Permeable void-free interface for all-solid-state alkali-ion polymer batteries.

All-solid-state batteries suffer from a loss of contact between the electrode and electrolyte particles, leading to poor cyclability. Here, a void-free ion-permeable interface between the solid-state polymer electrolyte and electrode is constructed in situ during cycling using charge/discharge voltage as the stimulus. During the charge-discharge, the permeation phase fills the voids at the interface and penetrates the electrode, forming strong bonds with the cathode and effectively mitigating the contact problem. Our all-solid-state potassium ion polymer batteries maintain high Coulombic efficiency more than 2000 cycles at a high operating voltage of 4.5 volt and stably cycle more than 500 cycles even at 4.6 volt. Our rational design for mitigating the contact problem is versatile, as demonstrated by the scalability of all-solid-state graphite-based polymer potassium-ion pouch cells and all-solid-state lithium-ion polymer batteries.