Breaking Voltage Limitations: Triethyl Phosphate-Engineered PVDF-Based Electrolytes with Dual-Interphase Stabilization for 4.7 V-Class Quasi-solid-state Lithium Metal Batteries

The advancement of high-voltage solid-state electrolytes constitutes a pivotal challenge for realizing practical solid-state lithium metal batteries (SSLMBs). This work overcomes intrinsic voltage constraints in conventional dimethylformamide-processed poly(vinylidene fluoride) quasi-solid-state polymer electrolytes (SPEs) through molecular engineering of triethyl phosphate (TEP) as a high-band-gap solvent. First-principles calculations demonstrate TEP's exceptional frontier orbital configuration, featuring a 9.4 eV HOMO-LUMO gap, thus expanding the electrochemical window to 4.8 V, an enhancement of 0.5 V compared to DMF-based systems (4.3 V). Leveraging this design, the optimized SPEs enable the stable operation of Li||NCM811 cells at ultrahigh voltages up to 4.7 V. Remarkably, these cells exhibit excellent long-term cycling stability, capacity retentions of 88.2% (1800 cycles at 4.2 V) and 86.8% (900 cycles at 4.5 V) are achieved. Even under the ultrahigh voltage of 4.7 V, the batteries maintain remarkable cycling stability, successfully completing 500 cycles and showcasing exceptional performance. Multiscale analysis reveals dual interfacial stabilization mechanisms: a TEP-derived Li₃PO₄-rich cathode interphase suppressing structural degradation coupled with a 25 nm crystalline Li₂O-dominated anode interphase inhibiting dendrites. This molecular design paradigm establishes a pathway toward 4.7 V-class SSLMBs through interfacial architecture stabilization.