全固态锂电池界面科学问题的原子尺度原位电镜研究

All solid state Li-ion batteries (ASSLIBs) are considered to be the ultimate solution to the safety hazard of LIBs using liquid electrolyte. However, the energy density, power density and charge/discharge electrochemical properties of current ASSLIBs are far away from that required for commercialization. There are three critical problems that need to be resolved in ASSLIBs: the high interface resistance, interfacial electrochemical degradation and failure, and the interfacial mechanical failure. The interface reaction during battery cycling usually occurs under non-equilibrium conditions, and in-situ observations of which are very difficult, consequently, the reasons for the problems in ASSLIBs are still unclear, which prevents the development of ASSLIBs with better performance. We propose to use nanosphere lithography (NSL) as templates to prepare all solid state nanobatteries that can be incorporated into an aberration corrected TEM in Yanshan University to enable in-situ TEM studies of ASSLIBs. We will create a new technology to enable real time observation and analysis of interfacial phenomena in ASSLIBs while being cycled. Through simultaneous interface evolution investigations and electrochemical property study, we intend to understand the electron and ion transport properties of interfaces between electrodes and electrolyte; reveal the physical reasons for high interface impedance in ASSLIBs; understand the mechanisms of electrochemical degradation and failure and mechanical failure. Our studies will open a new window in studying the basic sciences of ASSLIBs and provide key scientific guidance in developing novel ASSLIBs with low interface resistance, high energy and power density, long cycle life and good safety.

全固态锂电池被认为是解决商用锂离子电池安全性隐患的理想方案。但是，目前全固态锂电池的能量和功率密度与产业化的指标差距很大，其中亟待解决的三个关键问题是电极和固体电解质的界面阻抗过高、界面电化学失效和界面机械失效。全固态锂电池充放电过程中界面反应发生在非平衡状态下，其原位实验观测非常困难，因此造成这些问题的机制至今尚不清楚，严重阻碍了全固态锂电池性能的进一步提高。本申请拟通过采用纳米球自组装模板法制备适于原位电镜观察用的全固态纳米电池样品，建立全固态电池在充放电过程中界面演化的原位动态电镜观察和解析的新方法。通过全固态电池在循环过程中界面演化和电化学性能的同步研究，在原子尺度上阐明电极和电解质界面层的离子和电子传输机理，揭示全固态电池高界面阻抗的物理起因、电化学降解和失效的微观过程、机械失效的物理机制，为研发低界面阻抗、高能量密度、高安全性、长寿命的新型全固态锂电池提供科学依据和设计策略。

全固态电池的高能量密度、高安全性的特点已经是未来电池的重要发展方向。在全固态电池设计中，金属锂具有高比容量（3860 mAh g‒1）和低电化学势（‒3.04 V相对于标准氢电极）的特点，是理想的高能量密度负极材料。然而在实际应用过程中，锂枝晶很容易在机械刚性的陶瓷基固态电解质中生长，最终导致电池短路，这很大程度上限制了全固态锂电池的商业化应用。尽管已有大量的研究者关注这一领域，但锂枝晶在固态电池中的生长问题至今还没有得到解决，且锂枝晶穿透固态电解质的机理至今尚无定论，特别是对于固态电解质裂纹扩展和锂沉积之间的动态相互作用还缺乏更深层次的认识。为此，本研究从锂枝晶问题的根源着手，建立起一种基于原位电镜生长稳定可控锂枝晶的实验方案，并发展出一套通过原位电镜对锂枝晶同时进行结构和力学性能表征的新技术。研究发现，锂枝晶在生长过程中可产生的应力高达130 MPa, 通过原位压缩实验发现其屈服强度更是高达244 MPa，这一数值远高于宏观金属锂，颠覆了研究者对锂枝晶力学性能的传统认知。相关实验结果发表在Nature Nanotechnology等杂志，得到了国内外同行的广泛关注。在此基础上，利用原位电镜技术实时观察了Li6.4La3Zr1.4Ta0.6O12固态电解质（LLZTO）内部裂纹扩展的动态过程，提出了锂金属在电解质内部沉积会产生巨大静水压力，这是导致固态电解质近表面产生“碗状”裂纹的根本原因。基于此，提出了降低固态电解质的电子电导和改善电解质近表面电场以抑制电解质破裂和防止电池短路的新观点。该项目不仅揭示了锂枝晶的切变模量、屈服强度和断裂强度等力学性能的机理，还建立起了全固态电解质力学性能、锂枝晶力学性能耦合和锂枝晶生长与传输的关联。相关研究成果可为固态电池中抑制锂枝晶的生长提供科学依据，为研发高能量密度和高安全性金属锂负极全固态电池提供科学依据和设计策略。