金属锂因其极高的理论比容量与极低的氧化还原电势成为了下一代高比能量二次电池的理想负极材料之一。然而，金属锂负极在充放电过程中存在着体积变化与不可控的的枝晶状生长等问题，其带来的不均匀内应力会进一步造成固态电解质膜（SEI）失效和死锂形成等连锁效应，最终使得电池的库伦效率降低、循环寿命缩短。阐明金属锂负极在充放电过程中的力-电化学动态耦合机制，进而从根源上解决以上问题，是推动金属锂负极实用化的关键。 针对金属锂电池中力-电化学动态耦合过程缺乏深入理解的问题，本研究基于应力耦合电化学反应动力学、离子输运、电荷守恒与力平衡等基础物理场理论，利用基于变形网格的有限元与相场法追踪锂沉积/脱出界面，提出了金属锂负极中的力-电化学模型，为金属锂负极的理论研究提供了新的工具。 针对锂的液固转化反应与枝晶形貌带来的内应力问题，本研究探究了不同锂枝晶形貌的形成机制，确定了电流密度的提高会使得离散状锂枝晶转向不利的团聚状锂枝晶；探究了SEI的动态稳定性影响机制，确定了结构均匀性为其关键影响因素，并提出3.0 GPa模量的机械强度设计要求；基于以上理论指导，设计了可容纳体积变化、降低真实电流密度并具有稳定SEI的复合金属锂负极，其优异的性能证明了理论策略的可行性。 面向电池的实用化，针对充放电过程中的外压力管理问题，本研究确定了锂沉积/脱出过程中外压力在不同电流密度、电解质模量下对于电化学性能、枝晶形貌、死锂量的影响机制，进而为外压力的优化提供了定量控制策略。 综上所述，本论文构建了金属锂负极中的力-电化学动态耦合模型，揭示了金属锂负极在电化学反应过程中的内应力影响机制与外压力调控机制，进而提出了高性能金属锂负极的材料设计策略与电池系统的外压力、充放电管理准则。这为基于金属锂负极的下一代二次电池的实际应用提供了多尺度、多维度的解决策略。
Lithium (Li) metal is considered an ideal anode material for the next-generation high-specific-energy rechargeable batteries due to its ultrahigh theoretical specific capacity and low redox potential. However, Li metal anodes suffer from volume changes and uncontrolled dendritic growth in working. The resulting inhomogeneous stress can further cause the failure of solid electrolyte interphase (SEI) and the formation of dead Li, which will eventually reduce the coulombic efficiency and shorten the cycle life of the Li metal batteries. Elucidating the mechano-electrochemical coupling mechanism in the working Li metal anode is essential to address these issues and promote the practical application of Li metal anodes.To reveal the mechano-electrochemical coupling mechanism of Li metal anodes, mechano-electrochemical models with the multiphysics of stress-coupled electrochemical reaction, ion transport, charge conservation, and mechanical balance are established using deformed mesh-based finite element methods and phase field methods, which provides a new tool for theoretical studies of Li metal anodes.To reveal the stress influence brought by the phase transformation and dendrites morphology, the dynamic evolution of Li dendrites is investigated at first. The increase in current density causes the change of discrete Li dendrites to aggregated Li dendrites. Further, the stability of SEI under plating stress is simulated. The structural uniformity is demonstrated as the key factor and a mechanical requirement of 3.0 GPa modulus is proposed. Based on the above theoretical guidance, a composite Li metal anode is designed. Its high performance proves the feasibility of the theoretical strategies.For the pressure management in practical batteries, the influence mechanism of external pressure on the electrochemical reaction, dendrite morphology, and dead Li under different current densities and electrolyte moduli is revealed, and thus quantitative optimization guidelines of external pressure are provided.In summary, mechano-electrochemical models are proposed and establied, revealing the influence mechanism of internal stress and external pressure in the working Li metal anodes. Corresponding material design strategies and cell management guidelines are thus poroposed for high performance Li metal batteries. This thesis provides a multi-scale and multi-dimensional strategy for the practical application of next-generation rechargeable batteries based on lithium metal anodes.
