Abstract
Tetragonal Na3SbS4 is synthesized as a new sodium superionic conductor. The discovery of Na vacancies experimentally verifies previous theoretical predictions. Na vacancies, distorted cubic sulphur sublattices and large Na atomic displacement parameters lead to the ionic conductivity as high as 3 mS cm-1, a value significantly higher than those of state-of-the-art sodium sulfide electrolytes.
Highlights
The growing demand for high capacity rechargeable batteries used in large-scale energy storage,[1] including electric vehicles and electrical grid energy storage, has promoted the development of sodium all-solid-state batteries.[2]
Arrhenius plot of the total ionic conductivity σ in the temperature range from 25 to 90 °C is depicted in Figure 3a for Na3SbS4
The ionic conductivity locates in the range from 3 mS cm−1 at 25 °C to 16 mS cm−1 at 90 °C, approaching to those of organic liquid electrolytes currently used.[2a]. This value is three orders of magnitude larger than that of tetragonal Na3PS4[8] and significantly higher than those of state-of-the-art sulfides with cubic structure.[9f,g] The activation energy Ea for the sodium-ion conduction were determined from the slope of the linear Arrhenius plot using the equation:[15] σ = σo exp(–Ea/kBT), where σo represents the pre-exponential parameter and kB the Boltzmann constant
Summary
The growing demand for high capacity rechargeable batteries used in large-scale energy storage,[1] including electric vehicles and electrical grid energy storage, has promoted the development of sodium all-solid-state batteries.[2]. The existence of Na vacancies in Na3SbS4 structure was revealed, experimentally verifying the vacancy theory recently proposed.[9g] This tetragonal Na3SbS4 demonstrates a high ionic conductivity of 3 mS cm−1 and is the fastest room temperature Na+ solid conductor to date.
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