Research On Structure And Electrochemical Performance Of Lithium Rich Manganese Based Cathode Materials Coated Molybdenum Oxides

Rechargeable lithium-ion batteries（LIBs）are popular in the field of electric vehicles（EVs）and hybrid and electric vehicles（HEVs）due to merits of high energy density and long cycling life.To meet the requirement of increasing commercial application for higher energy density of power batteries,compared with the traditional commercial cathode electrodes,such as LiFePO₄ and LiMn₂O₄,Li-Rich cathode material,denoted as x Li₂MnO₃?（1-x）LiMO₂（M=Ni,Co and Mn）,exhibiting reversible higher specific capacity and lower price,has become one of the promising power batteries.Unfortunately,suffering from substantial voltage fade and poor rate capability during continuous cycle and low first Coulombic efficiency lithium-rich materials undergoes a variety of adversities in face of practical application.In this paper,based on the molybdenum oxide coating modification,the reduced molybdenum oxide compounds were designed,further exploring anionic redox behavior involved to MoO₃/MoO_3-x coating layers and the special interface between the coating layers and the inner bulk phase in order to improve the electrochemical performance.Firstly,aimed to prepare the mixed valence solution of Mo⁵⁺/Mo⁶⁺by solvothermal method,alcohol as the reducing agent and solvent,meanwhile,different amounts of MoO₃ were warped on the surface of Li-Rich via traditional wet chemical method,consequently 2 wt.%of MoO₃ was excellent in the electrochemical performance.Combined the ex-situ measurements and the charge-discharge curves,Li-Rich@MoO₃,Li-Rich@MoO_3-x and corresponding pretreated materials were researched.The above results revealed that more anionic redox compensate charge,namely,“4.5 V”voltage platform strengthened upon the initial charge process,whether oxygen vacancies exist in the coating species or not,as long as the solution of Mo⁵⁺/Mo⁶⁺treated.The solution of Mo⁵⁺/Mo⁶⁺treatment,gives rise to induce reducing Mn in Li₂MnO₃,accompanied by the lattice distortion and enhanced covalency among Mn-O bonds.The charge-discharge curves display that the specific capacity of Li-Rich@MoO₃,Li-Rich@MoO_3-x is 266.2 mA h g^-1and 263.3 mA h g^-1,respectively,which is increased by 30.1 mA h g^-1 and 27.2 mA h g^-1 compared with the raw material.Next,the different mixed valence solutions of Mo⁴⁺/Mo⁶⁺were synthesized via hydrothermal method,tuning the amount of ethylene glycol,following Li-Rich coated various series of MoO₃/MoO₂ were synthesized by means of traditional wet chemical method.The physical measurements were combined to probe the mechanism.During the formation of MoO₃/MoO₂,various molybdenum ions were doped to the interface between the coating layer and the bulk phase,regulating the composition of the interface,resulting in affecting the chemical environment of the ligand.From the electrochemical data,appropriate interfacial components had the best cycle performance and rate performance.The capacity retention of the modified material was 90.5%at 1C after 300 cycles,elevate 41.6%compared with untreated sample.All in all,molybdenum oxide coating layers could improve the electrochemical performance,improving the performance of Li-Rich cathode materials take account into the material’s capacity and cycle stability.