Sodium-ion battery cell, sodium-ion battery and electric device

Abstract

This application provides a sodium-ion battery cell, a sodium-ion battery, and a power device, relating to the field of battery technology. The sodium-ion battery cell of this application includes a positive electrode sheet, which comprises a positive current collector and a positive active layer attached to the surface of the positive current collector. The positive active layer comprises sodium iron phosphate pyrophosphate and carbon nanotubes. The compaction density of the positive electrode sheet is not less than 1.9 g / cm³. 3 The sodium-ion battery cell of this application, by selecting sodium iron phosphate pyrophosphate as the positive electrode active material and adding carbon nanotubes, achieves a compaction density of the positive electrode sheet of not less than 1.9 g / cm³. 3 Without causing electrode breakage or delamination, the sodium-ion battery cell achieves good long-cycle performance while increasing its energy density.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a sodium-ion battery cell, a sodium-ion battery, and an electrical device. Background Technology

[0002] In recent years, polyanionic compounds, especially sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP), have been widely used as cathode materials for sodium-ion batteries due to their abundant resources, low cost, high operating voltage, good thermal stability, and good cycle performance. Currently, the main problem with NFPP sodium battery systems is their low energy density. To address this issue, increasing the compaction density of the cathode sheet is one of the most effective methods. However, due to the relatively high cohesive force of NFPP, high compaction (compaction density greater than 1.9 g / cm³) is challenging. 3 In such cases, electrode breakage or delamination can easily occur. Summary of the Invention

[0003] This application is made in view of the above-mentioned issues, and its purpose is to provide a sodium-ion battery cell, a sodium-ion battery and an electrical device, such that the sodium-ion battery cell has both high energy density and good long cycle performance.

[0004] The first aspect of this application provides a sodium-ion battery cell, which includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive active layer attached to the surface of the positive current collector. The positive active layer includes sodium iron phosphate pyrophosphate and carbon nanotubes. The compaction density of the positive electrode sheet is not less than 1.9 g / cm³. 3 .

[0005] The positive electrode active material of the positive electrode sheet is sodium iron phosphate pyrophosphate with a compaction density ≥ 1.9 g / cm³. 3 While the high energy density of the battery can be achieved under certain conditions, the strong cohesive force of sodium iron phosphate pyrophosphate makes the positive electrode prone to brittle fracture during preparation, or electrode detachment after a period of cycling, thus affecting the long-cycle performance of the battery system. In this application, by selecting sodium iron phosphate pyrophosphate as the positive electrode active material and adding carbon nanotubes to provide tensile strength, the compaction density can be made not less than 1.9 g / cm³. 3 Under these conditions, electrode breakage does not occur, which can improve the energy density of sodium-ion battery cells. Furthermore, after a period of cycling, the positive electrode does not experience electrode film detachment, thus ensuring good long-cycle performance of the sodium-ion battery cells.

[0006] In some embodiments, the compaction density of the positive electrode sheet is 1.9 g / cm³. 3 ~2.2g / cm3 Within the aforementioned compaction density range, the energy density of the battery can be relatively high. Furthermore, in conjunction with carbon nanotubes, the elongation of the positive electrode sheet can be reduced, allowing the battery to remain intact after a long period of cycling. This enables sodium-ion battery cells to simultaneously possess high energy density and excellent long-cycle performance.

[0007] In some embodiments, sodium iron phosphate pyrophosphate accounts for 96% to 97.2% of the total mass of the positive electrode active layer. Increasing the content of positive electrode active material helps to improve the energy density of the battery, but it also increases the cohesive force, making the positive electrode sheet more prone to brittle fracture during preparation and more likely to delaminate after cycling. In this application, sodium iron phosphate pyrophosphate is selected as the positive electrode active material, and carbon nanotubes are added, achieving a compaction density of not less than 1.9 g / cm³. 3 Furthermore, when the mass percentage of NFPP is not less than 96%, the positive electrode sheet can be kept from becoming brittle during preparation and is less prone to delamination after long cycles.

[0008] In some embodiments, the elongation of the positive electrode sheet is no higher than 0.7%. In the sodium-ion battery cell of this application, the addition of carbon nanotubes allows the positive electrode sheet to achieve a compaction density of no less than 1.9 g / cm³. 3 Under certain conditions, the elongation rate can be kept to no more than 0.7%, which makes the positive electrode sheet less prone to brittle breakage during preparation and less prone to delamination during battery cycling.

[0009] In some embodiments, carbon nanotubes include single-walled carbon nanotubes. Compared to multi-walled carbon nanotubes, single-walled carbon nanotubes have higher tensile strength, thereby allowing for better control of the elongation of the positive electrode and preventing film stripping after the battery has been cycled for a period of time.

[0010] In some embodiments, the diameter of the single-walled carbon nanotubes is no greater than 6 nm, and the length is 10 μm to 20 μm. By controlling the single-walled carbon nanotubes to have suitable diameter and length, the electrical conductivity of the single-walled carbon nanotubes can be significantly improved while ensuring high tensile strength.

[0011] In some implementations, the mass percentage of carbon nanotubes is 1% to 2% based on the total mass of the positive electrode active layer. By controlling the mass percentage of carbon nanotubes within a suitable range, the DC internal resistance (DCR) of sodium-ion battery cells during cycling can be effectively reduced, and the long-cycle performance of sodium-ion battery cells can be improved.

[0012] In some embodiments, sodium iron pyrophosphate has a charging capacity of 110 mAh / g to 130 mAh / g at a 0.33C rate and a discharging capacity of 90 mAh / g to 110 mAh / g at a 1C rate. By selecting sodium iron pyrophosphate with a charging and discharging capacity within an appropriate range, it is beneficial to further improve the energy density and long-cycle performance of sodium-ion battery cells.

[0013] In some embodiments, the positive electrode active layer further includes a dotted conductive agent. The dotted conductive agent can further improve the conductivity of the positive electrode.

[0014] In some embodiments, the mass percentage of the dotted conductive agent is 0.5% to 2% based on the total mass of the positive electrode active layer. By controlling the mass percentage of the dotted conductive agent within a suitable range, the conductivity of the positive electrode sheet can be improved while essentially not affecting the mass percentage of NFPP and carbon nanotubes.

[0015] In some embodiments, the dot-like conductive agent includes at least one of Superp, acetylene black, Ketjen black, carbon nanoparticles, or fullerene. All of these dot-like conductive agents can effectively improve the conductivity of the positive electrode.

[0016] The second aspect of this application provides a sodium-ion battery, including the sodium-ion battery cell of the first aspect of this application.

[0017] A third aspect of this application provides an electrical device, including a sodium-ion battery as described in the second aspect of this application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a sodium-ion battery according to one embodiment of this application.

[0019] Figure 2 yes Figure 1 An exploded view of a sodium-ion battery according to an embodiment of this application is shown.

[0020] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0021] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0022] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0023] Figure 6 This is a schematic diagram of an electrical device using a sodium-ion battery as a power source according to an embodiment of this application.

[0024] Figure 7This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at 500 magnification.

[0025] Figure 8 This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at 3K magnification.

[0026] Figure 9 This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at a magnification of 30K.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1 Sodium-ion battery; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Sodium-ion battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the sodium-ion battery cell, sodium-ion battery, and power-consuming device of this application, as well as methods for preparing electrode sheets. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a thorough understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

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

[0033] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] Polyanionic compounds, especially sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP), are widely used as cathode materials for sodium-ion batteries due to their abundant resources, low cost, high operating voltage, good thermal stability, and good cycle performance. Currently, the main problem with NFPP-type sodium battery long-cycle systems is their low energy density. To address this issue, increasing the compaction density of the cathode sheet is one of the most effective methods. However, due to the relatively high cohesive force of NFPP, a compaction density greater than 1.9 g / cm³ is challenging. 3 In some cases, although the battery can achieve high energy density, the positive electrode is prone to brittle fracture during processing, or the electrode may crack or peel off after cycling for a period of time, which affects the long-cycle performance of the battery system.

[0035] Based on this, this application provides a sodium-ion battery cell that, by selecting NFPP as the positive electrode active material and adding carbon nanotubes to provide a certain tensile strength, achieves a compaction density of not less than 1.9 g / cm³. 3 This improves the energy density of sodium-ion battery cells, and after a period of battery cycling, the positive electrode does not crack or peel off, ensuring that the sodium-ion battery cells have good long-cycle performance.

[0036] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0037] [Sodium-ion battery cell]

[0038] The first aspect of this application provides a sodium-ion battery cell, which includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive active layer attached to the surface of the positive current collector. The positive active layer includes sodium iron phosphate pyrophosphate and carbon nanotubes. The compaction density of the positive electrode sheet is not less than 1.9 g / cm³. 3 .

[0039] The battery cell, the most basic unit of a battery, includes an electrode assembly and an electrolyte (specifically, an electrolyte solution in this embodiment). The electrode assembly typically includes a positive electrode, a negative electrode, and a separator. The positive and negative electrodes are stacked sequentially, with a separator placed between them for isolation, resulting in a bare cell. Alternatively, the bare cell can be obtained after stacking or further winding. The bare cell is then placed in outer packaging, injected with electrolyte, and sealed to obtain the battery cell.

[0040] In this paper, compaction density refers to the mass of active material per unit volume of the electrode, and is one of the important reference indicators of the electrode's energy density. The compaction density of the positive electrode can be tested using any method known in the art. As an example, the method for testing the compaction density of the electrode may include the following steps: take an electrode with an area of ​​s1, measure its thickness as h1, and its weight as m1; take an aluminum foil of the same area, with a thickness as h2 and a weight as m2; the compaction density of the electrode = (m1-m2) / [s1×(h1-h2)], in g / cm³. 3 The measurement deviation of compacted density is within ±0.05 g / cm³. 3 Within the range.

[0041] Increasing the compaction density of the positive electrode sheet can improve the energy density of a sodium-ion battery cell. However, due to the large cohesive force of NFPP, a high compaction density (greater than 1.9 g / cm³) is difficult to achieve. 3 Sodium-ion battery systems are prone to electrode breakage or delamination after a period of cycling, especially systems with a high content of positive electrode active material (greater than 96%). In such cases, the positive electrode is susceptible to breakage during preparation, or cracking or delamination after cycling, further degrading the cycle performance of the sodium-ion battery. In this embodiment, NFPP is selected as the positive electrode active material, and carbon nanotubes are added. The carbon nanotubes effectively connect the particles of the positive electrode active material, effectively improving the tensile strength of the positive electrode and reducing the elongation, resulting in a compaction density of not less than 1.9 g / cm³. 3 This improves the energy density of sodium-ion battery cells, and after 500 cycles, the positive electrode does not experience electrode film detachment, ensuring that the sodium-ion battery cells have good long-cycle performance.

[0042] In this paper, tensile strength refers to the maximum stress a material can withstand before breaking. Carbon nanotubes have a small diameter and a relatively long length, i.e., a certain length-to-diameter ratio, thus exhibiting excellent tensile strength.

[0043] In some embodiments, the compaction density of the positive electrode sheet is 1.9 g / cm³. 3 ~2.2g / cm 3 As an example, the compaction density of the positive electrode sheet can be 1.9 g / cm³. 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 wait.

[0044] Within the aforementioned compaction density range, the positive electrode sheet is less prone to brittle fracture during preparation and less prone to delamination after cycling, thus effectively improving energy density while ensuring the cycle performance of sodium-ion battery cells.

[0045] In some embodiments, the mass percentage of sodium iron phosphate pyrophosphate is 96% to 97.2% based on the total mass of the positive electrode active layer. As examples, the mass percentage of sodium iron phosphate pyrophosphate may be 96.5%, 97.2%, etc.

[0046] When the content of NFPP as the positive electrode active material is very high (above 96%), the elongation of the positive electrode sheet is higher, making it more prone to brittle fracture during preparation and more susceptible to delamination after cycling. In this application, by selecting NFPP as the positive electrode active material and adding carbon nanotubes, a compaction density of not less than 2.1 g / cm³ is achieved. 3 Furthermore, when the mass percentage of NFPP is not less than 96%, the positive electrode sheet can be kept from becoming brittle during preparation and is less prone to delamination after long cycles.

[0047] In some implementations, the elongation of the positive electrode sheet is no higher than 0.7%. As an example, the elongation of the positive electrode sheet can be 0.7%.

[0048] Elongation, which refers to the ratio of the length change of an electrode under a certain pressure, is an important indicator for judging whether an electrode is prone to brittle fracture or delamination. Generally, when the elongation of an electrode is less than 0.7%, it indicates that the electrode is not prone to brittle fracture or delamination.

[0049] The above-mentioned elongation test method can be as follows: cut the electrode sheet to a specific length, denoted as L0, roll the electrode sheet under a certain pressure, and measure the length after rolling, denoted as L1. L1 / L0×100% is the elongation of the electrode sheet under this pressure condition. Test 3 times and take the average value.

[0050] In the sodium-ion battery cell of this application, the positive electrode sheet has a compaction density of not less than 1.9 g / cm³. 3 Under certain conditions, the elongation rate can be kept to no more than 0.7%, which makes it less likely for the positive electrode to detach.

[0051] In some implementations, carbon nanotubes include single-walled carbon nanotubes.

[0052] In this paper, carbon nanotubes are classified into single-walled carbon nanotubes and multi-walled carbon nanotubes based on the number of wall layers. Single-walled carbon nanotubes consist of a single layer of graphene sheets, while multi-walled carbon nanotubes contain multiple layers of graphene sheets.

[0053] Compared to multi-walled carbon nanotubes, single-walled carbon nanotubes have higher tensile strength, which allows for better control of the elongation of the positive electrode sheet.

[0054] In some embodiments, the diameter of the single-walled carbon nanotubes is no greater than 6 nm, and the length is 10 μm to 20 μm. As an example, the diameter of the single-walled carbon nanotubes is 6 nm, and the length is 10 μm to 15 μm.

[0055] By controlling the diameter and length of single-walled carbon nanotubes, the electrical conductivity of single-walled carbon nanotubes can be significantly improved while ensuring high tensile strength.

[0056] In some embodiments, the mass percentage of carbon nanotubes is 1% to 2% based on the total mass of the positive electrode active layer. For example, the mass percentage of carbon nanotubes may be 1% or 1.3%.

[0057] By controlling the mass ratio of carbon nanotubes within a suitable range, the DC internal resistance (DCR) of sodium-ion battery cells during cycling can be effectively reduced, thereby improving the cycling performance of sodium-ion battery cells.

[0058] In some embodiments, the positive electrode active material has a charging capacity of 110 mAh / g to 130 mAh / g at a 0.33C rate and a discharging capacity of 90 mAh / g to 110 mAh / g at a 1C rate.

[0059] In this paper, specific capacity refers to the ratio between the electrical capacity that an active material can release and the mass of that active material. A higher specific capacity indicates a greater electrical capacity per unit mass of active material. Specifically, charge specific capacity refers to the ratio of the maximum electrical capacity released by the active material during charging to the mass of the active material, while discharge specific capacity refers to the ratio of the maximum electrical capacity released by the active material during discharging to the mass of the active material. The charge / discharge specific capacity of the positive electrode can be tested using any method known in the art. As an example, the method for testing the charge / discharge specific capacity of the positive electrode may include the following steps: disassembling a sodium-ion battery cell, cutting the positive electrode into small discs, assembling them with sodium plates to form a coin cell, and then charging and discharging with a current of approximately 1.5A to determine the charge / discharge specific capacity.

[0060] By selecting the charging and discharging specific capacities of NFPP within an appropriate range, it is beneficial to improve the energy density of sodium-ion battery cells and enhance long-cycle performance.

[0061] In some embodiments, the positive electrode active layer further includes a dot-shaped conductive agent. As an example, the dot-shaped conductive agent includes at least one of Superp, acetylene black, Ketjen black, carbon nanodots, or fullerene.

[0062] Dot-shaped conductive agents can fill the spaces between NFPP particles, effectively shortening the ion transport path and forming a short-range conductive network, thereby further improving the electrochemical performance of the positive electrode.

[0063] In some embodiments, the mass percentage of the dot-shaped conductive agent is 0.5% to 2% based on the total mass of the positive electrode active layer. As examples, the mass percentage of the dot-shaped conductive agent can be 0.5%, 0.7%, 1.0%, 1.5%, 2%, etc.

[0064] By controlling the mass ratio of dotted conductive agent within a suitable range, the conductivity of the positive electrode can be improved without affecting the mass ratio of NFPP and carbon nanotubes.

[0065] For more detailed technical features of the various components in a sodium-ion battery cell, please refer to the following:

[0066] [Positive electrode plate]

[0067] In some embodiments, the positive current collector can be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, carbon-coated metal foil, and porous metal plate is independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite current collector formed by combining a metal foil with a polymer base film.

[0068] In some embodiments, the positive electrode film layer also includes an adhesive.

[0069] The binder refers to the material in the positive electrode film layer that acts as an adhesive (bonding the positive electrode film layer to the positive electrode current collector and bonding the positive electrode active materials together), also known as a binder or adhesive. For example, the binder content in the positive electrode film layer is 0.2wt%, 0.4wt%, 2wt%, or any value between the two above.

[0070] As an example, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0071] [Preparation method of positive electrode sheet]

[0072] The positive electrode sheet can be prepared by dispersing the above-mentioned components used to prepare the positive electrode sheet, such as NFPP, carbon nanotubes, dot conductive agents, binders and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0073] In some embodiments, the preparation method of the positive electrode sheet includes the following steps: dispersing NFPP, carbon nanotubes (with a diameter of no more than 6 nm and a length of 10 μm to 20 μm), dot-like conductive agent and binder in N-methylpyrrolidone (NMP) at a mass ratio of (96 to 97.2):(1 to 2):(0.5 to 2):(2 to 3) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing and other processes. As an example, the preparation method of the positive electrode sheet includes the following steps: dispersing NFPP (0.33C charging capacity of 121mAh / g and 1C discharge capacity of 98mAh / g), single-walled carbon nanotubes (tube diameter of 6nm and tube length of 10μm to 20μm), Superp and PVDF in N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:0.5:2 to form a positive electrode slurry; coating the positive electrode slurry onto aluminum foil, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0074] [Negative electrode plate]

[0075] A sodium-ion battery cell includes a negative electrode. During the charging and discharging process, active ions move back and forth between the positive and negative electrode plates, inserting and de-inserting.

[0076] The negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector.

[0077] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0078] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (sodium, sodium alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). When sodium or sodium alloy is used as the negative electrode current collector, since sodium or sodium alloy itself can also be used as a negative electrode active material, the negative electrode sheet may not contain a negative electrode active layer, and sodium or sodium alloy is both the current collector and the negative electrode active material.

[0079] In some embodiments, the negative electrode active layer includes a negative electrode active material, which may be a negative electrode active material known in the art for use in sodium-ion battery cells. The negative electrode active material may be a mixture or composite material formed from any one or more of carbon-based materials, alloy materials, titanium-based materials, and sodium metal. Carbon-based materials include, but are not limited to, graphite, soft carbon, hard carbon, carbon microspheres, and carbon fibers; alloy materials include, but are not limited to, sodium-tin alloys, sodium-germanium alloys, and sodium-antimony alloys; titanium-based materials include, but are not limited to, titanium dioxide, titanates, and titanium phosphates. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for sodium-ion battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0080] The mass content of the negative electrode active material in the negative electrode active layer can be set to 85% to 98%, preferably 95% to 98%, for example, any one of 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or any range between two.

[0081] In some embodiments, the negative electrode active layer may optionally 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).

[0082] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0084] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0085] [Electrolytes]

[0086] A sodium-ion battery cell includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0087] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0088] In some embodiments, the electrolyte salt may include sodium hexafluorophosphate (NaPF6), sodium difluorosulfonamide (NaFSI), sodium trifluoromethanesulfonate (NaOTf), sodium sulfide (Na2S), sodium chloride (NaCl), sodium fluoride (NaF), sodium sulfate (Na2SO4), sodium carbonate (Na2CO3), sodium phosphate (Na3PO4), sodium nitrate (NaNO3), sodium difluorooxalate borate (NaDFOB), sodium pyrophosphate (Na4P2O7), sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS), trisodium citrate, and sodium metaborate (NaBO2). Sodium borate (Na2B4O7), sodium molybdate (Na2MoO4), sodium tungstate (Na2WO4), sodium bromide (NaBr), sodium nitrite (NaNO2), sodium iodate (NaIO3), sodium iodide (NaI), sodium silicate (Na2SiO3), sodium lignosulfonate, sodium oxalate (Na2C2O4), sodium aluminate (NaAlO2), sodium methanesulfonate, sodium acetate (CH3COONa), sodium dichromate (Na2Cr2O7), sodium hexafluoroarsenate (NaAsF6), sodium tetrafluoroborate (NaBF4), and sodium perchlorate (NaClO4) are among the following:

[0089] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl ether (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, 2,2,2,2-trifluoroethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, methyl trifluoroethyl carbonate (FEMC), dioxolane (DOL), acetonitrile (AN), fluorobenzene, triethyl phosphate (TEP), sulfolane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, and N,N-dimethylacetamide.

[0090] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0091] The electrolyte can be prepared as follows: Dissolve the sodium salt of the electrolyte in the solvent in a protective atmosphere (such as argon, nitrogen, or helium) and stir until homogeneous.

[0092] [Isolation membrane]

[0093] The sodium-ion battery cell also includes a separator, which is disposed between the positive and negative electrodes. Its main function is to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0094] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0096] [Outer Packaging]

[0097] In some embodiments, a sodium-ion battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly comprising a positive electrode, a negative electrode, and a separator, as well as the electrolyte.

[0098] In some embodiments, the outer packaging of a sodium-ion battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a sodium-ion battery cell can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0099] This application does not impose any particular limitation on the shape of the sodium-ion battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured sodium-ion battery cell 5.

[0100] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The sodium-ion battery cell 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0101] [Battery Module]

[0102] Sodium-ion battery cells can be assembled into battery modules. A battery module can contain one or more sodium-ion battery cells, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0103] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple sodium-ion battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple sodium-ion battery cells 5 can be fixed in place using fasteners.

[0104] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0105] Sodium-ion batteries

[0106] The second aspect of this application provides a sodium-ion battery, which can be assembled from the above-mentioned battery modules. The sodium-ion battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0107] Figure 4 and Figure 5 This is an example of a sodium-ion battery 1. (See reference...) Figure 4 and Figure 5 The sodium-ion battery 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0108] It should be understood that in some embodiments, the sodium-ion battery 1 described above is also referred to as a sodium-ion battery pack. The individual battery cells 5 can be first assembled into a battery module 4, and the sodium-ion battery 1 is composed of the battery module 4. Alternatively, the sodium-ion battery 1 can be directly assembled from the individual battery cells 5, omitting the intermediate form of the battery module 4.

[0109] [Electrical appliances]

[0110] Furthermore, a third aspect of this application provides an electrical device, which includes at least one of the sodium-ion battery cell, battery module, or sodium-ion battery provided in this application. The sodium-ion battery cell, battery module, or sodium-ion battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0111] As an electrical device, sodium-ion battery cells, battery modules, or sodium-ion batteries can be selected according to their usage requirements.

[0112] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the sodium-ion battery cells in this device, a battery pack or battery module can be used.

[0113] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a thin and light design and can use sodium-ion battery cells as their power source.

[0114] Example

[0115] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0116] Example 1

[0117] This embodiment provides a sodium-ion battery cell, the preparation method of which includes the following steps:

[0118] (1) Preparation of positive electrode sheet

[0119] A positive electrode slurry was prepared by dissolving and mixing NFPP (charge capacity of 121 mAh / g at 0.33C and discharge capacity of 98 mAh / g at 1C), single-walled carbon nanotubes (diameter of 6 nm and length of 14 μm), Super P, and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:0.5:2. The positive electrode slurry was then coated onto a current collector aluminum foil, dried, and cold-pressed to form the positive electrode sheet.

[0120] (2) Preparation of negative electrode sheet

[0121] Hard carbon, carboxymethyl cellulose (CMC), and Super P were dissolved in deionized water at a mass ratio of 95:5:5 and stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was coated onto a current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0122] (3) Separating membrane

[0123] Polypropylene film is used as the separator.

[0124] (4) Electrolyte

[0125] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), sodium hexafluorophosphate (NaPF6) was dissolved in dimethyl ethylene glycol (DME) organic solvent and stirred until homogeneous to obtain the electrolyte with a sodium salt concentration of 1 mol / L as in Example 1.

[0126] (5) Sodium-ion battery

[0127] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the sodium-ion battery cell of Example 1.

[0128] The morphology of the positive electrode sheet in Example 1 was tested. A portion of the positive electrode film sample was obtained by scraping powder with a blade and photographing the sample using a scanning electron microscope (e.g., ZEISS Sigma 300). Figure 7 This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at 500 magnification. Figure 8 This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at 3K magnification. Figure 9This is a scanning electron microscope (SEM) image of the positive electrode sheet of Embodiment 1 of this application at 30K magnification. Figures 7 to 9 As can be seen, NFPP consists of regular spherical particles, with carbon nanotubes connecting the particles.

[0129] The preparation methods of sodium-ion battery cells in Examples 2-8 and Comparative Examples 1-3 are similar to those in Example 1, but the charge / discharge specific capacity and mass ratio of NFPP in step (1), the type, diameter, length, and mass ratio of carbon nanotubes, the mass ratio of Super P (SP), and the compaction density of the positive electrode sheet are adjusted, as detailed in Table 1. Specifically, Na3V2(PO4)3 was used to replace NFPP in Comparative Example 1, no carbon nanotubes were added in Comparative Example 2, and the compaction density of the positive electrode sheet in Comparative Example 3 was less than 1.9 g / cm³. 3 .

[0130] Table 1. Some preparation conditions of sodium-ion battery cells in the examples and comparative examples.

[0131]

[0132]

[0133] Performance testing

[0134] 1. Positive electrode plate testing

[0135] (1) Compacted density

[0136] After disassembling a sodium-ion battery following cycle performance testing, take the positive electrode sheet, define its area as s1, measure its thickness as h1, and its weight as m1. Take an aluminum foil of the same area, with a thickness of h2 and a weight of m2. The compaction density of the electrode sheet is calculated as (m1-m2) / [s1×(h1-h2)], in g / cm³. 3 .

[0137] (2) elongation

[0138] After disassembling the sodium-ion battery following cycle performance testing, take the positive electrode sheet and cut it to a specific length, denoted as L0. Roll the electrode sheet under a certain pressure and measure the length after rolling, denoted as L1. L1 / L0×100% is the elongation of the electrode sheet under this pressure condition. The test is performed 3 times, and the average value is taken.

[0139] (3) Whether the electrode is brittle and broken

[0140] At 25°C and 40% relative humidity, the positive electrode sheets prepared in the examples and comparative examples were cold-pressed to a certain compaction density. Then, the electrode sheets were cut into 20mm × 100mm sheets, folded in half, and rolled three times using a 2kg roller. The positive electrode sheets were then laid out and observed against a light source. If light was transmitted through an area exceeding 10% of the width, or if any area showed signs of breakage, the brittleness was considered insufficient for processing and was defined as brittle fracture (recorded as yes); otherwise, it was defined as non-brittle fracture (recorded as no).

[0141] (4) Whether the electrode has been delaminated

[0142] After disassembling the sodium-ion battery following cycle performance testing, take the positive electrode and observe it against a light source. If light is transmitted or broken in an area exceeding 10% of its width, it is defined as delamination (marked as yes); otherwise, it is defined as no delamination (marked as no).

[0143] 2. Sodium-ion battery cell testing

[0144] (1) Energy density

[0145] At 25°C, a sodium-ion battery cell was charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C. After resting for 5 minutes, the initial charge capacity was recorded. The cell was then discharged at a constant current of 1C to the discharge cutoff voltage of 1.5V, and the discharge capacity was recorded. Energy density = discharge capacity / mass of positive electrode active material, in Wh / kg. The energy density after the 500th charge-discharge cycle was obtained after 500 charge-discharge cycles of the sodium-ion battery cell.

[0146] (2) DC internal resistance (DCR)

[0147] At 25℃, the secondary battery is charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, and the voltage V1 is recorded. Then, it is discharged at a constant current of 1C to the discharge cutoff voltage of 1.5V, and the voltage V2 is recorded. The DC internal resistance DCR1 of the battery after the first cycle is obtained by calculating 3 × (V2 - V1) / C. After resting for 5 minutes (stabilization time), the above steps are repeated 500 times to obtain the DC internal resistance DCR of the sodium-ion battery cell after the 500th cycle. 500 .

[0148] (3) Cyclic performance (capacity retention)

[0149] At 25°C, the sodium-ion battery cells prepared in each embodiment and comparative example were charged at a constant current rate of 0.33C to the charging cutoff voltage of 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 1C to the discharge cutoff voltage of 1.5V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle, and the resulting capacity is recorded as the initial discharge capacity (C0). The batteries were subjected to cyclic charge-discharge tests according to this method, and the discharge capacity (C0) of the battery after the 500th cycle was recorded. 500 If P is the capacity retention rate of a sodium-ion battery cell after each cycle, then P is the capacity retention rate of the cell after each cycle. 500 =C 500 / C0×100%.

[0150] The performance test results are shown in Table 2.

[0151] Table 2 Performance test results of the examples and comparative examples

[0152]

[0153]

[0154] As can be seen from Tables 1 and 2, in Examples 1-8 of this application, by selecting NFPP as the positive electrode active material and adding carbon nanotubes, the compaction density of the positive electrode sheet is controlled to be greater than 1.9 g / cm³. 3 Under these conditions, the compaction elongation of the positive electrode sheet is relatively low, resulting in a higher energy density for the corresponding sodium-ion battery cell. After 500 cycles, the positive electrode sheet did not exhibit film detachment, and the DC internal resistance after 500 cycles was reduced, improving the capacity retention rate. Table 2 shows that in Examples 1-8, the compaction density of the positive electrode sheet is greater than 1.9 g / cm³. 3 Under these conditions, the energy density of a sodium-ion battery cell can reach as high as 110.3 Wh / kg; the compressibility elongation of the positive electrode can be less than 0.9%, and no film detachment occurs after 500 cycles. Furthermore, the DC internal resistance after 500 cycles can be as low as 4.2 Ω, and the capacity retention rate after 500 cycles can reach as high as 99.20%. Moreover, by controlling the carbon nanotubes to be single-walled carbon nanotubes with a diameter no greater than 6 nm, a length of 10 μm to 20 μm, and a mass percentage of no less than 1%, the elongation of the positive electrode can be further reduced, the DC internal resistance of the sodium-ion battery cell after cycling can be lowered, and the capacity retention rate can be improved.

[0155] Comparing the performance test results of Example 1 and Comparative Example 1, it can be seen that when the positive electrode active material is Na3V2(PO4)3, the compaction density is 2.1 g / cm³. 3Under these conditions, the elongation of the positive electrode increases, leading to brittle fracture. Furthermore, after 500 cycles, the positive electrode of the corresponding sodium-ion battery cell shows film detachment, resulting in high DC internal resistance and low capacity retention. Therefore, adding carbon nanotubes can achieve a compaction density of at least 1.9 g / cm³. 3 The technical solution is not applicable to other polyanionic cathode materials.

[0156] Comparing the performance test results of Example 1 and Comparative Example 2, it can be seen that when no carbon nanotubes are added to the positive electrode sheet, the compaction density is 2.1 g / cm³. 3 Under these conditions, the elongation of the positive electrode sheet increases significantly, leading to brittle fracture, and the energy density of the corresponding sodium-ion battery cell decreases. After 500 cycles, the positive electrode sheet delaminates, the DC internal resistance of the sodium-ion battery cell increases significantly, and the capacity retention rate decreases significantly.

[0157] A comparison of the performance test results of Example 1 and Comparative Example 3 shows that the compaction density of the positive electrode sheet is less than 1.9 g / cm³. 3 In this case, although the positive electrode sheet can be kept from breaking and the positive electrode sheet of the sodium-ion battery cell does not detach after 500 cycles, the energy density of the sodium-ion battery cell is significantly reduced, and the DC internal resistance is significantly increased after 500 cycles, resulting in a decrease in capacity retention.

[0158] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sodium-ion battery cell, characterized in that, The sodium-ion battery cell includes a positive electrode sheet, which includes a positive current collector and a positive active layer attached to the surface of the positive current collector. The positive active layer includes sodium iron phosphate pyrophosphate and carbon nanotubes. The compaction density of the positive electrode sheet is not less than 1.9 g / cm³. 3 .

2. The sodium-ion battery cell as described in claim 1, characterized in that, The compaction density of the positive electrode sheet is 1.9 g / cm³. 3 ~2.2g / cm 3 ; Or / and, based on the total mass of the positive electrode active layer, the mass percentage of sodium iron phosphate pyrophosphate is 96% to 97.2%; Or / and, the elongation of the positive electrode sheet is not higher than 0.7%.

3. The sodium-ion battery cell according to any one of claims 1 to 2, characterized in that, The carbon nanotubes include single-walled carbon nanotubes.

4. The sodium-ion battery cell as described in claim 3, characterized in that, The diameter of the single-walled carbon nanotube is no greater than 6 nm, and the length is 10 μm to 20 μm.

5. The sodium-ion battery cell according to any one of claims 1 to 4, characterized in that, The carbon nanotubes account for 1% to 2% of the total mass of the positive electrode active layer.

6. The sodium-ion battery cell according to any one of claims 1 to 5, characterized in that, The sodium iron pyrophosphate has a charging capacity of 110 mAh / g to 130 mAh / g at a 0.33C rate and a discharging capacity of 90 mAh / g to 110 mAh / g at a 1C rate.

7. The sodium-ion battery cell according to any one of claims 1 to 6, characterized in that, The positive electrode active layer also includes a dot-shaped conductive agent.

8. The sodium-ion battery cell as described in claim 7, characterized in that, Based on the total mass of the positive electrode active layer, the mass percentage of the dot-shaped conductive agent is 0.5% to 2%. Or / and, the dotted conductive agent includes at least one of Superp, acetylene black, Ketjen black, carbon nanodots, or fullerene.

9. A sodium-ion battery, characterized in that, Includes the sodium-ion battery cell as described in any one of claims 1 to 8.

10. An electrical device, characterized in that, Including the sodium-ion battery as described in claim 9.

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