Anion Redistribution in Solvation Structure Enables a Stable Graphite Cathode in Dual-Ion Batteries.

The electrochemical properties of anions as carriers in graphite-based dual-ion batteries (GDIBs) play an important role in achieving long cycling stability and high-rate performance. However, anion behavior in the electrolyte was neglected in previous studies. To balance high voltage and fast conduction, the anion behavior after introducing diluent in a highly concentrated electrolyte|high concentrated electrolyte (HCE) to form locally highly concentrated electrolyte|locally high concentrated electrolyte (LHCE) in GDIBs was deeply investigated. In contrast to the highly aggregated coordinated ion pairs in the HCE, more free anions can be attained in the LHCE without significant reunion. These free anions can rapidly migrate to the electrode surface under the electric field drive and then intercalate between graphite layers with a lower energy barrier. Meanwhile, an inorganic-rich interfacial layer with rapid ion conduction and a thinner thickness can be formed to prevent further decomposition of anions and stabilize the structure of the cathode. As a consequence, the dual-graphite DIBs achieved a superior capacity of 98.3% after 1000 cycles at a high rate of 200 mA g in LHCE, and the corresponding pouch cells exhibited a stable cycling process. This work advances the understanding of anion chemistry, enabling the regulation of the anion status to enhance the electrochemical performance of GDIBs.