Sodium battery cells, batteries and electrical devices

Abstract

The embodiments of the present application provide a sodium battery cell, a battery, and an electric device. The sodium battery cell includes a negative electrode sheet, a positive electrode sheet, and an electrolyte, the negative electrode sheet including a negative electrode current collector and a negative electrode film layer, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer, and at least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte includes a lithium-containing compound. The technical solution of the present application can improve the cycle performance of the sodium battery cell.

Description

[Technical Field]

[0001] This application relates to the technical field of batteries, and more particularly to sodium battery cells, batteries, and electrical devices. [Background technology]

[0002] In recent years, with the increasing development and application of lithium-ion batteries in portable electronic devices, high-power electric vehicles, large-scale energy storage power plants, and smart grids, the industry's demand for metallic lithium has been rising. However, due to the dwindling reserves of metallic lithium resources and the increasing difficulty of mining, current metallic lithium resources are no longer sufficient to meet the demands of the lithium battery industry. On the other hand, sodium, which belongs to the same group as lithium, has similar chemical properties and is abundant in reserves. Therefore, sodium-ion batteries, which operate on a similar principle to lithium-ion batteries, are currently being developed, and it is hoped that sodium-ion batteries will become an important complement to lithium-ion batteries in large-scale energy storage applications.

[0003] Therefore, improving the cycle performance of sodium-ion batteries is an urgent issue that needs to be resolved quickly. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] This application has been made in view of the above-mentioned problems, and aims to provide a sodium battery cell, a battery, and an electrical device that can improve cycle performance. [Means for solving the problem]

[0005] A first aspect of this application provides a sodium battery cell comprising a negative electrode sheet, a positive electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, and at least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte comprises a lithium-containing compound.

[0006] In the embodiments of this application, the sodium battery cell comprises a negative electrode sheet, a positive electrode sheet, and an electrolyte. The negative electrode sheet further comprises a negative electrode current collector and a negative electrode film layer, and the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer. At least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte contains a lithium-containing compound. By including a lithium-containing compound in at least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte of the sodium battery cell, a solid electrolyte interface film (SEI film) containing some alkyl lithium carbonate is formed in the sodium battery cell. Compared to an SEI film whose components are mostly alkyl sodium carbonate, an SEI film containing some alkyl lithium carbonate has lower solubility in the electrolyte, thereby improving the stability of the SEI film, reducing the probability of side reactions between the electrolyte and the negative electrode, extending the cycle life of the sodium battery, and thus improving the cycle performance of the sodium battery.

[0007] In one possible embodiment, the negative electrode film layer comprises a negative electrode active material core and the lithium-containing compound coating the negative electrode active material core.

[0008] In the embodiments of this application, when the negative electrode film layer of a sodium battery cell contains a lithium-containing compound, the lithium-containing compound and the negative electrode active material are configured such that the negative electrode active material forms a core, and the lithium-containing compound coats the negative electrode active material core. By including the negative electrode active material core and the lithium-containing compound that coats the negative electrode active material core in the negative electrode film layer, that is, by coating the negative electrode active material core with the lithium-containing compound, a stable lithium-containing compound can be formed by the SEI film when the SEI film is formed in the sodium battery, thereby improving the stability of the SEI film and the cycle performance of the battery.

[0009] In one possible embodiment, the negative electrode active material core comprises amorphous carbon.

[0010] In the embodiments of this application, by using amorphous carbon as the negative electrode active material of the sodium battery cell, sodium ions can be more effectively desorbed and inserted into the negative electrode active material, thereby further improving the performance of the sodium battery.

[0011] In one possible embodiment, the content of the lithium-containing compound in 100 parts by weight of the negative electrode film layer is 0.05 to 15 parts by weight, and selectively 0.1 to 5 parts by weight.

[0012] In the embodiments of this application, by setting the mass ratio of the lithium-containing compound in the negative electrode film layer to 0.05% to 15%, particularly 0.1% to 5%, a sufficient amount of lithium element is provided to the sodium battery, the solubility of the SEI film in the electrolyte of the sodium battery is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0013] In one possible embodiment, the content of the lithium-containing compound in 100 parts by weight of the positive electrode film layer is 0.1 to 20 parts by weight, and selectively 0.5 to 10 parts by weight.

[0014] In the embodiments of this application, by setting the mass ratio of the lithium-containing compound in the positive electrode film layer to 0.1% to 20%, particularly 0.5% to 10%, a sufficient amount of lithium element is provided to the sodium battery, the solubility of the SEI film in the electrolyte of the sodium battery is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0015] In one possible embodiment, the content of the lithium-containing compound in 100 parts by weight of the electrolyte is 0.01 to 15 parts by weight, and selectively 0.1 to 5 parts by weight.

[0016] In the embodiments of this application, by setting the mass ratio of the lithium-containing compound in the electrolyte to 0.01% to 15%, particularly 0.1% to 5%, a sufficient amount of lithium element is provided to the sodium battery, the solubility of the SEI film in the electrolyte is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0017] In one possible embodiment, the ratio of the mass content of lithium to the mass content of sodium in the negative electrode sheet is 0.0001 to 1, and selectively 0.01 to 0.5.

[0018] In the embodiments of this application, since sodium compounds in the SEI film are more soluble than lithium compounds, the ratio of the mass content of lithium to sodium in the negative electrode sheet directly determines the solubility of the SEI film in the electrolyte. When the ratio of the mass content of lithium to sodium in the negative electrode sheet is less than 0.0001, the SEI film consists almost entirely of sodium-containing compounds, and the SEI film continues to dissolve in the electrolyte. When the ratio of the mass content of lithium to sodium in the negative electrode sheet is greater than 1, the negative electrode sheet contains a large amount of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride. Because the radius of sodium ions is larger than the radius of lithium ions, the sodium ion conductivity of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride deteriorates, further severely worsening the interfacial impedance and affecting the output of the sodium battery. By setting the ratio of the mass content of lithium to the mass content of sodium in the negative electrode sheet of a sodium battery to 0.0001 to 1, particularly 0.01 to 0.5, the sodium battery can achieve both long cycle performance and high output.

[0019] In one possible embodiment, the lithium-containing compound comprises at least one of alkyl lithium carbonate, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, lithium hydroxide, lithium chloride, lithium perchlorate, lithium hexafluorophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

[0020] In embodiments of the present application, a lithium-containing compound is added to at least one of the positive electrode membrane layer, the negative electrode membrane layer, and the electrolyte. The lithium-containing compound comprises at least one selected from the group consisting of lithium alkyl carbonate, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, lithium hydroxide, lithium chloride, lithium perchlorate, lithium hexafluorophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate. Lithium in these lithium salt materials detaches from the materials and migrates into the electrolyte. Then, the lithium salt in the electrolyte undergoes a metathesis reaction with the sodium-containing compound at the negative electrode, which can effectively reduce the solubility of the SEI film in the electrolyte, and improve the stability of the SEI film and the battery performance.

[0021] In one possible embodiment, the electrolyte comprises fluoroethylene carbonate.

[0022] In embodiments of the present application, the lithium-containing compound material has high brittleness. During cycling, the volume of the active material expands, and the active material added with the lithium-containing compound cracks. By adding fluoroethylene carbonate to the electrolyte, an organic polymer can be formed on the negative electrode interface. The organic polymer has high toughness, enables the positive and negative electrode interfaces to withstand contraction, and can prevent cracking caused by expansion of the negative electrode material.

[0023] In one possible embodiment, based on 100 parts by weight of the electrolyte, the content of the fluoroethylene carbonate is 0.01 to 10 parts by weight, and optionally 0.1 to 5 parts by weight.

[0024] In the embodiments of this application, fluoroethylene carbonate is added to the electrolyte so that the positive or negative electrode active material to which the lithium-containing compound is added can withstand shrinkage. However, fluoroethylene carbonate has low thermal stability, and gas generation is severely worsened by acidic substances produced by its decomposition. Furthermore, if added in excess, a thick SEI film is formed, making it easy for sodium to precipitate in the sodium battery. By setting the mass content of fluoroethylene carbonate in the electrolyte to 0.01% to 10%, and especially to 0.1% to 5%, it is possible to not only enable the SEI film to withstand shrinkage, but also to avoid affecting the performance of the sodium battery.

[0025] A second aspect of this application provides a battery comprising a sodium battery cell described in any one embodiment of the first aspect of this application.

[0026] A third aspect of this application provides an electrical device comprising a sodium battery cell described in any one embodiment of the first aspect of this application or a battery described in the second aspect.

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application are briefly described below. The drawings described below represent only a few embodiments of this application, and it is clear that those skilled in the art will be able to obtain further drawings from these drawings without requiring any creative effort. [Brief explanation of the drawing]

[0028] [Figure 1] This is a schematic diagram of the structure of a sodium battery cell according to one embodiment of this application. [Figure 2] This is a schematic diagram of a sodium battery cell according to one embodiment of the present application. [Figure 3] This is a schematic diagram of the structure of a sodium battery cell according to another embodiment of this application. [Figure 4] This is a schematic diagram of the structure of a sodium battery according to one embodiment of this application. [Figure 5]This is a schematic diagram of the structure of an electrical device according to one embodiment of this application. [Modes for carrying out the invention]

[0029] In the following, embodiments of the electrode assemblies, battery cells, batteries, and electrical devices of this application will be described in detail with due reference to the drawings, although unnecessary details may be omitted. For example, detailed explanations of well-known matters and redundant explanations of structures that are actually the same may be omitted. Furthermore, the 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 described in the claims.

[0030] The “range” disclosed in this application is limited by a lower and upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundary of a particular range. The range thus limited may or may not include endpoint values ​​and can be combined arbitrarily; that is, either lower limit and any upper limit can be combined to form a single range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if the minimum range values ​​are 1 and 2 and the maximum range values ​​are 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 are all expected. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers from "0 to 5" are listed in this specification, and "0 to 5" is simply an abbreviated expression for combinations of these numbers. Also, when a parameter is described as being 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.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technological solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or selectively sequentially. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the fact that the method may further include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b).

[0034] Unless otherwise specified, the terms “include” and “inclusive” as used in this application may be in open or closed form. For example, “include” and “inclusive” may further include or include other components not listed, or they may include or include only the listed components.

[0035] As used in this application, the terms “greater than or equal to,” “less than or equal to,” “greater than,” and “less than” include numbers; for example, “at least one” means one or more, and “at least one of A and B” means “A,” “B,” or “A and B.”

[0036] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0037] Sodium batteries have a structure similar to lithium batteries and include a positive electrode, a negative electrode, and an electrolyte for transporting sodium ions, all of which can be inserted and removed. Similar to lithium batteries, during the initial charging process, the products of reductive decomposition of the electrolyte form a solid electrolyte interfacial film (SEI film) at the negative electrode interface to prevent further reductive decomposition of the electrolyte. Therefore, the performance of this SEI film layer directly affects the performance of the sodium battery.

[0038] The main components of the SEI film formed at the negative electrode interface of a sodium battery are alkyl sodium carbonate, sodium carbonate, and sodium fluoride. Compared to alkyl lithium carbonate, the main component of the SEI film in a lithium battery, alkyl sodium carbonate, the main component of the SEI film in a sodium battery, has a higher solubility in the electrolyte. As a result, the electrolyte continuously reacts with the negative electrode, making the SEI film in a sodium battery very unstable, and the cycle performance of the sodium battery does not easily meet practical requirements.

[0039] Currently, there are several technical means to solve the above problems: (1) Adding fluoroethylene carbonate (FEC) to the electrolyte. FEC can synergistically interact with the electrolyte and improve the stability of the SEI in sodium batteries. However, the polymerized organic material formed by the reduction of FEC at the negative electrode severely worsens the internal resistance of the battery, and furthermore, these sodium-containing organic materials still have a strong dissolving ability in the electrolyte, so the improvement in the battery's cycle performance is not significant. (2) Constructing organic structures / graphene organic composite materials to reduce the dissolution of the SEI film in the electrolyte. However, both organic structures and graphene are expensive and unsuitable for large-scale application in industrial production. (3) Coating the outside of the negative electrode material with a layer of fluorine-containing compound to contribute to better formation of the SEI film in sodium batteries. However, the process of coating the outside of the carbon negative electrode material with a layer of fluorine-containing compound is complex and still expensive, and the improvement in cycle performance is not significant. Therefore, how to give sodium batteries suitable cycle performance is an important technical challenge that urgently needs to be solved.

[0040] The sodium battery cell, battery, and electrical device of this application will be described below with reference to the drawings.

[0041] The sodium batteries described in this application include sodium-ion batteries and sodium metal batteries, and although the following embodiments will describe sodium-ion batteries as an example, the technical solutions of this application are not limited to sodium-ion batteries.

[0042] [Sodium battery cell]

[0043] A first aspect of this application provides a sodium battery cell, and Figure 1 is a schematic diagram of the structure of a sodium battery cell according to one embodiment of this application. As shown in Figure 1, the sodium battery cell 100 includes a negative electrode sheet 121, a positive electrode sheet 123, an electrolyte and a separator 122, the negative electrode sheet 121 includes a negative electrode current collector and a negative electrode film layer, the positive electrode sheet 123 includes a positive electrode current collector and a positive electrode film layer, the negative electrode film layer, Positive At least one of the electrode film layer and the electrolyte contains a lithium-containing compound.

[0044] Negative electrode film layer, Positive The lithium-containing compound is included in at least one of the electrode film layer and the electrolyte. In other words, by adding a lithium-containing compound to the sodium battery cell 100, the cycle performance of the sodium battery cell 100 can be improved.

[0045] In the above solution, a lithium-containing compound is included in at least one of the negative electrode film layer, positive electrode film layer, and electrolyte of the sodium battery cell 100, thereby forming an SEI film containing some alkyl lithium carbonate and lithium fluoride on the sodium battery cell 100. Compared to an SEI film whose components are mostly alkyl sodium carbonate, an SEI film containing some alkyl lithium carbonate and lithium fluoride has lower solubility in the electrolyte, improves the stability of the SEI film, reduces side reactions between the electrolyte and the negative electrode, extends the cycle life of the sodium battery, and thus improves the cycle performance of the sodium battery.

[0046] Typically, a sodium battery cell 100 includes a positive electrode sheet 123, a separator 122, a negative electrode sheet 121, and an electrolyte. During charging and discharging of the battery, active ions reciprocate between the positive and negative electrodes, undergoing desorption and insertion. The electrolyte plays a role in conducting ions between the positive and negative electrodes, and the separator 122 is placed between the positive electrode sheet 123 and the negative electrode sheet 121, primarily serving to prevent short circuits between the positive and negative electrodes while also allowing ions to pass through.

[0047] It should be explained here that the terms "positive electrode sheet" and "negative electrode sheet" used in the embodiments of this application refer to the entire positive electrode sheet and negative electrode sheet, including the active material, current collector, or other additives.

[0048] In some embodiments, the negative electrode film layer includes a negative electrode active material core and a lithium-containing compound that coats the negative electrode active material core.

[0049] In the above-described method, when the negative electrode film layer of the sodium battery cell 100 contains a lithium-containing compound, the lithium-containing compound and the negative electrode active material are configured such that the negative electrode active material forms the core, and the lithium-containing compound coats the negative electrode active material core. By including the negative electrode active material core and the lithium-containing compound coating the negative electrode active material core in the negative electrode film layer, that is, by coating the negative electrode active material core with the lithium-containing compound, a stable lithium-containing compound is formed by the SEI film when the SEI film is formed in the sodium battery, thereby improving the stability of the SEI film and the cycle performance of the sodium battery.

[0050] In the embodiments of this application, the coating of the negative electrode active material core with a lithium-containing compound may be continuous or discontinuous, and this application does not limit this.

[0051] In the embodiments of this application, the lithium-containing compound may be directly and uniformly mixed with the negative electrode active material.

[0052] In some embodiments, the negative electrode active material core contains amorphous carbon.

[0053] In the above method, by using amorphous carbon as the negative electrode active material of the sodium battery cell 100, sodium ions can be more effectively detached and inserted into the negative electrode active material, thereby further improving the performance of the sodium battery.

[0054] In some embodiments, the content of the lithium-containing compound in 100 parts by weight of the negative electrode film layer is 0.05 to 15 parts by weight, and selectively 0.1 to 5 parts by weight.

[0055] In the above method, by setting the mass ratio of the lithium-containing compound in the negative electrode film layer to 0.05% to 15%, particularly 0.1% to 5%, a sufficient amount of lithium element is provided to the sodium battery cell 100, the solubility of the SEI film in the electrolyte of the sodium battery is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0056] In some embodiments, the lithium-containing compound content in 100 parts by weight of the positive electrode film layer is 0.1 to 20 parts by weight, and selectively 0.5 to 10 parts by weight.

[0057] In the above method, by setting the mass ratio of the lithium-containing compound in the positive electrode film layer to 0.1% to 20%, particularly 0.5% to 10%, a sufficient amount of lithium element is provided to the sodium battery cell 100, the solubility of the SEI film in the electrolyte of the sodium battery is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0058] In the embodiments of this application, the lithium-containing compound may be directly and uniformly mixed with the positive electrode active material.

[0059] In some embodiments, the content of the lithium-containing compound in 100 parts by weight of the electrolyte is 0.01 to 15 parts by weight, and selectively 0.1 to 5 parts by weight.

[0060] In the above method, by setting the mass ratio of the lithium-containing compound in the electrolyte to 0.01% to 15%, particularly 0.1% to 5%, sufficient lithium elements are provided to the sodium battery cell 100, the solubility of the SEI film of the sodium battery in the electrolyte is reduced to the maximum extent, and the performance of the sodium battery can be further improved.

[0061] In the embodiments of this application, the lithium-containing compound may be added directly to the electrolyte.

[0062] In some embodiments, the ratio of the mass content of lithium to the mass content of sodium in the negative electrode sheet 121 is 0.0001 to 1, and selectively 0.01 to 0.5.

[0063] In the above scheme, since sodium compounds in the SEI film dissolve more easily than lithium compounds, the ratio of lithium to sodium mass content in the negative electrode sheet 121 directly determines the solubility of the SEI film in the electrolyte. If the ratio of lithium to sodium mass content in the negative electrode sheet 121 is less than 0.0001, the SEI film consists almost entirely of sodium-containing compounds, and the SEI film continues to dissolve in the electrolyte. If the ratio of lithium to sodium mass content in the negative electrode sheet 121 is greater than 1, the negative electrode sheet 121 contains a large amount of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride. Because the radius of sodium ions is larger than the radius of lithium ions, the sodium ion conductivity of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride deteriorates, further severely worsening the interfacial impedance and affecting the output of the sodium battery. By setting the ratio of lithium mass content to sodium mass content in the negative electrode sheet 121 of the sodium battery to 0.0001 to 1, and especially to 0.01 to 0.5, the sodium battery can achieve both high cycle performance and high output.

[0064] It should be explained here that the sodium battery state at the specified lithium-sodium mass ratio refers to the state after the first charge-discharge cycle of the sodium battery cell 100, that is, the state of the sodium battery cell 100 after the SEI formation stage.

[0065] In some embodiments, the lithium-containing compound includes at least one of alkyl lithium carbonate, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, lithium hydroxide, lithium chloride, lithium perchlorate, lithium hexafluorophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

[0066] In the above method, a lithium-containing compound is added to at least one of the positive electrode film layer, negative electrode film layer, and electrolyte. The lithium-containing compound includes at least one of the following: alkyl lithium carbonate, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, lithium hydroxide, lithium chloride, lithium perchlorate, lithium hexafluorophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate. The lithium in these lithium salt materials is released from the material and moves into the electrolyte. The lithium salt in the electrolyte then undergoes a metathesis reaction with the sodium-containing compound at the negative electrode, effectively reducing the solubility of the SEI film in the electrolyte and improving the stability of the SEI film and the performance of the battery.

[0067] In some embodiments, the electrolyte contains fluoroethylene carbonate.

[0068] In the above method, the lithium-containing compound material is highly brittle, and during the cycling process, the volume of the active material expands, causing the active material to rupture. By adding fluoroethylene carbonate to the electrolyte, an organic polymer can be formed at the negative electrode interface. This organic polymer has high toughness, allowing the positive and negative electrode interface to withstand contraction and preventing rupture due to expansion of the negative electrode material.

[0069] In some embodiments, the content of fluoroethylene carbonate in 100 parts by weight of electrolyte is 0.01 to 10 parts by weight, and selectively 0.1 to 5 parts by weight.

[0070] In the above method, fluoroethylene carbonate is added to the electrolyte so that the positive or negative electrode active material, to which the lithium-containing compound is added, can withstand contraction. However, fluoroethylene carbonate has low thermal stability, and the acidic substances produced by its decomposition severely worsen gas generation. Furthermore, if added in excess, a thick SEI film is formed, making it easy for sodium in the sodium battery to precipitate. By setting the mass content of fluoroethylene carbonate in the electrolyte to 0.01% to 10%, and especially 0.1% to 5%, it becomes possible to not only have the fluoroethylene carbonate play a role in withstanding the contraction of the SEI film, but also to avoid affecting the performance of the sodium battery.

[0071] [Positive electrode sheet]

[0072] The positive electrode sheet 123 includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer contains a positive electrode active material, and the positive electrode film layer may also contain the lithium-containing compound described in the above embodiment.

[0073] For example, a positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0074] In some embodiments, the positive electrode 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 material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0075] In some embodiments, the positive electrode active material may be any positive electrode active material known in the art for batteries. For example, the positive electrode active material may comprise at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventional materials usable as battery positive electrode active materials may be used. These positive electrode active materials may be used individually or in combination of two or more.

[0076] In some embodiments, the transition metal in the sodium transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2 (where M includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≦1である)である。

[0077] In some embodiments, the polyanionic compound is a sodium ion, a transition metal ion, and a tetrahedral (YO4) ion. n- The compound may have an anion unit. The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y may be at least one of P, S, and Si, and n is (YO4) n-represents the valence. The polyanionic compound may be a compound having sodium ions, transition metal ions, tetrahedral (YO4) n- anion units and halogen anions. The transition metal may be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may be at least one selected from P, S and Si, and n represents the valence of (YO4) n- and the halogen may be at least one selected from F, Cl and Br. The polyanionic compound may be a compound having sodium ions, tetrahedral (YO4) n- anion units, polyhedral units (ZO y ) m+ and optional halogen anions. Y may be at least one selected from P, S and Si, n represents the valence of (YO4) n- Z represents a transition metal, and may be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents the valence of (ZO y ) m+ and the halogen may be at least one selected from F, Cl and Br. The polyanionic compounds are, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM’PO4F (M' is one or more selected from V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y (0≦y≦1) is at least one of the foregoing.

[0078] In some embodiments, the Prussian blue-based compound is a compound having sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The Prussian blue-based compound is, for example, Na a Me b Me' c(CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 <a≦2、0<b<1、0<c<1である。

[0079] In some embodiments, the cathode film layer selectively further comprises a conductive agent. For example, 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.

[0080] In some embodiments, the positive electrode film layer selectively further comprises a binder. For example, 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 fluorine-containing acrylate resins.

[0081] In this application, the positive electrode sheet 123 may be manufactured by conventional methods of the art. For example, the positive electrode film layer is usually obtained by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode material, a selective conductive agent, a selective binder, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP).

[0082] The positive electrode sheet 123 of this application does not exclude other additional functional layers other than the positive electrode film layer. For example, in some embodiments, the positive electrode sheet 123 of this application further includes a conductive undercoat (e.g., consisting of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode film layer and provided on the surface of the positive electrode current collector. In some other embodiments, the positive electrode sheet 123 of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0083] [Negative electrode sheet]

[0084] The negative electrode sheet 121 includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer contains a negative electrode active material, and the negative electrode film layer may also contain the lithium-containing compound described in the above embodiment.

[0085] For example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0086] 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 layer 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 (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0087] In some embodiments, the negative electrode active material may be any negative electrode active material known in the art for batteries. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials. The silicon-based material may be at least one selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxygen compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials usable as battery negative electrode active materials may be used. These negative electrode active materials may be used individually or in combination of two or more types.

[0088] In some embodiments, the negative electrode film layer further selectively comprises a binder. The binder may be at least one selected from 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).

[0089] In some embodiments, the negative electrode film layer further selectively comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode film layer selectively further comprises other auxiliary agents, such as thickeners (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0091] In this application, the negative electrode sheet 121 may be manufactured by conventional methods of the art. For example, the negative electrode film layer is usually obtained by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode material, a selective conductive agent, a selective binder, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP).

[0092] [Electrolyte]

[0093] The electrolyte plays a role in conducting ions between the positive electrode sheet 123 and the negative electrode sheet 121. In the embodiments of this application, the electrolyte may include fluoroethylene carbonate (FEC) and the lithium-containing compound described in any of the embodiments above.

[0094] In some embodiments, the electrolyte comprises an organic solvent, a sodium electrolyte salt, and a selective additive, the types of which are not specifically limited and can be selected as needed.

[0095] In some embodiments, the electrolyte salt may include, for example, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. The electrolyte salt may be used individually or two or more simultaneously.

[0096] In some embodiments, the organic solvent may include, but is not limited to, at least one of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The organic solvent may be used individually or in combination of two or more. Selectively, two or more organic solvents may be used simultaneously.

[0097] In some embodiments, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives that can improve certain performance characteristics of the battery, such as additives that can improve the overcharge performance of the battery, or additives that can improve the high-temperature or low-temperature performance of the battery.

[0098] In some embodiments, the additives include, but are not limited to, at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (DTD), propylene sulfate, ethylene sulfite (ES), 1,3-propanesultone (PS), 1,3-propensultone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0099] The electrolyte may be prepared by conventional methods in this field. For example, an electrolyte may be obtained by homogeneously mixing an organic solvent, a sodium electrolyte salt, and a selective additive. The order in which each material is added is not particularly limited; for example, the electrolyte may be obtained by adding the sodium electrolyte salt and the selective additive to the organic solvent and mixing them homogeneously, or by first adding the sodium electrolyte salt to the organic solvent, and then adding the selective additive to the organic solvent and mixing them homogeneously.

[0100] [Separator]

[0101] The separator is provided between the positive electrode sheet 123 and the negative electrode sheet 121, and its main role is to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through. This application does not particularly limit the type of separator, and any known porous structure separator having good chemical and mechanical stability may be selected.

[0102] In some embodiments, the material of the separator may be one or more selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the material of each layer may be the same or different. In some embodiments, the separator may be further provided with an organic / inorganic composite coating, including a ceramic particle coating and a metal oxide coating.

[0103] In some embodiments, the positive electrode sheet 123, the negative electrode sheet 121, and the separator can be manufactured as an electrode assembly 12 by a winding process or a lamination process.

[0104] In some embodiments, the sodium battery cell 100 may include an outer casing. This casing can be used to enclose the electrode assembly 12 and the electrolyte.

[0105] In some embodiments, the outer casing of the sodium battery cell 100 may be a hard case, such as a rigid plastic case, an aluminum case, or a steel case. The outer casing of the sodium battery cell 100 may also be a soft pack, such as a bag-shaped soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] This application does not particularly limit the shape of the sodium battery cell 100, and it may be cylindrical, rectangular, or any other shape. For example, Figure 2 is a schematic diagram of a sodium battery cell according to one embodiment of this application.

[0107] Figure 3 is a schematic diagram of the structure of a sodium battery cell according to another embodiment of this application. In some embodiments, the casing may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround the housing cavity. The housing 11 has an opening that communicates with the housing cavity, and the cover plate 13 is provided to cover the opening and seal the housing cavity. The positive electrode, negative electrode and solid electrolyte can be formed into an electrode assembly 12 by a winding process or a lamination process. The electrode assembly 12 is sealed within the housing cavity. The number of electrode assemblies 12 contained in the sodium battery cell 100 may be one or more, and can be selected as required by those skilled in the art.

[0108] In some embodiments, sodium battery cells may be assembled as a battery module, and the number of sodium battery cells included in the battery module may be one or more, and a person skilled in the art can select the specific number based on the application and capacity of the battery module.

[0109] Figure 4 is a schematic diagram of the structure of a battery 400 according to one embodiment of this application. As shown in Figure 4, in the battery 400, a plurality of sodium battery cells 100 may be arranged sequentially along the length of the battery 400. Of course, they may be arranged in any other way. Furthermore, the plurality of sodium battery cells 400 may be fixed via fasteners.

[0110] Referring to Figure 4, the battery 400 may include a battery box and a plurality of sodium battery cells 100 provided in the battery box. The battery box includes an upper box 401 and a lower box 402, the upper box 401 covering the lower box 402 and being provided to form a sealed space for housing the sodium battery cells 100. The plurality of sodium battery cells 100 may be arranged within the battery box in any manner.

[0111] Furthermore, this application further provides an electrical device comprising at least one of the sodium battery cells or batteries provided herein. The sodium battery cell or battery may be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0112] For example, Figure 5 is a schematic diagram of the structure of a vehicle according to one embodiment of this application. As shown in Figure 5, the vehicle 1 may be a fuel vehicle, a natural gas vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid electric vehicle, or a range extender vehicle, etc. A motor 500, a controller 600, and a battery 400 may be provided inside the vehicle 1, and the controller 600 is used to control the power supply of the battery 400 to the motor 500. For example, the battery 400 can be provided at the bottom, front, or rear of the vehicle 1. The battery 400 is used to supply power to the vehicle 1, for example, as the operating power source of the vehicle 1, the battery 400 is used to meet the demands of the vehicle 1's circuit system, such as starting the vehicle 1, navigation, and operating power during driving. In another embodiment of this application, the battery 400 can not only be the operating power source of the vehicle 1, but can also be used as the driving power source of the vehicle 1, providing driving power to the vehicle 1 by substituting or partially substituting fuel or natural gas.

[0113] The electrical device may be selected from a sodium battery cell or a battery depending on the usage requirements.

[0114] The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the demand for high output and high energy density of the battery in the electrical device, sodium battery cells or batteries may be used.

[0115] Other examples of devices may include mobile phones, tablet computers, and laptop computers. Such devices are typically required to be lightweight and thin, and may use battery cells as a power source.

[0116] [Examples]

[0117] Examples of the present application are described below. The examples described below are illustrative and are for interpretive purposes only, and should not be understood as limiting the present application. Unless otherwise specified in the examples, specific techniques or conditions are described in the technical or technical instructions or product descriptions in the literature in the art. Unless otherwise specified, the reagents or equipment used are all common commercially available products.

[0118] [Example 1]

[0119] 1) Manufacturing of sodium-ion batteries

[0120] 1.1) Production of the positive electrode: The positive electrode active material was prepared by dissolving the active material, sodium vanadium phosphate (Na3V2(PO4)3), the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), in a weight ratio of 90%:5%:5% in the solvent N-methylpyrrolidone (NMP), and thoroughly stirring to ensure uniform mixing. The positive electrode active material was uniformly coated onto aluminum foil, which served as the positive electrode current collector, and then subjected to baking, cold pressing, and cutting to obtain a positive electrode sheet.

[0121] 1.2) Manufacturing of the negative electrode: Active material: hard carbon, lithium nitrate; conductive agent: acetylene black; binder: styrene-butadiene rubber (SBR); thickener: sodium carboxymethylcellulose (CMC) -Na The materials were mixed uniformly with an appropriate amount of deionized water in a weight ratio of 89.5%:0.5%:4%:4%:2% to obtain a negative electrode active material. The negative electrode active material was then coated onto a Cu foil, and subsequently baked, cold pressed, and cut to obtain a negative electrode sheet.

[0122] 1.3) Separator manufacturing: A porous polymer film of PE was used as the separator.

[0123] 1.4) Electrolyte: Ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a mass ratio of 30%:70%, dissolved in 1M NaPF6, and uniformly stirred.

[0124] 1.5) Assembly: The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator interposed between the positive and negative electrodes to act as a separator. The assembly was then wound up to obtain the electrode assembly, and the electrolyte was added. Subsequently, the assembly was hot-pressed at 100°C and 250 MPa for 2 minutes to obtain a sodium-ion battery.

[0125] [Example 2]

[0126] The manufacturing process for the sodium-ion battery in Example 2 involves the following components in the negative electrode active material: hard carbon as the active material, lithium nitrate, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener. -Na The results were almost the same as in Example 1, except that the mass ratio of the components was set to 89%:1%:4%:4%:2%.

[0127] [Example 3]

[0128] The manufacturing process for the sodium-ion battery in Example 3 involves using hard carbon as the active material, lithium nitrate as the active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener in the negative electrode active material. -Na Except for setting the mass ratio of ) to 85%:5%:4%:4%:2%, this is almost the same as Example 1.

[0129] [Example 4]

[0130] The manufacturing process for the sodium-ion battery in Example 4 involves using hard carbon as the active material, lithium nitrate as the active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener in the negative electrode active material. -Na The method is almost the same as in Example 1, except that the mass ratio of the components is set to 80%:10%:4%:4%:2%.

[0131] [Example 5]

[0132] The manufacturing process for the sodium-ion battery in Example 5 involves the following components in the negative electrode active material: hard carbon as the active material, lithium nitrate, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener. -Na The method is almost the same as in Example 1, except that the mass ratio of the components is set to 87%:3%:4%:4%:2%.

[0133] [Example 6]

[0134] The manufacturing process for the sodium-ion battery in Example 6 is as follows: (1) The negative electrode active material consists of hard carbon as the active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener. -Na (1) The cathode active material is composed of the active material sodium vanadium phosphate (Na3V2(PO4)3), lithium iron phosphate (LiFePO4), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 85%:5%:5%:5%, otherwise it is almost the same as Example 1.

[0135] [Example 7]

[0136] The manufacturing process for the sodium-ion battery in Example 7 is as follows: (1) The negative electrode active material consists of hard carbon as the active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickener. -Na (2) It is composed of 90%:4%:4%:2% by mass, and is almost the same as Example 1 except that 0.8 wt% LiPF6 is added to the electrolyte.

[0137] [Example 8]

[0138] The manufacturing process for the sodium-ion battery in Example 8 is almost the same as that in Example 7, except that 1 wt% LiPF6 was added to the electrolyte.

[0139] [Example 9]

[0140] The manufacturing process for the sodium-ion battery in Example 9 is almost the same as that of Example 8, except that 0.1 wt% FEC was added to the electrolyte.

[0141] [Example 10]

[0142] The manufacturing process for the sodium-ion battery in Example 10 is almost the same as that of Example 8, except that 1 wt% FEC was added to the electrolyte.

[0143] [Example 11]

[0144] The manufacturing process for the sodium-ion battery in Example 11 is almost the same as that of Example 8, except that 3 wt% FEC was added to the electrolyte.

[0145] [Example 12]

[0146] The manufacturing process for the sodium-ion battery in Example 12 is almost the same as that of Example 8, except that 5 wt% FEC was added to the electrolyte.

[0147] [Example 13]

[0148] The manufacturing process for the sodium-ion battery in Example 13 is almost the same as that of Example 8, except that 10 wt% FEC was added to the electrolyte.

[0149] [Comparative Example 1]

[0150] The manufacturing process for the sodium-ion battery in Comparative Example 1 involves the following materials: the negative electrode active material is hard carbon, the conductive agent is acetylene black, the binder is styrene-butadiene rubber (SBR), and the thickener is sodium carboxymethylcellulose (CMC). -Na It is almost the same as Example 1, except that it is composed of ) in a mass ratio of 90%:4%:4%:2%.

[0151] [Comparative Example 2]

[0152] The manufacturing process for the sodium-ion battery in Comparative Example 2 is almost the same as that of Example 1, except that 1 wt% polystyrene (PS) is added to the electrolyte.

[0153] [Comparative Example 3]

[0154] The manufacturing process for the sodium-ion battery in Comparative Example 3 is almost the same as that of Example 1, except that 1 wt% ethylene sulfate (DTD) is added to the electrolyte.

[0155] [Comparative Example 4]

[0156] The manufacturing process for the sodium-ion battery in Comparative Example 4 is almost the same as that of Example 1, except that 1 wt% FEC was added to the electrolyte.

[0157] 2) Characterization of the performance of sodium-ion batteries

[0158] 2.1) Capacity Retention Rate: At room temperature, a manufactured sodium-ion battery was left for 5 minutes, then charged with a constant current at a 1C rate to 4.2V, then charged with a constant voltage until the current fell to 0.05C or less, left for 5 minutes, and finally discharged with a constant current at a 1C rate to 2.0V. This was defined as one charge-discharge cycle. The discharge capacity in this test was defined as the discharge capacity of the first cycle of the sodium-ion battery. The sodium-ion battery was repeated 800 times, and the discharge capacity of each cycle was recorded. The capacity retention rate (%) of a sodium-ion secondary battery after 800 cycles at 1C / 1C at room temperature is calculated as: Discharge capacity at the 800th cycle / Discharge capacity at the first cycle × 100%. The measurement results are shown in Table 1.

[0159] 2.2) DC impedance measurement: under room temperature conditions, sodium The ion battery is left standing for 5 minutes, then charged with a constant current at a rate of 1C to 4.2V, and further charged with a constant voltage until the current drops below 0.05C. sodium The state of charge (SOC) of the ion battery was set to 100%. After standing for 5 minutes, constant current discharge was performed at a rate of 1C. sodium The state of charge (SOC) of the ion battery was adjusted to 50%. sodium The ion battery was left to stand for another 10 minutes, and then discharged at a constant current of 4C for 30 seconds. The voltage U1 at the last second of standing, the voltage U2 at the last second of constant current discharge at 4C, and the current I at constant current discharge at 4C were recorded. sodium The DC impedance R = (U1 - U2) / I was obtained after 30s constant current discharge of an ion battery at 25°C, 50% SOC, and a 4C rate. The measurement results are shown in Table 1.

[0160] 2.3) Li / Na ratio in the negative electrode sheet: At room temperature, a sodium-ion battery was charged with a constant current of 1C to 4.2V, then charged with a constant voltage at 4.2V until the current fell below 0.05C, and then discharged to 2.0V at 0.33C. After full discharge, the sodium-ion battery was disassembled, the negative electrode sheet was removed, and then the negative electrode sheet was analyzed by inductively coupled plasma atomic emission spectrometry according to EPA 6010D-2014. Extreme The lithium and sodium content in the sample was measured, and then the wtr (W) = Li content / Na content was calculated. The measurement results are shown in Table 1.

[0161] [Table 1]

[0162] As can be seen from Examples 1-5 and Comparative Examples 1-4, compared to general sulfur-containing compounds PS or DTD, adding lithium nitrate to a sodium-ion battery effectively improves the internal resistance of the battery, improves the capacity retention rate, and enhances the cycle performance of the sodium-ion battery.

[0163] As can be seen from Examples 1 to 5, when the Li / Na ratio in the negative electrode sheet is less than 0.001, that is, when the lithium content in the negative electrode sheet is too low, the improvement in the cycle performance of the sodium-ion battery is not significant. However, when the Li / Na ratio in the negative electrode sheet is greater than 1, that is, when the lithium content in the negative electrode sheet is too high, the negative electrode interface impedance deteriorates. Therefore, by maintaining the Li / Na ratio between 0.001 and 1, it is possible not only to improve the cycle performance of the sodium-ion battery but also to avoid affecting other aspects of the sodium-ion battery's performance.

[0164] As can be seen from Examples 6 and 7, the cycle performance of sodium-ion batteries can also be improved by adding lithium-containing compounds to the positive electrode and electrolyte.

[0165] As can be seen from Examples 8-13, the cycle performance of a sodium-ion battery can be further improved by adding FEC in a mass content of 0.1% to 5%.

[0166] As can be seen from Examples 1 to 13, several lithium-containing compounds, such as lithium nitrate, lithium iron phosphate, and lithium hexafluorophosphate, can all play a role in improving the cycle performance of sodium-ion batteries.

[0167] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and all embodiments having substantially the same technical idea and achieving the same function and effect within the scope of the technical solution of this application are included in the technical scope of this application. Furthermore, other forms that are constructed by adding various modifications to the embodiments that a person skilled in the art could conceive of, and by combining some of the components of the embodiments, are also included in the scope of this application, without departing from the gist of this application. [Explanation of Symbols]

[0168] 11 cabinets 12 Electrode assembly 13 Lid plate 100 sodium battery cells 121 Negative electrode sheet 122 Separator 123 Positive electrode sheet 400 batteries 401 Top Box 402 Lower Box 500 motor 600 Controllers

Claims

1. It includes a negative electrode sheet, a positive electrode sheet, and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer. At least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte contains a lithium-containing compound. A sodium battery cell wherein the negative electrode film layer comprises a negative electrode active material core and the lithium-containing compound coating the negative electrode active material core.

2. The sodium battery cell according to claim 1, wherein the negative electrode active material core contains amorphous carbon.

3. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in the negative electrode film layer 100 parts by weight is 0.05 to 15 parts by weight.

4. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in the negative electrode film layer 100 parts by weight is 0.1 to 5 parts by weight.

5. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in the positive electrode film layer 100 parts by weight is 0.1 to 20 parts by weight.

6. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in the positive electrode film layer 100 parts by weight is 0.5 to 10 parts by weight.

7. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in 100 parts by weight of the electrolyte is 0.01 to 15 parts by weight.

8. The sodium battery cell according to claim 1 or 2, wherein the content of the lithium-containing compound in 100 parts by weight of the electrolyte is 0.1 to 5 parts by weight.

9. The sodium battery cell according to claim 1 or 2, wherein the ratio of the mass content of lithium to the mass content of sodium in the negative electrode sheet is 0.0001 to 1.

10. The sodium battery cell according to claim 1 or 2, wherein the ratio of the mass content of lithium to the mass content of sodium in the negative electrode sheet is 0.01 to 0.

5.

11. The sodium battery cell according to claim 1 or 2, wherein the lithium-containing compound comprises at least one of alkyl lithium carbonate, lithium fluoride, lithium carbonate, lithium sulfate, lithium nitrate, lithium hydroxide, lithium chloride, lithium perchlorate, lithium hexafluorophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

12. The sodium battery cell according to claim 1 or 2, wherein the electrolyte contains fluoroethylene carbonate.

13. The sodium battery cell according to claim 12, wherein the content of fluoroethylene carbonate in 100 parts by weight of the electrolyte is 0.01 to 10 parts by weight.

14. The sodium battery cell according to claim 12, wherein the content of fluoroethylene carbonate in 100 parts by weight of the electrolyte is 0.1 to 5 parts by weight.

15. A battery comprising a sodium battery cell according to claim 1 or 2.

16. An electrical device comprising the battery described in claim 15.

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