Sodium-ion battery and preparation method of modified positive electrode active material thereof

Abstract

The application belongs to the field of sodium ion battery positive electrode materials, and specifically provides a modified positive electrode active material of a sodium ion battery and a preparation and application thereof. X After the TMO2 layered oxide and the modifier are mixed, positive pressure calcination treatment is performed, and the modified positive electrode active material of the sodium ion battery is obtained; Na X In the TMO2 layered oxide, the TM is one or more of Ni, Fe, Mn, Cu, Ca, Mg, Ti, Al, Zn, Zr, Sn, Sb and W; x is 0.5-1; the modifier is M a N b O c Y d ; M is at least one of Sn, In and Cd; N is at least one of Ga, Sb, Ba, Al, Ti, Zr, La, Ce, Mo, W, Au, Sr, Hf and Ta; Y is at least one of F, Cl, Br and I; 0

Description

Technical Field

[0001] This invention belongs to the field of sodium secondary battery technology, specifically relating to the field of cathode materials. Background Technology

[0002] Layered oxide cathode materials for sodium-ion batteries possess advantages such as high energy density, high operating voltage, and simple fabrication processes, making them one of the most widely used and promising key materials in the sodium-ion battery field. Currently, with the development of sodium-ion batteries, the requirements for battery energy density are becoming increasingly stringent. While increasing the charging cut-off voltage of layered oxides can improve their specific capacity, it will inevitably lead to a decrease in cycle and rate performance. The irreversible phase transition at high charging cut-off voltage and the thickening of the electrolyte-electrolyte interface film due to side reactions at the material-electrolyte interface are the main reasons affecting the material's cycle and rate performance. Therefore, coating and gradient doping modifications of layered oxide cathode materials are necessary.

[0003] Surface modification, such as coating the surface of layered oxide cathode materials with metal oxides ZrO2, metal fluorides AlF3, metal phosphates NaPO4, etc., can prevent the dissolution of transition metals, reduce adverse side reactions at the electrolyte-cathode interface, and improve the cycle stability of the material.

[0004] Currently, the cathode surface coating materials used in industrial production both domestically and internationally are mainly metal oxides. The surface coating purpose is achieved by mixing and sintering the coating material and the cathode active material. At the same time, the metal oxides can be gradient-doped into the surface of the matrix material, improving irreversible phase transitions and further enhancing the high-voltage stability of the material.

[0005] For example, Chinese patent document CN114613981A discloses a zinc-doped zinc oxide-coated manganese-based morphological oxide material, its preparation method and application, specifically describing a scheme in which sodium source, nickel source, copper source, zinc source and manganese source are mixed by ball milling in a certain stoichiometric ratio and then calcined at high temperature. Chinese patent document CN116314640A discloses a layered oxide cathode material for sodium-ion batteries. Specifically, it discloses that a nickel source, sodium source, manganese source, iron source, Me source, and additives and dopants are mixed uniformly in a certain proportion to obtain a mixture. The mixture is then sintered for the first time in an air or oxygen atmosphere, followed by heating and reaction for a period of time, then heating again and continuing to sinter. After sintering, the mixture is cooled to the furnace exit temperature, and finally removed from the furnace, crushed, and sieved to obtain a first-sintered product. The first-sintered product is then mixed with a surface modifier, mixed uniformly, and heated to the reaction temperature in an air or oxygen atmosphere for a second sintering. After the second sintering, the mixture is cooled to the furnace exit temperature, removed from the furnace, crushed, and sieved to obtain a second-sintered product. Subsequently, the second product is mixed uniformly with a coating agent and then sintered for the third time in an air or oxygen atmosphere. The third-sintered product is then sieved to obtain an O3 or P2 type layered oxide cathode material.

[0006] In summary, although existing coating methods can improve high-voltage performance to some extent, they inevitably reduce material capacity and conductivity, making it difficult to simultaneously achieve high voltage, high rate, fast charging, and low-temperature performance. Summary of the Invention

[0007] To address the problem that existing cathode active materials struggle to simultaneously achieve high voltage, fast charging, and low-temperature performance, the primary objective of this invention is to provide a method for preparing a modified cathode active material, aiming to provide a cathode active material for sodium-ion batteries that balances excellent fast charging performance.

[0008] The second objective of this invention is to provide the modified positive electrode active material prepared by the aforementioned method and its application in sodium-ion batteries.

[0009] A third objective of this invention is to provide a sodium-ion battery comprising the modified positive electrode active material, and the same as the positive electrode and the positive electrode material.

[0010] Existing coating technologies can improve voltage to some extent, but they easily compromise fast charging and capacity performance, making it difficult to balance high voltage, fast charging, and low-temperature performance. To address this issue, this invention, after in-depth research, provides the following improvement:

[0011] A method for preparing a modified positive electrode active material for sodium-ion batteries, wherein Na... X The TMO2 layered oxide is mixed with a modifier and subjected to positive pressure calcination to obtain the product.

[0012] Na XIn the TMO2 layered oxide, the TM is one or more of Ni, Fe, Mn, Cu, Ca, Mg, Ti, Al, Zn, Zr, Sn, Sb, and W; x is 0.5 to 1;

[0013] The modifier is M a N b O c Y d ; M is at least one of Sn, In, and Cd; N is at least one of Ga, Sb, Ba, Al, Ti, Zr, La, Ce, Mo, W, Au, Sr, Hf, and Ta; Y is at least one of F, Cl, Br, and I; 0 < a ≤ 1; b is 0 to 0.5; d is 0 to 0.5; c is 2 to 0.5d.

[0014] In this invention, M a N b O c Y d is innovatively used as an external modifier to conduct positive-pressure thermal modification on the Na X TMO2 layered oxide. In this way, low-impedance gradient doping and coating of the material can be achieved based on the in-to-out embedding method, and then the high-voltage, fast-charging, and low-temperature performance of the prepared material can be improved.

[0015] In this invention, the Na X TMO2 layered oxide can be any active material that needs to be modified and is applicable in the field of sodium batteries, and it can be obtained based on existing principles and methods. For example, it can be obtained by sintering a Na source and a TM source.

[0016] In this invention, the Na source includes at least one of sodium carbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium chloride, and sodium fluoride.

[0017] In this invention, the TM source is at least one of the carbonate, hydroxide, organic acid salt, and oxide of the TM element;

[0018] In this invention, the TM includes at least one of Ni, Fe, and Mn, and also selectively includes one or more of Cu, Ca, Mg, Ti, Al, Zn, Zr, Sn, Sb, and W.

[0019] In this invention, the molar ratio of Na / TM in the Na source and the TM source is 0.5 - 1.07; further, it can be 1 to 1.05.

[0020] In this invention, the sintering temperature is 800 to 1500 °C, and further, it can be 1000 to 1400 °C.

[0021] In this invention, the sintering time is 10 to 15 hours.

[0022] In this invention, the type of modifier and its external-to-internal embedded thermal modification method are key to improving the high-voltage, fast-charging and low-temperature performance of materials by synergistic solid gradient infiltration and uniform surface coating, reducing interlayer interface impedance, and optimizing ion and electron conduction networks and efficiency.

[0023] As an optional solution, the modifier is SnO2, In2O3, CdO, or SnO. 2-0.5d F d InO 2-0.5d F d CdO 2- 0.5d Br d Sn a Sb b O2, In a Sn b O2, In a Cd b O2, Sn a Sr b O2, In a Ga b O2, Sn a La b Ba c O2, Sn a Ce b O2, In a Ce b O2, In a Sn b O 2-0.5d F d Sn a Sb b O 2-0.5d F d At least one of them.

[0024] Furthermore, in the modifier, b and c are not simultaneously zero. In this invention, when b and c are not simultaneously zero, the fast-charging and low-temperature performance of the prepared material can be further optimized based on the hybridization of cations and / or anions in the modifier.

[0025] Furthermore, the modifier is SnO. 2-0.5d F d In a Sn b O 2-0.5d F dAt least one of the following. d is 0.1–0.6, more preferably 0.3–0.5. Studies have shown that the preferred modifier, combined with the positive pressure calcination process described in this invention, can further optimize the fast charging and low-temperature performance of the prepared material.

[0026] In this invention, the M a N b O c Y d Existing commercial products can be selected, or the product can be prepared based on conventional solid-phase synthesis methods. For example, when the M... a N b O c Y d When b and / or d in the formula are not 0, the formula can be obtained by sintering a source material containing the elements therein; wherein the calcination temperature is 800-1500℃ (more preferably 850-950℃); and the time is preferably 10-15h.

[0027] In this invention, the modifier is Na, calculated based on the molar mass of transition metals. X 1–5 mol% of the mixture of TMO2 layered oxide and modifier.

[0028] In this invention, the calcination temperature is 500-900℃ (more preferably 650-850℃), and the time is preferably 2-10h (more preferably 6-8h);

[0029] Preferably, the atmosphere during the calcination stage is an oxygen-containing atmosphere;

[0030] Preferably, the pressure during the calcination stage is +20 to +100 Pa.

[0031] The present invention also provides a modified positive electrode active material prepared by the preparation method described above.

[0032] The preparation method described in this invention can endow the prepared material with good interfacial structure relationship, and the material prepared by the method can unexpectedly take into account the advantages of excellent high voltage, fast charging and low temperature performance.

[0033] The present invention also provides an application of the modified positive electrode active material prepared by the above preparation method, which is used as a positive electrode active material for the preparation of sodium-ion batteries.

[0034] Based on conventional principles and methods, the present invention can use the modified positive electrode active material as a positive electrode active material to prepare sodium-ion batteries and their positive electrodes and positive electrode materials.

[0035] For example, in this invention, the modified positive electrode active material, binder, and conductive agent can be combined to obtain a positive electrode material, which can then be coated onto a current collector to form a positive electrode. The positive electrode, barrier layer, and negative electrode can be further combined to obtain a battery.

[0036] The present invention also provides a positive electrode material for sodium-ion batteries, which comprises the modified positive electrode active material described in the present invention.

[0037] The present invention also provides a positive electrode for a sodium-ion battery, which comprises the positive electrode material described in the present invention.

[0038] The present invention also provides a sodium-ion battery comprising the positive electrode described herein.

[0039] The sodium-ion battery and its positive electrode and positive electrode material described in this invention, except for the modified positive electrode active material described in this invention, can have other conventional components and parts.

[0040] Beneficial effects

[0041] This invention addresses the problem that conventional oxide coating modification of layered oxide cathode materials for sodium-ion batteries at high charge cutoff voltages results in unsatisfactory capacity and rate performance, and that modification methods struggle to balance high voltage and fast charging performance. The invention preferentially coats the layered oxide cathode material with conductive oxides and performs gradient doping modification, thereby improving the volume strain and interface problems of the layered oxide cathode material at high charge cutoff voltages while maintaining the original rate performance of the material.

[0042] Further optimization of the modifier can not only ensure the high chemical stability of the coating layer, but also improve its electronic (ionic) conductivity, construct a high conductivity (surface) interface, improve the rate performance of the layered oxide cathode material, and enable the prepared layered oxide cathode material to have high capacity, high rate, long cycle, excellent fast charging and low temperature performance under high voltage. Attached Figure Description

[0043] Figures 1-4 Scanning electron microscope images of Example 1, Comparative Example 1, Comparative Example 4 and Comparative Example 5; Detailed Implementation

[0044] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0045] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention and in its specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0046] The first aspect of this invention provides a method for preparing a layered oxide cathode material, comprising the following steps:

[0047] Step 1: Preparation of layered oxide Na X TMO2 cathode material:

[0048] Transition metal oxides are mixed with Na₂CO₃ and then calcined to obtain Na. X TMO2 is a layered oxide. The transition metal oxide and Na2CO3 can be mixed in a conventional ratio according to the art. According to an embodiment of the present invention, the transition metal oxide and Na2CO3 are mixed at a sodium to transition metal molar ratio of 0.5-1.07. The mixing parameters are not particularly limited, but the mixture should be homogeneous and free of white spots. According to an embodiment of the present invention, the mixing speed is 1500 rpm to 2500 rpm, and the mixing time is 5 to 15 minutes.

[0049] Further, in this invention, the transition metal oxide is one or more of NiO, Fe2O3, MnO, CuO, MgO, SnO2, Sb2O5, WO3, TiO2, ZnO, CaO, Al2O3, and ZrO2. According to embodiments of this invention, based on the molar mass of the transition metal in the precursor, the content of NiO is 5%-40%, the content of Fe2O3 is 10%-40%, the content of MnO2 is 10%-50%, and the content of CuO is...

[0050] 1%-10%, SnO2 content is 0.5%-5%, Sb2O5 content is 0.5%-7%, and MgO content is...

[0051] The content of Al2O3 is 0.3%-3%, the content of TiO2 is 1%-40%, the content of ZnO is 1%-10%, the content of CaO is 1%-5%, the content of ZrO2 is 1%-3%, and the content of WO3 is 1%-5%.

[0052] Furthermore, in the preparation of layered oxides, gradient sintering is adopted. The gradient sintering process specifically involves pre-sintering at 400-500℃ for 6-8 hours, followed by heating to 800-1200℃ and holding for 10-15 hours.

[0053] Step 2: Preparation of conductive oxide (modifier):

[0054] The conductive oxides described in this invention are cation- and anion-doped conductive oxides, mainly SnO2, In2O3, CdO, and SnO. 2-0.5d F d InO2-0.5d F d CdO 2-0.5d Br d Sn a Sb b O2, In a Sn b O2, In a Cd b O2, Sn a Sr b O2, In a Ga b O2, Sn a La b Ba c O2, Sn a Ce b O2, In a Ce b O2, In a Sn b O 2-0.5d F d Sn a Sb b O 2-0.5d F d At least one of them.

[0055] Furthermore, according to an embodiment of the present invention, the conductive oxide is prepared using a solid-state sintering method known in the art, and the specific steps are as follows:

[0056] The conductive oxide is obtained by mixing and sintering a source material containing elements; the mixing parameters are not particularly limited, as long as the mixture is uniform and free of white spots. According to an embodiment of the present invention, the mixing speed is 1500 rpm to 2500 rpm, the mixing time is 5 to 15 min; secondly, the sintering temperature is 800 to 1500 °C; and the sintering time is preferably 10 to 15 h.

[0057] Step 3: High-voltage, high-rate layered oxide cathode material

[0058] Layered oxide Na X The TMO2 cathode material and modifier are mixed uniformly, and then the mixture is sintered in a box furnace under an oxygen-containing atmosphere at a pressure of +20 to +100 Pa at 500 to 900 °C for 2 to 10 hours. The main layered oxide Na... X The molar mass ratio of TMO2 to the transition metal of the conductive oxide modifier is 99:1 to 95:5; the mixing equipment is a vertical mixer with a speed of 1000 rpm to 2000 rpm and a mixing time of 5 to 15 minutes.

[0059] The present invention will be described below through specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods that do not specifically describe conditions or steps are conventional methods, and the reagents and materials used can be obtained commercially.

[0060] Example 1

[0061] Step 1: Preparation of layered oxide cathode material

[0062] The transition metal oxides and Na2CO3 were prepared according to a sodium / transition metal molar ratio of 1.05:1.

[0063] The transition metal oxides include NiO, Fe2O3, MnO2, CuO, SnO2, Sb2O3, MgO, Al2O3, TiO2, ZnO, CaO, ZrO2, and WO3, with a molar ratio of 0.3:0.3:0.3:0.03:0.005:0.005:0.01:0.005:0.01:0.005:0.005:0.005:0.005.

[0064] The prepared oxide precursor and Na2CO3 were added to a high-speed mixer at a mixing speed of 2000 rpm for 10 min. The mixture was mixed evenly without any white spots. The mixture was pre-sintered at 500℃ for 8 h in an air box furnace, and then calcined at 1200℃ for 12 h. After cooling to room temperature in the furnace, the layered oxide was obtained after crushing with rollers and air jet milling.

[0065] Step 2: SnO 1.8 F 0.4 Preparation of conductive oxide (modifier) ​​powder

[0066] SnO2 powder with an F:Sn molar ratio of 4:10 and NH4F powder were added to a vertical mixer and mixed evenly at a speed of 2000 rpm for 10 minutes. The mixture was then sintered at 900℃ for 12 hours to obtain SnO2. 1.8 F 0.4 Conductive oxides.

[0067] Step 3:

[0068] The layered oxide (based on the molar amount of transition metal therein) and conductive oxide obtained in step 1 were mixed at a molar ratio of 98:2. The mixing machine was rotated at 1500 rpm and the mixing time was 10 min. After the mixing was completed, the mixture was sintered at 700℃ for 8 h in an air box furnace with a positive pressure of 60 Pa to obtain the conductive oxide-coated modified layered oxide cathode material.

[0069] Example 2:

[0070] Compared to Example 1, the only difference is that the layered oxide cathode material prepared in step 1 is changed. The difference in step 1 is as follows: transition metal oxides and Na2CO3 are mixed according to a sodium / transition metal molar ratio of 1.03; the transition metal oxides include NiO, Fe2O3 and MnO2 with a Ni:Fe:Mn molar ratio of 0.33:0.33:0.34. The prepared oxide precursor and Na2CO3 are added sequentially to a high-speed mixer at a mixing speed of 2000 rpm for 10 min, until the mixture is uniform and free of white spots. The mixture is pre-sintered at 500℃ for 8 h in an air box furnace, then calcined at 1300℃ for 11 h, cooled to room temperature in the furnace, and then crushed by roller crushing and air jet milling to obtain the layered oxide.

[0071] All other operations and parameters are the same as in Example 1.

[0072] Example 3: Case of changing the type of modifier

[0073] Compared to Example 1, the only difference is the change in the modifier; the experimental groups are as follows:

[0074] Group A: The modifier is SnO2; all other operations and parameters are the same as in Example 1;

[0075] Group B: The modifier is In2O3; all other operations and parameters are the same as in Example 1;

[0076] Group C: Modifier is ZnO 0.8 F 0.4

[0077] The preparation steps of the modifier are as follows: ZnO with an F:Zn molar ratio of 4:10 and NH4F powder are added to a vertical mixer and mixed evenly. The mixer speed is 2000 rpm and the mixing time is 10 min. Then the mixture is sintered at 850℃ for 14 h to obtain F-doped ZnO conductive oxide. Other operations and parameters are the same as in Example 1.

[0078] Group D: Modifier is In2SnO5

[0079] In2O3 powder with a molar mass ratio of In to Sn of 2:1 was added to a vertical mixer and mixed evenly. The mixer speed was 2000 rpm and the mixing time was 10 min. Then the mixture was sintered at 950℃ for 11 h to obtain In2SnO5 conductive oxide. Other operations and parameters were the same as in Example 1.

[0080] Group E: Modifier is In2SnO 4.8 F 0.4

[0081] In₂O₃, SnO₂, and NH₄F powders in a molar ratio of In:Sn:F = 20:10:4 were added to a vertical mixer and mixed evenly at 2000 rpm for 10 min. The mixture was then sintered at 900℃ for 12 h to obtain In₂SnO. 4.8 F 0.4 Conductive oxide; other operations and parameters are the same as in Example 1.

[0082] Example 4: Changing the amount of modifier

[0083] Compared with Example 1, the only difference is that in step 3, the molar ratio of the modifier to the transition metal element in the layered oxide obtained in step 1 is 4:96; all other operations and parameters are the same as in Example 1.

[0084] Example 5:

[0085] Compared to Example 1, the only difference is that the sintering conditions in step 3 were changed. The experimental groups were as follows:

[0086] Group A: Sintering temperature was 800℃, and time was 6 hours; other operations and parameters were the same as in Example 1.

[0087] Group B: Sintering pressure is +20 Pa; other operations and parameters are the same as in Example 1.

[0088] Comparative Example 1

[0089] Compared with Example 1, the only difference is that steps 2 and 3 are omitted, and the layered oxide obtained in step 1 is used directly as the active material. All other operations and parameters are the same as in Example 1.

[0090] Comparative Example 2

[0091] Compared with Example 1, the only difference is that ZnO is used as the modifier, and its dosage and other operations and parameters are the same as in Example 1.

[0092] Comparative Example 3

[0093] Compared with Example 1, the only difference is that the modifier is prepared in step 2 in advance, and the initiator is mixed with the raw material in step 1 and calcined together under the conditions of step 1, and then sintered in step 3 to obtain the composite material.

[0094] Comparative Example 4

[0095] Compared with Example 1, the only difference is that in step 3, no sintering process is performed; all other operations and parameters are the same as in Example 1.

[0096] Comparative Example 5

[0097] Compared with Example 1, the only difference is that in step 3, the sintering furnace is not set to positive pressure; all other operations and parameters are the same as in Example 1.

[0098] Test case

[0099] The conductive oxide-coated layered oxides from the examples and comparative examples were used as positive electrode materials to assemble half-cells. The modified positive electrode material, along with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF), were dispersed in a nitrogen-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1. The mixture was stirred until homogeneous to obtain an electrode slurry. This slurry was coated onto an aluminum foil surface, vacuum-baked at 80°C for 12 hours, rolled, and cut to obtain the positive electrode sheet. A sodium sheet negative electrode was used, and an electrolyte was formed by mixing 1 mol / L NaPF6 with a two-component mixed solvent at an EC:DMC ratio of 1:1 (v / v). A polypropylene microporous membrane was used as the separator, and the cells were assembled into CR2032 coin cells in an argon-filled glove box. The following tests were performed:

[0100] Rate capability: Constant current charge and discharge test was performed at 2-4.2V / 0.1 / 10C at 25℃.

[0101] Low-temperature performance: Constant current charge-discharge tests were conducted at -20℃ and 25℃ under a voltage range of 2–4.2V / 0.1C.

[0102] Cycling: 200 constant current charge-discharge cycles were performed at 25℃ and 2~4.2V / 1C.

[0103] The results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] from Figures 1 to 4The SEM images show that, compared to Comparative Example 1 (which did not undergo steps 2 and 3), Example 1 has a uniform and dense coating layer on the particle surface; Comparative Example 4 (which did not undergo the heat treatment in step 3) only has granular conductive oxides on the surface and no coating effect; while the surface of Comparative Example 5 (which did not use positive pressure heat treatment) has an uneven island-like coating. This indicates that the heat treatment in step 3 can regulate the surface structure, allowing the conductive oxides to coat the substrate material surface in situ, resulting in a higher adhesion, while the positive pressure setting can promote a more uniform and dense coating layer.

[0108] As can be seen from the examples and comparative examples, by using the special modifier described in this invention, based on the positive pressure sintering and infiltration process from the outside to the inside, the coating and gradient doping modification of the layered oxide cathode material by the conductive oxide can be optimized, while improving the volume strain and interface problems of the layered oxide cathode material under high charging cutoff voltage and maintaining the original rate performance of the material.

[0109] Furthermore, as demonstrated in Examples 1 and 2, using multi-doped bulk materials can yield superior rate capability and low-temperature performance. As demonstrated in Examples 1 and 3, using cation and / or anion hybrid modifiers, combined with the aforementioned outside-to-inside sintering coating and external diffusion gradient doping, can achieve superior fast-charging and low-temperature performance.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a modified positive electrode active material for sodium-ion batteries, characterized in that, Will Na X The TMO2 layered oxide and modifier are mixed and then subjected to positive pressure calcination to obtain the product. Na X In the TMO2 layered oxide, TM is one or more of Ni, Fe, Mn, Cu, Ca, Mg, Ti, Al, Zn, Zr, Sn, Sb, and W; and x is 0.5 to 1. The modifier is SnO 1.8 F 0.4 SnO2, In2O3, ZnO 0.8 F 0.4 In2SnO5, In2SnO 4.8 F 0.4 At least one of them; Na X The molar amount of TMO2 layered oxide is expressed as the molar amount of the transition metals therein, and the molar percentage of the modifier is Na. X 1-5 mol% of the mixture of TMO2 layered oxide and modifier. The calcination temperature is 500~900℃; The atmosphere during the calcination stage is an oxygen-containing atmosphere; The pressure during the calcination stage is +20 ~ +100 Pa.

2. The method for preparing the modified positive electrode active material for sodium-ion batteries as described in claim 1, characterized in that, The Na X TMO2 layered oxide was obtained by sintering using a Na source and a TM source; The Na source comprises at least one of sodium carbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium chloride, and sodium fluoride; The TM source is at least one of the following: carbonate, hydroxide, organic acid salt, and oxide of TM element; The TM contains at least one of Ni, Fe, and Mn, and selectively contains one or more of Cu, Ca, Mg, Ti, Al, Zn, Zr, Sn, Sb, and W; The molar ratio of Na / TM in the Na source and TM source is 0.5~1.

07.

3. The method for preparing the modified positive electrode active material for sodium-ion batteries as described in claim 2, characterized in that, The sintering temperature is 800~1500℃; The sintering time is 10~15 h.

4. The method for preparing the modified positive electrode active material for sodium-ion batteries as described in claim 1, characterized in that, The modifier is SnO 1.8 F 0.4 In2SnO 4.8 F 0.4 At least one of them.

5. The method for preparing the modified positive electrode active material for sodium-ion batteries as described in claim 1, characterized in that, The modifier is obtained by mixing and calcining a source material containing the elements therein; wherein the calcination temperature is 800~1500℃ and the time is 10~15 h.

6. The method for preparing the modified positive electrode active material for sodium-ion batteries as described in claim 1, characterized in that, The calcination time is 2 to 10 hours.

7. A modified positive electrode active material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of a modified positive electrode active material prepared by the preparation method according to any one of claims 1 to 6, characterized in that, It is used as a positive electrode active material in the preparation of sodium-ion batteries.

9. A positive electrode material for a sodium-ion battery, characterized in that, The modified positive electrode active material is prepared by the preparation method according to any one of claims 1 to 6.

10. A positive electrode for a sodium-ion battery, characterized in that, It includes the cathode material as described in claim 9.

11. A sodium-ion battery, characterized in that, It includes the positive electrode as described in claim 10.

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