A thick electrode and its preparation method and application

Abstract

The present invention provides a thick electrode and its preparation method and application, which relate to the field of lithium-ion battery technology. Specifically, the thick electrode comprises the following steps of preparing: fully mixing the electrode active component, lithium salt, conductive agent, adhesive and solvent, heating the mixed slurry to 110°C to 180°C, compounding the hot mixed slurry with a current collector, and obtaining a thick electrode after cooling. The preparation method provided by the present invention avoids the defects of easy cracking, poor adhesion, and inability to industrialize production that may exist in conventional processes when preparing thick electrodes; the thick electrode provided by the present invention has the effect of improving the efficiency of ionic conductivity and electronic conductivity, so that the thick electrode has the effects of improved charging capacity and improved rate performance. At the same time, the preparation process of the present invention does not require N-methylpyrrolidone, and does not require baking or sintering steps for the electrode sheets, does not emit unsafe gases, is more environmentally friendly and safe, and can be mass-produced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a thick electrode and a preparation method and application thereof. Background Art

[0002] The active material content in lithium-ion battery electrodes determines the battery's output capacity and energy density. Thick electrode design means higher energy output can be achieved, so thick electrodes have broad application prospects in the lithium battery field. However, in thick electrodes, the proportion of inactive materials (such as current collectors and separators) is low, the thickness of the electrode increases, and the tortuosity of the electrode increases, which reduces the wettability of the electrolyte (the surface of the electrode is well wetted by the electrolyte, but there may be more closed pores inside the electrode, making it impossible for the electrolyte to penetrate). Ultimately, this leads to an increase in the migration path of ions in the thick electrode, or the main material performance cannot be fully utilized, resulting in a reduced battery charging capacity.

[0003] For the preparation of thick electrodes, the following methods and processes are often used: 1) Conventional wet coating method: First, the electrode raw materials are fully mixed in a solvent, and then phase transfer, extrusion and other methods are used to coat them on the current collector. Subsequently, the solvent is removed in the oven section to obtain the electrode. However, this method is not easy to dry when the coating thickness increases, and it is easy to crack and peel off after drying. 2) Dry mixing method: First, the electrode raw materials are fully mixed in a dry state, and then an adhesive is added and fully stirred or ground. The mixed material is then repeatedly rolled over a roller to allow the adhesive to fully stretch and bond the main material, and finally the electrode of the desired thickness is obtained and composited with the current collector. Dry mixing does not have the problem of cracking, but when the thickness of the electrode increases, there are defects such as loose contact between the material and the current collector, and even falling off. 3) Other preparation processes such as plasma sintering technology, template method, carbon nanotube array, and biomass sintering produce thick electrodes that are suitable for small-batch preparation and are not suitable for existing battery mass production lines.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first objective of the present invention is to provide a method for preparing thick electrodes to address the drawbacks of conventional electrode preparation processes in the prior art, which are difficult to adapt to thick electrodes. Furthermore, the first objective of the present invention is to provide a method for preparing thick electrodes to address the drawbacks of thick electrodes, which suffer from poor electrochemical performance due to their thickness and high tortuosity, which is limited by the transport of ions and electrons and the rapid degradation of their capacity. To achieve the above objectives, the present invention employs the following technical solutions:

[0006] A method for preparing a thick electrode comprises the following steps: fully mixing electrode active components, lithium salt, conductive agent, adhesive and solvent, heating the mixed slurry to 110°C to 180°C, compounding the heated mixed slurry with a current collector, and cooling to obtain a thick electrode.

[0007] Preferably, the electrode active component includes at least one of lithium cobalt oxide, lithium iron phosphate, ternary materials (such as NCM811, NCM622, NCM523, etc.), lithium-rich manganese-based materials or lithium manganese oxide; or, the electrode active component includes at least one of graphite material, amorphous carbon, titanium oxide or silicon-carbon composite material.

[0008] Preferably, the lithium salt is at least one of lithium tetrafluoroborate (LiBF4), lithium bissulfonyl imide (LiFSI), lithium difluorophosphate (LiPF2O2), lithium bis(trifluoromethane)sulfonyl imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium dioxalatoborate (LiDFOB), 4,5-dicyano-trifluoromethylimidazolium lithium (LiDTI), lithium perchlorate (LiClO4) or lithium hexafluoroarsenate (LiAsF6).

[0009] Preferably, the conductive agent includes at least one of conductive carbon black, industrial furnace black, high temperature graphitized carbon black, acetylene black, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and single-layer or multi-layer graphene.

[0010] Preferably, the adhesive includes at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), vinylidene fluoride (VF2), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), polyamide (PAI), polyvinyl alcohol (PVA), polyethyleneimine (PEI) or polyimide (PI).

[0011] Preferably, the solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl butyrate (MB), ethyl propionate (EP), dimethyl sulfoxide (DMSO), acetophenone, benzoate and ethyl benzoate; more preferably, the boiling point of the solvent is ≥150°C.

[0012] More preferably, the solvent comprises ethylene carbonate and propylene carbonate, and the volume ratio of the ethylene carbonate to the propylene carbonate is 1:1.

[0013] The second object of the present invention is to provide a thick electrode prepared by the method for preparing the thick electrode;

[0014] Preferably, the thick electrode is a positive electrode or a negative electrode of a lithium ion battery.

[0015] Preferably, the thickness of the thick electrode is 100 μm to 1000 μm.

[0016] The third object of the present invention is to provide the use of the thick electrode in the field of lithium-ion batteries; including but not limited to the preparation of lithium-ion batteries containing the thick electrode, the preparation of electrical appliances containing the thick electrode, etc., all fall within the use of the present invention.

[0017] Compared with the prior art, the present invention has the following advantages: the preparation method provided by the present invention avoids the defects that may exist in conventional processes for preparing thick electrodes, such as easy cracking, poor adhesion, and inability to industrialize production; the thick electrode produced by the present invention has solid-state porous properties, which improves the efficiency of ionic and electronic conductivity, thereby improving the charging capacity and rate performance of the thick electrode. At the same time, the preparation process of the present invention does not require solvents such as N-methylpyrrolidone (NMP), saving costs, and does not require baking or sintering of the electrode sheets, eliminating the emission of unsafe gases, making it more environmentally friendly and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A performance comparison chart of gram capacity versus number of cycles for the test example is disclosed;

[0020] Figure 2 A performance comparison chart of area capacity-cycle number in the test example is disclosed. DETAILED DESCRIPTION

[0021] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0022] The present invention is carried out through the following specific implementation methods: A method for preparing a thick electrode comprises the following steps: fully mixing an electrode active component, a lithium salt, a conductive agent, an adhesive and a solvent, heating the mixed slurry to 110°C to 180°C, compounding the heated mixed slurry with a current collector, and obtaining a thick electrode after cooling.

[0023] It should be noted that the "heating the mixed slurry to 110°C to 180°C" is the only heating operation involved in the present invention, that is, the preparation method of the thick electrode in the present invention does not contain a drying step; at the same time, the thick electrode prepared by the present invention does not require other heating operations (such as conventional steps such as baking or sintering) when assembling the battery.

[0024] It should also be noted that when performing the operation of "raising the temperature of the mixed slurry to 110° C. to 180° C.", the operator should perform the operation of "compounding the mixed slurry with the current collector" as quickly as possible, that is, ensure that the mixed slurry is compounded while hot.

[0025] When the temperature is raised, a specific adhesive can dissolve in a specific organic solvent and form a gel, but at room temperature the adhesive is separated from the solvent and forms a continuous adhesive-solvent network, which is a network interwoven structure of a bicontinuous electrolyte. At high temperatures, the adhesive-solvent gel structure is manifested as: the homogenized glue is mixed with the electrode raw material and forms a cross-linked structure, and when the temperature drops to room temperature, the adhesive is separated from the solvent, and the adhesive plays a conventional bonding role. At this time, the separated solvent is evenly fixed in the internal pores of the thick electrode and acts as an electrolyte. Specifically, the adhesive in the present invention forms a uniform suspension with the electrode active component, lithium salt, conductive agent and solvent, and when the suspension is cooled, the adhesive phase separates, carrying away the electrode active component particles and lithium salt to form a continuous adhesive (electrode active component and lithium salt)-solvent (conductive agent) network.

[0026] As a preferred embodiment, the temperature of the mixed slurry is 112°C to 172°C; specifically, it includes but is not limited to: 112, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 172 (°C); as a more preferred embodiment, the temperature of the mixed slurry is 112°C to 145°C, at which temperature the adhesive can be repeatedly softened at high temperature, and its fluidity makes it easy to apply.

[0027] As a preferred embodiment, the thickness of the thick electrode includes but is not limited to 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 (μm).

[0028] As a preferred embodiment, the raw material components of the thick electrode include: by weight percentage, 60% to 98% of electrode active components, 0.1% to 40% of conductive agent and 0.1% to 40% of binder, and solvent, and the solvent accounts for 5% to 50% of the total mass of the active component, conductive agent and binder; as a preferred embodiment, the molar mass of the lithium salt in the solvent is 0.1 mol / L to 8 mol / L.

[0029] As a preferred embodiment, the composite of the mixed slurry and the current collector includes: applying the mixed slurry to the current collector, or rolling the mixed slurry and then bonding it to the current collector.

[0030] As a preferred embodiment, the current collector includes but is not limited to copper foil, aluminum foil, carbon-coated copper foil, carbon-coated aluminum foil, composite copper foil, composite aluminum foil, molybdenum foil or stainless steel sheet.

[0031] As a preferred embodiment, the thorough mixing includes: firstly mixing the electrode active component, the conductive agent, and the adhesive for a first time, and then adding the lithium salt solution consisting of the lithium salt and the solvent, and mixing for a second time to obtain the mixed slurry.

[0032] As a preferred embodiment, after the mixed slurry is heated, the mixed slurry is compounded with the current collector as much as possible before it is cooled down, that is, the "hot mixed slurry is compounded with the current collector". Those skilled in the art should complete this operation in a relatively short time, and the slight cooling of the mixed slurry that is inevitably caused during the compounding process with the current collector does not affect the implementation of the technical solution of the present invention.

[0033] As a preferred embodiment, the lithium salt includes at least one of lithium bis(trifluoromethane)sulfonyl imide, lithium hexafluorophosphate or lithium bis(oxalatoborate); as a more preferred embodiment, the lithium salt is lithium bis(trifluoromethane)sulfonyl imide, which is insensitive to moisture; and when lithium hexafluorophosphate or lithium bis(oxalatoborate) is selected, the moisture requirements for the operating process environment will be more stringent, such as the preparation, coating, slicing and other processes of the positive electrode slurry need to be in a relatively dry test environment.

[0034] Example 1

[0035] The active material, conductive agent, lithium salt and adhesive are dissolved in a solvent, the temperature is raised to 112°C, and stirring is continued to obtain a uniformly mixed gel mixture, which is coated on the current collector copper foil while hot with a coating thickness of 100 μm. After cooling, the following eight thick electrodes of this embodiment are obtained (the eight thick electrodes correspond to embodiments 1-1, 1-2... to 1-8, and the specific raw material components of each are recorded in Table 1 below).

[0036] The percentage values given for the active material, conductive agent, and binder refer to their respective weight percentages, and the sum of the weight percentages of the active material, conductive agent, and binder is guaranteed to be 100%. The molar concentration given for the lithium salt refers to the molar concentration of the lithium salt in the solvent.

[0037] Table 1

[0038]

[0039]

[0040] Example 2

[0041] It is basically the same as Example 1-2, with the only difference being that the temperature is raised to 150° C., the coating thickness is 500 μm, and the thick electrode of this example is obtained.

[0042] Example 3

[0043] It is basically the same as Example 1-2, except that the temperature is raised to 172° C., the coating thickness is 1000 μm, and the thick electrode of this example is obtained.

[0044] Comparative Example 1

[0045] conv (60 μm) electrode: Lithium iron phosphate (96.5%), conductive carbon black (1.5%) and polyvinylidene (2%) were thoroughly mixed in the solvent N-methylpyrrolidone to form the positive electrode slurry; the positive electrode slurry was coated on the current collector aluminum foil with a coating thickness of 60 μm, and then dried in an oven at 100°C to remove the solvent and obtain the electrode.

[0046] Comparative Example 2

[0047] conv (125 μm) electrode: exactly the same as Comparative Example 1, except that the coating thickness is 125 μm.

[0048] Test example

[0049] The thick electrodes prepared in the above-mentioned embodiments and comparative examples were compared in terms of their double charge performance. The test method was as follows: within a specific voltage test range of the battery, charge and discharge were performed at rates of C / 20, C / 10, C / 5, C / 2, 1C, 2C, 3C, 5C, and 10C, respectively. Each rate was cycled five times, with a 10-minute interval between each charge and discharge cycle. The gram capacity of each embodiment and comparative example during each cycle was recorded, and the average gram capacity obtained from the five cycles was calculated, as shown in Table 1 below.

[0050] like Figure 1 The figure shows a scatter plot comparison of the average value of the gram capacity and the number of cycles of Examples 1-2, Comparative Example 1 and Comparative Example 2.

[0051] At the same time, in this test example, the area capacity of Examples 1-2, Comparative Example 1 and Comparative Example 2 at different charge and discharge rates (similarly, the average value is measured in five cycle tests), the scatter plot comparison of the average area capacity and the number of cycles is shown in FIG. Figure 2 shown.

[0052] Table 1

[0053]

[0054]

[0055] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a thick electrode, characterized in that: The method comprises the following steps: fully mixing electrode active components, lithium salt, conductive agent, adhesive and solvent, heating the mixed slurry to 110°C to 180°C, compounding the heated mixed slurry with a current collector, and cooling the mixed slurry to obtain a thick electrode; The adhesive comprises at least one of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, vinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, polyamide, polyvinyl alcohol, polyethylene imine or polyimide; The solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl butyrate, ethyl propionate, dimethyl sulfoxide, acetophenone, benzoate and ethyl benzoate.

2. The method for preparing a thick electrode according to claim 1, wherein: The electrode active component includes at least one of lithium cobalt oxide, lithium iron phosphate, ternary materials, lithium-rich manganese-based materials or lithium manganate; Alternatively, the electrode active component includes at least one of graphite material, amorphous carbon, titanium oxide or silicon-carbon composite material.

3. The method for preparing a thick electrode according to claim 1, wherein: The lithium salt includes at least one of lithium tetrafluoroborate, lithium bissulfonyl imide, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonyl imide, lithium hexafluorophosphate, lithium bisoxalatoborate, lithium 4,5-dicyano-trifluoromethylimidazolium, lithium perchlorate or lithium hexafluoroarsenate.

4. The method for preparing a thick electrode according to claim 1, wherein: The conductive agent includes at least one of conductive carbon black, industrial furnace black, high temperature graphitized carbon black, acetylene black, carbon nanofiber, single-walled carbon nanotube, multi-walled carbon nanotube, single-layer or multi-layer graphene.

5. The method for preparing a thick electrode according to claim 1, wherein: The boiling point of the solvent is ≥150°C.

6. The method for preparing a thick electrode according to claim 1, wherein: The solvent includes ethylene carbonate and propylene carbonate, and the volume ratio of the ethylene carbonate to the propylene carbonate is 1:

1.

7. A thick electrode produced by the method for producing a thick electrode according to any one of claims 1 to 6.

8. The thick electrode according to claim 7, characterized in that The thick electrode is a positive electrode or a negative electrode of a lithium ion battery.

9. The thick electrode according to claim 7, characterized in that The thickness of the thick electrode is 100 μm to 1000 μm.

10. Use of the thick electrode according to claim 7 in the field of lithium-ion batteries.

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