Principle of flatulence of lithium titanate battery

　　Academics believe that the reason why lithium titanate/NCM battery gas is more serious than graphite/NCM is that lithium titanate cannot form an SEI film on its surface to inhibit its reaction with the electrolyte like graphite anode system batteries. During the charge and discharge process, the electrolyte is always in direct contact with the surface of Li4Ti5O12, causing the electrolyte to continue to reduce and decompose on the surface of the Li4Ti5O12 material. This may be the root cause of the bloating of the Li4Ti5O12 battery.

　　The important components of gas are H2, CO2, CO, CH4, C2H6, C2H4, C3H8, etc. When lithium titanate is immersed in the electrolyte alone, only CO2 appears. After it is made into a battery with NCM materials, the gases that appear include H2, CO2, CO and a small amount of gaseous hydrocarbons. After the battery is made into a battery, only CO2 appears during the cycle. H2 will only appear during charging and discharging, and the content of H2 in the gas that appears at the same time exceeds 50%. This indicates that H2 and CO gases will appear during the charge and discharge process.

　　LiPF6 has the following equilibrium in the electrolyte:

　　PF5 is a strong acid that easily causes the decomposition of carbonates, and the amount of PF5 increases as the temperature increases. PF5 helps the electrolyte decompose and produce CO2, CO and CxHy gases. According to relevant studies, the appearance of H2 comes from trace amounts of water in the electrolyte, but generally the water content in the electrolyte is about 20×10–6, which contributes very little to the production of H2. Wu Kai of Shanghai Jiao Tong University used graphite/NCM111 as the battery in his experiment, and concluded that the source of H2 is the decomposition of carbonate under high voltage.

　　2. Suppression of flatulence in lithium titanate ion batteries

　　At present, there are three main solutions to suppress the flatulence of lithium titanate batteries. First, the processing and modification of LTO anode materials, including improving preparation methods and surface modifications; second, developing electrolytes that match the LTO anode, including Additives and solvent systems; third, improve battery process technology.

　　(1) Improve the purity of raw materials and prevent the introduction of impurities during the manufacturing process. Impurity particles will not only catalyze the classification of electrolytes to produce gas, but will also greatly reduce the performance, cycle life and safety of lithium-ion batteries. Therefore, the introduction of impurities into the battery must be reduced as much as possible.

　　(2) The surface of lithium titanate is covered with nanocarbon particles. The apparent reason for the formation of gas in the negative electrode LTO is that the SEI film is formed slowly and less, resulting in the flatulence phenomenon that will accompany it throughout its life. Research has found that establishing an isolation layer between lithium titanate and the electrolyte interface (such as constructing a nanocarbon coating layer on the surface of lithium titanate (LTO/C), synergizes with the solid electrolyte interface (SEI) film formed on the coating layer - On the one hand, it reduces the contact area between the LTO material and the electrolyte and prevents the occurrence of gas.

　　On the other hand, the carbon itself can form an SEI film to make up for the shortcomings of LTO, and can also enhance the conductivity of the LTO material. The above research results are of great significance in solving the gas generation behavior of lithium titanate batteries, and can promote the design, large-scale application and development of high-energy lithium titanate power lithium batteries.

　　(3) Improve electrolyte functionality. Regarding the development of new electrolytes, many patents tend to use additives to promote the formation of a dense SEI film on the surface of LTO to suppress the occurrence of side reactions at the interface between LTO and electrolyte. Certain electrolyte additives, such as fluorinated carbonates and phosphates, are beneficial to forming a stable SEI film on the surface of the positive electrode, reducing the dissolution of metal ions on the surface of the positive electrode, thereby reducing the occurrence of gas.

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

　　(4) Positive electrode surface coating. Covering the surface of the positive electrode with a stable compound, such as alumina, can effectively inhibit the dissolution of metal ions. However, an overly complex coating layer will inhibit the deintercalation of lithium ions and affect the electrochemical performance of the material.

　　(5) Improve battery production technology. When producing batteries, it is necessary to control the environmental humidity and the introduction of moisture during operation. It can be seen from the cause of the gas that the moisture in the air reacts with the cathode material to form lithium carbonate and accelerates the decomposition of the electrolyte to generate carbon dioxide. In addition, the lithium titanate material itself is extremely water-absorbent (it needs to be operated in a dry room). After the negative electrode piece absorbs moisture, it will react with PF5 that appears from the reversible decomposition of the electrolyte to generate H2, so strict moisture control is crucial. .

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