Electrode plate, secondary battery and electronic equipment

Abstract

The invention provides an electrode plate, a secondary battery and electronic equipment, the electrode plate comprises a current collector and electrode film layers, and the electrode film layers comprise a first electrode film layer and a second electrode film layer; the first electrode film layer is located on at least one surface of the current collector, and the first electrode film layer comprises a gel polymer; the second electrode film layer is located on the surface of the first electrode film layer away from the current collector; wherein the swelling degree of the gel polymer in the lithium salt solution is q, q is larger than or equal to 200% and smaller than or equal to 1500%, a solvent of the lithium salt solution is composed of ethylene carbonate and diethyl carbonate according to the mass ratio of 1: 1, and the concentration of lithium salt in the lithium salt solution is 1 mol / L. The secondary battery provided by the invention can give consideration to high energy density, high dynamic performance and high rate performance.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode sheet, a secondary battery, and an electronic device. Background Art

[0002] Lithium-ion batteries are widely used in digital electronic products, energy storage, drones, power tools, electric vehicles and other products due to their high energy density, long cycle life, high safety, fast charging ability and other characteristics. At present, the requirements for secondary batteries tend to be higher energy density. The ways to improve the energy density of secondary batteries mainly include positive and negative electrode main materials with high specific capacity and high tap density of positive and negative electrodes. When the theoretical specific capacity of the material is fully utilized, high tap density becomes an inevitable development trend for high-energy-density secondary batteries. However, high tap density reduces the pores between the main particles of the electrode sheet, reduces the liquid storage space of the electrode sheet, and the electrolyte free around the electrode sheet during the charge and discharge cycle of the secondary battery cannot be replenished in time, resulting in an increase in the electrolyte diffusion resistance in the later stage of the cycle, affecting the cycle performance of the secondary battery. Summary of the Invention

[0003] The present application provides an electrode sheet, a secondary battery, and an electronic device.

[0004] In a first aspect, the present application provides an electrode sheet, which includes a current collector and an electrode film layer. The electrode film layer includes a first electrode film layer and a second electrode film layer. The first electrode film layer is located on at least one surface of the current collector. The first electrode film layer includes a gel polymer. The second electrode film layer is located on the surface of the first electrode film layer away from the current collector. Wherein, the swelling degree of the gel polymer in the lithium salt solution is q, 200% ≤ q ≤ 1500%, the solvent of the lithium salt solution is composed of ethylene carbonate and diethyl carbonate according to a mass ratio of 1:1, and the concentration of the lithium salt in the lithium salt solution is 1 mol / L.

[0005] According to the embodiments of the present application, by adding a gel polymer to the first negative electrode film layer at the bottom layer of the electrode film layer, the gel polymer has a good adsorption effect on the electrolyte, and can adsorb and store the electrolyte in the spatial network structure of the gel polymer. Thus, the problem of lack of liquid at the bottom layer of the electrode sheet can be improved. And because the gel polymer has good liquid locking ability, it can make the bottom layer of the electrode sheet have a good electrolyte infiltration effect during the charge and discharge cycle of the secondary battery. Thus, the problem of insufficient embedding of active ions caused by lack of liquid at the bottom layer of the high-tap-density electrode sheet can be reduced, and the cycle performance of the secondary battery can be improved. At the same time, the electrolyte adsorbed and fixed in the spatial network structure of the gel polymer has a good contact and infiltration effect with the electrode active material, enabling the active ions to have a high transmission rate, thereby improving the kinetic performance of the secondary battery.

[0006] In some embodiments, 500% ≤ q ≤ 1000%. Thereby, the swelling rate of the secondary battery can be further reduced, while being beneficial to improving the cycling performance of the secondary battery.

[0007] In some embodiments, the peel strength between the electrode film layer and the current collector is F, and 10 N / m ≤ F ≤ 40 N / m. Thereby, the swelling stress of the electrode plate during the insertion / extraction of active ions can be evenly dispersed, the swelling of the secondary battery can be reduced, and at the same time, the risk of rupture and detachment of the electrode film layer can be reduced, and the cycling performance of the secondary battery can be improved.

[0008] In some embodiments, the Young's modulus of the standard gel film made of the gel polymer is E, and 0.012 MPa ≤ E ≤ 4 MPa. Thereby, the first electrode film layer can better disperse the swelling stress, reduce the swelling deformation of the electrode plate during the insertion / extraction of active ions, and further reduce the swelling rate of the secondary battery.

[0009] In some embodiments, based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W%, and 1 ≤ W ≤ 5. Thereby, the swelling stress of the first electrode film layer during the insertion / extraction of active ions can be better dispersed, and the cyclic swelling of the electrode plate can be reduced; at the same time, the first electrode layer can have a high active material content, enabling the secondary battery to have a high energy density.

[0010] In some embodiments, the gel polymer includes one or more of acrylic polymer gels, acrylate polymer gels, amide-functionalized polyolefin gels, polyethylene ether gels, polystyrene gels, and polyvinylpyrrolidone gels.

[0011] In some embodiments, the porosity of the first electrode film layer is Optionally, Thereby, the first electrode film layer can have a high tap density, and the first electrode film layer can have good electrolyte wettability, which is beneficial to enabling the secondary battery to have a high energy density while improving its cycling performance.

[0012] In some embodiments, the porosity of the second electrode film layer is Thereby, the electrode plate can have a better electrolyte wetting effect, and at the same time, the electrode plate can maintain an appropriate tap density, which is beneficial to further improving the kinetic performance and cycling performance of the secondary battery.

[0013] In some embodiments, the thickness of the first electrode film layer is H1, and the thickness of the second electrode film layer is H2, and H1 ≤ H2. Thereby, the electrode plate can take into account good wettability and a high tap density, which is beneficial to enabling the secondary battery to maintain a high energy density while having improved cycling performance.

[0014] In some embodiments, 0.2 ≤ H1 / H2 ≤ 1.

[0015] In some embodiments, the electrode sheet is a positive electrode sheet, and the tap density of the electrode sheet is PD1 g / cm 3 ; based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W1%, and 0.3 ≤ W1 / PD1 ≤ 1.1. This can make the gel polymer content in the first electrode film layer appropriate, further improve the electrolyte infiltration effect of the bottom layer of the positive electrode film, and improve the cycling performance of the secondary battery.

[0016] In some embodiments, the electrode sheet is a negative electrode sheet, and the tap density of the negative electrode sheet is PD2 g / cm 3 ; based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W2%, and 1 ≤ W2 / PD2 ≤ 4. This can make the gel polymer content in the first electrode film layer appropriate, further improve the electrolyte wettability of the bottom layer of the negative electrode film, and improve the cycling performance of the secondary battery.

[0017] In a second aspect, the present application provides a secondary battery including the electrode sheet according to the embodiments of the first aspect of the present application.

[0018] In a third aspect, the present application provides an electronic device including the secondary battery according to the embodiments of the second aspect of the present application. Detailed Embodiments

[0019] In the present specification, the embodiments or implementation manners are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

[0020] In the description of the present specification, the description of reference terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of the present application. In the present specification, the schematic expressions of the above terms do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0021] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0022] In the description of the present application, "normal temperature" refers to 10 - 35 °C.

[0023] In the present application, the battery may include a lithium-ion secondary battery, a lithium-ion primary battery, a lithium-sulfur battery, a sodium-lithium ion battery, a sodium-ion battery, a magnesium-ion battery, etc., and the embodiments of the present application do not limit this. The battery may be in a cylindrical shape, a flat shape, a cuboid shape or other shapes, etc., and the embodiments of the present application do not limit this either.

[0024] As described in the background art section, increasing the compaction density of the electrode sheet to improve the energy density of the secondary battery will result in poor electrolyte wettability of the electrode sheet, especially at the bottom layer of the electrode sheet (the position close to the current collector). Due to the reduction of porosity, the space for accommodating the electrolyte decreases, and it is difficult for the bottom layer of the electrode sheet to be sufficiently wetted by the electrolyte. An ion bridge break will form at the liquid-deficient area, and the polarization impedance will continuously increase, resulting in insufficient embedding of active ions in the bottom layer and precipitation of surface active ions, leading to the cycle decay of the secondary battery; in the later stage of cycling, due to the continuous increase in the diffusion resistance of the electrolyte, the transmission rate of active ions will become slower, affecting the kinetic performance of the secondary battery.

[0025] Based on this, the embodiments of the present application provide an electrode sheet. By adding a gel polymer with good liquid absorption and liquid locking functions to the bottom layer of the electrode sheet, the problem of liquid deficiency in the bottom layer of the electrode sheet can be improved, and further the cycle performance and kinetic performance of the secondary battery can be improved.

[0026] [Electrode Sheet]

[0027] The embodiments of the first aspect of the present application provide an electrode sheet, which includes a current collector and an electrode film layer. The electrode film layer includes a first electrode film layer and a second electrode film layer; the first electrode film layer is located on at least one surface of the current collector, and the first electrode film layer includes a gel polymer; the second electrode film layer is located on the surface of the first electrode film layer away from the current collector; wherein, the swelling degree of the gel polymer in the lithium salt solution is q, 200% ≤ q ≤ 1500%, the solvent of the lithium salt solution is composed of ethylene carbonate and diethyl carbonate according to a mass ratio of 1:1, and the concentration of the lithium salt in the lithium salt solvent is 1 mol / L.

[0028] In this application, a gel polymer refers to an organic polymer having a gel form. This organic polymer has a three-dimensional network structure in which media such as electrolytes can be accommodated. According to an embodiment of this application, by adding a gel polymer to a first negative electrode film layer located at the bottom layer of an electrode film layer, the gel polymer has a good adsorption effect on the electrolyte, and can adsorb and store the electrolyte in the three-dimensional network structure of the gel polymer. Thereby, the problem of liquid shortage at the bottom layer of the electrode plate can be improved. And because the gel polymer has good liquid locking ability, during the charge and discharge cycle of the secondary battery, the bottom layer of the electrode plate can have a good electrolyte infiltration effect. Thereby, the problem of insufficient embedding of active ions caused by liquid shortage at the bottom layer of the high-pressure dense electrode plate can be reduced, and the cycle performance of the secondary battery can be improved; at the same time, the electrolyte adsorbed and fixed in the three-dimensional network structure of the gel polymer has a good contact and infiltration effect with the electrode active material, enabling the active ions to have a high transmission rate, thereby improving the kinetic performance of the secondary battery.

[0029] In this application, the gel polymer can be obtained by polymerization of corresponding gel monomers. For example, the gel monomers can be added to the first negative electrode film layer, and then the gel polymer formed in the first negative electrode film layer through initiation of polymerization. It can be understood that the gel monomers in this application refer to organic small molecules that can be polymerized to form gel polymers, and the methods for initiating the polymerization of gel monomers can adopt methods known in the art, such as photo-initiated polymerization, thermal-initiated polymerization, initiator-initiated polymerization, etc.

[0030] In some embodiments, the swelling degree q of the gel polymer satisfies: 500% ≤ q ≤ 1000%. As an example, q can be 500%, 600%, 700%, 800%, 900%, 1000%, or a range composed of any of the above values.

[0031] According to an embodiment of this application, when the swelling degree of the gel polymer is within the above range, it has better liquid absorption and locking ability, can better adsorb and fix the electrolyte, and improve the electrolyte wettability of the bottom layer of the electrode plate; at the same time, the gel polymer can have higher mechanical strength, and can disperse the swelling stress during the insertion / extraction process of active ions. Thereby, the swelling rate of the secondary battery can be reduced, and at the same time, it is beneficial to improve the cycle performance of the secondary battery.

[0032] In some embodiments, the peel strength between the electrode film layer and the current collector is F, and 10 N / m ≤ F < 40 N / m. As an example, F can be 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, or a range composed of any of the above values. Optionally, 15 N / m ≤ F < 35 N / m.

[0033] According to the embodiments of the present application, when the peel strength between the electrode film layer and the current collector is within the above range, the electrode film layer and the current collector can have a relatively high bonding strength, so that the expansion stress of the electrode plate during the insertion / extraction of active ions can be evenly dispersed, the expansion of the secondary battery can be reduced, and at the same time, the risk of rupture and detachment of the electrode film layer can be reduced, and the cycle performance of the secondary battery can be improved.

[0034] It can be understood that the bonding performance of the gel polymer can be adjusted by changing parameters such as the type, molecular weight, and crosslinking degree of the gel polymer, and then the peel strength between the electrode film layer and the current collector can be adjusted.

[0035] In the present application, the peel strength between the electrode film layer and the current collector can be further calculated by measuring the force required to peel the negative electrode film layer from the negative electrode current collector, and can be determined by using methods and instruments known in the art. For example, a tensile testing machine can be used for determination.

[0036] In some embodiments, the Young's modulus of the standard adhesive film made of the gel polymer is E, and 0.02 MPa < E < 4 MPa. As an example, E can be 0.02 MPa, 0.05 MPa, 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, or a range composed of any of the above values. Optionally, E can be 0.05 MPa - 0.8 MPa.

[0037] According to the embodiments of the present application, when the Young's modulus of the standard adhesive film made of the gel polymer is within the above range, the gel polymer has a good ability to resist elastic deformation. Adding it to the first electrode film layer can enable the first electrode film layer to better disperse the expansion stress, thereby reducing the expansion deformation of the electrode plate during the insertion / extraction of active ions and further reducing the expansion rate of the secondary battery.

[0038] It can be understood that parameters such as the swelling degree and Young's modulus of the gel polymer can be adjusted by changing the structural data such as the type, molecular weight, crosslinking degree, and crystallinity of the gel polymer. In the embodiments of the present application, if parameters such as the swelling degree and Young's modulus of the gel polymer change, it can be considered that the above changes are made by adjusting at least one of the parameters such as the type, molecular weight, crosslinking degree, and crystallinity of the gel polymer.

[0039] In some embodiments, based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W%, and 1 ≤ W ≤ 5. As an example, W can be 1, 2, 3, 4, 5, or a range composed of any of the above values. Optionally, 2 ≤ W ≤ 4.

[0040] According to the embodiments of the present application, when the mass ratio of the gel polymer in the first negative electrode film layer is within the above range, the gel polymer can better disperse the swelling stress of the first electrode film layer during the insertion / extraction of active ions, reducing the cyclic swelling of the electrode tab; at the same time, the first electrode layer can have a high active material content, enabling the secondary battery to have a high energy density.

[0041] In some embodiments, the gel polymer may include one or more of acrylic polymer gels, acrylate polymer gels, amide-functionalized polyolefin gels, polyethylene ether gels, polystyrene gels, and polyvinylpyrrolidone gels.

[0042] It can be understood that the above-listed gel polymers may be the corresponding gel polymer bodies or derivatives of the corresponding gel polymers.

[0043] In some embodiments, the porosity of the first electrode film layer is As an example, it may be 25%, 22%, 20%, 18%, 15%, 12%, 10%, 8%, 5%, 3%, 2%, 1%, or a range composed of any of the above values. Optionally,

[0044] According to the embodiments of the present application, by limiting the porosity of the first electrode film layer within the above range, the first electrode film layer can have a high tap density, and the first electrode film layer can have good electrolyte wettability, which is beneficial to improving the cyclic performance of the secondary battery while enabling it to have a high energy density.

[0045] In some embodiments, when the electrode tab is a positive electrode tab, the porosity of the first electrode film layer is As an example, it may be 25%, 22%, 20%, 18%, 15%, 12%, 10%, 8%, 5%, 3%, 2%, 1%, or a range composed of any of the above values. Optionally,

[0046] In some embodiments, when the electrode tab is a negative electrode tab, the porosity of the first electrode film layer is As an example, it may be 25%, 22%, 20%, 18%, 15%, 12%, 10%, 8%, 5%, 3%, 2%, 1%, or a range composed of any of the above values. Optionally,

[0047] In some embodiments, the porosity of the second electrode film layer is As an example, It can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, or a range composed of any of the above values.

[0048] According to the embodiments of the present application, limiting the porosity of the second electrode film layer within the above range can enable the electrode sheet to have a better electrolyte infiltration effect, and at the same time, the electrode sheet can maintain an appropriate compaction density, which is beneficial to further improving the kinetic performance and cycling performance of the secondary battery.

[0049] In some embodiments, when the electrode sheet is a positive electrode sheet, the porosity of the second electrode film layer is As an example, when the electrode sheet is a positive electrode sheet, the porosity of the second electrode film layer It can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range composed of any of the above values.

[0050] In some embodiments, when the electrode sheet is a negative electrode sheet, the porosity of the second electrode film layer is As an example, when the electrode sheet is a negative electrode sheet, the porosity of the second electrode film layer It can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 38%, 40%, 42%, 45%, or a range composed of any of the above values. Optionally,

[0051] In some embodiments, the thickness of the first electrode film layer is H1, and the thickness of the second electrode film layer is H2, and H1 ≤ H2.

[0052] In some embodiments, 0.2 ≤ H1 / H2 ≤ 1. As an example, the value of H1 / H2 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a range composed of any of the above values. Optionally, 0.4 ≤ H1 / H2 ≤ 0.8.

[0053] According to the embodiments of the present application, when the ratio of the thicknesses of the first electrode film layer and the second electrode film layer is within the above range, the electrode sheet can take into account good wettability and a relatively high compaction density, which is beneficial to enabling the secondary battery to maintain a relatively high energy density while having improved cycling performance. When the value of H1 / H2 is relatively large, the proportion of the gel polymer in the electrode film layer is relatively high, resulting in a decrease in the energy density of the secondary battery; when the value of H1 / H2 is relatively small, the content of the bottom electrolyte is insufficient, and the electrolyte wettability of the bottom layer of the electrode sheet is poor, which is not conducive to the improvement of the cycling performance of the secondary battery.

[0054] When the electrode sheet is a positive electrode sheet, the thickness of the first electrode film layer is H 11, the thickness of the second electrode film layer is H 21 ; H 11 can satisfy: 16.4μm ≤ H 11 ≤ 48μm. As an example, H 11 can be 16.4μm, 16.5μm, 17μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 45μm, 48μm, or a range composed of any of the above values. Optionally, 20μm ≤ H 11 ≤ 45μm.

[0055] H 21 can satisfy: 46μm ≤ H 21 ≤ 81.6μm. As an example, H 21 can be 46μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 81μm, 81.5μm, 81.6μm, or a range composed of any of the above values. Optionally, 55μm ≤ H 21 ≤ 80μm.

[0056] When the electrode plate is a negative electrode plate, the thickness of the first electrode film layer is H 12 , and the thickness of the second electrode film layer is H 22 ; H 12 can satisfy: 15μm ≤ H 12 ≤ 45μm. As an example, H 12 can be 15μm, 20μm, 25μm, 0μm, 35μm, 40μm, 45μm, or a range composed of any of the above values. Optionally, 20μm ≤ H 12 ≤ 40μm.

[0057] H 22 can satisfy: 45μm ≤ H 22 ≤ 84μm. As an example, H 22 can be 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 84μm, or a range composed of any of the above values. Optionally, 50μm ≤ H 22 ≤ 80μm.

[0058] In this application, the thicknesses of the first electrode film layer and the second electrode film layer can be measured by methods and instruments known in the art. For example, it can be measured and analyzed by observing the cross-sectional SEM (scanning electron microscope) image of the negative electrode sheet, or a laser thickness gauge can also be used for measurement. In this application, the cross-section of the negative electrode sheet can be subjected to microscopic morphology detection, the interfaces between the layers in the negative electrode sheet can be observed, and then the thicknesses of the layers can be determined. In this application, the cross-section of the negative electrode sheet refers to the cross-section formed by slicing along the thickness direction of the negative electrode sheet. Instruments such as a focused electron beam (FIB) electron microscope (such as the FEI Scios2HiVa device, etc.) and an ion cross-section polisher (such as the IB-09010CP type argon ion cross-section polisher of JEOL Company, etc.) can be used to polish the cross-section to obtain a clear cross-section. In addition, the cross-section of the negative electrode sheet can also be observed for microscopic morphology and combined with composition analysis, such as energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) analysis, etc. to determine the element types to confirm the element composition in each layer of the negative electrode sheet.

[0059] It can be understood that the electrode sheet in this application can be a positive electrode sheet or a negative electrode sheet.

[0060] In some embodiments, the electrode sheet in the embodiments of this application is a positive electrode sheet, and correspondingly, the electrode film layer is a positive electrode film layer.

[0061] The tap density of the positive electrode sheet is PD1 g / cm 3 ; Based on the total mass of the first electrode film layer, the mass ratio of the gel polymer is W1%, and 0.3 ≤ W1 / PD1 ≤ 1.1. As an example, the value of W1 / PD1 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, or the range composed of any of the above numerical values. Optionally, 0.5 ≤ W1 / PD1 ≤ 0.9.

[0062] According to the embodiments of this application, limiting the ratio of the content of the gel polymer in the first electrode film layer to the tap density of the first electrode film layer within the above range can make the first electrode film layer have an appropriate content of the gel polymer, thereby better improving the electrolyte infiltration effect of the bottom layer of the positive electrode film layer and improving the cycle performance of the secondary battery.

[0063] In some embodiments, the tap density PD1 g / cm of the positive electrode sheet 3 can satisfy: PD1 ≥ 3. Optionally, 3.3 ≤ PD1 ≤ 4.8.

[0064] The positive electrode film layer includes a positive electrode active material.

[0065] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of their modified compounds, etc. Examples of the lithium-containing phosphate with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0066] It can be understood that when the electrode sheet is a positive electrode sheet, both the first electrode film layer and the second electrode film layer include the positive electrode active material, and the types of the positive electrode active material in the first electrode film layer and the second electrode film layer can be the same or different.

[0067] In some embodiments, the electrode sheet in the embodiments of the present application is a negative electrode sheet, and correspondingly, the electrode film layer is a negative electrode film layer.

[0068] The compaction density of the negative electrode sheet is PD2 g / cm3 ; Based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W2%, and 1 ≤ W2 / PD2 ≤ 4. As an example, the value of W2 / PD2 can be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or a range composed of any of the above values. Optionally, 1.5 ≤ W2 / PD2 ≤ 3.

[0069] According to the embodiments of the present application, limiting the ratio of the content of the gel polymer in the first electrode film layer to the compaction density of the first electrode film layer within the above range can make the first electrode film layer have an appropriate content of the gel polymer, thereby better improving the electrolyte wettability of the bottom layer of the negative electrode film layer and improving the cycling performance of the secondary battery.

[0070] In some embodiments, the compaction density PD2 of the negative electrode tab is g / cm 3 can satisfy: PD2 ≥ 0.8. Optionally, 1 ≤ PD2 ≤ 1.6.

[0071] The negative electrode film layer includes a negative electrode active material.

[0072] The negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0073] In some embodiments, the electrode film layer may further include a binder. The binder can be a commonly used binder in the art, and there is no specific limitation on the specific type.

[0074] As an example, the binder may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, hexafluoropropylene, tetrafluoropropylene, trifluoropropylene, hexafluorobutadiene, hexafluoroisobutene, trifluoroethylene, trifluorochloroethylene, polytetrafluoroethylene, hydroxyalkyl methyl cellulose, styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene. The alkyl group in the hydroxyalkyl methyl cellulose includes at least one of methyl, ethyl, propyl, and butyl.

[0075] In some embodiments, the electrode film layer may further include a conductive agent. The conductive agent can be a commonly used conductive agent in the art, and there is no specific limitation on the specific type.

[0076] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (single-walled carbon nanotubes, multi-walled carbon nanotubes or few-walled carbon nanotubes), graphene and carbon nanofibers.

[0077] In some embodiments, the current collector may include current collectors commonly used in the art, and there is no limitation on the specific type.

[0078] Exemplarily, the current collector may be a metal foil or a composite current collector. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] As an example, the electrode sheet is a positive electrode sheet and the current collector is an aluminum foil. As another example, the electrode sheet is a negative electrode sheet and the current collector is a copper foil.

[0080] It can be understood that when the electrode sheet is a negative electrode sheet, both the first electrode film layer and the second electrode film layer include a negative active material, and the types of the negative active material in the first electrode film layer and the second electrode film layer may be the same or different.

[0081] [Secondary battery]

[0082] Embodiments of the second aspect of the present application provide a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. At least one of the positive electrode sheet and the negative electrode sheet is the positive electrode sheet provided by the embodiments of the first aspect of the present application.

[0083] According to the present application, at least one of the positive electrode and the negative electrode of the secondary battery is the positive electrode sheet provided by the embodiments of the first aspect of the present application or the positive electrode sheet obtained by the preparation method of the second aspect of the present application. The electrode sheet has been described and explained in detail above and will not be repeated here. It can be understood that the secondary battery of the present application can achieve the beneficial effects of the second aspect and the third aspect of the present application.

[0084] Separator

[0085] The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through. The present application has no particular limitation on the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0086] In some embodiments, the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited thereto. Optionally, the material of the separator can include polyethylene and / or polypropylene. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the separator.

[0087] Electrolyte

[0088] The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The electrolyte that can be used in the secondary battery of the present application can be an electrolyte known in the prior art.

[0089] In some embodiments, the electrolyte can include an organic solvent, an electrolyte salt, and an optional additive. The types of the organic solvent, the lithium salt, and the additive are not specifically limited and can be selected according to requirements.

[0090] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte salt can include a lithium salt. As an example, the lithium salt includes but is not limited to at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDODFP (lithium difluoro(dioxalato)phosphate), and LiOTFP (lithium tetrafluoro(oxalato)phosphate). The above lithium salts can be used alone or two or more of them can be used simultaneously.

[0091] In some embodiments, the secondary battery is a sodium-ion battery, and the electrolyte salt can include a sodium salt. As an example, the sodium salt can be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0092] In some embodiments, by way of example, the organic solvent includes but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE). The above organic solvents can be used alone or two or more of them can be used simultaneously. Optionally, two or more of the above organic solvents are used simultaneously.

[0093] In some embodiments, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include additives that can improve certain battery performances, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0094] By way of example, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), propylene sulfate, ethylene sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0095] The electrolyte can be prepared by a conventional method in the art. For example, the organic solvent, the electrolyte salt, and the optional additive can be mixed uniformly to obtain the electrolyte. There is no particular limitation on the addition order of each material. For example, the electrolyte salt and the optional additive are added to the organic solvent and mixed uniformly to obtain the electrolyte; or, the electrolyte salt is first added to the organic solvent, and then the optional additive is added to the organic solvent and mixed uniformly to obtain the electrolyte.

[0096] [Preparation Method of Secondary Battery]

[0097] An embodiment of the third aspect of the present application provides a preparation method of a secondary battery, which can be used to prepare the secondary battery of the embodiment of the second aspect of the present application.

[0098] The preparation method of the secondary battery can include the following steps:

[0099] S100, respectively provide a first electrode paste containing a gel monomer and a second electrode paste without a gel monomer;

[0100] S200, use a dual - nozzle coater to simultaneously coat the first electrode paste and the second electrode paste on at least one surface of the current collector to form a first electrode film layer and a second electrode film layer, with the first electrode film layer located between the current collector and the second electrode film layer, and then obtain an electrode sheet after drying, cold pressing, and slitting;

[0101] S300, arrange the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator located between the positive electrode sheet and the negative electrode sheet, and wind to obtain a wound electrode assembly; or stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator located between the positive electrode sheet and the negative electrode sheet, to obtain a stacked electrode assembly; wherein, at least one of the positive electrode sheet and the negative electrode sheet is the electrode sheet prepared as above;

[0102] S400, place the electrode assembly in a housing, inject electrolyte and then encapsulate it, and let it stand at the initiation temperature to initiate the polymerization of the gel monomer; wherein, the electrolyte includes an initiator for initiating the polymerization of the gel monomer.

[0103] According to the embodiments of the present application, when preparing a secondary battery, by adding a gel monomer to the first negative electrode film layer, a raw material basis that can polymerize to form a gel polymer is introduced into the first negative electrode film layer. During the process of the electrolyte infiltrating the negative electrode sheet after injecting the electrolyte, the initiator contained in the electrolyte can initiate the polymerization of the gel monomer at the corresponding initiation temperature, and then form a gel polymer in the first negative electrode film layer. And because the gel monomer and the electrode active material are uniformly distributed in the first electrode film layer, the formed gel polymer can well coat the electrode active material, so that the electrode active material in the first electrode film layer is uniformly dispersed in the spatial network structure of the gel polymer. Thus, the gel polymer can better disperse the swelling stress of the electrode active material during the insertion / extraction process of active ions, reducing the swelling; at the same time, the electrolyte adsorbed in the spatial network structure of the gel polymer can better contact and infiltrate the electrode active material, improving the problem of lack of liquid at the bottom layer of the electrode sheet, making the electrode sheet have better electrolyte wettability, and further enabling the secondary battery to have both improved cycle performance and high energy density. Therefore, the preparation method provided by the third - aspect embodiments of the present application can be used to prepare the secondary battery of the second - aspect embodiments of the present application.

[0104] It can be understood that in the embodiments of the present application, the initiation temperature can be determined according to the specific type of the gel monomer, and different gel monomers may have different initiation polymerization temperatures.

[0105] As an example, the initiation temperature can be 50°C - 80°C. For example, the initiation temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or a range composed of any of the above values.

[0106] In some embodiments, the gel monomer can include one or more of acrylic acid and its derivatives, acrylate esters and their derivatives, amidated acrylic acid and its derivatives, amidated olefins and their derivatives, vinyl ethers and their derivatives, and vinyl pyrrolidone.

[0107] As an example, the gel monomer can include one or more of methyl methacrylate, acrylic acid, N-isopropylacrylamide, 2-hydroxyethyl methacrylate, N,N-dimethylacrylamide, 2-hydroxypropyl methacrylate, polyethylene glycol dimethacrylate, hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl acrylate, polyethylene glycol-picolinate, such as vinyl methyl ether, such as butyl acrylate, styrene, acrylamide, and vinyl pyrrolidone.

[0108] In some embodiments, the initiator can include one or more of azobisisobutyronitrile (AIBN), ammonium persulfate (APS), potassium persulfate (KPS), azobiscyclohexanecarbonitrile (ACCN), benzoyl peroxide (BPO), dicumyl peroxide (DCP), and di-tert-butyl peroxide (DTBP).

[0109] It can be understood that in the embodiments of the present application, the dosage of the initiator can be determined according to the content of the gel monomer respectively, so that the gel monomer in the electrode sheet is completely polymerized, and at the same time, the residual amount of the initiator in the electrolyte is minimized.

[0110] In some embodiments, based on the total mass of the electrolyte, the mass ratio of the initiator can be 0.1% - 0.5%. As an example, the mass ratio of the winner can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or a range composed of any of the above values.

[0111] [Electronic device]

[0112] An embodiment of the fourth aspect of the present application provides an electronic device, which includes the secondary battery of the embodiment of the third aspect of the present application or the secondary battery obtained by the preparation method according to the embodiment of the third aspect of the present application.

[0113] According to the present application, since the electronic device includes the secondary battery of any embodiment of the third aspect, the electronic device has the beneficial effects of the third aspect.

[0114] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0115] Embodiment

[0116] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation of the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0117] Sampling of electrode sheet

[0118] Under the condition of 25 °C, the secondary battery is discharged at a constant current of 0.5C until the discharge cut-off voltage. The lithium-ion battery is disassembled in an argon atmosphere, and the electrode plate is soaked in a dimethyl carbonate solvent for 2 h and dried at 60 °C for 1 h to obtain the negative electrode plate. Among them, the discharge cut-off voltage of the lithium-ion battery in the embodiments and comparative examples of the present application is 3.0V. It can be understood that when the voltage range marked on the outer package of the factory battery is 3.0V to 4.5V, the charge cut-off voltage is 4.5V and the discharge cut-off voltage is 3.0V. Unless otherwise specified, the charge cut-off voltage of the secondary battery as an example in the present application is 4.5V and the discharge cut-off voltage is 3.0V.

[0119] Unless otherwise specified, the following test methods are carried out using the electrode plates obtained in the above manner.

[0120] Test of peel strength F

[0121] The electrode plate is cut into a spline with a size of 100 mm × 20 mm and pasted on double-sided tape. The roller is rolled back and forth on the spline 4 times. One end of the spline is clamped on the tensile machine fixture, and it is stretched at 180 °C. The tensile machine is turned on for testing, and the electrode plate is pulled at a constant speed of 5 mm / min until the electrode film layer is peeled off from the current collector. When it is visually observed that the current collector surface is exposed after peeling, the test is completed, and the peeling strength of the electrode film layer is calculated after the test is completed.

[0122] Determination of compaction density of electrode film layer

[0123] Use a pole piece punching machine to punch the electrode film into small discs with a diameter of 14 mm. Take 10 small discs and weigh their mass, which is recorded as m1 (unit: g). Use a micrometer to test the thickness of the electrode film, and take the average value of the 10 thickness points, which is recorded as D1 (unit: cm). Calculate the compaction density PD (g / cm) of the electrode film according to the following formula: 3 )=m1×1540.25×100 / D1.

[0124] Determination of porosity of electrode film layer

[0125] Refer to the national standard GB / T24586-2009 "Determination of apparent density, true density and porosity of iron ore" test method, the equipment model used is: II 1340 fully automatic true density meter uses gas replacement method to test the porosity of electrode plates to obtain the overall porosity of electrode film layer. The second electrode film layer on the upper electrode film layer is peeled off to obtain the first electrode film layer, and then the porosity of the first electrode film layer is measured by the above method. Determination and calculation of the pores of the second electrode film layer using the density method

[0126] Determination of swelling degree of gel polymer

[0127] Sample preparation: Cut the gel film into a regular shape of 10×10 mm, with a thickness of 0.5 mm, ensuring thickness uniformity (deviation <5%). Weigh after drying ((W0), accurate to 0.1 mg);

[0128] Swelling process: The sample was completely immersed in a lithium salt solution (1 mol / L lithium hexafluorophosphate added to a solution of ethylene carbonate and diethyl carbonate mixed in a mass ratio of 1:1) at 25±0.5°C for 24 hours until swelling equilibrium was reached. After being taken out, the surface liquid was dried within 10 seconds and weighed (W1);

[0129] Calculation of swelling degree: The swelling degree was calculated according to the following formula: swelling degree q (%) = (W1-W0) / W0×100%. Three samples were tested in parallel in each group, and the average value was taken after eliminating the data with deviation >10%.

[0130] Determination of gel polymer content

[0131] Bisect the electrode film layer on the counter electrode tab in the thickness direction, and collect the part with the nearest half thickness to the surface of the counter electrode tab as the upper layer sample, and the remaining part as the lower layer sample. Refer to JY-T0589.5-2020 General Rules for Thermal Analysis Methods, and use a thermal analyzer to test the change of the mass of the electrode film layer powder with temperature. The model of the thermal analyzer equipment is STA449F3, using an N2 inert atmosphere, the test temperature is from 35°C to 600°C, the heating rate is 5°C / min, the purge gas flow rate is 60 mL / min, and the protective gas flow rate is 20 mL / min;

[0132] First, obtain the thermal decomposition temperature range T and mass loss m2 of the second electrode film layer (upper layer) sample (sample mass is M2), compare the mass decomposition curves of the first electrode film layer (lower layer) sample (sample mass is M1) at different temperatures, and take the mass loss m1 in the decomposition temperature range of 200°C - 450°C, and calculate the mass fraction W1(%) of the gel polymer = m1 / M1×100%. If T is within the range of 200°C - 450°C, then W1(%) = (m1 / M1 - m2 / M2)×100%.

[0133] Determination of gel polymer type

[0134] After fully discharging the secondary battery to 3V, take out the electrode assembly and put it into a centrifuge. Set the rotation speed to 4000 rpm and the running time to 10 min to centrifuge out the gel polymer swollen with the electrolyte. After collection, test the liquid chromatography. Through the functional group matching of the chromatograph, reverse the classification of the polymer, and then test the Young's modulus of this kind of substance.

[0135] Determination of Young's modulus of gel polymer

[0136] Adopt the tensile test method to make the gel polymer into a standard rubber film (25 mm×5 mm, the thickness is controlled within 0.5 mm - 2 mm, and the thickness deviation ≤5%). Conduct a vertical tensile test on a universal material testing machine, fix one end of the rubber film on the horizontal tabletop, and pull the other end perpendicular to the horizontal tabletop. The tensile rate is 5 mm / min, and measure and calculate the Young's modulus of the gel polymer.

[0137] Energy density test

[0138] At 25 °C, the length, width and thickness of the secondary battery are measured and the volume V (L) of the secondary battery is calculated; the lithium-ion secondary battery is charged at a constant current of 0.05C until the voltage reaches 4.50V (i.e., the full charge voltage), and then charged at a constant voltage of 4.5V until the current reaches 0.025C (the cut-off current) to make the lithium-ion battery reach the full charge state. The battery is left standing for 10 min, and then discharged at a rate of 0.2C until the voltage reaches 3.0V, and left standing for 5 min to obtain the discharge energy Q of the secondary battery. The volume energy density (Wh / L) of the secondary battery = Q / V.

[0139] Kinetic performance test

[0140] At 25 °C, the lithium-ion battery to be tested is charged at a constant current of 0.05C until the voltage reaches 4.50V (i.e., the full charge voltage), and then charged at a constant voltage of 4.5V until the current reaches 0.025C (the cut-off current) to make the lithium-ion battery reach the full charge state. The battery is left standing for 10 min, and then discharged at a rate of 0.2C until the voltage reaches 3.0V, and left standing for 5 min. At this time, the obtained discharge capacity is D ω . The lithium-ion battery to be tested is charged at a constant current of 0.05C until the voltage reaches 4.5V (i.e., the full charge voltage), and then charged at a constant voltage of 4.5V until the current reaches 0.025C (the cut-off current) to make the lithium-ion battery reach the full charge state. The battery is left standing for 10 min, and then discharged at a rate of 3.0C until the voltage reaches 3.0V, and left standing for 5 min. At this time, the obtained discharge capacity is D1. Then the 3C discharge rate = D1 / D0×100%.

[0141] Cycling performance test

[0142] At 25 °C, the secondary battery is charged at a constant current of 4C until 4.5V, then charged at a constant voltage of 4.5V until the current reaches 0.05C, and then discharged at a constant current of 0.5C until 3.0V. The charge and discharge cycle is carried out three times according to the above method, and the discharge capacity and the thickness of the secondary battery after the third cycle are recorded; continue the charge and discharge cycle, and record the discharge capacity and the thickness of the secondary battery after the 600th cycle.

[0143] Cycle capacity retention rate = (discharge capacity after 500 cycles / discharge capacity after 3 cycles) × 100%;

[0144] Swelling rate = (thickness of the secondary battery after 500 cycles / thickness of the secondary battery after 3 cycles) × 100%.

[0145] Example 1-1

[0146] Preparation of positive electrode sheet

[0147] Mix the cathode active material lithium cobalt oxide (LiCoO₂), conductive agent conductive carbon black, binder polyvinylidene fluoride (PVDF), and gel monomer methyl methacrylate in a mass ratio of 94.6:1.2:1.2:3, add them to the solvent N-methylpyrrolidone (NMP), control the solid content to be 70%, and stir and mix evenly to obtain the first cathode slurry;

[0148] Mix the cathode active material lithium cobalt oxide (LiCoO₂), conductive agent conductive carbon black, binder polyvinylidene fluoride (PVDF) in a mass ratio of 97.6:1.2:1.2, add them to the solvent N-methylpyrrolidone (NMP), control the solid content to be 70%, and stir and mix evenly to obtain the second cathode slurry;

[0149] Use a double-layer coating nozzle to spray the first cathode slurry on the surface of the cathode current collector aluminum foil, and spray the second cathode slurry on the surface of the first cathode slurry. After drying, form the first cathode film layer and the second cathode film layer respectively; through cold pressing and slitting, obtain the cathode pole piece. The size of the cathode pole piece is 42mm×49mm, and the total thickness of the coated cathode film layer is 108μm.

[0150] Preparation of negative electrode sheet

[0151] Mix the anode active material silicon-carbon composite material, conductive agent carbon nanotubes (multi-walled carbon nanotubes), binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, and gel monomer methyl methacrylate in a mass ratio of 94.3:0.2:1.3:1.2:3, and disperse them in deionized water to form the first anode slurry;

[0152] Mix the anode active material silicon-carbon composite material, conductive carbon nanotubes (multi-walled carbon nanotubes), binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose in a mass ratio of 97.3:0.2:1.3:1.2, and disperse them in deionized water to form the second anode slurry;

[0153] Use a double-layer coating nozzle to spray the first anode slurry on the surface of the anode current collector copper foil, and spray the second anode slurry on the surface of the first anode slurry. After drying, form the first anode film layer and the second anode film layer respectively; through cold pressing and slitting, obtain the anode pole piece. The size of the anode pole piece is 43mm×50mm, the total thickness of the anode film layer is 90μm, and the thickness ratio of the first anode film layer to the second anode film layer is 1:2.

[0154] Preparation of electrolyte

[0155] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a mass ratio of 20:30:20:28:2 to obtain an organic solvent. Then, lithium hexafluorophosphate, the above-prepared organic solvent, and the initiator azobisisobutyronitrile (AIBN) are mixed to form an electrolyte with a lithium salt concentration of 1 mol / L. Based on the total mass of the electrolyte, the mass proportion of the initiator in the electrolyte is 0.2%.

[0156] Preparation of separator

[0157] A polyethylene (PE) separator layer with a thickness of 7 μm is selected.

[0158] Preparation of secondary battery

[0159] The positive electrode plate, the separator, and the negative electrode plate are stacked in sequence, with the separator placed between the positive and negative electrode plates to play a role in isolation, obtaining a stacked electrode core with 14 layers of stacking, and the positive electrode plate is the outermost layer; after welding the electrode tabs, the bare electrode core is placed in an outer packaging foil aluminum-plastic film, dehydrated at 80 °C, then the electrolyte is injected and encapsulated, and after processes such as standing at room temperature for 48H, formation, standing at 60 °C for 24H, degassing, and shaping, a lithium-ion secondary battery is obtained. The thickness of the secondary battery body is 52 mm, the width is 57 mm, and the length is 75 mm.

[0160] Examples 1-2 to 1-16

[0161] Except for adjusting the parameters of the electrode plates according to Table 1, the rest are the same as those in Example 1-1.

[0162] Comparative Examples 1-1 to 1-2

[0163] Except for adjusting the parameters of the electrode plates according to Table 1, the rest are the same as those in Example 1-1.

[0164] Comparative Example 1-3

[0165] The difference from Example 1-1 is that: an equal mass of positive electrode active material is used to replace the gel polymer in the first positive electrode layer, and an equal mass of negative electrode active material is used to replace the gel polymer in the first negative electrode layer. See Table 1 for details, and the rest are the same as those in Example 1-1.

[0166]

[0167]

[0168]

[0169] Examples 2-1 to 2-8

[0170] Except for adjusting the parameters of the electrode sheet and the electrolyte according to Table 2, the rest are the same as in Example 1-1.

[0171] Table 2

[0172]

[0173] The test results of the secondary batteries in each example and comparative example are shown in Table 3 in detail.

[0174] Table 3

[0175]

[0176]

[0177] Referring to Tables 1 to 3, it can be seen from Examples 1-1 to 1-24, Examples 2-1 to 2-8, and Comparative Examples 1-1 to 1-3 that in the examples, the bottom layers of the positive electrode sheet and the negative electrode sheet both contain a gel polymer and the swelling degree of the gel polymer is within the range defined in the present application. There is a high peel strength between the positive electrode film layer and the negative electrode film layer and the current collector, which indicates that adding a gel polymer to the bottom layer of the electrode film layer can improve the bonding strength of the electrode film layer and reduce the risk of the electrode film layer falling off. At the same time, the 3C discharge rate, the capacity retention rate after 500 charge-discharge cycles, and the swelling of the secondary battery in the examples are all better than those in the comparative examples, which indicates that the secondary battery in the examples has improved kinetic performance and cycling performance compared with the comparative examples.

[0178] The swelling degree of the gel polymer affects the electrolyte wettability of the bottom layer of the electrode film layer, and further affects the rate performance of the secondary battery. Combining Examples 1-1 to 1-5 and Comparative Examples 1-1 and 1-2, it can be seen that when the swelling degree of the gel polymer is within the range defined in the present application, it is beneficial to maintain the structural integrity of the negative electrode sheet, the discharge rate and the cycle capacity retention rate of the secondary battery are relatively high, and the cycle expansion rate is low, indicating that the secondary battery has improved cycle performance and rate performance.

[0179] The porosity and the compaction density of the electrode film layer affect the electrolyte wettability and the ion transport rate of the electrode sheet, and further affect the rate performance and the cycle performance of the secondary battery. Combining Examples 1-6 to 1-14, it can be seen that when the porosity / compaction density of the positive electrode sheet and / or the negative electrode sheet is within the range defined in the present application, the secondary battery has a high energy density, and at the same time, the discharge rate and the cycle capacity retention rate of the secondary battery are relatively high, and the secondary battery has improved cycle performance and high rate performance.

[0180] The thickness of the electrode film layer also affects the electrolyte wettability of the electrode sheet and the ion transport rate, thereby affecting the rate performance and cycle performance of the secondary battery. Combining Examples 1-15 to 1-18, it can be seen that when the thickness of the positive electrode film layer / negative electrode film layer is within the scope of this application, the charging rate and cycle capacity retention rate of the secondary battery are both good, indicating that the secondary battery has high rate performance and improved cycle performance.

[0181] The content of the gel polymer in the electrode film layer affects the electrolyte wettability of the electrode sheet and the bonding performance of the electrode film layer on the surface of the current collector, thereby affecting the rate performance and cycle performance of the secondary battery. Combining Examples 1-19 to 1-24, when the content of the gel polymer in the positive electrode sheet / negative electrode sheet is within the scope defined in this application, the bonding strength between the electrode film layer and the current collector is high, and the energy density, discharge rate, and cycle capacity retention rate of the secondary battery are all high, indicating that the secondary battery takes into account high energy density, high rate performance, and improved cycle performance.

[0182] When preparing a secondary battery, the addition amount of the initiator in the electrolyte affects the polymerization degree of the gel polymer in the electrode film layer, thereby affecting the rate performance and cycle performance of the secondary battery. When the addition amount of the initiator is small, the gel monomers in the electrode film layer cannot be completely polymerized, the liquid retention effect of the electrode film layer is poor, and the rate performance of the secondary battery will decline; when the addition amount of the initiator is large, the proportion of the initiator in the electrolyte is high, and the proportion of the lithium salt and the additive decreases, resulting in a decline in the cycle performance of the secondary battery. Combining Example 1-1 and Examples 2-1 to 2-4, when the addition amount of the initiator in the electrolyte is within the scope of this application, the discharge rate and cycle capacity retention rate of the secondary battery are high, indicating that the secondary battery has improved cycle performance and high rate performance.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them; although the technical solutions of this application have been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrode sheet, characterized in that, The electrode tab includes a current collector and an electrode film layer, and the electrode film layer includes a first electrode film layer and a second electrode film layer; The first electrode film layer is located on at least one surface of the current collector, and the first electrode film layer includes a gel polymer; the second electrode film layer is located on the surface of the first electrode film layer away from the current collector; wherein, The swelling degree of the gel polymer in the lithium salt solution is q, 200% ≤ q ≤ 1500%, the solvent of the lithium salt solution is composed of ethylene carbonate and diethyl carbonate in a mass ratio of 1:1, and the concentration of the lithium salt in the lithium salt solution is 1 mol / L.

2. The electrode sheet according to claim 1, characterized in that, 500％≤q≤1000％。 3. The electrode sheet according to claim 1, wherein The peel strength between the electrode film layer and the current collector is F, 10 N / m ≤ F ≤ 40 N / m.

4. The electrode sheet according to claim 1, characterized in that, The Young's modulus of the standard gel film made of the gel polymer is E, 0.02 MPa ≤ E ≤ 4 MPa.

5. The electrode sheet according to claim 1, wherein Based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W%, 1 ≤ W ≤ 5.

6. The electrode sheet according to claim 1, wherein The gel polymer includes one or more of acrylic polymer gel, acrylate polymer gel, amide-functionalized polyolefin gel, polyvinyl ether gel, polystyrene gel, and polyvinylpyrrolidone gel.

7. The electrode sheet according to claim 1, characterized in that, The porosity of the first electrode film layer is Optionally, 8. The electrode sheet according to claim 1, characterized in that, The porosity of the second electrode film layer is 9. The electrode sheet according to claim 1, wherein The thickness of the first electrode film layer is H1, and the thickness of the second electrode film layer is H2, H1 ≤ H2.

10. The electrode sheet according to claim 9, characterized in that, 0.2 ≤ H1 / H2 ≤ 1.

11. The electrode sheet according to any one of claims 1-10, characterized in that, The electrode sheet is a positive electrode sheet, and the compaction density of the electrode sheet is PD1 g / cm 3 ; Based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W1%, and 0.3 ≤ W1 / PD1 ≤ 1.

1.

12. The electrode sheet according to any one of claims 1-10, characterized in that, The electrode plate is a negative electrode plate, and the compaction density of the negative electrode plate is PD2 g / cm 3 ; based on the total mass of the first electrode film layer, the mass percentage of the gel polymer is W2%, and 1 ≤ W2 / PD2 ≤ 4.

13. A secondary battery, characterized in that, Including the electrode tab according to any one of claims 1-12.

14. An electronic device, characterized in that, Including the secondary battery according to claim 13.

Images