混合溶剂对溶胶-凝胶法制备的Li_3V_2(PO_4)_3/C高倍率性能的影响

Effects of Mixed Solvents on the High-Rate Performance of Li_3V_2(PO_4)_3/C Prepared by Sol-Gel Method

以有机-水为混合溶剂,采用溶胶-凝胶法制备锂离子电池正极材料Li3V2(PO4)3/C,选取乙醇、乙二醇和1,2-丙二醇为有机溶剂,聚丙烯酸(PAA)为碳源和螯合剂.通过X射线衍射(XRD)、扫描电镜(SEM)、恒流充放电以及循环伏安测试等方法,研究了产物的结构形貌及电化学性能.XRD测试结果表明所有溶剂制备的样品结晶良好,有机溶剂的加入不影响Li3V2(PO4)3材料的晶型结构.恒流充放电结果表明有机溶剂的加入改善了材料的电化学性能.以1,2-丙二醇-水为溶剂的样品电化学性能最好,在3.0-4.5V电压范围内,0.1C(1C=150mA·g-1)倍率首次放电比容量为132.89mAh·g-1,10C倍率首次放电比容量达125.42mAh·g-1,循环700周后容量保持率为95.79%,具有良好的倍率性能与循环性能;在3.0-4.8V电压范围内倍率性能较差.扫描电镜结果表明混合溶剂制备的样品呈片状和针状,这种形状有利于锂离子的扩散,因此提高了材料的电化学性能.

A Li3V2（PO4）3/C composite cathode material was obtained by a sol-gel method using deionized water and organic solvents as mixed solvents. Ethanol, ethylene glycol, and 1,2-propylene glycol were used as the organic solvents and polyacrylic acid （PAA） was used as the chelating agent and carbon source. The structure, morphology, and electrochemical performance of the synthesized materials were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, charge-discharge tests, and cyclic voltammetry. XRD analysis showed that all the materials were well crystallized and that the addition of organic solvents did not affect the crystal structure of Li3V2（PO4）3. The results of galvanostatic cycling showed that the electrochemical performance of the products was improved by the addition of organic solvents. The material synthesized using 1,2-propylene glycol had the best electrochemical performance. It exhibited an initial discharge capacity of 132.89 mAh·g-1 at 0.1C （1C=150 mA·g-1） in the voltage range of 3.0-4.5 V. The initial discharge capacity was as high as 125.42 mAh·g-1 upon discharging at 10C, and it had a capacity retention of 95.79% after 700 cycles. These results indicate a good rate and cycling performance in the voltage range of 3.0-4.5 V; while in the voltage range of 3.0-4.8 V, it exhibits a bad rate performance. SEM images indicated that the sample prepared using the mixed solvents had a flake-like and needle-like shape, which facilitates the interface ion-transfer process and thus improves the overall electrochemical properties.