Lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion battery. The lithium ion battery comprises a negative plate, a positive plate, a diaphragm and an electrolyte, the negative plate comprises a negative current collector; the first negative electrode film layer is arranged on at least one surface of the negative electrode current collector in the thickness direction, and the first negative electrode film layer comprises a first monomer, a first conductive agent and a first binder; the second negative electrode film layer is arranged on the surface, far away from the negative electrode current collector, of the first negative electrode film layer, and the second negative electrode film layer comprises a negative electrode active material, a second monomer, a second conductive agent and a second binder. The electrolyte comprises a solvent, a lithium salt and a catalyst, and the catalyst is used for promoting any one of the first monomer and the second monomer to be polymerized into a polymer. The positive electrode, the negative electrode and the electrolyte interface are blocked before the positive electrode releases oxygen, and the heat production reaction is inhibited, so that the heat production in the thermal runaway process of the battery cell is reduced, and the safety performance is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium-ion battery. Background Art

[0002] In order to further improve the energy density of batteries, high nickel cathode materials have attracted widespread attention due to their high specific capacity and high platform voltage. However, with the increase of Ni content in the ternary cathode, its thermal stability decreases significantly, and it releases a large amount of O at high temperature. 2 , O 2 It will further react with EC in the electrolyte and Li embedded in the negative electrode to generate intense heat and cause thermal runaway. In addition, before the positive electrode releases oxygen, the SEI on the negative electrode surface will decompose at around 100°C, and then the electrolyte will react with the negative electrode to generate a large amount of alkane and olefin gases, which will aggravate the positive electrode oxygen release and increase the degree of thermal runaway. Summary of the invention

[0003] In view of this, the present invention provides a lithium ion battery. The present invention blocks the interface between the positive electrode, the negative electrode and the electrolyte before the positive electrode releases oxygen, inhibits the occurrence of heat generation reaction, thereby reducing the heat generation during the thermal runaway process of the battery cell and improving safety performance.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a lithium ion battery, which includes a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte;

[0006] The negative electrode sheet includes:

[0007] Anode current collector;

[0008] A first negative electrode film layer, the first negative electrode film layer is arranged on at least one surface of the negative electrode current collector in the thickness direction, and the first negative electrode film layer comprises a first monomer, a first conductive agent and a first binder;

[0009] A second negative electrode film layer, the second negative electrode film layer is arranged on a surface of the first negative electrode film layer away from the negative electrode current collector, the second negative electrode film layer comprising a negative electrode active material, a second monomer, a second conductive agent and a second binder;

[0010] The electrolyte includes a solvent, a lithium salt and a catalyst, and the catalyst is used to promote polymerization of any one of the first monomer and the second monomer into a polymer.

[0011] In a preferred embodiment of the present invention, the positive electrode sheet comprises:

[0012] Positive electrode current collector;

[0013] A positive electrode film layer, which is disposed on at least one surface of the positive electrode current collector in the thickness direction, and the positive electrode film layer includes a positive electrode active material, a third monomer, a third conductive agent and a third binder;

[0014] The catalyst in the electrolyte is used to promote the polymerization of the third monomer into a polymer.

[0015] In an embodiment of the present invention, the first monomer, the second monomer and the third monomer independently include at least one of styrene, acrylamide, N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-(1,3-phenylene)bismaleimide and N,N'-(4-methyl-1,3-phenylene)bismaleimide.

[0016] Preferably, the thickness of the first negative electrode film layer is 0.5-3 μm.

[0017] Preferably, the mass ratio of the first monomer, the first conductive agent and the first binder in the first negative electrode film layer is (30-50): (40-70): (2-10).

[0018] Preferably, the thickness of the second negative electrode film layer is 50-100 μm.

[0019] Preferably, the mass ratio of the negative electrode active material, the second monomer, the second conductive agent and the second binder in the second negative electrode film layer is (90-96): (2-5): (0.8-2): (1-3).

[0020] In an embodiment of the present invention, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon oxide, and silicon carbon.

[0021] In an embodiment of the present invention, the first conductive agent and the second conductive agent each independently include at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene.

[0022] In an embodiment of the present invention, the first binder and the second binder independently include at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacryloyl, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate, and guar gum.

[0023] In an embodiment of the present invention, a first projection of the first negative electrode film layer in the thickness direction of the negative electrode current collector coincides with a second projection of the second negative electrode film layer in the thickness direction of the negative electrode current collector, and the area of ​​the first projection is equal to the area of ​​the second projection.

[0024] In an embodiment of the present invention, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0025] In an embodiment of the present invention, the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene.

[0026] In an embodiment of the present invention, the third binder includes at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate, and guar gum.

[0027] Preferably, the thickness of the positive electrode film layer is 40 to 80 μm.

[0028] Preferably, the mass ratio of the positive electrode active material, the third monomer, the third conductive agent and the third binder in the positive electrode film layer is (92-96): (2-5): (0.8-2): (0.9-2).

[0029] In an embodiment of the present invention, the catalyst includes at least one of barbituric acid, azobisisobutyronitrile, and dibenzoyl peroxide.

[0030] Preferably, the mass proportion of the catalyst in the electrolyte is 3% to 6%.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The monomers in the positive and negative electrode sheets of the present invention can be rapidly polymerized with the catalyst in the electrolyte at high temperature to generate a cross-linked network polymer, which can effectively cover the interface between the positive and negative electrode particles and inhibit the heat generated by various side reactions; in addition, there is a first negative electrode film layer rich in monomers under the negative electrode active layer of the negative electrode sheet, which will polymerize to form an insulating layer before the diaphragm fails, avoiding short-circuit heat generation caused by the contact between the positive and negative electrodes, thereby controlling the heat generation of the battery cell at high temperature as a whole, thereby achieving the effect of improving safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of the negative electrode sheet;

[0034] Figure 2 Schematic diagram of the structure of the positive electrode.

[0035] The reference numerals are as follows:

[0036] 11, negative electrode current collector;

[0037] 12, a first negative electrode film layer;

[0038] 13. Second negative electrode film layer

[0039] 21, positive electrode current collector;

[0040] 22. Positive electrode film layer. DETAILED DESCRIPTION

[0041] The present invention discloses a negative electrode sheet, a positive electrode sheet and a lithium-ion battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the above. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0042] In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes, and do not indicate or imply relative importance.

[0043] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0044] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0048] The "high temperature" mentioned in the present invention refers to a temperature greater than or equal to 130°C, for example 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, etc.

[0049] Specifically, the present invention adopts the following technical solutions:

[0050] The present invention provides a lithium ion battery, which includes a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte;

[0051] The negative electrode sheet includes:

[0052] Anode current collector;

[0053] A first negative electrode film layer, the first negative electrode film layer is arranged on at least one surface of the negative electrode current collector in the thickness direction, and the first negative electrode film layer comprises a first monomer, a first conductive agent and a first binder;

[0054] A second negative electrode film layer, the second negative electrode film layer is arranged on a surface of the first negative electrode film layer away from the negative electrode current collector, the second negative electrode film layer comprising a negative electrode active material, a second monomer, a second conductive agent and a second binder;

[0055] The electrolyte includes a solvent, a lithium salt and a catalyst, and the catalyst is used to promote polymerization of any one of the first monomer and the second monomer into a polymer.

[0056] In the present invention, the second negative electrode film layer is the negative electrode active layer. A small amount of monomers is added without affecting the electrical performance. Under the action of the catalyst in the electrolyte, the monomers in the second negative electrode film layer can quickly generate a cross-linked network polymer layer on the surface of the negative electrode active material at high temperature to block the interface, block the direct contact between the negative electrode and the electrolyte, and alleviate the mutual crosstalk caused by gas production between the positive and negative electrodes, isolate the solid-liquid and solid-gas interfaces, and inhibit the heat generation of side reactions.

[0057] However, the amount of monomer added to the negative electrode active layer is small, and it cannot completely achieve electrical insulation. Therefore, it is necessary to set the first negative electrode film layer to avoid internal short circuit. The monomer content in the first negative electrode film layer is high. At high temperatures, the monomers in the first negative electrode film layer can quickly polymerize to form an insulating layer with electrical insulation. When the temperature exceeds 150°C and the diaphragm begins to fail, the monomers in the first negative electrode film layer have polymerized into an electrical insulation network, cutting off the electron transmission between the second negative electrode film layer and the negative electrode current collector. Therefore, even when the positive and negative electrodes are in direct contact, heat will not be generated due to internal short circuits. The heat generated by side reactions and internal short circuits are effectively controlled. Therefore, the thermal stability of the battery cell is effectively improved, and the degree of thermal runaway is greatly reduced.

[0058] In the embodiment of the present invention, a monomer may be added to the positive electrode sheet, or may not be added to the positive electrode sheet. Preferably, a monomer is added.

[0059] In a preferred embodiment of the present invention, the positive electrode sheet comprises:

[0060] Positive electrode current collector;

[0061] A positive electrode film layer, which is disposed on at least one surface of the positive electrode current collector in the thickness direction, and the positive electrode film layer includes a positive electrode active material, a third monomer, a third conductive agent and a third binder;

[0062] The catalyst in the electrolyte is used to promote the polymerization of the third monomer into a polymer.

[0063] In the present invention, a small amount of monomers is added to the positive electrode film layer without affecting the electrical performance. Under the action of the catalyst in the electrolyte, the monomers in the positive electrode film layer can generate a polymer interface layer on the surface of the positive electrode active material at high temperature, inhibiting the release of oxygen from the high-nickel positive electrode, blocking the direct contact between the positive electrode and the electrolyte, blocking the reaction of oxygen and the electrolyte, isolating the solid-liquid and solid-gas interfaces, and inhibiting the heat generation of side reactions.

[0064] In an embodiment of the present invention, the first monomer, the second monomer and the third monomer independently include at least one of styrene, acrylamide, N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-(1,3-phenylene)bismaleimide and N,N'-(4-methyl-1,3-phenylene)bismaleimide.

[0065] Preferably, the thickness of the first negative electrode film layer is 0.5 to 3 μm. Exemplarily, the thickness of the first negative electrode film layer is any value among 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any value within the range of values ​​composed of any two of the above values. When the thickness of the first negative electrode film layer is too thick, it will increase the difficulty of electron transmission, increase the internal resistance of the battery cell, and affect the performance of the battery cell. When the thickness of the first negative electrode film layer is too thin, the first negative electrode film layer cannot form an effective insulating layer, and the heat generated by side reactions and internal short circuits cannot be effectively controlled.

[0066] Preferably, the mass ratio of the first monomer, the first conductive agent and the first binder in the first negative electrode film layer is (30-50): (40-70): (2-10). Exemplarily, the mass ratio of the first monomer, the first conductive agent and the first binder is any value in 30:70:2, 50:40:10, 30:65:5, 50:45:5, 40:55:5 or any value in the range of any two of the above values. When the amount of the first monomer added is small, the difficulty of monomer polymerization increases, the first negative electrode film layer cannot form an effective insulating layer, and the heat generated by side reactions and internal short circuits cannot be effectively controlled. When the amount of the first monomer added is large, due to the poor conductivity of the monomer, the overall internal resistance of the battery cell increases significantly. Although the safety performance is greatly improved, during the charge and discharge process of the battery cell, due to the excessive internal resistance, the capacity cannot be fully utilized, and the temperature rise of the charge and discharge battery cell is large, which affects the service life.

[0067] Preferably, the thickness of the second negative electrode film layer is 50-100 μm. Exemplarily, the thickness of the second negative electrode film layer is any value among 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any value within the range of any two of the above values.

[0068] Preferably, the coating surface density of the second negative electrode film layer is 80 to 170 g / m 2 For example, the coating surface density of the second negative electrode film layer is 80 g / m 2 , 90g / m 2 , 100g / m 2 , 110g / m 2 , 120g / m 2 , 130g / m 2 , 140g / m 2 , 150g / m 2 , 160g / m 2 , 170g / m 2 Any value in or any value in the range consisting of any two of the above values.

[0069] Preferably, the mass ratio of the negative electrode active material, the second monomer, the second conductive agent and the second binder in the second negative electrode film layer is (90-96): (2-5): (0.8-2): (1-3). Exemplarily, the mass ratio of the negative electrode active material, the second monomer, the second conductive agent and the second binder is any value in 90:5:0.8:3, 96:2:2:1, 94.5:2:1:2.5, 91.5:5:1:2.5, 92.5:4:1:2.5 or any value in the range of any two of the above values. When the amount of the second monomer added is small, the difficulty of monomer polymerization increases, the polymer interface layer cannot effectively cover the interface of the negative electrode active material, and the heat generated by side reactions and internal short circuits cannot be effectively controlled. When a large amount of the second monomer is added, the overall internal resistance of the battery cell increases significantly due to the poor conductivity of the monomer. Although the safety performance is greatly improved, the capacity cannot be fully utilized during the charge and discharge process of the battery cell due to the excessive internal resistance, and the temperature rise of the charge and discharge battery cell is large, affecting the service life.

[0070] In an embodiment of the present invention, the negative electrode active material includes but is not limited to at least one of graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon oxide, and silicon carbon.

[0071] In an embodiment of the present invention, the first conductive agent and the second conductive agent independently include but are not limited to at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene.

[0072] In an embodiment of the present invention, the first binder and the second binder independently include but are not limited to at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate, and guar gum.

[0073] In an embodiment of the present invention, a first projection of the first negative electrode film layer in the thickness direction of the negative electrode current collector coincides with a second projection of the second negative electrode film layer in the thickness direction of the negative electrode current collector, and the area of ​​the first projection is equal to the area of ​​the second projection.

[0074] In an embodiment of the present invention, the negative electrode current collector is copper foil.

[0075] Preferably, the thickness of the negative electrode current collector is 4 to 10 μm. Exemplarily, the thickness of the negative electrode current collector is any value among 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value within the range of any two of the above values.

[0076] In an embodiment of the present invention, the positive electrode active material includes but is not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0077] In an embodiment of the present invention, the third conductive agent includes but is not limited to at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene.

[0078] In an embodiment of the present invention, the third binder includes but is not limited to at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate, and guar gum.

[0079] Preferably, the thickness of the positive electrode film layer is 40-80 μm. Exemplarily, the thickness of the positive electrode film layer is any value among 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or any value within the range formed by any two of the above values.

[0080] Preferably, the coating surface density of the positive electrode film layer is 130 to 260 g / m 2 For example, the coating surface density of the positive electrode film layer is 130 g / m 2 , 140g / m 2 , 150g / m 2 , 160g / m 2 , 170g / m 2 , 180g / m 2 , 190g / m 2 , 200g / m 2 , 220g / m 2 , 240g / m 2 , 260g / m 2 Any value in or any value in the range consisting of any two of the above values.

[0081] Preferably, the mass ratio of the positive electrode active material, the third monomer, the third conductive agent and the third binder in the positive electrode film layer is (92-96): (2-5): (0.8-2): (0.9-2). Exemplarily, the mass ratio of the positive electrode active material, the third monomer, the third conductive agent and the third binder is any value in 92:5:0.8:2, 96:2:2:0.9, 95:2:1.5:1.5, 92:5:1.5:1.5, 93:4:1.5:1.5 or any value in the range of any two of the above values. When the amount of the third monomer added is small, the difficulty of monomer polymerization increases, the polymer interface layer cannot effectively cover the interface of the positive electrode active material, and the heat generated by side reactions and internal short circuits cannot be effectively controlled. When a large amount of the third monomer is added, the overall internal resistance of the battery cell increases significantly due to the poor conductivity of the monomer. Although the safety performance is greatly improved, the capacity cannot be fully utilized during the charge and discharge process of the battery cell due to the excessive internal resistance, and the temperature rise of the charge and discharge battery cell is large, affecting the service life.

[0082] In another embodiment of the present invention, no monomer is added to the positive electrode sheet. The positive electrode film layer includes a positive electrode active material, a third conductive agent and a third binder. Preferably, the mass ratio of the positive electrode active material, the third conductive agent and the third binder in the positive electrode film layer is (92-96): (0.8-2): (0.9-2).

[0083] In an embodiment of the present invention, the positive electrode current collector is aluminum foil.

[0084] Preferably, the thickness of the positive electrode current collector is 8 to 20 μm. Exemplarily, the thickness of the positive electrode current collector is any value among 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any value within the range of any two of the above values.

[0085] In the embodiment of the present invention, the catalyst includes but is not limited to at least one of barbituric acid, azobisisobutyronitrile and dibenzoyl peroxide. Any catalyst that can catalyze the polymerization of monomers into polymers is within the protection scope of the present invention.

[0086] Preferably, the mass proportion of the catalyst in the electrolyte is 3% to 6%. Exemplarily, the mass proportion of the catalyst in the electrolyte is any value among 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or any value within the range of any two of the above values. When the amount of catalyst added is small, the difficulty of monomer polymerization increases, the polymer interface layer cannot effectively cover the positive and negative electrode interfaces, and the first negative electrode film layer cannot form an effective insulating layer, and the heat generated by side reactions and internal short circuits cannot be effectively controlled. When the amount of catalyst added is large, due to the poor conductivity of the catalyst, the overall internal resistance of the battery cell increases significantly. Although the safety performance is greatly improved, during the charge and discharge process of the battery cell, due to the excessive internal resistance, the capacity cannot be fully utilized, and the temperature rise of the charge and discharge battery cell is large, which affects the service life.

[0087] In an embodiment of the present invention, the solvent includes but is not limited to at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, and fluoroethylene carbonate.

[0088] In an embodiment of the present invention, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

[0089] Preferably, the concentration of the lithium salt in the electrolyte is 1 to 1.4 mol / L. Exemplarily, the concentration of the lithium salt in the electrolyte is any one of 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, and 1.4 mol / L, or any value within the range of any two of the above values.

[0090] In an embodiment of the present invention, the diaphragm is not particularly limited. In a specific embodiment of the present invention, the diaphragm includes a base film and a coating. Preferably, the thickness of the base film is 7 to 15 μm, and the material of the base film includes polyethylene and / or polypropylene. Preferably, the thickness of the coating is 1 to 8 μm, and the material of the coating includes but is not limited to one or more of aluminum oxide, titanium dioxide, zirconium oxide, barium titanate, lithium aluminate, lithium lanthanum titanate, lithium aluminum titanium phosphate, and lithium lanthanum zirconate.

[0091] In an embodiment of the present invention, the lithium-ion battery further includes an aluminum shell.

[0092] In the embodiment of the present invention, the battery structure includes but is not limited to button batteries, soft-pack batteries, cylindrical batteries, etc.

[0093] The reagents, instruments or materials used in the present invention can be obtained through commercial channels.

[0094] The present invention will be further described below in conjunction with embodiments:

[0095] Embodiment 1:

[0096] 1. Preparation of negative electrode

[0097] Preparation of the first negative electrode film layer: A 6μm copper foil was selected as the negative electrode current collector. The monomer N,N'-(4,4'-methylenediphenyl) bismaleimide, the conductive agent conductive carbon black, the binder sodium carboxymethyl cellulose and styrene-butadiene rubber (SBR) were added into deionized water at a mass ratio of 30:65:2:3. The solid content was controlled to be 30%. After being evenly dispersed, it was coated on the surfaces of both sides of the copper foil and dried to complete the preparation of the first negative electrode film layer. The thickness of the first negative electrode film layer was 3μm.

[0098] Preparation of the second negative electrode film layer: graphite is selected as the negative electrode active material, N,N'-(4,4'-methylenediphenyl) bismaleimide is selected as the monomer, conductive carbon black is selected as the conductive agent, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are selected as the binder. The negative electrode active material, monomer, conductive agent, CMC, and SBR are mixed in a mass ratio of 94.5:2:1:1:1.5, and deionized water is added and stirred to form a uniform and stable negative electrode slurry. The solid content is controlled to be 50%, and the negative electrode slurry is evenly coated on the surface of the first negative electrode film layer, and the coating surface density is 99g / m 2 After rolling, the thickness of the second negative electrode film layer is 65 μm. The structural diagram of the negative electrode sheet is shown in Figure 1 shown.

[0099] 2. Preparation of positive electrode

[0100] The positive electrode active material is lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn0.1 O 2 The monomer is N,N'-(4,4'-methylenediphenyl) bismaleimide, the conductive agent is conductive carbon black SP and carbon nanotubes (mass ratio 10:1), the binder is PVDF5130, and the positive electrode current collector is 10μm aluminum foil. The positive electrode active material, monomer, conductive agent and binder are mixed in a ratio of 95:2:1.5:1.5, and NMP is added and stirred to form a uniform and stable positive electrode slurry. The solid content is controlled to 75%, and the positive electrode slurry is evenly coated on the positive electrode current collector. The coating surface density is 156g / m 2 The thickness of the positive electrode film after rolling is 50μm. The structural diagram of the positive electrode sheet is as follows Figure 2 shown.

[0101] 3. Selection of diaphragm

[0102] A polypropylene film is selected as the separator base film with a thickness of 12 μm, and the surface of the base film facing the positive electrode is coated with 3 μm alumina ceramic.

[0103] 4. Battery cell assembly process

[0104] Arrange the positive electrode sheet, separator, negative electrode sheet and separator in sequence, and use winding as the assembly method.

[0105] Preparation of electrolyte: LiPF 6 LiPF is dissolved in a solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1. 6 The concentration was 1.2 mol / L, and catalysts barbituric acid and azobisisobutyronitrile were added (mass ratio 3:1), and the catalyst accounted for 3% of the total mass of the electrolyte.

[0106] The electrolyte was injected into the dry battery cell, and after soaking for 24 hours, the battery cell was formed at 45°C. The formation process was as follows: charge at 0.05C to 3.4V, and then charge at 0.2C to 3.75V. The battery cell was completed after aging at room temperature for 24 hours.

[0107] Embodiment 2:

[0108] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0109] The first negative electrode film layer: the monomer, the conductive agent, the binder sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are in a mass ratio of 50:45:2:3;

[0110] The second negative electrode film layer: the mass ratio of negative electrode active material, monomer, conductive agent, binder CMC, and binder SBR is 91.5:5:1:1:1.5;

[0111] Positive electrode film layer: the mass ratio of positive electrode active material, monomer, conductive agent and binder is 92:5:1.5:1.5;

[0112] In the electrolyte, the catalyst accounts for 6% of the total mass of the electrolyte.

[0113] Embodiment 3:

[0114] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0115] The monomers in the positive and negative electrodes are replaced with styrene;

[0116] The first negative electrode film layer: the monomer, the conductive agent, the binder sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are in a mass ratio of 40:55:2:3;

[0117] The second negative electrode film layer: the mass ratio of negative electrode active material, monomer, conductive agent, binder CMC, and binder SBR is 92.5:4:1:1:1.5;

[0118] Positive electrode film layer: the mass ratio of positive electrode active material, monomer, conductive agent and binder is 93:4:1.5:1.5;

[0119] In the electrolyte, the catalyst accounts for 5% of the total mass of the electrolyte.

[0120] Embodiment 4:

[0121] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0122] The monomers in the positive and negative electrodes are replaced with N,N'-(1,2-phenylene)bismaleimide;

[0123] The catalyst in the electrolyte was replaced with barbituric acid and dibenzoyl peroxide (mass ratio 3:1).

[0124] Embodiment 5:

[0125] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0126] The thickness of the first negative electrode film layer is 0.5 μm.

[0127] Embodiment 6:

[0128] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0129] The second negative electrode film coating surface density is 83g / m 2 , the thickness of the second negative electrode film layer after rolling is 50μm;

[0130] Positive electrode coating surface density 130g / m 2 , the thickness of the positive electrode film after rolling is 40μm.

[0131] Embodiment 7:

[0132] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0133] The second negative electrode film coating surface density is 166g / m 2 , the thickness of the second negative electrode film layer after rolling is 100 μm;

[0134] Positive electrode coating surface density 260g / m 2 , the thickness of the positive electrode film after rolling is 80μm.

[0135] Embodiment 8:

[0136] The other conditions of this embodiment are the same as those of embodiment 1, except that:

[0137] No monomer N,N'-(1,2-phenylene)bismaleimide is added to the positive electrode sheet.

[0138] Comparative Example 1:

[0139] The other conditions of this comparative example are the same as those of Example 1, except that the monomers in the positive and negative electrodes and the catalyst in the electrolyte are eliminated.

[0140] Comparative Example 2:

[0141] The other conditions of this comparative example and Example 1 remain unchanged, except that the first negative electrode film layer is eliminated.

[0142] Comparative Example 3:

[0143] The other conditions of this comparative example and Example 1 remain unchanged, except that:

[0144] The first negative electrode film layer: the monomer, the conductive agent, the binder sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are in a mass ratio of 10:85:2:3;

[0145] The second negative electrode film layer: the mass ratio of negative electrode active material, monomer, conductive agent, binder CMC, and binder SBR is 95.5:1:1:1:1.5;

[0146] Positive electrode film layer: the mass ratio of positive electrode active material, monomer, conductive agent and binder is 96:1:1.5:1.5;

[0147] In the electrolyte, the catalyst accounts for 1% of the total mass of the electrolyte.

[0148] Comparative Example 4:

[0149] The other conditions of this comparative example and Example 1 remain unchanged, except that:

[0150] The first negative electrode film layer: the monomer, the conductive agent, the binder sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are in a mass ratio of 60:35:2:3;

[0151] The second negative electrode film layer: the mass ratio of negative electrode active material, monomer, conductive agent, binder CMC, and binder SBR is 86.5:10:1:1:1.5;

[0152] Positive electrode film layer: the mass ratio of positive electrode active material, monomer, conductive agent and binder is 87:10:1.5:1.5;

[0153] In the electrolyte, the catalyst accounts for 8% of the total mass of the electrolyte.

[0154] Comparative Example 5:

[0155] The other conditions of this comparative example and Example 1 remain unchanged, except that the thickness of the first negative electrode film layer is 6 μm.

[0156] Battery performance test

[0157] The battery cells prepared in the above examples and comparative examples were subjected to the following tests to evaluate the internal resistance and safety performance of the battery cells.

[0158] DCR test: At 25℃ and 50% SOC, discharge the battery cell at 1C for 30s. The voltage difference divided by the current value is the DC internal resistance DCR. The smaller the DCR value, the smaller the internal resistance of the battery cell.

[0159] ARC test: The battery cell is heated from 25°C until failure, and the heating rate at each temperature point is recorded during the test, and the temperature at the thermal runaway point T is compared. 2 (heating rate up to 1℃ / s) and the highest temperature T during thermal runaway 3 ; T 2 The higher the temperature, the higher the thermal runaway temperature of the battery cell, which means the better the thermal stability of the battery cell; T 3 The higher the temperature, the more severe the thermal runaway of the battery cell.

[0160] The test results are summarized in Table 1:

[0161] Table 1

[0162]

[0163]

[0164] As shown in Table 1, Examples 1 to 8 are preferred schemes, in which the ratio of monomers to catalysts is controlled within a specified range, and the effect on the internal resistance of the battery cell is small, and the normal charging and discharging of the battery cell will not be affected. In addition, during the thermal runaway test, when the temperature exceeds 130°C, the catalyst triggers a rapid polymerization reaction of the monomers in the electrode sheet, and a polymer interface layer is generated on the surface of the active material, blocking the direct contact between the positive and negative electrodes and the electrolyte, and alleviating the mutual crosstalk caused by the gas production between the positive and negative electrodes, thereby greatly reducing the heat generation. In addition, when the temperature exceeds 150°C and the diaphragm begins to fail, the monomers of the first negative electrode film layer have been polymerized into an electrically insulating network, cutting off the electron transmission between the second negative electrode film layer and the current collector. Therefore, even when the positive and negative electrode sheets are in direct contact, heat will not be generated due to an internal short circuit, and the heat generated by the side reactions and the internal short circuit are effectively controlled. Therefore, the thermal stability of the battery cell is effectively improved, and the degree of thermal runaway is greatly reduced.

[0165] It can be seen from Example 1 and Comparative Example 1 that when no monomer is added to the battery cell, the heat generated by the side reactions and internal short circuits at high temperatures cannot be effectively controlled, the thermal stability of the battery cell cannot be effectively improved, and the degree of thermal runaway is severe.

[0166] It can be seen from Example 1 and Comparative Example 2 that when the negative electrode does not have the first negative electrode film layer, although the positive and negative electrode interfaces are effectively protected, when the diaphragm fails, the short circuit between the positive and negative electrodes cannot be effectively controlled, which will cause the battery cell temperature to rise rapidly and cause thermal runaway.

[0167] It can be seen from Example 1 and Comparative Example 3 that when the amount of monomer and catalyst added to the battery cell is small, the difficulty of monomer polymerization increases, the polymer interface layer cannot effectively cover the positive and negative electrode interfaces, and the first negative electrode film layer cannot form an effective insulating layer, and the heat generated by side reactions and internal short circuits cannot be effectively controlled. Although there is a certain improvement compared to Comparative Example 1, the effect is not obvious.

[0168] It can be seen from Example 1 and Comparative Example 4 that when the amount of monomers and catalysts added to the battery cell is relatively large, the overall internal resistance of the battery cell increases significantly due to the poor conductivity of the monomers and catalysts. Although the safety performance is greatly improved, during the charge and discharge process of the battery cell, the capacity cannot be fully utilized due to the excessive internal resistance, and the temperature rise of the charge and discharge battery cell is relatively large, which affects the service life.

[0169] It can be seen from Example 1 and Comparative Example 5 that when the thickness of the first negative electrode film layer is too thick, it will increase the difficulty of electron transmission, increase the internal resistance of the battery cell, and affect the performance of the battery cell.

[0170] It can be seen from Example 1 and Example 8 that in Example 8, since no monomer is added to the positive electrode and only the negative electrode is added, although the effect of suppressing the heat generation of side reactions is worse than that of Example 1, it is greatly improved compared with Comparative Example 1.

[0171] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte; The negative electrode sheet comprises: Anode current collector; A first negative electrode film layer, the first negative electrode film layer is disposed on at least one surface of the negative electrode current collector in a thickness direction, the first negative electrode film layer comprising a first monomer, a first conductive agent and a first binder; A second negative electrode film layer, the second negative electrode film layer is arranged on a surface of the first negative electrode film layer away from the negative electrode current collector, the second negative electrode film layer comprising a negative electrode active material, a second monomer, a second conductive agent and a second binder; The electrolyte includes a solvent, a lithium salt and a catalyst, and the catalyst is used to promote polymerization of any one of the first monomer and the second monomer into a polymer.

2. The lithium-ion battery according to claim 1, characterized in that The positive electrode sheet comprises: Positive electrode current collector; A positive electrode film layer, the positive electrode film layer is arranged on at least one surface of the positive electrode current collector in the thickness direction, the positive electrode film layer comprises a positive electrode active material, a third monomer, a third conductive agent and a third binder; The catalyst is used to promote the polymerization of the third monomer into a polymer.

3. The lithium-ion battery according to claim 2, characterized in that: The first monomer, the second monomer and the third monomer independently include at least one of styrene, acrylamide, N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-(1,3-phenylene)bismaleimide and N,N'-(4-methyl-1,3-phenylene)bismaleimide.

4. The lithium-ion battery according to claim 1, characterized in that: The thickness of the first negative electrode film layer is 0.5 to 3 μm; Preferably, the mass ratio of the first monomer, the first conductive agent and the first binder in the first negative electrode film layer is (30-50): (40-70): (2-10).

5. The lithium-ion battery according to claim 1, characterized in that: The thickness of the second negative electrode film layer is 50-100 μm; Preferably, the mass ratio of the negative electrode active material, the second monomer, the second conductive agent and the second binder in the second negative electrode film layer is (90-96): (2-5): (0.8-2): (1-3).

6. The lithium-ion battery according to claim 1, characterized in that The negative electrode active material includes at least one of graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon oxide, and silicon carbon; Preferably, the first conductive agent and the second conductive agent independently include at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene; Preferably, the first binder and the second binder independently include at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate and guar gum.

7. The lithium-ion battery according to claim 1, characterized in that: A first projection of the first negative electrode film layer in the thickness direction of the negative electrode current collector coincides with a second projection of the second negative electrode film layer in the thickness direction of the negative electrode current collector, and an area of ​​the first projection is equal to an area of ​​the second projection.

8. The lithium-ion battery according to claim 2, characterized in that: The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; Preferably, the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotube or graphene; Preferably, the third binder includes at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, polyacrylamide, styrene-butadiene rubber, sodium alginate, and guar gum.

9. The lithium-ion battery according to claim 2, characterized in that: The thickness of the positive electrode film layer is 40 to 80 μm; Preferably, the mass ratio of the positive electrode active material, the third monomer, the third conductive agent and the third binder in the positive electrode film layer is (92-96): (2-5): (0.8-2): (0.9-2).

10. The lithium ion battery according to claim 1, characterized in that: The catalyst comprises at least one of barbituric acid, azobisisobutyronitrile and dibenzoyl peroxide; Preferably, the mass percentage of the catalyst in the electrolyte is 3% to 6%.

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