Low-LUMO Orotic Acid Enables Li₃N-Embeded Solid Electrolyte Interphase for Stable All-Solid-State Lithium Metal...

Biomacromolecules hold promise as sustainable fillers to address the challenges of low ionic conductivity and interfacial instability in polymer electrolytes, yet their structural complexity obscures in-depth mechanistic understanding. Herein, small biomolecules are strategically incorporated, which retain the key functional groups of biomacromolecules, as highly effective fillers for polymer electrolytes. Orotic acid (OA), a small-molecule building block of ribonucleic acid, enhances lithium (Li) ion conductivity by facilitating the dissociation of lithium bis(trifluoromethanesulfonyl)imide without compromising the crystallinity of the polyethylene oxide (PEO) matrix. The amide-rich conjugated structure endows OA with a low lowest unoccupied molecular orbital energy level, promoting its preferential decomposition to form a lithium nitride (Li₃N) embedded solid electrolyte interphase. This dual-function mechanism enables the OA-optimized PEO electrolyte to achieve 95.2% capacity retention after 350 cycles (0.5 C, initial capacity: 148 mAh g^-1) and >80% retention after 600 cycles (1.0 C, initial capacity: 128.6 mAh g^-1) in Li||LiFePO₄ cells.