Sodium battery positive electrode with conductive water absorption buffer structure and preparation method and application thereof

Abstract

The invention belongs to the field of sodium-ion batteries, and relates to a preparation method and application of a composite sodium-ion battery positive electrode with a water absorption buffer structure, the sodium-ion battery positive electrode comprises a metal current collector, a first positive electrode material layer, a conductive water absorption buffer layer and a second positive electrode material layer which are arranged in sequence; the conductive water absorption buffer layer contains a solid water absorbent and can absorb moisture in the positive electrode material layer, so that the influence of the moisture on the positive electrode material is avoided; the conductive water-absorbing buffer layer contains a large amount of conductive carbon, so that a network buffer structure can be formed, and volume expansion of the positive electrode material layer in the circulation process is relieved; the conductive water absorption buffer layer is located between the two positive electrode material layers and can absorb moisture of the upper layer and the lower layer at the same time, and the water absorption efficiency is improved; the sodium-ion battery assembled by the invention has relatively good moisture influence resistance and volume expansion influence resistance, has relatively high cycle stability, and has practical industrial application value.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries, and relates to a method for preparing a composite sodium ion battery positive electrode with a water absorption buffer structure and an application thereof, and specifically relates to a method for preparing a highly air-stable composite positive electrode with a water absorption buffer layer structure and a highly stable sodium ion battery comprising the composite positive electrode. Background Art

[0002] Lithium-ion batteries have been widely used in daily life due to their high energy density and high charge and discharge rate characteristics. However, the content of lithium in the earth's crust is only 0.0065%, and it faces the risk of depletion. Therefore, sodium-ion batteries came into being. The content of sodium in the earth's crust is as high as 2.74%, and it has similar physical and chemical properties to lithium. Therefore, sodium-ion batteries are considered to be a potential alternative to lithium-ion batteries.

[0003] However, the positive electrode materials of sodium-ion batteries are relatively sensitive to air, and the humidity requirements for assembly and application environments are relatively high. Unlike lithium-ion positive electrode materials, after the surface of sodium-ion positive electrode materials adsorb water molecules, the sodium ions inside the material exchange with the protons in the adsorbed water at a fast rate, inducing the precipitation of sodium ions in the material body, resulting in changes in the bulk crystal structure. During the preparation and use of sodium-ion batteries, due to environmental and seasonal factors, trace amounts of water will always be adsorbed, resulting in sodium-ion battery performance attenuation and inconsistency, hindering the further industrial application of sodium-ion batteries.

[0004] Therefore, it is urgent to develop a low-cost sodium-ion battery with a conductive water-absorbing buffer structure to improve the effect of moisture on the positive electrode of the sodium-ion battery and improve the water resistance and stability of the sodium-ion battery. Summary of the invention

[0005] The purpose of the present invention is to provide a sodium battery positive electrode with resistance to moisture, reduced volume expansion, stable cycle and high electrochemical stability in view of the deficiencies in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention is to provide a sodium battery positive electrode with a conductive water absorption buffer structure, comprising: a metal current collector, a first positive electrode material layer, a conductive water absorption buffer layer and a second positive electrode material layer arranged in sequence;

[0008] Wherein, the first positive electrode material layer and the second positive electrode material layer include: a sodium ion battery positive electrode material, a first conductive carbon and a first binder;

[0009] The conductive water-absorbing buffer layer includes: a water-absorbing agent, a second conductive carbon and a second adhesive.

[0010] Preferably, the metal current collector is selected from aluminum sheet, copper sheet or steel sheet.

[0011] Preferably, the sodium ion battery positive electrode material is a layered positive electrode material Na x At least one of MO2, polyanion material, and Prussian blue material.

[0012] More preferably, the layered cathode material Na x M in MO2 is at least one of Ni, Co, Mn, Fe, and Cu.

[0013] Preferably, the water absorbing agent comprises at least one of calcium oxide, calcium chloride and sodium hydroxide.

[0014] Preferably, the first conductive carbon comprises: at least one of carbon nanotubes, Super P, and KB;

[0015] The second conductive carbon includes at least one of carbon nanotubes, Super P, and KB.

[0016] Preferably, in the first positive electrode material layer and the second positive electrode material layer, the mass ratio of the sodium ion battery positive electrode material, the first conductive carbon and the first binder is 6-9.6:0.2-2:0.2-2; in the conductive water-absorbing buffer layer, the mass ratio of the water absorbent, the second conductive carbon and the second binder is 3-6:3-6:0.2-2.

[0017] The second aspect of the present invention is to provide a method for preparing the above-mentioned sodium battery positive electrode, the steps comprising:

[0018] S1, mixing the sodium ion battery positive electrode material, the first conductive carbon and the first binder to prepare a positive electrode slurry; applying the positive electrode slurry to one side of the metal current collector, and obtaining a single-layer electrode sheet consisting of the first positive electrode material layer and the metal current collector after drying;

[0019] S2, mixing the water absorbent, the second conductive carbon and the second binder to obtain a conductive water absorbent slurry; applying the conductive water absorbent slurry to one side of the first positive electrode material layer, and drying to obtain a double-layer electrode sheet consisting of the conductive water absorbent buffer layer, the first positive electrode material layer and the metal current collector;

[0020] S3, applying the positive electrode slurry in step S1 to one side of the conductive water-absorbing buffer layer, and obtaining the sodium battery positive electrode composed of the second positive electrode material layer, the conductive water-absorbing buffer layer, the first positive electrode material layer and the metal current collector after drying.

[0021] More preferably, the coating thickness of the positive electrode slurry is 20 μm-60 μm, and the coating thickness of the conductive water-absorbing slurry is 10 μm-50 μm.

[0022] More preferably, in step S1 to step S3, the drying temperature is 60°C-120°C.

[0023] The third aspect of the present invention is to provide an application of the above-mentioned sodium battery positive electrode in the preparation of a sodium ion secondary battery.

[0024] The fourth aspect of the present invention is to provide a sodium ion secondary battery, comprising: a sodium battery negative electrode, an electrolyte and a sodium battery positive electrode; wherein the sodium battery negative electrode comprises: at least one of a sodium sheet, hard carbon, a transition metal oxide, and a transition metal sulfide; the electrolyte comprises: at least one of an ester electrolyte and an ether electrolyte; and the sodium battery positive electrode is the above-mentioned sodium battery positive electrode.

[0025] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0026] (1) The conductive water-absorbing buffer layer contains a solid water-absorbing agent, which can absorb the moisture in the positive electrode material layer to prevent the moisture from affecting the positive electrode material.

[0027] (2) The conductive water-absorbing buffer layer contains a large amount of conductive carbon, which can form a network buffer structure to alleviate the volume expansion of the positive electrode material layer during the cycle.

[0028] (3) The conductive water-absorbing buffer layer is located between the two layers of positive electrode material and can absorb moisture from both layers at the same time, thereby improving the water absorption efficiency.

[0029] (4) The conductive water-absorbing buffer layer contains a large amount of conductive carbon and a network structure, which can quickly transmit electrons and ions and improve the battery rate performance.

[0030] (5) The sodium ion battery assembled in the present invention has good resistance to the influence of moisture and volume expansion, has high cycle stability, and has practical industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the basic structure of a positive electrode of a sodium battery in one embodiment of the present invention;

[0032] Figure 2 1 is a charge and discharge curve of a sodium ion secondary battery in one embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0036] Example 1

[0037] This embodiment provides a sodium ion secondary battery and a preparation method thereof, the steps comprising:

[0038] S1. Na2Fe2(SO4)3, carbon nanotubes (CNT), and binder PVDF are mixed in a mass ratio of 7:2:1, and stirred on a magnetic stirrer for 24 hours to fully mix the three materials to obtain a positive electrode slurry; the positive electrode slurry is applied on the surface of an aluminum foil with a scraper to a coating thickness of 60 μm, and vacuum dried at 80°C for 24 hours to obtain a single-layer electrode sheet consisting of the first positive electrode material layer and the metal current collector;

[0039] S2. Mix CaO solid water absorbent, CNT and PVDF in a mass ratio of 6:3:1, stir on a magnetic stirrer for 24 hours to fully mix the three materials to obtain a conductive water absorbent slurry; use a scraper to apply the conductive water absorbent slurry on one side of the first positive electrode material layer to a coating thickness of 40 μm, and vacuum dry at 80° C. for 24 hours to obtain a double-layer electrode sheet consisting of the conductive water absorbent buffer layer, the first positive electrode material layer and the metal current collector;

[0040] S3. Use a scraper to coat the positive electrode slurry in step S1 to one side of the conductive water-absorbing buffer layer with a coating thickness of 60 μm, and vacuum dry at 80° C. for 24 hours to obtain the sodium battery positive electrode composed of the second positive electrode material layer, the conductive water-absorbing buffer layer, the first positive electrode material layer and the metal current collector.

[0041] S4. The sodium battery positive electrode prepared in step S3 is used as the positive electrode, the hard carbon is used as the negative electrode, and the commercial sodium battery liquid electrolyte is used as the electrolyte to assemble a sodium ion battery.

[0042] The sodium ion battery was cycled at 2-4.5V to obtain a charge and discharge curve, such as Figure 2 As shown, it can be seen that the sodium ion battery has a higher specific capacity and an abnormal curve without the influence of moisture.

[0043] Example 2

[0044] This embodiment provides another sodium ion secondary battery and a preparation method thereof, the steps comprising:

[0045] S1, Na 0.67 Ni 0.33 Mn 0.677 O2, CNT, and PVDF are mixed in a mass ratio of 8:1:1, and stirred on a magnetic stirrer for 24 hours to fully mix the three materials to obtain a positive electrode slurry; the positive electrode slurry is coated on the surface of an aluminum foil with a scraper to a coating thickness of 50 μm, and vacuum dried at 80° C. for 24 hours to obtain a single-layer electrode sheet consisting of the first positive electrode material layer and the metal current collector;

[0046] S2, mixing CaCl2 solid water absorbent, CNT, and PVDF in a mass ratio of 5:4:1, stirring on a magnetic stirrer for 24 hours to fully mix the three materials to obtain a conductive water absorbent slurry; using a scraper to apply the conductive water absorbent slurry on one side of the first positive electrode material layer to a coating thickness of 30 μm, and vacuum drying at 80° C. for 24 hours to obtain a double-layer electrode sheet consisting of the conductive water absorbent buffer layer, the first positive electrode material layer, and the metal current collector;

[0047] S3. Use a scraper to coat the positive electrode slurry in step S1 to one side of the conductive water-absorbing buffer layer with a coating thickness of 60 μm, and vacuum dry at 80° C. for 24 hours to obtain the sodium battery positive electrode composed of the second positive electrode material layer, the conductive water-absorbing buffer layer, the first positive electrode material layer and the metal current collector.

[0048] S4, the sodium battery positive electrode prepared in step S3 is used as the positive electrode, the Na sheet is used as the negative electrode, and 1M NaPF6 (solvent: diethylene glycol dimethyl ether, C6H 14 O3) as the electrolyte and assembled into a sodium ion battery.

[0049] Comparative Example 1

[0050] This comparative example provides another sodium ion secondary battery, which does not contain a conductive water-absorbing buffer layer, and the remaining steps are the same as those of Example 1.

[0051] Comparative Example 2

[0052] This comparative example provides another sodium ion secondary battery, which does not contain a conductive water-absorbing buffer layer, and the remaining steps are the same as those of Example 2.

[0053] Detection Example

[0054] The sodium battery positive electrodes prepared in Examples 1-2 and Comparative Examples 1-2 were exposed to air for 2 hours and then transferred to the assembled sodium ion batteries in a dry environment for charge and discharge tests. The charge and discharge rate was 0.1C and the test temperature was 25°C. The test results are shown in Table 1.

[0055] Table 1

[0056]

[0057] From Table 1 and Figure 2 It can be seen that under normal air conditions, the sodium ion battery prepared using the sodium battery positive electrode of the present invention has the characteristics of anti-air sensitivity, absorption of internal moisture in the material, and relief of volume expansion, showing a high charge and discharge specific capacity and 99% Kunlun efficiency, indicating that the active material layer is not affected by moisture and volume expansion; Comparative Examples 1-2 do not have a conductive water-absorbing buffer layer, and due to the influence of moisture and volume expansion, the battery exhibits a low theoretical specific capacity and low coulombic efficiency; Compared with Comparative Examples 1-2, Examples 1-2 can avoid the influence of moisture on the positive electrode material, relieve the volume expansion of the positive electrode material layer during the cycle, and exhibit high specific capacity and coulombic efficiency; Examples 1 and 2 were tested twice, and it can be seen that the sodium battery positive electrode of the present invention has good consistency, and the prepared sodium ion batteries also exhibit high specific capacity and coulombic efficiency.

[0058] In summary, the conductive water-absorbing buffer layer introduced into the positive electrode of the sodium battery of the present invention contains a solid water-absorbing agent, a conductive carbon network buffer structure and a sandwich electrode structure, which can avoid the influence of moisture on the positive electrode material, alleviate the volume expansion of the positive electrode material layer during the cycle, and quickly transmit electrons and ions, thereby improving the air tolerance and electrochemical performance of the positive electrode of the sodium battery.

[0059] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A sodium battery positive electrode having a conductive water-absorbing buffer structure, characterized in that: include: A metal current collector, a first positive electrode material layer, a conductive water-absorbing buffer layer and a second positive electrode material layer are sequentially arranged; Wherein, the first positive electrode material layer and the second positive electrode material layer include: a sodium ion battery positive electrode material, a first conductive carbon and a first binder; The conductive water-absorbing buffer layer includes: a water-absorbing agent, a second conductive carbon and a second adhesive.

2. The sodium battery positive electrode according to claim 1, characterized in that: The metal current collector is selected from aluminum sheet, copper sheet or steel sheet.

3. The sodium battery positive electrode according to claim 1, characterized in that: The positive electrode material of the sodium ion battery is a layered positive electrode material Na x At least one of MO2, polyanion material, and Prussian blue material.

4. The sodium battery positive electrode according to claim 3, characterized in that: Layered cathode material Na x M in MO2 is at least one of Ni, Co, Mn, Fe, and Cu.

5. The sodium battery positive electrode according to claim 1, characterized in that: The water absorbing agent includes at least one of calcium oxide, calcium chloride and sodium hydroxide.

6. The sodium battery positive electrode according to claim 1, characterized in that: The first conductive carbon comprises: at least one of carbon nanotubes, Super P, and KB; The second conductive carbon includes at least one of carbon nanotubes, Super P, and KB.

7. The sodium battery positive electrode according to claim 1, characterized in that: In the first positive electrode material layer and the second positive electrode material layer, the mass ratio of the sodium ion battery positive electrode material, the first conductive carbon and the first binder is 6-9.6:0.2-2:0.2-2; in the conductive water-absorbing buffer layer, the mass ratio of the water absorbent, the second conductive carbon and the second binder is 3-6:3-6:0.2-2.

8. A method for preparing a positive electrode for a sodium battery according to any one of claims 1 to 7, characterized in that the steps include: S1, mixing the sodium ion battery positive electrode material, the first conductive carbon and the first binder to prepare a positive electrode slurry; applying the positive electrode slurry to one side of the metal current collector, and obtaining a single-layer electrode sheet consisting of the first positive electrode material layer and the metal current collector after drying; S2, mixing the water absorbent, the second conductive carbon and the second binder to obtain a conductive water absorbent slurry; applying the conductive water absorbent slurry to one side of the first positive electrode material layer, and drying to obtain a double-layer electrode sheet consisting of the conductive water absorbent buffer layer, the first positive electrode material layer and the metal current collector; S3, applying the positive electrode slurry in step S1 to one side of the conductive water-absorbing buffer layer, and obtaining the sodium battery positive electrode composed of the second positive electrode material layer, the conductive water-absorbing buffer layer, the first positive electrode material layer and the metal current collector after drying.

9. Use of the sodium battery positive electrode according to any one of claims 1 to 7 in the preparation of a sodium ion secondary battery.

10. A sodium ion secondary battery, characterized in that: include: A sodium battery negative electrode, an electrolyte and a sodium battery positive electrode; wherein the sodium battery negative electrode comprises: at least one of sodium sheet, hard carbon, transition metal oxide, and transition metal sulfide; the electrolyte comprises: at least one of an ester electrolyte and an ether electrolyte; the sodium battery positive electrode is the sodium battery positive electrode as described in any one of claims 1 to 7.

Images