Carbon-coated pyrophosphate doped vanadium manganese sodium phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a carbon-coated pyrophosphate doped vanadium manganese phosphate positive electrode material and a preparation method thereof. Pyrophosphate radicals are doped to phosphate radical anion sites of sodium vanadium manganese phosphate (Na < 3.5 > Mn < 0.5 > V < 1.5 > (PO < 4 >) < 3 >) through a sol-gel method and a high-temperature calcination method, and the sodium ion battery positive electrode material pyrophosphate radical doped sodium vanadium manganese phosphate (Na < 3.5 + x > Mn < 0.5 > V < 1.5 > (PO < 4 >) < 3-x > (PO < 7 >) < x / C) (0 lt, x < = 1) is obtained. By introducing P2O74 <-> into the lattice structure of the vanadium manganese sodium phosphate, the crystal structure can be stabilized, the structural deformation in the charging and discharging process can be reduced, and a relatively large channel is provided for rapid migration of sodium ions, so that the doped vanadium manganese sodium phosphate has excellent large current property and cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, and specifically relates to a carbon-coated sodium vanadium manganese phosphate (Na₂O₃) doped with pyrophosphate. 3.5 Mn 0.5 V 1.5 (PO4)3 / C) cathode material and its preparation method. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have attracted more attention due to their advantages such as low cost and abundant resources. However, compared to the ionic radius of lithium (0.76 Å), the ionic radius of sodium (1.02 Å) is larger, resulting in slower diffusion kinetics of sodium ions within the bulk phase of the electrode material. This ultimately leads to lower cycle stability and energy density in sodium-ion batteries compared to lithium-ion batteries. The cathode material is crucial in determining the battery's energy density and electrochemical performance. Currently, cathode materials under research can be divided into three main categories: transition metal oxides, polyanionic compounds, and Prussian blue analogues. These cathode materials show promising applications in sodium-ion batteries. Among polyanionic compounds, fast-ion conductor polyanionic compounds have attracted considerable attention due to their tunable chemical composition, structural flexibility, and good electrochemical compatibility with sodium ions. Sodium vanadium manganese phosphate (Na₂O₃) is a prime example. 3.5 Mn 0.5 V 1.5 (PO4)3) exhibits high discharge capacity, discharge plateau, and good structural stability, but its cycle performance and rate performance still need further improvement. This invention modifies the material through ion doping and carbon coating. The stable and robust PO bonds endow the material with excellent chemical and structural stability, while the open framework allows for rapid and reversible insertion / extraction of sodium ions within the lattice, increasing the lattice volume and improving structural stability, thereby significantly enhancing Na+ performance. 3.5 Mn 0.5 V 1.5 Electrochemical performance of (PO4)3 / C. Summary of the Invention

[0003] This invention aims to address the problems of poor electronic conductivity, rate performance, and cycle performance of existing sodium-ion battery cathode materials, such as sodium vanadium manganese phosphate, and provides a pyrophosphate-doped Na... 3.5 Mn 0.5 V 1.5 A method for preparing (PO4)3 / C cathode materials with good electrochemical performance was presented. This method is simple, and the prepared doped materials exhibit advantages such as long cycle life, high capacity, and good rate performance under high voltage, significantly improving the electrochemical performance of sodium vanadium manganese phosphate (Na). 3.5 Mn 0.5 V 1.5(PO4)3 / C Electrochemical Performance. The molecular formula of the sodium manganese vanadium phosphate cathode material doped with pyrophosphate radicals involved in this invention is Na 3.5+x Mn 0.5 V 1.5 (PO4) 3-x (P2O7) x / C (0 < x ≤ 1). The specific steps of the preparation method of the sodium manganese vanadium phosphate doped with pyrophosphate radicals are as follows:

[0004] (1) Weigh the sodium source compound, manganese source compound, vanadium source compound, phosphorus source compound, and pyrophosphate radical compound according to the molar ratio of Na:Mn:V:PO4 3- :P2O7 4- = (3.5 + x):0.5:1.5:(3 - x):x (0 < x ≤ 1), and dissolve them in a certain amount of complexing agent aqueous solution (the molar ratio of the complexing agent to vanadium is 1.0 - 2.5:1). Under the reduction of the complexing agent and heating the solution, a precursor gel is obtained;

[0005] (2) After drying the precursor gel described in (1), place it in an inert atmosphere and calcine it. Heat it to 350 °C at a heating rate of 3 - 10 °C / min, and roast it for 3 - 6 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 carbon-coated doped sodium manganese vanadium phosphate (Na 3.5+x Mn 0.5 V 1.5 (PO4) 3-x (P2O7) x / C) material.

[0006] The sodium source is one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium carbonate, sodium citrate, sodium sulfate, sodium dihydrogen phosphate, and sodium bicarbonate;

[0007] The manganese source is one or more of manganese nitrate, manganese acetate, manganese chloride, and manganese sulfate;

[0008] The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, vanadyl sulfate, and vanadium trioxide;

[0009] The complexing agent is one or more of citric acid, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid;

[0010] The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid, and sodium dihydrogen phosphate;

[0011] The pyrophosphate radical source is one or more of sodium pyrophosphate, ammonium pyrophosphate, pyrophosphoric acid, and nucleotide pyrophosphate;

[0012] The inert atmosphere is one or both of nitrogen and argon.

[0013] This invention involves reacting water-soluble substances such as sodium, manganese, vanadium, phosphorus, and pyrophosphate compounds with a complexing agent. Pyrophosphate partially replaces the phosphate anions in sodium vanadium manganese phosphate, resulting in a uniformly dispersed reaction mixture at the molecular level. The preparation process is simple and requires minimal time. After high-temperature calcination, the in-situ carbon coating enhances electronic conductivity and inhibits particle growth. The pyrophosphate replacement of the phosphate anions in sodium vanadium manganese phosphate stabilizes the crystal structure, reduces structural deformation during charging and discharging, and provides a larger channel for the rapid migration of sodium ions, thereby enhancing the doping of sodium vanadium manganese phosphate (Na). 3.5 Mn 0.5 V 1.5 (PO4)3 / C exhibits excellent high current performance and cycle stability. Attached Figure Description

[0014] Figure 1 This is Example 1 of the present invention for the preparation of Na. 3.7 Mn 0.5 V 1.5 (PO4) 2.8 (P2O7) 0.2 XRD pattern of / C composite material.

[0015] Figure 2 This is Example 2 of the present invention for the preparation of Na4Mn. 0.5 V 1.5 (PO4) 2.5 (P2O7) 0.5 XRD pattern of / C composite material.

[0016] Figure 3 This is Example 3 of the present invention for the preparation of Na. 4.3 Mn 0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 / C First charge / discharge curves at 2.5-4.3 V and 0.5C.

[0017] Figure 4 This is Example 3 of the present invention for the preparation of Na. 4.3 Mn 0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 Cyclic performance curves of / C at 2.5-4.3 V and 1C. Detailed Implementation

[0018] Example 1:

[0019] (1) Dissolve 0.5849 g ammonium metavanadate, 0.4085 g manganese acetate tetrahydrate, 1.0736 g ammonium dihydrogen phosphate, 0.7929 g sodium acetate, 1.6221 g sodium pyrophosphate and 2.1014 g citric acid in 30 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 -46 ℃ and dry for 72 hours.

[0020] (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 3 hours. Then, it was heated to 850 °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. 3.7 Mn 0.5 V 1.5 (PO4) 2.8 (P2O7) 0.2 / C composite material. Figure 1 for Na 3.7 Mn 0.5 V 1.5 (PO4) 2.8 (P2O7) 0.2 XRD pattern of / C composite material.

[0021] Na, the positive electrode material of sodium-ion batteries 3.7 Mn 0.5 V 1.5 (PO4) 2.8 (P2O7) 0.2 C, conductive agent Super P, and binder PVDF were ground thoroughly in an agate mortar at a mass ratio of 8:1:1 until uniformly mixed. The mixture was then transferred to a sample vial, and an appropriate amount of NMP solution was added to form an electrode slurry. After stirring evenly on a magnetic stirrer, the slurry was uniformly coated onto aluminum foil and dried in a 110 ℃ oven for 12 h. The dried electrode was then cut into 12 mm round electrodes using a slicer, rolled, and weighed. The resulting electrode was used as the positive electrode, with a sodium sheet as the negative electrode, a GF / D glass fiber membrane as the glass fiber, and 1 mol / L NaClO4 (DMC:EC:EMC=1:1:1, 2 wt% FEC) as the electrolyte. The cells were assembled into a CR2016 button cell in a glove box protected by high-purity argon (moisture and oxygen content both less than 0.1 ppm). After the cells were allowed to stand for 12 h, they were tested using a Newway testing system at 25 ℃ (voltage range 2.5~4.3V vs. NaClO4). + The Na prepared using the method of this invention was subjected to constant current charge-discharge testing.3.7 Mn 0.5 V 1.5 (PO4) 2.8 (P2O7) 0.2 The cathode material for the / C sodium-ion battery has a first-cycle discharge specific capacity of 108.5 mAh / g at 1C, and a discharge specific capacity of 96.9 mAh / g after 50 cycles, with a retention rate of 89.3%.

[0022] Example 2:

[0023] (1) Dissolve 0.5849 g ammonium metavanadate, 0.2817 g manganese sulfate pentahydrate, 0.9586 g ammonium dihydrogen phosphate, 0.5466 g sodium acetate, 0.7434 g sodium pyrophosphate and 1.6811 g citric acid in 50 ml deionized water and place it in a constant temperature water bath at 90 ℃. 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 -46 ℃ and dry it for 72 hours.

[0024] (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 Na4Mn. 0.5 V 1.5 (PO4) 2.5 (P2O7) 0.5 / C composite material. Figure 2 Na4Mn 0.5 V 1.5 (PO4) 2.5 (P2O7) 0.5 XRD pattern of / C composite material.

[0025] Na4Mn, the positive electrode material for sodium-ion batteries 0.5 V 1.5 (PO4) 2.5 (P2O7) 0.5C, conductive agent Super P, and binder PVDF were ground thoroughly in an agate mortar at a mass ratio of 8:1:1 until uniformly mixed. The mixture was then transferred to a sample vial, and an appropriate amount of NMP solution was added to form an electrode slurry. After stirring evenly on a magnetic stirrer, the slurry was uniformly coated onto aluminum foil and dried in a 110 ℃ oven for 12 h. The dried electrode was then cut into 12 mm round electrodes using a slicer, rolled, and weighed. The resulting electrode was used as the positive electrode, with a sodium sheet as the negative electrode, a GF / D glass fiber membrane as the glass fiber, and 1 mol / L NaClO4 (DMC:EC:EMC=1:1:1, 2 wt% FEC) as the electrolyte. The cells were assembled into a CR2016 button cell in a glove box protected by high-purity argon (moisture and oxygen content both less than 0.1 ppm). After the cells were allowed to stand for 12 h, they were tested using a Newway testing system at 25 ℃ (voltage range 2.5~4.3V vs. NaClO4). + The Na₄Mn₄ prepared by the method of this invention was subjected to constant current charge-discharge testing. 0.5 V 1.5 (PO4) 2.5 (P2O7) 0.5 The first charge-discharge curve at 0.5C and the first discharge specific capacity at 1C are 103.8 mAh / g. After 50 cycles, the discharge specific capacity is still as high as 99.6 mAh / g, with a capacity retention rate of 96.0%.

[0026] Example 3:

[0027] (1) Dissolve 0.5849 g ammonium metavanadate, 0.2817 g manganese sulfate pentahydrate, 1.0736 g ammonium dihydrogen phosphate, 1.6221 g sodium acetate, 0.2974 g sodium pyrophosphate and 2.1014 g citric acid in 40 ml deionized water, place in a constant temperature water bath at 75 ℃ 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 -46 ℃ and dry for 72 hours.

[0028] (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. 4.3 Mn 0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 / C composite material.

[0029] Na, the positive electrode material of sodium-ion batteries 4.3 Mn0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 C, conductive agent Super P, and binder PVDF were ground thoroughly in an agate mortar at a mass ratio of 8:1:1 until uniformly mixed. The mixture was then transferred to a sample vial, and an appropriate amount of NMP solution was added to form an electrode slurry. After stirring evenly on a magnetic stirrer, the slurry was uniformly coated onto aluminum foil and dried in a 110 ℃ oven for 12 h. The dried electrode was then cut into 12 mm round electrodes using a slicer, rolled, and weighed. The resulting electrode was used as the positive electrode, with a sodium sheet as the negative electrode, a GF / D glass fiber membrane as the glass fiber, and 1 mol / L NaClO4 (DMC:EC:EMC=1:1:1, 2 wt% FEC) as the electrolyte. The cells were assembled into a CR2016 button cell in a glove box protected by high-purity argon (moisture and oxygen content both less than 0.1 ppm). After the cells were allowed to stand for 12 h, they were tested using a Newway testing system at 25 ℃ (voltage range 2.5~4.3V vs. NaClO4). + Constant current charge-discharge test was performed on / Na). Figure 3 and Figure 4 Na 4.3 Mn 0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 The initial charge-discharge curves of / C at 2.5-4.3 V and 0.5C, and the cycle performance curves at 1C. Na prepared using the method of this invention. 4.3 Mn 0.5 V 1.5 (PO4) 2.2 (P2O7) 0.8 The discharge specific capacity of / C at 1C is 90.4 mAh / g in the first cycle, and the discharge specific capacity after 50 cycles is still as high as 86.7 mAh / g, with a capacity retention rate of 96.0%.

[0030] 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 carbon-coated pyrophosphate-doped sodium manganese phosphate cathode material, characterized in that... The molecular formula of the pyrophosphate-doped sodium vanadium manganese phosphate is Na. 3.5+x Mn 0.5 V 1.5 (PO4) 3-x (P2O7) x / C, where 0 <x≤0.1。 2. The sodium vanadium manganese phosphate (Na) doped with pyrophosphate according to claim 1 3.5 Mn 0.5 V 1.5 The method for preparing (PO4)3 / C cathode material is characterized by: The specific steps are as follows: (1) Weigh a sodium source compound, a manganese source compound, a vanadium source compound, a phosphorus source compound, and a pyrophosphate compound in a molar ratio of Na:Mn:V:PO4 3- :P2O7 4- =(3.5 + x):0.5:1.5:(3 - x):x (0 < x ≤ 0.1), and dissolve them in a certain amount of aqueous solution of a complexing agent (where the molar ratio of the complexing agent to vanadium is 1.0 - 2.5:1). Under the reduction of the complexing agent and the condition of heating the solution, 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 3-10 °C / min and calcine for 3-6 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. 3.5+x Mn 0.5 V 1.5 (PO4) 3-x (P2O7) x / C material; The sodium source is one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium carbonate, sodium citrate, sodium sulfate, sodium dihydrogen phosphate, and sodium bicarbonate. The manganese source is one or more of manganese nitrate, manganese acetate, manganese chloride, and manganese sulfate; The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, vanadium oxysulfate, and vanadium trioxide. The complexing agent is one or more of citric acid, tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid; 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; The pyrophosphate source is one or more of sodium pyrophosphate, ammonium pyrophosphate, pyrophosphate, and nucleotide pyrophosphate esters. The inert atmosphere is one or both of nitrogen and argon.

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