| CPC H01M 4/525 (2013.01) [C01G 53/50 (2013.01); H01B 1/08 (2013.01); H01M 4/131 (2013.01); H01M 4/133 (2013.01); H01M 4/134 (2013.01); H01M 4/139 (2013.01); H01M 4/366 (2013.01); H01M 4/505 (2013.01); H01M 6/164 (2013.01); H01M 10/0525 (2013.01); C01P 2002/74 (2013.01); H01M 2004/028 (2013.01)] | 22 Claims |

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1. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution:
wherein:
the positive electrode comprises a positive electrode active material comprising a positive electrode active material particle, the positive electrode active material particle comprising lithium cobalt oxide, magnesium, and aluminum,
a magnesium concentration in a surface portion of the positive electrode active material particle is higher than a magnesium concentration in an inner portion of the positive electrode active material particle,
in an EDX linear analysis of the positive electrode active material particle, a concentration peak of aluminum is located in a deeper region than a concentration peak of magnesium,
the positive electrode active material has an O3 crystal structure when a charge depth of the positive electrode active material is 0.06 or less,
an X-ray diffraction pattern of the positive electrode active material has at least a first diffraction peak at 2θ of 19.30+0.20° and a second diffraction peak at 2θ of 45.55=0.10° when the positive electrode is analyzed by powder X-ray diffraction by using CuKal ray, when a battery comprising the positive electrode and a counter electrode of lithium is charged at 4.6V, and
the electrolyte solution comprises vinylene carbonate.
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