A sodium-ion battery cathode material and a sodium-ion battery

Abstract

This invention discloses a sodium-ion battery cathode material and a sodium-ion battery, relating to the field of sodium-ion batteries. The cathode material described in this invention can exist stably in aqueous solution, effectively solving the inaccuracy of testing residual alkali on the surface of sodium-ion cathode materials in aqueous solution, providing technical support for the development of water washing processes for sodium-ion cathode materials, and further improving the viscosity stability of the slurry material in air. This results in sodium-ion batteries equipped with this cathode material having higher discharge capacity, laying the foundation for the application of sodium-ion batteries in the energy storage field.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, specifically to a sodium-ion battery cathode material and a sodium-ion battery. Background Technology

[0002] With societal development, the excessive consumption of fossil fuels has led to increasingly severe energy shortages and environmental pollution, seriously impacting the sustainable development of human society. Therefore, vigorously developing renewable energy sources such as solar, wind, and tidal power has become an inevitable trend. However, renewable energy power generation (wind, solar, etc.) is discontinuous and unstable, making grid connection difficult. Thus, large-scale energy storage technology is a bottleneck for the widespread application of renewable energy, requiring low-cost, environmentally friendly energy storage materials and technologies to provide continuous and stable energy output. Among various energy storage methods, lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their advantages such as high charge / discharge voltage, no memory effect, high energy density, low self-discharge, and long lifespan. However, lithium resources are limited in quantity and extremely unevenly distributed, severely restricting their application in large-scale energy storage.

[0003] Sodium-ion batteries are gradually becoming a research hotspot in the field of large-scale energy storage due to the abundance of sodium (Na in the Earth's crust is 1000 times more abundant than Li), its uniform distribution, and its low cost. However, Na has a larger ionic radius than Li, and the atomic occupancy in similar structures will differ, meaning that lithium-ion battery cathode materials cannot be directly applied as sodium-ion battery cathode materials. Therefore, finding suitable electrode materials for sodium-ion batteries is crucial for their practical application and industrialization. Layered transition metal oxides have advantages such as high reversible capacity, suitable operating voltage, and simple synthesis methods, making them a promising cathode material for sodium-ion batteries. Currently, layered sodium-ion oxides face three major challenges: irreversible phase transitions during charge and discharge, instability of the electrode-electrolyte interface under high voltage, and poor air stability during storage and preparation. Regarding the air stability issue, although a few studies mention mechanisms such as surface decomposition, oxygen oxidation, water intercalation, and proton intercalation into the sodium layer, researchers from Xiamen University, the Institute of Chemistry of the Chinese Academy of Sciences, the Institute of Physics of the Chinese Academy of Sciences, and Dalhousie University have proposed some layered oxide materials that are stable in air. However, to date, researchers lack a deep and systematic understanding of the reaction mechanism of layered sodium ion oxides in humid air, and the design principles of air-stable layered sodium ion oxides remain a blank, which greatly hinders the development and practical application of this type of material.

[0004] Moreover, common transition metal oxide sodium salts are unstable in aqueous solutions. With the increase of relative humidity and the presence of carbon dioxide, the structure of the exposed layered oxides undergoes more drastic changes. Sodium elements in the bulk phase dissolve in water, leading to problems such as a decrease in the sodium content of transition metal oxide sodium salts, an increase in the pH value of the aqueous solution, and the inability to accurately test the residual alkali content on the surface of the cathode material in an aqueous system. This further limits the possibility of reducing the residual alkali on the surface of transition metal oxide sodium salts through water washing processes. Furthermore, it leads to an increase in viscosity after the material is slurryed and exposed to air and moisture, rendering it unusable. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a sodium-ion battery cathode material and a sodium-ion battery. The sodium-ion battery cathode material is a cathode material that is stable in aqueous solution. Specifically, the sodium-ion cathode material is a sodium salt of a transition metal oxide and has a layered structure.

[0006] The technical solution of the present invention is as follows:

[0007] This invention provides a sodium-ion battery cathode material, wherein the sodium-ion battery cathode material has a layered structure and a molecular formula as shown in formula (1):

[0008] Na α A β Ni x Mn y Fe z O γ Equation (1)

[0009] In formula (1), element A is selected from at least one of Ca, Ce, Pr, La, Nd, and Ni;

[0010] 0<α≤1, 0<β≤0.3, 1.7<γ<3.5, x+y+z=1, 0≤x<1, 0<y≤1 / 2, 0<z≤1 / 2.

[0011] In this embodiment of the invention, when x = 0, that is, iron-manganese composite hydroxide (Fe 0.5 Mn 0.5 The cathode material Na can be prepared by mixing sodium carbonate, calcium oxalate, and nickel oxide in a molar ratio of (OH)₂, sodium carbonate, calcium oxalate, and nickel oxide (1:0.33:0.02:0.3). 0.66 Ca 0.02 Ni 0.3 Mn 0.5 Fe 0.5 O2.

[0012] Preferably, element A is selected from at least one of Pr, Ce, La, and Nd.

[0013] Preferably, 0.66 < α ≤ 0.95, 0.02 < β ≤ 0.3, γ = 2, x + y + z = 1, 1 / 4 ≤ x ≤ 1 / 3, 1 / 3 ≤ y ≤ 1 / 2, 1 / 4 ≤ z ≤ 1 / 3.

[0014] The present invention also provides a method for preparing the sodium-ion battery cathode material, comprising the following steps: mixing sodium salt, transition metal compound or transition metal composite hydroxide and structural stabilizer, and performing a heat treatment reaction to obtain the sodium-ion battery cathode material; using an A ion radius to sodium ion radius ratio of 0.95 to 1.05, the equivalent ion radius is more easily embedded into the crystal lattice during the material preparation process, thereby changing the local electron distribution, increasing the lattice energy and making it more stable.

[0015] The sodium salt is sodium carbonate;

[0016] The transition metal compound is at least one of iron oxide, ferrous oxide, and manganese oxide; and / or a transition metal complex hydroxide, wherein the transition metal complex hydroxide is obtained by dissolving a water-soluble transition metal salt in water, adding an alkaline solution, stirring, and filtering; the water-soluble transition metal salt is at least two of water-soluble iron salt, water-soluble manganese salt, and water-soluble nickel salt.

[0017] The structural stabilizer is at least one of calcium carbonate, calcium oxalate, cerium carbonate, lanthanum oxalate, neodymium oxalate, and praseodymium oxalate.

[0018] Preferably, the water-soluble iron salt is at least one of ferric sulfate and ferric sulfate hydrate; the water-soluble manganese salt is at least one of manganese sulfate and manganese sulfate hydrate; and the water-soluble nickel salt is at least one of nickel sulfate and nickel sulfate hydrate.

[0019] The metal element of the additive is introduced in situ into the transition metal compound by co-precipitation, the steps of which are as follows: water-soluble nickel salt, water-soluble manganese salt, and water-soluble iron salt are dissolved in deionized water, NaOH is dissolved in deionized water, and the three solutions are simultaneously added dropwise to a stirrer to react and obtain the iron-manganese-nickel composite hydroxide. The iron-manganese-nickel composite hydroxide is then filtered, washed, and dried before use.

[0020] The specific steps of coprecipitation and solid-state sintering are as follows:

[0021] Water-soluble iron salts and water-soluble manganese salts are dissolved in deionized water, and NaOH is dissolved in deionized water. The two solutions are simultaneously added dropwise to a stirrer for reaction and filtration to obtain the iron-manganese composite hydroxide. After filtering, washing, and drying the iron-manganese composite hydroxide, it is mixed with sodium salt, structural stabilizer, and additives and then calcined to obtain the cathode material.

[0022] The mixing method is ball milling, sand milling, or high-speed mixing, and the mixing time is 5-20 hours.

[0023] Preferably, when a transition metal compound is used, the temperature of the heat treatment reaction is 800°C to 900°C, and the reaction time is 15 to 25 hours.

[0024] Preferably, the temperature of the heat treatment reaction is 840–870°C, and the reaction time is 18–20 hours.

[0025] When using transition metal composite hydroxides, the heat treatment reaction is performed by first pre-sintering and then high-temperature sintering; the pre-sintering temperature is 400-600℃ and the pre-sintering time is 4-10h; the high-temperature sintering temperature is 800-1000℃ and the high-temperature sintering time is 8-22h.

[0026] Preferably, the high-temperature sintering time is 15 to 20 hours.

[0027] Preferably, the mass ratio of the transition metal compound to the additive, sodium salt, and structural stabilizer is 7-95:3-60:1, and the mass ratio of the transition metal compound to the additive is 1:0-1.

[0028] The additive is nickel oxide.

[0029] The present invention also provides a positive electrode, the positive electrode comprising a positive electrode current collector and the sodium-ion battery positive electrode material disposed on one or both surfaces of the positive electrode current collector.

[0030] The present invention also provides a sodium-ion battery, including the aforementioned positive electrode.

[0031] The present invention also provides a detection method that can quickly determine whether sodium in the bulk phase of the positive electrode material is stable in water, comprising the following steps:

[0032] The cathode material is ground and sieved through a 100-200 mesh to obtain a sieved cathode material sample. A slurry of a certain concentration is prepared using deionized water. Under constant temperature conditions, the slurry is stirred and sonicated for 30 seconds. The pH value of the slurry is measured using a pH meter and recorded as m1. The pH value of the slurry is measured again after stirring and sonicating for 5 minutes and recorded as m2. The pH value of the slurry is measured again after sonicating for 5 minutes and recorded as m3. If |m1-m2|≤0.2 and |m2-m3|≤0.05, then the cathode material is stable in the aqueous solution.

[0033] The slurry includes a sieved positive electrode, deionized water, and a dispersant;

[0034] The positive electrode material has a mass fraction of 8% to 20%, preferably 10% to 15%.

[0035] The dispersant is one or more of sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate;

[0036] The mass fraction of the dispersant is 1-5%, preferably 2-3%;

[0037] The stirring can be a magnetic stirrer or an electric stirrer, with a speed of 100-300 r / min, preferably 150 r / min;

[0038] The ultrasonic frequency is 10-30 kHz, preferably 20-25 kHz;

[0039] The constant temperature is 20-30°C, preferably 25°C.

[0040] The beneficial effects of this invention are as follows: By introducing a structural stabilizer, this invention simply and effectively improves the instability of sodium elements in the bulk phase of transition metal oxide sodium salts in aqueous solutions, which gradually dissolves. This provides technical support for the development of methods for testing the residual alkali content of cathode materials using aqueous solutions as solvents and for the material washing process. This method is highly universal and applicable to both solid-phase and liquid-phase synthesis. This invention also provides a rapid detection method to determine the bulk elemental stability of cathode materials.

[0041] The cathode material described in this invention can exist stably in aqueous solution, effectively solving the inaccuracy of testing residual alkali on the surface of sodium-ion cathode materials in aqueous solution. This provides technical support for the development of water washing processes for sodium-ion cathode materials and further improves the viscosity stability of the slurry material in air. Consequently, sodium-ion batteries equipped with this cathode material have higher discharge capacity, laying the foundation for the application of sodium-ion batteries in the energy storage field.

[0042] The raw materials mentioned above, not shown in the examples, and related derivatives can also achieve the aforementioned beneficial effects. Attached Figure Description

[0043] Figure 1 Electron micrograph of the cathode material (D1-1) prepared for Comparative Example 1.

[0044] Figure 2 Electron micrograph of the cathode material (D2-1) prepared for Comparative Example 2.

[0045] Figure 3 The image shows the XRD patterns of the cathode materials (D2-1 and D2-2) in Comparative Example 2.

[0046] Figure 4 The graph shows the discharge capacity variation of the cathode materials (D1-1 and D1-2) prepared for Comparative Example 1.

[0047] Figure 5 Cyclic performance diagrams of the cathode materials (D1-1 and D1-2) prepared for Comparative Example 1.

[0048] Figure 6 The graph shows the discharge capacity variation of the cathode materials (S7-1 and S7-2) prepared in Example 7.

[0049] Figure 7 The diagram shows the cycle performance of the cathode materials (S7-1 and S7-2) prepared in Example 7. Detailed Implementation

[0050] Comparative Example 1

[0051] FeSO4·7H2O and MnSO4·H2O in a molar ratio of 1:1 were dissolved in deionized water to prepare a 1.5 mol / L metal salt solution. 90 g of sodium hydroxide was dissolved in 540 g of deionized water to prepare a 2 mol / L alkaline solution. The metal salt solution and alkaline solution were added dropwise to a reaction vessel, and the reaction was stirred for 4 hours. The mixture was then rapidly filtered using vacuum filtration to form a filter cake, which was washed three times with 0.5 L of deionized water. After drying in a 120℃ forced-air oven, the iron-manganese composite hydroxide Fe was obtained. 1 / 2Mn 1 / 2 (OH)₂. Iron-manganese composite hydroxide and sodium carbonate were added to a mixer at a molar ratio of 1:0.33, and zirconium balls were added for mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 500℃ at 5℃ / min and held for 5 hours. Then, the temperature was increased to 870℃ at 5℃ / min and held for 22 hours to obtain the cathode material Na. 0.66 Mn 0.5 Fe 0.5 O2(D1-1).

[0052] When the above cathode material was tested using a Shimadzu XRD-6000 instrument, a distinct 002 characteristic peak was observed, indicating that it is a layered material.

[0053] The above-mentioned positive electrode material (D1-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity D1-1 is obtained by coin cell testing.

[0054] Test method: Under constant temperature conditions, after stirring and sonicating for 30 seconds, use a pH meter to test the pH value of the slurry and record the value m1. After stirring and sonicating for 5 minutes, test the pH value of the slurry again and record the data m2. After sonicating for 5 minutes, test the pH value of the slurry again and record the data m3. If |m1-m2|≤0.2 and |m2-m3|≤0.05, then the positive electrode material is stable in the aqueous solution.

[0055] The above-mentioned positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The above test method was used to test the slurry with a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 1.

[0056] Table 1

[0057] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 12.65 13.05 13.30

[0058] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (D1-2) was obtained. The above cathode material was tested using a Shimadzu XRD-6000 instrument, and the 002 characteristic peak and obvious impurity peaks were observed, indicating that the material has impurity phases and is unstable.

[0059] The above-mentioned positive electrode material (D1-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity D1-2 is obtained by coin cell testing.

[0060] Comparative Example 2

[0061] FeSO4·7H2O, MnSO4·H2O, and NiSO4·6H2O in a molar ratio of 1:2:1 were dissolved in deionized water to prepare a 1.5 mol / L metal salt solution. 90 g of sodium hydroxide was dissolved in 540 g of deionized water to prepare a 2 mol / L alkaline solution. The metal salt solution and alkaline solution were added dropwise to a reaction vessel, and the reaction was stirred for 4 hours. After filtration, washing, and drying, the iron-manganese-nickel composite hydroxide Ni was obtained. 0.25 Mn 0.5 Fe 0.25 (OH)2. Iron-manganese-nickel composite hydroxide and sodium carbonate were added to a mixer at a molar ratio of 1:0.4, and zirconium balls were added for mixing, with a ball-to-material ratio of 3:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 500℃ at 5℃ / min and held for 6 hours. Then, the temperature was increased to 870℃ at 5℃ / min and held for 20 hours to obtain the cathode material Na. 0.8 Mn 0.5 Fe 0.25 Ni 0.25 O2(D2-1).

[0062] When the above cathode material was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that it is a layered material.

[0063] The above-mentioned positive electrode material (D2-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test D2-1.

[0064] The above positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 2.

[0065] Table 2

[0066] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 12.85 13.15 13.25

[0067] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (D2-2) was obtained. The above cathode material was tested using a Shimadzu XRD-6000 instrument, and the 003 characteristic peak and obvious impurity peaks were observed, indicating that the material has impurity phases and is unstable.

[0068] The above-mentioned positive electrode material (D2-2), conductive agent, and binder were mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared into a sheet and dried, a positive electrode sheet was made. Using metallic sodium as the negative electrode, the capacity of D2-2 was obtained by coin cell testing.

[0069] Comparative Example 3

[0070] Ferrous oxide, manganese oxide, sodium carbonate, and nickel oxide in a molar ratio of 1:1:1.5:1 were added to a mixer, and zirconium balls were added for further mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace, heated to 870℃ at a rate of 5℃ / min, and held for 18 hours to obtain the cathode material NaNi. 1 / 3 Mn 1 / 3 Fe 1 / 3 O2(D3-1),

[0071] When the above cathode material (D3-1) was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that it is a layered material.

[0072] The above-mentioned positive electrode material (D3-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test D3-1.

[0073] The above positive electrode material was mixed with deionized water at a mass ratio of 1:20 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a magnetic stirrer and a pH meter. The results are shown in Table 3.

[0074] Table 3

[0075] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 12.85 13.13 13.33

[0076] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (D3-2) was obtained. The above cathode material was tested using a Shimadzu XRD-6000 instrument, and the 003 characteristic peak and obvious impurity peaks were observed, indicating that the material has impurity phases and is unstable.

[0077] The above-mentioned positive electrode material (D3-2), conductive agent, and binder were mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet was made. Using metallic sodium as the negative electrode, the capacity of D3-2 was obtained by coin cell testing.

[0078] Example 1

[0079] The iron-manganese composite hydroxide (Fe) prepared in Comparative Example 1 0.5 Mn 0.5 (OH)2), sodium carbonate, and calcium oxalate were added to a mixer in a molar ratio of 1:0.33:0.02, and zirconium balls were added for mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 500℃ at 5℃ / min and held for 5 hours. Then, the temperature was increased to 870℃ at 5℃ / min and held for 22 hours to obtain the positive electrode material Na. 0.66 Ca 0.02 Mn 0.5 Fe 0.5 O2(S1-1).

[0080] The above-mentioned positive electrode material (S1-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity S1-1 is obtained by coin cell testing.

[0081] The above positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 4.

[0082] Table 4

[0083] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 10.85 10.85 10.84

[0084] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S1-2) was obtained. The above cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 002 characteristic peak was observed. The absence of impurity peaks at the angle indicates that the material has no impurity phase and its structure is stable.

[0085] The above-mentioned positive electrode material (S1-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity S1-2 is obtained by coin cell testing.

[0086] Example 2

[0087] The iron-manganese composite hydroxide (Fe) prepared in Comparative Example 1 0.5 Mn 0.5 (OH)2), sodium carbonate, calcium oxalate, and nickel oxide were added to a mixer in a molar ratio of 1:0.33:0.02:0.3. Zirconium balls were added and mixed, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 400℃ at 5℃ / min and held for 4 hours. Then, the temperature was increased to 840℃ at 5℃ / min and held for 18 hours to obtain the cathode material Na. 0.66 Ca 0.02 Ni 0.3 Mn 0.5 Fe 0.5 O2(S2-1).

[0088] When the above cathode material was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that it is a layered material.

[0089] The above-mentioned positive electrode material (S2-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S2-1 is obtained by coin cell testing.

[0090] The above positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 5.

[0091] Table 5

[0092] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 10.80 10.81 10.81

[0093] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S2-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0094] The above-mentioned positive electrode material (S2-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S2-2 is obtained by coin cell testing.

[0095] Example 3

[0096] The iron-manganese-nickel composite hydroxide Ni prepared in Comparative Example 2 0.25 Mn 0.5 Fe 0.25 (OH)2. Iron-manganese-nickel composite hydroxide, sodium carbonate, and neodymium oxalate were added to a mixer in a molar ratio of 1:0.4:0.1. Zirconium balls were added and mixed, with a ball-to-material ratio of 3:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 400℃ at 5℃ / min and held for 6 hours. Then, the temperature was increased to 800℃ at 5℃ / min and held for 8 hours. The cathode material Na was obtained under a pure oxygen atmosphere. 0.8 Nd 0.2 Mn 0.5 Fe 0.25 Ni 0.25 O2(S3-1).

[0097] When the above cathode material was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that it is a layered material.

[0098] The above-mentioned positive electrode material, conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared into a sheet and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, a coin cell test capacity S3-1 is prepared.

[0099] The above positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 6.

[0100] Table 6

[0101] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 10.95 10.96 10.96

[0102] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S3-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0103] The above-mentioned positive electrode material (S3-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S3-2 is obtained by coin cell testing.

[0104] Example 4

[0105] The iron-manganese-nickel composite hydroxide Ni prepared in Comparative Example 2 0.25 Mn 0.5 Fe 0.25 (OH)2. Iron-manganese-nickel composite hydroxide, sodium carbonate, and lanthanum oxalate were added to a mixer in a molar ratio of 1:0.4:0.05. Zirconium balls were added and mixed, with a ball-to-material ratio of 3:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace. The temperature was increased to 500℃ at 5℃ / min and held for 6 hours. Then, the temperature was increased to 900℃ at 5℃ / min and held for 22 hours to obtain the cathode material Na. 0.8 La 0.1 Mn 0.5 Fe 0.25 Ni 0.25 O2(S4-1).

[0106] When the above cathode material (S4-1) was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that it is a layered material.

[0107] The above-mentioned positive electrode material (S4-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test S4-1.

[0108] The above positive electrode material was mixed with deionized water at a mass ratio of 1:15 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 7.

[0109] Table 7

[0110] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 11.05 11.05 11.05

[0111] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S4-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0112] The above-mentioned positive electrode material (S4-2), conductive agent, and binder were mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared into a sheet and dried, a positive electrode sheet was made. Using metallic sodium as the negative electrode, the capacity of S4-2 was obtained by coin cell testing.

[0113] Example 5

[0114] FeO, MnO, Na₂CO₃, CaCO₃, and NiO in a molar ratio of 1:1:1.475:0.075:1 were added to a mixer, and zirconium balls were added for further mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace, heated to 870℃ at a rate of 5℃ / min, and held for 18 hours to obtain the cathode material Na. 0.95 Ca 0.025 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2(S5-1),

[0115] The above-mentioned positive electrode material (S5-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test S5-1.

[0116] The above positive electrode material (S5-1) was mixed with deionized water at a mass ratio of 1:20 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 8.

[0117] Table 8

[0118] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 11.02 11.03 11.03

[0119] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S5-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0120] The above-mentioned positive electrode material (S5-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S5-2 is obtained by coin cell testing.

[0121] Example 6

[0122] FeO, MnO, Na₂CO₃, Ce(CO₃)₂, and NiO in a molar ratio of 1:1:1.41:0.03:1 were added to a mixer, and zirconium balls were added for further mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace, heated to 900℃ at a rate of 5℃ / min, and held for 18 hours to obtain the cathode material Na. 0.94 Ce 0.02 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2(S6-1),

[0123] The above-mentioned positive electrode material (S6-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test S6-1.

[0124] The above-mentioned positive electrode material (S6-1) was mixed with deionized water at a mass ratio of 1:20 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 9.

[0125] Table 9

[0126] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 10.93 10.93 10.93

[0127] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S6-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0128] The above-mentioned positive electrode material (S6-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S6-2 is obtained by coin cell testing.

[0129] Example 7

[0130] FeO, MnO, Na2CO3, La2(C2O4)3, and NiO in a molar ratio of 1:1:1.41:0.03:1 were added to a mixer, and zirconium balls were added for further mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace, heated to 800℃ at a rate of 5℃ / min, and held for 18 hours to obtain the cathode material Na. 0.94 La 0.02 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2(S7-1),

[0131] The above-mentioned positive electrode material (S7-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test S7-1.

[0132] The above-mentioned positive electrode material (S7-1) was mixed with deionized water at a mass ratio of 1:20 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 10.

[0133] Table 10

[0134] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 11.00 11.01 11.01

[0135] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S7-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0136] When the above cathode material (S7-2) was tested using a Shimadzu XRD-6000 instrument, a distinct 003 characteristic peak was observed, indicating that the layered material was not damaged.

[0137] The above-mentioned positive electrode material (S7-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S7-2 is obtained by coin cell testing.

[0138] Example 8

[0139] FeO, MnO, Na2CO3, Pr2(C2O4)3, and NiO in a molar ratio of 1:1:1.41:0.03:1 were added to a mixer, and zirconium balls were added for further mixing, with a ball-to-material ratio of 2:1. After mixing for 4 hours, the sample was removed and placed in a muffle furnace, heated to 870℃ at a rate of 5℃ / min, and held for 15 hours to obtain the cathode material Na. 0.94 Pr 0.02 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2(S8-1),

[0140] The above-mentioned positive electrode material (S8-1), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made, and sodium metal is used as the negative electrode to prepare the coin cell capacity test S8-1.

[0141] The above positive electrode material (S8-1) was mixed with deionized water at a mass ratio of 1:20 to form a slurry. The test method in Comparative Example 1 was used to test the slurry using a Sinochem MSP-2C magnetic stirrer and a Mettler Toledo FE-20 pH meter. The results are shown in Table 11.

[0142] Table 11

[0143] Stirring time 30 seconds 5 minutes 10 minutes slurry pH value 11.00 11.01 11.01

[0144] The above slurry was dried, ground, and pulverized in a forced-air oven at 120°C, and then heat-treated in a muffle furnace at 250°C for 5 hours. After cooling, the cathode material (S8-2) was obtained. The cathode material was tested using a Shimadzu XRD-6000 instrument, and a distinct 003 characteristic peak was observed. There were no impurity peaks at the angle, indicating that the material did not contain any impurity phases and had a stable structure.

[0145] The above-mentioned positive electrode material (S8-2), conductive agent, and binder are mixed and stirred in a mass ratio of 9:0.5:0.5. After being prepared and dried, a positive electrode sheet is made. Using metallic sodium as the negative electrode, the capacity of S8-2 is obtained by coin cell testing.

[0146] Table 12

[0147]

[0148] In Comparative Examples 1-3 and Examples 1-8, the capacity obtained by the coin cell test was 0.2C discharge capacity, as shown in Table 12. This indicates that when a structural stabilizer is added, the cathode material can exist stably in an aqueous solution, effectively solving the inaccuracy of testing residual alkali on the surface of the sodium ion cathode material in an aqueous solution. At the same time, it further improves the viscosity stability of the slurry material in air, resulting in a sodium ion battery equipped with this cathode material having a higher discharge capacity.

[0149] from Figures 1-3 It can be seen that the cathode material prepared in the comparative proportion cannot exist stably in aqueous solution, and there is a significant difference in the morphology of the cathode material before and after drying into a slurry. Meanwhile, from... Figures 4-7 It can be seen that the capacity and cycle performance (approximately 83%) of the cathode material prepared in the comparative example decreased sharply after being made into a slurry and then dried, while the capacity and cycle performance (approximately 93%) of the cathode material prepared in the example did not change significantly before and after being made into a slurry and then dried.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, Includes the following steps: Sodium salt, transition metal compound or transition metal complex hydroxide, and structural stabilizer are mixed and subjected to heat treatment reaction to obtain the sodium-ion battery cathode material. The sodium-ion battery cathode material has a layered structure, and its molecular formula is shown in formula (1): Na α A β Ni x Mn y Fe z O γ Formula (1), In equation (1), element A is selected from at least one of Pr, Ce, La, and Nd; 0.66<α≤0.95, 0.02<β≤0.3, γ=2, x+y+z=1, 1 / 4≤x≤1 / 3, 1 / 3≤y≤1 / 2, 1 / 4≤z≤1 / 3; the ratio of the radius of element A to the radius of element sodium is 0.95~1.05; The sodium salt is sodium carbonate; The transition metal compound is at least one of iron oxide, ferrous oxide, and manganese oxide; and / or a transition metal complex hydroxide, wherein the transition metal complex hydroxide is obtained by dissolving a water-soluble transition metal salt in water, adding an alkaline solution, stirring, and filtering; the water-soluble transition metal salt is at least two of water-soluble iron salt, water-soluble manganese salt, and water-soluble nickel salt. The structural stabilizer is at least one of cerium carbonate, lanthanum oxalate, neodymium oxalate, and praseodymium oxalate. The positive electrode material is stable in aqueous solution, as shown by the following steps: the positive electrode material is ground and sieved through a 100-200 mesh to obtain a sieved positive electrode material sample; a slurry of a certain concentration is prepared using deionized water; under constant temperature conditions, the slurry is stirred and sonicated for 30 seconds, and the pH value of the slurry is measured using a pH meter and recorded as value m1; the slurry is stirred and sonicated for 5 minutes, and the pH value of the slurry is measured again and recorded as data m2; the slurry is sonicated for 5 minutes, and the pH value of the slurry is measured again and recorded as data m3; and |m1-m2|≤0.2 and |m2-m3|≤0.05 are calculated. When using transition metal compounds, the temperature of the heat treatment reaction is 840~870℃ and the reaction time is 18~20 hours; When using transition metal composite hydroxides, the heat treatment reaction is performed by first pre-sintering and then high-temperature sintering; the pre-sintering temperature is 400~600℃ and the pre-sintering time is 4~10h; the high-temperature sintering temperature is 800~1000℃ and the high-temperature sintering time is 15~20h.

2. The preparation method according to claim 1, characterized in that, The water-soluble iron salt is at least one of ferric sulfate and ferric sulfate hydrate; the water-soluble manganese salt is at least one of manganese sulfate and manganese sulfate hydrate; the water-soluble nickel salt is at least one of nickel sulfate and nickel sulfate hydrate.

3. The preparation method according to claim 1, characterized in that, The mixing method is ball milling or sand milling, and the mixing time is 5-20 hours.

4. A positive electrode, the positive electrode comprising a positive electrode current collector and a sodium-ion battery positive electrode material prepared by any one of claims 1 to 3 disposed on one or both surfaces of the positive electrode current collector.

5. A sodium-ion battery, characterized in that, Includes the positive electrode as described in claim 4.

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