A Biocompatible Deep Eutectic Electrolyte Enables Ultra-Fast Charging in Lithium-Ion Batteries

Lithium-ion batteries are of great significance in improving people's lives by offering reliable, long-lasting, and high-capacity power solutions. However, safety concerns, particularly those related to electrolyte leakage under harsh conditions, pose significant obstacles to their practical applications. In this context, a biocompatible deep eutectic electrolyte (DEE) is presented formulated by blending 2,6-dimethylpyrazine (DMPY)—a natural ingredient approved by the World Health Organization (WHO) due to its natural origin—with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in specific molar ratios. Benefitting from its abundant N atoms, DMPY molecule effectively drives Li─N coordination with Li⁺ cations, forms hydrogen bonds with TFSI⁻ anions, and consequently enhances the dissociation of LiTFSI—all of which trigger the formation of DEE. This DEE solution demonstrates remarkable performance characteristics, including a high Li⁺ transference number (0.67), substantial ion conductivity (0.57 mS cm⁻¹ at 30 °C), and moderate oxidation voltage (4.10 V vs Li/Li⁺). These attributes are complemented by remarkable interface stability and long-term cycling stability across a broad range of rates, notably at a rate of 10 C, ascribed to the generation of a robust organic–inorganic gradient solid-electrolyte interphase. This work opens intriguing perspectives to design novel electrolytes for the demanded performance of lithium-ion batteries while ensuring good biocompatibility.