锂离子电池用LiVPO4F/C 基正极材料的制备和性能

摘要

LiVPO4F/C-based material was prepared by heating a precursor, which was obtained through ball milling with slurry of H2C2O4·2H2O, NH4H2PO4, NH4VO3 and LiF. In this process, H2C2O4·2H2O was used as a reducing agent as well as carbon source. The properties of the precursor and the prepared sample were characterized by TG-DTA, XRD, SEM, TEM and C−S analysis. XRD analysis shows that the precursor is amorphous and the prepared LiVPO4F sample coexists with Li3V2(PO4)3, as well as a small amount of V2O3. Homogeneous powders with an average particle size of 2μm are observed by TEM. HRTEM image shows that the crystal particles are coated by amorphous carbon uniformly, with a coating layer of about 2 nm. The synthesized material shows the specific discharge capacities of 151.3 and 102.5 mA·h/g at 0.1C and 10C respectively, in the voltage range of 3.0−4.4 V, and it keeps 90.4%of initial discharge capacity at 10C after 50 cycles. V3+/V4+redox peaks corresponding to both LiVPO4F and Li3V2(PO4)3 are seen clearly in the CV curve.%将H2C2O4·2H2O, NH4H2PO4, NH4VO3和 LiF通过球磨反应、烧结，合成了 LiVPO4F/C 基正极材料。在这个过程中，草酸起还原剂和碳源的作用，利用热重、 X 射线衍射、扫描电镜、透射电镜和碳−硫分析等手段对合成的前驱体和材料进行检测和分析。XRD分析表明，球磨反应后所得到的前驱体为无定形态，而烧结后的材料中除了LiVPO4F的衍射峰外，还存在Li3V2(PO4)3和V2O3衍射峰。材料颗粒均匀，尺寸约2μm。透射电镜分析表明，合成的材料颗粒表面包裹着一层约2 nm厚的无定形碳。在截止电压3.0~4.4 V时，合成的材料在0.1C和10C倍率下的放电比容量分别为151.3和102.5 mA·h/g。在10C倍率下循环50次后容量保持率为90.4%。在LiVPO4F 和Li3V2(PO4)3的循环伏安曲线中可以明显看到V3+/V4+的氧化还原峰。