Importance

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Abstract

The present invention provides an electrodeposited copper foil having a tensile strength of at least 300 MPa and elongation rate of at least 3.0% after heat treatment at 350° C. for 1 hour and provides a copper foil which prevents the breakage of a current collector (copper foil) while maintaining adhesiveness between the current collector (copper foil) and the active material in response to substantial expansion and contraction of a Si or Sn alloy-based active material. The foil is an electrodeposited copper foil having a roughened surface, the tensile strength of the copper foil being at least 300 MPa after heating at 350° C. for 1 hour, the elongation rate being at least 3.0% after heating at 350° C. for 1 hour, and respective surface area ratios (actual surface area/geometric surface area) of both sides of the copper foil (the side that is roughened and the side that is not roughened) being from 1.6 to 2.2. The electrodeposited copper foil is produced with an electrolyte in which from 3 to 20 ppm of organic additives of one or more compounds selected from compounds having a structure with an SH group binding to a heterocycle containing N or thiourea-based compounds is added to a copper sulfate-based electrolyte, and then from 0 to 12 ppm of hydroxyethyl cellulose or a low-molecular weight glue, and from 10 to 80 ppm of chlorine ions are added thereto.

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First Claim