Synthesis And Electrochemical Performance Modification Of Li-rich Mn-based Cathode Material Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ For Lithium-ion Batteries

Lithium-rich Mn-based cathode material?LMR?Li1.2Ni0,13Co0.13Mn0.54O2 possesses the advantages of high discharge capacity,low cost and environment-friendly,which is a promising candidate of the next generation cathode materials for Li-ion batteries.Despite these merits,LMR also suffer from a lot of drawbacks,including poor rate performance,unsatisfactory cycle stability and serious voltage decay during charge/discharge process,hindering its practical applications.In order to overcome these shortcomings,this thesis attempts to modify the electrochemical performance of Li1.2Nio.,3Co0.13Mn0.54O2 through a series of routes,such as compositing method with the two-dimensional MXene material Ti₃C₂T_x,elemental doping method with aluminium and selecting diferent manganese compound as the the raw materials,and so on.The specific research content of this thesis is as follows:Li_1.2Ni_0.13Co_0.13Mn_0.54O₂/Ti₃C₂T_x?LMR/TC?composite materials have been synthesized through mixing LMR particles with TC nanosheets.The effects of Ti₃C₂T_x nanosheets on the electrochemical properties of the composites were studied.The results show that the imbedded Ti₃C₂T_x nanosheets can enhance the electronic and ionic conductivity of LMR considerably,make its structure more stable during charge/discharg process,and eventually the composite cathode materials deliver an improved electrochemical property,especially the rate performance and cycle stability.The first discharge capacity of 5wt%Ti₃C₂T_x composite material reaches 279.9 mAh g^-1 at 0.1 C,and the-first coulombic efficiency is 81.8%.After 50 cycles,the capacity of the composite material still maintains 256.8 mAh g^-1,and the capacity retention is 91.7%.A series of Al-doped Li-rich Mn-based materials Li1.2NiO.13Co0.13Mn0.54O2 were synthesized by a combustion method.The influences of A1 substitution for Li on the the structural,morphological and electrochemical properties of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode material have been investigated.The results show that a proper A1 dopant in Li1.2Ni0.13Co0.13Mno.54O2 lattice can effectively improve the electrochemical properties of the material,especially the cycling and rating performance.Among the series samples,the material Al-LMR with 0.02 A1 doping content delivers the best electrochemical performance.The first discharge capacity of Al-LMR at 0.1 C is 269.4 mAh g^-1 and even after 150 cycles,its capacity at 0.5 C can still maintain 182.1 mAh g^-1 with a capacity retention of 98%.However,the initial specific capacity of the undoped material is only 241.5 mAh g^-1 at 0.1 C,and its capacity at 0.5 C can only maintain 129.8 mAh g^-1 with a capacity retention of 92%after 150 cycles.A series of Li-rich manganese-based materials Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ were synthesized via combustion method using different manganese compounds as the raw materials.The influence of different manganese sources on the electrochemical properties of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ were studied in detailed.The results show that the material N-LMR synthesized from Mn?NO3?2·4H2O manganese sources had a much better electrochemical properties than that of materials synthesized from Mn?CH3CO2?2·4H2O?LMR?and MnCO3?C-LMR?.At 0.1 C,the first discharge specific capacities of N-LMR,LMR and C-LMR were 313 mAh g^-1,242.2 mAh g^-1 and 226 mAh g^-1,respectively.The discharge specific capacity of N-LMR exceeded 300 mAh g^-1 at 0.2 C rate,and can reach 132.1 mAh g^-1 even at 5 C current density.However,the capacities of LMR and C-LMR at 0.2 C and 5 C are only 173.7,208.6 mAh g^-1 and 29.4,101 mAh g^-1,respectively.