Synthesis And Modification Of Li₂FeSiO₄and Li[Li_0.2Co_0.13Ni_0.13Mn_0.54]O₂Cathode Materials By Sol-gel Method

Silicate Li2FeSiO4and lithium-rich layered Li[Li0.2Co0.13Ni0.13Mn0.54]O2oxides havepotential applications for next-generationlithium ion batteries due to their high theoreticalspecific capacity as cathode materials. However, it is difficult to synthesize the pureLi2FeSiO4phase, low conductivity, poor rate capability due to its low conduction, limitingitsapplication. Also, lithium-rich layered Li[Li0.2Co0.13Ni0.13Mn0.54]O2exhibits a grandual decayof both capacity and voltage during long cycles, although it posseses high specific capacity. Inthis study, in order to attack these problems, we investigate the wet-chemical synthesisprocess, micro-nanostructure,and electrochemical properties of Li2FeSiO4andLi[Li0.2Co0.13Ni0.13Mn0.54]O2cathode materials.Through investigating the synthesis process of the materials, the Li2FeSiO4/Cnanocomposite materialswere obtained using PEO-PPO-PEO triblock copolymer (P123) ascarbon source by sol-gel method. It shows that the Li2FeSiO4/C nanocomposite anneled at650℃exhibits the best electrochemical performance. The initial charge and dischargecapacities are163.7mAh/g and172mAh/g at0.1C, respectively. In addition,it is found thathydrothermal treatment benefits to controlling particle morphology and size, but it wouldbring impurities to the composites. Finally, the Li2FeSiO4/C nanocomposite can be used as thenegative electrode material. The initial charge-discharge capacity are451mAh/g and840mAh/g at the current density of50mA/g, respectively，and the material exhibits good cyclestability.Based on above synthesis process, the Mn doped Li2FeSiO4/C nanocomposite powder withgood dispersion was obtained though hydrothermal treatment, followed by calination at670℃. This material shows a slightly higher discharging votage. In addition, in order todope P in Si site, P2O5is introduced into the Li2FeSiO4/C nanocomposite. As a result, theLi2FeSiO4/C nanocomposite containing P2O5exhibits better cycle stability at high rates.Optium P2O5content should be less than10%, otherwise excess of the P2O5would reduce thecapacity of the material.The lithium-rich layered Li[Li0.2Co0.13Ni0.13Mn0.54]O2materials wereprepared usingethylene diamine tetraacetic acid (EDTA) as complexing agent by sol-gel method. However, it shows poor cycling performance due to the agglomeration of the material particles. By fillingthe precursor solution into PMMA template, the material possesse dispersed and uniformparticles with a size of approximately100nm, improving electrochemical cycleability. Theinitial charge-discharge capacity are330mAh/g and280mAh/g at the current density of40mA/g, respectively，with capacity retention near to71%.