WO2023184208A1

WO2023184208A1 - Binder, electrochemical device and electronic device

Info

Publication number: WO2023184208A1
Application number: PCT/CN2022/083966
Authority: WO
Inventors: 程宝校
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2023-10-05
Also published as: CN116195099A

Abstract

Provided in the present application are a binder, an electrochemical device and an electronic device, the binder having the advantages of both a high strength and a high toughness. During the process of cyclic expansion of negative electrode active material particles (such as a silicon-based material), the binder can effectively release stress and maintain the integrity of the bonded molecular network; and when the expansion of the negative electrode active material particles exceeds the binding limit of the binder, the binder can provide sufficient toughness, thereby reducing the possibility of damage to the bonding interface caused by crushing of the binder. When the binder of the present application is used in an electrochemical device, the cycle performance and the expansion performance of the electrochemical device can be effectively improved. Moreover, the binder of the present application has high flexibility, such that a negative electrode plate has machining advantages during a rolling process, and the risk of machining problems, such as overvoltage, decarburization and edge material falling is reduced; as a result, the machining performance of the electrochemical device is improved.

Description

An adhesive, electrochemical device and electronic device

Technical field

This application relates to the field of electrochemistry, specifically to a binder, an electrochemical device and an electronic device.

Background technique

As one of the negative active materials of lithium-ion batteries (electrochemical devices), silicon-based materials have the advantages of high specific capacity, low cost, and abundant storage in nature. However, silicon-based materials are used as negative active materials in lithium-ion batteries. During the charging and discharging process of lithium-ion batteries, huge volume effects are prone to occur, causing the volume expansion rate to be as high as more than 300%. The high volume expansion rate of lithium-ion batteries will cause the active material particles to rupture, thereby destroying the conductive network and the positive electrode/negative electrode structure. As a result, the cycle performance of the lithium-ion battery will be seriously affected.

At present, in order to alleviate the volume expansion of lithium-ion batteries caused by silicon-based materials, high-modulus binders are often used. However, high-modulus binders are too brittle and lack toughness, which affects the processing performance and performance of lithium-ion batteries. Cycling performance is affected.

Contents of the invention

The present application provides a binder, an electrochemical device and an electronic device to improve the cycle performance of the electrochemical device.

It should be noted that in the following content, the present application is explained using a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to lithium ion batteries. The specific technical solutions are as follows:

The first aspect of this application provides a binder, which includes anionic polymers and organic amine cationic polymers. The anionic polymers include carboxylate polymers, sulfonate polymers and modified polymers thereof. at least one of them.

The inventor has discovered through extensive research that there is a synergistic effect between the above-mentioned anionic polymers and organic amine cationic polymers, so that the binder formed by cross-linking the two can combine It has the advantages of high strength and high toughness. During the cyclic expansion process of negative active material particles (such as silicon-based materials), the binder can effectively release stress and maintain the integrity of the bonded molecular network. When the expansion of each negative active material particle exceeds the constraints of the binder, At its limit, the adhesive can provide sufficient toughness to reduce the possibility of bond interface failure due to adhesive fragmentation. Applying the binder of the present application to an electrochemical device can improve the cycle performance and expansion performance of the electrochemical device.

It should be noted that the above modified polymer is based on a carboxylate polymer or a sulfonate polymer and is prepared by a modification method such as free radical polymerization or graft modification.

In one embodiment of the present application, the mass ratio W1 of the anionic polymer to the organic amine cationic polymer is (55-90): (10-45), and the carboxyl anion (-COO ^- ) in the anionic polymer is and/or the sulfonate anion (-SO ₃ ^- ) and the amine cation (-NH ₃ ⁺ , -NH ₂ ⁺ -, R ₄ N ⁺ (R is a C ₅ to C ₈ alkane) in the organic amine cationic polymer The molar ratio M1 of base)) is (1-10):1. When the mass ratio of the anionic polymer to the organic amine cationic polymer, or the molar ratio of the carboxyl anions and/or sulfonate anions in the anionic polymer to the amine cations in the organic amine cationic polymer is outside the above range , the number of carboxyl anions and/or sulfonate anions in the anionic polymer is out of balance with the amine cations in the organic amine cationic polymer, and the modulus of the formed binder is weakened, which affects the expansion of the binder to the negative active material. The binding effect. The mass ratio of the anionic polymer to the organic amine cationic polymer, and the molar ratio of the carboxyl anions and/or sulfonate anions in the anionic polymer to the amine cations in the organic amine cationic polymer are simultaneously controlled within the above ranges. Within, the quantity ratio of carboxyl anions and/or sulfonate anions and amine cations is reasonable, and cross-linking groups can be formed between each group to the greatest extent. In this way, the bond formed has the advantages of both high strength and high toughness. During the cyclic expansion process of negative active material particles (such as silicon-based materials), the binder can effectively release stress and maintain the integrity of the bonding molecular network. When the negative active material particles expand beyond the binding limit of the binder, When the bonding agent is used, the adhesive can provide sufficient toughness to reduce the possibility of bonding interface damage due to the fragmentation of the adhesive. Applying this binder to an electrochemical device can effectively improve the cycle performance and expansion performance of the electrochemical device.

In one embodiment of the present application, the molar percentage M1 of anionic monomers containing carboxyl anions and/or sulfonate groups is 25% to 60% based on the total number of moles of monomers constituting the anionic polymer. Regulating the molar percentage of monomers containing carboxyl anions and/or sulfonate anions within the above range is more conducive to a reasonable ratio of the number of carboxyl anions and/or sulfonate anions to amino cations, and each group can form cross-linking groups to the greatest extent. In this way, the bond formed has the advantages of both high strength and high toughness. During the cyclic expansion process of negative active material particles (such as silicon-based materials), the binder can effectively release stress and maintain the integrity of the bonded molecular network. When the negative active material particles expand beyond the binding limit of the binder, When the bonding agent is used, the adhesive can provide sufficient toughness to reduce the possibility of bonding interface damage due to the fragmentation of the adhesive. Applying this binder to an electrochemical device can effectively improve the cycle performance and expansion performance of the electrochemical device.

In this application, based on the total number of moles of monomers constituting the organic amine cationic polymer, the molar percentage M2 of the monomer containing the amine cation is not particularly limited, as long as the purpose of this application can be achieved. For example, M2 can be 10% to 100%.

In one embodiment of the present application, the anionic polymer includes at least one of a polymer copolymerized from an anionic monomer and a non-anionic monomer, lithium carboxymethyl cellulose or sodium carboxymethyl cellulose. The anionic monomer is lithium acrylate, sodium acrylate, lithium methacrylate, sodium methacrylate, lithium styrenesulfonate, sodium styrenesulfonate, and sodium 2-acrylamide-2-methylpropanesulfonate. At least one non-anionic monomer includes at least one of acrylonitrile, acrylate, acrylamide and other acrylic derivatives. The above-mentioned "other acrylic derivatives" refer to acrylic derivatives other than acrylate and acrylamide.

In one embodiment of the present application, the organic amine cationic polymer includes at least one of polyquaternary ammonium salt, polyethylenimine (PEI) or cationic polyacrylamide. Among them, polyquaternary ammonium salts include poly3-(methacrylamido)propyl-trimethylammonium chloride, polyacryloyloxyethyltrimethylammonium chloride or polydiallyldimethylchloride. At least one kind of ammonium. It should be noted that the above-mentioned "cationic polyacrylamide" is prepared by copolymerization of acrylamide and cationic monomers or by Mannich reaction of polyacrylamide. The above-mentioned cationic monomers include methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, and acrylamidopropyltrimethylammonium chloride. At least one of ammonium or 2-(N,N-dimethylamino)ethyl methacrylate. This application has no special restrictions on the specific material types of cationic polyacrylamide, as long as the purpose of this application can be achieved.

The above-mentioned Mannich reaction is a well-known Mannich reaction in the art (referred to as Mannsch reaction, also known as amine methylation reaction).

The inventor found that when a combination of the above-mentioned anionic polymer and an organic amine cationic polymer is used as a binder, it is beneficial to obtain a binder with higher strength and toughness. Moreover, the above types of anionic polymers and organic amine cationic polymers are easy to obtain, which is more conducive to commercialization.

In one embodiment of the present application, the weight average molecular weight M _W1 of the anionic polymer is 400,000 to 2,000,000, and the weight average molecular weight M _W2 of the organic amine cationic polymer is 10,000 to 100,000. The weight average molecular weight of anionic polymers and organic amine cationic polymers directly affects the integrity and toughness of the cross-linked structural network. Without affecting the processing performance of the binder, the weight average molecular weight of anionic polymers and organic amine cationic polymers Controlling the weight average molecular weight within the above range is more conducive to obtaining a binder with higher strength and toughness, thereby more effectively preventing damage to the bonding interface caused by binder rupture. Applying this binder to an electrochemical device can effectively improve the cycle performance and expansion performance of the electrochemical device.

In one embodiment of the present application, the adhesive meets at least one of the following conditions: (1) The adhesive film elastic modulus of the adhesive is 8 GPa to 15 GPa. (2) The adhesive film tensile strength at break is 60MPa to 140MPa; (3) The adhesive film elongation at break is 5% to 30%. Regulating at least one of the adhesive film elastic modulus, adhesive film tensile strength at break, and adhesive film elongation at break within the above range indicates that the relationship between amino cations, carboxyl anions, and/or sulfonate anions is There is electrostatic cross-linking between them to form a cross-linked molecular network, so that the binder has the advantages of both high strength and high toughness. During the expansion process of the negative active material particles bound by it, it can effectively release stress and maintain the negative electrode. The sheet integrity provides sufficient toughness to prevent the binder from breaking and causing damage to the bonding interface when the negative active material particles expand beyond the binding limit. Applying this binder to an electrochemical device can effectively improve the cycle performance and expansion performance of the electrochemical device.

In one embodiment of the present application, the solid content of the binder is 5 to 30 wt%, the pH of the binder is 6 to 9, and the viscosity of the binder is 8000 mPa·s to 50000 mPa·s. Controlling the solid content, pH and viscosity of the binder within the above range is more conducive to improving the processing performance of the negative electrode piece, thereby improving the processing performance of the electrochemical device.

In one embodiment of the present application, the swelling degree of the adhesive film in the electrolyte is 1% to 5%, and the solubility of the adhesive film in the electrolyte is less than 3%. This application has no particular limitation on the type of the above-mentioned electrolyte solution, and it can be an electrolyte solution known in the art. The swelling degree and solubility of the adhesive film in the electrolyte are within the above range, indicating that the adhesive film has good stability in the electrolyte. Applying this binder to electrochemical devices is more conducive to improving the safety performance of electrochemical devices.

A second aspect of the present application provides an electrochemical device, which includes a negative electrode piece. The negative electrode piece includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes any of the above. The binder in the embodiment; based on the mass of the negative active material layer, the mass percentage content W2 of the binder is 1% to 8%. If the binder content is too low, the bonding effect will not be achieved; if the binder content is too high, the energy density of the electrochemical device will be reduced. Applying the binder within the above mass percentage range to the negative electrode sheet can give full play to the advantages of high modulus and high toughness of the binder, thereby improving the cycle performance and performance of the electrochemical device using the negative electrode sheet. The expansion performance is effectively improved. It also enables electrochemical devices to have good energy density.

The negative electrode current collector of this application is not particularly limited, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 130 μm.

In one embodiment of the present application, the mass percentage content W3 of silicon in the negative active material layer is 1% to 60% based on the total mass of the negative active material layer. When the silicon element content in the negative active material layer is less than 1%, it is not conducive to improving the cycle life and capacity of the electrochemical device. When the silicon content in the negative active material layer is greater than 60%, the negative active material layer will expand too much during the cycle of the electrochemical device, which will exceed the binding limit of the negative active material by the binder and affect the cycle performance of the electrochemical device. and electrochemical properties such as capacity. Regulating the mass percentage of silicon in the negative active material layer within the above range is more conducive to improving the cycle performance and expansion performance of the electrochemical device.

This application has no special restrictions on the type of negative active material, as long as the mass percentage of silicon in the negative active material layer is 1% to 60%, and the purpose of this application can be achieved. For example, the negative active material includes at least one of graphite, hard carbon, silicon, silicon carbon, or silicon oxide. The use of the above-mentioned types of negative electrode active materials is beneficial to improving the specific capacity of the negative electrode; further, when the above-mentioned types of negative electrode active materials are used and bonded using the binder of the present application, the obtained negative electrode sheet can effectively The occurrence of binder fragmentation and bonding interface damage is reduced, and the electrochemical device using the negative electrode piece has better cycle performance. In one embodiment of the present application, the negative active material layer has a compacted density of 1.45g/cm ³ to 1.85g/cm ³ . When the compaction density of the negative active material layer is controlled within the above range, the risk of breakage of each negative active material particle is reduced, which can improve the interface stability of the negative active material layer. At the same time, the contact between each negative active material particle is better, which is beneficial to Improve the conductivity of the conductive network and better regulate the interface stability of the negative active material layer. As a result, the cycle performance and expansion performance of the electrochemical device using the negative electrode piece are improved.

In one embodiment of the present application, the negative active material layer includes a negative active material, and the average particle size Dv50 of the negative active material is 5 μm to 40 μm. The Dv50 of the negative active material is controlled within the above range, and the binder has a good coating effect on the negative active material. If the particle size of the negative electrode active material is greater than 40 μm, it is easy to cause the binder to cover the negative electrode active material in a too small area, thus affecting the binding force of the negative electrode piece. “Dv50” in this application refers to the particle size corresponding to 50% of the cumulative volume from the small particle size side in the volume-based particle size distribution curve.

In one embodiment of the present application, the cohesive force of the negative electrode piece is 20 N/m to 100 N/m. The cohesion control of the negative active material layer is within the above range, which indicates that the negative electrode piece has good cohesion, stabilizes the structure of the negative electrode piece, and is more conducive to improving the cycle performance and expansion performance of the electrochemical device using the negative electrode piece. The above-mentioned "cohesive force of the negative electrode sheet" usually refers to the adhesive force within the negative active material layer.

In one embodiment of the present application, the bonding force of the negative electrode piece is 10 N/m to 850 N/m. The bonding force of the negative electrode piece is within the above range, indicating that there is good bonding force between the negative electrode active material layer and the negative electrode current collector, which is more conducive to the stability of the negative electrode piece structure and also makes the electrochemical device using the negative electrode piece The cycle performance and expansion performance are improved.

The electrochemical device of this application also includes a positive electrode piece, a separator, an electrolyte, etc. This application has no special restrictions on the positive electrode piece, a separator, and an electrolyte, as long as the purpose of this application can be achieved.

For example, a positive electrode plate typically includes a positive current collector and a positive active material layer. The positive electrode current collector is not particularly limited and can be any positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, composite current collector, etc. The positive active material layer includes a positive active material. The positive active material is not particularly limited and can be a known positive active material in the art, for example, including lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, At least one of lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganate, lithium iron manganese phosphate or lithium titanate. In this application, the thickness of the positive electrode current collector and the positive electrode active material layer is not particularly limited, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material layer is 25 μm to 100 μm.

Optionally, the positive electrode tab may further include a conductive layer located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in this field. The conductive layer includes conductive agent and conductive layer adhesive. The conductive agent is not particularly limited and may be any conductive agent or combination thereof known to those skilled in the art. For example, at least one of a zero-dimensional conductive agent, a one-dimensional conductive agent, or a two-dimensional conductive agent may be used. Preferably, the conductive agent may include at least one of conductive carbon black, conductive graphite, carbon fiber, carbon nanotube, vapor grown carbon fiber (VGCF) or graphene. The amount of conductive agent used is not particularly limited and can be selected based on common knowledge in the art.

The conductive layer adhesive is not particularly limited and may be a conductive layer adhesive known to those skilled in the art or a combination thereof. For example, polyacrylate, polyimide, polyamide, polyamide-imide, polyamide-imide, or polyamide-imide may be used. At least one of vinylidene fluoride (PVDF), styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethylcellulose or lithium carboxymethylcellulose.

The isolation membrane in the electrochemical device of the present application is used to separate the positive electrode piece and the negative electrode piece, prevent internal short circuit of the electrochemical device, allow electrolyte ions to pass freely, and complete the electrochemical charge and discharge process. In this application, the isolation film is not particularly limited as long as it can achieve the purpose of this application. For example, polyethylene (PE), polypropylene (PP)-based polyolefin (PO) isolation films, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyacyl Imine film (PI), polyamide film (PA), spandex film, aramid film, woven film, non-woven film (non-woven fabric), microporous film, composite film, separator paper, rolled film or spun film At least one of the others. For example, the isolation film may include a base material layer and a surface treatment layer. The base material layer can be a non-woven fabric, film or composite film with a porous structure. The material of the base material layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. kind. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the base material layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and an inorganic layer binder. The inorganic particles are not particularly limited. For example, they can be selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, At least one of nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The inorganic layer binder is not particularly limited, and may be selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, and polyethylene. At least one of pyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( At least one of vinylidene fluoride-hexafluoropropylene), etc.

The electrolyte in the electrochemical device of the present application includes lithium salt and non-aqueous solvent.

This application has no special restrictions on the lithium salt. For example, the lithium salt is selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), tetrafluoroborate Lithium phenylboron (LiB(C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium triflate (LiCF ₃ SO ₃ ), lithium bistrifluoromethanesulfonyl imide (LiN At least one of (SO ₂ CF ₃ ) ₂ ), LiC (SO ₂ CF ₃ ) ₃ , lithium hexafluorosilicate (LiSiF ₆ ), lithium bisoxaloborate (LiBOB) or lithium difluoroborate (LiF ₂ OB) . For example, LiPF ₆ can be used as the lithium salt because it has high ionic conductivity and improves the cycle performance of the electrochemical device.

This application has no particular limitation on the non-aqueous solvent. For example, the non-aqueous solvent may be at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may be at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound. Examples of the above chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or carbonic acid. At least one of methyl ethyl ester (EMC). Examples of the cyclic carbonate compound are at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate. Ethyl ester, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-dicarbonate At least one of fluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone , at least one of decanolide, valerolactone, mevalonolactone or caprolactone. Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethane At least one of oxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. Examples of other organic solvents mentioned above are propyl propionate, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl -At least one of 2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester. Based on the quality of the electrolyte, the total content of the above-mentioned non-aqueous solvent is 5% to 90%, such as 5%, 10%, 15%, 25%, 25%, 30%, 35%, 40%, 45%, 25% , 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or any range in between.

The electrochemical device of the present application is not particularly limited and may include any device that undergoes electrochemical reactions. In some embodiments, the electrochemical device may include, but is not limited to: a lithium metal secondary battery, a lithium ion battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, and the like.

The preparation process of the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, it may include but is not limited to the following steps: stack the positive electrode sheets, separators, and negative electrode sheets in order, and stack the positive electrode sheets as needed. The winding, folding and other operations obtain an electrode assembly with a wound structure. The electrode assembly is placed in a packaging case, the electrolyte is injected into the packaging case and sealed to obtain an electrochemical device; or, the positive electrode piece, separator and negative electrode piece are Stack them in order, and then use tape to fix the four corners of the entire laminated structure to obtain an electrode assembly of the laminated structure. Place the electrode assembly into the packaging shell, inject the electrolyte into the packaging shell and seal it, to obtain an electrochemical device. In addition, overcurrent prevention components, guide plates, etc. can also be placed in the packaging case as needed to prevent pressure rise inside the electrochemical device and overcharge and discharge.

A third aspect of the present application provides an electronic device, which includes the electrochemical device in any of the preceding embodiments. The electronic device has good cycle performance and expansion performance.

The electronic device of the present application is not particularly limited and may be used in any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset , VCR, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, power-assisted bicycle, bicycle , lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

The present application provides a binder, an electrochemical device and an electronic device, wherein the binder has the advantages of high strength and high toughness. During the expansion process of the negative active material particles (such as silicon-based materials) bonded by the binder, the stress can be effectively released and the integrity of the molecular network can be maintained. When the negative active material particles expand beyond the binding limit of the binder, When the bonding agent is used, the adhesive can provide sufficient toughness to reduce the possibility of bonding interface damage due to the fragmentation of the adhesive. Applying the binder of the present application to an electrochemical device can effectively improve the cycle performance and expansion performance of the electrochemical device. Moreover, the binder of the present application has high flexibility, which allows the negative electrode sheet to have processing advantages during the rolling process, reducing the risk of processing problems such as overpressure, decarburization, and edge shedding, thereby improving the electrochemical device processing performance.

Description of drawings

In order to explain the embodiments of the present application and the technical solutions of the prior art more clearly, the drawings needed to be used in the embodiments and the prior art are briefly introduced below. Obviously, the drawings in the following description are only for the purpose of explaining the embodiments and the technical solutions of the prior art. For some embodiments of the application, those of ordinary skill in the art can also obtain other drawings based on these drawings.

Figure 1 is a schematic diagram of the intermolecular interaction of the adhesive in this application.

Detailed ways

In order to make the purpose, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application fall within the scope of protection of this application.

Hereinafter, the present application will be specifically described based on examples, but the present application is not limited to these examples. It should be noted that in the specific embodiments of the present application, a lithium ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium ion batteries.

In the following examples and comparative examples, the reagents, materials and instruments used are all commercially available unless otherwise specified.

Test Methods:

Test of Dv50 of negative active material:

Use a laser particle size analyzer to test the Dv50 of the negative active material.

Test of compacted density of negative active material layer:

The compacted density Pa of the negative active material layer is calculated by the formula: Pa=Ma/Va. In the formula, Ma is the mass of the negative active material layer, unit: g; Va is the volume of the negative active material layer, unit: cm ³ , where the volume Va is the area Sa of the negative active material layer and the thickness of the negative active material layer. product.

Test of elastic modulus:

TA dynamic thermomechanical analyzer DMA850; constant strain mode test;

Test steps: Dry the adhesive at 120°C to prepare a 120μm thick adhesive film, cut it into a sample with width × length = 8mm × 40mm, and fix the sample along the length direction between the upper and lower clamps of the dynamic thermomechanical analyzer. , the upper clamp does not move, the lower clamp applies a sinusoidal strain to the sample, and the sinusoidal stress of the sample response is tested. Modulus of elasticity = (stress/strain) cos δ. δ: Stress-strain phase difference.

Tests of tensile breaking strength and elongation at break:

Universal testing machine; tensile mode testing.

Test steps: Dry the adhesive at 120°C to prepare a 300 μm thick adhesive film, cut it into a sample of width × length = 1.5cm × 4cm, and fix the sample along the length direction between the upper and lower clamps of the universal testing machine. The initial distance between the upper and lower clamps is L0, the lower clamp does not move, and the upper clamp stretches at a constant rate of 50mm/min until the sample breaks. At this time, the distance between the upper and lower clamps is L1, and the elongation at break = (L1-L0)/L0×100%; Tensile breaking strength = breaking tensile force/cross-sectional area of the film, where the cross-sectional area of the film is film thickness × width.

Test of swelling/solubility of binder electrolyte:

Select a sample film with width × length × thickness = 1.5cm × 1.5cm × (50 to 200) μm. Weigh the mass of the film before infiltration, and then soak the film in the electrolyte of the corresponding comparative example or example at 60°C for 48 hours. , then dry the solvent on the surface of the film, weigh the mass of the swollen adhesive film, and then bake the film at 105°C for 2 hours, weigh w2, and calculate the swelling degree of the sample according to the following formula. In order to ensure the test results For reliability, each sample should be measured at least three times during testing.

Swelling degree=(w1-w0)/w0

Solubility=(w0-w2)/w0

Among them, w0 represents the mass of the sample film before soaking, w1 represents the mass of the sample after soaking, and w2 represents the mass of the sample after drying.

Test of cohesion:

The negative electrode piece was dried in a 60°C oven for 15 hours, cut into 1.5cm×11cm strips, and subjected to a 180° peeling test.

Test steps: Use double-sided tape to paste the cut negative electrode piece on the 3cm × 15cm steel plate. Paste the high-viscosity green glue on the surface of the electrode piece. Roll it with a small stick 7 to 8 times to fix the steel plate in tension. In the lower clamp of the machine, the upper clamp clamps the green glue, and peels off 50mm at a constant speed of 50mm/min in the direction parallel to the negative electrode piece. The stress and displacement data are obtained. The cohesion of the negative active material layer = stress/displacement.

Adhesion test:

Test steps: Use double-sided tape to paste the cut negative electrode piece on a 3cm × 15cm steel plate, roll it with a small stick 7 to 8 times, use a tensile machine to perform a peeling test, and fix the steel plate in the lower clamp of the tensile machine. , bend the negative electrode piece 180°, clamp the negative electrode piece with the upper clamp, peel off 50mm at a constant speed of 50mm/min in the direction parallel to the negative electrode piece, and obtain the stress and displacement data, the negative electrode active material layer and the negative electrode current collector. Bonding force = stress/displacement.

Expansion performance test:

The thickness of the lithium-ion battery with state of charge (SOC) = 25% is measured using a battery thickness measuring machine (manufacturer: Shenzhen Aotomei Automation Technology Co., Ltd., model: PPG650gf), recorded as T1; then, the lithium-ion battery is Charge to 4.35V at 0.5C and discharge to 3.0V at a current of 0.5C. This is a charge and discharge cycle. Measure the thickness of the lithium-ion battery every 50 laps until the lithium-ion battery is tested for 200 laps and record the final lithium-ion battery. Thickness is T200.

Expansion rate=(T200-T1)/T1×100%.

Test of cycle performance:

The test temperature is 25°C, charge to 4.45V at a constant current of 0.5C, charge to 0.025C at a constant voltage, and discharge to 3.0V at a rate of 0.5C after letting it stand for 5 minutes. The capacity obtained in this step is the initial capacity C1. After 200 cycles and 500 cycles of 0.5C charge/0.5C discharge cycle testing, the capacities C200 and C500 of the lithium-ion battery are calculated respectively. If the number of cycles does not reach 500 laps, it will be calculated as 200 laps.

Each example and comparative example is calculated based on 200 cycles, and the cycle capacity retention rate=C200/C1×100%.

Example 1

Mix poly(lithium acrylate-acrylonitrile-acrylamide) and PEI at a mass ratio W1 of 90:10, stir for 2 hours, and set aside. Among them, the weight average molecular weight M _W1 of poly(lithium acrylate-acrylonitrile-acrylamide) is 700000, and the weight average molecular weight M _W2 of PEI is 50000; the molar ratio N of carboxyl anions to amino cations is 8.84:1; based on poly( The number of monomer moles of lithium acrylate-acrylonitrile-acrylamide), the molar percentage content of lithium acrylate M1 is 50%, the molar percentage content of acrylonitrile is 30%, and the molar percentage content of acrylamide is 20%; based on The number of moles of ethyleneimine, the molar percentage M2 of monomer ethyleneimine containing amino cations is 30%; the solid content of the binder is 20wt%, the pH is 7.5, and the viscosity is 30000mPa·s.

Mix the negative active material graphite and SiO (mass percentage of silicon W3: 15%), the conductive agent conductive carbon black, and the binder prepared above, so that the mass ratio of graphite, SiO, conductive carbon black, and binder is The ratio is 70:15:10:5, then add deionized water as the solvent to prepare a negative electrode slurry with a solid content of 70wt%, stir evenly, and evenly coat the negative electrode slurry on one surface of the copper foil with a thickness of 10 μm. on the negative electrode, and dried at 110°C to obtain a negative electrode piece with a coating thickness of 150 μm coated with the negative active material layer on one side. Then, repeat the above coating steps on the other surface of the negative electrode piece to obtain a double-sided coating. A negative electrode plate covered with a layer of negative active material. Cold-press and cut the negative electrode sheet into sheets with specifications of 76 mm × 851 mm for use. Among them, the Dv50 of the negative active material is 10 μm, and the compacted density of the negative active material layer is 1.75g/cm ³ .

Mix the positive active material lithium cobalt oxide, the conductive agent conductive carbon black, and the positive electrode binder PVDF so that the mass ratio of lithium cobalt oxide, conductive carbon black, and PVDF is 97.5:1.0:1.5, and then add N-methylpyrrolidone (NMP ) as a solvent, prepare a positive electrode slurry with a solid content of 75wt%, and stir evenly. Coat the positive electrode slurry evenly on one surface of the aluminum foil with a thickness of 12 μm, and dry it at 90°C to obtain a positive electrode sheet with a coating thickness of 100 μm. Then repeat the above steps on the other surface of the positive electrode sheet. , obtaining a positive electrode sheet coated with a positive electrode active material layer on both sides. Cold-press and cut the positive electrode sheet into sheets with specifications of 74mm×867mm for use.

In a dry argon atmosphere, mix the organic solvents EC, EMC and DEC according to the mass ratio of 30:50:20, then add LiPF ₆ to the organic solvent to dissolve and mix evenly to obtain an electrolyte, in which LiPF ₆ is in the electrolyte The molar concentration is 1.15mol/L.

Using a PE porous polymer film with a thickness of 15 μm as the isolation film, stack the positive electrode piece, isolation film, and negative electrode piece prepared above in order, so that the isolation film is between the positive and negative electrodes to play an isolation role, and winding to obtain Electrode assembly. The electrode assembly is placed in the outer packaging, the prepared electrolyte is injected and packaged, and the lithium-ion battery is obtained through processes such as formation, degassing, and trimming.

Example 2 to Example 4

The rest was the same as in Example 1 except that the mass ratio W1 of poly(lithium acrylate-acrylonitrile-acrylamide) and PEI and the molar ratio N of carboxyl anions and amino cations were adjusted according to Table 1.

Example 5 to Example 6

The rest is the same as Example 2 except that the molar percentage M1 of the carboxyl anion-containing monomer lithium acrylate is adjusted according to Table 1.

Example 7 to Example 10

Except that the type of anionic polymer was adjusted according to Table 1, the rest was the same as Example 2.

Example 11 to Example 12

Except that the type of organic amine cationic polymer is adjusted according to Table 1, the rest is the same as Example 2.

Example 13 to Example 14

The rest were the same as Example 2 except that the weight average molecular weight M _W1 of the anionic polymer and the weight average molecular weight M _W2 of the organic amine cationic polymer were adjusted according to Table 1.

Example 15 to Example 16

The rest is the same as in Example 2 except that the mass percentage content W2 of the binder based on the mass of the negative active material layer is adjusted according to Table 1.

Example 17 to Example 19

The rest is the same as in Example 2 except that the mass percentage content W3 of silicon in the negative active material layer is adjusted according to Table 1.

Example 20 to Example 21

Except that the Dv50 of the negative active material was adjusted according to Table 1, the rest was the same as in Example 2.

Example 22 to Example 23

Except that the compaction density of the negative active material layer is adjusted according to Table 1, the rest is the same as in Example 2.

Comparative example 1

Except that it does not contain organic amine cationic polymer, the rest is the same as Example 1.

Comparative example 2

It is the same as Example 1 except that it does not contain an anionic polymer.

The preparation parameters of each embodiment and comparative example are shown in Table 1 below, and the test results are shown in Table 2 below:

Table 2

It can be seen from Examples 1 to 4, Comparative Examples 1 and 2 that the anionic polymer and the organic amine cationic polymer are combined according to the mass ratio W1 and the carboxyl anion and/or the sulfonate anion within the scope of the present application. The storage modulus, tensile breaking strength and breaking elongation of the adhesive film of the adhesive prepared after being mixed with amine cations at a molar ratio of N are significantly improved. The inventor believes that there is a synergistic effect between anionic polymers and organic amine cationic polymers within the mass ratio W1 of the present application and the molar ratio N of carboxyl anions and/or sulfonate anions to amine cations, so that the anionic The binder formed by cross-linking the polymer and the organic amine cationic polymer has both high strength and Advantages of high toughness. The bonding force and cohesion of the negative electrode sheet using the binder of the present application are significantly improved. The cycle performance and expansion performance of lithium-ion batteries using this negative electrode piece have also been significantly improved.

The molar percentage M1 of the monomeric lithium acrylate containing carboxyl anions, based on the moles of lithium acrylate, also generally affects the cycle performance and swelling performance of the lithium-ion battery. It can be seen from Example 2, Example 5 and Example 6 that the storage modulus, tensile elongation at break, and breaking strength can all be achieved by using a binder with a molar percentage M1 within the scope of the present application. improvement. The negative electrode piece using this binder has high adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The types of anionic polymers and organic amine cationic polymers often also affect the cycle performance and swelling performance of lithium-ion batteries. It can be seen from Example 2, Example 7 to Example 12 that the binders using anionic polymers and organic amine cationic polymers within the scope of the present application can achieve storage modulus, tensile strength, etc. Improvement of elongation at break and strength at break. The negative electrode piece using this binder has high adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The weight average molecular weight of anionic polymers and organic amine cationic polymers also generally affects the cycle performance and swelling performance of lithium-ion batteries. It can be seen from Example 2, Example 13 and Example 14 that the storage modulus, Improvement of tensile elongation at break and breaking strength. The negative electrode piece using this binder has high adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The mass percentage W2 of the binder in the negative active material layer usually also affects the cycle performance and expansion performance of the lithium-ion battery. It can be seen from Example 2, Example 15 and Example 16 that the negative electrode sheet using the mass percentage W2 of the binder in the negative active material layer is within the scope of the present application has a higher bonding force. and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The mass percentage W3 of silicon in the negative active material layer usually also affects the cycle performance and expansion performance of lithium-ion batteries. It can be seen from Example 2, Example 17 to Example 19 that the negative electrode piece with a mass percentage W3 of silicon in the negative active material layer within the scope of the present application has higher adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The average particle size Dv50 of the negative active material usually also affects the cycle performance and expansion performance of lithium-ion batteries. It can be seen from Example 2, Example 20 and Example 21 that the negative electrode piece using an average particle size Dv50 of the negative active material within the scope of the present application has high adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The compaction density of the negative active material layer also generally affects the cycle performance and swelling performance of lithium-ion batteries. It can be seen from Example 2, Example 22 and Example 23 that the negative electrode piece with a compacted density of the negative active material layer within the scope of the present application has higher adhesion and cohesion. Lithium-ion batteries using this negative electrode plate have good cycle performance and expansion performance.

The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims

A binder comprising an anionic polymer and an organic amine cationic polymer, the anionic polymer comprising at least one of carboxylate polymers, sulfonate polymers and modified polymers thereof .
The adhesive according to claim 1, wherein the adhesive satisfies at least one of the following conditions (a) to (b):

(a) The mass ratio of the anionic polymer to the organic amine cationic polymer is (55-90): (10-45);

(b) The molar ratio of the carboxyl anions and/or sulfonate anions in the anionic polymer to the amine cations in the organic amine cationic polymer is (1-10):1.
The binder according to claim 2, wherein the molar percentage of the carboxyl anion and/or the sulfonate anionic monomer is included based on the total number of moles of monomers constituting the anionic polymer. is 25% to 60%.
The binder according to claim 1, wherein the anionic polymer includes a polymer copolymerized from an anionic monomer and a non-anionic monomer, lithium carboxymethyl cellulose or carboxymethyl cellulose At least one of sodium;

The anionic monomer includes lithium acrylate, sodium acrylate, lithium methacrylate, sodium methacrylate, lithium styrenesulfonate, sodium styrenesulfonate or sodium 2-acrylamide-2-methylpropanesulfonate. At least one of the non-anionic monomers includes at least one of acrylonitrile, acrylate, acrylamide and other acrylic derivatives.
The adhesive according to claim 1, the organic amine cationic polymer includes at least one of polyquaternary ammonium salt, polyethyleneimine or cationic polyacrylamide;

The polyquaternary ammonium salt includes poly-3-(methacrylamido)propyl-trimethylammonium chloride, polyacryloyloxyethyltrimethylammonium chloride or polydiallyldimethyl chloride At least one kind of ammonium.
The binder according to claim 1, wherein the weight average molecular weight of the anionic polymer is 400,000 to 2,000,000, and the weight average molecular weight of the organic amine cationic polymer is 10,000 to 100,000.
The adhesive according to claim 1, wherein the adhesive satisfies at least one of the following conditions:

(1) The adhesive film elastic modulus is 8GPa to 15GPa;

(2) The adhesive film tensile breaking strength is 60MPa to 140MPa;

(3) The adhesive film has a film elongation at break of 5% to 30%.
The adhesive according to claim 1, wherein the solid content of the adhesive is 5wt% to 30wt%, the pH of the adhesive is 6 to 9, and the viscosity of the adhesive is 8000mPa· s to 50000mPa·s.
The adhesive according to claim 1, wherein the swelling degree of the adhesive film in the electrolyte is 1% to 5%, and the solubility of the adhesive film in the electrolyte is less than 3%.
An electrochemical device, comprising a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising claims 1 to 9 The adhesive described in any one of them;

The mass percentage of the binder is 1% to 8% based on the total mass of the negative active material layer.
The electrochemical device according to claim 10, wherein the mass percentage of silicon in the negative active material layer is 1% to 60% based on the total mass of the negative active material layer.
The electrochemical device of claim 10, wherein the negative active material layer has a compacted density of 1.45 to 1.85 g/cm 3 .
The electrochemical device according to claim 10, wherein the negative active material layer includes a negative active material having an average particle diameter Dv50 of 5 μm to 40 μm.
The electrochemical device according to claim 10, wherein the cohesive force of the negative electrode piece is 20 N/m to 100 N/m.
The electrochemical device according to claim 10, wherein the adhesive force of the negative electrode piece is 10 N/m to 850 N/m.
An electronic device comprising the electrochemical device according to any one of claims 10 to 15.