A secondary battery and electrical equipment

Abstract

This application discloses a secondary battery and an electrical device. The secondary battery includes a positive electrode, a separator, and a negative electrode arranged sequentially. The separator includes a substrate and an adhesive coating disposed on the surface of the substrate. The adhesive coating includes a first adhesive, the primary particles of which have an average particle size of 0.02–0.5 μm, and the secondary particles of which have an average particle size of 0.5–10 μm. The surface roughness of the positive electrode is 0.1–6.5 μm, and the surface roughness of the negative electrode is 0.5–12 μm. The adhesive coating surface of the separator in this application is microscopically uneven, exhibiting high roughness. Simultaneously, the positive and negative electrodes are also configured as interfaces with a certain degree of roughness (i.e., their surfaces are microscopically uneven). Therefore, when the separator is bonded to the electrodes (positive and negative electrodes), a strong anchoring is formed between the separator and the electrodes, improving the bonding strength and tightness between the adhesive coating and the electrodes, reducing the battery's internal resistance, and increasing cycle life.

Description

Technical Field

[0001] This application relates to the field of batteries, and specifically discloses a secondary battery and an electrical device. Background Technology

[0002] Currently, rechargeable batteries have become a key industry in the new energy sector, widely used not only in fields such as 3C digital products but also in the electric vehicle industry. The cycle life and safety of rechargeable batteries are crucial prerequisites for their acceptance.

[0003] In secondary batteries, especially lithium-ion batteries, lithium ions are transported between the positive electrode, negative electrode, and separator via the electrolyte during charging and discharging. It is crucial to ensure a good bonding interface between the separator and the electrodes. The bonding coating on the separator surface forms an adhesive bond with the electrodes, and the bond strength significantly impacts the entire lifespan of the lithium-ion battery. Insufficient bonding strength between the separator and the electrodes leads to a poor bonding interface, hindering lithium-ion transport and significantly affecting the battery's lifespan.

[0004] Furthermore, during use, especially in the actual operating conditions of lithium-ion batteries used in electric vehicles, lithium-ion batteries are continuously subjected to vibrations and potentially severe impacts under extreme conditions. This can easily lead to misalignment of the positive and negative electrodes, causing short circuits and safety accidents. The separator, as the physical barrier between the positive and negative electrodes, plays a crucial role in preventing electrode misalignment due to vibration. Strengthening the bond between the separator and the electrodes improves the safety performance of lithium-ion batteries under operating conditions. Summary of the Invention

[0005] This application provides a secondary battery and an electrical device, aiming to solve the technical problems of poor electrochemical performance and poor safety performance of existing secondary batteries, which are caused by poor bonding strength between the electrode and the separator, resulting in obstructed ion transport and easy misalignment of the electrode.

[0006] In view of this, this application provides a secondary battery, wherein a positive electrode, a separator, and a negative electrode are sequentially disposed thereon;

[0007] The diaphragm includes a substrate and an adhesive coating disposed on the surface of the substrate. The adhesive coating includes a first adhesive, wherein the average particle size of the primary particles of the first adhesive is 0.02–0.5 μm, and the average particle size of the secondary particles of the first adhesive is 0.5–10 μm. The surface roughness of the positive electrode is 0.1–6.5 μm, and the surface roughness of the negative electrode is 0.5–12 μm.

[0008] Furthermore, the positive electrode sheet includes a positive active material, the negative electrode sheet includes a negative active material, the particle Dv50 of the positive active material is 1-8 μm, and the particle Dv50 of the negative active material is 4-17 μm.

[0009] Furthermore, the ratio of the average particle size of the positive electrode active material particles Dv50 to the average particle size of the primary particles of the first binder, and the ratio of the average particle size of the negative electrode active material particles Dv50 to the average particle size of the primary particles of the first binder are both ≥10; the ratio of the average particle size of the positive electrode active material particles Dv50 to the average particle size of the secondary particles of the first binder, and the ratio of the average particle size of the negative electrode active material particles Dv50 to the average particle size of the secondary particles of the first binder are both ≥0.5.

[0010] Furthermore, the adhesive coating further includes a second adhesive, wherein the first adhesive includes at least one of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), a copolymer derivative of vinylidene fluoride, and a copolymer derivative of tetrafluoroethylene; and the second adhesive includes at least one of polyethylene glycol, polymethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyacrylic acid, polyvinyl acetate, acrylate multi-component copolymers, styrene-butadiene latex, styrene-acrylic latex, polyvinyl alcohol, and sodium carboxymethyl cellulose.

[0011] Furthermore, the negative electrode sheet includes a negative electrode binder, which contains at least one group selected from -COOH, -OH, C=O, C=C, and -NH2.

[0012] Furthermore, the thickness of the adhesive coating is 0.5–10 μm, and the areal density of the adhesive coating is 0.2–1.5 g / m³. 2 .

[0013] Furthermore, the substrate includes one or more of polyethylene, polypropylene, PET nonwoven fabric, PVDF, and polyimide porous membrane.

[0014] Furthermore, the diaphragm also includes an inorganic material layer disposed between the substrate and the adhesive coating. The inorganic material layer contains inorganic materials, including at least one selected from alumina, boehmite, silicon dioxide, calcium sulfate, magnesium sulfate, and magnesium hydroxide.

[0015] Furthermore, the first adhesive is embedded to a depth of 0.1–2 μm into the surface of the positive electrode and to a depth of 0.5–5 μm into the surface of the negative electrode.

[0016] This application also provides an electrical device that includes the aforementioned secondary battery, which is used as a power supply for the electrical device.

[0017] The secondary battery and electrical device provided in this application have a high roughness due to the fact that the average particle size of the primary particles of the first binder in the separator is 0.02–0.5 μm, and the average particle size of the secondary particles is 0.5–10 μm. This results in a microscopically uneven surface with high roughness for the adhesive coating of the separator. Simultaneously, the positive and negative electrode plates are also designed with a certain degree of surface roughness (i.e., their surfaces are microscopically uneven). Therefore, when the separator is bonded to the electrode plates (positive and negative electrode plates), the first binder particles of the separator can embed into the electrode plates. The bonding coating forms a strong anchor with the electrode, thereby improving the bonding strength between the bonding coating and the electrode. It can also further improve the tightness between the electrode and the separator. Therefore, during the charge and discharge cycle of the secondary battery, the lithium ion transport rate between the positive and negative electrode is faster, reducing the internal resistance of the secondary battery and improving the cycle performance of the secondary battery. In addition, due to the improved bonding strength, the positive and negative electrode can be prevented from misaligning under strong vibration, avoiding short circuits in the secondary battery and improving safety performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a partial structure of a secondary battery in one embodiment.

[0019] Figure 2 This is a schematic diagram of the electrode interface and the adhesive coating interface structure in one embodiment. Detailed Implementation

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0021] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0022] In one embodiment, this application provides a secondary battery, which includes a positive electrode, a separator, and a negative electrode arranged sequentially.

[0023] The separator includes a substrate and an adhesive coating disposed on the surface of the substrate. The adhesive coating includes a first adhesive, wherein the primary particles of the first adhesive have an average particle size of 0.02 to 0.5 μm, and the secondary particles of the first adhesive have an average particle size of 0.5 to 10 μm. The adhesive coating is used to bond the positive electrode and the negative electrode to both sides of the separator.

[0024] The surface roughness of the positive electrode is 0.1–6.5 μm; the surface roughness of the negative electrode is 0.5–12 μm.

[0025] In this embodiment, the positive and negative electrode sheets are bonded together by an adhesive coating on the surface of the separator, with the separator serving both as a separator and a bond. The primary particles of the first adhesive in the separator have an average particle size of 0.02–0.5 μm, and the secondary particles have an average particle size of 0.5–10 μm, resulting in a microscopically uneven surface on the adhesive coating of the separator, giving it a suitable surface roughness of 0.2–0.9 μm. Simultaneously, the positive and negative electrode sheets are also configured as interfaces with a certain degree of roughness (i.e., their surfaces are microscopically uneven). Specifically, the average particle size of the primary particles of the first adhesive in this application can be any one of 0.02μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, and 0.5μm, or a range between any two values. The average particle size of the secondary particles of the first adhesive can be any one of 0.5μm, 1μm, 2μm, 5μm, 8μm, and 10μm, or a range between any two values. With the above configuration, when the separator is bonded to the electrodes (positive electrode and negative electrode), the first adhesive particles of the separator can be embedded into the electrodes, forming a strong anchoring between the adhesive coating and the electrodes. This improves the bonding strength between the adhesive coating and the electrodes, and further enhances the tightness between the electrodes and the separator. Therefore, during the charge-discharge cycle of the secondary battery, the lithium ion transport rate between the positive and negative electrodes is faster, reducing the internal resistance of the secondary battery and improving its cycle performance. Furthermore, due to the increased bonding strength, misalignment of the positive and negative electrodes can be prevented under strong vibration, avoiding short circuits and improving safety. In this embodiment, the positive electrode contains a positive active material, which may include one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium iron phosphate. The negative electrode contains a negative active material, which may include one or more of graphite, graphite / silicon composite material, and lithium titanate. To obtain electrodes with different roughnesses, the roughness of the electrode can be controlled by changing the particle size of the active material (positive or negative electrode active material), or by controlling the rolling pressure on the electrode during the rolling process. Alternatively, the particle size of the active material and the rolling pressure can be adjusted simultaneously to control the roughness of the electrode.

[0026] The testing method for the surface roughness of the electrode (positive or negative electrode) and the separator is as follows: The roughness used in this application is the arithmetic mean roughness Sa. Specifically, the electrode (or separator) surface is first 3D scanned using a Keyence VHX-7000 scanner, with a scanning area of ​​5mm*5mm. Then, the surface is calculated using computer software, and multiple parallel samples are continuously tested and calculated. The average value of the multiple parallel samples is the electrode roughness. The testing method for the average particle size of the primary particles of the first adhesive in the bonding coating is as follows: The bonding coating on the separator surface is photographed using an SEM device, and the average value of multiple primary particles (the longest dimension of a sphere or approximately a sphere) is calculated using a scale as the average particle size of the primary particles. The testing method for the average particle size of the secondary particles of the first adhesive in the bonding coating is as follows: The coating on the separator surface is photographed using an SEM device, and the average value of multiple secondary particles (the longest dimension of a sphere or approximately a sphere) is calculated using a scale as the average particle size of the secondary particles.

[0027] To better embed the first binder particles of the adhesive coating into the gaps on the electrode surface, achieving higher anchoring force and tightness, in another embodiment, the positive electrode includes a positive active material, and the negative electrode includes a negative active material. The particle size distribution (Dv50) of the positive active material is 1–8 μm, and the particle size distribution (Dv50) of the negative active material is 4–17 μm. The Dv50 of the positive and negative active materials being within the aforementioned ranges can complement the average particle size of the primary and secondary particles of the first binder, thereby enhancing the anchoring force and improving the bonding strength.

[0028] To further enhance the anchoring force and optimize the particle size selection of the primary and secondary particles of the positive electrode active material, negative electrode active particles, and the first binder, in another embodiment, the ratio of the average particle size of the positive electrode active material particles Dv50 to the average particle size of the primary particles of the first binder, and the ratio of the average particle size of the negative electrode active material particles Dv50 to the average particle size of the primary particles of the first binder are both ≥10; the ratio of the average particle size of the positive electrode active material particles Dv50 to the average particle size of the secondary particles of the first binder, and the ratio of the average particle size of the negative electrode active material particles Dv50 to the average particle size of the secondary particles of the first binder are both ≥0.5.

[0029] In some embodiments, the first adhesive is embedded to a depth of 0.1–2 μm into the surface of the positive electrode and to a depth of 0.5–5 μm into the surface of the negative electrode. The adhesion force between the separator and the positive electrode is 1–15 N / m, and the adhesion force between the separator and the negative electrode is 0.5–6 N / m.

[0030] The testing procedure for the depth of the first adhesive embedded in the electrode surface (positive electrode surface or negative electrode surface) is as follows: Take out the positive electrode + separator + negative electrode unit from the discharged battery. During sampling, ensure that the separator and the electrode remain bonded and not loose. Cut the positive electrode + separator + negative electrode unit with argon ion cross-section. Take SEM images of the cut unit cross-section. Record the depth of the adhesive coating embedded in the electrode with a ruler. Collect 15 data points and take the average value as the first adhesive embedding depth value.

[0031] In some embodiments, the adhesive coating further includes a second adhesive. The first adhesive includes at least one selected from polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), copolymer derivatives of vinylidene fluoride, and copolymer derivatives of tetrafluoroethylene. The second adhesive includes one or more selected from polyethylene glycol, polymethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyacrylic acid, polyvinyl acetate, acrylate multi-component copolymers, styrene-butadiene latex, styrene-acrylic latex, polyvinyl alcohol, and sodium carboxymethyl cellulose. In this embodiment, the first and second adhesives are combined to form the adhesive coating, further improving the adhesion performance of the adhesive coating and thus increasing the adhesion strength with the electrode.

[0032] In some embodiments, the positive electrode sheet includes a positive electrode binder, and the negative electrode sheet includes a negative electrode binder, wherein the negative electrode binder contains at least one group selected from -COOH, -OH, C=O, C=C, and -NH2. For example, the negative electrode binder includes one or more of polyurethane, polymethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyacrylic acid, polyvinyl acetate, acrylate copolymers, styrene-butadiene latex, styrene-acrylic latex, polyvinyl alcohol, and sodium carboxymethyl cellulose. The positive electrode binder includes polyvinylidene fluoride or a copolymer derivative of polyvinylidene fluoride.

[0033] In another embodiment, the first or second adhesive composition of the adhesive coating on the separator facing the positive electrode and the adhesive coating on the separator facing the negative electrode can be the same or different. To improve the bonding strength between the separator and the electrode, the adhesive in the adhesive coating can form hydrogen bonds with the positive and negative electrode adhesives at the interface. In this embodiment, the positive and negative electrode adhesives are used in conjunction with the adhesive in the separator adhesive coating, so that hydrogen bonds are formed between the separator and the electrode due to the interaction of the adhesives, effectively improving the bonding strength between the electrode and the separator.

[0034] Considering cost and adhesion strength, in some embodiments, the adhesive coating covers 5%-80% of the substrate surface, preferably 30%-60%. In some embodiments, the thickness of the adhesive coating is 0.5-10 μm, and the areal density of the adhesive coating is 0.2-1.5 g / m³. 2 The aforementioned range of adhesive coating thickness and areal density allows for both low battery internal resistance and effective adhesion.

[0035] In some embodiments, the substrate of this application includes one or more of polyethylene, polypropylene, PET nonwoven fabric, PVDF, and polyimide porous membrane. The substrate composed of the above materials has the advantages of wide availability and good film-forming effect. To improve the thermal stability and mechanical strength of the diaphragm, in another embodiment, the diaphragm further includes an inorganic material layer disposed between the substrate and the adhesive coating. The inorganic material layer includes inorganic materials, including at least one of alumina, boehmite, silica, calcium sulfate, magnesium sulfate, and magnesium hydroxide.

[0036] In order to enable lithium ions to shuttle quickly through the separator during the charge-discharge cycle of the secondary battery and reduce the internal resistance of the separator, in some embodiments, the thickness of the substrate is 4 to 20 μm and the porosity of the substrate is 30% to 70%.

[0037] On the other hand, this application also provides an electrical device that includes a secondary battery for use as a power source for the device. The electrical device includes at least electric vehicles, mobile phones, tablets, VR devices, and smartwatches.

[0038] The secondary battery provided in this application uses a matching device for the separator and the electrode, which can improve the bonding strength between the separator and the electrode, prevent misalignment caused by vibration, and prevent short circuits in the battery. In addition, it can also improve the tightness between the separator and the electrode, reduce the DC internal resistance of the secondary battery, and improve cycle life.

[0039] To clearly understand the technical solution of this application, the following detailed description of this application is provided in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0040] Example 1

[0041] 1) Preparation of the positive electrode: LiNi with a mass ratio of 96:2:2 0.6 Co 0.2 Mn 0.2 After O2 (Dv50 is 4μm), PVDF and SP are mixed evenly, they are placed in NMP solvent and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, and after drying, rolling and slitting, a positive electrode sheet with a surface roughness of 2.8μm is obtained.

[0042] 2) Preparation of negative electrode sheet: Graphite (Dv50 is 6μm), sodium carboxymethyl cellulose, polyethylene glycol and SP are mixed evenly in a mass ratio of 94:2:1:3 and then stirred evenly in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of copper foil, and after drying, rolling and cutting, a negative electrode sheet with a surface roughness of 6μm is obtained.

[0043] 3) Preparation of the diaphragm: PVDF-HFP (with an average primary particle size of 0.2 μm and an average secondary particle size of 4 μm) and polyethylene glycol were mixed uniformly at a mass ratio of 1:1 to obtain a coating slurry. The slurry was then coated onto both sides of a 13 μm thick PE substrate containing an inorganic material layer (for 9 μm PE substrates, 2 μm of alumina was coated on each side). The coating density was 1.0 g / m³. 2 The coating thickness on one side is 2μm.

[0044] 4) Preparation of secondary batteries: The positive electrode, negative electrode, and separator obtained above are wound into a core, which is then further shaped, tab welded, fitted into a square aluminum shell, baked, injected with electrolyte, packaged, left to stand, and formed to obtain the finished secondary battery. The adhesive in the separator is embedded to a depth of 0.1–2 μm into the surface of the positive electrode and 0.5–5 μm into the surface of the negative electrode.

[0045] Example 2

[0046] Similar to Example 1, except that the average particle size of the primary PVDF-HFP particles in step 3 is 0.02 μm.

[0047] Example 3

[0048] Similar to Example 1, except that the average particle size of the primary PVDF-HFP particles in step 3 is 0.1 μm.

[0049] Example 4

[0050] Similar to Example 1, except that the average particle size of the primary PVDF-HFP particles in step 3 is 0.5 μm.

[0051] Example 5

[0052] Similar to Example 1, except that the average particle size of the secondary particles of PVDF-HFP in step 3 is 0.8 μm.

[0053] Example 6

[0054] Similar to Example 1, except that the average particle size of the secondary particles of PVDF-HFP in step 3 is 3 μm.

[0055] Example 7

[0056] Similar to Example 1, except that the average particle size of the secondary particles of PVDF-HFP in step 3 is 8 μm.

[0057] Example 8

[0058] Similar to Example 1, except that the average particle size of the secondary particles of PVDF-HFP in step 3 is 10 μm.

[0059] Example 9

[0060] Similar to Example 1, except that the average particle size of the primary particles in PVDF-HFP is 0.15 μm, and the average particle size of the secondary particles is 2.5 μm, and the LiNi... 0.6 Co 0.2 Mn 0.2 The Dv50 of O2 is 2μm, the Dv50 of graphite is 5μm, the surface roughness of the positive electrode is 0.8μm, and the surface roughness of the negative electrode is 2.9μm.

[0061] Example 10

[0062] Similar to Example 1, except that the average particle size of the primary particles in PVDF-HFP is 0.08 μm, and the average particle size of the secondary particles is 1 μm, and the LiNi... 0.6 Co 0.2 Mn 0.2 The Dv50 of O2 is 1 μm, the Dv50 of graphite is 4 μm, the surface roughness of the positive electrode is 0.3 μm, and the surface roughness of the negative electrode is 3.2 μm.

[0063] Example 11

[0064] Similar to Example 1, except that the average particle size of the primary particles in PVDF-HFP is 0.3 μm, and the average particle size of the secondary particles is 6 μm, and the LiNi... 0.6 Co 0.2 Mn 0.2 The Dv50 of O2 is 8 μm, the Dv50 of graphite is 17 μm, the surface roughness of the positive electrode is 6.5 μm, and the surface roughness of the negative electrode is 10.2 μm.

[0065] Example 12

[0066] Similar to Example 1, except that the average particle size of the primary particles in PVDF-HFP is 0.18 μm, and the average particle size of the secondary particles is 7 μm, while that of LiNi is... 0.6 Co 0.2 Mn 0.2The Dv50 of O2 is 5 μm, the Dv50 of graphite is 14 μm, the surface roughness of the positive electrode is 4.2 μm, and the surface roughness of the negative electrode is 8.5 μm.

[0067] Examples 13 to 16

[0068] Similar to Example 1, except that positive electrode sheets with different surface roughness are obtained by adjusting the rolling parameters of the positive electrode sheet.

[0069] Examples 17-20

[0070] Similar to Example 1, except that negative electrode sheets with different surface roughness are obtained by adjusting the rolling parameters of the negative electrode sheet.

[0071] Example 21

[0072] Similar to Example 1, except that the total coating thickness of the coating slurry is 0.5 μm.

[0073] Example 22

[0074] Similar to Example 1, except that the total coating thickness of the coating slurry is 3 μm.

[0075] Example 23

[0076] Similar to Example 1, except that the total coating thickness of the coating slurry is 6 μm.

[0077] Example 24

[0078] Similar to Example 1, except that the total coating thickness of the coating slurry is 10 μm.

[0079] Example 25

[0080] Similar to Example 1, except that the total coating density of the coating slurry is 0.2 g / m³. 2 .

[0081] Example 26

[0082] Similar to Example 1, except that the total coating density of the coating slurry is 1.5 g / m³. 2 .

[0083] Example 27

[0084] Similar to Example 1, except that PVdF-HFP is replaced with PTFE (polytetrafluoroethylene).

[0085] Example 28

[0086] Similar to Example 1, except that PVdF-HFP is replaced with PVdF (polyvinylidene fluoride).

[0087] Example 29

[0088] Similar to Example 1, except that polyethylene glycol is replaced with polyacrylate.

[0089] Example 30

[0090] Similar to Example 1, except that polyethylene glycol is replaced with polyacrylic acid.

[0091] Example 31

[0092] Similar to Example 1, except that polyethylene glycol is not added in step 3.

[0093] Comparative Example 1

[0094] Similar to Example 1, except that the average particle size of the PVDF-HPF secondary particles is 0.1 μm, and the LiNi... 0.6 Co 0.2 Mn 0.2 The Dv50 of O2 is 0.1 μm, the Dv50 of graphite is 2 μm, the surface roughness of the positive electrode is 0.1 μm, and the surface roughness of the negative electrode is 0.8 μm.

[0095] Comparative Example 2

[0096] Similar to Comparative Example 1, except that the coating slurry does not contain polyethylene glycol.

[0097] Comparative Example 3

[0098] Similar to Example 1, except that in step 3, there are no secondary PVDF-HFP particles in the coating slurry (the primary particles are prevented from agglomerating by introducing electrostatics), and there is no polyethylene glycol.

[0099] The relevant parameters of the separators, positive electrode plates, and negative electrode plates prepared in the above embodiments and comparative examples are recorded in Table 1. The peel strength between the separator and the electrode plates (positive electrode plate and negative electrode plate), as well as the DC resistance and cycle life of the secondary battery, were tested, and the relevant data are recorded in Table 2.

[0100] The test method is as follows: 1) Separator and electrode peel strength test: After discharging the battery to the cutoff voltage of 3.2V, the battery is disassembled to obtain the bonding unit of separator / positive electrode / separator / negative electrode. The bonding unit is cut into 50mm wide strips. After the electrolyte on the surface of the bonding unit evaporates, the separator and electrode are subjected to a 180° peel tensile test using a universal tensile testing machine. The tensile speed is 50mm / min and the tensile stroke is 100mm. The force detected when the positive electrode (negative electrode) is peeled off is the peel strength. The bonding strength values ​​of separator and positive electrode, and separator and negative electrode are obtained in this way.

[0101] 2) Battery DCR test: Under 25℃ conditions, the battery is charged and discharged three times at a rate of 1C / 1C. The average of the three capacities is taken as the actual capacity C0 of the battery. The battery is then adjusted to 50% SOC state according to the actual capacity C0. The battery is discharged at a current of 4C for 10s, and the voltage difference before and after discharge is recorded. DCR is defined as the ratio of the voltage difference before and after discharge to the current, i.e., DCR=ΔU / I.

[0102] 3) Battery cycle life test: Under conditions of 25℃ and 45℃ respectively, the battery is cycled to 80% capacity retention at a charge / discharge current of 1C / 1C from 0 to 100% SOC, and the number of cycles at this time is recorded.

[0103] Table 1. Relevant parameters of the separators, positive electrode sheets, and negative electrode sheets prepared in each embodiment and comparative example.

[0104]

[0105]

[0106] Table 2 shows the peel strength between the separator and the electrode (positive electrode and negative electrode) prepared in each embodiment and comparative example, as well as the DC resistance and cycle life of the secondary battery.

[0107]

[0108]

[0109] As can be seen from the data in the table above, this application improves the bonding strength between the separator and the electrode by matching the particle size of the adhesive particles in the separator bonding coating with the surface roughness of the positive and negative electrode sheets. This is beneficial for reducing the DC internal resistance of the battery and improving the cycle life of the battery.

[0110] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery characterized by comprising: The positive electrode sheet, the separator, and the negative electrode sheet are sequentially arranged. The separator comprises a substrate and a bonding coating layer arranged on the surface of the substrate, and the bonding coating layer comprises a first binder, the average particle size of primary particles of the first binder is 0.02-0.5 μm, and the average particle size of secondary particles of the first binder is 0.5-10 μm. The surface roughness of the positive electrode sheet is 0.1-6.5 μm, and the surface roughness of the negative electrode sheet is 0.5-12 μm. The positive electrode sheet comprises a positive electrode active material, and the negative electrode sheet comprises a negative electrode active material, the particle Dv50 of the positive electrode active material is 1-8 μm, and the particle Dv50 of the negative electrode active material is 4-17 μm. The ratio of the particle Dv50 of the positive electrode active material to the average particle size of the primary particles of the first binder and the ratio of the particle Dv50 of the negative electrode active material to the average particle size of the primary particles of the first binder are both ≥10, and the ratio of the particle Dv50 of the positive electrode active material to the average particle size of the secondary particles of the first binder and the ratio of the particle Dv50 of the negative electrode active material to the average particle size of the secondary particles of the first binder are both ≥0.

5.

2. The secondary battery according to claim 1, characterized by The bonding coating layer further comprises a second binder, the first binder comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, a copolymer derivative of polyvinylidene fluoride, and a copolymer derivative of polytetrafluoroethylene, and the second binder comprises at least one of polyethylene glycol, polymethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyacrylic acid, polyvinyl acetate, an acrylate-based multi-copolymer, butyl benzene latex, benzene propyl latex, polyvinyl alcohol, and sodium carboxymethyl cellulose.

3. The secondary battery according to claim 2, characterized by The negative electrode sheet comprises a negative electrode binder, and the negative electrode binder contains at least one of -COOH, -OH, C=O, C=C, and -NH2.

4. The secondary battery according to claim 1, characterized by The thickness of the adhesive coating is 0.5 to 10 μm, and the area density of the adhesive coating is 0.2 to 1.5 g / m 2 .

5. The secondary battery according to any one of claims 1 to 4, characterized by, The substrate comprises one or more of polyethylene, polypropylene, PET non-woven fabric, PVDF, and polyimide porous membrane.

6. The secondary battery according to claim 5, characterized by The separator further comprises an inorganic material layer arranged between the substrate and the bonding coating layer, and the inorganic material layer contains an inorganic material, and the inorganic material comprises at least one of alumina, boehmite, silicon dioxide, calcium sulfate, magnesium sulfate, and magnesium hydroxide.

7. The secondary battery according to claim 1, characterized by The first binder is embedded in the surface of the positive electrode sheet to a depth of 0.1-2 μm and in the surface of the negative electrode sheet to a depth of 0.5-5 μm.

8. An electric device, characterized by The secondary battery comprises the secondary battery of any one of claims 1-7, and the secondary battery is used as a power supply for the power consumption device.

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