Positive active material and preparation method thereof, electrochemical battery, battery module, battery pack, and apparatus
This application provides a positive active material and a preparation method thereof, an electrochemical battery, a battery module, a battery pack, and an apparatus. The positive active material includes an inner core and a coating layer, where the coating layer coats a surface of the inner core. The inner core is selected from a ternary material with a molecular formula of Li 1+a [Ni x Co y Mn z M b M′ c ]O 2−d Y d , where distribution of each of the doping elements M, M′, and Y in the inner core meets the following condition: there is a reduced mass concentration gradient from an outer side of the inner core to a center of the inner core. The positive active material herein features high gram capacity, high structural stability, and high thermal stability, so that the electrochemical battery has excellent cycle performance and storage performance and high initial discharge gram capacity.
1. A positive active material, comprising:
an inner core; and
a coating layer that coats a surface of the inner core, wherein
the inner core is selected from a ternary material with a molecular formula of Li 1+a [Ni x Co y Mn z M b M′ c ]O 2−d Y d , wherein a doping element M is selected from one or more of Zr, Ti, Te, Ca, and Si; a doping element M′ is selected from one or more of Mg, Zn, Al, B, Ce, and Fe; a doping element Y is selected from one or more of F, Cl, and Br; −0.1≤a≤0.2, 0<d≤0.1, 0.7≤x<1, 0<y<0.3, 0<z<0.3, 0<b≤0.1, 0<c≤0.1 and x+y+z+b+c=1; and distribution of each of the doping elements M, M′, and Y in the inner core meets the following condition: there is a reduced mass concentration gradient from an outer side of the inner core to a center of the inner core;
the coating layer is made of a material that is an oxide of a coating element M″, and M″ is selected from one or more of Mg, Zn, Al, B, Ce, and Fe; and
a mass ratio of the coating element M″ in the coating layer to the doping element M′ in the inner core is 1:1 to 1:5.
2. The positive active material according to claim 1 , wherein within a thickness range from an outermost side of the positive active material to a ⅕ average particle size of the positive active material in a direction towards the inner core, a sum of masses of M, M′, Y, and M″ is more than 50% of a total mass of M, M′, Y, and M″ in the positive active material.
3. The positive active material according to claim 2 , wherein the sum of masses of M, M′, Y, and M″ is more than 55% of the total mass of M, M′, Y, and M″ in the positive active material.
4. The positive active material according to claim 2 , wherein in the thickness range from the outermost side of the positive active material to a ⅔ average particle size of the positive active material in the direction towards the inner core, the sum of the masses of M, M′, Y, and M″ is more than 90% of the total mass of M, M′, Y, and M″ in the positive active material.
5. The positive active material according to claim 2 , wherein the sum of the masses of M, M′, Y, and M″ is more than 93% of the total mass of M, M′, Y, and M″ in the positive active material.
6. The positive active material according to claim 1 , wherein the coating element M″ in the coating layer is the same as the doping element M′ in the inner core.
7. The positive active material according to claim 1 , wherein based on the total mass of the positive active material,
a mass concentration of the doping element M in the inner core is 100 ppm to 3000 ppm;
a mass concentration of the doping element M′ in the inner core is 100 ppm to 3000 ppm; and
a mass concentration of the coating element M″ in the coating layer is 100 ppm to 3000 ppm.
8. The positive active material according to claim 1 , wherein
an average particle size D50 of the positive active material is 8 μm to 20 μm, and a thickness T of the coating layer is 0.001 μm to 0.5 μm.
9. The positive active material according to claim 8 , wherein 0.005≤T/D50≤0.02.
10. The positive active material according to claim 1 , wherein the positive active material contains lithium impurity, the lithium impurity comprises lithium hydroxide and lithium carbonate, and a concentration of the lithium impurity is less than or equal to 1500 ppm.
11. An electrochemical battery, comprising a positive active material, the positive active material comprising:
an inner core; and
a coating layer that coats a surface of the inner core, wherein
the inner core is selected from a ternary material with a molecular formula of Li 1+a [Ni x Co y Mn z M b M′ c ]O 2−d Y d , wherein a doping element M is selected from one or more of Zr, Ti, Te, Ca, and Si; a doping element M′ is selected from one or more of Mg, Zn, Al, B, Ce, and Fe; a doping element Y is selected from one or more of F, Cl, and Br; −0.1≤a≤0.2, 0<d≤0.1, 0.7≤x<1, 0<y<0.3, 0<z<0.3, 0<b≤0.1, 0<c≤0.1 and x+y+z+b+c=1; and distribution of each of the doping elements M, M′, and Y in the inner core meets the following condition: there is a reduced mass concentration gradient from an outer side of the inner core to a center of the inner core;
the coating layer is made of a material that is an oxide of a coating element M″, and M″ is selected from one or more of Mg, Zn, Al, B, Ce, and Fe; and
a mass ratio of the coating element M″ in the coating layer to the doping element M′ in the inner core is 1:1 to 1:5.
12. A battery module, comprising the electrochemical battery according to claim 11 , used as a battery cell.
13. A battery pack, comprising the battery module according to claim 12 .
14. An apparatus, comprising the electrochemical battery according to claim 11 , wherein the electrochemical battery is used as a power supply of the apparatus.
15. The apparatus according to claim 14 , wherein the apparatus is one selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric vessel, and an energy storage system.