Why does the l lithium-titanate battery swell?

Lithium titanate (Li4Ti5O12 commonly known as LTO) space group belongs to Fd3m. because of its unique three-dimensional lithium ion diffusion channel, it has excellent power characteristics and high temperature performance. At the same time, the lithium titanate crystal structure can maintain a high stability volume change of less than 1% in the lithium ion deintercalation cycle, which lays a foundation for lithium titanate to become an important negative electrode material.

More importantly, it eliminates the safety hazard of the battery and is called the safest lithium battery anode material. The physical structure of lithium titanate is suitable as a negative electrode material for lithium batteries, so what is its electrochemical property? Compared with the carbon anode material, the lithium titanate has a higher potential of 1.55 Vvs Li+/Li, a theoretical capacity of 175 MAH/G, an open circuit voltage of 2.4 V, and a lower energy density and voltage platform.

Lithium-titanate battery has the advantages of high safety, large rate charging, long cycle life, etc. However, when lithium titanate is used as the negative electrode, the battery has serious flatulence during the charge and discharge cycle, and is more serious at high temperatures. Although the research on flatulence of lithium-titanate battery has never stopped, including carbon coating modification, hybridization, nanocrystallization, etc., its flatulence problem has not been completely solved, which hinders the market promotion of lithium titanate battery.

Expansion mechanism of lithium-titanate battery

The academic community believes that the lithium flattening of lithium titanate/NCM batteries is more serious than graphite/NCM. Lithium titanate cannot form an SEI film on the surface of the graphite negative electrode system to inhibit its reaction with the electrolyte. During the charging and discharging process, the electrolyte is always in direct contact with the surface of Li4Ti5O12, which causes the electrolyte to continuously reduce and decompose 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 and the like. When lithium titanate is separately immersed in the electrolyte, only CO2 is produced. After the NCM material is prepared into a battery, the generated gas includes H2, CO2, CO, and a small amount of gaseous hydrocarbons, and after being fabricated into a battery, it is only in circulation. At the time of charge and discharge, H2 is generated, and at the same time, the content of H2 exceeds 50%. This indicates that H2 and CO gases will be produced during charge and discharge.

PF5 is a strong acid that easily causes decomposition of carbonates, and the amount of PF5 increases with increasing temperature. PF5 helps the electrolyte to decompose, producing CO2, CO and CxHy gases. According to the related research, the production of H2 is derived from trace water in the electrolyte, but the water content in the electrolyte is generally about 20×10–6, which contributes very little to the production of H2. Wu Kai's experiment at Shanghai Jiaotong University used graphite/NCM111 as the battery, and concluded that the source of H2 is the decomposition of carbonate at high voltage.

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