Secondary battery, negative pole piece and electric device

Abstract

The invention relates to a secondary battery, a negative pole piece 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 first binder, and the first binder comprises polyrotaxane.

Description

[0001] Related applications

[0002] This application is a divisional application of the Chinese patent application filed by the applicant on June 15, 2023, with application number 2023107123961 and entitled "Secondary Battery, Negative Electrode Sheet and Electrical Device". Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a secondary battery, a negative electrode sheet, 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, a negative electrode, and an electrical 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 first binder, the first binder including polyrotaxane.

[0008] Not wishing to be limited by any theory, the negative electrode sheet in the aforementioned secondary battery of this application incorporates polyrotaxane as a binder in its conductive coating. Polyrotaxane comprises linear molecules and cyclic molecules interwoven with the linear molecules. The cyclic molecules can freely shuttle and rotate around the axis of the linear molecules. This cyclic sliding motion gives the polyrotaxane a large degree of internal freedom, endowing the polymer network formed by the polyrotaxane with exceptional elasticity, which can better polymerize and bind the conductive agent. Furthermore, during the charge and discharge process of the secondary battery, the conductive coating containing polyrotaxane acts as a nucleation layer for the deposition of metals such as sodium and lithium, improving the uniformity of the metal layer deposited on the surface of the conductive coating, effectively suppressing the growth of metal dendrites, and improving the cycle performance of the negative electrode-less secondary battery.

[0009] 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.

[0010] 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.

[0011] In any embodiment of this application, the polyrotaxane comprises a linear molecule, a cyclic molecule pierced through the linear molecule, and a capping group connected to the linear molecule;

[0012] Wherein, the cyclic molecule includes at least one of crown ethers, macrocyclic amides, and cyclodextrins; and / or,

[0013] The linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane, and polyvinyl polypropylene.

[0014] In any embodiment of this application, the end-capping group includes at least one of sulfonate and amino groups;

[0015] Optionally, the capping agent providing the capping group includes at least one of sulfonate capping agents and amino-containing capping agents; more preferably, the capping agent includes at least one of 3,5-dinitrobenzenesulfonate, 3,5-ditrifluoromethylbenzenesulfonate, 1-naphthol-3-sulfonate, 2,4-dinitroaniline and 1-aminoanthracene.

[0016] In any embodiment of this application, the conductive coating further includes a second adhesive;

[0017] Optionally, the second adhesive includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, and sodium alginate;

[0018] Alternatively, the second adhesive may include at least one of sodium carboxymethyl cellulose and polyacrylic acid.

[0019] In any embodiment of this application, the mass content of the polyrotaxane in the total amount of the first adhesive and the second adhesive is 2% to 10%; optionally, it is 4% to 8%.

[0020] In any embodiment of this application, the conductive agent includes at least one selected from carbon nanotubes, graphene, conductive carbon black, conductive graphite, acetylene black, Ketjen black, and carbon fiber; and / or,

[0021] In the conductive coating, the mass content of the conductive agent is 1% to 80%; optionally, it is 5% to 40%.

[0022] 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.

[0023] In any embodiment of this application, the areal density of the conductive coating is (0.2mg~5mg) / 1540.25mm. 2 The dosage can be selected as (0.5 mg~3 mg) / 1540.25mm. 2 .

[0024] In a second aspect, this application provides a negative electrode sheet, comprising a negative current collector and a conductive coating disposed on at least one surface of the negative current collector, the conductive coating comprising a conductive agent and a first binder, the first binder comprising polyrotaxane.

[0025] In a third aspect, this application provides an electrical device comprising the secondary battery described in the first aspect of this application. Attached Figure Description

[0026] 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.

[0027] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0028] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0029] 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;

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0032] The embodiments 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.

[0033] 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.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] 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 mention that the method may also include step (c) indicates 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.

[0037] 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.

[0038] 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).

[0039] 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).

[0040] Secondary batteries

[0041] 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.

[0042] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions move back and forth between the positive and negative electrodes, inserting and extracting.

[0043] Negative electrode sheet

[0044] One embodiment of this application provides a 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 includes a conductive agent and a first binder, the first binder including polyrotaxane.

[0045] As can be understood, polyrotaxane comprises a linear molecule, a cyclic molecule threaded onto the linear molecule, and end-capping groups connected to the linear molecule. The end-capping groups prevent the cyclic molecule from slipping off the linear molecule. In other words, the linear molecule acts as an axis, passing through the cavity of the cyclic molecule, and the end of the axis has end-capping groups as a plug.

[0046] Not wishing to be limited by any theory, the negative electrode sheet in the aforementioned secondary battery of this application incorporates polyrotaxane as a binder in its conductive coating. Polyrotaxane comprises linear molecules and cyclic molecules interwoven with the linear molecules. The cyclic molecules can freely shuttle and rotate around the axis of the linear molecules. This cyclic sliding motion gives the polyrotaxane a large degree of internal freedom, endowing the polymer network formed by the polyrotaxane with exceptional elasticity, which can better polymerize and bind the conductive agent. Furthermore, during the charge and discharge process of the secondary battery, the conductive coating containing polyrotaxane acts as a nucleation layer for the deposition of metals such as sodium and lithium, improving the uniformity of the metal layer deposited on the surface of the conductive coating, effectively suppressing the growth of metal dendrites, and improving the cycle performance of the negative electrode-less secondary battery.

[0047] In addition, the conductive coating on the negative electrode sheet can promote the uniform deposition of the metal layer on its surface, effectively suppress the growth of metal dendrites, thereby improving the problem of metal dendrites piercing the separator and causing short circuits and thermal runaway in the battery, and improving the safety performance of the battery.

[0048] 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.

[0049] 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, and is not required during the fabrication of the negative electrode.

[0050] Optionally, the metal layer is a metal layer formed of at least one element selected from sodium, lithium, and potassium. As an example, the metal layer may be a sodium layer, a lithium layer, or a potassium layer, or it may be a lithium-sodium composite metal layer.

[0051] 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.

[0052] In some embodiments, the cyclic molecules in the polyrotaxane include at least one of crown ethers, macrocyclic amides, and cyclodextrins.

[0053] Cyclodextrins possess abundant -OH groups, and the hydrogen bonds between these -OH groups form nanochannels that can provide directional transport pathways for active particles such as sodium and lithium ions, thereby better promoting the uniform deposition of metals such as sodium and lithium on the conductive coating. Furthermore, the cyclodextrin can be at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0054] Compared to cyclodextrins, crown ethers are formed by oxygen atoms linked by alkyl chains (CH2-CH2-O). Sodium ions and lithium ions can be transported between or within chain segments through a transient dynamic process of complexation / decomplexation with ether oxygen atoms in the amorphous regions of the chain segments. This enables the directional transport of active ions such as sodium and lithium ions, and better promotes the uniform deposition of metals such as sodium and lithium on conductive coatings.

[0055] The presence of hydrogen bonds between cyclic amide molecules and linear molecules in macrocyclic amides creates nanochannels that can provide directional transport pathways for active ions such as sodium and lithium ions, promoting the uniform deposition of metals such as sodium and lithium on conductive coatings.

[0056] Furthermore, the parent ring structure of macrocyclic amides is shown below:

[0057] .

[0058] In some embodiments, the linear molecules in the polyrotaxane are linear polymers. As examples, linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane, and polyvinyl polypropylene.

[0059] Furthermore, the end-capping group includes at least one of sulfonate and amino groups. The sulfonate group not only serves as the end-capping group but also possesses good proton conductivity, which can improve the conductivity of the conductive coating.

[0060] It is understandable that the higher the conductivity of the conductive coating, the lower its film resistance. Film resistance can be measured using any known method.

[0061] Furthermore, the capping agent providing the capping group includes at least one of sulfonate capping agents and amino-containing capping agents.

[0062] As an example, the end-capping agent providing the end-capping group includes at least one selected from 3,5-dinitrobenzenesulfonate, 3,5-ditrifluoromethylbenzenesulfonate, 1-naphthol-3-sulfonate, 2,4-dinitroaniline, and 1-aminoanthracene. Specifically, 3,5-dinitrobenzenesulfonate is such as sodium 3,5-dinitrobenzenesulfonate, 3,5-ditrifluoromethylbenzenesulfonate is such as sodium 3,5-ditrifluoromethylbenzenesulfonate, and 1-naphthol-3-sulfonate is such as sodium 1-naphthol-3-sulfonate.

[0063] Polyrotaxane can be commercially available or prepared in-house. In some embodiments, polyrotaxane can be prepared by the following method:

[0064] The linear and cyclic molecular compounds are mixed in a solvent, and a capping agent is added to carry out a capping reaction. Furthermore, the capping reaction temperature is 20–80°C.

[0065] Among them, linear molecular compounds include, but are not limited to, at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane and polyvinyl polypropylene; cyclic molecular compounds include, but are not limited to, at least one of crown ethers, macrocyclic amides and cyclodextrins.

[0066] In some embodiments, the conductive coating further includes a second binder. Optionally, the second binder includes at least one selected from sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, and sodium alginate. The combination of the second binder and the first binder provides better adhesion, thereby enabling the conductive agent to bond better.

[0067] Alternatively, the second binder may include at least one of sodium carboxymethyl cellulose and polyacrylic acid.

[0068] Furthermore, in the total amount of the first adhesive and the second adhesive, the mass content of polyrotaxane is 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%; it can be selected as 4% to 8%, or it can be a range consisting of any two of the above values.

[0069] In some embodiments, the total amount of the first adhesive and the second adhesive accounts for 20% to 99% of the mass content of the conductive coating, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90%, 95%, 99%, and can be selected as 60% to 95%, or can be any range formed by any two of the above point values.

[0070] 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.

[0071] In some embodiments, the conductive agent in the conductive coating has a mass content of 1% to 80%; optionally, it has a mass content of 5% to 40%.

[0072] 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.

[0073] In some embodiments, the areal density of the conductive coating is (0.2 mg to 5 mg) / 1540.25 mm. 2 The dosage can be selected as (0.5 mg~3 mg) / 1540.25mm. 2 .

[0074] 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.

[0075] The aforementioned negative electrode sheet can be prepared by the following method. This preparation method includes the following steps S10~S20:

[0076] S10. The conductive agent, the first binder and the solvent are mixed, and optionally a second binder is also added to obtain a primer slurry.

[0077] Furthermore, the solvent used in S10 may be water, an organic solvent, or a mixture of both, depending on the requirements of the adhesive. For example, if the second adhesive is styrene-butadiene rubber, the solvent may be water. Alternatively, if the second adhesive is polyvinylidene fluoride, the solvent may be an organic solvent, such as NMP (N-methylpyrrolidone).

[0078] S20. Apply the primer slurry obtained in step S10 to at least one surface of the negative electrode current collector to form a conductive coating.

[0079] The secondary battery using the above-mentioned negative electrode is a metal battery.

[0080] Positive electrode sheet

[0081] 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.

[0082] 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.

[0083] 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.

[0084] As an example, the positive electrode active material may include a sodium-ion active material, which may be a positive electrode active material known in the art for sodium-ion batteries. 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 are compounds composed of sodium, transition metals, and cyanide ions, such as Na4Fe2(CN)6, Na4Fe(CN)6, Na... 1.72MnFe2(CN)6, NaMnMn(CN)6, NaNiFe(CN)6, etc.; oxide type, with the chemical formula NaxMO2, where 0 < x ≤ 1 and M is a transition metal element. It 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, which are relatively abundant in resources, are the 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 polyanionic compound type, with the chemical formula Na x M y [(XO m ) n- z , where M is a metal ion with variable valence states, and X is an element such as P, S, and V. It is composed of sodium, transition metals, and anions. 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).

[0085] As an example, the positive electrode active material may include a lithium ion active material. The lithium ion active material includes, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels. [[ID=​​​​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.

[0088] Furthermore, the positive electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] electrolytes

[0093] 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.

[0094] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0095] In some embodiments, the electrolyte salt includes at least one of a sodium electrolyte salt and a lithium electrolyte salt.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In some embodiments, the solvent in the electrolyte includes at least one of ether solvents, ester solvents, and sulfone solvents.

[0100] 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.

[0101] 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.

[0102] 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).

[0103] As examples, sulfone solvents include sulfolane, dimethyl sulfone, methyl ethyl sulfone, and dimethyl sulfoxide (DMSO).

[0104] 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.

[0105] Separating membrane

[0106] 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.

[0107] 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.

[0108] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] In some implementations, refer to Figure 2 The 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.

[0113] 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.

[0114] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0115] 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.

[0116] Another example device could be a mobile phone, tablet, laptop, etc.

[0117] Unless otherwise specified, all of the above-mentioned raw materials can be obtained through commercial purchase.

[0118] 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.

[0119] To better illustrate the present invention, the following embodiments are provided for further explanation. The specific embodiments are as follows.

[0120] Description of the polyrotaxane used in each example:

[0121] Cyclodextrin-type polyrotaxanes: the cyclic molecules are cyclodextrins, and the linear molecules are polyethylene glycols;

[0122] Crown ether polyrotaxanes: cyclic molecules are crown ethers, and linear molecules are polyethylene glycol;

[0123] Macrocyclic amide polyrotaxanes: The cyclic molecules are macrocyclic amides, and the linear molecules are polyethylene glycol.

[0124] The end-capping agents corresponding to the end-capping groups of each polyrotaxane are shown in Table 1.

[0125] Example 1

[0126] 1) Preparation of negative electrode sheet

[0127] 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 binder comprised 60% of the total mass of the binder and conductive agent; it consisted of a first binder (polyrotaxane) and a second binder (polyacrylic acid); the polyrotaxane comprised 5% of the total binder mass. The conductive coating had a thickness of 0.8 μm and an areal density of 2 mg / 1540.25 mm. 2 .

[0128] 2) Preparation of positive electrode sheet

[0129] 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.

[0130] 3) Preparation of electrolyte

[0131] 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, which is the electrolyte of Example 1.

[0132] 4) Separating membrane

[0133] Polypropylene film is used as the separator.

[0134] 5) Preparation of sodium batteries

[0135] 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.

[0136] Examples 2-20

[0137] It is basically the same as Example 1, except that some parameters are different as shown in Table 1.

[0138] Specifically, compared with Example 1, the only difference between Examples 2 to 5 is the amount of polyrotaxane added in the conductive coating, that is, the mass percentage of polyrotaxane in the total binder is different;

[0139] Compared with Example 1, the only difference between Examples 6 and 7 is the type of end-capping agent used in the polyrotaxane;

[0140] Compared with Example 1, the only difference between Examples 8-10 is that other types of adhesives of equal mass are used instead of polyacrylic acid in Example 1;

[0141] Compared with Examples 1 and 8-10, the only difference between Examples 11-14 is that the same mass of crown ether polyrotaxane is used instead of cyclodextrin-type polyrotaxane.

[0142] Compared with Examples 1 and 8-10, the only difference between Examples 15-18 is that the same mass of macrocyclic amide polyrotaxane is used instead of cyclodextrin-type polyrotaxane.

[0143] Compared with Example 1, the only difference between Examples 19 and 20 is the thickness and areal density of the conductive coating;

[0144] Compared with Example 1, the only difference between Examples 21 and 22 is that other types of conductive agents of the same mass are used instead of the conductive agent in Example 1.

[0145] Comparative Example 1

[0146] 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.

[0147] Comparative Example 2

[0148] It is basically the same as Example 1, except that polyrotaxane is omitted from the adhesive and replaced with an equal mass of polyacrylic acid.

[0149] Comparative Examples 3-5

[0150] The results are basically the same as in Example 1, except that an equal mass of the mixture is used instead of the polyrotaxane in Example 1, as shown in Table 1.

[0151] The following is a battery performance test.

[0152] 1) Coulomb efficiency

[0153] 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.

[0154] Sodium battery coulombic efficiency = initial discharge capacity (Cd1) / initial charge capacity (Cc1)

[0155] The testing process for other embodiments and comparative examples is the same as above.

[0156] 2) Capacity retention rate

[0157] 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:

[0158] Capacity retention rate = discharge capacity after n cycles (Cdn) / discharge capacity in the first cycle (Cd1).

[0159] The testing process for other embodiments and comparative examples is the same as above.

[0160] 3) Sodium dendrite grade

[0161] 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:

[0162] 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;

[0163] 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;

[0164] 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;

[0165] Grade 3 sodium precipitation: Sodium precipitation is present but the above-mentioned criteria for grades 0 to 2 are not met.

[0166] Table 1

[0167]

[0168]

[0169] The following is a film resistance test of the negative electrode.

[0170] Test method: The film resistance R of the negative electrode is tested using a HIOKI BT23562 internal resistance tester. The upper and lower sides of the negative electrode are clamped between the two conductive terminals of the tester and pressure is applied to fix it. The diameter of the conductive terminals is 14mm and the applied pressure is 25MPa. The film resistance of the negative electrode is then measured.

[0171] Test subjects: negative electrode sheets (same size and shape) prepared in Examples 1 and 6-7.

[0172] The film resistance test results of the negative electrode are shown in Table 2:

[0173] Table 2

[0174]

[0175] As shown in Table 1, compared with the comparative examples, the addition of polyrotaxane as a binder in each embodiment of this application not only improves the coulombic efficiency and cycle capacity retention rate, but also greatly improves the degree of sodium precipitation.

[0176] A comparison of Examples 1-5 shows that, with other conditions remaining unchanged, the coulombic efficiency and cycle capacity retention of the battery are good when the mass percentage of polyrotaxane in the total binder is in the range of 2% to 10%, and there is no obvious sodium precipitation problem. Furthermore, when the mass percentage of polyrotaxane in the total binder is in the range of 4% to 8%, the coulombic efficiency and cycle capacity retention of the battery are even better, and the sodium precipitation level is lower.

[0177] A comparison of Examples 1 and 6-7 shows that different types of end-capping agents in polyrotaxane all achieve good coulombic efficiency and cycle capacity retention, and there is no obvious sodium precipitation problem. Furthermore, as shown in Table 2, the preferred end-capping agent in polyrotaxane is sodium 3,5-ditrifluoromethylbenzenesulfonate, which has good proton conductivity and can improve the conductivity of the conductive coating.

[0178] A comparison of Examples 1, 8-10, 11-14, and 15-18 shows that different types of polyrotaxanes using different second binders all achieve good coulombic efficiency and cycle capacity retention, and there is no obvious sodium precipitation problem. Furthermore, using polyacrylic acid or sodium carboxymethyl cellulose as the second binder results in batteries with even better coulombic efficiency and cycle capacity retention.

[0179] A comparison of Examples 1 and 19-20 shows that different thicknesses and areal densities of the conductive coating all achieve good coulombic efficiency and cycle capacity retention, and there is no obvious sodium deposition problem; furthermore, the battery with a conductive coating thickness of 0.6-2 μm has better coulombic efficiency and cycle capacity retention.

[0180] A comparison of Examples 1 and Examples 21-22 shows that using different types of conductive agents all yielded good coulombic efficiency and cycle capacity retention, and there was no obvious sodium precipitation problem.

[0181] 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.

[0182] 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 device includes a negative electrode sheet, which 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, a first binder, and a second binder mixed together. The first binder includes polyrotaxane, and the second binder includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, and sodium 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 polyrotaxane comprises a linear molecule, a cyclic molecule entangled on the linear molecule, and a capping group connected to the linear molecule; Wherein, the cyclic molecule includes at least one of crown ethers, macrocyclic amides, and cyclodextrins; and / or, The linear molecules are linear polymers; optionally, the linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, and polydimethylsiloxane.

5. The secondary battery as described in claim 4, characterized in that, The terminating group includes at least one of sulfonate and amino groups; Optionally, the capping agent providing the capping group includes at least one of sulfonate capping agents and amino-containing capping agents; more preferably, the capping agent includes at least one of 3,5-dinitrobenzenesulfonate, 3,5-ditrifluoromethylbenzenesulfonate, 1-naphthol-3-sulfonate, 2,4-dinitroaniline and 1-aminoanthracene.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The second adhesive includes at least one of sodium carboxymethyl cellulose and polyacrylic acid.

7. The secondary battery as described in claim 6, characterized in that, In the total amount of the first adhesive and the second adhesive, the mass content of the polyrotaxane is 2% to 10%; optionally, it is 4% to 8%.

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, acetylene black, Ketjen black, and carbon fiber; and / or, In the conductive coating, the mass content of the conductive agent is 1% to 80%; optionally, it is 5% to 40%.

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 0.5mg / 1540.25mm. 2 ~3mg / 1540.25mm 2 .

11. A negative electrode sheet, characterized in that, The device includes 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, a first binder, and a second binder mixed together. The first binder includes polyrotaxane, and the second binder includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber, and sodium alginate.

12. 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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