Secondary battery and electric apparatus containing same

Abstract

Provided in the present disclosure are a secondary battery and an electric apparatus containing same. The secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative current collector and a negative film layer, which is arranged on at least one surface of the current collector and comprises a negative active material and a conductive agent, the powder conductivity σ of the negative active material is greater than or equal to 80 S / cm but less than or equal to 106 S / cm, and the compaction density of the negative film layer is 1.35 g / cm3 to 1.50 g / cm3. The negative electrode sheet is conducive to alleviating a black-spot phenomenon of a secondary battery and improving the cycle performance and dynamic performance of the secondary battery.

Description

Secondary battery and electric device containing same

[0001] Cross-references

[0002] The present disclosure claims priority to Chinese Patent Application No. 202311677390.1, filed on December 7, 2023, entitled “Secondary Battery and Electrical Device Containing the Same,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device containing the same. Background Art

[0004] In recent years, secondary batteries have been increasingly used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. Therefore, higher requirements are placed on the performance of secondary batteries.

[0005] During the use or storage of secondary batteries, due to a series of complex chemical and physical reactions inside the battery, certain failure phenomena such as black spots and lithium precipitation often occur, which seriously reduce the performance of the secondary battery. The negative electrode active material is one of the important raw materials of secondary batteries and has a great impact on the electrical performance of secondary batteries. The failure of graphite negative electrode materials mainly occurs on the surface of graphite, resulting from the electrochemical reaction between the graphite surface and the electrolyte to form a solid electrolyte interface phase (SEI), and ultimately affects the cycle performance of the secondary battery. Therefore, it is necessary to provide a secondary battery that can improve the black spot phenomenon of secondary batteries.

[0006] Summary of the Invention

[0007] The present disclosure provides a secondary battery having good cycle performance and kinetic performance and can reduce the black spot phenomenon on the surface of the negative electrode of the secondary battery.

[0008] The secondary battery provided by the present disclosure includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the current collector and including a negative electrode active material, the negative electrode active material having a compacted density of 1.5 g / cm 3 The powder conductivity σ measured under the test conditions is greater than or equal to 80S / cm and less than or equal to 106S / cm; the compaction density of the negative electrode film layer is 1.35g / cm 3 -1.50g / cm 3 .

[0009] Adjusting the powder conductivity σ of the negative electrode active material and the compaction density of the negative electrode film layer can ensure good electrical contact and conductive network between the negative electrode active material particles in the negative electrode sheet, alleviate the problem of delayed gas production caused by delayed SEI film formation in some active material particles during the formation process, and the black spot defect caused by the inability of active ions to be embedded in the active material due to gas barrier, and alleviate the lithium plating problem caused by the active ion content in the battery cell being greater than the acceptable amount of the negative electrode, which helps to improve the cycle performance and kinetic performance of the secondary battery.

[0010] In any embodiment, the powder conductivity σ is 83 S / cm-104 S / cm, which is beneficial to further improve the conductivity of the negative electrode active material, improve the black spot phenomenon, and enhance the cycle performance of the secondary battery.

[0011] In any embodiment, the compaction density of the negative electrode film layer is 1.40-1.50 g / cm 3 , which can further improve the energy density of secondary batteries.

[0012] In any embodiment, the negative electrode active material satisfies at least one of the following conditions:

[0013] (1) Volume distribution particle size D of the negative electrode active material V 1 is 1.4μm-3.0μm, optional is 1.7μm-2.7μm;

[0014] (2) Volume distribution particle size D of the negative electrode active material V 50 is 12μm-18μm, optional is 12.9μm-14.5μm;

[0015] (3) The particle size distribution of the negative electrode active material (D V 90-D V 10) / D V 50 is 1.3-1.8, optional is 1.35-1.70.

[0016] Control volume distribution particle size D V 1. It can reduce the excessive active sites on the surface of the negative electrode active material and the irreversible active ion consumption caused by the excessive content of small particles; it also helps to improve the conductive network between the negative electrode active material particles, and also helps the secondary battery to have good cycle performance and alleviate the black spot phenomenon. Control the volume distribution particle size D V50 helps to obtain sufficient active sites, reduce the inhibitory effect on the deintercalation rate of active ions, and improve the kinetic performance of secondary batteries; controlling the particle size distribution of negative electrode active materials helps to improve the particle size distribution concentration of negative electrode active materials, reduce the side reactions of negative electrode active materials with excessively large and excessively small particle sizes in the electrochemical reaction, comprehensively improve the cycle performance and kinetic performance of secondary batteries, and further reduce the black spot phenomenon.

[0017] In any embodiment, the tap density of the negative electrode active material is 1.25 g / cm 3 -1.45g / cm 3 , optional 1.29g / cm 3 -1.41g / cm 3 Adjusting the tap density of the negative electrode active material can make the negative electrode active materials of different particle sizes well dispersed in the negative electrode sheet, so that there are sufficient contact sites and good electrical contact between the negative electrode active material particles, and the active ions are well embedded and released between the negative electrode active materials, reducing the precipitation of active ions and the black spot phenomenon of the negative electrode sheet.

[0018] In any embodiment, the specific surface area of ​​the negative electrode active material is 0.8 m 2 / g-1.4m 2 / g, optional 0.9m 2 / g-1.3m 2 Adjusting the specific surface area of ​​the negative electrode active material is beneficial to increasing the contact sites and surface active sites between the negative electrode active material particles, increasing the conductivity of the negative electrode active material and improving the transport performance of active ions, thereby improving the cycle performance of the secondary battery.

[0019] In any embodiment, the gram capacity of the negative electrode active material is 335 mAh / g-350 mAh / g, optionally 340.5 mAh / g-347.5 mAh / g, thereby improving the energy density of the secondary battery and enhancing its cycle performance.

[0020] In any embodiment, the surface density of the negative electrode film layer in the negative electrode sheet is 7 mg / cm 2 -15mg / cm 2 , which can increase the energy density of secondary batteries and improve the cycle performance of secondary batteries.

[0021] In any embodiment, the negative electrode active material includes artificial graphite.

[0022] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present disclosure.

[0024] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present disclosure shown in FIG. 1 .

[0025] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0026] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0027] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0028] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0029] FIG7 shows the cycle curves of Example 2 and Comparative Example 1 of the present disclosure.

[0030] Description of reference numerals:

[0031] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0032] Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device disclosed in the present invention are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0033] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] Unless otherwise specified, the terms "include" and "comprising" mentioned in this disclosure may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0038] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery's charge and discharge process, active ions (e.g., lithium ions, sodium ions) are embedded and extracted between the positive and negative electrodes. The electrolyte conducts active ions between the positive and negative electrodes. The separator is placed between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0040] During the formation stage of a secondary battery, an electrochemical reaction occurs between the negative electrode active material and the electrolyte to form a solid electrolyte interface (SEI), accompanied by the generation of gas. During this process, some of the negative electrode active material particles have poor electrical contact with the surrounding particles. During the formation process, the electrochemical reaction between the graphite material and the electrolyte is not timely, and a complete SEI film cannot be formed in time, resulting in a lag in the formation of the SEI film and gas production. The gas generated by this lag cannot be discharged in time with the formation process and is retained between the negative electrode plate and the separator, hindering the charging process in which the active ions in this area escape from the positive electrode, pass through the separator, and embed into the negative electrode, resulting in black spot defects. This causes some of the negative electrode active materials to be unable to effectively participate in the charge and discharge cycle of the secondary battery. The positive electrode active ion content in the secondary battery is greater than the maximum acceptable active ion content of the negative electrode, causing some active ions to precipitate on the negative electrode surface and lose their electrical activity, resulting in a decrease in the capacity of the battery cell and rapid decay in cycle performance.

[0041] [Secondary battery]

[0042] The present disclosure provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material. 3 The powder conductivity σ measured under the test conditions is greater than or equal to 80S / cm and less than or equal to 106S / cm; and the compaction density of the negative electrode film layer is 1.35g / cm 3 -1.50g / cm 3 .

[0043] By adjusting the powder conductivity σ of the negative electrode material and the compaction density of the negative electrode film layer, the active material particles in the negative electrode sheet have good electrical contact and conductive network, which can slow down the gas production lag caused by the delayed formation of SEI film in some negative electrode active material particles during the formation process, thereby reducing the black spot defects caused by the inability of active ions to be deintercalated due to gas barrier and reducing the lithium plating problem of the secondary battery, reducing the irreversible consumption of active ions, and improving the cycle performance and kinetic performance of the secondary battery.

[0044] In this paper, the powder conductivity σ is the conductivity of the negative electrode active material at a compacted density of 1.5 g / cm 3 The powder conductivity σ measured under the test conditions can be measured using methods known in the art. For example, it can be measured using the following method:

[0045] At 25°C, using the FT-8100A four-probe powder test platform, refer to the four-probe method in GBT 30835-2014 for the determination of powder conductivity; weigh 1g of the test sample powder and place it in a cylindrical metal mold with a height of 25mm and a diameter of 12mm; press the lower electrode of the mold, and when the upper electrode is pressed to the table, the sample begins to be compressed. The pressure is maintained for 30s so that the sample thickness is maintained at 0.147±0.002. Then, the negative electrode active material is measured by the four-probe powder method at 1.50g / cm 3 Powder conductivity at compacted density.

[0046] In some embodiments, the negative electrode active material has a compaction density of 1.5 g / cm 3 The powder conductivity σ measured under the test conditions is 83S / cm-104S / cm. In some embodiments, the negative electrode active material has a compaction density of 1.5g / cm 3 The powder conductivity σ measured under the test conditions is 85S / cm-100S / cm, 90S / cm-104S / cm, 85S / cm-104S / cm, or 95S / cm-100S / cm. Adjusting the powder conductivity of the negative electrode active material helps further improve the electrical contact between the negative electrode active material particles, improve the conductivity of the negative electrode active material, reduce the black spot phenomenon, and improve the cycle performance of the secondary battery.

[0047] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.50g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.43g / cm 3 , 1.44g / cm 3 -1.50g / cm 3 , 1.41g / cm3 -1.50g / cm 3 or 1.40g / cm 3 -1.45g / cm 3 In some embodiments, the compaction density of the negative electrode film layer is 1.41 g / cm 3 , 1.42g / cm 3 , 1.44g / cm 3 , 1.45g / cm 3 , 1.46g / cm 3 , 1.47g / cm 3 , 1.48g / cm 3 , 1.49g / cm 3 , or a range between any two values. Adjusting the compaction density of the negative electrode film can further improve the energy density of the secondary battery, the diffusion channels for active ions in the secondary battery, and the mobility of active ions. It can also alleviate the rapid capacity decay caused by the precipitation of active ions on the negative electrode surface due to insufficient charge and discharge capacity in the late cycle, thereby improving the cycle performance and fast charging performance of the secondary battery.

[0048] The compacted density of the negative electrode film layer can be measured using methods known in the art. As an example, a negative electrode sheet test sample with an area of ​​S is weighed using an electronic balance, with the weight recorded as W1. The thickness of the negative electrode sheet is measured using a caliper to obtain the thickness T1 of the negative electrode sheet. The weighed electrode sheet film layer is then wiped off, and the weight of the negative electrode current collector is weighed as W2. The thickness of the negative electrode current collector is also measured using a caliper to obtain the thickness T2 of the negative electrode current collector. The compacted density of the negative electrode film layer is then calculated as PD = (W1-W2) / [(T1-T2)×S].

[0049] In some embodiments, the surface density of the negative electrode film layer is 7 mg / cm 2 -15mg / cm 2 , 8mg / cm 2 -15mg / cm 2 , 9mg / cm 2 -15mg / cm 2 , 7mg / cm 2 -13mg / cm 2 In some embodiments, the surface density of the negative electrode sheet is 13.0 mg / cm 2 , 12mg / cm 2 、11mg / cm 2 、10mg / cm 2 , 9mg / cm 2 , 8mg / cm 2 , 7mg / cm 2Adjusting the surface density of the negative electrode sheet helps to increase the energy density of the secondary battery and improve the cycle performance of the secondary battery.

[0050] In the present disclosure, the areal density of the negative electrode film layer can be measured using methods known in the art. As an example, a cold-pressed negative electrode sheet is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1. The negative electrode film layer of the weighed negative electrode sheet is then wiped off and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1.

[0051] In some embodiments, the volume distribution particle size D of the negative electrode active material is V 1 is 1.4 μm-3.0 μm, and can be 1.7 μm-2.7 μm, 1.8 μm-2.7 μm, 1.71 μm-2.58 μm. In some embodiments, the volume distribution particle size D of the negative electrode active material is V 1 is 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm or any range between two values. Small-particle negative electrode active materials have a large specific surface area and many surface active sites. They are more likely to form byproducts at the active sites during the cycle, resulting in increased active ion consumption and deterioration of cycle performance. Adjust the volume distribution particle size D of the negative electrode active material V 1. It helps to reduce the content of small particle negative electrode active materials, reduce the irreversible consumption of active ions, and improve the cycle performance of secondary batteries. At the same time, it adjusts the volume distribution particle size D V 1. It can further improve the diffusion channels of active ions in secondary batteries, improve the migration performance of active ions and prevent the rapid capacity decay caused by the precipitation of active ions in the late cycle.

[0052] In some embodiments, the volume distribution particle size D of the negative electrode active material is V 50 is 12 μm-18 μm, and can be 14 μm-16.5 μm, 12 μm-14 μm, 12.9 μm-14.5 μm. In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material is 12.9 μm, 13 μm, 15 μm, 16 μm, 17 μm or a range between any two values. Adjust the volume distribution particle size Dv50 of the negative electrode active material V 50 helps to improve the specific surface area of ​​the negative electrode active material and provide sufficient surface active sites, shorten the migration path of active ions, promote the insertion and extraction of active ions, and improve the conductivity of the negative electrode active material and the power performance of the secondary battery.

[0053] In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 1.3-1.8, and can be optionally 1.35-1.70 or 1.35-1.60. In some embodiments, the particle size distribution of the negative electrode active material is 1.4, 1.45, 1.5, 1.55, 1.65, 1.7, 1.75, or a range between any two values. Adjusting the particle size distribution of the negative electrode active material can control the content of small particles in the negative electrode active material and make the particle size distribution of the negative electrode active material more concentrated, which is beneficial to reducing the irreversible active ion consumption caused by excessive small particle content; it also helps to improve the conductive network between the negative electrode active material particles, which can improve the cycle performance and power performance of the secondary battery.

[0054] In the present disclosure, the volume distribution particle size D of the negative electrode active material is V 10. D V 50. D V 90 represents the particle size corresponding to the cumulative volume distribution percentages of the material reaching 10%, 50%, and 90%, respectively. These can be measured using instruments and methods known in the art. For example, a laser particle size analyzer can be used in accordance with GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0055] In some embodiments, the tap density of the negative electrode active material is 1.25 g / cm 3 -1.45g / cm 3 , optional 1.25g / cm 3 -1.35g / cm 3 , 1.29g / cm 3 -1.41g / cm 3 , 1.25g / cm 3 -1.41g / cm 3 In some embodiments, the tap density of the negative electrode active material is 1.28 g / cm 3 , 1.30g / cm 3 , 1.33g / cm 3 , 1.40g / cm 3 , 1.42g / cm 3Or the range between any two values. When the tap density of the negative electrode active material is within a suitable range, the smaller-sized negative electrode active material particles can be well dispersed between the larger-sized negative electrode active material particles, filling the gaps between the larger-sized negative electrode active material particles and increasing the contact sites between the negative electrode active material particles. This not only improves the conductivity of the negative electrode active material particles, but also facilitates the embedding and extraction of active ions in the negative electrode active material, reduces the precipitation of active ions and the black spot phenomenon of the negative electrode sheet, and thus improves the cycle performance of the secondary battery.

[0056] Herein, the tap density can be measured using methods known in the art. For example, it can be measured using a powder tap density tester (such as Dandong Better BT-301) with reference to GB / T 5162-2006.

[0057] In some embodiments, the specific surface area of ​​the negative electrode active material is 0.8 m 2 / g-1.4m 2 / g, optional 0.9m 2 / g-1.3m 2 / g, 0.95m 2 / g-1.1m 2 / g, 0.97m 2 / g-1.1m 2 In some embodiments, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g, 1.05m 2 / g, 1.1m 2 / g, 1.15m 2 / g, 1.2m 2 / g, 1.25m 2 / g, 1.30m 2 / g, 1.35m 2 / g or the range between any two values. Adjusting the specific surface area of ​​the negative electrode active material is beneficial to improving the degree of overlap between the negative electrode active material particles, increasing the contact sites and surface active sites of the negative electrode active material, improving the conductivity of the negative electrode active material and the transport performance of active ions, and improving the cycle performance and power performance of the secondary battery.

[0058] As used herein, the term "specific surface area" refers to the total surface area of ​​all particles per gram of material. The specific surface area of ​​graphite materials can be measured using instruments and methods known in the art. For example, the specific surface area of ​​the negative electrode active material can be measured using a surface area analyzer (Micromeritics TriStar 3020, USA) using the nitrogen adsorption / desorption method, referring to the specific surface area determination method in GB / T 19587-2017. The negative electrode active material is dried in a vacuum drying oven, placed in a sample tube, and measured using the analyzer.

[0059] In some embodiments, the negative electrode active material has a gram capacity of 335 mAh / g to 350 mAh / g. As used herein, the term "gram capacity" refers to the ratio of the amount of charge released by the graphite material to the mass of the graphite material. Generally speaking, a higher gram capacity is associated with a higher energy density of the secondary battery.

[0060] In some embodiments, the gram capacity of the negative electrode active material is 340.5 mAh / g-347.5 mAh / g, for example, 344.7 mAh / g, 345.5 mAh / g, 344.9 mAh / g, 345.9 mAh / g, which helps to improve the energy density of the secondary battery and enhance the cycle performance of the secondary battery.

[0061] The gram capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly stirred and mixed with the conductive agent carbon black and polyvinylidene fluoride (PVDF) in a suitable amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform anode slurry. The anode slurry is evenly coated on the surface of the anode current collector copper foil and dried and cold-pressed. An electrolyte is then injected using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator. The electrolyte formulation used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to form an organic solvent, and LiPF6 is dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the charge capacity was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite anode active material sample is the gram capacity of the graphite anode active material.

[0062] In the present disclosure, the negative electrode active material can be prepared using a method comprising the following steps:

[0063] Providing raw materials; processing the raw materials to obtain a precursor; graphitizing the precursor to obtain a graphitized product; and demagnetizing to obtain a negative electrode active material.

[0064] In some embodiments, the feedstock includes at least one of petroleum coke, needle coke, and pitch coke.

[0065] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0066] In this article, the term "needle coke" refers to coal tar pitch or petroleum pitch, which, after undergoing liquid phase carbonization to generate an anisotropic mesophase, can produce coke with a needle-like texture through processes such as high-temperature carbonization.

[0067] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0068] In some embodiments, the feedstock comprises petroleum coke.

[0069] Petroleum coke has excellent anisotropy, which is conducive to the preparation of low-graphitization and low-expansion graphite materials, which is conducive to the long cycle life of the battery. At the same time, petroleum coke has high compaction density and high gram capacity, which is conducive to improving the energy density of the battery. In addition, the source of petroleum coke is more extensive, which is conducive to industrial production.

[0070] The above-mentioned raw materials generally include at least one of mosaic, regional, and fibrous structures. Generally, based on the morphological characteristics and isochromatic zone size of the char material under a polarizing microscope, isochromatic zones with a size less than 30 μm are classified as mosaic; isochromatic zones with a size greater than 30 μm are classified as regional; and anisotropic banded isochromatic zones are classified as fibrous.

[0071] In some embodiments of the present disclosure, based on the total volume of the raw material structure, the volume proportion of the mosaic and regional structures in the raw material is greater than or equal to 60%, and can be optionally 65%-80%.

[0072] In the present disclosure, the volume proportion of mosaic and regional structures in the raw materials can be tested using methods known in the art. As an example, according to the provisions of GB 1997-89, the raw materials are crushed to 1mm and mixed, and 40g to 50g of them are separated. 4g to 5g of 0.07mm to 1.0mm grade samples are taken through a square hole sieve for slice making. According to the provisions of MT 116.1-86, powder coke and block coke films are prepared. The diameter of the powder coke film shall not be less than 22mm, and the volume occupied by the cement shall be less than 1 / 3. The sample is placed on a slide with clay, flattened, and then placed on the stage for focusing. After calibrating the microscope, the polarizer and analyzer are adjusted to make them orthogonal. Insert the azurite inspection plate (1λ) so that the field of view shows the interference color of first-order red. Determine the step length of the moving ruler to ensure that more than 400 effective measuring points are evenly distributed, with a point spacing of 0.3 to 0.5mm and a line spacing of 0.5 to 0.8mm. Starting from one end of the sample, determine the microstructure category under the intersection of the crosshairs, and divide the number of effective measuring points of the mosaic-type and regional-type optical tissues by the total number of statistical testing points as the volume proportion of the mosaic-type and regional-type structures in the raw material.

[0073] In some embodiments, crushing is the process of reducing the particle size of the raw material, and the raw material can be crushed by any mechanical device such as a crusher, a mechanical mill, etc.

[0074] Classification is the process of adjusting the particle size distribution of the raw materials to obtain a precursor that meets the required particle size. The particle size and distribution of the precursor can be controlled by adjusting the classification frequency and air flow rate. In some embodiments, the classification frequency is 40 Hz to 50 Hz, and the air damper opening is 20% to 70%.

[0075] In some embodiments, the D of the precursor V 50 Particle size is 10.0μm~25.0μm.

[0076] In some embodiments, the D of the precursor V The particle size is 10.0 μm, 13.0 μm, 15.0 μm, 17.0 μm, 20.0 μm, 23.0 μm, 25.0 μm or any range therebetween.

[0077] In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 1.05-1.75.

[0078] In some embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is 1.05, 1.15, 1.25, 1.35, 1.45, 1.55, 1.65, 1.75 or any range therebetween.

[0079] In some embodiments, the tap density of the precursor is 0.5 g / cm 3 ~2g / cm 3 .

[0080] In some embodiments, the tap density of the precursor is 0.5 g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 , 1.5g / cm 3 , 1.8g / cm 3 or any range of values ​​between them.

[0081] In some embodiments, a low-temperature carbonization treatment may be performed before the graphitization treatment. In some embodiments, the low-temperature carbonization temperature is 900° C. to 1300° C., and the low-temperature carbonization time is 24 hours to 240 hours.

[0082] In some embodiments, the temperature of the low-temperature carbonization may be selected to be 900° C., 1000° C., 1100° C., 1200° C., 1300° C., or any range therebetween.

[0083] In some embodiments, the low-temperature carbonization time may be 24 h, 50 h, 75 h, 100 h, 150 h, 200 h, 240 h, or any range therebetween.

[0084] In this article, the term "graphitization treatment" refers to the heat treatment process of carbon materials. Under the action of high temperature, the carbon material transforms from a two-dimensional carbon network structure to a three-dimensional ordered structure through "microcrystal" growth.

[0085] In some embodiments, the maximum power of the graphitization process is 70% to 90% of the rated power of the graphitization process equipment.

[0086] In some embodiments, the maximum power of the graphitization process is 70%, 75%, 80%, 85%, 90%, or any range therebetween, of the rated power of the graphitization process equipment. It is understood that the graphitization process equipment refers to any device capable of performing graphitization, including but not limited to Acheson furnaces, box furnaces, internal furnaces, continuous graphitization furnaces, electric calcining furnaces, medium-frequency furnaces, and tubular furnaces. The rated power of graphitization process equipment produced by different manufacturers may vary, and the rated power can be selected based on actual conditions.

[0087] In some embodiments, the graphitization treatment equipment is an inner string furnace, and the rated power of the inner string furnace is 25000-32000 W. The graphitization treatment time can be 10 hours to 30 hours, and optionally 15 hours to 25 hours.

[0088] In some embodiments, the graphitization treatment equipment is an Acheson furnace, and the rated power of the Acheson furnace is 28,000-30,000 W. The graphitization treatment time can be 30 hours to 50 hours, and optionally 40 hours to 50 hours.

[0089] The maximum power of the graphitization treatment adopted in the present disclosure needs to be lower than the rated power of the graphitization treatment equipment to achieve uniformity of the thermal field during the graphitization treatment process.

[0090] In some embodiments, the maximum power of the graphitization process may be 20,000W-25,000W.

[0091] In some embodiments, the maximum power of the graphitization process may be 20,000 W, 21,000 W, 22,000 W, 22,500 W, 23,000 W, 23,500 W, 24,000 W, 25,000 W, or any range therebetween.

[0092] By controlling the maximum power of the graphitization treatment, the degree of graphitization of the graphite material during the heat treatment process can be effectively controlled. While the internal area of ​​the graphite material particles is highly graphitized, a uniform disordered layer is formed on the surface of the body, which is beneficial to improving the cycle stability of the secondary battery.

[0093] In some embodiments, during the graphitization process, the maximum power is maintained at a constant power for a period of 10 hours to 50 hours. In some embodiments, the maximum power is maintained at a constant power for a period of 10 hours, 13 hours, 16 hours, 19 hours, 22 hours, 25 hours, 28 hours, 31 hours, 33 hours, 36 hours, 39 hours, 42 hours, 45 hours, 48 ​​hours, 50 hours, or any range therebetween.

[0094] In some embodiments, the temperature of the graphitization treatment is 2600°C to 3000°C.

[0095] In some embodiments, the temperature of the graphitization treatment is 2600° C., 2700° C., 2800° C., 2900° C., 3000° C., or any range therebetween.

[0096] The appropriate graphitization treatment temperature and the appropriate graphitization treatment time are not likely to cause excessive rearrangement of the precursor, resulting in a high specific surface area of ​​the graphite material after graphitization and deterioration of high-temperature performance; they can also effectively improve the graphitization degree of the graphite material, thereby facilitating the simultaneous improvement of the high-temperature storage and cycle life of the secondary battery.

[0097] [Negative electrode]

[0098] As an example of a negative electrode sheet, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0099] In some embodiments, the negative electrode film layer includes a graphite material prepared by the method described in the first aspect of the present disclosure, thereby enabling the secondary battery to have both good cycle performance and kinetic performance.

[0100] In some embodiments, the negative electrode active material comprises one of artificial graphite, natural graphite, soft carbon, hard carbon, and mesocarbon microbeads. In some embodiments, the negative electrode active material comprises artificial graphite.

[0101] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned graphite materials. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0102] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0104] In some embodiments, the negative electrode plate further includes a conductive agent, which includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the conductive agent comprises carbon black. In some embodiments, the conductive agent comprises carbon nanotubes. In some embodiments, the conductive agent comprises carbon black and carbon nanotubes. These conductive agents are widely available and have excellent conductivity, which helps control the production cost of secondary batteries and improve the conductivity of the negative electrode.

[0106] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0107] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0108] [Positive electrode]

[0109] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0110] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0111] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0113] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0114] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0116] [Electrolytes]

[0117] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0118] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0119] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0120] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0121] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0122] [Isolation film]

[0123] In some embodiments, the secondary battery further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0124] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0125] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0126] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0127] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] In addition, the secondary battery, battery module, battery pack, and electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0129] In one embodiment of the present disclosure, a secondary battery is provided.

[0130] The present disclosure has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example.

[0131] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0132] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0133] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0134] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0135] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0136] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0137] In addition, the present disclosure further provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present disclosure. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but is not limited thereto.

[0138] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0139] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0140] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0141] Example

[0142] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0143] 1. Test Method

[0144] 1. Particle size test of powder

[0145] Determination method: Refer to GB / T 19077-2016 particle size distribution laser diffraction method, use the Master Size 3000 laser particle size analyzer of Malvern Instruments Co., Ltd., UK, to obtain the volume distribution particle size D V 10. D V 50. D V 90 and D V 1.

[0146] 2. Powder conductivity test of powder

[0147] Under 25℃, the FT-8100A four-probe powder test platform was used to prepare the sample according to the four-probe method in GBT 30835-2014 on the determination of powder conductivity. 1g of the test sample powder was weighed and placed in a cylindrical metal mold with a height of 25mm and a diameter of 12mm. The lower electrode of the mold was pressed, and when the upper electrode was pressed to the table, the sample began to be compressed. The pressure was maintained for 30s so that the sample thickness was maintained at 0.147±0.002. Then, the carbon material was measured by the four-probe powder method at 1.50g / cm 3 Powder conductivity under powder compaction.

[0148] 3. Specific surface area test of powder

[0149] The specific surface area of ​​the negative electrode active material was measured by the nitrogen adsorption / desorption method using a specific surface area analyzer (Micromeritics TriStar 3020, USA) with reference to the specific surface area determination method in GB / T 19587-2017: the negative electrode active material was dried in a vacuum drying oven and placed in a sample tube, which was then measured in the analyzer.

[0150] 4. Tap density test of powder

[0151] With reference to GB / T 5162-2006 and GB / T 24533-2009, a powder tap density tester (such as Dandong Better BT-301) was used to measure the tap density with the following measurement parameters: vibration frequency 250±15 times / min, amplitude 3±0.2mm, vibration number 5000 times, and graduated cylinder 25mL.

[0152] 5. Negative electrode active material gram capacity test

[0153] The gram capacity can be measured using any method known in the art. For example, a graphite anode active material sample can be thoroughly stirred and mixed with the conductive agent carbon black and polyvinylidene fluoride (PVDF) in a suitable amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform anode slurry. The anode slurry is evenly coated on the surface of the anode current collector copper foil and dried and cold-pressed. An electrolyte is then injected using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator. The electrolyte formulation used is as follows: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to form an organic solvent, and LiPF6 is dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells are assembled in an argon-protected glove box. At 25°C, the prepared button cell was first discharged at a constant current of 0.05C to 0.005V, then discharged at a constant current of 10μA to 0.005V. The cell was allowed to rest for 5 minutes, and the first-cycle discharge capacity was recorded. The cell was then charged at a constant current of 0.1C to 2.0V, and the charge capacity was recorded. The ratio of the charge capacity of the button cell to the mass of the graphite anode active material sample is the gram capacity of the graphite anode active material.

[0154] 6. Compaction density test of negative electrode film layer

[0155] Use an electronic balance to weigh a negative electrode sheet sample with an area of ​​S, denoted as W1. Use a caliper to measure the thickness of the negative electrode sheet, T1. Then, wipe off the weighed electrode film and weigh the negative electrode current collector, denoted as W2. Use a caliper to measure the thickness of the negative electrode current collector, T2. The compacted density of the negative electrode film layer, PD, is calculated as (W1-W2) / [(T1-T2)×S].

[0156] 7. High temperature cycle performance test

[0157] At 60°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 3.65V. They were then charged at a constant voltage of 3.65V to a current ≤ 0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the discharge capacity (C1) of the first cycle was recorded. This charge and discharge cycle was repeated until the battery capacity decayed to 80% of the initial capacity (C1). The test was then stopped, and the number of test cycles was recorded.

[0158] 8. Black spot test

[0159] At 25° C., the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 3.65V, and then disassembled in a dry room to observe whether there were black spots on the surface of the negative electrode.

[0160] (1) The total area of ​​black spots / total area of ​​the negative electrode is ≤1%, and the area of ​​black spots in a single electrode is ≤8% of the area of ​​a single electrode.

[0161] (2) 1% < total area of ​​black spots / total area of ​​negative electrode ≤ 3%, or 8% < area of ​​black spots in a single electrode / area of ​​a single electrode ≤ 15% is defined as secondary black spots;

[0162] (3) The total area of ​​black spots / total area of ​​the negative electrode is greater than 3%, or the area of ​​black spots in a single electrode / area of ​​a single electrode is greater than 15%, which is defined as level 3 black spots.

[0163] 9. Dynamic performance test

[0164] At 25°C, the secondary battery was charged to 3.65V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.50V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0165] Then the secondary battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 in sequence to a negative electrode cutoff potential of 3.5V or 0V (whichever is reached first). After each charging is completed, it is necessary to discharge it to 2.5V at 1C0. The negative electrode potential corresponding to charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge) at different charging rates is recorded, and the charging rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charging rate is the charging window under the SOC state, which is recorded as C 10％SOC 、C 20％SOC 、C 30％SOC 、C 40％SOC 、C 50％SOC 、C 60％SOC 、C 70％SOC 、C 80％SOC According to the formula (60 / C 10％SOC +60 / C 20％SOC +60 / C 30％SOC +60 / C 40％SOC +60 / C 50％SOC +60 / C 60％SOC +60 / C 70％SOC +60 / C 80％SOC ) × 10% to calculate the charging time T for the secondary battery from 10% SOC to 80% SOC (assuming no lithium deposition in the secondary battery), in minutes. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0166] 2. Preparation Method of Negative Electrode Active Materials

[0167] 1. Preparation of negative electrode active material H1

[0168] Petroleum coke, containing 67% mosaic and regional structures, was coarsely crushed, sieved, shaped, and graded. During the grading process, the classifier's induced draft frequency was controlled to remove fines (powder with a volume distribution particle size Dv50 of 3-7 μm), representing 25% of the total mass of the petroleum coke feedstock. This yielded a precursor with a volume distribution particle size Dv50 of 15.2 μm and a particle size distribution ratio (Dv90-Dv10) / Dv50 of 1.45.

[0169] The precursor was graphitized in an Acheson furnace at a temperature of 2800°C and a maximum power of 21000W. After maintaining the maximum power constant for 48 hours, the surface temperature of the graphite crucible of the Acheson furnace was cooled to 250°C to obtain an intermediate product.

[0170] The obtained intermediate product was sieved and demagnetized to obtain the negative electrode active material graphite H1.

[0171] 2. Preparation of negative electrode active material H2

[0172] The preparation process of negative electrode active material H2 is similar to that of H1, with the following differences:

[0173] The same raw materials are used, and after crushing, shaping and grading, without removing fine powder during the grading process, the negative electrode active material H2 is obtained after the same graphitization and screening demagnetization process.

[0174] 3. Preparation of negative electrode active material H3

[0175] The preparation process of negative electrode active material H3 is similar to that of H1, with the following differences:

[0176] During the classification process, fine powder accounting for 16% of the total mass of the petroleum coke raw material is removed, and then the negative electrode active material H3 is obtained through the same graphitization and screening demagnetization steps.

[0177] 4. Preparation of negative electrode active material H4

[0178] The preparation process of negative electrode active material H4 is similar to that of H1, with the following differences:

[0179] During the classification process, fine powder accounting for 20% of the total mass of the petroleum coke raw material is removed, and then the active material H4 is obtained through the same graphitization and screening demagnetization steps.

[0180] 5. Preparation of negative electrode active material H5

[0181] The preparation process of negative electrode active material H5 is similar to that of H1, with the following differences:

[0182] During the classification process, fine powder accounting for 35% of the total mass of the petroleum coke raw material was removed, and then the active material H5 was obtained through the same graphitization and screening demagnetization steps.

[0183] The negative electrode active materials H1-H5 were tested using the above method, and the parameter test results are shown in Table 1:

[0184] Table 1

[0185] 3. Preparation of Secondary Batteries

[0186] Example 1

[0187] 1) Preparation of negative electrode sheet

[0188] The prepared negative electrode active material, conductive agent carbon black Super P, thickener sodium carboxymethyl cellulose, and binder styrene butadiene rubber were mixed in a mass ratio of 96:1:1.2:1.8, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system became uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained after drying, cold pressing, and slitting. The compacted density of the negative electrode sheet was 1.50g / cm 3 , with a surface density of 9.50 mg / cm 2 .

[0189] 2) Preparation of positive electrode sheet

[0190] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone was added. The mixture was stirred in a vacuum mixer until the system was uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained after drying, cold pressing, and slitting. The compacted density of the positive electrode sheet is 2.5g / cm 3 , with a surface density of 19.5 mg / cm 2 .

[0191] 3) Preparation of electrolyte

[0192] In an argon atmosphere glove box with a water content of <10 ppm, 8% lithium hexafluorophosphate (LiPF6), 2% vinylene carbonate (VC), 30% ethylene carbonate (EC), 30% ethyl methyl carbonate (EMC), and the remainder is supplemented with diethyl carbonate (DEC) to 100%, and mixed to obtain the corresponding electrolyte.

[0193] 4) Isolation film

[0194] A polypropylene film is selected as the isolation film.

[0195] 5) Preparation of secondary batteries

[0196] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0197] Examples 2 to 6 and Comparative Examples 1 to 4

[0198] The preparation methods of the secondary batteries of Examples 2 to 6 and Comparative Examples 1 to 4 were similar to the preparation method of the secondary battery of Example 1, except that the negative electrode active materials and secondary battery preparation parameters were adjusted. The test results of the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 4 using the above method are shown in Table 2 below:

[0199] Table 2

[0200] As can be seen from Examples 1 to 6, the powder conductivity σ of the negative electrode active material is greater than or equal to 80 S / cm and less than or equal to 106 S / cm, and the compaction density of the negative electrode film layer is 1.35 g / cm 3 -1.50g / cm 3 The black spot phenomenon is effectively improved, and the secondary battery has both good cycle times and charging time.

[0201] As shown in Examples 1-2 and Comparative Example 1, when the compaction density of the negative electrode film layer is less than 1.35 g / cm³, the electrical contact between the negative electrode active material particles deteriorates and the energy density of the secondary battery is low, resulting in a decrease in the number of cycles of the secondary battery and an increase in the black spot phenomenon. Figure 7 shows the cycle curves of Example 2 and Comparative Example 1, showing that the cycle performance of the secondary battery of Example 2 is significantly better than that of Comparative Example 1.

[0202] It can be seen from Examples 1-2 and Comparative Example 2 that the compaction density of the negative electrode film layer is higher than 1.50 g / cm 3 When the density is increased, the electrical contact between the active materials of the negative electrode film layer is improved, which can improve the black spot phenomenon; however, the increase in compaction density leads to a significant deterioration in kinetics and a significant extension of the charging time, which in turn leads to rapid decay in the late cycle and reduces the cycle performance of the secondary battery.

[0203] It can be seen from Examples 1 to 6 and Comparative Example 3 that the negative electrode active material in Comparative Example 3 has a relatively high fine powder content, resulting in its powder conductivity σ being less than or equal to 80 S / cm; although the fine powder in the active material can improve the electrical contact between the active materials, excessive fine powder will clog the pores, significantly prolonging the charging time, and further leading to rapid decay in the late cycle, affecting the cycle performance of the secondary battery.

[0204] It can be seen from Examples 1 to 6 and Comparative Example 4 that the fine powder content in the negative electrode active material in Comparative Example 4 is relatively low, resulting in its powder conductivity σ being greater than 106 S / cm, the electrical contact and conductive network between the negative electrode active materials being deteriorated, the irreversible consumption of active ions in the secondary battery being increased, affecting the charge and discharge performance and capacity of the secondary battery, resulting in a significant decrease in the number of cycles and the generation of severe black spot phenomenon.

[0205] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the current collector and comprising a negative electrode active material, wherein: The negative electrode active material has a compaction density of 1.5 g / cm 3 The powder conductivity σ measured under the test conditions is 80S / cm-106S / cm; and the compaction density of the negative electrode film layer is 1.35g / cm 3 -1.50g / cm 3 .

2. The secondary battery according to claim 1, wherein The powder conductivity σ is 83S / cm-104S / cm.

3. The secondary battery according to claim 1 or 2, wherein: The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.50g / cm 3 .

4. The secondary battery according to any one of claims 1 to 3, wherein The negative electrode active material satisfies at least one of the following conditions: (1) Volume distribution particle size D of the negative electrode active material V 1 is 1.4μm-3.0μm, optional is 1.7μm-2.7μm; (2) Volume distribution particle size D of the negative electrode active material V 50 is 12μm-18μm, optional is 12.9μm-14.5μm; (3) The particle size distribution of the negative electrode active material (D V 90-D V 10) / D V 50 is 1.3-1.8, optional is 1.35-1.

70.

5. The secondary battery according to any one of claims 1 to 4, wherein The tap density of the negative electrode active material is 1.25 g / cm 3 -1.45g / cm 3 , optional 1.29g / cm 3 -1.41g / cm 3 .

6. The secondary battery according to any one of claims 1 to 5, wherein The specific surface area of ​​the negative electrode active material is 0.8 m 2 / g-1.4m 2 / g, optional 0.9m 2 / g-1.3m 2 / g.

7. The secondary battery according to any one of claims 1 to 6, wherein The gram capacity of the negative electrode active material is 335 mAh / g-350 mAh / g, and can be optionally 340.5 mAh / g-347.5 mAh / g.

8. The secondary battery according to any one of claims 1 to 7, wherein The surface density of the negative electrode plate is 7 mg / cm 2 -15mg / cm 2 .

9. The secondary battery according to any one of claims 1 to 8, wherein The negative electrode active material includes artificial graphite.

10. An electrical device, wherein: A secondary battery selected from any one of claims 1 to 9.

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