Tunable Stabilization of Cuprous Ions via Kinetic and Thermodynamic Control of Cu Electrodeposition in Non-Aqueous Media

In this work, significant stabilization of Cu⁺ ions is achieved in non-aqueous electrolytes containing TFSI^- and Cl^- anions with diglyme as solvent. When Cl^- is absent, stabilization of Cu⁺ occurs due to the very low stability constant of Cu²⁺ in diglyme. However, in the presence of relatively low Cl^- concentrations (i.e., equimolar relative to Cu²⁺), both Cu⁺ and Cu²⁺ form extremely stable Cu^2+/+[Cl^-] complexes resulting in a ∼1200 mV negative shift of the Cu^+/0 redox couple relative to that of more easily reduced Cu⁺[TFSI^-][Cl^-] complexes. These results suggest that the lower solvation energies and wider electrochemical stability windows of non-aqueous solvents relative to water enable anions to play a much more significant role in guiding complexation behavior─providing new possibilities for (electro)chemical stabilization of reactive intermediates and highlighting the wealth of unexplored opportunities for electrolyte design in non-aqueous systems.