Method of making negative electrode

Abstract

[Problem] To provide a negative electrode collector for lithium ion secondary batteries, having a high strength and a large discharge capacity. [Means for Resolution] A negative electrode collector using a copper-covered steel foilfor carrying a negative electrode active material for lithium ion secondary batteries, which has a steel sheetas the core material thereof and has, on both surfaces thereof, a copper covering layerhaving a mean thickness tof from 0.02 to 5.0 μm on each surface, and of which the total mean thickness, t, including the copper covering layeris from 3 to 100 μm with t/t of at most 0.3. To the steel sheet, for example, applicable is common steel, austenitic stainless steel or ferritic stainless steel. The copper covering layeris, for example, a copper electroplating layer (including one rolled after plating). On the surface of the copper covering layer, for example, a carbon-based active material layer that has been densified through strong roll pressing is formed, and the copper-covered steel foiland the carbon-based active material layer constitute the negative electrode collector.