Negative electrode material, negative electrode sheet and secondary battery

Abstract

The negative electrode material comprises a core body and a carbon coating layer coating at least part of the surface of the core body, the core body comprises a matrix and an active substance, the matrix is provided with holes, at least part of the active substance is arranged in the holes of the matrix, the negative electrode material is subjected to an infrared spectroscopic analysis test, and the carbon coating layer is a carbon coating layer coating at least part of the surface of the core body. The area of the telescopic vibration peak at the wavenumber of 2896 + / -10 cm <-1 > is S1; the sum of the areas of the telescopic vibration peaks at the wave numbers of 2924 + / -10 cm <-1 > and 2853 + / -10 cm <-1 > is S2; the area of the telescopic vibration peak at the wave number of 2960 + / -10 cm <-1 > is S3; the S1, the S2 and the S3 meet the following condition: # imgabs0 #. The negative plate and the secondary battery are based on the negative electrode material and have relatively good electrochemical performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a negative electrode material, a negative electrode sheet and a secondary battery. Background Art

[0002] With the rapid development of emerging fields such as new energy vehicles, smart homes, and the Internet of Things, the requirements for battery performance are increasing. Traditional graphite negative electrode materials have advantages such as high efficiency and stable charge and discharge platform. However, the low gram capacity hinders the further application of graphite in high-demand fields. Compared with graphite, silicon materials have a larger theoretical specific capacity and have the potential to be used as negative electrode materials. However, silicon negative electrode materials have problems such as low conductivity and large cycle volume change, which limit their performance in practical applications.

[0003] The composite of silicon and porous carbon materials can inhibit the volume expansion of silicon and improve its conductivity. However, in the composite process of silicon and porous carbon materials, silicon particles are generally exposed on the surface of porous carbon materials. In the subsequent aqueous homogenization and battery cycle, the silicon particles on the surface will contact the water and electrolyte in the slurry, causing gas production. In addition, the silicon particles on the surface lack the synergistic effect of the skeleton and the coating layer, and are prone to shedding, which affects the cycle life of the battery. Summary of the invention

[0004] In view of this, the present application provides a negative electrode material, a negative electrode sheet and a secondary battery to solve at least one of the above problems.

[0005] To achieve the above object, the present application provides a negative electrode material, including a core body and a carbon coating layer covering at least part of the surface of the core body, wherein the core body includes a matrix and an active substance, the matrix has pores, and at least part of the active substance is arranged in the pores of the matrix. The negative electrode material is tested by infrared spectroscopy analysis, and the result is that at a wave number of 2896±10 cm -1 The area of ​​the stretching vibration peak at 1 ; at wave number 2924±10 cm -1 and 2853±10 cm -1 The sum of the areas of the stretching vibration peaks at 2 ; At wave number 2960±10cm -1 The area of ​​the stretching vibration peak at is S 3 ; S 1 , S 2 and S 3 satisfy: .

[0006] In some possible implementations, the substrate has a specific surface area of ​​500 m 2 / g to 2000 m 2 / g.

[0007] In some possible implementations, the total pore volume of the matrix is ​​0.5 cm 3 / g to 2.0 cm 3 / g.

[0008] In some possible implementations, the average pore size of the matrix is ​​0.1 nm to 8 nm.

[0009] In some possible implementations, the average particle size of the active material is 0.1 nm to 100 nm.

[0010] In some possible implementations, the thickness of the carbon coating layer is 0.1 nm to 2000 nm.

[0011] In some possible implementations, the specific surface area of ​​the negative electrode material is 1 m 2 / g to 10 m 2 / g.

[0012] In some possible implementations, the powder conductivity of the negative electrode material is 0.05 S / m to 5 S / m.

[0013] In some possible implementations, the median particle size D of the negative electrode material is V 50 is 3 μm to 15 μm.

[0014] In some possible implementations, the substrate includes a carbon material, and the carbon material includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers, and graphene.

[0015] In some possible implementations, the matrix includes a non-carbon material, and the non-carbon material includes at least one of metal oxides, silicides, silicates, phosphates, titanates and aluminum borates; the metal oxides include one or more of aluminum oxide, zirconium oxide, germanium dioxide and manganese dioxide; the silicides include one or more of silicon carbide and silicon nitride; the silicates include one or more of cordierite, mullite and zeolite; the phosphates include one or more of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate and lanthanum phosphate; the titanates include one or more of calcium titanate, iron titanate, lithium titanate and barium titanate.

[0016] In some possible implementations, the active material includes one or more of Si, Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu.

[0017] In some possible implementations, the carbon material of the carbon coating layer includes one or more of amorphous carbon and graphitized carbon.

[0018] In some possible implementations, the matrix includes a carbon matrix, the active substance includes a silicon material, the silicon material includes one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon, and based on the mass of the negative electrode material, the mass proportion of carbon element in the negative electrode material is 30% to 70%.

[0019] In some possible implementations, based on the mass of the negative electrode material, the mass proportion of hydrogen element in the negative electrode material is less than or equal to 5%.

[0020] In some possible implementations, based on the mass of the negative electrode material, the mass proportion of silicon element in the negative electrode material is 30% to 80%.

[0021] The present application also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises the above-mentioned negative electrode material.

[0022] The present application also provides a secondary battery, comprising the above-mentioned negative electrode sheet.

[0023] In this application, the negative electrode material was tested by infrared spectroscopy analysis at a wave number of 2896 ± 10 cm -1 The area of ​​the stretching vibration peak at is S 1 ; at wave number 2924±10 cm -1 and 2853±10 cm -1 The sum of the areas of the stretching vibration peaks at 2 ; at wave number 2960±10 cm -1 The area of ​​the stretching vibration peak at is S 3 ; The S 1 , S 2 and S 3 satisfy: According to the inventor's reasonable speculation, at wave number 2896±10 cm -1 The stretching vibration peak at is the stretching vibration peak of -CH, at wave number 2924±10 cm -1 and 2853±10 cm -1 The stretching vibration peak at -CH 2 The stretching vibration peak is at wave number 2960±10 cm -1 The stretching vibration peak at -CH 3Stretching vibration peaks of methyl, methylene and methine groups. By setting methyl, methylene and methine groups on the carbon coating layer of the negative electrode material, the methyl group helps to improve the stability of the negative electrode material and adjust the wettability of the negative electrode material in the aqueous slurry, and the methylene and methine groups help to make the negative electrode material have more electron transmission paths. By setting methyl, methylene and methine groups on the carbon coating layer of the negative electrode material, the methyl group helps to improve the stability of the negative electrode material and adjust the wettability of the negative electrode material in the aqueous slurry, and the methylene and methine groups help to make the negative electrode material have more electron transmission paths. The stretching vibration peak area S of methyl, methylene and methine groups under infrared spectroscopy analysis test 3 , S 2 and S 1 satisfy On the one hand, it can reduce the gas production behavior of the active substances in the negative electrode material and alleviate the expansion volume effect of the negative electrode material, which is beneficial to improving the cycle stability of the resulting secondary battery. On the other hand, it can enhance the conductivity of the material, thereby maintaining or improving the electronic conductivity of the negative electrode sheet, which is beneficial to the rapid transport of electrons in the secondary battery to adapt to the rapid charging and discharging process and obtain a higher specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a secondary battery provided in one embodiment of the present application during charging.

[0025] Figure 2 A schematic diagram of the structure of a secondary battery provided in one embodiment of the present application during discharge.

[0026] Figure 3 This is the Gaussian fitting result of the infrared spectrum of the negative electrode material provided in one embodiment of the present application.

[0027] Main component symbols Electrode assembly 100 Positive electrode 101 Negative electrode 102 Isolation film 103. DETAILED DESCRIPTION

[0028] The embodiments of the present application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present application; in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other; many specific details are elaborated in the following description to facilitate a full understanding of the present application, and the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0029] An embodiment of the present application provides a secondary battery, comprising a housing, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are both located in the housing.

[0030] The outer shell may be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), for example, a soft-pack battery. In other embodiments, it may also be a steel shell battery, an aluminum shell battery, etc.

[0031] See also Figure 1 and Figure 2 The electrode assembly 100 includes a positive electrode sheet 101, a negative electrode sheet 102 and a separator 103. The separator 103 is disposed between the positive electrode sheet 101 and the negative electrode sheet 102. When an electrolyte (not shown) is provided, when charging, refer to Figure 1 , active ions (such as lithium ions) are deintercalated from the lattice of the positive electrode material (such as the lithiated intercalation compound) of the positive electrode sheet 101, pass through the separator 103 through the electrolyte, reach the negative electrode sheet 102 and insert into the lattice of the negative electrode material. Figure 2 , active ions (such as lithium ions) are deintercalated from the lattice of the negative electrode material of the negative electrode sheet 102, pass through the isolation membrane 103 through the electrolyte, reach the positive electrode sheet 101 and are embedded in the lattice of the positive electrode material (such as the lithiated intercalation compound), generating electrons that travel from the negative electrode sheet 102 through the external circuit to the positive electrode sheet 101, and the reverse movement of the electrons forms an electric current that can be used by electrical appliances.

[0032] In some embodiments, the electrode assembly 100 may be a laminated structure, which is formed by alternately stacking the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by stacking the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102 in sequence and then winding them.

[0033] Positive electrode The positive electrode sheet 101 includes a positive electrode current collector and a positive electrode material active layer provided on at least one surface of the positive electrode current collector. The positive electrode current collector may be made of aluminum foil or nickel foil, or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode material active layer contains a positive electrode active material, and the positive electrode active material includes a compound that reversibly embeds and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode active material may include but is not limited to lithium cobalt oxide (LiCoO 2 ), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn 2 O 4 ), lithium nickel manganese oxide (LiNi0.5 Mn 1.5 O 4 ) or lithium iron phosphate (LiFePO 4 ) at least one of.

[0034] The positive electrode material active layer also includes a binder to bond the positive electrode active material particles to facilitate the formation of a film layer, and at the same time, it can also improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the binder may include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon.

[0035] The positive electrode material active layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0036] Negative plate The negative electrode sheet 102 includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or may be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0037] The negative electrode material includes a core body and a carbon coating layer covering at least part of the surface of the core body, the core body includes a matrix and an active substance, the matrix has pores, at least part of the active substance is arranged in the pores of the matrix, and the negative electrode material is tested by infrared spectroscopy analysis at a wave number of 2896±10 cm -1 The area of ​​the stretching vibration peak at is S 1 ; at wave number 2924±10 cm -1 and 2853±10cm -1 The sum of the areas of the stretching vibration peaks at 2 ; at wave number 2960±10 cm -1 The area of ​​the stretching vibration peak at is S 3 ; S 1 , S 2 and S3 satisfy: .

[0038] According to the inventor's reasonable speculation, at wave number 2896±10 cm -1 The stretching vibration peak at is the stretching vibration peak of -CH, at wave number 2924±10 cm -1 and 2853±10 cm -1 The stretching vibration peak at -CH 2 The stretching vibration peak is at wave number 2960±10cm -1 The stretching vibration peak at -CH 3 stretching vibration peak.

[0039] The negative electrode material of the present application has a carbon coating layer, and a methyl group is provided on the carbon coating layer. The methyl group is an electron donating group, and its carbon atom has a relatively high electronegativity compared to a hydrogen atom, so the electron cloud in the methyl group will be biased toward its carbon atom, so that the carbon atom of the methyl group carries a partial negative charge. When the methyl group participates in the formation of a carbon chain, this negative charge effect will be transmitted along the carbon chain, so that the electron cloud density on the carbon atom connected to the methyl group increases, and the electron cloud density on the carbon atom away from the methyl group will be relatively reduced. Thus, dynamic electron cloud density and charge distribution changes are caused on the carbon chain, which helps to alleviate the local charge concentration phenomenon on the carbon chain, so as to help reduce the tension and energy instability inside the molecule. In addition, the σ electrons of the CH bond in the methyl group can overlap with the π electrons of the unsaturated bonds on the adjacent carbon chain, forming a hyperconjugated effect, reducing internal energy, and making the entire molecule more stable. In addition, methyl is a non-polar group, which is not conducive to the formation of hydrogen bonds and has a certain hydrophobicity. The negative electrode slurry system (negative electrode material active substance, conductive agent, binder, etc.) usually uses water as a solvent to form a water-washed slurry. The hydrophobicity of methyl can adjust the wettability and dispersibility of the negative electrode material in the aqueous slurry. When the methyl is coated on the active material (such as silicon particles) attached to the surface of the substrate, it helps to reduce the risk of side reactions of the active material in the aqueous slurry (such as gas production of silicon particles). The carbon coating layer of the present application also includes methylene and methine, both of which have relatively higher reactivity than methyl. The difference in reactivity may change the molecular structure or electron transmission path of the material in some chemical reactions. The higher reactivity of methylene and methine can provide more flow paths for the electrons of the negative electrode material, thereby helping to improve the conductivity of the negative electrode material.

[0040] The present application further defines that under infrared spectroscopy testing, methyl (-CH 3 ), methylene (-CH 2) and the peak area of ​​the methine (-CH) stretching vibration peak. The above relationship can characterize the content relationship of methyl, methylene and methine on the carbon coating. Specifically, infrared spectroscopy testing is based on the vibration and rotational energy level transitions that occur when molecules absorb infrared light of a specific wavelength. The vibration energy level transition of a molecule refers to the relative movement of atoms in the molecule near the equilibrium position. These vibration modes include normal vibrations (such as stretching vibrations and angular vibrations) and deformation vibrations. During the vibration process, if the dipole moment of the molecule changes, the molecule will absorb infrared light of a specific frequency and produce a vibration transition. Gaussian fitting of the infrared spectrum of the negative electrode material can obtain the methine (-CH), methylene (-CH 2 ) and methyl (-CH 3 ) of the stretching vibration peak area S 1 , S 2 and S 3 , see Figure 3 , at wave number 2896±10 cm -1 There is a stretching vibration peak of -CH at wave number 2924±10 cm -1 and 2853±10 cm -1 Existence-CH 2 The stretching vibration peak is at wave number 2960±10 cm -1 Existence-CH 3 The stretching vibration peak area of ​​-CH in the negative electrode material is S 1 , -CH 2 The sum of the stretching vibration peak areas is S 2 , -CH 3 The stretching vibration peak area is S 3 . Indicates from -CH 3 The content of H atoms (methyl hydrogen), Indicates from -CH 2 The content of H atoms (methylene hydrogen), represents the content of H atoms (methyl hydrogen) from -CH. In this case, the formula represents the proportion of methyl hydrogen in the sum of methyl hydrogen, methylene hydrogen and methine hydrogen. The present application found that when the formula satisfies the above numerical range, that is, When the negative electrode material is used, it is beneficial to exert the structural stability and hydrophobicity of the methyl group, and exert the reactivity of the methylene or methine group. On the one hand, it can reduce the gas generation behavior of the active material in the negative electrode material and alleviate the expansion volume effect of the negative electrode material, thereby improving the cycle stability of the obtained secondary battery. On the other hand, it can enhance the conductivity of the material, thereby maintaining or improving the electronic conductivity of the negative electrode sheet prepared by the negative electrode material, which is beneficial to the rapid transportation of electrons in the secondary battery to adapt to the rapid charge and discharge process and obtain a higher specific capacity. Overall, it helps to achieve a better balance between stability and conductivity of the negative electrode material.

[0041] It should be noted that when When it is greater than the upper limit, it means that there are excessive methyl groups on the coating layer, or the content of methylene or methyne is too low. It is understandable that too many methyl groups will increase the steric hindrance of the coated matrix (such as carbon matrix), thereby affecting the approach and reaction of other functional groups or molecules, reducing the electron flow path, and generating the risk of reducing the overall conductivity of the negative electrode material. This is not conducive to the reaction activity of the negative electrode material, affects the conductivity, and may cause the capacity and first coulomb efficiency of the battery prepared by the negative electrode material to decrease. When the formula When it is less than the lower limit, it means that the methyl content on the coating layer is small, or the methylene or methyne content is too high. Too few methyl groups will reduce the contribution of methyl groups to the stability of carbon materials, which is not conducive to the cycle stability of negative electrode materials. At the same time, too many methylene or methyne groups will bring about excessive reaction activity, which is not conducive to the chemical stability of negative electrode materials and may cause the cycle stability of batteries prepared with negative electrode materials to decrease.

[0042] In some embodiments, the infrared spectrum of the negative electrode material of the present application is obtained (such as Figure 3 ) and S 1 , S 2 and S 3 The analytical tests include: Step 1: Analyze using a Thermo Fisher Nicolet iS50 Fourier transform infrared spectrometer with an infrared light source wavelength of 400 cm -1 Up to 4000 cm -1 , detector is DTGS KBr, beam splitter is KBr, resolution is 2 cm -1 , and obtain the analysis data.

[0043] Step 2: Use OMNIC software to analyze the analytical data and obtain the preliminary peak positions of hydrocarbon groups.

[0044] Step 3: Use Origin software to analyze the preliminary peak position results and obtain the peak positions of methine (-CH), methylene (-CH 2 ) and methyl (-CH 3) of the stretching vibration peak position and peak area S 1 , S 2 and S 3 .

[0045] See also Figure 3 The peak formed by the first curve relative to the baseline is the preliminary peak position of the hydrocarbon group obtained by OMNIC software analysis, and the peak formed by the third curve relative to the baseline is the methylene (-CH 2 ), the peak formed by the fourth curve relative to the baseline is the stretching vibration peak of the methine (-CH), and the peak formed by the fifth curve relative to the baseline is the stretching vibration peak of the methyl (-CH 3 ) and calculate the peak area; wherein the second curve appears simultaneously with the third curve, the fourth curve and the fifth curve after analysis during the analysis process, and the higher the overlap between the second curve and the first curve, the more accurate the analysis results of the third curve, the fourth curve and the fifth curve are, and the present application Figure 3 , the second curve substantially coincides with the first curve.

[0046] In some embodiments, the infrared spectrum test may specifically include: taking 1 mg to 2 mg of the sample and grinding it appropriately in an agate mortar, then mixing it evenly with dry potassium bromide powder (about 100 mg, particle size 200 mesh), putting it into a mold, and pressing it into tablets on a tablet press for testing. The analysis was performed using a Thermo Fisher Nicolet iS50 Fourier transform infrared spectrometer, and the light source used was an infrared light source (400 cm -1 Up to 4000 cm -1 ), detector is DTGS KBr, beam splitter is KBr, resolution is 2 cm -1, then sample and complete the test. Use OMNIC software to preliminarily determine the relevant peak positions. The peak position results obtained are fitted by Origin software. The fitting process is as follows: import the infrared test data processed by OMNIC into Origin and draw a graph. In the Origin menu bar, click Analysis, Peak and Baseline, Peak Analysis in turn. After opening the dialog box, select "Peak Fitting" in the pop-up window, select "User Defined" for baseline mode, uncheck "Enable Automatic Search", select "Clear All" for the number of points to be found, and then click Add to add manually. After clicking Add, double-click at both ends of the curve to add points. After adding, click the Finish button in the upper left corner, click Next, select "Interpolation" for connection method, and select "Spline Curve" for interpolation method. The points will be connected in the form of a curve, then click Next, select "Automatically subtract baseline", flatten the baseline, click Next, uncheck "Allow automatic search", select "Add", and double-click to take points at the expected peak position on the curve according to the peak position in the OMNIC software. Click Next, and you can see the automatically generated peak (similar to Figure 3 ), click the fitting control, and you can see the peaks close to the imported peaks (similar to Figure 3 Click "1 iteration" and click repeatedly. During the iteration process, the "automatically generated peaks" will be automatically adjusted to make the "peaks close to the imported peaks" match the imported peaks more closely until "fit convergence" is displayed. The curve obtained after the fit converges ( Figure 3 The second curve in ) is compared with the original data ( Figure 3 The higher the overlap, the better the fitting effect. Click Finish to obtain the fitting curve and fitting data, that is, the methine (-CH), methylene (-CH 2 ) and methyl (-CH 3 ) (corresponding to the fourth curve, the third curve and the fifth curve respectively) and the peak area S 1 , S 2 and S 3 .

[0047] In some embodiments, the specific surface area of ​​the substrate is 500 m 2 / g to 2000 m 2 / g. For example, the specific surface area of ​​the matrix can be 500 m 2 / g, 600 m 2 / g, 800 m 2 / g, 1000 m 2 / g, 1200 m 2 / g, 1400 m 2 / g, 1600 m 2 / g、1800m 2 / g, 2000 m 2 / g or any value within the range formed by any two of the above values. Controlling the specific surface area of ​​the substrate within the above range is conducive to the uniform dispersion and stable attachment of the active material (such as silicon particles) on the substrate, thereby reducing the risk of the active material falling off the substrate and improving the stability and durability of the active material.

[0048] In some embodiments, the total pore volume of the matrix is ​​0.5 cm 3 / g to 2.0 cm 3 / g. For example, the total pore volume of the matrix can be 0.5 cm 3 / g, 0.8 cm 3 / g, 1 cm 3 / g, 1.2 cm 3 / g, 1.5 cm 3 / g, 1.8 cm 3 / g, 2 cm 3 / g or any value within the range formed by any two of the above values. When the matrix has abundant pores, these pores can accommodate the active material and reserve space for the volume expansion of the accommodated active material. It can be understood that when the matrix and the active material form a composite material, at least part of the active material is deposited in the pores of the matrix, so the total pore volume of the composite material formed will be less than the total pore volume of the initial matrix. In some embodiments, the average pore size of the matrix is ​​0.1 nm to 8 nm. For example, the average pore size of the matrix can be 0.1 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, or any value within the range formed by any two of the above values. The average pore size of the matrix is ​​controlled within the above range, indicating that the pores of the matrix include relatively more micropores (pores with a pore size of less than or equal to 2 nm), and also include at least one or more of mesopores (pores with a pore size greater than 2 nm and less than or equal to 50 nm) and macropores (pores with a pore size greater than 50 nm). The micropores in the matrix can reduce the aggregation of active substances in the matrix, increase the content of active substances in the matrix and the uniformity of the distribution of active substances, thereby improving the specific capacity and mechanical properties of the obtained negative electrode material. Mesopores or macropores with relatively large pore sizes can reserve sufficient buffer space for the volume expansion of active materials, effectively alleviate the volume expansion of active materials, and reduce the risk of excessive local expansion stress caused by uneven volume changes of active materials in the negative electrode material during the cycle, which may lead to rupture and pulverization of the negative electrode material. This is beneficial to improving the particle structure stability and cycle stability of the negative electrode material.

[0049] In some embodiments, the average particle size of the active material is 0.1 nm to 100 nm. For example, the average particle size of the active material can be 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 65 nm, 80 nm, 95 nm, 100 nm, or any value within the range formed by any two of the above values. By setting the average particle size of the active material within the above range, the mechanical stress of the active material (such as silicon particles) when the volume expands can be reduced, so that the secondary battery maintains a good battery capacity, and reduces irreversible capacity loss, and can also shorten the electron and ion transmission path. At the same time, the size of the active material is reduced, and the gap between adjacent active material particles is increased, which can reserve space for the volume expansion of the active material.

[0050] In some embodiments, the thickness of the carbon coating layer is 0.1 nm to 2000 nm. For example, the thickness of the carbon coating layer can be 0.1 nm, 0.5 nm, 1 nm, 30 nm, 60 nm, 100 nm, 150 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1200 nm, 1700 nm, 2000 nm, or any value within the range formed by any two of the above values. The carbon coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas produced by the reaction of the dissolved active substances (such as silicon particles) with the electrolyte. Controlling the thickness of the carbon coating layer within the above range is beneficial to maintaining the stability of the particle structure of the negative electrode material during the cycle, can reduce the exposed active substances on the surface of the negative electrode material, reduce the risk of generating a large amount of SEI during the charge and discharge process due to the exposed active substances, and improve the specific capacity and electrochemical performance of the negative electrode material.

[0051] In some embodiments, the specific surface area of ​​the negative electrode material is 1 m 2 / g to 10 m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g or any value within the range formed by any two of the above values. When the specific surface area of ​​the negative electrode material is large, the SEI film on the surface of the negative electrode material will consume excessive lithium salts, and the volume effect is likely to cause electrical separation between particles, resulting in reduced reversible capacity and coulombic efficiency of the battery. Therefore, the specific surface area of ​​the negative electrode material in this embodiment is small, which is conducive to improving the capacity of the first discharge ratio and the first coulombic efficiency of the battery.

[0052] In some embodiments, the powder conductivity of the negative electrode material is 0.05 S / m to 5 S / m. For example, the powder conductivity of the negative electrode material can be 0.05 S / cm, 0.1 S / cm, 0.3 S / cm, 0.5 S / cm, 1 S / cm, 1.5 S / cm, 2 S / cm, 3 S / cm, 4 S / cm, 5 S / cm, or any value within the range formed by any two of the above values.

[0053] In some embodiments, the median particle size D of the negative electrode material is V 50 is 3 μm to 15 μm. For example, the median particle size D of the negative electrode material V 50 can be 3 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm or any value within the range formed by any two of the above values. Controlling the median particle size of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material. Median particle size D V 50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%.

[0054] In some embodiments, the substrate includes a carbon material, and the carbon material includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers, and graphene. When the substrate is a carbon material, the above material can provide pore distribution sites for the active substance and form a conductive network.

[0055] In other embodiments, the matrix includes non-carbon materials, and the non-carbon materials include at least one of metal oxides, silicides, silicates, phosphates, titanates, and aluminum borates; metal oxides include one or more of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide; silicides include one or more of silicon carbide and silicon nitride; silicates include one or more of cordierite, mullite, and zeolites; phosphates include one or more of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate; titanates include one or more of calcium titanate, iron titanate, lithium titanate, and barium titanate. The selection of the above materials by non-carbon materials is conducive to optimizing the transmission path of lithium ions, improving the diffusion rate and embedding efficiency of lithium ions, and improving electrochemical performance.

[0056] In some embodiments, the active material includes one or more of Si, Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu.

[0057] In some embodiments, the carbon material of the carbon coating layer includes one or more of amorphous carbon and graphitized carbon. In some embodiments, the carbon coating layer can be a single-layer carbon coating layer formed by the above-mentioned single material, or a carbon coating layer formed by a combination of the above-mentioned multiple materials, or a single material can form a multi-layer carbon coating layer, or a multi-layer carbon coating layer can be formed by multiple materials, etc. The layer structure of the carbon coating layer can be selected according to actual needs. It can be understood that when the carbon coating layer is a multi-layer coating structure, its density is higher. The carbon coating layer located on the surface of the substrate is conducive to improving the stability and conductivity of the substrate. The carbon coating layer can also coat the active material exposed on the surface of the substrate, reduce the continuous oxidation of the exposed active material during the placement process, and reduce the risk of reducing the specific capacity and the first coulomb efficiency (ICE) of the negative electrode material. The carbon coating layer can also reduce the direct contact between the active material and the electrolyte, improve the stability of the SEI film, and thus improve the first coulomb efficiency of the negative electrode material.

[0058] In some embodiments, the matrix of the negative electrode material includes a carbon matrix, and the active material includes a silicon material, and the silicon material includes one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon. When the active material includes a silicon material, the silicon material is used as a component of the negative electrode active material, which can increase the specific capacity of the negative electrode material and thus increase the energy density of the secondary battery. Preferably, the silicon material includes amorphous silicon. When the active material includes amorphous silicon, amorphous silicon expands isotropically during the lithium insertion process, which can reduce the collapse of pores in the negative electrode material, inhibit the rapid attenuation of the specific capacity of the negative electrode material, and is more conducive to improving the lithium insertion cycle performance of the negative electrode material.

[0059] In some embodiments, based on the mass of the negative electrode material, the mass percentage of carbon elements in the negative electrode material is 30% to 70%. For example, the mass percentage of carbon elements in the negative electrode material can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or any value within the range formed by any two of the above values. Silicon material and porous carbon material are compounded to obtain a silicon-carbon composite material, which helps to alleviate the volume expansion of silicon materials. Carbon elements include a carbon matrix and a carbon coating layer. When the mass percentage of carbon elements is within this range, sufficient carbon-based substrates can be established to provide sufficient distribution sites for active substances, which is conducive to forming an effective conductive network and improving electrical conductivity and cycle stability.

[0060] In some embodiments, based on the mass of the negative electrode material, the mass percentage of hydrogen in the negative electrode material is less than or equal to 5%. For example, the mass percentage of hydrogen in the negative electrode material can be 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or any value within the range formed by any two of the above values. The hydrogen in the negative electrode material mainly comes from the methyl, methylene and methine groups on the carbon coating layer. Controlling the hydrogen within the above range is conducive to the formation of appropriate contents of methyl, methylene and methine groups, thereby helping to improve the chemical stability and reactivity of the negative electrode material as a whole.

[0061] In some embodiments, based on the mass of the negative electrode material, the mass percentage of silicon in the negative electrode material is 30% to 80%. For example, the mass percentage of silicon in the negative electrode material can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value within the range formed by any two of the above values. When the mass percentage of silicon is within this range, the lithium battery composed of the negative electrode material can store a higher amount of electricity, that is, the first discharge specific capacity is higher.

[0062] The negative electrode active material layer also includes a binder to bind the negative electrode active material particles to facilitate the formation of a film layer, and can also improve the binding force between the negative electrode material active layer and the negative electrode current collector. In some embodiments, the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin or nylon, etc.

[0063] The negative electrode active material layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0064] Isolation film The isolation membrane 103 includes a membrane layer with a porous structure, and its material includes but is not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the isolation membrane 103 can be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0065] Electrolyte The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The electrolyte can be in one or more of a gel state, a solid state, and a liquid state. In some embodiments, the electrolyte is an electrolyte. The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. In some embodiments, the electrolyte includes a lithium salt and an organic solvent. The lithium salt can be selected from, but is not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium tetraphenylborate (LiB(C 6 H 5 ) 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO 2 CF 3 ) 2 、Tris(trifluoromethylsulfonyl)methyllithium(LiC(SO 2 CF 3 ) 3 ), lithium bis(oxalatoborate) (LiBOB) and lithium difluorophosphate (LiPO 2 F 2 ) in one or more. For example, the lithium salt is selected from LiPF 6 The organic solvent may be a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, other organic solvents or a combination thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0066] One embodiment of the present application also provides a method for preparing the above-mentioned negative electrode material, comprising: The first step is to provide a substrate, wherein the substrate has holes.

[0067] In some embodiments, providing a substrate includes high temperature treatment, activation and acid washing of a substrate precursor to obtain a substrate having pores. Taking a carbon substrate as an example, a carbon source precursor material is subjected to high temperature carbonization treatment to obtain a carbon-based carbonized material, the carbon-based carbonized material is mixed with an activator, and a porous carbonaceous material, i.e., a carbon substrate having pores, is obtained after high temperature activation and acid washing.

[0068] In some embodiments, the carbon source precursor includes one or more of a biomass-based precursor, a resin-based precursor, a coal-based precursor, a petroleum-based precursor, and a polymer-based precursor. Among them, the biomass precursor may include one or more of coconut shell, straw, fruit shell, sugar, starch, and bamboo; the resin-based precursor may include one or more of phenolic resin and epoxy resin; the coal-based precursor may include one or more of coal tar, needle coke, and anthracite; the petroleum-based precursor may include one or more of petroleum coke, asphalt, and heavy oil; the polymer-based precursor may include one or more of polyfurfural, polyimide, polyacrylonitrile, polyvinylidene fluoride, polystyrene, and polyvinyl chloride.

[0069] In some embodiments, the carbonization process is carried out under an inert atmosphere, wherein the oxygen content is maintained at less than or equal to 500 ppm, and the pressure in the furnace chamber of the carbonization process is maintained at 1 torr to 200 torr. Wherein, the inert atmosphere gas includes one or more of nitrogen, helium, neon, argon, krypton and xenon. In some embodiments, the carbonization temperature is 400°C to 2000°C, preferably 600°C to 1200°C. In some embodiments, the carbonization time is 1 h to 48 h, preferably 2 h to 8 h.

[0070] In some embodiments, the activator in the activation process includes one or more of an alkaline activator, a gas activator, a salt activator, and an acidic activator. Among them, the alkaline activator may include one or more of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, calcium oxide, magnesium oxide, triethylamine, tetraethylamine, pyridine, and imidazole; the gas activator may include one or more of water vapor, oxygen, and carbon dioxide; the salt activator may include one or more of zinc chloride, potassium chloride, and sodium chloride; the acidic activator may include one or more of sulfuric acid, phosphoric acid, and nitric acid.

[0071] In some embodiments, the activation treatment temperature in the activation process is 600° C. to 1400° C. In some embodiments, the activation treatment time in the activation process is 2 h to 48 h.

[0072] Step 2: Deposit active substances in the matrix to obtain a core body.

[0073] In some embodiments, depositing the active material in the matrix includes placing the matrix in a gas phase carrier atmosphere of the active material, causing the gas phase carrier of the active material to be pyrolyzed at high temperature, and causing the active material to be deposited on the matrix. Taking the carbon matrix and silicon particles as an example, since the carbon matrix has pores and the silicon particles can be obtained by high temperature pyrolysis of the silicon source gas, the carbon matrix is ​​placed in a silicon source gas atmosphere, and the deposition of the silicon source gas atmosphere at high temperature can make some silicon particles deposited in the pores of the carbon matrix to obtain a silicon-carbon composite material. Among them, the silicon source gas can include one or more of monosilane, disilane, isosilane and trisilane. In some embodiments, the concentration of the silicon source gas is 10% to 60%. In some embodiments, the deposition temperature is 400 ℃ to 700 ℃, and the deposition time is 1 h to 48 h.

[0074] Step 3: Mix the core with the reaction gas and perform heat treatment, the reaction gas includes carbon source gas, hydrogen and inert gas, the volume proportion of hydrogen in the reaction gas is greater than or equal to 5% and less than or equal to 30%, the heat treatment temperature is greater than or equal to 500 ° C and less than or equal to 800 ° C, and the heat treatment time is greater than or equal to 2 h and less than or equal to 48 h, to obtain the negative electrode material. For example, the volume proportion of hydrogen in the reaction gas can be 5%, 10%, 15%, 20%, 25%, 30% or any value within the range of any two of the above values. The heat treatment temperature can be 500 ° C, 550 ° C, 600 ° C, 650 ° C, 700 ° C, 750 ° C, 800 ° C or any value within the range of any two of the above values. The heat treatment time can be 2h, 6h, 12h, 18h, 24h, 30h, 36h, 42h, 48h or any value within the range of any two of the above values.

[0075] Taking silicon-carbon composite materials as an example, by mixing silicon-carbon composite materials with carbon source gas and heat treating them, a negative electrode material can be obtained in which the surface of the carbon matrix or the surface of silicon particles attached to the surface of the carbon matrix is ​​coated with a carbon coating layer, and the carbon coating layer has methyl, methyne and methylene groups. Further heat treatment is carried out in an appropriate amount of hydrogen atmosphere, and hydrogen can adjust the concentration of atomic hydrogen or ionic hydrogen in the entire reaction gas, showing a hydrogenation process and a dehydrogenation process. Hydrogenation can cause active hydrogen atoms or ions to react with groups on the surface of the carbon material, such as the transformation of methyne and methylene to methyl; dehydrogenation at high temperature can cause methyl to gradually remove hydrogen atoms and transform into methyne and methylene, and at the same time, methyne and methylene will also remove hydrogen. By controlling the hydrogen concentration within a suitable range, the content of methyl, methylene and methyne on the carbon coating of the negative electrode material can be adjusted. In this way, the carbon coating layer is coated on the surface of the carbon matrix, or on the surface of the silicon particles attached to the surface of the carbon matrix. The stability and hydrophobicity of the negative electrode material are adjusted by the methyl structure, and the reactivity and conductivity of the negative electrode material are adjusted by the methylene or methyne structure, which is beneficial to improve the problems of unstable structure and poor conductivity of silicon-carbon composite negative electrode materials.

[0076] Controlling the volume proportion of hydrogen, the heat treatment temperature and the heat treatment time within the above range can control the content of methyl, methylene and methine on the carbon coating layer of the obtained negative electrode material, so as to facilitate obtaining a negative electrode material whose methyl, methylene and methine contents meet the preset relationship and range. In the above preparation process, when there is a lack of hydrogen in the atmosphere, the methyl in the material mainly comes from the cracking of the carbon source, and the overall content is less; when the proportion of hydrogen in the provided atmosphere is too small, the hydrogenation process in the reaction system is weak, and the low hydrogen concentration is conducive to breaking the original thermodynamic equilibrium, which is more conducive to the occurrence of the dehydrogenation process, so that the methyl content is less. When the proportion of hydrogen in the provided atmosphere is too large, the proportion of methyl in the material will increase due to the strong hydrogenation process. In addition, when the heat treatment temperature is too low, or when the heat treatment time is too short, the carbon source gas is not cracked sufficiently. Since the carbon source gas cracking reaction fails to fully proceed to the expected stage, intermediates or by-products containing methyl are produced. These methyl groups generally come from the incomplete cracking process of the carbon source gas molecules and are retained in the product under the influence of the reaction conditions, which will lead to an increase in the proportion of methyl. When the heat treatment temperature is too high, the dehydrogenation process is more obvious, which reduces the methyl content. Excessively high temperature may also cause the internal structure of the carbon material to become too fragile and the stability to decrease.

[0077] In some embodiments, the volume proportion of the carbon source gas in the reaction gas is greater than or equal to 10% and less than or equal to 50%, and the volume proportion of the inert gas in the reaction gas is greater than or equal to 20% and less than or equal to 85%.

[0078] In some embodiments, the carbon source gas includes one or more of methane, acetylene, ethylene, ethane, propane, propylene, benzene, toluene, xylene, ethanol, cyclohexane, methanol, and acetone.

[0079] In some embodiments, the inert gas includes one or more of nitrogen, helium, neon, argon, and krypton.

[0080] The scheme of the present application will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be construed as limiting the present application. Unless otherwise stated, the reagents, software and instruments not specifically stated in the following embodiments are all conventional commercial products or open source.

[0081] Embodiment 1: This example provides a negative electrode material and a lithium ion battery based on the negative electrode material.

[0082] (1) The method for preparing the negative electrode material includes: S1, placing a certain amount of fruit shells in a carbonization furnace and carbonizing them at 900 °C for 8 h to obtain a carbon-based carbonized material; S2, placing the carbon-based carbonized material obtained in S2 in a mixed atmosphere of 15% water vapor and 85% nitrogen for activation treatment, the activation temperature is 900 ° C, the activation time is 24 h, the activated material is ultrasonically stirred in a 40% hydrochloric acid aqueous solution, vacuum filtered, washed with pure water until the pH is neutral, and dried to obtain a carbon substrate with pores; S3, transferring the carbon substrate with holes obtained in S2 to a CVD device, maintaining the silane concentration at 25%, the reaction temperature at 550°C, and the reaction time at 10 h to obtain a silicon-carbon composite material; S4. Place the silicon-carbon composite material obtained in step S3 in a reaction furnace, introduce a reaction gas with a composition of nitrogen: acetylene: hydrogen = 70%: 15%: 15%, and perform heat treatment at a temperature of 700°C for 4 hours. Screen and grade the obtained material to obtain a negative electrode material.

[0083] (2) A method for preparing a lithium-ion battery based on the above negative electrode material comprises: The above-mentioned negative electrode materials, conductive carbon black and carboxymethyl cellulose were thoroughly stirred in a mixed solution of deionized water and anhydrous ethanol in a mass ratio of 7:2:1, evenly coated on copper foil, vacuum dried at 100 °C, cut into circular electrode sheets, and then assembled into button cells in a glove box with lithium metal as the counter electrode and tested. The separator used was Celgard C2400, and the electrolyte was 1.0 M LiPF6 solution of EC, PC and DEC (volume ratio of EC: PC: DEC = 3:1:6).

[0084] Embodiment 2: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: acetylene: hydrogen = 50%: 40%: 10%.

[0085] Embodiment 3: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: acetylene: hydrogen = 50%: 20%: 30%.

[0086] Embodiment 4: The difference from Example 1 is that in S4, the heat treatment temperature is adjusted to 600°C.

[0087] Embodiment 5: The difference from Example 1 is that in S4, the heat treatment time is adjusted to 8 h.

[0088] Embodiment 6: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: propane: hydrogen = 70%: 15%: 15%.

[0089] Embodiment 7: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: cyclohexane: hydrogen = 70%: 15%: 15%, and the cyclohexane in the mixed gas is connected to the reactor through an external bubbling device; and the heat treatment time is adjusted to 8 h.

[0090] Embodiment 8: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen:acetylene:hydrogen=85%:10%:5%.

[0091] Embodiment 9: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen:acetylene:hydrogen=30%:40%:30%.

[0092] Comparative Example 1: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: acetylene = 75%: 25%.

[0093] Comparative Example 2: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen:acetylene:hydrogen=25%:25%:50%.

[0094] Comparative Example 3: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen: acetylene: hydrogen = 50%: 25%: 25%, and the heat treatment temperature is adjusted to 400°C.

[0095] Comparative Example 4: The difference from Example 1 is that in S4, the composition of the reaction gas is adjusted to nitrogen:acetylene:hydrogen=50%:25%:25%, and the heat treatment time is adjusted to 1 h.

[0096] The negative electrode materials obtained in the above examples 1-9 and comparative examples 1-4 were subjected to performance tests, and the test methods were as follows: Test method for total pore volume and proportion of matrix and negative electrode material after removing active substances: The total pore volume of the matrix refers to the total pore volume per unit mass of the matrix, and the total pore volume of the matrix can be measured by gas adsorption measurement. Nitrogen adsorption is a technique that characterizes the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases until the saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms enables the determination of the pore volume and pore size distribution, as well as the proportion of the respective pore volumes of micropores, mesopores and macropores in the total pore volume. Among them, the method of removing active substances from negative electrode materials (taking silicon materials as an example) is as follows: add 1 M concentrated nitric acid to the negative electrode material and soak it for 4 hours, then drip a 20% mass fraction HF acid solution into the negative electrode material drop by drop, which will produce yellow smoke. Repeat the dripping several times until no yellow smoke is produced in the solution; finally, use 1 M concentrated nitric acid to digest the residue, then wash and dry it to obtain the negative electrode material after removing the silicon material.

[0097] The test method of the median particle size of the negative electrode material is as follows: the particle size distribution range of the negative electrode material is tested by Malvern laser particle size analyzer (Mastersizer3000), and the volume-based cumulative particle size distribution of the particle size distribution is measured by laser diffraction method, D V 10 represents the particle size corresponding to the cumulative particle size distribution percentage of the powder reaching 10%, D V 50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, D V 90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

[0098] Carbon coating thickness: The material was sectioned using a FIB-SEM device, 10 particles were randomly selected in the SEM, and the carbon coating thickness of each particle was measured three times to obtain the average thickness of the carbon coating.

[0099] Powder conductivity test: The four-probe method is used to determine the volume resistivity of the sample. The MCP-PD51 powder conductivity meter of Mitsubishi Chemical of Japan can measure the conductivity of the powder at five pressure points of 4 KN, 8 KN, 12 KN, 16 KN, and 20 KN, and then the computer automatically calculates the resistivity of the powder.

[0100] The mass content test method of carbon element is as follows: Using the G4 ICARUS HF infrared carbon-sulfur analyzer from Bruker of Germany, the sample is burned under high temperature and oxygen-rich conditions, and the carbon element it contains is oxidized into carbon dioxide. The generated gas enters the infrared detector with the carrier gas, and the carbon content can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

[0101] The test method for the mass content of silicon element is as follows: Nanyang Xinyu's SA2-9-17TP box-type atmosphere furnace is used to burn in an oxygen atmosphere so that the silicon in the sample reacts into silicon dioxide, and the carbon is burned and converted into carbon dioxide and discharged. The silicon content is calculated by weighing.

[0102] Test method for mass content of hydrogen element: Using German Verder ONH 2000 oxygen, nitrogen and hydrogen element analyzer, the method for detecting the mass proportion of hydrogen element in negative electrode material includes heating and melting the negative electrode material and flux (nickel) in a graphite crucible in a pulse electrode furnace under inert gas (He or Ar) to release hydrogen; after hydrogen passes through rare earth copper oxide, water vapor is generated, and the water infrared detector outputs the electrical signal of water, which is compared with the electrical signal of known hydrogen standard substance / sample to obtain the hydrogen content.

[0103] Specific surface area test method: The specific surface area of ​​the powder sample was tested by gas adsorption method (nitrogen adsorption multi-point BET) at low temperature controlled by liquid nitrogen cooling using the American Micromeritics TriStar 3000 & 3020 specific surface area and pore size analyzer.

[0104] Testing method for average particle size of material particles: The material particles are observed by field emission scanning electron microscopy or transmission electron microscopy, and the particle sizes of 5-10 material particles are directly measured by a scale. The average value of the particle sizes is taken as the average particle size of the final material particles.

[0105] The present application also conducted a test method for the gas production of the negative electrode materials obtained in Examples 1-9 and Comparative Examples 1-4: (1) 5 g of the negative electrode material was placed in a sealed container, and deionized water was added until the remaining volume above the container was 60 mL; (2) the container was sealed, mixed evenly, and stored at room temperature for one day; (3) after 24 hours, the container was shaken again to disperse the precipitate into the liquid; (4) the lid of the container was opened, and the concentration of hydrogen was detected with a hydrogen detector, and converted to cc / (kg·day).

[0106] The stretching vibration peak area S of the negative electrode material 1 , S 2 and S 3 The test method is described in the manual and will not be repeated here.

[0107] The present application further conducts electrochemical performance tests on the lithium-ion batteries obtained in Examples 1-9 and Comparative Examples 1-4, mainly including: using the Blue Electric CT2001A battery testing system, the first coulomb efficiency is tested according to the test method described in the silicon-carbon national standard GB / T38823-2020, the capacity retention rate is tested according to the test method described in the national standard GB / T36276-2018, and the expansion rate of the negative electrode sheets in these lithium-ion batteries is detected after 50 cycles of charge and discharge. The expansion rate is calculated by observing the electrode sheet using a scanning electron microscope, and the average particle size of the silicon particles before lithium insertion is obtained according to the corresponding scale as D 1 After the charge and discharge cycle, the battery was disassembled, the electrode was cleaned with DEC, and the electrode was observed with a scanning electron microscope. According to the corresponding scale, the average particle size of the silicon particles after lithium insertion was obtained as D 2 ; Considering the silicon particles as spherical structures, the expansion rate is D 2 / D 1 -1.

[0108] Please refer to Table 1 for some of the preparation conditions of Examples 1-9 and Comparative Examples 1-4 of the present application, and please refer to Table 2 for the above test results.

[0109] Table 1. Partial preparation conditions of Examples 1-9 and Comparative Examples 1-4 of the present application Table 2. Test results of negative electrode materials and lithium-ion batteries of Examples 1-9 and Comparative Examples 1-4 of the present application The negative electrode materials of Examples 1-9 of the present application meet the requirements , having a relatively low specific surface area and gas production, and a small degree of expansion during the charge and discharge cycle. The carbon coating layer in these negative electrode materials is provided with a suitable content of methyl, methylene and methine, which helps to improve the stability and conductivity of the carbon matrix and reduce the gas production of silicon particles and the side reaction with the electrolyte, so that the lithium ion batteries of Examples 1-9 have a higher capacity and first coulomb efficiency, and have good cycle stability during the charge and discharge cycle.

[0110] Compared with Example 1: Comparative Example 1: Due to the lack of hydrogen in the mixed gas during carbon coating, the methyl groups in the coating layer mainly come from the cracking of the carbon source, and the overall content is relatively small, resulting in the negative electrode material <0.1. In the carbon coating layer, the methyl content is too low, which affects the chemical stability of the obtained negative electrode material, significantly increases the gas production of silicon particles, and significantly increases the expansion degree of the pole piece during the charge and discharge cycle, affecting the electrochemical performance of the obtained lithium-ion battery.

[0111] In Comparative Example 2, since the mixed gas contains excessive hydrogen during carbon coating, the hydrogenation effect of hydrogen is dominant during the coating process, causing excessive methine and methylene groups to be converted into methyl groups, resulting in excessive methyl groups being formed on the carbon coating layer, while the content of methylene and methine groups is relatively insufficient. >0.5, the reaction activity of the group decreases, and the electron transmission path is relatively reduced, resulting in a decrease in the conductivity of the negative electrode material, affecting the electronic conductivity of the resulting lithium-ion battery, thereby causing a significant decrease in the capacity and first coulombic efficiency of the battery prepared from the negative electrode material.

[0112] In Comparative Examples 3 and 4, due to insufficient heat treatment temperature and time during carbon coating, the carbon source gas was not fully cracked. Since the carbon source gas cracking reaction failed to proceed to the expected stage, intermediates or by-products containing methyl groups were generated and retained in the product under the influence of the reaction conditions, resulting in an increase in the proportion of methyl groups in the obtained coating layer, resulting in When the reaction activity of the group is lower than 0.5, the electron transmission path is relatively reduced, resulting in a decrease in the conductivity of the negative electrode material, affecting the electronic conductivity of the obtained lithium-ion battery, thereby reducing the capacity and the first coulombic efficiency.

[0113] The above results show that the carbon coating of the negative electrode material includes methyl, methylene and methine. The stretching vibration peak area S of methyl, methylene and methine on the carbon coating of the negative electrode material is quantitatively analyzed by infrared spectroscopy. 3 , S 2 and S 1 , and satisfy it , which is conducive to exerting the structural stability and hydrophobicity of the methyl group, and exerting the reactivity of the methylene or methine group, and improving the chemical stability and conductivity of the obtained negative electrode material as a whole, and improving the capacity and first coulomb efficiency of the obtained secondary battery. Thus, the problems in the prior art that the negative electrode material matrix is ​​unstable and the active material is exposed on the surface of the matrix, affecting the battery cycle stability and conductivity, are improved.

[0114] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises a core and a carbon coating layer covering at least part of the surface of the core, the core comprises a matrix and an active substance, the matrix has pores, at least part of the active substance is arranged in the pores of the matrix, and the negative electrode material is tested by infrared spectroscopy analysis at a wave number of 2896±10 cm -1 The area of ​​the stretching vibration peak at wave number 2924±10 cm -1 and 2853±10 cm -1 The sum of the stretching vibration peak areas at wave number 2960 ± 10 cm -1 The area of ​​the stretching vibration peak at is S3; S1, S2 and S3 satisfy: .

2. The negative electrode material according to claim 1, characterized in that The substrate satisfies at least one of the following conditions: (1) The specific surface area of ​​the substrate is 500 m 2 / g to 2000 m 2 / g; (2) The total pore volume of the matrix is ​​0.5 cm 3 / g to 2.0 cm 3 / g; (3) The average pore size of the matrix is ​​0.1 nm to 8 nm.

3. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following conditions: (1) The average particle size of the active substance is 0.1 nm to 100 nm; (2) The thickness of the carbon coating layer is 0.1 nm to 2000 nm.

4. The negative electrode material according to claim 1, characterized in that The negative electrode material satisfies at least one of the following conditions: (1) The specific surface area of ​​the negative electrode material is 1 m 2 / g to 10 m 2 / g; (2) The powder conductivity of the negative electrode material is 0.05 S / m to 5 S / m; (3) Median particle size D of the negative electrode material V 50 is 3 μm to 15 μm.

5. The negative electrode material according to claim 1, characterized in that The substrate includes one or both of carbon material and non-carbon material; The carbon material includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers and graphene; The non-carbon material includes at least one of metal oxides, silicides, silicates, phosphates, titanates and aluminum borates; the metal oxide includes one or more of aluminum oxide, zirconium oxide, germanium dioxide and manganese dioxide; the silicide includes one or more of silicon carbide and silicon nitride; the silicate includes one or more of cordierite, mullite and zeolite; the phosphate includes one or more of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate and lanthanum phosphate; the titanate includes one or more of calcium titanate, iron titanate, lithium titanate and barium titanate.

6. The negative electrode material according to claim 1, characterized in that The active material includes one or more of Si, Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P and Cu.

7. The negative electrode material according to claim 1, characterized in that The carbon material of the carbon coating layer includes one or more of amorphous carbon and graphitized carbon.

8. The negative electrode material according to claim 1, characterized in that The matrix includes a carbon matrix, the active material includes a silicon material, the silicon material includes one or more of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon, and the negative electrode material further satisfies at least one of the following conditions: (1) Based on the mass of the negative electrode material, the mass proportion of carbon element in the negative electrode material is 30% to 70%; (2) Based on the mass of the negative electrode material, the mass proportion of hydrogen element in the negative electrode material is less than or equal to 5%; (3) Based on the mass of the negative electrode material, the mass proportion of silicon element in the negative electrode material is 30% to 80%.

9. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, characterized in that: The negative electrode active material layer comprises the negative electrode material according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 9.

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