COPPER FOIL FOR NEGATIVE ELECTRODE CURRENT COLLECTOR OF LITHIUM ION SECONDARY BATTERY, NEGATIVE ELECTRODE MATERIAL OF LITHIUM ION SECONDARY BATTERY, AND METHOD FOR SELECTING NEGATIVE ELECTRODE CURRENT COLLECTOR OF LITHIUM ION SECONDARY BATTERY

摘要

A copper foil for a negative electrode current collector of a lithium ion secondary battery enables prevention of deformation of the current collector even if the charge/discharge operation is repeatedly carried out. In a copper foil for a negative electrode current collector of a lithium ion secondary battery, a 10 mm wide test specimen composed of the copper foil is subjected to a tensile test, a maximum strain loaded on the copper foil is 30 N or higher in a region where "Value L" represented by the following expression is 0.8 or more in a strain-stress curve obtained in the tensile test where O is the starting point of the curve, PQ is the load at a point Q on the curve and EQ is an elongation at a point Q on the curve Value   L = ( area   of   triangle   OQE Q ) ( area   of   region   OQE Q )   ...  ( 1 )