CN110993942B

CN110993942B - High-performance sodium-deficient cathode material and sodium-ion battery

Info

Publication number: CN110993942B
Application number: CN202010002741.9A
Authority: CN
Inventors: 马吉伟; 穆罕默德·哈杜奇; 侯景荣; 黄云辉
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2020-01-02
Filing date: 2020-01-02
Publication date: 2021-09-03
Anticipated expiration: 2040-01-02
Also published as: CN110993942A

Abstract

The invention provides a high-performance sodium-deficient cathode materialAnd a sodium ion battery, belonging to the field of inorganic materials. The invention provides a high-performance sodium-deficient cathode material, which has the following chemical formula: na (Na)_4‑x□xFeV(PO₄)₃Wherein, 0<x is less than or equal to 0.6. The invention provides a positive electrode of a sodium ion battery, which comprises the following raw materials: na (Na)_4‑x□xFeV(PO₄)₃At least one conductive material, and at least one polymer binder. The invention not only reduces the manufacturing cost of NASICON type phosphate, but also stimulates the electrochemical activity of more than 2 sodium ions in the NASICON type phosphate structure, and shows extremely high stability, excellent rate performance and excellent coulomb efficiency in a sodium ion battery. The sodium ion battery provided by the invention has higher working voltage and good cycle performance.

Description

High-performance sodium-deficient cathode material and sodium-ion battery

Technical Field

The invention relates to a high-performance sodium-deficient cathode material and a sodium ion battery, belonging to the field of inorganic materials.

Background

At present, the demand of society for electronic equipment, electric vehicles and smart grids is continuously increasing, so that the development of low-cost high-performance energy storage systems becomes a major problem (Tarascon and Armand, 2001; Dunn, Kamath and Tarascon, 2011). Lithium Ion Batteries (LIBs) are widely used in the fields of mobile electronic products, electric vehicles and the like, however, for large-scale energy storage systems such as smart grids and the like, the content and cost of main materials of the batteries in the earth become key factors influencing the development of the large-scale energy storage systems. The cost of lithium resources in the crust is currently increasing year by year as demand increases due to limited reserves and uneven distribution of the resources (Tarascon, 2010). Therefore, it is urgent to find other low-cost battery systems to replace lithium ion batteries. Sodium Ion Batteries (SIBs) have a wide sodium reserve and relatively low cost and are currently promising rechargeable batteries (Slateret al, 2013; Hwang, Myung and Sun, 2017). However, one of the challenges faced by sodium ion batteries is how to construct an electrode material that has excellent electrochemical properties and can be practically applied.

Many efforts have been made by researchers to develop electrode materials, particularly positive electrode materials, for novel sodium ion batteries. At present, the methodThere are two classes of positive electrode materials that have received great attention, the layered oxides of sodium and the polyanionic materials, respectively. In this regard, there are many reports on layered oxides (Doubaji et al, 2014; Hwang et al, 2019; Xiao et al, 2019) and polyanionic materials such as phosphates (Jian et al, 2012; Kim et al, 2013), fluorophosphates and sulfates (Barpanda et al, 2014; Dwibedi et al, 2016; Lander, Tarascon and Yamada, 2018). The layered oxide is known for its high capacity, but its cycling performance is poor (Kleiner et al, 2018), while the polyanionic material has higher working voltage and good cycling performance, showing better application prospects (Zhu et al, 2017; Yan et al, 2019). Among all polyanionic compounds, phosphate has attracted much attention because it has good structural stability due to its P — O bond, as compared to sulfate, which has low thermal decomposition and high water reactivity. The NASICON structure in phosphate has been extensively studied and is of the general formula Na₃M₂(PO₄)₃(M ═ transition metal). One of the widely studied materials, Na₃V₂(PO₄)₃The cathode material is a cathode material (Jianan et al, 2012,2013; Zhu et al, 2014; Xianghua Zhuang et al, 2019; Xinxin Zhuang et al, 2019) with good application prospect, and the electrochemical performance of the cathode material is equal to that of V³⁺/V⁴⁺Redox reactions around 3.4V are involved (Jian et al, 2012, 2013). However, the price of V salt is higher, which leads to higher cost of manufacturing electrode material.

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 method for producing a compound₃V₂(PO₄)₃Using Fe in each unit of the (NVP) structure²⁺And Na⁺Co-substitution of V³⁺Thereby preparing the high-performance sodium-deficient cathode material and simultaneously providing a sodium ion battery using the material as a cathode.

The invention provides a high-performance sodium-deficient cathode material which is characterized by having the following chemical formula: na (Na)_4-x□_xFeV(PO₄)₃Wherein, 0<x≤0.6。

The invention provides a high-performance sodium-deficient cathode material, which is also characterized in that the preparation method comprises the following steps: step 1, adding 1 part of NH by mol₄VO₃Dissolving in a solution containing a reducing agent to obtain a solution A; step 2, adding 1 part of Fe (NO) by mol₃)₃·9H₂O and 2 parts by mol of Na₂CO₃Dissolving in water to obtain solution B; step 3, mixing the solution A and the solution B, and adding 3 parts by mole of NH₄H₂PO₄Heating at 65-75 deg.c until the system is gel to obtain precursor; and 4, carrying out heat treatment on the precursor to obtain the high-performance sodium-deficient cathode material.

The invention provides a sodium ion battery, which is provided with a positive electrode, a negative electrode and an electrolyte, and is characterized in that the positive electrode comprises the following raw materials: a high performance sodium-deficient cathode material, at least one conductive material, and at least one polymeric binder.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: the preparation method of the positive electrode comprises the following steps: step 1, adding Na_4-x□_xFeV(PO₄)₃Dissolving the conductive material and the polymer adhesive in a solvent to obtain slurry; and 2, coating the slurry on a current collector, and removing the solvent to obtain the anode.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein, Na is contained in the positive electrode_4-x□_xFeV(PO₄)₃The content is 70 wt% -90 wt%.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein the conductive material is conductive carbon.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein the polymer binder is polyvinylidene fluoride or polytetrafluoroethylene.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein the electrolyte is an inorganic sodium conductor, a sodium conductive polymer or an electrolyte containing sodium salt.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein, when the electrolytic material is liquid, the battery also has a diaphragm, and the diaphragm is glass fiber.

In the sodium ion battery provided by the invention, the sodium ion battery also has the following characteristics: wherein the negative electrode is made of metallic sodium or a carbon-based material.

Action and Effect of the invention

According to the high-performance sodium-deficient cathode material, Fe is used²⁺And Na⁺Co-substitution of V³⁺. Therefore, not only the manufacturing cost of NASICON-type phosphate is reduced, but also the electrochemical activity of more than 2 sodium ions in the NASICON-type phosphate structure is stimulated, and extremely high stability, excellent rate performance and excellent coulombic efficiency are exhibited in the sodium ion battery.

According to the sodium ion battery of the present invention, Na is used_3.4□_0.6FeV(PO₄)₃

(NFVP) is used for preparing the positive electrode material, so that the sodium-ion battery provided by the invention has higher working voltage and good cycle performance.

Drawings

FIG. 1 is an XRD experimental spectrum and a simulation spectrum of NFVP prepared in example 1 of the present invention;

FIG. 2 is a schematic polyhedral diagram, a schematic Na atom position and an environmental diagram of an NFVP crystal produced in example 1 of the present invention;

FIG. 3 is an XPS spectrum of the 2p orbital of Fe in NFVP obtained in example 1 of the present invention;

FIG. 4 shows Fe 2p in NFVP prepared in example 1 of the present invention_3/2XPS nuclear level spectral fit of the rail;

FIG. 5 is an XPS fit spectrum of O1s and V2 p in NFVP from example 1 of the present invention;

FIG. 6 is an XPS fit spectrum of P2P in NFVP prepared in example 1 of the present invention;

FIG. 7 is a Scanning Electron Microscope (SEM) image of an NFVP made in example 1 of the present invention;

FIG. 8a is a constant current charging and discharging curve chart of the sodium ion battery provided in example 2 of the present invention when the voltage window is 1.5V-4.4V;

FIG. 8b is the CV plot of the first five cycles of the NFVP scan rate at 0.1mV/s over a voltage window of 1.5V to 4.4V in the sodium ion battery provided in example 2 of the present invention;

FIG. 9a is a constant current charging and discharging curve chart of the sodium ion battery provided in example 2 of the present invention when the voltage window is 2V-3.8V;

FIG. 9b is a CV graph of the first five cycles of the NFVP in a sodium ion battery provided in example 2 of the present invention over a voltage window of 2V to 3.8V at a scan rate of 0.1 mV/s;

fig. 10 is a graph of the rate performance of NFVP in a sodium-ion battery provided in example 2 of the present invention; and

fig. 11 is a graph showing the cycling performance of NFVP in the sodium-ion battery provided in example 2 of the present invention.

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>

This example provides a high performance sodium-deficient cathode material, which has a structural formula of Na_3.4□_0.6FeV(PO₄)₃(NFVP) is prepared by a sol-gel method in this example, and may be prepared by a solid-phase reaction method, a sintering method, or a solvothermal method in another example.

In this example, in Na_3.4□_0.6FeV(PO₄)₃The preparation method comprises the following steps:

step 1, NH is carried out at the temperature of 80 DEG C₄VO₃(241.86mg,2.068mmol) was dissolved in 20mL of ultrapure water containing citric acid (1.6g) as a reducing agent to give solution A;

step 2, adding Fe (NO)₃)₃·9H₂O (835.29mg,2.068mmol) and Na₂CO₃ (438.28mg,4.135mmol) in 40mL of ultrapure water to obtain a solution B;

step 3, mixing the solution A and the solution B, stirring for 30 minutes, and adding NH₄H₂PO₄(713.49mg,6.202mmol) is heated to 70 ℃ until the system is gelatinous, and a precursor is obtained;

s4, keeping the temperature of the precursor at 200 ℃ for 4 hours to obtain solid powder, and heating the solid powder at 650 ℃ for 24 hours under argon to obtain Na_3.4□_0.6FeV(PO₄)₃。

< example 2>

This example provides a sodium ion battery having an NFVP electrode as the positive electrode comprising the high performance sodium-deficient positive electrode material provided in example 1, a metal sodium as the counter electrode, and 1M sodium perchlorate (NaClO) containing 5 wt% of vinyl fluoride carbonate (FEC) as the electrolyte₄) The diaphragm was glass fiber (GF/D, Whatman). The button cells (CR2025) were assembled in a glove box filled with argon.

In other embodiments, the electrolyte may be a solid composed of an inorganic sodium conductor or a sodium conductive polymer, or may be a solution in which a sodium salt is dissolved. In a solution in which the sodium salt is dissolved, preferably NaPF₆、NaClO₄And the like, the solvent may be selected from organic carbonate type solvents containing unsaturated cyclic carbonate groups (e.g., ethylene carbonate, propylene carbonate, butylene carbonate, ethylene fluorocarbon and propylene fluorocarbon) or unsaturated acyclic carbonates (e.g., dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and fluorinated acyclic carbonates, etc.), and some ester type solvents are also suitable for use in combination with carbonates (e.g., propyl propionate, ethyl propionate, etc.).

Wherein the NFVP electrode is composed of 70 wt% Na prepared in example 1_3.4□_0.6FeV(PO₄)₃20% by weight of conductive carbon black (Super P), 10% by weight of polyvinylidene fluoride (PVDF, binder).

In this embodiment, the preparation method of the NFVP electrode includes the following steps:

step 1, adding Na_4-x□_xFeV(PO₄)₃Conductive carbon black (Super product of Timcal)

) And polyvinylidene fluoride (PVDF, binder) is dissolved in a proper amount of N-methyl-2-pyrrolidone (NMP) to obtain slurry;

step 2, coating the slurry on an aluminum foil, wherein the coating amount is controlled to be 1.0-1.2mg/cm²Drying to remove the solvent, and cutting into round pieces with diameter of 8mm to obtain the anode.

< test example 1>

For the high-performance sodium-deficient cathode material Na prepared in example 1_3.4□_0.6FeV(PO₄)₃(NFVP) was subjected to multiple characterizations as follows:

quantitative analysis of NFVP was performed by Agilent ICP-OES spectrometer, and the results showed that Na, Fe, V, P, 3.39:0.98:1.03:3.07, which confirmed synthesis of Na_3.4FeV(PO4)₃. To demonstrate the phase purity of the target compound, high-precision X-ray powder diffraction was performed at room temperature using a Rigaku Ultima type IV X-ray diffractometer in a scanning mode of theta-theta with a radiation source of Cu

Data are collected in 0.015 ° steps over an angle range of 2 θ of 10 ° ≦ 2 θ ≦ 100 °.

FIG. 1 is an XRD experimental spectrum and a simulation spectrum of NFVP prepared in example 1 of the present invention.

The structural refinement of NFVP is carried out by the Rietveld method (Rietveld,1969) using a phosphate like NASICON type such as Na₄Fe²⁺Fe³⁺(PO₄)₃(Hatert,2009) was used as a control, and as shown in FIG. 1, the refined sodium-deficient phosphate crystal structure obtained was of the trigonal system with space group R c. The refinement results show that atoms V1 and Fe1 share this particular position of 12c in the final crystallographic model, and the occupancy is 50% each. The sodium atoms Na1 and Na2 are located at specific positions 6b and 18e, respectively. The occupancy rates of Na1 and Na2 after refinement were 92.75% and 83%, respectively, so the final material had the formula Na_3.4□_0.6FeV(PO₄)₃Deletion of 0.6 Na⁺. The experimental spectrum and the calculation spectrum of the refined crystal structure can be well matched.

Fig. 2 is a polyhedral schematic diagram, a Na atom position and an environmental schematic diagram of the NFVP crystal produced in example 1 of the present invention.

As shown in fig. 2, the crystal structure of NFVP is a typical NASICON structure, which is composed of shared angular positions of PO4 tetrahedra and (Fe/V) O6 octahedra, i.e., forming so-called "lantern units" (masquerier et al, 2000). The connection of the structural units by the corners creates a three-dimensional open framework. An atom of Na1 located between two lantern units and an atom of oxygen (Na 1-O2.468 (6)

) To form a hexa-coordinated and octa-coordinated Na2 atom (Na 2-O-2.440 (4) -2.906(6)

) The same z position as the phosphorus atom, and specific crystallographic data and structural refinement details are shown in table 1.

TABLE 1 Crystal data, data Collection and Structure refinement details of NFVP

FIG. 3 is an XPS spectrum of the 2p orbital of Fe in NFVP prepared in example 1 of the present invention. FIG. 4 shows Fe 2p in NFVP prepared in example 1 of the present invention_3/2XPS nuclear power level spectral fit of the orbits. FIG. 5 is an XPS fit spectrum of O1s and V2 p in NFVP from example 1 of the present invention. FIG. 6 is an XPS fit spectrum of P2P in NFVP obtained in example 1 of the present invention.

X-ray photoelectron spectroscopy (XPS) was performed on a photoelectron spectrometer model ESCALAB 250Xi using an Al K α source.

As shown in FIG. 3, due to spin-orbit coupling, the Fe 2p spectrum has two parts, including Fe 2p_3/2And Fe 2p_1/2Two core energy levels. To demonstrate the oxidation state of iron in NFVP, fitting spectra using Gupta and sen (gs) multiplets gave better results; this method was first used by Grosvenor et al (Grosvenor et al, 2004) and published as a rational fit procedure for Fe 2p3/2 spectra (Mullet, Khare and Ruby, 2008; Biesinger et al, 2011).

As shown in FIG. 4, in this study, Fe 2p_3/2In addition to the surface peaks, Fe is used for spectrum fitting²⁺And Fe³⁺The fitting was performed for three and four multiplets. Table 2 summarizes the fitting results. Obtained Fe²⁺/Fe³⁺The ratio was 0.4/0.6, which is consistent with the refinement results.

As shown in FIG. 5, it can be clearly seen that the broad peaks at 523.24eV and 516.36eV correspond to V2 p_1/2And V2 p_3/2Core energy level of V³⁺The characteristics of (1). The peak of V2 p is broadened and has a lower binding energy, which is consistent with the vanadium (III) based compounds reported in the literature (Silversmit et al, 2004; Chen et al, 2018; Xinxin Zhang et al, 2019).

As shown in FIG. 6, fitting the XPS spectra of P2P, the peaks at 133.41eV and 132.53 eV can correspond to P2P respectively_1/2And P2P_3/2Between the energy levels, a splitting energy of 0.88eV is generated, indicating the presence of a phosphate radical, i.e., PO₄ ^3-。

TABLE 2 high spin Fe in NFVP²⁺And Fe³⁺GS MultiPeak fitting parameters of Components

FIG. 7 is a Scanning Electron Microscope (SEM) image of the NFVP produced in example 1 of the present invention.

The powder morphology was characterized using a Zeiss Supra model 55 Scanning Electron Microscope (SEM), as shown in FIG. 7. The formation of agglomerated nanoparticles in the microporous structure can be clearly observed in the SEM image.

< test example 2>

The sodium ion battery prepared in example 2 was subjected to a constant current cyclic charge and discharge test and a cyclic voltammetry test.

Fig. 8a is a constant current charging and discharging curve diagram of the sodium ion battery provided by the embodiment 2 of the invention when the voltage window is 1.5V-4.4V. Fig. 8b is a CV graph of the first five cycles of the NFVP scan rate of 0.1mV/s over a voltage window of 1.5V to 4.4V in a sodium-ion battery provided in example 2 of the present invention. Fig. 9a is a constant current charging and discharging curve diagram of the sodium ion battery provided by the embodiment 2 of the invention when the voltage window is 2V-3.8V. Fig. 9b is a CV graph of the first five cycles of the NFVP scan rate of 0.1mV/s over a voltage window of 2V to 3.8V in a sodium-ion battery provided in example 2 of the present invention.

In this example, a constant current cyclic charge and discharge test was performed using a NEWARE cell test system. As shown in FIG. 8, the cell test was conducted at 0.5C in a voltage range of 1.5-4.4V (1C corresponds to 2 Na exchanges in 1 hour)⁺) Is carried out at a current density of (1). The first charge and discharge capacity is 163.5 and 170mA/g, that is to say, about 2.95Na is removed during charge and discharge⁺Then insert about 3.06Na⁺. The reversible capacity at the fifth cycle was 161 mAh/g. The initial coulombic efficiency of this material was as high as 96.2%, indicating low initial sodium loss, which also makes this new NASICON phosphate promising for the positive electrode of SIB full cells.

As shown in FIG. 8, CV measurements taken over a voltage range of 1.5-4.4V at a scan rate of 0.1mV/s highlighted three oxidation peaks, at 2.55, 3.48 and 4.04V, respectively, for Fe²⁺/Fe³⁺、V³⁺/V⁴⁺And V⁴⁺/V⁵A redox couple.

At the same rate we studied the electrochemical performance at a voltage window of 2-3.8V, as shown in FIG. 9, where it can be clearly observed that the reversible capacity is 118mAh/g due to about 2.13Na extraction/insertion⁺Has high stability. The overlapping CV curves also demonstrate that NFVP has very high stability over this voltage range.

Fig. 10 is a graph of the rate performance of NFVP in the sodium-ion battery provided in example 2 of the present invention.

As shown in fig. 10, the rate performance of the NFVP electrode was tested at different current rates in a voltage window of 2-3.8V, with the highest current being 10C (1.1A/g), demonstrating excellent rate performance of NFVP.

In this test example, cyclic voltammetry was performed using a Bio-Logic VMP-3 type electrochemical workstation. As shown in fig. 11, after a plurality of charge and discharge cycles of NFVP at 5C (550mA/g), the capacity of 99.42% can be maintained after 300 cycles, i.e. the capacity is 108mAh/g after 300 cycles, which proves that the material has stable cycling performance, and also has excellent coulomb efficiency (about 100%).

Effects and effects of the embodiments

According to the high-performance sodium-deficient cathode material related to example 1, Fe is used²⁺And Na⁺Co-substitution of V³⁺. Therefore, not only the manufacturing cost of NASICON-type phosphate is reduced, but also the electrochemical activity of more than 2 sodium ions in the NASICON-type phosphate structure is stimulated, and extremely high stability, excellent rate performance and excellent coulombic efficiency are exhibited in the sodium ion battery.

According to the sodium ion battery of example 2, Na is used_3.4□_0.6FeV(PO₄)₃The positive electrode material is prepared, so that the sodium ion battery provided by the example 2 has higher working voltage and good cycle performance.

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 high-performance sodium-deficient cathode material is characterized by having the following chemical formula:

Na_3.4□_0.6Fe²⁺ _0.4Fe³⁺ _0.6V³⁺(PO₄)₃，

the preparation method of the high-performance sodium-deficient cathode material comprises the following steps:

step 1, adding 1 part of NH by mol₄VO₃Dissolving in a solution containing a reducing agent to obtain a solution A;

step 2, adding 1 part of Fe (NO) by mol₃)₃·9H₂O and 2 parts by mol of Na₂CO₃Dissolving in water to obtain solution B;

step 3, mixing the solution A and the solution B, and adding 3 parts by mole of NH₄H₂PO₄Heating at 65-75 deg.c until the system is gel to obtain precursor;

and 4, carrying out heat treatment on the precursor to obtain the high-performance sodium-deficient cathode material.

2. A sodium ion battery having a positive electrode, a negative electrode and an electrolyte, characterized in that:

wherein, the raw materials of the positive electrode comprise: the high performance sodium-deficient positive electrode material of claim 1, at least one electrically conductive material, and at least one polymeric binder.

3. The sodium-ion battery of claim 2, wherein:

the preparation method of the positive electrode comprises the following steps:

step 1, adding Na_3.4□_0.6Fe²⁺ _0.4Fe³⁺ _0.6V³⁺(PO₄)₃Dissolving the conductive material and the polymer adhesive in a solvent to obtain slurry;

and 2, coating the slurry on a current collector, and removing the solvent to obtain the anode.

4. The sodium-ion battery of claim 2, wherein:

wherein Na in the positive electrode_3.4□_0.6Fe²⁺ _0.4Fe³⁺ _0.6V³⁺(PO₄)₃The content is 70 wt% -90 wt%.

5. The sodium-ion battery of claim 2,

wherein the conductive material is conductive carbon.

6. The sodium-ion battery of claim 2,

wherein the polymer binder is polyvinylidene fluoride or polytetrafluoroethylene.

7. The sodium-ion battery of claim 2,

wherein the electrolyte is an inorganic sodium conductor, a sodium conductive polymer or an electrolyte containing sodium salt.

8. The sodium-ion battery of claim 2,

wherein, when the electrolyte material is liquid, the battery further has a separator, and the separator is glass fiber.

9. The sodium-ion battery of claim 2,

wherein the negative electrode is made of metallic sodium or a carbon-based material.