Sodium ion battery positive electrode sheet and sodium ion battery

Abstract

A sodium ion battery positive electrode sheet and a sodium ion battery. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, a first additive and a second additive, the first additive being at least one of boric acid, metaboric acid and a borate, and the second additive being a hydrophobic polymer.

Description

Sodium ion battery positive electrode sheet and sodium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure is based on the Chinese patent application with application number 202410253367.8, application date March 5, 2024, and invention name “Sodium ion battery positive electrode sheet and sodium ion battery”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a sodium ion battery positive electrode sheet and a sodium ion battery. Background Art

[0004] In recent years, sodium-ion batteries (Na-ion batteries), due to their abundant resources and environmentally friendly properties, have seen an increasingly wide range of applications, including in low-speed electric vehicles and large-scale energy storage systems. With the industry's growing attention to Na-ion batteries, both their technology and applications have rapidly developed, placing higher demands on their performance.

[0005] At present, the positive electrode materials of sodium-ion batteries have poor air stability and are easy to react with water, which will undoubtedly increase the production, transportation and storage costs of the materials, and will have adverse effects on the battery's first coulomb effect and cycle performance after absorbing water.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems, and its object is to provide a sodium ion battery positive electrode sheet that can improve the first coulomb effect and cycle performance of a secondary battery, and a sodium ion battery including the positive electrode sheet.

[0008] To achieve the above objectives, the present disclosure provides, in a first aspect, a sodium-ion battery positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, a first additive, and a second additive. The first additive comprises at least one of boric acid, metaboric acid, and a borate; and the second additive comprises a hydrophobic polymer.

[0009] The surface of the positive electrode material of sodium-ion batteries easily reacts with water to form residual alkali, leading to the loss of active sodium ions. The first additive disclosed in this disclosure can react with the residual alkali on the material surface to form a weak acid sodium salt, releasing more sodium ions during the battery's charge and discharge process, thereby improving the battery's initial coulombic efficiency and cycle performance. The second additive can reduce the positive electrode slurry's ability to adsorb water during the coating process, thereby reducing the water content of the positive electrode layer and the reaction between the positive electrode material and water molecules. The two additives work synergistically to improve the initial coulombic efficiency and cycle performance of the sodium-ion battery.

[0010] In some embodiments, the hydrophobic polymer includes at least one of polyethylene, polypropylene, polystyrene, polyacrylonitrile, polydimethylsiloxane, polymethyl methacrylate, polytetrafluoroethylene, polyamide, polycarbonate, and a conjugated polymer. These hydrophobic polymers have low surface energy and good hydrophobicity, which can reduce the adsorption of water on the surface of the positive electrode.

[0011] In some embodiments, the first additive includes boric acid, and the second additive includes polyacrylonitrile. Polyacrylonitrile has a high dielectric constant, which facilitates more uniform sodium deposition. Its abundant C≡N groups can generate strong dipole-dipole interactions with C=O groups, significantly reducing side reactions of active sodium. Furthermore, the combined use of these two specific additives can improve the uniformity of slurry coating. Polyacrylonitrile has good dispersion in the electrode layer, effectively regulating the deposition behavior of sodium ions during charge and discharge, thereby further improving the initial coulombic efficiency and cycle performance of the sodium-ion battery.

[0012] In some embodiments, the mass content of the first additive is 0.5 wt% to 1 wt% relative to the mass of the positive electrode film layer. By optimizing the content of the first additive within the above range, the viscosity of the slurry can be adjusted and the fluidity of the slurry can be improved, thereby enhancing coating uniformity and obtaining an excellent positive electrode sheet, which is beneficial for improving the initial coulombic efficiency and cycle performance of the sodium-ion battery.

[0013] In some embodiments, the mass content of the second additive is 1 wt% to 2 wt% relative to the mass of the positive electrode film layer. By ensuring that the content of the second additive is within the above range, the adsorption of water on the surface of the positive electrode plate can be sufficiently reduced, and the initial coulombic efficiency and cycle performance of the sodium ion battery can be effectively improved.

[0014] In some embodiments, the positive electrode film layer further includes a binder, and the binder has a mass content of 7 wt % to 10 wt % relative to the mass of the positive electrode film layer. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0015] In some embodiments, the coating weight per unit area of ​​the positive electrode sheet is 0.130 mg / mm 2 ~0.227mg / mm 2 .

[0016] In some embodiments, the compacted density of the positive electrode sheet is 1.8 g / cm 3 ~2.5g / cm 3 .

[0017] A second aspect of the present disclosure provides a sodium ion battery, comprising the positive electrode sheet of the first aspect of the present disclosure, wherein the sodium ion battery has excellent first coulombic efficiency and cycle performance.

[0018] In some embodiments, the sodium ion battery is a negative electrode-less sodium ion battery.

[0019] A third aspect of the present disclosure provides an electric device including the secondary battery according to the second aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0021] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 1 .

[0022] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0023] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0024] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0025] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0026] Explanation of the accompanying drawings: 1. battery pack; 2. upper case; 3. lower case; 4. battery module; 5. battery cell; 51. housing; 52. electrode assembly; 53. top cover assembly. DETAILED DESCRIPTION

[0027] Below, embodiments of the sodium ion battery positive electrode sheet and sodium ion battery disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0028] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3,1-4,1-5,2-3,2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0030] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0032] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0033] At present, the positive electrode materials of sodium-ion batteries have poor air stability and are easily reacted with water to generate residual alkali such as NaOH, Na2CO3, and NaHCO3, resulting in the loss of active sodium ions and affecting the battery's initial coulombic efficiency and cycle performance.

[0034] In view of this, the first aspect of the present disclosure provides a sodium ion battery positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, a first additive and a second additive, the first additive is at least one of boric acid, metaboric acid, and borate; the second additive is a hydrophobic polymer.

[0035] The first additive disclosed herein is at least one of boric acid, metaboric acid, and a borate. The first additive reacts with residual alkali on the surface of the material to form a weak acid sodium salt, releasing more sodium ions during the battery's charge and discharge process, thereby improving the battery's initial coulombic efficiency and cycle performance. Boric acid has lubricating properties, which can reduce the viscosity of the positive electrode slurry and increase its fluidity, improving the adhesion and brittleness of the electrode sheet, and effectively reducing the breakage and powder loss of the electrode sheet after cold pressing. The resulting positive electrode sheet helps improve battery cycle performance.

[0036] In addition, the borate may be, for example, lithium borate, sodium borate, potassium borate, calcium borate, etc. Preferably, the borate is sodium borate, which has a sodium supplementing effect.

[0037] In addition, the present disclosure also includes that the second additive is a hydrophobic polymer. The lower the surface energy of the hydrophobic polymer, the better the hydrophobicity. By adding the second additive, the adsorption capacity of the positive electrode surface to water can be reduced, thereby reducing the water content of the positive electrode layer, thereby reducing the reaction between the positive electrode material in the electrode layer and water.

[0038] In some embodiments, the hydrophobic polymer includes at least one of polyethylene, polypropylene, polystyrene, polyacrylonitrile, polydimethylsiloxane, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polycarbonate, or a conjugated polymer. Among them, polyacrylonitrile is preferred. The interaction between polyacrylonitrile having a strong electron-withdrawing group (C≡N) and C=O in the carbonate solvent can form a more stable SEI film, which can improve the uniform deposition of sodium ions at the negative electrode and inhibit the growth of sodium dendrites, further improving the first coulombic efficiency and cycle performance of the sodium ion battery.

[0039] In some embodiments, the first additive includes boric acid, and the second additive includes polyacrylonitrile. Polyacrylonitrile has a high dielectric constant, which facilitates more uniform sodium deposition. Its abundant C≡N groups can interact with C═O groups in the electrolyte to reduce side reactions of active sodium. Furthermore, the combination of these two specific additives can improve the uniformity of slurry coating. Polyacrylonitrile has good dispersion in the electrode layer, effectively regulating the deposition behavior of sodium ions during charge and discharge, thereby further improving the initial coulombic efficiency and cycle performance of the sodium-ion battery.

[0040] In some embodiments, the mass content of the first additive relative to the mass of the positive electrode film layer is 0.5wt% to 1wt%, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, etc., preferably 0.6wt% to 0.8wt%. By ensuring that the content of the first additive is within the above range, the alkalinity of the slurry can be neutralized, reacting with the residual alkali on the surface of the material to form a weak acid sodium salt, thereby releasing more active sodium ions.

[0041] In some embodiments, the mass content of the second additive relative to the mass of the positive electrode film layer is 1.0 wt% to 2.0 wt%, for example, 1.1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, etc., preferably 1.4 wt% to 1.8 wt%. By setting the content of the second additive within the above range, the hydrophobicity of the positive electrode sheet can be improved, which can effectively improve the initial coulombic efficiency and cycle performance of the sodium ion battery.

[0042] In some embodiments, as the positive electrode active material of the sodium ion battery, a positive electrode active material for sodium ion batteries known in the art can be used. As an example, the positive electrode active material can include sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, etc.

[0043] In some embodiments, the positive electrode film layer further includes a binder, and the mass content of the binder relative to the mass of the positive electrode film layer is 7wt% to 10wt%, optionally 7wt% to 9wt%. There is no particular limitation on the type of binder, as long as it is a binder commonly used in positive electrode sheets, it can be used, for example, it can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. In some embodiments, the binder is polyvinylidene fluoride.

[0044] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0045] In some embodiments, the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0046] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0047] In some embodiments, the coating weight per unit area of ​​the positive electrode sheet is 0.130 mg / mm 2 ~0.227mg / mm 2 The compacted density of the pole piece is 1.8g / cm 3 ~2.5g / cm 3 .

[0048] In addition, a second aspect of the present disclosure provides a sodium ion battery comprising the positive electrode sheet of the first aspect of the present disclosure. The sodium ion battery has reduced gas generation during high-temperature storage and has an excellent cycle life.

[0049] In addition to the aforementioned positive electrode, the sodium-ion battery disclosed herein also includes the following negative electrode, electrolyte, and separator. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0050] Negative electrode

[0051] In one embodiment, the sodium ion battery is a negative electrode-free sodium ion battery. Wherein, no negative electrode means that in the initial state, the negative electrode structure only includes a current collector but no active material. After the first charge is completed, the metal in the positive electrode material migrates to the surface of the negative electrode current collector, and a metal layer is formed on the negative electrode current collector. During the charging process, the metal electrolyte ions in the electrolyte combine with electrons on the surface and / or in the pores of the negative electrode current collector, and deposition occurs. During the discharge process, the deposited layer on the surface of the negative electrode current collector peels off and dissolves back into metal electrolyte ions and electrons, returning to the positive electrode, and so on. Compared with traditional secondary batteries, the energy density of negative electrode-free secondary batteries is further improved, the safety and stability are also higher, and the weight and volume are smaller.

[0052] In the present disclosure, the first coulombic efficiency and cycle performance of the negative electrode-free sodium ion battery can be improved by making the negative electrode-free sodium ion battery include the positive electrode plate of the first aspect of the present disclosure.

[0053] In one embodiment, the negative electrode plate may also be of a traditional structure, that is, including a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0054] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0055] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0056] In some embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The above-mentioned silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The above-mentioned tin-based material can be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0057] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0058] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0059] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0060] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0061] electrolytes

[0062] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0063] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. The sodium salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. Organic solvents include, but are not limited to, 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), methyl ethyl sulfone (EMS), diethyl sulfone (ESE) or at least one of ether solvents. Ether solvents may include cyclic ethers and / or chain ethers. Specific examples of cyclic ethers include, but are not limited to, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), etc. Specific examples of chain ethers include, but are not limited to, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), and the like.

[0064] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0065] Isolation film

[0066] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0067] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0068] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0069] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0070] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0071] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0072] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the above opening to close the above receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the above-mentioned receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0073] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0074] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0075] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0076] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0077] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0078] In addition, the third aspect of the present disclosure further provides an electric device, which includes the sodium ion battery provided in the second aspect of the present disclosure. The battery can be used as a power source for the above-mentioned electric device, and can also be used as an energy storage unit for the above-mentioned electric device. The above-mentioned electric device may include an electric vehicle, an energy storage system, etc., but is not limited thereto. As the above-mentioned electric device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0079] Figure 6 shows an example of an electric device. This device is 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 secondary battery, a battery pack or battery module can be used.

[0080] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0081] Example

[0082] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0083] Example 1.

[0084] (1) Preparation of positive electrode sheet

[0085] The polyvinylidene fluoride (PVDF) binder, the first additive boric acid and the second additive polyacrylonitrile (PAN) are fully dissolved in N-methylpyrrolidone, and the conductive agent carbon black and the positive electrode active material phosphate sodium salt Na4Fe3(PO4)2(P2O7) (abbreviated as NFPP) are added to make a uniformly dispersed slurry. The above slurry is evenly coated on the surface of the aluminum foil, and then transferred to a vacuum drying oven for complete drying to form a positive electrode film layer on the surface of the aluminum foil. The obtained pole piece is rolled and then punched to obtain a positive pole piece. Among them, relative to the total mass of the positive electrode film layer, it contains 7.7% by mass of polyvinylidene fluoride (PVDF) binder, 0.8% by mass of boric acid, 1.5% by mass of PAN, 10% by mass of carbon black conductive agent and 80% by mass of positive electrode active material.

[0086] (2) Preparation of negative electrode sheet

[0087] Single-walled carbon nanotubes and carboxymethyl cellulose (CMC) are evenly mixed in an appropriate amount of deionized water as a solvent at a mass ratio of 0.5:2 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector copper foil. A negative electrode active material layer is formed on both sides of the negative electrode current collector through drying and cold pressing. Finally, the negative electrode sheet is obtained through striping and cutting processes.

[0088] (3) Preparation of electrolyte

[0089] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent ethylene glycol dimethyl ether and stirred evenly to obtain an electrolyte with a sodium salt concentration of 0.5 mol / L.

[0090] (4) Isolation film: Polypropylene film is used as the isolation film.

[0091] (5) Preparation of sodium ion batteries

[0092] The positive electrode sheet, separator, and negative electrode sheet are wound in sequence, with the separator placed between the positive and negative electrode sheets to serve as an isolation layer. The electrolyte is then added to form a soft-pack battery.

[0093] Examples 2-6

[0094] A sodium ion battery was prepared in the same manner as in Example 1 except that the type of the first additive or the second additive was changed as shown in Table 1.

[0095] Comparative Example 1

[0096] A sodium ion battery was prepared in the same manner as in Example 1 except that the first additive and the second additive were not added.

[0097] Comparative Example 2

[0098] A sodium ion battery was prepared in the same manner as in Example 1 except that the second additive was not added.

[0099] Comparative Example 3

[0100] A sodium ion battery was prepared in the same manner as in Example 1 except that the first additive was not added.

[0101] Performance Testing

[0102] [1] Water content of positive electrode

[0103] Water content (ug / g) indicates the mass of water per unit mass of sample. It is measured using a Metrohm instrument (model 831) based on GB / T 11133-2015. The solid sample is heated and purged with dry gas into the titration vessel of a Karl Fischer coulometer for titration. The result is converted to the water content of the solid sample.

[0104] Calculation formula: Water content = (sample moisture value - blank moisture value) / sample mass.

[0105] Among them, the blank moisture value represents the moisture value in the environment.

[0106] [2] First Coulombic efficiency

[0107] The sodium ion battery was charged at 45°C with a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and the charge capacity C0 was recorded; then the battery was discharged at a constant current of 1C to 1.5V, and the first cycle discharge capacity D0 was recorded. The first coulombic efficiency was recorded as D0 / C0×100%.

[0108] [3]Capacity retention rate

[0109] The sodium ion battery is charged at 45°C at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V until the current drops to 0.05C, and then discharged at a constant current of 1C to 1.5V to obtain the first cycle discharge capacity (Cd1); this charge and discharge is repeated until the nth cycle, and the discharge capacity of the sodium battery after n cycles is obtained, recorded as Cdn, and the sodium battery capacity retention rate is calculated according to the following formula:

[0110] Capacity retention after 500 cycles (%) = discharge capacity after 500 cycles (Cd 500 ) / first cycle discharge capacity (Cd1)×100%.

[0111] Table 1

[0112] In the table: PAN represents polyacrylonitrile; PDMS represents polydimethylsiloxane; PMMA represents polymethyl methacrylate; PA represents polyamide;

[0113] It can be seen from Table 1 above that, compared with Comparative Examples 1 to 3, in Examples 1 to 6, by including the first additive and the second additive in the positive electrode sheet, the battery achieves excellent first coulombic efficiency and cycle performance under the synergistic effect of the two.

[0114] Examples 7-10

[0115] A sodium ion battery was prepared in the same manner as in Example 1 except that the content of the first additive or the second additive was changed as shown in Table 2 (the total amount of the binder, the first additive, and the second additive was 10% relative to the total mass of the positive electrode film layer).

[0116] Table 2

[0117] As can be seen from Table 2, relative to the mass of the positive electrode film layer, the content of the first additive is 0.5% to 1%, and the content of the second additive is 1% to 2%, both of which can reduce the water content of the electrode and improve the first coulombic efficiency and cycle performance of the battery.

[0118] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A sodium ion battery positive electrode plate, wherein: The device comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, a first additive and a second additive; The first additive includes at least one of boric acid, metaboric acid, and borate; The second additive includes a hydrophobic polymer.

2. The sodium ion battery positive electrode sheet according to claim 1, wherein: The hydrophobic polymer includes at least one of polyethylene, polypropylene, polystyrene, polyacrylonitrile, polydimethylsiloxane, polymethyl methacrylate, polytetrafluoroethylene, polyamide, polycarbonate or a conjugated polymer.

3. The sodium ion battery positive electrode sheet according to claim 1 or 2, wherein: The first additive includes boric acid, and the second additive includes polyacrylonitrile.

4. The sodium ion battery positive electrode sheet according to any one of claims 1 to 3, wherein: The mass content of the first additive is 0.5 wt % to 1 wt % relative to the mass of the positive electrode film layer.

5. The sodium ion battery positive electrode sheet according to any one of claims 1 to 4, wherein: The mass content of the second additive is 1 wt% to 2 wt% relative to the mass of the positive electrode film layer.

6. The sodium ion battery positive electrode sheet according to any one of claims 1 to 5, wherein: The positive electrode film layer further includes a binder, and the mass content of the binder is 7 wt % to 10 wt % relative to the mass of the positive electrode film layer.

7. The sodium ion battery positive electrode sheet according to claim 6, wherein: The binder includes at least one of polyvinylidene fluoride, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

8. The sodium ion battery positive electrode sheet according to any one of claims 1 to 7, wherein: The coating weight per unit area of ​​the positive electrode sheet is 0.130 mg / mm 2 ~0.227mg / mm 2 .

9. The sodium ion battery positive electrode sheet according to any one of claims 1 to 8, wherein: The compaction density of the positive electrode sheet is 1.8 g / cm 3 ~2.5g / cm 3 .

10. A sodium ion battery, wherein: A sodium ion battery positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 9.

11. The sodium ion battery according to claim 10, wherein: The sodium ion battery is a negative electrode-free sodium ion battery.

12. An electrical device, wherein: Including the sodium ion battery according to claim 10 or 11.

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