Lithium-ion Battery Cathode Material Li <sub> Fesio <sub>, 2 </ Sub> 4 </ Sub> Modified Research

The development of rechargeable lithium-ion batteries and cathode materials are reviewed in detail. With the advantages of high safety, non-toxicity, low cost and abundant recource, Li₂FeSiO₄ has been considered as a promising cathode material on lithium-ion batteries. Synthesis of materials, modification process, structure characterization, electrochemical behaviors of Li₂FeSiO₄ has been involved in this study.Li₂FeSiO₄ doped with Ni was synthesized via a solid-state reaction. The precursor was characterized by TG/DTA, and the effort of Ni content on physical structure and electrochemical performance of Li₂FeSiO₄ has been investigated by XRD, SEM and electrochemical methods. The results suggested that Ni doping has increased the charge-discharge capacity, improved the cycle performance. Li₂Fe_0.7Ni_0.3SiO₄ shows the highest discharge capacity and the best cyclying stability.Li₂Fe_1-xMn_xSiO₄/C was synthesized using sucrose as carbon source and reductant, and the effort of doping amount, sintering temperature, sintering time and Li/Si ratio on Li₂Fe_1-xMn_xSiO₄/C's performance were systematically researched. The optimized Li₂Fe_0.9Mn_0.1SiO₄/C sample was synthesized at 600℃for 16h and a Li/Si moral ratio of 2.04. It delivered an initial capacity of 149.8mAh·g^-1 between 1.5V and 4.8V at C/16 rate and a capacity retention ratio of 90.1% after 30 cycles. Rate capability and cycle performance at high temperature of Li₂Fe_0.9Mn_0.1SiO₄/C synthesized at the optimum conditions were also studied. Cycle performance become worse with increasing the discharge rate, electrochemical performance of Li₂Fe_0.9Mn_0.1SiO₄/C at high temperature were markedly improved. It showed a flat potential plateau and the discharge capacity retention ratio remained 94.2% after 30 cycles.Li₂Fe_0.9Mn_0.1SiO₄/C with different content of sucrose and glucose were prepared. The grain size and tap density of Li₂Fe_0.9Mn_0.1SiO₄/C decreased with the increasing carbon content. Compared with Li₂Fe_0.9Mn_0.1SiO₄/C using sucrose as carbon source, that using glucose displayed smaller particles and more homogeneous distribution, the sample with 15% carbon exhibited excellent performance, with an initial discharge capacity of 154.7mAh·g^-1 and a capacity retention rate of 92.2% after 30 cycles.The lithium deintercalation-intercalation kinetics of pure Li₂FeSiO₄ and modified materials were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and potential step chronoamperometry methods, and a fitting equivalent circuit diagram was built. The results further proved the modified Li₂FeSiO₄ had better electrochemical performance than the pristine one.