Designing low-strain cathode materials for long-life all-solid-state batteries

Abstract

All-solid-state batteries (ASSBs) represent the next generation of technology, offering tremendous potential in safety and energy density. However, successfully integrating high-capacity cathode materials without compromising long-term stability remains a formidable challenge. The insertion of a large quantity of lithium ions easily induces high strain in the crystal structure, potentially disrupting the cathode's integrity and the cathode–solid electrolyte interface. This, in turn, can adversely affect the energy density and lifespan of ASSBs. In order to help alleviate the mechanical degradation of cathodes, it is necessary to design low-strain materials that exhibit minimal or even zero volume change during Li-ion extraction and insertion. In this review, the critical problems associated with high-strain cathodes in ASSBs are outlined, pinpointing the origins of strain and their detrimental impact on material failure and the degradation of solid–solid interfaces. Subsequently, the design principles of low-strain cathode materials are critically reviewed and discussed, including selecting transition metal ions with only t_2g electronic configuration or isotropic atomic arrangements, introducing the pinning effect by integrating strain-retardant heteroatoms or phases into the bulk phase, manipulating the different domains to mitigate the cooperative Jahn–Teller distortion, and designing nanosized and single-crystal cathode materials to suppress the intergranular and intragranular crack. Ultimately, this review offers insights and recommendations for future research aimed at designing low-strain cathode materials and at the operation of high-energy-density ASSBs under low external pressure conditions.