Secondary batteries and electrical devices containing them

Abstract

This application provides a secondary battery and an electrical device containing the same. The secondary battery includes a negative electrode sheet, which comprises: a negative current collector; a first negative electrode film layer disposed on at least one surface of the negative current collector, the first negative electrode film layer comprising a first negative electrode active material and a first conductive polymer, wherein the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, where A ≤ 6%; and a second negative electrode film layer disposed on the surface of the first negative electrode film layer, the second negative electrode film layer comprising a second negative electrode active material and a second conductive polymer, wherein the mass percentage of the second conductive polymer in the second negative electrode film layer is denoted as B; then the negative electrode sheet satisfies: A > B. This secondary battery possesses both excellent maximum charge rate and long cycle life.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery and an electrical device containing the same. Background Technology

[0002] In recent years, the application range of lithium-ion batteries has become increasingly wide. For example, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. The widespread use of lithium-ion batteries has led to increasingly higher requirements for the overall performance of batteries. More and more application scenarios require power batteries to have both high energy density and good charge and discharge characteristics.

[0003] As one of the most critical components of lithium-ion batteries, the design of the negative electrode directly affects the battery's performance, especially its charging-related characteristics. Optimizing the negative electrode design to achieve a battery that balances energy density and kinetic performance is a common challenge in the industry.

[0004] In view of this, it is indeed necessary to provide a secondary battery that can solve the above problems. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of the prior art by providing a secondary battery, a method for preparing the same, and an apparatus containing the secondary battery, with the aim of improving the maximum charging rate and long-term cycle life of the secondary battery.

[0006] The inventors of this application have discovered that by layering conductive polymers onto the negative electrode, the problem of insufficient negative electrode kinetics caused by different polarization degrees of conductive polymers in the thickness direction of thick electrodes in the prior art can be effectively solved. Using the technical solution of this invention to prepare the negative electrode sheet, under sufficient cell kinetics, the solid content of the active material in the slurry is maximized, the auxiliary material cost is minimized, and the maximum charge rate and long-term cycle life of the secondary battery are improved.

[0007] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising: a negative electrode current collector; a first negative electrode film layer disposed on at least one surface of the negative electrode current collector, the first negative electrode film layer comprising a first negative electrode active material and a first conductive polymer, wherein the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, A≤6%; and a second negative electrode film layer disposed on the surface of the first negative electrode film layer, the second negative electrode film layer comprising a second negative electrode active material and a second conductive polymer, wherein the mass percentage of the second conductive polymer in the second negative electrode film layer is denoted as B; then the negative electrode sheet satisfies: A>B.

[0008] A second aspect of this application provides a method for preparing a secondary battery, comprising preparing the negative electrode sheet of the secondary battery through 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; 2) A second negative electrode film layer comprising a second negative electrode active material is formed on the first negative electrode film layer; The first negative electrode film layer includes a first negative electrode active material and a first conductive polymer, and the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, where A≤6%; the second negative electrode film layer includes a second negative electrode active material and a second conductive polymer, and the mass percentage of the second conductive polymer in the second negative electrode film layer is denoted as B; satisfying: A>B.

[0009] 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.

[0010] Compared with the prior art, this application includes at least the following beneficial effects: The negative electrode of the secondary battery of this application includes a multi-layered structure, and the content of conductive polymer in each layer is controlled to be different during the design. This allows the negative electrode of the secondary battery to achieve the maximum solid content of the active material in the slurry while minimizing the cost of auxiliary materials, under sufficient cell dynamics. This results in the secondary battery having both good maximum charge rate and long cycle life. The device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0013] Figure 2 This is an exploded view of one embodiment of the secondary battery of this application.

[0014] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0015] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0016] Figure 5 yes Figure 4 The exploded diagram.

[0017] Figure 6 This is a schematic diagram of one embodiment of the electrical device that uses a secondary battery as a power source according to this application. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] Secondary batteries 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.

[0023] [Negative electrode plate] As one of the most critical components of lithium-ion batteries, the design of the negative electrode directly affects the battery's performance. Currently, conductive polymers are widely used in the coating and modification of positive and negative electrode materials in lithium-ion batteries to improve the battery's electrochemical performance. Specifically, coating the negative electrode surface with conductive polymers improves lithium plating and acts as a binder to improve the cell's rate performance. However, the introduction of conductive polymers leads to a decrease in the proportion of active material, resulting in a decrease in the capacity and energy density of cells with the same casing. Secondly, the process cost of coating the negative electrode material with conductive polymers is high, and the thickness and uniformity of the coating layer cannot be guaranteed. This results in poor consistency of the negative electrode powder, hindering mass production. Thirdly, as a surface coating layer, conductive polymers often use organic free radical groups as side chains and conjugated polymers as the main chain, resulting in low conductivity of the synthesized polymer coating layer, further reducing the battery's actual specific capacity and energy density.

[0024] To address the aforementioned problems, the inventors conducted extensive research and provided a negative electrode sheet. Specifically, the negative electrode sheet in the secondary battery of this application comprises: a negative current collector; a first negative electrode film layer disposed on at least one surface of the negative current collector, the first negative electrode film layer comprising a first negative electrode active material and a first conductive polymer, wherein the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, and A≤6%; a second negative electrode film layer disposed on the surface of the first negative electrode film layer, the second negative electrode film layer comprising a second negative electrode active material and a second conductive polymer, wherein the mass percentage of the second conductive polymer in the second negative electrode film layer is denoted as B; the negative electrode sheet satisfies: A>B.

[0025] The inventors discovered that when the negative electrode sheet meets the above design conditions, it can solve the problem of insufficient kinetics due to different polarization degrees in the thickness direction of the thick-coated electrode. This allows the cell kinetics to be sufficient, while maximizing the slurry solid content of the active material and minimizing the cost of auxiliary materials. As a result, the secondary battery has both a good maximum charge rate and a long cycle life.

[0026] In some preferred embodiments, the mass percentage A of the first conductive polymer in the first negative electrode film layer satisfies: 1% ≤ A ≤ 5%. For example, the range of A can be 1.2% ≤ A ≤ 4%, 1% ≤ A ≤ 3%, 1.5% ≤ A ≤ 4%, 2% ≤ A ≤ 4%, 2% ≤ A ≤ 3%, etc.

[0027] In some preferred embodiments, the mass percentage B of the second conductive polymer in the second negative electrode film layer satisfies: B≤4%; optionally, 0.2%≤B≤3%. For example, the range of B can be 0.5%≤B≤3%, 1.0%≤B≤3%, 1.5%≤B≤3%, 1.5%≤B≤2%, etc.

[0028] Through in-depth research, the inventors have discovered that, in addition to meeting the above design conditions, the negative electrode active material and negative electrode film of this application can optionally meet one or more of the following parameters, which can further improve the performance of the secondary battery.

[0029] In some preferred embodiments, the mass ratio A of the first conductive polymer in the first negative electrode film and the mass ratio B of the second conductive polymer in the second negative electrode film satisfy A / B≤10; optionally, A / B≤5.

[0030] In some preferred embodiments, the first conductive polymer and the second conductive polymer are each independently selected from one or more of polyaniline (PANI), polypyrrole (PPy), polythiophene (PTPh) and its derivatives, poly(3,4-ethylenedioxythiophene) (PEDOT), polyacetylene, polyphenylene, and polyphenylacetylene.

[0031] In some preferred embodiments, both the first active material and the second negative electrode active material comprise artificial graphite.

[0032] In some preferred embodiments, the volume average particle size Dv of the first negative electrode active material 50 The volume average particle size Dv of the second negative electrode active material is greater than that of the second negative electrode active material. 50 When the volume distribution particle size D of the first negative electrode active material V 50 is greater than the volume distribution particle size D of the second negative electrode active material VAt 50%, the matching degree between the concentration gradient distribution of active ions during battery charging and discharging is good, which can effectively improve the maximum charging rate of the battery. In addition, the particle size of the first negative electrode active material is larger, with more vacancies available to receive active ions, i.e., a larger specific capacity, which is beneficial to improving the battery's mass energy density. At the same time, the particle size of the second negative electrode active material is smaller, with more adhesion sites for the binder on its surface. The degree of particle breakage during cold pressing is less, reducing the probability of the material forming new surfaces. Therefore, it has a strong conductivity of electrons during battery charging and discharging and can effectively suppress the "broken bridge" phenomenon of the electrolyte, which can further improve the battery's cycle life.

[0033] In some preferred embodiments, the volume average particle size Dv of the first negative electrode active material 50 Available in 6μm-15μm ranges, with optional 8μm-12μm; and / or, The volume average particle size Dv of the second negative electrode active material 50 The range is 0.5μm-8μm; 4μm-6μm is also available.

[0034] In some preferred embodiments, the specific surface area (SSA) of the first negative electrode active material is smaller than that of the second negative electrode active material. When the specific surface area (SSA) of the first negative electrode active material is smaller than that of the second negative electrode active material, the maximum charge rate and cycle life of the battery can be further improved.

[0035] In some preferred embodiments, the specific surface area (SSA) of the first negative electrode active material is 0.5 m². 2 / g-2 m 2 / g, optional 1 m 2 / g-1.5 m 2 / g; and / or, The specific surface area (SSA) of the second negative electrode active material is 1.5 m². 2 / g -5m 2 / g, 2m optional 2 / g - 3m 2 / g.

[0036] In some preferred embodiments, the OI value of the first negative electrode active material is greater than the OI value of the second negative electrode active material. When the OI value of the first negative electrode active material is greater than the OI value of the second negative electrode active material, the maximum charge rate and cycle life of the battery can be further improved.

[0037] In some preferred embodiments, the OI value of the first negative electrode active material is 4-20, optionally 5-10; and / or, The OI value of the second negative electrode active material is 0.5-10, and can be selected as 1-4.

[0038] In some preferred embodiments, the thickness of the first negative electrode film is denoted as H1, and the thickness of the second negative electrode film is denoted as H2. Then the secondary battery satisfies: 0.5≤H1 / H2≤3; optionally, 0.8≤H1 / H2≤1.5.

[0039] In some preferred embodiments, the thickness of the first negative electrode film is denoted as H1, where 20 μm ≤ H1 ≤ 110 μm; and / or, The thickness of the second negative electrode film is denoted as H2, where 20μm≤H2≤110μm.

[0040] In some preferred embodiments, the first negative electrode active material and / or the second negative electrode active material further include one or more of natural graphite, hard carbon, and silicon-based materials.

[0041] In any embodiment of the present invention, the active material layer may be three, four, five or more layers, and the content of conductive polymer in each layer may vary, which is understandable to those skilled in the art and will not be elaborated here.

[0042] In this application, the type of conductive polymer can be determined using methods known in the art. For example, the type of conductive polymer can be determined by testing the infrared spectrum of the material and identifying its characteristic peaks. Specifically, the organic particles can be analyzed by infrared spectroscopy using instruments and methods known in the art, such as an infrared spectrometer, like the Nicolet IS10 Fourier transform infrared spectrometer, according to the general rules of GB / T6040-2002 Infrared Spectroscopic Analysis Methods. Optionally, photoelectron spectroscopy (XPS) can also be used to determine the type of substance, according to the measurement methods of ISO16531-2013 / ISO 16243-2011.

[0043] Furthermore, the content of conductive polymer can be determined using methods known in the art, such as surface elemental analysis (EDS) to confirm the content of characteristic elements of the conductive polymer, such as nitrogen. The characteristic elements in different layers will have relatively large differences, for example, the content can be obtained by testing according to the measurement method of GB / T 25189-2010 / ASTM E1508-1998(2008).

[0044] In this application, the Dv50 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, it can be tested using a laser particle size analyzer (such as a MalvernMaster Size 3000) in accordance with the standard GB / T 19077.1-2016.

[0045] The physical definition of Dv50 is as follows: Dv50: The particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material.

[0046] In this application, the specific surface area (SSA) 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, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0047] In this application, the OI value of the negative electrode active material = C 004 / C 110 C 004 C is the peak area of ​​the diffraction peak of the 004 crystal plane of the negative electrode active material. 110 This represents the peak area of ​​the 110 crystal plane diffraction peak of the negative electrode active material. In the testing, X-ray diffraction analysis can be performed according to standard JISK 0131-1996 using an X-ray diffractometer (e.g., a Bruker D8 Discover X-ray diffractometer). In the X-ray diffraction analysis, a copper target can be used as the anode target, and a 0.02 mm thick Ni filter can be used to filter CuK. β , with CuK α The radiation source is a ray, and the wavelength of the ray is λ = 1.5418 Å (take K). α1 and K α2 The weighted average value of the X-ray diffractometer is used. The scanning 2θ angle range is 20° ~ 80°, and the scanning rate is 4° / min. Specifically, in this application, the OI value test method for the negative electrode active material is as follows: the negative electrode active material is directly placed in an X-ray diffractometer, and the peak area C of its 004 crystal plane diffraction peak is obtained by X-ray diffraction analysis. 004 And the peak area C of the 110 crystal plane diffraction peak 110 OI value = C 004 / C 110 .

[0048] Generally, when the negative electrode active layer material is artificial graphite, the 2θ angle corresponding to the 004 crystal plane of the artificial graphite is 53.5° - 55.5° (e.g., 54.5°); the 2θ angle corresponding to the 110 crystal plane of the artificial graphite is 76.5° - 78.5° (e.g., 77.4°).

[0049] 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 μm.

[0050] In this application, the thicknesses of the first and second negative electrode films can be measured using a scanning electron microscope (such as a ZEISS Sigma300). As an example, the testing method can be 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 power supply to the argon ion cross-section polisher (e.g., IB-19500CP) is turned 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.

[0051] 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.

[0052] When the test sample is taken from the cold-pressed negative electrode film, as an example, the sampling can be performed according to the following steps: (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 should not exceed the boundary between the first negative electrode film layer and the second negative electrode film layer. (2) Secondly, when sampling the first negative electrode active material, since there may be an interfusion 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 interfusion layer at the same time), in order to ensure the accuracy of the test, when sampling the first negative electrode active material, the interfusion layer can be scraped off first, and then the powder of the first negative electrode active material can be scraped off and sampled. (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, dried, and then each negative electrode active material after drying is 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.

[0053] 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.

[0054] All negative electrode active materials used in this application are commercially available.

[0055] In the secondary battery of this application, the negative electrode film layer can be disposed on one surface of the negative electrode current collector, or it can be disposed on both surfaces of the negative electrode current collector simultaneously.

[0056] Furthermore, the negative electrode sheet of this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may also include a conductive undercoat layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the second negative electrode film layer. In other embodiments, the negative electrode sheet of this application also includes a protective layer covering the surface of the first negative electrode film layer.

[0057] It should be noted that the parameters of each negative electrode film layer given in this application (such as film layer thickness, areal density, compaction density, etc.) refer to the parameter range of a single-sided film layer. When the negative electrode film layer is disposed on two 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 layer thickness, areal density, and other ranges mentioned in this application refer to the film layer parameters after cold pressing and compaction and used for assembling the battery.

[0058] 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.

[0059] In the secondary battery of this application, the first negative electrode film layer and / or the second negative electrode film layer typically comprise a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and are typically formed by coating and drying a negative electrode film layer slurry. The negative electrode film layer slurry coating is typically formed by dispersing the negative electrode active material and optional conductive agents and binders in a solvent and stirring until homogeneous. The solvent may be, for example, N-methylpyrrolidone (NMP) or deionized water. Other optional additives may include thickeners and dispersants (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0060] 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.

[0061] 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).

[0062] In the secondary battery of this application, the first negative electrode active material and / or the second negative electrode active material, in addition to the negative electrode active materials described above, may optionally include 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. The preparation methods of these materials are well known and can be obtained commercially. Those skilled in the art can make appropriate selections based on the actual usage environment.

[0063] In the secondary battery of this application, the negative electrode sheet does not exclude other additional functional layers besides the aforementioned negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may further include a conductive coating (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the first film layer. In other embodiments, the negative electrode sheet of this application may further include a protective layer disposed on the surface of the second film layer.

[0064] [Positive electrode plate] In the secondary battery of this application, the positive electrode 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.

[0065] 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.

[0066] 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 depositing metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0067] In the secondary battery of this application, the positive electrode active material may be any positive electrode active material known in the art for use in secondary batteries. For example, 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 may 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 may 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.

[0068] 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. 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.

[0069] 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.

[0070] In the secondary battery of this application, the positive electrode film layer may optionally include a binder and a conductive agent.

[0071] As an example, the binder used for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0072] 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.

[0073] [Electrolytes] 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).

[0074] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0075] 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).

[0076] 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).

[0077] 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.

[0078] [Isolation membrane] Secondary batteries using electrolytes, as well as 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.

[0079] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven 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.

[0080] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0081] 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.

[0082] 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).

[0083] 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 This is an example of a square-structured secondary battery 5.

[0084] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 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 plate 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in 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.

[0085] 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.

[0086] Figure 3This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0087] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0088] 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.

[0089] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0090] Methods for preparing secondary batteries A second aspect of this application provides a method for preparing a secondary battery, comprising preparing the negative electrode sheet of the secondary battery through 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; 2) A second negative electrode film layer comprising a second negative electrode active material is formed on the first negative electrode film layer; The first negative electrode film layer includes a first negative electrode active material and a first conductive polymer, and the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, where A≤6%; the second negative electrode film layer includes a second negative electrode active material and a second conductive polymer, and the mass percentage of the second conductive polymer in the second negative electrode film layer is denoted as B; satisfying: A>B.

[0091] In the above preparation steps, the first negative electrode film layer and the second negative electrode film layer can be coated simultaneously or in two separate applications; preferably, the first negative electrode film layer and the second negative electrode film layer are coated simultaneously. Simultaneous coating in one application improves the adhesion between the upper and lower negative electrode film layers, which helps to further improve the cycle performance of the battery.

[0092] Besides the method for preparing the negative electrode sheet of this application, other structures and preparation methods of the secondary battery of this application are known. For example, the positive electrode sheet of this application can be prepared as follows: the positive active material and optional conductive agents (such as carbon materials such as carbon black), binders (such as PVDF), etc., are mixed and dispersed in a solvent (such as NMP), stirred evenly, coated on the positive current collector, and dried to obtain the positive electrode sheet. Metal foils such as aluminum foil or porous metal plates can be used as the positive current collector. When manufacturing the positive electrode sheet, positive electrode tabs can be obtained in the uncoated areas of the positive current collector by punching or laser die-cutting.

[0093] Finally, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrode assembly is formed by winding (or stacking). 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.

[0094] Device 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 by the method described in 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.

[0095] 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.

[0096] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0097] Figure 6 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.

[0098] 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.

[0099] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0100] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents, first active materials, and second active materials used in the embodiments are commercially available or synthesized by conventional methods, as are the instruments used in the embodiments.

[0101] Preparation of primary and secondary batteries Example 1 1) Preparation of positive electrode sheet LiNi, the positive electrode 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 95:3:2. The slurry was then coated onto an aluminum foil substrate. The resulting material was dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The areal density of the positive electrode film was 194 g / m³. 2 The compacted density is 3.4 g / cm³. 3 .

[0102] 2) Preparation of negative electrode sheet Step 1: Preparation of negative electrode slurry 1: The first negative electrode active material, conductive polymer polyaniline (PANI), binder (SBR), thickener (CMC-Na), and conductive carbon black (Super-P) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 89.5:6:2:1:1.5 to prepare negative electrode slurry 1. The first negative electrode active material is artificial graphite, and its Dv50 is 10 μm and BET is 1 μm. 2 / g, powder OI is 4.

[0103] The second step is to prepare negative electrode slurry 2: The second negative electrode active material, conductive polymer polyaniline (PANI), binder SBR, thickener (CMC-Na), and conductive carbon black (Super-P) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 91.5:4:2:1:1.5 to prepare negative electrode slurry 2. The second negative electrode active material is artificial graphite, and its Dv50 is 4 μm and BET is 2 μm. 2 / g, powder OI is 8.

[0104] 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 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 areal density of the negative electrode film layers (including the first and second negative electrode film layers) is 118 g / m³. 2 The compacted density is 1.65 g / cm³. 3 .

[0105] 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.

[0106] 3) Separating membrane PE film was selected as the separator.

[0107] 4) Preparation of electrolyte 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.

[0108] 5) Battery manufacturing 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, injected with the electrolyte, and after processes such as encapsulation, settling, formation, and aging, a secondary battery is obtained.

[0109] Examples 2-13 and Comparative Examples 1-4 The secondary batteries of Examples 2-13 and Comparative Examples 1-4 are prepared by methods similar to those of the secondary battery of Example 1. The different product parameters are detailed in Table 1.

[0110] II. Testing Section 1. Maximum charging rate At 25°C, the secondary batteries prepared in the examples and comparative examples were fully charged at xC and fully discharged at 1C 10 times. Then, the batteries were fully charged at xC, and the negative electrode was disassembled to observe the lithium deposition on the surface of the negative electrode. If no lithium deposition occurred on the negative electrode surface, the charging rate xC was increased in increments of 0.1C until lithium deposition occurred on the negative electrode surface. The test was then stopped, and the charging rate (x-0.1)C at this point was the maximum charging rate of the battery.

[0111] 2. Cyclic performance At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current rate of 1 C to the charging cutoff voltage of 4.2V, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2.8V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0112] III. Test Results of Each Embodiment and Comparative Example 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 Table 1 below.

[0113] First, it can be seen from the data of Example 1 and Comparative Example 1 that the secondary battery can have both good maximum charge rate and cycle performance only when both the first negative electrode active material and the second negative electrode active material contain conductive polymer molecules, and the mass percentage A of the first conductive polymer ≤ 6%, and the mass percentage A of the first conductive polymer in the first negative electrode film is greater than the mass percentage B of the second conductive polymer in the second negative electrode film.

[0114] When the negative electrode active material does not contain conductive polymer (Comparative Example 1), the battery's maximum charge rate and cycle performance are both poor. Comparative Example 4 shows that when both the first and second negative electrode active materials contain polymers, but the content of conductive polymers is too high, especially in the first negative electrode film layer, the battery's maximum charge rate and cycle performance are extremely poor. This is because, on the one hand, a high content of conductive polymers results in poor dispersion of the negative electrode active material, leading to decreased conductivity of the electrode. On the other hand, an excessively high content of conductive polymers reduces the weight ratio of the main materials, which is detrimental to increasing battery capacity.

[0115] When both the first and second negative electrode active materials comprise polymers, but the mass percentage (A) of the first conductive polymer in the first negative electrode film is less than or equal to the mass percentage (B) of the second conductive polymer in the second negative electrode film (Comparative Examples 2 and 3), the battery's maximum charge rate and cycle performance are both poor. This is because the current density distribution is uneven along the electrode thickness direction; the closer to the current collector, the worse the kinetics. Therefore, more conductive polymer is needed to improve the cell's performance.

[0116] Furthermore, comparing the data from Examples 1-11 reveals that, in terms of both maximum charge rate and cycle performance, excessively high or low levels of conductive polymer content are detrimental. With the same total conductive polymer content, distributing it across different layers, and assuming the mass percentage of the first conductive polymer A ≤ 6% and A is greater than B, the ratio of A to B also has a certain impact on battery performance; particularly when 1% ≤ A ≤ 3%, 0.5% ≤ B ≤ 3%, and 2 ≤ A / B ≤ 5, the maximum charge rate and cycle performance of the battery are significantly improved.

[0117] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0118] Table 1

Claims

1. A secondary battery, comprising a negative electrode, said negative electrode comprising: Negative electrode current collector; A first negative electrode film layer is disposed on at least one surface of the negative electrode current collector. The first negative electrode film layer includes a first negative electrode active material and a first conductive polymer, and the mass percentage of the first conductive polymer in the first negative electrode film layer is denoted as A, where A≤6%. The second negative electrode film layer is disposed on the surface of the first negative electrode film layer. The second negative electrode film layer includes a second negative electrode active material and a second conductive polymer, and the mass ratio of the second conductive polymer in the second negative electrode film layer is denoted as B. Then the negative electrode plate satisfies: 2≤A / B≤10; The first conductive polymer and the second conductive polymer are each independently selected from one or more of polyaniline, polypyrrole, polythiophene and its derivatives, polyacetylene, polyphenylene, and polyphenylacetylene; both the first negative electrode active material and the second negative electrode active material contain artificial graphite; the volume average particle size Dv of the first negative electrode active material is... 50 The volume average particle size Dv of the second negative electrode active material is 6μm-15μm. 50 The range is 0.5μm-8μm.

2. The secondary battery according to claim 1, wherein, 1%≤A≤5%。 3. The secondary battery according to claim 1, wherein, 1%≤A≤3%。 4. The secondary battery according to claim 1, wherein, B≤3%。 5. The secondary battery according to claim 1, wherein, 0.5%≤B≤3%。 6. The secondary battery according to claim 1, wherein, 2≤A / B≤5.

7. The secondary battery according to claim 1, wherein, The first conductive polymer and the second conductive polymer are each independently selected from poly(3,4-ethylenedioxythiophene).

8. The secondary battery according to claim 1, wherein, The volume average particle size Dv of the first negative electrode active material 50 The volume average particle size Dv of the second negative electrode active material is greater than that of the second negative electrode active material. 50 .

9. The secondary battery according to claim 1, wherein, The volume average particle size Dv of the first negative electrode active material 50 8μm - 12 μm; and / or, The volume average particle size Dv of the second negative electrode active material 50 It is 4μm-6μm.

10. The secondary battery according to claim 1, wherein, The specific surface area of ​​the first negative electrode active material is smaller than that of the second negative electrode active material.

11. The secondary battery according to claim 1, wherein, The specific surface area of ​​the first negative electrode active material is 0.5 m². 2 / g-2 m 2 / g; and / or, The specific surface area of ​​the second negative electrode active material is 1.5 m². 2 / g -5m 2 / g.

12. The secondary battery according to claim 1, wherein, The specific surface area of ​​the first negative electrode active material is 1 m². 2 / g-1.5 m 2 / g; and / or, The specific surface area of ​​the second negative electrode active material is 2m². 2 / g - 3m 2 / g.

13. The secondary battery according to claim 1, wherein, The OI value of the first negative electrode active material is 4-20; and / or, The OI value of the second negative electrode active material is 0.5-10.

14. The secondary battery according to claim 1, wherein, Let the thickness of the first negative electrode film be denoted as H1, and the thickness of the second negative electrode film be denoted as H2. Then the secondary battery satisfies: 0.5≤H1 / H2≤3.

15. The secondary battery according to claim 14, wherein, The secondary battery satisfies the following condition: 0.8 ≤ H1 / H2 ≤ 1.

5.

16. The secondary battery according to claim 1, wherein, The thickness of the first negative electrode film is denoted as H1, where 20 μm ≤ H1 ≤ 110 μm; and / or, The thickness of the second negative electrode film is denoted as H2, where 20μm≤H2≤110μm.

17. The secondary battery according to claim 1, wherein, The first negative electrode active material and / or the second negative electrode active material further include one or more of natural graphite, hard carbon, and silicon-based materials.

18. An electrical device comprising a secondary battery according to any one of claims 1-17.

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