Electron Beam Modification of Solid Polymer Electrolytes for Solid‐State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) offer flexibility and processability but suffer from low ionic conductivity and inadequate mechanical strength. Here, a facile, solvent‐free electron beam (EB) irradiation method is introduced to modify poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMATFSI)‐based SPEs for lithium metal batteries. At an optimal dose, EB irradiation simultaneously generates polar carbonyl groups and induces a crosslinked network. The carbonyl groups facilitate lithium‐ion transport and contribute to forming a robust, Li 2 O‐rich solid electrolyte interphase. Concurrently, the crosslinked architecture enhances mechanical integrity and suppresses the growth of lithium dendrites. As a result, Young's modulus increases from 170 to 921 MPa, ionic conductivity rises from 4.7 × 10 −4 to 8.2 × 10 −4 S cm −1 , the lithium‐ion transference number ( t Li + ) improves from 0.29 to 0.48, and the dielectric constant increases from 6.5 to 16.6. Consequently, Li||Li symmetric cells with modified SPE cycle stably for 2000 h (0.05 mA cm −2 ), 600 h (0.1 mA cm −2 ), and 180 h (0.2 mA cm −2 ), with a critical current density of 1.1 mA cm −2 . Li||NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) full cells deliver 83.7% capacity retention after 300 cycles at 1C and superior rate performance. This work demonstrates that EB irradiation is a promising and effective strategy for developing high‐performance solid‐state lithium metal batteries.