Power battery cathode material dispute

New energy vehicles are the direction of automobile development. Power batteries are the heart of new energy vehicles. Their technological level and industrial development are of great significance for the large-scale application of electric vehicles. With the increasing concentration of the power battery industry and the gradual maturity of the technology route, the future power battery will develop toward a safer, longer life, and faster charging speed.

At present, there are many technical routes for power battery cathode materials, mainly focusing on lithium iron phosphate, ternary materials lithium cobalt oxide and lithium manganate. Then with the continuous advancement of technology, which kind of cathode material technology route is in the power battery Is the field more competitive?

1, lithium iron phosphate

Due to its good safety, long cycle life, abundant raw material resources and no environmental pollution, lithium iron phosphate has been sought after by many power battery manufacturers headed by BYD. The success of China's lithium iron phosphate technology route is unexpected for foreign mainstream power battery manufacturers.

There are many advantages of lithium iron phosphate, but the disadvantages are also obvious. In addition to the extremely poor cycle performance at low temperatures, the main drawback is its low conductivity and tap density, and its energy density is only 120-150wh/kg. At the end of 2016, the state introduced subsidies for power batteries according to energy density, which may hinder the development of lithium iron phosphate power batteries. However, the use of lithium iron phosphate on electric buses is irreplaceable, and the market space is still broad in the future.

At present, battery manufacturers using lithium iron phosphate include BYD, Peking University First, Shenzhen Water Code and Hefei Guoxuan and so on. In the future, lithium iron phosphate will develop in the direction of increasing energy density. It is conceivable to use additives such as graphene and carbon nanotubes to increase the rate capacity, or to increase the voltage with lithium manganese iron phosphate, thereby increasing the energy density by 15-20%.

2. Lithium cobaltate and lithium nickelate

Lithium cobaltate is the first lithium battery cathode material for commercial application. The first generation of commercial lithium ion battery is the lithium cobalt oxide lithium ion battery that SONY introduced to the market in 1990, and then it has been widely used in consumer products application.

However, the biggest disadvantage of lithium cobaltate is that the mass specific capacity is low, and the theoretical limit is 274mAh/g. For structural stability considerations, only 137mAh/g can be achieved in practical applications. At the same time, due to the relatively low reserves of cobalt on the earth, the cost of lithium cobalt oxide is high, and it is difficult to spread in large scale in the field of power batteries.

Similar to lithium cobaltate, the ideal lithium nickelate is a hexagonal layer structure of α-NaFeO2 type. The theoretical capacity of lithium nickelate cathode material is 275mAh/g, which can reach 180-200mAh/g, and the average lithium insertion potential is about 3.8V. Compared with lithium cobaltate, nickel has a larger reserve than cobalt and is relatively cheaper. However, lithium nickelate is difficult to synthesize and has poor cycle performance. Pure phase lithium nickelate is not practical.

3. Lithium manganate

Lithium manganate is very close to the currently used lithium cobalt oxide and ternary materials. Its battery production process is very mature. The power battery production line is basically compatible with the existing production line. In particular, Japan and South Korea intend to use 18650 type batteries to form a power battery module. The technical idea makes the production of lithium manganate power battery easier to achieve.

The biggest disadvantage of lithium manganate is its poor temperature cycling performance, but it also has its own unique advantages compared to lithium iron phosphate.

(1) The volumetric specific energy of lithium manganate is better than lithium iron phosphate

The capacity of lithium manganate is about 25% lower than that of lithium iron phosphate, but its voltage is 15% higher than lithium iron phosphate, and the compaction density of lithium manganate is about 40% higher. Therefore, the volume specific energy of lithium manganate is higher than that of iron phosphate lithium 25-30%.

(2) The consistency of lithium manganate is better than that of lithium iron phosphate

Since the lithium manganate product does not contain carbon, the performance parameters of the product are stable and the consistency is very favorable for the production of the power battery.

At present, Sonny of Japan, China CITIC Guoan, Suzhou Xingheng and other enterprises are developing and producing lithium manganate power batteries, and there will be a good market in the future in low-speed electric vehicles and electric vehicles with low cruising range.

4. Ternary materials

The ternary materials are mainly nickel-cobalt lithium aluminate (NCA) and nickel-cobalt-manganate (NCM). Among them, NCA is the material with the highest specific capacity among commercial cathode materials.

Nickel cobalt cobalt aluminate (NCA)

Because Co and Ni have similar electronic configurations, similar chemical properties, and small differences in ion size, lithium nickelate and lithium cobaltate can be equivalently substituted to form a continuous solid solution and maintain a layered α-NaFeO 2 structure, in order to obtain A more stable high-nickel solid solution material, in addition to the addition of cobalt, can further improve the stability and safety of the material, thus forming a lithium cobalt aluminum aluminate ternary material.

Although NCA has a high specific capacity, its shortcomings are also obvious. The future development trend is to develop high-nickel low-cobalt NCA to reduce cost and increase capacity; and to develop high-pressure real NCA to increase the volume ratio; in addition, the coating process is used to reduce NCA sensitivity to humidity.

At present, the United States Tesla is using NCA cathode material power battery, the technology is in the leading position. Japan's 18650battery with NCA and silicon carbon anode combination has a capacity of up to 3500mAh and a cycle life of more than 2000 times. Various indications are that NCA is positive. Materials are highly competitive in power battery applications.

Lithium nickel cobalt manganese oxide (NCM)

Nickel-cobalt-manganese hydride (NCM) ternary material has the advantages of high specific capacity, long cycle life, good safety and low price, but it also has the disadvantages of relatively low platform and low initial charge and discharge efficiency.

Currently, nickel-cobalt-manganese hydride (NCM) is mainly used in South Korea LG, Zhejiang Weihong Power and Zhuhai Yinlong. In the future, the development trend of NCM is mainly to produce low-cobalt layered ternary materials. The main reason is that cobalt is a scarce resource. Reducing the amount can reduce the cost; the other direction is to develop a high-nickel layered ternary material. Although the high-nickel system is difficult to synthesize and is prone to lithium-nickel mixing, the increase in nickel content can significantly increase the gram capacity, and the high-nickel system is the power, one of the ideal materials for batteries. In addition, NCM should also pay attention to the problem of water absorption of materials.

At this stage, some domestic manufacturers adopt the technical route of ternary NCM/lithium titanate anode combination to avoid the problem of poor safety and cycleability caused by the formation of lithium dendrites that may exist in the carbon anode. The power battery produced by this module has the characteristics of good safety, high charge-discharge rate and long cycle life (up to 5000-10000 times), and thus has attracted much attention in the field of power batteries.

Sum up

Policy trends, the future power battery industry market is broad, the average annual growth rate of new energy vehicle power battery market in the three years can reach about 50%, but the entire battery industry is fiercely competitive, industry integration is continuing, the power battery market demand will further Concentrate on the dominant companies.

In terms of technical routes, the current cathode materials for commercial lithium-ion power batteries are mainly lithium manganate (LMO), lithium iron phosphate (LFP), and ternary materials (NMC). Each material has its own advantages and disadvantages, and it has its own application areas and market needs. Among them, power tools, HEVs and electric bicycles are the main application areas of LMO. New energy public transportation buses and taxis will still be dominated by LFP. In the future, the most likely situation in the field of power batteries will be that lithium iron phosphate and ternary materials will go hand in hand.

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