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

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 )