New Additives to Improve Cycle Performance of Lithium Ion Battery Under High Voltage Conditions

Abstract

Lithium ion batteries (LIBs) are one of the most versatile secondary batteries with high energy density and high power output.Recently the degradation of LIBs cycle durability has appeared to be one of the significant issues under the use of high voltage conditions.The capacity of LIBs is dramatically decreased after a cycle test in a range of 3.0-4.5 V. The additives for cathodes named “Multi Capture Powder (MCP)” have been developed herein.MCP is capable of capturing metal ions and refraining from cathode decompositions of fluorine compounds.Mechanisms of the effects of MCP on the improvement of LIBs’ cycle performance are different from those of cathode materials examined so far. In case of LiCoO2 (LCO) /graphite cells with 5% MCP added to the cathode, theircapacity retentions have increased by about 10% after 300 cycles under 2.5-4.35 V conditions. Electrochemical impedances between the LCO cathodes with MCP and the graphite anodes after the cycle tests were drastically decreased in comparison with the cells without MCP. In order to clarify the mechanism for the improvement of the capacity retention, the cathodes with/without MCP and the anodes were pulled out of the cells after the cycle tests.The capacity of both the LCO cathodes with /without MCP and the graphite anodes were measured before/after the cycle testsunder 0.2, 0.5 and 1.0 CA conditions with a Li counter electrode. According to the capacity measurements, the cathode materials including MCP mitigate the capacity loss significantly although the dominent factor of the capacity loss of the cells results in the degradation of the cathodes with/without MCP. After the cycle tests, X-ray diffraction angles for the (003) plane of cathode active materials were shifted to lower than their initial ones before the cycle tests. The shift of the diffraction angles for the cathodes with MCP was smaller than that of those of the cathodes without MCP. MCP plays an important role in improving capacity retention under high voltage cycle test conditions.