Sodium-ion battery electrolyte, sodium-ion battery comprising the electrolyte and electronic device

Abstract

The application relates to the field of electrochemistry, in particular to a sodium ion battery electrolyte, a sodium ion battery containing the electrolyte and an electronic device. The electrolyte contains a sodium salt, an ether solvent and an additive; the additive comprises a sulfur-based additive and / or a nitrogen-based additive; the sulfur-based additive comprises at least one of 1,3-propane sultone, ethylene sulfite and propylene-1,3-sulfonic acid lactone; the nitrogen-based additive comprises at least one of ethyl nitrate, propyl nitrate, sodium nitrate, potassium nitrate and bismuth nitrate; the electrolyte of the application is an ether-based electrolyte obtained through the synergistic cooperation of a sodium salt, an ether solvent and a sulfur-based additive and / or a nitrogen-based additive, which can be used as a negative electrode-free sodium ion battery electrolyte, has high discharge capacity, excellent cycle performance and rate performance and exhibits good electrochemical performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a sodium-ion battery electrolyte, a sodium-ion battery containing the electrolyte, and an electronic device. Background Technology

[0002] The application of ether-based electrolytes in sodium-ion batteries is one of the important areas of battery technology development today. With the continuous growth of energy demand and increasing environmental pressure, people have placed higher demands on battery performance, efficiency, and environmental friendliness. Among these, sodium-ion batteries have received widespread attention due to their high energy density, low cost, and environmental friendliness. Summary of the Invention

[0003] The purpose of this application is to provide a sodium-ion battery electrolyte, a sodium-ion battery containing the electrolyte, and an electronic device. According to a first aspect of this application, this application provides a sodium-ion battery electrolyte, the electrolyte containing sodium salt, ether solvent and additives; the additives include sulfur-based additives and / or nitrogen-based additives; the sulfur-based additives include at least one of 1,3-propanesulfonyl lactone, ethylene sulfate, and propenyl-1,3-sulfonyl lactone. The nitrogen-based additives include at least one of ethyl nitrate, propyl nitrate, sodium nitrate, potassium nitrate, and bismuth nitrate. In some embodiments of this application, the concentration of the sodium salt in the ether-based electrolyte is 0.1 mol / L to 0.8 mol / L. In some embodiments of this application, the volume fraction of the ether solvent in the electrolyte is 10% to 90%.

[0004] In some embodiments of this application, the additive accounts for 0.02% to 1.5% of the total mass of the electrolyte.

[0005] In some embodiments of this application, the sodium salt includes NaPF6 and NaBF4, and the molar ratio of NaPF6 and NaBF4 is (7-9):1.

[0006] In some embodiments of this application, the ether solvent includes diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, wherein the volume ratio of diethylene glycol dimethyl ether to tetraethylene glycol dimethyl ether is (8-10):1.

[0007] In some embodiments of this application, the additives include sulfur-based additives and nitrogen-based additives, wherein the sulfur-based additives account for 0.05% to 2% of the total mass of the electrolyte, and the nitrogen-based additives account for 0.05% to 2% of the total mass of the electrolyte.

[0008] According to a second aspect of this application, this application provides a sodium-ion battery containing an electrolyte as described in any one of the first aspects.

[0009] In some embodiments of this application, the sodium-ion battery further includes a positive electrode and a negative electrode. The negative electrode is composed of a metal foil current collector and a conductive bonding layer disposed on its surface. Furthermore, the negative electrode does not include a negative electrode active material for reversibly storing and releasing sodium ions.

[0010] According to a third aspect of this application, this application provides an electronic device comprising a sodium-ion battery as described in any of the second aspects.

[0011] Beneficial effects: The electrolyte of this application, obtained by the synergistic combination of sodium salt, ether solvent, sulfur-based additives and / or nitrogen-based additives, is an ether-based electrolyte that can be used as an electrolyte for a negative electrode-free sodium-ion battery. It has high discharge capacity, excellent cycle performance and rate performance, and exhibits good electrochemical performance. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0013] Figure 1 The graph shows the 0.5C cycle performance of the ether-based electrolytes used in Examples 2, 7, and Comparative Example 1 in a sodium-ion battery without a negative electrode. Figure 2 These are the charge-discharge curves of Example 2 at different rates. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0015] It should be noted that, in the specific implementation of this application, a pouch battery is used as a specific example, but the specific use of this application may also include other types of batteries.

[0016] Ether-based electrolytes play a crucial role in sodium-ion batteries due to their unique physicochemical properties. Their application helps improve battery cycle performance and safety. The low viscosity of ether-based electrolytes reduces internal battery resistance, thereby increasing charge-discharge efficiency. Simultaneously, their excellent chemical stability effectively prevents safety accidents such as leakage and explosions during charge-discharge processes. Furthermore, from a technological development perspective, the research and development of ether-based electrolytes has become an important direction for improving the performance of sodium-ion batteries.

[0017] Currently, the applicable scenarios and optimal ratios for different types of ether-based electrolytes are still unclear, thus requiring extensive experimentation to explore the optimal formulation. Although ether-based electrolytes show great promise for application in sodium-ion batteries, further solutions are needed to address issues such as performance stability, interface compatibility, and safety risks in practical applications.

[0018] The design of a cathode-less sodium-ion battery eliminates the need for negative electrode active materials (such as hard carbon), allowing for more positive electrode active material to be accommodated within the same volume or weight. During the first charge, all sodium from the positive electrode is deposited onto the negative electrode current collector as an active material to participate in subsequent reactions. Without the "space-occupying" and capacity limitations of negative electrode materials, the types and amounts of raw materials used are reduced, lowering material costs. A cathode-less sodium-ion battery forms a sodium metal negative electrode during the first charge, and sodium is deposited on the current collector during subsequent cycles. With proper electrolyte design, sodium deposition behavior can be better controlled, reducing dendrite formation and other issues, thus lowering safety risks. In sodium-ion battery production, the negative electrode fabrication process is complex and requires high standards for coating uniformity and rolling density. A cathode-less sodium-ion battery only requires processing the current collector before assembling the positive electrode and separator, significantly reducing process steps, facilitating large-scale production, and improving quality control.

[0019] This application provides a sodium-ion battery electrolyte with high ionic conductivity, low viscosity, and good chemical stability. At the same time, the electrolyte of this application can improve the electrochemical performance and safety performance of negative electrode-free sodium-ion batteries.

[0020] To achieve the above-mentioned objectives of this application, the technical solution adopted in this application is as follows: According to a first aspect of this application, this application provides a sodium-ion battery electrolyte, the electrolyte containing sodium salt, ether solvent and additives; the additives include sulfur-based additives and / or nitrogen-based additives; the sulfur-based additives include at least one of 1,3-propanesulfonyl lactone, ethylene sulfate, and propenyl-1,3-sulfonyl lactone. The nitrogen-based additives include at least one of ethyl nitrate, propyl nitrate, sodium nitrate, potassium nitrate, and bismuth nitrate.

[0021] In this application, the ether-based electrolyte exhibits high ionic conductivity and low viscosity, enabling it to provide higher energy density and faster charge / discharge rates in electrodeless sodium-ion batteries. Furthermore, the ether-based electrolyte demonstrates excellent chemical stability, maintaining stable electrochemical performance over a wide temperature range, which is crucial for improving the practicality and reliability of electrodeless sodium-ion batteries.

[0022] The application of ether-based electrolytes in sodium-ion batteries has significant advantages, as follows: The high ionic conductivity of ether-based electrolytes helps to improve the energy density of sodium-ion batteries, thereby increasing the battery's range; the low viscosity of ether-based electrolytes helps to improve ion migration rate, thereby accelerating the battery's charge and discharge speed; the chemical stability of ether-based electrolytes enables sodium-ion batteries to exhibit better stability during cycling, extending the battery's lifespan.

[0023] Ether-based electrolytes maintain stable electrochemical performance at high temperatures, reducing the risk of battery thermal runaway. Furthermore, ether-based electrolytes exhibit good compatibility with electrode materials, minimizing the possibility of internal short circuits within the battery.

[0024] Ether-based electrolytes are typically prepared using environmentally friendly raw materials and do not produce harmful substances during use, making them environmentally friendly. Furthermore, ether-based electrolytes are recyclable, reducing battery manufacturing costs and meeting the requirements of sustainable development.

[0025] In this application, the sulfur-based additive can form a nitrogen-rich SEI film on the negative electrode surface, physically blocking the migration of polysulfides to the negative electrode, inhibiting the polysulfide shuttle effect, and reducing the loss of active materials. - Anions participate in Na + The solvated sheath layer reduces the proportion of free solvent molecules, regulates the solvation structure, and inhibits the dissolution of polysulfides. Simultaneously, it can form a stable positive electrode electrolyte interface (CEI), reducing the formation and dissolution of polysulfides and enhancing interface stability. Furthermore, the NO produced by the decomposition of sulfur-based additives... x The gas can dilute the flammable gas in the electrolyte, reducing the risk of thermal runaway.

[0026] Nitrogen-based additives significantly improve battery performance in ether-based electrolytes by regulating solvation structure, optimizing electrode interface chemistry, and suppressing side reactions. Their core advantages include: suppressing lithium / sodium dendrite growth by decomposing on the negative electrode surface to form a Na3N-rich SEI film, thus inhibiting metal dendrite growth; nitrate esters can delay electrolyte decomposition through free radical capture mechanisms, suppressing phase transitions and oxygen evolution in positive electrode materials (such as high-nickel NCM); nitrogen-containing additives (such as propyl nitrate) have high decomposition temperatures, forming a stable CEI film at high temperatures to suppress electrolyte oxidation and gas generation.

[0027] In some embodiments of this application, the concentration of the sodium salt in the ether-based electrolyte is 0.1 mol / L to 0.8 mol / L; in some specific embodiments, the concentration includes values ​​within the range of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, or any combination of these values.

[0028] In some embodiments of this application, the volume fraction of the ether solvent in the electrolyte is 10% to 90%. In some specific embodiments, the volume fraction includes values ​​within the range of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any combination of these values.

[0029] In some embodiments of this application, the additive accounts for 0.02% to 1.5% of the total mass of the electrolyte. In some specific embodiments, the additive accounts for 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or any value within the range of any two of these values.

[0030] In some embodiments of this application, the molar ratio of NaPF6 to NaBF4 is (7-9):1; in some specific embodiments, the molar ratio of NaPF6 to NaBF4 can be 7:1, 7.5:1, 8:1, 8.5:1, 9:1, or any value within the range of any two of these values.

[0031] In some embodiments of this application, the ether solvent includes diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, wherein the volume ratio of diethylene glycol dimethyl ether to tetraethylene glycol dimethyl ether is (8-10):1. In some specific embodiments, the volume ratio of diethylene glycol dimethyl ether to tetraethylene glycol dimethyl ether can be 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or a value within any range of two of these values.

[0032] In some embodiments of this application, the additives include sulfur-based additives and nitrogen-based additives. The sulfur-based additives account for 0.05% to 2% of the total mass of the electrolyte. In some specific embodiments, the sulfur-based additives account for 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, or any value within the range of any two of these values.

[0033] In some embodiments of this application, the nitrogen-based additive accounts for 0.05% to 2% of the total mass of the electrolyte.

[0034] In some embodiments of this application, and in some specific embodiments, the content ratio of the nitrogen-based additive relative to the total mass of the electrolyte can be 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, or a value within the range of any two of these values.

[0035] According to a second aspect of this application, this application provides a sodium-ion battery containing an electrolyte as described in any one of the first aspects.

[0036] In some embodiments of this application, the sodium-ion battery further includes a positive electrode and a negative electrode. The negative electrode is composed of a metal foil current collector and a conductive bonding layer disposed on its surface. Furthermore, the negative electrode does not include a negative electrode active material for reversibly storing and releasing sodium ions.

[0037] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, or a polymer substrate coated with a conductive metal, etc.

[0038] A layer of resin-based carbon can be coated on the negative electrode current collector. In some specific embodiments, the thickness of the resin-based carbon is 0.5μm to 2μm. Resin-based carbon refers to a functional coating composed of a polymer resin binder and a conductive carbon material.

[0039] In some specific embodiments, the polymeric resin adhesive refers to one or a mixture of several of polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylonitrile (PAN), and styrene-butadiene rubber (SBR), which provides strong adhesion after curing.

[0040] In some specific embodiments, the conductive carbon material refers to one or a mixture of several of the following: conductive carbon black, acetylene black, Super P, Ketjen black, carbon nanotubes, and graphene, which serves to form a three-dimensional conductive network in the coating.

[0041] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a layer of positive active material disposed on at least one surface of the positive current collector. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil is aluminum foil. In some embodiments, the secondary battery is a sodium-ion battery, and the positive active material may include at least one of layered oxides and polyanionic materials.

[0042] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 15 μm, preferably 8 μm to 13 μm.

[0043] The secondary battery of this application also includes a separator for separating the positive and negative electrode plates, preventing short circuits in the sodium-ion battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material includes, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes. The sodium-ion battery of this application also includes a packaging bag for containing the positive electrode plate, separator, negative electrode plate, electrolyte, and other components known in the art in the sodium-ion battery. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0044] According to a third aspect of this application, this application provides an electronic device comprising a sodium-ion battery as described in any of the second aspects.

[0045] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0046] Example The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0047] The test methods and equipment used in the embodiments and comparative examples of this application are as follows: 1. Electrical performance testing The electrolytes of Examples 1-21 and Comparative Examples 1-6 were prepared and injected into sodium-ion pouch cells. After immersion at 45°C, electrochemical performance tests were conducted on a Newway battery tester. The cells were charged to 3.4V at 0.1C constant current and constant voltage, and discharged to 2.2V at 0.2C constant current to determine the initial discharge capacity and initial efficiency of the cells. After three cycles at 0.2C at room temperature, the capacity retention rate after cycling was determined by cycling at 0.5C. In Table 2, 85@92.4% of Example 1 indicates that the capacity retention rate is 92.4% after 85 cycles at 0.5C.

[0048] Example 1 <Preparation of Negative Electrode Sheets> Carbon-coated copper foil is used as the basic foil material and is die-cut into electrode sheets of 96mm×126mm.

[0049] <Preparation of the positive electrode> The positive electrode material, sodium iron pyrophosphate, conductive agent, and binder were mixed stepwise in a mass ratio of 95.5:2:2.5. N-methylpyrrolidone (NMP) was used as a solvent. The binder, conductive agent, and sodium iron pyrophosphate were added in sequence, and the viscosity and solid content were adjusted to obtain a positive electrode slurry with a solid content of 59wt%. After coating, rolling, slitting, and sheet forming, a positive electrode sheet with a thickness of 150μm and a size of 93mm×123mm was obtained.

[0050] <Preparation of Electrolyte> Electrolyte was prepared in a dew point room at 25±3℃ and a dew point of -55±3℃. Diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) were mixed in a volume ratio of 9:1, and 1 L of the mixture was added in small amounts several times while stirring to dissolve it into the mixed solvent. After complete dissolution, 0.2 mol of NaBF4 was added and stirred to dissolve it. After complete dissolution, 0.5% ethylene sulfate (DTD) (additive) was added by mass and mixed evenly to obtain the electrolyte ready for use.

[0051] <Preparation of the diaphragm> A 9μm thick polyethylene diaphragm is used, with a 3μm ceramic layer on one side of the diaphragm.

[0052] <Preparation of Sodium-ion Batteries> The prepared positive electrode sheet, separator, and carbon-coated copper foil are stacked in sequence. There are separators on both sides of the positive electrode and the carbon-coated copper foil. There are 29 positive electrode sheets and 30 carbon-coated copper foil sheets. The stacked sheets are used to obtain a soft-pack battery. After welding the tab sheets, the stacked core is put into an aluminum-plastic film packaging bag and placed in a nitrogen vacuum oven at 100°C for 24 hours to remove moisture. After baking, the moisture content is <300ppm. The prepared electrolyte is injected. After vacuum sealing, impregnation, formation, and capacity testing, a sodium-ion soft-pack battery is obtained and tested.

[0053] Examples 2 to 21 Except for adjusting the preparation parameters according to Table 1, the remaining parameters of Examples 2 to 21 are the same as those of Example 1, specifically: Example 2 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0054] Example 3 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% propenyl-1,3-sulfonyl lactone (PST). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0055] Example 4 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0056] Example 5 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% sodium nitrate (NaNO3). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0057] Example 6 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% propyl nitrate (C3H7ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0058] Example 7 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% potassium nitrate (KNO3). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The resulting pouch cell was then tested.

[0059] Example 8 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% bismuth nitrate (Bi(NO3)3). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0060] Example 9 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additives: 0.3% 1,3-propanesulfonyl lactone (PS) and 0.2% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0061] Example 10 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additives: 0.3% propenyl-1,3-sulfonyl lactone (PST) and 0.2% propyl nitrate (C3H7ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0062] Example 11 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.01% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0063] Example 12 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.01% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0064] Example 13 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additives: 0.005% 1,3-propanesulfonyl lactone (PS) and 0.005% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0065] Example 14 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 2% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0066] Example 15 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 2% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0067] Example 16 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additives: 1.0% 1,3-propanesulfonyl lactone (PS) and 1.0% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0068] Example 17 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 1.0 mol / L sodium hexafluorophosphate (NaPF6); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% sodium nitrate (NaNO3). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The resulting pouch cell is then tested.

[0069] Example 18 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 1.0 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0070] Example 19 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 1.0 mol / L sodium perchlorate (NaClO4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.5% sodium nitrate (NaNO3). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0071] Example 20 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salts: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: 100% triethylene glycol dimethyl ether (G3); additive: 0.5% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The resulting pouch cell is then tested.

[0072] Example 21 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salts: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: 100% dimethyl ethylene glycol (DME); additive: 0.5% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0073] Comparative Examples 1 to 6 Except for adjusting the preparation parameters according to Table 1, the remaining parameters of Comparative Examples 1 to 6 are the same as those of Example 1, specifically: Comparative Example 1 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1. In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode. The battery is assembled into a pouch cell for testing.

[0074] Comparative Example 2 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.005% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0075] Comparative Example 3 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 0.005% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0076] Comparative Example 4 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 2.5% 1,3-propanesulfonyl lactone (PS). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0077] Comparative Example 5 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additive: 2.5% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0078] Comparative Example 6 This embodiment provides an ether-based, negative electrode-free sodium-ion battery electrolyte with the following specific components: sodium salt: 0.8 mol / L sodium hexafluorophosphate (NaPF6) and 0.2 mol / L sodium tetrafluoroborate (NaBF4); solvent: diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME) in a volume ratio of 9:1; additives: 1.25% 1,3-propanesulfonyl lactone (PS) and 1.25% ethyl nitrate (C2H5ONO2). In this embodiment, sodium iron pyrophosphate is used as the positive electrode, and carbon-coated copper foil is used as the negative electrode, assembled into a pouch cell for testing.

[0079] Table 1

[0080]

[0081] Figure 1 The graph shows the 0.5C cycle performance of the ether-based electrolytes used in Examples 2, 7, and Comparative Example 1 in a cathode-free sodium-ion battery. In Comparative Example 1, due to the excessively high concentration of NaPF6 and the absence of NaBF4, the stability of the solvated structure in the electrolyte was poor, leading to a decrease in capacity retention to 83.2% after 30 cycles. Example 2 showed a capacity retention of 83.8% after 248 cycles, higher than Example 7, indicating that the electrolyte system of Example 2 has better electrochemical performance in a cathode-free sodium-ion battery. However, the ether-based electrolyte of Example 7 showed higher capacity retention in the first 80 cycles than Example 2, indicating that the NO3- of C2H5ONO2... - Anionic partial substitution of ether solvents into Na + Solvating the inner side of the sheath improves ion diffusion and increases the capacity retention rate during battery cycling, but the large gas production in the later stages of cycling leads to faster capacity loss. Figure 2 These are the charge-discharge curves of Example 2 at different rates. The charge-discharge curves of the cells with increased rates only show slight differences in capacity.

[0082] The ether-based electrolytes obtained in Examples 1 to 7 and Comparative Examples 1 to 2 were used in negative electrode-free sodium-ion soft-pack batteries. Electrochemical performance tests were conducted on a Newway battery tester to determine the initial discharge capacity and capacity retention. The relevant parameters and properties of the active materials prepared in the above examples and comparative examples were tested using the above test methods. The results are shown in Table 2. Table 2

[0083] As can be seen from the table above, the ether-based electrolyte obtained by using the present invention can be used as an electrolyte for a negative electrode-free sodium-ion battery. It has high discharge capacity, excellent cycle performance and rate performance, and exhibits good electrochemical performance, indicating that the technical solution adopted in this application effectively improves battery performance.

[0084] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention are protected by the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that the electrolyte contains a sodium salt, an ether solvent, and additives; the additives include sulfur-based additives and / or nitrogen-based additives; the sulfur-based additives include at least one of 1,3-propanesulfonyl lactone, ethylene sulfate, and propenyl-1,3-sulfonyl lactone. The nitrogen-based additives include at least one of ethyl nitrate, propyl nitrate, sodium nitrate, potassium nitrate, and bismuth nitrate.

2. The electrolyte according to claim 1, characterized in that the concentration of the sodium salt in the ether-based electrolyte is 0.1 mol / L to 0.8 mol / L.

3. The electrolyte according to claim 1, characterized in that the volume fraction of the ether solvent in the electrolyte is 10% to 90%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that the content of the additive relative to the total mass of the electrolyte is 0.02% to 1.5%.

5. The electrolyte according to any one of claims 1 to 3, characterized in that the sodium salt comprises NaPF6 and NaBF6. 4， The molar ratio of NaPF6 and NaBF4 is (7-9):

1.

6. The electrolyte according to any one of claims 1 to 3, characterized in that the ether solvent includes diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, wherein the volume ratio of diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether is (8 to 10):

1.

7. The electrolyte according to any one of claims 1 to 3, characterized in that the additives include the sulfur-based additives and the nitrogen-based additives, wherein the sulfur-based additives account for 0.05% to 2% of the total mass of the electrolyte, and the nitrogen-based additives account for 0.05% to 2% of the total mass of the electrolyte.

8. A sodium-ion battery, characterized in that, It contains the electrolyte as described in any one of claims 1-7.

9. The sodium-ion battery according to claim 8, characterized in that, The sodium-ion battery further includes a positive electrode and a negative electrode. The negative electrode is composed of a metal foil current collector and a conductive bonding layer disposed on its surface. Furthermore, the negative electrode does not include a negative electrode active material for reversibly storing and releasing sodium ions.

10. An electronic device, characterized in that, The electronic device includes a sodium-ion battery as described in any one of claims 8-9.

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