Battery negative electrode, secondary battery, negative electrode material and preparation method of negative electrode material

Abstract

The invention discloses a battery negative electrode, a secondary battery, a negative electrode material and a preparation method of the negative electrode material. The negative electrode material comprises an inner core which at least comprises a silicon-containing material; a cover layer containing at least a polymer having an amide group; wherein the covering layer is used for covering the inner core. The preparation method has the beneficial effects that the polymer covers the inner core during reaction, so that the problem caused by expansion of the inner core during charging and discharging is effectively solved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a battery negative electrode, a secondary battery, a negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have become an integral part of our daily lives, driven by technological advancements and increasing environmental protection requirements. Graphite-based anode materials are traditionally used, offering advantages such as low volume change during lithiation, low potential, stable structure, and low cost. Currently, demands for higher energy density in lithium batteries are increasing to extend battery life. Silicon-based anode materials, with their high reversible capacity, are considered the next generation of anode materials that can replace graphite and be widely adopted.

[0003] However, silicon-based negative electrode materials have a large volume expansion during the charging and discharging process. The volume expansion will cause the destruction of the solid electrolyte interface film, constantly exposing the fresh material surface, resulting in the repeated formation of the solid electrolyte interface film and the continuous consumption of electrolyte, accelerating the attenuation of material performance and battery capacity. Summary of the Invention

[0004] In view of this, the present application provides a battery negative electrode, a secondary battery, a negative electrode material and a preparation method thereof, aiming to solve the above-mentioned technical problems.

[0005] In a first aspect, the present application provides a negative electrode material comprising:

[0006] a core comprising at least a silicon-containing material;

[0007] a covering layer comprising at least a polymer having amide groups;

[0008] The covering layer covers the core; and the chromaticity of the negative electrode material ranges from 15 to 50.

[0009] Optionally, in some embodiments of the present application, the particle size of the negative electrode material ranges from 4 μm to 8 μm.

[0010] Optionally, in some embodiments of the present application, the carbon content of the negative electrode material ranges from 3% to 8%.

[0011] Optionally, in some embodiments of the present application, the specific surface area of ​​the negative electrode material is in the range of 0.5 m 2 / g to 1m 2 / g.

[0012] Optionally, in some embodiments of the present application, the pH value of the negative electrode material ranges from 3 to 6.

[0013] Optionally, in some embodiments of the present application, the silicon-containing material is selected from one or more of silicon-oxygen materials and silicon-carbon materials.

[0014] Optionally, in some embodiments of the present application, the mass ratio of the covering layer in the negative electrode material ranges from 0.1% to 10%.

[0015] Optionally, in some embodiments of the present application, the covering layer is obtained by reacting at least a first substance and a second substance, the first substance is a polymer having an amino group, the second substance is an organic substance having a carboxyl group, and the mass ratio of the first substance to the second substance ranges from 0.2 to 10.

[0016] In a second aspect, the present application provides a battery negative electrode, comprising: a foil material and a slurry layer; wherein the slurry layer is made of the negative electrode material as described above.

[0017] Optionally, in some embodiments of the present application, the indentation hardness of the negative electrode ranges from 0.5 to 5;

[0018] Optionally, in some embodiments of the present application, the elastic recovery rate of the negative electrode ranges from 71 to 89.

[0019] Optionally, in some embodiments of the present application, the peel strength of the slurry layer of the negative electrode ranges from 3.0 N / m to 9.0 N / m.

[0020] In a third aspect, the present application provides a method for preparing a negative electrode material, comprising: providing a silicon-containing material to form a core; covering the core with a polymer having an amide group to form a covering layer; wherein the chromaticity value of the negative electrode material prepared by the preparation method ranges from 17 to 36.

[0021] Optionally, in some embodiments of the present application, the core is covered with a polymer having an amide group to form a covering layer, comprising:

[0022] mixing the silicon-containing material and the first substance in a solvent to obtain a first solution;

[0023] adding a second substance to the first solution and reacting the second substance with the first substance to obtain a second solution;

[0024] Stirring the second solution and then drying it to obtain a dry product;

[0025] The dried product is subjected to a heat treatment under a preset atmosphere to obtain the negative electrode material.

[0026] Optionally, in some embodiments of the present application, the first substance is a polymer having an amino group, and the second substance is an organic substance having a carboxyl group; the mass ratio of the first substance to the second substance ranges from 0.2 to 10.

[0027] Optionally, in some embodiments of the present application, the solvent is deionized water;

[0028] Optionally, in some embodiments of the present application, the stirring time of the stirring process ranges from 1 h to 5 h;

[0029] Optionally, in some embodiments of the present application, the gas of the preset atmosphere includes one or more of nitrogen and argon;

[0030] Optionally, in some embodiments of the present application, the heating temperature of the heat treatment ranges from 150° C. to 250° C.;

[0031] Optionally, in some embodiments of the present application, the heating time of the heating treatment ranges from 1 hour to 6 hours.

[0032] In a fourth aspect, the present application provides a secondary battery, comprising the above-mentioned negative electrode material, the above-mentioned battery negative electrode, or the negative electrode material prepared by the above-mentioned preparation method.

[0033] The beneficial effect of the present application is that the problem caused by the expansion of the silicon-containing core during charging and discharging is effectively solved by covering the silicon-containing core with the polymer during the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 is a schematic structural diagram of the negative electrode material provided in some embodiments of the present application;

[0036] Figure 2 is an SEM image of the negative electrode material provided in some embodiments of the present application;

[0037] Figure 3 Schematic diagram of the main steps of the negative electrode material preparation method provided in some embodiments of the present application;

[0038] Figure 4 1 is the infrared spectrum of Comparative Example 1 and Example 1 in the present application;

[0039] Figure 5 1 is the corresponding relationship curve between indentation depth and pressure of Comparative Example 1 and Example 1 in this application;

[0040] Figure 6 1 is a curve showing the corresponding relationship between the capacity retention rate and the number of cycles of Comparative Example 1 and Example 1 in the present application;

[0041] Figure 7 This is the corresponding relationship curve between A / B and indentation hardness of Examples 17, 21 to 30 in this application.

[0042] Figure 8 This is the corresponding relationship curve between A / B and elastic recovery rate of Examples 17, 21 to 30 in this application.

[0043] Figure 9 This is the corresponding relationship curve between A / B and peel strength of Examples 17, 21 to 30 in this application.

[0044] Figure 10 This is the corresponding relationship curve between A / B and gram performance of Examples 17, 21 to 30 in this application.

[0045] Figure 11 This is the corresponding relationship curve between A / B and capacity retention rate of Examples 17, 21 to 30 in this application.

[0046] The meaning of the reference numerals in the figures:

[0047] 100. Negative electrode material; 110. Core; 120. Covering layer. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of a device in actual use or operation, specifically in the drawing directions of the accompanying drawings; whereas "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "including" means "including but not limited to." Terms such as first, second, and third are used merely as labels and do not impose numerical requirements or establish a sequence.

[0051] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0052] In this application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or plural, respectively.

[0053] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0054] As a first aspect, refer to Figure 1 As shown, the present application provides a negative electrode material comprising: a core, comprising at least a silicon-containing material; a covering layer, comprising at least a polymer having an amide group; wherein the covering layer covers the core; the chromaticity value range of the negative electrode material is 15 to 50, and can further be 17 to 36; or, further, it can also be 16, 20, 24, 28, 33, 37, 41, 44, 47, 49 and the numerical range between any two of them.

[0055] Figure 2This is the SEM image of the negative electrode material provided in Example 1 of the present application, referring to Figure 2 As shown, the microstructure of the powder of the negative electrode material has a core and a covering layer.

[0056] In some embodiments of the present application, the particle size of the negative electrode material ranges from 4 μm to 8 μm.

[0057] In some embodiments of the present application, the carbon content of the negative electrode material ranges from 3% to 8%.

[0058] In some embodiments of the present application, the specific surface area of ​​the negative electrode material is in the range of 0.5 m 2 / g to 1m 2 / g.

[0059] In some embodiments of the present application, the pH value of the negative electrode material ranges from 3 to 6.

[0060] In some embodiments of the present application, the silicon-containing material is selected from at least one of a silicon-oxygen material and a silicon-carbon material.

[0061] In some embodiments of the present application, the mass ratio of the covering layer in the negative electrode material ranges from 0.1% to 10%, and can further range from 2% to 8%.

[0062] In some embodiments of the present application, the covering layer is obtained by reacting at least a first substance and a second substance, the first substance is a polymer having an amino group, and the second substance is an organic substance having a carboxyl group. The mass ratio of the first substance to the second substance ranges from 0.2 to 10, and can further be 3 to 4, or 0.25 to 0.5, or specifically 2.5.

[0063] As a second aspect, the present application also provides a battery negative electrode, comprising: a foil material and a slurry layer; wherein the slurry layer is made of the above-mentioned negative electrode material.

[0064] In some embodiments of the present application, the indentation hardness of the battery negative electrode ranges from 0.5 to 5; further optionally, it can be 0.8 to 3.8, and further can be 1.0, 1.2, 1.3, 1.5, 1.8, 2.0, 2.2, 2.8 and the numerical range between any two of them.

[0065] In some embodiments of the present application, the elastic recovery rate of the battery negative electrode ranges from 71 to 89; further optionally from 71 to 86; further, it can be 71.5, 72.6, 73.4, 75.1, 76.7, 78.1, 81.3, 84.1 and the numerical range between any two of them.

[0066] In some embodiments of the present application, the peel strength of the slurry layer of the battery negative electrode ranges from 3.0 N / m to 9.0 N / m.

[0067] As a third aspect, refer to Figure 3 As shown, the present application provides a method for preparing a negative electrode material, which specifically includes the following steps:

[0068] S100: providing a silicon-containing material to form a core;

[0069] S200: Covering the inner core with a polymer having an amide group to form a covering layer.

[0070] Among them, the chromaticity value range of the negative electrode material is 17 to 36.

[0071] In some implementations of the present application, S200 specifically includes:

[0072] S210: mixing a silicon-containing material and a first substance in a solvent to obtain a first solution;

[0073] S220: adding a second substance to the first solution and reacting with the first substance to obtain a second solution;

[0074] S230: stirring the second solution and then drying it to obtain a dry product;

[0075] S240: The dried product is subjected to a heat treatment under a preset atmosphere to obtain a negative electrode material.

[0076] In some embodiments of the present application, the first substance is a polymer having an amino group, and the second substance is an organic substance having a carboxyl group; the mass ratio of the first substance to the second substance ranges from 0.2 to 10.

[0077] In some embodiments of the present application, the solvent is deionized water.

[0078] In some embodiments of the present application, the stirring time of the stirring process ranges from 1 hour to 5 hours.

[0079] In some embodiments of the present application, the gas of the preset atmosphere includes one or more of nitrogen and argon.

[0080] In some embodiments of the present application, the heating temperature of the heat treatment ranges from 150°C to 250°C.

[0081] In some embodiments of the present application, the heating time of the heating treatment ranges from 1 hour to 6 hours.

[0082] As a fourth aspect, the present application provides a secondary battery, comprising the above-mentioned negative electrode material, the above-mentioned battery negative electrode, or the negative electrode material prepared by the above-mentioned preparation method.

[0083] As a specific solution, the preparation method of the present application is as follows:

[0084] A first substance containing amino groups (ranging from 0.1 g to 10 g) is dissolved in a desolvent (such as deionized water), stirred until the first substance is dissolved, and then a certain amount (100 g) of silicon-containing material (such as silicon dioxide) particles are added and stirred and dispersed to obtain a first product.

[0085] A second substance containing a carboxylic acid group (ranging from 0.1 g to 10 g) is added to the first product, followed by stirring and dispersion (duration ranging from 1 h to 5 h), and finally rotary evaporation and drying to remove the solvent to obtain a second product (powder state).

[0086] The second product is transferred to a sealed container, and an inert gas (such as nitrogen or argon) is injected into the sealed container to form an inert atmosphere, so that the temperature inside the sealed container is raised to a set temperature (ranging from 150°C to 250°C), thereby heating the second product to a set time (1h to 6h), and the first substance and the second substance undergo dehydration reaction of the amino and carboxyl groups at high temperature; after the set time is met, it is naturally cooled (cooled to room temperature) to obtain the negative electrode material (powder state) of the present application.

[0087] The first substance may be an amino polymer selected from or including one or more of polyacrylamide, polymethacrylamide, poly(N-methylpropyleneamine), poly(N-methylacrylamide), polyethyleneimine, polyamino-modified silicone, and polyglucosamine.

[0088] The second substance may be an acidic substance containing a carboxylic acid group, such as citric acid, 3,4,5-trihydroxybenzoic acid, polyacrylic acid, or poly(4-vinylbenzoic acid).

[0089] By adopting the above preparation method, the first substance, the second substance and the silicon-containing material are mixed as designed and sintered, so that a network structure based on the first substance and the second substance can be formed on the particle surface of the silicon-containing material.

[0090] The second substance plays an important role in the covering layer. Since the second substance has a carboxylic acid group, this property enables it to interact with the first substance containing an amino group (such as polyacrylamide, polymethacrylamide, etc.).

[0091] The carboxylic acid group and the amino group can form hydrogen bonds or undergo amidation reactions, thereby establishing a chemical bond between the first and second substances. This complementary chemical structure ensures that the two can be tightly bound together to form a stable polymer network structure.

[0092] Furthermore, when the first substance and the second substance are mixed, they act together on the surface of the silicon-containing core to form a dense polymer network covering layer; the covering layer not only fits tightly to the silicon-containing core, but also effectively prevents the silicon-containing core from falling off due to volume changes during charging and discharging.

[0093] Because the polymer network has a certain degree of elasticity and toughness, it can adapt to the volume changes of the silicon-containing core, thereby maintaining the integrity and stability of the covering layer.

[0094] Furthermore, the introduction of a capping layer significantly enhances the electrochemical performance of silicon-based materials. The capping layer reduces direct contact between the silicon-containing core and the electrolyte, thereby lowering interfacial resistance and improving charge transfer efficiency. Furthermore, the capping layer prevents the silicon-containing core from pulverizing and shedding during charge and discharge, maintaining unobstructed access for electrons and ions, ensuring that the silicon-based material can continue to deliver its effective electrochemical capacity.

[0095] In addition, since the polymer network has a certain buffering effect, it can reduce the stress generated by the silicon-containing core during volume change, thereby extending the cycle life and stability of silicon-based materials.

[0096] The detection method involved in this application is described in detail as follows.

[0097] Indentation hardness and elastic recovery rate test

[0098] The powder material, conductive agent superP, and LA133 adhesive were mixed into a slurry in a ratio of 75:15:10 and evenly applied to the copper foil. After drying, it was prepared into a negative electrode plate, and a silicon oxide plate with a thickness of 50μm was prepared. The prepared plate was tested using a Shimadzu ultra-micro dynamic hardness tester DUH-211. Fifteen test sites were randomly selected on each plate to ensure that the test sites were fully representative of the sample. The indentation hardness (Hit) was calculated according to the load-unloading curve formula 1: The indentation hardness (Hit) is defined as the value measuring the resistance to semi-permanent deformation or damage.

[0099] Hit=Fmax / Ap (Formula 1)

[0100] Where, Fmax is the maximum test force, and Ap is the projected area of ​​contact between the indenter and the test piece.

[0101] The elastic recovery rate (Rer) is calculated using the load-unloading curve formula 2: When the test force is fixed at 1 mN and the change in the indentation depth is measured, the relative change in the indentation depth (elastic recovery rate) can be calculated.

[0102] Rer=(h1-h2) / h1 (Formula 2)

[0103] h1: The indentation depth when the set test force is reached, h2: The indentation depth maintained when the test force drops to 0.

[0104] Median particle size (D50) test

[0105] Particle size was measured using an MS3000 laser particle size analyzer. The principle is to measure the intensity of scattered light when a laser beam passes through a dispersed particle sample. The particle size distribution of the material is then simulated based on the scattering spectrum. D represents the particle size corresponding to the 50% cumulative particle size distribution percentage for a sample.

[0106] McAb surface area test

[0107] The nitrogen adsorption-desorption test (BET method) was performed using a Micromeritics TriStar II 3030 fully automatic specific surface area and porosity analyzer to measure the amount of gas adsorbed on the solid surface at different relative pressures at constant temperature and low temperature. The monolayer adsorption amount of the sample was obtained and the specific surface area of ​​the material was calculated.

[0108] Pole peel strength test

[0109] The prepared negative electrode material was mixed with graphite in a ratio of 9:1. The mixture was then mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6), and carbon black (SP) in a ratio of 92:2:2:2:2 in an aqueous solvent to form a slurry. The slurry was then evenly coated onto copper foil and dried to form the electrode. A mirror-finished steel plate was wiped with alcohol. Double-sided tape was applied to the mirror-finished copper plate, ensuring a firm bond and free of bubbles. The electrode plate prepared as described above was cut into strips of 25 mm wide and 220 mm long, respectively. The powder-coated side was adhered to the steel plate with double-sided tape, parallel to the plate. The electrode was rolled back and forth three times using an automatic roller press. The stripper was turned on, the stripping speed set to 100 mm / min, the lower clamp clamped the steel plate, and the upper clamp clamped the electrode. The test was then reset and the test was started using a Shimadzu AG-X50N stripper. Each material was tested five times, and the average value was taken. The peel strength was calculated according to the formula: T = P / B, where T represents the peel strength (N / m), P is the average peel force (N), and B is the sample test width (m).

[0110] pH test

[0111] The powder particles were fully mixed with water, and then the pH value of the aqueous solution was measured using a PHS-3C pH meter.

[0112] Chroma test

[0113] Bake the sample to be tested in an oven at 100°C for 24 hours to remove excess moisture, weigh 1g of powder and 10mL of commercial electrolyte LBC3401A57 and mix them, seal the container, and let it stand for 48 hours. Clean the cuvette with anhydrous ethanol and wipe it dry with a dust-free cloth. Wait 5 minutes for the anhydrous ethanol to completely evaporate. Pour ultrapure water into the cuvette to 2 / 3 of its height, press the Zero key to zero, pour out the ultrapure water in the cuvette, then clean it with anhydrous ethanol, wipe it dry with a dust-free cloth, wait 5 minutes for the cuvette to completely dry, and after drying, pour 2 / 3 of the volume of the sample to be tested into the cuvette and place it in the sample compartment. Use the PFXi195-1 automatic colorimeter to test the sample and perform automatic testing. After the results are out, read the data and record the measurement results displayed on the instrument.

[0114] Carbon content test

[0115] Using the German Airt infrared carbon and sulfur analyzer G4ICARUSHF / CS-i, the sample is burned in a high-temperature, oxygen-rich state. The carbon element it contains is oxidized into carbon dioxide and enters the infrared detector with the carrier gas. By quantitatively analyzing the changes in the infrared absorption wavelength intensity of the carbon dioxide signal, the instrument automatically calculates the carbon content.

[0116] First cycle capacity test after power off

[0117] The powder material, conductive agent superP and LA133 adhesive were mixed into a slurry in a ratio of 75:15:10 and evenly coated on a copper foil. After drying, the negative electrode was prepared and assembled into a button battery in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixed solution of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and fluorinated ethylene carbonate, with a volume ratio of 3:3:3:1), and the counter electrode used was a metal lithium sheet. The initial charge and discharge capacity of the button battery was tested on the Blue Electric Battery Test Cabinet M340A.

[0118] Cyclic performance test

[0119] The prepared negative electrode material was mixed with graphite in a ratio of 9:1, then mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6), and carbon black (SP) in a ratio of 92:2:2:2:2 in an aqueous solvent to form a slurry. The slurry was then evenly coated onto copper foil and dried to form a negative electrode sheet. Finally, the negative electrode sheets were assembled into button cells in an Ar atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and fluorinated ethylene carbonate, in a volume ratio of 3:3:3:1), and the counter electrode used was a metallic lithium sheet. The battery was cycled for 50 cycles in the voltage range of 0.005 V to 1.5 V at a current density of 50 mA / g. The 50-cycle capacity retention rate is calculated as the discharge capacity at the 50th cycle / the discharge capacity at the first cycle*100%.

[0120] Infrared spectroscopy FITR-ATR test

[0121] Place the powder sample to be tested on the crystal surface of the optical platform of an infrared spectrometer (ATR) (model is20). Open the infrared ATR test software and set the test parameters to 4 resolution and 32 scans. After starting the instrument, rotate the knob above the reflector to press the sample to ensure full contact with the lower emission hole, and begin data collection. After the test is completed, the sample's infrared spectrum information is obtained.

[0122] The technical solution of the present application is described below with reference to embodiments and comparative examples.

[0123] Example 1:

[0124] 5g of polyacrylamide was dissolved in deionized water and stirred to dissolve. 100g of pure silicon-containing core was then added and dispersed. 2g of citric acid was then added and stirred for 1 hour. The solvent was then removed by rotary evaporation to obtain a composite. The composite was transferred to a sealed container, purged with nitrogen to create an inert atmosphere, heated to 160°C for 4 hours, and finally cooled to room temperature to obtain the target product, which is the prepared negative electrode material. The product was evaluated for basic physicochemical properties, electrical performance, and full battery performance.

[0125] Example 2: The difference from Example 1 is that polyacrylamide is replaced by polymethacrylamide.

[0126] Example 3: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylpropyleneamine).

[0127] Example 4: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylacrylamide).

[0128] Example 5: The difference from Example 1 is that polyacrylamide is replaced by polyethyleneimine.

[0129] Example 6: The difference from Example 1 is that polyacrylamide is replaced by polybisaminopropylsiloxane.

[0130] Example 7: The difference from Example 1 is that citric acid is replaced by 3,4,5-trihydroxybenzoic acid.

[0131] Example 8: The difference from Example 1 is that citric acid is replaced by polyacrylic acid.

[0132] Example 9: The difference from Example 1 is that polyacrylamide is replaced by polymethacrylamide, and citric acid is replaced by 3,4,5-trihydroxybenzoic acid.

[0133] Example 10: The difference from Example 1 is that polyacrylamide is replaced by polymethacrylamide, and citric acid is replaced by polyacrylic acid.

[0134] Example 11: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylpropyleneamine), and citric acid is replaced by 3,4,5-trihydroxybenzoic acid.

[0135] Example 12: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylpropyleneamine), and citric acid is replaced by polyacrylic acid.

[0136] Example 13: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylacrylamide), and citric acid is replaced by 3,4,5-trihydroxybenzoic acid.

[0137] Example 14: The difference from Example 1 is that polyacrylamide is replaced by poly(N-methylacrylamide), and citric acid is replaced by polyacrylic acid.

[0138] Example 15: The difference from Example 1 is that polyacrylamide is replaced by polyethyleneimine, and citric acid is replaced by 3,4,5-trihydroxybenzoic acid.

[0139] Example 16: The difference from Example 1 is that polyacrylamide is replaced by polyethyleneimine, and citric acid is replaced by polyacrylic acid.

[0140] Example 17: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 10g.

[0141] Example 18: The difference from Example 1 is that the amount of citric acid is changed from 2g to 1g.

[0142] Example 19: The difference from Example 1 is that the heating temperature is changed from 160°C to 200°C.

[0143] Example 20: The difference from Example 1 is that the heating time is changed from 4 hours to 6 hours.

[0144] Example 21: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 2g.

[0145] Example 22: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 3g.

[0146] Example 23: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 4g.

[0147] Example 24: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 6g.

[0148] Example 25: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 7g.

[0149] Example 26: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 8g.

[0150] Example 27: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 9g.

[0151] Example 28: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 1g.

[0152] Example 29: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 0.5g.

[0153] Example 30: The difference from Example 1 is that the amount of polyacrylamide is changed from 5g to 0.2g.

[0154] Comparative Example 1: Silica particles not coated with any polymer were subjected to basic physicochemical properties, charge-discharge performance, and full battery evaluation.

[0155] Comparative Example 2: Unlike Example 1, no carboxylic acid-containing organic compound was added. Specifically, 5g of polyacrylamide was dissolved in deionized water and stirred to dissolve. Pure silicon-containing cores were then added and dispersed, followed by rotary drying to remove the solvent water. A composite was obtained. The composite was then transferred to a sealed container, purged with nitrogen to create an inert atmosphere. The temperature was raised to 160°C for 4 hours, and finally cooled to room temperature to obtain the target product, polymer-coated silicon-based particles. Basic physicochemical properties, electrical performance, and full battery evaluation were performed on the product.

[0156] Comparative Example 3: Unlike Example 1, no amino-containing polymer was added. Specifically, 2 g of citric acid was dissolved in deionized water, stirred to dissolve, and then the pure silicon-containing core was added and dispersed. The mixture was then rotary dried to remove the solvent water to obtain a composite. The composite was then transferred to a sealed container, purged with nitrogen to create an inert atmosphere, heated to 160°C for 4 hours, and finally cooled to room temperature to obtain the negative electrode material. The product was evaluated for basic physicochemical properties, electrical charge performance, and full battery performance.

[0157] Comparative Example 4: The difference from Example 1 is that the added polymer does not contain amino groups. Specifically, 5g of polyethylene oxide was dissolved in deionized water and stirred to dissolve. Then, a pure silicon-containing core was added and stirred and dispersed. 2g of citric acid was added and stirred and dispersed for 1 hour. The solvent water was then removed by rotary evaporation to obtain a composite. The composite was transferred to a sealed container, purged with nitrogen to form an inert atmosphere, heated to 160°C, heated for 4 hours, and finally cooled to room temperature to obtain the target product, silicon-based particles covered with polymer. The product was evaluated for basic physicochemical properties, electrical performance, and full battery performance.

[0158] Refer to Table 1 and Figure 4 It can be seen from the infrared spectra of uncovered silicon-based particles and polymer-covered silicon-based particles that the polymer-covered silicon-based particles show unique infrared characteristic peaks at 1654cm-1 and 1588cm-1, which are significantly different from the uncovered silicon-containing core.

[0159] The experimental data of the above examples are shown in Table 1 and Table 2.

[0160] Table 1 shows the A / B, D50, chromaticity, pH, and carbon content data of the examples and comparative examples.

[0161] Table 2 shows the indentation hardness, elastic recovery rate, peel strength, specific surface area, first-cycle gram capacity, and capacity retention rate of the examples and comparative examples.

[0162] In Table 1 and Table 2, A / B represents the mass ratio of the first substance to the second substance.

[0163] Reference Figure 2 as well as Figure 5 It can be seen from the indentation hardness and elastic recovery rate diagram of the negative electrode material without covering and the negative electrode material covered with polymer that the indentation hardness Hit of the negative electrode material covered with polymer is 1.5N / mm 2 , the elastic recovery rate Rer is 74.9%, which is significantly different from the result of the uncovered negative electrode material.

[0164] Refer to Table 2 and Figure 6It can be seen from the charge-withdrawal cycle curves of the uncovered negative electrode material and the polymer-covered negative electrode material that the charge-withdrawal capacity retention rate of the polymer-covered negative electrode material after 50 cycles is 88.4%, which is much higher than the charge-withdrawal capacity retention rate of the uncovered negative electrode material, which is only 79.2%.

[0165] The negative electrode material of the present application can improve the cycle stability of the battery negative electrode and reduce the consumption rate of active lithium ions in the electrochemical cycle of silicon-based negative electrode lithium batteries.

[0166] Since polyamide polymer has good flexibility, it can adjust the hardness of the surface layer of the silicon-containing core to keep it in the appropriate hardness range. That is, the silicon-containing core will not be rigidly broken due to large phase change volume changes and stress due to high hardness; on the contrary, it will not be structurally unstable due to mutual squeezing and deformation due to too low hardness.

[0167] At the same time, compared with simple carbon coating, flexible polymers have better elasticity, so that the covered silicon-containing core can still recover reversibly after being subjected to large strain, buffering the large volume and stress changes generated during the deintercalation and extraction of lithium from the silicon-containing core.

[0168] The silicon-containing core of the present application has an amide polymer covering layer on its surface that has a certain interaction with the electrolyte. The covered silicon-containing core will not be easily affected by the electrolyte, positive and negative electrode active particles and their electrochemical side reaction products, which are generally acidic products such as HF, PF5, POF3, and even corrosion or decomposition, thereby protecting the structure of the silicon-containing core in the covering layer and improving the electrochemical cycle stability of the silicon-containing core.

[0169] In the amide polymers of the present application, the N, O, and H of the amide groups can produce multi-site hydrogen bonding with the O and other groups on the surface of the silicon-containing core, and can produce hydrogen bonding with the hydroxyl and carbonyl groups on the surface of the silicon-containing core, which is also conducive to the dispersion and adsorption of the amide polymer on the surface of the silicon-containing core.

[0170] Amide polymers are often used as flocculants and viscose because they have good adhesive properties, which are conducive to bonding the silicon-containing core and preventing the silicon-containing core from falling off during phase change and volume change, resulting in failure of the contact path of electrons or ions and the inability to exert effective electrochemical capacity. This is particularly effective in improving the cyclic stability of silicon-based materials with large charge and discharge volume change rates.

[0171] The covering layer of the present application is a polymer, and the required amount is small, generally between 0.1% and 10%. Therefore, it has a small impact on the first cycle capacity of the battery, but the effective role it plays is obvious, especially in the cycle performance of the battery, which can significantly improve the battery charge and discharge cycle performance based on the battery negative electrode.

[0172] The battery negative electrode protected by the present application, due to the polymer covering the surface, can appropriately adjust the rigidity of the surface layer and enhance the elasticity, thereby buffering the expansion of the battery negative electrode during charging and discharging, reducing the failure of electron-ion contact and particle crushing deterioration of the silicon-containing core in the electrode, making the capacity of the battery negative electrode more stable and enhancing the electrochemical cycle stability.

[0173] After the covered finished product is made into an electrode, the basic data of the indentation hardness Hit of the electrode is in the range of 0.5 to 5, and the recovery rate Rer is between 71 and 89, which is significantly different from the uncovered pure silicon core.

[0174] The structural characteristics of the second substance, such as citric acid, 3,4,5-trihydroxybenzoic acid, and polyacrylic acid, are all small molecule compounds or high molecular weight polymers containing carboxylic acid groups. The abundant carboxylic acid groups in these substances can interact with polymer A (amino polymers such as polyacrylamide and polymethacrylamide), forming chemical cross-links and thus enhancing the stability and cohesion of the polymer network structure. This interaction helps form a more compact and elastic coating on the surface of the silicon-containing core.

[0175] Secondly, the addition of a second substance can further adjust the rigidity and elasticity of the surface layer. By optimizing the type and dosage of the second substance, the physicochemical properties of the coating can be manipulated, ensuring both a certain degree of rigidity to maintain structural stability and good elasticity to buffer the volume expansion of the battery's negative electrode during charge and discharge. This regulatory effect helps reduce electron-ion contact failure and particle pulverization degradation of the silicon-containing core in the electrode, thereby improving the electrochemical cycling stability of the battery's negative electrode. Furthermore, the structure and properties of the second substance directly influence the indentation hardness and elastic recovery rate of the finished product after coating, once fabricated into a pole piece. Specifically, careful selection of the second substance can ensure that the coated silicon-containing core exhibits a more optimal mechanical response when subjected to external forces. This is reflected in the pole piece's indentation hardness (Hit) ranging from 0.5 to 5 and its recovery rate (Rer) ranging from 71 to 89, which are significantly different and superior to those of the uncoated pure silicon-containing core. This improved mechanical property helps enhance the stability and durability of the battery's negative electrode during charge and discharge.

[0176] The secondary material plays a crucial role in the surface coating of the battery's negative electrode. Its structural characteristics and properties not only influence the stability and cohesion of the coating, but also directly determine the mechanical and electrochemical properties of the silicon-containing core in the electrode. Careful design and optimization of the selection and dosage of the secondary material can significantly improve the electrochemical cycling stability and service life of the battery's negative electrode.

[0177] After the covered finished product is made into an electrode, the basic data range of the indentation hardness Hit of the electrode is 0.5-5, and the recovery rate Rer is between 71 and 89, which is significantly different from the uncovered pure silicon core.

[0178] In addition, after the battery negative electrode protected by the present application is covered with a polymer, the polymer has certain adhesive properties, and the adhesive properties of the silicon-containing core after the coverage are improved, and it will adhere to other particles on the surface, making the particle size larger and the specific surface area smaller.

[0179] After the finished product is made into a pole piece, the unrolled peel strength of the pole piece is between 3.0-9.0N / m, the average particle size D50 of the silicon core is between 4-8um, and the specific surface area S is between 0.5-1m 2 / g, which is somewhat different from the uncovered pure silicon-containing core.

[0180] The battery negative electrode protected in this application, after being coated with a polymer, can interact with the electrolyte, protecting the silicon-containing core within the coating layer, allowing the silicon-containing core to remain stable during long-term immersion in the battery electrolyte, significantly improving the cycle stability of the battery negative electrode. In addition, when the polymer-coated negative electrode material is in a polar solvent, such as water, the interaction between the polymer and the polar solvent causes changes in ion ionization.

[0181] The finished product after covering is immersed in electrolyte for 48 hours, and the color range is 15 Hazen to 40 Hazen. In water, the pH is between 3 and 6, which is somewhat different from the uncovered pure silicon-containing core.

[0182] The battery negative electrode protected by this application, after being covered with a polymer, will increase the carbon content of the silicon-containing core because the polymer contains a large number of carbon atoms, such as polyamide. It should be noted that the uncovered silicon-containing core has a certain carbon content due to the carbon layer on the surface, but it is relatively low. In addition, since the polymer itself is a non-electrochemically active substance, that is, lithium will not be deintercalated during the charge and discharge process and the capacity cannot be exerted, the battery negative electrode covered with the polymer will have a lower gram capacity. However, the polymer coverage improves the electrochemical stability of the battery negative electrode during the charge and discharge process, which is manifested as an increase in the cycle capacity retention rate.

[0183] The finished product after covering has a carbon content between 3% and 8%, a first-cycle capacity between 1400Ah / g and 1650mAh / g, and a cycle retention rate of 85% to 95% after 50 cycles of power deduction, which is somewhat different from the uncovered silicon-containing core.

[0184] The polymer used for covering in this application is mainly polyamide. After repeated verification by multiple tests, the silicon-containing core after covering shows specific spectral peaks in the infrared spectral characteristic area, which are 1650cm -1to 1660cm -1 、1580cm -1 to 1590cm -1 This corresponds to the characteristic functional groups NH and C=O in the polymer structure, which is a polymer feature not found in pure silicon-containing cores or silicon-containing cores covered by other materials. In addition, the polymer covered by this application is used in an amount of 0.1-10%.

[0185] The finished product after covering is 1650cm -1 to 1660cm -1 、1580cm -1 to 1590cm -1 It shows unique infrared characteristic peaks, which are clearly distinguishable from the uncovered silicon-containing core.

[0186] Reference Figures 7 to 11 As shown, changes in the value of A / B will affect the chromaticity and corresponding performance, so choosing a suitable value of A / B can take into account multiple performances. In addition, the present application can more directly reflect the performance impact of the covering layer through chromaticity, and chromaticity is relatively easier to sample and test on the production line, so there is no need to evaluate the effect of the negative electrode material through testing after the battery is manufactured.

[0187] Table 1

[0188]

[0189]

[0190] Table 2

[0191]

[0192]

[0193] The above is a detailed introduction to the technical solutions provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes: a core comprising at least a silicon-containing material; a covering layer comprising at least a polymer having amide groups; The covering layer covers the core; and the chromaticity of the negative electrode material ranges from 15 to 50.

2. The negative electrode material according to claim 1, wherein: in, The median particle size of the negative electrode material ranges from 4 μm to 8 μm; And / or, the carbon content of the negative electrode material is in the range of 3% to 8%; And / or, the specific surface area of ​​the negative electrode material is in the range of 0.5m 2 / g to 1m 2 / g; And / or, the pH value of the negative electrode material ranges from 3 to 6.

3. The negative electrode material according to claim 1, wherein: in, The silicon-containing material is selected from one or more of silicon-oxygen materials and silicon-carbon materials; And / or, the mass ratio of the covering layer in the negative electrode material is in the range of 0.1% to 10%; And / or, in the infrared spectrum of the negative electrode material, at a wave number of 1650 cm -1 to 1660cm -1 、1580cm -1 to 1590cm -1 There are infrared characteristic peaks at the positions of And / or, the covering layer is obtained by reacting at least a first substance and a second substance, the first substance is a polymer having an amino group, the second substance is an organic substance having a carboxyl group, and the mass ratio of the first substance to the second substance ranges from 0.2 to 10.

4. A battery negative electrode, characterized in that: The battery negative electrode comprises: a foil material and a slurry layer; Wherein, the slurry layer is made of the negative electrode material according to any one of claims 1 to 3.

5. The battery negative electrode according to claim 4, characterized in that: in, The indentation hardness of the negative electrode ranges from 0.5 to 5; And / or, the elastic recovery rate of the negative electrode is in the range of 71 to 89; And / or, the peel strength of the slurry layer of the negative electrode ranges from 3.0 N / m to 9.0 N / m.

6. A method for preparing a negative electrode material, characterized in that: The preparation method comprises: providing a silicon-containing material to form the core; Covering the core with a polymer having an amide group to form a covering layer; The chromaticity of the negative electrode material prepared by the preparation method ranges from 17 to 36.

7. The preparation method according to claim 6, Its characteristics are: Wherein, the use of a polymer having an amide group to cover the core to form a covering layer comprises: mixing the silicon-containing material and the first substance in a solvent to obtain a first solution; adding a second substance to the first solution and reacting the second substance with the first substance to obtain a second solution; Stirring the second solution and then drying it to obtain a dry product; The dried product is subjected to a heat treatment under a preset atmosphere to obtain the negative electrode material.

8. The preparation method according to claim 7, characterized in that: in, The first substance is a polymer having an amino group, and the second substance is an organic substance having a carboxyl group; the mass ratio of the first substance to the second substance ranges from 0.2 to 10.

9. The preparation method according to claim 6, characterized in that: in, The solvent is deionized water; And / or, the stirring time of the stirring process ranges from 1 hour to 5 hours; And / or, the gas of the preset atmosphere includes one or more of nitrogen and argon; And / or, the heating temperature of the heat treatment ranges from 150° C. to 250° C.; And / or, the heating time of the heating treatment ranges from 1 hour to 6 hours.

10. A secondary battery, characterized in that: in, The secondary battery comprises: the negative electrode material according to any one of claims 1 to 3, the battery negative electrode according to any one of claims 4 to 5, or the negative electrode material prepared by the preparation method according to any one of claims 6 to 9.

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