锂金属负极三维多孔Cu@Li2O-LiZn骨架层的一体化设计与储锂性能研究

Lithium metal would be the optimal choice as an anode material for high-energy-density lithium metal based batteries owing to its ultra-high specific capacity and the lowest electrochemical potential of all. However, uncontrolled dendritic-lithium growth during cycling, the unstable electrode/electrolyte interface and the huge volume change of lithium anode severely prevent its practical applications in lithium metal batteries. Therefore, the design concept of this project is directed against the aforementioned main problems of lithium metal anode to reasonably synthesize special three dimensional (3D) porous Cu@Li2O-LiZn nanoparticle-assembled granular film with controllable thickness, composition and porosity as a stable scaffold layer for lithium anode through a self-developed plasma-gas-aggregation-type cluster beam deposition technique. The mechanism of the as-derived interfacial scaffold layer of lithium metal anode on the uniform lithium deposition without dendrite during cycling is investigated systematically, the influence of the artificial Li2O layer on the composition, structure and stability of solid electrolyte interphase (SEI) film and its improvement on the Coulombic efficiency of lithium metal anode are studied in depth, and he effect of the thickness and pore structure of the 3D porous scaffold layer on the capacity of the deposited lithium and the structural stability of the electrode are discussed elaborately. After that, the application of the optimized lithium metal anode in lithium metal full batteries will be investigated, which will provide the experimental and theoretical foundations for lithium metal anode from the experimental study to the practical application.

锂金属负极具有极高的理论比容量和最负的电势等优点，是高能量密度锂金属电池负极的最佳选择，然而循环过程中锂枝晶的不可控生长、不稳定的电极/电解液界面以及电极巨大的体积变化的问题严重制约其应用。本项目针对锂负极存在的主要问题进行合理设计，拟采用自行研制、具有特色的纳米粒子束流复合沉积系统，利用纳米粒子组装颗粒膜的独特多孔结构，实现厚度、成分和孔隙可控的锂负极三维多孔Cu@Li2O-LiZn骨架层的一体化构筑。系统研究锂负极表面修饰骨架层对循环过程中锂均匀沉积的引导作用和对枝晶生长的抑制机理，深入研究人造Li2O界面层构筑对界面SEI膜组成、结构和稳定性的影响规律及其对库伦效率的改善作用，探明骨架层的厚度与孔结构对沉积锂的容纳规律和电极结构的稳定作用，探究获得具有高安全性、高库伦效率和循环稳定的锂负极的有效途径，并考察该锂负极在全电池中的应用，为其从实验探究向实际应用的迈进提供实验和理论依据。

锂金属负极具有高比容量和低电位等优点，能够大幅提升锂金属电池的能量密度。针对锂金属负极循环过程中锂枝晶的不可控生长、电极界面副反应严重以及体积效应大等问题，本项目采用自行研制的纳米粒子束流沉积技术，首先制备出了Cu@ZnO核壳结构纳米颗粒组装多孔膜；接着通过实验参数优化，并结合原位预锂化策略，实现了厚度、成分和孔隙可调的Cu@Li2O-LiZn三维多孔骨架层的可控制备，详细研究了骨架层成分与微观结构等对锂金属负极电化学性能的影响机制。研究结果表明：原位形成的LiZn合金对锂呈现出高的表面能和低的扩散能垒，从而降低了锂金属成核过电位；Li2O作为人工固态电解质界面层具有高的离子导电率，能够均匀界面锂离子通量，从而降低了界面电荷转移阻抗和界面副反应；骨架层多孔结构缓解了锂沉积/溶解过程中剧烈的体积变化，提高了电极结构稳定性，最终有效提升了锂金属负极的库仑效率与循环稳定性。在此基础上，对三维多孔骨架的几何结构、材料构成和界面化学进行优化，设计制备出了具有亲锂/憎锂/亲锂多梯度ZnO/PAN/ZnO和Si/CNF/ZnO三维多孔骨架。该亲锂多梯度结构具有锂枝晶“自修复”功能，实现了高沉积容量（30 mAh/cm2）条件下锂金属的均匀沉积/溶解，显著提升了锂金属全电池的电化学性能。同时，本项目进一步设计制备了一种具有多孔结构的Zn纳米粒子组装膜作为隔膜修饰层，有效引导了锂金属在隔膜表面进行反向沉积，并分散电极/电解液界面的锂离子通量，不仅获得了均匀致密的柱状锂沉积形貌，而且调节了潜在的锂枝晶生长方向，从面向隔膜方向转变为面向集流体方向，从而解决了其穿透隔膜导致的安全隐患难题。