Secondary battery and electric device

Abstract

The invention relates to a negative pole piece, a secondary battery and an electric device. The secondary battery comprises a negative pole piece, the negative pole piece comprises a negative current collector and a conductive coating arranged on at least one surface of the negative current collector, the conductive coating comprises a conductive agent and a binder, and the binder comprises glyceride.

Description

[0001] Related applications

[0002] This application is a divisional application of the Chinese patent application filed by the applicant on June 16, 2023, with application number 2023107184077 and entitled "Secondary Battery and Power Consumption Device". Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a secondary battery and an electrical device. Background Technology

[0004] Secondary batteries are widely used in various consumer electronics products and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect.

[0005] In pursuit of high energy density, metal batteries in the secondary battery market have attracted considerable attention due to their high energy density. Taking sodium metal batteries as an example, the anode-less sodium metal battery eliminates the need for initial anode active material, not only increasing energy density but also reducing production costs. However, without the protection of anode active material, uneven sodium deposition and dendrite formation occur on the anode side during cycling, resulting in poor cycle stability and significant challenges to cycle life. Summary of the Invention

[0006] Therefore, it is necessary to provide a secondary battery and power supply device that can improve cycle stability.

[0007] A first aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a conductive coating disposed on at least one surface of the negative current collector, the conductive coating including a conductive agent and a binder, the binder including a glycerol ester.

[0008] Not wishing to be limited by any theory, the negative electrode sheet in the aforementioned secondary battery of this application includes a binder in its conductive coating comprising glycerol ester. This type of binder not only possesses good adhesion but also has fewer active protons compared to polyacrylic acid, reducing side reactions between the conductive coating and the electrolyte, thereby improving the electrochemical performance of the battery. Simultaneously, compared to polyacrylate, glycerol ester contains glycerol ester groups, resulting in better adhesion and mechanical properties. During the charging and discharging process of the secondary battery, as metals are repeatedly deposited or peeled off from the surface of the conductive coating on the negative electrode sheet, the conductive coating can better act as a nucleation layer for the deposition of metals such as sodium and lithium. This improves the uniformity of the metal layer deposited on the conductive coating surface, effectively suppresses the growth of metal dendrites, and improves the cycle performance of the negative electrode-less secondary battery.

[0009] In addition, the conductive coating of the negative electrode sheet, as a nucleation layer of the metal layer, can effectively suppress the growth of metal dendrites, improve the problem of metal dendrites piercing the separator and causing short circuits and thermal runaway in the battery, and improve the safety performance of the battery.

[0010] In any embodiment of this application, the negative electrode sheet further includes a metal layer disposed on the surface of the conductive coating away from the negative current collector.

[0011] In any embodiment of this application, the metal layer is a metal layer formed of at least one element selected from sodium, lithium, and potassium.

[0012] In any embodiment of this application, the glyceride is a water-soluble glyceride;

[0013] Optionally, the glyceride includes at least one of polyglycerol acrylate, polyglycerol methacrylate, carboxymethyl cellulose glyceride, and glycerol alginate.

[0014] In any embodiment of this application, the glyceride contains a free carboxyl group;

[0015] Optionally, the acid value of the glyceride is a, where 0 < a ≤ 0.5 mg KOH / g; or optionally 0.2 mg KOH / g ≤ a ≤ 0.4 mg KOH / g.

[0016] In any embodiment of this application, the hydroxyl value of the glyceride is (10~20) mgKOH / g, and may be (10~15) mgKOH / g.

[0017] In any embodiment of this application, the mass content of the adhesive in the total mass of the adhesive and the conductive agent is 20% to 99%; optionally, it is 50% to 70%.

[0018] In any embodiment of this application, the conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, acetylene black, Ketjen black, and carbon fiber.

[0019] In any embodiment of this application, the thickness of the conductive coating is 0.2 μm to 5 μm, and can be selected as 0.6 μm to 2 μm.

[0020] In any embodiment of this application, the areal density of the conductive coating is (0.2~5) mg / 1540.25 mm². 2 The dosage can be selected as (0.5~3) mg / 1540.25 mm. 2 .

[0021] In a second aspect, this application provides an electrical device comprising the secondary battery described in the first aspect of this application. Attached Figure Description

[0022] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0023] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0024] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0025] Figure 3 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0028] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0036] Secondary batteries

[0037] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be activated and the battery to continue to be used.

[0038] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte.

[0039] Negative electrode sheet

[0040] One embodiment of this application provides a negative electrode sheet, including a negative electrode current collector and a conductive coating disposed on at least one surface of the negative electrode current collector. The conductive coating includes a conductive agent and a binder, the binder including a glycerol ester. The conductive coating does not contain any negative electrode active material.

[0041] It is understood that the above conductive coating does not contain negative electrode active material, that is, the formed negative electrode sheet is an electrode sheet without negative electrode active material.

[0042] Not wishing to be limited by any theory, the negative electrode sheet in the aforementioned secondary battery of this application includes a binder in its conductive coating comprising glycerol ester. This type of binder not only possesses good adhesion but also has fewer active protons compared to polyacrylic acid, reducing side reactions between the conductive coating and the electrolyte, thereby improving the electrochemical performance of the battery. Simultaneously, compared to polyacrylate, glycerol ester contains glycerol ester groups, resulting in better adhesion and mechanical properties. During the charging and discharging process of the secondary battery, as metals are repeatedly deposited or peeled off from the surface of the conductive coating on the negative electrode sheet, the conductive coating can better act as a nucleation layer for the deposition of metals such as sodium and lithium. This improves the uniformity of the metal layer deposited on the conductive coating surface, effectively suppresses the growth of metal dendrites, and improves the cycle performance of the negative electrode-less secondary battery.

[0043] In addition, the conductive coating of the negative electrode sheet, as a nucleation layer of the metal layer, can effectively suppress the growth of metal dendrites, improve the problem of metal dendrites piercing the separator and causing short circuits and thermal runaway in the battery, and improve the safety performance of the battery.

[0044] It is worth noting that in the secondary battery of this application, the negative electrode does not contain negative electrode active material during the battery manufacturing stage. During continuous charging and discharging, active ions such as sodium ions and lithium ions are repeatedly deposited or stripped onto the conductive coating. Understandably, these active ions originate from the positive electrode active material.

[0045] The negative electrode current collector can be a conventional metal foil or a composite current collector. Composite current collectors can be formed by depositing a metal material on a polymer substrate. For example, the negative electrode current collector can be copper foil, aluminum foil, etc.

[0046] In some embodiments, the glycerol ester is a water-soluble glycerol ester. This allows for the preparation of the conductive coating using water as a solvent to prepare the conductive paste, resulting in low cost and environmental friendliness.

[0047] Furthermore, the glycerol esters include at least one of polyglycerol acrylate, polyglycerol methacrylate, carboxymethyl cellulose glycerol ester, and glycerol alginate ester. These glycerol esters form a three-dimensional network of cross-linked and reinforced binders with good mechanical properties through a low-temperature esterification reaction between polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, or alginate and glycerol.

[0048] In some embodiments, the glycerol ester contains free carboxyl groups. The free carboxyl groups can anchor the conductive agent to the surface of the negative electrode current collector, enhancing the adhesion of the conductive agent to the negative electrode current collector, improving the stability of the negative electrode sheet, increasing the stability of nucleation, and thus extending the cycle life of the battery.

[0049] Furthermore, the acid value of the glycerol ester is 'a', where 0 < a ≤ 0.5 mg KOH / g. If the acid value of the glycerol ester is > 0.5 mg KOH / g, the excess carboxyl groups will catalyze the hydrolysis of the ester, thereby accelerating the adhesion failure of the adhesive and causing the conductive coating to easily peel off from the current collector during charging and discharging.

[0050] In some embodiments, the hydroxyl value of the glycerol ester is (10~20) mgKOH / g. If the hydroxyl value is less than 10 mgKOH / g, it indicates that the esterification crosslinking density of the glycerol ester is insufficient, which will reduce the adhesion of the conductive agent to the current collector; if the hydroxyl value is greater than 20 mgKOH / g, the degree of esterification crosslinking of the glycerol ester is large, which will also lead to a decrease in the mechanical toughness of the binder and an increase in the fragility of the conductive coating.

[0051] In this paper, the hydroxyl value was measured according to ASTM E222-17, and the acid value was measured according to ISO 3682-1996.

[0052] Furthermore, the molecular weight of carboxymethyl cellulose glycerol ester can range from 120,000 to 650,000, with a degree of substitution of 0.5 to 0.9. If the substitution is too high, the hygroscopicity and hydrophilicity will be stronger, leading to excessively high water content in the negative electrode sheet, potentially causing severe battery side reactions and affecting battery performance. If the substitution is too low, the strong oleophilicity of carboxymethyl cellulose affects the dispersibility of water-soluble binders and conductive agents, and the adhesion between the conductive coating and the negative electrode current collector. The molecular weight of carboxymethyl cellulose glycerol ester also affects the slurry viscosity and its dispersibility with the conductive agent. If the molecular weight of carboxymethyl cellulose glycerol ester is too small, its binding strength to the conductive agent will decrease; if the molecular weight of carboxymethyl cellulose glycerol ester is too large, the system viscosity will be too high, resulting in poor dispersion of the conductive agent and easy agglomeration.

[0053] As an example, carboxymethyl cellulose glyceride has a molecular weight of 350,000 and a degree of substitution of 0.7.

[0054] In some embodiments, the adhesion force between the negative current collector and the conductive coating is 1.5N to 5N.

[0055] In some embodiments, the mass content of the adhesive in the total mass of the adhesive and conductive agent is 20% to 99%; optionally, it is 50% to 70%. As an example, the mass content of the adhesive in the total mass of the adhesive and conductive agent is 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99%, or it can be a range consisting of any two of the above values.

[0056] In some embodiments, the conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, acetylene black, Ketjen black, and carbon fiber.

[0057] In some embodiments, the thickness of the conductive coating is 0.2 μm to 5 μm, for example, 0.2 μm, 0.4 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm; it can be selected as 0.6 μm to 2 μm, or it can be any range consisting of any two of the above values. If the thickness of the conductive coating is too thin, it cannot function as a good nucleation layer; if the thickness of the conductive coating is too thick, it will hinder ion migration, thereby reducing the uniformity of sodium deposition; it will also reduce the energy density of the battery.

[0058] In some embodiments, the areal density of the conductive coating is (0.2~5) mg / 1540.25 mm. 2 The dosage can be selected as (0.5~3) mg / 1540.25 mm. 2 .

[0059] Areal density is calculated using the following formula: Areal density = Mass of conductive coating / Area of ​​conductive coating. Wherein, the mass of the conductive coating = Total mass of the electrode containing the conductive coating - Mass of the negative electrode current collector, which can be measured using conventional mass testing methods such as a balance, and the area can be measured using an electrode size detection system.

[0060] The aforementioned negative electrode sheet can be prepared by the following method. This preparation method includes the following steps S10~S20:

[0061] S10. Mix the conductive agent, binder and solvent to obtain a conductive coating.

[0062] Furthermore, the solvent used in S10 includes water.

[0063] S20. The conductive coating obtained in step S10 is applied to at least one surface of the negative electrode current collector to form a conductive coating.

[0064] The secondary battery using the above-mentioned negative electrode is a metal battery.

[0065] In some embodiments, the negative electrode in the secondary battery further includes a metal layer disposed on the surface of the conductive coating away from the negative electrode current collector. This metal layer can be formed by the deposition of active ions from the positive electrode active material during the charging and discharging process of the secondary battery.

[0066] Optionally, the metal layer is a metal layer formed of at least one element selected from sodium, lithium, and potassium.

[0067] Positive electrode sheet

[0068] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector. The positive electrode film layer includes a positive electrode active material.

[0069] The positive electrode current collector can be a conventional metal foil or a composite current collector, wherein the composite current collector can be formed by depositing a metal material on a polymer substrate. As an example, the positive electrode current collector can be an aluminum foil.

[0070] The specific type of positive electrode active material can be any active material known in the art that can be used for positive electrode sheets in secondary batteries, and those skilled in the art can select according to actual needs.

[0071] As an example, the positive electrode active material may include a sodium ion active material, and the sodium ion active material may adopt the positive electrode active material for sodium ion batteries well-known in the art. As an example, the sodium ion active material may include at least one of the following materials: Prussian blue (PBA) type, with the chemical formula (NaxMA[MB(CN)6]·zH2O, where MA and MB are transition metal ions, which is a compound composed of sodium, transition metal and cyanide, such as Na4Fe2(CN)6, Na4Fe(CN)6, Na 1.72 MnFe2(CN)6, NaMnMn(CN)6, NaNiFe(CN)6, etc.; oxide type, with the chemical formula NaxMO2, 0 < x ≤ 1, M is a transition metal element, which is composed of transition metal oxides. The variable-valence transition metals involved mainly include vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu). Among them, manganese and iron with relatively rich resources are most commonly used. For example, NaCrO2, NaMnO2, NaMnO2, Na 0.61 Ti 0.48 Mn 0.52 O2, Na[Fe 0.5 Co 0.5 O2, NaMnO2, Na[Ni 0.25 Fe 0.5 Mn 0.25 O2, etc.; and polyanion compound type, with the chemical formula Na x M y [(XO m ) n- z , M is a metal ion with variable valence states, X is an element such as P, S and V, which is composed of sodium, transition metal and anions. Among them, the transition metals mainly include iron, vanadium, cobalt, etc., and the anions mainly include phosphate, pyrophosphate, fluorophosphate and sulfate, such as NaMnFe2(PO4)6, Na2MnP2O7, Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na3V2(PO4)2F3, Na4Co3(PO4)2(P2O7).

[0072] ​As an example, the positive electrode active material may include lithium-ion active materials, including but not limited to lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and one or more of their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and one or more of their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and one or more of their modified compounds. All of these materials are commercially available.

[0073] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0074] Furthermore, the positive electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0075] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0076] As an example, the adhesive may be one or more of the following: styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0077] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then obtaining the positive electrode sheet through processes such as drying and cold pressing. As an example, the solvent includes N-methylpyrrolidone.

[0078] electrolytes

[0079] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The type of electrolyte can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0080] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0081] In some embodiments, the electrolyte salt includes at least one of a sodium electrolyte salt and a lithium electrolyte salt.

[0082] Optionally, the electrolyte sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonylimide, sodium difluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium di(trifluoromethanesulfonyl)imide, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0083] Optionally, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0084] Furthermore, in the electrolyte, the concentration of the electrolyte salt is 0.5 mol / L to 8 mol / L, optionally 1 mol / L to 4 mol / L.

[0085] In some embodiments, the solvent in the electrolyte includes at least one of ether solvents, ester solvents, and sulfone solvents.

[0086] Optionally, the solvent in the electrolyte may include an ether solvent. Ether solvent molecules in the electrolyte can build a stable electrode / electrolyte interface on the metal surface of the negative electrode of the secondary battery, forming a stable solid electrolyte interface (SEI) and reducing electrochemical polarization.

[0087] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.

[0088] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butene carbonate (BC), vinylene carbonate (VC), propyleneene carbonate, fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propanesulfonate lactone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0089] As examples, sulfone solvents include sulfolane, dimethyl sulfone, methyl ethyl sulfone, and dimethyl sulfoxide (DMSO).

[0090] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0091] Separating membrane

[0092] In some embodiments, the secondary battery also includes a separator. The separator is disposed between the positive electrode and the negative electrode, serving as a separator. This application can use any known porous separator with good chemical and mechanical stability.

[0093] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0094] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0095] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0096] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0097] The shape of the secondary battery in this application embodiment can be cylindrical, square, or other arbitrary shapes. For example... Figure 1 This is an example of a square-structured secondary battery 1.

[0098] In some implementations, refer to Figure 2The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. The aforementioned gel electrolyte is impregnated in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to specific practical needs.

[0099] In addition, the present invention also provides an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack provided by the present invention. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0100] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0101] Figure 3 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0102] Another example device could be a mobile phone, tablet, laptop, etc.

[0103] Unless otherwise specified, all of the above-mentioned raw materials can be obtained through commercial purchase.

[0104] To make the objectives, technical solutions, and advantages of this invention clearer and more concise, the invention is described using the following specific embodiments, but the invention is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of the invention and can be used to describe the invention, but should not be construed as limiting the scope of the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0105] To better illustrate the present invention, the following embodiments are provided for further explanation. The specific embodiments are as follows.

[0106] Example 1

[0107] 1) Preparation of negative electrode sheet

[0108] The binder and conductive agent were added to water and stirred to form a uniform conductive slurry. This slurry was then coated onto the surface of a copper foil and transferred to a vacuum drying oven for complete drying to form a conductive coating. The coating was then die-cut to obtain the negative electrode sheet. The parameters of the binder, conductive agent, and conductive coating are shown in Table 1. The binder content refers to the mass percentage of binder in the total mass of the binder and conductive agent. The areal density of the conductive coating is 2 mg / 1540.25 mm². 2 .

[0109] 2) Preparation of positive electrode sheet

[0110] 10 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 10 wt% carbon black conductive agent and 80 wt% positive electrode active material Na4Fe3(PO4)2P2O7 were added to prepare a uniformly dispersed slurry. The slurry was uniformly coated on the surface of aluminum foil and then transferred to a vacuum drying oven for complete drying. The resulting electrode was rolled and then punched to obtain the positive electrode sheet.

[0111] 3) Preparation of electrolyte

[0112] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate was dissolved in the organic solvent ethylene glycol dimethyl ether and stirred until homogeneous to obtain an electrolyte with a sodium hexafluorophosphate concentration of 1.0 mol / L.

[0113] 4) Separating membrane

[0114] A 10μm thick polypropylene membrane was used as the separator.

[0115] 5) Preparation of sodium batteries

[0116] The positive electrode, separator, and negative current collector are stacked in sequence, with the separator positioned between the positive and negative current collectors to provide isolation. The electrolyte is then added to assemble the stacked battery.

[0117] Other embodiments

[0118] It is basically the same as Example 1, except that some parameters are different as shown in Table 1.

[0119] Specifically, compared with Example 1, the only difference between Examples 2 to 4 is the specific type of adhesive used.

[0120] Compared with Example 1, the only difference between Examples 5 and 6 is the type of conductive agent.

[0121] Compared with Example 1, the only difference between Examples 7 and 8 is that the hydroxyl value of the polyacrylic acid triglyceride is different.

[0122] Compared with Example 1, the only difference between Examples 7 and 8 is that the acid value of the polyacrylic acid triglyceride is different.

[0123] Compared with Example 1, the only difference between Examples 11 to 13 is the mass content of the adhesive.

[0124] Compared with Example 1, the only difference between Examples 14 and 15 is the thickness of the conductive coating.

[0125] Comparative Example 1

[0126] It is basically the same as Example 1, except that the conductive coating is omitted and only the copper foil in Example 1 is used as the negative electrode.

[0127] Comparative Examples 2-4

[0128] The process is essentially the same as in Example 1, except that the type of adhesive is different. See Table 1 for details.

[0129] The following is a performance test of the negative electrode sheet.

[0130] Specifically, the adhesion force between the negative electrode current collector and the conductive coating in the negative electrode sheets of each embodiment and comparative example was tested, and the test method is as follows:

[0131] 1. Cutting the electrode sheets

[0132] Take the negative electrode sheet and cut it into 400mm long and 50mm wide pieces using a custom die.

[0133] 2. Attach and fix the electrode plates

[0134] Take a flat, thin steel plate, approximately 200-300mm long and 50mm wide. First, apply a strip of double-sided tape (longer than the sample test length, and the same width as the electrode) to the center of the steel plate, smoothing it firmly to ensure it adheres tightly to the center. Peel off the double-sided tape and attach the negative electrode to the tape. It is crucial to ensure a perfect fit between the negative electrode and the tape; otherwise, the width of the peel force test will change, resulting in inaccurate test values ​​and the peel curve showing jumps or waves.

[0135] 3. Installation and Testing

[0136] The tensile testing machine has two clamps, one above the other. One end of the negative electrode sheet, which is fixed to the steel plate, is secured to the clamp on the tensile testing machine, and the other end is secured to the other clamp. After securing the test sample, first calibrate and zero the sample, then set the test width, electrode peeling length to 100mm, and peeling speed to 800mm / min. Then begin the test to obtain the adhesion force between the negative current collector and the conductive coating in the negative electrode sheet.

[0137] The following is a battery performance test.

[0138] 1) Coulomb efficiency

[0139] Taking Example 1 as an example, the prepared sodium battery was charged to 3.7V at 25°C with a constant current of 1 / 3C, and then charged at a constant voltage of 3.7V until the current dropped to 0.05C to obtain the initial charge capacity (Cc1); then discharged to 2.5V with a constant current of 1 / 3C to obtain the initial discharge capacity (Cd1), and the coulombic efficiency of the sodium battery was calculated according to the following formula.

[0140] Sodium battery coulombic efficiency = initial discharge capacity (Cd1) / initial charge capacity (Cc1)

[0141] The testing process for other embodiments and comparative examples is the same as above.

[0142] 2) Capacity retention rate

[0143] Taking Example 1 as an example, the sodium battery is charged at 25°C with a constant current of 1C to 3.7V, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged at a constant current of 1C to 2.5V, obtaining the first discharge capacity (Cd1); this charging and discharging is repeated until the nth cycle, obtaining the discharge capacity of the sodium battery after n cycles, denoted as Cdn, and the capacity retention rate of the sodium battery is calculated according to the following formula:

[0144] Capacity retention rate = discharge capacity after n cycles (Cdn) / discharge capacity in the first cycle (Cd1).

[0145] The testing process for other embodiments and comparative examples is the same as above.

[0146] 3) Sodium dendrite grade

[0147] The sodium battery, after 100 cycles, was disassembled in an argon atmosphere glove box (H₂O < 0.1 ppm, O₂ < 0.1 ppm). A clearly deposited metal layer, namely a sodium metal layer, was observed on the surface of the negative electrode. Based on the morphology of the sodium metal layer on the surface of the negative electrode, the degree of sodium dendrite precipitation was determined visually. The evaluation criteria are as follows:

[0148] Grade 0 sodium deposition: The sodium metal layer is deposited evenly and flatly (densely) on the entire surface of the negative electrode, with no visible uneven areas;

[0149] Grade 1 Sodium Deposition: The maximum area of ​​a single non-uniform sodium deposition zone in the sodium metal layer on the entire negative electrode surface is ≤2*2 mm. 2 The number of non-uniform sodium deposition areas in the sodium metal layer on the entire negative electrode surface is ≤5;

[0150] Grade 2 sodium precipitation: 2*2mm 2 The maximum area of ​​a single non-uniform sodium deposition region in the sodium metal layer on the entire negative electrode surface is ≤5*5 mm. 2 The number of non-uniform sodium deposition areas in the sodium metal layer on the entire negative electrode surface is ≤5;

[0151] Grade 3 sodium precipitation: Sodium precipitation is present but the above-mentioned criteria for grades 0 to 2 are not met.

[0152] Table 1

[0153]

[0154] As shown in Table 1, Comparative Example 1, without a conductive coating, exhibits low coulombic efficiency and cycle capacity retention, and suffers from severe sodium deposition issues. Comparative Examples 1 and 2, using polyacrylic acid or carboxymethyl cellulose as binders, show improved coulombic efficiency and cycle capacity retention compared to Comparative Example 1; however, the sodium deposition problem remains unresolved. Comparative Example 4, using polybutyl acrylate as a binder, achieves battery performance comparable to Comparative Example 1. Comparative Examples 2 and 4 only enhanced the adhesion of the conductive agent to the current collector, and their adhesion strength is still slightly lower than that of this application. This application, while enhancing the adhesion of the conductive coating to the current collector, also improves the mechanical properties of the conductive coating. The combined effect of these two improvements enhances the overall stability of the negative electrode sheet, thereby mitigating the problem of uneven sodium deposition.

[0155] Compared to the comparative examples, the embodiments of this application use glycerol ester as a binder, which not only improves coulombic efficiency and cycle capacity retention, but also greatly improves the degree of sodium precipitation.

[0156] Specifically, compared with Example 1, the only difference between Examples 2 to 4 is the specific type of binder. The results show that Examples 1 to 4 all achieved good coulombic efficiency and cycle capacity retention, and there was no obvious sodium precipitation problem. Furthermore, compared with Example 4, the batteries of Examples 1 to 3 have better coulombic efficiency and cycle capacity retention, and lower sodium precipitation level.

[0157] Compared with Example 1, the only difference between Examples 5 and 6 is the type of conductive agent. The results show that all examples achieved good coulombic efficiency and cycle capacity retention, and there was no obvious sodium precipitation problem. Furthermore, compared with Examples 5 and 6, the battery of Example 1 has better coulombic efficiency and cycle capacity retention, and a lower sodium precipitation level.

[0158] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A secondary battery, characterized in that, The secondary battery is a metal battery. The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a conductive coating disposed on at least one surface of the negative current collector, the conductive coating includes a conductive agent and a binder, the binder includes glycerol ester, and the glycerol ester includes at least one of polyglycerol acrylate, polyglycerol methacrylate, carboxymethyl cellulose glycerol ester and glycerol alginate.

2. The secondary battery as described in claim 1, characterized in that, The negative electrode sheet further includes a metal layer, which is disposed on the surface of the conductive coating away from the negative current collector.

3. The secondary battery as described in claim 2, characterized in that, The metal layer is formed from at least one element selected from sodium, lithium, and potassium.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The polyglycerol acrylate includes polyglycerol triacrylate, the polymethacrylate includes polymethacrylate triacrylate, the carboxymethyl cellulose glycerol includes carboxymethyl cellulose triacrylate, and the alginate glycerol includes alginate triacrylate.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The glyceride contains a free carboxyl group; Optionally, the acid value of the glyceride is a, where 0 < a ≤ 0.5 mg KOH / g; or optionally 0.2 mg KOH / g ≤ a ≤ 0.4 mg KOH / g.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The hydroxyl value of the glyceride is (10~20) mgKOH / g, and can be selected as (10~15) mgKOH / g.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, In the total mass of the adhesive and the conductive agent, the mass content of the adhesive is 20% to 99%; optionally 30% to 90%, and more preferably 50% to 70%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The conductive agent includes at least one of carbon nanotubes, graphene, conductive carbon black, conductive graphite, and carbon fiber. Optionally, the conductive agent includes at least one of carbon nanotubes, graphene, conductive graphite, acetylene black, Ketjen black, and carbon fiber.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The thickness of the conductive coating is 0.2μm to 5μm, and can be selected as 0.6μm to 2μm.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The areal density of the conductive coating is 0.2 mg / 1540.25 mm. 2 ~5mg / 1540.25mm 2 The option is 0.5 mg / 1540.25 mm. 2 ~3mg / 1540.25mm 2 .

11. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 10.

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