New Strategy for Polysulfide Protection Based on Atomic Layer Deposition of TiO2 onto Ferroelectric‐Encapsulated Cathode: Toward Ultrastable Free‐Standing Room Temperature Sodium–Sulfur Batteries

Abstract The room temperature (RT) sodium–sulfur batteries (Na–S) hold great promise for practical applications including energy storage and conversion due to high energy density, long lifespan, and low cost, as well based on the abundant reserves of both sodium metal and sulfur. Herein, freestanding (C/S/BaTiO 3 )@TiO 2 (CSB@TiO 2 ) electrode with only ≈3 wt% of BaTiO 3 additive and ≈4 nm thickness of amorphous TiO 2 atomic layer deposition protective layer is rational designed, and first used for RT Na–S batteries. Results show that such cathode material exhibits high rate capability and excellent durability compared with pure C/S and C/S/BaTiO 3 electrodes. Notably, this CSB@TiO 2 electrode performs a discharge capacity of 524.8 and 382 mA h g −1 after 1400 cycles at 1 A g −1 and 3000 cycles at 2 A g −1 , respectively. Such superior electrochemical performance is mainly attributed from the “BaTiO 3 ‐C‐TiO 2 ” synergetic structure within the matrix, which enables effectively inhibiting the shuttle effect, restraining the volumetric variation and stabilizing the ionic transport interface.