Sodium-ion battery positive electrode material, preparation method thereof and sodium-ion battery

Abstract

The application relates to the technical field of sodium ion batteries, and discloses a sodium ion battery positive electrode material, a preparation method thereof and a sodium ion battery. The method for preparing the sodium ion battery positive electrode material comprises the following steps: mixing a positive electrode material precursor, a sodium source and an additive, and then performing first sintering, wherein the additive is an oxygen-containing compound of a metal; grinding the first sintering product in the presence of mixed gas to obtain a matrix; wherein the surface residual sodium hydroxide D1 and sodium carbonate D2 of the first sintering product and the surface residual sodium hydroxide D3 and sodium carbonate D4 of the matrix satisfy the following conditions: 0.1wt% <= D1-D3 <= 0.5wt%, and 0.13wt% <= D4-D2 <= 1.5wt%; and mixing the matrix and a coating aid, and then performing second sintering. The sodium ion battery positive electrode material prepared by the method has good structural stability and cycle stability, and the processing cost is low.

Description

Technical Field

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

[0002] Sodium-ion batteries, characterized by high safety, long cycle life, and wide temperature range, have attracted increasing attention and research from researchers. Currently, the main cathode materials for sodium-ion batteries include layered transition metal oxides, Prussian blue compounds, and polyanionic compounds. Among these, layered transition metal oxides are considered promising cathode materials for sodium-ion batteries due to their simple synthesis, easily tunable composition, and relatively high energy density. However, these materials generally suffer from poor structural and interfacial stability, easily undergoing irreversible phase transitions under deep desodiumization, resulting in low coulombic efficiency and rapid capacity decay. Improving the cycle stability of cathode materials has become a key requirement for driving the technological and industrial development of sodium-ion batteries.

[0003] Sodium-ion batteries are primarily targeted at two-wheeled vehicles, A00-class cars, and energy storage, markets that largely overlap with those of lithium iron phosphate materials. As lithium salt prices decline and stabilize, the cost advantage of sodium-ion batteries in raw materials is gradually diminishing. To further promote the development of sodium-ion batteries, further cost reductions are necessary.

[0004] Therefore, there is an urgent need to develop a sodium-ion battery cathode material with low material processing cost and good cycle performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high processing cost and unsatisfactory cycle performance of sodium-ion battery cathode materials in existing technologies, and to provide a sodium-ion battery cathode material, its preparation method, and a sodium-ion battery. The sodium-ion battery cathode material prepared by the method of this invention exhibits good structural stability and cycle stability, and has low processing cost.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a sodium-ion battery cathode material, the method comprising:

[0007] (1) The cathode material precursor, sodium source and additive are mixed and then subjected to a first sintering, wherein the additive is an oxygen-containing compound of metal.

[0008] (2) In the presence of a mixed gas, the first sintered product is ground to obtain a matrix;

[0009] Wherein, the residual sodium hydroxide D1 and sodium carbonate D2 on the surface of the first sintered product and the residual sodium hydroxide D3 and sodium carbonate D4 on the surface of the matrix satisfy the following: 0.1wt% ≤ D1-D3 ≤ 0.5wt%, 0.13wt% ≤ D4-D2 ≤ 1.5wt%;

[0010] (3) The matrix and coating agent are mixed and then a second sintering is performed.

[0011] Preferably, the volume fraction of carbon dioxide in the mixed gas is 0.03%-0.1%.

[0012] Preferably, the temperature of the mixed gas is 10℃-40℃.

[0013] Preferably, the relative humidity of the mixed gas is 20%-90%.

[0014] Preferably, the solid-gas mass ratio of the first sintered product to the mixed gas is 1:0.1-10.

[0015] Preferably, in the precursor and additive, the ratio of the total molar amount of oxygen to the total molar amount of metal elements is ≥1.5.

[0016] The second aspect of the present invention provides a sodium-ion battery cathode material prepared by the method described in the first aspect above.

[0017] A third aspect of the present invention provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery positive electrode material described in the second aspect.

[0018] Through the above technical solution, the present invention has the following beneficial effects:

[0019] The method for preparing sodium-ion battery cathode materials provided by this invention increases the Na content on the surface of the cathode material matrix by controlling the contact between the first sintering product and the mixed gas. + / H + The degree of ion exchange and residual sodium conversion effectively reduces the content of residual sodium hydroxide on the substrate surface. Further coating the cathode material substrate surface creates a favorable coating structure, further consuming the residual sodium. The cathode material prepared using the method described in this invention has advantages such as high structural stability and air stability, small volume change during cycling, and high cycle retention. Preferably, by controlling the ratio of oxygen atoms to metal atoms in the precursor and additives, the participation of molecular oxygen during cathode material synthesis is reduced, effectively lowering processing costs. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.

[0021] Figure 1 This is a SEM image of the sodium-ion battery cathode material prepared in Example 1 of the present invention;

[0022] Figure 2 This is a SEM image of the sodium-ion battery cathode material prepared in Comparative Example 1 of this invention.

[0023] Figure 3 The capacity curves are for batteries composed of sodium-ion battery cathode materials prepared in Examples 1, 5, 6, 7 and Comparative Example 1 of this invention.

[0024] Figure 4 The curves show the 50-cycle retention rates of batteries composed of sodium-ion battery cathode materials prepared in Examples 1, 5, 6, 7 and Comparative Example 1 of this invention. Detailed Implementation

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] The first aspect of this invention provides a method for preparing a sodium-ion battery cathode material, the method comprising:

[0027] (1) The cathode material precursor, sodium source and additive are mixed and then subjected to a first sintering, wherein the additive is an oxygen-containing compound of metal.

[0028] (2) In the presence of a mixed gas, the first sintered product is ground to obtain a matrix;

[0029] Wherein, the residual sodium hydroxide D1 and sodium carbonate D2 on the surface of the first sintered product and the residual sodium hydroxide D3 and sodium carbonate D4 on the surface of the matrix satisfy the following: 0.1wt% ≤ D1-D3 ≤ 0.5wt%, 0.13wt% ≤ D4-D2 ≤ 1.5wt%;

[0030] (3) The matrix and coating agent are mixed and then a second sintering is performed.

[0031] In this invention, the method for producing the sodium-ion battery cathode material increases the Na content on the substrate surface by controlling the contact between the first sintering product and the mixed gas. + / H +The increased ion exchange and residual sodium conversion effectively reduce the residual sodium hydroxide content on the substrate surface. Furthermore, coating the cathode material substrate surface creates a favorable coating structure, further consuming the residual sodium. The cathode material prepared using the method described in this invention exhibits good cycle performance and low processing cost.

[0032] In this invention, the difference (D1-D3) between the residual sodium hydroxide on the surface of the first sintered product and the residual sodium hydroxide on the surface of the matrix can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, or any value within the range of any two of the above values, preferably 0.2wt% ≤ D1-D3 ≤ 0.4wt%; the difference (D4-D2) between the residual sodium hydroxide on the surface of the matrix and the residual sodium hydroxide on the surface of the first sintered product can be 0.13wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, or any value within the range of any two of the above values, preferably 0.2wt% ≤ D4-D2 ≤ 1wt%.

[0033] In some embodiments of the present invention, preferably, the volume fraction of carbon dioxide in the mixed gas is 0.03%-0.1%, for example, it can be 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065%, 0.07%, 0.075%, 0.08%, 0.085%, 0.09%, 0.095%, 0.1%, or any value within the range of any two of the above values, preferably 0.05%-0.08%. Using the above-preferred volume fraction of carbon dioxide in the mixed gas is beneficial for promoting Na+ formation on the surface of the matrix material. + / H + Ion exchange.

[0034] In some embodiments of the present invention, preferably, the temperature of the mixed gas can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any value within a range of any two of the above values, preferably 15°C-35°C. In the present invention, using the above-mentioned preferred temperature of the mixed gas is more conducive to maintaining the structural stability of the material.

[0035] In some embodiments of the present invention, preferably, the relative humidity of the mixed gas is 20%-90%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value within the range of any two of the above values, preferably 35%-75%. In the present invention, using the above-mentioned preferred relative humidity of the mixed gas is beneficial to promoting the replacement of sodium ions on the surface of the substrate material with hydrogen ions in the mixed gas environment, improving the degree of residual sodium conversion on the substrate surface, and facilitating the formation of a more stable surface structure, thereby improving the cycle stability of the battery.

[0036] In this invention, a temperature and humidity measuring instrument is used to measure the temperature and relative humidity of the mixed gas.

[0037] In this invention, preferably, the mixed gas comprises carbon dioxide and water vapor. Its content satisfies the aforementioned carbon dioxide volume fraction and relative humidity range. The mixed gas may also contain nitrogen, rare gases, and other gases. In this invention, the content of nitrogen, rare gases, and other gases in the mixed gas is not particularly limited, as long as the content of carbon dioxide and water in the mixed gas meets the aforementioned range. In some preferred embodiments, the types of gases contained in the mixed gas are the same as those in air, and the content of carbon dioxide and water in the mixed gas meets the aforementioned range defined in this invention.

[0038] In some embodiments of the present invention, preferably, the solid-gas mass ratio of the first sintered product and the mixed gas is 1:0.1-10, for example, it can be 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10, or any value within any range of any two of the above values, preferably 1:2.5-7.5. Using the above-mentioned preferred solid-gas mass ratio is beneficial for more effectively controlling the reaction rate and sintering efficiency.

[0039] In this invention, the mixed gas is used to aid in the pulverization of materials during the grinding process and also serves as a conveying medium. Controlling the volume fraction of carbon dioxide in the mixed gas, the temperature of the mixed gas, the relative humidity of the mixed gas, and the solid-gas mass ratio of the first sintering product to the mixed gas within the aforementioned preferred ranges is more conducive to promoting Na… + / H + The degree of ion exchange and residual sodium conversion improves the structural stability and air stability of the material, thereby further improving the electrochemical performance of the cathode material and enhancing the cycle performance and capacity retention of the battery.

[0040] In this invention, the grinding method in step (2) is not particularly limited, but is preferably mechanical grinding and / or air jet grinding, more preferably air jet grinding. The above grinding method is more conducive to promoting the replacement of sodium ions on the surface of the substrate material with hydrogen ions in the mixed gas environment, improving the degree of residual sodium conversion on the substrate surface, so that D1, D2, D3 and D4 meet the aforementioned specific range, which is conducive to forming a more stable surface structure, thereby improving the cycle stability of the battery.

[0041] In some embodiments of the present invention, preferably, the ratio of the total molar amount of oxygen to the total molar amount of metal elements in the cathode material precursor and additives is ≥1.5, more preferably ≥2. In the present invention, by controlling the ratio of oxygen atoms to metal atoms in the cathode material precursor and additives within the above-mentioned preferred range, it is beneficial to reduce the participation of molecular oxygen during the cathode material synthesis process, reduce the need for additional oxygen supply, thereby reducing energy consumption and production costs, and also facilitating the formation of a more stable crystal structure and improving the electrochemical performance of the battery.

[0042] In some embodiments of the present invention, preferably, the molar ratio of the cathode material precursor to the additive, calculated in terms of metal elements, is 1:0.001-0.02. For example, it can be 1:0.001, 1:0.002, 1:0.004, 1:0.006, 1:0.008, 1:0.01, 1:0.015, 1:0.02, or any value within the range of any two of the above values, preferably 1:0.001-0.01. Using the above-mentioned preferred molar ratio is beneficial for improving the cycle stability and capacity retention of the battery.

[0043] In some embodiments of the present invention, preferably, the molar ratio of the cathode material precursor (calculated as metal element) to the sodium source (calculated as sodium element) is 1:0.67-1.1, more preferably 1:0.9-1.05. Using the above-mentioned preferred molar ratio helps to ensure a moderate sodium ion content and improve the electrochemical performance of the battery.

[0044] In this invention, the type of cathode material precursor has a wide range of selection. Preferably, the cathode material precursor is selected from oxygen-containing compounds of transition metals, more preferably from at least one of oxides, hydroxides, and carbonates of transition metals, and more preferably from hydroxides of transition metals. The type of oxide of transition metal has a wide range of selection. Preferably, the transition metal in the oxide of transition metal is selected from at least one of Ni, Mn, Fe, Ti, Zr, Cu, Zn, Co, Y, W, Mo, and Nb.

[0045] In this invention, when the cathode material precursor contains two or more transition metals, the cathode material precursor can be a composition of an oxygen-containing compound containing two or more transition metals, or it can be an oxide containing two or more transition metals.

[0046] In some embodiments of the present invention, preferably, the chemical formula of the positive electrode material precursor is Ni. x Mn y M z (OH)2, where 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.8, and x+y+z=1.

[0047] In this invention, the type of M has a wide range of selection. Preferably, M is selected from at least one of Fe, Ti, Zr, Cu, Zn, Co, Al, Mg, Ce, Sr, Ca, Ba, Y, W, La, Mo, Sn, Se and Nb, and more preferably from at least one of Fe, Ti, Zr, Al, Mg, Y and W.

[0048] In this invention, the types of oxygen-containing compounds of the metal are selected from a wide range. Preferably, the oxygen-containing compound of the metal in step (1) is selected from at least one of metal oxides, hydroxides, and carbonates, and is preferably a metal oxide.

[0049] In this invention, preferably, the metal in step (1) includes at least one metal element with a valence state greater than or equal to +4.

[0050] In this invention, the range of metal elements with a valence state greater than or equal to +4 is relatively wide. Preferably, the metal elements with a valence state greater than or equal to +4 are selected from at least one of Group IVA, Group VA, Group IVB, and Group VIB, and more preferably from at least one of Ti, Zr, Ce, W, La, and Sn, with Ti being even more preferred. In this invention, the type of metal element in the additive can be the same as or different from the type of metal element in the coating agent.

[0051] In this invention, the mixing method and conditions in step (1) are not particularly limited, as long as the cathode material precursor, sodium source, and additives can be mixed evenly. Preferably, the mixing conditions in step (1) include: a mixing time of 0.2-2 hours and a rotation speed of 300-1000 rpm. The mixing described in this invention is preferably carried out in a high-speed mixer.

[0052] In this invention, the conditions for the first sintering of the cathode material precursor, sodium source, and additives have a wide range of selection. Preferably, the conditions for the first sintering include: a temperature of 800℃-1100℃, more preferably 900℃-1050℃; and a time of 6h-20h, more preferably 8h-12h. Using the above-mentioned preferred first sintering conditions is more conducive to forming a stable crystal structure and improving the stability of the material. The first sintering of this invention is preferably carried out in a sintering kiln.

[0053] In this invention, preferably, the first sintering is carried out in the presence of a gas. The gas in this invention can be compressed air and / or oxygen, preferably compressed air.

[0054] In this invention, the type of coating aid is not particularly limited, and various coating aids conventionally used in the art can be used in this invention. Preferably, the coating aid is selected from oxides containing the element G.

[0055] In this invention, the type of element G has a wide range of selection. Preferably, the element G is selected from at least one of Mn, Ti, Zr, Cu, Zn, Co, Al, Mg, Ce, Sr, Ca, Ba, Y, W, La, Mo, Sn, Se, and Nb, more preferably from at least one of Mn, Ti, Zr, Al, Mg, Y, and W, and even more preferably from Zr. Using the above-mentioned preferred types of element G is beneficial for optimizing the electrochemical performance of the cathode material.

[0056] In this invention, the amount of the coating agent has a wide range of selection. Preferably, the mass ratio of the matrix (based on the first sintered product obtained in step (1)) to the coating agent (based on metal elements) is 1:0.001-0.02, more preferably 1:0.002-0.015, and even more preferably 1:0.005-0.015. Controlling the amount of the coating agent within the above-mentioned preferred range is beneficial to further improve the structural stability and air stability of the cathode material, and further improve the cycle stability of the battery.

[0057] In this invention, the mixing method and conditions in step (2) are not particularly limited, as long as the matrix and coating agent can be mixed evenly. Preferably, the mixing conditions in step (2) include: a mixing time of 0.2-2 hours and a rotation speed of 300-1000 rpm. The mixing in this invention is preferably carried out in a high-speed mixer.

[0058] In this invention, the conditions for the second sintering of the matrix and coating agent have a wide range of selection. Preferably, the conditions for the second sintering include: a temperature of 300℃-900℃, more preferably 500℃-700℃; and a time of 5h-12h, more preferably 6h-9h. Using the above-mentioned preferred second sintering conditions is more conducive to enhancing the bonding force between the coating layer and the matrix, ensuring the uniformity and stability of the coating layer, and further improving the electrochemical performance of the material. The second sintering of this invention is preferably carried out in a sintering kiln.

[0059] In this invention, preferably, the second sintering is carried out in the presence of a gas. The gas used in this invention is preferably compressed air.

[0060] In this invention, preferably, the method further includes: pulverizing the second sintered product. The invention does not particularly limit the specific operating conditions for the pulverization; the aim is simply to separate the adhering particles in the second sintered product. Those skilled in the art can adjust the conditions according to actual needs.

[0061] In a preferred embodiment of the present invention, the method for preparing the sodium-ion battery cathode material includes:

[0062] (1) The cathode material precursor, sodium source and additive are mixed and then subjected to a first sintering, wherein the additive is an oxygen-containing compound of metal; the ratio of the total molar amount of oxygen to the total molar amount of metal in the cathode material precursor and additive is ≥1.5.

[0063] (2) In the presence of a mixed gas, the first sintered product is ground to obtain a matrix;

[0064] Wherein, the residual sodium hydroxide D1 and sodium carbonate D2 on the surface of the first sintered product and the residual sodium hydroxide D3 and sodium carbonate D4 on the surface of the matrix satisfy the following: 0.1wt% ≤ D1-D3 ≤ 0.5wt%, 0.13wt% ≤ D4-D2 ≤ 1.5wt%;

[0065] The volume fraction of carbon dioxide in the mixed gas is 0.03%-0.1%; the temperature of the mixed gas is 10℃-40℃; and the relative humidity of the mixed gas is 20%-90%.

[0066] (3) The matrix and coating agent are mixed and then a second sintering is performed.

[0067] The second aspect of the present invention provides a sodium-ion battery cathode material prepared by the method described in the first aspect above.

[0068] A third aspect of the present invention provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery positive electrode material described in the second aspect above.

[0069] The present invention will be described in detail below through embodiments.

[0070] Unless otherwise specified, the raw materials used in the following examples and comparative examples are all commercially available.

[0071] Example 1

[0072] (1) Weigh out 5000g of Ni 0.33 Fe 0.33 Mn 0.34 (OH)2 cathode material precursor, 3001g of Na2CO3 and 31g of TiO2 were added to a high-speed mixer for mixing. The uniformly mixed material was then placed in a roller kiln, and compressed air was introduced into the bottom of the kiln. The kiln was kept at a temperature of 1000℃ for 8 hours. After the reaction was completed, the first sintered product was obtained. The molar ratio of cathode material precursor to TiO2 (calculated as metal element) was 1:0.007, and the molar ratio of cathode material precursor to Na2CO3 (calculated as sodium element) was 1:1.025. The residual NaOH (D1) content on the surface of the first sintered product was determined to be 3020ppm and the residual Na2CO3 (D2) content was 5010ppm by potentiometric titration.

[0073] (2) The first sintered product obtained in step (1) is ground by air jet milling. During the grinding process, a mixed gas with a temperature of 25°C, a relative humidity of 55%, and a CO2 volume content of 0.065% is introduced into the grinding chamber at a solid-to-gas ratio of 5.05 to grind and transport the material, thereby obtaining a pulverized positive electrode material matrix. The residual NaOH (D3) content on the matrix surface is 205 ppm and the residual Na2CO3 (D4) content on the matrix surface is 9007 ppm, as determined by potentiometric titration.

[0074] (3) Add 64.8g of ZrO2 and the matrix obtained in step (2) into a high-speed mixer and mix evenly. Then place the material in a roller kiln, introduce compressed air into the bottom of the kiln, and keep it at 600℃ for 6 hours. After the reaction is completed, crush it to obtain sodium-ion battery cathode material.

[0075] The SEM image of the sodium-ion battery cathode material prepared in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that the coating additives are evenly distributed on the substrate surface, and the surface of the coated sodium-ion battery cathode material is smooth.

[0076] Example 2

[0077] The method described in Example 1 is different,

[0078] In step (2), a mixed gas with a temperature of 30°C, a relative humidity of 40%, and a CO2 volume content of 0.08% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 3. The content of residual NaOH on the substrate surface was measured to be 210 ppm and the content of residual Na2CO3 on the substrate surface was 9020 ppm by potentiometric titration.

[0079] Example 3

[0080] The method described in Example 1 is different,

[0081] In step (2), a mixed gas with a temperature of 20°C, a relative humidity of 70%, and a CO2 volume content of 0.05% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 7. The content of residual NaOH on the substrate surface was measured to be 207 ppm and the content of residual Na2CO3 on the substrate surface was 9008 ppm by potentiometric titration.

[0082] Example 4

[0083] The method described in Example 1 is different,

[0084] In step (2), a mixed gas with a temperature of 10°C, a relative humidity of 90%, and a CO2 volume content of 0.1% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 0.1. The content of residual NaOH on the substrate surface was measured to be 1009 ppm and the content of residual Na2CO3 on the substrate surface was 7710 ppm by potentiometric titration.

[0085] In step (3), the amount of ZrO2 used is 65g.

[0086] Example 5

[0087] The method described in Example 1 is different,

[0088] In step (2), a mixed gas with a temperature of 40°C, a relative humidity of 20%, and a CO2 volume content of 0.03% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 10. The content of residual NaOH on the substrate surface was measured to be 211 ppm and the content of residual Na2CO3 on the substrate surface was 10025 ppm by potentiometric titration.

[0089] In step (3), the amount of ZrO2 used is 72g.

[0090] Example 6

[0091] The method described in Example 1 is different,

[0092] In step (2), a mixed gas with a temperature of 10°C, a relative humidity of 20%, and a CO2 volume content of 0.1% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 0.1. The content of residual NaOH on the substrate surface was measured to be 2015 ppm and the content of residual Na2CO3 on the substrate surface was 6311 ppm by potentiometric titration.

[0093] In step (3), the amount of ZrO2 used is 64.4g.

[0094] Example 7

[0095] The method described in Example 1 is different,

[0096] In step (2), a mixed gas with a temperature of 40°C, a relative humidity of 90%, and a CO2 volume content of 0.1% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 10. The content of residual NaOH on the substrate surface was measured to be 208 ppm and the content of residual Na2CO3 on the substrate surface was 12022 ppm by potentiometric titration.

[0097] In step (3), the amount of ZrO2 used is 86.4g.

[0098] Example 8

[0099] The method described in Example 1 is different,

[0100] (1) Weigh 917g of NiO, 980g of Fe2O3, 1100g of MnO2, 2021g of Na2CO3 and 20.8g of TiO2 respectively and add them to a high-speed mixer and mix them evenly. Then, place the evenly mixed material in a roller kiln and introduce compressed air into the bottom of the kiln. The kiln is kept at a temperature of 1000℃ for 8 hours. After the reaction is completed, the first sintered product is obtained. The total molar ratio of NiO, Fe2O3 and MnO2 (calculated as metal elements) to TiO2 (calculated as titanium elements) is 1:0.007, and the total molar ratio of NiO, Fe2O3 and MnO2 (calculated as metal elements) to Na2CO3 (calculated as sodium elements) is 1:1.025. The residual NaOH content on the surface of the first sintered product is 3009ppm and the residual Na2CO3 content on the surface of the first sintered product is 6015ppm by potentiometric titration.

[0101] (2) The first sintered product obtained in step (1) was ground by air jet milling. During the grinding process, a mixed gas with a temperature of 25°C, a relative humidity of 55%, and a CO2 volume content of 0.065% was introduced into the grinding chamber at a solid-to-gas ratio of 5.05 to grind and transport the material, thereby obtaining the pulverized positive electrode material precursor. The residual NaOH content on the substrate surface was measured to be 207 ppm and the residual Na2CO3 content on the substrate surface was 10017 ppm by potentiometric titration.

[0102] (3) Add 48.5 ZrO2 and the matrix obtained in step (2) into a high-speed mixer and mix evenly. Then place the material in a roller kiln, introduce compressed air into the bottom of the kiln, and keep it at 600℃ for 6 hours. After the reaction is completed, crush it to obtain sodium-ion battery cathode material.

[0103] Example 9

[0104] The method described in Example 8 differs in that...

[0105] In step (1), 1100g of MnO2 is replaced with 998.5g of Mn2O3. The molar ratio of the total number of NiO, Fe2O3, and Mn2O3 (calculated as metal elements) to TiO2 (calculated as titanium) is 1:0.007, and the molar ratio of the total number of NiO, Fe2O3, and Mn2O3 (calculated as metal elements) to Na2CO3 (calculated as sodium) is 1:1.025. Compressed air is replaced with oxygen. The residual NaOH content on the surface of the first sintered product is 3013ppm and the residual Na2CO3 content on the surface of the first sintered product is 6008ppm, as determined by potentiometric titration.

[0106] (2) The content of residual NaOH on the substrate surface was 205 ppm and the content of residual Na2CO3 on the substrate surface was 10012 ppm, as determined by potentiometric titration.

[0107] Comparative Example 1

[0108] The method described in Example 1 is different,

[0109] In step (2), a mixed gas with a temperature of 40°C, a relative humidity of 99%, and a CO2 volume content of 0.1% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 10. The content of residual NaOH on the substrate surface was measured to be 3006 ppm and the content of residual Na2CO3 on the substrate surface was 13012 ppm by potentiometric titration.

[0110] In step (3), the amount of ZrO2 used is 122.2g.

[0111] SEM images of the sodium-ion battery cathode material prepared in this comparative example are shown below. Figure 2As shown, by Figure 2 It can be seen that excessive contact with H2O and CO2 leads to a decrease in the amount of Na in the material. + A significant amount of sodium is released, resulting in a high total residual sodium content and a rough surface morphology after coating.

[0112] Comparative Example 2

[0113] (1) Weigh 917g of NiO, 980g of Fe2O3, 998.5g of Mn2O3, 2021g of Na2CO3 and 20.8g of TiO2 respectively and add them to a high-speed mixer and mix them evenly. Then, place the evenly mixed material in a roller kiln and introduce compressed air into the bottom of the kiln. The kiln is kept at a temperature of 1000℃ for 8 hours. After the reaction is completed, the first sintered product is obtained. The residual NaOH content on the surface of the first sintered product is 5006ppm and the residual Na2CO3 content on the surface of the first sintered product is 10007ppm by potentiometric titration.

[0114] (2) The first sintered product obtained in step (1) is ground by air jet milling. During the grinding process, ordinary industrial compressed gas is introduced into the grinding chamber to grind and transport the material to obtain the pulverized positive electrode material matrix. The residual NaOH content on the matrix surface is 5020ppm and the residual Na2CO3 content on the matrix surface is 10006ppm by potentiometric titration.

[0115] (3) Add 80.6g of ZrO2 and the matrix obtained in step (2) into a high-speed mixer and mix evenly. Then place the material in a roller kiln, introduce compressed air into the bottom of the kiln, and keep it at 600℃ for 6 hours. After the reaction is completed, crush it to obtain sodium-ion battery cathode material.

[0116] Comparative Example 3

[0117] The method described in Example 1 is different,

[0118] In step (2), a mixed gas with a temperature of 40°C, a relative humidity of 90%, and a CO2 volume content of 0.01% was introduced into the pulverizing chamber according to a solid-to-gas ratio of 0.1. The content of residual NaOH on the substrate surface was measured to be 5011 ppm and the content of residual Na2CO3 on the substrate surface was 5006 ppm by potentiometric titration.

[0119] In step (3), the amount of ZrO2 used is 83.7g.

[0120] Application examples

[0121] The cathode materials obtained in the examples and comparative examples were used to fabricate batteries and test their electrical performance, as detailed below:

[0122] The sodium-ion battery positive electrode material, polyvinylidene fluoride, and conductive carbon black prepared in the above embodiments and comparative examples were mixed in a mass ratio of 90:5:5. NMP (N-methylpyrrolidone) was added, and the mixture was magnetically stirred to form a slurry. The slurry was then coated onto aluminum foil and dried at 100°C to form a positive electrode sheet. Using the positive electrode sheet, sodium sheet as the negative electrode sheet, electrolyte, and separator as raw materials, a button cell battery was assembled in a glove box.

[0123] The charge-discharge capacity was tested at 25°C with a charge-discharge voltage of 2-4V and a rate of 0.1C. Cycle performance was tested after 50 cycles at 1C. The test results for the coin cells are shown in Table 1. The capacity curves of the batteries composed of the sodium-ion battery cathode materials prepared in Examples 1, 5-7, and Comparative Example 1 are shown in Table 1. Figure 3 As shown; the 50-cycle curves of batteries composed of sodium-ion battery cathode materials prepared in Examples 1, 5-7, and Comparative Example 1 are shown in the figure. Figure 4 As shown.

[0124] Table 1

[0125]

[0126]

[0127] As can be seen from the results in Table 1, the method for preparing sodium-ion cathode materials provided by the present invention effectively improves the structural stability of the cathode material by appropriately contacting the first sintering product with a specific mixed gas. It has the advantages of excellent capacity and cycle performance, low processing cost, and is easy to use in industrial-scale production.

[0128] Based on Example 1, Comparative Examples 1-3, and Table 1, it can be seen that compared with Example 1, the residual NaOH content hardly decreased, while the residual Na2CO3 content increased significantly, resulting in a higher total residual sodium content, which reduced capacity retention and cycle performance. Comparative Example 2 used ordinary industrial compressed gas for grinding, instead of the mixed gas provided by this invention, resulting in almost no change in the residual sodium content on the material surface, leading to low capacity retention and poor cycle performance. Comparative Example 3 used a mixed gas with a low carbon dioxide content, which failed to effectively grind Na2CO3 on the surface of the cathode material substrate. + / H + Ion exchange results in an increased content of residual sodium hydroxide on the matrix surface, leading to lower capacity retention and poorer cycling performance.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The method includes: (1) The cathode material precursor, sodium source and additive are mixed and then subjected to a first sintering, wherein the additive is an oxygen-containing compound of metal. (2) In the presence of a mixed gas, the first sintered product is ground to obtain a matrix; Wherein, the residual sodium hydroxide D1 and sodium carbonate D2 on the surface of the first sintered product and the residual sodium hydroxide D3 and sodium carbonate D4 on the surface of the matrix satisfy the following: 0.1wt% ≤ D1-D3 ≤ 0.5wt%, 0.13wt% ≤ D4-D2 ≤ 1.5wt%; (3) The matrix and coating agent are mixed and then a second sintering is performed.

2. The method according to claim 1, wherein, The residual sodium hydroxide D1 and sodium carbonate D2 on the surface of the first sintered product and the residual sodium hydroxide D3 and sodium carbonate D4 on the surface of the matrix satisfy the following: 0.2wt% ≤ D1-D3 ≤ 0.4wt%, 0.2wt% ≤ D4-D2 ≤ 1wt%.

3. The method according to claim 1 or 2, wherein, The volume fraction of carbon dioxide in the mixed gas is 0.03%-0.1%, preferably 0.05%-0.08%; Preferably, the temperature of the mixed gas is 10℃-40℃, more preferably 15℃-35℃; Preferably, the relative humidity of the mixed gas is 20%-90%, more preferably 35%-75%; Preferably, the solid-gas mass ratio of the first sintered product to the mixed gas is 1:0.1-10, and more preferably 1:2.5-7.

5.

4. The method according to any one of claims 1-3, wherein, In the cathode material precursor and additives, the ratio of the total molar amount of oxygen to the total molar amount of metal elements is ≥1.5, preferably ≥2. Preferably, the molar ratio of the cathode material precursor to the additive, calculated in terms of metal elements, is 1:0.001-0.02, more preferably 1:0.001-0.01; Preferably, the molar ratio of the cathode material precursor (calculated as metal element) to the sodium source (calculated as sodium element) is 1:0.67-1.1, more preferably 1:0.9-1.

05.

5. The method according to any one of claims 1-4, wherein, The cathode material precursor is selected from oxygen-containing compounds of transition metals, preferably from at least one of oxides, hydroxides and carbonates of transition metals; Preferably, the chemical formula of the cathode material precursor is Ni. x Mn y M z (OH)2, where 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.8, and x+y+z=1; Preferably, M is selected from at least one of Fe, Ti, Zr, Cu, Zn, Co, Al, Mg, Ce, Sr, Ca, Ba, Y, W, La, Mo, Sn, Se, and Nb; Preferably, the oxygen-containing compound of the metal in step (1) is selected from at least one of metal oxides, hydroxides and carbonates; Preferably, the metal in step (1) includes at least one metallic element with a valence state greater than or equal to +4; Preferably, the metal element with a valence state greater than or equal to +4 is selected from at least one of Group IVA, Group VA, Group IVB and Group VIB, and is preferably selected from at least one of Ti, Zr, Ce, W, La and Sn.

6. The method according to any one of claims 1-5, wherein, The coating agent is selected from oxides containing the element G; Preferably, the element G is selected from at least one of Mn, Ti, Zr, Cu, Zn, Co, Al, Mg, Ce, Sr, Ca, Ba, Y, W, La, Mo, Sn, Se and Nb, and more preferably from at least one of Mn, Ti, Zr, Al, Mg, Y and W.

7. The method according to any one of claims 1-6, wherein, The mass ratio of the matrix to the coating agent, based on the first sintered product obtained in step (1) and based on the metal element content, is 1:0.001-0.02, preferably 1:0.002-0.

015.

8. The method according to any one of claims 1-7, wherein, The conditions for the first sintering include: a temperature of 800℃-1100℃, preferably 900℃-1050℃; and a time of 6h-20h, preferably 8h-12h. Preferably, the conditions for the second sintering include: a temperature of 300℃-900℃, more preferably 500℃-700℃; and a time of 5h-12h, more preferably 6h-9h.

9. The sodium-ion battery cathode material prepared by the method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery cathode material as described in claim 9.

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