基于改性的硫化物固态电解质体系的锂硫电池性能研究

In recent years, all-solid-state lithium ion batteries are attracting more attention due to high power density and high safety. As an important part of the battery, the inorganic solid state electrolytes are hot and significant issues because of their advantages over the molten and aqueous electrolytes, such as high safety, good capacity retention. Among them, lots of attention was paid to sulfide solid electrolyte system, showing a promising application potential in all-solid-state lithium batteries.. In this project, sulfide solid electrolyte system with great application value in lithium-sulfur battery, for example, a new electrolyte (100-x) Li10GeP2S12·xLi10GeP2O12 would be prepared via high-energy ball milling and solid state sintering, thus obtaining enhanced ionic conductivity. The new compound system would be studied from phase analysis, crystal structure and microstructure analysis, composition analysis and transport properties by using XRD, SEM, XPS, ICP, Raman, electrochemical workstation and other experimental methods. The conduction mechanics and behavior of improved properties, including ionic conductivity and electrochemical stability would be analyzed, demonstrating the conduction essence and building the principle for improving the ionic conductivity in the inorganic solid state.electrolytes. On the basis, all-solid-state battery would be assembled and examined using the improved sulfide solid electrolyte and LLZO electrolyte membrane which can suppress the shuttle effect in lithium-sulfur battery. Finally, the cycle life, electrochemical stability and other properties would be measured. The project has important practical and scientific significance to suppress the shuttle effect, to solve the safety problems in lithium-sulfur battery, and to promote the application of all-solid-state lithium batteries in the new energy automobile industry.

该项目利用高能球磨法和固相烧结法等工艺以期制备出在锂硫电池中具有巨大应用价值的硫化物无机固态电解质，如制备出一种新型的电解质(100-x)Li10GeP2S12·xLi10GeP2O12，以达到提高电导率的目的。利用XRD、SEM、TEM、XPS、ICP、Raman、电化学工作站等实验手段，对新的化合物体系进行物相分析、晶体结构和微观组织分析、组分分析以及电导率测量等，并分析其显著提高离子电导率和电化学稳定性等性质的物理机制，从而获得能够显著提高无机固体电解质电导率的理论基础和实验技术。然后，利用优化后的硫化物固态电解质和能有效抑制锂硫电池穿梭效应的LLZO（Li7La3Zr2O12）陶瓷隔膜组装成全固态锂硫电池，测量该电池的循环寿命和电化学稳定性等电池性能。该项目对解决当前锂硫电池存在的穿梭效应和安全隐患问题及促进锂电池动力源应用于新能源汽车行业具有重要的实践和科学意义。

全固态锂电池因为其高能量密度和高安全性受到科研工作者广泛关注，其中Li2S-P2S5固态电解质具有较高的离子电导率和良好的机械性质，成为全固态电池中最有前景的电解质材料之一。然而其空气稳定极差、合成工艺复杂等因素极大地阻碍硫化物电解质的大规模应用。原子掺杂作为简单高效的改性方法，对于Li2S-P2S5固态电解质空气稳定性能及电学性能的提高起到重要的作用。. 基于此，本基金主要研究内容分为三个部分：改善制备工艺制备出电导率优异且重现性好的Li2S-P2S5固态电解质。经过前期大量实验摸索，研究团队得到性能优异且稳定的80Li2S-20P2S5固态电解质，其阻抗值稳定在103Ω，电导率为1.54×10-4Scm-1；通过原子掺杂改善LPS体系固态电解质电学性能以及空气稳定性能。LPS与双原子掺杂LPS-GeO2、LPS-Bi2Se3体系均呈Li2S结晶态，且内部存在P2S74-、PS43-、P2S64-高导电玻璃相，同时双原子掺杂后的LPS固态电解质形貌均一、缺陷更少、界面更紧密。双原子掺杂LPS体系能够明显改善其离子电导率及电子绝缘性，其中80Li2S-17P2S5-3GeO2的离子电导率最高为6.066×10-4Scm-1，而80Li2S-16P2S5-4Bi2Se3阻抗仅仅为52.74Ω，离子电导率达到3.01×10-3Scm-1且组装成锂对称电池稳态电流仅仅为10-10A，同时在-0.5V-5V宽电压窗口下具有更出色的电化学稳定性；优化创新测试方法，通过计算模拟方法验证团队的猜想及实验结果。我们创新性地通过传感仪器TH2828测试固态电解质片在空气中阻抗变化分析其空气稳定性，根据结果可以看出双原子掺杂后的体系在空气中更稳定，H2S释放量明显减少，且在湿度环境下依旧保持着优异的化学稳定性。通过密度泛函理论（DFT）第一原理计算可以得出，双原子掺杂LPS体系能够拓宽Li+传输通道，使得LPS体系结构对Li+的束缚作用减弱，离子迁移率大大增加，同时对水的吸附能增大，与水反应势垒增大，进而提高LPS体系空气稳定性。计算模拟结果与实验结果相符，再次验证双原子掺杂能够明显改善LPS体系性能。. 通过本项目研究，全面总结出双原子掺杂改善LPS基固态电解质性能的规律及理论，为硫化物固态电解质电导率的提高、稳定性的改善提供理论依据和实践指导。