Li-Ion Transfer Mechanism of Ambient-Temperature Solid Polymer Electrolyte toward Lithium Metal Battery

The low ionic conductivity and short service life of solid polymer electrolytes (SPEs) limit the application of ambient-temperature polymer lithium metal batteries, which is perhaps a result of the inherent restricted segment movement of the polymer at room temperature. Herein, an ambient-temperature dual-layer solid polymer electrolyte is developed and the related working mechanisms are innovatively investigated. In the strategy, poly(propylene carbonate) (PPC)/succinonitrile (SN) contacts with the cathode while polyethylene oxide (PEO)/Li₇La₃Zr₂O₁₂ is adopted near the anode. Molecular dynamics simulations demonstrate the formation of solvated sheath-like structure [SN···Li⁺], which demonstrates strong interaction with polymers (PPC···[SN···Li⁺]/PEO···[SN···Li⁺]). Further density functional theory calculations show that these structures, allow rapid transport of Li ions through polymer segments. These results are confirmed with Fourier transform infrared spectroscopy and nuclear magnetic resonance. Therefore, the Li-ion transport mechanism for ambient-temperature SPEs can be reasonably revealed. Remarkably, the binding energy between PPC and SN is stronger than that of PEO, which helps avoid the parasitic reaction between SN and Li. A low overpotential of 55 mV is exhibited for Li/Li symmetrical cells after 1000 h. Notably, a capacity retention of 86.3% is maintained for LiNi_0.6Co_0.2Mn_0.2O₂/Li cell at 25 °C, implying good application potential in ambient-temperature high voltage lithium metal batteries.