WO2024093126A1 - 一种层状钠电正极材料及其制备方法和应用 - Google Patents

一种层状钠电正极材料及其制备方法和应用 Download PDF

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WO2024093126A1
WO2024093126A1 PCT/CN2023/086087 CN2023086087W WO2024093126A1 WO 2024093126 A1 WO2024093126 A1 WO 2024093126A1 CN 2023086087 W CN2023086087 W CN 2023086087W WO 2024093126 A1 WO2024093126 A1 WO 2024093126A1
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positive electrode
sodium
electrode material
layered sodium
layered
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French (fr)
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奚凯颖
张艳鑫
赵泽锋
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横店集团东磁股份有限公司
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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
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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 embodiments of the present application relate to the technical field of sodium ion batteries, for example, a layered sodium battery positive electrode material and a preparation method and application thereof.
  • Lithium-ion batteries which have high energy density, small and light appearance, and long cycle life, have achieved great commercial success in the portable electronic devices and hybrid electric vehicle markets, and have been widely popularized and entered thousands of households.
  • the price of lithium-ion batteries is not advantageous, and the uneven distribution of lithium resources in the earth's crust greatly limits the application of lithium-ion batteries in fixed energy storage systems. Therefore, sodium-ion batteries, which are abundant in resources and low in price, are considered by researchers to be the future replacement for lithium-ion batteries, and have broad prospects in the fields of fixed energy storage and electric vehicles.
  • layered transition metal oxides have a simple synthesis process, a wide range of component selection space and structural diversity, can provide batteries with high specific capacity and excellent cycle life, and lay the foundation for the practical application of sodium-ion batteries.
  • researchers have found that layered positive electrode materials have a relatively complex structural rearrangement in the process of sodium insertion and extraction, which will lead to slow reaction kinetics, which is one of the key factors affecting the electrochemical performance of sodium-ion batteries.
  • Cao et al. https://doi.org/10.1039/C6TA10818K
  • NCM O3-type layered transition metal oxide NaCr 1/3 Fe 1/3 Mn 1/3 O 2
  • Mn ions were doped into the chromium-based layered material to achieve performance improvement.
  • the capacity of this material decayed to 53% of the first cycle capacity after 35 cycles, proving that doping with manganese ions is not the optimal design strategy.
  • the iron-based layered oxide positive electrode active material includes an iron-based layered oxide NaFexM1yO2 , wherein the NaFexM1yO2 contains a doping element M2 and a doping element Re, wherein x>y; M1 is selected from at least one of Ni, Mn, Cu and Co, the doping element M2 is selected from at least one of Mg, Al, Ti and Zr, and the doping element Re is selected from at least one of rare earth elements.
  • the positive electrode material prepared by this application has a low gram capacity and does not show an improvement in the cycle life of the material.
  • the application adopts a co-precipitation preparation process, which is complicated to operate, and the addition of a precipitant may cause excessive local concentration, agglomeration or uneven composition.
  • the embodiment of the present application provides a layered sodium positive electrode material and its preparation method and application.
  • the present application designs a layered sodium positive electrode material with a structure of Na y Cr 1-x M x O 2 by doping transition metals Ru and Ti.
  • the synergistic effect of Ru and Ti can not only inhibit the negative phase change of the layered sodium positive electrode material, but also improve the structural stability of the layered sodium positive electrode material under the broadened working electrochemical window.
  • this strategy can improve the electrochemical performance of the battery, obtain excellent capacity reversibility and excellent cycle stability, and has good application prospects.
  • an embodiment of the present application provides a layered sodium cathode material, wherein the chemical formula of the layered sodium cathode material is Na y Cr 1-x M x O 2 , wherein 0.1 ⁇ x ⁇ 0.3, 0.7 ⁇ y ⁇ 0.9, and M is a transition metal;
  • the transition metals include Ru and Ti.
  • the present invention doped transition metals Ru and Ti to form a new type of layered sodium positive electrode material.
  • the irreversible migration of transition metal ions from the transition metal layer to the sodium layer is suppressed, the transmission channel of sodium ions is unblocked, and the layer structure is prevented from being irreversibly migrated.
  • It can prevent the negative phase transition of layered sodium battery positive electrode materials, and improve the structural stability of the materials while broadening the working electrochemical window of layered sodium battery positive electrode materials, so that the electrochemical performance of the fabricated sodium ion battery is improved, thereby obtaining excellent capacity reversibility and outstanding cycle stability, and has good application prospects.
  • 0.1 ⁇ x ⁇ 0.3 for example, it can be 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28 or 0.3, etc.
  • 0.7 ⁇ y ⁇ 0.9 for example, it can be 0.7, 0.73, 0.75, 0.78, 0.8, 0.83, 0.85, 0.88 or 0.9, etc.
  • n is greater than 0.1, that is, the Ti content is too high, the original crystal phase structure of the layered sodium positive electrode material will be changed; and when the Ti content is too low, the improvement effect of doping element Ti on increasing the charge cut-off voltage is limited.
  • 0.8 ⁇ y ⁇ 0.9 for example, it may be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89 or 0.9, etc.
  • the chemical formula of the layered sodium cathode material is Na 0.9 Cr 0.9 Ru 0.06 Ti 0.04 O 2 .
  • the layered sodium cathode material has a hexagonal crystal structure and is in a granular form.
  • the average particle size of the layered sodium cathode material is 0.5-8 ⁇ m, for example, it can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8, etc.
  • an embodiment of the present application provides a method for preparing the layered sodium positive electrode material as described in the first aspect, the preparation method comprising:
  • the sodium source, chromium source, ruthenium source and titanium source are mixed and ground according to a stoichiometric ratio, and then calcined to obtain a layered sodium positive electrode material.
  • the present application adopts this preparation method to form a ruthenium and titanium doped layered sodium positive electrode material.
  • This method not only has a simple process flow and low cost, but also the microscopic discrete particles in the preparation process will gradually form a continuous solid layered structure at high temperature, thereby obtaining a stable sodium-containing hexagonal crystal system.
  • Layered oxides with space group structures have laid a good foundation for the subsequent realization of low-cost, high-performance sodium-ion batteries.
  • the ruthenium source comprises ruthenium oxide and/or ruthenium salt.
  • the ruthenium oxide comprises RuO 2 .
  • the ruthenium salt includes RuX 4 , wherein X includes any one of Cl, Br or I or a combination of at least two thereof, for example, RuCl 4 , RuBr 4 or RuI 4 .
  • the titanium source comprises titanium oxide and/or titanium salt.
  • the titanium oxide comprises TiO 2 .
  • the titanium salt includes TiX' 4 , wherein X' includes any one of Cl, Br or I or a combination of at least two thereof, for example, it may be TiCl 4 , TiBr 4 or TiI 4 .
  • the sodium source comprises sodium salt
  • the sodium salt comprises any one or a combination of at least two of Na2CO3 , NaHCO3 or NaCl , for example, a combination of Na2CO3 and NaHCO3 , a combination of NaHCO3 and NaCl, a combination of Na2CO3 and NaCl, or a combination of Na2CO3 , NaHCO3 and NaCl, etc.
  • the chromium source comprises chromium oxide
  • the chromium oxide comprises Cr 2 O 3 and/or CrO 2 .
  • the grinding method is ball milling.
  • the ball-to-material ratio of the ball mill is 1:(3-5), for example, it can be 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, etc.
  • the ball-to-material ratio refers to the ratio of the total mass of the mixed material to the total mass of the grinding balls.
  • the ball milling speed is 400-600 rpm, for example, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm.
  • the ball milling time is 5-10 h, for example, it can be 5 h, 5.3 h, 5.6 h, 5.9 h, 6.2 h, 6.5 h, 6.8 h, 7.1 h, 7.4 h, 7.7 h, 8 h, 8.3 h, 8.6 h, 8.9 h, 9.2 h, 9.5 h, 9.8 h or 10 h, etc.
  • the calcination temperature is 700-1200°C, for example, it may be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C, etc.
  • the heating rate of the calcination is 1-10°C/min, for example, it can be 1°C/min, 2°C/min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 7°C/min, 8°C/min, 9°C/min or 10°C/min, etc.
  • the calcination time is 5-25 h, such as 5 h, 10 h, 15 h, 20 h or 25 h.
  • the calcination atmosphere is an inert atmosphere
  • the gas in the inert atmosphere includes any one of argon, nitrogen or helium, or a combination of at least two of them.
  • the calcination is repeated 1-3 times, for example, 1 time, 2 times or 3 times.
  • the furnace may be cooled before calcination.
  • the mixing and grinding are followed by tableting.
  • the tabletting pressure is 5-10 MPa, for example, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, etc.
  • the preparation method comprises the following steps:
  • step (2) (2) calcining the intermediate material of step (1) in an inert atmosphere at a temperature of 700-1200° C. for 5-25 hours to obtain a layered sodium positive electrode material.
  • an embodiment of the present application provides a sodium ion battery, wherein the positive electrode of the sodium ion battery includes the layered sodium positive electrode material as described in the first aspect.
  • transition metals Ru and Ti are introduced to dope the layered sodium cathode material.
  • the synergistic effect of the two in the layered structure can inhibit the negative phase transition of the material and improve the structural stability of the material under the broadened electrochemical window of 1.5-3.92V, thereby avoiding damage to the electrochemical performance of the material;
  • the layered sodium positive electrode material provided in the embodiments of the present application enables the sodium ion battery to exhibit excellent electrochemical performance.
  • the discharge specific capacity at an ultra-large rate of 50C can reach 108.3 mAh/g, and the capacity retention rate can reach 81.3% after an ultra-long cycle of up to 1000 cycles at 10C, which reflects excellent cycle stability.
  • the charging voltage is increased to 3.92 V, the capacity can reach 141.3 mAh/g at a rate of 1C, which reflects excellent Capacity reversibility.
  • FIG1 is an X-ray powder diffraction spectrum of the layered sodium positive electrode material provided in Example 1 of the present application, wherein the inset is a sodium-containing hexagonal crystal system Schematic diagram of the structure of layered sodium cathode materials with space group structure.
  • FIG. 2 is a charge and discharge curve of the first three cycles of a sodium ion battery made of a layered sodium positive electrode material provided in Example 1 of the present application.
  • FIG3 is a differential specific capacity curve of a sodium ion battery made of a layered sodium positive electrode material provided in Example 1 of the present application.
  • FIG4 is a rate curve of a sodium ion battery made of a layered sodium positive electrode material provided in Example 1 of the present application at different current densities.
  • FIG5 is a cycle curve of a sodium ion battery made of a layered sodium positive electrode material provided in Example 1 of the present application under 10C high rate charge and discharge.
  • FIG6 is an AC impedance spectrum of a sodium ion battery made of a layered sodium positive electrode material provided in Example 1 of the present application after 50 cycles and a fitting curve obtained by equivalent circuit fitting.
  • This embodiment provides a layered sodium positive electrode material.
  • the chemical formula of the sodium positive electrode material is Na 0.9 Cr 0.9 Ru 0.06 Ti 0.04 O 2 , and the average particle size is 4 ⁇ m.
  • This embodiment also provides a method for preparing a layered sodium positive electrode material, the preparation method comprising: follow these steps:
  • step (3) placing the sheet sample obtained in step (2) in a tubular furnace, heating to 750°C at a rate of 2°C/min in an argon atmosphere, calcining for 5 hours, cooling to room temperature with the furnace, grinding the disc into powder, and then pressing it into a tablet under a pressure of 10 MPa, heating to 950°C at a rate of 7°C/min in a nitrogen atmosphere, calcining for 20 hours, and cooling to room temperature with the furnace to obtain a layered sodium positive electrode material.
  • FIG1 shows an X-ray powder diffraction spectrum of the layered sodium positive electrode material provided in this embodiment. It can be seen from the figure that the diffraction peak is obvious and has a high intensity, indicating that the sample has good crystallinity. In addition, it has a hexagonal crystal system. The characteristic peaks of the space group indicate that the sample has a layered structure. In addition, the inset in Figure 1 is a sodium-containing hexagonal crystal system. Schematic diagram of the structure of layered sodium cathode materials with space group structure, where the spheres in the octahedron are transition metal atoms and the spheres between the layers are sodium ions.
  • the layered sodium cathode material obtained in this example was used to assemble button cells and perform electrochemical performance tests, specifically:
  • the method of assembling a button cell comprises the following steps:
  • step (B) The electrode sheet obtained in step (A) was used as the positive electrode, metallic sodium was used as the negative electrode, glass fiber filter paper was used as the isolation membrane, and 1 M NaPF 6 (NaPF 6 was dissolved in a polyester (PC) mixed solution with 5 wt % fluoroacetate (FEC) added) solution was used as the electrolyte to assemble a button cell in a glove box filled with argon.
  • PC polyester
  • FEC fluoroacetate
  • Electrochemical testing methods include:
  • FIG2 shows the charge-discharge curves of the first three cycles of the sodium ion battery made of the layered sodium positive electrode material provided in this embodiment. It can be seen from the figure that the operating voltage window of the sodium ion battery made of the positive electrode material obtained in this embodiment is widened to 1.5-3.92V, and the sodium ion battery exhibits high energy density within this range. Its first-cycle discharge specific capacity is as high as 141.3 mAh/g; in addition, the obtained sodium-ion battery was subjected to three charge and discharge tests, and its charge and discharge curves basically overlapped, showing strong symmetry, that is, the charge and discharge process of the obtained sodium-ion battery is highly reversible.
  • FIG3 shows the differential specific capacity curve of the sodium ion battery made of the layered sodium positive electrode material provided in this embodiment. It can be seen from the figure that the redox peaks of the sodium ion battery can correspond one to one, reflecting the symmetry of the electrochemical curve.
  • FIG4 shows the rate curve of the sodium ion battery made of the layered sodium positive electrode material provided in this embodiment at different current densities. It can be seen from the figure that the discharge specific capacity of the sodium ion battery at 1C, 2C, 5C, 10C, 20C and 50C is 140.9mAh/g, 134.4mAh/g, 129.7mAh/g, 123.3mAh/g, 114.9mAh/g and 108.3mAh/g respectively. At the same time, after the sodium ion battery is charged and discharged at a high current density, it returns to the cycle at a 1C rate, and the capacity can be restored to 138.2mAh/g, which reflects the structural stability of the layered sodium positive electrode material under high rate charge and discharge test conditions.
  • the Land BT 2001A battery test system was used to perform charge and discharge tests in the voltage range of 1.5-3.8V, and Figure 5 was obtained. As shown in Figure 5, after an ultra-long cycle of up to 1000 cycles, the sodium ion battery still has a discharge specific capacity of 98.8mAh/g, providing a capacity retention rate of up to 81.3%.
  • Figure 6 shows the AC impedance spectrum of the sodium ion battery made of the layered sodium-ion cathode material provided in this embodiment after 50 cycles and the fitting curve fitted by the equivalent circuit.
  • the AC impedance spectrum consists of two semicircles (high and medium frequency) and a slant line (low frequency), wherein the semicircle in the ultra-high frequency region and the intercept of the Z' axis represent the solution impedance ( Rs ), and the sizes of the two semicircles from the high frequency region to the medium frequency region represent the interface impedance ( Rf ) and the charge mass transfer impedance ( Rct ), respectively.
  • the slant line in the low frequency region corresponds to the Warburg impedance, which is related to the diffusion process of sodium ions in the layered sodium-ion cathode material.
  • Table 1 is a statistical table of equivalent circuit parameters of sodium ion batteries after 50 cycles and sodium ion diffusion coefficients calculated by Warburg impedance, as shown below.
  • the R ct of the layered sodium cathode material is 465.2 ⁇ , which is almost unchanged compared to the R ct before the cycle, which confirms the excellent cycle stability of the layered sodium cathode material; after 50 cycles, the sodium ion diffusion coefficient of the layered sodium cathode material is still 7.89 ⁇ 10 -13 cm 2 s -1 , which is at a relatively high level. This result can correspond to the high discharge capacity retention rate and excellent rate performance of the layered sodium cathode material at high rates.
  • the layered sodium cathode material has a lower charge mass transfer impedance and a higher sodium ion diffusion coefficient after the cycle. This result confirms that multi-element doping is more conducive to the diffusion of Na + in the layered cathode material, which is also the reason why the layered sodium cathode material has such a high rate performance.
  • This embodiment provides a layered sodium positive electrode material.
  • the chemical formula of the sodium positive electrode material is Na 0.8 Cr 0.8 Ru 0.12 Ti 0.08 O 2 , and the average particle size is 2 ⁇ m.
  • This embodiment also provides a method for preparing a layered sodium positive electrode material, the preparation method comprising the following steps:
  • step (3) placing the sheet sample obtained in step (2) in a tubular furnace, heating to 700°C at a rate of 1°C/min in an argon atmosphere, calcining for 7 hours, cooling to room temperature with the furnace, grinding the disc into powder, and then pressing it into a tablet under a pressure of 10 MPa, heating to 900°C at a rate of 6°C/min in a helium atmosphere, calcining for 18 hours, and cooling to room temperature with the furnace to obtain a layered sodium positive electrode material.
  • This embodiment provides a layered sodium positive electrode material, the chemical formula of the sodium positive electrode material is Na 0.85 Cr 0.85 Ru 0.1 Ti 0.05 O 2 , and the average particle size is 6 ⁇ m.
  • This embodiment also provides a method for preparing a layered sodium positive electrode material, the preparation method comprising: follow these steps:
  • step (3) placing the sheet sample obtained in step (2) in a tubular furnace, heating to 800°C at a rate of 3°C/min in an argon atmosphere, calcining for 10 h, cooling to room temperature with the furnace, grinding the disc into powder, and then pressing it into a tablet under a pressure of 10 MPa, heating to 1000°C at a rate of 8°C/min in an argon atmosphere, calcining for 15 h, and cooling to room temperature with the furnace to obtain a layered sodium positive electrode material.
  • This embodiment provides a layered sodium positive electrode material.
  • the chemical formula of the sodium positive electrode material is Na 0.7 Cr 0.7 Ru 0.2 Ti 0.1 O 2 , and the average particle size is 0.5 ⁇ m.
  • This embodiment also provides a method for preparing a layered sodium positive electrode material, the preparation method comprising the following steps:
  • step (3) placing the sheet sample obtained in step (2) in a tubular furnace, heating the sample to 850°C at a rate of 4°C/min in an argon atmosphere, calcining for 15 h, cooling the sample to room temperature with the furnace, grinding the disc into powder, and pressing the tablet under a pressure of 10 MPa, heating the sample to 1100°C at a rate of 9°C/min in a nitrogen atmosphere, calcining for 10 h, and cooling the sample to room temperature with the furnace to obtain a layered sodium positive electrode material.
  • This embodiment provides a layered sodium positive electrode material.
  • the chemical formula of the sodium positive electrode material is Na 0.75 Cr 0.75 Ru 0.18 Ti 0.07 O 2 , and the average particle size is 8 ⁇ m.
  • This embodiment also provides a method for preparing a layered sodium positive electrode material, the preparation method comprising the following steps:
  • step (3) placing the sheet sample obtained in step (2) in a tubular furnace, heating to 900°C at a rate of 5°C/min in an argon atmosphere, calcining for 20 hours, cooling to room temperature with the furnace, grinding the disc into powder, and then pressing it into a tablet under a pressure of 10 MPa, heating to 1200°C at a rate of 10°C/min in an argon atmosphere, calcining for 5 hours, and cooling to room temperature with the furnace to obtain a layered sodium positive electrode material.
  • step (3) the flake sample is calcined at 750° C. for 25 h and the calcination is not repeated.
  • step (3) the calcination is performed at 600° C. for 5 h and at 950° C. for 20 h.
  • step (3) the calcination is performed at 750° C. for 5 h and at 1300° C. for 20 h.
  • Example 1 The difference between this comparative example and Example 1 is that the chemical formula of the layered sodium positive electrode material in this comparative example is Na 0.95 Cr 0.95 O 2 , and RuO 2 and TiO 2 are not added in step (1) of the preparation method, and their molar amounts are evenly distributed to Na 2 CO 3 and Cr 2 O 3 .
  • Example 1 The difference between this comparative example and Example 1 is that the chemical formula of the layered sodium positive electrode material in this example is Na 0.9 Cr 0.9 Ru 0.1 O 2 , and TiO 2 is not added in step (1) of the preparation method, and its molar amount is allocated to RuO 2 .
  • Example 1 The difference between this comparative example and Example 1 is that the chemical formula of the layered sodium positive electrode material in this example is Na 0.9 Cr 0.9 Ti 0.1 O 2 , and RuO 2 is not added in step (1) of the preparation method, and its molar amount is allocated to TiO 2 .
  • Example 1 The difference between this comparative example and Example 1 is that Ti is replaced by Mn, and the raw material TiO 2 is replaced by MnO 2 .
  • Example 1 The difference between this comparative example and Example 1 is that the chemical formula of the layered sodium positive electrode material is Na 0.9 Cr 0.6 Ru 0.11 Ti 0.09 O 2 .
  • the layered sodium cathode materials provided in Examples 2-10 and Comparative Examples 1-5 were assembled into button cells, and the electrochemical performance was tested in an operating voltage window of 1.5-3.92V.
  • the layered sodium positive electrode material provided in the present application makes the sodium ion battery charge and discharge process highly reversible, and has the characteristics of high specific capacity, strong symmetry and high cycle stability.
  • the discharge specific capacity at an ultra-large rate of 50C can reach 108.3mAh/g; the capacity retention rate can reach 81.3% after an ultra-long cycle of up to 1000 cycles at 10C; when the charging voltage is increased to 3.92V, the capacity at a rate of 1C can reach 141.3mAh/g, reflecting excellent capacity reversibility.
  • Example 1 By comparing the data results of Example 1 with those of the comparative examples, it can be seen that the optimization effect of single metal doping or other combined multi-metal doping on the material is worse than the co-doping of Ru and Ti provided in the present application, and when the amount of doping is too much, the original crystal phase structure of the layered sodium positive electrode material will be changed, and the first cycle discharge specific capacity will be greatly reduced.
  • the present application by introducing transition metals Ru and Ti to form an O3 phase positive electrode material, exerts the synergistic effect of multiple transition metal cations in the layered structure, effectively improving the structural stability of the layered sodium positive electrode material under the broadened working voltage window of 1.5-3.92V, thereby improving the electrochemical performance of sodium ion batteries, and has good application prospects.
  • the present application adopts a mixed grinding and calcination method to form a ruthenium and titanium doped layered sodium positive electrode material. This method is not only simple in process and low in cost, but also in the preparation process, the microscopic discrete particles will gradually form a continuous solid layered structure at high temperature, thereby obtaining a stable sodium-containing hexagonal system. Layered oxides with space group structures have laid a good foundation for the subsequent realization of low-cost, high-performance sodium-ion batteries.
  • the present application uses the above-mentioned embodiments to illustrate the process method of the present application, but the present application is not limited to the above-mentioned process steps, that is, it does not mean that the present application must rely on the above-mentioned process steps to be implemented.
  • the technicians in the relevant technical field should understand that any improvement to the present application, the equivalent replacement of the raw materials selected in the present application, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present application.

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Abstract

本文公布一种层状钠电正极材料及其制备方法和应用，所述层状钠电正极材料的化学式为NayCr1-xMxO2，其中0.1≤x≤0.3，0.7≤y≤0.9，M为过渡金属；所述惰性过渡金属包括Ru和Ti。本申请通过掺杂过渡金属Ru和Ti设计了一种结构为NayCr1-xMxO2的层状钠电正极材料，Ru和Ti的协同作用不仅可以抑制层状钠电正极材料的负面相变，提升层状钠电正极材料在拓宽的工作电化学窗口下的结构稳定性，而且此策略可以改善电池的电化学性能，获得优异的容量可逆性和卓越的循环稳定性，具有良好的应用前景。

Description

一种层状钠电正极材料及其制备方法和应用 技术领域
本申请实施例涉及钠离子电池技术领域，例如一种层状钠电正极材料及其制备方法和应用。
背景技术
近年来，二次电池作为一种用于整合可再生能源的成功储能技术，其小巧的尺寸适合在分布式场所使用，并且能减缓太阳能、风电场的输出波动，受到了研究者的广泛关注。能量密度高、外观小巧轻便、循环寿命长的锂离子电池在便携式电子设备以及混合动力电动汽车市场取得了巨大的商业成功，并得到了广泛普及，走进了千家万户。但是对于固定式大规模电力存储设备而言，锂离子电池的价格不占优势，并且在地壳中的锂资源分布不均，这些问题极大地限制了锂离子电池在固定式储能系统的应用。因此，资源丰富，价格低廉的钠离子电池被研究者认为是锂离子电池的未来取代者，在固定式储能和电动汽车领域拥有广阔的前景。
在钠离子电池正极材料的选择中，层状过渡金属氧化物合成工艺简单，拥有广阔的组分选择空间以及结构多样性，能为电池提供高比容量和优异的循环寿命，为钠离子电池投入实际应用奠定了基础。但是研究者发现层状正极材料在脱嵌钠的过程中存在着较为复杂的结构重排，会导致反应动力学滞缓，这是影响钠离子电池电化学性能的关键因素之一。在O3相的NaFeO2、NaTiO2、NaVO2和NaCrO2中，研究者发现当层状材料充电到高电压时，过渡金属离子从过渡金属层板向钠层发生不可逆的迁移，阻塞了钠离子的传输通道。这种高截止电压下产生的负面相变行为会对材料的电化学性能造成严重的损害。
目前，曹等人(https://doi.org/10.1039/C6TA10818K)公开了一种新型的O3型层状过渡金属氧化物NaCr1/3Fe1/3Mn1/3O2(NCFM)作为正极材料，即将Mn离子掺杂到铬基层状材料中，实现性能的改善，然而这种材料在循环35圈后容量衰减到了首圈容量的53％，证明锰离子的掺杂并不是最优的设计策略。
王等人(https://doi.org/10.1038/ncomms7954)提供了一种通过掺杂过渡金属离子Ti，将铬基层状材料的电压窗口拓宽到2.5-3.8V的策略。该正极材料是P 相结构，在P相材料中几乎不存在离子迁移现象，因为铬离子很难迁移到棱柱配位体中。此外，该正极材料的放电比容量仅为80mAh/g，无法满足当今对电池高能量密度的要求。
CN113716622A公开了一种铁基层状氧化物正极活性材料及其制备方法和应用。所述铁基层状氧化物正极活性材料包括铁基层状氧化物NaFexM1yO2，所述NaFexM1yO2中包含掺杂元素M2和掺杂元素Re，其中，x＞y；M1选自Ni、Mn、Cu和Co中的至少一种，所述掺杂元素M2选自Mg、Al、Ti和Zr中的至少一种，所述掺杂元素Re选自稀土元素中的至少一种。该申请制得的正极材料克容量较低且并未表现出材料的循环寿命得到改善。此外，该申请采用共沉淀法制备工艺，操作复杂，且沉淀剂的加入可能会使局部浓度过高，产生团聚或使得组成不够均匀。
因此，研究一种新型结构的层状钠电正极材料来抑制负面相变，拓宽层状钠电正极材料的工作电压窗口，进而获得优异的容量可逆性、高比容量和卓越的循环稳定性等电化学性能，是亟待解决的技术问题。
发明内容
以下是对本文详细描述的主题的概述。本概述并非是为了限制权利要求的保护范围。
本申请实施例提供一种层状钠电正极材料及其制备方法和应用。本申请通过掺杂过渡金属Ru和Ti设计了一种结构为NayCr1-xMxO2的层状钠电正极材料，Ru和Ti的协同作用不仅可以抑制层状钠电正极材料的负面相变，提升层状钠电正极材料在拓宽的工作电化学窗口下的结构稳定性，而且此策略可以改善电池的电化学性能，获得优异的容量可逆性和卓越的循环稳定性，具有良好的应用前景。
第一方面，本申请实施例提供一种层状钠电正极材料，所述层状钠电正极材料的化学式为NayCr1-xMxO2，其中0.1≤x≤0.3，0.7≤y≤0.9，M为过渡金属；
所述过渡金属包括Ru和Ti。
本申请掺杂过渡金属Ru和Ti形成了一种新型结构的层状钠电正极材料，通过发挥过渡金属Ru和Ti在层状结构中的协同作用，抑制了过渡金属离子从过渡金属层板向钠层的不可逆迁移，疏通了钠离子的传输通道，进而防止了层 状钠电正极材料的负面相变，并在拓宽层状钠电正极材料的工作电化学窗口的同时提升了材料的结构稳定性，使得制成的钠离子电池的电化学性能得到改善，从而获得优异的容量可逆性和卓越的循环稳定性，具有良好的应用前景。
本申请中，若只掺杂过渡金属Ru，则最高充电截止电压仅能到达3.8V，改善效果并不明显。
本申请中，0.1≤x≤0.3，例如可以是0.1、0.13、0.15、0.18、0.2、0.23、0.25、0.28或0.3等。
本申请中，过渡金属的含量过多，即x大于0.3时，会导致导致有效克容量降低，能量密度无法满足应用端的需求，并且价态无法守恒，无法制备得到纯度较高的材料；而当过渡金属的含量过少时，则过渡金属在层状钠电正极材料中的作用不明显，难以防止层状钠电正极材料的负面相变。
本申请中，0.7≤y≤0.9，例如可以是0.7、0.73、0.75、0.78、0.8、0.83、0.85、0.88或0.9等。
优选地，所述层状钠电正极材料的化学式为NayCr1-m-nRumTinO2，其中0.01≤m≤0.2，例如可以是0.01、0.03、0.06、0.09、0.12、0.15、0.18或0.2等，0.01≤n≤0.1，例如可以是0.01、0.02、0.03、0.04、0.05、0.06、0.07、0.08、0.09或0.1等，m+n＝x。
本申请中，若n大于0.1，即Ti的含量过高时，则会改变层状钠电正极材料的原始晶体相结构；而当Ti含量过低时，掺杂元素Ti对提高充电截止电压的改善效果有限。
优选地，0.8≤y≤0.9，例如可以是0.8、0.81、0.82、0.83、0.84、0.85、0.86、0.87、0.88、0.89或0.9等。
优选地，所述层状钠电正极材料的化学式为Na0.9Cr0.9Ru0.06Ti0.04O2。
优选地，所述层状钠电正极材料具有六方晶体结构，且呈现颗粒状。
优选地，所述层状钠电正极材料的平均粒径为0.5-8μm，例如可以是0.5、1、1.5、2、2.5、3、3.5、4、4.5、5、5.5、6、6.5、7、7.5或8等。
第二方面，本申请实施例提供一种如第一方面所述的层状钠电正极材料的制备方法，所述制备方法包括：
将钠源、铬源、钌源和钛源按照化学计量比混合并研磨，煅烧后得到层状钠电正极材料。
本申请采用此制备方法形成了钌和钛掺杂的层状钠电正极材料，此方法不仅工艺流程简单，成本较低，而且制备过程中微观的离散颗粒在高温下会逐渐形成连续的固态层状结构，从而得到稳定的含钠六方晶系空间群结构的层状氧化物，这为后续实现低成本、性能优异的钠离子电池奠定了良好的基础。
优选地，所述钌源包括钌氧化物和/或钌盐。
优选地，所述钌氧化物包括RuO2。
优选地，所述钌盐包括RuX4，其中X包括Cl、Br或I中的任意一种或至少两种的组合，例如可以是RuCl4、RuBr4或RuI4等。
优选地，所述钛源包括钛氧化物和/或钛盐。
优选地，所述钛氧化物包括TiO2。
优选地，所述钛盐包括TiX'4，其中X'包括Cl、Br或I中的任意一种或至少两种的组合，例如可以是TiCl4、TiBr4或TiI4等。
优选地，所述钠源包括钠盐，所述钠盐包括Na2CO3、NaHCO3或NaCl中的任意一种或至少两种的组合，例如可以是Na2CO3与NaHCO3的组合，NaHCO3与NaCl的组合，Na2CO3与NaCl的组合或Na2CO3、NaHCO3与NaCl的组合等。
优选地，所述铬源包括铬氧化物，所述铬氧化物包括Cr2O3和/或CrO2。
优选地，所述研磨的方式为球磨。
优选地，所述球磨的球料比为1:(3-5)，例如可以是1:3、1:3.5、1:4、1:4.5或1:5等。
本申请中，球料比是指混合物料的总质量与研磨球的总质量的比值。
优选地，所述球磨的速率为400-600rpm，例如可以是400rpm、450rpm、500rpm、550rpm或600rpm等。
优选地，所述球磨的时间为5-10h，例如可以是5h、5.3h、5.6h、5.9h、6.2h、6.5h、6.8h、7.1h、7.4h、7.7h、8h、8.3h、8.6h、8.9h、9.2h、9.5h、9.8h或10h等。
优选地，所述煅烧的温度为700-1200℃，例如可以是700℃、750℃、800℃、850℃、900℃、950℃、1000℃、1050℃、1100℃、1150℃或1200℃等。
本申请中，煅烧的温度过高，则浪费能耗，容易损坏烧结设备，对实验室存在安全隐患；而当煅烧的温度过低时，则无法烧结得到纯的O3相结构，存在前驱体杂质。
优选地，所述煅烧的升温速率为1-10℃/min，例如可以是1℃/min、2℃/min、3℃/min、4℃/min、5℃/min、6℃/min、7℃/min、8℃/min、9℃/min或10℃/min等。
优选地，所述煅烧的时间为5-25h，例如5h、10h、15h、20h或25h等。
优选地，所述煅烧的气氛为惰性气氛，所述惰性气氛中的气体包括氩气、氮气或氦气中的任意一种或至少两种的组合。
优选地，所述煅烧重复1-3次，例如可以是1次、2次或3次等。
本申请中，示例性的，每次煅烧后可以等炉冷却后再煅烧。
优选地，所述混合并研磨后进行压片。
优选地，所述压片的施加压力为5-10Mpa，例如可以是5Mpa、6Mpa、7Mpa、8Mpa、9Mpa、10Mpa等。
作为优选的技术方案，所述制备方法包括以下步骤：
(1)将钠源、铬源、钌源和钛源按照化学计量比混合，以400-600rpm的速率球磨5-10h并在5-10MPa的压力下压片，得中间材料；
(2)将步骤(1)所述中间材料在惰性气氛中进行煅烧，煅烧的温度为700-1200℃，时间为5-25h，得到层状钠电正极材料。
第三方面，本申请实施例提供一种钠离子电池，所述钠离子电池的正极中包括如第一方面所述的层状钠电正极材料。
本申请所述的数值范围不仅包括上述列举的点值，还包括没有列举出的上述数值范围之间的任意的点值，限于篇幅及出于简明的考虑，本申请不再穷尽列举所述范围包括的具体点值。
相对于相关技术，本申请实施例具有以下有益效果：
(1)本申请实施例通过引入过渡金属Ru和Ti对层状钠电正极材料进行掺杂，二者在层状结构中的协同作用可以抑制材料的负面相变，提升材料在拓宽的电化学窗口1.5-3.92V下的结构稳定性，从而避免对材料的电化学性能造成损害；
(2)本申请实施例所提供的层状钠电正极材料使得钠离子电池表现出优异的电化学性能，在50C超大倍率下的放电比容量可达108.3mAh/g，在10C且高达1000圈的超长循环后容量保持率可达81.3％，体现了卓越的循环稳定性；当充电电压提升到3.92V时，在1C的倍率下容量可达141.3mAh/g，体现了优异的 容量可逆性。
(3)本申请实施例表明掺杂多种过渡金属的方法在优化钠离子电池储能器件性能上具有良好的应用前景。
在阅读并理解了附图和详细描述后，可以明白其他方面。
附图说明
附图用来提供对本文技术方案的进一步理解，并且构成说明书的一部分，与本申请的实施例一起用于解释本文的技术方案，并不构成对本文技术方案的限制。
图1为本申请实施例1提供的层状钠电正极材料的X射线粉末衍射谱图，其中的插图是含钠六方晶系空间群结构的层状钠电正极材料的结构示意图。
图2为本申请实施例1提供的层状钠电正极材料制成的钠离子电池的前三圈充放电曲线。
图3为本申请实施例1提供的层状钠电正极材料制成的钠离子电池的微分比容量曲线。
图4为本申请实施例1提供的层状钠电正极材料制成的钠离子电池在不同电流密度下的倍率曲线。
图5为本申请实施例1提供的层状钠电正极材料制成的钠离子电池在10C高倍率充放电下的循环曲线。
图6为本申请实施例1提供的层状钠电正极材料制成的钠离子电池在循环50圈后的交流阻抗谱和通过等效电路拟合的拟合曲线。
具体实施方式
下面通过具体实施方式来进一步说明本申请的技术方案。本领域技术人员应该明了，所述实施例仅仅是帮助理解本申请，不应视为对本申请的具体限制。
实施例1
本实施例提供了一种层状钠电正极材料，所述钠电正极材料的化学式为Na0.9Cr0.9Ru0.06Ti0.04O2，平均粒径为4μm。
本实施例还提供了一种层状钠电正极材料的制备方法，所述制备方法包括 以下步骤：
(1)按照摩尔比9:9:1.2:0.8称取相应质量的Na2CO3、Cr2O3、RuO2和TiO2加入到玛瑙球磨罐中，再向其中加入总质量为混合物料总质量4倍的研磨球，在400rpm速度下球磨10h，将上述前驱体物料混合均匀；
(2)将球磨后的混合物料在10MPa压力下压制成直径为16mm的圆片；
(3)将步骤(2)所得片状样品放置于管式炉内，在氩气气氛下以2℃/min的速率升温至750℃，煅烧5h，随炉冷却至室温，将圆片研磨成粉末，再在10MPa压力下压片，在氮气气氛下以7℃/min的速率升温至950℃，煅烧20h，随炉冷却至室温，得到层状钠电正极材料。
图1示出了本实施例提供的层状钠电正极材料的X射线粉末衍射谱图，从图中可以看出，衍射峰明显且强度较高，表明样品的结晶性良好，此外，具有六方晶系空间群的特征峰，说明样品为层状结构。此外，图1中的插图为含钠六方晶系空间群结构的层状钠电正极材料结构示意图，其中八面体中的球体为过渡金属原子，层间的球体为钠离子。
采用本实施例所得的层状钠电正极材料组装成扣式电池并进行电化学性能测试，具体地：
组装扣式电池的方法包括以下步骤：
(A)按照质量比为7:2:1混合本实施例所得的层状钠电正极材料、乙炔黑和聚偏二氟乙烯，并加入溶剂N-甲基吡咯烷酮，均匀涂覆在铝箔上，经制浆、涂片、干燥等工艺流程即得到复合物正极，用压片机刻成直径为12mm的圆片；
(B)以步骤(A)所得电极片作为正极，以金属钠作为负极，以玻璃纤维滤纸作为隔离膜，以1M的NaPF6(NaPF6溶解于加入了5wt％氟代乙酸酯(FEC)的聚酯(PC)混合溶液)溶液作为电解液，在充满氩气的手套箱内组装成扣式电池。
电化学测试的方式包括：
(一)比容量测试
图2示出了本实施例提供的层状钠电正极材料制成的钠离子电池在的前三圈充放电曲线，由图可知，采用本实施例所得正极材料制成的钠离子电池的工作电压窗口被拓宽到1.5-3.92V，并在此范围内钠离子电池表现出高能量密度， 其首圈放电比容量高达141.3mAh/g；此外，对所得钠离子电池作3次充放电测试，其充放电曲线基本重合，展现出强对称性，即所得钠离子电池的充放电过程高度可逆。
(二)对称性测试
图3示出了本实施例提供的层状钠电正极材料制成的钠离子电池的微分比容量曲线，从图中可以看出，钠离子电池的氧化还原峰可一一对应，体现了电化学曲线的对称性。
(三)倍率测试
图4示出了本实施例提供的层状钠电正极材料制成的钠离子电池在不同电流密度下的倍率曲线，由图可知，钠离子电池在1C、2C、5C、10C、20C和50C下的放电比容量分别为140.9mAh/g、134.4mAh/g、129.7mAh/g、123.3mAh/g、114.9mAh/g和108.3mAh/g。同时，钠离子电池在高电流密度下充放电后，重新回到1C倍率下循环，容量可以回复到138.2mAh/g，体现了层状钠电正极材料在大倍率充放电测试条件下的结构稳定性。
(四)稳定性测试
用Land BT 2001A型号电池测试系统在1.5-3.8V电压范围内进行充放电测试，得到图5。由图5可知，在高达1000圈的超长循环后，钠离子电池依然拥有98.8mAh/g的放电比容量，可提供高达81.3％的容量保持率。
(五)阻抗测试
测试条件：交流电压为5mV，频率为0.01Hz-105Hz；
图6示出了本实施例提供的层状钠电正极材料制成的钠离子电池在循环50圈后的交流阻抗谱和通过等效电路拟合的拟合曲线，由图可知，交流阻抗谱图由两个半圆(高，中频)和一条斜线(低频)组成，其中超高频区的半圆和Z'轴的截点代表溶液阻抗(Rs)，从高频区到中频区的两个半圆大小分别代表界面阻抗(Rf)和电荷传质阻抗(Rct)，低频区的斜线对应于Warburg阻抗，与钠离子在层状钠电正极材料中的扩散过程相关。
表1为钠离子电池在50圈循环后的等效电路参数以及通过Warburg阻抗计算得到的钠离子扩散系数的统计表，如下所示。
表1
由表1可知，循环50圈后，层状钠电正极材料的Rct为465.2Ω，与循环前的Rct相比几乎没有衰减，这与层状钠电正极材料优异的循环稳定性相互印证；层状钠电正极材料经过50圈循环后钠离子扩散系数仍有7.89×10-13cm2s-1，处于较高的水准，这一结果可以对应于该层状钠电正极材料在高倍率下的放电容量保持率较高，倍率性能优异。此外，该层状钠电正极材料在循环后拥有较低的电荷传质阻抗，并且钠离子扩散系数较高，这个结果证实了多元素掺杂更加有利于Na+在层状正极材料中的扩散，这也是层状钠电正极材料具有这么高倍率性能的原因。
实施例2
本实施例提供了一种层状钠电正极材料，所述钠电正极材料的化学式为Na0.8Cr0.8Ru0.12Ti0.08O2，平均粒径为2μm。
本实施例还提供了一种层状钠电正极材料的制备方法，所述制备方法包括以下步骤：
(1)按照摩尔比1:2:0.3:0.2称取相应质量的Na2CO3、CrO2、RuCl3和TiO2加入到玛瑙球磨罐中，再向其中加入总质量为混合物料总质量3.5倍的研磨球，在450rpm速度下球磨8h，将上述前驱体物料混合均匀；
(2)将球磨后的混合物料在8MPa压力下压制成直径为16mm的圆片；
(3)将步骤(2)所得片状样品放置于管式炉内，在氩气气氛下以1℃/min的速率升温至700℃，煅烧7h，随炉冷却至室温，将圆片研磨成粉末，再在10MPa压力下压片，在氦气气氛下以6℃/min的速率升温至900℃，煅烧18h，随炉冷却至室温，得到层状钠电正极材料。
实施例3
本实施例提供了一种层状钠电正极材料，所述钠电正极材料的化学式为Na0.85Cr0.85Ru0.1Ti0.05O2，平均粒径为6μm。
本实施例还提供了一种层状钠电正极材料的制备方法，所述制备方法包括 以下步骤：
(1)按照摩尔比8.5:8.5:2:1称取相应质量的Na2CO3、Cr2O3、RuO2和TiCl4加入到玛瑙球磨罐中，再向其中加入总质量为混合物料总质量4.5倍的研磨球，在500rpm速度下球磨7h，将上述前驱体物料混合均匀；
(2)将球磨后的混合物料在7MPa压力下压制成直径为16mm的圆片；
(3)将步骤(2)所得片状样品放置于管式炉内，在氩气气氛下以3℃/min的速率升温至800℃，煅烧10h，随炉冷却至室温，将圆片研磨成粉末，再在10MPa压力下压片，在氩气气氛下以8℃/min的速率升温至1000℃，煅烧15h，随炉冷却至室温，得到层状钠电正极材料。
实施例4
本实施例提供了一种层状钠电正极材料，所述钠电正极材料的化学式为Na0.7Cr0.7Ru0.2Ti0.1O2，平均粒径为0.5μm。
本实施例还提供了一种层状钠电正极材料的制备方法，所述制备方法包括以下步骤：
(1)按照摩尔比7:3.5:2:1称取相应质量的NaCl、Cr2O3、RuO2和TiBr4加入到玛瑙球磨罐中，再向其中加入总质量为混合物料总质量3倍的研磨球，在550rpm速度下球磨6h，将上述前驱体物料混合均匀；
(2)将球磨后的混合物料在6MPa压力下压制成直径为16mm的圆片；
(3)将步骤(2)所得片状样品放置于管式炉内，在氩气气氛下以4℃/min的速率升温至850℃，煅烧15h，随炉冷却至室温，将圆片研磨成粉末，再在10MPa压力下压片，在氮气气氛下以9℃/min的速率升温至1100℃，煅烧10h，随炉冷却至室温，得到层状钠电正极材料。
实施例5
本实施例提供了一种层状钠电正极材料，所述钠电正极材料的化学式为Na0.75Cr0.75Ru0.18Ti0.07O2，平均粒径为8μm。
本实施例还提供了一种层状钠电正极材料的制备方法，所述制备方法包括以下步骤：
(1)按照摩尔比14:7.5:3.6:1.4称取相应质量的NaHCO3、Cr2O3、RuBr3和TiO2加入到玛瑙球磨罐中，再向其中加入总质量为混合物料总质量5倍的研磨球，在600rpm速度下球磨5h，将上述前驱体物料混合均匀；
(2)将球磨后的混合物料在5MPa压力下压制成直径为16mm的圆片；
(3)将步骤(2)所得片状样品放置于管式炉内，在氩气气氛下以5℃/min的速率升温至900℃，煅烧20h，随炉冷却至室温，将圆片研磨成粉末，再在10MPa压力下压片，在氩气气氛下以10℃/min的速率升温至1200℃，煅烧5h，随炉冷却至室温，得到层状钠电正极材料。
实施例6
本实施例与实施例2的不同之处为，本实施例中层状钠电正极材料的化学式为Na0.8Cr0.8Ru0.192Ti0.008O2。
其余制备方法和参数与实施例2保持一致。
实施例7
本实施例与实施例2的不同之处为，本实施例中层状钠电正极材料的化学式为Na0.8Cr0.8Ru0.08Ti0.12O2。
其余制备方法和参数与实施例2保持一致。
实施例8
本实施例与实施例1的不同之处为，步骤(3)中片状样品在750℃下煅烧25h，不再重复煅烧。
其余制备方法和参数与实施例1保持一致。
实施例9
本实施例与实施例1的不同之处为，步骤(3)中在600℃下煅烧5h，在950℃下煅烧20h。
其余制备方法和参数与实施例1保持一致。
实施例10
本实施例与实施例1的不同之处为，步骤(3)中在750℃下煅烧5h，在1300℃下煅烧20h。
其余制备方法和参数与实施例1保持一致。
对比例1
本对比例与实施例1的不同之处为，本对比例中层状钠电正极材料的化学式为Na0.95Cr0.95O2，则所述制备方法的步骤(1)中不添加RuO2和TiO2，并将其摩尔量平均分给Na2CO3和Cr2O3。
其余制备方法和参数与实施例1保持一致。
对比例2
本对比例与实施例1的不同之处为，本实施例中层状钠电正极材料的化学式为Na0.9Cr0.9Ru0.1O2，则所述制备方法的步骤(1)中不添加TiO2，并将其摩尔量分给RuO2。
其余制备方法和参数与实施例1保持一致。
对比例3
本对比例与实施例1的不同之处为，本实施例中层状钠电正极材料的化学式为Na0.9Cr0.9Ti0.1O2，则所述制备方法的步骤(1)中不添加RuO2，并将其摩尔量分给TiO2。
其余制备方法和参数与实施例1保持一致。
对比例4
本对比例与实施例1的不同之处为，Ti替换为Mn，原料TiO2替换为MnO2。
其余制备方法和参数与实施例1保持一致。
对比例5
本对比例与实施例1的不同之处为，所述层状钠电正极材料的化学式为Na0.9Cr0.6Ru0.11Ti0.09O2。
其余制备方法和参数与实施例1保持一致。
性能测试
按照实施例1中提供的扣式电池的制备方法将实施例2-10和对比例1-5提供的层状钠电正极材料组装成扣式电池，并在1.5-3.92V的工作电压窗口下进行电化学性能测试。
测试结果如表2所示。
表2

分析：
由各实施例可知，本申请所提供的层状钠电正极材料使得钠离子电池充放电过程高度可逆，具有高比容量、强对称性和高循环稳定性等特点，在50C超大倍率下的放电比容量可达108.3mAh/g；在10C且高达1000圈的超长循环后容量保持率可达81.3％的；当充电电压提升到3.92V时，在1C的倍率的容量可达141.3mAh/g，体现了优异的容量可逆性。通过实施例1与各对比例的数据结果对比可知，单金属掺杂或其他组合的多金属掺杂对于材料的优化效果均差于本申请提供的Ru和Ti的共掺杂，且掺杂的量过多时，会改变层状钠电正极材料的原始晶体相结构，大幅度降低首圈放电比容量。
由此可见，本申请通过引入过渡金属Ru和Ti以形成O3相正极材料，发挥了多种过渡金属阳离子在层状结构中的协同作用，有效提升了层状钠电正极材料在拓宽的工作电压窗口1.5-3.92V下的结构稳定性，从而改善了钠离子电池的电化学性能，具有良好的应用前景。此外，本申请采用混合研磨并煅烧的方式形成钌和钛掺杂的层状钠电正极材料，此方法不仅工艺简单，成本较低，而且制备过程中微观的离散颗粒在高温下会逐渐形成连续的固态层状结构，进而得到稳定的含钠六方晶系空间群结构的层状氧化物，这为后续实现低成本、性能优异的钠离子电池奠定了良好的基础。
申请人声明，本申请通过上述实施例来说明本申请的工艺方法，但本申请并不局限于上述工艺步骤，即不意味着本申请必须依赖上述工艺步骤才能实施。所属技术领域的技术人员应该明了，对本申请的任何改进，对本申请所选用原料的等效替换及辅助成分的添加、具体方式的选择等，均落在本申请的保护范围和公开范围之内。

Claims (15)

  1. 一种层状钠电正极材料，其中，所述层状钠电正极材料的化学式为NayCr1-xMxO2，其中0.1≤x≤0.3，0.7≤y≤0.9，M为过渡金属；
    所述过渡金属包括Ru和Ti。
  2. 根据权利要求1所述的钠电正极材料，其中，所述层状钠电正极材料的化学式为NayCr1-m-nRumTinO2，其中0.01≤m≤0.2，0.01≤n≤0.1，m+n＝x。
  3. 根据权利要求1或2所述的钠电正极材料，其中，0.8≤y≤0.9。
  4. 根据权利要求1-3任一项所述的钠电正极材料，其中，所述层状钠电正极材料的化学式为Na0.9Cr0.9Ru0.06Ti0.04O2。
  5. 根据权利要求1-4任一项所述的钠电正极材料，其中，所述层状钠电正极材料具有六方晶体结构，且呈现颗粒状；
    优选地，所述层状钠电正极材料的平均粒径为0.5-8μm。
  6. 一种如权利要求1-5任一项所述的层状钠电正极材料的制备方法，其包括：
    将钠源、铬源、钌源和钛源按照化学计量比混合并研磨，煅烧后得到层状钠电正极材料。
  7. 根据权利要求6所述的制备方法，其中，所述钌源包括钌氧化物和/或钌盐。
  8. 根据权利要求7所述的制备方法，其中，所述钌氧化物包括RuO2；
    优选地，所述钌盐包括RuX4，其中X包括Cl、Br或I中的任意一种或至少两种的组合。
  9. 根据权利要求6-8任一项所述的制备方法，其中，所述钛源包括钛氧化物和/或钛盐；
    优选地，所述钛氧化物包括TiO2；
    优选地，所述钛盐包括TiX'4，其中X'包括Cl、Br或I中的任意一种或至少两种的组合。
  10. 根据权利要求6-9任一项所述的制备方法，其中，所述钠源包括钠盐，所述钠盐包括Na2CO3、NaHCO3或NaCl中的任意一种或至少两种的组合；
    优选地，所述铬源包括铬氧化物，所述铬氧化物包括Cr2O3和/或CrO2。
  11. 根据权利要求6-10任一项所述的制备方法，其中，所述研磨的方式为球磨；
    优选地，所述球磨的球料比为1:(3-5)；
    优选地，所述球磨的速率为400-600rpm；
    优选地，所述球磨的时间为5-10h。
  12. 根据权利要求6-11任一项所述的制备方法，其中，所述煅烧的温度为700-1200℃；
    优选地，所述煅烧的升温速率为1-10℃/min；
    优选地，所述煅烧的时间为5-25h；
    优选地，所述煅烧的气氛为惰性气氛，所述惰性气氛中的气体包括氩气、氮气或氦气中的任意一种或至少两种的组合；
    优选地，所述煅烧重复1-3次。
  13. 根据权利要求6-12任一项所述的钠电正极材料，其中，所述混合并研磨后进行压片；
    优选地，所述压片的施加压力为5-10MPa。
  14. 根据权利要求6-13任一项所述的制备方法，其中，所述制备方法包括以下步骤：
    (1)将钠源、铬源、钌源和钛源按照化学计量比混合，以400-600rpm的速率球磨5-10h并在5-10MPa的压力下压片，得中间材料；
    (2)将步骤(1)所述中间材料在惰性气氛中进行煅烧，煅烧的温度为700-1200℃，时间为5-25h，得到层状钠电正极材料。
  15. 一种钠离子电池，其中，所述钠离子电池的正极中包括如权利要求1-5任一项所述的层状钠电正极材料。
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