Sodium metal battery and electric device

Abstract

The application provides a sodium metal battery and an electric device. The sodium metal battery comprises a separator film and an electrolyte, the separator film comprises a base film and a solid electrolyte layer on at least one surface of the base film, and the solid electrolyte layer comprises a binder, wherein the binder comprises polyvinylidene fluoride; and the electrolyte comprises a non-aqueous solvent and a sodium salt dissolved in the non-aqueous solvent, and the sodium salt comprises sodium tetrafluoroborate. Thus, the sodium metal battery provided by the application has good cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a sodium metal battery and an electrical device. Background Technology

[0002] Sodium metal batteries are rechargeable batteries that rely on the transfer of ions between the positive and negative electrodes to achieve charging and discharging. Since the negative electrode of a sodium metal battery is metallic sodium, the reaction occurring on the negative electrode side involves the deposition and stripping of metallic sodium. During charging and discharging, the sodium ion flux varies at different locations on the surface of the sodium metal negative electrode, resulting in uneven deposition and the formation of protruding deposits on the negative electrode side. Once these protrusions form, the tip effect further intensifies them, eventually forming dendritic deposits, i.e., sodium dendrites. The continuously growing sodium dendrites can pierce the separator, causing direct contact between the positive and negative electrodes, leading to a short circuit. Once an internal short circuit occurs, the battery capacity rapidly decays within a relatively short number of cycles, resulting in a significant decrease in cycle performance. Therefore, to improve the cycle performance of sodium metal batteries, higher requirements are placed on the selection of materials and the structural design of sodium metal batteries. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a sodium metal battery that aims to improve the cycle performance of the battery.

[0004] To achieve the above objectives, a first aspect of this application provides a sodium metal battery, comprising a separator and an electrolyte. The separator comprises a base film and a solid electrolyte layer located on at least one surface of the base film. The solid electrolyte layer comprises an adhesive, wherein the adhesive comprises polyvinylidene fluoride. The electrolyte comprises a non-aqueous solvent and a sodium salt dissolved in the non-aqueous solvent, wherein the sodium salt comprises sodium tetrafluoroborate.

[0005] This application includes at least the following beneficial effects: the electrolyte of this application includes sodium tetrafluoroborate, which has good compatibility with sodium metal, and sodium tetrafluoroborate can form a NaBO-containing electrolyte on the negative electrode side surface. x The inorganic solid electrolyte interphase (SEI) film between Na and F; the SEI film can prevent sodium metal from contacting PVDF on the solid electrolyte layer, thereby suppressing the occurrence of side reactions, allowing the solid electrolyte layer to function normally and enabling it to conduct Na. + This improves the uniformity of sodium metal deposition on the negative electrode side surface, thereby improving the battery's cycle performance.

[0006] In some embodiments, the concentration of sodium tetrafluoroborate in the electrolyte is 0.1 mol / L to 0.3 mol / L. This can further improve the cycle performance of the battery.

[0007] In some embodiments, the concentration of sodium tetrafluoroborate in the electrolyte is 0.15 mol / L to 0.25 mol / L. This can further improve the cycle performance of the battery.

[0008] In some embodiments, the non-aqueous solvent includes linear ether solvents and cyclic ether solvents. This can further improve the cycle performance of sodium metal batteries. This application uses a combination of linear and cyclic ether solvents as the non-aqueous solvent for the electrolyte, which has good compatibility with sodium metal. The solubility of NaBF4 in cyclic ether solvents is relatively low, therefore it needs to be combined with a linear ether solvent with strong sodium salt dissolution ability. Secondly, cyclic ether solvents have a weak solvation effect, further promoting the oxidation of BF4. - Enter Na + The solvation shell allows for the preferential formation of a NaBO-containing layer on the negative electrode side surface during formation. x SEI films with Na-F. Weak solvation of cyclic ether solvents and BF4. - High donor numbers synergistically promote BF4 - Enter Na + The solvated shell is used to improve the effect of NaBF4 on battery cycle performance.

[0009] In some embodiments, the cyclic ether solvent includes at least one selected from tetrahydrofuran, methyltetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, and 1,3-dioxane. This can further enhance the effect of NaBF4 on improving battery cycle performance.

[0010] In some embodiments, the volume fraction of the cyclic ether solvent is 10%-50% based on the total volume of the non-aqueous solvent. This can further enhance the effect of NaBF4 on improving battery cycle performance.

[0011] In some embodiments, the volume fraction of the cyclic ether solvent is 15%-30% based on the total volume of the non-aqueous solvent. This balances the solubility and weak solvation effect of the non-aqueous solvent, thereby improving the battery cycle performance.

[0012] In some embodiments, the linear ether solvent includes at least one selected from 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, and diethylene glycol dibutyl ether. Therefore, a linear ether solvent suitable for sodium metal battery systems can be selected to improve the dissolution effect of sodium salts.

[0013] In some embodiments, the solid electrolyte layer comprises a solid electrolyte, which includes oxide ceramic particles with the chemical formula Na. 1+x Zr2Si x P 3-x O 12 Where x ranges from 0 to 3. Therefore, selecting suitable oxide ceramic particles can improve the conductivity of Na. + The ability to improve the uniformity of sodium metal deposition on the negative electrode side surface can thus improve the cycle performance of the battery.

[0014] In some embodiments, the oxide ceramic particles may further be doped with X ions at the atomic sites of Zr, wherein X includes at least one of Mg, Ca, Sr, Ba, Sc, Zn, La, and Yb. This improves the ionic conductivity of the oxide ceramic particles, thereby enhancing the conduction of Na+. + This improves the uniformity of sodium metal deposition on the negative electrode surface, thereby enhancing the battery's cycle performance.

[0015] In some embodiments, the mass ratio of the oxide ceramic particles to the binder is (15-25):1. Therefore, by selecting a suitable mass ratio of oxide ceramic particles to binder, the oxide ceramic particles can be firmly adhered to the surface of the release membrane.

[0016] In some embodiments, the thickness of the solid electrolyte layer is 1 μm-5 μm. Therefore, selecting a suitable thickness for the solid electrolyte layer can improve Na... + This improves the conductivity of sodium metal, thereby enhancing the uniformity of sodium metal deposition on the negative electrode surface and thus improving the cycle performance of the battery.

[0017] In some embodiments, the sodium salt further includes sodium hexafluorophosphate. Therefore, this application utilizes sodium hexafluorophosphate, which has good compatibility with sodium metal; NaBF4 has low solubility in the electrolyte and needs to be used in conjunction with NaPF6 to increase the Na concentration in the electrolyte. + The concentration of electrolyte helps improve electrolyte performance and battery electrochemical characteristics.

[0018] In some embodiments, the concentration of sodium hexafluorophosphate in the electrolyte is 0.6 mol / L to 1.8 mol / L. Therefore, controlling the concentration of sodium hexafluorophosphate in the electrolyte can improve the performance of the electrolyte and the electrochemical characteristics of the battery.

[0019] In some embodiments, the electrolyte comprises: a linear ether solvent, a cyclic ether solvent, sodium hexafluorophosphate, and sodium tetrafluoroborate. Thus, the combination of linear ether solvents, cyclic ether solvents, sodium hexafluorophosphate, and sodium tetrafluoroborate is suitable for sodium metal battery systems to improve battery cycle performance.

[0020] In some embodiments, the base film includes at least one of glass fiber film, nonwoven film, polyethylene film, polypropylene film, and polyvinylidene fluoride film.

[0021] In some embodiments, the sodium metal battery includes a negative electrode-free sodium metal battery. This application is applicable to negative electrode-free sodium metal battery systems, which can improve the uniformity of sodium metal deposition and thus improve the cycle performance of negative electrode-free sodium metal batteries.

[0022] In a second aspect, this application provides an electrical device including the sodium metal battery of the first aspect. Thus, the electrical device possesses all the features and advantages of the aforementioned sodium metal battery, which will not be repeated here. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a sodium metal battery according to one embodiment of this application.

[0024] Figure 2 yes Figure 1 An exploded view of a sodium metal battery according to an embodiment of this application is shown.

[0025] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0026] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0027] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0028] Figure 6 This is a schematic diagram of an electrical device using a sodium metal battery as a power source according to an embodiment of this application.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Sodium metal battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0031] The embodiments of the sodium metal battery and power-consuming device of this application are hereby specifically disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0032] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

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

[0035] 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.

[0036] One of the main reasons why the sodium ion flux varies at different locations on the negative electrode surface of a sodium metal battery is that sodium ions (Na...) + When passing through the separator, the ionic insulating properties of the separator framework affect the Na+. + Na accumulates in the pores of the separating membrane. + After passing through the isolation membrane, these crowded Na + Na tends to accumulate near the pores of the membrane, leading to... + Non-uniform aggregation occurs on the negative electrode side; this non-uniform aggregation is particularly severe under high current density conditions; Na + Non-uniform aggregation on the negative electrode side leads to the formation of a strong space charge near the negative electrode, which promotes the growth of sodium dendrites and may subsequently cause an internal short circuit in the battery. Therefore, if Na... + The ability to uniformly pass through the separator and be delivered to the negative electrode side surface is key to improving battery cycle performance.

[0037] In order to make Na + It can pass uniformly through the separator and be transported to the negative electrode side. An effective strategy is to set a substrate with excellent Na+ on the separator. + A solid electrolyte layer with oxide ceramic particles exhibiting conductive properties. The solid electrolyte layer with oxide ceramic particles can promote the conduction of Na+. + To facilitate the drainage of Na+ accumulated in the pores of the membrane. + Increase Na + The uniform charge distribution behind the separator allows for more uniform deposition of sodium metal on the negative electrode surface. Oxide ceramic particles need to be mixed with a binder to enhance their adhesion, ensuring a firm bond between the oxide ceramic particles and the separator surface. However, when polyvinylidene fluoride (PVDF) is used as a binder, PVDF undergoes side reactions with the reactive sodium metal, limiting the application of solid-state electrolyte layers in sodium metal batteries.

[0038] Based on this, this application proposes a sodium metal battery, including a separator and an electrolyte. The separator includes a base film and a solid electrolyte layer located on at least one surface of the base film. The solid electrolyte layer includes an adhesive, wherein the adhesive includes polyvinylidene fluoride. The electrolyte includes a non-aqueous solvent and a sodium salt dissolved in the non-aqueous solvent, wherein the sodium salt includes sodium tetrafluoroborate.

[0039] In sodium metal battery systems, the compatibility between sodium salts and metallic sodium must be considered first, i.e., side reactions between sodium salts and metallic sodium should be minimized. The embodiments of this application use sodium tetrafluoroborate (NaBF4) as the sodium salt, which has good compatibility with metallic sodium. NaBF4 containing boron and fluorine is introduced into the electrolyte. -Having a high number of donors means BF4 - It can provide more electron pairs with Na + They form a strong interaction, therefore, BF4 - Can enter Na + The solvation shell can preferentially form a NaBO-containing layer on the negative electrode side surface during formation. x Inorganic solid electrolyte interphase (SEI) membrane with Na-F.

[0040] XPS testing is a surface analysis technique that determines the elemental composition of a sample surface by measuring the energy distribution of photoelectrons emitted when X-rays excite the sample surface. The testing instrument is an Axis Supra / Supra+ X-ray photoelectron spectrometer, conforming to standard GB / T 33502-2017. XPS testing revealed that the SEI film contains boron and fluorine.

[0041] The SEI film can prevent contact between sodium metal and PVDF on the solid electrolyte layer, thus suppressing side reactions and allowing the solid electrolyte layer to function normally, enabling it to conduct sodium. + This improves the uniformity of sodium metal deposition on the negative electrode side surface, thereby improving the battery's cycle performance.

[0042] Anode-free sodium metal batteries are a novel sodium metal battery technology. Because they lack sodium metal sheets and other negative electrode active materials, anode-free sodium metal batteries can reduce the overall weight and volume of the battery, resulting in higher energy density. During the first charge and discharge cycle, sodium ions in the positive electrode active material are reduced and deposited on the undercoat layer on the negative electrode side, forming metallic sodium, which serves as the negative electrode of the anode-free sodium metal battery. Therefore, anode-free sodium metal batteries place higher demands on the uniformity of sodium metal deposition. This application is applicable to anode-free sodium metal battery system, which can improve the uniformity of sodium metal deposition, thereby improving the cycle performance of the anode-free sodium metal battery.

[0043] In some embodiments, the concentration of sodium tetrafluoroborate in the electrolyte is 0.1 mol / L to 0.3 mol / L. In the embodiments of this application, the concentration of sodium tetrafluoroborate in the electrolyte is the initial concentration of the electrolyte. By controlling the concentration of sodium tetrafluoroborate in the electrolyte, BF4 can be further promoted. - NaBO-containing compounds are formed on the negative electrode side surface. x The SEI film of Na-F further suppresses the occurrence of side reactions, thereby improving the uniformity of sodium metal deposition on the negative electrode side surface and improving the cycle performance of the battery.

[0044] As an example, the concentration of sodium tetrafluoroborate in the electrolyte can be 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.20 mol / L, 0.22 mol / L, 0.24 mol / L, 0.26 mol / L, 0.28 mol / L, or 0.3 mol / L.

[0045] In some embodiments, the concentration of sodium tetrafluoroborate in the electrolyte is 0.15 mol / L to 0.25 mol / L. This can improve the effect of NaBF4 on battery cycle performance.

[0046] In some embodiments, the non-aqueous solvent includes linear ether solvents and cyclic ether solvents. In sodium metal battery systems, the compatibility of the non-aqueous solvent and metallic sodium needs to be considered. The embodiments of this application use a combination of linear ether solvents and cyclic ether solvents as the non-aqueous solvent for the electrolyte, exhibiting good compatibility with sodium metal. Since the solubility of NaBF4 in cyclic ether solvents is relatively low, it is necessary to combine it with a linear ether solvent that has a strong ability to dissolve sodium salts; secondly, cyclic ether solvents have a weak solubilizing effect, making NaBF4 more soluble in sodium. + The surrounding solvated shell forms a weak coordination structure, which further promotes the BF4 - Enter Na + The solvation shell allows for the preferential formation of a NaBO-containing layer on the negative electrode side surface during formation. x SEI films with Na-F. Weak solvation of cyclic ether solvents and BF4. - High donor numbers synergistically promote BF4 - Enter Na + The solvated shell is used to improve the effect of NaBF4 on battery cycle performance.

[0047] In some embodiments, the cyclic ether solvent includes at least one selected from tetrahydrofuran, methyltetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxopentane, and 1,3-dioxane. Therefore, a cyclic ether solvent suitable for sodium metal battery systems can be selected to promote BF4… - Enter Na + The solvation shell enhances the effect of NaBF4 on improving battery cycle performance.

[0048] In some embodiments, the volume fraction of cyclic ether solvents is 10%-50% based on the total volume of non-aqueous solvents. It is understood that the portion of the non-aqueous solvent excluding cyclic ether solvents is the linear ether solvent. This balances the solubility and weak solvation effect of the non-aqueous solvent, thereby improving the battery cycle performance.

[0049] As an example, the volume fraction of cyclic ether solvents can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, depending on the total volume of the non-aqueous solvent.

[0050] In some embodiments, the volume fraction of the cyclic ether solvent is 15%-30% based on the total volume of the non-aqueous solvent. This further balances the solubility and weak solvation effect of the non-aqueous solvent, thereby improving the battery cycle performance.

[0051] In some embodiments, the linear ether solvent includes at least one selected from 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, and diethylene glycol dibutyl ether. Therefore, a linear ether solvent suitable for sodium metal battery systems can be selected to improve the dissolution effect of sodium salts.

[0052] In some embodiments, the sodium salt also includes sodium hexafluorophosphate. In sodium metal battery systems, the compatibility of the sodium salt and metallic sodium must first be considered. The embodiments of this application use sodium hexafluorophosphate (NaPF6) as the sodium salt, which has good compatibility with sodium metal. NaBF4 has low solubility in the electrolyte and needs to be used in conjunction with NaPF6 to increase the Na concentration in the electrolyte. + The concentration of electrolyte helps improve electrolyte performance and battery electrochemical characteristics.

[0053] In some embodiments, the concentration of sodium hexafluorophosphate in the electrolyte is 0.6 mol / L to 1.8 mol / L. In the embodiments of this application, the concentration of sodium hexafluorophosphate in the electrolyte is the initial concentration of the electrolyte. By controlling the concentration of sodium hexafluorophosphate in the electrolyte, the performance of the electrolyte and the electrochemical characteristics of the battery can be improved.

[0054] As an example, the concentration of sodium hexafluorophosphate in the electrolyte can be 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, or 1.8 mol / L.

[0055] In some embodiments, the electrolyte includes linear ether solvents, cyclic ether solvents, sodium hexafluorophosphate, and sodium tetrafluoroborate. In sodium metal battery systems, the compatibility of sodium salts, non-aqueous solvents, and sodium metal must first be considered. In this embodiment, sodium hexafluorophosphate and sodium tetrafluoroborate are used as sodium salts, and linear ether solvents and cyclic ether solvents are used as non-aqueous solvents, both of which exhibit good compatibility with sodium metal. Secondly, the weak solvation of cyclic ether solvents and BF4... - High donor numbers synergistically promote BF4 - Enter Na +The solvation shell allows for the preferential formation of a NaBO-containing layer on the negative electrode side surface during formation. x The SEI film, along with the Na-F layer, prevents contact between sodium metal and PVDF on the solid electrolyte layer, thus suppressing side reactions and allowing the solid electrolyte layer to function properly, enabling it to conduct Na+. + To improve the uniformity of sodium metal deposition on the negative electrode surface, thereby improving the battery's cycle performance. NaBF4 has poor solubility in cyclic ether solvents, requiring the use of linear ether solvents with strong sodium salt dissolving capabilities; and sodium hexafluorophosphate is also used to improve electrolyte performance and battery electrochemical characteristics.

[0056] Therefore, the combination of linear ether solvents, cyclic ether solvents, sodium hexafluorophosphate, and sodium tetrafluoroborate can be applied to sodium metal battery systems to improve battery cycle performance.

[0057] In some embodiments, the solid electrolyte layer includes a solid electrolyte, which comprises oxide ceramic particles with the chemical formula Na. 1+x Zr2Si x P 3-x O 12 Where x is 0-3. Na oxide ceramic particles 1+ x Zr2Si x P 3-x O 12 (0≤x≤3) possesses excellent ionic conductivity and high Na+. + The transfer number allows for the construction of three-dimensional fast Na+ in solid electrolyte layers. + Channel networks help Na + Redistribution after passing through the base membrane to enhance Na + The uniformity of distribution guides Na + Smooth migration improves the uniformity of sodium metal deposition, thereby enhancing battery cycle performance. Furthermore, even in localized areas where sodium dendrites appear, the hard barrier formed by the oxide ceramic particles inhibits further dendrite growth. This barrier protects the separator, reducing the risk of internal short circuits in the battery. Therefore, selecting suitable oxide ceramic particles can improve their sodium conductivity. + The ability to improve the uniformity of sodium metal deposition on the negative electrode side surface can thus improve the cycle performance of the battery.

[0058] As an example, the oxide ceramic particles could be NaZr2P3O 12 Na2Zr2SiP2O 12 Na3Zr2Si3PO 12 Na4Zr2Si3O12 or Na3Zr2Si2PO 12 .

[0059] In some embodiments, the oxide ceramic particles may further be doped with X ions at the Zr atomic sites, where X includes at least one of Mg, Ca, Sr, Ba, Sc, Zn, La, and Yb. This improves the ionic conductivity of the oxide ceramic particles, thereby enhancing the conduction of Na+. + This improves the uniformity of sodium metal deposition on the negative electrode surface, thereby enhancing the battery's cycle performance.

[0060] As an example, oxide ceramic particles can be Na 3.4 La 0.4 Zr 1.6 Si2PO 12 Na 3.4 Sr 0.4 Zr 1.6 Si2PO 12 Na 3.4 Zn 0.4 Zr 1.6 Si2PO 12 Na 3.4 Yb 0.4 Zr 1.6 Si2PO 12 or Na2La 0.4 Zr 1.6 Si2PO 12 .

[0061] In some embodiments, the mass ratio of oxide ceramic particles to binder is (15-25):1. Therefore, by selecting a suitable mass ratio of oxide ceramic particles to binder, the oxide ceramic particles can be firmly adhered to the surface of the release membrane.

[0062] As an example, the mass ratio of oxide ceramic particles to binder can be 15:1, 17:1, 19:1, 21:1, 23:1 or 25:1.

[0063] In some embodiments, the thickness of the solid electrolyte layer is 1 μm-5 μm. Therefore, selecting a suitable thickness for the solid electrolyte layer can improve the performance of Na+. + This improves the conductivity of sodium metal, thereby enhancing the uniformity of sodium metal deposition on the negative electrode surface and thus improving the cycle performance of the battery.

[0064] In some embodiments, the base film includes at least one of glass fiber film, nonwoven film, polyethylene film, polypropylene film, and polyvinylidene fluoride film.

[0065] This application does not impose any particular restrictions on the type of base membrane; any known porous base membrane with good chemical and mechanical stability can be selected.

[0066] In some embodiments, the base film can be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0067] In addition, the sodium metal battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0068] In one embodiment of this application, a sodium metal battery is provided.

[0069] Typically, a sodium metal battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, sodium ions transfer back and forth between the positive and negative electrodes to achieve charging and discharging. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0070] [Positive electrode plate]

[0071] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0072] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0073] In this application, BF4 - Not only can it form a NaBO-containing structure at the negative electrode x The Na-F SEI film can also form a positive electrode electrolyte interface (CEI) film on the positive electrode side surface. The CEI film can reduce the side reactions of PVDF on the positive electrode side, thereby reducing the consumption of active sodium.

[0074] 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.).

[0075] In some embodiments, when the battery is a sodium metal battery, the positive electrode active material may be a positive electrode active material known in the art for sodium metal batteries.

[0076] As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue sodium compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0077] In some embodiments, the transition metal in the sodium transition metal oxide can be at least one selected from Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu. The chemical formula of the sodium transition metal oxide can satisfy Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0078] In some embodiments, the polyanionic compound may be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si; n represents (YO4). n- The price state.

[0079] In some embodiments, the polyanionic compound may also have sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n-The valence state of halogens can include at least one of F, Cl, and Br.

[0080] In some embodiments, the polyanionic compound may also be a tetrahedral compound containing sodium ions (YO4). n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. M may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may include at least one of P, S and Si, and n represents (YO4). n- The valence state, Z represents transition metal, m represents (ZO) y ) m+ The valence state of halogens can include at least one of F, Cl, and Br.

[0081] As an example, polyanionic compounds can satisfy the chemical formulas NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0082] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0083] As an example, Prussian blue compounds can satisfy the chemical formula Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0084] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Na content changes when the positive electrode active material is applied to the battery system.

[0085] In the list of positive electrode active materials for sodium metal batteries in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0086] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] 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.

[0089] [Negative electrode plate]

[0090] In some implementations, when the battery is a sodium metal battery, the negative electrode can be a sodium metal sheet, or a composite material or alloy containing sodium metal.

[0091] In some implementations, when the battery is a sodium metal battery without a negative electrode, it does not use sodium metal sheets or other negative electrode active materials. Instead, it uses only a negative electrode current collector as the negative electrode. Sodium plating is completed during the first charge, and the negative electrode returns to the positive electrode during discharge, thus achieving charge-discharge cycles. Because there is no negative electrode material and only a negative electrode current collector is used, the sodium metal battery without a negative electrode can effectively overcome the defects of sodium metal batteries and achieve a higher energy density than that of sodium metal negative electrodes.

[0092] 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] In some embodiments, a base coating is provided on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the base coating is provided on either or both of the opposite surfaces of the negative electrode current collector.

[0094] In some embodiments, the base coating can be a metal layer with a body-centered cubic structure, including any one of α-Fe, V, Nb, Cr, Mo, Ta, and W.

[0095] In some embodiments, the primer layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0096] In some embodiments, the base coating may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] In some embodiments, the base coating may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0098] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a base coating slurry; coating the base coating slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet of the sodium metal battery without a negative electrode can be obtained.

[0099] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0100] In some embodiments, the sodium metal battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0101] In some embodiments, the outer packaging of a sodium metal battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a sodium metal battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0102] This application does not impose any particular limitation on the shape of the sodium metal battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1This is an example of a square-structured sodium metal battery.

[0103] 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 metal 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.

[0104] In some embodiments, sodium metal batteries can be assembled into battery modules, and the number of sodium metal 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.

[0105] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple sodium metal 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, the multiple sodium metal batteries 5 can be fixed in place using fasteners.

[0106] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of sodium metal batteries 5 are received.

[0107] 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.

[0108] 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.

[0109] In a second aspect, this application provides an electrical device including the sodium metal battery of the first aspect. Thus, the electrical device possesses all the features and advantages of the aforementioned sodium metal battery, which will not be repeated here. As the electrical device, a sodium metal battery, a battery module, or a battery pack can be selected according to its usage requirements.

[0110] 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 high power and high energy density requirements of sodium metal batteries for this device, a battery pack or battery module can be used.

[0111] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a thin and light design and can use sodium metal batteries as their power source.

[0112] Example

[0113] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0114] I. Preparation of Sodium Metal Batteries

[0115] Example 1

[0116] 1) Preparation of positive electrode sheet

[0117] 10 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 10 wt% carbon black conductive agent and 80 wt% positive electrode active material (NaNi) were added. 0.20 Fe 0.22 Cu 0.13 Mn 0.45 A uniformly dispersed slurry was prepared. The slurry was then evenly coated onto the surface of aluminum foil and completely dried in a vacuum drying oven. The resulting electrode was rolled and then punched to obtain the positive electrode. The compacted density of the positive electrode was 2.8 g / cm³. 3 The coating weight is 10 mg / cm³. 2 The coating thickness is 35.7 μm.

[0118] 2) Preparation of negative electrode sheet

[0119] 5g of carboxymethyl cellulose (CMC) was dissolved in 1000mL of water, and then 5g of single-walled carbon nanotubes were added. After ultrasonic dispersion, a slurry was prepared. The slurry was then coated onto the surface of a copper foil and completely dried in a vacuum drying oven. Afterward, it was slit and die-cut to obtain a negative electrode sheet without a negative electrode structure. The coating weight of the negative electrode was 0.1mg / cm³. 2 The coating thickness is approximately 1 μm.

[0120] 3) Separating membrane

[0121] A 12μm thick polyethylene film was selected as the separator.

[0122] First, 5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and then 95 wt% oxide ceramic solid electrolyte particles Na3Zr2Si2PO were added. 12 A uniformly dispersed slurry was prepared. The slurry was then evenly coated onto both sides of a 12 μm polyethylene membrane using a coating method, and subsequently transferred to a vacuum drying oven for complete drying. The membrane was then die-cut to obtain the desired separator. In the separator, the thickness of the solid electrolyte layer on one side of the polyethylene membrane was 1 μm.

[0123] 4) Preparation of electrolyte

[0124] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene glycol dimethyl ether (DME) and 1,3-dioxane were used as non-aqueous solvents, with DME comprising 70% by volume and 1,3-dioxane comprising 30% by volume. Sodium hexafluorophosphate (NaPF6) was then dissolved in the non-aqueous solvent to form an electrolyte with a concentration of 1 mol / L. The solution was stirred until homogeneous. Sodium tetrafluoroborate (NaBF4) was then added to the electrolyte with a concentration of 0.2 mol / L, and the solution was stirred until homogeneous to obtain the desired electrolyte.

[0125] 5) Battery manufacturing

[0126] 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 metal battery without a negative electrode.

[0127] Examples 2-33

[0128] The sodium metal batteries provided in Examples 2-33 are prepared in the same way as those in Example 1. The specific differences are shown in Table 1.

[0129] Comparative Examples 1-3

[0130] The sodium metal batteries provided in Comparative Examples 1-3 were prepared using the same method as those in Example 1, with specific differences shown in Table 1.

[0131] The relevant parameters of the sodium metal batteries in Examples 1-33 and Comparative Examples 1-3 are shown in Table 1 below.

[0132]

[0133]

[0134]

[0135] II. Performance Testing

[0136] 1. Testing Method

[0137] (1) Gas production volume test

[0138] Before capacity testing, the cell volume (V1) was measured using the water displacement method at 25°C. The sodium-ion battery 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 at 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) after storage, and the gas production of the sodium-ion battery was calculated using the following formula:

[0139] Gas production = [Cell volume after storage (V2) - Cell volume before storage (V1)] / Cell capacity C d1 The lower the gas production, the better the chemical stability of the battery.

[0140] (2) Storage capacity retention rate

[0141] The sodium-ion battery was charged at 25°C with a constant current of 0.2C to 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and finally discharged at a constant current of 0.2C to 1.5V. The discharge capacity (C) before storage 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℃ 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-ion battery according to the following formula:

[0142] Storage capacity retention rate = C d2 / C d1 ×100%. Among them, the higher the capacity retention rate, the better the battery's long-term cycle stability and the higher its reliability.

[0143] (3) Cyclic performance test

[0144] At 25°C, the prepared battery was left to stand for 30 minutes, then charged to 3.65V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage of 3.65V. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the initial capacity (C0). After standing for 1 hour, it was charged to 3.65V with a constant current of 0.33C again, and then charged to 0.05C with a constant voltage of 3.65V until the current dropped to 0.05C. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the process capacity (C1). The above steps were repeated for the same battery, and the number of cycles N when the cycle capacity decayed to 80% was recorded.

[0145] 2. Test Results

[0146] The sodium-ion batteries obtained in Examples 1-33 and Comparative Examples 1-3 were subjected to performance tests. The test results are shown in Table 2 below.

[0147] Table 2: Performance test results of Examples 1-33 and Comparative Examples 1-3

[0148]

[0149]

[0150] As shown in Table 2, the number of cycles for batteries in Examples 1-33 is greater than that for Comparative Examples 1-3, indicating that the cycle performance of batteries in Examples 1-33 is better than that of Comparative Examples 1-3. Therefore, the solid electrolyte layer formed on the surface of the base film and the sodium tetrafluoroborate added to the electrolyte in this application can improve the cycle performance of sodium metal batteries. Meanwhile, Examples 1-33 exhibit lower gas production and higher capacity retention, indicating that the sodium metal batteries of this application have good long-term cycle stability and high reliability.

[0151] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sodium metal battery, characterized in that, Including the separator and electrolyte, The separator includes a base membrane and a solid electrolyte layer on at least one surface of the base membrane, the solid electrolyte layer including an adhesive, wherein the adhesive includes polyvinylidene fluoride; The electrolyte includes a non-aqueous solvent and a sodium salt dissolved in the non-aqueous solvent, the sodium salt including sodium tetrafluoroborate.

2. The sodium metal battery according to claim 1, characterized in that, The concentration of sodium tetrafluoroborate in the electrolyte is 0.1 mol / L to 0.3 mol / L.

3. The sodium metal battery according to claim 2, characterized in that, The concentration of sodium tetrafluoroborate in the electrolyte is 0.15 mol / L to 0.25 mol / L.

4. The sodium metal battery according to any one of claims 1-3, characterized in that, The non-aqueous solvents include linear ether solvents and cyclic ether solvents.

5. The sodium metal battery according to claim 4, characterized in that, The cyclic ether solvents include at least one of tetrahydrofuran, methyltetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, and 1,3-dioxane.

6. The sodium metal battery according to any one of claims 4-5, characterized in that, Based on the total volume of the non-aqueous solvent, the volume fraction of the cyclic ether solvent is 10%-50%.

7. The sodium metal battery according to claim 6, characterized in that, Based on the total volume of the non-aqueous solvent, the volume fraction of the cyclic ether solvent is 15%-30%.

8. The sodium metal battery according to any one of claims 4-7, characterized in that, The linear ether solvents include at least one 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, and diethylene glycol dibutyl ether.

9. The sodium metal battery according to any one of claims 1-8, characterized in that, The solid electrolyte layer includes a solid electrolyte, which comprises oxide ceramic particles with the chemical formula Na. 1+ x Zr2Si x P 3-x O 12 , where x is 0-3.

10. The sodium metal battery according to claim 9, characterized in that, The oxide ceramic particles may also be doped with X ions at the atomic sites of Zr, wherein X includes at least one of Mg, Ca, Sr, Ba, Sc, Zn, La, and Yb.

11. The sodium metal battery according to any one of claims 9-10, characterized in that, The mass ratio of the oxide ceramic particles to the binder is (15-25):

1.

12. The sodium metal battery according to any one of claims 1-11, characterized in that, The thickness of the solid electrolyte layer is 1μm-5μm.

13. The sodium metal battery according to any one of claims 1-12, characterized in that, The sodium salt also includes sodium hexafluorophosphate.

14. The sodium metal battery according to claim 13, characterized in that, The concentration of sodium hexafluorophosphate in the electrolyte is 0.6 mol / L to 1.8 mol / L.

15. The sodium metal battery according to any one of claims 1-14, characterized in that, The electrolyte includes: linear ether solvents, cyclic ether solvents, sodium hexafluorophosphate, and sodium tetrafluoroborate.

16. The sodium metal battery according to any one of claims 1-15, characterized in that, The base membrane includes at least one of glass fiber membrane, non-woven fabric membrane, polyethylene membrane, polypropylene membrane, and polyvinylidene fluoride membrane.

17. The sodium metal battery according to any one of claims 1-16, characterized in that, The sodium metal battery includes a sodium metal battery without a negative electrode.

18. An electrical appliance, characterized in that, Including the sodium metal battery according to any one of claims 1-17.

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