Abstract: An evaluation method of a negative electrode active material for secondary battery includes measuring an X-ray diffraction of a battery cell stored in a charged state; calculating intensity integrals of extracted diffraction peaks, where the extracted diffraction peaks are extracted from X-ray diffraction peaks for a carbon interlayer compounds and a decomposed products contained respectively in a negative electrode active layer of a negative electrode from the measured X-ray diffraction; calculating a reaction rate constant k1 for the carbon interlayer compounds or a reaction rate constant k?1 for the decomposed products of the carbon interlayer compounds from the calculated intensity integral; and evaluating a material suitability of the negative electrode active material contained in the negative electrode active layer based on the calculated reaction rate constant.

Abstract: A lithium secondary battery and a manufacturing method thereof, wherein the lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a lithium iron phosphate-based compound having an amorphous-content index (AI) of 0.28 or less, preferably 0.20 to 0.28, and more preferably 0.20 to 0.27, as defined by the disclosed Equation (1).