Power battery cathode material: lithium-rich manganese base

At present, the hot energy battery in the new energy automobile industry is lithium iron phosphate battery and ternary battery, and the lithium-rich manganese-based battery that is expected to be high is still not warm. The electric vehicle resource network was informed that in the 310th batch of new car announcements announced by the Ministry of Industry and Information Technology in July, lithium-rich manganese-based batteries appeared in the supporting list, which was provided by Zhejiang Youyou Power. The supporting model was Jiangsu Luzhou Zhouxin Energy Vehicle Co., Ltd. The production of the local land RQ5026XXYEVZ1 pure electric van and the new Japan XRF5032XXYBEV pure electric van transporter produced by Xinri (Wuxi) Development Co., Ltd., this is the first time in China and the world.

Unlimited lithium-rich manganese base

China attaches great importance to the new energy automobile industry and ranks new energy vehicles as one of the seven strategic emerging industries. For new energy vehicles, regardless of the country's support policies, the key factor in determining its development is still to meet the needs of consumers. At present, due to the level of power battery technology, most commercialized pure electric vehicles still have low cruising range. Consumers have serious “mileage anxiety” and their purchasing desire is not strong. According to the electric vehicle resource network, the pure electric vehicle has a battery life of 320 kilometers, which can meet the needs of most consumers. The battery life reaches 600 kilometers, which is close to the cruising range of the fuel tank full of oil, in order to eliminate the consumer's “mileage anxiety”. ". Therefore, the development of a new generation of high energy density power batteries is an inevitable requirement and trend for the future development of power batteries.

As far as the technology of the current industry is concerned, the technology for reducing the mass of the inactive material of the battery to increase the energy density of the power battery has reached the peak. It is more effective to increase the energy density of the power battery by using the positive and negative materials with higher energy density. . According to the electric vehicle resource network, among the known cathode materials, the lithium-rich manganese-based cathode material has a discharge specific capacity of up to 300 mAh/g, which is the discharge specific capacity of cathode materials such as lithium iron phosphate and ternary materials which have been commercialized. Doubled, it is very suitable for the new generation of high energy density power lithium battery cathode material. Lithium-rich manganese-based materials have the advantages of low cost, high capacity, non-toxic safety, etc., and are used as positive electrode materials to meet the requirements of power batteries in electric vehicles and other fields. After solving the related technical problems, the lithium-rich manganese-based cathode material has the absolute advantage of discharge specific capacity, which will be beneficial to the large-scale promotion of electric vehicles.

Lithium-rich manganese-based synthesis method and existing problems

Lithium-rich manganese-based cathode materials mainly have the following synthesis methods:

First, the co-precipitation method, the coprecipitation method is to uniformly mix several transition metal ions at the atomic level, and the morphology of the sample is easy to form a regular sphere, and the particle size distribution is uniform.

Second, the sol-gel method, the lithium-rich manganese-based synthesized by the method has relatively good electrochemical performance, but the morphology of the product is difficult to control, and it is often required to spend a large amount of expensive organic acid or alcohol, and the cost is high.

Third, the solid phase method, the solid phase method requires a good mixing of the raw materials, and it is necessary to ensure sufficient diffusion of several transition metal ions during the calcination process.

The lithium-rich manganese-based cathode material has an absolute advantage in discharge specific capacity, but there is still a long way to go before it can be applied to a power battery because it has the following technical problems:

First, the irreversible capacity of the first cycle is relatively large. Studies have shown that its first coulombic efficiency is usually 75%, and after modification, it can reach about 88%. This is because when charging for more than 4.5V for the first time, O2- in the crystal lattice is accompanied by Li+ to Li? In the form of O, in order to maintain the balance of charge, the transition metal ions in the surface layer migrate to the bulk phase, occupying the octahedral position left by Li+, which leads to the inability of Li+ to completely re-emerge during discharge, resulting in irreversible capacity loss. Therefore, when designing the battery industry, enterprises must consider the first-use efficiency of the positive electrode and avoid the formation of metallic lithium dendrites due to insufficient design of the negative electrode.

Second, the voltage platform is down, and the cycle stability is poor. Due to the migration of Mn ions into the lithium vacancies in the lithium layer during charging and discharging, the layered structure of the material gradually transforms into a spinel-like phase. In addition, due to the high working voltage window of the material, the full battery voltage range must be set at 2.0~4.7V, and most of the commercial electrolytes still cannot meet the demand. In general, the voltage window during the cycle test is set at 2.5 to 4.5 V, thus limiting the high specific energy advantage of the lithium-rich manganese-based positive electrode material. Therefore, the lithium-rich manganese-based cathode material needs to be modified by surface coating, bulk phase doping, particle nanocrystallization and the like. In addition, a matching high pressure electrolyte is also used.

Third, storage performance and coating performance are relatively poor. Storage performance is a key factor affecting the practical use of the cathode material. During the production, storage, transportation and battery manufacturing process, the physical and chemical properties of the cathode material must be stable. Related studies have shown that since the lithium-rich manganese-based positive electrode material has a large alkalinity and a rough surface, it is easier to absorb moisture than a positive electrode material such as lithium cobaltate. Therefore, in the preparation process of the power battery, moisture must be strictly controlled to avoid coating, problems such as decreased adhesion during the process and flatulence of the battery.

Although there are still various problems in the development of lithium-rich manganese base, this time, the first match can be said to let us see the dawn of commercialization of lithium-rich manganese, whether lithium-rich manganese-based can become the mainstream cathode material in the future, we look and look forward to it.

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