Negative electrode sheet, preparation method thereof and lithium ion battery containing the same

Abstract

The present disclosure provides a negative electrode sheet, a preparation method thereof and a lithium ion battery containing the same. The negative electrode sheet includes a negative electrode current collector, where the negative electrode current collector includes a single-sided coating area and a double-sided coating area; in the double-sided coating area, second coating layers are disposed on both side surfaces of the negative electrode current collector, respectively, wherein each of the second coating layers includes a first negative electrode active material layer and a second negative electrode active material layer, the second negative electrode active material layer is disposed on a surface of the negative electrode current collector, and the first negative electrode active material layer is disposed on a surface of the second negative electrode active material layer.

Claims

1. A winding negative electrode sheet, comprising a negative electrode current collector, wherein the negative electrode current collector comprises a single-sided coating area and a double-sided coating area; in the single-sided coating area, a first coating layer is disposed on a side surface of the negative electrode current collector and comprises a first negative electrode active material layer; in the double-sided coating area, second coating layers are disposed on both side surfaces of the negative electrode current collector, respectively, wherein each of the second coating layers comprises a first negative electrode active material layer and a second negative electrode active material layer, the second negative electrode active material layer is disposed on a surface of the negative electrode current collector, and the first negative electrode active material layer is disposed on a surface of the second negative electrode active material layer; the first negative electrode active material layer comprises a first negative electrode active material, the second negative electrode active material layer comprises a second negative electrode active material, and a reception speed of lithium ions of the first negative electrode active material is greater than a reception speed of lithium ions of the second negative electrode active material.

2. The negative electrode sheet according to claim 1, wherein a particle size distribution of the first negative electrode active material forming the first negative electrode active material layer is: 3 μm<D.sub.10<4 μm, 5 μm<D.sub.50<8 μm, 10 μm<D.sub.90<13 μm; a particle size distribution of the second negative electrode active material forming the second negative electrode active material layer is: 5 μm<D.sub.10<8 μm, 11 μm<D.sub.50<14 μm, 20 μm<D.sub.90<25 μm.

3. The negative electrode sheet according to claim 1, wherein the first negative electrode active material layer of the first coating layer is connected to the first negative electrode active material layer of the second coating layer.

4. The negative electrode sheet according to claim 2, wherein the first negative electrode active material layer of the first coating layer is connected to the first negative electrode active material layer of the second coating layer.

5. The negative electrode sheet according to claim 1, wherein a thickness of the first coating layer and thicknesses of the second coating layers are the same.

6. The negative electrode sheet according to claim 2, wherein a thickness of the first coating layer and thicknesses of the second coating layers are the same.

7. The negative electrode sheet according to claim 3, wherein a thickness of the first coating layer and thicknesses of the second coating layers are the same.

8. The negative electrode sheet according to claim 1, wherein in the double-sided coating area, thicknesses of the second coating layers on both sides of the negative electrode current collector are the same.

9. The negative electrode sheet according to claim 2, wherein in the double-sided coating area, thicknesses of the second coating layers on both sides of the negative electrode current collector are the same.

10. The negative electrode sheet according to claim 3, wherein in the double-sided coating area, thicknesses of the second coating layers on both sides of the negative electrode current collector are the same.

11. The negative electrode sheet according to claim 1, wherein in the second coating layers, a thickness of the first negative electrode active material layer is 5-30 μm, a thickness of the second negative electrode active material layer is 90-115 μm; and a sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer is 95-120 μm.

12. The negative electrode sheet according to claim 2, wherein in the second coating layers, a thickness of the first negative electrode active material layer is 5-30 μm, a thickness of the second negative electrode active material layer is 90-115 μm; and a sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer is 95-120 μm.

13. The negative electrode sheet according to claim 3, wherein in the second coating layers, a thickness of the first negative electrode active material layer is 5-30 μm, a thickness of the second negative electrode active material layer is 90-115 μm; and a sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer is 95-120 μm.

14. The negative electrode sheet according to claim 1, wherein the first negative electrode active material layer further comprises a first conductive agent and a first adhesive agent; a mass percentage of each component in the first negative electrode active material layer is: 70-99 wt % of the first negative electrode active material, 0.5-15 wt % of the first conductive agent, and 0.5-15 wt % of the first adhesive agent; wherein, a particle size distribution of the first negative electrode active material is: 3 μm<D.sub.10<4 μm, 5 μm<D.sub.50<8 μm, and 10 μm<D.sub.90<13 μm.

15. The negative electrode sheet according to claim 2, wherein the first negative electrode active material layer further comprises a first conductive agent and a first adhesive agent; a mass percentage of each component in the first negative electrode active material layer is: 70-99 wt % of the first negative electrode active material, 0.5-15 wt % of the first conductive agent, and 0.5-15 wt % of the first adhesive agent; wherein, a particle size distribution of the first negative electrode active material is: 3 μm<D.sub.10<4 μm, 5 μm<D.sub.50<8 μm, and 10 μm<D.sub.90<13 μm.

16. The negative electrode sheet according to claim 3, wherein the first negative electrode active material layer further comprises a first conductive agent and a first adhesive agent; a mass percentage of each component in the first negative electrode active material layer is: 70-99 wt % of the first negative electrode active material, 0.5-15 wt % of the first conductive agent, and 0.5-15 wt % of the first adhesive agent; wherein, a particle size distribution of the first negative electrode active material is: 3 μm<D.sub.10<4 μm, 5 μm<D.sub.50<8 μm, and 10 μm<D.sub.90<13 μm.

17. The negative electrode sheet according to claim 1, wherein the second negative electrode active material layer further comprises a second conductive agent and a second adhesive agent; a mass percentage of each component in the second negative electrode active material layer is: 70-99 wt % of the second negative electrode active material, 0.5-15 wt % of the second conductive agent, and 0.5-15 wt % of the second adhesive agent; wherein a particle size distribution of the second negative electrode active material is: 5 μm<D.sub.10<8 μm, 11 μm<D.sub.50<14 μm, and 20 μm<D.sub.90<25 μm.

18. The negative electrode sheet according to claim 2, wherein the second negative electrode active material layer further comprises a second conductive agent and a second adhesive agent; a mass percentage of each component in the second negative electrode active material layer is: 70-99 wt % of the second negative electrode active material, 0.5-15 wt % of the second conductive agent, and 0.5-15 wt % of the second adhesive agent; wherein a particle size distribution of the second negative electrode active material is: 5 μm<D.sub.10<8 μm, 11 μm<D.sub.50<14 μm, and 20 μm<D.sub.90<25 μm.

19. The negative electrode sheet according to claim 3, wherein the second negative electrode active material layer further comprises a second conductive agent and a second adhesive agent; a mass percentage of each component in the second negative electrode active material layer is: 70-99 wt % of the second negative electrode active material, 0.5-15 wt % of the second conductive agent, and 0.5-15 wt % of the second adhesive agent; wherein a particle size distribution of the second negative electrode active material is: 5 μm<D.sub.10<8 μm, 11 μm<D.sub.50<14 μm, and 20 μm<D.sub.90<25 μm.

20. A lithium-ion battery, comprising the negative electrode sheet according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a structure of a negative electrode sheet according to a preferred embodiment of the present disclosure, where 1 is a first negative electrode active material layer, and 2 is a second negative electrode active material layer; and

(2) FIG. 2 is a structure of a regular negative electrode sheet.

DETAILED DESCRIPTION OF EMBODIMENTS

(3) The present disclosure will be further described in detail with reference to specific embodiments hereinafter. It should be understood that the following embodiments are only illustratively explicating and explaining the present disclosure, and should not be interpreted as limiting the protection scope of the present disclosure. All technologies implemented based on the foregoing contents of the present disclosure fall within the scope intended to protect by the present disclosure.

(4) The experiment methods used in the following embodiments are conventional methods unless otherwise specified; the reagents, materials, or the like, used in the following embodiments can be all obtained from commercial sources unless otherwise specified.

(5) In the description of the present disclosure, it should be noted that the terms “first”, “second”, or the like, are only used for descriptive purpose, and do not indicate or imply relative importance.

(6) The negative electrode sheet prepared in the following embodiments is used for a battery of model 386283, where a distance between a negative electrode tab disposed in a tab area and a single-sided coating area is 35.5±0.5 mm, and a length of the single-sided coating area is 113±2 mm, a length of a current collector is 885±2 mm, and a width of the current collector is 773±2 mm.

Embodiment 1

(7) The first step: prepare a slurry forming a first negative electrode active material layer: add a first negative electrode active material (artificial graphite), a first conductive agent (conductive carbon black) and a first adhesive agent (sodium carboxymethyl cellulose) into a stirring tank according to a mass ratio of 97:1.5:1.5, add deionized water to prepare the slurry forming the first negative electrode active material layer, a solid content of the negative electrode slurry is 40 wt %˜45 wt %; where a particle size distribution of the first negative electrode active material is: 3 μm<D.sub.10<4 μm, 5 μm<D.sub.50<8 μm, 10 μm<D.sub.90<13 μm.

(8) The second step: prepare a slurry forming a second negative electrode active material layer: add a second negative electrode active material (artificial graphite), a second conductive agent (conductive carbon black) and a second adhesive agent (sodium carboxymethyl cellulose) into a stirring tank according to a mass ratio of 97:1.5:1.5, add deionized water to prepare the slurry forming the second negative electrode active material layer, a solid content of the negative electrode slurry is 40 wt % to 45 wt %; where the particle size distribution of the second negative electrode active material is: 5 μm<D.sub.10<8 μm, 11 μm<D.sub.50<14 μm, 20 μm<D.sub.90<2 5 μm.

(9) The third step: use a double-layer coating machine to coat the slurry forming the first negative electrode active material layer and the slurry forming the second negative electrode active material layer on surfaces of the negative electrode current collector, specifically:

(10) as shown in FIG. 1, on a side surface M of the negative electrode current collector, the slurry forming the first negative electrode active material layer and the slurry forming the second negative electrode active material layer are coated altogether from end A of the negative electrode current collector, where the slurry forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry forming the first negative electrode active material layer is away from the negative electrode current collector; the coating of the slurry forming the second negative electrode active material layer is ended at end B, the coating of the slurry forming the first negative electrode active material layer is kept and ended at end C, where an area between end A and end B is the double-sided coating area, an area between end B and end C is the single-sided coating area, the thickness of the first coating layer of the single-sided coating area and the thicknesses of the second coating layers of the double-sided coating area are the same;

(11) on the other side surface N of the negative electrode current collector, the slurry forming the first negative electrode active material layer and the slurry forming the second negative electrode active material layer are coated altogether from end E of the negative electrode current collector, where the slurry forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry forming the first negative electrode active material layer is away from the negative electrode current collector; and the coating of the slurry forming the second negative electrode active material layer is ended at end D, or, the slurry forming the first negative electrode active material layer and the slurry forming the second negative electrode active material layer are coated altogether from end D of the negative electrode current collector, where the slurry forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry forming the first negative electrode active material layer is away from the negative electrode current collector; and the coating of the slurry forming the second negative electrode active material layer is ended at end E; a line connecting end E and end A is perpendicular to the negative electrode current collector, a line connecting end D and end B is perpendicular to the negative electrode current collector, to ensure that of the tab area, the single-sided coating area and the double-sided coating area are formed in the negative electrode sheet; the prepared negative electrode sheet is dried at a temperature of 100° C.

(12) The fourth step: prepare a positive electrode sheet: use lithium cobalt oxide as a positive electrode active material, and then add it along with a conductive agent (acetylene black) and an adhesive agent (polyvinylidene fluoride) into a stirring tank according to a mass ratio of 97.2:1.5:1.3, add NMP solvent, stir well, go through a 200-mesh screen to obtain a positive electrode slurry, where a solid content of the positive electrode slurry is 70 wt %˜75 wt %, and then use a coating machine to coat the slurry on an aluminum foil, dry it at 120° C. to obtain the positive electrode sheet.

(13) The fifth step: assemble a battery cell: wind the negative electrode sheet prepared in the first to third steps above, the positive electrode sheet prepared in the fourth step and a separator together to form a roll core, which is packaged with an aluminum plastic film, baked to remove moisture and then injected with electrolytic solution, and applied with a hot-press forming process to form the battery cell.

Embodiments 2-3 and Comparative Examples 1-2

(14) The other operation steps are the same as Embodiment 1, the only difference lies in that the thickness of the single-sided coating area, and the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer of the double-sided coating area are different, which is specifically shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Structural parameters of the negative electrode sheet of Embodiments 1-3 and Comparative Examples 1-2 Double-sided coating area The thickness of the The thickness of the first negative second negative electrode active electrode active Single-sided coating material layer material layer area Embodiment 1  5 μm 115 μm First negative electrode active material layer 120 μm Embodiment 2 15 μm 105 μm First negative electrode active material layer 120 μm Embodiment 3 30 μm  90 μm First negative electrode active material layer 120 μm Comparative 0 120 μm First negative electrode Example 1 active material layer 120 μm Comparative 120 μm  0 First negative electrode Example 2 active material layer 120 μm

(16) The negative electrode sheets prepared in the embodiments have the same compaction density, and assembled into a soft-packed battery cell of model 386283. An energy density is tested by charging and discharging with 0.2 C/0.2 C at 25° C., each of the prepared soft-packed battery cell is charged with 2.5 C or discharged with 0.7 C at 25° C., and the battery is disassembled under different circulation counts to confirm a lithium deposition of the single-sided coating area of the negative electrode of the battery and the negative electrode surface. The disassembling result and energy density are shown in Table 2 below.

(17) TABLE-US-00002 TABLE 2 The energy density of the battery and the lithium deposition, capacity retention rate and inflation data of the single-sided coating area of the negative electrode during a cycling process of the embodiments Lithium Deposition 300 T 500 T 1000 T Single- Single- Single- 300 T 500 T 1000 T 1000 T Energy sided sided sided Negative Negative Negative Capacity Density coating coating coating Electrode Electrode Electrode Retention 1000 T Items Wh/L area area area Surface Surface Surface Rate Inflation Embodiment 1 693 No No No No No Slight 83.01% 9.85% Lithium Lithium Lithium Lithium Lithium Lithium Deposition Deposition Deposition Deposition Deposition Deposition Embodiment 2 692 No No No No No No 84.32% 9.63% Lithium Lithium Lithium Lithium Lithium Lithium Deposition Deposition Deposition Deposition Deposition Deposition Embodiment 3 689 No No No No No No 86.09% 9.01% Lithium Lithium Lithium Lithium Lithium Lithium Deposition Deposition Deposition Deposition Deposition Deposition Comparative 690 Slight Lithium Severe No Slight Lithium 80.23% 11.15% Example 1 Lithium Deposition Lithium Lithium Lithium Deposition Deposition Deposition Deposition Deposition Comparative 675 No No No No No No 87.35% 8.95% Example 2 Lithium Lithium Lithium Lithium Lithium Lithium Deposition Deposition Deposition Deposition Deposition Deposition

(18) In Table 2, the single-sided coating area has slight lithium deposition indicates that the single-sided coating area has a lithium deposition area takes up less than 10% of a total area of the single-sided coating area; the single-sided coating area has lithium deposition indicates that the lithium deposition area of the single-sided coating area takes up 10%-30% of the total area of the single-sided coating area; the single-sided coating area has severe lithium deposition indicates that the lithium deposition area of the single-sided coating area takes up greater than 50% of the total area of the single-sided coating area;

(19) the negative electrode surface has slight lithium deposition indicates that a lithium deposition area takes up less than 10% of a total area of the negative electrode; the negative electrode surface has lithium deposition indicates that the lithium deposition area takes up 10% to 30% of the total area of the negative electrode; the negative electrode surface has severe lithium deposition indicates that lithium deposition area takes up more than 50% of the total area of the negative electrode.

(20) It can be seen from Table 2 that the battery cell prepared using the method of the present disclosure can effectively improve the problem of lithium deposition of the single-sided coating area of the negative electrode of the conventional winding structural lithium ion battery without reducing the energy density of the battery, improve the circulation lifetime of the lithium ion battery, improve the circulation inflation, and improve the fast-charging performance of the lithium-ion battery. Although mere use of a negative electrode active material with better dynamic property and smaller particle size can effectively improve the problem of lithium deposition of the single-sided coating area of the negative electrode during long circulation process, it greatly reduces its energy density.

(21) The implementations of the present disclosure have been illustrated above. However, the present disclosure is not limited to the above-mentioned implementations. Any modification, equivalent replacement, improvement, or the like, made within the spirit and the principle of the present disclosure shall fall within the protection scope of the present disclosure.