Negative electrode material, preparation method thereof and lithium ion battery

Abstract

The present application discloses a negative electrode material, a preparation method thereof, and a lithium ion battery. The negative electrode material includes a carbon material, and the carbon material has pores, and the pores have the following characteristics: pores with a pore diameter of more than 3 nm and less than 1000 nm, the pore volume obtained by mercury porosimetry is V1, and V1 < 0.1 mL / g; pores with a pore diameter of more than 3 nm and less than 400 nm, the pore volume obtained by mercury porosimetry is V2, and the ratio range of V2 / V1 satisfies 40% - 70%; pores with a pore diameter of more than 3 nm and less than 500 nm, the pore volume obtained by mercury porosimetry is V3, and the ratio range of V3 / V1 satisfies ≥60%.

Description

Technical Field

[0001] This application relates to the technical field of anode materials for lithium-ion batteries. More specifically, this application relates to an anode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Graphite is the mainstream anode material for lithium-ion batteries in the current market. According to different sources, graphite can be further divided into artificial graphite and natural graphite. Among them, artificial graphite occupies most of the power battery market due to its good cycle stability. The advantages of natural graphite are high capacity and low carbon emissions, but its cycle life is relatively short. Currently, natural graphite usually adopts a surface coating modification method, coating an amorphous carbon layer on its surface to isolate the electrolyte from the natural graphite in the battery to improve its performance. This method is simple to operate and low in cost, and is widely used in the modification of natural graphite anode materials. However, since the coating agent cannot completely cover the outer surface of natural graphite (especially the surface of flake graphite inside spherical graphite), this causes the electrolyte to gradually penetrate to the surface of these uncoated natural graphite during the cycle, continuously generating SEI (solid electrolyte interface) and the electrolyte continuously embedding into the natural graphite layer structure, which will consume a large amount of active lithium, damage the natural graphite structure, and lead to continuous capacity attenuation. Therefore, in view of this, it is necessary to develop a new natural graphite modification method. Densify or isotropize natural graphite particles and perform pore size regulation treatment to reduce the porosity of natural spherical graphite particles while reducing the particle orientation, thereby reducing the expansion rate of the material and improving the cycle performance of the material.

[0003] Based on this, it is necessary to provide an anode material and a preparation method thereof, so that the cycle life and fast charging performance of the battery prepared therefrom are improved, and the orientation and expansion rate are also improved. Summary of the Invention

[0004] In order to solve at least one or more of the above-mentioned technical problems, this application proposes solutions for anode materials, preparation methods of anode materials, and lithium-ion batteries in multiple aspects.

[0005] According to one aspect of this application, an anode material is provided. The anode material includes a carbon material. Among them, the carbon material has pores, and the pores have the following characteristics: pores with a pore diameter of more than 3 nm and less than 1000 nm, the pore volume obtained by mercury porosimetry is V1, and V1 < 0.1 mL / g; pores with a pore diameter of more than 3 nm and less than 400 nm, the pore volume obtained by mercury porosimetry is V2, and the ratio range of V2 / V1 satisfies 40% - 70%; pores with a pore diameter of more than 3 nm and less than 500 nm, the pore volume obtained by mercury porosimetry is V3, and the ratio range of V3 / V1 satisfies ≥ 60%.

[0006] According to an embodiment of the present application, in the XRD pattern of the negative electrode material, there is a 004 peak between 2θ of 54° - 55°, and the intensity of the 004 peak is I 004 ; there is a 110 peak between 2θ of 77° - 78°, and the intensity of the 110 peak is I 110 ; the ratio of the two intensities I 004 / I 110 ≤3.0.

[0007] According to an embodiment of the present application, the negative electrode material includes at least one of the following characteristics:

[0008] a. BET specific surface area ≤ 3.0 m 2 / g;

[0009] b. The range of volume median particle size Dv50 is 5μm - 25μm;

[0010] c. The range of tap density is 1.5 - 2.1 g / cc;

[0011] d. The range of bulk density is 0.9 - 1.2 g / cc;

[0012] e. The range of fixed carbon content ≥ 99.94%.

[0013] According to an embodiment of the present application, the carbon material includes natural graphite.

[0014] According to another aspect of the present application, a method for preparing a negative electrode material is provided, including: the first step of selecting a carbon material raw material and performing crushing and spheroidization treatment on the carbon material raw material; the second step of performing pore regulation treatment on the carbon material obtained in the first step; the third step of performing high-temperature heat treatment on the carbon material obtained in the second step. The pore regulation treatment includes any one or a combination of at least two of adding a modifier, fusion heating, autoclave heating, rolling, cold isostatic pressing treatment, hot isostatic pressing treatment, or molding pressing treatment.

[0015] According to an embodiment of the present application, the carbon material raw material is selected from one or more of natural spherical graphite, natural flake graphite, or microcrystalline graphite.

[0016] According to an embodiment of the present application, in the first step, after the spheroidization treatment, a purification treatment step is further included.

[0017] According to an embodiment of the present application, in the second step, the pore regulation treatment includes adding a modifier, and the modifier is selected from any one or a combination of at least two of 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, tannic acid.

[0018] According to an embodiment of the present application, in the third step, it includes at least one of the following features:

[0019] a. The high-temperature heat treatment is carried out at a temperature of 600°C - 3000°C;

[0020] b. The high-temperature heat treatment is carried out in an inert gas atmosphere, and the inert gas is any one or a combination of at least two of helium, neon, argon, nitrogen or krypton.

[0021] According to another aspect of the present application, a lithium-ion battery is provided, which includes the negative electrode material of any of the foregoing embodiments or the negative electrode material prepared by the preparation method of any of the foregoing embodiments.

[0022] The technical solution of the embodiment of the present application reduces the pore volume of the negative electrode material, and at the same time adjusts the pore size distribution of the residual pores. It not only maintains the low pore volume of the negative electrode material, improves the cycle life of the negative electrode material and reduces the expansion rate, but also retains some mesopores to maintain the rapid transmission of lithium ions in the material. By regulating the pore volume and pore volume distribution of the negative electrode material, the technical solution of the embodiment of the present application reduces the orientation of the negative electrode material, effectively reduces the expansion of the negative electrode material during cycling and improves the long cycle life of the battery, and at the same time keeps the negative electrode material with a low impedance, effectively improving the fast charging performance of the material. Description of the Drawings

[0023] By reading the following detailed description with reference to the drawings, the above and other objects, features and advantages of the exemplary embodiments of the present application will become easy to understand. In the drawings, several embodiments of the present application are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0024] Figure 1 A schematic diagram of a battery in a discharged state is shown;

[0025] Figure 2 A pore volume distribution diagram of the carbon materials of Example 1 and Comparative Example 1 of the present application is shown. Detailed Embodiments

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0027] It should be understood that the terms "including" and "comprising" used in the specification and claims of the present application indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0028] It should also be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. As used in the specification and claims of the present application, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms. It should be further understood that the term "and / or" used in the specification and claims of the present application refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0029] As used in this specification and the claims, the term "if" can be interpreted as "when...", "once", "in response to determining", or "in response to detecting" according to the context. Similarly, the phrase "if determined" or "if [the described condition or event] is detected" can be interpreted as meaning "once determined", "in response to determining", "once [the described condition or event] is detected", or "in response to detecting [the described condition or event]" according to the context.

[0030] The following will describe in detail the specific implementation manners of the present application with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents, and equipment used in the embodiments of the present application are all obtained through conventional commercial channels.

[0031] An embodiment of the present application provides a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), including a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing.

[0032] The housing can be a packaging bag obtained by encapsulating with a packaging film (such as an aluminum-plastic film), such as when the secondary battery is a soft-pack battery. In some other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0033] Figure 1A schematic diagram of a battery in a discharged state, i.e., during operation, is shown. As shown in the figure, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120, and a separator 130. The separator is disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a stacked structure, which is formed by alternately laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence. In some other embodiments, the electrode assembly can also be a wound structure, which is formed by laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence and then winding them.

[0034] Positive electrode sheet

[0035] The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 disposed on at least one surface of the positive electrode current collector. The positive electrode current collector can be made of aluminum foil, nickel foil, etc., or can be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that can reversibly intercalate and deintercalate metal ions. In some embodiments, the positive electrode active material can 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 electrode active material can include but not limited to at least one of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4).

[0036] Negative electrode sheet

[0037] The negative electrode sheet 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 made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, or can be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0038] During battery operation, i.e., when the battery is in a discharged state, metal ions 140 (such as lithium ions) in the negative electrode escape from the lattice of the negative electrode material, pass through the electrolyte / separator 130, and intercalate into the lattice of the positive electrode material.

[0039] 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 escape from the lattice of the positive electrode material, pass through the electrolyte / separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to intercalate into the lattice of the negative electrode material.

[0040] As metal ions reciprocate between the positive electrode and the negative electrode, the battery can achieve the discharge and charging processes in thousands of cycles.

[0041] The present application provides a negative electrode material, which includes a carbon material; wherein, the carbon material has pores, and the pores have the following characteristics: pores with a pore diameter of more than 3 nm and less than 1000 nm, the pore volume obtained by mercury porosimetry is V1, and V1 < 0.1 mL / g; pores with a pore diameter of more than 3 nm and less than 400 nm, the pore volume obtained by mercury porosimetry is V2, and the ratio range of V2 / V1 satisfies 40% - 70%; pores with a pore diameter of more than 3 nm and less than 500 nm, the pore volume obtained by mercury porosimetry is V3, and the ratio range of V3 / V1 satisfies ≥60%.

[0042] In the process of spheroidization of the existing natural graphite negative electrode material, due to the curling and stacking of the scales, many pores are formed inside the particles of the spherical graphite, and the pore volume and specific surface area of the material are relatively high, and there are also many surface defects. The technical solution of the present application reduces the pore volume of the material and controls the pore size distribution of the residual pores at the same time. It not only maintains the low pore volume of the material, improves the cycle life of the material and reduces the cycle expansion, but also retains some mesopores to maintain the rapid transmission of lithium ions in the material. The technical solution of the present application reduces the orientation of the material by regulating the pore volume and pore volume distribution; the lower pore volume and specific pore volume distribution can effectively reduce the expansion of the negative electrode material during cycling and improve the long cycle life of the battery, while keeping the material with a low impedance and effectively improving the fast charging performance of the material. When the pore volume and pore volume distribution do not meet the target range, it will increase the contact and consumption between the material and the electrolyte, form a thicker SEI film, reduce the amount of electrolyte, resulting in a significant decrease in the cycle life of the material, an increase in the pole piece expansion rate, and at the same time, the larger pore diameter may lead to a decrease in the mechanical stability of the electrode material, thus affecting the cycle life and safety of the battery.

[0043] Specifically, when V1≥0.1 mL / g, the contact between the carbon material and the electrolyte increases, consuming more electrolyte, resulting in less electrolyte and a thicker SEI film, thus significantly reducing the cycle life of the material and increasing the swelling rate of the electrode sheet. When V2 / V1<40% or V3 / V1<60%, the pores inside the material are overly concentrated in the range of pore diameters from 500 nm to 1000 nm. The overly large pore diameters may reduce the mechanical stability of the electrode material and increase the contact and consumption of the electrolyte, thereby affecting the cycle life and safety of the battery. When V2 / V1>70%, the pores inside the material are overly concentrated in the range of pore diameters from 3 nm to 400 nm. The overly small pore diameters are not conducive to the rapid transmission of lithium ions, resulting in a large impedance of the material, accelerating the temperature rise of the battery, accelerating the decomposition and consumption of the electrolyte, leading to a large swelling rate of the electrode sheet of the material and a decrease in the cycle retention rate of the battery.

[0044] In some embodiments, in the XRD spectrum of the negative electrode material (XRD is the abbreviation of "X-ray diffraction": X-ray diffraction is an optical analysis method detected by an instrument. When monochromatic X-rays are irradiated onto a powder crystal sample, if the angle between a set of plane nets of one crystal grain and the incident X-rays is θ and the diffraction condition is satisfied, diffraction occurs at the diffraction angle 2θ), there is a 004 peak between 2θ of 54° - 55°, and the intensity of the 004 peak is I 004 ; there is a 110 peak between 2θ of 77° - 78°, and the intensity of the 110 peak is I 110 ; the ratio of the two intensities I 004 / I 110 ≤3.0. Exemplarily, I 004 / I 110 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 composed of the above arbitrary values. The technical solution of the present application regulates the pore size distribution, reduces the orientation of the material, is conducive to the rapid transmission 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 transmission of lithium ions, the impedance of the material is large, the temperature rise of the battery is accelerated, the decomposition and consumption of the electrolyte are accelerated, the swelling rate of the material will become large, thus affecting the cycle life of the battery.

[0045] In some embodiments, the BET specific surface area of the negative electrode material ≤3.0 m 2 / g. Exemplarily, it can be 3.0 m 2 / g, 2.9m 2 / g, 2.8m 2 / g, 2.7m2 / g, 2.6 m 2 / g, 2.5 m 2 / g, 2.4 m 2 / g, 2.3 m 2 / g, 2.0 m 2 / g, 1.5 m 2 / g, 1.0 m 2 / g, 0.5 m 2 / g or any value within the range composed 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 exhibit a higher initial Coulombic efficiency, resulting in an improvement in the cycle life of the battery prepared from the anode material and better high-temperature storage performance.

[0046] In some embodiments, the volume median diameter Dv50 of the anode material ranges from 5 μm to 25 μm, and can be, for example, 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 composed of any of the above values. If the average particle size of the anode material < 5 μm, it is not conducive to the rapid transport of lithium ions in the anode material, resulting in an increase in the material impedance and a decrease in the cycle retention rate of the battery. If the average particle size of the anode material > 25 μm, the particle size of the anode material is too large, resulting in a relatively large space between the anode material 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 exhibit a higher initial Coulombic efficiency, resulting in an improvement in the cycle life of the battery prepared from the anode material and better high-temperature storage performance.

[0047] In some embodiments, the tap density of the anode material ranges from 1.5 - 2.1 g / cc, and the tap density of the anode material can be, for example, 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 composed of any of the above values. When the tap density falls within the above range, the material has a relatively high tap density, resulting in an improvement in the energy density of the battery prepared from the anode material.

[0048] In some embodiments, the tap density of the negative electrode material ranges from 0.9 to 1.2 g / cc. Exemplarily, the compression density of the negative electrode material can 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 composed of any of the above values. When the tap density falls within the above range, the material has a relatively high tap density, such that the slurry prepared from the negative electrode material during the preparation of the negative electrode slurry has good stability and consistency.

[0049] In some embodiments, the fixed carbon content of the negative electrode material ranges from ≥99.94%. Exemplarily, the fixed carbon content of the negative electrode material can be 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, or any value within the range composed of any of the above values. When the fixed carbon content falls within the above range, the relatively high fixed carbon content enables the negative electrode material to have a relatively high capacity, and at the same time enables the battery prepared therefrom to have good high-temperature storage performance.

[0050] In some embodiments, the pole piece expansion rate of the negative electrode pole piece made of the negative electrode material after 20 cycles is <27%. Exemplarily, it can be 26.5%, 26%, 25.5%, 25%, 24.5%, 24%, 23.5%, 23%, 22.5%, 22%, 21%, 20%, or any value within the range composed of any of the above values. The pole piece expansion rate after 20 cycles reflects the expansibility of the material during use. In this application, by regulating the pore volume and pore distribution, the negative electrode pole piece made of the negative electrode material of this application has significantly reduced expansibility.

[0051] In some embodiments, the capacity retention rate of the soft-pack battery made of the negative electrode material at 1C / 1C for 300 cycles is >85%. Exemplarily, it can be 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or any value within the range composed of any of the above values. The capacity retention rate at 1C / 1C for 300 cycles reflects the cycling performance of the material during use. In this application, by regulating the pore volume and pore distribution, the capacity retention rate of the battery made of the material is significantly improved.

[0052] In some embodiments, the carbon material includes natural graphite. In this application, by regulating the pore volume and pore distribution, the pores of the natural graphite are reduced, the natural graphite is densified or made isotropic, while maintaining a certain number of mesopores, thereby reducing the expansion rate of the material and improving the cycling performance of the material.

[0053] Figure 2 The pore volume distribution diagrams of Example 1 of the present application and Comparative Example 1 are shown.

[0054] The present application also provides a method for preparing a negative electrode material, including: the first step S1 of selecting a carbon material raw material and performing crushing and spheroidization treatment on the carbon material raw material; the second step S2 of performing pore regulation treatment on the carbon material obtained in the first step; the third step S3 of performing high-temperature heat treatment on the carbon material obtained in the second step; the pore regulation treatment includes any one or a combination of at least two of adding a modifier, fusion heating, autoclave heating, roll pressing, cold isostatic pressing treatment, hot isostatic pressing treatment, or molding treatment.

[0055] Through steps such as pore regulation treatment, the technical solution of the present application precisely regulates the pore volume and pore size distribution of the material. On the one hand, it maintains a low pore volume of the material, 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 transmission of lithium ions in the material, so that the material has a low impedance and effectively improves the fast charging performance of the material.

[0056] In some embodiments, in the first step, the selected carbon material raw material can 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.

[0057] In some embodiments, in the first step, the crushing is performed by mechanical crushing.

[0058] In some embodiments, in the first step, after the spheroidization treatment, a purification treatment step is further included. Preferably, the purification treatment is performed by acid purification treatment.

[0059] In some embodiments, the carbon material obtained in the first step is spherical natural graphite with a Dv50 of 5 μm - 25 μm; preferably, the carbon material obtained in the first step is spherical natural graphite with a Dv50 of 9 μm - 18 μm.

[0060] In some embodiments, in the second step, preferably, the pore regulation treatment includes any one or a combination of at least two of adding a modifier, fusion heating, cold isostatic pressing treatment, or molding treatment. For example, the pore regulation treatment is a combination of first cold isostatic pressing treatment and then adding a modifier. First performing cold isostatic pressing treatment can make the total pore volume smaller and make the material densified; then adding a modifier and performing heat treatment can keep a certain number of mesopores in the material, which is beneficial to the transmission of lithium ions and improves the fast charging performance of the material. The method of first molding treatment and then adding a modifier can also achieve the above-described technical effects.

[0061] In some embodiments, in the second step, the pore regulation treatment is a combination of first cold isostatic pressing treatment and then adding a modifier. Specifically, the carbon material obtained in the first step is placed in a cold isostatic press for treatment, and the working pressure of the cold isostatic press is 60 MPa - 70 MPa; the specific setting of the pressure curve is: the pressure rises from 0 MPa to 20 MPa - 30 MPa in 8 min - 12 min, the holding time is 5 min - 10 min, rises to 60 MPa - 70 MPa in 25 - 45 min, and the holding time is 5 min - 8 min to obtain massive graphite; after crushing the massive graphite, graphite with a Dv50 of 9 μm - 16 μm is obtained, and it is mixed with the modifier in a mass ratio of 100:5 - 20.

[0062] In some embodiments, in the second step, the pore regulation treatment is a combination of first molding pressing treatment and then adding a modifier. Specifically, the carbon material obtained in the first step is placed in a molding press for treatment, and the working pressure of the molding press is 20 MPa - 25 MPa; the specific setting of the pressure curve is: the pressure rises from 0 MPa to 10 MPa - 15 MPa in 8 min - 12 min, the holding time is 4 min - 5 min, rises to 20 MPa - 25 MPa in 15 min - 20 min, and the holding time is 10 min - 15 min to obtain massive graphite; after crushing the massive graphite, graphite with a Dv50 of 5 μm - 20 μm is obtained, and it is mixed with the modifier in a mass ratio of 100:5 - 20.

[0063] In some embodiments, in the second step, the pore regulation treatment is a combination of first adding a modifier and then fusion heating. Specifically, the carbon material obtained in the first step is mixed with the modifier in a mass ratio of 100:5 - 20, placed in a fusion machine, heated at a heating rate of 3 °C / min - 7 °C / min to 180 °C - 220 °C, with a rotation speed of 1800 r / min - 2200 r / min, held for 1.5 hours - 2.5 hours, and then cooled to room temperature.

[0064] In some embodiments, in the second step, the pore regulation treatment includes adding a modifier. The modifier is selected from any one or a combination of at least two of 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, tannic acid. Preferably, the modifier is selected from any one or a combination of at least two of resin, coal tar pitch, petroleum pitch, mesophase pitch. Preferably, the addition amount of the modifier is 5 wt% - 20 wt% based on the weight of the carbon material.

[0065] In some embodiments, in the third step, the high-temperature heat treatment is carried out at a temperature of 600°C - 3000°C; exemplarily, the temperature of the high-temperature heat treatment can be 800°C, 1000°C, 1200°C, 1500°C, 1800°C, 2100°C, 2300°C, 2500°C, 2800°C or any value within the range formed by any two of the above values.

[0066] 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 maintaining a constant temperature at 200°C for 25 min - 35 min, heating to 600°C at a heating rate of 1.5°C / min - 2.5°C / min, and maintaining a constant temperature at 600°C for 25 min - 35 min, heating to 1000°C - 1200°C at a heating rate of 8°C / min - 12°C / min, and maintaining a constant temperature at 1000°C - 1200°C for 180 min - 220 min.

[0067] In some embodiments, specifically, in the third step, the temperature curve of the high-temperature heat treatment can be: heating to 1200°C at a heating rate of 8°C / min - 12°C / min, and maintaining a constant temperature at 1200°C for 25 min - 35 min, heating to 1800°C at a heating rate of 8°C / min - 12°C / min, heating to 2300°C - 2800°C at a heating rate of 15°C / min - 25°C / min, and maintaining a constant temperature at 2300°C - 2800°C for 50 min - 70 min.

[0068] In some embodiments, in the third step, the high-temperature heat treatment 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 protection of the inert gas atmosphere is beneficial to the material preparation process.

[0069] According to another aspect of the present application, a lithium-ion battery is provided, which includes the aforementioned negative electrode material or the negative electrode material prepared according to the aforementioned preparation method. The above lithium-ion battery has reduced expansibility, and at the same time has good cycle life and fast charging performance.

[0070] Specific examples and comparative examples

[0071] Example 1

[0072] First step S1: Select natural flake graphite and perform mechanical crushing, spheroidization, and acid purification treatments to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 9 μm.

[0073] Second step S2: Put the above-mentioned high-purity spherical natural graphite into a cold isostatic press for treatment. The working pressure of the isostatic press is set as follows: the pressure rises from 0 MPa to 30 MPa in 10 minutes, stays at 30 MPa for 5 minutes, rises to 60 MPa in 25 minutes, and stays for 8 minutes to obtain massive graphite. Crush the massive graphite. After crushing, graphite with a median particle volume diameter Dv50 of 9 μm is obtained. Mix the obtained graphite and pitch in a mass ratio of 100:10.

[0074] Third step S3: Then heat the mixed material at a high temperature of 1200 °C in a nitrogen atmosphere to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: heat to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 minutes, heat to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 minutes, heat to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 200 minutes.

[0075] Example 2

[0076] First step S1: Select natural flake graphite and perform mechanical crushing, spheroidization, and acid purification treatments to obtain high-purity spherical natural graphite with a median particle volume diameter Dv50 of 18 μm.

[0077] Second step S2: Put the above-mentioned high-purity spherical natural graphite into a molding press for treatment. The working pressure is set as follows: the pressure rises from 0 MPa to 10 MPa in 10 minutes, stays at 10 MPa for 5 minutes, rises to 20 MPa in 15 minutes, and stays for 10 minutes to obtain massive graphite. Crush the massive graphite. After crushing, graphite with a median particle volume diameter Dv50 of 18 μm is obtained. Mix the obtained graphite and pitch in a mass ratio of 100:5.

[0078] Third step S3: Then heat the mixed material at a high temperature of 1000 °C in a nitrogen atmosphere to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: heat to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 minutes, heat to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 minutes, heat to 1000 °C at a heating rate of 10 °C / min and keep it at 1000 °C for 200 minutes.

[0079] Example 3

[0080] First step S1: Select natural flake graphite and perform mechanical crushing and spheroidization to obtain high-purity spherical natural graphite with a median particle volume diameter Dv50 of 17 μm.

[0081] Second step S2: Mix the obtained graphite and pitch at a mass ratio of 100:6 and put them into a fusion machine, heat to 200°C at a rate of 5°C / min, rotate at 2000 r / min, hold for 2 hours, and then cool to room temperature.

[0082] Third step S3: Then heat the mixed material at a high temperature of 1200°C to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: Heat to 200°C at a heating rate of 5°C / min and hold at 200°C for 30 min, heat to 600°C at a heating rate of 2°C / min and hold at 600°C for 30 min, heat to 1200°C at a heating rate of 10°C / min and hold at 1200°C for 200 min.

[0083] Example 4

[0084] First step S1: Select microcrystalline graphite, mechanically crush and spheroidize it to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 10 μm.

[0085] Second step S2: Put the above high-purity spherical natural graphite into a cold isostatic press for treatment. The working pressure of the isostatic press is set as follows: The pressure rises from 0 MPa to 20 MPa in 10 min, holds at 20 MPa for 5 min, rises to 50 MPa in 20 min, holds for 10 min, rises to 80 MPa in 10 min, holds for 5 min, rises to 120 MPa in 15 min, holds for 5 min, rises to 150 MPa in 10 min, and holds for 1 min to obtain massive graphite. Crush and pulverize the massive graphite, and after pulverization, obtain graphite with a volume median diameter Dv50 of 10 μm. Mix the obtained graphite and pitch at a mass ratio of 100:20.

[0086] Third step S3: Then heat the mixed material at a high temperature of 2800°C to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: Heat to 1200°C at a heating rate of 10°C / min and hold at 1200°C for 30 min, heat to 1800°C at a heating rate of 10°C / min, and heat to 2800°C at a heating rate of 20°C / min and hold for 60 min.

[0087] Example 5

[0088] First step S1: Select natural flake graphite, mechanically crush, spheroidize and acid-purify it to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 16 μm.

[0089] Second step S2: Put the above-mentioned high-purity spherical natural graphite into a cold isostatic press for treatment. The working pressure of the isostatic press is set as follows: the pressure rises from 0 MPa to 30 MPa in 10 minutes, remains at 30 MPa for 5 minutes, rises to 70 MPa in 45 minutes, and remains for 5 minutes to obtain massive graphite. Crush the massive graphite. After crushing, graphite with a median volume particle size Dv50 of 16 μm is obtained. Mix the obtained graphite and phenolic resin at a mass ratio of 100:8.

[0090] Third step S3: Then heat the mixed material at a high temperature of 2300 °C to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: Heat it to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 30 minutes, heat it to 1800 °C at a heating rate of 10 °C / min, and heat it to 2300 °C at a heating rate of 20 °C / min and keep it at a constant temperature for 60 minutes.

[0091] Example 6

[0092] First step S1: Select natural flake graphite, and through mechanical crushing, spheroidization, and acid purification, obtain high-purity spherical natural graphite with a median volume particle size Dv50 of 10 μm and Dv90 / Dv10 = 2.0.

[0093] Second step S2: Put the above-mentioned high-purity spherical natural graphite into a cold isostatic press for treatment. The working pressure of the isostatic press is set as follows: the pressure rises from 0 MPa to 50 MPa in 30 minutes, remains for 10 minutes, rises to 150 MPa in 30 minutes, remains for 5 minutes, rises to 200 MPa in 25 minutes, and remains for 1 minute to obtain massive graphite. Crush the massive graphite. After crushing, graphite with a median volume particle size Dv50 of 10 μm and Dv90 / Dv10 = 2.0 is obtained. Mix the obtained graphite and pitch at a mass ratio of 100:15.

[0094] Third step S3: Then heat the mixed material at a high temperature of 1200 °C to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: Heat it to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 minutes, heat it to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 minutes, heat it to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 200 minutes.

[0095] Comparative example 1

[0096] First step S1: Select natural flake graphite, and through mechanical crushing, spheroidization, and acid purification treatment, obtain high-purity spherical natural graphite with a median volume particle size Dv50 of 9 μm.

[0097] Compared with the embodiment, the second step S2 of simplification is as follows: mix this high-purity spherical natural graphite and pitch at a mass ratio of 100:10.

[0098] The third step S3: Then heat-treat the mixed material at a high temperature of 1200 °C in a nitrogen atmosphere to obtain a carbon material. The specific temperature curve of the high-temperature treatment is as follows: heat it to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 min, heat it to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 min, heat it to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 200 min.

[0099] Comparative Example 2

[0100] The first step S1: Select natural flake graphite and perform mechanical crushing, spheroidization, and acid purification treatments to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 18 μm.

[0101] Do not perform the second step S2 and directly perform the third step S3: Heat-treat this high-purity spherical natural graphite at a high temperature of 1000 °C in a nitrogen atmosphere to obtain a carbon material. The specific temperature curve of the high-temperature treatment is as follows: heat it to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 min, heat it to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 min, heat it to 1000 °C at a heating rate of 10 °C / min and keep it at 1000 °C for 200 min.

[0102] Comparative Example 3

[0103] The first step S1: Select natural flake graphite and perform mechanical crushing, spheroidization, and acid purification treatments to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 18 μm.

[0104] Compared with the embodiment, the second step S2 of simplification is as follows: mix this high-purity spherical natural graphite and pitch at a mass ratio of 100:15.

[0105] The third step S3: Then, the mixed material is treated at a high temperature of 1200 °C under a nitrogen atmosphere. After depolymerization, a carbon material is obtained (in the above text, "depolymerization" means that after natural graphite and pitch are mixed and carbonized, some graphite particles are bonded together due to the adhesiveness of the pitch, and the bonded particles need to be separated by mechanical equipment). The specific temperature curve for the high-temperature treatment is as follows: Heat to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 min, heat to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 min, heat to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 200 min.

[0106] Comparative Example 4

[0107] The first step S1: Select natural flake graphite and perform mechanical crushing, spheroidization, and acid purification treatments to obtain high-purity spherical natural graphite with a volume median diameter Dv50 of 18 μm.

[0108] The second step S2: Mix this high-purity spherical natural graphite and pitch in a mass ratio of 100:6, and then put the mixed material into a cold isostatic press for treatment. The working pressure of the isostatic press is set as follows: The pressure rises from 0 MPa to 30 MPa in 10 min, the holding time at 30 MPa is 5 min, it rises to 60 MPa in 25 min, and the holding time is 8 min to obtain massive graphite.

[0109] The third step S3: Perform high-temperature treatment at 1200 °C under a nitrogen atmosphere to obtain a carbon material. The specific temperature curve for the high-temperature treatment is as follows: Heat to 200 °C at a heating rate of 5 °C / min and keep it at 200 °C for 30 min, heat to 600 °C at a heating rate of 2 °C / min and keep it at 600 °C for 30 min, heat to 1200 °C at a heating rate of 10 °C / min and keep it at 1200 °C for 200 min. Crush the massive graphite, and after crushing, obtain graphite with a volume median diameter Dv50 of 18 μm for the particle volume.

[0110] The test methods adopted in this application are as follows:

[0111] Use a Malvern laser particle size analyzer MS 3000 to test the volume median diameter Dv50 of the material;

[0112] Use a Tristar device from Micromeritics for specific surface area testing.

[0113] The pore volume was measured using a mercury intrusion porosimeter Micromeritics AutoPore IV 9500, and the pore volume within the pore size range of 3 - 1000 nm, the pore volume within the pore size range of 3 - 400 nm, the pore volume within the pore size range of 3 - 500 nm, etc. were determined.

[0114] XRD test was carried out using an X-ray diffractometer, and the ratio of the intensities of the 004 peak (2θ = 54.6°) and the 110 peak (2θ = 77.4°) was selected to obtain the value of the powder orientation (I 004 / I 110 ).

[0115] The expansion rate of the electrode was tested using the test device and system disclosed in the patent application CN201920973729.5 to test the expansion rate of the electrode after 20 cycles.

[0116] The compaction density of the material under a pressure of 1.0 T was tested using an automatic compaction density meter.

[0117] The tapped density of the material was tested using an American Quantachrome Auto Tap instrument, with a sampling volume of 100 mL, 1000 vibration times, and a vibration frequency of 260 times / min.

[0118] The fixed carbon content was tested with reference to GB / T 3521 - 2008 "Chemical Analysis Method of Graphite".

[0119] Battery test: The provided carbon material, conductive agent SP, CMC, and SBR were mixed in a mass ratio of 95.9:1.0:1.3:1.8 and then coated on a copper foil to obtain a negative electrode sheet; the positive 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 then coated on an aluminum foil to obtain a positive electrode sheet; the electrolyte was 1 mol / L LiPF6 + EC + EMC, and the separator was a three-layer PP / PE / PP separator. A soft-pack battery of about 38 mAh was made to test the full-cell performance of the material. The test method for the 1C / 1C capacity retention rate was: continuous charge and discharge at 1C for 300 cycles.

[0120] Table 1 shows the test results of each example and comparative example.

[0121] Table 1

[0122]

[0123] As can be seen from the results in the above table, the carbon material prepared by this solution meets the requirement that V1 is reduced to <0.1 mL / g, the ratio range of V2 / V1 meets 40% - 70%, and at the same time the ratio range of V3 / V1 meets ≥60%; the carbon material formed in this way has an overall lower pore volume, where the pore diameters are mostly concentrated in the range of 3 nm - 500 nm, and there are also appropriate pores with a medium pore diameter of 400 - 500 nm and appropriate pores with a larger pore diameter of 500 nm - 1000 nm, which not only ensures the rapid transmission of lithium ions but also ensures the more stable structure of the material; the pole piece expansion of the material in the battery after 20 weeks is significantly decreased, reduced to less than 27%, and can be as low as 23.8% at the lowest; the capacity retention rate after 300 cycles is increased by more than 5%, effectively reducing the expansion of the negative electrode material during cycling and improving the long cycle life of the battery, and at the same time keeping the material with a lower impedance, effectively improving the fast charging performance of the material.

[0124] From the results of Comparative Examples 1, 2 and Examples 1, 2, it can be seen that since V1 > 0.1 mL / g in Comparative Examples 1 and 2, it leads to more contact between the material and the electrolyte, consuming more electrolyte, resulting in less electrolyte and a thicker SEI film. Even if V2 / V1 meets 40% - 70% and V3 / V1 meets >60%, it will still lead to a significant decrease in the cycle life of the material and an increase in the pole piece expansion rate.

[0125] From the result of Comparative Example 3 (V2 / V1 < 40%, V3 / V1 < 60%), it is found that although only V1 < 0.1 mL / g is satisfied, but when V2 / V1 is not in the range of 40% - 70% and V3 / V1 ≥ 60% at the same time, although the carbon material has an overall lower pore volume, too many pores inside the material are concentrated in the range of 500 nm - 1000 nm. The too large pore diameter may lead to a decrease in the mechanical stability of the electrode material, while increasing the contact and consumption of the electrolyte, and also resulting in a significant decrease in the cycle life of the material and an increase in the pole piece expansion rate, thus affecting the cycle life and safety of the battery.

[0126] From the result of Comparative Example 4 (V2 / V1 > 70%), it is found that when only V1 < 0.1 mL / g and V3 / V1 ≥ 60% are satisfied, but V2 / V1 is not in the range of 40% - 70% at the same time, there will be too few pores with a pore diameter of 500 nm - 1000 nm inside the material, and too many pores are concentrated in the range of 3 nm - 400 nm. The too small pore diameter is not conducive to the rapid transmission of lithium ions, making the material impedance larger, accelerating the battery temperature rise, accelerating the decomposition and consumption of the electrolyte, resulting in a still larger pole piece expansion rate of the material and a lower 300 - cycle retention rate.

[0127] The above experimental data shows that when the carbon material meeting the characteristics of this application is used as the negative electrode of a lithium - ion battery, it can effectively reduce the pole piece expansion and improve the cycle life of the battery.

[0128] Although several embodiments of the present 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 changes, variations, and alternative methods may occur to those skilled in the art without departing from the spirit and scope of the present application. It should be understood that various alternatives to the embodiments of the present application described herein may be employed in practicing the present application. The appended claims are intended to define the scope of the present application and thus cover equivalents or alternatives within the scope of these claims.

Claims

1. A negative electrode material, the negative electrode material comprising a carbon material, characterized in that, The carbon material has pores, and the pores have the following characteristics: pores with a pore diameter of 3 nm or more and 1000 nm or less, the pore volume obtained by mercury porosimetry is V1, and V1 < 0.1 mL / g; pores with a pore diameter of 3 nm or more and 400 nm or less, the pore volume obtained by mercury porosimetry is V2, and the ratio range of V2 / V1 satisfies 40% - 70%; pores with a pore diameter of 3 nm or more and 500 nm or less, the pore volume obtained by mercury porosimetry is V3, and the ratio range of V3 / V1 satisfies ≥60%; In the XRD pattern of the negative electrode material, there is a 004 peak at a diffraction peak angle 2θ between 54° and 55°, and the intensity of the 004 peak is There is a 110 peak at a diffraction peak angle 2θ between 77° and 78°, and the intensity of the 110 peak is The ratio of the two intensities .

2. The negative electrode material according to claim 1, wherein The negative electrode material includes at least one of the following characteristics: a. BET specific surface area ≤ 3.0 ; b. The range of the volume median diameter Dv50 is 5 μm - 25 μm; c. The range of the tap density is 1.5 - 2.1 g / cc; d. The range of the bulk density is 0.9 - 1.2 g / cc; e. The range of the fixed carbon content is ≥99.94%.

3. The negative electrode material according to claim 1 or 2, characterized in that, The carbon material includes natural graphite.

4. A method for preparing a negative electrode material, characterized in that, Including: The first step is to select a carbon material raw material and perform crushing and spheroidization treatment on the carbon material raw material; The second step is to perform pore regulation treatment on the carbon material obtained in the first step; The third step is to perform high-temperature heat treatment on the carbon material obtained in the second step; The pore regulation treatment is either cold isostatic pressing treatment or molding pressing treatment first, and then a modifier is added; wherein, the pressure curve of the cold isostatic pressing treatment is: the pressure rises from 0 MPa to 20 MPa - 30 MPa in 8 min - 12 min, the holding time is 5 min - 10 min, the pressure rises from 20 MPa - 30 MPa to 60 MPa - 70 MPa in 25 - 45 min, and the holding time is 5 min - 8 min; or the pressure curve of the molding pressing treatment is: the pressure rises from 0 MPa to 10 MPa - 15 MPa in 8 min - 12 min, the holding time is 4 min - 5 min, the pressure rises from 10 MPa - 15 MPa to 20 MPa - 25 MPa in 15 min - 20 min, and the holding time is 10 min - 15 min; The temperature curve of the high-temperature heat treatment is: heat to 200 °C at a heating rate of 3 °C / min - 7 °C / min and keep it at 200 °C for 25 min - 35 min, heat from 200 °C to 600 °C at a heating rate of 1.5 °C / min - 2.5 °C / min and keep it at 600 °C for 25 min - 35 min, heat from 600 °C to 1000 °C - 1200 °C at a heating rate of 8 °C / min - 12 °C / min, and keep it at 1000 °C - 1200 °C for 180 min - 220 min.

5. The preparation method according to claim 4, characterized in that, In the first step, the carbon material raw material is selected from one or more of natural spherical graphite, natural flake graphite or microcrystalline graphite.

6. The preparation method according to claim 4 or 5, characterized in that In the first step, after the spheroidization treatment, there is also a step of performing purification treatment.

7. The preparation method according to claim 4 or 5, characterized in that, In the second step, the pore regulation treatment includes adding a modifier, and the modifier is selected from any one or a combination of at least two of resin, coal tar pitch, petroleum pitch, mesophase pitch, coal tar, glucose, sucrose, starch, polydopamine, polyvinyl alcohol, polypyrrole, polyethylene glycol, anthracene, aniline, citric acid, acetic acid, tannic acid.

8. The preparation method according to claim 4 or 5, characterized in that, In the third step, it includes at least one of the following features: a. The high-temperature heat treatment is carried out at a temperature of 600°C - 3000°C; b. The high-temperature heat treatment is carried out in an atmosphere of an inert gas, and the inert gas is any one or a combination of at least two of helium, neon, argon, nitrogen or krypton.

9. A lithium-ion battery, characterized in that the lithium-ion battery includes the negative electrode material described in any one of claims 1 to 3 or the negative electrode material prepared by the preparation method described in any one of claims 4 to 8.

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