Exploring the Active Roles of Fluorinated Ionic Polyacrylamide Copolymer on Electrolyte Performance Improvement for Lithium Metal Batteries.

Polymer electrolytes have attracted wide attention for improving the interfacial stability and safety of lithium metal batteries (LMBs). Understanding how the polymer chemical structure influences the ion conduction/environment, and electrochemical properties is quite important. Herein, fluorinated polyacrylamide-based ionic copolymer was constructed with liquid carbonate electrolyte by in situ photopolymerization to form gel polymer electrolyte (GPE) named MTA. The copolymer skeleton in MTA effectively coordinates with Li+ weakly and immobilizes TFSI- anion, resulting in rapid Li+ conduction (6.9 × 10- 4 S cm- 1) and high Li+ transference number (0.56). Meanwhile, the copolymer chain also interacts with liquid electrolyte molecules, thus improving the Li+ solvation environment with more TFSI- anions involved. This tuned Li+ solvation environment contributes to stable and LiF/Li3N-rich solid electrolyte interphase (SEI) on lithium metal. As a result, the Li/MTA/Li symmetric cell shows outstanding long cycling stability over 2500 h. Moreover, Li/MTA/NCM811 cell shows capacity retention of 96% after 100 cycles at 0.2 C. Li/MTA/LiCoO2 cell cycles stably over 120 cycles at 0.2 C. The cathode electrolyte interphase (CEI) on NCM811 is uniform and LiF-rich. At 0.1 C, the Li/MTA/NCM811 pouch cell retains 87% of its capacity after 50 cycles. It also proves good safety and could work under bending and cutting.