Fast Potassium‐Ion Conduction in K3LnSi3O9 (Ln = Y and Gd) Enabled by P‐Doping Toward Ultrastable Quasi‐Solid‐State Batteries

/PB cell achieves a remarkable cycling performance at a high current density of 1 C (500 cycles, 95.9% capacity retention). These results would no doubt boost research for high-safety and high-energy-density solid-state potassium-ion batteries.