CN112751003B - Carbon-coated lithium iron phosphate and preparation method thereof, lithium iron phosphate positive plate and lithium iron phosphate battery - Google Patents
Carbon-coated lithium iron phosphate and preparation method thereof, lithium iron phosphate positive plate and lithium iron phosphate battery Download PDFInfo
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Abstract
The invention provides carbon-coated lithium iron phosphate, a preparation method of the carbon-coated lithium iron phosphate, and a lithium iron phosphate positive plate and a lithium iron phosphate battery which are prepared by taking the carbon-coated lithium iron phosphate as a raw material, and the method comprises the following steps: s1, preparing graphene oxide dispersion liquid; s2, mixing and stirring ethylenediaminetetraacetic acid and ferric nitrate, and standing to obtain a solution containing a complex; s3, mixing and stirring the solution containing the complex obtained in the step S2 and the graphene oxide dispersion liquid obtained in the step S1 to obtain a mixed liquid; s4, performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain micron lithium iron phosphate; s5, adding the micron lithium iron phosphate obtained in the step S4 into the mixed solution obtained in the step S3, stirring and standing; and S6, transferring the mixture obtained in the step S5 to a hydrothermal reaction kettle for hydrothermal reaction, taking out the mixture after the hydrothermal reaction is finished, and naturally cooling, filtering and draining the mixture to obtain the carbon-coated lithium iron phosphate.
Description
Technical Field
The invention relates to the technical field of lithium iron phosphate materials, in particular to carbon-coated lithium iron phosphate and a preparation method thereof, a lithium iron phosphate positive plate and a lithium iron phosphate battery.
Background
Lithium iron phosphate is an electrode material of a lithium ion battery and has a chemical formula of LiFePO4The lithium ion battery is mainly used for various lithium ion batteries. NTT since 1996 in Japan was first exposed to AyMPO4(A is an alkali metal, M is a combination of CoFe: LiFeCoPO4) After the positive electrode material of the olivine-structured lithium battery, research group of john.b. goodenough et al, texas state university, 1997, also reported LiFePO4Reversibly incorporate into and extract from the lithium.
The lithium iron phosphate is used as the anode material of the electrode, has higher reversible charge-discharge specific capacity, has the advantages of wide raw material source, low pollution, good safety, long cycle life and the like, and is an ideal anode material of the power-shaped and energy-storage lithium ion battery at present. But the conductivity of the material is low due to the self structure of the material, and high-rate charge and discharge cannot be realized.
Disclosure of Invention
The invention aims to provide carbon-coated lithium iron phosphate and a preparation method thereof, a lithium iron phosphate positive plate and a lithium iron phosphate battery.
The embodiment of the invention is realized by the following technical scheme:
the invention provides a preparation method of carbon-coated lithium iron phosphate, which comprises the following steps:
s1, preparing graphene oxide dispersion liquid;
s2, mixing and stirring ethylenediaminetetraacetic acid and ferric nitrate, and standing to obtain a solution containing a complex;
s3, mixing and stirring the solution containing the complex obtained in the step S2 and the graphene oxide dispersion liquid obtained in the step S1 to obtain a mixed liquid;
s4, performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain micron lithium iron phosphate;
s5, adding the micron lithium iron phosphate obtained in the step S4 into the mixed solution obtained in the step S3, stirring and standing;
and S6, transferring the mixture obtained in the step S5 to a hydrothermal reaction kettle for hydrothermal reaction, taking out the mixture after the hydrothermal reaction is finished, and naturally cooling, filtering and draining the mixture to obtain the carbon-coated lithium iron phosphate.
The invention also provides a preparation method of the carbon-coated lithium iron phosphate.
The third aspect of the invention provides a lithium iron phosphate positive plate made of the carbon-coated lithium iron phosphate.
The invention provides a lithium iron phosphate battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate is the lithium iron phosphate positive plate.
The technical scheme of the embodiment of the invention at least has the following advantages and beneficial effects:
the carbon-coated lithium iron phosphate prepared by the preparation method provided by the invention takes the graphene oxide as a medium, and coats the organic carbon source ethylene diamine tetraacetic acid on the surface of the lithium iron phosphate to improve the conductivity of the material, and the reducibility of the ethylene diamine tetraacetic acid can also prevent Fe2+And oxidizing, and, the range-limiting effect of graphene oxide can prevent the particle size grow of lithium iron phosphate, and then has prevented that the transfer distance grow of lithium ion from leading to the conductivity to reduce, in addition, have the iron ion on the complex that forms after ethylenediamine tetraacetic acid and the iron nitrate complex, iron on the complex and the iron phosphate lithium take place electrostatic adsorption with the carboxylic acid group on the graphene oxide respectively, make ethylenediamine tetraacetic acid can wrap up in lithium iron phosphate's surface more steadily from this, promote lithium iron phosphate's conductivity.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The invention provides a preparation method of carbon-coated lithium iron phosphate, which comprises the following steps:
s1, preparing graphene oxide dispersion liquid;
in step S1, the method specifically includes:
s11, adding 16-18 parts by weight of graphene oxide powder into 100 parts by weight of water, and performing ultrasonic dispersion;
s12, adding hydrochloric acid dropwise into the solution obtained in the step S11, and adjusting the pH value of the solution to 3-5.
Through the treatment, the size of the graphene oxide sheets in the dispersion liquid can reach 200-300 nm, and the size of the graphene oxide can be screened by adjusting the pH value of the dispersion liquid because the large-size graphene oxide exists in an alkaline environment and the small-size graphene oxide exists in an acidic environment.
S2, mixing and stirring 10-12 parts by weight of ethylenediamine tetraacetic acid and 10-12 parts by weight of ferric nitrate, and standing to obtain a solution containing a complex;
s3, mixing and stirring the solution containing the complex obtained in the step S2 and the graphene oxide dispersion liquid obtained in the step S1 to obtain a mixed liquid;
the purpose of this step is to make iron in the complex and carboxylic acid groups on graphene oxide generate electrostatic adsorption, so that ethylenediaminetetraacetic acid and graphene oxide are stably connected together.
S4, performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain 1-2 micron lithium iron phosphate;
the purpose of limiting the size of the micron lithium iron phosphate to 1-2 microns is to enable the micron lithium iron phosphate to be matched with graphene oxide with the size of 200-300 nanometers, a complex containing ethylene diamine tetraacetic acid is stably connected with the graphene oxide through electrostatic interaction, then carboxylic acid groups on the graphene oxide and iron on the micron lithium iron phosphate generate electrostatic adsorption, so that the ethylene diamine tetraacetic acid is stably coated on the surface of the micron lithium iron phosphate and is not easy to fall off, in addition, the graphene oxide is coated on the surface of the micron lithium iron phosphate, the size of the micron lithium iron phosphate is prevented from being increased through the domain limiting effect, and the transfer distance of lithium ions is ensured not to be increased.
S5, adding the micron lithium iron phosphate obtained in the step S4 into the mixed solution obtained in the step S3, stirring and standing;
and S6, transferring the mixture obtained in the step S5 to a hydrothermal reaction kettle for hydrothermal reaction, taking out the mixture after the hydrothermal reaction is finished, and naturally cooling, filtering and draining the mixture to obtain solid powder.
Wherein the reaction temperature of the hydrothermal reaction is 120-160 ℃, and the reaction time is 2-3 hours.
The hydrothermal reaction is the assembly process of graphene oxide with ethylene diamine tetraacetic acid and micron lithium iron phosphate, iron on the micron lithium iron phosphate and carboxylic acid groups on the graphene oxide generate electrostatic adsorption, so that the graphene oxide with smaller size is adsorbed on the surface of the micron lithium iron phosphate with larger size, the ethylene diamine tetraacetic acid is further coated on the surface of the micron lithium iron phosphate as a carbon shell, and the reducibility of the ethylene diamine tetraacetic acid can effectively prevent Fe from being generated on the first hand2+The oxidation takes place, and the introduction of second aspect carbon shell has promoted the holistic electric conductive property of material, and the stable shell structure of third aspect oxidation graphite alkene formation on micron lithium iron phosphate's surface utilizes the confinement effect to make lithium iron phosphate's size keep in less scope, has guaranteed promptly that lithium ion's transmission distance can not grow.
S7, putting the solid powder obtained in the step S6 into deionized water, then adding carbon nanofibers, ultrasonically mixing, filtering and draining to obtain the carbon nanofiber composite material.
Wherein, the diameter of the carbon nanofiber is 50 nanometers, and the length is 300 nanometers.
Wherein the addition amount of the solid powder is 50 parts by weight, and the addition amount of the carbon nanofiber is 20 parts by weight.
Through the electrostatic adsorption between the carboxylic acid group on the carbon nanofiber and the iron on the lithium iron phosphate, different particles are connected together, and the carbon nanofiber is wound with each other, so that the structure of the material is firmer, and the carbon nanofiber has good conductivity, and the conductivity of the material is further improved.
The invention provides carbon-coated lithium iron phosphate in a second aspect, which is prepared by the preparation method.
The third aspect of the present invention provides a lithium iron phosphate positive plate, which is prepared from the above carbon-coated lithium iron phosphate, and the specific preparation method is as follows:
mixing and stirring 10 parts by weight of polyvinylidene fluoride, 10 parts by weight of carbon nano tubes and 26 parts by weight of N-methyl pyrrolidone to obtain mixed slurry, then adding 40 parts by weight of carbon-coated lithium iron phosphate into the mixed slurry, stirring and dispersing to obtain conductive slurry, coating the conductive slurry on the surface of an aluminum foil current collector, and rolling to obtain the lithium iron phosphate positive plate.
The invention provides a lithium iron phosphate battery, which comprises a negative plate, a diaphragm, electrolyte and the lithium iron phosphate positive plate, and is assembled and molded by conventional means in the field.
Example 1
Firstly, preparing graphene oxide dispersion liquid, adding 17 parts by weight of graphene oxide powder into 100 parts by weight of water, performing ultrasonic dispersion, then dropwise adding hydrochloric acid into the solution, adjusting the pH value of the solution to be 4, obtaining graphene oxide sheets with the size of 250 nanometers, and standing for later use; mixing and stirring 11 parts by weight of ethylenediamine tetraacetic acid and 11 parts by weight of ferric nitrate to obtain a solution containing a complex; mixing the solution containing the complex with the graphene oxide dispersion liquid, stirring and standing to obtain a mixed solution; performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain micrometer lithium iron phosphate with the size of 1.5 micrometers; and adding 10 parts by weight of the micron lithium iron phosphate into the mixed solution, stirring, then transferring to a hydrothermal reaction kettle for hydrothermal reaction, wherein the reaction temperature is 140 ℃, the reaction time is 2 hours, after the reaction is finished, taking out, naturally cooling, filtering and draining to obtain solid powder, taking 50 parts by weight of the solid powder, putting into 100 parts by weight of deionized water, then adding 20 parts by weight of carbon nanofiber (the diameter is 50 nanometers, the length is 300 nanometers), ultrasonically mixing, taking out, filtering and drying to obtain the carbon-coated lithium iron phosphate A1.
Example 2
Firstly, preparing graphene oxide dispersion liquid, adding 16 parts by weight of graphene oxide powder into 100 parts by weight of water, performing ultrasonic dispersion, then dropwise adding hydrochloric acid into the solution, adjusting the pH value of the solution to be 3, obtaining graphene oxide sheets with the size of 200 nanometers, and standing for later use; mixing and stirring 10 parts by weight of ethylenediamine tetraacetic acid and 10 parts by weight of ferric nitrate to obtain a solution containing a complex; mixing the solution containing the complex with the graphene oxide dispersion liquid, stirring and standing to obtain a mixed solution; performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain 1-micron lithium iron phosphate; and adding 10 parts by weight of the micron lithium iron phosphate into the mixed solution, stirring, then transferring to a hydrothermal reaction kettle for hydrothermal reaction, wherein the reaction temperature is 120 ℃, the reaction time is 3 hours, after the reaction is finished, taking out, naturally cooling, filtering and draining to obtain solid powder, taking 50 parts by weight of the solid powder, putting into 100 parts by weight of deionized water, then adding 20 parts by weight of carbon nanofiber (the diameter is 50 nanometers, the length is 300 nanometers), ultrasonically mixing, taking out, filtering and drying to obtain the carbon-coated lithium iron phosphate A2.
Example 3
Firstly, preparing graphene oxide dispersion liquid, adding 18 parts by weight of graphene oxide powder into 100 parts by weight of water, performing ultrasonic dispersion, then dropwise adding hydrochloric acid into the solution, adjusting the pH value of the solution to be 5 to obtain graphene oxide sheets with the size of 300 nanometers, and standing the graphene oxide sheets for later use; mixing and stirring 12 parts by weight of ethylenediamine tetraacetic acid and 12 parts by weight of ferric nitrate to obtain a solution containing a complex; mixing the solution containing the complex with the graphene oxide dispersion liquid, stirring and standing to obtain a mixed solution; performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain 2-micrometer lithium iron phosphate; and adding 10 parts by weight of the micron lithium iron phosphate into the mixed solution, stirring, then transferring to a hydrothermal reaction kettle for hydrothermal reaction, wherein the reaction temperature is 160 ℃, the reaction time is 2 hours, after the reaction is finished, taking out, naturally cooling, filtering and draining to obtain solid powder, taking 50 parts by weight of the solid powder, putting into 100 parts by weight of deionized water, then adding 20 parts by weight of carbon nanofiber (the diameter is 50 nanometers, the length is 300 nanometers), ultrasonically mixing, taking out, filtering and drying to obtain the carbon-coated lithium iron phosphate A3.
Comparative example 1
The remaining characteristics were the same as in example 1, except that the amount of graphene oxide powder added was 5 parts by weight, to obtain lithium iron phosphate D1.
Comparative example 2
The remaining characteristics were the same as in example 1, except that the amount of graphene oxide powder added was 30 parts by weight, to obtain lithium iron phosphate D2.
Comparative example 3
The remaining characteristics were the same as in example 1, except that the PH of the solution was adjusted to 2 to obtain lithium iron phosphate D3.
Comparative example 4
The remaining characteristics were the same as in example 1, except that hydrochloric acid was not added to the prepared graphene oxide dispersion liquid, and lithium iron phosphate D4 was obtained even when the ph of the dispersion liquid was neutral.
Comparative example 5
The remaining characteristics were the same as in example 1, except that the amount of ethylenediaminetetraacetic acid added was 3 parts by weight, to obtain lithium iron phosphate D5.
Comparative example 6
The remaining characteristics were the same as in example 1, except that the amount of ethylenediaminetetraacetic acid added was 20 parts by weight, to obtain lithium iron phosphate D6.
Comparative example 7
The remaining characteristics were the same as in example 1, except that iron nitrate was not added, and lithium iron phosphate D7 was obtained.
Comparative example 8
The other characteristics are the same as those of example 1, except that the size of lithium iron phosphate is controlled to 400 nm when ball milling is performed on the lithium iron phosphate, so that lithium iron phosphate D8 is obtained.
Comparative example 9
The remaining characteristics were the same as in example 1, except that sucrose was substituted for ethylenediaminetetraacetic acid, which also served as an organic carbon source, to produce lithium iron phosphate D9.
Comparative example 10
The remaining characteristics were the same as in example 1, except that carbon nanofibers were not added, and lithium iron phosphate D10 was prepared.
Comparative example 11
The remaining characteristics were the same as in example 1, except that the carbon nanofibers had a length of 50 nm and a diameter of 8 nm, to produce lithium iron phosphate D11.
Comparative example 12
The remaining characteristics were the same as in example 1, except that the carbon nanofibers were 800 nm in length and 50 nm in diameter, to produce lithium iron phosphate D12.
Comparative example 13
The lithium iron phosphate was not treated and was designated as lithium iron phosphate D13.
Examples of the experiments
The lithium iron phosphate positive plate is prepared by taking the lithium iron phosphate prepared in the above examples 1-3 and comparative examples 1-10 as a raw material, and assembled into a lithium iron phosphate battery.
Mixing and stirring 10 parts by weight of polyvinylidene fluoride, 10 parts by weight of carbon nano tubes and 26 parts by weight of N-methyl pyrrolidone to obtain mixed slurry, then adding 40 parts by weight of lithium iron phosphate into the mixed slurry, stirring and dispersing to obtain conductive slurry, coating the conductive slurry on the surface of an aluminum foil current collector, and rolling to obtain the lithium iron phosphate positive plate.
Using artificial graphite as negative electrode material and LiPF6The conductivity of the batteries prepared by using/EC + DEC (volume ratio 1: 1) as the electrolyte and Celgard 2400 membrane as the separator is tested, and the data are shown in Table 1.
TABLE 1 Battery conductivity test data
As can be seen from the data in table 1, the conductivity of the batteries prepared using the carbon-coated lithium iron phosphate prepared in examples 1 to 3 as a raw material is significantly better than that of the batteries prepared in comparative examples 1 to 13.
The effective content of the graphene oxide in the D1 is too low, so that the carbon shell coated on the surface of the micron lithium iron phosphate is reduced, and the conductivity of the material is reduced.
Due to the fact that the addition amount of the graphene oxide is too large, a carbon shell formed on the surface of the micrometer lithium iron phosphate is too compact, flowing of electrolyte is blocked, and therefore the conductivity of the material is reduced.
D3 is because the pH value of the solution is too low, leads to the undersize of the graphene oxide sheet, and then makes the effective amount of ethylene diamine tetraacetic acid that the graphene oxide sheet can adsorb reduce, thereby makes the conductivity of material lower.
D4 is not added with hydrochloric acid, so that the graphene oxide sheet is oversized, the number of graphene oxide sheets adsorbed on the surface of micrometer lithium iron phosphate is reduced, and the conductivity of the material is too low.
D5 because the addition of EDTA is too little, EDTA mainly plays the role of organic carbon source, so that the carbon shell coated on the surface of the micron lithium iron phosphate is reduced, and the conductivity of the material is reduced.
D6 also causes the carbon shell formed on the surface of the micron lithium iron phosphate to be too dense due to the excessive addition of the ethylene diamine tetraacetic acid, so that the flow of the electrolyte is blocked, and the conductivity of the material is reduced.
Since no ferric nitrate is added to D7, ethylenediaminetetraacetic acid cannot form a complex and is not stably adsorbed on the surface of lithium iron phosphate, resulting in a decrease in the conductivity of the material.
D8 has a small surface area due to the undersize of lithium iron phosphate, thereby reducing the carbon shell that can adsorb on its surface, resulting in a lower conductivity of the material.
In D9, sucrose cannot be complexed with ferric nitrate, and therefore, sucrose cannot be stably adsorbed on the surface of lithium iron phosphate to perform the function of carbon coating, and thus the conductivity of the material is low.
D10 has low conductivity compared with A1-A3 because no carbon nano fiber is added.
D11 is short in length of the carbon nanofibers, so that the distance between lithium iron phosphate particles is too small, the flowing of electrolyte is influenced, and the conductivity is reduced.
D12, the length of the carbon nanofiber is too long, so that the lithium ion transmission distance is increased, and the conductivity of the material is affected.
D13 selects unmodified lithium iron phosphate as a raw material, and the conductivity of the material is lower than that of A1-A3.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A preparation method of carbon-coated lithium iron phosphate is characterized by comprising the following steps:
s1, preparing graphene oxide dispersion liquid;
s2, mixing and stirring ethylenediaminetetraacetic acid and ferric nitrate, and standing to obtain a solution containing a complex;
s3, mixing and stirring the solution containing the complex obtained in the step S2 and the graphene oxide dispersion liquid obtained in the step S1 to obtain a mixed liquid;
s4, performing ball milling on the lithium iron phosphate, and then performing spray granulation to obtain micron lithium iron phosphate;
s5, adding the micron lithium iron phosphate obtained in the step S4 into the mixed solution obtained in the step S3, stirring and standing;
s6, transferring the mixture obtained in the step S5 to a hydrothermal reaction kettle for hydrothermal reaction, taking out the mixture after the hydrothermal reaction is finished, and naturally cooling, filtering and draining the mixture to obtain solid powder;
in step S1, the method specifically includes:
s11, adding 16-18 parts by weight of graphene oxide powder into 100 parts by weight of water, and performing ultrasonic dispersion;
s12, dropwise adding hydrochloric acid into the solution obtained in the step S11, and adjusting the pH value of the solution to 3-5;
wherein, in the graphene oxide dispersion liquid, the size of the graphene oxide sheet is 200-300 nanometers;
wherein, in the step S2, the addition amount of the ethylene diamine tetraacetic acid is 10 to 12 parts by weight, and the addition amount of the ferric nitrate is 10 to 12 parts by weight;
in step S4, the size of the lithium iron phosphate micrometers is 1 to 2 micrometers.
2. The method for preparing carbon-coated lithium iron phosphate according to claim 1, further comprising step S7:
and (5) putting the solid powder obtained in the step S6 into deionized water, then adding carbon nanofibers, carrying out ultrasonic mixing, filtering and draining to obtain the carbon nanofiber.
3. The method for preparing carbon-coated lithium iron phosphate as claimed in claim 1, wherein in step S6, the hydrothermal reaction temperature is 120-160 ℃ and the reaction time is 2-3 hours.
4. A carbon-coated lithium iron phosphate produced by the method for producing a carbon-coated lithium iron phosphate according to any one of claims 1 to 3.
5. A lithium iron phosphate positive electrode sheet characterized by being produced from the carbon-coated lithium iron phosphate according to claim 4.
6. A lithium iron phosphate battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, and is characterized in that the positive plate is the lithium iron phosphate positive plate in claim 5.
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