合成及其性能
(中南大学 化学化工学院， 长沙 410083)
摘 要: 以LiOH·H2O、 V2O5和NH4H2PO4为原料， C为还原剂， 采用高温固相法合成了锂离子电池正极材料磷酸钒锂（Li3V2(PO4)3）。考察了合成温度等条件对产物组成和晶相的影响。 结果表明： 随着焙烧温度的升高， 杂相的衍射峰相对强度逐渐减弱， 当煅烧温度达到800 ℃时， 杂相衍射峰消失， 所得样品为纯相的Li3V2(PO4)3样品； 按Li、 V、 P的摩尔比为3∶2∶3将原料在800 ℃下焙烧24 h， 合成得到正极材料。 该材料在0.1 C充放电制度下， 首次充电比容量达到135 mA·h/g， 首次放电比容量130 mA·h/g， 充放电效率达96.3％； 经过20次循环后， 放电容量仍然高达110 mA·h/g。 对经过20次循环后的样品进行了X射线衍射分析，结果发现， 经过20次循环后样品仍然具有单斜晶体结构， 样品各主要衍射峰强度都急剧减弱， 说明样品在充放电过程中晶体结构发生了变化；采用最小二乘法对样品充放电前后的晶胞参数进行了计算， 发现样品在经过充放电循环后晶胞参数都有不同程度的增加， 晶胞体积增大0.6％左右。
关键字: Li3V2(PO4)3；正极材料； NASCION结构
cathode materials Li3V2(PO4)3 for
lithium-ion batteries
（ School of Chemistry and Chemical Engineering,
Central South University, Changsha, 410083, China）
Abstract: The cathode material Li3V2(PO4)3 was prepared by solid-state reaction of LiOH·H2O, V2O5 and NH4H2PO4, with carbon as the reduction agent. The effects of reaction conditions such as temperature on the structure were investigated by X-ray diffractrometry. The results show that the sample synthesized from the raw materials with molar ratio of Li, V and P of 3∶2∶3 at 800 ℃ for 24 h has a pure monoclinic crystal structure, which derives a initial discharge specific capacity of 130 mA·h/g. After charged/discharged at 0.1 C rate for 20 cycles, the sample retaines a discharge specific capacity of 110 mA·h/g. XRD patterns show that it retains monoclinic crystal structure, but the intensity of diffraction declines sharply. Least square method was used to calculate the unit-cell parameters of the sample before and after cycling, it is found that all of the parameters increase to some extend, and the unit-cell volume increases by 0.6%.
Key words: Li3V2(PO4)3; cathode materials; NASCION structure
