Unveiling the Anionic Redox Chemistry in Phosphate Cathodes for Sodium-Ion Batteries

摘要

Anionic redox chemistry has aroused increasing attention in sodium-ionbatteries (SIBs) by virtue of the appealing additional capacity. However, up tonow, anionic redox reaction has not been reported in the mainstreamphosphate cathodes for SIBs. Herein, the ultrathin VOPO_4 nanosheets arefabricated as promising cathodes for SIBs, where the oxygen redox reaction isfirst activated accompanied by reversible ClO_4~? (from the electrolyte)insertion/extraction. As a result, the VOPO_4 cathode harvests a record-highcapacity (168 mAh g~(?1) at 0.1 C) among its counterparts ever reported.Moreover, the ClO_4~? insertion efficiently expands the interlayer spacing ofVOPO_4 and accelerates the ion diffusion, enabling an unprecedentedly highrate performance (69 mAh g~(?1) at 30 C). Via systematic ex situcharacterizations and theoretical computations, the anionic redox chemistryand charge storage mechanism upon cycling are thoroughly elucidated. Thisstudy opens up a new avenue toward high-energy phosphate cathodes forSIBs by triggering anionic redox reactions.