SO42-掺杂对Nasicon型Li3Fe2(PO4)3正极材料电化学性能的影响

采用溶胶-凝胶法用S\begin{array}{c}{O}_4^{2-}\end{array}部分代替Li₃Fe₂(PO₄)₃中的P\begin{array}{c}{O}_4^{3-}\end{array}阴离子制得Li_3-xFe₂(PO₄)_3-x(SO₄)_x(x=00.90)正极材料, 通过X射线衍射、 充放电技术、 循环伏安特性测试及电化学阻抗谱表征了掺杂材料的相组成及电化学性能. 结果表明, S\begin{array}{c}{O}_4^{2-}\end{array}主要以固溶形式存在于Li₃Fe₂(PO₄)₃中, 产物中还伴有少量Fe₂O₃第二相析出. S\begin{array}{c}{O}_4^{2-}\end{array}掺杂使Li₃Fe₂(PO₄)₃的放电容量呈抛物线形规律变化, 并在掺杂浓度x=0.60时达到最佳值, 该样品在0.5C倍率下的首次放电容量为111.59 mA·h/g, 比未掺杂的样品提高了18.4%; 60次循环充放电后的容量保持率为96%; 将该样品的放电倍率由0.5C逐渐提高至5C, 再降至0.5C, 并在每个倍率下循环10次, 材料的最终放电容量仍能达到首次放电容量的97%. 导致这些变化的原因是S\begin{array}{c}{O}_4^{2-}\end{array}掺杂使材料的氧化还原性能增强, 电池内阻减小, 极化程度降低及Li⁺扩散系数增大.

Effect of SO42- Doping on Electrochemical Properties of the Nasicon Li3Fe2(PO4)3 Cathode†

Effect of S\begin{array}{c}{O}_4^{2-}\end{array} doping on electrochemical properties of the Li₃Fe₂(PO₄)₃ cathode materials was studied. Phase constitutents and electrochemical properties of the Li_3-xFe₂(PO₄)_3-x(SO₄)_x(x=00.90) materials were characterized by XRD, charge-discharge technology, cyclic voltammetry and electrochemical impedance spectrum. The results proved that the added S\begin{array}{c}{O}_4^{2-}\end{array} anions mainly dissolved in the Li₃Fe₂(PO₄)₃ compound, concomitant with the secondary phase, Fe₂O₃. Introduction of the S\begin{array}{c}{O}_4^{2-}\end{array} anions resulted in a parabolic variation of discharging capacity for the Li₃Fe₂(PO₄)₃ compound, and that the sample with the S\begin{array}{c}{O}_4^{2-}\end{array} content(x) of 0.60 exhibited the best performance. Its initial discharging capacity was about 111.59 mA·h/g at a rate of 0.5C, and this value was 18. 4% higher than that without any S\begin{array}{c}{O}_4^{2-}\end{array}. After 60 charge-discharge cycles, its capacity retention was around 96% at a rate of 0.5C. Moreover, 97% of the initial capacity was obtained for this material by gradually increasing discharging rates from 0.5C to 5C, and then decreasing back to 0.5C, together with 10 charging-discharging cycles at each rate. Above-mentioned improvement in electrochemical properties for the S\begin{array}{c}{O}_4^{2-}\end{array} substituted samples should result from their enhanced redox ability, decreased internal resistance and polarization, and increased Li⁺ diffusion coefficients of the batteries.