With the recent accelerated reduction in the size and weight of mobile information terminals such as cellular phones, notebook computers, and smartphones, secondary batteries serving as driving power supplies for such mobile information terminals have been required to have a higher capacity. Nonaqueous electrolyte secondary batteries, which are charged and discharged by the movement of lithium ions between positive and negative electrodes, have a high energy density and a high capacity and therefore are widely used as driving power supplies for the above mobile information terminals.
Furthermore, nonaqueous electrolyte secondary batteries have recently attracted attention as power supplies for driving, for example, power tools, electric vehicles (EVs), and hybrid electric vehicles (HEVs, PHEVs) and are promising for various uses.
Such power supplies for driving are required to have a higher capacity that allows long-term operation and improved output characteristics in the case where charge and discharge are repeatedly performed with a large current within a relatively short time. A higher capacity needs to be achieved while output characteristics during charge and discharge with a large current are maintained.
For example, PTL 1 proposes a positive electrode active material containing lithium carbonate as means for improving high-temperature storage characteristics and load characteristics. PTL 2 proposes a lithium manganese oxide modified with an oxide containing tungsten as means for maintaining a high discharge capacity during discharge with a large current.