With the wider adaptation of electric vehicles (EV) by the general population, the Lithium-ion battery cell technology used in them becomes even more important. Lithium-ion batteries are a family of batteries that use different anode and cathode materials and each of them has its own advantages and disadvantages. The parameters considered to evaluate Li-ion battery technology are performance, safety, cost, and electric car range. There are five principle battery technologies used in EV’s and they are the following.
Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) – NCA
Lithium Nickel Cobalt Aluminum Oxide batteries have been around since 1999, and they are used for special applications. They have good specific energy i.e. energy per unit mass and good specific power i.e. power to weight ratio combined with long battery life span. This is an improvement over lithium nickel oxide battery, and adding aluminum gives it better stability. Its high energy and power densities along with a long life span makes it a good candidate for application in EV power trains. However, lower safety and higher cost compared to other EV battery technologies makes it a less attractive proposition.
Lithium Manganese Oxide (LiMn2O4) – LMO
Lithium Manganese spinel cathode type Li-ion batteries are one of the older forms, and they are still used today because of the lower internal resistance and better current flow management. They also have the added advantage of, better thermal stability and safety with moderate heat buildup. Due to these advantages, they can be fast-charged and allows high current discharge, making them useful in hybrid and electric vehicles. Moreover, their design flexibility allows engineers to modify for a longer life span, high specific power or high specific energy. Therefore, even though they offer moderate overall performance newer designs offer better safety, specific power, and life span.
Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) – NMC
Lithium Nickel Manganese Cobalt Oxide, Li-ion systems are one of the most successful technologies because they can be tailor-made to function as Power cells or Energy cells. This is because of combining nickel and manganese in the cathode where nickel has high specific energy but poor stability, whereas manganese forms a spinal structure giving low internal resistance but with low specific energy. Hence, combining them works by augmenting each other’s weaknesses. As a result, they are a popular choice in e-bikes, power tools, and other electric power trains.
There are different ratios of NMC cathode combinations resulting in varying cost and performance. The first type is, one-third nickel, one-third manganese and one-third cobalt achieving a ratio of 1-1-1 offering a blend that lowers the raw material cost especially of the expensive cobalt. The other type is 5parts Nickel, 3 parts Cobalt and 2 parts Manganese or NCM with a ratio of 5-3-2 and other combinations are also possible according to requirements.
Battery manufacturers are shifting to Nickel based cathode systems, and away from Cobalt systems due to the high cost of cobalt. Also, the NMC system has better performance with excellent specific energy coupled with a low rate of self-heatng. Moreover, Nickel, Manganese and Cobalt can be blended in a wide variety of ways to suit a range of applications in energy storage systems and automotive energy storage in a small electric carrequiring frequent cycling.
Lithium Titanate (Li2TiO3) – LTO
In LTO Li-ion batteries the graphite in the anode is replaced by Lithium Titanate and it forms a spinel structure, whereas the cathode is LMO or NMC. Because of this, it can be fast-charged, has a high current discharge capacity and has double the cycle count than an average Li-ion battery. Besides, it has better thermal stability at higher temperatures and zero-strain property over conventional cobalt-blended Li-ion with graphite anode. Due to the above mentioned qualities, it has excellent low-temperature performance, better safety and a long life span making them useful in the electric power train. However, it is expensive and has low specific energy compared to the NMC Li-ion battery system.
Lithium Iron Phosphate (LiFePO4) – LFP
Lithium Phosphate offers good electrochemical performance, with low resistance when used as cathode material for Li-ion battery system. Li-phosphate systems can tolerate fully charged conditions, can be kept at high voltage for a longer time and less stressed out than other Li-ion battery systems. As a tradeoff to these benefits, they have lower specific energy than cobalt blended batteries.
Similar to other batteries, cold temperature and elevated temperature reduce the service life of these batteries as well. However, they have higher self-discharge rates compared to other Li-ion batteries and can result in balancing issues when it ages. One of their biggest drawbacks is low moisture tolerance and this reduces the battery cycle. Even though they are tolerant of overcharging, have excellent safety, long life span, they have moderate specific energy with increased self-discharge. Because of this, they are primarily used for energy storage, portable and stationary charging requiring high load currents and endurance.
With the increasing number of manufactures entering into EV segment more advances and breakthroughs in Li-ion battery technology can be expected in the future.