A mixed-anion strategy for constructing rapid ion-conducting Na solid-state electrolyte

Abstract

To advance the development of all-solid-state Na-ion batteries (ASSNIBs), optimal Na solid-state electrolyte (SSE) materials must meet critical requirements, including high ionic conductivity (>10 −3 ​S ​cm −1 ), low electronic conductivity (<10 −10 ​S ​cm −1 ), and cost-effectiveness (<$50 ​kg −1 ). In this study, we present a mixed-anion strategy for designing SSEs containing earth-abundant elements only. Density functional theory (DFT) and bond valence site energy (BVSE) calculations show that Na 2 ZrO 3 offers better electrochemical stability but poor Na ​ + ​conductivity compared to Na 2 ZrCl 6 . Mixed-anion SSE Na 2 ZrCl 6-4x O 2x has the potential for combining the strengths of high electrochemical stability of the oxide and high ionic conductivity of the halide. The optimal composition Na 2 ZrCl 3 O 1.5 synthesized by a mechanochemical method exhibits a high ionic conductivity of 5.17 ​× ​10 −5 ​S ​cm −1 at room temperature, nearly an order of magnitude improvement over Na 2 ZrCl 6 and orders of magnitude higher than that of Na 2 ZrO 3 . This enhancement is attributed to the more disordered phase within Na 2 ZrCl 3 O 1.5 . Cost analysis reveals that Na 2 ZrCl 6-4x O 2x can be produced at a large scale and low cost (≤£25.53/kg). These findings pave the way for the mixed-anion strategy for developing high-performing SSE materials for ASSNIBs. Combining theoretical calculations and experimental approaches to design and synthesise doped Na solid-state electrolyte material with high ionic conductivity and electrochemical stability. • Na 2 ZrCl 6-4x O 2x solid-state electrolyte (SSE) contains earth-abundant elements only. • Na 2 ZrCl 6-4x O 2x combines high ion conductivity of halide and high stability of oxide. • Optimal composition Na 2 ZrCl 3 O 1.5 exhibits the highest ion conductivity. • Enhanced ionic conductivity due to more disordered phase with anion doping.

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