Green Polymer Electrolytes Based on Polycaprolactones for Solid‐State High‐Voltage Lithium Metal Batteries

Solid polymer electrolytes (SPEs) have attracted considerable attention for high energy solid‐state lithium metal batteries (LMBs). In this work, potentially ecofriendly, solid‐state poly( ε ‐caprolactone) (PCL)‐based star polymer electrolytes with cross‐linked structures (xBt‐PCL) are introduced that robustly cycle against LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) composite cathodes, affording long‐term stability even at higher current densities. Their superior features allow for sufficient suppression of dendritic lithium deposits, as monitored by 7 Li solid‐state NMR. Advantageous electrolyte|electrode interfacial properties derived from cathode impregnation with 1.5 wt% PCL enable decent cell performance until up to 500 cycles at rates of 1C (60 °C), illustrating the high potential of PCL‐based SPEs for application in high‐voltage LMBs.