摘要/Abstract

采用高温固相法合成了固态电解质Li₁₀GeP₂S₁₂，其室温离子电导率为2.02×10^-3 S/cm，并组装了LiNbO₃@LiNi_1/3Co_1/3Mn_1/3O₂/Li₁₀GeP₂S₁₂/Li全固态电池.恒流充放电测试表明全固态电池首次放电容量121.2 mAh/g，库伦效率40周后稳定在99.8%左右，循环100周后容量保持率达93.7%.电化学阻抗谱的测试结果表明，其典型的阻抗谱图由高频区半圆（HFS）、中频区半圆（MFS）和低频区斜线（LFL）组成，其中，HFS归属于电解质阻抗（R_el//Q_el），MFS归属于电荷传递过程（R_ct//Q_dl），LFL归属于锂离子的固态扩散过程.通过选取适当的等效电路，对实验所得的电化学阻抗谱数据进行拟合，并分析了R_el和R_ct随电极电位的变化规律.
关键词: 全固态电池, Li₁₀GeP₂S₁₂, 电化学阻抗谱, 电荷传递电阻
All-solid-state batteries will be the main direction of lithium-ion batteries in the future. Current research mainly focuses on improving the conductivity of solid-state electrolytes, but there are few studies on the electronic and ionic transport in all solid state batteries. In this paper, we synthesized Li₁₀GeP₂S₁₂ through high temperature solid phase method. The ionic conductivity of Li₁₀GeP₂S₁₂ at room temperature is 2.02×10^-3 S/cm and it's activation energy calculated from Arrhenius plots is 29.8 kJ/mol. The all solid-state battery of LiNbO₃@LiNi_1/3Co_1/3Mn_1/3O₂/Li₁₀GeP₂S₁₂/Li was successfully fabricated and characterized by galvanostatic charge/discharge (DC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The first discharge capacity of the all-solid-state battery is 121.2 mAh/g, the coulombic efficiency stabilize at 99.8% after 40 weeks and the capacity retention rate is 93.7% after 100 weeks. After analyzing the electrochemical impedance spectroscopy, the typical impedance spectra of the battery is composed of high frequency semicircle (HFS), middle frequency semicircle (MFS) and low frequency line (LFL). And HFS belongs to the impedance of electrolyte (R_el), MFS belongs to charge transfer impedance (R_ct) and LFL belongs to diffusion process of lithium ion in active material. The continuous increase of R_el between 3.8 V and 4.3 V is due to the decomposition of LGPS to GeS₂, S and P₂S₅ at high potential, which results in the decrease of grain conductivity. On the other hand, the voltage range of 3.8~4.3 V is near the charging and discharging plateau at which concentration polarization is large. The stress in the crystal may lead to the breakup of some grains which resulting in the generation of more grain boundaries and the increase of grain boundary impedance. According to the fitting results of R_ct, we find that R_ct decreases with the increase of potential until 4.3 V at which R_ct reaches the minimum value in the first process of charging and it is a reversible process while discharging.
Key words: all solid state batteries, Li₁₀GeP₂S₁₂, electrochemical impedance spectroscopy, charge transfer resistance


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