Battery

A battery comprising a positive electrode,

• wherein the positive electrode comprises a positive electrode active material,
• wherein the positive electrode active material comprises a first region and a second region,
• wherein the first region comprises first lithium, cobalt, magnesium, and oxygen,
• wherein the second region comprises second lithium, cobalt, and oxygen,
• wherein the first region is closer to a surface of the positive electrode active material than the second region is,
• wherein fluorine is adsorbed onto the surface of the positive electrode active material,
• wherein the fluorine is bonded to the first lithium,
• wherein the first region has a thickness greater than or equal to 2 nm and less than or equal to 20 nm, and
• wherein the magnesium has a concentration higher than 0 atomic % and lower than or equal to 10 atomic %.

A battery comprising a positive electrode,

• wherein the positive electrode comprises a positive electrode active material,
• wherein the positive electrode active material comprises cobalt, nickel, and lithium,
• wherein the positive electrode active material comprises a first region and a second region, the first region comprising at least part of a surface of the positive electrode active material, the second region being located inward from the first region,
• wherein a ratio of the number of atoms of the nickel of the first region to the number of atoms of the cobalt of the first region is less than 1,
• wherein a ratio of the number of atoms of the nickel of the second region to the number of atoms of the cobalt of the second region is less than the ratio of the number of the atoms of the nickel of the first region to the number of the atoms of the cobalt of the first region, and
• wherein when the battery undergoes a nail penetration test for short-circuiting the battery without undergoing a charge and discharge cycle test, the battery does not ignite.

A battery comprising a positive electrode,

• wherein the positive electrode comprises a positive electrode active material,
• wherein the positive electrode active material comprises a first region and a second region,
• wherein the first region comprises lithium, cobalt, magnesium, and oxygen,
• wherein the second region comprises lithium, cobalt, and oxygen,
• wherein the first region is closer to a surface of the positive electrode active material than the second region is,
• wherein in the positive electrode active material at a distance less than 2 cm from a nail hole due to a nail penetration test, a ratio of an atomic concentration of oxygen to an atomic concentration of cobalt is less than 1.3, and
• wherein in the positive electrode active material at a distance more than or equal to 2 cm from the nail hole, a ratio of an atomic concentration of oxygen to an atomic concentration of cobalt is greater than or equal to 1.3.

A battery comprising a positive electrode, a negative electrode, and an electrolyte solution,

• wherein the positive electrode comprises a positive electrode active material,
• wherein the negative electrode comprises a negative electrode active material,
• wherein the positive electrode active material comprises a first region and a second region,
• wherein the first region comprises cobalt, magnesium, fluorine, and oxygen,
• wherein the second region comprises cobalt and oxygen,
• wherein the first region is closer to a surface of the positive electrode active material than the second region is,
• wherein the negative electrode active material comprises graphite,
• wherein the electrolyte solution comprises a mixed organic solvent, and
• wherein when the battery in a fully charged state undergoes a nail penetration test in which a nail diameter is 3 mm and a nail penetration speed is 5 mm/sec, a voltage of the battery decreases from a first voltage Vb to a second voltage Vc and then exceeds the second voltage Vc.

A battery comprising a positive electrode, a negative electrode, and an electrolyte solution,

• wherein the positive electrode comprises a positive electrode active material,
• wherein the negative electrode comprises a negative electrode active material,
• wherein the positive electrode active material comprises a first region and a second region,
• wherein the first region comprises cobalt, magnesium, fluorine, and oxygen,
• wherein the second region comprises cobalt and oxygen,
• wherein the first region is closer to a surface of the positive electrode active material than the second region is,
• wherein the negative electrode active material comprises graphite,
• wherein the electrolyte solution comprises a mixed organic solvent, and
• wherein when the battery in a fully charged state undergoes a nail penetration test in which a nail diameter is 3 mm and a nail penetration speed is 5 mm/sec after undergoing a charge and discharge cycle test in an environment at 45° C., a voltage of the battery decreases to Vc and remains at the Vc.