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.