Secondary battery, pole piece, preparation method and electric device

Abstract

The invention discloses a secondary battery, a pole piece, a preparation method and an electric device. The secondary battery comprises a positive electrode and a negative electrode, a pole piece of at least one of the positive electrode and the negative electrode comprises a current collector and an active layer loaded on the current collector, the active layer comprises fibers and an electrode active material, the length-diameter ratio of the fibers is not less than 50, and the content of the fibers in the active layer is 1-2.5 wt%. According to the secondary battery, the active layer can be formed by adopting the slurry containing no binder under the condition of ensuring the performance of the pole piece, so that the secondary battery has better environmental protection performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a secondary battery, a pole piece, a preparation method and an electric device. BACKGROUND

[0002] Lithium ion batteries are widely used in various electric devices to provide electric energy due to their high energy density and specific energy, wide operating temperature range and other advantages. Secondary batteries such as lithium ion batteries have electrode active materials loaded on the electrodes, and the charging and discharging of the batteries are realized through the embedding and de-embedding of energy storage ions such as lithium ions. The active materials are usually compounded on the carrier structure such as the current collector in the form of an active material layer. In addition to the positive or negative active material, the active material layer also contains components such as conductive agents, dispersants, and binders. In order to improve the polarity and obtain good adhesion, most traditional binders contain fluorine elements, but the binders containing fluorine elements have poor environmental performance.

[0003] Therefore, the current secondary battery, pole piece, preparation method and electric device still need to be improved. SUMMARY

[0004] In view of the above problems, the present application provides a secondary battery, a preparation method and an electric device. The pole piece of the secondary battery can form an active layer using a slurry without a binder, while ensuring the performance of the pole piece, and therefore has better environmental performance.

[0005] In one aspect of the present application, a secondary battery is provided. The secondary battery includes a positive electrode and a negative electrode, and the pole piece of at least one of the positive electrode and the negative electrode includes a current collector and an active layer loaded on the current collector, the active layer including fibers and electrode active materials, the aspect ratio of the fibers being not less than 50, and the content of the fibers in the active layer being 1-2.5wt%. The pole piece of the secondary battery uses fibers to form a three-dimensional structure to load electrode active materials, forming a connection network similar to a bridge to reliably fix the electrode active materials in the active layer, so that the use of F-containing binders can be avoided, and the secondary battery has better environmental performance.

[0006] According to an embodiment of the present application, the content of F elements in the active layer is less than 0.05%. Thus, the secondary battery has better environmental performance.

[0007] According to an embodiment of the present application, the active layer does not contain a binder. Thus, the secondary battery has better environmental performance.

[0008] According to an embodiment of the present application, the length of the fibers is 30-200μm, and the diameter of the fibers is 0.5-5μm. Thus, the bridge effect of the fibers in connecting the electrode active materials can be further improved, and the performance of the secondary battery can be improved.

[0009] According to an embodiment of the present application, the fiber includes at least one of cellulose fiber, aramid fiber, carbon nanotube, and carbon fiber. Thus, the performance of the electrode sheet of the secondary battery can be further improved.

[0010] According to an embodiment of the present application, the active layer includes 96-99 wt% of the electrode active material, 1-2.5 wt% of the fiber, 0-1.5 wt% of the conductive agent, and optionally a dispersant.

[0011] According to an embodiment of the present application, the content of the fiber in the active layer is 1.5-2 wt%, the diameter of the fiber is 0.5-1.5 μm, and the length of the fiber is 100-200 μm. Thus, the electrode sheet can have better adhesion and tensile strength.

[0012] According to an embodiment of the present application, the electrode sheet is a negative electrode sheet, and the electrode active material includes at least one of graphite, silicon-carbon material, and silicon negative electrode material. Thus, the secondary battery can be applied to a wider system.

[0013] According to an embodiment of the present application, the electrode sheet satisfies at least one of the following conditions: the adhesion of the electrode sheet is not less than 10 N / m; the tensile strength of the electrode sheet is not less than 8-12%; and the area reduction of the electrode sheet is 8-12%. Thus, the secondary battery can have better service life and safety.

[0014] In another aspect of the present application, an electrode sheet is provided. The electrode sheet includes a current collector and an active layer loaded on the current collector, the active layer including fiber and electrode active material, the fiber having an aspect ratio of not less than 50, and the content of the fiber in the active layer being 1-2.5%. The electrode sheet has at least one of the advantages of reliable mechanical performance, more environmental protection, etc.

[0015] According to an embodiment of the present application, the electrode sheet satisfies at least one of the following conditions: the fiber is nanofiber; the length of the fiber is 30-200 μm, and the diameter of the fiber is 0.5-1.5 μm; the fiber includes at least one of cellulose fiber, aramid fiber, carbon nanotube, and carbon fiber; the content of the fiber in the active layer is 1.5-2 wt%; the active layer includes 96-99 wt% of the electrode active material, 1-2.5 wt% of the fiber, and 0-1.5 wt% of the conductive agent; and the electrode active material includes at least one of graphite, silicon-carbon material, and silicon negative electrode material.

[0016] In still another aspect of the present application, a method for preparing a pole piece is provided. The method comprises: mixing a dispersed fiber and an electrode active material to form a slurry; extruding the slurry into a piece to form an active layer precursor, and compounding the active layer precursor to a current collector to form an active layer, the fiber has an aspect ratio of not less than 50, and the content of the fiber in the active layer is 1.0-2.5 wt%. The method can simply obtain a pole piece with certain bonding force, and the pole piece has good environmental protection performance.

[0017] According to the embodiments of the present application, the fiber is provided by a fiber-containing raw material, and the fiber-containing raw material satisfies at least one of the following conditions: the viscosity is not more than 70 Cp; and the solid content of the fiber-containing raw material is not less than 10%. Thus, the pole piece can be more simply obtained.

[0018] According to the embodiments of the present application, the method satisfies at least one of the following conditions: the solid content of the slurry is 70-80%; the dispersion treatment is performed by using a double-planet disperser; the extruding into a piece is performed at room temperature, and the compounding to the current collector comprises pressing the active layer precursor obtained by the extruding into a piece on the current collector and drying, and the temperature of the drying is 50-70°C. Thus, the pole piece can be more simply obtained.

[0019] In still another aspect of the present application, an electric device is provided. The electric device comprises the secondary battery as described above, and the secondary battery is used for providing electric energy. BRIEF DESCRIPTION OF DRAWINGS

[0020] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not to be considered limitations of the present application. Moreover, in the drawings, like reference numerals refer to similar components throughout the several views. In the drawings:

[0021] Figure 1 Structure schematic diagram of the pole piece in some embodiments of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and thus only serve as examples, and cannot limit the protection scope of the present application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0026] 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).

[0027] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0028] Furthermore, with the development of power batteries, users' requirements for power battery performance have also increased across the board. In addition to the basic performance requirements of batteries, safety, environmental protection, and other performance characteristics have also become important indicators for measuring the performance of power batteries.

[0029] This application presents a secondary battery and electrode with an active layer containing extremely low or even no sulfur (F) content, as well as an electrode and secondary battery containing this active layer. Therefore, this electrode exhibits good environmental performance. Furthermore, by adjusting the composition of the active layer and selecting specific fibers to form a three-dimensional structured load electrode active material, this application can ensure the basic performance of the electrode without using binders and enables electrode fabrication processes.

[0030] The electrode sheet disclosed in this application can be used in secondary batteries such as lithium-ion batteries. For ease of understanding, the electrode sheet containing the above-described active layer will be described first below:

[0031] According to some embodiments of this application, reference is made to Figure 1 The electrode sheet proposed in this application includes a current collector 200 and an active layer 100 loaded on the current collector 200. The active layer 100 includes fibers 10 and electrode active material 20. The aspect ratio of the fibers in the active layer 100 is not less than 50, and the fiber content in the active layer 100 is 1-2.5 wt%. In the electrode sheet proposed in this application, the electrode active material 20 is mounted on a three-dimensional structure composed of fibers 10. The fibers 10 are used to form a supporting bridge structure connecting the electrode active materials 20, thereby avoiding the use of binders containing fluorine (F) and having better environmental performance.

[0032] This application employs fibers to form a bridge-like connection structure on the surface of the current collector, supporting the active layer and connecting the load and electrode active material. This avoids the use of fluorine-containing adhesives while maintaining adequate adhesion and strength of the electrode. Therefore, it offers a more environmentally friendly advantage. Furthermore, when the fiber's aspect ratio is not less than 50, i.e., when the fiber has a large aspect ratio, it facilitates the formation of a bridge structure that better supports the electrode active material and helps improve the adhesion between the active layer and the current collector. By controlling the fiber content in the active layer, sufficient adhesion can be ensured in the obtained electrode, reducing the probability of defects such as delamination during electrode preparation. Simultaneously, it provides sufficient toughness to the active layer, alleviating problems such as electrode breakage due to high brittleness.

[0033] Therefore, the electrode proposed in this application can achieve the electrode manufacturing process without using an F-containing binder. The adhesion and electrical properties of the electrode can meet the current requirements of secondary batteries for electrodes, and it can be adapted to a variety of industrialized secondary battery systems, thus having good application prospects.

[0034] In some examples, the aspect ratio of a fiber can be determined using information from scanning electron microscope (SEM) images. For instance, the aspect ratio can be determined using software such as Avizo 3D based on the SEM images. Alternatively, multiple fibers can be selected within the field of view of the SEM images, and their lengths and diameters measured separately. The average of these multiple aspect ratios is then determined as the fiber's aspect ratio. The number of fibers selected can be 5 or more, specifically 10 or more, 20 or more, or 50 or more.

[0035] In some examples, the fiber content in the active layer can be determined using methods such as thermal analysis. For instance, the fiber content can be calculated using thermogravimetric analysis (TGA) based on the weight loss of each component in the active layer at different temperatures. The weight loss temperatures of different components in the active layer can be determined by performing TGA on each component individually. Alternatively, the fiber content can be obtained by monitoring mass loss during programmed temperature rise using methods such as thermal analyzer-mass spectrometry (TMS).

[0036] In some examples, the electrode may be free of binders. For instance, it may be free of fluorine-containing polytetrafluoroethylene (PTFE) binders or fluorine-free polyacrylic binders. Here, "free of binders" specifically refers to conventional, non-fibrous electrode binders, such as the PTFE and polyacrylic binders listed above. Specifically, for example, the binder content in the active layer is less than 0.1 wt%, and the fiber content used in this application should not be considered as the binder content. The fluorine content in the active layer is less than 0.05 wt%. This allows the electrode to have better environmental performance.

[0037] According to embodiments of this application, the fibers can be small in diameter. For example, a diameter between a few nanometers and a few micrometers can be selected. Smaller diameter fibers better meet the requirement of an aspect ratio of not less than 50 and also better adapt to electrode active particles. In some examples, the fiber length can be 30-200 μm, and the fiber diameter can be 0.5-5 μm. When the fiber size is within the above range, a three-dimensional structure capable of effectively carrying electrode active materials can be formed, alleviating problems such as uneven loading of active material in the active layer caused by fiber agglomeration. Furthermore, when the fiber meets the above requirements, the formed bridge structure can effectively carry most current electrode active materials. That is, the fiber can provide an effective network structure for most current electrode active materials, such as adapting to various positive electrode active particles, such as lithium iron phosphate and ternary materials. It can also adapt to negative electrode active materials with different particle sizes, such as carbon negative electrode materials, silicon-carbon materials, and silicon negative electrode materials.

[0038] According to embodiments of this application, the specific chemical composition of the fiber is not particularly limited, and may include at least one of cellulose fiber, aramid fiber, carbon nanotube, and carbon fiber. In some embodiments, fibers with active groups on their surface, such as carboxyl groups and hydroxyl groups, may be selected. These fibers can interact better with electrode active materials and also have the advantage of lower cost.

[0039] According to embodiments of this application, the fiber content in the active layer can be 1-2.5 wt%, specifically 1.5-2 wt%. When the fiber content is within the above range, it can provide the active layer with a three-dimensional structure with better mechanical strength, further improve the adhesion of the electrode, and reduce the probability of defects such as delamination during the preparation of the electrode. At the same time, it can provide sufficient toughness to the active layer, alleviating problems such as easy breakage of the electrode due to its high brittleness.

[0040] According to embodiments of this application, the active layer comprises 96-99 wt% of the electrode active material, 1-2.5 wt% of the fiber, and 0-1.5 wt% of a conductive agent. The conductive agent can be selected from materials such as Super P, carbon nanofibers (VGCF), and carbon nanotubes (CNTs). When the content of each component of the active layer is within the above range, especially when the fiber content meets the above range, the formed electrode can have better mechanical properties, such as electrode adhesion. A content of 96-99 wt% of electrode active material allows the electrode to be formed through simpler operations, thereby reducing the difficulty of the electrode manufacturing process, reducing production costs, and maintaining good electrical performance.

[0041] In some examples, to further improve the flexibility of the electrode, the active layer may further include a dispersant. When the electrode is applied to a wound-cell secondary battery, the electrode containing the dispersant can have better flexibility to adapt to the shape of the wound-cell battery. Specifically, the dispersant includes a polyacrylic acid dispersant, and the mass percentage of the dispersant in the active layer can be 0.15%-0.25 wt%.

[0042] According to embodiments of this application, the specific type and size of the electrode active material in the active layer can be selected according to actual needs. The electrode sheet provided in this application uses fibers with the aforementioned characteristics, which can be well matched with most electrode active materials. Therefore, the size and chemical composition of the electrode active material can be selected within a wider range. For example, in some examples, the electrode sheet can be a negative electrode sheet, and the electrode active material includes at least one of graphite, silicon-carbon materials, and silicon negative electrode materials. For example, the electrode active material may include a mixture of graphite and silicon-carbon materials, or the electrode active material may include one or more graphite materials.

[0043] According to embodiments of this application, the electrode may also have an adhesion strength of not less than 10 N / m. This further improves the lifespan of the electrode, reduces the probability of active layer peeling, and thus increases the lifespan of the secondary battery utilizing this electrode.

[0044] According to an embodiment of this application, the tensile strength of the electrode can be not less than 0.3 MPa. This allows the electrode to have good mechanical strength.

[0045] According to an embodiment of this application, the cross-sectional shrinkage rate of the electrode is 8-12%. This allows the formed electrode to have better performance, for example.

[0046] In this application, the aforementioned physical properties of the electrode can be controlled by adjusting the aspect ratio, content, and composition of the fibers in the active layer. In some examples, cellulose fibers with a diameter in the nanometer range and a length greater than 20 μm, for example, between 50 μm and 200 μm, specifically 100-200 μm, can be used to form a three-dimensional network structure in the active layer of the electrode. In this electrode, the fiber content in the active layer can be 1-2.5%, for example, 1.5-2 wt%. The electrode active material can be a negative electrode active material, and the active layer contains a conductive agent and optionally a dispersant. The electrode obtained thereby can meet the aforementioned physical property requirements, thus possessing at least one of the advantages of being more environmentally friendly, having a longer service life, reliable mechanical properties, being obtainable through a simple manufacturing process, and having a high yield.

[0047] In another aspect of this application, a secondary battery is proposed. The secondary battery includes a positive electrode and a negative electrode. At least one of the positive and negative electrodes comprises a current collector and an active layer loaded on the current collector. The active layer comprises fibers and an electrode active material. The aspect ratio of the fibers is not less than 50, and the fiber content in the active layer is 1-2.5 wt%.

[0048] This secondary battery has at least one of the following advantages: it is more environmentally friendly, has a longer service life, reliable electrode mechanical properties, can be obtained through a simple manufacturing process, and has a high yield rate.

[0049] According to some examples of this application, the electrode of the secondary battery can be the aforementioned electrode. In some examples, the electrode can be a negative electrode. Thus, the fibers in the aforementioned electrode can be used to form a three-dimensional network structure, effectively carrying the electrode active material. While maintaining the mechanical strength and electrical performance of the electrode to meet the requirements of the secondary battery, this electrode can also improve the environmental performance of the secondary battery.

[0050] Specifically, the fibers in the active layer of the electrode of this secondary battery are nanofibers. In some embodiments, the fiber length is 30-200 μm and the fiber diameter is 0.5-1.5 μm; the fiber may include cellulose fibers. For example, it may include cellulose fibers of one or more sizes, or modified or unmodified cellulose fibers. The fiber content in the active layer may be 1-2.5 wt%, for example, 1.5-2 wt%. In some specific examples, the active layer of the electrode may include 96-99 wt% electrode active material, 1-2.5 wt% fibers, and 0-1.5 wt% conductive agent. The electrode active material includes at least one of graphite, silicon carbide, and silicon anode materials.

[0051] The aforementioned electrode can provide a more environmentally friendly positive or negative electrode for secondary batteries. Furthermore, this electrode is compatible with various electrolyte systems and positive electrode active particles, thus enabling the secondary battery to be used in a variety of battery systems. For example, this electrode can be used as a negative electrode, compatible with various positive electrode materials, such as lithium iron phosphate and ternary cathode materials. The negative electrode active material can be selected from graphite and silicon-carbon materials, and it exhibits good compatibility with electrolytes of various compositions.

[0052] In some embodiments, the electrode of this battery can have good tensile strength and adhesion. Therefore, the mechanical properties and service life of the secondary battery can be well guaranteed. For example, the tensile strength of the electrode can be no less than 0.3 MPa, and the adhesion strength can be no less than 10 N / m. This mechanical property is suitable for various types of secondary batteries and ensures battery life. The electrical performance of the secondary battery also remains at a good level, demonstrating that replacing the F-containing binder in the active layer with fiber does not affect the performance of the electrode.

[0053] In another aspect of this application, a method for preparing an electrode sheet is proposed. The electrode sheet prepared by this method can be the electrode sheet described above. Specifically, the method may include mixing dispersed fibers and electrode active materials to form a slurry, extruding the slurry into sheets to form an active layer precursor, and then laminating it onto a current collector to form an active layer. The aspect ratio of the fibers is not less than 50, and the fiber content in the active layer is 1-2.5%. This method can easily obtain the aforementioned electrode sheet.

[0054] The method proposed in this application can prepare the electrode sheet through a process similar to dry pressing. This method is simple to operate and effectively allows the fibers in the slurry to form a three-dimensional structure capable of carrying the electrode active material. The resulting active layer composite has sufficient adhesion to the current collector and ensures that the electrical properties of the obtained electrode sheet meet the requirements.

[0055] According to embodiments of this application, the method can use a liquid fiber-containing raw material to provide the fibers in the active layer. This is more conducive to the full dispersion of the fibers. For example, a liquid fiber-containing raw material containing solvents such as water can be used. The viscosity of the fiber-containing raw material can be no greater than 70 Cp. Fiber-containing raw materials with a viscosity meeting this requirement can be more easily and fully dispersed, and can better form the bridging three-dimensional structure connecting the electrode active materials in subsequent steps.

[0056] Viscosity

[0057] In this application, viscosity is referred to as dynamic viscosity, expressed in Cp. Viscosity Cp accurately assesses the rheological properties of a liquid, providing reliable parameter support for fiber selection. Those skilled in the art can convert it to Ps·s or mPa·s as needed. This viscosity is measured at temperature, specifically according to the standard GB / T1548-2004.

[0058] In some embodiments, the solid content of the fiber-containing raw material can be controlled within a range of not less than 10%. When the solid content of the fiber-containing raw material is higher than 10%, an active layer precursor with a certain water content can be obtained through simple processing, which helps to simplify the operation of the method. For example, the solid content can be 10-50%. Increasing the solid content of the fiber-containing raw material improves the manufacturability of the method, is more conducive to forming an active layer precursor with certain self-supporting properties, and can further improve the uniformity of dispersion of the fiber-containing raw material and the electrode active material.

[0059] For example, in some specific embodiments, the method can first mix fiber-containing raw materials, electrode active materials, and other components of the active layer (such as conductive agents, dispersants, etc.) to obtain a slurry for preparing the active layer. The formed slurry can be directly pressed to obtain an active layer precursor with a certain water content. At this time, because the slurry contains fibers, the active layer precursor can have self-supporting properties. Subsequently, the active layer precursor can be composited with a current collector. The composite with the current collector can be achieved by pressing. After drying, the aforementioned electrode sheet can be obtained.

[0060] In some specific embodiments, the solid content of the slurry can be 70-80%. When the solid content of the slurry is within the above range, the quality of the electrode obtained by this method can be further improved, and the yield can be increased. Specifically, an appropriate solid content can reduce the occurrence of incomplete coating on the electrode surface and alleviate the problem of decreased electrode adhesion.

[0061] In some embodiments, the fibrous raw material can be pre-dispersed before mixing with the electrode active material. Specifically, the dispersion treatment can be performed using a dual planetary disperser. This facilitates the formation of a more uniform system, resulting in an electrode with better performance. Extrusion of the slurry into sheets can be performed at room temperature, for example, pressing in the range of 10-40°C. Some of the solvent in the slurry, such as water, can be removed during pressing, and the resulting active layer precursor may contain a certain amount of residual solvent. Subsequently, the active layer precursor can be composited onto the current collector. Specifically, the active layer precursor obtained from the extrusion can be pressed onto the current collector and dried at a temperature of 50-70°C. This allows for a simpler method of obtaining the electrode.

[0062] In another aspect, this application proposes an electrical device. This device includes the aforementioned secondary battery for providing electrical energy. Thus, the device possesses all the features and advantages of the aforementioned battery, which will not be repeated here. In general, this device can utilize the aforementioned battery to provide electrical energy, and therefore has a reliable lifespan and good environmental performance.

[0063] In this application, the electrical device can be such as a mobile phone, tablet, laptop, electric toy, power tool, electric vehicle, electric car, ship, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0064] 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.

[0065] Example 1

[0066] A 10% solids-content aqueous solution of cellulose fibers (50 μm in length and 1 μm in diameter) was dispersed using a double planetary dispersion method and then mixed with a negative electrode active material (graphite) to form an aqueous slurry with a solids content of 75%. This slurry was extruded into sheets at room temperature, pressed onto copper foil, and dried at 70°C to form an electrode sheet. The active layer of the electrode sheet contained 97.1% graphite, 0.4% Super P conductive agent, and 1.75% fiber.

[0067] Example 2

[0068] The remaining operations are the same as in Example 1, except that the cellulose fiber used has a filament length of 100 μm.

[0069] Example 3

[0070] The remaining operations are the same as in Example 1, except that a cellulose aqueous solution with a solid content of 50% is used.

[0071] Example 4

[0072] The remaining operations are the same as in Example 1, except that the amount of solvent (water) is adjusted to prepare a slurry with a solid content of 60%.

[0073] Example 5

[0074] The remaining operations are the same as in Example 1, except that the amount of cellulose solution is adjusted so that the cellulose content in the formed active layer is 2.5%.

[0075] Example 6

[0076] The remaining operations are the same as in Example 1, except that the amount of cellulose solution is adjusted so that the cellulose content in the formed active layer is 1%.

[0077] Comparative Example 1

[0078] The remaining operations are the same as in Example 1, except that the cellulose fibers used have a filament length of 20 μm and a diameter of 1 μm.

[0079] Comparative Example 2

[0080] The remaining operations are the same as in Example 1, except that the amount of cellulose solution is adjusted so that the cellulose content in the formed active layer is 0.5%.

[0081] Comparative Example 3

[0082] The remaining operations are the same as in Example 1, except that the amount of cellulose solution is adjusted so that the cellulose content in the formed active layer is 3%.

[0083] The performance of the electrodes obtained in the examples and comparative examples was tested.

[0084] 1) Reduction of area test

[0085] The positive electrode sheets prepared in the examples and comparative examples were cut into test specimens with a size of 20mm × 100mm for later use.

[0086] The positive electrode sheet was stretched along its length until it broke using a universal testing machine (INSTRON 5969) at a stretching rate of 50 mm / min.

[0087] The reduction of area is calculated using the following formula:

[0088] Reduction of area (%) = [(A0-A) / A0] × 100%;

[0089] A0 represents the cross-sectional area of ​​the sample before stretching, and A represents the cross-sectional area of ​​the necked-out portion after stretching and fracture.

[0090] Three samples were taken from each group for testing, and the average value was taken.

[0091] 2) Electrode adhesion

[0092] The test was conducted according to the method of national standard GB2792-1998. The 180° peel strength of the electrode was tested using a universal testing machine (INSTRON 5969) at a tensile rate of 50 mm / min.

[0093] The operating procedure is as follows: Take a sample with a width of 30mm and a length of 100mm-160mm. Apply special double-sided adhesive tape to a steel plate. The tape should be 20mm wide and 90mm-150mm long. Place the positive electrode film layer of the previously cut electrode sample onto the double-sided adhesive tape, and then roll it three times in the same direction using a 2kg roller. Fix a paper strip with a width equal to the electrode and a length of 250mm below the current collector of the electrode, and secure it with wrinkle adhesive. Turn on the equipment power; the indicator light will illuminate. Adjust the limit block to the appropriate position. Secure the end of the steel plate without the electrode attached using the lower clamp. Fold the paper strip upwards and secure it with the upper clamp. Use the up and down buttons on the manual controller attached to the tensile testing machine to adjust the clamp position. Then perform the test and read the values. Divide the force when the electrode is in equilibrium by the width of the tape to obtain the electrode adhesion force per unit length, which characterizes the bonding strength between the positive electrode film layer and the current collector. Take three samples from each group for testing and take the average value.

[0094] Battery manufacturing

[0095] Secondary batteries were fabricated using the electrodes obtained in the examples and comparative examples. The battery fabrication process is as follows:

[0096] [Positive electrode plate]

[0097] The positive electrode active material, conductive agent carbon black Super P, binder CMC and solvent are mixed and stirred evenly in a mass ratio of 8:1:1:10 to obtain a positive electrode slurry; the positive electrode slurry is then uniformly coated on one surface of the current collector (copper foil), and then dried, cold pressed and cut to obtain a positive electrode sheet.

[0098] [Isolation membrane]

[0099] Polypropylene film is used as the separator.

[0100] Electrolyte

[0101] LiPF6 with a concentration of 1 mol / L was used as the electrolyte (the solvents were EC and EMC, with a volume ratio of 3:7).

[0102] [Negative electrode plate]

[0103] The electrodes prepared using the examples and comparative examples are negative electrode sheets.

[0104] The obtained positive electrode, separator (porous polyethylene film), and negative electrode are cut into round pieces and arranged in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation. The separator is impregnated with the electrolyte and then compacted to obtain a button lithium-ion battery.

[0105] Battery performance test

[0106] DC Impedance (DCR) Test

[0107] The DCR (Discharge-Responsive Characteristic) tester was used for testing. Before performing the Hybrid Pulse Power Characteristic (HPPC) test, the cell was discharged at 25°C at a 1C rate, then fully charged at a constant current and voltage, and left to rest for 1 hour to restore the electrochemical and thermal equilibrium state, recorded as 100% SOC. The open-circuit voltage (OCV) value at 100% SOC was recorded. The HPPC test was performed according to the recommended pulse rate (1C rate) to obtain the charge-discharge DCR at 100% SOC.

[0108] The electrode parameters obtained from the above embodiments and comparative examples are shown in Table 1 below:

[0109] Table 1

[0110]

[0111] The results of the electrode tests and battery tests are shown in Table 2 below:

[0112] Table 2

[0113] Manufacturability Strength / MPa Adhesion / (N / m) Shrinkage on break DCR / mΩ Example 1 ★☆ 0.35 20.3 9.03％ 422.13 Example 2 ★★★ 0.86 49.6 8.81％ 422.82 Example 3 ★★ 0.45 22.8 8.90％ 422.13 Example 4 ★ 0.23 11.8 9.63％ 422.13 Example 5 ★★☆ 0.66 31.5 8.40％ 428.26 Example 6 ★ 0.23 11.5 9.76％ 417.47 Comparative Example 1 ☆ 0.04 2.60 / / Comparative Example 2 ☆ / / / / Comparative Example 3 ★ 0.45 23.4 7.91％ 435.80

[0114] Table 2 above quantifies manufacturability, with ★ representing 1 and ☆ representing 0.5. A higher number indicates stronger manufacturability and a lower probability of problems such as electrode delamination or electrode breakage during manufacturing. When manufacturability is less than or equal to 0.5, the electrode cannot be manufactured.

[0115] Referring to the test results of the above embodiments and comparative examples, it can be seen that the electrode bonding strength obtained in the embodiments is greater than 10 N / m, which can meet the requirements of the anode electrode manufacturing process. Comparative Example 1 uses cellulose with a length of 20 μm, and the aspect ratio is less than 50, which leads to a decrease in the strength and bonding strength of the electrode and poor manufacturability; Comparative Example 2 has too little cellulose added, and is not manufacturable; Comparative Example 3 has too much cellulose added, and although it is manufacturable, the electrical properties are 3% higher than those of Example 1 (DCR), and the section shrinkage rate is less than 8%, making the electrode brittle and easy to break.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery characterized by comprising: The electrode includes a positive electrode and a negative electrode, at least one of the positive electrode and the negative electrode includes: a current collector, and an active layer loaded on the current collector, the active layer including fibers and an electrode active material, the fibers having an aspect ratio of not less than 50, the content of the fibers in the active layer being 1-2.5wt%.

2. The secondary battery according to claim 1, characterized by The content of F element in the active layer is less than 0.05%.

3. The secondary battery according to claim 1 or 2, characterized by The active layer does not contain a binder.

4. The secondary battery according to any one of claims 1 to 3, characterized by The length of the fibers is 30-200μm; The diameter of the fibers is 0.5-5μm.

5. The secondary battery according to any one of claims 1 to 4, characterized by The fibers include at least one of cellulose fibers, aramid fibers, carbon nanotubes, and carbon fibers.

6. The secondary battery according to any one of claims 1 to 5, characterized by The active layer includes 96-99wt% of the electrode active material, 1-2.5wt% of the fibers, 0-1.5wt% of a conductive agent, and optionally a dispersant.

7. The secondary battery according to claim 6, characterized by The content of the fibers in the active layer is 1.5-2wt%, the diameter of the fibers is 0.5-1.5μm, and the length of the fibers is 100-200μm.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The electrode active material includes at least one of graphite, silicon-carbon materials, and silicon negative electrode materials.

9. The secondary battery according to any one of claims 1 to 8, characterized by, At least one of the following conditions is met: The adhesive force of the electrode is not less than 10N / m; The tensile strength of the active layer is not less than 0.3MPa; The electrode has a cross-section shrinkage rate of 8-12%.

10. A pole piece characterized by, The electrode includes: a current collector, and an active layer loaded on the current collector, the active layer including fibers and an electrode active material, the fibers having an aspect ratio of not less than 50, the content of the fibers in the active layer being 1-2.5wt%.

11. The pole piece of claim 10, wherein At least one of the following conditions is met: The fibers are nanofibers; The length of the fibers is 30-200μm, and the diameter of the fibers is 0.5-1.5μm; The fibers include at least one of cellulose fibers, aramid fibers, carbon nanotubes, and carbon fibers; The active layer includes 96-99wt% of the electrode active material, 1-2.5wt% of the fibers, and 0-1.5wt% of a conductive agent; The content of the fibers in the active layer is 1.5-2wt%; The electrode active material includes at least one of graphite, silicon-carbon materials, and silicon negative electrode materials.

12. A method of making a pole piece, characterized by, The method includes: mixing the dispersed fibers and the electrode active material to form a slurry; extruding the slurry into a sheet to form an active layer precursor, and compounding the active layer precursor to a current collector to form an active layer, The fibers have an aspect ratio of not less than 50, and the content of the fibers in the active layer is 1-2.5wt%.

13. The method of claim 12, wherein, The fibers are provided by a fiber-containing raw material, and the fiber-containing raw material meets at least one of the following conditions: The viscosity is not more than 70Cp; The solid content of the fiber-containing raw material is not less than 10%.

14. The method according to claim 12 or 13, characterized in that, The method meets at least one of the following conditions: The solid content of the slurry is 70-80%; The dispersion treatment is performed by using a double-planet disperser; The extruding into a sheet is performed at room temperature, and the compounding to the current collector includes pressing the active layer precursor obtained by the extruding into a sheet on the current collector and drying, and the temperature of the drying is 50-70℃.

15. An electrical device, comprising: The power consuming device comprises the secondary battery as claimed in any one of claims 1 to 9, and the secondary battery is used to provide electric energy.

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