Binder, method for producing the same, negative electrode sheet, secondary battery, and battery pack

Abstract

The application provides a binder and a preparation method thereof, a negative electrode sheet, a secondary battery and a battery pack, wherein the binder comprises a polymer, and the polymer comprises a structural unit shown in formula (I), wherein R1 is at least one selected from -COOH, -COOLi and -COONa; R2 and R3 are independently selected from a polar group or a rigid group, and R2 and R3 are not simultaneously the polar group or the rigid group.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, and particularly relates to a binder and a preparation method thereof, a negative electrode sheet, a secondary battery and a battery pack. BACKGROUND

[0002] Secondary batteries (for example, lithium ion batteries) have the advantages of large energy density, small self-discharge and light weight, and are widely used in the field of energy storage devices and the like.

[0003] The negative electrode sheet, as a main structural part of the secondary battery, plays an important role in the performance of the secondary battery. With the increasing requirement for the performance of the secondary battery, how to improve the flexibility of the negative electrode sheet and reduce the cracking and powder dropping of the negative electrode sheet has become a problem to be solved. SUMMARY

[0004] In order to solve the above technical problems, the present application discloses a binder and a preparation method thereof, a negative electrode sheet, a secondary battery and a battery pack, so as to improve the flexibility, peeling strength and cohesion of the negative electrode sheet, thereby improving the capacity retention rate and energy efficiency of the secondary battery.

[0005] In a first aspect, the present application provides a binder, which comprises a polymer, and the polymer comprises a structural unit represented by formula (I),

[0006]

[0007] wherein R1 is selected from at least one of -COOH, -COOLi and -COONa;

[0008] R2 and R3 are independently selected from a polar group or a rigid group, and R2 and R3 are not simultaneously a polar group or a rigid group;

[0009] 2≤x≤10.

[0010] In some embodiments of the present application, the molar ratio of the rigid group to the polar group in the binder is 0.1-9:1.

[0011] In some embodiments of the present application, the molar ratio of the rigid group to the polar group in the binder is 0.1-9:1. x H 2x the molar ratio of the rigid group to the polar group in the binder is 0.1-9:1.

[0012] In some embodiments of the present application, the polar group comprises at least one of -OH, -COOH, -OCH2COOCH3, -OCONH2 and -OCH2NHCOOH.

[0013] In some embodiments of this application, the rigid group includes groups formed from cyclodextrin compounds.

[0014] In some embodiments of this application, the cyclodextrin compounds include at least one selected from α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, methyl-β-cyclodextrin, hydroxyethyl-β-cyclodextrin, 2,6-di-O-methyl-β-cyclodextrin, and carboxymethyl-β-cyclodextrin.

[0015] Secondly, this application provides a method for preparing an adhesive as described in the first aspect, comprising the following steps:

[0016] Carboxymethyl cellulose was subjected to oxidative ring-opening treatment and etherification treatment to obtain modified carboxymethyl cellulose;

[0017] The modified carboxymethyl cellulose was grafted onto the cellulose under catalytic conditions using cyclodextrin compounds and polar group compounds to obtain the binder.

[0018] In some embodiments of this application, the grafting reaction is carried out at a temperature of 160°C to 200°C, for a reaction time of 20 min to 40 min, and the pH of the reaction system is 2.5 to 3.0.

[0019] In some embodiments of this application, the polar group compound is selected from at least one of 1,2,3,4-butanetetracarboxylic acid, dimethylacetamide, maleamic acid, N-BOC-ethyl oxalamide, alanylglutamine, dimethyl 1,3-propanone dicarboxylic acid, and triethyl methanetricarboxylic acid; the catalyst is selected from at least one of sodium hypophosphite monohydrate, sodium hypochlorite, and sodium borohydride.

[0020] Thirdly, this application provides a secondary battery, including the negative electrode sheet described in the first aspect, or the negative electrode sheet prepared by the preparation method described in the second aspect.

[0021] Fourthly, this application provides a battery pack including a housing and at least one secondary battery as described in the third aspect, the secondary battery being housed within the housing.

[0022] Fifthly, this application provides an electrical device including the secondary battery described in the third aspect or the battery pack described in the fourth aspect.

[0023] Compared with the prior art, this application has at least the following beneficial effects:

[0024] This application provides an adhesive and its preparation method, a negative electrode sheet, a secondary battery, and a battery pack. The adhesive comprises a polymer containing structural units as shown in formula (I). The long chains of the polymer include straight or branched carbon segments with 2 to 10 carbon atoms, which are flexible carbon segments that increase the mobility of the molecular chain and isolate hydroxyl groups (-OH), thereby reducing hydrogen bond formation and improving the flexibility of the negative electrode sheet. The polar and rigid groups in the side chains of the polymer improve the adhesive properties of the adhesive, thereby increasing the peel strength of the negative electrode sheet. The adhesive with the structure of this application improves the flexibility, peel strength, and cohesiveness of the negative electrode sheet, reducing problems such as cracking and powder shedding, thereby improving the capacity retention and energy efficiency of the secondary battery. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application;

[0027] Figure 2 This is a schematic diagram of the structure of an energy storage system according to one embodiment of this application;

[0028] Figure 3 The Fourier transform infrared (FTIR) spectra of the adhesives of Example 1 and Comparative Example 1 of this application are shown.

[0029] Figure 4a This is a cross-sectional image of the negative electrode sheet before wetting in Comparative Example 1, polished and scanned electron microscope (CP-SEM) image.

[0030] Figure 4b This is the CP-SEM image of the negative electrode sheet after wetting in Comparative Example 1;

[0031] Figure 5a This is a CP-SEM image of the negative electrode sheet before wetting in Example 3;

[0032] Figure 5b This is a CP-SEM image of the negative electrode sheet after impregnation in Example 3.

[0033] Explanation of reference numerals in the attached drawings: 1-Energy storage device, 2-Power conversion device, 3-First user load, 4-Second user load, 400-Energy storage system, 410-High voltage cable, 420-First power conversion device, 430-Second power conversion device. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (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, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0039] 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.

[0040] In related technologies, traditional carboxymethyl cellulose (CMC) is composed of D-glucose units linked by β(1→4) glycosidic bonds. This type of CMC monomer contains two hydroxyl groups (-OH), hydrogen bonds exist between molecules, and the molecular chain is not easy to rotate, resulting in high rigidity. When applied to negative electrode sheets, it can easily cause the negative electrode sheets to become hard and brittle and break, affecting the capacity retention rate and energy efficiency of lithium-ion batteries.

[0041] In view of this, this application provides an adhesive comprising a polymer, the polymer comprising the structural unit shown in formula (I).

[0042]

[0043] R1 is selected from at least one of -COOH, -COOLi and -COONa;

[0044] R2 and R3 are independently selected from polar groups or rigid groups, and R2 and R3 are not both polar groups or rigid groups at the same time;

[0045] 2≤x≤10.

[0046] For the structural unit shown in formula (Ⅰ), R2 and R3 are not simultaneously polar or rigid groups. For example, when R2 is a polar group, R3 is a rigid group; when R2 is a rigid group, R3 is a polar group. This is because polar groups can appropriately increase the formation of intramolecular or intermolecular hydrogen bonds, improve the adhesive strength of the binder, and thus improve the peel strength of the negative electrode sheet; while rigid groups have large steric hindrance, which can effectively reduce the rotation of molecular bonds, increase molecular rigidity, and improve the cohesive force of the negative electrode sheet. Therefore, the introduction of polar and rigid groups into the binder can simultaneously improve the peel strength and cohesive force of the negative electrode sheet. The cohesive force in this application refers to the attraction and aggregation forces between the molecules of the binder itself.

[0047] The polymer of this application forms straight or branched carbon segments with 2 to 10 carbon atoms in its long chain. These carbon segments are flexible and can improve the flexibility of the negative electrode sheet. This is likely because these carbon segments can increase the mobility of the molecular chain and isolate hydroxyl groups, reducing the formation of hydrogen bonds and thus reducing the rigidity of the binder. The side chains of the polymer of this application have polar and rigid groups, which can improve the peel strength and cohesive force of the negative electrode sheet. This is likely because these polar and rigid groups can improve the adhesive properties of the binder and increase the rigidity of the binder molecules, thereby improving the peel strength and cohesive force of the negative electrode sheet. Under the combined effect of R2, R3 and the flexible carbon segments, the binder of this application can simultaneously improve the flexibility, peel strength and cohesive force of the negative electrode sheet, thereby improving the capacity retention and energy efficiency of the lithium-ion battery.

[0048] In some embodiments of this application, the molar ratio of rigid groups to polar groups in the binder is 0.1 to 9:1. For example, the molar ratio of rigid groups to polar groups in the binder is 0.1:1, 0.5:1, 1:1, 2:1, 4:1, 5:1, or 9:1. By controlling the molar ratio of rigid groups to polar groups in the binder within the above range, polar groups can appropriately increase the formation of intramolecular or intermolecular hydrogen bonds, improve the bonding strength of the binder, and thus improve the peel strength of the negative electrode sheet. However, if the proportion of polar groups is too large, too many active functional groups will be introduced into the binder, and the binder will produce more side reactions with the electrolyte during cycling, affecting the electrical performance of the lithium-ion battery. Rigid groups have large steric hindrance, which can effectively reduce the rotation of molecular bonds, increase molecular rigidity, and improve the cohesion of the negative electrode sheet. However, if the proportion of rigid groups is too large, it will lead to excessive steric hindrance between chains, hindering the formation of intermolecular hydrogen bonds, resulting in a loss of peel strength.

[0049] In some embodiments of this application, the rigid groups in the adhesive are related to -C x H 2x The molar ratio of -carbon segments is 2 to 5:1. For example, the rigid groups in the adhesive and -C x H 2x The molar ratio of the -carbon segments is 2:1, 3:1, 4:1, or 5:1. This application can regulate the ratio of rigid groups to -C segments during binder modification, thereby controlling the interaction between the rigid groups and the -C segments. x H 2x The molar ratio of carbon segments is within the above range. If the proportion of flexible carbon segments is too high, the binder structure is easily damaged, resulting in a significant decrease in the binder's adhesive strength; if the proportion of flexible carbon segments is too low, the binder is easily made too hard and brittle, failing to achieve the desired flexibility of the negative electrode sheet. This application addresses this by incorporating flexible C2-C segments into the middle of the long cellulose chain. 10 Chain segments, and regulate rigid groups and -C x H 2x When the molar ratio of carbon segments is within the above range, it can effectively increase the mobility of the molecular chain and isolate hydroxyl groups, thereby reducing the formation of hydrogen bonds and improving the flexibility of the negative electrode sheet.

[0050] In some embodiments of this application, the polar groups include at least one selected from hydroxyl (-OH), carboxylate (-COOH), ester (-OCH2COOCH3), amide (-OCONH2), and urethane (-OCH2NHCOOH). When the adhesive contains the above-mentioned polar groups, it is beneficial to improve the adhesive's bonding performance.

[0051] In some embodiments of this application, the rigid group includes a group formed from a cyclodextrin compound. The cyclodextrin compound is a cyclic oligosaccharide comprising the structural unit shown in formula (II):

[0052]

[0053] In some embodiments of this application, the cyclodextrin compounds include at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, methyl-β-cyclodextrin, hydroxyethyl-β-cyclodextrin, 2,6-di-O-methyl-β-cyclodextrin, and carboxymethyl-β-cyclodextrin.

[0054] The inventors discovered that traditional lithium-ion battery electrode materials suffer from drawbacks such as relatively low flexibility and brittleness. The aqueous binder used in the negative electrode sheet, due to its high hydrogen bond content, is also brittle, and its interfacial adhesion significantly decreases after rolling. This results in poor adhesion between the negative electrode active material layer and the negative electrode current collector, leading to insufficient contact. This not only causes the negative electrode sheet to crack and the active material to detach after folding, bending, and stretching, which is detrimental to the processing and later application of lithium-ion batteries, but also affects the cycle performance and lifespan of the batteries. Therefore, related technologies add small-molecule plasticizers, such as butanediol, during the preparation of the negative electrode sheet to improve this situation. However, butanediol is environmentally polluting and increases production costs.

[0055] In view of the above, this application provides a method for preparing the adhesive according to any of the above embodiments, comprising the following steps:

[0056] Main chain modification: Carboxymethyl cellulose was subjected to oxidative ring-opening treatment and etherification treatment to obtain modified carboxymethyl cellulose;

[0057] Side chain modification: Under catalytic conditions, modified carboxymethyl cellulose is grafted with cyclodextrin compounds and polar group compounds to obtain a binder.

[0058] In the main chain modification step, carboxymethyl cellulose (CMC) can be oxidized and ring-opened using an ethanol solution of sodium hypochlorite. The purpose is to break the carbon-carbon bonds at positions 2 and 3 in some of the ring structures of CMC, generating long carbon segments, i.e., flexible carbon segments. The length and ring-opening ratio of the carbon segments can be controlled by adjusting parameters such as the concentration of sodium hypochlorite, stirring temperature, and stirring time. In the etherification process, CMC can first be alkalized with an ethanol solution of sodium hydroxide, and then etherified with an ethanol solution of chloroacetic acid. The purpose is to generate ether bonds during the modification process so that CMC can be connected with other structural units through ether bonds.

[0059] In the side-chain modification step, maintaining the system at a low temperature of 3℃ to 5℃ during catalyst addition, followed by heating to carry out the grafting reaction, can ensure a gentle reaction, reduce side reactions, and thus improve the product yield.

[0060] In some embodiments of this application, the grafting reaction temperature is 160℃~200℃, the reaction time is 20min~40min, and the pH value of the reaction system is 2.5~3.0. This facilitates the full grafting of rigid and polar groups to obtain the binder of this application.

[0061] In some embodiments of this application, the polar group compound is selected from at least one of 1,2,3,4-butanetetracarboxylic acid (BTCA), dimethylacetamide (DMAC), maleic acid, N-BOC-ethyl oxalamide, alanylglutamine (L-Ala-Gln), dimethyl 1,3-propanone dicarboxylate, and triethyl methanetricarboxylate; the catalyst is selected from at least one of sodium hypophosphite monohydrate, sodium hypochlorite, and sodium borohydride. This facilitates the full grafting of rigid and polar groups to obtain the binder of this application.

[0062] This application does not impose any particular limitation on the method for controlling the ratio of rigid groups to polar groups in the binder, as long as the binder of this application can be obtained. For example, when the relative content of cyclodextrin compounds in the reactants is higher, the proportion of rigid groups in the binder is higher; when the relative content of polar group compounds in the reactants is higher, the proportion of polar groups in the binder is higher.

[0063] This application addresses the regulation of rigid groups and flexible carbon segments (-C) in adhesives. x H 2x -) There are no particular limitations on the proportioning method, as long as the binder of this application can be obtained. For example, increasing the molar ratio of sodium hypochlorite or cyclodextrin compounds to modified CMC can increase the flexible carbon segments (-C... x H 2x -) or the ratio of rigid groups. For example, when the molar ratio of sodium hypochlorite:cyclodextrin compound:modified CMC is 1:4:4, the ratio of rigid groups to flexible carbon segments (-C) is... x H 2x -) The ratio is approximately 4:1.

[0064] The binder preparation method provided in this application modifies CMC to form a polymer formed by polymerizing the structural units shown in formula (I). When this polymer is used as a binder, it has flexible carbon segments, polar groups and rigid groups. The binder prepared by this method has better flexibility and adhesion performance. Therefore, when the binder is applied to the negative electrode sheet, it can simultaneously improve the flexibility and peel strength of the negative electrode sheet, thereby improving the capacity retention rate and energy efficiency of the lithium-ion battery.

[0065] 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.

[0066] 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 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 can achieve 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.

[0067] This application also provides a secondary battery, including the negative electrode sheet described in any of the above embodiments.

[0068] The secondary 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.

[0069] 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 100μm to 200μm.

[0070] In this application, the positive electrode active material layer includes a positive electrode active material. This application does not have any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, it may include at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0071] In this application, the positive electrode active material layer may also include a positive electrode binder. This application does not have any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of fluorinated resin, polypropylene resin, fiber-type binder, rubber-type binder or polyimide-type binder.

[0072] 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.

[0073] The secondary 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.

[0074] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, separator and negative electrode in sequence, and winding and folding them 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 secondary battery.

[0075] This application also provides a battery pack, including a housing and at least one secondary battery as described in any of the above embodiments, the secondary battery being housed within the housing. The battery pack with this secondary battery exhibits excellent performance, which is beneficial for its use. Housed within the housing, the battery is secured and protected, thus extending the battery pack's lifespan. It is understood that the battery pack may contain one or more secondary batteries, and when the battery pack contains multiple secondary batteries, these batteries can be connected in at least one manner, such as parallel or series connection.

[0076] This application also provides an electrical device including a secondary battery or battery pack as described in any of 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 secondary battery or battery pack 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 terminal of the secondary battery or battery pack is used to electrically connect to the positive terminal of the electrical device body, and the negative terminal of the secondary battery or battery pack is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0077] The electrical equipment covered by this application may include, but is not limited to: containers, household energy storage systems, 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.

[0078] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application, and this application... Figure 1 The implementation plan is illustrated using the residential energy storage scenario in user-side energy storage as an example. The energy storage device in this application is not limited to the residential energy storage scenario.

[0079] This application provides a residential energy storage system, which includes a power conversion device 2 (photovoltaic panel), a first user load 3 (streetlight), a second user load 4 (e.g., household appliances such as air conditioners), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 1 is used to store this electrical energy and supply it to streetlights and household appliances during periods of high electricity prices, or to provide power during power outages / power failures.

[0080] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 400 according to one embodiment of this application, and this application Figure 2 The implementation plan is illustrated using the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1 in this application is not limited to the power generation / distribution side energy storage scenario.

[0081] This application provides an energy storage system 400, which includes a high-voltage cable 410, a first power conversion device 420, a second power conversion device 430, and the energy storage device 1 provided in this application. During power generation, the first power conversion device 420 and the second power conversion device 430 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable 410 and supplied to the power consumption side of the distribution network. When the power load is low and the first power conversion device 420 and the second power conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1, along with the high-voltage cable 410, in a grid-connected mode to supply power to the power consumption side. This provides various services such as peak shaving, frequency regulation, and backup for the power grid operation, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0082] Optionally, the first power conversion device 420 and the second power conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0083] The number of energy storage devices 1 can be multiple, and these devices can be connected in series or in parallel. The multiple energy storage devices 1 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" refers to two or more. An energy storage box can also be provided outside the energy storage device 1 to house it.

[0084] Optionally, the energy storage device 1 may include, but is not limited to, a single battery cell, a battery module, a battery pack, or a battery system. A single battery cell may be a rechargeable battery of this application; a battery module may be a rechargeable battery module formed by connecting multiple rechargeable batteries of this application in series or parallel; a battery pack may be a battery pack of this application; and a battery system may be a charging and discharging system including the rechargeable batteries or battery pack of this application. The actual application form of the energy storage device 1 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 1. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 1 is a single battery cell, the energy storage device 1 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0085] Example

[0086] 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.

[0087] Example 1

[0088] <Preparation of Adhesive>

[0089] <Main chain modification>

[0090] The raw carboxymethyl cellulose (CMC) was pre-dried at 110°C for 4 hours. The dried CMC was then added to a 0.8% (w / v) sodium hypochlorite ethanol solution to obtain a mixed solution, wherein the molar ratio of sodium hypochlorite to CMC was 1:4. The mixed solution was stirred at 45°C for 6 hours. Subsequently, the pH value was adjusted to 7.0 using a 1% (w / v) sulfuric acid solution, and then a 17.5% (w / v) sodium hydroxide ethanol solution was added. The mixture was stirred at 45°C for 3 hours to perform alkalization treatment until the pH value reached 10. Then, a 1% (w / v) chloroacetic acid ethanol solution was added, and the mixture was stirred at 76°C for 30 minutes to perform etherification treatment. Finally, the pH value was adjusted to 7.0 using a 1% (w / v) sulfuric acid solution, and the mixture was dried at 110°C to obtain solid modified CMC.

[0091] <Sidechain Modification>

[0092] β-Cyclodextrin (i.e., cyclodextrin compounds), 1,2,3,4-butanetetracarboxylic acid (BTCA, i.e., polar group compounds), and modified CMC were weighed at a molar ratio of 1.5:1:1.5. First, β-cyclodextrin and BTCA were mixed to obtain a mixture. Then, the mixture was added to 75% ethanol to obtain a first mixture. Next, the weighed modified CMC was added to the first mixture to obtain a second mixture. The pH of the second mixture was adjusted to 2.7 using a 1% (w / v) sulfuric acid solution. Then, sodium hypophosphite monohydrate, a catalyst, was added at 5°C. The concentration of the catalyst in the second mixture was 1 wt%. Subsequently, the second mixture containing the catalyst was subjected to a grafting reaction at 180°C for 30 min under a nitrogen atmosphere. After the reaction, sufficient ethanol was added to precipitate the product. The product was then obtained by filtration and freeze-drying, which is the binder.

[0093] <Preparation of Negative Electrode Sheets>

[0094] Artificial graphite (anode active material), water-based binder (polyacrylic acid), conductive carbon black (Super-P), and the prepared binder were mixed in a mass ratio of 96:2:1:1. Deionized water was then added as a solvent 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 used as a negative electrode 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.

[0095] <Preparation of the positive electrode>

[0096] Lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and PVDF binder were mixed at a mass ratio of 94:3:3. Then, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 60 wt%, which was stirred evenly. 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.

[0097] <Preparation of Electrolyte>

[0098] 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.

[0099] <Preparation of the diaphragm>

[0100] A porous polyethylene (PE) film with a thickness of 16 μm was used as the separator.

[0101] <Preparation of Lithium-ion Batteries>

[0102] 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.

[0103] Examples 2 to 5

[0104] Except for the section on "Preparation of Adhesives", where the molar ratio of rigid groups to polar groups in the adhesive is controlled according to Table 1 by adjusting the amount of cyclodextrin compounds and polar group compounds added, the rest is the same as in Example 1.

[0105] Examples 6 to 8

[0106] In addition to adjusting the molar ratio of sodium hypochlorite, cyclodextrin compounds, and modified CMC in the <Preparation of Adhesive> section (when the molar ratios of sodium hypochlorite, cyclodextrin, and modified CMC are 1:2:2, 1:3:3, and 1:5:5, respectively, the molar ratio of rigid groups to flexible carbon segments is 2:1, 3:1, and 5:1), the ratio of rigid groups to flexible carbon segments (-C) in the adhesive is controlled according to Table 1. x H 2x Except for the molar ratio of -), it is the same as in Example 1.

[0107] Examples 9 to 10

[0108] Except for the preparation of the binder, in which the types of reactants are controlled according to Table 1, the rest is the same as in Example 1.

[0109] Examples 11-12

[0110] Except for the section on "Preparation of Adhesives", where the types of polar group compounds are controlled according to Table 1, the rest is the same as in Example 1.

[0111] Examples 13-14

[0112] Except for the section on "Preparation of Binders", where the types of cyclodextrin compounds are controlled according to Table 1, the rest is the same as in Example 1.

[0113] Examples 15-16

[0114] Except for the control of the reaction temperature, reaction time and pH value of the reaction system in the <Preparation of Adhesive> section according to Table 2, the rest is the same as in Example 1.

[0115] Comparative Example 1

[0116] Except for the fact that CMC is not modified in the <Preparation of Adhesive> section, the rest is the same as in Example 1.

[0117] Comparative Example 2

[0118] Except for the omission of the side chain modification step in the preparation of the binder, i.e., the modified CMC obtained after the main chain modification step is used directly as the binder, the rest is the same as in Example 1.

[0119] Comparative Example 3

[0120] Except for omitting the "Main Chain Modification" step in "Preparation of Binder" and replacing the modified CMC with the original CMC in "Side Chain Modification", the rest is the same as in Example 1.

[0121] Test methods and equipment:

[0122] The molar ratio of polar groups to rigid groups in the adhesive, and the ratio of rigid groups to -C x H 2x - Molar ratio test of carbon segments:

[0123] The ratio of polar groups, rigid groups, and flexible carbon segments in the binder is obtained by detecting the content of these three components.

[0124] 1. Detection of polar group content

[0125] The nitrogen content in the obtained binder was determined using the Kjeldahl method, thus obtaining the content of polar groups incorporated. The specific procedure is as follows: The binder sample was placed in a Kjeldahl flask, and a 98% sulfuric acid solution was added. The sample was heated to obtain a mixture. Potassium sulfate was added to the mixture to raise the boiling point of the intermediate product, converting the nitrogen in the sample into ammonium sulfate. The decomposition process reached its endpoint when the mixture became colorless and transparent. A small amount of sodium hydroxide was added to the resulting solution, and then the ammonium salt was converted into ammonia by distillation. The total ammonia content was determined by back titration, thus obtaining the nitrogen content of the sample. The end of the condenser was immersed in a boric acid solution; the generated ammonia reacted with the boric acid, and the excess boric acid was titrated with sodium carbonate under the indication of methyl orange. This yielded the total nitrogen content of the sample, i.e., the content of polar groups incorporated into the sample.

[0126] 2. Detection of rigid functional groups

[0127] Rigid cyclodextrins contain a specific number of hydroxyl groups. The content of rigid groups can be determined by measuring the hydroxyl content in the binder sample using the acetylation method. The specific procedure is as follows: Weigh an appropriate amount of binder sample into an Erlenmeyer flask, add 25 mL of acetic anhydride pyridine solution (40% concentration), install the reflux condenser, and slowly shake the flask until the sample is completely dissolved. Place the flask in an oil bath and reflux at 115℃±5℃ for 1 hour. After the reaction is complete, remove the flask, add 10 mL of distilled water from the top of the condenser, and then immerse the flask in the oil bath for 10 minutes while continuously shaking. After the reaction is complete, remove the reflux apparatus, allow the reaction solution to cool to room temperature, add 10 drops of phenolphthalein indicator, and titrate with sodium hydroxide-ethanol standard titration solution until a faint red color persists for 30 seconds as the endpoint. A blank test is performed simultaneously. The acetylation reagent reacts with the hydroxyl groups in the sample to induce acylation. Hydrolysis is then performed to decompose the remaining acetic anhydride. The generated acetic acid is titrated with a sodium hydroxide-ethanol standard solution. A blank test is also performed. The hydroxyl content of the sample is calculated from the difference in the volume of NaOH consumed between the sample test group and the blank test group. The specific calculation is as follows:

[0128]

[0129] Wherein: [OH] refers to the hydroxyl content of the obtained sample, in mol / g; V1 refers to the volume of NaOH standard solution consumed by the blank solution, in mL; V2 refers to the volume of NaOH standard solution consumed by the sample, in mL; m refers to the sample amount, in g; C1 refers to the concentration of the NaOH standard solution, in mol / L.

[0130] 3. Detection of open-ring carbon segments

[0131] After the binder main chain undergoes oxidation and ring-opening, two aldehyde groups are formed in situ. The content of aldehyde groups in the sample structure can be determined by the hydroxylamine hydrochloride-potentiometric titration method to obtain the amount of flexible carbon chain incorporation. The test principle is as follows: First, the active amino group on the hydroxylamine hydrochloride and the aldehyde group on the binder react for a certain period of time. Then, the amount of HCl released and the amount of NaOH consumed are determined by potentiometric titration using NaOH aqueous solution. The aldehyde group concentration is then calculated. The specific process is as follows: Take about 0.1g of binder sample and add it to 25mL of 0.25mol / L hydroxylamine hydrochloride-methyl orange solution. Stir thoroughly for 2h to dissolve it into a homogeneous solution. Use about 0.1mol / L standard NaOH aqueous solution as the titrant and determine the amount of HCl generated in the solution by potentiometric titration. The aldehyde group concentration is then calculated based on the amount of NaOH consumed. For specific calculation methods, please refer to the paper: Determination of aldehyde concentration on oxidized sodium alginate by hydroxylamine hydrochloride-potentiometric titration, Chinese Journal of Analysis Laboratory, Vol.27.Suppl.2008-5.

[0132] Peel strength test:

[0133] 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. One corner of the torn negative electrode sheet is 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.

[0134] Warpage test:

[0135] The negative electrode sheet was baked at 110℃ for 3 hours. Then, the negative electrode sheet was cut into electrode samples of 15cm×5cm. The electrode samples were placed on the edge of the platform, and one end of the electrode sample was pressed with a glass plate so that the other end of the electrode sample hung down naturally. The size of the angle between the electrode sample and the horizontal plane was observed.

[0136] Three-point bending test:

[0137] 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±0.5mm. 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.

[0138] Cyclic performance test:

[0139] The lithium-ion battery was cycled at 25°C using 0.5P charging and discharging, 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 energy efficiency and capacity retention of the lithium-ion battery after 300 cycles were tested using a constant current method. Energy efficiency = (300th cycle discharge energy / 300th cycle charging energy) × 100%; Capacity retention = (300th cycle discharge capacity / 2nd cycle discharge capacity) × 100%.

[0140] Electrode porosity test:

[0141] Comparative Example 1 and Example 3 were selected as control groups. The negative electrode sheets after rolling (before impregnation) and the fully discharged negative electrode sheets disassembled after lithium-ion battery cycling (after impregnation) were tested using mercury intrusion porosimetry, specifically referring to the national standard GB / T 21650.1-2008, "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Methods—Part 1: Mercury Intrusion Porosimetry." Additionally, the four groups of negative electrode sheets were baked at 110℃ for 8 hours until the electrolyte completely evaporated. The negative electrode sheets were cut into 10cm × 10cm samples, and the cross-sectional morphology of the samples was characterized by cross-sectional polishing-scanning electron microscopy (CP-SEM).

[0142] Table 1. Preparation parameters of Examples 1-14 and Comparative Examples 1-3

[0143]

[0144] In Table 1, " / " indicates that no relevant preparation parameters exist.

[0145] Table 2 Preparation parameters of Examples 1, 15-16

[0146] Reaction temperature (°C) Reaction time (min) pH of the reaction system Example 1 180 30 2.7 Example 15 160 40 3.0 Example 16 200 20 2.5

[0147] Table 3 Performance data for each embodiment and comparative example

[0148]

[0149] As can be seen from Examples 1-16 and Comparative Examples 1-3, the binder of Comparative Example 1 was unmodified. Although its peel strength was high, its warpage was low and its three-point bending pressure value was high, indicating that its negative electrode sheet had low flexibility and high rigidity, resulting in low capacity retention and energy efficiency of its lithium-ion battery. The binder of Comparative Example 2 was modified only in the main chain and not in the side chain. Although its warpage was high and its three-point bending pressure value was low, indicating that its negative electrode sheet had high flexibility, its peel strength was very low, resulting in low energy efficiency and capacity retention of its lithium-ion battery. The binder of Comparative Example 3 was modified only in the side chain and not in the main chain. Although its peel strength was high, its warpage was too low and its three-point bending pressure value was too high, indicating that its negative electrode sheet had low flexibility. The low rigidity and high strength of the original material resulted in low capacity retention and energy efficiency in lithium-ion batteries. However, the binder in this application not only modified the main chain but also the side chain, enabling the negative electrode sheet to maintain good flexibility while possessing high peel strength. This effectively alleviates powder shedding and cracking caused by the hardness and brittleness of the negative electrode sheet during rolling and winding. It also reduces the problem of insufficient adhesion between the negative electrode active material and the negative electrode current collector due to binder floating after impregnation and during cycling, thus improving the capacity retention of the lithium-ion battery. Furthermore, the good peel strength and flexibility increase the compaction density of the negative electrode sheet, thereby improving the energy efficiency of the lithium-ion battery. In summary, the binder in this application can simultaneously improve the energy efficiency and capacity retention of lithium-ion batteries, making it more suitable for energy storage devices.

[0150] The ratio of rigid groups to polar groups, and the ratio of rigid groups to -C x H 2x The ratio of carbon segments, the type of reactants, the type of polar group compounds, and the type of cyclodextrin compounds also typically affect the performance of the binder. As can be seen from Examples 1 to 14, adjusting the ratio of rigid groups to polar groups, and the ratio of rigid groups to -C segments can significantly influence the binder's performance. x H 2x Within the scope of this application, the proportion of carbon segments, the types of reactants, the types of polar group compounds, and the types of cyclodextrin compounds, when the binder is applied to the negative electrode sheet, is beneficial to obtaining a negative electrode sheet with good peel strength and flexibility, thereby improving the energy efficiency and capacity retention of lithium-ion batteries.

[0151] The reaction temperature, reaction time, and pH value of the reaction system during the modification process also typically affect the performance of the binder. As can be seen from Examples 1, 15, and 16, by adjusting the above preparation parameters within the scope of this application, the binder obtained, when applied to the negative electrode sheet, is beneficial for obtaining a negative electrode sheet with good peel strength and flexibility, thereby improving the energy efficiency and capacity retention of the lithium-ion battery.

[0152] Figure 3 These are the Fourier transform infrared (FTIR) spectra of the adhesives prepared in Example 1 and Comparative Example 1 of this application. Figure 3 As can be seen from this, the FTIR spectrum of Comparative Example 1 is at 3273 cm⁻¹. -1 and 2918cm -1 The vicinity exhibits characteristic spectral bands, belonging to the stretching vibrations of -OH and CH, respectively, at 1591 cm⁻¹. -1 and 1418cm -1 For the asymmetric / symmetric stretching vibration of COO-, 1033 cm⁻¹ -1 This is the asymmetric stretching vibration of COC; the aforementioned characteristic bands can still be observed in the FTIR spectrum of Example 1, except that, unlike Comparative Example 1, the band at 1451 cm⁻¹ is... -1 The bending vibration of the NH group in the amide bond, 1321 cm⁻¹ -1 The stretching vibration of CN indicates the presence of polar amide bonds in the adhesive of this application.

[0153] Table 4 shows the porosity changes of the negative electrode sheets in Comparative Example 1 and Example 3 before and after impregnation.

[0154]

[0155] As can be seen from Table 4, the porosity of the negative electrode sheet in Comparative Example 1 decreased after wetting compared to before wetting; Figure 5a , Figure 5b It can be seen that the porosity of the negative electrode sheet in Example 3 is significantly higher after wetting compared to before wetting, indicating that the binder of this application can effectively increase the electrolyte retention of the lithium-ion battery when applied to the negative electrode sheet. Lithium-ion batteries with poor electrolyte retention exhibit greater polarization and faster degradation during cycling, and their internal resistance also increases significantly. This finding is consistent with the electrical performance test results.

[0156] Figure 4a This is the CP-SEM image of the negative electrode sheet before wetting in Comparative Example 1. Figure 4b This is the CP-SEM image of the negative electrode sheet after wetting in Comparative Example 1; Figure 5a This is a CP-SEM image of the negative electrode sheet before wetting in Example 3. Figure 5bThis is a CP-SEM image of the negative electrode sheet after impregnation in Example 3. After SEM observation of the negative electrode sheets before and after cycling in Comparative Example 1 and Example 3, it was found that... Figure 4a and Figure 4b The density of pores in the negative electrode sheet of Comparative Example 1 decreased after wetting; Reference Figure 5a and Figure 5b In Example 3, the pore density of the negative electrode increased after wetting. The above SEM observation results confirm that the porosity of the negative electrode of this application increases after wetting, thereby increasing the electrolyte retention capacity of the lithium-ion battery and improving the electrical performance of the lithium-ion battery.

[0157] The present application discloses an adhesive and its preparation method, a negative electrode sheet, a secondary battery, and a battery pack. 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 comprises a polymer, the polymer comprising the structural unit shown in formula (I), Equation (I) R1 is selected from at least one of -COOH, -COOLi and -COONa; R2 and R3 are independently selected from polar groups or rigid groups, and R2 and R3 are not both polar groups or rigid groups at the same time; 2≤x≤10； The rigid groups include groups formed from cyclodextrin compounds.

2. The adhesive according to claim 1, characterized in that, The molar ratio of the rigid group to the polar group in the adhesive is 0.1 to 9:

1.

3. The adhesive according to claim 1, characterized in that, The rigid groups and -C in the adhesive x H 2x - The molar ratio of carbon segments is 2~5∶1.

4. The adhesive according to any one of claims 1 to 3, characterized in that, The polar group includes at least one of -OH, -COOH, -OCH2COOCH3, -OCONH2 and -OCH2NHCOOH.

5. The adhesive according to claim 1, characterized in that, The cyclodextrin compounds include at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, methyl-β-cyclodextrin, hydroxyethyl-β-cyclodextrin, 2,6-di-O-methyl-β-cyclodextrin, and carboxymethyl-β-cyclodextrin.

6. A method for preparing an adhesive as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Carboxymethyl cellulose was subjected to oxidative ring-opening treatment and etherification treatment to obtain modified carboxymethyl cellulose; The modified carboxymethyl cellulose was grafted onto the cellulose under catalytic conditions using cyclodextrin compounds and polar group compounds to obtain the binder.

7. The preparation method according to claim 6, characterized in that, The grafting reaction was carried out at a temperature of 160℃ to 200℃, for a reaction time of 20 min to 40 min, and the pH of the reaction system was 2.5 to 3.

0.

8. The preparation method according to claim 6, characterized in that, The polar group compound is selected from at least one of 1,2,3,4-butanetetracarboxylic acid, dimethylacetamide, maleamic acid, N-BOC-oxalamidoethyl ester, alanylglutamine, dimethyl 1,3-propanone dicarboxylic acid, and triethyl methanetricarboxylic acid; the catalyst is selected from at least one of sodium hypophosphite monohydrate, sodium hypochlorite, and sodium borohydride.

9. A negative electrode sheet, characterized in that, The present invention includes 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 5, or the binder is prepared by the method of preparing the binder according to any one of claims 6 to 8.

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

11. A battery pack, characterized in that, It includes a housing and at least one secondary battery as described in claim 10, the secondary battery being housed within the housing.

12. An electrical appliance, characterized in that, Includes the secondary battery of claim 10 or the battery pack of claim 11.

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