Sodium battery monomer, battery and electric device

Abstract

The embodiment of the invention provides a sodium battery monomer, a battery and an electric device. The sodium battery monomer comprises a negative pole piece, a positive pole piece and electrolyte, the negative pole piece comprises a negative current collector and a negative film layer; the positive pole piece comprises a positive current collector and a positive film layer; at least one of the negative electrode film layer, the positive electrode film layer and the electrolyte comprises a lithium-containing compound. According to the technical scheme, the cycle performance of the sodium battery monomer can be improved.

Description

Sodium battery cells, batteries and electrical devices Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a sodium battery cell, a battery, and an electrical device. Background Art

[0002] In recent years, with the gradual development and application of lithium-ion batteries, from portable electronic devices to high-power electric vehicles, large-scale energy storage power stations, and smart grids, the demand for lithium metal has increased across various industries. However, with the decline in lithium metal reserves and the increasing difficulty of mining, the current lithium metal resources can no longer meet the needs of the lithium battery industry. Sodium, which is in the same main group as lithium, has similar chemical properties and abundant reserves. Therefore, sodium-ion batteries, which operate on similar principles to lithium-ion batteries, are currently being developed and are expected to serve as an important supplement to lithium-ion batteries in large-scale energy storage applications.

[0003] Therefore, how to improve the cycle performance of sodium-ion batteries is an urgent problem that needs to be solved.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a sodium battery cell, a battery and an electrical device, wherein the cycle performance of the sodium battery cell can be improved.

[0006] The first aspect of the present application provides a sodium battery cell, comprising: a negative electrode plate, a positive electrode plate and an electrolyte; the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer; the positive electrode plate 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 comprises a lithium-containing compound.

[0007] In an embodiment of the present application, a sodium battery cell includes a negative electrode sheet, a positive electrode sheet, and an electrolyte; further, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer, and 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 includes a lithium-containing compound. By making at least one of the negative electrode film layer, the positive electrode film layer, and the electrolyte of the sodium battery cell include a lithium-containing compound, the sodium battery cell will form a solid electrolyte interface film (SEI film) including some alkyl lithium carbonate. Compared with the SEI film whose components are almost all sodium alkyl carbonate, the SEI film including some alkyl lithium carbonate has a lower solubility in the electrolyte, which can improve the stability of the SEI film and reduce the probability of side reactions between the electrolyte and the negative electrode, thereby extending the cycle life of the sodium battery, that is, improving the cycle performance of the sodium battery.

[0008] In a possible implementation, the negative electrode film layer includes a negative electrode active material core and the lithium-containing compound coating the negative electrode active material core.

[0009] In the embodiments of the present application, when the negative electrode film layer of a sodium battery cell includes a lithium-containing compound, the lithium-containing compound and the negative electrode active material are configured as follows: the negative electrode active material serves as a core, and the lithium-containing compound coats the negative electrode active material core. By providing the negative electrode film layer with the negative electrode active material core and the lithium-containing compound coating the negative electrode active material core, i.e., by coating the negative electrode active material core with the lithium-containing compound, a more stable lithium-containing compound can be formed in the SEI film when the sodium battery forms the SEI film, thereby improving the stability of the SEI film and enhancing the battery's cycling performance.

[0010] In one possible implementation, the negative electrode active material core includes amorphous carbon.

[0011] In the embodiment of the present application, by making the negative electrode active material of the sodium battery monomer amorphous carbon, sodium ions can be better intercalated and deintercalated in the negative electrode active material, thereby further improving the performance of the sodium battery.

[0012] In a possible embodiment, based on 100 parts by weight of the negative electrode film layer, the content of the lithium-containing compound is 0.05-15 parts by weight, optionally 0.1-5 parts by weight.

[0013] In the embodiment of the present application, by making the mass proportion of the lithium-containing compound in the negative electrode film layer 0.05%-15%, especially 0.1%-5%, sufficient lithium elements can be provided for the sodium battery, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0014] In a possible implementation, based on 100 parts by weight of the positive electrode film layer, the content of the lithium-containing compound is 0.1-20 parts by weight, optionally 0.5-10 parts by weight.

[0015] In the embodiment of the present application, by making the mass proportion of the lithium-containing compound in the positive electrode film layer 0.1%-20%, especially 0.5%-10%, sufficient lithium elements can be provided for the sodium battery, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0016] In a possible implementation, based on 100 parts by weight of the electrolyte, the content of the lithium-containing compound is 0.01-15 parts by weight, optionally 0.1-5 parts by weight.

[0017] In the embodiment of the present application, by making the mass proportion of the lithium-containing compound in the electrolyte 0.01%-15%, especially 0.1%-5%, sufficient lithium elements can be provided for the sodium battery, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0018] In a possible embodiment, in the negative electrode plate, the ratio of the mass content of lithium to the mass content of sodium is 0.0001-1, optionally 0.01-0.5.

[0019] In the embodiments of the present application, sodium compounds in the SEI film are more soluble than lithium compounds. Therefore, the ratio of the mass content of lithium to sodium in the negative electrode 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 is less than 0.0001, the SEI film is almost entirely composed of sodium compounds, and the SEI film will continue to dissolve in the electrolyte. When the ratio of the mass content of lithium to sodium in the negative electrode is greater than 1, the negative electrode 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 that of lithium ions, this will cause the conductivity of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride to sodium ions to deteriorate, which in turn will seriously deteriorate the interfacial impedance and affect the power of the sodium battery. By setting the ratio of the mass content of lithium to the mass content of sodium in the negative electrode of the sodium battery to 0.0001-1, particularly 0.01-0.5, the sodium battery can achieve both long cycle performance and high power.

[0020] In one possible embodiment, 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 bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

[0021] In an embodiment of the present application, a lithium-containing compound is added to at least one of the positive electrode film layer, the negative electrode film layer and the electrolyte, and 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 bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate. The lithium in these lithium salt materials will be released from the material and migrate into the electrolyte. Then, the lithium salt in the electrolyte undergoes a double decomposition reaction with the sodium-containing compound on the negative electrode, which can effectively reduce the solubility of the SEI film in the electrolyte, thereby improving the stability of the SEI film and improving the battery performance.

[0022] In one possible implementation, the electrolyte includes fluoroethylene carbonate.

[0023] In the examples of this application, the lithium-containing compound material is brittle. During cycling, the active material expands, which can cause the active material to which the lithium-containing compound is added to break. By adding fluoroethylene carbonate to the electrolyte, an organic polymer can be formed at the negative electrode interface. This organic polymer has good toughness, allowing the interface between the positive and negative electrodes to withstand contraction, thereby preventing the negative electrode material from breaking due to expansion.

[0024] In one possible implementation, based on 100 parts by weight of the electrolyte, the content of the fluoroethylene carbonate is 0.01-10 parts by weight, optionally 0.1-5 parts by weight.

[0025] In the embodiments of the present application, fluoroethylene carbonate is added to the electrolyte to enable the positive or negative active material to which a lithium-containing compound is added to withstand shrinkage. However, fluoroethylene carbonate has poor thermal stability, and the acidic substances produced by decomposition can seriously worsen gas production. In addition, excessive addition will form a thicker SEI film, which can easily lead to sodium precipitation in sodium batteries. By setting the mass content of fluoroethylene carbonate in the electrolyte to 0.01%-10%, especially 0.1%-5%, fluoroethylene carbonate can not only play its role in making the SEI film resistant to shrinkage, but also prevent it from affecting the performance of the sodium battery.

[0026] A second aspect of the present application provides a battery, comprising the sodium battery cell according to any one of the embodiments in the first aspect of the present application.

[0027] A third aspect of the present application provides an electrical device comprising the sodium battery cell according to any one of the embodiments of the first aspect of the present application or the battery according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0029] FIG1 is a schematic structural diagram of a sodium battery cell according to an embodiment of the present application;

[0030] FIG2 is a schematic diagram of a sodium battery cell according to an embodiment of the present application;

[0031] FIG3 is a schematic structural diagram of a sodium battery cell according to another embodiment of the present application;

[0032] FIG4 is a schematic structural diagram of a sodium battery according to an embodiment of the present application;

[0033] FIG5 is a schematic structural diagram of an electric device according to an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following describes in detail embodiments of the electrode assembly, battery cell, battery, and electrical device of the present application, with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of specific range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0039] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0040] The terms "above", "below", "greater than" or "less than" as used in this application are inclusive of the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0041] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0042] Sodium batteries have a similar structure to lithium batteries, consisting of a positive electrode capable of intercalating and deintercalating sodium ions, a negative electrode, and an electrolyte for transporting sodium ions. Similar to lithium batteries, during the initial charge, the products of electrolyte reduction and decomposition form a solid electrolyte interface (SEI) film on the negative electrode interface, preventing further reduction and decomposition of the electrolyte. Therefore, the performance of this SEI film directly affects the performance of the sodium battery.

[0043] The SEI film formed at the negative electrode interface of sodium batteries is primarily composed of sodium alkyl carbonate, sodium carbonate, and sodium fluoride. Compared to lithium alkyl carbonate, the primary SEI component of lithium batteries, sodium alkyl carbonate, the primary SEI component of sodium batteries, has a greater solubility in the electrolyte. Consequently, the electrolyte continuously reacts with the negative electrode, making the SEI film of sodium batteries highly unstable and limiting their cycle performance to meet practical application requirements.

[0044] At present, the main technical means to solve the above problems are as follows: (1) Adding fluoroethylene carbonate (FEC) to the electrolyte. FEC can synergize with the electrolyte to improve the stability of the SEI of sodium batteries. However, the polymerized organic matter formed by the reduction of FEC at the negative electrode will seriously deteriorate the internal resistance of the battery. In addition, these sodium-containing organic matter still has a strong solubility in the electrolyte, and the battery cycle performance is not significantly improved. (2) Constructing organic framework / graphene composite organic materials to reduce the dissolution of SEI film in the electrolyte, but the cost of organic framework and graphene is relatively high, and it is not suitable for large-scale application in industrial production. (3) Coating a layer of fluorine-containing compound on the outside of the negative electrode material to help the SEI film in the sodium battery form better, but the process of coating a layer of fluorine-containing compound on the outside of the carbon negative electrode material is complicated, the cost is still very high, and the cycle performance is not significantly improved. Therefore, how to make sodium batteries have better cycle performance is an important technical problem that needs to be solved urgently.

[0045] The sodium battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0046] The sodium batteries described in this application include sodium ion batteries and nanometal batteries. The following embodiments are described using sodium ion batteries as an example, but the technical solutions of this application are not limited to sodium ion batteries.

[0047] [Sodium battery cell]

[0048] In a first aspect, the present application provides a sodium battery cell. FIG1 is a schematic structural diagram of a sodium battery cell according to one embodiment of the present application. As shown in FIG1 , 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; and at least one of the negative electrode film layer, the negative electrode film layer, and the electrolyte includes a lithium-containing compound.

[0049] Enabling at least one of the negative electrode film layer, the negative electrode film layer, and the electrolyte to include a lithium-containing compound, that is, adding a lithium-containing compound to the sodium battery cell 100 , can improve the cycle performance of the sodium battery cell 100 .

[0050] In the above solution, by including a lithium-containing compound in at least one of the negative electrode film layer, positive electrode film layer, and electrolyte of the sodium battery cell 100, the sodium battery cell 100 forms an SEI film comprising a portion of lithium alkyl carbonate and lithium fluoride. Compared to an SEI film composed almost entirely of sodium alkyl carbonate, an SEI film comprising a portion of lithium alkyl carbonate and lithium fluoride has lower solubility in the electrolyte. This improves the stability of the SEI film and reduces the probability of side reactions between the electrolyte and the negative electrode, thereby extending the cycle life of the sodium battery, that is, improving the cycling performance of the sodium battery.

[0051] Typically, a sodium battery cell 100 includes a positive electrode sheet 123, a separator 122, a negative electrode sheet 121, and an electrolyte. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator 122, located between the positive and negative electrodes 123 and 121, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0052] It should be noted here that the “positive electrode sheet” and “negative electrode sheet” mentioned in the embodiments of the present application refer to the positive electrode sheet and the negative electrode sheet as a whole including active materials, current collectors or other additives.

[0053] In some embodiments, the negative electrode film layer includes a negative electrode active material core and a lithium-containing compound coating the negative electrode active material core.

[0054] In the above embodiment, when the negative electrode film layer of the sodium battery cell 100 includes a lithium-containing compound, the lithium-containing compound and the negative electrode active material are configured as follows: the negative electrode active material serves as a core, and the lithium-containing compound coats the negative electrode active material core. By ensuring that the negative electrode film layer includes the negative electrode active material core and the lithium-containing compound coating the negative electrode active material core, i.e., by coating the negative electrode active material core with the lithium-containing compound, a more stable lithium-containing compound can be formed within the SEI film during formation of the sodium battery, thereby enhancing the stability of the SEI film and improving the cycling performance of the sodium battery.

[0055] In the embodiments of the present application, the lithium-containing compound coating of the negative electrode active material core may be continuous coating or discontinuous coating, which is not limited in the present application.

[0056] In the embodiment of the present application, the lithium-containing compound can be directly and evenly mixed with the negative electrode active material.

[0057] In some embodiments, the negative active material core includes amorphous carbon.

[0058] In the above solution, by making the negative electrode active material of the sodium battery cell 100 amorphous carbon, sodium ions can be better intercalated and deintercalated in the negative electrode active material, thereby further improving the performance of the sodium battery.

[0059] In some embodiments, based on 100 parts by weight of the negative electrode film layer, the content of the lithium-containing compound is 0.05-15 parts by weight, optionally 0.1-5 parts by weight.

[0060] In the above scheme, by making the mass proportion of the lithium-containing compound in the negative electrode film layer 0.05%-15%, especially 0.1%-5%, sufficient lithium elements can be provided to the sodium battery cell 100, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0061] In some embodiments, based on 100 parts by weight of the positive electrode film layer, the content of the lithium-containing compound is 0.1-20 parts by weight, optionally 0.5-10 parts by weight.

[0062] In the above scheme, by making the mass proportion of the lithium-containing compound in the positive electrode film layer 0.1%-20%, especially 0.5%-10%, sufficient lithium elements can be provided to the sodium battery cell 100, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0063] In the embodiment of the present application, the lithium-containing compound can be directly and evenly mixed with the positive electrode active material.

[0064] In some embodiments, based on 100 parts by weight of the electrolyte, the content of the lithium-containing compound is 0.01-15 parts by weight, alternatively 0.1-5 parts by weight.

[0065] In the above scheme, by making the mass proportion of the lithium-containing compound in the electrolyte 0.01%-15%, especially 0.1%-5%, sufficient lithium elements can be provided to the sodium battery cell 100, so as to minimize the solubility of the SEI film of the sodium battery in the electrolyte, thereby further improving the performance of the sodium battery.

[0066] In the embodiment of the present application, the lithium-containing compound can be directly added to the electrolyte.

[0067] In some embodiments, in the negative electrode sheet 121 , the ratio of the mass content of lithium to the mass content of sodium is 0.0001-1, and optionally 0.01-0.5.

[0068] In the above scheme, sodium compounds in the SEI film are more soluble than lithium compounds. Therefore, the ratio of the mass content of lithium to sodium in the negative electrode plate 121 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 plate 121 is less than 0.0001, the SEI film is almost entirely composed of sodium compounds and will continue to dissolve in the electrolyte. When the ratio of the mass content of lithium to sodium in the negative electrode plate 121 is greater than 1, the negative electrode plate 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 that of lithium ions, this will cause the conductivity of lithium-containing compounds such as alkyl lithium carbonate, lithium carbonate, and lithium fluoride to sodium ions to deteriorate, which will seriously deteriorate the interfacial impedance and affect the power 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 121 of the sodium battery to 0.0001-1, particularly 0.01-0.5, the sodium battery can have both longer cycle performance and higher power.

[0069] It should be noted that the sodium battery state of the lithium-to-sodium mass ratio defined herein refers to the state in which the sodium battery cell 100 has undergone the first charge-discharge cycle, that is, the charge-discharge cycle of the sodium battery cell 100 after the SEI formation stage.

[0070] 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 bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

[0071] In the above scheme, by adding a lithium-containing compound to at least one of the positive electrode film layer, the negative electrode film layer and the electrolyte, 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 bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate. The lithium in these lithium salt materials will be released from the material and migrate into the electrolyte. Then, the lithium salt in the electrolyte undergoes a double decomposition reaction with the sodium-containing compound on the negative electrode, which can effectively reduce the solubility of the SEI film in the electrolyte, thereby improving the stability of the SEI film and improving the battery performance.

[0072] In some embodiments, the electrolyte includes fluoroethylene carbonate.

[0073] In the above scheme, the lithium-containing compound is brittle, and the active material expands during cycling, which can cause the active material to fracture. By adding fluoroethylene carbonate to the electrolyte, an organic polymer can be formed at the negative electrode interface. This organic polymer has good toughness, allowing the interface between the positive and negative electrodes to withstand contraction, thereby preventing the negative electrode material from fracturing due to expansion.

[0074] In some embodiments, based on 100 parts by weight of the electrolyte, the content of fluoroethylene carbonate is 0.01-10 parts by weight, optionally 0.1-5 parts by weight.

[0075] In the above scheme, fluoroethylene carbonate is added to the electrolyte to make the positive or negative electrode active material containing a lithium compound resistant to shrinkage. However, fluoroethylene carbonate has poor thermal stability, and the acidic substances produced by decomposition can seriously worsen gas production. Furthermore, excessive addition can form a thicker SEI film, which can easily lead to sodium precipitation in sodium batteries. By limiting the mass content of fluoroethylene carbonate in the electrolyte to 0.01% to 10%, particularly 0.1% to 5%, fluoroethylene carbonate can both exert its role in making the SEI film resistant to shrinkage and prevent it from affecting the performance of the sodium battery.

[0076] [Positive electrode]

[0077] The positive electrode sheet 123 includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material and may also include the lithium-containing compound described in the above embodiments.

[0078] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0079] 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 base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the positive electrode active material may be a battery positive electrode active material known in the art. For example, the positive electrode active material may include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, this application is not limited to these materials; other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used singly or in combination.

[0081] 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. For example, the sodium transition metal oxide is Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0082] In some embodiments, the polyanionic compound may be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- The polyanionic compound can also be a compound with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds of anion units and halogen anions. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y may include at least one of P, S and Si, and n represents (YO4) n- The halogen may include at least one of F, Cl and Br. The polyanionic compound may also have sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y may include at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, including at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m represents (ZO y ) m+The halogen may be at least one of F, Cl and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0083] In some embodiments, the Prussian blue compound may be a compound having sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein 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.

[0084] In some embodiments, the positive electrode film layer may further include 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.

[0085] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0086] The positive electrode sheet 123 in this application can be prepared according to conventional methods in the art. For example, the positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0087] The positive electrode plate 123 of the present application does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode plate 123 of the present application also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode plate 123 of the present application also includes a protective layer covering the surface of the positive electrode film layer.

[0088] [Negative electrode]

[0089] The negative electrode sheet 121 includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material and may further include the lithium-containing compound described in the above embodiment.

[0090] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0091] 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 base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0093] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0094] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0096] The negative electrode sheet 121 in this application can be prepared according to conventional methods in the art. For example, the negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0097] [Electrolyte]

[0098] The electrolyte plays a role in conducting ions between the positive electrode sheet 123 and the negative electrode sheet 121. In the embodiment of the present application, the electrolyte may include fluoroethylene carbonate (FEC) and the lithium-containing compound described in any of the above embodiments.

[0099] In some embodiments, the electrolyte includes an organic solvent, a sodium electrolyte salt, and optional additives. The types of the organic solvent, the sodium electrolyte salt, and the additives are not particularly limited and can be selected according to needs.

[0100] In some embodiments, the electrolyte salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. The above electrolyte salts may be used alone or in combination of two or more.

[0101] In some embodiments, as an example, the organic solvent includes but is not limited to at least one of 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 above organic solvents can be used alone or in combination. Alternatively, two or more organic solvents are used in combination.

[0102] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0103] In some embodiments, as examples, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0104] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, a sodium electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the sodium electrolyte salt and the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the sodium electrolyte salt can be first added to the organic solvent, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0105] [Isolation film]

[0106] The separator is disposed between the positive electrode sheet 123 and the negative electrode sheet 121. It primarily prevents short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not specifically limit the type of separator; any known porous separator with good chemical and mechanical stability may be used.

[0107] In some embodiments, the material of the isolation membrane can be selected from one or more of, but not limited to, glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the isolation membrane can also be provided with an organic / inorganic composite coating, including a ceramic particle coating or a metal oxide coating.

[0108] In some embodiments, the positive electrode sheet 123 , the negative electrode sheet 121 , and the separator can be formed into the electrode assembly 12 by a winding process or a lamination process.

[0109] In some embodiments, the sodium battery cell 100 may include an outer packaging that can be used to encapsulate the electrode assembly 12 and the electrolyte.

[0110] In some embodiments, the outer packaging of the sodium battery cell 100 may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the sodium battery cell 100 may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] The present application has no particular limitation on the shape of the sodium battery cell 100 , which can be cylindrical, square, or any other shape. For example, FIG2 is a schematic diagram of a sodium battery cell according to an embodiment of the present application.

[0112] Figure 3 is a schematic structural diagram of a sodium battery cell according to another embodiment of the present application. In some embodiments, the outer packaging may include a shell 11 and a cover plate 13. Specifically, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode, the negative electrode and the solid electrolyte can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The number of electrode assemblies 12 contained in the sodium battery cell 100 can be one or more, and those skilled in the art can select according to specific actual needs.

[0113] In some embodiments, sodium battery cells can be assembled into a battery module. The number of sodium battery cells contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0114] Figure 4 is a schematic diagram of the structure of a battery 400 according to one embodiment of the present application. As shown in Figure 4 , in battery 400, multiple sodium battery cells 100 may be arranged sequentially along the length of battery 400. Of course, any other arrangement is also possible. Furthermore, the multiple sodium battery cells 400 may be secured together using fasteners.

[0115] Continuing with FIG4 , a battery 400 may include a battery box and a plurality of sodium battery cells 100 disposed within the battery box. The battery box includes an upper case 401 and a lower case 402. The upper case 401 can cover the lower case 402 and form an enclosed space for accommodating the sodium battery cells 100. The plurality of sodium battery cells 100 may be arranged in any manner within the battery box.

[0116] In addition, the present application also provides an electrical device, which includes at least one of the sodium battery cells or batteries provided in the present application. The sodium battery cells or batteries can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (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.

[0117] For example, Figure 5 is a structural diagram of a vehicle according to an embodiment of the present application. As shown in Figure 5, vehicle 1 can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 can be provided inside the vehicle 1, and the controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 can be provided at the bottom, front or rear of the vehicle 1. The battery 400 can be used to power the vehicle 1. For example, the battery 400 can be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements of the vehicle 1 during startup, navigation and operation. In another embodiment of the present application, the battery 400 can not only serve as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0118] As the electrical device, a sodium battery cell or a battery can be selected according to its usage requirements.

[0119] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of the battery, a sodium battery cell or battery can be used.

[0120] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0121] [Example]

[0122] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0123] [Example 1]

[0124] 1) Preparation of sodium ion batteries

[0125] 1.1) Preparation of the positive electrode: The active material sodium vanadium phosphate (Na3V2(PO4)3), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 90%:5%:5%, and the mixture is thoroughly stirred and mixed to prepare the positive electrode active material; the positive electrode active material is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0126] 1.2) Preparation of negative electrode: Active material hard carbon, lithium nitrate, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener carbon methyl cellulose sodium (CMC) are fully stirred and mixed in a proper amount of deionized water solvent system in a weight ratio of 89.5%:0.5%:4%:4%:2% to obtain negative electrode active material, and the negative electrode active material is coated on Cu foil, and then dried, cold pressed, and cut to obtain negative electrode sheets.

[0127] 1.3) Preparation of diaphragm: PE porous polymer film is used as the isolation membrane.

[0128] 1.4) Electrolyte: Mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 30%:70%, dissolve in 1M NaPF6, and stir evenly.

[0129] 1.5) Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide separation. Winding is then performed to form an electrode assembly, and electrolyte is added. The sodium-ion battery is then hot-pressed at 100°C and 250 MPa for 2 minutes.

[0130] [Example 2]

[0131] The preparation process of the sodium ion battery of Example 2 is basically the same as that of Example 1, except that the mass ratio of the active material hard carbon, lithium nitrate, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) in the negative electrode active material is 89%:1%:4%:4%:2%.

[0132] [Example 3]

[0133] The preparation process of the sodium ion battery of Example 3 is basically the same as that of Example 1, except that the mass ratio of the active material hard carbon, lithium nitrate, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) in the negative electrode active material is 85%:5%:4%:4%:2%.

[0134] [Example 4]

[0135] The preparation process of the sodium ion battery of Example 4 is basically the same as that of Example 1, except that the mass ratio of the active material hard carbon, lithium nitrate, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) in the negative electrode active material is 80%:10%:4%:4%:2%.

[0136] [Example 5]

[0137] The preparation process of the sodium ion battery of Example 5 is basically the same as that of Example 1, except that the mass ratio of the active material hard carbon, lithium nitrate, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) in the negative electrode active material is 87%:3%:4%:4%:2%.

[0138] [Example 6]

[0139] The preparation process of the sodium ion battery of Example 6 is basically the same as that of Example 1, except that: (1) the negative electrode active material is composed of the active material hard carbon, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carbon methyl cellulose (CMC) in a mass ratio of 90%:4%:4%:2%; (2) the positive electrode 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%.

[0140] [Example 7]

[0141] The preparation process of the sodium ion battery of Example 7 is basically the same as that of Example 1, except that: (1) the negative electrode active material is composed of an active material hard carbon, a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR), and a thickener sodium carbon methyl cellulose (CMC) in a mass ratio of 90%:4%:4%:2%; and (2) 0.8 wt% of LiPF6 is added to the electrolyte.

[0142] [Example 8]

[0143] The preparation process of the sodium ion battery of Example 8 is basically the same as that of Example 7, except that 1 wt% of LiPF6 is added to the electrolyte.

[0144] [Example 9]

[0145] The preparation process of the sodium ion battery of Example 9 is basically the same as that of Example 8, except that 0.1 wt % FEC is added to the electrolyte.

[0146] [Example 10]

[0147] The preparation process of the sodium ion battery of Example 10 is basically the same as that of Example 8, except that 1 wt% FEC is added to the electrolyte.

[0148] [Example 11]

[0149] The preparation process of the sodium ion battery of Example 11 is basically the same as that of Example 8, except that 3 wt % FEC is added to the electrolyte.

[0150] [Example 12]

[0151] The preparation process of the sodium ion battery of Example 12 is basically the same as that of Example 8, except that 5 wt% FEC is added to the electrolyte.

[0152] [Example 13]

[0153] The preparation process of the sodium ion battery of Example 13 is basically the same as that of Example 8, except that 10 wt % FEC is added to the electrolyte.

[0154] [Comparative Example 1]

[0155] The preparation process of the sodium ion battery of Comparative Example 1 is basically the same as that of Example 1, except that the negative electrode active material is composed of an active material hard carbon, a conductive agent acetylene black, a binder styrene butadiene rubber (SBR), and a thickener carbon methyl cellulose sodium (CMC) in a mass ratio of 90%:4%:4%:2%.

[0156] [Comparative Example 2]

[0157] The preparation process of the sodium ion battery of Comparative Example 2 is basically the same as that of Example 1, except that 1 wt % of polystyrene (PS) is added to the electrolyte.

[0158] [Comparative Example 3]

[0159] The preparation process of the sodium ion battery of Comparative Example 3 is basically the same as that of Example 1, except that 1 wt % of diethyl sulfate (DTD) is added to the electrolyte.

[0160] [Comparative Example 4]

[0161] The preparation process of the sodium ion battery of Comparative Example 4 is basically the same as that of Example 1, except that 1 wt % FEC is added to the electrolyte.

[0162] 2) Performance characterization of sodium ion batteries

[0163] 2.1) Capacity Retention: At room temperature, the prepared sodium-ion battery was left for 5 minutes, then charged at a constant current rate of 1C to 4.2V. It was then charged at a constant voltage rate until the current was less than or equal to 0.05C and left for 5 minutes. It was then discharged at a constant current rate of 1C to 2.0V. This constitutes one charge-discharge cycle. The discharge capacity at this time is the discharge capacity of the sodium-ion battery in the first cycle. The sodium-ion battery was subjected to this cycle 800 times, and the discharge capacity was recorded each time. The capacity retention (%) of the sodium-ion secondary battery after 800 cycles of 1C / 1C at room temperature = discharge capacity at the 800th cycle / discharge capacity at the first cycle × 100%. See Table 1 for test results.

[0164] 2.2) DC impedance test: At room temperature, allow the lithium-ion battery to rest for 5 minutes, charge at a constant current rate of 1C to 4.2V, and then charge at a constant voltage until the current is less than or equal to 0.05C, so that the lithium-ion battery's state of charge (SOC) is 100%. After resting for 5 minutes, discharge at a constant current rate of 1C to adjust the lithium-ion battery's SOC to 50%. Allow the lithium-ion battery with a 50% SOC to rest for another 10 minutes, and discharge at a constant current rate of 4C for 30 seconds. Record the voltage U1 at the last 1 second of rest, the voltage U2 at the last 1 second of 4C constant current discharge, and the current I of 4C constant current discharge. The DC impedance R of the lithium-ion battery at 25°C, 50% SOC, and 4C constant current discharge for 30 seconds is (U1-U2) / I. See Table 1 for the test results.

[0165] 2.3) Li / Na Ratio in the Negative Electrode: At room temperature, charge the sodium-ion battery at a constant current of 1C to 4.2V, then charge at a constant voltage of 4.2V until the current is less than 0.05C, and then discharge at 0.33C to 2.0V. Disassemble the fully discharged sodium-ion battery, remove the negative electrode, and measure the lithium and sodium contents of the negative electrode membrane using inductively coupled plasma atomic emission spectrometry according to EPA6010D-2014. W is calculated as Li content / Na content. See Table 1 for test results.

[0166] Table 1: Performance of sodium ion batteries of Examples 1-13 and Comparative Examples 1-4

[0167] Combining Examples 1-5 and Comparative Examples 1-4, it can be seen that compared with the commonly used sulfur-containing compounds PS or DTD, adding lithium nitrate to sodium ion batteries can effectively improve the internal resistance of the battery and improve the capacity retention rate to improve the cycle performance of the sodium ion battery.

[0168] Combining Examples 1-5, it can be seen that when the Li / Na ratio in the negative electrode is less than 0.001, that is, the lithium content in the negative electrode is too low, the cycle performance of the sodium-ion battery is not significantly improved; when the Li / Na ratio in the negative electrode is greater than 1, that is, the lithium content in the negative electrode is too high, the negative electrode interface impedance is deteriorated. Therefore, by maintaining the Li / Na ratio between 0.001 and 1, the cycle performance of the sodium-ion battery can be improved without affecting other aspects of the sodium-ion battery performance.

[0169] From Examples 6 and 7, it can be seen that adding lithium-containing compounds to the positive electrode and the electrolyte can also improve the cycle performance of the sodium ion battery.

[0170] In combination with Examples 8-13, it can be seen that further adding FEC with a mass content of 0.1%-5% to the sodium ion battery can further improve the cycle performance of the sodium ion battery.

[0171] It can be seen from Examples 1-13 that various lithium-containing compounds, such as lithium nitrate, lithium iron phosphate and lithium hexafluorophosphate, can play a role in improving the cycle performance of sodium ion batteries.

[0172] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, any implementation method having substantially the same structure as the technical concept and exerting the same effect is included in the technical scope of the present application. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A sodium battery cell, comprising: Negative electrode sheet, positive electrode sheet and electrolyte; The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer; 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 includes a lithium-containing compound.

2. The sodium battery cell according to claim 1, wherein: The negative electrode film layer includes a negative electrode active material core and the lithium-containing compound coating the negative electrode active material core.

3. The sodium battery cell according to claim 2, wherein: The negative electrode active material core includes amorphous carbon.

4. The sodium battery cell according to any one of claims 1 to 3, wherein: Based on 100 parts by weight of the negative electrode film layer, the content of the lithium-containing compound is 0.05-15 parts by weight, and optionally 0.1-5 parts by weight.

5. The sodium battery cell according to claim 1, wherein: Based on 100 parts by weight of the positive electrode film layer, the content of the lithium-containing compound is 0.1-20 parts by weight, and optionally 0.5-10 parts by weight.

6. The sodium battery cell according to claim 1, wherein: Based on 100 parts by weight of the electrolyte, the content of the lithium-containing compound is 0.01-15 parts by weight, and optionally 0.1-5 parts by weight.

7. The sodium battery cell according to any one of claims 1 to 6, wherein: In the negative electrode plate, the ratio of the mass content of lithium to the mass content of sodium is 0.0001-1, and optionally 0.01-0.

5.

8. The sodium battery cell according to any one of claims 1 to 7, wherein: 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 bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium iron phosphate, lithium cobaltate, lithium nickel manganese cobalt oxide, and lithium manganate.

9. The sodium battery cell according to any one of claims 1 to 8, wherein: The electrolyte includes fluoroethylene carbonate.

10. The sodium battery cell according to claim 9, wherein: Based on 100 parts by weight of the electrolyte, the content of the fluoroethylene carbonate is 0.01-10 parts by weight, and optionally 0.1-5 parts by weight.

11. A battery comprising the sodium battery cell according to any one of claims 1 to 10.

12. An electrical device comprising the battery as claimed in claim 11.

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