Hf < 4 + > doped vanadium manganese sodium phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses an Hf < 4 + > doped vanadium manganese sodium phosphate positive electrode material and a preparation method thereof. Hf < 4 + > is doped to the manganese site of sodium vanadium manganese phosphate Na4MnV (PO4) 3 through a sol-gel method and a high-temperature roasting method, and the sodium ion battery positive electrode material Hf < 4 + > doped sodium vanadium manganese phosphate Na4-2xMn < 1-x > Hf < x > V (PO4) 3 (0 lt, x is smaller than or equal to 0.1) is obtained. By introducing Hf < 4 + > into the lattice structure of vanadium manganese sodium phosphate, the ginger-Taylor effect of Mn < 3 + > can be weakened, and the interplanar spacing can be increased, so that the purposes of improving the stability of the crystal structure and expanding a sodium ion diffusion channel are achieved, the diffusion rate of sodium ions is further remarkably improved, and the stability of the crystal structure is favorably maintained; and the rate capability and the cycle performance of the vanadium manganese sodium phosphate are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, and specifically relates to an Hf 4+ Doped sodium manganese phosphate cathode material and its preparation method. Background Technology

[0002] The global energy system is accelerating its transformation towards a green and low-carbon direction. Renewable energy technologies, represented by photovoltaic and wind power generation, are developing rapidly. At the same time, emerging fields such as new energy vehicles and smart grids are placing higher demands on efficient energy storage systems. Although lithium-ion batteries have become the main power source for mobile electronic devices and electric vehicles due to their advantages of good cycle stability and high energy density, the sustainable development of lithium-ion batteries is severely constrained by disadvantages such as scarce lithium resources (global reserves are only about 0.0065%), uneven geographical distribution (lithium resources are highly concentrated in Bolivia, Chile, and Argentina), and large price fluctuations.

[0003] Against this backdrop, sodium-ion batteries, due to their similar working principle to lithium-ion batteries and the abundance of sodium resources (containing 2.64% of the Earth's crust), have become the most promising alternative technology to lithium-ion batteries. However, for sodium-ion batteries to achieve commercial application, key technological bottlenecks still need to be overcome, such as insufficient energy density (currently around 100-150 Wh / kg) and short cycle life (generally <2000 cycles). Among these, the cathode material, as the core element determining battery performance, is directly related to the technological breakthrough of sodium-ion batteries. Currently, research on cathode materials for sodium-ion batteries mainly focuses on three categories: Prussian blue analogs, layered oxides, and polyanionic compounds. However, the water of crystallization in Prussian blue analogs severely affects their cycle performance, and layered oxides suffer from poor structural stability. Polyanionic compound cathode materials, on the other hand, are highly favored due to their significant advantages in thermal stability and cycle performance. Sodium vanadium phosphate (Na3V2(PO4)3) is currently a relatively well-studied polyanionic compound cathode material, exhibiting good cycle stability and high operating voltage, and has broad application prospects. However, the expensive and somewhat toxic nature of vanadium resources limits the widespread application of sodium vanadium phosphate. Sodium manganese vanadium phosphate (Na4MnV(PO4)3), obtained by partially replacing V with inexpensive and environmentally friendly Mn, offers advantages in terms of environmental friendliness, energy density, and cost. This invention utilizes Hf at the manganese sites of Na4MnV(PO4)3. 4+ Doping can weaken Mn 3+ The Ginger-Taylor effect can inhibit the migration of V from the transition metal layer to the sodium layer, and can also expand the lattice volume of the material while improving structural stability, thereby enhancing the electrochemical performance of sodium vanadium manganese phosphate. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method for improving the electrochemical performance of sodium manganese vanadium phosphate cathode material by doping Hf at the manganese site in view of the problem of poor cycle performance of the existing sodium manganese vanadium phosphate cathode material in terms of material structure design. This method has a simple process, and the prepared sodium manganese vanadium phosphate has the advantages of long cycle life, excellent rate performance and high capacity, significantly improving the electrochemical performance of sodium manganese vanadium phosphate. 4+

[0005] The Hf-doped sodium manganese vanadium phosphate involved in the present invention 4+ has a molecular formula of Na 4-2x Mn 1-x Hf x V(PO4)3(0 < x ≤ 0.1). The specific steps of the preparation method of the Hf-doped sodium manganese vanadium phosphate are as follows: 4+ (1) Weigh the sodium source compound, vanadium source compound, manganese source compound, hafnium source compound, and phosphorus source compound according to the molar ratio of Na:V:Mn:Hf:P = (4 - 2x):1:(1 - x):x:3 (0 < x ≤ 0.1), and dissolve them in a certain amount of complexing agent aqueous solution (where the molar ratio of the complexing agent to vanadium is 1.2 - 2:1). Under the action of the complexing agent and the condition of heating the solution, a precursor gel is obtained;

[0007] (2) After drying the precursor gel in (1), place it in an inert atmosphere and carry out calcination. Heat it to 350 °C at a heating rate of 2 - 10 °C / min, and calcine for 3 - 7 hours. Then heat it to 650 °C - 850 °C at a heating rate of 2 - 10 °C / min, and keep it at a constant temperature for 8 - 12 hours. Then cool it naturally to room temperature to obtain the Na 4-2x 1-x Mn x Hf 4+ V(PO4)3 material.

[0008] The sodium source is one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium carbonate, sodium citrate, and sodium bicarbonate;

[0009] The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, and vanadium trioxide;

[0010] The manganese source is one or more of manganese nitrate, manganese acetate, and manganese chloride;

[0011] The hafnium source is one or more of hafnium chloride, hafnium nitrate, hafnium acetate, and hafnium carbonate;

[0012] The complexing agent is one or more of citric acid, sodium citrate, ammonium citrate, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid;

[0013] ​​The phosphorus source is one or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid, and sodium dihydrogen phosphate;

[0014] The inert atmosphere is one or both of nitrogen and argon.

[0015] This invention involves reacting water-soluble substances such as vanadium, manganese, hafnium, sodium, and phosphorus source compounds with a complexing agent to achieve uniform dispersion of the reactants at the molecular level. The preparation process is simple, requires less time, and yields products with small particle sizes. After high-temperature calcination, the in-situ carbon coating enhances electronic conductivity and inhibits particle growth. (The last sentence appears to be incomplete and possibly refers to a specific process involving Hf.) 4+ Doping the manganese sites in sodium vanadium manganese phosphate can weaken the Mn content. 3+ The Ginger-Taylor effect can also suppress the migration of V from the transition metal layer to the sodium layer, thereby improving the stability of the crystal structure and expanding the sodium ion diffusion channel, thus giving doped sodium vanadium manganese phosphate excellent rate performance and cycle stability. Attached Figure Description

[0016] Figure 1 The Hf prepared in Example 1 of this invention 4+ Sodium vanadium manganese phosphate (Na) 3.95 Mn 0.975 Hf 0.025 XRD pattern of V(PO4)3.

[0017] Figure 2 The Hf prepared in Example 2 of this invention 4+ Sodium vanadium manganese phosphate (Na) 3.93 Mn 0.965 Hf 0.035 XRD pattern of V(PO4)3.

[0018] Figure 3 The Hf prepared in Example 2 of this invention 4+ Sodium vanadium manganese phosphate (Na) 3.93 Mn 0.965 Hf 0.035 The first charge-discharge curve of V(PO4)3 at 1C.

[0019] Figure 4 The Hf prepared in Example 3 of this invention 4+ Sodium vanadium manganese phosphate (Na) 3.91 Mn 0.955 Hf 0.045 Cyclic performance curve of V(PO4) at 1C. Detailed Implementation

[0020] Example 1:

[0021] (1) Dissolve 0.5850 g ammonium metavanadate, 1.1950 g manganese acetate tetrahydrate, 0.04004 g hafnium chloride, 1.7255 g ammonium dihydrogen phosphate, 1.6203 g sodium acetate and 1.0508 g citric acid in 60 ml deionized water to prepare a mixed salt solution. Place the solution in an 80 ℃ constant temperature water bath and stir continuously until a blue gel is formed. Then transfer the blue gel to a refrigerator and freeze it into ice cubes. Place the ice cube gel in a vacuum freeze dryer at -50 ℃ and dry for 72 hours.

[0022] (2) The dry gel obtained in step (1) was heated to 350 °C in an argon atmosphere at a heating rate of 3 °C / min and calcined for 6 hours. Then, it was heated to 650 °C at a heating rate of 5 °C / min and calcined for 12 hours. Then, it was naturally cooled to room temperature in the furnace to obtain Na. 3.95 Mn 0.975 Hf 0.025 V (PO4)3. Figure 1 Here is the XRD pattern of the material.

[0023] Na, the positive electrode material of sodium-ion batteries 3.95 Mn 0.975 Hf 0.025 V(PO4)3 / C, conductive agent Super P, and binder PVDF were weighed in a mass ratio of 8:1:1 and mixed evenly in an agate mortar. An appropriate amount of NMP solution was added to prepare an electrode slurry. After stirring evenly, the slurry was coated evenly onto aluminum foil and dried in a 120 ℃ forced-air oven. After drying, the electrode sheets were cut into 12 mm round electrodes, rolled, and weighed. The resulting electrode sheets were used as the positive electrode, with metallic sodium as the negative electrode and glass fiber as the separator. A CR2016 button cell was assembled in a glove box filled with high-purity argon (moisture and oxygen content both less than 0.1 ppm). The cell was tested using a Newway testing system at 25 ℃ (voltage range 2.5~3.8 V vs. Na). + The Na prepared using the method of this invention was subjected to constant current charge-discharge testing. 3.95 Mn 0.975 Hf 0.025 The V(PO4)3 sodium-ion battery cathode material has a first-cycle discharge specific capacity of 94.1 mAh / g at 1C, and a discharge specific capacity of 86.6 mAh / g after 100 cycles, with a retention rate of 92.0%.

[0024] Example 2:

[0025] (1) Dissolve 0.5850 g ammonium metavanadate, 0.8438 g manganese nitrate, 0.0561 g hafnium chloride, 1.7255 g ammonium dihydrogen phosphate, 1.6150 g sodium acetate and 1.6813 g citric acid in 65 ml of deionized water and place it in a constant temperature water bath at 85 °C. Stir the solution continuously until a blue gel is formed. Then transfer the blue gel to a refrigerator and freeze it into ice cubes. Place the ice cube gel in a vacuum freeze dryer at -50 °C and dry it for 72 hours.

[0026] (2) The dry gel obtained in step (1) was heated to 350 °C in an argon atmosphere at a heating rate of 5 °C / min and calcined for 5 hours. Then, it was heated to 750 °C at a heating rate of 5 °C / min and calcined for 12 hours. Then, it was naturally cooled to room temperature in the furnace to obtain Na. 3.93 Mn 0.965 Hf 0.035 V (PO4)3. Figure 2 Here is the XRD pattern of the material.

[0027] Na, the positive electrode material of sodium-ion batteries 3.93 Mn 0.965 Hf 0.035 V(PO4)3, conductive agent Super P, and binder PVDF were weighed in a mass ratio of 8:1:1 and mixed evenly in an agate mortar. Then, an appropriate amount of NMP solution was added to form an electrode slurry. After stirring evenly, the slurry was evenly coated onto aluminum foil and dried in a 120 ℃ forced-air oven. After drying, the electrode sheets were cut into 12 mm round electrodes, rolled, and weighed. The resulting electrode sheets were used as the positive electrode, with metallic sodium as the negative electrode and glass fiber as the separator. A CR2016 button cell was assembled in a glove box filled with high-purity argon (moisture and oxygen content both less than 0.1 ppm). The cell was tested using a Newway testing system at 25 ℃ (voltage range 2.5~3.8 V vs Na). + The Na prepared using the method of this invention was subjected to constant current charge-discharge testing. 3.93 Mn 0.965 Hf 0.035 The discharge specific capacity of V(PO4)3 at 1C is 88.1 mAh / g in the first cycle, and the discharge specific capacity after 100 cycles is still as high as 84.9 mAh / g, with a capacity retention rate of 96.5%. Figure 3 The first charge-discharge curve of this material under 1C conditions is shown.

[0028] Example 3:

[0029] (1) Dissolve 0.5850 g vanadium pentoxide, 1.1704 g manganese chloride tetrahydrate, 0.07207 g hafnium chloride, 1.7255 g ammonium dihydrogen phosphate, 1.6039 g sodium acetate and 2.1016 g citric acid in 70 ml of deionized water, place it in a constant temperature water bath at 90 ℃ and stir continuously until a blue gel is formed. Then transfer the blue gel to a refrigerator and freeze it into ice cubes. Then place the ice cube gel in a vacuum freeze dryer at -50 ℃ and dry it for 72 hours.

[0030] (2) The dry gel obtained in step (1) was heated to 350 °C in an argon atmosphere at a heating rate of 5 °C / min and calcined for 6 hours. Then, it was heated to 850 °C at a heating rate of 5 °C / min and calcined for 11 hours. Then, it was naturally cooled to room temperature in the furnace to obtain Na. 3.91 Mn 0.955 Hf 0.045 V(PO4)3 / C composite material.

[0031] Na, the positive electrode material of sodium-ion batteries 3.91 Mn 0.955 Hf 0.045 V(PO4)3, conductive agent Super P, and binder PVDF were weighed in a mass ratio of 8:1:1 and mixed evenly in an agate mortar. Then, an appropriate amount of NMP solution was added to form an electrode slurry. After stirring evenly, the slurry was evenly coated onto aluminum foil and dried in a 120 ℃ forced-air oven. After drying, the electrode sheets were cut into 12 mm round electrodes, rolled, and weighed. The resulting electrode sheets were used as the positive electrode, with metallic sodium as the negative electrode and glass fiber as the separator. A CR2016 button cell was assembled in a glove box filled with high-purity argon (moisture and oxygen content both less than 0.1 ppm). The cell was tested using a Newway testing system at 25 ℃ (voltage range 2.5~3.8 V vs Na). + The Na prepared using the method of this invention was subjected to constant current charge-discharge testing. 3.91 Mn 0.955 Hf 0.045 The discharge specific capacity of V(PO4)3 at 1C is 99.6 mAh / g in the first cycle, and the discharge specific capacity after 100 cycles is still as high as 97.4 mAh / g, with a capacity retention rate of 97.8%. Figure 4 This is a graph showing the cycling performance of the material under 1C conditions.

[0032] Since there are many embodiments of the present invention, they will not be listed one by one here. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A type of Hf 4+ The doped sodium manganese phosphate cathode material is characterized by... The Hf 4+ The molecular formula of doped sodium manganese vanadium phosphate is Na. 4-2x Mn 1-x Hf x V(PO4)3, where 0 <x≤0.1。 2. The Hf according to claim 1 4+ The preparation method of sodium manganese phosphate doped cathode material is characterized by: The specific steps are as follows: (1) Weigh a sodium source compound, a vanadium source compound, a manganese source compound, a hafnium source compound, and a phosphorus source compound according to a molar ratio of Na:V:Mn:Hf:P = (4 - 2x):1:(1 - x):x:3 (0 < x ≤ 0.1), and dissolve them in a certain amount of an aqueous solution of a complexing agent (where the molar ratio of the complexing agent to vanadium is 1.2 - 2:1). Under the action of the complexing agent and with the solution heated, a precursor gel is obtained; (2) After drying the precursor gel described in (1), place it under an inert atmosphere and calcine it. Heat it to 350 °C at a heating rate of 2-10 °C / min and calcine for 3-7 hours. Then heat it to 650 °C-850 °C at a heating rate of 2-10 °C / min and hold it at that temperature for 8-12 hours. Then cool it naturally to room temperature to obtain Na. 4-2x Mn 1-x Hf x V(PO4)3 material; The sodium source is one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium carbonate, sodium citrate, and sodium bicarbonate; The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, and vanadium trioxide; The manganese source is one or more of manganese nitrate, manganese acetate, and manganese chloride; The hafnium source is one or more of hafnium chloride, hafnium nitrate, hafnium acetate, and hafnium carbonate; The complexing agent is one or more of citric acid, sodium citrate, ammonium citrate, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid; The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid, and sodium dihydrogen phosphate; The inert atmosphere is one or two of nitrogen and argon.

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