Phase-regulated ultrathin PVDF-based electrolytes for dynamic dendrite suppression in solid-state lithium metal batteries

The pursuit of safer batteries has driven significant research efforts toward solid-state lithium metal cells. To achieve an energy density comparable to that of liquid electrolyte-based cells, the development of ultrathin and lightweight solid electrolytes with superior performance is essential. However, fabricating solid electrolytes with thicknesses comparable to those of commercial separators (~ 10 μm) used in liquid systems remains challenging because of the increased risk of short circuits caused by dendrite growth. In this study, we present a polymer-based solid-state electrolyte composed of a 7.3 μm-thick ultrathin poly(vinylidene fluoride) (PVDF) film embedded with highly oriented Ti₃C₂T_x (T_x represents abundant surface functional groups) nanoflakes. Functionalized nanoflakes induce PVDF β-phase formation through hydrogen bonding, significantly improving dielectric and piezoelectric properties. These improvements enable a Li⁺ transfer number of 0.83 and ~ 10-fold enhancement in piezoelectric response. A high Li⁺ transfer number reduces polarization by suppressing space-charge formation during Li plating. Simultaneously, when the electrolyte senses strain accumulation from inevitable Li protrusions, the piezoelectric-induced electric field promptly alleviates the localized overpotential, dynamically promoting uniform Li deposition. Consequently, these electrolytes exhibit exceptional compatibility with Li anode, enabling long-term cycling under various conditions. The symmetric Li||Li cells demonstrate stable operation for over 3000 h without any micro-short circuits, whereas the LiFePO₄||Li full cells maintain high Coulombic efficiency (> 99.7%) and good stability through 300 cycles at 1 C.