CN111747394A

CN111747394A - NASICON type high-performance fluorophosphate and sodium ion battery

Info

Publication number: CN111747394A
Application number: CN202010644854.9A
Authority: CN
Inventors: 马吉伟; 侯景荣; 穆罕默德·哈杜奇; 黄云辉
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2020-07-07
Filing date: 2020-07-07
Publication date: 2020-10-09

Abstract

The invention provides a NASICON type high-performance fluorophosphate and sodium ion battery, belonging to the field of energy materials. The NASICON type high-performance fluorophosphate provided by the invention has the chemical formula as follows: na (Na)₄MV(PO₄)_3‑xF_3xWherein M is Mn or Ni, 0<x is less than or equal to 0.15, and the synthesis is carried out by a sol-gel method. The material is similar to the NASICON structure, the induction effect is enhanced by introducing a strong electronegative atom F, and when the obtained material is used as the positive electrode material in the sodium ion battery, the positive electrode material shows a higher and more stable working voltage platform, a larger specific capacity and cycling stabilityAnd is stronger. The sodium ion battery provided by the invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode, the negative electrode and the electrolyte contain the materials. Wherein the positive electrode material comprises the NASICON type high performance fluorophosphate, a conductive material and a polymer binder.

Description

NASICON type high-performance fluorophosphate and sodium ion battery

Technical Field

The invention relates to a NASICON type high-performance fluorophosphate and sodium ion battery, belonging to the field of energy materials.

Background

Since the 20 th century, human society has entered a stage of high-speed increase of demand for energy, but the development of a part of the society has been restricted by the accompanying energy crisis and environmental pollution problems, and new energy is characterized by immediacy and intermittency, so that the development of a new energy conversion system for storing and utilizing new energy is imminent.

Currently, lithium ion batteries are widely commercialized, but the use cost of lithium ion batteries is rising year by year due to the fact that the content of lithium resources in the earth crust is not abundant and the distribution is not uniform, and the development of the next generation of ion batteries to replace lithium batteries is not slow.

The sodium ion battery is concerned about due to the similar working principle with the lithium ion battery, and sodium element has wide distribution and larger reserve in the earth, and the cost is lower, so the sodium ion battery is expected to be applied to the aspects of large-scale energy storage facilities and the like. Sodium ion batteries are one of the major members of the late lithium era, but have certain defects in kinetics due to their larger ionic radius and molar mass, and researchers have made many efforts and extensive studies in relevant aspects, and the research focus has been on electrode materials, particularly positive electrode materials. Among many positive electrode materials, polyanion materials are greatly regarded as having higher working voltage and excellent cycle performance. However, although such important electrode materials have good application prospects, the synthesis and electrochemical performance of the electrode materials cannot meet the commercial standards, and further optimization is needed.

In polyanionic oxides, the sodium super-ion conductor has a three-dimensional open framework structure, Na⁺Can be rapidly inserted and removed in different spatial directions, thereby having higher ionic conductivity and the general formula of the ionic conductivity is Na₃M₂(PO₄)₃Wherein M is a transition metal. One material that has been extensively studied in NASICON is Na₃V₂(PO₄)₃. The material is a positive electrode material with wide application prospectAnd has better cycling stability and rate capability. However, as the research proceeds, Na₃V₂(PO₄)₃The lower voltage platform reduces the energy density, and meanwhile, the V element is expensive and toxic; while the NASICON structure was found to be suitable for a variety of transition metals, researchers have envisioned replacing the more expensive V with a cheaper metal ion³ ⁺Thereby reducing cost and increasing voltage by introducing other elements.

We have found that by adding Na to the phosphate₄MV(PO₄)₃A certain proportion of F is doped into a unit with a (M is Mn or Ni) structure to replace partial oxygen atoms to develop a new NASICON type phosphate material, so that the conductivity and the working voltage of the material are further improved, and the obtained new material has better electrochemical performance.

Disclosure of Invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a NASICON-type high-performance fluorophosphate material having a higher and more stable operating voltage plateau and a larger specific capacity, and a sodium ion battery containing the same.

The invention provides NASICON type high-performance fluorophosphate which has the characteristics that the molecular formula is as follows: na (Na)₄MV(PO4)_3-xF_3xWherein M is Mn or Ni, 0<x≤0.15。

The NASICON-type high-performance fluorophosphate provided by the present invention may also have a feature that it is synthesized by a sol-gel method.

The NASICON type high-performance fluorophosphate provided by the invention also has the characteristics that the preparation method comprises the following steps: step 1, adding NH₄VO₃Dissolving in a solution containing a reducing agent to obtain a solution A; step 2, mixing (CH)₃COO)₂Mn·4H₂O or (CH)₃COO)₂Ni·4H₂O，CH₃COONa and NaF are dissolved in water to obtain a solution B; step 3, mixing the solution A and the solution B, and stirring to obtain a mixed solution; step 4, adding NH into the mixed solution₄H₂PO₄And addHeating until it becomes a gel; and 5, heating the gel to obtain solid powder, and heating the solid powder under protective gas to obtain the NASICON type high-performance fluorophosphate.

The NASICON-type high-performance fluorophosphate provided by the present invention may further have a feature that the reducing agent in step 1 is citric acid.

The present invention also provides a sodium ion battery having features comprising: a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode contains one of the NASICON type high performance fluorophosphates.

The sodium ion battery provided by the invention can also be characterized in that the NASICON type high-performance fluorophosphate accounts for 70-90% of the mass of the positive electrode.

In the sodium-ion battery provided by the present invention, there may be further provided a feature wherein, when the electrolyte is a liquid, the sodium-ion battery further includes a separator.

The sodium ion battery according to the present invention may further have a feature in that the positive electrode is mainly composed of any one of the NASICON-type high-performance fluorophosphates, a conductive material, and a polymer binder.

In the sodium ion battery provided by the present invention, there may be further provided a feature wherein the conductive material is carbon black.

The sodium ion battery provided by the present invention may further have a feature in that the polymer binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

Action and Effect of the invention

According to the NASICON type high performance fluorophosphate according to the present invention, since a strong electronegative atom F is introduced to form an M-O-F bond, the covalent bond in M-O is weakened, and the induction effect is enhanced. Therefore, when the F-doped material is used for the anode, the material has a higher and more stable working voltage platform, a larger specific capacity and stronger cycling stability.

Drawings

FIG. 1a shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) An experimental spectrum and a fitting spectrum of powder X-ray diffraction;

FIG. 1b is an experimental and fitted graph of X-ray diffraction of NASICON-type high performance fluorophosphate powder prepared in accordance with the present invention and example 2;

FIG. 1c is an experimental and fitted graph of X-ray diffraction of NASICON-type high performance fluorophosphate powder prepared in accordance with the present invention and example 1;

FIG. 1d is an experimental and fitted graph of X-ray diffraction of NASICON-type high performance fluorophosphate powder prepared in accordance with the present invention and example 3;

FIG. 2 is a graph showing the trend of the NASICON type high performance fluorophosphate refinement lattice parameter obtained in examples 1 to 3 of the present invention;

FIG. 3 is a graph showing phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) Comparative first-cycle charge-discharge plots of NASICON-type high performance fluorophosphates prepared in examples 1-3;

FIG. 4 is a schematic representation of a polyhedron and a schematic representation of the Na atom position and environment of a NASICON type high performance fluorophosphate crystal obtained in example 1 of the present invention;

FIG. 5 is an XPS fit spectrum of the Mn 2p orbital in NASICON-type high performance fluorophosphates prepared in example 1 of the present invention;

FIG. 6 is an XPS fit spectrum of the V2p orbital in NASICON-type high performance fluorophosphates prepared in example 1 of the present invention;

FIG. 7 is an XPS fit spectrum of the P2P orbital in NASICON-type high performance fluorophosphates prepared in example 1 of the present invention;

FIG. 8 is an XPS fit spectrum of the F1 s orbit of NASICON type high performance fluorophosphates prepared in example 1 of the present invention;

FIG. 9 shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) Scanning electron microscopy images of (a);

FIG. 10 is a scanning electron microscope photograph of a NASICON type high performance fluorophosphate obtained in example 1 of the present invention;

FIG. 11a is phosphorus in comparative example 1 of the present inventionAcid salt (Na)₄MnV(PO₄)₃) Constant current charging and discharging curve of (1);

FIG. 11b shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) dQ/dV graph of (1);

FIG. 12a is a constant current charge-discharge curve of a NASICON type high performance fluorophosphate obtained in example 1 of the present invention;

FIG. 12b is a dQ/dV plot of a NASICON-type high performance fluorophosphate salt made in example 1 of the present invention;

FIG. 13 shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) Cycle performance profile of the NASICON type high performance fluorophosphate obtained in example 1.

Detailed Description

In order to make the technical means, the creation features, the achievement purposes and the effects of the invention easy to understand, the invention is specifically described below by combining the embodiment and the attached drawings.

< example 1>

The embodiment provides a NASICON type high-performance fluorophosphate, and the preparation method comprises the following steps:

step 1, 0.243g NH₄VO₃Dissolving in 20mL of a solution containing 1.6g of citric acid at 80 ℃, and obtaining a solution A;

step 2, add 0.509g (CH)₃COO)₂Mn·4H₂O、0.656g CH₃COONa and 0.013g NaF were dissolved in 40mL of ultrapure water, referred to as solution B;

step 3, A, B solution was mixed and stirred for 30 minutes, then 0.705g NH was added₄H₂PO₄And heating the mixed solution to 80 ℃ until the mixed solution becomes gel;

and 4, heating the obtained gel at 200 ℃ for 4 hours to obtain solid powder, and heating the powder at 700 ℃ for 12 hours under nitrogen to obtain the NASICON type high-performance fluorophosphate disclosed by the invention, wherein a polyhedral schematic diagram and a Na atom position and environment schematic diagram of the NASICON type high-performance fluorophosphate are shown in FIG. 4.

NASICON type high performance fluorophosphorus from example 1 was analyzed by Agilent ICP-OES spectrometerAnalysis of acid salts revealed that NASICON-type high-performance fluorophosphate (Na) according to the present invention was synthesized when Na, Mn, V, and P were 3.92:0.99:0.99:2.88₄MV(PO4)_3-xF_3x) Wherein x is 0.05 and the specific chemical formula is Na₄MnV(PO₄)_2.95F_0.15(note NMVPF 0.15).

< example 2>

This example provides a high performance fluorophosphate (Na) of the NASICON type as described in the present invention₄MV(PO4)_3- _xF_3x) Wherein x is 0.01, and the specific chemical formula is Na₄MnV(PO₄)_2.99F_0.03(note as NMVPF0.03) the procedure was carried out according to the preparation procedure in example 1.

< example 3>

This example provides a high performance fluorophosphate (Na) of the NASICON type as described in the present invention₄MV(PO4)_3- _xF_3x) Wherein x is 0.1, and the specific chemical formula is Na₄MnV(PO₄)_2.9F_0.3(note as NMVPF0.3), the procedure was performed according to the preparation procedure in example 1.

< comparative example 1>

This comparative example provides a phosphate salt (Na)₄MnV(PO₄)₃) The preparation method comprises the following steps:

step 1, 0.242g NH₄VO₃Dissolving in 20mL of a solution containing 1.6g of citric acid at 80 ℃, and obtaining a solution A;

step 2, add 0.507g (CH)₃COO)₂Mn·4H₂O、0.679g CH₃COONa is dissolved in 40mL of ultrapure water and is called solution B;

step 3, A, B solution was mixed and stirred for 30 minutes, then 0.714g NH was added₄H₂PO₄And heating the mixed solution to 80 ℃ until the mixed solution becomes gel;

step 4, heating the obtained gel at 200 ℃ for 4 hours to obtain solid powder, and heating the powder at 700 ℃ for 12 hours under nitrogen to obtain phosphate (Na)₄MnV(PO₄)₃)。

< test example 1>

X-ray diffraction (XRD) testing

Powder X-ray diffraction (XRD) test and structure refinement were performed on the compounds obtained in comparative example 1 and examples 1 to 3, and the test and refinement results are shown in fig. 1 and 2.

FIG. 1a, FIG. 1b, FIG. 1c, FIG. 1d are respectively the phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) The experimental pattern and the fitting pattern of the NASICON type high performance fluorophosphate powder X-ray diffraction obtained in example 2, example 1 and example 3.

As shown in fig. 1a, fig. 1b, fig. 1c, and fig. 1d, the experimental spectrum and the calculated spectrum of the refined crystal structure can be well matched, and the specific crystal unit cell parameters and the refinement results are shown in table 1.

FIG. 2 is a graph showing the tendency of the NASICON type high performance fluorophosphate refined lattice parameter obtained in examples 1-3 of the present invention to change.

As shown in fig. 2, the cell parameters a and c are inversely related, and the cell volume V is approximately positively related to the cell parameter a. V decreases with increasing amount of fluorine until x reaches 0.1, at which point V reaches a minimum

And c varies inversely with a.

TABLE 1 comparison of NMVP and NMVPF unit cell parameters with different amounts of F incorporation

< test example 3>

X-ray photoelectron spectroscopy (XPS) test

The compound obtained in example 1 was subjected to X-ray photoelectron spectroscopy, and the results are shown in FIGS. 5 to 8.

FIG. 5 is an XPS fit spectrum of the Mn 2p orbital in NASICON type high performance fluorophosphates prepared in example 1 of the present invention.

As shown in FIG. 5, Mn 2p is highResolution XPS spectra split into two peaks (Mn 2 p) due to spin-orbit coupling_1/2And Mn 2p_3/2)。Mn 2p_1/2(653.4eV) and Mn 2p_3/2The binding energy of (640.9eV) indicates that the valence of Mn is divalent; the satellite peak at 646.4eV appears, also demonstrating the presence of divalent manganese.

FIG. 6 is an XPS fitting spectrum of a NASICON type high performance fluorophosphate V2p prepared in example 1 of the present invention.

As shown in FIG. 6, peaks appear at the binding energies of 523.57eV and 516.50eV, respectively corresponding to V2p_1/2And V2p_3/2Core energy level of V³⁺The characteristics of (1).

FIG. 7 is an XPS fitting spectrum of a NASICON type high performance fluorophosphate P2P prepared in example 1 of the present invention.

As shown in FIG. 7, the peaks at 133.66eV and 132.84eV can correspond to P2P, respectively_1/2And P2P_3/2Core energy level of (C), demonstrating the presence of phosphorus-containing atoms (PO)₄ ^3-) The environment of (2).

FIG. 8 is an XPS fitting spectrum of NASICON type high performance fluorophosphate F1 s prepared in example 1 of the present invention.

As shown in fig. 8, a peak of F1 s was detected at 684.25eV, confirming the presence of elemental fluorine in the sample.

< test example 4>

Scanning Electron Microscope (SEM) testing

The compounds obtained in comparative example 1 and example 1 were subjected to scanning electron microscopy and the results are shown in FIGS. 9 to 10.

FIG. 9 shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) Scanning Electron Microscope (SEM) images of (a).

As shown in FIG. 9, phosphate (Na) is shown₄MnV(PO₄)₃) The particle size of the electron microscope image of (1) is about 200-500nm, and the formation of relatively non-uniform bulk nanoparticles can be clearly observed.

FIG. 10 is a Scanning Electron Microscope (SEM) image of a NASICON type high performance fluorophosphate produced in example 1 of the present invention.

As shown in figure 10 of the drawings,shows an electron microscope image of a NASICON type high performance fluorophosphate, compared to the phosphate (Na) of comparative example 1₄MnV(PO₄)₃) With similar particle size and morphology.

< test example 5>

Electrochemical performance testing of materials

The electrode materials of the sodium-ion batteries prepared in example 1 and comparative example 1 are respectively assembled in 2 button batteries, and the preparation method of the button batteries is as follows:

the electrode active material prepared in example 1 or comparative example 1, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were weighed and mixed in a mass ratio of 7:2:1, and uniformly distributed in n-methyl-2-pyrrolidone (NMP) solvent to prepare electrode slurry, the obtained battery slurry was coated on an aluminum foil, and then dried in vacuum at 120 ℃ for 12 hours, after which the dried slurry was cut into disks having a diameter of 8 mm. The electrolyte is 1M NaClO dissolved in 100% Polycarbonate (PC)₄5 wt% of vinyl fluoride carbonate (FEC) was added. Glass fiber (GF/D, Whatman) was used as a membrane and sodium metal was used as a counter electrode. A button cell (CR2025) was assembled in a glove box filled with argon gas.

Performing constant current circulation charge and discharge test by adopting a NEWARE cell test system; cyclic voltammetry tests were performed using a Bio-Logic VMP-3 electrochemical workstation.

The test results are shown in fig. 3 and fig. 11-13.

FIG. 3 is a graph showing phosphate (Na) in comparative example 1₄MnV(PO₄)₃) Comparative first-cycle charge-discharge graphs of NASICON-type high performance fluorophosphates prepared in examples 1-3.

As shown in FIG. 3, the original undoped F phosphate (Na)₄MnV(PO₄)₃) The capacity during the first charge and discharge is about 76mAh/g, the capacity is gradually increased along with the increase of the fluorine doping amount, the capacity reaches the maximum value when x is 0.05, the capacity is about 105mAh/g, and the specific capacity is increased by about 38%; the voltage plateau also rises slightly and as the fluorine content continues to increase, the capacity begins to drop, so further tests were performed with x equal to 0.05 as an example.

FIG. 11a shows the phosphate salt of comparative example 1 according to the invention(Na₄MnV(PO₄)₃) Constant current charging and discharging curve.

As shown in FIG. 11a, phosphate (Na)₄MnV(PO₄)₃) The first charge and discharge capacity was 88.6mAh/g and 76.2mAh/g, the reversible capacity at the fifth cycle was 71mAh/g, and the initial coulombic efficiency was about 86%.

FIG. 11b shows phosphate (Na) in comparative example 1 of the present invention₄MnV(PO₄)₃) dQ/dV graph of (a).

As shown in FIG. 11b, two oxidation peaks were observed, at 3.38V and 3.62V, respectively, corresponding to V³⁺/V⁴⁺And Mn²⁺/Mn³⁺A redox couple.

FIG. 12a is a constant current charge-discharge curve of a NASICON type high performance fluorophosphate obtained in example 1 of the present invention.

As shown in FIG. 12a, the NASICON type high performance fluorophosphate had first charge and discharge capacities of 113.7mAh/g and 105.4mAh/g, a reversible capacity of 102mAh/g at the fifth cycle, and an initial coulombic efficiency of the material as high as 92.7%, which is higher than that of the phosphate without F (Na + doped phosphate)₄MnV(PO₄)₃) This material also demonstrates a lower initial sodium loss compared to the larger boost, making this new NASICON phosphate promising for use in the positive electrode of sodium ion batteries.

FIG. 12b is a dQ/dV plot of a NASICON-type high performance fluorophosphate salt made in example 1 of the present invention.

As shown in FIG. 12b, two oxidation peaks are shown, at 3.42 and 3.62V, respectively, corresponding to V³⁺/V⁴⁺、Mn²⁺/Mn³⁺Redox couple, material doped with F, V³⁺/V⁴⁺Is gradually increased, while Mn²⁺/Mn³⁺The potential change is not large.

FIG. 13 shows phosphate (Na) in comparative example 1₄MnV(PO₄)₃) Cycle performance profile of the NASICON type high performance fluorophosphate obtained in example 1.

As shown in FIG. 13, the NASICON-type high performance fluorophosphates remained approximately 82.6% in capacity after 250 cycles, i.e., 250The capacity of the material after the circulation is 86.72mAh/g, which proves that the material has stable circulation performance, while the capacity of the material without F is only 41.78mAh/g after 250 cycles, and the capacity retention rate is only 54.9%. At the same time, the coulombic efficiency of NMVPF0.15 was comparable to phosphate (Na) during 250 cycles₄MnV(PO₄)₃) And is also more stable.

Effects and effects of the embodiments

According to the NASICON type high performance fluorophosphates according to examples 1-3, since when a strongly electronegative atom F is introduced to form an M-O-F bond, the covalent bond in M-O is weakened and the inducing effect is enhanced, and the electronegativity is enhanced after F replaces part of oxygen atoms. Therefore, when the material doped with F is used for the anode, a higher and more stable working voltage platform and a larger specific capacity are provided, the cycling stability is stronger, and the material also shows better electrochemical performance when used for a sodium ion battery.

The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.

Claims

1. A NASICON type high performance fluorophosphate, which is characterized in that the molecular formula is as follows: na (Na)₄MV(PO₄)_3-xF_3x，

Wherein M is Mn or Ni, and x is more than 0 and less than or equal to 0.15.

2. The NASICON-type high performance fluorophosphate according to claim 1, characterized in that it is synthesized by a sol-gel method.

3. The NASICON-type high performance fluorophosphate according to claim 1, characterized in that the preparation method comprises the following steps:

step 1, adding NH₄VO₃Dissolving in a solution containing a reducing agent to obtain a solution A;

step 2, mixing (CH)₃COO)₂Mn·4H₂O or (CH)₃COO)₂Ni·4H₂O，CH₃COONa and NaF are dissolved in water to obtain a solution B;

step 3, mixing the solution A and the solution B, and stirring to obtain a mixed solution;

step 4, adding NH into the mixed solution₄H₂PO₄And heating until it becomes a gel;

and 5, heating the gel to obtain solid powder, and heating the solid powder under protective gas to obtain the NASICON type high-performance fluorophosphate.

4. The NASICON-type high performance fluorophosphate according to claim 3, characterized in that:

wherein the reducing agent is citric acid.

5. A sodium ion battery, comprising: a positive electrode, a negative electrode, and an electrolyte,

wherein the positive electrode contains the NASICON-type high performance fluorophosphate according to any one of claims 1 to 4.

6. The sodium-ion battery of claim 5, wherein:

wherein the NASICON type high-performance fluorophosphate accounts for 70-90% of the mass of the positive electrode.

7. The sodium-ion battery of claim 5, wherein:

wherein, when the electrolyte is a liquid, the sodium-ion battery further comprises a separator.

8. The sodium-ion battery of claim 5, wherein:

wherein the positive electrode is mainly composed of the NASICON type high performance fluorophosphate according to any one of claims 1 to 4, a conductive material, and a polymer binder.

9. The sodium-ion battery of claim 8, wherein:

wherein the conductive material is carbon black.

10. The sodium-ion battery of claim 8, wherein:

wherein the polymer adhesive is at least one of polyvinylidene fluoride, polytetrafluoroethylene and sodium carboxymethyl cellulose.