CN113062013B

CN113062013B - Lithium vanadate with indium-cerium or indium-doped nanofiber structure and preparation method and application thereof

Info

Publication number: CN113062013B
Application number: CN202110280606.5A
Authority: CN
Inventors: 潘安强; 万远浪; 谢雪芳
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-03-16
Filing date: 2021-03-16
Publication date: 2022-04-12
Anticipated expiration: 2041-03-16
Also published as: CN113062013A

Abstract

The invention discloses lithium vanadate with an indium-cerium or indium-doped nanofiber structure, and a preparation method and application thereof₃VO₄Calcining the precursor in inert gas to obtain the indium cerium or indium doped Li with fiber structure₃VO₄A material. The unique fiber network conductive structure is beneficial to effective infiltration of electrolyte, and can ensure that the electrolyte is fully contacted with active substances, thereby improving the electrochemical performance of the material. The fiber network indium cerium or indium doped Li prepared by the invention₃VO₄The lithium ion electrode material has good electrochemical performance, simple process and mild conditions.

Description

Lithium vanadate with indium-cerium or indium-doped nanofiber structure and preparation method and application thereof

Technical Field

The invention belongs to the technical field of preparation of lithium battery electrodes, and particularly relates to lithium vanadate with an indium-cerium or indium-doped nanofiber structure, and a preparation method and application thereof.

Background

Li₃VO₄Because of its high energy density, low redox potential (0.5-1V vs. Li)⁺and/Li), has small strain during charge and discharge and is easy to synthesize, and has been widely studied as a negative electrode material of a lithium ion battery. When 3 lithium ions are inserted, the theoretical capacity can reach 540mAh g^-1. However, the electron conductivity of the material is poor, Li⁺The diffusion coefficient of the ions is low, the rate capability is poor when the ions are used as the lithium ion battery electrode, and the morphology is difficult to regulate and control. Therefore, researchers have focused on Li with different morphologies, micro-nano structures, high capacity and high rate performance₃VO₄And (5) developing materials.

Nano-fiberThe structure has a large specific surface area, can be fully contacted with electrolyte, provides more reaction sites, and further obtains higher electrochemical specific capacity. Liang et al (Advanced Energy Materials 10.20 (2020)) synthesizes Cr and Si co-doped Li by electrostatic spinning with lithium acetate and ammonium metavanadate as lithium source and vanadium source respectively₃VO₄The material shows excellent electrochemical performance when used as a lithium ion battery cathode, and is similar to LiFePO₄The specific energy density of the matched and assembled full battery is LiFePO₄/Li₄Ti₅O₁₂2.3 times of the total weight of the powder. But the preparation process is complex, the energy consumption is large, and the time consumption is long. The invention provides a synthetic nanofiber structure doped Li₃VO₄And the synthesis of doped Li in this document₃VO₄Compared with the method, the preparation period is obviously shortened, the energy consumption is obviously reduced, the process is easier to realize and control, the synthesized product has uniform particle size and good dispersibility, the rate capability and the capacity of the product are obviously improved, and the voltage range of 0.01-3V is 100mA g^-1The discharge capacity reaches 569mAh g under the current density^-1After 100 cycles, the capacity retention rate is close to 100%. Even if the current density is increased to 5000mA g in the test voltage range of 0.2-3V^-1The capacity of the material can still reach 335.2mAh g^-1. Undoped pure phase Li reported in Yang et al (ChemElectrochem 6.15(2019))₃VO₄In the test voltage range of 0.2-3V, 200mA g^-1At current density of (3), pure phase Li₃VO₄Has a capacity of only 94.1mAh g^-1. While the doped Li in the invention₃VO₄The electrochemical performance of the material is also obviously superior to that reported in other documents of the same type, and the material has good application prospect.

Disclosure of Invention

The invention provides indium-cerium or indium-doped Li with a nanofiber structure₃VO₄Lithium ion electrode material and preparation and application thereof. Synthetic fibrous doped Li₃VO₄The material has uniform size, large specific surface area and good electrochemical performance.

The object of the invention is thus achieved.

Li with indium-cerium or indium-doped nanofiber structure₃VO₄The preparation method comprises the following steps:

(1) dissolving lithium salt in an organic solvent to form a transparent solution;

(2) dissolving citric acid, ascorbic acid and vanadium salt in the lithium salt transparent solution obtained in the step (1), and heating and stirring to form a dark brown solution;

(3) adding soluble indium salt or a mixture of the soluble indium salt and the soluble cerium salt and organic matters into the mixed solution obtained in the step (2), and continuously heating and stirring to obtain an electrostatic spinning precursor solution;

(4) spinning the electrostatic spinning precursor solution obtained in the step (3);

(5) further calcining the product obtained in the step (4) in nitrogen or inert gas to obtain Li with an indium-cerium or indium-doped nanofiber structure₃VO₄。

The preparation method is characterized in that the raw materials are mixed,

the lithium salt in the step (1) comprises: at least one of lithium acetate, lithium hydroxide, lithium carbonate and lithium oxalate.

The organic solvent in the step (1) comprises: at least one of ethanol, glacial acetic acid, N-dimethylformamide and deionized water.

The vanadium salt in the step (2) comprises: at least one of ammonium metavanadate and vanadyl acetylacetonate.

And (3) the organic matter is a high molecular organic matter with a thickening effect. Preferably: at least one of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol and polymethyl methacrylate.

The preparation method is characterized in that the raw materials are mixed,

the addition amount of the lithium salt in the step (1) is 0.15-0.7 g.

Adding the organic solvent into the mixture in the step (1) with the volume not exceeding 14mL, preferably 12mL, heating and stirring the mixture at the temperature: 45-55 ℃.

The preparation method is characterized in that the raw materials are mixed,

the addition amount of the vanadium salt in the step (2) is 0.1-0.8 g, the addition amount of citric acid is not more than 0.5g, preferably 0.3278g, the addition amount of ascorbic acid is not more than 0.5g, preferably 0.5g, the heating and stirring temperature is as follows: 45-55 ℃ for at least 1 h.

The preparation method is characterized in that the raw materials are mixed,

the mol weight of the added soluble indium salt In the step (3) is calculated according to the mol weight of the indium element and the lithium element In the lithium salt In the step (1), and the In is not more than 5 percent of the mol weight of the Li, preferably 3 to 4 percent, and more preferably 3.4 percent; the soluble cerium salt is added in a molar amount of 0 to 0.8%, preferably 0.6 to 0.7%, and more preferably 0.64% of the molar amount of the Li, calculated as the molar amount of the cerium element and the lithium element in the lithium salt in the step (1).

The soluble indium salt is preferably indium sulfate, indium nitrate and indium acetate, and is further preferably indium sulfate; the soluble cerium salt is preferably ceric sulfate Ce (SO)₄)₂Or cerous sulfate with crystal water, cerous nitrate, and cerous acetate, and more preferably cerous sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O)。

The ratio of the organic matter to the total added mass of the soluble indium salt in the step (3) is not more than 13: 1, preferably 10 to 11: 1, more preferably 10: 1; heating and stirring temperature: the temperature is 45-55 ℃, and the time is at least 2h, preferably 2-4 h, and further preferably 3 h.

The preparation method is characterized in that the raw materials are mixed,

the electrostatic spinning high voltage in the step (4) is positive voltage of 5-15 kV, preferably 13-15 kV, further preferably 15kV, and the negative voltage is 0-2 kV, preferably-1-1.5 kV, further preferably-1 kV, and the forward speed of the needle tube is 0.05-0.15 mm/min, preferably 0.060-0.065 mm/min, further preferably 0.065 mm/min; the distance between the needle head and the roller is 12-20 cm, preferably 15-17 cm, and further preferably 15 cm.

The preparation method is characterized in that the raw materials are mixed,

in the step (5), the calcining atmosphere is Ar and N₂、H₂+ Ar, the calcination temperature is 500-800 ℃, preferably 600-700 ℃, and further preferably 700 ℃; the heat preservation time is 3-12 h, preferably 3-10 h, and further preferably 3 h; the heating rate is 1-5 ℃/min, preferably 2-3 ℃/min.

The preparation method preferably comprises the following steps: dissolving lithium acetate in alcohol, glacial acetic acid,Stirring the solution composed of deionized water at 45-55 ℃ to form a transparent solution; adding citric acid, ascorbic acid and ammonium metavanadate into the transparent solution, and continuously stirring for at least 6 hours to form a dark brown solution; finally, respectively adding soluble cerium salt and soluble indium salt, or single soluble indium salt and polyvinylpyrrolidone into the dark brown solution, and stirring for at least 2h to obtain an electrostatic spinning precursor solution; further calcining in nitrogen or inert gas after electrostatic spinning to obtain Li with indium-cerium or indium-doped nanofiber structure₃VO₄。

It is further preferred that 0.5733g of lithium acetate is first dissolved in a solution consisting of 8.875mL of ethanol, 0.955mL of glacial acetic acid, and 4mL of deionized water, and stirred at 50 ℃ and 600r/min for 10min to form a clear solution. 0.3278g of citric acid monohydrate, 0.5g of ascorbic acid and 0.2925g of ammonium metavanadate were then added to the clear solution and stirring was continued for 6h to give a dark brown solution. Finally 0.02273g ceric sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O), 0.07767g of indium sulfate, or 0.07767g of indium sulfate alone and 0.8g of polyvinylpyrrolidone (PVP) were added to the dark brown solution, respectively, and stirred for 3 hours to obtain an electrospinning precursor solution. The positive pressure of the electrostatic spinning is 15kV, the negative pressure is-1 kV, the distance between the needle head of the injector and the aluminum foil is 15cm, and the advancing speed of the needle tube is 0.065 mm/min. The obtained spinning product is put in a tube furnace in Ar atmosphere and is kept at 650 ℃ for 10h to obtain the required indium cerium or indium doped Li₃VO₄Material (LICPO), heating rate 2 deg.C/min.

The invention surprisingly finds that the system of lithium hydroxide, vanadyl acetylacetonate and N, N-dimethylformamide is adopted, so that all raw materials can be put together for rapid dissolution without step-by-step dissolution, and citric acid and ascorbic acid are not added, thereby greatly saving reaction raw materials and operation steps. Thus, a second Li of indium cerium or indium doped nanofiber structure is provided₃VO₄The preparation method comprises the following steps:

adding soluble indium salt or mixture of soluble indium salt and soluble cerium salt, lithium hydroxide and vanadyl acetylacetonate into N, N-dimethylformamide at 45-55 deg.CStirring for at least 3h to form a dark brown solution; finally, adding polyvinylpyrrolidone and polyacrylonitrile, and continuously stirring for at least 2 hours to obtain an electrostatic spinning precursor solution; further calcining in nitrogen or inert gas after electrostatic spinning to obtain Li with indium-cerium or indium-doped nanofiber structure₃VO₄。

The adding amount of the lithium hydroxide is 0.15-0.7 g.

The volume of the N, N-dimethylformamide is not more than 14mL, preferably 12 mL;

the addition amount of the vanadyl acetylacetonate is 0.1-0.8 g.

The mol weight of the soluble indium salt is calculated according to the mol weight of the indium element and the lithium element In the lithium salt In the step (1), and the In is not more than 5 percent of the mol weight of the Li, preferably 3 to 4 percent, and more preferably 3.4 percent; the soluble cerium salt is added in a molar amount of 0 to 0.8%, preferably 0.6 to 0.7%, and more preferably 0.64% of the molar amount of the Li, calculated as the molar amount of the cerium element and the lithium element in the lithium salt in the step (1).

The ratio of the polyvinylpyrrolidone to the polyacrylonitrile to the total mass of the soluble indium salt is not more than 13: 1, preferably 10 to 11: 1, more preferably 10: 1;

the electrostatic spinning high voltage is positive voltage of 5-15 kV, preferably 13-15 kV, further preferably 15kV, the negative voltage is 0-2 kV, preferably-1-1.5 kV, further preferably-1 kV, the forward pushing speed of the needle tube is 0.05-0.15 mm/min, preferably 0.060-0.065 mm/min, further preferably 0.065 mm/min; the distance between the needle head and the roller is 12-20 cm, preferably 15-17 cm, and further preferably 15 cm.

The calcining atmosphere is Ar and N₂、H₂+ Ar, the calcination temperature is 500-800 ℃, preferably 600-700 ℃, and further preferably 700 ℃; the heat preservation time is 3-12 h, preferably 3-10 h, and further preferably 3 h; the heating rate is 1-5 ℃/min, preferably 2-3 ℃/min.

Further preferably: 0.02273g ceric sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O) and 0.07767g of indium sulfate, or 0.07767g of indium sulfate alone, with 0.3672g of lithium hydroxide, 0.6629g of vanadyl acetylacetonate, were added to 12mL of N, N-dimethylformamide(DMF). Stirring at 50 deg.C and 600r/min for 3h to form a dark brown solution. And finally, adding 0.5g of polyvinylpyrrolidone (PVP) and 0.5g of Polyacrylonitrile (PAN), and continuously stirring for 3 hours to obtain the electrostatic spinning precursor solution. The positive pressure of electrostatic spinning is about 13kV, the negative pressure is-1 kV, the distance between a syringe needle and an aluminum foil is 15cm, and the advancing speed of a needle tube is 0.060 mm/min. The obtained spinning product is put in a tube furnace in Ar atmosphere and is kept at 700 ℃ for 3h to obtain the required indium cerium or indium doped Li₃VO₄The material temperature rise rate is 3 ℃/min.

The invention also provides the Li with the indium-cerium or indium-doped nanofiber structure prepared by the method₃VO₄。

The invention also provides Li with the indium-cerium or indium-doped nanofiber structure₃VO₄The application in the preparation of lithium ion battery electrodes.

The invention provides indium cerium or indium doped Li with synthetic fiber network structure₃VO₄The method has the following advantages:

1. the synthetic process can be realized in one step, and the synthetic product has controllable appearance, simple process and short time.

2. The synthesized product has special shape and is Li with a fiber network structure₃VO₄Realize Li₃VO₄And (5) regulating and controlling the appearance.

3. The synthesized product has uniform particle size distribution and large specific surface area, and has high specific capacity and excellent rate performance when being applied to a lithium ion battery.

Drawings

FIG. 1 shows doping of the nanofiber-like structure with Li in example 1₃VO₄XRD pattern of (a);

FIG. 2 shows doping of the nanofiber-like structure with Li in example 1₃VO₄In the voltage range of 0.01-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 3 shows doping of the nanofiber-like structure with Li in example 1₃VO₄In the voltage range of 0.2-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 4 shows doping of the nanofiber-like structure with Li in example 2₃VO₄In the voltage range of 0.01-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 5 shows doping of the nanofiber-like structure with Li in example 3₃VO₄Scanning electron microscope pictures and element distribution; wherein A, B, C and D respectively represent vanadium, oxygen, indium and cerium;

FIG. 6 shows doping of the nanofiber-like structure with Li in example 3₃VO₄In the voltage range of 0.2-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 7 shows doping of the nanofiber-like structure with Li in example 4₃VO₄Scanning electron microscope pictures;

FIG. 8 shows doping of the nanofiber-like structure with Li in example 4₃VO₄In the voltage range of 0.2-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 9 shows doped Li of comparative example 1₃VO₄Scanning electron microscope pictures;

FIG. 10 shows Li doping of comparative example 1₃VO₄In the voltage range of 0.01-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 11 is a Li-doped comparative example 2₃VO₄Scanning electron microscope pictures;

FIG. 12 is a Li-doped comparative example 2₃VO₄In the voltage range of 0.2-3V and 50-5000 mAg^-1Rate capability under conditions;

FIG. 13 is a Li-doped comparative example 3₃VO₄Scanning electron microscope pictures;

FIG. 14 is a Li-doped comparative example 3₃VO₄In the voltage range of 0.2-3V, 1000mAg^-1Cycling performance under conditions;

FIG. 15 is Li doping of comparative example 4₃VO₄Scanning electron microscope pictures;

FIG. 16 is a Li-doped comparative example 5₃VO₄Scanning electron microscope pictures.

Detailed Description

The following examples are intended to further illustrate the invention without limiting it.

Example 1

0.5733g of lithium acetate were first dissolved in a solution of 8.875mL of ethanol, 0.955mL of glacial acetic acid, and 4mL of deionized water, and stirred at 50 ℃ and 600r/min for 10min to form a clear solution. 0.3278g of citric acid monohydrate, 0.5g of ascorbic acid and 0.2925g of ammonium metavanadate were then added to the clear solution and stirring was continued for 6h (it was found that for the reaction system of this example, at least 6h of stirring time was required, otherwise the desired morphology could not be obtained, comparative examples with insufficient stirring time are given later), resulting in a dark brown solution. Finally 0.02273g ceric sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O), 0.07767g of indium sulfate and 0.8g of polyvinylpyrrolidone (PVP) are respectively added into the dark brown solution, and stirred for 3h to obtain an electrostatic spinning precursor solution.

The positive pressure of the electrostatic spinning is 15kV, the negative pressure is-1 kV, the distance between the needle head of the injector and the aluminum foil is 15cm, and the advancing speed of the needle tube is 0.065 mm/min. The obtained spinning product is put in a tube furnace in Ar atmosphere and is kept at 650 ℃ for 10h to obtain the required doped Li₃VO₄Material (LICPO), heating rate 2 deg.C/min.

The obtained sample was analyzed by an X-ray diffraction analyzer of Japan science D/max-2500 type, and the obtained results are shown in FIG. 1. Doping the obtained Li₃VO₄The material is prepared by uniformly mixing 70 wt.% of preparation material, 20 wt.% of conductive carbon black (Super P) and 10 wt.% of polyvinylidene fluoride (PVDF), preparing slurry, uniformly coating the slurry on copper foil, vacuum drying, and assembling a button cell by using a lithium sheet as a counter electrode to perform rate performance test. The voltage ranges of the multiplying power performance test are 0.01-3V and 0.2-3V respectively, and the current density is 50-5000 mA g^-1. The results of the rate capability test are shown in fig. 2 and 3, and it can be seen that the prepared doped Li is prepared under the conditions of deep discharge or shallow discharge₃VO₄The materials all show significant rate advantages. Even if the current density is increased to 5000mA g in the test voltage range of 0.2-3V^-1The capacity of the material can still reach 335.2mAh g^-1。

Example 2

The procedure of this example is exactly the same as example 1, with only the doping salt selection being different. The doping salt is only selected to be doped with indium sulfate with the same dosage as that of the embodiment 1, and the required doped Li is obtained after calcination₃VO₄Material (LIVO).

The obtained materials were assembled into button cells according to the method of example 1 for rate performance testing. The voltage range of the multiplying power performance test is 0.01-3V, and the current density is 50-5000 mA g^-1. The rate capability test result is shown in FIG. 4, and it can be seen that only indium is selected to dope Li₃VO₄By electrospinning and subsequent calcination steps, doped Li with excellent rate properties can be obtained as such₃VO₄A material.

Example 3

0.3672g of lithium hydroxide, 0.6629g of vanadyl acetylacetonate, 0.02273g of ceric sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O), 0.07767g of indium sulfate were added to 12mL of N, N-Dimethylformamide (DMF). Stirring at 50 deg.C and 600r/min for 3h to form a dark brown solution. And finally, adding 0.5g of polyvinylpyrrolidone (PVP) and 0.5g of Polyacrylonitrile (PAN), and continuously stirring for 3 hours to obtain the electrostatic spinning precursor solution.

The positive pressure of electrostatic spinning is about 13kV, the negative pressure is-1 kV, the distance between a syringe needle and an aluminum foil is 15cm, and the advancing speed of a needle tube is 0.060 mm/min. The obtained spinning product is put in a tube furnace in Ar atmosphere and is kept at 700 ℃ for 3h to obtain the required doped Li₃VO₄The temperature rise rate of the material (LICPO-1) is 3 ℃/min.

The morphology and the particle size of the sample are observed by using a Nova NanoSEM 230 scanning electron microscope of FEI company in America, and the element distribution of the selected area of the sample is observed by using EDS. The sample morphology was found to be a fibrous network-like structure with a uniform size distribution (fig. 5). The obtained materials were assembled into button cells according to the method of example 1 for rate performance testing. The voltage range of the multiplying power performance test is 0.2-3V, and the current density is 50-5000 mA g^-1. The results of the rate capability test are shown in FIG. 6, which shows that after the reaction system is changed, the reaction steps and time are greatly simplified and shortened, and the material consumption is reducedUnder the premise of electrostatic spinning and subsequent calcining steps, doped Li with excellent rate capability can be obtained₃VO₄A material.

Example 4

This example is exactly the same as example 3, only the doping salt is selected differently, and only the same amount of indium sulfate as example 3 is selected for doping.

The morphology and particle size of the samples were observed using a Nova NanoSEM 230 scanning electron microscope, FEI, usa. It can be found that the sample morphology is a fiber network structure, the product particles are uniformly attached to the fiber surface, and the size distribution of the product particles is uniform (fig. 7), and the uniformly distributed particles provide more electrochemical reaction sites, which is very helpful for improving the electrochemical performance of the material. The obtained material (LIVO-1) was assembled into a button cell according to the method of example 1 for rate performance test. The voltage range of the multiplying power performance test is 0.2-3V, and the current density is 50-5000 mA g^-1. The results of the rate capability test are shown in fig. 8. The test data in connection with example 3 can further confirm that the doped Li with excellent rate capability can be obtained by electrostatic spinning and subsequent calcining steps on the premise of greatly simplifying and shortening reaction steps and time and reducing material consumption after the reaction system is changed₃VO₄A material. Meanwhile, the test data of the comparative example 3 and the comparative example 4 show that in the reaction system, the indium is singly doped and the Li co-doped with the indium and the cerium is adopted₃VO₄Compared with the material, the former has more excellent electrochemical performance. Such results indicate that Li doping can be carried out in such a reaction system to obtain excellent rate capability₃VO₄When the material is prepared, ceric sulfate (Ce (SO) can be avoided₄)₂·4H₂O), only indium sulfate is selected for doping, which is certainly very advantageous for further reducing the consumption of raw materials and manufacturing cost.

Comparative example 1

This comparative example is exactly the same as example 1, only doped with salts, and only ceric sulfate tetrahydrate (Ce (SO) was chosen in the same amount as example 1₄)₂·4H₂O) single doping of cerium。

The morphology and particle size of the samples were observed using a Nova NanoSEM 230 scanning electron microscope, FEI, usa. It was found that the morphology of the sample exhibited significant melt crosslinking of the fibers and the fiber structure was completely destroyed (fig. 9). Doping the obtained Li₃VO₄Materials (LCVO) button cells were assembled for rate capability testing according to the method of example 1. The test voltage range is 0.01-3V, and the current density is 50-5000 mA g^-1. The results of the rate capability test are shown in fig. 10, and it can be found that the rate capability is significantly reduced and the capacity fading is fast compared with example 1. Therefore, the exploration of the invention can find that the Li which is singly doped with indium and is codoped with indium and cerium₃VO₄Compared with the material, the cerium is singly doped with Li₃VO₄The electrochemical performance of the material is far inferior to that of the former two doping materials.

Comparative example 2

This comparative example is exactly the same as the procedure of example 1, with only the vanadium salt being different, the vanadium salt being vanadyl acetylacetonate.

The morphology and particle size of the samples were observed using a Nova NanoSEM 230 scanning electron microscope, FEI, usa. The sample morphology was found to fail to exhibit a fibrous structure (fig. 11), indicating that the vanadium salt selection has a significant impact on the formation of the sample fibrous structure. Doping the obtained Li₃VO₄The material (LICCO-2) was assembled into button cells for rate capability testing according to the method of example 1. The test voltage range is 0.2-3V, and the current density is 50-5000 mAg^-1. The results of the rate capability test are shown in fig. 12, and it can be found that the rate capability is significantly reduced and the capacity fading is rapid compared to example 1. This indicates that vanadyl acetylacetonate, a source of vanadium, is not suitable for the reaction system of example 1.

Comparative example 3

0.5733g of lithium acetate were first dissolved in a solution of 0.955mL glacial acetic acid and 12mL of N-Dimethylformamide (DMF) and stirred at 50 ℃ and 600r/min for 10min to form a clear solution. 0.2925g of ammonium metavanadate, 0.05g of multi-wall carbon nano-tube and 0.02273g of ceric sulfate tetrahydrate (Ce (SO)₄)₂·4H₂O), 0.07767g of indium sulfate were added to the clear solution. In thatStirring at 50 deg.C and 600r/min for 3h to obtain black solution. And finally, adding 0.4g of polyvinylpyrrolidone (PVP) and 0.3g of Polyacrylonitrile (PAN), and continuously stirring for 3 hours to obtain the electrostatic spinning precursor solution.

The positive pressure of electrostatic spinning is about 13kV, the negative pressure is-1 kV, the distance between a syringe needle and an aluminum foil is 15cm, and the advancing speed of a needle tube is 0.060 mm/min. Presintering the obtained spinning product in a muffle furnace in air atmosphere at 200 ℃ for 60 min. Then keeping the temperature for 3 hours at 700 ℃ in Ar atmosphere in a tube furnace to obtain the required doped Li₃VO₄Material (LICGO-3), heating rate 3 deg.C/min.

When the morphology and the particle size of a sample are observed by using a Nova NanoSEM 230 scanning electron microscope of FEI company in America, the morphology of the sample can be found to be in a structure that fibers are crosslinked with irregular spherical particles (figure 13), and the occurrence of the irregular spherical particles can cause the structure part of a fiber conductive network to be damaged, block an electron transmission channel and cause the electrochemical performance of the material to be reduced. Doping the obtained Li₃VO₄The materials were assembled into button cells according to the method of example 1 for battery cycling performance testing. The test voltage range is 0.2-3V, and the current density is 1000mAg^-1. The results of the performance test are shown in FIG. 14, and it can be found that the material is 1000mA g^-1The capacity of the battery is obviously reduced compared with that of the battery in the embodiment 1, and the specific discharge capacity is only kept at 209.5mAh g after 500 cycles^-1Left and right.

The carbon nano tube belongs to a dopant for enhancing the performance of the conventional electrode material, but the performance of the product is influenced by adding the carbon nano tube into the reaction system of the invention.

Comparative example 4

This comparative example is exactly the same as example 1 procedure except that the stirring time before the salt and organic addition was varied. After stirring for 2h, ceric sulfate tetrahydrate (Ce (SO) was added in the same amount as in example 1₄)₂·4H₂And O), adding indium sulfate and polyvinylpyrrolidone (PVP) into the dark brown solution, and continuously stirring for 3 hours to obtain the electrostatic spinning precursor solution. The spinning conditions and calcination conditions were the same as in example 1.

The morphology and particle size of the samples were observed using a Nova NanoSEM 230 scanning electron microscope, FEI, usa. The sample morphology was found to fail to exhibit the expected fiber structure (fig. 15), and the results in the comparative examples illustrate that the mixing time has a significant impact on the formation of the sample fiber structure, i.e., insufficient mixing time would prevent the material from producing the desired fiber morphology.

Comparative example 5

This comparative example is identical to the procedure of example 1, with a different stirring time before the addition of the doping salts and organic substances. And only adding indium sulfate and polyvinylpyrrolidone (PVP) with the same dosage as in example 1 into the dark brown solution after stirring for 2h, and continuously stirring for 3h to obtain an electrostatic spinning precursor solution. The spinning conditions and calcination conditions were the same as in example 1.

The morphology and particle size of the samples were observed using a Nova NanoSEM 230 scanning electron microscope, FEI, usa. The sample morphology can be found to exhibit a fibrous structure as a whole (fig. 16), but the size distribution is not uniform, and part of the sample cannot form the expected fibrous structure, and it can be seen that more particles with different sizes and irregular shapes are distributed in the sample morphology, and the irregular structure of the part reduces the electrochemical performance of the material to a certain extent. The results in the comparative examples further illustrate that the stirring time has a significant effect on the formation of the fibrous structure of the sample.

There are many other embodiments of the invention and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention, which should be construed as being limited only by the claims.

Claims

1. A preparation method of lithium vanadate with an indium-cerium or indium-doped nanofiber structure is characterized by comprising the following steps:

(1) dissolving lithium salt in an organic solvent or deionized water to form a transparent solution;

(2) dissolving citric acid, ascorbic acid and vanadium salt in the lithium salt transparent solution obtained in the step (1), and heating and stirring for at least 6 hours to form a dark brown solution; the vanadium salt in the step (2) is ammonium metavanadate;

(3) adding soluble indium salt or a mixture of the soluble indium salt and the soluble cerium salt and organic matters into the mixed solution obtained in the step (2), and continuously heating and stirring for at least 2 hours to obtain an electrostatic spinning precursor solution;

(5) the product obtained in the step (4) is added in Ar and N₂Or H₂And+ Ar, further calcining to obtain Li with indium-cerium or indium-doped nanofiber structure₃VO₄。

2. The method of claim 1, wherein In the soluble indium salt In step (3) is added In a molar amount of not more than 5% of the molar amount of Li In terms of the molar amount of indium and lithium In the lithium salt In step (1), and Ce occupies 0 to 0.8% of the molar amount of Li In terms of the molar amount of cerium and lithium In the lithium salt In step (1).

3. The method of claim 2 wherein the soluble indium salt of step (3) is added In a molar amount of from 3% to 4% of the molar amount of Li, calculated as the molar amount of indium element relative to the molar amount of lithium element In the lithium salt of step (1); the mol weight of the soluble cerium salt is calculated according to the mol weight of cerium element and lithium element in the lithium salt in the step (1), and Ce occupies 0.6-0.7% of the mol weight of Li.

4. The method of claim 3 wherein the soluble indium salt of step (3) is added In a molar amount, calculated as the molar amount of indium element relative to the molar amount of lithium element In the lithium salt of step (1), In being 3.4% of the molar amount of Li; the soluble cerium salt is added in a molar amount, calculated by the molar amount of the cerium element and the lithium element in the lithium salt in the step (1), wherein Ce accounts for 0.64 percent of the molar amount of Li.

5. The production method according to claim 1,

adding the organic matter and the soluble indium salt in the step (3) by mass ratio of not more than 13: 1; heating and stirring temperature: 45-55 ℃.

6. The production method according to claim 5,

adding the organic matter and the soluble indium salt in a mass ratio of 10-11: 1; the heating and stirring time is 2-4 h.

7. The production method according to claim 6,

adding the organic matter and the soluble indium salt in the step (3) by the mass ratio of 10: 1; the mixture is heated and stirred for 3 hours.

8. The preparation method according to claim 1, wherein the high voltage of the electrostatic spinning in the step (4) is 5-15 kV positive voltage, 0-2 kV negative voltage, and the forward speed of the needle tube is 0.05-0.15 mm/min; the distance between the needle head and the roller is 12-20 cm.

9. The preparation method according to claim 8, wherein the electrospinning high voltage in the step (4) is positive voltage of 13-15 kV, the negative voltage is-1-1.5 kV, and the forward speed of the needle tube is 0.060-0.065 mm/min; the distance between the needle head and the roller is 15-17 cm.

10. The preparation method according to claim 9, wherein the electrospinning high voltage in the step (4) is positive voltage of 15kV, negative voltage of-1 kV, and the forward pushing speed of the needle tube is 0.065 mm/min; the distance from the needle to the roller was 15 cm.

11. The preparation method according to claim 1, wherein the calcination temperature in the step (5) is 500 to 800 ℃; the heat preservation time is 3-12 h; the heating rate is 1-5 ℃/min.

12. The preparation method according to claim 11, wherein the calcination temperature in the step (5) is 600-700 ℃; the heat preservation time is 3-10 h; the heating rate is 2-3 ℃/min.

13. The method according to claim 12, wherein the calcination temperature in the step (5) is 700 ℃; the heat preservation time is 3 h.

14. The production method according to claim 1,

the lithium salt in the step (1) comprises: at least one of lithium acetate, lithium hydroxide, lithium carbonate and lithium oxalate, wherein the organic solvent comprises: at least one of ethanol, glacial acetic acid and N, N-dimethylformamide;

and (3) the organic matter is a high molecular organic matter with a thickening effect.

15. The method of claim 14,

the macromolecular organic matter with thickening effect comprises at least one of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol and polymethyl methacrylate.

16. The method of claim 14, comprising the steps of:

dissolving lithium acetate in a solution composed of ethanol, glacial acetic acid and deionized water, and stirring at 45-55 deg.C to form a transparent solution; adding citric acid, ascorbic acid and ammonium metavanadate into the transparent solution, and continuously stirring for at least 6 hours to form a dark brown solution; finally, respectively adding soluble cerium salt and soluble indium salt, or single soluble indium salt and polyvinylpyrrolidone into the dark brown solution, and stirring for at least 2h to obtain an electrostatic spinning precursor solution; further calcining in nitrogen or inert gas after electrostatic spinning to obtain Li with indium-cerium or indium-doped nanofiber structure₃VO₄。

17. A preparation method of lithium vanadate with an indium-cerium or indium-doped nanofiber structure is characterized by comprising the following steps:

adding soluble indium salt or a mixture of the soluble indium salt and the soluble cerium salt, lithium hydroxide and vanadyl acetylacetonate into N, N-dimethylformamide, and stirring at 45-55 ℃ for at least 3 hours to form a dark brown solution; finally adding polyvinylpyrrolidone and polyacrylonitrile, and thenStirring for at least 2h to obtain an electrostatic spinning precursor solution; further calcining in nitrogen or inert gas after electrostatic spinning to obtain Li with indium-cerium or indium-doped nanofiber structure₃VO₄。

18. An indium cerium or indium doped nanofiber structured Li prepared by the method of any one of claims 1-17₃VO₄。

19. The Li of claim 18 in a form of an indium-cerium or indium-doped nanofiber structure₃VO₄The application in the preparation of lithium ion battery electrodes.