Negative pole piece, secondary battery and electric device

Abstract

The invention discloses a negative pole piece, a secondary battery and a power utilization device, the negative pole piece comprises a negative current collector, a first negative active material layer and a second negative active material layer, and the first negative active material layer and the second negative active material layer are arranged in the thickness direction of the negative current collector. The first negative electrode active material layer is positioned between the negative electrode current collector and the second negative electrode active material layer; the first negative electrode active material layer comprises graphite, the graphite is of a porous structure, the graphite is provided with an inner area and an outer layer area arranged on the periphery of the inner area, and at least part of pores of the outer layer area are filled with a graphitized filling agent; and the second negative electrode active material layer comprises regenerated graphite. Through the cooperation of the first negative electrode active material layer and the second negative electrode active material layer, the consumption of active lithium can be reduced, the storage performance of the battery is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] Graphite is one of the main negative electrode active materials of batteries. Among them, recycled graphite is produced by recycling and regenerating waste graphite negative electrodes, which is beneficial to saving resources and protecting the environment. However, during use, recycled graphite has poor storage performance, which will reduce the storage performance of the battery and affect the battery life. Summary of the Invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate that can improve the storage performance of the battery and extend the service life of the battery.

[0004] In order to achieve the above-mentioned objectives, embodiments of the present application provide a negative electrode plate, a secondary battery, and an electrical device.

[0005] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer, wherein in a thickness direction of the negative electrode current collector, the first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer;

[0006] The first negative electrode active material layer includes graphite, the graphite has a porous structure, the graphite has an inner region and an outer region disposed around the inner region, and at least part of the pores of the outer region are filled with a graphitized filler;

[0007] The second negative electrode active material layer includes recycled graphite.

[0008] Therefore, in the technical solution of the embodiment of the present application, a first negative electrode active material layer is arranged between the negative electrode current collector and the second negative electrode active material layer containing recycled graphite, and the first negative electrode active material layer includes graphite. The graphite has a porous structure, and at least part of the pores in the outer layer are filled with graphitized fillers. The outer layer of the graphite has fewer pores, a dense structure, and fewer surface defects, which can effectively reduce the side reactions between the electrolyte and the surface of the negative electrode active material, reduce the consumption of active lithium, and thereby improve the storage performance of the battery and extend the service life of the battery; at the same time, the graphite has a high degree of graphitization, which can increase the energy density of the battery; in addition, compared with recycled graphite, graphite has a higher compaction density. The first negative electrode active material layer containing graphite is located between the second negative electrode active material layer and the negative electrode current collector, which helps to reasonably distribute the gaps in the entire electrode, enhance the infiltration effect of the electrolyte, improve the dynamics of the battery, and ensure the cycle performance of the battery.

[0009] In any embodiment, the filler includes a graphitizable high molecular polymer, which can fill the pores of the graphite and achieve graphitization, thereby making the outer layer of the graphite denser and reducing surface defects.

[0010] In any embodiment, the filler includes at least one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile. When the filler includes at least one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile, the filling effect can be adjusted by adjusting the type of filler.

[0011] In any embodiment, the outer layer region is the region of the graphite from the surface to 2.5 μm, which can improve the storage performance of the battery and extend the service life of the battery.

[0012] In any embodiment, the total pore area of ​​the inner region is S1, and the total pore area of ​​the outer region is S2, where S1>S2. A portion of the pores in the outer region are filled with a graphitized filler, so that the total pore area of ​​the inner region is larger than the total pore area of ​​the outer region. This can improve the storage performance of the battery and extend the battery life. Furthermore, the S1 / S2 ratio of graphite is low, making graphite more readily available.

[0013] In any embodiment, 1.5≤S1 / S2≤500. When 1.5≤S1 / S2≤500, the storage performance of the battery can be improved and the battery life can be extended. Optionally, 1.5≤S1 / S2≤45, a more suitable S1 / S2 range, is conducive to improving the storage performance of the battery and extending the battery life.

[0014] In any embodiment, the graphitization degree of the graphite is greater than that of the regenerated graphite. When the graphitization degree of the graphite is greater than that of the regenerated graphite, the energy density of the battery can be increased.

[0015] In any embodiment, the graphite has a degree of graphitization greater than or equal to 95%. When the graphitization degree of graphite is greater than or equal to 95%, the energy density of the battery can be improved; optionally, the graphitization degree of graphite is 95.5% to 98.0%, which is a more suitable range of the graphitization degree of graphite, which is conducive to improving the energy density of the battery; and / or,

[0016] The graphitization degree of the regenerated graphite is less than or equal to 94%. When the graphitization degree of the regenerated graphite is less than or equal to 94%, the energy density of the battery can be taken into account; optionally, the graphitization degree of the regenerated graphite is 91% to 94%, which is a more suitable range of graphitization degree of the regenerated graphite, which is conducive to improving the energy density of the battery.

[0017] In any embodiment, the average particle size D of the graphite v50 is greater than or equal to 16μm. When the average particle size D of graphite v 50 is greater than or equal to 16 μm, the energy density and storage performance of the battery can be improved; Optionally, the average particle size D of the graphite v 50 is 16.5μm~20.0μm, the more suitable average particle size D of graphite v 50 range, which is beneficial to improving the energy density and storage performance of the battery.

[0018] In any embodiment, the graphite has a gram capacity of greater than or equal to 360 mAh / g. When the graphite has a gram capacity of greater than or equal to 360 mAh / g, the energy density of the battery can be increased. Optionally, the graphite has a gram capacity of 363 mAh / g to 370 mAh / g, which is a more suitable range for graphite gram capacity, and is conducive to improving the energy density of the battery.

[0019] In any embodiment, the compacted density of the graphite under a pressure of 50,000 N is less than or equal to 2.08 g / cm 3 When the compaction density of graphite under a pressure of 50,000 N is less than or equal to 2.08 / cm 3 Optionally, the compaction density of the graphite under a pressure of 50000N is 1.90g / cm 3 ~2.05g / cm 3 The more suitable compaction density range of graphite under a pressure of 50,000N is beneficial to improving the energy density of the battery.

[0020] In any embodiment, the initial weight loss temperature of the regenerated graphite is 610°C to 715°C. When the initial weight loss temperature of the regenerated graphite is 610°C to 715°C, the regenerated graphite has a relatively stable structure, which can improve the storage performance of the battery. Optionally, the initial weight loss temperature of the regenerated graphite is 620°C to 710°C. This more suitable initial weight loss temperature range of the regenerated graphite is conducive to improving the storage performance of the battery.

[0021] In any embodiment, the powder resistivity of the regenerated graphite is between 0.005Ω / cm and 0.025Ω / cm. When the powder resistivity of the regenerated graphite is between 0.005Ω / cm and 0.025Ω / cm, it is beneficial to improve the electrical contact between the particles in the negative electrode sheet, thereby improving the dynamic performance of the battery. Optionally, the powder resistivity of the regenerated graphite is between 0.005Ω / cm and 0.020Ω / cm, which is a more suitable range of powder resistivity for the regenerated graphite, and is beneficial to improving the dynamic performance of the battery.

[0022] In any embodiment, the average particle size D of the regenerated graphite v 50 is greater than or equal to 12μm. When the average particle size D of the regenerated graphitev 50 is greater than or equal to 12 μm, the energy density and storage performance of the battery can be improved; Optionally, the average particle size D of the regenerated graphite v 50 is 12μm~25μm, the average particle size D of the more suitable regenerated graphite v 50 range, which is beneficial to improving the energy density and storage performance of the battery.

[0023] In any embodiment, the gram capacity of the regenerated graphite is greater than or equal to 340 mAh / g. When the gram capacity of the regenerated graphite is greater than or equal to 340 mAh / g, the energy density of the battery can be improved. Optionally, the gram capacity of the regenerated graphite is within a range of 340 mAh / g to 353 mAh / g, which is a more suitable range for the gram capacity of the regenerated graphite and is conducive to improving the energy density of the battery.

[0024] In any embodiment, the surface of the regenerated graphite has conductive carbon, which can improve the cycle performance of the battery.

[0025] In any embodiment, the regenerated graphite has a carbon coating layer. When the regenerated graphite has a carbon coating layer, the energy density, storage performance, and kinetic performance of the battery can be improved.

[0026] In any embodiment, the compaction density of the negative electrode sheet is greater than or equal to 1.50 g / cm 3 When the compaction density of the negative electrode is greater than or equal to 1.50g / cm 3 When the negative electrode is 1.50 g / cm2, the energy density of the battery can be increased; optionally, the compaction density of the negative electrode is 1.50 g / cm2. 3 ~1.75g / cm 3 , a more suitable compaction density range of the negative electrode sheet is beneficial to improving the energy density of the battery.

[0027] In any embodiment, the surface density of the negative electrode sheet is greater than or equal to 6.0 mg / cm 2 When the surface density of the negative electrode is greater than or equal to 6.0 mg / cm 2 When the energy density of the battery is increased, the surface density of the negative electrode sheet can be increased. 2 ~13.0mg / cm 2 , a more suitable surface density range of the negative electrode sheet is beneficial to improving the energy density of the battery.

[0028] In any embodiment, the method for preparing graphite comprises the following steps:

[0029] The natural spherical graphite is mixed with fillers and treated at low temperature to obtain an intermediate product;

[0030] The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite.

[0031] Natural spherical graphite has a porous structure. By mixing natural spherical graphite with a filler, and sequentially subjecting the mixture to low-temperature treatment and high-temperature graphitization treatment, at least part of the pore structure of the outer layer of the natural spherical graphite is filled with the graphitized filler, thereby obtaining graphite that can be used for the first negative electrode active material layer.

[0032] In any embodiment, in the step of mixing natural spherical graphite with a filler and treating at low temperature to obtain an intermediate product:

[0033] The filler includes at least one of petroleum asphalt, high molecular polymer and resin. When the filler includes at least one of petroleum asphalt, coal-based asphalt and polyacrylonitrile, the filling effect can be adjusted by adjusting the type of filler; and / or,

[0034] The mass ratio of the natural spherical graphite to the filler is 100:(15-40). When the mass ratio of the natural spherical graphite to the filler is 100:(15-40), the filling effect can be adjusted by adjusting the mass ratio of the natural spherical graphite to the filler; and / or,

[0035] The temperature of the low temperature treatment is 300° C. to 1000° C. When the temperature of the low temperature treatment is 300° C. to 1000° C., the filling of the filler can be promoted to achieve a filling effect; and / or,

[0036] The low temperature treatment time is 1 hour to 5 hours. When the low temperature treatment time is 1 hour to 5 hours, the filling of the filler can be promoted to achieve the filling effect.

[0037] In any embodiment, in the step of subjecting the intermediate product to high-temperature graphitization to obtain the graphite:

[0038] The temperature of the high-temperature graphitization treatment is 2000° C. to 2800° C. When the temperature of the high-temperature graphitization treatment is 2000° C. to 2800° C., the graphitization effect can be achieved; and / or,

[0039] The high-temperature graphitization treatment time is 2 hours to 6 hours. When the high-temperature graphitization treatment time is 2 hours to 6 hours, the graphitization effect can be achieved.

[0040] In a second aspect, an embodiment of the present application provides a secondary battery comprising the negative electrode sheet of the first aspect of the present application.

[0041] In a third aspect, an embodiment of the present application provides an electrical device comprising the secondary battery according to the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1Schematic diagram of a secondary battery according to one embodiment of the present application.

[0043] Figure 2 yes Figure 1 FIG. 1 is an exploded view of a secondary battery according to an embodiment of the present application.

[0044] Figure 3 Schematic diagram of a battery module according to one embodiment of the present application.

[0045] Figure 4 Schematic diagram of a battery pack according to one embodiment of the present application.

[0046] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0047] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0048] Description of reference numerals:

[0049] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0050] The following specifically discloses the embodiments of the positive electrode material and its preparation method, positive electrode sheet, battery and electrical device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure 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 application and are not intended to limit the subject matter described in the claims.

[0051] " range " disclosed in the present application 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 the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, 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 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, 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.

[0052] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0053] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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.

[0055] Graphite is one of the main negative electrode active materials of batteries. Among them, recycled graphite is produced by recycling and regenerating waste graphite negative electrodes, which is beneficial to saving resources and protecting the environment. However, during use, recycled graphite has poor storage performance, which will reduce the storage performance of the battery and affect the battery life.

[0056] Based on this, in the first aspect, the present application proposes a negative electrode plate that can improve the storage performance of the battery and extend the service life of the battery.

[0057] Surprisingly, in a first aspect, embodiments of the present application provide a negative electrode sheet, comprising a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer, wherein in the thickness direction of the negative electrode current collector, the first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer;

[0058] The first negative electrode active material layer includes graphite, the graphite has a porous structure, the graphite has an inner region and an outer region disposed around the inner region, and at least part of the pores of the outer region are filled with a graphitized filler;

[0059] The second negative electrode active material layer includes recycled graphite.

[0060] In the technical solution of the embodiment of the present application, a first negative electrode active material layer is arranged between the negative electrode current collector and the second negative electrode active material layer containing recycled graphite. The first negative electrode active material layer includes graphite. The graphite has a porous structure. At least part of the pores in the outer layer are filled with graphitized fillers. The outer layer of the graphite has fewer pores, a dense structure, and fewer surface defects, which can effectively reduce the side reactions between the electrolyte and the surface of the negative electrode active material, reduce the consumption of active lithium, and thus improve the storage performance of the battery and extend the service life of the battery; at the same time, the graphite has a high degree of graphitization, which can increase the energy density of the battery; in addition, compared with recycled graphite, graphite has a higher compaction density. The first negative electrode active material layer containing graphite is located between the second negative electrode active material layer and the negative electrode current collector, which helps to reasonably distribute the gaps in the entire electrode, enhance the infiltration effect of the electrolyte, improve the dynamics of the battery, and ensure the cycle performance of the battery.

[0061] In any embodiment, the filler includes a graphitizable high molecular polymer, which can fill the pores of the graphite and achieve graphitization, thereby making the outer layer of the graphite denser and reducing surface defects.

[0062] In any embodiment, the filler includes at least one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile. When the filler includes at least one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile, the filling effect can be adjusted by adjusting the type of filler; the filler can be any one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile, a combination of any two, or a combination of all three.

[0063] In any embodiment, the outer layer region is the region of the graphite from the surface to 2.5 μm, which can improve the storage performance of the battery and extend the service life of the battery.

[0064] In any embodiment, the total pore area of ​​the inner region is S1, the total pore area of ​​the outer region is S2, and S1>S2. A portion of the pores in the outer region are filled with a graphitized filler to increase the total pore area of ​​the inner region to a greater extent than that of the outer region, thereby improving the storage performance of the battery and extending the battery life.

[0065] In any embodiment, 1.5≤S1 / S2≤500. When 1.5≤S1 / S2≤500, the storage performance of the battery can be improved and the service life of the battery can be extended. The value of S1 / S2 can be 1.5, 3, 4.5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 150, 200, 250, 300, 350, 400, 450 or 500. Optionally, 1.5≤S1 / S2≤45, a more suitable S1 / S2 range, is conducive to improving the storage performance of the battery and extending the service life of the battery. At the same time, the S1 / S2 value of graphite is lower, and graphite is more readily available.

[0066] It should be noted that the total pore area (S1) of the inner region is the total area of ​​the pores in the corresponding part of the inner region on the cross section of the graphite, and the total pore area (S2) of the outer region is the total area of ​​the pores in the corresponding part of the outer region on the cross section of the graphite; the above-mentioned total pore area can be determined by the following method: first, a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher of JEOL Company of Japan) can be used to prepare a cross section of the graphite; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope of ZEISS Company of Germany) is used to scan the cross section of the graphite; finally, the pore area of ​​any one hole in the cross section of the graphite is calculated by image processing software (such as AVIZO) to obtain the total pore area (S1) of the inner region and the total pore area (S2) of the outer region, and the ratio of the total pore area of ​​the inner region to the total pore area of ​​the outer region (the value of S1 / S2) can be obtained. Exemplarily, a binder can be mixed evenly with graphite powder and then coated on copper foil to prepare a sample, or samples can be obtained from different areas of the negative electrode sheet in a secondary battery, and at least 5 positions (such as 5, 10, 15, or more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and cross sections of at least 10 particles (such as 10, 20, 50, or more particles) are randomly selected from the scanning electron microscope image of each cross section. According to the above definition, image processing software is used to obtain and calculate the total pore area S1' of the inner region and the total pore area S2' of the outer region of each particle cross section, and thereby obtain the S1' / S2' value of each particle cross section, and then calculate the arithmetic mean of S1' / S2' of all measured particle cross sections as the S1 / S2 value of the graphite.

[0067] In any embodiment, the graphitization degree of the graphite is greater than that of the regenerated graphite. When the graphitization degree of the graphite is greater than that of the regenerated graphite, the energy density of the battery can be increased.

[0068] In any embodiment, the graphitization degree of the graphite is greater than or equal to 95%. When the graphitization degree of the graphite is greater than or equal to 95%, the energy density of the battery can be improved. The graphitization degree of the graphite can be 95%, 95.5%, 96%, 96.8%, 97.3%, 98% or 98.5%. Optionally, the graphitization degree of the graphite is 95.5% to 98.0%. The more suitable range of the graphitization degree of the graphite is conducive to improving the energy density of the battery; and / or,

[0069] The graphitization degree of the regenerated graphite is less than or equal to 94%. When the graphitization degree of the regenerated graphite is less than or equal to 94%, the energy density of the battery can be taken into consideration; the graphitization degree of the regenerated graphite can be 90%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5% or 94%. Optionally, the graphitization degree of the regenerated graphite is 91% to 94%, which is a more suitable range of graphitization degree of the regenerated graphite, which is conducive to improving the energy density of the battery.

[0070] In any embodiment, the average particle size D of the graphite v 50 is greater than or equal to 16μm. When the average particle size D of graphite v When the average particle size of graphite is greater than or equal to 16 μm, the energy density and storage performance of the battery can be improved; the average particle size of graphite D v 50 can be 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm or 22 μm; optionally, the average particle size Dv50 of the graphite is 16.5 μm to 20.0 μm, and the more suitable average particle size Dv50 of the graphite is 16.5 μm to 20.0 μm. v 50 range, which is beneficial to improving the energy density and storage performance of the battery.

[0071] In any embodiment, the gram capacity of the graphite is greater than or equal to 360 mAh / g. When the gram capacity of the graphite is greater than or equal to 360 mAh / g, the energy density of the battery can be increased. The gram capacity of the graphite can be 360 ​​mAh / g, 363 mAh / g, 366 mAh / g, 370 mAh / g, or 373 mAh / g. Optionally, the gram capacity of the graphite is 363 mAh / g to 370 mAh / g, which is a more suitable range of gram capacity of the graphite, which is conducive to improving the energy density of the battery.

[0072] In any embodiment, the compacted density of the graphite under a pressure of 50,000 N is less than or equal to 2.08 g / cm3 When the compaction density of graphite under a pressure of 50,000 N is less than or equal to 2.08 / cm 3 The energy density of the battery can be increased. The compaction density of graphite under a pressure of 50,000 N can be 1.87 g / cm 3 、1.90g / cm 3 、1.93g / cm 3 , 1.97g / cm 3 , 2.01g / cm 3 , 2.05g / cm 3 or 2.08g / cm 3 Optionally, the compacted density of the graphite under a pressure of 5000kg is 1.90g / cm 3 ~2.05g / cm 3 The more suitable compaction density range of graphite under a pressure of 50,000N is beneficial to improving the energy density of the battery.

[0073] In any embodiment, the initial weight loss temperature of the regenerated graphite is 610°C to 715°C. When the initial weight loss temperature of the regenerated graphite is 610°C to 715°C, the regenerated graphite has a relatively stable structure, which can improve the storage performance of the battery. The initial weight loss temperature of the regenerated graphite can be 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C or 715°C; optionally, the initial weight loss temperature of the regenerated graphite is 620°C to 710°C. The more suitable initial weight loss temperature range of the regenerated graphite is conducive to improving the storage performance of the battery.

[0074] In any embodiment, the powder resistivity of the regenerated graphite is 0.005Ω / cm to 0.025Ω / cm. When the powder resistivity of the regenerated graphite is 0.005Ω / cm to 0.025Ω / cm, it is beneficial to improve the electrical contact between the particles in the negative electrode plate, thereby improving the dynamic performance of the battery. The powder resistivity of the regenerated graphite can be 0.005Ω / cm, 0.08Ω / cm, 0.012Ω / cm, 0.016Ω / cm, 0.020Ω / cm, or 0.025Ω / cm. Optionally, the powder resistivity of the regenerated graphite is 0.005Ω / cm to 0.020Ω / cm, which is a more suitable range of powder resistivity of the regenerated graphite, and is beneficial to improving the dynamic performance of the battery.

[0075] In any embodiment, the average particle size D of the regenerated graphite v 50 is greater than or equal to 12μm. When the average particle size D of the regenerated graphite v When the particle size is greater than or equal to 12 μm, the energy density and storage performance of the battery can be improved; the average particle size of the regenerated graphite Dv 50 can be 12 μm, 15 μm, 19 μm, 22 μm, 25 μm or 28 μm; optionally, the average particle size D of the regenerated graphite v 50 is 12μm~25μm, which is a more suitable average particle size Dv50 range of recycled graphite, which is beneficial to improving the energy density and storage performance of the battery.

[0076] In any embodiment, the gram capacity of the regenerated graphite is greater than or equal to 340 mAh / g. When the gram capacity of the regenerated graphite is greater than or equal to 340 mAh / g, the energy density of the battery can be improved. The gram capacity of the regenerated graphite can be 340 mAh / g, 343 mAh / g, 347 mAh / g, 350 mAh / g, 353 mAh / g, 357 mAh / g, or 360 mAh / g. Optionally, the gram capacity of the regenerated graphite is 340 mAh / g to 353 mAh / g, which is a more suitable gram capacity range for the regenerated graphite and is conducive to improving the energy density of the battery.

[0077] In any embodiment, the surface of the regenerated graphite has conductive carbon, which can improve the cycle performance of the battery.

[0078] In any embodiment, the regenerated graphite has a carbon coating layer. When the regenerated graphite has a carbon coating layer, the energy density, storage performance, and kinetic performance of the battery can be improved.

[0079] In any embodiment, the compaction density of the negative electrode sheet is greater than or equal to 1.50 g / cm 3 When the compaction density of the negative electrode is greater than or equal to 1.50g / cm 3 When the negative electrode is compacted, the energy density of the battery can be increased; the compaction density of the negative electrode can be 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 or 1.80g / cm 3 ; Optionally, the compaction density of the negative electrode sheet is 1.55g / cm 3 ~1.75g / cm 3 , a more suitable compaction density range of the negative electrode sheet is beneficial to improving the energy density of the battery.

[0080] In any embodiment, the surface density of the negative electrode sheet is greater than or equal to 6.0 mg / cm 2 When the surface density of the negative electrode is greater than or equal to 6.0 mg / cm 2When the surface density of the negative electrode sheet is 6.0g / cm 2 , 7.0g / cm 2 , 8.0g / cm 2 , 9.0g / cm 2 、10g / cm 2 、11g / cm 2 , 12g / cm 2 、13.0g / cm 2 or 14.0g / cm 2 ; Optionally, the surface density of the negative electrode sheet is 6.0g / cm 2 ~13.0g / cm 2 , a more suitable surface density range of the negative electrode sheet is beneficial to improving the energy density of the battery.

[0081] In any embodiment, the method for preparing graphite comprises the following steps:

[0082] The natural spherical graphite is mixed with fillers and treated at low temperature to obtain an intermediate product;

[0083] The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite.

[0084] Natural spherical graphite has a porous structure. By mixing natural spherical graphite with a filler, and sequentially subjecting the mixture to low-temperature treatment and high-temperature graphitization treatment, at least part of the pores in the outer layer of the natural spherical graphite are filled with the graphitized filler, thereby obtaining graphite that can be used for the first negative electrode active material layer.

[0085] In any embodiment, in the step of mixing natural spherical graphite with a filler and treating at a low temperature to obtain an intermediate product:

[0086] The filler includes at least one of petroleum asphalt, a high molecular weight polymer, and a resin. When the filler includes at least one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile, the filling effect can be adjusted by adjusting the type of filler; the filler can be any one of petroleum asphalt, coal-based asphalt, and polyacrylonitrile, a combination of any two, or a combination of all three; and / or,

[0087] The mass ratio of the natural spherical graphite to the filler is 100:(15-40). When the mass ratio of the natural spherical graphite to the filler is 100:(15-40), the filling effect can be adjusted by adjusting the mass ratio of the natural spherical graphite to the filler; the mass ratio of the natural spherical graphite to the filler can be 100:15, 100:28, 100:40; and / or,

[0088] The temperature of the low temperature treatment is 300°C to 1000°C. When the temperature of the low temperature treatment is 300°C to 1000°C, the filling of the filler can be promoted to achieve a filling effect; the temperature of the low temperature treatment can be 300°C, 400, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C; and / or,

[0089] The low temperature treatment time is 1 hour to 5 hours. When the low temperature treatment time is 1 hour to 5 hours, the filling of the filler can be promoted to achieve a filling effect. The low temperature treatment time can be 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.

[0090] In any embodiment, in the step of subjecting the intermediate product to high-temperature graphitization to obtain the graphite:

[0091] The temperature of the high-temperature graphitization treatment is 2000°C to 2800°C. When the temperature of the high-temperature graphitization treatment is 2000°C to 2800°C, the graphitization effect can be achieved; the temperature of the high-temperature graphitization treatment can be 2000°C, 2200°C, 2400°C, 2600°C or 2800°C; and / or,

[0092] The high-temperature graphitization treatment time is 2 hours to 6 hours. When the high-temperature graphitization treatment time is 2 hours to 6 hours, the graphitization effect can be achieved; the high-temperature graphitization treatment time can be 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0093] As an example, the negative electrode current collector has two opposite surfaces in its thickness direction, and the first negative electrode active material layer and the second negative electrode active material layer are disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0094] 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.).

[0095] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0096] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0098] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the first negative electrode active material layer and the second negative electrode active material layer, 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 first negative electrode slurry and a second negative electrode slurry; the first negative electrode slurry is coated on the negative electrode current collector to form a first negative electrode active material layer, and the second negative electrode slurry is then coated on the first negative electrode active material layer to form a second negative electrode active material layer. After drying, cold pressing and other processes, a negative electrode sheet having the first negative electrode active material layer and the second negative electrode active material layer can be obtained.

[0099] In a second aspect, an embodiment of the present application provides a secondary battery comprising the negative electrode sheet of the first aspect of the present application.

[0100] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0101] 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.

[0102] 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.

[0103] 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.).

[0104] In some embodiments, the secondary battery may be a lithium-ion battery, and the positive electrode active material may be a positive electrode active material for lithium-ion batteries 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 application 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 / 3Mn 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 Co 0.25 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 0.05O2) 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0109] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0114] 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.

[0115] 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.

[0116] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0117] 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.

[0118] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 1 The secondary battery 5 is a square structure as an example.

[0119] In some embodiments, reference 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 form 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.

[0120] 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.

[0121] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0122] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0123] 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.

[0124] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0125] In a third aspect, an embodiment of the present application provides an electrical device, including the electrochemical device of the second aspect of the present application.

[0126] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. 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.

[0127] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0128] Figure 6 This is 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.

[0129] 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.

[0130] Example

[0131] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0132] The preparation method of regenerated graphite comprises the following steps:

[0133] S1. Crushing the waste negative electrode sheets, classifying and screening them, separating the copper foil from the negative electrode material I, and obtaining the negative electrode material I;

[0134] S2, putting the negative electrode material I obtained in step S1 into a rotary kiln for oxidation treatment to remove organic impurities, thereby obtaining the negative electrode material II; wherein the furnace tube speed of the rotary kiln is 2r / min to 6r / min, and the rotary kiln is introduced with gas, wherein the gas includes at least one of air, oxygen and carbon dioxide, and the flow rate of the gas is 1m 3 / h~9m 3 / h, the oxidation treatment temperature is 300°C-800°C, and the time is 1h-5h;

[0135] S3. Mix the negative electrode material II obtained in step S2 with an acid solution, react for 0.5h to 6h, and then filter, wash with water, and dry to obtain regenerated graphite; wherein the acid solution includes at least one of hydrofluoric acid, nitric acid, and hydrochloric acid.

[0136] After step S3, the following steps may also be included:

[0137] S4: mixing the regenerated graphite obtained in step S3 with 2.5 μm to 5.0 μm petroleum coke pitch, and carbonizing the mixture under inert gas to obtain regenerated graphite having a carbon coating layer; wherein the carbonization temperature is 1000° C. to 1300° C., and the time is 1 hour to 4 hours.

[0138] The parameters of the negative electrode active materials of Examples 1 to 21 and Comparative Examples 1 to 3 of the present application are as shown in Table 1, wherein the gram capacity of graphite is 366 mAh / g, and the compaction density under a pressure of 50,000 N is 1.97 g / cm 3 The powder resistivity of the recycled graphite is 0.012Ω / cm, the gram capacity is 347mAh / g, the outer layer region of the graphite is the region composed of the graphite from the surface to 2.5μm, and the rest is the internal region. For example, the negative electrode sheets of Comparative Examples 1 to 2 are single-layer negative electrode active material layers, and the negative electrode active material layer includes recycled graphite. The first negative electrode active material layer of Comparative Example 3 includes graphite, and the second negative electrode active material layer includes recycled graphite. At least part of the pores in the outer layer region of the graphite in Examples 1 to 21 are filled with graphitized petroleum asphalt, and the graphite in Comparative Example 3 is not filled.

[0139] Table 1 Negative electrode plate parameters and test results of Examples 1 to 21 and Comparative Examples 1 to 3

[0140]

[0141] Example 22

[0142] A method for preparing graphite comprises the following steps:

[0143] The natural spherical graphite is mixed with a filler and subjected to low-temperature treatment to obtain an intermediate product; wherein the filler is petroleum asphalt, the mass ratio of the natural spherical graphite to the filler is 100:5, the temperature of the low-temperature treatment is 300° C., and the time is 1 hour;

[0144] The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite, wherein the temperature of the high-temperature graphitization treatment is 2000° C. and the time is 2 hours.

[0145] Example 23

[0146] A method for preparing graphite comprises the following steps:

[0147] The natural spherical graphite and the filler are mixed and low-temperature treated to obtain an intermediate product; wherein the filler is coal-based pitch, the mass ratio of the natural spherical graphite to the filler is 100:28, the temperature of the low-temperature treatment is 600°C, and the time is 3 hours;

[0148] The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite, wherein the temperature of the high-temperature graphitization treatment is 2400° C. and the time is 4 hours.

[0149] Example 24

[0150] A method for preparing graphite comprises the following steps:

[0151] The natural spherical graphite and the filler are mixed and subjected to low-temperature treatment to obtain an intermediate product; wherein the filler is polyacrylonitrile, the mass ratio of the natural spherical graphite to the filler is 100:40, and the temperature of the low-temperature treatment is 1000° C. and the time is 5 hours;

[0152] The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite, wherein the temperature of the high-temperature graphitization treatment is 2800° C. and the time is 6 hours.

[0153] Performance testing:

[0154] The negative electrode sheets of Examples 1 to 21 and Comparative Examples 1 to 3 were prepared into secondary batteries, wherein the preparation method is as follows:

[0155] Preparation of negative electrode sheet

[0156] For Examples 1 to 21 and Comparative Example 3:

[0157] The graphite of Examples 1 to 21 and Comparative Example 3, conductive carbon black (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water was added as a solvent, and the mixture was stirred in a vacuum stirrer until the system became homogeneous to obtain a first negative electrode slurry;

[0158] The regenerated graphite of Examples 1 to 21 and Comparative Example 3, conductive carbon black (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water was added as a solvent, and the mixture was stirred in a vacuum stirrer until the system became homogeneous to obtain a second negative electrode slurry;

[0159] The first negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil to form a first negative electrode active material layer, and then the second negative electrode slurry is coated on the first negative electrode active material layer to form a second negative electrode active material layer. After drying, cold pressing and cutting, the negative electrode sheet is obtained.

[0160] For Comparative Examples 1 to 2:

[0161] The regenerated graphite of Comparative Examples 1 to 2, the conductive agent conductive carbon black (Super P), the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water was added as a solvent, and the mixture was stirred under a vacuum mixer until the system became uniform to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on the surface of the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet was obtained.

[0162] Preparation of positive electrode

[0163] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 ), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and solvent N-methylpyrrolidone (NMP) is added. The mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0164] Preparation of electrolyte

[0165] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then lithium hexafluorophosphate (LiPF6) is dissolved in the organic solvent to obtain an electrolyte; wherein the concentration of LiPF6 is 1 mol / L.

[0166] Isolation film: Polyethylene film is selected as the isolation film.

[0167] Preparation of secondary batteries

[0168] The positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a battery cell; the battery cell is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0169] Perform the following test:

[0170] (1) Energy density test of secondary batteries

[0171] At 25°C, charge the secondary battery at a constant current of 1 / 3C to the upper limit voltage, then charge at a constant voltage to a current of 0.05C. Let it stand for 5 minutes, and then discharge it at a constant current of 1 / 3C to the lower limit voltage. Record the discharge energy of the secondary battery at this time. Calculate the energy density of the secondary battery, where the energy density of the secondary battery = battery discharge energy / mass of the secondary battery, in Wh / kg.

[0172] (2) Storage performance test of secondary batteries

[0173] At 25°C, charge the secondary battery at a constant current of 1C to the upper limit voltage, then charge at a constant voltage to a current of 0.05C. After standing for 5 minutes, discharge the secondary battery at a constant current of 1C to the lower limit voltage. Record the discharge capacity at this time, which is the discharge capacity before storage.

[0174] At 25°C, the secondary battery was charged at a constant current of 1C to an upper limit voltage, and then charged at a constant voltage to a current of 0.05C; thereafter, the secondary battery was stored in a constant temperature box at 60°C for 150 days.

[0175] Capacity retention rate (%) of the secondary battery after storage at 60° C. for 150 days = discharge capacity after storage / discharge capacity before storage × 100%.

[0176] The test results of Examples 1 to 21 and Comparative Examples 1 to 3 are shown in Table 1.

[0177] As can be seen from Table 1, through Examples 1 to 21 and Comparative Examples 1 to 3, it can be seen that a first negative electrode active material layer is arranged between the negative electrode current collector and the second negative electrode active material layer containing regenerated graphite, and the first negative electrode active material layer includes graphite. The graphite has a porous structure, and at least part of the pores in the outer layer region is filled with a graphitized filler. The total pore area of ​​the inner region is greater than the total pore area of ​​the outer layer region. The outer layer region of the graphite has fewer pores, a dense structure, and fewer surface defects, which can effectively reduce the side reactions between the electrolyte and the surface of the negative electrode active material, reduce the consumption of active lithium, and thereby improve the storage performance of the battery and extend the service life of the battery; at the same time, the graphite has a high degree of graphitization, which can increase the energy density of the battery.

[0178] It can be seen from Examples 5 and 9 to 10 that the average particle size D of graphite v 50 is greater than or equal to 16 μm, which is beneficial to improving the energy density and storage performance of the battery; it can be seen from Examples 5 and 11 to 12 that the graphitization degree of graphite is greater than or equal to 95%, which is beneficial to improving the energy density of the battery; it can be seen from Examples 5 and 13 to 14 that the average particle size D of the regenerated graphite v50 is greater than or equal to 12 μm, which is beneficial to improving the energy density and storage performance of the battery; it can be seen from Example 5 and Examples 15 to 18 that when the initial weight loss temperature of the regenerated graphite is 610°C to 715°C, it is beneficial to improving the storage performance of the battery; it can be seen from Example 5 and Examples 19 to 20 that the graphitization degree of the regenerated graphite is less than or equal to 94%, which is beneficial to taking into account the energy density of the battery; it can be seen from Example 5 and Example 21 that the regenerated graphite has a carbon coating layer, which can improve the cycle performance of the battery while ensuring the energy density of the battery.

[0179] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer is located between the negative electrode current collector and the second negative electrode active material layer in the thickness direction of the negative electrode current collector; The first negative electrode active material layer includes graphite, the graphite has a porous structure, the graphite has an inner region and an outer region disposed around the inner region, and at least part of the pores of the outer region are filled with a graphitized filler; The second negative electrode active material layer includes recycled graphite.

2. The negative electrode sheet according to claim 1, wherein: The filler includes a graphitizable high molecular polymer.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The filler includes at least one of petroleum asphalt, coal-based asphalt and polyacrylonitrile.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The outer layer region is the region of the graphite from the surface to 2.5 μm.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The total pore area of ​​the inner region is S1, and the total pore area of ​​the outer region is S2, where S1>S2.

6. The negative electrode sheet according to claim 5, wherein: 1.5≤S1 / S2≤500.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The graphitization degree of the graphite is greater than the graphitization degree of the regenerated graphite.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The graphitization degree of the graphite is greater than or equal to 95%; and / or, The graphitization degree of the regenerated graphite is less than or equal to 94%.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein: The average particle size D of the graphite v 50 is greater than or equal to 16μm.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The gram capacity of the graphite is greater than or equal to 360 mAh / g.

11. The negative electrode sheet according to any one of claims 1 to 10, wherein: The compacted density of the graphite under a pressure of 50,000 N is less than or equal to 2.08 g / cm 3 .

12. The negative electrode sheet according to any one of claims 1 to 11, wherein: The initial weight loss temperature of the regenerated graphite is 610° C. to 715° C.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein: The powder resistivity of the regenerated graphite is 0.005Ω / cm to 0.025Ω / cm.

14. The negative electrode sheet according to any one of claims 1 to 13, wherein: The average particle size Dv50 of the regenerated graphite is greater than or equal to 12 μm.

15. The negative electrode sheet according to any one of claims 1 to 14, characterized in that: The gram capacity of the regenerated graphite is greater than or equal to 340 mAh / g.

16. The negative electrode sheet according to any one of claims 1 to 15, characterized in that: The surface of the regenerated graphite has conductive carbon.

17. The negative electrode sheet according to any one of claims 1 to 16, wherein: The regenerated graphite has a carbon coating layer.

18. The negative electrode sheet according to any one of claims 1 to 17, wherein: The compaction density of the negative electrode plate is greater than or equal to 1.50g / cm 3 .

19. The negative electrode sheet according to any one of claims 1 to 18, wherein: The surface density of the negative electrode plate is greater than or equal to 6.0 mg / cm 2 .

20. The negative electrode sheet according to any one of claims 1 to 19, wherein: The method for preparing the graphite comprises the following steps: The natural spherical graphite is mixed with fillers and treated at low temperature to obtain an intermediate product; The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite.

21. The negative electrode sheet according to claim 20, wherein: In the step of mixing natural spherical graphite with a filler and treating at low temperature to obtain an intermediate product: The filler includes at least one of petroleum asphalt, coal-based asphalt and polyacrylonitrile; and / or, The mass ratio of the natural spherical graphite to the filler is 100:(15-40); and / or, The temperature of the low temperature treatment is 300°C to 1000°C; and / or, The low temperature treatment time is 1 hour to 5 hours.

22. The negative electrode sheet according to claim 20 or 21, wherein: The intermediate product is subjected to high-temperature graphitization treatment to obtain the graphite: The temperature of the high temperature graphitization treatment is 2000° C. to 2800° C.; and / or, The high-temperature graphitization treatment lasts for 2 hours to 6 hours.

23. A secondary battery, characterized in that: Comprising the negative electrode sheet as described in any one of claims 1 to 22.

24. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 23.

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