Stack pressure-A critical strategy and challenge in performance optimization of solid state batteries

Abstract

Due to their excellent energy density, solid-state batteries (SSBs) are expected to play an important role in future energy storage and transportation fields. However, the practical application of SSBs still faces many challenges, including poor contact at the electrode - solid electrolyte (SE) interface, inferior interfacial stability, and low ionic conductivity of SE and electrode materials, which further affect the capacity, C-rate performance, cycle life and safety of SSBs. It has been demonstrated that appropriate stack pressure is a critical factor in improving interfacial contact quality, enhancing interfacial stability, and increasing ionic conductivity of materials in SSBs. To this end, this paper comprehensively summarizes the important role and challenges of stack pressure in the performance optimization of SSBs. First, the effects and mechanisms of stack pressure on the interfacial contact quality of SSBs are analyzed, including the anode-SE interface and the cathode-SE interface, as well as how stack pressure should be applied to improve interfacial contact quality. Then, the effects and mechanisms of stack pressure on the interfacial stability of SSBs are analyzed, including the stabilizing effect on lithium deposition/stripping and the inhibiting effect on lithium dendrites, as well as how stack pressure should be applied to enhance interfacial stability. Next, the effects of stack pressure on SE materials and electrode materials are analyzed, proposing that the ionic conductivity and cyclic stability of SSBs can be increased by pressure-affected parameters such as porosity and volume change rates of SE and electrode materials. With respect to the high demand for stack pressure in SSBs, methods and strategies that can effectively reduce the stack pressure are further discussed, including the adoption of novel interfaces, novel materials, and novel processes. The directions for future research and development are prospected at last.