Electrochemical behavior of CuF2 as reversible cathode in an organic liquid electrolyte for room-temperature fluoride-shuttle batteries

CuF2 is considered a promising positive electrode material for fluoride-shuttle batteries (FSBs). Herein, the electrochemical compatibility of CuF2 in an organic liquid electrolyte comprising equal concentrations (0.25 M) of lithium bis(oxalato)borate (LiBOB) and triphenylboroxine (TPhBX) in addition to saturated CsF salt in tetraethylene glycol dimethyl ether (G4) solution (LiBOB0.25/TPhBX0.25/sat_CsF/G4) was investigated for potential use in FSBs. CuF2 in the LiBOB0.25/TPhBX0.25/sat_CsF/G4 system exhibited comparable initial discharge and charge capacities of 330 and 240 mAh g−1, respectively. While XRD shows that some CuF2 in the inner region of the electrode remains unreacted, XPS analysis clearly confirms the success of the conversion reaction at the electrode surface. In addition, almost no Cu was found in the LiBOB0.25/TPhBX0.25/sat_CsF/G4 electrolyte system in discharged and charged cells. Therefore, since the dissolution of CuF2 and metallic Cu is alleviated through the use of the LiBOB0.25/TPhBX0.25/sat_CsF/G4 electrolyte, LiBOB0.25/TPhBX0.25/sat_CsF/G4 is a promising organic electrolyte system for FSBs.