A winding battery cell, a preparation process and a high-power aqueous sodium salt battery

Abstract

A structure of water-based sodium salt battery prepared by a winding process with a self-supporting flexible thick electrode, the main features and advantages include: a) continuous self-supporting flexible thick electrode sheet, which can be wound into a roll, produced by continuous winding, high production efficiency; b) the length of the electrode and the current collector can be freely adjusted according to the design specifications of the wound battery, which is convenient to control and realize the output of different specifications; c) and the current collector is protected against corrosion, the wound battery only needs to be cut once for each positive and negative electrode, and the entire battery structure only has two cut surfaces of the positive and negative current collectors, greatly reducing the risk of current collector corrosion; d) the tab and the current collector are integrated, without the need for welding tabs inside the electrode sheet, which can effectively reduce the battery resistance and facilitate molding.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage batteries, in particular to a wound cell, a preparation process and a high-power water-based sodium salt battery. BACKGROUND

[0002] The mainstream energy storage battery cells in the industry can be divided into wound process and laminated process according to the manufacturing process. The wound process is widely used due to its easy manufacturing and high production efficiency. However, the size and capacity of lithium batteries are generally small due to safety requirements. For example, the largest cylindrical lithium battery currently available has a diameter of 46 mm and a height of 80 mm (model 46800). Water-based sodium salt batteries use neutral sodium salt solution as electrolyte, which inherently has the advantages of safety, environmental protection and long life. This system not only avoids the flammable problem of organic electrolyte, but also overcomes the shortcomings of high pollution, short life (such as lead-acid batteries) and high price (lithium-ion batteries) of traditional water-based batteries. It is one of the ideal systems that can meet the requirements of large-scale energy storage technology. If the wound process is applied to the preparation of water-based sodium salt batteries, it will not be limited by the size and safety of the battery. In theory, large-size, high-capacity, safe and environmentally friendly water-based sodium salt batteries can be prepared, and the assembly efficiency of the battery can be greatly improved.

[0003] Chinese patent application publication No. CN109755473A (application No. 201811630834.5) relates to a dry method for preparing a lithium battery electrode. The electrode film strip prepared by the dry method has a thickness of 50-100 microns. The electrode film strip is compounded onto the electrode current collector by high-temperature rolling to obtain a wound lithium battery electrode. Chinese patent application publication No. CN112687833A (application No. 202011553241.0) relates to a dry electrode tab preparation method, an electrode tab prepared by the method and its use. The raw material powder is mixed, heated and fiberized to obtain a tab powder. The tab powder is sequentially subjected to vertical and horizontal roller pressing to obtain a film. The film and the foil are fed into a laminating roller to form an electrode tab. Chinese utility model patent authorization announcement No. CN213660479U relates to a multi-tab wound battery. The multi-tab design increases the number of tabs and adopts an integrated molding method with the current collector. However, the tabs cannot be completely integrated with the current collector due to tab welding and tab protection glue.

[0004] The conventional preparation method has the following problems: 1) at present, the electrode preparation basically adopts a wet forming process, that is, the process procedures of preparing slurry, coating, drying and rolling, a large amount of organic solvent or deionized water is used in the process, there are problems of solvent recovery difficulty, high energy consumption in the drying process, easy cracking of the electrode sheet, low electrode density and the like; 2) the existing winding process technology is to coat or hot-press composite active material on the aluminum foil (copper foil) current collector, although the product has high efficiency and good consistency, the winding process is difficult to be applied to thick electrodes due to the existence of the difference between the inner and outer curvatures, and is mainly applied to thin electrode batteries; the production efficiency of the laminated sheet is low, the production control is relatively complicated, there are difficulties in detection, operation and statistics for at least dozens of electrode sheets of each battery, and the product consistency is difficult to control; 3) the current most commonly used current collector of the water-based sodium salt battery is stainless steel, and corrosion protection needs to be performed on the aluminum foil, if there are more edge cutting of the laminated battery electrode sheet, especially the edge cutting section of the current collector is easy to be corroded by the salt solution, in order to eliminate the influence of the corrosion of the edge cutting section of the current collector, more processes and equipment are needed, and the process is more complicated. SUMMARY

[0005] The application creates a structure of a water-based sodium salt battery prepared by winding process with a self-supporting flexible thick electrode, and the main features and advantages include: a) continuous self-supporting flexible thick electrode sheet, the thick electrode sheet can be wound into a roll shape, and the continuous winding method is used for production, so that the production efficiency is high; b) the length of the electrode and the current collector can be freely adjusted according to the design specifications of the wound battery, so that the control is facilitated, and different specification product outputs are realized; c) the current collector is protected against corrosion, the wound battery only needs to be cut once for each of the positive and negative electrodes, and the whole battery structure only has two cutting sections of the positive and negative current collectors, so that the risk of corrosion of the current collector is greatly reduced; d) the tab and the current collector are integrated, and the tab does not need to be welded inside the electrode sheet, so that the battery internal resistance can be effectively reduced, and the molding is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 It is a winding schematic diagram, in which: 1-flexible positive thick electrode sheet; 2-flexible negative thick electrode sheet; 3-composite current collector; 4-separator; 5-winding core.

[0007] Figure 2 It is a schematic diagram of the composite current collector structure I, in which: 6-conductive film; 7-aluminum foil (tab end).

[0008] Figure 3 It is a schematic diagram of the composite current collector structure II, in which: 6-conductive film; 7-aluminum foil (tab end).

[0009] Figure 4 It is a cross-sectional view of the wound battery.

[0010] Figure 5A It is a cycle life curve diagram of the battery assembled by using the composite current collector structure II.

[0011] Figure 5B The diagram shows the rate discharge performance of a two-cell battery with a composite current collector structure. Detailed Implementation

[0012] This invention creates a structure for fabricating an aqueous sodium-ion battery using a self-supporting flexible thick electrode through a winding process. Its main features and advantages include: a) a continuous, self-supporting flexible thick electrode sheet that can be wound into a roll, resulting in high production efficiency through continuous winding; b) the lengths of the electrodes and current collectors can be freely adjusted according to the design specifications of the wound cell, facilitating control and enabling the output of products with different specifications; c) the current collector is protected against corrosion, requiring only one cutting of each of the positive and negative electrodes in the wound cell, resulting in only two cut surfaces for the entire cell structure, significantly reducing the risk of current collector corrosion; d) the tabs and current collector are integrated into a single structure, eliminating the need to weld tabs inside the electrode sheet, effectively reducing the battery's internal resistance and facilitating molding.

[0013] The technical solution adopted in this invention is: a wound battery cell, comprising a positive electrode group, a negative electrode group, a separator, and a core. The positive electrode group is composed of two layers of flexible positive electrode sheets and a layer of composite current collector arranged in an alternating superimposed structure. The negative electrode group is composed of two layers of flexible negative electrode sheets and a layer of composite current collector arranged in an alternating superimposed structure. The positive electrode group, the negative electrode group, and the two separator layers are alternately superimposed and then wound by the core. The separator is wound between the positive electrode group and the negative electrode group, and the positive electrode group is wound outside the negative electrode group. The composite current collector in the positive electrode group and the negative electrode group is the same material. The composite current collector in the positive and negative electrode groups can use the entire aluminum foil as a full tab, or the composite current collector in the positive and negative electrode groups can be cut into multiple aluminum foil tabs. The tab spacing is calculated according to the design diameter of the wound battery cell, so that the inner and outer layers of the tabs overlap during the winding process of the composite current collector. A manufacturing process and an aqueous sodium salt battery are disclosed. The specific process involves stacking raw materials in the order of negative electrode assembly, separator, positive electrode assembly, and separator, winding them into a cylindrical or elliptical cylinder, placing them in a cylindrical or square plastic shell, and injecting an aqueous electrolyte to obtain an aqueous sodium salt battery.

[0014] The flexible positive or negative electrode sheet of this invention uses positive or negative electrode active materials, carbon black as a conductive agent, and polytetrafluoroethylene emulsion (PTFE emulsion) as the main binder. The PTFE in the mixture is fiberized through a high-shear process, and then pressed into a self-supporting electrode sheet using a roll pressing process. The electrode sheet has a uniform thickness and can be continuously manufactured. The electrode sheet thickness is 0.1mm-5mm, preferably 1-2.5mm; the active material loading is 0.1-5g / cm³. 2 Preferred concentration: 0.15–2 g / cm³ 2 Porosity 30%-50%, preferably 35%-45%.

[0015] The positive active material described in the present application is selected from, but not limited to, MnO2, NaMnO2, KMnO2, a compound containing a tetrahedral or octahedral anion structural unit, a Prussian blue analogue, and NaMFe(CN)6 (M = Ni, Co, Fe, Cu).

[0016] The negative active material described in the present application is selected from, but not limited to, a phosphate compound, NaTi2(PO4)3, Na3V2(PO4)3, a metal oxide, MoO3, Na2V6O 16 , activated carbon, and a Prussian blue analogue.

[0017] The winding core described in the present application is a plastic round tube, which can be a polyethylene round tube, a polypropylene round tube, a polyvinyl chloride round tube, etc., and the outer diameter of the round tube is 10-60 mm.

[0018] The aqueous electrolyte described in the present application is a sodium salt aqueous solution, and the sodium salt can be one or more of sodium sulfate, sodium chloride, and sodium acetate.

[0019] The winding process described in the present application is specifically as follows: the negative electrode group, the separator, the positive electrode group, and the separator are stacked in order, and are wound into a cylindrical or elliptical cylindrical shape by winding the winding core, and then are placed in a plastic outer shell in the shape of a cylinder or a square shell, and the aqueous electrolyte is injected.

[0020] The present application has the following advantages: 1) The electrode manufacturing process does not use solvent, and the binder exists in the form of fibers, and the active carbon particles and the conductive agent particles are in closer contact, and the electrode has high density, good conductivity, good electrode toughness, high density, high capacity, and the carbon powder is not easy to fall off, and the cycle life is long; 2) The positive and negative electrode groups adopt the same kind of composite current collector, and a plurality of aluminum foil tabs are obtained by die cutting or cutting directly on the aluminum foil, or the entire aluminum foil is directly used as a full tab, and there is no need to weld tabs inside the electrode sheet, which can effectively reduce the internal resistance of the battery and facilitate the molding; 3) The cutting of the stacking method needs long-term precise control, and each composite current collector and flexible large electrode sheet needs to be cut around, and the cross section, material falling, burr, and other conditions of the product need to be controlled, and the consistency of the electrode sheet is required to be higher, and the cutting of the winding method is mainly at the two nodes of the start and termination of the winding of the electrode core, which can greatly reduce the risk of corrosion of the current collector by the electrolyte; 4) The active material and the current collector do not go through a coating process or are integrated by pressing, and the flexible large electrode sheet and the composite current collector are separately wound, which avoids the wrinkling and deformation of the separator and the large electrode sheet caused by the difference in internal and external curvature during winding, and the length of the winding can be flexibly cut, so that the size of the winding can be flexibly adjusted according to the capacity requirement.

[0021] In one embodiment, the size and capacity of the green high-safety electrode winding structure of the water-based sodium salt battery of the present application can be flexibly adjusted as needed; the diameter is 7-500 cm, the height is 14-200 cm, the height-length ratio is 2:1-20:1, the capacity is 1 Ah-ten thousand Ah, and the energy efficiency is >80%. There is no hidden danger such as heating, burning, and explosion under high rate and extreme use conditions.

[0022] In one embodiment, the winding cell of the present application uses a high-toughness, high-density, high-conductivity, high-load, self-supporting thick electrode, the electrode sheet thickness is 0.1 mm-5 mm, the active material load is 0.1-5 g / cm 2 , and the porosity is 30%-50%.

[0023] In one embodiment, the winding cell of the present application uses a corrosion-resistant current collector: composed of a metal current collector and an outer anti-corrosion conductive layer. The metal current collector can be aluminum, copper, nickel, etc.; the anti-corrosion conductive layer is a conductive organic film, such as a polyethylene conductive film, a polypropylene conductive film, an ethylene-vinyl acetate conductive film, a polyaniline conductive film, a polypyrrole conductive film, a polyphenylene sulfide conductive film, etc.

[0024] In one embodiment, the positive and negative electrode flexible large electrode sheets and the composite current collector of the present application can be individually wound into a roll shape, and the position and shape of each roll-shaped body during the cell winding process are adjusted according to the winding curvature, avoiding multiple bending and thickness change regions in the length direction of the entire electrode sheet, especially the small-angle bending region near the middle of the winding core. Due to uneven winding curvature and shape change, it is easy to cause the wrinkling and deformation of the separator and the electrode sheet, and the positive and negative electrodes cannot be effectively contacted, resulting in a reaction dead zone.

[0025] In one embodiment, the flexible positive or negative large electrode sheet of the present application is prepared by using a positive or negative active material, carbon black as a conductive agent, and PTFE as a main binder, fiberizing the PTFE in the mixture through a high shear process, and pressing into a self-supporting electrode sheet through a rolling process. The thickness of the electrode sheet is uniform, and continuous production can be realized.

[0026] In one embodiment, the tab and the current collector of the present application are integrated, without the need to weld the tab inside the electrode sheet, which can effectively reduce the internal resistance of the battery and facilitate molding; and the current collector is protected against corrosion, and the winding cell only needs to be cut once for each of the positive and negative electrodes, and the entire cell structure only has two cut surfaces of the positive and negative current collectors, greatly reducing the risk of current collector corrosion.

[0027] In one embodiment, the negative electrode group and the positive electrode group of the present application are thick electrodes with a self-supporting structure, and are individually wound into a roll shape without being first integrated with the composite current collector. The flexible thick electrode sheet and the composite current collector are individually wound into a roll shape, avoiding the wrinkling and deformation of the separator and the thick electrode sheet caused by the difference between the inner and outer curvatures during winding.

[0028] In one embodiment, the positive and negative electrode sheets of the present application have the same size, there is no mutual wrapping problem, the length of the electrode and the current collector can be freely adjusted according to the design specification of the wound battery, which is convenient for control and realizes the output of different specifications of products.

[0029] The present application can be better understood by referring to the following examples. Those skilled in the art will understand that the following examples are merely illustrative of the present application and are not intended to limit the scope of the present application. The scope of the present application is defined by the claims hereinafter. DETAILED DESCRIPTION

[0031] Example 1. A winding process of a water-based sodium salt battery, comprising the following steps:

[0032] 1) According to the size requirements of the wound battery, the cutting position, cutting size and cutting shape of the positive and negative aluminum foils are defined respectively to prepare the corresponding specification of aluminum foil (tab end) 7, and the tab spacing is calculated according to the design diameter of the wound battery;

[0033] 2) The aluminum foil (tab end) 7 is attached to the conductive film 6 through conductive adhesive, as shown in Figure 2 The conductive film completely wraps the aluminum foil, and the aluminum tab end is exposed, to prepare the composite current collector 3;

[0034] 3) The positive active material, carbon black as conductive agent, and polytetrafluoroethylene emulsion (PTFE emulsion) as main binder are mixed uniformly, and are pressed into a self-supporting flexible positive thick electrode sheet 1 by high shear and rolling process, with a thickness of 2 mm, an active material loading of 0.37 g / cm 2 , and a porosity of 38%. The negative active material, carbon black as conductive agent, and polytetrafluoroethylene emulsion (PTFE emulsion) as main binder are mixed uniformly, and are pressed into a self-supporting flexible negative thick electrode sheet 2 by high shear and rolling process, with a thickness of 1.9 mm, an active material loading of 0.27 g / cm 2 , and a porosity of 40%.

[0035] 4) The battery is wound by alternately stacking the positive electrode group, the negative electrode group and two layers of separator 4 as shown in Figure 1 , and then winding through the winding core 5 with an outer diameter of 50 mm. The positive electrode group includes the flexible positive thick electrode sheet 1 and the composite current collector 3, and the negative electrode group includes the flexible negative thick electrode sheet 2 and the composite current collector 3. During the winding process, the inner layer of the tab and the outer layer of the tab overlap, and the positive and negative tabs are staggered. The diameter of the battery is 16 cm, and the height is 30 cm.

[0036] 5) A water-based sodium salt battery is prepared by using sodium chloride aqueous solution as electrolyte, with a capacity of 90 Ah.

[0037] Example 2. A winding process of a high-power aqueous sodium salt battery, comprising the following steps:

[0038] 1) The aluminum foil (tab end) 7 is attached to the conductive film 6 by conductive adhesive, as shown in Figure 3 The conductive film completely wraps the aluminum foil, and the entire aluminum foil is directly exposed as the tab end to produce a composite current collector 3;

[0039] 2) The positive active material, carbon black as conductive agent, and polytetrafluoroethylene emulsion (PTFE emulsion) as the main binder are mixed uniformly, and a self-supporting flexible positive thick electrode sheet 1 is pressed by high shear and rolling process, with a thickness of 1.2 mm, an active material loading of 0.23 g / cm 2 , and a porosity of 40.6%. The negative active material, carbon black as conductive agent, and polytetrafluoroethylene emulsion (PTFE emulsion) as the main binder are mixed uniformly, and a self-supporting flexible negative thick electrode sheet 2 is pressed by high shear and rolling process, with a thickness of 1.2 mm, an active material loading of 0.16 g / cm 2 , and a porosity of 39.8%.

[0040] 3) The cell is formed by alternately stacking the positive electrode group, negative electrode group, and two layers of separator 4, as shown in Figure 1 , and then winding by the winding core 5. The positive electrode group includes the flexible positive thick electrode sheet 1 and the composite current collector 3, and the negative electrode group includes the flexible negative thick electrode sheet 2 and the composite current collector 3; Figure 4 The positive and negative tabs are offset in opposite directions during the winding process. The cell diameter is 11 cm, and the height is 25 cm.

[0041] 4) An aqueous sodium salt battery is prepared using a sodium sulfate aqueous solution as the electrolyte, with a capacity of 70 Ah. The battery is subjected to standard charge and discharge and different rate discharge tests according to the rated capacity of 0.2C (14 Ah). The standard charge is performed at 25°C with a charging current of 0.2C (14 A) and constant current charging to a cutoff voltage of 1.85V, with a 10-minute rest. The standard discharge is performed at 25°C with a discharging current of 0.2C (14 A) and constant current discharging to a cutoff voltage of 1.1V, with a 10-minute rest. The test data are shown in Figure 5A and 5B .

[0042] Due to the use of full-tab structure, there is no need for tab welding, and the battery internal resistance is 0.12 mΩ. The battery 0.2C (14 Ah) charge-discharge cycle capacity retention rate is 88.24% after 3915 cycles, and the rate discharge performance is good. The data are shown in Table 1 below.

[0043] Table 1: Rate discharge performance

[0044]

[0045]

[0046] Note: The battery was charged under standard charge conditions at 25°C to a cut-off voltage of 1.85V at a charge current of 0.2C (14A), then discharged to a cut-off voltage of 1.1V at different conditions, and the capacity ratio was shown in the above table. The discharge capacity at 25°C, 0.2C (14A) was taken as 100% capacity.

[0047] The documents or published articles cited in this patent application are incorporated by reference as part of this application to more fully describe the state of the art to which this invention pertains. Also, the transitional terms "comprises", "comprising", or "characterized by" are synonymous with "containing" or "including" or "characterized as" and are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

Claims

1. A wound battery cell, characterized in that, The battery includes a positive electrode assembly, a negative electrode assembly, a separator, and a core. The positive electrode assembly consists of two layers of flexible thick positive electrode sheets and a layer of composite current collector arranged in an alternating superimposed structure. The negative electrode assembly consists of two layers of flexible thick negative electrode sheets and a layer of composite current collector arranged in an alternating superimposed structure. The positive electrode assembly, the negative electrode assembly, and the two layers of separator are alternately superimposed and then wound by the core. The separator is wound between the positive electrode assembly and the negative electrode assembly, and the positive electrode assembly is wound outside the negative electrode assembly. The composite current collector in the positive electrode assembly and the negative electrode assembly is made of the same material. The composite current collector in the positive and negative electrode assemblies can be made by directly using the entire aluminum foil as a tab, or the composite current collector in the positive and negative electrode assemblies can be cut into multiple aluminum foil tabs. The tab spacing is calculated according to the design diameter of the wound battery cell, so that the inner and outer layers of the tabs overlap during the winding process of the composite current collector. The flexible positive electrode sheet contains a positive electrode active material selected from MnO2, NaMnO2, KMnO2, compounds containing tetrahedral or octahedral anionic structural units and Prussian blue analogues, carbon black as a conductive agent, polytetrafluoroethylene emulsion as the main binder, and PTFE in the mixture is fiberized by a high shear process and then pressed into a self-supporting electrode sheet by a roll pressing process. The flexible negative electrode thick sheet contains a negative electrode active material selected from phosphate compounds, metal oxides, activated carbon and Prussian blue analogues, carbon black as a conductive agent, polytetrafluoroethylene emulsion as the main binder, and PTFE in the mixture is fiberized by a high shear process and then pressed into a self-supporting electrode sheet by a roll pressing process. The battery cell uses a corrosion-resistant current collector: it consists of a metal current collector and an outer anti-corrosion conductive layer. The metal current collector can be aluminum, copper, or nickel; the anti-corrosion conductive layer can be a polyethylene conductive film, a polypropylene conductive film, an ethylene-vinyl acetate conductive film, a polyaniline conductive film, a polypyrrole conductive film, or a polyphenylene sulfide conductive film. Both the negative electrode assembly and the positive electrode assembly are thick electrodes with self-supporting structures, rolled up individually, and not first combined with the composite current collector.

2. The wound battery cell as described in claim 1, characterized in that, The thick electrode sheet has a thickness of 0.1mm–5mm, an active material loading of 0.1-5g / cm², and a porosity of 30%-50%.

3. The wound battery cell as described in claim 1, characterized in that, The wound battery cell is a plastic round tube, which can be a polyethylene round tube, a polypropylene round tube, or a polyvinyl chloride round tube, with an outer diameter of 10mm–60mm.

4. The wound battery cell as described in claim 1, characterized in that, Both the positive and negative flexible thick electrode sheets and the composite current collector can be individually wound into rolls. During the winding process of the battery cell, the position and shape of each roll change are adjusted automatically according to the winding curvature, avoiding multiple bending and thickness variation areas in the entire electrode sheet along its length.

5. A method for preparing the battery cell of claim 1, the method comprising stacking the negative electrode assembly, the separator, the positive electrode assembly, and the separator in the order of stacking them together, winding them into a cylindrical or elliptical cylinder by winding, placing them into a cylindrical or square plastic shell, and injecting an aqueous electrolyte to obtain an aqueous sodium salt battery. The electrode tab and current collector are integrated into one structure, eliminating the need to weld the electrode tab inside the electrode sheet; The current collector is protected against corrosion. The wound cell only needs to be cut once for the positive and negative electrodes. The entire cell structure has only two cut surfaces for the positive and negative current collectors, which greatly reduces the risk of corrosion of the current collector. Both the negative electrode assembly and the positive electrode assembly are thick electrodes with self-supporting structures, rolled up individually, and not first combined with the composite current collector.

6. The method as described in claim 5, characterized in that, The flexible thick electrode sheet and the composite current collector are individually rolled up.

7. The method as described in claim 5, characterized in that, The positive and negative electrode plates are the same size and there is no problem of mutual coverage. The length of the electrodes and current collectors can be freely adjusted according to the design specifications of the wound cell, which is convenient for control and can realize the output of products of different specifications.

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