Negative active material, negative pole piece comprising same, electrochemical device and electronic equipment
By forming a composite coating layer on the surface of silicon-based anode materials, the problems of volume expansion and interface stability of silicon-based anode materials during cycling are solved, achieving adaptive absorption of the electrode structure and improvement of battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-03-17
AI Technical Summary
Existing silicon-based anode materials suffer from volume expansion and poor interface stability during cycling, leading to electrode structure collapse and reduced capacity retention. Current solutions cannot achieve dynamic stress absorption while maintaining electrode integrity.
A composite coating structure is adopted, including conductive material, soluble organic phase and binder. A dense shell is formed on the surface of silicon-based material through spray drying process to ensure the integrity of the conductive network during the electrode preparation stage. After the battery is injected with electrolyte, the soluble organic phase is selectively dissolved to form an elastic conductive skeleton that adaptively absorbs silicon volume deformation.
It significantly improves the stability of the electrode structure, suppresses electrode expansion, optimizes the conductive network, enhances the energy density and cycle performance of the battery, and reduces the formation of lithium dendrites.
Smart Images
Figure SMS_1 
Figure SMS_2 
Figure SMS_3
Abstract
Description
Technical Field
[0001] This application relates to the field of electrochemical energy storage technology, and in particular to negative electrode active materials and negative electrode sheets, electrochemical devices and electronic devices containing the same. Background Technology
[0002] Currently, silicon-based anode materials have become a key focus of lithium battery research due to their high specific capacity, but there are two major technical bottlenecks: ① Cyclic volume expansion: The volume of silicon particles changes greatly during charging and discharging, leading to the pulverization of active materials and the breakage of conductive networks; ② Poor interface stability: Repeated expansion and contraction during use causes the electrode structure to collapse, reducing the capacity retention rate.
[0003] Existing solutions such as carbon coating and nano-sizing can alleviate expansion, but they cannot achieve dynamic stress absorption while maintaining electrode integrity. Summary of the Invention
[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a negative electrode active material, a negative electrode sheet containing the same, an electrochemical device, and an electronic device. The negative electrode active material provided by this application can adaptively absorb silicon volume deformation during cycling, reduce electrode expansion, and improve battery energy density.
[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: The first aspect of this application provides a negative electrode active material, including a silicon-based material and a composite coating layer disposed on the outer surface of the silicon-based material, wherein the composite coating layer includes a conductive material, a soluble organic phase and a binder; The water solubility of the soluble organic phase at 25 °C is <0.001 mg / mL.
[0006] As an embodiment of this application, the conductive material includes at least one of carbon nanotubes, graphene nanosheets, conductive carbon black, and nanowires.
[0007] As an embodiment of this application, the soluble organic phase includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide-styrene block copolymer, sulfonated polyaniline, stearic acid and its derivatives.
[0008] As an embodiment of this application, the adhesive includes at least one of styrene-butadiene rubber and its derivatives, polyacrylic acid and its derivatives, and polyurethane and its derivatives.
[0009] As an embodiment of this application, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, and silicon.
[0010] As an embodiment of this application, the negative electrode active material satisfies: 0.41≤D1 / D2≤0.97.
[0011] As a preferred embodiment of this application, the negative electrode active material satisfies: 0.7≤D1 / D2≤ 0.9, where D1 is the Dv50 particle size of the silicon-based material and D2 is the Dv50 particle size of the negative electrode active material.
[0012] As an embodiment of this application, D1 conforms to the condition 2 μm ≤ D1 ≤ 7.2 μm.
[0013] As an embodiment of this application, D2 conforms to 4.9μm≤D2≤10μm.
[0014] As an embodiment of this application, D1 = 5.6-7.2 μm.
[0015] As an embodiment of this application, D2 = 8-8.5 μm.
[0016] As an embodiment of this application, the soluble organic phase in the composite coating layer has a mass percentage content of 30-60%.
[0017] As an embodiment of this application, the mass percentage of conductive material in the composite coating layer is 5-50%.
[0018] As an embodiment of this application, the adhesive content in the composite coating layer is 10-50% by mass.
[0019] As an embodiment of this application, the elastic modulus of the composite coating layer is Ec, and 0.05Gpa≤Ec≤8.0Gpa.
[0020] As an embodiment of this application, the preparation method of the negative electrode active material of this application includes the following steps: S1. The silicon-based material is surface-treated with a strong oxidizing agent, and then the surface-treated silicon-based material, conductive material, and soluble organic phase are uniformly dispersed in an aqueous solution containing a binder to obtain a slurry. S2. The slurry is cured by spray drying to obtain the negative electrode active material.
[0021] As an embodiment of this application, in S1, the solid content of the slurry is 10-45wt%, and the viscosity of the slurry is 100-3000 mPa·s; As an embodiment of this application, in S2, the inlet temperature of the spray dryer is 150-200 ℃, and the atomization pressure is 2-5 bar.
[0022] A second aspect of this application provides a negative electrode sheet comprising the negative electrode active material as described above.
[0023] A third aspect of this application provides an electrochemical device comprising a negative electrode as described above.
[0024] A fourth aspect of this application provides an electronic device including the electrochemical device described above.
[0025] Compared with the prior art, the beneficial effects of this application are as follows: This application provides a negative electrode active material with a specific composite coating layer, achieved through a specific conductive material, a soluble organic phase, and a binder: (1) During the electrode preparation stage, the integrity of the composite coating layer can be maintained to ensure the construction of the conductive network between the particles of the negative electrode active material in the negative electrode; (2) After the battery is filled with electrolyte, the soluble phase in the composite coating layer is selectively dissolved, and the remaining conductive material and binder form an elastic conductive skeleton. (3) When the negative electrode active material of this application is used in the negative electrode sheet and battery, it can adaptively absorb silicon volume deformation during cycling, suppress electrode structure damage, reduce electrode expansion and increase energy density. Detailed Implementation
[0026] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; and unless otherwise specified, the materials and reagents used are commercially available.
[0027] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.
[0028] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.
[0029] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available, and the components and raw materials used in each parallel experiment are the same.
[0030] In the following description, all figures disclosed herein are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values with a lower limit RL and an upper limit RU is disclosed, any values falling within that range are specifically disclosed. Specifically, the following values within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable with a 1% increment from 1% to 100%, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values defined by the two R values as defined above are also specifically disclosed.
[0031] General definition The term "negative electrode active material" (also known as anodic active material) is defined as a material that is electrochemically active in a negative electrode or anode, as used herein and in the claims. An active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.
[0032] The term "silicon-based materials" is defined as a general term for a class of materials with silicon as the core component, including but not limited to silicon-carbon, silicon-oxygen, and silicon, which generally have hydroxyl groups (-OH) on their surface. In the field of electrochemical energy storage, it specifically refers to material systems that are used as negative electrode active materials and have silicon as the main active component.
[0033] The term "composite coating" as used herein and in the claims refers to a continuous or semi-continuous layer structure formed by a combination of two or more materials and wrapped around the surface of a core material.
[0034] The term "soluble organic phase" as used herein and in the claims refers to a functional component with an organic compound at its core, which is soluble in a specific solvent to form a homogeneous and stable system.
[0035] The term "Dv50 particle size" as used herein and in the claims refers to the median particle size as a percentage of particle volume, where 50% of the particles in a particle group are smaller than this particle size and 50% of the particles are larger than this particle size.
[0036] I. Negative electrode plate In some embodiments, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.
[0037] In some embodiments, the negative electrode current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate. In this application, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application, such as copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a composite current collector, etc.
[0038] To address the issues of volume expansion and poor stability in current silicon-based anode materials during cycling, this application provides an anode active material comprising a silicon-based material and a composite coating layer disposed on the outer surface of the silicon-based material, wherein the composite coating layer comprises a conductive material, a soluble organic phase, and a binder. The water solubility of the soluble organic phase at 25 °C is <0.001 mg / mL.
[0039] This application designs a composite coating structure on the surface of a silicon-based material, combining conductive materials, a soluble organic phase, and a binder. During the electrode fabrication stage, the integrity of the composite coating layer can be maintained, ensuring the construction of a conductive network between the particles of the negative electrode active material. When applied to a battery, after electrolyte injection, the soluble organic phase in the composite coating layer can be selectively dissolved, and the remaining part forms a stable elastic conductive interconnect framework. This structure can adaptively absorb the deformation of silicon volume during battery cycling, suppressing electrode structure damage.
[0040] The ternary composite coating structure provided in this application significantly reduces the resistance increase after the soluble organic phase is dissolved in the electrolyte and can absorb >88% of the expansion stress, thus significantly improving the stability of the electrode structure. On the other hand, it optimizes the percolation threshold of the conductive network and creates pores in the electrode sheet by means of the dissolution transformation method, forming a fast ion channel and improving the kinetic performance. The composite coating layer of this application can also suppress lithium dendrites. During use, lithium dendrites have difficulty breaking through the loose and elastic conductive network layer structure formed after dissolution, thus comprehensively solving the problem that existing silicon-based anodes cannot achieve dynamic stress absorption while maintaining electrode integrity.
[0041] In some embodiments, the conductive material includes at least one of carbon nanotubes (CNTs), graphene nanosheets (GNPs), conductive carbon black (Super P), and nanowires.
[0042] In some embodiments, the soluble organic phase includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene oxide-styrene block copolymer (PEO-PS), sulfonated polyaniline, stearic acid and its derivatives, wherein stearic acid and its derivatives include, but are not limited to, stearic acid, sodium stearate, glyceryl monostearate, polyethylene glycol-15 hydroxystearate, etc.
[0043] Regarding the selection of the soluble phase, since inorganic salts precipitate in the form of crystals and cannot achieve good adhesion to silicon-based materials, it is not conducive to the construction of an elastic conductive network between particles. This application selected the above-mentioned specific soluble organic substances as the soluble phase, whose water solubility at 25 °C is all <0.001 mg / mL; and at 45 °C, the above-mentioned soluble organic phase materials can achieve more than 99% dissolution after being treated in N-methylpyrrolidone (NMP), ethylene carbonate (EC) or dimethyl carbonate (DMC) for 24 h.
[0044] In some embodiments, the adhesive includes at least one of styrene-butadiene rubber (SBR) and its derivatives, polyacrylic acid (PAA) and its derivatives, and polyurethane (PU) and its derivatives.
[0045] In some embodiments, the styrene-butadiene rubber and its derivatives include, but are not limited to, styrene-butadiene rubber, carboxylated styrene-butadiene rubber (XSBR), hydroxylated styrene-butadiene rubber (HSBR), epoxy-modified styrene-butadiene rubber (ESBR), etc.; the polyacrylic acid and its derivatives include, but are not limited to, polyacrylic acid, carboxylated polyacrylic acid, hydroxylated polyacrylic acid, silane-modified polyacrylic acid, etc.; the polyurethane and its derivatives include, but are not limited to, polyurethane, hydroxyl-terminated polyurethane prepolymer, carboxyl-modified polyurethane, epoxy-modified polyurethane, etc.
[0046] This application selects the above-mentioned type of elastic binder, which has moderate elasticity after curing. It can adapt to the volume change of silicon-based materials through elastic deformation, reduce expansion, and enhance the stability and cycle reliability of the electrode structure.
[0047] In some embodiments, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, and silicon.
[0048] In some embodiments, the negative electrode active material satisfies: 0.41≤D1 / D2≤0.97, for example, it can be a range of 0.41, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.71, 0.75, 0.80, 0.85, 0.90, 0.97 or any two of these values.
[0049] In some embodiments, the negative electrode active material satisfies: 0.7≤D1 / D2≤0.9, where D1 is the Dv50 particle size of the silicon-based material and D2 is the Dv50 particle size of the negative electrode active material.
[0050] In some implementations, D1 conforms to 2 μm ≤ D1 ≤ 7.2 μm, and can be, for example, a range of 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 4.8 μm, 5.0 μm, 5.5 μm, 5.6 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.2 μm, or any two of these values. In some implementations, D2 conforms to 4.9μm≤D2≤10μm, and can be, for example, a range of 4.9μm, 5.0μm, 5.5μm, 6.0μm, 6.2μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, or any two of these values.
[0051] In some of these embodiments, D1 = 5.6-7.2 μm.
[0052] In some of these embodiments, D2 = 8-8.5 μm.
[0053] This application controls the particle size of the provided negative electrode active material by controlling the preparation process. If the particle size is too large, it may affect the compaction density and energy density of the electrode; if the particle size is too small, the specific surface area will be too large, and side reactions will increase. At the same time, the thickness of the composite coating layer is controlled by adjusting the particle size relationship between the silicon-based material core and the final negative electrode active material (i.e., the quantitative relationship between D1 and D2 mentioned above): when the coating layer is too thick, it will cause ED damage; if it is too thin, it will lead to the inability to achieve a good absorption deformation effect, resulting in an increased expansion rate during use.
[0054] In some embodiments, the soluble organic phase in the composite coating layer has a mass percentage content of 30-60%, for example, it can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any two of these values.
[0055] In some embodiments, the conductive material in the composite coating layer has a mass percentage content of 5-50%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any two of these values.
[0056] In some embodiments, the adhesive in the composite coating layer has a mass percentage content of 10-50%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range of any two values therein.
[0057] In some embodiments, the elastic modulus of the composite coating is Ec, and 0.05 Gpa ≤ Ec ≤ 8.0 Gpa.
[0058] The elastic modulus of the composite coating layer can be controlled within a certain range by adjusting the amount of specific elastic binder and the preparation steps. When Ec > 8, the elastic modulus is too large, and the composite coating layer cannot be compressed during normal charging and discharging, which is not conducive to suppressing volume expansion. On the other hand, if the elastic modulus is too small, the structural stability of the composite coating layer will decrease.
[0059] In some embodiments, the preparation method of the negative electrode active material of this application includes the following steps: S1. The silicon-based material is surface-treated with a strong oxidizing agent, and then the surface-treated silicon-based material, conductive material, and soluble organic phase are uniformly dispersed in an aqueous solution containing a binder to obtain a slurry. S2. The slurry is cured by spray drying to obtain the negative electrode active material.
[0060] The method for preparing the negative electrode active material provided in this application first involves surface treatment of the silicon-based material with a strong oxidizing agent such as concentrated H2SO4 or H2O2, resulting in abundant hydroxyl groups (-OH) on its surface, with a hydroxyl density reaching 4.0-5.0 OH / nm. 2 These hydroxyl groups are the basis for the subsequent chemical bonding between the silicon-based material and the composite coating layer. When preparing the slurry, it is necessary to ensure that it does not separate after standing for 24 hours. The silicon-based material, conductive material and binder are stably dispersed in the slurry without phase separation, which is a prerequisite for obtaining uniform coating.
[0061] The preparation process mainly utilizes the high-temperature instantaneous curing characteristics of spray drying. Under high imported temperatures, the soluble organic phase rapidly melts or softens, forming a dense, physically cross-linked "shell" on the surface of the silicon-based material along with an elastic binder and conductive materials, thus "locking" the water-soluble components inside. This shell effectively resists solvent erosion and maintains structural integrity during subsequent electrode slurry mixing (usually using an aqueous solvent).
[0062] In some embodiments, in S1, the solid content of the slurry is 10-45 wt%, and the viscosity of the slurry is 100-3000 mPa·s.
[0063] The solid content of the slurry can control the thickness and coating condition of the coating layer: if the solid content is too high and the viscosity is too high, the slurry will be difficult to atomize, the coating layer will be too thick, affecting ion diffusion and reducing electrical performance; if the solid content is too low and the viscosity is too low, the composite coating layer will be too thin or discontinuous, resulting in poor buffering effect and affecting the expansion inhibition performance.
[0064] In some embodiments, in S2, the inlet temperature of the spray dryer is 150-200 °C, and the atomization pressure is 2-5 bar.
[0065] The temperature control of the spray drying inlet affects the melt crosslinking of the soluble organic phase and the binder: if the temperature is too high, the organic phase may be degraded or over-crosslinked, affecting its solubility in the electrolyte; if the temperature is too low, the composite coating layer may not be fully cured and have poor structural strength.
[0066] The atomization pressure of spray drying can control the particle size of the formed negative electrode active material: if the particle size is too large, it will affect the compaction density and energy density of the electrode sheet; if the particle size is too small, the specific surface area will be too large, and the side reactions will increase.
[0067] II. Electrochemical Device This application provides an electrochemical device including a negative electrode as described above. In some embodiments, the electrochemical device further includes a positive electrode, a separator, and an electrolyte.
[0068] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.
[0069] positive electrode The electrochemical device of this application includes a positive electrode, wherein the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.
[0070] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.
[0071] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.
[0072] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.
[0073] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive material.
[0074] diaphragm The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.
[0075] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.
[0076] electrolyte The liquid electrolyte (electrolyte) may include organic solvents and lithium salts. The use of organic solvents is not limited, as long as they can dissolve the first and second network frameworks of this application and can serve as a medium for the movement of ions participating in the electrochemical reaction of the battery.
[0077] III. Electronic Equipment This application provides an electronic device, including the electrochemical device described above.
[0078] The electronic device described in this application is not particularly limited and may be any electronic device known in the prior art.
[0079] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.
[0080] The following uses a secondary battery as an example and combines specific embodiments to illustrate the preparation of a secondary battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.
[0081] In the following examples and comparative examples, the battery disassembly and pretreatment methods are as follows: the battery is frozen at -20 ℃ for 12 hours, then dissected at room temperature, and the electrode sheets are dried in a vacuum drying oven for 12 hours to remove residual electrolyte; In the following examples and comparative examples, the Dv50 particle size of the negative electrode active material was tested using a laser particle size analyzer (Malvern Mastersizer 3000). The test conditions were: the dispersion medium was deionized water, ultrasonic dispersion for 5 minutes, and the test temperature was 25 °C. In the following examples and comparative examples, the mass percentage of conductive materials and binders in the composite coating layer was determined by thermogravimetric analysis (TGA) under the following conditions: in a nitrogen atmosphere, the temperature was increased at a rate of 10 °C / min from room temperature to 800 °C, and the content of each component was calculated by mass loss.
[0082] In the following examples and comparative examples, the elastic modulus of the composite coating was tested using a nanoindenter (Hysitron TI950). The test conditions were: a diamond conical indenter, a load of 10 mN, a test depth of 1 μm, and the average value of 5 test points.
[0083] Example 1 This application discloses a method for preparing a secondary battery, comprising the following steps: (I) Preparation of the negative electrode (1) A method for preparing negative electrode active materials, comprising the following steps: S1. The silicon-based material is surface-treated with a strong oxidizing agent, and then the surface-treated silicon-based material, conductive material, and soluble organic phase are uniformly dispersed in an aqueous solution containing a binder to obtain a slurry with a solid content of 25 wt% and a viscosity of 1500 mPa·s. The silicon-based material is CVD silicon-carbon with a Dv50 of 6μm (D1). The soluble organic phase is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP). The conductive material is carbon nanotubes (CNT) and graphene nanosheets (GNP) in a mass ratio of 1:1. The binder is styrene-butadiene rubber (SBR). S2. The slurry is cured using a spray drying process, with the inlet temperature set at 180 ℃ and the atomization pressure at 3 bar, to obtain the negative electrode active material.
[0084] (2) Mix 50 mg of the negative electrode active material, 5 mg of CNT, 2 mg of sodium carboxymethyl cellulose (CMC) and 10 mL of deionized water obtained in step (1) evenly, coat it on copper foil, and then dry, roll and cut it to obtain the negative electrode sheet. (II) Preparation of the positive electrode: The positive electrode active material is LiCoO2, with a mass ratio of 90:5:5 (active material: conductive agent Super P: binder PVDF), and the slurry solid content is 40wt%. (III) Membrane: 17 μm polypropylene microporous membrane (iv) Electrolyte: 1.0 M LiPF6, solvent is EC / DEC (1:1 v / v); (v) Battery assembly: Stack the positive electrode, separator and negative electrode in sequence, put them into the aluminum-plastic film, inject the electrolyte, and let them stand for 12 hours before charging and discharging test.
[0085] Examples 2-9 The difference between Examples 2-9 and Example 1 lies in changing the Dv50 (D1) of the silicon-based material, adjusting the atomization pressure of the spray drying process, changing the Dv50 (D2) of the negative electrode active material, and / or changing the type of silicon-based material. The specific parameter changes are shown in Table 1.
[0086] Table 1 Examples 10-18 The difference between Examples 10-18 and Example 1 lies in the fact that the proportions of the soluble organic phase, binder, and conductive material are changed, thereby changing the mass percentage of the three components in the composite coating layer. Alternatively, the type of conductive material or the type of soluble organic phase may be changed, thereby changing the percentage content of each component and / or component in the composite coating layer. The specific parameter changes are shown in Table 2.
[0087] Table 2 Examples 19-22 The difference between Examples 19-22 and Example 1 is that the type of adhesive is changed or the inlet temperature of the spray drying process is changed, thereby changing the elastic modulus. The specific parameter changes are shown in Table 3.
[0088] Table 3 Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the soluble organic phase component was replaced with an equal mass of the soluble salt lithium hexafluorophosphate (LiPF6).
[0089] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the soluble organic phase component was replaced with an equal mass of polyvinylidene fluoride (PVDF).
[0090] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that no binder is added.
[0091] Example of effect To investigate the performance of the negative electrode active material and battery provided in this application, the following tests were conducted: (1) Battery charge-discharge cycle test: 0.5C charge-discharge cycle test was conducted at room temperature to test energy density, first efficiency, and capacity retention rate after 100 cycles; (2) Electrode volume expansion rate: The electrode volume expansion rate after cycling was monitored in situ using a laser displacement sensor (accuracy 0.1μm); (3) Resistance change rate after dissolution: The resistance change rate of the battery 12 hours after electrolyte injection was calculated by electrochemical impedance spectroscopy (EIS).
[0092] The results of the above performance tests are shown in Table 4.
[0093] Table 4 As shown in Table 4: In Examples 1-9, the battery performance was optimal when D1 / D2 was in the range of 0.7-0.9. In Examples 10-18, the proportion of the formed elastic conductive network could be comprehensively controlled to improve battery performance when the content of the soluble organic phase was 30-60%, the content of the conductive material was 5-50%, and the content of the binder was 10-50%. In Examples 19-22, the battery performance was relatively good when the elastic modulus was in the range of 0.05-8.0 GPa. Compared with Example 1, Comparative Examples 1-3 showed increased electrode expansion, decreased energy density, increased resistivity change rate, and significantly decreased battery cycle performance, indicating that the specific component selection and control in this application are crucial to battery performance.
[0094] In summary, this application provides a negative electrode active material that combines conductive materials, a soluble organic phase, and a binder. Through specific component selection and control of component ratios and particle size, it achieves the following: during electrode fabrication, it maintains the integrity of the composite coating layer to ensure the construction of a conductive network between the negative electrode active material particles; after battery electrolyte injection, the soluble phase in the composite coating layer selectively dissolves, leaving the remaining conductive material and binder to form an elastic conductive framework; when the negative electrode active material of this application is used in negative electrode sheets and batteries, it can adaptively absorb silicon volume deformation during cycling, suppress electrode structure damage, reduce electrode expansion, increase energy density, and improve battery cycle performance, showing great application potential.
[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.
Claims
1. A negative electrode active material, characterized by, A silicon-based material and a composite coating layer disposed on an outer surface of the silicon-based material, the composite coating layer comprising an electrically conductive material, a soluble organic phase, and a binder; The soluble organic phase has a water solubility of <0.001 mg / mL at 25 °C.
2. The negative electrode active material according to claim 1, wherein The electrically conductive material comprises at least one of carbon nanotubes, graphene nanoplatelets, conductive carbon black, and nanometal wires.
3. The negative electrode active material according to claim 1, wherein The soluble organic phase comprises at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide-styrene block copolymer, sulfonated polyaniline, and stearic acid and derivatives thereof.
4. The negative electrode active material according to claim 1, wherein The binder comprises at least one of styrene-butadiene rubber and derivatives thereof, polyacrylic acid and derivatives thereof, and polyurethane and derivatives thereof.
5. The negative active material according to claim 1, wherein The silicon-based material comprises at least one of silicon-carbon, silicon-oxygen, and silicon.
6. The negative electrode active material according to claim 1, wherein The negative electrode active material satisfies 0.41≤D1 / D2≤0.97; D1 is a Dv50 particle size of the silicon-based material; and D2 is a Dv50 particle size of the negative electrode active material.
7. The negative electrode active material according to claim 1, characterized by The D1 satisfies 2 μm≤D1≤7.2 μm. And / or, the D2 satisfies 4.9 μm≤D2≤10 μm.
8. The negative electrode active material according to claim 1, wherein The mass percentage content of the soluble organic phase in the composite coating layer is 30-60 %; And / or, the mass percentage content of the electrically conductive material in the composite coating layer is 5-50 %; And / or, the mass percentage content of the binder in the composite coating layer is 10-50 %.
9. The negative electrode active material according to claim 1, wherein The composite coating layer has an elastic modulus Ec, and 0.05 Gpa≤Ec≤8.0 Gpa.
10. A negative electrode sheet characterized by comprising: The negative electrode active material as claimed in any one of claims 1-9.
11. An electrochemical device, characterized by, The negative electrode sheet as claimed in claim 10.
12. An electronic device, comprising: The electrochemical device as claimed in claim 11.