Bilayer electrolyte for a lithium battery

A battery comprising an electrolyte film placed between a positive electrode and a negative electrode formed from a lithium or lithium alloy film, wherein:

• the electrolyte film is a composite film comprising a layer known as layer N and a layer known as layer P, wherein:
• each of the layers P and N is composed of a solid solution of a lithium salt in a polymer material, the lithium salt being the same in both layers, the polymer material content being at least 60% by weight, and the lithium salt content being from 5 to 25% by weight;
• the polymer material of the layer P comprises from 35 to 60% by weight of a solvating polymer and from 25 to 60% by weight of a nonsolvating polymer, from 5 to 20% by weight of lithium salt, and from 0 to 10% by weight of an additive, the weight ratio of the two polymers being such that the solvating polymer forms a continuous network;
• the polymer material of the layer N comprises from 60 to 85% by weight of a solvating polymer and from 0 to 12% by weight of a nonsolvating polymer, from 15 to 25% by weight of lithium salt, and from 0 to 15% by weight of an additive, the weight ratio of the two polymers being such that the solvating polymer forms a continuous network, and the nonsolvating polymer does not form a continuous network;
• and
• each of the layers P and N is free from any aprotic liquid;
• and
• the layer N of the composite film is adjacent to the negative electrode and the layer P of the composite film is adjacent to the positive electrode, said positive electrode being in contact with a current collector.