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

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a secondary battery, a negative electrode plate and an electrical device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect.

[0003] In pursuit of high energy density, metal batteries in secondary batteries have attracted people's attention due to their high energy density. Taking sodium metal batteries as an example, the negative electrode-free sodium metal battery eliminates the use of initial negative electrode active materials, which not only improves the energy density of the battery, but also reduces the battery production cost. However, without the protection of the negative electrode active material on the negative electrode side, uneven sodium is continuously deposited on the negative electrode side during the cycle process, and sodium dendrites are formed, resulting in poor cycle stability of the negative electrode-free sodium metal battery, and its cycle life faces great challenges. Summary of the invention

[0004] Based on this, it is necessary to provide a secondary battery, a negative electrode plate and an electrical device that can improve cycle stability.

[0005] In a first aspect of the present application, a secondary battery is provided, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a conductive coating provided on at least one surface of the negative electrode current collector, wherein the conductive coating comprises a conductive agent and a first binder, and the first binder comprises a polyrotaxane.

[0006] Without wishing to be limited to any theory, the negative electrode plate in the above-mentioned secondary battery of the present application has a conductive coating with polyrotaxane added as a binder. The polyrotaxane includes linear molecules and cyclic molecules threaded on the linear molecules, wherein the cyclic molecules can freely shuttle along the axis of the "linear molecules" and rotate around the axis. This ring sliding motion allows the polyrotaxane to have a large internal degree of freedom, giving the polymer network formed by the polyrotaxane extraordinary elasticity, which can better polymerize and bond the conductive agent. In addition, 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, which can improve the uniformity of the metal layer deposited on the surface of the conductive coating, effectively inhibit the growth of metal dendrites, and improve the cycle performance of the secondary battery without a negative electrode.

[0007] In any embodiment of the present application, the negative electrode plate further includes a metal layer, and the metal layer is disposed on a surface of the conductive coating layer away from the negative electrode current collector.

[0008] In any embodiment of the present application, the metal layer is a metal layer formed of at least one element selected from the group consisting of sodium, lithium and potassium.

[0009] In any embodiment of the present application, the polyrotaxane includes a linear molecule, a cyclic molecule inserted on the linear molecule, and a capping group connected to the linear molecule;

[0010] Wherein, the cyclic molecule comprises at least one of crown ether, macrocyclic amide and cyclodextrin; and / or,

[0011] The linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane and polyethylene-based polypropylene.

[0012] In any embodiment of the present application, the end-capping group includes at least one of a sulfonate group and an amino group;

[0013] Optionally, the capping agent providing the capping group includes at least one of a sulfonate capping agent and an amino-containing capping agent; more optionally, the capping agent includes at least one of 3,5-dinitrobenzenesulfonate, 3,5-ditrifluoromethylbenzenesulfonate, 1-naphthol-3-sulfonate, 2,4-dinitroaniline and 1-aminoanthracene.

[0014] In any embodiment of the present application, the conductive coating further comprises a second binder;

[0015] Optionally, the second binder includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber and sodium alginate;

[0016] More optionally, the second binder includes at least one of sodium carboxymethyl cellulose and polyacrylic acid.

[0017] In any embodiment of the present application, the mass content of the polyrotaxane in the total amount of the first binder and the second binder is 2% to 10%; optionally 4% to 8%.

[0018] In any embodiment of the present application, 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,

[0019] In the conductive coating, the mass content of the conductive agent is 1% to 80%; optionally 5% to 40%.

[0020] In any embodiment of the present application, the thickness of the conductive coating is 0.2 μm to 5 μm, and can be optionally 0.6 μm to 2 μm.

[0021] In any embodiment of the present application, the surface density of the conductive coating is (0.2 mg to 5 mg) / 1540.25 mm 2, optional: (0.5mg~3mg) / 1540.25mm 2 .

[0022] In a second aspect of the present application, a negative electrode plate is provided, comprising a negative electrode current collector and a conductive coating disposed on at least one surface of the negative electrode current collector, wherein the conductive coating comprises a conductive agent and a first binder, and the first binder comprises a polyrotaxane.

[0023] In a third aspect of the present application, an electrical device is provided, wherein the electrical device comprises the secondary battery provided in the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0025] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0026] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0027] Figure 3 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0028] Description of reference numerals:

[0029] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0030] Hereinafter, the embodiments of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

[0036] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0037] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0038] Secondary battery

[0039] A secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.

[0040] Generally, a secondary battery includes a positive electrode, a negative electrode and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode and the negative electrode.

[0041] Negative electrode

[0042] An embodiment of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a conductive coating disposed on at least one surface of the negative electrode current collector. The conductive coating comprises a conductive agent and a first binder, and the first binder comprises a polyrotaxane.

[0043] It can be understood that the polyrotaxane includes a linear molecule, a cyclic molecule threaded on the linear molecule, and a capping group connected to the linear molecule, and the capping group can prevent the cyclic molecule from sliding off the linear molecule. In other words, the linear molecule is an axis that passes through the cavity of the cyclic molecule, and the end of the axis has a capping group as a plug.

[0044] Without wishing to be limited to any theory, the negative electrode plate in the above-mentioned secondary battery of the present application has a conductive coating with polyrotaxane added as a binder. The polyrotaxane includes linear molecules and cyclic molecules threaded on the linear molecules, wherein the cyclic molecules can freely shuttle along the axis of the "linear molecules" and rotate around the axis. This ring sliding motion allows the polyrotaxane to have a large internal degree of freedom, giving the polymer network formed by the polyrotaxane extraordinary elasticity, which can better polymerize and bond the conductive agent. In addition, 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, which can improve the uniformity of the metal layer deposited on the surface of the conductive coating, effectively inhibit the growth of metal dendrites, and improve the cycle performance of the secondary battery without a negative electrode.

[0045] In addition, the conductive coating provided on the above-mentioned negative electrode plate can promote the uniform deposition of the metal layer on its surface, effectively inhibit the growth of metal dendrites, thereby improving the problem of metal dendrites piercing the isolation membrane to cause short circuit in the battery and induce thermal runaway, thereby improving the safety performance of the battery.

[0046] It is worth noting that in the secondary battery of the present application, during the preparation stage of the battery, the negative electrode sheet does not contain negative electrode active materials. During the continuous charging and discharging process, active ions such as sodium ions and lithium ions are repeatedly deposited or stripped on the conductive coating. It is understandable that these active ions are derived from the positive electrode active materials.

[0047] In some embodiments, the negative electrode plate in the secondary battery further includes a metal layer, which is disposed on the surface of the conductive coating away from the negative electrode current collector. The metal layer can be deposited by active ions in the positive electrode active material during the charge and discharge process of the secondary battery, and the metal layer does not need to be disposed during the preparation process of the negative electrode plate.

[0048] 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 may be a lithium-sodium composite metal layer.

[0049] The negative electrode current collector may be a conventional metal foil or a composite current collector. The composite current collector may be formed by placing a metal material on a polymer substrate. As an example, the negative electrode current collector may be copper foil, aluminum foil, etc.

[0050] In some embodiments, the cyclic molecules in the polyrotaxane include at least one of crown ethers, macrocyclic amides and cyclodextrins.

[0051] Among them, cyclodextrin has abundant -OH groups, and the nanochannels formed by hydrogen bonds between these -OH groups can provide a directional transmission path for active particles such as sodium ions 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.

[0052] Compared to cyclodextrins, crown ethers are composed of oxygen atoms connected by alkyl chains (CH 2 -CH 2 -O), sodium ions and lithium ions can be transported between or within the chain segment molecules through the instantaneous dynamic process of complexation / decomplexation with the ether oxygen atoms in the amorphous region of the chain segment, thereby achieving the directional transport of active ions such as sodium ions and lithium ions, and better promoting the uniform deposition of metals such as sodium and lithium on the conductive coating.

[0053] There is hydrogen bonding between cyclic amide molecules and linear molecules in macrocyclic amides. The formed nanochannels can provide directional transmission paths for active ions such as sodium ions and lithium ions, promoting the uniform deposition of metals such as sodium and lithium on the conductive coating.

[0054] Further, the parent ring structure of the macrocyclic amide is shown below:

[0055]

[0056] In some embodiments, the linear molecules in the polyrotaxane are linear polymers. As an example, the linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane and polyethylene polypropylene.

[0057] Furthermore, the end-capping group includes at least one of a sulfonate group and an amino group, wherein the sulfonate group not only can be used as an end-capping group, but also has good proton conductivity, and can improve the conductivity of the conductive coating.

[0058] It is understood that the greater the conductivity of the conductive coating, the smaller its sheet resistance. The sheet resistance can be measured by any known method.

[0059] Furthermore, the capping agent providing the capping group includes at least one of a sulfonate capping agent and an amino-containing capping agent.

[0060] As an example, the capping agent providing the capping group includes at least one of 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.

[0061] The polyrotaxane can be purchased commercially or prepared in-house. In some embodiments, the polyrotaxane can be prepared by the following preparation method:

[0062] The linear molecular compound and the cyclic molecular compound are mixed in a solvent, and a capping agent is added to carry out a capping reaction. Furthermore, the temperature of the capping reaction is 20 to 80°C.

[0063] Among them, the linear molecular compounds include but are not limited to at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane and polyethylene polypropylene; the cyclic molecular compounds include but are not limited to at least one of crown ethers, macrocyclic amides and cyclodextrins.

[0064] In some embodiments, the conductive coating further comprises a second binder. Optionally, the second binder comprises at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber and sodium alginate. The second binder and the first binder have better bonding properties when used in combination, thereby enabling the conductive agent to bond better.

[0065] More optionally, the second binder includes at least one of sodium carboxymethyl cellulose and polyacrylic acid.

[0066] Furthermore, in the total amount of the first binder and the second binder, the mass content of the polyrotaxane is 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%; it can be optionally 4% to 8%, or it can be a range consisting of any two of the above point values.

[0067] In some embodiments, the total amount of the first binder and the second binder accounts for 20% to 99% of the mass content in the conductive coating, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90%, 95%, 99%, and can be optionally 60% to 95%, or can be a range consisting of any two of the above point values.

[0068] 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.

[0069] In some of the embodiments, in the conductive coating, the mass content of the conductive agent is 1% to 80%; optionally 5% to 40%.

[0070] In some embodiments, the thickness of the conductive coating is 0.2 μm to 5 μm, such as 0.2 μm, 0.4 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm; it can be 0.6 μm to 2 μm, or it can be a range consisting of any two of the above point values. If the thickness of the conductive coating is too thin, it cannot serve 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.

[0071] In some embodiments, the surface density of the conductive coating is (0.2 mg to 5 mg) / 1540.25 mm 2 , optional: (0.5mg~3mg) / 1540.25mm 2 .

[0072] The surface density is calculated according to the following formula: Surface density = mass of conductive coating / area of ​​conductive coating. Among them, the mass of conductive coating = total mass of the electrode sheet containing conductive coating - mass of negative electrode current collector, which can be tested by conventional mass testing methods such as balance, and the area can be measured by electrode sheet size detection system.

[0073] The above-mentioned negative electrode sheet can be prepared by the following preparation method. The preparation method comprises the following steps S10 to S20:

[0074] S10, mixing the conductive agent, the first binder and the solvent, and optionally adding a second binder to obtain a primer slurry.

[0075] Further, the solvent used in S10 is water or an organic solvent, or a mixed solvent of the two, according to the requirements of the binder. As an example, the second binder is styrene-butadiene rubber, and the solvent may be water. As an example, the second binder is polyvinylidene fluoride, and the solvent may be an organic solvent, such as NMP (N-methylpyrrolidone).

[0076] S20, coating the primer slurry obtained in step S10 on at least one surface of the negative electrode current collector to form a conductive coating.

[0077] The secondary battery using the above-mentioned negative electrode plate is a metal battery.

[0078] Positive electrode

[0079] In a secondary battery, a positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0080] The positive electrode current collector may be a conventional metal foil or a composite current collector, wherein the composite current collector may be formed by placing a metal material on a polymer substrate. As an example, the positive electrode current collector may be an aluminum foil.

[0081] The specific type of the positive electrode active material can be any active material known in the art that can be used for a positive electrode sheet of a secondary battery, and those skilled in the art can select it according to actual needs.

[0082] As an example, the positive electrode active material may include a sodium ion active material, and the sodium ion active material may be a positive electrode active material for a sodium ion battery 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 a chemical formula of (NaxMA[MB(CN) 6 ]·zH 2 O, wherein MA and MB are transition metal ions, which are compounds composed of sodium, transition metals and cyanide, such as Na 4 Fe 2 (CN)6 , Na 4 Fe(CN) 6 , Na 1.72 MnFe 2 (CN) 6 , NaMnMn(CN) 6 , NaNiFe(CN) 6 etc.; oxide type, chemical formula NaxMO 2 , 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, which are relatively rich in resources, are the most commonly used. For example, NaCrO 2 , NaMnO 2 , NaMnO 2 , Na 0.61 Ti 0.48 Mn 0.52 O 2 , Na[Fe 0.5 Co 0.5 O 2 , NaMnO 2 , Na[Ni 0.25 Fe 0.5 Mn 0.25 O 2 etc.; and polyanion compound type, 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. It is composed of sodium, transition metals 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 NaMnFe 2 (PO 4 ) 6 , Na 2 MnP 2 O 7 , Na 3 V 2 (PO 4 ) 3 , Na 2 Fe 2 (SO 4 ) 3 , NaFePO 4 , Na 3 V 2 (PO 4 ) 2 F​3 、Na 4 Co 3 (PO 4 ) 2 (P 2 O 7 ).

[0083] As an example, the positive electrode active material may include a lithium ion active material, which includes, but is not limited to, one or more of lithium transition metal oxides, lithium 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 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 iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof. These materials can all be obtained commercially.

[0084] It is understood that in some examples, the positive electrode active material may include both sodium ion active material and lithium ion active material.

[0085] In some embodiments, the modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0086] Furthermore, the positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0087] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0088] As an example, the binder can be one or more of 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).

[0089] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. As an example, the solvent includes N-methylpyrrolidone.

[0090] Electrolytes

[0091] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The type of electrolyte can be selected according to the needs. For example, the electrolyte can be liquid, gel or all-solid.

[0092] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0093] In some of these embodiments, the electrolyte salt includes at least one of an electrolyte sodium salt and an electrolyte lithium salt.

[0094] Optionally, the electrolyte sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethylsulfonate, sodium difluorophosphate, sodium difluorooxalatoborate, sodium dioxalatoborate, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorodioxalatophosphate and sodium tetrafluorooxalatophosphate.

[0095] 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 trifluoromethylsulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0096] Further, in the electrolyte solution, the concentration of the electrolyte salt is 0.5 mol / L to 8 mol / L, and optionally 1 mol / L to 4 mol / L.

[0097] In some embodiments, the solvent in the electrolyte includes at least one of an ether solvent, an ester solvent, and a sulfone solvent.

[0098] Optionally, the solvent in the electrolyte includes an ether solvent. The ether solvent molecules in the electrolyte can construct a stable electrode / electrolyte interface on the metal surface of the negative electrode plate of the secondary battery, forming a stable solid electrolyte interface (SEI) and reducing electrochemical polarization.

[0099] 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.

[0100] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), propylene 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-propane sultone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP) and ethyl butyrate (EB).

[0101] As examples, the sulfone-based solvents include sulfolane, dimethyl sulfone, methyl ethyl sulfone, and dimethyl sulfoxide (DMSO).

[0102] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0103] Isolation film

[0104] In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode plate and the negative electrode plate to perform a separation function. The separator of the present application may be any known porous structure separator with good chemical stability and mechanical stability.

[0105] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0106] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0107] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0108] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0109] The shape of the secondary battery in the embodiment of the present application can be cylindrical, square or any other shape. Figure 1 The secondary battery 1 is a square structure as an example.

[0110] In some embodiments, reference Figure 2 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The above-mentioned gel electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0111] In addition, the present invention further provides an electrical device, which includes at least one of the secondary battery, battery module, or 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, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0112] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0113] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0114] As another example, the device may be a mobile phone, a tablet computer, a laptop computer, etc.

[0115] Unless otherwise specified, the above raw materials can be obtained from the market.

[0116] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0117] In order to better illustrate the present invention, the present invention is further described below in conjunction with the embodiments. The following are specific embodiments.

[0118] Description of the polyrotaxanes used in each example:

[0119] Cyclodextrin-type polyrotaxane: the cyclic molecule is cyclodextrin and the linear molecule is polyethylene glycol;

[0120] Crown ether polyrotaxane: the cyclic molecule is the crown ether, and the linear molecule is polyethylene glycol;

[0121] Macrocyclic amide polyrotaxane: the cyclic molecule is macrocyclic amide and the linear molecule is polyethylene glycol.

[0122] The capping agents corresponding to the capping groups of each polyrotaxane are shown in Table 1.

[0123] Example 1

[0124] 1) Preparation of negative electrode sheet

[0125] Add the binder and the conductive agent to water and stir to form a uniform conductive slurry. Coat the conductive slurry on the surface of the copper foil, transfer it to a vacuum drying oven and completely dry it to form a conductive coating, and then punch it to obtain the negative electrode sheet. Among them, in the total mass of the binder and the conductive agent, the total mass content of the binder is 60%; the binder is divided into the first binder polyrotaxane and the second binder polyacrylic acid; in the total amount of the binder, the mass content of the polyrotaxane is 5%. The thickness of the conductive coating is 0.8μm, and the surface density is 2mg / 1540.25mm 2 .

[0126] 2) Preparation of positive electrode

[0127] 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 Na 4 Fe 3 (PO 4 ) 2 P 2 O 7A uniformly dispersed slurry is prepared. The slurry is evenly coated on the surface of the aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained electrode is rolled and then punched to obtain a positive electrode.

[0128] 3) Preparation of electrolyte

[0129] In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), dissolving sodium hexafluorophosphate sodium salt in an organic solvent of ethylene glycol dimethyl ether and stirring evenly to obtain an electrolyte with a sodium hexafluorophosphate sodium salt concentration of 1.0 mol / L, i.e., the electrolyte of Example 1.

[0130] 4) Isolation film

[0131] Polypropylene film is used as the isolation film.

[0132] 5) Preparation of sodium battery

[0133] The positive electrode sheet, separator, and negative electrode current collector are stacked in order, with the separator located between the positive electrode and the negative electrode current collector to play a role of isolation, and the electrolyte is added to assemble into a laminated battery.

[0134] Embodiments 2 to 20

[0135] It is basically the same as Example 1, except that some parameters shown in Table 1 are different.

[0136] Specifically, compared with Example 1, the difference between Examples 2 to 5 is only that the amount of polyrotaxane added to the conductive coating is different, specifically, the mass proportion of the polyrotaxane in the total binder is different;

[0137] Compared with Example 1, the difference between Examples 6 and 7 is only that the types of end-capping agents in the polyrotaxane are different;

[0138] Compared with Example 1, the difference between Examples 8 to 10 is that other types of binders of equal mass are used to replace the polyacrylic acid in Example 1;

[0139] Compared with Examples 1 and 8 to 10, the only difference between Examples 11 to 14 is that the cyclodextrin polyrotaxane is replaced by the crown ether polyrotaxane of the same mass;

[0140] Compared with Examples 1 and 8 to 10, respectively, the only difference between Examples 15 to 18 is that the cyclodextrin polyrotaxane is replaced by a macrocyclic amide polyrotaxane of equal mass;

[0141] Compared with Example 1, the only difference between Examples 19 and 20 is that the thickness and surface density of the conductive coating are different;

[0142] Compared with Example 1, the only difference between Examples 21 and 22 is that other types of conductive agents of equal mass are used to replace the conductive agent in Example 1.

[0143] Comparative Example 1

[0144] 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 plate.

[0145] Comparative Example 2

[0146] The method is basically the same as Example 1, except that the polyrotaxane is omitted from the binder and replaced by polyacrylic acid of the same mass.

[0147] Comparative Examples 3 to 5

[0148] It is basically the same as Example 1, except that a mixture of equal mass is used to replace the polyrotaxane in Example 1, as shown in Table 1.

[0149] The following is a battery performance test.

[0150] 1) Coulomb efficiency

[0151] Taking Example 1 as an example, the prepared sodium battery is charged to 3.7V at a constant current of 1 / 3C at 25°C, and then charged at a constant voltage of 3.7V until the current drops to 0.05C to obtain the first charging capacity (Cc1); then discharged to 2.5V at a constant current of 1 / 3C to obtain the first discharge capacity (Cd1), and the coulombic efficiency of the sodium battery is calculated according to the following formula.

[0152] Sodium battery coulombic efficiency = first discharge capacity (Cd1) / first charge capacity (Cc1)

[0153] The testing processes of other embodiments and comparative examples are the same as above.

[0154] 2) Capacity retention rate

[0155] Taking Example 1 as an example, the sodium battery is charged to 3.7V at a constant current of 1C at 25°C, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the first cycle discharge capacity (Cd1); the charging and discharging are repeated to the nth cycle, and the discharge capacity of the sodium battery after n cycles is obtained, which is recorded as Cdn, and the sodium battery capacity retention rate is calculated according to the following formula:

[0156] Capacity retention rate = discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd1).

[0157] The testing processes of other embodiments and comparative examples are the same as above.

[0158] 3) Sodium dendrite level

[0159] The sodium battery after 100 cycles was placed in an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm) was disassembled, and a metal layer, namely a sodium metal layer, was clearly deposited on the surface of the negative electrode. Based on the morphology of the sodium metal layer on the surface of the negative electrode, the level of sodium dendrite precipitation in the sodium metal layer was determined by visual inspection. The evaluation criteria are as follows:

[0160] Level 0 sodium precipitation: The sodium metal layer on the entire surface of the negative electrode is evenly deposited (dense), with no uneven areas visible to the naked eye;

[0161] Level 1 sodium precipitation: The maximum area of ​​a single uneven uniform sodium deposition area in the sodium metal layer on the entire negative electrode surface is ≤ 2*2mm 2 , the number of sodium uneven deposition areas of the sodium metal layer on the surface of the entire negative electrode plate is ≤5;

[0162] 2nd level sodium precipitation: 2*2mm 2 <The maximum area of ​​a single sodium uneven deposition area of ​​the sodium metal layer on the entire negative electrode surface ≤5*5mm 2 , the number of sodium uneven deposition areas of the sodium metal layer on the surface of the entire negative electrode plate is ≤5;

[0163] Level 3 sodium precipitation: Sodium precipitation occurs and the above-mentioned judgment conditions of levels 0 to 2 are not met.

[0164] Table 1

[0165]

[0166]

[0167] The following is the film resistance test of the negative electrode.

[0168] Test method: Use Hioki BT23562 internal resistance tester to test the diaphragm resistance R of the negative electrode. Clamp the upper and lower sides of the negative electrode between the two conductive terminals of the tester and apply pressure to fix it. The diameter of the conductive terminals is 14mm and the applied pressure is 25MPa. The diaphragm resistance of the negative electrode is measured.

[0169] Test object: negative electrode sheets prepared in Example 1 and Examples 6-7 (same size and shape).

[0170] The test results of the film resistance of the negative electrode are shown in Table 2:

[0171] Table 2

[0172] Group Example 1 Example 6 Example 7 Diaphragm resistor 58.9mΩ 76.5mΩ 89.2mΩ

[0173] It can be seen from Table 1 that, compared with the comparative examples, the addition of polyrotaxane as a binder in the embodiments of the present application not only improves the coulombic efficiency and the cycle capacity retention rate, but also greatly improves the degree of sodium precipitation.

[0174] From a comparison of Examples 1 to 5, it can be seen that, when other conditions remain unchanged, the mass proportion of polyrotaxane in the total binder is in the range of 2% to 10%, good coulombic efficiency and cycle capacity retention rate are achieved, and there is no obvious sodium precipitation problem; further, when the mass proportion of polyrotaxane in the total binder is in the range of 4% to 8%, the coulombic efficiency and cycle capacity retention rate of the battery are better, and the sodium precipitation level is lower.

[0175] From the comparison between Example 1 and Examples 6 to 7, it can be seen that different types of end-capping agents in the polyrotaxane all achieved good coulombic efficiency and cycle capacity retention rate, and there was no obvious sodium precipitation problem; further, from Table 2, it can be seen that the end-capping agent in the polyrotaxane is preferably sodium 3,5-ditrifluoromethylbenzenesulfonate, which has good proton conductivity and can improve the conductivity of the conductive coating.

[0176] From the comparison among Examples 1, 8 to 10, 11 to 14, and 15 to 18, it can be seen that different types of polyrotaxanes adopt different second binders, all of which achieve good coulombic efficiency and cycle capacity retention rate, and have no obvious sodium precipitation problem; further, when the second binder adopts polyacrylic acid or sodium carboxymethyl cellulose, the coulombic efficiency and cycle capacity retention rate of the obtained battery are better.

[0177] From the comparison between Example 1 and Examples 19 to 20, it can be seen that the different thicknesses and surface densities of the conductive coating all achieve good coulombic efficiency and cycle capacity retention rate, and there is no obvious sodium precipitation problem; further, when the thickness of the conductive coating is within the range of 0.6 to 2 μm, the coulombic efficiency and cycle capacity retention rate of the battery are better.

[0178] Comparison of Example 1 and Examples 21 to 22 shows that the use of different types of conductive agents can achieve good coulombic efficiency and cycle capacity retention rate, and there is no obvious sodium precipitation problem.

[0179] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0180] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings can be used to interpret the content of the claims.

Claims

1. A secondary battery, It is characterized in that The invention comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a conductive coating disposed on at least one surface of the negative electrode current collector, wherein the conductive coating comprises a conductive agent and a first binder, and the first binder comprises a polyrotaxane.

2. The secondary battery according to claim 1, It is characterized in that The negative electrode plate further includes a metal layer, and the metal layer is disposed on a surface of the conductive coating layer away from the negative electrode current collector.

3. The secondary battery according to claim 2, It is characterized in that The metal layer is a metal layer formed of at least one element selected from the group consisting of sodium, lithium and potassium.

4. The secondary battery according to claim 1, It is characterized in that The polyrotaxane includes a linear molecule, a cyclic molecule inserted on the linear molecule, and a capping group connected to the linear molecule; Wherein, the cyclic molecule comprises at least one of crown ether, macrocyclic amide and cyclodextrin; and / or, The linear molecules include at least one of polyethylene glycol, polypropylene glycol, polyisoprene, polyisobutylene, polybutadiene, polytetrahydrofuran, polyacrylate, polydimethylsiloxane and polyethylene-based polypropylene.

5. The secondary battery according to claim 4, It is characterized in that The end-capping group includes at least one of a sulfonate group and an amino group; Optionally, the capping agent providing the capping group includes at least one of a sulfonate capping agent and an amino-containing capping agent; more optionally, 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, It is characterized in that The conductive coating further includes a second binder; Optionally, the second binder includes at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyvinylidene fluoride, styrene-butadiene rubber and sodium alginate; More optionally, the second binder includes at least one of sodium carboxymethyl cellulose and polyacrylic acid.

7. The secondary battery according to claim 6, It is characterized in that In the total amount of the first binder and the second binder, the mass content of the polyrotaxane is 2% to 10%, and can be optionally 4% to 8%.

8. The secondary battery according to any one of claims 1 to 5 and 7, It is 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 5% to 40%.

9. The secondary battery according to any one of claims 1 to 5 and 7, It is characterized in that The thickness of the conductive coating is 0.2 μm to 5 μm, and can be optionally 0.6 μm to 2 μm.

10. The secondary battery according to any one of claims 1 to 5 and 7, It is characterized in that The surface density of the conductive coating is (0.2mg-5mg) / 1540.25mm 2 , optional: (0.5mg~3mg) / 1540.25mm 2 .

11. A negative electrode sheet, It is characterized in that The invention comprises a negative electrode current collector and a conductive coating disposed on at least one surface of the negative electrode current collector, wherein the conductive coating comprises a conductive agent and a first binder, and the first binder comprises a polyrotaxane.

12. An electrical device, It is characterized in that The electric device comprises the secondary battery according to any one of claims 1 to 10.

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