When a conductive agent is added, the blending ratios of the positive electrode active material, binder, and conductive agent are preferably 77% by mass to 95% by mass, 2% by mass to 20% by mass, and 3% by mass to 15% by mass, respectively. When the content of the conductive agent is 3% by mass or more, the above-described effects can be achieved. By setting the amount of the positive electrode conductive agent to 15% by mass or less, the decomposition of a nonaqueous electrolyte on the surface of the positive electrode conductive agent in high-temperature storage can be reduced.
The current collector is preferably an aluminum foil, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.
The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm to 20 μm, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of the transition metal such as iron, copper, nickel, or chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.
The positive electrode is produced by, for example, suspending a positive electrode active material, a binder, and as necessary a conductive agent in an appropriate solvent to prepare a slurry, applying the slurry to a positive electrode current collector, drying the coating to form a positive electrode layer, and then pressing the layer. Alternatively, the positive electrode may be also produced by forming an active material, a binder, and as necessary a conductive agent into pellets to produce a positive electrode layer, and placing it on a current collector.
3) Nonaqueous Electrolyte