De-transition-metallization of cathode materials for constructing high-performance solid-state electrolytes in potassium-ion batteries

The development of potassium-ion batteries (KIBs) for grid-scale energy storage requires high-performance solid-state electrolytes (SSEs) that facilitate efficient K⁺ migration. However, the large ionic radius of K⁺ hinders the direct application of Li-/Na-ion SSE analogues in KIBs, presenting substantial challenges for SSE design. This study utilizes a de-transition-metallization (DTM) strategy, which involves substituting transition metals in KIB cathodes with main-group elements to design customized SSEs. First-principles calculations reveal that polyanionic KMPO₄A (M = Si, Ge, Sn, Al, Ga, and In; A = O/F) derivatives inherit the KTiOPO₄-type structure of cathodes, exhibiting thermodynamic stability due to the high anion coordination of K⁺. DTM eliminates transition-metal 3d-orbital contributions, widening band gaps to 3.13-5.32 eV (insulating behavior) while retaining helical 1D K⁺ migration channels. KMPO₄F displays enhanced ionic mobility, characterized by low diffusion barriers (<0.15 eV). Notably, KInPO₄F achieves a diffusion barrier of 0.04 eV, highlighting the intrinsic benefits of fluoride-based frameworks in promoting efficient K⁺ migration. The wide electrochemical windows of 4.80 V for KMPO₄F ensure compatibility with high-voltage cathodes. This work positions DTM as a rational and effective strategy for developing KIB SSEs, identifying polyanionic materials as premier candidates for designing high-safety and high-energy-density storage systems.