Study On Fabrication Of High Capacity Cathode And Anode Materials For Lithium Ion Secondary Battery

With the development of electronic products and electric vehicle technology in daily life, the lithium ion secondary battery becomes research focus. The key materials of lithium ion secondary battery are the cathode materials and anode materials. Their capacity directly affects the battery application in new technology. In order to make the application of lithium ion secondary battery become more widespread, the development of cathode materials and anode materials which have high capacity and good cycle stability become very necessary.Currently. Lithium iron phosphate is a promising cathode material candidate for lithium rechargeable batteries attribute to its safety and cycle stability. In the third chapter,we used nano-Fe2O3 as raw materials to synthesis nano-LiFePO4/C by the traditional carbon thermal reduction method. The as-prepared LiFePO4/C can keep 152.6 mAh/g after 10 cycles under 5 C. Considering the high cost, the nano Fe2O3 was not suitable for mass production. In the fourth chapter, we used normal Fe2O3 as raw materials, in order that the larger particles of normal Fe2O3 weren’t reacted completely. Hydrogen gas was injected into the tube furnace to build a reduction atmosphere. We discussed the relationship between hydrogen content and performance. LiFePO4/C had the best performance, which capacity reached 162 mAh/g at 0.1 C when the H2 volume content is 8%.Nickel manganese cathode materials attract most of interesting due to its high charge and discharge voltage and high capacity. We synthesized successfully nickel manganese oxide as the precursor for LiNi0.5Mn0.5O2 with layered structure similar as NaFeO2 using spray drying method. LiNi0.5Mn0.5O2 was doped with MgO to improve the electrochemical performance. As the doped sample has better charge-discharge properties and cycle performance, their discharge capacity is 197.85 mAh/g at 0.1 C and remains rarely after 10 cycles. But the cycle performance is not ideal at a higher rate (1 C). The first cycle can still remain 195 mAh/g, but the discharge capacity quickly reduced to 168 mAh/g after 3 circles.In the sixth chapter, carbon coating macroporous Mn2P2O7 composite particles were fabricated by hydrothermal method. The Mn2P2O7/C electrodes exhibited initial reversible capacities of 466 mAh/g and after 20 cycles it could deliver 329.8 mAh/g of discharge capacity better than Mn2P2O7 without carbon-coated. As we know, our samples have good discharge capacity at a current density of 100 mA/g.