Negative pole piece, battery, energy storage device and electric equipment

Abstract

The invention provides a negative electrode piece, a battery, an energy storage device and electric equipment, the negative electrode piece comprises a negative electrode current collector, at least one surface of the negative electrode current collector is provided with a negative electrode material layer, the negative electrode material layer comprises a negative electrode material, hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene-butadiene rubber, and based on the mass of the negative electrode material layer, the hyperbranched carboxymethyl cellulose and the lithiated polyacrylic acid are compounded. The mass percentage content of hyperbranched carboxymethyl cellulose is a, 0.1% < = a < = 0.5%, the mass percentage content of lithiated polyacrylic acid is b, 1% < = b < = 1.7%, and 0.4% < = c < = 1%.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a negative electrode plate, a battery, an energy storage device and an electrical equipment. Background Art

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

[0003] The negative electrode is one of the main structures of secondary batteries and is crucial to the performance of secondary batteries. With the increasing application of secondary batteries in large-scale energy storage, electric vehicles and other fields, the requirements for battery cycle life are constantly increasing. However, during long-term charging and discharging, the negative electrode material will undergo volume changes, resulting in the stripping of the negative electrode material and the limitation of the lithium ion diffusion rate, which affects the rate performance and cycle performance of the secondary battery. Summary of the invention

[0004] In order to solve the above technical problems, the present application discloses a negative electrode plate, a battery, an energy storage device and an electrical equipment to improve the structural stability of the negative electrode plate and the lithium ion diffusion rate, thereby improving the rate performance and cycle performance of the secondary battery.

[0005] In the first aspect, the present application provides a negative electrode plate, including a negative electrode current collector, at least one side of the negative electrode current collector having a negative electrode material layer, the negative electrode material layer including a negative electrode material, hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene butadiene rubber, wherein, based on the mass of the negative electrode material layer, the mass percentage of the hyperbranched carboxymethyl cellulose is a, 0.1%≤a≤0.5%, the mass percentage of the lithiated polyacrylic acid is b, 1%≤b≤1.7%, and the mass percentage of the cross-linked styrene butadiene rubber is c, 0.4%≤c≤1%.

[0006] In some embodiments of the present application, the viscosity of the hyperbranched carboxymethyl cellulose is η, 80000 mPa·s≤η≤100000 mPa·s.

[0007] In some embodiments of the present application, the glass transition temperature of the cross-linked styrene butadiene rubber is Tg, the swelling rate of the cross-linked styrene butadiene rubber is S, Tg≥15°C, and S≤60%.

[0008] In some embodiments of the present application, the negative electrode material layer also includes a conductive agent. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode material is d, 96%≤d≤99%, and the mass percentage of the conductive agent is e, 0.5%≤e≤1%.

[0009] In some embodiments of the present application, the cross-linked styrene-butadiene rubber includes at least one of the following features: a), the glass transition temperature of the cross-linked styrene-butadiene rubber is Tg, 15°C≤Tg≤20°C; b) The glass transition temperature of the cross-linked styrene-butadiene rubber is Tg, 20%≤S≤60%.

[0010] In a second aspect, the present application provides a method for preparing a negative electrode sheet as described in the first aspect, comprising the following steps: Mixing 2-hydroxy-5-ethylbenzoic acid, an initiator and a first solvent, and performing a polymerization reaction to obtain hyperbranched carboxymethyl cellulose; The hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, cross-linked styrene-butadiene rubber, negative electrode material and conductive agent are mixed with a second solvent to form a negative electrode slurry, and the negative electrode slurry is coated on at least one surface of a negative electrode current collector to form a negative electrode material layer.

[0011] In some embodiments of the present application, the molar ratio of the 2-hydroxy-5-ethylbenzoic acid, the initiator and the first solvent is 1: (0.04-0.06): (15-25).

[0012] In some embodiments of the present application, the preparation method includes at least one of the following features: a), the reaction temperature of the polymerization reaction is 65°C to 75°C, and the reaction time is 20h to 30h; b), in some embodiments of the present application, the first solvent includes N,N-dimethylformamide; c), the initiator includes azobisisobutyronitrile; d) The second solvent comprises water.

[0013] In a third aspect, the present application provides a battery, comprising the negative electrode plate described in the first aspect, or comprising the negative electrode plate prepared by the preparation method described in the second aspect.

[0014] In a fourth aspect, the present application provides an energy storage device, comprising a housing and at least one battery as described in the third aspect, wherein the battery is accommodated in the housing.

[0015] In a fifth aspect, the present application provides an electrical device, comprising the energy storage device described in the fourth 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: The present application provides a negative electrode plate, a battery, an energy storage device and an electrical equipment, wherein the negative electrode material layer comprises a negative electrode material, hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene-butadiene rubber. Based on the mass of the negative electrode material layer, the mass percentage of the hyperbranched carboxymethyl cellulose is a, 0.1%≤a≤0.5%, the mass percentage of the lithiated polyacrylic acid is b, 1%≤b≤1.7%, and the mass percentage of the cross-linked styrene-butadiene rubber is c, 0.4%≤c≤1%. The hyperbranched carboxymethyl cellulose of the present application has high viscosity characteristics, and the cross-linked styrene butadiene rubber has high cross-linking and high viscosity characteristics. By regulating the content of the hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, and cross-linked styrene butadiene rubber within the above range, the above materials can form an effective connection between the particles of the negative electrode material (such as graphite) to maintain the stability of the negative electrode plate structure, and will not over-coat the negative electrode material particles, thereby providing more channels for the diffusion of lithium ions, which is beneficial to the improvement of the rate performance and the reduction of impedance of the secondary battery. Through the synergistic effect of the hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene butadiene rubber of the present application, when the volume of the negative electrode material in the negative electrode material layer changes during the charge and discharge process of the secondary battery, the stress generated can be effectively buffered, the structural stability of the negative electrode plate can be maintained, and electrons and lithium ions can be smoothly transmitted in the negative electrode plate, thereby improving the rate performance and cycle performance of the secondary battery, which is beneficial to improving the operating stability and service life of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a household energy storage system according to an implementation scheme of the present application; Figure 2 A schematic diagram of the structure of a commercial energy storage system according to an implementation scheme of the present application.

[0019] Explanation of the accompanying drawings: 1-energy storage device, 2-electric energy conversion device, 3-first user load, 4-second user load, 400-commercial energy storage system, 410-high voltage cable, 420-first electric energy conversion device, 430-second electric energy conversion device. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0022] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0023] In addition, the terms "installed", "set", "provided with", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0024] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0025] It should be noted that, in the present application, a lithium-ion battery is used as an example of a secondary battery to explain the present application, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0026] The inventors have found that when faced with large stress changes, the thickening and dispersion effects of ordinary carboxymethyl cellulose (CMC) gradually weaken, resulting in a decrease in the bonding force between the negative electrode material particles, which is prone to agglomeration and shedding, affecting the structural stability of the negative electrode plate; in addition, after the lithium-ion battery undergoes multiple charge and discharge cycles, the internal structure of the negative electrode plate gradually changes, and ordinary polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) cannot maintain a strong bond between the negative electrode material layer and the negative electrode current collector, resulting in a gradual increase in the internal resistance of the negative electrode plate, which in turn leads to a decrease in the charge and discharge efficiency of the lithium-ion battery, especially under high-rate charge and discharge conditions, the problem of insufficient bonding performance is more prominent, limiting the performance of the lithium-ion battery; in addition, in the existing negative electrode material layer, there is a lack of effective synergistic mechanism between auxiliary materials such as carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber, and these components cannot form an organic whole. When dealing with a complex battery charge and discharge environment, they cannot give full play to their respective advantages, thereby limiting the further improvement of the cycle performance of the lithium-ion battery.

[0027] In view of this, the present application provides a negative electrode plate, which includes a negative electrode current collector, at least one side of the negative electrode current collector has a negative electrode material layer, the negative electrode material layer includes a negative electrode material, hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene butadiene rubber, wherein, based on the mass of the negative electrode material layer, the mass percentage of the hyperbranched carboxymethyl cellulose is a, 0.1%≤a≤0.5%, preferably, 0.1%≤a≤0.2%; the mass percentage of the lithiated polyacrylic acid is b, 1%≤b≤1.7%, preferably, 1%≤b≤1.3%; the mass percentage of the cross-linked styrene butadiene rubber is c, 0.4%≤c≤1%, preferably, 0.4%≤c≤0.7%. For example, a is 0.1%, 0.2%, 0.3% or 0.5%; b is 1%, 1.3%, 1.5% or 1.7%; c is 0.4%, 0.5%, 0.7% or 1%. By regulating the contents of hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, and cross-linked styrene-butadiene rubber within the above ranges, the above materials can form effective connections between the particles of the negative electrode material (such as graphite) to maintain the stability of the negative electrode plate structure, and will not over-coat the negative electrode material particles, thereby providing more channels for the diffusion of lithium ions, which is beneficial to the improvement of the rate performance and the reduction of the impedance of the lithium-ion battery. This may be because the hyperbranched structure of the hyperbranched carboxymethyl cellulose enables it to construct a more stable three-dimensional network structure in the negative electrode plate; on the one hand, the lithiated polyacrylic acid improves the ionic conductivity of the polyacrylic acid, which is beneficial to the rapid transmission of lithium ions inside the negative electrode plate; on the other hand, the interaction between the lithiated polyacrylic acid and the negative electrode material and other auxiliary materials in the negative electrode plate is enhanced, which can better play the role of bonding. The cross-linked styrene butadiene rubber has a high degree of cross-linking and a high bonding strength, and can build a strong bonding bridge between the negative electrode material and the negative electrode current collector, effectively resisting the volume change stress of the negative electrode during the charge and discharge process, and maintaining the integrity of the negative electrode structure; and the three-dimensional network structure formed by the hyperbranched carboxymethyl cellulose provides a stable support framework for the lithiated polyacrylic acid and the cross-linked styrene butadiene rubber. The lithiated polyacrylic acid fills the gaps in the three-dimensional network structure with its enhanced ionic conductivity and bonding properties, further strengthening the connection between the negative electrode materials and promoting the transmission of lithium ions; the cross-linked styrene butadiene rubber tightly bonds the negative electrode material to the negative electrode current collector, and at the same time interweaves with the hyperbranched carboxymethyl cellulose and the lithiated polyacrylic acid to form a tight and stable whole. It can be seen that the present application can effectively buffer the stress generated when the volume of the negative electrode material in the negative electrode material layer changes during the charging and discharging process of the lithium-ion battery through the synergistic effect of hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene butadiene rubber, maintain the structural stability of the negative electrode plate, and enable electrons and lithium ions to be smoothly transmitted in the negative electrode plate, thereby improving the rate performance and cycle performance of the lithium-ion battery, and can also reduce the impedance of the lithium-ion battery, which is beneficial to improving the operating stability and service life of the energy storage device.

[0028] In some embodiments of the present application, the viscosity of the hyperbranched carboxymethyl cellulose is η, 80000 mPa·s≤η≤100000 mPa·s. For example, η is 80000 mPa·s, 85000 mPa·s, 90000 mPa·s, 95000 mPa·s or 100000 mPa·s. By regulating the viscosity η within the above range, the high viscosity of the hyperbranched carboxymethyl cellulose effectively enhances the interaction between the negative electrode material particles, making the negative electrode material particles more evenly dispersed in the negative electrode material, preventing particle agglomeration and sedimentation, thereby constructing a more stable three-dimensional network structure in the negative electrode sheet, and will not affect the uniformity of the coating process or hinder the transmission of lithium ions in the negative electrode sheet due to excessive viscosity. The rate performance and cycle stability of the lithium-ion battery are reduced.

[0029] In some embodiments of the present application, the glass transition temperature of the cross-linked styrene butadiene rubber is Tg, the swelling rate of the cross-linked styrene butadiene rubber is S, Tg ≥ 15 ° C, and S ≤ 60%. For example, Tg is 15 ° C, 16 ° C, 17 ° C, 18 ° C, 19 ° C or 20 ° C; S is 20%, 30%, 40%, 50% or 60%. In other embodiments of the present application, 15 ° C ≤ Tg ≤ 20 ° C; in other embodiments of the present application, 20% ≤ S ≤ 60%. The cross-linked styrene butadiene rubber with the above glass transition temperature range has a high degree of cross-linking, which is conducive to building a stronger bonding bridge between the negative electrode material and the negative electrode current collector; the cross-linked styrene butadiene rubber with the above swelling rate range has a high bonding strength characteristic, which is conducive to resisting the volume change stress of the negative electrode plate during the charge and discharge process and maintaining the integrity of the negative electrode plate structure.

[0030] In some embodiments of the present application, the negative electrode material layer also includes a conductive agent. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode material is d, 96%≤d≤99%, and the mass percentage of the conductive agent is e, 0.5%≤e≤1%. For example, d is 96%, 97%, 98% or 99%; e is 0.5%, 0.7%, 0.8% or 1%. By regulating the content of the negative electrode material and the conductive agent within the above range, it is beneficial to improve the energy density of the lithium-ion battery, and the addition of the conductive agent also improves the electronic and lithium ion conductivity of the negative electrode sheet. In addition, the conductive agent forms a conductive network between the negative electrode material particles, which improves the electron transfer efficiency; and the addition of the conductive agent optimizes the pore structure of the negative electrode sheet and promotes the diffusion of lithium ions. In practical applications, by regulating the content of the negative electrode material and the conductive agent within the above range, the energy density and rate performance of the lithium-ion battery can be significantly improved, while the cycle stability of the lithium-ion battery can be improved.

[0031] In a second aspect, the present application provides a method for preparing a negative electrode sheet according to any of the above embodiments, comprising the following steps: Step A, mixing 2-hydroxy-5-ethylbenzoic acid, an initiator and a first solvent, and obtaining hyperbranched carboxymethyl cellulose through polymerization reaction; Step B, mixing hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, cross-linked styrene-butadiene rubber, negative electrode material and conductive agent with a second solvent to form a negative electrode slurry, and coating the negative electrode slurry on at least one surface of the negative electrode current collector to form a negative electrode material layer.

[0032] Exemplarily, step A specifically includes the following steps: The 2-hydroxy-5-ethylbenzoic acid monomer, the initiator and the first solvent are sequentially added to a dry three-necked flask equipped with a stirrer, a thermometer and a reflux condenser, and nitrogen is introduced to replace the air for 20min~40min, and the oil bath is slowly heated to 65℃~75℃, and the reaction is stirred at this temperature for 20h~30h. After the reaction is completed, the reaction solution is cooled to room temperature, and then slowly added dropwise to anhydrous ether for precipitation. After the precipitation is complete, the precipitate is collected by suction filtration and dried in a vacuum drying oven at 40℃ for 45h~50h to obtain hyperbranched carboxymethyl cellulose.

[0033] Among them, the structural formula of 2-hydroxy-5-ethylbenzoic acid is as follows:

[0034] The hyperbranched carboxymethyl cellulose prepared in step A of the present application can act like a "central hub" with branches extending from the center in all directions, and can interact with multiple negative electrode material particles, conductive agents and binders at the same time; and, both hyperbranched carboxymethyl cellulose and PAA are rich in carboxylic acid groups (-COOH), which can form a composite network by hydrogen bonding or dissociation into carboxyl groups (-COO-) and cross-linking with cations to enhance the stability of the negative electrode slurry and improve the mechanical strength of the negative electrode sheet; whereas linear polymers (such as carboxymethyl cellulose, methyl cellulose or sodium alginate) mainly exert their effects through the entanglement of chain molecules. Compared with linear polymers, hyperbranched carboxymethyl cellulose has more contact points with surrounding components and a higher interaction efficiency.

[0035] In step B, the lithiated polyacrylic acid can be prepared by using an existing lithiated process. For example, polyacrylic acid can be mixed with a lithium hydroxide solution and reacted to obtain lithiated polyacrylic acid; alternatively, commercially available lithiated polyacrylic acid can be used, and this application has no particular restrictions; the cross-linked styrene-butadiene rubber can use commercially available styrene-butadiene rubber that meets the above-mentioned glass transition temperature range and swelling rate range, and this application has no particular restrictions.

[0036] In some embodiments of the present application, the molar ratio of 2-hydroxy-5-ethylbenzoic acid, the initiator and the first solvent is 1: (0.04~0.06): (15~25). By regulating the above components within the scope of the present application, the polymerization reaction is facilitated to proceed fully.

[0037] In some embodiments of the present application, the reaction temperature of the polymerization reaction is 65° C. to 75° C., and the reaction time is 20 h to 30 h, which is conducive to the full progress of the polymerization reaction.

[0038] In some embodiments of the present application, the first solvent includes N,N-dimethylformamide, the initiator includes azobisisobutyronitrile, and the second solvent includes water.

[0039] The present application has no particular restrictions on the method for regulating the viscosity of the hyperbranched carboxymethyl cellulose, as long as the purpose of the present application can be achieved. During the polymerization reaction, the viscosity of the hyperbranched carboxymethyl cellulose usually increases with the extension of the reaction time and / or the increase of the reaction temperature. Based on this, the present application can regulate the viscosity of the hyperbranched carboxymethyl cellulose by regulating the reaction time and / or the reaction temperature during the polymerization reaction.

[0040] The preparation method of the negative electrode sheet of the present application is based on the preparation of negative electrode slurry based on components such as hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, cross-linked styrene butadiene rubber, and then the negative electrode slurry is applied to at least one surface of the negative electrode current collector to form a negative electrode material layer. The prepared negative electrode sheet has high structural stability and good electron and lithium ion transmission performance. When the negative electrode sheet is used in a lithium ion battery, the rate performance and cycle performance of the lithium ion battery are improved.

[0041] When preparing the negative electrode sheet, it may also include processes such as cold pressing, stripping, cutting, and welding the electrode ears. There is no special limitation in this application, as long as the negative electrode sheet can be obtained.

[0042] The negative electrode material layer of the present application can be arranged on one surface or two surfaces in the thickness direction of the negative electrode current collector. In the present application, the negative electrode material layer is arranged on the surface of the negative electrode current collector, that is, the negative electrode material layer can be arranged in a partial area of ​​one surface of the negative electrode current collector, or it can be arranged in the entire area of ​​one surface of the negative electrode current collector. The present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can include but is not limited to copper foil, copper alloy foil, nickel foil or composite current collector, etc. In the present application, there is no special restriction on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4μm~12μm.

[0043] In the present application, the negative electrode material layer includes a negative electrode material, wherein the negative electrode material is not particularly limited as long as the purpose of the present application can be achieved, for example, it can include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, hard carbon, silicon, and silicon-carbon composite materials; the conductive agent is not particularly limited as long as the purpose of the present application can be achieved, for example, it can include at least one of conductive carbon black, carbon nanotubes and graphene.

[0044] The present application also provides a battery, comprising the negative electrode sheet described in any of the above embodiments.

[0045] The battery of the present application may further include a positive electrode plate, a separator and an electrolyte, wherein the separator is located between the positive electrode plate and the negative electrode plate to play an isolating role.

[0046] The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet usually includes a positive current collector and a positive electrode material layer. The positive electrode material layer can be arranged on one surface in the thickness direction of the positive current collector, or on two surfaces in the thickness direction of the positive current collector. In the present application, the positive electrode material layer is arranged on the surface of the positive current collector, that is, the positive electrode material layer can be arranged in a partial area of ​​one surface of the positive current collector, or in the entire area of ​​one surface of the positive current collector. The present application has no special restrictions on the positive current collector, as long as the purpose of the present application can be achieved, for example, it can include but is not limited to aluminum foil, aluminum alloy foil or composite current collector. In the present application, there is no special restriction on the thickness of the positive current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 8μm~13μm. The single-sided thickness of the positive electrode material layer of the present application can be 100μm~200μm.

[0047] In the present application, the positive electrode material layer includes positive electrode materials. The present application has no particular limitation on the positive electrode materials as long as the purpose of the present application can be achieved. 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 iron manganese phosphate.

[0048] In the present application, the positive electrode material layer may also include a positive electrode binder. The present application has no particular limitation on the positive electrode binder as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of fluorine-containing resins, polypropylene resins, fiber-type binders, rubber-type binders or polyimide-type binders.

[0049] The present application has no particular restrictions on the diaphragm, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film 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, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0050] The present application has no particular restrictions on the diaphragm, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film 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, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0051] The battery of the present application also includes an electrolyte. The present application has no particular restrictions on the electrolyte, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. 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) or fluoroethylene carbonate (FEC) is mixed in a certain mass ratio or volume ratio to obtain a non-aqueous organic solvent, and then a lithium salt is added to dissolve and mix evenly. The present application has no restrictions on the type of lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(oxalate borate) (LiBOB) or lithium difluoroborate.

[0052] The present application has no particular limitation on the concentration of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. Taking LiPF6 as an example, the concentration of LiPF6 in the electrolyte is 1 mol / L to 2 mol / L, for example, the concentration of LiPF6 is 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L.

[0053] The battery of the present application also includes a shell, and the present application has no particular limitation on the shell, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved. For example, the shell may include an aluminum-plastic film.

[0054] The present application does not particularly limit the preparation method of the battery, and a preparation method known in the art can be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain a bare cell with a wound structure, placing the bare cell in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a battery.

[0055] The present application also provides an energy storage device, including a housing and at least one battery in any of the above embodiments, wherein the battery is contained in the housing. The energy storage device having the battery has excellent performance, which is beneficial to the use of the energy storage device. By containing the battery in the housing, the fixation and protection of the battery can be increased, thereby improving the service life of the energy storage device. It is understandable that the energy storage device may have one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries may be connected in at least one of parallel and series connection.

[0056] The present application also provides an electrical device, including the energy storage device in the above-mentioned implementation scheme, which is conducive to improving the product competitiveness and performance of the electrical device. In an optional implementation scheme, 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 implementation scheme, the electrical device body includes a positive electrode of the device and a negative electrode of the device, the positive electrode plate of the battery in the energy storage device is used to electrically connect to the positive electrode of the device body of the electrical device, and the negative electrode plate of the battery in the energy storage device is used to electrically connect to the negative electrode of the device body of the electrical device, so as to supply power to the electrical device.

[0057] The electrical equipment of the present application may include but is not limited to: containers, battery vehicles, electric vehicles, ships, spacecraft, electric toys and electric tools, etc., wherein spacecrafts include airplanes, rockets, space shuttles and spacecrafts, etc., electric toys include fixed or mobile electric toys, such as electric car toys, electric ship toys and electric airplane toys, etc., and electric tools include metal cutting power tools, grinding power tools, assembly power tools and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers.

[0058] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a household energy storage system according to an implementation scheme of the present application, and the present application Figure 1 The implementation plan is described using a household energy storage scenario in user-side energy storage as an example, but the energy storage device of the present application is not limited to the household energy storage scenario.

[0059] The present application provides a household energy storage system, which includes an energy conversion device 2 (photovoltaic panel), a first user load 3 (street lamp), a second user load 4 (such as air conditioner and other household appliances), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be mounted on an outdoor wall by wall hanging. Specifically, the photovoltaic panel can convert solar energy into electrical energy during the period of low electricity prices. The energy storage device 1 is used to store the electrical energy and supply it to street lamps and household appliances for use during peak electricity prices, or to supply power when the power grid is out of power / power outage.

[0060] See also Figure 2 , Figure 2 A schematic diagram of a commercial energy storage system 400 according to an embodiment of the present application. Figure 2 The implementation plan is described using the shared energy storage scenario on the generation / distribution side as an example, and the energy storage device 1 of the present application is not limited to the energy storage scenario on the generation / distribution side.

[0061] The present application provides a commercial energy storage system 400, which includes: a high-voltage cable 410, a first electric energy conversion device 420, a second electric energy conversion device 430 and an energy storage device 1 provided in the present application. In the case of power generation, the first electric energy conversion device 420 and the second electric energy conversion device 430 are used to convert other forms of energy into electric energy, which are connected to the high-voltage cable 410 and supplied to the power distribution network for use. When the power load is low and the first electric energy conversion device 420 and the second electric energy conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, thereby reducing the wind and solar power abandonment rates and improving the problem of new energy power generation and consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1 in conjunction with the high-voltage cable 410 in a grid-connected mode to the power consumption side, thereby providing peak load regulation, frequency regulation, standby and other services for the power grid operation, giving full play to the peak load regulation of the power grid, promoting peak load shaving and valley filling of the power grid, and alleviating the power supply pressure of the power grid.

[0062] Optionally, the first electric energy conversion device 420 and the second electric energy 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 electric energy.

[0063] The number of energy storage devices 1 can be multiple, and multiple energy storage devices 1 are connected in series or in parallel. Multiple energy storage devices 1 are supported and electrically connected by isolation plates (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 accommodate the energy storage device 1.

[0064] Optionally, the energy storage device 1 may include but is not limited to a battery module, a battery pack, a battery system, etc. Among them, the battery module may be a battery module formed by connecting multiple batteries of the present application in series / parallel, the battery pack may include multiple batteries of the present application, and the battery system may be a charging and discharging system including the battery or battery pack of the present application.

[0065] The actual application form of the energy storage device 1 provided in the embodiment of the present application may be, but is not limited to, the listed products, and may also be other application forms. The embodiment of the present application does not strictly limit the application form of the energy storage device 1. The embodiment of the present application only takes the energy storage device 1 as a multi-core battery as an example for explanation. When the energy storage device 1 includes a single cell, the single cell may be at least one of a cylindrical battery, a square battery, and the like.

[0066] Example Hereinafter, the embodiments of the present application will be described in more detail with reference to preparation examples, examples and comparative examples. Various tests and evaluations were performed according to the following methods.

[0067] Example 1 <Preparation of Hyperbranched Carboxymethyl Cellulose> 2-Hydroxy-5-ethylbenzoic acid monomer, initiator azobisisobutyronitrile and solvent N,N-dimethylformamide were weighed in a molar ratio of 1:0.05:20, and then the weighed raw materials were added to a dry three-necked flask equipped with a stirrer, a thermometer and a reflux condenser, nitrogen was introduced to replace the air for 30 minutes, the oil bath was slowly heated to 70°C, and the reaction was stirred at this temperature for 24 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and then slowly added dropwise to 500 mL of anhydrous ether for precipitation. After the precipitation was complete, the precipitate was collected by suction filtration and dried in a vacuum drying oven at 40°C for 48 hours to obtain hyperbranched carboxymethyl cellulose.

[0068] <Preparation of negative electrode sheet> The prepared hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid (model: Huitian New Materials 1208), cross-linked styrene butadiene rubber (model: Yanyi New Materials BONE Z8), negative electrode material artificial graphite and conductive agent acetylene black were mixed in a mass ratio of 0.1:1.3:0.7:97.1:0.8, deionized water was added, and a negative electrode slurry with a solid content of 60wt% was prepared, and stirred evenly; the negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and the coating thickness was 190μm, first vacuum dried at 80℃ for 12h, then vacuum dried at 120℃ for 8h, and rolled to form a negative electrode sheet. Among them, the viscosity η of the hyperbranched carboxymethyl cellulose, the glass transition temperature Tg of the cross-linked styrene butadiene rubber, and the swelling rate S are shown in Table 2.

[0069] <Preparation of Electrolyte> In an argon atmosphere glove box with a moisture content of ≤1ppm, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1, and then lithium salt LiPF6 was added and dissolved in the above solvent, and the electrolyte was obtained after mixing evenly. Among them, the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0070] <Assembly of lithium-ion batteries> The prepared negative electrode sheet and lithium sheet are placed in a press for pressing, and then a puncher is used to cut a circular negative electrode sheet with a diameter of 15 mm and a circular lithium sheet with a diameter of 15 mm. The circular negative electrode sheet, separator and circular lithium sheet are then stacked in order so that the separator is placed between the circular negative electrode sheet and the circular lithium sheet to play an isolating role. The prepared electrolyte is then injected to assemble a lithium-ion battery.

[0071] Embodiment 2 to Embodiment 8 Except that in <Preparation of Negative Electrode Sheet>, the contents of components such as hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, and cross-linked styrene-butadiene rubber are adjusted according to Table 1, the rest is the same as Example 1.

[0072] Embodiment 9 to Embodiment 12 Except that in <Preparation of Negative Electrode Plate>, hyperbranched carboxymethyl cellulose of corresponding viscosity and cross-linked styrene-butadiene rubber of corresponding glass transition temperature and swelling rate are selected according to Table 2, the rest is the same as Example 1.

[0073] Comparative Example 1 Except that in <Preparation of Negative Electrode Sheet>, the hyperbranched CMC is replaced by ordinary CMC, the lithiated PAA is replaced by ordinary PAA, and the cross-linked modified SBR is replaced by ordinary SBR, the rest is the same as Example 4.

[0074] Comparative Example 2~Comparative Example 3 Except that in <Preparation of Negative Electrode Sheet>, the contents of components such as hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, and cross-linked styrene-butadiene rubber are adjusted according to Table 1, the rest is the same as Example 1.

[0075] Table 1: Relevant preparation parameters of Examples 1 to 8 and Comparative Examples 1 to 3

[0076] Table 2: Relevant preparation parameters of Example 1, Example 9 to Example 12

[0077] Test methods and equipment: Carboxymethyl cellulose viscosity test: Dissolve carboxymethyl cellulose in water to form an aqueous solution with a mass concentration of 1%, then stir at room temperature until completely dissolved, let stand to defoam, use a rotational viscometer (such as Brookfield viscometer), select rotor No. 4 and test at a speed of 12 rpm, start the viscometer, and record the viscosity value (in mPa·s) after the reading stabilizes. Measure each sample 3 times and take the average value as the final result.

[0078] Styrene butadiene rubber glass transition temperature test: Cut the styrene butadiene rubber sample into small pieces and ensure that the surface is flat. Then put 10 mg of the styrene butadiene rubber sample into the sample cell of the differential scanning calorimeter (DSC). Set the test temperature range (e.g. -100°C ~ 100°C) and the heating rate (e.g. 10°C / min). Test in a nitrogen atmosphere and record the DSC curve. Determine the glass transition temperature (Tg) of the styrene butadiene rubber by the inflection point of the DSC curve.

[0079] Styrene butadiene rubber swelling rate test: Cut the styrene butadiene rubber sample into small pieces (e.g. 10 mm × 10 mm × 2 mm), weigh it using an analytical balance and record the initial mass, recorded as m1; soak the styrene butadiene rubber sample in a solvent (e.g. toluene), place it in a constant temperature device, set the temperature to 25°C, soak it for 24 hours, take out the sample, gently wipe off the residual solvent on the surface with filter paper, weigh it immediately using an analytical balance and record the mass after swelling, recorded as m2. Calculate the swelling rate, S= ×100%. Each sample was measured 3 times and the average value was taken as the final result.

[0080] Rate performance test: Under 25℃ environment, the lithium-ion battery is charged to 3.65V at 0.5C rate, and after standing for 30min, it is discharged to 2.0V at 0.5C rate, and the discharge capacity is recorded as Q1, in Ah; then, the lithium-ion battery is allowed to stand for 30min, and then the lithium-ion battery is charged to 3.65V at 2C rate, and after standing for 30min, it is discharged to 2.0V at 2C rate, and the discharge capacity is recorded as Q2, in Ah.

[0081] 2C rate efficiency of lithium-ion battery = (Q2 / Q1)×100%.

[0082] Cycle performance test: The test temperature is 25°C. The lithium-ion battery is charged to 3.65V at a constant current of 0.5 times (C). After standing for 10 minutes, it is discharged to 2.5V at 0.5C. The capacity obtained in this step is the initial discharge capacity C0. A cycle test of 0.5C charge / 0.5C discharge is performed for 600 cycles, and the discharge capacity of the 600th cycle is recorded. Cycle capacity retention rate = (discharge capacity of the 600th cycle / initial discharge capacity C0) × 100%.

[0083] DC resistance (DCR) test: The test temperature is 25℃. The lithium-ion battery is charged to 3.65V at a constant current of 0.5 times (C), then charged to a current of 0.05C at a constant voltage of 3.65V, and then left to stand for 30 minutes. Then, it is cycled 9 times according to the following process: discharge at a constant current of 0.1C for 60 minutes, stand for 60 minutes, record the voltage V1 after standing for 60 minutes, then discharge at a constant current of 1.07C for 30 seconds, record the voltage V2 at the end of discharge; then stand for 40 seconds, and then charge at a constant current of 1.07C for 30 seconds, and stand for 10 minutes. The state of charge (SOC) after the end of the 5th cycle discharge is taken as the 50% SOC of the lithium-ion battery. According to the V1 and V2 recorded in the 5th cycle, the discharge DCR is calculated according to the following formula: DCR=(V1-V2) / I, where I=1.07C.

[0084] Table 3: Performance data of various embodiments and comparative examples

[0085] It can be seen from Examples 1 to 8 and Comparative Examples 1 to 3 that when only ordinary CMC, ordinary PAA and ordinary SBR are used to prepare the negative electrode sheet (for example, Comparative Example 1), the rate energy efficiency and cycle capacity retention rate of the lithium ion battery are low, and the DCR is high; when the content of hyperbranched carboxymethyl cellulose, the content of lithiated polyacrylic acid and the content of cross-linked SBR are too low or too high (for example, Comparative Example 2, Comparative Example 3), the rate energy efficiency and cycle capacity retention rate of the lithium ion battery are low, and the DCR is high, indicating that when the content of the above three components is too low or too high, it is not conducive to the synergistic effect of the three components; and the lithium ion battery of the present application exhibits higher rate energy efficiency, cycle capacity retention rate and lower DCR.

[0086] The viscosity of the hyperbranched carboxymethyl cellulose, the glass transition temperature of the cross-linked styrene butadiene rubber, and the swelling rate of the cross-linked styrene butadiene rubber usually also affect the performance of the negative electrode plate, thereby affecting the performance of the lithium-ion battery. It can be seen from Examples 1 and 9 to 12 that, based on the components and contents of the hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, and cross-linked SBR in this application, by regulating the above parameters within the scope of this application, it is beneficial to obtain a lithium-ion battery with good rate performance, cycle performance, and low DC impedance.

[0087] The above is a detailed introduction to a negative electrode plate, a battery, an energy storage device and an electrical equipment disclosed in the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core inventions of the embodiments of the present application. At the same time, for those skilled in the art, according to the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector, at least one side of which has a negative electrode material layer, wherein the negative electrode material layer comprises a negative electrode material, hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid and cross-linked styrene-butadiene rubber, wherein: Based on the mass of the negative electrode material layer, the mass percentage of the hyperbranched carboxymethyl cellulose is a, 0.1%≤a≤0.5%, the mass percentage of the lithiated polyacrylic acid is b, 1%≤b≤1.7%, and the mass percentage of the cross-linked styrene-butadiene rubber is c, 0.4%≤c≤1%.

2. The negative electrode sheet according to claim 1, characterized in that: The viscosity of the hyperbranched carboxymethyl cellulose is η, 80000 mPa·s≤η≤100000 mPa·s.

3. The negative electrode sheet according to claim 1, characterized in that: The glass transition temperature of the cross-linked styrene butadiene rubber is Tg, the swelling rate of the cross-linked styrene butadiene rubber is S, Tg≥15°C, and S≤60%.

4. The negative electrode sheet according to claim 1, characterized in that: The negative electrode material layer also includes a conductive agent. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode material is d, 96%≤d≤99%, and the mass percentage of the conductive agent is e, 0.5%≤e≤1%.

5. The negative electrode sheet according to claim 3, characterized in that: The cross-linked styrene-butadiene rubber comprises at least one of the following features: a), the glass transition temperature of the cross-linked styrene-butadiene rubber is Tg, 15°C≤Tg≤20°C; b) The swelling rate of the cross-linked styrene-butadiene rubber is S, 20%≤S≤60%.

6. A method for preparing a negative electrode sheet according to any one of claims 1 to 5, characterized in that: The following steps are involved: Mixing 2-hydroxy-5-ethylbenzoic acid, an initiator and a first solvent, and performing a polymerization reaction to obtain hyperbranched carboxymethyl cellulose; The hyperbranched carboxymethyl cellulose, lithiated polyacrylic acid, cross-linked styrene-butadiene rubber, negative electrode material and conductive agent are mixed with a second solvent to form a negative electrode slurry, and the negative electrode slurry is coated on at least one surface of a negative electrode current collector to form a negative electrode material layer.

7. The preparation method according to claim 6, characterized in that: The molar ratio of the 2-hydroxy-5-ethylbenzoic acid, the initiator and the first solvent is 1: (0.04-0.06): (15-25).

8. The preparation method according to claim 6, characterized in that: The preparation method comprises at least one of the following features: a), the reaction temperature of the polymerization reaction is 65°C to 75°C, and the reaction time is 20h to 30h; b), the first solvent includes N,N-dimethylformamide; c), the initiator includes azobisisobutyronitrile; d) The second solvent comprises water.

9. A battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet as described in any one of claims 1 to 5, or a negative electrode sheet made by the method for making a negative electrode sheet as described in any one of claims 6 to 8.

10. An energy storage device, characterized in that: The invention comprises a casing and at least one battery according to claim 9, wherein the battery is accommodated in the casing.

11. An electrical device, characterized in that: It includes the energy storage device as described in claim 10, and the energy storage device supplies power to the electrical equipment.

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