Method for forming a Li-ion battery cell

A Li-ion battery cell includes cathode and anode materials, a separator, and an electrolyte including a mixture of a polyethylene oxide and an oxide of formula LivLasZnOn. A method of forming the cell includes the following successive cycling steps: (a) at least two successive charge and discharge cycles of the cell at a first cycling rate C/x, the charge/discharge steps being limited in time to x/2; (b) at least two successive charge and discharge cycles of the cell at a second charging rate C/y, different from the first cycling rate, where y is lower than x, the charge/discharge steps being limited in time to y/2; and (c) at least two successive charge and discharge cycles of the cell at a third cycling rate C/z different from the first and second charging rates, where z is lower than x and y, the charge/discharge steps being limited in time to z/2.