ELECTROCHEMICAL DEVICE AND ELECTRONIC DEVICE

Abstract

An electrochemical device includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative active material. A specific surface area of the negative active material is A m.sup.2/g and 0.3≤A≤4. The electrolyte includes fluorocarboxylate and fluorocarbonate. Based on a mass of the electrolyte, a mass percent of the fluorocarboxylate is X % and a mass percent of the fluorocarbonate is Y %, 5≤Y≤70, and the electrochemical device satisfies 50≤X+Y≤85, and 6≤Y/A≤200. The synergy between the negative active material and the electrolyte can effectively improve cycle performance of the electrochemical device under high voltages, and alleviate lithium plating of the negative electrode.

Claims

1. An electrochemical device, comprising a negative electrode plate and an electrolyte; wherein the negative electrode plate comprises a negative active material, a specific surface area of the negative active material is A m.sup.2/g and 0.3≤A≤4; the electrolyte comprises fluorocarboxylate and fluorocarbonate; and, based on a mass of the electrolyte, a mass percent of the fluorocarboxylate is X % and a mass percent of the fluorocarbonate is Y %, 5≤Y≤70, and 50≤X+Y≤85, and 6≤Y/A≤200.

2. The electrochemical device according to claim 1, wherein the fluorocarboxylate comprises at least one selected from the group consisting of ethyl difluoroacetate, difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, ethyl trifluoroacetate, and trifluoroethyl acetate.

3. The electrochemical device according to claim 1, wherein a number of carbon atoms in the fluorocarbonate is less than or equal to 7, and the fluorocarbonate comprises cyclic fluorocarbonate and/or chain fluorocarbonate.

4. The electrochemical device according to claim 1, wherein the fluorocarbonate comprises fluoroethylene carbonate and/or difluoroethylene carbonate.

5. The electrochemical device according to claim 1, wherein the fluorocarbonate comprises at least one selected from the group consisting of bis(2,2,2-trifluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, methyl trifluoroethyl carbonate, methyl difluoroethyl carbonate, and methyl-fluoroethyl carbonate.

6. The electrochemical device according to claim 1, wherein the electrolyte further comprises a nitrile compound, a number of cyano groups in the nitrile compound is 1 to 6, and, based on the mass of the electrolyte, a mass percent of the nitrile compound is Z %, wherein 0.1≤Z≤10 and 0.5≤Y/Z≤120.

7. The electrochemical device according to claim 6, wherein 0.3≤Z≤8 and 5≤Y/Z≤120.

8. The electrochemical device according to claim 6, wherein the nitrile compound comprises at least one selected from the group consisting of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tri(2-cyanooxy)propane, ethylene glycol bis(propionitrile) ether, and fumaronitrile.

9. The electrochemical device according to claim 1, wherein a conductivity of the electrolyte is greater than or equal to 5.5 mS/cm.

10. The electrochemical device according to claim 1, wherein the negative active material comprises graphite and/or a silicon-based material.

11. The electrochemical device according to claim 1, wherein the negative active material comprises a silicon-based material; and carbon or Me.sub.xO.sub.y exists on a surface of the silicon-based material, wherein Me comprises at least one selected from the group consisting of Al, Si, Mn, V, Cr, Co, and Zr, 1≤x≤2, and 1≤y≤3.

12. The electrochemical device according to claim 1, wherein the electrochemical device further comprises a separator, and the separator satisfies at least one of the following conditions (a) to (c): (a) an air permeability of the separator is 50 s/100 cm.sup.3 to 700 s/100 cm.sup.3; (b) a thickness of the separator is 5 μm to 30 μm; (c) a pore size of the separator is greater than 0.005 μm and less than or equal to 1 μm.

13. The electrochemical device according to claim 12, wherein at least one surface of the separator is covered with a coating, the coating comprises inorganic particles, and the inorganic particles comprise at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

14. The electrochemical device according to claim 1, wherein a charge cut-off voltage of the electrochemical device is 4.2 V to 5 V.

15. An electronic device, comprising an electrochemical device, the electrochemical device comprising a negative electrode plate and an electrolyte; wherein the negative electrode plate comprises a negative active material, a specific surface area of the negative active material is A m.sup.2/g and 0.3≤A≤4; the electrolyte comprises fluorocarboxylate and fluorocarbonate; and, based on a mass of the electrolyte, a mass percent of the fluorocarboxylate is X % and a mass percent of the fluorocarbonate is Y %, 5≤Y≤70, and 50≤X+Y≤85, and 6≤Y/A≤200.

16. The electronic device according to claim 15, wherein the fluorocarboxylate comprises at least one selected from the group consisting of ethyl difluoroacetate, difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, ethyl trifluoroacetate, and trifluoroethyl acetate.

17. The electronic device according to claim 15, wherein the fluorocarbonate comprises at least one selected from the group consisting of bis(2,2,2-trifluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, methyl trifluoroethyl carbonate, methyl difluoroethyl carbonate, and methyl-fluoroethyl carbonate.

18. The electronic device according to claim 15, wherein the electrolyte further comprises a nitrile compound, a number of cyano groups in the nitrile compound is 1 to 6, and, based on the mass of the electrolyte, a mass percent of the nitrile compound is Z %, wherein 0.1≤Z≤10 and 0.5≤Y/Z≤120; wherein the nitrile compound comprises at least one selected from the group consisting of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tri(2-cyanooxy)propane, ethylene glycol bis(propionitrile) ether, and fumaronitrile.

19. The electronic device according to claim 15, wherein a conductivity of the electrolyte is greater than or equal to 5.5 mS/cm.

20. The electronic device according to claim 15, wherein the electrochemical device further comprises a separator, and the separator satisfies at least one of the following conditions (a) to (c): (a) an air permeability of the separator is 50 s/100 cm.sup.3 to 700 s/100 cm.sup.3; (b) a thickness of the separator is 5 μm to 30 μm; (c) a pore size of the separator is greater than 0.005 μm and less than or equal to 1 μm.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following describes this application in more detail with reference to embodiments. Evidently, the described embodiments are merely a part of but not all of the embodiments of this application. All other embodiments derived by a person of ordinary skill in the art based on the embodiments of this application without making any creative efforts fall within the protection scope of this application.

[0047] It needs to be noted that in specific embodiments of this application, this application is construed by using a lithium-ion battery as an example of the electrochemical device, but the electrochemical device according to this application is not limited to the lithium-ion battery.

Embodiments

[0048] The implementations of this application are described below in more detail with reference to embodiments and comparative embodiments. Various tests and evaluations are performed in accordance with the following methods.

[0049] Test Methods and Devices:

[0050] Evaluation of the Cycle Performance:

[0051] Putting the lithium-ion battery into a 45° C. thermostat, and leaving the battery to stand for 30 minutes so that the temperature of the lithium-ion battery is constant. Charging, after the lithium-ion battery reaches a constant temperature, the lithium-ion battery at a constant current of 1 C at 45° C. until the voltage reaches 4.45 V, and then charging the battery at a constant voltage of 4.45 V until the current reaches 0.025 C. Leaving the battery to stand for 30 minutes, and then discharging the battery at a constant current of 1 C until the voltage reaches 3.0 V, thereby completing a charge-and-discharge cycle. Repeating the foregoing charge-and-discharge process, and calculating the capacity retention rate of the battery at the end of 500 cycles.

[0052] Calculating the capacity retention rate of the cycled lithium-ion battery by the following formula:

Capacity retention rate=(500.sup.th-cycle discharge capacity/first-cycle discharge capacity)×100%.

[0053] Method for Determining a Lithium Plating Phenomenon of the Lithium-Ion Battery:

[0054] Putting the lithium-ion battery into a 0° C. thermostat, and leaving the battery to stand for 60 minutes so that the temperature of the lithium-ion battery is constant. Charging, after the lithium-ion battery reaches a constant temperature, the lithium-ion battery at a constant current of 1 C at 0° C. until the voltage reaches 4.45 V, and then charging the battery at a constant voltage of 4.45 V until the current reaches 0.025 C. Leaving the battery to stand for 5 minutes, and then discharging the battery at a constant current of 1 C until the voltage reaches 3.0 V, thereby completing a charge-and-discharge cycle. Subsequently, charging the lithium-ion battery at a constant current of 1 C until the voltage reaches 4.45 V, and then charging the battery at a constant voltage of 4.45 V until the current reaches 0.025 C, so as to obtain a fully charged battery cycled for 10 cycles. Disassembling the battery in a drying room with a humidity less than 5%, and taking photos to record the status of the negative electrode plate.

[0055] Determining severity of lithium plating of the lithium-ion battery according to the following criteria:

[0056] No lithium plating: No lithium is deposited on the surface of the negative electrode plate;

[0057] Slight lithium plating: The lithium deposition area on the surface of the negative electrode plate is less than 10%;

[0058] Moderate lithium plating: The lithium deposition area on the surface of the negative electrode plate is 10% to 30%; and

[0059] Severe lithium plating: The lithium deposition area on the surface of the negative electrode plate is greater than 30%.

[0060] Measurement of the Air Permeability:

[0061] Measuring the air permeability of a separator of a disassembled battery with an air permeameter, where the air column volume of the air permeameter is 100 cm.sup.3, and the test area of the separator is 6.45 cm.sup.2. Keeping the separator absolutely flat during the test. Repeating the test for 3 times, and averaging out the measured values to obtain a final air permeability value.

[0062] Measurement of the Conductivity of the Electrolyte:

[0063] Putting 50 ml of electrolyte of a disassembled battery into a 100 ml beaker, and leaving the beaker to stand in a 25° C. water bath for 30 minutes. Subsequently, measuring the conductivity of the electrolyte at 25° C. by using a conductivity meter (model DDS-307, manufactured by Shanghai Leici). Repeating the test for 3 times, and averaging out the measured values to obtain a conductivity value of the electrolyte.

Embodiment 1

[0064] <Preparing a Positive Electrode Plate>

[0065] Mixing lithium cobalt oxide (LiCoO.sub.2) as a positive active material, conductive carbon black (Super P) as a conductive agent, and polyvinylidene difluoride as a binder at a mass ratio of 96:2:2, adding N-methyl-pyrrolidone (NMP), and mixing well with a vacuum mixer to obtain a positive slurry, in which the solid content is 70 wt %. Coating one surface of a 12-μm-thick positive current collector aluminum foil with the positive slurry evenly, and drying the aluminum foil at 120° C. for 1 hour to obtain a positive electrode plate coated with a 110-μm-thick positive material layer on a single side. Repeating the foregoing steps on the other surface of the aluminum foil to obtain a positive electrode plate coated with the positive active material on both sides. Subsequently, performing cold calendering, cutting, and slitting, and drying under vacuum conditions at 120° C. for 1 hour to obtain a positive electrode plate of 74 mm×867 mm in size.

[0066] <Preparing a Negative Electrode Plate>

[0067] Mixing silicon-based material SiO particles and graphite at a mass ratio of 15:85 to obtain a negative active material. Mixing the negative active material, a conductive agent Super P, a thickener sodium carboxymethyl cellulose (CMC), and a binder styrene butadiene rubber (SBR) at a mass ratio of 85:2:13. Adding deionized water, and mixing well with a vacuum mixer to obtain a negative slurry, in which the solid content is 75 wt %. Coating one surface of a 12-μm-thick negative current collector copper foil with the negative slurry evenly, and drying the copper foil at 120° C. to obtain a negative electrode plate coated with a 130-μm-thick negative material layer on a single side. Repeating the foregoing steps on the other surface of the copper foil to obtain a negative electrode plate coated with the negative active material on both sides. Subsequently, performing cold calendering, cutting, and slitting, and drying under vacuum conditions at 120° C. for 1 hour to obtain a negative electrode plate of 74 mm×867 mm in size. The specific surface area of the negative active material is 0.5 m.sup.2/g. The silicon-based particles are obtained by mixing Si and SiO.sub.2 at a molar ratio of 1:1.

[0068] <Preparing an Electrolyte>

[0069] Mixing fluorocarboxylate, difluoroethyl acetate, fluorocarbonate, fluoroethylene carbonate (FEC), and diethyl carbonate in a dry argon atmosphere glovebox to obtain a basic organic solvent, and then adding lithium hexafluorophosphate (LiPF.sub.6) into the basic organic solvent to dissolve, and mixing well to obtain an electrolyte. Based on the massy of the electrolyte, the mass percent of difluoroethyl acetate is 20 wt %, the mass percent of fluoroethylene carbonate is 30 wt %, the mass percent of LiPF.sub.6 is 12.5 wt %, and the remainder is diethyl carbonate.

[0070] <Preparing a Separator>

[0071] Using a 30-μm-thick polypropylene film as a separator, of which the pore size is 0.008 μm and the air permeability is 650 s/100 cm.sup.3.

[0072] <Preparing a Lithium-Ion Battery>

[0073] Stacking the prepared positive electrode plate, the separator, and the negative electrode plate sequentially in such a way that the separator is located between the positive electrode plate and the negative electrode plate to serve a function of separation, and winding the stacked structure to obtain an electrode assembly. Putting the electrode assembly into an aluminum plastic film package, drying the packaged electrode assembly, and then injecting the electrolyte. Performing vacuum sealing, static standing, chemical formation, degassing, and edge trimming to obtain a lithium-ion battery. The conditions of chemical formation are: charging the battery at a constant current of 0.02 C until the voltage reaches 3.3 V, and then charging the battery at a constant current of 0.1 C until the voltage reaches 3.6 V.

[0074] Table 1 shows parameters and evaluation results of Embodiments 1 to 18 and Comparative Embodiments 1 to 6.

[0075] Embodiments 1 to 16 and Comparative Embodiments 1 to 5 make changes on the basis of Embodiment 1 according to the parameters in the table. Embodiment 17 is identical to Embodiment 2 except the following steps: depositing Al.sub.2O.sub.3 on the surface of the silicon-based particles by using an atomic layer deposition (ALD) technique, and then mixing the silicon-based particles containing Al.sub.2O.sub.3 on the surface with graphite to obtain a negative active material, where the deposition thickness of Al.sub.2O.sub.3 on the surface of silicon-based particles is 35 nm. Embodiment 18 is identical to Embodiment 2 except the following steps: depositing amorphous carbon on the surface of the silicon-based particles by using an atomic layer deposition (ALD) technique, and then mixing the silicon-based particles containing amorphous carbon on the surface with graphite to obtain a negative active material, where the thickness of amorphous carbon on the surface of silicon-based particles is 35 nm.

TABLE-US-00001 TABLE 1 Specific surface area of negative Conductivity Fluorocarboxylate Fluorocarbonate active Capacity Lithium of Content Content X + Y material A retention deposition electrolyte Type X (%) Type Y (%) (%) (m.sup.2/g) Y/A rate (%) test (mS/cm) Embodiment Difluoroethyl 20 FEC 30   50   0.5 60   50 No 6.7  1 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   0.5 70   52 No 6.8  2 acetate lithium plating Embodiment Difluoroethyl 40 FEC 35   75   0.5 70   58 No 7    3 acetate lithium plating Embodiment Difluoroethyl 15 FEC 70   85   0.5 140    61 No 5.6  4 acetate lithium plating Embodiment Difluoroethyl 50 FEC 5   55   0.5 10   61 No 6.1  5 acetate lithium plating Embodiment Difluoroethyl 25 FEC 60   85   0.3 200    62 No 5.7  6 acetate lithium plating Embodiment Difluoroethyl 30 + 10 FEC 25   65   0.5 50   65 No 6.8  7 acetate + lithium monofluoroethyl plating acetate Embodiment Difluoroethyl 20 + 20 FEC 25   65   0.5 50   63 No 6.2  8 acetate + ethyl lithium trifluoroacetate plating Embodiment Ethyl 40 FEC 25   65   0.5 50   61 No 5.7  9 trifluoroacetate lithium plating Embodiment Difluoroethyl 40 DFEC + 10 + 20 70   0.5 60   65 Slight 6.3 10 acetate FEC lithium plating Embodiment Difluoroethyl 30 FEC + 20 + 15 65   0.5 70   63 No 6.7 11 acetate bis(2,2,2- lithium trifluoroethyl) plating Embodiment Difluoroethyl 30 + 30 DFEC + 10 + 15 85   0.5 50   65 Slight 6.5 12 acetate + ethyl methyl lithium trifluoroacetate trifluoroethyl plating carbonate Embodiment Difluoroethyl 30 FEC 35   65   0.3 116.67  50 Slight 6.8 13 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   1   35   55 No 6.8 14 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   2   17.50 59 No 6.8 15 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   4    8.75 51 Slight 6.8 16 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   0.5 70   60 Slight 6.8 17 acetate lithium plating Embodiment Difluoroethyl 30 FEC 35   65   0.5 70   65 Slight 6.8 18 acetate lithium plating Comparative Difluoroethyl 35 FEC 25   60   0.1 250    40 Moderate 6.4 Embodiment acetate lithium  1 plating Comparative Difluoroethyl 35 FEC 25   60   6    4.17 41 Slight 6.4 Embodiment acetate lithium  2 plating Comparative Difluoroethyl 20 FEC 20   40   0.5 40   47 Severe 6   Embodiment acetate lithium  3 plating Comparative Difluoroethyl 80 FEC 3.5 83.5  0.5 7   41 Moderate 5.7 Embodiment acetate lithium  4 plating Comparative Difluoroethyl  5 FEC 80   85   0.5 170    35 Severe 5.6 Embodiment acetate lithium  5 plating Note: “/” in Table 1 indicates nonexistence of the corresponding preparation parameter or substance.

[0076] Referring to Table 1, as can be seen from Embodiments 1 to 16 and Comparative Embodiments 1 to 5, when the mass percent Y of fluorocarbonate, the total mass percent (X+Y) of the fluorocarboxylate and fluorocarbonate, the specific surface area A of the negative active material, and the Y/A ratio fall within the range specified herein, the capacity retention rate of the electrochemical device can be increased without greatly affecting the conductivity of the electrolyte.

[0077] As can be seen from Embodiments 1 to 16 and Comparative Embodiments 1 and 2, when the specific surface area A of the negative active material and the Y/A ratio fall within the range specified herein, the capacity retention rate of the electrochemical device is increased significantly.

[0078] As can be seen from Embodiments 1 to 16 and Comparative Embodiment 3, when the total mass percent (X+Y) of the fluorocarboxylate and fluorocarbonate falls within the range specified herein, the capacity retention rate of the electrochemical device is increased significantly, and the lithium plating of the negative electrode plate is alleviated significantly.

[0079] As can be seen from Embodiments 1 to 16 and Comparative Embodiments 4 and 5, when the mass percent Y of the fluorocarbonate falls within the range specified herein, the capacity retention rate of the electrochemical device can be increased, and the lithium plating of the negative electrode can be alleviated.

[0080] As can be seen from Embodiments 2, 17, and 18, when the negative electrode includes silicon-based particles and the surface of the silicon-based particles contains the material provided in this application, the capacity retention rate of the electrochemical device can be further increased.

[0081] Table 2 shows parameters and evaluation results of Embodiments 2 and 5 and Embodiments 19 to 29.

[0082] In Embodiments 19 to 29, on the basis of Embodiment 2, the content of fluorocarboxylate and the content of fluorocarbonate are adjusted according to the parameters in Table 2, and nitrile compounds are further added according to the types and content shown in Table 2.

TABLE-US-00002 TABLE 2 Conductivity Nitrile compound of Capacity Lithium Content electrolyte retention deposition X (%) Y (%) Type Z (%) Y/Z (mS/cm) rate (%) test Embodiment 30 35 / / / 6.8 52 No  2 lithium plating Embodiment 50  5 / / / 6.1 61 No  5 lithium plating Embodiment 30 35 Succinonitrile 0.3 116.7  6.7 57 No 19 lithium plating Embodiment 30 35 Succinonitrile 1   35   6.3 61 No 20 lithium plating Embodiment 30 35 Succinonitrile 4    8.75 6.0 69 No 21 lithium plating Embodiment 30 35 Succinonitrile 10   3.5 5.6 63 Slight 22 lithium plating Embodiment 30 35 Succinonitrile + 2 + 2  8.75 6.0 69 No 23 adiponitrile lithium plating Embodiment 30 35 Succinonitrile + 3 + 1  8.75 6.0 68 No 24 1,3,6- lithium hexanetricarbonitrile plating Embodiment 30 35 1,3,6- 2 + 2  8.75 6.1 67 No 25 hexanetricarbonitrile + lithium 1,2,3-tris plating (2-cyanooxy) propane Embodiment 30 35 Succinonitrile + 2 + 2 + 1 7   5.9 70 No 26 1,3,6- lithium hexanetricarbonitrile + plating 1,2,3-tris (2-cyanooxy) propane Embodiment 50  5 Succinonitrile 10   0.5 5.5 62 Slight 27 lithium plating Embodiment 30 35 Succinonitrile 0.2 175    6.8 51 No 28 lithium plating Embodiment 50  5 Succinonitrile 16.7  0.3 4.4 53 Moderate 29 lithium plating Note: “/” in Table 2 indicates nonexistence of the corresponding preparation parameter or substance.

[0083] Referring to Table 2, as can be seen from Embodiment 2 and Embodiments 19 to 26, the nitrile compound added in the electrolyte can further increase the capacity retention rate of the electrochemical device.

[0084] As can be seen from Embodiments 19 to 29, when the value of Y/Z falls within the range specified herein, the lithium plating of the negative electrode plate can be alleviated on the basis of improving the capacity retention rate of the electrochemical device. As can be seen from Embodiments 19 to 27 and Comparative Embodiment 29, when the mass percent Z of the nitrile compound falls within the range specified herein, the capacity retention rate of the electrochemical device can be increased, and the lithium plating of the negative electrode can be alleviated.

[0085] As can be seen from Embodiments 19 to 22, when the total mass percent (X+Y) of fluorocarbonate and fluorocarboxylate in the electrolyte remains unchanged, the mass percent Z of the nitrile compound is excessively high or the Y/Z ratio is excessively low, the conductivity of the electrolyte shows a tendency to decrease gradually, the capacity retention rate of the electrochemical device cannot be further improved, and slight lithium plating occurs on the negative electrode plate.

[0086] Table 3 shows parameters and evaluation results of Embodiment 3 and Embodiments 30 to 37.

[0087] Embodiments 30 to 37 make changes on the basis of Embodiment 3 according to the parameters in the table. Embodiment 37 is identical to Embodiment 34 except the following steps: mixing Al.sub.2O.sub.3, water, and polyvinyl alcohol at a mass ratio of 10:30:1 to obtain a coating slurry, and then coating one surface of the separator with the coating slurry by a thickness of 2 and drying the separator at 120° C. Repeating the foregoing steps on the other surface of the separator to obtain a separator coated on both sides.

TABLE-US-00003 TABLE 3 Pore size of Thickness of Air permeability Capacity separator separator of separator retention rate Lithium (μm) (μm) (s/100 cm.sup.3) (%) deposition test Embodiment 3 0.008 30 650 58 No lithium plating Embodiment 30 0.005 30 710 50 No lithium plating Embodiment 31 0.008 28 690 57 No lithium plating Embodiment 32 0.008 25 500 60 No lithium plating Embodiment 33 0.01 25 351 61 No lithium plating Embodiment 34 0.1 10 60 65 No lithium plating Embodiment 35 0.8 35 48 51 No lithium plating Embodiment 36 1.1 4 45 50 No lithium plating Embodiment 37 0.1 10 65 69 No lithium plating Note: “/” in Table 3 indicates nonexistence of the corresponding preparation parameter or substance.

[0088] The thickness, pore size, and air permeability of the separator usually also affect the comprehensive performance such as capacity retention rate of the electrochemical device. Referring to Table 3, when the thickness, pore size, and air permeability of the separator are set to fall within the ranges specified herein, all the resulting electrochemical devices achieve a high capacity retention rate.

[0089] The coating disposed on the surface of the separator usually also affects the comprehensive performance such as capacity retention rate of the electrochemical device. As can be seen from Embodiments 34 and 37, when the coating includes the inorganic particles provided in this application, the capacity retention rate of the electrochemical device can be further increased.

[0090] What is described above is merely preferred embodiments of this application, but is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application still fall within the protection scope of this application.