A negative electrode material, a negative electrode sheet, and a battery

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode material, a negative electrode sheet comprising the negative electrode material and a battery. The negative electrode material has a core-shell structure, the shell comprises a carbon layer, the core comprises porous carbon and silicon particles distributed in the pores of the porous carbon, and the negative electrode material has a weight gain peak in the micro-derivative thermogravimetric curve between 400-900 DEG C. The negative electrode material has high structural stability, can provide a buffer space for the expansion of the silicon particles, the negative electrode sheet prepared from the negative electrode material has high capacity and high initial coulomb efficiency, and the battery prepared from the negative electrode sheet has good rate performance, high cycle capacity retention rate and low expansion rate.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a negative electrode material, a negative electrode sheet including the negative electrode material, and a battery. Background Technology

[0002] The rapid development of new energy technologies such as electronic devices, electric vehicles, and energy storage power stations has placed increasingly higher demands on the energy density of lithium-ion batteries. Currently, graphite is used as the anode material in lithium-ion batteries. However, with continuous advancements in manufacturing processes, the actual performance of graphite is gradually approaching its theoretical limits, hindering further development. In the exploration of next-generation high-energy-density battery materials, silicon-based anodes, with their theoretical capacity ten times that of graphite anodes, have become a key research focus. However, silicon-based anodes experience a volume expansion rate exceeding 300% after full lithium intercalation, easily leading to problems such as particle pulverization, electrode structure damage, and repeated rupture and growth of the surface SEI film, severely restricting their practical application. Furthermore, silicon is a semiconductor material with low electronic and ionic conductivity, resulting in poor rate performance.

[0003] To address these issues, the industry has proposed coating silicon particles with a carbon layer to improve conductivity and prevent direct contact between the electrolyte and silicon particles. However, for conventional carbon-coated silicon-based materials, the core still exhibits a significant volume expansion rate after lithium intercalation. The surface carbon layer deforms along with the core during this expansion, potentially leading to cracking or detachment from the core surface. This makes it difficult to effectively suppress side reactions that occur after the electrolyte and silicon particles come into contact in the long term.

[0004] Therefore, it is very important to invent a battery with better rate performance, higher cycle capacity retention, and lower expansion rate. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a negative electrode material, a negative electrode sheet including the negative electrode material, and a battery. The negative electrode material of this invention has high structural stability and can provide buffer space for the expansion of silicon particles; the negative electrode sheet obtained from the negative electrode material of this invention has high specific capacity and high initial coulombic efficiency; the battery obtained from the negative electrode sheet of this invention has good rate performance, high cycle capacity retention, and low expansion rate.

[0006] The inventors of this invention have discovered that by improving the structural stability of silicon particles, the specific capacity and initial coulombic efficiency of the negative electrode can be increased, thereby improving the rate performance, cycle capacity retention, and reducing the expansion rate of the battery.

[0007] Through further in-depth research, the inventors of this invention discovered that, in order to improve the structural stability of silicon particles, a specific structure can be used to provide buffer space for the volume expansion of silicon particles, reducing the overall expansion rate of the material, thereby improving the specific capacity and initial coulombic efficiency of the negative electrode, enhancing the rate performance and cycle capacity retention of the battery, and reducing the battery's expansion rate. The inventors of this invention, through extensive and in-depth research, have identified a specific structure that can provide buffer space for the volume expansion of silicon particles.

[0008] To achieve the above objectives, the first aspect of the present invention provides a negative electrode material having a core-shell structure, the shell comprising a carbon layer, the core comprising porous carbon and silicon particles distributed in the pores of the porous carbon, and the micro-quotient thermogravimetric curve of the negative electrode material having a weight gain peak between 400-900℃.

[0009] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the first aspect of the present invention.

[0010] A third aspect of the present invention provides a battery comprising the negative electrode material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0011] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0012] (1) The negative electrode material of the present invention has good structural stability;

[0013] (2) The negative electrode sheet of the present invention has high specific capacity;

[0014] (3) The negative electrode of the present invention has high initial coulombic efficiency;

[0015] (4) The battery of the present invention has good rate performance;

[0016] (5) The battery of the present invention has a high cycle capacity retention rate;

[0017] (6) The battery of the present invention has a low volume expansion rate.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] Figure 1 The image shown is an X-ray powder diffraction (XRD) pattern of a negative electrode material according to an embodiment of the present invention.

[0020] Figure 2 The thermogravimetric (TG) curve and thermogravimetric derivative (DTG) curve of the negative electrode material of one embodiment are shown.

[0021] Figure 3The thermogravimetric (TG) curve and thermogravimetric derivative (DTG) curve of the negative electrode material of Example 1 of the present invention are shown.

[0022] Figure 4 The discharge curves of batteries prepared using the negative electrode materials of Example 1 and Comparative Example 1 of this invention at different rates. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] The first aspect of the present invention provides a negative electrode material having a core-shell structure, the shell comprising a carbon layer, the core comprising porous carbon and silicon particles distributed in the pores of the porous carbon, and the micro-quotient thermogravimetric curve of the negative electrode material having a weight gain peak between 400-900℃.

[0025] Existing silicon-carbon composite materials often form a carbon coating layer on the surface of silicon particles through chemical vapor deposition or polymer pyrolysis. However, even if the carbon coating layer formed in this way is relatively dense at the beginning, it will expand along with the silicon particle core during the expansion of the silicon particles. This can easily cause the carbon coating layer to fall off or peel off from the silicon particle surface, resulting in the electrolyte coming into direct contact with the silicon particles. The electrolyte reduces and produces a passivation film on the surface of the silicon particles. As the cycle continues, the passivation film will also repeatedly rupture and grow as the silicon particle core expands and contracts, thereby consuming the active lithium in the battery and generating additional gas, which in turn causes the battery capacity to continuously decrease and the thickness to continuously increase.

[0026] The inventors of this invention have discovered that by depositing silicon particles into the pores of porous carbon to form silicon-carbon composite particles, the unfilled voids in the porous carbon can be used to buffer the volume expansion of silicon particles during lithium insertion and extraction. This reduces the overall volume change rate of the silicon-carbon composite particles during lithium insertion and extraction, improving the structural stability of the silicon-carbon composite particles and avoiding the problem of surface coating failure caused by excessive expansion of silicon particles. Furthermore, by setting a dense carbon layer on the surface of the silicon-carbon composite particles, the reduction and decomposition of the electrolyte can be effectively reduced, thereby further improving the cycle stability of the battery.

[0027] In this invention, by employing the above-described method to improve the stability of the negative electrode material structure, the negative electrode material can achieve better stability than existing technologies. To further improve the effect, one or more of the technical features can be further optimized.

[0028] The carbon layer can partially or completely cover the outer surface of the silicon-carbon composite particles. When the carbon layer partially covers the surface of the silicon-carbon composite particles, the carbon layer can at least cover the pores where silicon particles are distributed. Thus, the carbon layer, as a shell, can prevent the electrolyte from directly contacting the silicon particles, reduce the reduction and decomposition of the electrolyte, and thereby improve the cycle stability of the battery.

[0029] In thermogravimetric analysis (TGA) conducted under air or oxygen atmosphere, the derivative thermogravimetric (DTG) curve of the aforementioned negative electrode material exhibits a weight gain peak between 400 and 900 °C. For example, as... Figure 2 As shown, it can be seen that there is a weight gain peak in its thermogravimetric (DTG) curve between 400-900℃.

[0030] In one example, the derivative thermogravimetric curve (DTG) of the negative electrode material exhibits a weight gain peak between 400 and 900 °C and at least one weight loss peak (e.g., one or two weight loss peaks) in the temperature range below the temperature corresponding to the weight gain peak. The DTG curve is a curve representing the first derivative of the thermogravimetric curve (TG). Both the weight gain peak and the weight loss peak are located between 400 and 900 °C, and the weight loss peak occurs before the position of the weight gain peak.

[0031] In one example, the thermogravimetric analysis results of the negative electrode material in an air or oxygen atmosphere show that its derivative thermogravimetric (DTG) curve has a weight gain peak between 400-900°C and a weight loss peak in the temperature range below the corresponding temperature of the weight gain peak.

[0032] When the DTG curve of the negative electrode material under air or oxygen atmosphere conditions shows a weight gain peak between 400-900℃, it can effectively improve the stability of the negative electrode material and effectively alleviate the expansion of silicon, reduce the contact reaction with the electrolyte surface, thereby improving the cycle life of the negative electrode material and reducing the expansion rate.

[0033] Preferably, the weight loss peak appears as a weight gain peak between 400-900°C. The presence of at least one weight loss peak (e.g., one or two weight loss peaks) in a temperature range below the corresponding weight gain peak further indicates that the shell comprises a relatively dense carbon layer. This is because the weight loss peak may be formed due to the weight loss of the negative electrode material caused by the combustion of the carbon layer in air or oxygen. If there is no carbon layer on the surface or the carbon layer is not dense enough, more oxygen molecules will penetrate the carbon layer and come into contact with silicon. These oxygen molecules will oxidize the silicon before the carbon begins to burn, resulting in weight gain and thus offsetting the weight loss caused by carbon combustion. Consequently, the weight loss peak will not appear before the weight gain peak. Therefore, the presence of at least one weight loss peak (e.g., one or two weight loss peaks) in a temperature range below the corresponding weight gain peak can effectively improve the stability of silicon, while avoiding contact between the core and the electrolyte, and improving the initial coulombic efficiency of the negative electrode.

[0034] For example, such as Figure 3 As shown, the mass change rate of the differential thermogravimetric (DTG) curve between 400-900℃ forms multiple peaks. One of the peaks has a positive value greater than zero, indicating that the peak is a weight gain peak. In the temperature range below the weight gain peak, there is a negative peak with a value less than zero, which is a weight loss peak. It can be seen that there is a relatively dense carbon layer on the surface of the negative electrode material.

[0035] In this invention, the thermogravimetric (TG) curve and thermogravimetric derivative (DTG) curve of the negative electrode material can be obtained by thermogravimetric analysis, for example, using a Shimadzu DTG-60 thermogravimetric analyzer. The sample amount used for testing is 5 mg, with air or oxygen as the atmosphere, a heating rate of 10 °C / min, and a test range of 20 °C-900 °C.

[0036] In one example, the porous carbon has a pore size of less than 10 nm (e.g., 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm).

[0037] In one example, the porous carbon has a pore size of 1 nm to 5 nm.

[0038] In one example, the porous carbon has a pore size of less than 10 nm, and / or the median particle size D of the silicon particles is... v 50 ranges from 0.1nm to 10000nm.

[0039] In one example, the median particle size D of the silicon particles v 50 ranges from 0.1nm to 10000nm (e.g., 0.1nm, 0.5nm, 1nm, 5nm, 10nm, 50nm, 100nm, 500nm, 1000nm, 5000nm, 10000nm, 5000nm, 10000nm).

[0040] It should be noted that when the median particle size D of the silicon particles... v Even when the diameter of the silicon particles is greater than that of the porous carbon, the silicon particles can still be distributed within the pores of the porous carbon. Because the pore size of the porous carbon limits the width of the silicon particles but not their length, the silicon particles distributed within the pores of the porous carbon may grow into larger rod-shaped or dendritic shapes along the carbon pores. Therefore, the median particle size of the silicon particles can be larger than the pore size of the porous carbon.

[0041] In one example, the median particle size D of the silicon particles v 50 represents 100nm to 8000nm.

[0042] According to one specific embodiment, the porous carbon has a pore volume greater than 0.3 cm³. 3 / g (e.g., 0.4cm) 3 / g, 0.5cm 3 / g, 1cm 3 / g, 1.5cm 3 / g、2cm 3 / g, 2.5cm 3 / g, 3cm 3 / g).

[0043] In one example, the porous carbon has a pore volume greater than 0.5 cm³. 3 / g.

[0044] According to one specific embodiment, the negative electrode material exhibits a diffraction peak in the range of 2θ = 28.4° ± 0.5° during X-ray powder diffraction (XRD) testing. The half-width at half-maximum (FWHM) of this diffraction peak, expressed in 2θ degrees as B, satisfies the condition 0.3° ≤ B ≤ 10°. The FWHM represents the peak width at half the height of the diffraction peak.

[0045] In the example, such as Figure 1As shown, diffraction peaks exist within the range of 2θ = 28.4° ± 0.5°. When the negative electrode material exhibits diffraction peaks within this range in XRD testing, it indicates the presence of silicon. When the full width at half maximum (FWHM) B of the diffraction peaks satisfies 0.3° ≤ B ≤ 10°, it indicates that the silicon particles in the negative electrode material have moderate crystallinity and grain size. Moderate crystallinity and grain size result in better lithium-ion transport speed and specific capacity. When B < 0.3°, it indicates that the silicon particles in the negative electrode material have high crystallinity and large grain size. Higher crystallinity of silicon particles leads to relatively slower lithium-ion transport speed within their lattice, and the larger silicon grains experience greater volume expansion after lithium intercalation, which can easily damage the structure of porous carbon particles. When B>10°, it indicates that the silicon particles in the negative electrode material have very small grain size or low silicon content. The smaller grain size of silicon results in a lower packing density, which in turn leads to a lower filling rate of silicon particles in the limited pores of porous carbon, resulting in a lower specific capacity of the negative electrode material.

[0046] In one instance, B satisfies 0.5°≤B≤6°.

[0047] In this invention, the 2θ characteristic diffraction peaks are measured using X-ray diffraction (XRD), for example, using a Shimadzu XRD-6100 X-ray diffractometer, with a sample volume of 0.5 g / cm³. 2 The Kα line of Cu was used as the incident X-ray. The working voltage of the X-ray source was 40 kV, the test power was 2 kW, 2θ was used as the abscissa and the unit was °, the signal intensity was used as the ordinate, the test range was 10° to 80°, the scanning rate was 4° / min, and the data point interval was 0.02°.

[0048] According to one specific embodiment, in the negative electrode material, the weight ratio x of silicon to carbon satisfies 0.33≤x≤3 (e.g., 0.33, 0.5, 0.8, 1, 1.5, 2, 2.5, 3).

[0049] When the weight ratio x of silicon to carbon in the negative electrode material satisfies 0.33 ≤ x ≤ 3, the negative electrode material achieves a relative balance between high specific capacity and high structural stability. When x < 0.33, the silicon content in the negative electrode material is too low, resulting in a low specific capacity that is difficult to meet the high energy density requirements of lithium-ion batteries. When x > 3, the silicon content in the negative electrode material is too high, leading to a large volume change rate during lithium insertion / extraction and a low structural stability of the particles, which is also difficult to meet the high cycle stability requirements of lithium-ion batteries.

[0050] In one example, the weight ratio x of silicon to carbon in the negative electrode material satisfies 0.5 ≤ x ≤ 2.

[0051] In this invention, the relative content of silicon and carbon elements in the negative electrode material can be analyzed by X-ray fluorescence (XRF) or energy dispersive spectroscopy (EDS), for example, using a Thermo Fisher X-ray fluorescence spectrometer or an Oxford energy dispersive spectroscopy spectrometer.

[0052] According to one specific embodiment, the thickness of the carbon layer is 1-15 nm (e.g., 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm). When the thickness of the carbon layer is within the above-mentioned specific range, the carbon layer has stronger conductivity and is less prone to breakage, thereby improving the initial coulombic efficiency of the negative electrode. When the thickness of the carbon layer is less than 1 nm, the conductivity of the negative electrode material decreases; when the thickness of the carbon layer is greater than 15 nm, the carbon content in the material becomes too high, resulting in a lower specific capacity of the negative electrode material.

[0053] In one example, the thickness of the carbon layer is 2-10 nm. A carbon layer thickness of 2-10 nm further enhances the conductivity of the carbon layer, makes it less prone to breakage, and also provides higher specific capacity.

[0054] According to one specific embodiment, the median particle size D of the porous carbon v 50 ranges from 1μm to 15μm (e.g., 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm).

[0055] In one example, the median particle size D of the porous carbon v 50 is 3μm to 12μm.

[0056] In one example, the specific surface area of ​​the porous carbon is 300-1800 m². 2 / g(300m 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1800m 2 / g).

[0057] In one example, the specific surface area of ​​the porous carbon is 500-1600 m². 2 / g.

[0058] In this invention, the specific surface area and pore volume of the porous carbon are measured using the Brunauer-Emmett-Teller (BET) test method. For example, a Tri Star II specific surface area analyzer is used for measurement.

[0059] According to one specific embodiment, the median particle size D of the negative electrode material v 50 ranges from 1μm to 20μm (e.g., 1μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 17μm, 20μm).

[0060] In one example, the median particle size D of the negative electrode material v 50 is 3μm to 15μm.

[0061] In this invention, the median particle size Dv50 of the negative electrode material is measured using a laser particle size distribution method. For example, a Malvern particle size analyzer is used for measurement, and the testing steps are as follows: the negative electrode material is dispersed in deionized water containing a dispersant (e.g., nonylphenol polyoxyethylene ether, content 0.02-0.03 wt%) to form a mixture, the mixture is sonicated for 2 minutes, and then placed in a Malvern particle size analyzer for testing.

[0062] In one example, the specific surface area of ​​the negative electrode material is 0.1-25 m². 2 / g (e.g., 0.1m 2 / g, 0.5m 2 / g、1m 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g).

[0063] In one example, the specific surface area of ​​the negative electrode material is 0.5-20 m². 2 / g.

[0064] The negative electrode material can be prepared by the following method:

[0065] a) The porous carbon material is placed in a vapor deposition furnace, and then silane gas is introduced. The temperature is increased to cause the silane to decompose and produce silicon particles, which are deposited in the pores of the porous carbon to obtain silicon-carbon composite particles as the core.

[0066] b) Place the silicon-carbon composite particles in a vapor deposition furnace, continue to introduce acetylene gas, and raise the temperature to cause the acetylene gas to decompose and produce carbon particles, which are then deposited on the surface of the silicon-carbon particles to form a carbon layer.

[0067] The porous carbon material can be a commercially available porous carbon material, such as activated carbon purchased from Aladdin.

[0068] In one example, the silane gas is selected from one or more of silane, trichlorosilane, and trifluorosilane.

[0069] In one example, the silane pyrolysis conditions are: a temperature of 400-800°C (e.g., 400°C, 500°C, 600°C, 700°C, 800°C) and a time of 6-10 hours.

[0070] In one example, the conditions for acetylene gas pyrolysis are: temperature 600-1000℃ (e.g., 600℃, 700℃, 800℃, 900℃, 1000℃) and time 30 min-2 h.

[0071] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the first aspect of the present invention.

[0072] The materials used in the negative electrode sheet, except for the negative electrode material in the negative electrode active material layer, can all be made in accordance with the methods in this field, and can all achieve higher specific capacity and higher first coulombic efficiency.

[0073] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode material.

[0074] In one example, the negative electrode active material layer also includes graphite.

[0075] In one instance, the graphite is synthetic graphite and / or natural graphite.

[0076] According to one specific embodiment, based on the total weight of the negative electrode material and the graphite, the weight content of the negative electrode material is 3 to 90 wt% (e.g., 3 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%), and the weight content of the graphite is 10 to 97 wt% (e.g., 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, 97 wt%).

[0077] In one example, based on the total weight of the negative electrode material and the graphite, the weight content of the negative electrode material is 5-80 wt%, and the weight content of the graphite is 20-95 wt%.

[0078] In one example, the negative electrode active material layer includes a conductive agent and a binder.

[0079] In one example, the conductive agent is selected from one or more of carbon black (SuperP), acetylene black, Ketjen black, carbon fiber, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0080] In one example, the adhesive is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, and epoxy resin.

[0081] In one example, the negative current collector is selected from one or more of copper foil, carbon-coated copper foil, and perforated copper foil.

[0082] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode material and the graphite is 70wt% to 99wt%, the weight content of the conductive agent is 0.5wt% to 15wt%, and the weight content of the binder is 0.5wt% to 15wt%.

[0083] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode material and the graphite is 80wt% to 98wt%, the weight content of the conductive agent is 1wt% to 10wt%, and the weight content of the binder is 1wt% to 10wt%.

[0084] The negative electrode sheet can be prepared using methods known in the art, or it can be prepared in the following ways:

[0085] The negative electrode material, the graphite, the conductive agent and the binder are mixed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on at least one side of the negative electrode current collector, dried and sliced, then transferred to a vacuum oven for drying, and finally rolled and slit.

[0086] In one example, the drying temperature is 80-120°C.

[0087] In one example, the drying conditions are: temperature 80-120°C, time 8-12h.

[0088] The negative electrode sheet of the present invention improves specific capacity and first coulombic efficiency by including the negative electrode active material layer of the negative electrode material described in the present invention.

[0089] A third aspect of the present invention provides a battery, wherein the negative electrode of the battery is the negative electrode described in the second aspect of the present invention.

[0090] The materials used in the battery, except for the negative electrode, can all be manufactured in accordance with the methods described in this field, and can all achieve better rate performance, higher cycle capacity retention, and lower expansion rate.

[0091] The battery can be a lithium-ion battery.

[0092] In one example, the battery includes a positive electrode, an electrolyte, and a separator.

[0093] The positive electrode sheet can be a conventional positive electrode sheet in the art. For example, the positive electrode sheet includes a positive current collector and a positive active material layer coated on at least one side of the positive current collector, and the positive active material layer includes a positive electrode material.

[0094] In one example, the positive current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, and perforated aluminum foil.

[0095] In one example, the cathode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobalt oxide, nickel-cobalt-manganese ternary materials, nickel-manganese / cobalt-manganese / nickel-cobalt binary materials, lithium manganese oxide, and lithium-rich manganese-based materials.

[0096] The electrolyte can be a conventional electrolyte in the art, for example, the electrolyte is a non-aqueous electrolyte, and the electrolyte includes a carbonate solvent and a lithium salt.

[0097] In one example, the carbonate solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0098] In one example, the lithium salt is selected from one or more of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB, and LiDFOB.

[0099] The diaphragm can be a conventional diaphragm in the art, for example, the diaphragm is selected from polyethylene and / or polypropylene.

[0100] The battery casing may include one of aluminum-plastic film, aluminum alloy, and stainless steel.

[0101] The battery of the present invention, by containing the negative electrode sheet described herein, improves the rate performance and cycle capacity retention of the battery, and reduces battery expansion.

[0102] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0103] The following examples illustrate the negative electrode material and negative electrode sheet of the present invention.

[0104] Example 1

[0105] (1) Preparation of ingredients

[0106] Porous carbon: 30g, pore size 2nm, pore volume 0.65cm³ 3 / g, median particle size 6μm, specific surface area 1200m² 2 / g;

[0107] Silane gas: Trichlorosilane

[0108] Acetylene

[0109] Anode material: 50 parts by weight;

[0110] Graphite: 46.5 parts by weight of artificial graphite;

[0111] Conductive agent: SuperP 0.3 parts by weight;

[0112] Adhesive: 1.6 parts by weight of sodium carboxymethyl cellulose and 1.6 parts by weight of styrene-butadiene rubber;

[0113] Negative current collector: copper foil thickness is 8μm.

[0114] (2) Preparation of negative electrode materials

[0115] Porous carbon was placed in a vapor deposition furnace, and silane gas with a flow rate of 300 sccm was introduced. The temperature was then raised to 500°C to cause the silane to decompose. The decomposition time was controlled to be 8 hours. After the decomposition was completed, the silane was stopped, and the temperature was raised to 700°C. Acetylene gas with a flow rate of 100 sccm was introduced, and the acetylene decomposition time was controlled to be 1 hour.

[0116] (3) Preparation of negative electrode

[0117] The prepared negative electrode material, artificial graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and SuperP were mixed, and deionized water was added. The mixture was then stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both sides of a negative electrode current collector with a thickness of [thickness value missing]. The areal density of the negative electrode slurry coated on the surface of the negative electrode current collector was 11.0 mg / cm³. 2 The negative electrode current collector coated with negative electrode slurry is transferred to an 80°C oven and dried for 12 hours. Then, it is rolled and slit to obtain the negative electrode sheet.

[0118] Example 2

[0119] This embodiment is based on Embodiment 1, except that the conditions for silane cracking are adjusted, with the temperature adjusted to 700°C and the time adjusted to 10 hours, and the conditions for acetylene gas cracking are adjusted, with the temperature adjusted to 800°C. See Table 1 for details.

[0120] Example 3

[0121] This embodiment is based on Embodiment 1, except that the silane gas is changed to methanesilane, as detailed in Table 1.

[0122] Example 4

[0123] This embodiment is based on Embodiment 1, except that the pore size of the porous carbon is adjusted to 9 nm, as detailed in Table 1.

[0124] Example 5

[0125] This embodiment is based on Embodiment 1, except that the pore volume of the porous carbon is adjusted to 0.4 cm³. 3 / g, see Table 1 for details.

[0126] Example 6 group

[0127] This set of examples illustrates the effects of changing the median particle size of porous carbon.

[0128] Example 6a

[0129] This embodiment is based on Example 1, except that the median particle size of the porous carbon is adjusted to 10 μm, as detailed in Table 1.

[0130] Example 6b

[0131] This embodiment is based on Example 1, except that the median particle size of the porous carbon is adjusted to 15 μm, as detailed in Table 1.

[0132] Example 7

[0133] This embodiment is based on Embodiment 1, except that the specific surface area of ​​the porous carbon is adjusted to 800 m². 2 / g, see Table 1 for details.

[0134] Example 8 group

[0135] This set of examples is used to illustrate the effects of changes in at least one of the following when the conditions for silane pyrolysis are changed: median particle size of silicon particles, half-width at half-maximum (B) of diffraction peaks, and weight ratio of silicon to carbon (x).

[0136] Example 8a

[0137] This embodiment is based on Embodiment 1, except that the temperature for silane pyrolysis is adjusted to 1000°C, as detailed in Table 1.

[0138] Example 8b

[0139] This embodiment is based on Example 1, except that the silane pyrolysis time is adjusted to 16 hours, as detailed in Table 1.

[0140] Example 8c

[0141] This embodiment is based on Embodiment 1, except that the silane pyrolysis time is adjusted to 1 hour, as detailed in Table 1.

[0142] Example 9 group

[0143] This set of examples is used to illustrate the effects of changes in at least one of the following when the conditions for acetylene gas pyrolysis are altered: the thickness of the carbon layer, the full width at half maximum (FWHM) of the diffraction peak (B), and the weight ratio of silicon to carbon (x).

[0144] Example 9a

[0145] This embodiment is based on Embodiment 1, except that the temperature for acetylene gas pyrolysis is adjusted to 1500℃, as detailed in Table 1.

[0146] Example 9b

[0147] This embodiment is based on Embodiment 1, except that the acetylene gas cracking time is adjusted to 5 hours, as detailed in Table 1.

[0148] Example 9c

[0149] This embodiment is based on Embodiment 1, except that the acetylene gas cracking time is adjusted to 0.3 h, as detailed in Table 1.

[0150] Comparative Example 1

[0151] This comparative example is based on Example 1, except that acetylene is not introduced for cracking during the preparation of the negative electrode material, as detailed in Table 1.

[0152] Comparative Example 2

[0153] 30g of commercial 100nm silicon particle powder was placed in a vapor deposition furnace, the temperature was raised to 700℃, acetylene gas with a flow rate of 100sccm was introduced, and the acetylene decomposition time was controlled to be 1h.

[0154] Table 1

[0155]

[0156]

[0157] * indicates the same as in Example 1

[0158] Preparation Example

[0159] (1) The materials obtained in the examples and comparative examples were used to prepare coin half-cells in the following manner.

[0160] 1) Mix the negative electrode material, artificial graphite, SuperP, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a weight ratio of 50:46.5:1.6:1.6:0.3, add deionized water, and mix evenly under the action of a vacuum mixer to obtain the negative electrode slurry;

[0161] 2) The negative electrode slurry was coated onto copper foil, dried in an oven at 80°C, and then transferred to a vacuum oven at 100°C for 12 hours to obtain an areal density of approximately 6.0 mg / cm³. 2 The negative electrode plate;

[0162] 3) In a dry environment, place the negative electrode sheet at approximately 1.3 g / cm³. 3 The compacted material is rolled and then formed into negative electrode discs with a diameter of 12mm using a stamping machine;

[0163] 4) In the glove box, a negative electrode disc is used as the working electrode, a lithium metal sheet is used as the counter electrode, and a polyethylene membrane with a thickness of 20μm is used as the separator. Electrolyte is added to assemble a coin cell half battery.

[0164] (2) Batteries were prepared using the materials obtained from the examples and comparative examples in the following manner.

[0165] 1) Preparation of positive electrode sheet

[0166] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), acetylene black, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. The coated aluminum foil was baked in an oven, then dried in an oven at 120°C for 8 hours. Afterward, it was rolled and slit to obtain the desired positive electrode sheet. The positive electrode sheet was smaller than the negative electrode sheet, and its reversible capacity per unit area was 4% lower than that of the negative electrode sheet.

[0167] 2) Preparation of negative electrode sheet

[0168] The negative electrode sheets obtained from the above embodiments and comparative examples were used respectively.

[0169] 3) Diaphragm

[0170] A polyethylene diaphragm with a thickness of 8μm was selected.

[0171] 4) Preparation of lithium-ion batteries

[0172] The positive electrode sheet from step 1), the separator from step 3), and the negative electrode sheet from step 2) are stacked in sequence, ensuring that the separator is positioned between the positive and negative electrodes to provide isolation. Then, the cells are wound to obtain bare cells. The bare cells are placed in an aluminum-plastic film casing, and electrolyte is injected into the dried cells. After vacuum sealing, settling, formation, shaping, and sorting, the desired battery is obtained.

[0173] Test case

[0174] (1) Specific capacity and initial coulombic efficiency tests were performed on the coin cell.

[0175] The performance of the coin cell was tested using the LAND testing system at a temperature of 25°C. Specifically:

[0176] Lithium was inserted to 0.005V with a current of 0.1mA and allowed to stand for 10 min. Lithium was then inserted to 0.005V with a current of 0.05mA and allowed to stand for 10 min. Lithium was then de-lithiated to 1.5V with a current of 0.1mA to obtain the initial lithium insertion / de-lithiation capacity. The specific capacity of the negative electrode was obtained by dividing the initial lithium insertion / de-lithiation capacity by the mass of the negative electrode material in the negative electrode wafer. The initial coulombic efficiency of the negative electrode was obtained by dividing the initial de-lithiation capacity by the initial lithium insertion capacity. The results are shown in Table 2.

[0177] (2) Performance testing of lithium-ion batteries

[0178] The battery performance was tested using the LAND testing system at a temperature of 25°C.

[0179] (2.1) Nominal capacity test

[0180] Charged at a constant current of 0.7C to 4.45V, then charged at a constant voltage of 0.05C, left to stand for 10 minutes, and discharged at 0.2C to 3.0V to obtain the discharge capacity. This discharge capacity is recorded as the nominal capacity. The results are shown in Table 2.

[0181] (2.2) Energy density test

[0182] The energy of the battery is calculated by multiplying the nominal capacity by the average discharge voltage, and the energy density of the battery is calculated by dividing the energy of the battery by the volume of the battery. The results are shown in Table 2.

[0183] (2.3) Capacity retention test

[0184] The battery was charged at a constant current of 1.5C to 4.45V, then charged at a constant voltage of 0.05C, left to stand for 10 minutes, discharged at 1C to 3.0V, and left to stand for 10 minutes. This charge-discharge cycle was repeated. The highest discharge capacity in the first three weeks was taken as the initial capacity of the battery. The ratio of the capacity after 500 cycles to the initial capacity was recorded as the capacity retention rate of the battery. The results are shown in Table 2.

[0185] (2.4) Volume expansion rate test

[0186] The battery was charged at a constant current of 0.7C to 3.85V and then at a constant voltage of 0.01C. The thickness of the battery at this point was measured and taken as the initial thickness. The thickness of the battery was measured after 500 cycles. The difference between this thickness and the initial thickness was divided by the initial thickness to obtain the volume expansion rate of the battery. The results are shown in Table 2.

[0187] (2.5) Determination of the ratio of 1C discharge capacity to 0.2C discharge capacity

[0188] The charge-discharge cycle was repeated three times: constant current charging at 0.7C to 4.45V, constant voltage charging at 0.05C, resting for 10 minutes, discharging at 0.2C to 3.0V, and resting for 10 minutes. The cycle was then repeated again for three weeks. The highest discharge capacity in the first three weeks was the 0.2C discharge capacity, and the highest discharge capacity in the subsequent three weeks was the 1C discharge capacity. The results are shown in Table 2.

[0189] The results are recorded in Table 2.

[0190] Table 2

[0191]

[0192] As can be seen from Table 2, and through the comparative examples and embodiments, the negative electrode material of the embodiments shows an improvement in the initial coulombic efficiency, a significant improvement in the capacity retention rate of the battery made from the negative electrode material of the embodiments, a significant reduction in the volume expansion rate, and an improvement in the ratio of 1C discharge capacity to 0.2C discharge capacity. This indicates that the negative electrode material of the present invention, as well as the negative electrode sheet and battery including the negative electrode material, improves the initial coulombic efficiency of the negative electrode sheet, improves the cycle capacity retention rate and rate performance of the battery, and reduces the volume expansion rate of the battery by improving the structural stability of the negative electrode material.

[0193] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material comprises a silicon-carbon composite material having a core-shell structure. The shell includes a carbon layer, and the core includes porous carbon and silicon particles distributed in the pores of the porous carbon. The porous carbon consists of porous carbon particles. The differential thermogravimetric curve of the negative electrode material shows a weight gain peak between 400-900℃ and at least one weight loss peak in the temperature range below this weight gain peak. In X-ray powder diffraction testing, the negative electrode material exhibits a diffraction peak in the range of 2θ = 28.4° ± 0.5°. The half-width at half-maximum (FWHM) of this diffraction peak, expressed in 2θ degrees, is B. B satisfies 0.3° ≤ B ≤ 10°. The median particle size D of the negative electrode material is... v 50 represents 1μm to 20μm.

2. The negative electrode material according to claim 1, wherein, The differential thermogravimetric curve of the negative electrode material was obtained by thermogravimetric analysis. The sample amount used for testing was 5 mg, the atmosphere was air or oxygen, the heating rate was 10℃ / min, and the test range was 20℃-900℃. And / or, the X-ray powder diffraction test of the negative electrode material is performed using X-ray diffraction analysis, with the Kα line of Cu as the incident X-ray, the working voltage of the X-ray source being 40kV, the test power being 2kW, the abscissa being 2θ with the unit being °, the ordinate being the signal intensity, the test range being 10° to 80°, the scan rate being 4° / min, and the data point interval being 0.02°.

3. The negative electrode material according to claim 1, wherein, The porous carbon has a pore volume greater than 0.3 cm³. 3 / g.

4. The negative electrode material according to claim 3, wherein, The porous carbon has a pore volume greater than 0.5 cm³. 3 / g.

5. The negative electrode material according to claim 1, wherein, B satisfies 0.5°≤B≤6°.

6. The negative electrode material according to claim 1, wherein, The porous carbon has a pore size of less than 10 nm, and / or the median particle size D of the silicon particles. v 50 ranges from 0.1nm to 10000nm.

7. The negative electrode material according to claim 1, wherein, In the negative electrode material, the weight ratio x of silicon to carbon satisfies 0.33 ≤ x ≤ 3.

8. The negative electrode material according to claim 7, wherein, 0.5≤x≤2。 9. The negative electrode material according to claim 1, wherein, The median particle size Dv50 of the silicon particles is greater than the pore size of the porous carbon.

10. The negative electrode material according to any one of claims 1-9, wherein, The thickness of the carbon layer is 1-15 nm.

11. The negative electrode material according to claim 10, wherein, The thickness of the carbon layer is 2-10 nm.

12. The negative electrode material according to claim 1, wherein, The median particle size D of the porous carbon v 50 is 1μm to 15μm; And / or, the specific surface area of ​​the porous carbon is 300-1800 m². 2 / g.

13. The negative electrode material according to claim 1, wherein, The specific surface area of ​​the negative electrode material is 0.1-25m². 2 / g.

14. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material according to any one of claims 1-13.

15. A battery, characterized in that, The battery comprises the negative electrode material according to any one of claims 1-13 and / or the negative electrode sheet according to claim 14.

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