Study On The Safety Performances Of Lithium Battery With Composite Cathode System

Research on the safety performance of lithium battery with composite cathode system was made.Firstly,LiMn₂O₄ and Li[Ni_0.5Co_0.2Mn_0.3]O₂ were used as composite cathode materials according to the ratio of quality of Li[Ni_0.5Co_0.2Mn_0.3]O₂:LiMn₂O₄?10:0,8:2,7:3,5:5,0:10?.Five groups composite cathode materials were tested to determine the optimal composition ratio.Secondly,the composite cathode materials of the optimum ratio was made into soft package of laminated type lithium battery.The safety performance of the composite cathode system was improved by ceramic-coated separator.Finally,the effects of the core structure and the battery shell material in the production process on the safety of the composite cathode system lithium battery were studied.The optimal ratio of composite cathode materials was determined by electrochemical performance study.The results show that with the increase of Li[Ni_0.5Co_0.2Mn_0.3]O₂,the cycle performance of the composite cathode materials is improved.The ratio of 8:2composite cathode materials shows good cycle characteristics.The retention of specific capacity is 84.8%after 50 cycles.The composite cathode materials with the ratio of 8:2exhibits good rate characteristics.The capacity retention rate is still 93.9%at 2 C discharge rate.Thus,the ratio of 8:2 is the optimum composite cathode material system..The effect of the separator on the safety performance of the composite cathode material lithium battery was studied.The surface temperature rise of battery with ceramic-coated separator are reduced by 36°C,27°C and 38.7°C than the battery with PE separator,respectively,during the safety test of acupuncture,heavy impact and 5 V overcharging.It indicats that the safety performance of the battery is significantly improved through the use of ceramic-coated separator to replace the PE separator.Therefore,the ceramic-coated separator can significantly improve the safety performance of the composite cathode system lithium battery.Effects of the core structure and the battery shell material in the production process on the safety of the composite cathode system lithium battery were studied.Compared with the wound type cell structure,it is found that the cell structure of the laminated presents some advantages of small internal resistance and good heat dissipation performance.Thereby the safety performance of the battery is improved.The wound-type battery occurs the phenomenon of smoke and combustion,respectively,while the battery of laminated structure do not appear the phenomenon of smoke in the test of acupuncture and 5 V overcharging.Compared with the nickel-plated steel,aluminum-plastic composite film with some advantages of good ductility,low mechanical strength,which make the battery show better safety performance in the acupuncture experiment.The steel battery of 18650-type occurs the phenomenon of violent fire burning,and safety valve spewing in the acupuncture test.While the wound-type battery only smoke and there is no open flame phenomenon.