POSITIVE ELECTRODE MATERIAL AND PREPARATION METHOD THEREOF, POSITIVE ELECTRODE PLATE, SECONDARY BATTERY, AND ELECTRICAL DEVICE

1 . A positive electrode material, comprising:

a sodium-containing positive electrode material substrate; and

a coating layer, covering at least a part of a surface of the sodium-containing positive electrode material substrate, wherein the coating layer comprises Na x M y O 2 , wherein M comprises at least one of B, Si, or P, x>0, and y>0.

2 . The positive electrode material according to claim 1 , wherein the coating layer comprises:

a transition layer relatively close to the sodium-containing positive electrode material substrate, wherein the transition layer comprises an element M-doped region; and

an oxide layer relatively away from the sodium-containing positive electrode material substrate, wherein the oxide layer comprises Na x M y O 2 .

3 . The positive electrode material according to claim 2 , wherein the positive electrode material satisfies at least one of following conditions:

a content of residual alkali on a surface of the positive electrode material is 0.5 wt % to 5.5 wt %; and

based on a total mass of the coating layer, a mass percent of the element M in the doped region is greater than a mass percent of the element M in the oxide layer.

4 . The positive electrode material according to claim 1 , wherein the positive electrode material satisfies at least one of following conditions:

the sodium-containing positive electrode material substrate comprises one or more of a layered oxide, a Prussian blue compound, or a polyanionic compound;

the sodium-containing positive electrode material substrate is a micron-scale particle, and an average particle diameter of the micron-scale particle is 1 μm to 25 μm;

a mass percent of the coating layer in the positive electrode material is 0.001% to 3%; and

a thickness of the coating layer is 0.5 nm to 30 nm.

5 . A positive electrode plate, comprising the positive electrode material according to claim 1 .

6 . A secondary battery, comprising the positive electrode plate according to claim 5 .

7 . An electrical device, comprising the secondary battery according to claim 6 .

8 . A method for preparing a positive electrode material, comprising:

providing a sodium-containing positive electrode material substrate; and

performing surface heat treatment on the sodium-containing positive electrode material substrate by using vapor of a coating modifier, so as to form a Na x M y O 2 -containing coating layer on at least a part of the surface of the sodium-containing positive electrode material substrate and obtain a positive electrode material, wherein M comprises at least one of B, Si, or P, x>0, and y>0.

9 . The method according to claim 8 , wherein the performing the surface heat treatment on the sodium-containing positive electrode material substrate by using the vapor of the coating modifier comprises:

sintering the sodium-containing positive electrode material substrate and the coating modifier, causing the sodium-containing positive electrode material substrate to contact and react with the vapor of the coating modifier, and forming a transition layer and an oxide layer on at least a part of the surface of the sodium-containing positive electrode material substrate, wherein:

the transition layer is relatively close to the sodium-containing positive electrode material substrate, and the oxide layer is relatively far away from the sodium-containing positive electrode material substrate; and

the transition layer comprises an element M-doped region, and the oxide layer comprises Na x M y O 2 .

10 . The method according to claim 8 , wherein the method satisfies at least one of following conditions:

the coating modifier comprises one or more of a boric acid, a boron oxide, a silicic acid, or ammonium dihydrogen phosphate;

the sodium-containing positive electrode material substrate comprises one or more of a layered oxide, a Prussian blue compound, or a polyanionic compound, and is optionally an O3-type layered oxide;

a mass ratio between the coating modifier and the sodium-containing positive electrode material substrate is m, satisfying: 0<m<2; and

during the sintering, the coating modifier is in a solid phase or a liquid phase.

11 . The method according to claim 8 , wherein sintering the sodium-containing positive electrode material substrate and the coating modifier comprises:

providing a first container, wherein the first container contains the coating modifier and a second container, the second container contains the sodium-containing positive electrode material substrate, and a gas phase of the first container communicates with a gas phase of the second container; and

sintering the first container.

12 . The method according to claim 11 , wherein providing the first container comprises:

providing a second container;

placing the second container into the first container; and

laying the coating modifier in at least a part of a region between the first container and an outer wall of the second container.

13 . The method according to claim 12 , wherein the first container and the second container each is independently a crucible.

14 . The method according to claim 11 , wherein the method satisfies at least one of following conditions:

the sintering is performed at a temperature of T 1 , 0<T 1 <2000° C.; and

the sintering continues for a time of t 1 , 0<t 1 <36 h.

15 . The method according to claim 8 , wherein sintering the sodium-containing positive electrode material substrate and the coating modifier comprises:

heat-treating the coating modifier to form vapor of the coating modifier;

passing the vapor of the coating modifier into a rotary kiln containing the sodium-containing positive electrode material substrate; and

sintering the vapor of the coating modifier passed into the rotary kiln and the sodium-containing positive electrode material substrate.

16 . The method according to claim 15 , wherein the method satisfies at least one of following conditions:

the sintering is performed at a temperature of T 2 , 0<T 2 <1000° C.; and

the sintering continues for a time of t 2 , 0<t 2 <36 h.

17 . The method according to claim 15 , wherein the method satisfies at least one of following conditions:

the heat treatment is performed at a temperature of T 3 , 300<T 3 <2000° C.;

a rotation speed of the rotary kiln is R, 0 r/min<R≤15 r/min; and

a flow rate of the vapor of the coating modifier is v, 0 ml/min<v≤5 ml/min.