Positive electrode active material, method for manufacturing positive electrode active material, and secondary battery

A lithium-ion secondary battery comprising a positive electrode,

• wherein the positive electrode comprises a positive electrode active material comprising a positive electrode active material particle,
• wherein the positive electrode active material particle comprises lithium cobalt oxide,
• wherein the positive electrode active material particle comprises magnesium, aluminum, and fluorine,
• wherein, in EDX linear analysis of the positive electrode active material particle, a peak of aluminum is located in a deeper region than a peak of magnesium,
• when the positive electrode of the lithium-ion secondary battery is subjected to an X-ray diffraction measurement under a measurement condition, an X-ray diffraction pattern shows a first diffraction peak at 2θ=19.30°±0.2° and a second diffraction peak at 2θ=45.55°±0.1°,
• the measurement condition comprising:
• manufacturing a CR2032 type coin cell using the positive electrode of the lithium-ion secondary battery, a lithium metal as a counter electrode, an electrolyte solution, a polypropylene separator, a positive electrode can, and a negative electrode can;
• subjecting the coin cell to constant current charging at 25° C. until a voltage value reaches 4.6 V with a current value of 0.5 C, where 1 C is set to 137 mA/g which is a current value per unit mass of the positive electrode active material;
• after the constant current charging, subjecting the coin cell to constant voltage charging until a current value reaches 0.01 C with the voltage value of 4.6 V;
• after the constant voltage charging, taking out the positive electrode by disassembling the coin cell in an argon atmosphere;
• washing the positive electrode with dimethyl carbonate in an argon atmosphere;
• and
• performing the X-ray diffraction measurement using a CuKα1 ray in an argon atmosphere,
• wherein the electrolyte solution comprises 1 mol/L lithium hexafluorophosphate as an electrolyte, and a solution in which ethylene carbonate and diethyl carbonate at a volume ratio of 3:7 and vinylene carbonate at 2 wt % are mixed, and
• wherein the positive electrode can and the negative electrode can are formed of stainless steel.