阅读说明：本技术 一种碳包覆磷酸钒钛锰钠微米球及其制备方法与应用 (Carbon-coated vanadium-titanium-manganese-sodium phosphate micro-spheres and preparation method and application thereof ) 是由 麦立强 朱婷 胡平 周亮 于 2021-07-29 设计创作，主要内容包括：本发明提供了一种碳包覆磷酸钒钛锰钠微米球及其制备方法与应用,制备方法包括步骤：将碳源、钒源、锰源、钠源、磷酸二氢钠和二(2-羟基丙酸)二氢氧化二铵合钛加入去离子水中,搅拌溶解后进行喷雾干燥,获得前驱体；将所述前驱体在预设条件下进行煅烧,得到碳包覆磷酸钒钛锰钠微米球。本发明采用喷雾干燥技术制备碳包覆磷酸钒钛锰钠微米球,制备方法简单,产品的产率高、环境友好、成本低廉；制备的微米球作为钠离子电池正极材料可实现多电子电化学反应,表现出高的放电中压和可逆比容量,在能量密度、循环稳定性和倍率性能上均具有明显优势。(The invention provides a carbon-coated vanadium titanium manganese phosphate sodium microsphere and a preparation method and application thereof, wherein the preparation method comprises the following steps: adding a carbon source, a vanadium source, a manganese source, a sodium source, sodium dihydrogen phosphate and di (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium into deionized water, stirring and dissolving, and then carrying out spray drying to obtain a precursor; and calcining the precursor under a preset condition to obtain the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres. The carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres are prepared by adopting a spray drying technology, the preparation method is simple, the yield of the product is high, the environment is friendly, and the cost is low; the prepared microsphere can realize multi-electron electrochemical reaction when being used as a sodium ion battery anode material, shows high discharge medium voltage and reversible specific capacity, and has obvious advantages in energy density, cycling stability and rate capability.)

1. A preparation method of carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres is characterized by comprising the following steps:

s1, adding a carbon source, a vanadium source, a manganese source, a sodium source, sodium dihydrogen phosphate and di (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium into deionized water, stirring and dissolving, and then carrying out spray drying to obtain a precursor;

and S2, calcining the precursor under a preset condition to obtain the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres.

2. The method of claim 1, wherein the carbon source in step S1 comprises one of citric acid, acetic acid, glucose, sucrose powder and polyvinylpyrrolidone, the vanadium source comprises one of ammonium metavanadate, vanadium acetylacetonate and vanadyl acetylacetonate, the manganese source comprises one of manganese acetate, manganese nitrate and manganese acetylacetonate, and the sodium source comprises one of sodium acetate, sodium citrate and sodium bicarbonate.

3. The method according to claim 1, wherein the sodium source, the manganese source, the titanium bis (2-hydroxypropionate) dihydroxide, the vanadium source, and the sodium dihydrogen phosphate are selected from the group consisting of Na, Mn, Ti, V, NaH in step S1₂PO₄In terms of molar ratio of Na, Mn, Ti, V and NaH₂PO₄In the range of 0: 1: 0.5: 1 to 0.5: 1: 0.5: 3.

4. The production method according to claim 3, wherein a mass ratio of the total mass of the sodium source, the manganese source, the titanium bis (2-hydroxypropionate) dihydrogenoxide, the vanadium source, and the sodium dihydrogenphosphate to the carbon source is in a range of 9.0: 1.0 to 9.9: 0.1.

5. The method according to any one of claims 1 to 4, wherein the spray drying in step S1 employs a drying temperature in the range of 160 ℃ to 220 ℃, a circulating gas flow in the range of 80% to 100%, and a sample injection pump in the range of 2% to 25%.

6. The method according to claim 5, wherein the preset conditions in step S2 include: under the protection of inert gas, the temperature rise rate of the tube furnace is 2 ℃ for min^-1To 10 ℃ for min^-1In the range of 600 ℃ to 750 ℃, and in the range of 4h to 12 h.

7. A carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere, which is characterized by being prepared by the preparation method of the carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere as claimed in any one of claims 1 to 6.

8. The carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres of claim 7, wherein the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres are prepared by the method of claim 7The chemical formula of the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres is Na_3+xMnTi_1-xV_x(PO₄)₃C, wherein, 0<x≤0.5。

9. The carbon-coated vanadium titanium manganese sodium phosphate microspheres of claim 7, wherein the carbon-coated vanadium titanium manganese sodium phosphate microspheres have a diameter in the range of 0.2 μ ι η to 8 μ ι η.

10. Use of carbon-coated vanadium titanium manganese phosphate microspheres according to any one of claims 7 to 9 as positive active material for sodium-ion batteries.

Technical Field

The invention relates to the technical field of nano materials and electrochemistry, in particular to a carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere and a preparation method and application thereof.

Background

Lithium ion batteries, one of the most important representatives of clean energy, have the characteristics of high energy density, long cycle life, simplicity and portability, and become the first choice for power storage systems in the past 30 years. However, the shortage of lithium resources and high cost greatly limit the application of lithium in the field of large-scale energy storage, and therefore, the development of novel efficient energy storage batteries with low cost is urgent. The sodium and the lithium are in the same main group, the sodium and the lithium have similar chemical characteristics, and meanwhile, the sodium resource is high in abundance, wide in distribution and low in raw material cost. Therefore, sodium ion batteries are considered to be one of the first choice in future large-scale energy storage systems, and have become a hot spot and a leading edge of research in the field of current energy storage materials and devices.

In the whole energy storage system of the sodium-ion battery, the anode material has important influence on key indexes such as the working voltage, the energy density, the power density and the cycle life of the battery. Due to the radius of sodium ionFar greater than the radius of lithium ionThis makes the resistance of sodium ions during intercalation/deintercalation greater, and the damage to the electrode material structure is also more serious. Among many cathode materials, polyanionic sodium fast ion conductor phosphate is one of the most promising materials because of its unique sodium ion conductor (NASICON) structure, high theoretical energy density, good thermodynamic stability, and large internal ion diffusion channel.

However, the intrinsic electronic conductivity of the material is low, so that the coulombic efficiency of the material is low, and the cycling stability of the material is poor. Therefore, how to improve the cycling stability of the material and improve the rate capability becomes the focus of the current research work.

Disclosure of Invention

In view of the above, the invention aims to provide a carbon-coated vanadium titanium manganese phosphate microsphere, a preparation method and an application thereof, so as to solve the problems of low discharge platform, insufficient specific capacity, poor rate capability, rapid capacity attenuation and the like of the conventional NASICON type sodium ion battery anode material.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a preparation method of carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres comprises the following steps:

s1, adding a carbon source, a vanadium source, a manganese source, a sodium source, sodium dihydrogen phosphate and di (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium into deionized water, stirring and dissolving, and then carrying out spray drying to obtain a precursor;

and S2, calcining the precursor under a preset condition to obtain the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres.

Optionally, in step S1, the carbon source includes one of citric acid, acetic acid, glucose, sucrose powder and polyvinylpyrrolidone, the vanadium source includes one of ammonium metavanadate, vanadium acetylacetonate and vanadyl acetylacetonate, the manganese source includes one of manganese acetate, manganese nitrate and manganese acetylacetonate, and the sodium source includes one of sodium acetate, sodium citrate and sodium bicarbonate.

Optionally, the sodium source, the manganese source, the titanium bis (2-hydroxypropionate) dihydroxide, the vanadium source, and the sodium dihydrogen phosphate are replaced by Na, Mn, Ti, V, NaH in step S1₂PO₄In a molar ratio of Na to Mn to Ti to V to NaH₂PO₄In the range of 0: 1: 0.5: 1 to 0.5: 1: 0.5: 3.

Optionally, the mass ratio of the total mass of the sodium source, the manganese source, the titanium bis (2-hydroxypropionate) dihydroxide, the vanadium source, and the sodium dihydrogen phosphate to the carbon source is in the range of 9.0: 1.0 to 9.9: 0.1.

Optionally, the spray drying in step S1 uses a drying temperature in the range of 160 ℃ to 220 ℃, a circulating gas flow in the range of 80% to 100%, and a sample injection pump in the range of 2% to 25%.

Optionally, the preset condition in step S2 includes: under the protection of inert gas, the temperature rising rate of the tube furnace is within the range of 2 ℃/min to 10 ℃/min, the calcining temperature is within the range of 600 ℃ to 750 ℃, and the calcining time is within the range of 4h to 12 h.

The invention also aims to provide carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres prepared by the preparation method of the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres.

Optionally, the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres have a chemical formula of Na_3+xMnTi_1-xV_x(PO₄)₃C, wherein, 0<x≤0.5。

Optionally, the carbon-coated vanadium titanium manganese phosphate sodium microspheres have a diameter in a range of 0.2 μm to 8 μm.

The third purpose of the invention is to provide the application of the carbon-coated vanadium titanium manganese phosphate sodium microspheres as the positive electrode active material of the sodium ion battery.

Compared with the prior art, the carbon-coated vanadium-titanium-manganese-sodium phosphate micro-spheres and the preparation method and application thereof provided by the invention have the following advantages:

(1) the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres are prepared by adopting a spray drying technology, can realize multi-electron electrochemical reaction when being used as a positive electrode material of a sodium ion battery, show high discharge medium voltage and reversible specific capacity, and have obvious advantages in energy density, cycling stability and rate capability.

(2) The preparation method is simple, the product yield is high, the environment is friendly, the cost is low, the potential of large-scale generation and application is realized, the market popularization is facilitated, and the preparation method has wide application prospects in the field of sodium ion battery application.

Drawings

FIG. 1 is Na according to the present invention_3.2MnTi_0.8V_0.2(PO₄)₃/C、Na₃MnTi(PO₄)₃/C、 Na₄MnV(PO₄)₃XRD pattern of/C;

FIG. 2 is Na according to the example of the present invention_3.2MnTi_0.8V_0.2(PO₄)₃TEM image of/C;

FIG. 3 is Na according to the example of the present invention_3.2MnTi_0.8V_0.2(PO₄)₃/C、Na₃MnTi(PO₄)₃/C、 Na₄MnV(PO₄)₃SEM picture of/C;

FIG. 4 is Na according to the example of the present invention_3.2MnTi_0.8V_0.2(PO₄)₃/C、Na₃MnTi(PO₄)₃/C、 Na₄MnV(PO₄)₃At 50mA g of/C^-1A charge-discharge curve graph of the second circle under the current density;

FIG. 5 shows Na according to the example of the present invention_3.2MnTi_0.8V_0.2(PO₄)₃/C、Na₃MnTi(PO₄)₃/C、 Na₄MnV(PO₄)₃Rate performance graph of/C.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the description of the present invention, it should be noted that the terms "first" and "second" mentioned in the embodiments of the present invention are only used for descriptive purposes and are not to be construed as indicating or implying relative importance or implicit to indicate the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. The term "in.. range" as used herein includes both end values, e.g., "in the range of 1 to 100" includes both end values of 1 and 100.

In the description of embodiments of the present application, the description of the term "some embodiments" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same implementation or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

In the sodium ion positive electrode material, polyanion is polymerizedThe daughter sodium fast ion conductor phosphate is one of the most valuable materials due to its unique NASICON structure, high theoretical energy density, good thermodynamic stability and large internal ion diffusion channels. Wherein, Na₃V₂(PO₄)₃Is the most widely researched NASICON sodium ion battery anode material at present, and the theoretical specific capacity of the NASICON sodium ion battery anode material is 117mAh g^-1And has a stable voltage platform at 3.4V. But the V voltage platform is limited, which forces people to develop NASICON type anode materials with better performance and more safety and environmental protection. Recently, Na₄MnV(PO₄)₃And Na₃MnTi(PO₄)₃Two NASICON phosphates have been reported in succession, in which Mn not only increases the discharge medium voltage of the material but also reduces the raw material cost to some extent and is safe, and thus are attracting attention.

However, the electron transfer number of the active metal participating in the reaction of the material is not high, and the electron conductivity is generally low, which seriously affects the full exertion of the electrochemical performance.

In order to solve the above problems, an embodiment of the present invention provides a method for preparing carbon-coated vanadium titanium manganese phosphate microspheres, including the following steps:

s1, adding a carbon source, a vanadium source, a manganese source, a sodium source, sodium dihydrogen phosphate and di (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium into deionized water, stirring and dissolving, and then carrying out spray drying to obtain a precursor;

and S2, calcining the precursor under preset conditions to obtain the carbon-coated vanadium titanium manganese phosphate sodium microspheres.

Specifically, in step S1, the carbon source includes one of citric acid, acetic acid, glucose, sucrose powder and polyvinylpyrrolidone, the vanadium source includes one of ammonium metavanadate, vanadium acetylacetonate and vanadyl acetylacetonate, the manganese source includes one of manganese acetate, manganese nitrate and manganese acetylacetonate, and the sodium source includes one of sodium acetate, sodium citrate and sodium bicarbonate.

The invention realizes the uniform atomization drying of the mixed solution by utilizing the spray drying technology, and the spherical solution can be collected by the rapid volatilization of the solventPrecursor, high-temperature treating the precursor in inert atmosphere to obtain carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres (Na) with typical NASICON structure_3+xMnTi_1-xV_x(PO₄)₃/C micron ball electrode material). The preparation method is simple, the product yield is high, the environment is friendly, the cost is low, the potential of large-scale generation and application is realized, the marketization popularization is facilitated, and the preparation method has wide application prospects in the application field of sodium ion batteries.

Wherein in step S1, the sodium source, the manganese source, the bis (2-hydroxypropionic acid) diammonium bihydroxide titanium, the vanadium source and the sodium dihydrogen phosphate are selected from Na, Mn, Ti, V and NaH₂PO₄In terms of molar ratio of Na, Mn, Ti, V and NaH₂PO₄In the range of 0: 1: 0.5: 1 to 0.5: 1: 0.5: 3.

The mass ratio of the total mass of the sodium source, the manganese source, the titanium source, the bis (2-hydroxypropionic acid) diammonium titanium dihydroxide, the vanadium source and the sodium dihydrogen phosphate to the carbon source is in the range of 9.0: 1.0 to 9.9: 0.1.

The invention can optimize the material structure by adjusting the ratio of vanadium and titanium in the material, and can obviously improve the discharge medium voltage of the material, particularly the energy density of the material.

In step S1, the drying temperature for spray drying is 160-220 deg.C, the circulating gas flow is 80-100%, and the sample injection pump is 2-25%.

Specifically, in step S2, the preset conditions for calcining the precursor include: under the protection of inert gas, the temperature rising rate of the tube furnace is within the range of 2 ℃/min to 10 ℃/min, the calcining temperature is within the range of 600 ℃ to 750 ℃, and the calcining time is within the range of 4h to 12 h.

The precursor provided by the invention is sintered in one step to obtain Na_3+xMnTi_1-xV_x(PO₄)₃The active substance of the/C micron sphere is coated by in-situ carbon, the specific surface area is increased, a plurality of reaction active sites are provided, the conductivity, the electrochemical reaction platform and the specific capacity of the material are improved, the infiltration of electrolyte is facilitated, and the energy density has outstanding advantages.

The embodiment of the invention also provides a carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere which is prepared by adopting the preparation method of the carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere. Na (Na)_3+xMnTi_1-xV_x(PO₄)₃the/C is in microsphere shape, the diameter of the microsphere is different, and the diameter is in the range of 0.2-8 μm.

The chemical formula of the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres is Na_3+xMnTi_1-xV_x(PO₄)₃C, wherein, 0<x≤0.5。

The embodiment of the invention also provides application of the carbon-coated vanadium titanium manganese phosphate sodium microspheres as a sodium ion battery positive electrode active material, can realize multi-electron electrochemical reaction (more than 3), shows high discharge medium voltage and reversible specific capacity, and has obvious advantages in energy density, cycling stability and rate capability. The problems that the existing NASICON type sodium ion battery anode material is low in discharge platform, not high in specific capacity, poor in rate capability, rapid in capacity attenuation and the like are solved.

On the basis of the above embodiments, the present invention is further illustrated below by combining the preparation method of carbon-coated vanadium titanium manganese phosphate microspheres. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are examples of experimental procedures not specified under specific conditions, generally according to the conditions recommended by the manufacturer. Unless otherwise indicated, percentages and parts are by mass.

Example 1

The embodiment provides a preparation method of carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres, which comprises the following steps:

1) sequentially adding 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder, 1mmol of ammonium metavanadate, 1mmol of sodium acetate and 4mmol of bis (2-hydroxypropionic acid) diammonium hydrogen oxide titanium into 100mL of deionized water, and stirring at room temperature for 30min to dissolve to obtain a mixed solution; then carrying out spray drying on the mixed solution, wherein the spray drying temperature is 160 ℃, the circulating air flow is 90%, and the sampling pump is 5%, so as to obtain a precursor;

2) calcining the prepared precursor in a tube furnace at 650 deg.C for 6h under argon atmosphere at a heating rate of 3 deg.C for 3 min^-1The final calcined product is the carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres Na_3.2MnTi_0.8V_0.2(PO₄)₃/C(650℃)。

Comparative example 1 of example 1

The comparative example 1 provides a preparation method of a microsphere, comprising the following steps:

1) sequentially adding 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder and 5mmol of bis (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium and stirring at room temperature for 30min to dissolve to obtain a mixed solution; then carrying out spray drying on the mixed solution, wherein the spray drying temperature is 160 ℃, the circulating air flow is 90%, and the sampling pump is 5%, so as to obtain a precursor;

2) calcining the prepared precursor in a tube furnace at 650 deg.C for 6h under argon atmosphere at a heating rate of 3 deg.C for 3 min^-1The final calcined product is the microsphere Na₃MnTi(PO₄)₃/C(650℃)。

Comparative example 2 of example 1

The comparative example 2 provides a preparation method of a microsphere, comprising the following steps:

1) sequentially adding 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder, 5mmol of ammonium metavanadate and 5mmol of sodium acetate into 100mL of deionized water, and stirring at room temperature for 30min to dissolve to obtain a mixed solution; then carrying out spray drying on the mixed solution, wherein the spray drying temperature is 160 ℃, the circulating air flow is 90%, and the sampling pump is 5%, so as to obtain a precursor;

2) calcining the prepared precursor in a tube furnace at 650 deg.C for 6h under argon atmosphere at a heating rate of 3 deg.C for 3 min^-1The final calcined product is microsphere Na₄MnV(PO₄)₃/C(650℃)。

The products obtained in example 1, comparative example 1 and comparative example 2 were tested to obtain a graph of results as shown in FIGS. 1 to 3.

FIG. 1 is Na_3.2MnTi_0.8V_0.2(PO₄)₃/C(650℃)、Na₃MnTi(PO₄)₃/C(650℃)、 Na₄MnV(PO₄)₃X-ray diffraction Pattern (XRD) of/C (650 ℃), as can be seen in FIG. 1, Na₃MnTi(PO₄)₃C (650 ℃) microspheres, Na_3.2MnTi_0.8V_0.2(PO₄)₃C (650 ℃) microspheres and Na₄MnV(PO₄)₃The peak positions of the/C (650 ℃) microspheres are basically consistent, and are all typical NASICON structures.

FIG. 2 shows Na obtained in example 1_3.2MnTi_0.8V_0.2(PO₄)₃Transmission Electron Microscopy (TEM) image of/C (650 ℃ C.), as can be seen in FIG. 2, Na_3.2MnTi_0.8V_0.2(PO₄)₃the/C (650 ℃) is a spherical structure and can endow the material with larger specific surface area.

FIG. 3 is Na_3.2MnTi_0.8V_0.2(PO₄)₃/C(650℃)、Na₃MnTi(PO₄)₃/C(650℃)、 Na₄MnV(PO₄)₃Scanning Electron Microscopy (SEM) image of/C (650 ℃), as can be seen in FIG. 3, Na_3.2MnTi_0.8V_0.2(PO₄)₃the/C (650 ℃) micron sphere (as shown in figure 3 b) has spherical micron-sized morphology and good dispersibility, the diameter of the micron sphere is 0.2-8 mu m, and the result is compared with Na₃MnTi(PO₄)₃C (650 ℃ C.) (shown in FIG. 3 a) and Na₄MnV(PO₄)₃the/C (650 deg.C) (as shown in FIG. 3C) is substantially the same.

The products prepared in example 1, comparative example 1 and comparative example 2 are respectively used as positive active materials of sodium-ion batteries, and the method for preparing the sodium-ion batteries is as follows:

by using Na_3.2MnTi_0.8V_0.2(PO₄)₃The material comprises/C (650 ℃) micron spheres as an active material, acetylene black as a conductive agent, PVDF as a binder, the active material, the acetylene black and polytetrafluoroethyleneThe mass ratio is 70: 20: 10, a small amount of N-methylpyrrolidone NMP is added after the components are mixed according to the proportion, the mixture is uniformly subjected to ultrasonic treatment, an aluminum foil is coated to serve as a positive electrode plate of the sodium ion battery, and the coated positive electrode plate is placed in an oven at 80 ℃ and dried for 24 hours for later use. With 1M NaClO₄in EC + PC (1: 1) + 5% FEC solution as electrolyte, sodium sheet as negative electrode, Celgard as diaphragm, and 2016 positive and negative battery cases to assemble sodium ion button battery. Sodium ion batteries were tested and the results are shown in figures 4-5.

FIG. 4 is Na_3.2MnTi_0.8V_0.2(PO₄)₃/C(650℃)、Na₃MnTi(PO₄)₃/C(650℃)、 Na₄MnV(PO₄)₃At 50mA g/C (650 ℃ C.)^-1Second turn charge-discharge curve at current density, FIG. 5 is Na_3.2MnTi_0.8V_0.2(PO₄)₃/C(650℃)、Na₃MnTi(PO₄)₃/C(650℃)、 Na₄MnV(PO₄)₃A rate performance graph of/C (650 ℃).

As can be seen from FIG. 4, Na_3.2MnTi_0.8V_0.2(PO₄)₃The specific discharge capacity of the/C (650 ℃) micron ball can reach 172.6mAh g^-1Having a long and stable discharge plateau, i.e. Na, around 3.5V_3.2MnTi_0.8V_0.2(PO₄)₃The energy density of the electrochemical reaction process of 3.2 electrons of the/C (650 ℃) micron ball is up to 526Wh Kg^-1. As can be seen from FIG. 5, Na_3.2MnTi_0.8V_0.2(PO₄)₃the/C (650 ℃) micron ball electrode material has excellent rate performance.

And Na₃MnTi(PO₄)₃C (650 ℃ C.) and Na₄MnV(PO₄)₃the/C (650 ℃ C.) has an electrochemical platform position different from that of Na_3.2MnTi_0.8V_0.2(PO₄)₃The electrochemical reaction process of/C (650 ℃) is obviously different, namely the electrochemical performance of the microspheres prepared in comparative examples 1 and 2 is difficult to be matched with that of Na_3.2MnTi_0.8V_0.2(PO₄)₃the/C microsphere is comparable to the/C microsphere.

Example 2

The embodiment provides a preparation method of carbon-coated vanadium titanium manganese phosphate microspheres, and the difference between the embodiment and the embodiment 1 is as follows:

in the step 1), 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder, 1mmol of ammonium metavanadate, 1mmol of sodium acetate and 4mmol of bis (2-hydroxypropionic acid) diammonium hydrogen oxide titanium are sequentially added into 100mL of deionized water;

the other steps and parameters are the same as those of the example 1, and the final product is carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres Na_3.3MnTi_0.7V_0.3(PO₄)₃/C(650℃)。

Comparative example 1 of example 2

Adding 5mmol of bis (2-hydroxypropionic acid) diammonium dihydroxide titanium into the raw materials obtained in the step 1) without adding ammonium metavanadate and sodium acetate, and keeping other steps and parameters unchanged to obtain Na₃MnTi(PO₄)₃C (650 ℃ C.) microspheres.

Comparative example 2 of example 2

Adding 5mmol of ammonium metavanadate and 5mmol of sodium acetate into the raw materials in the step 1) without adding bis (2-hydroxypropionic acid) diammonium dihydroxide titanium, and keeping other steps and parameters unchanged to obtain Na₄MnV(PO₄)₃C (650 ℃ C.) microspheres.

Na prepared in example 2 and its comparative example_3.3MnTi_0.7V_0.3(PO₄)₃C (650 ℃) microspheres, Na₃MnTi(PO₄)₃C (650 ℃) microspheres, Na₄MnV(PO₄)₃the/C (650 ℃) micron balls are respectively used as the positive active materials of the sodium ion battery to assemble the sodium ion button half battery at 200mA g^-1And carrying out constant current charge and discharge test under the current density.

Found in the test, Na_3.3MnTi_0.7V_0.3(PO₄)₃The first discharge specific capacity of the/C (650 ℃) micron ball can reach 133.8mAh g^-1The electrochemical reaction of 3.3 electrons occurs, and the capacity can still be maintained at 114.4mAh g after 100 cycles^-1And the capacity retention rate after 200 cycles is 78.9%. In contrast, Na₄MnV(PO₄)₃At 200mA g/C (650 ℃ C.)^-1The first discharge specific capacity under the current density is 122.9 mAh g^-1However, the specific discharge capacity of the second circle is only 109.1mAh g^-1The capacity retention rate after 200 cycles is only 20.3%, and the performance is far inferior to Na_3.3MnTi_0.7V_0.3(PO₄)₃C (650 ℃ C.) microspheres.

Example 3

The embodiment provides a preparation method of carbon-coated vanadium titanium manganese phosphate microspheres, and the difference between the embodiment and the embodiment 1 is as follows:

in the step 1), 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder, 0.5mmol of ammonium metavanadate, 0.5mmol of sodium acetate and 4.5mmol of bis (2-hydroxypropionic acid) diammonium dihydrogen oxide titanium are sequentially added into 100mL of deionized water;

the other steps and parameters are the same as those of the example 1, and the final product is carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres Na_3.1MnTi_0.9V_0.1(PO₄)₃C (650 ℃ C.) microspheres.

Na prepared in example 3_3.1MnTi_0.9V_0.1(PO₄)₃the/C (650 ℃) micron ball is used as the positive active material of the sodium ion battery to assemble the sodium ion button half battery at 100mA g^-1And carrying out constant current charging and discharging tests under the current density.

Found in the test, Na_3.1MnTi_0.9V_0.1(PO₄)₃The first discharge specific capacity of the/C (650 ℃) micron ball can reach 165.2mAh g^-1After 100 cycles, the capacity can still be maintained at 142.4mAh g^-1(ii) a At 100mA g^-1The specific capacity of the first loop under the current density is 135.4mAh g^-1And the capacity retention rate after 300 cycles is 82.1%.

Example 4

The embodiment provides a preparation method of carbon-coated vanadium titanium manganese phosphate microspheres, and the difference between the embodiment and the embodiment 1 is as follows:

in the step 1), 10mmol of citric acid powder, 5mmol of manganese acetate powder, 15mmol of sodium dihydrogen phosphate powder, 0.5mmol of ammonium metavanadate, 0.5mmol of sodium acetate and 4.5mmol of bis (2-hydroxypropionic acid) diammonium hydrogen oxide titanium are sequentially added into 100mL of deionized water;

in the step 2), the calcining temperature is 600 ℃, and the calcining time is 6 hours;

the other steps and parameters are the same as those of the example 1, and the final product is carbon-coated vanadium-titanium-manganese-sodium phosphate microspheres Na_3.1MnTi_0.9V_0.1(PO₄)₃C (600 ℃) microspheres.

Na prepared in example 4_3.1MnTi_0.9V_0.1(PO₄)₃the/C (600 ℃) micron ball is used as the positive active material of the sodium ion battery to assemble the sodium ion button half battery, and the weight is 50mA g^-1And carrying out constant current charge and discharge test under the current density.

Found in the test, Na_3.1MnTi_0.9V_0.1(PO₄)₃The first discharge specific capacity of the/C (600 ℃) micron ball can reach 168mAh g^-1The capacity retention after 100 cycles was 78.2%.

Example 5

The embodiment provides a preparation method of carbon-coated vanadium titanium manganese phosphate microspheres, and the difference between the embodiment and the embodiment 1 is as follows:

in the step 2), the calcining temperature is 700 ℃, and the calcining time is 6 hours;

the other steps and parameters are the same as those in example 1, and the final product is carbon-coated vanadium-titanium-manganese-sodium phosphate micron Na_3.2MnTi_0.8V_0.2(PO₄)₃C (700 ℃) microspheres.

Na prepared in example 5_3.2MnTi_0.8V_0.2(PO₄)₃the/C (700 ℃) micron ball is used as the positive active material of the sodium ion battery to assemble the sodium ion button half battery, and the weight is 50mA g^-1And carrying out constant current charge and discharge test under the current density.

Found in the test, Na_3.2MnTi_0.8V_0.2(PO₄)₃The first discharge specific capacity of the/C (700 ℃) micron sphere can reach 168.8mAh g^-1The capacity retention rate after 100 cycles is 82.3%; at 100mA g^-1The specific capacity of the first loop under the current density is 128.4mAh g^-1And the capacity retention rate after 300 cycles is 81.8%.

In conclusion, the carbon-coated vanadium-titanium-manganese-sodium phosphate microsphere prepared by the invention can realize multi-electron electrochemical reaction (more than 3) by being applied as the positive electrode active material of the sodium ion battery, shows high discharge medium voltage and reversible specific capacity, and has obvious advantages in energy density, cycling stability and rate capability. And the material structure can be optimized by adjusting the ratio of vanadium to titanium in the material, and the discharge medium voltage and energy density of the material are improved.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.