锂离子电池因其能量密度高、循环寿命长的特点，是当今社会移动储能的首选技术。近年来，电动车和消费电子产品等对电池快速充电的需求日益迫切，而锂离子电池快充时易产生极化过大和负极析锂等问题，损害电池寿命和安全性。电池快充的限制主要在于锂离子在电极和电解液中有限的质量传递速率，以及锂离子跨越电极-电解液界面的传输阻力。其中，针对质量传递的研究较为深入，而关于界面离子传输机制和动力学改善策略的研究相对较少。因此，开展界面离子传输动力学的研究对于设计下一代快充锂离子电池具有重要意义。针对锂离子在负极侧脱溶剂化能垒高制约快充速度的问题，本文提出了弱溶剂化电解液的概念，并系统研究了其电化学性质。实验揭示了弱溶剂化电解液能够通过降低脱溶剂化能垒和离子跨固态电解质界面膜传输能垒协同提升锂离子嵌入负极的动力学，进而实现电池快充。本文进一步研究了弱溶剂化电解液中固态电解质界面膜的形核和生长机理及其调控手段，为快充电池的化成制度设计构建了理论基础。针对锂离子全电池器件，本文通过引入三电极系统和动态阻抗的技术手段，解耦了快充过程中的极化来源和限速步骤，确定了锂离子在正极-电解液界面的传输为快充的主要极化来源，而锂离子在负极-电解液界面的传输决定了电池是否析锂。通过电解液的合理设计，平衡了正负极侧界面离子传输能垒，实现了安时级软包和圆柱锂离子电池器件在10–25分钟内的安全快充。针对锂离子电池在低温下充电困难的问题，本文结合变温三电极阻抗测试和弛豫时间分布的分析方法，确定了商用电解液中的碳酸乙烯酯形成的高阻抗界面膜为低温充电的主要瓶颈。通过无碳酸乙烯酯电解液的设计，在负极表面构建了一层低温下具有高离子导率的界面膜，实现了锂离子软包电池在?60℃下的放电及?15℃下的稳定循环，拓展了二次锂离子电池的工作温度范围。综上所述，本文系统地研究了在快充锂离子电池中，界面离子传输过程的决速步、反应机制和提升策略，实现了安时级软包和圆柱锂离子电池器件的常温快充和低温充电，有助于推动下一代高功率锂离子电池的性能突破。
Lithium (Li)-ion battery (LIB) is the primary choice of portable energy storage in the modern society due to its high energy density and long cycle life. In recent years, the rapid spread of electric vehicles and consumer electronics have put forward increasingly urgent need for battery fast charging. However, current LIBs suffer from large polarization and anode Li plating during fast charging, endangering battery life and safety. Battery fast charging is mainly hindered by the limited rate of Li ion mass transport in electrodes and electrolytes, as well as its transfer across electrode/electrolyte interfaces. While Li ion mass transport has been thoroughly studied, the mechanism and improving strategy of interfacial Li ion transfer remain elusive. Therefore, understanding the kinetics of interfacial Li ion transfer is critical for next-generation fast charging battery design.The present research puts forward the concept of weakly-solvating electrolytes (WSEs) to tackle the issue of high Li ion desolvation energy barrier at the anode during fast charging. The electrochemical properties of WSE have been systematically studied, which revealed reduced energy barrier of Li ion desolvation and transport across the solid electrolyte interphase (SEI) as the main reason for the improved kinetics of Li ion intercalation into the anode. This study further elucidates the mechanism of SEI nucleation and growth in WSE and how this process could be regulated, building a theoretical foundation for designing formation protocols for fast charging LIBs.By introducing a three-electrode system and dynamic impedance technique, this research decouples various polarizations during fast charging of a full cell and identifies the rate-limiting step. Li ion transfer at the cathode/electrolyte interface is found to be a major contributor to cell polarization during fast charging, while Li ion transfer at the anode/electrolyte interface controls Li plating. By balancing the energy barrier of these two processes through electrolyte engineering, fast charging of Ah-level pouch and cylindrical LIB cells within 10–25 minutes is demonstrated.To improve the poor rechargeability of LIBs at sub-zero temperatures, this research identifies the highly resistive SEI induced by ethylene carbonate (EC)-based electrolytes as the key bottleneck by combining temperature-dependent 3-electrode impedance and distribution of relaxation times technique. A novel EC-free electrolyte creates a highly conducting SEI on the anode at low temperatures, which enables normal discharge of a Li-ion pouch cell at ?60℃ and stable cycling at ?15℃, widening the working temperature range of rechargeable LIBs.In summary, this thesis systematically studies the rate-limiting step, reaction mechanism and improving strategy of interfacial ion transport in fast charging LIBs. Based on these understandings, fast charging and low-temperature charging are successfully demonstrated in Ah-level pouch or cylindrical LIBs, which helps to push the performance of next-generation high-power LIBs through their limits.
