Solid Polymer Electrolyte with Dual Lewis‐Acid Filler for Ultra‐Stable Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are regarded as promising candidates that could address the safety concerns associated with liquid electrolytes. Nonetheless, SPEs are still confronting serious lithium dendrite issues, and there is a lack of systematic studies regarding the formation of lithium dendrites within SPEs. Herein, Sand equation is employed to elucidate the determinants of dendrite growth in SPEs, revealing that three factors including the Li⁺ transference number, Li⁺ diffusion coefficient, and Li⁺ concentration are positively correlated with Sand's time (τ) which determine the plating/striping behaviors of Li anode. More importantly, an effective and universal approach is proposed to construct dendrite-free polymer lithium metal batteries with dual-Lewis-acid materials such as Zinc Borate (ZB). Endowed with ZB materials, the PVDF-HFP based electrolyte possesses sufficient Li⁺ supply and swift transport channel and thus achieves an impressively high Li⁺ transference number of 0.9 and outstanding ionic conductivity at 30 °C (9.2 × 10^-4 S cm^-1), outperforming the polymer electrolytes with single Lewis-acid fillers. The electrolyte imparts the LFP//Li cell with exceptional capacity retention, showing almost no decay in discharge capacity even after 700, 500, and 300 cycles at 2 C, 3 C, and 5 C, respectively. Additionally, it capacitates the LiNi_0.6Mn_0.2Co_0.2O₂//Li cell to outperform by achieving over 1900 cycles at 1C and stably cycling under a cut-off voltage of 4.5V.