Is the new NASA battery a game-changer?
Mirko Vojnovic
Innovative Technical Program/Project Manager | Expert in Analog, Digital, and Mixed Hardware Systems | 21 Patents Holder
NASA recently announced the development of a new type of solid-state battery that packs twice as much energy per kilogram weight compared to standard lithium-ion batteries. This technology, NASA claims, can then be used for electric airplanes. Many readers immediately started commenting on how this technology can be used for and even revolutionize electric cars. But is this so?
Let’s explore.
A brief recap of the article
NASA has developed a groundbreaking solid-state sulfur selenium battery that could transform air travel by replacing traditional combustion engines with electric power. Current air travel heavily relies on fossil fuels, contributing to significant pollution. Electric airplanes exist, but their limited speed and range are attributed to the energy density of existing batteries. To become airborne, a plane needs a battery with an energy density of about 800 watt-hours per kilogram, a far cry from the 250 watt-hours per kilogram offered by lithium-ion batteries.
NASA's Solid-state Architecture Batteries for Enhanced Rechargeability and Safety (SABERS) project has been working on creating a battery suitable for aircraft. The new sulfur selenium prototype battery not only offers enhanced safety, being solid-state and non-flammable but also boasts a remarkable energy density of 500 watt-hours per kilogram, double that of conventional lithium-ion batteries. Moreover, it can discharge energy ten times faster than other solid-state batteries. Despite the higher energy release causing elevated temperatures, the sulfur selenium battery can withstand heat twice as effectively as lithium-ion batteries.
The research team reduced battery weight by 40%, potentially allowing more batteries on an aircraft and thereby enhancing the fuel capacities of electric airplanes. While these developments are promising, it will take time before these batteries are commercially viable for air travel. Solid-state batteries are expensive to produce, and any component introduced in commercial flights must undergo rigorous testing for approval. Despite these challenges, the progress made signifies a significant leap in energy storage technology, offering the possibility of revolutionizing air travel in the future.
Selenium Sulfur Battery Prototype
A?carefully crafted selenium sulfur battery prototype has an?energy density?of 1000 watt-hours/kg. It is approximately 40% lighter than conventional?lithium-ion batteries.
NASA's prototypes use a?solid-state electrolyte.?The cathode is made from?sulfur?and?selenium. ?This cathode incorporates NASA-patented holey graphene technology, which provides a highly conductive, low-weight electrode scaffold. The anode is made from?lithium metal.?Lithium?ions are the?charge carriers.
As promising cathode materials in lithium-sulfur batteries, sulfur-rich selenium sulfide (SexS1?x)/pyrolyzed polyacrylonitrile (pPAN) composites, denoted as SexS1?x@pPAN, can effectively alleviate the problem of polysulfide dissolution and deliver reliable performances. Nevertheless, the material properties essential to the electrochemical performance of SexS1?x@pPAN still require further studies. Herein, SexS1?x@pPAN materials were prepared?via?a simple calcination strategy using the commercial selenium sulfide (SeS2) as the sulfur and selenium source.
The prototype exceeds 1100 Wh/kg at a discharge rate of 0.4C and 804 Wh/kg at a discharge rate of 1C.
NOTE:? The "C" in 1C represents the battery's capacity. For example, if you have a battery with a capacity of 1000 milliampere-hours (mAh), 1C would mean discharging the battery at a rate of 1000mA, which would completely deplete its entire capacity in one hour. Correspondingly, 0.4C would mean that the battery is discharged at the rate of 400mA.
NASA's prototypes can be stacked without a casing. Case-free stackability means the battery's cooling systems can be smaller and lighter. Operating conventional batteries at full power causes rapid temperature increases. The prototype can operate at much higher temperatures than conventional lithium-ion batteries. In addition, they are less affected by pressure changes, which occur during takeoff and landing.
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Is there a problem with Selenium?
Using rare elements for mass-produced batteries may pose a supply problem.
Selenium is?rare, composing approximately 90 parts per billion of the crust of Earth. It is occasionally found uncombined, accompanying native sulfur, but more often, it is found in combination with heavy metals (copper, mercury, lead, or silver) in a few minerals. Selenium is mainly obtained as a byproduct in copper production.
The other problem with the newly proposed battery design is the usage of selenium sulfide (SeS2) in its production.
The United States Environmental Protection Agency (EPA) has determined that selenium sulfide (SeS2) is a probable human carcinogen. Selenium sulfide is the only selenium compound shown to cause cancer in animals. Selenium sulfide (SeS2) has been linked with the occurrence of liver and lung tumors in mice and rats following oral exposure. As a result, selenium sulfide is a Group B2 carcinogen, as per the EPA classification. Elemental selenium has low toxicity following oral administration.
Is there a problem with Sulfur?
Sulfur is the tenth most abundant element by mass in the universe and the fifth most abundant on Earth. Though sometimes found in pure, native form, sulfur on Earth usually occurs as sulfide and sulfate minerals.
Lithium-sulfur batteries are one of the most promising energy storage devices due to their high specific capacity and abundant natural reserves. However, early lithium-sulfur (Li-S) batteries did not perform well because sulfur species (polysulfides) dissolved into the electrolyte, causing its corrosion. This polysulfide shuttling effect negatively impacted battery life and lowered the number of times the battery can be recharged.
In Lithium Selenium Sulfur batteries, a separator is used to prevent short circuits by keeping positive and negative electrodes apart. This separator is coated with a mixed SeS2/KB coating. KB refers to Ketjen Black, a well-known conductive carbon material often used in battery applications. This coating can effectively stop the polysulfide shuttle and improve the performance of lithium-sulfur batteries through the physical barrier of KB and the strong adsorption of SeS2 in synergy with each other. Theoretical calculations and experiments show that SeS2 has a strong adsorption effect on polysulfides. The lithium-sulfur battery equipped with a SeS2/KB separator has excellent electrochemical performance, with a capacity decay rate of only 0.047 % per cycle.
How sulfur will behave in this new sulfur selenium battery is still to be determined by extended battery life testing.
Conclusion
In the pursuit of efficient energy storage solutions, the development of selenium sulfur batteries has emerged as a promising avenue. The challenges associated with the intricate behavior of sulfur have been met with rigorous scientific exploration. The innovative approach involving advanced coatings on separators demonstrates significant progress in overcoming these challenges.
However, integrating selenium sulfur batteries into the mass production of EVs is challenging. One primary concern lies in the scalability of production processes. The specialized coatings and materials used in these batteries, while enhancing performance, often require intricate manufacturing techniques. Scaling up these processes to meet the demands of mass production, especially when dealing with potential health hazards of selenium sulfide, presents a substantial challenge. Additionally, the scarcity of selenium raises questions about the long-term feasibility of widespread battery production.
Addressing these challenges is paramount as the industry continues to invest in research and development. Solutions must be sought not only to enhance performance but also to streamline manufacturing processes and ensure a stable supply chain. Collaborative efforts between researchers, manufacturers, and policymakers are essential to overcoming these hurdles for the growing EV market. Only through concerted technical advancements and strategic planning can we pave the way for a sustainable future in electric vehicle technology.