Secondary battery and electric device comprising same

Abstract

The present invention provides a negative electrode sheet, a secondary battery, and an electric device comprising same. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector; the negative electrode film layer has a first surface distant from the negative electrode current collector and a second surface opposite to the first surface; the thickness of the negative electrode film layer is denoted as H; a region within the thickness range from the first surface to 0.3H of the negative electrode film layer is denoted as a first region of the negative electrode film layer; a region within the thickness range from the second surface to 0.3H of the negative electrode film layer is denoted as a second region of the negative electrode film layer; and the content of a binder of the first region is less than the content of a binder of the second region. The secondary battery prepared from the negative electrode sheet has good cycle performance and dynamic performance.

Description

Secondary battery and electric device containing same

[0001] Cross-references

[0002] The present disclosure claims priority to Chinese Patent Application No. 202311678957.7, filed on December 7, 2023, entitled “Secondary Battery and Electrical Device Containing 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, as secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, the market has put forward higher demands on battery fast charging performance and cycle life.

[0005] Compared to power batteries, energy storage batteries have a longer cycle life. Increasing the energy density of secondary batteries helps improve their cycle life, but it can also reduce the mobility of active ions, affecting the kinetic performance of the secondary battery. This makes it difficult to achieve both cycle life and kinetic performance, hindering the use of energy storage secondary batteries.

[0006] Summary of the Invention

[0007] The present disclosure provides a secondary battery and an electric device including the same, wherein the secondary battery has both good cycle performance and dynamic performance.

[0008] The negative electrode plate provided in the first aspect of the present disclosure includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer. The binder content in the first area is less than the binder content in the second area, which is beneficial to adjusting the pore structure of the upper and lower layers of the negative electrode film layer, improving the kinetic difference between the upper and lower layers of the negative electrode film layer, so that the negative electrode plate has excellent kinetic performance, and thus the secondary battery has good fast charging performance.

[0009] In any embodiment, the first region includes a first binder, and the mass content of the first binder in the first region is 0.78%-2.0%, optionally 0.78%-1.4%, which can enable the first carbon-based material particles to have good cohesion and pore structure, improve the electrical contact between the first carbon-based materials and the migration performance of active ions in the first region.

[0010] In any embodiment, the second region includes a second binder, and the mass content of the second binder in the second region is 1.0%-3.0%, optionally 1.79%-2.32%. During the preparation of the negative electrode plate, the binder in the second region migrates to the first region as the solvent evaporates, which helps to reduce the difference in binder content between the first region and the second region of the negative electrode film layer. Compared with the negative electrode plate with a uniform binder mass content in the negative electrode film layer, the negative electrode plate provided by the present disclosure helps to improve the degree of blockage of the pore structure in the first region and improve the dynamic performance of the negative electrode plate; at the same time, it can also improve the electrical contact between the negative electrode film layer and the negative electrode current collector, and improve the electrical contact degradation caused by the shedding or breakage of the film layer in the second region due to insufficient binder content, so that the secondary battery has both good cycle performance and dynamic performance.

[0011] In any embodiment, the cohesive force of the first region is greater than or equal to 70 N / m and less than or equal to 125 N / m, and can be optionally 70 N / m-110 N / m, thereby further improving the pore structure of the first region and thus improving the dynamic performance.

[0012] In any embodiment, the cohesive force of the second region is greater than or equal to 138 N / m and less than or equal to 170 N / m, and can be optionally 145 N / m-170 N / m, which can further improve the overlap between the negative electrode active material particles and enhance the electrical contact between the particles; at the same time, it can inhibit the volume change of the negative electrode film layer, reduce the shedding of the negative electrode active material, and further improve the cycle performance of the secondary battery.

[0013] In any embodiment, the first region includes a first carbon-based material, the second region includes a second carbon-based material, and the first carbon-based material and the second carbon-based material are the same carbon-based material. In this case, the first carbon-based material or the second carbon-based material satisfies at least one of the following conditions:

[0014] (1) The volume distribution particle size Dv10 of the first carbon-based material or the second carbon-based material is greater than or equal to 4 μm, and can be optionally 4 μm-7 μm;

[0015] (2) the volume distribution particle size Dv50 of the first carbon-based material or the second carbon-based material is 7 μm-18 μm, optionally 8.0 μm-16.0 μm;

[0016] (3) The volume distribution particle size Dv90 of the first carbon-based material or the second carbon-based material is less than or equal to 40.0 μm, and can be optionally 15 μm-30.0 μm;

[0017] (4) the particle size distribution of the first carbon-based material or the second carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.6, optionally 1.10-1.55;

[0018] (5) The gram capacity of the first carbon-based material or the second carbon-based material is 310 mAh / g to 350 mAh / g;

[0019] (6) Both the first carbon-based material and the second carbon-based material include artificial graphite.

[0020] The first carbon-based material and the second carbon-based material have a good volume distribution particle size Dv50, which helps to increase the specific surface area of ​​the negative electrode active material, provide sufficient active sites and reduce the migration path of active ions, thereby improving the cycle performance and kinetic performance of the secondary battery; the appropriate volume distribution particle size Dv10 helps to reduce the side reactions of the negative electrode active material during the cycle, improve the irreversible consumption of active ions caused by the side reactions, and improve the cycle performance of the secondary battery; the appropriate volume distribution particle size Dv90 can reduce the loss of electrical contact caused by particle breakage of the larger particle size negative electrode active material during the cycle, so that the secondary battery has both good cycle performance and kinetic performance. The gram capacity of the first carbon-based material and the second carbon-based material within the said range is conducive to the transmission of active ions in the first region, can improve the kinetic performance of the secondary battery, and also helps to increase the overall energy density of the negative electrode sheet, while improving the cycle performance and kinetic performance of the secondary battery.

[0021] In any embodiment, the first region includes a first carbon-based material, the second region includes a second carbon-based material, and the first carbon-based material and the second carbon-based material are different carbon-based materials. In this case, the first carbon-based material satisfies at least one of the following conditions:

[0022] (1) The volume distribution particle size Dv10 of the first carbon-based material is greater than or equal to 3 μm, and can be selected from 3 μm to 7 μm;

[0023] (2) the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm-13.5 μm, optionally 7.5 μm-11.5 μm;

[0024] (3) the volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 30 μm, and can be optionally 15 μm-25 μm;

[0025] (4) the particle size distribution of the first carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.6, optionally 1.10-1.55;

[0026] (5) The gram capacity of the first carbon-based material is 315 mAh / g to 335 mAh / g;

[0027] (6) The first carbon-based material includes artificial graphite;

[0028] The second carbon-based material satisfies at least one of the following conditions:

[0029] (1) The volume distribution particle size Dv10 of the second carbon-based material is greater than or equal to 3.5 μm, and can be selected from 3.5 μm to 7 μm;

[0030] (2) the volume distribution particle size Dv50 of the second carbon-based material is 7.0 μm-14.0 μm, optionally 8.0 μm-12.0 μm;

[0031] (3) the volume distribution particle size Dv90 of the second carbon-based material is less than or equal to 28 μm, and can be optionally 13 μm-20 μm;

[0032] (4) the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.5, and can be optionally 1.1-1.3;

[0033] (5) The gram capacity of the second carbon-based material is 345 mAh / g-355 mAh / g;

[0034] (6) The second carbon-based material includes artificial graphite.

[0035] The volume distribution particle sizes Dv50, Dv10, and Dv90 of the first carbon-based material and the second carbon-based material as negative electrode active materials within the above ranges help provide sufficient active sites for active ions and reduce the migration paths of active ions, improve the irreversible consumption of active ions caused by side reactions, and reduce the loss of electrical contact caused by particle breakage of negative electrode active materials with larger particle sizes during the cycle, so that the secondary battery has both good cycle performance and kinetic performance. In addition, the gram capacity of the first carbon-based material within the above range is conducive to the transmission of active ions in the first region, which can improve the kinetic performance of the secondary battery; the gram capacity of the second carbon-based material within the above range helps to increase the overall energy density of the negative electrode sheet, while improving the cycle performance and kinetic performance of the secondary battery.

[0036] In any embodiment, under the condition that the first carbon-based material and the second carbon-based material are different carbon-based materials, the volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material, so that the porosity of the first region of the negative electrode film layer can be greater than or equal to the porosity of the second region, so that the pore structure between the particles of the first carbon-based material is not easily blocked, which is beneficial for the secondary battery to maintain good dynamic performance during long-term cycling.

[0037] In any embodiment, under the condition that the first carbon-based material and the second carbon-based material are different carbon-based materials, the gram capacity of the first carbon-based material is less than or equal to the gram capacity of the second carbon-based material. At this time, the powder compaction density of the first carbon-based material is less than or equal to the powder compaction density of the second carbon-based material, and the first region has a higher porosity than the second region; at the same time, the second region has a higher energy density than the first region, which is beneficial for the negative electrode to take into account both energy density and active ion transmission performance.

[0038] In any embodiment, the first binder and the second binder respectively include at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0039] In any embodiment, the compaction density of the negative electrode film layer is 1.30 g / cm 3 -1.60g / cm 3 ; and / or, the surface density of the negative electrode film layer is 7mg / cm 2 -15mg / cm 2 , which helps to improve the energy density of secondary batteries.

[0040] 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

[0041] FIG1 is a schematic diagram of a negative electrode sheet according to an embodiment of the present disclosure;

[0042] FIG2 is a schematic diagram of a negative electrode sheet according to an embodiment of the present disclosure;

[0043] FIG3 is a schematic diagram of a negative electrode sheet according to an embodiment of the present disclosure;

[0044] FIG4 is a schematic diagram of a secondary battery according to an embodiment of the present disclosure;

[0045] FIG5 is an exploded view of the secondary battery according to one embodiment of the present disclosure shown in FIG4 ;

[0046] FIG6 is a schematic diagram of a battery module according to an embodiment of the present disclosure;

[0047] FIG7 is a schematic diagram of a battery pack according to an embodiment of the present disclosure;

[0048] FIG8 is an exploded view of the battery pack shown in FIG7 according to an embodiment of the present disclosure;

[0049] FIG9 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0050] Description of reference numerals:

[0051] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover; 10 negative electrode sheet, 101 negative electrode current collector, 102 negative electrode film layer, 102a first surface, 102b second surface, 1021 second region, 1022 first region, 1023 middle region. DETAILED DESCRIPTION

[0052] 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.

[0053] " 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge process, active ions (lithium or sodium ions) are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is placed between the positive and negative electrodes, primarily to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0060] In a secondary battery, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a binder dispersed around the negative electrode active material, which allows the negative electrode active material particles to have bonding properties, inhibits the volume expansion of the negative electrode film layer during the cycle, and maintains the structural integrity of the negative electrode film layer. In the negative electrode film layer, there is a pore structure between the negative electrode active material particles, which is a pore that is not completely filled with solid matter. During the preparation of the secondary battery, the binder in the negative electrode film layer can migrate along the pore structure in the film layer toward the solvent volatilization direction (or away from the current collector direction) as the solvent evaporates, resulting in the binder content in the film layer area away from the current collector being higher than the binder content in the film layer area on the current collector surface. Excess binder can block the pore structure in the negative electrode film layer, affect the migration performance of active ions, and further affect the fast charging performance of the secondary battery.

[0061] [Secondary battery]

[0062] In order to achieve a balance between the cycle performance and fast charging performance of a secondary battery, the secondary battery provided by the present disclosure includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector. The negative electrode film has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface. The thickness of the negative electrode film (the thickness of the negative electrode film located on a single side of the negative electrode current collector) is recorded as H. The area within the thickness range from the first surface of the negative electrode film to 0.3H is recorded as the first area of ​​the negative electrode film, and the area within the thickness range from the second surface of the negative electrode film to 0.3H is recorded as the second area of ​​the negative electrode film. The binder content in the first area is less than the binder content in the second area, which is conducive to adjusting the pore structure of the upper and lower layers of the negative electrode film, reducing the degree of pore structure blockage in the first area, improving the kinetic difference between different areas of the negative electrode film, improving the kinetic performance of the negative electrode plate, and making the secondary battery have good fast charging performance.

[0063] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0064] Figures 1 to 3 illustrate schematic diagrams of the negative electrode sheet of the present disclosure. As shown in Figures 1 to 3, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film 102 has a first surface 102a distal from the negative electrode current collector 101 and a second surface 102b opposite the first surface 102a. The thickness of the negative electrode film 102 is denoted as H. The region from the second surface 102b of the negative electrode film to a thickness of 0.3H is denoted as the second region 1021 of the negative electrode film, and the region from the first surface 102a of the negative electrode film to a thickness of 0.3H is denoted as the first region 1022 of the negative electrode film.

[0065] In some embodiments, the first region includes a first adhesive and the second region includes a second adhesive.

[0066] In some embodiments, the mass content of the first binder in the first region is 0.78%-2.0%, optionally 0.78%-1.4%, 1.3%-1.8%, 1.2%-1.9%, 1.1%-1.7%. In some embodiments, the mass content of the first binder in the first region is 1.05%, 1.15%, 1.25%, 1.35%, 1.4%, 1.5%, 1.6%, 1.75%, 1.85%, 1.95%, or a range between any two of the above values. Adjusting the mass content of the first binder in the first region improves the overlap between the first carbon-based material particles, improves the cohesion and pore structure of the first region, and thereby improves the electrical contact between the first carbon-based materials and the migration performance of active ions in the first region.

[0067] In some embodiments, the mass content of the second binder in the second region is 1.0%-3.0%, optionally 1.79%-2.32%, 1.4%-2.5%, 1.3%-2.5%, 1.1%-2.8%, or 1.2%-2.9%. In some embodiments, the mass content of the second binder in the second region is 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.0%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.75%, 2.85%, 2.95%, or a range between any two of the above values. This helps to reduce the difference in binder content between the first region and the second region of the negative electrode film layer. Compared with the negative electrode sheet with uniform binder mass content in the negative electrode film layer, the negative electrode sheet provided by the present invention helps to improve the degree of blockage of the pore structure in the first region and improve the dynamic performance of the negative electrode sheet; at the same time, it also helps to improve the bonding performance between the negative electrode film layer and the negative electrode current collector, reduce the electrical contact degradation caused by the shedding or breakage of the film layer due to insufficient binder content in the second region, improve the cycle decline caused by electrical contact degradation, and enable the secondary battery to have both good cycle performance and dynamic performance.

[0068] In a secondary battery, the content of the binder in the first region and the second region can be measured using methods known in the art. For example, the following method can be used:

[0069] Take a clean copper foil and spread it flat on the table. Cut the negative electrode to be tested into 20cm×10cm pieces. Prepare a clean blade and scrape powder samples from the first and second areas of the negative electrode film layer respectively.

[0070] Sampling standard: Based on the thickness H of the negative electrode film layer, calculate the thickness from the first surface of the negative electrode film layer to 0.3H (this area is the first area), and the thickness from the second surface of the negative electrode film layer to 0.3H (this area is the second area). Scrape powder in the first area and the second area respectively as the first area sample and the second area sample, and store the collected samples in sealed bottles.

[0071] Weigh 50 mg of the collected first area sample and second area sample respectively, place them in an alumina crucible and shake them flat, use a thermogravimetric analyzer to detect the binder content in the samples (the atmosphere is a nitrogen atmosphere, and the nitrogen flow rate is 20 mL / min), and heat the samples from room temperature (25°C±5°C) to 600°C at a heating rate of 10°C / min. At this time, the mass percentage of the sample lost is the binder content in different areas.

[0072] Herein, the "pore structure" in the negative electrode sheet can be observed by methods known in the art, such as direct observation through an electron microscope image of a film cross section.

[0073] The first binder and the second binder each independently include 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).

[0074] In some embodiments, the first binder is styrene-butadiene rubber. In some embodiments, the second binder is styrene-butadiene rubber.

[0075] The negative electrode film layer contains a first carbon-based material and a second carbon-based material as negative electrode active materials, wherein the first region includes the first carbon-based material and the second region includes the second carbon-based material. The interaction force between the negative electrode active materials is cohesive force, which helps maintain the mechanical structural stability of the negative electrode film layer and inhibits the volume expansion of the negative electrode film layer, improves the electrical contact between the active materials in the negative electrode film layer, and improves the conductivity of the negative electrode film layer. Cohesive force can also affect the pore structure between the particles of the negative electrode film layer material, affect the kinetic performance of active ions in the negative electrode active material, and thus affect the fast charging performance of the secondary battery.

[0076] In some embodiments, the cohesion of the first region is less than the cohesion of the second region. In some embodiments, the cohesion of the first region is greater than or equal to 70 N / m and less than or equal to 125 N / m. In some embodiments, the cohesion of the second region is greater than or equal to 138 N / m and less than or equal to 170 N / m.

[0077] Adjusting the cohesive force between the first and second regions helps improve the structural stability of different regions of the negative electrode film layer and enhances electrical contact between the negative electrode active material particles. Furthermore, having the cohesive force of the first region smaller than that of the second region can improve the mobility of active ions in the first region, resulting in good conductivity and excellent kinetic performance for the overall negative electrode film layer.

[0078] The cohesive force between the first region and the second region affects the performance of the secondary battery. This may be because during the preparation of the negative electrode, the binder in the negative electrode slurry floats (or migrates) to the surface of the electrode film layer as the solvent evaporates during the drying process, resulting in excessive binder content and reduced pore structure in the first region, which hinders electrolyte infiltration and ion transport, and cannot exert the fast charging performance of the first carbon-based material; and the too little binder content in the second region reduces the adhesion (or cohesion) between the second carbon-based material particles. As the material volume expands and contracts due to the embedding and extraction of active ions during the cyclic charge and discharge process, the bonding strength between the second carbon-based material particles is further deteriorated, causing some of the second carbon-based material particles to detach or fall off in the later stage of the cycle, losing electrical contact with the surrounding materials, resulting in rapid decay of the battery cell capacity.

[0079] In some embodiments, the cohesion of the first region is 70 N / m-110 N / m. In some embodiments, the cohesion of the first region is 80 N / m-125 N / m, 80 N / m-110 N / m, 73 N / m-109 N / m, or 95 N / m-115 N / m. In some embodiments, the cohesion of the first region is 75 N / m, 85 N / m, 90 N / m, 96 N / m, 103 N / m, 105 N / m, 108 N / m, 110 N / m, 113 N / m, 114 N / m, 116 N / m, 117 N / m, 118 N / m, or a range between any two of the above values, which can further improve the structural stability of the first region and the migration performance of active ions.

[0080] In some embodiments, the cohesion of the second region is 145N / m-170N / m. In some embodiments, the cohesion of the second region is 140N / m-170N / m, 140N / m-165N / m, 143N / m-170N / m or 140N / m-162N / m. In some embodiments, the cohesion of the second region is 141N / m, 147N / m, 150N / m, 153N / m, 155N / m, 158N / m, 162N / m, 164N / m, 168N / m, 170N / m or a range between any two of the above values. This helps to further improve the degree of overlap between the second carbon-based material particles and improve the conductivity of the negative electrode film layer; at the same time, maintain the structural stability of the second region, reduce the loss of electrical contact due to the shedding of the second carbon-based material particles, and further improve the cycle performance of the secondary battery.

[0081] Cohesion can be measured using methods known in the art. For example, it can be measured using the following method:

[0082] Double-sided tape was used to attach to a steel plate. A 20 cm long and 20 mm wide strip of the negative electrode was affixed to the double-sided tape. A copper foil tape (width × length = 20 mm × 80 mm) for testing the cohesion of the negative electrode was centered and applied to the strip, covering it. A 20 mm × 60 mm strip of white paper was cut and inserted between the strip and the single-sided tape, with an overlap of approximately 15 mm. The strip was rolled back and forth four times under 2 kg of pressure. The paper was clamped in the fixture of a tensile testing machine (Instron 3365). The machine was turned on and the paper strip was slowly pulled at a speed of 50 mm / min, with a displacement of 60 mm. The cohesion at this location was measured in N / m.

[0083] The first carbon-based material and the second carbon-based material have good powder characteristics. In some embodiments, the volume distribution particle size Dv10 of the first carbon-based material is greater than or equal to 3.0 μm. In some embodiments, the volume distribution particle size Dv10 of the first carbon-based material is greater than or equal to 4.0 μm. In some embodiments, the volume distribution particle size Dv10 of the first carbon-based material is 3.0 μm-7 μm, 4.0 μm-7 μm, or 4.0 μm-6.5 μm. In some embodiments, the volume distribution particle size Dv10 of the first carbon-based material is 3.0 μm, 4.0 μm, 4.4 μm, 4.6 μm, 4.7 μm, 4.8 μm, 5.0 μm, 5.3 μm, 5.7 μm, 6.1 μm, 6.0 μm, 6.5 μm, 6.8 μm or a range between any two of the above values, thereby reducing the side reactions of the first carbon-based material with smaller particle size during the cycle, reducing the irreversible consumption of active ions, and improving the cycle performance of the secondary battery.

[0084] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm-18 μm. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 7 μm-18.0 μm. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm-13.5 μm. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm-16.0 μm, 8.5 μm-14.3 μm, 9.6 μm-14.3 μm, 7.5 μm-11.5 μm, 7.5 μm-10.5 μm, 8.0 μm-11.5 μm, 8.5 μm-11 μm. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm, 6.0 μm, 7.0 μm, 7.8 μm, 8.3 μm, 8.8 μm, 9.0 μm, 9.2 μm, 9.6 μm, 9.8 μm, 10.0 μm, 10.3 μm, 10.7 μm, 11.2 μm, 12.2 μm, 12.9 μm, 13.1 μm, 13.7 μm, 14.3 μm, or a range between any two of the above values. The volume distribution particle size Dv50 can affect the specific surface area of ​​the negative electrode active material, thereby affecting the number of active sites for the negative electrode active material to interact with active ions. Adjusting the volume distribution particle size Dv50 helps to obtain suitable active sites, which can reduce side reactions caused by too many active sites and reduce irreversible consumption of active ions; it can also reduce the inhibition of secondary battery cycle performance caused by too few active sites. Adjusting the volume distribution particle size Dv50 of the first carbon-based material helps to improve the consumption and migration performance of active ions in the first region, so that the secondary battery can have both cycle performance and fast charging performance.

[0085] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 40 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 30 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 15 μm-30.0 μm, 15 μm-25 μm, 18 μm-28.9 μm, 16.9 μm-28.9 μm. In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 15.7 μm, 16.1 μm, 16.9 μm, 17.3 μm, 17.9 μm, 19.0 μm, 20.9 μm, 21.2 μm, 22.4 μm, 23.6 μm, 25.7 μm, 26.5 μm, 27.7 μm, 28.9 μm, 29.2 μm or a range between any two of the above values. During cycling, larger particles (particularly secondary particles) in the negative electrode active material expand and contract as active ions are embedded and extracted. This makes the bridges within the particles more susceptible to breaking, leading to particle rupture and loss of electrical contact between the negative electrode active material particles. Adjusting the volume distribution particle size (Dv90) of the first carbon-based material helps improve the conductivity of the first region in the negative electrode film layer, thereby improving the cycling performance of the secondary battery.

[0086] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is 0.9-1.6, optionally 1.10-1.55, 1.1-1.45, 1.2-1.5, 1.3-1.55. In some embodiments, the particle size distribution of the first carbon-based material is 1.05, 1.15, 1.2, 1.25, 1.30, 1.35, 1.40, 1.45, 1.55 or a range between any two of the above values. The particle size distribution reflects the degree of concentration and dispersion of the particle size distribution of the first carbon-based material particles. Adjusting the particle size distribution of the first carbon-based material helps to control the content of the volume distribution particle size Dv10 and the volume distribution particle size Dv90 in the first carbon-based material, thereby reducing the impact of the two on the cycle performance of the secondary battery.

[0087] In some embodiments, the volume distribution particle size Dv10 of the second carbon-based material is greater than or equal to 3.5 μm. In some embodiments, the volume distribution particle size Dv10 of the second carbon-based material is greater than or equal to 4.0 μm. In some embodiments, the volume distribution particle size Dv10 of the second carbon-based material is 3.5 μm-7 μm, which can be optionally 4.0 μm-7 μm, 3.0 μm-6.2 μm or 4.6 μm-6.2 μm. In some embodiments, the volume distribution particle size Dv10 of the second carbon-based material is 3.5 μm, 4.0 μm, 4.5 μm, 4.6 μm, 4.8 μm, 5.3 μm, 6.2 μm, 6.7 μm or a range between any two of the above values. Thereby reducing the irreversible consumption of active ions in the second region and improving the cycle performance of the secondary battery.

[0088] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 7.0 μm-18.0 μm. In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 7.0 μm-14.0 μm. In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 8.0 μm-16.0 μm, 8.0 μm-12.0 μm, 8.5 μm-14.5 μm, 9.5 μm-14.3 μm, 9.5 μm-11.5 μm, 9.0 μm-12.5 μm, 9.6 μm-14.3 μm. In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 7.5 μm, 8.8 μm, 9.2 μm, 9.7 μm, 10.0 μm, 10.3 μm, 10.5 μm, 10.7 μm, 10.9 μm, 11.2 μm, 11.8 μm, 12.0 μm, 12.2 μm, 13.5 μm, 14.1 μm, 17.6 μm, or a range between any two of the above values. Adjusting the volume distribution particle size Dv50 of the second carbon-based material can reduce the path of active ion embedding and de-embedding, help improve the consumption and migration performance of active ions in the second region, and enable the secondary battery to have both cycle performance and fast charging performance.

[0089] In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is less than or equal to 40.0 μm. In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is less than or equal to 28.0 μm. In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is 15 μm-30.0 μm, 13 μm-20.0 μm, 16 μm-30 μm, 18 μm-28.9 μm or 16.9 μm-28.9 μm. In some embodiments, the volume distribution particle size Dv90 of the second carbon-based material is 16.4 μm, 17.6 μm, 18.3 μm, 19.7 μm, 20.6 μm, 22.1 μm, 24.5 μm, 26.4 μm, 27.3 μm, 28.2 μm, 29.6 μm or a range between any two of the above values. It helps to improve the conductivity of the second region in the negative electrode film layer, thereby improving the cycle performance of the secondary battery.

[0090] In some embodiments, the particle size distribution of the second carbon-based material is 0.9-1.6. In some embodiments, the particle size distribution of the second carbon-based material is 0.9-1.5. In some embodiments, the particle size distribution of the second carbon-based material is 1.1-1.55, 1.1-1.4, 1.1-1.3, 1.0-1.6, 1.0-1.5, 1.1-1.5, 1.3-1.55. In some embodiments, the particle size distribution of the second carbon-based material is 1.05, 1.15, 1.2, 1.25, 1.3, 1.35, 1.45, 1.55 or a range between any two of the above values. Adjusting the particle size distribution of the second carbon-based material helps to control the content of volume distribution particle size Dv10 and volume distribution particle size Dv90 in the second carbon-based material, reducing the impact of the two on the cycle performance of the secondary battery.

[0091] In the present disclosure, the volume distribution particle sizes Dv10, Dv50, and Dv90 of the carbon-based negative electrode material represent the particle sizes corresponding to the cumulative volume distribution percentages of the material reaching 10%, 50%, and 90%, respectively, and can be measured using instruments and methods known in the art. For example, the measurement can be performed using a laser particle size analyzer in accordance with GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0092] In the negative electrode sheet, the increase in the gram capacity of the negative electrode active material helps to improve the energy density and cycle performance of the secondary battery. However, the crystal interplanar spacing of the high-gram capacity negative electrode active material is reduced, which is not conducive to the deintercalation of active ions, making it difficult for the secondary battery to exert its fast charging performance. In the later stages of the cycle, it is very easy to experience an accelerated decline in cycle performance due to insufficient kinetics. In order to take into account the energy density, fast charging and cycle performance of the secondary battery, in some embodiments, the gram capacity of the first carbon-based material is less than or equal to the gram capacity of the second carbon-based material. In this article, "gram capacity" refers to the ratio of the capacitance that can be released by the carbon-based negative electrode active material to the mass of the carbon material.

[0093] In some embodiments, the gram capacity of the first carbon-based material is 310mAh / g-350mAh / g. In some embodiments, the gram capacity of the first carbon-based material is 315mAh / g-335mAh / g. In some embodiments, the gram capacity of the first carbon-based material is 310mAh / g-340mAh / g, 310mAh / g-330mAh / g, 300mAh / g-340mAh / g. In some embodiments, the gram capacity of the first carbon-based material is 315mAh / g, 320mAh / g, 325mAh / g, 330mAh / g, 335mAh / g, 345mAh / g, 350mAh / g, or a range between any two of the above values.

[0094] In some embodiments, the gram capacity of the second carbon-based material is 310mAh / g-355mAh / g. In some embodiments, the gram capacity of the second carbon-based material is 310mAh / g-350mAh / g. In some embodiments, the gram capacity of the second carbon-based material is 345mAh / g-355mAh / g. In some embodiments, the gram capacity of the second carbon-based material is 340mAh / g-355mAh / g or 340mAh / g-350mAh / g. In some embodiments, the gram capacity of the second carbon-based material is 315mAh / g, 319mAh / g, 343mAh / g, 348mAh / g, 350mAh / g, 355mAh / g, 353mAh / g or a range between any two of the above values. At this time, the crystal interplanar spacing of the first carbon-based material is larger, and the powder compaction density of the first carbon-based material is less than or equal to the powder compaction density of the second carbon-based material, so that the first region has more pore structure and higher porosity relative to the second region, which can improve the transport performance of active ions in the first region. At the same time, the second region has a higher energy density than the first region, which can improve the overall energy density of the negative electrode plate, so that the negative electrode plate can take into account both energy density and fast charging performance.

[0095] 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.

[0096] In some embodiments, the first carbon-based material and the second carbon-based material both include artificial graphite.

[0097] In some embodiments, the first carbon-based material and the second carbon-based material are the same carbon-based material, and the first carbon-based material or the second carbon-based material satisfies at least one of the following conditions:

[0098] (1) The volume distribution particle size Dv10 of the first carbon-based material or the second carbon-based material is greater than or equal to 4 μm, and can be optionally 4 μm-7 μm;

[0099] (2) the volume distribution particle size Dv50 of the first carbon-based material or the second carbon-based material is 7 μm-18 μm, optionally 8.0 μm-16.0 μm;

[0100] (3) The volume distribution particle size Dv90 of the first carbon-based material or the second carbon-based material is less than or equal to 40.0 μm, and can be optionally 15 μm-30.0 μm;

[0101] (4) the particle size distribution of the first carbon-based material or the second carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.6, optionally 1.10-1.55;

[0102] (5) The gram capacity of the first carbon-based material or the second carbon-based material is 310 mAh / g to 350 mAh / g;

[0103] (6) Both the first carbon-based material and the second carbon-based material include artificial graphite.

[0104] A good volume distribution particle size Dv50 helps to increase the specific surface area of ​​the negative electrode active material, provide sufficient active sites and reduce the migration path of active ions, thereby improving the cycle performance and kinetic performance of the secondary battery; a suitable volume distribution particle size Dv10 helps to reduce the side reactions of the negative electrode active material during the cycle, improve the irreversible consumption of active ions caused by side reactions, and improve the cycle performance of the secondary battery; a suitable volume distribution particle size Dv90 can reduce the loss of electrical contact caused by particle breakage of negative electrode active materials with larger particle sizes during the cycle, so that the secondary battery has both good cycle performance and kinetic performance. The gram capacity of the first carbon-based material and the second carbon-based material within the above range is conducive to the transmission of active ions in the first region, can improve the kinetic performance of the secondary battery, and also helps to increase the overall energy density of the negative electrode sheet, while improving the cycle performance and kinetic performance of the secondary battery.

[0105] In some embodiments, the first carbon-based material and the second carbon-based material are different carbon-based materials, and the first carbon-based material satisfies at least one of the following conditions:

[0106] (1) The volume distribution particle size Dv10 of the first carbon-based material is greater than or equal to 3 μm, and can be selected from 3 μm to 7 μm;

[0107] (2) the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm-13.5 μm, optionally 7.5 μm-11.5 μm;

[0108] (3) the volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 30 μm, and can be optionally 15 μm-25 μm;

[0109] (4) the particle size distribution of the first carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.6, optionally 1.10-1.55;

[0110] (5) The gram capacity of the first carbon-based material is 315 mAh / g to 335 mAh / g;

[0111] (6) The first carbon-based material includes artificial graphite;

[0112] The second carbon-based material satisfies at least one of the following conditions:

[0113] (1) The volume distribution particle size Dv10 of the second carbon-based material is greater than or equal to 3.5 μm, and can be selected from 3.5 μm to 7 μm;

[0114] (2) the volume distribution particle size Dv50 of the second carbon-based material is 7.0 μm-14.0 μm, optionally 8.0 μm-12.0 μm;

[0115] (3) the volume distribution particle size Dv90 of the second carbon-based material is less than or equal to 28 μm, and can be optionally 13 μm-20 μm;

[0116] (4) the particle size distribution of the second carbon-based material (Dv90-Dv10) / Dv50 is 0.9-1.5, and can be optionally 1.1-1.3;

[0117] (5) The gram capacity of the second carbon-based material is 345 mAh / g-355 mAh / g;

[0118] (6) The second carbon-based material includes artificial graphite.

[0119] The volume distribution particle sizes Dv50, Dv10, and Dv90 of the first carbon-based material and the second carbon-based material within the above ranges help provide sufficient active sites for active ions and reduce the migration paths of active ions, thereby improving the irreversible consumption of active ions due to side reactions and reducing the loss of electrical contact caused by particle breakage of larger-particle-sized negative electrode active materials during the cycle, thereby enabling the secondary battery to have both good cycle performance and kinetic performance. In addition, the gram capacity of the first carbon-based material within the above range is conducive to the transmission of active ions in the first region, thereby improving the kinetic performance of the secondary battery; the gram capacity of the second carbon-based material within the above range helps to increase the overall energy density of the negative electrode sheet, while improving the cycle performance and kinetic performance of the secondary battery.

[0120] In some embodiments, when the first carbon-based material and the second carbon-based material are different carbon-based materials, the volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material. The smaller particle size helps to improve the pore structure in the membrane layer, making the porosity of the first region higher than the porosity of the second region, making the pore structure in the first region less likely to be clogged, facilitating the migration of active ions, and improving the kinetic performance of the secondary battery during long-term cycling.

[0121] In some embodiments, under the condition that the first carbon-based material and the second carbon-based material are different carbon-based materials, the gram capacity of the first carbon-based material is less than or equal to the gram capacity of the second carbon-based material. At this time, the powder compaction density of the first carbon-based material is less than or equal to the powder compaction density of the second carbon-based material, and the first region has a higher porosity than the second region; at the same time, the second region has a higher energy density than the first region, which is beneficial for the negative electrode to take into account both energy density and active ion transmission performance.

[0122] In some embodiments, the first carbon-based material and / or the second carbon-based material can be prepared using a method comprising the following steps: providing a raw material; processing the raw material to obtain a precursor; and graphitizing and post-processing the precursor to obtain a graphite material.

[0123] In some embodiments, the feedstock comprises at least one of petroleum coke, needle coke, and pitch coke.

[0124] As used herein, the term "petroleum coke" refers to coke formed by carbonizing petroleum residue or petroleum asphalt at high temperatures.

[0125] 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.

[0126] As used herein, the term "pitch coke" refers to the solid material produced by carbonizing coal tar pitch at high temperatures.

[0127] In some embodiments, the raw material is petroleum coke. Petroleum coke has excellent graphitization performance and low thermal expansion coefficient, which is conducive to obtaining graphite materials with excellent rate performance and cycle stability, and the raw material cost is low, saving costs.

[0128] In some embodiments, the raw material is needle coke. Needle coke has a number of advantages, including low thermal expansion coefficient, low porosity, low sulfur, low ash, low metal content, high electrical conductivity, and easy graphitization. The graphite material produced after graphitization can achieve a high ultimate compaction density and exhibit a low cyclic expansion rate.

[0129] 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.

[0130] In some embodiments of the present disclosure, the raw material is petroleum coke, and 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 60%-80%, which is conducive to obtaining a graphite material with a low oil absorption value. However, if the area proportion of the mosaic and regional structures is too high, it will affect the gram capacity of the graphite material and the energy density of the battery.

[0131] In some embodiments of the present disclosure, the raw material is needle coke, and based on the total volume of the raw material structure, the volume proportion of the fiber-type structure in the raw material is greater than or equal to 40%, and can be optionally 45%-70%. This is beneficial to improving the compaction density and gram capacity of the graphite material, so that the graphite material retains a high degree of integrity during the compaction process, and the battery has a good energy density while having a long cycle life. Raw materials with a volume proportion of the fiber-type structure within the above range have both low cost and good gram capacity of the graphite, and the battery cell has a kinetic window for the entire life cycle, thereby comprehensively improving the long-term cycle life and electrochemical performance of the battery.

[0132] In the present disclosure, the volume proportion of mosaic, regional and fiber structures in the raw material can be tested by methods known in the art. As an example, according to the provisions of GB 1997-89, the raw material is crushed to 1mm and mixed, and 40g-50g is separated. A square hole sieve is used to take 4g-5g of 0.07mm-1.0mm grade samples for film making; according to the provisions of MT 116.1-86, powder coke and block coke optical films are prepared. The diameter of the powder coke optical 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 placed on the stage for focus. 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 the 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 0.3-0.5mm and a line spacing of 0.5-0.8mm. Starting from one end of the sample, determine the microstructure type under the intersection of the crosshairs, and divide the number of effective measuring points of the mosaic-type, regional-type and fiber-type optical tissues by the total number of statistical testing points as the volume proportion of the mosaic-type, regional-type and fiber-type structures in the raw material.

[0133] In some embodiments, the raw material may further meet the following requirements: sulfur content ≤ 0.7%, ash content ≤ 0.50%, and volatile matter content ≤ 8% ≤ 15%.

[0134] In some embodiments, the processing of raw materials specifically includes: crushing the raw materials, shaping them, grading them, removing fine powder after crushing, and obtaining a precursor.

[0135] The volume distribution particle size Dv50 of the precursor is 8.0-16.0 μm, and / or (Dv90-Dv10) / Dv50 of the precursor is 1.10-1.70.

[0136] In some embodiments, the volume distribution particle size Dv50 of the precursor can be selected as 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm or 16.0 μm, or a range between any two of the above values.

[0137] Controlling the Dv50 of the precursor within a suitable range is beneficial to controlling the Dv50 of the graphite material within a suitable range, reducing the path of active ion embedding and de-embedding, improving the transmission performance of active ions and electrons, improving the rate performance of the battery, and helping to reduce the side reactions of the graphite material and the irreversible consumption of active ions during the cycle, thereby improving the cycle performance and storage performance of the secondary battery.

[0138] In some embodiments, (Dv90-Dv10) / Dv50 of the precursor may be 1.10, 1.20, 1.30, 1.40, 1.50, 1.60 or 1.70, or a range between any two of the above values.

[0139] Controlling the (Dv90-Dv10) / Dv50 of the precursor within a suitable range is beneficial to controlling the (Dv90-Dv10) / Dv50 of the graphite material within a suitable range, which is beneficial for the negative electrode film layer to have a suitable pore structure, thereby reducing the difficulty of ion liquid phase transmission and improving the rate performance of the secondary battery; in addition, the graphite material can also have good particle stacking properties, which is beneficial to improving the compaction density of the negative electrode film layer, thereby further improving the energy density of the secondary battery.

[0140] In some embodiments, during the step of crushing the raw material, a crusher, such as a jaw crusher, can be used to crush the coke raw material. For example, the raw material can be crushed to a predetermined particle size and then sieved, such as through a 3-20 mesh screen.

[0141] In some embodiments, in the step of shaping the raw material, a shaping machine can be used to shape the crushed raw material. The shaping process can reduce burrs on the surface of the crushed raw material.

[0142] In some embodiments, during the step of classifying the raw materials, an air classifier can be used to classify the shaped raw materials. Optionally, the induced air frequency can be greater than or equal to 20 Hz, and the classification frequency can be greater than or equal to 35 Hz. Classification can reduce the content of large particles and fine powder in the resulting precursor.

[0143] The raw materials are crushed, shaped and classified to obtain a primary particle precursor.

[0144] In some embodiments, the primary particle precursor can be granulated to obtain a secondary particle precursor. A binding material can be added for granulation, and the binding material can use any substance known in the art that can be used to prepare negative electrode active materials, for example, one or more of coal tar, petroleum asphalt, polymer compounds and resins. After the binding material is heated and melted, the viscosity is not high and good fluidity is maintained, which can reduce the agglomeration of the raw material particles in the subsequent preparation process, thereby reducing the problems of increased surface defects and increased surface active sites of the carbon-based negative electrode active material particles due to the need to add a depolymerization process.

[0145] "Primary particles" generally refer to individual, small crystal grains. In some cases, even in amorphous particles, when there are both primary particles and agglomerated particles, the primary particles can also be referred to as primary particles. Agglomerated particles formed by the agglomeration of multiple primary particles or primary particles are referred to as "secondary particles."

[0146] In some embodiments, the prepared secondary particles may be shaped and graded. In some embodiments, the volume distribution particle size Dv50 of the secondary particle precursor is 11 μm-15 μm, optionally 12 μm-15 μm, 11.5 μm-15.5 μm, 12.5 μm-15 μm, 11 μm-14.5 μm, or 12 μm-14 μm.

[0147] By adjusting the particle size of the secondary particle precursor within the above range, it is helpful to control the particle size of the secondary particles in the negative electrode active material and improve the kinetic performance and cycle performance of the secondary battery.

[0148] In some embodiments, a carbonization treatment is included before the graphitization treatment. In some embodiments, the treatment temperature of the carbonization treatment is 950° C. to 1350° C. In some embodiments, the treatment temperature of the carbonization treatment can be selected from 950° C., 1000° C., 1100° C., 1200° C., 1300° C., or 1350° C., or a range between any two of the above values.

[0149] The carbonization treatment may be performed before the graphitization treatment, after the graphitization treatment, or both before and after the graphitization treatment.

[0150] 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.

[0151] In some embodiments, the maximum power of the graphitization process is 70%-90% of the rated power of the equipment. In some embodiments, the maximum power of the graphitization process is 70%, 75%, 80%, 85%, 90% of the rated power, or any range therebetween. It is understood that graphitization processing equipment refers to any device capable of performing graphitization processing, including but not limited to Acheson furnaces, box furnaces, internal series furnaces, continuous graphitization furnaces, electric calcining furnaces, medium frequency furnaces, tubular furnaces, and the like. The rated power of graphitization processing equipment produced by different manufacturers may vary, and the rated power can be selected based on actual conditions.

[0152] In some embodiments, the graphitization treatment equipment is an internal string furnace, and the rated power of the internal string furnace is 20000W-32000W. The graphitization treatment time is 10h-30h, and can be optionally 15h-25h;

[0153] 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 is 30 hours to 50 hours, and can be optionally 40 hours to 50 hours.

[0154] The maximum power of the graphitization treatment equipment used in the present disclosure needs to be lower than the rated power of the graphitization treatment equipment to achieve uniformity of the temperature field during the graphitization treatment process.

[0155] In some embodiments, the maximum power of the graphitization treatment is 21000 W to 25000 W. In some embodiments, the maximum power of the graphitization treatment can be 23000 W, 23500 W, 24000 W, 24500 W, 25000 W, or any range therebetween.

[0156] By controlling the maximum power of the graphitization treatment, the graphitization degree of the graphite material during the heat treatment process can be effectively controlled, so that the graphite material has a graphitization degree within a suitable range, which is conducive to obtaining a graphite material that takes into account both cycle stability and high gram capacity.

[0157] In some embodiments, the maximum power constant power duration of the graphitization treatment is 10 hours to 50 hours.

[0158] In some embodiments, the constant power duration of the maximum power of the graphitization treatment is 10 h, 15 h, 20 h, 45 h, 50 h, or any range therebetween.

[0159] The appropriate graphitization treatment time is 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; it can also effectively improve the graphitization degree of the graphite material, thereby facilitating the simultaneous improvement of the energy density and cycle life of the secondary battery.

[0160] In some embodiments, the graphitization equipment is a graphitization furnace, the graphitization treatment temperature is 2500° C. to 3000° C., and the constant temperature treatment time is 9 hours to 50 hours. In some embodiments, the graphitization furnace treatment temperature is 2600° C. to 3000° C., and the constant temperature treatment time is 10 hours to 50 hours.

[0161] In some embodiments, the graphitized product after the graphitization treatment is subjected to post-processing to obtain a graphite material, wherein the post-processing includes screening and demagnetization.

[0162] In some embodiments, the graphitized product after the graphitization treatment is subjected to a fusion treatment and a pitch coating treatment to obtain a graphite material. In some embodiments, the fusion treatment frequency is 20-40 Hz, and / or the fusion treatment time is 5-15 minutes.

[0163] The purpose of spheroidization and de-edgeing can be achieved by subjecting the graphitized product to fusion treatment before asphalt coating treatment. On the one hand, the intermediate obtained by fusion spheroidization has a relatively regular structure, which can improve the powder compaction density of the intermediate. On the other hand, the small particles of graphite produced by de-edgeing can fill the voids in the intermediate material, further improving the powder compaction density of the intermediate. The fusion treatment can effectively compensate for the adverse effects of asphalt coating treatment on the powder compaction density of the material, which is conducive to obtaining a negative electrode film layer with a high compaction density, and is conducive to obtaining a graphite material with high energy density and excellent rate performance.

[0164] In some embodiments, the frequency of the fusion process may be selected to be 20 Hz, 25 Hz, 30 Hz, 35 Hz, or 40 Hz, or a range between any two of the above values.

[0165] The frequency of the fusion process affects the powder compaction density and specific surface area of ​​the graphite material. A high fusion process frequency can increase the powder compaction density of the graphite material while also preventing damage to the processing equipment caused by an excessively high fusion process frequency. In addition, a high fusion process frequency can also increase the specific surface area of ​​the graphite material and improve the material's rate performance.

[0166] In some embodiments, the fusion treatment time is 5-15 minutes. In some embodiments, the fusion treatment time can be selected from 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, or a range between any two of the above values.

[0167] In some embodiments, the asphalt-coated product may be post-processed.

[0168] In some embodiments, the graphite material can be obtained by mixing the primary graphitized particles and the secondary graphitized particles in a predetermined ratio. In some embodiments, the primary graphitized particles and the secondary graphitized particles are mixed in a mass ratio of (1:1) to (6:4). In some embodiments, the obtained primary graphitized particles and the secondary graphitized particles are mixed in a mass ratio of 50:50, 54:46, or 60:40.

[0169] In some embodiments, the primary graphitized particles and the secondary graphitized particles may be mixed and then post-processed.

[0170] In the present disclosure, as shown in FIG. 1 to FIG. 3 , the negative electrode film layer 102 further includes a middle region 1023 located between the first region 1022 of the negative electrode film layer and the second region 1021 of the negative electrode film layer and having a thickness of 0.4H.

[0171] In some embodiments, the intermediate region includes the first carbon-based material and / or the second carbon-based material. For example, as shown in FIG3 , the intermediate region 1023 may be the same as the first region 1022 in composition, whereby the first carbon-based material is distributed in the thickness direction of the negative electrode film layer 102 within the range of the thickness from the first surface 102a of the negative electrode film layer to 0.7H; or, as shown in FIG2 , the intermediate region 1023 may be the same as the second region 1021 in composition, whereby the second carbon-based material is distributed in the thickness direction of the negative electrode film layer 102 within the range of the thickness from the second surface 102b of the negative electrode film layer to 0.7H; or, as shown in FIG1 , the intermediate region 1023 includes both the first carbon-based material and the second carbon-based material. In this case, the intermediate region 1023 includes both a layer structure having the first carbon-based material and a layer structure having the second elastic carbon-based material, and the two-layer structure may further have a layer interface.

[0172] In some embodiments, the compaction density of the negative electrode film layer is 1.30 g / cm 3 -1.60g / cm 3 For example, the compaction density of the negative electrode film layer is 1.43 g / cm 3 , 1.45g / cm 3 , 1.53g / cm 3 , 1.50g / cm 3 、1.58g / cm 3 Or the range between any two of the above values.

[0173] In the present disclosure, the compaction density of the negative electrode film layer can be tested using methods known in the art. As an example, an electronic balance is used to weigh a negative electrode sheet test sample with an area of ​​S, and the weight is recorded as W1. The thickness of the negative electrode sheet T1 is measured using a caliper. The weighed electrode sheet film layer is then wiped off, the weight of the negative electrode current collector is weighed, recorded as W2, and the thickness of the negative electrode current collector T2 is measured using a caliper. The compaction density of the negative electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0174] 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 film layer is 13.0 mg / cm 2 , 12mg / cm 2 、11mg / cm 2 、10mg / cm 2 , 9mg / cm 2 , 8mg / cm 2 , 7mg / cm 2 Adjusting the surface density of the negative electrode film layer helps to increase the energy density of the secondary battery and improve the cycle performance of the secondary battery.

[0175] In this 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.

[0176] Excessively high electrode compaction density and / or surface density are not conducive to the migration of active ions in the negative electrode. Adjusting the compaction density and / or surface density of the negative electrode film layer can reduce the impact on the active ion migration performance and improve the energy density of the secondary battery.

[0177] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0178] 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, other 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.

[0179] 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.).

[0180] In some embodiments, the negative electrode film 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.

[0181] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0182] 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.

[0183] [Positive electrode]

[0184] 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.

[0185] 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.

[0186] 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.).

[0187] 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 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] [Electrolytes]

[0192] 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.

[0193] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] [Isolation film]

[0198] 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.

[0199] 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.

[0200] 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.

[0201] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0202] 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.

[0203] 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.

[0204] 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, FIG4 shows a secondary battery 5 having a square structure as an example.

[0205] In some embodiments, referring to Figure 5, 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.

[0206] 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.

[0207] Figure 6 shows an example battery module 4. Referring to Figure 6 , 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 using fasteners.

[0208] 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.

[0209] 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.

[0210] Figures 7 and 8 illustrate an example battery pack 1. Referring to Figures 7 and 8 , 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 positioned 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.

[0211] 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.

[0212] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0213] Figure 9 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.

[0214] 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.

[0215] Example

[0216] 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.

[0217] 1. Test Method

[0218] 1. Particle size test and particle size distribution test of powder

[0219] Determination method: Referring to GB / T 19077-2016 particle size distribution laser diffraction method, a Master Size 3000 laser particle size analyzer such as Malvern Instruments Ltd. of the United Kingdom was used for determination to obtain volume distribution particle diameters Dv10, Dv50, Dv90, and particle size distribution.

[0220] 2. Negative electrode active material gram capacity test

[0221] A graphite anode active material sample, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly stirred in an appropriate amount of NMP solvent at a mass ratio of 91.6:1.8:6.6 to form a uniform anode slurry. The slurry was evenly coated on the surface of the anode current collector copper foil, dried, and cold-pressed. A lithium metal sheet was then used as the counter electrode, and a polypropylene (PP) film was used as the separator. An electrolyte solution was then injected. The electrolyte formulation used was as follows: LiPF6 was dissolved in an organic solvent prepared by mixing dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) at a weight ratio of 1:1:1 to prepare an electrolyte solution with a concentration of 1.0 mol / L. CR2430 button cells were then 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.

[0222] 3. Cycle performance test of secondary batteries

[0223] At 60°C, the batteries prepared in the 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 of ≤0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge-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.

[0224] 4. Dynamic performance test of secondary batteries

[0225] 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.

[0226] 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 discharged 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 C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, C90% SOC, ...110% SOC, C120% SOC, C130% SOC, C140% SOC, C150% SOC, C160% SOC, C170% SOC, C180% SOC, C190% SOC, C20% SOC, C210% SOC, C220% SOC, C230% SOC, C240% SOC, C250% SOC, C260% SOC, C270% SOC, C300% SOC, C310% SOC, C320% SOC, C330% At 80% SOC, the charging time T (in minutes) required for the secondary battery to charge from 10% SOC to 80% SOC (assuming lithium deposition does not occur in the secondary battery) is calculated using the formula (60 / C10% SOC + 60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0227] 2. Preparation Method of Negative Electrode Active Materials

[0228] Preparation Example 1

[0229] The negative electrode active material H1 is prepared by a method comprising the following steps:

[0230] The petroleum coke with a mosaic and regional structure accounting for 66% was coarsely crushed, and then the coarsely crushed material was crushed and sieved. The sieved material was shaped and graded. During the classification process, fine powder (powder with a volume distribution particle size Dv50 of 3μm-7μm) accounting for 26% of the total mass of the petroleum coke raw material was removed. The classification frequency during the classification process was 35Hz-45Hz, and a precursor with a volume distribution particle size Dv50 of 15.2μm and a particle size distribution (Dv90-Dv10) / Dv50 of 1.44 was obtained;

[0231] The precursor was graphitized using an Acheson furnace with a maximum power of 21,000 W. After maintaining a constant power of the maximum power for 48 hours, the furnace mouth temperature of the Acheson furnace was cooled to 300° C. to obtain an intermediate product; the intermediate product was sieved and demagnetized to obtain a graphite negative electrode active material.

[0232] Preparation Example 2

[0233] The preparation process of the negative electrode active material H2 is similar to that of Preparation Example 1, with the following differences: the raw material used is needle coke with a fiber-type structure accounting for 44%, the volume distribution particle size Dv50 of the precursor is 9.6 μm, and the particle size distribution (Dv90-Dv10) / Dv50 is 1.31; the precursor is then placed in a kiln for pre-carbonization treatment, and during the pre-carbonization treatment, the temperature is raised to 950°C at a heating rate of 5°C / min and kept warm for 20 hours.

[0234] The precursor was graphitized in a continuous graphitization furnace at a temperature of 2600°C. After constant temperature treatment for 10 hours, the material temperature was lowered to 300°C to obtain a graphitized product.

[0235] The graphitized product is sieved and demagnetized, and then added into a high-speed fusion machine for fusion treatment to obtain an intermediate. The fusion frequency is 40 Hz, and the fusion time is 10 min. The intermediate is mixed with asphalt, wherein the mass ratio of the intermediate to the asphalt is 98%:2%. After being fully mixed, it is carbonized at 1150°C for 2 hours. After the demagnetization process, the graphite material H2 is obtained.

[0236] Preparation Example 3

[0237] The preparation process of the negative electrode active material H3 is similar to that of Preparation Example 1. After the needle coke raw material with a fiber structure of 63% is crushed and graded, the crushed material is further shaped and finely powdered using a shaping machine to obtain the first precursor. The volume distribution particle size Dv50 of the first precursor is 8.9μm, the particle size distribution (Dv90-Dv10) / Dv50 is 1.33, and the tap density of the first precursor is 0.64g / cm 3 .

[0238] The first precursor is granulated and reformed in a reactor to obtain a second precursor having a volume distribution particle size Dv50 of 14.0 μm;

[0239] The first precursor and the second precursor were placed in a kiln for carbonization treatment at a temperature of 1100°C and a high temperature zone time of 24 hours to obtain a first intermediate product and a second intermediate product. The tap density of the first intermediate product was 0.95 g / cm 3 The tap density of the second intermediate product is 0.90g / cm 3 ;

[0240] The first intermediate product and the second intermediate product are graphitized at a temperature of 2800°C, respectively. The graphitization treatment device is an internal string furnace with a rated power of 28000W. The maximum power of the graphitization treatment is 21500W. The constant power time of the maximum power is maintained for 28 hours, and primary particles and secondary particles are obtained respectively.

[0241] The primary particles and secondary particles were mixed uniformly in a mass ratio of 50:50, and sieved with a 325-mesh sieve to obtain the final product graphite material H3.

[0242] After testing, the powder characteristics and gram capacity of the negative electrode active material are shown in Table 1:

[0243] Table 1

[0244] 3. Preparation method of secondary battery

[0245] Example 1

[0246] 1) Preparation of negative electrode sheet

[0247] Material H1, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene butadiene rubber are fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 97.0:1:1.2:0.8 to form a first slurry. Material H1, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene butadiene rubber are fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 95.5:1:1.2:2.3 to form a second slurry. The second slurry is coated on the negative electrode current collector copper foil. After the drying step, the first slurry is again coated on the electrode containing the second carbon-based material through a coating device. The negative electrode is obtained by cold pressing and cutting. The first slurry is dried to form a first region, and the second slurry is dried to form a second region. The coating weight of the first slurry and the second slurry is the same. The compaction density of the negative electrode film layer is 1.50g / cm 3 , the surface density is 9.49 mg / cm 2 .

[0248] 2) Preparation of positive electrode sheet

[0249] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder PVDF 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 , the surface density is 19.48 mg / cm 2 .

[0250] 3) Preparation of electrolyte

[0251] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Vinylene carbonate (VC) was then added, and the VC content was 2% of the total mass of the electrolyte.

[0252] 4) Isolation film

[0253] A polypropylene film is selected as the isolation film.

[0254] 5) Preparation of secondary batteries

[0255] 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 an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0256] Examples 2 to 7 and Comparative Examples 1 to 2

[0257] The secondary batteries of Examples 2-7 and Comparative Examples 1-2 were prepared similarly to Example 1, except that the type of negative electrode active material and the binder mass content were adjusted. The binder mass content was adjusted by adjusting the amount of negative electrode active material used. For details, see Table 2-1.

[0258] Table 2-1

[0259] The binder content and performance test of the secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 were measured using the above test method. The results are shown in Table 2-2 below:

[0260] Table 2-2

[0261] Comparative Examples 3 to 5

[0262] The preparation method of Comparative Example 3 is similar to that of Example 1, but the coating method is adjusted:

[0263] 1) Preparation of negative electrode sheet

[0264] Material H1, conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent in a weight ratio of 96.3:1:1.2:1.5 to form a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, dried, cold pressed, and cut to obtain a negative electrode sheet. The compacted density of the negative electrode film layer was 1.50 g / cm3 , the surface density is 9.48mg / cm 2 .

[0265] Comparative Examples 4 and 5 were prepared similarly to Comparative Example 3, except that the type of negative electrode active material was modified. Specific preparation parameters, binder mass content in the electrode sheet, and secondary battery performance test results are shown in Table 3.

[0266] Table 3

[0267] When the negative electrode active material and electrode design are identical, the electrode cohesion is related to the type and content of the binder in the negative electrode film. For the same binder type, the greater the binder content between particles, the higher the interparticle bonding strength, or cohesion.

[0268] It can be seen from Examples 1-4 and Comparative Example 1 that when the same negative electrode active material is used in the first region and the second region, in the prepared negative electrode sheet, the binder content in the first region is lower than the binder content in the second region, the cohesion of the first region is smaller than the cohesion of the second region, and the prepared secondary battery has both good cycle performance and fast charging performance.

[0269] It can be seen from Examples 5-7 and Comparative Example 2 that the volume distribution particle size Dv50 of the negative electrode active material in the first region is smaller than the volume distribution particle size Dv50 of the negative electrode active material in the second region. In the prepared negative electrode sheet, the binder content in the first region is lower than the binder content in the second region, the binder content in the first region is lower than the binder content in the second region, the cohesion in the first region is smaller than the cohesion in the second region, and the prepared secondary battery also has good cycle performance and fast charging performance.

[0270] It can be seen from Examples 1-7 and Comparative Examples 1-2 that when the mass content of the binder in the first region is in the range of 0.78%-1.37% and the mass content of the binder in the second region is in the range of 1.79%-2.35%, the secondary battery can have both good cycle performance and fast charging performance.

[0271] As can be seen from Example 1 and Comparative Example 3, Example 3 and Comparative Example 4, and Example 4 and Comparative Example 5, secondary batteries without a secondary coating process for the negative electrode film cannot achieve both cycling performance and fast-charging performance. This indicates that during the drying process of the electrode, the binder migrates to the first region of the film layer as the solvent evaporates, resulting in a higher binder content in the first region than in the second region. This affects the migration of lithium ions in the negative electrode film layer, and thus affects the cycling performance and fast-charging performance of the secondary battery.

[0272] 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 includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, and the binder content in the first area is less than the binder content in the second area.

2. The secondary battery according to claim 1, wherein The first region includes a first binder, and the mass content of the first binder in the first region is 0.78%-2.0%, and optionally 0.78%-1.4%.

3. The secondary battery according to claim 1 or 2, wherein: The second region includes a second binder, and the mass content of the second binder in the second region is 1.0%-3.0%, and optionally 1.79%-2.32%.

4. The secondary battery according to any one of claims 1 to 3, wherein The cohesive force of the first region is greater than or equal to 70 N / m and less than or equal to 125 N / m, and can be optionally 70 N / m-110 N / m.

5. The secondary battery according to any one of claims 1 to 3, wherein The cohesive force of the second region is greater than or equal to 138 N / m and less than or equal to 170 N / m, and can be optionally 145 N / m-170 N / m.

6. The secondary battery according to any one of claims 1 to 5, wherein The first region includes a first carbon-based material, the second region includes a second carbon-based material, and the first carbon-based material and the second carbon-based material are the same carbon-based material.

7. The secondary battery according to claim 6, wherein The first carbon-based material or the second carbon-based material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv10 of the first carbon-based material or the second carbon-based material is greater than or equal to 4 μm, and can be 4 μm-7 μm; (2) the volume distribution particle size Dv50 of the first carbon-based material or the second carbon-based material is 7 μm-18 μm, and can be 8.0 μm-16.0 μm; (3) The volume distribution particle size Dv90 of the first carbon-based material or the second carbon-based material is less than or equal to 40.0 μm, and can be optionally 15 μm-30.0 μm; (4) Particle size distribution of the first carbon-based material or the second carbon-based material (Dv90-Dv10) / Dv50 0.9-1.6, optional 1.10-1.55; (5) The gram capacity of the first carbon-based material or the second carbon-based material is 310 mAh / g to 350 mAh / g; (6) Both the first carbon-based material and the second carbon-based material include artificial graphite.

8. The secondary battery according to any one of claims 1 to 5, wherein The first region includes a first carbon-based material, the second region includes a second carbon-based material, and the first carbon-based material and the second carbon-based material are different carbon-based materials.

9. The secondary battery according to claim 8, wherein The first carbon-based material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv10 of the first carbon-based material is greater than or equal to 3 μm, and can be selected from 3 μm to 7 μm; (2) the volume distribution particle size Dv50 of the first carbon-based material is 5.5 μm-13.5 μm, and can be optionally 7.5 μm-11.5 μm; (3) The volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 30 μm, and can be optionally 15 μm-25 μm; (4) the particle size distribution (Dv90-Dv10) / Dv50 of the first carbon-based material is 0.9-1.6, and can be 1.10-1.55; (5) The gram capacity of the first carbon-based material is 315 mAh / g-335 mAh / g; (6) The first carbon-based material includes artificial graphite.

10. The secondary battery according to claim 8 or 9, wherein: The second carbon-based material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv10 of the second carbon-based material is greater than or equal to 3.5 μm, and can be selected from 3.5 μm to 7 μm; (2) the volume distribution particle size Dv50 of the second carbon-based material is 7.0 μm-14.0 μm, and can be 8.0 μm-12.0 μm; (3) The volume distribution particle size Dv90 of the second carbon-based material is less than or equal to 28 μm, and can be optionally 13 μm-20 μm; (4) the particle size distribution (Dv90-Dv10) / Dv50 of the second carbon-based material is 0.9-1.5, and can be 1.1-1.3; (5) The gram capacity of the second carbon-based material is 345 mAh / g-355 mAh / g; (6) The second carbon-based material includes artificial graphite.

11. The secondary battery according to any one of claims 8 to 10, wherein The volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material.

12. The secondary battery according to any one of claims 8 to 11, wherein The gram capacity of the first carbon-based material is less than the gram capacity of the second carbon-based material.

13. The secondary battery according to any one of claims 1 to 12, wherein: The first binder and the second binder each independently include at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

14. The secondary battery according to any one of claims 1 to 13, wherein The compaction density of the negative electrode film layer is 1.30 g / cm 3 -1.60g / cm 3 and / or, The surface density of the negative electrode film layer is 7 mg / cm 2 -15mg / cm 2 .

15. An electrical device, wherein: The invention comprises the secondary battery according to claims 1 to 14.

Images