CR1632 battery companies encounter technical difficulties in deploying high-nickel batteries

High-nickel batteries, as the name suggests, are batteries with a high proportion of nickel in power batteries. The main domestic models are NCM523, and now various power battery companies are actively deploying NCM811. What do these numbers mean? They represent the proportion of nickel, cobalt, and manganese in power batteries, respectively. The proportion of nickel in NCM811 is as high as 80%. High nickel means that power batteries can have higher energy density and lower cobalt content. High-nickel batteries can meet the two major needs of current power batteries at the same time, improving energy density and reducing material costs. Major power battery manufacturers will naturally actively deploy. However, there are some inevitable technical difficulties in the road to mass production and commercialization of high-nickel batteries.

The increase in nickel content in ternary materials can bring higher energy density, but the stability of positive electrode materials will also decrease with the increase in nickel, which is mainly manifested in capacity loss during cyclic charging and accelerated capacity decay under high temperature environment. The main factors causing capacity loss are cation mixing, stress-induced microcracks, impurities introduced in the production process, and redistribution of conductive carbon black. Among them, the most significant factors affecting the accelerated capacity attenuation are cation mixing and stress-induced microcracks. The Electric Vehicle Resource Network will focus on analyzing these two factors.

Cation mixing: refers to the fact that the volume of divalent nickel ions is similar to that of lithium ions. When lithium ions are released in large quantities during the discharge process, the lithium insertion capacity changes due to external factors. During charging and discharging, the lithium deintercalation pressure on the surface of the positive electrode material is the largest and the speed is the fastest, so the surface often changes the surface lattice due to cation mixing, which is also called surface reconstruction.

The higher the nickel content, the greater the probability of cation mixing. There are several ways to reduce the occurrence of cation mixing:

1. Improving technology to reduce the formation of divalent nickel ions can fundamentally reduce the probability of cation mixing.

2. Doping with magnesium ions. Magnesium ions are similar in volume to divalent nickel ions, and magnesium ions will occupy the vacancies left by Li earlier than divalent nickel ions to prevent nickel ions from entering. Most importantly, magnesium ions do not directly participate in the charging and discharging process, and can maintain structural stability after embedding.

3. Improve the preparation technology, adjust the molar ratio of nickel to lithium in the raw materials of the positive electrode materials, and reduce the influence of the raw materials on the cation mixing.

Microcrack generation: The volume of high-nickel positive electrode materials will change during charging and discharging. The higher the nickel content, the greater the volume expansion ratio. The generation of microcracks will also be affected by the potential at the end of charging and discharging. Therefore, the working voltage of the nickel-based layered oxide positive electrode should not exceed 4.1V to prevent the occurrence of irreversible phase changes and reduce internal stress. When the microcracks on the crystals begin to separate from the crystals, the grains of the high-nickel positive electrode material will be subjected to greater volume changes. In the process of volume cycle changes, there is a high probability that microcracks will occur inside the grains, and the distance between the grains will gradually increase, and the grains will separate from the positive electrode and exist independently. More and more crystal faces are released from the electrolyte, which will affect the lithium ions, increase their resistance to diffusion on the electrode, and cause capacity loss during the charging cycle.

The formation of microcracks is mainly suppressed by weakening the phase change trend of the single-cell voltage. Currently, there are mainly the following methods:

1. Suppressing the doping of magnesium ions in the cation mixing can play a role in reducing the generation of microcracks.

2. Optimizing the preparation technology, preparing the high-nickel positive electrode material into a two-phase composite material with Li2MnO3 structural units uniformly embedded inside, which can reduce volume changes.

Summary: Since nickel is cheaper than cobalt, the raw material cost of high-nickel batteries is relatively low, but the Electric Vehicle Resource Network believes that power battery companies need to overcome the above technical difficulties if they want to mass-produce and commercialize high-nickel batteries. Due to the existence of these difficulties, the production difficulty of high-nickel positive electrode materials has increased, the raw material cost has decreased, and the production cost has increased, so the final cost of high-nickel batteries will not drop significantly. However, judging from the overall trend of the power battery industry, the development of high-nickel batteries is imperative.

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