Molecularly engineered gel electrolyte bridges high voltage and lithium-metal stability

As lithium metal batteries (LMBs) move toward higher energy density, pairing lithium-metal anodes with high-voltage Ni-rich cathodes such as NCM811 remains challenging because conventional electrolytes struggle to simultaneously withstand oxidative conditions at the cathode and maintain stable lithium deposition at the anode. Researchers from North China Electric Power University, Southern University of Science and Technology, the Chinese Academy of Sciences, Sunwoda Mobility Energy Technology, and Sun Yat-Sen University have developed an in situ cross-linked polyurethane gel electrolyte that tackles these conflicting requirements through coordinated molecular- and atomic-level regulation. 

Why This Electrolyte Matters

Conventional ether-based electrolytes offer favorable compatibility with lithium metal but generally have limited electrochemical stability at high voltages, while ester-based electrolytes provide a wider stability window but strongly coordinate Li⁺, increasing the desolvation barrier and compromising lithium-metal interfaces. This intrinsic trade-off becomes particularly severe in Li||NCM811 batteries operating at high voltage. The new polyurethane strategy integrates complementary polymer segments within a single cross-linked network to address both sides of the electrolyte–electrode interface. 

Innovative Design and Mechanism

The resulting G-P3 AR electrolyte combines polyether and polyester segments with an atomic-scale boron-based anion-regulating unit. Polyester segments broaden the HOMO–LUMO gap and improve oxidation resistance, extending the electrochemical stability window to 4.97 V, while polyether segments exhibit weaker Li⁺ binding and facilitate faster desolvation. Meanwhile, sp²-hybridized boron Lewis-acid centers immobilize TFSI⁻ and DFOB⁻ anions, increasing the Li⁺ transference number to 0.78. Hydrogen bonding between polyurethane chains and solvent molecules further reconstructs the Li⁺ solvation sheath, promotes anion participation, and favors the formation of inorganic-rich SEI and CEI layers.  

Outstanding Performance

The molecularly regulated electrolyte delivers 0.78 mS cm^-1 ionic conductivity at 25 °C and substantially lowers the Li⁺ desolvation activation energy to 38.9 kJ mol^-1. Li||Li symmetric cells operate stably for more than 1000 h at 0.5 mA cm^-2 and 0.5 mAh cm^-2. In Li||NCM811 cells, the electrolyte achieves 157.7 mAh g^-1 at 2 C, with the capacity recovering to 205.7 mAh g^-1 when the rate returns to 0.1 C. At 0.5 C charge/1 C discharge, the cell retains 81.7% of its capacity after 500 cycles, compared with 73.5% for the conventional liquid electrolyte. 

Applications and Future Outlook

The electrolyte also demonstrates promise under more demanding practical conditions. A high-loading NCM811 cell with an areal capacity of 2 mAh cm^-2 retains 76.6% capacity after 200 cycles, while a pouch cell maintains 85.5% retention after 50 cycles and can power an LED even under bending, puncturing, and shearing. By simultaneously regulating polymer structure, Li⁺ solvation, anion distribution, and electrode interphases, this work provides a practical molecular-design strategy for safer and more durable high-energy lithium-metal batteries.