Composite binder and manufacturing method of the same, and electrochemical device

Abstract

To provide a composite binder and a manufacturing method of the same, and an electrochemical device.SOLUTION: A composite binder has a core-shell structure, the core of the core-shell structure is a phase change material, a phase change temperature of the phase change material is -10 to 70°C, and the shell of the core-shell structure is a polymer binder. A manufacturing method of a composite binder includes a step of subjecting a mixture of an oil phase and an aqueous phase to shear processing, and subjecting it to polymerization reaction. The oil phase contains a phase change material and a raw material of the polymer binder, the raw material of the polymer binder contains at least a monomer, and the aqueous phase contains water and an emulsifier. The composite binder obtained by the composite binder manufacturing method is applied to an electrochemical device (for example, battery), which controls heat environment of an electrode sheet according to a demand while holding inherent adhesive performance, and can improve performances such as high temperature and low temperature, quick charge and safety of a cell.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a composite binder, a method for producing the same, and an electrochemical device. [Background technology]

[0002] Lithium / sodium-ion batteries are important electrochemical energy storage devices that are widely used in fields such as electronic consumer goods, new energy vehicles, and power storage devices. Lithium ions reversibly intercalate into and deintercalate from the active material through the electrolyte-active material interface, thereby completing the battery's charge-discharge cycle. However, to achieve excellent battery performance, the temperature (thermal) environment of the cell is very strict. High-temperature environments accelerate the rate of electrolyte side reactions, ultimately deteriorating long-term cycle performance. Low-temperature environments slow the lithium ion migration rate, increasing the activation energy of interfacial migration reactions, increasing internal resistance, and exacerbating lithium deposition. Furthermore, even at room temperature, high-rate charge-discharge or long-term charge-discharge cycles can cause strong thermal shock, making the battery susceptible to temperature spikes and thermal runaway.

[0003] However, current battery thermal management is limited to the module / pack level, and in most cases, liquid cooling is used. There is no method yet available to adjust heat according to demand in real time from within the electrode sheet and provide a uniform and consistent thermal environment for battery operation. Summary of the Invention [Problem to be solved by the invention]

[0004] To address the gap in the field of thermal management at the electrode sheet and cell scale in existing batteries, the present invention provides a composite binder, a manufacturing method thereof, and an electrochemical device. The composite binder can adjust the thermal environment of the electrode sheet according to demand, based on the existing electrode sheet manufacturing process, and improve the cell's performance in high and low temperature, fast charging, safety, etc. [Means for solving the problem]

[0005] In a first aspect, the present invention provides a composite binder, the composite binder having a core-shell structure, The core of the core-shell structure includes a phase change material, and the phase change temperature of the phase change material is -10 to 70°C; The shell of the core-shell structure comprises a polymeric binder.

[0006] In a second aspect, the present invention provides a method for producing the aforementioned composite binder, the method comprising the steps of: The method includes a step of shearing the mixture of the oil phase and the water phase to cause a polymerization reaction to produce the composite binder. wherein the oil phase contains a phase change material and raw materials for the polymer binder, and the raw materials for the polymer binder contain at least a monomer; The aqueous phase comprises water and an emulsifier.

[0007] In a third aspect, the present invention provides an electrochemical device, which employs the composite binder described above in a manufacturing process for an electrode sheet of the electrochemical device. [Effects of the Invention]

[0008] The positive advances of the present invention include the following: The present invention provides a composite binder with a core-shell structure, consisting of a phase-change material as the core and a polymer binder as the shell. The phase-change material has a specific phase change temperature. The composite binder maintains its inherent binding properties while undergoing a phase change in response to changes in the external environmental temperature (battery temperature), thereby dissipating or absorbing heat. This directly and efficiently controls temperature at the electrode sheet level, mitigating issues such as thermal shock, and improving battery performance in areas such as fast charging, high-low temperature, cycle life, and safety. Furthermore, the composite binder is compatible with existing electrode sheet manufacturing processes, eliminating the need for equipment modifications or upgrades. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an SEM image of the composite binder in Example 1. [Figure 2] 1 is a TEM image of the composite binder in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be further described through the following examples, but the present invention is not limited to the scope of the examples. In the following examples, experimental methods for which specific conditions are not specified are selected according to conventional methods and conditions or product instructions.

[0011] Composite Binder

[0012] In the composite binder according to the first aspect of the present invention, the composite binder has a core-shell structure, The core of the core-shell structure is a phase change material, and the phase change temperature of the phase change material is -10 to 70°C; The shell of the core-shell structure is a polymeric binder. In the present invention, the core-shell structure can be an ordered structure formed by covering the core layer material with the shell layer material.

[0013] In the present invention, the phase change material refers to a substance that can undergo a first-order phase transition and release latent heat, i.e., a substance that can change form and provide latent heat with a change in temperature. The process in which a phase change material changes from solid to liquid (melting) or from liquid to solid (solidification) is called the phase change process, and during this process, the phase change material absorbs or releases a large amount of latent heat. Accordingly, the temperature at which the phase change material undergoes the phase change process is called the phase change temperature.

[0014] In the present invention, the phase change temperature of the phase change material is −10 to 70°C. Based on the requirements of actual applications, those skilled in the art can select a composite binder containing a phase change material with a corresponding temperature range, or can choose to mix composite binders containing phase change materials with different temperature ranges. For example, if a phase change material with a phase change temperature of −10 to 25°C is selected, the phase change material can undergo a liquid-to-solid phase transition and release latent heat when the battery is transferred from a room temperature environment to a cold environment, thereby achieving the effect of preheating the battery. Furthermore, if a phase change material with a phase change temperature of 50 to 70°C is selected, the phase change material can undergo a solid-to-liquid phase transition and absorb latent heat when the battery is transferred from a room temperature environment to a high temperature environment, thereby reducing the battery temperature and avoiding safety issues caused by excessive battery temperature.

[0015] In some embodiments, the phase change temperature of the phase change material is 25 to 50°C, e.g., 25 to 30°C, 35 to 40°C, or 45 to 50°C. This temperature range is most favorable for long-term battery charging and discharging in a room-temperature environment. Temperature increases occur during the battery charging and discharging process. For example, in a 25°C environment (typically considered the optimal operating temperature for a battery), for a battery based on LFP (lithium iron phosphate) or NCM (nickel-cobalt-manganese peroxide ternary material) chemistry, the battery temperature typically increases by 10 to 25°C during a charging process at a multiplication factor of 1C. During this process, the phase change material effectively absorbs some of the heat, improving battery performance.

[0016] In the present invention, the phase change material is C 10 ~C 24 It can be selected from long chain alkanes and mixtures thereof.

[0017] In some embodiments, the phase change material is paraffin, and the paraffin has a phase change temperature of 5-10°C, 20-25°C, 25-30°C, 35-40°C, or 45-50°C. The paraffin may refer to a mixture of alkanes with different carbon numbers, where alkanes with different carbon numbers have different melting points. That is, those skilled in the art can select different alkanes according to their actual needs, thereby obtaining paraffins with different melting points.

[0018] In the present invention, the particle size of the composite binder may be 0.1 to 10 μm, for example, 0.4 μm.

[0019] In the present invention, the mass ratio of the core to the shell in the core-shell structure may be (1:10) to (4:1), preferably (1:1) to (4:1), for example, 1.5:1 or 2:1.

[0020] In the present invention, the thickness of the shell of the core-shell structure may be 0.01 to 1 μm, for example, 20 nm, 30 nm, 40 nm, or 60 nm.

[0021] In the present invention, the polymer binder may be a crosslinked polymer or a non-crosslinked polymer. When the polymer binder is a non-crosslinked polymer, its weight average molecular weight is optionally 70,000 to 500,000 g / mol.

[0022] Manufacturing method of composite binder

[0023] In the method for producing a composite binder according to the second aspect of the present invention, the method for producing the composite binder comprises the following steps: The method includes a step of shearing the mixture of the oil phase and the water phase to cause a polymerization reaction to produce the composite binder. the oil phase includes a phase change material and a raw material for the polymer binder, the raw material for the polymer binder including at least a monomer; The aqueous phase comprises water and an emulsifier.

[0024] In the present invention, the monomer may be a monoene type monomer or a non-polyene type monomer, and those skilled in the art will understand the specific meaning thereof.

[0025] In the present invention, the mass of the oil phase is calculated as the total mass of the phase-change material and the monomer, and the mass of the aqueous phase is calculated as the total mass of water. The mass ratio of the oil phase to the aqueous phase may be 1:(1 to 10), preferably 1:(1 to 7), for example, 1:1.3, 1:1.7, 1:2.0, 1:3.3, 1:4.0, or 1:6.7.

[0026] In the present invention, the shearing step can be performed using a high-shear liquid-liquid dispersing device. Optionally, the high-shear liquid-liquid dispersing device includes one of a high-speed shearer, a high-pressure homogenizer, a cell disrupter, and a super-gravity field generator. For example, it is a high-speed shearer or an ultrasonic cell disrupter.

[0027] In some embodiments, the shear rate of the high-speed shear machine is 2000 to 5000 rpm.

[0028] In some embodiments, the power output of the ultrasonic cell disrupter is 150-600W, optionally 200-500W, for example 400W.

[0029] In the present invention, the shearing time may be 5 to 15 minutes.

[0030] In the present invention, the temperature of the shearing treatment may be ambient temperature.

[0031] In the present invention, the temperature of the polymerization reaction may be 50°C to 85°C, for example, 75°C.

[0032] In the present invention, the polymerization reaction time may be 6 to 12 hours, for example, 10 hours.

[0033] In the present invention, the polymerization reaction may be carried out under stirring.

[0034] In the present invention, an inert gas such as nitrogen may be continuously introduced into the polymerization reaction process.

[0035] In the present invention, a drying step may be further included after the polymerization reaction step.

[0036] In the present invention, the monomer may be one or more selected from butyl acrylate, hydroxyethyl acrylate, methacrylic acid ester, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, styrene, vinyl toluene, tert-butyl styrene, and N-hydroxymethyl acrylamide.

[0037] In some embodiments, the monomers are styrene, hydroxyethyl acrylate, and butyl acrylate, and the weight ratio of the styrene, hydroxyethyl acrylate, and butyl acrylate is optionally 50:40:10.

[0038] In the present invention, the emulsifier may be a polymer emulsifier, where the polymer has a molecular weight of 1,000 to 50,000 g / mol.

[0039] The polymeric emulsifier (emulsifier for polymer polymerization process) used in the present invention has the inherent emulsifying properties of an emulsifier, while also having a soft texture and further improving the binding strength of the polymeric binder in the shell layer. Optionally, the emulsifier is one or more selected from the group consisting of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, nonylphenol polyoxyethylene ether, OP surfactants, Span surfactants, Tween surfactants, and sodium dodecylbenzenesulfonate.

[0040] In some embodiments, the emulsifier is sodium dodecyl sulfate.

[0041] In the present invention, the raw materials for the polymer binder may further include an initiator. The initiator may be an azo-based initiator and / or a peroxide-based initiator having a water solubility of 0.5 g / kg water or less at 25°C. The azo-based initiator may optionally include azobisisobutyronitrile and / or azobisisoheptonitrile. The peroxide-based initiator may optionally include one or more selected from benzoyl peroxide, ammonium persulfate, and potassium persulfate.

[0042] In some embodiments, the initiator is azobisisobutyronitrile.

[0043] In the present invention, the raw material of the polymer binder may further include a crosslinking agent, which is a crosslinking agent commonly selected in the art, and is generally one or more selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, allyl methacrylate, ethylene glycol diacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, hexanediol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane, and pentaerythritol tetramethacrylate.

[0044] In some embodiments, the crosslinker is divinylbenzene.

[0045] In the present invention, the aqueous phase may further contain one or more selected from the group consisting of a dispersant, a polymerization inhibitor, and a metal salt.

[0046] The dispersant can improve the stability of large-sized latex particles. The dispersant is a common dispersant in this field, and is generally one or more selected from polyvinyl alcohol, magnesium hydroxide, calcium carbonate, calcium phosphate, silica sol, polyvinylpyrrolidone, styrene-maleic anhydride copolymer, and carboxymethyl cellulose. For example, polyvinyl alcohol.

[0047] Here, the polymerization inhibitor is a polymerization inhibitor commonly used in the art, and is generally selected from nitrites and / or potassium dichromate, such as sodium nitrite.

[0048] The metal salt can reduce the diffusion of highly water-soluble monomers into the aqueous phase, trap free radicals in the aqueous phase, and improve the synthesis efficiency of the phase change composite binder. The metal salt is a common metal salt in the art and is generally an ionic compound, such as sodium chloride.

[0049] In the present invention, the weight ratio of the phase-change material to the monomer may be (10-400):100, preferably (100-400):100, for example, 150:100 or 200:100.

[0050] In the present invention, the weight ratio of the emulsifier to water may be (0.01-5):(150-2000), preferably (0.01-5):(150-1000), for example, 0.01:400, 0.01:500, or 0.01:1000.

[0051] 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. Any ratio can be selected, such as (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.

[0052] In some embodiments, the aqueous phase contains a dispersant, an emulsifier, a metal salt, a polymerization inhibitor, and water, wherein the weight ratio of the dispersant, emulsifier, metal salt, polymerization inhibitor, and water is (1-50):(0.01-5):(0.5-5):(0.01-2):(150-2000). Any ratio can be selected, such as (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.

[0053] Electrochemical Equipment

[0054] In the electrochemical device according to the third aspect of the present invention, the electrode sheet is produced by using the composite binder described above, which is the composite binder provided by the present invention or the composite binder produced by the method for producing the composite binder of the present invention.

[0055] In the present invention, the electrode sheet is preferably a negative electrode sheet.

[0056] In the present invention, the electrochemical device may be a sodium ion battery or a lithium ion battery.

[0057] In some embodiments, the electrochemical device is a lithium ion battery, the lithium ion battery comprising the negative electrode sheet, the positive electrode sheet, a separator, and an electrolyte.

[0058] Negative electrode sheet

[0059] 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 includes a negative electrode active material and the composite binder, and may further include a conductive agent and / or a thickener, as necessary.

[0060] Here, the negative electrode active material may be a negative electrode active material commonly used in the art for manufacturing negative electrode sheets, such as one or more materials selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, lithium metal, and silicon-based materials.

[0061] The conductive agent is a reagent that ensures that the electrode has good charge / discharge performance, and can be selected from the following: graphite-based materials, such as natural graphite or artificial graphite; carbon black-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers, such as carbon fibers or 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; or conductive polymers, such as polyphenylene derivatives.

[0062] The thickener can increase the viscosity of the system of components in the negative electrode layer, and may be a thickener commonly used in the art for manufacturing negative electrode sheets, such as sodium carboxymethylcellulose (CMC).

[0063] In some embodiments, the negative electrode material is graphite, the conductive agent is carbon black, and the thickener is CMC, and the mass ratio of the graphite, carbon black, composite binder, and CMC in the negative electrode material layer is optionally 96:1:2:1.

[0064] In some embodiments, the negative electrode sheet is prepared by mixing the negative electrode active material, the conductive agent, the composite binder, the thickener, and a solvent to obtain a negative electrode slurry, and then coating the negative electrode slurry on a negative electrode current collector, followed by drying, cold pressing, and slitting to produce the negative electrode sheet.

[0065] Here, the solvent may be any solvent commonly used in the art, such as deionized water.

[0066] Positive electrode sheet

[0067] In the present invention, the positive electrode sheet can 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 includes a positive electrode active material, and if necessary, a conductive agent and / or a binder can be further added. Here, the positive electrode active material can be one commonly used in the art, and includes, but is not limited to, one or more of lithium iron phosphate (LiFePO4, LFP), lithium manganese iron phosphate, ternary positive electrode materials, and lithium-rich manganese-based materials. The ternary positive electrode material can be, 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)

[0068] The conductive agent is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. For example, the following can be used: Graphite is, for example, natural graphite or artificial graphite; Carbon-based materials are, for example, carbon black (Super P), acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; Metal powder or metal fiber is, for example, copper, nickel, aluminum, or silver; Conductive whiskers are, for example, zinc oxide whiskers or potassium titanate whiskers; Conductive metal oxides are, for example, titanium dioxide; or Conductive polymers are, for example, polyphenylene derivatives.

[0069] The binder enhances the bonding between the positive electrode active materials and the adhesion between the positive electrode active material and the positive electrode current collector, and there are no particular limitations on the type of binder. The binder may be a binder commonly used in the art or the composite binder described above. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. Any one of these or a mixture of two or more thereof may be used.

[0070] 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 the LFP, Super P, and PVDF in the positive electrode material layer can be optionally selected to be 97:1:2.

[0071] 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 the NCM622, Super P, and PVDF in the positive electrode material layer can be arbitrarily selected to be 97:1:2.

[0072] In some embodiments, the positive electrode sheet is manufactured by the following manufacturing method.

[0073] The positive electrode active material, the conductive agent, the binder, and the solvent are mixed to obtain a positive electrode slurry, which is then applied to a positive electrode current collector, dried, cold-pressed, and cut to produce the positive electrode sheet.

[0074] Here, the solvent may be an organic solvent commonly used in the art for preparing a positive electrode sheet slurry, such as one or more selected from N-methylpyrrolidone (NMP), DMAC, and acetone.

[0075] In the present invention, the positive and negative electrode current collectors may be made of any material that is highly conductive and does not undergo chemical changes, depending on actual needs. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon may be used. Alternatively, aluminum or stainless steel materials that have been surface-treated with carbon, nickel, titanium, or silver may be used. To improve the adhesion of the positive and negative electrode active materials, the surfaces of the positive and negative electrode current collectors may be finely embossed. The positive and negative electrode current collectors may be in various forms, such as a film, sheet, foil, mesh, or porous body.

[0076] electrolyte

[0077] In the present invention, the electrolyte may be any electrolyte commonly used in the art for lithium ion secondary battery cells, and generally includes a non-aqueous solvent and a lithium salt.

[0078] Here, the non-aqueous solvent is selected from, for example, carbonate ester solvents. Specifically, the carbonate ester solvent may be one or more selected from 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), and butylene carbonate (BC).

[0079] In some embodiments, the non-aqueous solvent is ethylene carbonate and propylene carbonate, optionally in a volume ratio of 1:1.

[0080] Here, the lithium salt may be a lithium salt commonly used in the art, such as LiPF6.

[0081] In the present invention, the method for preparing the electrolyte solution may be a method commonly used in the art, for example, by dissolving the lithium salt in the non-aqueous solvent.

[0082] Separator

[0083] In the present invention, the separator may be a common one in the art, for example, a polypropylene (PP) separator or a polyethylene (PE) separator is selected and used.

[0084] In some embodiments, the lithium ion battery is manufactured by the following manufacturing method.

[0085] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially wound or stacked, and then placed in a battery case. The electrolyte is injected, and the lithium ion battery is manufactured through forming and sealing processes.

[0086] Based on common knowledge in the art, the above optional conditions can be arbitrarily combined to obtain preferred embodiments of the present invention.

[0087] The reagents and materials used in the present invention are conventional reagents and materials, all of which are commercially available.

[0088] Example 1

[0089] Step (1): 2 parts by mass of divinylbenzene, 0.5 parts by mass of azobisisobutyronitrile, 200 parts by mass of paraffin (phase change temperature is 35-40°C; since the phase change process is a continuous change process, the phase change temperature here can only be controlled within a certain range rather than a specific point value; the same applies 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.

[0090] Step (2): 10 parts by mass of polyvinyl alcohol, 0.01 parts by mass of sodium dodecyl sulfate, 1 part by mass of sodium chloride, and 0.01 parts by mass of sodium nitrite are dispersed or dissolved in 1000 parts by mass of deionized water to form an aqueous phase.

[0091] Step (3): The oil and water phases are mixed and the resulting mixture is sheared in a cell disruptor (400 W) for 5 to 15 minutes to obtain an oil / water dispersion, which resembles small oil droplets (containing paraffin and polymerized monomers) dispersed in water.

[0092] Step (4): The oil / water dispersion is heated to 75°C and polymerized for 10 hours (during which time the polymerized monomer undergoes a polymerization reaction around the paraffin material, forming a polymerized binder that encases the paraffin material. Nitrogen gas is continuously introduced during the polymerization process, and moderate stirring is performed at the same time to prevent excessive aggregation between the synthesized binders). The reaction is then stopped, and an emulsion of the composite binder is obtained. (Note that since the boiling point of the reactants is much higher than the polymerization temperature, there is almost no loss of raw materials.)

[0093] 0.01 mL of the composite binder emulsion was taken, diluted 5 to 10 times, and dried. The results of scanning electron microscope (SEM) and electron microscope (TEM) scans of the obtained composite binder are shown in Figures 1 and 2, respectively. The particle diameter of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 2:1, and the shell layer thickness was 30 nm.

[0094] Here, the particle diameter and the shell layer thickness are average values obtained by selecting at least 50 composite binder particles and photographing them under an SEM or TEM electron microscope.

[0095] Example 2 Based on Example 1, the other conditions are not changed, and only the amount of paraffin used in step (1) is changed to 150 parts by mass. The particle size of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 1.5:1, and the shell layer thickness was 40 nm.

[0096] Example 3 Step (1): A composite binder is prepared based on Example 1, with the other conditions unchanged, except that the paraffin in step (1) of Example 1 is replaced with a paraffin having a phase change temperature of 5 to 10° C. The particle size of the obtained composite binder is 0.4 μm, the core-shell mass ratio is 2:1, and the shell layer thickness is 30 nm. Step (2): The composite binder of step (1) and Example 1 is mixed in a mass ratio of 1:1 and used as a binder.

[0097] Example 4 Step (1): A composite binder was prepared based on Example 1, with the other conditions unchanged, except that the paraffin used in step (1) of Example 1 was replaced with a paraffin having a phase change temperature of 5 to 10°C, and the amount of paraffin used was 150 parts by mass. The particle size of the resulting composite binder was 0.4 μm, the core-shell mass ratio was 1.5:1, and the shell layer thickness was 40 nm. Step (2): The composite binder of step (1) and Example 2 is mixed in a mass ratio of 1:1 and used as a binder.

[0098] Example 5 Based on Example 1, the other conditions are not changed, and only the paraffin in step (1) of Example 1 is changed to a paraffin having a phase change temperature of 45 to 50°C. The particle size of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 2:1, and the shell layer thickness was 30 nm.

[0099] Example 6 Based on Example 2, the other conditions are not changed, and only the paraffin in step (1) of Example 1 is changed to a paraffin having a phase change temperature of 45 to 50°C. The particle size of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 1.5:1, and the shell layer thickness was 40 nm.

[0100] Example 7 Based on Example 1, the other conditions are not changed, and only the paraffin in step (1) of Example 1 is changed to a paraffin having a phase change temperature of 20 to 25°C. The particle size of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 2:1, and the shell layer thickness was 30 nm.

[0101] Example 8 Based on Example 1, the other conditions are not changed, and only the paraffin in step (1) of Example 1 is changed to a paraffin having a phase change temperature of 25 to 30°C. The particle size of the obtained composite binder was 0.4 μm, the core-shell mass ratio was 2:1, and the shell layer thickness was 30 nm.

[0102] Comparative Example 1 Styrene butadiene rubber (ZEON-451B), a common binder, is used as the binder, and no phase change material is added.

[0103] Comparative Example 2 Based on Example 1, other conditions were not changed, and the emulsifier sodium dodecyl sulfate in step (2) of Example 1 was not added. It is not possible to produce a composite binder.

[0104] Effect Example 1

[0105] 1. Preparation of Lithium-ion Battery

[0106] (1) Preparation of positive electrode sheet: The positive electrode active material (LFP or NCM622), conductive carbon black Super P, and binder PVDF are added to an appropriate amount of NMP solvent in a weight ratio of 97:1:2, and thoroughly stirred to form a uniform, stable positive electrode slurry with a viscosity of 4000-8000 mPa·s. The slurry is allowed to stand for 48 hours to ensure there are no abnormal phenomena such as gelation, separation, or sedimentation. The positive electrode slurry is uniformly applied to an Al foil current collector, dried, and then cold-rolled to the designed compaction density. After punching and cutting, the positive electrode sheet is obtained.

[0107] (2) Preparation of negative electrode sheet: The negative electrode active material (graphite), conductive agent (carbon black), binder (composite binder in Examples 1-14 / conventional binder in Comparative Example 1), and thickener (CMC) were added to an appropriate amount of water solvent in a weight ratio of 96:1:2:1 and thoroughly stirred to form a uniform negative electrode stable slurry. The negative electrode slurry was uniformly applied to a Cu foil current collector, dried, and then cold-rolled to the designed compaction density. After punching / cutting, different negative electrode sheets were obtained.

[0108] (3) Preparation of electrolyte: Equal volumes of ethylene carbonate and propylene carbonate are mixed, and an appropriate amount of lithium hexafluorophosphate salt is uniformly dissolved in the mixed solvent to obtain a 1 mol / L electrolyte solution.

[0109] (4) Preparation of separator: Select a separator made of PP material.

[0110] (5) Preparation of Lithium-ion Battery: Using the conventional lithium-ion battery manufacturing process, a positive electrode sheet, a separator, and a different negative electrode sheet are wound or stacked to form a battery element, which is then placed in a battery case, after which an electrolyte is injected, followed by chemical formation and sealing processes, to obtain a lithium-ion battery containing a different composite binder.

[0111] 2. Measurement of capacity retention rate

[0112] (1) Cyclic discharge capacity retention test at 45℃: The lithium ion batteries containing the binders obtained in each of the examples and comparative examples were subjected to repeated charge-discharge cycles. Specifically, the first cycle included: Step a.: The fabricated lithium-ion battery is allowed to stand at 45°C for 30 minutes. Step b: Discharge the battery at a constant current of 1C to the end-of-discharge voltage, then leave it for 30 minutes. Step c.: Charge the battery at a constant current of 1C up to the end-of-charge voltage, then continue constant voltage charging until the current reaches 0.05C, and let it rest for 5 minutes. Step d: Discharge the battery at a constant current of 1 C to the end-of-discharge voltage and let it stand for 5 minutes. The discharge capacity measured here is designated as Cap1. Then, the above steps a, c, and d are repeated to repeat the charge-discharge cycle. The discharge capacity measured at the 800th cycle is defined as Cap800, and the capacity retention rate at 800 cycles is (Cap800 / Cap1) × 100%. Here, the end-of-charge voltage of the battery using LFP as the positive electrode material is 3.65 V and the end-of-discharge voltage is 2.5 V, and the end-of-charge voltage of the battery using NCM622 as the positive electrode material is 4.25 V and the end-of-discharge voltage is 2.8 V. The same applies below.

[0113] (2) Cyclic discharge capacity retention test at 25°C: The lithium ion batteries containing the binders obtained in each of the examples and comparative examples were subjected to repeated charge-discharge cycles. Specifically, the first cycle included: Step a.: The fabricated lithium-ion battery is allowed to stand at 25°C for 30 minutes. Step b: Discharge the battery at a constant current of 1C to the end-of-discharge voltage, then leave it for 30 minutes. Step c.: Charge the battery at a constant current of 1C up to the end-of-charge voltage, then continue constant voltage charging until the current reaches 0.05C, and let it rest for 5 minutes. Step d: Discharge the battery at a constant current of 1 C to the end-of-discharge voltage and let it stand for 5 minutes. The discharge capacity measured here is designated as Cap1. Then, repeat the above steps a, c, and d to repeat the charge-discharge cycle. The discharge capacity measured at the 800th cycle is Cap800, and the capacity retention rate at 800 cycles is (Cap800 / Cap1) × 100%.

[0114] The results obtained are shown in Table 1.

[0115] [Table 1]

[0116] Here, an LFP battery is a battery manufactured using LFP as a positive electrode active material, and an NCM battery is a battery manufactured using NCM as a positive electrode active material.

[0117] From the data in Table 1, it can be seen that after the composite binder obtained in the embodiment of the present invention is further fabricated into an LFP battery, it can guarantee a cyclic discharge capacity retention of 91% or more at 25° C. and a cyclic discharge capacity retention of 85% or more at 45° C. At the same time, after it is further fabricated into an NCM battery, it can guarantee a cyclic discharge capacity retention of 85% or more at 25° C. and a cyclic discharge capacity retention of 79% or more at 45° C.

[0118] Here, for LFP batteries, because the battery itself has excellent high-temperature resistance, the amount of phase-change material added does not have a significant effect when the phase-change temperature of the phase-change material is fixed. Regarding the phase-change temperature of the phase-change material, when a phase-change material with a phase-change temperature of 20 to 25°C is included, the resulting LFP battery can maintain a cyclic discharge capacity retention rate equivalent to that of an existing conventional binder (Comparative Example 1). As the phase-change temperature increases up to 40°C, the cyclic discharge capacity retention rate at 45°C remains at a similar level, while the cyclic discharge capacity retention rate at 25°C increases accordingly until it reaches equilibrium. Selecting a higher phase-change temperature (45 to 50°C) significantly improves the cyclic discharge capacity retention rate at 45°C, but at this point, the temperature difference between the measurement temperature and the phase-change temperature is too large, resulting in a slight decrease in the cyclic discharge capacity retention rate at 25°C. However, it is still superior to the conventional binder (Comparative Example 1).

[0119] Here, for NCM batteries, the effect of the amount of phase change material added is more pronounced than for LFP batteries when the phase change temperature of the phase change material is fixed because the battery itself has relatively poor high-temperature resistance. As the phase change temperature increases from 25°C to 40°C, the cyclic discharge capacity retention at 45°C always remains at a level comparable to that of the conventional binder (Comparative Example 1), but the cyclic discharge capacity retention at 25°C increases accordingly until it reaches equilibrium, both of which are superior to that of the conventional binder (Comparative Example 1). Selecting a higher phase change temperature (45-50°C) significantly improves the cyclic discharge capacity retention at 45°C, but at this point, the temperature difference between the measurement temperature and the phase change temperature is too large, resulting in a slight decrease in the cyclic discharge capacity retention at 25°C. However, the performance level remains comparable to that of the conventional binder (Comparative Example 1).

[0120] The above results indicate that the battery fabricated with the composite binder of the present invention can adjust the internal temperature of the battery under different temperature environments based on the properties of the internal phase change material, i.e., directly and efficiently control the temperature at the electrode sheet scale, mitigate thermal shock, and improve the battery's performance in terms of fast charging, high and low temperature, cycling, safety, etc. [Industrial Applicability]

[0121] The composite binder of the present invention can be used in electrode sheets and is compatible with existing electrode sheet manufacturing processes.

Claims

1. A composite binder comprising: The composite binder has a core-shell structure, The core of the core-shell structure has a phase change temperature of -10 to 70 ｏ C, A composite binder, wherein the shell of the core-shell structure contains a polymer binder.

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

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

4. A method for producing the composite binder according to any one of claims 1 to 3, comprising: subjecting the mixture of the oil phase and the water phase to shearing treatment and then carrying out a polymerization reaction to produce the composite binder; the oil phase includes a phase change material and a raw material for the polymer binder, the raw material for the polymer binder including at least a monomer; The method for producing a composite binder, wherein the aqueous phase contains water and an emulsifier.

5. The method for producing a composite binder according to claim 4, wherein the method satisfies one or more of the following conditions (a) to (f): (a) The mass ratio of the oil phase to the aqueous phase is 1:(1 to 10), where the mass of the oil phase is calculated as the total mass of the phase change material and the monomer, and the mass of the aqueous phase is calculated as the total mass of water. (b) The shearing time is 5 to 15 minutes. (c) The temperature of the shearing treatment is the ambient temperature. (d) The temperature of the polymerization reaction is 50 to 85°C. (e) The polymerization reaction time is 6 to 12 hours. (f) In the polymerization process, an inert gas is continuously introduced.

6. The method for producing a composite binder according to claim 4, wherein the method for producing a composite binder satisfies one or more of the following conditions (a) to (c): (a) The monomer is at least one selected from the group consisting of butyl acrylate, hydroxyethyl acrylate, methacrylic acid ester, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, styrene, vinyl toluene, tert-butyl styrene, and N-hydroxymethyl acrylamide. (b) the raw materials for the polymeric binder further comprise an initiator. (c) the raw materials for the polymeric binder further include a crosslinking agent.

7. The method for producing a composite binder according to claim 6, wherein the method for producing a composite binder satisfies one or two of the following conditions (a) to (b): (a) The initiator is selected from azo-based initiators and peroxide-based initiators. (b) The crosslinking agent is at least one selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, allyl methacrylate, ethylene glycol diacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, neopentyl glycol dimethacrylate, hexanediol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane, and pentaerythritol tetramethacrylate.

8. The method for producing a composite binder according to claim 4, wherein the method for producing a composite binder satisfies one or two of the following conditions (a) to (b): (a) The emulsifier is one or more selected from the group consisting of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, nonylphenol polyoxyethylene ether, OP surfactants, Span surfactants, Tween surfactants, and sodium dodecylbenzenesulfonate. (b) The aqueous phase further contains one or more selected from the group consisting of a dispersant, a polymerization inhibitor, and a metal salt, the dispersant is one or more selected from the group consisting of polyvinyl alcohol, magnesium hydroxide, calcium carbonate, calcium phosphate, silica sol, polyvinylpyrrolidone, styrene-maleic anhydride copolymer, and carboxymethyl cellulose, the polymerization inhibitor is a nitrite and / or potassium dichromate, and the metal salt is an ionic compound.

9. The method for producing a composite binder according to claim 8, wherein the method for producing a 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 the water is (0.01-5):(150-2000). (c) the oil phase comprises a crosslinking agent, an initiator, a phase change material, and a monomer, and the weight ratio of the crosslinking agent, the initiator, the phase change material, and the monomer is (0.5-3):(0.1-3):(10-400):

100. (d) The aqueous phase contains a dispersant, an emulsifier, a metal salt, a polymerization inhibitor, and the water, and the weight ratio of the dispersant, the emulsifier, the metal salt, the polymerization inhibitor, and the water is (1 to 50):(0.01 to 5):(0.5 to 5):(0.01 to 2):(150 to 2000).

10. 1. An electrochemical device comprising: An electrochemical device, characterized in that the composite binder according to any one of claims 1 to 3 is employed in the manufacturing process of an electrode sheet.

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