全固态锂离子电池固-固界面交互作用机制的研究

All-solid-state Li-ion battery has become an important research focus in the fields of electrochemical power sources due to high safety, high energy density and wide operating temperature. With the occurrence of solid electrolyte possessing highly ionic conductivity, the key to develop all-solid-state Li-ion batteries is to understand the interactions and mitigate Li-ion transfer obstacles at the solid-solid interfaces between electrolyte and electrode. This project will form Li-O-containing compounds on the surface of Li10GeP2S12 electrolyte grains, considering pure ionic conduction of the Li-O-containing compounds, small difference of chemical potential between the compounds and high-voltage cathodes as well as mixed anion effect. Better insights into the role of the electrolyte modification are therefore needed to elucidate in the interface interactions of Li10GeP2S12 electrolyte/high-voltage cathode and Li10GeP2S12 electrolyte/low-voltage anode. Li-ion transport thermodynamics at the interface of modified Li10GeP2S12 electrolyte/electrodes will be analyzed. Also, this project will propose the decisive mechanisms of the interface interactions that govern the performance degradation of the batteries containing modified Li10GeP2S12 electrolyte during their charge-discharge cycles. From a scientific point of view, these researches would enrich the interfacial interactions of the solid-solid contacts in all-solid-state batteries as well as the effect of the interactions on the electrochemical performance of the batteries. In the meanwhile, surface design and interface control of the Li10GeP2S12-like solid electrolytes would be directed. Consequently, it is of great signification in offering key theoretical understanding and experimental evidence from this project for technology progress and future applications of all-solid-state rechargeable Li-ion batteries.

全固态锂离子电池具有安全性高、比能量大、工作温度区间广等优势，是化学电源领域的研究热点。随着高离子电导率固态电解质的成功研制，电解质与电极固-固界面的物质相互作用及锂离子传输障碍成为制约全固态锂离子电池发展的关键。本项目拟在Li10GeP2S12电解质表面形成纯离子导电、相近于高电位正极化学势和混合阴离子效应的含锂氧化合物，探索电解质表面改性对Li10GeP2S12/高电位正极和Li10GeP2S12/低电位负极的界面交互作用的影响，分析改性Li10GeP2S12电解质/正负电极固-固界面的锂离子传导热动力学，并在充放电过程中得出影响电池性能衰减的固-固界面交互作用的决定因素。这既丰富全固态电池固-固界面交互作用及其对电池电化学性能影响机制的理论，又能指导Li10GeP2S12类硫化物固体电解质的表面设计和相关的界面控制，为实现全固态锂离子电池技术进步和未来应用提供有力的理论和实验依据。

Li10GeP2S12（LGPS）硫化物固态电解质的离子电导率可以与液态电解质的相媲美，为其全固态锂离子电池的成功研制带来了希望，目前亟待解决的问题是LGPS硫化物固态电解质与电极固-固界面的物质相互作用及锂离子传输障碍。本项目首先利用阴离子掺杂构筑了一系列改性LGPS材料，建立改性LGPS材料的微观结构、化学成分、锂离子电导率、导锂活化能等理化性质的相互联系，发现Li3PO4掺杂阻碍了锂离子在LGPS固态电解质中的传导，而LiBr掺杂由于相对较大的Br-部分取代S2-而有益于锂离子的传导，同时在改性LGPS中形成了硫银锗矿Li6PS5Br新相，这可能能够提高LGPS相关的界面稳定性；然后针对改性Li10GeP2S12固态电解质与高电位正极、低电位负极之间组建的新型固-固界面，发现将LiBr添加到LGPS中，可以很好地提高LGPS与、NCA 正极、Li-In负极之间的界面锂离子传导动力学，并明显提高LGPS与Li金属的化学相容性；最后利用高电位正极、改性Li10GeP2S12固态电解质、低电位负极，构建新型全固态电池，结果表明，NCA/改性LGPS /Li-In全固态电池在室温充放电循环100次后表现出良好的循环稳定性，容量保持率高达73.2%，这些研究为获取高能量密度、高电压及长寿命等优异性能的全固态电池打下良好基础。