Non-aqueous electrolyte secondary battery and method for producing non-aqueous electrolyte secondary battery

A method for producing a non-aqueous electrolyte secondary battery that comprises

• a flat-shaped wound electrode body in which a belt-shaped positive electrode plate and a belt-shaped negative electrode plate are wound, with a belt-shaped separator being intervened therebetween;
• a non-aqueous electrolyte;
• and
• a battery case that houses the wound electrode body and the non-aqueous electrolyte,
• the negative electrode plate comprising a negative electrode core and a negative electrode active material layer formed on the negative electrode core, and
• the negative electrode active material layer having a length of at least 20 cm in a winding axis direction of the wound electrode body,
• the method comprising:
• an assembling step of placing the wound electrode body and the non-aqueous electrolyte in the battery case to construct a secondary battery assembly;
• a first step of performing initial charging on the secondary battery assembly, wherein the secondary battery assembly is charged so that the state of charge (SOC) of the secondary battery assembly is 50% or less;
• and
• a second step, wherein the secondary battery assembly after the first step is maintained in a state with a SOC of 50% or less and a temperature of 50° C. or lower and this state is maintained for at least 72 hours.