极片面密度和压实密度对Li_3V_2(PO_4)_3/C电化学性能的影响

Effect of electrode plate surface density and press density on electrochemical performance of Li_3V_2(PO_4)_3/C

采用溶胶-凝胶法合成Li_3V_2(PO_4)_3/C正极材料,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、充放电循环测试、电化学阻抗谱(EIS)、循环伏安(CV)等手段研究极片面密度和压实密度对Li_3V_2(PO_4)_3/C电化学性能的影响。结果表明:Li_3V_2(PO_4)_3/C的倍率性能随着面密度的增加而变差,且面密度越大极化现象越严重,20C时放电比容量差距高达22.8(mA·h)/g。EIS分析结果表明:随着面密度的增加,电荷转移阻抗增大,锂离子表观扩散系数降低。当极片压实密度过高或过低时,Li_3V_2(PO_4)_3/C的倍率性能均较差,压力为20 MPa时放电比容量最高,20C时放电比容量为94.0(mA·h)/g,而0和35 MPa时放电比容量仅70(mA·h)/g左右。EIS和CV测试结果表明:极片压实密度较小和较大的情况均不利于电荷和锂离子的转移。

Li3V2（PO4）3/C anode material was prepared by sol-gel method.The effects of surface density and press density of the cathode electrode on electrochemical performance of Li3V2（PO4）3/C were characterized by X-ray diffractometry（XRD）,scanning electron microscopy（SEM）,galvanostatic charge-discharge test,electrochemical impedance spectroscopy（EIS） and cyclic voltammetry（CV）.The results show that the rate capability of Li3V2（PO4）3/C electrode becomes worse with the increase of surface density,delivering a discharge specific capacity gap of as high as 22.8（mA·h）/g at 20 C,and is accompanied by a more severe polarization.The EIS results show that the charge transfer resistance increases and apparent lithium ion diffusion coefficient decreases with the increase of surface density.Besides,the rate capability of Li3V2（PO4）3/C is poor when the press density is either too low or too high.It is evidenced that Li3V2（PO4）3/C electrode pressed at the pressure of 20 MPa can provide the highest discharge capacity of 94.0（mA·h）/g at20 C,but only about 70（mA·h）/g at 0 and 35 MPa.The results of EIS and CV show that it is not conductive to the transformation of charge and lithium ion under too high or too low press density.