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采用溶胶-凝胶法制备锂离子电池正极材料Li_3V_2(PO_4)_3/C.通过恒电流充放电测试、循环伏安(CV)、电化学阻抗谱(EIS)等方法,研究了Li_3V_2(PO_4)_3/C在不同电压区间的电化学行为(3.0-4.5 V和3.0-4.8 V).结果表明,3.0-4.8 V电压区间的循环性能和倍率性能均不及3.0-4.5 V电压区间的.3.0-4.5 V区间0.1C(1C=150m A·g~(-1))倍率首次放电比容量为127.0 mAh·g~(-1),循环50次后容量保持率为99.5%,而3.0-4.8 V区间的分别为168.2 mAh·g~(-1)和78.5%.经过高倍率测试后再回到0.1C倍率充放电,3.0-4.5 V和3.0-4.8 V的放电比容量分别为初始0.1C倍率的99.0%和80.7%.经过3.0-4.8 V电压区间测试后,少部分第三个锂离子能够在低于4.5V的电压脱出,使3.0-4.5 V电压区间的放电比容量提升了7.4%.CV结果表明3.0-4.8 V区间的容量损失主要表现为第一个锂离子的不可逆损失.极片的X射线衍射(XRD)和X射线光电子能谱(XPS)分析测试结果表明经过3.0-4.8 V测试后,Li_3V_2(PO_4)_3的结构发生了轻微的改变.电感耦合等离子体(ICP)测试结果表明循环后的电解液中含有少量的V.结构变形和V溶解可能是Li_3V_2(PO_4)_3在3.0-4.8 V区间容量衰减的主要原因.
Li_3V_2 (PO_4) _3 / C was prepared by sol-gel method. The effects of Li_3V_2 (PO_4) _3 / C were investigated by means of constant current charge and discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) (3.0-4.5 V and 3.0-4.8 V). The results show that the cycling performance and rate performance in the voltage range of 3.0-4.8 V are not as good as the 3.0-4.5 V voltage range, The first discharge capacity at a rate of 0.1C (1C = 150m A · g -1) in the 4.5 V range was 127.0 mAh · g -1. After 50 cycles, the capacity retention was 99.5%, while that of 3.0-4.8 V The range of 168.2 mAh · g ~ (-1) and 78.5% respectively.After the high rate test and then back to the 0.1C charge and discharge, 3.0-4.5 V and 3.0-4.8 V discharge capacity were the initial 0.1C rate Of 99.0% and 80.7%, respectively.After a period of 3.0-4.8 V, a small part of the third lithium ion could be released at a voltage lower than 4.5V, increasing the specific discharge capacity in the voltage range of 3.0-4.5 V by 7.4%. CV results show that the capacity loss in the interval of 3.0-4.8 V is mainly the irreversible loss of the first lithium ion.The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis of the pole pieces show that after 3.0 The structure of Li_3V_2 (PO_4) _3 changed slightly after -4.8 V test.The results of inductively coupled plasma (ICP) test showed that there was a small amount of V. The structural deformation and V dissolution of Li_3V_2 (PO_4) ) _3 The main reason for the capacity decay in the 3.0-4.8 V range.