Research On Synthesis And Surface Modifition Of Cathode Materials LiNi_0.5Mn_1.5O₄ For Lithiun-ion Batteries

Lithium-ion batteries have been widely used in portable electronic devices,electric vehicles,and large-scale energy storage devices due to their advantages of high-energy and high-power densities.Among the numerous cathode materials,lithium nickel manganese oxide(LiNi0.5Mn1.5O4)with a 3D li-ion diffusion framework has received significant attention because of its relatively high operation potential(-4.8V vs.Li/Li+)and a larger specific capacity(650Wh/g).Unfortunately,LiNi0.5Mn1.5O4 also suffers from poor rate capablity and unsatisfied cyclic stability.In this work,the electrochemical performances of LiNi0.5Mn1.5O4 cathode materials ha-ve been improved by surface modfcation and the main work is divided into two parts as follows,Firstly,zero-gap PbPdO2 oxides were coated on LiNi0.5Mn1.5O4 surface via sol-gel method.The structual propetries and surface morphologies of the as-prepared composites were systematically characterize with X-ray diffraction,scanning electron microscopy,Raman spectroscopy,and electron energy spectroscopy.The effect of PbPdo2 surface-modification on the electrochemical performance of LiNi0.5Mn1.5O4 was investigated by charge-discharge test,electrochemical impedance spectroscopy(EIS)and Cyclic voltammograms(CV).It was found that PbPdO2 surface-modification improved significantly rate capablity and cycling stability of LiNi0.5Mn1.5O4 cathode materials.Analysis from electrochemical performances and Kelvin probe force microscopy measurements indicates that the enhancement of electrochemical performance is mainly attributed to smaller polarization and charge transfer resistances induced by high-conductivity PbPdO2 surface-modification.Secondly,surface-sulfidized LiNi 0.5 Mn 1.5 O 4 cathode materials are successfully synthesized through electrostatic interactions.The results show that the surface-sulfidized LiNi0.5Mn1.5O4 exhibits a superior electrochemical performance in terms of the rate capability,cycling stability and thermal stability.A discharge capacity of 93.4 mAhg-1 can be still delivered at 2 C after 2500 cycles,with a capacity retention of 74.9%of the stable capacity.However,the capacity retention rate of LiNi0.5Mn1.5O4 sample was only 45.3%at 2C after 1800 times cycles.Electrochemical performance tests and Kelvin probe force microscopy results showed that the enhancement of electrochemical performance and thermal stability was mainly attributable to the fact that the surface-sulfidized layer against HF attack,reduced the work function of the material.and promotes the diffusion kinetics of lithium ions.