Secondary negative-electrode-free sodium metal battery and electric equipment

Abstract

The invention provides a secondary negative-electrode-free sodium metal battery and electric equipment, and relates to the field of sodium metal batteries. The secondary negative-electrode-free sodium metal battery comprises a diaphragm and a positive plate, the diaphragm comprises a first coating layer, a base material and a second coating layer which are stacked, the base material comprises any one of a PP film, a PE film and a PP and PE composite film, and a material for forming the first coating layer and a material for forming the second coating layer are selected from at least one of boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, aluminum oxide and magnesium oxide; the positive plate comprises a positive active layer, and the positive active layer comprises a sodium salt additive. The diaphragm can inhibit the growth of sodium dendrites, prevent the sodium dendrites from puncturing the diaphragm, reduce the risk of short circuit in the battery, and improve the safety performance of the battery. Moreover, the sodium salt additive introduced in the invention can ensure the stability of the positive electrode material structure in the repeated sodium intercalation and deintercalation process of the positive electrode, can also provide a part of consumed sodium source, and is beneficial to improving the cycle efficiency of the battery.

Description

Technical Field

[0001] The present application relates to the field of sodium metal batteries, and in particular to a secondary negative electrode-free sodium metal battery and electrical equipment. Background Art

[0002] With the widespread application of lithium-ion battery technology, its importance in the field of energy storage has become increasingly prominent. However, the widespread adoption of lithium-ion batteries has also raised concerns about the risk of lithium resource depletion. Global lithium resource reserves are limited and unevenly distributed, which makes the cost and sustainability of lithium-ion batteries a challenge. In contrast, sodium resources have become a potential alternative to lithium-ion batteries due to their abundance and low cost. Sodium-ion batteries have shown significant cost advantages and provide new possibilities for large-scale energy storage applications.

[0003] Despite their numerous advantages, sodium-ion batteries (SIBs) have several performance limitations. Specifically, the capacities of both the cathode and anode of SIBs are lower than those of lithium-ion batteries, and the higher redox potential of the sodium anode results in a relatively low energy density. This limitation limits their application in high-energy applications.

[0004] In order to overcome these challenges, researchers have been continuously exploring and optimizing the composition and structure of sodium-ion batteries. Among them, the negative electrode-free sodium metal battery has attracted widespread attention as a new battery design. This battery removes the traditional hard carbon negative electrode and utilizes the Na released by the positive electrode active material. + Sodium metal is deposited directly on the negative electrode current collector. This design not only reduces the battery's volume and mass, but also significantly improves the energy density of sodium batteries. Furthermore, since all active sodium ions originate from the positive electrode material, the manufacturing process of a negative electrode-free sodium metal battery is more convenient and safer.

[0005] However, anode-free sodium metal batteries also face several technical challenges during the charge and discharge process. Among them, the repeated deposition and stripping of sodium metal on the anode current collector easily leads to the formation and accumulation of sodium dendrites. These sodium dendrites can not only pierce the separator and cause a battery short circuit, but can also cause a large amount of dead sodium to accumulate, thereby reducing the battery's cycle life. Furthermore, the rapid growth of sodium dendrites and the volume expansion of sodium metal increase the safety risks of the battery. Summary of the Invention

[0006] The purpose of this application is to provide a secondary negative electrode-free sodium metal battery and electrical equipment to solve the above problems.

[0007] To achieve the above objectives, this application adopts the following technical solutions:

[0008] A secondary negative electrode-free sodium metal battery, comprising: a separator and a positive electrode sheet;

[0009] The diaphragm includes a substrate, a first coating layer, and a second coating layer, wherein the first coating layer and the second coating layer are respectively located on opposite sides of the substrate; wherein the substrate includes any one of a PP film, a PE film, and a composite film of PP and PE, and the material forming the first coating layer and the material forming the second coating layer are independently selected from at least one of boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, aluminum oxide, and magnesium oxide;

[0010] The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer contains a sodium salt additive.

[0011] According to an embodiment of the present application, the thickness of the substrate is 14-20 μm;

[0012] And / or, the thickness of the first coating layer and the thickness of the second coating layer are independently selected from 1-4 μm.

[0013] According to an embodiment of the present application, the sodium salt additive includes at least one of sodium borate, sodium tetrafluoroborate, sodium tetrakis(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium sodium tetrafluoroborate, and sodium difluorooxalatoborate;

[0014] And / or, the sodium salt additive accounts for 0.5-3 wt % of the mass of the positive electrode active layer.

[0015] According to an embodiment of the present application, the positive electrode active layer further includes 90-97 wt % of a positive electrode active material, 1-3 wt % of a conductive agent, and 1-5 wt % of a binder.

[0016] According to an embodiment of the present application, the positive electrode active material includes any one of a polyanionic compound and a layered metal oxide;

[0017] And / or, the polyanionic compound includes at least one of NaFePO4, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2FeP2O7, Na4Fe3(PO4)2P2O7, and NaFe(SO4)3;

[0018] And / or, the layered metal oxide comprises NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2、Na 2 / 3 Mn 1 / 2 Fe 1 / 4 Co 1 / 4 O2、Na 0.9 Cu 0.22 Fe 0.3 Mn 0.48 At least one of O2;

[0019] The conductive agent includes at least one of Super P, Ketjen black, acetylene black, carbon nanotubes, and graphene;

[0020] And / or, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, sodium alginate, and polyolefin binders.

[0021] According to an embodiment of the present application, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode active layer is formed on the surface of the positive electrode current collector;

[0022] The positive electrode current collector includes any one of aluminum foil, carbon-coated aluminum foil, and aluminum mesh.

[0023] According to an embodiment of the present application, the secondary negative electrode-free sodium metal battery further includes an electrolyte;

[0024] The electrolyte includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, sulfolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0025] According to an embodiment of the present application, the electrolyte includes a sodium salt;

[0026] The solubility of the sodium salt in the electrolyte is 0.5-2.0M;

[0027] The sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium difluorobisoxalatophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium trifluoromethanesulfonate.

[0028] According to an embodiment of the present application, the secondary negative electrode-free sodium metal battery further includes a negative electrode current collector;

[0029] The negative electrode current collector includes carbon-coated aluminum foil.

[0030] The present application also provides an electrical device, which includes the secondary negative electrode-free sodium metal battery described above.

[0031] Compared with the prior art, the advantages of this application include:

[0032] The separator of the present application includes a first coating layer and a second coating layer, which significantly enhances the uniformity of the current density distribution on the negative electrode side, which is conducive to a more uniform deposition of the sodium layer. In addition, the separator structure of the present application can effectively inhibit the growth of sodium dendrites, prevent them from piercing the separator, reduce the risk of internal short circuits in the battery, and further improve the safety performance of the battery. The present application introduces a sodium salt additive into the positive electrode. On the one hand, it can ensure the stability of the positive electrode material structure during the repeated sodium insertion and removal process of the positive electrode. On the other hand, it can provide a portion of the consumed sodium source, which helps to improve the cycle efficiency of the battery.

[0033] The diaphragm and sodium salt additive of the present application cooperate with each other in terms of function. On the one hand, the design of the diaphragm of the present application ensures the uniform deposition of sodium ions and can also effectively inhibit the growth of dendrites, which is beneficial to improving the safety performance of the battery; on the other hand, the introduction of sodium salt additives in the positive electrode is beneficial to improving the stability of the positive electrode structure and replenishing the sodium source, which significantly improves the cycle performance of the battery. The combination of the diaphragm of the present application and the sodium salt additive jointly improves the electrochemical performance and safety performance of the battery, opening up a new path for the development and application of high electrochemical performance and high safety batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0035] Figure 1 1 is a graph showing the relationship between the capacity retention rate and the number of cycles of the battery of Example 1 at 0.5C;

[0036] Figure 2 The charge and discharge curves of the battery of Example 1 at 0.2C, 0.5C, and 1C are shown. DETAILED DESCRIPTION

[0037] As used herein:

[0038] As used herein, the terms "comprises," "including," "having," "containing" or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0039] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0040] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0041] In order to better illustrate the technical solution provided by this application, before the embodiments, an overall description of the technical solution is first given, as follows:

[0042] Existing negative electrode-free sodium metal batteries have problems such as sodium dendrites easily piercing the diaphragm during the charge and discharge process, and the accumulation of dead sodium reduces the cycle life of the battery; at the same time, the excessive growth of sodium dendrites and the volume expansion of sodium metal increase the safety risks of sodium metal batteries.

[0043] In order to improve the above technical problems, the present application provides a secondary negative electrode-free sodium metal battery, comprising: a separator and a positive electrode sheet;

[0044] The diaphragm includes a substrate, a first coating layer, and a second coating layer, wherein the first coating layer and the second coating layer are respectively located on opposite sides of the substrate; wherein the substrate includes any one of a PP film, a PE film, and a composite film of PP and PE, and the material forming the first coating layer and the material forming the second coating layer are independently selected from at least one of boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, aluminum oxide, and magnesium oxide;

[0045] The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer contains a sodium salt additive.

[0046] The first coating layer and the second coating layer in the diaphragm of the present application both exhibit excellent thermal stability, chemical stability and high strength properties. This unique design ensures that the diaphragm is effectively coated and protected on both the side facing the positive electrode sheet and the side facing the negative electrode current collector. In particular, the coating layer facing the negative electrode side can effectively inhibit sodium dendrites from piercing the diaphragm, which can prevent the battery from thermal runaway. The coating layer facing the positive electrode side makes full use of the high chemical stability of the coating material to cope with the high voltage and strong oxidizing environment in the positive electrode area, significantly enhancing the antioxidant capacity of the diaphragm, which is beneficial to improving the cycle life of the battery. The synergistic effect between the first coating layer and the second coating layer not only enhances the overall performance of the diaphragm, but also plays a key role in effectively reducing adverse phenomena such as micro-short circuits and self-discharge of the battery, thereby greatly improving the safety performance of the battery. This innovative design provides a new solution for building high-performance, high-safety batteries. At the same time, the first coating layer material and the second coating layer material have a high specific surface area, which makes the diaphragm of the present application have good wettability and liquid retention properties to the electrolyte. With the same injection volume, the flowing electrolyte in the battery is relatively reduced, which can alleviate the side reaction between sodium metal and electrolyte to a certain extent.

[0047] In general, the diaphragm of the present application can significantly improve the uniformity of the current density on the negative electrode side, thereby promoting a more uniform deposition of the sodium layer, and effectively inhibiting the penetration of sodium dendrites into the diaphragm, thereby enhancing the safety and performance of the battery. The sodium salt additive of the present application can effectively maintain the stability of the structure during the repeated deintercalation of sodium in the positive electrode; moreover, the sodium salt additive can also serve as a supplementary source to provide sodium ions that are partially consumed due to recycling, thereby improving the overall performance and cycle life of the battery. The diaphragm of the present application and the sodium salt additive cooperate with each other to effectively improve the electrochemical performance and safety performance of the battery.

[0048] According to the embodiments of the present application, the thickness of the substrate is 14-20 μm. Substrates within this thickness range have good air permeability and strength. If the substrate thickness is too thin, it is easy to cause substrate defects, resulting in low battery yield. If the substrate thickness is too thick, it will cause a decrease in battery capacity, and an excessively thick substrate will increase raw material costs.

[0049] For example, the thickness of the substrate may be 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value between 14 and 20 μm.

[0050] And / or, the thickness of the first coating layer and the thickness of the second coating layer are independently selected from 1-4 μm. When the thickness of the first coating layer and the thickness of the second coating layer are within the above range, the strength of the diaphragm can be effectively improved, and the penetration of sodium dendrites can be effectively blocked. At the same time, the battery's liquid absorption capacity can be increased, and the cycle stability is better. If the thickness of the first coating layer and the second coating layer is too small, there may be defects in some parts of the diaphragm that are not covered by the coating and are easily punctured by dendrites. If the thickness of the first coating layer and the thickness of the second coating layer are too large, problems such as warping and curling of the diaphragm are likely to occur.

[0051] The thickness of the first coating layer and the thickness of the second coating layer can be 1 μm, 2 μm, 3 μm, 4 μm or any value between 1 and 4 μm.

[0052] According to an embodiment of the present application, the sodium salt additive includes at least one of sodium borate, sodium tetrafluoroborate, sodium tetrakis(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium sodium tetrafluoroborate, and sodium difluorooxalatoborate;

[0053] And / or, the sodium salt additive accounts for 0.5-3 wt % of the mass of the positive electrode active layer.

[0054] For example, the sodium salt additive accounts for 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3 wt% or any value between 0.5-3 wt% of the mass of the positive electrode active layer.

[0055] According to an embodiment of the present application, the positive electrode active layer further includes 90-97 wt % of a positive electrode active material, 1-3 wt % of a conductive agent, and 1-5 wt % of a binder.

[0056] Furthermore, the positive electrode active layer includes 90-97 wt % of a positive electrode active material, 1-3 wt % of a conductive agent, 1-5 wt % of a binder, and 0.5-3 wt % of a sodium salt additive.

[0057] For example, the content of the positive electrode active material in the positive electrode active layer can be 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt% or any value between 90-97wt%;

[0058] The content of the conductive agent in the positive electrode active layer can be 1wt%, 2wt%, 3wt% or any value between 1-3wt%;

[0059] The content of the binder in the positive electrode active layer may be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt% or any value between 1 and 5 wt%.

[0060] According to an embodiment of the present application, the positive electrode active material includes any one of a polyanionic compound and a layered metal oxide;

[0061] And / or, the polyanionic compound includes at least one of NaFePO4, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2FeP2O7, Na4Fe3(PO4)2P2O7, and NaFe(SO4)3;

[0062] And / or, the layered metal oxide comprises NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2、Na 2 / 3 Mn 1 / 2 Fe 1 / 4 Co 1 / 4 O2、Na 0.9 Cu 0.22 Fe 0.3 Mn 0.48 At least one of O2;

[0063] The conductive agent includes at least one of Super P, Ketjen black, acetylene black, carbon nanotubes, and graphene;

[0064] And / or, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, sodium alginate, and polyolefin binders.

[0065] According to an embodiment of the present application, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode active layer is formed on the surface of the positive electrode current collector;

[0066] The positive electrode current collector includes any one of aluminum foil, carbon-coated aluminum foil, and aluminum mesh.

[0067] The electrolyte of the existing negative electrode-free sodium metal battery is easily catalyzed and decomposed by metallic sodium during storage, resulting in an increase in internal resistance and easily causing poor storage. To improve this technical problem, in some embodiments, the secondary negative electrode-free sodium metal battery also includes an electrolyte; the electrolyte includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, cyclopentane, tetrahydrofuran, and 2-methyltetrahydrofuran. The electrolyte of the present application has excellent performance when applied to negative electrode-free sodium metal batteries. It can stabilize the SEI and CEI interfaces. The negative electrode side effectively inhibits the formation of dead sodium and sodium dendrites, repairs cracks formed during the deposition and stripping of metallic sodium, and the positive electrode side protects the structural integrity of the positive electrode and hinders the dissolution of transition metal ions, thereby improving the cycle life of the battery. The solution of the present application can alleviate the catalytic decomposition reaction between the liquid electrolyte and metallic sodium, thereby improving the cycle stability and storage performance of the negative electrode-free sodium metal battery.

[0068] According to an embodiment of the present application, the electrolyte includes a sodium salt;

[0069] The solubility of the sodium salt in the electrolyte is 0.5-2.0M; for example, the solubility of the sodium salt in the electrolyte can be 0.5M, 1.0M, 1.5M, 2.0M or any value between 0.5-2.0M.

[0070] The sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium difluorobisoxalatophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium trifluoromethanesulfonate.

[0071] According to an embodiment of the present application, the secondary negative electrode-free sodium metal battery further includes a negative electrode current collector;

[0072] The negative electrode current collector includes carbon-coated aluminum foil.

[0073] In some embodiments, a secondary negative electrode-free sodium metal battery can be prepared by stacking and winding a positive electrode sheet, a separator, and a negative electrode current collector in sequence, and assembling them with an electrolyte to obtain a secondary negative electrode-free sodium metal battery.

[0074] After the battery prepared by the above method is filled with liquid and formed at 40-60°C, the initial charge and discharge efficiency can reach more than 90%. Moreover, the battery formed in the present application can achieve a charge and discharge efficiency of 98-100% when cycled at room temperature, with high reversible capacity.

[0075] Secondary negative electrode-free sodium metal batteries include cylindrical batteries or soft-pack batteries.

[0076] The present application also provides an electrical device, which includes the secondary negative electrode-free sodium metal battery described above.

[0077] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0078] Example 1

[0079] 1) The positive electrode active material Na4Fe3(PO4)2P2O7, the conductive agent Super-P, the conductive agent CNTs, the binder PVDF, and the sodium salt additive NaBF4 were mixed in a mass ratio of 93.7:1.5:1.0:2.3:1.5. The solvent NMP was added and the mixture was evenly dispersed to obtain a positive electrode slurry. The prepared positive electrode slurry was coated on aluminum foil using a coater and dried in a forced air oven at 100°C to obtain a coated positive electrode. The coated positive electrode was then roller-pressed and slit to obtain a positive electrode sheet.

[0080] 2) Diethylene glycol dimethyl ether is used as an electrolyte solvent, and NaBF4 accounting for 1 wt% of the total electrolyte mass is added as an additive. NaPF6 and NaOTF are selected as sodium salts. NaPF6 and NaOTF are configured into a 1.5 M electrolyte in a mass ratio of 1:1, stirred until fully dissolved, and mixed evenly to obtain an electrolyte.

[0081] 3) Slicing the carbon-coated aluminum foil into strips to serve as the negative electrode current collector, wherein the carbon-coated aluminum foil comprises an aluminum foil and two carbon-coated layers located on opposite sides of the aluminum foil, the thickness of the aluminum foil is 13 μm, and the thickness of the two carbon-coated layers is 1 μm;

[0082] 4) The diaphragm includes a substrate and a first coating layer and a second coating layer located on opposite sides of the substrate, wherein the substrate is a PP film with a thickness of 16 μm, the first coating layer is aluminum oxide with a thickness of 2 μm, and the second coating layer is aluminum oxide with a thickness of 2 μm;

[0083] 5) The positive electrode sheet, separator, and negative electrode current collector were wound and assembled into an 18650 battery, which was then filled with electrolyte and completely sealed for electrochemical performance testing.

[0084] 6) After the battery is filled with liquid and left to stand at 45℃ for 24 hours, it is placed on the shelf for formation. The formation voltage range is 3.65-2.0V, the formation current is 0.2C, and the formation temperature is 45℃.

[0085] Example 2

[0086] Other parameters are the same as those in Example 1, except that the base material in the diaphragm is a PP film with a thickness of 14 μm, and the first coating layer in the diaphragm and the second coating layer in the diaphragm are both 1 μm of aluminum oxide.

[0087] Example 3

[0088] Other parameters are the same as those in Example 1, except that the base material in the diaphragm is a PP film with a thickness of 20 μm, and the first coating layer in the diaphragm and the second coating layer in the diaphragm are both 4 μm aluminum oxide.

[0089] Example 4

[0090] Other parameters are the same as those in Example 1, except that the first coating layer in the diaphragm and the second coating layer in the diaphragm are both boehmite.

[0091] Example 5

[0092] The remaining parameters are the same as those in Example 1, except that the sodium salts NaPF6 and NaOTF in the electrolyte are configured in a mass ratio of 1:1 to form a 0.5 M electrolyte.

[0093] Example 6

[0094] The remaining parameters are the same as those in Example 1, except that the sodium salts NaPF6 and NaOTF in the electrolyte are configured in a mass ratio of 1:1 to form a 2.0 M electrolyte.

[0095] Example 7

[0096] The remaining parameters are the same as those in Example 1, except that: NaPF6 and NaFSI are selected as sodium salts in the electrolyte, and NaPF6 and NaFSI are configured into a 1.5M electrolyte in a mass ratio of 1:1.

[0097] Comparative Example 1

[0098] The other parameters are the same as those in Example 1, except that: there is only one coating layer in the diaphragm of Comparative Example 1. Specifically, the diaphragm of Comparative Example 1 includes a substrate and a coating layer located on one surface of the substrate. The substrate is a PP film with a thickness of 16 μm, and the coating layer is aluminum oxide with a thickness of 2 μm. The aluminum oxide is on the positive electrode.

[0099] Comparative Example 2

[0100] Other parameters are the same as those in Example 1, except that the first coating layer and the second coating layer of the diaphragm are both 0.8 μm aluminum oxide.

[0101] Comparative Example 3

[0102] Other parameters are the same as those in Example 1, except that the first coating layer and the second coating layer of the diaphragm are both 4.5 μm aluminum oxide.

[0103] Comparative Example 4

[0104] Other parameters are the same as those in Example 1, except that the material used for the separator is different from that in Example 1, and the separator is made of non-woven fabric with a thickness of 20 μm.

[0105] Comparative Example 5

[0106] Other parameters are the same as those in Example 1, except that no NaBF4 is added to the electrolyte as an additive.

[0107] The electrochemical performance tests were performed on the batteries of Examples 1-7 and Comparative Examples 1-5. The test results are shown in Table 1. The test method is as follows:

[0108] 1. Chemical process:

[0109] 1. Let it stand for 1 minute;

[0110] 2. 0.05C constant current charging for 2h, voltage limit 3.65V;

[0111] 3. 0.1C constant current charging for 1h, voltage limit 3.65V;

[0112] 4. Charge at a constant current of 0.2C to 3.65V. The total charge capacity from 1 to 4 is recorded as C0. 5. Let stand for 10 minutes.

[0113] 6. Discharge at a constant current of 0.2C to 2.0V, and record the discharge capacity as C1;

[0114] 7. Let it stand for 10 minutes;

[0115] 8. Constant current charging to 3.65V, current 0.2C;

[0116] 9. Let it stand for 10 minutes and remove from the shelf.

[0117] 2. Storage at 60℃ for 7 days:

[0118] Take the formed battery;

[0119] 1. 0.2C constant current charging to 3.65V;

[0120] 2. Remove from the shelf and store in a 60°C constant temperature oven for 7 days;

[0121] 3. Take out and cool to room temperature;

[0122] 4. Discharge at a constant current of 0.2C to 2.0V, and record the discharge capacity as C2;

[0123] 5. Let it stand for 10 minutes;

[0124] 6. 0.2C constant current charge to 3.65V;

[0125] 7. Let it stand for 10 minutes;

[0126] 8. Discharge at 0.2C constant current to 2.0V, and record the discharge capacity as C3;

[0127] 9. Let it stand for 10 minutes and remove from the shelf.

[0128] 3. Cycle test steps:

[0129] 1. Let it stand for 1 minute;

[0130] 2. 0.5C constant current charging, voltage limit 3.4V;

[0131] 3. Let it stand for 10 minutes;

[0132] 4. Discharge at a constant current of 0.5C to 2.0V, and record the discharge capacity as C4.

[0133] 5. Let it stand for 10 minutes;

[0134] 6. Remove from shelf after cycling until discharge capacity is less than 80%*C4.

[0135] First effect = C1 / C0*100%;

[0136] Gram capacity = C1 / mass of active material of a single positive electrode; capacity retention after 7 days storage at 60°C = C2 / C1 * 100%;

[0137] Capacity recovery rate after storage at 60°C for 7 days = C3 / C1*100%.

[0138] Table 1 Comparison of electrochemical performance of Examples 1-7 and Comparative Examples 1-5

[0139]

[0140] The test performance of the battery of Example 1 is as follows Figure 1 、 Figure 2 As shown in Table 1-2.

[0141] Figure 1 This is the cycle diagram of the test under 0.5C 3.4-2.0V, Figure 1 It can be seen that the battery prepared according to the conditions of Example 1 has good cycle stability, and the capacity retention rate after 1000 cycles can reach 80%.

[0142] Figure 2 The charge and discharge curves of the battery in Example 1 at 0.2C, 0.5C, and 1C are shown, and the test voltage range is 3.4-2.0V. Figure 2 It can be seen that the battery of Example 1 can be stably charged and discharged at 0.2C-1C, and has good rate capability.

[0143] The safety performance test of the battery prepared in Example 1 was performed. The specific method is as follows:

[0144] The short-circuit test is conducted at room temperature of approximately 25±5°C. The positive and negative terminals of a fully charged battery are connected together with an external resistance load of 80±20mΩ, creating an external short circuit. The test terminates when the battery ignites, explodes, leaks, or is fully discharged to a voltage below 0.1V and the battery temperature drops to ±10°C below the ambient temperature. The short-circuit test passes if there is no explosion, no fire, and the battery surface temperature does not exceed 150°C.

[0145] The over-discharge test method is to fully discharge the battery cell and then charge it with 1C reverse polarity for 90 minutes. The over-discharge test passing standard is: no explosion, no fire.

[0146] The vibration test method involves mounting a standard-charged battery cell on a vibration table and vibrating it in the X, Y, and Z directions for 30 minutes each, with an amplitude of 1.6mm and a frequency range of 10Hz to 55Hz, varying by 1Hz per minute. The vibration test passing criteria include no leakage, no explosion, and no fire.

[0147] The drop test method is as follows: the battery is fully charged according to standard charging conditions and then dropped from a height of 1.0m onto a concrete floor. The battery is dropped once on each end surface and twice on the cylindrical surface, for a total of four drops. The drop test passing criteria are: no leakage, no explosion, and no fire.

[0148] The squeeze test method is as follows: After fully charging the battery cell, place it between two squeeze plates. Press the plates perpendicular to the battery plates at a speed of (5±1) mm / s until the squeeze force reaches 13.0±0.78 kN. The squeeze test passing criteria are: no explosion and no fire.

[0149] The heavy object impact test method is as follows: After fully charging the battery cell to a standard standard, place it on a platform. A metal rod with a diameter of 15.8±0.2mm is placed horizontally at the geometric center of the battery cell. A 9.1±1.0kg weight is then dropped from a height of 610±25mm to impact the battery with the metal rod. The battery is observed for 6 hours. The passing criteria for the heavy object impact test are: no explosion and no fire.

[0150] The thermal abuse test method is as follows: After the fully charged battery reaches room temperature, it is placed in a circulating air oven and heated from room temperature to 150±2°C at a rate of 5±2°C / minute. The battery is then kept at 150±2°C for 30 minutes. The passing criteria for the thermal abuse test are: no explosion and no fire.

[0151] The needle penetration test involves penetrating a fully charged single cell with a high-temperature resistant steel needle (5-8mm in diameter, with a 45-50° cone angle and a smooth surface free of rust, oxide, or oil) at a speed of 20-30mm / s, perpendicular to the battery. The penetration point should be near the geometric center of the punctured surface. The needle remains in the battery for one hour. The passing criteria for the needle penetration test are: no explosion or fire.

[0152] The safety test results of the battery of Example 1 are shown in Table 2.

[0153] Table 2 Safety test results of the battery in Example 1

[0154]

[0155]

[0156] As can be seen from Table 2, the battery prepared in Example 1 can pass safety tests such as short circuit test, free drop test, heavy object impact test, vibration test, over-discharge test, extrusion test, 150°C thermal shock test, and needle penetration test.

[0157] Depend on Figure 1 , Figure 2 As well as the results in Table 1 and Table 2, the comparison of the experimental conditions of Examples 1-7 and Comparative Examples 1-5 shows that the introduction of a coating layer coated with a specific material on both sides of the diaphragm, the introduction of a sodium salt additive in the positive electrode, and the use of the double-salt ether electrolyte of the present application can effectively improve the performance of the negative electrode-free sodium metal battery. The first coating layer and the second coating layer of the diaphragm significantly enhance the uniformity of the current density distribution on the negative electrode side, which is conducive to a more uniform deposition of the sodium layer, can effectively inhibit the growth of sodium dendrites, prevent them from piercing the diaphragm, reduce the risk of internal short circuits in the battery, and further improve the safety performance of the battery. The introduction of a sodium salt additive in the positive electrode can, on the one hand, ensure the stability of the positive electrode material structure during the repeated deintercalation of sodium in the positive electrode, and on the other hand, can provide a portion of the consumed sodium source, which helps to improve the cycle efficiency of the battery. In combination with the electrolyte system of the present application, compared with traditional carbonate solvents, ether solvents have higher reduction stability and better Na metal compatibility, and can construct a thin and strong SEI film; the addition of NaBF4 can reduce the desolvation energy and has a higher ion transport capacity, thereby improving the reversibility of sodium plating / stripping. The combination of double salts can generate a stable SEI layer rich in B / F inorganics on the negative electrode surface, effectively improving the cycle performance of negative electrode-free sodium batteries.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0159] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form distinct embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A secondary negative electrode-free sodium metal battery, characterized in that: include: diaphragm and positive electrode; The diaphragm includes a substrate, a first coating layer and a second coating layer, wherein the first coating layer and the second coating layer are respectively located on opposite sides of the substrate; wherein the substrate includes any one of a PP film, a PE film, and a composite film of PP and PE, and the material forming the first coating layer and the material forming the second coating layer are independently selected from at least one of boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, aluminum oxide, and magnesium oxide; The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer contains a sodium salt additive.

2. The secondary negative electrode-free sodium metal battery according to claim 1, characterized in that: The thickness of the substrate is 14-20 μm; And / or, the thickness of the first coating layer and the thickness of the second coating layer are independently selected from 1-4 μm.

3. The secondary negative electrode-free sodium metal battery according to claim 1, characterized in that: The sodium salt additive includes at least one of sodium borate, sodium tetrafluoroborate, sodium tetrakis(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium sodium tetrafluoroborate, and sodium difluorooxalatoborate; And / or, the sodium salt additive accounts for 0.5-3 wt % of the mass of the positive electrode active layer.

4. The secondary negative electrode-free sodium metal battery according to claim 3, characterized in that: The positive electrode active layer further comprises 90-97 wt % of a positive electrode active material, 1-3 wt % of a conductive agent, and 1-5 wt % of a binder.

5. The secondary negative electrode-free sodium metal battery according to claim 4, characterized in that: The positive electrode active material includes at least one of a polyanionic compound and a layered metal oxide; And / or, the polyanionic compound includes at least one of NaFePO4, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2FeP2O7, Na4Fe3(PO4)2P2O7, and NaFe(SO4)3; And / or, the layered metal oxide comprises NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2、Na 2 / 3 Mn 1 / 2 Fe 1 / 4 Co 1 / 4 O2、Na 0.9 Cu 0.22 Fe 0.3 Mn 0.48 At least one of O2; And / or, the conductive agent includes at least one of Super P, Ketjen black, acetylene black, carbon nanotubes, and graphene; And / or, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, sodium alginate, and polyolefin binders.

6. The secondary negative electrode-free sodium metal battery according to claim 1, characterized in that: The positive electrode sheet further includes a positive electrode current collector, and the positive electrode active layer is formed on the surface of the positive electrode current collector; The positive electrode current collector includes any one of aluminum foil, carbon-coated aluminum foil, and aluminum mesh.

7. The secondary negative electrode-free sodium metal battery according to claim 1, characterized in that: The secondary negative electrode-free sodium metal battery further includes an electrolyte; The electrolyte includes a non-aqueous solvent, and the non-aqueous solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane, sulfolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

8. The secondary negative electrode-free sodium metal battery according to claim 7, characterized in that: The electrolyte includes a sodium salt; The solubility of the sodium salt in the electrolyte is 0.5-2.0M; And / or, the sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium difluorobisoxalatophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium trifluoromethanesulfonate.

9. The secondary negative electrode-free sodium metal battery according to any one of claims 1 to 8, characterized in that: The secondary negative electrode-free sodium metal battery further includes a negative electrode current collector; The negative electrode current collector includes carbon-coated aluminum foil.

10. An electrical device, characterized in that: The electrical equipment includes the secondary negative electrode-free sodium metal battery according to any one of claims 1 to 9.

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