Secondary battery and electrical device

Abstract

The present disclosure provides a secondary battery and an electrical device. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer comprises a first region and a second region. The first region is located between the second region and the negative electrode current collector. The first region comprises a first negative electrode active material. The second region comprises a second negative electrode active material. A powder OI value of the second negative electrode active material is less than a powder OI value of the first negative electrode active material. The first negative electrode active material comprises a first artificial graphite having an La(110) of 130-175 nm and an Lc(002) of 30-42 nm.

Description

Secondary batteries and electrical appliances

[0001] Cross-reference to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411215915.4, filed on August 30, 2024, entitled “Secondary Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and more particularly to a secondary battery and an electrical device. Background Technology

[0004] In recent years, with the increasingly wide range of applications, secondary 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 secondary batteries, higher requirements have been placed on their energy density and kinetic performance. Summary of the Invention

[0005] This disclosure is made in view of the above-mentioned problems, and its object is to provide a secondary battery and an electrical device. The secondary battery of this disclosure has high energy density, excellent kinetic performance, and good cycle performance.

[0006] To achieve the above objectives, this disclosure provides a secondary battery, including a negative electrode sheet, which includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector. The negative electrode film layer includes a first region and a second region, with the first region located between the second region and the negative current collector. The first region includes a first negative electrode active material, and the second region includes a second negative electrode active material. The powder OI value of the second negative electrode active material is lower than that of the first negative electrode active material. The first negative electrode active material includes first 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 the first artificial graphite, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the first artificial graphite. Therefore, the secondary battery can achieve both high energy density and excellent kinetic performance.

[0007] In some embodiments, the La(110) of the first artificial graphite is 132nm-172nm, and / or the Lc(002) is 30nm-36nm. This is beneficial for the secondary battery to have a high energy density.

[0008] In some implementations, La(110) / Lc(002) is 3.5-5.5. This is beneficial for improving the energy density of the secondary battery.

[0009] In some embodiments, La(110) / Lc(002) is 4.5-5.5. This is beneficial for increasing the specific capacity of the first negative electrode active material and for improving the energy density of the secondary battery.

[0010] In some embodiments, charge-discharge tests were conducted on coin cells prepared from the first artificial graphite at lithium delithiation rates of 0.1C and lithium insertion rates of 0.05C, respectively, yielding charge-discharge curves in the range of 0.005V-2.0V. In the discharge curve, a lithium insertion plateau was observed in the voltage range of 0.005V-0.070V, and the discharge capacity corresponding to the lithium insertion plateau accounted for more than 43% of the total discharge capacity X of the coin cell. Therefore, the first artificial graphite exhibits a high specific capacity, which is beneficial for improving the energy density of the secondary battery.

[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. Therefore, the high specific capacity of the first artificial graphite is beneficial for improving the energy density of the secondary battery.

[0012] In some embodiments, the specific capacity of the first negative electrode active material is greater than or equal to the specific capacity of the second negative electrode active material. In some embodiments, the specific capacity of the first negative electrode active material is ≥359 mAh / g; and / or, the specific capacity of the second negative electrode active material is 353 mAh / g-359 mAh / g. This is beneficial for improving the kinetic performance of the secondary battery while also increasing its energy density. In some embodiments, the specific capacity of the first negative electrode active material is 359 mAh / g-366 mAh / g; and / or, the specific capacity of the second negative electrode active material is 354.6 mAh / g-356.8 mAh / g.

[0013] In some embodiments, the degree of graphitization of the first negative electrode active material is greater than that of the second negative electrode active material. In some embodiments, the degree of graphitization of the first negative electrode active material is 94.0%-96.0%; and / or, the degree of graphitization of the second negative electrode active material is 93.5%-95.5%. This is beneficial for the first negative electrode active material to have high compaction density and specific capacity, and improves the transport efficiency of active ions in the second negative electrode active material, thereby improving the energy density and kinetic performance of the secondary battery.

[0014] In some embodiments, the degree of graphitization of the first negative electrode active material is 94.2%-95.8%; and / or, the degree of graphitization of the second negative electrode active material is 93.7%-95.3%.

[0015] In some embodiments, the powder compaction density of the first negative electrode active material at 50,000 N pressure is greater than that of the second negative electrode active material at 50,000 N pressure. This is beneficial for improving the energy density of the secondary battery and enhancing its kinetic performance.

[0016] In some embodiments, the powder compaction density of the first negative electrode active material under 50,000 N pressure is 1.95 g / cc to 2.04 g / cc; and / or, the powder compaction density of the second negative electrode active material under 50,000 N pressure is 1.75 g / cc to 1.94 g / cc.

[0017] In some embodiments, the first artificial graphite comprises secondary particles. This is beneficial for improving the isotropy of the first negative electrode active material, reducing reversible expansion, and improving cycle performance.

[0018] In some embodiments, the powder OI value of the first negative electrode active material is 5.0-20.5; and / or, the powder OI value of the second negative electrode active material is 2.5-6.5. This facilitates the dispersion of lithium intercalation expansion, thereby improving the cycle performance of the secondary battery. Furthermore, it helps to improve the isotropy of the second negative electrode active material, thus improving the kinetic performance of the secondary battery.

[0019] In some embodiments, the powder OI value of the first negative electrode active material is 5.5-19.5; and / or, the OI value of the second negative electrode active material is 2.8-6.3.

[0020] In some embodiments, the volumetric particle size distribution (Dv50) of the second negative electrode active material is 10.0 μm-15.5 μm; and / or, the particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95-1.3. This is beneficial for improving the kinetic performance of the secondary battery.

[0021] In some embodiments, the volumetric particle size distribution Dv50 of the second negative electrode active material is 11.0 μm-14.5 μm; and / or, the particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95-1.25.

[0022] In some embodiments, the volume distribution of particles with a diameter greater than 6.5 μm and less than 22.5 μm in the second negative electrode active material accounts for ≥75%. This is beneficial for increasing the compaction density of the negative electrode film, thereby improving the energy density of the secondary battery.

[0023] In some embodiments, the volume distribution of particles with a diameter greater than 6.5 μm and less than 22.5 μm in the second negative electrode active material is 75%-90%.

[0024] In some embodiments, the second negative electrode active material includes a second artificial graphite and a third artificial graphite, wherein the second artificial graphite comprises primary particles and the third artificial graphite comprises secondary particles. This allows the second negative electrode active material to achieve both excellent kinetic performance and high energy density.

[0025] In some embodiments, the mass ratio of the second artificial graphite to the third artificial graphite in the second negative electrode active material is 1:9 to 3:7. This allows the second negative electrode active material to achieve a balance between good kinetic performance, high energy density, and good cycle performance.

[0026] In some embodiments, the mass ratio of the second artificial graphite to the third artificial graphite in the second negative electrode active material is 1:9 to 1:3.

[0027] In some embodiments, the La(110) of the first artificial graphite is greater than that of the second artificial graphite, and the La(110) of the first artificial graphite is greater than that of the third artificial graphite. In some embodiments, the La(110) of the second artificial graphite is 100-140 nm, and the Lc(002) is 25-32 nm. In some embodiments, the La(110) of the third artificial graphite is 90-130 nm, and the Lc(002) is 26-34 nm. This is beneficial for maintaining a better porosity distribution in the negative electrode sheet and improving the cell's dynamic performance.

[0028] In some embodiments, the volumetric particle size distribution (Dv50) of the second artificial graphite is 7 μm-9 μm, and the Dv1 is 3 μm-5.5 μm; and / or, the volumetric particle size distribution (Dv50) of the third artificial graphite is 13 μm-18 μm. This is beneficial for improving the kinetic performance of the secondary battery and increasing its energy density.

[0029] In some embodiments, the OI value of the second artificial graphite powder is 7-10; and / or, the OI value of the third artificial graphite powder is 2-5. This is beneficial for improving the kinetic and cycle performance of the secondary battery.

[0030] In some embodiments, the specific capacity of the second artificial graphite is 354.1 mAh / g to 359.6 mAh / g; and / or, the specific capacity of the third artificial graphite is 353.0 mAh / g to 358.2 mAh / g. This is beneficial for improving the energy density of the secondary battery.

[0031] In some embodiments, the second artificial graphite has a powder compaction density of 1.72 g / cc to 1.92 g / cc under a pressure of 50,000 N; and / or, the third artificial graphite has a powder compaction density of 1.75 g / cc to 1.95 g / cc under a pressure of 50,000 N. This is beneficial for increasing the compaction density of the negative electrode film, thereby improving the energy density of the secondary battery.

[0032] In some embodiments, the volumetric particle size distribution (Dv50) of the first artificial graphite is 14.5 μm-18.0 μm. This is beneficial for improving the energy density of the secondary battery. In some embodiments, the volumetric particle size distribution (Dv50) of the first artificial graphite is 15.0 μm-17.5 μm.

[0033] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.25. This is beneficial for improving the kinetics of the first artificial graphite. In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.20.

[0034] In some embodiments, the specific surface area of ​​the first artificial graphite is 0.8 m². 2 / g-2.1m 2 / g. This is beneficial for improving the initial coulombic efficiency and kinetic performance of the secondary battery. In some embodiments, the specific surface area of ​​the first synthetic graphite is 1.0 m². 2 / g-1.9m 2 / g.

[0035] In some embodiments, the first negative electrode material and / or the second negative electrode active material further include silicon. This is beneficial for further improving the energy density of the secondary battery.

[0036] A second aspect of this disclosure provides an electrical device that includes a secondary battery as described in the first aspect of this disclosure. Since the electrical device of this disclosure includes the secondary battery provided herein, it has at least the same advantages as a secondary battery. Attached Figure Description

[0037] Figure 1 is a schematic diagram of one embodiment of the negative electrode sheet of this disclosure.

[0038] Figure 2 is a schematic diagram of a battery cell according to one embodiment of the present disclosure.

[0039] Figure 3 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 2.

[0040] Figure 4 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0041] Figure 5 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0042] Figure 6 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 5.

[0043] Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0044] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 10 Negative electrode sheet; 101 Negative current collector; 102 Negative electrode film; 102a First surface; 102b Second surface; 1021 First region; 1022 Second region; 1023 Intermediate region. Detailed Implementation

[0045] Hereinafter, embodiments of the secondary battery and electrical device of this disclosure are specifically disclosed in detail with appropriate reference to the accompanying drawings. 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.

[0046] 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.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0049] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0050] 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.

[0051] 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.

[0052] Currently, in order to obtain secondary batteries with high kinetics, some reports have proposed surface coating of graphite materials. However, the surface coating method leads to a decrease in the specific capacity and electrode compaction density of the material, which affects the energy density of the secondary battery.

[0053] Based on this, the present disclosure proposes a secondary battery and an electrical device, thereby enabling the secondary battery to achieve both high energy density and excellent kinetic performance.

[0054] This disclosure does not impose any particular restrictions on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, etc.

[0055] Typically, a single rechargeable battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, 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 while allowing ions to pass through.

[0056] Negative electrode sheet

[0057] In the secondary battery disclosed herein, the negative electrode sheet includes 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 first region and a second region. The first region is located between the second region and the negative current collector. The first region includes a first negative electrode active material, and the second region includes a second negative electrode active material. The powder OI value of the second negative electrode active material is less than the powder OI value of the first negative electrode active material. The first negative electrode active material includes a first artificial graphite. The La(110) of the first 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 the carbon material, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the carbon material.

[0058] In this disclosure, the negative electrode film layer includes a first region and a second region. The first region is located between the second region and the negative electrode current collector; that is, the first region is located on the side of the negative electrode film layer closer to the negative electrode current collector, and the second region is located on the side of the negative electrode film layer away from the negative electrode current collector. FIG1 shows a schematic diagram of one embodiment of the negative electrode sheet of this disclosure. As shown in FIG1, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b disposed opposite to the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H. The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer located on one side of the negative electrode current collector. The region from the second surface 102b of the negative electrode film layer to a thickness of 0.3H is denoted as the first region 1021 of the negative electrode film layer. The region extending from the first surface 102a of the negative electrode film to a thickness of 0.3H is designated as the second region 1022 of the negative electrode film. The first region 1021 includes a first negative electrode active material, and the second region 1022 includes a second negative electrode active material. The region between the first region 1021 and the second region 1022 is designated as the intermediate region 1023. It is readily understood that the intermediate region 1023 may contain only the first negative electrode active material, only the second negative electrode active material, both the first and second negative electrode active materials, or other negative electrode active materials known in the art besides the first and second negative electrode active materials disclosed herein.

[0059] It should be understood that in the embodiment shown in FIG1, the second surface 102b is in contact with the upper surface of the negative electrode current collector 101, but the structure of the negative electrode sheet of this disclosure is not limited thereto. For example, there may be an additional layer between the negative electrode film layer 102 and the negative electrode current collector 101. In this case, the second surface 102b is not in direct contact with the negative electrode current collector 101.

[0060] It should also be understood that although Figure 1 shows clear boundaries between the areas, such clear interfaces may not exist in the product.

[0061] In this disclosure, by setting the negative electrode film layer as a double layer, the negative electrode sheet can still maintain a good pore structure, low tortuosity, short ion transport path, and high ion conduction efficiency even at a high compaction density. This is beneficial for the secondary battery to achieve both high energy density and excellent kinetic performance. Furthermore, by making the powder OI value of the second negative electrode active material located in the second region lower than that of the powder OI value of the first negative electrode active material located in the first region, the negative electrode active material in the second region preferentially intercalates active ions, which is beneficial for the negative electrode film layer to maintain excellent kinetic performance. Therefore, it is beneficial for the secondary battery to achieve both high energy density and excellent kinetic performance.

[0062] In this disclosure, the first negative electrode active material includes a first artificial graphite, wherein the La(110) of the first 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 the carbon material, and Lc(002) represents the crystallite size along the c-axis in the (002) crystal plane of the carbon material.

[0063] In this disclosure, the increase in La of the 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 both the specific capacity and powder compaction density of the artificial graphite. When the 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 ensuring that the La (110) and Lc (002) of the first artificial graphite are within the aforementioned specific ranges, the development of graphite grains in the material is better, which is beneficial for the intercalation of active ions, thereby improving the specific capacity of the first negative electrode active material. The negative electrode active material located in the first region has high specific capacity and high compaction density, which is beneficial for the secondary battery to have high energy density. For example, the La(110) of the first artificial graphite can be a value between 130nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 175nm, or any two of these values. Additionally, the Lc(002) of the first artificial graphite can be a value between 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, or any two of these values.

[0064] In some embodiments, the La(110) of the first artificial graphite is 132nm-172nm, and / or the Lc(002) is 30nm-36nm. By keeping the La(110) and Lc(002) of the first artificial graphite within the above ranges, it is beneficial to improve the specific capacity and compaction density of the first negative electrode active material, thereby contributing to a high energy density in the secondary battery.

[0065] In some embodiments, the La(110) / Lc(002) ratio of the first artificial graphite is 3.5-5.5. A higher La(110) / Lc(002) ratio indicates better grain development and fewer microcrystals in the graphite material, resulting in fewer grain boundaries and thus 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. This disclosure ensures that the La(110) / Lc(002) ratio of the first artificial graphite is within the aforementioned range, which is beneficial for improving the specific capacity of the first negative electrode active material, thereby 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 consisting of any two of these values. In some alternative embodiments, the La(110) / Lc(002) ratio of the first artificial graphite is 4.5-5.5.

[0066] In some embodiments, charge-discharge tests are performed on the coin cell prepared from the first 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-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.

[0067] 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, a lithium metal sheet is used as the electrode... A polyethylene (PE) film was used as a separator, and the above electrolyte was assembled into a CR2430 coin cell in an argon-protected glove box. 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 5 minutes, it was discharged again at a constant current rate of 50μA to 0.005V. After standing for 5 minutes, it was discharged again at a constant current rate of 10μA to 0.005V. Then it was charged at a constant current rate of 0.1C to 2.0V. The relationship between the charge and discharge capacity of the carbon material and the voltage was obtained, i.e., the charge and discharge curve.

[0068] In this disclosure, a coin cell prepared from a first type of artificial graphite was subjected to the aforementioned charge-discharge test, resulting in charge-discharge curves. In the discharge curve, the discharge capacity corresponding to the lithium intercalation plateau within the voltage range of 0.005V to 0.070V accounted for more than 43% of the total discharge capacity of the coin cell. The high specific capacity of the first type 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 0.005V-0.07V) is formed during lithium intercalation, the greater the corresponding 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 a value within a range of any two of these values. 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%.

[0069] In some embodiments, the specific capacity of the first negative electrode active material located in the first region is greater than or equal to the specific capacity of the second negative electrode active material located in the second region, thereby improving the energy density of the secondary battery. The specific capacity of the first negative electrode active material is 359 mAh / g or more. By keeping the specific capacity of the first negative electrode active material within the above range, it is beneficial to increase the specific capacity of the negative electrode film, thereby increasing the energy density of the secondary battery. Exemplarily, the specific capacity of the first negative electrode active material 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 between any two of these values. In some optional embodiments, the specific capacity of the first negative electrode active material is 359 mAh / g to 366 mAh / g.

[0070] In some embodiments, the specific capacity of the second negative electrode active material is 353 mAh / g to 359 mAh / g. By keeping the specific capacity of the second negative electrode active material within this range, it is beneficial to improve the kinetic performance of the secondary battery while simultaneously increasing its energy density. Exemplarily, the specific capacity of the second negative electrode active material can be 353 mAh / g, 354 mAh / g, 355 mAh / g, 356 mAh / g, 357 mAh / g, 358 mAh / g, 359 mAh / g, or a value within a range of any two of these values. In some optional embodiments, the specific capacity of the second negative electrode active material is 354.6 mAh / g to 356.8 mAh / g.

[0071] In some embodiments, the degree of graphitization of the first negative electrode active material is greater than that of the second negative electrode active material. The degree of graphitization of the first negative electrode active material is 94.0%-96.0%. By keeping the degree of graphitization of the first negative electrode active material within the above range, it is beneficial for the first negative electrode active material to have a high compaction density and specific capacity, thereby improving the energy density of the secondary battery. Exemplarily, the degree of graphitization of the first negative electrode active material can be 94.0%, 94.5%, 95.0%, 95.5%, 96.0%, or a value between any two of these values. In some optional embodiments, the degree of graphitization of the first negative electrode active material is 94.2%-95.8%.

[0072] In some embodiments, the degree of graphitization of the second negative electrode active material is 93.5%-95.5%. By placing the second negative electrode active material within this range, it is beneficial to improve the transport efficiency of active ions in the second negative electrode active material, thereby improving the kinetic performance of the secondary battery. Exemplarily, the degree of graphitization of the second negative electrode active material can be 93.5%, 94.0%, 94.5%, 95.0%, 95.5%, or a value within a range of any two of these values. In some optional embodiments, the degree of graphitization of the second negative electrode active material is 93.7%-95.3%.

[0073] In some embodiments, the powder compaction density of the first negative electrode active material at 50,000 N pressure is greater than that of the second negative electrode active material at 50,000 N pressure. In this disclosure, the higher powder compaction density of the first negative electrode active material is beneficial for increasing the specific capacity of the negative electrode film, thereby improving the energy density of the secondary battery. The lower powder compaction density of the second negative electrode active material is beneficial for improving the kinetic performance of the secondary battery.

[0074] In some embodiments, the powder compaction density of the first negative electrode active material at a pressure of 50,000 N is 1.95 g / cc to 2.04 g / cc. Maintaining the powder compaction density of the first negative electrode active material within this range is beneficial for increasing the compaction density of the negative electrode film, thereby improving the energy density of the secondary battery. For example, the powder compaction density of the first negative electrode active material at a pressure of 50,000 N 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.

[0075] In some embodiments, the powder compaction density of the second negative electrode active material under 50,000 N pressure is 1.75 g / cc to 1.94 g / cc. For example, the powder compaction density of the second negative electrode active material under 50,000 N pressure can be 1.75 g / cc, 1.76 g / cc, 1.78 g / cc, 1.80 g / cc, 1.82 g / cc, 1.84 g / cc, 1.86 g / cc, 1.88 g / cc, 1.90 g / cc, 1.92 g / cc, 1.94 g / cc, or any two values ​​between them.

[0076] In some embodiments, the first artificial graphite comprises secondary particles. The first artificial graphite is predominantly composed of secondary particles; for example, more than 80% of the first artificial graphite particles are secondary particles. Exemplarily, 80%, 85%, or 90% of the first artificial graphite particles are secondary particles. This is beneficial for improving the isotropy of the first negative electrode active material, reducing reversible expansion, and improving cycle performance.

[0077] In some embodiments, the powder OI value of the first negative electrode active material is 5.0-20.5. Maintaining the powder OI value of the first negative electrode active material within this range facilitates the dispersion of lithium intercalation expansion, thereby improving the cycle performance of the secondary battery. Exemplarily, the powder OI value of the first negative electrode active material can be 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, 10.5, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 19.5, 20.0, 20.5, or a value within a range of any two of these values. In some optional embodiments, the powder OI value of the first negative electrode active material is 5.5-19.5.

[0078] In some embodiments, the OI value of the second negative electrode active material is 2.5-6.5. An appropriate OI value is beneficial for improving the isotropy of the second negative electrode active material, allowing active ions to intercalate and deintercalate from various directions. This increases the number of intercalation and deintercalation channels for active ions in the particles of the second negative electrode active material, thus improving the kinetic performance of the secondary battery. For example, the OI value of the second negative electrode active material can be 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, or a value within a range of any two of these values. In some embodiments, the OI value of the second negative electrode active material is 2.8-6.3.

[0079] In some embodiments, the volumetric particle size distribution Dv50 of the second negative electrode active material is 10.0 μm-15.5 μm. By keeping the volumetric particle size distribution Dv50 of the second negative electrode active material within this range, it is beneficial to improve the transport performance of active ions and electrons in the negative electrode film, thereby further improving the kinetic performance of the secondary battery. Exemplarily, the particle size distribution Dv50 of the second negative electrode active material can be 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, or a value within a range consisting of any two of these values. In some optional embodiments, the volumetric particle size distribution Dv50 of the second negative electrode active material is 11.0 μm-14.5 μm.

[0080] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95-1.3. 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 transport performance of active ions and electrons in the negative electrode film, thereby enhancing the kinetic performance of the secondary battery. For example, the particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 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 second negative electrode active material is 0.95-1.25.

[0081] In some embodiments, the volume distribution percentage of particles with a diameter greater than 6.5 μm and less than 22.5 μm in the second negative electrode active material is greater than or equal to 75%. Maintaining the volume distribution percentage of the second negative electrode active material within this range is beneficial for increasing the compaction density of the negative electrode film, thereby improving the energy density of the secondary battery. Exemplarily, the volume distribution percentage of particles with a diameter greater than 6.5 μm and less than 22.5 μm in the second negative electrode active material can be 75%, 80%, 85%, 90%, 95%, or a value within a range of any two of these figures. In some optional embodiments, the volume distribution percentage of particles with a diameter greater than 6.5 μm and less than 22.5 μm in the second negative electrode active material is 75%-90%.

[0082] In some embodiments, the second negative electrode active material comprises a second artificial graphite and a third artificial graphite, wherein the second artificial graphite comprises primary particles and the third artificial graphite comprises secondary particles. By comprising primary particles of the second artificial graphite and secondary particles of the third artificial graphite in the second negative electrode active material, it is advantageous to achieve both excellent kinetic performance and high energy density. During the charging process of the secondary battery, active ions preferentially intercalate on the side away from the current collector; therefore, by positioning the second negative electrode active material in the second region, the kinetics of the secondary battery can be further improved.

[0083] In some embodiments, the second artificial graphite is predominantly composed of primary particles; for example, more than 80% of the second artificial graphite particles are primary particles. Exemplarily, 80%, 85%, or 90% of the second artificial graphite particles are primary particles. The third artificial graphite is predominantly composed of secondary particles; for example, more than 80% of the third artificial graphite particles are secondary particles. Exemplarily, 80%, 85%, or 90% of the third artificial graphite particles are secondary particles.

[0084] In some embodiments, the mass ratio of the second artificial graphite to the third artificial graphite in the second negative electrode active material is from 1:9 to 3:7. By keeping the mass ratio of the second artificial graphite to the third artificial graphite within the above range, it is beneficial to adjust the powder OI value and powder compaction density of the second negative electrode active material, thereby enabling the second negative electrode active material to achieve a balance between good kinetic performance, high energy density, and good cycle performance. Exemplarily, the mass ratio of the second artificial graphite to the third artificial graphite can be 3:7, 1:3, 1:4, 5:17, 1:9, or a value within a range of any two of these ratios. In some optional embodiments, the mass ratio of the second artificial graphite to the third artificial graphite is from 1:9 to 1:3.

[0085] In some embodiments, the La(110) of the first artificial graphite is greater than that of the second artificial graphite, and the La(110) of the first artificial graphite is greater than that of the third artificial graphite. The La(110) of the second artificial graphite is 100-140 nm, and the Lc(002) is 25-32 nm. The La(110) of the third artificial graphite is 90-130 nm, and the Lc(002) is 26-34 nm. This is advantageous for balancing high specific capacity and kinetic performance.

[0086] In some embodiments, the volumetric particle size distribution (Dv50) of the second artificial graphite is 7 μm-9 μm, and the Dv1 is 3 μm-5.5 μm. Exemplarily, the volumetric particle size distribution (Dv50) of the second artificial graphite is 7 μm, 7.5 μm, 8 μm, 8.5 μm, or 9.0 μm, and the Dv1 is 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or 6.0 μm. Optionally, the Dv1 is 3.0 μm-5.5 μm. By ensuring the particle size of the second artificial graphite is within the above range, it is beneficial to reduce the distance of the solid-phase diffusion path of active ions in the primary particles, thereby increasing the insertion / extraction rate of active ions and thus improving the kinetic performance of the secondary battery. Furthermore, it is beneficial to increase the number of active ions inserted into the primary particles, thereby increasing the specific capacity of the negative electrode active material and improving the energy density of the secondary battery. In some embodiments, the volumetric particle size distribution (Dv50) of the third artificial graphite is 13 μm-18 μm. For example, the particle sizes are 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, and 18 μm. By ensuring that the volume distribution particle size of the third type of artificial graphite is within the above range, it is beneficial to improve the isotropy of the negative electrode active material, increase the number of active ion insertion / extraction channels in the negative electrode active material, and improve the transport efficiency of active ions and electrons, thereby enhancing the kinetic performance of the secondary battery.

[0087] In some embodiments, the OI value of the second artificial graphite powder is 7-10, exemplarily a value between 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, or any two of these values. By ensuring the OI value of the second artificial graphite powder is within this range, it is beneficial to improve the conductivity of the second negative electrode active material, thereby improving the kinetic and cycle performance of the secondary battery. In some embodiments, the OI value of the third artificial graphite powder is 2-5, exemplarily a value between 2, 3, 4, 5, or any two of these values. By ensuring the OI value of the third artificial graphite powder is within this range, it is beneficial to improve the isotropy of the second negative electrode active material, increase the number of active ion insertion / extraction channels, increase the number of active sites in the negative electrode film, thereby improving the kinetic performance of the secondary battery.

[0088] In some embodiments, the specific capacity of the second artificial graphite is 354.1 mAh / g to 359.6 mAh / g; and / or, the specific capacity of the third artificial graphite is 353.0 mAh / g to 358.2 mAh / g. By ensuring that the specific capacity of the second and / or third artificial graphite is within the aforementioned range, it is beneficial to increase the specific capacity of the negative electrode active material, thereby improving the energy density of the secondary battery. Exemplarily, the specific capacity of the second artificial graphite is 354.1 mAh / g, 355.2 mAh / g, 356.3 mAh / g, 357.4 mAh / g, 358.5 mAh / g, 359.6 mAh / g, or a value within a range consisting of any two of these values. For example, the specific capacity of the third artificial graphite can be 353.0 mAh / g, 354.1 mAh / g, 355.2 mAh / g, 356.3 mAh / g, 357.4 mAh / g, 358.2 mAh / g, or a value between any two of these values.

[0089] In some embodiments, the compacted density of the second artificial graphite powder at a pressure of 50,000 N is 1.72 g / cc to 1.92 g / cc, exemplarily, a value between 1.72 g / cc, 1.75 g / cc, 1.76 g / cc, 1.77 g / cc, 1.78 g / cc, 1.79 g / cc, 1.80 g / cc, 1.81 g / cc, 1.83 g / cc, 1.85 g / cc, 1.87 g / cc, 1.89 g / cc, 1.90 g / cc, 1.92 g / cc, or any two of these values. In some embodiments, the powder compaction density of the third artificial graphite at a pressure of 50,000 N is 1.75–1.95 g / cc, exemplarily within the range of 1.75 g / cc, 1.76 g / cc, 1.77 g / cc, 1.78 g / cc, 1.79 g / cc, 1.80 g / cc, 1.81 g / cc, 1.83 g / cc, 1.85 g / cc, 1.87 g / cc, 1.89 g / cc, 1.90 g / cc, 1.92 g / cc, 1.95 g / cc, or any two of these values. By ensuring that the powder compaction density of the second and / or third artificial graphite is within the aforementioned range, it is beneficial to increase the compaction density of the negative electrode film layer, thereby improving the energy density of the secondary battery.

[0090] In some embodiments, the volumetric particle size distribution (Dv50) of the first artificial graphite is 14.5 μm-18.0 μm. Exemplarily, the volumetric particle size distribution (Dv50) of the first 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 volumetric particle size distribution (Dv50) of the first artificial graphite is 15.0 μm-17.5 μm. This is beneficial for increasing the powder compaction density of the first artificial graphite, thereby improving the energy density of the secondary battery.

[0091] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.25. Exemplarily, the particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is a value between 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, or any two of these values. In some alternative embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.20. This is beneficial for improving the kinetics of the first artificial graphite.

[0092] In some embodiments, the specific surface area of ​​the first artificial graphite is 0.8 m². 2 / g-2.1m 2 / g. By ensuring the specific surface area of ​​the first artificial graphite is within the aforementioned range, on the one hand, the first artificial graphite can possess 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 ​​the first 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 value within a range of any two of these values. In some alternative embodiments, the specific surface area of ​​the first synthetic graphite is 1.0 m². 2 / g-1.9m 2 / g.

[0093] In some embodiments, the first negative electrode active material and / or the second negative electrode active material further include silicon. Adding silicon to the first negative electrode active material and / or the second negative electrode active material is beneficial for further improving the energy density of the secondary battery. Exemplarily, the silicon may be derived from one or more of nano-silicon materials, silicon suboxide materials, and silicon-carbon composite materials. In some embodiments, the silicon content is less than or equal to 30 wt% relative to the total mass of the negative electrode film. Exemplarily, the silicon content may be a value between 30 wt%, 25 wt%, 20 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, 0.1 wt% relative to the total mass of the negative electrode film, or any two of these values. In some alternative embodiments, the silicon content is 3 wt% to 10 wt% relative to the total mass of the negative electrode film.

[0094] 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. The negative electrode active material is tested using an X-ray diffractometer (such as a Bruker D8 Discover). The test can be performed according 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 of the carbon material, and the peak intensity and full width at half maximum (FWHM) of the diffraction peak corresponding to the (002) crystal plane, and then calculated according to the Scherrer formula.

[0095] In this disclosure, the OI value of the powder of materials (first negative electrode active material, second negative electrode active material, first artificial graphite, second artificial graphite, third artificial graphite, etc.) refers to the graphite orientation degree of the material, describing the uniformity of crystal orientation in the graphite material particles. The powder OI value of the material is the ratio of the peak area of ​​surface (004) to the peak area of ​​surface (110) obtained by testing the material by X-ray diffraction. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction pattern of the powder sample. According to OI value = I 004 / I 110 The OI value of the powder in the sample was calculated. 004 I is the integrated area of ​​the diffraction peak of the crystalline carbon 004 crystal plane in the powder sample.110 This represents the integrated area of ​​the diffraction peaks on the crystalline carbon-110 plane in the powder sample. In the X-ray diffraction analysis of this disclosure, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0096] In this disclosure, the powder compaction density of the materials (first negative electrode active material, second negative electrode active material, first artificial graphite, second artificial graphite, third artificial graphite, etc.) is the mass per unit volume of the powder under specified conditions, and 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) in accordance with 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.

[0097] In this disclosure, the volume distribution particle sizes Dv1, Dv10, Dv50, and Dv90 of the materials (e.g., the first negative electrode active material, the second negative electrode active material, the first artificial graphite, the second artificial graphite, the third artificial graphite, etc.) represent the particle sizes corresponding to the cumulative volume distribution percentages of the materials reaching 1%, 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 the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0098] In this disclosure, the volume distribution percentage of particles with a diameter greater than 6.5 μm and less than 22.5 μm can be determined using the following method: Particle size can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The volume distribution percentage X corresponding to particles with a diameter less than or equal to 6.5 μm and the volume distribution percentage Y corresponding to particles with a diameter less than 22.5 μm are tested. The volume distribution percentage of particles with a diameter greater than 6.5 μm and less than 22.5 μm is calculated using the formula (YX)*100%.

[0099] In this disclosure, the specific capacity of the materials (first negative electrode active material, second negative electrode active material, first artificial graphite, second artificial graphite, third 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 first discharged at 25°C with a constant current of 0.15 mA to 0.005 V, allowed to stand for 10 minutes, and then discharged at a constant current of 50 μA to 0.005 V. After standing for 10 minutes, they were discharged at a constant current of 10 μA to 0.005 V, and the first discharge capacity of the coin cells was recorded. Subsequently, they were charged at a constant current of 0.3 mA to 2.0 V, and the first charge capacity of the coin cells was recorded. The ratio of the charge capacity to the sample mass is the specific capacity of the corresponding material (negative electrode active material, first artificial graphite, second artificial graphite, third artificial graphite, etc.).

[0100] In this disclosure, the degree of graphitization of materials (first negative electrode active material, second negative electrode active material, first artificial graphite, second artificial graphite, third artificial graphite, etc.) 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, an X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing, and the testing can be referenced 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).

[0101] In this disclosure, the thickness of the negative electrode film layer has a meaning known in the art and can be tested using methods known in the art, such as a micrometer (e.g., a Mitutoyo 293-100 with an accuracy of 0.1 μm). The thickness range given in this disclosure refers to the thickness range of the negative electrode film layer on one side of the negative electrode current collector.

[0102] In this disclosure, primary particles and secondary particles have meanings known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0103] Preparation method of negative electrode sheet

[0104] The negative electrode sheet in this disclosure can be prepared in the following manner: a first slurry containing a first negative electrode active material and a second slurry containing a second negative electrode active material are provided; the first slurry is coated on a negative electrode current collector, the second slurry is coated on the first slurry, and after drying and cold pressing, a negative electrode sheet is obtained.

[0105] The preparation method of the first negative electrode active material in this disclosure includes the following steps:

[0106] The first preparation steps of artificial graphite:

[0107] 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%;

[0108] Granulation step: Mix the shaped material with the first binder to obtain granulated material;

[0109] Graphitization step: The granulated material is subjected to a first graphitization treatment at 3000℃-3200℃ to obtain a first artificial graphite with La(110) of 130nm-175nm and Lc(002) of 30nm-42nm, which serves as the first negative electrode active material.

[0110] 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.

[0111] 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, volatile components refer to hydrocarbons with low molecular weight, such as light alkanes. The sulfur content and volatile content of the calcined needle coke are within the above ranges, resulting in better purity of the raw material. This is beneficial for grain development during graphitization, reduces the number of defects during graphitization, increases the degree of graphitization of artificial graphite and the La(110) value of artificial graphite, thereby improving the specific capacity and compaction density of the negative electrode film and increasing the energy density of the secondary battery.

[0112] 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 the artificial graphite, thereby increasing the specific capacity of the first artificial graphite and improving the energy density of the secondary battery. Exemplarily, the graphitization temperature can be 3000℃, 3050℃, 3100℃, 3150℃, 3200℃, or a value within a range consisting of any two of these values.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] In some embodiments, the softening point of the first binder is 180°C-270°C. 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 first binder is within the above range, the molecular weight and content of the polycyclic aromatic hydrocarbons in the first binder are large, which is beneficial to improving the adhesion of the first binder, reducing the amount of the first binder used in the granulation step, thereby increasing the specific capacity and compaction density of the first artificial graphite. Exemplarily, the softening point of the first binder can be 180°C, 200°C, 220°C, 240°C, 260°C, 270°C, or a value between any two of these values.

[0117] In some embodiments, the coking value of the first binder is 50%-70%. 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 first binder within the above range is beneficial for improving the specific capacity and compaction density of the first artificial graphite, thereby increasing the energy density of the secondary battery.

[0118] In some embodiments, the mass ratio of the shaping material to the first binder is 100:(6-12). A ratio of shaping material to the first binder within the above range is beneficial for reducing the amount of residual carbon from the first binder, increasing the specific capacity and compaction density of the first artificial graphite, and thus improving the energy density of the secondary battery.

[0119] In some embodiments, prior to the graphitization step, the granulated material is pre-carbonized to obtain an intermediate. The pre-carbonization step helps reduce volatile components in the first binder, thereby reducing the impurity content in the first artificial graphite, increasing the specific capacity and compaction density of the first artificial graphite, and improving the energy density of the secondary battery.

[0120] In some embodiments, the pre-carbonization temperature is 1000°C-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.

[0121] 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 two of these values.

[0122] In some embodiments, pre-carbonization is performed under a protective atmosphere, which may, for example, be nitrogen or argon. In an alternative embodiment, pre-carbonization is performed under a nitrogen atmosphere.

[0123] In some embodiments, the volumetric particle size distribution (Dv50) of the intermediate is 15 μm-18 μm. Having the intermediate particle size within this range is beneficial for increasing the particle size of the first artificial graphite, thereby increasing the specific capacity of the first artificial graphite and improving the energy density of the secondary battery.

[0124] 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 for 1-4 hours. The surface micro-oxidation treatment of artificial graphite can increase oxidized functional groups on the surface of the artificial graphite, enhance the bonding force between artificial graphite particles and between artificial graphite and the binder, reduce rebound effect, thereby improving the powder compaction density of the artificial graphite and thus increasing the energy density of the secondary battery.

[0125] The preparation method of the second negative electrode active material in this disclosure includes the following steps:

[0126] The second artificial graphite preparation steps are as follows: the second raw material with a sulfur content of less than or equal to 1.5% by mass is crushed, shaped, graded and screened, and then graphitized at 3000℃-3200℃ to produce primary particles, which are used as the second artificial graphite.

[0127] The third artificial graphite preparation steps are as follows: the third raw material with a sulfur content of less than or equal to 1.5% by mass is crushed and shaped to obtain primary particles, then a second binder is added for granulation, and then the third graphitization is carried out at 3000℃-3200℃ to produce secondary particles, which are used as the third artificial graphite.

[0128] Mixing step: The second artificial graphite and the third artificial graphite are mixed to obtain the second negative electrode active material; wherein, the powder OI value of the second negative electrode active material is 2.5-6.5, and the powder compaction density of the negative electrode active material under 50000N pressure is 1.75g / cc-1.94g / cc.

[0129] In this disclosure, in the aforementioned second and / or third artificial graphite preparation steps, the second and / or third graphitization is performed at 3000°C-3200°C. Exemplarily, the second and / or third graphitization can be performed at temperatures between 3000°C, 3050°C, 3100°C, 3150°C, 3200°C, or any two of these values.

[0130] Those skilled in the art can adjust the graphitization time as needed. In some embodiments, the processing time for the second and / or third graphitization can be 4-60 hours. For example, when the raw material is low-sulfur needle coke, the graphitization temperature is 3100°C, and the graphitization time can be 12 hours, 24 hours, or 36 hours.

[0131] By mixing second and third artificial graphite, the primary particles of the second artificial graphite have a smaller particle size and higher powder compaction density, while the secondary particles of the third artificial graphite have higher isotropy. This results in an OI value of 2.5-6.5 for the second negative electrode active material and a powder compaction density of 1.75 g / cc-1.94 g / cc under 50,000 N pressure. This facilitates the utilization of the high capacity, high compaction density, and excellent kinetic performance of the second negative electrode active material, leading to high energy density and excellent kinetic performance in the secondary battery. The smaller particle size of the second artificial graphite can fill the gaps between the secondary particles of the third artificial graphite in the negative electrode active material, playing a supporting and dispersing role. This improves the structural stability and processing performance of the second negative electrode active material, reduces the amount of dispersant and suspending agent in the negative electrode film, increases the active sites of the second negative electrode active material, thereby improving the kinetic performance of the secondary battery and increasing the proportion of negative electrode active material in the second negative electrode film, thus increasing the energy density of the secondary battery.

[0132] In some embodiments, in the second artificial graphite preparation step, a second graphitization is performed to produce primary particles with a volume distribution particle size Dv50 of 7 μm-9 μm and Dv1 of 3 μm-5.5 μm, which serve as the second artificial graphite. In the second artificial graphite preparation step, a classifier is used to prepare primary particles with a volume distribution particle size Dv50 of 7 μm-9 μm and Dv1 of 3 μm-5.5 μm. The smaller particle size of the primary particles helps to reduce the distance of the solid-phase diffusion path of active ions within the primary particles, increasing the intercalation and deintercalation rate of active ions, thereby improving the kinetic performance of the secondary battery. Furthermore, making the volume distribution particle size Dv1 of the primary particles 3 μm-5.5 μm helps to increase the number of intercalated active ions in the primary particles, thereby increasing the specific capacity of the second negative electrode active material and improving the energy density of the secondary battery.

[0133] In some embodiments, in the preparation step of the third artificial graphite, the third raw material is crushed and shaped to obtain primary particles with a volume distribution particle size Dv50 of 7μm-9μm; then, a binder is added for granulation, and third graphitization is carried out at 3000℃-3200℃ to produce secondary particles with a (Dv90-Dv10) / Dv50 ratio of 1.0-1.25 and a Dv50 of 13μm-18μm, thus obtaining the third artificial graphite. In the preparation step of the third artificial graphite, preparing secondary particles with a Dv50 of 13μm-18μm is beneficial to improving the isotropy of the second negative electrode active material, increasing the number of active ion insertion / extraction channels in the second negative electrode active material, and improving the transport efficiency of active ions and electrons, thereby improving the kinetic performance of the secondary battery.

[0134] In this disclosure, the second and / or third raw materials can be any raw materials known in the art for preparing artificial graphite, without particular limitation. Exemplarily, the second and / or third raw materials may include one or more of petroleum coke, calcined petroleum coke, needle coke, calcined needle coke, pitch coke, and metallurgical coke; optionally, the raw materials may include one or more of petroleum coke, needle coke, and calcined needle coke. In one embodiment, the second and / or third raw material is needle coke.

[0135] In some embodiments, the sulfur content in the second and / or third raw materials is ≤0.6% by mass, and the volatile components are ≤7% by mass. Here, volatile components refer to volatile organic compounds, such as alkanes, aromatics, and lipids. Having the sulfur content and volatile components of the second and / or third raw materials within the above-mentioned ranges is beneficial for reducing impurities in the resulting second and third artificial graphite, increasing the graphitization degree of the negative electrode active material, and thus improving the energy density of the secondary battery.

[0136] In this disclosure, grading and screening can be performed using equipment known in the art, without particular limitation. In some embodiments, grading and screening can be performed using a classifier. Exemplarily, the classifier is selected from cyclone classifiers and airflow classifiers.

[0137] In this disclosure, the second binder in the third artificial graphite preparation step can be any binder known in the art, without particular limitation. Exemplarily, the second binder may include one or more of oily asphalt, coal-based pitch, and polymers. In some embodiments, the softening point of the second binder in the third artificial graphite preparation step is ≥150°C. Using a binder with a softening point within the above range results in a high coking value, facilitates graphitization, and is beneficial for increasing the powder compaction density of the third artificial graphite, thereby increasing the specific capacity of the negative electrode active material and improving the energy density of the secondary battery. In some optional embodiments, the softening point of the binder is 150°C-280°C. For example, the softening point of the adhesive may be a value between 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or any two of these values.

[0138] In some embodiments, during the third artificial graphite preparation step, the mass percentage of the second binder relative to the mass of the primary particles is 8%-14%. Maintaining the mass of the binder within this range facilitates better adhesion and improves the isotropy of the secondary particles. Exemplarily, the mass percentage of the second binder relative to the mass of the primary particles can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or a value within a range of any two of these values.

[0139] In some embodiments, the ratio of the second artificial graphite to the third artificial graphite in the mixing step is from 1:9 to 3:7. Maintaining the mass ratio of the second artificial graphite to the third artificial graphite within this range facilitates the adjustment of the powder OI value and powder compaction density of the second negative electrode active material, thereby enabling the second negative electrode active material to achieve a balance between good kinetic performance, high energy density, and good cycle performance. Exemplarily, the mass ratio of the second artificial graphite to the third artificial graphite can be 3:7, 1:3, 1:4, 5:17, 1:9, or a value within a range of any two of these ratios. In one embodiment, the mass ratio of the second artificial graphite to the third artificial graphite is from 1:9 to 1:3. In an optional embodiment, the mass ratio of the second artificial graphite to the third artificial graphite is 1:3.

[0140] 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.).

[0141] In some embodiments, a first negative electrode active material, along with optional conductive agents, optional binders, and other optional additives, can be dispersed in a solvent (e.g., deionized water) to form a first slurry. A second negative electrode active material, along with optional conductive agents, optional binders, and other optional additives, can be dispersed in a solvent (e.g., deionized water) to form a second slurry. The binder can 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), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS). The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0142] Positive electrode sheet

[0143] 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 the positive electrode active material of the first aspect of the present disclosure.

[0144] 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.

[0145] 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.).

[0146] 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.

[0147] 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.

[0148] 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 processes.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] electrolytes

[0155] 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.

[0156] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] Separating membrane

[0161] 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.

[0162] 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.

[0163] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0164] 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.

[0165] 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.

[0166] 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 2 shows a square battery cell 5 as an example.

[0167] In some embodiments, referring to FIG3, 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.

[0168] 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.

[0169] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, 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.

[0170] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0171] 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.

[0172] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, 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.

[0173] 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.

[0174] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0175] Figure 7 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.

[0176] 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.

[0177] Example

[0178] 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.

[0179] Preparation of the first negative electrode active material

[0180] Material 1-1

[0181] 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;

[0182] Step 2: Using granulated asphalt with a softening point of 200℃ as the first binder, the above-mentioned shaping material is granulated together in a granulation kettle to obtain granulated material, wherein the mass ratio of the shaping material to the first binder is 100:8.

[0183] Step 3: The above granulated material is pre-carbonized at 1150°C for 2 hours under a nitrogen atmosphere to obtain an intermediate.

[0184] Step 4: The above intermediate was graphitized at a high temperature of 3020℃. The graphitized particles were sieved and demagnetized to obtain the first artificial graphite with La(110) of 131.7nm and Lc(002) of 32.5nm, which was used as the first negative electrode active material 1-1.

[0185] Materials 1-2 to 1-4 and Materials 1-1' to 1-2'

[0186] The preparation methods of materials 1-2 to 1-4 and materials 1-1' to 1-2' are similar to those of material 1-2. The difference is that the raw material type and graphitization temperature are adjusted so that the La(110), Lc(002), La / Lc, powder OI value, specific capacity, powder compaction density and Dv50 of materials 1-2 to 1-4 and materials 1-1' to 1-2' are the values ​​shown in Table 1.

[0187] The above materials were tested according to the following methods, and the results are shown in Table 1.

[0188] Tests of La(110), Lc(002), and La / Lc of the material:

[0189] 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 X-ray diffraction pattern of the powder sample was obtained by scanning with a 2θ angle range of 20°-80° and a scanning rate of 4° / min. The La(110), Lc(002), and La / Lc of the material were calculated using the following formulas:

[0190] La calculation formula:

[0191] 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.

[0192] Lc calculation formula:

[0193] 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.

[0194] Testing of the powder OI value of the material:

[0195] Following the test method for lattice parameters of artificial graphite in JB / T 4220-2011, a Bruker D8 Discover X-ray diffractometer was used for testing. A copper target was used as the anode target, and CuKα rays were used as the radiation source. The wavelength of the rays was... The X-ray diffraction pattern of the material was obtained by scanning with a 2θ angle range of 20°-80° and a scanning rate of 4° / min. The integrated area I of the diffraction peaks on the crystalline carbon 004 plane in the powder sample was calculated based on the X-ray diffraction pattern. 004 The integrated area I of the diffraction peaks of the crystalline carbon 110 crystal plane in the powder sample. 110 The OI value of powder is calculated using the formula OI = I 004 / I 110 To calculate.

[0196] Testing of material specific capacity:

[0197] 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.

[0198] At 25°C, the prepared coin cell was first discharged to 0.005V with a constant current of 0.15mA, and allowed to stand for 5 minutes. Then, it was discharged to 0.005V with a constant current of 50μA, allowed to stand for 5 minutes, and then discharged to 0.005V with a constant current of 10μA. The first discharge capacity of the coin cell was recorded. After that, it was charged to 2.0V with a constant current of 0.3mA, 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.

[0199] The proportion of lithium intercalation capacity in the platform to the total capacity X

[0200] 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%.

[0201] Testing the compacted density of powder materials:

[0202] 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.

[0203] Testing of particle size distribution in materials:

[0204] Dv50 test: The test was conducted using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0205] (Dv90-Dv10) / Dv50: Referring to GB / T 19077-2016 Particle size distribution laser diffraction method, the values ​​of Dv90, Dv50 and Dv10 were measured by a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK, and the value of (Dv90-Dv10) / Dv50 was calculated.

[0206] Table 1

[0207] Preparation of the second negative electrode active material

[0208] (1) Preparation of the second artificial graphite

[0209] Material a-1

[0210] Step 1: The needle-shaped raw coke (sulfur content of 0.5% and volatile matter of 5%) is mechanically crushed and shaped, and then classified by an air classifier to remove small particles, thus obtaining the shaped material.

[0211] Step 2: The above-mentioned shaped material is graphitized at a high temperature of 3100℃ in an Atchison graphitization furnace for 36 hours; the graphitized particles are sieved and demagnetized to obtain primary particles with Dv50 of 7μm and Dv1 of 3.5μm as the second artificial graphite (material a-1).

[0212] Materials a-2 to a-3

[0213] The preparation methods of materials a-2 to a-3 are similar to those of material a-1. The difference lies in adjusting the type of raw materials and the graphitization temperature. The Dv1, Dv50, powder OI value, specific capacity and powder compaction density of materials a-2 to a-3 are shown in Table 2.

[0214] Table 2

[0215] (2) Preparation of the third type of artificial graphite

[0216] Material b-1

[0217] Step 1: The needle-shaped raw coke (sulfur content 0.5%, volatile matter 5%) is crushed and shaped using an air jet mill to obtain primary particles with a Dv50 of 8.0 μm.

[0218] Step 2: Using oily asphalt with a softening point of 180℃ as a binder, the above-mentioned primary particles are granulated together in a granulation reactor to obtain granulated material. The amount of binder added is 10% relative to the total weight of the granulated material.

[0219] Step 3: Graphitize the above granulated material at 3100℃ for 36 hours; sieve and demagnetize the graphitized particles to obtain secondary particles with a Dv50 of 14.5μm, which are used as the third artificial graphite (material b-1).

[0220] Materials b-2 to b-3

[0221] The preparation methods of materials b-2 to b-3 are similar to those of material b-1. The difference is that the raw materials and graphitization temperature of materials b-2 to b-3 are adjusted so that the Dv50, powder OI value, specific capacity and powder compaction density under 50000N pressure are the values ​​shown in Table 3.

[0222] The particle size, OI value, specific gravity, and powder compaction density of the material were tested using the same method as the third type of artificial graphite mentioned above, and the test results are recorded in Table 3.

[0223] Table 3

[0224] (3) Preparation of the second negative electrode active material

[0225] The second artificial graphite and the third artificial graphite were mixed according to the mass ratio shown in Table 4 below to obtain the second negative electrode active material.

[0226] The test was conducted using the same testing method as described above, and the test results are shown in Table 4.

[0227] Table 4

[0228] Example 1

[0229] (1) Preparation of the first negative electrode active material slurry

[0230] The first negative electrode active material, 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 slurry of the first negative electrode active material.

[0231] (2) Preparation of the second negative electrode active material slurry

[0232] The above-mentioned second negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97.4:1:0.7:0.9 to form the first negative electrode active material slurry.

[0233] (3) Preparation of negative electrode sheet

[0234] A first negative electrode active material slurry and a second negative electrode active material slurry are simultaneously extruded using a dual-cavity coating device, with a mass ratio of 1:1. The first negative electrode active material slurry is coated onto the negative electrode current collector copper foil, i.e., the first negative electrode active material slurry is coated in the first region, and the second negative electrode active material slurry is coated onto the first negative electrode active material slurry, i.e., the second negative electrode active material slurry is coated in the second region. After drying and cold pressing, the negative electrode sheet is obtained.

[0235] (4) Preparation of positive electrode sheet

[0236] 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.

[0237] (5) Preparation of lithium-ion batteries

[0238] A 7μm polyethylene membrane is used as the separator. PVDF slurry is sprayed on both sides of the separator, and an alumina ceramic coating of 1μm is sprayed on one side. The ceramic coating side corresponds to the cathode electrode.

[0239] 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.

[0240] 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.

[0241] Examples 2-4

[0242] The battery preparation methods in Examples 2-4 are similar to those in Example 1, except that the types of the first and second negative electrode active materials are adjusted in the negative electrode preparation steps, as shown in Table 5.

[0243] Comparative Example 1

[0244] The battery preparation method of Comparative Example 1 is similar to that of Example 1, except that in the preparation step of the negative electrode sheet, the second negative electrode active material slurry is coated on the first region and the first negative electrode active material slurry is coated on the second region.

[0245] Comparative Example 2

[0246] The battery preparation method of Comparative Example 2 is similar to that of Example 1, except that in the preparation step of the negative electrode sheet, the first negative electrode active material and the second negative electrode active material are mixed and coated on the negative electrode current collector to form a single layer of negative electrode film.

[0247] Comparative Example 3

[0248] The battery preparation method of Comparative Example 3 is similar to that of Example 1, except that in the preparation step of the negative electrode sheet, only the first negative electrode active material 1-1 is used to form a single layer of negative electrode film on the negative electrode current collector.

[0249] Comparative Example 4

[0250] The battery preparation method of Comparative Example 4 is similar to that of Example 1, except that in the preparation step of the negative electrode sheet, only the second negative electrode active material 2-1 is used to form a single layer of negative electrode film on the negative electrode current collector.

[0251] Comparative Examples 5-6

[0252] The battery preparation methods of Comparative Examples 5-6 are similar to those of Example 1, except that the types of the first and second negative electrode active materials are adjusted in the negative electrode preparation steps, as shown in Table 5.

[0253] Performance testing

[0254] (1) Energy density

[0255] 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 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 5.

[0256] (2) Fast charging performance test of secondary batteries

[0257] At 25°C, the secondary battery was charged to 3.65V at a constant current of 0.33C, then charged to 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.0V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0258] Then, the secondary battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, and 3.0C0 until it reached 3.65V or 0V negative terminal cutoff potential (whichever comes first). After each charge, it was discharged to 2.0V at 1C0. The state of charge (SOC) was recorded at different charging rates until it reached 10%, 20%, 30%, ..., 80%. The negative electrode potential corresponding to the state of charge (SOC) is plotted, and the charge rate-negative electrode potential curves are obtained for different SOC states. After linear fitting, the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charge rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC, respectively. The charging time T (assuming no lithium plating in the secondary battery) from 10%SOC to 80%SOC is calculated using the following formula, in minutes. The shorter the charging time, the better the kinetic performance of the secondary battery.

[0259] T=(60 / C10%SOC+60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%

[0260] (3) Cyclic performance test of secondary batteries

[0261] At 45℃, the secondary battery was charged at a constant current of 1C to the upper limit of 3.65V (corresponding to 100% SOC), then charged at a constant voltage to a current of 0.05C. After resting for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.5V (corresponding to 0% SOC), and the discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The secondary battery was subjected to a cyclic charge-discharge test using the above method, and the discharge capacity after each cycle was recorded.

[0262] The capacity retention rate (%) of a secondary battery after 1000 cycles at 45℃ = discharge capacity after 1000 cycles / discharge capacity of the first cycle × 100%.

[0263] The performance of the secondary batteries prepared in the above embodiments and comparative examples was tested, and the results are shown in Table 5.

[0264] Table 5

[0265] As can be seen from the data in Table 5, compared with Comparative Examples 1 to 6, the negative electrode sheet prepared in the embodiments of this disclosure has a double-layer design. The first region uses a first negative electrode active material with high energy density, and the second region uses a second negative electrode active material with high isotropy and high powder compaction density. Thus, the secondary battery can take into account high energy density, excellent kinetic performance and high cycle performance.

[0266] Examples 5-11

[0267] The battery preparation methods in Examples 5-11 are similar to those in Example 1, except that, in the preparation steps of the negative electrode sheet, the type of the second negative electrode active material and the mass ratio of the first negative electrode active material and the second negative electrode active material are adjusted as shown in Table 6.

[0268] The performance of the secondary batteries prepared in the above embodiments was tested, and the results are shown in Table 6.

[0269] Table 6

[0270] As can be seen from the data in Table 6, the secondary batteries prepared in the embodiments of this disclosure can achieve a balance between high energy density, excellent kinetic performance, and high cycle performance.

[0271] 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 secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector, the negative electrode film layer comprising a first region and a second region, the first region being located between the second region and the negative current collector, the first region comprising a first negative electrode active material, the second region comprising a second negative electrode active material, the powder OI value of the second negative electrode active material being less than the powder OI value of the first negative electrode active material, the first negative electrode active material comprising a first artificial graphite, the first artificial graphite having a La(110) of 130nm-175nm and an Lc(002) of 30nm-42nm, La(110) representing the crystallite size along the a-axis in the (110) crystal plane of the first artificial graphite, and Lc(002) representing the crystallite size along the c-axis in the (002) crystal plane of the first artificial graphite.

2. The secondary battery according to claim 1, wherein, The first artificial graphite has a La(110) of 132nm-172nm and / or an Lc(002) of 30nm-36nm.

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

5.

4. The secondary battery according to any one of claims 1-3, wherein, The ratio of La(110) / Lc(002) is 4.5-5.

5.

5. The secondary battery according to any one of claims 1-4, wherein, Charge-discharge tests were conducted on the coin cell prepared from the first 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-0.070V, 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 secondary battery 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 secondary battery according to any one of claims 1-6, wherein, The specific capacity of the first negative electrode active material is greater than or equal to the specific capacity of the second negative electrode active material.

8. The secondary battery according to any one of claims 1-7, wherein, The specific capacity of the first negative electrode active material is ≥359 mAh / g; and / or, The specific capacity of the second negative electrode active material is 353mAh / g-359mAh / g.

9. The secondary battery according to any one of claims 1-8, wherein, The specific capacity of the first negative electrode active material is 359 mAh / g-366 mAh / g; and / or, The specific capacity of the second negative electrode active material is 354.6 mAh / g-356.8 mAh / g.

10. The secondary battery according to any one of claims 1-9, wherein, The degree of graphitization of the first negative electrode active material is greater than that of the second negative electrode active material.

11. The secondary battery according to any one of claims 1-10, wherein, The degree of graphitization of the first negative electrode active material is 94.0%-96.0%; and / or, The degree of graphitization of the second negative electrode active material is 93.5%-95.5%.

12. The secondary battery according to any one of claims 1-11, wherein, The graphitization degree of the first negative electrode active material is 94.2%-95.8%; and / or, The degree of graphitization of the second negative electrode active material is 93.7%-95.3%.

13. The secondary battery according to any one of claims 1-12, wherein, The compacted density of the first negative electrode active material under 50,000 N pressure is greater than that of the second negative electrode active material under 50,000 N pressure.

14. The secondary battery according to any one of claims 1-13, wherein, The first negative electrode active material has a powder compaction density of 1.95 g / cc - 2.04 g / cc under a pressure of 50,000 N; and / or, The second negative electrode active material has a powder compaction density of 1.75 g / cc to 1.94 g / cc under a pressure of 50,000 N.

15. The secondary battery according to any one of claims 1-14, wherein, The first artificial graphite comprises secondary particles.

16. The secondary battery according to any one of claims 1-15, wherein, The powder OI value of the first negative electrode active material is 5.0-20.5; and / or, The OI value of the second negative electrode active material powder is 2.5-6.

5.

17. The secondary battery according to any one of claims 1-16, wherein, The powder OI value of the first negative electrode active material is 5.5-19.5; and / or, The OI value of the second negative electrode active material is 2.8-6.

3.

18. The secondary battery according to any one of claims 1-17, wherein, The volume distribution particle size Dv50 of the second negative electrode active material is 10.0 μm-15.5 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95-1.

3.

19. The secondary battery according to any one of claims 1-18, wherein, The volumetric particle size Dv50 of the second negative electrode active material is 11.0 μm-14.5 μm; and / or, The particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material is 0.95-1.

25.

20. The secondary battery according to any one of claims 1-19, wherein, In the second negative electrode active material, the volume distribution ratio of particles with a particle size greater than 6.5 μm and less than 22.5 μm is ≥75%.

21. The secondary battery according to any one of claims 1-20, wherein, In the second negative electrode active material, the volume distribution ratio of particles with a particle size greater than 6.5 μm and less than 22.5 μm is 75%-90%.

22. The secondary battery according to any one of claims 1-21, wherein, The second negative electrode active material includes a second artificial graphite and a third artificial graphite, wherein the second artificial graphite comprises primary particles and the third artificial graphite comprises secondary particles.

23. The secondary battery according to claim 22, wherein, In the second negative electrode active material, the mass ratio of the second artificial graphite to the third artificial graphite is 1:9 to 3:

7.

24. The secondary battery according to claim 22 or 23, wherein, In the second negative electrode active material, the mass ratio of the second artificial graphite to the third artificial graphite is 1:9 to 1:

3.

25. The secondary battery according to any one of claims 22-24, wherein, The La(110) of the first artificial graphite is greater than the La(110) of the second artificial graphite, and the La(110) of the first artificial graphite is greater than the La(110) of the third artificial graphite.

26. The secondary battery according to any one of claims 22-25, wherein, The second artificial graphite has a La(110) of 100-140 nm and an Lc(002) of 25-32 nm.

27. The secondary battery according to any one of claims 22-26, wherein, The third artificial graphite has a La(110) of 90-130 nm and an Lc(002) of 26-34 nm.

28. The secondary battery according to any one of claims 22-27, wherein, The second artificial graphite has a volume distribution particle size Dv50 of 7 μm-9 μm and a Dv1 of 3 μm-5.5 μm; and / or, The volumetric particle size Dv50 of the third artificial graphite is 13μm-18μm.

29. The secondary battery according to any one of claims 22-28, wherein, The second artificial graphite powder has an OI value of 7-10; and / or, The OI value of the third artificial graphite powder is 2-5.

30. The secondary battery according to any one of claims 22-29, wherein, The specific capacity of the second artificial graphite is 354.1 mAh / g to 359.6 mAh / g; and / or, The specific capacity of the third type of artificial graphite is 353.0 mAh / g to 358.2 mAh / g.

31. The secondary battery according to any one of claims 22-30, wherein, The second type of artificial graphite has a powder compaction density of 1.72 g / cc to 1.92 g / cc under a pressure of 50,000 N; and / or, The compacted density of the third type of artificial graphite powder under a pressure of 50,000 N is 1.75 g / cc to 1.95 g / cc.

32. The secondary battery according to any one of claims 1-31, wherein, The first artificial graphite satisfies one or more of the following conditions. (1) The volume distribution particle size Dv50 of the first artificial graphite is 14.5μm-18.0μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.25; (3) The specific surface area of ​​the first artificial graphite is 0.8 m². 2 / g-2.1m 2 / g.

33. The secondary battery according to any one of claims 1-32, wherein, The first artificial graphite satisfies at least one or more of the following conditions. (1) The volume distribution particle size Dv50 of the first artificial graphite is 15.0μm-17.5μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the first artificial graphite is 0.90-1.20; (3) The specific surface area of ​​the first artificial graphite is 1.0 m². 2 / g-1.9m 2 / g.

34. The secondary battery according to any one of claims 1-33, wherein, The first negative electrode material and / or the second negative electrode active material further include silicon.

35. An electrical device comprising a secondary battery as described in any one of claims 1-34.

Images