Electrode assembly and lithium-ion battery

1. An electrode assembly, comprising a positive electrode plate, a separator, and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active substance layer provided on at least one surface of the negative electrode current collector and comprising a negative electrode active substance;

and

the negative electrode plate further comprises a lithium metal layer provided on a surface of the negative electrode active substance layer on a side farther away from the negative electrode current collector, wherein the lithium metal layer is formed by a plurality of regular or irregular strip-shaped lithium-rich regions, and the plurality of lithium-rich regions present a discontinuous pattern of spaced distribution in a length direction of the negative electrode plate; and

the electrode assembly further satisfies that: negative electrode capacity per unit area/positive electrode capacity per unit area=1.2 to 2.1 and negative electrode capacity per unit area/(positive electrode capacity per unit area+capacity of the lithium metal layer on the surface of the negative electrode active substance layer per unit area×80%)≥1.10, wherein a width of each lithium-rich region is 0.2 mm to 2 mm, and a distance between every two adjacent lithium-rich regions is 0.25 to 2 times an average width of the adjacent two lithium-rich regions.

2. The electrode assembly according to claim 1 , wherein an included angle between a length direction of the lithium-rich regions and the length direction of the negative electrode plate is 45° to 135°.

3. The electrode assembly according to claim 2 , wherein an included angle between the length direction of the lithium-rich regions and the length direction of the negative electrode plate is 60° to 120°.

4. The electrode assembly according to claim 1 , wherein in a length direction of the lithium-rich regions, a ratio of a length of a negative electrode active substance layer region covered with a lithium metal layer to a length of a negative electrode active substance layer region not covered with a lithium metal layer is not less than 20:1.

5. The electrode assembly according to claim 4 , wherein in the length direction of the lithium-rich regions, the lithium-rich regions fully cover the negative electrode active substance layer.

6. The electrode assembly according to claim 1 , wherein a mass of the lithium metal layer is 0.5% to 5% of a total mass of the negative electrode active substance layer.

7. The electrode assembly according to claim 6 , wherein the mass of the lithium metal layer is 1% to 5% of the total mass of the negative electrode active substance layer.

8. The electrode assembly according to claim 1 , wherein a material of the lithium-rich regions is lithium foil, lithium mesh, or lithium powder.

9. The electrode assembly according to claim 1 , wherein the negative electrode active substance is selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microbead, nano carbon, elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon alloy, elemental tin, a tin-oxygen compound, a tin-carbon composite, a tin alloy, and lithium titanate.

10. The electrode assembly according to claim 9 , wherein the negative electrode active substance comprises at least graphite.

11. A lithium-ion battery, comprising an electrode assembly, a battery casing, and an electrolyte, wherein the electrode assembly is the electrode assembly according to claim 1 , and after the electrode assembly is installed into the battery casing and the electrolyte is injected, at least a part of lithium in the lithium metal layer on the surface of the negative electrode active substance layer is pre-intercalated under an action of the electrolyte, and is distributed in the negative electrode active substance layer in a form of a first lithium intercalation compound.

12. The lithium-ion battery according to claim 11 , wherein the first lithium intercalation compound comprises LiC x , wherein x=12 to 120.

13. The lithium-ion battery according to claim 11 , wherein after the electrode assembly is installed into the battery casing and the electrolyte is injected, a part of lithium in the lithium metal layer on the surface of the negative electrode active substance layer further forms a second lithium intercalation compound under the action of the electrolyte and exists on the surface of the negative electrode active substance layer, and the second lithium intercalation compound presents a discontinuous pattern of spaced distribution on the surface of the negative electrode active substance layer.

14. The lithium-ion battery according to claim 13 , wherein a position of the second lithium intercalation compound on the surface of the negative electrode active substance layer is the same as that of the lithium metal layer.

15. The lithium-ion battery according to claim 13 , wherein the second lithium intercalation compound comprises one or more of a lithium nitrogen compound, lithium carbonate, and lithium oxide.