Amide-functionalized copolymer electrolyte with high ionic conductivity and transference number for high-performance lithium metal batteries

Solid polymer electrolytes are regarded as promising candidates for high-energy-density lithium metal batteries, yet they typically suffer from a trade-off between ionic conductivity and lithium-ion transference number, alongside interfacial instability. In this work, a molecular engineering strategy is proposed by copolymerizing an amide-functionalized acrylate monomer, bis[2-(acrylamido)ethyl] heptanedioate, into a polyacrylate backbone. Theoretical calculations and spectroscopic analyses reveal that the incorporated amide groups establish a hydrogen bonding network interacting preferentially with succinonitrile and bis(trifluoromethanesulphonyl)imide anions. This interaction effectively anchors the solvent molecules and anions to the polymer chain, thereby restricting anion mobility while facilitating Li+ dissociation. Therefore, the optimized copolymer electrolyte achieves a high room-temperature ionic conductivity of 0.92 mS·cm-1 and a remarkable Li+ transference number of 0.82. Moreover, the hydrogen-bond-modulated solvation structure promotes the formation of contact ion pairs and aggregates, which subsequently induces the formation of a robust inorganic-rich (LiF/Li3N) solid electrolyte interphase. As a result, the Li||Li symmetric cell demonstrates stable cycling for over 1,700 h at a current density of 0.5 mA·cm-2. The Li||LiNi0.8Co0.1Mn0.1O2 full cell delivers an initial discharge capacity of 220.8 mAh·g-1 at 0.1 C and exhibits superior long-term cyclability (85.3% capacity retention after 500 cycles at 1 C). This work highlights the critical role of intermolecular hydrogen bonding in designing advanced electrolytes for next-generation batteries.