What's a lithium-rich manganese base?

At present, the more hot power batteries in the new energy automotive industry are lithium iron phosphate batteries and ternary batteries. Lithium-rich manganese batteries that have been placed in high hopes have not been heated. The electric vehicle resources network learned that in the 310th batch of new vehicles publicized by the Ministry of Industry and Information Technology in July, Fulithium-manganese batteries appeared in the supporting list, which was provided by Zhejiang Yuyou Power. The supporting model is the Xinri XRF5032XXYBEV pure electric van produced by Jiangsu Lujianzhou New Energy Vehicle Co., Ltd., which produces the local brand RQ5026XXYEVZ1 pure electric van and Xinri(Wuxi) Development Co., Ltd.. For the first time, this is the first time in China or the world.

Lithium-rich manganese base with unlimited future

China attaches great importance to the new energy car industry and lists new energy vehicles as one of the seven strategic emerging industries. For new energy vehicles, regardless of national support policies, the key factor that determines their development is whether they can meet the needs of consumers. At present, due to the level of power cell technology, most commercial pure electric vehicles still have low mileage, and consumers have serious "mileage anxiety" about them. The electric vehicle resource network learned that the pure electric vehicle has a range of 320 kilometers, which can meet the needs of most consumers; The endurance of 600 kilometers, close to the mileage of the fuel truck under full oil, can eliminate consumers ' "mileage anxiety." Therefore, the development of a new generation of power cells with high energy density is an inevitable requirement and trend for the future development of power cells.

As far as the current industry is concerned, the technology of reducing the mass of the inactive material of the core to increase the energy density of the power cell has reached its peak. It is more effective to increase the energy density of the power cell by using a positive and negative material with higher energy density. The electric vehicle resources network learned that among the known positive electrode materials, the discharge ratio of lithium-rich manganese-based positive electrode materials is as high as 300 mAh/g, which is the current commercial application of lithium iron phosphate and ternary materials. About twice the discharge ratio, It is very suitable for making a new generation of high-energy density-powered lithium battery positive electrode material. Lithium-rich manganese based materials have the advantages of low cost, high capacity, non-toxic safety, etc.. The use of cathode materials can meet the requirements of power batteries in electric vehicles and other fields. After solving the related technical problems, lithium-rich manganese positive electrode material has the absolute advantage of discharge specific capacity will be conducive to the large-scale promotion of electric vehicles.

Synthetic Methods and Problems of Lithium-rich Manganese Base

Lithium-rich manganese positive electrode materials mainly have the following synthesis methods:

Co-precipitation method. Co-precipitation method is the uniform mixing of several transition metal ions at the atomic level, the shape of the sample is easy to form a regular spherical, and the particle size distribution is uniform.

Sol-gel method. The electrochemical properties of the lithium-rich manganese base synthesized by this method are relatively good, but the morphology of the product is not easy to control. It often requires a large amount of expensive organic acids or alcohols, and the cost is high.

Third, the solid phase method. The solid phase method requires a good mixture of raw materials and a sufficient diffusion of several transition metal ions during calcination.

Lithium-rich manganese positive electrode material has an absolute advantage over capacity, but it still has a long way to go to apply it to power batteries because it still has the following technical problems:

First, the irreversible capacity of the first cycle is relatively large. Studies show that the first Coulomb efficiency is usually 75 %, and after modification, it can reach about 88 %. This is because when the first charge is above 4.5 V, O2-in the lattice is accompanied by Li + to Li? The form of O is removed. In order to maintain the balance of the charge, the transition metal ions on the surface will migrate to the body phase, occupying the octahedral position left by Li +, resulting in Li + being unable to fully return during discharge, resulting in irreversible capacity loss. Therefore, when enterprises design battery industry, they must take into account the first use efficiency of positive poles and avoid the formation of lithium dendrites due to the lack of negative electrode quality design.

Second, the voltage platform drops, and the cyclic stability performance is poor. Due to the migration of Mn ions to lithium vacancies in the lithium layer during the process of charging and discharging, the layered structure of the material is gradually converted to spinel phase. In addition, due to the high operating voltage window of the material, the voltage range of the entire battery must be set at 2.0 to 4.7 V in order to fully play its capacity. At present, most commercial electrolytes still can not meet the demand. In general, the voltage window is set at 2.5 to 4.5 V during cyclic testing, thus limiting the use of high-specific energy advantages of lithium-rich manganese-based cathode materials. Therefore, it is necessary to modify the lithium-rich manganese base positive electrode materials by surface coating, body phase doping, and particle nanocrystallization. In addition, matching high-pressure electrolytes are also used.

Third, the storage performance and coating performance are relatively poor. Storage performance is a key factor affecting the practicability of cathode materials. All physical and chemical properties of cathode materials must remain stable during production, storage, transportation and battery manufacturing. Related studies have shown that due to the large alkalinity and rough surface of lithium-rich manganese positive electrode materials, it is easier to absorb moisture than lithium cobalt isopolar materials, so water must be strictly controlled during the preparation of power cells. In order to avoid the problem of reduced adhesion and battery gas in the coating process.

Although there are still various problems in the development of lithium-rich manganese base, this time the first set of products can be seen as a glimpse of the commercialization of lithium-rich manganese base. Whether or not lithium-rich manganese is a mainstream positive material in the future, we look forward to it.

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