Sodium ion secondary battery and electrical device

Abstract

The present application provides a sodium ion secondary battery, characterized in that it comprises: a shell; a cover plate assembly, the cover plate assembly is covered on the shell to form an accommodation space; and an electrode assembly and an electrolyte accommodated in the accommodation space; the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode collector and a positive electrode active layer arranged on at least one surface of the positive electrode collector, the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material is selected from one or more of layered oxides and polyanion oxides; the surface density of the positive electrode active layer is 240g / m 2 ~350g / m 2 The sodium ion conductivity of the electrolyte is 3mS to 7mS / cm. By setting the positive electrode active layer and the sodium ion conductivity of the electrolyte, the sodium ion secondary battery can maintain high safety performance while taking into account the cycle performance.

Description

Technical Field

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

[0002] In the field of electrochemical energy storage, secondary batteries provide an efficient and reliable energy storage solution. Secondary batteries have become one of the preferred technologies for energy storage systems due to their ultra-long cycle life, excellent safety and cost-effectiveness. These batteries can release energy during peak loads on the grid or store energy when there is excess renewable energy generation, thereby improving the stability and reliability of the grid. In addition, secondary batteries have strong environmental adaptability and can operate in extreme temperatures, making them suitable for energy storage projects in various climate conditions.

[0003] In the field of electric vehicles (EVs), secondary batteries are core components that directly affect the vehicle's range, safety and cost. Lithium iron phosphate batteries are favored for their high energy density, fast charging capabilities and low self-discharge rate. These characteristics enable electric vehicles to provide a driving experience comparable to traditional fuel vehicles while reducing the impact on the environment. With the advancement of technology, the energy density of lithium iron phosphate batteries continues to increase, which helps to increase the range of electric vehicles and meet consumer demand.

[0004] In recent years, with the development of new energy vehicles and the rapid development of electrochemical energy storage, the application background technology of secondary batteries in the field of electrochemical energy storage and electric vehicles is multifaceted. They not only provide efficient energy solutions, but also promote the development and innovation of related technologies. As the demand for sustainable energy and clean transportation grows, secondary battery technology will continue to play a key role in these fields.

[0005] With the large-scale application of secondary batteries, the market has increasingly higher requirements for the performance and safety of secondary batteries. Among them, cycle performance and safety performance have become key issues in industry research. Summary of the invention

[0006] In order to achieve the above objectives, the present application provides a sodium ion secondary battery with higher safety performance.

[0007] The present application provides a sodium ion secondary battery, characterized in that it comprises: a shell; a cover plate assembly, the cover plate assembly is covered on the shell to form an accommodation space; and an electrode assembly and an electrolyte accommodated in the accommodation space; the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode collector and a positive electrode active layer arranged on at least one surface of the positive electrode collector, the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material is selected from one or more of layered oxides and polyanion oxides; the surface density of the positive electrode active layer is 240g / m 2 ~350g / m 2 ; The sodium ion conductivity of the electrolyte is 3mS~7mS / cm.

[0008] In the embodiments of the present application, by setting the positive electrode active layer and setting the sodium ion conductivity of the electrolyte, the sodium ion secondary battery can maintain high safety performance while taking into account the cycle performance.

[0009] Preferably, the surface density of the positive electrode active layer is 240 g / m 2 ~330g / m 2 .

[0010] Preferably, the surface density of the positive electrode active layer is 3mS to 7mS / cm.

[0011] Preferably, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material is selected from one or more of hard carbon and soft carbon.

[0012] Furthermore, the positive electrode active material comprises layered oxide and polyanion compound; the layered oxide accounts for 70-90% of the total mass of the positive electrode active material; the polyanion compound accounts for 10-30% of the total mass of the positive electrode active material.

[0013] Furthermore, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer; the first positive electrode active layer includes a first positive electrode active material, which is a layered oxide; the second positive electrode active layer includes a second positive electrode active material, which is a polyanion compound.

[0014] Preferably, the surface density of the first positive electrode active layer is 215 g / m 2 ~315g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~35g / m 2 .

[0015] Preferably, the surface density of the first positive electrode active layer is 215 g / m 2 ~300g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~30g / m 2 .

[0016] In the embodiments of the present application, by providing a first positive electrode active layer of a layered oxide and a second positive electrode active layer of a polyanion compound on the positive electrode sheet, the sodium ion battery has both a higher energy density and better safety performance.

[0017] Furthermore, the battery further comprises an additive, wherein the additive is provided in one or more of the positive electrode active material, the negative electrode active material and the electrolyte.

[0018] Preferably, the additive is sodium bicarbonate.

[0019] Preferably, the additive is disposed in the positive electrode coating, the negative electrode coating and / or the electrolyte.

[0020] Preferably, when the additive is disposed in the positive electrode coating, the additive accounts for 0.5 to 3 wt % of the total mass of the positive electrode active material.

[0021] Preferably, when the additive is disposed in the negative electrode coating, the additive accounts for 0.5 to 3 wt % of the total mass of the negative electrode active material.

[0022] Preferably, when the additive is provided in the electrolyte, the additive accounts for 0.5-3 wt % of the total mass of the electrolyte.

[0023] In the embodiments of the present application, by providing additives in the positive electrode slurry, the negative electrode slurry, and the electrolyte, the gas production inside the battery can be accelerated when the battery thermally runs away and the pressure is released, thereby achieving rapid pressure release, preventing thermal runaway and heat spread, and improving the safety performance of the battery.

[0024] Another object of the present application is to provide an electrical device comprising the above-mentioned sodium ion secondary battery.

[0025] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present invention, the following will briefly describe the drawings required for describing the embodiments. It should be understood that these drawings are only for the convenience of technicians to understand the present invention more easily, and are not intended to limit the scope of the present invention.

[0027] Figure 1is an overall exploded view of a sodium ion secondary battery according to an embodiment of the present application;

[0028] Figure 2 is a schematic diagram of an electrode assembly of a sodium ion secondary battery according to an embodiment of the present application;

[0029] Figure 3 is a schematic diagram of a pole piece of a sodium ion secondary battery according to an embodiment of the present application;

[0030] Figure 4 Schematic diagram of a pole piece of a sodium ion secondary battery according to another embodiment of the present application.

[0031] Like reference symbols refer to like parts throughout the drawings.

[0032] Reference numerals: 100 - electrode assembly; 110 - positive electrode plate; 111 - positive electrode current collector; 112 - first positive electrode active layer; 113 - second positive electrode active layer; 120 - negative electrode plate; 130 - separator; 200 - housing; 300 - cover plate assembly. DETAILED DESCRIPTION

[0033] In order to make the invention purpose, technical solution and beneficial technical effect of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, implementation methods and advantages described in the present application may be compatible and / or may be combined together.

[0034] Unless otherwise specified, the meanings of the technical terms in this specification are the same as those generally understood by those skilled in the art.

[0035] The invention relates to a sodium ion secondary battery and an electric device comprising the sodium ion secondary battery.

[0036] The present invention will be described in detail below.

[0037] Sodium ion secondary battery

[0038] In a first aspect, the present invention relates to a sodium ion secondary battery, such as Figure 1 As shown, it includes: a shell 200, which is surrounded by a bottom surface and a side surface and has an opening; a cover assembly 300, which is covered on the shell opening and forms an accommodation space with the shell; and an electrode assembly 100 and an electrolyte accommodated in the accommodation space; the sodium ion conductivity of the electrolyte is 3mS~7mS / cm; Figure 2 As shown, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120 and a separator 130, and the separator 130 is located between the positive electrode sheet 110 and the negative electrode sheet 120; Figure 3As shown, the positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 disposed on at least one surface of the positive electrode current collector. The surface density of the positive electrode active layer is 240 g / m 2 ~350g / m 2 ; By matching the positive electrode surface density with the sodium ion electrolyte, the sodium ion secondary battery can maintain high safety performance while taking into account the cycle performance.

[0039] In some sodium ion secondary batteries of the present application, the sodium ion conductivity of the electrolyte is 3mS to 7mS / cm, preferably 4mS to 6mS / cm. As an example, the sodium ion conductivity of the electrolyte can be 3mS / cm, 4mS / cm, 5mS / cm, 6mS / cm, 7mS / cm, or within the range defined by any two of them.

[0040] In some sodium ion secondary batteries of the present application, the surface density of the positive electrode active layer is 240 g / m 2 ~350g / m 2 , preferably 240g / m 2 ~330g / m 2 As an example, the surface density of the positive electrode active layer can be 240 g / m 2 , 250g / m 2 , 260g / m 2 , 270g / m 2 , 280g / m 2 , 290g / m 2 , 300g / m 2 , 310g / m 2 , 320g / m 2 , 330g / m 2 , 340g / m 2 , 350g / m 2 or within the range defined by any two of them.

[0041] In some sodium ion secondary batteries of the present application, the positive electrode active material includes one or more of a layered oxide and a polyanion compound. When the positive electrode active material of the sodium ion secondary battery is selected from a layered oxide and a polyanion compound, the layered oxide accounts for 70 to 90% of the total mass of the positive electrode active material; the polyanion compound accounts for 10 to 30% of the total mass of the active material; the layered oxide and the polyanion compound are mixed to form a positive electrode slurry, and the prepared sodium ion secondary battery takes into account both high energy density and good safety performance.

[0042] In some sodium ion batteries of the present application, the positive electrode active coating is provided in two layers, such as Figure 4The positive electrode sheet of the sodium ion secondary battery shown in the figure comprises a first positive electrode active layer and a second positive electrode active layer; the active slurry of the first positive electrode active layer comprises a layered oxide, the active slurry of the second positive electrode active layer comprises a polyanion compound, and the surface density of the first positive electrode active layer is 215 g / m 2 ~315g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~35g / m 2 Preferably, the surface density of the first positive electrode active layer is 215 g / m 2 ~300g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~30g / m 2 A polyanion active layer and a layered oxide active layer are arranged on the current collector on the positive electrode; the sodium ion battery has both high safety performance and high energy density.

[0043] In some sodium ion secondary batteries of the present application, an additive is also provided, and the additive can produce gas when heated, and the additive is selected from sodium bicarbonate. The additive is provided in the battery, which can accelerate the gas production inside the battery when the battery is thermally runaway and depressurized, realize rapid depressurization, prevent thermal runaway, and improve the safety performance of the battery.

[0044] In some sodium ion secondary batteries of the present application, the positive electrode plate includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer includes a positive active material, and an additive is disposed in the positive active material, wherein the additive accounts for 0.5 to 3%wt of the total mass of the positive active material. As an example, the value of the additive in the total mass of the positive active material may include but is not limited to 0.5wt%, 1wt%, 2wt%, 3wt% or the range defined by any two of them.

[0045] In some sodium ion secondary batteries of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, and an additive is disposed in the negative electrode active material, wherein the additive accounts for 0.5 to 3%wt of the total mass of the negative electrode active material. As an example, the value of the additive in the total mass of the negative electrode active material may include but is not limited to 0.5wt%, 1wt%, 2wt%, 3wt% or the range defined by any two of them.

[0046] In some sodium ion secondary batteries of the present application, the additive is disposed in the electrolyte, wherein the additive accounts for 0.5 to 3%wt of the total mass of the electrolyte. As an example, the value of the additive accounting for the total mass of the electrolyte may include but is not limited to 0.5wt%, 1wt%, 2wt%, 3wt% or the range defined by any two of them.

[0047] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0048] Positive electrode

[0049] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer arranged on at least one surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material. The positive electrode active material is selected from one or more of layered oxides and polyanion compounds.

[0050] There is no particular limitation on the positive electrode current collector, and the positive electrode current collector commonly used by those skilled in the art may be used. As an example, the positive electrode current collector may be a metal foil such as aluminum foil, nickel foil, or a composite current collector. 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), 1,3-propane sultone (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0051] The positive electrode sheet can be prepared according to the method commonly used in the art.

[0052] For example, the positive electrode can be formed by uniformly dispersing a positive electrode active material, a conductive agent, and a binder in a solvent (eg, N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; coating the slurry on a positive electrode current collector, drying, and pressing.

[0053] Alternatively, the positive electrode can also be formed by uniformly dispersing the positive electrode active material, the conductive agent, and the binder in a solvent (e.g., N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; casting the positive electrode slurry on a separate carrier, drying, separating the obtained positive electrode film from the carrier and laminating it on a positive electrode current collector.

[0054] Negative electrode

[0055] The negative electrode plate may be a metal sodium plate, or may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0056] The negative electrode current collector is not particularly limited, and the negative electrode current collector commonly used by those skilled in the art can be used. As an example, the negative electrode current collector can be a metal foil such as copper foil, or a composite current collector. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0057] In some embodiments, the negative electrode active material may be an active material commonly used by those skilled in the art. For example, the negative electrode active material may be one or more of mesophase microcarbon beads (MCMB), hard carbon, and soft carbon.

[0058] In some embodiments, the negative electrode active material may be present in an amount of 70-96 wt %, for example 80-90 wt %, based on the total weight (dry weight) of the negative electrode active material layer.

[0059] In addition to the negative electrode active material, the negative electrode active material layer may further include a binder, a conductive agent and any other optional auxiliary agents such as a thickener.

[0060] There is no particular requirement for the negative electrode conductive agent. As an example, the conductive agent can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0061] In some embodiments, the conductive agent may be present in an amount of 1 to 10 wt %, for example 2 to 5 wt %, based on the total weight (dry weight) of the negative electrode active material layer.

[0062] There is no special requirement for the negative electrode binder. As an example, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), styrene butadiene rubber (SBR), water-based acrylic resin and carboxymethyl cellulose (CMC).

[0063] In some embodiments, the binder may be present in an amount of 1 to 10 wt %, for example 2 to 5 wt %, based on the total weight (dry weight) of the negative electrode active material layer.

[0064] The negative electrode can be prepared according to a method commonly used in the art.

[0065] For example, the negative electrode can be formed by uniformly dispersing the negative electrode active material and optional conductive agent, binder and thickener in a solvent (such as N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, drying, and pressing.

[0066] Alternatively, the negative electrode can also be formed by uniformly dispersing the negative electrode active material and optional conductive agent, binder and thickener in a solvent (e.g., N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; casting the negative electrode slurry on a separate carrier, drying, separating the obtained negative electrode film from the carrier and laminating it on a negative electrode current collector.

[0067] Electrolyte

[0068] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte is not particularly limited and can be selected according to needs.

[0069] In some embodiments, the electrolyte includes an organic aprotic solvent and an electrolyte sodium salt.

[0070] In some embodiments, the solvent can be selected from one or more 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), fluoroethylene carbonate (FEC), 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), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0071] In some embodiments, the electrolyte sodium salt can be selected from one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroborate (NaBF6), sodium bis(trifluoromethylsulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium trifluoromethylsulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0072] In some embodiments, the concentration of sodium ions in the electrolyte is 0.2 to 2 mol / L, for example, 0.5-1.0 mol / L.

[0073] In some embodiments, the electrolyte may further include additives, for example, additives that help negative electrode film formation or positive electrode film formation, and additives that can improve battery performance, such as additives that improve high or low temperature performance of the battery.

[0074] Diaphragm

[0075] The separator is not particularly limited, and a commonly used porous structure separator with electrochemical stability and chemical stability can be used, for example, it can be a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0076] Example 1

[0077] Preparation of positive electrode

[0078] 96wt% of layered oxide as positive electrode active material, 2.3wt% of carbon black as conductive agent, 1.3wt% of polyvinylidene fluoride PVDF as binder and 0.4wt% of oxalic acid were mixed and uniformly dispersed in N-methylpyrrolidone solvent to obtain positive electrode slurry, and then the positive electrode slurry was coated on both sides of the current collector aluminum foil, dried at 100°C, and then rolled and cut to obtain the positive electrode sheet. The double-sided surface density of the active area of ​​the positive electrode sheet is 350g / m 2 .

[0079] Preparation of negative electrode

[0080] 95.6wt% of hard carbon as negative electrode active material, 1.4wt% of carbon black as conductive agent, and 3wt% of polyvinylidene fluoride (PVDF) as binder are mixed and evenly dispersed in N-methylpyrrolidone solvent to obtain negative electrode slurry. The negative electrode slurry is then coated on both sides of the current collector aluminum foil, dried at 90°C, and then rolled and cut to obtain negative electrode sheets.

[0081] Electrolyte preparation.

[0082] 1M sodium hexafluorophosphate NaPF6 was dissolved in propylene carbonate PC / ethyl methyl carbonate EMC (volume ratio of 1:1) to obtain a mixed solution, and then 5wt% of vinyl sulfate DTD and 5wt% of fluoroethylene carbonate FEC were added to the mixed solution relative to the total weight of the final electrolyte, and the electrolyte was obtained after uniform dispersion. Among them, the sodium ion conductivity of the electrolyte was 7mS / cm.

[0083] Preparation of isolation membrane

[0084] A polyethylene (PE) film coated with nano-aluminum oxide was used as the separator.

[0085] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked and wound in order to obtain a wound electrode assembly. The electrode assembly is added to an outer square aluminum shell, and the electrolyte is injected after drying. After standing, forming, aging, secondary injection, sealing, and capacity separation, a sodium ion secondary battery is obtained.

[0086] Example 2

[0087] The difference from Example 1 is that the double-sided surface density of the active area of ​​the positive electrode sheet is 330g / m 2 .

[0088] Example 3

[0089] The difference from Example 1 is that the double-sided surface density of the active area of ​​the positive electrode sheet is 310g / m 2 .

[0090] Example 4

[0091] The difference from Example 1 is that the double-sided surface density of the active area of ​​the positive electrode sheet is 240g / m 2 .

[0092] Implementation 5

[0093] The difference from Example 2 is that the sodium ion conductivity of the electrolyte is 6 mS / cm.

[0094] Implementation 6

[0095] The difference from Example 2 is that the sodium ion conductivity of the electrolyte is 5 mS / cm.

[0096] Implementation 7

[0097] The difference from Example 4 is that the sodium ion conductivity of the electrolyte is 4 mS / cm.

[0098] Implementation 8

[0099] The difference from Example 4 is that the sodium ion conductivity of the electrolyte is 3 mS / cm.

[0100] Implementation 9

[0101] The difference from Example 1 is that the steps for preparing the positive electrode sheet are as follows:

[0102] 96 wt % of layered oxide as a positive electrode active material, 2.3 wt % of carbon black as a conductive agent, 1.3 wt % of polyvinylidene fluoride PVDF as a binder, and 0.4 wt % of oxalic acid were mixed and uniformly dispersed in an N-methylpyrrolidone solvent to obtain a first positive electrode slurry.

[0103] 96 wt % of a polyanion compound as a positive electrode active material, 2.3 wt % of carbon black as a conductive agent, 1.3 wt % of polyvinylidene fluoride PVDF as a binder, and 0.4 wt % of oxalic acid were mixed and uniformly dispersed in an N-methylpyrrolidone solvent to obtain a second positive electrode slurry.

[0104] The first positive electrode slurry is first coated on both sides of the current collector aluminum foil to form a first positive electrode active layer. The surface density of the first positive electrode active layer is 215g / m 2 ; The second positive electrode slurry is coated on the surface of the first positive electrode active layer to form a second positive electrode active layer, and the surface density of the second positive electrode active layer is 25g / m 2 ; Then, after drying at 100°C, rolling and slitting, the positive electrode sheet can be obtained. The double-sided surface density of the active area of ​​the positive electrode sheet is 240g / m 2 .

[0105] Implementation 10

[0106] The difference from Example 9 is that the surface density of the first positive electrode active layer is 300 g / m 2 ; The second positive electrode slurry is coated on the surface of the first positive electrode active layer to form a second positive electrode active layer, and the surface density of the second positive electrode active layer is 30g / m 2 The double-sided surface density of the active area of ​​the positive electrode is 330g / m 2

[0107] Comparative Example 1

[0108] The difference from Example 1 is that the double-sided surface density of the active area of ​​the positive electrode sheet is 200g / m 2 .

[0109] Comparative Example 2

[0110] The difference from Example 1 is that the sodium ion conductivity of the electrolyte is 6 mS / cm.

[0111] The sodium ion secondary batteries prepared in the examples and comparative examples were subjected to power performance tests and safety performance tests (thermal runaway tests and needle puncture tests), respectively. The test results are shown in Table 1.

[0112] (1) Power performance test method: The battery cell is discharged at a 2C rate to the lower limit voltage of the discharge, and the lower limit voltage is set to 2V; let it stand for 10 minutes; the battery cell is charged at a 2C rate constant current constant voltage method to the battery charging upper limit voltage, and the upper limit voltage is set to 4V, and let it stand for 10 minutes; the above steps are repeated 10 times, and then the battery cell is removed and disassembled to observe whether there is sodium precipitation on the negative electrode sheet. If sodium precipitation occurs, it means that the battery does not support 2C rate charging and discharging, and the power performance is poor.

[0113] (2) Safety performance (thermal runaway) test method: According to the thermal runaway test method in 6.7.4.2 of GB / T 36276-2023, if a battery cell has thermal runaway and either fire or explosion occurs, it will fail.

[0114] (3) Overcharge test: According to the overcharge performance test method in 6.7.1.1 of GB / T 36276-2023 standard, at 25°C, charge the battery cell at a constant current and constant voltage of 0.33C to an upper cut-off voltage of 4V, then charge at a constant voltage to a current of 0.05C, then charge the battery cell at a constant current of 1C for 1h or until the voltage of the battery cell reaches 1.5 times the upper cut-off voltage (i.e. 4V). When any of the conditions are met, stop charging, then leave it alone for 1h to observe whether the battery cell fails. The judgment standard for battery cell failure is: no fire and no explosion. The number of battery cell samples is 20, and the pass rate of the battery cell overcharge test is counted.

[0115] Table 1

[0116]

[0117]

[0118] It can be seen from Table 1 that the surface density of the positive electrode active layer is 240g / m 2 ~350g / m 2 When the lithium ion conductivity of the electrolyte is between 3mS / cm and 7mS / cm, the battery can have both good cycle performance and good safety performance. It can also be seen from Table 1 that a layered oxide active layer and a polyanion compound active layer are provided on the positive electrode sheet, and the surface density of the layered oxide active layer is set at 215g / m 2 ~300g / m 2 , the polyanion compound oxide layer is set at 25g / m 2 ~30g / m 2 When charged, the sodium-ion secondary battery has better overcharge performance, which greatly improves the safety performance of the battery.

[0119] The present application also provides an electric device, which includes a sodium ion secondary battery of any of the above embodiments. Since the sodium ion secondary battery of the embodiment of the present application can take into account the long cycle characteristics of the energy storage battery and the high safety requirements of the power battery, and the electric device of the embodiment of the present application includes the above sodium ion secondary battery, the electric device of the embodiment of the present application has the advantage of strong safety, which will not be elaborated here.

[0120] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A sodium ion secondary battery, characterized in that: include: case; A cover plate assembly, the cover plate assembly is covered on the shell to form an accommodating space; as well as An electrode assembly and an electrolyte contained in the accommodation space; The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material is selected from one or more of layered oxides and polyanion oxides; The surface density of the positive electrode active layer is 240 g / m 2 ~350g / m 2 ; The sodium ion conductivity of the electrolyte is 3mS to 7mS / cm.

2. The sodium ion secondary battery according to claim 1, characterized in that: The surface density of the positive electrode active layer is 240 g / m 2 ~330g / m 2 .

3. The sodium ion secondary battery according to claim 1, characterized in that: The sodium ion conductivity of the electrolyte is 4mS to 6mS / cm.

4. The sodium ion secondary battery according to claim 1, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the negative electrode active material is selected from one or more of hard carbon and soft carbon.

5. The sodium ion secondary battery according to claim 1, characterized in that: The positive electrode active material comprises layered oxide and polyanion compound; the layered oxide accounts for 70-90% of the total mass of the positive electrode active material; the polyanion compound accounts for 10-30% of the total mass of the positive electrode active material.

6. The sodium ion secondary battery according to claim 1, characterized in that: The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer; the first positive electrode active layer includes a first positive electrode active material, which is a layered oxide; the second positive electrode active layer includes a second positive electrode active material, which is a polyanion compound.

7. The sodium ion secondary battery according to claim 6, characterized in that: The surface density of the first positive electrode active layer is 215 g / m 2 ~315g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~35g / m 2 .

8. The sodium ion secondary battery according to claim 7, characterized in that: The surface density of the first positive electrode active layer is 215 g / m 2 ~300g / m 2 The surface density of the second positive electrode active layer is 25g / m 2 ~30g / m 2 .

9. The sodium ion secondary battery according to any one of claims 1 to 8, characterized in that: It also includes additives; the additives are arranged in the positive electrode coating, the negative electrode coating and / or the electrolyte; when the additives are arranged in the positive electrode coating, the additives account for 0.5 to 3 wt% of the total mass of the positive electrode active material; when the additives are arranged in the negative electrode coating, the additives account for 0.5 to 3 wt% of the total mass of the negative electrode active material; when the additives are arranged in the electrolyte, the additives account for 0.5 to 3 wt% of the total mass of the electrolyte.

10. An electrical device, characterized in that: A sodium ion secondary battery comprising any one of claims 1 to 9.

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