Tailored Organic Electrode Material Compatible with Sulfide Electrolyte for Stable All-Solid-State Sodium Batteries.

All-solid-state sodium batteries (ASSSBs) with nonflammable electrolytes and ubiquitous sodium resource are a promising solution to the safety and cost concerns for lithium-ion batteries. However, the intrinsic mismatch between low anodic decomposition potential of superionic sulfide electrolytes and high operating potentials of sodium-ion cathodes leads to a volatile cathode-electrolyte interface and undesirable cell performance. Here we report a high-capacity organic cathode, Na4 C6 O6 , that is chemically and electrochemically compatible with sulfide electrolytes. A bulk-type ASSSB shows high specific capacity (184 mAh g-1 ) and one of the highest specific energies (395 Wh kg-1 ) among intercalation compound-based ASSSBs. The capacity retentions of 76 % after 100 cycles at 0.1 C and 70 % after 400 cycles at 0.2 C represent the record stability for ASSSBs. Additionally, Na4 C6 O6 functions as a capable anode material, enabling a symmetric all-organic ASSSB with Na4 C6 O6 as both cathode and anode materials.