Sodium secondary battery, electrolyte, and electric device

Abstract

The invention discloses a sodium secondary battery, electrolyte and electric equipment, the sodium secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector, at least one side of the positive current collector is provided with a positive active material layer, and the positive active material layer comprises a positive active material; the negative electrode plate comprises a negative electrode current collector, and metal sodium is formed on the negative electrode current collector through in-situ deposition when the sodium secondary battery is charged; the invention discloses a lithium ion battery, which comprises an electrolyte, the electrolyte comprises a phosphate ester additive, and based on the total mass of the electrolyte, the mass ratio of the phosphate ester additive is 0.2%-5%. Therefore, the side reaction between the positive electrode active material and the electrolyte is reduced, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to sodium secondary batteries, electrolytes, and electrical equipment. Background Technology

[0002] Batteries are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. In sodium-based secondary batteries without a negative electrode, the solvent easily reacts with the positive electrode active material during cycling, reducing the battery's cycle stability. Summary of the Invention

[0003] The first aspect of this application provides a sodium secondary battery, comprising: a positive electrode sheet including a positive current collector, wherein at least one side of the positive current collector has a positive active material layer, the positive active material layer comprising a positive active material; a negative electrode sheet including a negative current collector, wherein metallic sodium is deposited in situ on the negative current collector during charging; and an electrolyte comprising an ether solvent and a phosphate ester additive, wherein the phosphate ester additive accounts for 0.2%-5% of the total mass of the electrolyte. Therefore, during the cycling process of the sodium secondary battery, the ether solvent has good compatibility with the negative electrode, and the phosphate ester additive can form a stable positive electrolyte interphase (CEI) film on the surface of the positive electrode, reducing direct contact between the positive active material and the electrolyte, reducing side reactions between the positive active material and the electrolyte, and improving the cycle performance of the battery.

[0004] According to some embodiments of this application, the mass percentage of the phosphate ester additive is 1%-3.5% based on the total mass of the electrolyte. Therefore, by keeping the content of the phosphate ester additive within the above range, the probability of the phosphate ester additive reacting with the sodium metal at the negative electrode is reduced, thereby minimizing its impact on the capacity of the sodium secondary battery.

[0005] According to some embodiments of this application, the phosphate ester additive includes compounds represented by Formula 1:

[0006]

[0007] R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

[0008] According to some embodiments of this application, the phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

[0009] Therefore, the aforementioned types of phosphate ester additives can oxidize and decompose on the positive electrode surface to form a CEI film, reducing side reactions between the positive electrode active material and the electrolyte, and improving the cycle performance of the battery.

[0010] According to some embodiments of this application, the phosphate ester additive includes one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate. This reduces side reactions between the positive electrode active material and the electrolyte, while also facilitating uniform sodium deposition at the negative electrode, reducing sodium dendrite formation, minimizing active sodium loss, and improving battery cycle performance.

[0011] According to some embodiments of this application, the ether solvent includes one or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane. This improves the compatibility between the electrolyte and the sodium metal anode.

[0012] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes NaPF6. Therefore, the electrolyte has good compatibility with sodium metal, improving the compatibility between the electrolyte and the negative electrode sodium metal.

[0013] According to some embodiments of this application, the molar concentration of NaPF6 in the electrolyte is 0.5 mol / L-2 mol / L. This improves the ionic conductivity of the electrolyte.

[0014] According to some embodiments of this application, the positive electrode active material includes NaMO2, wherein M includes one or more of T, V, Cr, Mn, Fe, Co, Ni, and Cu. This improves the energy density of the battery.

[0015] According to some embodiments of this application, at least one side of the negative electrode current collector has an interface modification layer, which includes a binder and a conductive agent. This improves the electronic conductivity of the negative electrode.

[0016] According to some embodiments of this application, the thickness of the interface modification layer is 0.5 μm-2 μm. This improves the electronic conductivity of the negative electrode.

[0017] According to some embodiments of this application, the positive electrode sheet satisfies one or more of the following conditions: the compaction density of the positive electrode sheet is 2.5 g / cm³. 3 -3.5g / cm 3 The coating weight of the positive electrode sheet is 5 mg / cm³. 2 -30mg / cm 2 This increases the energy density of sodium secondary batteries.

[0018] According to some embodiments of this application, the negative electrode sheet satisfies one or more of the following conditions: the compaction density of the negative electrode sheet is 1 g / cm³. 3 -2g / cm 3 The coating weight of the negative electrode sheet is 0.1 mg / cm³. 2 -0.2mg / cm 2 This increases the energy density of sodium secondary batteries.

[0019] A second aspect of this application provides an electrolyte comprising an ether solvent and a phosphate ester additive, wherein the phosphate ester additive accounts for 0.2%-5% of the total mass of the electrolyte. Therefore, during battery cycling, the phosphate ester additive can form a stable CEI film on the positive electrode surface, reducing direct contact between the positive electrode active material and the electrolyte, reducing side reactions between the positive electrode active material and the electrolyte, and improving the battery's cycle performance.

[0020] According to some embodiments of this application, the mass percentage of the phosphate ester additive is 1%-3.5%. Therefore, when the sodium secondary battery is a sodium battery without a negative electrode, by keeping the content of the phosphate ester additive within the above range, the probability of the phosphate ester additive reacting with the sodium metal of the negative electrode is reduced, thereby reducing the impact on the capacity of the sodium secondary battery.

[0021] According to some embodiments of this application, the phosphate ester additive includes compounds represented by Formula 1:

[0022]

[0023] R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

[0024] According to some embodiments of this application, the phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

[0025] Therefore, the aforementioned types of phosphate ester additives can oxidize and decompose on the positive electrode surface to form a CEI film, reducing side reactions between the positive electrode active material and the electrolyte, and improving the cycle performance of the battery.

[0026] According to some embodiments of this application, the phosphate ester additive includes one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate. This reduces side reactions between the positive electrode active material and the electrolyte, while also facilitating uniform sodium deposition at the negative electrode, reducing sodium dendrite formation, minimizing active sodium loss, and improving battery cycle performance.

[0027] According to some embodiments of this application, the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane. This improves the compatibility between the electrolyte and the sodium metal anode.

[0028] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes NaPF6. Therefore, the electrolyte formed by the electrolyte salt has good compatibility with sodium metal, reducing the compatibility issues between the electrolyte and the negative electrode sodium metal.

[0029] According to some embodiments of this application, the molar concentration of NaPF6 in the electrolyte is 0.5 mol / L-2 mol / L. This improves the ionic conductivity of the electrolyte.

[0030] A third aspect of this application provides an electrical device, including the sodium secondary battery provided in the first aspect of this application.

[0031] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0033] Figure 1 This is a schematic diagram of a sodium secondary battery according to one embodiment of this application.

[0034] Figure 2 yes Figure 1 An exploded view of a sodium secondary battery according to an embodiment of this application is shown.

[0035] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0038] Figure 6This is a schematic diagram of an electrical device using a sodium secondary battery as a power source according to an embodiment of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Sodium secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0041] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0047] Currently, ether-based solvent systems are used as electrolytes in sodium-based secondary batteries without a negative electrode, considering their compatibility with sodium metal. However, ether-based solvents have a low oxidation potential window. In oxide-based sodium-based battery systems, the positive electrode active material exhibits strong oxidizing properties under full charge conditions. Consequently, ether-based solvents easily react with the oxide positive electrode active material during cycling, leading to the loss of both the positive electrode active material and active sodium, thus reducing the cycle stability of the sodium-based secondary battery.

[0048] This application proposes a sodium-ion secondary battery. Based on the use of ether solvents, a phosphate ester additive is added to the electrolyte. During battery cycling, the phosphate ester additive can oxidize and decompose on the positive electrode surface to form a stable CEI film, effectively reducing direct contact between the ether solvent and the positive electrode active material, reducing side reactions between the positive electrode active material and the ether solvent, reducing the consumption of active sodium, and improving the battery's cycle performance. The addition of the phosphate ester additive to the electrolyte also helps to form a uniform sodium metal layer on the negative electrode, reducing sodium dendrite growth, reducing active sodium loss due to internal short reactions, and reducing battery gas production. Simultaneously, by forming a stable CEI film on the positive electrode surface, the dissolution of transition metals in the positive electrode active material can also be reduced, reducing the loss of positive electrode active material and improving the battery's cycle performance.

[0049] The sodium secondary battery proposed in this application can be used in electrical devices that use sodium secondary batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0050] The first aspect of this application provides a sodium secondary battery, comprising: a positive electrode sheet including a positive current collector, wherein at least one side of the positive current collector has a positive active material layer, the positive active material layer comprising a positive active material; a negative electrode sheet including a negative current collector, wherein metallic sodium is deposited in situ on the negative current collector during charging; and an electrolyte comprising an ether solvent and a phosphate ester additive, wherein the mass percentage of the phosphate ester additive is 0.2%-5% based on the total mass of the electrolyte. Therefore, during the cycling process of the sodium secondary battery, the ether solvent and the negative electrode sodium metal exhibit good compatibility, and the phosphate ester additive can form a stable CEI film on the positive electrode surface, reducing direct contact between the positive active material and the electrolyte, reducing side reactions between the positive active material and the electrolyte, reducing the consumption of active sodium, reducing transition metal dissolution, reducing battery gas production, and improving the battery's cycle performance. By keeping the content of phosphate ester additives within the above range, the cycle performance of the battery can be improved while reducing the risk of excessive phosphate ester additives reacting with sodium metal at the negative electrode, thus reducing the impact on the capacity of sodium secondary batteries.

[0051] As an example, based on the total mass of the electrolyte, the mass percentage of the phosphate ester additive can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or a range of any of the above values. According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the phosphate ester additive is 1%-3.5%. Therefore, while improving the cycle performance of the sodium secondary battery, the probability of reaction between the phosphate ester additive and the sodium metal at the negative electrode is reduced, thereby increasing the capacity of the sodium secondary battery.

[0052] In this application, the detection method for phosphate ester additives is as follows: Detection is performed by gas chromatography-mass spectrometry (GC-MS). After disassembling the sodium secondary battery, a portion of the electrolyte is taken and separated using gas chromatography. The separated substances are then detected and identified by mass spectrometry. The phosphate ester additives are separated in gas chromatography and then subjected to qualitative and quantitative analysis based on the mass-to-charge ratio of their fragment ions in the mass spectrometer.

[0053] According to some embodiments of this application, the phosphate ester additive includes compounds represented by Formula 1:

[0054]

[0055] R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

[0056] According to some embodiments of this application, the phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

[0057] Therefore, the aforementioned types of phosphate ester additives can oxidize and decompose on the positive electrode surface to form a CEI film, reducing side reactions between the positive electrode active material and the electrolyte, and improving the cycle performance of the battery.

[0058] According to some embodiments of this application, the phosphate ester additive includes one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate. This reduces side reactions between the positive electrode active material and the electrolyte, while also facilitating uniform sodium deposition at the negative electrode, reducing sodium dendrite formation, minimizing active sodium loss, and improving battery cycle performance.

[0059] According to some embodiments of this application, the ether solvent includes one or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane. This improves the compatibility between the electrolyte and the sodium metal anode.

[0060] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes NaPF6. Therefore, the electrolyte formed by the electrolyte salt has good compatibility with sodium metal, improving the compatibility between the electrolyte and the negative electrode sodium metal.

[0061] According to some embodiments of this application, the molar concentration of NaPF6 in the electrolyte can be 0.5 mol / L to 2 mol / L. This improves the ionic conductivity of the electrolyte.

[0062] As an example, the molar concentration of NaPF6 in the electrolyte can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.4 mol / L, 1.7 mol / L, or 2 mol / L, or a range of any of the above values.

[0063] According to some embodiments of this application, the electrolyte may further include NaBF4, and the molar concentration of NaBF4 in the electrolyte is 0.01 mol / L-0.4 mol / L. This improves the ionic conductivity of the electrolyte.

[0064] As an example, the molar concentration of NaBF4 in the electrolyte can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or 0.4 mol / L, or a range of any of the above values.

[0065] According to some embodiments of this application, the positive electrode active material includes NaMO2, wherein M includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Therefore, when the above-mentioned material is used as the positive electrode active material in a sodium secondary battery and an ether solvent is used as the electrolyte, even if the positive electrode active material has strong oxidizing properties under full charge conditions, the presence of phosphate ester additives in the electrolyte, through the formation of a CEI film on the positive electrode surface, can reduce side reactions between the positive electrode active material and the ether solvent, thereby improving the cycle performance of the sodium secondary battery.

[0066] According to some embodiments of this application, the positive electrode active material includes NaMO2, wherein M includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Therefore, when the positive electrode contains the above-mentioned positive electrode active material, phosphate ester additives can form a CEI film on the positive electrode surface, which can reduce side reactions between the positive electrode active material and the ether solvent, thereby improving the cycle performance of the sodium secondary battery.

[0067] 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 (aluminum, aluminum 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.).

[0068] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0069] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] 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.

[0071] According to some embodiments of this application, when the positive electrode active material includes NaMO2, the compaction density of the positive electrode sheet can be 2.5 g / cm³. 3 -3.5g / cm 3 For example, it could be 2.5 g / cm³. 3 2.7g / cm 3 2.9g / cm 3 3.1g / cm 3 3.3g / cm 3 3.5g / cm 3 The range can be any of the values ​​mentioned above. This increases the energy density of the sodium-based secondary battery without a negative electrode.

[0072] In this application, the compaction density of the positive electrode sheet is determined by measuring the mass of the positive electrode sheet per unit area (g / cm³). 2 The positive electrode thickness (cm) was determined by the number of sampling points > 14. The compaction density PD of the positive electrode is calculated as: PD = (mass of the positive electrode per unit area, g / cm³) 2 ) / Thickness of positive electrode (cm).

[0073] According to some embodiments of this application, the coating weight of the positive electrode sheet can be 5 mg / cm³. 2 -30mg / cm 2 For example, it could be 5 mg / cm³. 2 10mg / cm 2 15mg / cm 2 20mg / cm 2 25mg / cm 2 Or 30mg / cm 2 The range can be any of the values ​​mentioned above. This increases the energy density of the sodium-based secondary battery without a negative electrode.

[0074] It should be noted that the coating weight of the positive electrode film referred to here refers to the coating weight of the positive electrode film on one side of the positive electrode current collector.

[0075] In this application, a fixed-size mold is used to punch and coat the middle area and the tab area. The mass of the positive active material layer on both sides of the positive electrode sheet in the middle area is m1, and the mass of the positive film layer on both sides of the positive electrode sheet in the tab area is m2. The coating mass of one side of the positive film layer is ((m1-m2) / 2) / S, where S is the mold area.

[0076] According to some embodiments of this application, at least one side of the negative electrode current collector has an interface modification layer, which includes a binder and a conductive agent. This improves the electronic conductivity of the negative electrode.

[0077] According to some embodiments of this application, the thickness of the interface modification layer can be 0.5 μm-2 μm. This improves the electronic conductivity of the negative electrode.

[0078] As an example, the thickness of the interface modification layer can be 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm or 2μm, or can be a range of any of the above values.

[0079] In this application, the longitudinal section of the negative electrode sheet along its thickness direction can be obtained by plasma, and the thickness of the interface modification layer can be obtained by scanning electron microscopy (SEM).

[0080] According to some embodiments of this application, the compaction density of the negative electrode sheet can be 1 g / cm³. 3 -2g / cm 3 For example, it could be 1g / cm³ 3 1.2g / cm 3 1.4g / cm 3 1.6g / cm 3 1.8g / cm 3 or 2g / cm 3 The range can be any of the values ​​mentioned above. This increases the energy density of the sodium-based secondary battery without a negative electrode.

[0081] In this application, the compaction density of the negative electrode sheet is determined by measuring the mass of the negative electrode sheet per unit area (g / cm³). 2 The density of the negative electrode sheet (PD) is determined by the negative electrode sheet thickness (cm) (number of sampling points > 14). The compaction density PD of the negative electrode sheet is calculated as: PD = (mass of the negative electrode sheet per unit area) g / cm³. 2 ) / Thickness of negative electrode sheet (cm).

[0082] According to some embodiments of this application, the coating weight of the negative electrode sheet can be 0.1 mg / cm³. 2 -0.2mg / cm 2 For example, it could be 0.1 mg / cm³. 20.12 mg / cm 2 0.14 mg / cm 2 0.16 mg / cm 2 0.18 mg / cm 2 Or 0.2 mg / cm 2 The range can be any of the values ​​mentioned above. This increases the energy density of sodium secondary batteries.

[0083] It should be noted that the coating weight of the negative electrode film referred to here refers to the coating weight of the negative electrode film on one side of the negative electrode current collector.

[0084] In this application, a fixed-size die is used to punch and coat the middle area and the tab area. The mass of the negative active material layer on both sides of the negative electrode sheet in the middle area is m1, and the mass of the negative film layer on both sides of the negative electrode sheet in the tab area is m2. The coating mass of one side of the negative film layer is ((m1-m2) / 2) / S, where S is the die area.

[0085] 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.).

[0086] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0087] In some embodiments, the sodium 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.

[0088] In some embodiments, the material of the separator can be selected from one or more 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.

[0089] In some implementations, the sodium secondary battery can be a sodium metal battery.

[0090] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0091] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0092] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured sodium secondary battery.

[0094] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 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 plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 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 sodium 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.

[0095] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a 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.

[0096] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple sodium 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 sodium secondary batteries 5 can be fixed in place using fasteners.

[0097] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of sodium secondary batteries 5 are received.

[0098] 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.

[0099] 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.

[0100] A second aspect of this application provides an electrolyte comprising an ether solvent and a phosphate ester additive, wherein the phosphate ester additive comprises 0.2%-5% of the total mass of the electrolyte. As an example, the phosphate ester additive may comprise 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5% of the total mass of the electrolyte, or any range thereof. According to some embodiments of this application, the phosphate ester additive comprises 1%-3.5% of the total mass of the electrolyte. This improves the cycle performance of the sodium secondary battery while reducing the probability of reaction between the phosphate ester additive and the sodium metal at the negative electrode, thereby increasing the capacity of the sodium secondary battery.

[0101] According to some embodiments of this application, the phosphate ester additive includes compounds represented by Formula 1:

[0102]

[0103] R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

[0104] According to some embodiments of this application, the phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

[0105] Therefore, the aforementioned types of phosphate ester additives can oxidize and decompose on the positive electrode surface to form a CEI film, reducing side reactions between the positive electrode active material and the electrolyte, and improving the cycle performance of the battery.

[0106] According to some embodiments of this application, the phosphate ester additive includes one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate. This reduces side reactions between the positive electrode active material and the electrolyte, while also facilitating uniform sodium deposition at the negative electrode, reducing sodium dendrite formation, minimizing active sodium loss, and improving battery cycle performance.

[0107] According to some embodiments of this application, the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane. This improves the compatibility between the electrolyte and the sodium metal anode.

[0108] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes NaPF6. Therefore, the electrolyte has good compatibility with sodium metal, improving the compatibility between the electrolyte and the negative electrode sodium metal.

[0109] According to some embodiments of this application, the molar concentration of NaPF6 in the electrolyte is 0.5 mol / L-2 mol / L. This improves the ionic conductivity of the electrolyte.

[0110] As an example, the molar concentration of NaPF6 in the electrolyte can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.4 mol / L, 1.7 mol / L, or 2 mol / L, or a range of any of the above values.

[0111] According to some embodiments of this application, the electrolyte may further include NaBF4, and the molar concentration of NaBF4 in the electrolyte is 0.01 mol / L-0.4 mol / L. This improves the ionic conductivity of the electrolyte.

[0112] As an example, the molar concentration of NaBF4 in the electrolyte can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or 0.4 mol / L, or a range of any of the above values.

[0113] A third aspect of this application provides an electrical device, including the sodium secondary battery provided in the first aspect of this application.

[0114] The electrical device includes one or more of the sodium secondary batteries, battery modules, or battery packs provided in this application. The sodium secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0115] As the electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0116] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density batteries, a battery pack or battery module can be used.

[0117] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0118] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0119] Example 1

[0120] 1. Preparation of positive electrode sheet

[0121] NaNi, the positive electrode active material 0.20 Fe 0.22 Cu 0.13 Mn 0.45 O2, polyvinylidene fluoride (PVDF) binder, and carbon black conductive agent are dissolved in N-methylpyrrolidone at a mass ratio of 80:10:10 to form a uniformly dispersed slurry. This slurry is then evenly coated onto the surface of aluminum foil and transferred to a vacuum drying oven for complete drying. The resulting electrode is then rolled and punched to obtain the positive electrode sheet, which has a compacted density of 2.8 g / cm³. 3 The coating weight is 10 mg / cm³. 2 .

[0122] 2. Preparation of negative electrode sheet

[0123] Sodium carboxymethyl cellulose and single-walled carbon nanotubes were dissolved in water at a mass ratio of 50:50, and then ultrasonically dispersed to prepare a slurry. The slurry was then coated onto the surface of copper foil, transferred to a vacuum drying oven for complete drying, and subsequently slit and die-cut to prepare a negative electrode sheet without a negative electrode structure. The compacted density of the negative electrode sheet was 1.2 g / cm³. 3 The coating weight is 0.1 mg / cm³. 2 .

[0124] 3. Preparation of electrolyte

[0125] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene glycol dimethyl ether (DME) and ethylene glycol diethyl ether (DEE) are mixed at a volume ratio of 50:50. Then, a certain amount of sodium hexafluorophosphate (NaPF6) is dissolved in the above mixed solvent and stirred evenly. The molar concentration of sodium hexafluorophosphate is 1 mol / L. Subsequently, trimethyl phosphate is added to the electrolyte. Based on the total mass of the electrolyte, the mass ratio of trimethyl phosphate is 0.2%. The mixture is stirred evenly to form the final electrolyte for use.

[0126] 4. Separating membrane

[0127] Polypropylene film is used as the separator.

[0128] 5. Preparation of sodium-based secondary batteries without negative electrodes

[0129] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a sodium-free negative electrode secondary battery product.

[0130] The preparation methods of sodium-free secondary batteries in Examples 2-12 and Comparative Examples 1-4 are the same as those in Example 1, with the differences detailed in Table 1.

[0131] Example 12

[0132] The preparation method of the sodium-free secondary battery is the same as in Example 1, except that the mass ratio of trimethyl phosphate to triethyl phosphate in the electrolyte is 1:1.

[0133] Table 1

[0134]

[0135]

[0136] Performance testing

[0137] 1. Storage capacity retention rate

[0138] The sodium-ion secondary battery without a negative electrode was charged to 3.65V at a constant current of 0.2C at 25°C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and finally discharged to 1.5V at a constant current of 0.2C. The discharge capacity (C) before storage was obtained. d1 Then, the battery was charged again with a constant current of 0.2C to 3.65V, followed by constant voltage charging at 3.65V until the current dropped to 0.05C. The battery was then stored in a 60℃ constant temperature chamber for 30 days. After removal, the battery was placed at 25℃ and charged with a constant current of 0.2C to 3.65V, followed by constant voltage charging at 3.65V until the current dropped to 0.05C, and then discharged with a constant current of 0.2C to 1.5V. The discharge capacity (C) after storage was obtained. d2 And calculate the capacity retention rate of the sodium-free secondary battery according to the following formula:

[0139] Storage capacity retention rate = C d2 / C d1 ×100%.

[0140] 2. Cyclic performance test

[0141] At 25°C, the prepared sodium secondary battery without a negative electrode was allowed to stand for 30 minutes, then discharged at a constant current of 0.33C to 3.65V, followed by charging at a constant voltage of 3.65V until the current dropped to 0.05C. After standing for 1 hour, it was discharged at a constant current of 0.33C to 1.5V to obtain the initial capacity (C0). After standing for 1 hour, it was charged again at a constant current of 0.33C to 3.65V, followed by charging at a constant voltage of 3.65V until the current dropped to 0.05C. After standing for 1 hour, it was discharged at a constant current of 0.33C to 1.5V to obtain the process capacity (C1). The above steps were repeated for the same battery, and the process capacity (C1) of the battery was recorded after the 200th cycle. 200 The capacity retention rate after 200 cycles = C 200 / C0×100%.

[0142] 3. Gas production volume test during storage

[0143] Before capacity testing, the cell volume (V1, mL) was measured using the water displacement method at 25°C. The sodium-ion secondary battery without a negative electrode was charged to 3.65V at a constant current of 0.2C at 25°C, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and finally discharged to 1.5V at a constant current of 0.2C. The discharge capacity before storage (C) was obtained. d1Then, the battery was charged again with a constant current of 0.2C to 3.65V, followed by constant voltage charging at 3.65V until the current dropped to 0.05C. The battery was then stored in a 60℃ constant temperature chamber for 30 days. After removal, the battery was placed at 25℃ to test the cell volume (V2, mL) after storage, and the gas production of the sodium-ion secondary battery without a negative electrode was calculated using the following formula: Gas production = [V2 - V1] / C d1 .

[0144] The test results of sodium-free secondary batteries in Examples 1-12 and Comparative Examples 1-4 are shown in Table 2.

[0145] Table 2

[0146]

[0147]

[0148] As can be seen from the comparison between Examples 1-12 and Comparative Examples 1-4, the battery proposed in this application produces less gas and has better storage and cycle performance. This indicates that by using an ether solvent and simultaneously adding a phosphate ester additive to the electrolyte, and controlling the content of the phosphate ester additive, the side reactions between the positive electrode active material and the ether solvent, and between the negative electrode sodium metal and the ether solvent, are reduced during battery cycling, thus reducing the consumption of active sodium.

[0149] As can be seen from the comparison between Examples 1-5 and Comparative Examples 2 and 4, by controlling the content of phosphate ester additives, a battery with low gas production and excellent cycle storage performance can be obtained, reducing the risk of excessive phosphate ester additives reacting with sodium metal in the negative electrode.

[0150] As can be seen from Examples 6-9 and Example 12, different types of phosphate ester additives can all reduce battery gas production and improve battery cycle storage performance.

[0151] As can be seen from Examples 10 and 11, batteries with low gas production and excellent cycle and storage performance can be obtained by using different types of ether solvents in the electrolyte.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery, characterized in that, include: A positive electrode sheet, the positive electrode sheet including a positive current collector, the positive current collector having a positive active material layer on at least one side, the positive active material layer including a positive active material; The negative electrode includes a negative current collector, and metallic sodium is deposited in situ on the negative current collector during charging of the sodium secondary battery. The electrolyte comprises an ether solvent and a phosphate ester additive, wherein the phosphate ester additive accounts for 0.2%-5% of the total mass of the electrolyte.

2. The sodium secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the phosphate ester additive accounts for 1%-3.5% of the total mass.

3. The sodium secondary battery according to claim 1 or 2, characterized in that, The phosphate ester additives include compounds represented by Formula 1: R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

4. The sodium secondary battery according to any one of claims 1-3, characterized in that, The phosphate ester additives include one or more of the following: trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

5. The sodium secondary battery according to any one of claims 1-4, characterized in that, The phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

6. The sodium secondary battery according to any one of claims 1-5, characterized in that, The ether solvents include one or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane.

7. The sodium secondary battery according to any one of claims 1-6, characterized in that, The electrolyte also includes an electrolyte salt, which includes NaPF6.

8. The sodium secondary battery according to claim 7, characterized in that, The molar concentration of NaPF6 in the electrolyte is 0.5 mol / L to 2 mol / L.

9. The sodium secondary battery according to any one of claims 1-8, characterized in that, The positive electrode active material includes NaMO2, wherein M includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu.

10. The sodium secondary battery according to any one of claims 1-9, characterized in that, At least one side of the negative electrode current collector has an interface modification layer, which includes an adhesive and a conductive agent.

11. The sodium secondary battery according to claim 10, characterized in that, The thickness of the interface modification layer is 0.5μm-2μm.

12. The sodium secondary battery according to any one of claims 1-11, characterized in that, The positive electrode sheet satisfies one or more of the following conditions: The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 -3.5g / cm 3 ; The coating weight of the positive electrode sheet is 5 mg / cm³. 2 -30mg / cm 2 .

13. The sodium secondary battery according to any one of claims 1-12, characterized in that, The negative electrode sheet satisfies one or more of the following conditions: The compaction density of the negative electrode sheet is 1 g / cm³. 3 -2g / cm 3 ; The coating weight of the negative electrode sheet is 0.1 mg / cm³. 2 -0.2mg / cm 2 .

14. An electrolyte, characterized in that, It includes ether solvents and phosphate ester additives, with the phosphate ester additives accounting for 0.2%-5% of the total mass of the electrolyte.

15. The electrolyte according to claim 14, characterized in that, The phosphate ester additives account for 1%-3.5% of the total mass.

16. The electrolyte according to claim 14 or 15, characterized in that, The phosphate ester additives include compounds represented by Formula 1: R1, R2, and R3 each independently include an alkyl group with 1 to 8 carbon atoms.

17. The electrolyte according to any one of claims 14-16, characterized in that, The phosphate ester additives include one or more of the following: trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, and trioctyl phosphate.

18. The electrolyte according to any one of claims 14-17, characterized in that, The phosphate ester additives include one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

19. The electrolyte according to any one of claims 14-18, characterized in that, The ether solvents include one or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran, and 1,3-dioxane.

20. The electrolyte according to any one of claims 14-19, characterized in that, The electrolyte also includes an electrolyte salt, which includes NaPF6.

21. The electrolyte according to claim 20, characterized in that, The molar concentration of NaPF6 in the electrolyte is 0.5 mol / L to 2 mol / L.

22. An electrical appliance, characterized in that, Includes the sodium secondary battery according to any one of claims 1-13.

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