Silicon-carbon negative electrode material, preparation method thereof, secondary battery and electric device

Abstract

The application provides a silicon-carbon negative electrode material, a preparation method thereof, a secondary battery and an electric device. The silicon-carbon negative electrode material comprises carbon fibers and carbon-coated silicon particles located inside the carbon fibers, the carbon fibers are overlapped with each other to form a layered porous network structure, and the silicon-carbon negative electrode material satisfies the following relationship: 4 < a x b x c < 15; wherein a is a half-height width of a G peak in a Raman spectrum of the silicon-carbon negative electrode material; b is a ratio of a D peak intensity to a G peak intensity in the Raman spectrum of the silicon-carbon negative electrode material; and c is a Poisson ratio of the silicon-carbon negative electrode material. ‑1 The application designs the structure of the silicon-carbon negative electrode, coats the silicon with carbon, embeds the silicon inside the carbon fibers, and further overlaps the carbon fibers to form a layered porous network film structure. Meanwhile, the parameters of the silicon-carbon negative electrode material are reasonably controlled to satisfy a specific relationship, which can effectively relieve the volume expansion of the material, improve the conductivity of the material, and improve the cycle performance and rate performance of the material.

Description

Technical Field

[0001] This application relates to the field of anode material technology, and in particular to a silicon-carbon anode material, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-ion rechargeable batteries are the main energy storage devices in the current new energy field. The low capacity of carbon materials, the primary commercially available anode material, has limited the development of lithium-ion rechargeable batteries. Silicon anodes have the highest theoretical specific capacity, but their volume expansion during charge and discharge can reach up to 300%, and silicon has low intrinsic conductivity. The huge volume effect during charge and discharge can cause the electrode material structure to collapse, even peeling off from the current collector, resulting in deterioration of electrochemical performance. Traditional coating methods for electrode structures contain a large proportion of inert components, such as metal current collectors, conductive agents, and binders, increasing both battery weight and internal resistance.

[0003] Therefore, it is necessary to modify the negative electrode material of secondary batteries and design it rationally to improve the overall performance of secondary batteries, such as conductivity, cycle performance, and rate performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery with excellent cycle performance and rate performance.

[0005] To achieve the above objectives, a first aspect of this application provides a silicon-carbon anode material, comprising carbon fibers and carbon-coated silicon particles located within the carbon fibers, wherein the carbon fibers overlap to form a layered porous network structure, and the silicon-carbon anode material satisfies the following relationship:

[0006] 4 <a×b×c<15;

[0007] Among them, a cm -1 The full width at half maximum (FWHM) of the G peak in the Raman spectrum of the silicon-carbon anode material;

[0008] b is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the silicon-carbon anode material;

[0009] c represents the Poisson's ratio of the silicon-carbon anode material.

[0010] As an embodiment of this application, the D peak of the silicon-carbon anode material in the Raman spectrum emerges at 1300 cm⁻¹. -1 ~1380cm -1 .

[0011] As an embodiment of this application, the G peak of the silicon-carbon anode material in the Raman spectrum is located at 1520 cm⁻¹. -1 ~1590cm -1 .

[0012] As an embodiment of this application, the silicon-carbon anode material satisfies: 10cm -1 ≤a≤25cm -1 .

[0013] As an embodiment of this application, the silicon-carbon anode material satisfies: 0.6≤b≤1.5.

[0014] As an embodiment of this application, the silicon-carbon anode material satisfies: 0 < c ≤ 0.5.

[0015] As an embodiment of this application, based on the silicon-carbon anode material, the weight percentage of silicon is 2-15%.

[0016] As an embodiment of this application, based on the silicon-carbon anode material, the weight percentage of the carbon fiber is 35-78%.

[0017] As an embodiment of this application, based on the silicon-carbon anode material, the weight percentage of the carbon coating layer in the carbon-coated silicon particles is 20-50%.

[0018] A second aspect of this application also provides a method for preparing the silicon-carbon anode material described in the first aspect of this application, comprising the following steps:

[0019] After the silicon source and the first carbon source are mixed evenly in a solvent, the second carbon source is added and mixed evenly to form a colloidal precursor solution. The colloidal precursor solution is electrospinned into a film and carbonized to prepare the silicon-carbon anode material.

[0020] The first carbon source is a polar carbon-containing macromolecule that forms a carbon coating layer in carbon-coated silicon particles; the second carbon source is a precursor polymer that forms carbon fibers.

[0021] As an embodiment of this application, the first carbon source includes at least one of epoxy resin, cellulose, and polyvinylidene fluoride.

[0022] As an embodiment of this application, the second carbon source includes at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylonitrile.

[0023] A third aspect of this application provides a secondary battery, the secondary battery comprising a positive electrode, an electrolyte, a separator, and a negative electrode, the negative electrode comprising a negative current collector and a negative active material layer comprising the silicon-carbon negative electrode material described in the first aspect of this application disposed on at least one surface of the negative current collector.

[0024] A fourth aspect of this application also provides an electrical device, which includes the secondary battery described in the third aspect of this application.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This application designs the structure of a silicon-carbon anode by coating silicon with carbon and embedding it inside carbon fibers. The carbon fibers are then overlapped to form a layered, porous, mesh-like thin film structure. At the same time, by reasonably controlling the parameters of the silicon-carbon anode material (such as the ratio of the D peak intensity to the G peak intensity in the Raman spectrum, the full width at half maximum (FWHM) of the G peak, and the Poisson's ratio) to satisfy specific relationships, the volume expansion of the material can be effectively mitigated, the conductivity of the material can be improved, and the cycle performance and rate performance can be enhanced. Detailed Implementation

[0027] To better illustrate the purpose, technical solutions, and advantages of this invention, specific embodiments will be used to further explain the invention below. However, these embodiments do not limit the invention in any way. The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] 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.

[0029] 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.

[0030] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0031] The first aspect of this application provides a silicon-carbon anode material, the silicon-carbon anode material comprising carbon fibers and carbon-coated silicon particles located inside the carbon fibers, the carbon fibers overlapping each other to form a layered porous network structure, and the silicon-carbon anode material satisfying the following relationship:

[0032] 4 <a×b×c<15;

[0033] Among them, a cm -1 The full width at half maximum (FWHM) of the G peak in the Raman spectrum of the silicon-carbon anode material;

[0034] b is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the silicon-carbon anode material;

[0035] c represents the Poisson's ratio of the silicon-carbon anode material.

[0036] This application designs the structure of a silicon-carbon anode by coating silicon with carbon and embedding it inside carbon fibers. The carbon fibers are then overlapped to form a layered, porous, mesh-like thin film structure. At the same time, by reasonably controlling the parameters of the silicon-carbon anode material (such as the ratio of the D peak intensity to the G peak intensity in the Raman spectrum, the full width at half maximum (FWHM) of the G peak, and the Poisson's ratio) to satisfy specific relationships, the volume expansion of the material can be effectively mitigated, the conductivity of the material can be improved, and the cycle performance and rate performance can be enhanced.

[0037] It should be noted that the silicon-carbon anode material of this application is in the form of a fibrous film. The carbon fiber matrix therein can be used as part of the anode active material and can also be used as a current collector. Therefore, the silicon-carbon anode material of this application can be pressed into a sheet and used as a negative electrode sheet without being loaded onto the surface of a metal current collector.

[0038] In some embodiments, the D peak of the silicon-carbon anode material in the Raman spectrum emerges at 1300 cm⁻¹. -1 ~1380cm -1 .

[0039] In some embodiments, the G peak of the silicon-carbon anode material in the Raman spectrum emerges at 1520 cm⁻¹. -1 ~1590cm -1 .

[0040] In some embodiments, the silicon-carbon anode material satisfies: 10cm -1 ≤a≤25cm -1 In this application, a (unit: cm) -1 The value 'a' represents the full width at half maximum (FWHM) of the G peak in the Raman spectrum of the silicon-carbon anode material, i.e., the difference between the two wavelengths corresponding to half the intensity of the G peak. The FWHM 'a' is related to the defect concentration and disorder of the hard carbon material in the silicon-carbon anode material. Specifically, the defect concentration of the hard carbon material affects the obstruction of lithium-ion migration in the solid phase, thus affecting the kinetic performance of the hard carbon material; simultaneously, the disorder of the hard carbon material reflects, to some extent, the capacity of the silicon-carbon anode material. When the G peak intensity 'a' of the silicon-carbon anode material is within the above range, the defect concentration and disorder of the carbon material are moderate, and lithium-ion secondary batteries using this silicon-carbon anode material as the anode active material exhibit superior first-cycle coulombic efficiency and cycle rate performance. For example, the value of 'a' can specifically be 10.5 cm⁻¹. -1 11.0cm -114.5cm -1 16.2cm -1 18.3cm -1 25.0cm -1 The value in the range of any one or any two values ​​is further preferably 12cm. -1 ≤a≤20cm -1 .

[0041] In some embodiments, the silicon-carbon anode material satisfies: 0.6 ≤ b ≤ 1.5, more preferably 0.8 ≤ b ≤ 1.2. For example, the value of b can specifically be any one or any two values ​​from 0.75, 0.99, 1.05, 1.31, 1.39, and 1.50. b = ID / IG represents the defect concentration of the silicon-carbon anode material, which is the ratio of the D peak intensity (represented by ID) to the G peak intensity (represented by IG) in the Raman spectrum of the silicon-carbon anode material. When the value of b is within the above-mentioned suitable range, the silicon-carbon anode material has a suitable defect concentration and a moderate number of active reaction sites, which can effectively balance the contradiction between side reactions and lithium storage capacity during the charging and discharging process of lithium-ion secondary batteries, resulting in a battery with first-cycle coulombic efficiency and long cycle life.

[0042] In some embodiments, the silicon-carbon anode material satisfies: 0 < c ≤ 0.5, preferably 0.4 ≤ c ≤ 0.49. c is the Poisson's ratio of the silicon-carbon anode material, which is the elastic coefficient of the material's deformation and is positively correlated with the material's bending effect. Silicon-carbon anode materials within this Poisson's ratio range possess sufficient flexibility, and during the charging and discharging process of a lithium-ion secondary battery, the specific distribution between the carbon fibers and carbon-coated silicon particles in the silicon-carbon anode material can effectively buffer the volume change of silicon during charging and discharging. The combination of carbon fibers and carbon-coated silicon particles also greatly improves the conductivity of the silicon-carbon anode material, thereby significantly enhancing the cycle performance and rate performance of the lithium-ion secondary battery. For example, the value of c can be any one of 0.30, 0.35, 0.39, 0.45, 0.48, or 0.49, or a range between any two values.

[0043] In some embodiments, based on the silicon-carbon anode material, the weight percentage of silicon is 2-15%, exemplarily any one of 2%, 10%, and 15%, or a range between any two values. Silicon has a higher ability to insert and extract lithium ions, thus improving the energy storage capacity of lithium batteries. However, during the lithium ion insertion and extraction process, its volume expands, which affects the cycle life and rate performance of lithium-ion secondary batteries. A suitable silicon content in the anode material allows the prepared lithium-ion secondary battery to possess both high first-cycle coulombic efficiency and high rate performance.

[0044] In some embodiments, based on the silicon-carbon anode material, the weight percentage of the carbon coating layer in the carbon-coated silicon particles is 20% to 50%, specifically any one of 20%, 30%, and 50%, or a range between any two values.

[0045] In some embodiments, based on the silicon-carbon anode material, the weight percentage of the carbon fiber is 35% to 78%, and specifically, it can be any one of 35%, 40%, 60%, and 78%, or a range between any two values.

[0046] The ratio of the two carbon materials and silicon in the silicon-carbon anode material affects its structure, especially the integrity of the carbon coating, which in turn affects its cycle performance. The parameters of the silicon-carbon anode material can be adjusted to control the proportions of each component within a suitable range, thereby ensuring its excellent electrochemical performance.

[0047] The second aspect of this application provides a method for preparing the silicon-carbon anode material described in the first aspect of this application, comprising the following steps:

[0048] After the silicon source and the first carbon source are mixed evenly in a solvent, the second carbon source is added and mixed evenly to form a colloidal precursor solution. The colloidal precursor solution is electrospun into a film and carbonized to prepare the silicon-carbon anode material. The first carbon source is a polar carbon macromolecule that forms a carbon coating layer in the carbon-coated silicon particles. The second carbon source is a precursor polymer that forms carbon fibers.

[0049] In some embodiments, the first carbon source includes at least one of epoxy resin, cellulose, and polyvinylidene fluoride. The first carbon source forms a carbon coating layer in the carbon-coated silicon particles.

[0050] In some embodiments, the second carbon source includes at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylonitrile. The second carbon source can form a carbon fiber matrix.

[0051] In some embodiments, the silicon source includes at least one of silicates, elemental silicon, and silicon dioxide; preferably silicates, which have better compatibility with the first and second carbon sources, and the resulting silicon-carbon anode material has a more uniform structural distribution. The silicates include at least one of sodium silicate, lithium silicate, potassium silicate, and ammonium silicate.

[0052] In some embodiments, the solvent includes at least one selected from water, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, and ethylene carbonate. Conventional electrospinning solvents in the art can be used in this application.

[0053] In some embodiments, the mass concentration of the silicon source in the colloidal precursor solution is 1% to 20%.

[0054] In some embodiments, the parameters of the electrospinning are: glue pushing speed 0.1-0.5 mL / h, spinning distance 10-20 cm, spinning voltage 10-25 kV, and collector rotation speed 150-300 rpm.

[0055] In some embodiments, the carbonization process parameters are: heating rate of 2-10℃ / min; carbonization temperature of 800-1100℃; and carbonization time of 1-4h.

[0056] A third aspect of this application provides a secondary battery, the secondary battery comprising the silicon-carbon anode material described in the first aspect of this application, specifically: the secondary battery comprises a positive electrode, an electrolyte, a separator, and a negative electrode formed from the silicon-carbon anode material described in the first aspect of this application.

[0057] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer containing a negative active material.

[0058] The type of positive current collector is not specifically limited and can be selected according to actual needs.

[0059] The positive electrode current collector may include, but is not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and composite materials formed by polymers and metal layers. In some embodiments, aluminum foil is preferably used as the positive electrode current collector.

[0060] In this application, the type of positive electrode active material is not limited and can be selected according to actual needs. For example, the positive electrode active material can be lithium iron phosphate, lithium manganese iron phosphate, or ternary positive electrode material. The positive electrode active material may also contain doping elements and / or coating elements. There are no special requirements for doping elements and / or coating elements, as long as they can make the positive electrode active material more stable.

[0061] In addition, the positive electrode active material layer also contains at least one of a conductive agent, a binder, and a thickener.

[0062] Commonly used battery conductive agents, binders, and thickeners in this field can all be used in this application.

[0063] In some embodiments, the conductive agent includes, but is not limited to, at least one of graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0064] In some embodiments, the adhesive includes, but is not limited to, at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer.

[0065] In some embodiments, the thickener includes, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0066] In some embodiments, there is no limitation on the type of solvent used to form the positive electrode slurry and / or negative electrode slurry, as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, the negative electrode active material, the conductive agent, the binder, or the dispersant.

[0067] In the secondary battery described in this application, the type of separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene membrane, a polyethylene membrane, a polyvinylidene fluoride membrane, a spandex membrane, an aramid membrane, or a multilayer composite membrane modified with a coating.

[0068] In the secondary battery described in this application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0069] In some embodiments, the preparation of a secondary battery includes: stacking a positive electrode, a separator, and a negative electrode in sequence, with the separator acting as a separator between the positive and negative electrodes; then winding the battery into a square bare battery; inserting it into a battery casing; baking it at 65–95°C to remove water; injecting electrolyte; sealing the battery; and then performing processes such as standing, hot and cold pressing, formation, clamping, and capacity testing to obtain a secondary battery.

[0070] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch, made of plastic, such as one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate. The shape of the secondary battery is not particularly limited; it may be cylindrical, square, or any other arbitrary shape.

[0071] A fourth aspect of this application provides an electrical device comprising the secondary battery described in the third aspect. The electrical device can be an application device such as a vehicle, mobile phone, portable device, laptop, ship, spacecraft, electric toy, and power tool. Vehicles can be new energy vehicles, including pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles; spacecraft include airplanes, rockets, space shuttles, and spacecraft; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. The embodiments of this application do not impose special limitations on the above-described device.

[0072] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0073] Example 1

[0074] A silicon-carbon anode material is provided, and the preparation method of the silicon-carbon anode material specifically includes the following steps:

[0075] Weigh the raw materials according to the proportions in Table 1. Add epoxy resin (i.e., the aforementioned first carbon source) and sodium silicate to a 66.67 wt% ethanol aqueous solution, mix them evenly, add polyvinylpyrrolidone (i.e., the aforementioned second carbon source), ultrasonically stir for 30 min, and stir at room temperature for 12 h to form a homogeneous colloidal precursor solution (the mass concentration of sodium silicate in the colloidal precursor solution is 1.70 wt%).

[0076] The prepared colloidal precursor solution was injected into a syringe, and electrospinning was performed with a pushing speed of 0.25 mL / h, a spinning distance of 15 cm, a spinning voltage of 15 kV, and a collector rotation speed of 200 rpm. The resulting product was collected and dried in a drying oven at 50 °C for 12 h, and then placed in an argon atmosphere tube furnace and heated to 1000 °C at 5 °C / min, held at that temperature for 2 h, and cooled to room temperature (25 ± 5 °C) to obtain the silicon-carbon anode material. The characterization of the relevant parameters of the obtained silicon-carbon anode material is detailed in Table 1.

[0077] Examples 2-13, Comparative Examples 1-2

[0078] A series of silicon-carbon anode materials are provided and prepared according to the method of Example 1. By changing the type and proportion of raw materials, electrospinning parameters (including spinning distance, etc.), carbonization temperature and time, etc. in Example 1, silicon-carbon anode materials with different parameters are obtained. The parameters of the obtained silicon-carbon anode materials are detailed in Table 1.

[0079] Comparative Example 3

[0080] A silicon-carbon anode material is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that the epoxy resin (first carbon source) is replaced with an equal mass of polyvinylpyrrolidone (second carbon source), and the electrospinning parameters and carbonization temperature are adjusted to ensure that the relationship between the parameters satisfies the same calculated value of a×b×c as in Example 1.

[0081] Comparative Example 4

[0082] A silicon-carbon anode material is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that the second carbon source, polyvinylpyrrolidone, is replaced with an equal mass of epoxy resin (first carbon source), that is, no second carbon source, polyvinylpyrrolidone, is added. The electrospinning parameters and carbonization temperature are adjusted to ensure that the relationship between the parameters satisfies the same calculated value of a×b×c as in Example 1.

[0083] Comparative Example 5

[0084] A silicon-carbon anode material is provided, which is prepared according to the method of Comparative Example 3. The difference from Comparative Example 3 is that the electrospinning parameters and carbonization temperature are adjusted to ensure that the relationship between the parameters is a×b×c<4.

[0085] Comparative Example 6

[0086] A silicon-carbon anode material is provided, which is prepared according to the method of Comparative Example 4. The difference from Comparative Example 3 is that the electrospinning parameters and carbonization temperature are adjusted to ensure that the relationship between the parameters a×b×c>15.

[0087] Parameters related to silicon-carbon anode materials:

[0088] 1) In this application, the proportion of each component in the silicon-carbon anode material product can be calculated by thermogravimetric differential thermal analysis (TG-DTA). The specific calculation method is as follows: the silicon-carbon anode material is tested under an argon atmosphere to obtain a thermogravimetric differential thermal curve. Then, the content of silicon material and carbon material is calculated based on the weight loss curve. Then, the content of carbon fiber matrix and coated carbon layer is further calculated based on the ratio of the two carbon sources. The specific results are detailed in Table 1.

[0089] 2) In this application, the specific conditions for Raman spectroscopy testing of the silicon-carbon anode material are as follows: the material is placed under a Raman spectrometer and tested at a constant temperature of 25°C. The ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the material is b: b = I D / I G , among which, I D This represents the intensity of the D peak in the Raman spectrum of the material. The D peak has a wavelength of 1350 cm⁻¹ in the Raman spectrum. -1 Nearby (1300cm selected in this application) -1 -1380cm -1 (within the range); I G This represents the intensity of the G peak in the Raman spectrum of the material. The G peak has a wavelength of 1580 cm⁻¹ in the Raman spectrum. -1 Nearby (1520cm selected in this application) -1 -1590cm -1 (within the range);

[0090] 3) Poisson's ratio c: The test results were obtained by using a tensile testing machine according to the method in the standard GB / T3354-2014. The tensile rate was 50 mm / min and the test temperature was room temperature (i.e., 25±5℃). The test results are detailed in Table 1.

[0091] Table 1 Parameters of silicon-carbon anode materials

[0092]

[0093] The silicon-carbon anode materials provided in the above embodiments and comparative examples were used to prepare batteries, and their electrochemical performance was tested. The specific preparation process includes the following steps:

[0094] Preparation of positive electrode sheet

[0095] Lithium iron phosphate (LiFePO4), a positive electrode active material, acetylene black (acetylene black), PVP (polyvinylidene fluoride), and polyvinylidene fluoride (PVDF) (a binder) were dispersed in NMP at a mass ratio of 96:1.2:1:1.8 to prepare a slurry. This slurry was then coated onto both sides of an aluminum foil. After baking, rolling, and cutting, the positive electrode sheet (area density 0.22 g / 1540.25 mm²) was obtained. 2 );

[0096] Preparation of negative electrode sheet

[0097] The silicon-carbon anode active materials prepared in the above examples and comparative examples were compacted to obtain anode sheets (area density 0.135 g / 1540.25 mm²). 2 );

[0098] Preparation of electrolyte

[0099] EC and DMC were mixed at a volume ratio of 1:1, and then lithium hexafluorophosphate was added in a glove box to prepare an electrolyte with a concentration of 1 mol / L.

[0100] Battery assembly

[0101] The prepared positive electrode sheet, polyethylene separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, a bare cell is obtained. The bare cell is placed in an outer packaging shell, vacuum dried, and then injected with electrolyte. After standing, formation, shaping, and capacity testing, a secondary battery is obtained.

[0102] The performance of the secondary batteries obtained in the above embodiments and comparative examples was tested. The specific test items, test methods, and results are as follows:

[0103] 1. Cyclic performance test:

[0104] The secondary battery was placed in a charge-discharge test chamber at a constant temperature of 25°C, with a charge rate of 1C and a discharge rate of 1C. Cyclic testing was performed within a voltage range of 2.5 to 3.65V. When the capacity dropped to 80% of the initial capacity, the test was stopped, and the first discharge capacity and the number of cycles were recorded.

[0105] Take the negative electrode plate before and after the secondary battery cycle, place the negative electrode plate under a resistance meter to measure the resistance value of the electrode plate, and record the initial electrode plate resistance (ρ0) and the electrode plate resistance after the cycle (ρ...). t ), and calculate the rate of change of resistance of the negative electrode = (ρ t )-ρ0) / ρ0*100%;

[0106] 2. Ratio Performance Test:

[0107] The secondary battery was placed in a charge-discharge test cabinet and kept at a constant temperature of 25°C. The charging rate was 1C, and the discharging rates were 1C and 5C. After 5 cycles in the voltage range of 2.5 to 3.65V, the capacity at different rates was recorded and denoted as C1 and C5, respectively. The capacity retention rate at 5C rate was calculated as C5 / C1*100%.

[0108] 3. Bending stiffness: Take an electrode made of this material, place the electrode under a bending test machine, and use the 2-point bending test method to determine the bending stiffness of the electrode according to DIN 53121 or ISO 5628 standards.

[0109] Table 2. Performance test results of the negative electrode sheets and batteries prepared in the examples and comparative examples.

[0110]

[0111]

[0112] The results above show that:

[0113] From the above embodiments and comparative examples, it can be seen that by designing the structure of the silicon-carbon anode, silicon is coated with carbon and embedded inside the carbon fibers, and the carbon fibers are further overlapped to form a layered, porous, mesh-like thin film structure. At the same time, by reasonably controlling the parameters of the silicon-carbon anode material (such as the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum, the full width at half maximum (FWHM) of the G peak, and the Poisson's ratio) to satisfy specific relationships, the volume expansion of the material can be effectively mitigated, the conductivity of the material can be improved, and the cycle performance and rate performance can be enhanced.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention 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 the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material comprises carbon fibers and carbon-coated silicon particles located inside the carbon fibers, wherein the carbon fibers overlap to form a layered porous network structure; based on the silicon-carbon anode material, the weight percentage of silicon is 2-15%, the weight percentage of carbon fibers is 35-78%, and the weight percentage of the carbon coating layer in the carbon-coated silicon particles is 20-50%; the silicon-carbon anode material satisfies the following relationship: 4 <a×b×c<15; acm -1 The full width at half maximum (FWHM) of the G peak in the Raman spectrum of the silicon-carbon anode material satisfies: 10 cm⁻¹ -1 ≤a≤25cm -1 ; b is the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the silicon-carbon anode material, satisfying: 0.6≤b≤1.5; c is the Poisson's ratio of the silicon-carbon anode material, satisfying: 0 < c ≤ 0.

5.

2. The silicon-carbon anode material according to claim 1, characterized in that, In the Raman spectrum, the D peak of the silicon-carbon anode material emerges at 1300 cm⁻¹. -1 ~1380cm -1 .

3. The silicon-carbon anode material according to claim 1, characterized in that, In the Raman spectrum, the G peak of the silicon-carbon anode material emerges at 1520 cm⁻¹. -1 ~1590cm -1 .

4. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: After the silicon source and the first carbon source are mixed evenly in a solvent, the second carbon source is added and mixed evenly to form a colloidal precursor solution. The colloidal precursor solution is electrospinned into a film and carbonized to prepare the silicon-carbon anode material. The first carbon source is a polar carbon-containing macromolecule that forms a carbon coating layer in carbon-coated silicon particles; the second carbon source is a precursor polymer that forms carbon fibers.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, The first carbon source includes at least one of epoxy resin, cellulose, and polyvinylidene fluoride.

6. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, The second carbon source includes at least one of polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylonitrile.

7. A secondary battery, comprising a positive electrode, an electrolyte, a separator, and a negative electrode, characterized in that, The negative electrode sheet comprises the silicon-carbon negative electrode material as described in any one of claims 1 to 3.

8. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 7.

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