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