Positive electrode additives and their preparation methods, positive electrode sheets, secondary batteries and battery packs

Abstract

This application provides a positive electrode additive and its preparation method, a positive electrode sheet, a secondary battery, and a battery pack, wherein the positive electrode additive includes a fluorohydrazone compound represented by Formula I or Formula II. In Formula I, R1, R2, and R3 are each independently selected from -H or -F, and R1, R2, and R3 are not simultaneously -H; R4 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups. In Formula II, R5, R6, and R7 are each independently selected from -H or -F, and R5, R6, and R7 are not simultaneously -H; R8 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a positive electrode additive and its preparation method, a positive electrode sheet, a secondary battery, and a battery pack. Background Technology

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

[0003] As people's requirements for the performance of secondary batteries increase, not only are high energy density required, but also stable cycle performance. Therefore, how to improve the electrolyte wettability of the positive electrode to improve the cycle performance of secondary batteries has become an urgent problem to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses a positive electrode additive and its preparation method, a positive electrode sheet, a secondary battery, and a battery pack, which improves the electrolyte wettability of the positive electrode sheet, thereby enhancing the cycle performance of the secondary battery.

[0005] In a first aspect, this application provides a positive electrode additive comprising a fluorohydrazone compound represented by Formula I or Formula II:

[0006]

[0007] In Formula I, R1, R2, and R3 are each independently selected from -H or -F, and R1, R2, and R3 are not simultaneously -H. R4 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

[0008] In Formula II, R5, R6, and R7 are each independently selected from -H or -F, and R5, R6, and R7 are not simultaneously -H. R8 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

[0009] In some embodiments of this application, the compound of formula I is selected from at least one of the following compounds:

[0010]

[0011] The compound of formula II is selected from at least one of the following compounds:

[0012]

[0013] Secondly, this application provides a positive electrode sheet, including a positive current collector, wherein at least one side of the positive current collector has a positive active material layer, the positive active material layer including a positive active material and the positive additive described in the first aspect.

[0014] In some embodiments of this application, the mass percentage of the fluorohydrazone compound is 0.3% to 1.5% based on the mass of the positive electrode active material layer.

[0015] In some embodiments of this application, the mass percentage of the fluorohydrazone compound is 0.5% to 1.2% based on the mass of the positive electrode active material layer.

[0016] In some embodiments of this application, the compaction density of the positive electrode active material layer is 1.6 g / cm³. 3 ~1.8g / cm 3 .

[0017] In some embodiments of this application, the porosity of the positive electrode active material layer is 26.5% to 28.5%.

[0018] Thirdly, this application provides a method for preparing a positive electrode additive as described in the first aspect, comprising the following steps:

[0019] Benzoylhydrazide, fluoroacetophenone or their derivatives are mixed in a molar ratio of 1:1.1 to 1:1.7 and then added to anhydrous ethanol.

[0020] Fluorohydrazone compounds are obtained by heating under acidic or alkaline conditions at a temperature of 110℃~120℃ for 3.5h~4.5h under reflux.

[0021] In some embodiments of this application, the fluoroacetophenone or its derivatives are selected from at least one of p-fluoroacetophenone or its derivatives, m-fluoroacetophenone or its derivatives, and o-fluoroacetophenone or its derivatives.

[0022] In some embodiments of this application, under acetic or formic acid conditions, compound I is obtained; under alkaline conditions, compound II is obtained.

[0023] Fourthly, this application provides a secondary battery, including the positive electrode sheet described in the second aspect.

[0024] In some embodiments of this application, the liquid retention coefficient of the secondary battery is 3.50 to 3.85.

[0025] Fifthly, this application provides a battery pack including a housing and at least one secondary battery as described in the fourth aspect, the secondary battery being housed within the housing.

[0026] In a sixth aspect, this application provides an electrical device including the secondary battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0027] Compared with the prior art, this application has at least the following beneficial effects:

[0028] This application provides a positive electrode additive and its preparation method, a positive electrode sheet, a secondary battery, and a battery pack. The fluorine element in the fluorohydrazone compound of the positive electrode additive balances excess protons in the electrolyte, stabilizing the structure of the positive electrode sheet and reducing the surface tension of the electrolyte on the surface of the positive electrode active material, thereby increasing the wetting rate of the electrolyte on the positive electrode sheet. Furthermore, since fluorine has a similar ionic radius to oxygen, during secondary battery cycling, the fluorine element in the fluorohydrazone compound can partially replace the lattice oxygen sites in the metal oxide of the positive electrode active material, forming metal-F bonds. The formation of metal-F bonds facilitates the generation of a stable metal oxide / hydroxide phase structure, thereby reducing the dissolution of metal ions from the positive electrode active material layer and providing higher lattice energy and a smaller polarization tendency, thus improving the cycle performance of the secondary battery. Additionally, the fluorohydrazone compound contains a benzene ring, which has a protective effect on the positive electrode active material, slowing down the collapse rate of the positive electrode active material during cycling, thereby improving the cycle performance of the secondary battery. Therefore, this application improves the electrolyte wetting performance of the positive electrode by leveraging the synergistic effect of fluorine and benzene rings in the fluorohydrazone compound on the positive electrode, thereby enhancing the cycle performance of the secondary battery. Attached Figure Description

[0029] 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.

[0030] Figure 1 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application;

[0031] Figure 2 This is a schematic diagram of the energy storage system according to one embodiment of this application;

[0032] Figure 3 These are schematic diagrams illustrating the electrolyte wetting properties of Examples 1, 2, and 5.

[0033] Figure 4 This is a schematic diagram of the liquid retention coefficient of the secondary battery in Examples 1, 2, 5 and Comparative Example 1;

[0034] Figure 5 This is a schematic diagram of the EIS (Electrochemical Impedance Spectroscopy) test results for Examples 1, 2, 5, and Comparative Example 1.

[0035] 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

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The inventors discovered that uneven electrolyte wetting leads to irregular reactions in the positive electrode, which may affect the cycle life of lithium-ion batteries. Furthermore, incomplete electrolyte wetting can affect the performance of lithium-ion batteries, promoting the formation of lithium metal dendrites and creating safety hazards. Positive electrode wettability is considered a crucial factor in developing high-performance lithium-ion batteries. Two main factors influence positive electrode wettability: accelerating the wetting rate and achieving sufficient wetting. Lithium-ion batteries are a gap-pore structure (one of the dual-medium types). Currently, the typical wetting process involves injecting the electrolyte into the cell using an injection gun and then allowing it to stand at room temperature. To allow the electrolyte to fully penetrate the electrode, the standing time is several hours to tens of hours. However, a slow wetting process can easily destabilize the formation of the CEI (Cathode Electrolyte Interphase) film between the positive electrode and the electrolyte, thus affecting the cycle life of the lithium-ion battery. In addition, in order to improve the energy density of lithium-ion batteries, it is usually necessary to reduce the porosity of the positive electrode active material layer. This also increases the risk of pore blockage, which slows down the electrolyte wetting process and makes the electrolyte wettability worse.

[0043] In view of this, this application provides a positive electrode additive comprising a fluorohydrazone compound represented by Formula I or Formula II:

[0044]

[0045] In Formula I, R1, R2, and R3 are each independently selected from -H or -F, and R1, R2, and R3 are not simultaneously -H. R4 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

[0046] In Formula II, R5, R6, and R7 are each independently selected from -H or -F, and R5, R6, and R7 are not simultaneously -H. R8 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

[0047] Wherein, when R4 is selected from alkyl, R4 can be methyl; similarly, when R8 is selected from alkyl, R8 can be methyl.

[0048] The cathode additive of this application is a fluorohydrazone compound, which includes fluorine and a benzene ring. The fluorine can balance excess protons in the electrolyte, stabilizing the structure of the cathode and reducing the surface tension of the electrolyte on the cathode active material, thereby increasing the wetting rate of the electrolyte on the cathode. Furthermore, fluorine has a similar ionic radius to oxygen. During lithium-ion battery cycling, the fluorine in the fluorohydrazone compound can partially replace the lattice oxygen sites in the metal oxide of the cathode active material, forming metal-F bonds. The formation of metal-F bonds is conducive to the formation of a stable metal oxide / hydroxide phase structure, thereby reducing the dissolution of metal ions from the cathode active material layer and providing higher lattice energy and lower polarization tendency, thus improving the cycle performance of the lithium-ion battery. In addition, the fluorohydrazone compound contains a benzene ring, which has a protective effect on the cathode active material and can slow down the collapse rate of the cathode active material during cycling, thereby improving the cycle performance of the lithium-ion battery. Therefore, this application improves the electrolyte wetting performance of the positive electrode by leveraging the synergistic effect of fluorine and benzene rings in the fluorohydrazone compound on the positive electrode, thereby enhancing the cycle performance of the lithium-ion battery.

[0049] In some embodiments of this application, the compound of formula I is selected from at least one of the following compounds:

[0050]

[0051] The compound of formula II is selected from at least one of the following compounds:

[0052]

[0053] The cathode additives of this application include compounds of formula I-1, I-2, and I-3, or compounds II-1, II-2, and II-3. These compounds contain fluorine and abundant benzene rings. The synergistic effect of fluorine and benzene rings improves the electrolyte wetting performance of the cathode electrode, thereby enhancing the cycle performance of the lithium-ion battery.

[0054] This application also provides a positive electrode sheet, including a positive current collector, at least one side of which has a positive active material layer, the positive active material layer including a positive active material and a positive additive of any of the above embodiments.

[0055] The positive electrode of this application contains a positive electrode additive, a fluorohydrazone compound, which includes fluorine and a benzene ring. The fluorine can balance excess protons in the electrolyte, stabilizing the structure of the positive electrode and reducing the surface tension of the electrolyte on the surface of the positive electrode active material, thereby increasing the wetting rate of the electrolyte on the positive electrode. Furthermore, fluorine has a similar ionic radius to oxygen. During lithium-ion battery cycling, the fluorine in the fluorohydrazone compound can partially replace the lattice oxygen sites in the metal oxide of the positive electrode active material, forming metal-F bonds. The formation of metal-F bonds is conducive to the formation of a stable metal oxide / hydroxide phase structure, thereby reducing the dissolution of metal ions from the positive electrode active material layer and providing higher lattice energy and lower polarization tendency, thus improving the cycle performance of the lithium-ion battery. In addition, the fluorohydrazone compound contains a benzene ring, which has a protective effect on the positive electrode active material, slowing down the collapse rate of the positive electrode active material during cycling, thereby improving the cycle performance of the lithium-ion battery. Therefore, this application improves the electrolyte wetting performance of the positive electrode by leveraging the synergistic effect of fluorine and benzene rings in the fluorohydrazone compound on the positive electrode, thereby enhancing the cycle performance of the lithium-ion battery.

[0056] In some embodiments of this application, the mass percentage of the fluorohydrazone compound is 0.3% to 1.5%, preferably 0.5% to 1.2%, based on the mass of the positive electrode active material layer. For example, the mass percentage of the fluorohydrazone compound is 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.35%, 1.5%, or any range thereof.

[0057] The inventors discovered that when the mass percentage of fluorohydrazone compounds is too low (e.g., below 0.3%), it is difficult to effectively improve the electrolyte wetting performance of the positive electrode; when the mass percentage of fluorohydrazone compounds is too high (e.g., above 1.5%), the relative content of the positive electrode active material in the positive electrode decreases, which is detrimental to improving the energy density of lithium-ion batteries and also increases costs. This application, by controlling the content of fluorohydrazone compounds within the above-mentioned range, can both improve the electrolyte wetting performance of the positive electrode and facilitate the production of lithium-ion batteries with high energy density. When the mass percentage of fluorohydrazone compounds is between 0.5% and 1.2%, the positive electrode exhibits excellent electrolyte wetting performance, while the lithium-ion battery also has lower impedance, which is beneficial for further improving the cycle performance of the lithium-ion battery.

[0058] In some embodiments of this application, the compaction density of the positive electrode active material layer is 1.6 g / cm³. 3 ~1.8g / cm 3 For example, the compaction density of the positive electrode active material layer is 1.6 g / cm³. 3 1.65g / cm3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 Or any range thereof. When the compaction density of the positive electrode active material layer is too low (e.g., below 1.6 g / cm³), 3 This is detrimental to improving the energy density of lithium-ion batteries; when the compaction density of the positive electrode active material layer is too high (e.g., higher than 1.8 g / cm³), it hinders the improvement of the energy density of lithium-ion batteries. 3 If the porosity of the positive electrode active material layer is too low, it will hinder the improvement of the electrolyte wetting performance of the positive electrode sheet. This application improves the electrolyte wetting performance of the positive electrode sheet and facilitates the production of lithium-ion batteries with high energy density by adjusting the compaction density of the positive electrode active material layer within the above-mentioned range.

[0059] In some embodiments of this application, the porosity of the positive electrode active material layer is 26.5% to 28.5%. For example, the porosity of the positive electrode active material layer is 26.5%, 27%, 27.5%, 28%, 28.5%, or any range therebetween. When the porosity of the positive electrode active material layer is too low (e.g., below 26.5%), the pores in the positive electrode active material layer are easily blocked, resulting in a slower wetting process of the electrolyte on the positive electrode sheet, which is detrimental to improving the electrolyte wetting performance of the positive electrode sheet. When the porosity of the positive electrode active material layer is too high (e.g., above 28.5%), it is detrimental to improving the strength of the positive electrode sheet. This application, by controlling the porosity of the positive electrode active material layer within the above-mentioned range, is beneficial to both improving the electrolyte wetting performance of the positive electrode sheet and improving the strength of the positive electrode sheet, thereby improving the electrolyte retention capacity and cycle stability of the lithium-ion battery.

[0060] It is understood that the compaction density of the positive electrode active material layer usually increases with the increase of the rolling pressure, and the porosity usually decreases with the increase of the rolling pressure. This application can adjust the compaction density and porosity of the positive electrode active material layer by adjusting the rolling pressure.

[0061] In this application, the positive electrode active material layer can be disposed on one surface or on two surfaces along the thickness direction of the positive electrode current collector. The positive electrode active material layer is disposed on the surface of the positive electrode current collector; that is, it can be disposed on a portion or the entire surface of one surface. The positive electrode current collector is not particularly limited in this application, as long as it achieves the purpose of this application; for example, it can be, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collectors. The thickness of the positive electrode current collector is not particularly limited in this application, as long as it achieves the purpose of this application; for example, a thickness of 8 μm to 12 μm is acceptable.

[0062] This application does not impose any particular restriction on the type of positive electrode active material in the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide. By selecting the above-mentioned positive electrode active materials, it is beneficial to obtain lithium-ion batteries with high energy density and excellent cycle performance, making them more suitable for application in energy storage devices.

[0063] The positive electrode sheet of this application also includes a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder is selected from at least one of polyvinylidene fluoride (PVDF) and polyimide, and the conductive agent includes conductive carbon black or carbon nanotubes.

[0064] This application also provides a method for preparing the positive electrode additive according to any of the above embodiments, comprising the following steps:

[0065] Step A: Mix benzoyl hydrazide, fluoroacetophenone or its derivatives in a molar ratio of 1:1.1 to 1:1.7 and then add them to anhydrous ethanol;

[0066] Step B: Under acidic or alkaline conditions, heat under reflux at a temperature of 110℃~120℃ for 3.5h~4.5h to obtain fluorohydrazone compounds.

[0067] In step A of this application, by adjusting the molar ratio of benzoyl hydrazine, fluoroacetophenone, or their derivatives within the aforementioned range, complete condensation of fluoroacetophenone or its derivatives is facilitated, thereby increasing the yield of the reaction product. This application does not impose any particular limitation on the amount of anhydrous ethanol added, as long as the reactants are sufficiently dissolved in the anhydrous ethanol.

[0068] In step B of this application, by adjusting the heating temperature and reflux time within the above range, it is beneficial to ensure that benzoyl hydrazine reacts fully with fluoroacetophenone or its derivatives, thereby further improving the yield of the reaction product.

[0069] After the reaction is complete, step C may also be included:

[0070] The organic solvent is removed by vacuum distillation, and the crude product is washed repeatedly with cold methanol solution. The washed crude product is then recrystallized in anhydrous ethanol to obtain the purified fluorohydrazone.

[0071] In some embodiments of this application, fluoroacetophenone or its derivatives are selected from any one of p-fluoroacetophenone or its derivatives, m-fluoroacetophenone or its derivatives, and o-fluoroacetophenone or its derivatives.

[0072] In some embodiments of this application, under acetic or formic acid conditions, compound I is obtained; under alkaline conditions, compound II is obtained.

[0073] Acylhydrazone groups typically exist in two tautomers: enol and keto. In this application, the fluoroacylhydrazone compound can be the enol form shown in Formula I, or it can also be the keto form shown in Formula II. Generally, reaction under acetic or formic acid conditions yields the compound of Formula I; reaction under alkaline conditions yields the compound of Formula II. The alkaline solution can be a 15wt%–20wt% sodium hydroxide solution. The difference between acidic and alkaline conditions allows for different forms of the complex; that is, the enol form under acidic conditions and the keto form under alkaline conditions, making the product more controllable and improving purity.

[0074] This application provides a method for preparing a positive electrode additive, which involves a condensation reaction of benzoyl hydrazine, fluoroacetophenone, or their derivatives to generate a fluorohydrazone compound. This method has the advantages of readily available reactants, simple reaction steps, easily controllable reaction parameters, and high product yield. When the obtained fluorohydrazone compound is applied to the positive electrode, it improves the electrolyte wetting performance of the positive electrode, thereby enhancing the cycle performance of the lithium-ion battery.

[0075] This application also provides a secondary battery, including the positive electrode sheet described in any embodiment of this application.

[0076] In some embodiments of this application, the liquid retention coefficient of the secondary battery is 3.50 to 3.85. For example, the liquid retention coefficient is 3.50, 3.55, 3.60, 3.70, 3.80, 3.85, or any range thereof. It is evident that the secondary battery of this application has excellent liquid retention capacity, which is beneficial for improving the cycle performance of the secondary battery.

[0077] The secondary battery of this application also includes a negative electrode sheet. This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet typically includes a negative current collector and a negative active material layer. The negative active material layer can be disposed on one or both surfaces along the thickness direction of the negative current collector. In this application, the negative active material layer is disposed on the surface of the negative current collector; that is, the negative active material layer can be disposed on a portion of one surface of the negative current collector, or it can be disposed on the entire surface of one surface of the negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative current collector, as long as it achieves the purpose of this application; for example, a thickness of 4 μm to 12 μm. The thickness of the negative active material layer in this application can be 60 μm to 120 μm.

[0078] In this application, the negative electrode active material layer includes a negative electrode active material. There are no particular limitations on the negative electrode active material, as long as it can achieve the purpose of this application. For example, it may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon-carbon.

[0079] In this application, the negative electrode active material layer may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, it may include at least one of acrylate, polyamide, polyimide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0080] The secondary battery of this application also includes a separator. This application does not impose any particular limitation on the separator; those skilled in the art can choose one according to actual needs, as long as it achieves the purpose of this application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0081] The secondary battery of this application also includes an electrolyte. This application does not impose any particular limitation on the electrolyte; those skilled in the art can choose according to actual needs, as long as it achieves the purpose of this application. For example, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), or fluoroethylene carbonate (FEC) can be mixed in a certain mass or volume ratio to obtain a non-aqueous organic solvent, and then a lithium salt can be added to dissolve and mix evenly. This application does not limit the type of lithium salt, as long as it achieves the purpose of this application. For example, 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 dioxolane-borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of lithium salt in the electrolyte, as long as the purpose of this application can be achieved. For example, the concentration of lithium salt can be from 1.0 mol / L to 2.0 mol / L.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Please see Figure 1 , Figure 1 This is a structural schematic diagram 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.

[0088] 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.

[0089] Please see Figure 2 , Figure 2 This is a structural schematic diagram 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.

[0090] 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 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.

[0091] 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.

[0092] 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.

[0093] 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. 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.

[0094] Example

[0095] 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.

[0096] Preparation Example 1

[0097] Step A: Mix benzoyl hydrazide and p-fluoroacetophenone at a molar ratio of 1:1.5, and then mix the resulting mixture with anhydrous ethanol at a volume ratio of 1:20.

[0098] Step B: In the presence of acetic acid, heat under reflux at 120°C for 4 hours;

[0099] Step C: Remove the organic solvent by vacuum distillation, wash the crude product three times with cold methanol solution, and then recrystallize the washed crude product in anhydrous ethanol to obtain the purified compound I-1.

[0100] Preparation Example 2

[0101] Except for replacing p-fluoroacetophenone with m-fluoroacetophenone in step A to obtain compound I-2, the rest is the same as in preparation example 1.

[0102] Preparation Example 3

[0103] Except for replacing p-fluoroacetophenone with o-fluoroacetophenone in step A to obtain compound I-3, the rest is the same as in preparation example 1.

[0104] Preparation Example 4

[0105] Except for step B, where the reaction is carried out in a 20 wt% sodium hydroxide solution to obtain compound II-1, the preparation method is the same as in Example 1.

[0106] Preparation Example 5

[0107] Except for step A, in which p-fluoroacetophenone was replaced with m-fluoroacetophenone to obtain compound II-2, the heating temperature was 110°C, and the heating was refluxed for 3.5 h, the rest of the preparation was the same as in Preparation Example 4.

[0108] Preparation Example 6

[0109] Except for step A, in which p-fluoroacetophenone was replaced with o-fluoroacetophenone to obtain compound II-3, the heating temperature was 110°C, and the heating was refluxed for 4.5 h, the rest of the preparation was the same as in Preparation Example 4.

[0110] Example 1

[0111] <Preparation of the positive electrode>

[0112] Lithium iron phosphate (LiFePO4) as the positive electrode active material, conductive carbon black (Super-P) as the conductive agent, PVDF as the binder, and compound I-1 obtained in Preparation Example 1 were mixed in a mass ratio of 95:2:2.5:0.5. Then, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 70 wt%, and the mixture 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. The slurry was dried at 85°C and then rolled to obtain the positive electrode sheet. The thickness of the positive electrode active material layer was 100 μm, and the compaction density was 1.7 g / cm³. 3 The porosity is 28.07%.

[0113] <Preparation of Negative Electrode Sheets>

[0114] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC) thickener, Super-P conductive carbon black, and styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 96:2:1:1. Deionized water was added to prepare a negative electrode slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector, dried at 85°C, and then rolled to obtain the negative electrode sheet. The thickness of the negative electrode active material layer was 62 μm, and the compaction density was 3.7 g / cm³. 3 .

[0115] <Preparation of Electrolyte>

[0116] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:4:3, dissolved, and thoroughly stirred. The mixture was then placed at 5°C or lower for 12 hours. Lithium salt LiPF6 was then added, and the mixture was thoroughly mixed to obtain the electrolyte. The molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0117] <Preparation of the diaphragm>

[0118] A porous polymeric polypropylene (PP) film with a thickness of 10 μm was used as the separator.

[0119] <Preparation of a full cell>

[0120] 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 cell. The bare cell is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, and formation processes, a full cell with a capacity of 3.2 Ah is obtained.

[0121] <Preparation of Button Cells>

[0122] The positive electrode is punched into a 12mm diameter circular positive electrode sheet, and a 12mm diameter circular lithium sheet is used as the negative electrode sheet. The circular positive electrode sheet, separator, and circular lithium sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets to act as a separator. Then, the prepared electrolyte is injected to assemble a coin cell.

[0123] Examples 2 to 5

[0124] Except for adjusting the content of compound I-1 according to Table 1 in the <Preparation of Positive Electrode> section, the rest is the same as in Example 1.

[0125] Examples 6 to 20

[0126] Except for adjusting the type and content of the fluorohydrazone compound according to Table 1 in the <Preparation of Positive Electrode> section, the rest is the same as in Example 1.

[0127] Examples 21-22

[0128] Except for adjusting the compaction density and porosity of the positive electrode active material layer according to Table 2 in the <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1.

[0129] Comparative Examples 1 to 3

[0130] Except for adjusting the content of compound I-1 according to Table 1 in the <Preparation of Positive Electrode> section, the rest is the same as in Example 1.

[0131] Test methods and equipment:

[0132] Electrolyte wetting performance test of positive electrode sheet:

[0133] The positive electrode sheets from Examples 1, 2, and 5 were cut into strips 0.5 cm wide and 15 cm long. (Reference) Figure 3 Fix it with tape and a glass plate, then drip 11 drops of electrolyte at the same position, and record the wetting distance of the electrolyte after 10 minutes.

[0134] Lithium-ion battery liquid retention coefficient test:

[0135] At 25°C, the lithium-ion batteries (full cells) prepared in each embodiment and comparative example were formed and weighed, denoted as m1. Then, after evacuation and top-side sealing, the weight of the lithium-ion battery was recorded as m2. The weight of the lithium-ion battery without electrolyte injection was m3. Therefore, Δm = m1 - (m1 - m2) - m 3＝ m2-m3, where Δm represents the mass of electrolyte retained in the lithium-ion battery. The electrolyte retention coefficient = Δm / rated capacity of the lithium-ion battery, with units of g / Ah.

[0136] EIS test:

[0137] At 25°C, the lithium-ion batteries (full cells) prepared in each example and comparative example were connected to an electrochemical workstation and scanned from a high frequency of 800 kHz to a low frequency of 50 mHz with an AC amplitude of 10 mV to obtain electrochemical impedance spectroscopy curves.

[0138] Cyclic performance test:

[0139] At 25°C, the lithium-ion batteries (button cells) prepared in each embodiment and comparative example were charged to 3.65V at a constant current of 0.5P, and then discharged to 2.5V at a constant power of 0.5P; this constitutes one charge-discharge cycle. The capacity retention rate of the battery after N charge / discharge cycles was calculated.

[0140] The capacity retention rate (%) of a lithium-ion battery after N cycles = discharge capacity of the Nth cycle / discharge capacity of the first cycle × 100%.

[0141] Compacted density test:

[0142] The compaction density of the positive electrode active material layer is calculated using the following expression: P = m / V. Where P represents the compaction density of the positive electrode active material layer, m represents the mass of the positive electrode active material layer (in grams), and V represents the volume of the positive electrode active material layer (in centimeters). 3 Wherein, volume V is the product of the area of ​​the positive electrode active material layer and the thickness of the positive electrode active material layer.

[0143] Porosity test:

[0144] The positive electrode sheet was polished by ion polishing (CP), and then backscattered X-ray spectroscopy (EDS) was used to take a picture. The porosity of the positive electrode sheet was calculated using ImageJ software.

[0145] Table 1. Preparation parameters of Examples 1-20 and Comparative Examples 1-3

[0146]

[0147]

[0148] Note: In Table 1, " / " indicates that the relevant preparation parameters do not exist.

[0149] Table 2. Relevant preparation parameters for Examples 1-5 and Examples 21-22

[0150] <![CDATA[Apparent density of the positive electrode active material layer (g / cm 3 )]]> Porosity Example 1 1.7 28.07％ Example 2 1.7 27.05％ Example 3 1.7 26.63％ Example 4 1.7 28.42％ Example 5 1.7 25.21％ Example 21 1.6 29.07％ Example 22 1.8 26.21％ Comparative Example 1 1.7 29.43％

[0151] Table 3 Performance data for each embodiment and comparative example

[0152]

[0153]

[0154] Figure 3 This is a schematic diagram of the electrolyte wetting performance of Examples 1, 2, and 5. As can be seen from the figure, with the increase of the fluorohydrazone compound content, the wetting area of ​​the positive electrode sheet (the dark area of ​​the strip-shaped positive electrode sheet in the figure) becomes longer, and the wetting effect is improved, indicating that the fluorohydrazone compound of this application can improve the electrolyte wetting performance of the positive electrode sheet.

[0155] Figure 4 This is a schematic diagram showing the liquid retention coefficient of lithium-ion batteries in Examples 1, 2, 5, and Comparative Example 1. (Combined with...) Figure 4 As shown in Table 3, Examples 1, 2, 5, and Comparative Example 1 demonstrate that, compared to Comparative Example 1 without the addition of the fluorohydrazone compound, Examples 1, 2, and 5 exhibit significantly improved electrolyte retention coefficients and cycle performance. This indicates that the present application improves the electrolyte wetting performance of the positive electrode sheet through the synergistic effect of the fluorine element and benzene ring in the fluorohydrazone compound, thereby enhancing the cycle performance of the lithium-ion battery.

[0156] Based on the data in Table 3, and from Examples 1-5, Comparative Examples 2 and 3, it can be seen that when the content of fluorohydrazone compounds is too low (e.g., Comparative Example 2), it is difficult to effectively improve the electrolyte wetting performance of the positive electrode, resulting in a low liquid retention coefficient for the lithium-ion battery. When the mass percentage content of fluorohydrazone compounds is too high (e.g., Comparative Example 3), the relative content of the positive electrode active material in the positive electrode decreases, which is not conducive to improving the energy density of the lithium-ion battery. Furthermore, due to the small particle size of fluorohydrazone compounds, excessive fluorohydrazone compounds can clog the positive electrode active material layer, leading to excessively low porosity of the positive electrode active material layer. In contrast, the liquid retention coefficient and 300-cycle capacity retention rate of Examples 1-5 are significantly improved. Therefore, by controlling the content of fluorohydrazone compounds within the scope of this application, it is possible to improve the electrolyte wetting performance of the positive electrode, obtain a lithium-ion battery with high energy density, and improve the cycle stability of the lithium-ion battery.

[0157] Figure 5 This is a schematic diagram of the EIS test results for Examples 1, 2, 5, and Comparative Example 1. From... Figure 5 It can be seen that the impedance of Examples 1 and 2 is significantly lower than that of Comparative Example 1, and the impedance of Examples 1 and 2 is also lower than that of Example 5. This indicates that controlling the content of fluorohydrazone compounds within the range of 0.5% to 1.2% is beneficial to reducing the impedance of lithium-ion batteries.

[0158] Based on the data in Table 3, it can be seen from Examples 6 to 20 that by controlling the type and content of fluorohydrazone compounds within the scope of this application, it is beneficial to obtain lithium-ion batteries with excellent liquid retention performance and cycle stability.

[0159] The porosity and compaction density of the positive electrode active material layer also typically affect the performance of lithium-ion batteries. Combining the data in Tables 2 and 3, it can be seen from Examples 1 to 5 that the porosity of the positive electrode active material layer decreases with increasing fluorohydrazone compound content. This may be because the fluorohydrazone compound has a small particle size, making it easier to fill the pores of the positive electrode active material layer. However, by controlling the fluorohydrazone compound content within the scope of this application, it is possible to improve the liquid retention performance of the lithium-ion battery while balancing its cycle performance. As can be seen from Examples 1 and 21-22, controlling the compaction density of the positive electrode active material layer within the scope of this application is beneficial for obtaining lithium-ion batteries with excellent liquid retention performance and cycle stability.

[0160] The above provides a detailed description of a positive electrode additive and its preparation method, positive electrode sheet, secondary battery, and battery pack disclosed in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode plate, characterized in that, The present invention includes a positive current collector, wherein at least one side of the positive current collector has a positive active material layer, the positive active material layer comprising a positive active material and a positive additive, the positive additive comprising a fluorohydrazone compound represented by Formula I or Formula II. Formula I, Formula II; In Formula I, R1, R2, and R3 are each independently selected from -H or -F, and R1, R2, and R3 are not simultaneously -H. R4 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups. In Formula II, R5, R6, and R7 are each independently selected from -H or -F, and R5, R6, and R7 are not simultaneously -H. R8 is selected from substituted or unsubstituted alkyl, halogen, or nitro groups.

2. The positive electrode sheet according to claim 1, characterized in that, The compound of formula I is selected from at least one of the following compounds: Equation I-1, Equation I-2, Equation I-3; The compound of formula II is selected from at least one of the following compounds: Formula II-1 Formula II-2 Formula II-3.

3. The positive electrode sheet according to claim 1, characterized in that, Based on the mass of the positive electrode active material layer, the mass percentage of the fluorohydrazone compound is 0.3% to 1.5%.

4. The positive electrode sheet according to claim 1, characterized in that, Based on the mass of the positive electrode active material layer, the mass percentage of the fluorohydrazone compound is 0.5% to 1.2%.

5. The positive electrode sheet according to claim 1, characterized in that, The compaction density of the positive electrode active material layer is 1.6 g / cm³. 3 ~1.8 g / cm 3 .

6. The positive electrode sheet according to claim 5, characterized in that, The porosity of the positive electrode active material layer is 26.5%~28.5%.

7. A method for preparing a positive electrode sheet as described in any one of claims 1 to 6, characterized in that, The preparation of the positive electrode additive includes the following steps: Benzoylhydrazide, fluoroacetophenone or their derivatives are mixed in a molar ratio of 1:1.1 to 1:1.7 and then added to anhydrous ethanol. Fluorohydrazone compounds are obtained by heating under acidic or alkaline conditions at a temperature of 110°C to 120°C for 3.5 to 4.5 hours under reflux for 3.5 hours.

8. The preparation method according to claim 7, characterized in that, The fluoroacetophenone or its derivatives are selected from at least one of p-fluoroacetophenone or its derivatives, m-fluoroacetophenone or its derivatives, and o-fluoroacetophenone or its derivatives.

9. The preparation method according to claim 7, characterized in that, Under acetic acid or formic acid conditions, compound of formula I is obtained; Under alkaline conditions, compound of formula II was obtained.

10. A secondary battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 6.

11. The secondary battery according to claim 10, characterized in that, The liquid retention coefficient of the secondary battery is 3.5~3.

85.

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

13. An electrical appliance, characterized in that, It includes the secondary battery as described in claim 10 or 11, or the battery pack as described in claim 12.

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