Method for improving stripping force of pole piece through morphology regulation and control, carbon-coated current collector, positive pole piece and battery

Abstract

The invention discloses a method for improving stripping force of a pole piece through morphology regulation and control, a carbon-coated current collector, a positive pole piece and a battery, and the method comprises the following steps: S1, preparing an initial carbon-coated current collector, namely coating a current collector with carbon-coated slurry, and drying to prepare the current collector with a carbon-coated layer; and S2, putting the initial carbon-coated current collector into a selenylation solution containing Ni < 2 + > ions and Fe < 2 + > ions, and carrying out heating treatment to obtain the morphology-controlled carbon-coated current collector. By adopting a surface topography regulation and control technology, the bonding strength between the carbon-coated current collector and the positive electrode active material is improved, so that the cycle performance of the lithium battery is improved, and the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for improving the peeling force of a pole piece by morphology control, a carbon-coated current collector, a positive pole piece and a battery. Background Art

[0002] Lithium-ion batteries (LIBs), due to their excellent performance, have found widespread application in consumer electronics, transportation, power tools, and energy storage systems. In lithium battery manufacturing, aluminum foil current collectors serve as a crucial carrier for the positive electrode material, forming the electrode structure through compounding with the active material. To improve battery rate performance, the industry currently widely utilizes carbon-coated aluminum foil current collector technology. This technology significantly enhances the current collector's conductivity and interfacial stability by coating the aluminum foil surface with a conductive carbon layer.

[0003] However, in practical applications, insufficient adhesion between the carbon coating and the aluminum foil substrate leads to two key problems: first, coating peeling is prone to occur during the coating process of the positive electrode active material, affecting the integrity of the electrode structure; second, interfacial stratification during cycling exacerbates the increase in contact resistance, leading to accelerated battery capacity decay. To address the above technical bottlenecks, the development of new carbon-coated aluminum foil current collectors with high interfacial bonding strength has become a key research direction for improving the cycle life of lithium batteries. By optimizing the coating formulation and surface treatment process, and enhancing the mechanical interlocking effect and chemical bonding between the carbon layer and the aluminum foil, it is expected to achieve a synergistic improvement in electrode structural stability and battery cycle life. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the peeling force of a pole piece by morphology control, a carbon-coated current collector, a positive pole piece and a battery, so as to solve the above problems.

[0005] To achieve the above object, the technical solution provided by the present invention is:

[0006] A first aspect of the present application provides a method for improving the peeling force of an electrode by morphology control, comprising the following steps:

[0007] S1: preparing an initial carbon-coated current collector, wherein the initial carbon-coated current collector is prepared by coating a carbon-coated slurry on the current collector and drying the slurry to form a current collector having a carbon-coated layer;

[0008] S2: Place the initial carbon-coated current collector into a 2+ ions, Fe 2+ The carbon-coated current collector with controlled morphology is obtained by heat treatment in a selenized solution of ions.

[0009] To optimize the above technical solutions, specific measures taken also include:

[0010] The thickness of the carbon coating layer is 0.4-0.8 μm.

[0011] The carbon-coated slurry is formed by mixing a carbon-coated conductive material, a wetting agent, and a binder; the carbon-coated conductive material is selected from at least one of carbon powder, graphite powder, carbon nanofiber, conductive carbon black, and carbon nanotube.

[0012] Furthermore, the carbon-coated conductive material is carbon powder and graphite powder, and the ratio of carbon powder to graphite powder is 7-10:1-3.

[0013] Furthermore, the Ni 2+ ions, Fe 2+ The heat treatment is carried out in the selenide solution of the ions by heating in an oil bath at a heating temperature of 85 to 95° C. and a treatment time of 5 to 7 hours.

[0014] Furthermore, the Ni 2+ ions, Fe 2+ In the selenide solution of ions, Ni 2+ The ion content is 0.3~0.5mM / ml, Fe 2+ The content of ions is 0.3~0.5mM / ml, Se 4+ The ion content is 0.6-1 mM / ml, and the solvent is anhydrous ethanol or isopropanol.

[0015] As preferably, the Ni 2+ ions, Fe 2+ The selenized solution of ions also contains anhydrous lithium chloride, the content of anhydrous lithium chloride is 0.03~0.06mM / ml

[0016] The second aspect of the present application provides a carbon-coated current collector, which is a morphology-controlled carbon-coated current collector prepared by the above method.

[0017] The third aspect of the present application provides a positive electrode sheet comprising the above-mentioned carbon-coated current collector.

[0018] A fourth aspect of the present application provides a battery comprising the above-mentioned positive electrode sheet.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention has developed a carbon-coated current collector with high adhesion properties. By adopting surface morphology control technology, the bonding strength between the carbon-coated current collector and the positive electrode active material is improved, thereby improving the cycle performance and service life of the lithium battery:

[0021] By manipulating the surface morphology of the carbon-coated current collector, increasing the coupling sites with the active material, and improving the surface roughness of the material, this design can strengthen the mechanical anchoring effect between the active material and the current collector and reduce the interfacial contact impedance.

[0022] Add transition metal element Ni into selenide solution by oil bath heating method 2+ ions and Fe 2+ ions, inducing the growth of a porous ultra-thin nanosheet structure on the surface of the material, which significantly improves the surface roughness of the carbon-coated current collector and greatly increases the binding sites with the active material, thereby effectively enhancing the peeling strength between the two. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : Morphology of ultrathin nanosheets on the carbon-coated current collector of the present invention. DETAILED DESCRIPTION

[0024] The above contents of the present invention are further described in detail below in the form of specific implementation methods, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments. All technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0025] The experimental methods used in the following examples are conventional methods unless otherwise specified, and the reagents, methods and equipment used are conventional reagents, methods and equipment in the art unless otherwise specified.

[0026] For the sake of simplicity, this document only specifically discloses some numerical values ​​and optional ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range. Similarly, any upper limit can be combined with any other upper limit to form an unspecified range; the optional items in the optional range can also be combined arbitrarily.

[0027] The present invention provides a method for improving the peeling force of a pole piece by morphology control, comprising the following steps:

[0028] S1: preparing an initial carbon-coated current collector, wherein the initial carbon-coated current collector is formed by coating a carbon-coated slurry on the current collector and drying the slurry to form a current collector having a carbon-coated layer;

[0029] S2: Place the initial carbon-coated current collector into a 2+ ions, Fe 2+ The carbon-coated current collector with controlled morphology is obtained by heat treatment in a selenized solution of ions.

[0030] The thickness of the carbon coating layer is 0.4 to 0.8 μm.

[0031] The carbon-coated slurry is formed by mixing a carbon-coated conductive material, a wetting agent and a binder; the carbon-coated conductive material is selected from at least one of carbon powder, graphite powder, carbon nanofiber, conductive carbon black and carbon nanotube.

[0032] Preferably, the carbon-coated conductive material is carbon powder and graphite powder, and the ratio of carbon powder to graphite powder is 7-10:1-3.

[0033] The preparation process of the initial carbon-coated current collector is exemplified as follows:

[0034] The binder is mixed and diluted with water; half of the carbon-coated conductive material is added and dispersed at a high speed of 2000-2600 rpm / min for 25-35 minutes; the other half of the carbon-coated conductive material is added and dispersed at a high speed of 2000-2600 rpm / min for 50-70 minutes; water is added to dilute and dispersed at a high speed of 2000-2600 rpm / min for 25-35 minutes; a pH regulator is added to adjust the pH to 5-7, which is weakly acidic; a wetting agent is added and stirred at a low speed of 10-15 rpm / min for 30-45 minutes; the material is discharged and homogenized; the slurry is coated on a current collector; and it is dried to obtain an initial carbon-coated current collector.

[0035] Add Ni 2+ ions, Fe 2+ The heat treatment is carried out in the selenide solution of the ions by heating in an oil bath at a heating temperature of 85 to 95° C. and a treatment time of 5 to 7 hours.

[0036] In some embodiments, Ni 2+ ions, Fe 2+ In the selenide solution of ions, Ni 2+ The ion content is 0.3~0.5mM / ml, Fe 2+ The content of ions is 0.3~0.5mM / ml, Se 4+ The ion content is 0.6-1 mM / ml, and the solvent is anhydrous ethanol or isopropanol.

[0037] Contains Ni 2+ ions, Fe 2+ The ion selenide solution also contains anhydrous lithium chloride, and the content of anhydrous lithium chloride is 0.03-0.06 mM / ml.

[0038] The present invention also provides a carbon-coated current collector, which is a morphology-controlled carbon-coated current collector prepared by the above method.

[0039] The present invention increases the roughness of the carbon coating surface, increases the coupling points between the positive electrode active material and the carbon-coated aluminum foil current collector, and increases the contact area and embedding degree with the positive electrode active material during rolling, thereby improving the peeling force between the carbon coating layer and the positive electrode active material.

[0040] The surface roughness of the carbon coating layer refers to the unevenness and roughness of the carbon coating surface. It has an important impact on the adhesion and performance of the carbon coated aluminum foil. The surface roughness of the carbon coating layer will affect the adhesion, that is, the higher the surface roughness of the carbon coating layer, the stronger the adhesion, because the rough surface provides more mechanical locking points, which enhances the adhesion between the carbon coating layer and the aluminum foil.

[0041] The experimental method for morphology control of the present invention is oil bath heating method. Most carbon-coated current collectors are water-based coatings, which themselves do not have any water resistance. Therefore, the present invention configures a non-aqueous oil-based solvent solution.

[0042] The morphology control of the present invention is to grow porous ultra-thin nanosheet morphology on the surface of the carbon-coated current collector. During the material growth, the Ni-Se mixed solution will grow irregular nanosheet morphology on the substrate at a certain temperature and time. 2+ Doping with elements can enrich the morphology, increase the number of nanosheets, and increase the density of nanosheets. It is worth noting that Fe 3+ This function is not available.

[0043] Fe 2+ ions and Ni 2+ Ions also have a certain synergistic effect, because Fe 2+ ions and Ni 2+ The different ionic radii of the ions lead to lattice distortion during co-deposition, forming a local stress field, inhibiting the isotropic growth of the material, promoting the formation of a two-dimensional layered structure, and inducing the generation of a porous structure. The two ions form different selenide nuclei in the solution, and the difference in their interfacial energy prompts the nanosheets to grow in a non-coherent manner, forming a porous cross-linked network and increasing the specific surface area.

[0044] Furthermore, by adding anhydrous lithium chloride (LiCl), LiCl, as a precipitation plasticizer, can effectively stabilize the morphological growth, so that the secondary growth morphology is more closely integrated with the carbon-coated current collector substrate.

[0045] The present invention also provides a positive electrode sheet comprising the above-mentioned carbon-coated current collector.

[0046] The present invention also provides a battery comprising the above-mentioned positive electrode sheet.

[0047] The technical solution of the present invention is further described in detail below with reference to specific embodiments:

[0048] Experimental preparation and experimental materials:

[0049] Selenium dioxide (SeO2), purchased from Sinopharm Group, AR (Shanghai trial), ≥99.0% 50g, material code 80113915; nickel nitrate hexahydrate (Ni(NO3)2·6H2O), purchased from Sinopharm Group AR (Shanghai trial), ≥98.0% 500g, material code 10014360; ferrous sulfate heptahydrate (FeSO4·7H2O), purchased from Sinopharm Group AR (Shanghai trial), 99.0~101.0% 100g, material code 10012116; anhydrous lithium chloride (LiCl), 99% (Wokai) 100g, material code XW01744741807.

[0050] Example 1

[0051] (1) Preparation of initial carbon-coated current collector:

[0052] Mix deionized water with PAA to reduce the solid content of the binder;

[0053] Add half of the first conductive agent and half of the second conductive agent, and disperse at a high speed of 2300 rpm / min in a 200L Double Star stirring tank for 30 minutes;

[0054] Add the other half of the first conductive agent and the other half of the second conductive agent, and disperse at a high speed of 2300 rpm / min in a 200L Double Star stirring tank for 60 minutes;

[0055] Add appropriate amount of deionized water to reduce the slurry concentration, and disperse at high speed of 2300 rpm / min in a 200L Double Star stirring tank for 30 minutes;

[0056] Add pH adjuster to adjust pH to 6.

[0057] Add wetting agent, stir at low speed of 12 rpm / min in a 200L Double Star stirring tank for 40 minutes, and then discharge;

[0058] The slurry was homogenized twice in a homogenizer at a pressure of 300 bar;

[0059] The slurry is evenly coated on an aluminum functional current collector and dried to obtain a conventional carbon-coated current collector sample.

[0060] The first conductive agent is carbon powder, the second conductive agent is graphite powder, and the ratio of the two is; PAA is selected as the carbon coating slurry binder, the thickness of the single-sided carbon coating layer is selected to be 0.5μm, the wetting agent accounts for 10%, and the wetting agent is modified polyether siloxane.

[0061] (2) Preparation of selenization solution:

[0062] Prepare selenium dioxide solution by taking 80 mM selenium dioxide powder and dissolving it in 50 ml of anhydrous ethanol solution. Stir magnetically at 600 rpm for 15 minutes until the material is completely dissolved.

[0063] Prepare transition metal solution: dissolve 40 mM nickel nitrate hexahydrate in 25 mL of anhydrous ethanol solution, stir magnetically at 600 rpm for 10 min until the material is completely dissolved; dissolve 40 mM ferrous sulfate heptahydrate in 25 mL of anhydrous ethanol solution, stir magnetically at 600 rpm for 10 min until the material is completely dissolved; mix the two solutions, and disperse them ultrasonically at a frequency of 2000 Hz for 10 min;

[0064] After mixing the transition metal solution and selenium dioxide solution, stir them magnetically at 600 rpm for 20 minutes to ensure complete mixing of the materials.

[0065] 5 mM LiCl was dissolved in 10 mL of anhydrous ethanol, and the solution was transferred to the mixed solution after magnetic stirring at 600 r / min for 30 minutes. After ultrasonic dispersion at a frequency of 2000 Hz for 15 minutes, the prepared selenide solution was obtained.

[0066] (3) Oil bath surface morphology control:

[0067] Place the carbon-coated current collector aluminum foil at the bottom of a beaker, transfer the selenide solution into the beaker, seal the beaker with a sealer and a heat-resistant PE bag, transfer the beaker to a container filled with silicone oil, heat in an oven at 90°C for 6 hours, and then remove the sample after cooling.

[0068] After taking out the sample, rinse it with anhydrous ethanol and transfer it to a vacuum drying oven at 50°C to dry overnight. The sample has completed morphological reconstruction. Scanning the sample surface with a scanning electron microscope or an atomic force microscope reveals dense ultrathin nanosheet morphology.

[0069] (4) Preparation of positive electrode sheet:

[0070] The positive electrode slurry was prepared with PVDF: lithium iron phosphate: carbon black = 2:97:1; the positive electrode slurry was coated on the carbon-coated aluminum foil prepared by the above method and baked at 120℃ for 20 minutes; the electrode was coated with 2.35g / cm 2 The positive electrode active material and the carbon-coated layer are pressed together by roller pressing with a compaction density of 1000 nm. The electrode sheet is cut into 12*2 cm pieces and placed in a vacuum drying oven for later use.

[0071] Preparation of lithium batteries:

[0072] Preparation of the positive electrode sheet: The positive electrode sheet is prepared using the above steps; Preparation of the negative electrode sheet: Using copper foil as the negative electrode current collector, silicon as the negative electrode active material, and carbon black as the conductive agent, a negative electrode active material layer is formed on the surface of the negative electrode current collector to prepare the negative electrode sheet.

[0073] Preparation of electrolyte: Propylene carbonate, ethylene carbonate, and ethyl methyl carbonate were mixed thoroughly in a mass ratio of 1:1:1 to obtain a carbonate solvent. LiPF6 was added to the carbonate solvent to prepare 1 mol·L -1 LiPF6 carbonate solution is used as the electrolyte of lithium-ion battery.

[0074] Assembly of lithium-ion batteries: The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order to prepare a bare cell; the bare cell is placed in the outer packaging shell of the lithium battery, and after drying, the electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0075] Test the electrode peeling force and lithium battery cycle performance of the samples.

[0076] Comparative Example 1

[0077] Compared with Example 1, the selenide solution of this comparative example is replaced by "taking 40 mM ferrous sulfate heptahydrate, dissolving it in 25 mL of anhydrous ethanol solution, stirring it with a magnetic stirrer at 600 r / min for 10 min until the material is completely dissolved" with "taking 25 mL of anhydrous ethanol solution". The rest is the same as Example 1, i.e., no Fe is added. 2+ ion.

[0078] Comparative Example 2

[0079] In the selenide solution of this comparative example, compared with Example 1, the following sequence is replaced by “take 40 mM nickel nitrate hexahydrate, dissolve it in 25 mL of anhydrous ethanol solution, stir it with magnetic stirring at 600 r / min for 10 min, and wait until the material is completely dissolved”. The rest is the same as Example 1, i.e., no Ni is added. 2+ ion.

[0080] Comparative Example 3

[0081] Compared with Example 1, the selenium solution in this comparative example is the same as that in Example 1, except that “5 mM LiCl is dissolved in 10 mL of anhydrous ethanol, magnetically stirred at 600 r / min for 30 min, and then the solution is transferred to the mixed solution” is replaced by “10 mL of anhydrous ethanol solution is taken and transferred to the mixed solution”.

[0082] Comparative Example 4

[0083] The thickness of the carbon coating layer on the single side of the comparative example is 0.2 μm, and the other aspects are the same as those in Example 1.

[0084] Comparative Example 5

[0085] This comparative example uses a carbon-coated current collector without morphology control as a comparison, and adopts the same initial carbon-coated current collector as step (1) of Example 1.

[0086] Test method:

[0087] Pole peeling force test:

[0088] The prepared positive electrode sheet was attached to the test board with 2 cm 3M double-sided tape, the active material on the positive electrode sheet was separated from the carbon coating layer, and the tape was attached to the carbon-coated aluminum foil, and the 180° electrode peeling force was tested on a tensile testing machine.

[0089] Lithium battery cycle performance test:

[0090] The battery was tested at room temperature (25°C). The button-type symmetrical battery was charged at constant current and constant voltage to 3-4.5V at rates of 0.2C, 0.3C, 0.5C, 1C, 2C, 3C, and 5C, with a cut-off current of 0.15-3A. The button-type symmetrical battery was then discharged at constant current to 3-4.5V at rates of 0.2C, 0.3C, 0.5C, 1C, 2C, 3C, and 5C, with this being considered one charge-discharge cycle. The button-type symmetrical battery was charged and discharged for 100 cycles in accordance with the above method, and the discharge capacity of the button-type symmetrical battery before and after the cycle was measured. The capacity retention rate of the button-type symmetrical battery after 100 cycles was calculated according to the following formula: Capacity retention rate after 100 cycles (%) = (discharge capacity at the 100th cycle / initial discharge capacity) × 100%.

[0091] Comparison of test results:

[0092] Table 1

[0093] serial number Pole peeling force (mΩ) Cycle performance (%) Example 1 52.7 88.0 Comparative Example 1 35.2 82.7 Comparative Example 2 12.3 67.5 Comparative Example 3 50.2 84.8 Comparative Example 4 42.0 61.8 Comparative Example 5 11.5 57.3

[0094] Comparing Example 1 with Comparative Example 1 and Comparative Example 2, the 2+ ions, the electrode peeling force is significantly reduced, while without adding Ni 2+ ions, the electrode peeling force is reduced more significantly; in the absence of Fe 2+ ions and Ni 2+ ions, irregular nanosheet morphology grows on the substrate, and Fe 2+ ions and Ni 2+ The ions need to exist at the same time to have a better effect. The two may produce a certain synergistic effect, promoting the formation of a two-dimensional layered structure, inducing the generation of a pore structure, forming a porous cross-linked network, and increasing the specific surface area.

[0095] Comparing Example 1 with Comparative Example 3, the electrode peeling force without adding LiCl is lower than that of Example 1 with adding LiCl. LiCl, as a precipitation plasticizer, can effectively stabilize the morphology growth, so that the secondary growth morphology is more closely integrated with the carbon-coated current collector substrate. Adding LiCl is the preferred embodiment of the present invention.

[0096] Comparing Example 1 with Comparative Example 4, when the thickness of the current collector carbon coating layer is reduced to 0.2 μm, the degree of surface modification is limited, so the test results are not good; after experimental research, when the thickness of the carbon coating layer is in the range of 0.4 to 0.8 μm, the effect of the present invention can be obtained.

[0097] Comparing Example 1 with Comparative Example 5, using the carbon-coated current collector without morphology control as a comparison, the solution of the present invention significantly increases the peel strength between the carbon-coated current collector and the active material. The highly adhesive carbon-coated current collector sample effectively increases the number of battery cycles, thereby increasing the life of the lithium battery.

[0098] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent replacement and improvement made by any technician familiar with the profession to the above embodiment without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the peeling force of a pole piece by morphology control, characterized in that: The following steps are involved: S1: preparing an initial carbon-coated current collector, wherein the initial carbon-coated current collector is prepared by coating a carbon-coated slurry on the current collector and drying the slurry to form a current collector having a carbon-coated layer; S2: Place the initial carbon-coated current collector into a 2+ ions, Fe 2+ The carbon-coated current collector is heated in a selenized solution containing ions to obtain a morphology-controlled carbon-coated current collector.

2. The method for improving electrode peeling force by morphology control according to claim 1, characterized in that: The thickness of the carbon coating layer is 0.4-0.8 μm.

3. The method for improving electrode peeling force by morphology control according to claim 1, characterized in that: The carbon-coated slurry is formed by mixing a carbon-coated conductive material, a wetting agent, and a binder; the carbon-coated conductive material is selected from at least one of carbon powder, graphite powder, carbon nanofiber, conductive carbon black, and carbon nanotube.

4. The method for improving electrode peeling force by morphology control according to claim 3, characterized in that: The carbon-coated conductive material is carbon powder and graphite powder, and the ratio of the carbon powder to the graphite powder is 7-10:1-3.

5. The method for improving electrode peeling force by morphology control according to claim 1, characterized in that: The Ni 2+ ions, Fe 2+ The heat treatment is carried out in the selenide solution of the ions by heating in an oil bath at a heating temperature of 85 to 95° C. and a treatment time of 5 to 7 hours.

6. The method for improving electrode peeling force by morphology control according to claim 1, characterized in that: The Ni-containing 2+ ions, Fe 2+ In the selenide solution of ions, Ni 2+ The ion content is 0.3~0.5mM / ml, Fe 2+ The content of ions is 0.3~0.5mM / ml, Se 4+ The ion content is 0.6-1 mM / ml, and the solvent is anhydrous ethanol or isopropanol.

7. The method for improving electrode peeling force by morphology control according to claim 1, characterized in that: The Ni-containing 2+ ions, Fe 2+ The ion selenide solution also contains anhydrous lithium chloride, and the content of anhydrous lithium chloride is 0.03-0.06 mM / ml.

8. A carbon-coated current collector, characterized in that: A morphology-controlled carbon-coated current collector prepared by the method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: Comprising the carbon-coated current collector according to claim 8.

10. A battery, characterized in that: Contains the positive electrode sheet according to claim 9.

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