Study On Lithium-ion Battery System Based On High-voltage Cathode Material

Spinel structure Li_zNi_xMn2-xO₄ were synthesized by high-temperature solid-phase method,with Li2CO₃ as lithium source, NiO as nickel source and Mn3O₄ as manganese source, determining the best material ratio and calcined system, to improve its electrochemical performance, and 14500 full cell with Li_1.04Ni_0.4Mn_1.56O₄ as cathode was assumed. To improve the electrochemistry performance of Li_1.04Ni_0.4Mn_1.56O₄, it was blended with Li FePO₄/C. Samples were observed by scanning electron microscope（SEM） and examined by X-ray diffraction pattern（XRD） and electrochemical performance tests（charge-discharge and cycle test）.To acquire Li_zNi_xMn_2-xO₄ which had the best performance we designed contrast experiments based on important factors such as nickel contents, overdose ratio of lithium source, the ratio of Ni/Mn and different calcined system. And results showed that discharge capacity and cycle retention of the material was better after two step calcination, which meaned the material has been calcined under 850 °C for 8 h firstly and then be calcined under 850 °C for 2 h secondly. The results showed that when the lithium source of Li2CO₃ excesses 0.04, nickel content of 0.4 and Ni/Mn of 0.4:1.56 in spinel LizNixMn2-xO₄,sample had the best performance, which first discharge capacity under 0.2 C was 134.5 mA h·g-1. Its discharge capacity under 1 C was 133.1 mA h·g-1, which was reduced to 131.7 m A h·g-1 after 80 cycles with 98.9% cycle retention rate.We researched full cell performance of Li_1.04Ni_0.4Mn_1.56O₄ which had the best electrochemical performance with graphite as nagtive, to determine the optimum parameters of cathode pole piece. The process parameters just as follows: the ratio of cathode and anode was 1:1.08, active substance content was 92.5%, KS-6 content was 2.5%, S-P content was 1.5%. The results showed that its double surface density was 316g·m-2, compacted density was 2.9g·cm-3, internal resistance was 35 mΩ, practical discharge capacity was 435.4 m A h under 0.5 C, discharge capacity under 1 C was 424.4 mA h, which was reduced to 153.4 mA h after 100 cycles with 36.2% cycle retention rate.Solid phase synthesis of LiFePO₄/C was blended with spinel Li_1.04Ni_0.4Mn_1.56O₄ which had the best electrochemical performance according to the mass ratio, to determine the optimal ratio of mixing material. The testing results showed when the mixing ratio was 2:3(Li_1.04Ni_0.4Mn_1.56O₄:LiFePO₄), after wet ball grindling 1h, the blending material had the best electrochemical performance which first discharge capacity under 0.2C was 163.6 mAh·g-1. Its discharge capacity under 1C was 139.4 mAh·g-1, which was reduced to 130.7 mAh·g-1 after 100 cycles with 93.7% cycle retention rate. Blending material complemented each other’s disadvantages.