A Cross‐Linked Flexible Metaferroelectrolyte Regulated by 2D/2D Perovskite Heterostructures for High‐Performance Compact Solid‐State Sodium Batteries

To address the issues of limited ionic conductivity and poor interface stability at room and low temperatures in solid-state electrolytes, a robust intrinsic ferroelectrolyte or nanoferroelectrolyte strategy for engineering solid-state flexible ferroelectric composite electrolytes utilizing strongly coupled intrinsic ion conducting 2D/2D sodium-rich anti-perovskite (NaRAP)/ferroelectric perovskite heterostructures is introduced. Herein, highly scalable PVDF-based metaferroelectrolytes with Na2.99Ba0.005OCl/Ca2Na2Nb5O16 - (CNNO-) nanosheets into a ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix, through an in situ cross-linking and spontaneous bridging method, for compact solid-state sodium batteries (SSBs), are reported. Benefiting from unique well-dispersed 3D ferroelectric coupled network and the Na2.99Ba0.005OCl/CNNO--induced PVDF-HFP ferroelectric β phase, the Na+ flux is regulated, thereby inhibiting Na dendrite growth at the interface. Notably, the optimized PH-5% NC metaferroelectrolyte exhibits rapid ion transport (1.11 × 10-4 S cm-1 at 25 °C), a wide electrochemical window (> 4.8V), superior conformal mechanical compatibility, improved flexibility, good elasticity and flame retardancy. The solid-state Na3V2(PO4)3/PH-5% NC/Na batteries present a stable cycling performance (remaining 56.4 mAh g-1 after 500 cycles at 1 C) even at 0 °C, potential for cost-effective, safe, stable and compact SSB energy storage over 600 Wh L-1, vastly surpassing 365 Wh L-1 of the current commercial sodium-ion liquid-electrolyte batteries.