Negative electrode material, preparation method thereof, and battery

Abstract

The application provides a negative electrode material and a preparation method and a battery thereof, the negative electrode material comprising graphite and amorphous carbon on at least part of the surface of the graphite; the negative electrode material is measured by X-ray diffraction, and the interlayer spacing d1 of the crystal face of the (002) plane of the negative electrode material is nm; after the negative electrode material is heat-treated at a temperature of 650 DEG C for 30 minutes in an oxygen-containing atmosphere, the heat-treated negative electrode material is measured by X-ray diffraction, the interlayer spacing d2 of the crystal face of the (002) plane of the negative electrode material is nm, and 0.98 <= d2 / d1 <= 1. The negative electrode material and the preparation method and the battery thereof have the advantages that the binding force between the graphite and the surface amorphous carbon in the negative electrode material is improved, and the negative electrode material can have high gram capacity, excellent rate performance and cycle stability.

Description

Technical Field

[0001] This application relates to the field of graphite materials technology, specifically to negative electrode materials and their preparation methods, and batteries. Background Technology

[0002] Graphite anode materials, as lithium-ion battery anode materials, have advantages such as wide availability of raw materials, low price, low and stable discharge platform, and high reversible capacity. However, with the rapid development of lithium-ion batteries and the new energy industry, higher requirements have been placed on graphite anode materials in terms of capacity, rate capability, and cycle performance. Due to the anisotropy of graphite, i.e., the difference in lithium-ion transport rate between perpendicular and parallel to the graphite layer, the internal transport of lithium ions is hindered, thus limiting the high-rate fast-charging performance of graphite anode materials.

[0003] Currently, amorphous carbon layers can be prepared by coating carbon source materials such as pitch / phenolic resin to adjust the compatibility between graphite and electrolyte, thereby improving lithium-ion transport efficiency. However, the bonding force between the coated carbon layer and graphite is relatively poor, and it will fall off during actual use as lithium insertion and extraction proceeds, leading to SEI film recombination and regeneration, which affects the battery's lifespan and capacity. Summary of the Invention

[0004] This application provides a negative electrode material and its preparation method, and a battery. The bonding force between graphite in the negative electrode material and the amorphous carbon on the surface is improved, and the negative electrode material can have both high specific capacity, excellent rate performance and cycle stability.

[0005] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising graphite and amorphous carbon located on at least a portion of the surface of the graphite;

[0006] The interlayer spacing d1 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction.

[0007] After the negative electrode material was heat-treated at 650°C for 30 minutes in an oxygen-containing atmosphere, the interlayer spacing d2 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction, and 0.98≤d2 / d1≤1.

[0008] In some implementations, 0.336 ≤ d1 < 0.35.

[0009] In some embodiments, the half-width at half-maximum (WHM) of the diffraction peak of the negative electrode material (002) is w1; the half-width at half-maximum (WHM) of the diffraction peak of the negative electrode material (002) after heat treatment at 800°C for 1 hour in an oxygen-containing atmosphere is w2, and 1 < w1 / w2 ≤ 5, as determined by X-ray diffraction.

[0010] In some embodiments, amorphous carbon located on at least a portion of the surface of the graphite forms a disordered carbon layer.

[0011] In some embodiments, the thickness of the disordered carbon layer is D μm.

[0012] In some embodiments, the graphite has a radius of R μm and D / R ≤ 0.05.

[0013] In some implementations, 0.01 ≤ D ≤ 0.3.

[0014] In some embodiments, the graphite includes synthetic graphite and / or natural graphite.

[0015] In some embodiments, after the negative electrode material is heat-treated at 650°C for 30 minutes in an oxygen-containing atmosphere, the thermal weight loss rate of the negative electrode material is 0.01% to 0.2%.

[0016] In some embodiments, the amorphous carbon is generated in situ from the graphite after grinding.

[0017] In some embodiments, the amorphous carbon accounts for 0.1 wt% to 1.5 wt% of the mass of the negative electrode material.

[0018] In some embodiments, Raman spectroscopy is used to test the particle surface of the negative electrode material at a depth of 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G , 1.05≤I D / I G ≤2.80.

[0019] In some embodiments, the specific surface area of ​​the negative electrode material is 0.9 m². 2 / g~3.0m 2 / g.

[0020] In some embodiments, the tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 .

[0021] In some embodiments, the negative electrode material has a powder conductivity of 280 S / cm to 800 S / cm under a pressure of 20 kN.

[0022] In some embodiments, the particle size D of the negative electrode material 50 The size ranges from 10μm to 20μm.

[0023] Secondly, this application provides a method for preparing a negative electrode material, the method comprising:

[0024] A dispersion of graphite raw material, layer expander and solvent is subjected to intermittent ball milling under a protective atmosphere. The intermittent ball milling process includes alternating ball milling and cooling sections to obtain a wet material.

[0025] The wet material is dried to remove the solvent, thus obtaining the negative electrode material.

[0026] In some embodiments, the diameter of the grinding balls used in the intermittent ball milling process is 3 mm to 10 mm.

[0027] In some embodiments, the mass ratio of the graphite raw material to the grinding balls used in the intermittent ball milling process is 1:(5-10).

[0028] In some embodiments, the layer-expanding agent includes at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecylamine hydrochloride, and octadecylamine acetate.

[0029] In some embodiments, the mass ratio of the graphite raw material to the layer expander is 100:(0.1 to 1).

[0030] In some embodiments, the ball milling operation period lasts 15 to 30 minutes, and the cooling period lasts 5 to 10 minutes.

[0031] In some embodiments, the rotational speed during the intermittent ball milling process is 100 rpm to 200 rpm, and the total ball milling time is 4 h to 12 h.

[0032] In some embodiments, the graphite raw material includes synthetic graphite and / or natural graphite.

[0033] In some embodiments, the graphitization degree of the graphite raw material is ≥93.5%.

[0034] Thirdly, this application provides a battery comprising the negative electrode material described in the first aspect and the negative electrode material prepared by the preparation method described in the second aspect.

[0035] The technical solution of this application has at least the following beneficial effects:

[0036] The negative electrode material provided in this application includes graphite and amorphous carbon located on at least a portion of the surface of the graphite. X-ray diffraction was used to determine the interlayer spacing d1 nm of the (002) plane of the negative electrode material. After heat treatment at 650°C for 30 minutes in an oxygen-containing atmosphere, the interlayer spacing d2 nm of the (002) plane of the negative electrode material was 0.98 ≤ d2 / d1 ≤ 1. The difference in interlayer spacing before and after heat treatment was minimal, indicating a high bonding strength between the amorphous carbon and graphite. After heat treatment in an oxygen-containing atmosphere, only a portion of the amorphous carbon on the graphite surface reacted, leaving a large amount of amorphous carbon. This amorphous carbon facilitates the insertion and extraction of lithium ions into and out of the graphite lattice during charging and discharging, improving the rate performance of the negative electrode material. Especially under high-rate charging and discharging conditions, lithium ions can enter the graphite more quickly through the amorphous carbon, contributing to fast charging and high-current discharge of the battery made from the negative electrode material. In addition, due to the high bonding strength between amorphous carbon and graphite, amorphous carbon is not easily detached during charging and discharging, which reduces side reactions between the negative electrode material and the electrolyte and helps to improve the cycle stability and capacity retention of the negative electrode material.

[0037] The method for preparing the anode material provided in this application involves using intermittent ball milling to transform the ordered carbon on the surface of graphite raw materials into disordered carbon (i.e., amorphous carbon), that is, generating amorphous carbon in situ on the surface of the graphite raw materials. Furthermore, under the action of a layer-expanding agent, the interlayer spacing of the amorphous carbon on the graphite raw material surface is increased, providing a wider channel for lithium-ion insertion and extraction, thus improving the rate performance of the anode material. The anode material prepared by this method exhibits stronger bonding between the in-situ generated amorphous carbon and the ordered carbon in the graphite raw material. The amorphous carbon is also less prone to detachment during charge and discharge, reducing side reactions between the anode material and the electrolyte. This results in a cathode material that combines high specific capacity, excellent rate performance, and cycle stability. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the discharge state of a battery provided in an embodiment of this application.

[0039] Figure 2 XRD pattern of amorphous carbon on the surface of the negative electrode material provided in the embodiments of this application. Detailed Implementation

[0040] To better illustrate this application and facilitate understanding of its technical solutions, the following detailed description is provided. However, the following embodiments are merely simplified examples and do not represent or limit the scope of protection of this application. The scope of protection of this application is determined by the claims.

[0041] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising graphite and amorphous carbon located on at least a portion of the surface of the graphite;

[0042] The interlayer spacing d1 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction.

[0043] After the negative electrode material was heat-treated at 650°C for 30 minutes in an oxygen-containing atmosphere, the interlayer spacing d2 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction, and 0.98≤d2 / d1≤1.

[0044] The negative electrode material comprises graphite and amorphous carbon located on at least a portion of the surface of the graphite. X-ray diffraction was used to determine the interlayer spacing d1 nm of the (002) facet of the negative electrode material; after heat treatment at 650°C for 30 minutes, the interlayer spacing d2 nm of the (002) facet of the negative electrode material was 0.98 ≤ d2 / d1 ≤ 1. The difference in interlayer spacing before and after heat treatment was minimal, indicating a high bonding strength between the amorphous carbon and graphite. Even after heat treatment, the graphite surface still possesses a large amount of amorphous carbon, providing more transport channels for lithium ions. This makes it easier for lithium ions to insert into and extract from the graphite lattice during charging and discharging, improving the rate performance of the negative electrode material. Especially under high-rate charge and discharge conditions, lithium ions can enter the graphite more quickly through the amorphous carbon, contributing to fast charging and high-current discharge of the battery made from the negative electrode material. In addition, due to the high bonding strength between amorphous carbon and graphite, the anode material is not easily broken or pulverized during the electrode rolling process, and the amorphous carbon is not easily detached during the charging and discharging process. This reduces the side reactions between the anode material and the electrolyte, which helps to improve the cycle stability and capacity retention of the anode material.

[0045] In some embodiments, d2 / d1 can specifically be 0.98, 0.985, 0.988, 0.99, 0.995, 0.998, 1.0, or any value between them, and is not limited thereto. This application controls the d2 / d1 ratio within the above range. Due to the strong bonding between amorphous carbon and graphite, some amorphous carbon can still be retained on the graphite surface after heat treatment; and the difference between the carbon interlayer spacing of amorphous carbon and the carbon interlayer spacing of graphite is small. When the d2 / d1 ratio is too small, the difference in interlayer spacing of the crystal planes of the anode material before and after heat treatment increases, indicating that most of the amorphous carbon has pyrolyzed and volatilized, leading to a reduction in the remaining amorphous carbon on the graphite surface, a reduction in lithium-ion transport channels, and a decrease in the rate performance of the anode material.

[0046] In some implementations, 0.336 ≤ d1 < 0.350, and the interlayer spacing of the crystal planes of the negative electrode material (002) can be 0.336 nm, 0.338 nm, 0.34 nm, 0.342 nm, 0.345 nm, 0.346 nm, 0.348 nm, 0.349 nm or any value between them, without limitation here.

[0047] In some embodiments, the half-width at half-maximum (WHM) of the diffraction peak of the (002) crystal plane of the negative electrode material is w1; the WHM of the negative electrode material after heat treatment at 800℃ for 1 hour is w2 as determined by X-ray diffraction, where 1 < w1 / w2 ≤ 5, and w1 / w2 can specifically be 1.1, 1.5, 2, 2.5, 3, 3.5, 4, 5, or any value between them, without limitation here. It should be noted that the WHM of the diffraction peak of the (002) crystal plane of the negative electrode material refers to the width corresponding to half the peak intensity of the (002) crystal plane diffraction peak in the X-ray diffraction pattern of the negative electrode material. After heat treatment, the full width at half maximum (FWHM) of the (002) crystal plane diffraction peak decreases. This is because after heat treatment at 800℃ in an oxygen-containing atmosphere, the disordered carbon layer on the surface completely decomposes, exposing the graphite core. At this time, the (002) crystal plane diffraction peak measured by X-ray diffraction is a highly ordered graphitized graphite core with higher crystallinity, thus resulting in a smaller peak width. When the w1 / w2 ratio is ≤1, the graphitization degree of the negative electrode material surface is high, and the disorder degree is low, increasing the difficulty of lithium ion insertion, affecting kinetic performance, and reducing the fast-charging performance of the negative electrode material. When the w1 / w2 ratio is >5, there are too many defects on the graphite surface, increasing the specific surface area of ​​the negative electrode material, intensifying the side reactions between the electrolyte and the negative electrode material, increasing the irreversible consumption of active lithium ions, decreasing the initial coulombic efficiency of the negative electrode material, and deteriorating the cycle performance. This application controls the w1 / w2 ratio within the above range, and the graphite surface is coated with amorphous carbon material, which can reduce the occurrence of side reactions, improve the lithium ion insertion / extraction rate, and enhance the first coulombic efficiency and rate performance of the anode material.

[0048] In some embodiments, the graphite includes artificial graphite and / or natural graphite. Natural graphite is flake graphite, a natural crystalline graphite with a fish-scale-like shape, belonging to the hexagonal crystal system, and exhibiting a layered structure. It possesses excellent properties such as high-temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance. Artificial graphite is a graphite material obtained by carbonizing organic matter and then subjecting it to high-temperature graphitization treatment.

[0049] In some embodiments, the graphite is spherical graphite.

[0050] In some embodiments, the graphitization degree of the graphite is ≥93.5%, specifically it can be 93.5%, 94%, 95%, 96%, 96.5%, 97%, 98%, 99%, or any value between them, and is not limited thereto. Controlling the graphitization degree of the graphite within the above range in this application is beneficial for electron transfer within the graphite lattice, which can reduce the internal resistance of the battery made from the negative electrode material and improve the charge-discharge efficiency.

[0051] In some embodiments, amorphous carbon located on at least a portion of the surface of the graphite forms a disordered carbon layer.

[0052] In some embodiments, the thickness of the disordered carbon layer is D μm, where 0.01 ≤ D ≤ 0.3. Specifically, it can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or any value between them, and is not limited thereto. Controlling the thickness of the disordered carbon layer within the above range is beneficial for improving the lithium-ion transport power of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and improving the initial coulombic efficiency.

[0053] In some embodiments, the radius of the graphite is R μm, and the D / R ratio is ≤0.05. Specifically, the D / R ratio can be 0.05, 0.04, 0.03, 0.02, 0.01, 0.005, or any value between them, and is not limited thereto. When the D / R ratio is too large, the thickness of the disordered carbon layer on the graphite surface is too large, the lithium-ion intercalation potential decreases, the side reactions between the negative electrode material and the electrolyte intensify, the specific capacity of the negative electrode material decreases, and the energy density also decreases.

[0054] In some embodiments, after heat-treating the negative electrode material at 650°C for 30 minutes in an oxygen-containing atmosphere, the thermal weight loss rate of the negative electrode material is 0.01% to 0.2%, specifically 0.01%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, or 0.2%, or any value between them. If the thermal weight loss rate is too high, excessive decomposition of amorphous carbon on the surface of the negative electrode material occurs. The poor bonding force between amorphous carbon and graphite makes it easy for amorphous carbon to detach during charge and discharge, leading to repeated formation of the SEI film and accelerated capacity decay of the negative electrode material.

[0055] In some embodiments, the amorphous carbon is generated in situ from the graphite after grinding. The mass percentage of the amorphous carbon in the negative electrode material is 0.1 wt% to 1.5 wt%, specifically 0.1%, 0.5%, 1.0%, 1.5%, or any value between them. The appropriate amount of amorphous carbon generated in situ on the graphite surface can improve the conductivity of the graphite negative electrode material, reduce side reactions between graphite and the electrolyte, and improve the specific capacity, rate performance, and cycle capacity retention of the negative electrode material.

[0056] In some embodiments, Raman spectroscopy is used to test the particle surface of the negative electrode material at a depth of 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G , 1.05≤I D / I G ≤2.80. I D / I G The specific values ​​can be 1.05, 1.1, 1.2, 1.5, 1.8, 2.0, 2.3, 2.5, 2.6, or 2.8, etc. Controlled within the above range, the carbon layer on the graphite surface has a high degree of structural disorder, which can improve the wettability of the contact interface between the negative electrode material and the electrolyte, reduce the occurrence of interfacial side reactions of the negative electrode material, reduce the consumption of irreversible active lithium ions, improve the lithium ion transport power, reduce the interfacial impedance of the contact interface, and improve the first coulombic efficiency and electrochemical performance of the negative electrode material.

[0057] In some embodiments, the particle size D of the negative electrode material 50 The particle size distribution is 10 μm to 20 μm, specifically 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, or any value between them; no specific limitation is made here. It should be noted that the cumulative particle size distribution of the volume standard determined by laser diffraction is D. 50 This indicates the particle size corresponding to a cumulative particle size distribution percentage of 50%.

[0058] In some embodiments, the specific surface area of ​​the negative electrode material is 0.9 m². 2 / g~3.0m 2 / g; specifically, it can be 0.9m 2 / g, 1.0m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 2.8m 2 / g, 3.0m 2 / g or any value between them, without limitation. Controlling the specific surface area of ​​the negative electrode material within the above range reduces side reactions between the negative electrode material and the electrolyte, which is beneficial to improving the initial coulombic efficiency of the negative electrode material.

[0059] In some embodiments, the tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm3 Specifically, it could be 0.8 g / cm³. 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 Or any value between them, without limitation.

[0060] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 280 S / cm to 800 S / cm, specifically 280 S / cm, 300 S / cm, 400 S / cm, 500 S / cm, 700 S / cm, 800 S / cm, or any value between them, and is not limited thereto. The conductivity of the negative electrode material in this application is improved, and the powder conductivity of the negative electrode material is also effectively improved.

[0061] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0062] Step S10: Under a protective atmosphere, the dispersion of graphite raw material, layer expander and solvent is subjected to intermittent ball milling treatment, the intermittent ball milling treatment including alternating ball milling operation section and cooling section, to obtain wet material;

[0063] Step S20: The wet material is dried to remove the solvent, thereby obtaining the negative electrode material.

[0064] The method for preparing the anode material provided in this application involves using intermittent ball milling to transform the ordered carbon on the surface of graphite raw materials into disordered carbon (i.e., amorphous carbon), that is, generating amorphous carbon in situ on the surface of the graphite raw materials. Furthermore, under the action of a layer-expanding agent, the interlayer spacing of the amorphous carbon on the graphite raw material surface is increased, providing a wider channel for lithium-ion insertion and extraction, thus improving the rate performance of the anode material. The anode material prepared by this method exhibits stronger bonding between the in-situ generated amorphous carbon and the ordered carbon in the graphite raw material. The amorphous carbon is also less prone to detachment during charge and discharge, reducing side reactions between the anode material and the electrolyte. This results in a cathode material that combines high specific capacity, excellent rate performance, and cycle stability.

[0065] The preparation method of this application is explained in detail below with reference to the embodiments:

[0066] Step S10: Under a protective atmosphere, the dispersion of graphite raw material, layer expander and solvent is subjected to intermittent ball milling treatment, the intermittent ball milling treatment including alternating ball milling operation section and cooling section, to obtain wet material.

[0067] In some embodiments, the graphite includes artificial graphite and / or natural graphite. Natural graphite is flake graphite, a natural crystalline graphite with a fish-scale-like shape, belonging to the hexagonal crystal system, and exhibiting a layered structure. It possesses excellent properties such as high-temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance. Artificial graphite is a graphite material obtained by carbonizing organic matter and then subjecting it to high-temperature graphitization treatment.

[0068] In some embodiments, the graphite is spherical graphite.

[0069] In some embodiments, the particle size D50 of the graphite raw material is 10 μm to 20 μm, more specifically, it can be 10 μm, 12 μm, 13 μm, 15 μm, 18 μm, 20 μm or any value between them, without limitation. Controlling the particle size of the graphite raw material within the above range is beneficial for balancing processing performance, capacity, and rate performance.

[0070] In some embodiments, the graphitization degree of the graphite raw material is ≥93.5%, specifically it can be 93.5%, 94%, 95%, 96%, 96.5%, 97%, 98%, 99%, or any value between them, and is not limited thereto. Controlling the graphitization degree of graphite within the above range in this application is beneficial for electron transfer within the graphite lattice, which can reduce the internal resistance of the battery made from the negative electrode material and improve the charge-discharge efficiency.

[0071] In some embodiments, the solvent includes at least one selected from water, ethanol, acetone, benzene, toluene, quinoline, tetrahydrofuran, and carbon tetrachloride. Preferably, the solvent is ethanol.

[0072] In some embodiments, the layer-expanding agent includes at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecylamine hydrochloride, and octadecylamine acetate. Preferably, the layer-expanding agent includes hexadecyltrimethylammonium chloride.

[0073] In some embodiments, the mass ratio of graphite raw material to layer expander is 100:(0.1 to 1), specifically 100:0.1, 100:0.2, 100:0.3, 100:0.5, 100:1 or any value between them, which is not limited here.

[0074] In some embodiments, the dispersion is mixed by at least one of mechanical stirring and ultrasonic mixing. Specifically, mechanical stirring can be either magnetic stirring or propeller stirring.

[0075] In some embodiments, the mass ratio of the graphite raw material to the grinding balls used in the intermittent ball milling process is 1:(5-10), specifically 1:5, 1:6, 1:8, 1:9, 1:10 or any value between them, which is not limited here.

[0076] In some embodiments, the diameter of the grinding balls used in the intermittent ball milling process is 3mm to 10mm, specifically 3mm, 4mm, 5mm, 6mm, 8mm, 10mm or any value between them, and is not limited here.

[0077] In some specific embodiments, the grinding balls used in the intermittent ball milling process include a first ball with a diameter of 10 mm, a second ball with a diameter of 5 mm, and a third ball with a diameter of 3 mm, wherein the mass ratio of the first ball to the second ball and the third ball is (0-1):(1-3):1.

[0078] In some embodiments, the grinding balls and grinding jars are made of stainless steel.

[0079] In some embodiments, the equipment used for the intermittent ball milling process includes at least one of a planetary ball mill, a stirred ball mill, and a drum ball mill, preferably a planetary ball mill.

[0080] In some implementations, the volume of the dispersion does not exceed half the volume of the ball mill jar.

[0081] In some embodiments, the ball milling operation period lasts 15 to 30 minutes, and the cooling period lasts 5 to 10 minutes. This application controls the alternation of the ball milling and cooling periods to reduce the oxidation of graphite raw materials and ensure the capacity utilization of the negative electrode material.

[0082] In some implementations, the total ball milling time is 4h to 12h, specifically 4h, 5h, 6h, 8h, 10h, 12h or any value between them, and is not limited here.

[0083] In some embodiments, the rotational speed during the intermittent ball milling process is 100 rpm to 200 rpm, specifically 100 rpm, 120 rpm, 140 rpm, 150 rpm, 180 rpm, 200 rpm or any value between them, without limitation.

[0084] In some embodiments, the protective atmosphere includes at least one of argon, nitrogen, helium, and neon.

[0085] In this application, by controlling the addition ratio of graphite raw material and layer expander, the diameter of the grinding balls, the time, and the grinding state during ball milling, the energy generated by ball milling can be controlled. During ball milling, the grinding balls move randomly and collide with the particles, thereby generating energy input to the graphite particle surface, breaking interlayer bonds, increasing the interlayer spacing, and breaking intralayer covalent bonds, causing the long-range ordered structure to break. Furthermore, due to the attenuation of energy input from the outside to the inside, the carbon atoms on the surface of the graphite raw material gradually transform from an ordered structure to a gradient disordered structure, without easily affecting the ordered lamellar structure of the graphite raw material core. This results in the surface of the ball-milled particles having amorphous carbon with appropriate thickness, uniform distribution, and high bonding strength. The uniformly coated disordered carbon layer has a larger interlayer spacing, which is beneficial for lithium ion insertion and extraction. In addition, the high bonding strength can effectively alleviate the expansion of graphite during lithium ion insertion and extraction, enhancing structural stability. Therefore, the amorphous carbon generated in situ on the graphite surface by ball milling can simultaneously improve its cycle stability and kinetic performance.

[0086] Step S20: The wet material is dried to remove the solvent, thereby obtaining the negative electrode material.

[0087] In some embodiments, the drying method includes at least one of water bath heating drying and vacuum drying.

[0088] In some embodiments, the dried product is further subjected to sieving and demagnetization.

[0089] In some embodiments, the screening method is any one of a fixed screen, drum screen, resonant screen, roller screen, vibrating screen, and chain screen, and the screening mesh size is 200-500 mesh, specifically 200 mesh, 300 mesh, 400 mesh, or 500 mesh, etc. Controlling the particle size of the negative electrode material within the above range is beneficial to improving the processing performance of the negative electrode material. Preferably, the screening mesh size is 325 mesh.

[0090] In some implementations, the demagnetizing equipment is any one of a permanent magnet drum magnetic separator, an electromagnetic iron separator, and a pulsed high-gradient magnetic separator. Demagnetization is used to control the magnetic content of graphite materials, reduce the impact of magnetic materials on the charging and discharging of lithium-ion batteries, and ensure the safety of the batteries during use.

[0091] Thirdly, embodiments of the present invention also provide a battery. Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1As shown, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0092] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0093] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0094] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0095] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0096] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0097] In some embodiments, the negative electrode current collector 201 may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which may be the graphite material described in the first aspect or the graphite material prepared by the aforementioned preparation method.

[0098] The battery provided in this application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid-state electrolyte battery, etc., and is not limited thereto.

[0099] The embodiments of the present invention will be further described below with reference to several examples.

[0100] The embodiments in this patent are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. Where there is no conflict, the embodiments and features of the embodiments of this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of this application; the described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments of this application are further described below with reference to several examples.

[0101] Example 1

[0102] (1) Take 50g of graphite raw material (D 50 Add 10.00 μm of ethanol, 0.5 g of layer expander, and 20 mL of anhydrous ethanol to a beaker, and stir with an electric stirrer at room temperature for 30 min until a uniform dispersion is obtained. Then, mix the dispersion with 250 g of stainless steel grinding balls (5 mm diameter, 3 mm diameter, mass ratio 1:1).

[0103] Place the material into the grinding jar of a planetary ball mill, fill it with nitrogen, set the ball mill speed to 100 rpm, each ball mill cycle consists of 30 minutes of ball milling and 10 minutes of cooling, and the total ball milling time is 4 hours to obtain wet material.

[0104] (2) After vacuum drying of the wet material, it is then sieved and demagnetized to obtain the negative electrode material.

[0105] According to the preparation process of Example 1, the following examples and comparative examples were prepared, and the specific process parameters are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] Comparative Example 1

[0110] The difference from Example 1 is that the artificial graphite is not ball-milled.

[0111] Comparative Example 2

[0112] The difference from Example 13 is that the natural graphite is not ball-milled.

[0113] Comparative Example 3

[0114] Take 50g of graphite raw material (D50 is 10.00μm), 1.5g of asphalt and 20mL of ethanol and stir to mix to obtain a coating agent. Mix the dispersion with the graphite raw material and use high-speed stirring in the liquid phase to uniformly coat the surface of the graphite particles with the coating agent. Then, after high-temperature carbonization, the negative electrode material is obtained. The negative electrode material includes graphite and its surface amorphous carbon layer.

[0115] Test methods

[0116] (1) Test method for particle size of negative electrode material:

[0117] The particle size distribution range of the anode material was tested using a Marlven Mastersizer 3000 laser particle size analyzer.

[0118] (2) Test method for specific surface area of ​​negative electrode material:

[0119] The specific surface area of ​​the negative electrode material was measured using a high-precision dynamic specific surface area analyzer (JW-DX).

[0120] (3) Test method for tap density of negative electrode material:

[0121] The graphite anode material was naturally filled into a 100mL graduated cylinder and placed in the sample chamber of the tap density meter. After vibrating 1000 times, the sample was removed and its volume and mass were recorded. The tap density can then be calculated according to the mass-volume ratio. The testing equipment model was Quantachrome DAT-6-220.

[0122] (4) Test method for the thickness of disordered carbon layer in negative electrode material:

[0123] The negative electrode material powder was prepared into a SEM cross-section sample, and the average thickness D of the disordered carbon layer and the radius R of the graphite were measured by SEM.

[0124] (5) Test method for disorder of negative electrode materials:

[0125] Raman spectroscopy revealed that the negative electrode material was located at 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G .

[0126] (6) XRD testing method for negative electrode materials:

[0127] XRD testing was performed using an Xpert PRO XRD instrument. The peak intensity and full width at half maximum (FWHM) of the 002 peak of the anode material were measured based on its XRD spectrum. The interlayer spacing d was calculated using the X-ray diffraction angle, X-ray wavelength, and Bragg's equation (2dsinθ = nλ). 002 The unit is

[0128] (7) Test of the mass content of amorphous carbon in the negative electrode material:

[0129] A certain amount of sample is placed in a constant temperature chamber with air in the atmosphere. The chamber is heated to a constant temperature of 800℃ and kept at that temperature for 60 minutes. The mass difference of the sample before and after heating is the mass of amorphous carbon.

[0130] (8) Powder conductivity

[0131] The test sample is placed in a circular mold cavity. Four equally spaced probes, numbered 1, 2, 3, and 4, are fixed on a ceramic disc at the bottom center of the mold cavity. In the mold cavity filled with the sample, a cylindrical top post with ceramic probes of the same diameter as the mold cavity is used to apply pressure to the sample, causing the four probe electrodes on the ceramic disc at the bottom of the sample to come into close contact and be gradually pressed together. A current I passes between probes numbered 1 and 4, and a potential difference V is generated between probes numbered 2 and 3. By using the dynamic four-probe method to test the resistance of the circular block material under different pressures, the resistivity and conductivity of the powder sample under different pressures can be accurately calculated.

[0132] (9) Test method for thermal weight loss rate of negative electrode material:

[0133] A certain amount of sample M is placed in a constant temperature chamber with air atmosphere. The chamber temperature is kept constant at 650℃ for 30 minutes. The mass difference m of the sample before and after heating is measured. The thermal weight loss rate is m / M×100%.

[0134] (10) Battery performance testing methods:

[0135] The negative electrode materials prepared in each embodiment and comparative example were used as active materials. They were mixed and slurryed according to a mass ratio of negative electrode material: conductive carbon black: CMC: SBR = 95.4:1.2:1.4:2. The coating surface density was 6.5±0.1 mg / cm², and the roller-pressed compaction density was 1.50±0.02 g / cc. The coin cell half-cells were subjected to rate performance testing at 25±2℃, obtaining the specific capacity and coulombic efficiency at 0.1C, 0.2C, and 1C.

[0136] 1) Rate testing conditions: ① Discharge to 0.01V at 0.1C, maintain constant voltage to 0.01C, then charge to 1.5V at 0.1C; ② Discharge to 0.01V at 0.2C, maintain constant voltage to 0.01C, then charge to 1.5V at 0.2C; ③ Discharge to 0.01V at 1C, maintain constant voltage to 0.01C, then charge to 1.5V at 0.2C. The 1C / 0.2C discharge capacity retention rate can be calculated by dividing the 1C discharge capacity by the 0.2C discharge capacity.

[0137] 2) Room temperature cycling performance test conditions: ① Discharge at 0.1C to 0.01V, maintain voltage to 0.01C, charge at 0.1C to 1.5V; ② Discharge at 0.2C to 0.01V, maintain voltage to 0.01C, charge at 0.2C to 1.5V; ③ Discharge at 1C to 0.01V, maintain voltage to 0.01C, charge at 0.2C to 1.5V. ④ Repeat step ③ until 100 cycles are reached. The room temperature cycling capacity retention rate is obtained by dividing the 1C discharge capacity at 100 cycles by the 1C discharge capacity at the first cycle. The electrochemical testing platform is Blue Electric CT3002A.

[0138] The performance test results of the negative electrode materials obtained in the above embodiments (Examples 1 to 14 are abbreviated as S1 to S14) and comparative examples (Comparative Examples 1 to 3 are abbreviated as D to D3) are shown in Table 2 below.

[0139] Table 2. Test results of physicochemical properties of the examples and comparative examples.

[0140]

[0141] Table 3. Electrochemical performance test results of the examples and comparative examples.

[0142]

[0143]

[0144] The negative electrode material prepared in this application includes graphite and amorphous carbon located on at least a portion of the surface of the graphite. X-ray diffraction was used to determine the interlayer spacing d1 nm of the (002) facet of the negative electrode material. After heat treatment at 650°C for 30 minutes, the interlayer spacing d2 nm of the (002) facet of the negative electrode material was 0.98 ≤ d2 / d1 ≤ 1. The difference in interlayer spacing before and after heat treatment is minimal because the amorphous carbon in this application is generated in situ from graphite through grinding, increasing the bonding strength between the amorphous carbon and graphite. Even after heat treatment, the graphite surface still has a large amount of amorphous carbon, providing more transport channels for lithium ions. This makes it easier for lithium ions to insert into and extract from the graphite lattice during charging and discharging, improving the rate performance of the negative electrode material. Especially under high-rate charging and discharging conditions, lithium ions can enter the graphite more quickly through the amorphous carbon, contributing to fast charging and high-current discharge of the battery made from the negative electrode material.

[0145] According to the test data of Examples 1 to 3, as the amount of layer expander added increases, the content of amorphous carbon on the surface of graphite particles also increases. Although there will be a slight loss of capacity, the presence of more amorphous carbon can provide more transport channels for lithium ions, thus improving the rate performance of the anode material.

[0146] According to the test data of Examples 3 and 4-7, as the ball milling speed or ball milling time increases, the amorphous carbon content on the surface of the graphite particles also increases, and the rate performance of the negative electrode material is improved.

[0147] According to the test data of Examples 3 and 8, as the ball-to-particle ratio increases, the energy input of the grinding balls to the graphite particles increases, the amorphous carbon content on the graphite surface increases, and the rate performance of the negative electrode material improves. Furthermore, according to the test data of Examples 8 and 9-10, as the ball milling speed increases, the disorder on the graphite particle surface further increases, and the rate performance of the negative electrode material is further improved compared to Example 8.

[0148] According to the test data of Examples 3 and 11-12, changing the grinding ball ratio and increasing the proportion of large-size grinding balls will significantly increase the energy input to graphite particles, further increase the disorder on the surface of graphite particles, and improve the rate performance. However, excessive disorder will lead to a certain degree of decrease in the initial discharge capacity and initial efficiency. The overall performance can be adjusted by changing the grinding ball ratio according to the requirements.

[0149] According to the test data of Examples 3 and 13-14, the preparation method of this application can effectively modify the surface of graphite particles by using different types of graphite raw materials and different types of layer expanders, thereby increasing the amorphous carbon content on the graphite surface and improving the rate performance of the negative electrode material.

[0150] According to the test data of Comparative Example 1 and Example 1, and Comparative Example 2 and Example 13, without ball milling the graphite raw material, the ordered structure on the surface of the graphite particles is difficult to be effectively adjusted, and there is not enough amorphous carbon to increase the lithium-ion diffusion path, resulting in a significant decrease in the rate performance of the anode material.

[0151] Based on the test data of Comparative Example 3 and Example 10, it can be seen that Comparative Example 3 used a liquid-phase carbon coating process to coat the surface of graphite particles with a layer of amorphous carbon. The coating amount was close to, or even slightly more than, that of Example 10, and the coating integrity was high. However, using ordinary liquid-phase coating resulted in low bonding strength, and the amorphous carbon was prone to detachment during charge and discharge, leading to a significant increase in thermal weight loss compared to Example 10. Although the initial efficiency and capacity of the negative electrode material in Comparative Example 3 were higher than those in Example 10, its rate performance was significantly lower. According to the cycle performance test, the coin cells made of the negative electrode materials of Comparative Example 3 and Example 10 were cycled for 100 cycles under the conditions of 1C discharge / 0.2C charge. The capacity retention rates of the coin cells made of the negative electrode materials of Comparative Example 3 and Example 10 were measured to be 95.2% and 97.7%, respectively. The capacity retention rate of Comparative Example 3 was significantly lower than that of the battery of Example 10. This is because the amorphous carbon on the graphite surface of Example 10 has a strong bonding force with the graphite, and the amorphous carbon is not easy to fall off during the charge and discharge process, which reduces the side reactions between the negative electrode material and the electrolyte and helps to improve the cycle stability and capacity retention rate of the negative electrode material.

[0152] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes graphite and amorphous carbon located on at least a portion of the surface of the graphite; The interlayer spacing d1 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction. After the negative electrode material was heat-treated at 650°C for 30 minutes in an oxygen-containing atmosphere, the interlayer spacing d2 nm of the (002) plane of the negative electrode material was determined by X-ray diffraction, and 0.98≤d2 / d1≤1.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1)0.336≤d1＜0.35； (2) The half-width of the diffraction peak of the (002) crystal plane of the negative electrode material was measured by X-ray diffraction, and the half-width of the diffraction peak of the (002) crystal plane of the negative electrode material was measured by X-ray diffraction, and the half-width of the diffraction peak of the (002) crystal plane of the negative electrode material was measured by X-ray diffraction, and the half-width of the diffraction peak of the (002) crystal plane of the negative electrode material was measured by X-ray diffraction, and 1 < w1 / w2 ≤ 5.

3. The negative electrode material according to claim 1, characterized in that, Amorphous carbon located on at least a portion of the surface of the graphite forms a disordered carbon layer, the thickness of which is D μm, and the negative electrode material satisfies at least one of the following characteristics: (1) The radius of the graphite is Rμm, and D / R≤0.05; (2)0.01≤D≤0.3； (3) The graphite includes artificial graphite and / or natural graphite.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that, After heat-treating the negative electrode material at 650°C for 30 minutes in an oxygen-containing atmosphere, the thermal weight loss rate of the negative electrode material is 0.01% to 0.2%.

5. The negative electrode material according to any one of claims 1 to 3, characterized in that, The amorphous carbon is generated in situ from the graphite after grinding, and / or the mass percentage of the amorphous carbon in the negative electrode material is 0.1wt% to 1.5wt%.

6. The negative electrode material according to any one of claims 1 to 3, characterized in that, The particle surface of the negative electrode material was measured using Raman spectroscopy at a depth of 1300 cm⁻¹. -1 ~1350cm -1 The peak area of ​​the D characteristic peak within the range and the peak area located at 1500 cm⁻¹ -1 ~1580cm -1 The peak area ratio of the G characteristic peak within the range is I D / I G , 1.05≤I D / I G ≤2.

80.

7. The negative electrode material according to any one of claims 1 to 3, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The specific surface area of ​​the negative electrode material is 0.9 m². 2 / g~3.0m 2 / g; (2) The tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 ; (3) The negative electrode material has a powder conductivity of 280 S / cm to 800 S / cm under a pressure of 20 kN; (4) The particle size D of the negative electrode material 50 The size ranges from 10μm to 20μm.

8. A method for preparing a negative electrode material, characterized in that, The preparation method includes: A dispersion of graphite raw material, layer expander and solvent is subjected to intermittent ball milling under a protective atmosphere. The intermittent ball milling process includes alternating ball milling and cooling sections to obtain a wet material. The wet material is dried to remove the solvent, thus obtaining the negative electrode material.

9. The preparation method according to claim 8, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The diameter of the grinding balls used in the intermittent ball milling process is 3mm to 10mm; (2) The mass ratio of the graphite raw material to the grinding balls used in the intermittent ball milling process is 1:(5-10); (3) The layer-expanding agent includes at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecylamine hydrochloride, and octadecylamine acetate; (4) The mass ratio of the graphite raw material to the layer expander is 100:(0.1~1); (5) The time for the ball mill running section is 15 min to 30 min, and the time for the cooling section is 5 min to 10 min; (6) The rotation speed during the intermittent ball milling process is 100 rpm to 200 rpm, and the total ball milling time is 4 h to 12 h; (7) The graphite raw materials include artificial graphite and / or natural graphite; (8) The graphitization degree of the graphite raw material is ≥93.5%.

10. A battery, characterized in that, The battery comprises the negative electrode material according to any one of claims 1 to 7 or the negative electrode material prepared by the preparation method according to any one of claims 8 to 9.

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