Anion coordination-regulated multi-element synergistic electrolyte for high-voltage lithium-ion batteries

This research explores the structural and interfacial regulation mechanisms of multi-element synergistic electrolytes for high voltage LiNi x Co y Mn 1-x-y O 2 (NCM) lithium ion batteries through a combined simulation-experiment approach. Theoretical calculations revealed that difluoroxalate borate ion (DFOB − ) exhibit a pronounced negative electrostatic potential distribution, with a binding energy to Li + (-110.26 kJ/mol) higher than conventional carbonate solvents (e.g., DMC, FEC), thus dominating the formation of anion-enriched solvation sheaths and significantly reducing Li + desolvation energy barriers (<30 kJ/mol). Raman spectroscopy and molecular dynamics simulations confirmed that LiDFOB introduction facilitates the transition of solvation structures from solvent-separated ion pairs (SSIPs) to contact ion pairs (CIPs) and aggregates (AGGs), with CIPs/AGGs proportion increasing from 29 % to 39 %, effectively suppressing LiPF 6 hydrolysis and mitigating electrode structural damage caused by solvent co-intercalation. Electrochemical tests demonstrated that the optimized 0.5 PB modified electrolyte(0.5 M lithium hexafluorophosphate+0.5 M lithium difluoro(oxalato)borate dissolved in a mixed solvent of dimethyl carbonate: fluoroethylene carbonate: propyl p-toluene sulfonate in a ratio of 3:1:1) enabled NCM811||Li half-cells to achieve 88 % capacity retention after 100 cycles at 4.5 V high voltage (versus 58 % for control group), along with stable lithium metal anode cycling for 500 h at 1 mA·cm −2 . Interface analysis revealed that DFOB⁻ and PPTs preferentially undergo redox reactions to form inorganic-rich cathode electrolyte interphase (CEI) films containing borides (LiₓBOyFz) and sulfonates (ROSO₂Li). On the anode side, synergistic effects of DFOB⁻, Propyl p-toluene sulfonate (PPTs) and FEC generate LiF/sulfur/boride-enriched composite solid electrolyte interface (SEI) layers, effectively suppressing transition metal dissolution and graphite structural degradation. This work provides a novel paradigm of "anion coordination-solvation structure-interface functionalization" for high-voltage lithium-ion batteries."