Hydrothermal Synthesis Of Lithium Rich Layered-spinel Composite Cathode Material And Its Electrochemical Performance

In recent years, lithium rich layered cathode materialxLi2MnO3-(1-x)Li(Mn0.5Ni0.5)O2has been extensively investigated for its advantagesof high discharge specific capacity, low cost, environment friendly, which wasconsidered as the most suitable cathode material for electric vehicles. However, thekey issues of large initial irreversible capacity, poor rate performance and capacityfading during cycling hinder the application of the cathode material. Thus, it is veryimportant to explore new cathode materials with high capacity, high cycleperformance and high rate performance.Lithium rich layered oxide/graphene composite was synthesised by hydrothermalmethod, and the effect of graphene content on the electrochemical performance of thecomposite was investigated. Lithium rich layered-spinel composite was synthesisedby hydrothermal method followed by calcination. The morphologies, microstructureand electrochemical performance of the layered-spinel composite were compared withthose of the single spinel and layered material. The influence of process parameterssuch as hydrothermal reaction temperature, time and calcination temperature on thecontents of layered phase and spinel phase have been studied.The results show that (1) Lithium rich layered cathode is comprised ofnanoparticles with the size below100nm, and the optimized process parameters arehydrothermal temperature of180°C and hydrothermal reaction time of10h.(2) Theaddition of graphene can improve the electrochemical performance for its superiorconductivity and high specific surface area. The sample containing4wt%grapheneexhibits the best performance.(3) The first-cycle efficiency and cycle stability oflayered-spinel composite are significantly improved, the efficiency rises from71%to90%and discharge capcacity keeps at227mAh g-1after50cycles, while the capacityloss ratio of layered cathode is34.3%. The result also indicates the layered-spinelcomposite could decrease the Rctof layered structure. The Rctof the composites is103.2Ω cm2after cycled10th, while Rctof layered structure is613.7Ω cm2.(4) Spinelcontent could be controlled by preparation technique, and spinel content decreaseswith the hydrothermal time and increasing reaction temperature.