Secondary battery, method for manufacturing the same, and device including the same
By using a specific range of natural and artificial graphite as active materials in the negative electrode of the secondary battery, a gradient pore distribution is formed, which solves the problem of insufficient kinetic performance and cycle life of the secondary battery at high energy density, and achieves better battery performance and safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CONTEMPORARY AMPEREX TECHNOLOGY CO LTD
- Filing Date
- 2020-04-30
- Publication Date
- 2026-07-10
Smart Images
Figure CN116741938B_ABST
Abstract
Description
[0001] This application is a divisional application of the invention patent application "Secondary Battery, Method for Preparing the Secondary Battery and Apparatus Containing the Secondary Battery", filed on April 30, 2020, with application number 202080005908.5 (international application number PCT / CN2020 / 088255). Technical Field
[0002] This application belongs to the field of electrochemical technology, and more specifically, relates to a secondary battery and an apparatus containing the secondary battery. Background Technology
[0003] Secondary batteries are widely used in various consumer electronics products and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect.
[0004] With the continuous development of the new energy industry, people have put forward higher requirements for the use of secondary batteries. How to make secondary batteries have higher energy density while taking into account other electrochemical performance remains a key challenge in the field of secondary batteries.
[0005] In view of this, it is indeed necessary to provide a rechargeable battery that can take into account multiple performance characteristics in order to meet the needs of customers. Summary of the Invention
[0006] In view of the technical problems existing in the background art, this application provides a secondary battery and an apparatus containing the same, which aims to enable the secondary battery to have high energy density while also taking into account good dynamic performance and long cycle life.
[0007] To achieve the aforementioned objective, a first aspect of this application provides a secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer, the negative electrode film layer comprising a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer being disposed on at least one surface of the negative current collector and comprising a first negative electrode active material, the second negative electrode film layer being disposed on the first negative electrode film layer and comprising a second negative electrode active material; the first negative electrode active material comprising natural graphite, and the first negative electrode active material satisfying: 6 mΩ·cm ≤ A ≤ 12 mΩ·cm; the second negative electrode active material comprising artificial graphite, and the second negative electrode active material satisfying: 13 mΩ·cm ≤ B ≤ 20 mΩ·cm; wherein, A is the powder resistivity of the first negative electrode active material tested at 8 MPa pressure, and B is the powder resistivity of the second negative electrode active material tested at 8 MPa pressure.
[0008] A second aspect of this application provides a method for manufacturing a secondary battery, comprising preparing the negative electrode sheet of the secondary battery through the following steps:
[0009] 1) A first negative electrode film layer comprising a first negative electrode active material is formed on at least one surface of the negative electrode current collector, wherein the first negative electrode active material comprises natural graphite, and the first negative electrode active material satisfies: 6mΩ·cm≤A≤12mΩ·cm;
[0010] 2) A second negative electrode film layer comprising a second negative electrode active material is formed on the first negative electrode film layer. The second negative electrode active material comprises artificial graphite, and the second negative electrode active material satisfies: 13mΩ·cm≤B≤20mΩ·cm;
[0011] in,
[0012] A represents the powder resistivity of the first negative electrode active material tested under a pressure of 8 MPa.
[0013] B represents the powder resistivity of the second negative electrode active material tested under a pressure of 8 MPa.
[0014] A third aspect of this application provides an apparatus comprising a secondary battery as described in the first aspect of this application or a secondary battery manufactured according to the method described in the second aspect of this application.
[0015] Compared with the prior art, this application includes at least the following beneficial effects:
[0016] In the secondary battery of this application, the negative electrode sheet includes a first negative electrode film layer and a second negative electrode film layer, and specific negative electrode active materials are selected in each negative electrode film layer. Through the rational design of the upper and lower layers, the secondary battery of this application achieves high energy density while also maintaining good kinetic performance and long cycle life. The device of this application includes the aforementioned secondary battery, and therefore has at least the same advantages as the aforementioned secondary battery. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.
[0018] Figure 2 This is a schematic diagram of one embodiment of the negative electrode sheet in the secondary battery of this application.
[0019] Figure 3 This is a schematic diagram of another embodiment of the negative electrode sheet in the secondary battery of this application.
[0020] Figure 4 This is an exploded view of one embodiment of the secondary battery of this application.
[0021] Figure 5 This is a schematic diagram of one embodiment of the battery module.
[0022] Figure 6 This is a schematic diagram of one embodiment of the battery pack.
[0023] Figure 7 yes Figure 6 The exploded diagram.
[0024] Figure 8 This is a schematic diagram of one embodiment of the device for using a secondary battery as a power source according to this application.
[0025] The reference numerals in the attached figures are explained as follows:
[0026] 1 Battery Pack
[0027] 2 upper box
[0028] 3 lower box
[0029] 4 Battery Modules
[0030] 5. Secondary batteries
[0031] 51. Housing
[0032] 52 Electrode Assembly
[0033] 53 Cover plate
[0034] 10 Negative electrode sheet
[0035] 101 Negative Electrode Current Collector
[0036] 102 Second negative electrode film layer
[0037] 103 First negative electrode film layer Detailed Implementation
[0038] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.
[0039] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.
[0040] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.
[0041] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).
[0042] Secondary batteries
[0043] The first aspect of this application provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode.
[0044] [Negative electrode plate]
[0045] In the secondary battery of this application, the negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on at least one surface of the negative current collector and includes a first negative electrode active material. The second negative electrode film layer is disposed on the first negative electrode film layer and includes a second negative electrode active material. The first negative electrode active material includes natural graphite and satisfies the following condition: 6 mΩ·cm ≤ A ≤ 12 mΩ·cm. The second negative electrode active material includes artificial graphite and satisfies the following condition: 13 mΩ·cm ≤ B ≤ 20 mΩ·cm. Wherein, A is the powder resistivity of the first negative electrode active material tested at 8 MPa pressure, and B is the powder resistivity of the second negative electrode active material tested at 8 MPa pressure.
[0046] The inventors discovered that when the first negative electrode active material includes natural graphite and the second negative electrode active material includes artificial graphite, and the first and second negative electrode active materials have a specific range of powder resistivity, the active sites of the upper and lower film layers in the negative electrode film can be reasonably matched, which is beneficial to improving the dynamic performance of the battery. At the same time, the specific design of the upper and lower layer materials can also form a gradient pore distribution, effectively improving the wetting performance of the electrolyte, enhancing the liquid phase conduction of active ions, and thus improving the cycle life of the battery.
[0047] In some preferred embodiments, the first negative electrode active material satisfies: 8mΩ·cm ≤ A ≤ 11mΩ·cm.
[0048] In some preferred embodiments, the second negative electrode active material satisfies: 14mΩ·cm≤B≤18mΩ·cm.
[0049] Through in-depth research, the inventors have discovered that, in addition to satisfying the above design, the negative electrode film layer of this application can further improve the battery performance if it optionally satisfies one or more of the following parameters.
[0050] In some preferred embodiments, 1.4 ≤ B / A ≤ 3; more preferably, 1.5 ≤ B / A ≤ 2.0. When B / A is controlled within the given range, the gradient resistance of the upper and lower negative electrode active materials can be better matched. This allows the active ions extracted from the positive electrode to diffuse more quickly and orderly into the interior of the bottom negative electrode active material particles, reducing the risk of lithium plating during battery cycling, lowering polarization, and further improving the battery's cycle performance and safety performance.
[0051] In some preferred embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the first negative electrode active material is smaller than the particle size distribution (Dv90-Dv10) / Dv50 of the second negative electrode active material.
[0052] In some preferred embodiments, the particle size distribution of the first negative electrode active material can be 1.0≤(Dv90-Dv10) / Dv50≤1.5, more preferably 1.0≤(Dv90-Dv10) / Dv50≤1.3.
[0053] In some preferred embodiments, the particle size distribution of the second negative electrode active material can be 1.0≤(Dv90-Dv10) / Dv50≤2, more preferably 1.2≤(Dv90-Dv10) / Dv50≤1.7.
[0054] When the particle size distribution of the first negative electrode active material is smaller than that of the second negative electrode active material, the fine powder content in the upper and lower negative electrode active materials is better matched. On the one hand, this effectively regulates the diffusion rate of active ions within different particles, making the intercalation and deintercalation stress comparable, reducing the expansion of the electrode during battery cycling, and thus further improving the battery's cycle performance. On the other hand, it effectively regulates the diffusion path of active ions, which is conducive to the rapid diffusion of active ions in the electrode, thereby further improving the battery's kinetic performance. In addition, the particle size distribution of the upper and lower negative electrode active materials within the given range is also conducive to increasing the compaction density of the negative electrode film, thereby further improving the battery's energy density.
[0055] In some preferred embodiments, the volume average particle size D of the first negative electrode active material V 50 can be 15μm to 19μm, more preferably 16μm to 18μm.
[0056] In some preferred embodiments, the volume average particle size D of the second negative electrode active material V50 can be 14μm to 18μm, more preferably 15μm to 17μm.
[0057] When the volume average particle size D of the first negative electrode active material and / or the second negative electrode active material V When 50 is within the given range, it helps to control the powder resistivity of the upper and lower negative electrode active materials within the range given in this application, thereby further improving the dynamic performance of the battery.
[0058] In some preferred embodiments, the volume average particle size D of the first negative electrode active material V 50 is greater than the volume average particle size D of the second negative electrode active material. V 50.
[0059] When the volume average particle size D of the first negative electrode active material V 50 is greater than the volume average particle size D of the second negative electrode active material. V At 50, the capacity difference between the upper and lower active materials can be reduced, the risk of lithium plating during battery cycling can be reduced, and the cycle performance of the battery can be further improved.
[0060] In some preferred embodiments, the compaction density of the first negative electrode active material powder under a force of 50,000 N can be 1.85 g / cm³. 3 ~2.1g / cm 3 More preferably, it is 1.9 g / cm³. 3 ~2.0g / cm 3 .
[0061] In some preferred embodiments, the compaction density of the second negative electrode active material powder under a force of 50,000 N can be 1.7 g / cm³. 3 ~1.9g / cm 3 More preferably 1.8 g / cm³ 3 ~1.9g / cm 3 .
[0062] The inventors discovered that when the powder compaction density of the upper and lower negative electrode active materials is within the given range under a force of 50,000 N, it helps to control the powder resistivity of the upper and lower negative electrode active materials within the range given in this application. At the same time, the powder compaction of the upper and lower graphite materials is reasonably matched, which is conducive to the formation of gradient pores in the electrode sheet, resulting in a smaller resistance to liquid phase conduction of active ions, and further improving the dynamic performance of the battery.
[0063] In some preferred embodiments, the degree of graphitization of the first negative electrode active material can be 95% to 98%; more preferably 96% to 97%.
[0064] In some preferred embodiments, the degree of graphitization of the second negative electrode active material can be 90% to 95%, more preferably 91% to 93%.
[0065] The inventors discovered that when the graphitization degree of the upper and lower negative electrode active materials is within the given range, it helps to control the powder resistivity of the upper and lower negative electrode active materials within the range given in this application. At the same time, the crystal structure of the upper and lower graphite materials is reasonably matched, which effectively improves the solid-phase diffusion rate of active ions during charge-discharge cycles and reduces the side reactions of the battery during charge-discharge cycles, thereby further improving the kinetic performance and cycle performance of the battery.
[0066] In some preferred embodiments, the morphology of the first negative electrode active material can be one or more of spherical and near-spherical shapes. This effectively improves the anisotropy of the first negative electrode active material, thereby further improving the electrochemical expansion and electrode processing performance of the battery.
[0067] In some preferred embodiments, the morphology of the second negative electrode active material is one or more of block and sheet shapes. In this case, the porosity between the particles of the second negative electrode active material can be effectively improved. The block and sheet structures easily create a "bridging" effect between particles, which is beneficial to the transport of lithium ions wetted by the electrolyte, thereby further improving the kinetic performance of the battery.
[0068] In some preferred embodiments, at least a portion of the surface of the first negative electrode active material has an amorphous carbon coating layer.
[0069] In some preferred embodiments, the surface of the second negative electrode active material does not have an amorphous carbon coating layer.
[0070] In some preferred embodiments, the natural graphite accounts for ≥50% of the mass of the first negative electrode active material, more preferably 80% to 100%.
[0071] In some preferred embodiments, the artificial graphite accounts for ≥80% by mass in the second negative electrode active material, more preferably 90% to 100%.
[0072] In this application, the powder resistivity of the negative electrode active material has a meaning known in the art and can be tested using methods known in the art. For example, the four-probe method, specifically referring to GB / T 30835-2014, is used with an ST2722-SZ powder resistivity meter: a certain amount of the sample powder to be tested is weighed and placed in a special mold, and the test pressure is set to obtain the powder resistivity under different pressures. In this application, the test pressure can be set to 8 MPa.
[0073] In this application, the material D V10. D V 50 and Dv90 both have meanings known in the art and can be tested using methods known in the art. For example, they can be measured using a laser diffraction particle size distribution measuring instrument (such as Mastersizer 3000) according to the particle size distribution laser diffraction method (see GB / T19077-2016 for details). Here, Dv10 refers to the particle size corresponding to a cumulative volume percentage of 10%; Dv50 refers to the particle size corresponding to a cumulative volume percentage of 50%, i.e., the median particle size of the volume distribution; and Dv90 refers to the particle size corresponding to a cumulative volume percentage of 90%.
[0074] In this application, the compacted density of the powder has a well-known meaning and can be tested using methods known in the art. For example, it can be tested using an electronic pressure testing machine (such as UTM7305) according to GB / T 24533-2009: a certain amount of powder is placed on a special compaction mold, different pressures are set, and the thickness of the powder under different pressures can be read on the equipment, and the compacted density under different pressures can be calculated. In this application, the pressure is set to 50000N.
[0075] In this application, the degree of graphitization of the material has a meaning known in the art and can be tested using methods known in the art. For example, the degree of graphitization can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be referenced in JISK 0131-1996 and JB / T 4220-2011 to measure d. 002 The size is then determined according to the formula G = (0.344 - d). 002 The degree of graphitization is calculated by d / (0.344-0.3354)×100%, where d 002 It is the interlayer spacing in the crystal structure of a material, expressed in nanometers (nm).
[0076] In this application, the morphology of the material has a meaning known in the art and can be tested using methods known in the art. For example, the material can be adhered to conductive adhesive, and the morphology of the particles can be tested using a scanning electron microscope (such as a ZEISS Sigma300). The testing method can be referred to JY / T010-1996.
[0077] It should be noted that the above-mentioned tests on various parameters of the negative electrode active material can be conducted by sampling before coating or by sampling from the negative electrode film layer after cold pressing.
[0078] When the test sample is taken from the negative electrode film layer after cold pressing, as an example, the sampling can be performed according to the following steps:
[0079] (1) First, select any cold-pressed negative electrode film layer and take a sample of the second negative electrode active material (you can use a blade to scrape the powder for sampling). The scraping depth does not exceed the boundary between the first negative electrode film layer and the second negative electrode film layer.
[0080] (2) Secondly, when sampling the first negative electrode active material, since there may be an inter-fusion layer in the boundary area between the first negative electrode film layer and the second negative electrode film layer during the cold pressing process of the negative electrode film layer (that is, the first active material and the second active material exist in the inter-fusion layer at the same time), in order to ensure the accuracy of the test, when sampling the first negative electrode active material, the inter-fusion layer can be scraped off first, and then the powder of the first negative electrode active material can be scraped off and sampled.
[0081] (3) The first and second negative electrode active materials collected above are placed in deionized water, and the first and second negative electrode active materials are filtered and dried. Then, the dried negative electrode active materials are sintered at a certain temperature and time (e.g., 400℃, 2h) to remove the binder and conductive carbon, thus obtaining the test samples of the first and second negative electrode active materials.
[0082] During the above sampling process, an optical microscope or a scanning electron microscope can be used to help determine the location of the boundary between the first negative electrode film layer and the second negative electrode film layer.
[0083] Both the natural and artificial graphite used in this application are commercially available.
[0084] In a preferred embodiment of this application, the thickness of the negative electrode film is ≥50μm, preferably 60μm to 75μm. It should be noted that the thickness of the negative electrode film refers to the total thickness of the negative electrode film (i.e., the sum of the thicknesses of the first negative electrode film and the second negative electrode film).
[0085] In a preferred embodiment of this application, the areal density of the negative electrode film is 9 mg / cm³. 2 ~14mg / cm 2 More preferably 11 mg / cm³ 2 ~13mg / cm 2 It should be noted that the areal density of the negative electrode film layer refers to the areal density of the entire negative electrode film layer (i.e., the sum of the areal densities of the first negative electrode film layer and the second negative electrode film layer).
[0086] In a preferred embodiment of this application, the thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 1:1.01 to 1:1.1, more preferably 1:1.02 to 1:1.06.
[0087] When the thickness of the upper and lower layers is within the given range, it is beneficial to form a gradient pore distribution between the upper and lower layers, which reduces the liquid phase conduction resistance of active ions extracted from the positive electrode on the surface of the negative electrode film, and prevents ions from accumulating on the surface and causing lithium plating problems. At the same time, the uniform diffusion of active ions in the film layer helps to reduce polarization, further improving the kinetic performance and cycle performance of the battery.
[0088] In a preferred embodiment of this application, two circular regions of equal area are randomly selected on the negative electrode sheet, respectively denoted as the first region and the second region. The center distance between the first region and the second region is 20cm. The electrode resistance R11 of the first region and the electrode resistance R12 of the second region satisfy: |R11-R12|≤3mΩ·cm; more preferably, |R11-R12|≤1mΩ·cm.
[0089] The small resistance difference between any two circular regions of equal area with a center-to-center distance of 20 cm on the negative electrode sheet indicates minimal resistance fluctuation, suggesting good dispersion uniformity of the first and second materials in the negative electrode film. This improves the compaction density, cycle stability, and electrolyte distribution uniformity at various locations on the negative electrode sheet. Consequently, the active ion transport and electronic conduction performance at different locations on the negative electrode sheet are essentially at the same level, thus enhancing capacity utilization, cycle and storage life, and kinetic performance at all locations on the negative electrode sheet. The good overall consistency of the negative electrode sheet further improves the energy density, high-temperature performance, and low-temperature power performance of the secondary battery.
[0090] The electrode resistance of the negative electrode has a well-known meaning in the art and can be tested using methods known in the art. For example, a BER1300 multi-functional electrode resistance meter can be used for testing. First, the negative electrode is cut into a sample of a certain size (a small circle with a diameter of 40 mm); the sample is placed between two probes, and the test results are recorded. To ensure the accuracy of the test results, multiple sets (e.g., 5 sets) of samples can be taken simultaneously, and the average value of the multiple sets of samples can be calculated as the test result.
[0091] In this application, the thickness of the negative electrode film can be measured using a micrometer, for example, a micrometer of model Mitutoyo293-100 with an accuracy of 0.1 t.
[0092] In this application, the thicknesses of the first and second negative electrode films can be measured using a scanning electron microscope (e.g., Sigma 300). Sample preparation is as follows: First, the negative electrode sheet is cut into a sample of a certain size (e.g., 2cm × 2cm), and then fixed to the sample stage with paraffin wax. Next, the sample stage is installed in the sample holder and locked in place. The argon ion cross-section polisher (e.g., IB-19500CP) is powered on and a vacuum is applied (e.g., 10...). -4 Set the argon flow rate (e.g., 0.15 MPa), voltage (e.g., 8 kV), and polishing time (e.g., 2 hours), and adjust the sample stage to swing mode to begin polishing. Sample testing can refer to JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 10) different regions can be randomly selected from the sample to be tested for scanning. At a certain magnification (e.g., 500x), the thicknesses of the first and second negative electrode films in the scale test areas are read, and the average value of the test results of multiple test areas is taken as the average thickness of the first and second negative electrode films.
[0093] In this application, the areal density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, take a negative electrode sheet that has been coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), cut it into small circular pieces with an area of S1, weigh it, and record its weight as M1. Then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0. The areal density of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1. To ensure the accuracy of the test results, multiple groups (e.g., 10 groups) of samples can be tested, and the average value can be calculated as the test result.
[0094] The compaction density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, the areal density and thickness of the negative electrode film can be obtained first using the test methods described above. The compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film.
[0095] In this application, the first negative electrode film layer and / or the second negative electrode film layer typically include a negative electrode active material as well as optional binders, optional conductive agents and other optional additives.
[0096] As an example, conductive agents may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0097] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).
[0098] As an example, other optional additives may include thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.
[0099] In this application, in addition to the graphite material specified above, the first and / or second negative electrode active materials may optionally contain a certain amount of other commonly used negative electrode active materials, such as soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, or several thereof. The silicon-based material may be selected from elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys, or several thereof. The tin-based material may be selected from elemental tin, tin oxide compounds, and tin alloys, or several thereof. These materials are commercially available. Those skilled in the art can make appropriate selections based on the actual application environment.
[0100] In the secondary battery of this application, the negative electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the negative electrode current collector can be copper foil.
[0101] It is understandable that the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.
[0102] Figure 2 A schematic diagram of one embodiment of the negative electrode 10 of this application is shown. The negative electrode 10 is composed of a negative current collector 101, a first negative electrode film layer 103 disposed on two surfaces of the negative current collector, and a second negative electrode film layer 102 disposed on the first negative electrode film layer 103.
[0103] Figure 3 A schematic diagram of another embodiment of the negative electrode 10 of this application is shown. The negative electrode 10 is composed of a negative current collector 101, a first negative electrode film layer 103 disposed on one surface of the negative current collector, and a second negative electrode film layer 102 disposed on the first negative electrode film layer 103.
[0104] It should be noted that the parameters of each negative electrode film layer (such as film thickness, areal density, etc.) given in this application refer to the parameter range of a single film layer. When the negative electrode film layer is simultaneously disposed on both surfaces of the negative electrode current collector, the film layer parameters on either surface that meet the requirements of this application are considered to fall within the protection scope of this application. Furthermore, the film thickness, areal density, and other ranges mentioned in this application refer to the film layer parameters after cold pressing and compaction and used for battery assembly.
[0105] [Positive electrode plate]
[0106] In the secondary battery of this application, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and including a positive electrode active material.
[0107] It is understandable that the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer can be laminated on either or both of the two opposite surfaces of the positive current collector.
[0108] In the secondary battery of this application, the positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.
[0109] In the secondary battery of this application, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.
[0110] In some preferred embodiments, to further improve the energy density of the battery, the positive electrode active material may include one or more of the lithium transition metal oxides and their modified compounds represented by Formula 1.
[0111] Li a Ni b Co c M d O e A f Formula 1,
[0112] In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.
[0113] In this application, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.
[0114] In the secondary battery of this application, the positive electrode film layer may optionally include a binder and / or a conductive agent.
[0115] As an example, the binder used for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
[0116] As an example, the conductive agent used for the positive electrode film may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
[0117] [Electrolytes]
[0118] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).
[0119] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.
[0120] In some embodiments, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).
[0121] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).
[0122] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.
[0123] [Isolation membrane]
[0124] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.
[0125] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.
[0126] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.
[0127] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
[0128] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 A square-structured secondary battery 5 is shown as an example.
[0129] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.
[0130] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.
[0131] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.
[0132] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.
[0133] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
[0134] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.
[0135] Methods for preparing secondary batteries
[0136] In a second aspect of this application, a method for preparing a secondary battery is provided, comprising preparing the negative electrode sheet of the secondary battery through the following steps:
[0137] 1) A first negative electrode film layer comprising a first negative electrode active material is formed on at least one surface of the negative electrode current collector. The first negative electrode active material comprises natural graphite and satisfies 6mΩ·cm≤A≤12mΩ·cm, where A is the powder resistivity of the first negative electrode active material tested under a pressure of 8MPa.
[0138] 2) A second negative electrode film layer comprising a second negative electrode active material is formed on the first negative electrode film layer. The second negative electrode active material comprises artificial graphite and satisfies 13mΩ·cm≤B≤20mΩ·cm, where B is the powder resistivity of the second negative electrode active material tested under a pressure of 8MPa.
[0139] In the process of preparing a secondary battery, by controlling and adjusting the composition of the first negative electrode active material, the composition of the second negative electrode active material, and their respective powder resistivity, the active sites in the negative electrode film can be kept within a suitable range, which is beneficial to improving the kinetic performance of the battery. At the same time, the specific design of the upper and lower layer materials can also form a gradient pore distribution, effectively improving the wetting performance of the electrolyte and enhancing the liquid phase conduction of active ions, thereby improving the cycle life of the battery.
[0140] In the preparation method of the secondary battery of this application, the first negative electrode active material slurry and the second negative electrode active material slurry can be coated simultaneously at one time or coated in two separate times.
[0141] In some preferred embodiments, the first negative electrode active material slurry and the second negative electrode active material slurry are coated simultaneously in one step. Simultaneous coating in one step can improve the adhesion between the upper and lower negative electrode film layers, which helps to further improve the cycle performance of the battery.
[0142] Apart from the method for preparing the negative electrode sheet, the structure and preparation method of the secondary battery of this application are known in themselves.
[0143] As an example, the construction and preparation method of the secondary battery of this application can be as follows:
[0144] First, the positive electrode sheet of the battery is prepared according to conventional methods in the art. This application does not limit the positive active material used in the positive electrode sheet. Typically, conductive agents (such as carbon materials such as carbon black) and binders (such as PVDF) are added to the aforementioned positive active materials. Other additives, such as PTC thermistor materials, may also be added as needed. These materials are usually mixed together and dispersed in a solvent (such as NMP), stirred evenly, and then uniformly coated onto the positive current collector. After drying, the positive electrode sheet is obtained through processes such as cold pressing. Metal foil such as aluminum foil or porous metal plates can be used as the positive current collector. Typically, during the fabrication of the positive electrode sheet, a positive electrode film layer is not formed on a portion of the current collector, leaving a portion of the current collector as the positive electrode lead portion. Of course, the lead portion can also be added later.
[0145] Then, prepare the negative electrode sheet (as the negative electrode sheet) of this application as described above.
[0146] Finally, the positive electrode, separator, and negative electrode can be stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrode assembly is wound (or stacked) to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.
[0147] Device
[0148] A third aspect of this application provides an apparatus. This apparatus includes a secondary battery as described in the first aspect of this application or a secondary battery prepared according to the method of the second aspect of this application. The secondary battery can be used as a power source for the apparatus or as an energy storage unit for the apparatus. The apparatus of this application uses the secondary battery provided in this application and therefore has at least the same advantages as the secondary battery.
[0149] The device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
[0150] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.
[0151] Figure 8 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high rate capability and high energy density of the secondary battery, a battery pack or battery module can be used.
[0152] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.
[0153] The beneficial effects of this application are further illustrated below with reference to the embodiments.
[0154] Example
[0155] To make the inventive purpose, technical solution, and beneficial technical effects of this application clearer, the following describes this application in further detail with reference to embodiments. However, it should be understood that the embodiments of this application are merely for explaining this application and are not intended to limit this application, and the embodiments of this application are not limited to the embodiments given in the specification. Unless otherwise specified, specific experimental or operating conditions in the embodiments are prepared under conventional conditions or according to the conditions recommended by the material supplier.
[0156] Preparation of primary and secondary batteries
[0157] Example 1
[0158] 1) Preparation of positive electrode sheet
[0159] LiNi, a lithium-nickel-cobalt-manganese ternary active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in N-methylpyrrolidone solvent at a weight ratio of 94:3:3. The slurry was then coated onto an aluminum foil substrate, and the positive electrode sheet was obtained through drying, cold pressing, slitting, and cutting. The areal density of the positive electrode film was 17.5 mg / cm³. 2 The compacted density is 3.4 g / cm³. 3 .
[0160] 2) Preparation of negative electrode sheet
[0161] The first step is to prepare negative electrode slurry 1: The first negative electrode active material, natural graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na), and conductive carbon black (Super P) are weighed and added to a mixing tank in a weight ratio of 96.2:1.8:1.2:0.8 along with deionized water in a specific order to prepare negative electrode slurry 1. The powder resistivity of natural graphite, tested at 8 MPa, is 6.1 mΩ·cm.
[0162] The second step is to prepare negative electrode slurry 2: The second negative electrode active material, artificial graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na), and conductive carbon black (Super P) are weighed and added to a mixing tank in a weight ratio of 96.2:1.8:1.2:0.8 along with deionized water in a specific order to prepare negative electrode slurry 2. The resistivity of the artificial graphite powder tested at 8 MPa is 16.1 mΩ·cm.
[0163] The third step involves simultaneously extruding negative electrode slurry 1 and negative electrode slurry 2 using a dual-cavity coating device. Negative electrode slurry 1 is coated onto the negative electrode current collector to form a first negative electrode film layer, and negative electrode slurry 2 is coated onto the first negative electrode film layer to form a second negative electrode film layer. The mass ratio of the first to the second negative electrode film layer is 1:1; the areal density of the negative electrode film layer is 11.5 mg / cm³. 2 The compaction density of the negative electrode film is 1.65 g / cm³. 3 .
[0164] The fourth step involves baking the coated wet film in an oven at different temperature zones to obtain a dry electrode sheet, followed by cold pressing to obtain the required negative electrode film layer, and then slitting, cutting and other processes to obtain the negative electrode sheet.
[0165] 3) Separating membrane
[0166] PE film was selected as the separator.
[0167] 4) Preparation of electrolyte
[0168] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.
[0169] 5) Battery manufacturing
[0170] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is then placed in an outer package, and the electrolyte is added. After processes such as encapsulation, settling, formation, and aging, a secondary battery is obtained.
[0171] The secondary batteries of Examples 2-22 and Comparative Examples 1-4 are prepared in a similar manner to the secondary battery of Example 1, but the composition of the battery electrodes and the product parameters are adjusted. The different product parameters are detailed in Tables 1 to 2.
[0172] II. Performance Parameter Testing Methods
[0173] The test methods for the parameters of the negative electrode active material and the parameters of the battery structure are described above in this application specification. The performance test methods for the secondary battery are as follows.
[0174] 1) Battery kinetic performance testing (room temperature lithium plating performance)
[0175] In an environment of 25°C, the batteries of each embodiment and comparative example were subjected to charge-discharge tests. A constant current discharge of 1.0C (i.e., the current value required to completely discharge the theoretical capacity within 1 hour) was used to discharge the battery until the discharge cutoff voltage reached 2.8V. Then, a constant current charge of 1.0C was used to charge the battery until the charging cutoff voltage reached 4.2V, followed by constant voltage charging until the current reached 0.05C, at which point the battery was fully charged. After the fully charged battery was allowed to rest for 5 minutes, it was discharged at a constant current of 1.0C until the discharge cutoff voltage. The discharge capacity at this point was the actual capacity of the battery at 1.0C, denoted as C0. The battery was then charged at a constant current of xC0 until the upper limit of the cutoff voltage, followed by constant voltage charging until the current reached 0.05C0. After resting for 5 minutes, the battery was disassembled to observe the lithium deposition at the interface. If no lithium deposition was observed on the negative electrode surface, the charging rate was increased and the test was repeated until lithium deposition occurred on the negative electrode surface. The maximum charging rate at which no lithium deposition occurred on the negative electrode surface was recorded to characterize the battery's kinetic performance.
[0176] 2) High-temperature cycle performance test of the battery
[0177] The first charge and discharge cycle was performed at 60℃. Constant current and constant voltage charging was conducted at a charging current of 1.0C (the current value required to completely discharge the theoretical capacity within 1 hour) until the charging cutoff voltage reached 4.2V. Then, constant current discharging was performed at a discharging current of 1.0C until the discharging cutoff voltage reached 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. Subsequently, continuous charge-discharge cycles were performed, recording the discharge capacity value of each cycle. The capacity retention rate of the Nth cycle was calculated as (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%. When the cycle capacity retention rate dropped to 80%, the number of battery cycles was recorded.
[0178] III. Test Results of Each Embodiment and Comparative Example
[0179] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.
[0180] First, from the data in Examples 1-10 and Comparative Examples 1-4 in Table 1, it can be seen that only when the natural graphite in the first negative electrode active material satisfies 6 mΩ·cm ≤ A ≤ 12 mΩ·cm and the artificial graphite in the second negative electrode active material simultaneously satisfies 13 mΩ·cm ≤ B ≤ 20 mΩ·cm, can the secondary battery simultaneously possess high cycle performance and excellent fast-charging performance (kinetic performance). The secondary battery exhibits optimal overall performance at 8 mΩ·cm ≤ A ≤ 11 mΩ·cm and 14 mΩ·cm ≤ B ≤ 18 mΩ·cm. In particular, the secondary battery performs even better when 1.5 ≤ B / A ≤ 2.0.
[0181] Furthermore, a comparison of Examples 11-18 and Examples 19-22 in Table 2 shows that the particle size distribution (Dv90-Dv10) / Dv50 of the negative electrode active material also has a significant impact on battery performance. Under the premise that 6 mΩ·cm ≤ A ≤ 12 mΩ·cm and 13 mΩ·cm ≤ B ≤ 20 mΩ·cm, the particle size distribution (Dv90-Dv10) / Dv50 of the first negative electrode active material is preferably smaller than that of the second negative electrode active material; otherwise, the cycle performance and kinetic performance will be relatively poor (Examples 20, 21). As shown in Table 2, the battery exhibits better overall performance when the particle size distribution of the first negative electrode active material is 1.0≤(Dv90-Dv10) / Dv50≤1.5, preferably 1.0≤(Dv90-Dv10) / Dv50≤1.3; and / or the particle size distribution of the second negative electrode active material is 1.0≤(Dv90-Dv10) / Dv50≤2, preferably 1.2<(Dv90-Dv10) / Dv50≤1.7.
[0182] Based on the data in Tables 1 and 2, it can be seen that in order to maintain a high energy density while also ensuring good kinetic performance and a long cycle life, the secondary battery should meet the following requirements: 6mΩ·cm≤A≤12mΩ·cm and 13mΩ·cm≤B≤20mΩ·cm.
[0183] It should also be noted that, based on the disclosure and guidance in the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, this application is not limited to the specific embodiments disclosed and described above, and some modifications and changes to this application also fall within the protection scope of the claims of this application. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on this application.
[0184]
[0185]
Claims
1. A secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer, the negative electrode film layer comprising a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer being disposed on at least one surface of the negative current collector and comprising a first negative electrode active material, the second negative electrode film layer being disposed on the first negative electrode film layer and comprising a second negative electrode active material. The first negative electrode active material includes natural graphite, and the first negative electrode active material satisfies: 6 mΩ•cm≤A≤12 mΩ•cm; The second negative electrode active material includes artificial graphite, and the second negative electrode active material satisfies: 13 mΩ•cm≤B≤20 mΩ•cm; in, A represents the powder resistivity of the first negative electrode active material tested under a pressure of 8 MPa. B represents the powder resistivity of the second negative electrode active material tested at a pressure of 8 MPa. The particle size distribution (Dv90 - Dv10) / Dv50 of the first negative electrode active material is smaller than that of the particle size distribution (Dv90 - Dv10) / Dv50 of the second negative electrode active material.
2. The secondary battery according to claim 1, wherein, 8 mΩ•cm≤A≤11 mΩ•cm; and / or, 14 mΩ•cm≤B≤18 mΩ•cm.
3. The secondary battery as described in claim 1, wherein, 1.4≤B / A≤3.
4. The secondary battery as described in claim 3, wherein, 1.5≤B / A≤2.
0.
5. The secondary battery according to claim 2, wherein, The natural graphite constitutes 80% to 100% of the first negative electrode active material by mass; and / or, The artificial graphite accounts for 90% to 100% of the mass of the second negative electrode active material.
6. The secondary battery according to any one of claims 1 to 5, wherein, The particle size distribution of the first negative electrode active material is 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.5; and / or, The particle size distribution of the second negative electrode active material is 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.
7. The secondary battery as described in claim 6, wherein, The particle size distribution of the first negative electrode active material is 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.3; and / or, The particle size distribution of the second negative electrode active material is 1.2 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.
7.
8. The secondary battery as described in claim 1, wherein, The volume average particle size D of the first negative electrode active material V 50 is greater than the volume average particle size D of the second negative electrode active material. V 50.
9. The secondary battery according to claim 1, wherein, The volume average particle size D of the first negative electrode active material V 50 represents 15 μm to 19 μm; and / or, The volume average particle size D of the second negative electrode active material V 50 is 14 μm ~ 18 μm.
10. The secondary battery according to claim 9, wherein, The volume average particle size D of the first negative electrode active material V 50 is 16 μm ~ 18 μm; and / or, The volume average particle size D of the second negative electrode active material V 50 is 15 μm ~ 17 μm.
11. The secondary battery as claimed in claim 1, wherein, The first negative electrode active material also satisfies one or more of the following (1) to (4): (1) The compaction density of the first negative electrode active material powder under a force of 50,000 N is 1.85 g / cm³. 3 ~ 2.1g / cm 3 ; (2) The graphitization degree of the first negative electrode active material is 95% ~ 98%; (3) The morphology of the first negative electrode active material is one or more of spherical and near-spherical shapes; (4) At least a portion of the surface of the first negative electrode active material has an amorphous carbon coating layer.
12. The secondary battery as claimed in claim 11, wherein, The compacted density of the first negative electrode active material under a force of 50,000 N is 1.9 g / cm³. 3 ~ 2.0 g / cm 3 ; and / or The graphitization degree of the first negative electrode active material is 96% to 97%.
13. The secondary battery according to claim 1, wherein, The second negative electrode active material also satisfies one or more of the following conditions (1) to (4): (1) The compaction density of the second negative electrode active material under a force of 50,000 N is 1.7 g / cm³. 3 ~ 1.9 g / cm 3 ; (2) The degree of graphitization of the second negative electrode active material is 90%~95%; (3) The morphology of the second negative electrode active material is one or more of the following: block and sheet; (4) The surface of the second negative electrode active material does not have an amorphous carbon coating layer.
14. The secondary battery according to claim 13, wherein, The second negative electrode active material has a powder compaction density of 1.8 g / cm³ under a force of 50,000 N. 3 ~ 1.9 g / cm 3 ; and / or The graphitization degree of the second negative electrode active material is 91% to 93%.
15. The secondary battery according to claim 1, wherein, The secondary battery also satisfies one or more of the following (1) to (3): (1) The thickness of the negative electrode film is ≥50μm; (2) The areal density of the negative electrode film is 9 mg / cm³. 2 ~ 14mg / cm 2 ; (3) The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 1:1.01~1:1.
1.
16. The secondary battery according to claim 15, wherein, The secondary battery also satisfies one or more of the following (1) to (3): (1) The thickness of the negative electrode film is 60 μm ~ 75 μm; (2) The areal density of the negative electrode film is 11 mg / cm³. 2 ~ 13mg / cm 2 ; (3) The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 1:1.02~1:1.
06.
17. The secondary battery according to claim 1, wherein, When two circular regions of equal area are randomly selected on the negative electrode film layer, and denoted as the first region and the second region respectively, the center distance between the first region and the second region is 20cm. The electrode resistance R11 of the first region and the electrode resistance R12 of the second region satisfy: |R11-R12|≤3 mΩ•cm.
18. The secondary battery according to claim 17, wherein, The electrode resistance R11 in the first region and the electrode resistance R12 in the second region satisfy the following condition: |R11-R12|≤1 mΩ•cm.
19. The secondary battery according to claim 1, wherein, The secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and including a positive electrode active material. The positive electrode active material includes one or more of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds.
20. The secondary battery according to claim 19, wherein, The positive electrode active material includes one or more of the lithium transition metal oxides and their modified compounds shown in Formula 1. Li a Ni b Co c M d O e A f Formula 1 In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.
21. A method for manufacturing a secondary battery, comprising preparing the negative electrode sheet of the secondary battery by the following steps: 1) A first negative electrode film layer comprising a first negative electrode active material is formed on at least one surface of the negative electrode current collector, wherein the first negative electrode active material comprises natural graphite, and the first negative electrode active material satisfies: 6 mΩ•cm≤A≤12 mΩ•cm; 2) A second negative electrode film layer comprising a second negative electrode active material is formed on the first negative electrode film layer. The second negative electrode active material comprises artificial graphite, and the second negative electrode active material satisfies: 13 mΩ•cm≤B≤20 mΩ•cm; in, A represents the powder resistivity of the first negative electrode active material tested under a pressure of 8 MPa. B represents the powder resistivity of the second negative electrode active material tested at a pressure of 8 MPa. The particle size distribution (Dv90 - Dv10) / Dv50 of the first negative electrode active material is smaller than that of the particle size distribution (Dv90 - Dv10) / Dv50 of the second negative electrode active material.
22. An apparatus, characterized in that: Includes the secondary battery according to any one of claims 1 to 20 or the secondary battery manufactured according to the method of claim 21.