Composite binder, preparation method thereof and electrochemical device

Abstract

The invention provides a composite binder, a preparation method thereof and an electrochemical device. The composite binder has a core-shell structure; wherein the core of the core-shell structure is a phase change material, and the phase change temperature of the phase change material is-10 DEG C to 70 DEG C; and the shell of the core-shell structure is a polymer binder. The preparation method comprises the following steps: carrying out shearing treatment on a mixture of an oil phase and a water phase, and carrying out polymerization reaction, wherein the oil phase comprises a phase change material and a raw material of a polymer binder, and the raw material of the polymer binder at least comprises a monomer; the aqueous phase includes water and an emulsifier. When the obtained composite binder is applied to an electrochemical device (such as a battery), the inherent binding performance can be maintained, meanwhile, the thermal environment of a pole piece is regulated and controlled according to needs, and the high and low temperature, fast charging, safety and other performance of a battery cell are improved.

Description

Technical Field

[0001] The invention relates to a composite adhesive and a preparation method thereof, and an electrochemical device. Background Art

[0002] Lithium / sodium ion batteries are an important electrochemical energy storage device that has been widely used in consumer electronics, new energy vehicles, power storage devices and other fields. Lithium ions reversibly embed / de-embed the active material through the electrolyte-active material interface, thereby completing the battery charge and discharge process. However, excellent battery performance has extremely stringent requirements on the temperature (thermal) environment of the battery cell: high temperature environment will aggravate the degree of electrolyte side reactions, and ultimately deteriorate long-term cycle performance; low temperature environment will reduce the lithium ion migration rate and the activation energy of the interface transfer reaction, increase the internal resistance, and aggravate the lithium precipitation phenomenon. In addition, even at room temperature, high-rate charging and discharging or long-term charging and discharging will still cause strong thermal shock, which is prone to temperature surge and thermal runaway.

[0003] However, current thermal management of batteries is limited to the module / pack level, and liquid cooling is often used. There is no method for real-time, on-demand thermal regulation within the electrode to provide a uniform and constant thermal environment for battery operation. Summary of the Invention

[0004] To address the gap in thermal management for both electrode and cell scale in existing batteries, the present invention provides a composite adhesive, its preparation method, and an electrochemical device. This composite adhesive, while adapting to existing electrode preparation processes, can regulate the electrode thermal environment as needed, improving battery cell performance in terms of high and low temperature tolerance, fast charging, and safety.

[0005] In a first aspect, the present invention provides a composite adhesive having a core-shell structure; wherein

[0006] The core of the core-shell structure comprises a phase change material, and the phase change temperature of the phase change material is -10°C to 70°C;

[0007] The shell of the core-shell structure includes a polymer binder.

[0008] In a second aspect, the present invention provides a method for preparing the composite adhesive as described above, the method for preparing the composite adhesive comprising the following steps:

[0009] Shearing the mixture of the oil phase and the water phase and subjecting it to polymerization reaction to obtain the composite adhesive;

[0010] Wherein, the oil phase comprises a phase change material and a raw material of the polymer binder, and the raw material of the polymer binder comprises at least a monomer;

[0011] The aqueous phase includes water and an emulsifier.

[0012] In a third aspect, the present invention provides an electrochemical device, wherein the composite binder as described above is used in the preparation process of the electrode plate.

[0013] The positive progress effect of the present invention is:

[0014] The present invention provides a composite adhesive with a core-shell structure with a phase change material as the core and a polymer adhesive as the shell. The phase change material has a specific phase change temperature. The composite adhesive can maintain its inherent bonding properties while undergoing phase change according to changes in the external ambient temperature (battery temperature), thereby releasing or absorbing heat, directly and efficiently regulating the temperature at the electrode level, alleviating problems such as thermal shock, and improving the battery's fast charging, high and low temperature, cycling, and safety performance. It is compatible with existing electrode manufacturing processes and does not require equipment modification or upgrading. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the SEM image of the composite adhesive in Example 1.

[0016] Figure 2 This is the TEM image of the composite adhesive in Example 1. DETAILED DESCRIPTION

[0017] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0018] Composite adhesive

[0019] In the composite adhesive described in the first aspect of the present invention, the composite adhesive has a core-shell structure; wherein,

[0020] The core of the core-shell structure is a phase change material, and the phase change temperature of the phase change material is -10°C to 70°C;

[0021] The shell of the core-shell structure is a polymer binder.

[0022] In the present invention, the core-shell structure may be an ordered assembly structure formed by a shell material covering a core material.

[0023] In the present invention, the term "phase change material" refers to a substance capable of undergoing a primary phase transition, releasing latent heat. This refers to a substance that changes form with temperature and provides latent heat. The process by which a phase change material changes from solid to liquid (melting) or from liquid to solid (solidifying) is called a phase change. During this process, the phase change material absorbs or releases a significant amount of latent heat. Accordingly, the temperature at which the phase change material undergoes this phase change is referred to as the phase transition temperature.

[0024] In the present invention, the phase change temperature of the phase change material is -10℃~70℃. Those skilled in the art can select a composite binder containing a phase change material in the corresponding temperature range according to the needs of actual application, or can choose to mix composite binders containing phase change materials in different temperature ranges for use. For example, a phase change material with a phase change temperature of -10℃~25℃ is selected. When the battery enters a cold environment from a normal temperature environment, the phase change material can be transformed from liquid to solid, releasing latent heat, which has the effect of preheating the battery. For another example, a phase change material with a phase change temperature of 50℃-70℃ is selected. When the battery enters a high temperature environment from a normal temperature environment, the phase change material can be transformed from solid to liquid, absorbing latent heat, reducing the battery temperature, and avoiding safety problems caused by excessively high battery temperatures.

[0025] In some embodiments, the phase change temperature of the phase change material is 25°C-50°C, for example, 25°C-30°C, 35°C-40°C or 45-50°C. This temperature range is the temperature range that is most conducive to long-term charging and discharging of the battery under normal temperature conditions. The battery will heat up during charging and discharging. For example, in an environment of 25°C (25°C is generally considered to be the optimal operating temperature of the battery), such as LFP (lithium iron phosphate) and NCM (nickel cobalt manganese peroxide ternary material) chemical system batteries, the battery temperature will generally rise by 10°C to 25°C during 1C rate charging. During this process, the phase change material can effectively absorb part of the heat to improve battery performance.

[0026] In the present invention, the phase change material can be selected from C 10 -C 24 Long-chain alkanes and mixtures thereof.

[0027] In some embodiments, the phase change material is paraffin wax, and the phase change temperature of the paraffin wax can be 5°C-10°C, 20°C-25°C, 25°C-30°C, 35°C-40°C, or 45-50°C. The paraffin wax can refer to a mixture of alkanes with different numbers of carbon atoms; wherein alkanes with different numbers of carbon atoms have different melting points, that is, those skilled in the art can select different alkanes according to actual needs to obtain paraffin waxes with different melting points.

[0028] In the present invention, the particle size of the composite binder may be 0.1-10 μm, for example, 0.4 μm.

[0029] In the present invention, in the core-shell structure, the mass ratio of the core to the shell can be (1:10)-(4:1), preferably (1:1)-(4:1), for example 1.5:1 or 2:1.

[0030] In the present invention, the shell thickness of the core-shell structure may be 0.01-1 μm, for example, 20 nm, 30 nm, 40 nm or 60 nm.

[0031] In the present invention, the polymer binder may be a cross-linked polymer or a non-cross-linked polymer; when the polymer binder is a non-cross-linked polymer, its weight average molecular weight may optionally be 7w-50w g / mol.

[0032] Preparation method of composite adhesive

[0033] In the preparation method of the composite adhesive according to the second aspect of the present invention, the preparation method of the composite adhesive comprises the following steps:

[0034] Shearing the mixture of the oil phase and the water phase and subjecting it to polymerization reaction to obtain the composite adhesive;

[0035] Wherein, the oil phase includes a phase change material and a raw material of the polymer binder, and the raw material of the polymer binder includes at least a monomer;

[0036] The aqueous phase includes water and an emulsifier.

[0037] In the present invention, the monomer may be a monoene monomer, not a polyene monomer, and those skilled in the art will know its specific meaning.

[0038] In the present invention, the mass of the oil phase is calculated based on the total mass of the phase change material and the monomer, and the mass of the aqueous phase is calculated based on the total mass of water. The mass ratio of the oil phase to the aqueous phase can be 1:(1-10), preferably 1:(1-7), for example, 1:1.3, 1:1.7, 1:2.0, 1:3.3, 1:4.0 or 1:6.7.

[0039] In the present invention, the shear treatment step can be performed using a strong shear liquid-liquid dispersion device. Optionally, the strong shear liquid-liquid dispersion device includes one of a high-speed shearing machine, a high-pressure homogenizer, a cell crusher and a high-gravity field generating device, such as a high-speed shearing machine or an ultrasonic cell crusher.

[0040] In some embodiments, the shearing speed of the high-speed shearing machine is 2000-5000 rpm.

[0041] In some embodiments, the power of the ultrasonic cell disruptor is 150-600W, optionally 200-500W, such as 400W.

[0042] In the present invention, the shearing treatment time may be 5-15 minutes.

[0043] In the present invention, the temperature of the shearing treatment may be ambient temperature.

[0044] In the present invention, the polymerization reaction temperature may be 50°C-85°C, for example 75°C.

[0045] In the present invention, the polymerization reaction time may be 6-12 hours, for example 10 hours.

[0046] In the present invention, the polymerization reaction can be carried out under stirring.

[0047] In the present invention, an inert gas such as nitrogen may be continuously introduced during the polymerization reaction.

[0048] In the present invention, the polymerization step may be followed by a drying step.

[0049] In the present invention, the monomer can be selected from one or more of butyl acrylate, hydroxyethyl acrylate, methacrylate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, styrene, vinyltoluene, tert-butylstyrene and N-hydroxymethyl acrylamide.

[0050] In some embodiments, the monomers are styrene, hydroxyethyl acrylate and butyl acrylate; the mass ratio of styrene, hydroxyethyl acrylate and butyl acrylate is optionally 50:40:10.

[0051] In the present invention, the emulsifier may be a polymer emulsifier, where the polymer means an emulsifier having a molecular weight of 1000-50000 g / mol.

[0052] The polymer emulsifier (emulsifier used in polymer polymerization processes) used in the present invention has the emulsifying properties of the emulsifier itself and a soft texture, which can further enhance the bonding strength of the shell polymer binder. Optionally, the emulsifier is selected from one or more of sodium lauryl sulfate, hexadecyltrimethylammonium bromide, polyoxyethylene terephthalate, OP surfactants, span surfactants, tween surfactants, and sodium dodecylbenzene sulfonate.

[0053] In some embodiments, the emulsifier is sodium lauryl sulfate.

[0054] In the present invention, the raw materials of the polymer binder may further include an initiator. The initiator may be an azo initiator and / or a peroxide initiator having a water solubility of less than or equal to 0.5 g / kg water at 25°C. The azo initiator may optionally include azobisisobutyronitrile and / or azobisisoheptanenitrile; the peroxide initiator may optionally include one or more of benzoyl peroxide, ammonium persulfate, and potassium persulfate.

[0055] In some embodiments, the initiator is azobisisobutyronitrile.

[0056] In the present invention, the raw materials of the polymer binder may further include a cross-linking agent. The cross-linking agent may be a conventional cross-linking agent in the art, generally selected from one or more of divinylbenzene, ethylene glycol dimethacrylate, allyl methacrylic acid, ethylene glycol diacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, dimethacrylate adipate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane, and pentaerythritol tetramethacrylate.

[0057] In some embodiments, the cross-linking agent is divinylbenzene.

[0058] In the present invention, the aqueous phase may further include one or more of a dispersant, a polymerization inhibitor and a metal salt.

[0059] The dispersant can improve the stability of large-size latex particles. The dispersant can be a conventional dispersant in the art, generally selected from one or more of polyvinyl alcohol, magnesium hydroxide, calcium carbonate, calcium phosphate, silica sol, polyvinyl pyrrolidone, styrene-maleic anhydride copolymer and carboxymethyl cellulose, such as polyvinyl alcohol.

[0060] The polymerization inhibitor may be a conventional polymerization inhibitor in the art, generally selected from nitrite and / or potassium dichromate, such as sodium nitrite.

[0061] The metal salt can reduce the diffusion of highly water-soluble monomers in the aqueous phase, capture free radicals in the aqueous phase, and improve the synthesis efficiency of the phase change composite adhesive. The metal salt can be a conventional metal salt in the art, generally an ionic compound such as sodium chloride.

[0062] In the present invention, the weight ratio of the phase change material to the monomer may be (10-400):100, preferably (100-400):100, such as 150:100 or 200:100.

[0063] In the present invention, the weight ratio of the emulsifier to water can be (0.01-5):(150-2000), preferably (0.01-5):(150-1000), for example 0.01:400, 0.01:500 or 0.01:1000.

[0064] In some embodiments, the oil phase comprises the crosslinker, initiator, phase change material and monomer; wherein the weight ratio of the crosslinker, initiator, phase change material and monomer is (0.5-3):(0.1-3):(10-400):100, optionally (0.5-3):(0.1-3):(100-400):100, for example, 2:0.5:150:100, 2:0.5:200:100 or 2:0.5:400:100.

[0065] In some embodiments, the aqueous phase comprises a dispersant, an emulsifier, a metal salt, an inhibitor, and water; wherein the weight ratio of the dispersant, the emulsifier, the metal salt, the inhibitor, and the water is (1-50):(0.01-5):(0.5-5):(0.01-2):(150-2000), optionally (1-50):(0.01-5):(0.5-5):(0.01-2):(150-1000), for example, 10:0.01:1:0.01:400, 10:0.01:1:0.01:500, or 10:0.01:1:0.01:1000.

[0066] electrochemical devices

[0067] In the electrochemical device described in the third aspect of the present invention, the electrode plates are prepared using the composite binder described above, which is the composite binder provided by the present invention or prepared by the method for preparing the composite binder of the present invention.

[0068] In the present invention, the electrode plate is preferably a negative electrode plate.

[0069] In the present invention, the electrochemical device may be a sodium ion battery or a lithium ion battery.

[0070] In some embodiments, the electrochemical device is a lithium-ion battery; the lithium-ion battery comprises the negative electrode sheet, the positive electrode sheet, the separator and the electrolyte.

[0071] Negative electrode

[0072] In the present invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and the composite binder, and a conductive agent and / or thickener may be further added as needed.

[0073] The negative electrode active material may be a negative electrode active material conventionally used in the art for preparing negative electrode sheets, such as one or more of natural graphite, artificial graphite, soft carbon, hard carbon, lithium metal and silicon-based materials.

[0074] Among them, the conductive agent is a reagent used to ensure that the electrode has good charge and discharge performance, and can be selected from: graphite materials, such as natural graphite or artificial graphite; carbon black materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers, metal fibers; metal powders, such as carbon fluoride powder, aluminum powder or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium dioxide; and conductive polymers, such as polyphenylene derivatives.

[0075] The addition of the thickener can increase the system viscosity of the components in the negative electrode material layer, and can be a thickener conventionally used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0076] In some embodiments, the negative electrode material is graphite, the conductive agent is carbon black, and the thickener is CMC; the mass ratio of the graphite, carbon black, composite binder and CMC in the negative electrode material layer is optionally 96:1:2:1.

[0077] In some embodiments, the negative electrode sheet is prepared by the following method: the negative electrode active material, the conductive agent, the composite binder, the thickener and the solvent are mixed to obtain a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet is obtained through drying, cold pressing and slitting processes.

[0078] The solvent may be conventional in the art, such as deionized water.

[0079] Positive electrode

[0080] In the present invention, the positive electrode sheet may include a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector; the positive electrode material layer contains a positive electrode active material, and a conductive agent and / or a binder may be further added as needed. The positive electrode active material may be conventional in the art, including but not limited to one or more of lithium iron phosphate (LiFePO4, LFP), lithium iron manganese phosphate, ternary positive electrode material and lithium-rich manganese-based material; the ternary positive electrode material is, for example, NCM622 (Li (Ni 0.6 Co 0.2 Mn 0.2 )O2) or NCM811(Li(Ni 0.8 Co 0.1 Mn 0.1 )O2).

[0081] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0082] Wherein, the binder plays a role in improving the bonding effect between the positive electrode active materials and the adhesion effect between the positive electrode active material and the positive electrode current collector, and its type is not particularly limited. The binder may be a conventional binder in the art, or it may be a composite binder as described above. Specific examples of the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers, and any one thereof or a mixture of two or more thereof may be used.

[0083] In some embodiments, the positive electrode active material is LFP, the conductive agent is Super P, and the binder is PVDF; the mass ratio of LFP, Super P, and PVDF in the positive electrode material layer is optionally 97:1:2.

[0084] In some embodiments, the positive electrode active material is NCM622, the conductive agent is Super P, and the binder is PVDF; the mass ratio of NCM622, Super P, and PVDF in the positive electrode material layer is optionally 97:1:2.

[0085] In some embodiments, the positive electrode sheet is prepared by the following preparation method:

[0086] The positive electrode active material, the conductive agent, the binder and the solvent are mixed to obtain a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector, and the positive electrode sheet is obtained through drying, cold pressing and slitting processes.

[0087] The solvent may be an organic solvent conventionally used in the art for preparing positive electrode sheet slurry, for example, one or more selected from N-methylpyrrolidone (NMP), DMAC and acetone.

[0088] In the present invention, materials that do not cause chemical changes and have high conductivity can be used for both the positive and negative electrode current collectors without restriction, depending on actual needs. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver, can be commonly used. To enhance the adhesion of the positive and negative electrode active materials, micro-embossing can be formed on the surface of the positive and negative electrode current collectors. The positive and negative electrode current collectors can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0089] electrolyte

[0090] In the present invention, the electrolyte may be an electrolyte conventionally used in lithium-ion secondary battery cells in the art, generally comprising a non-aqueous solvent and a lithium salt.

[0091] Wherein, the non-aqueous solvent is, for example, selected from carbonate solvents. Specifically, the carbonate solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), polyethylene carbonate (PEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC).

[0092] In some embodiments, the non-aqueous solvent is ethylene carbonate and propylene carbonate; the volume ratio of ethylene carbonate to propylene carbonate is optionally 1:1.

[0093] The lithium salt may be a conventional lithium salt in the art, such as LiPF6.

[0094] In the present invention, the preparation method of the electrolyte can be conventional in the art, for example, comprising: dissolving the lithium salt in the non-aqueous solvent.

[0095] diaphragm

[0096] In the present invention, the diaphragm can be conventional in the art, for example, a polypropylene (PP) diaphragm or a polyethylene (PE) diaphragm.

[0097] In some embodiments, the lithium ion battery is prepared by the following preparation method:

[0098] The positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence, and then placed in a battery casing, injected with the electrolyte, and subjected to formation and sealing processes to obtain the lithium-ion battery.

[0099] On the basis of conforming to the common sense in this field, the above optional conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0100] The reagents and raw materials used in the present invention are conventional reagents and raw materials, all of which are commercially available.

[0101] Example 1

[0102] (1) 2 parts by mass of divinylbenzene, 0.5 parts by mass of azobisisobutyronitrile, 200 parts by mass of paraffin wax (phase transition temperature is 35° C.-40° C.; since the phase transition process is a continuous change process, the phase transition temperature here can only be controlled within a certain range rather than a specific point value, the same below), and 100 parts by mass of monomers (50 parts by mass of styrene, 40 parts by mass of hydroxyethyl acrylate, and 10 parts by mass of butyl acrylate) are mixed to form an oil phase;

[0103] (2) dispersing or dissolving 10 parts by mass of polyvinyl alcohol, 0.01 parts by mass of sodium lauryl sulfate, 1 part by mass of sodium chloride, and 0.01 parts by mass of sodium nitrite in 1000 parts by mass of deionized water to form an aqueous phase;

[0104] (3) mixing the oil phase and the aqueous phase, and shearing the mixture in a cell crusher (400W) for 5-15 minutes to obtain an oil / water dispersion system, forming small oil droplets (including paraffin and polymer monomers) similar to those dispersed in water;

[0105] (4) The oil / water dispersion system is heated to 75°C and polymerized for 10 hours (during which time the polymer monomers undergo a polymerization reaction around the paraffin material to form a polymer binder that wraps the paraffin material. Nitrogen is continuously introduced during the polymerization process and appropriate stirring is performed to prevent excessive agglomeration of the synthesized binder). The reaction is then stopped to obtain a composite binder emulsion. (Note: The boiling point of the reactants is much higher than the polymerization temperature, and there is almost no loss of raw materials.)

[0106] Take 0.01mL of composite adhesive emulsion, dilute it 5-10 times and dry it. The SEM electron microscope and TEM electron microscope scanning results of the composite adhesive are as follows: Figure 1 and Figure 2 The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 2:1, and a shell thickness of 30 nm.

[0107] The particle size and shell thickness are average values obtained by selecting at least 50 composite binder particles and photographing SEM electron microscope or TEM electron microscope scans.

[0108] Example 2

[0109] On the basis of Example 1, other conditions were kept unchanged, and only the amount of paraffin wax in step (1) was changed to 150 parts by mass.

[0110] The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 1.5:1, and a shell thickness of 40 nm.

[0111] Example 3

[0112] (1) Based on Example 1, other conditions remained unchanged, and only the paraffin wax in step (1) was changed to a paraffin wax with a phase transition temperature of 5°C-10°C to prepare a composite adhesive. The obtained composite adhesive had a particle size of 0.4 μm, a core-shell mass ratio of 2:1, and a shell thickness of 30 nm.

[0113] (2) The composite adhesive prepared in step (1) and Example 1 were blended in a mass ratio of 1:1 and used as an adhesive.

[0114] Example 4

[0115] (1) Based on Example 1, other conditions remained unchanged, except that the paraffin wax in step (1) was changed to a paraffin wax with a phase transition temperature of 5°C-10°C and an amount of 150 parts by mass to prepare a composite adhesive. The resulting composite adhesive had a particle size of 0.4 μm, a core-shell mass ratio of 1.5:1, and a shell thickness of 40 nm.

[0116] (2) The composite adhesive of step (1) and Example 2 was blended in a mass ratio of 1:1 and used as an adhesive.

[0117] Example 5

[0118] On the basis of Example 1, other conditions remain unchanged, and only the paraffin in step (1) is changed to paraffin with a phase transition temperature of 45°C-50°C.

[0119] The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 2:1, and a shell thickness of 30 nm.

[0120] Example 6

[0121] On the basis of Example 2, other conditions remain unchanged, and only the paraffin in step (1) is changed to paraffin with a phase transition temperature of 45°C-50°C.

[0122] The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 1.5:1, and a shell thickness of 40 nm.

[0123] Example 7

[0124] On the basis of Example 1, other conditions remain unchanged, and only the paraffin in step (1) is changed to paraffin with a phase transition temperature of 20°C-25°C.

[0125] The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 2:1, and a shell thickness of 30 nm.

[0126] Example 8

[0127] On the basis of Example 1, other conditions remain unchanged, and only the paraffin in step (1) is changed to paraffin with a phase transition temperature of 25°C-30°C.

[0128] The obtained composite binder has a particle size of 0.4 μm, a core-shell mass ratio of 2:1, and a shell thickness of 30 nm.

[0129] Comparative Example 1

[0130] Conventional adhesive styrene-butadiene rubber (ZEON-451B) is used as the adhesive, without adding phase change material.

[0131] Comparative Example 2

[0132] On the basis of Example 1, other conditions were kept unchanged and no emulsifier sodium lauryl sulfate was added in step (2).

[0133] A composite adhesive cannot be produced.

[0134] Effect Example 1

[0135] 1. Lithium-ion battery preparation

[0136] (1) Preparation of positive electrode sheet:

[0137] The positive electrode active material (LFP or NCM622), conductive carbon black Super P, and binder PVDF were thoroughly stirred in an appropriate amount of solvent NMP at a weight ratio of 97:1:2 to form a uniform, stable positive electrode slurry with a viscosity of 4000-8000 mPa·s. The slurry was allowed to stand for 48 hours without any abnormalities such as gelation, delamination, or sedimentation. The positive electrode slurry was evenly coated on an Al foil current collector, dried, and cold-pressed to the designed compaction density. After die-cutting / slitting, the positive electrode sheets were obtained.

[0138] (2) Preparation of negative electrode sheet:

[0139] The negative electrode active material (graphite), conductive agent (carbon black), binder (i.e., the composite binder in Examples 1-14 / the conventional binder in Comparative Example 1), and thickener (CMC) were thoroughly stirred and mixed in an appropriate amount of aqueous solvent at a weight ratio of 96:1:2:1 to form a uniform, stable negative electrode slurry. The negative electrode slurry was evenly coated on a Cu foil current collector, dried, and cold-pressed to the designed compaction density. After die-cutting / slitting, different negative electrode sheets were obtained.

[0140] (3) Preparation of electrolyte:

[0141] Equal volumes of ethylene carbonate and propylene carbonate were mixed, and then an appropriate amount of lithium hexafluorophosphate was uniformly dissolved in the mixed solvent to obtain a 1 mol / L electrolyte.

[0142] (4) Diaphragm preparation:

[0143] Use PP material diaphragm.

[0144] (5) Lithium-ion battery preparation:

[0145] Using conventional lithium-ion battery manufacturing technology, the positive electrode sheet, separator, and different negative electrode sheets are wound or stacked into a bare battery cell, which is placed in a battery casing, then injected with electrolyte, and then carried out formation and sealing processes to obtain a lithium-ion battery containing different composite binders.

[0146] 2. Capacity retention test

[0147] (1) Cyclic discharge capacity retention test at 45°C:

[0148] Lithium-ion batteries containing the binders obtained in each example and comparative example were subjected to repeated charge and discharge cycles. The first cycle specifically comprised the following steps: a. The prepared lithium-ion batteries were allowed to rest at 45°C for 30 minutes; b. The batteries were discharged at a constant current of 1C to the battery's discharge cutoff voltage, followed by a rest period of 30 minutes; c. The batteries were charged at a constant current of 1C to the battery's charge cutoff voltage, then charged at a constant voltage until the current was less than 0.05C, followed by a rest period of 5 minutes; and d. The batteries were discharged at a constant current of 1C to the battery's discharge cutoff voltage, followed by a rest period of 5 minutes. The measured discharge capacity was designated as Cap1.

[0149] Then, the above steps a, c, and d are repeated to perform repeated charge and discharge cycles. The discharge capacity measured at the 800th time is counted as Cap800, and the capacity retention rate after 800 cycles is: (Cap800 / Cap1)*100%.

[0150] Among them, the battery with LFP as the positive electrode material has a charge end voltage of 3.65V and a discharge end voltage of 2.5V; the battery with NCM622 as the positive electrode material has a charge end voltage of 4.25V and a discharge end voltage of 2.8V. The same applies to the following.

[0151] (2) Cyclic discharge capacity retention test at 25°C:

[0152] Lithium-ion batteries containing the binders obtained in each example and comparative example were subjected to repeated charge and discharge cycles. The first cycle specifically comprised the following steps: a. The prepared lithium-ion batteries were allowed to rest at 25°C for 30 minutes; b. The batteries were discharged at a constant current of 1C to the battery's discharge cutoff voltage, followed by a rest period of 30 minutes; c. The batteries were charged at a constant current of 1C to the battery's charge cutoff voltage, then charged at a constant voltage until the current was less than 0.05C, followed by a rest period of 5 minutes; and d. The batteries were discharged at a constant current of 1C to the battery's discharge cutoff voltage, followed by a rest period of 5 minutes. The measured discharge capacity was designated as Cap1.

[0153] Then, the above steps a, c, and d are repeated to perform repeated charge and discharge cycles. The discharge capacity measured at the 800th time is counted as Cap800, and the capacity retention rate after 800 cycles is: Cap800 / Cap1*100%.

[0154] The results are shown in Table 1.

[0155] Table 1. Performance of lithium-ion batteries containing binders in Examples and Comparative Examples

[0156]

[0157] Among them, LFP battery is a battery made with LFP as the positive electrode active material, and NCM battery is a battery made with NCM as the positive electrode active material.

[0158] According to the data in Table 1, the composite binder obtained in the embodiment of the present invention can ensure that the cycle discharge capacity retention rate at 25°C is more than 91% and the cycle discharge capacity retention rate at 45°C is more than 85% after being further made into LFP batteries. At the same time, after being further made into NCM batteries, the cycle discharge capacity retention rate at 25°C is more than 85% and the cycle discharge capacity retention rate at 45°C is more than 79%.

[0159] Among them, for LFP batteries, based on the good high temperature resistance of the battery itself, when the phase change temperature of the phase change material is fixed, the amount of phase change material added will not have a significant effect. As for the phase change temperature of the phase change material, when containing a phase change material with a phase change temperature of 20-25°C, the resulting LFP battery can maintain a cycle discharge capacity retention rate equivalent to that of the existing conventional binder (Comparative Example 1); as the phase change temperature rises to 40°C, its cycle discharge capacity retention rate at 45°C always remains at a considerable level, but the cycle discharge capacity retention rate at 25°C increases to equilibrium; when a higher phase change temperature (45-50°C) is further selected, its cycle discharge capacity retention rate at 45°C is significantly increased, but at this time, due to the large temperature difference between the detection temperature and the phase change temperature, the cycle discharge capacity retention rate at 25°C decreases slightly, but is still better than the conventional binder (Comparative Example 1).

[0160] Among them, for NCM batteries, based on the relatively poor high temperature resistance of the battery itself, when the phase change temperature of the phase change material is fixed, the influence of the amount of phase change material added is more obvious than that of LFP batteries. As the phase change temperature increases from 25°C to 40°C, its cyclic discharge capacity retention rate at 45°C always remains at a level comparable to that of the conventional binder (Comparative Example 1), but the cyclic discharge capacity retention rate at 25°C increases to equilibrium, and is better than that of the conventional binder (Comparative Example 1); when a higher phase change temperature (45-50°C) is further selected, its cyclic discharge capacity retention rate at 45°C is significantly increased, but at this time, due to the large temperature difference between the detection temperature and the phase change temperature, the cyclic discharge capacity retention rate at 25°C decreases slightly, but still maintains a level comparable to that of the conventional binder (Comparative Example 1).

[0161] In summary, it can be shown that the battery made of the composite binder of the present invention, based on the characteristics of the internal phase change material, can regulate the internal temperature of the battery under different temperature environments, that is, it can directly and efficiently regulate the temperature at the pole piece scale, alleviate thermal shock, and improve the battery's fast charging, high and low temperature, cycle, safety and other performance.

Claims

1. A composite adhesive, characterized in that: The composite binder has a core-shell structure; wherein, The core of the core-shell structure comprises a phase change material, and the phase change temperature of the phase change material is -10°C to 70°C; The shell of the core-shell structure includes a polymer binder.

2. The composite adhesive according to claim 1, wherein The composite binder satisfies one or more of the following conditions (a)-(e): (a) the particle size of the composite binder is 0.1-10 μm; (b) In the core-shell structure, the mass ratio of the core to the shell is (1:10)-(4:1); (c) the shell thickness of the core-shell structure is 0.01-1 μm; (d) the phase change temperature of the phase change material is 25°C-50°C; (e) The phase change material is selected from C 10 -C 24 Long-chain alkanes and any mixtures thereof.

3. The composite adhesive according to claim 1, wherein The phase change temperature of the phase change material is 25-30°C, 35-40°C or 45-50°C.

4. A method for preparing the composite adhesive according to any one of claims 1 to 3, characterized in that: The preparation method of the composite adhesive comprises the following steps: Shearing the mixture of the oil phase and the water phase and subjecting it to polymerization reaction to obtain the composite adhesive; Wherein, the oil phase includes a phase change material and a raw material of the polymer binder, and the raw material of the polymer binder includes at least a monomer; The aqueous phase includes water and an emulsifier.

5. The method for preparing the composite adhesive according to claim 4, wherein: The preparation method of the composite binder satisfies one or more of the following conditions (a) to (f): (a) the mass of the oil phase is calculated based on the total mass of the phase change material and the monomer, the mass of the aqueous phase is calculated based on the total mass of water, and the mass ratio of the oil phase to the aqueous phase is 1:(1-10); (b) the shearing treatment time is 5-15 min; (c) the shearing treatment is performed at ambient temperature; (d) the polymerization reaction temperature is 50° C.-85° C.; (e) the polymerization reaction time is 6-12h; (f) Inert gas is continuously introduced during the polymerization reaction.

6. The method for preparing the composite adhesive according to claim 4, wherein: The preparation method of the composite binder satisfies one or more of the following conditions (a)-(c): (a) the monomer is selected from one or more of butyl acrylate, hydroxyethyl acrylate, methacrylate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, styrene, vinyl toluene, tert-butylstyrene and N-hydroxymethyl acrylamide; (b) the raw materials of the polymer binder further include an initiator; (c) The raw materials of the polymer binder further include a cross-linking agent.

7. The method for preparing the composite adhesive according to claim 6, wherein: The preparation method of the composite binder satisfies one or both of the following conditions (a)-(b): (a) the initiator is selected from azo initiators and peroxide initiators; (b) The crosslinking agent is selected from one or more of divinylbenzene, ethylene glycol dimethacrylate, allyl methacrylate, ethylene glycol diacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, adipate dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane and pentaerythritol tetramethacrylate.

8. The method for preparing the composite adhesive according to claim 4, wherein: The preparation method of the composite binder satisfies one or both of the following conditions (a)-(b): (a) the emulsifier is selected from one or more of sodium lauryl sulfate, cetyltrimethylammonium bromide, polyoxyethylene terephthalate, OP surfactant, Span surfactant, Tween surfactant and sodium dodecylbenzene sulfonate; (b) the aqueous phase further comprises one or more of a dispersant, an inhibitor and a metal salt; wherein the dispersant is selected from one or more of polyvinyl alcohol, magnesium hydroxide, calcium carbonate, calcium phosphate, silica sol, polyvinyl pyrrolidone, styrene-maleic anhydride copolymer and carboxymethyl cellulose; the inhibitor is selected from nitrite and / or potassium dichromate; and the metal salt is an ionic compound.

9. The method for preparing the composite adhesive according to claim 8, wherein: The preparation method of the composite binder satisfies one or more of the following conditions (a) to (d): (a) the weight ratio of the phase change material to the monomer is (10-400):100; (b) the weight ratio of the emulsifier to water is (0.01-5):(150-2000); (c) the oil phase comprises a cross-linking agent, an initiator, a phase change material, and a monomer; wherein the weight ratio of the cross-linking agent, the initiator, the phase change material, and the monomer is (0.5-3):(0.1-3):(10-400):100; (d) The aqueous phase comprises a dispersant, an emulsifier, a metal salt, an inhibitor and water; wherein the weight ratio of the dispersant, the emulsifier, the metal salt, the inhibitor and the water is (1-50):(0.01-5):(0.5-5):(0.01-2):(150-2000).

10. An electrochemical device, characterized in that The composite binder according to any one of claims 1 to 3 is used in the preparation process of the electrode plate.

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