Positive pole piece, sodium ion battery and electric device

Abstract

The embodiment of the invention discloses a positive pole piece, a sodium ion battery and an electric device. The positive pole piece comprises a positive current collector; the positive electrode film layer is arranged on the surface of at least one side of the positive electrode current collector, the positive electrode film layer comprises an oxygen absorbent, and anions of the oxygen absorbent have reducibility. When the positive pole piece is applied to the sodium-ion battery, the oxygen release phenomenon of the positive pole can be effectively improved, and the safety performance of the sodium-ion battery is improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a positive electrode sheet, a sodium-ion battery, and an electrical device using the same. Background Art

[0002] With the rapid development of social economy, energy and environment have become the focus of increasing concern. Among them, sodium-ion batteries with rich element reserves have been deeply studied and developed in recent years and are widely used in fields such as energy storage and electronic products.

[0003] Some positive electrode active materials of sodium-ion batteries may generate oxygen during the cycling process or in some extreme usage scenarios, which has an adverse effect on the cycling stability of sodium-ion batteries. Moreover, in some high-temperature or thermal runaway scenarios, the oxygen released by the positive electrode is likely to react with the active sodium inside the sodium-ion battery, triggering serious safety accidents. Therefore, how to improve the oxygen release phenomenon of the positive electrode and enhance the safety performance of sodium-ion batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a positive electrode sheet, a sodium-ion battery, and an electrical device using the same. The positive electrode sheet can effectively improve the oxygen release phenomenon of the positive electrode and enhance the safety performance of sodium-ion batteries.

[0005] In a first aspect, a positive electrode sheet is provided, including: a positive electrode current collector; a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including an oxygen absorber, and the anion of the oxygen absorber having reducibility.

[0006] In an embodiment of the present application, an oxygen absorber with a reducible anion is introduced into the positive electrode sheet. Once the positive electrode active material releases oxygen, the oxygen absorber in the positive electrode film layer can react with the oxygen, and its reducible anion can be oxidized by the oxygen, thereby consuming the oxygen released by the positive electrode active material. Thus, the oxygen release phenomenon of the positive electrode sheet during the cycling process can be effectively improved, and the safety performance of sodium-ion batteries can be enhanced.

[0007] In an implementable manner, the anion includes at least one of sulfite, phosphite, polyphosphate, and metaphosphate.

[0008] In an embodiment of the present application, inorganic anions with reducibility are selected. When the positive electrode releases oxygen, the reducibility of the inorganic anions can be used to react with the oxygen to consume the oxygen, and it has little impact on the DCR of sodium-ion batteries, reducing the DCR growth rate of sodium-ion batteries while enhancing the safety performance of sodium-ion batteries.

[0009] In an implementable manner, the cation of the oxygen absorber includes at least one of potassium ions and sodium ions.

[0010] In one possible implementation, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a transition metal oxide.

[0011] In one possible implementation, on the positive electrode sheet per unit area, the mass a of the positive electrode active material and the mass b of the oxygen scavenger satisfy: 18 ≤ (a:b) ≤ 189; optionally, 37 ≤ (a:b) ≤ 189.

[0012] In one possible implementation, the positive electrode film layer includes a positive electrode active material layer, and the positive electrode active material layer includes the positive electrode active material and the oxygen scavenger.

[0013] In one possible implementation, the mass fraction m of the oxygen scavenger in the positive electrode active material layer 1 satisfies: 0.5% ≤ m 1 ≤ 5%; optionally, 0.5% ≤ m 1 ≤ 2.5%.

[0014] In one possible implementation, the positive electrode film layer includes: a positive electrode active material layer and a positive electrode coating layer, and the positive electrode active material layer is disposed between the positive electrode current collector and the positive electrode coating layer; the positive electrode active material layer includes the positive electrode active material, and the positive electrode coating layer includes the oxygen scavenger.

[0015] In one possible implementation, the mass fraction m of the oxygen scavenger in the positive electrode coating layer 2 satisfies: 70% ≤ m 2 ≤ 99%; optionally, 80% ≤ m 2 ≤ 95%.

[0016] In one possible implementation, the thickness d of the positive electrode coating layer satisfies: 3 μm ≤ d ≤ 15 μm; optionally, 3 μm ≤ d ≤ 12 μm.

[0017] In one possible implementation, the average volume particle size Dv50 of the oxygen scavenger satisfies: 0.1 μm ≤ Dv50 ≤ 20 μm; optionally, 0.2 μm ≤ Dv50 ≤ 10 μm.

[0018] In one possible implementation, the positive electrode film layer further includes: phosphate and / or sulfate.

[0019] In a second aspect, a sodium ion battery is provided, and the sodium ion battery includes the positive electrode sheet in any possible implementation manner of the first aspect.

[0020] In a third aspect, an electrical device is provided, and the electrical device includes the sodium ion battery in any possible implementation manner of the third aspect. Description of the Drawings

[0021] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments of the present application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other accompanying drawings can be obtained based on the accompanying drawings without creative efforts.

[0022] Figure 1 It is a schematic diagram of a sodium-ion battery cell according to an embodiment of the present application.

[0023] Figure 2 It is a schematic diagram of a sodium-ion battery module according to an embodiment of the present application.

[0024] Figure 3 It is a schematic diagram of a sodium-ion battery according to an embodiment of the present application.

[0025] Figure 4 It is another schematic diagram of a sodium-ion battery according to an embodiment of the present application. Detailed implementation manners

[0026] Hereinafter, the embodiments of the positive electrode material, positive electrode sheet, sodium-ion battery, and electrical device of the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0027] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] In the description of this application, it should be noted that unless otherwise stated, the meaning of "a plurality of" is more than two; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", etc. is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to this application. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0029] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0030] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0032] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally recognized meanings in the art.

[0033] If mentioned, "oxygen scavenger" refers to a substance that can absorb oxygen or react with oxygen in a battery. For example, salts with reducing properties, etc.

[0034] If mentioned, "reducibility" refers to the ability of a substance to lose electrons in a chemical reaction.

[0035] If mentioned, "transition metal oxide" refers to a compound composed of sodium and an oxide containing transition metal elements. The transition metal elements can be, for example, one or several of Fe, Co, Ni, Cu, Zn, V, Cr, Mn. Structurally, sodium transition metal oxides can have a layered structure, etc.

[0036] Generally, a battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions shuttle between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short - circuit between the positive and negative electrodes, and at the same time allows active ions to pass through. In some embodiments, the above - mentioned battery cell is also referred to as a secondary battery.

[0037] During the charging process of a sodium - ion battery, sodium ions are removed from the positive electrode active material, move and intercalate into the negative electrode material; during the discharging process, sodium ions are removed from the negative electrode material, move and intercalate into the positive electrode active material.

[0038] It should be understood that the "intercalation" process described in this application refers to the process in which sodium ions intercalate into the positive electrode active material and the negative electrode material due to an electrochemical reaction. The "removal" and "de - intercalation" processes described in this application refer to the process in which sodium ions are removed from the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0039] The positive electrode active material is one of the key factors affecting the development of sodium-ion batteries. Layered transition metal oxides are used as positive electrode materials in sodium-ion batteries due to their high sodium storage capacity. The positive electrode active material, especially layered transition metal oxides, may undergo a phase change during the cycling process of sodium-ion batteries or in some relatively extreme usage scenarios, and oxygen in the lattice is released to generate oxygen gas. In other words, the phenomenon of oxygen release from the positive electrode occurs. On the one hand, the irreversible oxygen release behavior of the positive electrode active material during the cycling process destroys the structure of the positive electrode active material, affecting the cycling stability of sodium-ion batteries; on the other hand, sodium dendrites may be generated on the surface of the negative electrode active material during the cycling process of sodium-ion batteries, damaging the SEI film on the surface of the negative electrode and thus coming into contact with the oxygen released from the positive electrode; or the oxygen released from the positive electrode comes into contact with metallic sodium at the negative electrode, and a violent redox reaction will occur, generating a large amount of heat and triggering serious safety accidents, threatening the safety performance of sodium-ion batteries. Especially in some extreme usage scenarios, the positive electrode active material is more likely to release oxygen. For example, in the case of thermal runaway of sodium-ion batteries, the violent redox reaction caused by the oxygen release behavior of the positive electrode will exacerbate the thermal runaway of sodium-ion batteries. Therefore, improving the phenomenon of oxygen release from the positive electrode of sodium-ion batteries is of great significance for enhancing the safety performance of sodium-ion batteries.

[0040] In view of this, the present application provides a positive electrode sheet, a sodium-ion battery, and an electrical device. An oxygen absorbent with a reducing anion is introduced into the positive electrode sheet, which can effectively improve the phenomenon of oxygen release from the positive electrode and enhance the cycling performance and safety performance of sodium-ion batteries.

[0041] Next, the electrode materials, positive electrode sheet, negative electrode sheet, separator, electrolyte, etc. in the sodium-ion battery will be introduced in detail.

[0042] [Positive Electrode Sheet]

[0043] First of all, the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one side surface of the positive electrode current collector. The positive electrode film layer includes an oxygen absorbent, and the anion of the oxygen absorbent has reducibility.

[0044] As an example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film layer can be disposed on either or both of the two opposite surfaces of the positive electrode current collector. In this embodiment, by introducing an oxygen absorbent with a reducing anion into the positive electrode film layer, the anion can be oxidized by the oxygen released when the positive electrode releases oxygen, thereby consuming the oxygen released from the positive electrode. Thus, the phenomenon of oxygen release from the positive electrode is improved, which helps to enhance the safety performance of sodium-ion batteries.

[0045] Optionally, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum 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.).

[0046] In one embodiment, the anion includes at least one of sulfite, phosphite, polyphosphate, and metaphosphate.

[0047] The above-mentioned reducing inorganic anions are more likely to react with oxygen and can consume oxygen when oxygen is released at the positive electrode, thereby improving the safety performance of the sodium-ion battery. Moreover, sulfate and phosphate formed after the oxidation of the above-mentioned inorganic anions are not likely to undergo other side reactions in the sodium-ion battery and hardly have an adverse effect on the electrochemical performance of the sodium-ion battery. Furthermore, when oxygen is not released at the positive electrode of the sodium-ion battery, introducing the above-mentioned inorganic anions into the sodium-ion battery hardly affects the electrochemical performance of the sodium-ion battery (for example, the Direct Current Resistance (DCR)), which helps to reduce the growth rate of DCR during the cycling process of the sodium-ion battery. Excessive DCR or too large a growth rate during the cycling process of the sodium-ion battery poses a serious threat to its power performance and cycling life. Therefore, the embodiments of the present application can also help improve the power performance and cycling life of the sodium-ion battery while improving the safety performance of the sodium-ion battery by selecting the above-mentioned inorganic anions.

[0048] In one embodiment, the cation of the oxygen scavenger includes at least one of potassium ions and sodium ions.

[0049] In the positive electrode active material of the sodium-ion battery, sodium ions exist in various forms. Therefore, in this embodiment, by selecting sodium ions or potassium ions with physical and chemical properties close to those of sodium ions as the cations of the oxygen scavenger, it is more beneficial to the compatibility between the oxygen scavenger and the positive electrode active material.

[0050] In one embodiment, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a transition metal oxide.

[0051] The positive electrode active material may include one or several of transition metal oxides. As an example, the transition metal oxide may be a transition metal oxide with sodium ions, such as sodium copper iron manganese, sodium iron nickel manganese, etc. However, the present application is not limited to these materials, and other materials that can be used as the positive electrode active material of a sodium ion battery may also be used. These positive electrode active materials may be used alone, or two or more of them may be used in combination.

[0052] In one embodiment, on the positive electrode sheet per unit area, the mass a of the positive electrode active material and the mass b of the oxygen absorbent satisfy: 18 ≤ (a:b) ≤ 189; optionally, 37 ≤ (a:b) ≤ 189.

[0053] It should be understood that the ratio of a:b being 18 can be understood as the ratio of a:b being 18:1. Specifically, a:b may be 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 37, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, 189, or its value is within the range obtained by combining any two of the above values.

[0054] In one embodiment, the positive electrode film layer includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material and an oxygen absorbent.

[0055] Specifically, the positive electrode film layer may only include the positive electrode active material layer. In this case, the oxygen absorbent can be directly mixed with the positive electrode active material and coated onto the positive electrode current collector together to form the positive electrode active material layer. Thus, the oxygen absorbent exists in the positive electrode active material layer and can react with oxygen when the positive electrode releases oxygen, thereby improving the phenomenon of oxygen release from the positive electrode.

[0056] In one embodiment, the mass fraction m of the oxygen absorbent in the positive electrode active material layer 1 satisfies: 0.5% ≤ m 1 ≤ 5%; optionally, 0.5% ≤ m 1 ≤ 2.5%.

[0057] Specifically, m 1 can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 3.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or its value is within the range obtained by combining any two of the above values.

[0058] In one embodiment, the positive electrode active material layer and the positive electrode coating are provided, and the positive electrode active material layer is disposed between the positive electrode current collector and the positive electrode coating; the positive electrode active material layer includes a positive electrode active material, and the positive electrode coating includes an oxygen absorber.

[0059] Specifically, the positive electrode film layer may further include a positive electrode coating. The positive electrode active material layer is disposed on the current collector, and the positive electrode coating is disposed on the positive electrode active material layer. In this case, the oxygen absorber can be provided as a coating in the positive electrode film layer and can also react with oxygen when oxygen is released from the positive electrode, thereby improving the phenomenon of oxygen release from the positive electrode.

[0060] In one example, the slurry corresponding to the positive electrode active material layer and the slurry corresponding to the positive electrode coating can be coated onto the positive electrode current collector together. In another example, the slurry corresponding to the positive electrode active material layer and the slurry corresponding to the positive electrode coating can also be coated onto the positive electrode current collector separately. For example, first, the slurry corresponding to the positive electrode active material layer is coated onto the positive electrode current collector to form the positive electrode active material layer, and then the slurry corresponding to the positive electrode coating is coated onto the positive electrode active material layer to form a positive electrode film layer including the positive electrode active material layer and the positive electrode coating. Another example is that after forming the positive electrode active material layer, after cold pressing the positive electrode current collector and the positive electrode active material layer, the slurry corresponding to the positive electrode coating can be coated onto the positive electrode active material layer to form the positive electrode coating.

[0061] In an implementable manner, the mass fraction m of the oxygen absorber in the positive electrode coating 2 satisfies: 70% ≤ m 2 ≤ 99%; optionally, 80% ≤ m 2 ≤ 95%.

[0062] Specifically, m 2It can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or its value is within the range obtained by combining any two of the above values. The slurry corresponding to the positive electrode coating includes an oxygen absorbent and a binder, m 2 It can also be approximately the mass fraction of the oxygen absorbent in the slurry corresponding to the positive electrode coating.

[0063] In this embodiment, the content of the oxygen absorbent in the positive electrode coating can be adjusted by controlling the mass fraction of the oxygen absorbent, and then the content of the oxygen absorbent in the positive electrode sheet can be adjusted. For example, when the loading amount of the positive electrode active material in the positive electrode sheet is large, increasing the mass fraction of the oxygen absorbent can better improve the oxygen release phenomenon of the positive electrode.

[0064] In an implementable manner, the thickness d of the positive electrode coating satisfies: 3μm ≤ d ≤ 15μm; optionally, 3μm ≤ d ≤ 12μm.

[0065] Specifically, d can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or its value is within the range obtained by combining any two of the above values.

[0066] In this embodiment, when the mass fraction of the oxygen absorbent in the positive electrode coating is constant, the content of the oxygen absorbent in the positive electrode sheet can be controlled by adjusting the thickness of the positive electrode coating. For example, when the loading amount of the positive electrode active material in the positive electrode sheet is large, appropriately increasing the thickness of the positive electrode coating can better improve the oxygen release phenomenon of the positive electrode. In addition, the positive electrode coating cannot be too thick, as being too thick may affect the interfacial reaction of the positive electrode sheet.

[0067] In an implementable manner, the average volume particle size Dv50 of the oxygen absorbent satisfies: 0.1μm ≤ Dv50 ≤ 20μm; optionally, 0.2μm ≤ Dv50 ≤ 10μm.

[0068] Specifically, Dv50 can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or its value is within the range obtained by combining any two of the above values.

[0069] When the positive electrode active material layer includes an oxygen scavenger, an oxygen scavenger with a smaller Dv50 can be selected. When the Dv50 of the oxygen scavenger is smaller, the oxygen scavenger can adsorb or coat more uniformly on the surface of the positive electrode active material, react with oxygen when oxygen is generated in the positive electrode active material, play a better role in improving / inhibiting oxygen release from the positive electrode, and help improve the safety performance of the sodium-ion battery.

[0070] In an implementable embodiment, the positive electrode film layer further includes: phosphate and / or sulfate.

[0071] Taking the positive electrode film layer including at least one of phosphite, polyphosphate, and metaphosphate as an example. Once oxygen release occurs at the positive electrode during the cycling of the sodium-ion battery, the released oxygen will undergo a redox reaction with phosphite, polyphosphate, and metaphosphate in the positive electrode film layer, and phosphite, polyphosphate, and metaphosphate will be oxidized to phosphate. Thus, for the positive electrode plate after cycling, the positive electrode film layer can also include phosphate, such as sodium phosphate. Similarly, sulfite will be oxidized to sulfate, thereby forming the corresponding sulfate.

[0072] Optionally, the positive electrode active material may not only include transition metal oxides, but may also include one or several of polyanion-type compounds and Prussian blue-type compounds. As an example, the polyanion-type compound may be a class of compounds having sodium ions, transition metal ions, and tetrahedral anion units. For example, sodium iron phosphate (NaFePO 4 ), sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 ), etc. The Prussian blue-type compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions.

[0073] Optionally, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0074] Optionally, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the positive electrode sheet can be prepared in the following manner: dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, oxygen scavenger, additive, conductive agent, binder, and any other components, in a solvent (such as NMP) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0076] In some other embodiments, the positive electrode sheet can also be prepared in the following manner: dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, additive, conductive agent, binder, and any other components, in a solvent (such as NMP) to form a positive electrode slurry 1; dispersing the oxygen scavenger and the binder in a solvent to form a positive electrode slurry 2; coating the positive electrode slurry 1 on the positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode active material layer is formed on the positive electrode current collector, and then coating the positive electrode slurry 2 on the positive electrode active material layer, and after drying, the positive electrode sheet can be obtained. It should be understood that the cold pressing process can also be set after coating the positive electrode slurry 2 and drying.

[0077] [Negative electrode sheet]

[0078] The negative electrode sheet generally includes a negative electrode current collector, or includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode material, and the negative electrode material includes a negative electrode active material.

[0079] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer can be provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0080] Optionally, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0081] Optionally, the negative electrode active material may adopt a negative electrode active material known in the art for sodium ion batteries. For example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, mesophase microbeads (MCMB), hard carbon, and soft carbon. Again, for example, in a sodium metal battery, the negative electrode active material may include at least one of the following materials: sodium metal, a carbon-based material or metal deposited with sodium metal, an alloy material, a composite material containing sodium metal, an alloy material containing sodium metal, etc. However, the present application is not limited to these materials, and other materials that can be used as the negative electrode active material of sodium ion batteries may also be used. These negative electrode active materials may be used alone, or two or more of them may be used in combination.

[0082] In one embodiment, the sodium ion battery may be a sodium metal battery, that is, the negative electrode tab of the sodium ion battery is the negative electrode current collector. In other words, the negative electrode current collector directly serves as the negative electrode tab of the battery, and this type of sodium ion battery may also be referred to as a "negative-free battery". During the charging process, sodium ions released from the positive electrode tab are deposited on the negative electrode current collector to form a sodium metal negative electrode. In the sodium metal negative electrode, sodium metal is the negative electrode active material. In some other embodiments, in order to ensure the normal use of the negative electrode tab or facilitate the deposition of sodium metal on the negative electrode current collector, a conductive film layer may be provided on the negative electrode current collector.

[0083] Optionally, the negative electrode material further includes a conductive agent, and the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] Optionally, the negative electrode material further includes a binder, and the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0085] The above-mentioned negative electrode tab can be prepared by conventional methods in the art. For example, a copper foil or a copper foil provided with a conductive film layer on at least one surface thereof may be used as the negative electrode tab. The conductive film layer may be provided on at least one surface of the negative electrode current collector by methods such as physical vapor deposition (PVD), spin coating, electroplating, chemical vapor deposition (CVD), etc.

[0086] For another example, the components for preparing the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, can also be dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0087] [Electrolyte]

[0088] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0089] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0090] Optionally, the electrolyte salt includes NaPF 6 , NaBCl 4 , NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 etc.

[0091] Optionally, the solvent includes a carbonate or an ether solvent. The carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and chain-like dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc.; the ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, etc.

[0092] Optionally, the electrolytic solution may also optionally include an electrolytic solution additive. For example, the electrolytic solution additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0093] [Separator]

[0094] In some embodiments, the sodium-ion battery further includes a separator. There is no special limitation on the type of separator in this application. For example, the separator can be a separator film. The separator film can be any well-known porous structure separator film with good chemical stability and mechanical stability.

[0095] Optionally, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0096] In some embodiments, the above-mentioned positive electrode sheet, negative electrode sheet, and separator may be made into an electrode assembly by a winding process or a stacking process.

[0097] In some embodiments, the battery cell may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0098] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be cited.

[0099] This application has no particular limitation on the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 100 of a sodium-ion battery with a square structure as an example.

[0100] Figure 2 is a battery module 200 of a sodium-ion battery as an example. Referring to Figure 2 , in the battery module 200, a plurality of battery cells 100 may be arranged in sequence along the length direction of the battery module 200. Of course, they may also be arranged in any other arbitrary manner. Further, the plurality of battery cells 100 may be fixed by fasteners.

[0101] Optionally, in one embodiment, the battery module 200 may further include a housing having an accommodation space, and a plurality of battery cells 100 are accommodated in the accommodation space.

[0102] Optionally, in one embodiment, the above-mentioned battery module 200 may further be assembled into a sodium-ion battery. The number of battery modules 200 included in the sodium-ion battery may be one or more, and those skilled in the art may select the specific number according to the application and capacity of the battery.

[0103] Figure 3 and Figure 4 is a sodium-ion battery 300 as an example. Referring to Figure 3 and Figure 4, in the sodium-ion battery 300, a battery box and a plurality of battery modules 200 disposed in the battery box may be included. The battery box includes an upper box body 301 and a lower box body 302. The upper box body 301 can cover the lower box body 302 and form a closed space for accommodating the battery modules 200. The plurality of battery modules 200 can be arranged in the battery box in any manner.

[0104] It should be understood that in some other embodiments, the above sodium-ion battery 300 is also referred to as a sodium-ion battery pack. The battery cells 100 can first form battery modules 200, and the sodium-ion battery 300 is composed of the battery modules 200. It is also possible to directly form the sodium-ion battery 300 from the battery cells 100, omitting the intermediate form of the battery modules 200.

[0105] In addition, the present application also provides an electrical device. The electrical device includes at least one of the battery cells 100 of the sodium-ion battery provided by the present application, the battery modules 200 of the sodium-ion battery, or the sodium-ion battery 300. The battery cells 100, the battery modules 200, or the sodium-ion battery 300 can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0106] As the electrical device, the number of the battery cells 100, the battery modules 200, or the sodium-ion battery 300 can be selected according to its usage requirements.

[0107] As an example of the electrical device. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, the sodium-ion battery 300 or the battery module 200 can be adopted.

[0108] As another example of the device, it can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinning, and the battery cell 100 can be adopted as the power source.

[0109] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those not specified in the embodiments in terms of specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For those reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial procurement.

[0110] [Examples and Comparative Examples]

[0111] Example 1

[0112] (1) Preparation of the positive electrode sheet

[0113] The positive electrode active material NaNi 0.4 Fe 0.2 Mn 0.4 O 2 , sodium phosphite as an oxygen absorber with a Dv50 of 2.5 μm, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were thoroughly stirred in an appropriate amount of NMP to form a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil positive electrode current collector, and after drying and rolling, a positive electrode sheet was obtained.

[0114] Among them, the loading amount of the positive electrode active material on the positive electrode sheet was 0.35 g / 1540.25 mm 2 , and the mass fraction m 1 of the oxygen absorber in the positive electrode active material layer was 1.5%.

[0115] (2) Preparation of the negative electrode sheet

[0116] Carbon nanotubes and sodium alginate were added to deionized water and stirred to form a uniform slurry. The slurry was coated on a copper foil, and after drying and cold pressing, a "negative electrode-free" negative electrode sheet was obtained.

[0117] Alternatively, further, the above-mentioned "negative electrode-free" sheet after drying and cold pressing was cut. This sheet was assembled with the positive electrode sheet and the separator into a battery cell, and the assembled battery cell was charged at a constant current of 0.5C to 3.8V, thereby pre-depositing sodium metal on this sheet; after the battery cell was fully charged, this fully charged sheet was taken out in a glove box and used as the negative electrode sheet.

[0118] (3) Assembly of the sodium-ion battery

[0119] The above positive electrode sheet, PE separator, and negative electrode sheet were stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet. After the stacking process, an electrode assembly was formed. The electrode assembly was placed in a packaging shell, and a NaPF 6 electrolyte with a concentration of 1 mol / L was added. After processes such as encapsulation, formation, and standing, a sodium-ion battery was obtained.

[0120] Example 2

[0121] Compared with Example 1, in Example 2, m 1 was 0.5%.

[0122] Example 3

[0123] Compared with Example 1, in Example 3, m1 is 5%.

[0124] Example 4

[0125] Compared with Example 1, in Example 4, the oxygen absorbent is sodium sulfite with Dv50 of 2.5 μm (in the example where another oxygen absorbent is mixed in the positive electrode active material, the specific substance B is given).

[0126] Example 5

[0127] Compared with Example 1, in Example 5, when preparing the positive electrode plate, the positive electrode active material NaNi 0.4 Fe 0.2 Mn 0.4 O 2 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred evenly in an appropriate amount of NMP according to a mass ratio of 95:2.5:2.5 to form positive electrode slurry 1. After coating positive electrode slurry 1 on the positive electrode current collector aluminum foil, it is dried and cold-pressed to form a positive electrode active material layer on the positive electrode current collector. Then, sodium phosphite with Dv50 of 1 μm as the oxygen absorbent and the binder are dissolved in an appropriate amount of NMP and fully stirred evenly to form positive electrode slurry 2. Positive electrode slurry 2 is coated on the positive electrode active material layer and dried to form a positive electrode plate. The positive electrode film layer of this positive electrode plate includes a positive electrode active material layer and a positive electrode coating layer.

[0128] Among them, the loading amount of the positive electrode active material on the positive electrode plate is 0.35 g / 1540.25 mm 2 , and the mass fraction m 2 of the oxygen absorbent in the positive electrode coating layer is 80%, and the thickness d of the positive electrode coating layer is 5 μm.

[0129] Example 6

[0130] Compared with Example 5, in Example 6, m 2 = 90.0%.

[0131] Example 7

[0132] Compared with Example 5, in Example 7, m 2 = 95.0%.

[0133] Example 8

[0134] Compared with Example 5, in Example 8, d = 3 μm.

[0135] Example 9

[0136] Compared with Example 5, in Example 9, d = 12 μm.

[0137] Example 10

[0138] Compared with Example 5, in Example 10, the oxygen scavenger is sodium sulfite with a Dv50 of 1 μm.

[0139] Comparative Example 1

[0140] Compared with Example 1, there is no oxygen scavenger in the positive electrode film layer of Comparative Example 1.

[0141] Table 1 Product parameters of examples and comparative examples Oxygen absorber Position Dv50 <![CDATA[m 1 > <![CDATA[m 2 > d Example 1 Sodium phosphite Positive electrode active material layer 2.5μm 1.5％ / / Example 2 Sodium phosphite Positive electrode active material layer 2.5μm 0.5％ / / Example 3 Sodium phosphite Positive electrode active material layer 2.5μm 5％ / / Example 4 Sodium sulfite Positive electrode active material layer 2.5μm 1.5％ / / Example 5 Sodium phosphite Positive electrode coating 1μm / 80％ 5μm Example 6 Sodium phosphite Positive electrode coating 1μm / 90％ 5μm Example 7 Sodium phosphite Positive electrode coating 1μm / 95％ 5μm Example 8 Sodium phosphite Positive electrode coating 1μm / 80％ 3μm Example 9 Sodium phosphite Positive electrode coating 1μm / 80％ 12μm Example 10 Sodium sulfite Positive electrode coating 1μm / 80％ 5μm Comparative Example 1 / / / / / /

[0142] In Table 1, "Position" represents the position of the oxygen scavenger in the positive electrode film layer, "Dv50" represents the average volume particle size of the oxygen scavenger, "m 1 " represents the mass fraction of the oxygen scavenger in the positive electrode active material layer, "m 2 " represents the mass fraction of the oxygen scavenger in the positive electrode coating, and "d" represents the thickness of the positive electrode coating.

[0143] The performance test results of the sodium-ion batteries in the above examples and comparative examples are shown in Table 2 in detail.

[0144] Table 2 Performance test results of batteries in different examples and comparative examples

[0145] In Table 2, "Detection of the components of the positive electrode film layer after 50 cycles of high-voltage cycling" means that the sodium-ion battery is subjected to a cycling test at a charging voltage of 4.2 V. After 50 cycles, the sodium-ion battery is disassembled, and the components in the positive electrode film layer are detected. Substances related to the oxygen scavenger detected should be understood that the positive electrode film layer after cycling also includes positive electrode active materials, or components of the SEI film such as sodium fluoride and sodium carbonate, which exist in both the examples and the comparative examples, so they are omitted in Table 2. "Temperature rise per cycle" represents the temperature rise of the first cycle during the cycling of the sodium-ion battery. "DCR growth rate" represents the growth rate of the DCR of the sodium-ion battery after 50 cycles compared to the initial DCR before cycling. The specific detection process will be introduced later and will not be elaborated here.

[0146] According to the comparative analysis of the examples and comparative examples, in Examples 1-4, 6-9, after the sodium-ion battery is cycled, sodium phosphate can be detected in the positive electrode film layer by XRD, indicating that whether it is sodium phosphite in the positive electrode active material layer or sodium phosphite in the positive electrode coating, redox reactions have occurred during the cycling of the sodium-ion battery, generating sodium phosphate. In Example 5 and Example 10, after the sodium-ion battery is cycled, sodium sulfate is also detected in the positive electrode film layer by XRD, indicating that sodium sulfite in the positive electrode active material layer or the positive electrode coating has also undergone a redox reaction to generate sodium sulfate. In the comparative examples, no oxygen scavenger was added, and there was no oxygen scavenger that could undergo a redox reaction with oxygen during the cycling of the sodium-ion battery. Therefore, no corresponding phosphate or sulfate was detected in the positive electrode film layer. From the perspective of the temperature rise in the first cycle, the temperature rise per cycle in the examples is lower than that in the comparative examples. This shows that oxygen evolution may occur at the positive electrode in the comparative examples, and the released oxygen may trigger side reactions and release heat, resulting in a higher temperature rise per cycle in the comparative examples. In the examples, the oxygen scavenger reacts with oxygen and is consumed, resulting in a lower temperature rise per cycle. This shows that by introducing an oxygen scavenger into the positive electrode film layer, the phenomenon of oxygen evolution at the positive electrode can be effectively improved, and the safety performance of the sodium-ion battery can be effectively enhanced. From the perspective of the DCR growth rate, the DCR growth rates in the examples are lower than those in the comparative examples. This shows that by introducing inorganic oxygen scavengers such as phosphites and sulfites into the positive electrode film layer in the examples, while improving oxygen evolution at the positive electrode and enhancing the safety performance of the sodium-ion battery, the DCR growth of the sodium-ion battery can be reduced, thereby helping to improve the power performance and service life of the sodium-ion battery. The possible principle is that the inorganic oxygen scavengers such as phosphites and sulfites added in the examples react with oxygen during the cycling of the sodium-ion battery to generate the corresponding phosphates and sulfates. Phosphates and sulfates themselves have relatively high ionic conductivities, which are helpful for improving the ionic conductivity of the positive electrode film layer in the negative electrode film layer, thereby reducing the DCR growth rate of the sodium-ion battery. In addition, these phosphates and sulfates can also participate in the interfacial reaction between the positive electrode active material and the electrolyte. In other words, they participate in the formation of the positive electrode SEI film, thereby increasing the content of inorganic components in the SEI film, improving the ionic conductivity of the SEI film, and thus improving the ionic conductivity of the positive electrode film layer and reducing the DCR growth rate of the sodium-ion battery. In the comparative examples, no oxygen scavenger was added, and no corresponding phosphates and sulfates were generated during the cycling process. The main components in the positive electrode SEI film are substances such as sodium carbonate and sodium fluoride. The ionic conductivity of carbonates is lower than that of phosphates and sulfates. Therefore, the comparative examples show a higher DCR growth rate, which is not conducive to the power performance of the sodium-ion battery and has an adverse effect on its cycle life.

[0147] It should be understood that the single-cycle temperature rise of the battery is mainly affected by the electrode active material. For sodium-ion batteries, without changing the charge-discharge conditions, in other cycle numbers except the first cycle, the value of the single-cycle temperature rise may fluctuate around the value of the first-cycle temperature rise. Therefore, the first-cycle temperature rise can be used to represent the single-cycle temperature rise of sodium-ion batteries.

[0148] According to the comparative analysis of Examples 1-3, 5-7, whether it is the scheme of introducing an oxygen absorber into the positive electrode active material layer or the scheme of introducing an oxygen absorber into the positive electrode coating, when the loading amount of the positive electrode active material is certain, as the mass fraction of the oxygen absorber increases, the single-cycle temperature rise of the sodium-ion battery decreases, and the DCR growth rate decreases. This shows that increasing the mass fraction of the oxygen absorber within an appropriate range helps to reduce the single-cycle temperature rise and DCR growth rate of the sodium-ion battery, improve the safety performance of the sodium-ion battery while reducing the adverse effects of DCR growth on the sodium-ion battery. In addition, the mass fraction of the oxygen absorber should not be too high because the oxygen absorber does not belong to the active material and does not contribute to the capacity.

[0149] According to the comparative analysis of Examples 5, 8-9, when the mass fraction of the oxygen absorber in the positive electrode coating is certain, the thicker the positive electrode coating, the higher the content of the oxygen absorber in the positive electrode film layer, and the lower the single-cycle temperature rise and DCR growth rate of the sodium-ion battery. This shows that it is verified that increasing the thickness of the positive electrode coating within an appropriate range helps to reduce the single-cycle temperature rise and DCR growth rate of the sodium-ion battery, improve the safety performance of the sodium-ion battery while reducing the adverse effects of DCR growth on the sodium-ion battery. In addition, the thickness of the positive electrode coating cannot be too thick, as it may affect the interfacial reaction of the positive electrode plate.

[0150] Examples 4 and 10 show an example of sodium sulfite as an oxygen absorber, indicating that sodium sulfite as an oxygen absorber can also achieve a similar effect to sodium phosphite.

[0151] Next, the test methods for the physical parameters and performance parameters involved in the embodiments of the present application will be introduced.

[0152] 1. Test method for average volume particle size (Dv50)

[0153] The average volume particle size of the material can be tested using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration should ensure a light obscuration of 8-12%), add 20 ml of deionized water, and ultrasonicate for 5 min (53 KHz / 120 W) externally to ensure complete dispersion of the sample, and then measure the sample according to the standard of GB / T19077-2016 / ISO 13320:2009.

[0154] 2. Component detection of the positive electrode film layer

[0155] The components of the positive electrode film layer can be detected by any possible means in the art. For example, methods such as XRD, AES, and XPS can be used to detect the components in the positive electrode film layer.

[0156] The following takes XRD as an example for illustration: Take an appropriate amount of the sample to be tested and place it in the sample groove of the glass slide and press it into a tablet. Then place the sample on the sample holder of the XRD diffractometer and close the sample chamber door. Set the detection parameters on the computer software. For example, the scanning angle range is (5° - 90°), and the scanning rate is (0.02° / min - 10° / min). Then start the test. After the test is completed, the measured data can be compared with the standard card in Jade, and the physical images present in the sample can be judged according to the positions of the three strongest peaks, peak intensities, and elemental qualitative analysis.

[0157] 3. Detection of the mass content of the oxygen absorber

[0158] The value content of the oxygen absorber in the positive electrode active material layer or the positive electrode coating can be detected by any possible means in the art. As introduced in the previous text, continue to illustrate with XRD as an example.

[0159] When the positive electrode active layer includes an oxygen absorber, take the prepared positive electrode plate, scrape an appropriate amount of the material of the positive electrode active layer, and through XRD testing, the XRD peaks of each component in the positive electrode active material layer can be obtained. According to the fact that the intensity of the XRD peak is proportional to the content of this component, the mass content of the oxygen absorber compared to the positive electrode active material layer can be measured by the internal standard method.

[0160] Similarly, when the positive electrode coating includes an oxygen absorber, take the prepared positive electrode plate, scrape the positive electrode coating on the surface of the positive electrode plate for XRD detection, and the mass content of the oxygen absorber compared to the positive electrode coating can be measured.

[0161] 4. High-voltage cycling process of the sodium-ion battery

[0162] At 25°C, charge the sodium-ion battery monomer at a constant current rate of 0.33C until the voltage reaches 4.2V, then charge at a constant voltage of 4.2V until the current reaches 1C, then let it stand for 5 minutes, discharge at a constant current rate of 0.33C until the voltage reaches 1.5V, and then let it stand for 5 minutes. This is a cycle of charge and discharge process.

[0163] 5. Test method for single-loop temperature rise

[0164] Before charging and discharging, a temperature sensing wire is placed on the top cover of the sodium-ion battery, and the thermometer at this time is the starting temperature of the first circle. At 25 °C, the sodium-ion battery is charged at a constant current of 0.33C until the voltage reaches 4.2V, then charged at a constant voltage of 4.2V until the current is 1C, then left standing for 5 minutes, discharged at a constant current of 0.33C until the voltage reaches 1.5V, and then left standing for 5 minutes. This is a cycle of charging and discharging. The temperature at this time is recorded as the end temperature of the first circle of discharge, and the single-circle temperature rise = the end temperature of the first circle of discharge - the starting temperature of the first circle.

[0165] 6. Test method for DCR

[0166] The test method for DCR can refer to the method in the "Performance Test Specification for High-Power Lithium-Ion Power Batteries for HEV", and make slight adjustments to the test parameters to test the DCR of the sodium-ion battery.

[0167] For example, discharge the sodium-ion battery at a constant current of 1C until the cut-off voltage of 2.0V, leave it standing for 1h, then charge it at a constant current of 1C for 18 minutes, adjust the SOC to 30%, leave it standing for 1h, then charge it at a constant current of 3C for 1.5 minutes, and then leave it standing for 1h. Then discharge it at a current of 9C for 0.5 minutes, leave it standing for 1h, charge it at a constant current of 1C for 6 minutes, adjust the SOC of the sodium-ion battery to 40%, and leave it standing for 1h.

[0168] Repeat the above process until the SOC is 70%, and the DCR data of the sodium-ion battery is obtained by calculating through the following formula. R = ΔU / ΔI

[0169] Among them, represents the voltage drop within 5s at the start of discharge, and represents the change value of the current within 5s at the start of discharge.

[0170] Perform a DCR test on the sodium-ion battery before cycling, and the initial DCR before cycling is measured as R 0 , perform a DCR test on the sodium-ion battery again after 50 cycles, and the DCR after cycling is measured as R 50 , the DCR growth rate of the sodium-ion battery = [(R 50 - R 0 ) / R 0 × 100%.

[0171] Although the present application has been described with reference to the preferred embodiments, various improvements can be made to it and components therein can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, the positive electrode plate comprises: a positive current collector; a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising an oxygen scavenger, and the anion of the oxygen scavenger having reducibility.

2. The positive electrode plate according to claim 1, characterized in that, the anion comprises at least one of sulfite, phosphite, polyphosphate, and metaphosphate.

3. The positive electrode plate according to claim 1 or 2, characterized in that, the cation of the oxygen scavenger comprises at least one of potassium ion and sodium ion.

4. The positive electrode plate according to any one of claims 1-3, characterized in that, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a transition metal oxide.

5. The positive electrode plate according to claim 4, characterized in that, on the positive electrode plate per unit area, the mass a of the positive electrode active material and the mass b of the oxygen scavenger satisfy: 18 ≤ (a:b) ≤ 189; optionally, 37 ≤ (a:b) ≤ 189.

6. The positive electrode plate according to any one of claims 1-5, characterized in that, the positive electrode film layer comprises a positive electrode active material layer, and the positive electrode active material layer comprises the positive electrode active material and the oxygen scavenger.

7. The positive electrode plate according to claim 6, characterized in that, The mass fraction m of the oxygen absorbent in the positive electrode active material layer 1 satisfies: 0.5% ≤ m 1 ≤ 5%; optionally, 0.5% ≤ m 1 ≤ 2.5%.

8. The positive electrode plate according to any one of claims 1-5, characterized in that, the positive electrode film layer comprises: a positive electrode active material layer and a positive electrode coating, the positive electrode active material layer being disposed between the positive current collector and the positive electrode coating; the positive electrode active material layer comprises the positive electrode active material, and the positive electrode coating comprises the oxygen scavenger.

9. The positive electrode plate according to claim 8, characterized in that, The mass fraction m of the oxygen absorbent in the positive electrode coating 2 satisfies: 70% ≤ m 2 ≤ 99%; optionally, 80% ≤ m 2 ≤ 95%.

10. The positive electrode plate according to claim 8 or 9, characterized in that, the thickness d of the positive electrode coating satisfies: 3 μm ≤ d ≤ 15 μm; optionally, 3 μm ≤ d ≤ 12 μm.

11. The positive electrode plate according to any one of claims 1-10, characterized in that, the average volume particle size Dv50 of the oxygen scavenger satisfies: 0.1 μm ≤ Dv50 ≤ 20 μm; optionally, 0.2 μm ≤ Dv50 ≤ 10 μm.

12. The positive electrode plate according to any one of claims 2-11, characterized in that, the positive electrode film layer further comprises: phosphate and / or sulfate.

13. A sodium-ion battery, characterized in that, the sodium-ion battery comprises the positive electrode plate according to any one of claims 1-12.

14. An electrical device, characterized in that, the electrical device comprises the sodium-ion battery according to claim 13.

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