Stable Dendrite-Free Sodium-Sulfur Batteries Enabled by a Localized High-Concentration Electrolyte

Ambient-temperature sodium-sulfur batteries are an appealing, sustainable, and low-cost alternative to lithium-ion batteries due to their high material abundance and specific energy of 1274 W h kg^-1. However, their viability is hampered by Na polysulfide (NaPS) shuttling, Na loss due to side reactions with the electrolyte, and dendrite formation. Here, we demonstrate that a solid-electrolyte interphase rich in inorganic components can be realized at both the sulfur cathode and the Na anode by tweaking the solvation structure of the electrolyte. This transforms the sulfur redox process from conventional dissolution-precipitation chemistry into a quasi-solid-state reaction, which eliminates NaPS shuttling and facilitates dendrite-free Na-metal plating and stripping. With the solvated ionic liquid electrolyte structure, a high initial capacity of 922 mA h g^-1 with a capacity fade of as low as 0.10% per cycle over 300 cycles was achieved. The scalability of this approach to pouch cells with practically necessary parameters demonstrates its potential for practical viability.