Synthesis And Electrochemical Performances Of Li_1.27Cr_0.2Mn_0.53O₂ Cathode Material

The lithium-rich layered solid solution material as a new type of lithium ion positive-level material with a relatively high specific capacity.Lithium-enriched layered solid solution material has attracted people’s attention as a new type of lithium-ion positive-stage material with higher specific capacity and higher working voltage.However,such high irreversible capacity for the first time and low electronic conductivity make it unable to obtain good rate performance.At the same time,structural changes occur during charge and discharge,making its power density significantly.Lowering has seriously hindered its practical application.Therefore,the synthesis process optimization and further modification of the lithium-enriched solid solution material are required.In this work,layered Li_1.27Cr_0.2Mn_0.53O₂ powder synthesized by solid phase method were attempted to confirm the importance of Cr³⁺/Cr⁶⁺redox pairs in the electrochemical process,the Mn ions will not participate in the charging/discharging reactions.The Mn element keeps the valence（Mn4+）unchanged and plays a role in stabilizing the structure of the material This graded material was synthesized by different calcinations temperature（900°C,950°C,1000°C）.The electrochemical properties of the resulting materials at three synthesis temperatures were:171.4mAh/g,195.2mAh/g and 180.6mAh/g,respectively.It was found by the results that the layered Li_1.27Cr_0.2Mn_0.53O₂ cathode delivered high capacity close to the theoretical value and good capacity retention of 95.1%after 100 cycles.Such good electrochemical behavior can be attributed to the Cr³⁺/Cr⁶⁺redox pairs rather than Mn ions,as confirmed by XPS investigations.To further improve the performance of the material,we prepared Li_1.27-xRb_xCr_0.2Mn_0.53O₂and Li_1.27Cr_0.2Mn_0.53-xCu_xO₂ cathode materials by substituting different positions of Rb ions and Cu ions for the material.It was found that the initial specific capacity,coulombic efficiency and rate performance were improved by Rb doping.Among the prepared cathode samples,the Rb_0.03Li_1.24Cr_0.2Mn_0.53O₂ material presented the best results.The material showed an initial discharging capacity of 224.9mAh/g,the capacity retention of 98.8%after 50 cycles and excellent performance of 92.0mAh/g at 5C rate.Li_1.27Cr_0.2Mn_0.53-xCu_xO₂ material was also prepared in the study.Through the replacement of Cu ions,the electrochemical properties of the materials were modified.The substitution of Cu ions also greatly improves the electrochemical performance of the material.On the one hand,the initial discharge specific capacity of the sample Li_1.27Cr_0.2Mn_0.5Cu_0.03O₂ reached230.6mAh/g at 0.1C.In terms of rate,when the cycle is performed at 0.2C rate,the specific discharge capacity of the material is about 200mAh/g,and when the rate performance is increased to 2C,the specific discharge capacity of the material is about 150mAh/g.At a rate of 5C,the sample with 3%doping has a specific discharge capacity of 97.9mAh/g which has obvious application value.