三元掺杂改性锂离子电池正极材料Li_3V_2(PO_4)_3

Triple-Cation-Doped Li_3V_2(PO_4)_3 Cathode Material for Lithium Ion Batteries

以柠檬酸为螯合剂和还原剂,NH4VO3为钒源,通过溶胶-凝胶法制备了锂离子电池正极材料Li3V2(PO4)3及其三元掺杂体系Li2.85Na0.15V1.9Al0.1(PO4)2.9F0.1.分别采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、能量损失谱(EELS)、拉曼(Raman)光谱、扫描电子显微镜(SEM)、X射线能谱(EDS)、恒流充放电、循环伏安(CV)和交流阻抗谱(EIS)等技术对材料的微观结构、颗粒形貌和电化学性能进行分析.结果表明:在残余碳包覆的基础上,Na、Al、F三元掺杂有利于稳定Li3V2(PO4)3的晶体结构,进一步减少颗粒团聚和提升材料导电特性,促进第三个锂离子的脱出和嵌入,从而显著改善Li3V2(PO4)3的实用电化学性能.未经掺杂的Li3V2(PO4)3原粉在1/9C、1C和6C倍率下的可逆比容量分别为141、119和98 m Ah g–1,而三元掺杂改性材料在1/9C、1C、8C和14C倍率下的比容量分别为172、139、119和115 m Ah g–1.在1C倍率下循环300圈后,掺杂体系的比容量依然高达118 m Ah g–1,比原粉高出32.6%.值得注意的是,这种三元掺杂还使Li3V2(PO4)3的多平台放电曲线近似转变为一条斜线,显示出可能不同的储锂机制.

Li3V2（PO4）3 and its triple-cation-doped counterpart Li2.85Na0.15V1.9Al0.1（PO4）2.9F0.1 were prepared by a conventional sol-gel method. The effect of Na-Al-F co-doping on the physicochemical properties, especially the electrochemical performance of Li3V2（PO4）3, were investigated by X-ray diffraction（XRD）, high-resolution transmission electron microscopy（HRTEM）, electron energy loss spectroscopy（EELS）, Raman spectroscopy,scanning electron microscopy（SEM）, X-ray energy dispersive spectroscopy（EDS）, galvanostatic charge/discharge, cyclic voltammetry（CV）, and electrochemical impedance spectroscopy（EIS）. It was found that combined with surface coating from residual carbon, this triple-cation co-doping stabilizes the crystalline structure of Li3V2（PO4）3, suppresses secondary particle agglomeration, and improves the electric conductivity.Moreover, reversible deinsertion/insertion of the third lithium ion at deeper charge/discharge is enabled by such doping. As a consequence, the practical electrochemical performance of Li3V2（PO4）3 is significantly improved. The specific capacity of the doped material at a low rate of 1/9C is 172 mAh·g^-1 and it maintains115 mAh·g^-1 at a rate of 14 C, while the specific capacities of the undoped sample at 1/9C and 6C are only141 and 98 mAh·g^-1, respectively. After 300 cycles at 1C rate, the doped material has a capacity of 118 mAh·g^-1, which is 32.6% higher than that of the undoped counterpart. It is also noteworthy that the multiplateau discharge curve of Li3V2（PO4）3 transforms to a slope-like curve, indicating the possibility of a different lithium intercalation mechanism after this co-doping.