Dendrite-free, interfacially compatible Na2ZrCl6 composite halide solid-state electrolyte for solid-state sodium-ion batteries

Abstract

Low ionic conductivity and poor interfacial stability restrict the practical application of all-solid-state sodium-ion batteries (ASSSIBs). To solve these issues, a facile strategy involving the use of an inorganic–organic composite solid electrolyte (SE) composed of Na₂ZrCl₆ and polyacrylonitrile (PAN) is proposed. The introduction of Na₂ZrCl₆ results in a reduction in the crystallinity of PAN, which creates numerous pathways for Na⁺ ions migration and significantly enhances the ionic conductivity of SE. When utilized in a Na‖Na symmetric cell, the Na₂ZrCl₆–PAN SE exhibited good interfacial stability, with no Na dendrite formation even after 5000 h of Na electroplating/stripping. In addition, non-in situ X-ray diffraction, X-ray photoelectron spectroscopy, and in situ AC impedance tests confirmed the favorable interfacial stability of the Na₂ZrCl₆–PAN SE in contact with Na metal and Na₃V₂(PO₄)₃ (NVP). Furthermore, Na|Na₂ZrCl₆–PAN|NVP ASSSIBs exhibit outstanding electrochemical performance. The battery achieves an initial discharge capacity of 80.7 mA h g⁻¹ at 1 C, which remains at 69.2 mA h g⁻¹ after 500 cycles. Additionally, all-solid-state SIBs with a hard carbon (HC)|Na₂ZrCl₆–PAN|NVP ASSSIB configuration demonstrate excellent electrochemical cycling stability.