A method is provided for forming a rechargeable metal-ion battery with a non-aqueous hybrid ion electrolyte. The method provides a transition metal hexacyanometallate (TMHCM) cathode (AXM1YM2Z(CN)N.MH2O), where “A” is from a first group of metals, and M1 and M2 are transition metals. The electrolyte includes a first type of cation from the first group of metals, different than “A”. The method connects the cathode and anode to external circuitry to perform initial charge/discharge operations. As a result, a hybrid ion electrolyte is formed including the first type of cation and “A” cations. Subsequently, cations are inserted into the anode during charging, which alternatively may be only “A” cations, only the first type of cation, or both the “A” cations and the first type of cation. Only “A” cations, only the first type, or both “A” and the first type of cation are inserted into the TMHCM during discharge.