Negative-electrode-free sodium battery positive electrode material as well as synthesis method and application thereof

Abstract

The invention belongs to the technical field of sodium-ion battery positive electrode materials, and particularly provides a negative-electrode-free sodium-ion battery positive electrode material and a synthesis method and application thereof, and the negative-electrode-free sodium-ion battery positive electrode material is of a core-shell structure with NaNi < x > Fe < y > Mn < z > M < 1-x-y-z > O as a core and Na < alpha > Mn < beta > O < gamma > F < 2-gamma > as a shell; m is selected from one or more of Sn, Pb, In, Bi, Sb, Zn and Au; wherein 0 < = x < = 1, 0 < = y < = 1, 0 < = z < = 1, x + y + z < 1, alpha > = 1.1, beta > = 1, and gamma > = 0. The positive electrode material prepared by the invention has the advantages of high capacity retention ratio and good cycling stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium-ion battery cathode materials, in particular to a negative-electrode-free sodium battery cathode material and a synthesis method and application thereof. BACKGROUND

[0002] To meet the growing demand for energy storage, sodium-ion batteries have been considered as an attractive alternative to lithium-ion batteries due to their abundant resources and cost-effectiveness. Sodium-ion battery technology urgently needs high-capacity and long-life cathode materials to meet large-scale applications, especially in electrochemical energy storage and conversion systems.

[0003] In recent years, the negative-electrode-free design has been proposed as an innovative technical path, which eliminates the need for pre-installed negative electrode materials by directly depositing metallic sodium on the current collector to form the negative electrode. This not only simplifies the battery structure, but also significantly improves the energy density and cost-effectiveness. However, this technology puts forward more stringent requirements for the cathode material, which needs to have both sodium source supply and high-capacity storage functions, and needs to compensate for the irreversible capacity loss of sodium metal deposition and inhibit phase transition during high operating voltage operation. Patent CN119361665A improves the surface stability of the material by doping, and improves the capacity and cycle performance at high voltage by coating to isolate the electrolyte from the material. Patent CN119008906A prepared the cathode material can realize stable charge and discharge up to 4.7V. This cathode material can consume part of the residual alkali, so that it remains stable in the electrolyte, and reduces the cycle deterioration caused by material phase transition.

[0004] However, the above-mentioned patents have a big problem in the negative-electrode-free battery system. During the operation of the battery, part of the Na in the cathode material is deposited on the negative electrode, and the deposition is not dense and uniform, which is easy to induce dendrites. In dynamic cycling, problems such as continuous SEI loss, poor sodium deposition / peeling reversibility, and current collector mechanical failure will inevitably occur, which will further accelerate the destruction of the cathode material structure and shorten the battery life. Therefore, the high capacity, long cycle, and low gas production performance of the negative-electrode-free sodium battery cathode material at high voltage become the key to breaking through these bottlenecks, which will lay the foundation for the commercialization of negative-electrode-free sodium batteries. SUMMARY

[0005] In order to further improve the performance of the negative-electrode-free sodium-ion battery cathode material, the application provides a negative-electrode-free sodium battery cathode material and a synthesis method and application thereof.

[0006] The application first provides a negative-electrode-free sodium battery cathode material, which is a NaNi x Fe y Mn z M 1-x-y-z O as the core, Na α Mn β Oγ F 2-γ core-shell structure of a shell; M is selected from one or more of Sn, Pb, In, Bi, Sb, Zn, Au; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z<1 and α≥1.1, β≥1, γ≥0.

[0007] The application provides a synthesis method of a positive electrode material of a sodium battery without a negative electrode, comprising the following steps: S1: a precursor and a sodium compound are weighed according to a molar ratio of 1:1, a sodium metal ion compound is added, the mixture is mechanically mixed uniformly, and the mixed powder is calcined to obtain NaNi x Fe y Mn z M 1-x-y-z O2 material; M is selected from one or more of Sn, Pb, In, Bi, Sb, Zn, Au; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z<1 and α≥1.1, β≥1, γ≥0; S2: a sodium source, a manganese source and a fluorine source are dissolved in anhydrous ethanol according to a certain proportion, magnetic stirring is performed for 30 min, citric acid is added and stirring is continued for 1 h to obtain a precursor solution; the NaNi x Fe y Mn z M 1-x-y-z O2 material is added into the precursor solution, and stirring is performed to form a gel; S3: the gel is vacuum dried, and then calcined in an air atmosphere, and after cooling, crushing and sieving, the positive electrode material of the sodium battery without a negative electrode is obtained.

[0008] Further, in the step S1, the precursor is one of Ni 0.4 Fe 0.2 Mn 0.4 (OH)2, Ni 0.5 Fe 0.2 Mn 0.3 (OH)2, Ni 0.33 Fe 0.33 Mn 0.33 (OH)2.

[0009] Further, in the step S1, the sodium compound is one or more of Na2CO3, NaHCO3, NaOH and NaNO3.

[0010] Further, in the step S1, the sodium metal ion compound is one or more of a Sn, Pb, In, Bi, Sb, Zn and Au-containing compound. And / or, in step S1, the amount of sodium-loving metal ion compound added is 0.03-0.05% molar.

[0011] Furthermore, in step S1, the calcination temperature is 700~1000℃, the heating rate is 3~10℃ / min, and the calcination time is 10~16h.

[0012] Furthermore, in step S2, the sodium source is one or more of Na2CO3, NaHCO3, NaOH, and NaNO3; And / or, in step S2, the manganese source is one or more of Mn(NO3)2‧4H2O, MnSO4‧H2O, and MnCl2‧4H2O; And / or, in step S2, the fluorine source is one or more of NH4F, NH3HF, NH4HF2, and NaF; And / or, in step S2, the molar ratio of sodium source, manganese source and fluorine source is α: β: γ: 2-γ, where 1.1≤α≤1.5, 0≤β≤1, 0≤γ≤2; And / or, in step S2, the amount of citric acid added is 5-20% of the total molar mass of sodium, manganese, and fluorine.

[0013] Furthermore, in step S3, the calcination temperature is 400~900℃, the heating rate is 3~5℃ / min, and the calcination time is 4~10h.

[0014] This application also provides an application of a negative electrode-free sodium-ion battery positive electrode material, wherein the negative electrode-free sodium-ion battery positive electrode material prepared by the above-mentioned negative electrode-free sodium-ion battery positive electrode material or by the above-mentioned synthesis method is used to make a sodium-ion battery positive electrode sheet, which is suitable for negative electrode-free sodium-ion batteries.

[0015] Furthermore, the negative electrode-free sodium-ion battery also includes a negative electrode current collector, an electrolyte, and a separator.

[0016] Furthermore, the negative electrode current collector is selected from carbon-coated aluminum foil; And / or, the concentration of sodium salt in the electrolyte is 0.1-5 mol / L; And / or, the sodium salt is any one or more of NaClO4, NaPF6, and NaTFSI; And / or, the electrolyte includes an organic solvent, which is any one or more of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

[0017] Compared with the prior art, this application has the following beneficial effects: 1. This application innovatively proposes a cathode material suitable for sodium-free batteries and its synthesis method. A core-shell structure cathode material with a sodium-rich outer layer and an inner layer doped with sodium-loving metal ions is designed. The sodium-rich outer shell serves as a sodium source, compensating for irreversible capacity loss during the first cycle; the sodium-loving metal-ion-doped core plays a dual role: firstly, it stabilizes the main structure, withstanding volume changes caused by Na insertion and extraction; secondly, it guides the uniform deposition of sodium ions at the negative electrode interface, thereby improving the battery's initial efficiency, cycle stability, and safety. This cathode material exhibits excellent performance for sodium-free batteries.

[0018] 2. The outer shell of the positive electrode material in this application is constructed with a sodium-rich composition. Its function is to act as an endogenous "sodium compensator" during the first charge, releasing active sodium ions to the outside. After these sodium ions migrate to the negative electrode through the electrolyte, the sodium-loving metal ions in the core induce a uniform sodium ion flow at the negative electrode interface, promoting uniform sodium deposition, thereby synergistically improving the cycle life and safety of the entire battery.

[0019] 3. The positive electrode material shell structure prepared in this application introduces fluorine, which can enhance the interfacial stability between the coating layer and the electrolyte, reduce the dissolution of transition metals and side reactions, effectively suppress the release of lattice oxygen under high operating voltage, and improve the cycle life and cycle stability of the negative electrode-free battery. The positive electrode material synthesis method of this application can show unique application value in the field of negative electrode-free sodium batteries. Attached Figure Description

[0020] Figure 1 This is a SEM image of the core-shell structure cathode material in Example 14 of this application.

[0021] Figure 2 Capacity curve of the electrodeless coin cell prepared in Example 14 of this application. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0025] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0026] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0027] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0028] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0030] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0031] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0032] This application, based on extensive experimental research, provides a sodium-based cathode material without a negative electrode, using NaNi... x Fe y Mn z M 1-x-y-z O is the nucleus, Na α Mn β O γ F 2-γ It has a core-shell structure; M is selected from one or more of Sn, Pb, In, Bi, Sb, Zn, and Au; Where 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z<1 and α≥1.1, β≥1, γ≥0.

[0033] Furthermore, the core is a high-capacity O3-type layered metal oxide sodium-ion battery cathode material.

[0034] Furthermore, the shell is a two-dimensional layered fluorine oxide Na, designed with fluorine doping and sodium richness. α Mn β O γ F 2-γ .

[0035] This application provides a method for synthesizing a sodium-ion battery cathode material without a negative electrode, comprising the following steps: S1: Weigh the precursor and sodium compound in a molar ratio of 1:1, add the sodium-loving metal ion compound, mechanically mix thoroughly, and then calcine the mixed powder to obtain NaNi. x Fe y Mn zM 1-x-y-z O2 materials; S2: Dissolve sodium, manganese, and fluorine sources in anhydrous ethanol in a certain proportion, stir magnetically for 30 min, add citric acid and continue stirring for 1 h to obtain the precursor solution; NaNi x Fe y Mn z M 1-x-y-z O2 material is added to the above precursor solution and stirred to form a gel; S3: The gel is vacuum dried, then calcined in air, cooled, pulverized, and sieved to obtain the final product.

[0036] Furthermore, in step S1, the precursor is Ni. 0.4 Fe 0.2 Mn 0.4 (OH)2, Ni 0.5 Fe 0.2 Mn 0.3 (OH)2, Ni 0.33 Fe 0.33 Mn 0.33 One of (OH)2.

[0037] Furthermore, in step S1, the sodium compound is one or more of Na2CO3, NaHCO3, NaOH, and NaNO3.

[0038] In some specific embodiments, generally speaking, when the sodium compound is selected as Na2CO3 in step S1, better experimental results can be obtained.

[0039] Furthermore, in step S1, the sodium-loving metal ion compound is one or more compounds containing Sn, Pb, In, Bi, Sb, Zn, and Au; Na + The redox potential of / Na is 2.71V, and the doping concentration is <0.1mol%; And / or, in step S1, the amount of sodium-loving metal ion compound added is 0.03-0.05% molar.

[0040] In some specific embodiments, in step S1, the amount of sodium-loving metal ion compound added is based on sodium-loving metal ions, and the amount added can be 0.03%, 0.035%, 0.04%, 0.045%, or 0.05%.

[0041] In some specific embodiments, when the sodium-loving metal ion compound in step S1 is a compound containing Sb and Zn, better experimental results can be obtained.

[0042] Furthermore, in step S1, the calcination temperature is 700~1000℃, the heating rate is 3~10℃ / min, and the calcination time is 10~16h.

[0043] In some specific embodiments, the calcination temperature in step S1 can be 700℃-800℃, 800℃-900℃, 900℃-1000℃, 700℃-900℃, or 800℃-1000℃. More preferably, the calcination temperature in step S1 can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃.

[0044] In some specific embodiments, the heating rate in step S1 can be 3~5℃ / min, 4~6℃ / min, 5~7℃ / min, 7~9℃ / min, or 9~10℃ / min. The heating speed in step S1 can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min.

[0045] In some specific embodiments, the calcination time in step S1 can be 10~12h, 12~14h, or 14~16h.

[0046] Under normal circumstances, in step S1, when the calcination temperature is 800℃-1000℃, the heating rate is 5℃ / min, and the holding time is 10-12h, better experimental results can be obtained.

[0047] Furthermore, in step S2, the sodium source is one or more of Na2CO3, NaHCO3, NaOH, and NaNO3; And / or, in step S2, the manganese source is one or more of Mn(NO3)2‧4H2O, MnSO4‧H2O, and MnCl2‧4H2O; And / or, in step S2, the fluorine source is one or more of NH4F, NH3HF, NH4HF2, and NaF; And / or, in step S2, the molar ratio of sodium source, manganese source and fluorine source is α: β: γ: 2-γ, where 1.1≤α≤1.5, 0≤β≤1, 0≤γ≤2; And / or, the amount of citric acid added in step S2 is 5-20% of the total molar mass of sodium, manganese, and fluorine.

[0048] In some specific embodiments, when the sodium source is Na2CO3, the manganese source is MnSO4‧H2O, and the fluorine source is NaF in step S2, better technical effects can be achieved.

[0049] In some specific implementations, the amount of citric acid added in step S2 can be 5-8%, 8-12%, 12-15%, 15-17%, 17-19%, or 19-20% of the total molar mass of sodium, manganese, and fluorine. Generally, adding citric acid in step S2 at 5-10% of the total molar mass of sodium, manganese, and fluorine yields better experimental results.

[0050] Furthermore, in step S3, the calcination temperature is 400~900℃, the heating rate is 3~5℃ / min, and the calcination time is 4~10h.

[0051] In some specific embodiments, the calcination temperature in step S3 can be 400℃-500℃, 500℃-600℃, 600℃-700℃, 700℃-800℃, or 800℃-900℃. More preferably, the calcination temperature in step S3 can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃.

[0052] In some specific embodiments, the heating rate in step S3 can be 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min.

[0053] In some specific embodiments, the calcination time in step S3 can be 4~6h, 6~8h, or 8~10h.

[0054] This application also provides an application of a negative electrode-free sodium-ion battery positive electrode material, wherein the negative electrode-free sodium-ion battery positive electrode material prepared by the above-mentioned negative electrode-free sodium-ion battery positive electrode material or by the above-mentioned preparation method is used to make a sodium-ion battery positive electrode sheet, which is suitable for negative electrode-free sodium-ion batteries.

[0055] Furthermore, the negative electrode-free sodium-ion battery also includes a negative electrode current collector, an electrolyte, and a separator.

[0056] Furthermore, the negative electrode current collector is selected from carbon-coated aluminum foil; And / or, the concentration of sodium salt in the electrolyte is 0.1-5 mol / L; And / or, the sodium salt is any one or more of NaClO4, NaPF6, and NaTFSI; In some specific embodiments, when the sodium salt is NaClO4, better technical effects can be obtained.

[0057] And / or, the electrolyte includes an organic solvent, which is any one or more of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

[0058] In some specific embodiments, the organic solvent is a combination of propylene carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0059] In some specific embodiments, the concentration of sodium salt in the electrolyte can be 0.1-0.5 mol / L, 0.5-1 mol / L, 1-1.5 mol / L, 1.5-2 mol / L, 2-2.5 mol / L, 2.5-3 mol / L, 3-3.5 mol / L, 3.5-4 mol / L, 4-4.5 mol / L, or 4.5-5 mol / L.

[0060] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0061] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0062] Example 1 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 and Na2CO3 were weighed out in a molar ratio of 1:1, and 0.05% of the molar amount of Sb2O5 was added. After mechanically mixing until uniform, the mixed powder was calcined in air at a rate of 5℃ / min to 800℃ for 10 hours to obtain NaNi. 0.4 Fe 0.2 Mn 0.4 Sb 0.05O2 material (NFMS); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1: 1: 1: 1, stir magnetically for 30 min, add 20% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. NaNi 0.4 Fe 0.2 Mn 0.4 Sb 0.05 O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that the NFMS particles are uniformly coated by the gel. S3: The gel-coated NFMS was vacuum dried at 120℃ for 12h to remove residual ethanol; then calcined in air at 800℃ for 10h, and naturally cooled to room temperature. After crushing and sieving, a core-shell structured anode-free sodium-ion battery cathode material was finally obtained, which can be used to make anode sheets for sodium-ion batteries and is suitable for anode-free sodium-ion batteries.

[0063] Example 2 The difference between the synthesis method of the negative electrode-free sodium-ion battery positive electrode material in this embodiment and that in Example 1 is that: in step S1, the precursor is Ni. 0.5 Fe 0.2 Mn 0.3 (OH)2, the rest are the same.

[0064] Example 3 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed out in a molar ratio of 1:1, and 0.05% of the molar amount of Sb2O5 was added. After mechanically mixing until uniform, the mixed powder was calcined in air at a rate of 5℃ / min to 800℃ for 10 hours to obtain NaNi. 0.4 Fe 0.2 Mn 0.4 Sb 0.05 O2 material (NFMS); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1: 1: 1: 1, stir magnetically for 30 min, add 20% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. NaNi0.4 Fe 0.2 Mn 0.4 Sb 0.05 O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that the NFMS particles are uniformly coated by the gel. S3: The gel-coated NFMS was vacuum dried at 120℃ for 12h to remove residual ethanol; then calcined in air at 800℃ for 10h, and naturally cooled to room temperature. After crushing and sieving, a core-shell structured anode-free sodium-ion battery cathode material was finally obtained, which can be used to make anode sheets for sodium-ion batteries and is suitable for anode-free sodium-ion batteries.

[0065] Example 4 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 3 in that: in step S1, the sodium-loving metal ion compounds added are Sb2O5 and Zn(NO3)2, while the rest are the same.

[0066] Example 5 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed in a molar ratio of 1:1, and 0.03% (Sb+Zn) molar amounts of Sb2O5 and Zn(NO3)2 were added. After mechanical mixing until homogeneous, the mixed powder was calcined in air at a rate of 5℃ / min to 800℃ for 10 hours to obtain Na1Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material (NFMSZ); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1: 1: 1: 1, stir magnetically for 30 min, add 20% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. Na1Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that NFMSZ particles are uniformly coated by the gel. S3: The gel-coated NFMSZ was vacuum dried at 120℃ for 12h to remove residual ethanol; then calcined in air at 800℃ for 10h, and naturally cooled to room temperature. After crushing and sieving, a core-shell structured anode-free sodium-ion battery cathode material was finally obtained, which can be used to make anode sheets for sodium-ion batteries and is suitable for anode-free sodium-ion batteries.

[0067] Example 6 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 5 in that the calcination temperature in step S1 is 950°C, while the rest are the same.

[0068] Example 7 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 5 in that the calcination temperature in step S1 is 900°C, while the rest are the same.

[0069] Example 8 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 7 in that the heat preservation time in step S1 is 12 hours, while the rest are the same.

[0070] Example 9 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed in a molar ratio of 1:1, and 0.03% (Sb+Zn) molar amounts of Sb2O5 and Zn(NO3)2 were added. After mechanical mixing until homogeneous, the mixed powder was calcined in air at a rate of 5℃ / min to 900℃ for 12 hours to obtain Na1Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material (NFMSZ); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1.2: 0.8: 1: 1, stir magnetically for 30 min, add 20% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. Na1Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that NFMSZ particles are uniformly coated by the gel. S3: The gel-coated NFMSZ was vacuum dried at 120℃ for 12h to remove residual ethanol; then calcined in air at 800℃ for 10h, and naturally cooled to room temperature. After crushing and sieving, a core-shell structured anode-free sodium-ion battery cathode material was finally obtained, which can be used to make anode sheets for sodium-ion batteries and is suitable for anode-free sodium-ion batteries.

[0071] Example 10 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 9 in that the molar ratio of Na: Mn: O: F in step S2 is 1.2: 0.8: 1.5: 0.5, while the rest are the same.

[0072] Example 11 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed in a molar ratio of 1:1, and 0.03% (Sb+Zn) molar amounts of Sb2O5 and Zn(NO3)2 were added. After mechanical mixing until homogeneous, the mixed powder was calcined in air at a rate of 5℃ / min to 900℃ for 12 hours to obtain Na1Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material (NFMSZ); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1.2: 0.8: 1.5: 0.5. Stir magnetically for 30 min, add 5% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. Na1Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that NFMSZ particles are uniformly coated by the gel. S3: The gel-coated NFMSZ was vacuum dried at 120℃ for 12h to remove residual ethanol; then calcined in air at 800℃ for 10h, and naturally cooled to room temperature. After crushing and sieving, a core-shell structured anode-free sodium-ion battery cathode material was finally obtained, which can be used to make anode sheets for sodium-ion batteries and is suitable for anode-free sodium-ion batteries.

[0073] Example 12 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 11 in that: in step S2, 10% citric acid (total molar mass of sodium, manganese, and fluorine) is added and the mixture is stirred for 1 hour, while the rest are the same.

[0074] Example 13 The method for synthesizing the negative electrode-free sodium-ion battery positive electrode material in this embodiment includes the following steps: S1: The precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed in a molar ratio of 1:1, and 0.03% (Sb+Zn) molar amounts of Sb2O5 and Zn(NO3)2 were added. After mechanical mixing until homogeneous, the mixed powder was calcined in air at a rate of 5℃ / min to 900℃ for 12 hours to obtain Na1Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material (NFMSZ); S2: Dissolve sodium carbonate, manganese sulfate, and sodium fluoride in anhydrous ethanol with a molar ratio of Na: Mn: O: F = 1.2: 0.8: 1.5: 0.5. Stir magnetically for 30 min, add 10% citric acid (total molar mass of sodium, manganese, and fluorine) and continue stirring for 1 h to form a stable metal-citric acid chelate, thus obtaining the precursor solution. Na1Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 Sb 0.02 Zn 0.01 O2 material is added to the above precursor solution, stirred in a 60°C water bath and ethanol is evaporated until a viscous gel is formed, ensuring that NFMSZ particles are uniformly coated by the gel. S3: The gel-coated NFMSZ was vacuum dried at 120℃ for 12h to remove residual ethanol; then it was calcined in air at 700℃ for 10h. After crushing and sieving, a core-shell structured sodium-ion battery cathode material with no negative electrode was finally obtained, which can be used to make sodium-ion battery cathode sheets and is suitable for sodium-ion batteries without negative electrodes.

[0075] Example 14 The method for synthesizing the negative electrode-free sodium-ion positive electrode material in this embodiment differs from that in Example 13 in that the calcination time in step S3 is 8 hours, while the rest are the same.

[0076] Comparative Example 1 Ni precursor 0.4 Fe 0.2 Mn 0.4 (OH)₂ and sodium carbonate were weighed out in a molar ratio of 1:0.8. A mixture of Na and Mn in a molar ratio of 1.2:0.8 was added and dissolved together in anhydrous ethanol. The mixture was magnetically stirred for 30 min. The ethanol was then evaporated in a 60°C water bath. The resulting powder was sintered in air at a rate of 5°C / min to 800°C and held for 10 hours to obtain a sodium-ion battery cathode material suitable for use with sodium-ion batteries without a negative electrode.

[0077] Comparative Example 2: Ni precursor 0.33 Fe 0.33 Mn 0.33 (OH)₂ and sodium carbonate were weighed out in a molar ratio of 1:0.8. A mixture of Na:Mn:O:F in a molar ratio of 1.2:0.8:1.5:0.5 was added and dissolved together in anhydrous ethanol. The mixture was magnetically stirred for 30 min. The ethanol was then evaporated while stirring in a 60°C water bath. The resulting powder was sintered in air at a rate of 5°C / min to 800°C and held for 10 hours to obtain a sodium-ion battery cathode material suitable for use with sodium-ion batteries without a negative electrode.

[0078] Comparative Example 3: According to the molecular formula Na 0.8 Ni 0.33 Fe 0.33 Mn 0.33 O2, the precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)₂ and Na₂CO₃ were weighed and mixed evenly at a total metal atom to sodium atom molar ratio of 1:0.8. The mixed powder was then sintered at 900℃ for 12 hours to obtain a primary sintered cathode material. The above sintered cathode material was then pulverized and sieved, and a raw material with a Na:Mn:O:F molar ratio of 1.2:0.8:1.5:0.5 was added. The mixture was then sintered a second time at 600℃ for 6 hours. After pulverization and sieving, a sodium-ion battery cathode material suitable for use with sodium-ion batteries without a negative electrode was finally obtained.

[0079] Comparative Example 4: (1) Ni precursor 0.33 Fe 0.33 Mn0.33 (OH)₂ and sodium carbonate were weighed in a molar ratio of 1:1, mechanically mixed evenly, and then the mixed powder was sintered at 900°C in air for 12 hours to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NFM) materials; (2) The raw materials with a molar ratio of Na: Mn: O: F of 1: 1: 1: 1 were dissolved in anhydrous ethanol and magnetically stirred for 30 min. The ethanol was then stirred and evaporated in a water bath at 60°C. After mixing with NFM material, the mixture was sintered at 600°C for 10 hours in an air atmosphere and naturally cooled to room temperature. After crushing and sieving, a sodium-ion battery cathode material suitable for a structure without a negative electrode sodium battery was finally obtained.

[0080] Comparative Example 5: According to the molecular formula Na 0.8 Ni 0.33 Fe 0.33 Mn 0.33 O2, the precursor Ni 0.33 Fe 0.33 Mn 0.33 (OH)2 and Na2CO3 were weighed and mixed evenly according to a 1:1 molar ratio of total metal atoms to sodium atoms. The mixed powder was then sintered at 900℃ for 12 hours to obtain a primary sintered material. The raw material with a Na:Mn:O:F molar ratio of 1.2:0.8:1.5:0.5 was then sintered at 600℃ for 6 hours to obtain a secondary sintered material. The positive electrode materials obtained from the two sintering processes were mechanically mixed evenly and then sintered at 400℃ for 6 hours. After crushing and sieving, a sodium-ion battery positive electrode material suitable for a structure without a negative electrode sodium battery was finally obtained.

[0081] Performance testing 1. The cathode materials of Examples 1-14 and Comparative Examples 1-5 were subjected to X-ray diffraction, electron microscopy, specific surface area, and powder compaction tests. The specific test results are shown in Table 1 and... Figures 1-2 As shown.

[0082] 2. Take the positive electrode materials from Examples 1-14 and Comparative Examples 1-5, grind them through a 200-mesh sieve, then mix them with SP (conductive carbon black) and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1, add NMP (N-methylpyrrolidone) and stir to form a slurry, coat it onto aluminum foil, and then dry, punch, and press to form a sodium-ion battery positive electrode material. Use metallic sodium as the negative electrode, glass fiber (Whatman GF / D brand) as the separator, and the negative electrode current collector is selected from carbon-coated aluminum foil; the sodium salt in the electrolyte includes any one or more of NaClO4, NaPF6, and NaTFSI; the organic solvent includes any one or more of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether. CR2025 button batteries were assembled in an argon-filled glove box for charge-discharge testing. Under conditions of 100 mA / g and a voltage range of 2~4.2V, the charge-discharge capacity and cycle performance were tested first at 0.2C for two cycles, and then at 1C.

[0083] Table 1. Test data of cathode materials in Examples 1-14 and Comparative Examples 1-5 analyze Figure 1 As can be seen, the cathode material of Example 14 of this application has a regular core-shell structure, better crystallinity, and the particle morphology shows a more regular crystal phase.

[0084] analyze Figure 2 As can be seen from the specific capacitance curves, the electrochemical performance of the sodium-ion battery cathode material prepared in Example 14 of this application is significantly better than that of Comparative Examples 1-5. This is because the sodium-rich surface layer of the core-shell structured sodium-ion battery cathode material prepared in the embodiments of this invention can provide more reversible sodium ion insertion / extraction, which not only increases the theoretical capacity but also allows excess sodium ions to fill interlayer vacancies, suppressing transition metal migration and lattice distortion. Simultaneously, the core, as the main body of the electrochemical reaction, ensures structural stability under high-voltage deep sodium removal, effectively suppressing unfavorable phase transitions and lattice oxygen evolution during cycling. By doping with specific sodium-loving metal ions, sodium ions can be guided to deposit uniformly at the negative electrode interface, demonstrating clear commercial prospects and potentially becoming a core driving force for the large-scale application of sodium batteries.

[0085] Example 14, as the optimal solution, has a greater advantage in core parameter matching compared with other examples: Examples 1-4 use non-111 type precursors or only single Sb doping, without optimizing secondary sintering parameters, and do not reflect the synergistic effect of 111 precursor, Sb / Zn co-doping and secondary sintering. However, the 111 precursor in Example 14 is adapted to 0.03% Sb / Zn co-doping, which is more conducive to structural stability and SEI film optimization. Examples 5-8 are prone to sodium volatilization or core-shell layer cracking due to excessively high secondary sintering temperature, excessively high primary sintering temperature or excessively long holding time. The primary and secondary sintering temperatures and times in Example 14 effectively avoid this problem. In Examples 9-13, the imbalance of Na:Mn:O:F ratio or excessive citric acid content and excessive secondary sintering time affect the coating uniformity and interface characteristics. The ratio adaptation and parameter simplification in Example 14 can better ensure the integrity of the core and shell. Compared to the comparative examples, Comparative Examples 1-2, lacking Sb / Zn co-doping and employing one-step sintering, did not form a core-shell structure and could not meet the interface requirements of a cathode-free sodium electrode. The co-doping and core-shell design of Example 14 can reduce side reactions. Comparative Example 3, lacking co-doping and employing a low secondary sintering temperature, had a less dense core-shell layer. In contrast, the secondary sintering parameters of Example 14 resulted in a stronger bond between the core-shell and the substrate. Comparative Examples 4-5, lacking co-doping and employing non-in-situ mixing, had structures prone to stratification. The in-situ gel coating and co-doping synergistic effect of Example 14 significantly improved the capacity retention rate of the cathode-free system.

[0086] In summary, the core-shell structured sodium-ion battery cathode material prepared in this application, suitable for use without a sodium-containing negative electrode, uses a sodium-rich outer shell as a sodium source to compensate for the irreversible capacity loss during the first cycle. The shell layer F... - Replace part of O 2- The strong Mn-F bond suppresses oxygen evolution under high voltage; the core doped with sodium-loving metal ions plays a dual role: first, it stabilizes the main structure and withstands the volume changes caused by Na insertion and extraction; second, it guides sodium ions to be uniformly deposited at the negative electrode interface, thereby improving the battery's first efficiency, cycle stability and safety. It shows excellent performance in positive electrode materials for negative electrode sodium batteries.

[0087] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A sodium-ion battery positive electrode material without a negative electrode, characterized in that: NaNi x Fe y Mn z M 1-x-y-z O is the nucleus, Na α Mn β O γ F 2-γ It has a core-shell structure; M is selected from one or more of Sn, Pb, In, Bi, Sb, Zn, and Au; Where 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z<1 and α≥1.1, β≥1, γ≥0.

2. A method for synthesizing a sodium-ion battery cathode material without a negative electrode, characterized in that: Includes the following steps: S1: Weigh the precursor and sodium compound in a molar ratio of 1:1, add the sodium-loving metal ion compound, mechanically mix thoroughly, and then calcine the mixed powder to obtain NaNi. x Fe y Mn z M 1-x-y-z O2 material; M is selected from one or more of Sn, Pb, In, Bi, Sb, Zn, and Au; wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z<1 and α≥1.1, β≥1, γ≥0; S2: Dissolve sodium, manganese, and fluorine sources in anhydrous ethanol in a certain proportion, stir magnetically for 30 min, add citric acid and continue stirring for 1 h to obtain the precursor solution; NaNi x Fe y Mn z M 1-x-y-z O2 material is added to the above precursor solution and stirred to form a gel; S3: The gel is vacuum dried, then calcined in air, cooled, pulverized, and sieved to obtain the final product.

3. The method for synthesizing the negative electrode-free sodium-ion cathode material according to claim 2, characterized in that: In step S1, the sodium compound is one or more of Na2CO3, NaHCO3, NaOH, and NaNO3; And / or, in step S1, the precursor is Ni 0.4 Fe 0.2 Mn 0.4 (OH)2, Ni 0.5 Fe 0.2 Mn 0.3 (OH)2, Ni 0.33 Fe 0.33 Mn 0.33 One of (OH)2.

4. The method for synthesizing the negative electrode-free sodium-ion cathode material according to claim 2, characterized in that: In step S1, the sodium-loving metal ion compound is one or more compounds containing Sn, Pb, In, Bi, Sb, Zn, and Au; And / or, in step S1, the amount of sodium-loving metal ion compound added is 0.03-0.05% molar.

5. The method for synthesizing the negative electrode-free sodium-ion cathode material according to claim 1, characterized in that: In step S1, the calcination temperature is 700~1000℃, the heating rate is 3~10℃ / min, and the calcination time is 10~16h.

6. The method for synthesizing the negative electrode-free sodium-ion cathode material according to claim 1, characterized in that: In step S2, the sodium source is one or more of Na2CO3, NaHCO3, NaOH, and NaNO3; And / or, in step S2, the manganese source is one or more of Mn(NO3)2‧4H2O, MnSO4‧H2O, and MnCl2‧4H2O; And / or, in step S2, the fluorine source is one or more of NH4F, NH3HF, NH4HF2, and NaF; And / or, in step S2, the molar ratio of sodium source, manganese source and fluorine source is α: β: γ: 2-γ, where 1.1≤α≤1.5, 0≤β≤1, 0≤γ≤2; And / or, in step S2, the amount of citric acid added is 5-20% of the total molar mass of sodium, manganese, and fluorine.

7. The method for synthesizing the negative electrode-free sodium-ion cathode material according to claim 1, characterized in that: In step S3, the calcination temperature is 400~900℃, the heating rate is 3~5℃ / min, and the calcination time is 4~10h.

8. An application of a sodium-ion battery positive electrode material without a negative electrode, characterized in that: The sodium-ion battery cathode material without negative electrode as described in claim 1 or prepared by any of the synthesis methods described in claims 2-7 is used to make a sodium-ion battery cathode sheet, which is suitable for sodium-ion batteries without negative electrode.

9. The application of the negative electrode-free sodium-ion cathode material according to claim 8, characterized in that: The negative electrode-free sodium-ion battery also includes a negative electrode current collector, an electrolyte, and a separator.

10. The application of the negative electrode-free sodium-ion cathode material according to claim 9, characterized in that: The negative electrode current collector is selected from carbon-coated aluminum foil; And / or, the concentration of sodium salt in the electrolyte is 0.1-5 mol / L; And / or, the sodium salt is any one or more of NaClO4, NaPF6, and NaTFSI; And / or, the electrolyte includes an organic solvent, which is any one or more of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, and diethylene glycol diethyl ether.

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