A Biosourced and Self‐Healable Polymer Electrolyte for Potassium Batteries

Potassium‐ion batteries offer a cost‐effective and sustainable alternative to large‐scale energy storage, yet electrolyte design remains a critical bottleneck. Here, we introduce a UV‐cured gel‐polymer electrolyte (GPE) that exploits bio‐derived lignin microparticles as a key functional component (as a microfiller) in potassium batteries. Far beyond acting as a passive additive, the microsized lignin phase actively engineers the polymer network, suppressing crystallinity, unlocking high chain mobility, reinforcing mechanical integrity, and enabling fast and homogeneous K + transport. Combined with ureidopyrimidinone methacrylate, polycaprolactone diol di‐methacrylate, and polyethylene glycol, and plasticized by a potassium‐based liquid electrolyte, this architecture yields an ionic conductivity that surpasses conventional separators swollen with liquid electrolyte. The resulting GPE delivers 134 mAh·g −1 at 0.1 A·g −1 with 100% retention over 1000 cycles, and introduces the first self‐healing electrolyte ever reported for potassium batteries, maintaining 86% capacity after intentional membrane damage. By demonstrating that lignin microstructuring is a powerful and unexplored design lever for K‐ion electrolytes, this work opens new possible routes toward safe, high‐performance, and long‐lived potassium batteries for stationary applications.