CN113054184A - Symmetric sodium-ion battery and preparation method thereof - Google Patents

Symmetric sodium-ion battery and preparation method thereof Download PDF

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CN113054184A
CN113054184A CN201911378487.6A CN201911378487A CN113054184A CN 113054184 A CN113054184 A CN 113054184A CN 201911378487 A CN201911378487 A CN 201911378487A CN 113054184 A CN113054184 A CN 113054184A
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sodium
negative electrode
equal
positive electrode
ion battery
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CN113054184B (en
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钱韫娴
邓永红
王军
康媛媛
马鑫
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Shenzhen Capchem Technology Co Ltd
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Shenzhen Capchem Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

In order to solve the problem of slow diffusion of sodium ions in the conventional symmetric sodium ion battery, the invention provides a symmetric sodium ion battery which comprises a positive electrode, a negative electrode and electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, the positive electrode comprises a positive electrode material, the negative electrode comprises a negative electrode material, and active materials of the positive electrode material and the negative electrode material both comprise a general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5. Meanwhile, the invention also discloses a preparation method of the symmetrical sodium-ion battery. The symmetrical sodium ion battery provided by the invention adopts the general formula Na7±xV3±y(P2O7)4The sodium pyrophosphate is used as a positive electrode active material and a negative electrode active material and hasThe faster sodium ion de-intercalation capability is beneficial to improving the rate discharge capability, and meanwhile, the symmetric sodium ion battery has excellent cycle stability.

Description

Symmetric sodium-ion battery and preparation method thereof
Technical Field
The invention belongs to the technical field of symmetric sodium-ion batteries, and particularly relates to a symmetric sodium-ion battery and a preparation method thereof.
Background
Lithium ion batteries have been rapidly developed in the fields of electric vehicles and energy storage due to the advantages of environmental friendliness, high energy density and power density, and the like. However, as the demand for lithium ion batteries is increasing due to social development, the high cost of lithium ion batteries has become a major problem. In recent years, sodium ion batteries have been considered as a new battery most likely to replace lithium ion batteries due to their low cost. The low cost of the sodium-ion battery is embodied in the following aspects: sodium is stored in vast quantities on earth and widely distributed in the form of salts on land and in the sea; with the advance of research on sodium ion positive electrode materials, more mature cobalt-free layered positive electrode materials have been developed nowadays; in addition, another advantage of low cost of the sodium ion battery is the utilization of the current collector, and since sodium ions cannot form alloy with aluminum, the traditional copper negative current collector in the lithium ion battery can be replaced by aluminum foil with low price in the sodium ion battery. Therefore, the sodium ion battery has great advantages in cost, and especially, with the increasing price of lithium in the future, the sodium ion battery has more prominent and important application prospects in the fields of electric automobiles and large-scale energy storage batteries.
The common cathode materials of the existing sodium ion battery are hard carbon, titanium-containing oxide and the like. Common cathode materials include Prussian blue, phosphate systems and layered sodium transition metal oxides (chemical formula: Na)xTMO2Wherein TM represents transition metal such as Mn, Ni, Fe, Ti and V). However, the asymmetric sodium ion battery composed of different anode and cathode materials has complex process and high cost. The existing symmetrical sodium-ion battery uses a single active material as a positive electrode material and a negative electrode material at the same time, can simplify the battery design and reduce the production cost, but the requirement of the symmetrical sodium-ion battery on the electrode material is higher, and the common electrode material is difficult to be applied to the symmetrical sodium-ion battery. In the sodium ion battery bodyThe electrode of the existing symmetric sodium-ion battery is reported to be mainly P2-Na0.66LixMn0.5Ti0.5O2，O3-Na0.8Ni0.4Ti0.6O2，Na3Co0.5Mn0.5Ti(PO4)3，P2-Na0.66Ni0.17Co0.17Ti0.66O2，Na2.55V6O16·0.6H2O，P2-Na0.6[Cr0.6Ti0.4]O2，Na2VTi(PO4)3And Na3V2(PO4)3These materials are used. However, these materials suffer from slow diffusion of sodium ions, e.g., Qiuyue Wang et al tested Na3V2(PO4)3As the migration rate of sodium ions as an electrode material, Na was obtained as a result of low carbon content3V2(PO4)3The migration velocity of sodium ions as an electrode material was 10-13To 10-15.5cm2s-1And at high carbon content, Na3V2(PO4)3The migration speed of sodium ions as electrode material can only reach 10-12.7To 10-15.1cm2s-1Therefore, the sodium ion migration speed of the electrode material is low, the use of the battery under large current is not facilitated, the battery cannot meet the requirements of high-rate large-current charging and discharging, and the application of the sodium ion battery in the fields of electric automobiles and large-scale energy storage batteries is not facilitated.
Disclosure of Invention
The invention provides a symmetric sodium-ion battery and a preparation method thereof, aiming at the problem that the existing symmetric sodium-ion battery has slow sodium ion diffusion.
The technical scheme adopted by the invention for solving the technical problems is as follows:
in one aspect, the invention provides a symmetric sodium-ion battery, which comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, the positive electrode comprises a positive electrode material, and the negative electrode comprises a negative electrodeThe active materials of the positive electrode material and the negative electrode material both comprise a general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
Optionally, the active materials of the positive electrode material and the negative electrode material further include carbon, the carbon is coated on the sodium pyrophosphate, and the content of the carbon in the active materials is 0-15 wt.%.
Optionally, the positive electrode material further comprises a positive electrode conductive agent and a positive electrode binder, and in the positive electrode material, the mass fraction of the positive electrode active material is greater than or equal to 70%;
the positive electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nano tubes and graphene;
the positive adhesive comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
Optionally, the negative electrode material further comprises a negative electrode conductive agent and a negative electrode binder, and in the negative electrode material, the mass fraction of the negative electrode active material is greater than or equal to 70%;
the negative electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nano tubes and graphene;
the negative electrode binder comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
Optionally, the electrolyte comprises a solvent comprising one or more of EC, PC, DEC, DMC, EMC.
In another aspect, the present invention provides a method for preparing a symmetric sodium-ion battery as described above, comprising the following steps:
mixing the sodium source precursor, the vanadium source precursor and the phosphoric acid source precursor, and calcining in a protective atmosphere to obtain the general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to0.5；
Preparing a working electrode by adopting an active material comprising the sodium pyrophosphate, preparing a sodium metal battery by adopting sodium metal as a counter electrode, discharging, charging, and taking out the working electrode;
and respectively taking the two working electrodes as a positive electrode and a negative electrode to be assembled with electrolyte together to obtain the symmetrical sodium-ion battery.
Optionally, the sodium source precursor comprises one or more of sodium acetate, sodium oxalate, sodium carbonate and sodium hydroxide, the vanadium source precursor comprises one or more of vanadium pentoxide, vanadium dioxide and ammonium metabisulfite, and the phosphoric acid source precursor comprises one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or sodium phosphate.
Optionally, the mixing molar ratio of the sodium element of the sodium source precursor, the vanadium element of the vanadium source precursor and the phosphorus element of the phosphoric acid source precursor is 7 ± x: 3 +/-y: 8, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
Optionally, when the materials are mixed, a carbon compound is further added, wherein the carbon compound accounts for 0-20 wt% of the total mixed materials, and the carbon compound comprises one or more of citric acid and glucose.
Optionally, the temperature of the calcination operation is 200-750 ℃, the calcination time is 1-22 h, and after the calcination is completed, the sodium pyrophosphate is washed in water bath at the temperature of 20-100 ℃.
The symmetrical sodium ion battery provided by the invention adopts the general formula Na7±xV3±y(P2O7)4Experiments show that compared with the existing symmetric sodium ion battery adopting other electrode materials, the positive electrode material and the negative electrode material obtained by the invention have higher sodium ion de-intercalation capability, are beneficial to improving the rate discharge capability, and can meet the requirements of high-rate heavy-current charging and discharging of the obtained symmetric sodium ion batteryRing stability.
Drawings
FIG. 1 is an XRD spectrum provided in examples 1 to 3 of the present invention;
FIG. 2 shows Na in examples 1 to 4 of the present invention7±xV3±y(P2O7)4The crystal structure of (a);
FIG. 3 shows Na provided in example 3 of the present invention6.88V2.81(P2O7)4Electron microscope photograph of (1);
FIG. 4 is a sample thermogravimetric plot provided in example 3 of the present invention;
FIG. 5 shows a composition containing Na according to example 5 of the present invention6.88V2.81(P2O7)4GITT plots for positive electrode testing of active materials;
FIG. 6 shows a sample containing Na according to example 5 of the present invention6.88V2.81(P2O7)4The first three-turn charge-discharge curve of the positive electrode test of the active material;
FIG. 7 shows a composition containing Na according to example 5 of the present invention6.88V2.81(P2O7)4GITT plots for negative electrode testing of active materials;
FIG. 8 shows a sample containing Na according to example 5 of the present invention6.88V2.81(P2O7)4The first three-turn charge-discharge curve of the negative electrode test of the active material;
FIG. 9 shows a sample containing Na according to example 5 of the present invention6.88V2.81(P2O7)4A rate performance graph of positive or negative electrode testing of the active material;
FIG. 10 shows a sample containing Na according to example 5 of the present invention6.88V2.81(P2O7)4Cycle performance plot at 0.5C for positive or negative electrode test of active materials;
FIG. 11 shows a sample containing Na according to example 5 of the present invention6.88V2.81(P2O7)4Cycle performance plot at 2C for positive or negative electrode test of active materials;
fig. 12 is a discharge curve of the symmetric sodium-ion battery provided in example 6 at different current densities;
fig. 13 is a graph of the cycling performance of the symmetric sodium-ion battery provided in example 6.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
An embodiment of the invention provides a symmetric sodium-ion battery, which comprises a positive electrode, a negative electrode and electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, the positive electrode comprises a positive electrode material, the negative electrode comprises a negative electrode material, and active materials of the positive electrode material and the negative electrode material both comprise a general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
The symmetrical sodium ion battery provided by the invention adopts the general formula Na7±xV3±y(P2O7)4Experiments show that compared with the existing symmetric sodium ion battery adopting other electrode materials, the positive electrode material and the negative electrode material obtained by the invention have higher sodium ion de-intercalation capability, are beneficial to improving the rate discharge capability, and can meet the requirements of high-rate heavy-current charging and discharging of the obtained symmetric sodium ion battery.
In some embodiments, the active materials of the positive electrode material and the negative electrode material further comprise carbon coated on the sodium pyrophosphate, and the content of carbon in the active materials is 0-15 wt.%.
In some embodiments, the carbon comprises one or more of graphite, graphene, hard carbon, nanocarbon, fibrous carbon, amorphous carbon.
In some embodiments, the positive electrode material further comprises a positive electrode conductive agent and a positive electrode binder, and the mass fraction of the active material in the positive electrode material is greater than or equal to 70%. If the amount of the active material added is too low, the energy density of the battery tends to decrease.
The positive electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nanotubes and graphene.
The positive adhesive comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
In some embodiments, the negative electrode material further comprises a negative electrode conductive agent and a negative electrode binder, and the mass fraction of the active material in the negative electrode material is greater than or equal to 70%. If the amount of the active material added is too low, the energy density of the battery tends to decrease.
The negative electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nanotubes and graphene.
The negative electrode binder comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
In some embodiments, the electrolyte comprises a solvent comprising one or more of EC (ethylene carbonate), PC (propylene carbonate), DEC (diethyl carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate).
In some embodiments, the electrolyte further comprises additives, and the additives can be various electrolyte additives in the art, such as FEC (fluoroethylene carbonate).
In some embodiments, the symmetric sodium-ion battery further comprises a positive current collector and a negative current collector, wherein the positive material is disposed on the positive current collector, and the negative material is disposed on the negative current collector.
The positive electrode current collector and the negative electrode current collector may be independently selected from a sheet structure or a foamed porous structure, for example, when the positive electrode current collector has a sheet structure, the positive electrode material may be coated on the surface of the positive electrode current collector in the form of slurry and dried to be molded; when the positive electrode current collector has a foam porous structure, the positive electrode material may be embedded in pores of the foam porous structure.
The positive electrode current collector and the negative electrode current collector may be selected from various types of conductive materials.
In a preferred embodiment, the positive electrode current collector and the negative electrode current collector are each selected from aluminum foil.
In some embodiments, the symmetric sodium-ion battery further comprises a separator between the positive electrode material and the negative electrode material.
Another embodiment of the present invention provides a method for preparing a symmetric sodium-ion battery as described above, comprising the following steps:
mixing the sodium source precursor, the vanadium source precursor and the phosphoric acid source precursor, and calcining in a protective atmosphere to obtain the general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5;
preparing a working electrode by adopting an active material comprising the sodium pyrophosphate, preparing a sodium metal battery by adopting sodium metal as a counter electrode, discharging, charging, and taking out the working electrode;
and respectively taking the two working electrodes as a positive electrode and a negative electrode to be assembled with electrolyte together to obtain the symmetrical sodium-ion battery.
In the preparation method, the compound of the general formula Na7±xV3±y(P2O7)4The working electrode of the sodium pyrophosphate and sodium metal are subjected to electrochemical pre-charging and discharging treatment to activate the working electrode, meanwhile, the surface of the working electrode is provided with a stable solid-liquid surface membrane, and the symmetrical sodium ion battery is assembled after the working electrode is taken out, so that the improvement of the cycle stability of the symmetrical sodium ion battery is facilitated.
In some embodiments, the "charge after discharge" condition is constant current charge after constant current discharge.
In some embodiments, the sodium source precursor comprises one or more of sodium acetate, sodium oxalate, sodium carbonate, sodium hydroxide, the vanadium source precursor comprises one or more of vanadium pentoxide, vanadium dioxide, and ammonium metavanadate, and the phosphoric acid source precursor comprises one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or sodium collodion phosphate.
In some embodiments, the sodium element of the sodium source precursor, the vanadium element of the vanadium source precursor, and the phosphorus element of the phosphoric acid source precursor are mixed at a molar ratio of 7 ± x: 3 +/-y: 8, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
In some embodiments, a carbon compound is added during the material mixing, and the carbon compound accounts for 0-20 wt% of the total mixed material.
In some preferred embodiments, the carbon compound comprises one or more of citric acid, glucose.
In some embodiments, the temperature of the calcination operation is 200 to 750 ℃ and the calcination time is 1 to 22 hours.
In some embodiments, after the calcination is completed, the sodium pyro-phosphate is washed in a water bath at a temperature of 20-100 ℃.
And (3) cleaning impurities in the calcined product through water bath, and improving the purity of the sodium pyrophosphate in the product.
The present invention will be further illustrated by the following examples.
Example 1
This example is used to illustrate the sodium pyrophosphate and the preparation method thereof adopted in the present invention, and includes the following steps:
anhydrous sodium acetate (CH)3COO) Na, ammonium metavanadate NH4VO3Phosphoric acid diamine NH4H2PO4According to the following steps: 3: mixing 8 mol ratio, 1g of citric acid and 0.2g of glucose, dissolving in 150ml of water, removing water from the obtained solution at 110 ℃, presintering the obtained powder at 300 ℃ for 2h in an argon atmosphere, sintering at 550 ℃ for 10h, cooling, and washing by a water bath at 40 ℃ to obtain a sample. The sample obtained was carbon-coated Na by ICP test6.60V2.58(P2O7)4The crystal structure was monoclinic, and the carbon content was 5 wt.%.
Example 2
This example is used to illustrate the sodium pyrophosphate and the preparation method thereof adopted in the present invention, and includes the following steps:
anhydrous sodium acetate (CH)3COO) Na, ammonium metavanadate NH4VO3Phosphoric acid diamine NH4H2PO4According to the following steps of 3: 1: mixing 3 mol ratio, 0.5g of citric acid and 1.5g of glucose, dissolving in 150ml of water, removing water from the obtained solution at 110 ℃, presintering the obtained powder at 300 ℃ for 2h in an argon atmosphere, sintering at 650 ℃ for 10h, cooling, and washing by using a water bath at 80 ℃ to obtain a sample. The sample obtained was carbon-coated Na by ICP test6.96V3.02(P2O7)4The crystal structure was monoclinic, and the carbon content was 8 wt.%.
Example 3
This example is used to illustrate the sodium pyrophosphate and the preparation method thereof adopted in the present invention, and includes the following steps:
anhydrous sodium acetate (CH)3COO) Na, ammonium metavanadate NH4VO3Phosphoric acid diamine NH4H2PO4According to the following steps: 1: mixing and dissolving 4 mol ratio, 2g of citric acid and 1g of glucose in 150ml of water, removing water from the obtained solution at 110 ℃, presintering the obtained powder at 300 ℃ for 2h in an argon atmosphere, sintering at 600 ℃ for 10h, cooling, and washing in a water bath at 80 ℃ to obtain a sample. The sample obtained was carbon-coated Na by ICP test6.88V2.81(P2O7)4. The crystal structure is monoclinic structure, and the carbon content is 12 wt.%.
Example 4
This example is used to illustrate the sodium pyrophosphate and the preparation method thereof adopted in the present invention, and includes the following steps:
mixing sodium carbonate Na2CO3Diammonium hydrogen phosphate (NH)4)2HPO4Sodium phosphate Na4P2O7With vanadium pentoxide2O5According to the following steps of 3: 12: 2: ball milling and mixing 3 mol ratio, dissolving in 150ml water, presintering the obtained powder for 1h at 400 ℃ in an argon atmosphere, sintering for 20h at 650 ℃, cooling, and washing in 80 ℃ water bath to obtain a sample. The sample obtained is Na by ICP test6.90V2.90(P2O7)4. The crystal structure is a monoclinic structure.
Example 5
This example is used to illustrate a sodium metal battery using sodium pyrophosphate as a positive electrode or a negative electrode and a preparation method thereof, and includes the following steps:
carbon-coated Na obtained in example 36.88V2.81(P2O7)4Mixing the active material with conductive carbon black and polyvinylidene fluoride (PVdF) adhesive according to the mass ratio of 8:1:1, dissolving the mixture in N-methylpyrrolidone (NMP) solvent to prepare slurry, coating the slurry on an aluminum foil, drying and cutting the aluminum foil to obtain the pole piece.
Assembling the obtained pole piece, sodium metal and a diaphragm into a sodium metal battery, wherein the solvent of the electrolyte of the sodium metal battery is an EC/PC mixture with the volume ratio of 1:1, and the solute is 1M NaPF6And 1 wt.% of FEC, and standing for 24h to obtain the sodium metal battery after the voltage is stabilized.
Example 6
This embodiment is used to illustrate a symmetric sodium-ion battery and a method for manufacturing the same disclosed in the present invention, and the method includes the following steps:
carbon-coated Na obtained in example 36.88V2.81(P2O7)4Mixing the active material with conductive carbon black and polyvinylidene fluoride (PVdF) adhesive according to the mass ratio of 8:1:1, dissolving the mixture in N-methylpyrrolidone (NMP) solvent to prepare slurry, coating the slurry on an aluminum foil, drying and cutting the aluminum foil to obtain the pole piece.
Assembling the obtained pole piece, sodium metal and a diaphragm into a sodium metal battery, wherein the solvent of the electrolyte of the sodium metal battery is an EC/PC mixture with the volume ratio of 1:1, and the solute is 1M NaPF6And 1 wt.% FEC, which was charged at 0.1C after standing for 24h for voltage stabilizationPerforming one-circle discharge and charge test under the current density to obtain Na with stable solid-liquid surface film and high coulombic efficiency6.88V2.81(P2O7)4And an electrode.
Will obtain Na6.88V2.81(P2O7)4One of the electrodes is used as a positive electrode, the other electrode is used as a negative electrode, and the electrodes and the diaphragm are assembled into a symmetrical sodium-ion battery.
Performance testing
First, Na prepared in example 1 to 36.60V2.58(P2O7)4、Na6.96V3.02(P2O7)4、Na6.88V2.81(P2O7)4The XRD spectrum obtained by X-ray diffraction is shown in figure 1. It can be seen that the crystal structure is shown in FIG. 2.
Second, the carbon-coated Na prepared in example 3 was used6.88V2.81(P2O7)4The microscopic topography map obtained by electron microscope observation is shown in FIG. 3.
Thirdly, carbon-coated Na prepared in example 36.88V2.81(P2O7)4Thermogravimetric analysis was performed, and the obtained thermogravimetric plot is shown in fig. 4, from which fig. 4 it can be seen that Na coated with carbon6.88V2.81(P2O7)4The content of C in the product is 12%.
Fourthly, Na coated by carbon6.88V2.81(P2O7)4The performance of the positive electrode of the sodium metal battery prepared in example 5 was tested as a positive electrode in the following manner: constant current intermittent titration (GITT) and charge and discharge tests were performed at a current density of 0.1C at 2.5-4.35V, and the test results are shown in FIG. 5, FIG. 6 and FIGS. 9-11.
The obtained GITT results are shown in FIG. 5, and the diffusion coefficient of sodium ions at the positive electrode is 3.3 x 10-3～4.4*10-9cm2The/s range, which is significantly higher than the sodium ion diffusion rate of other materials disclosed in the prior art as electrode materials. .
FIG. 6 is the charge-discharge curve of the first three circles of the positive electrode, the specific discharge capacity is about 60mAh/g, and the discharge voltage plateau is as high as 4.0V. The charge-discharge current density is improved, and the capacity of the charge-discharge current density is not obviously attenuated in the first three circles of charge-discharge processes.
As shown in fig. 9 to 11, the excellent rate performance of the material as a positive electrode is explained. The capacity retention rates of the alloy after being cycled for 400 circles at the current density of 0.5C and 500 circles at the current density of 2C are 94.5 percent and 87.9 percent respectively.
V, Na coated with carbon6.88V2.81(P2O7)4The sodium metal battery prepared in example 5 was tested for negative electrode performance in the following manner: constant current intermittent titration (GITT) and charge-discharge test are carried out at 0.5-2.5V and 0.1C current density. The test results are shown in FIGS. 7, 8 and 9 to 11.
The GITT results are shown in FIG. 7, where the diffusion coefficient of sodium ions in the negative electrode is 5.5 x 10-5～1.4*10-10cm2The/s range, which is significantly higher than the sodium ion diffusion rate of other materials disclosed in the prior art as electrode materials.
FIG. 8 is the charge-discharge curve of the first three circles of the negative electrode, and the specific charge capacity is about 68 mAh/g. The capacity of the lithium ion battery is not obviously attenuated by improving the charge and discharge current density.
As shown in fig. 9 to 11, the excellent rate performance of this material as a negative electrode is explained. The capacity retention rates of the lithium ion battery are 87% and 86.3% respectively after the lithium ion battery is cycled for 400 circles at a current density of 0.5C and is cycled for 500 circles at a current density of 2C.
Sixthly, the charge and discharge test is carried out on the symmetric sodium-ion battery prepared in the example 6, the test voltage range is 0.01-3.85V, and the test results are shown in fig. 12 and 13.
As can be seen from fig. 12 and 13, the discharge specific capacity of the symmetric sodium ion battery at 10C current density is as high as 45mAh/g, which indicates that the material system has excellent high-rate discharge capability, because pyrophosphate has a lower sodium ion transport barrier and a faster sodium ion transport capability than that of a phosphate crystal structure, and the phosphate crystal cannot realize high-rate charge and discharge due to the limited sodium ion transport capability; . In addition, the symmetric sodium-ion battery is cycled for 500 cycles under the current density of 2C, the capacity retention rate is as high as 81.7%, and the high-rate cycle performance is excellent. Compared with other symmetric sodium-ion battery systems, the energy density retention rate is more excellent due to the stability of the crystal structure.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. The symmetrical sodium-ion battery is characterized by comprising a positive electrode, a negative electrode and electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, the positive electrode comprises a positive electrode material, the negative electrode comprises a negative electrode material, and active materials of the positive electrode material and the negative electrode material both comprise a general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
2. The symmetric sodium-ion battery of claim 1, wherein the active materials of the positive electrode material and the negative electrode material further comprise carbon coated on the sodium pyrophosphate, and the content of carbon in the active materials is 0-15 wt.%.
3. The symmetric sodium-ion battery of claim 1 or 2, wherein the positive electrode material further comprises a positive electrode conductive agent and a positive electrode binder, and the mass fraction of the active material in the positive electrode material is greater than or equal to 70%;
the positive electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nano tubes and graphene;
the positive adhesive comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
4. The symmetric sodium-ion battery of claim 1 or 2, wherein the negative electrode material further comprises a negative electrode conductive agent and a negative electrode binder, and the mass fraction of the active material in the negative electrode material is greater than or equal to 70%;
the negative electrode conductive agent comprises one or more of carbon black, acetylene black, conductive graphite, carbon nano tubes and graphene;
the negative electrode binder comprises one or more of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, vinylidene fluoride and polytetrafluoroethylene.
5. The symmetric sodium-ion battery as claimed in claims 1-4, wherein the electrolyte comprises a solvent comprising one or more of EC, PC, DEC, DMC, EMC.
6. The method for preparing a symmetric sodium-ion battery according to any one of claims 1 to 5, comprising the following steps:
preparation of sodium pyrophosphate: mixing the sodium source precursor, the vanadium source precursor and the phosphoric acid source precursor, and calcining in a protective atmosphere to obtain the general formula Na7±xV3±y(P2O7)4The sodium alum pyrophosphate is shown, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5;
preparing a working electrode by adopting an active material comprising the sodium pyrophosphate, preparing a sodium metal battery by adopting sodium metal as a counter electrode, discharging, charging, and taking out the working electrode;
and respectively taking the two working electrodes as a positive electrode and a negative electrode to be assembled with electrolyte together to obtain the symmetrical sodium-ion battery.
7. The method of claim 6, wherein the sodium source precursor comprises one or more of sodium acetate, sodium oxalate, sodium carbonate, and sodium hydroxide, the vanadium source precursor comprises one or more of vanadium pentoxide, vanadium dioxide, and ammonium metavanadate, and the phosphoric acid source precursor comprises one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or sodium collophanate.
8. The method for preparing a symmetric sodium-ion battery according to claim 6 or 7, wherein the mixing molar ratio of the sodium element of the sodium-source precursor, the vanadium element of the vanadium-source precursor and the phosphorus element of the phosphoric-acid-source precursor is 7 ± x: 3 +/-y: 8, wherein x is more than or equal to 0 and less than or equal to 0.5; y is more than or equal to 0 and less than or equal to 0.5.
9. The method for preparing a symmetric sodium-ion battery according to claim 6, wherein a carbon compound is further added during material mixing, wherein the carbon compound accounts for 0-20 wt.% of the total mixed material, and the carbon compound comprises one or more of citric acid and glucose.
10. The method for preparing a symmetric sodium-ion battery according to claim 6, wherein the temperature of the calcination operation is 200-750 ℃, the calcination time is 1-22 h, and after the calcination is completed, the sodium pyrophosphate is washed in a water bath at a temperature of 20-100 ℃.
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