A composite sodium supplement agent, its preparation method, and a positive electrode sheet for sodium-ion batteries.

Abstract

This invention belongs to the field of sodium-ion battery technology, specifically relating to a composite sodium replenishing agent, its preparation method, and a positive electrode sheet for sodium-ion batteries. The composite sodium replenishing agent provided by this invention includes a fully sacrificial sodium replenishing agent and a non-fully sacrificial sodium replenishing agent. The fully sacrificial sodium replenishing agent has a porous structure, and the non-fully sacrificial sodium replenishing agent is loaded within the porous structure of the fully sacrificial sodium replenishing agent. This invention uses a fully sacrificial sodium replenishing agent with a porous structure as a carrier, which provides structural support. Loading the non-fully sacrificial sodium replenishing agent within the porous structure of the fully sacrificial sodium replenishing agent not only improves the cycle life of the battery cell but also significantly reduces gas production, simplifying the application of sodium replenishing agents.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a composite sodium supplementing agent, a preparation method thereof and a sodium ion battery positive electrode sheet. BACKGROUND

[0002] With the rapid development of renewable energy and the increasing demand for electric vehicles, sodium ion batteries have become a potential battery technology that attracts much attention due to their abundant raw materials, low cost and environmental friendliness. At present, significant progress has been made in the development of electrode materials and electrolytes for sodium ion batteries. However, they still face some key problems in practical applications, such as low energy density and poor cycle life, mainly due to the irreversible consumption of sodium ions during the first charge-discharge process. Specifically, this loss is mainly caused by the reduction and decomposition of the electrolyte on the negative electrode surface to form a solid electrolyte interface (SEI) film, accompanied by the irreversible consumption of sodium ions.

[0003] To solve these problems, sodium compensation strategies have attracted widespread attention due to their simple operation and easy expansion. Adding a sodium supplementing agent to the positive electrode is the most direct and universal method for sodium supplementation, which can effectively compensate for the loss of SEI and improve the energy density and cycle life of sodium batteries.

[0004] Therefore, there is an increasing demand for a sodium supplementing agent with excellent performance. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the present application proposes a composite sodium supplementing agent that not only improves the cycle life of the battery cell, but also significantly reduces the amount of gas produced, reducing the difficulty of applying the sodium supplementing agent.

[0006] The composite sodium supplementing agent of the present application comprises a full-sacrificial sodium supplementing agent and a non-full-sacrificial sodium supplementing agent, wherein the full-sacrificial sodium supplementing agent has a pore structure, and the non-full-sacrificial sodium supplementing agent is loaded in the pores of the full-sacrificial sodium supplementing agent.

[0007] Optionally, the full-sacrificial sodium supplementing agent comprises at least one of Na2C6O6, Na2C6H2O6, CH3COONa, PABZ-Na, EDTA-4Na, DTPA-5Na, Na2C4O4, Na2C2O4 or Na2C3O5.

[0008] And / or, the chemical formula of the non-full-sacrificial sodium supplementing agent is Na x M y O zM comprises at least one of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti or V, wherein 1≤x≤7, 0

[0009] Optionally, the mass ratio of the full-sacrificial sodium supplement agent and the non-full-sacrificial sodium supplement agent is (50-95%):(5-50%);

[0010] And / or, the pore diameter of the full-sacrificial sodium supplement agent is 10-40 μm;

[0011] And / or, the particle size of the non-full-sacrificial sodium supplement agent is 3-30 μm.

[0012] It can be understood that, in order to enable the non-full-sacrificial sodium supplement agent to be loaded in the pore of the full-sacrificial sodium supplement agent, the particle size of the non-full-sacrificial sodium supplement agent needs to be smaller than the pore diameter of the full-sacrificial sodium supplement agent.

[0013] The application further provides a preparation method of the composite sodium supplement agent, comprising the following steps:

[0014] (1) mixing the full-sacrificial sodium supplement agent and a template solution, and then performing a hydrothermal reaction, and after the reaction, performing washing, drying, calcination and grinding treatment to obtain the full-sacrificial sodium supplement agent containing a pore structure;

[0015] (2) mixing the full-sacrificial sodium supplement agent containing a pore structure prepared in the step (1) and the non-full-sacrificial sodium supplement agent in an inert atmosphere by ball milling.

[0016] Optionally, in the step (1), the template comprises at least one of sodium chloride, potassium chloride, mesoporous carbon, carbon nanotube, carbon black, carbon nanofiber, polystyrene ball, CTAB or PEG;

[0017] And / or, in the step (1), the molar ratio of the template to the full-sacrificial sodium supplement agent is 1-10:90-99.

[0018] Optionally, in the step (1), the temperature of the hydrothermal reaction is 80-180 ℃, and the time of the hydrothermal reaction is 6-20 h;

[0019] And / or, the washing comprises washing 2-3 times by using anhydrous ethanol and deionized water respectively;

[0020] And / or, the temperature of the drying is 60-150 ℃;

[0021] And / or, the temperature of the calcination is 100 ℃-600 ℃, the time of the calcination is 2-6 h, the calcination is performed in a muffle furnace, and the heating rate of the muffle furnace is 1-20 ℃ / min.

[0022] Optionally, in the step (2), the speed of the ball milling is 100-800 r / min, and the time of the ball milling is 0.5-5 h. The ball milling can fill the non-full sacrificial sodium supplement into the channel of the sacrificial sodium supplement.

[0023] Optionally, in the step (2), the inert atmosphere is nitrogen, argon or helium.

[0024] The application further provides a sodium ion battery positive electrode sheet, which comprises a positive electrode active material, a conductive agent, a binder, the composite sodium supplement or the composite sodium supplement prepared by the method described above, and a current collector.

[0025] Optionally, the mass ratio of the positive electrode active material, the conductive agent, the binder and the composite sodium supplement is (87-99):(0.1-5):(0.1-4):(0.8-4).

[0026] Optionally, the conductive agent comprises at least one of Super P, Ketjen black, acetylene black carbon black, carbon nanotubes, graphene, conductive graphite, carbon fibers, conductive carbon nanotubes or ordered mesoporous carbon.

[0027] A sodium ion battery comprises a sodium ion battery positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet comprises a negative electrode active material, a negative electrode conductive agent, a negative electrode thickening agent and a negative electrode binder in a mass ratio of (90-99):(1-3):(1-4):(1-4). The negative electrode conductive agent comprises at least one of Super P, Ketjen black, acetylene black carbon black, carbon nanotubes, graphene, conductive graphite, carbon fibers, conductive carbon nanotubes or ordered mesoporous carbon.

[0028] The above-mentioned positive electrode active material, binder, negative electrode active material, negative electrode thickening agent, negative electrode binder, electrolyte, separator and the like are not limited in material selection, and any positive electrode active material, binder, negative electrode active material, negative electrode thickening agent, negative electrode binder, electrolyte, separator and the like known in the art can be used.

[0029] The composite sodium supplement and the preparation method thereof have the following technical effects:

[0030] (1) The full sacrificial sodium supplement with a channel structure is used as a carrier, which can play a structural support role, and the non-full sacrificial sodium supplement is loaded in the channel of the full sacrificial sodium supplement, which can not only improve the cycle life of the battery cell, but also significantly reduce the gas production, and reduce the application difficulty of the sodium supplement;

[0031] (2) Further limit the mass ratio of the full-sacrificial sodium supplement agent and the non-full-sacrificial sodium supplement agent, and the pore diameter and the particle size of the non-full-sacrificial sodium supplement agent, which can ensure that the non-full-sacrificial sodium supplement agent is more fully loaded in the pore channel of the full-sacrificial sodium supplement agent. After the full-sacrificial sodium supplement agent is decomposed, the structure is distorted and a hole appears. At this time, the non-full-sacrificial sodium supplement agent can provide structural support to avoid the appearance of holes in the pole piece. Because of the existence of the non-full-sacrificial sodium supplement agent (which does not produce gas during decomposition), the gas production is less than that of the full-sacrificial sodium supplement agent alone. If the amount of the full-sacrificial sodium supplement agent is too much, it will cause the entire composite sodium supplement agent to produce a large amount of gas during decomposition, which will cause safety risks. If the amount of the full-sacrificial sodium supplement agent is too small, there will be a large amount of decomposition products after the entire composite sodium supplement agent is decomposed, which will occupy the weight of the battery cell and affect the energy density of the battery cell.

[0032] (3) The preparation method of the composite sodium supplement agent of the present application can make the non-full-sacrificial sodium supplement agent fully loaded in the pore channel structure of the full-sacrificial sodium supplement agent, and the preparation method is simple and easy to operate, which is convenient for popularization and application in industrial production. The molar ratio of the template agent and the full-sacrificial sodium supplement agent is limited. If the amount of the template agent is too much, it may accumulate in the pore channel, causing the pore diameter to shrink or the pore channel to be blocked. The template agent needs to be removed by calcination, solvent extraction or other methods. Excessive amount will cause residual risk (such as carbonization residue during calcination) or increase the number of washing times, affecting the purity of the product. At the same time, it will also cause the cost to increase. If the amount of the template agent is too small, it will cause uneven pore size distribution, or even unable to form regular pore channels.

[0033] (4) The composite sodium supplement agent is used in the positive pole piece of the sodium ion battery. During the charging process of the battery, the sodium supplement agent is decomposed to release active sodium ions to supplement sodium for the sodium ion battery, which can compensate for the loss of irreversible sodium during the first charge and discharge, and improve the capacity and cycle life of the sodium ion battery. DETAILED DESCRIPTION

[0034] The embodiments of the present application will be described in detail below. The embodiments are exemplary and are intended to explain the present application, but cannot be understood as a limitation of the present application.

[0035] The composite sodium supplement agent of the embodiment of the present application comprises a full-sacrificial sodium supplement agent and a non-full-sacrificial sodium supplement agent. The full-sacrificial sodium supplement agent has a pore channel structure, and the non-full-sacrificial sodium supplement agent is loaded in the pore channel of the full-sacrificial sodium supplement agent.

[0036] Fully sacrificial sodium replenishers refer to substances that release sodium into the battery through an irreversible electrochemical reaction to compensate for sodium loss during battery cycling. These substances cannot participate in the reversible charge-discharge process after the reaction; they have no decomposition products but produce a large amount of gas during decomposition. Non-fully sacrificial sodium replenishers, on the other hand, replenish sodium ions through a partially reversible electrochemical reaction. Their structure retains the ability to reversibly participate in charge-discharge after the reaction; these substances produce decomposition products, but produce almost no gas during decomposition.

[0037] In some embodiments, the sacrificial sodium supplement may optionally include at least one of Na2C6O6 (sodium roserin), Na2C6H2O6 (disodium tetrahydroxy-1,4-benzoquinone), CH3COONa (sodium acetate), PABZ-Na (sodium p-aminobenzoate), EDTA-4Na (tetrasodium ethylenediaminetetraacetate), DTPA-5Na (sodium diethylenetriaminepentaacetate), Na2C4O4 (sodium squartzate), Na2C2O4 (sodium oxalate), or Na2C3O5 (sodium acetone).

[0038] And / or, the chemical formula of the non-sacrificial sodium supplement is Na x M y O z M includes at least one of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, or V, wherein 1 ≤ x ≤ 7, 0 < y ≤ 1, and 2 ≤ z ≤ 8. Further optionally, the non-sacrificial sodium supplement includes at least one of Na2NiO2 (sodium nickelate), Na5FeO4 (sodium ferrite), Na6CoO4 (sodium cobaltate), or NaCrO2 (sodium chromate).

[0039] In some embodiments, optionally, the mass ratio of the sacrificial sodium supplement to the non-sacrificial sodium supplement is (50~95%):(5~50%), for example, 50%:50%, 60%:40%, 70%:30%, 80%:20%, 90%:10%, or 95%:5%, etc.

[0040] And / or, the pore diameter of the sacrificial sodium supplement is 10~40 μm, for example 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, etc.;

[0041] And / or, the particle size of the non-total sacrificial sodium supplement is 3~30 μm, for example 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 24 μm, 27 μm, 30 μm. It is understood that, in order for the non-total sacrificial sodium supplement to be loaded within the pores of the total sacrificial sodium supplement, the particle size of the non-total sacrificial sodium supplement needs to be smaller than the pore diameter of the total sacrificial sodium supplement.

[0042] This invention also provides a method for preparing a compound sodium supplement, comprising the following steps:

[0043] (1) The sacrificial sodium supplement and the template agent solution are mixed and subjected to hydrothermal reaction. After the reaction is completed, the mixture is washed, dried, calcined and ground to obtain a sacrificial sodium supplement containing a porous structure.

[0044] (2) The fully sacrificial sodium supplement with a porous structure and the non-fully sacrificial sodium supplement obtained in step (1) are ball-milled and mixed under an inert atmosphere.

[0045] In some embodiments, optionally, in step (1), the template agent includes at least one of sodium chloride, potassium chloride, mesoporous carbon, carbon nanotubes, carbon black, carbon nanofibers, polystyrene spheres, CTAB (hexadecyltrimethylammonium bromide) or PEG (polyethylene glycol);

[0046] And / or, in step (1), the molar ratio of the template agent to the sacrificial sodium supplement is 1~10:90~99, for example 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91, 10:90, etc.

[0047] In some embodiments, optionally, in step (1), the temperature of the hydrothermal reaction is 80~180℃, for example 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, etc., and the time of the hydrothermal reaction is 6~20h, for example 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, etc.;

[0048] And / or, the washing includes washing 2 to 3 times with anhydrous ethanol and deionized water respectively;

[0049] And / or, the drying temperature is 60~150℃, for example 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc.;

[0050] And / or, the calcination temperature is 100℃~600℃, for example 100℃, 200℃, 300℃, 400℃, 500℃, 600℃, etc., and the calcination time is 2~6h; the calcination is carried out in a muffle furnace, and the heating rate of the muffle furnace is 1~20℃ / min, for example 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min, 20℃ / min, etc.

[0051] In some embodiments, optionally, in step (2), the ball milling speed is 100~800 r / min, for example 100r / min, 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, 800r / min, etc., and the ball milling time is 0.5~5h, for example 0.5h, 1h, 2h, 3h, 4h, 5h, etc.

[0052] In some embodiments, optionally, in step (2), the inert atmosphere is nitrogen, argon or helium.

[0053] This invention also provides a sodium-ion battery positive electrode sheet, comprising a positive electrode active material, a conductive agent, a binder, the aforementioned composite sodium supplement agent or the composite sodium supplement agent prepared by the aforementioned preparation method, and a current collector.

[0054] In some embodiments, optionally, the mass ratio of the positive electrode active material, conductive agent, binder and composite sodium supplement is (87-99):(0.1-5):(0.1-4):(0.8-4).

[0055] In some embodiments, the conductive agent may optionally include at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes, or ordered mesoporous carbon.

[0056] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder in a mass ratio of (90-99):(1-3):(1-4):(1-4). The negative electrode conductive agent includes at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes, or ordered mesoporous carbon.

[0057] The selection of the above-mentioned positive electrode active material, binder, negative electrode active material, negative electrode thickener, negative electrode binder, electrolyte, separator, etc. is not limited, and they can all be any positive electrode active material, binder, negative electrode active material, negative electrode thickener, negative electrode binder, electrolyte, separator, etc. known in the art.

[0058] The technical effects of the compound sodium supplement and its preparation method of the present invention are as follows:

[0059] (1) Using a fully sacrificial sodium supplement with a pore structure as a carrier can play a structural support role. Loading a non-fully sacrificial sodium supplement in the pores of the fully sacrificial sodium supplement can not only improve the cycle life of the battery cell, but also significantly reduce the gas production, thus reducing the difficulty of applying the sodium supplement.

[0060] (2) Further limiting the mass ratio of the fully sacrificial sodium supplement and the non-fully sacrificial sodium supplement, as well as the pore diameter and particle size of the non-fully sacrificial sodium supplement, can ensure that the non-fully sacrificial sodium supplement is more fully loaded in the pores of the fully sacrificial sodium supplement. After the fully sacrificial sodium supplement decomposes, the structure becomes distorted and pores appear. At this time, the non-fully sacrificial sodium supplement can provide structural support to avoid pores appearing on the electrode. Because of the presence of the non-fully sacrificial sodium supplement (which does not produce gas after decomposition), the gas production is smaller than that of adding the fully sacrificial sodium supplement alone. If the amount of the fully sacrificial sodium supplement is too large, it will cause the decomposition of the entire composite sodium supplement to produce a large amount of gas, which will cause safety risks. If the amount of the fully sacrificial sodium supplement is too small, a large amount of decomposition products will exist after the entire composite sodium supplement decomposes, occupying the weight of the cell and affecting the energy density of the cell.

[0061] (3) The preparation method of the composite sodium supplement of the present invention enables the non-sacrificial sodium supplement to be fully loaded in the pore structure of the sacrificial sodium supplement, and the preparation method is simple and easy to operate, which is convenient for promotion and application in industrial production; and the molar ratio of template agent to sacrificial sodium supplement is limited. If the amount of template agent is too much, it may accumulate in the pores, resulting in pore size reduction or pore blockage. The template agent needs to be removed by calcination, solvent extraction and other methods. Excessive amount will lead to residual risk (such as carbonization residue during calcination) or increase the number of washing times, affecting the purity of the product; it will also lead to increased cost; if the amount of template agent is too little, it will lead to uneven pore size distribution, or even failure to form regular pores;

[0062] (4) The composite sodium replenishing agent is used in the positive electrode of the sodium-ion battery. During the battery charging process, the sodium replenishing agent decomposes and releases active sodium ions to replenish sodium for the sodium-ion battery, thereby making up for the irreversible sodium loss during the first charge and discharge and improving the capacity and cycle life of the sodium-ion battery.

[0063] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0064] Example 1

[0065] (1) Add sodium squartz (Na2C4O4) to a 0.1 mol / L CTAB solution and control the molar ratio of CTAB to sodium squartz to be 1:20 to form a mixture;

[0066] (2) The mixture obtained in (1) is transferred into a hydrothermal reactor lined with polytetrafluoroethylene and heated to 120°C at 5°C / min for 12 hours.

[0067] (3) After the hydrothermal reaction is completed, the reactor is naturally cooled. The reacted material is centrifuged, and the solid precipitate is taken out and washed twice with anhydrous ethanol and deionized water, respectively.

[0068] (4) Vacuum dry at 80℃ for 6h, grind into powder, then transfer the powder to a muffle furnace and calcine at 400℃ for 2h at a heating rate of 5℃ / min to remove the template agent;

[0069] (5) Grind into powder again to obtain Na2C4O4 powder with a porous structure and a pore diameter of 20μm;

[0070] (6) Na2C4O4 powder with a porous structure and Na2NiO2 are ball-milled at a mass ratio of 80:20. The mixture is ball-milled for 2 hours at a speed of 100 r / min under a nitrogen atmosphere. The D50 of Na2NiO2 is about 15 μm, and the composite sodium supplement Na2C4O4@Na2NiO2 is obtained.

[0071] The positive electrode active material Na4Fe3(PO4)2P2O7, the conductive agent Super P, the binder PVDF, and the composite sodium supplement agent Na2C4O4@Na2NiO2 are mixed in a mass percentage of 94%:2%:1%:3% until the system is homogeneous to obtain the positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet is obtained.

[0072] Example 2

[0073] The preparation method of this embodiment is the same as that of Example 1, except that Na2NiO2 in step (6) is replaced with Na5FeO4, and the D50 of Na5FeO4 is about 12μm, so as to obtain the composite sodium supplement Na2C4O4@Na5FeO4.

[0074] Example 3

[0075] (1) Add sodium oxalate (Na2C2O4) to 0.1 mol / L CTAB solution and control the molar ratio of CTAB to sodium oxalate to 1:20 to form a mixture;

[0076] (2) The mixture obtained in (1) is transferred into a hydrothermal reactor lined with polytetrafluoroethylene and heated to 120°C at 5°C / min for 12 hours.

[0077] (3) After the hydrothermal reaction is completed, the reactor is naturally cooled. The reacted material is centrifuged, and the solid precipitate is removed and washed three times with anhydrous ethanol and deionized water, respectively.

[0078] (4) Vacuum dry at 80℃ for 6h, grind into powder, then transfer the powder to a muffle furnace and calcine at 400℃ for 2h at a heating rate of 5℃ / min to remove the template agent.

[0079] (5) Grind into powder again to obtain Na2C2O4 powder with a porous structure and a pore diameter of 18μm;

[0080] (6) Na2C2O4 powder with a porous structure and Na2NiO2 are ball-milled at a mass ratio of 80:20. The mixture is ball-milled for 2 hours at a speed of 100 r / min under a nitrogen atmosphere. The D50 of Na2NiO2 is about 15 μm. The composite sodium supplement Na2C2O4@Na2NiO2 is obtained.

[0081] The positive electrode active material Na4Fe3(PO4)2P2O7, the conductive agent Super P, the binder PVDF, and the composite sodium supplement agent Na2C2O4@Na2NiO2 are mixed in a mass percentage of 94%:2%:1%:3% until the system is homogeneous to obtain the positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet is obtained.

[0082] Example 4

[0083] The preparation method of this embodiment is the same as that of Example 3, except that in step (6), Na2NiO2 is replaced with Na5FeO4, and the D50 of Na5FeO4 is about 12μm, so as to obtain the composite sodium supplement Na2C2O4@Na5FeO4.

[0084] Example 5

[0085] The preparation method of this embodiment is the same as that of Example 1, except that the mass ratio of Na2C4O4 to Na2NiO2 in step (6) is 95:5.

[0086] Example 6

[0087] The preparation method of this embodiment is the same as that of Example 1, except that the calcination temperature in step (4) is changed to 600℃ for 2h, and the rest of the experimental conditions remain unchanged. At this time, the diameter of the pores of the Na2C4O4 powder is 18μm.

[0088] Example 7

[0089] The preparation method of this embodiment is the same as that of Example 1, except that the calcination temperature in step (4) is changed to 400℃ for 6h, and the rest of the experimental conditions remain unchanged. At this time, the diameter of the pores of the Na2C4O4 powder is 17μm.

[0090] Comparative Example 1

[0091] In this comparative example, no sodium supplement is added to the positive electrode sheet. The positive electrode active material Na4Fe3(PO4)2P2O7, the conductive agent Super P, and the binder PVDF are mixed in a mass ratio of 97%:2%:1% until the system is homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry is uniformly coated on the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet is obtained.

[0092] Comparative Example 2

[0093] In this comparative example, sodium supplement Na2C4O4 was added separately to the positive electrode sheet. The positive active material Na4Fe3(PO4)2P2O7, conductive agent Super P, binder PVDF, and sodium supplement Na2C4O4 were mixed in a mass ratio of 94%:2%:1%:3% until the system was homogeneous, thus obtaining the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet was obtained.

[0094] Comparative Example 3

[0095] In this comparative example, sodium supplement Na2NiO2 was added separately to the positive electrode sheet. The positive electrode active material Na4Fe3(PO4)2P2O7, conductive agent Super P, binder PVDF, and sodium supplement Na2NiO2 were mixed in a mass ratio of 94%:2%:1%:3% until the system was homogeneous, thus obtaining the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet was obtained.

[0096] Comparative Example 4

[0097] In this comparative example, sodium supplement Na5FeO4 was added separately to the positive electrode sheet. The positive electrode active material Na4Fe3(PO4)2P2O7, conductive agent Super P, binder PVDF, and sodium supplement Na5FeO4 were mixed in a mass ratio of 94%:2%:1%:3% until the system was homogeneous, thus obtaining the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the sodium-ion battery positive electrode sheet was obtained.

[0098] Comparative Example 5

[0099] The composite sodium supplement in the positive electrode of this comparative example is obtained by directly mixing Na2C4O4 and Na2NiO2, which have no porous structure, at a mass ratio of 80:20. The preparation process of the positive electrode is the same as that in Example 1.

[0100] The positive and negative electrode sheets prepared in Examples 1-7 and Comparative Examples 1-5 were assembled, electrolyte was added, and cycle performance was tested in a Land CT2001A testing system within a reasonable voltage range. The specific test method was as follows: Charging method: After standing for 10 minutes, constant current charging was performed at 0.02C with a cutoff voltage of 2.0V, followed by standing for 10 minutes. Then, constant current charging was performed at 0.1C to 3.4V, followed by standing for 10 minutes. Finally, constant current and constant voltage charging was performed at 0.05C to 4.3V, with a cutoff current of 0.02C to obtain the charging capacity. Discharging method: The full cell was discharged at 0.05C to 1.5V to obtain the first-cycle discharge capacity. Cyclic performance test: The 1C / 1C cycle performance was tested within the voltage range of 1.5V-3.4V at room temperature. The results are shown in Table 1.

[0101] Table 1

[0102]

[0103] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0104] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a complexed sodium supplement, characterized by, The method comprises the following steps: (1) mixing a full-sacrificial sodium supplement and a template solution, and then performing a hydrothermal reaction, and then performing washing, drying, calcination and grinding to obtain a full-sacrificial sodium supplement with a pore structure; (2) mixing the full-sacrificial sodium supplement with a pore structure obtained in step (1) and a non-full-sacrificial sodium supplement in an inert atmosphere by ball milling; The composite sodium supplement prepared by the preparation method comprises a full-sacrificial sodium supplement and a non-full-sacrificial sodium supplement, the full-sacrificial sodium supplement has a pore structure, and the non-full-sacrificial sodium supplement is loaded in the pores of the full-sacrificial sodium supplement; the mass ratio of the full-sacrificial sodium supplement to the non-full-sacrificial sodium supplement is (50-95):(5-50).

2. The method of claim 1, wherein the sodium supplement is prepared by, The full-sacrificial sodium supplement comprises at least one of Na2C6O6, Na2C6H2O6, CH3COONa, PABZ-Na, EDTA-4Na, DTPA-5Na, Na2C4O4, Na2C2O4 or Na2C3O5; and / or, the non-full sacrificial sodium supplement has a chemical formula of Na x M y O z M includes at least one of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, or V, wherein 1≤x≤7, 0 3. The method for producing a complex sodium supplement according to claim 1 or 2, characterized by, The pore diameter of the full-sacrificial sodium supplement is 10-40 μm; And / or, the particle size of the non-full-sacrificial sodium supplement is 3-30 μm.

4. The method of claim 1, wherein the sodium-replenishing composite is prepared by the steps of: In step (1), the template comprises at least one of sodium chloride, potassium chloride, mesoporous carbon, carbon nanotubes, carbon black, carbon nanofibers, polystyrene balls, CTAB or PEG; And / or, in step (1), the molar ratio of the template to the full-sacrificial sodium supplement is 1-10:90-99.

5. The method of claim 1 or 4, wherein the sodium supplement is prepared by, In step (1), the temperature of the hydrothermal reaction is 80-180 ℃, and the time of the hydrothermal reaction is 6-20 h; And / or, the washing comprises washing 2-3 times with anhydrous ethanol and deionized water, respectively; And / or, the temperature of the drying is 60-150 ℃; And / or, the temperature of the calcination is 100 ℃-600 ℃, the time of the calcination is 2-6 h, the calcination is performed in a muffle furnace, and the heating rate of the muffle furnace is 1-20 ℃ / min.

6. The method of claim 1, wherein the sodium-replenishing composite is prepared by the steps of: In step (2), the speed of the ball milling is 100-800 r / min, and the time of the ball milling is 0.5-5 h.

7. A sodium-ion battery positive electrode sheet, characterized by, The positive electrode active material, the conductive agent, the binder and the composite sodium supplement have a mass ratio of (87-99):(0.1-5):(0.1-4):(0.8-4).

8. The sodium-ion battery cathode electrode sheet of claim 7, wherein, The conductive agent comprises at least one of Super P, Ketjen black, acetylene black carbon black, carbon nanotubes, graphene, conductive graphite, carbon fibers, conductive carbon nanotubes or ordered mesoporous carbon.

9. The sodium-ion battery cathode electrode of claim 7 or 8, wherein, ​

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