LITHIUM POLYMER BATTERY WORKING & CHARACTERISTICS

Batteries are the first practical way of generating electricity and were invented by Alessandro Volta. Before generators came into the scene, batteries were the main source of electricity till the end of the The ancient electric cars also used the semi-sealed wet cells. This background of the batteries was the key for the development of the LiPo cells. The discovery of the Lithium Polymer Battery cells came because of the Lithium-ion and lithium-metal cells as they went to depth in the 1980s. A significant, yet remarkable milestone was the first commercial Li-ion cell of Sony in 1991. There was a revolution thereafter which introduced a pouch form of battery called “LiPo”.

A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), is a rechageable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. High conductivity semisolid (gel) polymers form this electrolyte. These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, such as mobile devices, radio-controlled aircraft and some electric vehicles.

Design origin and terminology

Lithium polymer cells have evolved from lithium-ion and lithium-metal batteries. The primary difference is that instead of using a liquid lithium-salt electrolyte (such as LiPF6) held in an organic solvent such as EC/DMC/DEC, the battery uses a solid polymer electrolyte (SPE) such as Polyethylene oxide (PEO), Poly(acrylonitrile) (PAN), poly(methl methacrylate) (PMMA) or poly(vinylidene fluoride) (PVdF).

In the 1970s the original polymer design used a solid dry polymer electrolyte resembling a plastic-like film, replacing the traditional porous separator that is soaked with electrolyte.

The solid electrolyte can typically be classified as one of three types: dry SPE, gelled SPE and porous SPE. The dry SPE was the first used in prototype batteries, around 1978.

A typical cell has four main components: positive electrode, negative electrode, separator and electrode. The separator itself may be a polymer, such as a microporous film of polyethylene (PE) or polypropylene (PP); thus, even when the cell has a liquid electrolyte, it will still contain a "polymer" component. In addition to this, the positive electrode can be further divided into three parts: the lithium-transition-metal-oxide (such as LiCoO2 or LiMn2O4), a conductive additive, and a polymer binder of poly(vinylidene fluoride) (PVdF). The negative electrode material may have the same three parts, only with carbon replacing the lithium-metal-oxide. The main difference between lithium ion polymer cells and lithium ion cells is the physical phase of the electrolyte, such that LiPo cells use dry solid, gel-like electrolytes whereas Li-ion cells use liquid electrolytes.

A Lithium-ion battery, also known as the Li-ion battery, is a type of secondary (rechargeable) battery composed of cells in which lithium ions move from the anode through an electrolyte to the cathode during discharge and back when charging.?

A lithium-ion polymer (LiPo) battery (also known as Li-pol, lithium-poly, and other names) is a type of Li-ion battery with a polymer electrolyte instead of a liquid electrolyte. All LiPo batteries use a high-conductivity gel polymer as the electrolyte. Lithium polymer cells have evolved from lithium-ion and lithium-metal batteries. The primary difference between lithium-ion and Li-pol is that instead of using a liquid lithium-salt electrolyte (such as LiPF6) held in an organic solvent, the battery uses a solid polymer electrolyte (SPE) such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) or polyvinylidene fluoride (PVdF). LiPos provide higher specific energies than other lithium batteries, often used in systems where weight is an important factor, such as mobile devices, drones, and some electric vehicles.

The cathode is made of a composite material (an intercalated lithium compound) and defines the name of the Li-ion battery cell. The anode is usually made out of porous lithiated graphite. The electrolyte can be liquid, polymer, or solid. The separator is porous to enable the transport of lithium ions and prevents the cell from short-circuiting and thermal runaway.

Chemistry, performance, cost, and safety characteristics vary across types of lithium-ion batteries. Handheld electronics mostly use lithium polymer batteries (with a polymer gel as electrolyte), a lithium cobalt oxide (LiCoO2) cathode material, and a graphite anode, which offer high energy density.

Li-ion batteries, in general, have a high energy density, no memory effect, and low self-discharge. One of the most common types of cells is 18650 battery, which is used in many laptop computer batteries, cordless power tools, certain electric cars, electric kick scooters, most e-bikes, portable power banks, and LED flashlights. The nominal voltage is 3.7 V.

Note that non-rechargeable primary lithium batteries (like lithium button cells CR2032 3V) must be distinguished from secondary lithium-ion or lithium-polymer, which are rechargeable batteries. Primary lithium batteries contain metallic lithium, which lithium-ion batteries do not.

Composition of Lithium Polymer Battery

A typical lithium-ion cell contains:

• Cathode: ?The cathode is the positive or oxidizing electrode that acquires electrons from the external circuit and is reduced during the electrochemical reaction. In the case of lithium batteries, cathode materials are generally constructed from LiCoO2 or LiMn2O4. For the cathode, it is important to hold a large amount of lithium without significant change in structure, have good chemical and electrochemical stability with electrolyte, be a good electrical conductor and diffuser of lithium ions, and be of low cost.
• Anode: The anode is the negative or reducing electrode that releases electrons to the external circuit and oxidizes during an electrochemical reaction. One of the most common anode materials used today is lithiated graphite, LixC6, which is composed of graphite sheets intercalated with lithium. New materials, such as those based on Silicon and other elemental blends, are being researched. Lithiated graphite has a unit cell with an HCP structure.
• Separator. A separator is a permeable membrane placed between a battery’s anode and cathode. The main function of a separator is to keep the two electrodes apart to prevent electrical short circuits while also allowing the transport of ionic charge carriers that are needed to close the circuit during the passage of current in an electrochemical cell. Commercially available liquid electrolyte cells use microporous polyolefin materials, such as polyethylene (PE) or polypropylene (PP). Separators in Li-ions have to be electrochemically and chemically stable relative to the electrolyte and electrode materials. Functional separators that use MOF-coated membranes to perform the dual functions of the electrolyte and separator are being developed to support the design of high-performance Li-metal batteries for high-energy systems in electric vehicles and electric aircraft.
• Electrolyte: The choice of electrolyte in all batteries is critical for performance as well as safety. Most of the electrolytes used in commercial lithium-ion batteries are non-aqueous solutions, in which lithium hexafluorophosphate (LiPF6) salt dissolved in organic carbonates, in particular, mixtures of ethylene carbonate (EC) with dimethyl carbonate (DMC), propylene carbonate (PC), diethyl carbonate (DEC), and/or ethyl methyl carbonate (EMC). A good electrolyte must have low reactivity with other cell components, high ionic conductivity, low toxicity, a large window of electrochemical voltage stability (0-5V), and be thermally stable.

Internal Structure of?a Lithium Polymer Battery

Lithium Polymer Battery is a combination of a cylindrical and a rectangular shaped structure. The internal structure is bounded spirally that helps in creating a partition between the anode and the cathode portions of the battery by putting a concise and highly porous polyethylene layer between the two.

Lithium Polymer batteries work on the principle of using liquid electrolyte solution, so a portion of the battery is filled with organic liquid electrolyte solution. Also, to protect the battery from unprecedented incidents such as short circuit or explosions, safety valves, and PTC components are installed.

Followed by these, cells are installed either in a series or parallel to one another. The number of cells varies depending on the total voltage requirement of the battery. The voltage of one cell is 3.6V and the total voltage of the battery is the sum of the voltage of the cells installed.

The working principle of polymer lithium battery There are two types of lithium ion batteries: liquid lithium ion batteries and lithium polymer batteries. Among them, the liquid lithium ion battery refers to a secondary battery with Li+ intercalation compound as the positive and negative electrodes. The positive electrode adopts lithium compound LiCoO2, LiNiO2 or LiMn2O4, and the negative electrode adopts lithium carbon intercalation compound LixC6. A typical battery system is:

(-) C | LiPF6—EC+DEC | LiCoO2 (+)

Positive electrode reaction: LiCoO2 = Li1-xCoO2 + xLi+ + xe-

Negative reaction: 6C + xLi+ + xe- = LixC6

Total battery reaction: LiCoO2 + 6C = Li1-xCoO2 + LixC6

The principle of lithium polymer battery is the same as that of liquid lithium, but the main difference is that the electrolyte is different from liquid lithium. The main structure of the battery includes three elements:

Positive electrode,

Negative electrode

Electrolyte

The so-called lithium polymer battery refers to the use of polymer materials as the main battery system in at least one or more of these three main structures. In the lithium polymer battery system developed, polymer materials are mainly used for the positive electrode and electrolyte.

Cathode materials include conductive polymers or inorganic compounds commonly used in lithium-ion batteries. The electrolyte may use a solid or gel polymer electrolyte or an organic electrolyte. Generally, lithium ion technology uses liquid or gel electrolyte, so it needs high strength. The secondary packaging contains flammable active ingredients, which increase weight and limit size flexibility.

The shape of the new generation of lithium polymer battery is theoretically achievable, and the shape is diversified, which improves the flexibility of battery shape design, so that it can meet product needs, and make some shape and capacity batteries for application equipment developers. Provide a high degree of design flexibility and adaptability in the power supply solution to maximize its product performance. At the same time, the unit energy of lithium polymer batteries is 10% higher than that of general lithium ion batteries. Compared with lithium-ion batteries, its capacity and cycle life have been greatly improved.

Electrical data Some benchmark data for ‘standard’ Li-polymer cells:

Voltage level: 3.6 to 3.7 V (average voltage at 50% discharge depth/0.2 C).

Charging: Constant I / constant V, maximum charging voltage 4.2 V, for special cells up to 4.35/4.4 V, max. charging current 1 C, for larger cells 0.5 C.

Discharge: Min. voltage 3.0 V, currents up to 1 C (in some cases 2 C).

Temperature range: Charge: 0°C to +45°C, with reduced currents below 15°C. Discharge: -20°C to +60°C with suitably reduced voltage levels and capacities at low temperatures.

Cycles: Charge/discharge at 0.5C/0.5C, 80% residual capacity after 500 cycles.

The energy density of LiPo batteries ranges from 140 - 200+ Wh/kg in terms of weight and 250 - 350+ Wh/L for volume.

Differences between Li-Ion and Li-Polymer (LiPo) Battery

Based on the composition of ions that carry the electrolyte materials, Lithium Batteries can be classified as Lithium Ion and Lithium Polymer. Following are the points of difference between the two:

• Li-ion batteries use liquid electrolytes whereas LiPo batteries use solid gel like polymers that substitute the electrolytes.
• Li-ion batteries are relatively cheaper because of the higher energy density.
• LiPo Batteries are safer and light weight.
• LiPo Batteries are rechargeable and have a longer span of life once charged as compared to the Li-ion batteries which tend to lose charge even when not in use.

Voltage and state of charge

The voltage of a single LiPo cell depends on its chemistry and varies from about 4.2 V (fully charged) to about 2.7–3.0 V (fully discharged), where the nominal voltage is 3.6 or 3.7 volts (about the middle value of highest and lowest value) for cells based on lithium-metal-oxides (such as LiCoO2). This compares to 3.6–3.8 V (charged) to 1.8–2.0 V (discharged) for those based on lithium-iron-phosphate (LiFePO4).

The exact voltage ratings should be specified in product data sheets, with the understanding that the cells should be protected by an electronic circuit that won't allow them to overcharge nor over-discharge under use.

LiPo battery packs, with cells connected in series and parallel, have separate pin-outs for every cell. A specialized charger may monitor the charge on a per-cell basis so that all cells are brought to the same state of charge (SOC).

Applying pressure on LiPo cells

Unlike lithium-ion cylindrical and prismatic cells, which have a rigid metal case, LiPo cells have a flexible, foil-type (polymer laminate) case, so they are relatively unconstrained. Moderate pressure on the stack of layers that compose the cell results in increased capacity retention, because the contact between the components is maximised and delamination and deformation is prevented, which is associated with increase of cell impedance and degradation.

Applications

LiPo cells provide manufacturers with compelling advantages. They can easily produce batteries of almost any desired shape. For example, the space and weight requirements of mobile devices and notebook computers can be met. They also have a low self-discharge rate, which is about 5% per month.

Drones, radio controlled equipment and aircraft

LiPo batteries are now almost ubiquitous when used to power commercial and hobby drones (unmanned aerial vehicles), radio-controlled aircraft, radio-controlled cars and large scale model trains, where the advantages of lower weight and increased capacity and power delivery justify the price. Test reports warn of the risk of fire when the batteries are not used in accordance with the instructions.

The voltage for long-time storage of LiPo battery used in the R/C model should be 3.6~3.9V range per cell, otherwise it may cause damage to the battery.

LiPo packs also see widespread use in airsoft, where their higher discharge currents and better energy density has very noticeable performance gain (higher rate of fire).

Personal electronics

LiPo batteries are pervasive in mobile devices, power banks, very thin laptops computers, portable media players,, wireless controllers for video game consoles, wireless PC peripherals, electric cigarettes, and other applications where small form factors are sought and the high energy density outweighs cost considerations.

Electric vehicles

Hyundai uses this type of battery in some of its battery electric and hybrid vehicles, as well as Kia Motors in their battery electric Kia Soul. The Bolloré Bluecar, which is used in car sharing schemes in several cities, also uses this type of battery.

Uninterruptible power supply systems

Lithium-ion batteries are becoming increasingly more commonplace in Uninterruptible power supply (UPS) systems. They offer numerous benefits over the traditional VRA battery and with stability and safety improvements confidence in the technology is growing. Their power to size and weight ratio is seen as a major benefit in many industries requiring critical power back up including data centers where space is often at a premium. The longer cycle life, usable energy (Depth of discharge), and thermal runaway are also seen as a benefit for using Li-po batteries over VRLA batteries.

Jump starter

The battery used to start a vehicle engine is typically 12V or 24V, so a portable jump starter or battery booster uses three or six LiPo batteries in series (3S1P/6S1P) to start the vehicle in an emergency, instead of the other jump-start methods . The price of a lead-acid jump starter is less but they are bigger and heavier than comparable lithium batteries, and so such products have mostly switched to LiPo batteries or sometimes lithium iron phosphate batteries.

LiPo Battery Safety

LiPo batteries have a greater risk of fire and swelling than older technologies due to their internal chemistry. Operating the battery at or beyond its limits can lead to the accumulation of oxygen atoms and build up of Lithium Oxide (Li2O), which creates greater internal resistance. More internal resistance leads to more heat, and the thermal runaway cycle begins.

Once the battery pack starts to swell, this is a good indication that the battery is damaged beyond repair or has reached the end of its life cycle. Using it beyond this point will further increase its temperature and potentially lead to a fire.

For common LiPo batteries, the nominal or average voltage is 3.7 V/cell with a maximum voltage of 4.2 V/cell. After the cell is fully charged, it will briefly provide 4.2 V before dropping to 3.7 V for most of the battery life. It becomes dangerous to discharge the battery after the cell voltage has dropped below 3.2 V because the resistance in the battery increases, causing it to heat up and swell, resulting in damage.?

To avoid this, many motor manufacturers have added a low voltage cutoff (LVC) to their controls, which stops them from drawing charge after a certain threshold, usually in the range of 3.2 - 3.4 V. Overcharging a LiPo battery is equally dangerous and can result in overheating and even an explosion.

Lithium ion battery fires are classified as Class B flammable liquid fires, so a type ABC or BC fire extinguisher should be used to put them out. These extinguishers stop the chemical reaction from occurring and eventually put out the fire.

Polymer electrolytes

Polymer electrolytes can be divided into two large categories: dry solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE). In comparison to liquid electrolytes and solid organic electrolytes, polymer electrolyte offer advantages such as increased resistance to variations in the volume of the electrodes throughout the charge and discharge processes, improved safety features. excellent flexibility and processability.

Solid polymer electrolyte is initially defined as a polymer matrix swollen with lithium salts, which is now referred to as dry solid polymer electrolyte. Lithium salts are dissolved in the polymer matrix to provide ionic conductivity. Due to its physical phase, there is poor ion transfer resulting in poor conductivity at room temperature. In order to improve the ionic conductivity at room temperature, gelled electrolyte is added resulting in the formation of GPEs. GPEs are formed by incorporating an organic liquid electrolyte in the polymer matrix. Liquid electrolyte is entrapped by a small amount of polymer network, hence the properties of GPE is characterized by properties between those of liquid and solid electrolytes. The conduction mechanism is similar for liquid electrolytes and polymer gels, but GPEs have higher thermal stability and low volatile nature which also further contribute to safety.

Lithium cells with solid polymer electrolyte

Cells with solid polymer electrolytes have not reached full commercialization and are still a topic of research. Prototype cells of this type could be considered to be between a traditional lithium-ion battery (with liquid electrolyte) and a completely plastic, solid-state lithium-ion battery.

The simplest approach is to use a polymer matrix, such as polyvinylidene fluoride (PVdF) or poly(acrylonitrile) (PAN), gelled with conventional salts and solvents, such as LiPF6 in EC/DMC/DEC.

Nishi mentions that Sony started research on lithium-ion cells with gelled polymer electrolytes (GPE) in 1988, before the commercialization of the liquid-electrolyte lithium-ion cell in 1991. At that time polymer batteries were promising and it seemed polymer electrolytes would become indispensable. Eventually, this type of cell went into the market in 1998. However, Scrosati argues that, in the strictest sense, gelled membranes cannot be classified as "true" polymer electrolytes, but rather as hybrid systems where the liquid phases are contained within the polymer matrix. Although these polymer electrolytes may be dry to the touch, they can still contain 30% to 50% liquid solvent. In this regard, how to really define what a "polymer battery" is remains an open question.

Other terms used in the literature for this system include hybrid polymer electrolyte (HPE), where "hybrid" denotes the combination of the polymer matrix, the liquid solvent and the salt. It was a system like this that Bellcore used to develop an early lithium-polymer cell in 1996, which was called "plastic" lithium-ion cell (PLiON), and subsequently commercialised in 1999.

A solid polymer electrolyte (SPE) is a solvent-free salt solution in a polymer medium. It may be, for example, a compound of lithium bis(fluorosulfonyl)imide (LiFSI) and high molecular weight poly(ethylene oxide) (PEO), a high molecular weight poly(trimethylene carbonate) (PTMC), polypropylene oxide (PPO), poly[bis(methoxy-ethoxy-ethoxy)phosphazene] (MEEP), etc.

PEO exhibits most promising performance as a solid solvent for lithium salts, mainly due to its flexible ethylene oxide segments and other oxygen atoms that comprise strong donor character, readily solvating Li+ cations.

Other attempts to design a polymer electrolyte cell include the use of inorganic ionic liquids such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) as a plasticizer in a microporous polymer matrix like poly(vinylidene fluoride-co-hexafluoropropylene)/poly(methyl methacrylate) (PVDF-HFP/PMMA).

What is the spec of a LiPo battery?

A Lipo battery is constructed from separate cells, all connected to form the specific battery. One Lipo cell has a nominal voltage of 3.7V. When connecting these in series, the voltage increases, meaning you get 7.4V for a 2 cell battery, 11.1V for a 3 cell battery, 14.8V for a 4 cell battery etc.

What is the maximum voltage of a lithium polymer battery?

3.2v to 4.2v

The usable voltage range for a standard lipo battery cell is 3.2v to 4.2v. Any lower than 3.2v and the battery may be permanently damaged. Any higher than 4.2v and you significantly increase the risk of a battery bursting into flames.

A lithium polymer battery used to power a smartphone

Specific energy 100–265 W·h/kg (0.36–0.95 MJ/kg)

Energy density 250–670 W·h/L (0.90–2.63 MJ/L)

1. Voltage: The nominal single-cell voltage for Li-polymer cells is 3.6V, on average; the charge cut-off voltage is 3.0V; and the maximum charging voltage is 4.20V. On the market there are also cells with charging voltages of 4.35V and 4.40V. The required voltage should be defined. If a higher voltage is required, a series connection is possible. The mean voltages can then be represented by the factor N x 3.6V. This information is needed to design the electronics safely. For higher capacities, cells can also be connected in parallel. -

2. Currents: For discharging, the mean continuous currents should be given. The maximum pulse currents and the pulse lengths must be specified. The inrush currents and their lengths of duration in applications must be taken into account. Ideally, the current power load profiles of the application, taking temperatures into account as well, would be presented. The field of application and the prevailing temperature and environmental conditions play an important role. Low temperatures and higher currents lower the voltage level. The relationship between charge and required or desired currents must be taken into account. In principle, charging proceeds by the technical principle "constant current/constant voltage".

3. Temperature: The temperature conditions in the application area as well as during charging and discharging must be determined. This is necessary for cell selection and for possible adjustments. By default, Li-polymer batteries of today meet specifications for, among others, the following temperature ranges: a. Charging: 0°C to +45°C b. Discharging: -20°C to +60°C High and low temperatures affect the capacity. This must also be taken into consideration. For an extended temperature spectrum, special high-temperature cells, for example, are available. Similarly, some cells have been developed for lower temperatures or for higher currents.

4. Dimensions: To lay out the batteries correctly, the supplier must know the maximum dimensions of the installation space. Here it should be noted that Li-ion and Li-polymer cells swell up slightly over time. Over their lifetime, they can grow up to 10% thicker. The cause of this is related to chemical degradation. Even the degree of charge (30% or 60% on delivery and 100% after a full charge) affects the cell thickness and therefore the dimensions of the installation space. When specifying the maximum thickness after cycles, the degree of charge is always assumed to be full.

5. CAPACITY Battery capacity is given in mAh or Ah and can be used to estimate your flight time?(more on this later). Battery capacity is more specifically defined as the number of hours of current or power the battery can provide. Common units are the ampere-hour (Ah) and the watt-hour (Wh). If a battery has a capacity of 1 Ah, you can draw 1 A of current for one hour. If the capacity is 1 Wh, the battery would provide 1 W of power for one hour.

6. Safety: The parameters for the design of the protection electronics or safety circuit (Battery Management System = BMS, Protection Circuit Module = PCM) are of great importance. Deep discharge, short circuits and excessive currents and overcharging must be prevented. In this context, the supplier needs information about the current profile and the potential voltages desired during switch-off. The internal resistance of the battery should be known. For multi-cell batteries, a BMS with fuel gauging, balancing and communication via SMBus and I2C is recommended.

7. Other information: For softpacks that have protection circuit modules (PCM), cables and plugs, the parameters of the PCM should be precisely defined. (See point 6.) Alternatively, a standard PCM can be selected. It should also be specified whether a Negative Temperature Coefficient (NTC) should be taken into account. Standard parameters for resistance and temperature are: 10 kOhm 1%, Beta value 3435 1%. Alternatives can also be specified. Information about the cables (AWG, UL) and c

How to Read a LiPo Battery

LiPo batteries are labeled with a few important pieces of information, including: battery capacity, voltage, cell configuration and discharge rate

The advantages and disadvantages of lithium polymer battery

LITHIUM-ION POLYMER

Lithium ion polymer batteries are characterized by their:

• High energy density
• Easily customizable appearance & flexible design
• Small size & lightweight
• Good safety

Lithium ion polymer battery is one of lithium ion battery. But compare to liquid li-ion battery, it has high energy density, miniaturization, ultra-thin, lightweight, and also? high security and low cost, and other obvious advantages, is a new type of battery. here we summarize the advantages and disadvantages of lithium polymer batteries.

Advantage:

1.???? Safety performance is good

Lithium-ion polymer battery with aluminum composite flexible packaging in the structure, different from liquid metal case of batteries, in the event of a safety hazard, liquid batteries easy explosion, but lithium ion polymer battery most has meteorism.

2.???? More thin thickness, and can do more thin

Ultra-thin, batteries could assemble into a credit card. Ordinary liquid lithium battery use custom shell, after the plug is the method of the cathode, thickness of 3.6 mm the following technical bottlenecks, polymer batteries, there is no this problem, the thickness can be below 1 mm, can meet the demand of current mobile direction.

3.???? Light-weight

Lithium polymer battery using polymer electrolyte ?without metal shell as a protective outer packing. Same specifications of steel shell polymer battery weight is equal capacity lithium electric light 40%, a 20% aluminum battery light.

4.???? Big capacity

Lithium Polymer battery is the same size of the steel shell battery, the capacity is 10 to 15% more than high aluminum battery 5 ~ 10%, be the first choice of the color screen mobile phones and MMS, now on the market a new color and MMS phones are mostly used lithium polymer batteries

5.???? Small internal impedance

The internal resistance of the polymer batteries is less than liquid batteries, the current domestic internal resistance of the polymer batteries can even do below 35 m Ω, greatly reduced the battery power consumption, extend the standby time of mobile phone, can reach with international level. The support of large discharge current polymer li-ion battery, the ideal choice of remote control model to become the most promising alternative products of nimh batteries.

6.???? Shape can be customized

Manufacturers no need to limited to the standard shape, able to make the appropriate economic size. Lithium Polymer battery can increase or decrease the thickness of the batteries according to the customer's demand, the development of new batteries models, price cheap, open mold cycle is short, some even can be tailored according to the mobile phone shape, to make full use of the battery shell space, improve battery capacity

7.???? Better discharge characteristic

Li-Polymer battery using gel electrolyte, compared to liquid electrolyte, colloid electrolyte with smooth discharge characteristics and higher discharge platform.

8.???? Simple PCM design

Because of using polymer materials, which made batteries no fire, no explosion, batteries itself has enough safety, therefore, polymer battery protection circuit design can consider omitting PTC and fuse, thereby saving the cost of batter

Specific charge/discharge characteristics of a Lithium- Polymer(Li- Po) battery through experimental testing of a remote triggered Li- Po Battery.??Background and Theory

Lithium polymer batteries are??rechargeable battery?of?lithium-ion?technology in a?pouch format. Unlike cylindrical and prismatic cells, LiPos come in a soft package or pouch, which makes them lighter but also less rigid.

Each type of battery chemistry, whether it be Lithium-polymer, Lithium ion, nickel metal hydride, or others has specific characteristics that define its electrical operation, size, weight and other properties.

Charge and discharge curves - Lithium-polymer batteries have unique charge and discharge curves (voltage vs. time during charging and discharging). Amongst others, these curves can be used for:?

Quickly determining the State of Charge (SOC) of the battery based on its voltage, as used daily by billions of people all over the world to see how much battery is left on a laptop or mobile phone,

Determining the low-voltage cutoff at which?a battery voltage will fall below the value required for operating the electronics of portable devices,

Determining algorithms for safe charging and discharging since over-charging or over-discharging batteries can reduce the lifetime of batteries, damage them, or even lead to fire and explosion,

Understanding the float behavior of batteries, or how the voltage of a battery changes when a charge or discharge process is stopped.

Energy capacity vs. discharge rate is an?important design parameter for electric and hybrid vehicles with Lithium batteries, electric power tools, and portable electronics devices. The energy capacity vs. discharge rate affects the weight, size, and cost of a battery and device. Amongst others, this information is useful for:

Sizing a battery for an application, by understanding the usable capacity of the battery which changes as a function of the discharge rate,

Identifying the duration for which a device can operate off battery power by using the formula:?Time = Energy / Power = ((State of Charge of the battery in percentage) (Total Full Energy of the battery)) / (Loaded Voltage Current)

The life of LiPo battery vs DOD and discharge rate is shown in the below graph:

Introduction:

A battery is an electrochemical device in which electrical energy is converted and stored in chemical form for storage. The chemical energy can then be easily reconverted into electrical energy.

Two primary types of chemical batteries exist: Primary and secondary. A primary battery is not normally rechargeable and is designed to only last one discharge cycle, after which it must be replaced. Secondary batteries are rechargeable. They can be discharged and recharged repeatedly.

As we are all aware, a significant number of the modern electronic equipment we take for granted every day, such as mobile phones, laptop computers, music players, cameras and countless others are powered from rechargeable batteries.

Basic Battery Operation

Two electrodes (positive and negative, made of two chemically different materials) are separated by an electrolyte - a solution that easily conducts ions (charged particles)

An Electrical Load is applied to the cell, causing the cell to discharge.

• Electrons are pulled from the positive terminal of the battery through a chemical reaction between the ? positive terminal and the electrolyte
• Electrons flow through the electrical load
• Electrons return to the negative terminal
• Electrons are put back into the negative side of the battery through a chemical reaction between the ? ? negative terminal and the electrolyte
• Battery becomes discharged when the chemical reactions are not possible any longer ?￠a??a€? the ? ? ? ? chemicals have all been transformed into other chemicals that do not support electron producing ? chemical reactions

Rechargable Batteries

In many batteries, the chemical reactions are reversible when voltage is applied to the battery (Charging). Rechargeable batteries are also called Secondary batteries, as opposed to Primary batteries, which are single use only.

?More Battery Basics

The voltage of an individual cell is fixed by battery chemistry.

The current is a function of the rate of chemical reaction in the battery, which is characterized by the Equivalent Series Resistance (ESR). Then from Ohm law, we can see that for a fixed voltage, the current is controlled by the resistance.

?Current = Voltage / Resistance = V / ESR

The capacity of the battery is defined as

Capacity = (Voltage) * (Amp-hours).

?The Amp Hours is the number of Amps that a battery can produce for an hour OR? the number of hours a battery can produce one Amp.

For example, if the battery has a 10 Ah (Amp hour) rating, it can provide:1 Amp for 10 hoursOR10 Amps for 1 hour.The capacity is usually defined at a standard charge/discharge rate (C-rate), which is the the charge/discharge rate (in Amps) that the battery will provide for the specified # of hours. For example, under discharge, C/10 = 5.2 A implies that the battery will provide 5.2 Amps for 10 hours.

The capacity usually increases for lower charge/discharge currents and decreases for higher charge/discharge currents.

?Series and Parallel Connection

• When connected in series, the battery voltages add

Positive terminals of one battery connected to the negative of another, and so on

• When connected in parallel, the battery currents add

Positive terminals of all the batteries connected together, negatives all connected together

• Multiple cells are connected in?series?to obtain higher voltages

Connecting in Series (Double voltages, Same capacity (Ah) )

Series connection adds the voltage of two batteries, keeps the capacity as same (Ah).

For Example,

Two sets of batteries already connected in parallel are joined them together to form a series produces 12 V and 20 Ah.

?The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination.?

The lithium-polymer differentiates itself from conventional battery systems in the type of electrolyte used. This electrolyte resembles a plastic like film that does not conduct the electricity but allows the ion exchange. Since the metal casing is absent, it is much lighter than the Lithium ion battery.?

The lithium-polymer electrochemistry currently covers a wide range of active materials such as LiCoO2, LiNiO2, and its Co doped derivatives. Harding uses LiCoO2 chemistry?

Charging & Discharging Chemical Reaction

When Lithium Polymer cells are first charged, lithium ions are transferred from the layers of the lithium cobaltite to the carbon material that forms the anode.?

LiCoO2?+ 6C --> Li1-x?CoO2?+ LixC6?

Subsequent discharge and charge reactions are based on the motion of lithium ions between anode and cathode.

Li1-x?CoO2?+ LixC <----> Li?1-x +dx?CoO?2?+ Lix-dx?C

During charge/discharge Li+ ions are transported back and forth between two insertion electrodes.

Overcharge

A strict charging regime is necessary to properly and safely charge Lithium Polymer batteries. Most batteries contain a protective circuit to prevent overcharge and over discharge. This circuit limits the charge voltage to a maximum 4.2 Volts. The circuit also contains a thermal sensor, which disconnects charge if the temperature reaches 90 °C . If a cell is inadvertently overcharged, the cell may heat up and vent with a flame.?

LITHIUM POLYMER BATTERY'S SPECIFICATION PROVIDED BY MANUFACTURER

Battery Specification 3.7V 1200mAh

Lithium ion Polymer Battery Pack LP503759 1200mAh 3.7V with Protection Circuit Module(PCM). This data sheet describes the requirements and properties of lithium ion polymer rechargeable battery pack manufactured by LiPol Battery Co., Ltd-China

A Lipo battery is constructed from separate cells, all connected to form the specific battery. One Lipo cell has a nominal voltage of 3.7V. When connecting these in series, the voltage increases, meaning you get 7.4V for a 2 cell battery, 11.1V for a 3 cell battery, 14.8V for a 4 cell battery etc.

Electrical Specification

Rated Capacity: 1200mAh min, 1250mAh typ

Nominal Voltage: 3.7 V

Watt-Hour Rating: 4.4 Wh

Max. Operating Voltage Range: 2.75 V to 4.2 V

Max. Charge Voltage: 4.2V±50mV

Max. Charge Current: 600 mAh

Max. Continuous Discharge Current: 300 mAh

Discharge Cut Off: 2.75 V

Internal Impedance: < 200 mohm

Expected Cycle Life @(0.5C/0.5C) @23±5° 500 cycles

Protection

Overcharge Detection: 4.275 ±50mV (0.7 to 1.3sec. delay, release 4.275V ±50mV)

Overdischarge Detection:2.75V ±50mV (14 to 26msec. delay, resume 2.50V ±50mV)

Overcurrent Detection: 2A to 2.5A (8 to 16msec. delay)

Ambient Conditions

Charge Temp. Range: 0 to +45 C

Discharge Temp. Range: -20 to + 60 C

Storage Temp. Range: 1 year at - 20 to + 30 C > 70%

3 months at - 20 C to + 45 C

1 month at - 20 C to + 60 C > 70%