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Lithium titanate space group belongs to Fd3m, spinel structure. Due to its unique three-dimensional lithium ion diffusion channel, it has excellent power characteristics and high and low temperature performance. At the same time, the crystal structure of lithium titanate can maintain high stability during the lithium ion de-insertion cycle, and the volume change is less than 1%, which lays the foundation for lithium titanate to become an important anode material. Lithium titanate (Li4Ti5O12 commonly known as LTO) space group belongs to Fd3m, spinel structure. Because of its unique three-dimensional lithium ion diffusion channel, it has excellent power characteristics and high and low temperature performance. At the same time, the crystal structure of lithium titanate can maintain high stability during the lithium ion de-insertion cycle, and the volume change is less than 1%, which lays the foundation for lithium titanate to become an important anode material.

More importantly, it eliminates the potential safety hazard of the battery and is known as the safest anode material for lithium batteries. The physical structure of lithium titanate is suitable to be used as the anode material of lithium battery, so what is its electrochemical characteristics? Compared with carbon anode materials, lithium titanate has a higher potential of 1.55VvsLi+/Li, a theoretical capacity of 175mAh/g, an open-circuit voltage of 2.4V, and a lower energy density and voltage platform.

Lithium titanate battery has the advantages of high safety, high rate charging and long cycle life. However, when lithium titanate is used as the negative electrode, the battery will have serious gas expansion during the charging and discharging cycle, especially at high temperature. Although the research on the flatulence of lithium titanate batteries has never stopped, including carbon coating modification, hybridization, nanoization, etc., the flatulence problem has not been completely solved, which hinders the market promotion of lithium titanate batteries.

Academics believe that the reason why the expansion of lithium titanate/NCM battery is more serious than that of graphite/NCM battery is that lithium titanate can not form SEI film on its surface like graphite anode system battery to inhibit its reaction with electrolyte. During the charging and discharging process, the electrolyte always contacts the surface of Li4Ti5O12 directly, resulting in the continuous reduction and decomposition of the electrolyte on the surface of Li4Ti5O12 material, which may be the root cause of the flatulence of Li4Ti5O12 battery.

The main components of the gas are H2, CO2, CO, CH4, C2H6, C2H4, C3H8, etc. When lithium titanate is separately immersed in the electrolyte, only CO2 is generated. After it is prepared into a battery with NCM materials, the gas generated includes H2, CO2, CO and a small amount of gaseous hydrocarbons. After it is used as a battery, H2 will only be generated during cyclic charging and discharging. At the same time, the content of H2 in the gas generated exceeds 50%. This indicates that H2 and CO gas will be generated during charging and discharging.

LiPF6 has the following balance in the electrolyte:

PF5 is a strong acid, which is easy to cause the decomposition of carbonates, and the amount of PF5 increases with the increase of temperature. PF5 is conducive to the decomposition of electrolyte to produce CO2, CO and CxHy gas. According to relevant research, the generation of H2 comes from trace water in the electrolyte, but the water content in the electrolyte is generally 20 × About 10 – 6, contributing very little to the production of H2. Wu Kai of Shanghai Jiaotong University selected graphite/NCM111 as the battery in his experiment, and concluded that the source of H2 was the decomposition of carbonate under high voltage.

2、 Inflation inhibition of lithium titanate battery

At present, there are three main solutions to suppress the expansion of lithium titanate batteries. First, the processing and modification of LTO anode materials, including the improvement of preparation methods and surface modification; Second, develop the electrolyte that matches the LTO anode, including additives and solvent systems; Third, improve battery technology.

(1) Improve the purity of raw materials and avoid the introduction of impurities in the manufacturing process. Impurity particles will not only catalyze the grading of electrolyte to produce gas, but also greatly reduce the performance, cycle life and safety of lithium battery. Therefore, it is necessary to minimize the introduction of impurities in the battery.

(2) The surface of lithium titanate is covered with carbon nanoparticles. The apparent reason for the formation of gas in negative LTO is that the formation of SEI film is slow and less, which leads to the phenomenon of flatulence throughout its life. It was found that the solid electrolyte interface (SEI) film formed on the surface of lithium titanate (LTO/C) by building an insulating layer between the lithium titanate and the electrolyte interface (such as building a nano-carbon coating layer on the surface of lithium titanate (LTO/C)), on the one hand, reduced the contact area between the LTO material and the electrolyte, and prevented the generation of gas.

On the other hand, carbon itself can produce SEI film to make up for the deficiency of LTO, and can also enhance the conductivity of LTO materials. The above research results are of great significance to solve the gas generation behavior of lithium titanate battery and promote the design, large-scale application and development of high-energy lithium titanate power battery.

(3) Improve the function of electrolyte. For the development of new electrolyte, many patents tend to use additives to promote the formation of a dense SEI film on the surface of LTO to inhibit the occurrence of side reactions at the interface between LTO and electrolyte. Some electrolytic agent additives, such as fluorinated carbonate and phosphate, are conducive to the formation of stable SEI film on the surface of the positive electrode, reducing the dissolution of metal ions on the surface of the positive electrode, and thus reducing the generation of gas.

Film forming additives can also inhibit gas production. The added film forming additives include lithium borate, succinonitrile or adipic nitrile, compounds with R-CO-CH=N2 structure (where R is C1 to C8 alkyl or phenyl), cyclic phosphate, phenyl derivatives, phenylacetylene derivatives, LiF additives, etc. These film forming additives are conducive to the formation of SEI film on the LTO surface, and to some extent inhibit the occurrence of gas flatulence.

(4) Positive surface coating. Covering the surface of the positive electrode with stable compounds, such as aluminum oxide, can effectively inhibit the dissolution of metal ions. However, too complex coating layer will inhibit lithium ion de-insertion and affect the electrochemical performance of the material.

(5) Improve battery production process. During battery production, environmental humidity and water introduction during operation shall be controlled. From the cause of gas generation, water in the air will react with the cathode material to form lithium carbonate and accelerate the decomposition of electrolyte to generate carbon dioxide. In addition, lithium titanate material itself has extremely strong water absorption (needs to be operated in a dry room). After absorbing water, the negative electrode plate will react with the PF5 produced by the reversible decomposition of the electrolyte to generate H2, so strict water control is essential.

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