Quaternary metal co-doped sodium vanadium phosphate electrode material, preparation method and application of quaternary metal co-doped sodium vanadium phosphate electrode material in sodium-ion battery

Abstract

The invention discloses a quaternary metal co-doped sodium vanadium phosphate electrode material, a preparation method and application of a sodium ion battery, and belongs to the technical field of sodium ion batteries. The chemical formula of the electrode material is NaxVyAlaMnbCrcNid (PO4) 3, and x is greater than or equal to 3.0 and less than or equal to 3.6, 0.5 lt; y is less than or equal to 2.0, 0lt; (a, b, c or d) < = 0.2, and 1.5 < = (y + a + b + c + d) < = 2.0. The material has the characteristics of single phase, high crystallinity and uniform particle size. Charge compensation in the Na ion deintercalation process is achieved through a local electric field formed by the four elements of Al, Mn, Cr and Ni at the V site, the distortion degree of the crystal structure of the material in the charging and discharging process is reduced, and the lattice frame structure of the material is stabilized. Experiments show that the capacity retention rate of the electrode material reaches 98% (the specific capacity is 141 mA h / g) after circulation for 1500 times under the current of 10 C, the capacity retention rate of the electrode material is 96% (the specific capacity is 138 mA h / g) after circulation charge and discharge for 237 circles under the test current of 30 C, and the electrode material shows excellent transposable circulation stability in a symmetric sodium ion battery and is suitable for a high-performance sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical fields of new materials and sodium-ion battery technologies, and specifically relates to a quaternary metal co-doped sodium vanadium phosphate electrode material, a preparation method thereof, and an application thereof as a sodium-ion battery electrode material. Background Art

[0002] With the growing global demand for sustainable development and environmental protection, the development of efficient and economical energy storage systems has become one of the important technical challenges in the 21st century. Among numerous energy storage technologies, sodium-ion batteries have gradually become an important research direction in the fields of portable electronic devices and electric vehicles due to their advantages such as rich resources and low cost. However, sodium-ion batteries still face many technical bottlenecks in practical applications, especially the uncontrollable growth problem of sodium dendrites during the cycling process. The formation of sodium dendrites not only leads to the generation of "dead sodium", but may also pierce the separator, causing internal short circuits and thus bringing serious safety hazards.

[0003] To overcome the above problems, symmetric sodium-ion batteries (SSIBs) have emerged. SSIBs use the same material as both the positive electrode and the negative electrode, which can not only avoid the formation of sodium dendrites, but also reduce the side reactions between the electrode and the electrolyte, thus significantly improving the safety of the battery. In addition, due to the interchangeability of the positive and negative electrode materials, SSIBs have higher flexibility in circuit design, simplifying the manufacturing process and reducing the production cost. However, the voltage output of SSIBs is relatively low (usually below 4.0V), and the cycling performance is poor, which limits their energy density and practical application potential. Therefore, how to improve the voltage output and cycling stability of SSIBs has become the focus of current research.

[0004] Among numerous electrode materials, sodium vanadium phosphate Na3V2(PO4)3 with a NASICON structure has shown significant advantages in symmetric battery applications due to its multi-electron reaction characteristics. This material provides capacity through the V 2+ / V 3+ and V 3+ / V 4+ redox pairs at 1.6V and 3.4V potentials respectively, so it can be used as both the positive electrode and the negative electrode of SSIBs. In addition, the lantern-like structure of Na3V2(PO4)3 has abundant Na ion migration channels, which is beneficial to improving the ion migration rate. However, during the charge and discharge process of Na3V2(PO4)3, due to the large difference in the ionic radii of V 4+ and V 2+ ions, the unit cell volume changes significantly (about 10.8%), which in turn affects the structural stability and electrochemical cycling performance of the material.

[0005] To improve the structural stability of Na3V2(PO4)3 as an electrode material, researchers have proposed optimizing its cycling performance through a multi-metal ion doping strategy. Doping the V site with multiple metal elements can not only make full use of the capacity of the V element in the Na3V2(PO4)3 framework, but also optimize its lattice structure, enhance the ion diffusion rate and conductivity, thereby improving the overall sodium storage performance of Na3V2(PO4)3. Although the unique configurations and tunable electrochemical properties of multi-element doped Na3V2(PO4)3 materials bring new opportunities to break through the performance bottleneck of current symmetric electrode materials, how to improve the cycling stability of Na3V2(PO4)3 as an electrode material and increase its output energy through low-concentration metal element doping and reasonable structure design remains a technical problem to be solved urgently. Summary of the Invention

[0006] The purpose of the present invention is to provide a multi-metal co-doped sodium vanadium phosphate applicable to sodium-ion batteries and a preparation method thereof.

[0007] To achieve the purpose of the present invention, the following technical solutions are adopted: doping four elements of Al, Cr, Mn, and Ni with nearly equimolar ratios at the V site to form a combined site, obtaining a sodium-ion battery electrode material Na x V y Al a Mn b Cr c Ni d (PO4)3 (where 3.0 ≤ x ≤ 3.5, 0.5 < y ≤ 2.0, 0 < (a, b, c or d) ≤ 0.2, 1.5 ≤ (y + a + b + c + d) ≤ 2.0). This electrode material has a single phase, good crystallinity, and uniform particle size. At the same time, four metal elements with different electronegativities form a local electric field at the V site, compensating for the charge during the Na ion insertion and extraction reaction of this electrode material, effectively reducing the degree of crystal structure distortion during charge and discharge, and thus stabilizing its lattice framework structure. Therefore, Na x V y Al a Mn b Cr c Ni d (PO4)3 exhibits high specific capacity and excellent cycling stability in sodium-ion batteries.

[0008] According to the first aspect of the present application, a quaternary metal co-doped sodium vanadium phosphate electrode material is provided, and the chemical formula of the electrode material is Na x V y Al a Mn b Cr c Nid (PO4)3, where 3.0 ≤ x ≤ 3.5, 0.5 < y ≤ 2.0, 0 < (a, b, c or d) ≤ 0.2, and 1.5 ≤ (y + a + b + c + d) ≤ 2.0.

[0009] Optionally, the matrix structure of the quaternary metal co-doped sodium vanadium phosphate is a single-phase structure of Na3V2(PO4)3 with a space group of R-3c, and the atomic ratio of the elements at the V site is V:Al:Cr:Mn:Ni = 5.0 - 10.0:0.1 - 0.5:0.1 - 0.5:0.1 - 0.5:0.1 - 0.5.

[0010] Optionally, the electrode material is near-spherical quaternary metal co-doped sodium vanadium phosphate micro-particles with a small amount of carbon layer coated on the surface.

[0011] According to the second aspect of the present application, a preparation method of the above-mentioned quaternary metal co-doped sodium vanadium phosphate electrode material is provided, and the preparation method includes:

[0012] Step 1: Weigh the carbon source compound, sodium source compound, phosphorus source compound, vanadium source compound, aluminum source compound, chromium source compound, manganese source compound and nickel source compound in the required stoichiometric ratio, and gradually dissolve them in water and stir evenly to obtain a precursor mixed aqueous solution containing the required stoichiometric ratio.

[0013] Step 2: Add the required volume of polar solvent to the precursor mixed aqueous solution in Step 1, transfer it to a high-pressure reaction kettle and react at 160 - 200 °C for 10 - 16 h, and then place it in an oven at 60 - 100 °C to dry for 10 - 18 h to obtain a precursor powder.

[0014] Step 3: Perform two-step calcination on the precursor powder in Step 2: The first-step calcination is carried out under the condition of 200 - 500 °C, and the second-step calcination is carried out under the condition of 600 - 900 °C. After the second-step sintering, the quaternary metal co-doped sodium vanadium phosphate electrode material Na x V y Al a Mn b Cr c Ni d (PO4)3, where 3.0 ≤ x ≤ 3.5, 0.5 < y ≤ 2.0, 0 < (a, b, c or d) ≤ 0.2, and 1.5 ≤ (y + a + b + c + d) ≤ 2.0.

[0015] In a specific embodiment, the preparation method includes:

[0016] First step, prepare an aqueous solution A containing a vanadium source compound and a carbon source compound;

[0017] In the second step, an appropriate amount of aluminum source compound, manganese source compound, chromium source compound, and nickel source compound are weighed and added to solution A to obtain aqueous solution B;

[0018] In the third step, an aqueous solution C containing a sodium source compound and a phosphorus source compound is prepared;

[0019] In the fourth step, aqueous solution C is slowly added dropwise to aqueous solution B to obtain aqueous solution D;

[0020] In the fifth step, aqueous solution D is transferred to a hydrothermal reactor, an appropriate amount of polar solvent is added, heated for reaction, and after cooling, separated and dried to obtain an electrode precursor, denoted as powder E;

[0021] In the sixth step, powder E is sintered under a protective atmosphere, and after cooling, crushed, ground, and sieved to obtain a quaternary metal co-doped sodium vanadium phosphate electrode material;

[0022] In the seventh step, the prepared quaternary metal co-doped sodium vanadium phosphate material, conductive agent, and binder are weighed in a certain weight ratio, uniformly mixed with N-methylpyrrolidone solvent, coated on the surface of aluminum foil, dried and cut to be used as the positive electrode or negative electrode, or sodium metal is used as the negative electrode, or a negative electrode sheet made of commercial hard carbon material is used as the negative electrode, and a carbonate or ether electrolyte is used to assemble a button cell for testing, where 1C is set to 117.6 mA h / g.

[0023] Optionally, in aqueous solution A, the molar ratio of the carbon source compound to the vanadium source compound is 1-6:1.

[0024] Optionally, in aqueous solution B, the vanadium source compound is one or more mixtures of sodium vanadate, ammonium metavanadate, vanadium pentoxide, ammonium vanadate, and their hydrates; the aluminum source compound is one or more mixtures of aluminum chloride, aluminum oxide, aluminum acetate, aluminum nitrate, and their hydrates; the chromium source compound is one or more mixtures of chromium chloride, chromium sulfate, chromium nitrate, and their hydrates; the manganese source compound is one or more mixtures of manganese chloride, manganese sulfate, manganese acetate, manganese nitrate, and their hydrates; the nickel source compound is one or more mixtures of nickel nitrate, nickel sulfate, nickel chloride, nickel hydroxide, and their hydrates.

[0025] Optionally, in aqueous solution C, the sodium source compound is selected from one or more mixtures of anhydrous sodium carbonate, sodium hydroxide, sodium acetate, sodium alginate, sodium nitrate, sodium oxalate, and sodium citrate. The molar ratio of sodium element in the sodium source compound to phosphate radical in the phosphate: 1.0-1.2:1.0.

[0026] Optionally, in aqueous solution D, the molar ratio of V element, Al element, Mn element, Cr element, and Ni element is 1.0-2.0:0.01-0.05:0.01-0.05:0.01-0.05:0.01-0.05.

[0027] Optionally, in the aqueous solution D, the molar ratio of Na element, V element, Al element, Mn element, Cr element, Ni element, and phosphate group is 1.0 - 1.5: 0.5 - 1.0: 0.01 - 0.05: 0.01 - 0.05: 0.01 - 0.05: 0.01 - 0.05: 1.0 - 1.5.

[0028] Optionally, in the fourth step, heat the aqueous solution D: under the condition that the temperature is 60 - 100 °C, with a stirring speed of 100 - 400 r / min, magnetically stir for 1 - 4 h to obtain a uniformly mixed solution D.

[0029] Optionally, in the fifth step, heat by hydrothermal method: the volume of the polytetrafluoroethylene inner liner of the autoclave is selected to be 50 - 150 ml, the polar solvent is one or a mixture of tetrahydrofuran, acetonitrile, and ethylene glycol, the volume ratio of the polar solvent to the water in the aqueous solution D is 0.25 - 2.0: 1.0, heat to 160 - 200 °C at a heating rate of 0.3 - 1.0 °C / min, and heat for 10 - 16 h.

[0030] Optionally, in the fifth step, separate and dry: use a water pump or an oil pump in vacuum filtration, the detergent is absolute ethanol, the atmosphere in the oven is vacuum or air, the heating temperature is 60 - 100 °C, and the time is 10 - 18 h.

[0031] Optionally, in the sixth step, sinter the powder E: the protective atmosphere is nitrogen, argon, or a mixed gas of an inert atmosphere and a reducing gas; heat to 200 - 500 °C at a heating rate of 0.5 - 1.5 °C / min and pre-sinter for 2 - 6 h, then heat to 600 - 900 °C at a heating rate of 2.0 - 6.0 °C / min and sinter for 10 - 18 h; the cooling process is natural cooling.

[0032] According to the third aspect of the present application, a sodium-ion battery electrode sheet is provided, which is prepared from an electrode material, a conductive additive, a binder, and a solvent, and the electrode material is selected from the above-mentioned quaternary metal co-doped sodium vanadium phosphate symmetric electrode material.

[0033] According to the fourth aspect of the present application, a sodium-ion battery is provided, which consists of a positive electrode sheet, a separator, an organic electrolyte, and a negative electrode metal sodium, and the positive electrode sheet is the above-mentioned sodium-ion battery electrode sheet.

[0034] According to the fifth aspect of the present application, a symmetric sodium-ion battery is provided, which consists of a positive electrode sheet, a separator, an organic electrolyte, and a negative electrode sheet, and the positive electrode sheet and the negative electrode sheet are the above-mentioned sodium-ion battery electrode sheets.

[0035] According to the sixth aspect of the present application, an electrical device is provided, and the electrical device includes the above-mentioned sodium-ion battery or symmetric sodium-ion battery.

[0036] Compared with the prior art, the beneficial effects of the technical solution of the quaternary metal co-doped phosphate sodium ion battery electrode material, its preparation method and application provided by the present invention are as follows:

[0037] 1. The present invention provides a preparation method for synthesizing a quaternary metal co-doped phosphate electrode material with single phase, good crystallinity and uniform particle size, which is environmentally friendly and low in cost, and avoids the use of harmful chemical reagents and equipment waste.

[0038] 2. In the process of preparing the quaternary metal co-doped phosphate electrode material, only a very small amount of carbon source is used to coat the active substance of the electrode material, further improving the overall working voltage and energy density of the electrode.

[0039] 3. The present invention forms a combined site at the V site by four elements of Al, Mn, Cr, and Ni with nearly equimolar ratio. The local electronic structure generated by the mixing of multiple metal ions can compensate the charge in the reaction of sodium ion insertion and extraction of sodium vanadium phosphate material, effectively inhibiting the lattice volume change of the electrode material during charge and discharge at low and high voltages, and stabilizing the crystal structure of the material.

[0040] 4. In the test voltage range of 1.2 - 4.2V, the sodium ion battery assembled with a sodium foil as the negative electrode has a capacity retention rate of 98% (specific capacity is 141 mA h / g) after 1500 cycles of charge and discharge at a test current of 10C; after 237 cycles of charge and discharge at a test current of 30C, the capacity retention rate of the electrode material is 96% (specific capacity is 138 mA h / g), indicating that the synergistic effect of multi-metal doping has well improved the specific capacity and cycle stability of the sodium vanadium phosphate material.

[0041] 5. In the test voltage range of 1.2 - 4.0V, the symmetric sodium ion battery is subjected to a positive charge / negative charge transposition test (transposed every 100 cycles) at a test current of 10C. The capacity retention rates for every 100 cycles are 78%, 97%, 76%, and 82% respectively. After 400 cycles, the capacity retention rate of the symmetric sodium ion battery is 61%, and the specific capacity is 44 mA h / g, indicating that the synergistic effect of multi-metal doping enhances the structural stability of the sodium vanadium phosphate material in the symmetric sodium ion battery. Description of the Drawings

[0042] Figure 1 SEM image of the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 prepared in Example 1 of the present invention.

[0043] Figure 2 The XRD pattern of the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 prepared in Example 1 of the present invention.

[0044] Figure 3 The charge-discharge curves of the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 in the first three cycles at a test current of 1C.

[0045] Figure 4 The cycle performance graph of the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 at a test current of 10C.

[0046] Figure 5 The cycle performance graph of the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 at a test current of 30C.

[0047] Figure 6 The charge-discharge curves of the symmetric sodium-ion battery assembled with the quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 in the first three cycles at a test current of 1C.

[0048] Figure 7 The quaternary metal co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 assembled symmetric sodium-ion battery for the charge / discharge cycle performance graph at a test current of 10C.

[0049] Figure 8 Na of the quaternary metal co-doped sodium vanadium phosphate electrode material prepared in Example 2 of the present invention 3.26 V 1.55 Al 0.10 Mn 0.07 Cr 0.09 Ni 0.19 XRD pattern of (PO4)3.

[0050] Figure 9 Na of the quaternary metal co-doped sodium vanadium phosphate electrode material prepared in Example 3 of the present invention 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 XRD pattern of (PO4)3.

[0051] Figure 10 Na of the quaternary metal co-doped sodium vanadium phosphate electrode material prepared in Example 3 of the present invention 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 Charge / discharge curves of the first three cycles of (PO4)3 at a test current of 1C.

[0052] Figure 11 Na of the quaternary metal co-doped sodium vanadium phosphate electrode material prepared in Example 4 of the present invention 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 XRD pattern of (PO4)3.

[0053] Figure 12 Na of the quaternary metal co-doped sodium vanadium phosphate electrode material prepared in Example 4 of the present invention 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 Charge / discharge curves of the first three cycles of (PO4)3 at a test current of 1C.

[0054] Figure 13The sodium vanadium phosphate electrode material Na 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3 assembled into a symmetric sodium-ion battery at a test current of 1C, with the charge-discharge curves for the first three cycles. Detailed implementation manners

[0055] The present application will be described in detail below in conjunction with the embodiments, but the present application is not limited to these embodiments.

[0056] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels.

[0057] The present invention will be further described in detail below in conjunction with the drawings and the implementation manners:

[0058] Embodiment 1

[0059] A preparation method of a quaternary metal co-doped sodium vanadium phosphate electrode material, comprising the following steps:

[0060] In the first step, 0.018 mol of ammonium metavanadate and 0.040 mol of citric acid monohydrate are weighed and dissolved in 90 mL of deionized water, heated to 80 °C, and the stirring speed is set to 350 r / min and the time is 0.5 h to form an aqueous solution A;

[0061] In the second step, 0.0005 mol of aluminum nitrate nonahydrate, 0.0005 mol of chromium nitrate nonahydrate, 0.0005 mol of nickel nitrate hexahydrate, and 0.0005 mol of manganese acetate tetrahydrate are weighed and added to the solution A in sequence to obtain an aqueous solution B;

[0062] In the third step, 0.0155 mol of anhydrous sodium carbonate and 0.0300 mol of ammonium dihydrogen phosphate are weighed and dissolved in 20 mL of deionized water to form an aqueous solution C;

[0063] In the fourth step, the aqueous solution C is slowly (1 drop per second) added dropwise to the aqueous solution B to obtain an aqueous solution D;

[0064] In the fifth step, the aqueous solution D is heated in a water bath at 80 °C for 4 h, then transferred to a polytetrafluoroethylene inner liner, and 20 mL of tetrahydrofuran is added. The inner liner is sealed in a stainless steel outer shell and reacted in an oven at 180 °C for 12 h. After cooling to room temperature at a cooling rate of 0.55 °C / min, the product is filtered under reduced pressure, and then dried in vacuo at 80 °C for 12 h to obtain the electrode material precursor, denoted as powder G;

[0065] Step 6: The obtained powder G is pre-sintered in a high-purity argon atmosphere mixed with 10 wt% hydrogen at a gas flow rate of 20 sccm, a heating rate of 1 °C / min, and a temperature of 350 °C for 4 h, and then heated to 750 °C and sintered for 12 h. After cooling, it is crushed and ground to obtain Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 material;

[0066] As Figure 1 shown, the surface particle size of the Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 prepared by the above method is at the micron level;

[0067] As Figure 2 shown, the XRD pattern of the Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3 indicates that the crystal structure of this material is the Na3V2(PO4) structure of space group R-3c, and there are no other impurity phases. Table 1 shows the elemental content data measured by inductively coupled plasma optical emission spectrometry of the quaternary co-doped sodium vanadium phosphate electrode material Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 (PO4)3, indicating that the ratio of each element in the sample is basically consistent with the feeding ratio.

[0068] Table 1

[0069]

[0070] Step 7: Weigh the Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.040.3 g of (PO4)3 material, conductive agent acetylene black, and binder polyvinylidene fluoride were uniformly mixed with N-methyl P-pyrrolidone to form a slurry, which was then coated on the surface of aluminum foil. After drying and cutting, it was used as an electrode sheet. Using 1 mol / L NaPF6 / 100% diglyme as the electrolyte, a button cell was assembled.

[0071] The obtained Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 The (PO4)3 material electrode sheet was used as the positive electrode of a sodium-ion battery, and a sodium metal foil was used as the negative electrode to assemble a sodium-ion battery, which was tested in the voltage range of 1.2 - 4.2 V. As Figure 3 shown, at a 1C test current, the initial discharge specific capacity of the sodium-ion battery was 152 mA h / g. As Figure 4 shown, at a 10C test current and after 1500 cycles of charge and discharge, the capacity retention rate of the material was 98% (specific capacity was 141 mA h / g). As Figure 5 shown, at a 30C test current and after 237 cycles of charge and discharge, the capacity retention rate of the electrode material was 96% (specific capacity was 138 mA h / g).

[0072] The obtained Na 3.09 V 1.84 Al 0.05 Mn 0.05 Cr 0.02 Ni 0.04 The (PO4)3 material electrode sheet was used as the positive and negative electrodes to assemble a symmetric sodium-ion battery. As Figure 6 shown, in the voltage range of 1.2 - 4.0 V and at a 1C test current, the initial discharge specific capacity of the symmetric sodium-ion battery was 73 mA h / g. As Figure 7 shown, the symmetric sodium-ion battery was subjected to positive charge / negative charge tests (transposed every 100 cycles) at a 10C test current. The capacity retention rates for each 100 cycles were 78%, 97%, 76%, and 82% respectively. After 400 cycles, the total capacity retention rate of the symmetric sodium-ion battery was 61%, and the specific capacity was 44 mA h / g.

[0073] Example 2

[0074] A preparation method of a quaternary metal co-doped sodium vanadium phosphate electrode material, comprising the following steps:

[0075] First step: Weigh 0.007 mol of ammonium metavanadate and 0.020 mol of citric acid monohydrate, dissolve them in 90 mL of deionized water, heat to 80 °C, set the stirring speed at 350 r / min and the time at 0.5 h to form aqueous solution A;

[0076] Second step: Weigh 0.0005 mol of aluminum nitrate nonahydrate, 0.0005 mol of chromium nitrate nonahydrate, 0.0005 mol of nickel nitrate hexahydrate and 0.0005 mol of manganese acetate tetrahydrate respectively, and add them to solution A in sequence to obtain aqueous solution B;

[0077] Third step: Weigh 0.0065 mol of anhydrous sodium carbonate and 0.0120 mol of ammonium dihydrogen phosphate respectively, dissolve them in 20 mL of deionized water to form aqueous solution C;

[0078] Fourth step: Slowly (1 drop per second) drip aqueous solution C into aqueous solution B to obtain aqueous solution D;

[0079] Fifth step: Heat aqueous solution D in a water bath at 80 °C for 4 h, then transfer it to a polytetrafluoroethylene inner liner, and add 20 mL of tetrahydrofuran. Seal the inner liner into a stainless steel outer shell, react in an oven at 180 °C for 12 h, cool to room temperature at a cooling rate of 0.55 °C / min, filter the product under reduced pressure, and then dry it under 80 vacuum for 12 h to obtain the electrode material precursor, denoted as powder G;

[0080] Sixth step: In a high-purity argon atmosphere mixed with 10% hydrogen, with a gas flow rate of 20 sccm and a heating rate of 1 °C / min, pre-sinter the obtained powder G at 350 °C for 4 h, then heat it to 750 °C and sinter for 12 h. After cooling, crush and grind it to obtain the quaternary metal co-doped sodium vanadium phosphate Na 3.26 V 1.55 Al 0.10 Mn 0.07 Cr 0.09 Ni 0.19 (PO4)3 material;

[0081] Figure 8 For the XRD pattern of the quaternary metal co-doped sodium vanadium phosphate Na 3.26 V 1.55 Al 0.10 Mn 0.07 Cr 0.09 Ni 0.19 (PO4)3, it shows that the structure of this material is the Na3V2(PO4) structure with the space group R-3c and no other impurity phases exist. Table 2 shows the prepared quaternary co-doped sodium vanadium phosphate electrode material Na 3.26 V 1.55 Al 0.10 Mn 0.07Cr 0.09 Ni 0.19 The elemental content data measured by energy dispersive spectrometer of (PO4)3 indicates that the proportion of each element in the sample is basically consistent with the feeding ratio.

[0082] Table 2

[0083]

[0084] Example 3

[0085] A preparation method of a quaternary metal co-doped sodium vanadium phosphate electrode material, comprising the following steps:

[0086] First step, weigh 0.018 mol of ammonium metavanadate and 0.040 mol of citric acid monohydrate, dissolve them in 90 mL of deionized water, heat to 80 °C, set the stirring speed to 350 r / min and the time to 0.5 h to form aqueous solution A;

[0087] Second step, weigh 0.0005 mol of aluminum nitrate nonahydrate, 0.0005 mol of chromium nitrate nonahydrate, 0.0005 mol of nickel nitrate hexahydrate and 0.0005 mol of manganese acetate tetrahydrate respectively, and add them to solution A in sequence to obtain aqueous solution B;

[0088] Third step, weigh 0.0155 mol of anhydrous sodium carbonate and 0.0300 mol of ammonium dihydrogen phosphate respectively, dissolve them in 20 mL of deionized water to form aqueous solution C;

[0089] Fourth step, slowly (1 drop per second) drip aqueous solution C into aqueous solution B to obtain aqueous solution D;

[0090] Fifth step, heat aqueous solution D in a water bath at 80 °C for 4 h, transfer it to a polytetrafluoroethylene inner liner, and add 5 mL of tetrahydrofuran. Seal the inner liner into a stainless steel outer shell, react in an oven at 180 °C for 12 h, cool to room temperature at a cooling rate of 0.55 °C / min, filter the product under reduced pressure, and then dry it under vacuum at 80 °C for 12 h to obtain the electrode material precursor, denoted as powder G;

[0091] Sixth step, place the obtained powder G in a high-purity argon atmosphere mixed with 10% hydrogen, with a gas flow rate of 20 sccm and a heating rate of 1 °C / min, pre-sinter at 350 °C for 4 h, then heat up to 750 °C and sinter for 12 h. After cooling, crush and grind to obtain quaternary metal co-doped sodium vanadium phosphate Na 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 (PO4)3 material;

[0092] Figure 9 The Na prepared by the above method 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 (PO4)3 XRD pattern indicates that the structure of this material is the Na3V2(PO4) structure with the space group R-3c and no other impurity phases exist. Table 3 shows the Na of the prepared quaternary co-doped sodium vanadium phosphate electrode material 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 (PO4)3 elemental content data measured by energy dispersive spectrometer shows that the proportion of each element in the sample is basically consistent with the feeding ratio.

[0093] Table 3

[0094]

[0095] Step 7: Make the Na 3.08 V 1.79 Al 0.07 Mn 0.04 Cr 0.06 Ni 0.04 (PO4)3 electrode material into an electrode sheet by the same method as in Example 1, assemble it as the positive electrode into a sodium-ion battery and conduct electrochemical tests. As Figure 10 shown, at a 1C test current, the sodium-ion battery exhibits a relatively high initial specific capacity (147 mA h / g), showing excellent electrochemical performance.

[0096] Example 4

[0097] A preparation method of a quaternary metal co-doped sodium vanadium phosphate electrode material, comprising the following steps:

[0098] Step 1: Weigh 0.018 mol of ammonium metavanadate and 0.040 mol of citric acid monohydrate, dissolve them in 90 mL of deionized water, heat to 80 °C, set the stirring speed at 350 r / min and the time at 0.5 h to form aqueous solution A;

[0099] Step 2: Weigh 0.0005 mol of aluminum nitrate nonahydrate, 0.0005 mol of chromium nitrate nonahydrate, 0.0005 mol of nickel nitrate hexahydrate and 0.0005 mol of manganese acetate tetrahydrate respectively, and add them to solution A in sequence to obtain aqueous solution B;

[0100] Step 3: Weigh 0.0155 mol of anhydrous sodium carbonate and 0.0300 mol of ammonium dihydrogen phosphate separately, dissolve them in 20 mL of deionized water to form aqueous solution C;

[0101] Step 4: Slowly (1 drop per second) add aqueous solution C to aqueous solution B to obtain aqueous solution D;

[0102] Step 5: After heating aqueous solution D in a water bath at 80 °C for 4 h, transfer it to a polytetrafluoroethylene inner liner, and add 20 mL of tetrahydrofuran. Seal the inner liner in a stainless-steel outer shell, react in an oven at 180 °C for 12 h, cool to room temperature at a cooling rate of 0.55 °C / min, filter the product under reduced pressure, and then dry it under vacuum at 80 °C for 12 h to obtain the electrode material precursor, denoted as powder G;

[0103] Step 6: In an atmosphere of high-purity argon mixed with 10% hydrogen, with a gas flow rate of 20 sccm and a heating rate of 1 °C / min, pre-sinter the obtained powder G at 350 °C for 4 h, and then heat it up to 650 °C and sinter for 12 h. After cooling, crush and grind it to obtain the quaternary metal co-doped sodium vanadium phosphate Na 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3 material.

[0104] Figure 11 The XRD pattern of the quaternary metal co-doped sodium vanadium phosphate Na 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3 shows that the structure of this material is the Na3V2(PO4) structure with the space group R-3c and no other impurity phases. Table 4 shows the elemental content data measured by the energy dispersive spectrometer of the prepared quaternary co-doped sodium vanadium phosphate electrode material Na 3.2 V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3, indicating that the ratio of each element in the sample is basically consistent with the feeding ratio.

[0105] Table 4

[0106]

[0107] Step 7: The Na 3.2 V 1.57 Al0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3 was made into an electrode sheet in the same manner as in Example 1. As Figure 12 shown, the sodium-ion battery assembled with the electrode sheet as the positive electrode exhibited a high initial specific capacity (138 mA h / g) at a 1C test current, demonstrating excellent electrochemical performance. The obtained Na 3. 2V 1.57 Al 0.06 Mn 0.09 Cr 0.16 Ni 0.12 (PO4)3 electrode sheet was used as the positive and negative electrodes of a symmetric sodium-ion battery. As Figure 13 shown, the symmetric sodium-ion battery had a discharge specific capacity of 50 mA h / g for the first and the first three cycles at a 1C test current in the voltage range of 0.5 - 3.5V.

[0108] As described above, only several embodiments of the present application are provided, and it does not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A quaternary metal co-doped sodium vanadium phosphate electrode material, characterized in that: The chemical formula of the electrode material is Na x V y Al a Mn b Cr c Ni d (PO4)3, where 3.0 ≤ x ≤ 3.5; 0.5 < y ≤ 2.0; 0 < (a, b, c or d) ≤ 0.2; 1.5 ≤ (y + a + b + c + d) ≤ 2.

0.

2. The quaternary metal co-doped sodium vanadium phosphate electrode material according to claim 1, characterized in that: The electrode material has a space group R-3c The single-phase structure of Na3V2(PO4)3, the atomic ratio of V site is V:Al:Cr:Mn:Ni = 5.0 ~10.0:0.1 ~ 0.5:0.1 ~ 0.5:0.1 ~ 0.5:0.1 ~ 0.

5.

3. The method for preparing the quaternary metal co-doped sodium vanadium phosphate electrode material according to claim 1 or 2, characterized in that The following steps are involved: Step 1, weighing a carbon source compound, a sodium source compound, a phosphorus source compound, a vanadium source compound, an aluminum source compound, a chromium source compound, a manganese source compound and a nickel source compound in a required stoichiometric ratio, gradually dissolving them in deionized water, and stirring them evenly to obtain a precursor mixed aqueous solution; Step 2: Add a polar solvent to the precursor mixed aqueous solution, then transfer it to a high-pressure reactor, react at 160-200°C for 10-16 hours, and then place it in an oven at 60-100°C for 10-18 hours to obtain a precursor powder; Step 3: Perform two-step calcination on the precursor powder described in Step 2. The first-step calcination is carried out at 200 - 500 °C, and the second-step calcination is carried out at 600 - 900 °C. The target product Na x V y Al a Mn b Cr c Ni d (PO4)3, where 3.0 ≤ x ≤ 3.5; 0.5 < y ≤ 2.0; 0 < (a, b, c or d) ≤ 0.2; 1.5 ≤ (y + a + b + c + d) ≤ 2.

0.

4. The preparation method according to claim 3, characterized in that: The carbon source compound is selected from one or more mixtures of citric acid, glucose and ascorbic acid; The sodium source compound is selected from one or more mixtures of anhydrous sodium carbonate, anhydrous sodium hydroxide, sodium acetate, sodium alginate, sodium nitrate, sodium oxalate and sodium citrate; The vanadium source compound is selected from one or more mixtures of sodium vanadate, ammonium metavanadate, vanadium pentoxide, ammonium vanadate and hydrates thereof; The aluminum source compound is selected from one or more mixtures of aluminum chloride, aluminum oxide, aluminum acetate, aluminum nitrate and hydrates thereof; The chromium source compound is selected from one or more mixtures of chromium chloride, chromium sulfate, chromium nitrate and hydrates thereof; The manganese source compound is selected from one or more mixtures of manganese chloride, manganese sulfate, manganese acetate, manganese nitrate and hydrates thereof; The nickel source compound is selected from one or more mixtures of nickel nitrate, nickel sulfate, nickel chloride, nickel hydroxide and hydrates thereof.

5. The preparation method according to claim 3, characterized in that: In step 1, the molar ratio of the sodium element in the sodium source compound to the phosphate in the phosphorus source compound is: 1.0 ~ 1.2:1.

0.

6. The preparation method according to claim 3, characterized in that: In step 2, the polar solvent is selected from one or more mixtures of tetrahydrofuran, acetonitrile and ethylene glycol, and the volume ratio of the polar solvent to the deionized water in step 1 is 0.25-2.0:1.

0.

7. A sodium ion battery electrode sheet, prepared from an electrode material, a conductive additive, a binder and a solvent, characterized in that: The electrode material is selected from the quaternary metal co-doped sodium vanadium phosphate electrode material according to claim 1 or 2, or the quaternary metal co-doped sodium vanadium phosphate electrode material prepared by the preparation method according to any one of claims 4-6.

8. A sodium ion battery, comprising a positive electrode, a separator, an organic electrolyte and a negative electrode, characterized in that: The positive electrode is the sodium ion battery electrode sheet according to claim 7.

9. A symmetrical sodium ion battery, comprising a positive electrode, a separator, an organic electrolyte and a negative electrode, characterized in that: The positive electrode and the negative electrode are both the sodium ion battery electrode sheets as described in claim 7.

10. An electrical equipment, characterized in that: The electrical equipment comprises the sodium ion battery according to claim 8 or the symmetrical sodium ion battery according to claim 9.

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