CN116885168A - Preparation method of lithium iron phosphate/nitrogen doped carbon/nano carbon composite material, prepared material and application - Google Patents
Preparation method of lithium iron phosphate/nitrogen doped carbon/nano carbon composite material, prepared material and application Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 76
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 66
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 52
- 239000002131 composite material Substances 0.000 title claims abstract description 49
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 37
- 229910021392 nanocarbon Inorganic materials 0.000 title claims abstract description 30
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 26
- 239000000463 material Substances 0.000 title claims abstract description 25
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 19
- 238000000034 method Methods 0.000 claims abstract description 11
- 239000002028 Biomass Substances 0.000 claims description 32
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 30
- 229910021389 graphene Inorganic materials 0.000 claims description 30
- 239000000843 powder Substances 0.000 claims description 21
- 239000003575 carbonaceous material Substances 0.000 claims description 19
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 18
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 15
- 239000004202 carbamide Substances 0.000 claims description 15
- 239000003513 alkali Substances 0.000 claims description 14
- 238000001354 calcination Methods 0.000 claims description 12
- 239000002243 precursor Substances 0.000 claims description 12
- 239000000243 solution Substances 0.000 claims description 11
- 239000011259 mixed solution Substances 0.000 claims description 10
- 238000001694 spray drying Methods 0.000 claims description 10
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 9
- 239000002041 carbon nanotube Substances 0.000 claims description 9
- 239000007864 aqueous solution Substances 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 8
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 6
- 239000012298 atmosphere Substances 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 5
- 239000011268 mixed slurry Substances 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 5
- 239000007774 positive electrode material Substances 0.000 claims description 5
- 238000010257 thawing Methods 0.000 claims description 5
- 238000005406 washing Methods 0.000 claims description 5
- 229920002101 Chitin Polymers 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 239000002585 base Substances 0.000 claims description 3
- 229920002678 cellulose Polymers 0.000 claims description 2
- 239000001913 cellulose Substances 0.000 claims description 2
- 239000011261 inert gas Substances 0.000 claims description 2
- 238000004321 preservation Methods 0.000 claims description 2
- 238000005245 sintering Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 3
- 238000009792 diffusion process Methods 0.000 abstract description 9
- 239000002245 particle Substances 0.000 description 8
- 239000013078 crystal Substances 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 239000011149 active material Substances 0.000 description 3
- 239000008367 deionised water Substances 0.000 description 3
- 229910021641 deionized water Inorganic materials 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 238000007710 freezing Methods 0.000 description 3
- 230000008014 freezing Effects 0.000 description 3
- 125000004433 nitrogen atom Chemical group N* 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910010710 LiFePO Inorganic materials 0.000 description 2
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 239000012300 argon atmosphere Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 239000006245 Carbon black Super-P Substances 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 1
- 238000010951 particle size reduction Methods 0.000 description 1
- -1 polypropylene Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Classifications
-
- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- 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
- 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 preparation method of a lithium iron phosphate/nitrogen doped carbon/nano carbon composite material, a prepared material and application thereof. The composite material prepared by the method has higher conductivity and lithium ion diffusion rate, and can be used as the positive electrode of a lithium ion battery, so that the rate capability of the composite material can be obviously improved.
Description
Technical Field
The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a preparation method of a lithium iron phosphate/nitrogen doped carbon/nano carbon composite material, and a prepared material and application.
Background
Currently, lithium ion batteries have been widely used in 3C portable devices, electric car power systems and energy storage systems due to their high energy density and long service life, and lithium iron phosphate is an important positive electrode material for lithium ion batteries. The olivine structure of the lithium iron phosphate has the advantages of stable structure, stable charge/discharge platform, high theoretical specific capacity, good thermal stability and chemical stability, rich raw material sources, environmental friendliness and high safety performance. The inherent crystal structure of lithium iron phosphate determines its low electron conductivity and lithium ion diffusion rate, resulting in rapid capacity fade at high rates.
Aiming at the defects of the lithium iron phosphate, the electrical conductivity and the ion diffusion rate of the lithium iron phosphate are improved by coating, doping modification, particle size reduction and other aspects, so that the rate capability of the material is improved. Surface carbonaceous material coating is one of the effective methods for improving the conductivity of lithium iron phosphate materials, and by dispersing or coating a small amount of conductive carbon among particles and on the surfaces of the particles of the lithium iron phosphate materials, channels for electron transport can be effectively provided, the conductivity between lithium iron phosphate particles can be enhanced, and simultaneously, the polarization of electrodes can be reduced, thereby improving the electrochemical performance of the lithium iron phosphate materials. Based on the existing research, how to further improve the performance of lithium iron phosphate as a positive electrode material of a lithium ion battery becomes a problem expected to be solved by people.
Disclosure of Invention
The invention aims to provide a preparation method of a lithium iron phosphate/nitrogen doped carbon/nano carbon composite material, and the composite material prepared by the method has higher conductivity and lithium ion diffusion rate, and can be used as a positive electrode of a lithium ion battery to remarkably improve the rate capability of the lithium ion battery.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the preparation method of the lithium iron phosphate/nitrogen doped carbon/nano carbon composite material comprises the following steps:
step S1: dispersing biomass material powder in an aqueous solution of strong alkali and urea, adding a nano carbon material solution, and performing low-temperature freezing-thawing cycle to obtain a biomass/nano carbon material mixed solution, wherein the concentration of the strong alkali in the aqueous solution of the strong alkali and the urea is 0.2-3 mol/L, and the mass ratio of the strong alkali to the urea is 1-4:1;
step S2: adding lithium iron phosphate powder into the mixed solution, mixing to obtain lithium iron phosphate/biomass/nano carbon material mixed slurry, and then performing spray drying to obtain lithium iron phosphate/biomass/nano carbon composite material powder;
step S3: placing the composite material powder into a muffle furnace, and washing and drying the composite material powder after low-temperature calcination to obtain a lithium iron phosphate/nitrogen doped carbon/nano carbon composite material precursor, wherein the low-temperature calcination temperature is 200-380 ℃ and the calcination time is 1-12 hours;
step S4: and (3) placing the precursor into a tube furnace in an inert atmosphere environment, calcining in the inert atmosphere, wherein the sintering temperature is 600-1000 ℃, and the heat preservation time is 1-10 h, so as to obtain the lithium iron phosphate/nitrogen doped carbon/nano carbon composite material.
Preferably, the biomass material in the step S1 is one or a mixture of two of chitin and cellulose in any proportion.
Preferably, the strong base in step S1 is one or a mixture of two or more of sodium hydroxide, potassium hydroxide or lithium hydroxide in any proportion.
Preferably, the nano carbon material solution in the step S1 is an acidified carbon nanotube or graphene oxide aqueous solution.
Preferably, the concentration of the nano carbon material solution is 0.1-5 mg.mL -1 The mass ratio of the biomass material to the strong alkali is 1:4-12.
Preferably, in the step S3, parameters of spray drying are set as follows: the inlet temperature is 150-260 ℃, the outlet temperature is 80-130 ℃, the working pressure of the atomizer is 100-250 kPa, and the feeding rate is 60-200mL/h.
Preferably, the inert atmosphere in the step S4 is high-purity nitrogen or argon, and the heating rate is 2-10 ℃/min.
Preferably, in the step S2, the mass ratio of the lithium iron phosphate to the nano carbon material is 60-120:1
Two other objects of the invention are to provide the lithium iron phosphate/nitrogen doped carbon/nano carbon composite material prepared by the method and the application of the composite material as a positive electrode material of a lithium ion battery.
The invention has the following beneficial effects:
according to the invention, through a low-temperature freezing/dissolving method under an alkali/urea aqueous system, a biomass material and a nano carbon material form a mutually-interweaved multi-dimensional network structure carbonaceous material precursor through electrostatic, hydrogen bond and hydrophilic and hydrophobic interaction, and the precursor is coated on the surface of the lithium iron phosphate.
According to the invention, renewable natural biomass is taken as a nitrogen source, and the renewable natural biomass and lithium iron phosphate are calcined under inert gas to synthesize the biomass nitrogen-doped carbon-coated lithium iron phosphate composite material, so that the biomass raw material is wide in source, low in cost, renewable, environment-friendly and easy to obtain, and the hydrophilicity of nitrogen atoms in the biomass material in alkaline solution is beneficial to improving the wettability and the affinity to active materials, enhancing the interaction with positive electrode materials and reducing the diffusion activation energy of lithium ions; meanwhile, the affinity and wettability of the electrolyte are improved, so that the electron conduction and lithium ion diffusion performance in the lithium iron phosphate are improved. The nitrogen atoms can provide carriers for a carbon material conduction band of the surface layer of the lithium iron phosphate, so that the electronic conductivity of the material is improved, defects can be induced to reduce the activation energy of lithium ion diffusion, the diffusion kinetics of lithium ions is enhanced, the ionic conductivity and the electronic conductivity of the lithium iron phosphate are improved, and the rate capability of the material is improved.
The invention has simple process, easy large-scale preparation and good application prospect and industrialization potential. In addition, the preparation method provides a brand new way for the high added value utilization of biomass materials.
Drawings
FIG. 1 is an XRD spectrum of a lithium iron phosphate/nitrogen-doped carbon/graphene composite material prepared in example 1 of the present invention;
FIG. 2 is an SEM spectrum of a lithium iron phosphate/nitrogen doped carbon/graphene composite material prepared in example 1 of the present invention;
FIG. 3 is a charge/discharge curve of a half cell assembled from the lithium iron phosphate/nitrogen doped carbon/graphene composite material prepared in example 1 of the present invention at a 1C rate;
fig. 4 is a charge/discharge curve of a half cell assembled from the lithium iron phosphate/nitrogen doped carbon/graphene composite material prepared in example 1 of the present invention at a 5C rate.
Detailed Description
The invention is further illustrated by the following examples:
example 1 preparation example 1
2 g of cellulose powder was dispersed in 250mL of sodium hydroxide/urea in a mass ratio of 2:1, wherein the concentration of sodium hydroxide is 2mol/L, the concentration of sodium hydroxide is 20 g, the concentration of urea is 10 g, and the mass ratio of cellulose powder to sodium hydroxide is 1:10. 80mL of 1 mg/mL was added -1 The graphene oxide solution is subjected to low-temperature freezing-thawing cycle to obtain a uniform biomass/graphene oxide mixed solution, and the number of times of repeated low-temperature freezing/dissolving is 3.
Adding 8g of lithium iron phosphate powder into the mixed solution, and fully and uniformly mixing to obtain lithium iron phosphate/biomass/graphene oxide mixed slurry; then spray drying is carried out to obtain lithium iron phosphate/biomass/graphene oxide composite material powder; the working parameters of the spray dryer are set as follows: the inlet temperature is 180 ℃, the outlet temperature is 100 ℃, the working pressure of the atomizer is 120kPa, and the feeding rate is 60mL/h.
And (3) placing the powder obtained by spray drying into a muffle furnace, calcining at the low temperature of 250 ℃ for 3 hours, filtering and washing with deionized water for 3 times, transferring into a blast drying box, and drying at the temperature of 80 ℃ for 6 hours to obtain the lithium iron phosphate/nitrogen doped carbon/graphene composite material precursor.
And (3) placing the precursor of the lithium iron phosphate/nitrogen-doped carbon/graphene composite material into a tube furnace, heating to 600 ℃ at a speed of 3 ℃/min in an argon atmosphere, and preserving heat for 10 hours to obtain the lithium iron phosphate/nitrogen-doped carbon/graphene composite material.
XRD and SEM characterization were performed on the prepared lithium iron phosphate/nitrogen doped carbon/graphene composite material, and the results are shown in fig. 1 and 2.
As can be seen from the XRD pattern (FIG. 1), the sharp main characteristic diffraction peaks and LiFePO in the pattern 4 The standard PDF card (JCPDS No. 83-2092) of (B) corresponds well, indicating LiFePO in the composite material 4 The space group is Pmnb. Characteristic peaks at 2θ=17.1 °, 20.7 °, 25.5 °, 29.7 °, and 35.5 ° correspond to (200), (101), (111), (211), and (311) crystal planes, respectively. In addition, the three characteristic diffraction peaks, which occur at 2θ=15.2°,22.3 ° and 43.7 °, indicate that the biomass material in the composite material is fully carbonized to a nitrogen-doped carbon material and graphene oxide is reduced to graphene. The weaker and broad characteristic peak at 15.2 ° is attributed to the (001) peak of graphitized carbon nitride, indicating that the N atoms are doped into the graphitic carbon. The broad characteristic diffraction peak at 22.3 deg. indicates that the resulting carbon material is less graphitized. Based on the results, the prepared composite material is composed of lithium iron phosphate and carbon, and the thermal pyrolysis process realizes the transformation from the biomass material to the nitrogen-doped carbon material and the graphene oxide to the graphene. No other impurity peaks are found in the spectrum, which can indicate that the purity of the prepared material is higher.
As can be seen from the SEM image (fig. 2), there are a large number of net-like and flocculent substances on the surface and inside of the spherical particles, which are graphene obtained by reduction of nitrogen-doped carbon and graphene oxide generated after thermal decomposition of biomass. These carbon materials distributed on the surface and inside the particles, on the one hand, in LiFePO 4 The surface of the particles forms a good conductive network, so that the contact among the particles is enhanced, the conductivity among the particles is improved, a good channel is provided for the transmission of electrons in the charge/discharge process, and the polarization is reduced; on the other hand, coating LiFePO 4 The carbon layer on the surface of the particles can inhibit the growth of crystal grains in the crystal growth process, and reduce the size of the crystal grainsShortening the deintercalation path of lithium ions and improving the diffusion coefficient of lithium ions. The electrochemical lithium storage performance of the composite material can be further improved.
Example 2 preparation example 2
1 g of chitin powder was dispersed in 250mL of lithium hydroxide/urea with a mass ratio of 3:1, wherein the concentration of lithium hydroxide is 1mol/L, 12 g of lithium hydroxide, 4 g of urea and the mass ratio of chitin powder to lithium hydroxide is 1:12. 60mL of the solution was added at a concentration of 1.5 mg/mL -1 Acidifying the carbon nano tube aqueous solution, and obtaining a uniform biomass/carbon nano tube mixed solution after low-temperature freezing-thawing cycle, wherein the number of times of repeated low-temperature freezing/dissolving is 4.
Adding a certain amount of lithium iron phosphate powder of 6g into the mixed solution, and fully and uniformly mixing to obtain lithium iron phosphate/biomass/carbon nano tube mixed slurry; then spray drying is carried out to obtain lithium iron phosphate/biomass/carbon nano tube composite material powder; the working parameters of the spray dryer are set as follows: the inlet temperature is 150 ℃, the outlet temperature is 110 ℃, the working pressure of the atomizer is 100kPa, and the feeding rate is 70mL/h.
Placing the powder obtained by spray drying into a muffle furnace, calcining at 200 ℃ for 12 hours, filtering and washing with deionized water for 3 times, transferring into a blast drying oven, and drying at 80 ℃ for 6 hours; and obtaining the precursor of the lithium iron phosphate/nitrogen doped carbon/carbon nano tube composite material.
And (3) placing the precursor of the lithium iron phosphate/nitrogen-doped carbon/carbon nano tube composite material into a tube furnace, heating to 800 ℃ at a speed of 2 ℃/min in an argon atmosphere, and preserving heat for 5 hours to obtain the lithium iron phosphate/nitrogen-doped carbon/carbon nano tube composite material.
Example 3 preparation example 3
2 g of cellulose powder was dispersed in 250mL of sodium hydroxide/urea in a mass ratio of 1:1, wherein the concentration of sodium hydroxide is 1mol/L, 10 g of sodium hydroxide and 10 g of urea are contained, and the mass ratio of cellulose powder to sodium hydroxide is 1:5. 50mL of the solution with the concentration of 2 mg.mL is added -1 Graphene oxide solution is subjected to low-temperature freezing-thawing cycle to obtain uniform biomass/oxidationThe graphene mixed solution was repeatedly frozen/dissolved at low temperature for 3 times.
Adding a certain amount of 9g of lithium iron phosphate powder into the mixed solution, and fully and uniformly mixing to obtain lithium iron phosphate/biomass/graphene oxide mixed slurry; then spray drying is carried out to obtain lithium iron phosphate/biomass/graphene oxide composite material powder; the working parameters of the spray dryer are set as follows: the inlet temperature is 260 ℃, the outlet temperature is 130 ℃, the working pressure of the atomizer is 250kPa, and the feeding rate is 200mL/h.
Placing the powder obtained by spray drying into a muffle furnace, calcining at 380 ℃ for 1 hour, filtering and washing with deionized water for 3 times, transferring into a blast drying oven, and drying at 80 ℃ for 6 hours; and obtaining a precursor of the lithium iron phosphate/nitrogen doped carbon/graphene composite material.
And (3) putting the precursor of the lithium iron phosphate/nitrogen-doped carbon/nano carbon composite material obtained in the step into a tube furnace, heating to 1000 ℃ at a speed of 3 ℃/min in an argon gas atmosphere, and preserving heat for 1h to obtain the lithium iron phosphate/nitrogen-doped carbon/graphene composite material.
Example 4 electrochemical Effect test
Preparing an active material, a conductive agent (Super-P) and a binder (polyvinylidene fluoride, PVDF) into a positive electrode plate according to a mass ratio of 8:1:1 by taking the lithium iron phosphate/nitrogen doped carbon/graphene composite material prepared in the embodiment 1 as an electrochemical active material, taking the prepared lithium iron phosphate/nitrogen doped carbon/graphene electrode plate as a working electrode, taking a metal lithium plate as a counter electrode and an auxiliary electrode, and preparing 1mol L of ethylene carbonate and dimethyl carbonate (EC/DMC) by using an electrolyte according to a volume ratio of 1:1 -1 LiPF of (a) 6 Solution, celgard 2400 microporous polypropylene membrane as lithium ion battery separator, assembled half cell. At 1C (1c=170ma g -1 ) And constant current charge/discharge testing at 5C magnification, the results are shown in fig. 3 and 4. As can be seen from fig. 3 and 4, the lithium iron phosphate/nitrogen-doped carbon/graphene composite material prepared in example 1 has charge/discharge capacities of 156.02mAh g at 1C and 5C rates, respectively -1 And 154.75mAh g -1 ，127.02mAh g -1 And 126.77mAh g -1 . Lithium iron phosphate/nitrogen dopingThe carbon/graphene composite material exhibits excellent rate performance and electrochemical reversibility.
Claims (10)
1. The preparation method of the lithium iron phosphate/nitrogen doped carbon/nano carbon composite material is characterized by comprising the following steps of:
step S1: dispersing biomass material powder in an aqueous solution of strong alkali and urea, adding a nano carbon material solution, and performing low-temperature freezing-thawing cycle to obtain a biomass/nano carbon material mixed solution, wherein the concentration of the strong alkali in the aqueous solution of the strong alkali and the urea is 0.2-3 mol/L, and the mass ratio of the strong alkali to the urea is 1-4:1;
step S2: adding lithium iron phosphate powder into the mixed solution, mixing to obtain lithium iron phosphate/biomass/nano carbon material mixed slurry, and then performing spray drying to obtain lithium iron phosphate/biomass/nano carbon composite material powder;
step S3: placing the composite material powder into a muffle furnace, and washing and drying the composite material powder after low-temperature calcination to obtain a lithium iron phosphate/nitrogen doped carbon/nano carbon composite material precursor, wherein the low-temperature calcination temperature is 200-380 ℃ and the calcination time is 1-12 hours;
step S4: and (3) placing the precursor into a tube furnace, calcining in an inert gas atmosphere, wherein the sintering temperature is 600-1000 ℃, and the heat preservation time is 1-10 h, so as to obtain the lithium iron phosphate/nitrogen doped carbon/nano carbon composite material.
2. The method of manufacturing according to claim 1, characterized in that: the biomass material in the step S1 is one or a mixture of two of chitin and cellulose in any proportion, and the strong base is one or a mixture of more than two of sodium hydroxide, potassium hydroxide or lithium hydroxide in any proportion.
3. The method of manufacturing according to claim 1, characterized in that: the nano carbon material solution in the step S1 is an acidified carbon nano tube or graphene oxide aqueous solution, and the concentration of the nano carbon material solution is 0.1-5 mg.mL -1 The biomass materialThe mass ratio of the material to the strong base is 1:4-12.
4. The method of manufacturing according to claim 1, characterized in that: the concentration of the strong alkali in the aqueous solution of the strong alkali and the urea is 1-2 mol/L, and the mass ratio of the strong alkali to the urea is 1-3:1; the mass ratio of the biomass material to the strong alkali is 1:5-12; in the step S3, the low-temperature calcination temperature is 200-300 ℃.
5. The method according to claim 1, wherein in the step S2, parameters of spray drying are set as follows: the inlet temperature is 150-260 ℃, the outlet temperature is 80-130 ℃, the working pressure of the atomizer is 100-250 kPa, and the feeding rate is 60-200mL/h.
6. The preparation method according to claim 1, wherein the inert atmosphere in the step S4 is high-purity nitrogen or argon, and the heating rate is 2-10 ℃/min.
7. The preparation method according to claim 1, wherein in the step S2, the mass ratio of the lithium iron phosphate to the nanocarbon material is 60-120:1.
8. the method according to claim 7, wherein in the step S2, the mass ratio of the lithium iron phosphate to the nanocarbon material is 60-100:1.
9. a lithium iron phosphate/nitrogen doped carbon/nanocarbon composite material, characterized in that it is prepared by the preparation method according to any one of claims 1 to 8.
10. Use of the composite material according to claim 9 as a positive electrode material for a lithium ion battery.
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