CN114551882A - Ferric fluoride cathode material and preparation method and application thereof - Google Patents

Ferric fluoride cathode material and preparation method and application thereof Download PDF

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CN114551882A
CN114551882A CN202210030124.9A CN202210030124A CN114551882A CN 114551882 A CN114551882 A CN 114551882A CN 202210030124 A CN202210030124 A CN 202210030124A CN 114551882 A CN114551882 A CN 114551882A
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fluoride
iron
ferric
positive electrode
ferric fluoride
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袁中直
程节
朱立才
吴钰佳
潘燕霞
罗薪涛
黄于桐
周一凡
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South China Normal University
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    • 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
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    • H—ELECTRICITY
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Abstract

The invention provides an iron fluoride anode material and a preparation method and application thereof. The ferric fluoride anode material has a core-shell structure, a shell of the ferric fluoride anode material comprises a carbon-nitrogen nanocage, an inner core of the ferric fluoride anode material comprises ferric fluoride, and a gap is formed between the shell and the inner core to provide a certain space for volume expansion of the ferric fluoride in a reaction process, so that the result of improving the cycle performance of the ferric fluoride is achieved. In the preparation method, the fluorine source is adopted to generate hydrogen fluoride gas for fluorination, so that the precursor material can be effectively fluorinated. The ferric fluoride anode material has good electrochemical stability when being applied to a lithium battery.

Description

Ferric fluoride cathode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to an iron fluoride positive electrode material, and a preparation method and application thereof.
Background
In more than twenty years of the commercial development of lithium ion batteries, the capacity of the battery is limited by the breakthrough of the capacity of the anode material. Currently, researchers prefer ferric fluoride as a positive electrode material, which has the advantages of high specific capacity, thermal stability, cheap and easily available raw materials, but the application of ferric fluoride is limited by the disadvantages of poor conductivity, poor cycle performance due to volume expansion generated in the ferric fluoride reaction process, and the like. Researchers try to improve the performance of the iron fluoride by doping and compounding the iron fluoride and a carbon material with good conductivity, for example, a one-dimensional carbon nanowire, a two-dimensional carbon nanotube and three-dimensional graphene have a certain result, but the defects of poor cycle performance and the like caused by volume expansion in the reaction process of the iron fluoride are not well improved.
Researchers' synthesis of nano-FeF3In the/C composite positive electrode material, polytetrafluoroethylene is used as a fluorine source and a carbon source, and ferrocene and/or ferric chloride is used as an iron source, so that the polytetrafluoroethylene can provide the fluorine source and can be cracked to provide the carbon source due to the sublimation property of the polytetrafluoroethylene at low temperature, and the polytetrafluoroethylene and the iron source can obtain the ferric trifluoride composite positive electrode material with superfine nano particles in a 400 ℃ high-temperature closed reaction kettle. However, the decomposition of the carbon-containing organic matter and the synthesis of the ferric fluoride are carried out synchronously, the carbon is only subjected to in-situ compounding, the main structure is also composed of the ferric fluoride main body, and no limiting stress exists, so that the condition that the ferric fluoride undergoes volume expansion in the reaction process cannot be well controlled, and the cycle performance of the material is not well improved.
FeF synthesized by a liquid phase synthesis method from a carbon material and an iron salt has also been studied3·0.33H2The O carbon material, graphene or mesoporous carbon construct a conductive network on one hand, and the iron trifluoride nanocrystals grow on the pore channel structure of the graphene or mesoporous carbon on the other hand. Although the main structure of the material is graphene or mesoporous carbon with a conductive network, iron fluoride crystals are only attached to the structure of the carbon and cannot limit phase change stress in the charging and discharging processes, so that the volume expansion of the iron fluoride in the energy conversion process is caused, the material is pulverized, and the connectivity is interrupted; so that part of the ferric fluoride loses effective electric connection in the charging and discharging processes, the charging and discharging are incomplete, and the actual discharging capacity is lower than the theoretical capacity; eventually leading to less than good material cycle performance. In the iron-based fluoride particles composed of the porous octahedral carbon skeleton and the iron fluoride dispersed in the porous octahedral carbon skeleton, although the iron fluoride is confined in the porous octahedral carbon skeleton, a certain restriction is given to the volume expansion during the reaction of the iron fluoride, since the Fe-MOF is octahedral, a microstructure having a diameter of about 1 μm and a length of about 1.2 μm and the iron fluoride is dispersed in the microstructure, a good buffer space cannot be provided for the phase transition stress and the volume expansion during the reaction of the iron fluoride. There is room for improvement in the case where the volume expansion of iron fluoride occurs during the reaction and in the cycle performance of the material.
Aiming at the ferric fluoride, a preparation method is developed, which is green, environment-friendly and pollution-free, and particularly, a product which can improve the cycle performance influenced by the volume expansion in the ferric fluoride reaction process is prepared; therefore, the iron fluoride is used as the positive electrode active material to prepare the lithium ion battery with high specific energy and excellent cycle performance, and is vital to the wide application and the expected commercial development of the iron fluoride.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the invention provides the ferric fluoride anode material in the first aspect, which can well solve the problem of volume expansion caused by the ferric fluoride reaction process, provide a certain buffer space for the ferric fluoride anode material, avoid the collapse of the ferric fluoride anode material structure caused by the expansion of the ferric fluoride in the reaction process so as to influence the cycle performance of the lithium battery, and finally achieve the effect of improving the overall application performance of the ferric fluoride anode material in the lithium battery.
The second aspect of the invention provides a preparation method of the ferric fluoride cathode material.
A third aspect of the present invention provides a lithium battery.
According to a first aspect of the invention, an iron fluoride cathode material is provided, the iron fluoride cathode material has a core-shell structure, a shell of the iron fluoride cathode material comprises a carbon-nitrogen nanocage, an inner core of the iron fluoride cathode material comprises iron fluoride, and a gap is formed between the shell and the inner core.
Compared with a common carbon shell, the carbon-nitrogen nanocage can further improve the conductivity of the shell due to the existence of nitrogen elements, further improve the conductivity of the ferric fluoride anode material, and reserve enough gaps between the shell and the inner core, so that the problem of volume expansion caused by the ferric fluoride reaction process can be well solved, a certain buffer space is provided for the ferric fluoride nanocage, the phenomenon that the ferric fluoride anode material structure collapses to influence the cycle performance of the lithium battery due to the expansion of the ferric fluoride in the reaction process is avoided, and the effect of improving the overall application performance of the ferric fluoride anode material in the lithium battery is finally achieved.
In some embodiments of the invention, the size of the voids is from 120nm to 350 nm.
In some preferred embodiments of the present invention, the shell of the ferric fluoride cathode material has a thickness of 10nm to 50 nm.
In some more preferred embodiments of the present invention, the average particle size of the core of the iron fluoride positive electrode material is 100nm to 400 nm.
In some more preferred embodiments of the invention, the ferric fluoride positive electrode material is in the form of cubic or cuboidal particles; preferably, the average particle size of the ferric fluoride cathode material is 250nm to 700 nm.
In some more preferred embodiments of the present invention, the carbon-nitrogen nanocage is contained in the iron fluoride positive electrode material in an amount of 14 to 40% by mass.
In some more preferred embodiments of the present invention, the mass content of the iron fluoride in the iron fluoride positive electrode material is 60% to 86%.
According to a second aspect of the present invention, there is provided a method for preparing the ferric fluoride cathode material, comprising the steps of:
s1: dispersing iron oxide nano particles into a solvent, adding a carbon source, mixing, drying and calcining to obtain an iron oxide @ carbon nitrogen material;
s2: etching and drying the iron oxide @ carbon nitrogen material in an acid solution to obtain a precursor material;
s3: and carrying out fluorination reaction on the precursor material and a fluorine source to prepare the ferric fluoride anode material.
In the invention, micropores are formed on the carbon-nitrogen shell in the calcining process, so that a good ion channel can be provided for lithium ions; the double-continuous lithium ion and electron transmission channel is provided, so that the conductivity of the ferric fluoride anode material can be further improved, and the electrochemical activity is improved; the ferric oxide @ carbon nitrogen material is etched by the aid of the acid solution, a precursor material with a larger void volume can be obtained, and the finally prepared ferric fluoride anode material can bring a larger buffer space for volume expansion in the ferric fluoride reaction process.
In some embodiments of the invention, in S3, the fluorine source is at least one of gaseous hydrogen fluoride, ammonium bifluoride; ammonium bifluoride is preferred. The fluorine source can be decomposed to generate HF gas for fluorination reaction, and the solid-solid reaction provides anhydrous high-purity HF atmosphere for fluorination, so that the reaction rate is improved, and a product with good crystallinity is obtained; in the traditional fluorination method, HF liquid is directly adopted for fluorination, so that agglomeration is easy to cause, the fluorination effect is poor, and the safety is poor.
In some preferred embodiments of the present invention, in S3, the temperature of the fluorination reaction is 100 ℃ to 300 ℃; preferably 150 ℃ to 250 ℃.
In some more preferred embodiments of the present invention, in S3, the time for the fluorination reaction is 8 to 36 hours.
In some more preferred embodiments of the invention, S3 further comprises using NaH2PO4·2H2And O absorbs the tail gas generated by the fluorination reaction. Ammonia tail gas is generated in the fluorination reaction process, and NaH is adopted2PO4·2H2O and other substances which can absorb ammonia gas and do not react with HF gas can be absorbed, so that the fluorination process is environment-friendly and pollution-free, and the demand of green chemistry is met.
In some more preferred embodiments of the present invention, in S1, the iron oxide nanoparticles are cubic or cuboidal particles.
In some more preferred embodiments of the present invention, in S1, the iron oxide nanoparticles have a dispersion concentration of 0.005mol/L to 0.010 mol/L.
In some more preferred embodiments of the present invention, in S1, the mass ratio of the iron oxide nanoparticles to the carbon source is (1-3): 1.
in some more preferred embodiments of the present invention, in S1, the method for preparing the iron oxide nanoparticles comprises: and dropwise adding a solution containing hydroxide ions into the ferric salt solution for reaction and purification to obtain the ferric oxide nanoparticles.
In some more preferred embodiments of the invention, the molar ratio of iron ions in the iron salt to the hydroxide ions is 1: (3-5).
In some more preferred embodiments of the present invention, the concentration of the iron salt solution is 1.5mol/L to 2.0 mol/L.
In some more preferred embodiments of the present invention, in S1, the carbon source is dopamine.
In some more preferred embodiments of the present invention, in S1, the temperature of the calcination is 300 ℃ to 700 ℃; preferably 450 to 550 ℃.
In some more preferred embodiments of the present invention, in S2, the acid solution is at least one selected from a nitric acid solution, a hydrochloric acid solution, and a sulfuric acid solution.
In some more preferred embodiments of the present invention, in S2, the etching time is 0.5h to 5 h; preferably 1 to 3 hours.
According to a third aspect of the present invention, a lithium battery is provided, which includes a positive electrode plate, where the positive electrode plate includes a positive electrode current collector and an iron fluoride positive electrode material as described in the first aspect or an iron fluoride positive electrode material prepared by the method of the second aspect.
The invention has the beneficial effects that:
1. according to the ferric fluoride cathode material, enough part of gaps are reserved in a core-shell structure formed by taking ferric fluoride as an inner core and a carbon nitrogen nanometer cage as a shell to provide a certain space for the volume expansion of the ferric fluoride in the reaction process, so that the phenomenon that the lithium ion battery taking the ferric fluoride as the cathode material has poor cycle performance due to the collapse of the ferric fluoride cathode material structure caused by the expansion of the ferric fluoride in the reaction process is avoided, and the result of improving the cycle performance of the ferric fluoride is achieved.
2. In the preparation method of the ferric fluoride cathode material, the acid solution is adopted for one-step etching pore-forming, so that the ferric fluoride cathode material with a core-shell structure with large void volume can be obtained; and the preparation method is simple and easy to operate, meets the requirement of green chemistry, and is beneficial to promoting the application of the ferric fluoride anode material in the lithium battery.
3. In the preparation method, the fluorine source is adopted to generate hydrogen fluoride gas for fluorination, the precursor material can be effectively fluorinated, and NaH is adopted2PO4·2H2O absorbs tail gas generated in the fluorination reaction process, and the fluorination process is environment-friendly and pollution-free and meets the requirement of green chemistry.
4. When the ferric fluoride anode material is applied to a lithium battery, the initial discharge capacity is 229mAh/g, and the charge-discharge curves in subsequent cycles tend to be consistent, which shows that the ferric fluoride anode material has good electrochemical stability.
Drawings
The invention is further described with reference to the following figures and examples, in which:
FIG. 1 is a schematic diagram of the preparation of an iron fluoride cathode material according to an embodiment of the present invention;
FIG. 2 is a TEM image of an iron fluoride positive electrode material of example 1 of the present invention, wherein a is 0.5 μm; scale b is 100 nm;
FIG. 3 is a TEM image of an iron fluoride positive electrode material prepared by a comparative example of the present invention;
FIG. 4 is an XRD pattern of the iron fluoride positive electrode material of example 1 of the present invention;
FIG. 5 is an XRD pattern of an iron fluoride cathode material according to example 2 of the present invention;
FIG. 6 is an XRD pattern of an iron fluoride cathode material according to example 3 of the present invention;
FIG. 7 is a graph showing the charging and discharging curves of the ferric fluoride cathode material in example 1 of the present invention;
FIG. 8 is a discharge curve of the ferric fluoride cathode material of example 3 of the present invention.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
Fig. 1 shows a schematic diagram of a process for preparing an iron fluoride cathode material according to an embodiment of the present invention.
The iron oxide nanocubes used in the embodiments of the present invention may be commercially available, or may be prepared according to the following method:
preparing an iron oxide nanocube material: adding 50mL of deionized water into 0.1mol of ferric chloride hexahydrate, uniformly mixing to obtain a brown solution, then keeping the temperature of the brown solution at 75 ℃, dropwise adding 50mL of 5.4M sodium hydroxide solution into the brown solution at 75 ℃ under the condition of magnetic stirring, transferring the obtained solution into a reaction kettle, standing and reacting for 96 hours at 100 ℃, then filtering deionized water, washing for three times, and drying for 10 hours at 80 ℃ to obtain the iron oxide nanocube particles.
Example 1
The embodiment prepares the ferric fluoride cathode material, and the specific process is as follows:
s1: preparing the iron oxide @ carbon nitrogen nanocage with the core-shell structure: adding 400mg of iron oxide nanocubes into 500mL0.01M Tris-buffer salt solution, performing ultrasonic dispersion for 30min, then adding 200mg of dopamine hydrochloride into the solution, stirring for 10h, centrifuging, washing for 3 times by deionized water, drying at 80 ℃ for 10h, heating the obtained product from 25 ℃ to 550 ℃ at a speed of 3 ℃/min, and calcining at 550 ℃ for 3h to obtain iron oxide @ carbon nitrogen nanocubes with a core-shell structure;
s2: yolk-like-eggshell structure iron oxide @ carbon nitrogen nanocage material: reacting the core-shell structure iron oxide @ carbon nitrogen nanocage with 20mL of 4M hydrochloric acid under magnetic stirring for 1h, filtering a product after the reaction is finished, washing the product with deionized water for three times, and drying the product at 80 ℃ for 10h to obtain the yolk-like-eggshell structure iron oxide @ carbon nitrogen nanocage material;
s3: preparing an iron fluoride @ carbon nitrogen nanometer cage material with an egg yolk-egg shell structure: addition of NH4HF2Providing a fluorine source, reacting at 190 ℃ for 24h to fluorinate the iron oxide @ carbon nitrogen nanocage to obtain the iron fluoride @ carbon nitrogen nanocage with the core-shell structure, and using NaH2PO4·2H2And O, absorbing ammonia tail gas. The specific scheme is as follows: adding 8.14g of NH4HF2With 10.97g NaH2PO4·2H2And (3) placing O at the bottom of a 100mL reaction kettle, then placing a layer of filter paper on the mixture, then placing the filter paper folded twice above the filter paper, finally placing 0.5g of the core-shell structure iron oxide @ carbon nitrogen nanocage material into the folded filter paper, reacting for 24h at 190 ℃, taking out the product and weighing after the reaction kettle is cooled to room temperature. In order to improve the crystallinity of the product, the product is heated to 210 ℃ from 25 ℃ at the speed of 2 ℃/min and is calcined for 10h at 210 ℃, and the ferric fluoride cathode material is prepared.
Example 2
This example prepared an iron fluoride cathode material, which was different from example 1 in that the fluorination time in S3 was 12 hours, and the rest of the procedure was the same as example 1.
Example 3
In this example, an iron fluoride cathode material was prepared, and the preparation method is different from that of example 1 in that the fluorination method in S3 is specifically as follows:
s3: adding aqueous solution of hydrogen fluoride with the mass concentration of 40-50% to provide a fluorine source, reacting with the yolk shell structure iron oxide @ carbon nitrogen nano cage for 10h at 150 ℃, performing fluorination reaction to obtain the yolk shell structure iron fluoride @ carbon nitrogen nano cage material, heating the product from 25 ℃ to 150 ℃ at the speed of 2 ℃/min and calcining for 10h at 150 ℃ to obtain the iron fluoride cathode material.
Comparative example
This comparative example prepared an iron fluoride cathode material, which was different from example 1 in that fluorination was directly performed without etching in the preparation of the iron fluoride material of this comparative example, S2 was not included, and the rest of the operation was identical to example 1.
Test example 1
TEM images of the iron fluoride positive electrode materials obtained in example 1 and comparative example are shown in FIG. 2 (scale a is 0.5 μm; scale b is 100nm) and FIG. 3.
As can be seen from fig. 2, the ferric fluoride cathode material prepared in example 1 is a nanocube material with a cage structure, the average diameter of the core-shell structure ferric fluoride cathode material particles is 250nm to 700nm, the thickness of the carbon nitrogen shell is 10nm to 50nm, the average particle size of the ferric fluoride core is 100nm to 400nm, and the gap between the shell and the core occupies about half of the total volume of the material.
As can be seen from FIG. 3, the core-shell structured iron fluoride @ carbon nitrogen nanocage has an individual diameter of 250nm to 700nm, a carbon nitrogen shell of 10nm to 50nm, and no void volume, and the nanocube material with the core-shell structure can still be prepared by direct fluorination without etching in the comparative example. The iron fluoride anode material prepared by the comparative example cannot limit the phase change stress in the charging and discharging process, so that the iron fluoride undergoes volume expansion in the energy conversion process, the material is pulverized, and the connectivity is interrupted; so that part of the ferric fluoride loses effective electric connection in the charging and discharging processes, the charging and discharging are incomplete, and the actual discharging capacity is lower than the theoretical capacity; eventually leading to less than good material cycle performance.
The XRD patterns of the iron fluoride positive electrode materials obtained in examples 1 to 3 are shown in fig. 4 to 6, respectively.
As can be seen from fig. 4 to 6, the iron fluoride cathode materials having the core-shell structure can be prepared by different fluorination methods in examples 1 to 3.
Test example 2
In this test example, electrochemical performance of the ferric fluoride positive electrode materials prepared in examples 1 and 3 was tested, and the specific process was as follows:
assembling the battery: according to the iron fluoride cathode material: adhesive: acetylene black ═ 8: 1: grinding the mixture in an agate mortar for 30-60 min to obtain slurry, uniformly coating the slurry on an aluminum foil current collector, and pressing the aluminum foil current collector into a pole piece after vacuum drying. In a glove box filled with argon (H)2O<0.1ppm,O2<0.1ppm) prepared by taking the prepared pole piece as a research electrode, metal lithium as a counter electrode, a PP/PE/PP composite membrane as a diaphragm and LiPF6The electrolyte is assembled into a battery.
And (3) testing the battery performance: the conditions for the battery performance test were: 25 ℃; current densities of 0.1C, 0.2C, 0.5C, 1C, 2C; the voltage range is 2.0-4.2V.
The charging and discharging curves of the typical electrostatic current charging and discharging curve test of the iron fluoride cathode material prepared in the example 1 under the current of 0.2C are shown in FIG. 7.
As can be seen from fig. 7, the initial discharge capacity of the electrode of the ferric fluoride cathode material prepared in example 1 was 229 mAh/g. In the following circulation, the charge-discharge curves tend to be consistent, and the iron fluoride cathode material electrode with the core-shell structure has good electrochemical stability. Research and test verification result in: the yolk-like and eggshell composite material structure of the iron fluoride cathode material is beneficial to keeping the structural integrity of the iron fluoride substance in the reaction process of the iron fluoride substance, and improves the cycle performance of the iron fluoride active material while giving play to the advantage of high specific volume of the iron fluoride, so that a lithium battery applying the yolk shell structure iron fluoride @ carbon nitrogen nanocage material electrode has the advantages of high specific energy, long service life and the like.
The first-turn discharge curve of the typical electrostatic current charge-discharge curve test of the ferric fluoride cathode material prepared in the example 3 under the current of 0.1C is shown in FIG. 8.
As can be seen from FIG. 8, the specific discharge capacity of the electrode of the ferric fluoride cathode material prepared in example 3 is only 86.9mAh/g (the discharge performance at 0.1C current is stronger than that at 0.2C current), which is much smaller than 229mAh/g of example 1. As can be seen from fig. 6 and 8, in examples 1 and 3 of the present invention, the core-shell structure ferric fluoride cathode materials can be prepared by performing fluorination reactions using different fluorine sources, and both of them have electrochemical activity, but the ferric fluoride cathode material prepared in example 1 has more excellent electrochemical performance.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the embodiments, and various changes can be made without departing from the gist of the present invention within the knowledge of those skilled in the art. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims (10)

1. An iron fluoride positive electrode material characterized in that: the iron fluoride anode material is of a core-shell structure, a shell of the iron fluoride anode material comprises a carbon-nitrogen nanocage, an inner core of the iron fluoride anode material comprises iron fluoride, and a gap is formed between the shell and the inner core.
2. The iron fluoride positive electrode material according to claim 1, characterized in that: the size of the gap is 120 nm-350 nm.
3. The iron fluoride positive electrode material according to claim 1, characterized in that: the thickness of the shell of the ferric fluoride anode material is 10 nm-50 nm.
4. The iron fluoride positive electrode material according to claim 1, characterized in that: the average grain diameter of the inner core of the ferric fluoride anode material is 100 nm-400 nm.
5. The iron fluoride positive electrode material according to claim 1, characterized in that: the ferric fluoride cathode material is cubic or cube-like particles; preferably, the average particle size of the ferric fluoride cathode material is 250nm to 700 nm.
6. A method for producing an iron fluoride positive electrode material according to any one of claims 1 to 5, characterized in that: the method comprises the following steps:
s1: dispersing iron oxide nano particles into a solvent, adding a carbon source, mixing, drying and calcining to obtain an iron oxide @ carbon nitrogen material;
s2: etching and drying the iron oxide @ carbon nitrogen material in an acid solution to obtain a precursor material;
s3: and carrying out fluorination reaction on the precursor material and a fluorine source to prepare the ferric fluoride anode material.
7. The method for producing an iron fluoride positive electrode material according to claim 6, characterized in that: in S3, the fluorine source is at least one of hydrogen fluoride, ammonium fluoride, and ammonium bifluoride.
8. The method for producing an iron fluoride positive electrode material according to claim 6, characterized in that: in S3, the temperature of the fluorination reaction is 100-300 ℃.
9. The method for producing an iron fluoride positive electrode material according to claim 6, characterized in that: in S2, the etching time is 0.5 h-5 h; preferably 1 to 3 hours.
10. A lithium battery, characterized in that: the positive pole piece comprises a positive pole current collector and the ferric fluoride positive pole material which is arranged on the positive pole current collector and is prepared by the method for preparing the ferric fluoride positive pole material according to any one of claims 1 to 5 or the method for preparing the ferric fluoride positive pole material according to any one of claims 6 to 9.
CN202210030124.9A 2022-01-12 2022-01-12 Ferric fluoride cathode material and preparation method and application thereof Pending CN114551882A (en)

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