Solidification for solid-state lithium batteries with high energy density and long cycle life

Conventional lithium-ion batteries with inflammable organic liquid electrolytes are required to make a breakthrough regarding their bottlenecks of energy density and safety, as demanded by the ever-increasing development of electric vehicles and grids. In this context, solid-state lithium batteries (SSLBs), which replace liquid electrolytes with solid counterparts, have become a popular research topic due to their excellent potential in the realization of improved energy density and safety. However, in practice, the energy density of SSLBs is limited by the cathode mass loading, electrolyte thickness and anode stability. Moreover, the crucial interfacial issues related to the rigid and heterogeneous solid-solid contacts between the electrolytes and electrodes, including inhomogeneous local potential distributions, sluggish ion transport, side reactions, space charge barriers and stability degradation, severely deteriorate the cycle life of SSLBs. Solidification, which converts a liquid into a solid inside a solid battery, represents a powerful tool to overcome the aforementioned obstacles. The liquid precursors fully wet the interfaces and infiltrate the electrodes, followed by in-situ conformal solidification under certain conditions for the all-in-one construction of cells with highly conducting, closely contacted and sustainable electrode/electrolyte interfaces, thereby enabling high energy density and long cycle life. Therefore, in this review, we address the research progress regarding the latest strategies toward the solidification of the electrolyte layers and the interfaces between the electrodes and electrolytes. The critical challenges and future research directions are proposed for the solidification strategies in SSLBs from both science and engineering perspectives.