Next-generation solid-state batteries: Self-Healing Nano-Electrolytes

Abstract

Solid-state batteries (SSBs) are considered one of the most promising new battery technologies for replacing flammable liquid electrolytes with mechanically stiff, non-volatile solid conductors providing improved safety and increased energy density due to the lithium-metal anode. But the same constraint which ensures safety of solid electrolytes makes them brittle: repeated volumetric expansion and contraction of the electrodes during cycling create micro-cracks, voids and interfacial delamination that gradually block ionic transport pathways and lead to increased capacity fade. This paper describes self-healing nano-electrolytes, a new type of composite ionic conductors constructed by introducing into a polymer or polymer-ceramic matrix dynamic, reversibly bonded nanostructures such as hydrogen-bonded polymer networks, dynamic disulfide linkages, and core-shell ceramic nanoparticles. When damaged by mechanical force, the broken ionic pathway is bridged by the healing chemistry without any outside assistance. We review the design requirements of intrinsic and extrinsic self-healing systems, present representative synthesis pathways, and present illustrative electrochemical and mechanical performance data, such as Arrhenius conductivity behaviour, healing-efficiency kinetics, capacity retention across damage events and the effect of nanofiller loading on crack-healing performance. The results suggest that there is an optimum nanofiller loading that will maximize the benefits of the healing chemistry without being outweighed by agglomeration of the particles (around 5 % in the system studied). We end by discussing the remaining scientific and manufacturing challenges including scalability, healing-cycle durability and interfacial stability with lithium-metal anodes and present possible avenues for future research work in this fast-developing field.