CN116364923A - Carbon-nitrogen co-coated sodium iron pyrophosphate composite material, preparation method and application - Google Patents

Carbon-nitrogen co-coated sodium iron pyrophosphate composite material, preparation method and application Download PDF

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CN116364923A
CN116364923A CN202310170724.XA CN202310170724A CN116364923A CN 116364923 A CN116364923 A CN 116364923A CN 202310170724 A CN202310170724 A CN 202310170724A CN 116364923 A CN116364923 A CN 116364923A
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carbon
composite material
nitrogen
sodium
coated
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王广进
彭俊棋
徐绍霞
李喜飞
侯宁静
李默恒
王晓雪
王慧
席玉坤
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Sichuan Yinneng New Energy 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/626—Metals
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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

The invention discloses a carbon-nitrogen co-coated sodium iron pyrophosphate composite material, a preparation method and application thereof, wherein the molecular formula of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material is Na 4 Fe 3‑ x M x (PO 4 ) 2 P 2 O 7 and/C-N, wherein x is more than or equal to 0 and less than or equal to 3. According to the invention, through partial substitution of transition metal ions and co-cladding of sodium iron pyrophosphate by carbon and nitrogen, the electron structure is regulated and controlled from the intrinsic aspect, the energy gap of electron transition is reduced, the electrochemical reaction defect and active site of the electrode material are increased, and the discharge specific capacity and the cycling stability of the material are effectively improved.

Description

Carbon-nitrogen co-coated sodium iron pyrophosphate composite material, preparation method and application
Technical Field
The invention relates to the technical field of sodium ion battery anode materials, in particular to a carbon-nitrogen co-coated sodium iron pyrophosphate composite material, a preparation method and application.
Background
The green low-carbon transformation of energy is a necessary choice for sustainable development of China, and national energy safety and energy structure provide development demands for industrialization of sodium ion batteries. Currently, the world style is regulated, the energy supply and demand relation is changed, the energy resource constraint of China is increasingly aggravated, and the energy development faces a series of new problems and new challenges. The lithium ion battery is difficult to support and start the development of two industries of electric automobiles and power grid energy storage at the same time due to the limitation of nonuniform lithium resource reserves and distribution. Along with the acceleration of the 5G base station construction process, the requirement on the energy storage battery is greatly improved, so that the development of the sodium ion battery is brought into a new opportunity.
Compared with the traditional lithium ion battery anode materials, such as lithium cobaltate, lithium manganate, ternary materials and the like, the sodium iron pyrophosphate (Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Recorded as NFPP) due to its thermodynamic stability, higher theoretical capacity (129 mAh/g), moderate average operating potential (higher than 3.1V), at Na + The small volume change (4%) and low cost during de-intercalation is considered to be a very potential positive electrode material for Sodium Ion Batteries (SIBs). However, its inherent low conductivity and ion diffusion capability result in low discharge capacity and poor cycling stability, greatly limiting its wide practical application.
Disclosure of Invention
The invention aims to solve the defects in the prior art, and provides a carbon-nitrogen co-coated sodium iron pyrophosphate composite material, a preparation method and application thereof.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
in a first aspect, the invention provides a carbon-nitrogen co-coated sodium iron pyrophosphate composite material, wherein the molecular formula of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material is Na 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 and/C-N, wherein x is more than or equal to 0 and less than or equal to 3. Further, x is more than or equal to 0.03 and less than or equal to 3.
Optionally, the M is selected from one or more of Mn, co, ni, ti, mg, al and the like.
Optionally, the average particle size of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material is 2-10 mu m.
In a second aspect, the invention provides a preparation method of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material, which comprises the following steps:
s1, preparing a carbon-coated sodium ferric pyrophosphate composite material, wherein the molecular formula of the composite material is Na 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 and/C, wherein x is more than or equal to 0 and less than or equal to 3;
s2, dispersing the carbon-coated sodium ferric pyrophosphate composite material and conductive carbon in a nitrogen source, continuously and vigorously stirring to form a suspension, wherein the violent stirring speed is 700-1000 r/min, and drying the suspension in the stirring process to obtain powder;
and S3, calcining the powder in an inert atmosphere to obtain the carbon-nitrogen co-coated sodium ferric pyrophosphate composite material.
Optionally, in S1, x is more than or equal to 0.03 and less than or equal to 3.
Optionally, M of the molecular formula in S1 is selected from one or more of Mn, co, ni, ti, mg, al and the like.
Optionally, the average particle size of the S1 carbon-coated ferric sodium pyrophosphate composite material is 50 nm-10 mu m; further, the average particle diameter is 2 to 10 μm.
In the invention, the process for preparing the carbon-coated sodium iron phosphate composite material by S1 specifically comprises the following steps:
step 1: respectively dissolving sodium salt, ferric salt and/or M salt, phosphate and a carbon source in deionized water, and stirring to obtain a uniform mixed solution;
step 2: drying the mixed solution to obtain precursor powder;
step 3: calcining the precursor powder in an inert reducing atmosphere to obtain the Na 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 and/C composite material.
Wherein, optionally, the ratio of the amounts of sodium salt, ferric salt, M salt, phosphate and carbon source substances in the step 1 is 4 (3-x) x is 4:4, wherein, x is more than or equal to 0 and less than or equal to 3; further, x is more than or equal to 0.03 and less than or equal to 3. In some embodiments of the invention, the ratio of the amounts of the sodium salt, iron salt, msalt, phosphate, carbon source materials is 2:0:1.5:2:2; in some embodiments of the invention, the ratio of the amounts of the sodium salt, iron salt, msalt, phosphate, carbon source materials is 2:1.485:0.015:2:2.
Optionally, the sodium salt in the step 1 is one or more selected from sodium dihydrogen phosphate, sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate and sodium citrate.
Optionally, the ferric salt in step 1 is selected from one or more of ferrous acetate, ferric nitrate nonahydrate, ferrous oxalate and ferrous sulfate.
Optionally, the M salt in step 1 is selected from one or more of M acetate, M sulfate, M chloride, M nitrate, M tetrahydrate acetate, and M dihydrogen phosphate.
Optionally, the phosphate in step 1 is selected from one or more of sodium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and sodium pyrophosphate.
Optionally, the carbon source in step 1 is one or more selected from starch, citric acid, sucrose and glucose.
Alternatively, the drying in step 2 is spray drying or freeze drying. Further, the drying is a spray drying method.
Optionally, the inert reducing atmosphere in the step 3 is selected from one or more of nitrogen, argon and hydrogen. In some embodiments of the present invention, the inert reducing atmosphere is a mixture of argon and hydrogen, wherein the hydrogen is 5% by volume.
Optionally, the calcining in the step 3 is divided into two steps of presintering and high-temperature calcining, and the presintering conditions are as follows: the temperature rising rate is 1-5 ℃/min, the temperature is 250-350 ℃, and the heat preservation time is 3-10 h; further, the burn-in conditions are: heating rate is 2 ℃/min, temperature is 300 ℃, and heat preservation time is 6h. The high-temperature calcination conditions are as follows: the temperature rising rate is 1-5 ℃/min, the temperature is 550-600 ℃, the heat preservation time is 8-12 h, and the temperature is reduced along with the furnace; further, the high temperature calcination conditions are: heating rate is 2 ℃/min, temperature is 550 ℃, and heat preservation time is 8h.
Optionally, the carbon-coated sodium iron pyrophosphate composite anode material has a carbon content of 1-10 wt.%. Further, the carbon-coated sodium iron pyrophosphate composite anode material has a carbon content of 5wt.%.
Optionally, in S2, the conductive carbon is selected from one or more of conductive carbon black Super P, conductive graphite, VGCF, ketjen black.
Optionally, in the step S2, the mass ratio of the conductive carbon to the carbon coated sodium iron pyrophosphate composite material is 1:10-80; further, the mass ratio of the conductive carbon to the carbon coated ferric sodium pyrophosphate composite is any one or a numerical value between 1:10, 1:40 and 1:80.
Optionally, in the S2, the mass ratio of the carbon-coated ferric sodium pyrophosphate composite material to nitrogen in the nitrogen source is (0.3-3): 9-22.6; further, the mass ratio of the carbon-coated sodium iron pyrophosphate composite material to the nitrogen in the nitrogen source is a value of any one or two of 0.3:9, 3:22.6 and 3:11.3.
Optionally, in S2, the nitrogen source is N-methyl-2-pyrrolidone (NMP) or urea. Further, the nitrogen source is N-methyl-2-pyrrolidone (NMP), and the mass ratio of the carbon-coated ferric sodium pyrophosphate composite material to N-methyl-2-pyrrolidone (NMP) is (0.3-3) (64-160); further, the nitrogen source is urea, and the mass ratio of the carbon-coated ferric sodium pyrophosphate composite material to the urea is (0.3-3) (19.37-48.42).
Optionally, in S2, the dispersing is ultrasonic dispersing. Further, the temperature of the ultrasonic dispersion is room temperature, and the ultrasonic time is 2-4 hours. Ultrasonic dispersion is mainly based on ultrasonic cavitation of liquid, a large number of cavitation bubbles are generated in the liquid, and micro-jet flow is generated along with the generation and explosion of the cavitation bubbles, so that important solid particles in the liquid are smashed. Simultaneously, the solid and the liquid are fully mixed due to the vibration and the dispersion effect of the ultrasonic wave.
Further, in S2, the rotation speed of the vigorous stirring is one or two values of 700r/min, 800r/min, 900r/min and 1000r/min according to the overall apparent flow speed of the liquid, and the stirring time is one or two values of 18h, 24h and 36 h. Because the molecular weight of the positive electrode particles is far greater than that of the carbon particles, the positive electrode particles are extremely easy to settle, so that the positive electrode particles give larger kinetic energy to the positive electrode particles, so that the conductive carbon particles are more uniformly dispersed and dissolved among the positive electrode active particles, the conductive contact among active substances is increased, and the electronic conductivity is improved.
Optionally, in S2, the drying is spray drying.
Optionally, the inert atmosphere in S3 is selected from one or more of nitrogen, argon and hydrogen. Further, the inert reducing atmosphere is a mixed gas of argon and hydrogen, wherein the volume percentage of the hydrogen is 5%.
Optionally, the calcination temperature in the step S3 is 300-350 ℃, the heating rate is 1-5 ℃/min, and the time is 3-4 hours.
In a third aspect, the invention provides a sodium ion battery anode material, which comprises the carbon-nitrogen co-coated sodium iron pyrophosphate composite material or the carbon-nitrogen co-coated sodium iron pyrophosphate composite material obtained by the preparation method of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material.
In a fourth aspect, the invention provides a preparation method of the positive electrode material of the sodium ion battery, which comprises the following steps: and uniformly mixing the carbon-nitrogen co-coated sodium iron pyrophosphate composite material with a conductive agent and a binder, and coating the mixture on a positive current collector to prepare the positive electrode of the sodium ion battery.
Optionally, the positive electrode current collector is selected from at least one of aluminum, copper, iron, tin, zinc, nickel, titanium, manganese, lead, antimony, cadmium, gold, bismuth, and germanium.
Among them, the conductive agent and the binder may be materials known to those skilled in the art.
In a fifth aspect, the invention provides a carbon-nitrogen co-coated sodium iron pyrophosphate composite material, or a carbon-nitrogen co-coated sodium iron pyrophosphate composite material obtained by the preparation method of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material, or the sodium ion battery positive electrode material, or the application of the sodium ion battery positive electrode material obtained by the preparation method of the sodium ion battery positive electrode material in the preparation of a sodium ion battery.
Optionally, the application is specifically: dissolving the carbon-nitrogen co-coated sodium iron pyrophosphate composite material, conductive carbon black and PVDF binder in NMP according to the mass ratio of 8:1:1, fully stirring and mixing to obtain uniform slurry, coating the slurry on an aluminum foil to serve as a test electrode, taking metal sodium as a counter electrode, and taking 1M NaClO as electrolyte 4 The sodium ion half-cell was prepared by dissolving in a 1:1 volume ratio of Ethylene Carbonate (EC) and Propylene Carbonate (PC) solution and adding 5wt.% of fluoroethylene carbonate (FEC).
The beneficial effects of the invention are as follows:
the carbon-nitrogen co-cladding sodium iron pyrophosphate Na of the invention 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 The composite material of the/C-N (x is more than or equal to 0 and less than or equal to 3), the intrinsic electronic structure of the material is regulated and controlled through the doping of transition metal elements, and the electronic transition is reducedThe energy gap of the coating layer is greatly improved by introducing nitrogen atom doping into the carbon-coated layer, the electrochemical reaction defect and the active site of the electrode material are increased, and the conductivity of the material is greatly improved by cooperating the two aspects of modification.
According to the invention, in a preparation method of researching the carbon-nitrogen co-coated sodium ferric pyrophosphate composite material, creatively discovers that the carbon-coated sodium ferric pyrophosphate composite material and conductive carbon are dispersed in a nitrogen source, the carbon-coated sodium ferric pyrophosphate composite material is subjected to secondary carbon coating, meanwhile, nitrogen atom doping is introduced into a carbon coating layer, the electronic conductivity of the coating layer is greatly improved, then suspension is continuously and vigorously stirred at the rotating speed of 700-1000 r/min, the kinetic energy which is far greater than that of carbon particles and is extremely easy to settle is given to positive electrode particles, so that the conductive carbon particles are more uniformly dispersed and dissolved among the positive electrode active particles, the conductive contact among active substances is increased, the electronic conductivity is improved, and finally, the carbon-nitrogen co-coating is realized by secondary low-temperature calcination, and after secondary granulation and calcination are completed, the surface attachment of carbon-nitrogen co-coating or a little residual nitrogen-oxygen free radical is realized, so that the reaction site and the material are increased, and the discharge specific capacity and the cycling stability of the material are further improved. The method ensures the uniformity of coating, has good repeatability, simple operation and low energy consumption, and provides a new method for improving the electrochemical performance of the material. In addition, considering the actual combination condition, the solid powder can be completely dispersed in the liquid, and the liquid nitrogen source NMP is preferably selected, so that the uniformity of nitrogen atom doping is ensured.
In the preparation process of the carbon-coated sodium ferric pyrophosphate composite material, the inventor regulates and controls the intrinsic electronic structure of the material through doping of transition metal elements, improves the conductivity of the material, improves the electrochemical performance of the composite material, creatively discovers that a carbon source in the step 1 is taken as a raw material and is added at the beginning of synthesis, and the carbon coating is realized through an in-situ one-step method, so that the uniform mixing of the materials is ensured, the specific discharge capacity and the cycle stability of the positive electrode material are improved, meanwhile, the processing procedures are effectively reduced, the synthesis cost of the material is greatly reduced, and the formed carbon-coated sodium ferric pyrophosphate composite material is more beneficial to improving the electrochemical performance of the subsequent carbon-nitrogen co-coated sodium ferric pyrophosphate composite material.
The sodium ion battery anode material obtained by taking the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material as the anode active material has the discharge specific capacity of 117.0mAh/g at 0.1C, the capacity retention rate after 200 circles of 1C circulation is up to more than 97%, and the multiplying power and the circulation performance are obviously excellent.
Drawings
FIG. 1 shows Na prepared in example 3 of the present invention 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 XRD pattern of the C-N composite.
FIG. 2 shows Na prepared in example 3 of the present invention 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Microstructure scanning electron microscope image of the C-N composite material.
FIG. 3 is a view of Na prepared in example 3 of the present invention 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 And (3) a charge-discharge curve diagram of the sodium ion button cell assembled by the C-N composite material at the multiplying power of 0.1C.
FIG. 4 shows Na prepared in example 3 of the present invention 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C-N composite and Na prepared in comparative example 1 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 And (3) multiplying power performance diagram of the sodium ion button cell assembled by the composite material.
FIG. 5 shows Na prepared in example 3 of the present invention 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C-N composite and Na prepared in comparative example 1 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Cycling performance of sodium ion button cell assembled by/C composite material under 1C multiplying powerAnd (5) energy diagram.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments thereof in order to enable those skilled in the art to better understand the technical aspects of the invention.
Example 1
Preparation of Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 Composite material/C:
firstly, 2mmol of sodium dihydrogen phosphate, 1.5mmol of manganous acetate tetrahydrate and 2mmol of citric acid are taken and dissolved in deionized water, and a uniform mixed solution is obtained by stirring; spray drying the mixed solution to obtain precursor powder; presintering the material in a tubular furnace to 300 ℃ for 6 hours at a heating rate of 2 ℃/min, then heating the material to 600 ℃ for 10 hours at a high temperature calcining temperature, protecting the whole argon-hydrogen mixed gas (hydrogen contains 5%), heating the material at a heating rate of 2 ℃/min, and cooling the material along with the furnace to obtain the required Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 and/C composite material.
Preparing a carbon-nitrogen co-coated sodium ferric pyrophosphate composite material:
taking 300mg of Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 C and 7.5mg of conductive carbon black Super P (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 64g of NMP, performing ultrasonic dispersion at room temperature for 2 hours, and then continuing to vigorously stir at 900r/min for 18 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; calcining under argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating to 300 deg.C at a speed of 5 deg.C/min for 4 hr to obtain Na product 4 Mn 3 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 2
Preparation of Na 4 Mg 1.5 Ni 1 Al 0.5 (PO 4 ) 2 P 2 O 7 Composite material/C:
firstly, 2mmol of sodium dihydrogen phosphate and 0.75mmol of ethyl tetrahydrate are takenDissolving magnesium acid, 0.5mmol of nickel acetate tetrahydrate, 0.25mmol of aluminum chloride and 2mmol of citric acid in deionized water, and stirring to obtain a uniform mixed solution; spray drying the mixed solution to obtain precursor powder; presintering the material in a tubular furnace to 300 ℃ for 6 hours at a heating rate of 2 ℃/min, then heating the material to 550 ℃ for 12 hours at a high temperature calcining temperature, protecting the whole argon-hydrogen mixed gas (hydrogen contains 5%), heating the material at a heating rate of 2 ℃/min, and cooling the material along with the furnace to obtain the required Na 4 Mg 1.5 Ni 1 Al 0.5 (PO 4 ) 2 P 2 O 7 and/C composite material.
Preparing a carbon-nitrogen co-coated sodium ferric pyrophosphate composite material:
taking 3000mg of Na 4 Mg 1.5 Ni 1 Al 0.5 (PO 4 ) 2 P 2 O 7 30mg of conductive graphite and 45mg of VGCF (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 160g of NMP, performing ultrasonic dispersion at room temperature for 3 hours, and then continuing to vigorously stir at 800r/min for 24 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; calcining under argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating at a rate of 5 deg.C/min to 350 deg.C for 3 hr to obtain Na product 4 Mg 1.5 Ni 1 Al 0.5 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 3
Preparation of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Composite material/C:
firstly, 2mmol of sodium dihydrogen phosphate, 1.485mmol of ferric nitrate nonahydrate, 0.015mmol of manganous acetate tetrahydrate and 2mmol of citric acid are taken and dissolved in deionized water, and a uniform mixed solution is obtained by stirring; spray drying the mixed solution to obtain precursor powder; presintering in a tube furnace to 300 ℃ for 6 hours at a heating rate of 2 ℃/min, then calcining at high temperature and heating to 550 ℃ for 8 hours, and protecting argon-hydrogen mixture (hydrogen contains 5%) at a heating rate of 2 DEG CAfter cooling along with the furnace, the required Na is obtained 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 and/C composite material.
Preparing a carbon-nitrogen co-coated sodium ferric pyrophosphate composite material:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 75mg of Keqin black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 160g of NMP, performing ultrasonic dispersion for 4 hours at room temperature, and then continuing to vigorously stir at 700r/min for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; placing the mixture in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5 percent), calcining at the heating rate of 1 ℃/min to 350 ℃ for 3 hours to obtain the product
Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 4
The difference with example 3 is that in the process of preparing the sodium iron pyrophosphate composite material coated by carbon and nitrogen, the dosage of secondary conductive carbon is increased, and the method specifically comprises the following steps:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 300mg of ketjen black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:10), dispersing in 160g of NMP, performing ultrasonic dispersion for 4 hours at room temperature, and then continuing to vigorously stir at 700r/min for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; calcining in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating to 350 deg.C at a speed of 1 deg.C/min for 3 hr to obtain Na product 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 5
The difference with example 3 is only that in the process of preparing the sodium iron pyrophosphate composite material coated by carbon and nitrogen, the dosage of secondary conductive carbon is reduced, and the method specifically comprises the following steps:
3000mg of Na is taken 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 37.5mg of ketjen black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:80), dispersing in 160g of NMP, performing ultrasonic dispersion for 4 hours at room temperature, and then continuing to vigorously stir at 700r/min for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; placing the mixture in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5 percent), calcining at the heating rate of 1 ℃/min to 350 ℃ for 3 hours to obtain the product
Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 6
The difference with example 3 is that in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material, the dosage of NMP solvent is halved, and the specific steps are as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 75mg of Keqin black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 80g of NMP, performing ultrasonic dispersion for 4 hours at room temperature, and then continuing to vigorously stir at 700r/min for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; placing the mixture in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5 percent), calcining at the heating rate of 1 ℃/min to 350 ℃ for 3 hours to obtain the product
Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 7
The difference is that in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material, the ultrasonic dispersion is carried out for 2 hours, and then the magnetic stirring is carried out for 18 hours at 800r/min, and the specific steps are as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 75mg of Keqin black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 160g of NMP, performing ultrasonic dispersion for 2 hours at room temperature, magnetically stirring for 18 hours at 800r/min to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; calcining in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating to 350 deg.C at a speed of 1 deg.C/min for 3 hr to obtain Na product 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 8
The difference is that in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material, the calcination process is that the temperature is raised to 300 ℃ at 5 ℃/min and the calcination is carried out for 4 hours, and the specific steps are as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 75mg of Keqin black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), dispersing in 160g of NMP, performing ultrasonic dispersion for 4 hours at room temperature, and then continuing to vigorously stir at 700r/min for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; placing the mixture in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5 percent), calcining at the temperature rising speed of 5 ℃/min to 300 ℃ for 4 hours, and obtaining the product
Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Example 9
The difference from example 3 is only that ketjen black is replaced with conductive carbon black Super P during the preparation of the carbon-nitrogen co-coated sodium iron pyrophosphate composite.
Example 10
The difference from example 3 is only that in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material, the nitrogen source NMP is replaced by urea, and the specific steps are as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 C and 75mg of Keqin black (the mass ratio of conductive carbon to carbon coated ferric sodium pyrophosphate composite material is 1:40), and 48.42g of urea are dispersed in 200ml of deionized water (consistent with 160g of NMP nitrogen content), ultrasonic dispersion is carried out for 4 hours at room temperature, and then intense stirring is carried out for 36 hours at 700r/min to form uniform black suspension, and the suspension is subjected to spray drying in the stirring process to obtain black powder; calcining in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating to 350 deg.C at a speed of 1 deg.C/min for 3 hr to obtain Na product 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Comparative example 1
Preparation of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Composite material/C:
the preparation procedure is as in example 3.
Comparative example 2
The same as in example 3, except that Na was produced 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 In the process of the/C composite material, the adding time of citric acid as a carbon source is variable, and the concrete steps are as follows:
firstly, 2mmol of sodium dihydrogen phosphate, 1.485mmol of ferric nitrate nonahydrate and 0.015mmol of manganous acetate tetrahydrate are dissolved in deionized water and stirred to obtain a uniform mixed solution; spray drying the mixed solution to obtain precursor powder; presintering the powder in a tube furnace to 300 ℃ and preserving heat for 6 hours, wherein the heating rate is 2 ℃/min; adding 2mmol of citric acid for grinding after presintering, heating the mixture to 550 ℃ for 8 hours, keeping the temperature at a heating rate of 2 ℃/min, protecting the whole argon-hydrogen mixture (hydrogen contains 5%), and cooling along with a furnace to obtainNa is needed 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 and/C composite positive electrode material.
Comparative example 3
The difference is that in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material, the spray drying is directly carried out under the magnetic stirring at the low speed of 300r/min without carrying out the intense stirring at 700r/min for 36h after ultrasonic dispersion, and the method is concretely as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Dispersing ketjen black of/C and 75mg in NMP of 200ml, ultrasonic dispersing at room temperature for 4h to form uniform black suspension, and spray drying the suspension in 300r/min stirring process to obtain black powder; placing the mixture in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5 percent), calcining at the heating rate of 1 ℃/min to 350 ℃ for 3 hours to obtain the product
Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Comparative example 4
The difference from example 3 is that in the process of preparing the carbon-nitrogen co-coated sodium iron pyrophosphate composite material, the volume of NMP is beyond the scope of the invention, and the specific steps are as follows:
taking 3000mg of Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 dispersing/C and 75mg of Keqin black in 500ml of NMP, performing ultrasonic dispersion at room temperature for 4 hours, continuing to vigorously stir for 36 hours to form uniform black suspension, and performing spray drying on the suspension in the stirring process to obtain black powder; calcining in a tube furnace containing argon-hydrogen mixed atmosphere (hydrogen contains 5%), heating to 350 deg.C at a speed of 1 deg.C/min for 3 hr to obtain Na product 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 a/C-N composite.
Comparative example 5
In the same manner as in example 3,the only difference is that Na is prepared 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 In the process of the composite material/C, the sintering temperature is beyond the required range of the invention, and the method comprises the following steps:
firstly, 2mmol of sodium dihydrogen phosphate, 1.485mmol of ferric nitrate nonahydrate, 0.015mmol of manganous acetate tetrahydrate and 2mmol of citric acid are taken and dissolved in deionized water. After spray drying, a precursor powder is obtained. Presintering in a tube furnace to 300 ℃ for 6 hours, then calcining at high temperature to 800 ℃ for 6 hours, protecting argon-hydrogen mixture (hydrogen contains 5 percent) in the whole process, heating at a speed of 5 ℃/min, and cooling along with the furnace to obtain the required Na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 and/C composite positive electrode material.
Effect example 1XRD characterization
Na prepared in example 3 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 XRD testing (model: XRD-7000, cuK alpha, lambda=0.15406 nm, shimadzu, japan) was carried out on the/C-N composite material, and the 2 theta testing range was 5-65 deg.. The XRD pattern is shown in FIG. 1.
As can be seen from FIG. 1, na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 the/C-N composite positive electrode material shows high crystallinity Pn2 1 a space group pure phase crystal structure (PDF standard card number: PDF # 89-0579), no obvious impurity diffraction peak was observed.
Effect example 2 scanning electron microscope observation
Na prepared in example 3 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 The composite positive electrode material was subjected to scanning electron microscope observation (FESEM, JSM-6700F). The specific image is shown in fig. 2.
As can be seen from FIG. 2, na 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 The composite positive electrode material of/C-N is hollow spherical particle with particle size of 2-10 μm.
Effect example 3 electrochemical Performance test
Preparation of button cell: dissolving the composite material, conductive carbon black and PVDF binder in NMP according to the mass ratio of 8:1:1, fully stirring and mixing to obtain uniform slurry, coating the slurry on an aluminum foil to serve as a test electrode, and taking metal sodium as a counter electrode, wherein the electrolyte is 1M NaClO 4 Dissolved in a 1:1 volume ratio of Ethylene Carbonate (EC) and Propylene Carbonate (PC) solution and 5wt.% fluoroethylene carbonate (FEC) was added.
The composite materials prepared in examples and comparative examples were subjected to charge and discharge tests after assembled into button cells. The charge-discharge voltage range was 1.8-4.2V, the current 1C was 129mA/g, the test temperature was room temperature, and the results are shown in Table 1.
Table 1 electrochemical performance test
Figure BDA0004097992680000141
Figure BDA0004097992680000151
As can be seen from the electrochemical performance test of table 1, the composite material of the manganese-based phosphoric acid pyrophosphoric acid composite salt in example 1 and the composite material of the nickel-based composite salt in example 2 all exhibit relatively excellent electrochemical performance; the iron-based composite salts of examples 3 to 10 have more excellent electrochemical properties than the manganese-based pyrophosphoric acid composite salt of example 1 due to the low conductivity of the manganese-based pyrophosphoric acid composite salt and the high spin Mn at the time of oxidation 3+ The unique electronic configuration of (2) can lead to structural distortion, namely the ginger Taylor effect is generated, so that the performance of the device is limited; likewise, the composite material of the nickel-based composite salt of example 2 faces problems of phase transition and the like, but has potential value in studying its phase stability and kinetic effect on electrochemical reaction by cation substitution because of its high oxidation-reduction potential. In contrast, the stable crystal structure of the iron-based complex salt imparts excellent cycling stability, and thus is implementedThe composite materials of the iron-based composite salts of examples 3 to 10 were more excellent in electrochemical properties.
In addition, the preparation conditions in the preparation of the carbon-nitrogen co-coated sodium ferric pyrophosphate composite material are also extremely important for the electrochemical performance of the material, and as can be seen from examples 3 to 10, the obtained material has excellent electrochemical performance under the conditions of addition of the conductive carbon, addition of the nitrogen source, vigorous stirring speed and calcination. As can be seen from the comparison between the embodiment 3 and the embodiment 9, the dual-carbon composite conductive network formed by the secondary conductive carbon with higher conductivity is more beneficial to the improvement of the material performance. And the stirring rate in the process of preparing the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material has a decisive influence on the electrochemical performance of the obtained material, under the stirring rate defined by the invention, as the molecular weight of the positive electrode particles is far greater than that of the carbon particles, the positive electrode particles are extremely easy to settle, larger kinetic energy is given to the positive electrode particles, so that the conductive carbon particles are more uniformly dispersed and dissolved among the positive electrode active particles, the conductive contact among active substances is increased, the electronic conductivity is improved, and if the stirring rate is lower, as shown in comparative example 3, the kinetic energy required by molecular movement cannot be provided, and the conductive contact of the active substances is further influenced. For the nitrogen source content, if the nitrogen content is too high, as shown in comparative example 4, the whole skeleton structure of the carbon material is collapsed, defect sites are increased, the conductivity of the material is reduced, and the solid urea nitrogen source and the liquid NMP nitrogen source are selected differently, so that nitrogen doped carbon coating effects with different configurations are generated, and the performance of the material is also affected. With respect to the calcination conditions, a composite material excellent in electrochemical properties could be obtained under the calcination conditions defined in the present invention, which would otherwise directly affect the synthesis of the composite material as shown in comparative example 5. As can be seen from the comparison between the example 3 and the comparative example 1, the electrochemical performance of the carbon-nitrogen co-coated ferric sodium pyrophosphate composite material is obviously improved compared with that of the carbon-coated ferric sodium pyrophosphate composite material, which indicates that after nitrogen atoms are doped into the carbon material framework, more free electrons can be provided for the conduction band, so that the conductivity of the material is improved.
As can be seen from the comparison between the embodiment 3 and the comparative example 2, compared with the traditional method of adding the carbon source in the calcining process, the carbon source is added at the beginning of synthesis, and the carbon source is coated by an in-situ one-step method, so that an acidic environment is provided for the solution, the chemical reaction is facilitated, the uniformity of carbon atoms distributed in the material is improved, the electrochemical performance of the material can be improved finally, meanwhile, the processing procedures are reduced effectively, the synthesis cost of the material is reduced greatly, and the formed carbon-coated sodium ferric pyrophosphate composite material is more favorable for the subsequent preparation of the carbon-nitrogen co-coated sodium ferric pyrophosphate composite material.
Fig. 3 shows the charge and discharge curves of the assembled button cell at 0.1C rate for the carbon-nitrogen co-coated sodium iron pyrophosphate composite of example 3. A voltage plateau similar to NFPP in the literature is shown, indicating that trace manganese doping and carbon nitrogen co-cladding have no significant effect on the material voltage plateau.
FIG. 4 shows the Na of comparative example 1 and the carbon-nitrogen co-coated sodium iron pyrophosphate composite of example 3 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 And (3) multiplying power performance diagram of the sodium ion button cell assembled by the composite material. As can be seen from the graph, the carbon-nitrogen co-coated sodium iron pyrophosphate composite material of example 3 of the present invention has excellent rate capability, and has a specific discharge capacity of 95.9mAh/g even at a rate of 5C.
FIG. 5 shows the Na of comparative example 1 and the carbon-nitrogen co-coated sodium iron pyrophosphate composite of example 3 4 Fe 2.97 Mn 0.03 (PO 4 ) 2 P 2 O 7 Cycling performance graph of sodium ion button cell assembled with/C composite at 1C rate. Before the 1C formal cycle, 3 cycles are activated with a small current of 0.1C.
The data show that the carbon-nitrogen co-coated sodium ferric pyrophosphate composite material has excellent cycling stability, and the capacity retention rate after cycling for 200 circles under 1C is over 95 percent.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-mentioned preferred embodiment should not be construed as limiting the invention, and the scope of the invention should be defined by the appended claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.

Claims (10)

1. The carbon-nitrogen co-coated sodium iron pyrophosphate composite material is characterized in that the molecular formula of the carbon-nitrogen co-coated sodium iron pyrophosphate composite material is Na 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 and/C-N, wherein x is more than or equal to 0 and less than or equal to 3.
2. A method of preparing the composite material of claim 1, comprising the steps of:
s1, preparing a carbon-coated sodium ferric pyrophosphate composite material, wherein the molecular formula of the composite material is Na 4 Fe 3-x M x (PO 4 ) 2 P 2 O 7 and/C, wherein x is more than or equal to 0 and less than or equal to 3;
s2, dispersing the carbon-coated sodium ferric pyrophosphate composite material and conductive carbon in a nitrogen source, continuously and vigorously stirring to form a suspension, wherein the violent stirring speed is 700-1000 r/min, and drying the suspension in the stirring process to obtain powder;
and S3, calcining the powder in an inert atmosphere to obtain the carbon-nitrogen co-coated sodium iron pyrophosphate composite material.
3. The preparation method according to claim 2, wherein the S1 preparation process of the carbon-coated sodium iron pyrophosphate composite material specifically comprises the following steps:
step 1: respectively dissolving sodium salt, ferric salt and/or M salt, phosphate and a carbon source in deionized water, and stirring to obtain a uniform mixed solution;
step 2: drying the mixed solution to obtain precursor powder;
step 3: and calcining the precursor powder in an inert reducing atmosphere to obtain the carbon-coated sodium ferric pyrophosphate composite material.
4. The method according to claim 3, wherein the ratio of the amounts of sodium salt, iron salt, M salt, phosphate and carbon source in step 1 is 4 (3-x): x:4:4, wherein 0.ltoreq.x.ltoreq.3.
5. The preparation method according to claim 2, wherein in the S2, the mass ratio of the conductive carbon to the carbon-coated sodium iron pyrophosphate composite material is 1:10-80.
6. The method according to claim 2, wherein in S2, the mass ratio of the carbon-coated sodium iron pyrophosphate composite to nitrogen in the nitrogen source is (0.3 to 3): 9 to 22.6.
7. The preparation method according to claim 2, wherein the calcination temperature in S3 is 300-350 ℃, the temperature rising rate is 1-5 ℃/min, and the time is 3-4 hours.
8. A sodium ion battery cathode material, characterized by comprising the carbon-nitrogen co-coated sodium iron pyrophosphate composite material of claim 1 or the carbon-nitrogen co-coated sodium iron pyrophosphate composite material obtained by the preparation method of any one of claims 2 to 7.
9. A method for preparing the positive electrode material of the sodium ion battery as claimed in claim 8, comprising the following steps: and uniformly mixing the carbon-nitrogen co-coated sodium iron pyrophosphate composite material with a conductive agent and a binder, and coating the mixture on a positive current collector to prepare the positive electrode of the sodium ion battery.
10. The carbon-nitrogen co-coated sodium iron pyrophosphate composite material of claim 1, or the carbon-nitrogen co-coated sodium iron pyrophosphate composite material obtained by the preparation method of any one of claims 2 to 7, or the sodium ion battery positive electrode material of claim 8, or the application of the sodium ion battery positive electrode material obtained by the preparation method of the sodium ion battery positive electrode material of claim 9 in the preparation of sodium ion batteries.
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* Cited by examiner, † Cited by third party
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