Preparation method and application of sodium ion battery positive electrode material with multi-site doped NASICON structure

Abstract

The invention provides a preparation method and application of a multi-site doped NASICON structure sodium ion battery positive electrode material. The preparation method comprises the following steps: by taking carboxylated carbon nanotubes, citric acid monohydrate, vanadium pentoxide, sodium dihydrogen phosphate, manganese acetate tetrahydrate, potassium carbonate, sodium silicate nonahydrate and sodium acetate trihydrate as raw materials, magnetically stirring the raw materials in an oil bath pan at 80 DEG C by using a sol-gel method to uniformly mix the components, and volatilizing water to obtain dry gel; and then putting the precursor into a vacuum drying oven, drying for 12 hours at 80 DEG C, fully drying, and finally carrying out heat treatment for 6 hours at 700 DEG C under the protection of argon inert atmosphere in a tubular furnace, so as to obtain the multi-site doped NASICON structure positive electrode material. The preparation method has the characteristics of simplicity in operation and high product purity, shows excellent sodium storage property when being used as a sodium-ion battery identification material, and can provide reference for development of sodium-ion battery positive electrode materials and design of high-energy-density commercial batteries when being used as a novel NASICON structure electrode material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrode materials and electrochemical energy storage devices, and particularly relates to a preparation method of a novel multi-site doped NASICON structure sodium ion battery positive electrode material and application thereof. The material is obtained by a sol-gel method to obtain a precursor, and a high-purity phase material is obtained through corresponding heat treatment. When applied to a sodium ion battery positive electrode material, the material exhibits superior electrochemical sodium storage properties. BACKGROUND

[0002] With the rapid progress of society and the progress of science and technology, the demand for secondary batteries is increasing, but the safety of lithium ion batteries still has certain challenges. Sodium ion batteries, which have a similar working principle to lithium ion batteries, have good safety, and their raw materials are easy to obtain and low in cost, so they have advantages. In the field of large-scale energy storage, such as grid energy storage, solar energy and wind energy, they have excellent application potential.

[0003] Sodium superionic conductor (NASICON) structure materials have a stable three-dimensional structural framework with large sodium ion transmission channels between the frameworks, and are considered to be an extremely attractive sodium ion battery positive electrode material. Na3V2(PO4)3 material has a typical NASICON structure, has a high ion conductivity, and due to the covalent nature of the phosphorus-oxygen bond (P-O), it has a strong induction effect, so that the Na3V2(PO4)3 positive electrode material has a discharge platform as high as 3.4 V. However, due to the limited number of sodium ion migrations, the theoretical specific capacity of the Na3V2(PO4)3 positive electrode material is only 118 mAh g -1 , which limits the wide application of Na3V2(PO4)3 positive electrode materials in large-scale energy storage fields. The present application aims at the shortcomings of Na3V2(PO4)3 positive electrode materials, and combines the compatibility of the NASICON structure to dope different elements at different sites in the Na3V2(PO4)3 material. The metal K element replaces the Na element, the Mn element replaces the V element, and the non-metal Si replaces the P element to obtain a new material Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3. Benefiting from the synergistic effect of multi-site doping and the formation of a three-dimensional conductive network by carbon nanotubes, the material as a sodium ion battery positive electrode material can provide an ultra-high initial discharge capacity of 144.8 mAh g −1 at a rate of 0.2 C in the voltage range of 1.5-4.2 V, which is higher than the theoretical specific capacity of Na3V2(PO4)3 (118 mAh g -1), the capacity retention rate is 81.3% after 500 cycles of fast charging and discharging (6 minutes) at 10 C high rate, and even under the working condition of 3-minute charging and discharging, the reversible capacity can reach 64.7 mAh g -1 . SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a new NASICON structure positive electrode material and application thereof. Based on the openness and compatibility of Na3V2(PO4)3 structure, the present application respectively dopes appropriate K + , Mn 3+ and Si 5+ ions at Na + , V 2+ and P 4+ sites, in order to maintain the electrical neutrality of the compound, therefore, the number of sodium ions needs to be increased, and finally the molecular formula of the material is Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3. After doping, the material still maintains the NASICON of the trigonal system and the space group R-3c. Since the effective ionic radius of K + ion (1.38 Å, coordination number 6), Mn 2+ ion (0.83 Å, coordination number 6), Si 4+ (0.26 Å, coordination number 4) is greater than the effective ionic radius of Na + ion (1.02 Å, coordination number 6), V 3+ ion (0.64 Å, coordination number 6) and P 5+ ion (0.17 Å, coordination number 4), the unit cell volume (1474.4 Å 3 ) of the material obtained after doping is greater than the unit cell volume (1474.4 Å 3 ) of the original Na3V2(PO4)3, and the larger structure framework will be beneficial to the transmission of sodium ions. At the same time, carboxylated carbon nanotubes are added to form a three-dimensional conductive network, which is beneficial to the transmission, thereby improving the energy storage properties of the material. The obtained electrode has a reversible specific capacity of up to 144.8 mAh g -1 when charged and discharged in the voltage range of 1.5-4.2 V. The corresponding energy density is 498 Wh / kg, and even under the condition of 6-minute fast charging and discharging, the reversible capacity after 500 cycles of charging and discharging can still reach 83.7 mAh g -1 .

[0005] Preparation of multi-site doped NASICON structure Na 3.5 K0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 positive electrode material is as follows:

[0006] (1) 0.15 g of carboxylated carbon nanotubes is ultrasonically dispersed in 30 mL of deionized water;

[0007] (2) Citric acid monohydrate and V2O5 are stirred and dissolved in a ball mill tank containing 50 mL of deionized water according to the stoichiometric ratio, and placed in an 80 ℃ oil bath and continuously stirred by magnetic force;

[0008] (3) After all the substances in step (2) are dissolved, NaH2PO4, Mn(Ac)2·4H2O, K2CO3, Na2SiO3·9H2O and NaAc·3H2O are sequentially added according to the stoichiometric ratio, and stirring is continued for 20 minutes, then the carbon nanotube suspension obtained in step (1) is slowly added, and after stirring to evaporate the water, a dry gel is obtained, which is then vacuum dried at 80 ℃ for 12 hours to obtain a dried gel;

[0009] (4) The dry gel obtained in step (3) is thoroughly ground into powder, and then an appropriate amount of powder is weighed and pressed into a tablet using a Ф10 mm mold;

[0010] (5) The tablet pressed in step (4) is placed in a tube furnace and heat treated at 700 ℃ for 6 hours under an argon atmosphere, to obtain a multi-site doped NASICON structure Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material.

[0011] The method of the present application uses a sol-gel process to prepare a precursor of the Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material. Compared with the traditional high-temperature solid-phase synthesis process, the sol-gel process can realize mixing of reactants at the molecular level, can make the components more uniform, the particle size of the obtained product is relatively small, effectively shortens the transmission distance of sodium ions and electrons, and at the same time embeds carbon nanotubes to form a three-dimensional conductive network to improve the electronic conductivity of the material, thereby improving the rate characteristics of the electrode. This method is simple and easy to operate, the phase purity of the synthesized material is high, and has a positive reference significance for the synthesis of other electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a multi-site doped NASICON structured Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 Rietveld refinement plot of XRD data of the (P

[0013] Figure 2 is a multi-site doped NASICON structured Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 Scanning electron micrograph of the (P

[0014] Figure 3 is a multi-site doped NASICON structured Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 Voltage-capacity plot of the first cycle of the (P

[0015] Figure 4 is a multi-site doped NASICON structured Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 Cycle-discharge specific capacity plot of the (P

[0016] Figure 5 is a multi-site doped NASICON structured Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 Cycle performance plot of the (P DETAILED DESCRIPTION

[0017] The following is described in detail in the form of specific examples, which are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples, and the specific steps are as follows:

[0018] (1) 0.15 g of carboxylated carbon nanotubes were ultrasonically dispersed in 30 mL of deionized water;

[0019] (2) Citric acid monohydrate and V2O5 are stirred and dissolved in a ball mill tank containing 50 mL of deionized water in a 80 ℃ oil bath with continuous magnetic stirring;

[0020] (3) After all the dissolution in step (2), NaH2PO4, Mn(Ac)2·4H2O, K2CO3, Na2SiO3·9H2O and NaAc·3H2O are sequentially added in stoichiometric ratio and stirred for 20 minutes, then the carbon nanotube suspension obtained in step (1) is slowly added, and the dry gel is obtained after continuous stirring and evaporation of water, and then vacuum drying at 80 ℃ for 12 hours to obtain a dry gel;

[0021] (4) The dry gel obtained in step (3) is thoroughly ground into powder, and then an appropriate amount of powder is weighed and pressed into a tablet with a Ф10 mm mold;

[0022] (5) The tablet pressed in step (4) is placed in a tube furnace and heat treated at 700 ℃ for 6 hours under an argon atmosphere, and a multi-site doped NASICON structure Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material is obtained.

[0023] The Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material obtained by the present application, when used as a positive electrode material of a sodium ion battery, is prepared into an electrode according to the mass ratio of active material: superconducting carbon black: PVDF (binder) is 7:2:1. First, PVDF is placed in a 5 mL glass beaker, and an appropriate amount of N-methyl pyrrolidone (NMP) is added, and the mixture is stirred with a magnetic stirrer until the PVDF is completely dissolved; at the same time, the active electrode material and superconducting carbon black are mixed and ground in a mortar for 60 minutes, then taken out and placed in a glass beaker, stirred for 6 hours, and finally uniformly coated on the current collector aluminum foil, and placed in a vacuum drying oven at 80 ℃ for 12 hours, then taken out and sliced, and the circular piece area is 1.13 cm 2 Then the electrode sheet is compacted at a pressure of 4 MPa, and the active material after tabletting is used as the working electrode, a sodium metal sheet is used as the reference electrode, a glass fiber membrane (Whatman) is used as the separator, and a sodium perchlorate solution is used as the electrolyte, and the concentration of NaClO4 is 1 mol L -1, the battery shell is CR2032. CR2032 half battery is assembled and sealed in an argon-filled glove box, and the oxygen content and water content in the glove box are less than 0.1 ppm, wherein the charge and discharge capacity is calculated based on the mass of the active material.

[0024] Figure 1 Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material of the present application wp converges to 2.15%, indicating that the structure model is reasonable, the refinement result is reliable, and the material has a typical NASICON structure and a space group of R-3c.

[0025] Figure 2 Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material

[0026] Figure 3 Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 electrode at 0.5 C rate. In the voltage platform of 1.5-1.8 V, it corresponds to the reversible oxidation and reduction of V 2+ / V 3+ , in the voltage range of 3-3.75 V, it corresponds to the oxidation and reduction of V 3+ / V 4+ and Mn 2+ / Mn 3+ , and the platform between 3.8-4.2 V corresponds to the oxidation and reduction of V 3+ / V 4+ and Mn 2+ / Mn 3+ .

[0027] Figure 4 Na 3.5 K 0.05 Mn0.5 V 1.5 (P 0.95 Si 0.05 O4)3 electrode at a voltage range of 1.5~4.2 V, the average discharge specific capacity from 0.2 C to 20 C is 137.3, 121.9, 106.8, 89.8, 80.6, 74.1, 69.2, 64.7 mAh g -1 . At high rate of 20 C, the capacity is still as high as 64.7 mAh g -1 .

[0028] Figure 5 is Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 electrode at a voltage range of 1.5~4.2 V, the average discharge specific capacity from 0.2 C to 20 C is 137.3, 121.9, 106.8, 89.8, 80.6, 74.1, 69.2, 64.7 mAh g -1 . At high rate of 20 C, the capacity is still as high as 64.7 mAh g -1 .

Claims

1. A method for preparing a multi-site doped NASICON structured sodium-ion battery cathode material with a chemical formula of Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3, characterized in that, The specific steps of the preparation method are: (1) ultrasonic dispersion of 0.15 g carboxylated carbon nanotubes in 30 mL deionized water; (2) stirring citric acid monohydrate and V2O5 in a ball mill tank containing 50 mL deionized water according to the stoichiometric ratio, and placing in an 80 ℃ oil bath and continuously stirring with a magnetic stirrer; (3) after all the solubles in step (2) are dissolved, adding NaH2PO4, Mn(Ac)2·4H2O, K2CO3, Na2SiO3·9H2O and NaAc·3H2O according to the stoichiometric ratio in sequence and continuously stirring for 20 minutes, then slowly adding the carbon nanotube suspension obtained in step (1), continuously stirring to evaporate the water, obtaining a dry gel, and then vacuum drying at 80 ℃ for 12 hours to obtain a dried gel; (4) grinding the dry gel obtained in step (3) into powder, and then weighing an appropriate amount of powder and tabletting into a Ф10 mm mold; (5) The sheet pressed in step (4) is placed in a tube furnace and heat treated at 700 ℃ for 6 hours under an argon atmosphere to obtain a multi-site doped NASICON structure Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 material.

2. The material obtained by the method according to claim 1, characterized by: The multi-site doped NASICON structure Na 3.5 K 0.05 Mn 0.5 V 1.5 (P 0.95 Si 0.05 O4)3 cathode material is applied to a sodium ion battery cathode material.

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