Electrode plate, preparation method thereof, secondary battery and device

Abstract

The invention relates to an electrode plate, a preparation method thereof, a secondary battery and a device. The electrode pole piece comprises a composite current collector, wherein the composite current collector comprises a polymer layer and a metal layer arranged on the surface of the polymer layer; the dry electrode film is arranged on the surface of the metal layer, the dry electrode film comprises an active material and a binding agent, and the binding agent comprises a fiberizable binding agent and a first binding agent; wherein the compaction density of the dry electrode film is X g / cm < 3 >, the stripping force between the dry electrode film and the composite current collector is Y N / m, and Y / X is larger than or equal to 3 and smaller than or equal to 14. Therefore, the electrode plate provided by the invention has at least one of the following advantages: excellent processing matching performance, good electrical performance and safety performance, and lower cost.

Description

Technical Field

[0001] This application relates to the field of energy storage. Specifically, this application relates to an electrode sheet, a preparation method thereof, a secondary battery and a device. Background Art

[0002] As a new type of electrode sheet production process, the dry preparation of electrode sheets has attracted much attention in the lithium battery market because of its low energy consumption, low cost, and the better cell performance of the produced electrode sheets. Currently, dry electrodes are mainly formed by thermocompression lamination of dry electrode films (self-supporting films) and conventional current collectors (such as aluminum foils or copper foils). However, on the one hand, due to the easy extension of the dry electrode film under pressure, the rolling elongation rate does not match that of the conventional current collector, which affects the product yield; on the other hand, when a lithium battery assembled with a conventional current collector electrode sheet is deformed or punctured under a strong external force, it is very easy to catch fire and explode, causing serious harm to the surrounding area.

[0003] Therefore, the current electrode sheet, its preparation method, secondary battery and device still need to be improved. Summary of the Invention

[0004] The inventors found that, compared with conventional foil current collectors, composite current collectors are lighter, have excellent mechanical properties, better flexibility, high plasticity under pressure, and are more compatible with dry electrodes and processes under certain conditions. Moreover, the composite current collector has a three-layer structure composed of metal / polymer / metal, which provides insulation for the circuit system when the lithium battery starts to thermally runaway, thus reducing the probability of further runaway; in addition, due to the low density of the polymer, the composite current collector can also reduce the weight of the battery and improve the energy density; finally, the use of the polymer layer also reduces the use of metal foils, reducing the raw material cost and the large amount of energy consumption in the production of the corresponding metals. However, during the rolling process of the wet process, the composite current collector is prone to deformation, extension, and twisting under stress, resulting in low yield of electrode production, increased resistance, and unstable quality; in addition, the drying process of the wet-process electrode will also have a negative impact on the composite current collector, and the side effects need to be reduced by lowering the drying temperature or reducing the drying time. Therefore, the composite current collector has extremely high requirements for production processes and equipment, and perfect composite between organic polymer materials and metal materials needs to be achieved. Aiming at the deficiencies of the prior art, this application applies the composite current collector to the dry process. Utilizing the property that both the dry electrode film and the composite current collector have a certain degree of ductility, laminating the dry electrode film onto the surface of the composite current collector (such as including a polymer layer and a metal layer provided on the surface of the polymer layer) is a more suitable scenario for the application of the composite current collector. On the one hand, the dry process does not require the drying process of the electrode, avoiding the negative impact on the polymer layer in the composite current collector caused by long-term heating; on the other hand, during the lamination process of the dry process and the subsequent rolling process, by controlling an appropriate line pressure, the deformation of the composite current collector is prevented, improving the quality and yield of the electrode; at the same time, the composite current collector also brings higher energy density and higher safety performance to the dry electrode.

[0005] This application provides an electrode sheet, which includes: a composite current collector, the composite current collector includes a polymer layer and a metal layer provided on the surface of the polymer layer; a dry electrode film, the dry electrode film is provided on the surface of the metal layer, the dry electrode film includes an active material and a binder, and the binder includes a fibrillatable binder and a first binder; wherein, the compaction density of the dry electrode film is X g / cm 3 , and the peel force between the dry electrode film and the composite current collector is Y N / m, 3 ≤ Y / X ≤ 14.

[0006] The present application also provides a method for preparing an electrode pole piece, the method comprising: providing a composite current collector and a dry electrode film, wherein the composite current collector comprises a polymer layer and a metal layer disposed on the surface of the polymer layer, and the dry electrode film comprises an active material and a binder; forming the dry electrode film on the surface of the metal layer of the composite current collector by hot pressing to obtain the electrode pole piece; wherein the line pressure between rollers during the hot pressing is 0.01 t / cm to 0.5 t / cm.

[0007] The present application also provides a secondary battery, the secondary battery comprising the electrode pole piece described above or the electrode pole piece formed by the preparation method described above.

[0008] The present application also provides a device, the device comprising the secondary battery described above.

[0009] The beneficial effects of the present application are as follows:

[0010] The electrode pole piece of the present application forms the dry electrode film (dry self-supporting film) and the composite current collector by hot pressing and compounding, and by controlling the compaction density of the dry electrode film and the peel force between the dry electrode film and the composite current collector, at least one of the following advantages can be achieved: First, the dry process of the dry electrode film does not require the drying process of the pole piece, avoiding the negative impact on the polymer layer in the composite current collector caused by long-term heating; during the dry process compounding and subsequent rolling process, by controlling the appropriate line pressure, the deformation of the pole piece is prevented, and the quality and yield of the pole piece are improved; by utilizing the relatively high compaction density and good ductility of the dry electrode film itself, it better matches the processing characteristics of the composite current collector, avoiding overpressure deformation and distortion of the composite current collector. Second, compared with conventional current collectors (for example, the conventional positive current collector is aluminum foil or steel foil, and the negative current collector is copper foil), using the composite current collector can improve the safety of the battery cell - under acupuncture, and the composite current collector also brings higher energy density, higher safety performance, and lower cost to the dry pole piece. Third, the relatively high compaction density and good ductility of the dry electrode film itself better match the extension characteristics and processing characteristics of the composite current collector, avoiding overpressure deformation, distortion, and deterioration due to long-term heating of the composite current collector. Fourth, the hot pressing and compounding process between the dry electrode film and the composite current collector does not require excessive pressure, avoiding excessive extension deformation or damage of the dry electrode film or the current collector layer caused by overpressure, which affects the yield of the pole piece. Therefore, the combination of the two can greatly simplify the use conditions of the composite current collector, simplify the equipment, and compounding the composite current collector to the dry electrode film can achieve the optimization of process and performance. Thus, based on the above improvements, the electrode pole piece of the present application has at least one of the following advantages: excellent processing matchability, good electrical performance, safety performance, and lower cost. Detailed embodiments

[0011] For the sake of simplicity, only some numerical ranges are specifically disclosed in this application. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0012] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various common measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0013] The list of items connected by the terms "at least one of", "at least one", "at least one kind of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0014] The term "dry electrode film" is an electrode film combined with a binder matrix structure that is sufficient to support the film and maintain its shape, so that the electrode film can be independent without any external support elements, such as current collectors. For example, in the absence of other support elements, the dry electrode film can have sufficient strength to be rolled up, processed, and unfolded during the manufacturing process of the electrode plate.

[0015] The following further elaborates on this application in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate this application and not to limit the scope of this application.

[0016] I. Electrode Plate

[0017] This application provides an electrode plate, which includes: a composite current collector and a dry electrode film. The composite current collector includes a polymer layer and a metal layer provided on the surface of the polymer layer; the dry electrode film is provided on the surface of the metal layer, and the dry electrode film includes an active material and a binder, and the binder includes a fibrillatable binder and a first binder; wherein, the tap density of the dry electrode film is X g / cm 3, the peeling force between the dry electrode film and the composite current collector is Y N / m, and 3 ≤ Y / X ≤ 14.

[0018] In the electrode sheet of the present application, the dry electrode film (dry self-supporting film) and the composite current collector are formed by hot pressing and laminating. By controlling the compaction density of the dry electrode film and the peeling force between the dry electrode film and the composite current collector, at least one of the following advantages can be achieved: First, the dry process of the dry electrode film does not require the drying process of the electrode sheet, avoiding the negative impact on the polymer layer in the composite current collector caused by long-term heating; during the dry process lamination and subsequent rolling processes, by controlling the appropriate line pressure, the deformation of the electrode sheet is prevented, improving the quality and yield of the electrode sheet; by utilizing the relatively high compaction density and good ductility of the dry electrode film itself, it better matches the processing characteristics of the composite current collector, avoiding overpressure deformation and distortion of the composite current collector. Second, compared with conventional current collectors (for example, the conventional positive current collector is aluminum foil or steel foil, and the negative current collector is copper foil), using the composite current collector can improve the safety of the battery cell - under nail penetration. Moreover, the composite current collector also brings higher energy density, higher safety performance, and lower cost to the dry electrode sheet. Third, the relatively high compaction density and good ductility of the dry electrode film itself better match the extension characteristics and processing characteristics of the composite current collector, avoiding overpressure deformation, distortion, and deterioration due to long-term heating of the composite current collector. Fourth, the hot pressing and laminating process between the dry electrode film and the composite current collector does not require excessive pressure, avoiding excessive extension deformation or damage to the dry electrode film or the current collector layer caused by overpressure, which affects the yield of the electrode sheet. Therefore, the combination of the two can greatly simplify the usage conditions of the composite current collector and simplify the equipment. Combining the composite current collector with the dry electrode film can optimize the process and performance. Thus, based on the above improvements, the electrode sheet of the present application has at least one of the following advantages: excellent processing compatibility, good electrical performance, safety performance, and lower cost.

[0019] In the present application, the compaction density of the dry electrode film can be adjusted by conventional technical means in the art according to the characteristics of the selected active material, such as controlling the rolling pressure, rolling temperature, rolling speed, etc. of the electrode sheet to obtain the required compaction density.

[0020] In the present application, the composite current collector includes a polymer layer and a metal layer provided on the surface of the polymer layer. Compared with conventional foil current collectors (for example, the conventional positive current collector is aluminum foil or steel foil, and the negative current collector is copper foil), the composite current collector in the present application is lighter and has better flexibility, can improve the energy density, and at the same time can improve the safety - under nail penetration performance of the secondary battery using this electrode sheet, bringing higher safety.

[0021] In some embodiments, 3 ≤ Y / X ≤ 14. In some embodiments, Y / X is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or any value therebetween. Thus, when Y / X satisfies the above range, it is beneficial to the matching of the dry electrode film and the composite current collector. When the value of Y / X is too low, it will cause insufficient adhesion and an increase in interfacial impedance; when the value of Y / X is too high, it will cause too low a compaction density at the interface between the dry electrode film and the composite current collector, resulting in a high resistance and a low volumetric energy density.

[0022] In some embodiments, 1.4 ≤ X ≤ 3.7. In some embodiments, X is 1.4, 1.5, 1.7, 1.9, 2, 2.1, 2.3, 2.5, 3, 3.5, 3.7 or any value therebetween. Thus, if the compaction density of the dry electrode film is too high, the film will be too brittle to be wound and stored, and the ion transport impedance will be too large; if the compaction density of the dry electrode film is too low, the strength will be insufficient to be self-supporting, the conductivity will be too low, and the volumetric energy density of the battery will be too low.

[0023] In some embodiments, 3 ≤ Y ≤ 55. In some embodiments, Y is 3, 4, 5, 6, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or any value therebetween. Thus, if the peel force between the dry electrode film and the composite current collector is too high, more adhesion force is required, which will bring side effects such as a high interfacial resistance; if the peel force between the dry electrode film and the composite current collector is too low, the interface will be unstable and the interfacial impedance will be high.

[0024] In some embodiments, the rolling elongation rate of the dry electrode film is Z%, 0.2 ≤ Z ≤ 5.5. In some embodiments, Z is 0.2, 0.7, 1.0, 1.2, 1.5, 1.7, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or any value therebetween. Thus, if the rolling elongation rate of the dry electrode film is too high or too low, the active material will be separated from the composite current collector.

[0025] In some embodiments, the density of the active material is ρ g / cm 3 , 2 ≤ ρ ≤ 5. In some embodiments, ρ is 2, 2.2, 2.5, 3, 3.5, 3.6, 4, 4.5, 4.7, 5 or any value therebetween.

[0026] In some embodiments, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3. In some embodiments, (1 - X / ρ) × Z is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any value therebetween. Thus, when (1 - X / ρ) × Z satisfies the above range, it is beneficial to the matching of the dry electrode film and the composite current collector. When the value of (1 - X / ρ) × Z is too low, the electrode sheet will not be compacted enough, resulting in high resistance and low volume energy density; when the value of (1 - X / ρ) × Z is too high, the electrode sheet will be overextended and deformed until it breaks.

[0027] In some embodiments, the active material is a positive electrode active material or a negative electrode active material. In some embodiments, the positive electrode active material includes at least one of lithium nickel transition metal oxide and phosphate.

[0028] In some embodiments, the active material is a positive electrode active material, and the positive electrode active material includes lithium nickel transition metal oxide. In some embodiments, 3.4 ≤ X ≤ 3.7. In some embodiments, X is 3.4, 3.45, 3.5, 3.55, 3.55, 3.6, 3.65, 3.7 or any value therebetween. In some embodiments, 15 ≤ Y ≤ 55. In some embodiments, Y is 15, 20, 25, 30, 35, 40, 45, 50, 55 or any value therebetween. In some embodiments, 3 ≤ Y / X ≤ 14. In some embodiments, Y / X is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or any value therebetween. In some embodiments, 0.5 ≤ Z ≤ 4. In some embodiments, Z is 0.5, 0.7, 1.0, 1.2, 1.5, 1.7, 2, 2.2, 2.5, 2.7, 3, 3.2, 3.5, 3.7, 4 or any value therebetween. In some embodiments, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3. In some embodiments, (1 - X / ρ) × Z is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any value therebetween. In some embodiments, the density of the lithium nickel transition metal oxide is ρ g / cm 3 , 4 ≤ ρ ≤ 5. In some embodiments, ρ is 4, 4.2, 4.4, 4.6, 4.7, 4.8, 5 or any value therebetween. In some embodiments, ρ is 4.7.

[0029] In some embodiments, the active material is a positive electrode active material, and the positive electrode active material includes phosphate. In some embodiments, 2.1 ≤ X ≤ 2.6. In some embodiments, X is 2.1, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6 or any value therebetween. In some embodiments, 8 ≤ Y ≤ 30. In some embodiments, Y is 8, 9, 10, 15, 20, 25, 30 or any value therebetween. In some embodiments, 3 ≤ Y / X ≤ 14. In some embodiments, Y / X is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or any value therebetween. In some embodiments, 0.2 ≤ Z ≤ 2.2. In some embodiments, Z is 0.2, 0.4, 0.7, 1.0, 1.2, 1.5, 1.7, 2, 2.2 or any value therebetween. In some embodiments, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3. In some embodiments, (1 - X / ρ) × Z is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any value therebetween. In some embodiments, the density of the phosphate is ρ g / cm 3 , 3 ≤ ρ ≤ 4. In some embodiments, ρ is 3, 3.2, 3.4, 3.6, 3.8, 4 or any value therebetween. In some embodiments, ρ is 3.6.

[0030] In some embodiments, the active material is a negative electrode active material. 1.4 ≤ X ≤ 1.65. In some embodiments, X is 1.4, 1.45, 1.5, 1.55, 1.6, 1.65 or any value therebetween. In some embodiments, 3 ≤ Y ≤ 20. Y is 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or any value therebetween. In some embodiments, 3 ≤ Y / X ≤ 14. In some embodiments, Y / X is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or any value therebetween. In some embodiments, 2 ≤ Z ≤ 5.5. Z is 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or any value therebetween. In some embodiments, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3. In some embodiments, (1 - X / ρ) × Z is 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any value therebetween. In some embodiments, the density of the negative electrode active material is ρ g / cm 3 , 2 ≤ ρ ≤ 3. In some embodiments, ρ is 2, 2.2, 2.4, 2.6, 2.8, 3 or any value therebetween. In some embodiments, ρ is 2.2.

[0031] In some embodiments, the lithium nickel transition metal oxide includes LiNi x Co y M (1-x-y) O2, where M includes at least one of manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver, and niobium, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 < x + y ≤ 1. In some embodiments, x is 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any value therebetween. In some embodiments, y is 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any value therebetween. In some embodiments, the lithium nickel transition metal oxide includes at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, and lithium nickel manganese oxide. In some embodiments, the lithium nickel transition metal oxide includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0032] In some embodiments, the phosphate includes LiMn k B (1-k) PO4, where 0 ≤ k ≤ 1 and B includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead. In some embodiments, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or any value therebetween. In some embodiments, the phosphate includes at least one of lithium iron phosphate and lithium manganese iron phosphate. In some embodiments, the phosphate includes at least one of LiMn 0.6 Fe 0.4 PO4 and LiMn 0.8 Fe 0.2 PO4.

[0033] In some embodiments, the negative electrode active material includes at least one of a silicon-based material, a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. In some embodiments, the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide compound, and a silicon carbide compound; the carbon-based material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene; the tin-based material includes at least one of tin, a tin oxide, and a tin alloy; and the phosphorus-based material includes phosphorus and / or a phosphorus complex. In some embodiments, the negative electrode active material includes a carbon-based material and a silicon-based material. In some embodiments, the silicon-based material includes at least one of a silicon oxide compound and a silicon carbide compound, and the carbon-based material includes at least one of artificial graphite and natural graphite. In some embodiments, the negative electrode active material includes at least one of artificial graphite and natural graphite.

[0034] In some embodiments, based on the mass of the dry electrode film, the mass percentage of the active material is 90% to 99%. In some embodiments, based on the mass of the dry electrode film, the mass percentage of the active material is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value therebetween.

[0035] In some embodiments, the fibrillatable binder includes polytetrafluoroethylene (PTFE). In some embodiments, the fibrillatable binder is formed by in-situ fibrillation of fibrillatable particulate polymers. In this application, in-situ fibrillation means that the polymer particles gradually become fibrous under thermal and shear conditions after being mixed with other components such as the active material. In some embodiments, the particulate polymer includes polytetrafluoroethylene.

[0036] In some embodiments, the first binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyphenylene sulfide (PPS), polyethylene oxide (PEO), polypropylene (PP), polyethylene (PE), styrene-butadiene rubber (SBR), styrene-acrylonitrile copolymer (SAN), polyacrylonitrile (PAN), polyacrylate, and polyurethane (PU). It should be noted that the first binder is a thermoplastic adhesive, which does not form fibrous under thermal and shear conditions.

[0037] In some embodiments, the mass ratio of the fibrillatable binder to the first binder is 1:(0.25 to 4). In some embodiments, the mass ratio of the fibrillatable binder to the first binder is 1:0.25, 1:0.5, 1:0.8, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or any value therebetween.

[0038] In some embodiments, based on the mass of the dry electrode film, the mass percentage of the fibrillatable binder is 0.5% to 2%, and the mass percentage of the first binder is 0.5% to 2%. In some embodiments, based on the mass of the dry electrode film, the mass percentage of the fibrillatable binder is 0.5%, 0.7%, 0.9%, 1%, 1.5%, 2% or any value therebetween, and the mass percentage of the first binder is 0.5%, 0.7%, 0.9%, 1%, 1.5%, 2% or any value therebetween.

[0039] In some embodiments, the dry electrode film further includes a first conductive agent, and the first conductive agent includes at least one of carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, graphene, and carbon fiber; based on the mass of the dry electrode film, the mass percentage of the first conductive agent is 0.5% to 6%. In some embodiments, based on the mass of the dry electrode film, the mass percentage of the first conductive agent is 0.5%, 0.7%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% or any value therebetween.

[0040] In some embodiments, the thickness of the dry electrode film is 60 μm to 250 μm. In some embodiments, the thickness of the dry electrode film is 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 250 μm or any value therebetween.

[0041] In some embodiments, the dry electrode film does not contain detectable processing solvents, processing solvent residues, or processing solvent impurities.

[0042] In some embodiments, the polymer layer includes a polymer, or includes a polymer and a second conductive agent, wherein the polymer includes at least one of polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, polyamide, polyimide, polyvinyl chloride, polystyrene, polyvinylidene fluoride, and polytetrafluoroethylene, and the second conductive agent includes at least one of carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, graphene, carbon fiber, copper nanoparticles, and silver nanoparticles.

[0043] In some embodiments, the composite current collector includes a polymer layer and a metal layer disposed on the surface of the polymer layer. Based on the mass of the polymer layer, the mass percentage of the polymer is 70% to 100%, and the mass percentage of the second conductive agent is 0% to 30%. In some embodiments, based on the mass of the polymer layer, the mass percentage of the polymer is 70%, 75%, 80%, 85%, 90%, 95%, 100% or any value therebetween, and the mass percentage of the second conductive agent is 0%, 5%, 10%, 15%, 20%, 25%, 30% or any value therebetween. The composite current collector in the present application includes a polymer layer and a metal layer disposed on the surface of the polymer layer. Compared with conventional foil current collectors (for example, conventional positive current collectors are aluminum foil or steel foil, and negative current collectors are copper foil), the composite current collector in the present application is lighter and has better flexibility, can improve the energy density, and at the same time can improve the safety - needle puncture performance of the secondary battery using the electrode sheet, bringing higher safety.

[0044] In some embodiments, the thickness of the polymer layer is 3 μm to 10 μm. In some embodiments, the thickness of the polymer layer is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any value therebetween.

[0045] In some embodiments, the active material is a positive electrode active material, and the metal layer includes at least one of aluminum foil, aluminum alloy, stainless steel foil, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0046] In some embodiments, the active material is a negative electrode active material, and the metal layer includes at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam and copper foam.

[0047] In some embodiments, the thickness of the metal layer is 0.5 μm to 5 μm. In some embodiments, the thickness of the metal layer is 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4.5 μm, 5 μm or any value therebetween.

[0048] In some embodiments, metal layers are disposed on opposite sides of the polymer layer, and a dry electrode film is disposed on each metal layer. Specifically, metal layers are disposed on opposite sides of the polymer layer, and a dry electrode film is disposed on each metal layer.

[0049] In some embodiments, the composite current collector further includes a carbon layer disposed on the metal layer, wherein the carbon layer includes at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene. In some embodiments, the thickness of the carbon layer is 0.5 μm to 8 μm. In some embodiments, the thickness of the carbon layer is 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value therebetween. In some embodiments, the carbon layer further includes a carbon layer binder, and the carbon layer binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid and its copolymers, polyacrylate, sodium carboxymethyl cellulose, and polyacrylonitrile. In some embodiments, based on the mass of the carbon layer, the mass percentage of the carbon layer binder is 5% to 45%. In some embodiments, based on the mass of the carbon layer, the mass percentage of the carbon layer binder is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any value therebetween. Thus, by disposing the carbon layer on the metal layer, the impedance (DCR) of the secondary battery can be reduced, and the cycle life of the secondary battery can be improved.

[0050] II. Preparation Method of Electrode Plate

[0051] The present application also provides a method for preparing an electrode plate. The electrode plate prepared by this method can be the electrode plate described above, and thus can have all the characteristics and advantages of the electrode plate described above. In some embodiments, the method includes:

[0052] S100: Provide a composite current collector and a dry electrode film, wherein the composite current collector includes a polymer layer and a metal layer disposed on the surface of the polymer layer, and the dry electrode film includes an active material and a binder;

[0053] S200: Form the dry electrode film on the surface of the metal layer of the composite current collector by hot pressing to obtain an electrode plate; wherein the linear pressure between the rollers during hot pressing is 0.01 t / cm to 0.5 t / cm.

[0054] In some embodiments, the linear pressure between the rollers during hot pressing is 0.01 t / cm, 0.05 t / cm, 0.1 t / cm, 0.15 t / cm, 0.2 t / cm, 0.25 t / cm, 0.3 t / cm, 0.35 t / cm, 0.4 t / cm, 0.45 t / cm, 0.5 t / cm, or any value therebetween.

[0055] In some embodiments, the surface temperature of the rollers during hot pressing is 20°C to 130°C. In some embodiments, the surface temperature of the rollers during hot pressing is 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, or any value therebetween.

[0056] In some embodiments, the roll spacing in the hot pressing process is greater than or equal to 20% of the thickness of the dry electrode film.

[0057] In some embodiments, the dry electrode film is formed by the following steps: mixing an active material and a binder to form a first mixture, subjecting the first mixture to a shearing process to form a second mixture, and subjecting the second mixture to a roll pressing process to obtain the dry electrode film. Thus, after the shearing process, a second mixture containing a fibrillatable binder can be obtained, wherein the fibrillatable binder includes polytetrafluoroethylene (PTFE).

[0058] In some embodiments, the linear velocity of the shearing process is 10 m / s to 80 m / s, and the shearing temperature is 30°C to 120°C. In some embodiments, the linear velocity of the shearing process is 10 m / s, 20 m / s, 30 m / s, 40 m / s, 50 m / s, 60 m / s, 70 m / s, 80 m / s, or any value therebetween, and the shearing temperature is 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or any value therebetween.

[0059] In some embodiments, the linear pressure between the rolls in the roll pressing process is 0.1 t / cm to 2 t / cm, the roll surface temperature is 30°C to 180°C, and the roll spacing is greater than or equal to 20% of the thickness of the dry electrode film. In some embodiments, the linear pressure between the rolls in the roll pressing process is 0.1 t / cm, 0.2 t / cm, 0.4 t / cm, 0.5 t / cm, 0.6 t / cm, 0.8 t / cm, 1 t / cm, 1.2 t / cm, 1.4 t / cm, 1.6 t / cm, 1.8 t / cm, 2 t / cm, or any value therebetween, and the roll surface temperature is 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 140°C, 160°C, 180°C, or any value therebetween.

[0060] In some embodiments, neither the preparation method of the dry electrode film nor the steps of the hot pressing process for forming the dry electrode film on the surface of the metal layer of the composite current collector use a solvent. That is to say, the dry electrode film and the hot pressing process do not contain detectable processing solvents, processing solvent residues, or processing solvent impurities.

[0061] III. Secondary battery

[0062] The present application also provides a secondary battery, which includes the above electrode tab or the electrode tab formed by the above preparation method. The secondary battery includes a positive electrode tab and a negative electrode tab. In the above electrode tab or the electrode tab formed by the above preparation method, if the active material is a positive electrode active material, it serves as the positive electrode tab of the secondary battery; and / or, in the above electrode tab or the electrode tab formed by the above preparation method, if the active material is a negative electrode active material, it serves as the negative electrode tab of the secondary battery.

[0063] In some embodiments, the secondary battery further includes an electrolyte. The electrolyte includes a lithium salt, an organic solvent, and an additive.

[0064] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium bis(fluoromalonic acid)borate (LiBFMB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorodioxalate phosphate, and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI).

[0065] In some embodiments, based on the mass of the electrolyte, the mass percentage of the lithium salt is 4% - 25%. In some embodiments, the mass percentage of the lithium salt is 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value therebetween. In some embodiments, the mass percentage of the lithium salt is 6% - 18%.

[0066] In some embodiments, the organic solvent includes at least one of a chain carbonate and a cyclic carbonate. In some embodiments, the chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and fluorinated chain carbonate. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate. In some embodiments, the organic solvent further includes a non-fluorinated carboxylic acid ester, and the non-fluorinated carboxylic acid ester is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone.

[0067] In some embodiments, based on the mass of the electrolyte, the mass percentage of the organic solvent is 40% to 80%. In some embodiments, the mass percentage of the solvent is 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or any value therebetween. In some embodiments, the mass percentage of the solvent is 50% to 70%.

[0068] In some embodiments, the additive includes at least one of vinylene carbonate (VC), ethylene ethylene carbonate, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), succinonitrile, adiponitrile, glutaronitrile and hexane trinitrile. In some embodiments, the additive further includes at least one of methylene methylene disulfonate (MMDS), ethylene ethyl disulfonate, 1,3-propane sultone (1,3-PS), 1-propene-1,3-sultone (PST), 1,4-butane sultone (1,4-BS), vinylene sulfate (DTD), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), propylene sulfate (TS), ethylene sulfite (DTO), dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0069] In some embodiments, based on the mass of the electrolyte, the mass percentage of the additive is 0.05% to 10%. In some embodiments, the mass percentage of the additive is 0.05%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween. In some embodiments, the mass percentage of the additive is 0.1% to 5%.

[0070] In some embodiments, a separator is provided between the positive electrode sheet and the negative electrode sheet to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0071] For example, the separator may include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the base material layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0072] A surface treatment layer is provided on at least one surface of the base material layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0073] The inorganic layer includes inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0074] The polymer layer contains a polymer. The materials of the polymer include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, and poly(vinylidene fluoride - hexafluoropropylene).

[0075] In some embodiments, the method for preparing a secondary battery includes providing an electrode assembly, injecting electrolyte, encapsulating, and forming. In some embodiments, the temperature for forming is 40°C to 50°C, such as 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, or 49°C.

[0076] In some embodiments, forming includes: charging at a current of 0.05C to 4.25V and standing for 60 min at a temperature of 40°C to 50°C, such as 45°C, and a pressure of 150 kgf to 250 kgf, such as 210 kgf, then charging at 0.1C to 4.25V, and then discharging at 0.2C to 3.0V.

[0077] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some examples, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium - ion secondary battery, a lithium - polymer secondary battery, or a lithium - ion polymer secondary battery.

[0078] In some embodiments, the secondary battery may include an outer package. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch - type soft package. The material of the soft package can be a plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0079] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other arbitrary shape.

[0080] In some embodiments, the present application further provides a battery module. The battery module includes the secondary battery described above. Since the battery module of the present application employs the above secondary battery, it has at least the same advantages as the secondary battery. The number of secondary batteries included in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0081] In some embodiments, the present application further provides a battery pack, which includes the above battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0082] IV. Device

[0083] The present application further provides a device, which includes at least one of the above secondary battery, battery module, and battery pack. Thus, the device can have all the features and advantages of the secondary battery, battery module, or battery pack described above, which will not be elaborated herein.

[0084] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. To meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be employed.

[0085] In some other embodiments, the device can be a mobile phone, a tablet computer, a laptop computer, etc. Such a device usually requires a thin and light design, and a secondary battery can be used as the power source.

[0086] Examples and Comparative Examples

[0087] Example 1

[0088] Preparation method of dry-process positive electrode sheet:

[0089] Mix the positive active material LiFePO4 (LFP), the conductive agent Super-P (conductive carbon black), and the first binder polyvinylidene fluoride PVDF, add the fibrillatable binder PTFE (polytetrafluoroethylene) particles and mix evenly. The weight ratio of LFP, Super-P, PVDF, and PTFE is 96:1.5:1.5:1. Subject the obtained mixture to high-speed shearing, control the shear linear velocity at 40 m / s, the shear temperature at 60 °C, and the shear time at 18 min to achieve the purpose of PTFE fibrillation. Subject the fibrillated mixture to hot roll pressing, with the roll surface temperature at 60 °C and the linear pressure at 0.5 t / cm, to obtain a self-supporting electrode film (dry electrode film); subject the obtained dry electrode film to hot pressing with a composite current collector (PET polymer layer, double-sided Al metal layer), with the linear pressure between the rolls at 0.4 t / cm and the roll surface temperature set at 70 °C, to prepare a dry-process positive electrode sheet (the dry electrode film is double-sided).

[0090] The preparation steps of the wet-process negative electrode sheet are as follows: add the negative electrode active material graphite (Gr), the conductive agent acetylene black, the binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose CMC-Na, and the polyacrylic acid PAA in a weight ratio of 95:2:1.5:1:0.5 to deionized water, and after sufficient homogenization, coat it on a 9μm thick copper current collector, and then obtain the negative electrode sheet through drying, rolling, hot pressing and other steps.

[0091] Preparation of electrolyte: In a glove box filled with argon (H2O < 0.1ppm, O2 < 0.1ppm), fully dissolve the lithium salt LiPF6 in a mixed solution of EC / DEC / EMC (ethylene carbonate / diethyl carbonate / ethyl methyl carbonate) = 25 / 20 / 55 to prepare a 1 mol / L solution, and stir evenly to obtain the electrolyte.

[0092] Diaphragm: PE diaphragm is used.

[0093] Preparation of lithium-ion secondary battery: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to obtain a bare cell. The bare cell is placed in a punched aluminum-plastic film soft package shell, and after being fully dried, the prepared electrolyte is injected. The theoretical capacity of the battery is 200mAh. After the battery is placed at 45°C for 48 hours, formed, and sealed for the second time, conventional capacity division is performed.

[0094] Embodiment 2-3

[0095] The other steps in Examples 2 to 3 are the same as those in Example 1, except that the type and mass percentage of the fiberizable adhesive, the type and mass percentage of the first adhesive, the line pressure between the rollers during the hot pressing treatment, the roller surface temperature during the hot pressing treatment, etc. are different, as shown in Table 1 for details.

[0096] Example 4

[0097] Preparation method of dry positive electrode sheet:

[0098] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2O2 (NCM), conductive agent Super-P (conductive carbon black), and the first binder PVDF are mixed, and fibrillatable binder PTFE (polytetrafluoroethylene) particles are added and uniformly mixed. The weight ratio of NCM, Super-P, PVDF, and PTFE is 96:1.5:1:1.5. The obtained mixture is subjected to high-speed shearing, controlling the shear linear velocity to be 40 m / s, the shear temperature to be 60 °C, and the shear time to be 18 min to achieve the purpose of PTFE fibrillation. The fibrillated mixture is subjected to hot roll pressing treatment, with the roll surface temperature of 60 °C and the linear pressure of 0.5 t / cm, to obtain a self-supporting electrode film (dry electrode film); the obtained dry electrode film is hot-pressed with a composite current collector (PET polymer layer, double-sided Al metal layer), with the linear pressure between the rolls being 0.4 t / cm and the roll surface temperature being set to 70 °C to prepare a dry-type positive electrode plate (the dry electrode film is double-sided).

[0099] The preparation steps of the wet-type negative electrode plate are as follows: The negative electrode active material graphite (Gr), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickening agent sodium carboxymethyl cellulose CMC-Na, and polyacrylic acid PAA are added to deionized water according to the weight ratio of 95:2:1.5:1:0.5, and after sufficient homogenization, it is coated on a 9-μm-thick copper current collector, and then obtained the negative electrode plate through steps such as drying, roll pressing, and hot pressing.

[0100] Preparation of the electrolyte: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium salt LiPF6 is fully dissolved in a mixed solution of EC / DEC / EMC (ethylene carbonate / diethyl carbonate / ethyl methyl carbonate) = 25 / 20 / 55 to prepare a 1 mol / L solution, and after stirring evenly, the electrolyte is obtained.

[0101] Separator: A PE separator is used.

[0102] Preparation of the lithium-ion secondary battery: The positive electrode plate, separator, and negative electrode plate prepared above are sequentially stacked layer by layer, with the separator in the middle of the positive electrode plate and the negative electrode plate to obtain a bare battery core. The bare battery core is placed in a cut aluminum-plastic film soft package shell, and after sufficient drying, the above-prepared electrolyte is injected. The theoretical battery capacity is 200 mAh. After the battery is left at 45 °C for 48 h, formed, and secondarily sealed, it is subjected to conventional capacity grading.

[0103] Examples 5 - 6

[0104] In Examples 5 - 6, other steps are the same as those in Example 4, except that the type and mass percentage of the fibrillatable binder, the type and mass percentage of the first binder, the linear pressure between the rolls during the hot pressing treatment, the roll surface temperature during the hot pressing treatment, etc. are different. See Table 1 for details.

[0105] Example 7

[0106] Preparation method of dry-process negative electrode sheet:

[0107] Mix the negative active material graphite (Gr), conductive agent Super-P (conductive carbon black), and the first binder polyethylene (PE). Add fibrillatable binder PTFE (polytetrafluoroethylene) particles and mix evenly. The weight ratio of graphite, Super-P, PE, and PTFE is 96.5:1.5:1.5:0.5. Subject the obtained mixture to high-speed shearing, control the shear linear velocity at 40 m / s, the shear temperature at 60 °C, and the shear time at 18 min to achieve the purpose of PTFE fibrillation. Subject the fibrillated mixture to hot roll pressing, with the roll surface temperature at 60 °C and the linear pressure at 0.5 t / cm, to obtain a self-supporting electrode film (dry electrode film); subject the obtained dry electrode film to hot pressing with a composite current collector (PET polymer layer, double-sided Cu metal layer), with the linear pressure between the rolls at 0.3 t / cm and the roll surface temperature set at 70 °C, to prepare a dry-process negative electrode sheet.

[0108] Preparation steps of wet-process positive electrode sheet: Mix the positive active material LiFePO4 (LFP), CNT / SuperP, and polyvinylidene fluoride (PVDF) in NMP at a weight ratio of 96:0.6 / 0.9:2.5. After sufficient homogenization, coat it on an aluminum current collector with a thickness of 12 μm, and then obtain the LFP positive electrode sheet through steps such as drying, roll pressing, and hot pressing.

[0109] Preparation of electrolyte: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), fully dissolve lithium salt LiPF6 in a mixed solution of EC / DEC / EMC (ethylene carbonate / diethyl carbonate / ethyl methyl carbonate) = 25 / 20 / 55 to prepare a 1 mol / L solution, and stir evenly to obtain the electrolyte.

[0110] Separator: Use a PE separator.

[0111] Preparation of lithium-ion secondary battery: Stack the positive electrode sheet, separator, and negative electrode sheet prepared above layer by layer in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet, to obtain a bare battery core. Place the bare battery core in a cut aluminum-plastic film soft package shell, and after sufficient drying, inject the electrolyte prepared above. The theoretical battery capacity is 200 mAh. After the battery is left at 45 °C for 48 h, formed, and secondarily sealed, it undergoes conventional grading.

[0112] Example 8

[0113] In Example 8, other steps are the same as those in Example 7, except that the type and mass percentage of the fibrillatable binder, the type and mass percentage of the first binder, the nip pressure during the hot pressing process, the surface temperature of the rollers during the hot pressing process, the preparation steps of the wet-process positive electrode sheet, etc. are different. Specifically, see Table 1. Among them, the preparation steps of the wet-process positive electrode sheet are as follows:

[0114] The preparation steps of the wet-process positive electrode sheet are: The positive active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM), CNT (carbon nanotube conductive agent) / Super-P (conductive carbon black), and the binder polyvinylidene fluoride PVDF are mixed in a weight ratio of LiNi 0.6 Co 0.2 Mn 0.2 O2:CNT / Super-P:PVDF = 97:(0.6 / 0.9):1.5 in N-methylpyrrolidone NMP. After sufficient homogenization, it is coated on an aluminum current collector with a thickness of 12 μm, and then an NCM positive electrode sheet is obtained through steps such as drying, rolling, and hot pressing.

[0115] Example 9

[0116] In Example 9, other steps are the same as those in Example 8, except that the type and mass percentage of the fibrillatable binder, the type and mass percentage of the first binder, the nip pressure during the hot pressing process, the surface temperature of the rollers during the hot pressing process, etc. are different. Specifically, see Table 1.

[0117] Comparative Example 1

[0118] In Comparative Example 1, other steps are the same as those in Example 1, except that the type and mass percentage of the fibrillatable binder, the type and mass percentage of the first binder, the nip pressure during the hot pressing process, the surface temperature of the rollers during the hot pressing process, the preparation method of the positive electrode sheet, etc. are different. Specifically, see Table 1. Among them, the preparation method of the positive electrode sheet is as follows:

[0119] The preparation steps of the wet-process positive electrode sheet are: The positive active material LiFePO4 (LFP), CNT / SuperP, and polyvinylidene fluoride PVDF are mixed in a weight ratio of 96:0.6 / 0.9:2.5 in NMP. After sufficient homogenization, it is coated on an aluminum current collector with a thickness of 12 μm, and then an LFP positive electrode sheet is obtained through steps such as drying, rolling, and hot pressing.

[0120] Comparative Example 2

[0121] In Comparative Example 2, other steps are the same as those in Example 1, except that the type and mass percentage of the fibrillatable binder, the type and mass percentage of the first binder, the line pressure between rolls during hot pressing, the roll surface temperature during hot pressing, the preparation method of the positive electrode sheet, etc. are different, as shown in Table 1 specifically. Among them, the preparation method of the positive electrode sheet is as follows:

[0122] The preparation steps of the wet-process positive electrode sheet are as follows: The positive active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM), CNT (conductive carbon nanotubes) / Super-P (conductive carbon black), and the binder polyvinylidene fluoride PVDF are in a weight ratio of LiNi 0.6 Co 0.2 Mn 0.2 O2:CNT / Super-P:PVDF = 97:(0.6 / 0.9):1.5. They are fully homogenized in N-methylpyrrolidone NMP and then coated on a composite current collector (PET polymer layer, double-sided Al metal layer). Subsequently, through steps such as drying, rolling, and hot pressing, an NCM positive electrode sheet is obtained.

[0123] Testing methods

[0124] 1. Peel strength test

[0125] Stick the surface of a 15-mm-wide electrode sheet to an aluminum plate with 3M double-sided tape. Clamp the lower end of the aluminum plate with the lower chuck of a tensile testing machine, and clamp the foil with the upper chuck. Use the 180° peeling method to test the tensile force, read the tensile force value, and calculate the peel strength. The moving speed of the upper chuck of the tensile testing machine is 50 mm / min.

[0126] 2. Tensile strength test

[0127] Clamp a 15-mm-wide electrode sheet between the upper and lower chucks of a tensile testing machine. The distance between the chucks is 10 mm. Start the tensile mode and automatically obtain the tensile strength value from the tensile program of the tensile testing machine.

[0128] 3. Compaction density test of the electrode sheet

[0129] The compaction density of the electrode sheet = the single-sided areal density of the electrode sheet (g / cm 2) / Thickness of one side (cm). Among them, the areal density of the electrode: Cut a piece of the electrode, weigh its mass and record it as M1. Then scrape off the active material layer on the electrode, weigh its mass and record it as M2, and measure the area of the electrode and record it as V. When the active material layer is coated on one side of the electrode, scrape off the active material layer on one side of the electrode. The areal density of one side of the electrode = (M1 - M2) / V, and the thickness of one side of the active material layer is the total thickness of the electrode minus the thickness of the current collector (such as a composite current collector); when the active material layer is coated on both sides of the electrode, scrape off the active material layer on both sides of the electrode. The areal density of one side of the electrode = (M1 - M2) / 2V, and the thickness of one side of the active material layer is the total thickness of the electrode minus the thickness of the current collector (such as a composite current collector) first, and then divided by 2. Among them, the mass can be weighed by a standard balance, and the thickness can be measured by a micrometer. When the electrode is a positive electrode, the active material layer is a positive electrode active material layer, and the active material is a positive electrode active material; when the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the active material is a negative electrode active material.

[0130] 4. Impedance Test

[0131] Discharge the lithium-ion battery at a constant current of 1C to 2.5V at 25 ± 2°C, then charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage of 4.2V to 0.05C, and then discharge it at a constant current of 1C to 50% SOC. Let it stand for 60 min, record the voltage U1 after the standing ends, then discharge it at a constant current of 2C for 10 s, record the voltage U2 after the discharge ends, record the 2C current as I, and let it stand for 60 min. Calculate the discharge DCR (impedance) of the battery at 50% SOC according to the formula DCR = (U1 - U2) / I.

[0132] 5. Test Method for Rolling Elongation Rate:

[0133] Take the dry-process electrode film and the current collector, with a length of 100 - 1000 mm, the lengths are L0 and L1 respectively, and the thicknesses are t0 and t1 respectively; set a constant rolling gap t2, the upper limit of the rolling pressure is 2000 N / cm; the rolling wire speed is 1 m / min; measure the length L2 of the dry-process electrode film after being pressed, where: L1 > L0 + 10; t2 = t0 / 2 + t1; the rolling elongation rate = (L1 - L0) / L0 * 100%.

[0134] Test Results

[0135] Table 1

[0136]

[0137] Table 2

[0138]

[0139]

[0140] It can be seen from Examples 1 to 9 and Comparative Examples 1 to 6 that the present application can achieve at least one of the following advantages by forming the dry electrode film and the composite current collector by hot pressing and compounding, and by controlling the compaction density of the dry electrode film and the peeling force between the dry electrode film and the composite current collector: First, the deformation of the pole piece is prevented, the pole piece quality and yield are improved; the overpressure deformation and distortion of the composite current collector is avoided. Second, the use of the composite current collector can improve the safety of the battery cell-acupuncture, and the composite current collector also brings higher energy density, higher safety performance, and lower cost to the dry-process pole piece. Third, the higher compaction density and better ductility of the dry electrode film itself are more matched with the ductility and processing characteristics of the composite current collector, avoiding the overpressure deformation and distortion of the composite current collector and deterioration due to long-term heating. Fourth, the hot pressing composite process between the dry electrode film and the composite current collector does not require excessive pressure, which avoids excessive ductility, deformation or damage to the dry electrode film or current collector layer caused by overpressure, affecting the pole piece yield.

[0141] By comparing comparative examples 1 to 3, it can be seen that the compaction density of the dry electrode film and the peeling force between the dry electrode film and the composite current collector do not satisfy the preset relationship, and the ratio of the compaction density to the peeling force is too large, resulting in excessive extension of the composite current collector, which ultimately leads to a decrease in the tensile strength of the electrode and a decrease in the battery DCR.

[0142] Comparing Comparative Examples 4 to 6, it can be seen that the rolling process of the hot pressing treatment of the wet-process electrode causes excessive elongation of the composite current collector, which ultimately leads to a decrease in the tensile strength of the electrode and a decrease in the battery DCR.

[0143] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. An electrode tab, characterized in that, Comprising: A composite current collector, the composite current collector comprising a polymer layer and a metal layer disposed on the surface of the polymer layer; A dry electrode film, the dry electrode film being disposed on the surface of the metal layer, the dry electrode film comprising an active material and a binder, the binder comprising a fibrillatable binder and a first binder; Among them, the compaction density of the dry electrode film is X g / cm 3 , and the peel force between the dry electrode film and the composite current collector is Y N / m, where 3 ≤ Y / X ≤ 14.

2. The electrode tab according to claim 1, characterized in that, 1.4 ≤ X ≤ 3.7; and / or, 3 ≤ Y ≤ 55.

3. The electrode tab according to claim 1 or 2, characterized in that, The rolling elongation rate of the dry electrode film is Z%, and the density of the active material is ρ g / cm 3 , where 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3, 0.2 ≤ Z ≤ 5.5, and 2 ≤ ρ ≤ 5.

4. The electrode tab according to claim 3, characterized in that, The active material is a positive electrode active material or a negative electrode active material, the positive electrode active material comprising at least one of a lithium nickel transition metal oxide and a phosphate; the electrode sheet further satisfies at least one of the following conditions: (a) The active material is a positive electrode active material, the positive electrode active material comprising a lithium nickel transition metal oxide; wherein, 3.4 ≤ X ≤ 3.7; and / or, 15 ≤ Y ≤ 55; and / or, 3 ≤ Y / X ≤ 14; and / or, 0.5 ≤ Z ≤ 4; and / or, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3; and / or, 4 ≤ ρ ≤ 5; and / or (b) The active material is a positive electrode active material, the positive electrode active material comprising a phosphate; wherein, 2.1 ≤ X ≤ 2.6; and / or, 8 ≤ Y ≤ 30; and / or, 3 ≤ Y / X ≤ 14; and / or, 0.2 ≤ Z ≤ 2.2; and / or, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3; and / or, 3 ≤ ρ ≤ 4; and / or (c) The active material is a negative electrode active material; wherein, 1.4 ≤ X ≤ 1.65; and / or, 3 ≤ Y ≤ 20; and / or, 3 ≤ Y / X ≤ 14; and / or, 2 ≤ Z ≤ 5.5; and / or, 0.1 ≤ (1 - X / ρ) × Z ≤ 1.3; and / or, 2 ≤ ρ ≤ 3.

5. The electrode tab according to claim 4, characterized in that, The lithium nickel transition metal oxide includes LiNi x Co y M (1-x-y) at least one of O2, M includes at least one of manganese, iron, chromium, titanium, zinc, vanadium, aluminum, zirconium, cerium, magnesium, calcium, molybdenum, strontium, tungsten, copper, yttrium, lanthanum, gallium, silver and niobium, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 < x + y ≤ 1; and / or The phosphate includes LiMn k B (1-k) at least one of PO4, where 0 ≤ k ≤ 1, and B includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead; and / or The negative electrode active material comprises at least one of a silicon-based material, a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium, wherein the silicon-based material comprises at least one of silicon, a silicon alloy, a silicon oxide compound, and a silicon carbide compound, the carbon-based material comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene, the tin-based material comprises at least one of tin, a tin oxide, and a tin alloy, the phosphorus-based material comprises phosphorus and / or a phosphorus complex; and / or Based on the mass of the dry electrode film, the mass percentage of the active material is 90% - 99%; and / or The fibrillatable binder comprises polytetrafluoroethylene; and / or The first binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, polyphenylene sulfide, polyethylene oxide, polypropylene, polyethylene, styrene-butadiene rubber, styrene-acrylonitrile copolymer, polyacrylonitrile, polyacrylate, and polyurethane; and / or The mass ratio of the fibrillatable binder to the first binder is 1:(0.25 - 4); and / or Based on the mass of the dry electrode film, the mass percentage of the fibrillatable binder is 0.5% - 2%, and the mass percentage of the first binder is 0.5% - 2%; and / or The dry electrode film further includes a first conductive agent, which includes at least one of carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, graphene, and carbon fiber; based on the mass of the dry electrode film, the mass percentage of the first conductive agent is 0.5% to 6%; and / or The thickness of the dry electrode film is 60 μm to 250 μm; and / or The dry electrode film does not contain detectable processing solvents, processing solvent residues, or processing solvent impurities.

6. The electrode tab according to claim 4 or 5, characterized in that, The polymer layer includes a polymer, or includes a polymer and a second conductive agent. Among them, the polymer includes at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, polyamide, polyimide, polyvinyl chloride, polystyrene, polyvinylidene fluoride, and polytetrafluoroethylene, and the second conductive agent includes at least one of carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, graphene, carbon fiber, copper nanoparticles, and silver nanoparticles; based on the mass of the polymer layer, the mass percentage of the polymer is 70% to 100%, and the mass percentage of the second conductive agent is 0% to 30%; and / or The active material is a positive electrode active material, and the metal layer includes at least one of aluminum foil, aluminum alloy, stainless steel foil, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; and / or The active material is a negative electrode active material, and the metal layer includes at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, and copper foam; and / or The thickness of the polymer layer is 3 μm to 10 μm; and / or The thickness of the metal layer is 0.5 μm to 5 μm; and / or The metal layers are provided on both opposite sides of the polymer layer, and the dry electrode films are provided on each of the metal layers; and / or The composite current collector further includes a carbon layer provided on the metal layer, where the carbon layer includes at least one of carbon nanotubes, carbon black, acetylene black, Ketjen black, and graphene, and the thickness of the carbon layer is 0.5 μm to 8 μm.

7. A method for preparing an electrode tab, characterized in that, Including: Providing a composite current collector and a dry electrode film, where the composite current collector includes a polymer layer and a metal layer provided on the surface of the polymer layer, and the dry electrode film includes an active material and a binder; Forming the dry electrode film on the surface of the metal layer of the composite current collector by hot pressing to obtain the electrode sheet; Among them, the line pressure between the rollers of the hot pressing is 0.01 t / cm to 0.5 t / cm.

8. The preparation method according to claim 7, wherein, The surface temperature of the roller of the hot pressing is 20 °C to 130 °C; and / or The distance between the rollers of the hot pressing is greater than or equal to 20% of the thickness of the dry electrode film; and / or The dry electrode film is formed through the following steps: mixing and processing the active material and the binder to form a first mixture, subjecting the first mixture to shearing treatment to form a second mixture, and subjecting the second mixture to roll pressing treatment to obtain the dry electrode film; wherein, the linear velocity of the shearing treatment is 10 m / s to 80 m / s, and the shearing temperature is 30 °C to 120 °C; the linear pressure between rolls of the roll pressing treatment is 0.1 t / cm to 2 t / cm, and the roll surface temperature is 30 °C to 180 °C; and / or Neither the preparation method of the dry electrode film nor the step of the hot pressing treatment in which the dry electrode film is formed on the surface of the metal layer of the composite current collector uses a solvent.

9. A secondary battery, wherein, It includes the electrode tab according to any one of claims 1 to 6 or the electrode tab formed by the preparation method according to any one of claims 7 to 8.

10. A device, wherein, It includes the secondary battery according to claim 9.

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