A modifier for silicon-based anode materials, a modified silicon-based anode material and its application

Abstract

The present invention provides a modifier for silicon-based anode materials, a modified silicon-based anode material and its application. The modifier for silicon-based anode materials comprises a combination of a first polymer and a second polymer. The first polymer is a water-soluble polymer, and the second polymer is a water-insoluble polymer. The first polymer and the second polymer are dissolved in the same non-aqueous solvent. The modifier for silicon-based anode materials can uniformly coat the surface of the silicon-based material to obtain a modified silicon-based anode material with a polymer coating layer. In the preparation of the anode slurry, the first polymer dissolves to form a porous network-like coating structure on the surface of the silicon-based material, effectively alleviating the volume expansion of the silicon-based material during charge and discharge, preventing the pulverization and shedding of the material, and having excellent structural stability and cycling performance. At the same time, there are still a large number of conductive channels on the surface of the silicon-based material, which will not cause an increase in the impedance of the material, and has excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a modifier for silicon-based anode materials, a modified silicon-based anode material and its application. Background Art

[0002] With the rapid development of economy and technology, energy and environmental problems have become increasingly severe. New energy technologies have become one of the important research topics at present, and lithium-ion batteries, as a major branch of new energy technologies, have received much attention. In recent years, people's demand for the energy and safety of lithium-ion batteries has gradually increased. The endurance problem of electric vehicles and the lightweight development of consumer electronics such as mobile phones urgently require lithium-ion batteries to have a higher energy density. A lithium-ion battery is assembled from a positive electrode, a negative electrode, a separator and an electrolyte. The electrical performance of the battery is closely related to each part, and the properties of the positive and negative electrode materials directly affect the final performance of the lithium-ion battery. Currently, the commercially available negative electrode materials are mainly graphite. The theoretical specific capacity of graphite is 372 mAh / g. The specific capacity of graphite negative electrode materials has approached its theoretical value, and it is difficult to further improve, which restricts the development of lithium-ion batteries towards high energy density. Therefore, using negative electrode active materials with higher specific energy is the only way for the development of lithium-ion batteries.

[0003] Compared with graphite, silicon-based materials have obvious capacity advantages. Their theoretical specific capacity at room temperature is 3580 mAh / g, and the theoretical specific capacity at high temperature is 4200 mAh / g, which is about 10 times that of graphite. Moreover, the lithium insertion / extraction potential of silicon-based materials is relatively low (0.4 V), the reserves in nature are large, the sources are rich, and the processing cost is relatively low. It is recognized as the next-generation negative electrode material. However, as a lithium-ion battery negative electrode material, silicon-based materials have unavoidable defects: silicon-based materials will undergo serious volume changes during charge and discharge, and the volume expansion is about 400%, resulting in pulverization and separation between materials, damage to the battery electrode structure, and rapid attenuation of the battery capacity; at the same time, the volume effect of silicon makes it difficult to form a stable SEI film, resulting in continuous consumption of lithium ions and electrolytes, and low Coulomb efficiency; moreover, the electrical conductivity of silicon materials themselves is poor, obvious polarization phenomena occur during the cycle, the rate performance is not good, the conductivity is low, and lithium-ion batteries containing silicon-based negative electrode materials have serious problems in terms of aging degree and safety.

[0004] Coating or doping silicon-based materials with carbon materials is currently the main method to improve the performance of silicon-based materials. For example, CN104112847A discloses a silicon-based anode material, which includes carbon nanotubes with voids inside and nano-silicon particles located inside the carbon nanotubes. The mass percentage content of the nano-silicon particles is 30-70%, and the carbon nanotubes are nano-carbon nanotubes with a diameter of 10-100 nm. Since there are voids inside the carbon nanotubes, the silicon particles can be fixed in the limited space inside the carbon nanotubes, enabling the volume expansion or contraction of the silicon particles to occur within the limited space, which is beneficial to improving the capacity and cycle performance of lithium batteries. CN110550635A discloses a preparation method of a carbon-coated silicon oxide anode material. After crushing massive SiO into powder, it is mixed with asphalt and ball-milled to be homogeneous to form a mixed precursor. After high-temperature carbonization of the mixed precursor in a vacuum tube furnace, it is ball-milled and granulated to obtain a carbon-coated silicon monoxide composite anode material.

[0005] The composite material prepared by doping or coating the carbon material on the silicon-based material as described above combines the performance advantages of carbon and silicon, obtaining a negative electrode active material with better performance than pure silicon-based materials. However, the carbon material formed by high-temperature carbonization itself lacks ductility and cannot effectively absorb or digest the tension generated by the volume expansion of the silicon-based material during the charge and discharge process of the electrode, making it difficult to delay and prevent the pulverization of the negative electrode material, and not well solving the expansion problem of the silicon-based material. The cycle performance and reliability of the battery are still poor. Therefore, developing negative electrode materials with more excellent performance is the research focus in this field. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a modifier for silicon-based anode materials, a modified silicon-based anode material and its application. The modifier for silicon-based anode materials can effectively inhibit the volume expansion of silicon-based materials and will not cause an increase in impedance, significantly improving the cycle performance of the battery.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a modifier for silicon-based anode materials, and the modifier for silicon-based anode materials includes a combination of a first polymer and a second polymer. The first polymer is a water-soluble polymer, the second polymer is a water-insoluble polymer, and the first polymer and the second polymer are dissolved in the same non-aqueous solvent.

[0009] The modifier for silicon-based anode materials provided by the present invention comprises a combination of a water-soluble first polymer and a water-insoluble second polymer. The modifier for silicon-based anode materials can uniformly coat the surface of the silicon-based material to form a modified silicon-based anode material with a polymer coating layer. In the preparation of the anode slurry, the first polymer can dissolve in water (the solvent of the anode slurry) and fall off from the polymer coating layer, so that a porous network-like coating structure mainly composed of the second polymer is formed on the surface of the silicon-based material, alleviating the volume expansion of the silicon-based material during charge and discharge, preventing the pulverization and shedding of the material, and thus endowing the silicon-based anode material with excellent cycling performance. At the same time, due to the porous network structure of the coating layer on the surface of the silicon-based material in the battery, a large number of conductive channels still exist on the surface of the silicon-based anode material, which will not lead to an increase in the impedance of the material, and endows the material with excellent electrical conductivity and rate performance.

[0010] In the present invention, the first polymer is a water-soluble polymer, that is, the mass of the first polymer that can be dissolved in 100 g of water ≥ 1 g, that is, the solubility of the first polymer in water ≥ 1 g / 100 g.

[0011] In the present invention, the second polymer is a water-insoluble polymer, that is, the mass of the second polymer that can be dissolved in 100 g of water ≤ 0.01 g, that is, the solubility of the second polymer in water ≤ 0.01 g / 100 g.

[0012] In the present invention, the first polymer and the second polymer are dissolved in the same non-aqueous solvent, that is, the solubility of the first polymer and the second polymer in the same non-aqueous solvent is ≥ 1 g / 100 g.

[0013] Preferably, the first polymer comprises any one or a combination of at least two of polyvinyl alcohol, polyether polyol, polyvinylpyrrolidone, water-soluble alkyd resin, polyacrylamide or polyvinylcaprolactam.

[0014] Preferably, the polyether polyol comprises polyethylene glycol and / or polypropylene glycol, specifically comprising any one or a combination of at least two of polyethylene oxide, polypropylene oxide, (methoxy) polyethylene glycol or (methoxy) polypropylene glycol.

[0015] Preferably, the first polymer comprises any one or a combination of at least two of polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, (methoxy) polyethylene glycol, (methoxy) polypropylene glycol, water-soluble alkyd resin or polyvinylcaprolactam.

[0016] Preferably, the second polymer comprises any one or a combination of at least two of acrylonitrile-based polymers, (meth)acrylate-based polymers, styrene-based polymers, polyamides, epoxy resins, polyurethanes, polyhalogenated olefins or polyolefins.

[0017] In the present invention, the "polymer" in the second polymer includes homopolymers and / or copolymers. Taking the "(meth)acrylate-based polymer" as an example, the polymer can be a homopolymer of a (meth)acrylate monomer, or a copolymer of a (meth)acrylate monomer and other monomers, such as a (meth)acrylate-styrene copolymer, etc., or a copolymer of different (meth)acrylate monomers, such as a methyl (meth)acrylate-butyl (meth)acrylate copolymer, as long as the polymer contains a structural unit formed by a (meth)acrylate monomer. Other polymers have the same meaning and will not be elaborated for the sake of simplicity.

[0018] Preferably, the (meth)acrylate-based polymer includes any one or a combination of at least two of polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, or polybutyl acrylate.

[0019] Preferably, the polyhaloolefin includes any one or a combination of at least two of polyvinyl chloride, polytetrafluoroethylene, or polyvinylidene fluoride.

[0020] Preferably, the polyolefin includes any one or a combination of at least two of polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, or polyisoprene.

[0021] Preferably, the second polymer includes any one or a combination of at least two of polyacrylonitrile, polyurethane, polyamide, polymethyl methacrylate, polymethyl acrylate, polystyrene, polyisoprene, epoxy resin, or polyvinylidene fluoride.

[0022] In the present invention, in addition to the polymers listed above, the first polymer and the second polymer also include derivatives of each polymer. The derivatives include polymers with the same or similar main chain structure as the aforementioned polymers and formed by chemical modification.

[0023] Preferably, the mass ratio of the first polymer to the second polymer is 1:(0.01 - 99.00), for example, it can be 1:0.05, 1:0.10, 1:0.30, 1:0.50, 1:0.80, 1:1.00, 1:2.00, 1:3.00, 1:4.00, 1:5.00, 1:6.00, 1:7.00, 1:8.00, 1:9.00, 1:10.00, 1:20.00, 1:30.00, 1:40.00, 1:50.00, 1:60.00, 1:70.00, 1:80.00, or 1:90.00, etc. Further preferably, it is 1:(0.100 - 10.00), and even more preferably, it is 1:(0.50 - 3.00).

[0024] As a preferred technical solution of the present invention, the mass ratio of the first polymer to the second polymer is 1:0.1 - 1:10.0, and more preferably 1:0.5 - 1:3.0, so that the modifier for the silicon-based anode material can form a uniform and effective surface coating on the silicon-based material. During the preparation of the anode slurry, the first polymer dissolves in water and falls off, and finally a porous network-like coating structure mainly composed of the second polymer is formed on the silicon-based material, alleviating the volume expansion of the silicon-based material during charge and discharge cycles, having excellent cycle performance, and not causing an increase in impedance. If the mass ratio of the first polymer to the second polymer exceeds the aforementioned preferred range and the dosage of the first polymer is too large, a large amount of components in the polymer coating layer dissolve in water, and finally the coating structure formed on the silicon-based material is too porous and loose to effectively alleviate the volume expansion of the silicon-based material, resulting in poor cycle performance; if the dosage of the first polymer is too small, the coating structure finally formed on the silicon-based material is too dense, resulting in a decrease in conductivity and an increase in impedance, reducing the rate performance of the battery.

[0025] Preferably, the non-aqueous solvent includes any one or a combination of at least two of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, alcohol ether solvents, sulfone solvents, nitrogen-containing solvents or phenolic solvents, and preferably any one or a combination of at least two of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone solvents, sulfone solvents or nitrogen-containing solvents.

[0026] Preferably, the aromatic hydrocarbon solvents include any one or a combination of at least two of benzene, toluene or xylene.

[0027] Preferably, the aliphatic hydrocarbon solvents include any one or a combination of at least two of pentane, hexane, octane or petroleum ether.

[0028] Preferably, the alicyclic hydrocarbon solvents include any one or a combination of at least two of cyclopentane, cyclohexane or cycloheptane.

[0029] Preferably, the halogenated hydrocarbon solvents include any one or a combination of at least two of carbon tetrachloride, chlorobenzene, dichlorobenzene, dichloromethane or chloroform.

[0030] Preferably, the alcohol solvents include any one or a combination of at least two of methanol, ethanol, isopropanol or glycerol.

[0031] Preferably, the ether solvents include any one or a combination of at least two of diethyl ether, propylene oxide, tetrahydrofuran or dioxane.

[0032] Preferably, the ester solvent includes any one or a combination of at least two of methyl acetate, ethyl acetate, or propyl acetate.

[0033] Preferably, the ketone solvent includes any one or a combination of at least two of acetone, methyl n-butyl ketone, methyl isobutyl ketone, or cyclohexanone.

[0034] Preferably, the alcohol ether solvent includes any one or a combination of at least two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, or ethylene glycol monobutyl ether.

[0035] Preferably, the sulfone solvent includes dimethyl sulfoxide and / or sulfolane.

[0036] Preferably, the nitrogen-containing solvent includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, or pyridine.

[0037] Preferably, the phenolic solvent includes phenol and / or cresol.

[0038] Preferably, the non-aqueous solvent includes any one or a combination of at least two of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methylpyrrolidone (NMP), chloroform, dichloromethane, toluene, benzene, xylene, or acetone.

[0039] In a second aspect, the present invention provides an application of the modifier for silicon-based anode materials as described in the first aspect in silicon-based anode materials.

[0040] In a third aspect, the present invention provides a modified silicon-based anode material, which includes a silicon-based material and a polymer coating layer disposed on the surface of the silicon-based material; the material of the polymer coating layer is the modifier for silicon-based anode materials as described in the first aspect.

[0041] Preferably, the coating of the polymer coating layer on the silicon-based material includes full coating or partial coating.

[0042] Preferably, the silicon-based material includes any one or a combination of at least two of nanosilicon, microsilicon, porous silicon, amorphous silicon, or silicon oxide.

[0043] Among them, the silicon oxide is SiOx, 0 < x < 2. For example, x can be 0.1, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, or 1.8, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0044] Preferably, the silicon-based material is silicon oxide, and more preferably silicon monoxide particles.

[0045] Preferably, based on the mass of the silicon-based material being 100%, the mass of the modifier for the silicon-based anode material is 1-10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list all the specific point values included in the range.

[0046] In the present invention, the mass of the modifier for the silicon-based anode material is the total mass of the first polymer and the second polymer, which is calculated based on the solid content of the first polymer and the second polymer and does not include any solvents.

[0047] As a preferred technical solution of the present invention, in the modified silicon-based anode material, based on the mass of the silicon-based material being 100%, the mass of the modifier for the silicon-based anode material is 1-10%. It forms a uniform polymer coating layer on the surface of the silicon-based material and can dissolve and shed the first polymer during the preparation of the anode slurry, forming a porous network-like coating structure on the surface of the silicon-based material, inhibiting the volume expansion of the silicon-based material during charge and discharge cycles, and significantly improving the structural stability and cycling performance of the material. If the mass of the modifier for the silicon-based anode material is too small, an effective coating cannot be formed, and the volume expansion of the silicon-based material cannot be inhibited; if the mass of the modifier for the silicon-based anode material is too large and the thickness of the formed coating structure is too high, it will lead to an increase in impedance and affect the rate performance of the lithium-ion battery.

[0048] Fourthly, the present invention provides a preparation method of the modified silicon-based anode material as described in the third aspect. The preparation method includes: mixing the silicon-based material with a solution of the modifier for the silicon-based anode material to obtain a slurry; drying the slurry to obtain the modified silicon-based anode material.

[0049] Preferably, the solution of the modifier for the silicon-based anode material is a combination of the first polymer, the second polymer and a non-aqueous solvent.

[0050] Preferably, the mass ratio of the modifier for the silicon-based anode material (total mass of the first polymer and the second polymer) in the slurry to the mass of the silicon-based material is (0.01-0.10):1, for example, it can be 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1 or 0.09:1, etc.

[0051] Preferably, the inlet temperature of the spray drying is 200-300 °C, for example, it can be 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C or 290 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 230-270 °C.

[0052] Preferably, the outlet temperature of the spray drying is 100-200 °C, for example, it can be 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C or 190 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 130-170 °C.

[0053] Preferably, the pressure of the spray drying is 0.2-0.8 MPa, for example, it can be 0.25 MPa, 0.30 MPa, 0.35 MPa, 0.40 MPa, 0.45 MPa, 0.50 MPa, 0.55 MPa, 0.60 MPa, 0.65 MPa, 0.70 MPa or 0.75 MPa, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0054] Preferably, the feeding speed of the slurry in the spray drying is 5-15 mL / min, for example, it can be 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 11 mL / min, 12 mL / min, 13 mL / min or 14 mL / min, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0055] In the fifth aspect, the present invention provides a negative electrode material composition, and the negative electrode material composition includes the modified silicon-based negative electrode material as described in the third aspect.

[0056] Preferably, the negative electrode material composition includes a combination of a modified silicon-based negative electrode material, a conductive agent, a binder, and optionally a thickener.

[0057] In the sixth aspect, the present invention provides a negative electrode plate, and the negative electrode plate includes a current collector and a coating provided on the current collector, and the material of the coating includes the negative electrode material composition as described in the fifth aspect.

[0058] Preferably, the method for preparing the negative electrode plate includes: uniformly mixing the negative electrode material composition with water to obtain a negative electrode slurry; coating the negative electrode slurry on a current collector and drying to obtain the negative electrode plate.

[0059] Preferably, after drying, a step of rolling is further included.

[0060] In a seventh aspect, the present invention provides an electrochemical energy storage device, and the electrochemical energy storage device includes the negative electrode plate as described in the sixth aspect.

[0061] Preferably, the electrochemical energy storage device includes any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, a fuel cell, or a solar cell.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) The modifier for the silicon-based negative electrode material provided by the present invention includes a combination of a water-soluble first polymer and a water-insoluble second polymer, which are uniformly coated on the surface of the silicon-based material to obtain a modified silicon-based negative electrode material with a polymer coating layer. In the preparation of the negative electrode slurry, the first polymer dissolves and falls off from the polymer coating layer, forming a porous network-like coating structure mainly composed of the second polymer on the surface of the silicon-based material, thereby effectively alleviating the volume expansion of the silicon-based material during charge and discharge, preventing the pulverization and shedding of the material, and having excellent structural stability and cycling performance. At the same time, due to the porous network-like structure of the coating layer on the surface of the silicon-based material in the battery, a large number of conductive channels still exist on the surface of the silicon-based material, which will not cause an increase in the impedance of the material, and has excellent conductivity and rate performance.

[0064] (2) The modified silicon-based negative electrode material prepared by using the modifier for the silicon-based negative electrode material is used in the negative electrode plate and the lithium-ion battery. While significantly inhibiting the volume expansion of the silicon-based material, it has excellent conductivity, enabling the capacity retention rate of the lithium-ion battery to be > 89% after 100 cycles at room temperature, and the rate performance to be ≥ 80%, significantly improving the cycling performance of the lithium-ion battery. Specific Embodiments

[0065] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0066] As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or device containing the listed elements is not necessarily limited to those elements, but may also include other elements not explicitly listed or elements inherent to such composition, step, method, article, or device.

[0067] "Optional" or "any one" means that the matters or events described thereafter may or may not occur, and such description includes the cases where the events occur and the cases where the events do not occur.

[0068] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirements (i.e., the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity clearly refers only to the singular form.

[0069] The descriptions of the terms "one embodiment", "some embodiments", "exemplarily", "specific examples", or "some examples", etc. described in the present invention mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this article, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example.

[0070] Moreover, the technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0071] In the following specific embodiments of the present invention, the silicon-based material, the first polymer, and the second polymer used are all commercially available products. The silicon-based material is silicon oxide (SiOx, purchased from Global Graphene Group, USA, product number GA-K9C2), and the specific information of the first polymer and the second polymer is shown in Table 1 below:

[0072] Table 1

[0073]

[0074]

[0075] Example 1

[0076] A modifier for a silicon-based anode material, comprising a combination of polyvinyl alcohol (PVA-1788) and polyacrylonitrile, and the mass ratio of PVA-1788 to polyacrylonitrile is 1:1.

[0077] A modified silicon-based anode material includes silicon oxide and a polymer coating layer disposed on the surface of the silicon oxide; the material of the polymer coating layer is a modifier for the silicon-based anode material provided in this embodiment, and the preparation method is as follows: Dissolve 2.5 parts of PVA-1788 and 2.5 parts of polyacrylonitrile in 100 parts of a non-aqueous solvent (dimethyl sulfoxide), and add 95 parts of silicon oxide powder under stirring at 1000 rpm. After stirring for 30 minutes, a uniform slurry is obtained. Spray-dry the slurry, and set the parameters as follows: the inlet temperature is 250 °C, the outlet temperature is 150 °C, the feeding rate is 10 mL / min, and the air pressure is 0.5 MPa. After spraying, the collected particulate matter is the modified silicon-based anode material.

[0078] Examples 2-10, Comparative Examples 1-3

[0079] A modifier for a silicon-based anode material and a modified silicon-based anode material, the difference from Example 1 is only that the components in the modifier for the silicon-based anode material or the types of non-aqueous solvents are different, as shown in Table 2 specifically; The modifiers for the silicon-based anode materials provided in Examples 2-10 and Comparative Examples 1-3 are used to prepare the modified silicon-based anode materials, and the specific method is the same as that in Example 1.

[0080] Table 2

[0081]

[0082] In Table 2, "mass ratio" represents the mass ratio of the first polymer to the second polymer; "--" represents the non-existence of components / values, that is, the difference between Comparative Example 1 and Example 1 is only that polyacrylonitrile is replaced with an equal amount of PVA-1788, and the difference between Comparative Example 2 and Example 1 is only that PVA-1788 is replaced with an equal amount of polyacrylonitrile, and Comparative Example 3 is unmodified silicon oxide powder.

[0083] Application Examples 1-10, Comparative Application Examples 1-3

[0084] A negative electrode sheet includes a current collector (Cu foil) and a coating disposed on the current collector, and the material of the coating is a negative electrode material composition; the negative electrode material composition includes a silicon-based anode active material, artificial graphite, a conductive agent (conductive carbon black, SP), a binder (styrene-butadiene rubber, SBR), and a thickener (sodium carboxymethyl cellulose, CMC) with a mass ratio of 10:85:1.0:2.5:1.5; wherein, the silicon-based anode active materials are the modified silicon-based anode materials provided in Examples 1-10 and Comparative Examples 1-3 respectively.

[0085] Preparation of the negative electrode sheet: Mix silicon-based negative electrode active material, artificial graphite, SP, SBR, and CMC in a mass ratio of 10:85:1.0:2.5:1.5, add deionized water according to the proportion of the solid content of the system being 40 wt%, stir and mix well to make a uniform negative electrode slurry. After passing through a 100-mesh sieve, coat it on a negative electrode current collector Cu foil, dry it, and roll it with a roller at a unit length load of 10×10 4 N / m to obtain the negative electrode sheet.

[0086] A lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet is the aforementioned negative electrode sheet; the preparation method of the lithium-ion battery is as follows:

[0087] (1) Preparation of the positive electrode sheet: Mix a positive electrode active material (lithium iron phosphate), a conductive agent (conductive carbon black), and a binder (polyvinylidene fluoride, PVDF) in a mass ratio of 95.5:2.0:2.5, add NMP according to the proportion of the solid content of the system being 50 wt%, stir and mix well to make a uniform positive electrode slurry. After passing through a 100-mesh sieve, coat it on a positive electrode current collector Al foil, dry it, and roll it with a roller at a unit length load of 10×10 4 N / m to obtain the positive electrode sheet.

[0088] (2) Preparation of the negative electrode sheet: As described above;

[0089] (3) Separator: Use a PE porous polymer film (Shenzhen Xingyuan Material Technology Co., Ltd.) as the separator;

[0090] (4) Assembly of the lithium-ion battery: Wind the positive electrode sheet, the separator, and the negative electrode sheet in sequence to obtain an electric core; encapsulate the electric core with an aluminum-plastic film, bake to remove water, then inject the electrolyte, and after processes such as vacuum packaging, shelving, formation, secondary packaging, and shaping, obtain the lithium-ion battery.

[0091] Performance test:

[0092] (1) Room temperature cycle performance

[0093] Charge the above-prepared lithium-ion battery at a constant current of 0.33C to 4.2V, then charge it at a constant voltage until the cut-off current is 0.02C, and discharge it at 0.33C to 2.5V; set it aside for 5 minutes, charge it at a constant current of 0.33C to 4.2V, then charge it at a constant voltage until the cut-off current is 0.02C, and discharge it at 0.33C to 2.5V to perform initial adjustment.

[0094] At 25 °C, the initially adjusted lithium-ion battery is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage until the cut-off current of 0.02C, left standing for 5 minutes, and then discharged at a constant current of 1C to 2.5V, left standing for 5 minutes, and the initial cycle discharge capacity is measured; following this cycle, after 100 charge / discharge cycles, the 100th cycle discharge capacity is measured, and the cycle capacity retention rate of the 100th cycle is calculated using the following formula:

[0095] Capacity retention rate after 100 cycles (%) = 100% × Discharge capacity of the 100th cycle / Initial cycle discharge capacity.

[0096] (2) Rate performance

[0097] At 25 °C, the initially adjusted lithium-ion battery is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage until the cut-off current of 0.02C, left standing for 5 minutes, and then discharged at a constant current of 1C to 2.5V, left standing for 5 minutes, and the 1C discharge capacity is measured. Then it is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage until the cut-off current of 0.02C, left standing for 5 minutes, and then discharged at a constant current of 3C to 2.5V, left standing for 5 minutes, and the discharge capacity at the 3C rate is measured.

[0098] 3C capacity retention rate (%) = 100% × 3C discharge capacity / 1C discharge capacity.

[0099] The test results are shown in Table 3.

[0100] Table 3

[0101] First Polymer / Second Polymer Cycling Performance (%) Rate Performance (%) Example 1 PVA-1788 / Polyacrylonitrile 90.2 80.4 Example 2 PVA-0588 / Polyurethane 89.3 80.5 Example 3 Polyacrylamide / Polyamide 89.7 80.4 Example 4 Polyvinylpyrrolidone / PMMA 90.6 80.4 Example 5 mPEG / Polystyrene 91.1 80.3 Example 6 MPPG / Polyisoprene 92.0 80.2 Example 7 Water-soluble Alkyd Resin / Epoxy Resin 92.9 80.1 Example 8 Polyvinylcaprolactam / PVDF 93.8 80.0 Example 9 PVA-1788 / Polyacrylonitrile 86.6 79.9 Example 10 PVA-1788 / Polyacrylonitrile 89.0 75.3 Comparative Example 1 PVA-1788 85.8 79.2 Comparative Example 2 Polyacrylonitrile 86.5 65.1 Comparative Example 3 -- 85.4 79.2

[0102] Combined with the performance test data in Table 3, compared with the conventional silicon oxide negative electrode material in Comparative Example 3, the modified silicon-based negative electrode material prepared with the modifier for the silicon-based negative electrode material provided in Examples 1-8 of the present invention effectively alleviates the pulverization and shedding caused by volume expansion, has excellent structural stability and cycle performance, enables the lithium-ion battery containing it to have a capacity retention rate > 89% after 100 cycles at room temperature, and a rate performance ≥ 80%, and has excellent cycle performance and rate performance.

[0103] In the present invention, a water-soluble first polymer and a water-insoluble second polymer are combined in a specific ratio, so that the modifier for the silicon-based anode material uniformly coats the surface of the silicon-based material, forming a uniform polymer coating layer; in the preparation of the anode slurry, because the first polymer is soluble in water and the second polymer forms a porous network-like coating structure on the surface of the silicon-based material, the volume expansion of the silicon-based material during charge and discharge is alleviated, preventing the material from pulverization and shedding, thus having excellent cycling performance; at the same time, due to the network structure of the coating layer on the surface of the silicon-based material, a large number of conductive channels still exist on the surface of the silicon-based material, which will not cause an increase in the impedance of the material, and has excellent conductivity and rate performance. Combining the effect data of Examples 1-10, it can be seen that by adjusting the ratio of the first polymer to the second polymer, the cycling performance and rate performance of the modified silicon-based anode material and the battery can be optimized. However, if the dosage of the first polymer is too large (Example 9), a large amount of components in the polymer coating layer will dissolve in the anode slurry, and the coating structure on the silicon-based material is too small to effectively alleviate the volume expansion of the silicon-based material, resulting in a decrease in cycling performance; if the dosage of the first polymer is too small (Example 10), the coating structure finally formed on the silicon-based material is too dense, resulting in a decrease in conductivity and an increase in impedance, reducing the rate performance of the battery. In Comparative Example 1, PVA-1788 was used as the modifier for the silicon-based anode material, and a large amount of polyvinyl alcohol on the surface of the silicon-based material dissolved in the anode slurry, and did not form an effective coating on the silicon-based material, so it was unable to inhibit the pulverization caused by volume expansion, resulting in poor cycling performance; while in Comparative Example 2, polyacrylonitrile was used as the modifier for the silicon-based anode material, and the polymer coating layer on the surface of the silicon-based material was very dense, hindering the conductive channels and increasing the impedance of the material, resulting in a significant reduction in rate performance.

[0104] The applicant declares that the present invention uses the above examples to illustrate the modifier for the silicon-based anode material, the modified silicon-based anode material and its application of the present invention, but the present invention is not limited to the above examples, that is, it does not mean that the present invention must rely on the above examples to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negative electrode plate, characterized in that, the negative electrode plate includes a current collector and a coating disposed on the current collector, and the material of the coating includes a negative electrode material composition; the negative electrode material composition includes a modified silicon-based negative electrode material; the modified silicon-based negative electrode material includes a silicon-based material and a polymer coating layer disposed on the surface of the silicon-based material; the material of the polymer coating layer is a modifier for the silicon-based negative electrode material; the modifier for the silicon-based negative electrode material includes a combination of a first polymer and a second polymer; the first polymer is a water-soluble polymer, the second polymer is a water-insoluble polymer, and the first polymer and the second polymer are dissolved in the same non-aqueous solvent; the mass ratio of the first polymer to the second polymer is 1:(0.30 - 9.00); the second polymer includes any one or at least two combinations of acrylonitrile-based polymers, (meth)acrylate-based polymers, styrene-based polymers, polyamides, epoxy resins, polyurethanes or polyolefins; the modified silicon-based negative electrode material is prepared by the following preparation method: mixing the silicon-based material with a modifier solution for the silicon-based negative electrode material to obtain a slurry; drying the slurry to obtain the modified silicon-based negative electrode material; in the preparation of the negative electrode slurry, the first polymer dissolves and detaches from the polymer coating layer, so that a porous network-like coating structure mainly composed of the second polymer is formed on the surface of the silicon-based material.

2. The negative electrode plate according to claim 1, characterized in that, the first polymer includes any one or at least two combinations of polyvinyl alcohol, polyether polyol, polyvinylpyrrolidone, water-soluble alkyd resin, polyacrylamide or polyvinylcaprolactam.

3. The negative electrode plate according to claim 2, characterized in that, the polyether polyol includes polyethylene glycol and / or polypropylene glycol.

4. The negative electrode plate according to claim 1, characterized in that, the non-aqueous solvent includes any one or at least two combinations of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, alcohol ether solvents, sulfone solvents, nitrogen-containing solvents or phenolic solvents.

5. The negative electrode plate according to claim 4, characterized in that, the non-aqueous solvent includes any one or at least two combinations of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone solvents, sulfone solvents or nitrogen-containing solvents.

6. The negative electrode plate according to claim 4, characterized in that, the aromatic hydrocarbon solvents include any one or at least two combinations of benzene, toluene or xylene.

7. The negative electrode plate according to claim 4, characterized in that, the aliphatic hydrocarbon solvents include any one or at least two combinations of pentane, hexane, octane or petroleum ether.

8. The negative electrode plate according to claim 4, characterized in that, the alicyclic hydrocarbon solvents include any one or at least two combinations of cyclopentane, cyclohexane or cycloheptane.

9. The negative electrode plate according to claim 4, characterized in that, The halogenated hydrocarbon solvents include any one or a combination of at least two of carbon tetrachloride, chlorobenzene, dichlorobenzene, dichloromethane, or chloroform.

10. The negative electrode sheet according to claim 4, characterized in that the alcohol solvents include any one or a combination of at least two of methanol, ethanol, isopropanol, or glycerol.

11. The negative electrode sheet according to claim 4, characterized in that the ether solvents include any one or a combination of at least two of diethyl ether, propylene oxide, tetrahydrofuran, or dioxane.

12. The negative electrode sheet according to claim 4, characterized in that the ester solvents include any one or a combination of at least two of methyl acetate, ethyl acetate, or propyl acetate.

13. The negative electrode sheet according to claim 4, characterized in that the ketone solvents include any one or a combination of at least two of acetone, methyl n-butyl ketone, methyl isobutyl ketone, or cyclohexanone.

14. The negative electrode sheet according to claim 4, characterized in that the alcohol ether solvents include any one or a combination of at least two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, or ethylene glycol monobutyl ether.

15. The negative electrode sheet according to claim 4, characterized in that the sulfone solvents include dimethyl sulfoxide and / or sulfolane.

16. The negative electrode sheet according to claim 4, characterized in that The nitrogen-containing solvent includes N N-methylpyrrolidone, N,N N,N-dimethylformamide, N,N N,N-dimethylacetamide, acetonitrile or pyridine, or a combination of any one or at least two of them.

17. The negative electrode sheet according to claim 4, characterized in that the phenolic solvents include phenol and / or cresol.

18. The negative electrode sheet according to claim 1, characterized in that the silicon-based materials include any one or a combination of at least two of nanosilicon, microsilicon, porous silicon, amorphous silicon, or silicon oxide.

19. The negative electrode sheet according to claim 1, characterized in that based on the mass of the silicon-based materials being 100%, the mass of the modifier for the silicon-based negative electrode materials is 1-10%.

20. The negative electrode sheet according to claim 1, characterized in that the drying method is spray drying.

21. The negative electrode sheet according to claim 20, characterized in that the inlet temperature of the spray drying is 200-300 °C.

22. The negative electrode sheet according to claim 20, characterized in that the outlet temperature of the spray drying is 100-200 °C.

23. The negative electrode sheet according to claim 20, characterized in that the pressure of the spray drying is 0.2-0.8 MPa.

24. The negative electrode sheet according to claim 20, characterized in that the feeding rate of the slurry in the spray drying is 5-15 mL / min.

25. The negative electrode sheet according to claim 1, characterized in that the negative electrode material composition includes a combination of a modified silicon-based negative electrode material, a conductive agent, a binder, and a thickener.

26. An electrochemical energy storage device, characterized in that the electrochemical energy storage device includes the negative electrode sheet according to any one of claims 1-25.

27. The electrochemical energy storage device according to claim 26, characterized in that The electrochemical energy storage device includes any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, a fuel cell, or a solar cell.

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