Negative electrode material and preparation method thereof, and lithium ion battery

Abstract

The application relates to a negative electrode material and a preparation method thereof and a lithium ion battery, the negative electrode material comprising a graphite material, at least part of the surface of the graphite material being provided with a coating layer, the material of the coating layer comprising hard carbon, the median particle size of the negative electrode material being D2, the median particle size of the graphite material being D1, the median particle size D2 of the negative electrode material and the median particle size D1 of the graphite material satisfying the following relationship: D2-D1 <= 1 mu m (1). The hard carbon-coated graphite material of the application can obviously improve the low-temperature and fast-charging performance of the material, improve the stability of the charging and discharging cycles of the lithium ion battery, and effectively reduce the expansion rate of the negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of negative electrode material technology, and specifically relates to negative electrode materials and their preparation methods, and lithium-ion batteries. Background Technology

[0002] As the mainstream anode material for lithium-ion batteries, graphite anode materials have advantages such as high energy density, good cycle performance, mature preparation technology, and low manufacturing cost. However, with the increasing demands for fast charging in the consumer electronics and power battery fields, there is a general desire to improve fast charging capabilities under room temperature and low temperature conditions. This necessitates special design and processing of graphite anode materials to meet these requirements. Typically, a layer of soft or hard carbon is coated onto the surface of graphite to enhance the fast charging capability of graphite anode materials.

[0003] Currently, hard carbon coating processes include solid-phase coating and liquid-phase coating. Solid-phase coating typically uses a solid, plastic polymer resin as the coating agent, which is mixed with the graphite anode and heat-treated to turn the polymer into hard carbon. However, because the solid resin particles are too large after pulverization, it is difficult to mix evenly with graphite, failing to achieve uniform coating and easily causing agglomeration, affecting the initial coulombic efficiency and compaction density of the anode material. Liquid-phase coating generally disperses the graphite anode material in a polymer solution, then prepares the anode material through heating and drying. Due to the high viscosity of the polymer and its tendency to soften during drying, the polymer is prone to agglomeration during drying, and it easily expands during subsequent carbonization, affecting the initial coulombic efficiency and compaction density of the anode material.

[0004] Therefore, there is an urgent need for a hard carbon coating process that produces uniform coating and is not prone to agglomeration and expansion, as well as corresponding hard carbon coated graphite anode materials. Summary of the Invention

[0005] In order to overcome the above-mentioned defects, this application provides a negative electrode material and its preparation method, and a lithium-ion battery, wherein the thickness of the coating layer on the surface of the negative electrode material is controllable, which can improve the cycle stability of the negative electrode material and the fast charging performance under low temperature environment.

[0006] In a first aspect, a negative electrode material is provided, the negative electrode material comprising a graphite material, at least a portion of the surface of the graphite material having a coating layer, the coating layer being made of hard carbon, the median particle size of the negative electrode material being D2, the median particle size of the graphite material being D1, and the median particle size D2 of the negative electrode material and the median particle size D1 of the graphite material satisfying the following relationship:

[0007] D2-D1≤1μm (1).

[0008] In conjunction with the first aspect, the negative electrode material includes at least one of the following technical features (1) to (7):

[0009] (1) The median particle size D1 of the graphite material is 6 μm to 15 μm;

[0010] (2) The graphite material includes at least one of natural graphite and artificial graphite;

[0011] (3) The thickness of the coating layer is 20nm to 100nm;

[0012] (4) The carbon atom spacing of the coating layer is 0.36 nm to 0.38 nm;

[0013] (5) The nitrogen content in the coating layer is 0%wt to 5%wt;

[0014] (6) The coating layer is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532 nm at a depth of 1200 cm⁻¹. -1 Up to 1500cm -1 D-band was observed at 1500 cm. -1 Up to 1800cm -1 The peak area of ​​band G was observed, and the peak area of ​​band D was I. D With the peak area of ​​the G band I G The ratio between I D / I G The value is 1.5 to 3.0, and the standard deviation of the 30-point Raman ratio of the negative electrode material is less than or equal to 0.3.

[0015] (7) The hardness of the coating layer is 100 MPa to 150 MPa.

[0016] In conjunction with the first aspect, the negative electrode material includes at least one of the following technical features (1) to (4):

[0017] (1) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~2.0m 2 / g;

[0018] (2) The tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.2g / cm 3 ;

[0019] (3) The compaction density of the negative electrode material under 5T pressure is 1.7 g / cm³. 2 ~2.2g / cm 2 ;

[0020] (4) The median particle size D2 of the negative electrode material is 6μm to 16μm.

[0021] Secondly, embodiments of this application provide a method for preparing a negative electrode material, comprising the following steps:

[0022] Graphite material is added to a polymer solution and atomized to obtain a precursor of graphite material coated with polymer solution. The precursor is added to a polar solvent and the solvent is removed to obtain graphite material coated with polymer, wherein the polymer is insoluble in the polar solvent.

[0023] The polymer-coated graphite material is modified to obtain a cured material; and

[0024] The solidified material is carbonized to obtain the negative electrode material.

[0025] In conjunction with the second aspect, the method comprises at least one of the following technical features (1) to (6):

[0026] (1) The graphite material includes at least one of natural graphite and artificial graphite;

[0027] (2) The median particle size D1 of the graphite material is 6 μm to 15 μm;

[0028] (3) The polymer solution includes at least one of polyimide acid solution, polyethersulfone solution and polyvinylidene fluoride solution;

[0029] (4) The solid content in the polymer solution is 6% to 8%;

[0030] (5) The mass ratio of the graphite material to the polymer solution is (97:3) to (90:10);

[0031] (6) The solid content of the mixture formed after adding the graphite material to the polymer solution is 50% to 80%.

[0032] In conjunction with the second aspect, the method comprises at least one of the following technical features (1) to (3):

[0033] (1) The ratio of the volume V1 of the precursor of the graphite material coated by the polymer solution to the volume V2 of the graphite material is V1 / V2 = 1.01 to 1.1.

[0034] (2) The polar solvent includes at least one of water, ethanol, methanol and propylene glycol;

[0035] (3) The rate at which the precursor is added to the polar solvent is 10 mL / min to 50 mL / min.

[0036] In conjunction with the second aspect, the modification treatment includes:

[0037] The polymer-coated graphite material is dehydrated under vacuum conditions;

[0038] Alternatively, the graphite material coated with the polymer may be subjected to an oxidation treatment.

[0039] In conjunction with the second aspect, the method includes at least one of the following technical features (1) to (6):

[0040] (1) The vacuum pressure of the dehydration treatment is -0.1 MPa to 0.05 MPa;

[0041] (2) The temperature of the dehydration treatment is 150℃~200℃;

[0042] (3) The dehydration treatment time is 0.5h to 2h;

[0043] (4) The oxidation treatment temperature is 180℃~300℃;

[0044] (5) The oxidation treatment is carried out in an atmosphere with an oxygen content of 20% to 100%;

[0045] (6) The oxidation treatment time is 2h to 4h.

[0046] In conjunction with the second aspect, the method includes at least one of the following technical features (1) to (2):

[0047] (1) The carbonization temperature is 1000℃~1150℃;

[0048] (2) The carbonization atmosphere includes at least one of nitrogen, helium, neon, argon and krypton.

[0049] Thirdly, embodiments of this application provide a lithium-ion battery comprising a negative electrode material prepared according to the negative electrode material described in the first aspect or the preparation method described in the second aspect.

[0050] The technical solution of this application has at least the following beneficial effects:

[0051] The negative electrode material of this application has a median particle size that is not much different from the median particle size of the internally coated graphite material, indicating that the graphite material is tightly bonded to the coating layer on its surface, which can improve the cycle stability of the negative electrode material. Furthermore, the coating layer of the negative electrode material is hard carbon, which can improve the fast charging performance of the negative electrode material in low-temperature environments.

[0052] The preparation method provided in this application involves dispersing and atomizing graphite material and a polymer solution, then adding them to a polar solvent to uniformly coat the surface of graphite particles with the polymer. The polymer coating is then modified to shrink, cross-link, and solidify, preventing expansion during subsequent carbonization. This avoids the problems of excessively large specific surface area and low compaction and tap density of the negative electrode material. Furthermore, the modification treatment allows for a tighter bond between the polymer and graphite particles, thereby improving the strength of the coating layer and the cycle stability of the negative electrode material. The uniform coating of the graphite material with polymer, followed by carbonization to form hard carbon, significantly improves the fast-charging performance of the negative electrode material under low-temperature conditions, effectively reduces the expansion rate of the negative electrode material, and thus enhances the stability of lithium battery charge-discharge cycles. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 This is a flowchart of the preparation method of the negative electrode material in this application;

[0055] Figure 2 This is a SEM image of the negative electrode material prepared in Example 1 of this application;

[0056] Figure 3 The image shows the SEM image of the negative electrode material prepared in Comparative Example 3. Detailed Implementation

[0057] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0058] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0060] This application provides a negative electrode material, which includes graphite material. A coating layer is provided on the surface of the graphite material, and the coating layer is made of hard carbon. The median particle size of the negative electrode material is D2, and the median particle size of the graphite material is D1. The median particle size D2 of the negative electrode material and the median particle size D1 of the graphite material satisfy the following relationship:

[0061] D2-D1≤1μm (1).

[0062] In the above technical solution, the difference between the median particle size D2 of the negative electrode material and the median particle size D1 of the internally coated graphite material is less than or equal to 1 μm. Specifically, the difference between the median particle size D2 of the negative electrode material and the median particle size D1 of the internally coated graphite material can be 0 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1 μm, etc., or other values ​​within the above range, which are not limited here. The fact that the median particle size D2 of the negative electrode material and the median particle size D1 of the internally coated graphite material are not much different indicates that the graphite material and its surface coating layer are tightly bonded, which can improve the cycle stability of the negative electrode material. Moreover, the coating layer is hard carbon, which can improve the fast charging performance of the negative electrode material in low-temperature environments.

[0063] In some embodiments, the median particle size of the graphite material is 6 μm to 15 μm, the D10 of the graphite material is 2 μm to 10 μm, the D90 is 10 μm to 27 μm, and the Dmax is < 45 μm. Specifically, the median particle size of the graphite material can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm, etc., or other values ​​within the above range. No limitation is made here. Controlling the median particle size of the graphite material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0064] In some embodiments, the graphite material includes at least one of natural graphite and artificial graphite. Understandably, the graphite material can be natural graphite, artificial graphite, or a mixture of natural and artificial graphite.

[0065] In some embodiments, the thickness of the coating layer is 20nm to 100nm. Specifically, the thickness of the coating layer is 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm and 100nm, etc. Of course, it can also be other values ​​within the above range, which are not limited here. Controlling the thickness of the coating layer within the above range results in a smaller surface area, which is beneficial to improving the first efficiency of the negative electrode material.

[0066] In some embodiments, the carbon atom spacing of the coating layer is 0.36 nm to 0.38 nm. The carbon atom spacing of the coating layer can be 0.36 nm, 0.37 nm, and 0.38 nm, etc., or other values ​​within the above range. No limitation is made here. If the carbon atom spacing of the coating layer is within the above range, it can be confirmed that the carbon in the negative electrode material is hard carbon. Hard carbon can improve the fast charging performance of the negative electrode material, especially the fast charging performance under low temperature environment.

[0067] In some embodiments, the nitrogen content of the coating layer is 0%wt to 5%wt. Specifically, the nitrogen content of the coating layer can be 0%wt, 1%wt, 2%wt, 3%wt, 4%wt and 5%wt, etc. Of course, it can also be other values ​​within the above range, which are not limited here. Controlling the nitrogen content of the coating layer within the above range can improve the capacity and first-pass efficiency of the negative electrode material.

[0068] In some embodiments, the coating layer is shown in a Raman spectroscopy pattern obtained using a measurement light source with a wavelength of 532 nm at a 1200 cm⁻¹ depth. -1 Up to 1500cm -1 D-band was observed at 1500 cm. -1 up to 1800m -1 The peak area of ​​band G was observed, and the peak area of ​​band D was I. D With the peak area of ​​the G band I G The ratio between I D / I G The Raman ratio I was measured at 30 randomly selected points on the negative electrode material, ranging from 1.5 to 3.0. D / I G The standard deviation of the 30-point Raman ratio of the negative electrode material is less than or equal to 0.3. Specifically, the peak area of ​​the D band is I. D With the peak area of ​​the G band I G The ratio between I D / I G The values ​​can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0, or other values ​​within the above range; no specific limitation is made here. The peak area I of the D band... D With the peak area of ​​the G band I G The ratio between I D / I G Within the aforementioned range, it is evident that the coating effect of the negative electrode material in this application is good, thereby improving the initial efficiency, fast charging performance, expansion rate, and cycle life of the negative electrode material.

[0069] In some embodiments, the hardness of the coating layer is 100 MPa to 150 MPa, specifically 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, and 150 MPa, or other values ​​within the above range, which are not limited here. Understandably, controlling the hardness of the coating layer within the above range is beneficial for suppressing the volume expansion of the negative electrode material and for improving the cycle performance of the negative electrode material.

[0070] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~2.0m 2 / g, specifically 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Understandably, controlling the specific surface area of ​​the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0071] In some embodiments, the tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.2g / cm 3 Specifically, it could be 0.9 g / cm³. 3 1.0g / cm 3 1.1g / cm 3 and 1.2g / cm 3 Of course, other values ​​within the above range are also possible, and are not limited here. Understandably, controlling the tap density of the negative electrode material within the above range can improve the processing performance and volumetric energy density of the negative electrode material.

[0072] In some embodiments, the compaction density of the negative electrode material under 5T pressure is 1.7 g / cm³. 2 ~2.2g / cm 2 Specifically, it could be 1.7g / cm³ 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 and 2.2g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. Understandably, the compaction density of the negative electrode material is controlled within the above range. The higher the compaction density of the negative electrode material, the higher the energy density of the lithium-ion battery.

[0073] In some embodiments, the median particle size D2 of the negative electrode material is 6μm to 16μm. Specifically, the median particle size of the negative electrode material can be 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, etc., or other values ​​within the above range, which are not limited here. Controlling the median particle size of the negative electrode material within the above range is beneficial for the negative electrode material to possess both high compaction density and high fast charging capability.

[0074] This application provides a method for preparing a negative electrode material, such as... Figure 1 The diagram shown is a flowchart of the preparation process for the negative electrode material, including the following steps:

[0075] Step S100: Add graphite material to polymer solution, atomize to obtain a precursor of graphite material coated with polymer solution, add the precursor to polar solvent, remove solvent to obtain graphite material coated with polymer, wherein the polymer is insoluble in the above polar solvent.

[0076] Step S200: Modify the polymer-coated graphite material obtained in step S100 to obtain a cured material;

[0077] Step S300: Carbonize the solidified material obtained in step S200 to obtain the negative electrode material.

[0078] This application involves adding graphite material to a polymer solution and atomizing it to obtain a polymer-coated graphite precursor. Atomization improves the uniformity and controllability of polymer coating. Adding the precursor to a polar solvent allows the polymer, which is insoluble in polar solvents, to precipitate and tightly coat the graphite surface. Adding the polar solvent after atomization prevents particle adhesion and agglomeration. The polymer coated on the surface is then modified to shrink, cross-link, and solidify, preventing expansion during subsequent carbonization. This avoids the problems of excessively large specific surface area and low compaction and tap density of the negative electrode material. Furthermore, the modification process allows for a tighter bond between the polymer and graphite particles, thereby increasing the strength of the coating layer and improving the cycle stability of the negative electrode material. The uniform coating of the graphite surface with polymer, followed by carbonization, results in hard carbon. This preparation method significantly improves the fast-charging performance of the negative electrode material under low-temperature conditions, effectively reduces the expansion rate of the negative electrode material, and thus improves the stability of lithium battery charge-discharge cycles.

[0079] The preparation method of this application is described in detail below with reference to the embodiments:

[0080] Step S100: Add graphite material to polymer solution, stir, disperse and atomize to obtain a precursor of graphite material coated with polymer solution, add the precursor to polar solvent, remove the solvent to obtain graphite material coated with polymer, wherein the polymer is insoluble in the above polar solvent.

[0081] In the above steps, graphite material and polymer solution are atomized to obtain a precursor of graphite material coated with polymer solution, which is in the form of droplets, each droplet containing a graphite particle. The precursor of graphite material coated is added to a polar solvent. At the instant the polymer solution comes into contact with the polar solvent, the solvent in the polymer solution is miscible with the polar solvent, while the polymer is insoluble in the polar solvent, so that the polymer precipitates and tightly coats the surface of the graphite material. The coating method of this application has the advantages of good coating uniformity and tight coating.

[0082] In some embodiments, the graphite material includes at least one of natural graphite and artificial graphite. Understandably, the graphite material can be natural graphite, artificial graphite, or a mixture of natural and artificial graphite.

[0083] In some embodiments, the median particle size D50 of the graphite material is 6μm to 15μm, specifically 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm, etc., or other values ​​within the above range, which are not limited here. Controlling the median particle size of the graphite material within the above range is beneficial to improving the fast-charging performance of the negative electrode material.

[0084] In some embodiments, the polymer solution includes at least one of a polyimide solution, a polyethersulfone solution, and a polyvinylidene fluoride (PVDF) solution. The polymer in the polymer solution is soluble in an organic solvent but insoluble in a polar solvent (e.g., water), and the solvent in the polymer solution is soluble in a polar solvent (e.g., water). For example, a PVDF solution is obtained by dissolving PVDF in N,N-dimethylacetamide as a solvent, wherein PVDF is insoluble in water, while N,N-dimethylacetamide is soluble in water. In the polyimide solution, the solvent is N,N-dimethylformamide, and the solute is polyimide acid (PAA); in the polyethersulfone solution, the solvent is N,N-dimethylformamide, and the solute is polyethersulfone.

[0085] Understandably, in the preparation process of the negative electrode material of this application, nitrogen element in the negative electrode material is mainly introduced through the solute in the polymer solution. When the solute in the polymer solution is polyvinylidene fluoride, the negative electrode material does not contain N element.

[0086] In some embodiments, the solid content of the polymer solution is 6% to 8%, specifically 6%, 7%, and 8%, or other values ​​within the above range, which are not limited here. Controlling the solid content of the polymer solution within the above range is beneficial for the uniform coating of the graphite material by the polymer.

[0087] In some embodiments, the mass ratio of graphite material to polymer solution is (90-10):(97-3), specifically 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, and 90:10, etc., and other values ​​within the above range are also possible, without limitation. When the mass ratio of graphite material to polymer is greater than 97:3, it is difficult for the polymer to completely coat the graphite material; when the mass ratio of graphite material to polymer is less than 90:10, it is not conducive to improving the cycle performance of the negative electrode material.

[0088] In some embodiments, the solid content in the mixture formed after adding graphite material to the polymer solution is 50% to 80%. Specifically, the solid content can be 50%, 55%, 60%, 65%, 70%, 75%, and 80%, or other values ​​within the above range, which are not limited here. Controlling the solid content in the mixture formed after adding graphite material to the polymer solution is beneficial for improving atomization production efficiency.

[0089] In some embodiments, the stirring rate is 200 r / pm to 1000 r / pm, specifically 200, 300, 400 r / pm, 500 r / pm, 600 r / pm, 700 r / pm, 800 r / pm, 900 r / pm and 1000 r / pm, etc. Of course, other values ​​within the above range are also possible, and are not limited here.

[0090] In some embodiments, the stirring time is 0.5h to 2h, specifically 0.5h, 45min, 1h, 70min, 90min and 2h, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0091] Controlling the stirring rate and stirring time within the above range is beneficial to improving the uniformity of the graphite material coated by the polymer solution, and to ensuring that each precursor contains a graphite particle in the subsequent atomization.

[0092] In some embodiments, the atomization operation uses an atomizer or an electrostatic spraying device, which can disperse the graphite material and polymer solution into droplets through a nozzle or by using a high-speed airflow. Each droplet contains a graphite particle, thereby improving the uniformity of the polymer solution coating.

[0093] In some embodiments, the volume of the polymer solution-coated graphite precursor (droplet) is set as V1, and the volume of the graphite material is set as V2, with V1 / V2 = 1.01 to 1.1. Specifically, the ratio of the polymer solution-coated graphite precursor (droplet) volume V1 to the graphite material volume V2 can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, and 1.1, etc., or other values ​​within the above range, which are not limited here. The purpose of controlling the volume ratio of the polymer solution-coated graphite precursor to the graphite material is to ensure that each droplet contains at most one graphite particle.

[0094] In some embodiments, the precursor coated with graphite material is added to the polar solvent by spraying, which helps to increase the dispersibility of the graphite material and the polymer.

[0095] In some embodiments, the polar solvent includes at least one of water, ethanol, methanol, and propylene glycol, preferably water. Understandably, water not only dissolves well in the polymer solution but also saves costs and protects the environment.

[0096] In some embodiments, the rate at which the precursor is added to the polar solvent is 10 mL / min to 50 mL / min. The specific rate at which the graphite-coated precursor is added to the polar solvent can be 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, or 50 mL / min, etc., or other values ​​within the above range, which are not limited here. A rate greater than 50 mL / min results in excessively large atomized droplet volumes, leading to agglomeration; a rate less than 10 mL / min will affect production efficiency and increase production costs.

[0097] In some embodiments, the solvent removal step includes solid-liquid separation and washing. The solid-liquid separation method includes either centrifugal separation or filtration separation, preferably centrifugal separation, to separate the polymer coating the graphite material from the solvent (including the solvent in the polymer solution and additionally added polar solvent). During washing, deionized water is used to wash multiple times to remove impurities, thereby obtaining a graphite material with a uniformly coated surface of polymer.

[0098] Step S200: Modify the graphite material coated with polymer obtained in step S100 to obtain the cured material.

[0099] In some implementations, there are two ways to modify it:

[0100] (1) The graphite material coated with polymer in step S100 is dehydrated under vacuum conditions;

[0101] In some embodiments, the vacuum pressure for dehydration treatment is -0.1 MPa to 0.05 MPa. Specifically, the pressure can be -0.1 MPa, -0.05 MPa, 0.02 MPa, and 0.05 MPa, or other values ​​within the above range. No limitation is made here. By controlling the dehydration treatment pressure within the above range, the vaporization temperature of the water or volatile solvent in the polymer-coated graphite material decreases, allowing the polymer-coated graphite material to be rapidly dehydrated in a short time.

[0102] In some embodiments, the dehydration treatment temperature is 150℃~200℃, and the specific temperature can be 150℃, 160℃, 170℃, 180℃, 190℃ and 200℃, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0103] In some embodiments, the dehydration treatment time is 0.5h to 2h, and the specific temperature can be 0.5h, 1h, 1.5h and 2h, etc., or other values ​​within the above range, which are not limited here.

[0104] Controlling the dehydration temperature and time within the above range is beneficial for the dehydration, cross-linking and curing of the graphite material coated with polymer, so as to prevent it from expanding during subsequent carbonization. This avoids the problems of excessively large specific surface area and low compaction and tap density of the prepared negative electrode material.

[0105] (2) The graphite material coated with polymer in step S100 is subjected to oxidation treatment.

[0106] In some embodiments, the oxidation treatment temperature is 180℃~300℃. The specific oxidation temperature can be 180℃, 200℃, 220℃, 250℃ and 300℃, etc. Of course, it can also be other values ​​within the above range, which are not limited here. If the oxidation temperature is higher than 300℃, the specific surface area of ​​the prepared negative electrode material will be too large, which will affect its electrochemical performance. If the oxidation temperature is lower than 180℃, the polymer cannot form a cross-linked structure, and the cross-linking curing effect cannot be achieved.

[0107] In some embodiments, the oxidation treatment time is 2h to 4h. The specific oxidation time can be 2h, 2.5h, 3h, 3.5h and 4h, etc., or other values ​​within the above range, which are not limited here.

[0108] In some embodiments, the oxidation treatment is carried out in an atmosphere with an oxygen content of 20% to 100%. The specific oxygen content of the oxidation treatment atmosphere can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%, etc., or other values ​​within the above range. No limitation is made here. By limiting the oxygen content of the oxidation treatment atmosphere to the above range, the polymer can undergo an oxidation reaction to crosslink and cure, thereby avoiding the expansion of the polymer in subsequent reactions.

[0109] For example, the oxidation treatment atmosphere is an oxygen atmosphere or an air atmosphere. The air flow rate of the air atmosphere is 4L / min to 6L / min, and the specific flow rate can be 4L / min, 5L / min, and 6L / min, etc., or other values ​​within the above range, which are not limited here. The oxygen flow rate of the oxygen atmosphere is 2L / min to 4L / min, and the specific flow rate can be 2L / min, 3L / min, and 4L / min, etc., or other values ​​within the above range, which are not limited here.

[0110] This application modifies the polymer through low-temperature dehydration or low-temperature oxidation treatment, so that the particle size of the final anode material is not much different from that of the raw material, thus avoiding the problems of excessive specific surface area and low compaction and tap density of the final anode material. Moreover, the low-temperature dehydration or low-temperature oxidation treatment can make the polymer and graphite particles more tightly bonded, improve the strength of the coating layer, and thus improve the cycle stability of the material, which is beneficial to improving the cycle performance of the anode material.

[0111] Step S300: The solidified material obtained in step S200 is carbonized, broken up, and sieved to obtain the negative electrode material.

[0112] In some implementations, the carbonization equipment is a tunnel kiln, but other carbonization equipment can also be used, such as any one of tube furnaces, box furnaces, pusher kilns and roasting kilns.

[0113] In some embodiments, the carbonization temperature is 1000℃~1150℃, and the specific carbonization temperature can be 1000℃, 1030℃, 1050℃, 1080℃, 1100℃, 1130℃ and 1150℃, etc. Of course, it can also be other values ​​within the above range, which are not limited here. By controlling the carbonization temperature within the above range, the polymer on the surface of the graphite material is converted into hard carbon, thereby improving the fast charging performance of the negative electrode material under low temperature conditions.

[0114] In some embodiments, carbonization is carried out in a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, and krypton.

[0115] In some implementations, the disintegration method includes any one of vibration, crushing, and ultrasound.

[0116] The screening method can be any one of fixed screen, drum screen, resonant screen, roller screen, vibrating screen, and chain screen. In some embodiments, the screening mesh is 200 mesh to 500 mesh. Specifically, the screening mesh can be 200 mesh, 300 mesh, 400 mesh, 500 mesh, etc. Controlling the screening mesh within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0117] Thirdly, this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0118] The negative electrode sheet includes a current collector and a negative electrode active material layer. The negative electrode active material layer includes the negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes the aforementioned negative electrode material.

[0119] In some embodiments, the current collector of the negative electrode may include at least one of copper foil, aluminum foil, nickel foil, or fluorocarbon current collector. The binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, polystyrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. The conductive agent may include at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, and graphene.

[0120] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a conductive agent, and a binder. The positive electrode current collector may be an Al foil, or other positive electrode current collectors commonly used in the art may be used.

[0121] The conductive agent in the positive electrode sheet may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes. The binder in the positive electrode sheet may include at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The positive electrode active material includes, but is not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide. These positive electrode active materials may be doped or coated.

[0122] In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene comprises at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, are effective in preventing short circuits and can improve battery stability through a turn-off effect. In some embodiments, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.

[0123] In some embodiments, the lithium-ion battery may further include an electrolyte. In some embodiments, the electrolyte includes, but is not limited to, at least two of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP). Furthermore, the electrolyte may additionally include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or a dinitrile compound as an electrolyte additive. In some embodiments, the electrolyte also includes a lithium salt.

[0124] The positive electrode, separator, and negative electrode are sequentially wound or stacked to form an electrode assembly, which is then encapsulated in a film such as aluminum-plastic film. Electrolyte is injected, and the assembly is formed and sealed to produce a lithium-ion battery. The prepared lithium-ion battery is then subjected to performance and cycle tests.

[0125] Those skilled in the art will understand that the methods for preparing lithium-ion batteries described above are merely examples. Other methods commonly used in the art can be employed without departing from the disclosure of this application.

[0126] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0127] Example 1

[0128] (1) Artificial graphite with a median particle size of 13 μm was added to a polyimide solution with a solid content of 5% (DMF as solvent). The mass ratio of artificial graphite to polyimide solution was 95:5, so that the overall solid content reached 50%. The mixture was dispersed at high speed for 30 min at a rotation speed of 1000 r / min to obtain a well dispersed precursor. The well dispersed precursor was atomized into fine droplets using an electrostatic spraying device and sprayed into pure water at a flow rate of 40 mL / min. After centrifugation and washing with pure water 3 to 5 times, a polymer with a uniformly coated surface of graphite material was obtained.

[0129] (2) The polymer coated with graphite material is placed under vacuum and 200°C for 2 hours and the air flow rate is 6L / min to dehydrate the polyimide acid coated on the graphite surface and crosslink it into polyimide curing material.

[0130] (3) The solidified material was carbonized at 1150℃ for 2 hours under a nitrogen atmosphere to obtain the negative electrode material.

[0131] The SEM image of the negative electrode material prepared in this embodiment is shown below. Figure 2 As shown, by Figure 2 It can be seen that the negative electrode material particles are uniformly dispersed and there is no agglomeration.

[0132] The median particle size of the negative electrode material prepared in this embodiment is 13.1 μm, and the specific surface area is 0.9 m². 2 / g, the coating thickness is 70nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.0, the hardness of the coating layer is 130 MPa, and the specific surface area of ​​the negative electrode material is 0.9 m². 2 The tap density of the negative electrode material is 1.01 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.95 g / cm³. 2 .

[0133] Example 2

[0134] (1) Spherical natural graphite with a median particle size of 8 μm was added to polyethersulfone (PESF) with a solid content of 8% (NMP as solvent). The mass ratio of natural graphite to PESF solution was 95:5, resulting in an overall solid content of 70%. The mixture was dispersed at high speed for 1 hour at a rotation speed of 500 r / min to obtain a well-dispersed precursor. The well-dispersed precursor was atomized into fine droplets using an electrostatic spraying device and sprayed into pure water at a flow rate of 50 mL / min. After centrifugation and washing with pure water 5 to 7 times, a polymer with a uniformly coated surface of graphite material was obtained.

[0135] (2) The polymer coated with graphite material is placed in an air atmosphere at 300°C and heated for 0.5 h with an air flow rate of 4 L / min to dehydrate the polyethersulfone coated on the graphite surface and crosslink and cure to obtain a cured material.

[0136] (3) The solidified material was carbonized at 1150℃ for 2 hours under a nitrogen atmosphere, and the final negative electrode material was obtained after being dispersed by VC and sieved.

[0137] The median particle size of the negative electrode material prepared in this embodiment is 8.2 μm, and the specific surface area is 1.7 m². 2 / g, the coating thickness is 80nm, the carbon spacing of the coating is 0.37nm, the N content of the coating is 0%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.1, the hardness of the coating layer is 110 MPa, and the specific surface area of ​​the negative electrode material is 1.7 m². 2 The tap density of the negative electrode material is 1.05 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.97 g / cm³. 2 .

[0138] Example 3

[0139] (1) A mixture of spherical natural graphite and artificial graphite with a mass ratio of 1:99 and a median particle size of 12 μm was added to a PVDF solution with a solid content of 6% (NMP as solvent). The mass ratio of the spherical natural graphite and artificial graphite mixture to the PVDF polymer solution was 90:10, so that the overall solid content reached 80%. The mixture was dispersed at high speed for 2 hours at a rotation speed of 200 r / min to obtain a well dispersed precursor. The well dispersed precursor was atomized into fine droplets using an electrostatic spraying device and sprayed into pure water at a flow rate of 10 mL / min. After centrifugation and washing with pure water 3 to 5 times, a polymer with a uniformly coated graphite material was obtained.

[0140] (2) The polymer coated with graphite material is placed in an air atmosphere at 150°C and heated for 2 hours with an air flow rate of 5L / min to dehydrate the PVDF coated on the graphite surface and crosslink and cure to obtain a cured material.

[0141] (3) The solidified material is then carbonized at 1150℃ for 2 hours under a nitrogen atmosphere. After being dispersed by VC and sieved, the final product is obtained.

[0142] The median particle size of the negative electrode material prepared in this embodiment is 12.5 μm, and the specific surface area is 1.1 m². 2 / g, the coating thickness is 100nm, the carbon spacing of the coating is 0.37nm, the N content of the coating is 2%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.2, the hardness of the coating layer is 120 MPa, and the specific surface area of ​​the negative electrode material is 1.1 m². 2 The tap density of the negative electrode material is 0.97 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.93 g / cm³. 2 .

[0143] Example 4

[0144] Unlike Example 1, the mass ratio of artificial graphite to polyimide solution is 92:8.

[0145] The median particle size of the negative electrode material prepared in this embodiment is 13.4 μm, and the specific surface area is 0.85 m². 2 / g, the coating thickness is 90nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.5, the hardness of the coating layer is 140 MPa, and the specific surface area of ​​the negative electrode material is 0.85 m². 2 The tap density of the negative electrode material is 0.98 g / cm³. 3The compaction density of the negative electrode material under 5T pressure is 1.94 g / cm³. 2 .

[0146] Example 5

[0147] Unlike Example 1, the mass ratio of artificial graphite to polyimide solution was 97:3.

[0148] The median particle size of the negative electrode material prepared in this embodiment is 13 μm, and the specific surface area is 0.95 m². 2 / g, the coating thickness is 50nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 1.7, the hardness of the coating layer is 100 MPa, and the specific surface area of ​​the negative electrode material is 0.95 m². 2 The tap density of the negative electrode material is 1.03 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.97 g / cm³. 2 .

[0149] Example 6

[0150] Unlike Example 1, the mass ratio of artificial graphite to polyimide solution is 90:10.

[0151] The median particle size of the negative electrode material prepared in this embodiment is 13.5 μm, and the specific surface area is 0.8 m². 2 / g, the coating thickness is 120nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.8, the hardness of the coating layer is 140 MPa, and the specific surface area of ​​the negative electrode material is 0.8 m².2 The tap density of the negative electrode material is 0.95 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.91 g / cm³. 2 .

[0152] Example 7

[0153] Unlike Example 1, the mass ratio of artificial graphite to polyimide solution is 85:15.

[0154] The median particle size of the negative electrode material prepared in this embodiment is 14 μm, and the specific surface area is 0.8 m². 2 / g, the coating thickness is 240nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 3.0, the hardness of the coating layer is 150 MPa, and the specific surface area of ​​the negative electrode material is 0.8 m². 2 The tap density of the negative electrode material is 0.90 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.85 g / cm³. 2 .

[0155] Example 8

[0156] Unlike Example 1, the mass ratio of artificial graphite to polyimide solution was 99:1.

[0157] The median particle size of the negative electrode material prepared in this embodiment is 13 μm, and the specific surface area is 1.0 m². 2 / g, the coating thickness is 10nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 1%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I GThe specific surface area of ​​the negative electrode material is 1.0, the hardness of the coating layer is 10 MPa, and the specific surface area of ​​the negative electrode material is 1.0 m². 2 The tap density of the negative electrode material is 1.03 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 2.0 g / cm³. 2 .

[0158] Example 9

[0159] Unlike Example 1, the dehydration treatment temperature was 180°C.

[0160] The median particle size of the negative electrode material prepared in this embodiment is 13.1 μm, and the specific surface area is 0.91 m². 2 / g, the coating thickness is 75nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 Up to 1800cm -1 G-band was observed at 1200 cm. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.0, the hardness of the coating layer is 125 MPa, and the specific surface area of ​​the negative electrode material is 0.91 m². 2 / g, the tap density of the negative electrode material is 1.00 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.94 g / cm³. 2 .

[0161] Example 10

[0162] Unlike Example 1, the dehydration treatment temperature was 190°C.

[0163] The median particle size of the negative electrode material prepared in this embodiment is 190 μm, and the specific surface area is 0.9 m². 2 / g, the coating thickness is 72nm, the carbon spacing of the coating is 0.365nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between ID / I G The strength is 2.0, the hardness of the coating layer is 128 MPa, and the specific surface area of ​​the negative electrode material is 0.9 m². 2 The tap density of the negative electrode material is 1.01 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.95 g / cm³. 2 .

[0164] Example 11

[0165] Unlike Example 1, the dehydration treatment temperature was 300°C.

[0166] The median particle size of the negative electrode material prepared in this embodiment is 13 μm, and the specific surface area is 0.9 m². 2 / g, the coating thickness is 68nm, the carbon spacing of the coating is 0.368nm, the N content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.0, the hardness of the coating layer is 130 MPa, and the specific surface area of ​​the negative electrode material is 0.9 m². 2 The tap density of the negative electrode material is 1.01 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.95 g / cm³. 2 .

[0167] Example 12

[0168] Unlike Example 1, the dehydration treatment temperature was 100°C.

[0169] The median particle size of the negative electrode material prepared in this embodiment is 14 μm, and the specific surface area is 1.5 m². 2 / g, the coating thickness is 150nm, the carbon spacing of the coating is 0.365nm, the nitrogen content of the coating is 4%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band IG The ratio between I D / I G The strength is 2.0, the hardness of the coating layer is 10 MPa, and the specific surface area of ​​the negative electrode material is 1.5 m². 2 The tap density of the negative electrode material is 0.85 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.85 g / cm³. 2 .

[0170] Example 13

[0171] Unlike Example 1, step 2 uses a low-temperature oxidation process for modification.

[0172] Step 3 specifically involves placing the polymer coated with graphite material at 200°C for 4 hours in an air atmosphere to dehydrate and oxidize the polyimide acid coated on the graphite surface, crosslinking it into polyimide. Finally, the polymer is carbonized at 1150°C for 2 hours in a nitrogen atmosphere to obtain the negative electrode material.

[0173] The median particle size of the negative electrode material prepared in this embodiment is 13 μm, and the specific surface area is 1.0 m². 2 / g, the coating thickness is 70nm, the carbon spacing of the coating is 0.37nm, the N content of the coating is 3%wt, and the coating is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532nm at 1500cm. -1 G-band was observed at 1800 cm⁻¹ and at 1200 cm⁻¹. -1 Up to 1500cm -1 A D band was observed, and the peak area of ​​the D band was I. D With the peak area of ​​the G band I G The ratio between I D / I G The strength is 2.1, the hardness of the coating layer is 140 MPa, and the specific surface area of ​​the negative electrode material is 1.0 m². 2 The tap density of the negative electrode material is 1.02 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.96 g / cm³. 2 .

[0174] Comparative Example 1

[0175] The difference from Example 1 is that the low-temperature vacuum dehydration treatment is not performed; instead, the carbonization treatment is performed directly.

[0176] The negative electrode material prepared in this embodiment has a median particle size of 14.5 μm, a hardness of 50 MPa, and a specific surface area of ​​2.0 m². 2 The tap density of the negative electrode material is 0.87 g / cm³.3 The compaction density of the negative electrode material under 5T pressure is 1.86 g / cm³. 2 .

[0177] Comparative Example 2

[0178] The difference from Example 2 is that the low-temperature oxidation and dehydration treatment is not performed; instead, the carbonization treatment is performed directly.

[0179] The negative electrode material prepared in this embodiment has a median particle size of 14.5 μm, a hardness of 10 MPa, and a specific surface area of ​​2.0 m². 2 The tap density of the negative electrode material is 0.85 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.86 g / cm³. 2 .

[0180] Comparative Example 3

[0181] The difference from Example 1 is that the precursor in step (1) is atomized into fine droplets by an electrostatic spraying device and directly dried, i.e., spray drying, and then steps (2) and (3) are performed to obtain the negative electrode material.

[0182] The median particle size of the anode material prepared in this comparative example is 15.6 μm, the hardness is 100 MPa, and the specific surface area is 1.5 m². 2 The tap density of the negative electrode material is 0.79 g / cm³. 3 The compaction density of the negative electrode material under 5T pressure is 1.94 g / cm³. 2 .

[0183] Performance testing

[0184] (1) The hardness of the coating layer was tested using a Shimadzu DUH211 dynamic microhardness tester. The indenter was pressed into the sample by electromagnetic force, and the pressure was increased from 0 to a predetermined value in a certain proportion. During the process of the indenter pressing into the sample, the depth of the indenter into the sample was automatically measured and then converted into strength.

[0185] (2) Test of compaction density of negative electrode material: Measure the volume of a certain weight of powder under 5T pressure, and calculate the compaction density by compaction density = mass / volume.

[0186] (3) Full-cell performance testing: The negative electrode materials, conductive agents, and binders prepared in each example and comparative example were dissolved in a solvent at a mass ratio of 94:1:5, and the solid content was controlled at 50%. The mixture was coated onto a copper foil current collector, vacuum dried, and a negative electrode sheet was obtained. Then, a ternary positive electrode sheet NCM523 prepared by conventional mature technology, a 1mol / L LiPF6 / ethyl cellulose + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a casing were assembled into 18650 cylindrical cells using conventional production processes. The charge and discharge tests of the cylindrical cells were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd. Under normal temperature conditions, constant current charge and discharge were performed at 0.2C, and the charge and discharge voltage was limited to 2.75~4.2V to obtain the first reversible capacity, the first charge capacity, and the first discharge capacity. The first coulombic efficiency = first discharge capacity / first charge capacity. The 3C charging capacity retention rate can be calculated by dividing the charging capacity at 4.2V when charged at a 3C rate by the charging capacity at 0.2C rate.

[0187] Repeat the cycle 50 times. Use a micrometer to measure the thickness of the lithium-ion battery electrode at this time. The thickness of the battery electrode at the beginning is H1. The initial thickness of the battery electrode is H0. After 50 cycles, the expansion rate is (H1-H0) / H0×100%.

[0188] Repeat the cycle 100 times and record the discharge capacity as the remaining capacity of the lithium-ion battery; capacity retention rate = remaining capacity / initial capacity * 100%.

[0189] (4) Electrode performance test: The core-shell composite particles obtained in the various embodiments and comparative examples of this invention were used as the negative electrode active material. They were mixed according to the mass ratio of negative electrode active material: conductive carbon black: CMC: SBR = 95.3:1.5:1.4:1.8, and the mixture was coated onto copper foil using deionized water as the solvent. The coating surface density was 6.5 ± 0.1 mg / cm³. 2 After vacuum drying at 90℃, a negative electrode sheet was obtained, and the negative electrode sheet was rolled to a compaction density of 1.65±0.02g / cc. The negative electrode sheet, lithium sheet, electrolyte (1mol / L LiPF6, EC:EMC=1:1) and Celgard2400 separator were assembled into a 2016 type coin cell. The obtained battery was subjected to rate and cycle tests at 25±2℃. The rate test conditions were: ① 0.1C discharge to 0.01V, constant voltage for 5h; 0.1C charge to 1.5V; ② 0.2C discharge to 0.01V, constant voltage 0.01C; 0.2C charge to 1.5V, and the first week's charging specific capacity and first week's efficiency were tested respectively.

[0190] The results of the above performance tests are as follows:

[0191] Table 1. Performance Comparison Results

[0192]

[0193] As can be seen from the test data in Table 1, Examples 1-6 and 9-11 respectively used different graphite materials within the scope of this application to prepare anode materials, and their anode materials have good first-time efficiency and cycle performance.

[0194] In Example 7, the proportion of graphite added was too high, making it difficult for the polymer to completely coat the graphite, resulting in an oversized negative electrode material. In Example 8, the proportion of graphite added was too low, which was not conducive to improving the first discharge efficiency and cycle performance of the negative electrode.

[0195] The dehydration temperature in the preparation method of this application is too high (Example 12) or too low (Example 13), which makes the negative electrode material prone to expansion during subsequent carbonization, resulting in a lower specific capacity and initial efficiency compared to Example 1 of this application.

[0196] Comparative Examples 1 and 2 were not subjected to dehydration or oxidation treatment, resulting in graphite anode materials with larger dimensions. These materials were prone to expansion during subsequent carbonization, which reduced the cycle stability of the anode material products and hindered the improvement of fast-charging performance.

[0197] In Comparative Example 3, the precursor from step (1) was atomized into fine droplets using an electrostatic spraying device and directly spray-dried, followed by low-temperature modification treatment. Figure 2 This is a SEM image of the negative electrode material prepared in Example 1 of this application. Figure 3 This is a SEM image of the negative electrode material prepared in Comparative Example 3. Figure 2 and Figure 3 The comparison shows that the particle size of the negative electrode material obtained in Comparative Example 3 is significantly larger, and the dispersion is uneven with agglomeration, which affects the tap density and fast charging performance of the negative electrode material.

[0198] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0199] 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 material, and at least a portion of the surface of the graphite material is provided with a coating layer. The coating layer is made of hard carbon. The median particle size of the graphite material is D1, and the median particle size of the negative electrode material is D2. The median particle size D2 of the negative electrode material and the median particle size D1 of the graphite material satisfy the following relationship: （1）； The coating layer is shown in the Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 532 nm, at a wavelength of 1200 cm⁻¹. -1 Up to 1500cm -1 D-band was observed at 1500 cm. -1 Up to 1800cm -1 The peak area of ​​band G was observed, and the peak area of ​​band D was I. D With the peak area of ​​the G band I G The ratio between I D / I G The value is 1.5~3.0, and the standard deviation of the 30-point Raman ratio of the negative electrode material is less than or equal to 0.

3.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following technical features (1) to (6): (1) The median particle size D1 of the graphite material is 6µm~15µm; (2) The graphite material includes at least one of natural graphite and artificial graphite; (3) The thickness of the coating layer is 20nm~100nm; (4) The carbon atom spacing of the coating layer is 0.36 nm to 0.38 nm; (5) The nitrogen content in the coating layer is 0%wt~5%wt; (6) The hardness of the coating layer is 100MPa~150MPa.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes at least one of the following technical features (1) to (4): (1) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g ~2.0m 2 / g; (2) The tap density of the negative electrode material is 0.9 g / cm³. 3 ~1.2g / cm 3 ; (3) The compaction density of the negative electrode material under 5T pressure is 1.7 g / cm³. 2 ~2.2g / cm 2 ; (4) The median particle size D2 of the negative electrode material is 6µm ~ 16µm.

4. A method for preparing a negative electrode material, characterized in that, Includes the following steps: Graphite material is added to a polymer solution and atomized to obtain a precursor of graphite material coated with polymer solution. The precursor is added to a polar solvent and the solvent is removed to obtain graphite material coated with polymer, wherein the polymer is insoluble in the polar solvent. The polymer-coated graphite material is modified to obtain a cured material; and The solidified material is carbonized to obtain the negative electrode material.

5. The method according to claim 4, characterized in that, The method has at least one of the following technical features (1) to (6): (1) The graphite material includes at least one of natural graphite and artificial graphite; (2) The median particle size D1 of the graphite material is 6µm~15µm; (3) The polymer solution includes at least one of polyimide acid solution, polyethersulfone solution and polyvinylidene fluoride solution; (4) The solid content in the polymer solution is 6%~8%; (5) The mass ratio of the graphite material to the polymer solution is (97:3) to (90:10); (6) The solid content in the mixture formed after the graphite material is added to the polymer solution is 50%~80%.

6. The method according to claim 4, characterized in that, The method has at least one of the following technical features (1) to (3): (1) The ratio of the volume V1 of the precursor of the graphite material coated by the polymer solution to the volume V2 of the graphite material is V1 / V2 = 1.01~1.1; (2) The polar solvent includes at least one of water, ethanol, methanol and propylene glycol; (3) The rate at which the precursor is added to the polar solvent is 10 mL / min to 50 mL / min.

7. The method according to claim 4, characterized in that, The modification process includes: The polymer-coated graphite material is dehydrated under vacuum conditions; Alternatively, the graphite material coated with the polymer may be subjected to an oxidation treatment.

8. The method according to claim 7, characterized in that, The method includes at least one of the following technical features (1) to (6): (1) The vacuum pressure of the dehydration treatment is -0.1MPa to 0.05MPa; (2) The temperature of the dehydration treatment is 150℃~200℃; (3) The dehydration treatment time is 0.5h~2h; (4) The oxidation treatment temperature is 180℃~300℃; (5) The oxidation treatment is carried out in an atmosphere with an oxygen content of 20% to 100%; (6) The oxidation treatment time is 2h~4h.

9. The preparation method according to claim 4, characterized in that, The method comprises at least one of the following technical features (1) to (2): (1) The carbonization temperature is 1000℃~1150℃; (2) The carbonization atmosphere includes at least one of nitrogen, helium, neon, argon and krypton.

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

Images