Electrode, preparation method thereof and secondary battery

Abstract

The invention provides an electrode, a preparation method thereof and a secondary battery, and belongs to the technical field of secondary batteries. The preparation method of the electrode comprises the following steps: S1, powder and a solvent are mixed, the powder comprises an active material, a conductive agent and a binder, and a flocculent or dough-shaped mixture is obtained; s2, performing cold pressing on the mixture to obtain a semi-dry electrode film; s3, carrying out first hot pressing on the semi-dry electrode film to obtain a self-supporting electrode film; and S4, carrying out second hot pressing on the self-supporting electrode film and a current collector to obtain the electrode. The preparation method belongs to a semi-dry process, the process flow is simple, the equipment investment is low, the energy consumption is low, the prepared electrode is high in compaction density and good in uniformity, and a secondary battery composed of the electrode has high energy density, good cycle performance and relatively low manufacturing cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to an electrode, a preparation method thereof and a secondary battery. BACKGROUND

[0002] The electrode of a lithium ion battery is traditionally prepared by a wet process, which mainly includes the following steps: slurry preparation, slurry coating, electrode sheet drying, electrode sheet rolling, etc. Specifically, the wet process generally includes the following steps: dispersing an active material, a conductive agent, a binder, etc. in a solvent, stirring, preparing an electrode slurry, then uniformly coating the electrode slurry on a current collector by a coating method such as slot coating, and then feeding the coated electrode sheet into an oven for drying, and then rolling the dried electrode sheet by double rollers of a rolling machine to obtain an electrode sheet with a certain thickness.

[0003] It can be seen that the wet process for producing an electrode has a complex process flow, low production efficiency, large investment in plant and equipment, and huge energy consumption in the processes of slurry stirring and coating and electrode sheet drying after coating. In addition, when the positive electrode sheet is prepared by the wet process, a large amount of N-methyl pyrrolidone (NMP) is used as a solvent for the positive electrode slurry, and NMP is a toxic solvent that must be recovered, purified and reused, which will increase the manufacturing cost and bring environmental risks. Furthermore, when the electrode slurry is prepared by the wet process, the solvent in the electrode slurry accounts for 35wt% to 120wt% of the mass of the powder, and in the process of evaporation of the solvent in the electrode sheet drying, the binder is prone to float, which on the one hand will result in low content of the binder at the position where the active material contacts the current collector, and the active material is prone to peel off from the current collector, and the conductivity between the active material and the current collector decreases, and on the other hand, the binder is unevenly distributed in the electrode material, and the part with more binder has poor conductivity, and the above two aspects will result in increased internal resistance of the battery cell. Moreover, after the solvent in the electrode sheet drying is evaporated, a large number of pores will be left in the active material, resulting in low compaction density of the active material.

[0004] The dry process needs to apply high shear force to the mixture of the active material, the conductive agent and polytetrafluoroethylene (PTFE, binder) by using complex high-speed shearing equipment such as an air flow pulverizer, a screw extruder, a ball mill and an open mill, which requires high equipment, and the fibrillated powder material is prone to agglomeration, stratification and bridging in the production and transportation process, which will result in poor uniformity and consistency of the electrode. In the rolling process, the fibrillated powder material is too hard, which will result in excessive pressure on the rollers, and even deformation and powder falling of the self-supporting film of the electrode after rolling. SUMMARY

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose an electrode, its preparation method, and a secondary battery. The electrode preparation method has a simple process flow, uses less solvent and is environmentally friendly, consumes less energy, and produces an electrode with high compaction density and good uniformity. The battery has high energy density and good cycle performance.

[0006] This invention provides a method for preparing an electrode, comprising the following steps:

[0007] S1. Mix the powder and solvent to obtain a mixture in the form of flocculent material or dough; the powder includes active materials, conductive agents, and binders;

[0008] S2. The mixture is cold-pressed to obtain a semi-dry electrode film;

[0009] S3. The semi-dry electrode film is subjected to a first hot pressing to obtain a self-supporting electrode film;

[0010] S4. The self-supporting electrode film and the current collector are subjected to a second hot pressing to obtain the electrode.

[0011] The advantages and technical effects of the preparation method of this invention are as follows:

[0012] (1) The preparation method of the present invention belongs to the semi-dry process. When preparing the electrode, only a small amount of solvent needs to be added during the mixing process. The mixing equipment and mixing process are simple. The electrode is obtained by three rolling processes: cold pressing, first hot pressing, and second hot pressing. It can be seen that the preparation method of the present invention has a simple process flow, low equipment investment, low energy consumption, high compaction density and good uniformity of the electrode. The secondary battery composed of the electrode has high energy density and good cycle performance, and the manufacturing cost is low.

[0013] (2) Compared with the wet process disclosed in the related technology, the preparation method of the present invention has a simple mixing process, only requires the addition of a small amount of environmentally friendly solvent, without the need for a large amount of toxic solvent, and without the need for coating equipment and electrode drying equipment, which shortens the process flow, reduces equipment investment and energy consumption, and lowers manufacturing costs; in addition, the prepared electrode has a high compaction density, and the secondary battery composed of the electrode has a higher energy density and better cycle performance.

[0014] (3) Compared with the dry process disclosed in the related technology, the preparation method of the present invention has lower equipment requirements, better electrode processing performance, higher uniformity of electrode material, higher compaction density of prepared electrode, and higher energy density and better cycle performance of secondary battery composed using the electrode.

[0015] In some embodiments, the solvent is at least one of ethanol, isopropanol, n-propanol, diethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, dimethyl succinate, dimethyl glutarate, dimethyl adipate, and water.

[0016] In some embodiments, when the electrode is a positive electrode, the mass of the solvent is 3wt% to 30wt% of the mass of the powder.

[0017] In some embodiments, when the electrode is a negative electrode, the mass of the solvent is 3wt% to 50wt% of the mass of the powder.

[0018] In some embodiments, the thickness of the semi-dry electrode film is 0.5mm to 5mm.

[0019] In some embodiments, the thickness of the self-supporting electrode film is 0.1mm to 3mm.

[0020] In some embodiments, the temperature of the first heat pressing is 60℃ to 110℃.

[0021] In some embodiments, the temperature of the second heat pressing is 80℃ to 120℃.

[0022] In addition, the electrode prepared by the preparation method is also provided.

[0023] The electrode prepared by the preparation method has the advantages and technical effects that:

[0024] Compared with the electrodes prepared by the wet process and the dry process disclosed in the related art, the electrode prepared by the preparation method has lower manufacturing cost, higher energy density, and higher cycle performance.

[0025] In addition, the secondary battery including the electrode is also provided.

[0026] The secondary battery has the advantages and technical effects that:

[0027] Compared with the secondary battery assembled by the electrodes prepared by the wet process and the dry process disclosed in the related art, the secondary battery assembled by the electrode prepared by the preparation method has lower manufacturing cost, higher energy density, and higher cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flow chart of the preparation method of the electrode;

[0029] Figure 2 is a schematic diagram of the preparation process of the mixture;

[0030] Figure 3This is a schematic diagram of the preparation process of semi-dry electrode film and self-supporting electrode film;

[0031] Figure 4 This is a schematic diagram of the electrode fabrication process;

[0032] Explanation of reference numerals in the attached drawings: 1-mixing tank; 2-spray nozzle; 3-stirring paddle; 4-mixture; 5-feed trough; 6-push rod; 7-cold pressing roller; 8-semi-dry electrode film; 9-first hot pressing roller; 10-self-supporting electrode film; 11-first take-up roller; 12-current collector; 13-unwinding roller; 14-second hot pressing roller; 15-electrode; 16-second take-up roller. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] This invention provides a method for preparing an electrode, such as... Figure 1 As shown, it includes the following steps:

[0035] S1. Mix the powder and solvent to obtain a mixture in the form of flocculent material or dough; the powder includes active materials, conductive agents, and binders;

[0036] S2. The mixture is cold-pressed to obtain a semi-dry electrode film;

[0037] S3. The semi-dry electrode film is subjected to a first hot pressing to obtain a self-supporting electrode film;

[0038] S4. The self-supporting electrode film and the current collector are subjected to a second hot pressing to obtain the electrode.

[0039] The preparation method of this invention belongs to a semi-dry process. Only a small amount of solvent needs to be added during the mixing process when preparing the electrode. The mixing equipment and process are simple. The electrode is obtained through three rolling processes: cold pressing, first hot pressing, and second hot pressing. The preparation method of this invention has a simple process flow, requires little equipment investment, has low energy consumption, and produces electrodes with high compaction density and good uniformity. Secondary batteries composed using these electrodes have high energy density and good cycle performance, and the manufacturing cost is low.

[0040] To facilitate understanding of the preparation method of the embodiments of the present invention, the following description is provided in conjunction with the accompanying drawings. Figure 2is a schematic diagram of the mixing process. The powder is put into the mixing tank 1, and then the solvent is sprayed into the mixing tank 1 through the spraying nozzle 2 provided on the top of the mixing tank 1 while the powder is stirred by the stirring paddle 3 provided in the mixing tank 1, so that the powder and the solvent are mixed uniformly. After the spraying of the solvent is finished, the stirring can be continued for 1-2 hours, so that the solvent can sufficiently wet the powder, and the mixture 4 in the form of "dough" or "cake" is prepared.

[0041] Figure 3 is a schematic diagram of the preparation process of the semi-dry electrode film and the self-supporting electrode film. The mixture 4 is put into the feeding slot 5, and the mixture 4 is cold-pressed into the semi-dry electrode film 8 by the two cold-pressing rollers 7 under the pushing of the pushing rod 6. The semi-dry electrode film 8 with a specific thickness can be prepared by adjusting the pressure and the gap of the cold-pressing rollers 7. Then, the first hot-pressing is performed, for example, the semi-dry electrode film 8 is passed through the gap of the two first hot-pressing rollers 9, and the semi-dry electrode film 8 is hot-pressed to form the self-supporting electrode film 10. Since the solvent is volatilized by the heat during the hot-pressing of the semi-dry electrode film 8 by the first hot-pressing rollers 9, the self-supporting electrode film 10 close to the dry state is prepared, and the content of the solvent in the self-supporting electrode film is 0.5wt%-3wt%. The self-supporting electrode film 10 with a specific thickness can be prepared by adjusting the pressure and the gap of the first hot-pressing rollers 9. In addition, the volatilized solvent can be condensed and recovered by the condensing device (not shown) during the first hot-pressing. The self-supporting electrode film obtained by the cold-pressing and the first hot-pressing is fully contacted with the binder and the active material, the electrically conductive agent, and the self-supporting electrode film has high toughness and tensile strength. After the self-supporting electrode film 10 is cut by the cutting mechanism (not shown in the figure), the self-supporting electrode film 10 with a specific width can be wound on the first winding roller 11 for standby.

[0042] Figure 4 is a schematic diagram of the electrode preparation process. During the second hot-pressing, two rolls of the self-supporting electrode film 10 and one roll of the foil (current collector 12) are unwound by the unwinding roller 13, and then the "self-supporting electrode film-foil-self-supporting electrode film" is passed through the second hot-pressing roller 14 in the order of "self-supporting electrode film-foil-self-supporting electrode film". Under the action of the pressure and the temperature of the second hot-pressing roller 14, the two layers of the self-supporting electrode film are hot-pressed on both sides of the foil to form the electrode 15. During the passing of the "self-supporting electrode film-foil-self-supporting electrode film" through the second hot-pressing roller 14, the solvent in the self-supporting electrode film is completely evaporated, and the residual amount of the solvent in the prepared electrode is less than 100 ppm, 100 ppm=0.01wt%. In addition, the electrode 15 with a specific thickness can be prepared by adjusting the pressure and the gap of the second hot-pressing roller 14. Furthermore, the prepared electrode 15 can be wound on the second winding roller 16 for standby. It can be understood that if only the active layer is needed to be arranged on one side of the current collector, only one roll of the self-supporting electrode film and one roll of the foil (current collector) are needed to pass through the second hot-pressing roller in the order of "self-supporting electrode film-foil".

[0043] In some embodiments, the solvent may be at least one selected from ethanol, isopropanol, n-propanol, diethyl ether, ethylene glycol methyl ether, propylene glycol methyl ether, dimethyl succinate, dimethyl glutarate, dimethyl adipate, and water. All of these solvents are non-toxic and environmentally friendly. Considering environmental protection and the volatility of the solvent, ethanol or a mixture of ethanol and water is preferred.

[0044] When using a mixture of ethanol and water as a solvent, with a total solvent mass of 100 wt%, the ethanol content is 60 wt% to 100 wt%, and the water content is 0 wt% to 40 wt%. If the ethanol content is too low and the water content is too high, the solvent will not easily evaporate, making it difficult to form a self-supporting electrode film that is close to a dry state, and it is prone to sticking to the rollers.

[0045] In some embodiments, when the electrode is a positive electrode, the mass of the solvent is 3 wt% to 30 wt% of the powder mass, for example, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 12 wt%, 15 wt%, 18 wt%, 21 wt%, 25 wt%, 28 wt%, 30 wt%, etc. When the amount of solvent is too low, the mixture may not entirely form a "flour" or "dough" state, but a portion will remain in powder form, making it impossible to subsequently cold press to form a semi-dry electrode film. When the amount of solvent is too high, the mixture may not form a "flour" or "dough" state, but rather a slurry state, making it impossible to subsequently cold press to form a semi-dry electrode film, or requiring a large amount of energy for subsequent drying.

[0046] In some embodiments, when the electrode is a negative electrode, the mass of the solvent is 3 wt% to 50 wt% of the powder mass, for example, 3 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, etc. When the amount of solvent is too low, the mixture may not entirely form a "flour" or "dough" state, but a portion will remain in powder form, making it impossible to subsequently cold press to form a semi-dry electrode film. When the amount of solvent is too high, the mixture may not form a "flour" or "dough" state, but rather a slurry state, making it impossible to subsequently cold press to form a semi-dry electrode film, or requiring a large amount of energy for subsequent drying.

[0047] In the embodiments of the present invention, cold pressing in step S2 refers to the process of pressing loose powder composed of particles into a blank with a certain shape, size, strength and density under certain pressure and equipment at room temperature or below room temperature, such as 5°C, 10°C, 15°C, 20°C, 25°C, etc.

[0048] In some embodiments, the thickness of the semi-dry electrode film is 0.5 mm to 5 mm, such as 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, etc. When the semi-dry electrode film is too thin, it is not conducive to the formation of the semi-dry electrode film, and defects such as holes and cracks are prone to occur. When the semi-dry electrode film is too thick, the solvent evaporation efficiency is low when the semi-dry electrode film is cold-pressed, and it is not conducive to further rolling the semi-dry electrode film into a self-supporting electrode film with a target thickness (e.g., 0.1 mm to 3 mm).

[0049] In some embodiments, the thickness of the self-supporting electrode film is 0.1 mm to 3 mm, such as 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, etc. When the self-supporting electrode film is too thin, it is not conducive to improving the tensile strength of the self-supporting electrode film and the energy density of the battery cell. When the self-supporting electrode film is too thick, it is not conducive to forming an electrode with a target thickness (e.g., 50 μm to 1000 μm) during the second heat pressing.

[0050] In some embodiments, the temperature of the first heat pressing is 60°C to 110°C, such as 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, etc. When the temperature of the first heat pressing is too low, it is not conducive to the solvent evaporation to obtain a self-supporting electrode film close to a dry state, and the self-supporting electrode film is prone to sticking to the roller. When the temperature of the first heat pressing is too high, the solvent evaporates too quickly, and the self-supporting electrode film is prone to cracking and other defects.

[0051] In some embodiments, the content of the solvent in the self-supporting electrode film is 0.5 wt% to 3 wt%, such as 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, etc. When the content of the solvent in the self-supporting electrode film is too low, the self-supporting electrode film is prone to cracking and other defects. When the content of the solvent in the self-supporting electrode film is too high, the self-supporting electrode film is prone to sticking to the roller.

[0052] In some embodiments, the temperature of the second heat pressing is 80°C to 120°C. When the temperature of the second heat pressing is too low, the content of the solvent in the electrode tab is too high, which is not conducive to improving the energy density and cycle performance of the electrode tab. When the temperature of the second heat pressing is too high, it is not conducive to cost reduction and efficiency improvement.

[0053] In some embodiments, the content of the solvent in the electrode tab is 100 ppm or less. When the content of the solvent in the electrode tab is too high, it is not conducive to improving the energy density and cycle performance of the electrode tab.

[0054] In some embodiments, the thickness of the electrode is 50 μm to 1000 μm, for example, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, etc. When the thickness of the electrode is too thin, it is not conducive to improving the energy density of the battery cell. When the thickness of the electrode is too thick, it is not conducive to improving the power and cycle performance of the battery cell.

[0055] The preparation method of the embodiments of the present application can be applied to the preparation of positive electrode sheets and also to the preparation of negative electrode sheets. There is no particular limitation on the types and contents of the positive active material, the negative active material, the conductive agent and the binder, and materials and contents in the related art can be used. For example, the positive active material can be at least one of nickel cobalt lithium manganate, nickel cobalt lithium aluminate, lithium iron phosphate, lithium manganese phosphate, lithium nickel cobalt phosphate, lithium manganese iron phosphate and lithium-rich manganese-based positive electrode material. The negative active material can be at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, silicon-oxygen, silicon-carbon and lithium titanate. The conductive agent can be at least one of conductive carbon black (Super-P), acetylene black, carbon nanotube, carbon fiber and flaky graphite. The binder can be at least one of polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETEF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na). Taking the total mass of the active material, the conductive agent and the binder as 100 wt%, the content of the active material can be 80 wt% to 98 wt%, the content of the conductive agent can be 0.5 wt% to 10 wt%, and the content of the binder can be 3 wt% to 15 wt%.

[0056] In addition, the present application also provides an electrode obtained by the preparation method.

[0057] Compared with the electrodes obtained by the wet process and the dry process disclosed in the related art, the electrode obtained by the preparation method of the embodiments of the present application has lower manufacturing cost and higher energy density and cycle performance.

[0058] In addition, the embodiments of the present application also provide a secondary battery comprising the electrode sheet.

[0059] Compared with the secondary battery assembled by the electrodes obtained by the wet process and the dry process disclosed in the related art, the secondary battery assembled by the electrode obtained by the preparation method of the embodiments of the present application has lower manufacturing cost and higher energy density and cycle performance.

[0060] The present application will be described in detail below with reference to the embodiments and the accompanying drawings.

[0061] Embodiment 1

[0062] A method for preparing a positive electrode, the process being as follows:

[0063] S1. Add lithium nickel cobalt manganese oxide (positive electrode active material), carbon nanotubes (positive electrode conductive agent), and PTFE (positive electrode binder) into a mixing tank according to a mass ratio of 97wt%:0.5wt%:2.5wt%, and rotate the stirring paddle to stir and mix the positive electrode active material, positive electrode conductive agent, and positive electrode binder (positive electrode powder). The positive electrode powder is mixed for 1 h, after which ethanol (positive electrode solvent) is sprayed into the mixing tank through a spraying nozzle while stirring. The amount of positive electrode solvent sprayed is 10wt% of the mass of the positive electrode powder. After the spraying of the positive electrode solvent is completed, the stirring is continued for 1 h. The positive electrode solvent fully wets the positive electrode powder, and a surface-flocculated mixture is prepared.

[0064] S2. Add the mixture into a feeding chute. Under the pushing of the pushing rod, the mixture passes through the gap between two cold pressing rollers, and the mixture is cold-pressed into a semi-dry electrode film with a thickness of 1.5 mm.

[0065] S3. Pass the semi-dry electrode film through the gap between two first hot pressing rollers, and the temperature of the first hot pressing rollers is 100°C. After the first hot pressing, the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.28 mm. After the edges are cut, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0066] S4. After two rolls of self-supporting electrode film and one roll of aluminum foil (positive electrode current collector) are unwound by unwinding rollers, they pass through the gap between two second hot pressing rollers in the order of “self-supporting electrode film-aluminum foil-self-supporting electrode film”, and the temperature of the second hot pressing rollers is 115°C. After the second hot pressing, a positive electrode with a thickness of 262μm is obtained, and the positive electrode is wound on a second winding roller.

[0067] A method for preparing a negative electrode, the process being as follows:

[0068] S1. Add artificial graphite (negative electrode active material), conductive carbon black (negative electrode conductive agent), and PTFE (negative electrode binder) into a mixing tank according to a mass ratio of 96wt%:1wt%:3wt%, and rotate the stirring paddle to stir and mix the negative electrode active material, negative electrode conductive agent, and negative electrode binder (negative electrode powder). The negative electrode powder is mixed for 1 h, after which ethanol (negative electrode solvent) is sprayed into the mixing tank through a spraying nozzle while stirring. The amount of negative electrode solvent sprayed is 40wt% of the mass of the negative electrode powder. After the spraying of the negative electrode solvent is completed, the stirring is continued for 1 h. The negative electrode solvent fully wets the negative electrode powder, and a dough-like mixture is prepared.

[0069] S2. Add the mixture into a feeding chute. Under the pushing of the pushing rod, the mixture passes through the gap between two cold pressing rollers, and the mixture is cold-pressed into a semi-dry electrode film with a thickness of 1.8 mm.

[0070] S3. The semi-dry electrode film is passed through the nip of two first hot-press rollers, the temperature of which is 100°C, to form a self-supporting electrode film with a thickness of 0.35 mm after the first hot-pressing. After the edges of the self-supporting electrode film are trimmed, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0071] S4. The self-supporting electrode film and the current collector are subjected to a second hot-pressing to obtain an electrode:

[0072] Two rolls of the self-supporting electrode film and one roll of copper foil (negative current collector) are unwound by unwinding rollers, and are passed through the nip of two second hot-press rollers in the order of "self-supporting electrode film ~ copper foil ~ self-supporting electrode film", the temperature of the second hot-press rollers being 115°C. The above three-layer structure is subjected to the second hot-pressing to obtain a negative electrode with a thickness of 320 μm, which is wound on a second winding roller.

[0073] Application Example 1

[0074] The positive electrode, the negative electrode and the separator prepared in Example 1 are wound together to obtain a roll core, which is loaded into a square shell, electrolyte is injected, and a lithium ion battery is obtained after the shell is sealed with a cover plate.

[0075] Example 2

[0076] A method for preparing a positive electrode, the process being as follows:

[0077] S1. Lithium iron phosphate (positive active material), carbon nanotube (positive conductive agent) and PTFE (positive binder) are added into a mixing tank in a mass ratio of 96wt%: 1wt%: 3wt%, and the positive active material, the positive conductive agent and the positive binder (positive powder) are stirred and mixed by rotating the stirring paddle. The positive powder is stirred for 1 h, and then a mixture of ethanol and water (positive solvent) is sprayed into the mixing tank through a spraying nozzle while stirring. The mass ratio of ethanol to water in the positive solvent is 7:3, and the spraying amount of the positive solvent is 30wt% of the mass of the positive powder. After the spraying of the positive solvent is completed, the stirring is continued for 1 h to fully wet the positive powder, and a dough-like mixture is prepared.

[0078] S2. The mixture is added into a feeding chute, and the mixture is cold-pressed into a semi-dry electrode film with a thickness of 2 mm by passing through the nip of two cold-press rollers under the pushing of a pushing rod.

[0079] S3. The semi-dry electrode film is passed through the nip of two first hot-press rollers, the temperature of which is 110°C, to form a self-supporting electrode film with a thickness of 0.25 mm after the first hot-pressing. After the edges of the self-supporting electrode film are trimmed, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0080] S4. Two rolls of self-supporting electrode film, one roll of aluminum foil (positive current collector) are unwound by unwinding rollers, and pass through the nip of two second hot pressing rollers in the order of "self-supporting electrode film-aluminum foil-self-supporting electrode film", the temperature of the second hot pressing roller is 120°C, and the above three-layer structure obtains a positive electrode with a thickness of 244 μm after the second hot pressing, and the positive electrode is wound on a second winding roller.

[0081] A method for preparing a negative electrode, the process being as follows:

[0082] S1. Artificial graphite (negative active material), conductive carbon black (negative conductive agent), and PTFE (negative binder) are added into a mixing tank in a mass ratio of 97wt%:0.5wt%:2.5wt%, and the negative active material, negative conductive agent, and negative binder (negative powder) are stirred and mixed by rotating the stirring paddle, the mixing time of the negative powder is 1h, then ethanol (negative solvent) is sprayed into the mixing tank through a spraying nozzle while stirring, the spraying amount of the negative solvent is 38wt% of the mass of the negative powder, after the spraying of the negative solvent is completed, the stirring is continued for 1h, the negative solvent sufficiently wets the negative powder, and a dough-like mixture is prepared.

[0083] S2. The mixture is added into a feeding slot, and the mixture passes through the nip of two cold pressing rollers under the pushing of a pushing rod, and the mixture is cold-pressed into a semi-dry electrode film with a thickness of 1mm.

[0084] S3. The semi-dry electrode film passes through the nip of two first hot pressing rollers, the temperature of the first hot pressing roller is 110°C, and the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.22mm after the first hot pressing. After the edge is cut, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0085] S4. Two rolls of self-supporting electrode film, one roll of copper foil (negative current collector) are unwound by unwinding rollers, and pass through the nip of two second hot pressing rollers in the order of "self-supporting electrode film-copper foil-self-supporting electrode film", the temperature of the second hot pressing roller is 120°C, and the above three-layer structure obtains a negative electrode with a thickness of 170 μm after the second hot pressing, and the negative electrode is wound on a second winding roller.

[0086] Application Example 2

[0087] The positive electrode and the negative electrode prepared in Example 2 are wound together with a separator to prepare a roll core, the roll core is loaded into a square shell, an electrolyte is injected, and a lithium ion battery is obtained after sealing with a cover plate.

[0088] Example 3

[0089] A method for preparing a positive electrode, the process being as follows:

[0090] S1. Add lithium nickel cobalt manganese oxide (positive active material), carbon nanotubes (positive conductive agent), and PTFE (positive binder) into a mixing tank in a mass ratio of 96.5wt%:1wt%:2.5wt%, and rotate the stirring paddle to stir and mix the positive active material, positive conductive agent, and positive binder (positive powder) above. The positive powder mixing time is 1h. Then, while stirring, spray ethanol (positive solvent) into the mixing tank through a spray nozzle. The positive solvent spraying amount is 12wt% of the mass of the positive powder. After the positive solvent spraying is completed, continue stirring for 1h. The positive solvent fully wets the positive powder, and a surface-flocculated mixture is prepared.

[0091] S2. Add the mixture into a feeding chute. Under the pushing of the pushing rod, the mixture passes through the gap between two cold pressing rollers, and the mixture is cold pressed into a semi-dry electrode film with a thickness of 2mm.

[0092] S3. Pass the semi-dry electrode film through the gap between two first hot pressing rollers with a temperature of 105°C. After the first hot pressing, the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.35mm. After edge cutting, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0093] S4. Unwind two rolls of self-supporting electrode film and one roll of aluminum foil (positive current collector) through unwinding rollers. Pass them through the gap between two second hot pressing rollers in the order of “self-supporting electrode film-aluminum foil-self-supporting electrode film” with a temperature of 110°C. After the second hot pressing, the three-layer structure obtains a positive electrode with a thickness of 350μm. The positive electrode is wound on a second winding roller.

[0094] A method for preparing a negative electrode, the process being as follows:

[0095] S1. Add natural graphite (negative active material), conductive carbon black (negative conductive agent), and PTFE (negative binder) into a mixing tank in a mass ratio of 95.5wt%:0.5wt%:4wt%, and rotate the stirring paddle to stir and mix the negative active material, negative conductive agent, and negative binder (negative powder) above. The negative powder mixing time is 1h. Then, while stirring, spray ethanol (negative solvent) into the mixing tank through a spray nozzle. The negative solvent spraying amount is 45wt% of the mass of the negative powder. After the negative solvent spraying is completed, continue stirring for 1h. The negative solvent fully wets the negative powder, and a dough-like mixture is prepared.

[0096] S2. Add the mixture into a feeding chute. Under the pushing of the pushing rod, the mixture passes through the gap between two cold pressing rollers, and the mixture is cold pressed into a semi-dry electrode film with a thickness of 2.3mm.

[0097] S3. The semi-dry electrode film is passed through the nip of two first hot-press rollers, the temperature of which is 105°C, and after the first hot-pressing, the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.4 mm. After the edges of the self-supporting electrode film are trimmed, the self-supporting electrode film with a specific width is wound on the first winding roller.

[0098] S4. After two rolls of the self-supporting electrode film and one roll of the copper foil (negative current collector) are unwound by the unwinding roller, they are passed through the nip of two second hot-press rollers in the order of "self-supporting electrode film-copper foil-self-supporting electrode film", the temperature of the second hot-press rollers is 110°C, and after the second hot-pressing, the above three layers of structure form a negative electrode with a thickness of 432 μm, which is wound on the second winding roller.

[0099] Application Example 3

[0100] The positive electrode, the negative electrode and the separator prepared in Example 3 are wound together to form a roll core, which is loaded into a cylindrical shell, electrolyte is injected, and after the shell is sealed with a cover plate, a lithium ion battery is obtained.

[0101] Example 4

[0102] A method for preparing a positive electrode, the process being as follows:

[0103] S1. Lithium iron phosphate (positive active material), carbon nanotubes (positive conductive agent) and PTFE (positive binder) are added to a mixing tank in a mass ratio of 96wt%: 1wt%: 3wt%, and the above positive active material, positive conductive agent and positive binder (positive powder) are stirred and mixed by rotating the stirring paddle. The positive powder mixing time is 1 h, and then ethanol and water (positive solvent) are sprayed into the mixing tank through a spray nozzle while stirring. The mass ratio of ethanol to water in the positive solvent is 3:7, and the solvent spraying amount is 30wt% of the mass of the positive powder. After the positive solvent is sprayed, the stirring is continued for 1 h, and the positive solvent is fully wetted with the positive powder to prepare a dough-like mixture.

[0104] S2. The mixture is added to the feed chute, and under the pushing of the pushing rod, the mixture is cold-pressed through the gap of two cold-press rollers to form a semi-dry electrode film with a thickness of 2 mm.

[0105] S3. The semi-dry electrode film is passed through the nip of two first hot-press rollers, the temperature of which is 110°C, and after the first hot-pressing, the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.28 mm. After the edges of the self-supporting electrode film are trimmed, the self-supporting electrode film with a specific width is wound on the first winding roller.

[0106] S4. Two rolls of self-supporting electrode film, one roll of aluminum foil (positive current collector) are unwound by unwinding rollers, and pass through the nip of two second hot pressing rollers in the order of "self-supporting electrode film-aluminum foil-self-supporting electrode film", the temperature of the second hot pressing roller is 120°C, and the above three-layer structure obtains a positive electrode with a thickness of 253 μm after the second hot pressing, and the positive electrode is wound on a second winding roller.

[0107] A preparation method of a negative electrode, the process is as follows:

[0108] S1. Artificial graphite (negative active material), conductive carbon black (negative conductive agent), and PTFE (negative binder) are added into a mixing tank according to a mass ratio of 97wt%:0.5wt%:2.5wt%, and the negative active material, the negative conductive agent, and the negative binder (negative powder) are stirred and mixed by rotating a stirring paddle, the mixing time of the negative powder is 1h, then ethanol (negative solvent) is sprayed into the mixing tank through a spraying nozzle while stirring, the spraying amount of the negative solvent is 38wt% of the mass of the negative powder, after the spraying of the negative solvent is completed, the stirring is continued for 1h, the negative solvent sufficiently wets the negative powder, and a dough-like mixture is prepared.

[0109] S2. The mixture is added into a feeding slot, and the mixture passes through the nip of two cold pressing rollers under the pushing of a pushing rod, and the mixture is cold pressed into a semi-dry electrode film with a thickness of 1mm.

[0110] S3. The semi-dry electrode film passes through the nip of two first hot pressing rollers, the temperature of the first hot pressing roller is 110°C, and the semi-dry electrode film forms a self-supporting electrode film with a thickness of 0.22mm after the first hot pressing. After the self-supporting electrode film is trimmed, the self-supporting electrode film with a specific width is wound on a first winding roller.

[0111] S4. Two rolls of self-supporting electrode film, one roll of copper foil (negative current collector) are unwound by unwinding rollers, and pass through the nip of two second hot pressing rollers in the order of "self-supporting electrode film-copper foil-self-supporting electrode film", the temperature of the second hot pressing roller is 120°C, and the above three-layer structure obtains a negative electrode with a thickness of 170 μm after the second hot pressing, and the negative electrode is wound on a second winding roller.

[0112] Application Example 4

[0113] The positive electrode and the negative electrode prepared in Example 4 are wound together with a separator to prepare a roll core, the roll core is loaded into a square shell, an electrolyte is injected, and a lithium ion battery is obtained after sealing by using a cover plate.

[0114] Comparative Example 1

[0115] A preparation method of a positive electrode, the process is as follows:

[0116] S1. Add lithium nickel cobalt manganese oxide (positive active material), carbon nanotubes (positive conductive agent), and PVDF (positive binder, polyvinylidene fluoride) into a mixing tank in a mass ratio of 97.5wt%: 1wt%: 1.5wt%, and stir the positive active material, positive conductive agent, and positive binder (positive powder) by rotating the stirring paddle for 1 hour. Then, spray NMP (positive solvent) into the mixing tank through a spray nozzle while stirring, and the amount of positive solvent sprayed is 34wt% of the mass of the positive powder. After the spraying of the positive solvent is completed, continue stirring for 1 hour to obtain a positive slurry.

[0117] S2. Coat the positive slurry on both sides of an aluminum foil (positive current collector) through a slot coating device, and then dry at 110°C for 5 minutes. Then, pass the positive slurry through the gap between two cold pressing rollers to obtain a positive electrode with a thickness of 106μm. Finally, wind the positive electrode on a winding roller.

[0118] A method for preparing a negative electrode, the process being as follows:

[0119] S1. Add artificial graphite (negative active material), conductive carbon black (negative conductive agent), CMC (carboxymethyl cellulose sodium, negative binder), and SBR (styrene-butadiene rubber, negative binder) into a mixing tank in a mass ratio of 96wt%: 1wt%: 1wt%: 2wt%, and stir the negative active material, negative conductive agent, and negative binder (negative powder) by rotating the stirring paddle for 1 hour. Then, spray deionized water (negative solvent) into the mixing tank through a spray nozzle while stirring, and the amount of negative solvent sprayed is 92wt% of the mass of the negative powder. After the spraying of the negative solvent is completed, continue stirring for 1 hour to obtain a negative slurry.

[0120] S2. Coat the negative slurry on both sides of a copper foil (negative current collector) through a slot coating device, and then dry at 90°C for 5 minutes. Then, pass the negative slurry through the gap between two cold pressing rollers to obtain a negative electrode with a thickness of 132μm. Finally, wind the negative electrode on a winding roller.

[0121] Comparative Example 1

[0122] Wind the positive electrode and the negative electrode prepared in Comparative Example 1 together with a separator to obtain a winding core. Then, put the winding core into a square shell, inject an electrolyte, and seal the lithium ion battery after using a cover plate to seal the opening.

[0123] Comparative Example 2

[0124] A method for preparing a positive electrode, the process being as follows:

[0125] S1. Lithium iron phosphate (positive active material), carbon nanotubes (positive conductive agent), PVDF (positive binder) were added into a mixing tank according to a mass ratio of 97wt%: 1wt%: 2wt%, and the positive active material, positive conductive agent and positive binder (positive powder) were stirred and mixed by rotating the stirring paddle for 1h. Then, NMP (positive solvent) was sprayed into the mixing tank through a spray nozzle while stirring, and the amount of the positive solvent sprayed was 68wt% of the mass of the positive powder. After the spraying of the positive solvent was completed, the stirring was continued for 1h, and a positive slurry was prepared.

[0126] S2. The positive slurry was coated on both sides of an aluminum foil (positive current collector) by a slot coating device, and then dried at 120°C for 5min. Then, the positive slurry was passed through the gap between two cold pressing rollers, and a positive electrode with a thickness of 145μm was obtained after cold pressing. The positive electrode was wound on a winding roller.

[0127] A method for preparing a negative electrode, the process being as follows:

[0128] S1. Artificial graphite (negative active material), conductive carbon black (negative conductive agent), CMC (negative binder), SBR (negative binder) were added into a mixing tank according to a mass ratio of 96wt%: 1wt%: 1wt%: 2wt%, and the negative active material, negative conductive agent and negative binder (negative powder) were stirred and mixed by rotating the stirring paddle for 1h. Then, deionized water (negative solvent) was sprayed into the mixing tank through a spray nozzle while stirring, and the amount of the negative solvent sprayed was 105wt% of the mass of the negative powder. After the spraying of the negative solvent was completed, the stirring was continued for 1h, and a negative slurry was prepared.

[0129] S2. The negative slurry was coated on both sides of a copper foil (negative current collector) by a slot coating device, and then dried at 100°C for 5min. Then, the negative slurry was passed through the gap between two cold pressing rollers, and a negative electrode with a thickness of 100μm was obtained after cold pressing. The negative electrode was wound on a winding roller.

[0130] Comparative Example 2

[0131] The positive electrode and the negative electrode prepared in Comparative Example 2 were wound together with a separator to prepare a core, and the core was loaded into a square shell, electrolyte was injected, and a lithium ion battery was obtained after sealing with a cover plate.

[0132] Comparative Example 3

[0133] A method for preparing a positive electrode, the process being as follows:

[0134] S1. Add lithium nickel cobalt manganese oxide (positive active material), carbon nanotubes (positive conductive agent), and PVDF (positive binder) into a mixing tank in a mass ratio of 97.5wt%: 1wt%: 1.5wt%, and rotate the stirring paddle to mix the positive active material, positive conductive agent, and positive binder (positive powder) above. The mixing time of the positive powder is 1h. Then, while stirring, spray NMP (positive solvent) into the mixing tank through a spray nozzle. The amount of positive solvent sprayed is 42wt% of the mass of the positive powder. After the spraying of the positive solvent is completed, continue stirring for 1h to obtain a positive slurry.

[0135] S2. Coat the positive slurry on both sides of an aluminum foil (positive current collector) through a slot coating device, and then dry at 115℃ for 5min. Then, pass through the gap between two cold pressing rollers to obtain a positive electrode with a thickness of 130μm. The positive electrode is wound on a winding roller.

[0136] A method for preparing a negative electrode, the process being as follows:

[0137] S1. Add artificial graphite (negative active material), conductive carbon black (negative conductive agent), CMC (negative binder), and SBR (negative binder) into a mixing tank in a mass ratio of 96.5wt%: 0.5wt%: 1wt%: 2wt%, and rotate the stirring paddle to mix the negative active material, negative conductive agent, and negative binder (negative powder) above. The mixing time of the negative powder is 1h. Then, while stirring, spray deionized water (negative solvent) into the mixing tank through a spray nozzle. The amount of negative solvent sprayed is 100wt% of the mass of the negative powder. After the spraying of the negative solvent is completed, continue stirring for 1h to obtain a negative slurry.

[0138] S2. Coat the negative slurry on both sides of a copper foil (negative current collector) through a slot coating device, and then dry at 95℃ for 5min. Then, pass through the gap between two cold pressing rollers to obtain a negative electrode with a thickness of 153μm. The negative electrode is wound on a winding roller.

[0139] Application Comparative Example 3

[0140] The positive electrode and the negative electrode prepared in Application Comparative Example 3 are wound together with a separator to obtain a winding core. The winding core is loaded into a cylindrical shell, electrolyte is injected, and after sealing with a cover plate, a lithium ion battery is obtained.

[0141] Comparative Example 4

[0142] A method for preparing a positive electrode, the process being as follows:

[0143] S1. Add lithium nickel cobalt manganese oxide (positive active material), carbon nanotubes (positive conductive agent), and PTFE (positive binder) into a mixing tank in a mass ratio of 97wt%:0.5wt%:2.5wt%, and stir and mix the positive active material, positive conductive agent, and positive binder (positive powder) by rotating the stirring paddle. The positive powder mixing time is 1h. Then, while stirring, spray ethanol (positive solvent) into the mixing tank through the spray nozzle. The positive solvent spraying amount is 10wt% of the mass of the positive powder. After the positive solvent spraying is completed, continue stirring for 1h. The positive solvent fully wets the positive powder, and a dough-like mixture is prepared.

[0144] S2. Add the mixture into the feeding slot. Under the pushing of the pushing rod, the mixture passes through the gap between the two cold pressing rollers, and the mixture is cold pressed into a semi-dry electrode film with a thickness of 0.6mm. The semi-dry electrode film is wound on the first winding roller.

[0145] S3. After two rolls of semi-dry electrode film and one roll of aluminum foil (positive current collector) are unwound by the unwinding roller, they pass through the gap between the two hot pressing rollers in the order of “semi-dry electrode film-aluminum foil-semi-dry electrode film”. The temperature of the hot pressing roller is 115℃. A positive electrode with a thickness of 270μm is obtained. The positive electrode is wound on the second winding roller.

[0146] A method for preparing a negative electrode, the process being as follows:

[0147] S1. Add artificial graphite (negative active material), conductive carbon black (negative conductive agent), and PTFE (negative binder) into a mixing tank in a mass ratio of 96wt%:1wt%:3wt%, and stir and mix the negative active material, negative conductive agent, and negative binder (negative powder) by rotating the stirring paddle. The negative powder mixing time is 1h. Then, while stirring, spray ethanol (negative solvent) into the mixing tank through the spray nozzle. The solvent spraying amount is 40wt% of the mass of the negative powder. After the negative solvent spraying is completed, continue stirring for 1h. The negative solvent fully wets the negative powder, and a dough-like mixture is prepared.

[0148] S2. Add the mixture into the feeding slot. Under the pushing of the pushing rod, the mixture passes through the gap between the two cold pressing rollers, and the mixture is cold pressed into a semi-dry electrode film with a thickness of 0.8mm. The semi-dry electrode film is wound on the first winding roller.

[0149] S3. Hot press the semi-dry electrode film and the current collector to obtain an electrode:

[0150] After two rolls of semi-dry electrode film and one roll of copper foil (negative current collector) are unwound by the unwinding roller, they pass through the gap between the two hot pressing rollers in the order of “semi-dry electrode film-copper foil-semi-dry electrode film”. The temperature of the hot pressing roller is 115℃. A negative electrode with a thickness of 340μm is obtained. The negative electrode is wound on the second winding roller.

[0151] Application Comparative Example 4

[0152] The positive electrode, the negative electrode and the separator prepared in Application Comparative Example 4 were wound together to prepare a roll core, the roll core was loaded into a square shell, an electrolyte was injected, and after being sealed by using a cover plate, a lithium ion battery was obtained.

[0153] Comparative Example 5

[0154] A preparation method of a positive electrode, the process being as follows:

[0155] S1. Lithium nickel cobalt manganese oxide (positive electrode active material), carbon nanotubes (positive electrode conductive agent) and PTFE (positive electrode binder) were added into a mixing tank according to a mass ratio of 97wt%:0.5wt%:2.5wt%, and a stirring paddle was rotated to stir and mix the positive electrode active material, the positive electrode conductive agent and the positive electrode binder (positive electrode powder). The positive electrode powder was mixed for 1 h, and then ethanol (positive electrode solvent) was sprayed into the mixing tank through a spraying nozzle while stirring. The amount of the positive electrode solvent sprayed was 10wt% of the mass of the positive electrode powder. After the spraying of the positive electrode solvent was completed, the stirring was continued for 1 h. The positive electrode solvent was fully wetted to the positive electrode powder, and a dough-like mixture was prepared.

[0156] S2. The mixture was added into a feeding slot, and the mixture passed through the gap between two first hot pressing rollers under the pushing of a pushing rod. The temperature of the first hot pressing roller was 100°C. After the first hot pressing, the mixture formed a self-supporting electrode film with a thickness of 0.35 mm. After the edge was cut, the self-supporting electrode film with a specific width was wound on a first winding roller.

[0157] S3. Two rolls of the self-supporting electrode film and one roll of aluminum foil (positive electrode current collector) were unwound through unwinding rollers, and passed through the gap between two second hot pressing rollers in the order of “self-supporting electrode film-aluminum foil-self-supporting electrode film”. The temperature of the second hot pressing roller was 115°C. After the second hot pressing, the above three layers of structure obtained a positive electrode with a thickness of 266μm. The positive electrode was wound on a second winding roller.

[0158] A preparation method of a negative electrode, the process being as follows:

[0159] S1. Artificial graphite (negative electrode active material), carbon nanotubes (negative electrode conductive agent) and PTFE (negative electrode binder) were added into a mixing tank according to a mass ratio of 96wt%:1wt%:3wt%, and a stirring paddle was rotated to stir and mix the negative electrode active material, the negative electrode conductive agent and the negative electrode binder (negative electrode powder). The negative electrode powder was mixed for 1 h, and then ethanol (negative electrode solvent) was sprayed into the mixing tank through a spraying nozzle while stirring. The amount of the negative electrode solvent sprayed was 40wt% of the mass of the negative electrode powder. After the spraying of the negative electrode solvent was completed, the stirring was continued for 1 h. The negative electrode solvent was fully wetted to the negative electrode powder, and a dough-like mixture was prepared.

[0160] S2. The mixture is added into the feeding slot, and the mixture is pressed by the pushing rod to pass through the gap of two first hot-pressing rollers with a temperature of 100°C, and the first hot-pressing of the mixture forms a self-supporting electrode film with a thickness of 0.4 mm. After the edge cutting of the self-supporting electrode film, the self-supporting electrode film with a specific width is wound on the first winding roller.

[0161] S3. The self-supporting electrode film, a roll of copper foil (negative current collector) are unwound by the unwinding roller, and pass through the gap of two second hot-pressing rollers in the order of "self-supporting electrode film-copper foil-self-supporting electrode film" with a temperature of 115°C, and the above three-layer structure is second hot-pressed to obtain a negative electrode with a thickness of 330 μm, which is wound on the second winding roller.

[0162] Application Comparative Example 5

[0163] The positive electrode and the negative electrode prepared in the application comparative example 5 are wound together with the separator to prepare a roll core, and the roll core is loaded into a square shell, electrolyte is injected, and a lithium ion battery is obtained after sealing with a cover plate.

[0164] Performance test:

[0165] (1) Compaction density: take a certain area of the electrode sheet, weigh and measure the thickness, and the compaction density = (electrode sheet weight-foil weight) / electrode sheet area / (electrode sheet thickness-foil thickness)

[0166] (2) Energy density:

[0167] The battery is charged to the upper limit cutoff voltage at a 1C charging current, and is charged to 0.05C cutoff at constant voltage, and is rested for 10 min; the battery is discharged to the lower limit cutoff voltage at a 1C discharging current, and the battery discharging energy is recorded;

[0168] The energy density = battery discharging energy / battery weight. The upper limit cutoff voltage of the lithium nickel cobalt manganese oxide is 4.2V, the upper limit cutoff voltage of the lithium iron phosphate is 3.65V, the lower limit cutoff voltage of the lithium nickel cobalt manganese oxide is 2.75V, and the lower limit cutoff voltage of the lithium iron phosphate is 2.5V.

[0169] (3) Cycle number:

[0170] The battery is charged to the upper limit cutoff voltage at a 1C charging current, and is charged to 0.05C cutoff at constant voltage, and is rested for 10 min; the battery is discharged to the lower limit cutoff voltage at a 1C discharging current, and is rested for 10 min, and the discharging capacity is recorded. The above cycle process is one cycle. The above steps are repeated, and the discharging capacity of the battery in each cycle is recorded, until the discharging capacity decays to 80% of the discharging capacity of the first cycle, and the cycle number is recorded.

[0171] (4) The ratio of the sum of the material cost, energy consumption cost and direct labor cost of the manufacturing to the energy (Wh) of the output battery.

[0172] The process parameters of the electrode preparation method of each of the above embodiments and comparative examples are shown in Table 1, and the performance and manufacturing cost of the lithium ion battery of each of the above application examples and application comparative examples are shown in Table 2.

[0173] Table 1. Process parameters of the electrode preparation method of each of the embodiments and comparative examples

[0174]

[0175]

[0176] Table 2. Performance and manufacturing cost of the lithium ion battery of each of the application examples and application comparative examples

[0177]

[0178] As can be seen from the comparison of Example 4 and Comparative Example 2, compared with the wet process of Comparative Example 2, the tap density of the positive electrode and the negative electrode prepared by the semi-dry process of Example 4 is obviously higher, and compared with the lithium ion battery of Application Comparative Example 2, the energy density of the lithium ion battery of Application Example 4 is significantly improved, the cycle number is significantly increased, and the manufacturing cost is greatly reduced.

[0179] As can be seen from the comparison of Example 3 and Comparative Example 3, compared with the wet process of Comparative Example 3, the tap density of the positive electrode and the negative electrode prepared by the semi-dry process of Example 3 is obviously higher, and compared with the lithium ion battery of Application Comparative Example 3, the energy density of the lithium ion battery of Application Example 3 is significantly improved, the cycle number is significantly increased, and the manufacturing cost is greatly reduced.

[0180] Therefore, compared with the wet process in the related art, the semi-dry process of the embodiments of the present application has obvious advantages, which can improve the tap density of the electrode, improve the energy density and cycle performance of the secondary battery, and reduce the manufacturing cost of the secondary battery.

[0181] As can be seen from the comparison of Example 1 and Comparative Examples 4 and 5, when the cold pressing is omitted or the first hot pressing is omitted, the energy density of the lithium ion battery is significantly reduced, the cycle number is significantly reduced, and the manufacturing cost is greatly increased.

[0182] As can be seen from the comparison of Example 2 and Example 4, when the mixture of ethanol and water is used as the solvent, when the ratio of ethanol to water is 7:3, it is more beneficial to improve the energy density, cycle performance and reduce the manufacturing cost of the secondary battery than when the ratio of ethanol to water is 3:7.

[0183] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present disclosure. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terminology "comprising" is used in the disclosure as comprising but not limited to, that is, it is open-ended and does not exclude the presence of additional features, structures, materials, or characteristics.

[0184] Although the embodiments of the present disclosure have been shown and described above, it should be understood by those having ordinary skill in the art that the above-mentioned embodiments are exemplary and should not be construed as limiting the present disclosure, and those skilled in the art can make changes, modifications, replacements, and variations to the above-mentioned embodiments within the scope of the present disclosure.

Claims

1. A method of preparing an electrode, characterized by, The method comprises the following steps: S1. mixing a powder and a solvent to obtain a mixture in the form of a paste or a dough; the powder comprises an active material, a conductive agent, and a binder; S2. cold-pressing the mixture to obtain a semi-dry electrode film; S3. first heat-pressing the semi-dry electrode film to obtain a self-supporting electrode film; S4. second heat-pressing the self-supporting electrode film and a current collector to obtain an electrode.

2. The production method according to claim 1, characterized by, The solvent is at least one of ethanol, isopropanol, n-propanol, diethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, dimethyl succinate, dimethyl glutarate, dimethyl adipate, and water.

3. The preparation method according to claim 1, characterized in that, When the electrode is a positive electrode, the mass of the solvent is 3wt%-30wt% of the mass of the powder.

4. The method of claim 1, wherein, When the electrode is a negative electrode, the mass of the solvent is 3wt%-50wt% of the mass of the powder.

5. The process according to any one of claims 1 to 4, characterized in that, The thickness of the semi-dry electrode film is 0.5mm-5mm.

6. The method of any one of claims 1 to 4, wherein the method further comprises, The thickness of the self-supporting electrode film is 0.1mm-3mm.

7. The method of any one of claims 1 to 4, wherein the method further comprises the step of: The temperature of the first heat-pressing is 60℃-110℃.

8. The method of any one of claims 1 to 4, wherein, The temperature of the second heat-pressing is 80℃-120℃.

9. An electrode characterized by, The electrode obtained by the method of any one of claims 1-8.

10. A secondary battery characterized by comprising: The electrode tab comprises the electrode tab of any one of claims 1-9.

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