【文章简介】 固态电解质（SE）在很大程度上定义了全固态电池（ASSB）的性能，并有望提高其安全性，和电化学性能。近年来，它们的离子电导率有了很大提高，从而实现了更高的功率和能量密度。但是，更细微的参数（例如结晶度）也可能会影响电池的电化学性能。清华大学南策文院士，德国吉森大学Jürgen Janek教授，张闻博博士（现就职于德国大众电池卓越中心），张强教授，德国明斯特大学Wolfgang G. Zeier教授等人合作在著名能源材料国际期刊Advanced Energy Materials （IF=25.245）发表题为“Influence of Crystallinity of Lithium Thiophosphate Solid Electrolytes on the Performance of Solid-State Batteries”的文章。作者研究了化学计量相同但结晶度不同的硫代磷酸电解质和ASSB的性能之间的关系。在In / InLi | SE | LiCoO2 @ LiNb0.5Ta0.5O3模型电池中，使用玻璃/玻璃陶瓷SEs（例如75Li2S·25P2S5玻璃，70Li2S·30P2S5玻璃和Li6PS5Cl玻璃陶瓷）可实现更好的循环和倍率性能。这主要归因于与晶体SE对应物相比，玻璃/玻璃-陶瓷SE物理接触损失较小。此外，通过使用SE和碳复合材料作为正极，研究了典型正极电势下的SE分解。循环后，SE /碳复合正极中的晶体SE出现更大的体积变化和更严重的分解。晶态SEs显示出较高的电子部分电导率，这导致复合正极的分解程度更高。通过仔细选择具有适当机械和（电）化学性能的固体电解质，这项工作为ASSB的优化复合正极设计提供了启示。 【主要内容】
Figure 1. Cycling performance comparison of In/InLi | SE | LCO(coated)-SE ASSB cells at 0.1 C at 25 °C using a) 7525-glass (red) and β-Li3PS4 (cyan) as electrolytes, b) gc-LPSC (red) and c-LPSC (cyan) as electrolytes. Differential capacities of c) 7525-glass and d) β-Li3PS4 in ASSBs at the 1st and 100th cycles and e) c-LPSC and f) gc-LPSC in ASSBs at the 1st and 50th cycles.
Figure 2. Nyquist plots of a) In/InLi | 7525-glass | LCO(coated) and b) In/InLi | β-Li3PS4 | LCO(coated) cells after the 1st and 100th charge, and c) In/InLi | gc-LPSC | LCO(coated) and d) In | c-LPSC | LCO(coated) cells after the 1st and 50th charge at 0.1 C.
Figure 3. Rate capability comparisons of a) 7525-glass and β-Li3PS4, b) c-LPSC and gc-LPSC in ASSBs at 0.1 C, 0.2 C, 0.5 C, and 1 C (1 C corresponds to 1.21 mA cm–2). c) Cycling performance comparison of c-LPSC and gc-LPSC in ASSBs at 1 C. d) Charge/discharge curves for ASSBs using c-LPSC or gc-LPSC as SEs after 1st and 60th cycles at 1 C. Nyquist plots of e) In/InLi | gc-LPSC | LCO(coated) and f) In/InLi | c-LPSC | LCO(coated) cells after the 1st and 60th charge.
Figure 4. a) Interfacial resistance RLCO/SE between LCO(coated) and SE (c-LPSC/gc-LPSC). b) Warburg coefficients Dw of the ASSBs with c-LPSC and gc-LPSC as solid electrolytes, respectively.
Figure 5. Cyclic voltammetry tests—a) voltage steps and b) current response upon cycling—of ASSB cells using 7525-glass/C65 composite (red) and β-Li3PS4/C65 composite (blue) as working electrodes, and c) the corresponding pressure response. d,e) The SEM images of the corresponding composites after the CV tests. The cutoff voltage is set to be 2.7 V versus LTO, so the same as the electrochemical test with LCO(coated) as active material.
Figure 6. Normalized XP spectra of S 2p of a) β-Li3PS4/C65 and b) 7525-glass/C65 composite cathodes at different cut-off voltages versus LTO during the charge process, respectively. Simulated structures of c) β-Li3PS4 and d) 7525-glass. Lithium, phosphorus, and sulfur atoms are marked with green, purple, and yellow, respectively.
【结论】在gc-LPSC和c-LPSC、g-7525和β-Li3PS4、g-7030和Li7P3S11三种硫化物电解质体系，均发现采用玻璃或玻璃陶瓷的硫化物电解质在以In / InLi | SE | LCO(coated)为模型全固态电池显示出更高的库仑效率，缓慢地界面阻抗增长，以及更好的循环性能和倍率性能。在复合正极中，硫化物电解质与氧化物活性物质LCO之间的界面是决定因素。与玻璃（玻璃陶瓷）电解质相比，晶态的硫化物电解质在循环时，LCO与电解质之间的机械接触失效更为突出，这可能是导致它们性能差异的主要因素。 与7525-glass相比，使用β-Li3PS4的LTO | LGPS | SE / C65模型电池会产生更大的体积收缩和更多的裂纹和孔洞。从热力学角度看，理论计算和CV结果表明7525-glass电解质的电化学窗口比β-Li3PS4的电化学窗口略窄。但是，β-Li3PS4的分解比7525-glass要多，这是由于β-Li3PS4的电子电导率更高。通过非原位XPS表征得以揭示β-Li3PS4-C65正极循环过程中会形成更多的离子/电子绝缘多硫化物。 该工作加深了人们对不同电解质的（电）化学和机械性能对全固态电池影响的认识，这为设计高性能全固态电池开辟了一条新的途径。显然，单靠晶态硫化物电解质高的离子导电性不足以获得高性能正极。此外，还需要考虑更微妙的现象。 Shuo Wang, Wenbo Zhang, Xiang Chen, Dyuman Das, Raffael Ruess, Ajay Gautam, Felix Walther, Saneyuki Ohno, Raimund Koerver, Qiang Zhang, Wolfgang G. Zeier, Felix H. Richter, Ce‐Wen Nan, Jürgen Janek, Influence of Crystallinity of Lithium Thiophosphate Solid Electrolytes on the Performance of Solid‐State Batteries, Adv. Energy Mater., 2021, DOI:10.1002/aenm.202100654
