Secondary batteries and electrical devices

Abstract

This application discloses a secondary battery and an electrical device. The secondary battery includes electrode plates and a composite separator, the composite separator being located on one side of the electrode plates. The composite separator includes a first base film, a second base film, and a gel electrolyte located between the first and second base films. The gel electrolyte includes at least one of a polyether compound and a polyester compound. This secondary battery exhibits good cycle performance.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to secondary batteries and electrical devices. Background Technology

[0002] Rechargeable batteries, as important new energy storage devices, are widely used in various electrical devices to provide power. Furthermore, with the continuous development of battery technology, users' requirements for rechargeable batteries are also increasing, demanding higher capacity and longer cycle life. Moreover, when batteries are left unused for extended periods, the electrolyte concentrates at the bottom of the battery due to gravity. The battery electrode tips have limited capacity to absorb electrolyte, leading to electrolyte breakage at the battery tip. During charging and discharging, problems such as rapid cycle drops due to the lack of electrolyte bridging occur.

[0003] Therefore, the performance of current secondary batteries and electrical devices still needs improvement. Summary of the Invention

[0004] In view of the above problems, this application provides a secondary battery and an electrical device. The secondary battery has a composite separator, which enhances the adsorption and retention capacity of the electrolyte through the gel-like electrolyte within the composite separator. This alleviates the electrolyte breakage at the electrode tips during cycling caused by poor electrolyte retention at the electrode tips, thus affecting the cycle life of the secondary battery. Furthermore, the composite separator uses two base films to hold the gel-like electrolyte. On the one hand, this better limits the gel-like electrolyte, preventing it from detaching or peeling off during use. On the other hand, the two base films also isolate the gel-like electrolyte from the electrode phase of the secondary battery, avoiding the problem of reaction between the gel-like electrolyte and the electrode metal due to direct contact between the gel-like electrolyte and the battery electrode.

[0005] In one aspect of this application, a secondary battery is provided. The secondary battery includes electrode plates and a composite separator located on one side of the electrode plates. The composite separator includes a first base film, a second base film, and a gel electrolyte located between the first and second base films. The gel electrolyte includes at least one of a polyether compound and a polyester compound. This secondary battery exhibits good cycle performance.

[0006] According to embodiments of this application, the polyether compound includes at least one of polyethylene oxide, polyethylene oxide, polypropylene ether, polyetherketone, and polymethyl ether, and the polyester compound includes at least one of polymethyl methacrylate, polyethylene terephthalate, and polybutylene terephthalate. The gel electrolyte formed by the above compounds has good stability and good compatibility with the electrolyte.

[0007] According to embodiments of this application, the gel electrolyte can swell in the electrolyte by absorbing the electrolyte, and the mass and / or volume of the gel electrolyte after swelling is 1-5 times that of the gel electrolyte before swelling. Therefore, the gel electrolyte has good liquid absorption and retention properties.

[0008] According to embodiments of this application, the secondary battery further includes an electrolyte containing an ether compound, and the gel electrolyte comprises polyethylene oxide. Therefore, the gel electrolyte and the electrolyte exhibit good compatibility.

[0009] According to embodiments of this application, the composite membrane satisfies at least one of the following conditions: the thickness of the first base membrane and the second base membrane are each independently 5-20 μm, the porosity is each independently 35-42%, and the pore size is each independently 30-40 nm; the gel electrolyte is a gel layer formed between the first and second base membranes, and the thickness of the gel layer is 2-10 μm. This further improves the performance of the composite membrane.

[0010] According to an embodiment of this application, the height of the electrode sheet is not less than 100 mm. This further increases the capacity of the secondary battery.

[0011] According to an embodiment of this application, the electrode sheet includes a positive electrode sheet and a negative electrode sheet, and the composite separator is located between the positive electrode sheet and the negative electrode sheet. This further improves the performance of the secondary battery.

[0012] According to an embodiment of this application, the electrode sheet is a positive electrode sheet, and the composite separator further includes a negative electrode conductive layer, which includes a conductive coating and a metal foil, with one side of the conductive coating facing the first or second base film. This secondary battery can be a negative electrode-free system.

[0013] According to embodiments of this application, the secondary battery is a lithium-ion secondary battery or a sodium metal battery. This expands the application scenarios of the secondary battery.

[0014] In another aspect of this application, an electrical device is provided. This electrical device includes a secondary battery as described above, the secondary battery being used to provide electrical energy. Attached Figure Description

[0015] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0017] Figure 2 This is a schematic diagram of the structure of an electrical device according to some embodiments of this application. Detailed Implementation

[0018] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0020] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0024] In the description of the embodiments of this application, the technical terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0025] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0026] As mentioned earlier, since secondary batteries such as power batteries are usually not moved or repositioned during use, the electrolyte tends to concentrate at the bottom of the battery due to gravity as it sits for extended periods. Because the battery's separator and electrodes have limited capacity to absorb the electrolyte, an electrolyte break occurs at the top of the battery, leading to a rapid drop in electrolyte levels during charging and discharging due to the lack of an electrolyte bridge.

[0027] In view of this, this application proposes a secondary battery. The secondary battery includes electrode plates and a composite separator, the composite separator being located on one side of the electrode plates. The composite separator includes a first base film, a second base film, and a gel electrolyte located between the first base film and the second base film. The gel electrolyte includes at least one of a polyether compound and a polyester compound. This secondary battery exhibits good cycle performance.

[0028] The secondary battery proposed in this application employs a composite separator, in which a gel-like electrolyte is sandwiched between two base membranes. Polyether and polyester compounds, which have better compatibility with secondary battery systems, are used to form the gel electrolyte. This composite separator can be applied to a wider range of battery systems, such as lithium-ion batteries and sodium metal batteries. Compared to the traditional approach of simply adding a gel-like electrolyte to a secondary battery, the composite separator utilizes the first and second base membranes to better confine the gel-like electrolyte and prevent direct contact between the gel-like electrolyte and the electrode plates. Therefore, this secondary battery exhibits better cycle stability and effectively mitigates the problem of cycle performance being affected by electrolyte breakage.

[0029] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured lithium-ion secondary battery 1. (See reference...) Figure 1The outer packaging may include a housing 200 and a cover plate 300. The housing 200 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 200 has an opening communicating with the receiving cavity, and the cover plate 300 can be placed over the opening to close the receiving cavity. The electrode assembly 100 described above is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 100. The lithium-ion secondary battery 1 may contain one or more electrode assemblies 100, which can be selected by those skilled in the art according to specific practical needs.

[0030] According to embodiments of this application, the polyether compounds include at least one of polyethylene oxide, polyethylene oxide, polypropylene ether, polyetherketone, and polymethyl ether, and the polyester compounds include at least one of polymethyl methacrylate, polyethylene terephthalate, and polybutylene terephthalate. The gel electrolyte formed by the above compounds exhibits good stability and good compatibility with the electrolyte.

[0031] The aforementioned polymers exhibit good stability in electrolytes and possess a certain adsorption capacity for electrolytes. They also demonstrate good compatibility with commonly used electrolyte systems in secondary batteries, particularly those containing ether compounds. Polyether and polyester compounds allow small-molecule solvents in the electrolyte to better penetrate into the interior of the polymer, being "locked in" by the polyether or polyester compounds through mechanisms such as entering the gaps between polymer chains, thus achieving good liquid absorption and retention properties.

[0032] The gel electrolyte formed from the above-mentioned compounds exhibits good compatibility with electrolytes containing ethers, thus possessing high liquid absorption and retention properties. This can better alleviate or even solve the problem of electrolyte breakage at the battery head caused by insufficient electrolyte adsorption capacity of electrodes and conventional separators. The gel electrolyte formed from the above-mentioned polyether and / or polyester compounds exhibits good stability in electrolytes, especially those containing ethers. After immersion in the electrolyte for a certain period, the gel electrolyte shows no obvious gas production or discoloration. Furthermore, the above-mentioned polymers have good compatibility with the electrolyte, and the resulting gel electrolyte has good wettability in the electrolyte, with a contact angle of 40-55°. In some embodiments, the adsorption effect of the composite separator on the electrolyte can be judged by the degree of electrolyte diffusion on the surface of the composite separator. For example, the composite separator can be immersed in the electrolyte, and the degree of electrolyte diffusion on the surface of the composite separator can be observed. The higher the electrolyte diffusion height and the faster the diffusion rate, the better the adsorption effect of the composite separator on the electrolyte. For example, in some embodiments, the diffusion height of the electrolyte on the surface of the composite membrane can be no less than 1 cm. For example, in some embodiments, the diffusion height can reach 6 cm.

[0033] According to embodiments of this application, the gel electrolyte can swell in the electrolyte by absorbing the electrolyte, and the mass and / or volume of the gel electrolyte will increase accordingly after swelling. In some embodiments, the mass m2 of the swollen gel electrolyte can be 1-5 times the mass m1 of the gel electrolyte before swelling. Alternatively, the volume V2 of the swollen gel electrolyte can be 1-5 times the mass-volume V1 of the gel electrolyte before swelling. Thus, the gel electrolyte has good liquid absorption and retention properties.

[0034] According to embodiments of this application, the secondary battery further includes an electrolyte containing ether compounds. In some examples, the electrolyte may contain diethylene glycol dimethyl ether. Those skilled in the art will understand that the electrolyte may further include other solvents and conductive ionic salts, such as lithium salts. To further improve the performance of the secondary battery, the electrolyte may also contain, but is not limited to, volumetric or additive components that adjust the viscosity and conductivity of the electrolyte, and may also contain additives with functions such as inhibiting gas production and assisting in the formation of an SEI film.

[0035] In some embodiments of this application, the gel electrolyte can be a gel layer sandwiched between the first and second base membranes. The thickness of the gel layer is 2-10 μm. This further improves the performance of the composite membrane.

[0036] The gel layer may include polyethylene oxide. Specifically, a slurry can be formed by mixing polyethylene oxide and water in a mass ratio of (2-5):(5-8), and then depositing the slurry onto a first or second base film by means including but not limited to extrusion coating. The remaining base film can then be laminated to obtain a composite membrane.

[0037] According to the embodiments of this application, the specific types and chemical compositions of the first and second base films are not particularly limited, and those skilled in the art can select the first and second base films according to the actual situation. For example, in some embodiments, polyethylene separator films can be used as the first and second base films.

[0038] According to embodiments of this application, the same or different membrane materials can be selected as the first base membrane and the second base membrane. In some embodiments, the first base membrane and the second base membrane can be formed using the same membrane material. For example, in some embodiments, the thickness of the first and second base membranes can be independently 5-20 μm, the porosity can be independently 35-42%, and the pore size can be independently 30-40 nm. When the thickness, porosity, and pore size of the first and second base membranes are within the above ranges, the composite membrane can have a more reasonable thickness and better lithium-ion conductivity.

[0039] According to embodiments of this application, the height of the electrode plates in the secondary battery can be relatively high. Because the secondary battery incorporates a composite separator with good liquid retention properties, the height of the electrode plates can be no less than 100 mm, and more specifically, no less than 140 mm. For example, it can be 150 mm. This further increases the capacity of the secondary battery.

[0040] Those skilled in the art will understand that in the secondary battery of this application, the composite separator serves to absorb and retain the electrolyte in a gel-state electrolyte, thereby mitigating the electrolyte bridging problem caused by poor electrolyte adsorption capacity of the electrodes. Therefore, when the height of the electrode plates is high, the height of the composite separator, especially the height of the gel-state electrolyte in the composite separator, can also be high. For example, the height of the first and second base films in the composite separator can be the same as the height of the gel-state electrolyte, and the height of the composite separator can be slightly lower than the height of the electrode plates, or the same as the height of the electrode plates.

[0041] In some examples, the electrode sheet may have a current collector and an active layer located on the current collector. The height of the active layer may be slightly lower than the height of the current collector. The height of the composite separator may be such that it at least covers the active layer, i.e., the orthogonal projection of the composite separator onto the current collector completely covers the active layer. This allows the active material in the active layer to fully utilize its capacity.

[0042] In some embodiments, the heights of the first and second base films of the composite separator may be slightly higher than the height of the gel electrolyte. In this embodiment, the height of the gel electrolyte may be at least higher than the height of the active layer on the electrode sheet, that is, the orthogonal projection of the gel electrolyte onto the current collector covers the active layer.

[0043] According to embodiments of this application, the aforementioned secondary battery can be a lithium-ion secondary battery or a sodium metal battery. This expands the application scenarios of the secondary battery.

[0044] As mentioned above, the polymer used in the gel electrolyte of the secondary battery proposed in this application remains stable in various battery systems. Therefore, this secondary battery can be applied to lithium-ion battery and sodium metal battery systems. The gel electrolyte was also tested by immersion in a solution containing sodium sheets and electrolyte, and it showed no significant gas production or discoloration.

[0045] According to embodiments of this application, the secondary battery can be a system with a positive electrode and a negative electrode, or it can be a secondary battery without a negative electrode system.

[0046] Specifically, the electrode plates in this secondary battery can be positive and negative electrodes, with a composite separator located between them, separating them. Because the composite separator used in this application uses first and second base films to isolate the gel electrolyte and the electrodes, the more reactive groups in the gel electrolyte, such as residual hydroxyl groups in polyethers and polyester compounds, will not directly contact the electrode plates, thus preventing reactions between these more reactive groups and the electrode plates. This further improves the durability of the gel electrolyte in the composite separator, thereby enhancing the cycle performance of the secondary battery.

[0047] Alternatively, in some embodiments, the secondary battery can be a negative electrode-less system. In a negative electrode-less battery system, active intercalation / deintercalation ions, such as lithium ions, are initially stored in the positive electrode material. During the initial charging process, the lithium ions move from the positive electrode to the negative electrode and are in-situ electroplated on the negative electrode current collector, typically copper foil, to form a lithium metal layer. During subsequent discharge, the active lithium ions are stripped from the in-situ formed lithium layer. The negative electrode-less secondary battery system simplifies the negative electrode structure, minimizing the battery volume and thus improving energy density. However, since a negative electrode-less system requires the formation of a metal layer on the negative electrode side, a certain "gap" needs to be reserved on the negative electrode side for lithium ion deposition to form metallic lithium. Furthermore, since there is a possibility of lithium dendrites forming and piercing the separator during deposition on the negative electrode side, leading to a short circuit, sufficient gaps need to be reserved on the negative electrode side.

[0048] In general, the gap for lithium-ion deposition on the negative electrode side of a cathode-less system can be achieved in several ways: Firstly, an artificial interface layer can be formed on the current collector, such as depositing a thin Al₂O₃ artificial interface layer as an artificial SEI film to stabilize Li deposition. This uniform Al₂O₃ artificial SEI structure with a high band gap can create a certain space on the current collector surface and promote dense and uniform lithium deposition. Another way to reserve the gap is to use a three-dimensional (3D) negative electrode current collector: the current collector is modified with a conductive material that can form a three-dimensional network structure, such as conductive fibers. However, the above methods have limited effectiveness in mitigating dendrite puncture of the separator.

[0049] In some embodiments of this application, a composite separator with the aforementioned structure can be used in a negative electrode-free system. In these embodiments, the electrode sheet can be a positive electrode sheet. Since the composite separator has two base films, with a gel electrolyte further sandwiched between them, it can better provide space for lithium-ion deposition and prevent short circuits caused by dendrite puncture of the single-layer separator. Furthermore, compared to the aforementioned artificial interface layer and 3D current collector, the composite separator of this application can also be thicker, thereby reserving more sufficient gaps for metal deposition on the negative electrode side.

[0050] According to an embodiment of this application, in this embodiment, a negative electrode current collector can be further composited onto the composite separator. Specifically, the composite separator may further include a negative electrode conductive layer. The negative electrode conductive layer includes a conductive coating and a metal foil, with the conductive coating side facing the first or second base film. For example, the conductive coating can first be formed on the surface of a metal foil (used as a current collector) by means including but not limited to extrusion coating, such as coating a mixed slurry formed of conductive carbon black material and deionized water onto the surface of the copper foil. The thickness of the formed conductive coating is not particularly limited, for example, it can be 1-3 micrometers, such as about 2 micrometers. Subsequently, the structure with the conductive undercoat can be formed on the side of the base film away from the gel electrolyte by processes such as pressing.

[0051] In traditional negative electrode-less secondary batteries, the lack of an active layer on the negative electrode side results in poor electrolyte retention at the electrode tip, leading to rapid cycle degradation due to electrolyte breakage. This application addresses this issue by incorporating a conductive coating and metal foil onto one side of the base film, creating a composite structure that combines the functions of a separator and a negative electrode. This improves the electrolyte retention capacity on the negative electrode side, thus mitigating the problem of drastic cycle performance degradation caused by poor electrolyte retention.

[0052] In summary, the secondary battery proposed in this application, through its composite membrane structure, can better adsorb and retain electrolyte, thereby improving the cycle performance of the secondary battery.

[0053] In another aspect of this application, an electrical device is provided. This electrical device includes a secondary battery as described above, the secondary battery being used to provide electrical energy.

[0054] In this application, the electrical device can be such as a mobile phone, tablet, laptop, electric toy, power tool, electric vehicle, electric car, ship, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0055] As the electrical device, a sodium metal battery can be selected according to its usage requirements.

[0056] Figure 2 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of sodium metal batteries for this electrical device, a battery pack or battery module can be used.

[0057] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can utilize sodium metal batteries as their power source.

[0058] 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.

[0059] Example 1: Preparation of Lithium-ion Secondary Batteries

[0060] Preparation of positive electrode sheet:

[0061] Lithium iron phosphate (LiFePO4), carbon nanotubes (CNTs), and metahexafluorophosphate (PHPF) were thoroughly mixed in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 to form a uniform positive electrode slurry. This slurry was then coated onto the surface of an aluminum foil current collector. After drying, cold pressing, and die-cutting, a positive electrode sheet with a thickness of 200 μm was obtained. The coating weight of the positive electrode film on the positive electrode sheet was 350 mg / 1540 mm². 2

[0062] Preparation of negative electrode sheet: According to the mass ratio of graphite:carbon black:sodium carboxymethyl cellulose of 90:5:5, hard carbon, carbon black and sodium carboxymethyl cellulose are mixed and then added to a deionized water solvent system and stirred thoroughly to obtain a negative electrode slurry; coated on both sides of copper foil (side A and side B), dried at room temperature and then transferred to an oven at 120℃ for 1 hour, and after cold pressing and cutting, the negative electrode sheet is obtained.

[0063] Preparation of the composite separator: A polyethylene membrane is used as the first base membrane, with a thickness of 10-20 μm, a porosity of 35-42%, and a pore size of 35 nm. A gel layer with a thickness of 10 μm is coated on one side of the base membrane by extrusion coating. The gel layer is formed by coating a slurry of polyethylene oxide mixed with water at a mass ratio of 3:7. Subsequently, a second base membrane is laminated to the other side of the gel layer to form the composite separator. The parameters of the second base membrane are the same as those of the first base membrane.

[0064] Electrolyte preparation: In an argon-filled glove box with a water content of <1ppm, diethylene glycol dimethyl ether and tetrahydrofuran were mixed at a mass ratio of 1:3, and lithium hexafluorophosphate (LiPF6) with a concentration of 1.0mol / L was added. After stirring evenly, the electrolyte was obtained.

[0065] The positive electrode, separator, and negative electrode obtained in the above steps are stacked in sequence, and then the stacked components are wound to obtain the battery cell; the electrode assembly is placed in the housing, dried, and then injected with electrolyte; after formation, settling and other processes, the battery is obtained.

[0066] Example 2: Preparation of a Sodium Metal Battery Without a Negative Electrode

[0067] Preparation of the positive electrode sheet: Sodium iron pyrophosphate (positive electrode active material), carbon nanotubes (conductive agent), and metahexafluorophosphate (binder) were thoroughly mixed in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 to form a uniform positive electrode slurry. The positive electrode slurry was coated onto the surface of an aluminum foil current collector. After drying, cold pressing, and die-cutting, a positive electrode sheet with a thickness of 200 μm was obtained. The coating weight of the positive electrode film layer on the positive electrode sheet was 350 mg / 1540 mm². 2

[0068] Preparation of the composite separator: A polyethylene membrane is used as the first base membrane, with a thickness of 10-20 μm, a porosity of 35-42%, and a pore size of 35 nm. A gel layer with a thickness of 10 μm is coated on one side of the base membrane by extrusion coating. The gel layer is formed by coating a slurry of polyethylene oxide mixed with water at a mass ratio of 3:7. Subsequently, a second base membrane is laminated to the other side of the gel layer to form the composite separator. The parameters of the second base membrane are the same as those of the first base membrane.

[0069] 10 wt% conductive carbon black and an appropriate amount of deionized water are mixed to form a slurry, and then a conductive coating with a thickness of 2 μm is formed on the surface of copper foil by extrusion coating, and then laminated to one side of the second base film.

[0070] Preparation of electrolyte: In an argon-filled glove box with a water content of <1ppm, diethylene glycol dimethyl ether and tetrahydrofuran were mixed at a mass ratio of 1:3, and sodium hexafluorophosphate (NaPF6) with a concentration of 1.0mol / L was added. After stirring evenly, the electrolyte was obtained.

[0071] The positive electrode sheet and separator gel composite structure prepared in the above steps are stacked in sequence, so that the separator is between the positive electrode sheet and the copper foil and can isolate the positive electrode sheet and the copper foil. Then, the stacked components are wound to obtain the battery cell. The electrode assembly is placed in the shell, dried and injected with electrolyte. After formation, settling and other processes, a sodium metal battery without negative electrode is obtained.

[0072] Comparative Example 1

[0073] The remaining parameters are the same as in Example 1, except that the first base membrane of Example 1 is used as a diaphragm.

[0074] Comparative Example 2

[0075] The remaining parameters are the same as in Example 2, except that the first base membrane in Example 2 is used as a diaphragm.

[0076] Polymer wetting ability test:

[0077] The wetting ability of the polymer was tested using the contact angle: An automatic droplet method was used to ensure that the volume of each droplet was the same. The electrolyte in this example was dropped onto the gel layer surface of the composite separator. A high-resolution camera was used to ensure optical stability, and the droplets on the gel surface were photographed. The test results were analyzed in real time by measurement software to obtain the contact angle θ: the angle between the tangent line drawn at the gas-liquid interface at the gas-liquid-solid three-phase junction and the solid-liquid interface line on the liquid side. The contact angle measuring instrument (wetting contact angle measuring instrument) model: JY-JC2000C.

[0078] Polymer liquid absorption capacity test:

[0079] The composite diaphragms prepared in Examples 1 and 2 were cut into strips 10 cm long and 1 cm wide, and vertically immersed in a beaker containing electrolyte. The length of the strips below the electrolyte surface was 2 cm. The height of the electrolyte rising to the negative electrode bottom coating was recorded using an ultra-high time resolution camera, and the height of the electrolyte rising was recorded after xx hours.

[0080] First-time effect test:

[0081] The battery cells prepared in the examples and comparative examples were charged at room temperature at a rate of 0.33C to a voltage of 3.65V, and the initial charge capacity C1 was tested. Then, they were discharged at a rate of 0.33C to a voltage of 1.5V, and the initial discharge reversible capacity D1 was measured. The ratio of the initial discharge capacity D1 / C1 is the battery's first efficiency.

[0082] Cyclic performance test:

[0083] The battery cells prepared in the examples and comparative examples were charged at room temperature at a rate of 0.33C to a voltage of 3.65V, and then discharged at a rate of 0.33C to a voltage of 1.5V. The reversible capacity was measured as C0. This charging and discharging process was repeated until the discharge capacity C of a certain cycle was reached. n The total number of cycles until C0 ≤ 80% is recorded as X-Cycle. Where C... n It is the reversible capacity at the nth cycle.

[0084] Battery storage life test:

[0085] The cells prepared in the examples and comparative examples were charged at room temperature at a rate of 0.33C to a voltage of 3.65V, and then discharged at a rate of 0.33C to a voltage of 1.5V. The reversible capacity was measured as C0. The cells were then stored at 45°C and charged at a rate of 0.33C to a voltage of 3.65V every 30 days, followed by discharge at a rate of 0.33C to a voltage of 1.5V. The reversible capacity was measured as C. n Then C n / C0 yields the storage life degradation rate of a single battery cell. This is used to continuously store and repeatedly charge and discharge the battery until the discharge capacity C of a certain cycle is reached. n Until / C0 ≤ 80%. Record the number of days Dn the battery is stored.

[0086] The above standards were used to test the examples and comparative examples, and the test results are shown in Table 1 below.

[0087] Table 1

[0088]

[0089] As shown in Table 1 above, the gel electrolyte contained in the composite membranes of Examples 1 and 2 has a better contact angle, better electrolyte absorption capacity, and higher climbing height. The secondary batteries proposed in this application (Examples 1 and 2) have significantly improved cycle performance, cycle life, and first-time formation efficiency compared to the comparative examples.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, The device includes electrode plates and a composite separator, wherein the composite separator is located on one side of the electrode plates, and the composite separator includes a first base film, a second base film, and a gel electrolyte located between the first base film and the second base film. The gel electrolyte includes at least one of polyether compounds and polyester compounds.

2. The secondary battery according to claim 1, characterized in that, The polyether compound includes at least one of polyethylene oxide, polyethylene oxide, polypropylene ether, polyetherketone, and polymethyl ether. The polyester compounds include at least one of polymethyl methacrylate, polyethylene terephthalate, and polybutylene terephthalate.

3. The secondary battery according to claim 1 or 2, characterized in that, The gel electrolyte can swell in the electrolyte by absorbing the electrolyte, and the mass and / or volume of the gel electrolyte after swelling is 1-5 times that of the gel electrolyte before swelling.

4. The secondary battery according to claim 3, characterized in that, The secondary battery further includes an electrolyte containing ether compounds, and the gel electrolyte includes polyethylene oxide.

5. The secondary battery according to any one of claims 1-4, characterized in that, The composite diaphragm satisfies at least one of the following conditions: The thickness of the first base film and the second base film are independently 5-20 μm, the porosity is independently 35-42%, and the pore size is independently 30-40 nm. The gel electrolyte is a gel layer formed between the first and second base films, and the thickness of the gel layer is 2-10 μm.

6. The secondary battery according to any one of claims 1-5, characterized in that, The height of the electrode sheet is not less than 100mm.

7. The secondary battery according to any one of claims 1-6, characterized in that, The electrode plates include a positive electrode plate and a negative electrode plate, and the composite separator is located between the positive electrode plate and the negative electrode plate.

8. The secondary battery according to any one of claims 1-6, characterized in that, The electrode sheet is a positive electrode sheet, and the composite separator further includes a negative conductive layer. The negative conductive layer includes a conductive coating and a metal foil, and one side of the conductive coating is disposed facing the first or second base film.

9. The secondary battery according to any one of claims 1-8, characterized in that, The secondary battery is a lithium-ion secondary battery or a sodium metal battery.

10. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1-9, the secondary battery being used to provide electrical energy.

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