Battery cell, battery and electrical apparatus

Abstract

A battery cell, a battery and an electrical apparatus. The battery cell comprises an electrode assembly, the electrode assembly comprising a negative electrode sheet; the negative electrode sheet comprises a negative electrode film layer, the negative electrode film layer having a first surface away from a negative electrode current collector and a second surface opposite to the first surface, and the thickness of the negative electrode film layer being H; a region within a thickness range from the second surface of the negative electrode film layer to 0.3H is a first region of the negative electrode film layer, and a region within a thickness range from the first surface of the negative electrode film layer to 0.3H is a second region of the negative electrode film layer; the first region comprises a first active material, the first active material comprising first graphite; the second region comprises a second active material, the second active material comprising second graphite; in a longitudinal section view of the negative electrode sheet, the amount of pores inside a single particle of the second graphite is greater than the amount of pores inside a single particle of the first graphite. The length of the battery cell is a, the width of the battery cell is b, and the thickness of the battery cell is c, wherein a:b:c=(2000-500):(200-80):(25-8).

Description

Battery cells, batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 2024103631856, filed on March 28, 2024, entitled “Battery Cell, Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to a battery cell, a battery and an electrical device. Background Art

[0004] In recent years, batteries have been widely used in energy storage 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. With the development of society and the application of various fields, the requirements for battery volume energy density are becoming increasingly higher. By adjusting the battery cells to a long sheet structure, the battery integration and volume energy density can be improved. However, the long sheet structure of battery cells has insufficient heat dissipation area, resulting in a sharp increase in internal battery temperature during the cycle, which seriously affects the battery's performance and service life.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery and an electrical device, which can improve the volume energy density of the battery while effectively reducing the temperature rise of the battery cell, improving the bonding strength of the negative electrode sheet, and comprehensively improving the safety performance and performance of the battery.

[0007] A first aspect of the present application provides a battery cell, the battery cell comprising an electrode assembly; the electrode assembly comprising a negative electrode plate; the negative electrode plate comprising 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 disposed opposite to the first surface, the thickness of the negative electrode film layer on a single side of the negative electrode plate being denoted as H, The area from the second surface of the negative electrode film layer to the thickness range of 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area from the first surface of the negative electrode film layer to the thickness range of 0.3H is recorded as the second area of ​​the negative electrode film layer, wherein the first area includes a first active material, the first active material includes a first graphite, the second area includes a second active material, the second active material includes a second graphite, and in the longitudinal cross-section of the negative electrode plate, the pore volume inside a single particle of the second graphite is greater than the pore volume inside a single particle of the first graphite; the length of the battery cell is recorded as a, the width of the battery cell is recorded as b, and the thickness of the battery cell is recorded as c, wherein a:b:c=(2000~500):(200~80):(25~8).

[0008] The negative electrode plate of the present application includes multiple regions in the thickness direction. In the second region away from the current collector, a second graphite with a relatively large pore structure inside the particles is used, which can improve the thermal conductivity of the negative electrode film layer and effectively reduce the internal temperature rise phenomenon of the long-sheet battery cell; in the first region close to the current collector, a first graphite with a relatively small pore structure inside the particles is used, which can improve the adhesion between the first graphite and the current collector, reduce the powder loss of the negative electrode plate during the process and the demolding phenomenon during the battery cycle, and comprehensively improve the safety performance and performance of the battery.

[0009] In any embodiment, a is 500 mm to 2000 mm; and / or b is 80 mm to 200 mm; and / or c is 8 mm to 25 mm.

[0010] In any embodiment, a is 650 mm to 700 mm; and / or b is 110 mm to 120 mm; and / or c is 13 mm to 16 mm.

[0011] By controlling the length, width and height of the battery cell within an appropriate range, the battery cell has a relatively large heat dissipation area, which is beneficial to reducing the internal temperature rise of the battery cell. At the same time, it can also take into account the integration of long-sheet battery cells in the battery, which is beneficial to obtaining a battery with high energy density.

[0012] In any embodiment, the thickness of the negative electrode current collector is less than or equal to 6 μm.

[0013] In order to further improve the volume energy density of battery cells and batteries, the thickness of the negative electrode current collector can be reduced to increase the loading amount of active materials. However, reducing the thickness of the current collector will affect the toughness of the current collector, causing the elongation difference between the electrode film layer and the current collector to increase significantly during the cold pressing process, greatly increasing the risk of electrode breakage.

[0014] The present application adopts a first graphite with a relatively small pore structure inside the particles in the first region close to the current collector. The first graphite with a small pore structure has relatively small ductility under cold pressing pressure, which reduces the ductility of the electrode film layer, reduces the ductility difference between the electrode film layer and the current collector, and reduces the breakage phenomenon during the cold pressing process of the electrode.

[0015] In any embodiment, the thickness of the negative electrode current collector is 4 μm-5.8 μm.

[0016] When the thickness of the negative electrode current collector is within an appropriate range, it can take into account both the energy density of the battery cell and the risk of cold-pressed fracture, and comprehensively improve the performance and preparation performance of the battery cell.

[0017] In any embodiment, the first graphite includes artificial graphite, and the second graphite includes natural graphite.

[0018] In any embodiment, the first graphite is artificial graphite, and the second graphite is natural graphite.

[0019] The technical solution of adopting the first graphite including artificial graphite and the second graphite including natural graphite can achieve the design purpose of the pore volume inside the second graphite particles being greater than the pore volume inside the first graphite particles. At the same time, the crystal development of natural graphite is relatively complete and has excellent conductivity, which is beneficial to reducing the membrane resistance of the negative electrode plate and improving the rate performance of long-sheet battery cells. At the same time, artificial graphite has the advantages of high particle uniformity and high isotropy, and is not easy to break during the battery cycle, which is beneficial to improving the cycle stability of the negative electrode film layer, improving the cycle performance of the battery, and comprehensively improving the electrochemical performance of the battery cell.

[0020] In any embodiment, the artificial graphite and natural graphite satisfy at least one of the following conditions:

[0021] (1) The volume distribution particle size Dv50 of the artificial graphite is smaller than the volume distribution particle size Dv50 of the natural graphite;

[0022] (2) The specific surface area of ​​the artificial graphite is smaller than the specific surface area of ​​the natural graphite;

[0023] (3) The degree of graphitization of the artificial graphite is less than that of the natural graphite;

[0024] (4) The Raman spectrum of the artificial graphite is 1250 cm-1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is less than 1250cm in the Raman spectrum of the natural graphite. -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm - 1 The peak intensity Ig ratio is Id / Ig.

[0025] In any embodiment, the artificial graphite and natural graphite satisfy at least one of the following conditions:

[0026] (1) The volume distribution particle size Dv50 of the artificial graphite is 8 μm-12 μm; and / or, the volume distribution particle size Dv50 of the natural graphite is 15 μm-25 μm;

[0027] (2) The degree of graphitization of the artificial graphite is 80%-94%; and / or the degree of graphitization of the natural graphite is 92%-98%;

[0028] (3) The specific surface area of ​​the artificial graphite is 0.8m 2 / g-1.5m 2 / g; and / or, the specific surface area of ​​the natural graphite is 1.2 m 2 / g-2.0m 2 / g;

[0029] (4) The Raman spectrum of the artificial graphite is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.04-0.34; and / or, the Raman spectrum of the natural graphite at 1250cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.3-0.85.

[0030] In any embodiment, the first region and the second region satisfy at least one of the following conditions:

[0031] (1) The compacted density of the first region is 1.35 g / cm 3 -1.6g / cm 3; and / or, the compacted density of the second region is 1.45g / cm 3 -1.70g / cm 3 ;

[0032] (2) The surface density of the first region is 0.140 g / 1540 mm 2 -0.175g / 1540mm 2 ; and / or, the surface density of the second region is 0.150g / 1540mm 2 -0.185g / 1540mm 2 .

[0033] In any embodiment, the negative electrode film layer satisfies at least one of the following conditions:

[0034] (1) The surface density of the negative electrode film layer is 0.145g / 1540mm 2 -0.180g / 1540mm 2 ;

[0035] (2) The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.65g / cm 3 ;

[0036] (3) The thickness of the negative electrode film layer is 58 μm-91 μm.

[0037] In any embodiment, the first region comprises a first adhesive and the second region comprises a second adhesive;

[0038] The negative electrode sheet satisfies: w1% ≥ w2%,

[0039] Wherein, w1% is the mass percentage of the first binder, based on the total mass of the first region; w2% is the mass percentage of the second binder, based on the total mass of the second region.

[0040] By regulating the mass content of the binder in the first region to be higher than the mass content of the binder in the second region, the bonding force between the first region close to the current collector and the current collector can be improved, thereby reducing the powder loss of the negative electrode during the manufacturing process and the demolding phenomenon during the battery cycle, thereby improving the safety and performance of the battery cell.

[0041] In any embodiment, the w1% is 1.2%-2.0%; and / or the w2% is 0.8%-1.5%.

[0042] In any embodiment, the negative electrode plate further includes a negative electrode primer layer, which is located between the negative electrode current collector and the negative electrode film layer; the negative electrode primer layer includes a negative electrode primer layer binder and a negative electrode primer layer conductor.

[0043] Providing a primer layer in the negative electrode sheet can improve the conductivity of the current collector and the negative electrode film layer, which is beneficial to improving the rate performance and cycle performance of the battery.

[0044] In any embodiment, the negative electrode undercoat layer satisfies at least one of the following conditions:

[0045] (1) The thickness of the negative electrode bottom coating is 1 μm-3 μm;

[0046] (2) Based on the total mass of the negative electrode undercoat layer, the mass percentage of the negative electrode undercoat layer binder is 10%-50%; and / or, based on the total mass of the negative electrode undercoat layer, the mass percentage of the negative electrode undercoat layer conductive agent is 50%-90%.

[0047] In any embodiment, the electrode assembly further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector;

[0048] The thickness of the positive electrode current collector is less than or equal to 15 μm.

[0049] The thickness of the positive electrode current collector is within a smaller range, which can further improve the volume energy density of the battery cell and the battery.

[0050] In any embodiment, the thickness of the positive electrode current collector is 11 μm-14 μm.

[0051] When the thickness of the positive electrode current collector is within an appropriate range, it can further take into account the energy density of the battery cell and the risk of cold-pressed fracture, and comprehensively improve the use performance and preparation performance of the battery cell.

[0052] In any embodiment, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium iron phosphate and modified compounds thereof.

[0053] The positive electrode active material of lithium iron phosphate and its modified compounds has a stable structure and relatively little heat and gas generation during the battery cycle, and is suitable for long-sheet battery cells.

[0054] In any embodiment, the positive electrode film layer includes flaky graphite.

[0055] Flake graphite can improve the conductivity of the electrode and improve the rate performance of the battery cell.

[0056] In any embodiment, the flaky graphite includes primary particles.

[0057] The primary particles of flaky graphite have a small particle size, good dispersibility in the positive electrode slurry, and are evenly distributed in the positive electrode film layer, further improving the conductivity of the electrode.

[0058] In any embodiment, the positive electrode film layer satisfies at least one of the following conditions:

[0059] (1) The surface density of the positive electrode film layer is 0.320g / 1540mm 2 -0.380g / 1540mm 2 ;

[0060] (2) The compaction density of the positive electrode film layer is 2.35 g / cm 3 -2.85g / cm 3 ;

[0061] (3) The thickness of the positive electrode film layer is 70 μm-105 μm.

[0062] In any embodiment, the positive electrode plate further includes a positive electrode primer layer, which is located between the positive electrode current collector and the positive electrode film layer; the positive electrode primer layer includes a positive electrode primer layer binder and a positive electrode primer layer conductor.

[0063] Providing a primer layer in the positive electrode sheet can improve the conductivity of the current collector and the positive electrode film layer, which is beneficial to improving the rate performance and cycle performance of the battery cell.

[0064] In any embodiment, the positive electrode undercoat layer satisfies at least one of the following conditions:

[0065] (1) The thickness of the positive electrode bottom coating is 1 μm-3 μm;

[0066] (2) Based on the total mass of the positive electrode undercoat layer, the mass percentage of the positive electrode undercoat layer binder is 10%-50%; and / or, based on the total mass of the positive electrode undercoat layer, the mass percentage of the positive electrode undercoat layer conductive agent is 50%-90%.

[0067] In any embodiment, the electrode assembly includes a separator located between the negative electrode sheet and the positive electrode sheet, the separator includes a porous substrate and a composite coating, the composite coating is located on the side of the porous substrate facing the negative electrode sheet, and the composite coating includes an inorganic particle layer and an adhesive layer located on the side of the inorganic particle layer away from the porous substrate.

[0068] wherein the inorganic particle layer comprises aluminum oxide;

[0069] The adhesive layer includes polyvinylidene fluoride particles.

[0070] The positive electrode active material of the present application is a lithium iron phosphate series, which has relatively little volume expansion during the battery cycle. The negative electrode active material is a graphite material, which has a certain volume expansion during the battery cycle. In addition, in order to further improve the volume energy density of the battery cell, thinning the isolation membrane will be considered. Therefore, the composite coating is set on one side, and the composite coating is set to face the negative electrode plate. While alleviating the volume expansion of the negative electrode plate, it can also further improve the volume energy density of the battery cell.

[0071] The inorganic particle layer containing aluminum oxide on the isolation membrane can form a rigid skeleton, so that the isolation membrane has excellent thermal stability and dimensional stability at high temperatures, and can reduce the impact of temperature rise inside the long-sheet battery cell on the isolation membrane. At the same time, the adhesive layer containing polyvinylidene fluoride particles on the isolation membrane can improve the wetting ability and liquid retention ability of the isolation membrane. The polyvinylidene fluoride particles in direct contact with the negative electrode are softened by hot pressing during the battery assembly process, and the isolation membrane is bonded to the negative electrode, thereby increasing the hardness of the battery and improving the battery interface.

[0072] In any embodiment, the isolation film satisfies at least one of the following conditions:

[0073] (1) The thickness of the isolation film is 9 μm-12 μm;

[0074] (2) The thickness of the porous substrate is 6 μm-8 μm;

[0075] (3) The thickness of the adhesive layer is 0.8 μm-2 μm;

[0076] (4) The thickness of the inorganic particle layer is 0.8 μm-1.5 μm.

[0077] In any embodiment, the battery cell includes an outer packaging, and the outer packaging includes a material with a Brinell hardness of less than or equal to 30 HB.

[0078] The outer packaging is made of a material with a hardness of less than or equal to 30HB, which has the advantages of high safety factor, large battery capacity and diversified design, which is conducive to improving the integration of battery cells in secondary batteries and improving the volume energy density of the battery.

[0079] In any embodiment, the outer packaging comprises one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0080] In any embodiment, the electrode assembly includes a plurality of positive electrode sheets and a plurality of negative electrode sheets, the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked along the thickness direction of the battery cell, and the separator of the electrode assembly is continuous.

[0081] The electrode assembly adopts a lamination process, which can improve the space utilization of the battery cell and is suitable for long-sheet battery cells.

[0082] A second aspect of the present application provides a battery, comprising the battery cell described in the first aspect.

[0083] A third aspect of the present application provides an electrical device comprising the battery described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present application;

[0085] FIG2 is a schematic diagram of another embodiment of the negative electrode sheet of the present application;

[0086] FIG3 is a schematic diagram of another embodiment of the negative electrode sheet of the present application;

[0087] FIG4 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0088] FIG5 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0089] Reference numerals:

[0090] 10 negative electrode plate, 101 negative electrode current collector, 102 negative electrode film layer, 102a first surface,

[0091] 102b second surface, 1021 first area, 1022 second area, 1023 middle area,

[0092] 5 battery cells, 51 electrode terminals. DETAILED DESCRIPTION

[0093] Below, the embodiments of the battery cell, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0094] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0095] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0096] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0097] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0098] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0099] Unless otherwise specified, the term "or" is used in this application to be inclusive. 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).

[0100] In the existing technology, battery cells are adjusted to a long sheet structure to improve the integration of the battery and increase the volume energy density of the battery. However, the battery cells with a long sheet structure have the problem of insufficient heat dissipation area, which causes the temperature inside the battery to rise sharply during the cycle, thereby seriously affecting the battery's performance and service life.

[0101] Based on this, the present application provides a battery cell, the length of the battery cell is recorded as a, the width of the battery cell is recorded as b, and the thickness of the battery cell is recorded as c, wherein a:b:c=(2000~500):(200~80):(25~8).

[0102] In some embodiments, a:b:c can be selected from 2000:200:25, 2000:200:8, 2000:80:25, 2000:80:8, 500:200:25, 500:200:8, 500:80:25, 700:120:13, 700:120:16, 700:110:13, 700:110:16, 650:120:16, 650:110:13, 650:120:13, or any range therebetween.

[0103] The battery cell of the present application is a long sheet-type battery cell. When the long sheet-type battery cells are assembled to form a battery, the integration of the battery can be improved to obtain a battery with a high energy density.

[0104] The length a, width b, and thickness c of the battery cell 5 refer to the dimensions of the main body of the battery cell 5 in the length direction X, width direction Y, and thickness direction Z, which do not include the dimensions of the electrode terminals 51 protruding from the main body of the battery cell.

[0105] The two electrode terminals 51 are respectively located on both sides of the battery cell along the length direction X.

[0106] The thickness direction Z of the battery cell is the thickness direction of the negative electrode sheet.

[0107] The length a of a battery cell can be measured using a laser thickness gauge. Three to five random points can be selected during the test and the average value calculated. The width b of a battery cell can also be measured using a laser thickness gauge. Three to five random points can be selected during the test and the average value calculated. The thickness c of a battery cell can also be measured using a laser thickness gauge. Nine random points can be selected during the test and the average value calculated. The ratios of length, width, and thickness (a:b:c) within a battery cell can be calculated using the length a, thickness c, and width b obtained from the above tests.

[0108] As shown in FIG4 , the battery cell 5 includes an electrode assembly and an outer package.

[0109] The electrode assembly includes a negative electrode sheet. FIG. 1 to FIG. 3 are schematic diagrams of embodiments of the negative electrode sheet of the present application. As shown in Figures 1 to 3, the negative electrode plate 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b opposite to the first surface 102a. The thickness of the negative electrode film layer 102 on one side of the negative electrode plate is denoted as H. The region within a thickness range of 0.3H from the second surface 102b of the negative electrode film layer is denoted as a first region 1021 of the negative electrode film layer. The region within a thickness range of 0.3H from the first surface 102a of the negative electrode film layer is denoted as a second region 1022 of the negative electrode film layer. The first region 1021 includes a first active material, which includes a first graphite. The second region 1022 includes a second active material, which includes a second graphite. In a longitudinal cross-section of the negative electrode plate, the pore volume inside a single particle of the second graphite is greater than the pore volume inside a single particle of the first graphite.

[0110] The negative electrode current collector 101 has two opposite surfaces in its thickness direction. The negative electrode film layer 102 is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0111] In some embodiments, the intermediate region 1023 located between the first region 1021 and the second region 1022 includes the first active material and / or the second active material. For example, as shown in FIG1 , the intermediate region 1023 includes both the first active material and the second active material. In this case, the intermediate region 1023 includes both a layer structure comprising the first active material and a layer structure comprising the second active material. The two layer structures may also have a layer interface. Alternatively, as shown in FIG2 , the intermediate region 1023 may be compositionally identical to the first region 1021 , whereby the first active material is distributed over a thickness range of 0.7H from the second surface 102b of the negative electrode film layer. Alternatively, as shown in FIG3 , the intermediate region 1023 may be compositionally identical to the second region 1022 , whereby the second active material is distributed over a thickness range of 0.7H from the first surface 102a of the negative electrode film layer.

[0112] The comparison of the internal pore volume of a single particle of the first graphite in the first region and the internal pore volume of a single particle of the second graphite in the second region can be tested using any method known in the art, for example: the battery cell is disassembled to obtain a negative electrode sheet, the sheet is cut into 6 mm*6 mm pieces, and a cross-section polisher (e.g., an IB-09010CP argon ion cross-section polisher from JEOL, Japan) is used to prepare a cross section of the negative electrode sheet; then, referring to JY / T010-1996, a scanning electron microscope (e.g., a Sigma 5000 from ZEISS, Germany) is used to measure the cross section of the negative electrode sheet. A longitudinal cross-section of the negative electrode sheet was scanned using a 300-type scanning electron microscope; multiple test areas were randomly selected from the test sample, and images of the multiple test areas were obtained using a scanning electron microscope. Finally, the scanned images representing the interior of individual graphite particles in the first and second areas were threshold segmented using ImageJ software. The gray-white contrast area represented particles, and the black contrast area represented pores. The ratio of the area of ​​the black contrast area to the total area of ​​the individual graphite particles within the range of the individual graphite particles was used as the internal pore volume of the individual graphite particles. During the test, 10 first graphite particles in the first area and 10 second graphite particles in the second area were randomly selected to test the internal pore volume of the individual graphite particles, and then the average value was taken. The result of comparing the internal pore volume of the individual first graphite particles in the first area with the internal pore volume of the individual second graphite particles in the second area was obtained.

[0113] In the present application, the thickness H of the negative electrode film layer on one side of the negative electrode plate can be tested by methods known in the art. As an example, it is measured using a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0114] The negative electrode sheet of this application includes multiple regions along its thickness. A second graphite with relatively large pores within the particles is used in the second region away from the current collector. This improves the thermal conductivity of the negative electrode film layer and effectively reduces the internal temperature rise of long-sheet battery cells. A first graphite with relatively small pores within the particles is used in the first region near the current collector. This improves the adhesion between the first region and the current collector, reduces powder loss during the manufacturing process and film release during battery cycling, and comprehensively improves the safety and performance of the battery. Compared to single-layer sheets made from a single graphite material, this multi-layer design can improve the temperature rise of battery cells that are long in length and thin in thickness, and further improves the adhesion of the negative electrode film layer.

[0115] In some embodiments, the first graphite is artificial graphite or natural graphite, the second graphite is artificial graphite or natural graphite, and in the longitudinal cross-section of the negative electrode sheet, the pore volume inside a single particle of the second graphite is greater than the pore volume inside a single particle of the first graphite.

[0116] As mentioned above, by controlling the internal pore volume of a single particle of the second graphite to be greater than the internal pore volume of a single particle of the first graphite, the purpose of reducing the internal temperature rise of the battery cell and improving the adhesion of the negative electrode film layer can be achieved. There is no restriction on the type of the first graphite or the second graphite. For example, different preparation methods can be used to prepare artificial graphites with different internal pore volumes of particles. The second graphite uses artificial graphite with a larger internal pore volume of a single particle, and the first graphite uses artificial graphite with a smaller internal pore volume of a single particle.

[0117] In some embodiments, a is 500 mm to 2000 mm. In some embodiments, a is 650 mm to 700 mm.

[0118] In some embodiments, a can be selected as 500 mm, 600 mm, 700 mm, 800 mm, 900 mm, 1000 mm, 1100 mm, 1200 mm, 1300 mm, 1400 mm, 1500 mm, 1600 mm, 1700 mm, 1800 mm, 1900 mm, 2000 mm or any range therebetween.

[0119] In some embodiments, b is 80 mm to 200 mm. In some embodiments, b is 110 mm to 120 mm.

[0120] In some embodiments, b can be selected as 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, 200 mm or any range therebetween.

[0121] In some embodiments, the c is 8 mm to 25 mm. In some embodiments, the c is 13 mm to 16 mm.

[0122] In some embodiments, the c can be selected as 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm or any range of values ​​therebetween.

[0123] By controlling the length, width and height of the battery cell within an appropriate range, the battery cell has a relatively large heat dissipation area, which is beneficial to reducing the internal temperature rise of the battery cell. At the same time, it can also take into account the integration of long-sheet battery cells in the battery, which is beneficial to obtaining a battery with high energy density.

[0124] In some embodiments, the thickness of the negative electrode current collector is less than or equal to 6 μm.

[0125] In some embodiments, the thickness of the negative electrode current collector is any one of less than or equal to 6 μm, less than or equal to 5 μm, less than or equal to 4 μm, and less than or equal to 3 μm.

[0126] The thickness of the negative electrode current collector can be tested using methods known in the art. For example, it can be measured using a micrometer (eg, Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0127] In order to further improve the volume energy density of battery cells and secondary batteries, the thickness of the negative electrode current collector can be reduced. However, reducing the thickness of the current collector will reduce the toughness of the current collector, which will significantly increase the elongation difference between the electrode film layer and the current collector during the cold pressing process, and greatly increase the risk of electrode breakage.

[0128] The present application adopts a first graphite with a relatively small pore structure inside the particles in the first region close to the current collector. The first graphite with a small pore structure has relatively small ductility under cold pressing pressure, which reduces the ductility of the electrode film layer, reduces the ductility difference between the electrode film layer and the current collector, and reduces the breakage phenomenon during the cold pressing process of the electrode.

[0129] In some embodiments, the thickness of the negative electrode current collector is 4 μm-5.8 μm. In some embodiments, the thickness of the negative electrode current collector can be 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5.0 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, or any range therebetween.

[0130] When the thickness of the negative electrode current collector is within an appropriate range, it can take into account both the energy density of the battery cell and the risk of cold-pressed fracture, and comprehensively improve the performance and preparation performance of the battery cell.

[0131] In some embodiments, the first graphite includes artificial graphite, and the second graphite includes natural graphite.

[0132] By using artificial graphite as the first graphite and natural graphite as the second graphite, the design goal of the pore volume inside a single particle of the second graphite being greater than the pore volume inside a single particle of the first graphite can be achieved. At the same time, the crystal development of natural graphite is relatively complete, and it has excellent conductivity, which is beneficial to reducing the membrane resistance of the negative electrode plate and improving the rate performance of the long-sheet battery cell. At the same time, artificial graphite has the advantages of high particle uniformity and high isotropy, and is not easy to break during the battery cycle, which is beneficial to improving the cycle stability of the negative electrode film layer and improving the cycle performance of the battery.

[0133] The negative electrode film layer of the present application adopts a multi-layer structure design, and different film layers contain artificial graphite and natural graphite respectively, combining the respective advantages of artificial graphite and natural graphite to comprehensively improve the cycle performance and rate performance of the battery.

[0134] In some embodiments, the first graphite is artificial graphite and the second graphite is natural graphite, which can improve the cycle performance and rate performance of the battery.

[0135] In some embodiments, the weight content of the artificial graphite is greater than or equal to 80%, and can be 80% to 100%, based on the weight of the first active material. In some embodiments, the weight content of the artificial graphite can be 80%, 90%, 100%, or any range therebetween, based on the weight of the first active material.

[0136] In some embodiments, based on the mass of the second active material, the mass content of the natural graphite is greater than or equal to 80%, and can be optionally 80%-100%.

[0137] In some embodiments, based on the mass of the second active material, the mass content of the natural graphite may be 80%, 90%, 100%, or any range therebetween.

[0138] In some embodiments, the volume distribution particle size Dv50 of the artificial graphite is smaller than the volume distribution particle size Dv50 of the natural graphite.

[0139] Scrape the powder from the second region on the side of the negative electrode sheet away from the current collector, and monitor the thickness change with a micrometer. Control the scraping thickness at 0.3 hours so that all the scraped powder comes from the second region. Use strong tape to completely tear the negative electrode film from the current collector, scrape the powder from the first region on the side of the negative electrode film close to the current collector, and monitor the thickness change with a micrometer. Control the scraping thickness at 0.3 hours so that all the scraped powder comes from the first region. Weigh 50 mg of the collected first region sample and second region sample respectively. Filter the first region sample or the second region sample, dry it, and then sinter the dried sample at 400°C for 2 hours to remove the binder and conductive agent, thus obtaining the negative electrode active material of the first region or the second region.

[0140] As used herein, the term "Dv50" refers to the particle size corresponding to the cumulative volume distribution number of particles reaching 50% in a particle size distribution curve.

[0141] In this application, the volume distribution particle size Dv50 of the material can be measured using methods known in the art. As an example, referring to GB / T 19077-2016, it can be measured using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer produced by Malvern Instruments Ltd. in the UK.

[0142] Smaller particle size helps to improve the pore structure in the membrane layer, making the porosity of the second region higher than that of the first region, making the pore structure in the second region in direct contact with the electrolyte less likely to be blocked, which is beneficial to improving the wettability of the electrolyte and improving the dynamic performance of the battery during long-term cycling.

[0143] In some embodiments, the specific surface area of ​​the artificial graphite is smaller than the specific surface area of ​​the natural graphite.

[0144] In this application, the specific surface area of ​​artificial graphite and natural graphite can be measured using methods known in the art. As an example, the specific surface area is measured using nitrogen adsorption specific surface area analysis and calculation using the BET (Brunauer Emmett Teller) method, as described in GB / T 19587-2017. The test instrument can be a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0145] Natural graphite has a relatively large specific surface area and sufficient adsorption sites, which can promote the adsorption of active ions and improve the kinetic performance of the battery.

[0146] In some embodiments, the degree of graphitization of the artificial graphite is less than that of the natural graphite.

[0147] As used herein, the term "degree of graphitization" refers to an indicator measuring the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure.

[0148] In this application, the degree of graphitization of artificial graphite and natural graphite can be tested using methods known in the art. As an example, an X-ray diffractometer (such as a Bruker D8 Discover) is used for testing, with reference to JIS K0131-1996 and JB / T4220-2011, to determine the average interlayer spacing d002 of the (002) plane in the crystal structure of the graphite material. The degree of graphitization is then calculated using the formula g = (0.344 - d002) / (0.344 - 0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the (002) plane in the crystal structure of the graphite material expressed in nanometers (nm).

[0149] Active materials with low graphitization often have larger interlayer spacing, which facilitates the intercalation and deintercalation of active ions. The low graphitization of artificial graphite in the first region of the negative electrode, away from the current collector, improves battery kinetics while minimizing the volume expansion of the electrode caused by the intercalation and deintercalation of active ions, ultimately improving the battery's cycling stability.

[0150] In some embodiments, the Raman spectrum of the artificial graphite is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is less than 1250cm in the Raman spectrum of the natural graphite. -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio is Id / Ig.

[0151] In this application, the Id / Ig of the Raman spectra of artificial graphite and natural graphite can be tested by methods known in the art. As an example, this application refers to GB / T 40219-2021 and uses a LabRAM HR Evolution laser micro-Raman spectrometer for testing. A solid laser with a wavelength of 523 nm is used as the light source, with a beam diameter of 1.2 μm and a power of 1 mW. 100 points are collected in an area of ​​100 μm × 100 μm, and the Id / Ig of each point at 1250 cm is calculated. -1 Up to 1500cm -1The peak intensity Id (in the example, peak height) and 1500cm -1 to 1650cm -1 The ratio of Id / Ig of the peak intensity Ig (exemplified as peak height) is taken, and the median of the Id / Ig values ​​of 100 points is taken as the Id / Ig of the graphite material.

[0152] The Id / Ig of the Raman spectrum can be used to characterize the degree of disorder on the surface of the active material. The Id / Ig of natural graphite in the second region of the negative electrode, located away from the current collector, is greater than the Id / Ig of artificial graphite in the first region, which means that the active material in the second region outside the electrode has a higher average degree of disorder than the active material in the first region. In materials with high disorder, active ions are more easily embedded in and extracted from the active material, which can effectively reduce the volume expansion during the ion embedding and extraction process and improve the cycle performance of the battery; at the same time, the electrolyte is also more easily infiltrated with the active material, thereby improving the kinetic performance of the battery.

[0153] In some embodiments, the volume distribution particle size Dv50 of the artificial graphite is 8 μm-12 μm. In some embodiments, the volume distribution particle size Dv50 of the artificial graphite can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm or any range therebetween.

[0154] In some embodiments, the volume distribution particle size Dv50 of the natural graphite is 15 μm-25 μm. In some embodiments, the volume distribution particle size Dv50 of the natural graphite can be selected from 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or any range therebetween.

[0155] In some embodiments, the degree of graphitization of the artificial graphite is 80%-94%. In some embodiments, the degree of graphitization of the artificial graphite can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or any range therebetween.

[0156] In some embodiments, the degree of graphitization of the natural graphite is 92%-98%. In some embodiments, the degree of graphitization of the natural graphite can be 92%, 93%, 94%, 95%, 96%, 97%, 98% or any range therebetween.

[0157] In some embodiments, the specific surface area of ​​the artificial graphite is 0.8 m 2 / g-1.5m 2 In some embodiments, the specific surface area of ​​the artificial graphite can be 0.8m2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or any range of values ​​between them.

[0158] In some embodiments, the specific surface area of ​​the natural graphite is 1.2 m 2 / g-2.0m 2 In some embodiments, the specific surface area of ​​the natural graphite can be 1.2 m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g or any range of values ​​between them.

[0159] In some embodiments, the Raman spectrum of the artificial graphite is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig of the artificial graphite is 0.04-0.34. In some embodiments, the Raman spectrum of the artificial graphite at 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig can be selected as 0.04, 0.08, 0.12, 0.14, 0.18, 0.20, 0.24, 0.28, 0.30, 0.34 or any numerical range therebetween.

[0160] In some embodiments, the ratio of the peak intensity Id at 1250 cm-1 to 1500 cm-1 and the peak intensity Ig at 1500 cm-1 to 1650 cm-1 in the Raman spectrum of the natural graphite is 0.3-0.85. -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1The peak intensity Ig ratio Id / Ig can be selected as 0.30, 0.38, 0.42, 0.48, 0.50, 0.54, 0.58, 0.60, 0.64, 0.68, 0.72, 0.78, 0.80, 0.85 or any numerical range therebetween.

[0161] The parameters of the artificial graphite and natural graphite mentioned above may be design parameters in the process of preparing the negative electrode film layer, and may also include parameters of materials obtained by testing the negative electrode sheets obtained by disassembling the battery cells.

[0162] In some embodiments, the compacted density of the first region is 1.35 g / cm 3 -1.6g / cm 3 In some embodiments, the compacted density of the first region may be 1.35 g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 or any range of values ​​between them.

[0163] In some embodiments, the compacted density of the second region is 1.45 g / cm 3 -1.70g / cm 3 In some embodiments, the compacted density of the second region may be 1.45 g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 or any range of values ​​between them.

[0164] In some embodiments, the compacted density of the second region has a meaning well known in the art and can be tested using methods known in the art. The battery cell is disassembled to obtain the negative electrode pole piece, which is punched into small discs with an area of ​​S1. The discs are weighed and recorded as M1. The thickness H of the negative electrode film layer on one side is measured using a micrometer. Powder from the second region is scraped from the side of the negative electrode pole piece away from the current collector, and the thickness change is monitored using a micrometer. The scraped thickness is controlled to 0.3H so that all the scraped powder comes from the second region. The pole piece after the powder is scraped is weighed and recorded as M2. The compacted density of the second region P2 = (M1-M2) / (0.3H×S1).

[0165] In some embodiments, the compaction density of the first region has a meaning well known in the art and can be tested using methods known in the art. The battery cell is disassembled to obtain a negative electrode sheet, which is punched into small discs with an area of ​​S1. The thickness H of the negative electrode film layer on one side is measured using a micrometer. Powder from the first region is scraped from the side of the negative electrode sheet away from the current collector, and the thickness change is monitored using a micrometer. The scraped thickness is controlled to 0.7H, so that the remaining film layer is entirely the first region. The sheet after the powder is scraped is weighed and recorded as M3. The negative electrode film layer of the weighed negative electrode sheet is then completely wiped off, and the weight of the negative electrode current collector is weighed and recorded as M4. The compaction density of the first region P1 = (M3-M4) / (0.3H×S1).

[0166] Controlling the compaction density of the first region and the second region within an appropriate range can increase the compaction density of the negative electrode film layer and the energy density of the battery cell. At the same time, the appropriate compaction density also allows the electrolyte to fully infiltrate the negative electrode sheet during the cycle, thereby improving the cycle performance and rate performance of the battery.

[0167] In some embodiments, the surface density of the first region is 0.140 g / 1540 mm 2 -0.175g / mm 2 In some embodiments, the surface density of the first region may be 0.140 g / 1540 mm 2 、0.145g / mm 2 , 0.150g / 1540mm 2 、0.155g / mm 2 , 0.160g / 1540mm 2 、0.165g / mm 2 , 0.170g / 1540mm 2 、0.175g / mm 2 or any range of values ​​between them.

[0168] In some embodiments, the surface density of the second region is 0.150 g / mm 2 -0.185g / mm 2 In some embodiments, the surface density of the second region may be 0.150 g / 1540 mm 2 、0.155g / mm 2 , 0.160g / 1540mm 2 、0.165g / mm 2 , 0.170g / 1540mm 2 、0.175g / mm 2 , 0.180g / 1540mm 2 、0.185g / mm2 or any range of values ​​between them.

[0169] The areal density of the first region or the second region can be measured using methods known in the art. For example, using the longitudinal slice of the negative electrode obtained in the aforementioned test, the thickness of the first region mixed with the second region can be obtained, denoted as H1 and H2. Combined with the compacted density P1 of the first region or the compacted density P2 of the second region obtained in the aforementioned test, the coating areal density of the first region can be calculated as W1 = P1 × H1, and the coating areal density of the second region can be calculated as W2 = P2 × H2.

[0170] Controlling the coating surface density of the first region and the second region within an appropriate range can increase the coating surface density of the negative electrode film layer and improve the energy density of the battery cell. At the same time, the appropriate coating surface density also allows the electrolyte to fully infiltrate the negative electrode plate during the cycle, thereby improving the cycle performance and rate performance of the battery.

[0171] In some embodiments, the surface density of the negative electrode film layer is 0.145g / 1540mm 2 -0.180g / 1540mm 2 In some embodiments, the surface density of the negative electrode film layer can be 0.145 g / mm 2 , 0.150g / 1540mm 2 、0.155g / mm 2 , 0.160g / 1540mm 2 、 0.165g / mm 2 , 0.170g / 1540mm 2 、0.175g / mm 2 、0.180g / mm 2 or any range of values ​​between them.

[0172] The areal density of the negative electrode film layer can be measured using methods known in the art. For example, disassemble the battery cell to obtain the negative electrode pole piece, punch it into small discs with an area of ​​S1, and weigh this disc, recording it as M5. Then, wipe off the negative electrode film layer from the weighed negative electrode pole piece, and weigh the negative electrode current collector, recording it as M0. The areal density of the negative electrode film layer = (M5 - M0) / S1.

[0173] In some embodiments, the compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.65g / cm 3 In some embodiments, the compaction density of the negative electrode film layer can be 1.40 g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3, 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 or any range of values ​​between them.

[0174] The compacted density of the negative electrode film can be tested using methods known in the art. For example, disassemble the battery cell to obtain the negative electrode pole piece, punch it into small discs with an area of ​​S1, weigh it, record it as M5, and use a micrometer to measure the thickness H of the negative electrode film on one side. Then, wipe off the weighed pole piece and weigh the negative electrode current collector, record it as M0. The compacted density of the negative electrode film layer is then calculated as PD = (M5 - M0) / [H × S1].

[0175] In some embodiments, the thickness of the negative electrode film layer is 58 μm-91 μm. In some embodiments, the thickness of the negative electrode film layer can be selected from 58 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 91 μm, or any range therebetween.

[0176] The thickness of the negative electrode film layer can be tested using methods known in the art. For example, a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm) is used for measurement.

[0177] Controlling the coating surface density, compaction density or thickness of the negative electrode film layer within an appropriate range can increase the loading amount of the active material while allowing the electrolyte to fully infiltrate the negative electrode film layer, taking into account the energy density, rate performance and cycle performance of the battery.

[0178] The compaction density, coating surface density or thickness of the first region, the second region and the negative electrode film layer can be design parameters in the process of preparing the negative electrode film layer, and also include parameters obtained by testing the negative electrode sheets obtained by disassembling the battery cell.

[0179] In some embodiments, the first region comprises a first adhesive and the second region comprises a second adhesive;

[0180] The negative electrode sheet satisfies: w1% ≥ w2%,

[0181] Wherein, w1% is the mass percentage of the first binder, based on the total mass of the first region; w2% is the mass percentage of the second binder, based on the total mass of the second region.

[0182] The binder content in the first and second regions can be measured using methods known in the art. For example, the following method can be used: disassemble the battery cell to obtain the negative electrode sheet to be tested, cut the negative electrode sheet to be tested into 20 cm x 10 cm pieces, and prepare a clean blade to scrape powder samples from the first and second regions of the negative electrode film layer.

[0183] Scrape the powder from the second area of ​​the negative electrode sheet, away from the current collector. Monitor the thickness change with a micrometer and control the scraping thickness to 0.3 hours, ensuring that all the scraped powder comes from the second area. Use strong tape to completely tear the negative electrode film from the current collector. Scrape the powder from the first area of ​​the negative electrode film, close to the current collector, and monitor the thickness change with a micrometer. Control the scraping thickness to 0.3 hours, ensuring that all the scraped powder comes from the first area.

[0184] 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.

[0185] By regulating the mass content of the binder in the first region to be higher than the mass content of the binder in the second region, the bonding force of the first region close to the current collector can be improved, the powder loss of the negative electrode during the manufacturing process and the demolding phenomenon during the battery cycle can be reduced, and the safety and performance of the battery can be improved.

[0186] In some embodiments, the w1% is 1.2%-2.0%.In some embodiments, the w1% can be 1.2%, 1.4%, 1.6%, 1.8%, 2.0% or any range therebetween.

[0187] In some embodiments, the w2% is 0.8%-1.5%.In some embodiments, the w2% can be 0.8%, 1.0%, 1.2%, 1.4%, 1.5% or any range therebetween.

[0188] In some embodiments, the negative electrode plate further includes a negative electrode primer layer, which is located between the negative electrode current collector and the negative electrode film layer; the negative electrode primer layer includes a negative electrode primer layer binder and a negative electrode primer layer conductor.

[0189] Providing a primer layer in the negative electrode sheet can improve the conductivity and adhesion between the current collector and the negative electrode film layer, which is beneficial to improving the rate performance and cycle performance of the battery.

[0190] In some embodiments, the thickness of the negative electrode undercoat layer is 1 μm-3 μm. In some embodiments, the thickness of the negative electrode undercoat layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any range therebetween.

[0191] The thickness of the negative electrode undercoat layer can be tested using any method known in the art. For example, the thickness of the negative electrode undercoat layer can be tested from the longitudinal cross-section of the negative electrode sheet obtained above.

[0192] The thickness of the negative electrode bottom coating is within an appropriate range, which can improve the conductivity and adhesion between the current collector and the membrane layer, while also reducing the impact of an overly thick bottom coating on the energy density of the battery.

[0193] In some embodiments, the weight percentage of the negative electrode undercoat layer binder is 10%-50% based on the total weight of the negative electrode undercoat layer. In some embodiments, the weight percentage of the negative electrode undercoat layer binder is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any range therebetween based on the total weight of the negative electrode undercoat layer.

[0194] In some embodiments, the weight percentage of the conductive agent in the negative electrode undercoat layer is 50%-90% based on the total weight of the negative electrode undercoat layer. In some embodiments, the weight percentage of the conductive agent in the negative electrode undercoat layer can be 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any range therebetween, based on the total weight of the negative electrode undercoat layer.

[0195] By controlling the binder and conductive agent in the base coating within an appropriate range, the bonding force and conductivity between the current collector and the film layer can be taken into account, and the performance of the negative electrode sheet can be comprehensively improved.

[0196] In some embodiments, the negative electrode bottom coating binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS), but the embodiments of the present application are not limited to this.

[0197] In some embodiments, the negative electrode undercoat conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode undercoat may also optionally include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0198] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0199] In some embodiments, the first region, the second region, and the middle region of the negative electrode film layer may optionally further include a negative electrode conductor and / or a negative electrode binder.

[0200] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS), but the embodiments of the present application are not limited to this.

[0201] In some embodiments, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode film layer may also optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0202] In some embodiments, the negative electrode sheet can be prepared according to the following method: providing a first negative electrode slurry containing a first negative electrode active material and a second negative electrode slurry containing a second negative electrode active material; coating the first negative electrode slurry on a negative electrode collector, coating the second negative electrode slurry on the first negative electrode slurry, and obtaining a negative electrode sheet after drying and cold pressing.

[0203] In some embodiments, in some embodiments, the negative electrode sheet can be prepared according to the following method: providing a first negative electrode slurry containing a first negative electrode active material, a second negative electrode slurry containing a second negative electrode active material, and a negative electrode primer slurry; applying the negative electrode primer slurry on the negative electrode current collector, applying the first negative electrode slurry on the primer slurry, and applying the second negative electrode slurry on the first negative electrode slurry; after drying and cold pressing, a negative electrode sheet is obtained.

[0204] In some embodiments, the negative electrode undercoat layer binder, the negative electrode undercoat layer conductive agent, and optional auxiliary agents may be dispersed in a solvent (eg, deionized water) to form an undercoat slurry.

[0205] In some embodiments, the first negative electrode active material, an optional conductive agent, an optional binder, and other optional auxiliary agents may be dispersed in a solvent (eg, deionized water) to form a first negative electrode slurry.

[0206] In some embodiments, the second negative electrode active material, an optional conductive agent, an optional binder, and other optional auxiliary agents may be dispersed in a solvent (eg, deionized water) to form a second negative electrode slurry.

[0207] The first negative electrode slurry and the second negative electrode slurry can be applied simultaneously in one application or in two separate applications. In some embodiments, the first negative electrode slurry and the second negative electrode slurry are applied simultaneously in one application. Applying them simultaneously in one application can reduce the negative electrode film resistance, thereby further improving the power performance and cycle performance of the battery.

[0208] In some embodiments, the electrode assembly further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector;

[0209] The thickness of the positive electrode current collector is less than or equal to 15 μm.

[0210] In some embodiments, the thickness of the positive electrode current collector is any one of less than or equal to 15 μm, less than or equal to 14 μm, less than or equal to 13 μm, less than or equal to 12 μm, less than or equal to 11 μm, and less than or equal to 10 μm.

[0211] The thickness of the positive electrode current collector can be tested using methods known in the art. For example, it can be measured using a micrometer (eg, Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0212] The positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0213] When the thickness of the positive electrode current collector is within a smaller range, the volume energy density of the battery cell and the secondary battery can be further improved.

[0214] In some embodiments, the thickness of the positive electrode current collector is 11 μm-14 μm. In some embodiments, the thickness of the positive electrode current collector can be 11 μm, 12 μm, 13 μm, 14 μm, or any range therebetween.

[0215] When the thickness of the positive electrode current collector is within an appropriate range, it can further take into account the energy density of the battery cell and the risk of cold-pressed fracture, and comprehensively improve the use performance and preparation performance of the battery cell.

[0216] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0217] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium iron phosphate and modified compounds thereof.

[0218] In some embodiments, the modified compound of lithium iron phosphate includes a doped modified compound of lithium iron phosphate and a coated modified compound of lithium iron phosphate.

[0219] The doping modified compound of lithium iron phosphate refers to the modification elements doped into the lithium iron phosphate body, and the coating modified compound of lithium iron phosphate refers to the modification elements existing in the form of a coating layer on the surface of the lithium iron phosphate body. The modification elements include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, Ta, and C.

[0220] The positive electrode active material of lithium iron phosphate and its modified compounds has a stable structure and relatively little heat and gas generation during the battery cycle, and is suitable for long-sheet battery cells.

[0221] In some embodiments, the positive electrode film layer includes flaky graphite.

[0222] The flaky graphite in the positive electrode film layer can be tested using any method known in the art, for example: disassemble the battery cell to obtain the positive electrode sheet, cut the sheet into 6mm*6mm size, and use a cross-section polisher (for example, the IB-09010CP argon ion cross-section polisher of Japan's JEOL company) to prepare the cross section of the positive electrode sheet; then, referring to JY / T010-1996, use a scanning electron microscope (for example, the Sigma 300 scanning electron microscope of Germany's ZEISS company) to scan the longitudinal cross-section of the positive electrode sheet, and confirm the presence of flaky graphite from the cross-section. The flaky graphite has a layered structure, which resembles fish scales.

[0223] Flake graphite can improve the conductivity of the electrode and improve the rate performance of the battery cell.

[0224] In some embodiments, the flaky graphite includes primary particles.

[0225] As used herein, primary particles have a meaning well known in the art. "Primary particles" generally refer to non-agglomerated particles. Whether flaky graphite is a primary particle can be confirmed by using the longitudinal cross-section of the positive electrode sheet described above.

[0226] The primary particles of flaky graphite have a small particle size, good dispersibility in the positive electrode slurry, and are evenly distributed in the positive electrode film layer, further improving the conductivity of the electrode.

[0227] In some embodiments, the surface density of the positive electrode film layer is 0.320 g / 1540 mm 2 -0.380g / 1540mm 2 .

[0228] In some embodiments, the surface density of the positive electrode film layer can be selected to be 0.320g / 1540mm 2 , 0.330g / 1540mm 2 、0.340g / 1540mm 2 , 0.350g / 1540mm 2 , 0.360g / 1540mm 2 , 0.370g / 1540mm 2 , 0.380g / 1540mm 2 or any range of values ​​between them.

[0229] The areal density of the positive electrode film layer can be measured using methods known in the art. For example, disassemble the battery cell to obtain the positive electrode sheet, punch it into small discs with an area of ​​S1, and weigh them, recording them as M6. Then, wipe off the positive electrode film layer from the weighed positive electrode sheet, and weigh the positive current collector, recording it as M0. The areal density of the positive electrode film layer = (M6 - M0) / S1.

[0230] In some embodiments, the compaction density of the positive electrode film layer is 2.35 g / cm 3 -2.85g / cm 3 .

[0231] In some embodiments, the compaction density of the positive electrode film layer can be 2.35 g / cm 3 , 2.45g / cm 3 , 2.50g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3, 2.65g / cm 3 , 2.70g / cm 3 , 2.75g / cm 3 , 2.80g / cm 3 , 2.85g / cm 3 or any range of values ​​between them.

[0232] The compacted density of the positive electrode film can be measured using methods known in the art. For example, disassemble the battery cell to obtain the positive electrode sheet, punch it into small discs with an area of ​​S1, weigh it, record it as M5, and use a micrometer to measure the thickness T of the positive electrode film on one side. Then, wipe off the weighed electrode sheet and weigh the positive electrode current collector, record it as M0. The compacted density of the positive electrode film is then calculated as PD = (M5 - M0) / [T × S1].

[0233] In some embodiments, the thickness of the positive electrode film layer is 70 μm-105 μm. In some embodiments, the thickness of the positive electrode film layer can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 105 μm, or any range therebetween.

[0234] The thickness of the positive electrode film layer can be tested using methods known in the art. As an example, it can be measured using a micrometer (such as Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0235] The compaction density, coating area density or thickness of the positive electrode film layer can be either design parameters in the process of preparing the positive electrode film layer or parameters obtained by testing the positive electrode sheets obtained by disassembling the battery cells.

[0236] Controlling the coating surface density, compaction density or thickness of the positive electrode film layer within an appropriate range can increase the loading amount of the active material while allowing the electrolyte to fully infiltrate the positive electrode film layer, taking into account the battery's energy density, rate performance and cycle performance.

[0237] In some embodiments, the positive electrode plate further includes a positive electrode primer layer, which is located between the positive electrode current collector and the positive electrode film layer; the positive electrode primer layer includes a positive electrode primer layer binder and a positive electrode primer layer conductor.

[0238] Providing a primer layer in the positive electrode sheet can improve the conductivity and adhesion between the current collector and the positive electrode film layer, which is beneficial to improving the rate performance and cycle performance of the battery.

[0239] In some embodiments, the thickness of the positive electrode undercoat layer is 1 μm-3 μm. In some embodiments, the thickness of the positive electrode undercoat layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any range therebetween.

[0240] The thickness of the positive electrode undercoat layer can be tested using any method known in the art. For example, the thickness of the positive electrode undercoat layer can be tested from the longitudinal cross-section of the positive electrode sheet obtained above.

[0241] The thickness of the positive electrode bottom coating is within an appropriate range, which can improve the conductivity and adhesion between the current collector and the membrane layer, while also reducing the impact of an overly thick bottom coating on the energy density of the battery.

[0242] In some embodiments, the weight percentage of the positive electrode undercoat layer binder is 10%-50% based on the total weight of the positive electrode undercoat layer. In some embodiments, the weight percentage of the positive electrode undercoat layer binder is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any range therebetween based on the total weight of the positive electrode undercoat layer.

[0243] In some embodiments, the weight percentage of the conductive agent in the positive electrode undercoat layer is 50%-90% based on the total weight of the positive electrode undercoat layer. In some embodiments, the weight percentage of the conductive agent in the positive electrode undercoat layer can be 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any range therebetween, based on the total weight of the positive electrode undercoat layer.

[0244] By controlling the binder and conductive agent in the base coating within an appropriate range, the bonding force and conductivity between the current collector and the film layer can be taken into account, and the performance of the positive electrode sheet can be comprehensively improved.

[0245] In some embodiments, the positive electrode undercoat binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin, but the embodiments of the present application are not limited to this.

[0246] In some embodiments, the positive electrode undercoat conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0247] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. In some embodiments, as an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0248] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent.

[0249] In some embodiments, as examples, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0250] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, and positive electrode conductive agent in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0251] In some embodiments, the electrode assembly includes a separator located between the negative electrode sheet and the positive electrode sheet, the separator including a porous substrate and a composite coating, the composite coating located on a side of the porous substrate facing the negative electrode sheet, the composite coating including an inorganic particle layer and an adhesive layer located on a side of the inorganic particle layer away from the porous substrate.

[0252] wherein the inorganic particle layer comprises aluminum oxide;

[0253] The adhesive layer includes polyvinylidene fluoride particles.

[0254] The positive electrode active material of the present application is a lithium iron phosphate series, which has relatively little volume expansion during the battery cycle. The negative electrode active material is a graphite material, which has a certain volume expansion during the battery cycle. In addition, in order to further improve the volume energy density of the battery cell, thinning the isolation membrane will be considered. Therefore, the composite coating is set on one side and faces the negative electrode plate. While alleviating the volume expansion of the negative electrode plate, it can also further improve the volume energy density of the battery cell.

[0255] The inorganic particle layer containing aluminum oxide on the isolation membrane forms a rigid skeleton, which makes the isolation membrane have excellent thermal stability and dimensional stability at high temperature, and can reduce the impact of temperature rise inside the long-sheet battery cell on the isolation membrane. At the same time, the adhesive layer containing polyvinylidene fluoride particles on the isolation membrane can improve the wetting ability and liquid retention ability of the isolation membrane. The polyvinylidene fluoride particles in direct contact with the negative electrode are softened by hot pressing during the battery assembly process and adhere to the negative electrode, thereby increasing the hardness of the battery and improving the battery interface.

[0256] In some embodiments, the thickness of the isolation film is 9 μm-12 μm. In some embodiments, the thickness of the isolation film can be 9 μm, 10 μm, 11 μm, 12 μm, or any range therebetween.

[0257] In some embodiments, the thickness of the porous substrate is 6 μm to 8 μm. In some embodiments, the thickness of the porous substrate can be 6 μm, 7 μm, 8 μm, or any range therebetween.

[0258] In some embodiments, the thickness of the adhesive layer is 0.8 μm-2 μm. In some embodiments, the thickness of the adhesive layer can be 0.8 μm, 1 μm, 1.5 μm, 2 μm, or any range therebetween.

[0259] In some embodiments, the thickness of the inorganic particle layer is 0.8 μm-1.5 μm. In some embodiments, the thickness of the inorganic particle layer can be 0.8 μm, 1 μm, 1.5 μm, or any range therebetween.

[0260] The thickness of the isolation membrane, porous substrate, inorganic particle layer and adhesive layer can be tested using any method known in the art, for example: disassembling the battery cell to obtain the isolation membrane, cutting the isolation membrane with an ion beam cutter to form a cross section; then, using a scanning electron microscope to measure the thickness of the cross section of the isolation membrane and its various layers.

[0261] In some embodiments, the porous substrate comprises at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The porous substrate may be a single-layer film or a multi-layer composite film, without particular limitation. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0262] In some embodiments, the inorganic particle layer further includes a binder, and the binder can be selected from one or more of polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, and styrene-butadiene rubber.

[0263] In some embodiments, the adhesive layer further includes a binder, and the binder can be selected from one or more of polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, and styrene-butadiene rubber.

[0264] In some embodiments, the isolation membrane can be prepared according to the following method: providing an inorganic particle layer slurry containing aluminum oxide and a bonding layer slurry containing polyvinylidene fluoride particles; coating the inorganic particle layer slurry on a porous substrate, coating the bonding layer slurry on the inorganic particle layer slurry, and obtaining the isolation membrane after drying and cold pressing.

[0265] In some embodiments, alumina, a binder, and optional additives may be dispersed in a solvent (eg, deionized water) to form an inorganic particle layer slurry.

[0266] In some embodiments, polyvinylidene fluoride particles, a binder, and optional auxiliary agents may be dispersed in a solvent (eg, NMP) to form an adhesive layer slurry.

[0267] In some embodiments, the electrode unit includes an outer package, and the outer package includes a material with a Brinell hardness of less than or equal to 30 HB.

[0268] The Brinell hardness of the outer packaging material can be tested in accordance with the method specified in "GBT231-1984-Metal Brinell Hardness Test Method".

[0269] Optionally, the Brinell hardness of the outer packaging material is less than or equal to 30HB, that is, the hardness value measured by a quenched steel ball indenter is less than or equal to 30.

[0270] The outer packaging is made of a material with a Brinell hardness of less than or equal to 30HB, which has the advantages of high safety factor, large battery capacity and diversified design, which is conducive to improving the integration of battery cells in secondary batteries and improving the volume energy density of the battery.

[0271] In some embodiments, the outer packaging comprises one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0272] In some embodiments, the electrode assembly includes a plurality of positive electrode sheets and a plurality of negative electrode sheets, the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked along the thickness direction of the battery cell, and the separator of the electrode assembly is continuous.

[0273] The electrode assembly adopts a lamination process, with the positive and negative pole pieces alternately stacked along the thickness direction Z, which can improve the space utilization of the battery cell and is suitable for long-sheet battery cells.

[0274] In a battery cell, the number of electrode assemblies contained in the outer packaging may be one or more. When there are multiple electrode assemblies, the multiple electrode assemblies are arranged in sequence in the thickness direction Z of the battery cell.

[0275] Battery cells also include an electrolyte. The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0276] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0277] 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.

[0278] 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.

[0279] 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.

[0280] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator and negative electrode sheet can be formed into an electrode assembly through a lamination process, and the electrode assembly can be placed in an outer package, dried and injected with the above-mentioned electrolyte. After vacuum packaging, standing, formation and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0281] The batteries mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the batteries mentioned in this application may include battery cells, battery modules, or battery packs. A battery cell is the smallest unit that makes up a battery and independently performs charge and discharge functions. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or in parallel via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam. In some embodiments, the battery may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, and the like.

[0282] The battery cells mentioned in the embodiments of the present application may include lithium-ion battery cells

[0283] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0284] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0285] Figure 5 is a schematic diagram of an exemplary 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 this device, a battery pack or battery module may be used.

[0286] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0287] Example

[0288] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0289] 1. Preparation method

[0290] Example 1

[0291] 1) Preparation of negative electrode sheet

[0292] First slurry: artificial graphite, conductive agent carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC), binder styrene butadiene rubber (SBR) were mixed in a mass ratio of 96.5%:1.2%:0.8%:1.5%, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system was uniform to obtain the first slurry. The volume particle size Dv50 of the artificial graphite was 10 μm, and the BET specific surface area was 1.22 m 2 / g, the graphitization degree is 93.3%, and the Raman spectrum is 1250cm - 1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.08.

[0293] Second slurry: natural graphite, conductive agent carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC), binder styrene butadiene rubber (SBR) were mixed in a mass ratio of 97%:1.0%:0.8%:1.2%, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer until the system was uniform to obtain the second slurry. The volume particle size Dv50 of the natural graphite was 20 μm, and the BET specific surface area was 1.56 m 2 / g, the graphitization degree is 98.0%, and the Raman spectrum is 1250cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.36.

[0294] Negative electrode: The first slurry and the second slurry are extruded simultaneously through a dual-chamber coating device. The first slurry is coated on a copper foil with a thickness of 5μm, and the second slurry is coated on the first slurry; after drying, the electrode is obtained, wherein the coating weight of the first slurry is 0.150g / 1540mm 2The coating weight of the second slurry is 0.160g / 1540mm 2 The initial electrode is cold pressed, and the cold pressed electrode is trimmed, striped, cut and other processes to obtain the negative electrode.

[0295] 2) Positive electrode

[0296] LiFePO4 was mixed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 97:1:2, and an appropriate amount of solvent NMP was added and stirred to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of a 12 μm thick aluminum foil to form a positive electrode film layer. After drying and cold pressing, a positive electrode sheet was obtained, wherein the compaction density of the positive electrode film layer was 2.5 g / cm 3 .

[0297] 3) Electrolyte

[0298] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0299] 4) Isolation film

[0300] Alumina, acrylic block polymer dispersant, and polyvinylidene fluoride binder are dispersed in deionized water solvent in a weight ratio of 93:0.5:6.5 to form an inorganic particle layer slurry;

[0301] Dispersing polyvinylidene fluoride particles, N-dodecyldimethylamine, and polydimethylsiloxane in an acetone solvent at a mass ratio of 80:10:10 to form an adhesive layer slurry;

[0302] The inorganic particle layer slurry is coated on a porous polyethylene substrate, and the bonding layer slurry is coated on the inorganic particle layer slurry. After drying and cold pressing, an isolation film is obtained.

[0303] 5) Preparation of battery cells

[0304] The positive electrode sheet and the negative electrode sheet prepared above are assembled to obtain a laminated electrode assembly; the electrode assembly is placed in an aluminum-plastic film of a soft package material, and after drying, the electrolyte is injected, and after vacuum packaging, standing, and formation processes, a battery is obtained, wherein the adhesive layer of the isolation film is located on the side of the porous polyethylene facing the negative electrode sheet.

[0305] Examples 2-5

[0306] Compared with Example 1, Examples 2-5 adjust the length, width or height of the battery cells. See Table 1 for details.

[0307] Examples 6-8

[0308] Compared with Example 1, the thickness of the copper foil current collector was adjusted in Examples 6-8. See Table 1 for details.

[0309] Examples 9-10

[0310] Compared with Example 1, Examples 9-10 adjusted the coating surface density of the first slurry and the second slurry, see Table 1 for details.

[0311] Comparative Example 1

[0312] Compared with Example 1, the artificial graphite in the first slurry is replaced by the natural graphite, and the natural graphite in the second slurry is replaced by artificial graphite. For specific parameters, see Table 1.

[0313] Comparative Example 2

[0314] Compared with Example 1, the artificial graphite in the first slurry is replaced by the natural graphite. For specific parameters, see Table 1.

[0315] Comparative Example 3

[0316] Compared with Example 1, the natural graphite in the second slurry was replaced with artificial graphite. For specific parameters, see Table 1.

[0317] 2. Test Method

[0318] 1. Elongation of negative electrode membrane

[0319] The copper foil on both sides of the dried negative electrode sheet in the embodiment and comparative example was removed, and then three straight lines were drawn on the negative electrode sheet (the negative electrode sheet could not be pierced). The straight lines were parallel to the length direction of the negative electrode sheet. The lengths of the three straight lines were measured and recorded as L1, L2, and L3 respectively. The negative electrode sheet was placed on a cold press for cold pressing, so that the compaction density of the negative electrode film layer was 1.6 g / cm 3 Measure the lengths of these three straight lines after cold pressing and record them as L1', L2', and L3'. Calculate the elongation of the negative electrode film using the formula E = (L' - L) / L. The results are recorded as E1, E2, and E3, respectively. The average of these three values ​​is recorded as the elongation of the negative electrode film.

[0320] 2. Sheet resistance of the negative electrode

[0321] Cut the dried negative electrode film from the left, center, and right sides of the negative electrode into small discs with a diameter of 3mm. Turn on the Yuanneng Technology electrode resistance meter, place it in the appropriate position on the "probe" of the electrode resistance meter, click the "Start" button, and wait for the reading to stabilize before reading. Test two locations on each small disc. Calculate the average of the six measurements to obtain the film resistance of that electrode.

[0322] 3. Adhesion of negative electrode sheet

[0323] With reference to GB-T2790-1995 national standard "Test method for 180° peel strength of adhesives", the adhesion test process of the examples and comparative examples of the present application is as follows:

[0324] Use a razor blade to cut a sample 30mm wide and 100-160mm long. Apply a 20mm wide, 90-150mm long, double-sided tape to a steel plate. Place the negative electrode film layer of the previously cut electrode sample on the double-sided tape. Then, use a 2kg roller to roll the tape three times in the same direction. Secure a 250mm long paper tape, the same width as the electrode, to the electrode current collector and secure it with crepe adhesive. Turn on the Sansi tensile testing machine (sensitivity set to 1N), and when the indicator light comes on, adjust the stop block to the appropriate position. Secure the end of the steel plate not attached to the electrode with the lower clamp. Fold the paper tape upward and secure it with the upper clamp. Use the "up" and "down" buttons on the manual controller included with the tensile testing machine to adjust the position of the upper clamp. Then perform the test and read the value. The force at equilibrium on the electrode divided by the tape width is used as the bond strength per unit length of the electrode, which represents the bond strength between the negative electrode film and the current collector.

[0325] 4. Temperature rise inside the battery cell

[0326] During the stacking process of the positive and negative electrode sheets, a temperature-sensing wire was embedded. At an ambient temperature of 25°C, the battery cells were charged at a constant current of 0.33C to a voltage of 3.65V. Then, they were charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the cells were discharged at a constant current of 0.33C to a voltage of 2.5V. This constituted one charge-discharge cycle. During this charge-discharge cycle, the temperature rise of the large surface of the electrode assembly (i.e., the temperature difference before and after charge and discharge) was measured and recorded using the temperature-sensing wire.

[0327] 3. Analysis of test results of various embodiments and comparative examples

[0328] The battery cells of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0329] Table 1

[0330] Table 2

[0331] From the comparison of Examples 1-10 and Comparative Example 1, it can be seen that the internal pore volume of a single particle of the second graphite is greater than the internal pore volume of a single particle of the first graphite, which can effectively reduce the internal temperature rise of the battery cell, and at the same time improve the adhesion of the negative electrode pole piece, reduce the elongation of the negative electrode film layer, reduce the elongation difference between the current collector and the negative electrode film layer, reduce the risk of breaking the negative electrode current collector, and comprehensively improve the safety performance and performance of the battery cell.

[0332] Compared with Examples 1-10 and Comparative Example 2, compared with the natural graphite second graphite with a larger internal pore volume containing only a single particle in the negative electrode film layer, the negative electrode pole piece of the present application can improve the bonding strength of the negative electrode pole piece, reduce the elongation of the negative electrode film layer, reduce the elongation difference between the current collector and the negative electrode film layer, and reduce the risk of the negative electrode current collector breaking.

[0333] From the comparison of Examples 1-10 and Comparative Example 3, it can be seen that compared with the artificial graphite first graphite with a smaller internal pore volume containing only a single particle in the negative electrode film layer, the negative electrode plate of the present application can reduce the film resistance and reduce the internal temperature rise of the battery cell.

[0334] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: The battery cell includes an electrode assembly; the electrode assembly includes a negative electrode plate; 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, wherein 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 on one side of the negative electrode plate is recorded as H, the area within a thickness range from the second 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 a thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer. The first region includes a first active material, which includes a first graphite; the second region includes a second active material, which includes a second graphite; and in a longitudinal cross-section of the negative electrode sheet, the pore volume inside a single particle of the second graphite is greater than the pore volume inside a single particle of the first graphite; The length of the battery cell is recorded as a, the width of the battery cell is recorded as b, and the thickness of the battery cell is recorded as c, wherein a:b:c=(2000-500):(200-80):(25-8).

2. The battery cell according to claim 1, wherein: The a is 500mm-2000mm; and / or, the b is 80mm-200mm; and / or, the c is 8mm-25mm.

3. The battery cell according to claim 1, wherein: The a is 650mm-700mm; and / or, the b is 110mm-120mm; and / or, the c is 13mm-16mm.

4. The battery cell according to claim 1, wherein: The thickness of the negative electrode current collector is less than or equal to 6 μm.

5. The battery cell according to claim 1, characterized in that The thickness of the negative electrode current collector is 4 μm-5.8 μm.

6. The battery cell according to any one of claims 1 to 5, characterized in that: The first graphite includes artificial graphite, and the second graphite includes natural graphite.

7. The battery cell according to any one of claims 1 to 5, characterized in that: The first graphite is artificial graphite, and the second graphite is natural graphite.

8. The battery cell according to claim 7, characterized in that The artificial graphite and natural graphite meet at least one of the following conditions: (1) The volume distribution particle size Dv50 of the artificial graphite is smaller than the volume distribution particle size Dv50 of the natural graphite; (2) The specific surface area of ​​the artificial graphite is smaller than the specific surface area of ​​the natural graphite; (3) The degree of graphitization of the artificial graphite is less than that of the natural graphite; (4) The Raman spectrum of the artificial graphite is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is less than 1250cm in the Raman spectrum of the natural graphite. -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm - 1 The peak intensity Ig ratio is Id / Ig.

9. The battery cell according to claim 7, characterized in that: The artificial graphite and natural graphite meet at least one of the following conditions: (1) The volume distribution particle size Dv50 of the artificial graphite is 8 μm-12 μm; and / or the volume distribution particle size Dv50 of the natural graphite is 15 μm-25 μm; (2) The degree of graphitization of the artificial graphite is 80%-94%; and / or the degree of graphitization of the natural graphite is 92%-98%; (3) The specific surface area of ​​the artificial graphite is 0.8m 2 / g-1.5m 2 / g; and / or, the specific surface area of ​​the natural graphite is 1.2 m 2 / g-2.0m 2 / g; (4) The Raman spectrum of the artificial graphite is 1250 cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.04-0.34; and / or, the Raman spectrum of the natural graphite at 1250cm -1 Up to 1500cm -1 The peak intensity Id and 1500 cm -1 to 1650cm -1 The peak intensity Ig ratio Id / Ig is 0.3-0.

85.

10. The battery cell according to any one of claims 1 to 5, characterized in that: The first area and the second area satisfy at least one of the following conditions: (1) The compacted density of the first region is 1.35 g / cm 3 -1.6g / cm 3 ; and / or, the compacted density of the second region is 1.45g / cm 3 -1.70g / cm 3 ; (2) The surface density of the first region is 0.140 g / 1540 mm 2 -0.175g / 1540mm 2 ; and / or, the surface density of the second region is 0.150g / 1540mm 2 -0.185g / 1540mm 2 .

11. The battery cell according to any one of claims 1 to 5, characterized in that: The negative electrode film layer satisfies at least one of the following conditions: (1) The surface density of the negative electrode film layer is 0.145g / 1540mm 2 -0.180g / 1540mm 2 ; (2) The compaction density of the negative electrode film layer is 1.40 g / cm 3 -1.65g / cm 3 ; (3) The thickness of the negative electrode film layer is 58 μm-91 μm.

12. The battery cell according to any one of claims 1 to 5, characterized in that: The first region includes a first adhesive, and the second region includes a second adhesive; The negative electrode sheet satisfies: w1% ≥ w2%, Wherein, w1% is the mass percentage of the first binder, based on the total mass of the first region; w2% is the mass percentage of the second binder, based on the total mass of the second region.

13. The battery cell according to claim 12, characterized in that The w1% is 1.2%-2.0%; and / or, the w2% is 0.8%-1.5%.

14. The battery cell according to any one of claims 1 to 5, characterized in that: The negative electrode plate further includes a negative electrode primer layer, which is located between the negative electrode current collector and the negative electrode film layer; the negative electrode primer layer includes a negative electrode primer layer binder and a negative electrode primer layer conductor.

15. The battery cell according to claim 14, characterized in that The negative electrode undercoat layer satisfies at least one of the following conditions: (1) The thickness of the negative electrode bottom coating is 1 μm-3 μm; (2) Based on the total mass of the negative electrode undercoat layer, the mass percentage of the negative electrode undercoat layer binder is 10%-50%; and / or, based on the total mass of the negative electrode undercoat layer, the mass percentage of the negative electrode undercoat layer conductive agent is 50%-90%.

16. The battery cell according to any one of claims 1 to 5, characterized in that: The electrode assembly further includes a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector; The thickness of the positive electrode current collector is less than or equal to 15 μm.

17. The battery cell according to claim 16, characterized in that The thickness of the positive electrode current collector is 11 μm-14 μm.

18. The battery cell according to claim 16, characterized in that The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium iron phosphate and modified compounds thereof.

19. The battery cell according to claim 16, characterized in that The positive electrode film layer includes flaky graphite.

20. The battery cell according to claim 19, characterized in that The flaky graphite includes primary particles.

21. The battery cell according to claim 16, characterized in that The positive electrode film layer satisfies at least one of the following conditions: (1) The surface density of the positive electrode film layer is 0.320g / 1540mm 2 -0.380g / 1540mm 2 ; (2) The compaction density of the positive electrode film layer is 2.35 g / cm 3 -2.85g / cm 3 ; (3) The thickness of the positive electrode film layer is 70 μm-105 μm.

22. The battery cell according to claim 16, characterized in that The positive electrode plate further includes a positive electrode primer layer, which is located between the positive electrode current collector and the positive electrode film layer; the positive electrode primer layer includes a positive electrode primer layer binder and a positive electrode primer layer conductor.

23. The battery cell according to claim 22, characterized in that The positive electrode undercoat layer satisfies at least one of the following conditions: (1) The thickness of the positive electrode bottom coating is 1 μm-3 μm; (2) Based on the total mass of the positive electrode undercoat layer, the mass percentage of the positive electrode undercoat layer binder is 10%-50%; and / or, based on the total mass of the positive electrode undercoat layer, the mass percentage of the positive electrode undercoat layer conductive agent is 50%-90%.

24. The battery cell according to claim 16, characterized in that The electrode assembly includes a separator located between the negative electrode sheet and the positive electrode sheet, the separator includes a porous substrate and a composite coating, the composite coating is located on a side of the porous substrate facing the negative electrode sheet, and the composite coating includes an inorganic particle layer and an adhesive layer located on a side of the inorganic particle layer away from the porous substrate. wherein the inorganic particle layer comprises aluminum oxide; The adhesive layer includes polyvinylidene fluoride particles.

25. The battery cell according to claim 24, characterized in that The isolation film satisfies at least one of the following conditions: (1) The thickness of the isolation film is 9 μm-12 μm; (2) The thickness of the porous substrate is 6 μm-8 μm; (3) The thickness of the adhesive layer is 0.8 μm-2 μm; (4) The thickness of the inorganic particle layer is 0.8 μm-1.5 μm.

26. The battery cell according to any one of claims 1 to 5, characterized in that: The battery cell includes an outer package, and the outer package includes a material with a Brinell hardness of less than or equal to 30 HB.

27. The battery cell according to claim 26, characterized in that The outer packaging comprises one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate, and polybutylene succinate.

28. The battery cell according to any one of claims 1 to 5, characterized in that: The electrode assembly includes a plurality of positive electrode sheets and a plurality of negative electrode sheets, the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked along the thickness direction of the battery cell, and the separator of the electrode assembly is continuous.

29. A battery comprising the battery cell according to any one of claims 1 to 28.

30. An electrical device comprising the battery according to claim 29.

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