Negative electrode material, preparation method, and use

Abstract

The present application relates to the technical field of batteries, and in particular, to a negative electrode material, a preparation method, and a use. The negative electrode material comprises a silicon-carbon composite material; the silicon-carbon composite material comprises porous carbon and nano-silicon particles located in pores of the porous carbon; and the ratio of the end face area to the total area of the porous carbon is A, the ratio of the basal face area to the total area is B, and the ratio of the defect face area to the total area is C, wherein the following relational expressions are satisfied: A<B<C, 0≤A<40%, 0<B<40%, 40%<C<80%, 1<M<20, and M=(A+C) / B. By using the porous carbon characterized by the described ratio relationship, utilization efficiency of a silicon source is improved; pressure resistance of the negative electrode material is enhanced; and the negative electrode material exhibits low expansion performance, high capacity, excellent rate capability, and cycling performance.

Description

Negative electrode materials, preparation methods and applications

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202410362923.5, filed with the Patent Office of China on March 28, 2024, entitled “A negative electrode material, a preparation method thereof, and a secondary battery,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a negative electrode material, a preparation method and an application thereof. Background Art

[0004] With the rapid promotion of new energy sources such as electric vehicles, photovoltaic power generation, and wind power, the demand for using secondary batteries to store these energy sources is increasing. The negative electrode material of secondary batteries has a crucial impact on the overall battery performance.

[0005] Silicon anode materials undergo significant volume changes during battery charge and discharge, leading to the shedding and pulverization of active materials and even damage to the electrode structure, resulting in rapid capacity decay and severely restricting their industrial application. Carbon materials, on the other hand, have a stable structure, relatively small volume changes during charge and discharge, and good cycle stability. Furthermore, they share similar chemical properties to silicon. Silicon and carbon materials are often combined to create silicon-carbon composites to improve silicon's volume effect and enhance its electrochemical stability.

[0006] Silicon-carbon composite material is a secondary battery negative electrode material with good electrochemical properties, which can achieve high capacity, long life and excellent fast charge and discharge performance.

[0007] In view of this, this invention is proposed.

[0008] Summary of the Invention

[0009] The first purpose of the present disclosure is to provide a negative electrode material, which, by adopting porous carbon with a specific adsorption potential, is conducive to the deposition of nano-silicon particles in the porous carbon, thereby improving the utilization rate of the silicon source; the porous carbon has high compressive strength, thereby improving the pressure resistance and mechanical strength of the negative electrode material; and improves the volume expansion of the negative electrode material, thereby improving the capacity, rate performance and cycle performance.

[0010] The second object of the present disclosure is to provide a method for preparing a negative electrode material.

[0011] A third object of the present disclosure is to provide a secondary battery.

[0012] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions are adopted:

[0013] The present disclosure provides a negative electrode material, comprising a silicon-carbon composite material; the silicon-carbon composite material comprises porous carbon and nano-silicon particles located in the pores of the porous carbon;

[0014] The ratio of the end face area to the total area of ​​the porous carbon is A, the ratio of the base face area to the total area is B, and the ratio of the defect face area to the total area is C, and the following relationship is satisfied: <B<C,0≤A<40%,0<B<40%,40%<C<80%,1<M<20,M=(A+C) / B。

[0015] Furthermore, 1 <M<10。

[0016] Furthermore, 0≤A<20%, 20% <B<40%,40%<C<80%。

[0017] Furthermore, 0≤A<10%, 20% <B<40%,40%<C<80%。

[0018] Furthermore, the particle size Dv50 of the porous carbon is 3 to 10 μm.

[0019] Furthermore, the specific surface area of ​​the porous carbon is 1500 to 2200 m 2 / g;

[0020] And / or, the pore volume of the porous carbon is 0.8 to 1.2 cm 3 / g;

[0021] And / or, the microporosity of the porous carbon is 80% to 100%.

[0022] Furthermore, the negative electrode material also includes a carbon layer coated on the surface of the silicon-carbon composite material.

[0023] Furthermore, the test method for the ratio of the end face area to the total area, the ratio of the basal face area to the total area, and the ratio of the defective face area to the total area of ​​the porous carbon includes:

[0024] Nitrogen adsorption tests were performed at liquid nitrogen temperature (77.3 K) using a Micromeritics ASAP 2460 instrument. Prior to testing, the samples were degassed at 443 K until a static vacuum of less than 0.01 Torr was achieved. The adsorption potential distribution was calculated from the adsorption isotherms using the standard instrument software DFT. (NLDFT) software. Select "DFT surface energy" in the software and select "DFT Modified Density Functional" fitting model. The horizontal axis of the obtained data is energy (e / K) and the vertical axis is the cumulative pore area (m 2 / g), derived energy (e / K)-cumulative pore area (m2 / g)data;

[0025] The adsorption potential distribution centered on energy 50K~60K represents the basal plane, below 50K is the end plane, and above 60K is the defect plane; the calculation method is: in the nitrogen adsorption specific surface area test, the basal plane, end plane and defect plane are quantified by the nitrogen adsorption specific surface area through density functional theory, the total adsorption area corresponding to the total energy of the porous carbon (total cumulative pore area) is S, the accumulated pore area at 50K energy is A1, and the accumulated pore area at 60K energy is A2, then 50K~60K reflects the cumulative pore area J=A2-A1 of the basal plane, and the total area minus the accumulated pore area at 60K energy is the cumulative pore area Q of the defect plane; the proportion of different energy planes is reflected by the ratio of the cumulative area corresponding to the adsorption potential to the total surface area, then below 50K (end plane)=A1 / S, 50~60K (basal plane)=J / S, and above 60K (defect plane)=Q / S, and the sum of the three is 100%.

[0026] The present disclosure also provides a method for preparing the negative electrode material as described above, comprising the following steps:

[0027] The porous carbon is vapor-deposited in an atmosphere containing a silicon source to obtain a silicon-carbon composite material.

[0028] Furthermore, the method for preparing the negative electrode material further includes the following step: sintering the silicon-carbon composite material in an atmosphere containing a carbon source to obtain the negative electrode material.

[0029] The present disclosure also provides a negative electrode plate, comprising the negative electrode material as described above.

[0030] The present disclosure also provides a secondary battery comprising the negative electrode material as described above.

[0031] The present disclosure also provides an electrical device including the secondary battery described above.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] In the negative electrode material disclosed herein, by adopting porous carbon with a specific ratio relationship as a matrix, it is beneficial for nano-silicon particles to be deposited in the porous carbon, thereby improving the utilization rate of the silicon source; the porous carbon has high particle compressive strength, thereby improving the pressure resistance and mechanical strength of the negative electrode material, making it more pressure-resistant during electrode rolling; the porous carbon can be deformed without breaking, providing sufficient buffer space for the expansion of silicon, improving the volume expansion of the negative electrode material, and making it have low expansion; the ion diffusion performance of the negative electrode material is improved, and the capacity, initial charge and discharge performance, first coulomb efficiency, rate performance and cycle performance are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] FIG1 is a graph showing the compressive strength of porous carbon according to Example 2 of the present disclosure. DETAILED DESCRIPTION

[0036] The technical solutions of the present disclosure will be clearly and completely described below in conjunction with specific embodiments, but those skilled in the art will understand that the embodiments described below are part of the embodiments of the present disclosure, rather than all of the embodiments, and are only used to illustrate the present disclosure, and should not be considered as limiting the scope of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present disclosure. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0037] In some embodiments of the present disclosure, a negative electrode material is provided, comprising a silicon-carbon composite material; the silicon-carbon composite material comprises porous carbon and nano-silicon particles located in the pores of the porous carbon;

[0038] The ratio of the end face area to the total area of ​​porous carbon is A, the ratio of the base face area to the total area is B, and the ratio of the defect face area to the total area is C, and they satisfy the following relationship: A <B<C,0%≤A<40%,0%<B<40%,40%<C<80%,1<M<20,M=(A+C) / B。

[0039] The nano silicon particles in the negative electrode material of the present disclosure are silicon particles that are less than 100 nm in at least one dimension. For example, the particle size of the silicon nano particles can be 99 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1.5 nm, 1 nm, 0.5 nm, or a range consisting of any two of them. For example, a typical but non-limiting range can be less than 2 nm.

[0040] Porous carbon has two main types of surfaces: the basal plane and the end planes (edges). The ideal (defect-free and contaminant-free) basal plane surface is uniform (smooth) and consists only of carbon atoms; while the end plane (prismatic surface) is non-uniform (rough) and contains various surface groups in addition to carbon, mainly oxygen-containing groups.

[0041] The basal and end faces of porous carbon exhibit different physical and chemical behaviors in many ways, which also has a significant impact on the electrochemical reactivity of lithium-ion batteries. The surface groups and defects of porous carbon also have a significant impact on the performance of the resulting negative electrode material (silicon-carbon composite material). Porous carbon is used as a negative electrode material for lithium-ion batteries. The surface morphology and chemical properties of porous carbon have a significant impact on the formation of the solid electrolyte interface (SEI), the corresponding irreversible charge loss, and the overall electrochemical performance.

[0042] While the ideal basal surface is quite inert to gas treatment, the surface chemistry and morphology of non-basal surfaces (including end faces and defective surfaces) and anode performance can be significantly altered. This disclosure defines the proportion of basal surface area, end face area, and defective surface area within the total surface area of ​​porous carbon. Using porous carbon with these ratios can yield anode materials with superior performance.

[0043] The proportions (area ratios) of the end faces, basal faces, and defective faces of the porous carbon in the total surface of the porous carbon are calculated from their respective adsorption potential energies and obtained by the following method:

[0044] Definition of adsorption potential: There is an adsorption force field on the surface of the adsorbent. When the adsorbate molecules are adsorbed, adsorption work is required, also known as adsorption potential. It is the work done by the adsorption force to move 1 mol of gas from the space outside the range of the adsorption force to a certain point within the adsorption force field.

[0045] The test principle is as follows: During physical adsorption, the magnitude of the adsorption potential depends largely on the local density of the constituent atoms of the adsorbent. Basal surfaces, which offer a higher areal carbon density, will adsorb nitrogen more strongly than end surfaces, which have a lower density. Therefore, in the adsorption potential distribution, end surfaces are represented by lower surface energies. In contrast, lattice defects in porous carbon surfaces, such as surface groups or surface steps and dislocations, lead to increased "surface roughness," which also enhances adsorbent-adsorbate molecule interactions and results in higher adsorption potentials on defect surfaces than on basal surfaces, leading to stronger adsorption of nitrogen.

[0046] The test method is as follows: Nitrogen adsorption test is performed at liquid nitrogen temperature (77.3K) using a Micromeritics ASAP 2460 instrument; before testing, the sample is degassed at 443K until a static vacuum of less than 0.01 Torr is reached; the adsorption potential distribution is calculated based on the adsorption isotherm using standard instrument software DFT. (NLDFT) software. Select "DFT surface energy" in the software, select the "DFT Modified Density Functional" fitting model. The abscissa of the obtained data is energy (e / K), and the ordinate is the cumulative pore area (m 2 / g). Export the energy (e / K) - cumulative pore area (m 2 / g) data.

[0047] The end face and the defect face are non-basal planes. The adsorption potential of the end face in porous carbon is the weakest, the adsorption potential of the basal plane is in the middle, and the adsorption potential of the defect face is the highest. Definition: The adsorption potential distribution centered at an energy of 50K - 60K represents the basal plane, below 50K is the end face, and above 60K is the defect face. The calculation method is as follows: In the nitrogen adsorption specific surface area test, the basal plane, end face, and defect face are quantified by density functional theory from the nitrogen adsorption specific surface area. The total adsorption area corresponding to the total energy of the porous carbon (the total cumulative pore area) is S. The pore area accumulated at an energy of 50K is A1, and the pore area accumulated at an energy of 60K is A2. Then, the cumulative pore area J of the basal plane reflected by 50K - 60K = A2 - A1, and the cumulative pore area Q of the defect face is the total area minus the pore area accumulated at an energy of 60K. The proportion of different energy planes is reflected by the ratio of the cumulative area corresponding to the adsorption potential to the total surface area. Then, below 50K (end face) = A1 / S, 50 - 60K (basal plane) = J / S, above 60K (defect face) = Q / S, and the sum of the three is 100%.

[0048] In some embodiments of the present disclosure, typically but not limited to, for example, A can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 39% or a range value composed of any two of them; B can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 39% or a range value composed of any two of them; C can be 41%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 79% or a range value composed of any two of them.

[0049] The ratio range M of the proportion of the non-basal plane (A + C) to the proportion of the basal plane B satisfies 1 < M < 20. The ratio of the non-basal plane to the basal plane is an important factor determining the plane quality because the transmission of lithium ions during charge and discharge usually occurs through the end face rather than the basal plane.

[0050] The negative electrode material of the present disclosure, by adopting the porous carbon with specific ratio relationships characterized by the above nitrogen adsorption test, is conducive to the deposition of nano-silicon particles in the porous carbon, thereby improving the utilization rate of the silicon source; this porous carbon has high particle compressive strength, thereby improving the pressure resistance performance and mechanical strength of the negative electrode material, making it more resistant to pressure during the rolling of the electrode sheet; the porous carbon can deform without breaking, providing sufficient buffer space for the expansion of silicon, improving the volume expansion of the negative electrode material, and endowing it with low expansibility; it improves the ion diffusion performance of the negative electrode material, and enhances the capacity, initial charge-discharge performance, first Coulomb efficiency, rate performance, and cycle performance.

[0051] In some embodiments of the present disclosure, 1 < M < 10; typically but not limited to, for example, the value of M can be 1.1, 2, 3, 4, 5, 6, 7, 8, 9, 9.9 or the range value composed of any two of them.

[0052] In some embodiments of the present disclosure, 0 ≤ A < 20%, 20% < B < 40%, 50% < C < 80%.

[0053] In some embodiments of the present disclosure, 0 ≤ A < 10%, 20% < B < 40%, 50% < C < 80%; more preferably, 0 ≤ A < 5%; more preferably, A is 0.

[0054] When the adsorption potential A of the end face of the porous carbon tends to 0%, the morphology of the porous carbon particles tends to be spherical, with a higher packing density, better fluidity, and better coating uniformity compared to irregular carbon materials.

[0055] Among the ratios of the areas of each face of the porous carbon to the total surface area, when the strength of the defective face ratio C is enhanced relative to the end face ratio A and the basal face ratio B, the lattice defects in the porous carbon are high, such as surface groups, surface steps, and dislocations, resulting in an increase in "surface roughness", which is conducive to the deposition of the silicon source, so there will be a higher utilization rate of the silicon source; at the same time, with a rough surface, the porous carbon will have more active sites, which is conducive to the insertion and extraction of lithium ions.

[0056] In some embodiments of the present disclosure, the particle size Dv50 of the porous carbon is 3 - 10 μm; typically but not limited to, for example, the particle size Dv50 of the porous carbon can be 3 μm, 5 μm, 7 μm, 10 μm or the range value composed of any two of them.

[0057] In some embodiments of the present disclosure, the particle size Dv99 of the porous carbon is 10 to 25 μm; typically but not limitatively, for example, the particle size Dv99 of the porous carbon can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or a range of any two thereof.

[0058] In some embodiments of the present disclosure, the particle size Dn10 of the porous carbon is 0.5 to 5 μm; typically but not limitatively, for example, the particle size Dn10 of the porous carbon can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or a range of any two thereof.

[0059] In some embodiments of the present disclosure, the specific surface area (BET) of the porous carbon is 1500 to 2200 m 2 / g; Typical but non-limiting examples include porous carbon having a specific surface area of ​​1500 m 2 / g、1700m 2 / g、1900m 2 / g、2000m 2 / g、2200m 2 / g or a range consisting of any two of them.

[0060] In some embodiments of the present disclosure, the pore volume of the porous carbon is 0.8 to 1.2 cm 3 / g.

[0061] In some embodiments of the present disclosure, the microporosity of the porous carbon is 80% to 100%; alternatively, the microporosity of the porous carbon is 90% to 100%.

[0062] Microporosity refers to the percentage of pore volume with a pore diameter of less than 2 nm in porous carbon tested by nitrogen adsorption method to the total pore volume.

[0063] In some embodiments of the present disclosure, the compressive strength of the porous carbon is 50 to 400 MPa; optionally 100 to 400 MPa; more optionally 300 to 400 MPa.

[0064] The adsorption potential reflects the ratio of the end face, base face and defect face of porous carbon, and the matrix structure is related to pore formation. The porous carbon that meets the above ratio has higher mechanical strength.

[0065] In some embodiments of the present disclosure, the sphericity of the porous carbon is ≥0.85; typically but not limiting, for example, the sphericity of the porous carbon may be 0.85, 0.87, 0.90, 0.93, 0.95, 0.98, 1, and the like.

[0066] Sphericity refers to the following: The sphericity D of porous carbon is measured using a laser particle size analyzer (model BT-2900) based on the analysis method specified in GB / T 38887-2020. Specifically, the porous carbon solid powder is dispersed using electromagnetic vibration sampling and free-fall dispersion techniques. The sphericity D is then output using a high-speed CCD camera and image processing software with multi-threading and edge recognition technology.

[0067] When the sphericity D of the porous carbon is higher, it is beneficial to increase the pores between the porous carbon particles, thereby facilitating lithium ion transmission and improving the rate performance and cycle performance of the electrochemical device.

[0068] The pore volume of the porous carbon disclosed herein is 0.8 to 1.2 cm 3 / g, including macropores, mesopores and micropores, and the proportion of the pore volume of micropores is ≥80%; by regulating the pore volume of porous carbon and the proportion of the pore volume of micropores within the scope of the present disclosure, the pores of the porous carrier carbon material can provide sufficient buffer space for the expansion of silicon, thereby making the silicon-carbon composite material less likely to expand, further improving the cycle performance of the secondary battery.

[0069] The porous carbon disclosed in the present invention has a higher specific surface area, a higher microporosity, and better single-particle compressive strength. When preparing silicon-carbon composite materials, the utilization rate of silicon source gas can be significantly improved, and the prepared negative electrode can have low expansion performance. When used as the negative electrode active material of a secondary battery, it has a high capacity and can obtain good cycle characteristics and initial charge and discharge characteristics.

[0070] The highly microporous porous carbon disclosed in the present invention has high particle compressive strength, so it can be more pressure-resistant during pole piece rolling, thereby improving mechanical strength; the porous carbon can be deformed without breaking, and the porous carbon provides a high volume loading capacity.

[0071] In some embodiments of the present disclosure, the porous carbon includes at least one of biomass-derived carbon, resin-derived carbon, petroleum coke-derived carbon, coal-derived carbon, metal-modified carbon materials, and metal oxide-modified carbon materials.

[0072] In some embodiments of the present disclosure, porous carbon can be selected from commercially available products or prepared by methods known in the art, such as hydrothermal method, solvothermal method, electrochemical deposition method, powder metallurgy method, molten metal method, ion exchange method, activation method, etc.

[0073] In some embodiments of the present disclosure, the silicon content in the silicon-carbon composite material is 5 wt% to 85 wt%; typically but not limitatively, for example, the silicon content in the silicon-carbon composite material can be 5 wt%, 15 wt%, 25 wt%, 35 wt%, 45 wt%, 55 wt%, 65 wt%, 75 wt%, 85 wt% or a range of any two thereof.

[0074] In some embodiments of the present disclosure, in the negative electrode material, the mass percentage of the carbon layer is 1 wt% to 10 wt%; typically but not limitatively, for example, in the negative electrode material, the mass percentage of the carbon layer can be 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt% or a range of any two thereof.

[0075] In some embodiments of the present disclosure, in the negative electrode material, the sum of the mass percentages of the C element and the Si element is 100%.

[0076] In some embodiments of the present disclosure, the negative electrode material may contain other elements in addition to C and Si. Without being bound by theory, the other elements may be unavoidable impurities, lithiophilic substances, carbonaceous materials or other substances.

[0077] In some embodiments of the present disclosure, a method for preparing the above-mentioned negative electrode material is also provided, comprising the following steps:

[0078] The porous carbon is vapor-deposited in an atmosphere containing a silicon source to obtain a silicon-carbon composite material.

[0079] The silicon source gas is thermally decomposed at high temperature to form silicon element and then filled into porous carbon with a porous structure to obtain a silicon-carbon composite material, that is, porous carbon deposited with nano-silicon particles. This material has a high first coulombic efficiency and electrochemical performance.

[0080] In some embodiments of the present disclosure, the silicon source includes at least one of monosilane, disilane, monochlorosilane, and dichlorosilane.

[0081] In some embodiments of the present disclosure, the volume concentration of the silicon source in the atmosphere containing the silicon source is 1% to 60%.

[0082] In some embodiments of the present disclosure, the vapor deposition includes: heating to 400-700° C. and maintaining the temperature for 1-20 hours.

[0083] In some embodiments of the present disclosure, the heating rate during the vapor deposition process is 1-10° C. / min.

[0084] In some embodiments of the present disclosure, the vapor deposition reactor includes a box furnace, a rotary kiln, a tube furnace, a vacuum furnace, a roller kiln, a fluidized bed, or a plasma-enhanced chemical vapor deposition device.

[0085] In some embodiments of the present disclosure, the method for preparing the negative electrode material further includes the following step: sintering the silicon-carbon composite material in an atmosphere containing a carbon source to obtain the negative electrode material.

[0086] In some embodiments of the present disclosure, sintering includes: heating to 400-800° C. and maintaining the temperature for 1-20 hours.

[0087] In some embodiments of the present disclosure, the heating rate of the sintering process is 1-10° C. / min.

[0088] In some embodiments of the present disclosure, the carbon source includes at least one of methane, ethane, propane, isopropane, butane, isobutane, ethylene, propylene, acetylene, butene, vinyl chloride, vinyl fluoride, 1,1-difluoroethylene, ethyl chloride, pentachlorofluoroethane, difluoroethane, methyl chloride, methyl fluoride, difluoromethane, trifluoromethane, methylamine and formaldehyde.

[0089] In some embodiments of the present disclosure, the volume concentration of the carbon source in the atmosphere containing the carbon source is 1% to 50%.

[0090] Some embodiments of the present disclosure further provide a negative electrode plate comprising the negative electrode material as described above.

[0091] In some embodiments of the present disclosure, a secondary battery is further provided, comprising the above-mentioned negative electrode material.

[0092] In some embodiments of the present disclosure, the secondary battery includes a lithium-ion battery.

[0093] The use of the negative electrode material disclosed herein in a secondary battery is beneficial for improving the capacity, rate performance, and cycle performance of the battery.

[0094] Some embodiments of the present disclosure further provide an electrical device including the secondary battery described above.

[0095] In some specific embodiments of the present disclosure, a method for preparing porous carbon comprises the following steps: cutting 100 g of the stem of Eupatorium adenophorum into inch-long segments, washing and removing dust, and then soaking them in a 5 wt% to 30 wt% HCl solution for 0.5 to 48 hours, and then washing with distilled water to remove the HCl; drying them in an oven at 80°C, placing them in a microwave oven, heating them to 500°C at a rate of 5°C / min under a vacuum atmosphere, and keeping them warm for 2 hours, and then heating them to 900°C and carbonizing them for 5 hours to obtain porous carbon based on Eupatorium adenophorum.

[0096] The method for preparing porous carbon in the specific embodiments of the present disclosure is described using the above-mentioned method for preparing porous carbon as an example, but is not limited thereto, and any other method for preparing porous carbon may be used.

[0097] Example 1

[0098] The method for preparing the negative electrode material provided in this embodiment includes the following steps:

[0099] S1. Place 1 kg of porous carbon in a rotary kiln, heat to 100 ° C, keep warm for 30 minutes under vacuum, then introduce nitrogen protection, then raise the temperature to 450 ° C at a rate of 5 ° C / min, and introduce silane (SiH4) at a flow rate of 0.5 L / min for 4 hours, and close the silicon source valve;

[0100] In porous carbon, the ratio of the end face area to the total area is A, which is 6.40%, the ratio of the basal face area to the total area is B, which is 33.77%, and the ratio of the defect face area to the total area is C, which is 59.82%. M = (A + C) / B, and M is 1.96;

[0101] The particle size of the porous carbon is Dv50 is 6.6 μm, Dv99 is 16.2 μm, Dn10 is 3.3 μm, and the specific surface area is 1800 m 2 / g, pore volume is 0.82cm 3 / g.

[0102] S2. The temperature is then raised to 700°C, and acetylene (C2H2) and argon are introduced for 3 hours to obtain a negative electrode material with a silicon content of 48 wt%.

[0103] Example 2

[0104] The preparation method of the negative electrode material provided in this embodiment refers to that in Example 1, except that, in step S1, in the porous carbon, the ratio of the end face area to the total area is A, which is 0%, the ratio of the basal face area to the total area is B, which is 26.13%, and the ratio of the defective face area to the total area is C, which is 73.87%, and M = (A + C) / B, where M is 2.83;

[0105] The particle size of the porous carbon is Dv50 8.5 μm, Dv99 14.5 μm, Dn10 3.5 μm, and the specific surface area is 2100 m 2 / g, pore volume is 0.85cm 3 / g.

[0106] Example 3

[0107] The preparation method of the negative electrode material provided in this embodiment refers to that in Example 1, except that, in step S1, in the porous carbon, the ratio of the end face area to the total area is A, which is 0%, the ratio of the basal face area to the total area is B, which is 6.04%, and the ratio of the defective face area to the total area is C, which is 93.96%, and M = (A + C) / B, where M is 15.56;

[0108] The particle size of the porous carbon is Dv50 9.2 μm, Dv99 21 μm, Dn10 0.3 μm, and the specific surface area is 1150 m 2 / g, pore volume is 0.64cm 3 / g.

[0109] Example 4

[0110] The preparation method of the negative electrode material provided in this embodiment refers to that in Example 1, except that, in step S1, in the porous carbon, the ratio of the end face area to the total area is A, which is 13.5%, the ratio of the basal face area to the total area is B, which is 35.36%, and the ratio of the defective face area to the total area is C, which is 51.14%, and M = (A + C) / B, where M is 1.83;

[0111] The particle size of the porous carbon is Dv50 5.5 μm, Dv99 14.2 μm, Dn10 0.5 μm, and the specific surface area is 1873 m 2 / g, pore volume is 0.87cm 3 / g.

[0112] Example 5

[0113] The preparation method of the negative electrode material provided in this embodiment refers to that in Example 1, except that, in step S1, in the porous carbon, the ratio of the end face area to the total area is A, which is 20.03%, the ratio of the basal face area to the total area is B, which is 32.97%, and the ratio of the defective face area to the total area is C, which is 47%, and M = (A + C) / B, where M is 2.03;

[0114] The particle size of the porous carbon is Dv50 7.1 μm, Dv99 19.2 μm, Dn10 1.7 μm, and the specific surface area is 1790 m 2 / g, pore volume is 0.93cm 3 / g.

[0115] Example 6

[0116] The preparation method of the negative electrode material provided in this embodiment refers to that in Example 1, except that, in step S1, in the porous carbon, the ratio of the end face area to the total area is A, which is 5.45%, the ratio of the basal face area to the total area is B, which is 15.24%, and the ratio of the defective face area to the total area is C, which is 79.31%, and M = (A + C) / B, where M is 5.56;

[0117] The particle size of the porous carbon is Dv50 of 7.3 μm, Dv99 of 18 μm, Dn10 of 0.9 μm, and the specific surface area is 1920 m 2 / g, pore volume is 0.85cm 3 / g.

[0118] Comparative Example 1

[0119] The preparation method of the negative electrode material provided in this comparative example refers to Example 1, except that, in step S1, the porous carbon (manufacturer: Jiangxi Zichen Technology Co., Ltd.) has a ratio of the end face area to the total area (A) of 50.17%, a ratio of the basal surface area to the total area (B) of 26.38%, a ratio of the defective surface area to the total area (C) of 23.44%, M = (A + C) / B, and M is 2.79;

[0120] The particle size of porous carbon is Dv50 8.2 μm, Dv99 is 22 μm, Dn10 is 2.8 μm, and the specific surface area is 1452 m 2 / g, pore volume is 0.65cm 3 / g.

[0121] Test Example 1

[0122] The parameters of the porous carbon in Examples 1 to 6 and Comparative Example 1 are shown in Table 1. The compressive strength of the porous carbon in Example 2 is shown in FIG1 .

[0123] The compressive strength test method involves placing the particle sample to be tested in a fixture using a micro-compression testing machine and clamping it. Select the desired compressive strength test, set appropriate test parameters, and determine the material's compressive strength by characterizing the strength of the particle crushing.

[0124] Test principle: Select a flat indenter with a diameter of 50μm, use two indicators to clamp the sample in the middle, measure the sample in increments of 0.1μm (when using a x50 objective lens) until it increases to 200μm; apply a test force with a constant increasing rate to the sample and fix it between the upper pressure rod and the lower pressure plate; then automatically measure the deformation of the sample. The test force can be set at 9.8mN. Measure and record the pressure and deformation during the deformation process of the sample. The horizontal axis of the obtained data is the compression displacement, and the vertical axis is the test force. The test force at the inflection point of the curve is used to calculate the compressive strength of the material.

[0125] Table 1

[0126] Button-type half-cells were prepared using the negative electrode materials of Examples 1 to 6 and Comparative Example 1, respectively. The performance of each cell was tested, and the results are shown in Table 2.

[0127] Preparation method of coin-type half cell: The active material, SP, CNT, and PAA colloidal solution are mixed in a mass ratio of 80:9:1:10, made into a slurry with deionized water, uniformly coated on a copper foil, and vacuum dried at 80 °C for 24 h to obtain the battery electrode sheet for the experiment. Then, a lithium sheet is used as the counter electrode, and an electrolyte of 1.1 mol / L LiPF6 with a solvent of a four-component mixed solvent, ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 1:1:1:1 (volume ratio), and a polypropylene microporous film is used as the separator to assemble a CR2025-type coin-type half cell in a vacuum glove box.

[0128] The test method for battery performance is as follows: A battery test system (a multi-channel battery test system of Arbin in the United States for half-cell tests, and a Labstar (1200 / 780) type glove box of Braun in Germany) is used to test the capacity and the first charge-discharge efficiency (initial efficiency).

[0129] The test steps are: 0.1C DC to 5 mV, stand for 5 min; 0.02C DC to 5 mV, stand for 5 min; 0.01C DC to 5 mV, stand for 5 min; 0.1C CC to 0.8V, 0.1C CC to 2V.

[0130] Silane utilization rate % = [receiving material amount (g) × silicon content (%)] / [volume of silane introduced (L) × silane density (g / L)].

[0131] Table 2

[0132] As can be seen from Table 1, in Example 2, when A is equal to 0%, the porous carbon tends to be spherical, has a higher sphericity, and higher compressive strength. In Example 3, the C value is relatively high, M = 15.6, the pore volume of the porous carbon is relatively low, resulting in a relatively low capacity of the anode material. In Comparative Example 1, the relationship A < B < C is not met, M = 2.79, its compressive strength is poor, and the silane utilization rate is low.

[0133] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present disclosure, and are not intended to limit them; Although the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure. Industrial applicability

[0134] In the negative electrode material disclosed herein, by adopting porous carbon with a specific ratio relationship as a matrix, it is beneficial for nano-silicon particles to be deposited in the porous carbon, thereby improving the utilization rate of the silicon source; the porous carbon has high particle compressive strength, thereby improving the pressure resistance and mechanical strength of the negative electrode material, making it more pressure-resistant during electrode rolling; the porous carbon can be deformed without breaking, providing sufficient buffer space for the expansion of silicon, improving the volume expansion of the negative electrode material, and making it have low expansion; the ion diffusion performance of the negative electrode material is improved, and the capacity, initial charge and discharge performance, first coulomb efficiency, rate performance and cycle performance are improved.

Claims

1. A negative electrode material, characterized in that Comprising a silicon-carbon composite material; the silicon-carbon composite material comprises porous carbon and nano-silicon particles located in the pores of the porous carbon; The ratio of the end face area to the total area of ​​the porous carbon is A, the ratio of the base face area to the total area is B, and the ratio of the defect face area to the total area is C, and the following relationship is satisfied: <B<C,0≤A<40%,0<B<40%,40%<C<80%,1<M<20,M=(A+C) / B。 2. The negative electrode material according to claim 1, characterized in that 1<M<10。 3. The negative electrode material according to claim 1 or 2, characterized in that 0≤A<20%,20% <B<40%,40%<C<80%。 4. The negative electrode material according to claim 3, characterized in that 0≤A<10%,20% <B<40%,40%<C<80%。 5. The negative electrode material according to any one of claims 1 to 4, characterized in that The particle size Dv50 of the porous carbon is 3 to 10 μm.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that The specific surface area of ​​the porous carbon is 1500 to 2200 m 2 / g; And / or, the pore volume of the porous carbon is 0.8 to 1.2 cm 3 / g; And / or, the microporosity of the porous carbon is 80% to 100%.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that The negative electrode material further includes a carbon layer coated on the surface of the silicon-carbon composite material.

8. The negative electrode material according to any one of claims 1 to 7, characterized in that The method for testing the ratio of the end face area to the total area, the basal face area to the total area, and the defect face area to the total area of ​​the porous carbon includes: using a Micromeritics ASAP 2460 instrument to perform a nitrogen adsorption test at liquid nitrogen temperature (77.3K); before the test, the sample is degassed at 443K until a static vacuum of less than 0.01 Torr is reached; the adsorption potential distribution is calculated based on the adsorption isotherm, and the standard instrument software DFT is used. (NLDFT) software, select "DFT surface energy" in the software, select "DFT Modified Density Functional" fitting model, the horizontal axis of the obtained data is energy (e / K), and the vertical axis is the cumulative pore area (m 2 / g), derived energy (e / K)-cumulative pore area (m 2 / g) data; The adsorption potential distribution centered on energy 50K~60K represents the basal plane, below 50K is the end plane, and above 60K is the defect plane; the calculation method is: in the nitrogen adsorption specific surface area test, the basal plane, end plane and defect plane are quantified by the nitrogen adsorption specific surface area through density functional theory, the total adsorption area corresponding to the total energy of the porous carbon (total cumulative pore area) is S, the accumulated pore area at 50K energy is A1, and the accumulated pore area at 60K energy is A2, then 50K~60K reflects the cumulative pore area J=A2-A1 of the basal plane, and the total area minus the accumulated pore area at 60K energy is the cumulative pore area Q of the defect plane; the proportion of different energy planes is reflected by the ratio of the cumulative area corresponding to the adsorption potential to the total surface area, then below 50K (end plane)=A1 / S, 50~60K (basal plane)=J / S, and above 60K (defect plane)=Q / S, and the sum of the three is 100%.

9. The method for preparing the negative electrode material according to any one of claims 1 to 7, characterized in that: The steps include: The porous carbon is vapor-deposited in an atmosphere containing a silicon source to obtain a silicon-carbon composite material.

10. The method for preparing the negative electrode material according to claim 8, wherein: The method further comprises the following step: sintering the silicon-carbon composite material in an atmosphere containing a carbon source to obtain the negative electrode material.

11. A negative electrode plate, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 8.

12. A secondary battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 8.

13. An electrical equipment, characterized in that: The secondary battery according to claim 12 is included.

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