Study On The Failure Mechanism Of Lithium Ion Battery And Its Key Materials Under Severe Environmental Conditions

As a kind of clean and renewable energy source,lithium-ion battery has made great progress since its development.With the rapid development of all kinds of instruments and equipment powered by lithium-ion battery,the demand for high-energy,high efficiency and safety of lithium-ion batteries is increasing.However,in the past,researchers focused on the development of higher performance materials of lithium-ion batteries,but less on the failure of batteries.As a complicated energy storage device,lithium-ion battery has many hidden dangers that will endanger human safety.Therefore,it is necessary to explore the failure of lithium-ion batteries in various environments.Based on this,the electrochemical behavior,material interface behavior and crystal structure of lithium-ion battery were studied,tested and analyzed to obtain the failure mechanism of the battery at high temperature。And provide some help for the study of failure mechanism of lithium-ion battery at high temperature in the future.In the first part,CR 2032 button cells were used to assemble Li Co O₂and graphite half-cell to study the basic properties of the materials.Then Li Co O₂/graphite full cell was assembled to check out the electrochemical performance at 80°C.Compared with the electrochemical performance of the cell at room temperature,it is found that the cell capacity decays rapidly at high temperature.Through testing,we speculate that the reason for the failure of battery at 80°C is related to the electrode material and the interfacial film.In the second part,we have studied the crystal structure and the change of the interfacial film of Li Co O₂and graphite at 80°C.Compared with room temperature,the cell volume of Li Co O₂increases with cycle.The change of the structure of the materials makes it more difficult for the lithium ion to insertion and extraction,which greatly affects the cycle performance of the cell.SEM and XPS showed that the thickness of SEI film on the surface of Li Co O₂increased the diffusion impedance of the cell and eventually led to irreversible capacity loss.The anode electrode could directly observed the SEI film cracking and thickening through SEM and TEM,which also leads to the cell capacity degradation.From the results of the whole experiment,the failure of the Li Co O₂/graphite full cell at 80°C is due to the change of crystal structure and SEI of anode and cathode materials.By comparing with the electrochemical performance,material morphology and crystal structure of Li Co O₂/graphite full cell at room temperature,we analyzed the impact of high temperature on lithium-ion battery.And the results which we obtained can provide reference for future research in this area.It is helpful to develop the next generation of lithium-ion batteries with higher security and wider application.