| Lithium-ion batteries are booming in recent years due to its high energy density,long cycle life,excellent high and low temperature discharge performance,no memory effect and flexible design.As a consumer battery,the life of lithium-ion battery is usually one to three years,which can basically meet the needs of users.However,a longer life is needed to use as power batteries and energy storage batteries.The aging test of lithium-ion batteries under actual service conditions requires a long time,which results in the delay of performance feedback and seriously restricts the design and development of lithium-ion batteries.The key to solve this problem is to quickly evaluate the life of lithium-ion battery.Hence,taking accelerated life tests to predict the lifetime of lithium-ion batteries is worth-studying amd practical.In this work,the charge/discharge rates and electron irradiation coupled with charge/discharge rates are used as the accelerated aging conditions to study the the accelerated aging of 18650 lithium ion batteries.The battery is disassembled at the initial and the end of the cycle.Various physical and chemical characterizations were carried out to research the surface morphology,structure and composition of cathod/anode electrode before and after cycling.The aging behaviours and degradation mechanisms of 18650 lithium ion batteries were studied at 1.0C,1.2C,1.5C and 1.8C.With the increase of charge/discharge rates,the lifetime of the batteries is shortened,accompanying with the decrease of discharging platform and the rise of charging platform and battery polarization.Further,the time of the charging process and the capacity of the constant voltage charging process are positively related to the rate.Obviously,reasonable charge system is vital to the balance of fast charging and long cycle life of lithium ion batteries.The loss of active lithium and the structure deformation of cathode materials are the reasons for the degradation of positive electrode.The loss of active lithium leading to the decrease of available voltage range of positive electrode and the shift of positive electrode SOC is the major cause of the attenuation of cathode materials.The attenuation of negative electrode is mainly caused by the SEI film and the lithium deposit.Compared with the positive electrode,the non-uniform attenuation of the negative electrode is obvious,and the attenuation is more serious at the winding position of the electrode.Electron irradiation was successfully introduced into the accelerated life tests of batteries as an acceleration factor.The failure mechanism of 18650 lithium ion battery cycling under electron irradiation and cycled after irradiating at different charge/discharde rates(1.0C,1.2C,1.5C and 1.8C)was studied systematically.The failure of 18650 lithium ion batteries cycling under electron irradiation is due to the triggered CID.At the same rates,the batteries suffered electron irradiation reach the end of life faster.The loss of active lithium,the structural attenuation and particle crushing of cathodes materials,the dissolution of transition metal ions,SEI film and lithium deposit on the negative electrode surface are the common factors causing the capacity degradation of batteries.Different from the aging without electron irradiation,the rate aging coupled with electron irradiation increases the graphite layer spacing,and the graphite expands slightly. |
