Method for coating sodium ion battery polyanionic positive electrode material by using inorganic sulfur / selenium source

Abstract

The invention relates to the technical field of polyanionic sodium ion battery positive electrode materials, and discloses a method for coating a sodium ion battery polyanionic positive electrode material with an inorganic sulfur / selenium source. The method comprises the following steps: uniformly mixing a core material with an inorganic sulfur source or an inorganic selenium source, carrying out high-temperature calcination in a protective atmosphere, cooling, grinding and sieving to obtain the sulfur or selenium coated polyanionic sodium ion battery positive electrode material, and the core material is a compound of a polyanionic positive electrode material and carbon. The sulfur / selenium coating layer is formed on the surface of the polyanionic sodium ion battery positive electrode material, so that the electronic conductivity and the sodium ion diffusion rate of the positive electrode material can be improved, and the specific capacity, the rate capability and the cycling stability of the battery are improved; the material can be used as a protective layer to effectively isolate direct contact between a positive electrode material and electrolyte, so that the occurrence of interface side reaction is reduced; in addition, shedding of a positive active material can be reduced, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of polyanion type sodium ion battery positive electrode materials, and in particular to a method for coating a polyanion type sodium ion battery positive electrode material with an inorganic sulfur / selenium source. Background Art

[0002] Lithium-ion batteries have been widely used in commercial applications due to their long life, high specific capacity and high stability. However, the low content of lithium in the earth's crust makes it difficult to meet the growing demand. The content of sodium in the earth's crust is much higher than that of lithium. It is abundant in source and low in cost. As a potential alternative to lithium-ion batteries, sodium-ion batteries have broad application prospects.

[0003] At present, the cathode materials of sodium ion batteries mainly include transition metal oxides, polyanions, and Prussian blue compounds. Among them, polyanion cathode materials are the research hotspot in sodium ion battery cathode materials due to their good safety performance, high cycle stability, and easy control of material structure.

[0004] However, the existing polyanion-type sodium-ion battery cathode materials react with the electrolyte during use, resulting in interface damage, which leads to rapid capacity decay and poor cycle stability in sodium-ion batteries. Based on this, developing effective surface modification technology to improve the interface stability and electrochemical performance of cathode materials is crucial to promote the commercial application of sodium-ion batteries. Summary of the invention

[0005] The present application provides a method for coating a polyanion positive electrode material for a sodium ion battery using an inorganic sulfur / selenium source, aiming to solve the problem in the prior art that the polyanion positive electrode material for a sodium ion battery is easily reacted with an electrolyte, resulting in rapid capacity decay and poor cycle stability of the sodium ion battery.

[0006] In order to achieve the above objectives, the present application adopts the following technical solutions.

[0007] In a first aspect of the present application, a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source is provided, comprising:

[0008] The core material is mixed evenly with an inorganic sulfur source or an inorganic selenium source, calcined at high temperature under a protective atmosphere, and after cooling, ground and sieved to obtain a sulfur- or selenium-coated polyanion type sodium ion battery positive electrode material;

[0009] The core material is a composite of a polyanion positive electrode material and carbon.

[0010] Preferably, in the sulfur- or selenium-coated polyanion sodium ion battery positive electrode material, the coating layer accounts for 5 to 15 wt % of the mass of the core material.

[0011] Preferably, the general structural formula of the polyanionic cathode material is Na 4-y Fe 3-x M x (PO4) a (P2O7) b ;

[0012] Among them, 0≤x≤3; 0≤y≤3; 0≤a; b≤2; M includes at least one of Mn, Ni, Co, Cu, Ti, Zn, Mg, Al, Zr, Cr, Nb or Sc.

[0013] Preferably, in the core material, the mass ratio of the polyanionic positive electrode material to carbon is 4:1 to 20:7.

[0014] Preferably, the inorganic sulfur source includes at least one of sulfur powder, ferrous sulfide, sodium sulfide, ammonium bisulfate or sodium bisulfate;

[0015] The inorganic selenium source includes at least one of selenium powder, selenium trioxide, sodium selenide, sodium selenate or sodium selenite.

[0016] Preferably, the mass ratio of the core material to the inorganic sulfur or selenium source is 1:(0.1-5).

[0017] Preferably, the core material is mixed with the inorganic sulfur or inorganic selenium source by one or more of grinding, ultrasound, ball milling, sand milling, and magnetic stirring.

[0018] Preferably, the protective atmosphere is one or more of nitrogen, argon and hydrogen.

[0019] Preferably, the high temperature calcination, if an inorganic sulfur source is selected, the calcination temperature is 400-600° C., and the time is 1-5 hours;

[0020] If an inorganic selenium source is selected, the calcination temperature is 550-650°C and the time is 2-8 hours.

[0021] Preferably, the grinding is one or more of manual grinding, ball milling, sand milling, and air flow milling, and the mesh size during screening is 300-400.

[0022] Compared with the prior art, the beneficial effects of this application are:

[0023] The method of coating a polyanionic positive electrode material of a sodium ion battery with an inorganic sulfur / selenium source of the present application forms a sulfur / selenium coating layer on the surface of the positive electrode material of the polyanionic sodium ion battery, which can improve the electronic conductivity and sodium ion diffusion rate of the positive electrode material on the one hand, thereby improving the specific capacity, rate performance and cycle stability of the battery, and significantly improving the electrochemical performance; on the other hand, it can enhance the compatibility of the interface, and as a protective layer, it effectively isolates the direct contact between the positive electrode material and the electrolyte, reduces the occurrence of side reactions at the interface, and prolongs the cycle life of the battery; in addition, the sulfur / selenium coating layer can provide adhesion and protection, reduce the shedding of positive electrode active materials, and improve the cycle performance of the battery.

[0024] Compared with the traditional sulfur-carbon coating modification method, the present application has a simple process and is easy to control. The modifiers used in the sulfur / selenium coating layer are all inorganic components, which are low in cost, stable in nature and highly safe compared to organic components, and are conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a SEM spectrum of the sulfur-coated polyanionic cathode material prepared in Example 1;

[0027] Figure 2 The first cycle charge and discharge performance test results of the sodium ion battery prepared with the polyanion positive electrode materials of Example 1 and Comparative Example 1 are shown;

[0028] Figure 3 This is a graph showing the cycle performance test results of sodium ion batteries prepared using the polyanionic positive electrode materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are all open terms, meaning including but not limited to.

[0031] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0032] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0033] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0034] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present application are to be construed as specifically disclosing each intermediate value between the upper and lower limits of the scope. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present application. The upper and lower limits of these smaller ranges may be independently included or excluded in the scope.

[0036] Unless otherwise specified, the technical / scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0037] In a first aspect, the present application provides a method for coating a polyanionic cathode material for a sodium ion battery with an inorganic sulfur / selenium source, specifically comprising:

[0038] The core material is mixed evenly with an inorganic sulfur source or an inorganic selenium source, calcined at high temperature under a protective atmosphere, and after cooling, ground and sieved to obtain a sulfur- or selenium-coated polyanion type sodium ion battery positive electrode material;

[0039] Wherein, the core material is a composite of polyanion positive electrode material and carbon.

[0040] The present application coats a sulfur / selenium layer on the surface of a composite of a polyanionic positive electrode material and carbon. The sulfur / selenium coating layer can not only improve the electronic conductivity and sodium ion diffusion rate of the positive electrode material, thereby improving the specific capacity, rate performance and cycle stability of the battery, and significantly improving the electrochemical performance; the sulfur / selenium coating layer can also serve as a protective layer, effectively isolating the direct contact between the anionic positive electrode material and the electrolyte, reducing the occurrence of interfacial side reactions, and extending the cycle life of the battery; in addition, the sulfur / selenium coating layer can provide adhesion and protection, reduce the shedding of active substances, and improve the cycle performance of the battery.

[0041] In the present application, the general structural formula of the polyanionic cathode material is Na 4-y Fe 3-x M x (PO4) a (P2O7) b ;

[0042] Among them, 0≤x≤3; 0≤y≤3; 0≤a; b≤2; M includes at least one of Mn, Ni, Co, Cu, Ti, Zn, Mg, Al, Zr, Cr, Nb or Sc.

[0043] In the present application, in the core material, the mass ratio of the polyanionic positive electrode material to carbon is preferably 4:1 to 20:7.

[0044] In the present application, the sulfur source is inorganic sulfur, which is more stable than organic sulfur, and the obtained sulfur coating has better adhesion, which is beneficial to reduce the shedding of active substances and improve the cycle performance of the battery. The sulfur source includes at least one of sulfur powder, ferrous sulfide, sodium sulfide, ammonium hydrogen sulfate or sodium hydrogen sulfate.

[0045] In the present application, the selenium source is selected from inorganic selenium, which is more stable than organic selenium, and the obtained selenium coating layer has better adhesion, which is conducive to reducing the shedding of active substances and improving the cycle performance of the battery. The selenium source includes at least one of selenium powder, selenium trioxide, sodium selenide, sodium selenate or sodium selenite.

[0046] In the present application, the core material and the inorganic sulfur or inorganic selenium source are mixed by one or more of grinding, ultrasound, ball milling, sand milling, and magnetic stirring. The mass ratio of the core material to the sulfur source / selenium source is preferably 1: (0.1-5).

[0047] In the present application, calcination is preferably performed under a protective atmosphere, wherein the protective atmosphere is one or more of nitrogen, argon, and hydrogen.

[0048] In the present application, the calcination temperatures of the sulfur coating layer and the selenium coating layer are different. If a sulfur source is used to prepare the sulfur coating layer, the calcination temperature is 400-600°C for 1-5 hours; if a selenium source is used to prepare the selenium coating layer, the calcination temperature is 550-650°C for 2-8 hours. The heating rate is 2-8°C / min.

[0049] In the present application, the sulfur or selenium coated polyanion type sodium ion battery positive electrode material is obtained by grinding and screening the calcined product. The grinding can be performed by one or more of manual grinding, ball milling, sand milling or air flow milling; the sieve during the screening process is 300-400 mesh.

[0050] The present application discloses a method for coating a sodium ion battery polyanionic positive electrode material using an inorganic sulfur / selenium source. Compared with the traditional sulfur-carbon coating modification method, the process is simple and easy to control. The modifiers used in the sulfur / selenium coating layer are all inorganic components, which are low in cost, stable in nature and highly safe compared to organic components, and are conducive to large-scale industrial production.

[0051] The present application is further described below by way of examples.

[0052] Example 1

[0053] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0054] S1, preparation of core material:

[0055] Add 20mmol of anhydrous citric acid, 15mmol of ferric nitrate nonahydrate, and 20mmol of sodium dihydrogen phosphate dihydrate into 30ml of deionized water and stir magnetically at room temperature for 2h. Spray dry the resulting solution to obtain a precursor powder. Heat the precursor powder to 300℃ in a tubular furnace at a heating rate of 2℃ / min for 6 hours, and then heat to 550℃ for 8 hours, with argon-hydrogen mixed gas protection throughout the process; after cooling in the furnace, grind to obtain the core material, whose structural formula is Na4Fe3(PO4)2P2O7 / C;

[0056] S2, preparation of sulfur-coated polyanionic cathode material:

[0057] Na4Fe3(PO4)2P2O7 / C and sulfur powder were weighed at a mass ratio of 1:0.5; they were manually ground in an agate mortar for 30 minutes to obtain a semi-finished precursor powder; they were heated to 400°C at a heating rate of 2°C / min in a tubular furnace under the protection of an argon-hydrogen mixed gas and kept warm for 1 hour. After cooling with the furnace, a sulfur-coated polyanionic positive electrode material was obtained.

[0058] Example 2

[0059] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0060] S1, preparing the core material: the same as in Example 1;

[0061] S2, preparation of selenium-coated polyanion positive electrode material:

[0062] Na4Fe3(PO4)2P2O7 / C and selenium powder were weighed in a mass ratio of 1:2; ball milled at a speed of 300 rpm for 30 minutes to obtain a semi-finished precursor powder; heated to 600°C at a heating rate of 4°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 2 hours; after cooling with the furnace, a selenium-coated polyanionic positive electrode material was obtained.

[0063] Example 3

[0064] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0065] S1, preparation of core material:

[0066] Add 15mmol of anhydrous citric acid, 10mmol of ferric nitrate nonahydrate, and 15mmol of sodium dihydrogen phosphate dihydrate into 30ml of deionized water and stir magnetically at room temperature for 2h. Spray dry the resulting solution to obtain a precursor powder. Heat the precursor powder to 300℃ in a tubular furnace at a heating rate of 2℃ / min and keep it warm for 6 hours, then heat it to 500℃ and keep it warm for 8 hours, with argon and hydrogen mixed gas protection throughout the process; after cooling in the furnace, grind to obtain the core material, whose structural formula is Na3Fe2(PO4)P2O7 / C;

[0067] S2, preparation of sulfur-coated polyanionic cathode material:

[0068] Na3Fe2(PO4)P2O7 / C and sulfur powder were weighed in a mass ratio of 1:1; they were manually ground in an agate mortar for 30 minutes to obtain a semi-finished precursor powder; they were heated to 400°C at a heating rate of 4°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 1.5 hours. After cooling with the furnace, a sulfur-coated polyanionic positive electrode material was obtained.

[0069] Example 4

[0070] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0071] S1, preparing the core material: the same as in Example 3;

[0072] S2, preparation of selenium-coated polyanion positive electrode material:

[0073] Na3Fe2(PO4)P2O7 / C and selenium powder were weighed in a mass ratio of 1:5; ball milled at a speed of 500 rpm for 30 minutes to obtain a semi-finished precursor powder; heated to 650°C at a heating rate of 5°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 6 hours; after cooling with the furnace, a selenium-coated polyanionic positive electrode material was obtained.

[0074] Example 5

[0075] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0076] S1, preparation of core material:

[0077] 20mmol of anhydrous citric acid, 14.55mmol of ferric nitrate nonahydrate, 0.45mmol of cobalt acetate tetrahydrate and 20mmol of sodium dihydrogen phosphate dihydrate were added to 30ml of deionized water and magnetically stirred at room temperature for 2h. The resulting solution was spray dried to obtain a precursor powder. The precursor powder was first heated to 240℃ in a tubular furnace at a heating rate of 3℃ / min and kept warm for 6 hours, and then heated to 600℃ and kept warm for 10 hours, with argon-hydrogen mixed gas protection throughout the process; after cooling with the furnace, the core material was obtained after grinding, and its structural formula is Na4Fe 2.91 Co 0.09 (PO4)2P2O7 / C;

[0078] S2, preparation of sulfur-coated polyanionic cathode material:

[0079] Na4Fe 2.91 Co 0.09 (PO4)2P2O7 / C and sulfur powder were weighed in a mass ratio of 1:1; they were manually ground in an agate mortar for 30 minutes to obtain a semi-finished precursor powder; they were heated to 450°C at a heating rate of 3°C / min in a tubular furnace under the protection of an argon-hydrogen mixed gas and kept warm for 1.5 hours. After cooling with the furnace, a sulfur-coated polyanionic positive electrode material was obtained.

[0080] Example 6

[0081] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0082] S1, preparation of core material:

[0083] 20mmol of anhydrous citric acid, 13.8mmol of ferric nitrate nonahydrate, 0.75mmol of nickel acetate tetrahydrate, 0.45mmol of cobalt acetate tetrahydrate and 20mmol of sodium dihydrogen phosphate dihydrate were added to 30ml of deionized water and magnetically stirred at room temperature for 2h. The resulting solution was spray dried to obtain a precursor powder. The precursor powder was first heated to 300℃ in a tubular furnace at a heating rate of 4℃ / min and kept warm for 6 hours, and then heated to 550℃ and kept warm for 8 hours, with argon-hydrogen mixed gas protection throughout the process; after cooling with the furnace, the core material was obtained after grinding, and its structural formula is Na4Fe 2.76 Co 0.09 Ni 0.15 (PO4)2P2O7 / C;

[0084] S2, preparation of sulfur-coated polyanionic cathode material:

[0085] Na4Fe 2.76 Co 0.09 Ni 0.15 (PO4)2P2O7 / C and sulfur powder were weighed in a mass ratio of 1:4; they were manually ground in an agate mortar for 30 minutes to obtain a semi-finished precursor powder; they were heated to 500°C at a heating rate of 5°C / min in a tubular furnace under the protection of an argon-hydrogen mixed gas and kept warm for 4 hours. After cooling with the furnace, a sulfur-coated polyanionic positive electrode material was obtained.

[0086] Example 7

[0087] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0088] S1, preparation of core material: the same as in Example 1.

[0089] S2, preparation of sulfur-coated polyanionic positive electrode material: Na4Fe3(PO4)2P2O7 / C and sulfur powder are weighed in a mass ratio of 1:1, and the rest is the same as in Example 1.

[0090] Example 8

[0091] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0092] S1, preparation of core material: the same as Example 2.

[0093] S2, preparation of selenium-coated polyanion positive electrode material:

[0094] Na4Fe3(PO4)2P2O7 / C and selenium powder were weighed in a mass ratio of 1:1.5 and ball-milled at a speed of 500 rpm for 30 minutes to obtain a semi-finished precursor powder; it was heated to 550°C at a heating rate of 5°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 6 hours. After cooling with the furnace, a selenium-coated polyanionic positive electrode material was obtained.

[0095] Example 9

[0096] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0097] S1, preparation of core material: same as Example 3.

[0098] S2, preparation of sulfur-coated polyanionic cathode material:

[0099] Na3Fe2(PO4)P2O7 / C and sulfur powder were weighed at a mass ratio of 1:0.5; they were manually ground in an agate mortar for 30 minutes to obtain a semi-finished precursor powder; they were heated to 450°C at a heating rate of 3°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 3 hours. After cooling with the furnace, a sulfur-coated polyanionic positive electrode material was obtained.

[0100] Example 10

[0101] This embodiment provides a method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source, comprising:

[0102] S1, preparation of core material: same as Example 3.

[0103] S2, preparation of selenium-coated polyanion positive electrode material:

[0104] Na3Fe2(PO4)P2O7 / C and selenium trioxide were weighed in a mass ratio of 1:1.5 and ball-milled at a speed of 400 rpm for 30 minutes to obtain a semi-finished precursor powder; it was heated to 620°C at a heating rate of 5°C / min in a tubular furnace under the protection of an argon-hydrogen mixture and kept warm for 4 hours. After cooling with the furnace, a selenium-coated polyanionic positive electrode material was obtained.

[0105] Embodiment 11

[0106] The difference between Example 11 and Example 1 is that in step S2, the heating rate is 4°C / min, the temperature of the second calcination is 400°C and the time is 1 hour, and the rest is the same as Example 1.

[0107] Example 12

[0108] The difference between Example 12 and Example 1 is that in step S2, Na4Fe3(PO4)2P2O7 / C and sulfur powder are weighed in a mass ratio of 1:1.5, and the rest is the same as Example 1.

[0109] Comparative Example 1

[0110] The difference between Comparative Example 1 and Example 1 is that there is no step S2.

[0111] Comparative Example 2

[0112] The difference between Comparative Example 2 and Example 3 is that there is no step S2.

[0113] The sulfur-coated polyanionic cathode material prepared in Example 1 was tested for morphology, and its SEM spectrum is as follows: Figure 1 As shown. Figure 1 It can be seen that the prepared sulfur-coated polyanion material has a dense and uniform microscopic morphology, showing a spherical structure with a size of 0.5 to 2 μm. Since the present application adopts a multi-step sintering process from the preparation of the polyanion positive electrode material to the sulfur coating process, the spherical structure will agglomerate, and the overall size of the agglomerated material is less than 3 μm, and a small, dense and uniform sulfur-coated polyanion material is successfully synthesized.

[0114] The performance of the positive electrode materials prepared in Examples 1-12 and Comparative Examples 1-2 was evaluated by assembling positive electrode sheets and sodium ion batteries, respectively, and performing charge and discharge performance tests.

[0115] (1) Preparation of positive electrode sheet: 70 parts of positive electrode material, 20 parts of acetylene black and 10 parts of PVDF were dissolved in N-methylpyrrolidone to obtain battery positive electrode slurry; the battery positive electrode slurry was coated on the surface of aluminum foil with a coating amount of 2 mg / cm 2 , put it into a vacuum drying oven and vacuum dry it at 90°C for 10 hours, and use a mold to cut the electrode piece to obtain the positive electrode piece.

[0116] (2) Sodium ion battery assembly:

[0117] The positive electrode sheet is used as the positive electrode and the metallic sodium is used as the negative electrode; the electrolyte is 1 molL -1 The sodium salt of NaClO4 is dissolved in a mixed electrolyte of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1 and 5% fluoroethylene carbonate (FEC) is additionally added. The separator is glass fiber (GF / A), and a C2032 button cell is formed in a glove box filled with argon.

[0118] The battery was tested for electrical properties at 30°C and 1.8-4.2V using a CT-4008 battery testing system (Wuhan Blue Electric Electronics Co., Ltd.). The test results are shown in Table 1.

[0119] Table 1 Battery performance test data

[0120]

[0121]

[0122] As can be seen from Table 1, the sodium ion batteries prepared by the polyanion positive electrode materials coated with inorganic sulfur / selenium sources in the present application generally have an initial discharge capacity of more than 110 mAh / g, a first-week coulomb efficiency of more than 95%, and a capacity retention rate of more than 80% after 500 cycles, which are all higher than those of the uncoated polyanion positive electrode materials.

[0123] The sodium ion battery prepared in Example 1 and Comparative Example 1 was subjected to the first cycle charge and discharge test at 30°C, 1.8-4.2V, and 0.1C current density. The 1C current density was 129mAh / g. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the discharge capacity of the original sample is 103.06 mAh / g, and the discharge capacity of the sulfur-coated sample is 117.5 mAh / g, an increase of up to 12.3%. The above results show that the modification method of the present application can effectively improve the discharge capacity of the polyanion material.

[0124] The sodium ion batteries prepared in Example 1 and Comparative Example 1 were activated for 3 cycles at 30°C, 1.8-4.2V, and 0.1C current density, and then the cycle performance test results at 1C current density were 129mAh / g at 1C. Figure 3 As shown. Figure 3 It can be seen that the discharge capacity of the original sample at 1C current density is 93.21mAh / g, and after 500 cycles, the discharge capacity is 69.56mAh / g, and the capacity retention rate is 74.62%; the discharge capacity of the sulfur-coated sample is 103.36mAh / g, and after 500 cycles, the discharge capacity is 97.60mAh / g, and the capacity retention rate is 94.42%. The above results show that the modification method of the present application can effectively improve the cycle stability of the polyanion material.

[0125] The above test results show that the sulfur or selenium coating layer obtained by the preparation method of the present application is coated on the surface of the polyanion material, which can improve the electronic conductivity and sodium ion diffusion rate of the positive electrode material, effectively isolate the direct contact between the positive electrode material and the electrolyte, and reduce the occurrence of interfacial side reactions, thereby improving the battery's specific capacity, first-week coulomb efficiency and cycle stability.

[0126] Although the present application has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in the present application.

Claims

1. A method for coating a sodium ion battery polyanion positive electrode material using an inorganic sulfur / selenium source, characterized in that: include: The core material is mixed evenly with an inorganic sulfur source or an inorganic selenium source, calcined at high temperature under a protective atmosphere, and after cooling, ground and sieved to obtain a sulfur- or selenium-coated polyanion type sodium ion battery positive electrode material; The core material is a composite of a polyanion positive electrode material and carbon.

2. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: In the sulfur- or selenium-coated polyanion sodium ion battery positive electrode material, the sulfur or selenium coating layer accounts for 5 to 15 wt % of the core material mass.

3. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The general structural formula of the polyanionic cathode material is Na 4-y Fe 3-x M x (PO4) a (P2O7) b ; Among them, 0≤x≤3; 0≤y≤3; 0≤a; b≤2; M includes at least one of Mn, Ni, Co, Cu, Ti, Zn, Mg, Al, Zr, Cr, Nb or Sc.

4. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: In the core material, the mass ratio of the polyanion positive electrode material to carbon is 4:1 to 20:

7.

5. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The inorganic sulfur source includes at least one of sulfur powder, ferrous sulfide, sodium sulfide, ammonium bisulfate or sodium bisulfate; The inorganic selenium source includes at least one of selenium powder, selenium trioxide, sodium selenide, sodium selenate or sodium selenite.

6. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The mass ratio of the core material to the inorganic sulfur or selenium source is 1:(0.1-5).

7. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The core material is mixed with the inorganic sulfur or inorganic selenium source by one or more of grinding, ultrasound, ball milling, sand milling and magnetic stirring.

8. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The protective atmosphere is one or more of nitrogen, argon and hydrogen.

9. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The high temperature calcination, if an inorganic sulfur source is selected, the calcination temperature is 400-600°C and the time is 1-5h; If an inorganic selenium source is selected, the calcination temperature is 550-650°C and the time is 2-8 hours.

10. The method for coating a sodium ion battery polyanion positive electrode material with an inorganic sulfur / selenium source according to claim 1, characterized in that: The grinding is one or more of manual grinding, ball milling, sand milling, and air flow crushing, and the screen is 300-400 meshes during the screening process.

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