Moderately Solvating Ionic Liquid Electrolytes for High-Performance Lithium Metal Batteries

Development of ionic liquid electrolytes (ILEs) plays a key role in achieving high safety and high energy density in lithium metal batteries. While introducing cosolvents can reduce the viscosity of ILEs and enhance Li+ transport ability, the impact of the solvating ability of cosolvents on the solvation structure of ILEs remains unclear. In this work, we rationally design the solvating ILEs, with different solvation abilities of cosolvents, and reveal the correlation between solvation structure and electrochemical performance. We found that introducing cosolvents with moderate solvating ability, such as ethyl acetate (EA), into the ionic liquid electrolyte can regulate the solvation structure of ILEs, thereby optimizing Li+ transport ability and enhancing the stability of the electrode/electrolyte interface. With our designed ionic liquid electrolytes (ILEs), the Li||Ni0.8Co0.1Mn0.1O2 battery cell demonstrates exceptional capacity retention of 84.8% after 800 cycles at 1.0C, significantly outperforming the battery with a conventional ester electrolyte, which retains only 22.1% capacity. This study provides practical solutions and foundational guidance for the rational design of advanced ionic liquid electrolytes and the selection of cosolvents, advancing the development of high-safety and high-energy-density LMBs.