WO2023097984A1 - 一种正极材料及其制备方法、正极片以及钠离子电池 - Google Patents

一种正极材料及其制备方法、正极片以及钠离子电池 Download PDF

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WO2023097984A1
WO2023097984A1 PCT/CN2022/093421 CN2022093421W WO2023097984A1 WO 2023097984 A1 WO2023097984 A1 WO 2023097984A1 CN 2022093421 W CN2022093421 W CN 2022093421W WO 2023097984 A1 WO2023097984 A1 WO 2023097984A1
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positive electrode
electrode material
doping
sodium
material according
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French (fr)
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徐雄文
涂健
谢健
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湖南钠方新能源科技有限责任公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of battery materials, and in particular relates to a positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery.
  • the layered material used as a sodium-ion battery has certain similarities to the layered cathode material of a lithium-ion battery, but the situation is more complicated, such as richer phases, prone to phase change at lower charging voltages, and easy to occur Lattice loses oxygen, reacts with air to make the surface more alkaline, etc.
  • the layered materials used for the cathode of sodium-ion batteries generally use Mn element as the basic framework, and contribute capacity by doping electrochemically active elements such as Ni, Fe, Co, Cr, etc.
  • O3-type materials have the advantage of high capacity, but complex phase transitions will occur during cycling, resulting in lattice distortion and poor cycle performance.
  • the lattice is stabilized by doping inactive elements, but excessive doping will cause a decrease in capacity, and even cause performance degradation due to oxygen loss in the lattice, and doping with high-valent ions will reduce the sodium content in the sodium layer. Therefore, it is necessary to optimize the doping element, doping amount, and doping position.
  • One of the purposes of the present invention is to address the deficiencies of the prior art and provide a positive electrode material with a stable lattice structure and a surface doped structure covered with doping elements, which can effectively suppress harmful phase transitions during charging and discharging. , good stability, high specific capacity, good rate performance and cycle life.
  • a positive electrode material whose general chemical formula is Na nm A m Mn 1-xy M1 x M2 y O 2-z F z , the material is in O3 phase, where M1 is Fe, Ni, Cr, Cu, Co At least one, M2 is at least one of Li, Na, K, Mg, Ca, Sr, A is at least one of Nb, Ta, Zr, Mo, W, where 0.2 ⁇ x ⁇ 0.7, 0.01 ⁇ y ⁇ 0.1, x/(1-xy) ⁇ 0.5, 0 ⁇ z ⁇ 0.1, 0 ⁇ m ⁇ 0.05, 0.85 ⁇ n ⁇ 1.
  • the manganese-based layered positive electrode material of the present invention uses Mn element as the basic frame, and by combining the lattice doping and surface doping, the harmful phase transition in the charging and discharging process is suppressed, so that it maintains the O3 phase, and the elements Mn, M1 and M2 present an orderly distribution, and the elements of type A and element F are distributed on the surface of material particles in a gradient manner. function, inhibit the harmful phase transition of the material during charge and discharge, and inhibit the cracking of active particles, thereby improving the electrochemical performance of the material. Stabilize the crystal lattice of the material during charge and discharge, and improve its stability in the electrolyte and air, thereby improving the specific capacity, rate performance and cycle life of the material.
  • K1, K2, K3, and K4 are the valences of elements A, Mn, M1, and M2 in the positive electrode material, respectively.
  • the doping element M1 is an electrochemically active element, and the electrochemical activity means that the element can contribute capacity by changing the price during the charging and discharging process.
  • the doping element M2 is an electrochemically inactive element, and the electrochemical inactivity means that the element cannot contribute to the capacity by changing the price during the charging and discharging process.
  • This type of metal is easy to form ionic bonds with oxygen and fluorine in the crystal lattice, which is conducive to promoting the formation of O3 type layered structure;
  • this type of metal has a larger ionic radius (The radii of Li + , Na + , K + , Mg 2+ , Ca 2+ , and Sr 2+ are respectively ), much higher than the ionic radius of active metal M1 when charging (Fe 2+ , Ni 2+ , Cu 2+ , Cr 3+ , Co 3+ radii are respectively ), which can compensate the lattice distortion caused by the rapid decrease of the ion radius of the active metal M1 during charging, and suppress the slippage of the transition metal layer, thereby suppressing the harmful phase transition; (3)
  • This kind of ion doping can promote the redox reaction of M1, thereby activating the deintercalation of sodium ions in the sodium layer.
  • these elements belong to alkali metals and alkaline earth metals, according to the diagonal principle, Li + and Mg 2+ , Na + and Ca 2+ , K + and Sr 2+ have similar physical and chemical properties.
  • the positive electrode material includes lattice particles and a surface doping layer covering the surface of the lattice particles.
  • the present invention combines lattice doping and surface doping to suppress harmful phase transitions during charge and discharge, stabilize the lattice of the material during charge and discharge, and improve its stability in electrolyte and air, thereby improving The specific capacity, rate performance and cycle life of the material.
  • the layered anode material of the present invention is subjected to crystal lattice doping and surface modification, and the surface modification includes doping of type A elements on the surface sodium side and fluorine doping on the surface oxygen side.
  • the surface doped layer includes at least one of fluorine element or type A element.
  • the surface doping includes surface fluorine element doping or at least one doping of type A elements.
  • the doping of element F is located within 5-50 atomic layers of the surface of the lattice particles, and the content of F element gradually decreases from the outside to the inside.
  • the effects of surface gradient fluorine doping are: (1) Stabilize the surface structure and inhibit Harmful phase transition induced by the surface of the material; (2) a small amount of surface doping does not affect the diffusion of sodium ions inside the lattice, and does not affect the specific capacity of the material; (3) the F-rich surface is beneficial to improve the stability of the material in air , and the F-rich surface is easy to form surface fluoride in situ to improve the stability of the material in the electrolyte; (4) Fluorine, which is more electronegative than oxygen, forms a stronger ionic bond with metal M2, which is less electronegative , thereby stabilizing the surface structure of the material, further improving the stability of the material in electrolyte and air, and suppressing the surface phase transition.
  • the gradient doping of A-type elements wherein the A-type elements are at least one of Nb, Ta, Zr, Mo, and W, and the doping of A-type elements is located within 5 to 50 atomic layers of the particle surface, and from the outside
  • the effect of surface gradient A-type element doping is: (1) Element A acts as a pillar, inhibiting the lattice distortion of the sodium layer during desodiumization, stabilizing the surface structure, and inhibiting the (2) A small amount of surface doping does not affect the diffusion of sodium ions inside the lattice, and does not affect the specific capacity of the material; (3) Forming an appropriate amount of sodium vacancies in the sodium layer by doping can accelerate the diffusion of sodium ions in the lattice.
  • the fluorine content and/or the A-type element content of the surface doped layer decreases sequentially from the outside to the inside. Gradient doping on the surface of fluorine and A-type elements can control the harmful phase transition and improve the stability.
  • the particle size of the positive electrode material is 0.5 micron to 20 micron. Within this particle size range, it is beneficial to increase the compaction density of the electrode and improve the processing performance of the electrode.
  • the second object of the present invention is to provide a method for preparing positive electrode materials, which has simple and controllable process, low cost, short cycle, low energy consumption and is suitable for industrial production.
  • a method for preparing a positive electrode material comprising the steps of:
  • Step S1 using a synthetic method to prepare lattice particles Na n Mn 1-xy M1 x M2 y O 2 ;
  • Step S2 doping the lattice particles Na n Mn 1-xy M1 x M2 y O 2 with fluorine element and type A element to obtain Na nm A m Mn 1-xy M1 x M2 y O 2-z F z .
  • the invention has the advantages of simple and controllable process, low cost, short cycle, low energy consumption and suitability for industrialized production.
  • the surface doping process for A-type elements is generally to disperse Na n Mn 1-xy M1 x M2 y O 2 or Na n Mn 1-xy M1 x M2 y O 2 doped with surface F elements in an organic solvent, and then Add organic salts of A-type elements, stir and dry, and finally calcine in air or oxygen to achieve surface gradient doping of A-type elements, wherein the calcination temperature is 500°C to 700°C, and the calcination time is 2 to 10 hours.
  • the organic The solvent is selected from ethanol
  • the organic salt of the A-type element is selected from ethanol salt
  • the surface gradient doping of the element A is realized by adjusting the amount of the organic salt of the A-type element, roasting temperature and time; the surface doping process of the element F is generally To do this, mix Na n Mn 1-xy M1 x M2 y O 2 or surface A element-doped Na n Mn 1-xy M1 x M2 y O 2 with NH 4 F evenly, and then bake in air or oxygen atmosphere
  • the surface doping of element F, the calcination temperature is 300°C-500°C, the calcination time is 2-10 hours
  • the mixing method is preferably dry ball milling, by adjusting the amount of NH 4 F used, the calcination temperature and time to achieve surface gradient doping of element F.
  • the synthesis method in the step S1 includes solid phase method, co-precipitation method, spray drying method and sol-gel method.
  • the solid phase reaction method means that in the synthesis of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z , the compounds containing elements Na, Mn, M1, M2 are subjected to sand milling, ball milling, or high-mixing The process is mixed evenly, and then the solid phase reaction is carried out.
  • the compound is selected from but not limited to nitrates, acetates, carbonates, oxalates, hydroxides, oxides, and oxyhydroxides containing these elements , or its hydrate.
  • the solid phase reaction temperature is 600°C-1100°C
  • the reaction time is 3-24 hours
  • the reaction atmosphere is selected from air, oxygen, or compressed air.
  • Co-precipitation method means that in the synthesis of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z , the soluble salt containing Mn and M1 is dissolved in deionized water to prepare a salt solution, and a precipitant solution and a complex Mixture agent solution, then inject salt solution, precipitant solution and complexing agent solution into the reaction vessel simultaneously to obtain precipitation.
  • the salt solution is selected from chlorides, sulfates, nitrates, or hydrates thereof, the complexing agent solution is selected from ammonia, and the precipitation agent solution is selected from sodium hydroxide, An aqueous solution of potassium hydroxide, sodium carbonate, potassium carbonate, sodium oxalate, and potassium oxalate; preferably, the coprecipitation reaction temperature is 40°C to 60°C, and the pH value of the reaction solution depends on the precipitating agent.
  • the pH value is generally about 11. After the co-precipitation reaction, the precipitate is washed and dried, mixed evenly with the compound containing Na and M2, and then the solid-phase reaction is carried out.
  • the spray-drying method adopts the direct spray-drying method, in the synthesis of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z , the soluble compounds of Na, Mn, M1, M2 are dissolved in deionized water, After being fully mixed and uniform, the precursor is obtained by spray drying, and then the solid phase reaction is carried out.
  • the sol-gel method refers to that in the synthesis of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z , the nitrate or sulfate of Na, Mn, M1, M2 is dissolved in water 1.
  • a complexing agent such as citric acid, stir at 60°C to 90°C to obtain a gel, and then perform a solid phase reaction.
  • the step S2 it also includes adding 1 to 10 parts by weight of the sodium supplement agent to 100 to 110 parts by weight of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z Sodium treatment.
  • the sodium supplement agent to 100 to 110 parts by weight of Na nm A m Mn 1-xy M1 x M2 y O 2-z F z Sodium treatment.
  • high temperature can easily lead to sodium burning loss, and the amount of sodium needs to be supplemented so that the excess sodium is 1% to 10%.
  • the sodium replenishing agent comprises Na 2 S, a conductive agent and a catalyst
  • the conductive agent is selected from at least one of acetylene black, carbon nanotubes, carbon fibers, and graphene
  • the catalyst is a transition metal oxide, selected from From but not limited to at least one of CuO, MnO 2 , Mn 3 O 4 , NiO
  • the weight ratio of Na 2 S, conductive agent and catalyst is 1-2:0.01-0.1:0.01-0.1; preferably,
  • the weight ratio of the sodium replenishing agent to the layered active material is 1:100-10:100.
  • the sodium replenishment can effectively compensate for the loss of sodium in the negative electrode during the first charging and improve the first coulombic efficiency.
  • the sodium replenishing agent includes sodium sulfide, a conductive agent and a catalyst in a ratio of parts by weight of 1-2:0.01-0.1:0.01-0.1.
  • the third object of the present invention is to provide a positive electrode sheet with good electrochemical performance, stable structure and long service life in view of the deficiencies in the prior art.
  • a positive electrode sheet comprising a positive electrode current collector and a positive electrode active material arranged on at least one surface of the positive electrode current collector, the positive electrode active material includes the above-mentioned positive electrode material.
  • the positive electrode active material may be disposed on one surface of the positive electrode current collector, or may be disposed on both surfaces of the positive electrode current collector.
  • the fourth object of the present invention is to provide a sodium ion battery with high capacity, excellent rate performance and long cycle life in view of the deficiencies of the prior art.
  • a sodium ion battery comprising the above-mentioned positive electrode sheet.
  • a sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a diaphragm, an electrolyte, and a housing, the diaphragm separates the positive electrode sheet and the negative electrode sheet, and the casing combines the positive electrode sheet, the negative electrode sheet, the diaphragm, and the electrolytic The liquid seal wraps it up.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided with at least one surface of the negative electrode current collector, and the negative electrode active layer includes at least one negative electrode active material in soft carbon, hard carbon, or hard carbon/soft carbon composite materials.
  • organic solution containing an organic solvent, sodium salt, and additives is used as an organic electrolyte.
  • the organic solvent is selected from but not limited to at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
  • Sodium salts include at least one of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bistrifluoromethanesulfonimide, sodium bisfluorosulfonimide, sodium tetrafluoroborate, and sodium bisoxalate borate A sort of.
  • the beneficial effect of the present invention lies in: a positive electrode material of the present invention, through the uniform doping of M1 and M2 elements in the bulk phase of the material, and the surface doping of elements A and F, and both
  • the synergistic effect can effectively inhibit the harmful phase transition of the material during charge and discharge, and improve the stability of the material in the electrolyte and air.
  • the resulting material has high capacity, excellent rate performance and long cycle life.
  • the positive electrode material of the present invention has a stable lattice structure and a surface doping structure coated with doping elements, effectively inhibits harmful phase transitions during charge and discharge, has good stability, high specific capacity, good rate performance and cycle life.
  • FIG. 1 is an X-ray diffraction pattern of the O3 phase manganese-based layered positive electrode material prepared in Example 1 of the present invention.
  • Fig. 2 is a charge-discharge curve diagram of the O3 phase manganese-based layered positive electrode material prepared in Example 1 of the present invention.
  • Step S1 According to the stoichiometric ratio of Na 0.91 Nb 0.004 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.06 ]O 1.99 F 0.01 , the material is prepared by direct solid state reaction method and surface doping. According to the stoichiometric ratio, Na 2 CO 3 , Mn 2 O 3 , Fe 2 O 3 , NiO, Li 2 CO 3 were mixed evenly, and the precursor was obtained after ball milling. The ball milling time was 10 hours and the rotation speed was 400 rpm. The precursor was placed in a muffle furnace and calcined at 820°C for 10 hours in an air atmosphere to obtain a manganese-based layered material without surface doping.
  • Step S2 the above product is mixed with a certain amount of niobium ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Nb doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD, and it was O3 phase, as shown in Figure 1. According to the elemental analysis, the elements Mn, Fe, Ni, and Li are evenly distributed in the bulk phase of the material, and the elements Nb and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the propylene carbonate (PC)/ethyl methyl carbonate (EMC) solution of NaPF 6 is the electrolyte, and the weight of the above electrolyte added is 4% fluorinated ethylene carbonate (FEC), assembled button battery, and carried out charge and discharge test, the current density is 12mA/g, the voltage range is 1.5 ⁇ 3.9V, the charge and discharge curve is shown in Figure 2, and the specific capacity is 125mAh/g, The material has a capacity retention rate of 91% after 400 cycles.
  • PC propylene carbonate
  • EMC ethyl methyl carbonate
  • Step S1 According to the stoichiometric ratio of Na 0.86 Nb 0.002 [Mn 0.47 Fe 0.24 Ni 0.24 Li 0.05 ]O 1.995 F 0.005 , the material is prepared by co-precipitation method with solid phase reaction and surface doping. According to the stoichiometric ratio, NiSO 4 , MnSO 4 , and FeSO 4 were placed in deionized water and mixed evenly to obtain a salt solution with a total concentration of 1mol/L, and 0.5mol/L ammonia solution and 2mol/L NaOH solution were prepared as complexing agent and precipitating agent, and then inject the salt solution, complexing agent and precipitating agent into the reaction vessel at the same time to carry out co-precipitation reaction.
  • the resulting precipitate was centrifuged and dried, mixed with Na 2 CO 3 and Li 2 CO 3 in a measured ratio, then placed in a muffle furnace, and calcined at 820°C for 10 hours in an air atmosphere to obtain a non-surface-doped Manganese-based layered materials.
  • Step S2 the above product is mixed with a certain amount of niobium ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Nb doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and was O3 phase. According to the elemental analysis, the elements Mn, Fe, Ni, and Li are evenly distributed in the bulk phase of the material, and the elements Nb and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 90%.
  • Step S1 According to the stoichiometric ratio of Na 0.87 Nb 0.002 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.05 ]O 1.995 F 0.005 , the material is prepared by using a sol-gel method combined with solid phase reaction and surface doping.
  • NaNO 3 , LiNO 3 , Mn(NO 3 ) 2 , Ni(NO 3 ) 2 , Fe(NO 3 ) 2 were mixed in deionized water, stirred to obtain a sol, and then added citric acid, at 60 After fully stirring at °C to obtain a gel, then place it in a muffle furnace and bake at 810°C for 15 hours in an air atmosphere to obtain a manganese-based layered material without surface doping.
  • Step S2 the above product is mixed with a certain amount of niobium ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Nb doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. According to the elemental analysis, the elements Mn, Fe, Ni, and Li are evenly distributed in the bulk phase of the material, and the elements Nb and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 93%.
  • Step S1 According to the stoichiometric ratio of Na 0.88 Nb 0.002 [Mn 0.43 Fe 0.31 Cu 0.20 Li 0.06 ]O 1.997 F 0.003 , the material is prepared by co-precipitation method with solid phase reaction and surface doping. According to the stoichiometric ratio, CuSO 4 , MnSO 4 , and FeSO 4 were placed in deionized water and mixed evenly to obtain a salt solution with a total concentration of 1mol/L, and 0.5mol/L ammonia solution and 2mol/L NaOH solution were prepared as complexing agent and precipitating agent, and then inject the salt solution, complexing agent and precipitating agent into the reaction vessel at the same time to carry out co-precipitation reaction.
  • CuSO 4 , MnSO 4 , and FeSO 4 were placed in deionized water and mixed evenly to obtain a salt solution with a total concentration of 1mol/L, and 0.5mol/L ammonia solution and 2mol/L NaOH solution were prepared as complex
  • the resulting precipitate was centrifuged and dried, mixed with Na 2 CO 3 and Li 2 CO 3 in a measured ratio, then placed in a muffle furnace, and calcined at 820°C for 10 hours in an air atmosphere to obtain a non-surface-doped Manganese-based layered materials.
  • Step S2 the above product is mixed with a certain amount of niobium ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Nb doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and was O3 phase. According to the elemental analysis, the elements Mn, Fe, Cu, and Li are evenly distributed in the bulk phase of the material, and the elements Nb and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 91%.
  • Step S1 According to the stoichiometric ratio of Na 0.88 Ta 0.002 [Mn 0.43 Fe 0.27 Cr 0.04 Ni 0.20 Li 0.06 ]O 1.997 F 0.003 , the material is prepared by co-precipitation method combined with solid phase reaction and surface doping.
  • the resulting precipitate was centrifuged and dried, mixed with Na 2 CO 3 and Li 2 CO 3 in a measured ratio, then placed in a muffle furnace, and calcined at 820°C for 12 hours in an air atmosphere to obtain a non-surface-doped Manganese-based layered materials.
  • Step S2 the above product is mixed with a certain amount of tantalum ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Ta doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and was O3 phase. According to the elemental analysis, the elements Mn, Fe, Cr, Ni, and Li are evenly distributed in the bulk phase of the material, and the elements Ta and F present a gradient graduation on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 90%.
  • Step S1 According to the stoichiometric ratio of Na 0.85 Ta 0.004 [Mn 0.42 Fe 0.28 Ni 0.13 Cu 0.12 Mg 0.05 ]O 1.99 F 0.01 , the material is prepared by using a direct solid-state method combined with surface doping. According to the stoichiometric ratio, NaNO 3 , Mn 3 O 4 , Fe 3 O 4 , Ni(OH) 2 , MgO, and CuO were mixed evenly, and the precursor was obtained after ball milling. The ball milling time was 10 hours and the rotation speed was 400rpm. The precursor was placed in a muffle furnace and calcined at 820° C. for 15 hours in an air atmosphere to obtain a manganese-based layered material without surface doping.
  • Step S2 the above product is mixed with a certain amount of tantalum ethoxide in ethanol, stirred and dried at 60°C, and then calcined in air at 600°C for 5 hours to perform Ta doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. According to the elemental analysis, the elements Mn, Fe, Ni, Cu, and Mg are evenly distributed in the bulk phase of the material, and the elements Ta and F present a gradient graduation on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 92%.
  • Step S1 According to the stoichiometric ratio of Na 0.88 Zr 0.003 [Mn 0.42 Fe 0.31 Ni 0.11 Cu 0.11 Li 0.05 ]O 1.996 F 0.004 , the material is prepared by using a direct solid-state method combined with surface doping. According to the stoichiometric ratio, NaNO 3 , Mn 3 O 4 , Fe 3 O 4 , Ni(OH) 2 , LiNO 3 , and CuO were mixed evenly, and deionized water was used as the medium to obtain the precursor slurry after sand milling, in which The ball milling time is 3 hours, and the rotation speed is 2000rpm. The slurry obtained by sand milling is spray-dried to obtain a precursor.
  • the inlet temperature of the spray dryer is 180°C, and the outlet temperature is 110°C. Then the precursor is placed in a muffle furnace. After calcining at 820° C. for 15 hours in an air atmosphere, a manganese-based layered material without surface doping was obtained.
  • Step S2 Mix the above-mentioned product with a certain amount of zirconium ethoxide in ethanol, stir and dry at 60°C, and then bake in air at 600°C for 5 hours to perform Zr doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. According to the elemental analysis, the elements Mn, Fe, Ni, Cu, and Li are evenly distributed in the bulk phase of the material, and the elements Zr and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 90%.
  • Step S1 According to the stoichiometric ratio of Na 0.89 Zr 0.002 [Mn 0.42 Fe 0.31 Ni 0.05 Cu 0.16 Li 0.05 Mg 0.01 ]O 1.996 F 0.004 , the material is prepared by using a direct solid-state method combined with surface doping. According to the stoichiometric ratio, mix Na 2 CO 3 , MnO 2 , Fe 2 O 3 , NiO, CuO, Li 2 CO 3 , and MgO evenly, and use deionized water as the medium to obtain the precursor slurry after sand milling, in which The ball milling time is 4 hours, and the rotation speed is 2000rpm. The slurry obtained by sand milling is spray-dried to obtain a precursor. The inlet temperature of the spray dryer is 180°C, and the outlet temperature is 110°C. After calcining at 830° C. for 10 hours in an air atmosphere, a manganese-based layered material without surface doping was obtained.
  • Step S2 Mix the above-mentioned product with a certain amount of zirconium ethoxide in ethanol, stir and dry at 60°C, and then bake in air at 600°C for 5 hours to perform Zr doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. Elemental analysis shows that the elements Mn, Fe, Ni, Cu, Li, and Mg are evenly distributed in the bulk phase of the material, and the elements Zr and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 92%.
  • Step S1 According to the stoichiometric ratio of Na 0.85 Zr 0.002 [Mn 0.51 Fe 0.19 Ni 0.08 Cu 0.15 Li 0.07 ]O 1.996 F 0.004 , the material is prepared by direct solid-state method combined with surface doping. According to the stoichiometric ratio, Na 2 CO 3 , MnO 2 , Fe 2 O 3 , NiO, CuO, Li 2 CO 3 were mixed evenly, and deionized water was used as the medium to obtain the precursor slurry after sand milling.
  • the ball milling time For 4 hours, the rotation speed is 2000rpm, and the slurry obtained by sand grinding is spray-dried to obtain the precursor, wherein the inlet temperature of the spray dryer is 180°C, and the outlet temperature is 110°C, and then the precursor is placed in the muffle furnace, in the air atmosphere After calcination at 810°C for 15 hours, the manganese-based layered material without surface doping was obtained.
  • Step S2 Mix the above-mentioned product with a certain amount of zirconium ethoxide in ethanol, stir and dry at 60°C, and then bake in air at 600°C for 5 hours to perform Zr doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. According to the elemental analysis, the elements Mn, Fe, Ni, Cu, and Li are evenly distributed in the bulk phase of the material, and the elements Zr and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 91%.
  • Step S1 According to the stoichiometric ratio of Na 0.93 Zr 0.005 [Mn 0.46 Cr 0.18 Ni 0.14 Cu 0.16 Li 0.06 ]O 1.996 F 0.004 , the material is prepared by direct spray drying method combined with solid phase reaction and surface doping. According to the stoichiometric ratio, NaNO 3 , Mn(NO 3 ) 2 , Cr(NO 3 ) 3 , Ni(NO 3 ) 2 , Cu(NO 3 ) 2 , LiNO 3 were mixed in deionized water and stirred thoroughly to obtain Mix the solution, and then spray dry to obtain the precursor. The inlet temperature of the spray dryer is 180°C, and the outlet temperature is 110°C. Then, the obtained precursor is placed in a muffle furnace and roasted at 820°C for 15 hours in an air atmosphere to obtain The manganese-based layered material is not surface-doped.
  • Step S2 Mix the above-mentioned product with a certain amount of zirconium ethoxide in ethanol, stir and dry at 60°C, and then bake in air at 600°C for 5 hours to perform Zr doping on the surface. Then the above-mentioned product was mixed uniformly with a certain amount of NH 4 F, and baked at 400° C. for 5 hours in the air to perform F doping on the surface.
  • the product was analyzed by XRD and had an O3 phase. According to the elemental analysis, the elements Mn, Cr, Ni, Cu, and Li are evenly distributed in the bulk phase of the material, and the elements Zr and F present a gradient on the surface of the material, and the content gradually decreases from the outside to the inside.
  • the material prepared in this embodiment is used as the positive electrode, the sodium metal is used as the negative electrode, the glass fiber is the diaphragm, and the PC/EMC solution of NaPF 6 is the electrolyte, and the above-mentioned electrolyte weight is 4% of FEC, and a button cell is assembled for charging.
  • Discharge test the current density is 12mA/g, the voltage range is 1.5-3.9V, after 400 cycles, the capacity retention rate is 90%.
  • Example 1 The difference from Example 1 is that no lithium is doped during the preparation process, and the lithium part is replaced by the electrochemically active element Ni, that is, Na 0.75 Nb 0.004 [Mn 0.44 Fe 0.24 Ni 0.32 ]O 1.99 F 0.01 . Under the same test conditions as in Example 1, after 400 cycles, the capacity retention rate was 82%.
  • Example 1 The difference from Example 1 is that during the preparation process, Nb doping was not performed on the Na side surface, and Na 0.93 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.06 ]O 1.99 F 0.01 was obtained. Under the same test conditions as in Example 1, after 400 cycles, the capacity retention rate is 80%.
  • Example 1 The difference from Example 1 is that the surface is not doped with F during the preparation process, and Na 0.92 Nb 0.004 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.06 ]O 2 is obtained. Under the same test conditions as in Example 1, after 400 cycles, the capacity retention rate was 79%.
  • Example 1 The difference from Example 1 is that no F and Nb are doped on the surface during the preparation process, and Na 0.94 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.06 ]O 2 is obtained. Under the same test conditions as in Example 1, after 400 cycles, the capacity retention rate was 75%.
  • Example 1 The difference from Example 1 is that no lithium is doped during the preparation process, and the lithium part is replaced by the electrochemically active element Ni, that is, Na 0.75 Nb 0.004 [Mn 0.44 Fe 0.24 Ni 0.32 ]O 1.99 F 0.01 O 2 .
  • Example 1 The difference from Example 1 is that during the preparation process, the sodium side surface is doped with titanium to obtain Na 0.91 Ti 0.004 [Mn 0.44 Fe 0.24 Ni 0.26 Li 0.06 ]O 1.99 F 0.01 . Under the same test conditions as in Example 1, after 400 cycles, the capacity retention rate was 78%.
  • step (3) (1) In an environment of 25°C, discharge to 1.5V with a constant current rate of 0.2C, and let it stand for 5 minutes; (2) Charge to 3.9V with a constant current rate of 0.5C, and charge to The current is lower than 0.05C, and stand for 5 minutes; (3) discharge to 1.5V at a rate of 0.2C to obtain the discharge capacity at a rate of 0.2C; (4) repeat the above steps (2)-(3) and adjust The discharge rates in step (3) are respectively 0.5C, 1C, 1.5C and 2.0C to obtain the discharge capacities at different discharge rates. The discharge capacity obtained at each rate is compared with the discharge capacity obtained at 0.2C rate to compare the rate performance.
  • the positive electrode material prepared by the present invention has better electrochemical performance than the positive electrode material of the prior art, and the prepared sodium ion battery has good specific capacity, rate performance and cycle life. After 400 times of charging and discharging, the capacity retention rate is as high as 93%, and the 2C discharge capacity/0.2C discharge capacity is as high as 90.5%.
  • Example 1 From the comparison of Example 1 and Comparative Example 1, it can be concluded that the performance of the material prepared without doping A-type elements is poor, and the capacity retention rate decreases, indicating that the doping of A-type elements can improve the electrochemical performance of the material and increase the capacity retention rate.
  • Example 1 From the comparison of Example 1 and Comparative Example 2, it can be concluded that the performance of the material prepared without doping F element is worse, and the capacity retention rate drops greatly, indicating that the doping of F element can improve the capacity retention rate of the material, and the effect is relative to that of A The class element is larger.
  • Example 1 From the comparison of Example 1 and Comparative Example 3, it can be concluded that the performance of the material prepared without doping F elements and A-type elements is the worst, and the capacity retention rate drops the most, indicating that both F elements and A-type elements have an effect on the capacity retention rate of the material. Influence, the doping of the two can help to play a role and improve the capacity retention rate.
  • Example 1 From the comparison of Example 1 and Comparative Example 4, it can be concluded that the performance of the material prepared without doping the inactive element M2 is poor, and the capacity retention rate decreases. This is because the doping of the inactive element M2 can form stronger ionic bonds, thereby Stabilize the surface structure of the material, further improve the stability of the material in the electrolyte and air, and inhibit the surface phase transition, thereby improving the capacity retention rate of the material.

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Abstract

本发明属于电池材料技术领域，尤其涉及一种正极材料及其制备方法、正极片以及钠离子电池，其化学通式为Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z，该材料呈O3相，式中M1为Fe、Ni、Cr、Cu、Co中的至少一种，M2为Li、Na、K、Mg、Ca、Sr中的至少一种，A为Nb、Ta、Zr、Mo、W中的至少一种，其中0.2≤x≤0.7，0.01≤y≤0.1，x/(1-x-y)≥0.5，0<z≤0.1，0<m≤0.05，0.85≤n≤1。本发明的正极材料，具有稳定的晶格结构以及掺杂元素包覆的表面掺杂结构，有效抑制充放电过程中的有害相变，稳定性好，具有高的比容量，良好的倍率性能以及循环寿命。

Description

一种正极材料及其制备方法、正极片以及钠离子电池 技术领域
本发明属于电池材料技术领域，尤其涉及一种正极材料及其制备方法、正极片以及钠离子电池。
背景技术
随着汽车电动化的快速推进，对锂离子动力电池的需求巨大，导致锂资源供应日益紧张、价格居高不下。另一方面，随着国家“碳达峰，碳中和”大战略的推进，发展风光为主的清洁能源势在必行，为提高清洁能源的利用效率，必然要配置储能电池。鉴于目前储能电池中锂离子电池占主导地位，储能产业的快速发展同样加剧了锂资源的快速消耗。因此，开发后锂离子电池的新型储能电池迫在眉睫。钠离子电池具有安全性好、成本低、资源丰富，环境友好等综合优点，非常适合于大规模储能。对于开发钠离子电池，获得合适的正极材料是关键因素。层状材料具有容量较高、倍率性能好、循环寿命长等优点，适合作为钠离子电池正极材料。
用作钠离子电池的层状材料，相对于锂离子电池层状正极材料，具有一定的相似性，但情况更复杂，如物相更丰富、在较低充电电压下易发生相变、易发生晶格失氧、与空气接触发生反应造成表面碱性更强等。目前，用于钠离子电池正极的层状材料一般以Mn元素为基本框架，通过掺杂电化学活性元素如Ni、Fe、Co、Cr等来贡献容量。在层状材料中，O3型材料具有容量高的优点，但在循环过程中会发生复杂的相变，导致晶格发生畸变从而引发循环性能变差。通过掺杂非活性元素来稳定晶格，但过量掺杂会引起容量的降低，甚至会造成晶格失氧造成性能衰退，而且高价离子掺杂会造成钠层中钠含量的减少。因此，需要优化掺杂元素、掺杂量、掺杂位置。
发明内容
本发明的目的之一在于：针对现有技术的不足，而提供一种正极材料，具 有稳定的晶格结构以及掺杂元素包覆的表面掺杂结构，有效抑制充放电过程中的有害相变，稳定性好，具有高的比容量，良好的倍率性能以及循环寿命。
为了实现上述目的，本发明采用以下技术方案：
一种正极材料，其化学通式为Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z，该材料呈O3相，式中M1为Fe、Ni、Cr、Cu、Co中的至少一种，M2为Li、Na、K、Mg、Ca、Sr中的至少一种，A为Nb、Ta、Zr、Mo、W中的至少一种，其中0.2≤x≤0.7，0.01≤y≤0.1，x/(1-x-y)≥0.5，0<z≤0.1，0<m≤0.05，0.85≤n≤1。
本发明的锰基层状正极材料以Mn元素为基本框架，通过将晶格掺杂和表面掺杂结合，抑制充放电过程中的有害相变，使其保持O3相，晶格颗粒中元素Mn、M1、M2呈现有序分布，A类元素和元素F呈梯度分布于材料颗粒表面，通过元素M1和M2的体相掺杂及A类元素和元素F的表面梯度掺杂，以及它们之间协同作用，抑制该材料在充放电过程中的有害相变，抑制活性颗粒的开裂，从而提高材料的电化学性能。稳定材料在充放电过程中的晶格，并提高其在电解液和空气中的稳定性，从而提高材料的比容量、倍率性能以及循环寿命。本发明的正极材料整体呈电中性，电中性是指(n-m)+m×K1+(1-x-y)×K2+x×K3+y×K4＝(2-z)×2+z，其中K1、K2、K3、K4分别为元素A、Mn、M1、M2在正极材料中的化合价。当A类元素、M1、M2具有两个或两个以上的元素时，根据该正极材料电中性原理，正电荷数与负电荷数相等，即可得出关系式。
其中，掺杂元素M1为电化学活性元素，电化学活性是指该元素在充放电过程中可以通过变价贡献容量。
其中，掺杂元素M2为电化学非活性元素，电化学非活性是指该元素在充放电过程中不能通过变价贡献容量。这类金属掺杂的优点是：(1)这类金属易与晶格中的氧和氟形成离子键，有利于促进O3型层状结构的形成；(2)这类金属的离子半径较大(Li +、Na +、K +、Mg 2+、Ca 2+、Sr 2+的半径分别为
Figure PCTCN2022093421-appb-000001
Figure PCTCN2022093421-appb-000002
)，远高于活性金属M1充电时的离子半 径(Fe 2+、Ni 2+、Cu 2+、Cr 3+、Co 3+半径分别为
Figure PCTCN2022093421-appb-000003
Figure PCTCN2022093421-appb-000004
)，可以补偿充电时活性金属M1离子半径快速下降造成的晶格畸变，抑制过渡金属层的滑移，从而抑制有害相变；(3)低价元素的掺杂有利于促进Mn达到最稳定的四价态并提高Na含量，从而抑制三价锰的John-Teller效应并提高容量。(4)这类离子掺杂可以促进M1的氧化还原反应，从而激活钠层钠离子的脱嵌。(5)虽然这类元素分属碱金属和碱土金属元素，但根据对角线原则，Li +和Mg 2+、Na +和Ca 2+、K +和Sr 2+具有类似的物化性质。作为优选，0.01≤y≤0.1，再优选，0.03≤y≤0.09，在此范围内，可实现容量、工作电压和循环寿命的优化平衡，过高的掺杂量将引起电压下降、容量降低及晶格失氧。
优选地，所述正极材料包括晶格颗粒以及包覆于晶格颗粒表面的表面掺杂层。本发明通过将晶格掺杂和表面掺杂结合，抑制充放电过程中的有害相变，稳定材料在充放电过程中的晶格，并提高其在电解液和空气中的稳定性，从而提高材料的比容量、倍率性能以及循环寿命。本发明的层状正极材料进行晶格掺杂和表面修饰，表面修饰包括表面钠侧A类元素掺杂和表面氧侧氟掺杂。
优选地，表面掺杂层包括氟元素或A类元素中的至少一种。所述表面掺杂包括表面氟元素掺杂或A类元素中的至少一种掺杂。其中，元素F的掺杂位于晶格颗粒表面5～50个原子层内，且从外到内F元素含量逐渐减少，表面梯度氟掺杂的效果是：(1)稳定表面结构，抑制通常由材料表面引发的有害相变；(2)少量表面掺杂不影响钠离子在晶格内部的扩散，不影响材料的比容量；(3)富F的表面有利于提高材料在空气中的稳定性，且富F的表面易原位形成表面氟化物提高材料在电解液中的稳定性；(4)电负性比氧更大的氟与电负性较小的金属M2形成更强的离子键，从而稳定材料的表面结构，进一步提高材料在电解液和空气中的稳定性，并抑制表面相变。作为优选，0<z≤0.1，进一步优选，0.001≤z≤0.02，在此范围内，可实现比容量、循环寿命、倍率性能的优化平衡，并实现在空气中的稳定性。
其中，A类元素的梯度掺杂，其中A类元素为Nb、Ta、Zr、Mo、W中 的至少一种，A类元素的掺杂位于颗粒表面5～50个原子层内，且从外到内A元素的含量逐渐减少，表面梯度A类元素掺杂的效果是：(1)元素A起到支柱作用，抑制脱钠时钠层的晶格畸变，稳定表面结构，抑制通常由材料表面开始的有害相变；(2)少量表面掺杂不影响钠离子在晶格内部的扩散，不影响材料的比容量；(3)通过掺杂在钠层形成适量钠空位，从而加快钠离子在晶格表面的扩散，并促进体相钠离子扩散；(4)有利于提高材料在空气中和电解液中的稳定性。作为优选，0<m≤0.05，进一步优选，0.001≤m≤0.005，在此范围内，可实现比容量、循环寿命、倍率性能的优化平衡，并实现在空气中的稳定性。
优选地，所述表面掺杂层从外到内氟含量和/或A类元素含量依次减少。氟元素和A类元素表面梯度掺杂，有控抑制有害相变，提高稳定性。
优选地，所述正极材料的粒径为0.5微米～20微米。在此粒径范围内，有利于提高电极的压实密度，并提高电极的加工性能。
本发明的目的之二在于：针对现有技术的不足，而提供一种正极材料的制备方法，工艺简单可控、成本低、周期短、能耗低及适合工业化生产。
为了实现上述目的，本发明采用以下技术方案：
一种正极材料的制备方法，包括以下步骤：
步骤S1、使用合成法制备晶格颗粒Na nMn 1-x-yM1 xM2 yO 2；
步骤S2、对晶格颗粒Na nMn 1-x-yM1 xM2 yO 2进行氟元素掺杂和A类元素掺杂得到Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z。
本发明工艺简单可控、成本低、周期短、能耗低及适合工业化生产优点。对A类元素表面掺杂工艺一般为，将Na nMn 1-x-yM1 xM2 yO 2或表面F元素掺杂的Na nMn 1-x-yM1 xM2 yO 2分散于有机溶剂中，再加入A类元素的有机盐，经搅拌干燥、最后在空气或氧气中焙烧实现A类元素的表面梯度掺杂，其中焙烧温度为500℃～700℃，焙烧时间为2～10小时，所述有机溶剂选自乙醇，所述A类元素的有机盐选自乙醇盐，通过调节A类元素的有机盐的使用量、焙烧 温度和时间实现元素A的表面梯度掺杂；元素F表面掺杂工艺一般为，将Na nMn 1-x-yM1 xM2 yO 2或表面A元素掺杂的Na nMn 1-x-yM1 xM2 yO 2与NH 4F混合均匀，再在空气或氧气氛中焙烧进行F元素的表面掺杂，所述的焙烧温度为300℃～500℃，焙烧时间为2～10小时，所述的混合方式优选为干法球磨，通过调节NH 4F的使用量、焙烧温度和时间实现元素F的表面梯度掺杂。
优选地，所述步骤S1中合成法包括固相法、共沉淀法、喷雾干燥法、溶胶-凝胶法。
其中，固相反应法指在合成Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z中，将含元素Na、Mn、M1、M2的化合物经砂磨、球磨、或高混等工艺混合均匀，然后再进行固相反应，所述的化合物选自但不限于含这些元素的硝酸盐、醋酸盐、碳酸盐、草酸盐、氢氧化物、氧化物、羟基氧化物，或其水合物。作为优选，所述的固相反应温度为600℃～1100℃，反应时间为3～24小时，反应气氛选自空气、氧气、或压缩空气。
共沉淀法指在合成Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z中，将含Mn、M1的可溶性盐溶于去离子水中配制盐溶液，并配置沉淀剂溶液和络合剂溶液，然后将盐溶液、沉淀剂溶液和络合剂溶液同时注入反应容器中，得到沉淀。作为优选，所述的盐溶液，选自氯化物、硫酸盐、硝酸盐，或其水合物，所述的络合剂溶液，选自氨水，所述的沉淀剂溶液，选自氢氧化钠、氢氧化钾、碳酸钠、碳酸钾、草酸钠、草酸钾的水溶液；作为优选，所述的共沉淀反应温度为40℃～60℃，反应液的pH值视沉淀剂而定，当选用NaOH溶液作为沉淀剂时，pH值一般约为11。共沉淀反应后，将沉淀物经洗涤和干燥后，与含Na和M2的化合物混合均匀，然后再进行固相反应。
所述喷雾干燥法采用直接喷雾干燥法，在合成Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z中，将Na、Mn、M1、M2的可溶性化合物溶于去离子水中，充分混合均匀后，经喷雾干燥得到前驱体，然后再进行固相反应。
所述的溶胶-凝胶法，是指在合成Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z中，将Na、 Mn、M1、M2的硝酸盐或硫酸盐溶于水、经混合后形成溶胶，再加入络合剂如柠檬酸，在60℃～90℃下经搅拌得到凝胶，然后进行固相反应。
优选地，所述步骤S2后还包括将重量份为1～10份的补钠剂加入重量份为100～110份的Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z进行补钠处理。合成反应时，高温容易导致钠烧损，需要补充钠量，使钠过量1％～10％。其中，所述补钠剂包含Na 2S、导电剂和催化剂，所述导电剂选自乙炔黑、碳纳米管、碳纤维、石墨烯中的至少一种，所述催化剂为过渡金属氧化物，选自但不限于CuO、MnO 2、Mn 3O 4、NiO中的至少一种，所述Na 2S、导电剂和催化剂的重量比为1～2:0.01～0.1:0.01～0.1；作为优选，所述的补钠剂与层状活性材料的重量比为1:100～10:100，通过补钠，可有效弥补首次充电时在负极的钠损失，提高首次库仑效率。
优选地，所述补钠剂包括重量份数比为1～2:0.01～0.1:0.01～0.1的硫化钠、导电剂和催化剂。
本发明的目的之三在于：针对现有技术的不足，而提供一种正极片，具体良好的电化学性能，结构稳定，使用寿命长。
为了实现上述目的，本发明采用以下技术方案：
一种正极片，包括正极集流体以及设置在正极集流体至少一表面的正极活性材料，所述正极活性材料包括上述的正极材料。优选地，正极活性材料可以设置于正极集流体的一表面，可以设置于正极集流体的两表面。
本发明的目的之四在于：针对现有技术的不足，而提供一种钠离子电池，具有高的容量、优异的倍率性能和长的循环寿命。
为了实现上述目的，本发明采用以下技术方案：
一种钠离子电池，包括上述的正极片。具体地，一种钠离子电池，包括正极片、负极片、隔膜、电解液以及壳体，所述隔膜分隔所述正极片和所述负极片，壳体将正极片、负极片、隔膜和电解液封装包裹起来。其中，负极片包括负极集流体和设置有负极集流体至少一表面的负极活性层，负极活性层包括软 碳、硬碳、或硬碳/软碳复合材料中的至少一种负极活性材料。使用含有机溶剂、钠盐、添加剂的有机溶液作为有机电解液。其中，有机溶剂选自但不限于碳酸乙烯酯、碳酸丙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯中的至少一种。钠盐包括六氟磷酸钠、高氯酸钠、三氟甲磺酸钠、双三氟甲烷磺酰亚胺钠、双氟磺酰亚胺钠、四氟硼酸钠、双草酸硼酸钠中的至少一种。
相对于现有技术，本发明的有益效果在于：本发明的一种正极材料，通过M1和M2元素在材料体相中的均匀掺杂，以及元素A和F的表面掺杂，以及两者的协同作用，过可有效抑制材料在充放电过程中的有害相变，并改进材料在电解液和空气中的稳定性，所得材料具有高的容量、优异的倍率性能和长的循环寿命。本发明的正极材料具有稳定的晶格结构以及掺杂元素包覆的表面掺杂结构，有效抑制充放电过程中的有害相变，稳定性好，具有高的比容量，良好的倍率性能以及循环寿命。
附图说明
图1是本发明实施例1制备的O3相锰基层状正极材料的X射线衍射图谱。
图2是本发明实施例1制备的O3相锰基层状正极材料的充放电曲线图。
具体实施方式
下面结合具体实施方式和说明书附图，对本发明作进一步详细的描述，但本发明的实施方式并不限于此。
实施例1
步骤S1、按Na 0.91Nb 0.004[Mn 0.44Fe 0.24Ni 0.26Li 0.06]O 1.99F 0.01化学计量比，使用直接固相反应法及表面掺杂制备该材料。按化学计量比，将Na 2CO 3，Mn 2O 3、Fe 2O 3、NiO、Li 2CO 3混合均匀，经球磨后得到前驱体，其中球磨时间为10小时，转速为400rpm，再将前驱体置于马弗炉中，在空气氛中820℃下焙烧10小时后得到未表面掺杂的锰基层状材料。
步骤S2、再将上述产物与一定量乙醇铌在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Nb掺杂。然后将上述产物与 一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，为O3相，见图1。经元素分析，元素Mn、Fe、Ni、Li在材料体相中均匀分布，元素Nb和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的碳酸丙烯酯(PC)/碳酸甲乙酯(EMC)溶液为电解液，并加入上述电解液重量为4％的氟化碳酸乙烯酯(FEC)，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，充放电曲线如图2所示，比容量为125mAh/g，材料经400次循环，容量保持率为91％。
实施例2
步骤S1、按Na 0.86Nb 0.002[Mn 0.47Fe 0.24Ni 0.24Li 0.05]O 1.995F 0.005化学计量比，使用共沉淀法配合固相反应及表面掺杂制备该材料。按化学计量比，将NiSO 4、MnSO 4、FeSO 4置于去离子水中混合均匀，得到总浓度为1mol/L的盐溶液，配置0.5mol/L的氨水溶液和2mol/L的NaOH溶液分别作为络合剂和沉淀剂，然后将盐溶液、络合剂和沉淀剂同时注入反应容器中，进行共沉淀反应，共沉淀反应温度为50℃，通过调节NaOH溶液流速将pH值控制在11.0。将所得沉淀经离心分离、干燥后，与Na 2CO 3和Li 2CO 3按计量比混合，然后置于马弗炉中，在空气氛中820℃下焙烧10小时后得到未表面掺杂的锰基层状材料。
步骤S2、再将上述产物与一定量乙醇铌在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Nb掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，为O3相。经元素分析，元素Mn、Fe、Ni、Li在材料体相中均匀分布，元素Nb和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为90％。
实施例3
步骤S1、按Na 0.87Nb 0.002[Mn 0.44Fe 0.24Ni 0.26Li 0.05]O 1.995F 0.005化学计量比，使用溶胶-凝胶法结合固相反应及表面掺杂制备该材料。按化学计量比，将NaNO 3，LiNO 3、Mn(NO 3) 2、Ni(NO 3) 2、Fe(NO 3) 2混合于去离子水中，经搅拌得到溶胶，再加入柠檬酸，在60℃下经充分搅拌得到凝胶，然后置于马弗炉中，在空气氛中810℃下焙烧15小时后得到未表面掺杂的锰基层状材料。
步骤S2、再将上述产物与一定量乙醇铌在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Nb掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，具有O3相。经元素分析，元素Mn、Fe、Ni、Li在材料体相中均匀分布，元素Nb和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为93％。
实施例4
步骤S1、按Na 0.88Nb 0.002[Mn 0.43Fe 0.31Cu 0.20Li 0.06]O 1.997F 0.003化学计量比，使用共沉淀法配合固相反应及表面掺杂制备该材料。按化学计量比，将CuSO 4、MnSO 4、FeSO 4置于去离子水中混合均匀，得到总浓度为1mol/L的盐溶液，配置0.5mol/L的氨水溶液和2mol/L的NaOH溶液分别作为络合剂和沉淀剂，然后将盐溶液、络合剂和沉淀剂同时注入反应容器中，进行共沉淀反应，共沉淀反应温度为50℃，通过调节NaOH溶液流速将pH值控制在11.0。将所得沉淀经离心分离、干燥后，与Na 2CO 3和Li 2CO 3按计量比混合，然后置于马弗炉中，在空气氛中820℃下焙烧10小时后得到未表面掺杂的锰基层状材料。
步骤S2、再将上述产物与一定量乙醇铌在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Nb掺杂。然后将上述产物与 一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，为O3相。经元素分析，元素Mn、Fe、Cu、Li在材料体相中均匀分布，元素Nb和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为91％。
实施例5
步骤S1、按Na 0.88Ta 0.002[Mn 0.43Fe 0.27Cr 0.04Ni 0.20Li 0.06]O 1.997F 0.003化学计量比，使用共沉淀法配合固相反应及表面掺杂制备该材料。按化学计量比，将NiSO 4、MnSO 4、FeSO 4、Cr 2(SO 4) 3置于去离子水中混合均匀，得到总浓度为1mol/L的盐溶液，配置0.5mol/L的氨水溶液和2mol/L的NaOH溶液分别作为络合剂和沉淀剂，然后将盐溶液、络合剂和沉淀剂同时注入反应容器中，进行共沉淀反应，共沉淀反应温度为50℃，通过调节NaOH溶液流速将pH值控制在11.0。将所得沉淀经离心分离、干燥后，与Na 2CO 3和Li 2CO 3按计量比混合，然后置于马弗炉中，在空气氛中820℃下焙烧12小时后得到未表面掺杂的锰基层状材料。
步骤S2、再将上述产物与一定量乙醇钽在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Ta掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，为O3相。经元素分析，元素Mn、Fe、Cr、Ni、Li在材料体相中均匀分布，元素Ta和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为90％。
实施例6
步骤S1、按Na 0.85Ta 0.004[Mn 0.42Fe 0.28Ni 0.13Cu 0.12Mg 0.05]O 1.99F 0.01化学计量比，使用直接固相法结合表面掺杂制备该材料。按化学计量比，将NaNO 3，Mn 3O 4、Fe 3O 4、Ni(OH) 2、MgO、CuO混合均匀，经球磨后得到前驱体，其中球磨时间为10小时，转速为400rpm，再将前驱体置于马弗炉中，在空气氛中820℃下焙烧15小时后得到未表面掺杂锰基层状材料。
步骤S2、再将上述产物与一定量乙醇钽在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Ta掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，具有O3相。经元素分析，元素Mn、Fe、Ni、Cu、Mg在材料体相中均匀分布，元素Ta和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为92％。
实施例7
步骤S1、按Na 0.88Zr 0.003[Mn 0.42Fe 0.31Ni 0.11Cu 0.11Li 0.05]O 1.996F 0.004化学计量比，使用直接固相法结合表面掺杂制备该材料。按化学计量比，将NaNO 3，Mn 3O 4、Fe 3O 4、Ni(OH) 2、LiNO 3、CuO混合均匀，以去离子水为媒介，经砂磨后得到前驱体浆料，其中球磨时间为3小时，转速为2000rpm，将砂磨所得浆料经喷雾干燥得到前驱体，其中喷雾干燥仪的进口温度180℃，出口温度110℃，再将前驱体置于马弗炉中，在空气氛中820℃下焙烧15小时后得到未表面掺杂锰基层状材料。
步骤S2、再将上述产物与一定量乙醇锆在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Zr掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产 物经XRD分析，具有O3相。经元素分析，元素Mn、Fe、Ni、Cu、Li在材料体相中均匀分布，元素Zr和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为90％。
实施例8
步骤S1、按Na 0.89Zr 0.002[Mn 0.42Fe 0.31Ni 0.05Cu 0.16Li 0.05Mg 0.01]O 1.996F 0.004化学计量比，使用直接固相法结合表面掺杂制备该材料。按化学计量比，将Na 2CO 3，MnO 2、Fe 2O 3、NiO、CuO、Li 2CO 3、MgO混合均匀，以去离子水为媒介，经砂磨后得到前驱体浆料，其中球磨时间为4小时，转速为2000rpm，将砂磨所得浆料经喷雾干燥得到前驱体，其中喷雾干燥仪的进口温度180℃，出口温度110℃，再将前驱体置于马弗炉中，在空气氛中830℃下焙烧10小时后得到未表面掺杂锰基层状材料。
步骤S2、再将上述产物与一定量乙醇锆在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Zr掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，具有O3相。经元素分析，元素Mn、Fe、Ni、Cu、Li、Mg在材料体相中均匀分布，元素Zr和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为92％。
实施例9
步骤S1、按Na 0.85Zr 0.002[Mn 0.51Fe 0.19Ni 0.08Cu 0.15Li 0.07]O 1.996F 0.004化学计量比，使用直接固相法结合表面掺杂制备该材料。按化学计量比，将Na 2CO 3，MnO 2、 Fe 2O 3、NiO、CuO、Li 2CO 3混合均匀，以去离子水为媒介，经砂磨后得到前驱体浆料，其中球磨时间为4小时，转速为2000rpm，将砂磨所得浆料经喷雾干燥得到前驱体，其中喷雾干燥仪的进口温度180℃，出口温度110℃，再将前驱体置于马弗炉中，在空气氛中810℃下焙烧15小时后得到未表面掺杂锰基层状材料。
步骤S2、再将上述产物与一定量乙醇锆在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Zr掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，具有O3相。经元素分析，元素Mn、Fe、Ni、Cu、Li在材料体相中均匀分布，元素Zr和F在材料表面呈现梯度分度，从外到内含量逐渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为91％。
实施例10
步骤S1、按Na 0.93Zr 0.005[Mn 0.46Cr 0.18Ni 0.14Cu 0.16Li 0.06]O 1.996F 0.004化学计量比，使用直接喷雾干燥法结合固相反应及表面掺杂制备该材料。按化学计量比，将NaNO 3，Mn(NO 3) 2、Cr(NO 3) 3、Ni(NO 3) 2、Cu(NO 3) 2、LiNO 3混合于去离子水中，经充分搅拌后得到混合溶液，再经喷雾干燥得到前驱体，其中喷雾干燥仪的进口温度180℃，出口温度110℃，然后将所得前驱体置于马弗炉中，在空气氛中820℃下焙烧15小时后得到未表面掺杂锰基层状材料。
步骤S2、再将上述产物与一定量乙醇锆在乙醇中混合，在60℃下搅拌干燥后，在空气中600℃下焙烧5小时，进行表面Zr掺杂。然后将上述产物与一定量NH 4F混合均匀，在空气中400℃下焙烧5小时，进行表面F掺杂。产物经XRD分析，具有O3相。经元素分析，元素Mn、Cr、Ni、Cu、Li在材料体相中均匀分布，元素Zr和F在材料表面呈现梯度分度，从外到内含量逐 渐降低。以本实施例制备的材料作为正极，以金属钠为负极，玻璃纤维为隔膜，NaPF 6的PC/EMC溶液为电解液，并加入上述电解液重量为4％的FEC，装配纽扣电池，进行充放电测试，电流密度12mA/g，电压范围1.5～3.9V，经400次循环，容量保持率为90％。
实施例11
与实施例1的不同之处在于：制备过程中没有掺杂锂，锂部分由电化学活性元素Ni取代，即Na 0.75Nb 0.004[Mn 0.44Fe 0.24Ni 0.32]O 1.99F 0.01。在与实施例1相同的测试条件下，经过400次循环，容量保持率为82％。
其余与实施例1相同，这里不再赘述。
对比例1
与实施例1的不同之处在于：制备过程中没有进行Na侧表面掺Nb，得到Na 0.93[Mn 0.44Fe 0.24Ni 0.26Li 0.06]O 1.99F 0.01。在与实施例1相同的测试条件下，经过400次循环，容量保持率为80％
其余与实施例1相同，这里不再赘述。
对比例2
与实施例1的不同之处在于：制备过程中没有表面掺F，得到Na 0.92Nb 0.004[Mn 0.44Fe 0.24Ni 0.26Li 0.06]O 2。在与实施例1相同的测试条件下，经过400次循环，容量保持率为79％。
其余与实施例1相同，这里不再赘述。
对比例3
与实施例1的不同之处在于：制备过程中没有表面掺F和Nb，得到Na 0.94[Mn 0.44Fe 0.24Ni 0.26Li 0.06]O 2。在与实施例1相同的测试条件下，经过400次循环，容量保持率为75％。
其余与实施例1相同，这里不再赘述。
对比例4
与实施例1的不同之处在于：制备过程中没有掺杂锂，锂部分由电化学活 性元素Ni取代，即Na 0.75Nb 0.004[Mn 0.44Fe 0.24Ni 0.32]O 1.99F 0.01O 2。
其余与实施例1相同，这里不再赘述。
对比例5
与实施例1的不同之处在于：制备过程中进行钠侧表面掺钛，得到Na 0.91Ti 0.004[Mn 0.44Fe 0.24Ni 0.26Li 0.06]O 1.99F 0.01。在与实施例1相同的测试条件下，经过400次循环，容量保持率78％。
其余与实施例1相同，这里不再赘述。
性能测试：将实施例1-10以及对比例1-5制备出的正极材料以及将正极材料制备出钠离子电池进行测试，测试结果记录表1。
1、放电倍率测试：
(1)在25℃的环境中，以0.2C倍率恒流放电到1.5V，静置5分钟后；(2)以0.5C倍率恒流充电到3.9V，在3.9V恒压条件下充电到电流低于0.05C，静置5分钟；(3)以0.2C的倍率放电到1.5V以得到0.2C放电倍率下的放电容量；(4)通过重复前述步骤(2)-(3)且调整步骤(3)中的放电倍率分别为0.5C、1C、1.5C和2.0C以得到不同放电倍率下的放电容量。以每个倍率下得到的放电容量与0.2C倍率下得到的放电容量做比值，以比较倍率性能。
2、循环性能测试：
在25℃下，将钠离子二次电池以1C恒流充电至3.9V，之后以3.9V恒压充电至电流为0.05C，静置5min，然后以1C恒流放电至1.5V，此为一个充放电循环过程，此次的放电容量为首次循环的放电容量。将钠离子二次电池按照上述方法进行400次循环充放电测试，记录每一次循环的放电容量。循环容量保持率(％)＝第400次循环的放电容量/首次循环的放电容量×100％
表1
Figure PCTCN2022093421-appb-000005
Figure PCTCN2022093421-appb-000006
由上述表1可以得出，本发明的制备出的正极材料相对于现有技术的正极材料具有更好的电化学性能，制备出的钠离子电池具有良好的比容量、倍率性能以及循环寿命，经过400次充放电后容量保持率高达93％，2C放电容量/0.2C放电容量高达90.5％。
由实施例1-3对比得出，使用溶胶-凝胶法结合固相反应及表面掺杂制备该材料时，制备出的正极材料具有更好的电化学性能。
由实施例2、4、5对比得出，按Na 0.88Nb 0.002[Mn 0.43Fe 0.31Cu 0.20Li 0.06]O 1.997F 0.003化学计量比，使用共沉法配合固相反应及表面掺杂制备该材料时，制备出的正极材料具有更好的电化学性能。
由实施例6-9对比，Na 0.89Zr 0.002[Mn 0.42Fe 0.31Ni 0.05Cu 0.16Li 0.05Mg 0.01]O 1.996F 0.004按上述化学计量比制备出的正极材料性能更好。
由实施例1和10对比得出，使用固相法制备相对于喷雾干燥法制备更好，制备出的正极材料电化学性能更好。
由实施例1和对比例1对比得出，没有掺杂A类元素制备出的材料性能较差，容量保持率下降，说明A类元素掺杂能够提高材料的电化学性能，提高容量保持率。
由实施例1和对比例2对比得出，没有掺杂F元素制备出的材料性能更差，容量保持率下降较大，说明F元素掺杂能够提高材料的容量保持率，而影响相对于A类元素较大。
由实施例1和对比例3对比得出，没有掺杂F元素和A类元素制备出的材料性能最差，容量保持率下降最大，说明F元素以及A类元素对材料的容量保持率均有影响，二者掺杂能够协助发挥作用，提高容量保持率。
由实施例1和对比例4对比得出，没有掺杂非活性元素M2制备出的材料性能较差，容量保持率下降，这是因为非活性元素M2掺杂能够形成更强的离子键，从而稳定材料的表面结构，进一步提高材料在电解液和空气中的稳定性，并抑制表面相变，进而提高材料的容量保持率。
根据上述说明书的揭示和教导，本发明所属领域的技术人员还能够对上述实施方式进行变更和修改。因此，本发明并不局限于上述的具体实施方式，凡是本领域技术人员在本发明的基础上所作出的任何显而易见的改进、替换或变型均属于本发明的保护范围。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (11)

  1. 一种正极材料，其特征在于，其化学通式为Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z，该材料呈O3相，式中M1为Fe、Ni、Cr、Cu、Co中的至少一种，M2为Li、Na、K、Mg、Ca、Sr中的至少一种，A为Nb、Ta、Zr、Mo、W中的至少一种，其中0.2≤x≤0.7，0.01≤y≤0.1，x/(1-x-y)≥0.5，0<z≤0.1，0<m≤0.05，0.85≤n≤1。
  2. 根据权利要求1所述的正极材料，其特征在于，所述正极材料包括晶格颗粒以及包覆于晶格颗粒表面的表面掺杂层。
  3. 根据权利要求2所述的正极材料，其特征在于，所述表面掺杂层包括氟元素或A类元素中的至少一种。
  4. 根据权利要求3所述的正极材料，其特征在于，所述表面掺杂层从外到内氟含量和/或A类元素含量依次减少。
  5. 根据权利要求1所述的正极材料，其特征在于，所述正极材料的粒径为0.5微米～20微米。
  6. 一种正极材料的制备方法，其特征在于，包括以下步骤：
    步骤S1、使用合成法制备晶格颗粒Na nMn 1-x-yM1 xM2 yO 2；
    步骤S2、对晶格颗粒Na nMn 1-x-yM1 xM2 yO 2进行氟元素掺杂和A类元素掺杂得到Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z。
  7. 根据权利要求6所述的一种正极材料的制备方法，其特征在于，所述步骤S1中合成法包括固相法、共沉淀法、喷雾干燥法、溶胶-凝胶法。
  8. 根据权利要求6所述的一种正极材料的制备方法，其特征在于，所述步骤S2后还包括将重量份为1～10份的补钠剂加入重量份为100～110份的Na n-mA mMn 1-x-yM1 xM2 yO 2-zF z进行补钠处理。
  9. 根据权利要求8所述的一种正极材料的制备方法，其特征在于，所述补钠剂包括重量份数比为1～2:0.01～0.1:0.01～0.1的硫化钠、导电剂和催化剂。
  10. 一种正极片，其特征在于，包括正极集流体以及设置在正极集流体至少一表面的正极活性材料，所述正极活性材料包括权利要求1-5中任一项所述 的正极材料。
  11. 一种钠离子电池，其特征在于，包括权利要求10所述的正极片。
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