A compactable Na2.5PS3.5F0.5 electrolyte for solid-state sodium batteries

Solid-state sodium batteries (NaSSBs) hold great promise due to their large-scale energy storage properties. However, the widely used sulfide electrolyte, Na₃PS₄, shows severe interface reaction with the anode and can be easily penetrated by Na dendrites during cycling. Here we propose a new type of Na_2.5PS_3.5F_0.5 (NPSF) electrolyte with comprehensive advantages over Na₃PS₄. It demonstrates a Na⁺ conductivity of 0.27 mS cm⁻¹ and a low electronic conductivity of 3.9 × 10⁻⁶ mS cm⁻¹ at room temperature. Benefiting from F-doping, NPSF demonstrates superior mechanical compactability, thus obtaining a dense electrolyte pellet with minimal defects, through a simple cold-pressing process. The assembled symmetric battery with Na₁₅Sn₄ electrodes shows highly improved dendrite-resistant capability. Moreover, NPSF also exhibits increased electrochemical stability with Na₁₅Sn₄, enabling it to be a comprehensive upgrade over Na₃PS₄. A robust Na₁₅Sn₄/hard carbon composite electrode is further developed to pair with an NPSF electrolyte, where the assembled symmetric battery can demonstrate a high critical current density of 4.5 mA cm⁻². Integrated full batteries of NaSSBs with a series of oxide cathodes of the high-performance 4 V class are achieved with high specific energy and power densities, as well as a long cycle life of over 1000 cycles.