COMPREHENSIVE COVERAGE OF ELECTRIC VEHICLES
vijay tharad
Director Operations at Corporate Professional Academy for Technical Training & Career Development
Electric Vehicles
From time immemorial, man has been inventing newer machines to improve his living comfort and to have more productivity in factories. Electric vehicles were born around the middle period of the 19th century and modern Electric vehicles/Hybrid Electric vehicles were developed at the end of the 20th century. These Electric vehicles were seen as more comfortable and easier to operate compared with the ICE engine vehicles. But now the latter has created an environmental problem. In today’s quest to safeguard our environment and to have more ways to use sustainable and renewable energy sources, the automobile industry has the most important role to perform.
This industry is the most polluting in terms of tailpipe emissions from their products. Battery industries also have an important role to play. More and more batteries are used for applications like electric vehicles (Electric vehicles), renewable energy sources (RES) like solar and wind energies. Electric propulsion through batteries helps in reducing the pollution level in the atmosphere as well as operating costs. Moreover, it also reduces dependence on crude oil. Electric propulsion of vehicles is the most talked about topic today.
All auto manufacturers have their own design of electric vehicles and Electric vehicles batteries (EVB). Although the lead-acid battery was the most widely used EVB until recent times, Li-ion battery now has taken over the leading role. But considering the initial cost and safety aspects, the lead-acid battery cannot be dethroned completely until the cost of the Li-ion Electric vehicles battery pack comes down to an affordable level and the safety aspects are improved further.
All auto manufacturers have their own design of electric vehicles and Electric vehicles batteries (EVB). Although the lead-acid battery was the most widely used EVB until recent times, Li-ion battery now has taken over the leading role. But considering the initial cost and safety aspects, the lead-acid battery cannot be dethroned completely until the cost of the Li-ion Electric vehicles battery pack comes down to an affordable level and the safety aspects are improved further. Around the year 2010, the number of EVs on the roads stood at far less than 20,000 in the world. However, in the year 2019, the number had gone up by more than 400 times and was near seven million.
Nearly 80% of the air quality problems are related to automobile emission. In the industrialized countries of the West and Japan, it has been established that two-thirds of the CO, one-third of the nitrogen oxides, and nearly half of the hydrocarbons were due to the above-mentioned emissions. When such was the case with industrialized nations, it was no better in developing countries where environmental controls were not strictly enforced.
Inefficient ICE vehicles contributed significantly to air pollution even though the traffic density was lean. Apart from the above reasons, vehicular emissions produce large quantities of the “greenhouse gas” (GHG) i.e., CO2. On average, a car will produce nearly four times its weight of CO2. Vehicular emissions are responsible for 20, 24, and 26 per cent of all emissions of CO2 in the U.K, the USA and Australia, respectively. All these reasons and oil crises of the 1960s and 1970s and 1973 and 1979 were the real reasons behind the development of Electric vehicles and suitable Electric vehicles batteries.
Electric Vehicles - zero emission
An electric vehicle uses one or more electric motors powered by batteries alone for traction purposes (Pure Electric vehicles) with no internal combustion engine (ICE) whatsoever. Hence it has no tail-pipe emissions and so-known as or zero-emission vehicle (ZEEV). Hybrid electric vehicles (HEV) has two power sources, one with a high energy content (fossil fuel) and the other is a high-discharge rate battery. The topic of Electric vehicles and its variants is a vast one and shall be dealt with in detail separately. Suffice it here to know the brief definition of Electric vehicles and HEV.
Components of Pure Electric Vehicles
I. Electrical Energy Storage (Battery) II. Electronic control module (ECM) III. A battery management system (BMS ) IV. Electrical Drive train
Every electric car has a range indicator, and the range is displayed prominently on the dashboard. In some Electric vehicles, lights start flashing when about 25 km of a range is left.
Components of a Conventional Hybrid Electric Vehicles
I. Electrical Energy Storage (Battery) II. Chemical Energy Storage (Fuel tank) III. Electrical Drive train IV. Combustion Drive train
An introduction to batteries for electric vehicles
Characteristics required of an Electric Vehicle battery
There are several characteristics required of an Electric vehicles battery, but the following are of prime importance and provide a reasonably accurate assessment of battery feasibility. a. Initial purchase cost of the battery pack (cost per kWh, including all paraphernalia) b. Specific energy, which is an indicator of the size of the battery (Wh/kg) c. Specific power, which is an indicator of acceleration and hill-climbing ability (W/kg) d. Operating cost (cost/km/passenger) e. Long cycle life with maintenance-free characteristics f. Rapid rechargeability (80% within 10 minutes) g. Ability to absorb high currents during regenerative braking. h. Safety, dependability, and ease of recyclability.
Electric vehicles & Hybrid electric vehicles
In pure Electric vehicles, the power is to be supplied by the battery on a continuous mode. The energy capacity of the battery is so designed that it can supply this continuous discharge rating for the total designed range of the Electric vehicles. Usually, the Electric vehicles battery is not permitted to discharge beyond 80% of the capacity, so that its state of charge (SOC) will not drop below 20 to 25 %.
Electric vehicles battery range
This is to safeguard the battery against over-discharge and to avoid difficulties encountered in case the battery gets over-discharged. Moreover, the battery should also be able to accept the energy input from the regenerative braking system. If the battery is fully charged, the regenerative braking energy cannot be accepted by the battery. The current trend in the above-mentioned continuous discharge rate is one time the capacity rating. For example, if the capacity rating is 300 Ah, the discharge rate is 300 amperes. Invariably, an Electric vehicles battery will experience full discharge once in a day. Of course, it will receive the return energy from regenerative braking as when applied.
The mean percentage of regenerative energy is about 15%. This figure may go up to more than 40 % in some cases.? The regenerative power does not go beyond 40 kW.? Its highest value is at a particular deceleration.
Nowadays, Electric vehicles battery manufacturers claim a cycle life of about 1000 to > 10,000 cycles.
An electric car battery nominally requires a 36 to 40 kWh (usable energy capacity) battery for a round-trip range of 300 to 320 km. But most of the OEM makers specify more than this value, typically, 40 to 60 per cent more. This will compensate for the lowering of life due to cycling so that even after the warranted battery life, there is a safe margin of capacity for a normal operation of an EV. The 96-kWh battery in an EV has a usable capacity of 86.5 kWh.
Although today’s Li-ion cells easily deliver 170 Wh/kg specific energy, the pack’s specific energy comes down by 35 %. As a result, the overall specific energy reduces to 120 Wh/kg. In 2019, the pack percentage of non-cell components has come down to about 28% from about 35%. But technology innovations like cell-to-pack technology (eliminating the middle agent, the module) may further improve the specific energy of the future EV batteries. The current specific power characteristics of EV batteries is highly satisfactory and hence the R&D engineers and scientists are aiming at higher specific energies.
Electrical drive train in electric vehicles
Traction motors power all-electric vehicles. But there are controllers for manipulating the performance of the electric motors. There are two types of electric motors, AC and DC motors. The latter is easier to control and also are less costly; the disadvantages are their heavier weight and larger volume. The rapid advances in power electronics have added highly efficient AC motors with a wider window of operational range, but, with attendant higher cost. In the EV, the energy input to the motor is controlled by the highly complicated electronic circuit called electronic control module (ECM). The EV operator gives the input through the accelerator pedal.
Battery management system (BMS) in electric vehicles
Similar to the above-mentioned electronic control module, there is a control system for battery also, called a battery management system (BMS), which controls the performance of the EV battery. The BMS may also have separate electronics installed at the cell or module levels which monitor the temperature and voltage of the cells, often referred to as a voltage temperature monitor (VTM) board.
In addition to these, there will be a thermal management system, which may range from a passive solution such as using the enclosure as a thermal heat sink to an actively managed liquid- or air-cooled system that forces cooled (or heated) air or liquid through the battery pack. Switches to turn the current flow on and off and wiring are also part of the system. All of these different systems must come together into a single system solution for the battery function safely and meet its life and performance expectancies.
History of Electricity, Batteries, and Electric Vehicles
Electricity and Batteries
Why should we discuss the history of electric battery and electric vehicles? There is an old saying: “those who cannot remember the past are condemned to repeat it”. Hence it is worthwhile to have a basic understanding of how the technology evolved. This will play an important role in understanding its future path and what were the key stakeholders in making it truly successful. As stated by John Warner in his book on Li-ion batteries, “World Fairs of the time provide a good representation of the speed of technological innovation and change in the world in general” [1. John Warner, The Handbook of Lithium-Ion Battery Pack Design, Elsevier, 2015, page 14].
One can understand that world fairs provided a picture of those days about the status of different technologies. The development in battery technology was made possible only because of the availability, expansion, and growth of electricity and the network of electricity of those days. Here we have to understand that only because of the electricity “supply” the “demand” for the battery (energy storage) was created. Otherwise, energy storage may not have emerged at all.
When Was the Battery Invented?
One of the most remarkable and novel discoveries in the last 400 years was electricity. We might ask, “Has electricity been around that long?” The answer is yes, and perhaps much longer. Its practical use has only been at our disposal since the mid to late 1800s, and in a limited way at first. Some of the earliest public works gaining attention were streets lights in Berlin in 1882, lighting up the Chicago World’s Fair in 1893 with 250,000 light bulbs, and illuminating a bridge over the river Seine during the Paris 1900 World Fair.
The use of electricity may go back further. While constructing a railway in 1936 near Baghdad, workers uncovered what appeared to be a prehistoric battery, also known as the Parthian Battery. The object dates back to the Parthian empire and is believed to be 2,000 years old. The battery consisted of a clay jar that was filled with a vinegar solution into which an iron rod surrounded by a copper cylinder was inserted. This device produced 1.1 to 2.0 volts of electricity. Figure 1 illustrates the Parthian Battery.
Not all scientists accept the Parthian Battery as a source of energy. It is possible that the device was used for electroplating, adding a layer of gold or other precious metals to a surface. The Egyptians are said to have electroplated antimony onto copper over 4,300 years ago. Archeological evidence suggests the Babylonians were the first to discover and employ a galvanic technique in the manufacturing of jewelry by using an electrolyte based on grape juice to gold-plate stoneware. The Parthians, who ruled Baghdad (ca. 250 BC), may have used batteries to electroplate silver.
One of the earliest methods to generate electricity in modern times was by creating a static charge. In 1660, Otto von Guericke constructed an electrical machine using a large sulfur globe which, when rubbed and turned, attracted feathers and small pieces of paper. Guericke was able to prove that the sparks generated were electrical in nature.
In 1744, Ewald Georg von kleist developed the Leyden jar that stored static charge in a glass jar that was lined with metallic foil on the inside and outside of the container. Many scientists, including Peter van Musschenbroek, professor at Leiden, the Netherlands, thought that electricity resembled a fluid that could be captured in a bottle. They did not know that the two metallic foils formed a capacitor. When charged up with high voltage, the Leyden jar gave the gentlemen an unexplainable hefty shock when they touched the metallic foil.
The first practical use of static electricity was the “electric pistol” that Alessandro Volta (1745–1827) invented. He thought of providing long-distance communications, albeit only one Boolean bit. An iron wire supported by wooden poles was to be strung from Como to Milan, Italy. At the receiving end, the wire would terminate in a jar filled with methane gas. To signal a coded event, an electrical spark would be sent by wire to detonate the jar. This communications link was never built. Figure 2 shows a pencil rendering of Alessandro Volta.
In 1791, while working at Bologna University, Luigi Galvani discovered that the muscle of a frog would contract when touched by a metallic object. This phenomenon became known as animal electricity. Prompted by these experiments, Volta initiated a series of experiments using zinc, lead, tin and iron as positive plates (cathode); and copper, silver, gold and graphite as negative plates (anode). The interest in galvanic electricity soon became widespread.
Early Batteries
Volta discovered in 1800 that certain fluids would generate a continuous flow of electrical power when used as a conductor. This discovery led to the invention of the first voltaic cell, more commonly known as battery. Volta learned further that the voltage would increase when voltaic cells were stacked on top of each other. Figure 3.1 and 3.2 illustrate such a series connection.
Volta’s experiments with the electric battery in 1796.
Metals in a battery have different electron affinities. Volta noticed that the voltage potential of dissimilar metals became stronger the farther apart the affinity numbers moved. The first number in the metals listed below demonstrates the affinity to attract electrons; the second is the oxidation state.
The metals determine the battery voltage; they were separated with moist paper soaked in salt water.
In the same year, Volta released his discovery of a continuous source of electricity to the Royal Society of London. No longer were experiments limited to a brief display of sparks that lasted a fraction of a second; an endless stream of electric current now seemed possible.
France was one of the first nations to officially recognize Volta’s discoveries. This was during a time when France was approaching the height of scientific advancements. New ideas were welcomed with open arms as they helped to support of the country’s political agenda. In a series of lectures, Volta addressed the Institute of France. Napoleon Bonaparte participated in the experiments, drawing sparks from the battery, melting a steel wire, discharging an electric pistol and decomposing water into its elements (see Figure 4).
Figure 4: Volta’s experimentations at the Institute of France.Volta’s discoveries so impressed the world that in November 1800 the Institute of France invited him to lecture at events in which Napoleon Bonaparte participated. Napoleon helped with the experiments, drawing sparks from the battery, melting a steel wire, discharging an electric pistol and decomposing water into its elements
In 1800, Sir Humphry Davy, inventor of the miner’s safety lamp, began testing the chemical effects of electricity and found out that decomposition occurred when passing electrical current through substances. This process was later called electrolysis. He made new discoveries by installing the world’s largest and most powerful electric battery in the vaults of the Royal Institution of London, connecting the battery to charcoal electrodes produced the first electric light. Witnesses reported that his voltaic arc lamp produced “the most brilliant ascending arch of light ever seen.”
In 1802, William Cruickshank designed the first electric battery for mass production. He arranged square sheets of copper with equal-sized sheets of zinc placed into a long rectangular wooden box and soldered together. Grooves in the box held the metal plates in position. The sealed box was then filled with an electrolyte of brine, or watered-down acid. This resembled the flooded battery that is still with us today. Figure 5 illustrates his battery workshop.
Invention of the Rechargeable Battery
In 1836, John F. Daniell, an English chemist, developed an improved battery that produced a steadier current than earlier attempts to store electrical energy. In 1859, the French physician Gaston Planté invented the first rechargeable battery based on lead acid, a system that is still used today. Until then, all batteries were primary, meaning they could not be recharged.
In 1899, Waldmar Jungner from Sweden invented the nickel-cadmium (NiCd) battery that used nickel as the positive electrode (cathode) and cadmium as the negative (anode). High material costs compared to lead limited its use. Two years later, Thomas Edison replaced cadmium with iron, and this battery was called nickel-iron (NiFe). Low specific energy, poor performance at low temperature and high self-discharge limited the success of the nickel-iron battery. It was not until 1932 that Schlecht and Ackermann achieved higher load currents and improved the longevity of NiCd by inventing the sintered pole plate. In 1947, Georg Neumann succeeded in sealing the cell.
For many years, NiCd was the only rechargeable battery for portable applications. In the 1990s, environmentalists in Europe became concerned about the harm incurred when NiCd is carelessly disposed. The Battery Directive 2006/66/EC now restricts the sale of NiCd batteries in the European Union except for specialty industrial use for which no replacement is suitable. The alternative is nickel-metal-hydride (NiMH), a more environmentally friendly battery that is similar to NiCd.
Most research activities today revolve around improving lithium-based systems, first commercialized by Sony in 1991. Besides powering cellular phones, laptops, digital cameras, power tools and medical devices, Li-ion is also used for electric vehicle and satellites.. The battery has a number of benefits, most notably its high specific energy, simple charging, low maintenance and being environmentally benign.
Electricity Through Magnetism
Generating electricity through magnetism came relatively late. In 1820, André-Marie Ampère (1775–1836) noticed that wires carrying an electric current were at times attracted to, and at other times repelled from, one another. In 1831, Michael Faraday (1791–1867) demonstrated how a copper disc provided a constant flow of electricity while revolving in a strong magnetic field. Faraday, assisting Humphry Davy and his research team, succeeded in generating an endless electrical force as long as the movement between a coil and magnet continued. This led to the invention of the electric generator, as well as the electric motor by reversing the process.
Shortly thereafter, transformers were developed that converted alternating current (AC) to any desired voltage. In 1833, Faraday established the foundation of electromagnetism on which Faraday’s law is based. It relates to electromagnetism found in transformers, inductors and many types of electrical motors and generators. Once the relationship with magnetism was understood, large generators were built to produce a steady flow of electricity. Motors followed that enabled mechanical movement and Thomas Edison’s light bulb appeared to conquer darkness.
Early electrical plants produced direct current (DC) with distribution limitations of 3km (~2 miles) from the plant. In around 1886, the Niagara Falls Power Company (NFPC) offered $100,000 for a method to transmit electricity over a long distance. After much controversy and failed proposals, the world’s brightest minds met in London, England, and the prize was awarded to Nikola Tesla (1856–1943), a Serbian immigrant who created the AC transmission system. NRPC with Tesla as a consultant built a multi-phase AC system, delivering power from new Niagara power station as far as Buffalo, NY.
DC systems run on low voltage and require heavy wires; AC could be transformed to higher voltages for transmission over light wires and then reduced for use. Older folks supported DC while younger geniuses gravitated towards AC. Thomas Edison was dead set against AC, giving danger by electrocution as a reason.
The disagreement continued, but AC became the accepted norm that was also supported by Europe. George Westinghouse, an American inventor and manufacturer, began developing the Tesla system to the displeasure of Thomas Edison.
To everyone’s amazement, AC power lit up the Chicago World Fair in 1893 (Figure 7). Westinghouse then built three large generators to transform energy from the Niagara Falls to electricity. Three-phase AC technology developed by Tesla enabled the transmission of electric power over great distances cheaply. Electricity was thus made widely available to humanity to improve the quality of life.
Telecommunications by wire that was strung along railways operated mostly by primary batteries that needed frequent replacement. Telex, an early means to transmit data, was digital in that the batteries activated a series of relays. The price to send a message was based on the number of relay clicks required.
In the mid-1800s, telegraphy opened new careers for bright young men. Staff operating these devices moved into the growing middle class, far removed from mills and mines burdened with labor, dirt and danger. Steel magnate Andrew Carnegie recalled his early days as a telegraphy messenger: Alfred Hitchcock started his career as an estimator before becoming an illustrator.
The invention of the electronic vacuum tube in the early 1900s formed the significant next step towards high technology. It enabled frequency oscillators, signal amplifications and digital switching. This led to radio broadcasting in the 1920s and the first digital computer, called ENIAC, in 1946. The invention of the transistor in 1947 paved the way for the arrival of the integrated circuit 10 years later, and the microprocessor that ushered in the Information Age. This forever changed the way we live and work.
Humanity has become dependent on electricity and with increased mobility, people gravitate towards portable power involving the battery. As the battery improves further, more tasks will be made possible with this portable power source.
Fun facts on electric vehicles!!
Nickel Metal Hydride Battery Technology for electric vehicles
The invention of the Ni-MH battery system is a derivative of both Ni-Cd and Ni-H2 batteries. The Cd in the Ni-Cd system is considered a hazardous material. The associated advantages of the new system were the higher specific energy, lower pressures required and the cost of Ni-MH cells. The work was supported by two German auto makers over a period of 20 years
Energy producing electrochemical reactions: There is a lot of similarity between Ni-Cd and Ni-MH cells, except for the negative electrode. As in the case of Ni-Cd cells, during discharge, the positive active material (PAM), nickel oxyhydroxide, is reduced to nickel hydroxide. (Thus, the positive electrode behaves as a cathode):
NiOOH + H2O +e–? ?Discharge?Charge? ?Ni(OH)2 + OH–? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? E° = 0.52 Volt? ??
The negative active material (NAM), reacts as given below: (Thus the negative electrode behaves as an anode):
MH + OH– Discharge?Charge????M + H2O? + e–????????????????????????????????????????????????????????????? E° = -0.83 ?Volt
That is, desorption of hydrogen occurs during discharge.
The total reaction during discharge is
NiOOH + H2O + e–? Discharge?Charge???Ni(OH)2 + OH
MH + OH– ? Discharge?Charge???M + H2O? + e–
NiOOH + MH Discharge?Charge ?Ni(OH)2 + M? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?E° = 1.35 Volts
Please remember that
Cell voltage = VPositive – VNegative
Therefore 0.52 – (-0.83) = 1.35 V
Here it is to be noted that water molecules shown in the half cell reactions do not appear in the overall or total cell reaction. This is due to the electrolyte (aqueous potassium hydroxide solution) not participating in the energy-producing reaction and it is there only for conductivity purposes. Also, note that the aqueous solution of sulphuric acid used as an electrolyte in the lead-acid cells actually? is participating in the reaction as shown below:
?PbO2 + Pb + 2H2SO4?? Discharge?Charge? 2PbSO4?? + 2H2O
This is an important difference between lead-acid cells and alkaline cells.? The reverse process occurs during the charge reaction.
The sealed nickel-metal hydride cell uses an oxygen-recombination reaction similar to the one occurring in valve-regulated lead-acid (VRLA) cells, thus preventing the unwanted increase in the internal pressure which results from the generation of gases towards the end of the charge and particularly during overcharge.
During charge, PAM reaches full charge before the NAM and so the positive electrode begins to evolve oxygen.
4OH–? → 2H2O + O2 + 4e–
The gas thus evolved from the above reaction travels through the porous matrix of the separator to the NAM aided by the starved of electrolyte construction and by employing a suitable separator.
Because the O2 combines with the MH electrode to generate water on the negative electrode, the pressure build-up inside the battery is prevented.?? Even so, there is a safety valve in the case of an extended overcharge or charger malfunctioning.
4MH + O2 → 4M + 2H2O
Moreover, by design, the NAM is never allowed to come to full charge, thus preventing the possibility of hydrogen production. Additionally, it is very important to follow an intelligent charge algorithm to restrict the O2 generation beyond the capability of the cell’s recombination efficiency. This is also achieved by careful control of the two active materials proportion.
Readers can refer to the following for a detailed account of the Ni-MH batteries a. Chapter on Ni-MH batteries by Michael Fetcenko and John Koch in the Handbook b. Kaoru Nakajima and Yoshio Nishi Chapter 5 in: Energy Storage Systems for Electronics.
Lead acid battery technology in electric vehicles
The Advanced Lead Acid Battery Consortium (ALABC) [7. J.F. Cole, J. Power Sources, 40, (1992) 1-15] was set up in March 1992 to manage a 4-year Research Plan with a fund of US $ 19.3 million (Rs.48 crores approximately) for the development of high-performance EV lead-acid battery that will serve a significant share of the EV market in the short to mid-term.
ILZRO managed this consortium and is a partnership organization among the fourteen largest lead producers, twelve battery manufacturers, electric utilities, motor manufacturers, charger and coupling manufacturers, power-train suppliers, controller/electronics manufacturers, and EV trade organizations. The membership currently stands at 48, hailing from 13 countries. The ALABC (now CBI) has five critical research and development goals which have been included in Table 3. Advanced lead-acid batteries are capable of providing electric vehicles with daily commuting ranges of 90 miles or more, recharging times of a few minutes, and lifetimes of approximately 3 years.
The state of the technology of ALABC in 1998 indicates that, with the projects currently in train, valve-regulated lead-acid batteries with a performance characteristic of 48 Wh/kg, 150W/kg, a fast charge of 80% in 10 minutes, and cycle life of 800 are on schedule for development before the end of 1998. The achievement of such a performance will represent a spectacular advance by the lead-acid battery community during the course of the 1990s and offers the prospect of an electric automobile with a range per charge of over 100 miles, repeatable several times within a day and over 500 times during the lifetime of a battery pack.
Lithium-ion batteries in electric vehicles
How do Lithium Batteries Work?
Pioneering work of the lithium battery began in 1912 under G.N. Lewis, but it was not until the early 1970s that the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the 1980s but failed because of instabilities in the metallic lithium used as anode material. (The metal-lithium battery uses lithium as anode; Li-ion uses graphite as anode and active materials in the cathode.)
Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest specific energy per weight. Rechargeable batteries with lithium metal on the anode could provide extraordinarily high energy densities; however, it was discovered in the mid-1980s that cycling produced unwanted dendrites on the anode. These growth particles penetrate the separator and cause an electrical short. The cell temperature would rise quickly and approach the melting point of lithium, causing thermal runaway, also known as “venting with flame.” A large number of rechargeable metallic lithium batteries sent to Japan were recalled in 1991 after a battery in a mobile phone released flaming gases and inflicted burns to a man’s face.
The inherent instability of lithium metal, especially during charging, shifted research to a non-metallic solution using lithium ions. In 1991, Sony commercialized the first Li ion, and today this chemistry has become the most promising and fastest growing battery on the market. Although lower in specific energy than lithium-metal, Li ion is safe, provided the voltage and currents limits are being respected.
Credit for inventing the lithium-cobalt-oxide battery should go to John B. Goodenough (1922). It is said that during the developments, a graduate student employed by Nippon Telephone & Telegraph (NTT) worked with Goodenough in the USA. Shortly after the breakthrough, the student traveled back to Japan, taking the discovery with him. Then in 1991, Sony announced an international patent on a lithium-cobalt-oxide cathode. Years of litigation ensued, but Sony was able to keep the patent and Goodenough received nothing for his efforts. In recognition of the contributions made in Li-ion developments, the U.S. National Academy of Engineering awarded Goodenough and other contributors the Charles Stark Draper Prize in 2014. In 2015, Israel awarded Goodenough a $1 million prize, which he will donate to the Texas Materials Institute to assist in materials research.
The key to the superior specific energy is the high cell voltage of 3.60V. Improvements in the active materials and electrolytes have the potential to further boost the energy density. Load characteristics are good and the flat discharge curve offers effective utilization of the stored energy in a desirable and flat voltage spectrum of 3.70–2.80V/cell.
In 1994, the cost to manufacture Li-ion in the 18650 cylindrical cell was over US$10 and the capacity was 1,100mAh. In 2001, the price dropped to below $3 while the capacity rose to 1,900mAh. Today, high energy-dense 18650 cells deliver over 3,000mAh and the costs are dropping. Cost reduction, increased specific energy and the absence of toxic material paved the road to make Li-ion the universally accepted battery for portable applications, heavy industries, electric powertrains and satellites. The 18650 measures 18mm in diameter and 65mm in length.
Li-ion is a low-maintenance battery, an advantage that most other chemistries cannot claim. The battery has no memory and does not need exercising (deliberate full discharge) to keep it in good shape. Self-discharge is less than half that of nickel-based systems and this helps the fuel gauge applications. The nominal cell voltage of 3.60V can directly power mobile phones, tablets and digital cameras, offering simplifications and cost reductions over multi-cell designs. The drawbacks are the need for protection circuits to prevent abuse, as well as high price.
Types of Lithium-ion Batteries
Lithium-ion uses a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. (The anode of a discharging battery is negative and the cathode positive . The cathode is metal oxide and the anode consists of porous carbon. During discharge, the ions flow from the anode to the cathode through the electrolyte and separator; charge reverses the direction and the ions flow from the cathode to the anode. Figure 1 illustrates the process.
Li ion batteries come in many varieties but all have one thing in common – the “lithium-ion” catchword. Although strikingly similar at first glance, these batteries vary in performance and the choice of active materials gives them unique personalities.
Sony’s original lithium-ion battery used coke as the anode (coal product). Since 1997, most Li ion manufacturers, including Sony, shifted to graphite to attain a flatter discharge curve. Graphite is a form of carbon that has long-term cycle stability and is used in lead pencils. It is the most common carbon material, followed by hard and soft carbons. Nanotube carbons have not yet found commercial use in Li-ion as they tend to entangle and affect performance. A future material that promises to enhance the performance of Li-ion is graphene.
Figure 2 illustrates the voltage discharge curve of a modern Li-ion with graphite anode and the early coke version.
Several additives have been tried, including silicon-based alloys, to enhance the performance of the graphite anode. It takes six carbon (graphite) atoms to bind to a single lithium ion; a single silicon atom can bind to four lithium ions. This means that the silicon anode could theoretically store over 10 times the energy of graphite, but expansion of the anode during charge is a problem. Pure silicone anodes are therefore not practical and only 3–5 percent of silicon is typically added to the anode of a silicon-based to achieve good cycle life.
Using nano-structured lithium-titanate as an anode additive shows promising cycle life, good load capabilities, excellent low-temperature performance and superior safety, but the specific energy is low and the cost is high.
Experimenting with cathode and anode material allows manufacturers to strengthen intrinsic qualities, but one enhancement may compromise another. The so-called “Energy Cell” optimizes the specific energy (capacity) to achieve long runtimes but at lower specific power; the “Power Cell” offers exceptional specific power but at lower capacity. The “Hybrid Cell” is a compromise and offers a little bit of both.
Manufacturers can attain a high specific energy and low cost relatively easily by adding nickel in lieu of the more expensive cobalt, but this makes the cell less stable. While a start-up company may focus on high specific energy and low price to gain quick market acceptance, safety and durability cannot be compromised. Reputable manufacturers place high integrity on safety and longevity. Table 3 summarizes the advantages and limitations of Li-ion.
Most Li-ion batteries share a similar design consisting of a metal oxide positive electrode (cathode) that is coated onto an aluminum current collector, a negative electrode (anode) made from carbon/graphite coated on a copper current collector, a separator and electrolyte made of lithium salt in an organic solvent. Table 3 summarizes the advantages and limitations of Li-ion.
Advantages
Limitations
Table 3: Advantages and Limitations of Lithium-ion Batteries
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Types of Lithium-ion
Lithium-ion is named for its active materials; the words are either written in full or shortened by their chemical symbols. A series of letters and numbers strung together can be hard to remember and even harder to pronounce, and battery chemistries are also identified in abbreviated letters.
For example, lithium cobalt oxide, one of the most common Li-ions, has the chemical symbols LiCoO2 and the abbreviation LCO. For reasons of simplicity, the short form Li-cobalt can also be used for this battery. Cobalt is the main active material that gives this battery character. Other Li-ion chemistries are given similar short-form names. This section lists six of the most common Li-ions. All readings are average estimates at time of writing.
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Lithium Cobalt Oxide(LiCoO2) — LCO
Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Figure 1 illustrates the structure.
The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power). Like other cobalt-blended Li-ion, Li-cobalt has a graphite anode that limits the cycle life by a changing solid electrolyte interface (SEI), thickening on the anode and lithium plating while fast charging and charging at low temperature. Newer systems include nickel, manganese and/or aluminum to improve longevity, loading capabilities and cost.
Li-cobalt should not be charged and discharged at a current higher than its C-rating. This means that an 18650 cell with 2,400mAh can only be charged and discharged at 2,400mA. Forcing a fast charge or applying a load higher than 2,400mA causes overheating and undue stress. For optimal fast charge, the manufacturer recommends a C-rate of 0.8C or about 2,000mA. . The mandatory battery protection circuit limits the charge and discharge rate to a safe level of about 1C for the Energy Cell.
The hexagonal spider graphic (Figure 2) summarizes the performance of Li-cobalt in terms of specific energy or capacity that relates to runtime; specific power or the ability to deliver high current; safety; performance at hot and cold temperatures; life span reflecting cycle life and longevity; and cost. Other characteristics of interest not shown in the spider webs are toxicity, fast-charge capabilities, self-discharge and shelf life.
The Li-cobalt is losing favor to Li-manganese, but especially NMC and NCA because of the high cost of cobalt and improved performance by blending with other active cathode materials. (See description of the NMC and NCA below.)
Summary Table
Lithium Cobalt Oxide: LiCoO2 cathode (~60% Co), graphite anode Short form: LCO or Li-cobalt. Since 1991
Voltages 3.60V nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity) 150–200Wh/kg. Specialty cells provide up to 240Wh/kg.
Charge (C-rate) 0.7–1C, charges to 4.20V (most cells); 3h charge typical. Charge current above 1C shortens battery life. Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate)1C; 2.50V cut off. Discharge current above 1C shortens battery life.
Cycle life 500–1000, related to depth of discharge, load, temperature
Thermal runaway 150°C (302°F). Full charge promotes thermal runaway
Applications Mobile phones, tablets, laptops, cameras
Comments 2019 Update: Very high specific energy, limited specific power. Cobalt is expensive. Serves as Energy Cell. Market share has stabilized. Early version; no longer relevant.
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Lithium Manganese Oxide (LiMn2O4) — LMO
Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. In 1996, Moli Energy commercialized a Li-ion cell with lithium manganese oxide as cathode material. The architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and enhanced safety, but the cycle and calendar life are limited.
Low internal cell resistance enables fast charging and high-current discharging. In an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. It is also possible to apply one-second load pulses of up to 50A. A continuous high load at this current would cause heat buildup and the cell temperature cannot exceed 80°C (176°F). Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.
Figure 4 illustrates the formation of a three-dimensional crystalline framework on the cathode of a Li-manganese battery. This spinel structure, which is usually composed of diamond shapes connected into a lattice, appears after initial formation.
Li-manganese has a capacity that is roughly one-third lower than Li-cobalt. Design flexibility allows engineers to maximize the battery for either optimal longevity (life span), maximum load current (specific power) or high capacity (specific energy). For example, the long-life version in the 18650 cell has a moderate capacity of only 1,100mAh; the high-capacity version is 1,500mAh.
Figure 5 shows the spider web of a typical Li-manganese battery. The characteristics appear marginal but newer designs have improved in terms of specific power, safety and life span. Pure Li-manganese batteries are no longer common today; they may only be used for special applications.
Most Li-manganese batteries blend with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out the best in each system, and the LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which can be about 30 percent, provides high current boost on acceleration; the NMC part gives the long driving range.
Li-ion research gravitates heavily towards combining Li-manganese with cobalt, nickel, manganese and/or aluminum as active cathode material. In some architecture, a small amount of silicon is added to the anode. This provides a 25 percent capacity boost; however, the gain is commonly connected with a shorter cycle life as silicon grows and shrinks with charge and discharge, causing mechanical stress.
These three active metals, as well as the silicon enhancement can conveniently be chosen to enhance the specific energy (capacity), specific power (load capability) or longevity. While consumer batteries go for high capacity, industrial applications require battery systems that have good loading capabilities, deliver a long life and provide safe and dependable service.
Summary Table
Lithium Manganese Oxide: LiMn2O4 cathode. graphite anode Short form: LMO or Li-manganese (spinel structure) Since 1996
领英推荐
Voltages 3.70V (3.80V) nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity)100–150Wh/kg
Charge (C-rate) 0.7–1C typical, 3C maximum, charges to 4.20V (most cells) Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate)1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off
Cycle life 300–700 (related to depth of discharge, temperature)
Thermal runaway 250°C (482°F) typical. High charge promotes thermal runaway
Applications Power tools, medical devices, electric powertrains
Comments 2019 Update: High power but less capacity; safer than Li-cobalt; commonly mixed with NMC to improve performance. Less relevant now; limited growth potential.
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Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC
One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.
The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths.
NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. Cobalt is expensive and in limited supply. Battery manufacturers are reducing the cobalt content with some compromise in performance. A successful combination is NCM532 with 5 parts nickel, 3 parts cobalt and 2 parts manganese. Other combinations are NMC622 and NMC811. Cobalt stabilizes nickel, a high energy active material.
New electrolytes and additives enable charging to 4.4V/cell and higher to boost capacity. Figure 7 demonstrates the characteristics of the NMC.
There is a move towards NMC-blended Li-ion as the system can be built economically and it achieves a good performance. The three active materials of nickel, manganese and cobalt can easily be blended to suit a wide range of applications for automotive and energy storage systems (EES) that need frequent cycling. The NMC family is growing in its diversity.
Summary Table
Lithium Nickel Manganese Cobalt Oxide: LiNiMnCoO2. cathode, graphite anode Short form: NMC (NCM, CMN, CNM, MNC, MCN similar with different metal combinations) Since 2008
Voltages 3.60V, 3.70V nominal; typical operating range 3.0–4.2V/cell, or higher
Specific energy (capacity)150–220Wh/kg
Charge (C-rate)0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical. Charge current above 1C shortens battery life. Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate) 1C; 2C possible on some cells; 2.50V cut-off
Cycle life 1000–2000 (related to depth of discharge, temperature)
Thermal runaway210°C (410°F) typical. High charge promotes thermal runaway
Cost~$420 per kWh[1]
ApplicationsE-bikes, medical devices, EVs, industrial
Comments 2019 Update: Provides high capacity and high power. Serves as Hybrid Cell. Favorite chemistry for many uses; market share is increasing. Leading system; dominant cathode chemistry.
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Lithium Iron Phosphate(LiFePO4) — LFP
In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.
Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. . As a trade-off, its lower nominal voltage of 3.2V/cell reduces the specific energy below that of cobalt-blended lithium-ion. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception. Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. This can be mitigated by buying high quality cells and/or using sophisticated control electronics, both of which increase the cost of the pack. Cleanliness in manufacturing is of importance for longevity. There is no tolerance for moisture, lest the battery will only deliver 50 cycles. Figure 9 summarizes the attributes of Li-phosphate.
Li-phosphate is often used to replace the lead acid starter battery. Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series. Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge. Topping charge is applied to maintain full charge level and prevent sulfation on lead acid batteries.
With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage. At this point, the charge should be disconnected but the topping charge continues while driving. Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long road trip, could stress Li-phosphate. Time will tell how durable Li-Phosphate will be as a lead acid replacement with a regular vehicle charging system. Cold temperature also reduces performance of Li-ion and this could affect the cranking ability in extreme cases.
Summary Table
Lithium Iron Phosphate: LiFePO4 cathode, graphite anode Short form: LFP or Li-phosphate Since 1996
Voltages3.20, 3.30V nominal; typical operating range 2.5–3.65V/cell
Specific energy (capacity)90–120Wh/kg
Charge (C-rate)1C typical, charges to 3.65V; 3h charge time typical Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate)1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off (lower that 2V causes damage)
Cycle life2000 and higher (related to depth of discharge, temperature)
Thermal runaway270°C (518°F) Very safe battery even if fully charged
Cost~$580 per kWh[1]
ApplicationsPortable and stationary needing high load currents and endurance
Comments 2019 Update: Very flat voltage discharge curve but low capacity. One of safest Li-ions. Used for special markets. Elevated self-discharge. Used primarily for energy storage, moderate growth.
Table 10: Characteristics of Lithium Iron Phosphate
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See Lithium Manganese Iron Phosphate (LMFP) for manganese enhanced L-phosphate.
Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) — NCA
Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. Less flattering are safety and cost. Figure 11 summarizes the six key characteristics. NCA is a further development of lithium nickel oxide; adding aluminum gives the chemistry greater stability.
Summary Table
Lithium Nickel Cobalt Aluminum Oxide: LiNiCoAlO2 cathode (~9% Co), graphite anode Short form: NCA or Li-aluminum. Since 1999
Voltages3.60V nominal; typical operating range 3.0–4.2V/cell
Specific energy (capacity)200-260Wh/kg; 300Wh/kg predictable
Charge (C-rate)0.7C, charges to 4.20V (most cells), 3h charge typical, fast charge possible with some cells Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate)1C typical; 3.00V cut-off; high discharge rate shortens battery life
Cycle life500 (related to depth of discharge, temperature)
Thermal runaway150°C (302°F) typical, High charge promotes thermal runaway
Cost~$350 per kWh[1]
ApplicationsMedical devices, industrial, electric powertrain (Tesla)
Comments 2019 Update: Shares similarities with Li-cobalt. Serves as Energy Cell. Mainly used by Panasonic and Tesla; growth potential.
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Table 12: Characteristics of Lithium Nickel Cobalt Aluminum Oxide
Lithium Titanate (Li2TiO3) — LTO
Batteries with lithium titanate anodes have been known since the 1980s. Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. Li-titanate has a nominal cell voltage of 2.40V, can be fast charged and delivers a high discharge current of 10C, or 10 times the rated capacity. The cycle count is said to be higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge characteristics and obtains a capacity of 80 percent at –30°C (–22°F).
LTO (commonly Li4Ti5O12) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperature is also better than other Li-ion systems; however, the battery is expensive. At only 65Wh/kg, the specific energy is low, rivalling that of NiCd. Li-titanate charges to 2.80V/cell, and the end of discharge is 1.80V/cell. Figure 13 illustrates the characteristics of the Li-titanate battery. Typical uses are electric powertrains, UPS and solar-powered street lighting.
Summary Table
Lithium Titanate: Cathode can be lithium manganese oxide or NMC; Li2TiO3 (titanate) anode Short form: LTO or Li-titanate Commercially available since about 2008.
Voltages 2.40V nominal; typical operating range 1.8–2.85V/cell
Specific energy (capacity) 50–80Wh/kg
Charge (C-rate) 1C typical; 5C maximum, charges to 2.85V Charge must be turned off when current saturates at 0.05C.
Discharge (C-rate) 10C possible, 30C 5s pulse; 1.80V cut-off on LCO/LTO
Cycle life 3,000–7,000
Thermal runaway One of safest Li-ion batteries
Cost ~$1,005 per kWh[1]
Applications UPS, electric powertrain (Mitsubishi i-MiEV, Honda Fit EV), solar-powered street lighting
Comments 2019 Update: Long life, fast charge, wide temperature range but low specific energy and expensive. Among safest Li-ion batteries. Ability to ultra-fast charge; high cost limits to special application.
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Table 14: Characteristics of Lithium Nickel Cobalt Aluminum Oxide
Future Batteries
Figure 15 compares the specific energy of lead-, nickel- and lithium-based systems. While Li-aluminum (NCA) is the clear winner by storing more capacity than other systems, this only applies to specific energy. In terms of specific power and thermal stability, Li-manganese (LMO) and Li-phosphate (LFP) are superior. Li-titanate (LTO) may have low capacity but this chemistry outlives most other batteries in terms of life span and also has the best cold temperature performance. Moving towards the electric powertrain, safety and cycle life will gain dominance over capacity. (LCO stands for Li-cobalt, the original Li-ion.)
Figure 15: Typical specific energy of lead-, nickel- and lithium-based batteries.NCA enjoys the highest specific energy; however, manganese and phosphate are superior in terms of specific power and thermal stability. Li-titanate has the best life span. Courtesy of Cadex
Li-ion Lithium cobaltate (LCO) cell chemistry
The total reaction is???
C6 + LiCoO2 ? LixC6 + Li1-xCoO2 ?????
Ecell?????? = 3.8 – (0.1) = 3.7 V.
Li-ion cell of the LiFePO4 chemistry
The total reaction LiFePO4 + 6C →LiC6 + FePO4
Ecell?????? = 3.3 – (0.1) = 3.2 V
Era of Modern Electric Vehicles
It was really not until the 1990s that the major automakers work on hybrid and electric vehicles solutions began to produce results. In parallel with these advancements, the first commercial lithium-ion batteries were introduced to the market in 1991 and were quickly adopted. ?With the rapid spread of personal electronics, these high energy-density batteries became the energy storage solution of choice for many different applications from portable electronics to hybrid and electric vehicles.
The modern era of EVs was precipitated by the oil shortages in the 1970s.
Electric Vehicle (EV)
Transformation from the horse-drawn carriage to horseless transportation took its time when new technology arrived. The architecture and seating arrangements stayed the same for a while on early cars; only the horse was replaced with a motor. Figure 1 illustrates proud and well-to-do travelers on a horseless carriage, well elevated from the danger of horse’s hoofs and the grit from the street.
In the early 1900s, the electric vehicle was reserved for dignitaries the likes of Thomas Edison, John D. Rockefeller, Jr. and Clara Ford, the wife of Henry Ford. They chose this transportation for its quiet ride over the vibrating and polluting internal combustion engine. Environmentally conscious drivers are rediscovering the EV with a choice of many attractive products.
The EV culture is developing distinct philosophies, each satisfying a unique user group. This is visible with vehicle sizes and the associated batteries. The subcompact EV comes with a battery that has 12–18kWh, the mid-sized family sedan has a 22–32kWh pack, and the luxury models by Tesla stand alone with an oversized battery boasting 60–100kWh to provide extended driving range and achieve high performance.
The EV is said to replace cars with the internal combustion engine (ICE) by ca. 2040. Several technological improvements will be needed to make the electric powertrain practical and economical. Even with oil at $100 a barrel, the price of the EV batteries would need to fall by a factor of three and also offer ultra-fast charging. In terms of carbon footprint, the electricity used to power the EVs would need to come from renewable sources. Published reports say that emissions from EVs powered by America’s electricity grids are higher than those from an efficient ICE. Table 2 illustrates common EVs.
MODEL BATTERY
Toyota Prius PHEV 4.4kWh Li-ion, 18km (11 miles) all-electric range
Chevy Volt PHEV 16kWh, Li-manganese/NMC, liquid cooled, 181kg (400 lb), all electric range 64km (40 miles)
Mitsubishi iMiEV 16kWh; 88 cells, 4-cell modules; Li-ion; 109Wh/kg; 330V, range 128km (80 miles)
Smart Fortwo ED 16.5kWh; 18650 Li-ion, driving range 136km (85 miles)
BMW i3 Curb 1,365kg (3,000 lb) Since 2019: 42kWh, LMO/NMC, large 60A prismatic cells, battery weighs ~270kg (595 lb) driving range: EPA 246 (154 mi); NEDC 345km (215 mi); WLTP 285 (178 mi)
charge Nissan Leaf* 30kWh; Li-manganese, 192 cells; air cooled; 272kg
(600 lb), driving range up to 250km (156 miles)
Tesla S* Curb 2,100kg (4,630 lb) 70kWh and 90kWh, 18650 NCA cells of 3.4Ah; liquid cooled; 90kWh pack has 7,616 cells; battery weighs 540kg (1,200 lb); S 85 has up to 424km range (265 mi)
Tesla 3 Curb 1,872 kg (4072 lb) Since 2018, 75kWh battery, driving range 496km (310 mi); 346hp engine, energy consumption 15kWh /100km (24kWh/mi)
Chevy Bolt Curb 1,616kg; battery 440kg60kWh; 288 cells in 96s3p format, EPA driving rate 383km (238 miles); liquid cooled; 200hp electric motor (150kW)
* In 2015/16 Tesla S 85 increased the battery from 85kWh to 90kWh; Nissan Leaf from 25kWh to 30kWh.
The makers of Nissan Leaf, BMW i3 and other EVs use the proven lithium-manganese (LMO)battery with a NMC blend, packaged in a prismatic cell. (NMC stands for nickel, manganese, cobalt.) Tesla uses NCA (nickel, cobalt, aluminum) in the 18650 cell that delivers an impressive specific energy of 3.4Ah per cell or 248Wh/kg. To protect the delicate Li-ion from over-loading at highway speed, Tesla over-sizes the pack by a magnitude of three to four fold compared to other EVs.
The large 90kWh battery of the Tesla S Model (2015) provides an unparalleled driving range of 424km (265 miles), but the battery weighs 540kg (1,200 lb), and this increases the energy consumption to 238Wh/km (380Wh/mile), one of the highest among EVs
In comparison, the BMW i3 is one of the lightest EVs and has a low energy consumption of 160Wh/km (260Wh/mile). The car uses an LMO/NMC battery that offers a moderate specific energy of 120Wh/kg but is very rugged. The mid-sized 22kWh pack provides a driving range of 130–160km (80–100 miles). To compensate for the shorter range, the i3 offers REX, an optional gasoline engine that is fitted on the back. Table 3 compares the battery size and energy consumption of common EVs. The range is under normal non-optimized driving conditions.
EV MAKE BATTERY RANGE KM(MI) WH/KM (MI) ENERGYcost/KM(MI) BMW i3 (2019) 42kWh 345km (115) 165 (260) $0.033 ($0.052)GM Spark 21kWh 120km (75) 175 (280) $0.035 ($0.056
Fiat 500e 24kWh 135km (85) 180 (290) $0.0 36 ($0.058)
Honda Fit 20kWh 112km (70) 180 (290) $0.036 ($0.058)
Nissan Leaf 30kWh 160km (100) 190 (300) $0.038 ($0.06)
Mitsubishi MiEV 16kWh 85km (55) 190 (300) $0.038 ($0.06)
Ford Focus 23kWh 110km (75) 200 (320) $0.04 ($0.066)
Smart ED 16.5kWh 90km (55) 200 (320) $0.04 ($0.066)
Mercedes B 28kWh (31.5)*136km (85) 205 (330) $0.04 ($0.066)
Tesla S 60 60kWh 275km (170) 220 (350) $0.044 ($0.07)
Tesla S 85 90kWh 360km (225) 240 (380) $0.048 ($0.076)
Tesla 375kw 496 (310) 151 (242) $0.030 (0.048)
* Driving range limited to 28kWh; manual switch to 31.5kWh gives extra 16km (10 mile) spare
Clarification: The driving ranges in Tables 2 and 3 differ. This is less of an error than applying different driving conditions. Discrepancies also occur in topping charge, depth of discharge and fuel-gauging.
Note: Driving ranges are based on short duration and low speed. Stated distances per charge under true driving conditions are typical at 65%.
The cost of automotive lithium-ion batterers has fallen from about $1,000/kWh to a bit more than $100/kWh today. These cost reductions are attributed to incremental improvements in battery design and manufacturing efficiency, but few are credited to better battery chemistry. To further reduce cost, better battery chemistries are needed, but nothing is in the foreseeable future for the EV at time of writing.
In ca. 2016, the cost of an EV battery was about $350/kWh. Tesla managed to lower the price to $250/kWh using the 18650, a popular cell of which 2.5 billion were made in 2013. The 18650 in the current Tesla models is an unlikely choice as the cell was designed for portable devices such as laptops. Available since the early 1990s, the 18650 cell is readily available at a low cost. The cylindrical cell-design further offers superior stability over the prismatic and pouch cell, but the advantage may not hold forever as prismatic and pouch cells are improving. Large Li-ion cells are relatively new and have the potential for higher capacities and lower pack-cost as fewer cells are needed.
Prices are dropping and Bloomberg (December 2017) says that the average EV battery costs now $209 per kWh. This includes housings, wiring, BMS and plumbing, housekeeping that adds 20 percent to 40 percent to cell costs. Experts predict that the EV battery will drop below $100 per kWh by 2025. This will put the EV in par with a conventional powered vehicle of similar features. These price reductions do not apply to stationary battery systems that, according to Bloomberg, will command a 51 percent price premium over the EV because of lower volume.
All EV makers must provide an 8-year warranty or a mileage limit on their batteries. Tesla believes in their battery and offers 8 years with unlimited mileage. Figure 4 illustrates the battery that forms the chassis of the Tesla S Model. The Model S 85 contains 7,616 type 18650 cells in serial and parallel configuration. The smaller S-60 has 5,376 cells.
The 85kWh battery has 7,616 18650 cells in parallel/serial configuration. At $250 per kWh, the cost is lower than other Li-ion designs.
EV manufacturers calculate the driving range under the best conditions and according to reports, the distances traveled in the real-world can be 30–37 percent less than advertised. This may be due to the extra electrical loads such as headlights, windshield wipers, as well as cabin heating and cooling. Aggressive driving in a hilly countryside lowers the driving range further.
Cold temperature also reduces the driving range. What battery users may also overlook is the difficulty of charging when cold. Most Li-ion cannot be charged below freezing. To protect EV batteries, some packs include a heating blanket to warm the battery during cold temperature charging. A BMS may also administer a lower charge current when the battery is cold. Fast charging when cold promotes dendrite growth in Li-ion that can compromise battery safety
EV owners want ultra-fast charging and technologies are available but these should be used sparingly as fast charging stresses the battery. If at all possible, do not exceed a charge rate of 1C. Avoid full charges that take less than 90 minutes. Ultra-fast charging is ideal for EV drivers on the run and this is fine for occasional use. Some EVs keep a record of stressful battery events and this data could be used to nullify a warranty claim.
Estimating SoC has always been a challenge, and the SoC accuracy of a battery is not at the same level as dispensing liquid fuel. EV engineers at an SAE meeting in Detroit were surprised to learn that the SoC on some new BMS were off by 15 percent. This is hidden to the user; spare capacity makes up for a shortfall.
EV makers must further account for capacity fade in a clever and non-alarming way to the motorist. This is solved by oversizing the battery and only showing the driving range. A new battery is typically charged to 80 percent and discharged to 30 percent. As the battery fades, the bandwidth may expand to keep the same driving range. Once the full capacity range is needed, the entire cycle is applied. This will cause stress to the aging battery and shorten the driving ranges visibly. Figure 5 illustrates three SoH ranges of an EV fuel gauge.
A new EV battery only charges to about 80% and discharges to 30%. As the battery ages, more of the usable battery bandwidth is demanded, which will result in increased stress and enhanced aging.
Economics
On the surface, driving on electricity is cheaper than burning fossil fuel; however, low fuel prices, uncertainty about battery longevity, unfamiliarity with battery abuse tolerances and high replacement costs are factors that reduce buyer incentives to switch from a proven propulsion system to the electric drivetrain. The EV will always have shorter driving ranges than vehicles with ICE because oversizing the battery has a diminishing return. When the size is increased, batteries simply get too heavy, negatively affecting travel economics and driving range
Technology Roadmaps as part of the International Energy Agency (IEA) compares energy consumption and cost of gasoline versus electric propulsion;
An EV requires between 150Wh and 250Wh per kilometer depending on vehicle weight, speed and terrain. At an assumed consumption of 200Wh/km and electricity price of $0.20 per kWh, the energy cost to drive an EV translates to $0.04 per km. This compares to $0.06 per km for a similar-size gasoline-powered car and $0.05 per km for diesel. Price estimations exclude equipment costs, service and the eventual replacement of the product.
Battery endurance and cost will govern the success of the EV. A consumer market will likely develop for a light EV with a battery providing 160km (100 miles) driving range or less. This will be a subcompact commuter car owned by a driver who adheres to a tightly regimented driving routine and follows a disciplined recharging regime. According to research, 90 percent of commuting involves less than 30km. The EV market will also include high-end models for the ecology-minded wealthy wanting to reduce greenhouse gases.
Driving an EV only delivers optimal environmental benefit when charging with renewable resources. Burning coal and fossil fuel to generate electricity, as is done in many countries, does not reduce greenhouse gases. In the US, 50 percent of electricity is generated by burning coal, 20 percent by natural gas and 20 percent by nuclear energy. Renewable energy by hydro is 8 percent and solar/wind energy is only 2 percent.
Going electric also begs the question, “Who will pay for the roads in the absence of fuel tax?” Governments spend billions on road maintenance and expansions; the EV, and in part the PHEV, can use the infrastructure for free. This is unfair for folks using public transport as they pay double: first paying income tax to support the road infrastructures and second in purchasing the train fare.
The high cost of the EV against the lure of cheap and readily available fossil fuel will slow the transition to clean driving. Government subsidies may be needed to make “green” cars affordable to the masses, but many argue that such handouts should be directed towards better public transportation, systems that had been ignored in North America since the 1950s.
Guidelines for EV Batteries
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Charging an Electric Vehicle
If you own an EV, you want to pamper the battery and charge the car at home and at the office. The power requirements to charge a mid-sized EV is similar to that of an electric stove connected to a 40A, 240VAC circuit developing up to 9.6kW. Most mid-sized EVs carry a 6.6kW on-board charger designed for a 4- to 5-hour charge. (6.6kW is derived by multiplying 220V by 30A.)
On-board chargers are limited by cost, size and thermal issues. With the availability of three-phase AC power in most European residences, on-board chargers can be made smaller than with a two-phase system. Renault offers compact on-board chargers that range from 3–43kW.
The hookup to charge an EV is called the Electric Vehicle Service Equipment (EVSE). Except for Level 1, all must be installed by an electrician if not already available. There are three categories of charging.
Level 1: 1.5kW typical Cord-set connects to a regular household outlet of 115VAC, 15A (230VAC, ~6A in Europe). This singe-phase hookup produces about 1.5kW, and the charge time is 7 to 30 hours depending on battery size. Level 1 meets overnight charging needs for e-bikes, scooters, electric wheelchairs and PHEVs not exceeding 12kWh. EV driving range per minute charge: 130m (426 feet)
Level 2: 7kW typical Wall-mount; 230VAC, 30A two pole, charges a mid-sized EV in 4 to 5 hours. This is the most common home and public charging station for EVs. It produces about 7kW to feed the 6.6kW on-board EV charger. The cost to install a Level 2 EVSE is about $750 in materials and labor. Households with a 100A service should charge the EV after cooking and clothes-drying to prevent exceeding the allotted household power. EV driving range per minute charge: 670m (2,200 feet)
Level 3: 50kW typical (Tesla V2 stations charge at 120kW) DC Fast Charger; 400–600VDC, up to 300A; serves as ultra-fast charging by bypassing the on-board charger and feeding the power directly to the battery. Level 3 chargers deliver 50 kW of power than can go up to 120kW to fill a Li-ion battery to 80 percent in about 30 minutes. The power demand at 120kW is equal to five households. EV driving range per minute charge at 50kW: 4.6km (2.9 miles)
Extra Fast Charge: 150kW; up to 400kW (Tesla V3 stations charge at 250kW) 400kW charging stations will charge at a voltage of up to 800VDC. This results in high component costs and high power demand equal to 16 households. The stress factor of ultra-fast charging on the battery also plays a role. If possible, charge at a more regular rate. EV range per minute charge at 400kW: 37km (23 miles) (30km Tesla)
In the 1990s and 2000s, EV makers made a concerted effort to develop a universal charging port for EVs and this resulted in the SAE J1772, a 5-pin connector carrying AC and data. The drawback is a charge time pursuant to Level 2 that takes several hours.
EV makers agree that the future of the EV lies in fast charging. While Level 2 only gains about 40km (25 miles) per hour charge, DC Fast Charging fills the battery to 80 percent in 30 minutes. This changes the EV from a commuter car into a touring vehicle, and EV marketing has started to push the concept.
Japan was first to introduce DC Fast Charging by developing the CHAdeMO connector for the Nissan Leaf and Mitsubishi MiEV. JEVS (Japan Electric Vehicle Standard) specified the connector that includes two large DC pins with communications pins for the CAN-BUS. The CHAdeMO standard was formed by TEPCO (The Tokyo Electric Power Company), Nissan, Mitsubishi, Fuji Heavy Industries (manufacturer of Subaru vehicles) and Toyota in 2008. It charges a battery at 500VDC and 125A with up to 62.5kW charging power. CHAdeMO stands for “CHArge on the Move;” Figure 1 illustrates the plug.
Nissan and Mitsubishi lead DC fast charging and developed CHAdeMO. It fast-charges at 500VDC and 125A, developing up to 62.5kW of power.
While the CHAdeMO connector performs well, the West lobbied against it, citing “technical issues.” The reason for this may be the “not invented in my backyard” syndrome as well as a standard that favors certain brands of cars. SAE rejected CHAdeMO in favor of their version.
After much delay, the SAE International J1772 Committee released the SAE DC Fast Charging standard in 2012, a system that is also known as the Combo Charging System (CCS). The delay caused a setback in building the CHAdeMO infrastructure and some argue that the postponement was deliberate.
To keep compatibility with Level 2 charging, CCS is based on the existing J1772 connector by adding two DC pins. When charging on AC, the circular connector provides AC power and communications to govern voltage, charge rate and end-of-charge. DC Fast Charging uses the same communications protocol but adds the DC pins. Figure 2 illustrates the charging connectors for AC and DC charging with the vehicle inlet.
CCS allows Level 2 charging by connecting to the upper circular receptacle only, and Level 3 charging with a plug that includes the DC terminals. SAE J1772 divides charging into four levels:
The SAE Combo or CCS is the de facto global standard for Level 2 and 3 charging and Audi, BMW, Daimler, Ford, General Motors, Porsche and Volkswagen jointly announced their support in 2011. The Chevy Spark was the first EV to feature the SAE Combo in 2013. There is now talk to discontinue the CHAdeMO. To maintain compatibility with EVs featuring CHAdeMO, newer Nissan Leafs include an SAE J1772 port to allow Level 2 charging. Some charger manufacturers, including ABB, offer both charging plugs at their “pumps.”
Tesla Motors does not follow standards easily, and they came up with their own system. Their exclusive Supercharger fills a depleted battery to 80 percent in 40 minutes and gives a driving range of 270km. (Charging from 80–100 percent doubles the time.) While Tesla was criticized by some for introducing their Superchargers, others say that Tesla is way ahead of the game and did not want to wait for the world to get its standards right. Tesla is in discussions with Nissan and BMW to offer their Supercharger standard to these EV makers as well. They are also working on an inter-protocol charging adapter that can support the CHAdeMO and SAE J1772 systems.
Charging the Tesla S 85 on a Supercharger begins at a voltage of about 375V and 240A, consuming 90kW. As the battery fills, the voltage rises to about 390VDC and the current drops to roughly 120A. The initial 90kW into the 85kWh battery has a charge rate that is only slightly higher than 1C. After a brief moment, the C-rate falls to a comfortable 0.8C, and then goes down further, avoiding harmful battery stress that is related to ultrafast charging .
Battling three incompatible charging systems was not the plan for EV makers, but it occurred in part by not accepting available technologies and delaying their own standards. Tesla jumped ahead with their own technology and is investing heavily into building Superchargers and offering free charging; other EV makers have followed by also making charging free, at least for now. The resulting incompatibility has similarities with the railroads industry in the 1800s, when railway companies ran their trains on different track gauges. LP vs. 45 RPM, as well as Sony Beta vs. VHS are other examples of similar situation.
BMW with its SAE Combo Charging system chose 24kW rather than the more common 50kW for the DC Fast Charger. They reckon that 24 kW is cheaper, lighter and easier to install than a 50kW system. While 50kW would charge faster, the benefit is for a brief moment only before the charge acceptance degrades. Scaling down is especially apparent with the smaller i3 battery, as well as packs that cannot take the ultra-fast charge due to advanced age and other anomalies. Tests show that the 50 kW charger fills a battery to 80 percent in about 20 minutes; the 24 kW charger does it in roughly 30 minutes.
Doubling the power does not cut the charge time in half and moving up in the pyramid has diminishing returns. The main reason for powerful chargers relates to battery size. The BMW i3 carries a 22kW battery compared to the monster 85kW in the Tesla S 85. Both charging systems keep the charge C-rate at about 1C during DC fast charging to moderate battery stress levels.
DC fast charging is more complex in that it must evaluate the condition of the battery and apply a charge level that the battery can safely absorb. A cold battery must be charged slower than a warm one; the charge current must also be reduced when cells develop high internal resistance and when the balancing circuit can no longer compensate for cell mismatch. DC Fast Charging is not designed to fill the battery completely but to allow the vehicle to reach the next charging station. Using Level 2 is the preferred routine for everyday charging.
Table 3 summarizes the charge levels and times with Levels 1, 2 and 3. The charge times may not fully agree with advertised rates as the calculations are based on charging an empty battery to fully SoC; some EV makers consider the battery charged when it reaches 80 percent. The charge time also shortens as the battery fades because there is less to fill.
Table 3?summarizes the charge levels and times with Levels 1, 2 and 3. The charge times may not fully agree with advertised rates as the calculations are based on charging an empty battery to fully SoC; some EV makers consider the battery charged when it reaches 80 percent. The charge time also shortens as the battery fades because there is less to fill.
Charge levels Level 1 Cordset Level 2 wall mounted
1.5kW 120VAC, 15A 6.6kWh* 240VAC, 30A**
Driving Range 8km (5 mi) per 1h charge 36km (22 mi) per 1h charge
4.4kWh?Toyota Prius 4h 1 h
16kWhChevy Volt 12 h 3h
22kWh?BMW i3 15 h 4 h
32kWh?Nissan Leaf 16 h 5 h
60kWh?Chevy Bolt 40 h 10 h
90kWh?Tesla S 85 60 h 15 h
Table 3?summarizes the charge levels and times with Levels 1, 2 and 3. The charge times may not fully agree with advertised rates as the calculations are based on charging an empty battery to fully SoC; some EV makers consider the battery charged when it reaches 80 percent. The charge time also shortens as the battery fades because there is less to fill.
Charge levels Level 3 DC Fast Charge 20-120kW 400–600VDC, up to 300A
Driving Range 110, 270km (70, 168 mi) per 30min charge
4.4kWh?Toyota Prius N/A
16kWh?Chevy Volt N/A
22kWh?BMW i3 24kW: To 80% in 30 min
32kWh?Nissan Leaf 50kW: To 80% in 20 min
60kWh?Chevy Bolt 50kW: To 80% in 60min
90kWh?Tesla S 85 120kW: To 80% in 40 min
Table 3:?Estimated charging times on Electric Vehicle Service Equipment (EVSE).?EVs carry the charging circuit on board and the most common is the 6.6kW system, Tesla has 10kW charger.
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