Secondary battery, preparation method thereof and electric equipment

Abstract

The invention provides a secondary battery, a preparation method thereof and electric equipment, the secondary battery comprises a shell, at least one electrode assembly and an electrolyte, the electrode assembly and the electrolyte are arranged in the shell, and the electrode assembly comprises a positive pole piece, an isolating membrane and a negative pole piece which are stacked in sequence; a composite liquid storage structure is arranged between the electrode assembly and the shell, the composite liquid storage structure comprises a first layer and a second layer which are sequentially stacked in the direction, close to the shell, of the electrode assembly, the first layer comprises a flame-retardant layer, and the second layer comprises a liquid storage layer. According to the secondary battery provided by the invention, the problem that the capacity is quickly attenuated and even dives due to the lack of electrolyte in the circulation of the secondary battery can be effectively solved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a secondary battery and its preparation method and electrical equipment. Background Technology

[0002] A secondary battery is an electrochemical device that stores and releases electrical energy through reversible electrochemical reactions and can be used multiple times in charge-discharge cycles. During charge-discharge cycles, due to changes in the electrode material structure, the thickness of the secondary battery undergoes periodic expansion and contraction, much like breathing, a phenomenon known as the "breathing effect" of the secondary battery. This effect is more pronounced at higher energy densities. During this process, the negative electrode active material may crack and break, leading to continuous reaction between fresh exposed surfaces and the electrolyte to form an SEI film, resulting in excessive electrolyte consumption. This leads to electrolyte deficiency, a significant increase in internal resistance, and even abnormal capacity drops, greatly shortening battery life. Therefore, a simple and effective method is urgently needed to improve the problem of shortened battery life due to electrolyte deficiency during cycling. Summary of the Invention

[0003] This application aims to at least partially solve one of the technical problems in related technologies. This application proposes a secondary battery and its preparation method, as well as an electrical device thereof. The secondary battery proposed in this application can effectively solve the problem of rapid capacity decay or even a complete capacity drop due to lack of electrolyte during secondary battery cycling.

[0004] The first aspect of this application provides a secondary battery, the secondary battery including a housing, at least one electrode assembly and an electrolyte, the electrode assembly and the electrolyte being disposed within the housing, the electrode assembly including a positive electrode, a separator and a negative electrode stacked sequentially; a composite liquid storage structure is provided between the electrode assembly and the housing, the composite liquid storage structure including a first layer and a second layer stacked sequentially along the direction of the electrode assembly toward the housing, the first layer including a flame retardant layer and the second layer including a liquid storage layer.

[0005] The secondary battery proposed in this application incorporates a composite electrolyte storage structure between the electrode assembly and the casing. The second layer of this composite electrolyte storage structure absorbs excess electrolyte after the electrode assembly has been fully wetted, thus achieving electrolyte storage. During subsequent secondary battery cycles, the electrode assembly expands and compresses the composite electrolyte storage structure, allowing the discharged electrolyte to wet the electrode assembly, thereby continuously replenishing the secondary battery and mitigating the problem of electrolyte deficiency during cycling. Furthermore, the second layer provides a buffer space for electrode assembly expansion, further improving the battery's cycle life. In addition, the first layer of the composite electrolyte storage structure has a certain degree of flatness and hardness, preventing distortion and deformation of the positive and negative electrode plates due to uneven thickness during compression of the second electrolyte storage layer. Moreover, the first layer is made of flame-retardant material, which enhances the safety of the secondary battery to a certain extent. In summary, the secondary battery proposed in this application effectively solves the problem of rapid capacity decay or even a sharp drop in capacity due to electrolyte deficiency during secondary battery cycling.

[0006] According to some embodiments of this application, the flame-retardant layer comprises a flame-retardant material; the flame-retardant material is selected from one or more of epoxy resin, acrylonitrile-butadiene-styrene copolymer, and polycarbonate; preferably, the thickness of the first layer is 0.1 mm to 2 mm; preferably, the electrolyte storage layer comprises foam, preferably, the foam comprises one or more of polyurethane foam, polyester foam, rubber foam, polyvinyl chloride foam, and silicone foam; preferably, the porosity of the second layer is 10% to 96%; preferably, the negative electrode comprises a negative electrode active material layer, the thickness of the second layer is (0.05h to 0.5h) mm, where h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly, in mm. This can further improve the problem of insufficient electrolyte during cycling and increase the cycle life of the secondary battery.

[0007] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material, which includes one or more of lithium metal, graphite, silicon-based materials, and hard carbon. This can improve the energy density of the secondary battery.

[0008] According to some embodiments of this application, the secondary battery satisfies one or more of the following conditions: the liquid storage capacity of the second layer P = S·H·β / 1000ρ, where P is in g and S is the surface area of ​​the second layer in mm. 2 H is the thickness of the second layer in mm, β is the porosity of the second layer, and ρ is the density of the electrolyte in g / cm³. 3The second layer's liquid storage capacity is greater than or equal to the electrolyte replenishment volume. The negative electrode includes a negative electrode active material layer, and the thickness H of the second layer satisfies: H·β≥Φ·

h·(1-α)·(k1·φ+k2·ψ)

[0009] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; based on the total mass of the negative electrode active material, the mass percentage of the silicon-based material is 5%~95%, the liquid storage capacity P of the second layer is (0.05C~0.5C)g, and the thickness of the second layer is (0.05h~0.5h)mm, where C is the capacity of the secondary battery in Ah, and h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly in mm. Therefore, the energy density and cycle life of the secondary battery can be further improved.

[0010] According to some embodiments of this application, the liquid storage capacity of the second layer is 0.5g to 35g; and / or, the thickness of the second layer is 0.1mm to 5mm. This can further improve the energy density and cycle life of the secondary battery.

[0011] According to some embodiments of this application, the electrode assembly is a stacked structure or a wound structure. This can further improve the energy density and cycle life of the secondary battery.

[0012] According to some embodiments of this application, the composite electrolyte storage structure is disposed on both sides of the electrode assembly and arranged parallel to at least one positive electrode, the separator, and the negative electrode. This further improves the problem of electrolyte deficiency during cycling and increases the cycle life of the secondary battery.

[0013] The second aspect of this application provides a method for preparing the secondary battery provided in the first aspect of this application. The method includes: assembling a negative electrode, a separator, and a positive electrode to obtain an electrode assembly; fixing a composite liquid storage structure containing a first layer and a second layer on the surface of the electrode assembly; placing the electrode assembly containing the composite liquid storage structure in a housing and injecting electrolyte to obtain a secondary battery.

[0014] The secondary battery prepared in this application has a composite electrolyte storage structure between the electrode assembly and the casing. The second layer of the composite electrolyte storage structure can absorb excess electrolyte after the electrode assembly is fully wetted, thereby achieving the effect of storing electrolyte. During subsequent secondary battery cycles, the electrode assembly expands and compresses the composite electrolyte storage structure, and the discharged electrolyte can wet the electrode assembly, thereby achieving the purpose of continuous electrolyte replenishment for the secondary battery and improving the problem of electrolyte shortage during cycling. Furthermore, the second layer can also provide buffer space for the expansion of the electrode assembly, further improving the cycle life of the battery. The first layer of the composite electrolyte storage structure has a certain degree of flatness and hardness, which can avoid the distortion and deformation of the positive and negative electrode plates due to uneven thickness of the second layer during compression. Moreover, the first layer of the composite electrolyte storage structure is a flame-retardant material, which can improve the safety of the secondary battery to a certain extent. In addition, this preparation method can achieve the preparation of secondary batteries without making significant changes to the original secondary battery production process.

[0015] A third aspect of this application provides an electrical device, including the battery provided in the first aspect of this application. Attached Figure Description

[0016] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the electrode assembly of a square secondary battery provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the composite liquid storage structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram showing the positions of the electrode assembly and composite liquid storage structure provided in the embodiments of the present invention; Figure 4 This is a comparison chart of the cycle data of the secondary batteries in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0017] Figure label: 101 Electrode assembly; 102 First layer; 103 Second layer; 104 Composite liquid storage structure; 105 Electrode assembly equipped with composite liquid storage structure. Detailed Implementation

[0018] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0019] The first aspect of this application provides a secondary battery; please refer to [link / reference]. Figures 1-3 The secondary battery includes a casing, at least one electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are disposed within the casing. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked sequentially. A composite liquid storage structure is provided between the electrode assembly and the casing. The composite liquid storage structure includes a first layer and a second layer stacked sequentially along the direction of the electrode assembly toward the casing. The first layer includes a flame-retardant layer, and the second layer includes a liquid storage layer.

[0020] The secondary battery proposed in this application incorporates a composite electrolyte storage structure between the electrode assembly and the casing. The second layer of this composite electrolyte storage structure absorbs excess electrolyte after the electrode assembly has been fully wetted, thus achieving electrolyte storage. During subsequent secondary battery cycles, the electrode assembly expands and compresses the composite electrolyte storage structure, allowing the discharged electrolyte to wet the electrode assembly, thereby continuously replenishing the secondary battery and mitigating the problem of electrolyte deficiency during cycling. Furthermore, the second layer provides a buffer space for electrode assembly expansion, further improving the battery's cycle life. In addition, the first layer of the composite electrolyte storage structure has a certain degree of flatness and hardness, preventing distortion and deformation of the positive and negative electrode plates due to uneven thickness during compression of the second layer. Moreover, the first layer is made of flame-retardant material, which enhances the safety of the secondary battery to some extent. In summary, the secondary battery proposed in this application effectively solves the problem of rapid capacity decay or even a sharp drop in capacity due to electrolyte deficiency during secondary battery cycling.

[0021] When assembling the secondary battery modules according to this application, there is no need to use additional flame-retardant materials such as epoxy resin or foam cushioning materials, making the module assembly simpler and faster. Furthermore, this technical solution achieves the invention's objective without requiring significant changes to the existing secondary battery manufacturing process.

[0022] According to some embodiments of this application, the flame-retardant layer comprises a flame-retardant material; the flame-retardant material is selected from one or more of epoxy resin, acrylonitrile-butadiene-styrene copolymer, and polycarbonate. The first layer of the above material has a certain degree of flatness and hardness, which can avoid the distortion and deformation of the positive and negative electrode sheets caused by uneven thickness of the second layer during compression. Furthermore, the first layer of the above material is a flame-retardant material, which can improve the safety of the secondary battery to a certain extent.

[0023] According to some embodiments of this application, the thickness of the first layer is 0.1mm to 2mm. For example, the thickness of the first layer can be 0.1mm, 0.2mm, 0.5mm, 0.8mm, 1mm, 1.2mm, 1.5mm, 1.7mm, 2mm, or any combination of two of these values. Therefore, the first layer of the above material and thickness is insulating, incompressible, and possesses a certain degree of hardness and toughness. This further prevents the positive and negative electrode sheets from twisting or deforming due to uneven thickness during compression of the second layer of foam, thus improving the cycle life of the secondary battery. Furthermore, the first layer is made of flame-retardant material, which can improve the safety of the secondary battery to a certain extent. Controlling the thickness of the first layer within the above range avoids insufficient strength caused by an excessively thin first layer, ensuring that the second layer does not exhibit unevenness under stress, reducing damage such as deformation to the battery electrodes. It also avoids a decrease in the battery's gravimetric and volumetric energy density caused by an excessively thick first layer.

[0024] According to some embodiments of this application, the foam includes one or more of polyurethane foam, polyester foam, rubber foam, polyvinyl chloride foam, and silicone foam. Therefore, the foam made of the above materials has a strong ability to absorb electrolyte and strong stability in electrolyte. It can release electrolyte when under pressure to achieve the purpose of continuous electrolyte replenishment and improve the problem of lack of electrolyte in circulation.

[0025] According to some embodiments of this application, the porosity of the second layer is 10%-96%. As an example, the porosity of the second layer can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 96%, or any two of the above values. By controlling the porosity of the second layer within the above range, the second layer can fully absorb excess electrolyte. In subsequent secondary battery cycles, the electrode assembly expands and squeezes the composite electrolyte storage structure, thereby discharging electrolyte that can wet the electrode assembly, thus achieving the purpose of continuous electrolyte replenishment for the secondary battery, improving the problem of insufficient electrolyte during cycling, and increasing the cycle life of the secondary battery.

[0026] It is understandable that the porosity of the second layer can be determined by any of the following methods: liquid absorption method, buoyancy method, gas expansion method, microscopic image analysis method, etc.

[0027] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, and the thickness of the second layer is (0.05h~0.5h) mm, where h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly, in mm. For example, the thickness of the second layer can be 0.05h, 0.1h, 0.2h, 0.3h, 0.4h, 0.5h, or any combination of the above values. Therefore, during the charging process of the secondary battery, the volume expansion is mainly caused by the negative electrode. Thus, the total thickness of the negative electrode active material layer needs to be considered, and the thickness of the second layer should be controlled within the above range. The second layer can fully absorb excess electrolyte, and in subsequent secondary battery cycles, the expansion of the electrode assembly squeezes the composite electrolyte storage structure, thereby allowing the discharged electrolyte to wet the electrode assembly, achieving the purpose of continuous electrolyte replenishment for the secondary battery, improving the problem of insufficient electrolyte during cycling, and increasing the cycle life of the secondary battery. Furthermore, the second layer does not occupy excessive space inside the casing, ensuring that the secondary battery has excellent energy density.

[0028] It is understandable that there can be many layers of positive electrode, separator and negative electrode in the thickness direction of the electrode assembly. The total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly = the thickness of the negative electrode active material in a single negative electrode × the number of negative electrode layers.

[0029] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material, which includes one or more of lithium metal, graphite, silicon-based materials, and hard carbon; according to other embodiments of this application, the negative electrode active material includes one or more of lithium metal and silicon-based materials. Therefore, high-energy-density secondary batteries typically contain a large amount of silicon-based material or are lithium metal negative electrodes. Silicon-based materials or lithium metal negative electrodes exhibit more significant volume effects during charge and discharge, leading to cracks and breakage in silicon-based materials and the formation of a loose, porous structure on the surface of lithium negative electrodes. These negative electrodes consume electrolyte more significantly. Therefore, using a composite electrolyte storage structure in secondary batteries containing the aforementioned negative electrodes results in a more significant improvement in battery life.

[0030] According to some embodiments of this application, the liquid storage capacity of the second layer is P = S·H·β / 1000ρ, where P is in grams and S is the surface area of ​​the second layer in mm². 2 H is the thickness of the second layer in mm, β is the porosity of the second layer, and ρ is the density of the electrolyte in g / cm³. 3 .

[0031] According to some embodiments of this application, the liquid storage capacity of the second layer is greater than or equal to the replenishment amount of the electrolyte, thereby ensuring that there is sufficient electrolyte inside the shell and further improving the wetting performance of the electrolyte on the electrode assembly.

[0032] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, and the thickness H of the second layer satisfies: H·β≥Φ·

h·(1-α)·(k1·φ+k2·ψ)

[0033] It is understandable that the charging volume expansion coefficient can be determined by the following method: The negative electrode active material (such as graphite, hard carbon, silicon-based material) is mixed with conductive agent and binder, coated, rolled, dried and other processes to make a negative electrode sheet. The thickness of its initial active material layer is measured. Then, it is made into a coin cell with lithium metal. After charging, the battery is disassembled and the thickness of the negative electrode sheet after charging is measured. The charging volume expansion coefficient = the thickness of the negative electrode active material layer after charging / the thickness of the initial negative electrode active material layer.

[0034] The charging volume expansion coefficient of lithium metal is calculated as follows: the initial thickness of the lithium metal layer is measured, and then a coin cell is made with the positive electrode. After charging, the battery is disassembled, and the thickness of the lithium metal after charging is measured. The charging volume expansion coefficient is calculated as: the thickness of the lithium metal layer after charging / the initial thickness of the lithium metal layer.

[0035] According to some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; based on the total mass of the negative electrode active material, the mass percentage of the silicon-based material is 5%~95%, the liquid storage capacity P of the second layer is (0.05C~0.5C)g, and the thickness of the second layer is (0.05h~0.5h)mm, where C is the capacity of the secondary battery in Ah, and h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly in mm. As an example, based on the total mass of the negative electrode active material, the mass percentage of silicon-based material can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or any combination of two of the above values. The electrolyte storage capacity of the second layer can be 0.05C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, or any combination of two of the above values. The thickness of the second layer can be 0.05h, 0.1h, 0.2h, 0.3h, 0.4h, 0.5h, or any combination of two of the above values. Thus, matching the silicon content of the negative electrode with the electrolyte storage capacity and thickness of the second layer can improve the energy density of the secondary battery, avoid electrolyte deficiency, and improve the cycle performance of the secondary battery.

[0036] According to some embodiments of this application, the liquid storage capacity of the second layer is 0.5g to 35g, for example, it can be 0.5g, 1g, 5g, 10g, 15g, 20g, 25g, 30g, 35g or any two of the above values. Thus, the second layer is sufficient to absorb the excess electrolyte after the electrode assembly is fully wetted, thereby achieving the effect of storing electrolyte, and without causing poor wetting of the electrode assembly due to excessive liquid storage capacity, thereby improving the cycle performance of the secondary battery.

[0037] According to some embodiments of this application, the thickness of the second layer is 0.1mm to 5mm, for example, it can be 0.1mm, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm or any two of the above values. Thus, the second layer is sufficient to absorb the excess electrolyte after the electrode assembly is fully wetted, thereby achieving the effect of storing electrolyte, without being too thick and occupying too much weight of the secondary battery, thus affecting the energy density of the secondary battery.

[0038] According to some embodiments of this application, the electrode assembly is a stacked structure or a wound structure. Thus, the secondary battery with the stacked structure or wound structure is matched with the above-mentioned composite liquid storage structure, which can better give full play to the advantages of the stacked battery and further improve the energy density and cycle life of the secondary battery.

[0039] According to some embodiments of this application, the composite liquid storage structure is disposed on both sides of the electrode assembly and is arranged parallel to at least one positive electrode, the separator, and the negative electrode. Please refer to... Figure 3 The composite electrolyte storage structure is fixed (e.g., glued) to both sides of the large outer surface of the electrode assembly. Since the "breathing effect" of the expanded and contracted stacked electrode assembly generally occurs in the thickness direction, positioning the composite electrolyte storage structure nearly perpendicular to the thickness direction—that is, parallel to at least one of the positive electrode, the separator, and the negative electrode—allows it to withstand pressure during battery expansion, releasing some electrolyte and wetting the electrode assembly. This achieves continuous electrolyte replenishment for the secondary battery, improving the problem of electrolyte deficiency during cycling. Furthermore, the second layer provides a buffer space for electrode assembly expansion, further enhancing the battery's cycle life.

[0040] In a second aspect, this application proposes a method for preparing the aforementioned secondary battery. According to an embodiment of this application, the method includes: S1: Assemble the negative electrode, the separator, and the positive electrode to obtain the electrode assembly; S2: Fix the composite liquid storage structure containing the first layer and the second layer to the surface of the electrode assembly; S3: Place the electrode assembly containing the composite liquid storage structure into the housing, inject electrolyte, and obtain a secondary battery.

[0041] According to some embodiments of this application, the method can be carried out in the following steps: Z-shaped stacking of negative electrode sheet, separator and positive electrode sheet to obtain bare dry cell (electrode assembly); adhesive tape is used to attach and fix the composite electrolyte storage structure to both sides of the large outer surface of the bare dry cell; tab welding and shell encapsulation are performed on the bare dry cell after attaching the composite electrolyte storage structure; electrolyte is added to the encapsulated battery and it is sealed for the first time; after electrolyte injection, the battery is formed and sealed for the second time to obtain a lithium-ion battery.

[0042] In summary, the secondary battery preparation method proposed in this application provides a secondary battery with a composite electrolyte storage structure between the electrode assembly and the casing. The second layer of the composite electrolyte storage structure can absorb excess electrolyte after the electrode assembly is fully wetted, thereby achieving the effect of storing electrolyte. During subsequent secondary battery cycles, the electrode assembly expands and compresses the composite electrolyte storage structure, allowing the discharged electrolyte to wet the electrode assembly, thus achieving the purpose of continuous electrolyte replenishment and improving the problem of electrolyte deficiency during cycling. Furthermore, the second layer can also provide buffer space for the expansion of the electrode assembly, further improving the cycle life of the battery. In addition, this preparation method can achieve the preparation of secondary batteries without making significant changes to the original secondary battery manufacturing process.

[0043] As an example, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator located between the positive and negative electrodes. During the charging and discharging process of the secondary battery, active lithium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0044] According to some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes the aforementioned positive active material. The positive current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive current collector can be an aluminum foil.

[0045] According to some embodiments of this application, the positive electrode active materials include, but are not limited to, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium cobalt oxide.

[0046] According to some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin.

[0047] According to some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0048] According to some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0049] It should be noted that the features and advantages described above for the positive electrode active material and its preparation method also apply to this positive electrode sheet, and will not be repeated here.

[0050] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive electrode current collector can be a copper foil.

[0051] According to some embodiments of the present invention, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0052] According to some embodiments of the present invention, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0053] According to some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, and binder, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes.

[0054] According to some embodiments of the present invention, the negative electrode sheet may also be a lithium metal sheet.

[0055] According to further embodiments of the present invention, the type of separator is not particularly limited, and any known porous separator with good chemical and mechanical stability can be selected. As an example, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0056] According to some embodiments of the present invention, the electrolyte comprises a lithium salt and a solvent.

[0057] According to some specific embodiments of the present invention, the lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, or lithium bis(trifluoromethanesulfonyl)imide.

[0058] According to some specific embodiments of the present invention, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0059] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0060] It should be noted that the features and advantages described above for the positive electrode also apply to this battery, and will not be repeated here.

[0061] In a third aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device includes the battery described above. According to an embodiment of the invention, the electrical device may include, but is not limited to, mobile phones, laptops, electric vehicles, etc.

[0062] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0063] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0064] Example 1 (1) Preparation of bare dry cell 101 (electrode assembly): The positive electrode sheet containing ternary nickel cobalt manganese oxide (NCM9 system) (the positive electrode active layer is composed of NCM9 system (chemical formula LiNi)) is prepared. 0.915 Co 0.065 Mn 0.02 O2): SP:PVDF5130 = 97:1.4:1.6 (mass ratio), coating amount is 40mg / cm³ 2 Compacted density 3.5 g / cm³ 3The current collector is an aluminum foil with a thickness of 13 μm; the negative electrode sheet contains 15% silicon suboxide (the mass percentage of silicon-based material in the negative electrode active material is 15%), and the composition of the negative electrode active layer is graphite: silicon suboxide: SP (conductive carbon black): SWCNT (single-walled carbon nanotubes): CMC (carboxymethyl cellulose): PAA (polyacrylic acid): SBR (styrene-butadiene rubber) = 81.26: 14.34: 0.95: 0.05: 0.9: 1.3: 1.2 (mass ratio), with a compaction density of 1.52 g / cm³. 3 The current collector is a 4.5μm thick copper foil; the 2μm+12μm+2μm composite separator (composed of a 2μm thick ceramic coating, a 12μm thick base film and a 2μm thick ceramic coating stacked sequentially, purchased from Shenzhen Xingyuan Material Technology Co., Ltd., grade SH716W22) is stacked in a Z-shape to obtain a bare dry cell (N / P ratio is 1.05, and the designed capacity of the bare dry cell is 25Ah).

[0065] (2) A composite liquid storage structure consisting of an inner layer (first layer) of 1mm epoxy resin board and an outer layer (second layer) of 1mm thick open-cell polyurethane foam with a porosity of 50% is attached to the two outer surfaces of the bare dry cell 101. Then, the tabs are welded and the aluminum-plastic film shell is encapsulated. The designed liquid replenishment amount is 8g, and the liquid replenishment amount for each composite liquid storage structure is 4g. The liquid replenishment amount should be less than or equal to the liquid storage capacity P=5.43g of the composite liquid storage structure (P=S·H·β / 1000·ρ=5.43g, where S is the surface area of ​​the outer layer of the liquid storage layer, 7359mm²). 2 H is the thickness of the outer layer of the electrolyte (1 mm on one side, 2 mm in total on both sides; in the formula, H = 1 mm), β is the porosity of the outer layer of the electrolyte (60%), and ρ is the density of the electrolyte (1.23 g / cm³). 3 ), and H also satisfies H≥Φ·

h·(1-α)·(k1·φ+k2·ψ)

h·(1-α)·(k1·φ+k2·ψ)

h·(1-α)·(k1·φ+k2·ψ)

[0066] (3) Add electrolyte to the packaged battery (the amount of electrolyte is 43g, and the electrolyte composition is in the mass ratio of LiPF6:LiFSI:EC:EMC:DTD:FEC:PS:LiPO2F2=11:3:20:54:1.7:8:1.5:0.8 (wt%)) and seal it once.

[0067] (4) After the battery is filled with electrolyte, it is subjected to formation at room temperature for 48 hours (at a temperature of 45℃ and a pressure of 0.6MPa, it is charged at 0.2C to 4.25V, charged at constant voltage to 0.05C, left to stand for 20 minutes, discharged at 0.2C to 2.75V, left to stand for 20 minutes) and then sealed again to obtain a lithium-ion secondary battery.

[0068] Example 2 (1) Preparation of bare dry cell 101 (electrode assembly): The preparation of the positive electrode sheet is the same as in Example 1; the negative electrode sheet contains 5% silicon suboxide (the mass ratio of silicon-based material in the negative electrode active material is 5%), and the composition of the negative electrode active layer is graphite: silicon suboxide: SP (conductive carbon black): SWCNT (single-walled carbon nanotubes): CMC (carboxymethyl cellulose): PAA (polyacrylic acid): SBR (styrene-butadiene rubber) = 90.82: 4.78: 0.95: 0.05: 0.9: 1.3: 1.2 (mass ratio), and the compaction density is 1.52 g / cm³. 3 The current collector is a 4.5μm thick copper foil; the 2μm+12μm+2μm composite separator (composed of a 2μm thick ceramic coating, a 12μm thick base film and a 2μm thick ceramic coating stacked sequentially, purchased from Shenzhen Xingyuan Material Technology Co., Ltd., grade SH716W22) is stacked in a Z-shape to obtain a bare dry cell (N / P ratio is 1.05, and the designed capacity of the bare dry cell is 25Ah).

[0069] (2) A composite liquid storage structure consisting of an inner layer (first layer) of 1mm epoxy resin board and an outer layer (second layer) of 0.6mm thick open-pore polyurethane foam with a porosity of 43% is attached to the two outer surfaces of the bare dry cell 101, and then the tabs are welded and the aluminum-plastic film shell is encapsulated.

[0070] (3) and (4) are the same as in Example 1.

[0071] Example 3 (1) Preparation of bare dry cell 101 (electrode assembly): The preparation of the positive electrode sheet is the same as in Example 1; the negative electrode sheet contains 95% silicon suboxide (the mass ratio of silicon-based material in the negative electrode active material is 95%), and the composition of the negative electrode active layer is graphite: silicon suboxide: SP (conductive carbon black): SWCNT (single-walled carbon nanotubes): CMC (carboxymethyl cellulose): PAA (polyacrylic acid): SBR (styrene-butadiene rubber) = 4.78: 90.82: 0.95: 0.05: 0.9: 1.3: 1.2 (mass ratio), and the compaction density is 1.52 g / cm³. 3 The current collector is a 4.5μm thick copper foil; the 2μm+12μm+2μm composite separator (composed of a 2μm thick ceramic coating, a 12μm thick base film and a 2μm thick ceramic coating stacked sequentially, purchased from Shenzhen Xingyuan Material Technology Co., Ltd., grade SH716W22) is stacked in a Z-shape to obtain a bare dry cell (N / P ratio is 1.05, and the designed capacity of the bare dry cell is 25Ah).

[0072] (2) A composite liquid storage structure consisting of an inner layer (first layer) of 1mm epoxy resin board and an outer layer (second layer) of 3.5mm thick open-pore polyurethane foam with a porosity of 38% is attached to the two outer surfaces of the bare dry cell 101, and then the tabs are welded and the aluminum-plastic film shell is encapsulated.

[0073] (3) and (4) are the same as in Example 1.

[0074] Example 4 (1) Preparation of bare dry cell 101 (electrode assembly): The preparation of the positive electrode sheet is the same as in Example 1; the negative electrode sheet contains 50% silicon suboxide (the mass ratio of silicon-based material in the negative electrode active material is 50%), and the composition of the negative electrode active layer is graphite: silicon suboxide: SP (conductive carbon black): SWCNT (single-walled carbon nanotubes): CMC (carboxymethyl cellulose): PAA (polyacrylic acid): SBR (styrene-butadiene rubber) = 47.8: 47.8: 0.95: 0.05: 0.9: 1.3: 1.2 (mass ratio), and the compaction density is 1.52 g / cm³. 3 The current collector is a 4.5μm thick copper foil; the 2μm+12μm+2μm composite separator (composed of a 2μm thick ceramic coating, a 12μm thick base film and a 2μm thick ceramic coating stacked sequentially, purchased from Shenzhen Xingyuan Material Technology Co., Ltd., grade SH716W22) is stacked in a Z-shape to obtain a bare dry cell (N / P ratio is 1.05, and the designed capacity of the bare dry cell is 25Ah).

[0075] (2) The composite liquid storage structure, consisting of an inner layer (first layer) of 1mm epoxy resin board and an outer layer (second layer) of 2mm thick open-pore polyurethane foam with a porosity of 46%, is attached to the two outer surfaces of the bare dry cell 101, and then the tabs are welded and the aluminum-plastic film shell is encapsulated.

[0076] (3) and (4) are the same as in Example 1.

[0077] Example 5 (1) Preparation of bare dry cell 101 (electrode assembly): The preparation of the positive electrode sheet is the same as in Example 1; the negative electrode is a composite negative electrode of 50um lithium / 4.5μm copper foil; the 2μm+12μm+2μm composite separator (composed of a ceramic coating with a thickness of 2μm, a base film with a thickness of 12μm and a ceramic coating with a thickness of 2μm stacked in sequence, purchased from Shenzhen Xingyuan Material Technology Co., Ltd., brand name SH716W22) is Z-shaped stacked to obtain a bare dry cell (N / P ratio is 1.05, and the design capacity of the bare dry cell is 25Ah).

[0078] (2) A composite liquid storage structure consisting of an inner layer (first layer) of 1mm epoxy resin board and an outer layer (second layer) of 2.5mm thick open-pore polyurethane foam with a porosity of 70% is attached to the two outer surfaces of the bare dry cell 101, and then the tabs are welded and the aluminum-plastic film shell is encapsulated.

[0079] (3) and (4) are the same as in Example 1.

[0080] Comparative Example 1 The composite liquid storage structure of Comparative Example 1 does not have a first layer, but is otherwise the same as that of Example 1.

[0081] Comparative Example 2 Comparative Example 2 does not contain a composite liquid storage structure, but is otherwise the same as Example 1.

[0082] Comparative Example 3 Comparative Example 3 does not contain a composite liquid storage structure, but is otherwise the same as Example 2.

[0083] Comparative Example 4 Comparative Example 4 does not contain a composite liquid storage structure, but is otherwise the same as Example 3.

[0084] Comparative Example 5 Comparative Example 5 does not contain a composite liquid storage structure, but is otherwise the same as Example 4.

[0085] Comparative Example 6 Comparative Example 6 does not contain a composite liquid storage structure, but is otherwise the same as Example 5.

[0086] Performance testing (1) Record the electrolyte retention of the secondary battery. Electrolyte retention = total weight - weight of bare dry cell - weight of composite electrolyte structure - weight of tab - weight of casing. The data are shown in the table below.

[0087] (2) Battery cycle performance test: At 25℃±3℃, the battery was charged at 0.5C to 4.25V, kept constant at 0.05C, and left to stand for 15 minutes. It was then discharged at 0.5C to 2.75V and left to stand for 25 minutes. This cycle was repeated, and the capacity retention rate was calculated. Data are shown in Table 2 and... Figure 4 .

[0088] The test results of the batteries in the examples and comparative examples are shown in the table below.

[0089] Table 1

[0090] Table 2

[0091] As shown in Tables 1 and 2, when using the technical solution of this embodiment, compared with Comparative Example 2, in Table 2, it is shown that the excess electrolyte exceeding the inherent liquid absorption capacity of the battery cell will be eliminated, and the existing composite liquid storage structure can effectively absorb the excess electrolyte, thereby achieving the effect of storing electrolyte.

[0092] As shown in Table 2, the cycle life of the secondary battery in Comparative Example 1, which only contains a second layer of electrolyte storage structure or a composite electrolyte storage structure, is significantly improved. This is because the second layer of the composite electrolyte storage structure, attached to both sides of the large outer surface of the electrode assembly, has the ability to store electrolyte. During subsequent battery cycles, the electrode expands and squeezes the second layer of the electrolyte storage structure. The electrolyte discharged from the squeezed second layer can wet the electrode assembly, thereby achieving the purpose of continuously replenishing the electrolyte in the secondary battery. Furthermore, the second layer provides a buffer space for the expansion of the secondary battery, further improving the battery's cycle life.

[0093] As demonstrated in Example 1 and Comparative Example 1, the battery containing the first layer exhibits significantly better cycle performance than the battery without the first layer. This is because the first layer of the composite electrolyte storage structure possesses a certain degree of flatness and hardness, thus preventing adverse consequences such as electrode distortion and deformation caused by uneven thickness in the open-pore structure of the second layer during compression, thereby improving cycle performance. Furthermore, the first layer is made of flame-retardant material, which can enhance battery safety to a certain extent.

[0094] Table 3

[0095] Comparative Example 3 does not contain a composite liquid storage structure, but is otherwise the same as Example 2.

[0096] Table 4

[0097] As shown in Tables 3 and 4, when the silicon-based material content is 5%, the liquid storage structure can solve the problem of rapid capacity decay or even a sharp drop in capacity caused by lack of electrolyte during secondary battery cycling.

[0098] Table 5

[0099] Comparative Example 4 does not contain a composite liquid storage structure, but is otherwise the same as Example 3.

[0100] Table 6

[0101] As shown in Tables 5 and 6, when the silicon-based material content is 95%, the liquid storage structure can solve the problem of rapid capacity decay or even a sharp drop in capacity caused by lack of electrolyte during secondary battery cycling.

[0102] Table 7

[0103] Comparative Example 5 does not contain a composite liquid storage structure, but is otherwise the same as Example 4.

[0104] Table 8

[0105] As shown in Tables 7 and 8, when the silicon-based material content is 50%, the liquid storage structure can solve the problem of rapid capacity decay or even a sharp drop in capacity caused by lack of electrolyte during secondary battery cycling.

[0106] Table 9

[0107] In Example 5, the negative electrode is a lithium metal negative electrode, which was purchased from Tianjin Zhongneng Lithium Industry Co., Ltd. The thickness of the lithium metal layer is 50 μm. Comparative Example 6 does not contain a composite liquid storage structure, and is otherwise the same as Example 5.

[0108] Table 10

[0109] As shown in Tables 9 and 10, when lithium metal is used as the negative electrode, the liquid storage structure can solve the problem of rapid capacity decay or even a sharp drop in capacity caused by lack of electrolyte during secondary battery cycling.

[0110] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0111] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a casing, at least one electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are disposed inside the casing. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked in sequence. A composite liquid storage structure is provided between the electrode assembly and the housing. The composite liquid storage structure includes a first layer and a second layer stacked sequentially along the direction of the electrode assembly toward the housing. The first layer includes a flame-retardant layer, and the second layer includes a liquid storage layer.

2. The secondary battery according to claim 1, characterized in that, The flame-retardant layer includes a flame-retardant material; the flame-retardant material is selected from one or more of epoxy resin, acrylonitrile-butadiene-styrene copolymer, and polycarbonate. Preferably, the thickness of the first layer is 0.1mm to 2mm; Preferably, the liquid storage layer comprises foam, and more preferably, the foam comprises one or more of polyurethane foam, polyester foam, rubber foam, polyvinyl chloride foam, and silicone foam; Preferably, the porosity of the second layer is 10%-96%; Preferably, the negative electrode sheet includes a negative electrode active material layer, and the thickness of the second layer is (0.05h~0.5h) mm, where h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly, in mm.

3. The secondary battery according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes one or more of lithium metal, graphite, silicon-based materials, and hard carbon.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The secondary battery satisfies one or more of the following conditions: The liquid storage capacity of the second layer is P = S·H·β / 1000ρ, where P is in grams and S is the surface area of ​​the second layer in mm. 2 H is the thickness of the second layer in mm, β is the porosity of the second layer, and ρ is the density of the electrolyte in g / cm³. 3 ; The liquid storage capacity of the second layer is greater than or equal to the replenishment volume of the electrolyte; The negative electrode sheet includes a negative electrode active material layer, and the thickness H of the second layer satisfies: H·β≥Φ·【h·(1-α)·(k1·φ+k2·ψ)】, where β is the porosity of the second layer, Φ is the expansion coefficient of the negative electrode expansion buffer space, preferably 100%~120%; h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly, in mm, α is the porosity% of the negative electrode sheet, φ is the proportion of the volume of silicon-based material or lithium metal to the volume of the negative electrode sheet, ψ is the proportion of the volume of graphite or hard carbon to the volume of the negative electrode sheet, k1 is the charging volume expansion coefficient of silicon-based material or lithium metal, and k2 is the charging volume expansion coefficient of graphite or hard carbon.

5. The secondary battery according to any one of claims 1 to 3, characterized in that, The negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; Based on the total mass of the negative electrode active material, the mass ratio of the silicon-based material is 5%~95%, the liquid storage capacity of the second layer is P=(0.05C~0.5C)g, and the thickness of the second layer is (0.05h~0.5h)mm, where C is the capacity of the secondary battery in Ah, and h is the total thickness of the negative electrode active material layer in the thickness direction of the electrode assembly in mm.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, The second layer has a liquid storage capacity of 0.5g to 35g; and / or, The thickness of the second layer is 0.1mm to 5mm.

7. The secondary battery according to any one of claims 1 to 3, characterized in that, The electrode assembly has a stacked structure or a wound structure.

8. The secondary battery according to claim 7, characterized in that, The composite liquid storage structure is disposed on both sides of the electrode assembly and is arranged parallel to at least one of the positive electrode plates, the separator, and the negative electrode plate.

9. A method for preparing a secondary battery according to any one of claims 1 to 8, characterized in that, include: The negative electrode, the separator, and the positive electrode are assembled to obtain the electrode assembly. A composite liquid storage structure containing a first layer and a second layer is fixed on the surface of the electrode assembly; The electrode assembly containing the composite liquid storage structure is placed in the housing and an electrolyte is injected to obtain a secondary battery.

10. An electrical appliance, characterized in that, Includes the secondary battery according to any one of claims 1 to 8, or the secondary battery prepared by the method according to claim 9.

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