过渡金属离子在钛酸锂负极表面的沉积特性及其与电池性能的关系

The passive layer, which is generally called the solid electrolyte interface layer (SEI) covered on negative electrode, determines the dynamic stability of electrolyte/electrolyte interphase and the intercalation/deintercalation process, and plays a key role in the electrochemical performance of the lithium-ion battery. The “zero-strain” lithium titanate has attracted intensive attention on the fields of energy storage and electric vehicle due to its high safety and long lifetime. However, its practical application is severely hindered by its lack of theoretical basis on interface kinetics, and the existence and formation mechanism of the SEI film are still under hot debate nowadays. In this project, we intend to find the influence of the positive active materials on the SEI film of Li4Ti5O12 electrode through the deposited transition metal ions, which dissolves and diffuses from cathode materials. By using characterization methods of SEM, TEM, FIB, FTIR and FIB et al, we systematically investigate the evolution of the SEI film by subjecting the lithium-ion batteries to formation, cycling, and storing, taking several kinds of positve active materials as the cathode; combinging with the viriation characterisc of the dissolved and depostied transition metal ions, the mechanism of the formation and evolution of the SEI film are focused. Thereafter, the effects of the depostied transition metal ions on the interface kinetics are discussed basing on its impact on the battery performance（capacity, power, storage performance, cycle life, et al). The research results of this project will be benefitial to a better undestanding of the lithium titanate, and provide a certain theoretical support to the development and application of Li4Ti5O12 battery.

锂离子电池负极表面钝化膜决定了固液相界面的稳定性和嵌脱锂过程中的动力学，对电池的性能起决定性作用。零应变的钛酸锂材料由于其高安全性和长寿命，成为储能及电动汽车领域动力电池发展的重要方向，但复杂的界面成膜机理及作用机制成为该材料研发的瓶颈，制约了其实际应用。本课题从不同正极活性物质着手，着重考察过渡金属离子的溶解-沉积对界面钝化膜的影响机制：综合运用SEM、TEM、FIB、FTIR和XPS等检测手段分析不同正极活性物质与钛酸锂组成电池后负极界面在化成、循环和储存过程中的变化规律；结合过程中过渡金属离子在负极表面的沉积特性，研究过渡金属离子的沉积对界面钝化膜的生成、循环演变的作用机制；并综合过渡金属离子沉积对界面脱/嵌锂动力学的影响，揭示其与电池性能（容量、功率、储存性能、循环寿命等）间的内在联系，提高对钛酸锂基础理论的认识，从而为该类电池的研发与应用提供一定理论支撑。

零应变的钛酸锂（Li4Ti5O12，LTO）负极活性材料具有高安全性、长寿命、工作温度宽及快速充放电特性，在混合电动汽车及储能电池领域具有明显优势；负极表面钝化膜决定了固液相界面的稳定性和嵌脱锂过程中的动力学，对电池的性能起决定性作用。本课题采用不同正极材料与LTO电极匹配制成18650电池，研究不同化成制度和寿命不同检测阶段LTO电极表面沉积的过渡金属原子种类及含量，分析指出Ni、Co的溶解主要电解液中微量的HF腐蚀活性物质所致；Mn的溶解主要是Jahn-Teller效应引起的Mn3+溶解并在负极表面沉积，其中Ni、Co和Mn的电化学沉积在Li4Ti5O12不同晶面的反应活性存在差异，(111)晶面反应活性最高。基于XPS、XAS和XANES研究了充放电过程中LTO电极表面钝化膜的组成及循环演变机制：LTO电极在电池充放电过程中表面会形成钝化膜，该钝化膜随循环进行逐渐致密；膜组分在多次循环后会逐渐由可溶性的有机沉积物逐渐转化为不可溶的羧酸盐和碳酸盐。将界面钝化膜的形成与演变与界面副反应的控制有机关联，从LTO电极的制备工艺控制、电芯结构优化设计、活性材料的改性、电解液组分的筛选及优化、化成制度的改进等方面着手，综合制备长寿命、高功率、低气胀的18650型LTO电池。