Power battery manufacturers have begun to deploy 12V27A battery, but technical problems still exist

　　12V27A battery, as the name suggests, are batteries with a high proportion of nickel in power batteries. Currently, the main domestic models are NCM523, and now various power battery companies are actively deploying NCM811. What do these numbers mean? They respectively represent the proportions of nickel, cobalt and manganese in the power battery. 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. 12V27A battery can simultaneously meet the two major needs of current power batteries, improve energy density and reduce material costs. Naturally, major power battery manufacturers will actively deploy. However, there are some inevitable technical difficulties on the way to mass production and commercialization of 12V27A battery.

　　Increasing the nickel content in ternary materials can bring higher energy density, but the stability of the cathode material will also decrease with the increase in nickel, which is mainly manifested in capacity loss during cyclic charging and accelerated capacity attenuation in high temperature environments. The main factors causing capacity loss include cation mixing, stress-induced microcracks, impurities introduced during the production process, conductive carbon black redistribution, etc. Among them, the most significant impact on accelerated capacity attenuation is the mixing of cations and the generation of stress-induced microcracks. The reporter will focus on analyzing these two factors.

　　Cation mixing: refers to the fact that divalent nickel ions are similar in size to lithium ions. When a large number of lithium ions are released during the discharge process, the lithium insertion ability changes due to the influence of external factors. During charging and discharging, the lithium deintercalation pressure in the surface of the cathode material is the largest and the fastest. Therefore, the surface often changes the surface lattice due to the mixing of cations, which is also called surface reconstruction.

　　The higher the nickel content, the greater the chance 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. When doped with magnesium ions, the volumes of magnesium ions and divalent nickel ions are similar, and magnesium ions will seize the vacancies left by Li earlier than divalent nickel ions to prevent nickel ions from entering. The most important thing is that magnesium ions do not directly participate in the charge and discharge process, and can maintain structural stability after embedding.

　　3. Improve preparation technology, adjust the molar ratio of nickel and lithium in the cathode material raw materials, and reduce the impact of raw materials on cation mixing.

　　Generation of microcracks: The volume of high-nickel cathode materials changes during charge and discharge. The higher the nickel content, the greater the volume expansion ratio. The generation of microcracks is also affected by the potential at the end of charge and discharge. Therefore, the working voltage of the nickel-based layered oxide cathode should not exceed 4.1V in order to prevent the occurrence of irreversible phase transformation and reduce internal stress. When microcracks in the crystals and crystals begin to separate, the grains of the high-nickel cathode material are subject to greater volume variations. During the cyclic changes in volume, there is a high probability that microcracks will occur inside the crystal grains, and the distance between the crystal grains will gradually increase, causing the crystal grains to exist independently from the cathode. More and more crystal faces are released from the electrolyte, which will affect lithium ions and increase their resistance to diffusion on the electrode, causing capacity loss during charging cycles.

　　Suppressing the formation of microcracks is mainly solved by weakening the phase change tendency of the monomer voltage. Currently, there are mainly the following methods:

　　1. Suppressing magnesium ion doping in cation mixing can reduce the occurrence of microcracks.

　　2. Optimizing the preparation technology and preparing the high-nickel cathode material into a two-phase composite material with Li2MnO3 structural units evenly embedded inside can reduce volume changes.

　　Summary: Since nickel is cheaper than cobalt, the raw material cost of 12V27A battery is relatively low. However, the reporter believes that power battery companies need to overcome the above technical difficulties if they want to mass-produce and commercialize 12V27A battery. Due to the existence of these problems, the production of high-nickel cathode materials has become more difficult, the cost of raw materials has dropped, and the production cost has increased. Therefore, the final cost of 12V27A battery will not drop significantly. But judging from the overall trend of the power battery industry, the development of 12V27A battery is imperative.

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