Self-Healing and Flexible Ionic Gel Polymer Electrolyte Based on Reversible Bond for High-Performance Lithium Metal Batteries

Lithium metal is a promising anode material for manufacturing lithium batteries owing to its low density, low negative charge and high theoretical specific capacity. Unfortunately, the uneven lithium deposition at the lithium metal-electrolyte interface often leads to the growth of lithium dendrite structures, short circuit, excess heating and even explosion of lithium metal batteries (LMBs). Electrolyte is an important component in LMBs, which will affect the electrochemical performance, safety and cycle life of the battery. The liquid electrolytes with low safety and poor interface contact will limit the practical application of flexible LMBs.

Considering the inability of liquid electrolytes to prevent the formation and growth of lithium dendrites, gel electrolytes with remarkable electrochemical properties have emerged as a promising alternative. Ionic gel polymer electrolytes use the interaction between the ionic liquids and polymers to form ionic gel structures to improve the electrochemical performance of the battery. Nevertheless, most ionic gels are fragile and fail to withstand large deformation under continuous stretching and bending. Therefore, developing safer and more reliable electrolytes for LMBs is highly desirable.

Self-healing properties have continuously drawn research attention for preparing highly durable flexible materials for different applications. Lately, this concept has been extended to ionic gels, although there are still limited studies in this area. A notable challenge is preparing self-supporting ionic gels with high self-healing – efficiency without extra condition-. Besides, ionic gels formed by ionic liquids doped by self-healing soft polymer networks have exhibited excellent electrochemical and flexibility properties, making them suitable for improving the safety and performance of LMBs.

Herein, a team of researchers from Nanchang Hangkong University: Mr. Long Wan, Miss Xiaoyan Cao, Miss Xiaoyuan Xue, Professor Yongfen Tong, Professor Suqing Ci, Professor Hongbo Huang and Professor Dan Zhou designed an flexible ionic gel polymer electrolyte (IGPE) with self-healing ability to improve the safety, stability and performance of LMBs. The IGPE was prepared with imine cross-linkers and polyethylene glycol (PEG) via thermal cross-linking through a one-step reaction in the presence of ionic liquid electrolytes. The work is currently published in the journal, Energy Technology.

The authors demonstrated the novelty prepared IGPE with the excellent self-healing abilities, high ionic conductivity, good interfacial compatibility, high thermal and electrochemical stability. A Li/IGPE-50/LiFeO₄ battery using IGPE-50 as electrolyte was also fabricated, which exhibited excellent cyclic performance and rate capability. A coulombic efficiency of 99.6% and maximum discharge capacity of 154.8 mAhg^-1 were obtained at room temperature and 0.1 current rates.

In summary, the study by Nanchang Hangkong University scientists reported the successful design and preparation of IGPEs based on ionic liquids and reversible covalent imine polymer. Compared with the traditional liquid electrolytes, the unique structure of the IGPE endowed it with high ionic conductivity and self-healing abilities, whichcould optimize the stability, electrochemical performance and safety of the LMBs with the IGPEs as electroltyes. In a statement to Advances in Engineering, Professor Yongfen Tong, the corresponding author said the newly developed IGPEs are promising materials for fabricating stable, flexible and safe flexible LMBs for a wide range of applications.