空间高比能锂离子电池硅基负极预锂化过程及界面稳定化研究

To resolve fundamentally the bottleneck problems of high initial irreversible capacity and poor cycling stability of Si-based negative electrodes, this research is projected to systematically study the relevant theories and strategies for improving the overall performance of Si-based negative electrode from viewpoints of pre-lithiation of electrode (active material) and stabilization of interface between electrode and electrolyte solution. Based on the understanding of formation mechanism of irreversible lithium in Si-based electrode, the effective strategies and approaches for electrode pre-lithiation will be proposed and realized, and the functioning mechanism of pre-lithiation will be investigated. By modifying the Si-based electrode surface and introducing effective additives into electrolyte solution, a stable interface structure between Si-based negative electrode and electrolyte solution will be constructed to improve the long-term cycling stability of the electrode. Novel binders will be explored to enhance the electrode structural stability. According to the lithium storage characteristics of pre-lithiated Si electrode, the electrode structure will be optimized to accelerate the electrode reaction kinetics and improve the structural mechanic properties. We will also study the matching of pre-lithiated Si negative electrode with various positive electrodes and try to realize efficiently the performance modulation of full batteries with Si-based negative electrode under different operation conditions as space batteries. The synergism mechanism of various affecting factors and the long-term working performance of full battery with pre-lithiated Si-based negative electrode will be elucidated and characterized. The accomplishment of this research will provide fundamental knowledge and technical support for the development of high energy density and long cycle life batteries for space applications.

针对硅基负极首次不可逆大、循环性差的关键问题，本研究拟从硅负极材料（电极）预锂化和电极/电解液界面稳定化角度出发，系统研究改善硅基负极综合性能的相关理论和策略。基于对硅负极不可逆锂产生机制的认识，发展硅负极预锂化的有效策略和方法，研究预锂化作用机理；通过对硅基负极的表面改性以及电解液中引入有效添加剂，在硅基负极/电解液界面构筑稳定化结构，改善硅基负极的循环稳定性。发展新型电极粘结剂，提高电极的结构稳定性；基于预锂化硅负极的储锂特征，构筑电极合理结构，改善电极的反应动力学速率和结构力学特征。研究预锂化硅负极与正极材料的匹配关系；实现预锂化硅负极在全电池体系、空间电池工作环境下的电化学性能调控；研究预锂化硅负极电池中各因素的协同作用机制和长效工作特性。为高比能长寿命空间电池的开发提供理论基础和技术支持。

针对氧化亚硅基负极材料首次效率低、界面不稳定、循环性能差的关键科学问题，开展了系列研究工作。研究结果表明，在首次嵌锂过程中，氧化亚硅负极材料中生成的各种不可逆的锂硅酸盐是产生首次不可逆的主要来源，其他来源还包括锂硅合金中死锂以及生成SEI消耗的锂。引入过渡金属元素或化合物可以使部分硅酸锂活化，促使锂可逆脱出，提高材料的首次效率。预锂化是解决硅基负极首次不可逆问题的有效方法。在各种预锂化方式中，化学预锂化效率高性能稳定。过渡预锂化易导致电极SEI膜厚度增加，电池内阻增大，不利于电池倍率性能的发挥。硅基电极循环过程中性能衰减机理的研究显示，前10周的主要衰减原因是硅基材料结构的变化，10周之后的主导因素是硅基负极表面SEI膜的破损和重生造成的活性锂的损失。开发了高性能新型硅基负极材料，通过在SiOx基体中引入TiO2，制备了TiO2弥散与SiOx基质中的复合负极材料，显著提高了材料的材料内部电子和离子传输能力，改善电极的倍率特性，强化颗粒结构稳定性，并提高电极循环特性。设计并制备了蒲公英结构的SiOx/C负极材料，这种具有“应力自释放”结构特征的材料，具有较高的比容量（~1200 mAh/g）和优异的循环稳定性。预锂化后电极首次效率可达97%。.电解液和电极的双重添加剂（VC+LiNO3）可以增加SEI膜力学性能及离子传导性，显著改善硅负极界面稳定性。研究开发了具有高粘结性和离子传输能力的功能粘结剂，该粘结剂的使用可以显著提高电极的循环稳定性和倍率特性。利用Comsol-Multiphysics进行建模，优化了电极的面密度和孔隙率的设计，优化了正极材料、电极导电剂和电池电解液的结构和组成。在优化参数下制备的基于硅基负极和NCA正极材料的铝壳全电池，电池能量密度 293.8 Wh/kg，500次循环容量保持率91%。同时制备的全电池具有耐过充过放特性，并通过短路安全性测试。本项目研究中获得的系列科学和技术成果，对于空间高性能锂离子电池的发展和应用具有重要推动作用。