Binder, method for preparing the same, negative electrode sheet, battery, and energy storage device

Abstract

The application provides a binder and a preparation method thereof, a negative electrode sheet, a battery and an energy storage device, wherein the binder is a lignin graft modified acrylic polymer, monomers forming an acrylic polymer main chain include acrylate, acrylic acid, polyimide and methacrylonitrile; the mass percentage of lignin is 2% to 10% based on the total mass of the binder.

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 negative electrode sheet, a battery, 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] As a key structural component of secondary batteries, the negative electrode plays a crucial role in their performance. With increasing demands for battery performance, improving the flexibility of the negative electrode and reducing its cracking have become pressing issues. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses an adhesive and its preparation method, a negative electrode sheet, a battery, and an energy storage device, to improve the flexibility and peel strength of the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0005] In a first aspect, this application provides an adhesive, said adhesive being a lignin-grafted modified acrylic polymer, wherein: Monomers that form the backbone of acrylic polymers include acrylates, acrylic acid, polyimide, and methacrylonitrile; Based on the total mass of the binder, the lignin content is 2% to 10% by mass.

[0006] In some embodiments of this application, the acrylate content is 50% to 60% by mass, based on the total mass of the adhesive; And / or, based on the total mass of the adhesive, the mass percentage of the acrylic acid is 20% to 30%.

[0007] In some embodiments of this application, the polyimide content is 3% to 8% by mass, based on the total mass of the adhesive; And / or, based on the total mass of the adhesive, the mass percentage of the methacrylonitrile is 3% to 8%.

[0008] In some embodiments of this application, the acrylate includes at least one of butyl acrylate and isooctyl acrylate.

[0009] Secondly, this application provides a method for preparing an adhesive as described in the first aspect, comprising the following steps: Acrylate, acrylic acid, polyimide and methacrylonitrile were added to the emulsifier solution and mixed evenly to obtain a pre-emulsion. An ammonium persulfate aqueous solution was prepared as an initiator solution. A portion of the pre-emulsion and a portion of the initiator solution are added to the lignin solution, and the reaction is carried out at the target temperature for 25 min to 35 min to obtain a seed solution. The amount of the pre-emulsion added is 1 / 10 to 1 / 5 of the volume of the lignin solution, the amount of the initiator solution added is 1 / 3 to 1 / 2 of the volume of the lignin solution, and the target temperature is 76℃ to 80℃. Maintaining the target temperature, the remaining pre-emulsion and initiator solution are added dropwise to the seed solution, with the addition time controlled at 2.5h~3h, until the addition is completed; The reaction is continued at the target temperature for 0.8 h to 1.2 h. Then the reaction system is heated to 83 °C to 85 °C and matured for 25 min to 35 min to obtain an emulsion. The emulsion is then cooled and the pH value is adjusted to obtain the binder.

[0010] In some embodiments of this application, the steps of cooling and adjusting the pH value include: The emulsion was stirred and cooled to below 40°C, and the pH of the emulsion was adjusted to 7-8 using ammonia.

[0011] In some embodiments of this application, the emulsifier in the emulsifier solution includes at least one of sodium allyl hydroxypropyl sulfonate and alkylphenol polyoxyethylene ether.

[0012] Thirdly, this application provides a negative electrode sheet comprising the binder described in the first aspect.

[0013] Fourthly, this application provides a battery including the negative 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 negative electrode sheet, a battery, and an energy storage device. The adhesive is a lignin-grafted modified acrylic polymer. The monomers forming the main chain of the acrylic polymer include acrylate, acrylic acid, polyimide, and methacrylonitrile. The lignin content in the adhesive is 2% to 10% by mass. This allows the formation of a star-shaped or network structure with lignin as nodes and the acrylic polymer as branches, thereby improving the adhesive's bonding performance and flexibility. The adhesive with the structure of this application improves the flexibility and peel strength of the negative electrode sheet, reduces problems such as cracking and powder shedding during winding, and thus improves the cycle performance of the secondary battery. 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 This is the Fourier transform infrared (FTIR) spectrum of the adhesive of Example 3 of this application.

[0019] Explanation of reference numerals in the attached drawings: 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] 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.

[0022] 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.

[0023] This application provides an adhesive, which is a lignin-grafted modified acrylic polymer. The monomers forming the main chain of the acrylic polymer include acrylate, acrylic acid, polyimide, and methacrylonitrile. Based on the total mass of the adhesive, the lignin mass percentage is 2% to 10%. For example, the lignin mass percentage in the adhesive is 2%, 3%, 5%, 6%, 7%, 8%, or 10%. When the lignin content is too high (e.g., above 10%), it can easily lead to excessive steric hindrance in the adhesive, thereby reducing the intermolecular forces of the adhesive and decreasing the adhesive strength. When the lignin content is too low (e.g., below 2%), it is difficult to form π-π conjugated interactions with graphite, which also affects the adhesive strength of the adhesive.

[0024] The binder of this application enhances its affinity for graphite. The lignin within it is a three-dimensional, irregular network of aromatic polymers containing numerous benzene rings, which can generate π-π conjugated interactions with highly aromatic graphite. Due to this strong affinity, the lignin-containing binder solution can more effectively reduce interfacial energy and rapidly spread upon contact with the hydrophobic graphite surface, achieving rapid wetting. Furthermore, each binder molecule is "anchored" to multiple graphite particles through multiple benzene rings, forming a robust three-dimensional network steric hindrance that prevents graphite particles from re-aggregating under high shear forces or during resting, ensuring the long-term stability of the slurry and providing a more stable dispersion effect. Meanwhile, this strong anchoring effect prevents the binder from easily detaching from the active material when the negative electrode sheet is bent or the graphite expands in volume, thereby improving the flexibility and structural integrity of the negative electrode sheet and thus improving its mechanical properties. Furthermore, the acrylic polymer chains can tightly encapsulate the graphite particles and firmly bond with the current collector (e.g., copper foil) through intermolecular forces. The binder in this application is a lignin-grafted modified acrylic polymer, in which the acrylic polymer and lignin work synergistically to form a star-shaped or network structure with lignin as nodes and acrylic polymer as branches. This structure can tightly bind with graphite through benzene rings, enhance the toughness of the negative electrode sheet through a three-dimensional network, and improve the wettability of the slurry through polar groups, reducing problems such as cracking and powder shedding when the negative electrode sheet is wound thickly, thereby improving the cycle performance of the lithium-ion battery.

[0025] In some embodiments of this application, the mass percentage of acrylate is 50% to 60% based on the total mass of the binder; and / or, the mass percentage of acrylic acid is 20% to 30% based on the total mass of the binder. For example, the mass percentage of acrylate in the binder is 50%, 53%, 55%, 58%, or 50%, and the mass percentage of acrylic acid in the binder is 20%, 22%, 25%, 27%, or 30%. Acrylic acid and acrylates can provide a large number of hydrophilic functional groups such as carboxyl groups and ester groups. The binder of this application is a negative electrode binder and needs to be used in an aqueous system. If the content of acrylic acid and acrylates is too low, the relative content of lignin will increase. Since the benzene ring structure of lignin provides oleophilicity, the hydrophilicity of the binder will decrease, thereby affecting the dissolution and dispersion effect of the binder, which is not conducive to the preparation of the negative electrode slurry. The content of acrylate and acrylic acid within the above range is not only more conducive to the preparation of negative electrode slurry, but also helps to enhance the flexibility and affinity of the binder to the electrolyte while ensuring the high ionic conductivity of the binder, thereby improving the adhesion and electrolyte wettability of the electrode sheet, thus forming the main structure of the main chain in the modified acrylic polymer of this application.

[0026] In some embodiments of this application, the mass percentage of polyimide is 3% to 8% based on the total mass of the binder; and / or, the mass percentage of methacrylonitrile is 3% to 8% based on the total mass of the binder. For example, the mass percentage of polyimide in the binder is 3%, 4%, 5%, 6%, 7%, or 8%, and the mass percentage of methacrylonitrile in the binder is 3%, 4%, 5%, 6%, 7%, or 8%. Polyimide and methacrylonitrile have good affinity for the electrolyte, but their content should not be too high. Excessive content can cause side reactions during charge and discharge, thereby affecting the cycle performance of the lithium-ion battery. Within the above-mentioned ranges, the content of polyimide and methacrylonitrile can further impart good elasticity to the lignin-grafted modified acrylic polymer molecular chains, making the dried negative electrode sheet less prone to cracking during bending and rolling, and significantly improving its flexibility.

[0027] In some embodiments of this application, the acrylate includes at least one of butyl acrylate and isooctyl acrylate.

[0028] This application provides a method for preparing the adhesive according to any of the above embodiments, comprising the following steps: Step A, Preparation of pre-emulsion and initiator solution: Add acrylate, acrylic acid, polyimide and methacrylonitrile to the emulsifier solution, mix evenly to obtain pre-emulsion, and prepare ammonium persulfate aqueous solution as initiator solution; Step B, preparation of seed emulsion: Add part of the pre-emulsion and part of the initiator solution to the lignin solution and react at the target temperature for 25 min to 35 min to obtain the seed solution. The amount of pre-emulsion added is 1 / 10 to 1 / 5 of the volume of the lignin solution, and the amount of initiator solution added is 1 / 3 to 1 / 2 of the volume of the lignin solution. The target temperature is 76℃ to 80℃. Step C, graft copolymerization reaction: Maintain the target temperature and add the remaining pre-emulsion and initiator solution dropwise to the seed solution, controlling the dropwise addition time to be 2.5h~3h until the addition is complete; Step D, Incubation and Post-treatment: Maintain the target temperature and continue the reaction for 0.8h~1.2h to maximize the conversion rate. Then, raise the temperature of the reaction system to 83℃~85℃ and mature for 25min~35min to obtain an emulsion. After cooling and adjusting the pH value, the emulsion is used to obtain the binder.

[0029] In step A, the pre-emulsion can be mixed evenly by continuous high-speed shearing and stirring for 15 to 20 minutes; the solvent of the initiator solution is deionized water, and the mass concentration of ammonium persulfate is 0.5%; In step B, the reaction atmosphere can be a nitrogen atmosphere; the lignin can be a commercially available material, and this application does not have any particular restrictions.

[0030] In step C, stirring can be continued during the dropwise addition of the pre-emulsion and initiator solution to ensure a more complete reaction. In step D, the purpose of aging is to decompose the residual initiator, and heating is stopped after aging.

[0031] It should be noted that, since there is a certain loss of each raw material during the reaction process, the raw materials can be added in excess during preparation, for example, 10% excess raw materials can be added so that the content of each structural unit in the binder meets the scope of this application.

[0032] In some embodiments of this application, the steps of cooling and adjusting the pH value include: The emulsion was stirred and cooled to below 40°C, and the pH of the emulsion was adjusted to 7-8 using ammonia to increase the storage stability of the emulsion binder and adapt it to the battery slurry environment.

[0033] In some embodiments of this application, the emulsifier in the emulsifier solution includes at least one of sodium allyl hydroxypropyl sulfonate and alkylphenol polyoxyethylene ether.

[0034] The method for preparing the adhesive provided in this application obtains the adhesive of this application, namely, a lignin-grafted modified acrylic polymer, through a graft copolymerization reaction. It has the advantages of simple preparation process, no need for harsh reaction conditions, and wide availability of raw materials.

[0035] This application also provides a negative electrode sheet, including a negative current collector, at least one side of which has a negative active material layer, the negative active material layer including a negative active material and a binder, wherein the binder is the binder of any of the above embodiments, or the binder is prepared by the method of preparing the binder of any of the above embodiments.

[0036] The negative electrode active material layer of this application can be disposed on one or both surfaces of the negative electrode current collector in the 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 have any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be, 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 can achieve the purpose of this application; for example, a thickness of 4μm to 12μm. The single-sided thickness of the negative electrode active material layer in this application can be 70μm to 200μm.

[0037] In this application, the negative electrode material layer includes a negative electrode material. The negative electrode material is not particularly limited, as long as it can achieve the purpose of this application. For example, it can include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, silicon, and silicon-carbon, preferably graphite.

[0038] This application also provides a battery including the negative electrode sheet described in any of the above embodiments.

[0039] The battery of this application may also include a positive electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode and serves as a separator.

[0040] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet typically includes a positive current collector and a positive active material layer. The positive active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive current collector. In this application, the positive active material layer is disposed on the surface of the positive current collector, that is, the positive active material layer can be disposed on a portion of a surface of the positive current collector or on the entire surface of a surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application, it can be, for example, including but 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 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 active material layer in this application can be 60μm to 140μm.

[0041] The lithium-ion battery of this application also includes a separator. This application does not impose any particular limitation on the separator; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, the separator 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.

[0042] The battery of this application also includes an electrolyte. This application does not impose any particular limitations on the electrolyte; those skilled in the art can choose according to actual needs, as long as it achieves the purpose of this application. For example, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), or fluoroethylene carbonate (FEC) can be mixed in a certain mass or volume ratio to obtain a non-aqueous organic solvent, and then a lithium salt can be added to dissolve and mix evenly. This application does not limit the type of lithium salt, as long as it achieves the purpose of this application. For example, lithium salts may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(fluorosulfonyl)imide (LIFSI), lithium dioxalatoborate (LiBOB), or lithium difluoroborate.

[0043] This application does not impose any particular limitation on the concentration of lithium salt in the electrolyte, as long as the purpose of this application can be achieved. For example, the concentration of lithium salt can be 1.0 mol / L to 2.0 mol / L.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The electrical equipment in this application may include, but is not limited to: containers, 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.

[0049] 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.

[0050] 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 batteries as 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 batteries. 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.

[0051] 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.

[0052] In some embodiments, seeFigure 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Optionally, the individual cell can be, but is not limited to, at least one of cylindrical, prismatic, prismatic, or other shaped cells.

[0063] 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.

[0064] Example The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0065] Example 1 <Preparation of Adhesive> Pretreatment and dissolution of lignin: 2g of lignin (Shanghai Maclean Biochemical Technology Co., Ltd., CAS: 8068-05-1, model L832292) was added to a four-necked flask containing 50.0g of deionized water. The mixture was stirred and ammonia was slowly added dropwise to adjust the pH of the system to 9. Most of the lignin dissolved and formed a dark brown solution. Then the temperature was raised to 60℃ and the mixture was stirred continuously for 30min to completely dissolve and disperse the lignin, thus obtaining a lignin solution. Preparation of preemulsion: In another beaker, 1.0 g of sodium allyl hydroxypropyl sulfonate (COPS-1) and 0.5 g of alkylphenol polyoxyethylene ether (OP-10) were dissolved in 20.0 g of deionized water and stirred until completely dissolved to obtain an emulsifier aqueous solution; then 30 g of butyl acrylate, 15.5 g of acrylic acid, 3 g of polyimide and 3 g of methacrylonitrile were mixed evenly to obtain a mixed monomer. Under high speed stirring, the above mixed monomer was slowly added to the emulsifier aqueous solution and sheared and stirred at 1500 r / min for 15 min to obtain a uniform and stable preemulsion. Preparation of seed emulsion: Place a four-necked flask in a constant temperature water bath and add lignin solution. Add a portion of the pre-emulsion and initiator solution prepared above to the lignin solution. The amount of pre-emulsion added is 1 / 10 of the volume of the lignin solution, and the amount of initiator solution added is 1 / 3 of the volume of the lignin solution. Then, purge the air with nitrogen and start stirring slowly. Raise the temperature to 78°C and react for 30 minutes. When the viscosity of the system increases slightly, it indicates that the seed emulsion has been formed. Semi-continuous dropwise addition and graft copolymerization: Maintain the reaction temperature at 78°C and continuously purge with nitrogen gas. Simultaneously and slowly add the remaining pre-emulsion and the remaining initiator solution through two constant-pressure dropping funnels, completing the addition within 3 hours. Maintain a moderate stirring speed throughout the entire addition process to avoid splashing or agglomeration.

[0066] Insulation and curing and post-treatment: After the addition is complete, continue to keep the reaction at 78℃ for 1 hour to allow the monomers to react fully. Then, raise the temperature of the reaction system to 85℃ and continue curing for 30 minutes to obtain the emulsion. After the reaction is completed, stop heating, continue stirring and cool the emulsion to below 40℃. Then, adjust the pH of the emulsion to 8 with ammonia water, and filter it through a 200-mesh sieve to obtain the lignin-grafted acrylate copolymer emulsion.

[0067] <Preparation of Negative Electrode Sheets> Weigh the negative electrode active materials—artificial graphite, conductive carbon black (Super-P), styrene-butadiene rubber, and the prepared binder—in a mass ratio of 96.9:0.8:1.3:1. Add the artificial graphite and conductive agent to a mixing tank and disperse for 30 minutes. Then add the prepared binder and deionized water, kneading at a high solids content for 30 minutes. Next, add deionized water and continue stirring for 60 minutes to prepare a negative electrode slurry with a solids content of 40 wt%. Coat the prepared slurry evenly onto a 6 μm copper foil, then transfer it to a 100℃ vacuum oven and dry for 12 hours to completely remove the solvent. After cold pressing, slitting, and cutting, the negative electrode sheet is obtained. The single-sided thickness of the negative electrode active material layer is 70 μm.

[0068] <Preparation of the positive electrode> Lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and PVDF binder were mixed at a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a positive electrode slurry with a solid content of 60 wt%. The mixture was stirred until homogeneous. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil used as a 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.

[0069] <Preparation of Electrolyte> In an argon-atmosphere 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 1:1:1. Lithium salt LiPF6 was then added and dissolved in the solvent. After thorough mixing, an electrolyte was obtained. The molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0070] <Preparation of the diaphragm> A porous polyethylene (PE) film with a thickness of 16 μm was used as the separator.

[0071] <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.

[0072] Examples 2 to 13 Except for the section on "Preparation of Adhesive", where the amounts of lignin, acrylate, acrylic acid, polyimide, and methacrylonitrile in the adhesive are adjusted according to Table 1 by adjusting the amounts of each raw material added, the rest is the same as in Example 1.

[0073] Example 14 Except for replacing butyl acrylate with isooctyl acrylate in the <Preparation of Adhesive> section, the rest is the same as in Example 1.

[0074] Comparative Example 1 Except for the fact that lignin was not added in the <Preparation of Adhesive> section, and the amounts of acrylate and acrylic acid were adjusted so that their contents in the adhesive varied according to Table 1, the rest was the same as in Example 1.

[0075] Comparative Example 2 Except for the fact that lignin and methacrylonitrile were not added in the <Preparation of Adhesive> section, and the amounts of acrylate and acrylic acid were adjusted so that the contents of acrylate and acrylic acid in the adhesive varied according to Table 1, the rest was the same as in Example 1.

[0076] Comparative Example 3 Except for the section on "Preparation of Adhesive", where the amounts of lignin, acrylate, acrylic acid, polyimide, and methacrylonitrile in the adhesive are adjusted according to Table 1 by adjusting the amounts of each raw material added, the rest is the same as in Example 1.

[0077] Table 1: Preparation parameters for each example and comparative example

[0078] Test methods and equipment: Tests were conducted on the lignin content, acrylate content, acrylic acid content, polyimide content, and methacrylonitrile content of the adhesive. 1) Lignin content test: The acetyl bromide method was used to determine the lignin content in the binder. This method involves placing the sample in a mixed solution of acetyl bromide and glacial acetic acid to acetylate the phenolic hydroxyl groups of the lignin. The mass fraction of lignin is obtained by measuring the value of the maximum UV absorption peak at 280 nm in the resulting acetylated lignin solution. The specific steps are as follows: The binder sample (i.e., lignin-grafted modified acrylic polymer) is placed in a stoppered test tube with a small vent hole. 10 mL of freshly steamed acetyl bromide (concentrated to 25% with glacial acetic acid) is added, the tube is capped, and the mixture is shaken thoroughly. The tube is then placed in a 70°C constant temperature bath for 30 min, shaking once every 10 min. The tube is then immediately transferred to a 15°C ice water bath for cooling. In addition, 2 mol / L sodium hydroxide solution and glacial acetic acid were added to a volumetric flask. The reactants from the test tube were poured into the volumetric flask and rinsed with a small amount of glacial acetic acid. The mixture was cooled and shaken, and then diluted to the mark with glacial acetic acid. The absorbance was measured at ±280 nm using a UV-Vis spectrophotometer within 5 minutes. Based on the pre-determined ratio of different absorbance values ​​to lignin content, the lignin content in the binder was calculated using the measured absorbance values.

[0079] 2) Polyimide content test: The polyimide content was determined using the starch-cadmium iodide colorimetric method. Acetic acid buffer and bromine water were added sequentially to the adhesive. The amide groups reacted with the bromine water to form bromoamide. Sodium formate was then added to remove residual bromine. The bromoamide hydrolyzed to form hypobromic acid. Subsequently, a starch-cadmium iodide reagent was added, and iodide ions were oxidized to I₂ by hypobromic acid. The iodide ions and I₂ then formed I₃. - I3 - It can react with starch to form a blue starch-triiodine complex. The intensity of the color is directly proportional to the polyimide content. The absorbance is measured using a UV-Vis spectrophotometer. Based on the pre-determined ratio of different absorbance to polyimide content, the polyimide content in the adhesive is calculated from the measured absorbance.

[0080] 3) Methacrylonitrile content test: Polymethacrylonitrile standard and potassium thiocyanate were mixed and ground at different mass ratios, and then tested by infrared absorption spectroscopy to calculate the ratio coefficient of cyano to thiocyanate absorption values. The prepared adhesive sample was mixed and ground with potassium thiocyanate, and tested by infrared absorption spectroscopy to calculate the ratio of cyano to thiocyanate absorption values. Then, the mass ratio of methacrylonitrile units to potassium thiocyanate was calculated based on the ratio coefficient, thereby obtaining the content of cyano and methacrylonitrile in the adhesive.

[0081] 4) Acrylic acid content test: Accurately weigh 0.5 g of the adhesive sample and place it in an Erlenmeyer flask. Dissolve the sample in 100 mL of a mixture of isopropanol and water (60:40). Add one drop of phenolphthalein indicator and titrate with 0.1 mol·L⁻¹ sodium hydroxide solution. -1 Titrate to the endpoint and correct the titration result with a blank test. Each 1 mL of sodium hydroxide titrant (0.1 mol·L⁻¹) -1 This is equivalent to 7.206 mg of acrylic acid units, and the content of acrylic acid in the adhesive sample can be obtained from the titration results.

[0082] 5) Acrylate content test: Based on the above determination results of the contents of lignin, acrylic acid, polyimide, and methacrylonitrile, the content of acrylate in the adhesive can be calculated by subtracting the contents of the above substances from 100%.

[0083] Peel strength test: One side of the negative electrode sheet of the sample is adhered to a steel plate with double-sided tape. The steel plate is mounted on the fixed fixture at the bottom of the high-speed rail tensile testing machine (model HCF01747). After confirming that the bottom layer of the sample is firmly bonded to the steel plate, approximately 1 cm is torn along the interface between the negative electrode sheet and the double-sided tape at one end of the sample's length. This torn corner of the negative electrode sheet is then clamped onto the movable fixture at the top of the high-speed rail tensile testing machine. The sample preparation is complete. Test: Tension angle 90°, tension speed 50 mm / min, until the interface between the negative electrode sheet and the double-sided tape is completely separated. After separation, the negative electrode material layer is adhered to the surface of the double-sided tape, and the other side of the separated interface is at least partially exposed of the negative electrode current collector. Record the average load force (N) during the tensile process, divide it by the sample width to obtain the peel strength between the negative electrode active material layer and the negative electrode current collector, and then take the average value.

[0084] Three-point bending test: ① Bake the negative electrode at 110℃ for 3 hours, then cut the negative electrode into 15cm×5cm electrode samples using a cutter; ② Place the electrode samples into the fixture of a flexibility tester (model PY-H613); ③ Make the electrode sample at 90° with the test head, and press the test head vertically into the electrode sample to a depth of 8±0.5 mm. Record the maximum pressure value displayed by the test head sensor, which is the three-point bending pressure value, in mN. The smaller the value, the higher the flexibility of the electrode.

[0085] Cyclic performance test: At 25°C, the lithium-ion battery was subjected to charge-discharge cycles at 0.5C, with a charging cutoff voltage of 3.7V and a discharging cutoff voltage of 2.45V, until the battery capacity reached 60% of its initial capacity. Simultaneously, the capacity retention rate of the lithium-ion battery after 500 cycles was tested using a constant current method. The capacity retention rate was calculated as: (500th cycle discharge capacity / 2nd cycle discharge capacity) × 100%.

[0086] Table 2: Performance data of each embodiment and comparative example

[0087] As can be seen from Examples 1-14 and Comparative Examples 1-3, the binder of Comparative Example 1 did not introduce lignin, resulting in low peel strength and high three-point bending pressure, indicating that its negative electrode sheet has low flexibility and high rigidity, leading to a low capacity retention rate of its lithium-ion battery. The binder of Comparative Example 2 did not introduce lignin and methacrylonitrile, and although its peel strength was improved to some extent, its three-point bending pressure was even higher, indicating that its negative electrode sheet had even lower flexibility, leading to a low capacity retention rate of its lithium-ion battery. The binder of Comparative Example 3 had too high lignin content, resulting in a decrease in peel strength and affecting the capacity retention rate of the lithium-ion battery. In contrast, the binder of this application not only underwent main chain modification but also side chain modification, enabling the negative electrode sheet of this application to maintain good flexibility while having high peel strength. This reduces problems such as cracking and powder shedding when the negative electrode sheet is wound thick, thereby improving the capacity retention rate of the lithium-ion battery.

[0088] Figure 4 This is the Fourier transform infrared (FTIR) spectrum of the adhesive of Example 3 of this application. From... Figure 4 As can be seen from the image, the FTIR spectrum of Example 3 is at 3244 cm⁻¹. -1 The vicinity exhibits a characteristic spectral band, belonging to the stretching vibration of -OH, at 2940 cm⁻¹. -1 ~2855 cm -1 The stretching vibration of CH, 1706 cm -1 ~1547 cm -1 Asymmetric / symmetric stretching vibration at C=O, 1325 cm -1 This is an asymmetric stretching vibration of COC, 798 cm. -1 ~864 cm -1 The bending vibration of CH within the benzene ring, which is characteristic of lignin, indicates the presence of lignin in the binder of this application.

[0089] The present application discloses a binder and its preparation method, a negative electrode sheet, a battery, and an energy storage device. Specific examples have been used to illustrate the principles and implementation methods of the present 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 the present 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 the present application. Therefore, the content of this specification should not be construed as a limitation of the present application.

Claims

1. An adhesive, characterized in that, The adhesive is a lignin-grafted modified acrylic polymer, wherein: Monomers that form the backbone of acrylic polymers include acrylates, acrylic acid, polyimide, and methacrylonitrile; Based on the total mass of the binder, the lignin content is 2% to 10% by mass.

2. The adhesive according to claim 1, characterized in that, Based on the total mass of the adhesive, the mass percentage of the acrylate is 50% to 60%; And / or, based on the total mass of the adhesive, the mass percentage of the acrylic acid is 20% to 30%.

3. The adhesive according to claim 1, characterized in that, Based on the total mass of the adhesive, the polyimide content is 3% to 8% by mass; And / or, based on the total mass of the adhesive, the mass percentage of the methacrylonitrile is 3% to 8%.

4. The adhesive according to claim 1, characterized in that, The acrylate includes at least one of butyl acrylate and isooctyl acrylate.

5. A method for preparing an adhesive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Acrylate, acrylic acid, polyimide and methacrylonitrile were added to the emulsifier solution and mixed evenly to obtain a pre-emulsion. An ammonium persulfate aqueous solution was prepared as an initiator solution. A portion of the pre-emulsion and a portion of the initiator solution are added to the lignin solution, and the reaction is carried out at the target temperature for 25 min to 35 min to obtain a seed solution. The amount of the pre-emulsion added is 1 / 10 to 1 / 5 of the volume of the lignin solution, the amount of the initiator solution added is 1 / 3 to 1 / 2 of the volume of the lignin solution, and the target temperature is 76℃ to 80℃. Maintaining the target temperature, the remaining pre-emulsion and initiator solution are added dropwise to the seed solution, with the addition time controlled at 2.5h~3h, until the addition is complete; The reaction is continued at the target temperature for 0.8h to 1.2h. Then the reaction system is heated to 83℃ to 85℃ and matured for 25min to 35min to obtain an emulsion. The emulsion is then cooled and the pH value is adjusted to obtain the binder.

6. The preparation method according to claim 5, characterized in that, The steps for cooling and adjusting the pH value include: The emulsion was stirred and cooled to below 40°C, and the pH of the emulsion was adjusted to 7-8 using ammonia.

7. The preparation method according to claim 5, characterized in that, The emulsifier in the emulsifier solution includes at least one of sodium allyl hydroxypropyl sulfonate and alkylphenol polyoxyethylene ether.

8. A negative electrode sheet, characterized in that, include: A negative electrode current collector, wherein at least one side of the negative electrode current collector has a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material and a binder, wherein the binder is the binder according to any one of claims 1 to 4.

9. A battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. An energy storage device, characterized in that, It includes a housing and at least one battery as described in claim 9, the battery being housed within the housing.

11. An electrical appliance, characterized in that, The device includes the energy storage device of claim 10, wherein the energy storage device supplies power to the electrical equipment.

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