CN114784240B - Graphene-carbon coated lithium iron phosphate positive electrode material, and preparation method and application thereof - Google Patents
Graphene-carbon coated lithium iron phosphate positive electrode material, and preparation method and application thereof Download PDFInfo
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
Abstract
The invention discloses a graphene-carbon coated lithium iron phosphate positive electrode material, and a preparation method and application thereof, wherein the method comprises the following steps: (1) Placing the mixture of MgO and PEG in an inert atmosphere, and performing high-temperature pyrolysis to obtain graphene; (2) Mixing a lithium source, an iron source and a phosphorus source, and grinding to obtain a precursor; (3) Mixing graphene, a carbon source and a solvent, and stirring to obtain a dispersion liquid; (4) And mixing the precursor and the dispersion liquid, grinding, drying, and sintering at high temperature under an inert atmosphere to obtain the graphene-carbon coated lithium iron phosphate anode material. According to the invention, graphene generated by pyrolysis of MgO catalytic PEG under high-temperature conditions is of a thinner lamellar structure, and has higher graphitization degree, specific surface area and electron migration rate, and the graphene is used as a conductive network structure among lithium iron phosphate particles, so that the overall electron conductivity of the carbon-coated lithium iron phosphate anode material can be improved, and the multiplying power performance and the cycle performance of the carbon-coated lithium iron phosphate anode material serving as the anode material are improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a graphene-carbon coated lithium iron phosphate positive electrode material, and a preparation method and application thereof.
Background
The lithium ion battery has the advantages of quick charge and discharge, long cycle life, high output power, high average output voltage, environmental protection and the like, and has good development prospect in other electronic equipment such as electric automobiles, energy storage, notebook computers, unmanned aerial vehicles and the like. In lithium ion batteries, the positive electrode material is an important part that determines the performance of the battery. Currently, four common positive electrode materials of lithium ion batteries are lithium cobaltate, lithium iron phosphate, ternary positive electrode materials and lithium manganate, wherein, the lithium iron phosphate is considered as the best material for producing large-scale battery modules due to good cycle performance, thermal stability and low cost. However, the lithium iron phosphate with the olivine structure has lower electron conduction and ion conduction capacity, so that the lithium iron phosphate has lower energy density and poorer high-rate charge and discharge performance, and practical application is limited. Common ways to improve the performance of lithium iron phosphate include particle refinement, ion doping, and carbon coating. The current process technology for carbon coating the lithium iron phosphate is simpler, the carbon coating technology used in the traditional process cannot ensure that a complete carbon coating structure is obtained, and a conductive network between the carbon-coated lithium iron phosphate is absent, so that the improvement of the conductive performance of the lithium iron phosphate is not obvious, and the improvement effect of the multiplying power performance and the cycle performance is not obvious.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, one purpose of the invention is to provide a graphene-carbon coated lithium iron phosphate positive electrode material, a preparation method and application thereof, wherein graphene generated by pyrolysis of MgO catalyzed PEG under high temperature conditions is of a thinner lamellar structure, and has higher graphitization degree, higher specific surface area and higher electron migration rate.
In one aspect of the invention, a method of preparing a graphene-carbon coated lithium iron phosphate positive electrode material is provided. According to an embodiment of the invention, the method comprises:
(1) Placing the mixture of MgO and PEG in an inert atmosphere, and performing high-temperature pyrolysis to obtain graphene;
(2) Mixing a lithium source, an iron source and a phosphorus source, and grinding to obtain a precursor;
(3) Mixing the graphene, a carbon source and a solvent, and stirring to obtain a dispersion liquid;
(4) And mixing the precursor and the dispersion liquid, grinding, drying, and sintering at high temperature under an inert atmosphere to obtain the graphene-carbon coated lithium iron phosphate positive electrode material.
According to the method for preparing the graphene-carbon coated lithium iron phosphate anode material, in the step (1), mgO is adopted to catalyze PEG to crack hydrocarbon molecules under the high-temperature condition to generate carbon atoms, the carbon atoms are diffused, deposited and grown on the surface of MgO to form graphene sheets, and the thickness of the generated graphene sheets is about(about 10 nm) with a high degree of graphitization (I G /I D =1.0-1.2), higher specific surface area (1000-2000 m 2 /g) and a higher electron transfer rate (10 3 -10 6 S/m), the graphene is used as a conductive network structure among lithium iron phosphate particles, and the overall conductive capacity of the carbon-coated lithium iron phosphate positive electrode material can be improved, so that the rate performance and the cycle performance of the carbon-coated lithium iron phosphate positive electrode material as the positive electrode material are improved.
In addition, the method for preparing the graphene-carbon coated lithium iron phosphate cathode material according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the invention, in step (1), the pyrolysis temperature is 800-1200 degrees celsius and the pyrolysis time is 10-20 minutes.
In some embodiments of the invention, in step (1), the mass ratio of MgO to PEG is 1.5 (1-6).
In some embodiments of the present invention, in step (1), the graphene has a specific surface area of 1000-2000m 2 /g。
In some embodiments of the invention, the graphene has an electron mobility rate of 10 3 -10 6 S/m。
In some embodiments of the invention, in step (2), the molar ratio of the lithium element in the lithium source, the iron element in the iron source, and the phosphorus element in the phosphorus source is (0.95-1.1): 1:1.
in some embodiments of the invention, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate, and lithium acetate.
In some embodiments of the invention, the iron source is selected from at least one of ferrous oxalate, ferric acetate, ferric red, and ferrous phosphate.
In some embodiments of the invention, the phosphorus source is selected from at least one of monoammonium phosphate and diammonium phosphate.
In some embodiments of the invention, in step (3), the mass ratio of graphene to carbon source is (0.2-1): 1.
in some embodiments of the invention, the carbon source is selected from at least one of sucrose, glucose, and PEG.
In some embodiments of the invention, in step (4), the high temperature sintering is performed at a temperature of 400-800 degrees celsius for a time of 7-9 hours.
In some embodiments of the invention, the mass ratio of the graphene to the precursor is 1 (200-300).
In yet another aspect of the invention, a graphene-carbon coated lithium iron phosphate positive electrode material is provided. According to the embodiment of the invention, the graphene-carbon coated lithium iron phosphate positive electrode material is prepared by adopting the method described in the embodiment. Therefore, the overall electron conducting capacity of the carbon-coated lithium iron phosphate anode material is improved, and the rate performance and the cycle performance of the carbon-coated lithium iron phosphate anode material serving as the anode material are improved.
In a third aspect of the present invention, the present invention provides a positive electrode sheet. According to the embodiment of the invention, the positive plate is prepared from the graphene-carbon coated lithium iron phosphate positive electrode material obtained by the method in the embodiment, and therefore, the positive plate has all the advantages of the graphene-carbon coated lithium iron phosphate positive electrode material.
In a fourth aspect of the invention, the invention provides a lithium ion battery. According to an embodiment of the present invention, the lithium ion battery has the positive electrode sheet described in the above embodiment. Thus, the lithium battery has excellent cycle stability and rate performance.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
fig. 1 is a schematic flow chart of a method for preparing a graphene-carbon coated lithium iron phosphate positive electrode material according to an embodiment of the present invention;
fig. 2 is a TEM image of graphene prepared in example 1 of the present invention;
fig. 3 is a Raman diagram of graphene prepared in example 1 of the present invention;
FIG. 4 is N of graphene prepared in example 1 of the present invention 2 Adsorption and desorption test results are shown in a schematic diagram.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
In one aspect of the invention, a method of preparing a graphene-carbon coated lithium iron phosphate positive electrode material is provided. According to an embodiment of the present invention, referring to fig. 1, the method includes:
s100: placing the mixture of MgO and PEG under inert atmosphere, and high-temperature cracking
In this step, the mixture of MgO powder and PEG is subjected to high temperature pyrolysis under an inert atmosphere, so as to obtain graphene. The kind of the inert atmosphere is not particularly limited, and may be arbitrarily selected by those skilled in the art according to the actual circumstances, preferably N 2 . As a specific example, mgO powder and polyethylene glycol PEG are weighed in a certain proportion and mixed uniformly, and then the mixture is placed in the utilized N 2 Exhausting air and adding through pipe type furnaceIn a quartz tube heated to a certain temperature, cracking and carbonizing are carried out, the temperature is kept stable during the period, and N is continuously introduced into the quartz tube 2 。
According to one embodiment of the invention, the pyrolysis temperature is 800-1200 ℃, and the pyrolysis time is 10-20 minutes, so that graphene with higher graphitization degree and more complete carbon structure can be obtained. The inventor finds that if the high-temperature pyrolysis temperature is too low, the graphitization degree of the prepared graphene is low, the conductivity is poor, and if the high-temperature pyrolysis temperature is too high, the PEG decomposition speed is too high, so that a large amount of amorphous carbon is accumulated on the MgO surface to reduce the catalytic activity of the amorphous carbon; if the pyrolysis time is too short, insufficient PEG pyrolysis or incomplete conversion of non-static carbon into graphene may be caused, the yield may be reduced, and if the pyrolysis time is too long, the yield may not be affected, but the energy consumption may be increased.
According to still another embodiment of the present invention, the mass ratio of MgO to PEG is 1.5 (1-6), whereby a graphene sheet material having a high graphitization degree and a relatively complete carbon structure can be prepared with a certain yield. The inventors found that if the MgO content is too high, it causes Mgo waste, increases the difficulty in removing MgO in the later stage, and if the MgO content is too low, it causes the reduction of the conversion rate of PEG into graphene material.
According to another specific embodiment of the invention, the specific surface area of the graphene prepared by the step is 1000-2000m 2 And/g, thereby providing more electron and ion transport sites during charge and discharge.
According to another embodiment of the present invention, the electron migration rate of the graphene prepared by this step is 10 3 -10 6 S/m, whereby the electron transport rate can be increased.
In the embodiment of the invention, the method further comprises the following steps of: cooling the carbonized product after pyrolysis to room temperature, collecting the carbonized product, carrying out acid washing for a plurality of times by utilizing an acid solution (such as dilute hydrochloric acid), enabling the catalyst MgO to react with the acid solution and dissolve in the acid solution, finally washing in an ultrasonic machine by deionized water and absolute ethyl alcohol, and filtering to obtain a final product, namely the graphene.
In the embodiment of the invention, the source of MgO powder is not particularly limited, and the MgO powder can be purchased or synthesized by itself, and as a specific example, firstly, inorganic salt magnesium nitrate is crushed by a crusher, and the magnesium nitrate powder and polyethylene glycol PEG are mixed and kneaded into a mass according to a certain mass ratio, and then the mass is placed in a clean and dry beaker, sealed by a preservative film, and placed for more than 12 hours at normal temperature, so that the PEG and the magnesium nitrate powder are fully soaked; and then placing the mixture of the magnesium nitrate and the PEG in a muffle furnace, sintering for 1h at 550-650 ℃, and cooling to obtain the MgO powder.
S200: mixing lithium source, iron source and phosphorus source, grinding
In this step, a lithium source, an iron source, and a phosphorus source are mixed, and ground (coarse grinding and fine grinding) to obtain a precursor.
According to yet another specific embodiment of the present invention, the molar ratio of the lithium element in the lithium source, the iron element in the iron source, and the phosphorus element in the phosphorus source is (0.95-1.1): 1:1, thereby preparing a lithium iron phosphate product and ensuring sufficient conversion of a lithium source.
In the embodiment of the present invention, the specific kind of the above-mentioned lithium source is not particularly limited, and may be arbitrarily selected according to actual needs by those skilled in the art, and as a preferable embodiment, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate and lithium acetate.
In the embodiment of the present invention, the specific kind of the above-mentioned iron source is not particularly limited, and may be arbitrarily selected according to actual needs by those skilled in the art, and as a preferable scheme, the iron source is selected from at least one of ferrous oxalate, ferric acetate and ferrous phosphate.
In the embodiment of the present invention, the specific kind of the above-mentioned phosphorus source is not particularly limited, and may be arbitrarily selected by those skilled in the art according to actual needs, and as a preferable scheme, the phosphorus source is selected from at least one of monoammonium phosphate and diammonium phosphate.
S300: mixing the graphene, a carbon source and a solvent, and stirring
In this step, the graphene, a carbon source and a solvent are mixed and stirred for 1.5 to 2.5 hours to obtain a dispersion.
According to still another specific embodiment of the present invention, the mass ratio of the graphene to the carbon source is (0.2-1): 1, therefore, graphene-C coated lithium iron phosphate with proper specific surface area and good conductivity can be prepared, if the graphene is too low in ratio, the conductivity is not obviously improved, and if the graphene is too high in ratio, the specific surface area of the graphene-C coated lithium iron phosphate is too large, and particle agglomeration is easy to occur.
In the embodiment of the present invention, the specific kind of the above carbon source is not particularly limited, and may be arbitrarily selected according to actual needs by those skilled in the art, and as a preferred embodiment, the carbon source is at least one selected from sucrose, glucose and PEG.
In the embodiments of the present invention, the specific kind of the above-mentioned solvent is not particularly limited, and may be arbitrarily selected according to actual needs by those skilled in the art, so long as the effect of dispersing graphene and carbon source is achieved and it is easily removed in a subsequent drying step, such as ethanol.
S400: mixing the precursor and the dispersion, grinding, drying, and sintering at high temperature under inert atmosphere
In the step, the precursor and the dispersion liquid are mixed, the particle size of the precursor is reduced to 350-650nm through grinding (coarse grinding and fine grinding), the shape and the size of the precursor are more uniform, and the precursor particles with the surfaces coated with graphene and carbon sources are obtained after spray drying; sintering the precursor at high temperature in a high-temperature kiln in an inert gas atmosphere, generating lithium iron phosphate through oxidation-reduction reaction, and simultaneously forming amorphous carbon by high-temperature cracking of a carbon source, depositing the amorphous carbon on the surface of the lithium iron phosphate and growing to form a carbon coating layer; and cooling and crushing to obtain the graphene-carbon coated lithium iron phosphate anode material. The kind of the inert atmosphere is not particularly limited, and those skilled in the art can optionally select Ar, N according to the actual conditions 2 They are with H 2 Or other inert gas, preferably N 2 。
According to a further embodiment of the invention, the high temperature sintering is carried out at a temperature of 400-800 ℃ for a time of 7-9 hours, whereby a fine and uniform, relatively complete crystal form and Fe is obtained 3+ Lithium iron phosphate structure with few phase impurities. The inventors found that if the high temperature sintering temperature is too low, amorphous structure formation and nano Fe are caused 3+ If the high-temperature sintering temperature is too high, crystal particles are larger, and the particle size of a lithium iron phosphate finished product is increased; if the high-temperature sintering time is too short, incomplete transformation of the crystal form of the lithium iron phosphate and too small growth particle size of the finished product are caused, agglomeration is easy to occur, and if the high-temperature sintering time is too long, the growth of the particle size of the finished product of the lithium iron phosphate is too large, and the transmission capacity of electrons and ions is reduced.
According to another specific embodiment of the invention, the addition amount of the graphene accounts for 0.3-10% of the finished lithium iron phosphate product, so that graphene-C coated lithium iron phosphate with good conductivity and large specific surface area can be obtained. The mass ratio of the graphene to the precursor is limited to the above range because the inventors found that if the content of the graphene is too high, the specific surface area of the graphene-C coated lithium iron phosphate is too large, particle agglomeration is liable to be caused, and if the content of the graphene is too low, the improvement effect of the conductivity of the graphene-C coated lithium iron phosphate is not obvious.
According to the method for preparing the graphene-carbon coated lithium iron phosphate cathode material, in the step (1), graphene generated by pyrolysis of MgO catalytic PEG under high temperature conditions is of a thinner lamellar structure, and has higher graphitization degree, specific surface area and electron migration rate.
In yet another aspect of the invention, a graphene-carbon coated lithium iron phosphate positive electrode material is provided. According to the embodiment of the invention, the graphene-carbon coated lithium iron phosphate positive electrode material is prepared by adopting the method described in the embodiment. Therefore, the overall electron conducting capacity of the carbon-coated lithium iron phosphate anode material is improved, and the rate performance and the cycle performance of the carbon-coated lithium iron phosphate anode material serving as the anode material are improved.
In a third aspect of the present invention, the present invention provides a positive electrode sheet. According to the embodiment of the invention, the positive plate is prepared from the graphene-carbon coated lithium iron phosphate positive electrode material obtained by the method in the embodiment, and therefore, the positive plate has all the advantages of the graphene-carbon coated lithium iron phosphate positive electrode material.
In a fourth aspect of the invention, the invention provides a lithium ion battery. According to an embodiment of the present invention, the lithium ion battery has the positive electrode sheet described in the above embodiment. Thus, the lithium battery has excellent cycle stability and rate performance.
The following detailed description of embodiments of the invention is provided for the purpose of illustration only and is not to be construed as limiting the invention. In addition, all reagents employed in the examples below are commercially available or may be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated.
Example 1
The method comprises the following steps:
(1) Preparation of graphene: weighing MgO powder and polyethylene glycol PEG according to a certain proportion, and uniformly mixing, wherein the mass ratio of the MgO powder to the polyethylene glycol PEG is 1.5:6, then the mixture is placed in an already utilized N 2 Exhausting air, heating to 1000 deg.C in tube furnace, cracking and carbonizing for 10min while maintaining stable temperature and introducing N 2 . And taking out the quartz tube, cooling to room temperature, collecting carbonized products, and carrying out acid washing for a plurality of times by using dilute hydrochloric acid. Finally, washing the graphene with deionized water and absolute ethyl alcohol in an ultrasonic machine, and filtering to obtain a final product, namely graphene. TEM, raman and specific surface area tests were performed on the graphene. TEM image such as attachedAs shown in fig. 2, it can be seen from fig. 2 that the obtained carbon material is of a nano-scale lamellar structure and has a surface with a rich and dense pore structure. The Raman result analysis shown in fig. 3 can obtain that the carbon product has higher graphitization degree; from FIG. 4N 2 The adsorption and desorption test result can be analyzed to obtain the specific surface area of the carbon product reaching 1400m 2 And/g, illustrating that the carbon product obtained in this step is a lamellar graphene material having a high surface area.
(2) Preparation of graphene-carbon coated lithium iron phosphate: weighing lithium carbonate, iron red powder and ammonium dihydrogen phosphate in a certain proportion, mixing, dispersing, coarsely grinding and finely grinding to 500nm particle size by using a ball mill, wherein the molar ratio of lithium element in a lithium source to iron element in an iron source to phosphorus element in a phosphorus source is 1:1:1, obtaining a precursor; dispersing graphene into ethanol, and adding a carbon source, wherein the mass ratio of the graphene to the carbon source is 0.2:1, stirring for 2 hours, adding the mixture into a precursor, and carrying out coarse grinding and fine grinding by utilizing a ball mill, wherein the mass ratio of graphene to the precursor is 1:300. and (3) after spray drying, sintering in a high-temperature kiln at 800 ℃ for 8 hours under the protection of inert gas, and cooling and crushing to obtain the graphene-carbon coated lithium iron phosphate material.
(3) Conductivity test:
a: the graphene-carbon coated lithium iron phosphate material was subjected to a powder resistance test, and the powder resistance test results are shown in table 1.
B: the graphene-carbon coated lithium iron phosphate material is used as a positive electrode material, and the following lithium iron phosphate is adopted: conductive agent (SP): positive electrode binder (PVDF) =90%: 5%: the 5% by weight was dispersed in a stirring tank at 800rpm/min for 30 minutes to be uniformly mixed, and NMP was then added thereto and stirred at 2500rpm/min for 3 hours to prepare a slurry having a proper solid content (60%) and a proper fluidity (6000 mPa.s). The slurry conductivity was measured by a slurry resistivity tester after filtration through a 200 mesh screen, and the slurry conductivity test results are shown in table 2.
C: the graphene-carbon coated lithium iron phosphate material is used as a positive electrode material, and the following lithium iron phosphate is adopted: conductive agent (SP): positive electrode binder (PVDF) =90%: 5%: the 5% by weight was dispersed in a stirrer at 800rpm/min for 30 minutes to be uniformly mixed, and then N-methylpyrrolidone was added thereto, and stirred at 2500rpm/min for 3 hours to prepare a slurry having a proper solid content (60%) and a proper fluidity (6000 mPa.s). After being filtered by a 200-mesh screen, the carbon-coated aluminum foil is coated with a double-sided coating pole piece with certain coating quality by a transfer coater; after coating and drying, cold pressing the pole piece by using a roller press to obtain a rolled pole piece, and performing a diaphragm resistance test on the pole piece, wherein the diaphragm resistance test result is shown in Table 3.
Example 2
In the preparation process of graphene, the mass ratio of MgO powder to polyethylene glycol PEG is 1.5:6, cracking and carbonizing at 800 ℃ for 20min. In the preparation process of the graphene-carbon coated lithium iron phosphate, the mass ratio of graphene to a carbon source is 0.5:1, the mass ratio of the graphene to the precursor is 1:250, the high-temperature sintering temperature is 790 ℃, and the time is 9 hours. The other contents are the same as in example 1.
Example 3
In the preparation process of graphene, the mass ratio of MgO powder to polyethylene glycol PEG is 1.5:6, cracking and carbonizing at 1000 ℃ for 10min. In the preparation process of the graphene-carbon coated lithium iron phosphate, the mass ratio of graphene to a carbon source is 0.8:1, the mass ratio of the graphene to the precursor is 1:225, the high-temperature sintering temperature is 800 ℃, and the time is 7 hours. The other contents are the same as in example 1.
Example 4
In the preparation process of graphene, the mass ratio of MgO powder to polyethylene glycol PEG is 1.5:6, cracking and carbonizing at 1200 ℃ for 10min. In the preparation process of the graphene-carbon coated lithium iron phosphate, the mass ratio of graphene to a carbon source is 1:1, and the mass ratio of graphene to a precursor is 1:200. The other contents are the same as in example 1.
Comparative example 1
The comparative example was prepared by adding no graphene during the preparation of carbon-coated lithium iron phosphate, and the other contents were the same as in example 1.
TABLE 1
TABLE 2
TABLE 3 Table 3
As can be seen from tables 1-3, the powder resistivity and slurry resistivity of the graphene-carbon coated lithium iron phosphate materials of examples 1-4 were significantly reduced, and the sheet resistance of examples 1-4 was also significantly reduced, as compared to comparative example 1.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (9)
1. A method for preparing a graphene-carbon coated lithium iron phosphate positive electrode material, comprising the steps of:
(1) Placing a mixture of MgO and PEG in an inert atmosphere, and performing high-temperature pyrolysis, wherein the high-temperature pyrolysis temperature is 800-1200 ℃, and the high-temperature pyrolysis time is 10-20 minutes so as to obtain graphene;
the mass ratio of MgO to PEG is 1.5 (1-6); the specific surface area of the graphene is 1000-2000m 2 /g, the electron migration rate of the graphene is 10 3 -10 6 S/m；
(2) Mixing a lithium source, an iron source and a phosphorus source, and grinding to obtain a precursor;
(3) Mixing the graphene, a carbon source and a solvent, wherein the mass ratio of the graphene to the carbon source is (0.2-1) 1, and stirring to obtain a dispersion liquid;
(4) Mixing the precursor and the dispersion liquid, grinding, drying, and sintering at a high temperature of 400-800 ℃ in an inert atmosphere, wherein the high temperature sintering time is 7-9 hours, and the mass ratio of the graphene to the precursor is 1 (200-300), so as to obtain the graphene-carbon coated lithium iron phosphate positive electrode material.
2. The method according to claim 1, wherein in step (2), a molar ratio of lithium element in the lithium source, iron element in the iron source, and phosphorus element in the phosphorus source is (0.95-1.1): 1:1.
3. the method of claim 1, wherein the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium phosphate, and lithium acetate.
4. The method of claim 1, wherein the iron source is selected from at least one of ferrous oxalate, ferric acetate, and ferrous phosphate.
5. The method of claim 1, wherein the phosphorus source is selected from at least one of monoammonium phosphate and diammonium phosphate.
6. The method of claim 1, wherein the carbon source is selected from at least one of sucrose, glucose, starch, and PEG.
7. A graphene-carbon coated lithium iron phosphate positive electrode material, characterized in that the graphene-carbon coated lithium iron phosphate positive electrode material is prepared by the method of any one of claims 1 to 6.
8. The positive plate is characterized by being prepared from the graphene-carbon coated lithium iron phosphate positive material obtained by the method of any one of claims 1-6.
9. A lithium ion battery characterized in that it has the positive electrode sheet according to claim 8.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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