Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. A separator in the secondary battery comprises a base film layer. At least one surface of the base film layer is provided with a bonding layer, the bonding layer is composed of multiple bonding points, and the thickness of the bonding layer is 0.5 μm-5 μm. In the bonding layer, the longest diameter of a bonding point is 10 μm-400 μm, and the distance between adjacent bonding points is 100 μm-400 μm. An electrode sheet of the secondary battery comprises a current collector. At least one surface of the current collector is provided with an active layer, a partial region of a surface of the active layer is recessed inwards to form multiple scoring grooves, and the scoring grooves are arranged in the length direction of the electrode sheet. The width of each scoring groove is D1 mm, where 0.2≤D1≤1.5. The separator and the electrode sheet have good electrolyte transport capacity and storage capacity, and can enhance the cycle performance and fast charging performance of the secondary battery.

Description

Secondary batteries and electronic devices Technical Field

[0001] This application relates to the field of energy storage, and in particular to a secondary battery and electronic device. Background Technology

[0002] As the energy density of rechargeable batteries continues to increase, the requirements for the compaction density and coating density of battery electrodes are becoming increasingly stringent. This makes electrolyte transport within the electrodes an obstacle to improving fast-charging performance and long-cycle performance. The electrolyte is difficult to fully penetrate the inner layer of the electrode, and the electrode's electrolyte storage capacity is also reduced. This leads to the formation of a concentration gradient of lithium ions inside the rechargeable battery during use, resulting in concentration polarization and deterioration of the battery's cycle performance and fast-charging performance. Summary of the Invention

[0003] To address the aforementioned issues, this application provides a secondary battery and electronic device comprising a separator and electrodes. The separator and electrodes in the secondary battery of this application have excellent electrolyte transport and storage capabilities, which can enhance the cycle performance and fast charging performance of the secondary battery.

[0004] In a first aspect, this application provides a secondary battery comprising a separator and an electrode. The separator includes a base film layer, and at least one surface of the base film layer is provided with an adhesive layer. The adhesive layer is composed of multiple adhesive points, and the thickness of the adhesive layer is 0.5 μm to 5 μm. In the adhesive layer, the longest diameter of the adhesive point is 10 μm to 400 μm, and the distance between adjacent adhesive points is 100 μm to 400 μm. The secondary battery also includes an electrode comprising a current collector. At least one surface of the current collector is provided with an active layer. A portion of the surface of the active layer is recessed inward to form a plurality of grooves, which are arranged along the length direction of the electrode. The width of the grooves is D1 mm, and 0.2 ≤ D1 ≤ 1.5 mm.

[0005] Based on the separator of this application, the inventors discovered that because the adhesive layer in the separator is composed of adhesive points of 10μm to 400μm, and the distance between adjacent adhesive points is 100μm to 400μm, electrolyte transport channels can be formed in the adhesive layer. Furthermore, the adhesive points not only have good adhesion but also good electrolyte storage capacity. When at least one surface of the current collector of the electrode in the secondary battery is provided with an active layer, and a portion of the surface of the active layer is recessed inward to form several etched grooves, the etched grooves are arranged along the length direction of the electrode; the width of the etched grooves is D1mm, 0.2≤D1≤1.5. When the electrode meets these conditions, the fit between the electrode and the separator can improve the battery performance under high-current, high-speed charging and improve lithium plating. Therefore, the secondary battery of this application has good electrolyte transport and energy storage capacity, and the cycle performance and fast-charging performance of the secondary battery can be improved.

[0006] In one embodiment of this application, the longest diameter of the bonding point is 10 μm to 200 μm; and / or, the distance between adjacent bonding points is 150 μm to 300 μm.

[0007] Based on the above implementation scheme, the diaphragm has a stronger electrolyte transport capacity and a stronger electrolyte storage performance.

[0008] In one embodiment of this application, the thickness of the adhesive layer is 1 μm to 3 μm.

[0009] Based on the above implementation scheme, the separator that meets the requirements of this application can further improve the cycle performance and fast charging performance of the secondary battery.

[0010] In one embodiment of this application, the spacing between adjacent scribed grooves is D2mm, where 1≤D2≤3. This improves the fast-charging performance of the secondary battery and reduces lithium plating.

[0011] In one embodiment of this application, the adhesive layer comprises an aqueous polymer, wherein the monomers of the aqueous polymer include at least two selected from butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene, or vinylidene fluoride.

[0012] Based on the above implementation scheme, the aqueous polymer itself has good adhesive properties, and additional adhesives can be grafted onto the main chain and side chains of the aqueous polymer, which is beneficial to improving the adhesion of the adhesive layer.

[0013] In one embodiment of this application, the electrode is a negative electrode. This can improve the wetting of the negative electrode with the electrolyte, thereby increasing the electrolyte storage capacity of the negative electrode, which is beneficial to improving the cycle performance and fast charging performance of the secondary battery.

[0014] Based on the aforementioned electrode, the etched grooves serve both to guide the electrolyte flow along the grooves and to retain the electrolyte. Therefore, the electrode of this application possesses excellent electrolyte transport and storage capabilities, which is beneficial for improving the cycle performance and fast-charging performance of the secondary battery.

[0015] In one embodiment of this application, the thickness of the active layer is H1 μm, the depth of the scribe line groove is H2 μm, and 0.1 ≤ H2 / H1 ≤ 0.3.

[0016] Based on the above implementation scheme, when the depth of the groove and the thickness of the active layer conform to the above relationship, the electrode not only has a good liquid storage capacity, but also is not prone to lithium plating.

[0017] In one embodiment of this application, the projected area of ​​all the grooves on the surface of the current collector is 10% to 20% of the surface area of ​​the current collector.

[0018] Based on the above implementation scheme, the density of the grooves is moderate, and when the electrode is used in a secondary battery, the energy density of the secondary battery is not easily lost.

[0019] In one embodiment of this application, the secondary battery includes an electrolyte, a separator, and electrodes, with the separator and electrodes alternately stacked; or the secondary battery includes an electrolyte, a separator, and the aforementioned electrodes, with the separator and electrodes alternately stacked; or the secondary battery includes an electrolyte, the aforementioned separator, and electrodes, with the separator and electrodes alternately stacked. Therefore, the secondary battery of this application has good cycle performance and fast charging performance.

[0020] In one embodiment of this application, the area between adjacent grooves is a bonding area, and the bonding point is located in the bonding area.

[0021] Based on the above implementation scheme, the bonding points in the separator will not fall into the groove, so the groove can effectively carry out the function of transporting and storing electrolyte, which is beneficial to further improve the cycle performance and fast charging performance of the secondary battery.

[0022] Secondly, this application provides an electronic device that includes the aforementioned secondary battery.

[0023] Based on the above implementation scheme, the secondary battery has better cycle performance and fast charging performance.

[0024] This application provides a secondary battery comprising a separator and electrodes. The separator includes a base film layer, and at least one surface of the base film layer is provided with an adhesive layer. The adhesive layer consists of multiple adhesive points, and its thickness is 0.5 μm to 5 μm. The longest diameter of each adhesive point in the adhesive layer is 10 μm to 400 μm, and the distance between adjacent adhesive points is 100 μm to 400 μm. Because the adhesive layer in the separator of this secondary battery has transport channels, the separator has good performance in transporting and storing electrolyte. The electrodes include a current collector, and at least one surface of the current collector is provided with an active layer. A portion of the surface of the active layer is recessed inward to form several grooves, which are arranged along the length of the electrode. The width of each groove is D1 mm, 0.2 ≤ D1 ≤ 1.5, and the spacing between adjacent grooves is D2 mm, 1 ≤ D2 ≤ 3. Because the electrodes of this secondary battery contain grooves, the electrodes have good performance in transporting and storing electrolyte. This application can improve the cycle performance and fast charging performance of secondary batteries. Attached Figure Description

[0025] Figure 1 is a demonstration diagram of electrolyte transport rate testing according to an embodiment of this application;

[0026] Figure 2 is a CCD image of the adhesive layer in Embodiment 1-1 of this application;

[0027] Figure 3 shows the positive electrode in Embodiment 1-1 of this application. Embodiments of the present invention

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0030] Currently, to improve the energy density of secondary batteries to meet usage demands, the compaction density of the electrode sheets is continuously increased. However, this hinders electrolyte penetration, thus affecting the cycle performance and fast-charging performance of the secondary battery. Based on this, this application provides a separator, electrode sheets, and a secondary battery. The separator and electrode sheets of this application have excellent electrolyte transport and storage capabilities, and when used in secondary batteries, they can improve the cycle performance and fast-charging performance of the secondary battery. The technical solution of this application is described in detail below.

[0031] In a first aspect, this application provides a secondary battery comprising a separator, which includes a base film layer. At least one surface of the base film layer is provided with an adhesive layer, which is composed of multiple adhesive points. The thickness of the adhesive layer is 0.5 μm to 5 μm, preferably 1 μm to 3 μm, for example, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., or within a range of any two of the above values. In the adhesive layer, the longest diameter of each adhesive point is 10 μm to 400 mm. The diameter of the bonding points is μm, preferably 10μm to 200μm, for example, 10μm, 50μm, 100μm, 200μm, 300μm, 400μm, etc., or within any two of the above values. The distance between adjacent bonding points is 100μm to 400μm, preferably 150μm to 300μm, for example, 100μm, 120μm, 150μm, 250μm, 300μm, 350μm, 400μm, etc., or within any two of the above values. This application does not impose any particular limitation on the shape of the bonding points, as long as the purpose of this application is achieved.

[0032] It should be noted that, in this application, the "longest diameter of the bonding point" refers to the distance between the two points furthest apart in the projected shape of the bonding point within the base film layer. Specifically, when the projected shape of the bonding point is circular, the "longest diameter" refers to the diameter of the circle; when the projected shape is annular, the "longest diameter" refers to the radius of the great circle of the annulus; when the projected shape is elliptical, the "longest diameter" refers to the length of the major axis of the ellipse; and when the projected shape is square or rectangular, the "longest diameter" refers to the length of the diagonal of the square or rectangle. Furthermore, the "distance between adjacent bonding points" in this application is also relative to the projected shape, referring to the distance between the projections of two adjacent bonding points, which is the distance between the closest parts of the two projections.

[0033] It should also be noted that, in this application, "at least one surface of the base film layer is provided with an adhesive layer" means that the adhesive layer can be provided on one surface in the thickness direction of the base film layer, or on two surfaces in the thickness direction of the base film layer. This application does not have any particular limitations in this regard, as long as the purpose of this application can be achieved.

[0034] The inventors discovered that because the adhesive layer in the separator is composed of adhesive points of 10μm to 400μm, and the distance between adjacent adhesive points is 100μm to 400μm, electrolyte transport channels can be formed in the adhesive layer. Moreover, the adhesive points not only have good adhesion ability but also good electrolyte storage capacity. Therefore, the separator of this application has good electrolyte transport and storage capacity, and when used in secondary batteries, it can enhance the cycle performance and fast charging performance of secondary batteries.

[0035] In some embodiments of this application, to improve the adhesion performance of the adhesive layer, the adhesive layer includes an aqueous polymer. The monomers of the aqueous polymer include at least two selected from butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene, or vinylidene fluoride. Additional adhesives can be grafted onto the main chain and branches of the aqueous polymer, which is beneficial for improving the adhesion strength of the adhesive layer. Furthermore, the inventors tested the swelling properties of the aqueous polymer and found that when the equivalent particle size of the adhesive microspheres formed by the aqueous polymer is in the range of 0.2 μm to 3 μm, the glass transition temperature of the film made using the adhesive microspheres is in the range of 40°C to 55°C. Moreover, when the film is immersed in an electrolyte environment and stored at 60°C for 6 hours and 24 hours, the swelling rates are in the ranges of 40% to 60% and 60% to 80%, respectively. This indicates that the aqueous polymer has good adhesion performance and low volume change after electrolyte storage, thus making it less likely to clog the electrolyte transport channels in the membrane.

[0036] This application does not impose any particular restrictions on the material and thickness of the base membrane layer in the diaphragm, as long as the purpose of this application can be achieved. For example, the material of the diaphragm includes, but is not limited to, non-woven fabric, woven fabric, microporous membrane, etc.

[0037] In addition, this application generally uses a coating method to prepare the adhesive layer in the diaphragm, and the coating equipment is selected from gravure, microgravure, screen printing, and extrusion coating. To facilitate control over the number, spacing, and size of the adhesive points, as an example, a screen printing coating method is used to prepare the adhesive layer in a specific embodiment of this application. When using this method, the number, spacing, and size of the adhesive points in the adhesive layer can be changed by changing the screen printing plate with different mesh sizes.

[0038] Secondly, the secondary battery of this application includes an electrode sheet, which includes a current collector. At least one surface of the current collector is provided with an active layer. A portion of the surface of the active layer is recessed inward to form a plurality of grooves. The grooves are arranged along the length direction of the electrode sheet. The width of the grooves is D1mm, 0.2≤D1≤1.5, and the spacing between adjacent grooves is D2mm, 1≤D2≤3.

[0039] It should be noted that the aforementioned electrode can be either a positive or negative electrode. When it is a positive electrode, the current collector is a positive current collector, and the active layer is a positive active layer; when it is a negative electrode, the current collector is a negative current collector, and the active layer is a negative active layer. However, in actual operation, the positive electrode is generally provided with etched grooves. For ease of description, this application will not distinguish between positive and negative electrodes.

[0040] It should also be noted that, in this application, "at least one surface of the current collector is provided with an active layer" means that the active layer can be provided on one surface in the thickness direction of the current collector, or it can be provided on two surfaces in the thickness direction of the current collector. This application does not have any particular limitations in this regard, as long as the purpose of this application can be achieved.

[0041] In the electrode of this application, the etched grooves serve both to guide the electrolyte flow and to retain it, thus giving the electrode excellent electrolyte transport and storage capabilities, which is beneficial for improving the cycle performance and fast-charging performance of the secondary battery. Moreover, within the scope specified in this application, the greater the depth and width of the etched grooves, the stronger the electrolyte retention capacity.

[0042] Since setting grooves on the active layer can lead to the loss of material in the active layer, potentially affecting the energy density of the electrode and the secondary battery, in some embodiments of this application, the projected area of ​​all grooves on the current collector surface is 10% to 20% of the current collector surface area. This results in a more moderate groove density, minimizing the loss of energy density in the secondary battery. It should be noted that the "projected area of ​​all grooves on the current collector surface" is calculated based on the projected area of ​​grooves in all active layers of the electrode on the current collector surface. Specifically, the projected area of ​​grooves in one active layer is measured first, then the projected area of ​​grooves in another active layer is measured, and the two are added together. If the electrode has only one active layer, then the projected area of ​​grooves in that active layer on the current collector surface is the same as the projected area of ​​all grooves in the electrode on the current collector surface.

[0043] In addition, in some embodiments of this application, the thickness of the active layer is H1 μm, the depth of the groove is H2 μm, and 0.1 ≤ H2 / H1 ≤ 0.3. If the groove depth is too deep relative to the thickness of the active layer, it will impose high requirements on the consistency of the laser etching process and may easily expose the current collector, potentially leading to lithium plating, which is detrimental to the electrical performance of the secondary battery. If the groove depth is too shallow relative to the active layer, it may result in insufficient electrolyte introduction, failing to significantly improve the interface and having little effect on improving the cycle performance and fast charging performance of the secondary battery.

[0044] The positive and negative electrode plates will be explained in detail below:

[0045] Positive electrode sheet

[0046] In the positive electrode sheet, the components of the positive electrode active layer include a positive electrode active material, which can be any material capable of reversibly inserting and de-intercalating Li. + Na + Substances containing alkali metal ions are used to ensure the normal charging and discharging of the electrochemical device. For example, positive electrode active materials include, but are not limited to, at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, and ternary materials. Ternary materials include, but are not limited to, LiNi x Co y Mn z O2, LiNi x Co y Al z At least one of O2, etc., and the contents of Ni, Co, Mn, Al, etc., can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0047] In some embodiments of this application, the positive electrode active layer further includes a positive electrode conductive agent; this application does not limit the type of positive electrode conductive agent, and any known conductive material can be used. Specifically, the positive electrode conductive agent includes, but is not limited to, at least one of the following: acetylene black, Super-P carbon black, amorphous carbon such as needle coke, carbon nanotubes, or graphene.

[0048] In some embodiments of this application, the positive electrode active layer generally also contains a positive electrode binder. There are no particular restrictions on the type of positive electrode binder used in the manufacture of the positive electrode active layer. In the case of the coating method, any material that can be dissolved or dispersed in the liquid medium used in the electrode manufacturing process is acceptable. Positive electrode binders include, but are not limited to, any one or at least two of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions).

[0049] In the positive electrode sheet, there are no particular restrictions on the type of positive current collector; it can be any known material suitable for use as a positive current collector. Materials for the positive current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. Furthermore, to reduce the electronic contact resistance between the positive current collector and the positive active layer, conductive additives or conductive coatings can be applied to the surface of the positive current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture of inorganic oxides, conductive agents, and positive electrode binders.

[0050] In preparing the positive electrode sheet, the components of the aforementioned positive active layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry. This slurry is then coated onto a positive current collector and dried, forming the positive active layer on the current collector. Laser etching is then used to etch grooves onto the surface of the positive active layer, thus obtaining the positive electrode sheet. When preparing the positive electrode sheet using this method, the solvent in the positive electrode slurry is not particularly limited, as long as it can dissolve or disperse the aforementioned components. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methylpyrrolidone (NMP) and ethylene carbonate (EC). Alternatively, in preparing the positive electrode sheet, the components of the positive active layer can be dry-mixed to form a sheet, which is then pressed onto the positive current collector. Afterward, laser etching is used to etch grooves onto the surface of the positive active layer.

[0051] Negative electrode sheet

[0052] In the negative electrode sheet, the components of the negative electrode active layer include negative electrode active materials, and this application does not impose any particular limitation on the negative electrode active materials. Specifically, the negative electrode active materials may include at least one of carbon materials or silicon-based materials. More specifically, carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, or soft carbon; silicon-based materials include, but are not limited to, at least one of silicon, silicon-oxygen composite materials, or silicon-carbon composite materials.

[0053] In some embodiments of this application, the negative electrode active layer typically also contains a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, negative electrode conductive agents include, but are not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0054] In some embodiments of this application, the negative electrode active layer may also contain a negative electrode binder and a thickener. This application does not particularly limit the types of negative electrode binders and thickeners, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0055] In the negative electrode sheet, the material of the negative electrode current collector includes, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and this application does not have any particular limitations. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalamide).

[0056] Furthermore, in this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode active layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active layer is 30 μm to 160 μm.

[0057] In addition, similar to the preparation of the positive electrode sheet, the preparation of the negative electrode sheet can be achieved by either preparing a negative electrode slurry, coating the slurry onto a negative electrode current collector, and drying it to form a negative electrode active layer on the current collector, thus obtaining the negative electrode sheet; or by dry mixing the components of the negative electrode active layer to form a sheet, which is then pressed onto the negative electrode current collector to form the negative electrode active layer, thus obtaining the negative electrode sheet. Alternatively, laser etching can be used to etch grooves on the surface of the positive electrode active layer. The solvent in the negative electrode slurry includes any one of aqueous or organic solvents. Aqueous solvents include, but are not limited to, mixtures of alcohol and water or water itself. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In some other embodiments, when using aqueous solvents, the negative electrode slurry composition may also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting its viscosity. The types of thickeners in the negative electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0058] Thirdly, this application provides a secondary battery, which includes an electrolyte, a separator, and electrodes, wherein the separator and electrodes are alternately stacked; wherein the electrodes are alternately arranged as positive electrodes and negative electrodes.

[0059] In the secondary battery of this application, the separator can be a first-type separator, and the electrode can be a second-type electrode. The first-type separator and the second-type electrode can be used alone or simultaneously in the secondary battery. When used simultaneously, the cycle performance and fast-charging performance of the secondary battery are superior.

[0060] Furthermore, when both are used in a secondary battery, the area between adjacent grooves in the electrode is the bonding zone, and the bonding points in the separator are located in the bonding zone. Since the bonding points in the separator do not fall into the grooves, the grooves can effectively transport and store electrolyte, which is beneficial for further improving the cycle performance and fast-charging performance of the secondary battery.

[0061] electrolyte

[0062] Electrolytes play a role in transporting lithium ions and electrons, ensuring the formation of internal pathways in secondary batteries. Electrolytes typically contain lithium salts, solvents, and additives. It should be noted that this application does not impose specific restrictions on the amount of each component in the electrolyte, as long as the purpose of this application can be achieved.

[0063] Specifically, lithium salts can dissolve in solvents to form ionic conductors and be used as conductive media and lithium-ion transport media; lithium salts include, but are not limited to, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorooxalate-borate), and lithium bis(fluorosulfonyl)imide.

[0064] Solvents can dissolve lithium salts and additives. Solvents can be at least one of carbonates, carboxylic esters, ethers, and alcohols. Carbonates can be classified as cyclic carbonates and linear carbonates. Cyclic carbonates specifically include, but are not limited to, at least one of ethylene carbonate and propylene carbonate; linear carbonates specifically include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; carboxylic esters include, but are not limited to, at least one of methyl formate, methyl acetate, methyl butyrate, ethyl propionate, propyl propionate, and propyl acetate; ethers include, but are not limited to, at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane; and alcohols include, but are not limited to, at least one of ethanol, ethylene glycol, and glycerol.

[0065] Additives include, but are not limited to, nitriles, sulfones, sulfoxides, fluoronitriles, and fluoroesters.

[0066] The secondary battery of this application can be used in electronic devices. The application of the electrochemical device of this application is not particularly limited; it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0067] Example

[0068] The following uses a lithium-ion battery as an example to illustrate the implementation of the electrochemical device of this application in more detail through embodiments and comparative examples. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0069] Test methods and equipment:

[0070] Bonding point quantity detection:

[0071] A Keyence VHX5000 CCD (Charge-coupled Device) electron microscope was used to observe the diaphragm surface at 100x magnification and record the number of bonding points. Figure 2 is a CCD image of Example 1-1. As shown in Figure 2, the projected shape of the bonding points is annular.

[0072] The method for counting adhesive points in the area is as follows:

[0073] If the portion of an adhesive point that is not fully displayed in the selected area is less than 50% of the total number of adhesive points, it will not be counted in the total number. If it is equal to or greater than 50%, it will be counted as one adhesive point.

[0074] Electrolyte transfer rate test:

[0075] 1. Use the diaphragm or positive electrode as the test sample, and cut it into a sample 15mm wide and 100mm long for later use;

[0076] 2. Fix both ends of the sample and suspend the middle position. Use a 1ml syringe to drop the electrolyte into the middle position of the sample (as shown in Figure 1).

[0077] 3. Time for 1 minute and measure the distance the electrolyte diffuses along the length of the sample. Repeat this process three times for each sample and take the average value.

[0078] Fast charging performance test

[0079] Eight identical lithium-ion batteries were placed in a low-temperature environment of 12°C and left to stand for 1 hour to allow the lithium-ion batteries to reach a constant temperature. Then, the eight lithium-ion batteries were divided into four groups of two batteries each for testing. During the test, the four groups were cyclically charged and discharged at 1.5C, 2C, 2.5C, and 3C, respectively. After the cycle was completed, the lithium batteries were disassembled, and the lithium plating window of the lithium-ion battery was determined by comparing the purple spots produced on the negative electrode (i.e., the anode).

[0080] The specific steps for cyclic charging and discharging are as follows:

[0081] (1) Discharge at a constant current of 0.7C to 3.0V; (2) Let stand for 5 minutes; (3) Charge at a constant current of a fixed rate to 4.5V, and then charge at a constant voltage of 0.05C; (4) Let stand for 5 minutes; (5) Repeat steps (1) to (4) 10 times.

[0082] In step (3), the fixed multipliers are 1.5C, 2C, 2.5C, and 3C.

[0083] In the test results, a higher lithium plating window ratio indicates stronger fast charging capability. For the same lithium plating window ratio, a less severe degree of lithium plating and a smaller lithium plating area indicate stronger fast charging capability. Specifically, the fast charging capability is ranked from worst to best as follows: severe lithium plating across the entire anode surface < slight lithium plating across the entire anode surface < severe localized lithium plating on the anode < slight localized lithium plating on the anode < slight lithium plating on the anode < no lithium plating on the anode.

[0084] Cyclic performance test

[0085] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to reach a constant temperature. Then, the lithium-ion battery was discharged at a constant current of 0.2C to 3V, followed by a 5-minute rest period. The initial discharge capacity C0 of the lithium-ion battery was measured. Afterward, charging and discharging were performed, with each charge and discharge cycle counted as one cycle. 800 cycles were performed, and the discharge capacity C1 of the lithium-ion battery after 800 cycles was measured.

[0086] The charging process is as follows: (1) 3.5C constant current charging to 4.35V; (2) 3C constant current charging to 4.35V, constant voltage charging to 1.8C; (3) 1.8C constant current charging to 4.4V, constant voltage charging to 1.5C; (4) 1.5C constant current charging to 4.53V, constant voltage charging to 1.2C; (5) 1.2C constant current charging to 4.58V, constant voltage charging to 2100mA; (6) Sleep for 5 minutes; (7) 0.5C constant current charging to 4.53V, constant voltage charging to 0.05C. The discharging process is as follows: 0.7C constant current discharge to 3.0V.

[0087] Capacity retention rate after 800 cycles at 45℃ = C1 / C0 × 100%.

[0088] A higher capacity retention rate indicates better cycle performance of the lithium-ion battery.

[0089] Adhesion test

[0090] The adhesion between the separator and the positive or negative electrode was tested according to the national standard GB / T 2790-1995, which uses the 180° peel test standard. The separator and the positive or negative electrode were cut into 54.2mm×72.5mm samples. The separator and the positive or negative electrode were then laminated together using a hot press. The hot pressing conditions were: temperature 85℃, pressure 1MPa, and hot pressing time 85s. The laminated sample was then cut into 15mm×54.2mm strips, and the adhesion between the separator and the positive or negative electrode was tested according to the 180° peel test standard.

[0091] Adhesive layer thickness test

[0092] A cross-section was cut along the width direction of the separator sample (the length direction is the cell winding direction, and the width direction is perpendicular to the length direction), and then tested using a scanning electron microscope. The thickness of the adhesive layer in the region within 3 mm of the separator width direction (overhang region) was measured, and 5 measurement points were taken, and the average value was obtained as the thickness of the adhesive layer.

[0093] Example 1-1

[0094] <Preparation of the diaphragm>

[0095] 90g of polymer particles (weight-average molecular weight of 600,000, monomers in a 1:1 molar ratio of butadiene and methyl acrylate) were added to a stirrer, followed by 10g of sodium carboxymethyl cellulose. The mixture was stirred until homogeneous, then 5g of dimethylsiloxane (a wetting agent) was added, followed by deionized water and stirring. The viscosity of the slurry was adjusted to 2000mPa·s~5000mPa·s, with a solid content of 5%, resulting in the adhesive layer slurry. Subsequently, the adhesive layer slurry was uniformly coated onto both surfaces of a polyethylene base film using a screen printing method, with a coating weight of 0.4g / m². 2 After drying in an oven, an adhesive layer with a thickness of 3.2 μm will be formed on the surface of the base film.

[0096] <Preparation of Negative Electrode Sheets>

[0097] Artificial graphite, acetylene black, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96:1:1.5:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 70%. The slurry was then stirred uniformly using a vacuum mixer. The negative electrode slurry was uniformly coated onto one surface of an 8µm thick copper foil, dried at 110°C, and cold-pressed to obtain a negative electrode sheet with a 150µm negative electrode active layer on one side. The coating process was repeated on the other side of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode active layer. The negative electrode sheet was cut into 74mm × 867mm pieces and tabs were welded on for later use.

[0098] <Preparation of the positive electrode>

[0099] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a positive electrode slurry with a solid content of 75%. The slurry was then stirred uniformly using a vacuum mixer. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil with a thickness of 12µm, dried at 90℃, and cold-pressed to obtain a positive electrode current collector with a single-sided coating of a positive electrode active layer with a thickness H1 of 100µm. Then, a laser was used to etch grooves along the length of the positive electrode active layer on its surface. The width D1 of the grooves was 0.2mm, the spacing D2 between adjacent grooves was 1mm, and the depth H2 of the grooves was 10µm. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active layers and grooves, as shown in Figure 3. The positive electrode sheet was cut to a size of 74mm × 867mm and tabs were welded to the wide edge of the positive electrode sheet before use. The grooves in the two positive electrode active layers were observed using a CCD electron microscope, and the projected area of ​​all grooves on the current collector surface was measured to be 8%.

[0100] <Preparation of Electrolyte>

[0101] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2. Lithium hexafluorophosphate (LiPF6) was then added to the non-aqueous organic solvents, dissolved, and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 was 8%.

[0102] <Preparation of Lithium-ion Batteries>

[0103] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator and to prevent the bonding points in the separator from falling into the grooves of the positive electrode. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery.

[0104] Examples 1-2 to Examples 1-30

[0105] Except for adjusting the longest diameter of the bonding point, the spacing between adjacent bonding points, and the thickness of the bonding layer according to Table 1, the rest is basically the same as in Example 1-1.

[0106] Examples 1-31 to Examples 1-42

[0107] In addition to adjusting the thickness of the bonding layer in the positive electrode according to Table 1, and Apart from the parameters, the rest are basically the same as in Examples 1-29.

[0108] Comparative Examples 1 to 16

[0109] Except for adjusting the parameters in the positive electrode and the separator according to Table 1, the rest are basically the same as in Examples 1-29.

[0110] The preparation method of the positive electrode without grooves is as follows:

[0111] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a positive electrode slurry with a solid content of 75%. The mixture was then stirred evenly using a vacuum mixer. The positive electrode slurry was uniformly coated onto one surface of a 12µm thick aluminum foil, dried at 90°C, and cold-pressed to obtain a positive electrode current collector with a single-sided coating of a 100µm thick positive electrode active layer (H1). The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode active layer. The positive electrode sheet was cut to a size of 74mm × 867mm, and tabs were welded to the wide edges of the positive electrode sheet for later use.

[0112] In addition, by using a dot matrix coating method to apply the adhesive layer slurry during the preparation of the diaphragm, the adhesive layer can be free of discontinuous bonding points.

[0113] Table 1

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120] Examples 2-1 to 2-5

[0121] Except for adjusting the type of aqueous polymer in the diaphragm according to Table 2, and D1 and D2 in the negative electrode, the rest are basically the same as in Examples 1-35.

[0122] Table 2

[0123]

[0124] Note: In Table 2, the “longest diameter of the bonding point”, “distance between adjacent bonding points” and “thickness of the bonding layer” in Examples 2-1 to 2-5 are the same as those in Examples 1-35, so they are not described in Table 2.

[0125] Examples 3-1 to 3-14

[0126] Except for adjusting the parameters of the negative electrode according to Table 3, the rest is basically the same as in Examples 1-35.

[0127] Table 3

[0128]

[0129]

[0130] As shown in the table, when the secondary battery of this application meets the limitations of this application, its cycle performance and fast-charging performance can be improved. Specifically, when the longest diameter of the bonding point is 10μm to 200μm, or the distance between adjacent bonding points is 150μm to 300μm, the cycle performance and fast-charging performance of the secondary battery are better. In particular, when the range of 0.1 ≤ H2 / H1 in the negative electrode sheet is 0.1 to 0.3, or the projected area of ​​the groove on the current collector surface is 10% to 20% of the current collector surface area, the cycle performance and fast-charging performance of the secondary battery are better. Furthermore, the test results of the electrolyte transport rate show a positive correlation between the electrolyte transport rate and the cycle performance and fast-charging performance of the secondary battery.

[0131] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, comprising a separator and electrodes, characterized in that, The diaphragm includes a base film layer, and an adhesive layer is provided on at least one surface of the base film layer. The adhesive layer is composed of a plurality of adhesive points, and the thickness of the adhesive layer is 0.5 μm to 5 μm. In the adhesive layer, the longest diameter of the adhesive point is 10 μm to 400 μm, and the distance between adjacent adhesive points is 100 μm to 400 μm. The electrode includes a current collector, and at least one surface of the current collector is provided with an active layer. A portion of the surface of the active layer is recessed inward to form a plurality of grooves, which are arranged along the length of the electrode. The width of the grooves is D1 mm, and 0.2 ≤ D1 ≤ 1.

5.

2. The secondary battery according to claim 1, characterized in that, The longest diameter of the bonding point is 10 μm to 200 μm; and / or the distance between adjacent bonding points is 150 μm to 300 μm.

3. The secondary battery according to claim 1 or 2, characterized in that, The thickness of the adhesive layer is 1μm to 3μm.

4. The secondary battery according to claim 1, characterized in that, The adhesive layer comprises an aqueous polymer, wherein the monomers of the aqueous polymer include at least two of butadiene, acrylate, styrene, methacrylate, ethylene, propylene, or vinylidene fluoride.

5. The secondary battery according to claim 1, characterized in that, The thickness of the active layer is H1 μm, the depth of the scribed groove is H2 μm, and 0.1 ≤ H2 / H1 ≤ 0.

3.

6. The secondary battery according to claim 1, characterized in that, The projected area of ​​all the grooves on the surface of the current collector is 10% to 20% of the surface area of ​​the current collector.

7. The secondary battery according to claim 1, characterized in that, The electrode is a negative electrode.

8. The secondary battery according to claim 1, characterized in that, The spacing between adjacent scribed grooves is D2mm, where 1≤D2≤3.

9. The secondary battery according to claim 1, characterized in that, The area between adjacent grooves is a bonding area, and the bonding point is located in the bonding area.

10. An electronic device, characterized in that, It includes the secondary battery as described in any one of claims 1 to 9.

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