Long Cycle Life All-Solid-State Sodium Ion Battery.

All-solid-state sodium ion batteries (ASIBs) based on sulfide electrolytes are considered a promising candidate for large-scale energy storage. However, the limited cycle life of ASIBs largely restricts their practical application. Cycling-stable ASIBs can be achieved only if the designed cathode can simultaneously address challenges including insufficient interfacial contact, electrochemical and chemical instability between the electrode and electrolyte, and strain/stress during operation , rather than just addressing one or part of these challenges. Chevrel phase Mo6S8 has inherent high electronic conductivity and small volume change during sodiation/desodiation, and is chemically and electrochemically stable with the sulfide electrolyte, and therefore the only challenge of using Mo6S8 as the cathode for ASIBs is the insufficient contact between Mo6S8 and the solid electrolyte (SE). Herein, a thin layer of SE is coated on Mo6S8 using a solution method to achieve an intimate contact between Mo6S8 and the SE. Such a SE-coated Mo6S8 cathode enabled an ASIB with a high cycling performance (500 cycles), even much better than that of the liquid-electrolyte batteries with the Mo6S8 cathode. This work provides valuable insights for developing long-cycle life ASIBs.