LITHIUM ION SECONDARY BATTERY

摘要

Disclosed is a lithium ion secondary battery comprising a electrode plates group including a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode; a battery case for housing the electrode plates group; and a nonaqueous electrolyte solution containing a lithium salt dissolved in a nonaqueous solvent. The positive electrode comprises a positive electrode mix layer formed on a positive electrode collector, and the positive electrode mix layer contains a positive electrode active material and a conductive agent. The negative electrode comprises a negative electrode active material layer formed on a negative electrode collector. When such a lithium secondary battery is used for an HEV or the like, it is required high output characteristics enabling large current discharge such as an hour rate of 20-40C, though it is for a short time period such as 10 seconds or so. In the lithium secondary battery, 7-13% by weight of the positive electrode mix layer is composed of the conductive agent, the positive electrode mix layer have a porosity of 35-55%, and the concentration of lithium salt contained in the nonaqueous electrolyte solution is from 1.2 mol/L to 2 mol/L. Consequently, the output characteristics of the lithium secondary battery are improved.