Multifunctional Solvent Molecule Realizing High-Performance Elastic Polymer Electrolytes for Lithium Metal Batteries

Abstract

Solid-state polyurethane electrolytes offer excellent elasticity, which can significantly improve the interfacial ion transport of solid-state lithium metal batteries. However, pure polyurethane electrolytes suffer from poor Li+ conductivity. Herein, a multifunctional solvent molecule, trifluoro-N,N-dimethylacetamide (TFDMA), is introduced to modify the thermoplastic polyurethane (TPU) electrolyte, resulting in a composite electrolyte (TPU-TFDMA) with both high mechanical properties and good Li+ transport performance (ionic conductivity = 1.53 × 10–3 S cm–1 and Li+ transference number = 0.50). Experimental characterizations and theoretical simulations reveal that the presence of additional hydrogen-bonding interactions between TFDMA and the TPU chains not only maintains the mechanical strength of TPU but also enhances interfacial stability and effectively inhibits lithium dendrite growth. Furthermore, TFDMA promotes lithium salt dissociation and reduces the coordination between solvent molecules and Li+, facilitating Li+ desolvation and rapid diffusion. TFDMA also immobilizes TFSI–, thereby enhancing Li+ transport efficiency and contributing to the formation of stable and multifunctional interfaces between electrodes and electrolytes. Consequently, the TPU-TFDMA electrolytes enable the Li symmetric cell to stably work for over 2500 h and endow the LiFePO4 full cell with a reversible capacity of 130 mAh g–1 after 320 cycles at 0.5 C.