Composite positive electrode material and preparation method thereof, positive plate and battery

Abstract

In order to solve the problem that an existing sodium ion battery positive electrode material is poor in stability, the invention provides a composite positive electrode material and a preparation method thereof, a positive plate and a battery, the composite positive electrode material comprises a sodium positive electrode material and a coating layer, the coating layer contains a phosphate group and conductive carbon, the coating layer comprises a compact layer and a porous layer, and the porous layer is a porous layer. The surface of the sodium positive electrode material is coated with the compact layer, the surface of the compact layer is coated with the porous layer, and the conductive carbon and the phosphate groups are uniformly distributed in the compact layer and the porous layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a composite positive electrode material and a preparation method thereof, a positive electrode sheet, and a battery. Background Art

[0002] Due to the constraints of traditional fossil energy shortages and energy security, as well as the growing awareness of ecological and environmental protection, the sustainable development and storage of energy have received high attention worldwide. Among various energy storage systems, electrochemical energy storage systems (EES) are considered an effective method for balancing the cyclic characteristics of renewable energy due to their long service life, low cost, low investment, and easy installation. Secondary battery energy storage in electrochemical energy storage holds great potential. Among them, lithium-ion batteries dominate the energy storage market due to their high theoretical specific capacity and energy density. However, due to the limited and uneven distribution of lithium (Li) resources and the multifaceted consumption of lithium, and subject to objective factors such as lithium extraction technology, geographical environment, and transportation conditions, lithium resources in the power battery field remain a bottleneck. To alleviate this problem, it is currently proposed to replace lithium with abundant elements such as sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), and calcium (Ca) to prepare a new generation of low-cost, environmentally friendly secondary ion batteries. Sodium-ion batteries have attracted increasing attention and support from countries around the world.

[0003] Sodium-based layered oxide cathode material is one of the most critical materials for sodium-ion batteries, but existing sodium cathode materials are usually easily corroded by the electrolyte, resulting in structural decay and surface side reactions, which makes them less stable and leads to reduced battery cycle performance. Summary of the Invention

[0004] In response to the problem of poor stability of the positive electrode materials of existing sodium ion batteries, the present invention provides a composite positive electrode material and a preparation method thereof, a positive electrode sheet, and a battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows: In a first aspect, the present invention provides a composite positive electrode material, comprising a sodium positive electrode material and a coating layer, wherein the coating layer contains phosphate groups and conductive carbon, the coating layer comprises a dense layer and a porous layer, the dense layer is coated on the surface of the sodium positive electrode material, the porous layer is coated on the surface of the dense layer, and the conductive carbon and the phosphate groups are uniformly distributed in the dense layer and the porous layer.

[0006] Optionally, the density of the dense layer is 1.2-1.9 g / cm 3 , and / or, the porosity of the porous layer is 40%-70%.

[0007] Optionally, the thickness of the dense layer is 5-40 nm; the thickness of the porous layer is 10-20 nm; And / or, the mass content of the coating layer in the composite positive electrode material is 2.5%-5.0%.

[0008] In a second aspect, the present invention further provides a method for preparing the composite positive electrode material as described in any one of the above, comprising the following steps: Obtaining a sodium cathode material, a first organic phosphate solution, and a second organic phosphate solution; adding the sodium cathode material to the first organic phosphate solution to react, and then centrifuging and drying to obtain a primary coated sodium cathode material; adding the primary coated sodium cathode material to the second organic phosphate solution for dispersion to obtain a dispersion, and spray drying the dispersion to obtain a secondary coated sodium cathode material; The secondary coated sodium positive electrode material is calcined to obtain a composite positive electrode material.

[0009] Optionally, the mass concentration of the first organophosphate solution is 5%-10%, and the mass concentration of the second organophosphate is 10%-20%.

[0010] Optionally, the average particle size of the organic phosphate in the first organic phosphate is 5-50 nm, and the average particle size of the organic phosphate in the second organic phosphate is 50-200 nm.

[0011] Optionally, the mass ratio of the organic phosphate to the sodium positive electrode material in the first organic phosphate solution is 0.001-0.15, and the mass ratio of the organic phosphate to the initially coated sodium positive electrode material in the second organic phosphate solution is 0.05-0.2.

[0012] Optionally, the spray drying temperature is 200-400°C, and / or the calcination temperature is 500-700°C.

[0013] Optionally, the organic phosphates in the first organic phosphate solution and the second organic phosphate solution independently include at least one of sodium phytate, magnesium phytate, iron phytate, potassium phytate, barium phytate, copper phytate, calcium phytate, zinc phytate, and cobalt phytate.

[0014] In a third aspect, the present invention also provides a positive electrode sheet comprising a current collector and an active material layer arranged on at least one side of the current collector, wherein the active material layer comprises a composite positive electrode material as described in any one of the above items, or a composite positive electrode material prepared by a preparation method of a composite positive electrode material as described in any one of the above items.

[0015] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet as described above.

[0016] In the present invention, the coating layer has a composite coating structure with an inner dense layer and an outer porous layer. The dense layer can effectively isolate the air, improve the air stability of the material, inhibit the corrosion of the electrolyte, and reduce the interface side reaction. The porous layer enhances the mechanical buffering effect, can better protect the integrity of the electrode structure, and improve the battery cycle life. At the same time, the phosphate groups (PO4 3- ) can form strong covalent bonds with transition metals (such as Ni, Fe, and Mn) on the surface of the cathode material, not only inhibiting electrolyte corrosion and transition metal dissolution, but also forming a coating layer with both ionic and electronic conductivity through the phosphate groups and conductive carbon. Furthermore, the phosphate groups preferentially react with free acids (such as HF) in the electrolyte to form a stable NaPO4-F composite interface layer, further reducing transition metal dissolution and enhancing the stability of the electrode-electrolyte interface, significantly improving the overall performance of sodium-ion batteries. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] One embodiment of the present invention provides a composite positive electrode material, comprising a sodium positive electrode material and a coating layer, wherein the coating layer contains phosphate groups and conductive carbon, the coating layer comprising a dense layer and a porous layer, the dense layer coating the surface of the sodium positive electrode material, the porous layer coating the surface of the dense layer, and the conductive carbon and the phosphate groups are evenly distributed in the dense layer and the porous layer.

[0019] In this embodiment, the coating layer has a composite coating structure with an inner dense layer and an outer porous layer. The dense layer can effectively isolate the air, improve the air stability of the material, inhibit the corrosion of the electrolyte, and reduce the interface side reaction. The porous layer enhances the mechanical buffering effect, can better protect the integrity of the electrode structure, and improve the battery cycle life. At the same time, the phosphate groups (PO4 3- ) can form strong covalent bonds with transition metals (such as Ni, Fe, and Mn) on the surface of the cathode material, not only inhibiting electrolyte corrosion and transition metal dissolution, but also forming a coating layer with both ionic and electronic conductivity through the phosphate groups and conductive carbon. Furthermore, the phosphate groups preferentially react with free acids (such as HF) in the electrolyte to form a stable NaPO4-F composite interface layer, further reducing transition metal dissolution and enhancing the stability of the electrode-electrolyte interface, significantly improving the overall performance of sodium-ion batteries.

[0020] In some embodiments, the density of the dense layer is 1.2-1.9 g / cm 3 , and / or the porosity of the porous layer is 40%-70%. By limiting the density of the dense layer and the porosity of the porous layer to the above ranges, the dense layer can effectively isolate the air and inhibit electrolyte corrosion, and the porous layer provides an effective mechanical buffer for the sodium positive electrode material.

[0021] Specifically, the density of the dense layer includes but is not limited to 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.8 g / cm 3 or 1.9 g / cm 3 The porosity of the porous layer includes, but is not limited to, 40%, 43%, 46%, 49%, 52%, 55%, 58%, 61%, 64%, 67% or 70%.

[0022] In some embodiments, the thickness of the dense layer is 5-40 nm, and the thickness of the porous layer is 10-20 nm. By gradient-designing the thickness of the dense layer and the porous layer, the air stability of the composite cathode material is better guaranteed, and the ionic conductivity and electronic conductivity of the composite cathode material are also guaranteed.

[0023] Specifically, the thickness of the dense layer includes but is not limited to 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm, 17 nm, 20 nm, 23 nm, 26 nm, 29 nm, 32 nm, 35 nm, 38 nm or 40 nm. The thickness of the porous layer includes but is not limited to 10 nm, 12 nm, 14 nm, 16 nm, 18 nm or 20 nm.

[0024] In some embodiments, the mass content of the coating layer in the composite positive electrode material is 2.5%-5.0%. By limiting the mass content of the coating layer in the composite positive electrode material layer and further limiting the thickness of the coating layer, the composite positive electrode material can have good air stability, ionic conductivity, and electronic conductivity.

[0025] An embodiment of the present invention further provides a method for preparing the composite positive electrode material as described above, comprising the following steps: Obtaining a sodium cathode material, a first organic phosphate solution, and a second organic phosphate solution; adding the sodium cathode material to the first organic phosphate solution to react, and then centrifuging and drying to obtain a primary coated sodium cathode material; adding the primary coated sodium cathode material to the second organic phosphate solution for dispersion to obtain a dispersion, and spray drying the dispersion to obtain a secondary coated sodium cathode material; The secondary coated sodium positive electrode material is calcined to obtain a composite positive electrode material.

[0026] In this embodiment, centrifugation allows the first organic phosphate to be more densely coated on the surface of the sodium cathode material, forming a dense layer during the subsequent calcination process. During the secondary coating, spray drying is used to form a porous layer on the primary coated sodium cathode material. By calcining the secondary coated sodium cathode material, the organic phosphate in the coating layer converts into Na3PO4 and carbon, forming a composite coating layer with both ionic and electronic conductivity.

[0027] Specifically, the first organic phosphate solution and the second organic phosphate solution are prepared by dissolving organic phosphate in a mixed solution of deionized water and anhydrous ethanol (volume ratio 1:1), and uniformly dispersing by ultrasonication to obtain the organic phosphate solution.

[0028] Furthermore, the sodium cathode material is pretreated before coating, and the pretreatment steps are: putting the sodium cathode material into a mortar and grinding it for 30-60 minutes to make its particles evenly dispersed.

[0029] In some embodiments, the mass concentration of the first organophosphate solution is 5%-10%, and the mass concentration of the second organophosphate is 10%-20%. Using the first organophosphate at this mass concentration during the initial coating ensures uniform coating of the sodium cathode material and forms a dense layer after calcination. During the secondary coating, increasing the mass concentration of the second organophosphate solution creates an enhanced coverage on the surface of the initially coated sodium cathode material.

[0030] In some embodiments, the average particle size of the organic phosphate in the first organic phosphate is 5-50 nm, and the average particle size of the organic phosphate in the second organic phosphate is 50-200 nm. By using the above-mentioned gradient design for the particle size of the organic phosphate, a dense layer and a porous layer are formed on the surface of the sodium cathode material.

[0031] Specifically, the average particle size of the organophosphate in the first organophosphate includes, but is not limited to, 5 nm, 9 nm, 13 nm, 17 nm, 21 nm, 25 nm, 29 nm, 33 nm, 37 nm, 41 nm, 45 nm, 49 nm, or 50 nm. The average particle size of the organophosphate in the second organophosphate includes, but is not limited to, 50 nm, 54 nm, 58 nm, 62 nm, 66 nm, 70 nm, 74 nm, 78 nm, 82 nm, 86 nm, 90 nm, 94 nm, 98 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm.

[0032] In some embodiments, the mass ratio of the organophosphate to the sodium cathode material in the first organophosphate solution is 0.001-0.15, and the mass ratio of the organophosphate to the initially coated sodium cathode material in the second organophosphate solution is 0.05-0.2. By limiting the mass ratio of the organophosphate to the product to be coated, the uniformity of the dense layer and the porous layer is ensured, and the thickness of the dense layer and the porous layer is regulated.

[0033] In some embodiments, the spray drying temperature is 200-400° C., and / or the calcination temperature is 500-700° C. By regulating the spray drying temperature, the porosity of the porous layer can be regulated.

[0034] In some embodiments, the organophosphates in the first and second organophosphate solutions each independently include at least one of sodium phytate, magnesium phytate, iron phytate, potassium phytate, barium phytate, copper phytate, calcium phytate, zinc phytate, and cobalt phytate. The use of these organophosphates as the coating layer ensures both ionic and electronic conductivity of the coating layer after calcination, while also ensuring that the conductive carbon and phosphate groups are evenly distributed in the dense layer and the porous layer.

[0035] One embodiment of the present invention also provides a positive electrode sheet, including a current collector and an active material layer arranged on at least one side of the current collector, the active material layer including the composite positive electrode material as described in any one of the above items, or a composite positive electrode material prepared by the preparation method of the composite positive electrode material as described in any one of the above items.

[0036] An embodiment of the present invention provides a battery, comprising the positive electrode sheet as described above.

[0037] The present invention is further described below with reference to the following examples.

[0038] It should be noted that, although only sodium phytate is used as the phosphate in the following examples, other organic phosphates listed in the above description can produce similar coating effects.

[0039] Example 1 This embodiment is used to illustrate the composite positive electrode material and its preparation method, positive electrode sheet, and battery disclosed in the present invention.

[0040] Composite cathode materials The sodium cathode material was placed in an agate mortar and ground for 30-60 minutes to uniformly disperse the particles. The ground material was then added to a sodium phytate solution having a mass concentration of 10% to obtain a mixed solution. The mass ratio of sodium phytate to sodium cathode material was 0.1.

[0041] The mixed solution was placed on a magnetic stirrer, stirred and reacted at 40° C. for 7 h, then centrifuged, washed, and dried for 18 h to obtain a sodium positive electrode material coated with a sodium phytate inner layer.

[0042] The sodium cathode material coated with an inner layer of sodium phytate was added to a 15% sodium phytate solution, with a mass ratio of sodium phytate to the inner layer of sodium phytate-coated sodium cathode material of 0.1, and stirred to form a uniform dispersion. The dispersion was spray-dried to form a porous outer layer of sodium phytate coating on the surface of the material, thereby obtaining a gradient-coated sodium cathode material.

[0043] The gradient coated sodium positive electrode material is placed in a high temperature calcination furnace and calcined at 600°C to obtain a composite positive electrode material.

[0044] positive electrode The electrode was prepared by mixing the composite cathode material, SP, and PVDF in a weight ratio of 94:3:3. After mixing at 2000 rpm, the slurry was evenly coated on aluminum foil and vacuum-dried at 80°C overnight. The cathode sheets were then roll-pressed and slit.

[0045] negative electrode The negative electrode materials graphite: SP: CMC: SBR were mixed in a weight ratio of 92:3:1.5:3.5, and mixed at 1000 rpm. The resulting slurry was evenly coated on a copper foil and dried with air at 60°C for 24 hours. Subsequently, the negative electrode sheets were obtained by roller pressing and slitting. Battery production: The positive electrode sheet, separator, and negative electrode sheet are wound and stacked to form a bare cell. The bare cell is then placed in a pre-punched aluminum-plastic film and sealed on the top and sides. After liquid injection, resting, formation, capacity grading, and testing, the battery is complete.

[0046] Examples 2 to 14 The examples are used to illustrate the composite positive electrode material and its preparation method, negative electrode sheet, and battery disclosed in the present invention. Most of the steps in Example 1 are included, except that the formulation in Table 1 is used.

[0047] Comparative Examples 1-3 The comparative example is used to compare and illustrate the composite positive electrode material and its preparation method, negative electrode sheet, and battery disclosed in the present invention. It includes most of the operating steps in Example 1, except that the coating layer and formulation in Table 1 are used.

[0048] Table 1 Performance Testing 1. The composite positive electrode materials, positive electrode slurries, and batteries prepared in the above examples and comparative examples were subjected to the following performance tests: Slurry gelation test: record the time required for the above-mentioned positive electrode slurry to gel in an environment with a humidity of 10%; Cycling performance test: at 25°C, charge to 4.0V at 1C constant current, charge to 0.05C constant voltage, discharge to 2.0V at 1C constant current, repeat the cycle, and record the data after 1000 cycles. The test results are shown in Table 2.

[0049] Table 2 From the test results of the embodiments and comparative examples in Table 2, it can be seen that when the thickness of the inner coating layer is 40 nm, the thickness of the outer coating layer is 12 nm, and the mass ratio of the coating layer to the mass ratio of the positive electrode material is 4.5%, the battery cycle capacity retention rate is optimal; when the thickness of the inner coating layer is 5-40 nm, the thickness of the outer coating layer is 10-20 nm, and the mass ratio of the coating layer to the mass ratio of the positive electrode material is 2.5%-5.0%, a protective film that takes into account both density and electrode-electrolyte interface stability is formed on the surface of the composite positive electrode material, which can improve the cycle life of the battery.

[0050] From the test results of Examples 1 and 10 to 14, it can be seen that when the particle sizes of the first organic phosphate and the second organic phosphate increase in a gradient from the inside to the outside, the battery has a better cycle capacity retention rate.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite positive electrode material, characterized in that The invention comprises a sodium positive electrode material and a coating layer, wherein the coating layer contains phosphate groups and conductive carbon, the coating layer comprises a dense layer and a porous layer, the dense layer is coated on the surface of the sodium positive electrode material, the porous layer is coated on the surface of the dense layer, and the conductive carbon and the phosphate groups are uniformly distributed in the dense layer and the porous layer.

2. The composite cathode material according to claim 1, characterized in that The density of the dense layer is 1.2-1.9 g / cm 3 , and / or, the porosity of the porous layer is 40%-70%.

3. The composite cathode material according to claim 1 or 2, characterized in that The thickness of the dense layer is 5-40 nm; the thickness of the porous layer is 10-20 nm; And / or, the mass content of the coating layer in the composite positive electrode material is 2.5%-5.0%.

4. The method for preparing a composite positive electrode material according to any one of claims 1 to 3, wherein: The following steps are involved: Obtaining a sodium cathode material, a first organic phosphate solution, and a second organic phosphate solution; adding the sodium cathode material to the first organic phosphate solution to react, and then centrifuging and drying to obtain a primary coated sodium cathode material; adding the primary coated sodium cathode material to the second organic phosphate solution for dispersion to obtain a dispersion, and spray drying the dispersion to obtain a secondary coated sodium cathode material; The secondary coated sodium positive electrode material is calcined to obtain a composite positive electrode material.

5. The method for preparing a composite positive electrode material according to claim 4, wherein: The mass concentration of the first organic phosphate solution is 5%-10%, and the mass concentration of the second organic phosphate is 10%-20%.

6. The method for preparing a composite cathode material according to claim 4, wherein: The average particle size of the organic phosphate in the first organic phosphate is 5-50 nm, and the average particle size of the organic phosphate in the second organic phosphate is 50-200 nm.

7. The method for preparing a composite positive electrode material according to claim 4, wherein: The mass ratio of the organic phosphate to the sodium positive electrode material in the first organic phosphate solution is 0.001-0.15, and the mass ratio of the organic phosphate to the initially coated sodium positive electrode material in the second organic phosphate solution is 0.05-0.

2.

8. The method for preparing a composite cathode material according to claim 4, wherein: The spray drying temperature is 200-400°C, and / or the calcination temperature is 500-700°C.

9. The method for preparing a composite positive electrode material according to claim 4, wherein: The organic phosphates in the first organic phosphate solution and the second organic phosphate solution independently include at least one of sodium phytate, magnesium phytate, iron phytate, potassium phytate, barium phytate, copper phytate, calcium phytate, zinc phytate, and cobalt phytate.

10. A positive electrode sheet, characterized in that: The invention comprises a current collector and an active material layer provided on at least one side of the current collector, wherein the active material layer comprises the composite positive electrode material according to any one of claims 1 to 3, or the composite positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

11. A battery, characterized in that: Including the positive electrode sheet according to claim 10.

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