This standard systematically describes the method for determining the crystal structure of lithium-ion battery cathode materials using X-ray diffraction. It is applicable to various cathode materials such as lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate. Based on the diffraction phenomenon generated when X-rays pass through a crystal, the standard enables precise characterization of the material's crystal structure by analyzing the regular relationship between the diffraction pattern and the crystal structure, and calculating the interplanar spacing using Bragg's law. In the testing process, the core equipment is an X-ray diffractometer equipped with a high-stability X-ray tube and a high-voltage generator, which must be verified according to JJG 629 and calibrated annually using standard samples. Additionally, it must comply with the general principles of polycrystalline X-ray diffraction methods specified in JY/T 0587 and the relevant specifications for X-ray diffraction analysis of crystal structures of inorganic chemical products in GB/T 30904. By measuring and evaluating key parameters such as step size, weighted profile R-factor, and difference curves, this method provides a unified technical basis for the research, development, and quality control of cathode materials, ensuring the accuracy and comparability of test results.