锂离子电池负极材料Li3V2(BO3)3/C 复合材料的合成及电化学性能研究

本文以草酸锂、五氧化二钒、硼酸为原料，二水合草酸为碳原和还原剂，无水乙醇为分散剂，采用球磨法合成了Li₃V₂(BO₃)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 ℃下烧结10 h得到的样品电化学性能最佳，在50mA•g^-1电流密度下，首次充放电比容量分别为427.6mAh•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 %.

Synthesis and Electrochemical Properties ofLi3V2(BO3)3/C Anode Materials for Lithium-Ion Batteries

The Li₃V₂(BO₃)₃/C (LVB/C) composite materials were successfully synthesized in two steps：Firstly, a stoichiomertric mixture of Li₂C₂O₄, 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 ℃, 800 ℃ and 850 ℃ were selected based on TG-DTA analyses. The crystal structures,surface morphologies and carboncontents of the samples calcinated at five conditions, namely, a(750 ℃, 10 h), b(800 ℃, 10 h), c(850 ℃, 10 h), d(800 ℃, 5 h) and e(800 ℃, 15 h), were characterized by XRD, SEM and EDS, respectively. The results showed that the dominant phase of all the samples was (Li_0.31V_0.69)₃BO₅ withthe impureLi₃VO₄ phase in Samples a, b, c, and LiVO₂ 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 showedbetter crystallized and less-agglomerated particles. EDS data demonstrated that thecarbon, oxygen and vanadium elements were uniformly distributed in Sample b, and the carbon contentsin Samples a, b, c, d, e were 2.64 %, 1.17 %, 1.51 %, 1.97 %, 1.30 %, respectively. The electrochemical performances of Samples a, b, c, d and e were compared by obtaining the galvanostatic charge/discharge, cycling ability, cyclic voltammetry curves,and electrochemical impedance spectra. The resultsrevealed that Sample bachieved the optimal electrochemical performance. The initial charge/discharge capacities at a current density of 50mA•g^-1 were 427.6mAh•g^-1 and 669.1mAh•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.