Negative electrode sheet, secondary battery, electric device, and artificial graphite and preparation method therefor

Abstract

A negative electrode sheet, a secondary battery, an electric device, and artificial graphite and a preparation method therefor. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises artificial graphite. La (110) of the artificial graphite is 130 nm-175 nm, and Lc (002) thereof is 30 nm-42 nm, wherein La (110) represents the crystallite size along an a axis in the (110) crystal plane of the artificial graphite, and Lc (002) represents the crystallite size along a c axis in the (002) crystal plane of the artificial graphite.

Description

Negative electrode sheet, secondary battery, electrical device, artificial graphite and its preparation method

[0001] Cross-reference to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411214854.X, filed on August 30, 2024, entitled “Negative Electrode Sheet, Secondary Battery, Electrical Device, Artificial Graphite and Preparation Method Thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, an electrical device, artificial graphite, and a method for preparing the same. Background Technology

[0004] In recent years, with the increasingly wide range of applications, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. With the rapid development of rechargeable batteries, higher requirements have been placed on their energy density and other properties. Summary of the Invention

[0005] This disclosure is made in view of the above-mentioned problems, and its object is to provide a negative electrode sheet, a secondary battery, an electrical device, artificial graphite, and a method for preparing the same. The secondary battery of this disclosure has a high energy density.

[0006] To achieve the above objectives, this disclosure provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises artificial graphite, the artificial graphite having a La(110) of 130 nm-175 nm and an Lc(002) of 30 nm-42 nm, where La(110) represents the crystallite size along the a-axis in the (110) crystal plane of the artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the artificial graphite. In this disclosure, the graphite grains in the artificial graphite are well-developed, which is beneficial for the intercalation of active ions, thereby improving the specific capacity and compaction density of the negative electrode active material, and thus improving the energy density of the secondary battery.

[0007] In some embodiments, the La(110) of the artificial graphite is 132nm-172nm, and the Lc(002) is 30nm-36nm. This is beneficial for improving the specific capacity and compaction density of the negative electrode active material, thereby contributing to a high energy density in the secondary battery.

[0008] In some embodiments, La(110) / Lc(002) is 3.5-5.5. This is beneficial for increasing the specific capacity of the negative electrode active material and improving the energy density of the secondary battery.

[0009] In some implementations, La(110) / Lc(002) is 4.5-5.5.

[0010] In some embodiments, charge-discharge tests were conducted on coin cells made from artificial graphite under conditions of a delithiation rate of 0.1C and a lithium insertion rate of 0.05C, respectively, yielding charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau exists within the voltage range of 0.005V to 0.070V, and the discharge capacity corresponding to the lithium insertion plateau accounts for more than 43% of the total discharge capacity X of the coin cell. Therefore, artificial graphite has a high specific capacity, which is beneficial for improving the energy density of secondary batteries.

[0011] In some implementations, the discharge capacity corresponding to the lithium intercalation platform accounts for 43%-47% of the total discharge capacity of the coin cell.

[0012] In some embodiments, the specific capacity of the artificial graphite is 359 mAh / g or higher. This is beneficial for improving the energy density of the secondary battery. In some embodiments, the specific capacity of the artificial graphite is 359 mAh / g to 366 mAh / g.

[0013] In some embodiments, the degree of graphitization of the artificial graphite is 94.0%-96.0%. This is beneficial for the artificial graphite to have high compaction density and specific capacity, thereby improving the energy density of the secondary battery. In some embodiments, the degree of graphitization of the artificial graphite is 94.2%-95.8%.

[0014] In some embodiments, the compacted density of artificial graphite powder under 50,000 N pressure is 1.95-2.04 g / cc. This is beneficial for improving the energy density of secondary batteries.

[0015] In some implementations, artificial graphite comprises secondary particles.

[0016] In some embodiments, the volumetric particle size distribution (Dv50) of the artificial graphite is 14.5 μm-18.0 μm. This is beneficial for improving the energy density of the secondary battery.

[0017] In some implementations, the particle size distribution (Dv90-Dv10) / Dv50 of the artificial graphite is 0.9-1.25.

[0018] In some implementations, the specific surface area of ​​the artificial graphite is 0.8 m². 2 / g-2.1m 2 / g. On the one hand, it helps to reduce surface side reaction activity and improve the initial coulombic efficiency of the secondary battery; on the other hand, it helps to improve the transport performance of active ions and improve the kinetic performance of the secondary battery.

[0019] A second aspect of this disclosure also provides a secondary battery, including the negative electrode sheet described in the first aspect. Therefore, the secondary battery of this disclosure has a high energy density.

[0020] A third aspect of this disclosure also provides an electrical device that includes the secondary battery described in the second aspect. Since the electrical device of this disclosure includes the secondary battery provided herein, it has at least the same advantages as the secondary battery.

[0021] A fourth aspect of this disclosure also provides an artificial graphite, wherein the La(110) of the artificial graphite is 130 nm-175 nm, and the Lc(002) is 30 nm-42 nm, where La(110) represents the crystallite size along the a-axis in the (110) crystal plane of the artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the artificial graphite. This artificial graphite is beneficial for the intercalation of active ions and can improve the specific capacity and compaction density of the negative electrode active material.

[0022] In some implementations, La(110) / Lc(002) is 4.5-5.5.

[0023] In some embodiments, charge-discharge tests are performed on coin cells made of artificial graphite under conditions of 0.1C delithiation rate and 0.05C lithium insertion rate, respectively, to obtain charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau exists in the voltage range of 0.005V to 0.070V, and the discharge capacity corresponding to the lithium insertion plateau accounts for more than 43% of the total discharge capacity of the coin cell.

[0024] In some implementations, the specific capacity of the artificial graphite is 359 mAh / g or higher.

[0025] In some implementations, the degree of graphitization of the artificial graphite is 94.0%-96.0%.

[0026] In some embodiments, the compacted density of artificial graphite powder under a pressure of 50,000 N is 1.95 g / cc to 2.04 g / cc.

[0027] In some implementations, artificial graphite includes secondary artificial graphite particles.

[0028] The fifth aspect of this disclosure also provides a method for preparing artificial graphite, comprising the following steps:

[0029] Pretreatment steps: The calcined needle coke is crushed and shaped to obtain shaped material. The carbon content of the calcined needle coke is above 97%, the volatile component content is below 2%, and the sulfur content is below 0.5%.

[0030] Granulation step: Mix the shaping material with the granulating agent to obtain granulated material;

[0031] Graphitization step: The granulated material is graphitized at 3000℃-3200℃ to obtain artificial graphite with La(110) of 130nm-175nm and Lc(002) of 30nm-42nm.

[0032] Using the above method to prepare artificial graphite with high-purity raw materials is beneficial to reducing the number of impurities and defects in artificial graphite, increasing the graphitization degree and La(110) value of artificial graphite, thereby increasing the specific capacity and compaction density of the negative electrode film and improving the energy density of the secondary battery.

[0033] In some embodiments, the softening point of the granulating agent is 180°C-270°C. The aforementioned granulating agent has strong binding properties, which helps to reduce the amount of granulating agent used and increase the specific capacity and compaction density of artificial graphite.

[0034] In some embodiments, the coking value of the granulating agent is 50-70%. This is beneficial for improving the specific capacity and compaction density of artificial graphite, thereby increasing the energy density of secondary batteries.

[0035] In some embodiments, the mass ratio of shaping material to granulating agent is 100:(6-12). This is beneficial for improving the energy density of the secondary battery.

[0036] In some embodiments, the preparation method further includes pre-carbonizing the granulated material before the graphitization step to obtain an intermediate. The pre-carbonization step helps reduce the number of impurities and defects in the artificial graphite, thereby increasing the specific capacity and compaction density of the artificial graphite and improving the energy density of the secondary battery.

[0037] In some embodiments, the pre-carbonization treatment is carried out at a temperature of 1000-1500°C for 1-4 hours.

[0038] In some embodiments, the preparation method further includes subjecting the artificial graphite to a surface micro-oxidation treatment after the graphitization step. This is beneficial for increasing the compaction density of the artificial graphite powder, thereby improving the energy density of the secondary battery. Attached Figure Description

[0039] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0040] Figure 2 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 1.

[0041] Figure 3 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0042] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0043] Figure 5 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 4.

[0044] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0045] Figure 7 is a charge-discharge curve of the negative electrode sheet according to an embodiment of the present disclosure.

[0046] Figure 8 is an enlarged view of the charge-discharge curve of Figure 7 in the voltage range of 0.005V-0.5V.

[0047] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0048] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, secondary battery, and electrical device of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0049] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0052] Unless otherwise specified, all steps of this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0054] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0055] Unless otherwise specified, in this disclosure, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0056] Currently, the development of electric vehicles has placed higher demands on battery driving range, thus increasing the need for battery energy density. To obtain high-energy-density rechargeable batteries, some reports have suggested graphitizing artificial graphite raw materials with flake graphite. However, the high degree of graphitization of flake graphite makes it prone to graphite flake peeling during cycling, and flake graphite also undergoes significant volume expansion, which not only deteriorates cycle performance but also negatively impacts the energy density of the rechargeable battery.

[0057] Based on this, this disclosure proposes a negative electrode sheet, a secondary battery, an electrical device, an artificial graphite and its preparation method, thereby enabling the secondary battery to have high energy density.

[0058] Negative electrode sheet

[0059] This disclosure proposes a negative electrode sheet, including a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes artificial graphite. The artificial graphite has a La(110) of 130 nm-175 nm and an Lc(002) of 30 nm-42 nm. La(110) represents the crystallite size along the a-axis in the (110) crystal plane of the artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the artificial graphite.

[0060] In this disclosure, the increase in La (La) of artificial graphite indicates an increase in the size of the artificial graphite crystallites and an increase in the number of lithium intercalation sites on the surface of the artificial graphite, thus improving the specific capacity. Furthermore, the increased crystallite size also reduces the number of grain boundaries in the artificial graphite crystallites, resulting in an increase in the number of lithium intercalation sites. This reduces the adverse effects on specific capacity and powder compaction density, thereby improving the specific capacity and powder compaction density of the artificial graphite. When the Lc (Lc) of the artificial graphite is within the aforementioned range, it is beneficial to reduce the stacking of graphite crystallites, thereby reducing the number of grain boundaries between crystallites and increasing the number of lithium intercalation sites on the surface of the artificial graphite, thus improving the specific capacity of the artificial graphite. By making the La (110) of the artificial graphite 130nm-175nm and the Lc (002) 30nm-42nm, the development of graphite grains in the material is better, which is conducive to the intercalation of active ions, thereby improving the specific capacity and compaction density of the negative electrode active material, and thus improving the energy density of the battery.

[0061] The artificial graphite has a La(110) of 130nm-175nm and an Lc(002) of 30nm-42nm. For example, La(110) can be any value between 130nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 172nm, 173nm, 175nm, or any two of these values, and Lc(002) can be any value between 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, or any two of these values. Optionally, the artificial graphite has a La(110) of 132nm-172nm and an Lc(002) of 30nm-36nm. By keeping the La(110) and Lc(002) of artificial graphite within the above range, it is more beneficial to improve the specific capacity and compaction density of the negative electrode active material, thereby enabling the secondary battery to have a high energy density.

[0062] In this disclosure, the X-ray diffraction pattern of the artificial graphite does not show any obvious characteristic peaks corresponding to the (101) crystal plane of the 3R phase in the range of 43-44°, and the particle structure of the artificial graphite is a dense blocky structure.

[0063] In some embodiments, the La(110) / Lc(002) ratio of the artificial graphite is 3.5-5.5. By keeping the La(110) / Lc(002) ratio of the artificial graphite within the aforementioned range, the number of microcrystals in the graphite material is low, resulting in fewer grain boundaries between grains. This is beneficial for increasing the number of lithium intercalation sites on the surface of the artificial graphite, thereby improving the specific capacity of the negative electrode active material and thus increasing the energy density of the secondary battery. Exemplarily, La(110) / Lc(002) can be 3.5, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.5, or a value within a range of any two of these values. In some alternative embodiments, the La(110) / Lc(002) ratio in the artificial graphite is 4.5-5.5.

[0064] In some embodiments, charge-discharge tests are performed on coin cells made of artificial graphite under conditions of 0.1C delithiation rate and 0.05C lithium insertion rate, respectively, to obtain charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau exists in the voltage range of 0.005V-0.07V, and the discharge capacity corresponding to the lithium insertion plateau accounts for more than 43% of the total discharge capacity of the coin cell.

[0065] In this disclosure, the charge-discharge test is performed as follows: Sample powder, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed uniformly with solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to form a slurry; the prepared slurry is coated onto the surface of the negative electrode current collector copper foil and dried in an oven for later use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then, using a lithium metal sheet as the counter electrode, polyethylene... PE film was used as a separator and assembled with the electrolyte in an argon-protected glove box to form a CR2430 coin cell. After the obtained coin cell was left to stand for 12 hours, it was discharged at 25°C at a constant current rate of 0.05C to 0.005V. After standing for 10 minutes, it was discharged again at a constant current rate of 50μA to 0.005V. After standing for 10 minutes, it was discharged at a current of 10μA to 0.005V. During the charging process, it was charged at a rate of 0.1C to 2.0V. The relationship between the charge and discharge capacity and voltage of the artificial graphite was obtained, i.e., the charge and discharge curve.

[0066] In this disclosure, coin cells prepared from artificial graphite were subjected to the aforementioned charge-discharge tests, yielding charge-discharge curves. In the discharge curve, the discharge capacity corresponding to the lithium intercalation plateau within the voltage range of 0.005V-0.07V accounted for more than 43% of the total discharge capacity of the coin cell. The high specific capacity of artificial graphite is beneficial for improving the energy density of the secondary battery. Although the mechanism is not yet clear, the inventors believe that during the lithium intercalation process of graphite materials, as the amount of lithium ion intercalation increases, graphite intercalation compounds of different orders gradually form, such as LiC24, LiC12, and LiC6. The formation of graphite intercalation compounds of different orders corresponds to lithium intercalation plateaus within different voltage ranges in the charge-discharge curves of the graphite materials. Since the theoretical capacities of graphite intercalation compounds of different orders differ—for example, the theoretical capacity of LiC6 is 372 mAh / g, while that of LiCl2 is 186 mAh / g—the more LiC6 (i.e., the lithium intercalation platform corresponding to a voltage range of 0.005-0.07V) formed during lithium intercalation, the greater the capacity contribution, and thus the higher the specific capacity of the graphite material. Exemplarily, the proportion X can be 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any two of these values ​​within a range. In some embodiments, the proportion X of the discharge capacity corresponding to the lithium intercalation platform to the total discharge capacity of the coin cell is 43%-50%, optionally 43%-47%.

[0067] In some embodiments, the specific capacity of the artificial graphite is 359 mAh / g or higher. By ensuring the specific capacity of the artificial graphite is within the aforementioned range, it is beneficial to increase the specific capacity of the negative electrode film, thereby improving the energy density of the secondary battery. Exemplarily, the specific capacity of the artificial graphite can be 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, 364 mAh / g, 365 mAh / g, 366 mAh / g, 367 mAh / g, 368 mAh / g, 369 mAh / g, 370 mAh / g, or a value within a range of any two of these values. Optionally, the specific capacity of the artificial graphite is between 360 mAh / g and 366 mAh / g.

[0068] In some embodiments, the degree of graphitization of the artificial graphite is 94.0%-96.0%. By maintaining the degree of graphitization of the artificial graphite within this range, it is advantageous for the artificial graphite to possess high compaction density and specific capacity, thereby improving the energy density of the secondary battery. Exemplarily, the degree of graphitization of the artificial graphite can be 94.0%, 94.5%, 95.0%, 95.5%, 96.0%, or a value within a range of any two of these values. In some alternative embodiments, the degree of graphitization of the artificial graphite is 94.2%-95.8%.

[0069] In some embodiments, the compacted density of artificial graphite powder at 50,000 N pressure is 1.95-2.04 g / cc. Maintaining the compacted density of artificial graphite powder within this range is beneficial for increasing the compacted density of the negative electrode film, thereby improving the energy density of the secondary battery. For example, the compacted density of artificial graphite powder at 50,000 N pressure can be 1.95 g / cc, 1.96 g / cc, 1.97 g / cc, 1.98 g / cc, 1.99 g / cc, 2.00 g / cc, 2.01 g / cc, 2.02 g / cc, 2.03 g / cc, 2.04 g / cc, or any two values ​​between these values.

[0070] In some implementations, the artificial graphite includes secondary particles. This helps reduce the orientation of the structure, buffers volume changes during cycling, and improves structural stability, thereby enhancing lifespan performance.

[0071] In some embodiments, the volumetric particle size distribution (Dv50) of the artificial graphite is 14.5 μm to 18.0 μm. By ensuring the Dv50 of the artificial graphite is within this range, it is advantageous for the artificial graphite to possess high specific capacity and high powder compaction density, thereby improving the energy density of the secondary battery. Exemplarily, the Dv50 of the artificial graphite can be 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, or a value within a range of any two of these values. In some alternative embodiments, the Dv50 of the artificial graphite is 15.0 μm to 17.5 μm.

[0072] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the artificial graphite is 0.90-1.25. This is beneficial for increasing the compaction density of the negative electrode film and improving the energy density of the secondary battery. Furthermore, it facilitates the formation of a reasonable pore structure between the particles in the negative electrode film, improving the active ion and electron transport performance in the negative electrode film, thereby enhancing the kinetic performance of the secondary battery. Exemplarily, the particle size distribution (Dv90-Dv10) / Dv50 of the artificial graphite is 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, or a value within a range of any two of these values. In some optional embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the artificial graphite is 0.90-1.20.

[0073] In some implementations, the specific surface area of ​​the artificial graphite is 0.8 m². 2 / g-2.1m 2 / g. By ensuring the specific surface area of ​​artificial graphite is within the aforementioned range, on the one hand, artificial graphite can exhibit lower surface side reaction activity, thereby reducing the consumption of active ions during SEI film formation and improving the initial coulombic efficiency of the secondary battery; on the other hand, it can also possess higher active ion transport performance, improving the kinetic performance of the secondary battery. For example, the specific surface area of ​​artificial graphite can be 0.8m². 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g, 2.0m 2 / g、2.1m 2 / g or a range of values ​​between any two of them.

[0074] In this disclosure, the La(110) and Lc(002) of artificial graphite can be determined using instruments and methods known in the art. For example, the negative electrode sheet removed from a secondary battery can be cleaned with an organic solvent such as DMC and then dried. The cleaned negative electrode sheet is then immersed in NMP and ultrasonically treated to separate the copper foil, thus obtaining the negative electrode material. After drying the negative electrode material, it is calcined at 350°C-500°C, washed with water multiple times, and dried at 80°C to obtain the negative electrode active material. X-ray diffractometer (such as Bruker D8 Discover) is used for testing, and the testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the peak intensity and full width at half maximum (FWHM) of the diffraction peak corresponding to the (110) crystal plane and the peak intensity and full width at half maximum (FWHM) of the diffraction peak corresponding to the (002) crystal plane of artificial graphite, and then calculated according to the Scherrer formula.

[0075] In this disclosure, the powder compaction density of materials (negative electrode active materials, artificial graphite, etc.) is the mass per unit volume of the powder under specified conditions. It can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine) according to GB / T 24533-2009. An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 50,000 N, held for 30 seconds, then the pressure is released and held for 10 seconds. The compaction density of the powder under 50,000 N pressure is then recorded and calculated.

[0076] In this disclosure, the volume distribution particle sizes Dv10, Dv50, and Dv90 of materials (e.g., negative electrode active materials, artificial graphite, etc.) represent the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0077] In this disclosure, the specific capacity of the material (negative electrode active material, artificial graphite, etc.) is the ratio of the electrical capacity that the active material can release to the mass of the active material, and can be tested using methods known in the art. An exemplary test method is as follows: The sample powder is mixed evenly with a conductive agent, a binder, and optional other additives in a certain mass ratio with a solvent to form a slurry; the prepared slurry is coated on the surface of the negative electrode current collector copper foil and dried in an oven for later use; the electrolytic salt is dissolved in an organic solvent to prepare an electrolyte of a certain concentration; then, using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, the CR2430 coin cell is assembled with the electrolyte in an argon-protected glove box. After the obtained coin cells were allowed to stand for 12 hours, they were discharged at 25°C with a constant current of 0.15 mA to 0.005 V. After standing for 10 minutes, they were discharged again with a constant current of 50 μA to 0.005 V. After standing for 10 minutes, they were discharged again with a constant current of 10 μA to 0.005 V. Then, they were charged with a constant current of 0.3 mA to 2.0 V, and the charging capacity was recorded. The ratio of charging capacity to sample mass is the specific capacity of the corresponding material (negative electrode active material, artificial graphite, etc.).

[0078] In this disclosure, the degree of graphitization of a material (such as anode active materials and artificial graphite) is the proportion of carbon elements in the material existing in the form of a graphite structure, which can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011, to obtain the average interlayer spacing d of the C(002) crystal plane in the material's crystal structure. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the C(002) crystal plane in the material crystal structure, expressed in nanometers (nm).

[0079] In this disclosure, the term "secondary particle" has a meaning known in the art. A secondary particle refers to an aggregated particle composed of two or more primary particles. Primary particles, on the other hand, refer to non-aggregated particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0080] Preparation method of artificial graphite

[0081] The method for preparing artificial graphite in this disclosure includes the following steps:

[0082] Pretreatment steps: The calcined needle coke is crushed and shaped to obtain shaped material. The carbon content of the calcined needle coke is above 97%, the volatile component content is below 2%, and the sulfur content is below 0.5%.

[0083] Granulation step: Mix the shaping material with the granulating agent to obtain granulated material;

[0084] Graphitization step: The granulated material is graphitized at 3000℃-3200℃ to obtain artificial graphite with La(110) of 130nm-175nm and Lc(002) of 30nm-42nm.

[0085] In this disclosure, calcined needle coke is used as raw material. Calcined needle coke has a stronger needle-like structure and fewer interlocking structures. Using calcined needle coke as raw material helps to reduce the impurity content in artificial graphite, thereby improving the graphitization degree of artificial graphite.

[0086] In this disclosure, the carbon content of the calcined needle coke is 97% or more, the volatile content is 2% or less, and the sulfur content is 0.5% or less. Here, the volatile content refers to hydrocarbons with low molecular weight, such as light alkanes. When the sulfur content and volatile content of the calcined needle coke are within the above range, the purity of the raw material is better, which is conducive to grain development during graphitization, reduces the number of defects during graphitization, and improves the degree of graphitization and the La(110) value of artificial graphite. By making the La(110) of artificial graphite 130nm-175nm and the Lc(002) 30nm-42nm, the development of graphite grains in the material is better, which is conducive to the intercalation of active ions, thereby improving the specific capacity and compaction density of the negative electrode film and increasing the energy density of the secondary battery.

[0087] In this disclosure, the graphitization temperature is 3000℃-3200℃. A graphitization temperature within this range is beneficial for the growth and development of graphite grains, thereby increasing the La(110) value of the graphite material. Furthermore, it also helps to increase the degree of graphitization of artificial graphite, thereby increasing the specific capacity of artificial graphite and improving the energy density of secondary batteries. Exemplarily, the graphitization temperature can be 3000℃, 3050℃, 3100℃, 3150℃, 3200℃, or a value within a range consisting of any two of these values.

[0088] In this disclosure, high-purity raw materials are used and the graphitization temperature is controlled at 3000℃-3200℃, which is beneficial for the development of the 110 crystal plane of graphite grains along the a-axis direction during the graphitization process, thereby increasing the La(110) value of artificial graphite. In addition, it is also beneficial for reducing the number of defects during the graphitization process, which is beneficial for improving the energy density of secondary batteries.

[0089] Those skilled in the art can adjust the graphitization time as needed. For example, an Atchison graphitization furnace can be used for graphitization treatment, and the graphitization time can be 2-8 days when the temperature is above 2800°C.

[0090] In some embodiments, the volumetric particle size distribution (Dv50) of the shaping material is 9 μm-13 μm. Controlling the volumetric particle size distribution (Dv50) of the shaping material within the range of 9 μm-13 μm is beneficial for reducing the number of grain boundaries between crystals in artificial graphite, thereby increasing the specific capacity and powder compaction density of artificial graphite.

[0091] In some embodiments, the softening point of the granulating agent is 180℃-270℃. The softening point of the granulating agent refers to the temperature at which the granulating agent changes from a solid state to a softened state with a certain degree of fluidity. In this disclosure, the softening point can be tested using instruments and methods known in the art, for example, it can be determined according to GB / T4507-2014. When the softening point of the granulating agent is within the above range, the molecular weight and content of the polycyclic aromatic hydrocarbons in the granulating agent are large, which is beneficial to improving the adhesiveness of the granulating agent, reducing the amount of granulating agent used in the granulation step, reducing the residual carbon content of the granulating agent, thereby increasing the specific capacity and compaction density of the artificial graphite. Exemplarily, the softening point of the granulating agent can be 180℃, 200℃, 220℃, 240℃, 260℃, 270℃, or a value between any two of these values.

[0092] In some embodiments, the coking value of the granulating agent is 50%-70%. The coking value of the granulating agent refers to the percentage of the mass of the coke residue formed after heating, combustion, or other treatment of the granulating agent under specific experimental conditions, relative to the mass of the original sample. In this disclosure, the coking value can be tested using methods known in the art. Exemplarily, it can be determined with reference to GB / T 8727-2008. A coking value of the granulating agent within the above range is beneficial for improving the specific capacity and compaction density of artificial graphite, thereby increasing the energy density of the secondary battery.

[0093] In some embodiments, the mass ratio of shaping material to granulating agent is 100:(6-12). A ratio of shaping material to granulating agent within this range is beneficial for reducing the amount of residual carbon from the granulating agent, increasing the specific capacity and compaction density of artificial graphite, and thus improving the energy density of the secondary battery.

[0094] In some embodiments, the preparation method further includes pre-carbonizing the granulated material before the graphitization step to obtain an intermediate. Pre-carbonizing the granulated material helps remove volatile components from the raw material and promotes grain growth during subsequent graphitization, thereby increasing the specific capacity and compaction density of artificial graphite and improving the energy density of the secondary battery.

[0095] In some embodiments, the pre-carbonization temperature is 1000-1500°C. For example, the pre-carbonization temperature can be 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or any two of these values. By keeping the pre-carbonization temperature within this range, volatile components in the raw material can be sufficiently removed, which helps reduce the number of impurities and defects in the artificial graphite, thereby increasing the specific capacity of the artificial graphite. Additionally, pre-carbonization can increase the density of the raw material, allowing for a larger furnace charge during graphitization. In an optional embodiment, the pre-carbonization temperature is 1000°C-1100°C.

[0096] In some implementations, the pre-carbonization time is 1-4 hours. Exemplary pre-carbonization times can be 1 hour, 2 hours, 3 hours, 4 hours, or any range of two of these values.

[0097] In some embodiments, pre-carbonization is performed under a protective atmosphere, which may, for example, be nitrogen or argon. In one alternative embodiment, pre-carbonization is performed under a nitrogen atmosphere.

[0098] In some embodiments, the volumetric particle size distribution Dv50 of the intermediate is 15 μm-18 μm. An intermediate particle size within this range is beneficial for increasing the particle size of the artificial graphite, thereby increasing the specific capacity of the artificial graphite and improving the energy density of the secondary battery. Exemplarily, the volumetric particle size distribution Dv50 of the intermediate can be 15 μm, 16 μm, 17 μm, 18 μm, or a value within a range consisting of any two of these values.

[0099] In some embodiments, the preparation method further includes subjecting the artificial graphite to a surface micro-oxidation treatment after the graphitization step. In this disclosure, the surface micro-oxidation treatment can be performed using methods known in the art. Exemplarily, the surface micro-oxidation treatment can be performed on the artificial graphite at 700°C in an air atmosphere. The surface micro-oxidation treatment of artificial graphite increases the number of oxidized functional groups on the surface of the artificial graphite, enhances the bonding force between artificial graphite particles and between artificial graphite and the binder, reduces rebound, and is beneficial for increasing the compaction density of the artificial graphite powder, thereby improving the energy density of the secondary battery.

[0100] Secondary batteries

[0101] This disclosure also provides a secondary battery. The term "secondary battery" as used herein refers to a single battery cell, a battery module, or a battery pack. These are described below.

[0102] A single secondary battery cell includes a positive electrode, a negative electrode as described in this disclosure, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0103] In addition, the secondary battery and electrical device of this disclosure will be described below with appropriate reference to the accompanying drawings.

[0104] Negative electrode sheet

[0105] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0106] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0107] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0109] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0111] Positive electrode sheet

[0112] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0113] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0115] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM)622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0116] It should be noted that, in the embodiments of this disclosure, the above chemical formulas refer to the chemical formulas of the materials used in the secondary battery manufacturing process. In the positive electrode sheet, battery cell, and electrical device, due to processes such as formation and cycling, those skilled in the art will understand that the elements in the above chemical formulas may be lost. For example, in the positive electrode sheet, battery cell, and electrical device, due to processes such as cycling, oxygen elements in the positive electrode active material are lost, resulting in a decrease in the measured oxygen content in the positive electrode active material.

[0117] It should be noted that in the positive electrode, battery cell, and electrical equipment, lithium ions are consumed during formation and cycling processes, resulting in a decrease in the measured lithium content in the positive electrode active material. Conversely, if lithium is replenished to the positive and negative electrode, the measured lithium content in the positive electrode active material will increase after formation and cycling.

[0118] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this disclosure, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0119] In the examples of positive electrode active materials in this disclosure, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0120] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0121] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0123] electrolytes

[0124] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This disclosure does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0125] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0127] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0128] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0129] Separating membrane

[0130] In some embodiments, the battery cell also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0131] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0132] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0133] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0134] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0135] This disclosure does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0136] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0137] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0138] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0139] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0140] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0141] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0142] In addition, this disclosure also provides an electrical device, which includes a secondary battery provided by this disclosure. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0143] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0144] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0145] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0146] Example

[0147] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0148] Example 1

[0149] (1) Preparation of artificial graphite

[0150] Step 1: The oil-based calcined needle coke raw material (carbon content of 98.5%, volatile content of 1.0%, sulfur content of 0.5%) is crushed and shaped using an air jet mill to obtain a shaped material with a Dv50 of 11μm;

[0151] Step 2: Using granulated asphalt (softening point 200℃; coking value 60%) as a granulating agent, the above-mentioned shaping material is granulated together in a granulation kettle to obtain granulated material, wherein the mass ratio of shaping material to granulating agent is 100:8.

[0152] Step 3: The above granulated material is pre-carbonized at 1150℃ for 2 hours under a nitrogen atmosphere to obtain an intermediate (volume distribution particle size Dv50 is 16.5μm).

[0153] Step 4: The above intermediate was graphitized at a high temperature of 3020℃. The graphitized particles were then sieved and demagnetized to obtain artificial graphite. The La(110) and Lc(002) of the material were measured using the following method, and the results were: La(110) was 131.7 nm and Lc(002) was 32.5 nm.

[0154] (2) Preparation of negative electrode sheet

[0155] The above-mentioned artificial graphite, conductive agent Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.6:0.80:1.0:1.6 to form a negative electrode slurry. The negative electrode slurry was coated onto the negative electrode current collector copper foil by extrusion coating. After drying and cold pressing, the negative electrode sheet was obtained.

[0156] (3) Preparation of positive electrode sheet

[0157] Lithium iron phosphate, conductive carbon black, and PVDF were mixed in a mass ratio of 96.2:2:1.8, and then N-methylpyrrolidone solvent was added and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0158] (4) Preparation of lithium-ion batteries

[0159] A 12μm polyethylene film was used as the separator.

[0160] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0161] The positive and negative electrode sheets prepared above are placed in sequence, with the separator placed between the positive and negative electrode sheets to provide isolation. Then, the electrode assembly is wound up to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, a secondary battery is obtained.

[0162] Examples 2-6

[0163] The preparation methods of Examples 2-6 are similar to those of Example 1, except that the raw materials and graphitization temperature used in the preparation steps of artificial graphite are adjusted according to the values ​​in Table 1 below.

[0164] Comparative Examples 1-3

[0165] The preparation methods of Comparative Examples 1-3 are similar to those of Example 1, except that the raw materials and graphitization temperature used in the preparation steps of artificial graphite are adjusted according to the values ​​in Table 1 below.

[0166] Performance testing

[0167] The artificial graphite prepared in step (1) of Examples 1-6 and Comparative Examples 1-3 above was tested according to the following method, and the results are shown in Table 2.

[0168] Tests of La(110), Lc(002), and La / Lc of the material:

[0169] Following the testing method of JIS K 0131-1996, a Bruker D8 Discover X-ray diffractometer was used for testing, with a copper target as the anode and CuKα rays as the radiation source. The wavelength of the rays was... The X-ray diffraction pattern of the powder sample was obtained by scanning the 2θ angle range of 20°-80° at a scanning rate of 4° / min. The La(110) calculation formula is as follows:

[0170] Where: K is the shape factor, taken as 1.84; λ is the wavelength (nm); β110 is the full width at half maximum (FWHM) of the 110 crystal plane corresponding to ~43° in the X-ray diffraction pattern; θ110 is the diffraction angle corresponding to the 110 crystal plane in the X-ray diffraction pattern.

[0171] Lc(002) calculation formula:

[0172] Where: K is the shape factor, taken as 0.89; λ is the wavelength (nm); β002 is the full width at half maximum (FWHM) of the 002 crystal plane corresponding to ~26° in the X-ray diffraction pattern; θ002 is the diffraction angle corresponding to the 002 crystal plane in the X-ray diffraction pattern.

[0173] Testing of material specific capacity:

[0174] The prepared materials, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed with solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to form a slurry. The prepared slurry was coated on the surface of the negative electrode current collector copper foil and dried in an oven for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. The electrolyte was then assembled into a CR2430 coin cell in an argon-protected glove box. The resulting coin cell was left to stand for 12 hours.

[0175] At 25°C, the prepared coin cell was first discharged at a constant current of 0.15mA to 0.005V, allowed to stand for 5 minutes, then discharged at a constant current of 50μA to 0.005V, allowed to stand for 5 minutes, and then discharged at a constant current of 10μA to 0.005V. The first discharge capacity of the coin cell was recorded. After that, it was charged at a constant current of 0.3mA to 2.0V, and the first charge capacity of the coin cell was recorded. The ratio of the first charge capacity to the mass of the material is the material's specific capacity.

[0176] The proportion of lithium intercalation capacity in the platform to the total capacity X

[0177] CR2430 coin cells were prepared using the same method as described in the specific capacity test method above. After the CR2430 coin cells were left to stand for 12 hours, they were first discharged at 25°C with a constant current of 0.15 mA to 0.005 V, left to stand for 5 minutes, then discharged again with a constant current of 50 μA to 0.005 V, left to stand for 5 minutes, and then discharged again with a constant current of 10 μA to 0.005 V. Afterwards, they were charged with a constant current of 0.3 mA to 2.0 V, obtaining the relationship between the charge / discharge capacity and voltage, i.e., the charge / discharge curve. The lithium intercalation capacity of the lithium intercalation plateau appearing in the discharge curve within 0.005 V-0.070 V was denoted as C1, and the total lithium intercalation capacity within the range of 0.005 V-2.0 V was denoted as C2. The percentage of lithium intercalation capacity of the plateau is X = C1 / C2*100%.

[0178] The charge-discharge curves of the artificial graphite material prepared in Example 1, measured using the method described above, are shown in Figures 7 and 8. From Figures 7 and 8, the lithium intercalation capacity of the lithium intercalation plateau appearing within the 0.005V-0.070V range of the discharge curve can be denoted as C1, and the total lithium intercalation capacity within the 0.005V-2.0V range can be denoted as C2. Therefore, the lithium intercalation capacity percentage of the plateau is calculated to be X = 44.1%.

[0179] Testing the compacted density of powder materials:

[0180] A certain amount of powder is placed in a compaction mold, and then the mold is placed on a compaction density instrument. The pressure is set to 50000N. The thickness of the powder under this pressure (the thickness after depressurization) can be read on the instrument. The compaction density is calculated by ρ = m / v.

[0181] Testing of particle size distribution in materials:

[0182] Dv50 Test:

[0183] The volume distribution particle size Dv50 of the material can be tested using the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with the test method of GB / T 19077-2016.

[0184] The secondary batteries prepared in the above embodiments and comparative examples were tested according to the following methods, and the results are shown in Table 2.

[0185] Energy density testing

[0186] At 25℃, the secondary battery was charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1 / 3C to 2.5V. The battery discharge energy at this point was recorded. The battery discharge energy divided by the battery weight is the battery's gravimetric energy density, expressed in Wh / kg. Detailed measurement data are shown in Table 2.

[0187] Table 1

[0188] Table 2:

[0189] As can be seen from the data in Table 2, the artificial graphite prepared in Examples 1-6 of this disclosure has a higher specific capacity and powder compaction density than the artificial graphite prepared in Comparative Examples 1-2, and the secondary batteries of Examples 1-6 have a higher energy density than the secondary batteries of Comparative Examples 1-2. The secondary battery provided in this disclosure, made of artificial graphite with La(110) of 130nm-175nm and Lc(002) of 30nm-42nm, has a high energy density.

[0190] Examples 7-13

[0191] The preparation methods of Examples 7-13 are similar to those of Example 1, except that the granulating agent used in the preparation steps of artificial graphite and the mass ratio of shaping material to granulating agent are adjusted according to the values ​​in Table 3 below.

[0192] The artificial graphite and secondary battery prepared according to the above embodiments were tested according to the following method, and the results are shown in Table 3.

[0193] Table 3:

[0194] As shown in Table 3, by screening granulating agents with softening points and coking values ​​within a certain range, and by screening the mass ratio of shaping material and granulating agent within a certain range, it is possible to obtain artificial graphite with high specific capacity and high powder compaction density, thereby further improving the energy density of the secondary battery.

[0195] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material. The negative electrode active material includes artificial graphite, wherein the La(110) of the artificial graphite is 130nm-175nm, and the Lc(002) is 30nm-42nm. La(110) represents the crystallite size along the a-axis in the (110) crystal plane of artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of artificial graphite.

2. The negative electrode sheet according to claim 1, wherein, The artificial graphite has a La(110) of 132nm-172nm and an Lc(002) of 30nm-36nm.

3. The negative electrode sheet according to claim 1 or 2, wherein, La(110) / Lc(002) is 3.5-5.

5.

4. The negative electrode sheet according to claim 3, wherein, The ratio of La(110) / Lc(002) is 4.5-5.

5.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein, Charge-discharge tests were conducted on the coin cell made from the artificial graphite under conditions of a delithiation rate of 0.1C and a lithium insertion rate of 0.05C, respectively, to obtain charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau exists in the voltage range of 0.005V to 0.070V, and the discharge capacity corresponding to the lithium insertion plateau accounts for more than 43% of the total discharge capacity of the coin cell.

6. The negative electrode sheet according to claim 5, wherein, The discharge capacity corresponding to the lithium intercalation platform accounts for 43%-47% of the total discharge capacity of the coin cell.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein, The specific capacity of the artificial graphite is above 359 mAh / g.

8. The negative electrode sheet according to claim 7, wherein, The specific capacity of the artificial graphite is 359mAh / g-366mAh / g.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein, The degree of graphitization of the artificial graphite is 94.0%-96.0%.

10. The negative electrode sheet according to claim 9, wherein, The degree of graphitization of the artificial graphite is 94.2%-95.8%.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein, The compacted density of the artificial graphite powder under 50,000 N pressure is 1.95 g / cc - 2.04 g / cc.

12. The negative electrode sheet according to any one of claims 1 to 11, wherein, The artificial graphite comprises secondary particles.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein, The artificial graphite satisfies one or more of the following conditions: (1) The volume distribution particle size Dv50 of the artificial graphite is 14.5μm-18.0μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the artificial graphite is 0.9-1.25; (3) The specific surface area of ​​the artificial graphite is 0.8 m². 2 / g-2.1m 2 / g.

14. A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 13.

15. An electrical device comprising the secondary battery of claim 14.

16. An artificial graphite, wherein the La(110) of the artificial graphite is 130nm-175nm and the Lc(002) is 30nm-42nm, wherein La(110) represents the crystallite size along the a-axis in the (110) crystal plane of the artificial graphite and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the artificial graphite.

17. The artificial graphite according to claim 16, wherein, Charge-discharge tests were conducted on the coin cell made from the artificial graphite under conditions of 0.1C delithiation rate and 0.05C lithium insertion rate, respectively, to obtain charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau exists in the voltage range of 0.005V to 0.070V, and the discharge capacity corresponding to the lithium insertion plateau accounts for more than 43% of the total discharge capacity of the coin cell.

18. The artificial graphite according to claim 16 or 17, wherein, The specific capacity of the artificial graphite is above 359 mAh / g.

19. The artificial graphite according to any one of claims 16-18, wherein, The compacted density of the artificial graphite powder under 50,000 N pressure is 1.95 g / cc - 2.04 g / cc.

20. The artificial graphite according to any one of claims 16-19, wherein, The artificial graphite comprises secondary particles.

21. A method for preparing artificial graphite, comprising the following steps: Pretreatment step: The calcined needle coke is crushed and shaped to obtain shaped material. The calcined needle coke has a carbon content of more than 97%, a volatile component content of less than 2%, and a sulfur content of less than 0.5%. Granulation step: The shaping material is mixed with the granulating agent to obtain granulated material; Graphitization step: The granulated material is graphitized at 3000℃-3200℃ to obtain artificial graphite with La(110) of 130nm-175nm and Lc(002) of 30nm-42nm. La(110) represents the crystallite size along the a-axis in the (110) crystal plane of artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of artificial graphite.

22. The preparation method according to claim 21, wherein, The softening point of the granulating agent is 180℃-270℃.

23. The preparation method according to claim 21 or 22, wherein, The coking value of the granulating agent is 50%-70%.

24. The preparation method according to any one of claims 21-23, wherein, The mass ratio of the shaping material to the granulating agent is 100:(6-12).

25. The preparation method according to any one of claims 21-24, wherein, The preparation method further includes: Prior to the graphitization step, the granulated material is pre-carbonized to obtain an intermediate.

26. The preparation method according to claim 25, wherein, The pre-carbonization treatment temperature is 1000-1500℃, and the time is 1-4 hours.

27. The preparation method according to any one of claims 21-26, wherein, The preparation method further includes: after the graphitization step, subjecting the artificial graphite to surface micro-oxidation treatment.

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