Negative electrode sheet and battery

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode sheet and a battery. The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer comprises a first silicon-based material and a first binder, and the second negative electrode active material layer comprises a second silicon-based material and a second binder; the first binder comprises a cationic polymer electrolyte, and the second binder comprises an anionic polymer electrolyte; or the first binder comprises an anionic polymer electrolyte, and the second binder comprises a cationic polymer electrolyte. The negative electrode sheet adopts a double-layer coating mode, ion bonds are crosslinked through polymer electrolytes of different ion types in the two layers of active material layers, the flexibility of the electrode sheet can be improved, the expansion of the silicon-based material can be effectively inhibited, the surface tension of the electrode sheet is consistent, and the electrochemical performance of the battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode sheet and a battery. BACKGROUND

[0002] In recent years, many manufacturers have focused on silicon negative electrode batteries, and some silicon carbon or silicon oxide is added to graphite, but the problem is that the expansion of silicon materials causes material falling and large cycle loss. At present, most companies in the industry use an increased amount of binder to suppress the expansion of silicon, but too much binder will cause the internal resistance to rise and the electrical performance to decrease seriously.

[0003] Some companies use new binders. In a patent KR20220122818A of a South Korean company, a cross-linked copolymer is used as a silicon negative electrode binder. The cross-linked copolymer is prepared by cross-linking a side chain containing polyethylene glycol capped with a benzaldehyde group to a main chain side chain containing ethylene glycol chitosan. The cross-linked polymer contains imine bonds, which have excellent self-repairing ability, adhesion and mechanical strength, and can achieve the same effect without increasing the amount of use. However, the groups contained in this type of binder have strong adsorption to graphite or silicon, and the negative electrode slurry will cause abnormal gelation, which does not have a large production capacity.

[0004] Some companies propose to use a double-coating method to place the silicon-containing slurry in the bottom layer close to the current collector or the top layer far from the current collector. For example, in a patent CN116230867A of Tianjin Lishen, a double-coating process is used to make SiO x more distributed in the inner layer, and the volume expansion of SiO x is inhibited by the surface layer of graphite, and the overall conductivity of the negative electrode material is improved, and more binder and conductive agent are distributed in the inner layer to increase the adhesion of the composite negative electrode; for example, in a patent CN110148708A of Zhuhai Guanyu, it is proposed that the first coating layer is a bottom graphite coating layer close to the negative electrode current collector, and the second coating layer is a top silicon-containing coating layer far from the negative electrode current collector, and a double-coating technology is used to coat two kinds of slurry on the negative electrode current collector at the same time to obtain a double-coated negative electrode sheet with a silicon-containing coating layer in the top layer and a pure graphite layer in the bottom layer. However, simply placing the silicon-containing slurry in the bottom layer or the top layer cannot significantly improve the expansion of the silicon negative electrode, and it increases the difficulty of preparing the electrode sheet, and because the two layers of slurry have different compositions and different surface tensions, it is easy to form pits on the surface of the electrode sheet, which causes lithium precipitation. SUMMARY

[0005] Therefore, the application provides a negative electrode sheet and a battery. The negative electrode sheet adopts a double-layer coating method, the binders contained in the two active material layers are different ionic polymer electrolytes, and the ionic bonds are crosslinked by the different ionic polymer electrolytes, so that the flexibility of the electrode sheet is improved, the expansion of the silicon-based material is effectively inhibited, the surface tension of the electrode sheet is uniform, and the electrochemical performance of the battery is improved.

[0006] In order to achieve the above-mentioned purposes, the application provides the following technical solutions.

[0007] In a first aspect, the application provides a negative electrode sheet, which comprises:

[0008] (a) a negative current collector;

[0009] (b) a first negative active material layer, which is arranged on at least one surface of the negative current collector, and comprises a first silicon-based material and a first binder;

[0010] (c) a second negative active material layer, which is arranged on the surface of the first negative active material layer away from the negative current collector, and comprises a second silicon-based material and a second binder;

[0011] The first binder and the second binder are one of (i) or (ii) as follows:

[0012] (i) the first binder comprises a cationic polymer electrolyte, and the second binder comprises an anionic polymer electrolyte;

[0013] (ii) the first binder comprises an anionic polymer electrolyte, and the second binder comprises a cationic polymer electrolyte.

[0014] In an embodiment of the application, the mass percentage content of the cationic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m1, the mass percentage content of the anionic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m2, and m1 and m2 satisfy the following relationship:

[0015] 0≤|m1-m2| / m1≤20%;

[0016] and / or, 0≤|m1-m2| / m2≤20%;

[0017] and / or, m1 is 1.8% to 3.0%;

[0018] and / or, m2 is 1.8% to 3.0%.

[0019] In an embodiment of the present application, the cationic polymer electrolyte comprises at least one of cationic polyacrylamide, polyethyleneimine, cationic polyvinyl alcohol, polyvinylamide.

[0020] In an embodiment of the present application, the cationic group of the cationic polyacrylamide comprises at least one of imidazole group, pyridine group, piperidine group.

[0021] In a preferred embodiment of the present application, the first binder comprises the cationic polymer electrolyte, the cationic polymer electrolyte comprises the cationic polyacrylamide, and the cationic group of the cationic polyacrylamide comprises the imidazole group.

[0022] In an embodiment of the present application, the anionic polymer electrolyte comprises at least one of anionic epoxy resin, sodium polyacrylate, anionic polyacrylamide, anionic polyvinyl alcohol, sodium polystyrene sulfonate.

[0023] In an embodiment of the present application, the anionic group of the anionic epoxy resin comprises at least one of carboxyl group, phosphoric acid group, sulfonic acid group.

[0024] In an embodiment of the present application, the first negative electrode active material layer further comprises a first carbon-based material and a first conductive agent.

[0025] Preferably, the mass ratio of the first carbon-based material, the first silicon-based material, the first binder and the first conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5).

[0026] In an embodiment of the present application, the second negative electrode active material layer further comprises a second carbon-based material and a second conductive agent.

[0027] Preferably, the mass ratio of the second carbon-based material, the second silicon-based material, the second binder and the second conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5).

[0028] Preferably, the ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is (5-6):(4-5).

[0029] Preferably, the thickness of the first negative electrode active material layer is 70-110 μm.

[0030] Preferably, the thickness of the second negative electrode active material layer is 70-110 μm.

[0031] In a second aspect, the present application provides a battery comprising the negative electrode sheet as described above.

[0032] Compared with the prior art, the present application has the beneficial effects that:

[0033] 1、The silicon-containing negative electrode sheet of the present application adopts a double-layer coating method, and the binders contained in the first negative electrode active material layer and the second negative electrode active material layer are different ionic polymer electrolytes. First, unlike common binders, such binders are high-molecular electrolytes (also known as polymer electrolytes), which can be dissolved in water, dissociate into charges after being dissolved in water, and have excellent ion conductivity; second, before coating, the polymer electrolyte has a soft molecular chain, which can provide thickening effect after being dissolved and stretched in water, preventing slurry settlement; third, the polymer electrolyte is divided into anionic polymer electrolyte and cationic polymer electrolyte according to the charges dissociated in water, and the binders contained in the first negative electrode active material layer and the second negative electrode active material layer are different ionic polymer electrolytes, so that the anionic polymer electrolyte and the cationic polymer electrolyte are tightly combined due to the charge effect after coating, and form ionic bond cross-linking during the baking process, which imparts excellent flexibility to the negative electrode sheet after drying, effectively inhibits the expansion of silicon-based materials, and helps to improve the electrochemical performance of the battery.

[0034] 2、When the cationic polymer electrolyte is a cationic polyacrylamide, the amide bond of the cationic polyacrylamide has both carbonyl and imino groups, can undergo a reversible chemical reaction when the material is damaged, re-form chemical bonds, has a self-repairing function, thereby repairing the material, has a longer service life, and has more excellent durability and reliability.

[0035] 3、The main materials and proportions used in the upper and lower two layers of slurry of the present application are preferably kept consistent, only the binders in the upper and lower two layers of slurry are changed, which can make the surface tension of the electrode sheet consistent, make the surface of the electrode sheet flat, is not easy to cause lithium precipitation, and helps to improve the electrochemical performance of the battery.

[0036] Therefore, the present application can make the two layers of active material layers have higher adhesion, improve the flexibility of the electrode sheet, effectively inhibit the expansion of silicon-based materials, have a self-repairing function, and help to improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is a schematic view of the structure of the negative electrode sheet of the present application.

[0038] The reference signs are as follows:

[0039] 1, negative electrode current collector;

[0040] 2, first negative electrode active material layer;

[0041] 3, second negative electrode active material layer. DETAILED DESCRIPTION

[0042] The application discloses a negative pole piece and a battery, and those skilled in the art can refer to the content herein and appropriately improve process parameters to realize. It should be particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are all regarded as included in the application. The method and application of the application have been described through preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the method and application described herein without departing from the content, spirit and scope of the application, to realize and apply the technical solution of the application.

[0043] In the description of the present application, it should be pointed out that the terms "first", "second" and the like are only for the purpose of description, and do not indicate or imply relative importance.

[0044] In the description of the present application, the term "at least one of" or other similar terms connected to the list of items can 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 can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0045] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to include values approximately around the ranges or values. For ranges, the endpoints are included within the ranges, and the ranges are inclusive of the endpoints. For individual points, the value includes approximately the point. New ranges can be formed from the combination of the endpoints of the disclosed ranges or the individual points. These new ranges are to be considered disclosed herein.

[0046] If there is no special description, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0047] If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0048] If there is no special description, the "includes" and "contains" mentioned in the present application mean open type, and can also be closed type. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0049] Specifically, the application adopts the following technical solutions:

[0050] In a first aspect, the present application provides a negative electrode sheet, comprising:

[0051] (a) a negative current collector;

[0052] (b) a first negative active material layer, the first negative active material layer being disposed on at least one surface of the negative current collector, the first negative active material layer comprising a first silicon-based material and a first binder;

[0053] (c) a second negative active material layer, the second negative active material layer being disposed on a surface of the first negative active material layer away from the negative current collector, the second negative active material layer comprising a second silicon-based material and a second binder;

[0054] The first binder and the second binder are one of (i) or (ii) as follows:

[0055] (i) the first binder comprises a cationic polymer electrolyte, and the second binder comprises an anionic polymer electrolyte;

[0056] (ii) the first binder comprises an anionic polymer electrolyte, and the second binder comprises a cationic polymer electrolyte.

[0057] In the present application, the silicon-containing negative electrode sheet is coated in a double-layer manner, and the binders contained in the first negative active material layer and the second negative active material layer are polymer electrolytes of different ion types. In the first aspect, unlike common binders, such binders are high-molecular electrolytes (also known as polymer electrolytes), which can be dissolved in water, dissociate into charges after being dissolved in water, and have excellent ion conductivity. In the second aspect, before coating, the polymer electrolyte has a soft molecular chain, which can provide thickening effect after being dissolved and stretched in water to prevent slurry sedimentation. In the third aspect, the polymer electrolyte is divided into anionic polymer electrolytes and cationic polymer electrolytes according to the charges dissociated in water, and the binders contained in the first negative active material layer and the second negative active material layer are polymer electrolytes of different ion types. After coating, the anionic polymer electrolyte and the cationic polymer electrolyte are tightly combined due to charge effect, and form ionic bond cross-linking in the baking process, which endows the negative electrode sheet with excellent flexibility after drying, effectively inhibits the expansion of the silicon-based material, and helps to improve the electrochemical performance of the battery.

[0058] In an embodiment of the present application, the mass percentage content of the cationic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m1, the mass percentage content of the anionic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m2, and m1 and m2 satisfy the following relationship:

[0059] 0≤|m1-m2| / m1≤20%.

[0060] and / or, 0≤|m1-m2| / m2≤20%;

[0061] and / or, m1 is 1.8%~3.0%;

[0062] and / or, m2 is 1.8%~3.0%.

[0063] For example, the value of |m1-m2| / m1 or 0≤|m1-m2| / m2 is any of 0, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any value within the range formed by any two of the above values. When the value of |m1-m2| / m1 or 0≤|m1-m2| / m2 is greater than 20%, the combination of the cationic polymer electrolyte and the anionic polymer electrolyte is not sufficient, which results in poor flexibility.

[0064] In the embodiment of the present application, m1 is 1.8%~3.0%. For example, m1 is any of 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0% or any value within the range formed by any two of the above values. When m1 is less than 1.8%, the amount of the binder is too small, which results in a slurry with a viscosity that is too thin and causes sedimentation. When m1 is greater than 3.0%, the internal resistance is increased and the energy density is low.

[0065] In the embodiment of the present application, m2 is 1.8%~3.0%. For example, m2 is any of 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0% or any value within the range formed by any two of the above values. When m2 is less than 1.8%, the amount of the binder is too small, which results in a slurry with a viscosity that is too thin and causes sedimentation. When m2 is greater than 3.0%, the internal resistance is increased and the energy density is low.

[0066] In the embodiment of the present application, the cationic polymer electrolyte includes at least one of cationic polyacrylamide, polyethyleneimine, cationic polyvinyl alcohol, and polyvinylamide.

[0067] Preferably, the cationic polymer electrolyte includes cationic polyacrylamide. Compared with other cationic polymer electrolytes, the amide bond of cationic polyacrylamide has both carbonyl and imino groups, which can undergo reversible chemical reactions when the material is damaged, re-form chemical bonds, have a self-repairing function, repair the material, have a longer service life, and have more excellent durability and reliability.

[0068] In the embodiment of the present application, the cationic group of the cationic polyacrylamide includes at least one of imidazole group, pyridine group, and piperidine group.

[0069] In the preferred embodiment of the present application, the first adhesive comprises a cationic polymer electrolyte, the cationic polymer electrolyte comprises a cationic polyacrylamide, and the cationic groups of the cationic polyacrylamide comprise imidazole groups. In the above conditions, the polyacrylamide containing imidazole groups can be present in the first negative electrode active material layer, and the first negative electrode active material layer is close to the negative electrode current collector.

[0070] Preferably, the negative electrode current collector is a copper foil.

[0071] In the preferred embodiment of the present application, the imidazole groups are combined with the copper foil by coordination bond. The coordination bond mainly depends on the nitrogen atoms in the imidazole groups, which have unshared electron pairs and can participate in ring conjugation, reducing the electron density on the nitrogen atoms, making the hydrogen on this nitrogen atom easy to leave in the form of hydrogen ions, thereby forming a coordination bond with copper ions. This combination occurs instantaneously to generate a thin film layer with electrical conductivity, which is about 0.2-0.4 μm, and can make the first negative electrode active material layer and the negative electrode current collector copper foil tightly bonded, increase the peel strength, avoid the active material from falling off the negative electrode current collector, and increase the cycle life.

[0072] In the specific embodiment of the present application, the imidazole group introducing agent comprises 1-(2-methacryloyloxypropyl)-3-decylimidazole hydrochloride.

[0073] In the specific embodiment of the present application, the pyridine group introducing agent comprises 1-(1-pyridine-amido)-ethylene.

[0074] In the specific embodiment of the present application, the piperidine group introducing agent comprises 1-(1-piperidine-amido)-ethylene.

[0075] In the embodiment of the present application, the cationic polymer electrolyte comprises a first polymer group and a cationic group modified on the first polymer group.

[0076] As preferred, the mass ratio of the first polymer group to the cationic group is (1-10):1. Exemplarily, the mass ratio of the first polymer group to the cationic group is any one of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any value within the range formed by any two of the above values.

[0077] In the embodiment of the present application, the preparation monomer of the first polymer group comprises at least one of acrylamide, ethylene imine, ethylene alcohol, and ethylene amide.

[0078] In the embodiment of the present application, the anionic polymer electrolyte comprises at least one of an anionic epoxy resin, sodium polyacrylate, anionic polyacrylamide, anionic polyvinyl alcohol, and sodium polystyrene sulfonate.

[0079] Preferably, the anionic polymer electrolyte comprises an anionic epoxy resin. The anionic epoxy resin can react with various compounds containing active hydrogen, such as polyacrylamide, which can provide active functional groups to react with the anionic epoxy resin, introduce dynamic polyamide bonds, and make the formed compound have good toughness while maintaining three-dimensional crosslinking; in addition, when the cationic polymer electrolyte is selected as a cationic polymer electrolyte containing an imidazole group, the imidazole group can also promote the curing of the anionic epoxy resin. Imidazole is a five-membered compound containing two nitrogen atoms, one of which forms a secondary amine and the other forms a tertiary amine. This structure allows the imidazole group to act as a curing agent to rapidly cure the anionic epoxy resin, increase the reaction speed, and rapidly cure the active substance layer.

[0080] In an embodiment of the present application, the anionic group of the anionic epoxy resin comprises at least one of a carboxyl group, a phosphoric acid group, and a sulfonic acid group.

[0081] Preferably, the anionic group of the anionic epoxy resin comprises a carboxyl group. The reason why the anionic group of the anionic epoxy resin is preferably a carboxyl group is that the carboxyl group contains a carbonyl group and a hydroxyl group, has strong polarity, and can interact with the functional groups (hydroxyl groups, carboxyl groups, carbonyl groups, ketone groups, etc. For example, the main material comprises both carbon-based materials such as graphite and silicon-based materials, and the surface and interlayer defects of graphite are rich in oxygen-containing functional groups. These functional groups form a series of polar groups during sintering) on the surface of the main material, effectively dispersing carbon-based materials such as graphite.

[0082] In an embodiment of the present application, the anionic epoxy resin comprises at least one of a 2-carboxyl-diphenol propane epoxy resin, a 2-phosphoric acid-diphenol propane epoxy resin, and a 2-sulfonic acid-diphenol propane epoxy resin.

[0083] In a specific embodiment of the present application, the introducer of the carboxyl group comprises lactic acid.

[0084] In a specific embodiment of the present application, the introducer of the phosphoric acid group comprises a nucleotide.

[0085] In a specific embodiment of the present application, the introducer of the sulfonic acid group comprises sulfuric acid.

[0086] In an embodiment of the present application, the anionic polymer electrolyte comprises a second polymer group and an anionic group modified on the second polymer group.

[0087] As preferred, the molar ratio of the second polymer group to the anion group is (1-10):1. Exemplarily, the molar ratio of the second polymer group to the anion group is any one of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any value within the range formed by any two of the above values.

[0088] In an embodiment of the present application, the second polymer group comprises a bisphenol A type epoxy resin.

[0089] In an embodiment of the present application, the first negative active material layer further comprises a first carbon-based material and a first conductive agent.

[0090] As preferred, the mass ratio of the first carbon-based material, the first silicon-based material, the first binder and the first conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5). Exemplarily, the mass ratio of the first carbon-based material, the first silicon-based material, the first binder and the first conductive agent is any one of 75:20:1.8:1.5, 85:10:3:0.5, 80:15:2.4:1, 82.5:14.5:2:1, 82.5:14.5:1.8:1.2, 81.5:14.5:3:1 or any value within the range formed by any two of the above values.

[0091] In an embodiment of the present application, the second negative active material layer further comprises a second carbon-based material and a second conductive agent.

[0092] As preferred, the mass ratio of the second carbon-based material, the second silicon-based material, the second binder and the second conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5). Exemplarily, the mass ratio of the second carbon-based material, the second silicon-based material, the second binder and the second conductive agent is any one of 75:20:1.8:1.5, 85:10:3:0.5, 80:15:2.4:1, 82.5:14.5:2:1, 82.5:14.5:1.8:1.2, 81.5:14.5:3:1 or any value within the range formed by any two of the above values.

[0093] In a preferred embodiment of the present application, the main materials and their proportions used in the slurries of the first negative active material layer and the second negative active material layer are preferably kept consistent, only the binder in the upper and lower slurries is changed, which can make the surface tension of the pole piece consistent, make the surface of the pole piece flat, not easy to cause lithium precipitation, and help to improve the electrochemical performance of the battery.

[0094] In an embodiment of the present application, the first carbon-based material and the second carbon-based material independently comprise at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon and hard carbon.

[0095] In the embodiments of the present application, the first silicon-based material and the second silicon-based material independently comprise at least one of elemental silicon, silicon-oxygen, silicon-carbon, and silicon alloy.

[0096] In the embodiments of the present application, the first conductive agent and the second conductive agent independently comprise at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, and graphene.

[0097] Preferably, the ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is (5-6):(4-5). For example, the ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is any one of 5:5, 5.5:4.5, 6:4 or any value within the range formed by any two of the above values.

[0098] Preferably, the thickness of the first negative electrode active material layer is 70-110 μm. For example, the thickness of the first negative electrode active material layer is any one of 70 μm, 80 μm, 90 μm, 100 μm, 110 μm or any value within the range formed by any two of the above values.

[0099] Preferably, the thickness of the second negative electrode active material layer is 70-110 μm. For example, the thickness of the second negative electrode active material layer is any one of 70 μm, 80 μm, 90 μm, 100 μm, 110 μm or any value within the range formed by any two of the above values.

[0100] In a second aspect, the present application provides a battery comprising the negative electrode sheet as described above.

[0101] In the embodiments of the present application, the battery structure includes, but is not limited to, a button cell, a soft pack battery, a cylindrical battery, and the like.

[0102] The positive electrode sheet, the separator, and the electrolyte in the battery are not particularly limited in the present application, and can be selected by those skilled in the art according to actual needs, as long as the purpose of the present application can be achieved.

[0103] The reagents, instruments or materials used in the present application can be obtained through commercial channels.

[0104] The present application will be further described below in conjunction with examples:

[0105] Example 1:

[0106] 1. Preparation of the negative electrode sheet:

[0107] (1) Synthesis of imidazole polyacrylamide:

[0108] Dissolve acrylamide in deionized water, mix well, and cool to room temperature; pour the solution into a polymerization tank, fill with nitrogen, add 1-(2-methacryloyloxypropyl)-3-decyl imidazole hydrochloride as an imidazole-based initiator, and add sodium sulfite as an initiator; control the temperature at room temperature, and carry out polymerization reaction; after 10 h of reaction, a polymer colloid is obtained; dry and grind the reacted colloid to obtain imidazole polyacrylamide powder. The mass ratio of acrylamide, 1-(2-methacryloyloxypropyl)-3-decyl imidazole hydrochloride, sodium sulfite, and deionized water in the reaction system is 19:5:0.03:76.

[0109] (2) Synthesis of carboxyl epoxy resin:

[0110] Select bisphenol A type epoxy resin as the base material, lactic acid as the modifier, and quaternary ammonium salt as the catalyst; the molar ratio of bisphenol A type epoxy resin to lactic acid is 5:1, and the mass ratio of quaternary ammonium salt to the total mass of bisphenol A type epoxy resin and lactic acid is 0.2%; after dissolving in deionized water, heat; control the temperature at about 60°C in the early stage, and then to 100°C after 0.5 h and react for 3 h; after the reaction is completed, extract and dry to obtain carboxyl epoxy resin.

[0111] (3) Preparation of negative electrode slurry:

[0112] Mix graphite, silicon oxide, carbon black (SP), upper binder carboxyl epoxy resin (anionic polymer electrolyte), and deionized water in a solid mass ratio of 82.5:14.5:1:2:100 to obtain the upper layer negative electrode slurry.

[0113] Mix graphite, silicon oxide, carbon black (SP), lower binder imidazole polyacrylamide (cationic polymer electrolyte), and deionized water in a solid mass ratio of 82.5:14.5:1:2:100 to obtain the lower layer negative electrode slurry.

[0114] (4) Preparation of negative electrode sheet:

[0115] Use a double-layer die to coat the lower layer negative electrode slurry and the upper layer negative electrode slurry on both sides of the current collector (copper foil) at the same time; control the surface density ratio of the upper and lower layers to be 5:5; the thickness of the upper and lower coatings is 100 μm; after drying, rolling, and die cutting, the negative electrode sheet is obtained, and the structure is shown in Figure 1 .

[0116] 2. Preparation of positive electrode sheet:

[0117] (1) Preparation of positive electrode slurry:

[0118] Lithium iron phosphate (LFP), carbon black (SP), carbon nanotube (CNT), polyvinylidene fluoride (PVDF), N-methyl pyrrolidone (NMP) are mixed uniformly according to the mass ratio of 96:1.5:0.5:2.0:45 to obtain a positive electrode slurry.

[0119] (2) Preparation of the positive electrode tab:

[0120] The positive electrode slurry is uniformly coated on the aluminum foil current collector, and after drying, rolling, and die cutting, a positive electrode tab is obtained.

[0121] 3. Preparation of the battery:

[0122] The positive electrode tab, the negative electrode tab, and the separator are wound and assembled in the order of one layer of positive electrode, one layer of separator, and one layer of negative electrode. The assembled electrode roll is then packaged in an aluminum-plastic film, and an electrolyte is injected into the aluminum-plastic film. Then, formation, aging, and capacity distribution are performed, and finally, the aluminum-plastic film is sealed to obtain a battery.

[0123] Example 2:

[0124] The difference between this embodiment and Example 1 is that the upper binder is imidazole polyacrylamide (cationic polymer electrolyte), and the lower binder is carboxyl epoxy resin (anionic polymer electrolyte).

[0125] Example 3:

[0126] The difference between this embodiment and Example 1 is that the upper binder is polyethyleneimine (cationic polymer electrolyte), and the lower binder is sodium polyacrylate (anionic polymer electrolyte).

[0127] Example 4:

[0128] The difference between this embodiment and Example 1 is that the proportions of the components in the negative electrode slurry are different.

[0129] Graphite, silicon oxide, carbon black (SP), upper binder carboxyl epoxy resin (anionic polymer electrolyte), and deionized water are mixed uniformly according to the solid mass ratio of 82.5:14.5:1.2:1.8:100 to obtain an upper negative electrode slurry.

[0130] Graphite, silicon oxide, carbon black (SP), lower binder imidazole polyacrylamide (cationic polymer electrolyte), and deionized water are mixed uniformly according to the solid mass ratio of 82.5:14.5:1.2:1.8:100 to obtain a lower negative electrode slurry.

[0131] Example 5:

[0132] The difference between this embodiment and Example 1 is that the proportions of the components in the negative electrode slurry are different.

[0133] Graphite, silicon, carbon black (SP), upper layer binder carboxyl epoxy resin (anionic polymer electrolyte), deionized water were mixed uniformly according to the solid mass ratio of 81.5:14.5:1:3:100 to obtain the upper layer negative electrode slurry.

[0134] Graphite, silicon, carbon black (SP), lower layer binder imidazole polyacrylamide (cationic polymer electrolyte), deionized water were mixed uniformly according to the solid mass ratio of 81.5:14.5:1:3:100 to obtain the lower layer negative electrode slurry.

[0135] Comparative Example 1:

[0136] The difference between this comparative example and Example 1 is that the upper and lower layer negative electrode slurry formulations are consistent, and graphite, silicon, carbon black (SP), sodium carboxymethyl cellulose, butadiene rubber, deionized water are mixed uniformly according to the solid mass ratio of 82.5:14.5:1:1:1:100.

[0137] Comparative Example 2:

[0138] The difference between this comparative example and Example 1 is that the lower layer binder is imidazole polyacrylamide (cationic polymer electrolyte), and the upper layer negative electrode slurry is the same as Comparative Example 1.

[0139] Comparative Example 3:

[0140] The difference between this comparative example and Example 1 is that the upper layer binder is carboxyl epoxy resin (anionic polymer electrolyte), and the lower layer negative electrode slurry is the same as Comparative Example 1.

[0141] Comparative Example 4:

[0142] The difference between this comparative example and Example 1 is that the slurry is not layered, and graphite, silicon, carbon black (SP), imidazole polyacrylamide (cationic polymer electrolyte), carboxyl epoxy resin (anionic polymer electrolyte), deionized water are mixed uniformly according to the solid mass ratio of 82.5:14.5:1:1:1:100.

[0143] Performance test:

[0144] The negative electrode tabs and batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

[0145] (1) Peeling force: Fix the tab material area, tear the foil material at 90°, and the force measured at this time is the peeling force of the tab.

[0146] (2) Flexibility: Use different diameter winding needles to curl the tab, test the minimum diameter when the tab cracks, the smaller the diameter, the better the flexibility.

[0147] (3) Initial efficiency: after the battery is installed, 0.01C constant current charging is performed to the cut-off voltage 3.65V, the charge capacity is recorded, after standing, 0.33C discharging is performed to 2.5V, the discharge capacity is recorded, and the ratio of the first discharge and charge capacity is the initial efficiency.

[0148] (4) Full charge rebound rate: after the battery is installed, constant current and constant voltage charging is performed to the cut-off voltage 3.65V, the negative electrode sheet thickness is tested after disassembly, and the ratio of the thickness after rolling to the thickness after rolling is the full charge rebound rate.

[0149] (5) Internal resistance: the positive and negative electrodes of the battery are clamped using a multimeter, adjusted to test the internal resistance mode, and the internal resistance is obtained.

[0150] (6) Cycle number: the battery is repeatedly charged and discharged at a charge of 1C and a discharge of 1C, and the cycle number when the capacity retention rate is 80% is the cycle number.

[0151] Table 1

[0152]

[0153] By comparing the data of Examples 1-5 and Comparative Example 1, the peel strength of Examples 1-5 is high, the flexibility is good, the full charge rebound rate and internal resistance are also lower, the cycle number is greatly increased, and the overall performance is better than the industry standard.

[0154] Comparative Examples 1-3 have low peel strength, resulting in lower full charge rebound rate and cycle number, and higher internal resistance, poor fast charging ability.

[0155] Comparative Example 4 does not have upper and lower layers, anion polymer electrolyte (carboxyl epoxy resin) and cation polymer electrolyte (imidazole polyacrylamide) act early, resulting in the formation of flocculation, resulting in reduced adhesion, and the peel strength and cycle performance are the worst.

[0156] The above is only a preferred embodiment of the present application, it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized by, The negative electrode sheet comprises: (a) a negative current collector; (b) a first negative active material layer, the first negative active material layer being provided on at least one surface of the negative current collector, the first negative active material layer comprising a first silicon-based material and a first binder; (c) a second negative active material layer, the second negative active material layer being provided on a surface of the first negative active material layer away from the negative current collector, the second negative active material layer comprising a second silicon-based material and a second binder; the first binder comprises a cationic polymer electrolyte, the cationic polymer electrolyte comprising a cationic polyacrylamide, cationic groups of the cationic polyacrylamide comprising imidazole groups; the second binder comprises an anionic polymer electrolyte; the anionic polymer electrolyte comprises an anionic epoxy resin; anionic groups of the anionic epoxy resin comprising at least one of carboxyl groups, phosphoric acid groups, sulfonic acid groups.

2. The negative electrode sheet according to claim 1, characterized by, a mass percentage content of the cationic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m1, a mass percentage content of the anionic polymer electrolyte in the first negative active material layer or the second negative active material layer is denoted as m2, the m1 and the m2 satisfy the following relationship: 0≤|m1-m2| / m1≤20%; and / or, 0≤|m1-m2| / m2≤20%; and / or, the m1 is 1.8% to 3.0%; and / or, the m2 is 1.8% to 3.0%.

3. The negative electrode sheet according to claim 1, characterized by the first negative active material layer further comprises a first carbon-based material and a first conductive agent; a mass ratio of the first carbon-based material, the first silicon-based material, the first binder and the first conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5); and / or, the second negative active material layer further comprises a second carbon-based material and a second conductive agent; a mass ratio of the second carbon-based material, the second silicon-based material, the second binder and the second conductive agent is (75-85):(10-20):(1.8-3):(0.5-1.5).

4. The negative electrode sheet according to claim 1, wherein a ratio of a thickness of the first negative active material layer to a thickness of the second negative active material layer is (5-6):(4-5); and / or, the thickness of the first negative active material layer is 70-110 μm; and / or, the thickness of the second negative active material layer is 70-110 μm.

5. A battery, characterized by The battery comprises the negative electrode sheet according to any one of claims 1 to 4.

Images