Studies On The Modified Li₂FeSiO₄/C Composite Cathode Materials For Li-ion Battery

Recently secondaryLi-ion battery market growth is very rapid, especially for power battery market. Silicate cathode materials have prominent advantages applied in power battery, but no breakthrough have be made for the preparation method and the modification research, which greatly limits the application of such materials. In this work, we adopt the method combining sol-gel and high temperature carbon reduction to prepare the Li2FeSiO4/C composite cathode material, which is the most representative in silicate cathode materials. Meanwhile, Li2Fe0.5Mn0.5SiO4/C composite cathode materials were obtained with manganese metal ion doping. Finally quadrol was replaced by organic glucose to prepare complexation sol-gel, and Li2FeSiO4-xNy/C composite cathode materials with N-doping and oxygen vacancy were obtained. Such modified Li2FeSiO4/C composite cathode materials were characterized by TG, XRD, SEM, XPS, IR, AC impedance and charge-recharge electrochemical tests, indicating that:(1)The particle of Li2FeSiO4/C composite cathode material is uniform and the optimum calcining temperature is 700℃, the time is 12h.(2)Nanosize Li2FeSiO4/C composite cathode materials by addition of nanoscale conductivity carbon materials are prepared and singnificantly depends on the particle size and specific surface of the introduced carbon materials. The addition of different carbon can slightly change the structure of Li2FeSiO4/C, improving electronic conductivity and lithium ion release rate, and leading to the enhancement of the electrochemical properties.(3) For the Li2Fe0.5Mn0.5SiO4/BP2000 compound positive materials, they can acquire over a lithium-ion emerge-embedded capacity. At 0.1C ratio, the first charging capacity is 180mAh/g, and the discharging capacity is more than 140 mAh/g. After 50 cycles the capacity is 110 mAh/g with a 3.2 V platform.(4) For the Li2FeSiO4-xNy/C composite positive materials with oxygen vacancy by doping higher electrical negative N element, the first charging and discharging capacity at 0.1C ratio is more than 160 mAh/g, reducing the emerge-embedded voltage of second li-ion battery. The first charging and discharging capacity at 1C ratio is more than 140mAh/g, while it is more than 120 mAh/g after 10 cycles, indicating a very good performance at different charge/discharge rate and cycle life for such modified materials.