lifepo4 battery calb 200ah 3.2v.210mAh/g! The company breaks through the core technology of high-nickel single crystal materials

China's new energy vehicle market has developed rapidly in recent years. In 2018, China's new energy vehicle production and sales both exceeded 1.2 million units. China has become the world's largest new energy vehicle market. In the field of passenger cars, the cruising range of newly launched electric vehicles continues to increase, and the NEDC comprehensive operating range of many models

China's new energy vehicle market has developed rapidly in recent years. In 2018, China's new energy vehicle production and sales both exceeded 1.2 million units. China has become the world's largest new energy vehicle market. In the field of passenger cars, the cruising range of newly launched electric vehicles continues to increase. The NEDC comprehensive operating range of many models can reach up to more than 500km, which greatly improves the convenience of using electric vehicles.

The ever-increasing cruising range has also put forward higher and higher requirements for the energy density of power batteries. For example, among the new energy models announced by the National Development and Reform Commission in 2019, some models have a power battery system energy density of more than 180Wh/kg. This means The energy density of a power battery cell is required to be at least 250Wh/kg.

The core of improving the energy density of power batteries lies in the development of high-capacity positive and negative electrode materials. Let's take the positive electrode material as an example. The current mainstream positive electrode materials have gradually transitioned from the traditional NCM111 material to NCM523 and NCM622, and the capacity of the positive electrode material has increased from 140mAh/g. It has been increased to about 170mAh/g, and the energy density of the power battery has also been increased to 230-260Wh/kg.

To further improve the capacity of cathode materials, we can mainly proceed from two aspects: 1) Increase the Ni content. Higher Ni content can bring higher specific capacity. For example, the reversible capacity of NCM811 material can reach 190-207mAh/g. If further If the Ni content is increased to 0.9, the capacity can be further increased to about 210-220mAh/g [1, 2]; 2) Increase the charging voltage. The theoretical capacity of both NCM811 and NCM622 is around 270mAh/g without changing the material. Depending on the composition, the material capacity can be increased by increasing the charging voltage. For example, the capacity of NCM622 material at 4.3V is around 176mAh/g, but if the charging voltage is increased to 4.5V and 4.7V, its capacity can reach 201.3 and 218.1mAh/g[3].


However, while the above measures increase the capacity of the cathode material, they will also significantly reduce the cycle performance and safety performance of the cathode material. Taking the NCM622 material as an example, although the 4.7V cut-off voltage can bring the NCM622 material a specific capacity close to 220mAh/g, However, it will also lead to serious degradation of the material's cycle life. After 50 cycles at 55°C and a cut-off voltage of 4.7V in the half-cell system, the capacity retention rate of the NCM622 material is only 78.9%, which is much lower than that of the NCM622 material (96.3%) cycled at 4.3V [3]. Under high voltage The cycle stability of high-nickel materials faces severe challenges.


Increasing the Ni content also faces the same problem. Compared with NCM622 material, NCM900505 material not only has a significant decrease in cycle performance, but also has a significant decrease in thermal stability. Under high voltage, NCM900505 is significantly worse than NCM622 material in terms of thermal decomposition temperature and heat release [4], which corresponds to the poor safety of high-nickel materials in batteries.


These problems with high-nickel materials have seriously restricted the development of high-capacity battery products. The emergence of single-crystal materials has opened up a new direction for the development of high-capacity cathode materials. The so-called single-crystal materials are compared to traditional secondary particles. In terms of materials, traditional NCM materials are mostly secondary particles formed by agglomeration of primary particles of 200-300nm, while single-crystal materials are directly composed of independent crystals with a diameter of 2-5um. Due to higher crystallinity and more stability, Due to their layered structure and anisotropic characteristics, single crystal materials are superior to traditional secondary particle NCM materials in terms of cycle performance, thermal stability, gas production and other indicators [5].


Advantage 1: Improved cycle performance

The good structural stability of single crystal materials makes the materials have very good cycle stability. Taking single crystal NCM523 as an example, after 300 cycles (3-4.4V, C/2) at 40°C, the performance of single crystal NCM523 material batteries The capacity retention rate can still reach 98%, but even the capacity retention rate of secondary particle NCM523 material coated with Al2O3 is only 92% [5]. Under high temperature conditions of 55°C, this gap will be more obvious ( Single crystal >94%, secondary particles <85%).


Advantage 2: Reduced gas production

In recent years, as the energy density of power batteries continues to increase, the market share of soft-pack batteries with higher energy density has also expanded year by year. Compared with hard-shell batteries, soft-pack batteries are more sensitive to material gas production, so the gas production volume is also One of the important indicators to measure the stability of materials. Through float charging experiments, it can be found that the gas production volume of single crystal materials is very small [5]. The gas production volume of 100 hours of float charging at 4.4V, 4.5V and 4.6V voltages is only 0.01, 0.01 and 0.04ml, while under the same conditions, Al2O3 coating The gas production of the secondary particle NCM523 material battery reached 0.07, 0.27 and 0.62ml respectively, which once again shows that single crystal materials have great advantages in gas production.


Advantage 3: Improved thermal stability

Recently, many spontaneous combustion accidents of electric vehicles have brought the safety issue of electric vehicles to the forefront. We have already introduced that as the Ni content increases, the thermal stability of the material will decrease, and single crystal materials have a more stable crystal structure. Therefore, the thermal stability will be improved accordingly. The O2 release experiment shows that the single crystal NCM523 material not only has no O2 release near 80°C, but also has a higher O2 release peak temperature in the range of 200-350°C than the secondary particle NCM523 material. [5], which also shows that single crystal materials have certain advantages in thermal stability.


The advantages of single crystal materials in terms of high voltage, high temperature cycle stability, thermal stability, and gas production make it a high ground for competition among major material manufacturers. Domestic mainstream materials such as Dangsheng, Bamo and Shanshan Manufacturers have begun to launch single crystal NCM622 and NCM523 materials. However, compared with secondary particle materials, single crystal materials have slightly lower capacity [5]. Therefore, single crystal NCM622 materials cannot fully meet the needs of high specific energy batteries. Therefore, Major material manufacturers have been actively developing single crystal NCM811 materials with higher capacity.

Compared with NCM622 and NCM523, materials with relatively low Ni content, the preparation process of single crystal materials with high Ni system is significantly more difficult. Therefore, the research and development of single crystal materials is not going smoothly. Currently, there are only a few companies with the same level. High-end material manufacturers claim to have the ability to develop high-nickel single crystal ternary materials. High-nickel single crystal materials have also become an important criterion for measuring the technical level of material manufacturers, and there are even fewer battery manufacturers who have the ability to develop single crystal materials.

Wanxiang 123 is the world's top power battery manufacturer. With its profound technological accumulation in super lithium iron phosphate materials and high-performance battery systems, it firmly occupies the throne of the world's largest 48V system supplier. Starting from lithium iron phosphate batteries, "safety" has always been the core of Wanxiang's 123 battery development work. In the development of ternary batteries, Wanxiang has always adhered to the principle of "safety first". In order to solve the problem of ternary lithium ion Due to the contradiction between high energy density of batteries and long life and high safety, Wanxiang also launched the layout of single crystal high-nickel ternary materials early on and invested a lot of manpower and material resources in the research and development of high-nickel single crystal materials. After long-term basic research and development, scientists from Wanxiang 123 have recently successfully prepared a single-crystal high-nickel ternary material with a gram capacity of up to 210mAh/g (button battery 2.75-4.3V, 0.1C), which is comparable to domestic standards. The Ni83 single crystal material produced by a well-known material manufacturer is equivalent to the single crystal material prepared by Wanxiang in terms of capacity (207mAh/g). Wanxiang's high-nickel single crystal material has significant advantages in cycle life. After long-term technology accumulation, Wanxiang is now at the same level as current domestic mainstream material suppliers in the development of high-nickel single crystal materials.

The core of the preparation of single crystal materials lies in the sintering process, in which temperature control is the core. If the temperature is too low, it is not conducive to the full growth of the crystal. If the temperature is too high, O defects will easily occur inside the material, causing an increase in Li/Ni mixing in the material, affecting the material. performance. In order to promote the growth of crystals and reduce the risk of over-burning of the material, Wanxiang scientists prepared high-nickel single crystal ternary materials with good crystalline morphology by optimizing the amount of lithium and the sintering temperature.