Negative electrode material and lithium-ion battery

Abstract

Disclosed in the present application are a negative electrode material and a lithium-ion battery. The negative electrode material comprises a carbon material having pores therein. The pores are characterized in that the pore volume of pores having a pore diameter of 3 nm or more and 1000 nm or less as measured by means of mercury porosimetry is V1, where V1<0.1 mL / g; the pore volume of pores having a pore diameter of 3 nm or more and 400 nm or less as measured by means of mercury porosimetry is V2, and the range of the V2 / V1 ratio satisfies 40-70%; and the pore volume of pores having a pore diameter of 3 nm or more and 500 nm or less as measured by means of mercury porosimetry is V3, and the range of the V3 / V1 ratio satisfies ≥60%.

Description

Anode materials and lithium-ion batteries Cross-references to related applications

[0001] This application claims priority to Chinese patent application filed on December 16, 2024, with application number 202411850189.3 and entitled "Anode material and preparation method thereof and lithium-ion battery". Technical Field

[0002] This application relates to the field of lithium-ion battery anode materials technology. More specifically, this application relates to an anode material and a lithium-ion battery. Background Technology

[0003] Graphite is currently the mainstream anode material for lithium-ion batteries. Depending on its origin, graphite can be divided into artificial graphite and natural graphite. Currently, graphite is typically modified using surface coating methods, where an amorphous carbon layer is coated onto its surface to isolate the electrolyte from the graphite in the battery, thus improving its performance. This method is simple to operate, low in cost, and widely used in the modification of graphite anode materials. However, because the coating agent cannot completely cover the outer surface of the graphite, the electrolyte gradually penetrates into these uncoated graphite surfaces during cycling, continuously generating an SEI (solid electrolyte interface). The electrolyte continuously embeds itself into the graphite layer structure, consuming a large amount of active lithium, damaging the graphite structure, and leading to continuous capacity decay. Therefore, it is necessary to develop new graphite modification methods. Densification or isotropic treatment of graphite particles, as well as pore size control, can reduce the porosity and orientation of the graphite particles, thereby reducing the material's expansion rate and improving its cycle performance.

[0004] Therefore, there is a need to provide a negative electrode material that can improve the cycle life and fast charging performance of batteries made from it, as well as improve their orientation and expansion rate. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, this application proposes solutions for negative electrode materials and lithium-ion batteries in several aspects.

[0006] According to one aspect of this application, a negative electrode material is provided, the negative electrode material comprising a carbon material; wherein the carbon material has pores, the pores having the following characteristics: the pore volume of pores with a pore size of 3 nm or more and 1000 nm or less, as measured by mercury porosimetry, is V1, and V1 < 0.1 mL / g; the pore volume of pores with a pore size of 3 nm or more and 400 nm or less, as measured by mercury porosimetry, is V2, and the ratio of V2 / V1 is in the range of 40% to 70%; the pore volume of pores with a pore size of 3 nm or more and 500 nm or less, as measured by mercury porosimetry, is V3, and the ratio of V3 / V1 is in the range of ≥ 60%.

[0007] According to another aspect of this application, a lithium-ion battery is provided, comprising the negative electrode material of any of the foregoing embodiments.

[0008] The technical solution of this application reduces the pore volume of the negative electrode material and adjusts the pore size distribution of the residual pores. This maintains the low pore volume of the negative electrode material, improves its cycle life, and reduces its expansion rate, while retaining some mesopores to ensure rapid lithium-ion transport within the material. By controlling the pore volume and pore volume distribution of the negative electrode material, the technical solution of this application reduces the orientation of the negative electrode material, effectively reduces its expansion during cycling, and improves the battery's long cycle life. Simultaneously, it maintains low impedance in the negative electrode material, effectively improving its fast-charging performance. Attached Figure Description

[0009] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0010] Figure 1 shows a schematic diagram of a battery in a discharged state;

[0011] Figure 2 shows the pore volume distribution of carbon materials in Embodiment 1 and Comparative Example 1 of this application. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0014] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0015] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0016] The specific embodiments of this application are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the embodiments of this application are obtained through conventional commercial channels.

[0017] One embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing.

[0018] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0019] Figure 1 shows a schematic diagram of a battery in a discharged state, i.e., during operation. As shown, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator disposed between the positive and negative electrode sheets. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the positive electrode, separator, and negative electrode after they have been stacked in sequence.

[0020] Positive electrode film

[0021] The positive electrode 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector can be 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 and polymer substrate. The positive active layer contains a positive active material, which includes compounds that reversibly insert and extract metal ions. In some embodiments, the positive 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. In some embodiments, the positive 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).

[0022] negative electrode sheet

[0023] The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collectors, 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 includes a negative electrode material.

[0024] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, and are embedded in the lattice of the positive electrode material.

[0025] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to be embedded in the lattice of the negative electrode material.

[0026] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0027] This application provides a negative electrode material comprising carbon material; wherein the carbon material has pores, the pores having the following characteristics: the pore volume of pores with a pore size of 3 nm or more and 1000 nm or less, as measured by mercury porosimetry, is V1, and V1 < 0.1 mL / g; the pore volume of pores with a pore size of 3 nm or more and 400 nm or less, as measured by mercury porosimetry, is V2, and the ratio of V2 / V1 is in the range of 40% to 70%; the pore volume of pores with a pore size of 3 nm or more and 500 nm or less, as measured by mercury porosimetry, is V3, and the ratio of V3 / V1 is in the range of ≥ 60%.

[0028] For example, V2 / V1 is 40%, 41%, 43%, 45%, 47%, 49%, 50%, 51%, 53%, 55%, 57%, 59%, 60%, 61%, 63%, 65%, 67%, 69%, 70%, or any value within the range of any two of the above values; or within the range of 40% to 60%, or within the range of 50% to 70%, or within the range of 45% to 65%, or within the range of 50% to 60%, or within the range of 60% to 70%.

[0029] For example, V3 / V1 is 60%, 61%, 63%, 65%, 67%, 69%, 70%, 71%, 73%, 75%, 77%, 79%, 80%, or any value within the range of any two of the above values; or within the range of 60% to 70%, or within the range of 65% to 70%, or within the range of 65% to 80%, or within the range of 70% to 80%.

[0030] For example, V1 is 0.01 mL / g, 0.02 mL / g, 0.03 mL / g, 0.04 mL / g, 0.05 mL / g, 0.06 mL / g, 0.07 mL / g, 0.08 mL / g, 0.09 mL / g, 0.099 mL / g, or any value within the range of any two of the above values; or within the range of 0.01 mL / g to 0.09 mL / g, or within the range of 0.02 mL / g to 0.08 mL / g, or within the range of 0.04 mL / g to 0.07 mL / g, or within the range of 0.04 mL / g to 0.08 mL / g, or within the range of 0.05 mL / g to 0.099 mL / g.

[0031] The technical solution of this application reduces the pore volume of the material while controlling the pore size distribution of the residual pores. This maintains a low pore volume, improves the cycle life of the material, and reduces cycle expansion, while retaining some mesopores to ensure rapid lithium-ion transport within the material. By controlling the pore volume and pore volume distribution, the technical solution of this application reduces the orientation of the material. A lower pore volume and a specific pore volume distribution can effectively reduce the expansion of the negative electrode material during cycling and improve the battery's long cycle life, while maintaining low impedance and effectively improving the material's fast-charging performance. When the pore volume and pore volume distribution do not meet the target range, it increases the contact and consumption between the material and the electrolyte, resulting in a thicker SEI film, reduced electrolyte volume, and a significant decrease in the material's cycle life. Increased electrode expansion rate and larger pore size may also reduce the mechanical stability of the electrode material, thus affecting the battery's cycle life and safety.

[0032] Specifically, when V1 ≥ 0.1 mL / g, the increased contact between the carbon material and the electrolyte leads to greater electrolyte consumption, resulting in less electrolyte and a thicker SEI film. This significantly reduces the cycle life of the material and increases the electrode expansion rate. When V2 / V1 < 40% or V3 / V1 < 60%, the pores inside the material are excessively concentrated in the 500 nm to 1000 nm pore size range. Excessively large pore sizes may reduce the mechanical stability of the electrode material and increase electrolyte contact and consumption, thus affecting the battery's cycle life and safety. When V2 / V1 > 70%, the pores inside the material are excessively concentrated in the 3 nm to 400 nm pore size range. Excessively small pore sizes hinder the rapid transport of lithium ions, resulting in higher material impedance, accelerated battery temperature rise, and accelerated electrolyte decomposition and consumption. This leads to a larger electrode expansion rate and a lower battery cycle retention rate.

[0033] In some embodiments, in the XRD pattern of the negative electrode material (XRD is an abbreviation for "X-ray diffraction": X-ray diffraction is an optical analysis method detected by an instrument. When monochromatic X-rays are irradiated onto a powder sample, if the angle between a set of planes of one grain and the incident X-ray is θ, the diffraction condition is met, and diffraction occurs at the diffraction angle 2θ), there is a 004 peak between 54° and 55° of 2θ, and the intensity of the 004 peak is I. 004 It has a 110 peak between 77° and 78° of 2θ, and the intensity of the 110 peak is I. 110 The ratio of the two intensities I 004 / I 110 ≤3.0. For example, I 004 / I 110The value can be 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.8, 1.6, 1.4, 1.2, or any value within the range of any of the above values; or within the range of 1.0 to 3.0, or within the range of 1.5 to 3.0, or within the range of 2.0 to 3.0, or within the range of 2.5 to 3.0. The technical solution of this application reduces the orientation of the material by controlling the pore size distribution, which is beneficial to the rapid transport of lithium ions and can effectively improve the fast-charging performance of the material. When the ratio I... 004 / I 110 >3, the orientation of the material is enhanced, which is not conducive to the rapid transport of lithium ions. The material impedance is relatively large, which accelerates the temperature rise of the battery, accelerates the decomposition and consumption of the electrolyte, and leads to a larger expansion rate of the material, thus affecting the cycle life of the battery.

[0034] In some embodiments, the BET specific surface area of ​​the negative electrode material is ≤3.0 m². 2 / g, for example, can be 3.0m 2 / g, 2.9m 2 / g, 2.8m 2 / g, 2.7m 2 / g, 2.6m 2 / g, 2.5m 2 / g, 2.4m 2 / g, 2.3m 2 / g, 2.0m 2 / g, 1.5m 2 / g, 1.0m 2 / g, 0.5m 2 / g or any value within the range of any of the above values. When the BET specific surface area falls within the above range, a lower specific surface area is beneficial for the material to achieve a higher first coulombic efficiency, thereby improving the cycle life of the battery prepared with the negative electrode material and giving it better high-temperature storage performance.

[0035] In some embodiments, the volumetric median particle size Dv50 of the negative electrode material ranges from 5 μm to 25 μm, and can be exemplarily 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, or any value within the range of any of the above values. If the average particle size of the negative electrode material is <5 μm, it is not conducive to the rapid transport of lithium ions in the negative electrode material, resulting in increased material impedance and reduced cycle retention of the battery. If the average particle size of the negative electrode material is >25 μm, the particle size of the negative electrode material is too large, resulting in a large space between the particles, which may affect the mechanical properties of the material and thus affect the cycle life of the battery. When Dv50 falls within the above range, it is beneficial for the material to achieve a higher initial coulombic efficiency, thereby improving the cycle life of the battery prepared with the negative electrode material and providing better high-temperature storage performance.

[0036] In some embodiments, the compaction density of the negative electrode material ranges from 1.5 to 2.1 g / cc. The compaction density of the negative electrode material can, exemplarily, be 1.50 g / cc, 1.55 g / cc, 1.60 g / cc, 1.65 g / cc, 1.70 g / cc, 1.75 g / cc, 1.80 g / cc, 1.85 g / cc, 1.90 g / cc, 1.95 g / cc, 2.0 g / cc, 2.05 g / cc, 2.10 g / cc, or any value within the range of any of the above values. When the compaction density falls within the above range, the material has a higher compaction density, thereby improving the energy density of the battery prepared from the negative electrode material.

[0037] In some embodiments, the tap density of the negative electrode material ranges from 0.9 to 1.2 g / cc. The compaction density of the negative electrode material can, exemplarily, be 0.90 g / cc, 0.92 g / cc, 0.95 g / cc, 0.98 g / cc, 1.0 g / cc, 1.02 g / cc, 1.05 g / cc, 1.08 g / cc, 1.10 g / cc, 1.12 g / cc, 1.15 g / cc, 1.18 g / cc, 1.20 g / cc, or any value within the range of any of the above values. When the tap density falls within the above range, the material has a high tap density, resulting in a slurry with good stability and consistency prepared from the negative electrode material during the preparation of the negative electrode slurry.

[0038] In some embodiments, the fixed carbon content of the negative electrode material is ≥99.94%, and the fixed carbon content of the negative electrode material can be, for example, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, or any value within the range of any of the above values. When the fixed carbon content falls within the above range, a higher fixed carbon content results in a higher capacity for the negative electrode material, and also gives the battery made from it better high-temperature storage performance.

[0039] In some embodiments, the 20-cycle expansion rate of the negative electrode sheet made of the negative electrode material is <27%, which can be exemplarily 26.5%, 26%, 25.5%, 25%, 24.5%, 24%, 23.5%, 23%, 22.5%, 22%, 21%, 20%, or any value within the range of any of the above values. The 20-cycle expansion rate reflects the expansion property of the material during use. By controlling the pore volume and pore distribution, the negative electrode sheet made of the negative electrode material of this application exhibits a significantly reduced expansion property.

[0040] In some embodiments, the capacity retention rate of a pouch cell made of the negative electrode material after 300 cycles of 1C / 1C is >85%, which can be exemplarily 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or any value within the range of any of the above values. The capacity retention rate after 300 cycles of 1C / 1C reflects the cycling performance of the material in use. This application significantly improves the capacity retention rate of the battery made of the material by controlling the pore volume and pore distribution.

[0041] In some embodiments, the carbon material includes natural graphite. During the spheroidization process of existing natural graphite anode materials, numerous pores are formed within the spherical graphite particles due to the curling and stacking of the flakes. This results in high pore volume and specific surface area, as well as numerous surface defects. This application reduces the porosity of natural graphite and densifies or isotropicallyizes it by controlling the pore volume and distribution, while maintaining a certain number of mesopores, thereby reducing the material's expansion rate and improving its cycle performance.

[0042] In some embodiments, the carbon material includes a graphite core and a coating layer located on at least a portion of the surface of the graphite core.

[0043] In some embodiments, the coating layer comprises an amorphous carbon material.

[0044] Figure 2 shows the pore volume distribution of carbon materials in Embodiment 1 and Comparative Example 1 of this application.

[0045] This application also provides a method for preparing a negative electrode material, comprising: a first step S1, selecting carbon material raw materials and crushing and spherizing the carbon material raw materials; a second step S2, subjecting the carbon material obtained in the first step to pore control treatment; and a third step S3, subjecting the carbon material obtained in the second step to high-temperature heat treatment; wherein the pore control treatment includes any one or a combination of at least two of the following: adding a modifier, fusion heating, reactor heating, rolling, cold isostatic pressing, hot isostatic pressing, or molding.

[0046] The technical solution of this application precisely controls the pore volume and pore size distribution of the material through steps such as pore control treatment. On the one hand, it maintains a low pore volume, improves the cycle life of the material and reduces the expansion rate of the material. On the other hand, it retains some mesopores to ensure the rapid transport of lithium ions in the material, thereby making the material have low impedance and effectively improving the fast charging performance of the material.

[0047] In some embodiments, in the first step, the carbon material raw material selected may be highly crystalline graphite; the carbon material raw material is selected from one or more of natural spherical graphite, natural flake graphite, or microcrystalline graphite.

[0048] In some embodiments, the pulverization in the first step is carried out by mechanical pulverization.

[0049] In some embodiments, the first step, following the spheroidization process, further includes a purification process. Preferably, the purification process is an acid purification process.

[0050] In some embodiments, the carbon material obtained in the first step is spherical natural graphite with a Dv50 of 5μm-25μm; preferably, the carbon material obtained in the first step is spherical natural graphite with a Dv50 of 9μm-18μm.

[0051] In some embodiments, in the second step, preferably, the pore control treatment includes any one or a combination of at least two of the following: adding a modifier, fusion heating, cold isostatic pressing, or molding. For example, the pore control treatment can be a combination of cold isostatic pressing followed by adding a modifier. Cold isostatic pressing first reduces the total pore volume, making the material denser; then, adding the modifier followed by heat treatment maintains a certain number of mesopores in the material, which is beneficial for lithium-ion transport and improves the material's fast-charging performance. Molding followed by adding the modifier can also achieve the technical effects described above.

[0052] In some embodiments, in the second step, the pore control treatment is a combination of cold isostatic pressing followed by the addition of a modifier. Specifically, the carbon material obtained in the first step is placed in a cold isostatic press for processing, with the working pressure of the cold isostatic press being 60MPa-70MPa; the pressure curve is specifically set as follows: the pressure rises from 0MPa to 20MPa-30MPa in 8-12 minutes, held for 5-10 minutes, and then rises to 60MPa-70MPa in 25-45 minutes, held for 5-8 minutes, to obtain block graphite; the block graphite is then pulverized to obtain graphite with a Dv50 of 9μm-16μm, and mixed with a modifier at a mass ratio of 100:5-20.

[0053] In some embodiments, in the second step, the pore control treatment is a combination of molding treatment followed by the addition of a modifier. Specifically, the carbon material obtained in the first step is placed in a molding press for processing, with the working pressure of the molding press being 20MPa-25MPa; the pressure curve is specifically set as follows: the pressure rises from 0MPa to 10MPa-15MPa in 8-12 minutes, and is held for 4-5 minutes; then it rises to 20MPa-25MPa in 15-20 minutes, and is held for 10-15 minutes, to obtain block graphite; the block graphite is then pulverized to obtain graphite with a Dv50 of 5μm-20μm, and mixed with a modifier at a mass ratio of 100:5-20.

[0054] In some embodiments, in the second step, the pore conditioning treatment is a combination of adding a modifier followed by fusion heating. Specifically, the carbon material obtained in the first step is mixed with the modifier at a mass ratio of 100:5-20, placed in a fusion machine, heated to 180-220°C at a heating rate of 3-7°C / min and a rotation speed of 1800-2200 r / min, held for 1.5-2.5 hours, and then cooled to room temperature.

[0055] In some embodiments, the pore conditioning treatment in the second step includes adding a modifier. The modifier is selected from any one or a combination of at least two of the following: resin, coal tar pitch, petroleum pitch, mesophase pitch, coal tar or heavy oil, glucose, sucrose, starch, polydopamine, polyvinyl alcohol, polypyrrole, polyethylene glycol, anthracene, aniline, citric acid, acetic acid, and tannic acid. Preferably, the modifier is selected from any one or a combination of at least two of the following: resin, coal tar pitch, petroleum pitch, and mesophase pitch. Preferably, the amount of modifier added is 5 wt% to 20 wt% based on the weight of the carbon material.

[0056] In some embodiments, the high-temperature heat treatment in the third step is performed at a temperature of 600℃-3000℃; for example, the temperature of the high-temperature heat treatment can be 800℃, 1000℃, 1200℃, 1500℃, 1800℃, 2100℃, 2300℃, 2500℃, 2800℃ or any value within the range of any two of the above values.

[0057] In some embodiments, specifically, in the third step, the temperature curve of the high-temperature heat treatment can be: heating to 200°C at a heating rate of 3°C / min-7°C / min and holding at 200°C for 25min-35min; heating to 600°C at a heating rate of 1.5°C / min-2.5°C / min and holding at 600°C for 25min-35min; heating to 1000°C-1200°C at a heating rate of 8°C / min-12°C / min and holding at 1000°C-1200°C for 180min-220min.

[0058] In some embodiments, specifically, in the third step, the temperature curve of the high-temperature heat treatment can be: heating to 1200℃ at a heating rate of 8℃ / min-12℃ / min, and holding at 1200℃ for 25min-35min; heating to 1800℃ at a heating rate of 8℃ / min-12℃ / min; heating to 2300℃-2800℃ at a heating rate of 15℃ / min-25℃ / min, and holding at 2300℃-2800℃ for 50min-70min.

[0059] In some embodiments, the high-temperature heat treatment in the third step is carried out in an inert gas atmosphere. Preferably, the inert gas is any one or a combination of at least two of helium, neon, argon, nitrogen, or krypton. The protective atmosphere of an inert gas is beneficial to the material preparation process.

[0060] According to another aspect of this application, a lithium-ion battery is provided, comprising the aforementioned negative electrode material or a negative electrode material prepared according to the aforementioned preparation method. The aforementioned lithium-ion battery exhibits reduced swelling, while also possessing good cycle life and fast-charging performance.

[0061] Specific embodiments and comparative examples

[0062] Example 1

[0063] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 9μm.

[0064] Step S2: The high-purity spherical natural graphite is placed in a cold isostatic press for processing. The working pressure of the isostatic press is set as follows: the pressure increases from 0 MPa to 30 MPa in 10 minutes, and is held at 30 MPa for 5 minutes; then it increases to 60 MPa in 25 minutes and is held for 8 minutes, resulting in block graphite. The block graphite is then crushed and pulverized to obtain graphite with a median particle size (Dv50) of 9 μm. The obtained graphite is mixed with asphalt at a mass ratio of 100:10.

[0065] Step S3: The mixture is then subjected to high-temperature treatment at 1200℃ under a nitrogen atmosphere to obtain carbon material. The specific temperature curve for the high-temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min; heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min; heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200min.

[0066] Example 2

[0067] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 18μm.

[0068] Step S2: The high-purity spherical natural graphite is placed in a molding press for processing. The working pressure is set as follows: the pressure increases from 0 MPa to 10 MPa in 10 minutes, and is maintained at 10 MPa for 5 minutes; then, it increases to 20 MPa in 15 minutes and is maintained for 10 minutes, resulting in block graphite. The block graphite is then crushed and pulverized to obtain graphite with a median particle size (Dv50) of 18 μm. The obtained graphite is mixed with asphalt at a mass ratio of 100:5.

[0069] Step S3: Then, the mixture is subjected to high-temperature treatment at 1000℃ in a nitrogen atmosphere to obtain carbon material. The specific temperature curve for the high-temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min, heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min, heating to 1000℃ at a heating rate of 10℃ / min and holding at 1000℃ for 200min.

[0070] Example 3

[0071] Step S1: Select natural flake graphite and mechanically crush and spheroidize it to obtain high-purity spherical natural graphite with a median particle size Dv50 of 17μm.

[0072] Step S2: Mix the obtained graphite and asphalt at a mass ratio of 100:6 and put them into a fusion machine. Heat to 200°C at 5°C / min, rotate at 2000 r / min, maintain for 2 hours, and then cool to room temperature.

[0073] Step S3: Then the mixture is treated at a high temperature of 1200℃ to obtain carbon material. The specific temperature curve for the high temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min, heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min, heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200min.

[0074] Example 4

[0075] Step S1: Select microcrystalline graphite and mechanically crush and spheroidize it to obtain high-purity spherical natural graphite with a median particle size Dv50 of 10μm.

[0076] Step S2: The high-purity spherical natural graphite is placed in a cold isostatic press for processing. The working pressure of the isostatic press is set as follows: pressure increases from 0 MPa to 20 MPa in 10 minutes, held at 20 MPa for 5 minutes; pressure increases to 50 MPa in 20 minutes, held for 10 minutes; pressure increases to 80 MPa in 10 minutes, held for 5 minutes; pressure increases to 120 MPa in 15 minutes, held for 5 minutes; pressure increases to 150 MPa in 10 minutes, held for 1 minute, to obtain block graphite. The block graphite is crushed and pulverized to obtain graphite with a median particle size (Dv50) of 10 μm. The obtained graphite is mixed with asphalt at a mass ratio of 100:20.

[0077] Step S3: Then the mixture is treated at a high temperature of 2800℃ to obtain carbon material. The specific temperature curve for the high temperature treatment is as follows: heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 30min, heating to 1800℃ at a heating rate of 10℃ / min, heating to 2800℃ at a heating rate of 20℃ / min and holding at 2800℃ for 60min.

[0078] Example 5

[0079] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 16μm.

[0080] Step S2: The high-purity spherical natural graphite is placed in a cold isostatic press for processing. The working pressure of the isostatic press is set as follows: the pressure increases from 0 MPa to 30 MPa in 10 minutes, and is held at 30 MPa for 5 minutes; then, it increases to 70 MPa in 45 minutes and is held for 5 minutes, resulting in block graphite. The block graphite is then crushed and pulverized to obtain graphite with a median particle size Dv50 of 16 μm. The obtained graphite is mixed with phenolic resin at a mass ratio of 100:8.

[0081] The third step, S3, involves treating the mixture at a high temperature of 2300℃ to obtain carbon material. The specific temperature curve for the high-temperature treatment is as follows: heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 30 min, heating to 1800℃ at a heating rate of 10℃ / min, heating to 2300℃ at a heating rate of 20℃ / min, and holding at 2300℃ for 60 min.

[0082] Example 6

[0083] Step S1: Select natural flake graphite and mechanically crush, spheroidize, and acid-purify it to obtain high-purity spherical natural graphite with a median particle size Dv50 of 10μm and Dv90 / Dv10 = 2.0.

[0084] Step S2: The high-purity spherical natural graphite is placed in a cold isostatic press for processing. The working pressure of the isostatic press is set as follows: pressure increases from 0 MPa to 50 MPa in 30 minutes, held for 10 minutes; pressure increases to 150 MPa in 30 minutes, held for 5 minutes; pressure increases to 200 MPa in 25 minutes, held for 1 minute, to obtain block graphite. The block graphite is crushed and pulverized to obtain graphite with a median particle size Dv50 of 10 μm and Dv90 / Dv10 = 2.0. The obtained graphite is mixed with asphalt at a mass ratio of 100:15.

[0085] Step S3: Then the mixture is treated at a high temperature of 1200℃ to obtain carbon material. The specific temperature curve for the high temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min, heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min, heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200min.

[0086] Comparative Example 1

[0087] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 9μm.

[0088] Compared to the example, a simplified second step S2 is performed: the high-purity spherical natural graphite is mixed with bitumen at a mass ratio of 100:10.

[0089] Step S3: The mixture is then subjected to high-temperature treatment at 1200℃ under a nitrogen atmosphere to obtain carbon material. The specific temperature curve for the high-temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min; heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min; heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200min.

[0090] Comparative Example 2

[0091] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 18μm.

[0092] Without performing the second step S2, proceed directly to the third step S3: treat the high-purity spherical natural graphite at a high temperature of 1000℃ under a nitrogen atmosphere to obtain carbon material. The specific temperature curve for the high-temperature treatment is as follows: heat to 200℃ at a heating rate of 5℃ / min and hold at 200℃ for 30min; heat to 600℃ at a heating rate of 2℃ / min and hold at 600℃ for 30min; heat to 1000℃ at a heating rate of 10℃ / min and hold at 1000℃ for 200min.

[0093] Comparative Example 3

[0094] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 18μm.

[0095] Compared to the example, a simplified second step S2 is performed: the high-purity spherical natural graphite is mixed with asphalt at a mass ratio of 100:15.

[0096] Step S3: The mixture is then subjected to high-temperature treatment at 1200℃ in a nitrogen atmosphere to depolymerize and obtain carbon material (the “depolymerization” mentioned above refers to the fact that after the natural graphite and asphalt are mixed and carbonized, some graphite particles will stick together because of the adhesive properties of the asphalt, and mechanical equipment is needed to separate the sticky particles). The specific temperature curve for the high-temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30min, heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30min, heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200min.

[0097] Comparative Example 4

[0098] Step S1: Select natural flake graphite and process it through mechanical crushing, spheroidization, and acid purification to obtain high-purity spherical natural graphite with a median particle size Dv50 of 18μm.

[0099] Step S2: Mix the high-purity spherical natural graphite with asphalt at a mass ratio of 100:6, and then put the mixture into a cold isostatic press for processing. The working pressure of the isostatic press is set as follows: the pressure rises from 0 MPa to 30 MPa in 10 minutes, and is held at 30 MPa for 5 minutes. Then, the pressure rises to 60 MPa in 25 minutes and is held for 8 minutes to obtain block graphite.

[0100] Step S3: Carbon material is obtained by high-temperature treatment at 1200℃ under a nitrogen atmosphere. The specific temperature curve for this high-temperature treatment is as follows: heating to 200℃ at a heating rate of 5℃ / min and holding at 200℃ for 30 min; heating to 600℃ at a heating rate of 2℃ / min and holding at 600℃ for 30 min; heating to 1200℃ at a heating rate of 10℃ / min and holding at 1200℃ for 200 min. The block graphite is then crushed and pulverized to obtain graphite with a median particle size Dv50 of 18 μm.

[0101] The testing methods used in this application are as follows:

[0102] The volumetric median particle size (Dv50) of the material was tested using a Malvern Master Size 3000 laser particle size analyzer: The sample, a small amount of dispersant (a mixture of ethanol, pure water, and a low-foaming surfactant), and pure water were added to a 50 mL beaker. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The sample was then transferred to the sample cell of the laser particle size analyzer, and the pump speed was set to 2400–2500 r / min at a frequency of 19.5 Hz for particle size analysis. This application pertains to the cumulative volumetric particle size distribution statistics.

[0103] Specific surface area was tested using a Micromeritics Tristar instrument: nitrogen gas was used for testing, degassing temperature was 300℃, and degassing time was 1 h; P / P0 = 0-0.3, minimum equilibrium delay at P / P0 ≥ 0.995, time: 600 s. Adsorption isotherms were plotted by measuring the adsorption amount under different relative pressures (P / P0 = 0-0.3), and the specific surface area was calculated using the BET (Brunauer-Emmett-Teller) multilayer adsorption theory.

[0104] The pore volume was measured using a Micromeritics AutoPore IV 9500 mercury porosimeter, specifically within the pore size ranges of 3-1000 nm, 3-400 nm, and 3-500 nm. The testing method involved setting the pressure from 0.001 MPa to 600.0 MPa, with at least 15 points per order of magnitude, until the sample chamber was filled with mercury. The test was stopped once the set pressure was reached.

[0105] XRD analysis was performed using an X-ray diffractometer. The intensity ratio of the 004 peak (2θ between 54° and 55°) and the 110 peak (2θ between 77° and 78°) was calculated to obtain the powder orientation (I). 004 / I 110 The value of ).

[0106] The electrode expansion rate was tested using the testing device and system disclosed in patent application CN201920973729.5, which tested the electrode expansion rate for 20 cycles.

[0107] Electrode preparation and testing conditions: The provided negative electrode material, conductive agents SP, CMC, and SBR were mixed in a mass ratio of 95.9:1.0:1.5:2.0 and then coated onto copper foil to obtain the negative electrode sheet. The areal density of the negative electrode sheet was 7 mg / cm³. 2 The compacted density is 1.6 ± 0.03 g / cc, and the electrode diameter is 16 mm. The positive electrode active material NCM523, conductive agent SP, conductive agent CNTs, and PVDF are mixed evenly in a mass ratio of 97.5:1.0:0.5:1.5 and then coated onto aluminum foil to obtain the positive electrode sheet with a positive electrode areal density of 16.6 mg / cm³. 2 The compaction density is 3.8 g / cc, the electrode diameter is 16 mm, and the N / P ratio is 1.03 to 1.05. The electrolyte is 1 mol / L LiPF6 + EC + DMC + EMC, with additives VC / FEC (1 to 3%).

[0108] ●Charging and discharging steps:

[0109] Let it stand for 12 hours;

[0110] First cycle:

[0111] Charge at 0.01C constant current to the cutoff voltage for 30 minutes, charge at 0.05C constant current to the cutoff voltage for 30 minutes, charge at 0.1C constant current, charge at 4.2V constant voltage, discharge at 0.01C constant current to the cutoff voltage, and let stand for 5 minutes.

[0112] Discharge at a constant current of 0.1C to the cutoff voltage, and at a cutoff voltage of 3.0V, let stand for 5 minutes;

[0113] Second cycle:

[0114] Charge at a constant current of 0.2C, charge at a constant voltage of 4.2V, discharge at a constant current of 0.01C to the cutoff voltage, and let stand for 5 minutes;

[0115] Discharge at a constant current of 0.2C to the cutoff voltage, then at a cutoff voltage of 3.0V, and let stand for 5 minutes.

[0116] Cycles 3-20: Charge at 0.5C constant current, charge at 4.2V constant voltage, discharge at 0.01C constant current to cutoff voltage, and let stand for 5 minutes;

[0117] Discharge at a constant current of 0.5C to the cutoff voltage, and at a cutoff voltage of 3.0V, let stand for 5 minutes.

[0118] Thickness was measured using a Keyence GT2-71N sensor. The expansion rate was calculated as: thickness change / initial active layer thickness of the negative electrode * 100%. The thickness change value was the difference in thickness of the electrode before and after cycling.

[0119] The compaction density of the material under 1.0T pressure was tested using an automatic compaction density meter.

[0120] The tap density of the material was tested using a Quanta Auto Tap instrument from the United States. The sample size was 100 mL, the vibration was repeated 1000 times, and the vibration frequency was 260 times / min.

[0121] The fixed carbon content was tested in accordance with GB / T 3521-2008 "Methods for Chemical Analysis of Graphite".

[0122] Battery Testing: The provided negative electrode material, conductive agent SP, CMC, and SBR were mixed in a mass ratio of 95.9:1.0:1.3:1.8 and coated onto copper foil to obtain the negative electrode sheet. The positive electrode active material NCM523, conductive agent SP, conductive agent CNTs, and PVDF were mixed evenly in a mass ratio of 97.0:1.0:0.5:1.5 and coated onto aluminum foil to obtain the positive electrode sheet. The electrolyte was 1 mol / L LiPF6 + EC + EMC, and the separator was a PP / PE / PP three-layer separator. A soft-pack battery of approximately 38 mAh was fabricated to test the full-cell performance of the materials. The 1C / 1C capacity retention rate test method was as follows: continuous charge and discharge cycles of 1C and 1C were performed for 300 cycles.

[0123] Table 1 shows the test results for each embodiment and comparative example.

[0124] Table 1

[0125] The results in the table above show that the carbon material prepared using this method meets the following requirements: V1 is reduced to <0.1 mL / g, the V2 / V1 ratio ranges from 40% to 70%, and the V3 / V1 ratio ranges from ≥60%. The resulting carbon material exhibits a relatively low overall pore volume, with pore sizes mostly concentrated in the range of 3 nm to 500 nm. It also contains a suitable amount of pores with moderate sizes of 400 to 500 nm and a suitable amount of pores with larger sizes of 500 nm to 1000 nm, ensuring both rapid lithium-ion transport and a more stable material structure. The material shows a significant reduction in electrode expansion after 20 cycles in the battery, decreasing to less than 27%, with a minimum reduction to 23.8%. The capacity retention rate after 300 cycles is improved by more than 5%, effectively reducing the expansion of the negative electrode material during cycling and improving the battery's long cycle life. Simultaneously, the material maintains low impedance, effectively improving its fast-charging performance.

[0126] The results from Comparative Examples 1 and 2 and Examples 1 and 2 show that because V1 > 0.1 mL / g in Comparative Examples 1 and 2, the material has more contact with the electrolyte, which consumes more electrolyte. This results in less electrolyte and a thicker SEI film. Even if V2 / V1 meets 40% to 70% and V3 / V1 meets > 60%, the cycle life of the material will decrease significantly and the electrode expansion rate will increase.

[0127] The results of Comparative Example 3 (V2 / V1<40%, V3 / V1<60%) show that when only V1<0.1mL / g is satisfied, but V2 / V1 is in the range of 40% to 70% and V3 / V1≥60% are not simultaneously satisfied, although the carbon material has a low overall pore volume, too many pores inside the material are concentrated in the range of 500nm to 1000nm. The excessively large pore size may reduce the mechanical stability of the electrode material, increase the contact and consumption of electrolyte, and also lead to a significant decrease in the cycle life of the material and an increase in the electrode expansion rate, thereby affecting the cycle life and safety of the battery.

[0128] The results of Comparative Example 4 (V2 / V1>70%) show that if only V1<0.1mL / g and V3 / V1≥60% are satisfied, but V2 / V1 cannot be in the range of 40% to 70% at the same time, the number of pores with a diameter of 500nm to 1000nm inside the material will be too small, and too many pores will be concentrated in the range of 3nm to 400nm. The small pore size is not conducive to the rapid transport of lithium ions, resulting in a large material impedance, accelerating the temperature rise of the battery, accelerating the decomposition and consumption of the electrolyte, and resulting in a still large electrode expansion rate and a low 300-cycle retention rate.

[0129] The above experimental data demonstrate that when carbon materials conforming to the characteristics of this application are used as negative electrodes in lithium-ion batteries, they can effectively reduce electrode expansion and improve the cycle life of the battery.

[0130] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A negative electrode material, said negative electrode material comprising a carbon material, characterized in that, The carbon material contains pores, which have the following characteristics: the pore volume of pores with a diameter of 3 nm or more and less than 1000 nm, as measured by mercury porosimetry, is V1, and V1 < 0.1 mL / g; the pore volume of pores with a diameter of 3 nm or more and less than 400 nm, as measured by mercury porosimetry, is V2, and the ratio of V2 / V1 is in the range of 40% to 70%; the pore volume of pores with a diameter of 3 nm or more and less than 500 nm, as measured by mercury porosimetry, is V3, and the ratio of V3 / V1 is in the range of ≥ 60%.

2. The negative electrode material according to claim 1, characterized in that, V2 / V1 is 40%, 41%, 43%, 45%, 47%, 49%, 50%, 51%, 53%, 55%, 57%, 59%, 60%, 61%, 63%, 65%, 67%, 69%, 70%, or any value within the range of any two of the above values; or within the range of 40% to 60%, or within the range of 50% to 70%, or within the range of 45% to 65%, or within the range of 50% to 60%, or within the range of 60% to 70%.

3. The negative electrode material according to claim 1, characterized in that, V3 / V1 is 60%, 61%, 63%, 65%, 67%, 69%, 70%, 71%, 73%, 75%, 77%, 79%, 80%, or any value within the range of any two of the above values; or within the range of 60% to 70%, or within the range of 65% to 70%, or within the range of 65% to 80%, or within the range of 70% to 80%.

4. The negative electrode material according to claim 1, characterized in that, V1 is 0.01 mL / g, 0.02 mL / g, 0.03 mL / g, 0.04 mL / g, 0.05 mL / g, 0.06 mL / g, 0.07 mL / g, 0.08 mL / g, 0.09 mL / g, 0.099 mL / g, or any value within any two of the above values; or within the range of 0.01 mL / g to 0.09 mL / g, or within the range of 0.02 mL / g to 0.08 mL / g, or within the range of 0.04 mL / g to 0.07 mL / g, or within the range of 0.04 mL / g to 0.08 mL / g, or within the range of 0.05 mL / g to 0.099 mL / g.

5. The negative electrode material according to claim 1, characterized in that, In the XRD pattern of the negative electrode material, there is a 004 peak with a diffraction peak angle 2θ between 54° and 55°, and the intensity of the 004 peak is I. 004 The diffraction peak has a 110 peak with an angle 2θ between 77° and 78°, and the intensity of the 110 peak is I. 110 The ratio of the two intensities I 004 / I 110 ≤3.

0.

6. The negative electrode material according to claim 5, characterized in that, I 004 / I 110 It can be 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.8, 1.6, 1.4, 1.2, or any value within the range of any of the above values; or within the range of 1.0 to 3.0, or within the range of 1.5 to 3.0, or within the range of 2.0 to 3.0, or within the range of 2.5 to 3.

0.

7. The negative electrode material according to claim 1 or 5, characterized in that, The negative electrode material includes at least one of the following characteristics: a. BET specific surface area ≤ 3.0m² 2 / g; b. The volume median particle size Dv50 ranges from 5 μm to 25 μm.

8. The negative electrode material according to claim 1 or 5, characterized in that, The negative electrode material includes at least one of the following characteristics: c. The compaction density ranges from 1.5 g / cc to 2.1 g / cc; d. The tap density ranges from 0.9 g / cc to 1.2 g / cc.

9. The negative electrode material according to claim 1 or 5, characterized in that, The fixed carbon content of the negative electrode material is ≥99.94%.

10. The negative electrode material according to claim 1 or 5, characterized in that, The carbon material includes natural graphite.

11. The negative electrode material according to claim 1 or 5, characterized in that, The carbon material includes a graphite core and a coating layer located on at least a portion of the surface of the graphite core.

12. The negative electrode material according to claim 11, characterized in that, The coating layer comprises amorphous carbon material.

13. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 12.

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