锂离子电池负极材料Li_3V_2(BO_3)_3/C复合材料的合成及电化学性能研究

Syntheses and Electrochemical Properties of Li_3V_2(BO_3)_3/C Anode Materials for Lithium-Ion Batteries

本文以草酸锂、五氧化二钒、硼酸为原料,二水合草酸为碳源和还原剂,无水乙醇为分散剂,采用球磨法合成了Li_3V_2(BO_3)_3/C(LVB/C)复合材料前驱体,后经高温热处理得到LVB/C复合材料.采用TG-DTA技术对前驱体进行了热分析,通过XRD、SEM、EDS等技术研究了烧结条件对LVB/C材料的晶体结构、微观形貌、含碳量的影响.通过恒流充放电测试、循环性能测试、循环伏安测试和电化学阻抗测试等技术研究了烧结条件对LVB/C材料电化学性能的影响.电化学测试结果表明,800 o C下烧结10 h得到的样品电化学性能最佳,在50 mA·g^(-1)电流密度下,首次充放电比容量分别为427.6 mAh·g^(-1)和669.1 mAh·g^(-1),循环10次后,容量保持率分别为55.4%和35.2%.

The Li3V2（BO3）3/C（LVB/C） composite materials were successfully synthesized in two steps：Firstly, a stoichiomertric mixture of Li2 C2 O4, V2O5, H3BO3, H2C2O4·H2O and ethanol was thoroughly ball-milled to get the precursors. Secondly, the precursors were post-calcinated to get the ultimate products. The calcination temperatures of 750 oC, 800 oC and 850 oC were selected based on the TG-DTA analyses. The crystal structures, surface morphologies and carbon contents of the samples calcinated at five conditions, namely, a（750 oC, 10 h）, b（800 oC, 10 h）, c（850 oC, 10 h）, d（800 oC, 5 h） and e（800 oC, 15 h）, were characterized by XRD, SEM and EDS, respectively. The results showed that the dominant phase of all the samples was（Li0.31 V0.69）_3BO_5 with the impure Li3VO4 phase in Samples a, b, c, and Li VO2 phase in Samples a, b, d and e. All of the samples consisted of many cylindrical particles, polygonal particles and agglomerations, among which Sample b showed better crystallized and less-agglomerated particles. EDS data demonstrated that the carbon, oxygen and vanadium elements were uniformly distributed in Sample b, and the carbon contents in Samples a, b, c, d, and e were 2.64%, 1.17%, 1.51%, 1.97%, and 1.30%, respectively. The electrochemical performances of Samples a, b, c, d and e were compared by obtaining the galvanostatic charge/discharge, cycling ability, and cyclic voltammetry curves, and electrochemical impedance spectra. The results revealed that Sample b achieved the optimal electrochemical performance. The initial charge/discharge capacities at a current density of 50 m A·g-1 were 427.6 m Ah·g^（-1） and 669.1 mAh·g^（-1）,respectively. However, after 10 cycles, only 55.4% and 35.2% of the initial charge/discharge capacities were retained, which might be related to the phase transformation from crystalline to amorphous during the insertion and extraction of lithium ions.