All solid secondary battery, all solid secondary battery structure and preparation method for all solid secondary battery

An all solid secondary battery, comprising:

• a stack including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer;
• and
• an exterior casing material accommodating and sealing the stack,
• wherein:
• the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one surface or opposite surfaces of the positive electrode current collector,
• the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector,
• the first negative electrode active material layer does not contain a solid electrolyte or an amount of the solid electrolyte contained in the first negative electrode active material layer is 3 wt % or less of the total weight of the first negative electrode active material layer;
• the exterior casing material includes:
• a first exterior casing material disposed on a first surface of the stack adjacent to the negative electrode layer, and
• a second exterior casing material disposed on the second surface of
• the stack opposing the first surface,
• the first exterior casing material includes a cushioning layer,
• the cushioning layer has a compression recovery ratio in a thickness direction of 65% to 99%, the compression recovery ratio in the thickness direction being represented by Equation 3,
• Equation 3
• Compression recovery ratio =AA2/AA1×100C
• AA1 is a third stress measured at a first point which is reached by compression by 50% of an initial thickness, and
• AA2 is a fourth stress measured when a second point is reached by additional compression by 13.33% of the initial thickness from the first point, and then, after 60 seconds lapse at the second point, the first point is reached back by a relaxation from the second point.

A method of manufacturing an all solid secondary battery, the method comprising:

• providing an assembly;
• and
• preparing a sealed assembly by pressing and sealing the assembly,
• wherein:
• the assembly includes:
• a stack including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer;
• and
• an exterior casing material for accommodating and sealing the stack, the exterior casing material includes:
• a first exterior casing material disposed on a first surface of the stack adjacent to the negative electrode layer, and
• a second exterior casing material disposed on the second surface of the stack opposing the first surface,
• the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one surface or opposite surfaces of the positive electrode current collector,
• the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector,
• the first negative electrode active material layer does not contain a solid electrolyte or an amount of the solid electrolyte contained in the first negative electrode active material layer is 3 wt % or less of the total weight of the first negative electrode active material layer,
• the first exterior casing material includes a cushioning layer
• the cushioning layer has a stress relaxation rate of 3% to 25%, the stress relaxation rate being represented by Equation 2,
• Equation 2
• Stress relaxation rate = [(S1-S2)/S1] ×100
• SI indicates a first stress measured when a first point is reached by compression by 50% of an initial thickness and then a second point is reached from the first point by additional compression by 13.33% of the initial thickness, and
• S2 indicates a second stress measured after 60 seconds lapse from a time of measuring the first stress.