Secondary battery and preparation method thereof, negative pole piece and electric device

Abstract

The invention provides a secondary battery and a preparation method thereof, a negative pole piece and an electric device, the secondary battery comprises the negative pole piece, the negative pole piece comprises a negative current collector and a negative film layer arranged on at least one side of the negative current collector, the negative film layer comprises a negative active material, and the negative active material comprises a carbon material; at least part of the surface of the carbon material is coated with fibers, and the rebound rate of the negative pole piece is 20-40%.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a secondary battery and its preparation method, negative electrode sheet and power supply device. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] During the cycling process of rechargeable batteries, the negative electrode carbon material undergoes volume expansion, leading to pulverization. This volume expansion also causes electrode rebound, resulting in electrode corner breakage and increasing the safety risks of the rechargeable battery. Furthermore, it can cause the materials to lose electrical contact, leading to rapid capacity decay and deteriorating cycle stability. Therefore, reducing the volume expansion of the negative electrode carbon material during cycling, decreasing the electrode rebound rate, and improving the cycle performance and safety of the battery are urgent technical problems to be solved in the current application field of rechargeable batteries. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery, a negative electrode, and an electrical device, wherein the negative electrode of the secondary battery has a low rebound rate, and the secondary battery prepared thereby has excellent cycle performance and safety performance.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including a carbon material;

[0006] The carbon material has at least a portion of its surface covered with fibers, and the negative electrode has a rebound rate of 20%-40%.

[0007] In any embodiment, the rebound rate of the negative electrode is 25%-35%.

[0008] In the above scheme, the fiber is wound around the carbon material to bind the carbon material, which can effectively suppress the volume change of the carbon material during the process of intercalation and deintercalation of active ions, reduce the rebound rate of the electrode, reduce the possibility of electrode corner breakage, improve the safety performance of the battery, and at the same time reduce the phenomenon of carbon material pulverization during cycling, improve the adhesion between materials, thereby improving the cycle stability of the electrode and extending the battery life.

[0009] In any embodiment, the carbon material includes at least one of graphite and hard carbon materials.

[0010] In any embodiment, the tensile strength of the fiber is 550 MPa-2500 MPa.

[0011] When the tensile strength of the fiber is within a suitable range, it can effectively restrain the volume expansion of the matrix material, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0012] In any embodiment, the diameter of the fiber is 10nm-1000nm, and can be selected as 20nm-150nm.

[0013] When the diameter of the fiber is within a suitable range, the fiber has appropriate strength, enabling it to tightly wrap the carbon material. This helps to suppress the volume expansion of the carbon material, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0014] In any embodiment, the length of the fiber is 200 nm to 1 mm, and can be selected as 1 μm to 100 μm.

[0015] The fiber length is within a suitable range, which enables the fiber to wrap around the carbon material, suppress the volume expansion of the carbon material, reduce the rebound rate of the electrode, improve the cycle performance and safety performance of the battery, and at the same time enable the negative electrode slurry to have suitable dispersibility and filterability, broaden the process window of the negative electrode slurry and negative electrode sheet, improve the uniformity of the components such as the negative electrode active material and conductive agent in the negative electrode sheet, and improve the cycle performance of the battery.

[0016] In any embodiment, based on the mass of the negative electrode active material, the mass content of the fiber is 0.1% to 10%, optionally 0.5% to 2%.

[0017] When the fiber content is within a suitable range, it can suppress the volume expansion of the negative electrode active material, reduce the rebound rate of the electrode sheet, and improve the cycle performance and safety performance of the battery. At the same time, it can also facilitate the deintercalation and intercalation of active ions, improve the kinetic performance and cycle performance of the battery, and increase the loading of active materials in the negative electrode sheet, which is beneficial to improving the energy density of the battery.

[0018] In any embodiment, the fiber includes one or more of carbon nanotubes, carbon fibers, glass fibers, metal fibers, polymer fibers, and natural fibers.

[0019] In any embodiment, the fiber includes one or more of aramid fibers and lignocellulose fibers.

[0020] Aramid fibers and lignocellulose fibers have a certain degree of curvature, which allows them to adhere well to the surface of active material particles, forming a dense fiber coating layer. They can also maintain good encapsulation during cycling, thereby inhibiting the expansion of active material particles, reducing the rebound rate of the electrode, and improving the cycle performance and safety performance of the battery.

[0021] In any embodiment, the volume distribution particle size Dv50 of the carbon material is 10μm-20μm.

[0022] When the volume distribution particle size Dv50 of carbon material is within a suitable range, the fibers can be tightly wrapped around the carbon material, which can alleviate the volume expansion of carbon material during cycling, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0023] A second aspect of this application provides a method for preparing a secondary battery, comprising:

[0024] Fiber coating: The mixed slurry containing negative electrode active material and fiber is dried to obtain fiber-coated negative electrode active material particles.

[0025] Preparation of negative electrode sheet: A negative electrode slurry containing the fiber-coated negative electrode active material particles is coated on at least one surface of the negative electrode current collector to obtain a negative electrode sheet.

[0026] The rebound rate of the negative electrode sheet is 20%-40%;

[0027] Preparation of secondary batteries: Assemble electrode components, including negative electrode plates, into secondary batteries.

[0028] Using the above preparation method, fibers can be wound around the surface of the matrix material, which can effectively suppress the volume change of the matrix material during the process of active ion insertion and extraction, reduce the rebound rate of the electrode, reduce the possibility of electrode corner breakage, improve the safety performance of the battery, reduce the possibility of pulverization of the matrix material during cycling, improve the adhesion between materials, improve the cycle stability of the electrode, and extend the battery life.

[0029] In any embodiment, the drying method includes any one of spray drying, freeze drying, and oven drying; spray drying may be selected.

[0030] A third aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a carbon material;

[0031] The carbon material has at least a portion of its surface covered with fibers, and the negative electrode has a rebound rate of 20%-40%.

[0032] The fourth aspect of this application provides an electrical device, characterized in that it includes the secondary battery described in the first aspect, or a secondary battery obtained by the preparation method described in the second aspect, or a negative electrode sheet described in the third aspect. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0034] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0035] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0038] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0039] Figure 7 This is a scanning electron microscope image of the negative electrode active material prepared according to the embodiment of this application.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0042] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] During the cycling process of rechargeable batteries, the negative electrode carbon material undergoes volume expansion, which can lead to electrode rebound and breakage at the electrode corners, increasing the safety risks of the rechargeable battery. It can also cause the materials to lose electrical contact, resulting in rapid capacity decay and deteriorating cycle stability. Therefore, reducing the volume expansion of the negative electrode carbon material during cycling, decreasing the electrode rebound rate, and improving the cycle performance and safety of the battery are urgent technical problems to be solved in the current application field of rechargeable batteries.

[0050] To address the issue of volume expansion of negative electrode active materials during cycling, related technologies propose adding cross-linked binders. These binders solidify in situ, forming a three-dimensional network structure that binds the expansion of the material and the electrode. However, after solidification, cross-linked binders are often quite hard, increasing the brittleness of the electrode. This can easily lead to electrode breakage during coating and baking, causing safety issues. Therefore, reducing volume expansion during cycling, lowering the electrode rebound rate, and improving the cycle performance and safety of the battery without affecting electrode brittleness remains a pressing problem.

[0051] Based on this, this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including a carbon material;

[0052] The carbon material has at least a portion of its surface covered with fibers, and the negative electrode has a rebound rate of 20%-40%.

[0053] In some embodiments, fibers are wound around the surface of a carbon material.

[0054] In this paper, the rebound rate of the negative electrode sheet is used to evaluate the degree of expansion of the negative electrode sheet in the thickness direction under full charge.

[0055] In some implementations, the rebound rate of the negative electrode can be selected as any value from 20%, 25%, 28%, 30%, 35%, 40%, or a range of any two of these values.

[0056] By winding fibers around carbon materials, the carbon materials are effectively bound, which can effectively suppress the volume change of carbon materials during the process of active ion insertion and extraction, reduce the rebound rate of the negative electrode, reduce the probability of problems such as lithium plating and insufficient electrolyte, improve the cycle performance of the battery, and at the same time reduce the possibility of carbon material pulverization during cycling, improve the adhesion between materials, improve the cycle stability of the electrode, and extend the battery life. In addition, for wound batteries, this application can also reduce the rebound rate of the electrode by binding the volume expansion of the matrix material, reduce the possibility of electrode corner breakage, and improve the safety performance of the battery.

[0057] Meanwhile, compared to using cross-linked binders to slow down the volume expansion of the negative electrode active material, this application can effectively slow down the volume expansion of the material, reduce the rebound rate of the electrode, and improve the cycle performance of the battery by winding fibers on the surface of the carbon material without affecting the electrode.

[0058] In addition, the fibers on the surface of the negative electrode active material can provide certain active functional groups, which can interact with the binder in the electrode sheet. At the same time, the fibers can also increase the roughness of the negative electrode active material, strengthen the bonding effect of the binder on the material, improve the bonding effect between materials, improve the cohesion and adhesion of the electrode sheet, improve the cycle stability of the electrode sheet, and improve the cycle performance of the battery.

[0059] In some embodiments, the tensile strength of the fiber is 550 MPa-2500 MPa.

[0060] In this paper, the term "tensile strength" refers to the maximum stress at which a material fractures under a uniaxial uniform tensile load. Tensile strength is determined by the ratio of the maximum load P at fracture to the cross-sectional area F0 of the specimen. It reflects the maximum tensile stress that a material can withstand.

[0061] The tensile strength of fibers can be tested using methods and equipment known in the art. For example, the fiber to be tested is dissolved in deionized water to obtain a fiber dispersion; the fiber dispersion is then used to form a film in an oven, and after drying, a test film sample is obtained; the dried film is then tested for tensile strength according to the national standard GB / T1040.3-2006.

[0062] In some embodiments, the tensile strength of the fiber may be selected as any value or a range of any two of the following: 550 MPa, 600 MPa, 800 MPa, 1000 MPa, 1500 MPa, 2000 MPa, and 2500 MPa.

[0063] When the tensile strength of the fiber is within a suitable range, it can effectively restrain the volume expansion of the matrix material, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0064] In some embodiments, the diameter of the fiber is 10nm-1000nm, optionally 50nm-150nm. In some embodiments, the diameter of the fiber can be any value or a range of any two values ​​selected from 10nm, 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 800nm, 850nm, 900nm, 950nm, and 1000nm.

[0065] When the diameter of the fiber is within a suitable range, the fiber has high tensile strength and a certain degree of curvature, which allows the high-strength fiber to adhere tightly to the surface of the matrix material. The fiber achieves a tight wrapping of the matrix material, which helps to suppress the volume expansion of the matrix material, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0066] In some embodiments, the length of the fiber is 200 nm to 1 mm, and may be 1 μm to 100 μm. In some embodiments, the length of the fiber may be any value or a range of any two of the following: 200 nm, 500 nm, 1000 nm, 5 μm, 10 μm, 100 μm, 500 μm, 800 μm, and 1 mm.

[0067] When the fiber length is within a suitable range, the fiber has high tensile strength, enabling the intertwined fibers to tightly wrap around the surface of the carbon material, suppressing the volume expansion of the carbon material, reducing the rebound rate of the electrode, improving the cycle performance and safety performance of the battery, and at the same time giving the negative electrode slurry suitable dispersibility and filterability, broadening the process window and processing performance of the negative electrode slurry, improving the uniformity of components such as the negative electrode active material and conductive agent in the negative electrode sheet, and improving the cycle performance of the battery.

[0068] In some embodiments, based on the mass of the negative electrode active material, the mass content of the fiber is 0.1 wt% to 10 wt%, optionally 0.5% to 2%. In some embodiments, based on the mass of the negative electrode active material, the mass content of the fiber can be any value or a range of any two of the following: 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%.

[0069] When the fiber content is within a suitable range, it can suppress the volume expansion of the negative electrode active material, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery. At the same time, it is also conducive to the deintercalation and intercalation of active ions, which can help reduce the internal resistance of the battery, improve the kinetic performance and cycle performance of the battery, and increase the loading of active materials in the negative electrode, which can help improve the energy density of the battery.

[0070] In some embodiments, the fiber includes one or more of carbon nanotubes, carbon fibers, glass fibers, metal fibers, polymer fibers, and natural fibers.

[0071] In any embodiment, the fiber includes one or more of aramid fibers and lignocellulose fibers.

[0072] Aramid fibers and lignocellulose fibers have a certain degree of curvature, which allows them to adhere well to the surface of the matrix material. They can form a dense fiber coating layer on the matrix material and maintain good encapsulation during cycling, thereby inhibiting the expansion of the matrix material, reducing the rebound rate of the electrode, and improving the cycle performance of the battery.

[0073] In this article, aramid fibers include poly(p-phenylene terephthalamide) fibers and poly(m-phenylene isophthalamide) fibers.

[0074] Aramid fibers have high tensile strength and a certain degree of flexibility. During cycling, they can adhere to the surface of the matrix material, thereby inhibiting the volume expansion of the material and improving the cycle performance of the battery.

[0075] In this article, lignocellulose fiber refers to fiber obtained from natural wood materials through physical or chemical treatment.

[0076] In some embodiments, the fiber comprises aramid fiber with a tensile strength greater than or equal to 2000 MPa.

[0077] In some embodiments, the carbon material includes at least one of graphite and hard carbon.

[0078] The presence of benzene ring structures in aramid fibers allows them to interact with the six-membered ring structures on the surface of carbon materials, increasing the affinity between the fibers and the matrix materials. This enables the fibers to be tightly wrapped around the material surface, further suppressing the volume expansion of the material, reducing electrode rebound, and improving the cycle performance and safety performance of the battery.

[0079] The main chain of lignocellulose fiber includes a glucose structure and a six-membered ring structure, which can interact with the six-membered ring structure of carbon materials, increasing the affinity between the fiber and the matrix material. This allows the fiber to be tightly wrapped around the material surface, further suppressing the volume expansion of the material, reducing electrode rebound, and improving the cycle performance and safety performance of the battery.

[0080] In some embodiments, the volumetric particle size distribution (Dv50) of the carbon material is 10 μm-20 μm. In some embodiments, the volumetric particle size distribution (Dv50) of the carbon material can be selected as any value or a range of any two values ​​selected from 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, and 20 μm.

[0081] The "volume distribution particle size Dv50" in this application refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. As an example, the volume distribution particle size Dv50 of carbon materials can be determined using laser diffraction particle size analysis. Specifically, the volume distribution particle size Dv50 of carbon materials can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T 19077-2016.

[0082] When the volume distribution particle size Dv50 of carbon material is within a suitable range, the fibers can be tightly wrapped around the carbon material, which can alleviate the volume expansion of carbon material during cycling, reduce the rebound rate of the electrode, and improve the cycle performance and safety performance of the battery.

[0083] This application also provides a method for preparing a secondary battery, comprising:

[0084] Fiber coating: The mixed slurry containing negative electrode active material and fiber is dried to obtain fiber-coated negative electrode active material particles.

[0085] Preparation of negative electrode sheet: A negative electrode slurry containing the fiber-coated negative electrode active material particles is coated on at least one surface of the negative electrode current collector to obtain a negative electrode sheet.

[0086] The rebound rate of the negative electrode sheet is 20%-40%;

[0087] Preparation of secondary batteries: Assemble electrode components, including negative electrode plates, into secondary batteries.

[0088] Using the above preparation method, fibers can be wound around the surface of carbon materials, which can effectively suppress the volume change of carbon materials during the process of intercalation and deintercalation of active ions, reduce the rebound rate of the electrode, reduce the probability of problems such as lithium plating and insufficient electrolyte, improve the cycle performance of the battery, reduce the possibility of pulverization of carbon materials during cycling, improve the adhesion between materials, improve the cycle stability of the electrode, extend the battery life, and also reduce the possibility of electrode corner breakage by reducing the rebound rate of the electrode, thereby improving the safety performance of the battery.

[0089] In some embodiments, the specific steps for preparing the negative electrode active material are as follows:

[0090] Carbon materials are dispersed in a fiber dispersion to obtain a mixed slurry.

[0091] In some embodiments, the fibers are dissolved in an aqueous or oily solvent to obtain a fiber dispersion.

[0092] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0093] 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, the positive electrode film layer including a positive electrode active material.

[0094] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0095] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0097] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0098] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0100] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0101] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0102] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0104] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0106] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0107] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0108] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0109] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0110] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0111] 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 may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0112] In some embodiments, the secondary battery also includes a separator. 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.

[0113] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0114] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0115] In some embodiments, a secondary battery includes a positive electrode, an electrolyte, a separator, and a negative electrode as described in some examples.

[0116] In some implementations, the secondary battery includes a lithium-ion battery.

[0117] 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.

[0118] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0119] 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. For example, Figure 1This is an example of a square-structured secondary battery 5.

[0120] In some implementations, refer to Figure 2 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 selected by those skilled in the art according to specific practical needs.

[0121] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0122] Figure 3 This 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.

[0123] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0124] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0125] 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, 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.

[0126] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

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

[0128] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0129] 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.

[0130] Example

[0131] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0132] I. Preparation Method

[0133] Example

[0134] 1) Preparation of negative electrode active materials

[0135] One g of aramid fiber with a diameter of 50 nm, a length of 30 μm, and a tensile strength of 2500 MPa was dissolved in deionized water and stirred to obtain a fiber dispersion. Then, 99 g of graphite (with a volume distribution particle size Dv50 of 10–20 μm) was dissolved in the fiber dispersion to obtain a mixed slurry. The slurry was then dried by two-fluid spray drying to obtain fiber-coated negative electrode active material particles.

[0136] 2) Preparation of negative electrode sheet

[0137] Fiber-coated negative electrode active material particles, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose CMC-Na, and conductive carbon black are added to deionized water in a mass ratio of 96.2%:1.8%:1.0%:1.0% and mixed evenly to obtain a negative electrode slurry. The slurry is coated onto a negative electrode current collector, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0138] 2) Preparation of positive electrode sheet

[0139] Lithium iron phosphate, carbon black, and polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone at a mass ratio of 98%:1%:1% to obtain a positive electrode slurry. This slurry was then coated onto a positive electrode current collector, dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0140] 4) Separating membrane

[0141] Polypropylene film is used as the separator.

[0142] 5) Preparation of electrolyte

[0143] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and ethyl methyl carbonate (DMC) were mixed evenly. Ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and LiPF6 were dissolved in the above organic solvents to prepare an electrolyte with a LiPF6 concentration of 1 mol / L, thus obtaining the electrolyte of Example 1.

[0144] 6) Battery manufacturing

[0145] The positive electrode, separator, and negative electrode of Example 1 are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a battery cell, tabs are welded to the battery cell, and the battery cell is installed in an aluminum shell. Electrolyte is then injected and the shell is sealed. After processes such as settling, cold pressing, formation, shaping, and capacity testing, a lithium-ion secondary battery is obtained.

[0146] The specific preparation parameters for Examples 2-12 are shown in Table 1.

[0147] Comparative Example 1

[0148] The preparation parameters in Comparative Example 1 are basically the same as those in Example 1, but the negative electrode active material in Comparative Example 1 is graphite, that is, there is no fiber coating process on the graphite surface. The specific parameters are shown in Table 1.

[0149] II: Performance Testing

[0150] 1) Morphology of the negative electrode active material

[0151] The morphology of the negative electrode active material was measured using a Zeiss Sigma-300 scanning electron microscope at a voltage of 5 kV and a magnification of 10,000x.

[0152] 2) Negative electrode peeling force test

[0153] After cold pressing, the negative electrode sheet was cut into 15*2cm rectangular strips. After drying the strips in an 80℃ oven for 2 hours, the peel force between the active coating and the current collector was tested (3 to 5 electrode sheets were tested in each group, and the peel force was taken as the average of several groups of data).

[0154] 3) Rebound rate of the negative electrode sheet

[0155] The thickness of the negative electrode sheet was measured using a micrometer. The thickness of the negative electrode sheet after cold pressing was recorded as R (10 random tests were conducted, and the average value was taken). The battery cell was prepared according to the preparation method in the aforementioned embodiment. After formation and full charging, the thickness of the negative electrode sheet was measured and recorded as T (10 random tests were conducted, and the average value was taken). The rebound rate of the negative electrode sheet after full charging was calculated as S = (T / R-1)*100%.

[0156] 4) Cyclic performance

[0157] The secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 1 / 3C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 1 / 3C to the discharge cutoff voltage of 2.0V, 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.

[0158] 5) Cohesion test of negative electrode sheet

[0159] After cold pressing, the negative electrode sheet was cut into 15*2cm rectangular strips. The strips were dried in an 80℃ oven for 2 hours, and the cohesive force of the electrode sheet was tested. The cohesive force is the adhesion force between particles (3 to 5 electrode sheets were tested in each group, and the cohesive force was taken as the average value of several groups of data).

[0160] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0161] 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 the table below.

[0162] Table 1

[0163]

[0164]

[0165] Table 2

[0166]

[0167]

[0168] from Figure 7 The scanning electron microscope image shows that at least a portion of the surface of the graphite material is covered with fibers.

[0169] As can be seen from the above embodiments and comparative examples, coating the surface of carbon materials with fibers can effectively suppress the volume change of carbon materials during the process of intercalation and deintercalation of active ions, reduce the rebound rate of the electrode, and also improve the bonding force between the active material and the current collector, as well as between the active materials, thereby improving the cycle stability of the electrode and extending the battery life.

[0170] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a carbon material. The carbon material is at least partially coated with fibers, and the negative electrode sheet has a rebound rate of 20%-40%, preferably 25-35%.

2. The secondary battery according to claim 1, characterized in that, The carbon material includes at least one of graphite and hard carbon materials.

3. The secondary battery according to claim 1 or 2, characterized in that, The volumetric particle size Dv50 of the carbon material is 10μm-20μm.

4. The secondary battery according to claim 1 or 2, characterized in that, The tensile strength of the fiber is 550MPa-2500MPa.

5. The secondary battery according to claim 1 or 2, characterized in that, The diameter of the fiber is 10nm-1000nm.

6. The secondary battery according to any one of claims 1 to 2, characterized in that, The diameter of the fiber is 20nm-150nm.

7. The secondary battery according to any one of claims 1 to 2, characterized in that, The fiber has a length of 200 nm to 1 mm.

8. The secondary battery according to any one of claims 1 to 2, characterized in that, The length of the fiber is 1μm-100μm.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, Based on the mass of the negative electrode active material, the mass content of the fiber is 0.1 wt% to 10 wt%.

10. The secondary battery according to claim 9, characterized in that, The fiber content is 0.5% to 2% by mass.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The fibers include one or more of the following: carbon nanotubes, carbon fibers, glass fibers, metal fibers, polymer fibers, and natural fibers.

12. The secondary battery according to any one of claims 1 to 10, characterized in that, The fibers include one or more of aramid fibers and lignocellulose fibers.

13. A method for preparing a secondary battery, characterized in that, include: Fiber coating: The mixed slurry containing negative electrode active material and fiber is dried to obtain fiber-coated negative electrode active material particles. Preparation of negative electrode sheet: A negative electrode slurry containing the fiber-coated negative electrode active material particles is coated on at least one surface of the negative electrode current collector to obtain a negative electrode sheet. The rebound rate of the negative electrode sheet is 20%-40%; Preparation of secondary batteries: Assemble electrode components, including negative electrode plates, into secondary batteries.

14. The method for preparing a secondary battery as described in claim 13, characterized in that, The drying method includes any one of spray drying, freeze drying, and oven drying; spray drying may be selected.

15. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon material; The carbon material has at least a portion of its surface covered with fibers, and the negative electrode has a rebound rate of 20%-40%.

16. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1 to 12, or the secondary battery obtained by the preparation method according to any one of claims 13-14, or the negative electrode sheet according to claim 15.

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