| abstract |
PROBLEM TO BE SOLVED: To provide positive electrode active material particles with little deterioration. Alternatively, a power storage device with little deterioration is provided. Alternatively, a power storage device with high safety is provided. A first crystal grain, a second crystal grain, and a crystal grain boundary located between the first crystal grain and the second crystal grain are included. The crystal grain of 2 has lithium, a transition metal, and oxygen, and the crystal grain boundary has magnesium and oxygen, and the transition metal of the first crystal grain and the second crystal grain of The positive electrode active material particles have a region where the ratio of the atomic concentration of magnesium at the crystal grain boundaries to the atomic concentration is 0.010 or more and 0.50 or less. [Selection diagram] Figure 1 |