Method of producing a secondary battery, and secondary battery

A method of producing a secondary battery, the method comprising:

• preparing a battery architecture, the battery architecture comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode comprising a lithium-nickel-cobalt-manganese composite oxide, the negative electrode comprising a niobium-titanium composite oxide, and the electrolyte comprising one or more of first organic solvents having a viscosity of 1 cP or less;
• adjusting a positive electrode potential of the positive electrode to a range of 3.4 V or more and 3.9 V or less based on oxidation-reduction potential of lithium, and adjusting a negative electrode potential of the negative electrode to a range of 1.5 V or more and 2.0 V or less based on oxidation-reduction potential of lithium, thereby providing a potential adjusted state;
• and
• holding the battery architecture in the potential adjusted state at a holding temperature in a range of 50° C. or more and 90° C. or less.