Binder and preparation method thereof, positive pole piece and energy storage device

Abstract

The invention provides a binder and a preparation method thereof, a positive pole piece and an energy storage device, the binder comprises a polymer, the polymer comprises a structural unit represented by a formula (I) and a structural unit represented by a formula (II), and the polymer contains carboxyl functional groups. Formula (I) and formula (II) are shown in the description.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a binder and its preparation method, a positive electrode sheet, and an energy storage device. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have advantages such as high energy density, low self-discharge, and light weight, and are therefore widely used in energy storage devices and other fields.

[0003] The positive electrode, as a key structural component of a secondary battery, plays a crucial role in its performance. Currently, the commonly used non-fluorinated positive electrode binder is polyimide (PI). As a heat-resistant polymer material, polyimide exhibits excellent thermal stability due to its high molecular chain rigidity, but it still suffers from poor adhesion to the positive electrode and insufficient flexibility. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses an adhesive and its preparation method, a positive electrode sheet, and an energy storage device to improve the bonding performance and flexibility of polyimide, thereby enhancing the cycle performance of secondary batteries.

[0005] In a first aspect, this application provides an adhesive comprising a polymer, the polymer comprising structural units represented by formula (I) and structural units represented by formula (II), and the polymer containing carboxyl functional groups; Equation (Ⅰ), Formula (II); Where R1 is the reactive residue of dianhydride monomers, R2 is the reactive residue of diamine monomers, and 10≤x≤200.

[0006] In some embodiments of this application, the mass percentage of the structural unit represented by formula (I) in the polymer is 10% to 80%.

[0007] In some embodiments of this application, the mass percentage of the carboxyl functional group in the polymer is 0.35% to 1%.

[0008] In some embodiments of this application, the dianhydride monomers include at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 4,4'-oxophthalic anhydride; The diamine monomers include at least one of 4,4'-oxodiphenylamine and 3,3'-dimethylbenzidine, and at least one of 3,5-diaminobenzoic acid and 4,4'-diamino-3-carboxybiphenyl.

[0009] Secondly, this application provides a method for preparing an adhesive as described in the first aspect, comprising the following steps: Dihydride monomers, common diamine monomers, and carboxyl-containing diamine monomers are added to an organic solvent, and a first polymerization reaction is carried out at room temperature to obtain a polyamic acid solution. The polyamic acid and the flexible monomer are subjected to a second polymerization reaction at 120°C to 160°C, wherein the flexible monomer is a hydroxyl-terminated polyolefin; The second polymerization product is subjected to a thermal imidization reaction at 200℃~250℃ to obtain the binder.

[0010] In some embodiments of this application, the molar amount of the carboxyl-containing monomer is 0.1% to 10%, based on the sum of the molar amounts of the common dianhydride monomer and the carboxyl-containing diamine monomer.

[0011] In some embodiments of this application, the molar ratio of the polyamic acid to the flexible monomer is 60:1 to 10:7.

[0012] Thirdly, this application provides a positive electrode sheet, wherein at least one side of the positive current collector has a positive active material layer, the positive active material layer comprising a positive active material and a binder, the binder comprising the binder described in the first aspect, or the binder comprising a binder prepared by the method for preparing the binder described in the second aspect.

[0013] Fourthly, this application provides a battery including the positive electrode sheet described in the third aspect.

[0014] Fifthly, this application provides an energy storage device, including a housing and at least one battery as described in the fourth aspect, the battery being housed within the housing.

[0015] In a sixth aspect, this application provides an electrical device including the energy storage device described in the fifth aspect, wherein the energy storage device supplies power to the electrical device.

[0016] Compared with the prior art, this application has at least the following beneficial effects: This application provides an adhesive and its preparation method, a positive electrode sheet, and an energy storage device. The adhesive comprises a polymer, which includes structural units represented by formula (I) and structural units represented by formula (II). The polymer contains carboxyl functional groups, which enhance the interfacial adhesion of the adhesive, thereby improving the peel strength of the fluorine-free positive electrode sheet. Furthermore, the adhesive also contains flexible structural segments, which enhance the flexibility of the adhesive, thereby improving the interfacial stress buffering capacity of the fluorine-free positive electrode sheet. Additionally, the polyimide structure in the adhesive of this application has advantages such as high thermal stability, mechanical strength, and chemical corrosion resistance. The fluorine-free positive electrode sheet using the adhesive of this application exhibits better flexibility and peel strength, thereby improving the cycle performance of lithium-ion batteries based on fluorine-free positive electrode sheets. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of an energy storage system according to one embodiment of this application; Figure 2 This is a schematic diagram of the energy storage system according to another embodiment of this application; Figure 3 This is a schematic diagram of the energy storage system according to another embodiment of this application; Figure 4 The infrared spectrum of the adhesive prepared in Example 3; Figure 5 The electrochemical stability test results are for the binder prepared in Example 3; Figure 6 The results are the thermal stability test results of the adhesive prepared in Example 3.

[0019] Explanation of reference numerals in the attached drawings: 200-battery, 400-energy storage system, 410-first power conversion device, 420-first user load, 430-second user load, 440-energy storage device, 450-high voltage cable, 460-second power conversion device, 470-vehicle, 480-photovoltaic-energy storage-charging station. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0022] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0023] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0024] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, components, or parts (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, components, or parts. Unless otherwise stated, "a plurality of" means two or more.

[0025] It should be noted that this application uses lithium-ion batteries as an example of secondary batteries to explain the application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0026] Currently, the commonly used fluorinated cathode binder is polyvinylidene fluoride (PVDF), which refers to PVDF homopolymer or copolymer of PVDF and other small amounts of fluorinated vinyl monomers. PVDF maintains the stability of the electrode's mechanical structure and the battery's electrochemical performance during battery production and use. Although PVDF is not banned or restricted, the fluorides generated during its production may involve perfluorinated and polyfluoroalkyl substances (PFAS) chemicals. Therefore, it is necessary to develop non-fluorinated binders with good adhesion and flexibility for the preparation of fluorine-free cathode electrodes.

[0027] In view of this, this application provides an adhesive comprising a polymer, the polymer comprising structural units represented by formula (I) and structural units represented by formula (II), and the polymer containing carboxyl functional groups; Equation (Ⅰ), Formula (II); Where R1 is the reactive residue of dianhydride monomers, R2 is the reactive residue of diamine monomers, 10≤x≤200, and x is an integer.

[0028] The binder of this application is a polymer containing carboxyl functional groups. Due to the ionic and hydrogen bonding between the carboxyl functional groups and lithium iron phosphate, the interfacial adhesion of the binder is enhanced, thereby improving the peel strength of the fluorine-free positive electrode sheet. Furthermore, the binder also contains flexible structural segments, which enhance its flexibility and thus improve the interfacial stress buffering capacity of the fluorine-free positive electrode sheet. In addition, the polyimide structure in the binder of this application also has the advantages of high thermal stability, mechanical strength, and chemical corrosion resistance. The fluorine-free positive electrode sheet using the binder of this application exhibits better flexibility and peel strength, thereby improving the cycle performance of lithium-ion batteries based on fluorine-free positive electrode sheets.

[0029] In some embodiments of this application, the polymer contains structural units represented by formula (I) at a mass percentage of 10% to 80%, for example, 10%, 40%, 60%, or 80%. The structural units represented by formula (II) at a mass percentage of 20% to 90%, for example, 20%, 30%, 60%, or 90%. This allows the adhesive to maintain high bonding performance, flexibility, and low swelling.

[0030] In some embodiments of this application, the mass percentage of the carboxyl functional group is 0.35% to 1%, for example, the mass percentage can be 0.35%, 0.5%, 0.7% or 1%. In this way, the interfacial adhesion of the adhesive can be improved through the carboxyl functional group, while avoiding the problem of increased swelling degree of the adhesive due to excessive carboxyl content. In the structural unit represented by formula (II) above, some R2 contains carboxyl functional groups, and some R2 does not contain carboxyl functional groups. The R2 containing carboxyl functional groups is introduced by a carboxyl-containing diamine monomer, and the R2 without carboxyl functional groups is introduced by a common diamine monomer.

[0031] In some embodiments of this application, the dianhydride monomers include at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 4,4'-oxophthalic anhydride; Diamine monomers include at least one of 4,4'-oxodiphenylamine and 3,3'-dimethylbenzidine, and at least one of 3,5-diaminobenzoic acid and 4,4'-diamino-3-carboxybiphenyl (CAS: 873996-32-8).

[0032] In some embodiments of this application, R1 includes , ; R2 includes , , , , , , , .

[0033] This application provides a method for preparing the adhesive according to any of the above embodiments, comprising the following steps: Step A: Add dianhydride monomers, common diamine monomers and carboxyl-containing diamine monomers to an organic solvent and carry out the first polymerization reaction at room temperature to obtain a polyamic acid solution; Step B: The polyamic acid and the flexible monomer are subjected to a second polymerization reaction at 120°C to 160°C, wherein the flexible monomer is a hydroxyl-terminated polyolefin.

[0034] Step C: The second polymerization product is subjected to a thermal imidization reaction at 200℃~250℃ to obtain the binder.

[0035] In step A, dianhydride monomers include, but are not limited to, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) and 4,4'-oxophthalic anhydride (ODPA); diamine monomers include, but are not limited to, 4,4'-oxodiphenylamine (ODA) and 3,3'-dimethylbenzidine (DMBZ); and carboxyl-containing diamine monomers include, but are not limited to, 3,5-diaminobenzoic acid (DABA) and 4,4'-diamino-3-carboxybiphenyl. These carboxyl-containing diamine monomers can introduce carboxyl functional groups into the copolymer obtained from the first polymerization reaction. In this application, the dianhydride and diamine are generally mixed in a 1:1 molar ratio, and the carboxyl content in the polymer can be adjusted by adjusting the amount of carboxyl-containing diamine monomers added; the organic solvent includes, but is not limited to, N-methylpyrrolidone (NMP); and the first polymerization reaction time is 12-15 hours. Understandably, when the proportion of polyimide segments in the adhesive is large (e.g., greater than or equal to 80%), only a small amount of DABA is needed to meet the design requirements for carboxyl content; when the proportion of polyimide segments in the adhesive is small (e.g., less than or equal to 10%), a larger amount of DABA is needed to meet the design requirements for carboxyl content.

[0036] In step B, the second polymerization reaction is an addition condensation reaction between the polyimide and the flexible monomer, mainly through the formation of ester bonds (-CO-O-) between the carboxyl groups on the polyimide backbone and the hydroxyl groups (-OH) on the flexible monomer. For example, the carboxyl groups on the polyimide backbone form ester bonds with the hydroxyl groups on the terminal hydroxyl polyolefin segments. This application does not particularly limit the terminal hydroxyl polyolefin; it can be a commercially available material, as long as it achieves the purpose of this application. Exemplarily, the terminal hydroxyl polyolefin can be a long-chain polyolefin with 10 to 200 carbon atoms and hydroxyl groups at both ends.

[0037] In step C, the polyamic acid in the second polymerization product is converted into polyimide through thermal imidization, and a certain proportion of side chain carboxyl groups are introduced into the main chain of the polyimide; existing thermal imidization processes can be used, and this application does not make specific limitations.

[0038] In some embodiments of this application, the molar amount of the carboxyl-containing diamine monomer is 0.1% to 10% based on the sum of the molar amounts of the dianhydride monomer and the common diamine monomer. For example, the molar amount of the carboxyl-containing diamine monomer is 0.1%, 1%, 3%, 5%, or 10%. By controlling the amount of carboxyl-containing diamine monomer added within the above range, the content of carboxyl functional groups in the binder can be controlled.

[0039] In some embodiments of this application, the molar ratio of the polyamic acid to the flexible monomer is 60:1 to 10:7. For example, the molar ratio of the polyamic acid to the flexible monomer is 60:1, 10:1, 3:2, or 10:7. This allows for adjustment of the ratio of polyimide structural units to flexible structural segments in the polymer, which is beneficial for obtaining adhesives with high bonding performance and flexibility.

[0040] The binder preparation method provided in this application, using dianhydride monomers, common diamine monomers, carboxyl-containing diamine monomers, and flexible monomers as raw materials, produces a binder with high adhesion and flexibility, which enhances the interfacial adhesion of the binder and thus improves the peel strength of the fluorine-free positive electrode sheet. Furthermore, the polyimide structure in the binder prepared in this application also possesses advantages such as high thermal stability, mechanical strength, and chemical corrosion resistance. The fluorine-free positive electrode sheet using the binder of this application exhibits better flexibility and peel strength, thereby improving the cycle performance of lithium-ion batteries based on fluorine-free positive electrode sheets.

[0041] This application also provides a positive electrode sheet, including a positive current collector, at least one side of which has a positive active material layer, the positive active material layer including a positive active material and a binder, wherein the binder is the binder described in any of the above embodiments, or the binder is prepared by the binder preparation method of any of the above embodiments.

[0042] The positive electrode active material layer of this application can be disposed on one surface or on two surfaces along the thickness direction of the positive electrode current collector. In this application, the positive electrode active material layer is disposed on the surface of the positive electrode current collector; that is, the positive electrode active material layer can be disposed on a portion of a surface of the positive electrode current collector or on the entire surface of a surface of the positive electrode current collector. This application does not impose any particular limitation on the positive electrode current collector, as long as it achieves the purpose of this application; for example, it can be, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application; for example, a thickness of 8μm to 13μm. The single-sided thickness of the positive electrode active material layer in this application can be 100μm to 200μm.

[0043] This application also provides a battery including the positive electrode sheet described in any embodiment of this application.

[0044] The lithium-ion battery of this application also includes a negative electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode and plays a role in isolation.

[0045] This application does not impose any particular restrictions on the negative electrode sheet, as long as it can achieve the purpose of this application. For example, the negative electrode sheet usually includes a negative current collector and a negative active material layer.

[0046] The negative electrode active material layer can be disposed on one or both surfaces of the negative electrode current collector along its thickness direction. In this application, the negative electrode active material layer is disposed on the surface of the negative electrode current collector; that is, the negative electrode active material layer can be disposed on a portion of one surface of the negative electrode current collector, or it can be disposed on the entire surface of one surface of the negative electrode current collector. This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application; for example, a thickness of 4 μm to 12 μm. The single-sided thickness of the negative electrode active material layer in this application can be 70 μm to 200 μm.

[0047] In this application, the negative electrode active material layer includes a negative electrode active material. There are no particular limitations on the negative electrode active material, as long as it can achieve the purpose of this application. For example, it may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon-carbon.

[0048] In this application, the negative electrode active material layer may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, it may include at least one of acrylate, polyamide, polyimide, polyamide-imide, polyvinylidene fluoride (PVDF), styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0049] This application does not impose any particular limitation on the diaphragm; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0050] The battery of this application also includes a casing. This application does not impose any particular restrictions on the casing, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the casing may include an aluminum-plastic film.

[0051] This application does not impose any particular limitation on the battery preparation method; any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the battery preparation method includes, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the battery.

[0052] This application also provides an energy storage device, including a housing and at least one battery as described in any of the above embodiments, the battery being housed within the housing. The energy storage device with this battery exhibits excellent performance, which is beneficial for its use. Housing the battery within the housing increases its stability and protection, thereby extending the lifespan of the energy storage device. It is understood that the energy storage device may contain one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries can be connected in at least one manner, such as parallel or series connection.

[0053] This application also provides an electrical device including the energy storage device described in the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In an optional embodiment, the electrical device includes an electrical device body, and the energy storage device is used to supply power to the electrical device body. In an optional embodiment, the electrical device body includes a positive terminal and a negative terminal, the positive electrode of the battery in the energy storage device is used to electrically connect to the positive terminal of the electrical device body, and the negative electrode of the battery in the energy storage device is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0054] The electrical equipment in this application may include, but is not limited to: prefabricated energy storage cabins, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0055] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form for future applications. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels. Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0056] Taking electrochemical energy storage as an example, this solution provides an energy storage device 440, which is applied to an energy storage system 400. The energy storage device 440 is equipped with a set of chemical batteries, which mainly use the chemical elements in the battery 200 as the energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical battery. When the use of external electrical energy reaches its peak, the stored electrical energy is released for use, or transferred to places with a shortage of electricity for use.

[0057] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include: (1) Large-scale energy storage power stations (composed of multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy absorption capacity, reduces instantaneous power changes, reduces the impact on the power grid, improves the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation. (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption. (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system when the electricity price is low and discharging the energy storage system when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0058] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 1 This application Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 440 of this application is not limited to the home energy storage scenario.

[0059] This application provides an energy storage system 400, which includes a first power conversion device 410 (photovoltaic panel), a first user load 420 (household lighting fixture), a second user load 430 (e.g., household appliances such as air conditioners), and an energy storage device 440. The energy storage device 440 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 440 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 440 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0060] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 1 And this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 440 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0061] This application provides an energy storage system 400, which includes: a high-voltage cable 450, a first power conversion device 410, a second power conversion device 460, and an energy storage device 440 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 460 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 440 through grid connection. The energy storage device 440 is connected to the high-voltage cable and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power... The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 440 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 440 together with the high-voltage cable 450 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0062] In some embodiments on the distribution network side, the first power conversion device 410 can be a photovoltaic panel, and the energy storage device 440 is connected to the high-voltage cable 450 and installed downstream of the high-voltage cable 450 and between the user load. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 440, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 450 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0063] In some embodiments, see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 3 And this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 440 of this application is not limited to industrial and commercial energy storage scenarios.

[0064] This application provides an energy storage system 400, which includes: an energy storage device 440, a high-voltage cable 450, a factory equipped with a first power conversion device 410, a photovoltaic-energy storage-charging station 480, and a vehicle 470. In some embodiments of industrial and commercial scenarios, the first power conversion device 410 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 440 in the factory. In the event of a power grid failure, the energy storage device 440 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 440 in conjunction with the high-voltage cable 450 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 410 can also convert solar energy into electrical energy and store it in the energy storage device 440 of the photovoltaic-energy storage-charging station 480, which can then directly charge the vehicle 470, making it fast and convenient.

[0065] Optionally, the first power conversion device 410 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 460 may include, but is not limited to, a wind power conversion device. The first power conversion device 410 and the second power conversion device 460 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0066] Optionally, the energy storage device 440 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0067] Optionally, the energy storage device 440 may include, but is not limited to, individual batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of individual batteries. The actual application form of the energy storage device 440 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 440.

[0068] Optionally, the individual cell can be, but is not limited to, at least one of cylindrical, prismatic, prismatic, or other shaped cells.

[0069] Optionally, the single cell can be a rechargeable battery, which refers to a single cell that can be recharged after discharge to activate the active materials and continue to be used. The single cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0070] Example The following examples, embodiments, and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0071] Example 1 <Preparation of Adhesive> According to a molar ratio of 28:27:1:1, the following monomers were weighed: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 4,4'-oxodiphenylamine (ODA), 3,5-diaminobenzoic acid (DABA), and hydroxyl-terminated polyolefin (specifically hydroxyl polyenol with a weight-average molecular weight of 1000-50000; the molar molecular weight in this embodiment is 3000). Then, BPDA, ODA, and DABA were added together to... In N-methylpyrrolidone (NMP), a first polymerization reaction was carried out at room temperature for 12 hours to obtain a polyamic acid solution. Based on the sum of the molar amounts of dianhydride monomers and common diamine monomers, the molar amount of carboxyl diamine monomers was 1.8%. A second polymerization reaction was then carried out between the terminal hydroxyl polyolefin and the polyamic acid at 120°C. The second polymerization product was then thermally imidized at 250°C to obtain a polyolefin-modified polyimide. After removing the solvent under vacuum, a liquid binder was obtained. In this binder, the mass percentage of the polyimide segment was 80%, and the mass percentage of the flexible structural segment was 20%.

[0072] <Preparation of the positive electrode> By weight, 66 parts of lithium iron phosphate, 2 parts of the prepared binder, and 0.1 parts of polyvinylpyrrolidone dispersant (PVP) were dry-mixed for 30 min, then 21.9 parts of NMP were added and kneaded for 60 min, followed by high-speed dispersion of 10 parts of NMP for 100 min to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil for the positive electrode current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The single-sided thickness of the positive electrode active material layer was 100 μm.

[0073] <Preparation of Negative Electrode Sheets> Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC-Na) thickener, Super-P conductive carbon black, and styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 96:2:1:1. Deionized water was added to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The single-sided thickness of the negative electrode active material layer was 70 μm.

[0074] <Preparation of Electrolyte> In an argon-atmospheric glove box with a moisture content ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:2:1. Lithium salt LiPF6 was then added and dissolved in the solvent. The mixture was stirred until the lithium salt was completely dissolved, and then the first additive was added. After thorough mixing, the electrolyte was obtained. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0075] <Preparation of the diaphragm> A porous polyethylene (PE) membrane with a thickness of 16 μm was used as the separator.

[0076] <Preparation of Lithium-ion Batteries> The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic film packaging bag, vacuum dried, and then injected with electrolyte. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0077] Example 2 Except for the preparation of the adhesive, in which the molar ratio of dianhydride monomers, common diamine monomers, carboxyl-containing diamine monomers and hydroxyl-terminated polyolefins is adjusted to 28:27:1:6.4, thereby controlling the mass percentage of polyimide segments and flexible structural segments according to Table 1, the rest is the same as in Example 1.

[0078] Example 3 Except for the preparation of the adhesive, in which the molar ratio of dianhydride monomers, ordinary diamine monomers, carboxyl-containing diamine monomers and hydroxyl-terminated polyolefins is adjusted to 28:27:1:39, thereby controlling the mass percentage of polyimide segments and flexible structural segments according to Table 1, the rest is the same as in Example 1.

[0079] Example 4 Except for the preparation of the adhesive, in which the molar ratio of dianhydride monomers, ordinary diamine monomers, carboxyl-containing diamine monomers and hydroxyl-terminated polyolefins is adjusted to 14:13:1:19, thereby controlling the mass percentage of carboxyl functional groups in the adhesive according to Table 1, the rest is the same as in Example 3.

[0080] Example 5 Except for the preparation of the adhesive, in which the molar ratio of dianhydride monomers, ordinary diamine monomers, carboxyl-containing diamine monomers and hydroxyl-terminated polyolefins is adjusted to 10:9:1:13.5, thereby controlling the mass percentage of carboxyl functional groups in the adhesive according to Table 1, the rest is the same as in Example 3.

[0081] Examples 6 to 8 Except for the section on "Preparation of Adhesives", which adjusts the types of dianhydride monomers, common diamine monomers, and carboxyl-containing diamine monomers according to Table 1, the rest is the same as in Example 3.

[0082] Comparative Example 1 Except for replacing the binder with polyvinylidene fluoride (PVDF) in the <Preparation of Positive Electrode> section, the rest is the same as in Example 1.

[0083] Comparative Example 2 Except for the preparation of the adhesive, which differs from Example 1, the rest is the same as Example 1.

[0084] The preparation process of the adhesive is as follows: The dianhydride monomer BPDA and the diamine monomer ODA were weighed out at a molar ratio of 21:20. Then, BPDA and ODA were added together to N-methylpyrrolidone (NMP) and polymerized at room temperature for 12 hours to obtain a polyamic acid solution. The polyamic acid solution was then thermally imidized at 250°C to obtain polyimide. After removing the solvent under vacuum, the binder was obtained.

[0085] Table 1: Preparation parameters of Examples 1-8 and Comparative Examples 1-2

[0086] Note: In Table 1, " / " indicates that the relevant preparation parameters do not exist.

[0087] Test methods and equipment: Content testing of each structural unit in the adhesive: Peak area ratio method (semi-quantitative): Select a reference peak in the sample that does not change with the reaction or formulation. (e.g., C–H stretching of benzene ring 1508 cm) - ¹), Calculate the area ratio of the target peak to the reference peak: = / Content changes or reaction conversion rates are expressed as a ratio trend: Relative content or conversion rate = 样品 / 对照 ×100%.

[0088] The results are expressed as the peak area of ​​the target peak or the ratio of peak areas. The trend of functional group content changes or the degree of reaction is reflected by the rise and fall of the above ratio. This method is applicable to polymer systems containing imide, amide, carboxyl, aromatic ring and other structures, and can quickly assess the degree of imidization, the amount of carboxyl introduced and the degree of modification.

[0089] Adhesive swelling rate test: The adhesive was made into a film, and the initial mass of the film sample was weighed using a high-precision balance and recorded as W1. The film sample was then immersed in a mixed electrolyte solvent (specifically, dimethyl carbonate (DMC) : ethylene carbonate (EC) = 1 : 1) for 72 hours. After immersion, the sample was removed, excess solvent was absorbed from the surface with filter paper, and the mass of the sample was weighed again and recorded as W2. The swelling rate was calculated using the formula: Swelling rate = (W2 - W1) / W1 × 100%.

[0090] Electrode Softness Value Test: The positive electrode sheet was cut into samples of the same size (25mm × 130mm), with three parallel samples per group, for testing. The instrumental test was based on the stress-strain curve method. The instrument was fixed on the testing device, and the electric telescopic rod moved vertically at a certain speed (specifically 10mm / min), pressing down to the same depth (15mm). Simultaneously, the stress and strain (pressure-displacement) under different degrees of deformation were measured. By recording the correspondence between the vertical displacement value of the electric telescopic rod and the pressure value at its top, the "stress-strain curve" of the electrode sheet was obtained. The maximum force describes its flexibility; the higher the flexibility value, the worse the material's flexibility.

[0091] Electrode peel strength test: The positive electrode sheet was cut into samples of the same size (25mm×130mm), with three parallel samples in each group. The high-speed rail tensile testing machine was used to test the peeling angle at a tensile angle of 90° and a peeling speed of 50mm / min. The active material layer of the electrode sheet was peeled off from the current collector, and the peeling strength per unit width was recorded in N / m. The average value was then taken.

[0092] Infrared test: 15g of liquid binder was placed in a polytetrafluoroethylene container and dried to constant weight in a vacuum / normal pressure oven at 80℃. Approximately 0.1g of the film sample was cut and flattened to fit into an ATR mirror of an infrared spectrometer for infrared testing. Wavenumber range: 4000 cm⁻¹ - ¹~400 cm -1 Resolution: 1.5 cm -1 .

[0093] Electrochemical stability test: A film was prepared by applying a 100 μm doctor blade to an aluminum foil substrate using a mixture of binder and activated carbon at a liquid-to-solid mass ratio of 1:1. The film was dried at 80 °C to constant weight, and the coating quality and thickness (10 µm to 20 µm) were recorded. A coin cell was then fabricated using a lithium metal sheet as the counter electrode. The scan type was volumetric spectroscopy (CV), the potential range was 0–5 V, and the scan rate was CV 0.1 mV·s. - ¹.

[0094] Thermal stability test: 15g of liquid binder was placed in a polytetrafluoroethylene container and dried to constant weight in a vacuum / atmospheric pressure oven at 80℃. A sample of 5.00mg was taken (accurately weighed to 0.01mg). Atmosphere: nitrogen; heating rate: 10℃·min. - ¹, Temperature range: room temperature to 600°C, recording the change in mass with temperature.

[0095] Cyclic performance test: At 25℃, the lithium-ion battery was left to stand for 5 hours, then charged at a rate of 0.5P to 3.65V, left to stand for 10 minutes, then discharged at a rate of 0.5P to 2.5V, and left to stand for another 10 minutes. This charge-discharge cycle was repeated 800 times. The discharge capacity of the first charge-discharge cycle was recorded as C1, and the discharge capacity of the 800th charge-discharge cycle was recorded as C2. 800 Then the capacity retention rate of a lithium-ion battery after 800 cycles = (C 800 / C1)×100%.

[0096] Table 2: Performance data of each embodiment and comparative example

[0097] As can be seen from Examples 1 to 8 and Comparative Examples 1 to 2, when PVDF is used as a binder (e.g., Comparative Example 1), although its softness value is low and its flexibility is good, the swelling ratio of the binder is high and its peel strength is average, resulting in a low cycle capacity retention rate of the lithium-ion battery. This indicates that the PVDF-based binder is not resistant to electrolyte immersion. When the polyimide does not have carboxyl functional groups and flexible structural segments (e.g., Comparative Example 2), although its swelling ratio is low, its softness value is very high and its flexibility is poor, resulting in a low cycle capacity retention rate of the lithium-ion battery. The binder of this application has good resistance to electrolyte immersion, flexibility and peel strength, which improves the cycle performance of the lithium-ion battery.

[0098] The content of polyimide segments, carboxyl functional groups, and flexible structural segments in the adhesive usually also affect the performance of the adhesive. As can be seen from Examples 1 to 5, by adjusting the above parameters within the scope of this application, it is beneficial to obtain an adhesive with good resistance to electrolyte immersion, flexibility, and peel strength.

[0099] Examples 3 and 6-8 also show that the electrode flexibility varies when synthesizing PI with different dianhydride diamine monomers. The electrode with ether-containing dianhydride monomer ODA has better flexibility and less difference in adhesion.

[0100] Figure 4 The infrared spectrum of the adhesive prepared in Example 3 shows that the wavenumber is 3320 cm⁻¹. - ¹ The presence of a characteristic absorption peak for hydroxyl groups (–OH) near the molecule indicates the presence of a hydroxyl functional group; at a wavenumber of 1710 cm⁻¹ - ¹ The presence of a characteristic absorption peak for a carbonyl group (C=O) indicates the presence of carboxylic acid structures such as –COOH; at a wavenumber of 1635 cm⁻¹ - ¹ A carboxyl group (–COO) appears nearby. - The characteristic peaks of asymmetric stretching vibrations indicate the presence of carboxylates or carboxyl groups in the molecule; at a wavenumber of 1600 cm⁻¹ - ¹ The presence of a characteristic absorption peak near a carbon-carbon double bond (C=C), combined with multiple absorption bands, indicates the presence of an aromatic ring structure in the molecule; at a wavenumber of 1380 cm⁻¹ - ¹ The presence of a characteristic absorption peak near the carbon-nitrogen bond (C–N) indicates the presence of an imide ring structure in the molecule; at a wavenumber of 1100 cm⁻¹ - ¹ The presence of a characteristic absorption peak for an ether bond (C–O–C) nearby indicates that the molecule contains an ether structure.

[0101] Figure 5The figure shows the electrochemical stability test results of the binder prepared in Example 3. As can be seen from the figure, the current change is small in the voltage range of 0~4.5V, and it always remains within ±0.1 mA, indicating that the binder has good electrochemical stability in the conventional working voltage range; it can meet the usage requirements of the positive electrode working voltage window (≤4.5 V) of lithium-ion batteries and exhibits good electrochemical stability.

[0102] Figure 6 The figure shows the thermal stability test results of the binder prepared in Example 3. As can be seen from the figure, the binder has basically no significant weight loss before 300°C and has excellent thermal stability within the conventional lithium-ion battery processing and operating temperature range.

[0103] The above provides a detailed description of the adhesive, its preparation method, positive electrode sheet, and energy storage device disclosed in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A binder, characterized by The binder comprises a polymer, the polymer comprises structural units represented by formula (I) and structural units represented by formula (II), and the polymer contains a carboxyl functional group; Formula (I), Formula (II); wherein R1 is a reaction residue of a dianhydride monomer, R2 is a reaction residue of a diamine monomer, and 10≤x≤200.

2. The binder of claim 1, wherein, In the polymer, the mass percentage of the structural units represented by formula (I) is 10% to 80%.

3. The binder of claim 1, wherein, In the polymer, the mass percentage of the carboxyl functional group is 0.35% to 1%.

4. The binder of claim 1, wherein, The dianhydride monomer comprises at least one of 3,3',4,4'-diphenyltetracarboxylic dianhydride and 4,4'-oxydiphthalic anhydride. The diamine monomer comprises at least one of 4,4'-oxydianiline and 3,3'-dimethylbenzidine, and at least one of 3,5-diaminobenzoic acid and 4,4'-diamino-3-carboxy biphenyl.

5. A method of producing the binder as claimed in any one of claims 1 to 4, characterized in that The method comprises the following steps: adding a dianhydride monomer, a common diamine monomer, and a carboxyl-containing diamine monomer into an organic solvent to perform a first polymerization reaction at room temperature to obtain a polyamic acid solution; performing a second polymerization reaction of the polyamic acid and a flexible monomer at 120°C to 160°C, the flexible monomer being a hydroxyl-terminated polyolefin; performing a thermal imidization reaction of the second polymerization reaction product at 200°C to 250°C to obtain the binder.

6. The preparation method according to claim 5, characterized in that, Based on the sum of the molar amounts of the dianhydride monomer and the common diamine monomer, the molar amount of the carboxyl-containing diamine monomer is 0.1% to 10%.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the polyamic acid to the flexible monomer is 60:1 to 10:

7.

8. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises a positive electrode current collector, at least one surface of the positive electrode current collector having a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material and a binder, the binder comprising the binder of any one of claims 1 to 4, or the binder comprising the binder prepared by the method of any one of claims 5 to 7.

9. A battery, characterized by The positive electrode sheet comprises the binder of any one of claims 1 to 8.

10. An energy storage device, characterized by, The battery comprises the battery of claim 9.

11. An electrical device, characterized by The energy storage device comprises the battery of claim 10, and the energy storage device supplies power to the power-consuming device.

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