CN107394152B - High-conductivity graphene-based lithium iron phosphate spherical composite material, preparation method thereof and lithium ion battery comprising same - Google Patents

High-conductivity graphene-based lithium iron phosphate spherical composite material, preparation method thereof and lithium ion battery comprising same Download PDF

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CN107394152B
CN107394152B CN201710579932.XA CN201710579932A CN107394152B CN 107394152 B CN107394152 B CN 107394152B CN 201710579932 A CN201710579932 A CN 201710579932A CN 107394152 B CN107394152 B CN 107394152B
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graphene
iron phosphate
composite material
lithium iron
lithium
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CN107394152A (en
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王张健
杨顺毅
吴小珍
崔伟超
黄友元
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Jiangsu Beiteri Nano Technology Co ltd
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Shenzhen City Battery Nanometer Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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 high-conductivity graphene-based lithium iron phosphate spherical composite material, a preparation method thereof and a lithium ion battery containing the composite material. The high-conductivity graphene-based lithium iron phosphate spherical composite material is prepared by a series of technologies of graphene and LFP precursor molecule level mixing, spheroidization, CVD in-situ growth of graphene and the like, wherein the composite material contains two states of graphene, and one state is introduced in a precursor mixing stage; the other is grown on the surface of the material in situ, and specifically, the composite material comprises secondary spherical particles composed of primary particles and graphene grown on the surfaces of the secondary spherical particles; wherein the primary particles are lithium iron phosphate particles containing graphene. The graphene composite material is used as a positive active material to prepare a lithium ion battery, an additional conductive agent can be added or omitted, and the obtained lithium ion battery can well give consideration to the performances of gram capacity, low temperature, multiplying power, processing, circulation and the like of the material.

Description

High-conductivity graphene-based lithium iron phosphate spherical composite material, preparation method thereof and lithium ion battery comprising same
Technical Field
The invention belongs to the field of lithium ion battery anode materials, and particularly relates to a high-conductivity graphene-based lithium iron phosphate spherical composite material, a preparation method thereof and a lithium ion battery containing the composite material.
Background
Existing olivine-type LiFePO4(LFP) as the anode material of the lithium ion battery has the advantages of high theoretical capacity (170mAh/g), good cycle performance, stable structure, environmental protection, rich resources and the like, and is widely regarded; however, due to LiFePO4Has low electron conductivity by itself andthe lithium ion diffusion rate greatly limits the LiFePO4The exertion of electrochemical performance and the obstruction of LiFePO4The anode material is widely applied to power and start-stop power sources.
By subjecting LiFePO to4After a great deal of research, the control of the size and the shape of particles, surface coating and metal ion doping can effectively improve the LiFePO4In which small-particle LiFePO of regular shape is prepared4Can effectively shorten Li+The migration distance in the interior of the catalyst is increased, thereby increasing the LiFePO4Low temperature and rate of the material. Patent CN 102623701 a discloses a preparation method of a low-temperature type nano lithium iron phosphate cathode material, which is characterized in that a lithium iron phosphate material with primary particles of 60-70nm is prepared by a process technology of wet superfine grinding, spray drying, presintering, superfine grinding, spray drying, air crushing, primary low-temperature sintering and secondary high-temperature sintering, and the lithium iron phosphate material has excellent low-temperature performance, but the tap density is not high, the processing, high-temperature and cycle performances are not good, and simultaneously, the energy consumption is large due to too long working procedures, so that the lithium iron phosphate cathode material is not economical and environment-friendly.
In order to improve the tap density of the lithium iron phosphate, the preparation of the spherical lithium iron phosphate is a big direction. The existing method for preparing spherical lithium iron phosphate is mainly a liquid phase method, and the method is complex to operate, high in cost and not beneficial to industrial production. Patent CN 102642820 a discloses a method for preparing high-density spherical lithium iron phosphate, which is characterized in that the spherical lithium iron phosphate material prepared by the process technology of ball mill wet mixing, spray drying, presintering, wet grinding, spray drying and roasting has high tap density and good slurry fluidity, but the whole process is too long, the product consistency is not easy to control, the cost is high and the process is uneconomical. Patent CN 103996846 a discloses a method for preparing a lithium iron phosphate cathode material with controllable particle size, which prepares a spherical lithium iron phosphate material with a secondary particle size of 1-10um by a process technology of ultra-fine grinding, two-fluid spraying and high-temperature sintering, and the spherical lithium iron phosphate material has high gram volume and good rate capability, but the sphere is not compact and the tap density is not high.
The surface carbon coating is one of the commonly used methods for improving the electrochemical performance of the lithium iron phosphate material. The carbon-coated structures obtained in the currently customary synthesis processes are predominantly free ofThe shaped carbon is dominant. There are studies showing that Li+Ion in sp2Carbon to carbon ratio of structure sp3Easier diffusion in structural or amorphous carbon; and sp2Hybridized carbon has a conductivity greater than sp3Electrical conductivity of hybridized and disordered carbon. Carbon in graphene is completely sp2The lithium iron phosphate and the graphene exist in a form, so that the compounding of the lithium iron phosphate and the graphene is an effective means for improving the lithium ion diffusion rate and the electronic conductivity of the lithium iron phosphate material. Patent CN 105742629 a discloses an in-situ preparation method of a lithium iron phosphate/graphene composite as a positive electrode material of a lithium ion battery, wherein the prepared lithium iron phosphate/graphene composite has good electrical conductivity, good low-temperature and rate capability performance, but poor processability through a process technology of molecular mixing, drying and sintering of a graphene oxide conductive liquid and an LFP precursor. Patent CN 104934608A discloses a preparation method of graphene in-situ coated lithium ion battery cathode material, in which graphene is in-situ coated on the surface of LFP material powder, the growth uniformity of graphene is poor, and it is not obvious to improve the electrochemical performance of LFP.
Therefore, there is a need to develop a lithium iron phosphate spherical composite material that can satisfy all the properties of high capacity, low temperature, rate, processing, cycle, etc.
Disclosure of Invention
In view of the defects of the prior art, an object of the present invention is to provide a high-conductivity graphene-based lithium iron phosphate spherical composite material, a preparation method thereof, and a lithium ion battery comprising the composite material. The graphene-based lithium iron phosphate spherical composite material is used as a positive active material to prepare a lithium ion battery, and an additional conductive agent can be added or omitted, so that the obtained lithium ion battery can well give consideration to the performances of gram capacity, low temperature, multiplying power, processing, circulation and the like of the material.
In a first aspect, the present invention provides a graphene-based lithium iron phosphate spherical composite material, where the composite material includes secondary spherical particles composed of primary particles, and graphene grown on surfaces of the secondary spherical particles, and the primary particles include lithium iron phosphate particles of the graphene.
In the present invention, the "graphene grown on the surface of the secondary spherical particle" is preferably graphene grown on the surface of the secondary spherical particle by CVD in-situ.
Preferably, the primary particles have a particle size of 20-300nm, such as 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, 110nm, 125nm, 140nm, 150nm, 165nm, 180nm, 200nm, 220nm, 240nm, 260nm, 275nm, 285nm, 300nm, or the like.
Preferably, the secondary spherical particles have a median particle diameter of 3-9 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or 9 μm, and the like.
Preferably, the graphene comprised in the primary particles constitutes 1-5 wt.%, such as 1 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.% or 5 wt.%, etc., preferably 1-2 wt.%, of the total mass of the composite.
Preferably, the number of graphene layers grown on the surface of the secondary spherical particle is a single layer or less than 10 layers.
Preferably, the secondary median particle size of the composite material is 3-9 μm, such as 3 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or 9 μm, and the like.
Preferably, the powder conductivity of the composite material is above 1S/cm, such as 1S/cm, 3S/cm, 5S/cm, 7S/cm, 10S/cm or 12S/cm, and the like.
In a second aspect, the present invention provides a method of preparing a composite material according to the first aspect, the method comprising the steps of:
(1) preparing lithium iron phosphate precursor slurry containing graphene;
(2) spray drying to obtain a secondary spherical lithium iron phosphate precursor composed of primary particles;
(3) and (3) placing the secondary spherical lithium iron phosphate precursor in a reaction furnace, heating to 600-750 ℃, introducing an organic compound in a protective atmosphere, and carrying out in-situ growth of graphene to obtain the graphene-based lithium iron phosphate spherical composite material.
In the present invention, the temperature in step (3) is raised to 600-750 ℃, such as 600 ℃, 620 ℃, 630 ℃, 640 ℃, 650 ℃, 665 ℃, 680 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃ or 750 ℃ and so on.
In the method, the graphene and the lithium iron phosphate LFP precursor are added for molecular mixing, so that the problems that in the prior art, the conductivity is poor when the carbon content is low, and the internal hollow of the sphere is more and the tap density is not high when the carbon content is high in the process of preparing the nano-scale spherical LFP by using a conventional carbon source are solved.
According to the method, the graphene grows on the surface of the LFP sphere in situ by CVD in the sintering process of the spherical lithium iron phosphate precursor, so that agglomeration of primary particles during LFP sintering is inhibited, the conductivity of powder is increased by more than 100 times and can reach more than 1S/cm, and a conductive agent is not added in battery application, so that the slurry preparation solid content is further improved, and the method is economical and environment-friendly. In addition, in the application of the LFP battery, the surface of the LFP sphere is coated with a layer of graphene, so that the side reaction of LFP and electrolyte is well inhibited, and the high-temperature storage and high-temperature cycle performance of the LFP are obviously improved.
Compared with the conventional process of firstly sintering to prepare LFP powder and then growing graphene in situ on the surface, the method disclosed by the invention has the advantages of more uniform growth, simpler working procedures and better effect when the graphene is grown in the sintering process.
The composite material lithium iron phosphate prepared by the method has more compact internal particles and good conductivity, which is beneficial to better improving the processing performance of nano-scale LFP, reducing the internal resistance of LFP and improving the multiplying power and low-temperature performance of LFP.
Preferably, the lithium iron phosphate precursor slurry containing graphene in step (1) is a uniformly dispersed slurry.
As a preferred technical solution of the method of the present invention, the lithium iron phosphate precursor slurry containing graphene in step (1) is prepared by the following method:
(A) mixing a lithium source, iron phosphate, an optional dopant and an optional carbon source to obtain a mixture;
(B) and mixing the mixture with graphene, an optional dispersing agent and deionized water, and grinding and dispersing to obtain the lithium iron phosphate precursor slurry containing graphene.
Preferably, the lithium source, the iron phosphate and the optional dopant in step (a) are formulated according to a molar ratio of Li: Fe: P: M ═ 1.0-1.1: 1 (1-1.05): 0-2.0%, wherein M is a doping element in the dopant.
Preferably, the lithium source in step (a) includes any 1 or a combination of at least 2 of lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate or lithium fluoride, but is not limited to the above-mentioned lithium sources, and other lithium sources commonly used in the art to achieve the same effect can be used in the present invention.
Preferably, the dopant of step (a) is any 1 or a combination of at least 2 of Mg, Mn, Ti, V, Nb, Ni or Co compounds.
Preferably, in step (a), the percentage of the carbon source to the total mass is 0 wt.% to 1.5 wt.%, such as 0 wt.%, 0.2 wt.%, 0.5 wt.%, 0.7 wt.%, 1.0 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, or 1.5 wt.%, based on 100 wt.% of the total mass of the lithium source, iron phosphate, optional dopant, and optional carbon source. Wherein a percentage of 0 wt.% represents no carbon source added.
In the invention, the percentage of the carbon source in the total mass is the carbon content.
In the present invention, "alternative carbon source" means: the carbon source may or may not be added.
Preferably, the carbon source in step (a) includes 1 or a combination of at least 2 of ascorbic acid, cellulose, polypropylene, epoxy resin, sucrose, glucose, fructose, citric acid, polyethylene glycol, starch, and phenolic resin, but is not limited to the above-mentioned carbon sources, and other carbon sources commonly used in the art to achieve the same effect can be used in the present invention.
In the present invention, "optional dopants" means: the dopant may or may not be added.
Preferably, in step (B), the percentage of graphene to the mass of the mix is 0.1-1.5 wt.%, e.g., 0.1 wt.%, 0.5 wt.%, 0.7 wt.%, 0.8 wt.%, 1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, or 1.5 wt.%.
Preferably, in step (B), the percentage of dispersant to the mass of the mix is 0-2 wt.%, e.g., 0 wt.%, 0.5 wt.%, 0.7 wt.%, 1.0 wt.%, 1.2 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.8 wt.%, or 2.0 wt.%, etc. Wherein a percentage of 0 wt.% represents no dispersant added.
In the present invention, "optional dispersant" means: a dispersant may or may not be added.
Preferably, in step (B), the mass of the deionized water is 1-6 times of the mass of the mixture, such as 1 time, 1.2 times, 1.5 times, 2 times, 2.5 times, 3 times, 4 times, 4.5 times, 5 times, 5.5 times, or 6 times, etc.
Preferably, the graphene in the step (B) includes any 1 or a combination of at least 2 of graphene powder, graphene conductive liquid, and graphene oxide conductive liquid, but is not limited to the above-mentioned graphene, and other graphene commonly used in the art to achieve the same effect may also be used in the present invention.
Preferably, the dispersant in step (B) is any 1 or a combination of at least 2 of glucose, sucrose, polyethylene glycol, polyvinylpyrrolidone or polyvinyl alcohol.
Preferably, the milling dispersion time of step (B) is 2-20h, such as 2h, 4h, 5h, 8h, 10h, 12h, 15h, 16h, 18h or 20h, etc.
In a preferred embodiment of the method of the present invention, the spray drying in step (2) is any 1 of two-fluid, gas-electric combined two-fluid, and four-fluid spraying.
Preferably, when the spray drying is performed in the step (2), the inlet temperature of the spray dryer is 200-350 ℃, such as 200 ℃, 210 ℃, 225 ℃, 230 ℃, 240 ℃, 255 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃, 320 ℃, 330 ℃ or 350 ℃ and the like, and the outlet temperature is not lower than 70 ℃.
Preferably, the reaction furnace in the step (3) is a rotary furnace, and the rotary furnace rotates at a rotating speed of 1-10r/min, such as 1r/min, 2r/min, 3r/min, 5r/min, 6r/min, 7r/min, 8r/min, 8.5r/min, 9r/min, 10r/min and the like.
Preferably, the temperature rise rate of the reaction furnace in the step (3) is 1-10 ℃/min, such as 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, 7 ℃/min, 8 ℃/min or 10 ℃/min, and the like.
Preferably, the protective atmosphere in step (3) is a combination atmosphere of any 1 or at least 2 of an argon atmosphere, a nitrogen atmosphere, or a hydrogen atmosphere.
Preferably, the organic compound in step (3) includes any 1 or a combination of at least 2 of methane, ethane, ethylene, acetylene, acetone, benzene and toluene, but is not limited to the above-listed organic compounds, and other organic compounds commonly used in the art to achieve the same effect can also be used in the present invention.
Preferably, the flow rate of the organic compound introduced in step (3) is 0.1-5L/min, such as 0.1L/min, 0.5L/min, 1L/min, 1.3L/min, 1.6L/min, 2L/min, 2.5L/min, 3L/min, 3.5L/min, 4L/min, 4.5L/min, or 5L/min.
Preferably, the organic compound is introduced in step (3) for 0.5-10h, such as 0.5h, 1h, 1.5h, 2h, 2.3h, 3h, 4h, 4.5h, 5h, 6h, 6.5h, 7h, 8h, 9h or 10 h.
As a further preferred technical solution of the method of the present invention, the method comprises the steps of:
(1) mixing a lithium source, iron phosphate, a dopant and a carbon source to obtain a mixture;
(2) mixing the mixture with graphene, a dispersing agent and deionized water, and grinding and dispersing for 2-20h, wherein the mass of the deionized water is 1-6 times that of the mixture to obtain uniformly ground and dispersed slurry;
(3) spray drying the slurry which is uniformly ground and dispersed, wherein the inlet temperature of a spray dryer is 200-350 ℃, and the outlet temperature is not lower than 70 ℃, so as to obtain a secondary spherical lithium iron phosphate precursor composed of primary particles;
(4) and (3) placing the secondary spherical lithium iron phosphate precursor in a rotary furnace, rotating at 1-10r/min, heating to 600-750 ℃ at 1-10 ℃/min, continuously introducing organic compound gas at the flow rate of 0.1-5L/min for 0.5-10h under a protective atmosphere, and carrying out in-situ growth of graphene to obtain the graphene-based lithium iron phosphate spherical composite material.
In a third aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the composite material of the first aspect as an active material, and an additional conductive agent may or may not be added.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention prepares the high-conductivity graphene-based lithium iron phosphate spherical composite material by a series of technologies of graphene and LFP precursor molecule level mixing, spheroidization, CVD in-situ growth of graphene and the like, wherein the composite material comprises two states of graphene, one is graphene which forms primary particles together with lithium iron phosphate, and the other is a graphene layer which grows in situ on the surfaces of secondary spherical particles formed by the primary particles by CVD.
(2) By adding graphene into LFP precursor slurry, the compactness and conductivity among particles in the spherical LFP can be improved, and the tap density is 1.5g/cm3The method is beneficial to improving the processing performance of the nano-scale LFP, reducing the internal resistance of the LFP, improving the multiplying power and low-temperature performance of the LFP, and solving the problem that the conductivity is poor when the carbon content is low in the process of preparing the nano-scale spherical LFP by using a conventional carbon source in the prior art; more hollow parts in the sphere and low tap density when the carbon content is high.
(3) In the sintering process of the spherical LFP precursor, the graphene grows on the surface of the LFP sphere in situ by CVD, so that the agglomeration of primary particles during LFP sintering is inhibited, the conductivity is improved, and the powder conductivity can reach more than 1S/cm and is improved by more than 100 times; compared with conventional sintered LFP powder surface in-situ growth graphene, the graphene is more uniform in growth, simpler in process and better in effect. In the application of the LFP battery, the surface of the LFP sphere is coated with a layer of graphene, so that the side reaction of LFP and electrolyte is well inhibited, and the high-temperature storage and high-temperature cycle performance of the LFP are obviously improved. And because the conductivity is good, a conductive agent can not be added in the battery application, which is beneficial to further improving the solid content of the prepared slurry, and is economic and environment-friendly.
(4) The graphene-based lithium iron phosphate spherical composite material is used as a positive active material to prepare a lithium ion battery, and an additional conductive agent can be added or omitted. Under the condition of adding an external conductive agent, the capacity of the obtained lithium ion battery is more than 145mAh/g at 1C gram at normal temperature, the capacity retention rate is more than 92% at 1000 weeks at normal temperature, the capacity retention rate of 20℃/1C is more than 95%, and the temperature is-20 ℃: the capacity retention rate at 0.2C is more than 80%; under the condition of not adding an external conductive agent, the obtained lithium ion battery still has good capacity, cycle and low-temperature performance, the 1C gram capacity at normal temperature is more than 143mAh/g, the capacity retention rate at normal temperature is more than 90 percent at 1000 weeks, the 20℃/1C capacity retention rate is more than 91 percent, and the low temperature is-20 ℃: the capacity retention rate at 0.2C is more than 75%.
Drawings
Fig. 1 is an SEM image of a high-conductivity graphene-based lithium iron phosphate spherical composite material in example 1 of the present invention;
fig. 2 is a cross-sectional SEM of the high-conductivity graphene-based lithium iron phosphate spherical composite material in embodiment 1 of the present invention;
fig. 3 is a 0.1C first charge-discharge curve of the high-conductivity graphene-based lithium iron phosphate spherical composite material in embodiment 1 of the present invention;
fig. 4 is a 0.5C cycle performance curve of the high-conductance graphene-based lithium iron phosphate spherical composite material of embodiment 1 of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1
(1) Mixing lithium hydroxide monohydrate, iron phosphate, magnesium oxide and glucose, and blending according to a molar ratio of Li to Fe to P to Mg of 1.02 to 0.01 and a carbon content of 0.8 wt%;
(2) mixing the material (1) with a graphene conductive liquid, polyethylene glycol and deionized water, and grinding and dispersing for 10 hours to obtain slurry which is uniformly ground and dispersed and has a proper particle size, wherein the weight of the polyethylene glycol is 0.2% of the material (1), and the weight of the deionized water is 4 times of the material (1);
(3) carrying out gas-electric combined two-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 300 ℃, and the outlet temperature of the spray dryer is 100 ℃, so as to obtain a spherical lithium iron phosphate precursor with the secondary particle size of 5 mu m;
(4) and (3) placing the spherical lithium iron phosphate precursor in a rotary furnace, rotating at 1r/min, heating to 700 ℃ at 5 ℃/min, continuously introducing propylene gas at the flow rate of 0.5L/min for 2h, and carrying out in-situ growth of graphene to obtain the high-conductivity graphene-based lithium iron phosphate spherical composite material with the primary particle size of 70nm and the secondary particle size of 5 microns.
Fig. 1 is an SEM image of the high-conductivity graphene-based lithium iron phosphate spherical composite material in this example, and it can be seen from fig. 1 that the prepared material is spherical, the primary particle size is about 70nm, and the secondary particle size is about 5 μm.
Fig. 2 is a cross-sectional SEM of the high-conductivity graphene-based lithium iron phosphate spherical composite material in this embodiment, and it can be seen from fig. 2 that the primary particles inside the spheres are dense.
Fig. 3 is a 0.1C first charge-discharge curve of the high-conductivity graphene-based lithium iron phosphate spherical composite material in the embodiment of the present invention, and as can be seen from fig. 3, the capacity is very high, and the 0.1C first discharge capacity reaches 169.1 mAh/g.
Fig. 4 is a 0.5C cycle performance curve of the high-conductance graphene-based lithium iron phosphate spherical composite material in the embodiment of the present invention, and it can be seen from fig. 4 that the capacity is high and the cycle performance is good, the 0.5C first discharge capacity is 155.8mAh/g, and the capacity retention rate after 20 cycles is 104.2%.
Example 2
(1) Mixing lithium carbonate, iron phosphate, niobium oxalate and sucrose according to the mol ratio of Li to Fe to P to Nb of 1.02 to 1 to 1.03 to 0.005 and the carbon content of 0.7 wt.%;
(2) mixing the material (1) with a graphene oxide conductive liquid, polyvinyl alcohol and deionized water, and grinding and dispersing for 6 hours to obtain slurry with a proper particle size, wherein the weight of the polyvinyl alcohol is 0.25% of that of the material (1), and the weight of the deionized water is 4 times that of the material (1);
(3) carrying out two-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 260 ℃, the outlet temperature of the spray dryer is 70 ℃, and a spherical lithium iron phosphate precursor with the secondary particle size of 6 mu m is obtained;
(4) and (3) placing the spherical lithium iron phosphate precursor in a rotary furnace, rotating at 1.5r/min, heating to 700 ℃ at 10 ℃/min, continuously introducing acetylene gas at the flow rate of 1L/min for 1h, and carrying out in-situ growth of graphene to obtain the high-conductivity graphene-based lithium iron phosphate spherical composite material with the secondary particle size of 6 microns.
Example 3
(1) Mixing lithium carbonate, lithium hydroxide monohydrate, iron phosphate and citric acid according to a molar ratio of Li to Fe to P to M (0.5+0.53) to 1 to 1.02 to 0, wherein the doping element M is 0, and the carbon content is 0.5 wt%;
(2) mixing the material (1) with a graphene conductive liquid, polyvinylpyrrolidone and deionized water, and grinding and dispersing for 20 hours to obtain slurry which is uniformly dispersed and has a proper particle size, wherein the weight of the polyvinylpyrrolidone is 0.3% of that of the material (1), and the weight of the deionized water is 4 times that of the material (1);
(3) carrying out four-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 280 ℃, and the outlet temperature of the spray dryer is 80 ℃, so as to obtain a spherical lithium iron phosphate precursor with the secondary particle size of 6 mu m;
(4) and (3) placing the spherical lithium iron phosphate precursor in a rotary furnace, rotating at 2r/min, heating to 750 ℃ at 5 ℃/min, continuously introducing ethane gas at the flow rate of 0.1L/min for 2h, and carrying out in-situ growth of graphene, wherein the secondary particle size of the high-conductivity graphene-based lithium iron phosphate spherical composite material is 6 microns.
Example 4
(1) Mixing lithium hydroxide monohydrate, iron phosphate, titanium dioxide and glucose, and blending according to a molar ratio of Li to Fe to P to Ti of 1.0:1:1.05:0.05 and a carbon content of 1.5 wt.%;
(2) mixing the material (1) with graphene powder, polyvinyl alcohol and deionized water, and grinding and dispersing for 15 hours to obtain slurry with uniform grinding and dispersion and proper particle size, wherein the weight of the polyvinyl alcohol is 2% of that of the material (1), and the weight of the deionized water is 6 times that of the material (1);
(3) carrying out gas-electricity combined two-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 280 ℃, and the outlet temperature of the spray dryer is 80 ℃, so as to obtain a spherical lithium iron phosphate precursor with the secondary particle size of 4 mu m;
(4) and (3) placing the spherical lithium iron phosphate precursor in a rotary furnace, rotating at 3r/min, heating to 750 ℃ at the speed of 5 ℃/min, continuously introducing propylene gas at the flow rate of 2L/min for 5h, and carrying out in-situ growth of graphene to obtain the high-conductivity graphene-based lithium iron phosphate spherical composite material with the secondary particle size of 4 microns.
Example 5
(1) Mixing lithium hydroxide monohydrate, iron phosphate, vanadium oxide and glucose, and mixing according to a molar ratio of Li to Fe to P to V of 1.05 to 1 to 1.04 to 1 and a carbon content of 1 wt.%;
(2) mixing the material (1) with a graphene conductive liquid, glucose and deionized water, and grinding and dispersing for 4 hours to obtain slurry which is uniformly ground and dispersed and has a proper particle size, wherein the weight of the glucose is 1% of that of the material (1), and the weight of the deionized water is 2.5 times that of the material (1);
(3) carrying out gas-electric combined two-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 325 ℃, and the outlet temperature of the spray dryer is 90 ℃, so as to obtain a spherical lithium iron phosphate precursor with the secondary particle size of 5 mu m;
(4) and (3) placing the spherical lithium iron phosphate precursor in a rotary furnace, rotating at 5r/min, heating to 650 ℃ at 2 ℃/min, continuously introducing acetylene gas at the flow rate of 3L/min for 8h, and carrying out in-situ growth of graphene to obtain the high-conductivity graphene-based lithium iron phosphate spherical composite material with the secondary particle size of 5 microns.
Comparative example 1
(1) Adding lithium hydroxide monohydrate, ferric orthophosphate, magnesium oxide and glucose into a ball mill according to the mol ratio of Li, Fe, P, M being 1.02:0.01 and the carbon content being 1.6%, carrying out ball milling for 1h, and then carrying out superfine milling for 6h to obtain slurry with proper particle size;
(2) carrying out two-fluid spray drying on the obtained slurry, wherein the inlet temperature of a spray dryer is 280 ℃, the outlet temperature of the spray dryer is 100 ℃, and a spherical lithium iron phosphate precursor with the secondary particle size of 6 mu m is obtained;
(3) and (3) placing the spherical lithium iron phosphate precursor in a roller kiln, and sintering at 700 ℃ for 12h to prepare the spherical lithium iron phosphate material with the primary particle size of 100-300nm and the secondary particle size of 6 mu m.
The materials obtained in examples 1 to 5 and comparative example 1 were assembled into 18650PC as a positive electrode active material by the following method:
preparing a positive plate: in a 5L stirring machine, anode active material, binder PVDF and conductive agent super-P are mixed according to a ratio of 94:3:3 (in example 3, the anode active material and the binder PVDF are mixed according to a ratio of 97:3, a comparative experiment is carried out without using a conductive agent, and the result is marked as comparative example 3, in comparative example 1, the anode active material and the binder PVDF are mixed according to a ratio of 97:3, a comparative experiment is carried out without using a conductive agent, and the result is marked as comparative example 1), anode mixing is carried out under the oil system and vacuum conditions, uniform anode slurry is obtained, and the prepared anode slurry is uniformly coated on an anode current collector Al foil to obtain an anode piece.
Preparing a negative plate: and (2) carrying out negative electrode batching on graphite, a thickening agent CMC, a binder SBR and conductive carbon powder according to a weight ratio of 95:1:2:2 in a water system to obtain uniform negative electrode slurry, uniformly coating the prepared negative electrode slurry on a negative electrode current collector Cu foil, and cooling to obtain a negative electrode sheet.
Preparing a lithium ion battery: winding the positive plate, the negative plate and the diaphragm prepared according to the process to prepare a lithium ion core, and injecting a non-aqueous electrolyte to prepare the 18650PC cylindrical battery, wherein the non-aqueous electrolyte adopts LiPF with the concentration of 1.0mol/L6As the electrolyte, a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 was used as the nonaqueous solvent.
The lithium ion batteries prepared in the above examples and comparative examples were subjected to related processing and electrical property tests, and table 1 below shows corresponding test data.
TABLE 1
Figure BDA0001351987610000141
As can be seen from table 1, the high-conductivity graphene-based lithium iron phosphate spherical composite material prepared by mixing graphene and LFP precursor in a molecular scale, then spheroidizing the mixture, and then growing the graphene in situ by CVD according to the present invention can well give consideration to the properties of gram volume, low temperature, rate, processing, cycle, etc. of the material.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (28)

1. The graphene-based lithium iron phosphate spherical composite material is characterized by comprising secondary spherical particles consisting of primary particles and graphene growing on the surfaces of the secondary spherical particles;
wherein the primary particles are lithium iron phosphate particles containing graphene;
the graphene contained in the primary particles accounts for 1-5 wt.% of the total mass of the composite material;
the powder conductivity of the graphene-based lithium iron phosphate spherical composite material is more than 1S/cm;
the composite material is prepared by the following method, and the method comprises the following steps:
(1) preparing lithium iron phosphate precursor slurry containing graphene;
(2) spray drying to obtain a secondary spherical lithium iron phosphate precursor composed of primary particles;
(3) placing the secondary spherical lithium iron phosphate precursor in a reaction furnace, heating to 600-750 ℃, introducing an organic compound in a protective atmosphere, and carrying out in-situ growth of graphene to obtain the graphene-based lithium iron phosphate spherical composite material;
the lithium iron phosphate precursor slurry containing graphene in the step (1) is prepared by the following method:
(A) mixing a lithium source, iron phosphate, an optional dopant and an optional carbon source to obtain a mixture;
(B) and mixing the mixture with graphene, an optional dispersing agent and deionized water, and grinding and dispersing to obtain the lithium iron phosphate precursor slurry containing graphene.
2. The composite material according to claim 1, wherein the primary particles have a particle size of 20-300 nm.
3. The composite material according to claim 1, wherein the secondary spherical particles have a median particle size of 3-9 μm.
4. The composite material according to claim 1, wherein the graphene contained in the primary particles accounts for 1-2 wt.% of the total mass of the composite material.
5. The composite material according to claim 1, wherein the number of graphene layers grown on the surface of the secondary spherical particles is a single layer or less than 10 layers.
6. The composite material of claim 1, wherein the secondary median particle size of the composite material is 3-9 μm.
7. A preparation method of a graphene-based lithium iron phosphate spherical composite material, which is characterized in that the graphene-based lithium iron phosphate spherical composite material is the composite material according to any one of claims 1 to 6, and the method comprises the following steps:
(1) preparing lithium iron phosphate precursor slurry containing graphene;
(2) spray drying to obtain a secondary spherical lithium iron phosphate precursor composed of primary particles;
(3) placing the secondary spherical lithium iron phosphate precursor in a reaction furnace, heating to 600-750 ℃, introducing an organic compound in a protective atmosphere, and carrying out in-situ growth of graphene to obtain the graphene-based lithium iron phosphate spherical composite material;
the lithium iron phosphate precursor slurry containing graphene in the step (1) is prepared by the following method:
(A) mixing a lithium source, iron phosphate, an optional dopant and an optional carbon source to obtain a mixture;
(B) and mixing the mixture with graphene, an optional dispersing agent and deionized water, and grinding and dispersing to obtain the lithium iron phosphate precursor slurry containing graphene.
8. The method of claim 7, wherein step (A) the lithium source, iron phosphate, and optional dopant are formulated in a molar ratio of Li: Fe: P: M (1.0-1.1):1 (1-1.05): 0-0.02), wherein M is a doping element in the dopant.
9. The method of claim 7, wherein the lithium source of step (A) comprises any 1 or a combination of at least 2 of lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, or lithium fluoride.
10. The method of claim 7, wherein the dopant of step (A) is any 1 or a combination of at least 2 of Mg, Mn, Ti, V, Nb, Ni, or Co compounds.
11. The method according to claim 7, wherein in step (A), the carbon source accounts for 0-1.5 wt.% of the total mass of the lithium source, the iron phosphate, the optional dopant and the optional carbon source, based on 100 wt.% of the total mass.
12. The method of claim 7, wherein the carbon source of step (A) comprises 1 or a combination of at least 2 of ascorbic acid, cellulose, polypropylene, epoxy, sucrose, glucose, fructose, citric acid, polyethylene glycol, starch, phenolic resin.
13. The method of claim 7, wherein the percentage of graphene in the mixture mass in step (B) is 0.1-1.5 wt.%.
14. The method of claim 7, wherein the dispersant of step (B) is present in an amount of 0-2 wt.% based on the mass of the mix.
15. The method of claim 7, wherein the mass of the deionized water in step (B) is 1-6 times the mass of the mix.
16. The method according to claim 7, wherein the graphene in the step (B) comprises at least one of graphene powder and graphene conductive liquid.
17. The method of claim 7, wherein the dispersant of step (B) is any 1 or a combination of at least 2 of glucose, sucrose, polyethylene glycol, polyvinylpyrrolidone, or polyvinyl alcohol.
18. The method of claim 7, wherein the milling dispersion time of step (B) is 2-20 hours.
19. The method of claim 7, wherein the spray drying of step (2) is any 1 of two-fluid spray drying and four-fluid spray drying, and the two-fluid spray drying comprises gas-electric combined two-fluid spray drying.
20. The method as claimed in claim 7, wherein the step (2) is carried out at an inlet temperature of 200 ℃ to 350 ℃ and an outlet temperature of 70 ℃ or higher.
21. The method according to claim 7, wherein the reaction furnace in the step (3) is a rotary kiln, and the rotary kiln is rotated at a rotation speed of 1-10 r/min.
22. The method as claimed in claim 7, wherein the temperature rise rate of the reaction furnace in the step (3) is 1-10 ℃/min.
23. The method of claim 7, wherein the protective atmosphere of step (3) is a combination atmosphere of any 1 or at least 2 of an argon atmosphere, a nitrogen atmosphere, or a hydrogen atmosphere.
24. The method of claim 7, wherein the organic compound of step (3) comprises any 1 or a combination of at least 2 of methane, ethane, ethylene, acetylene, acetone, benzene, and toluene.
25. The method according to claim 7, wherein the flow rate of the organic compound in the step (3) is 0.1 to 5L/min.
26. The method as claimed in claim 7, wherein the time for introducing the organic compound in the step (3) is 0.5 to 10 hours.
27. The method according to any one of claims 7-26, characterized in that the method comprises the steps of:
(1) mixing a lithium source, iron phosphate, a dopant and a carbon source to obtain a mixture;
(2) mixing the mixture with graphene, a dispersing agent and deionized water, and grinding and dispersing for 2-20h, wherein the mass of the deionized water is 1-6 times that of the mixture to obtain uniformly ground and dispersed slurry;
(3) spray drying the slurry which is uniformly ground and dispersed, wherein the inlet temperature of a spray dryer is 200-350 ℃, and the outlet temperature is not lower than 70 ℃, so as to obtain a secondary spherical lithium iron phosphate precursor composed of primary particles;
(4) and (3) placing the secondary spherical lithium iron phosphate precursor in a rotary furnace, rotating at 1-10r/min, heating to 600-750 ℃ at 1-10 ℃/min, continuously introducing organic compound gas at the flow rate of 0.1-5L/min for 0.5-10h under a protective atmosphere, and carrying out in-situ growth of graphene to obtain the graphene-based lithium iron phosphate spherical composite material.
28. A lithium ion battery, characterized in that it comprises as active material a composite material according to any one of claims 1 to 6, without the addition of an external conductive agent.
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