Electrode binder as well as preparation method and application thereof

Abstract

The invention provides an electrode binder and a preparation method and application thereof, the preparation method of the electrode binder comprises the following steps: infiltrating a binding material with a fiber network structure in a solution containing a carbon source and a lithium salt, filling the lithium salt in the fiber network structure, and depositing the carbon source on the surface of the binding material to obtain a semi-finished product material; and carrying out heat treatment on the semi-finished product material to obtain the electrode binder. The electrode binder provided by the invention has good ionic conductivity and high-temperature performance, and can improve the rate capability and cycle performance of an electrode.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to an electrode binder, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries, as an important energy storage device, have a performance that is closely linked to the properties of their electrode materials. The performance of these materials has a crucial impact on the overall performance of the battery. Currently, dry-process electrode preparation typically involves raw materials including an active material (positive or negative electrode), a conductive agent, a binder, and a current collector. Binders are typically polymers with excellent chemical stability and electrical insulation properties.

[0003] However, the inherent properties of binders also present some problems, limiting their further application in lithium-ion batteries. For example, the addition of binders can reduce the charge-discharge efficiency and initial efficiency of the electrode. The high impedance and poor high-temperature performance of some binders also limit their application in lithium-ion batteries. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a method for preparing an electrode binder.

[0005] In addition, the embodiments of the present application further provide an electrode binder prepared by the aforementioned method for preparing the electrode binder, a dry-process electrode sheet using the electrode binder and a method for preparing the same, and an electrochemical device using the dry-process electrode sheet.

[0006] In a first aspect, an embodiment of the present application provides a method for preparing an electrode binder, which comprises the following steps: impregnating a binder material having a fiber network structure in a solution containing a carbon source and a lithium salt, so that the lithium salt is filled in the fiber network structure, and the carbon source is deposited on the surface of the binder material to obtain a semi-finished material; and heat-treating the semi-finished material to obtain the electrode binder.

[0007] In some possible embodiments, the pore size of the fiber network structure is 20 μm to 50 μm; the particle size of the carbon source is 50 μm to 100 μm; and the particle size of the lithium salt is 10 μm to 20 μm.

[0008] In some possible embodiments, the mass ratio of the binding material to the carbon source is 1:(0.4-0.8); and / or the mass ratio of the binding material to the lithium salt is 1:(0.2-0.6).

[0009] In some possible embodiments, the bonding material includes at least one of polytetrafluoroethylene, polyvinylidene fluoride and sodium carboxymethyl cellulose; the carbon source includes at least one of carbon black, graphite, activated carbon, carbon fiber and carbon composite material; the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium difluoro(bis(oxalatophosphate)) and lithium difluorophosphate.

[0010] In some possible embodiments, the soaking time is 12 hours to 36 hours; and / or the soaking temperature is 25° C. to 80° C.

[0011] In some possible embodiments, the heat treatment temperature is 60° C. to 100° C.; and / or the heat treatment time is 3 h to 6 h.

[0012] In a second aspect, an embodiment of the present application also provides an electrode binder, which is prepared by the aforementioned electrode binder preparation method, and the electrode binder includes a binding material having a fiber network structure, a carbon coating layer located on the surface of the binding material, and a lithium salt located inside the fiber network structure of the binding material.

[0013] In a third aspect, an embodiment of the present application further provides a dry electrode, which includes a current collector and an electrode active membrane arranged on the surface of the current collector, wherein the electrode active membrane includes an active material, a conductive agent and a binder, and the binder includes the aforementioned electrode binder.

[0014] In a fourth aspect, an embodiment of the present application also provides a method for preparing a dry electrode, which comprises the following steps: mixing a binder, a conductive agent and an active material, grinding and hot pressing to obtain an electrode active film, wherein the binder includes the aforementioned electrode binder; and stacking the current collector and the electrode active film and hot pressing to obtain the dry electrode.

[0015] In a fifth aspect, an embodiment of the present application further provides an electrochemical device, which includes the aforementioned dry electrode.

[0016] Compared to the prior art, the preparation method of the electrode binder provided in the embodiment of the present application is to soak the binder material having a fiber network structure in a solution containing a carbon source and a lithium salt, and then combine it with a heat treatment, so that the lithium salt is filled inside the fiber network structure and a carbon coating layer is formed on the surface of the binder material. First, due to the formation of the carbon coating layer on the surface of the binder material, the conductivity of the binder material surface is improved, the conductivity of the entire electrode sheet is increased, and the effect of high temperature on the binder material is reduced, thereby improving the conductivity and high temperature performance of the dry electrode. The lithium salt in the binder can offset the consumption of some active lithium ions in the electrode, while reducing the resistance to lithium ion transmission and improving the ionic conductivity of the electrode binder. Secondly, because the lithium salt is uniformly filled in the interior of the binder material, after the prepared dry electrode is injected with the electrolyte, the lithium salt in the electrode binder will be dissolved, forming gaps in the dry electrode, thereby achieving the purpose of uniformly creating pores in the dry electrode sheet, shortening the lithium ion transmission path, improving the lithium ion conductivity, and enabling the dry electrode to absorb and accommodate the electrolyte, improving the wettability and liquid retention of the dry electrode sheet. Therefore, the electrode binder of the present application has good ionic conductivity and high-temperature performance. When used in dry-process electrodes, it can improve the uniformity of lithium ion distribution and the transmission rate of lithium ions in the dry-process electrodes, and reduce the consumption of active lithium, thereby reducing battery impedance, improving the electrochemical performance of the battery, and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a process flow chart of a method for preparing an electrode binder provided in one embodiment of the present application.

[0018] Figure 2 A schematic diagram of an electrode active membrane provided in one embodiment of the present application.

[0019] Figure 3 This is a process flow chart of a method for preparing a dry electrode provided in one embodiment of the present application.

[0020] Figure 4 This is a rate performance test chart of the soft-pack batteries prepared with dry-process electrodes in Examples 1-9 and Comparative Example 1 of the present application.

[0021] Figure 5 This is a test chart of the cycle performance of soft-pack batteries prepared with dry-process electrodes in Examples 1-9 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0023] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the implementation methods of this application and the features in the implementation methods can be combined with each other unless there is a conflict; many specific details are set forth in the following description to facilitate a full understanding of this application, and the implementation methods described are only part of the implementation methods of this application, not all of the implementation methods.

[0024] See also Figure 1 As shown, the embodiment of the present application provides a method for preparing an electrode binder, which specifically includes the following steps: In step S11 , the adhesive material having a fiber network structure is immersed in a solution containing a carbon source and a lithium salt, so that the lithium salt is filled in the fiber network structure and the carbon source is deposited on the surface of the adhesive material to obtain a semi-finished material.

[0025] Specifically, a binder material with a fiber network structure is selected. This can be obtained by fiberizing the binder material, such as by mechanically shearing (stirring, rolling, or stretching) or hot pressing the binder material to impart a fiber network structure. During the infiltration process, the lithium salt in the solution enters the fiber network structure of the binder material, and the carbon source adsorbs on the surface of the binder material. Liquid-phase infiltration improves the sufficiency and uniformity of contact between the carbon source and lithium salt and the binder material. Furthermore, combining the carbon source and lithium salt with the binder material in a one-step process facilitates a simplified process flow.

[0026] In some embodiments, the pores of the fiber network structure can be 20 μm to 50 μm, which is advantageous in that the pores allow small particles (less than 20 μm) to penetrate while preventing large particles (over 50 μm) from entering the fiber network structure. The pores of the fiber network structure can illustratively be 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any value within a range of values ​​consisting of any two of the above values. The pores of the fiber network structure can further be 30 μm to 40 μm.

[0027] In some embodiments, the binder material may include at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and sodium carboxymethyl cellulose (CMC). These binders have high bond strength and good flexibility, which helps improve the processability of the electrode binder. Furthermore, the binder material may be PTFE, which has excellent chemical stability and electrical insulation properties. PTFE also has low surface energy and easily forms a fiber network structure, which helps improve the fiberization efficiency of the binder material and the efficiency of electrode binder preparation.

[0028] In some embodiments, the preparation method of the adhesive material having a fiber network structure (i.e., fiberization of the adhesive material) can include one of mechanical shearing, emulsion spinning, hot press stretching, electrospinning, and melt extrusion. Furthermore, the preparation method can include mechanical shearing and hot press stretching.

[0029] Exemplarily, the mechanical shearing method is used to prepare a bonding material having a fiber network structure, which specifically includes the following steps: Pretreatment: The bonding material powder is pretreated (such as drying) to remove moisture and other impurities.

[0030] Shearing: Use high shear equipment (such as twin-screw extruder, high-speed mixer, etc.) to shear the adhesive material powder. During the shearing process, the adhesive material is gradually stretched into fibers to obtain an adhesive material with a fiber network structure.

[0031] In some embodiments, the carbon source may include at least one of carbon black, graphite, activated carbon, carbon fiber, and carbon composite materials. The above carbon sources have good electrical conductivity, which is beneficial to improving the conductivity of the electrode binder.

[0032] In some embodiments, the carbon source particles may have a size of 50 μm to 100 μm, allowing them to be adsorbed on the surface of the binder material without penetrating the fiber network. Exemplarily, the carbon source particles may have a size of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any value within a range of any two of these values. Furthermore, the carbon source particles may have a size of 80 μm to 100 μm.

[0033] In some embodiments, the mass ratio of the binder material to the carbon source can be 1:(0.4-0.8). This facilitates moderate deposition of the carbon source on the binder material's surface, preventing a reduction in the binder material's modification effect due to a low carbon source content, and preventing a reduction in the binder material's viscosity and the lithium ion transfer efficiency during battery cycling due to an excessive carbon source content. Exemplary mass ratios of the binder material to the carbon source can be 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, or any value within a range of any two of these values. Furthermore, the mass ratio of the binder material to the carbon source can be 1:(0.5-0.6).

[0034] In some embodiments, the lithium salt may include at least one of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluoro(oxalato)borate (LiDFOB), lithium difluoro(bis(oxalatophosphate)) (LiDFBP), and lithium difluorophosphate (LiPO2F2). The above lithium salts can be dissolved in the electrolyte and have good high-temperature performance.

[0035] In some embodiments, the particle size of the lithium salt may be 10 μm to 20 μm. A smaller particle size allows the lithium salt to penetrate into the fiber network structure. Exemplarily, the particle size of the lithium salt may be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any value within a range consisting of any two of the above values. Further, the particle size of the lithium salt may be 10 μm to 15 μm.

[0036] In some embodiments, the mass ratio of the binder material to the lithium salt can be 1:(0.2-0.6). This facilitates the incorporation of an appropriate amount of lithium salt into the fiber network structure of the binder material, preventing the modification effect of the binder material from being reduced due to too little lithium salt, nor the weakening of the bonding performance of the binder material or the reduction of its electronic conductivity due to too much lithium salt. Exemplary mass ratios of the binder material to the lithium salt can be 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, or any value within a range of any two of these values. The mass ratio of the binder material to the lithium salt can further be 1:(0.4-0.6).

[0037] In some embodiments, the solution further contains a solvent, which is conducive to dissolving the lithium salt and allowing the lithium salt to fully enter the fiber network structure of the adhesive material. The solvent may include at least one of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0038] In some embodiments, the mass ratio of the binding material to the solvent may be 1:10, which is conducive to complete infiltration of the binding material and sufficient combination of the binding material with the carbon source and the lithium salt.

[0039] In some embodiments, the immersion time can be 12 to 36 hours, which facilitates sufficient contact between the binder material, carbon source, and lithium salt, thereby further improving the deposition of the carbon source and the amount of lithium salt entering the binder material. Exemplary immersion times can be 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, or any value within a range consisting of any two of these values. Furthermore, the immersion time can be 24 to 36 hours.

[0040] In some embodiments, the infiltration temperature can be 25°C~80°C. The wide temperature range design is conducive to improving the universality of the process. It also shows that the mixing and contact of the adhesive material, carbon source and lithium salt can be achieved at room temperature of 25°C, which facilitates the operation.

[0041] Step S12: heat-treating the semi-finished material to obtain the electrode binder.

[0042] Specifically, the above-mentioned semi-finished material is taken out and heat-treated, so that the lithium salt entering the interior of the adhesive material is filled in the fiber network structure of the adhesive material in a solid form, and the carbon source deposited on the surface of the adhesive material forms a carbon coating layer to wrap the adhesive material, thereby obtaining an electrode adhesive, which includes a bonding material with a fiber network structure, a carbon coating layer located on the surface of the bonding material, and a lithium salt located inside the fiber network structure of the bonding material.

[0043] In some embodiments, the temperature of the heat treatment can be 60°C to 100°C, which can effectively remove the solvent remaining in the semi-finished material and retain the carbon source and lithium salt. At the same time, the lower heat treatment temperature will not damage the semi-finished material. The temperature of the heat treatment can illustratively be 60°C, 70°C, 80°C, 90°C, 100°C or any value within the numerical range composed of any two of the above values. The temperature of the heat treatment can further be 70°C to 90°C.

[0044] In some embodiments, the heat treatment time can be 3 to 6 hours, which is conducive to further removing the solvent and obtaining a dry electrode binder. The heat treatment time can be 3 hours, 4 hours, 5 hours, 6 hours, or any value within a numerical range consisting of any two of the above values. The heat treatment time can further be 3 to 4 hours.

[0045] In some embodiments, the heat treatment can be performed in a vacuum drying oven. Specifically, the removed semi-finished product is placed in a vacuum drying oven for drying. The vacuum lowers the pressure inside the vacuum drying oven, thereby reducing the boiling point of the solvent, making it more volatile and accelerating the drying process. Furthermore, the vacuum environment reduces the oxygen content in the vacuum drying oven, preventing oxidation or deterioration of the semi-finished product during the drying process.

[0046] In some embodiments, after removing the semi-finished material, the semi-finished material can be air-dried to remove some of the solvent before heat treatment. For semi-finished materials obtained through immersion treatment, which have a high solvent content, air-drying them first can improve drying efficiency and shorten vacuum drying time.

[0047] Compared with the prior art, the preparation method of the electrode binder provided in the embodiment of the present application has the following beneficial effects: 1. By filling lithium salt inside the fiber network structure of the binder material: so that the lithium salt is uniformly distributed inside the binder material, thereby reducing the resistance, improving the transmission efficiency of lithium ions, and improving the ionic conductivity of the electrode binder.

[0048] 2. By forming a carbon coating layer on the surface of the binder material: the carbon coating layer has good electronic conductivity, which can reduce the lithium ion transmission resistance and improve the electronic conductivity of the electrode binder; the carbon coating layer can also achieve passivation of the binder material, reduce the reaction of the binder material with lithium ions in the electrolyte and active material during the cycle process, and reduce the consumption of active lithium; at the same time, the carbon coating on the surface of the binder material reduces the influence of temperature on the binder material and improves the high-temperature performance of the electrode binder.

[0049] 3. By using infiltration and heat treatment, the carbon source and lithium salt are efficiently combined with the binder material, thereby achieving double modification of the binder material and improving the overall conductivity and high-temperature performance of the electrode binder. The preparation method is simple and efficient, which is conducive to large-scale production of the electrode binder and has excellent commercialization prospects.

[0050] The application also provides an electrode binder prepared by the above-mentioned preparation method of the electrode binder, which comprises a binder material with a fiber network structure, a carbon coating layer on the surface of the binder material, and a lithium salt inside the fiber network structure of the binder material.

[0051] Compared with the prior art, the electrode binder has good conductivity and high-temperature performance, which can effectively improve the charge-discharge efficiency, initial efficiency, cycle performance and thermal stability of the electrode.

[0052] The application also provides a dry electrode, which comprises a current collector and an electrode active film arranged on the surface of the current collector. As shown in Figure 2 The electrode active film 100 comprises an active material 110, a conductive agent 120 and a binder 130, and the binder 130 comprises the above-mentioned electrode binder.

[0053] Since the electrode binder has a carbon coating layer, it can reduce the reaction of the binder material with lithium ions, reduce the consumption of lithium ions, and improve the conductivity of the binder material surface, reduce the lithium ion transmission resistance in the electrode, and reduce the influence of high temperature on the binder material, thereby improving the conductivity and high-temperature performance of the dry electrode.

[0054] The lithium salt in the electrode binder is evenly filled in the fiber network structure of the binder material, which is beneficial to improving the ionic conductivity of the dry electrode and reducing the electrode impedance. At the same time, it improves the uniformity of the lithium ion distribution in the dry electrode, reduces the situation where the lithium salt is directly added to the slurry during the electrode preparation process, resulting in uneven distribution of lithium salt inside the electrode sheet, further improves the conductivity of the dry electrode, thereby improving the electrochemical performance of the dry electrode and extending the service life of the dry electrode. In addition, after the dry electrode is injected with electrolyte, the lithium salt in the electrode binder will be dissolved, forming gaps in the dry electrode, thereby achieving the purpose of uniformly creating pores in the dry electrode sheet, allowing the dry electrode to absorb and accommodate electrolyte, improving the wettability and liquid retention of the dry electrode sheet, and at the same time reducing the environmental pollution problems caused by the dissolution or swelling of the binder material itself after injection.

[0055] See also Figure 3 As shown, the embodiment of the present application also provides a method for preparing a dry electrode, which specifically includes the following steps: Step S21 : mixing a binder, a conductive agent and an active material, grinding and hot pressing to obtain an electrode active film, wherein the binder includes the aforementioned electrode binder.

[0056] Specifically, the binder, the conductive agent and the active material are uniformly dispersed by high-speed air flow shearing, and the mixing time is 40 minutes to 100 minutes to obtain a mixture, wherein the binder includes the aforementioned electrode binder; the mixture is then ground until the particle size D50 is less than 10 μm; the ground mixture is hot rolled to obtain a self-supporting electrode active membrane that can maintain the membrane structure integrity and functionality without relying on external support.

[0057] In some embodiments, based on 100% of the total mass of the mixture, the content of the binder is 1.5% to 7.5%, the content of the conductive agent is 1.5% to 7.5%, and the content of the active material is 85% to 97%.

[0058] In some embodiments, the conductive agent may include at least one of carbon nanotubes, conductive carbon black, graphene, and the like.

[0059] In some embodiments, the active material may include a positive electrode material and a negative electrode material. Further, the positive electrode material may include at least one of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM) and nickel cobalt aluminum ternary material (NCA); the negative electrode material may include at least one of graphite material, silicon-based material, lithium titanate, metal oxide, alloy material and sulfide.

[0060] In some embodiments, the hot pressing temperature can be 90°C~250°C, which can effectively activate the bonding properties of the binder, so that the binder softens during the hot pressing process and is evenly distributed between the active material and the conductive agent, while avoiding excessively high temperatures that may cause material decomposition or performance degradation, thereby enhancing the mechanical strength and structural stability of the electrode active membrane.

[0061] In some embodiments, the number of hot pressing cycles may be 2 to 8 times. Multiple hot pressing cycles can gradually eliminate pores and defects in the electrode active membrane, improve the density and uniformity of the electrode active membrane, and thus improve the electrochemical performance of the electrode active membrane.

[0062] In some embodiments, the thickness of the electrode active membrane can be 90 μm to 150 μm, which is beneficial for the electrode active membrane to have both good energy density and rate performance. The thickness of the electrode active membrane can illustratively be 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, or any value within a numerical range consisting of any two of the above values. The thickness of the electrode active membrane can further be 120 μm to 150 μm.

[0063] Step S22: stacking the current collector and the electrode active membrane and then hot pressing them to obtain a dry electrode.

[0064] Specifically, two electrode active membranes are placed on the upper and lower surfaces of the current collector respectively for stacking, and hot pressing is performed using a multi-roll calendering process to obtain a dry electrode.

[0065] In some embodiments, the current collector may include at least one of copper foil, nickel foil, aluminum foil, silver foil, and gold foil. Furthermore, the current collector may be copper foil coated with a carbon layer, which is beneficial for further improving the conductivity of the dry electrode.

[0066] It is understood that the preparation methods of dry electrodes include but are not limited to the above methods. Preparation methods may also include powder tableting, spray drying, electrostatic spraying, and self-assembly, and the appropriate preparation process can be selected according to the specific materials and application requirements.

[0067] The present application also provides an electrochemical device (e.g., a lithium-ion battery) comprising the aforementioned dry-process electrode. The electrochemical device fabricated using the aforementioned dry-process electrode can reduce active lithium loss, reduce internal resistance, increase lithium ion transfer rate, and improve thermal stability, thereby exhibiting advantages such as high initial efficiency, high rate capability, and good high-temperature performance.

[0068] The electrode binder and its preparation method and application are further described below through specific examples.

[0069] Example 1 Preparation of electrode binder: Step S11: Immerse the PTFE, a binder material having a fiber network structure, in a solution containing a carbon source, conductive carbon black SP, and a lithium salt, LiTFSI, at room temperature for 12 hours. This allows the LiTFSI to fill the fiber network structure and deposit the SP on the surface of the PTFE, thereby obtaining a semi-finished material. The pore size of the fiber network structure is 20 μm to 50 μm; the particle size of the carbon source is 50 μm to 100 μm; the particle size of the lithium salt is 10 μm to 20 μm; the mass ratio of PTFE to conductive carbon SP is 1:0.5, and the mass ratio of PTFE to LiTFSI is 1:0.5. The preparation process of the PTFE binder material having a fiber network structure includes drying the PTFE powder and then shearing the PTFE powder using a high-speed mixer at 1000 rpm for 3 hours. During the shearing process, the PTFE is gradually elongated into fibers, thereby obtaining a binder material having a fiber network structure.

[0070] Step S12: After drying the semi-finished material, place it in a vacuum drying oven and heat treat it at 80° C. for 3 hours to obtain an electrode binder.

[0071] The electrode binder includes PTFE with a fiber network structure, a carbon coating layer located on the surface of the PTFE, and LiTFSI located inside the fiber network structure of the PTFE.

[0072] Preparation of dry electrode: Step S21: The binder, conductive agent SP, and active material graphite are evenly dispersed by high-speed air flow shearing, mixed for 50 minutes to obtain a mixture, and the mixture is ground to a particle size D50 of less than 10 μm; then hot pressed three times at 100° C. to obtain an electrode active membrane, wherein the binder is the aforementioned electrode binder, and based on the total mass of the mixture as 100%, the content of the binder is 5%, the content of SP is 5%, and the content of the active material graphite is 90%.

[0073] Step S22 , stacking the current collector carbon-coated copper foil and the electrode active membrane and then hot pressing them to obtain a dry-process electrode.

[0074] The dry-process electrode comprises a current collector carbon-coated copper foil and an electrode active membrane arranged on the surface of the current collector, wherein the electrode active membrane comprises graphite, SP and the aforementioned electrode binder.

[0075] Example 2 The difference between Example 2 and Example 1 is that in step S11, the lithium salt is LiFSI. The preparation methods of the remaining electrode binders and the preparation methods of the dry-process electrodes are basically the same as those in Example 1 and are not described in detail here.

[0076] Example 3 The difference between Example 3 and Example 1 is that in step S11, the carbon source is carbon fiber. The preparation method of the remaining electrode binder and the preparation method of the dry electrode are basically the same as those in Example 1 and are not described in detail here.

[0077] Example 4 The difference between Example 4 and Example 1 is that in step S11, the mass ratio of PTFE to conductive carbon SP is 1:0.4. The preparation methods of the remaining electrode binders and the dry electrode are basically the same as those in Example 1 and are not described in detail here.

[0078] Example 5 The difference between Example 5 and Example 1 is that in step S11, the mass ratio of PTFE to conductive carbon SP is 1:0.8. The preparation method of the remaining electrode binder and the preparation method of the dry electrode are basically the same as those in Example 1 and are not described in detail here.

[0079] Example 6 The difference between Example 6 and Example 1 is that in step S11, the mass ratio of PTFE to LiTFSI is 1:0.2. The preparation methods of the remaining electrode binders and the preparation methods of the dry-process electrodes are basically the same as those in Example 1 and are not described in detail here.

[0080] Example 7 The difference between Example 7 and Example 1 is that in step S11, the mass ratio of PTFE to LiTFSI is 1:0.6. The preparation methods of the remaining electrode binders and the preparation methods of the dry electrode are basically the same as those in Example 1 and are not described in detail here.

[0081] Example 8 The difference between Example 8 and Example 1 is that in step S11, the mass ratio of PTFE to conductive carbon SP is 1:0.2, and the mass ratio of PTFE to LiTFSI is 1:0.1. The preparation methods of the remaining electrode binders and the preparation methods of the dry-process electrodes are basically the same as those in Example 1 and are not described in detail here.

[0082] Example 9 The difference between Example 9 and Example 1 is that in step S11, the mass ratio of PTFE to conductive carbon SP is 1:1, and the mass ratio of PTFE to LiTFSI is 1:0.8. The preparation methods of the remaining electrode binders and the preparation methods of the dry-process electrodes are basically the same as those in Example 1 and are not described in detail here.

[0083] Comparative Example 1 In Comparative Example 1, unmodified PTFE was used as the electrode binder. The preparation method of the remaining dry-process electrodes is basically the same as that of Example 1 and will not be described in detail here.

[0084] The dry-process electrodes obtained in Examples 1-7 and Comparative Example 1 were prepared into electrochemical devices, and the following performance tests were performed on the electrode active membranes, dry-process electrodes, and electrochemical devices.

[0085] (1) Electrode active film thickness test: Use a thickness gauge to test the thickness of the electrode active film. Take 10 points of thickness measurement and calculate the thickness variance. The variance is the average of the square of the difference between the thickness measurement value of each point and the average thickness of the 10 points.

[0086] (2) Electrode active membrane resistance test: Use a multi-probe membrane resistance tester to prepare a 4cm×25cm sample of the electrode active membrane to be tested. Dry the sample at 85℃ under vacuum for more than 4 hours. The test pressure is 0.2~0.4Mpa, and the electrode active membrane resistance is tested.

[0087] (3) The dry-process electrodes are cut, punched, and dried in sequence, and assembled into symmetrical batteries and soft-pack batteries. The positive electrode uses an ordinary NCM623 positive electrode sheet, and the negative electrode is the dry-process electrode prepared above. The electrolyte is injected. After the injection is completed, it needs to be placed in a 45°C oven for 48 hours to ensure that the electrolyte is infiltrated into the electrode sheet.

[0088] Perform electrochemical impedance spectroscopy (EIS) test on the symmetrical battery: Use an electrochemical impedance spectrometer to perform EIS test on the assembled symmetrical battery. Place the sample in a constant temperature box at 25°C for testing to test the electrochemical impedance of the symmetrical battery.

[0089] Perform the first-efficiency performance test on the soft-pack battery: At 25°C, charge the soft-pack battery to 30% SOC at 0.1C, charge it to 50% SOC at 0.25C, fully charge it at 0.33C, and then discharge it at 0.33C to test the charge and discharge capacity of the battery and calculate the first-efficiency of the battery; Rate performance test of soft-pack batteries: At 25°C, a battery with a state of charge (SOC) of 0% (2.0V) was charged at 0.33C to 4.4V, then discharged at 1C to 2.5V. The discharge capacity at this point was recorded as C1. For the same battery, under the same test conditions, a battery with a state of charge (SOC) of 0% (2.0V) was charged at 0.33C to 100% (4.4V), then discharged at 2C to 2.5V. The discharge capacity at this point was recorded as C2. The discharge rate performance test indicator is capacity retention = C2 / C1 × 100%.

[0090] Cycling performance test of soft-pack batteries: In a 45°C constant temperature box, the soft-pack batteries were subjected to 1C / 1C charge and discharge cycles. The cycle test range was 3-97% SOC and the voltage range was 2.75-4.3V. Table 1 shows the thickness and resistivity test results of the electrode active film, and Table 2 shows the performance test results of the electrochemical device.

[0091] The above results show: As can be seen from Table 1, the thickness of the electrode active membranes of Examples 1-9 and Comparative Example 1 is relatively uniform. However, compared with the resistivity of the electrode active membrane in Comparative Example 1, which is as high as 2.4 mΩ, the resistivity of the electrode active membranes in Examples 1-9 is significantly reduced. Among them, the resistivity of the electrode active membrane in Example 1 is only 1.5 mΩ. In Example 3, the carbon source in the electrode active membrane is changed to carbon fiber, and the resistivity of the electrode active membrane is further reduced to only 1.42 mΩ.

[0092] Table 2 Combination Figure 4 and Figure 5 It can be seen that compared with Comparative Example 1, the ionic resistance (Rion) of the symmetrical battery prepared in Example 1 is reduced by 13.47%, indicating that a carbon coating layer is formed on the surface of the binding material PTFE, and lithium salt is added to the fiber network structure of the binding material PTFE for modification, thereby obtaining an electrode binder with good conductivity and high-temperature performance. When prepared as a dry electrode and applied to a battery, it can achieve the purpose of forming pores in the dry electrode during the battery preparation process, increase the wettability of the electrode, improve the liquid retention capacity of the electrode, shorten the ion transmission path, improve the ionic conductivity, and reduce the impedance. Therefore, the rate performance and high-temperature cycle performance of the soft-pack batteries prepared in Examples 1-9 are better than those in Comparative Example 1.

[0093] Compared with Example 1, after changing the type of lithium salt in Example 2, the performance is slightly worse than that of Example 1 because the conductivity of LiFSI is not as good as LiTFSI. However, compared with Comparative Example 1 prepared with LiTFSI with better conductivity, the performance is still improved.

[0094] Compared with Example 1, the conductive agent in Example 3 is changed to carbon fiber, and the conductivity of the electrode binder is further improved, thereby further reducing the resistance of the electrode active membrane and the ionic resistance of the prepared symmetrical battery.

[0095] In addition, on the basis of Embodiments 8-9, Embodiments 1, 4 and 5 further control the mass ratio of the binding material to the carbon source within the preset range 1:(0.4-0.8), which can further realize the synchronous improvement of the conductivity and high-temperature performance of the electrode binder, thereby further improving the high-temperature cycle performance and rate performance of the soft package battery. On the basis of Embodiments 8-9, Embodiments 1, 6 and 7 further control the mass ratio of the binding material to the lithium source within the preset range 1:(0.2-0.6), which can make the lithium salt further uniformly filled in the fiber network structure, improve the ion conductivity of the electrode binder, reduce the resistance, thereby further improving the high-temperature cycle performance of the soft package battery and prolonging the service life of the soft package battery.

[0096] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered to be within the protection scope of the present application.

Claims

1. A method for preparing an electrode binder, characterized in that: include: Immersing a bonding material having a fiber network structure in a solution containing a carbon source and a lithium salt, so that the lithium salt is filled in the fiber network structure and the carbon source is deposited on the surface of the bonding material, to obtain a semi-finished material; as well as The semi-finished material is heat-treated to obtain the electrode binder.

2. The method for preparing an electrode binder according to claim 1, wherein: The pore size of the fiber network structure is 20 μm to 50 μm; The particle size of the carbon source is 50 μm to 100 μm; The particle size of the lithium salt is 10 μm to 20 μm.

3. The method for preparing an electrode binder according to claim 1, wherein: The mass ratio of the binding material to the carbon source is 1:(0.4-0.8); and / or The mass ratio of the bonding material to the lithium salt is 1:(0.2-0.6).

4. The method for preparing an electrode binder according to claim 1, wherein: The bonding material includes at least one of polytetrafluoroethylene, polyvinylidene fluoride and sodium carboxymethyl cellulose; The carbon source includes at least one of carbon black, graphite, activated carbon, carbon fiber and carbon composite material; The lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium difluoro(bis(oxalatophosphate)), and lithium difluorophosphate.

5. The method for preparing an electrode binder according to claim 1, wherein: The infiltration time is 12h~36h; and / or The soaking temperature is 25°C to 80°C.

6. The method for preparing an electrode binder according to claim 1, wherein: The heat treatment temperature is 60°C to 100°C; and / or The heat treatment time is 3h~6h.

7. An electrode binder, characterized in that The electrode binder is prepared by the preparation method of the electrode binder according to any one of claims 1 to 6, and the electrode binder includes a binding material having a fiber network structure, a carbon coating layer located on the surface of the binding material, and a lithium salt located inside the fiber network structure of the binding material.

8. A method for preparing a dry electrode, characterized in that: include: mixing a binder, a conductive agent and an active material, grinding and hot pressing to obtain an electrode active film, wherein the binder comprises the electrode binder according to claim 7; as well as The current collector and the electrode active membrane are stacked and then hot-pressed to obtain the dry-process electrode.

9. A dry electrode, characterized in that: The dry electrode includes a current collector and an electrode active membrane disposed on the surface of the current collector. The electrode active membrane includes an active material, a conductive agent, and a binder. The binder includes the electrode binder according to claim 7.

10. An electrochemical device, characterized in that The electrochemical device comprises the dry electrode according to claim 9.

Images