Negative plate with composite structure, preparation method of negative plate, battery cell and lithium ion battery

Abstract

The invention discloses a composite structure negative plate and a preparation method thereof, a battery cell and a lithium ion battery. According to the composite structure negative plate provided by the invention, the empty foil area at the head part of the negative plate is coated with the compound of the high-molecular polymer and the carboxylated silicon dioxide, so that the problem of feeding curling and folding of a single fabric area at the head part of the negative plate when a lithium ion battery is wound is solved, the wrinkles of a battery cell are improved, and the proportion of the wrinkles of the wound battery cell is reduced; moreover, the high-molecular polymer / carboxylated nano silicon dioxide coated on the pole piece is subjected to a thermocuring reaction at a high formation temperature, so that a hydrogen bond cross-linking reaction of the high-molecular polymer and the carboxylated nano silicon dioxide is accelerated, a three-dimensional network is formed, the flatness of the lithium ion battery is improved, and the cyclic expansion rate of the battery is reduced. In addition, the opposite side empty foil region of the negative electrode single fabric region is coated with the high-molecular polymer / carboxylated nano silicon dioxide, so that the problem of lithium precipitation caused by overpressure of a single-sided region due to thickness change from the double-sided region to the single-sided region during rolling of the negative electrode can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery materials, and in particular to a composite structure negative electrode sheet and a preparation method thereof, a battery cell and a lithium ion battery. Background Art

[0002] Lithium ion batteries are widely used in products such as 3C, electric vehicles and power tools because of their advantages of high energy density, no memory effect, long cycle life, environmental friendliness and ability to adapt to various environments. The assembly process of lithium ion batteries mainly includes winding process and lamination process. Among them, when producing a wound lithium ion battery, the single-sided coated area at the head of the anode (negative electrode) is often prone to wrinkling and folding, resulting in poor wrinkling of the electrode sheets of the battery cell. In addition, soft-pack lithium ion battery cells often face problems such as poor flatness and high swelling rate caused by softening.

[0003] Therefore, it is of great significance to solve the existing problems that the single-sided coated area at the head of the anode is prone to wrinkling and folding, resulting in poor wrinkling of the electrode sheets of the battery cell, and to improve the flatness of the lithium ion battery and reduce the swelling rate of the battery. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a composite structure negative electrode sheet and a preparation method thereof, a battery cell and a lithium ion battery, aiming to solve the existing problems that the single-sided coated area at the head of the anode of the lithium ion battery is prone to wrinkling and folding, resulting in poor wrinkling of the electrode sheets of the battery cell, and the battery cell has poor flatness and high swelling rate.

[0005] In a first aspect of the present invention, a composite structure negative electrode sheet is provided. A composite material layer is coated on the empty foil area at the head of the negative electrode sheet. The composite material layer includes a composite of a high molecular polymer and carboxylated silica.

[0006] The composite structure negative electrode sheet according to the embodiments of the present invention has at least the following beneficial effects: The composite structure negative electrode sheet provided by the present invention can improve the problem of feeding curling and folding of the single-sided coating area at the head of the negative electrode sheet during the winding of the lithium-ion battery by coating a composite of a high molecular polymer and carboxylated silica in the empty foil area at the head of the negative electrode sheet. Coating the high molecular polymer / carboxylated nano-silica in the empty foil area can reduce the retraction and curling of the negative electrode sheet after cutting during winding, thereby improving the problems of electrode sheet wrinkles and folding defects in the battery cell. The composite structure negative electrode sheet can also improve the flatness of the soft-pack lithium-ion battery and reduce the cycle expansion rate of the battery. This is mainly because the high molecular polymer / carboxylated nano-silica coated on the electrode sheet undergoes a thermal curing reaction at the high temperature during formation, accelerating the hydrogen bond cross-linking reaction between the high molecular polymer and the carboxylated nano-silica. The cross-linked high molecular polymer and carboxylated nano-silica form a three-dimensional network, thereby improving the flatness of the lithium-ion battery. In addition, coating the high molecular polymer / carboxylated nano-silica in the empty foil area on the opposite side of the single-sided coating area of the negative electrode can also slow down the change in thickness from the double-sided area to the single-sided area during the rolling of the negative electrode, effectively avoiding the problem of lithium precipitation due to overpressure in the single-sided area caused by the above change. This is mainly because the extrusion force on the electrode sheet during the double-sided rolling of the negative electrode is relatively large. When transitioning to the single-sided rolling area, since the above composite is coated in the empty foil position, it can slow down the extrusion of the single-sided negative electrode coating by the rolling roller, so as not to damage the graphite interlayer structure at this position. Finally, the above composite structure negative electrode sheet reduces the stress curling at the head of the wound negative electrode sheet by coating the high molecular polymer / carboxylated nano-silica composite in the empty foil area at the head of the negative electrode sheet, improves the wrinkles of the battery cell, significantly reduces the proportion of wrinkles in the wound battery cell, effectively improves the flatness of the soft-pack lithium-ion battery, reduces the cycle expansion rate of the battery, and significantly improves the problem of lithium precipitation due to overpressure in the single-sided area of the negative electrode.

[0007] In some embodiments of the present invention, the high molecular polymer includes at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), or polycarbonate (PC), but is not limited thereto. In theory, any high molecular material that can swell in the lithium-ion battery electrolyte can be used as the material of the composite material layer of the present invention. The above high molecular materials can all undergo cross-linking reactions with the hydrogen bonds of carboxylated nano-silica to form a three-dimensional network, improving the flatness of the lithium-ion battery. Preferably, the high molecular polymer is polyethylene oxide (PEO).

[0008] In some embodiments of the present invention, a composite material layer is coated on the head empty foil area of the composite structure negative electrode sheet, and the composite material layer includes a composite of polyethylene oxide and carboxylated silica. By coating a composite of polyethylene oxide (PEO) and carboxylated silica on the misaligned end (i.e., the head empty foil area) of the long and short film surfaces coated on the negative electrode sheet, the present invention can slow down the lithium deposition problem caused by the change in thickness from the double-sided area to the single-sided area during the rolling process of the negative electrode sheet, reduce the stress curling at the head of the wound negative electrode sheet, and improve the folding of the battery core. The beneficial effects of the composite structure negative electrode sheet include: 1. It can improve the problem of the feeding curling and folding of the single-sided material area at the head of the negative electrode sheet during the winding of the soft-pack lithium-ion battery: Coating polyethylene oxide / carboxylated nano-silica in the empty foil area can reduce the retraction and curling of the negative electrode sheet after cutting during winding, thereby improving the folding and turning problems of the battery core electrode sheet. 2. It can improve the flatness of the soft-pack lithium-ion battery and reduce the cyclic expansion rate of the battery: The main reason is that the polyethylene oxide / carboxylated nano-silica undergoes a thermal curing reaction at the high temperature during formation, accelerating the hydrogen bond cross-linking reaction between the polyethylene oxide and the carboxylated nano-silica. The cross-linked polyethylene oxide and carboxylated nano-silica form a three-dimensional network, thereby improving the flatness of the lithium-ion battery. 3. Coating polyethylene oxide / carboxylated nano-silica in the empty foil area on the opposite side of the single-sided material area of the negative electrode can improve the lithium deposition problem caused by the change in thickness from the double-sided area to the single-sided area during the rolling of the negative electrode. This is mainly because the extrusion force on the electrode sheet is relatively large during the double-sided rolling of the negative electrode. When transitioning to the single-sided rolling area, since the empty foil position is coated with a composite of PEO and carboxylated silica, it can slow down the extrusion of the single-sided negative electrode coating by the rolling roller, so as not to damage the graphite interlayer structure at this position.

[0009] In some embodiments of the present invention, the molecular weight of the high molecular polymer is 100,000 to 500,000. By selecting a high molecular polymer with a specific molecular weight (100,000 to 500,000) to undergo a thermal curing reaction with carboxylated nano-silica at the high temperature during formation, the present invention can accelerate the hydrogen bond cross-linking reaction between the high molecular polymer and the carboxylated nano-silica, form a three-dimensional network, and further improve the flatness of the lithium-ion battery and reduce the expansion rate of the battery.

[0010] Specifically, the molecular weight of the polyethylene oxide is 100,000 to 500,000. When the molecular weight of the polyethylene oxide is between 100,000 and 500,000, the cross-linking effect is the best. This is because the composite of polyethylene oxide and carboxylated nano-silica presents a gel state after absorbing the electrolyte, thereby improving the flatness of the lithium-ion battery. When the molecular weight of the polyethylene oxide is lower than 100,000, the hydroxyl functional groups on the surface of the polyethylene oxide are few and the cross-linking degree with the carboxylated silica is low; while when the molecular weight of the polyethylene oxide is too large, the movement of its chain segments will be restricted, resulting in an increase in the hardness and rigidity of the composite of polyethylene oxide and carboxylated nano-silica in the electrolyte, and it cannot effectively improve the flatness of the battery core.

[0011] In some embodiments of the present invention, the carboxylated silica (COOH-SiO 2 ) is prepared by introducing a carboxyl (-COOH) functional group onto the surface of silica (SiO 2 ). Carboxylated silica is also known as carboxylated silica nanoparticles, carboxylated nano-silica microspheres, carboxylated silica gel, which is a product obtained by introducing carboxyl functional groups onto the surface of silica nanoparticles, and it contains specific functional group silicon-oxygen bonds (Si-O) and carboxyl (-COOH). This carboxylation can change the surface properties of silica, endowing it with the characteristics of carboxyl compounds, such as chemical reactivity with other molecules, water solubility, etc.

[0012] In some embodiments of the present invention, the particle size of the carboxylated silica is 1 - 100 nm.

[0013] In some embodiments of the present invention, the density of the carboxylated silica is 2.2 - 2.6 g / cm 3 .

[0014] In some embodiments of the present invention, the mass ratio of the polymer and the carboxylated silica is (1 - 4):(6 - 9). For example, the mass ratio of the polymer and the carboxylated silica can be 1:9, 2:8, 3:7, 4:6, and preferably 2:8.

[0015] Specifically, the mass ratio of polyethylene oxide and carboxylated silica is (1 - 4):(6 - 9), and preferably 2:8.

[0016] In some embodiments of the present invention, the thickness of the composite material layer is 4 - 8 μm, for example, it can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and preferably 6 μm. When the composite material layer is too thin, the material weight in the single-sided area of the negative electrode is too light to effectively improve the curling of the negative electrode; while when it is too thick, the increase in the coating thickness will affect the overall thickness of the battery cell, occupying space and affecting the overall volume energy density of the battery cell.

[0017] In some embodiments of the present invention, the composite structure negative electrode sheet further includes a negative electrode current collector and a negative electrode active material layer; the composite material layer is coated on the head empty foil area of the negative electrode current collector, and the negative electrode active material layer is coated on the area of the negative electrode current collector where the composite material layer is not coated.

[0018] Figure 1 The coating schematic diagram of one embodiment of the composite structure negative electrode sheet of the present invention is shown. In the figure, the negative electrode current collector is coated on both sides, the composite material layer is coated in area ①, and the negative electrode active material layer is coated in area ②.

[0019] In some specific embodiments of the present invention, the negative electrode current collector includes at least one of copper foil and composite copper foil.

[0020] In some specific embodiments of the present invention, the raw materials of the negative electrode active material layer include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0021] In the present invention, the negative electrode active material includes a silicon-based material, which may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, or a mixture of a silicon negative electrode material and other commonly used negative electrode active materials at present. The other negative electrode active materials include, but are not limited to, one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0022] The negative electrode conductive agent includes at least one of acetylene black, graphene, graphdiyne, carbon nanotubes, carbon fiber, and conductive carbon black. The present invention has no special requirements for the negative electrode conductive agent, and conventional conductive agents in the art can be applied.

[0023] The negative electrode binder includes at least one of polyvinylidene fluoride (PVDF) binder, sodium carboxymethyl cellulose (CMC) binder, styrene-butadiene rubber (SBR), or polyacrylate (PAA) binder. The present invention has no special requirements for the negative electrode binder, and conventional binders in the art can be applied.

[0024] In the second aspect of the present invention, a method for preparing the above composite structure negative electrode sheet is proposed, including the steps:

[0025] S100. Weigh a predetermined mass of a polymer and carboxylated silica, respectively prepare solutions and then mix them evenly to obtain a composite slurry;

[0026] S200. Coat the composite slurry on the uncoated area of the head of one side of the negative electrode current collector along the unwinding direction of the current collector, and dry it to form a composite material layer;

[0027] S300. Mix the negative electrode active material, conductive agent, and adhesive evenly and then prepare a negative electrode slurry, and coat the negative electrode slurry on the area of the negative electrode current collector that is not coated with the composite slurry, and dry it to obtain the composite structure negative electrode sheet.

[0028] The preparation method of the composite structure negative electrode sheet according to the embodiment of the present invention has at least the following beneficial effects: The preparation method provided by the present invention not only has a simple process, but also has mild reaction conditions, is compatible with the preparation processes of the original electrode sheets or battery cells, and has the potential for large-scale application.

[0029] Figure 2 The coating position of the composite slurry is shown as follows. As shown in the figure, the composite slurry is coated on the misaligned area of the anode's long and short sides (the misaligned area of the non-uniform film end of the anode), that is, the empty foil area at the head of the anode.

[0030] In some embodiments of the present invention, the polymer includes at least one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), or polycarbonate (PC), but is not limited thereto. In theory, any polymer material that can swell in the lithium-ion battery electrolyte can be used as the material for the composite material layer of the present invention. The above polymer materials can all undergo cross-linking reactions with the hydrogen bonds of carboxylated nano-silica to form a three-dimensional network, improving the flatness of the lithium-ion battery. Preferably, the polymer is polyethylene oxide (PEO).

[0031] In some embodiments of the present invention, the molecular weight of the polymer is 100,000 - 500,000. Specifically, the molecular weight of the polyethylene oxide is 100,000 - 500,000. By selecting a polymer with a specific molecular weight (100,000 - 500,000) (such as polyethylene oxide) in the present invention, a thermal curing reaction occurs with carboxylated nano-silica at the high temperature during formation, which can accelerate the hydrogen bond cross-linking reaction between polyethylene oxide and carboxylated nano-silica, form a three-dimensional network, and thus improve the flatness of the lithium-ion battery and reduce the expansion rate of the battery.

[0032] In some embodiments of the present invention, the carboxylated silica (COOH-SiO 2 ) is prepared by introducing a carboxyl (-COOH) functional group on the surface of silica (SiO 2 ). Carboxylated silica is also known as carboxylated silica nanoparticles, carboxylated nano-silica microspheres, or carboxylated silica gel. It is the product of introducing carboxyl functional groups onto the surface of silica nanoparticles, and it contains specific functional group silicon-oxygen bonds (Si-O) and carboxyl groups (-COOH). This carboxylation can change the surface properties of silica, endowing it with the characteristics of carboxyl compounds, such as chemical reactivity with other molecules and water solubility.

[0033] In some embodiments of the present invention, the particle size of the carboxylated silica is 1 - 100 nm.

[0034] In some embodiments of the present invention, the density of the carboxylated silica is 2.2 - 2.6 g / cm3 。

[0035] In some embodiments of the present invention, the mass ratio of the polymer and the carboxylated silica is (1-4):(6-9). For example, the mass ratio of the polymer and the carboxylated silica can be 1:9, 2:8, 3:7, 4:6, and preferably 2:8.

[0036] Specifically, the mass ratio of the polyethylene oxide and the carboxylated silica is (1-4):(6-9), and preferably 2:8.

[0037] In some embodiments of the present invention, the coating thickness of the composite slurry is 4-8 μm, and can be, for example, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and preferably 6 μm. When the coating thickness is too thin, the weight of the material in the single-sided area of the negative electrode is too light to effectively improve the curling of the negative electrode; while when the coating thickness is too thick, the increase in the coating thickness will affect the overall thickness of the battery cell, occupying space and affecting the overall volume energy density of the battery cell.

[0038] In some embodiments of the present invention, the coating length of the composite slurry is 2-2.5 times the width of the battery cell corresponding to the composite structure negative electrode sheet.

[0039] In some embodiments of the present invention, the coating width of the composite slurry is the same as the width of the negative electrode current collector.

[0040] In some embodiments of the present invention, the coating length of the composite slurry is 2-2.5 times the width of the battery cell after the negative electrode sheet is wound. Specifically, as Figure 3 shown in the figure, the wound battery cell is formed by winding the electrode sheet fold by fold, and each fold corresponds to approximately 1 time the width of the battery cell. Then, the coating length of the composite slurry is 2-2.5 times the length of one fold of the anode sheet ( Figure 3 the anode sheet shown in the figure is 10 folds, and the coating length is 2 folds).

[0041] In some specific embodiments of the present invention, the negative electrode current collector includes at least one of copper foil and composite copper foil.

[0042] In some specific embodiments of the present invention, the negative electrode active material includes a silicon-based material, which may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys, or a mixture of a silicon negative electrode material and other commonly used negative electrode active materials at present. The other negative electrode active materials include, but are not limited to, one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Among them, the graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0043] In some specific embodiments of the present invention, the conductive agent includes at least one of acetylene black, graphene, graphdiyne, carbon nanotubes, carbon fiber, and conductive carbon black. The present invention has no special requirements for the conductive agent, and conventional negative electrode conductive agents in the art can be applied.

[0044] In some specific embodiments of the present invention, the binder includes at least one of polyvinylidene fluoride (PVDF) binder, sodium carboxymethyl cellulose (CMC) binder, styrene-butadiene rubber (SBR), or polyacrylate (PAA) binder. The present invention has no special requirements for the binder, and conventional negative electrode binders in the art can be applied.

[0045] In a specific embodiment of the present invention, the method for preparing the composite structure negative electrode sheet includes the steps:

[0046] 1) Weigh a predetermined mass of polyethylene oxide (PEO) and add deionized water to prepare a polyethylene oxide solution with a molecular weight of 100,000 to 500,000;

[0047] 2) Weigh a predetermined mass of carboxylated silica and add deionized water, and stir well for 1 h to prepare a carboxylated silica solution;

[0048] 3) Mix the polyethylene oxide solution and the carboxylated silica solution evenly to obtain a composite slurry, and coat it on the misaligned area of the long and short sides of the negative electrode (i.e., the head empty foil area) with a coating thickness of 4 to 8 μm. After drying at 85°C, it is wound up and reserved;

[0049] 4) Mix the negative electrode active material, conductive agent, and adhesive evenly according to a predetermined mass ratio to prepare a negative electrode slurry, coat the negative electrode slurry on the area of the negative electrode current collector where the composite slurry is not coated, and after drying at 85°C, it is cold-pressed and cut for standby.

[0050] In the third aspect of the present invention, a battery cell is proposed, including the above-mentioned composite structure negative electrode sheet or the composite structure negative electrode sheet obtained by the above-mentioned preparation method.

[0051] Since the battery cell adopts all the technical solutions of the composite structure negative electrode sheet of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment. That is, by coating the polymer / carboxylated nano-silica composite on the head empty foil area of the negative electrode sheet, the stress curling at the head of the wound negative electrode sheet is reduced, the battery cell wrinkles are improved, the proportion of the wrinkles of the wound battery cell is significantly reduced, and the flatness of the soft-pack lithium-ion battery can be effectively improved, the cycle expansion rate of the battery is reduced, and the lithium deposition problem of the overvoltage in the single-sided area of the negative electrode is significantly improved.

[0052] In some embodiments of the present invention, the battery cell further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector.

[0053] In some specific embodiments of the present invention, the positive electrode current collector includes at least one of aluminum foil and composite aluminum foil.

[0054] In some specific embodiments of the present invention, the raw materials of the positive electrode active material layer include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0055] In the present invention, the positive electrode active material is a positive electrode active material commonly used in current lithium-ion batteries, including but not limited to compounds represented by the chemical formula such as Li x Ni h Co y M z O 2-d N d (where 0.95 ≤ x ≤ 1.2, h > 0, y ≥ 0, z ≥ 0, and h + y + z = 1, 0 ≤ d ≤ 1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) or a combination of one or more of the above compounds. The positive electrode active material may also be, including but not limited to, LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 、Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4, CuS 2 , FeS 2 , MoS 2 , NiS, TiS 2 or a combination of one or more of the above. The positive electrode active material may also be subjected to a modification treatment, and the method for modifying the positive electrode active material should be known to those skilled in the art. For example, methods such as coating and doping can be used to modify the positive electrode active material, and the materials used for the modification treatment can be a combination of one or more of, but not limited to, Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc.

[0056] The positive electrode conductive agent includes at least one of acetylene black, graphene, graphdiyne, carbon nanotubes, carbon fibers, and conductive carbon black. The present invention has no special requirements for the positive electrode conductive agent, and conventional conductive agents in the art can be applied.

[0057] The positive electrode binder includes at least one of a polyvinylidene fluoride (PVDF) binder, a sodium carboxymethyl cellulose (CMC) binder, a styrene-butadiene rubber (SBR), or a polyacrylate (PAA) binder. The present invention has no special requirements for the positive electrode binder, and conventional binders in the art can be applied.

[0058] In some embodiments of the present invention, the battery cell further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0059] In some embodiments of the present invention, the separator can be various materials suitable for lithium-ion battery separators in the art. For example, it can be a combination of one or more of, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. In actual production, the material and structure of the separator are not strictly limited. For example, it can be a multi-layer structure formed by laminating the above materials, or a single-layer structure formed by mixing the above materials, or a single-layer structure formed by a single material; as long as it can perform the basic function of the separator.

[0060] In a fourth aspect of the present invention, a lithium-ion battery is proposed, including the above battery cell.

[0061] Since the lithium-ion battery adopts all the technical solutions of the battery cell in the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, that is, effectively improving the flatness of the soft-pack lithium-ion battery and reducing the cyclic expansion rate of the battery.

[0062] In some embodiments of the present invention, the lithium-ion battery further includes an electrolyte, which infiltrates the positive electrode, the negative electrode, and the separator. The electrolyte includes an organic solvent, a lithium salt electrolyte, and an additive. Among them, the lithium salt electrolyte can be LiPF 6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF 4 , LiBOB, and LiPF 6 used in low-temperature electrolytes; it can also be at least one of LiBF 4 , LiBOB, LiPF 6 , and LiTFSI used in overcharge-proof electrolytes; it can also be at least one of LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , and LiN(CF 3 SO 2 ) 2 . The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DEC, DMC, or EMC; it can also be a carboxylic acid ester, including PP, MA, EA, EP, etc. The additive includes but is not limited to at least one of a film-forming additive, a conductive additive, a flame retardant additive, an overcharge prevention additive, an additive for controlling the content of H 2 O and HF in the electrolyte, an additive for improving low-temperature performance, and an aqueous safety additive.

[0063] In some embodiments of the present invention, the present invention also provides a secondary battery, including the above-mentioned battery cell. The battery cell proposed by the present invention can be applied not only to the above-mentioned lithium-ion battery, but also to other secondary batteries, including sodium-ion batteries, potassium-ion batteries, etc., without any limitation here.

[0064] In the fifth aspect of the present invention, there is provided an application of the above-mentioned lithium-ion battery in an energy storage device, an electrical device, or an electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The present invention will be further described below with reference to the drawings and embodiments, where:

[0066] Figure 1 is a coating schematic diagram of one embodiment of the composite structure negative electrode sheet of the present invention;

[0067] Figure 2 is a schematic diagram of the coating position of the composite slurry of the present invention on the anode;

[0068] Figure 3 is a schematic diagram of the coating length of the composite in the composite structure negative electrode sheet of the present invention;

[0069] Figure 4 Schematic diagram of the flatness of the cell test in Embodiment 1 of the present invention;

[0070] Figure 5 Schematic diagram of the flatness of the cell test in Comparative Example 1 of the present invention. Detailed implementation manners

[0071] The following will clearly and completely describe the concept of the present invention and the technical effects generated in combination with the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0072] In the description of the present invention, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0073] In the description of the present invention, unless otherwise specified, the numerical range "a~b" represents the abbreviated representation of any real number combination between a and b, where a and b are both real numbers. Unless otherwise specified, each reaction or operation step can be carried out in sequence or not in sequence. Preferably, the reaction method in the present invention is carried out in sequence.

[0074] In the following embodiments, if the specific technology or conditions are not indicated, they shall be carried out according to the technology or conditions described in the literature in the field or according to the product specification. All reagents or instruments without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0075] Embodiment 1

[0076] This embodiment provides a soft-pack lithium-ion battery.

[0077] 1. Preparation of the negative electrode sheet:

[0078] 1) Weigh 2 g of polyethylene oxide (PEO) (purchased from Aladdin Reagent (Shanghai) Co., Ltd.) and add 100 mL of deionized water to prepare a PEO solution with a concentration of 20 mg / mL, which is called Solution A, and the molecular weight of PEO is selected as 300,000.

[0079] 2) Weigh 8 g of carboxylated silica (purchased from Aladdin Reagent (Shanghai) Co., Ltd.) and place it in a beaker. Add 400 mL of deionized water and stir well for 1 h to prepare a PEO solution with a concentration of 20 mg / mL, which is designated as Solution B.

[0080] 3) Mix Solution A and Solution B evenly and coat the misaligned area on the long and short sides of the anode current collector copper foil, that is, Figure 1 the area ① shown in the figure. Control the coating thickness at 5 μm, and then dry it at 85 °C and wind it up for standby.

[0081] 4) Mix graphite, CMC, and binder evenly according to a mass ratio of 97.7:1.1:1.2 to prepare a lithium-ion battery negative electrode paste with a certain viscosity. Coat the paste on the current collector area that was not coated in Step 3, that is, Figure 1 the area ② shown in the figure. Dry it at 85 °C and then perform cold pressing and slitting for standby.

[0082] 2. Preparation of the positive electrode sheet:

[0083] Mix lithium iron phosphate, conductive agent Super-P, and binder polyvinylidene fluoride (PVDF) evenly according to a mass ratio of 97:1.5:1.5 to prepare a lithium-ion battery positive electrode paste with a certain viscosity. Coat the paste on the current collector aluminum foil, dry it at 85 °C, and then perform cold pressing and slitting for standby.

[0084] 3. Separator: The double sides of the PE-based film are coated with aluminum oxide / PVDF paste, dried, and slit for standby.

[0085] 4. Electrolyte: Dissolve lithium hexafluorophosphate (LiPF 6 ) in a mixed solvent composed of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (the mass ratio of the three is 1:2:1) to obtain an electrolyte with a concentration of 1 mol / L.

[0086] 5. Preparation of the lithium-ion battery:

[0087] Roll the above-mentioned positive electrode sheet, separator, negative electrode sheet, and electrolyte into a soft-pack battery, let it stand at room temperature for 24 h, and then at high temperature for 16 h for standby.

[0088] Example 2

[0089] This example provides a soft-pack lithium-ion battery, which is different from Example 1 in that the mass ratio of PEO to carboxylated silica is 1:9, with 1 g of PEO and 9 g of carboxylated silica.

[0090] The rest is the same as in Example 1 and will not be elaborated here.

[0091] Example 3

[0092] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the mass ratio of PEO to carboxylated silica is 3:7, with 3 g of PEO and 7 g of carboxylated silica.

[0093] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0094] Embodiment 4

[0095] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the mass ratio of PEO to carboxylated silica is 4:6, with 4 g of PEO and 6 g of carboxylated silica.

[0096] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0097] Embodiment 5

[0098] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the coating thickness in the misaligned area of the long and short sides of the electrode sheet (Area ①) is different. The coating thickness in this embodiment is 4 μm.

[0099] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0100] Embodiment 6

[0101] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the coating thickness in the misaligned area of the long and short sides of the electrode sheet (Area ①) is different. The coating thickness in this embodiment is 8 μm.

[0102] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0103] Embodiment 7

[0104] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the molecular weight of PEO is different. The molecular weight of PEO in this embodiment is 100,000.

[0105] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0106] Embodiment 8

[0107] This embodiment provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the molecular weight of PEO is different. The molecular weight of PEO in this embodiment is 500,000.

[0108] The rest is the same as that of Embodiment 1 and will not be elaborated here.

[0109] Comparative Example 1

[0110] This comparative example provides a soft-pack lithium-ion battery, which is different from Embodiment 1 in that the misaligned area of the long and short sides of the electrode sheet (Area ①) is not coated.

[0111] The rest is the same as in Example 1 and will not be elaborated here.

[0112] Comparative Example 2

[0113] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the silica is ordinary SiO 2 nanoparticles and is not carboxylated.

[0114] The rest is the same as in Example 1 and will not be elaborated here.

[0115] Comparative Example 3

[0116] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the mass ratio of PEO to carboxylated silica is 5:95, 5 g of PEO and 95 g of carboxylated silica.

[0117] The rest is the same as in Example 1 and will not be elaborated here.

[0118] Comparative Example 4

[0119] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the mass ratio of PEO to carboxylated silica is 6:4, 6 g of PEO and 4 g of carboxylated silica.

[0120] The rest is the same as in Example 1 and will not be elaborated here.

[0121] Comparative Example 5

[0122] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the molecular weight of PEO is different, and the molecular weight of PEO in this comparative example is 5000.

[0123] The rest is the same as in Example 1 and will not be elaborated here.

[0124] Comparative Example 6

[0125] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the molecular weight of PEO is different, and the molecular weight of PEO in this comparative example is 1 million.

[0126] The rest is the same as in Example 1 and will not be elaborated here.

[0127] Comparative Example 7

[0128] This comparative example provides a soft-pack lithium-ion battery, which is different from Example 1 in that: the coating thickness in the misaligned area (area ①) of the long and short sides of the electrode sheet is different, and the coating thickness in this comparative example is 16 μm.

[0129] The rest is the same as in Example 1 and will not be elaborated here.

[0130] Test Example

[0131] The soft-pack lithium-ion batteries of Examples 1-8 and Comparative Examples 1-7 were tested respectively:

[0132] Statistical analysis of the defective rate of wrinkles: 500 pcs of battery cores were produced using the negative electrode sheets in each example, and the produced battery cores were inspected comprehensively using an x-ray device. The number of defective products was counted, and the defective rate = the number of defective products / the number of products produced.

[0133] Flatness of the battery core (overall CV): A diaphragm of a thin-film pressure sensor was taken and placed between the layers of the battery core after formation. The mean value of the pressure tested at 1634 points was statistically analyzed, and the overall CV of the battery core was calculated using sigma. The overall CV of the battery core = sigma / mean.

[0134] Figure 4 The figure shows the flatness diagram of the battery core test of Example 1, Figure 5 which is the flatness diagram of the battery core test of Comparative Example 1.

[0135] The test results are shown in Table 1:

[0136] Table 1

[0137]

[0138]

[0139] As can be seen from Table 1 for Examples 1-4 and Comparative Example 1, when a composite of PEO and carboxylated silica is coated at the position of the empty foil in the single-sided area of the anode, the defective rate of wrinkles of the battery core is between 0.05% and 0.1%, which is much lower than 4.32% of Comparative Example 1. This is mainly because coating the composite of PEO and carboxylated silica at the position of the empty foil in the single-sided area of the anode reduces the stress curling at the head of the wound anode sheet, thereby improving the wrinkles of the battery core.

[0140] As can be seen from Table 1, coating the composite of PEO and carboxylated silica at the position of the empty foil in the single-sided area of the anode can also slow down the problem of lithium deposition due to overpressure in the single-sided area caused by the change in thickness from the double-sided to the single-sided area during the rolling process of the anode sheet. This is mainly because the extrusion force on the electrode sheet during double-sided rolling of the anode is relatively large. When transitioning to the single-sided rolling area, since the composite of PEO and carboxylated silica is coated at the position of the empty foil, it can slow down the extrusion of the single-sided area anode coating by the rolling roller, so as not to damage the graphite interlayer structure at this position.

[0141] As can be seen from Examples 1-4 and Comparative Examples 2-3 in Table 1, when the mass ratio of PEO to carboxylated silica is in the range of (1-4):(6-9), the overall CV of the battery cell can be improved. When the ratio is 2:8, the overall CV of the battery cell can reach an optimal value of 25.33%. This is mainly because the poly(ethylene oxide) / carboxylated nanosilica undergoes a thermal curing reaction at the high temperature during formation, which can accelerate the hydrogen bond cross-linking reaction between poly(ethylene oxide) and carboxylated nanosilica. The cross-linked poly(ethylene oxide) and carboxylated nanosilica form a three-dimensional network, thereby improving the flatness of the lithium-ion battery.

[0142] As can be seen from Examples 1, 5-6 and Comparative Example 6 in Table 1, when the coating thickness of the composite in Region ① is in the range of 4-8 μm, the effect of improving the defective rate of curling and wrinkling in the single-sided area and the flatness of the battery cell after formation in the manufacturing process is better, and the best effect is achieved at 6 μm. This is mainly because when the coating thickness is too thin, the weight of the material in the single-sided area of the anode is too light to effectively improve the anode curling; while when the coating thickness is too thick, the increase in the coating thickness will affect the overall thickness of the battery cell, occupying space and affecting the overall volume energy density of the battery cell.

[0143] As can be seen from Examples 1, 7-8 and Comparative Examples 4-5 in Table 1, the flatness of the battery cell after formation is also related to the molecular weight of PEO in the composite. When the molecular weight of poly(ethylene oxide) is in the range of 100,000-500,000, the cross-linking effect is the best. This is because the poly(ethylene oxide) / carboxylated nanosilica composite absorbs the electrolyte and presents a gel state, thereby improving the flatness of the lithium-ion battery. When the molecular weight of poly(ethylene oxide) is lower than 100,000, the number of hydroxyl functional groups on the surface of poly(ethylene oxide) is small and the cross-linking degree with carboxylated silica is low; while when the molecular weight of poly(ethylene oxide) is too large, the movement of its chain segments will be restricted, resulting in an increase in the hardness and rigidity of the poly(ethylene oxide) / carboxylated nanosilica composite in the electrolyte and unable to effectively improve the flatness of the battery cell.

[0144] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A composite structure negative electrode sheet, characterized in that: The head empty foil area of ​​the negative electrode sheet is coated with a composite material layer, and the composite material layer includes a composite of a high molecular polymer and carboxylated silicon dioxide.

2. The negative electrode sheet according to claim 1, characterized in that: The high molecular polymer includes at least one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polycarbonate; and / or, the molecular weight of the high molecular polymer is 100,000 to 500,000; and / or, the particle size of the carboxylated silicon dioxide is 1 to 100 nm; And / or, the density of the carboxylated silicon dioxide is 2.2 to 2.6 g / cm 3 .

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The mass ratio of the high molecular polymer to the carboxylated silicon dioxide is (1-4):(6-9).

4. The negative electrode sheet according to claim 1, characterized in that: The thickness of the composite material layer is 4-8 μm.

5. A method for preparing a composite structure negative electrode sheet according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: weighing a predetermined mass of a high molecular polymer and carboxylated silicon dioxide, respectively preparing them into solutions and then mixing them evenly to obtain a composite slurry; Applying the composite slurry to the empty foil area on one side of the head of the negative electrode current collector along the unwinding direction of the current collector, and drying to form a composite material layer; The negative electrode active material, the conductive agent and the adhesive are uniformly mixed to prepare a negative electrode slurry, and the negative electrode slurry is coated on the area of ​​the negative electrode current collector that is not coated with the composite slurry, and the composite structure negative electrode sheet is obtained after drying.

6. The preparation method according to claim 5, characterized in that: The high molecular polymer includes at least one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polycarbonate; and / or, the molecular weight of the high molecular polymer is 100,000 to 500,000; and / or, the particle size of the carboxylated silicon dioxide is 1 to 100 nm; And / or, the density of the carboxylated silicon dioxide is 2.2 to 2.6 g / cm 3 ; And / or, the mass ratio of the high molecular weight polymer to the carboxylated silica is (1-4):(6-9).

7. The preparation method according to claim 5, characterized in that: The coating thickness of the composite slurry is 4 to 8 μm; and / or the coating length of the composite slurry is 2 to 2.5 times the width of the battery cell corresponding to the composite structure negative electrode sheet.

8. A battery cell, characterized in that: It comprises the composite structure negative electrode sheet as described in any one of claims 1 to 4 or the composite structure negative electrode sheet obtained by the preparation method as described in any one of claims 5 to 7.

9. A lithium ion battery, characterized in that: Comprising the battery cell as claimed in claim 8.

10. Use of the lithium-ion battery according to claim 9 in an energy storage device, an electrical device or an electronic device.

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