Ionic Liquid Electrolytes for Anode-Free Lithium-ion Batteries (A Review)

Abstract Anode-free lithium-ion batteries (AFLBs) represent a paradigm shift in energy storage, promising significantly higher energy densities. However, the commercial realization of this technology is severely hindered by the uncontrolled growth of lithium dendrites. Ionic liquids (ILs) have emerged as a highly promising class of electrolytes to overcome these challenges, which unique physicochemical properties enable multiple mechanisms for the suppression of lithium dendrite growth. This review synthesizes current understanding of the application of IL electrolytes in AFLBs, with a particular emphasis on the mechanisms governing dendrite mitigation. Key mechanisms discussed include the formation of a robust and electrochemically stable solid electrolyte interphase (SEI), the physical impedance of dendrite propagation due to high viscosity and ionic strength, and mechanical suppression via composite systems. The report analyzes the key factors influencing battery performance, such as the physicochemical and electrochemical properties of ILs, and outlines the significant challenges that remain, including the trade-off between viscosity and ionic conductivity, interfacial compatibility, and the persistent need to achieve near-perfect Coulombic efficiency. Finally, an outlook on future research directions is provided, highlighting the need for rational design of novel IL structures and the development of hybrid electrolyte systems to unlock the full potential of anode-free battery technology.