Secondary battery, preparation method and battery pack

Abstract

The present invention provides a secondary battery, a method of manufacturing the same, and a battery pack, in a portion where a positive pole piece and a negative pole piece face each other, capacities of a negative active material and a positive active material are asymmetric, and a ratio N / P of a capacity N of the negative active material per unit area to a capacity P of the positive active material per unit area is less than 0.1. The problems that in the traditional battery field, fixed positive and negative electrode capacity design is difficult to meet requirements and is lack of flexibility are solved, the energy density and safety of the battery are improved, the cycle life of the battery is prolonged, high design flexibility and adaptability are provided, the battery is simplified, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a secondary battery, a preparation method and a battery pack. BACKGROUND

[0002] With the rapid development of renewable energy and electric vehicles, the requirements for battery performance are also increasing. In the field of traditional batteries, the matching degree of positive and negative electrode capacity is one of the important factors affecting battery performance. By reasonably designing and regulating the capacity ratio of positive and negative electrode materials (Negative / Positive, N / P), the optimization of battery capacity, energy density, cycle life and safety can be achieved, thereby promoting the progress of battery technology. The calculation formula of N / P is: N / P = negative surface density × active material ratio × active material specific discharge capacity / positive surface density × active material ratio × active material specific discharge capacity. Ideally, the positive and negative electrodes of the battery usually adopt symmetric capacity design, i.e. positive electrode capacity = negative electrode capacity, N / P = 1. In actual batteries, the symmetric design of positive and negative electrode capacity is affected by the following factors: ① positive and negative electrode material system: the charge and discharge platform, structural stability of the positive and negative electrode materials need to be considered; ② first efficiency of positive and negative electrode materials: all existing reactions, including conductive agent, binder, current collector, separator, and electrolyte, need to be considered. ③ Coating precision of equipment: ideal coating precision is 100%, if the coating precision is poor, it needs to be considered. ④ Attenuation rate of positive and negative electrode cycles: if the positive electrode attenuates quickly, the N / P ratio is designed to be lower, so that the positive electrode is in a shallow charge and discharge state, and vice versa if the negative electrode attenuates quickly, the N / P ratio is higher, so that the negative electrode is in a shallow charge and discharge state. ⑤ Rate performance to be achieved by the battery.

[0003] For the lithium ion battery using traditional graphite negative electrode or the sodium ion battery using hard carbon negative electrode, if the positive electrode capacity is excessive, the excessive lithium / sodium ions in the positive electrode cannot enter the negative electrode during charging, and lithium / sodium metal deposition is formed on the surface of the negative electrode to generate dendrites, which makes the battery cycle performance worse, and even causes internal short circuit of the battery, which leads to safety problems of the battery. Therefore, the negative electrode excess scheme is usually adopted. In this case, the capacity of the battery is limited by the positive electrode capacity, and the negative electrode capacity / positive electrode capacity ratio is greater than 1.0 (i.e. N / P ratio > 1.0). However, the negative electrode capacity cannot be excessive too much, because the excessive formation of SEI film (Solid Electrolyte Interphase) and other side reactions on the surface of the negative electrode will consume the active lithium in the positive electrode, resulting in the decrease of the initial coulombic efficiency; in addition, it will also cause the waste of negative electrode material, reduce the energy density of the battery, and increase the cost of the battery. Therefore, the capacity ratio of the positive electrode and the negative electrode needs to be accurately designed, which is generally between 1.03 and 1.5. However, for the battery using lithium titanate negative electrode, since the structure of lithium titanate is relatively stable, it has a high voltage platform, excellent cycle performance and will not cause lithium precipitation, the main reason for cycle failure is in the positive electrode end, and the design of the battery system can adopt the design method of slightly excessive positive electrode capacity and limited negative electrode capacity, and the N / P ratio is generally between 0.85 and 0.9. Therefore, in the traditional battery, the N / P ratio is generally 1±0.15, and the capacity of the positive electrode and the negative electrode is generally symmetrically designed. However, due to the complexity of the battery material system, the symmetric matching design of the capacity of the positive electrode and the negative electrode is a complex systematic engineering. In addition, in the actual application process of the battery, the charging and discharging mode and the use environment are complex and changeable, and the existing fixed capacity design of the positive electrode and the negative electrode cannot meet the requirements, and lacks flexibility. SUMMARY

[0004] The embodiments of the present application aim at the problems of the existing symmetric design of the capacity of the positive electrode and the negative electrode of the battery, the complex preparation method and the lack of flexibility, and provide a secondary battery with asymmetric capacity of the positive electrode and the negative electrode, a preparation method, a battery pack and an application. The energy density, safety and cycle life of the battery are improved, and high design flexibility and adaptability are provided, and the battery is simplified and the production cost is reduced.

[0005] To achieve the above-mentioned purpose, the technical solutions adopted by the embodiments of the present application are as follows:

[0006] In a first aspect, the embodiments of the present application provide a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and the negative electrode sheet and holds electrolyte.

[0007] In the part where the positive electrode sheet and the negative electrode sheet are opposite to each other, the capacity of the negative electrode active material and the positive electrode active material is asymmetric.

[0008] Preferably, the capacity per unit area of the negative active material N is in a ratio of ≤0.1 relative to the capacity per unit area of the positive active material P.

[0009] Preferably, the mass ratio of the positive active material to the negative active material is 5-200, and the thickness ratio of the positive electrode sheet to the negative electrode sheet is 2.5-20.

[0010] Preferably, the thickness of the positive electrode sheet is 50-500 μm, and the loading of the positive active material in the positive electrode sheet is 5-50 mg / cm 2 .

[0011] Preferably, the positive active material comprises one or more of sodium phosphite, sodium iron phosphate, sodium pyrophosphate iron phosphate, sodium pyrophosphate iron, sodium manganese oxide, sodium cobalt oxide, sodium iron oxide, fluorinated sodium phosphite, sodium iron sulfate, sodium nickel manganese oxide, sodium iron cobalt oxide, and sodium nickel cobalt manganese oxide.

[0012] Preferably, the positive electrode sheet further comprises a binder and a conductive agent.

[0013] Preferably, the negative electrode sheet is a porous structure for accommodating sodium metal deposited during charging of the battery, and the thickness of the negative electrode sheet is determined by the loading or the compaction density and thickness of the positive electrode sheet. Specifically, the thickness of the negative electrode sheet is ≥ positive active material surface loading × positive electrode sheet area × positive active material gram capacity × initial efficiency ÷ sodium metal specific capacity ÷ sodium metal density ÷ negative electrode sheet area ÷ negative electrode porosity; the thickness of the negative electrode sheet is ≥ positive active material compaction density × positive electrode sheet area × positive thickness × positive active material gram capacity × initial efficiency ÷ sodium metal specific capacity ÷ sodium metal density ÷ negative electrode sheet area ÷ negative electrode porosity; and the loading of the negative electrode sheet is ≤ positive active material surface loading × positive electrode sheet area × positive active material gram capacity × initial efficiency × 10% ÷ negative electrode specific capacity ÷ negative electrode area.

[0014] Preferably, the negative active material comprises a carbon material, and one or more of a metal, an alloy of a metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of a metal;

[0015] The carbon material comprises one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotube, carbon fiber, graphene, graphite, mesocarbon microbead, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon.

[0016] The metal comprises one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, and Ga.

[0017] Preferably, the negative electrode sheet is loaded by doctor blading, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation or 3D printing.

[0018] In a third aspect, an embodiment of the present application provides a preparation method of a secondary battery, comprising:

[0019] In step S1, a positive electrode active material, a conductive agent and a binder are mixed and stirred according to a preset first mass ratio, a solvent is added, and a positive electrode slurry is prepared; the positive electrode slurry is uniformly coated on two surfaces of a positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with the positive electrode slurry on both sides; the solvent is preferably N-methyl pyrrolidone or deionized water; the solid content of the positive electrode slurry is preferably 40-90wt%, more preferably 75wt%.

[0020] In step S2, a negative electrode active material and a binder are mixed and stirred according to a preset second mass ratio, a solvent is added, and a negative electrode slurry is prepared; the negative electrode slurry is uniformly coated on two surfaces of a negative electrode current collector aluminum foil to obtain a negative electrode sheet coated with the negative electrode slurry on both sides; the solvent is preferably deionized water or N-methyl pyrrolidone; the solid content of the negative electrode slurry is preferably 10-60wt%, more preferably 45wt%.

[0021] In step S3, the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked with the separator between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet and the negative electrode sheet are stacked in multiple layers or wound to obtain an electrode assembly; the electrode assembly is loaded into a housing assembly, and water is removed again, and the prepared electrolyte is injected, and the secondary battery is obtained through vacuum packaging, standing, formation and shaping processes. The number of stacked layers of the positive electrode sheet and the negative electrode sheet is selected according to actual conditions, and is preferably 2-50, more preferably 10 layers.

[0022] In a third aspect, an embodiment of the present application provides a battery pack comprising the secondary battery according to the first aspect of the present application.

[0023] The embodiment of the present application provides a secondary battery with a positive electrode capacity much higher than a negative electrode capacity, and the battery capacity is derived from the positive electrode. The negative electrode sheet has a porous structure for accommodating deposited sodium metal during charging of the battery, and provides a physical storage space for active sodium on the positive electrode side during deposition on the negative electrode side. When the thickness ratio of the positive electrode to the negative electrode is greater than 2.5, stable cycling of the secondary battery can be achieved, and the cycle life reaches 10,000 times.

[0024] The preparation method of the secondary battery provided by the embodiment of the present application overcomes the problem that the fixed positive and negative electrode capacity design in the conventional battery field is difficult to meet the requirements and lacks flexibility, improves the energy density, safety and cycle life of the battery, and provides high design flexibility and adaptability, simplifies the battery and reduces the production cost.

[0025] The battery pack comprising the secondary battery with asymmetric positive and negative electrode capacity provided by the embodiment of the present application has the same advantages of the secondary battery, and can meet the use requirements in the fields of renewable energy, consumer electronics and electric vehicles. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the secondary battery prepared by the embodiment 1 of the present application. DETAILED DESCRIPTION

[0027] The following non-limiting examples can make those skilled in the art more fully understand the present application, but do not limit the present application in any way. The following content is only an exemplary description of the scope of the present application, and those skilled in the art can make various changes and modifications to the present application according to the disclosed content, which should also belong to the scope of the present application claimed.

[0028] When the embodiment gives a numerical range, it should be understood that, unless otherwise stated by the present application, each numerical range and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0029] The present application will be further described in the following specific embodiments. The various chemical reagents used in the embodiments of the present application are obtained by conventional commercial routes unless otherwise specified.

[0030] In the conventional battery, the N / P ratio is generally 1±0.15, usually not more than 2, and the positive and negative electrode capacity is symmetrically designed. However, due to the complex battery material system, the symmetric matching design of the positive and negative electrode capacity is a complex systematic engineering. In addition, the charging and discharging mode and the complex and changeable use environment of the battery in the actual application process, the existing fixed positive and negative electrode capacity design is difficult to meet the requirements and lacks flexibility.

[0031] Therefore, the embodiment of the present application provides a secondary battery, a preparation method and a battery pack, which overcomes the problem that the fixed positive and negative electrode capacity design in the conventional battery field is difficult to meet the requirements and lacks flexibility, improves the energy density, safety and cycle life of the battery, and provides high design flexibility and adaptability, simplifies the battery and reduces the production cost.

[0032] In the embodiment of the application, the positive and negative electrode capacities of the secondary battery are asymmetric, the positive electrode capacity is much higher than the negative electrode capacity, and the N / P ratio is ≤0.1; the battery capacity is derived from the positive electrode, and the negative electrode mainly provides physical storage space for the active sodium on the positive electrode side when the active sodium is deposited on the negative electrode side; the mass ratio of the active materials of the positive electrode plate and the negative electrode plate is between 5-200, and the thickness ratio is between 2.5-20; preferably, the thickness of the positive electrode plate is 30-500 μm, and the loading of the positive electrode active material in the positive electrode plate is 2-50 mg / cm 2 The negative electrode plate is a porous structure for accommodating the deposited sodium metal during charging of the battery, and the thickness of the negative electrode plate is determined by the loading or the compaction density and thickness of the positive electrode plate. The positive electrode active material includes one or more of sodium phosphite, sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium manganese oxide, sodium cobalt oxide, sodium iron oxide, sodium phosphite fluoride, sodium iron sulfate, sodium nickel manganese oxide, sodium iron cobalt oxide, and sodium nickel cobalt manganese oxide. The positive electrode plate further includes a binder and a conductive agent. The negative electrode plate is a porous structure for accommodating the deposited sodium metal during charging of the battery, and the thickness of the negative electrode plate is determined by the loading or the compaction density and thickness of the positive electrode plate. The negative electrode active material includes a carbon material, and one or more of a metal, an alloy of a metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of a metal; the carbon material includes one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotubes, carbon fibers, graphene, graphite, mesocarbon microbeads, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon; the metal includes one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, Ga. The negative electrode plate is loaded by scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing.

[0033] Example 1

[0034] The embodiment provides a preparation method of a secondary battery, including:

[0035] Step S1, preparing the positive electrode sheet, the positive electrode active material (in this embodiment, sodium vanadium phosphate is selected), the conductive agent Super P, and the binder polyvinylidene difluoride (PVDF) are weighed according to the mass ratio of 97.5:1.0:1.5 (for example, 97.5 g of sodium vanadium phosphate, 1.0 g of Super P, and 1.5 g of PVDF), and then added into a 2L stirring tank for mechanical mixing. Subsequently, N-methylpyrrolidone (NMP) is added as a solvent to prepare a positive electrode slurry with a solid content of 75%, and the mixture is stirred for 2 hours to ensure uniform dispersion. Then, the stirred positive electrode slurry is uniformly coated on one surface of an aluminum foil positive electrode current collector with a thickness of 12 μm, and dried at 100°C to obtain a positive electrode sheet coated with a single layer of the positive electrode slurry (sodium vanadium phosphate). The surface loading of sodium vanadium phosphate on the positive electrode sheet is 14.0 mg / cm2, and the thickness of the dry film of the positive electrode sheet is measured to be 120 μm. The above steps are repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with a double layer of the positive electrode slurry (sodium vanadium phosphate). The positive electrode sheet is cold-pressed and cut into a 56 mm x 43 mm size for use.

[0036] Step S2, preparing the negative electrode sheet, the porous material coconut activated carbon, the conductive carbon, and the binder (carboxymethylcellulose sodium (CMC-Na) and polymerized styrene butadiene rubber (SBR)) are weighed according to the mass ratio of 85:5:5:5 (for example, 85 g of coconut activated carbon, 5 g of conductive carbon, 5 g of CMC-Na, and 5 g of SBR), and then added into a 2L stirring tank for mechanical mixing. Deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 45%, and the mixture is stirred for 2 hours to ensure uniform dispersion. The stirred negative electrode slurry is uniformly coated on one surface of an aluminum foil negative electrode current collector with a thickness of 12 μm, and dried at 80°C to obtain an electrode sheet coated with a single layer of the porous coconut activated carbon slurry. The surface loading of coconut activated carbon on the negative electrode sheet is 0.15 mg / cm2, and the thickness of the dry film of the negative electrode sheet is measured to be 21 μm. The above steps are repeated on the other surface of the negative electrode sheet to obtain an electrode sheet coated with a double layer of the porous coconut activated carbon slurry. After the coating is completed, the electrode sheet is cut into a 58 mm x 45 mm size for use. Unlike the positive electrode sheet, the negative electrode sheet does not undergo a rolling operation. 2

[0037] ​Step S3, preparation of electrolyte, in a glove box with dry argon atmosphere (H2O < 0.01 ppm, O2 < 0.01 ppm), organic solvents ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether after water removal with molecular sieves were mixed in a volume ratio of 1:1:2, then sodium salt sodium hexafluorophosphate (NaPF6) was added to the mixed organic solvent to dissolve and mix uniformly, to obtain an electrolyte with a sodium salt concentration of 1 mol / L, on this basis, 1 vol% FEC (Fluoroethylene carbonate) was added.

[0038] The separator was a polyethylene (PE) film with a thickness of 15 μm (provided by Celgard). The packaging material was a 113 μm aluminum-plastic composite film.

[0039] Preparation of a secondary battery, the positive electrode sheet, the separator and the negative electrode sheet prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role. After stacking 10 layers of positive and negative electrodes, an electrode assembly was obtained. The electrode assembly was loaded into an aluminum-plastic composite film, and water was removed at 80°C. The prepared electrolyte was injected, and vacuum packaging, standing, formation, shaping and other processes were carried out to obtain a soft-packaged secondary battery, as shown in Figure 1 .

[0040] Example 2

[0041] In this example, the positive electrode sheet, the electrolyte, and the preparation of the separator and the secondary battery were the same as in Example 1. Different from Example 1, the negative electrode sheet was prepared as follows:

[0042] Coconut shell activated carbon, magnesium oxide, conductive carbon, sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) were weighed according to a mass ratio of 85:5:5:1:4 (e.g. 85 g of coconut shell activated carbon, 5.0 g of MgO, 5 g of conductive carbon, 1 g of CMC and 4 g of SBR), added into a 2 L stirring tank for mechanical mixing, and deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 55%. The stirring was continued for 2 hours to ensure uniform dispersion. The stirred negative electrode slurry was uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm, and dried at 80°C to obtain a negative electrode sheet with a single-side coated porous coconut shell activated carbon slurry. The surface area load of the porous coconut shell activated carbon and magnesium oxide composite coating was 0.21 mg / cm 2 , and the thickness of the dry film of the negative electrode sheet was measured to be 18 μm. Then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-side coated porous coconut shell activated carbon slurry. After coating, the negative electrode sheet was cut into a size of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet did not undergo a rolling operation.

[0043] Example 3

[0044] In this embodiment, the negative electrode sheet, electrolyte, separator and secondary battery are prepared as in Example 1, except that the positive electrode sheet is prepared as follows:

[0045] The positive electrode active material sodium vanadium phosphate, conductive agent Super P and binder polyvinylidene fluoride (PVDF) are weighed in a mass ratio of 97.5:1.0:1.5 (for example, sodium vanadium phosphate 97.5 g, Super P 1.0 g, PVDF 1.5 g), and then added to a 2 L stirring tank for mechanical mixing. N-methyl pyrrolidone (NMP) is then added as a solvent in two portions to prepare a slurry with a solid content of 75%, and the mixture is stirred for 2 hours to ensure uniform dispersion. The stirred positive electrode slurry is then uniformly coated on one surface of an aluminum foil positive electrode current collector with a thickness of 12 μm, and dried at 100°C to obtain a positive electrode sheet coated with the positive electrode slurry on one surface. The surface loading of sodium vanadium phosphate on the positive electrode sheet is 28.0 mg / cm 2 The thickness of the dry film of the positive electrode sheet is measured to be 240 μm. The above steps are then repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with sodium vanadium phosphate on both surfaces. The positive electrode sheet is cold-pressed and cut into a 56 mm x 43 mm size for use.

[0046] Example 4

[0047] In this embodiment, the negative electrode sheet, electrolyte, separator and secondary battery are prepared as in Example 1, except that the positive electrode sheet is prepared as follows:

[0048] The positive electrode active material sodium vanadium phosphate, conductive agent Super P and binder polyvinylidene fluoride (PVDF) are weighed in a mass ratio of 97.5:1.0:1.5 (for example, sodium vanadium phosphate 97.5 g, Super P 1.0 g, PVDF 1.5 g), and then added to a 2 L stirring tank for mechanical mixing. N-methyl pyrrolidone (NMP) is then added as a solvent to prepare a slurry with a solid content of 75%, and the mixture is stirred for 2 hours to ensure uniform dispersion. The stirred positive electrode slurry is then uniformly coated on one surface of an aluminum foil positive electrode current collector with a thickness of 12 μm, and dried at 100°C to obtain a positive electrode sheet coated with the positive electrode slurry on one surface. The surface loading of sodium vanadium phosphate on the positive electrode sheet is 7.0 mg / cm 2 The thickness of the dry film of the positive electrode sheet is measured to be 60 μm. The above steps are then repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with sodium vanadium phosphate on both surfaces. The positive electrode sheet is cold-pressed and cut into a 56 mm x 43 mm size for use.

[0049] Example 5

[0050] In this embodiment, the positive electrode sheet, electrolyte, and separator and the preparation of the secondary battery are the same as in Example 4, except that the negative electrode sheet is prepared as follows:

[0051] The porous material coconut activated carbon, conductive carbon, binder (carboxymethyl cellulose sodium (CMC-Na) and polymerized styrene butadiene rubber (SBR)) were weighed according to the mass ratio of 85:5:2:3 (e.g. 85 g of coconut activated carbon, 5 g of conductive carbon, 2 g of CMC-Na, and 3 g of SBR), and then added to a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 60%, and the mixture was stirred for 2 hours to ensure uniform dispersion. The stirred negative electrode slurry was uniformly coated on one surface of a negative current collector aluminum foil with a thickness of 12 μm, and then dried at 80°C to obtain a single-sided porous coconut activated carbon slurry-coated electrode sheet with a surface loading of 1.29 mg / cm2. The thickness of the dry film of the negative electrode sheet was measured to be 24 μm. Subsequently, the above steps were repeated on the other surface of the negative electrode sheet to obtain a double-sided porous coconut activated carbon slurry-coated electrode sheet. After coating, the electrode sheet was cut into a size of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet was not subjected to a rolling operation.

[0052] Example 6

[0053] In this embodiment, the electrolyte, and separator and the preparation of the secondary battery are the same as in Example 1, except that,

[0054] Preparation of the positive electrode sheet:

[0055] The positive active material (sodium vanadium phosphate is selected in this embodiment), conductive agent Super P, and binder polyvinylidene difluoride (PVDF) are weighed according to the mass ratio of 97.5:1.0:1.5 (for example, 97.5 g of sodium vanadium phosphate, 1.0 g of Super P, and 1.5 g of PVDF), and then added into a 2-L stirring tank for mechanical mixing. N-methylpyrrolidone (NMP) is added as a solvent to prepare a positive electrode slurry with a solid content of 75%. After stirring for 2 hours, the slurry is uniformly dispersed. Subsequently, the stirred positive electrode slurry is uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 12 μm, and then dried at 100°C to obtain a positive electrode tab with single-side coated positive electrode slurry (sodium vanadium phosphate). The surface loading of sodium vanadium phosphate on the positive electrode tab is 50.0 mg / cm2, and the thickness of the dry film of the positive electrode tab is measured to be 500 μm. The above steps are repeated on the other surface of the positive electrode tab to obtain a positive electrode tab with double-side coated positive electrode slurry (sodium vanadium phosphate). After cold pressing, the positive electrode tab is cut into a specification of 56 mm x 43 mm for use.

[0056] Preparation of negative electrode tab:

[0057] The porous material coconut activated carbon, conductive carbon, and binders (carboxymethylcellulose sodium (CMC-Na) and polymerized styrene butadiene rubber (SBR)) are weighed according to the mass ratio of 80:5:6:9 (for example, 80 g of coconut activated carbon, 5 g of conductive carbon, 6 g of CMC-Na, and 9 g of SBR), and then added into a 2-L stirring tank for mechanical mixing. Deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 40%. After stirring for 2 hours, the slurry is uniformly dispersed. The stirred negative electrode slurry is uniformly coated on one surface of a negative current collector aluminum foil with a thickness of 12 μm, and then dried at 80°C to obtain an electrode tab with single-side coated porous coconut activated carbon slurry. The surface loading of coconut activated carbon on the electrode tab is 0.31 mg / cm2, and the thickness of the dry film of the negative electrode tab is measured to be 50 μm. The above steps are repeated on the other surface of the negative electrode tab to obtain an electrode tab with double-side coated porous coconut activated carbon slurry. After coating, the electrode tab is cut into a specification of 58 mm x 45 mm for use. Unlike the positive electrode tab, the negative electrode tab does not undergo a rolling operation.

[0058] Example 7

[0059] In this embodiment, the positive electrode tab, electrolyte, separator, and secondary battery are prepared in the same manner as in Example 1. Unlike Example 1, the negative electrode tab is prepared as follows:

[0060] The mesoporous carbon, indium powder, conductive carbon, and polybinder polyvinylidene fluoride (PVDF) are weighed according to the mass ratio of 80:10:5:5 (e.g., 80 g of mesoporous carbon, 10 g of In, 5 g of conductive carbon, and 5 g of PVDF), added into a 2 L stirring tank for mechanical mixing, N-methyl pyrrolidone is added as a solvent, and a negative electrode slurry with a solid content of 55% is prepared. The negative electrode slurry is stirred for 2 hours to make it uniformly dispersed. The stirred negative electrode slurry is uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm, and dried at 80°C to obtain a negative electrode sheet coated with mesoporous carbon and indium powder slurry on one side. The surface loading of mesoporous carbon and indium powder is 0.17 mg / cm 2 The thickness of the dry film of the negative electrode sheet is measured to be 23 μm. Then, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with mesoporous carbon and indium powder on both sides. After the coating is completed, the negative electrode sheet is cut into a specification of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet does not undergo a rolling operation.

[0061] Example 8

[0062] In this example, the preparation of the positive electrode sheet, electrolyte, and separator, and the secondary battery is the same as in Example 1. Unlike Example 1, the negative electrode sheet is prepared as follows:

[0063] The carbon nanotube, zinc iodide, conductive carbon, and polybinder polyvinylidene fluoride (PVDF) are weighed according to the mass ratio of 85:5:5:5 (e.g., 85 g of carbon nanotube, 5 g of ZnI2, 5 g of conductive carbon, and 5 g of PVDF), added into a 2 L stirring tank for mechanical mixing, N-methyl pyrrolidone is added as a solvent, and a negative electrode slurry with a solid content of 45% is prepared. The negative electrode slurry is stirred for 2 hours to make it uniformly dispersed. The stirred negative electrode slurry is uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm, and dried at 80°C to obtain a negative electrode sheet coated with carbon nanotube and zinc iodide slurry on one side. The surface loading of carbon nanotube and zinc iodide is 0.12 mg / cm 2 The thickness of the dry film of the negative electrode sheet is measured to be 16 μm. Then, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with carbon nanotube and zinc iodide on both sides. After the coating is completed, the negative electrode sheet is cut into a specification of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet does not undergo a rolling operation.

[0064] Example 9

[0065] In this example, the preparation of the positive electrode sheet, electrolyte, and separator, and the secondary battery is the same as in Example 1. Unlike Example 1, the negative electrode sheet is prepared as follows:

[0066] The graphite, activated carbon, conductive carbon, binder polyacrylic acid were weighed according to the mass ratio of 30:40:10:20 (for example, graphite 30 g, activated carbon 40 g, conductive carbon 10 g, PAA 20 g), and then added into a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 55%, and the slurry was stirred for 2 hours to make it uniformly dispersed. The well-stirred negative electrode slurry was uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm, and then dried at 80°C to obtain a negative electrode sheet coated with graphite and activated carbon slurry on one side, and the surface loading of the graphite and activated carbon composite coating was 0.15 mg / cm 2 The thickness of the dry film of the negative electrode sheet was measured to be 22 μm. Then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with graphite and activated carbon slurry on both sides. After the coating was completed, it was cut into a specification of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet did not undergo a rolling operation.

[0067] Comparative Example 1

[0068] In this example, the positive electrode, electrolyte, and separator and sodium battery were prepared as in Example 1, except that the negative electrode sheet was prepared as follows:

[0069] The porous material coconut activated carbon, conductive carbon, binder carboxymethyl cellulose sodium CMC and styrene-butadiene rubber SBR were weighed according to the corresponding mass ratio of 80:10:3:7 (for example, coconut activated carbon 80 g, conductive carbon 10 g, CMC 3 g, SBR 7 g), and then added into a 2 L stirring tank for mechanical mixing. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 60%, and the slurry was stirred for 2 hours to make it uniformly dispersed. The well-stirred negative electrode slurry was uniformly coated on one surface of a negative electrode current collector aluminum foil with a thickness of 12 μm, and then dried at 80°C to obtain a negative electrode sheet coated with porous coconut activated carbon slurry on one side, and the surface loading of the coconut activated carbon was 2.1 mg / cm 2 The thickness of the dry film of the negative electrode sheet was measured to be 300 μm. Then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with porous coconut activated carbon slurry on both sides. After the coating was completed, it was cut into a specification of 58 mm x 45 mm for use. Unlike the positive electrode sheet, the negative electrode sheet did not undergo a rolling operation.

[0070] Comparative Example 2

[0071] In this example, the electrolyte, and separator and secondary battery were prepared as in Example 1, except that the positive electrode sheet and the negative electrode sheet were prepared as follows.

[0072] The positive electrode sheet was prepared by weighing the corresponding mass of sodium vanadium phosphate, conductive agent Super P and binder polyvinylidene fluoride (PVDF) according to the mass ratio of 95:2.0:3.0 (for example, 95 g of sodium vanadium phosphate, 2.0 g of Super P and 3.0 g of PVDF), adding them into a 2 L stirring tank for mechanical mixing, adding N-methyl pyrrolidone (NMP) as a solvent, and adjusting the slurry to a solid content of 40% to make the slurry uniformly dispersed after stirring for 2 hours. Subsequently, the stirred positive electrode slurry was uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 12 μm, dried at 100 °C, and a single-sided coated positive electrode slurry positive electrode sheet was obtained, with a surface loading of sodium vanadium phosphate of 1.0 mg / cm 2 The thickness of the dry film of the positive electrode sheet was measured to be 10 μm. The above steps were then repeated on the other surface of the positive electrode sheet to obtain a double-sided coated sodium vanadium phosphate positive electrode sheet. The positive electrode sheet was cold-pressed and cut into a 56 mm x 43 mm size for use.

[0073] The negative electrode sheet was prepared by weighing the corresponding mass of porous material coconut activated carbon, conductive carbon, binder sodium carboxymethyl cellulose (CMC) and butadiene rubber (SBR) according to the mass ratio of 80:2:8:10 (for example, 80 g of coconut activated carbon, 2 g of conductive carbon, 8 g of CMC and 10 g of SBR), adding them into a 2 L stirring tank for mechanical mixing, adding deionized water as a solvent, adjusting the negative electrode slurry to a solid content of 50% to make the slurry uniformly dispersed after stirring for 2 hours. The stirred negative electrode slurry was uniformly coated on one surface of a negative current collector aluminum foil with a thickness of 12 μm, dried at 80 °C, and a single-sided coated porous coconut activated carbon slurry electrode sheet was obtained, with a surface loading of coconut activated carbon of 1.8 mg / cm 2 The thickness of the dry film of the negative electrode sheet was measured to be 200 μm. The above steps were then repeated on the other surface of the negative electrode sheet to obtain a double-sided coated porous coconut activated carbon slurry electrode sheet. After coating, it was cut into a 58 mm x 45 mm size for use. Unlike the positive electrode sheet, the negative electrode sheet did not undergo a rolling operation.

[0074] Comparative Example 3:

[0075] In this example, the positive electrode, electrolyte and separator, and sodium battery were prepared as in Example 1, except that, like the positive electrode sheet, the negative electrode sheet was subjected to a rolling operation.

[0076] The positive electrode capacity, negative electrode capacity, initial efficiency and cycle life of each example and comparative example are shown in Table 1:

[0077] Table 1

[0078]

[0079]

[0080] As can be seen from Table 1, the porous negative electrode design can realize the electrochemical device with the positive and negative electrode capacity asymmetry stated in the application, the battery capacity is derived from the positive electrode, the porous negative electrode does not provide capacity, only provides sodium deposition sites and physical storage space for sodium metal. When the positive and negative electrode thickness ratio is > 2.5, stable cycling of the secondary battery can be realized, and the cycle life reaches 10,000 times.

[0081] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and the negative electrode sheet and holds electrolyte. The capacity of the negative electrode active material and the positive electrode active material is asymmetric in the part where the positive electrode sheet and the negative electrode sheet are opposite to each other.

2. The secondary battery according to claim 1, characterized by The ratio N / P of the capacity per unit area of the negative electrode active material to the capacity per unit area of the positive electrode active material is less than or equal to 0.

1.

3. The secondary battery according to claim 2, characterized by The mass ratio of the positive electrode active material to the negative electrode active material is 5-200, and the thickness ratio of the positive electrode sheet to the negative electrode sheet is: 2.5-20。 4. The secondary battery according to claim 3, characterized by The thickness of the positive electrode tab is 50 to 500 μm, and the loading of the positive electrode active material in the positive electrode tab is 5 to 50 mg / cm2 2 .

5. The secondary battery according to claim 3, characterized by The positive electrode active material comprises one or more of sodium phosphite, sodium iron phosphate, sodium pyrophosphate iron phosphate, sodium pyrophosphate iron, sodium manganese oxygen, sodium cobalt oxygen, sodium iron oxygen, fluorinated sodium phosphite, sodium iron sulfate, sodium nickel manganese oxygen, sodium iron cobalt oxygen, and sodium nickel cobalt manganese oxygen.

6. The secondary battery according to claim 1, characterized by The positive electrode sheet further comprises a binder and a conductive agent.

7. The secondary battery according to claim 1, characterized by The negative electrode sheet is a porous structure for accommodating sodium metal deposited during charging of the battery, and the loading capacity of the negative electrode sheet is determined by the loading capacity or the compactness and thickness of the positive electrode sheet.

8. The secondary battery according to claim 1, characterized by The negative electrode active material comprises a carbon material and one or more of a metal, an alloy of the metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of the metal; The carbon material comprises one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotube, carbon fiber, graphene, graphite, mesocarbon microbead, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon. The metal comprises one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, and Ga.

9. The secondary battery according to claim 1, characterized by The negative electrode sheet is loaded by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing.

10. A method of producing the secondary battery according to any one of claims 1 to 8, characterized by, The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and the negative electrode sheet and holds electrolyte. The capacity of the negative electrode active material and the positive electrode active material is asymmetric in the part where the positive electrode sheet and the negative electrode sheet are opposite to each other. The ratio N / P of the capacity per unit area of the negative electrode active material to the capacity per unit area of the positive electrode active material is less than or equal to 0.

1. The mass ratio of the positive electrode active material to the negative electrode active material is 5-200, and the thickness ratio of the positive electrode sheet to the negative electrode sheet is:

11. A battery pack, characterized by The positive electrode active material comprises one or more of sodium phosphite, sodium iron phosphate, sodium pyrophosphate iron phosphate, sodium pyrophosphate iron, sodium manganese oxygen, sodium cobalt oxygen, sodium iron oxygen, fluorinated sodium phosphite, sodium iron sulfate, sodium nickel manganese oxygen, sodium iron cobalt oxygen, and sodium nickel cobalt manganese oxygen. The positive electrode sheet further comprises a binder and a conductive agent. The negative electrode sheet is a porous structure for accommodating sodium metal deposited during charging of the battery, and the loading capacity of the negative electrode sheet is determined by the loading capacity or the compactness and thickness of the positive electrode sheet. The negative electrode active material comprises a carbon material and one or more of a metal, an alloy of the metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of the metal; The carbon material comprises one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotube, carbon fiber, graphene, graphite, mesocarbon microbead, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon. The metal comprises one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, and Ga. The negative electrode sheet is loaded by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and the negative electrode sheet and holds electrolyte. The capacity of the negative electrode active material and the positive electrode active material is asymmetric in the part where the positive electrode sheet and the negative electrode sheet are opposite to each other. The ratio N / P of the capacity per unit area of the negative electrode active material to the capacity per unit area of the positive electrode active material is less than or equal to 0.

1. The mass ratio of the positive electrode active material to the negative electrode active material is 5-200, and the thickness ratio of the positive electrode sheet to the negative electrode sheet is: The positive electrode active material comprises one or more of sodium phosphite, sodium iron phosphate, sodium pyrophosphate iron phosphate, sodium pyrophosphate iron, sodium manganese oxygen, sodium cobalt oxygen, sodium iron oxygen, fluorinated sodium phosphite, sodium iron sulfate, sodium nickel manganese oxygen, sodium iron cobalt oxygen, and sodium nickel cobalt manganese oxygen. The positive electrode sheet further comprises a binder and a conductive agent. The negative electrode sheet is a porous structure for accommodating sodium metal deposited during charging of the battery, and the loading capacity of the negative electrode sheet is determined by the loading capacity or the compactness and thickness of the positive electrode sheet. The negative electrode active material comprises a carbon material and one or more of a metal, an alloy of the metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of the metal; The carbon material comprises one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotube, carbon fiber, graphene, graphite, mesocarbon microbead, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon. The metal comprises one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, and Ga. The negative electrode sheet is loaded by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and the negative electrode sheet and holds electrolyte. The capacity of the negative electrode active material and the positive electrode active material is asymmetric in the part where the positive electrode sheet and the negative electrode sheet are opposite to each other. The ratio N / P of the capacity per unit area of the negative electrode active material to the capacity per unit area of the positive electrode active material is less than or equal to 0.

1. The mass ratio of the positive electrode active material to the negative electrode active material is 5-200, and the thickness ratio of the positive electrode sheet to the negative electrode sheet is: The positive electrode active material comprises one or more of sodium phosphite, sodium iron phosphate, sodium pyrophosphate iron phosphate, sodium pyrophosphate iron, sodium manganese oxygen, sodium cobalt oxygen, sodium iron oxygen, fluorinated sodium phosphite, sodium iron sulfate, sodium nickel manganese oxygen, sodium iron cobalt oxygen, and sodium nickel cobalt manganese oxygen. The positive electrode sheet further comprises a binder and a conductive agent. The negative electrode sheet is a porous structure for accommodating sodium metal deposited during charging of the battery, and the loading capacity of the negative electrode sheet is determined by the loading capacity or the compactness and thickness of the positive electrode sheet. The negative electrode active material comprises a carbon material and one or more of a metal, an alloy of the metal, a halide, a sulfide, an oxide, a nitride, a selenide, a phosphide, a boride, and a hydride of the metal; The carbon material comprises one or more of hard carbon, soft carbon, amorphous carbon, carbon nanotube, carbon fiber, graphene, graphite, mesocarbon microbead, mesoporous carbon, carbon aerogel, carbon molecular sieve, and activated carbon. The metal comprises one or more of Sn, Ge, Bi, Si, Zn, Ca, Mg, Ti, Fe, Sb, Pb, and Ga. The negative electrode sheet is loaded by means of scraping, extrusion coating, spraying, brushing, roller coating, magnetron sputtering, spin coating, electron beam evaporation, thermal evaporation, or 3D printing. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode active material; the negative electrode sheet comprises a negative electrode active material; and the separator is arranged between the positive electrode sheet and

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