非平衡状态下钛基负极材料快速储锂机制的动态过程研究

Current understanding of ultrafast charging lithium-ion batteries (LIBs) is limited to the macroscopic aspects at equilibrium state. However, under fast charging, the reaction is far from the equilibrium state, limiting our understanding of dynamic fast charging process. Thus, a comprehensive study is urgently desired to reveal fundamental physicochemistry insights at non-equilibrium state, providing new perspectives to improve high-rate performance by rational materials design. To this end, in-situ microscopy is proposed to fundamentally understand the evolution of lithiation thermodynamic and kinetics during whole lithiation process, based on our developed elongated TiO2 nanostructure as the electrode platform. The goal of this proposal is to answer important scientific questions in high-rate electrochemistry: 1) Real-time capturing of the intermediate or metastable structures under fast charging and identifying key structures and limited-rate steps for determining the reaction rates; and identification and quantification of the electrode performance from each electrochemical reaction. 2) Building the relationship between material structure and the thermodynamic behavior, and monitoring their thermodynamic behavior change with cycling. This allows us to understand the correlations among thermodynamic behavior, electrode performance and safety issue for a battery system, delivering new methods and standards for evaluating the safety of fast charging LIBs. Combining with theoretical calculations, we are able to build the full picture of lithiation process at the atomic level for the non-equilibrium state under fast charging. This will provide strong scientific guidance for realizing safe and fast charging of LIBs in the future.

目前锂离子电池的电化学反应研究主要针对电极反应的平衡态，而对快充下远离平衡状态的电极反应过程研究相对较少，限制了对快充储锂过程中关键结构和锂化机制的认知。本项目以申请人研发的钛基负极超长纳米结构作为电极研究平台，通过材料结构设计与制备、构效关系研究来提升钛基负极的倍率性能。在此基础上，搭建原位表征平台对钛基负极在快充下的动力学和热力学过程中间态进行研究：1）实现对快充下中间态或亚稳态结构的实时捕获，揭示影响快充性能的关键结构和速控步骤，以及对电极性能的各个组成部分进行量化；2）建立电极材料结构与热力学行为的构效关系，以及循环过程中热力学行为变化与快充电极性能和安全性的对应关系，提出快充锂电池安全性的评价方法。结合理论计算，从微观尺度上解释锂离子在非平衡状态下的脱嵌机制，从而为实现安全快充的锂离子电池提供理论依据和设计思路。

电能和化学能的快速转化与存储是能源储存器件规模应用的核心技术，其关键是快充电极材料的设计和性能调控，钛基负极是最具代表性的快充型储能材料。本项目以提高储能材料内电子和锂离子的传输速率及储能器件的能量密度为目标，在新型快充钛基材料及其高容量复合负极的形成机制、储能机理及其性能调控方面取得了系统性的研究成果：(1) 开发了一种通用的搅拌溶剂热法及其后续真空煅烧法来合成出超长钛基氧化物纳米管及其复合结构(TiO2(B)、CoS2/TiO2(B)、Fe7S8/TiO2(B)、MoS2/TiO2(B)、MOF衍生碳/TiO2(B)及C@Si/TiNT、TiO2@C@MoS2)，充分发挥复合结构各组分性能的优点，各组分间性能互补，提升电极材料的整体性能；(2) 揭示了Peukert常数与锂离子电池中电极材料的相组成之间的相关性，发现提升复合电极中的电荷转移动力学可以有效降低 Peukert 常数，从而提高钛基负极的快充性能，为钛基负极快充提供了新的思路和理论依据；(3) 通过对不同充放电状态的钛基负极样品表面SEI膜的生长过程及演化机理的研究，揭示充放电过程中锂离子和电子传输机制和界面演化过程，为制备高功率密度和长循环寿命的新一代钛基二次电池及其电极材料其提供理论； (4) 通过原位XRD等技术手段分析嵌锂过程中间态对快充性能的影响规律，实现对快充下中间态结构的实时捕获，提出快充的决定步骤，指导氧化钛基负极材料设计和优化。本项目将为如何设计开发快充钛基负极材料及其高功率密度锂离子电池提供理论依据和重要借鉴。