Secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer contains a sodium ion active material. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer contains a carbon material. The electrolyte is arranged between the positive electrode sheet and the negative electrode sheet, and the electrolyte contains a sodium salt of boric acid.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, specifically to a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Sodium-ion batteries share similar working principles and manufacturing processes with lithium-ion batteries. Compared to lithium-ion batteries, sodium-ion batteries primarily use sodium salts as electrode materials, offering advantages such as lower cost and abundant resources compared to lithium sources, making them a promising alternative to lithium-ion batteries. However, sodium-ion batteries suffer from poor cycle performance, hindering their practical application. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery, a battery module, a battery pack, and an electrical device that can suppress sodium dendrite growth and improve the cycle performance of the secondary battery.

[0004] One aspect of this application provides a secondary battery, comprising:

[0005] A positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer contains sodium ion active material;

[0006] A negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector; the negative electrode film layer contains a carbon material; and

[0007] An electrolyte is disposed between the positive electrode and the negative electrode, and the electrolyte contains a sodium borate salt.

[0008] In the technical solution of the above-described embodiments of this application, the positive electrode active material layer contains sodium ion active material, and the negative electrode has a negative electrode film layer containing carbon material. The electrolyte contains sodium borate salt. The negative electrode film layer containing carbon material can provide sodium metal deposition sites. The sodium borate salt in the electrolyte can form an SEI film on the surface of the negative electrode. The negative electrode and the electrolyte work together to induce uniform sodium deposition, inhibit sodium dendrite growth, and thus greatly improve the cycle performance of the above-described secondary battery.

[0009] In some embodiments, the carbon material includes at least one of carbon nanotubes, graphene, hard carbon, and carbon black.

[0010] In some embodiments, the thickness of the negative electrode film is 0.5 μm to 15 μm;

[0011] Optionally, the thickness of the negative electrode film is 1 μm to 8 μm;

[0012] Optionally, the thickness of the negative electrode film is 4 μm to 7 μm.

[0013] By controlling the thickness of the negative electrode film within the above range, the surface of the negative electrode sheet has more sodium metal nucleation sites, and the overpotential for sodium nucleation on the negative electrode sheet is smaller, which is beneficial to suppressing the growth of sodium dendrites.

[0014] In some embodiments, the areal density of the negative electrode film is 0.6 g / m³. 2 ~13g / m 2 ;

[0015] Optionally, the areal density of the negative electrode film is 1 g / m³. 2 ~8g / m 2 .

[0016] By controlling the areal density of the negative electrode film within the above range, the surface of the negative electrode sheet has more sodium metal nucleation sites, and the overpotential for sodium nucleation on the negative electrode sheet is smaller, which is beneficial to suppressing the growth of sodium dendrites.

[0017] In some embodiments, the carbon material in the negative electrode film layer has a mass percentage of 60% to 98%;

[0018] Optionally, the carbon material in the negative electrode film layer has a mass percentage of 66% to 75%.

[0019] In some embodiments, the negative electrode film layer further contains a polymer binder;

[0020] Optionally, the polymer binder includes at least one of sodium cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, butadiene acrylate rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

[0021] In some embodiments, the polymer binder comprises 2% to 40% by mass in the negative electrode film layer;

[0022] Optionally, the polymer binder comprises 25% to 34% by mass in the negative electrode film layer.

[0023] In some embodiments, the sodium borate salt includes at least one of sodium difluoroborate, sodium tetrafluoroborate, sodium dioxalate borate, sodium difluorooxalate borate, sodium tetraphenylborate, sodium tetracyanoborate, sodium tetra(trifluoromethyl)borate, sodium bis(trifluoromethyl)difluoroborate, sodium pentafluoroethyl trifluoroborate, sodium dicyanoborate, sodium methoxytricyanoborate, sodium ethoxytricyanoborate, sodium tetramethoxyborate, sodium tetraethoxyborate, and sodium cyanotris(2,2,2-trifluoroethyl)borate.

[0024] Optionally, the sodium borate salt includes at least one of sodium difluorooxalate borate and sodium dioxalate borate.

[0025] The borate anions of the aforementioned sodium borate salts work synergistically with the negative electrode film layer of the negative electrode sheet to form a solid electrolyte interface (SEI) film on the surface of the negative electrode sheet, repairing the cracks formed during deposition and stripping, improving sodium deposition kinetics, and promoting uniform sodium deposition.

[0026] In some embodiments, the electrolyte is a liquid electrolyte;

[0027] Optionally, the solvent in the electrolyte includes ether solvents.

[0028] In some embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.

[0029] Optionally, the ether solvent includes ethylene glycol dimethyl ether.

[0030] Ether solvent molecules can build a stable electrode-electrolyte interface on the surface of the negative electrode, forming a stable solid electrolyte interphase (SEI) film and reducing electrochemical polarization.

[0031] In some embodiments, the molar concentration of the sodium borate salt in the electrolyte is 0.05 mol / L to 8 mol / L;

[0032] Optionally, the molar concentration of the sodium borate salt is 0.1 mol / L to 2 mol / L.

[0033] Typically, the molar concentration of sodium salts in electrolytes ranges from 0.5 mol / L to 8 mol / L. The aforementioned sodium borate salts can be used as main salts or additives in electrolytes.

[0034] In some embodiments, the electrolyte further includes at least one of sodium perchlorate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0035] In some embodiments, the overpotential of the secondary battery is less than or equal to 30mV. With an overpotential less than or equal to 30mV, the sodium metal deposition uniformity is better, effectively suppressing lithium dendrite growth and improving the cycle performance of the secondary battery.

[0036] Secondly, this application also provides a battery module comprising the secondary battery as described above.

[0037] Thirdly, this application also provides a battery pack comprising the battery module as described above.

[0038] Fourthly, this application also provides an electrical device, which includes at least one of the secondary battery, the battery module, and the battery pack described above, wherein the secondary battery is used to provide electrical energy.

[0039] Details of one or more embodiments of this application are set forth in the following drawings and description, and other features, objects and advantages of this application will become apparent from the specification, drawings and claims. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0041] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown;

[0042] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0043] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0044] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0045] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to an embodiment of this application.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device.

[0048] To better describe and illustrate embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the currently described embodiments and / or examples, or the best mode of these inventions as currently understood. Detailed Implementation

[0049] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] This application provides a secondary battery, and a battery module, battery pack, and electrical device using the secondary battery. This secondary battery is suitable for various battery-powered electrical devices, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, electric cars, ships, and spacecraft, including aircraft, rockets, space shuttles, and spacecraft.

[0052] The secondary battery, battery module, battery pack, and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0053] In one embodiment of this application, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode.

[0054] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; the negative electrode film layer contains carbon material. An electrolyte is disposed between the positive and negative electrode sheets, and the electrolyte contains a sodium borate salt.

[0055] Typically, active sodium ions on the positive electrode insert and extract back and forth between the positive and negative electrodes. During the charging process of a secondary battery, an electrochemical reaction occurs at the negative electrode, where sodium ions gain electrons and are reduced to sodium metal. Sodium metal directly serves as the active material of the negative electrode, thus exhibiting high energy density. However, uneven deposition of sodium metal on the surface of the negative electrode can easily lead to the formation of sodium dendrites, thereby affecting the cycle performance of the secondary battery.

[0056] In the technical solution of the above-described embodiments of this application, the positive electrode active material layer contains sodium ion active material, and the negative electrode has a negative electrode film layer containing carbon material. The electrolyte contains sodium borate salt. The negative electrode film layer containing carbon material can provide sodium metal deposition sites. The sodium borate salt in the electrolyte can form an SEI film on the surface of the negative electrode. The negative electrode and the electrolyte work together to induce uniform sodium deposition, inhibit sodium dendrite growth, and thus greatly improve the cycle performance of the above-described secondary battery.

[0057] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0058] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0059] In some embodiments, the carbon material includes at least one of carbon nanotubes, graphene, hard carbon, and carbon black.

[0060] In some embodiments, the thickness of the negative electrode film is 0.5 μm to 15 μm. Optionally, the thickness of the negative electrode film is 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, or 15 μm. Further, the thickness of the negative electrode film is 1 μm to 8 μm or 4 μm to 7 μm. Controlling the thickness of the negative electrode film within the above range results in a greater number of sodium nucleation sites on the surface of the negative electrode, leading to a lower sodium nucleation overpotential and thus inhibiting sodium dendrite growth. Excessive thickness of the negative electrode film reduces the energy density of the secondary battery; conversely, insufficient thickness results in fewer sodium nucleation sites on the surface of the negative electrode, leading to a poorer inhibition of sodium dendrite growth.

[0061] In some embodiments, the areal density of the negative electrode film is 0.6 g / m³. 2 ~13g / m 2 Optionally, the areal density of the negative electrode film is 0.6 g / m³. 2 1g / m 2 2g / m 2 4g / m 2 5g / m 26g / m 2 8g / m 2 10g / m 2 12g / m 2 Or 13g / m 2 Furthermore, the areal density of the negative electrode film is 1 g / m³. 2 ~8g / m 2 By controlling the areal density of the negative electrode film within the above-mentioned range, the surface of the negative electrode sheet has more sodium metal nucleation sites, and the overpotential for sodium nucleation on the negative electrode sheet is smaller, which is beneficial to suppressing the growth of sodium dendrites.

[0062] In some embodiments, the mass percentage of carbon material in the negative electrode film is 60% to 98%. Optionally, the mass percentage of carbon material in the negative electrode film is 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98%. Further, the mass percentage of carbon material in the negative electrode film is 66% to 75%.

[0063] In some embodiments, the negative electrode film layer further comprises a polymer binder. In some embodiments, the polymer binder includes at least one of sodium cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, butadiene acrylate rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

[0064] In some embodiments, the polymer binder constitutes 2% to 40% of the negative electrode film by mass. Optionally, the polymer binder constitutes 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40% of the negative electrode film by mass. Further, the polymer binder constitutes 25% to 34% of the negative electrode film by mass.

[0065] In some implementations, after the initial charge, the negative electrode also includes a layer of metallic sodium. The metallic sodium layer is deposited on the surface of the negative electrode film.

[0066] Positive electrode sheet

[0067] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0068] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0069] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on the polymer substrate. The polymer substrate includes substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0070] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in batteries. As an example, the sodium-ion active material may include at least one of the following: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0071] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0072] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0073] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0074] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO)y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0075] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤l).

[0076] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0077] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0078] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0080] electrolytes

[0081] The electrolyte acts as a conductor of ions between the positive and negative electrodes. In this application, the electrolyte contains a sodium borate salt. There are no specific limitations on the type of electrolyte in this application; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0082] In some embodiments, the sodium borate salts include at least one of sodium difluoroborate, sodium tetrafluoroborate (NaBF4), sodium dioxalate borate, sodium difluorooxalate borate, sodium tetraphenylborate (NaB(C6H5)4), sodium tetracyanoborate, sodium tetra(trifluoromethyl)borate, sodium bis(trifluoromethyl)difluoroborate, sodium pentafluoroethyl trifluoroborate, sodium dicyanoborate, sodium methoxytricyanoborate, sodium ethoxytricyanoborate, sodium tetramethoxyborate, sodium tetraethoxyborate, and sodium cyanotris(2,2,2-trifluoroethyl)borate.

[0083] Furthermore, the sodium borate salts include at least one of sodium difluorooxalate borate and sodium dioxalate borate.

[0084] The borate anions of the aforementioned sodium borate salts work synergistically with the negative electrode film to form a solid electrolyte interphase (SEI) film on the surface of the negative electrode. This repairs cracks formed during deposition and stripping, improves sodium deposition kinetics, and promotes uniform sodium deposition. Furthermore, fluorine-containing sodium borate salts can also form a NaF-containing SEI film on the surface of the negative electrode, further improving deposition kinetics.

[0085] In some embodiments, the electrolyte is a liquid electrolyte. Further, the solvent in the electrolyte includes ether solvents. Ether solvent molecules can build a stable electrode-electrolyte interface on the surface of the negative electrode, forming a stable solid electrolyte interphase (SEI) film and reducing electrochemical polarization.

[0086] In some embodiments, the ether solvent includes at least one selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether. Further, the ether solvent includes ethylene glycol dimethyl ether.

[0087] In some embodiments, the molar concentration of sodium borate in the electrolyte is 0.05 mol / L to 8 mol / L. Optionally, the molar concentration of sodium borate is 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, or 8 mol / L. Further, the molar concentration of sodium borate is 0.1 mol / L to 2 mol / L.

[0088] Typically, the molar concentration of sodium salt in an electrolyte is 0.5 mol / L to 8 mol / L. In this application, sodium borate salts can be used as the main salt or additive in the electrolyte.

[0089] In some embodiments, the electrolyte further includes at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), and sodium bis(trifluoromethanesulfonyl)imide (Na[(CF3SO2)2N]).

[0090] In some embodiments, the solvent in the electrolyte further includes at least one of ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, γ-butyrolactone, 1,3-propanesulfonate lactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and dimethyl sulfoxide.

[0091] 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.

[0092] Separating membrane

[0093] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0094] 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, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In some embodiments, the overpotential of the secondary battery is less than or equal to 30mV. With an overpotential of less than or equal to 30mV, the sodium metal deposition uniformity is better, effectively suppressing lithium dendrite growth and improving the cycle performance of the secondary battery.

[0096] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0097] 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.

[0098] 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.

[0099] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0100] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0101] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0102] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0103] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0104] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0105] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0106] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of 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.

[0107] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0108] Figure 6 This is an example of an electrical device 6. This electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0109] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0110] Example

[0111] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0112] Example 1:

[0113] Positive electrode preparation: 10 wt% polyvinylidene fluoride (PVDF) binder was fully dissolved in N-methylpyrrolidone (NMP), and 10 wt% carbon black conductive agent and 80 wt% positive electrode active material (Na4Fe3(PO4)2(P2O7)) were added to form a uniformly dispersed slurry. The slurry was uniformly coated onto 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.

[0114] Negative electrode preparation: 4 wt% hard carbon and 1.6 wt% sodium carboxymethyl cellulose (CMC-Na) polymer binder were added to water and stirred to form a uniform slurry. The slurry was coated onto the surface of copper foil, then transferred to a vacuum drying oven for complete drying, followed by punching to obtain the negative electrode sheet. The thickness of the negative electrode film on the negative electrode sheet was 5 μm, and the areal density was 5.6 g / m³. 2 .

[0115] Electrolyte preparation: Sodium difluorooxalate borate (NaDFOB) was dissolved in the organic solvent ethylene glycol dimethyl ether in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm) and stirred until homogeneous to obtain an electrolyte with a NaDFOB concentration of 1.5 mol / L.

[0116] Separator membrane: Polypropylene membrane is used as the separator membrane.

[0117] Secondary battery preparation: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative current collectors to provide isolation. Electrolyte is then injected to assemble the secondary battery.

[0118] Examples 2-5:

[0119] The difference between Examples 2-5 and Example 1 is that the hard carbon in the negative electrode sheet of Example 1 is replaced with other carbon materials. The carbon materials used in the negative electrode sheets of Examples 2-5 are recorded in Table 1.

[0120] Examples 6-9:

[0121] The difference between Examples 6-9 and Example 1 lies in the thickness and areal density of the negative electrode film. The thickness and areal density of the negative electrode film in Examples 6-9 are recorded in Table 1.

[0122] Examples 10-11:

[0123] The difference between Examples 10 and 11 and Example 1 lies in the different mass percentages of hard carbon in the negative electrode film. The mass percentages of hard carbon in the negative electrode film of Examples 10 and 11 are recorded in Table 1. The ratio of hard carbon to polymer binder during the preparation of the negative electrode sheet can be adjusted according to the mass ratio in Table 1.

[0124] Examples 12-18:

[0125] The difference between Examples 12-18 and Example 1 lies in the electrolyte composition. The electrolyte compositions of Examples 12-18 are recorded in Table 1.

[0126] Comparative Example 1:

[0127] The difference between Comparative Example 1 and Example 1 is that the negative electrode sheet is a copper current collector without a negative electrode film layer.

[0128] Comparative Example 2:

[0129] The difference between Comparative Example 2 and Comparative Example 1 is that NaDFOB in the electrolyte is replaced with NaPF6.

[0130] Comparative Example 3:

[0131] The difference between Comparative Example 3 and Example 1 is that NaDFOB in the electrolyte is replaced with NaPF6.

[0132] The compositions of the secondary batteries in Examples 1-18 and Comparative Examples 1-3 are recorded in Table 1.

[0133] Table 1. Composition of the secondary batteries in Examples 1-18 and Comparative Examples 1-3

[0134]

[0135]

[0136] Test section:

[0137] Overpotential test:

[0138] The prepared secondary battery was charged to 100μA at a constant current of 0.1C at 25℃, and the most negative potential obtained during the process was recorded as the overpotential.

[0139] Coulomb efficiency test:

[0140] The prepared secondary battery was charged to 3.7V at 25℃ 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 secondary battery was calculated according to the following formula.

[0141] Coulombic efficiency of a secondary battery = initial discharge capacity (Cd1) / initial charge capacity (Cc1).

[0142] Capacity retention test:

[0143] The secondary 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, yielding the initial discharge capacity (Cd1). This charging and discharging process is repeated until the nth cycle, yielding the discharge capacity of the secondary battery after n cycles, denoted as Cdn. The capacity retention rate of the secondary battery is then calculated using the following formula:

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

[0145] Sodium dendrite formation test:

[0146] After 100 cycles, the secondary battery was disassembled in a glove box (argon atmosphere, H2O < 0.1 ppm, O2 < 0.1 ppm). The surface morphology of the negative electrode was observed with the naked eye to determine whether sodium dendrites were formed.

[0147] The test results of the secondary batteries in Examples 1-18 and Comparative Examples 1-3 are recorded in Table 2.

[0148] Table 2 Electrochemical performance of secondary batteries in Examples 1-18 and Comparative Examples 1-3

[0149]

[0150] As can be seen from the data in Table 2, compared with the secondary batteries of Comparative Examples 1-3, the secondary batteries of Examples 1-18 have lower overpotentials (15mV-25mV), which is beneficial to improving the uniformity of sodium deposition on the negative electrode surface. The coulombic efficiency of the secondary batteries of Examples 1-18 is 88.7%-96.0%, and the capacity retention rate after 100 cycles is 81.6%-88.5%. After 100 cycles, no sodium dendrites are visible to the naked eye on the surface of the negative electrode. It can be seen that the secondary batteries of Examples 1-18 can significantly suppress sodium dendrite growth during cycling, and have high coulombic efficiency and good cycle performance.

[0151] Comparative Example 2 is a conventional sodium-ion battery with an overpotential of 40 mV, a coulombic efficiency of 81.1%, and a capacity retention of 71.7% after 100 cycles. Severe sodium dendrite formation was observed after 100 cycles. Comparative Example 1, based on Comparative Example 2, replaced the sodium salt with NaDFOB. The overpotential of the secondary battery decreased slightly, the coulombic efficiency was 83.2%, and the capacity retention after 100 cycles was 75.9%. While the coulombic efficiency and cycle performance were slightly improved, severe lithium dendrite formation remained. Comparative Example 3 differs from Example 1 in that the sodium salt in the electrolyte is NaPF6. Compared to the secondary battery in Comparative Example 1, the coulombic efficiency and cycle performance of the secondary battery in Comparative Example 3 are somewhat improved. However, compared to Example 1, the overpotential, coulombic efficiency, and cycle performance of the secondary battery in Comparative Example 3 are significantly deteriorated, and slight sodium dendrite formation was observed after 100 cycles.

[0152] 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.

[0153] The embodiments described above are merely illustrative of several implementation methods of this application, 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 this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A secondary battery, characterized in that, include: A positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer contains sodium ion active material; A negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; the negative electrode film layer contains carbon material, the thickness of the negative electrode film layer is 4 μm to 15 μm, and the areal density of the negative electrode film layer is 4 g / m³. 2 ~13g / m 2 ;and An electrolyte is disposed between the positive electrode and the negative electrode, and the electrolyte contains a sodium borate salt.

2. The secondary battery according to claim 1, characterized in that, The carbon material includes at least one of carbon nanotubes, graphene, hard carbon, and carbon black.

3. The secondary battery according to claim 1, characterized in that, The thickness of the negative electrode film is 4 μm to 8 μm.

4. The secondary battery according to claim 3, characterized in that, The thickness of the negative electrode film is 4 μm to 7 μm.

5. The secondary battery according to claim 1, characterized in that, The areal density of the negative electrode film is 4 g / m³. 2 ~8g / m 2 .

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The carbon material in the negative electrode film layer has a mass percentage of 60% to 98%.

7. The secondary battery according to claim 6, characterized in that, The carbon material in the negative electrode film layer has a mass percentage of 66% to 75%.

8. The secondary battery according to any one of claims 1 to 5, characterized in that, The negative electrode film layer also contains a polymer binder.

9. The secondary battery according to claim 8, characterized in that, The polymer binder includes at least one of sodium cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, butadiene acrylate rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

10. The secondary battery according to claim 8, characterized in that, The polymer binder has a mass percentage of 2% to 40% in the negative electrode film layer.

11. The secondary battery according to claim 10, characterized in that, The polymer binder has a mass percentage of 25% to 34% in the negative electrode film layer.

12. The secondary battery according to any one of claims 1 to 5, characterized in that, The sodium borate salts include at least one of sodium difluoroborate, sodium tetrafluoroborate, sodium dioxalate borate, sodium difluorooxalate borate, sodium tetraphenylborate, sodium tetracyanoborate, sodium tetra(trifluoromethyl)borate, sodium bis(trifluoromethyl)difluoroborate, sodium pentafluoroethyl trifluoroborate, sodium dicyanoborate, sodium methoxytricyanoborate, sodium ethoxytricyanoborate, sodium tetramethoxyborate, sodium tetraethoxyborate, and sodium cyanotris(2,2,2-trifluoroethyl)borate.

13. The secondary battery according to claim 12, characterized in that, The sodium borate salts include at least one of sodium difluorooxalate borate and sodium dioxalate borate.

14. The secondary battery according to any one of claims 1 to 5, characterized in that, The electrolyte is an electrolyte solution.

15. The secondary battery according to claim 14, characterized in that, The solvent in the electrolyte includes ether solvents.

16. The secondary battery according to claim 15, characterized in that, The ether solvents include at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.

17. The secondary battery according to claim 16, characterized in that, The ether solvents include ethylene glycol dimethyl ether.

18. The secondary battery according to any one of claims 15 to 17, characterized in that, In the electrolyte, the molar concentration of the sodium borate salt is 0.05 mol / L to 8 mol / L.

19. The secondary battery according to claim 18, characterized in that, The molar concentration of the sodium borate salt is 0.1 mol / L to 2 mol / L.

20. The secondary battery according to any one of claims 1 to 5, characterized in that, The electrolyte also includes at least one of sodium perchlorate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

21. The secondary battery according to any one of claims 1 to 5, characterized in that, The overpotential of the secondary battery is less than or equal to 30 mV.

22. A battery module, characterized in that, It includes the secondary battery as described in any one of claims 1 to 21.

23. A battery pack, characterized in that, It includes the battery module as described in claim 22.

24. An electrical appliance, characterized in that, The electrical device includes at least one of the secondary battery as described in any one of claims 1 to 21, the battery module as described in claim 22, and the battery pack as described in claim 23, wherein the secondary battery is used to provide electrical energy.

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