Secondary battery and electric device

Abstract

The invention relates to a secondary battery and an electric device, and belongs to the technical field of batteries. The secondary battery comprises a porous negative pole piece and a diaphragm, the porous negative pole piece comprises a current collector and a negative active layer arranged on at least one side surface of the current collector, and the negative active layer contains Si; a plurality of holes in the thickness direction are formed in the negative electrode active layer at intervals, and openings of the holes are located in the side, away from the current collector, of the negative electrode active layer; the puncture strength of the diaphragm is C gf; the mass content of Si in the negative electrode active layer is P%; the hole depth of the hole accounts for T% of the thickness of the negative electrode active layer; the secondary battery satisfies the following condition: T * P / C is more than 0.0025 and less than 2.78. The secondary battery has a low K value while maintaining high energy density and good fast charge performance.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a secondary battery and an electrical device. Background Art

[0002] With the development of new energy vehicles, electronic communication equipment and consumer digital products, consumers are increasingly demanding lithium-ion batteries with high energy density and fast charging performance. In order to improve the energy density of lithium-ion batteries, people have begun to replace commercial graphite electrodes with silicon-based negative electrodes with higher theoretical specific capacity, and combined with laser drilling technology to create a large number of micropores on the surface of the silicon-based negative electrode to form ion transmission channels to reduce the tortuosity of lithium ion diffusion to the deep negative electrode, thereby improving the fast charging performance of lithium-ion batteries. However, in actual applications, it is found that laser drilling on the surface of the silicon-based negative electrode will expose the silicon particles buried inside the pole piece to the pore interface, and the sharp and tiny silicon particles will easily pierce the diaphragm during the winding and formation process of the battery cell, which will cause a micro-short circuit inside the battery cell to cause self-discharge, thereby deteriorating the K value of the battery cell (the voltage drop of the battery per unit time, mV / h), causing the battery cell to fail. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies of the prior art and provide a secondary battery and an electrical device.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] In a first aspect, the present invention provides a secondary battery, comprising a porous negative electrode sheet and a separator;

[0006] The porous negative electrode sheet comprises a current collector and a negative electrode active layer disposed on at least one side of the current collector, wherein the negative electrode active layer comprises Si;

[0007] The negative electrode active layer is provided with a plurality of holes along the thickness direction at intervals, and the openings of the holes are located on a side of the negative electrode active layer away from the current collector;

[0008] The puncture strength of the separator is C gf; the mass content of Si in the negative electrode active layer is P%; the percentage of the pore depth to the thickness of the negative electrode active layer is T%;

[0009] The secondary battery satisfies: 0.0025<T*P / C<2.78;

[0010] Among them, 180≤C<250, 1<P≤6, 1<T≤30;

[0011] Or, 250≤C<400, 1<P≤10, 1<T≤50;

[0012] Or, 180≤C≤250, 6<P≤10, 1<T≤10.

[0013] As an embodiment of the present invention, 180≤C≤200, 2≤P≤6, and 10≤T≤30.

[0014] As an embodiment of the present invention, 250≤C≤300, 6≤P≤10, and 20≤T≤50.

[0015] As an embodiment of the present invention, 180≤C≤250, 6<P≤10, 5≤T≤10.

[0016] As an embodiment of the present invention, the thickness of the negative electrode active layer is 50 to 150 μm.

[0017] As an embodiment of the present invention, the surface density of the negative electrode active layer is 6 to 11 mg / mm 2 .

[0018] As an embodiment of the present invention, the pores have a pore diameter of 1 to 60 μm.

[0019] As an embodiment of the present invention, the hole spacing of the holes is 0.5 to 3 mm.

[0020] As an embodiment of the present invention, the Si in the negative electrode active layer exists in the form of silicon particles, and the particle size D of the silicon particles is V50 6~15μm.

[0021] As an embodiment of the present invention, the negative electrode active layer further includes a conductive agent, a binder and a thickener.

[0022] As an embodiment of the present invention, the conductive agent includes at least one of acetylene black, carbon nanotubes, graphene, and VGCF; the binder includes at least one of styrene-butadiene rubber, CMC, and PAA; and the thickener includes at least one of sodium carboxymethyl cellulose and CMC-Li.

[0023] As an embodiment of the present invention, the separator includes a polyolefin-based film and a coating provided on at least one surface of the polyolefin-based film; the coating includes at least one of PVDF and a ceramic material.

[0024] In a second aspect, the present invention provides an electrical device, comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention significantly reduces the risk of silicon particles exposed after laser drilling of silicon-based negative electrode plates piercing the diaphragm by regulating the puncture strength of the diaphragm in the secondary battery, as well as the pore depth and Si mass content of the pores in the negative electrode active layer in the porous negative electrode plate, so as to effectively suppress the self-discharge caused by micro-short circuits inside the battery, thereby making the battery have high energy density, good fast charging performance and low K value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the porous negative electrode plate in the secondary battery of the present invention. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, the purpose of which is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention, unless otherwise specified, are all commonly used common reagents and instruments.

[0029] According to a first aspect of the present invention, there is provided a secondary battery comprising a porous negative electrode sheet and a separator;

[0030] The porous negative electrode sheet comprises a current collector and a negative electrode active layer disposed on at least one side of the current collector, wherein the negative electrode active layer comprises Si;

[0031] The negative electrode active layer is provided with a plurality of holes along the thickness direction at intervals, and the openings of the holes are located on a side of the negative electrode active layer away from the current collector;

[0032] The puncture strength of the separator is C gf; the mass content of Si in the negative electrode active layer is P%; the percentage of the pore depth to the thickness of the negative electrode active layer is T%;

[0033] The secondary battery satisfies: 0.0025<T*P / C<2.78;

[0034] Among them, 180≤C<250, 1<P≤6, 1<T≤30;

[0035] Or, 250≤C<400, 1<P≤10, 1<T≤50;

[0036] Or, 180≤C≤250, 6<P≤10, 1<T≤10.

[0037] The present invention significantly reduces the risk of silicon particles exposed after laser drilling of silicon-based negative electrode sheets piercing the diaphragm by regulating the puncture strength of the diaphragm in the secondary battery, as well as the pore depth and Si mass content of the pores in the negative electrode active layer in the porous negative electrode sheet, so as to effectively suppress the self-discharge caused by micro-short circuits inside the battery, thereby enabling the battery to have high energy density, excellent fast charging performance and low K value.

[0038] Optionally, the puncture strength of the diaphragm may be any one of 80gf, 90gf, 100gf, 110gf, 120gf, 130gf, 140gf, 150gf, 160gf, 170gf, 180gf, 190gf, 200gf, 210gf, 220gf, 230gf, 240gf, 250gf, 260gf, 280gf, 300gf, and 350gf, or any two of the range values. The puncture strength of the diaphragm may be measured with reference to standard GB / T36363-2018.

[0039] Optionally, the mass content of Si in the negative electrode active layer can be any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two of the range values.

[0040] Optionally, the percentage of the pore depth to the thickness of the negative electrode active layer may be any one of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any two of the range values.

[0041] Preferably, 0.1≤T*P / C≤2, preferably 0.22≤T*P / C≤1.92.

[0042] Specifically, the secondary battery includes at least one of a wound soft-pack battery, a wound aluminum shell battery, a wound cylindrical battery, a laminated soft-pack battery, a laminated aluminum shell battery, and the like.

[0043] The secondary battery further comprises a positive electrode plate and an electrolyte, wherein the positive electrode active material in the positive electrode plate may comprise at least one of a nickel-cobalt-manganese ternary material, a lithium iron phosphate material, a lithium iron manganese phosphate material, and a lithium cobalt oxide material; the electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the lithium salt may be LiPF6 and / or LiBOB used in a high-temperature electrolyte; or may be at least one of LiBF4, LiBOB, and LiPF6 used in a low-temperature electrolyte; or may be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in an overcharge prevention electrolyte. At least one; it can also be at least one of LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2; the organic solvent can be cyclic carbonate, including PC, EC; it can also be chain carbonate, including DFC, DMC, or EMC; it can also be carboxylic acid esters, including MF, MA, EA, MP, etc.; the additives include but are not limited to at least one of film-forming additives, conductive additives, flame retardant additives, anti-overcharge additives, additives for controlling the content of H2O and HF in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0044] As an embodiment of the present invention, 180≤C≤200, 2≤P≤6, 10≤T≤30. Studies have found that when the puncture strength of the separator is low, the risk of exposed silicon particles piercing the separator can be better reduced by correspondingly reducing the mass content of Si in the negative electrode active layer and the depth of the laser-drilled holes, thereby significantly reducing the K value of the battery.

[0045] As an embodiment of the present invention, 250≤C≤300, 6≤P≤10, 20≤T≤50. Studies have found that when the puncture strength of the separator is high, by correspondingly increasing the mass content of Si in the negative electrode active layer and the depth of the laser-drilled hole, the deeper the drilling, the shorter the path for lithium ions to embed into the bottom layer of the anode sheet, reducing concentration polarization, and thus better increasing the charging performance of the battery.

[0046] As an embodiment of the present invention, 180≤C≤250, 6<P≤10, 5≤T≤10. Studies have found that when the mass content of Si in the negative electrode active layer is large, the exposure of silicon particles can be reduced by reducing the hole depth of laser drilling, and at the same time, with a separator with lower puncture strength, the risk of silicon particles piercing the separator can be effectively reduced, thereby maintaining a lower K value for the battery.

[0047] As an embodiment of the present invention, the thickness of the negative electrode active layer is 50-150 μm. Optionally, the thickness of the negative electrode active layer can be any one or any two of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, and 150 μm.

[0048] As an embodiment of the present invention, the surface density of the negative electrode active layer is 6 to 11 mg / mm 2 Optionally, the surface density of the negative electrode active layer can be 6 mg / mm 2 , 7mg / mm 2 , 8mg / mm 2 , 9mg / mm 2 , 10mg / mm 2 , 11mg / mm 2 The surface density in this range can not only meet the capacity requirements of the battery cell, but also help the battery cell maintain a good charging capacity and reduce concentration polarization.

[0049] As an embodiment of the present invention, the pore size is 1 to 50 μm. Optionally, the pore size can be any one of 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm, or any two of them. The pores within this pore size range are more conducive to improving the charging performance of the battery cell and can better reduce the diffusion path of lithium ions embedded in the deep anode.

[0050] As an embodiment of the present invention, the hole spacing of the holes is 0.5 to 3 mm. Optionally, the hole spacing of the holes can be any one of 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm or any two of them. The holes within this hole spacing range can make the battery cell have higher capacity and better charging performance.

[0051] As an embodiment of the present invention, the Si in the negative electrode active layer exists in the form of silicon particles, and the particle size D of the silicon particles is V50 Optionally, the particle size D of the silicon particles is V50 Specifically, the value may be within the range of any one or any two of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm.

[0052] As an embodiment of the present invention, the negative electrode active layer further includes a conductive agent, a binder and a thickener.

[0053] As an embodiment of the present invention, the conductive agent includes at least one of acetylene black, carbon nanotubes, graphene, and VGCF; the binder includes at least one of styrene-butadiene rubber, CMC, and PAA; and the thickener includes at least one of sodium carboxymethyl cellulose and CMC-Li.

[0054] As an embodiment of the present invention, the diaphragm includes a polyolefin base film and a coating provided on at least one side of the polyolefin base film; the coating includes at least one of PVDF and a ceramic material; the ceramic material includes at least one of boehmite, alumina, and silicon dioxide. Preferably, the coating is mainly composed of PVDF and the ceramic material in a mass ratio of 1:(0.5-1.5).

[0055] In a second aspect, the present invention provides an electrical device, comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0056] In order to clearly understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0057] Example 1

[0058] This embodiment provides a secondary battery, which is prepared by the following preparation method:

[0059] The positive electrode sheet, the separator, and the porous negative electrode sheet are stacked in order, with the separator being located between the positive electrode sheet and the porous negative electrode sheet, and the electrode assembly is obtained by winding; the electrode assembly is placed in a packaging shell, and the electrolyte is injected and packaged to obtain a secondary battery.

[0060] 1) The above-mentioned positive electrode sheet is prepared by the following preparation method:

[0061] The positive electrode active material (lithium cobalt oxide), conductive agent (acetylene black) and binder (polyvinylidene fluoride) are mixed in a mass ratio of 98:1.2:0.8 and added into N-methylpyrrolidone solvent and stirred thoroughly to obtain positive electrode slurry. The positive electrode slurry is then coated on the surface of Al foil (double-sided coating), and the positive electrode sheet is obtained after drying, rolling and slitting.

[0062] 2) The above-mentioned porous negative electrode sheet is prepared by the following preparation method:

[0063] The negative electrode active material (SiC anode composite material composed of silicon carbon and graphite, wherein the silicon carbon is provided by Beiterry and the graphite is provided by Zichen), the conductive agent (acetylene black), the binder (styrene-butadiene rubber), and the thickener (sodium carboxymethyl cellulose) are mixed in a mass ratio of 98:0.6:0.7:0.7, and then added into a deionized water solvent and stirred and mixed thoroughly to obtain a negative electrode slurry, and then the negative electrode slurry is coated on the surface of the Cu foil (double-sided coating), and after drying, rolling, and striping, a negative electrode sheet is obtained; then the negative electrode sheet is etched by a laser drilling field mirror device to obtain a porous negative electrode sheet (such as Figure 1 shown);

[0064] The thickness of the negative electrode active layer of the porous negative electrode sheet is 120 μm, the thickness of the double-sided coating after rolling is 104 μm, the thickness of the current collector copper foil is 4 μm, and the surface density is 9 mg / mm 2 .

[0065] 3) The above-mentioned diaphragm is prepared by the following preparation method:

[0066] PVDF and alumina are mixed in a mass ratio of 1:1, and then stirred and mixed thoroughly to obtain a coating slurry. The coating slurry is then coated on the surface of a polyethylene-based film using a gravure coating process, and a diaphragm is obtained after drying.

[0067] 4) The above electrolyte is prepared by the following preparation method:

[0068] LiPF6 and an organic solvent are evenly mixed in a mass ratio of 8:92 to obtain an electrolyte; wherein the organic solvent is obtained by compounding ethylene carbonate, diethyl carbonate, propylene carbonate, propyl propionate and vinylene carbonate in a mass ratio of 25:25:15:31:4.

[0069] Embodiments 2 to 10

[0070] Embodiments 2 to 10 provide a secondary battery, and the preparation method thereof is basically the same as that of Embodiment 1, except that the silicon-carbon content in the SiC anode material and the power of the laser drilling field mirror device are regulated during the preparation of the porous negative electrode plate, so that the mass content of Si in the negative electrode active layer of the porous negative electrode plate is different, and the depth and diameter of the holes formed by etching are different; and the annealing temperature of the base film during the preparation of the diaphragm is regulated to make the puncture strength of the diaphragm different.

[0071] Comparative Examples 1 to 4

[0072] Comparative Examples 1 to 4 provide a secondary battery, and the preparation method thereof is basically the same as that of Example 1, except that the power of the laser drilling field lens device during the preparation of the porous negative electrode plate is adjusted so that the hole depth and hole diameter of the holes formed by etching are different.

[0073] Comparative Examples 5-6

[0074] Comparative Examples 5 to 6 provide a secondary battery, the preparation method of which is basically the same as that of Example 2, except that the silicon-carbon content in the SiC anode material is regulated during the preparation of the porous negative electrode sheet so that the mass content of Si in the negative electrode active layer of the porous negative electrode sheet is different.

[0075] Comparative Examples 7 to 8

[0076] Comparative Examples 7 to 8 provide a secondary battery, and the preparation method thereof is substantially the same as that of Example 5, except that the puncture strength of the separator is different by adjusting the annealing temperature of the base film during the preparation of the separator.

[0077] Table 1 Examples 1 to 10 and Comparative Examples 1 to 8

[0078]

[0079]

[0080] T in Table 1 is the percentage of the pore depth of the pore to the thickness of the negative electrode active layer, %; P is the mass content of Si in the negative electrode active layer, %; C is the puncture strength of the diaphragm, gf; wherein the puncture strength of the diaphragm is measured with reference to standard GB / T36363-2018.

[0081] Performance Testing

[0082] 1) Battery K value: The secondary batteries in the embodiments and comparative examples are aged at high temperature (45°C) for 48 hours, and then aged at room temperature (25°C) for 48 hours, and then the open circuit voltage of the secondary battery is tested with a voltmeter, and the voltage at this time is recorded as OCV1; the secondary battery is then allowed to stand at room temperature (25°C) for 48 hours, and the open circuit voltage of the secondary battery is tested with a voltmeter after standing, and the voltage at this time is recorded as OCV2; according to K = (OCV1-OCV2) / 48, the unit is millivolt per hour (mV / h), the battery K value can be obtained.

[0083] 2) Energy density: The secondary batteries in the embodiments and comparative examples were subjected to charge and discharge cycle tests at 0.2C / 0.2C at 25°C and in the voltage range of 3.0 to 4.53V, and then the energy density of the secondary batteries was calculated according to the following formula: Energy density = discharge energy of the secondary battery at 0.2C (mAh)*1000 / volume of the secondary battery (mm 3 ); Volume of secondary battery (mm 3 ) = cell length (mm) * cell width (mm) * cell thickness (mm).

[0084] 3) Fast charging performance: The secondary batteries in the embodiments and comparative examples were subjected to charge and discharge cycle tests at 25°C and in the voltage range of 3.0 to 4.53V at rates of 1.0C, 1.2C, and 1.5C, respectively, for 50 cycles at each rate. After the test, the secondary batteries were disassembled and the anode plates were observed to see whether lithium was deposited. The fast charging performance of the secondary batteries was evaluated using the maximum rate corresponding to no lithium deposition.

[0085] Table 2 Performance of secondary batteries of various embodiments and comparative examples

[0086]

[0087]

[0088] According to the data in Table 2, the energy density of the secondary batteries in Examples 1 to 10 reaches 850 to 890Wh / L, and the fast charging performance reaches 1.0 to 1.5C. At the same time, the K values ​​are all below 0.08 (reaching 0.026 to 0.061), indicating that the secondary batteries of the present invention have a low K value while maintaining high energy density and good fast charging performance.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A secondary battery, characterized in that: Including a porous negative electrode sheet and a separator; The porous negative electrode sheet comprises a current collector and a negative electrode active layer disposed on at least one side of the current collector, wherein the negative electrode active layer comprises Si; The negative electrode active layer is provided with a plurality of holes along the thickness direction at intervals, and the openings of the holes are located on a side of the negative electrode active layer away from the current collector; The puncture strength of the separator is C gf; the mass content of Si in the negative electrode active layer is P%; the percentage of the pore depth to the thickness of the negative electrode active layer is T%; The secondary battery satisfies: 0.0025<T*P / C<2.78; Among them, 180≤C<250, 1<P≤6, 1<T≤30; Or, 250≤C<400, 1<P≤10, 1<T≤50; Or, 180≤C≤250, 6<P≤10, 1<T≤10.

2. The secondary battery according to claim 1, wherein: Among them, 180≤C≤200, 2≤P≤6, 10≤T≤30.

3. The secondary battery according to claim 1, wherein: Among them, 250≤C≤300, 6≤P≤10, 20≤T≤50.

4. The secondary battery according to claim 1, wherein: Among them, 180≤C≤250, 6<P≤10, 5≤T≤10.

5. The secondary battery according to claim 1, wherein: Satisfy at least one of the following: a. The thickness of the negative electrode active layer is 50 to 150 μm; b. The surface density of the negative electrode active layer is 6 to 11 mg / mm 2 ; c. The pore diameter is 1 to 60 μm; d. The hole spacing between the holes is 0.5 to 3 mm.

6. The secondary battery according to claim 1, wherein: The Si in the negative electrode active layer exists in the form of silicon particles, and the particle size D of the silicon particles is V50 6~15μm.

7. The secondary battery according to claim 1, wherein: The negative electrode active layer further comprises a conductive agent, a binder and a thickener.

8. The secondary battery according to claim 7, characterized in that The conductive agent includes at least one of acetylene black, carbon nanotubes, graphene, and VGCF; the binder includes at least one of styrene-butadiene rubber, CMC, and PAA; and the thickener includes at least one of sodium carboxymethyl cellulose and CMC-Li.

9. The secondary battery according to claim 1, wherein: The diaphragm includes a polyolefin base film and a coating disposed on at least one surface of the polyolefin base film; the coating includes at least one of PVDF and ceramic materials.

10. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 9, wherein the secondary battery is used as a power supply for the electrical device.

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