Synthesis And Electrochemical Performance Of High-voltage Cathode Materials For Lithium-ion Batteries

With the development and applications of lithium-ion batteries, high energydensity and power density lithium-ion batteries that are safe and environmentalfriendly will be the major trend in the development of battery industry. The cathodematerials acted as a key factor in lithium-ion batteries become more noteworthy.Therefore, developing new-type cathode materials with higher capacity and voltagehas become significant. In this paper, the synthesis and electrochemical performanceof three new high voltage cathode materials including LiCoPO₄, LiNi_0.5Mn_1.5O₄andLi₃V₂（PO₄）₃were investigated, specifically as follows:（1） Pure LiCoPO₄cathode material was synthesized by a sol-gel method. Thesynthesis conditions have been optimized by single factor experiment. It has beenfound that the sample synthesized at650℃for12h showed the bestelectrochemical performance, reaching the initial discharge capacities of132.4mAh·g^-1and122.7mAh·g^-1at0.1C and1C, respectively. Based on the galvanostaticcharged/discharged tests and electrochemical impendence spectra, the insert/deinsertmechanism of lithium ion and the main causes of capacity fading during cycling werediscussed in detail. In addition, the electrochemical performance of LiCoPO₄materialhas been improved by Al₂O₃（2） A sol-gel method was used to synthetize the high voltage cathode materialLiNi_0.5-xCr_xMn_1.5O₄. In the research of the electrochemical performance ofLiNi_0.5-xCr_xMn_1.5O₄, we found that the sample with the compositon ofLiNi_0.45Cr_0.05Mn_1.5O₄exhibited the best electrochemical properties, delivering thedischarge capacity of142.1mAh·g^-1after100cycles at the rate of1C. Besides, theelectrochemical performance of LiNi_0.45Cr_0.05Mn_1.5O₄/Li₄Ti₅O₁₂full cells withdifferent ratios （1:1.2,1:1and1:0.8） of the negative capacity （N） and positivecapacity （P） were investigated at different temperatures. The results indicated that thefull cells with N/P=1.2presented the best rate capability and cycle stability, exhibitingthe discharge capacities of107.4mAh·g^-1and63.7mAh·g^-1at0.5C and5C rates at 15℃,with excellent capacity retention of97.6%and94.2%after50cycles at1Crate under15℃and30℃, respectively. All these investigations provided a theorybasis for appling these cells on the applications of electric vehicle with high capacityand power battery.（3） A rapid sol-gel method for synthesizing Li₃V₂（PO₄）₃/C material was used inthis paper, and the elechechmical behavior of Li₃V₂（PO₄）₃/C cathode material underhigh voltage range （3.0-4.8V） was preliminarily studied. The results showed that thesample could reach a initial discharge capacity of158.9mAh·g^-1at the rate of0.5C,retaining115.8mAh·g^-1and100.7mAh·g^-1at5C and10C after200cycles, with thecapacity retention of83.4%and88.0%, respectively.