Negative plate of sodium ion battery as well as preparation method and application of negative plate

Abstract

The invention provides a negative electrode plate of a sodium ion battery and a preparation method and application thereof, the negative electrode plate of the sodium ion battery comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, and the negative electrode active layer comprises sodium deoxycholate. According to the negative plate of the sodium-ion battery as well as the preparation method and the application of the negative plate, the capacity and the cycle life of the sodium-ion battery can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a negative electrode sheet of a sodium ion battery and a preparation method and application thereof. Background Art

[0002] In order to meet the huge market demand, energy storage materials are not only evaluated based on electrochemical properties such as energy density and charge and discharge rate, but are gradually developing in the direction of abundant resources and environmental friendliness. Sodium-ion batteries have many advantages over lithium-ion batteries, such as abundant sodium resources, low cost, excellent rate performance, high and low temperature performance, and good safety performance.

[0003] At present, in the production of negative electrode sheets, deionized water is mainly used as a solvent, carboxymethyl cellulose (Sodium Carboxymethyl Cellulose, CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder to prepare negative electrode slurry. However, most of the negative electrode active materials of sodium ion batteries, such as hard carbon, soft carbon, etc., when prepared with water-based slurry, will have a large surface tension of the slurry and a small surface tension of the negative electrode collector, resulting in poor wettability of the negative electrode slurry on the surface of the negative electrode collector, and it is impossible to achieve uniform coating, which seriously affects the commercialization process of sodium ion batteries. Summary of the invention

[0004] The present invention provides a negative electrode sheet for a sodium ion battery and a preparation method and application thereof, which can effectively improve the dispersibility of the negative electrode slurry of the sodium ion battery, thereby improving the capacity and cycle life of the sodium ion battery.

[0005] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0006] The present invention provides a negative electrode sheet of a sodium ion battery, comprising a negative electrode current collector and a negative electrode active layer located on at least one surface thereof, wherein the negative electrode active layer comprises sodium deoxycholate.

[0007] In one embodiment of the present invention, the mass fraction of the sodium deoxycholate in the negative electrode active layer is 0.5% to 1%.

[0008] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, and the mass fraction of the negative electrode active material in the negative electrode active layer is 90% to 98%.

[0009] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode conductive agent, and the mass fraction of the negative electrode conductive agent in the negative electrode active layer is 1% to 2%.

[0010] In one embodiment of the present invention, the negative electrode active layer includes a thickener, and the mass fraction of the thickener in the negative electrode active layer is 1% to 2%.

[0011] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode binder, and the mass fraction of the negative electrode binder in the negative electrode active layer is 1% to 2%.

[0012] The present invention also provides a sodium ion battery, comprising the above-mentioned negative electrode sheet, a separator, a positive electrode sheet and an electrolyte.

[0013] The present invention also provides a method for preparing a negative electrode sheet of a sodium ion battery, which at least comprises:

[0014] The negative electrode active material, the negative electrode conductive agent, the thickener and sodium deoxycholate are mixed and stirred, and then the negative electrode solvent is added and kneaded to obtain a negative electrode slurry precursor;

[0015] Adding a negative electrode binder to the negative electrode slurry precursor to obtain a negative electrode slurry;

[0016] The negative electrode slurry is coated on at least one side of the negative electrode current collector, and then dried to obtain a negative electrode sheet.

[0017] In one embodiment of the present invention, the fineness of the negative electrode slurry is 10 μm to 20 μm.

[0018] In one embodiment of the present invention, the coating density of the negative electrode slurry is 6.8 mg / cm 2 ~10.2mg / cm 2 .

[0019] In summary, the present invention proposes a negative electrode sheet for a sodium ion battery, a preparation method and an application thereof. Adding sodium deoxycholate to the negative electrode slurry effectively increases the dispersion effect of the negative electrode active material in the negative electrode slurry, improves the wettability of the negative electrode slurry on the surface of the negative electrode current collector, thereby improving the capacity and cycle life of the sodium ion battery, and improving the economic benefits of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 FIG. 1 is a scanning electron microscope image of a negative electrode sheet of a sodium ion battery in one embodiment of the present invention.

[0022] Figure 2This is an energy spectrum analysis diagram of the negative electrode sheet of a sodium ion battery in one embodiment of the present invention.

[0023] Figure 3 This is a comparison chart of the fineness of negative electrode slurry in an embodiment of the present invention and a comparative example.

[0024] Figure 4 The figure is a comparison chart of the cycle performance of the sodium ion battery in one embodiment of the present invention and a comparative example. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0027] The technical solution of the present invention is further described in detail below in conjunction with several embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] The present invention provides an electronic device, which includes at least one sodium ion battery for providing electric energy. The electronic device in the present application is any electronic device, such as but not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera or a large household battery.

[0029] The present invention also proposes a sodium ion battery, comprising at least a positive electrode sheet, a separator and a negative electrode sheet. The battery cell of the sodium ion battery is, for example, a laminated battery cell or a wound structure core. In the present embodiment, the battery cell of the sodium ion battery is, for example, a laminated battery cell, and the separator is, for example, arranged between the positive electrode sheet and the negative electrode sheet. The negative electrode materials of sodium ion batteries are mainly divided into five types: carbon-based materials, titanium-based materials, alloy materials or organic compounds, etc., and carbon-based materials have a broader application basis due to their comprehensive cost-effectiveness advantages in terms of cost and performance. Hard carbon is considered to be the most promising negative electrode material due to its large interlayer spacing, numerous pores and many sodium embedded defects. The present invention uses hard carbon as the negative electrode active material to prepare the negative electrode sheet of the sodium ion battery to meet the growing demand for high-performance sodium ion batteries. The sodium ion battery proposed in the present invention can be applied to the above-mentioned various electronic devices.

[0030] See also Figure 1 As shown, the present invention proposes a negative electrode sheet of a sodium ion battery, the negative electrode sheet, for example, includes a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, wherein the material of the negative electrode current collector is, for example, copper foil or aluminum foil. In this embodiment, the material of the negative electrode current collector is, for example, aluminum foil, which reduces production costs and improves the commercial value of the sodium ion battery. The negative electrode active layer, for example, includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, a thickener and an additive, and the additive is sodium deoxycholate, etc. And the mass fraction of sodium deoxycholate in the negative electrode active layer is, for example, 0.5% to 1%. In a specific embodiment of the present invention, the mass fraction of sodium deoxycholate in the negative electrode active layer is, for example, 0.5%, 0.6% or 1%. In this embodiment, after adding sodium deoxycholate, the obtained negative electrode slurry has high wettability with the surface of the negative electrode current collector, and the negative electrode active material has high dispersion uniformity in the negative electrode active layer, thereby effectively improving the capacity and cycle life of the sodium ion battery. Among them, the negative electrode sheet provided by the present invention can be applied to the above-mentioned sodium ion battery, so the above-mentioned sodium ion battery at least has all the beneficial effects brought by the above-mentioned technical solutions related to the negative electrode sheet.

[0031] See also Figure 1 As shown, in one embodiment of the present invention, the negative electrode active material is, for example, selected as a carbon material, specifically, for example, hard carbon, and for example, a mixture of one or more of biomass hard carbon, organic hard carbon or coal-based hard carbon. The mass content of the negative electrode active material in the negative electrode active layer is, for example, 90% to 98%. In a specific embodiment of the present invention, the mass content of the negative electrode active material in the negative electrode active layer is, for example, 95.4%. The present invention does not limit the particle size of the negative electrode active material. In this embodiment, the average particle size of the negative electrode active material is, for example, less than 50 μm, which improves the wettability of the subsequently prepared negative electrode slurry and the negative electrode collector. In other embodiments, the type and particle size of the negative electrode active material are set according to other requirements.

[0032] See also Figure 1 As shown, in one embodiment of the present invention, the negative electrode conductive agent includes, for example, any one or more of conductive carbon black (Super P, SP), acetylene black, carbon nanotubes (Carbon Nanotube, CNT) or graphene. In a specific embodiment of the present invention, the negative electrode conductive agent is, for example, conductive carbon black. The mass content of the negative electrode conductive agent in the negative electrode active layer is, for example, 1% to 2%. In a specific embodiment of the present invention, the mass content of the negative electrode conductive agent in the negative electrode active layer is, for example, 1%. In other embodiments, the specific type and content of the negative electrode conductive agent are, for example, other options.

[0033] See also Figure 1 As shown, in one embodiment of the present invention, the negative electrode binder is, for example, a mixture of one or more aqueous binders such as styrene-butadiene rubber (SBR), aqueous polyacrylic acid derivative binder (PAAd) or polytetrafluoroethylene emulsion. In a specific embodiment of the present invention, the negative electrode binder is, for example, styrene-butadiene rubber. The mass content of the negative electrode binder in the negative electrode active layer is, for example, 1% to 2%. In a specific embodiment of the present invention, the mass content of the negative electrode binder in the negative electrode active layer is, for example, 2%, which effectively fixes the negative electrode active material and ensures the stability and reliability of the negative electrode sheet during the charge and discharge process. In other embodiments, the specific type and content of the negative electrode binder are, for example, other settings.

[0034] See also Figure 1 As shown, in one embodiment of the present invention, the negative electrode thickener is selected as a mixture of one or more of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na) or sodium alginate. The mass content of the negative electrode thickener in the negative electrode active layer is, for example, 1% to 2%. In a specific embodiment of the present invention, the mass content of the negative electrode thickener in the negative electrode active layer is, for example, 1%. In other embodiments, the specific type and content of the negative electrode thickener are, for example, other options.

[0035] The present invention also provides a method for preparing a negative electrode sheet of a sodium ion battery. The negative electrode sheet is obtained by the preparation method of steps S11 to S13.

[0036] Step S11, mixing and stirring the negative electrode active material, the conductive agent, the thickener and sodium deoxycholate, and then adding the negative electrode solvent to knead to obtain a negative electrode slurry precursor.

[0037] Step S12: adding a binder to the negative electrode slurry precursor to obtain a negative electrode slurry.

[0038] Step S13, coating the negative electrode slurry on at least one side of the negative electrode current collector, and drying to obtain a negative electrode sheet.

[0039] In one embodiment of the present invention, in step S11, the negative electrode active material, the conductive agent, the thickener and the sodium deoxycholate are stirred and mixed, wherein the mass ratio of the negative electrode active material, the conductive agent, the thickener and the sodium deoxycholate is, for example, (90-98): (1-2): (1-2): (0.5-1), and in a specific embodiment of the present invention, the mass ratio of the negative electrode active material, the conductive agent, the thickener and the sodium deoxycholate is, for example, 96.4: 1: 1: 0.6. The mixing and stirring time is, for example, 20 min to 60 min, and in a specific embodiment of the present invention, the mixing and stirring time is, for example, 30 min. After mixing, a negative electrode solvent is added to disperse the negative electrode active material, the conductive agent, the thickener and the sodium deoxycholate, and kneading is performed to obtain a negative electrode slurry precursor. Among them, the negative electrode solvent is, for example, selected from one or more aqueous solvents such as deionized water. In a specific embodiment of the present invention, the negative electrode solvent is, for example, selected from deionized water. The kneading time after adding the negative electrode solvent is, for example, 50 min to 70 min. In a specific embodiment of the present invention, the kneading time is, for example, 60 min, so that the negative electrode solvent can fully disperse the above materials.

[0040] In one embodiment of the present invention, in step S12, a binder is added to the negative electrode slurry precursor to obtain a negative electrode slurry, and after the binder is added, the negative electrode slurry is further dispersed for 2h to 3h to improve the dispersion uniformity of the negative electrode active material. In a specific embodiment of the present invention, the dispersion time of the negative electrode slurry is, for example, 2h. After dispersion, the fineness of the obtained negative electrode slurry is, for example, less than 20μm, the viscosity is, for example, 1000mPa·s to 9000mPa·s, and the solid content is 20% to 80%. In a specific embodiment of the present invention, the fineness of the obtained negative electrode slurry is, for example, 15μm, which improves the wettability of the negative electrode slurry and the negative electrode current collector in the subsequent coating process, and improves the dispersibility of the negative electrode active material in the negative electrode slurry. In step S13, the negative electrode slurry obtained in step S12 is coated on the negative electrode current collector, and the coating surface density is controlled at 6.8mg / cm 2 ~10.2mg / cm 2 , thereby ensuring the high energy density of the sodium ion battery obtained later. After applying the negative electrode slurry, the negative electrode current collector is placed in an oven for baking, and the baking temperature is set to 80°C to 120°C, and the baking time is set to 5h to 8h, to obtain a negative electrode sheet. In a specific embodiment of the present invention, the baking time is, for example, 100°C, and the baking time is, for example, 6h.

[0041] The present invention also provides a method for preparing a sodium ion battery. The sodium ion battery is obtained by the preparation method of steps S10 to S40.

[0042] Step S10: Mix the positive electrode active material, the conductive agent and the binder according to a set weight ratio, add them to the positive electrode solvent, and stir them under certain conditions until they are uniform to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector, and then dried, cold pressed and cut to obtain a positive electrode sheet.

[0043] Step S20, cold pressing and cutting the negative electrode sheets obtained in steps S11 to S13.

[0044] Step S30, mixing the organic solvents according to a proportion, adding sodium salt and other ingredients, and mixing evenly to obtain an electrolyte.

[0045] Step S40, stacking the separator and the positive electrode sheet and the negative electrode sheet prepared in steps S10 to S20, injecting the electrolyte prepared in step S30, and obtaining a sodium ion battery.

[0046] In one embodiment of the present invention, in step S10, the positive electrode current collector can be selected from aluminum foil, etc., and the thickness of the positive electrode current collector is, for example, 8μm to 15μm. In this embodiment, the positive electrode active material is, for example, one or more of Prussian blue compounds, sodium phosphate salts, sodium sulfate salts or layered oxygen-containing sodium salts, the positive electrode conductive agent is, for example, selected from any one or more of carbon black, acetylene black, carbon nanotubes (Carbon Nanotube, CNT) and graphene, etc., and the positive electrode binder is, for example, selected from one or more of oily binders such as polyvinylidene fluoride (Polyvinylidene Fluoride, PVDF) or a mixture of several. The material of the above-mentioned positive electrode active layer is, for example, dispersed in a positive electrode solvent to form a positive electrode slurry, which is coated on the positive electrode current collector, and the positive electrode solvent is, for example, selected from one or more of solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) or ethylene glycol dimethyl ether (EGDME). In a specific embodiment of the present invention, the positive electrode active material is selected as NaMn 0.33 F e0.33 Ni 0.33 O 2 The positive electrode conductive agent is selected as carbon black, the positive electrode binder is selected as polyvinylidene fluoride, and NaMn 0.33 F e0.33 Ni 0.33 O 2, carbon black and polyvinylidene fluoride are mixed in a mass ratio of, for example, 95.2:2.8:2, and then a positive electrode solvent is added and stirred until stable and uniform to obtain a positive electrode slurry, and the positive electrode slurry is coated on an aluminum foil. The aluminum foil is transferred to an oven at 80°C to 90°C and dried for 0.5h to 2h, and then a positive electrode sheet is obtained through cold pressing and slitting.

[0047] In one embodiment of the present invention, in step S20, the negative electrode sheet obtained in steps S11 to S13 is cold pressed and cut, and the size of the cut pieces is, for example, (3 to 10) cm. 2 ×(3~10)cm 2 The size of the positive electrode sheet obtained in step S10 is, for example, (3 to 10) cm 2 ×(3~10)cm 2 , and in this embodiment, the size of the positive electrode sheet is, for example, the same as the size of the negative electrode sheet.

[0048] In one embodiment of the present invention, in step S30, the sodium salt is selected from sodium hexafluorophosphate (LiPF 6 ), sodium perchlorate (Sodium perchlorate, NaClO 4 ), Sodium tetrafluoroborate (NaBF 4 ), sodium difluorosulfonymide (NaFSI), sodium bis(trifluoromethyl)sulfonamide (NaTFSI), or trifluoromethanesulfonic acid (NaSO 3 CF 3 In this embodiment, the sodium salt is selected from NaPF 6 , and the content of sodium salt in the electrolyte is, for example, 4wt% to 24wt%. The organic solvent is selected from any one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or polycarbonate (PC). In this embodiment, the organic solvent is, for example, a mixed solution of EC, EMC, DEC and PC, and the mass ratio of EC, EMC, DEC and PC is, for example, (2-4): (3-5): (2-4): (0-1).

[0049] In one embodiment of the present invention, in step S40, the diaphragm is, for example, selected from a polyethylene film (Polyethylene, PE) or a polypropylene film (Polypropylene, PP). The thickness of the diaphragm is, for example, 9μm to 18μm, the air permeability is, for example, 180s / 100m to 380s / 100mL, and the porosity is, for example, 30% to 50%. In this embodiment, the diaphragm is, for example, a composite diaphragm material of PP / PE / PP, and the surface of the diaphragm is, for example, sprayed with a binder PVDF. The positive and negative electrode sheets obtained in steps S10 to S20 are tightly stacked in the order of positive electrode sheet, diaphragm, and negative electrode sheet, and the electrolyte obtained in step S30 is injected into both sides of the diaphragm to form a battery core, and a sodium ion battery is obtained after stacking to the required number of layers.

[0050] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0051] Example 1

[0052] Preparation of negative electrode sheet: Add hard carbon, SP, CMC, and sodium deoxycholate into a blender and mix for 30 minutes, then add deionized water and knead for 60 minutes, and finally add a certain amount of SBR to disperse for 2 hours to obtain negative electrode slurry, and the mass ratio of hard carbon, SP, CMC, SBR and sodium deoxycholate is 95.4:1:1:2:0.6. The negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil, and dried in an oven at 80℃~120℃ for 6 hours, and then the negative electrode sheet is obtained through cold pressing and slitting.

[0053] Preparation of positive electrode: NaMn 0.33 Fe 0.33 Ni 0.33 O 2 , carbon black and PVDF are mixed in a mass ratio of 95.2:2.8:2, and a positive electrode solvent is added and stirred to obtain a positive electrode slurry. The positive electrode solvent is coated on the positive electrode current collector aluminum foil, and the aluminum foil is dried at room temperature and transferred to an oven at 80℃ to 90℃ for drying for 0.5h to 2h, and then the positive electrode sheet is obtained through cold pressing and slitting.

[0054] Preparation of electrolyte: Ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried sodium salt LiPF 6 Dispersed in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0055] Preparation of sodium ion battery: spray PVDF on the surface of the diaphragm, stack the positive electrode sheet, diaphragm and negative electrode sheet tightly together in sequence, inject the electrolyte on both sides of the diaphragm to obtain a battery cell, and after stacking to the required number of layers, a sodium ion battery is obtained.

[0056] Example 2

[0057] Preparation of negative electrode sheet: Add hard carbon, SP, CMC, and sodium deoxycholate into a blender and mix for 30 minutes, then add deionized water and knead for 60 minutes, and finally add a certain amount of SBR to disperse for 2 hours to obtain negative electrode slurry, and the mass ratio of hard carbon, SP, CMC, SBR and sodium deoxycholate is 95.5:1:1:2:0.5. The negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil, and dried in an oven at 80℃~120℃ for 6 hours, and then the negative electrode sheet is obtained through cold pressing and slitting.

[0058] The other operations are the same as those in Example 1.

[0059] Example 3

[0060] Preparation of negative electrode sheet: Add hard carbon, SP, CMC, and sodium deoxycholate into a blender and mix for 30 minutes, then add deionized water and knead for 60 minutes, and finally add a certain amount of SBR to disperse for 2 hours to obtain negative electrode slurry, and the mass ratio of hard carbon, SP, CMC, SBR and sodium deoxycholate is 95:1:1:2:1. The negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil, and dried in an oven at 80℃~120℃ for 6 hours, and then the negative electrode sheet is obtained through cold pressing and slitting.

[0061] The other operations are the same as those in Example 1.

[0062] Comparative Example 1

[0063] Preparation of negative electrode sheet: Add hard carbon, SP, and CMC into a mixer and mix for 30 minutes, then add deionized water and knead for 60 minutes, and finally add a certain amount of SBR to disperse for 2 hours to obtain negative electrode slurry, and the mass ratio of hard carbon, SP, CMC and SBR is 96:1:1:2. The negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil, and dried in an oven at 80℃~120℃ for 6 hours, and then the negative electrode sheet is obtained through cold pressing and slitting.

[0064] The other operations are the same as those in Example 1.

[0065] The negative electrode slurries, negative electrode sheets and sodium ion batteries obtained in Example 1 and Comparative Example 1 were tested.

[0066] Test the fineness of the negative electrode slurry.

[0067] Observe the scanning electron microscope and energy spectrum analysis diagram of the negative electrode.

[0068] To test the cycle capacity retention rate of the sodium ion battery, for example, within a voltage range of 1.5V to 4V, first use a current of, for example, 0.05C for formation, and then use a current of, for example, 1C to test the cycle retention rate of the battery.

[0069] See also Figure 1 and Figure 2 As shown, Figure 1 is a scanning electron microscope image of the negative electrode sheet obtained in Example 1, Figure 2 This is the energy spectrum analysis diagram of the negative electrode sheet obtained in Example 1. The energy spectrum analysis diagram of the negative electrode sheet shows that the negative electrode active layer is mainly composed of three elements: C, O and Na, proving that sodium deoxycholate can be used as an additive to prepare the negative electrode sheet of the sodium ion battery. And the scanning electron microscope image of the negative electrode sheet shows that the negative electrode active material hard carbon is uniformly dispersed in the negative electrode active layer, indicating that sodium deoxycholate as an additive can improve the dispersibility of the negative electrode active material in the negative electrode.

[0070] See also Figure 3 and Figure 4 As shown, Figure 3 This is a comparison chart of the fineness of the negative electrode slurry obtained in Example 1 and Comparative Example 1. The fineness of the negative electrode slurry in Example 1 reaches 15 μm, while the fineness of the negative electrode slurry in Comparative Example 1 is 35 μm, indicating that the introduction of sodium deoxycholate increases the dispersion performance of hard carbon in the negative electrode slurry. Figure 4 is the cycle capacity retention rate of the sodium ion batteries obtained in Example 1 and Comparative Example 1. After the cycle number of the sodium ion battery reaches 200, the cycle capacity retention rate of the sodium ion battery obtained in Example 1 is higher than the cycle capacity retention rate of the sodium ion battery obtained in Comparative Example 1. When the cycle number of the sodium ion battery in Example 1 reaches 400, the cycle capacity retention rate is still greater than 95%, indicating that the cycle performance of the sodium ion battery obtained by the present invention is improved, the service life of the sodium ion battery cell is extended, and the economic benefit of the sodium ion battery is greatly improved.

[0071] In summary, the present invention proposes a negative electrode sheet of a sodium ion battery, a preparation method and an application thereof, by introducing sodium deoxycholate as an additive into the negative electrode active layer, reducing the fineness of the negative electrode slurry, improving the wettability of the negative electrode slurry on the surface of the negative electrode current collector, solving the problem of uneven coating caused by poor wettability of the negative electrode slurry when coated on the surface of aluminum foil at a relatively low cost, and improving the electrochemical performance of the sodium ion battery. At the same time, sodium deoxycholate effectively increases the dispersion effect of the negative electrode active material in the negative electrode slurry, thereby improving the cycle capacity retention rate of the sodium ion battery and improving the economic benefits of the sodium ion battery. The method of the present invention for improving the uniformity of the dispersion of the negative electrode active material on the surface of the aluminum foil is simple and efficient, and is suitable for industrial applications.

[0072] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0073] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A negative electrode sheet for a sodium ion battery, It is characterized in that The invention comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active layer comprises sodium deoxycholate.

2. The negative electrode sheet of the sodium ion battery according to claim 1, It is characterized in that The mass fraction of the sodium deoxycholate in the negative electrode active layer is 0.5% to 1%.

3. The negative electrode sheet of the sodium ion battery according to claim 1, It is characterized in that The negative electrode active layer includes a negative electrode active material, and the mass fraction of the negative electrode active material in the negative electrode active layer is 90% to 98%.

4. The negative electrode sheet of the sodium ion battery according to claim 1, It is characterized in that The negative electrode active layer includes a negative electrode conductive agent, and the mass fraction of the negative electrode conductive agent in the negative electrode active layer is 1% to 2%.

5. The negative electrode sheet of the sodium ion battery according to claim 1, It is characterized in that The negative electrode active layer includes a thickener, and the mass fraction of the thickener in the negative electrode active layer is 1% to 2%.

6. The negative electrode sheet of the sodium ion battery according to claim 1, It is characterized in that The negative electrode active layer includes a negative electrode binder, and the mass fraction of the negative electrode binder in the negative electrode active layer is 1% to 2%.

7. A sodium ion battery, It is characterized in that The invention comprises the negative electrode sheet as claimed in any one of claims 1 to 6, and further comprises a separator, a positive electrode sheet and an electrolyte.

8. A method for preparing a negative electrode sheet for a sodium ion battery, It is characterized in that At least: The negative electrode active material, the negative electrode conductive agent, the thickener and sodium deoxycholate are mixed and stirred, and then the negative electrode solvent is added and kneaded to obtain a negative electrode slurry precursor; Adding a negative electrode binder to the negative electrode slurry precursor to obtain a negative electrode slurry; The negative electrode slurry is coated on at least one side of the negative electrode current collector, and then dried to obtain a negative electrode sheet.

9. The method for preparing the negative electrode sheet according to claim 8, It is characterized in that The fineness of the negative electrode slurry is 10 μm to 20 μm.

10. The method for preparing the negative electrode sheet according to claim 8, It is characterized in that The coating density of the negative electrode slurry is 6.8 mg / cm 2 ~10.2mg / cm 2 .

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