ELECTROCHEMICAL APPARATUS AND ELECTRONIC APPARATUS INCLUDING ELECTROCHEMICAL APPARATUS

Abstract

An electrochemical apparatus, including: a first electrode assembly including a first negative electrode plate having a first negative current collector with a first negative active material layer disposed on at least one surface; and a second electrode assembly including a second negative electrode plate having a second negative current collector with a second negative active material layer disposed on at least one surface. A coating weight W.sub.1f of the first negative active material layer and a coating weight W.sub.2f of the second negative active material layer satisfy: 30 mg/1540.25 mm.sup.2?W.sub.2f?W.sub.1f?100 mg/1540.25 mm.sup.2. By regulating a value of W.sub.2f?W.sub.1f to be within the above range, energy density of the electrochemical apparatus and swelling performance of the electrochemical apparatus can be improved while fast charging performance is satisfied.

Claims

1. An electrochemical apparatus, comprising: a packaging shell, wherein the packaging shell is provided with an accommodation cavity; and a first electrode assembly and a second electrode assembly, wherein the first electrode assembly and the second electrode assembly are disposed in the accommodation cavity; wherein the first electrode assembly comprises a first positive electrode plate and a first negative electrode plate, the first positive electrode plate comprises a first positive current collector and a first positive active material layer disposed on at least one surface of the first positive current collector, and the first negative electrode plate comprises a first negative current collector and a first negative active material layer disposed on at least one surface of the first negative current collector; the second electrode assembly comprises a second positive electrode plate and a second negative electrode plate, the second positive electrode plate comprises a second positive current collector and a second positive active material layer disposed on at least one surface of the second positive current collector, and the second negative electrode plate comprises a second negative current collector and a second negative active material layer disposed on at least one surface of the second negative current collector; and a difference between a coating weight W.sub.1f of the first negative active material layer and a coating weight W.sub.2f of the second negative active material layer satisfies: 30 mg/1540.25 mm.sup.2?W.sub.2f?W.sub.1f?100 mg/1540.25 mm.sup.2.

2. The electrochemical apparatus according to claim 1, wherein the electrochemical apparatus satisfies at least one of the following conditions: (1) the coating weight W.sub.1f of the first negative active material layer ranges from 50 mg/1540.25 mm.sup.2 to 140 mg/1540.25 mm.sup.2; or (2) a compaction density D.sub.1f of the first negative active material layer ranges from 1.5 g/cm.sup.3 to 1.8 g/cm.sup.3.

3. The electrochemical apparatus according to claim 1, wherein the electrochemical apparatus satisfies at least one of the following conditions: (3) the coating weight W.sub.2f of the second negative active material layer ranges from 130 mg/1540.25 mm.sup.2 to 170 mg/1540.25 mm.sup.2; or (4) a compaction density Der of the second negative active material layer ranges from 1.5 g/cm.sup.3 to 1.8 g/cm.sup.3.

4. The electrochemical apparatus according to claim 1, wherein the first negative active material layer comprises a first negative active material, the second negative active material layer comprises a second negative active material, and satisfying at least one of the following conditions: (a) a specific surface area BET.sub.1 of the first negative active material ranges from 1.6 m.sup.2/g to 2.0 m.sup.2/g; (b) a specific surface area BET.sub.2 of the second negative active material ranges from 0.6 m.sup.2/g to 1.1 m.sup.2/g; (c) the first negative active material comprises at least one of graphite or lithium titanate; or (d) the second negative active material comprises at least one of the graphite or a silicon-carbon composite material, and a mass percentage W.sub.Si of silicon in the silicon-carbon composite material ranges from 0.1% to 10%.

5. The electrochemical apparatus according to claim 4, wherein an average particle size Dv50.sub.?1 of the first negative active material ranges from 5 ?m to 15 ?m, and an average particle size Dv50.sub.?2 of the second negative active material ranges from 16 ?m to 25 ?m.

6. The electrochemical apparatus according to claim 1, wherein a difference between a coating weight Wiz of the first positive active material layer and a coating weight W.sub.2z of the second positive active material layer satisfies: 50 mg/1540.25 mm.sup.2?W.sub.2z?W.sub.1z?150 mg/1540.25 mm.sup.2.

7. The electrochemical apparatus according to claim 6, wherein the electrochemical apparatus satisfies at least one of the following conditions: (e) the coating weight Wiz of the first positive active material layer ranges from 150 mg/1540.25 mm.sup.2 to 250 mg/1540.25 mm.sup.2; (f) a compaction density D.sub.1z of the first positive active material layer ranges from 3.5 g/cm.sup.3 to 4.5 g/cm.sup.3; (g) the coating weight W.sub.2z of the second positive active material layer ranges from 250 mg/1540.25 mm.sup.2 to 315 mg/1540.25 mm.sup.2; or (h) a compaction density D.sub.2z of the second positive active material layer ranges from 3.5 g/cm.sup.3 to 4.5 g/cm.sup.3.

8. The electrochemical apparatus according to claim 1, wherein the first negative electrode plate is of a multi-tab structure or a tab center-positioned structure.

9. The electrochemical apparatus according to claim 1, wherein the accommodation cavity comprises a first cavity and a second cavity, a partition plate is provided between the first cavity and the second cavity, the first electrode assembly is disposed in the first cavity, and the second electrode assembly is disposed in the second cavity.

10. The electrochemical apparatus according to claim 9, wherein the partition plate comprises at least one of a polymer material or a metal material.

11. An electronic apparatus, comprising an electrochemical apparatus, the electrochemical apparatus comprises: a packaging shell, wherein the packaging shell is provided with an accommodation cavity; and a first electrode assembly and a second electrode assembly, wherein the first electrode assembly and the second electrode assembly are disposed in the accommodation cavity; wherein the first electrode assembly comprises a first positive electrode plate and a first negative electrode plate, the first positive electrode plate comprises a first positive current collector and a first positive active material layer disposed on at least one surface of the first positive current collector, and the first negative electrode plate comprises a first negative current collector and a first negative active material layer disposed on at least one surface of the first negative current collector; the second electrode assembly comprises a second positive electrode plate and a second negative electrode plate, the second positive electrode plate comprises a second positive current collector and a second positive active material layer disposed on at least one surface of the second positive current collector, and the second negative electrode plate comprises a second negative current collector and a second negative active material layer disposed on at least one surface of the second negative current collector; and a difference between a coating weight W.sub.1f of the first negative active material layer and a coating weight W.sub.2f of the second negative active material layer satisfies: 30 mg/1540.25 mm.sup.2?W.sub.2f?W.sub.1f?100 mg/1540.25 mm.sup.2.

12. The electronic apparatus according to claim 11, wherein the electrochemical apparatus satisfies at least one of the following conditions: (1) the coating weight W.sub.1f of the first negative active material layer ranges from 50 mg/1540.25 mm.sup.2 to 140 mg/1540.25 mm.sup.2; or (2) a compaction density Dir of the first negative active material layer ranges from 1.5 g/cm.sup.3 to 1.8 g/cm.sup.3.

13. The electronic apparatus according to claim 11, wherein the electrochemical apparatus satisfies at least one of the following conditions: (3) the coating weight W.sub.2f of the second negative active material layer ranges from 130 mg/1540.25 mm.sup.2 to 170 mg/1540.25 mm.sup.2; or (4) a compaction density D.sub.2f of the second negative active material layer ranges from 1.5 g/cm.sup.3 to 1.8 g/cm.sup.3.

14. The electronic apparatus according to claim 11, wherein the first negative active material layer comprises a first negative active material, the second negative active material layer comprises a second negative active material, and satisfying at least one of the following conditions: (a) a specific surface area BET.sub.1 of the first negative active material ranges from 1.6 m.sup.2/g to 2.0 m.sup.2/g; (b) a specific surface area BET.sub.2 of the second negative active material ranges from 0.6 m.sup.2/g to 1.1 m.sup.2/g; (c) the first negative active material comprises at least one of graphite or lithium titanate; or (d) the second negative active material comprises at least one of the graphite or a silicon-carbon composite material, and a mass percentage W.sub.Si of silicon in the silicon-carbon composite material ranges from 0.1% to 10%.

15. The electronic apparatus according to claim 14, wherein an average particle size Dv50.sub.?1 of the first negative active material ranges from 5 ?m to 15 ?m, and an average particle size Dv50.sub.?2 of the second negative active material ranges from 16 ?m to 25 ?m.

16. The electronic apparatus according to claim 11, wherein a difference between a coating weight W.sub.1z of the first positive active material layer and a coating weight W.sub.2z of the second positive active material layer satisfies: 50 mg/1540.25 mm.sup.2?W.sub.2z?W.sub.1z?150 mg/1540.25 mm.sup.2.

17. The electronic apparatus according to claim 16, wherein the electrochemical apparatus satisfies at least one of the following conditions: (e) the coating weight Wiz of the first positive active material layer ranges from 150 mg/1540.25 mm.sup.2 to 250 mg/1540.25 mm.sup.2; (f) a compaction density D.sub.1z of the first positive active material layer ranges from 3.5 g/cm.sup.3 to 4.5 g/cm.sup.3; (g) the coating weight W.sub.2z of the second positive active material layer ranges from 250 mg/1540.25 mm.sup.2 to 315 mg/1540.25 mm.sup.2; or (h) a compaction density D.sub.2z of the second positive active material layer ranges from 3.5 g/cm.sup.3 to 4.5 g/cm.sup.3.

18. The electronic apparatus according to claim 11, wherein the first negative electrode plate is of a multi-tab structure or a tab center-positioned structure.

19. The electronic apparatus according to claim 11, wherein the accommodation cavity comprises a first cavity and a second cavity, a partition plate is provided between the first cavity and the second cavity, the first electrode assembly is disposed in the first cavity, and the second electrode assembly is disposed in the second cavity.

20. The electronic apparatus according to claim 19, wherein the partition plate comprises at least one of a polymer material or a metal material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to clearly illustrate the technical solutions of the present application and the prior art, a brief description of drawings required in the embodiments and the prior art is set forth below.

[0043] Obviously, the drawings in the following description are merely illustrative of some embodiments of the present application.

[0044] FIG. 1 is a schematic diagram of an internal structure of an electrochemical apparatus according to an implementation solution of this application;

[0045] FIG. 2 is a schematic structural diagram of region A in FIG. 1;

[0046] FIG. 3 is a schematic structural diagram of a first positive electrode plate according to an implementation solution of this application; and

[0047] FIG. 4 is a schematic structural diagram of a first negative electrode plate in the solution in FIG. 3.

[0048] Reference numerals in specific implementations are as follows: [0049] 10Packaging shell, 21First electrode assembly, 211First positive electrode plate, 212First negative electrode plate, 22Second electrode assembly, 230Separator, 31First cavity, 32Second cavity, 40Partition plate, 51First positive electrode tab, 52First negative electrode tab, and 100Electrochemical apparatus.

DETAILED DESCRIPTION

[0050] In order to make the objective, technical solution, and advantages of this application clearer, this application is further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other technical solutions obtained by a person of ordinary skill in the art belong to the scope of protection of this application.

[0051] FIG. 1 is a schematic diagram of an internal structure of an electrochemical apparatus according to an implementation solution of this application. As shown in FIG. 1, the electrochemical apparatus 100 includes: a packaging shell 10, a first electrode assembly 21, and a second electrode assembly 22. The packaging shell 10 is provided with an accommodation cavity, and the accommodation cavity includes a first cavity 31 and a second cavity 32. A partition plate 40 is provided between the first cavity 31 and the second cavity 32, the first electrode assembly 21 is disposed in the first cavity 31, and the second electrode assembly 22 is disposed in the second cavity 32.

[0052] FIG. 2 is a schematic structural diagram of region A in FIG. 1. As shown in FIG. 2, a structure of the first electrode assembly 21 is a multi-tab structure. Specifically, in a jolly roll of the multi-tab structure formed by winding a first positive electrode plate 211, a separator 230, a first negative electrode plate 212, and a separator 230, the first positive electrode plate 211 includes a plurality of positive electrode tabs (not shown in the figure), and the first negative electrode plate 212 includes a plurality of negative electrode tabs 52. FIG. 3 is a schematic structural diagram of a first positive electrode plate according to some embodiments of this application. As shown in FIG. 3, a first positive electrode tab 51 is disposed between two ends in a length direction of a positive active material layer in the first positive electrode plate 211.

[0053] FIG. 4 is a schematic structural diagram of a first negative electrode plate according to some embodiments of this application. As shown in FIG. 4, a first negative electrode tab 52 is disposed between two ends in a length direction of a negative active material layer in the first negative electrode plate 212.

[0054] The structure of the first positive electrode plate 211 shown in FIG. 3 and the structure of the first negative electrode plate 212 shown in FIG. 4 are tab center-positioned structures.

[0055] It should be noted that in the specific implementations of the present application, the present application is explained by an example using a lithium-ion battery as an electrochemical apparatus, but the electrochemical apparatus of the present application is not limited to the lithium-ion battery.

EMBODIMENT

[0056] Implementations of this application are described in more details below with reference to embodiments and comparative embodiments. Various tests and evaluations are performed according to the following methods.

Measurement Methods and Devices

Coating Weight Measurement:

[0057] (1) Cut out an electrode plate sample by using a standard tool (with an area 1540.25 mm.sup.2), put the sample on a balance to obtain a weight denoted as m1, then wash an active material layer on the electrode plate, and put a current collector on the balance to obtain a weight denoted as m.sup.2.

[0058] (2) Coating weight calculation:

[0059] If the electrode plate is coated with an active material layer on one side, a coating weight=m1?m2.

[0060] If the electrode plate is coated with active material layers on both sides, a coating weight=(m1?m2)/2.

Compaction Density Measurement:

[0061] (1) Cut out a regular electrode plate, record an area S1 (cm.sup.2), and record a thickness H1 (?m) of the electrode plate.

[0062] (2) Weigh the electrode plate and record a weight as M1 (mg).

[0063] (3) Wash an active material layer on the electrode plate to leave only a current collector, weigh the current collector, record a weight M2 (mg), and measure a thickness H2 (?m) of the current collector.

[0064] (4) Calculate compaction density of the electrode plate: Compaction density (g/cm.sup.3)=10?(M1?M2)/(S1?(H2?H1))

Average Particle Size Measurement:

[0065] Measure an average particle size Dv50.sub.?1 of a first negative active material and an average particle size Dv50.sub.?2 of a second negative active material by using a laser particle size analyzer.

Capacity Ratio and Energy Density Measurement of a First Electrode Assembly:

[0066] First, the first electrode assembly and the second electrode assembly are respectively charged based on the following operation process, and then discharged, and discharge capacities of the first electrode assembly and the second electrode assembly are obtained.

[0067] (1) Charge the first electrode assembly: charge to 4.2 V at 6 C, then charge to 4.43 V at 4 C, then charge to 4.48 V at 3 C, and charge to 1 C at a constant voltage.

[0068] (2) Charge the second electrode assembly: charge to 4.2 V at 2 C, then charge to 4.45 V at 1.3 C, and charge to 0.05 C at a constant voltage.

[0069] (3) Discharge the first electrode assembly: discharge to 3.0 V with a constant current of 1 C to obtain the discharge capacity C1.

[0070] (4) Discharge the second electrode assembly: discharge to 3.0 V with a constant current of 0.5 C to obtain the discharge capacity C2.

Capacity ratio of first electrode assembly=C1/(C1+C2)?100%

[0071] After the charging step of the second electrode assembly of a lithium-ion battery is completed, measure a length L, a width W, and a height H of the lithium-ion battery by using a laser thickness gauge to obtain a volume V=L?W?H of the lithium-ion battery. Volumetric energy density (ED) of the lithium-ion battery can be calculated according to the following formula: ED (Wh/L)=(C1+C2)/V.

Thickness Swelling Rate Measurement:

[0072] Measure a thickness of a lithium-ion battery with state-of-charge (SOC)=0% by using a laser thickness gauge, where the thickness is denoted as T1, and then charge and discharge the first electrode assembly and the second electrode assembly in the lithium-ion battery for 500 cycles in the manner in <Capacity ratio and energy density measurement of a first electrode assembly>, and measure a final battery thickness as T500 by using the laser thickness gauge. Thickness swelling rate (%)=(T500?T1)/T1?100%

Embodiment 1-1

<Preparation of a First Negative Electrode Plate>

[0073] A first negative active material graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed in a mass ratio of 97:2:1, and deionized water is added, to prepare a slurry with a solid content of 70%, and the slurry is stirred evenly. The slurry is evenly coated on one surface of copper foil of a first negative current collector, and dried at 110? C., and then, and the above steps are repeated on the other surface of the copper foil of the first negative current collector, so that a first negative electrode plate coated with first negative active material layers on both sides is obtained. After the coating is completed, the first negative electrode plate is subjected to cold pressing and cut into a specification of 76 mm?851 mm, and tabs are welded for use. A coating weight W.sub.1f of the first negative active material layer is 120 mg/1540.25 mm.sup.2, a compaction density D.sub.1f of the first negative active material layer is 1.55 g/cm.sup.3, a specific surface area BET.sub.1 of the first negative active material is 1.9 m.sup.2/g, and an average particle size Dv50.1 of the first negative active material is 10 ?m.

<Preparation of a First Positive Electrode Plate>

[0074] A first positive active material lithium cobalt oxide (LiCoO.sub.2), a conductive agent conductive carbon black, and a binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.5:1.0:1.5, N-methylpyrrolidone (NMP) is added to prepare a slurry with a solid content of 75%, and the slurry is stirred evenly. The slurry is evenly coated on one surface of aluminum foil of a first positive current collector and dried at 130? C., and then, the above steps are repeated on the other surface of the aluminum foil of the first positive current collector, so that a positive electrode plate coated with first positive active material layers on both sides is obtained. After the coating is completed, the first positive electrode plate is subjected to cold pressing and cut into a specification of 74 mm?867 mm, and tabs are welded for use. A coating weight Wiz of the first positive active material layer is 220 mg/1540.25 mm.sup.2, and a compaction density of the first positive active material layer D.sub.1z is 4.05 g/cm.sup.3.

<Preparation of a Second Negative Electrode Plate>

[0075] A second negative active material graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed in a mass ratio of 97:2:1, and deionized water is added, to prepare a slurry with a solid content of 70%, and the slurry is stirred evenly. The slurry is evenly coated on one surface of copper foil of a second negative current collector and dried at 110? C., and then, the above steps are repeated on the other surface of the copper foil of the second negative current collector, so that a second negative electrode plate coated with second negative active material layers on both sides is obtained. After the coating is completed, the second negative electrode plate is subjected to cold pressing and cut into a specification of 76 mm?851 mm, and tabs are welded for use. A coating weight W.sub.2f of the second negative active material layer is 150 mg/1540.25 mm.sup.2, a compaction density Der of the second negative active material layer is 1.75 g/cm.sup.3, a specific surface area BET.sub.2 of the second negative active material is 0.9 m.sup.2/g, and an average particle size Dv50.sub.?2 of the second negative active material is 20 ?m.

<Preparation of a Second Positive Electrode Plate>

[0076] A second positive active material lithium cobalt oxide (LiCoO.sub.2), a conductive agent conductive carbon black, and a binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added, to prepare a slurry with a solid content of 75%, and the slurry is stirred evenly. The slurry is evenly coated on one surface of aluminum foil of a second positive current collector and dried at 130? C., and then, the above steps are repeated on the other surface of the aluminum foil of the second positive current collector, so that a positive electrode plate coated with second positive active material layers on both sides is obtained. After the coating is completed, the second positive electrode plate is subjected to cold pressing and cut into a specification of 74 mm?867 mm, and tabs are welded for use. A coating weight W.sub.2z of the second positive active material layer is 280 mg/1540.25 mm.sup.2, and a compaction density of the second positive active material layer D.sub.2z is 4.18 g/cm.sup.3

<Preparation of an Electrolyte Solution>

[0077] In the atmosphere of dry argon, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a mass ratio of EC:EMC:DEC-30:50:20 to obtain an organic solution, and then lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte solution in which a mass concentration of the lithium hexafluorophosphate is 12.5%.

<Preparation of a Separator>

[0078] A polypropylene (PP) film with a thickness of 14 ?m is adopted.

<Preparation of a First Electrode Assembly>

[0079] The first positive electrode plate, the separator, and the first negative electrode plate that are prepared above are stacked in order, so that the separator is located between the first positive electrode plate and the first negative electrode plate for separation, and winding is performed to obtain the first electrode assembly. A structure of the first electrode assembly is a tab center-positioned structure.

<Preparation of a Second Electrode Assembly>

[0080] The second positive electrode plate, the separator, and the second negative electrode plate that are prepared above are stacked in order, so that the separator is located between the second positive electrode plate and the second negative electrode plate for separation, and winding is performed to obtain the second electrode assembly.

<Preparation of a Lithium-Ion Battery>

[0081] A piece of outer packaging (an aluminum plastic film with a thickness of 150 ?m) molded through pouch forming is placed in a modular fixture, with a pouch surface facing upward, and the first electrode assembly is placed in the pouch. The second electrode assembly is placed on the first electrode assembly. Then, another piece of outer packaging (an aluminum plastic film with a thickness of 150 ?m) with a pouch facing down covers the second electrode assembly, positive and negative electrode tabs of the first electrode assembly and the second electrode assembly are led out, and other positions of the outer packaging are subjected to heat-sealing after the side of an electrolyte injection port is reserved, where a heat-sealing temperature is 180? C. and a heat-sealing pressure is 0.5 MPa. The electrolyte solution is injected through the electrolyte injection port, and vacuum packaging, standing, formation, degassing, trimming, and other processes are performed to obtain the lithium-ion battery.

Embodiment 1-2 to Embodiment 1-7 and Comparative Embodiment 1 and Comparative Embodiment 2

[0082] Except that the coating weight W.sub.1f of the first negative active material layer, the coating weight W.sub.2f of the second negative active material layer, the coating weight Wiz of the first positive active material layer, and the coating weight W.sub.2z of the second positive active material layer are adjusted according to Table 1, the rest are the same as those in Embodiment 1-1.

Embodiment 2-1 to Embodiment 2-6

[0083] Except that the specific surface area BET.sub.1 and the average particle size Dv50.sub.?1 of the first negative active material and the specific surface area BET.sub.2 and the average particle size Dv50.sub.?2 of the second negative active material are adjusted according to Table 2, the rest are the same as those in Embodiment 1-3.

Embodiment 3-1 to Embodiment 3-3

[0084] Except that the coating weight W.sub.1f of the first negative active material layer, the coating weight Wiz of the first positive active material layer, the coating weight W.sub.2f of the second negative active material layer, a type of the second negative active material, the specific surface area BET.sub.2 of the second negative active material, and the coating weight W.sub.2z of the second positive active material layer are adjusted according to Table 3, the rest are the same as those in Embodiment 1-3.

[0085] Relevant preparation parameters and performance parameters in Embodiment 1-1 to Embodiment 1-7 and Comparative Embodiment 1 and Comparative Embodiment 2 are shown in Table 1, relevant preparation parameters and performance parameters in Embodiment 2-1 to Embodiment 2-6 are shown in Table 2, and relevant preparation parameters and performance parameters in Embodiment 3-1 to Embodiment 3-3 are shown in Table 3.

TABLE-US-00001 TABLE 1 First negative active First positive active Second negative active Second positive material layer material layer material layer active material layer W.sub.1f (mg/ D.sub.1f W.sub.1z (mg/ D.sub.1z W.sub.2f (mg/ D2f W.sub.2z (mg/ 1540.25 mm.sup.2) (g/cm.sup.3) 1540.25 mm.sup.2) (g/cm.sup.3) 1540.25 mm.sup.2) (g/cm.sup.3) 1540.25 mm.sup.2) Embodiment 120 1.55 220 4.05 150 1.75 280 1-1 Embodiment 110 1.55 205 4.05 150 1.75 280 1-2 Embodiment 100 1.55 190 4.05 150 1.75 280 1-3 Embodiment 90 1.55 170 4.05 150 1.75 280 1-4 Embodiment 80 1.55 150 4.05 150 1.75 280 1-5 Embodiment 60 1.55 110 4.05 150 1.75 280 1-6 Embodiment 50 1.55 90 4.05 150 1.75 280 1-7 Comparative 120 1.55 220 4.05 130 1.75 240 Embodiment 1 Comparative 40 1.55 75 4.05 150 1.75 280 Embodiment 2 Second positive Capacity active material layer W.sub.2f ? W.sub.1f W.sub.2z ? W.sub.1z ratio of first Thickness Energy D.sub.2z (mg/1540.25 (mg/1540.25 electrode swelling density (g/cm.sup.3) mm.sup.2) mm.sup.2) assembly (%) rate (%) (Wh/L) Embodiment 4.18 30 60 40 5.2 630 1-1 Embodiment 4.18 40 75 38 4.7 632 1-2 Embodiment 4.18 50 90 36 4.5 635 1-3 Embodiment 4.18 60 110 34 4.2 638 1-4 Embodiment 4.18 70 130 32 3.9 640 1-5 Embodiment 4.18 90 170 30 3.8 650 1-6 Embodiment 4.18 100 190 28 4.3 645 1-7 Comparative 4.18 10 20 48 8.6 620 Embodiment 1 Comparative 4.18 110 205 25 5.4 610 Embodiment 2

TABLE-US-00002 TABLE 2 First negative Second negative W.sub.2f ? W.sub.2z ? Capacity active material active material W.sub.1f(mg/ W.sub.1z(mg/ ratio of first Thickness Energy BET.sub.1 Dv50.sub.?1 BET.sub.2 Dv50.sub.?2 1540.25 1540.25 electrode swelling density (m.sup.2/g) (?m) (m.sup.2/g) (?m) mm.sup.2) mm.sup.2) assembly (%) rate (%) (Wh/L) Embodiment 1-3 1.9 10 0.9 20 50 90 40 4.5 635 Embodiment 2-1 1.6 15 0.9 20 50 90 40 3.6 640 Embodiment 2-2 2.0 8 0.9 20 50 90 40 4.6 633 Embodiment 2-3 2.5 5 0.9 20 50 90 38 4.9 630 Embodiment 2-4 1.9 10 0.6 25 50 90 40 3.4 644 Embodiment 2-5 1.9 10 1.0 18 50 90 40 4.2 632 Embodiment 2-6 1.9 10 1.5 16 50 90 38 4.8 628

TABLE-US-00003 TABLE 3 First First Second negative positive negative active active active material material material layer First layer layer W.sub.1f(mg/ negative W.sub.1z(mg/ W.sub.2f(mg/ Second negative 1540.25 active 1540.25 1540.25 active material mm.sup.2) Type mm.sup.2) mm.sup.2) Type BET.sub.2(m.sup.2/g) Embodiment 1-3 100 Graphite 190 150 Graphite 0.9 Embodiment 3-1 90 Graphite 170 130 Silicon-carbon 1.1 composite material (W.sub.Si = 0.1%) Embodiment 3-2 100 Graphite 190 150 Silicon-carbon 1.1 composite material (W.sub.Si = 5%) Embodiment 3-3 110 Graphite 205 170 Silicon-carbon 1.1 composite material (W.sub.Si = 10%) Second positive active material Capacity layer W.sub.2f ? W.sub.2z ? ratio of W.sub.2z(mg/ W.sub.1f(mg/ W.sub.1z(mg/ first Thickness Energy 1540.25 1540.25 1540.25 electrode swelling density mm.sup.2) mm.sup.2) mm.sup.2) assembly rate (%) (Wh/L) Embodiment 1-3 280 50 90 40 4.5 635 Embodiment 3-1 250 40 80 38 3.3 640 Embodiment 3-2 270 50 80 36 3.5 645 Embodiment 3-3 290 60 85 42 3.6 648

[0086] It can be seen from Embodiment 1-1 to Embodiment 1-7 and Comparative Embodiment 1 and Comparative Embodiment 2 that, swelling performance and energy density of the lithium-ion battery vary with a difference W.sub.2f?W.sub.1f between the coating weight W.sub.1f of the first negative active material layer and the coating weight War of the second negative active material layer. A lithium-ion battery with W.sub.2f?W.sub.1f within the scope of this application has better swelling performance and better energy density than a lithium-ion battery with W.sub.2f?W.sub.1f<30 in Comparative Embodiment 1. Possible reasons are as follows: the coating weight War of the second negative active material layer is larger, in other words, in a same area, the second negative active material layer has more active materials than the first negative active material layer. Because accumulation between active material particles can provide more pores, when the first electrode assembly swells in a high-rate charge-discharge cycle process, the second negative active material layer can provide sufficient buffer space for the first electrode assembly, so that an overall volume increasing rate of the electrochemical apparatus is reduced, and swelling performance of the electrochemical apparatus is improved. By contrast, in Comparative embodiment 2 in which W.sub.2f?W.sub.1f>100, a low fast charging capacity cannot meet a requirement of a high-power consumption application. In addition, the coating weight W.sub.1f of a first negative active material layer is too small relative to the coating weight W.sub.2f of a second negative active material layer, which greatly reduces overall energy density of a lithium-ion battery, and when the coating weight W.sub.1f of the first negative active material layer<50 mg/1540.25 mm.sup.2, a degree of a side reaction between a surface of the first negative active material layer and an electrolyte solution increases, which also leads to a decrease in swelling performance.

[0087] It can be seen from Embodiment 1-3 and Embodiment 2-1 to Embodiment 2-6 that, there is more excellent swelling performance in Embodiment 1-3 and Embodiment 2-1 to Embodiment 2-2 with a first negative active material of which specific surface area BET.sub.1 ranges from 1.6 m.sup.2/g to 2.0 m.sup.2/g than in Embodiment 2-3. The reasons are as follows: when the specific surface area of the first negative active material is within the above range, a requirement on a lithium ion deintercalation rate during high-rate charging and discharging is met, thereby reducing a side reaction such as lithium plating. In addition, an increase of a side reaction, between a surface of the negative active material and an electrolyte solution during charging and discharging, due to an excessively large specific surface can be reduced, thereby improving the swelling performance. There is higher energy density in Embodiment 1-3, Embodiment 2-4, and Embodiment 2-5 with a second negative active material of which specific surface area BET.sub.2 ranges from 0.6 m.sup.2/g to 1.1 m.sup.2/g than in Embodiment 2-6. In addition, because a contact area with the electrolyte solution is small during charging and discharging, few side reactions occur, so that the good swelling performance is achieved.

[0088] It can be seen from Embodiment 1-3, and Embodiment 3-1 to Embodiment 3-3 that, there are also good swelling performance and higher energy density in Embodiment 3-1 to Embodiment 3-3 with a second negative active material of which type is of a silicon-carbon composite material and when W.sub.2f?W.sub.1f is within the scope of this application.

[0089] It should be noted that, in this specification, relational terms such as first and second are merely used to distinguish one entity from another entity, and do not necessarily require or imply any such actual relationship or order between these entities. Further, the terms include, contain, or any other variation thereof are intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also other elements that are not expressly listed, or further includes elements inherent to such article or device.

[0090] Each embodiment in this specification is described in a related manner, the same and similar parts between embodiments can refer to each other, and each embodiment focuses on differences with other embodiments.

[0091] The above description is only the preferred embodiment of the present application and is not be used to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application are to be included within the scope of protection of the present application.