Li-ion Batteries for EV and What to Improve?

| Jerry Huang

There are two main types of lithium batteries: Li-ion battery and lithium metal battery. So far the Li-ion batteries used for EVs are LFP (LiFePO4), NCM (LiNiMnCoO2), NCA, LCO (LiCoO2), LNO (LiNiO2), LMO (LiMn2O4, Li2MnO3) and LTO batteries.

Lithium metal battery was first invented by M. S. Whittingham in 1970, while this outdated type of lithium metal battery is usually not rechargeable. While a novel rechargeable Lithium metal battery, invented by SolidEnergy Systems that have overall advantages of light weight, double energy density of current li-ion battery, long life, reasonable cost and safer than ever, has come to a big scale application. Hopefully this will be the latest and next prevailing generation of lithium battery.

Wikipedia quote: Lithium-ion battery or Li-ion battery (LIB) is a type of rechargeable battery. Lithium-ion batteries are commonly used for portable electronics and electric vehicles and are growing in popularity for military and aerospace applications. A prototype Li-ion battery was developed by Akira Yoshino in 1985, based on earlier research by John Goodenough, Stanley Whittingham, Rachid Yazami and Koichi Mizushima during the 1970s–1980s, and then a commercial Li-ion battery was developed by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991.

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use lithium polymer batteries (with a polymer gel as electrolyte) with lithium cobalt oxide (LiCoO2) as cathode material, which offers high energy density, but presents safety risks, especially when damaged. Lithium iron phosphate (LiFePO4), lithium ion manganese oxide battery (LiMn2O4, Li2MnO3, or LMO), and lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) offer lower energy density but longer lives and less likelihood of fire or explosion. Such batteries are widely used for electric tools, medical equipment, and other roles. NMC and its derivatives are widely used in electric vehicles.

Research areas for lithium-ion batteries include extending lifetime, increasing energy density, improving safety, reducing cost, and increasing charging speed, among others. Research has been under way in the area of non-flammable electrolytes as a pathway to increased safety based on the flammability and volatility of the organic solvents used in the typical electrolyte. Strategies include aqueous lithium-ion batteries, ceramic solid electrolytes, polymer electrolytes, ionic liquids, and heavily fluorinated systems. (Wikipedia unquote)

The main lithium batteries for EV are NCA and NCM, with LFP as a minor option in world’s market in 2020. The energy density of an LFP single cell is usually about 110Wh/kg, very few can make it 190Wh/kg; while practically the energy density of an NCM single cell battery can be 200Wh/kg and hopefully it could be 300Wh/kg soon; but for NCA battery it can be around 300Wh/kg today. Tesla applies mostly NCA batteries from Panasonic and LG Chem, also NCM and LFP batteries from CATL in its global supply chain today.

LFP battery has an advantage of low cost and much better safety properties than NCA/NCM battery, while its comparatively low energy density is clearly a disadvantage.

For comparison of NCA and NCM battery, research and market application have shown that NCA lithium battery is lower in cost with less cobalt content, much better calendar life, much less degradation than NCM lithium battery, although NCA’s cycle life is less than that of NCM battery. Some of the NCA battery is used in solar energy storage in outer space with a lifespan as long as twenty years! The disadvantage of NCA battery rests on its safety factor, so far it is not as safe as NCM and LFP in high temperature circumstances. However researchers believe that NCA will become the first choice for EV in the near future as its safety and production improve.

Note: As basic lithium salts, lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium chloride, lithium acetate and lithium fluoride can be converted into various lithium compounds for electrolytes in lithium-ion battery manufacture. Find Poworks lithium salts here.