CN113054173B - Low-temperature lithium iron phosphate and preparation method and application thereof - Google Patents

Low-temperature lithium iron phosphate and preparation method and application thereof Download PDF

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CN113054173B
CN113054173B CN202110269414.4A CN202110269414A CN113054173B CN 113054173 B CN113054173 B CN 113054173B CN 202110269414 A CN202110269414 A CN 202110269414A CN 113054173 B CN113054173 B CN 113054173B
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iron phosphate
lithium iron
temperature
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layer
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CN113054173A (en
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万宁
李萍萍
王庆莉
彭家兴
杨茂萍
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Guoxuan High Tech Power Energy 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides low-temperature lithium iron phosphate and a preparation method and application thereof. The low-temperature lithium iron phosphate comprises lithium iron phosphate serving as an inner core and CuInS coated on the surface of the inner core2Layer and cladding on CuInS2LiTaO on the surface of the layer3And (3) a layer. The invention also provides a preparation method of the low-temperature lithium iron phosphate, which comprises the steps of sequentially preparing CuInS2Layer-coated lithium iron phosphate and LiTaO3Modified CuInS2And annealing the precursor of the layer-coated lithium iron phosphate to obtain the low-temperature lithium iron phosphate. The invention also provides a lithium ion battery anode material containing the low-temperature lithium iron phosphate. The lithium iron phosphate provided by the invention has high multiplying power and can keep good charge and discharge performance in a low-temperature environment.

Description

Low-temperature lithium iron phosphate and preparation method and application thereof
Technical Field
The invention relates to the field of lithium ion battery anode materials, in particular to low-temperature lithium iron phosphate and a preparation method and application thereof.
Background
Currently, there are many systems studied as positive electrode materials for lithium ion batteries, but only lithium cobaltate (LiCoO) is really used for large-scale industrialization2)、LiMn2O4、LiFePO4And a ternary composite oxide. LiCoO2The price is high, and the cost is high,poor safety, LiMn2O4Comparative LiCoO2Relatively cheap raw materials and slightly high thermal stability of the materials, but LiMn2O4Low capacity and poor high temperature performance. Novel ternary composite oxide Li1/3Co1/3Mn1/3O2With LiCoO2The battery has the same structure, has high energy density, but the ternary material has poor safety performance, which is a problem which always troubles the whole battery industry and is not completely solved so far. In 1997, the subject group of Goodenough reported for the first time that lithium ion cathode material LiFePO4The theoretical specific capacity is 170mAh/g which is larger than that of the commercialized LiCoO2Actual specific discharge capacity of (2). Also, LiFePO4Has good cycle performance and a stable discharge platform around 3.45V. LiFePO4The electrode material is mainly used in the current power battery, and has the main advantages of stable voltage platform, cheap and abundant raw materials, environmental friendliness, low toxicity and higher safety due to good high stability.
LiFePO4Is an orthorhombic olivine structure belonging to Pnmb space group and having a lattice constant of LiFePO4The crystal structure of the material can still keep stable at 400 ℃, so that the cycle performance and the safety of the material are greatly improved. Lithium ion in LiFePO4The one-dimensional channel migrates along the lattice, so that the diffusion rate is greatly limited, and the one-dimensional channel is easily blocked due to the occurrence of impurity defects, so that the ionic conductivity of the one-dimensional channel is further reduced. The bonding bond between O atom and Fe and P is very strong, so that LiFePO is formed4Structure and LiCoO2Compared with the laminated structure, the high-temperature-stability composite material has good high-temperature stability. However, strong P-O bonds also result in ion diffusion rates (10)-13-10-16cm-2·S-1) And electron conductivity (-10)-19cm-2·S-1)。
LiFePO4The lower ionic conductivity and electronic conductivity reduces the actual discharge capacity, the polarization phenomenon is serious, and the multiplying power and low-temperature performance are not ideal. Extensive and intensive studies have been made thereon to improve the electrochemical properties thereof by reducing the particle diameter; coating a conductive amorphous carbon net on the surfaceThe electronic conductivity can be improved, the growth of crystal grains can be inhibited, and the ionic conductivity is further effectively improved; the conductivity of P-type semiconductors is improved by doping Li or Fe with high-valent cations to form the P-type semiconductors. The modification modes have great influence on the ionic conductivity and the electronic conductivity of the composite material, so that the discharge capacity, the cycle life and the rate capability of the composite material are improved.
LiFePO4The synthetic raw material resource is rich, the cost is low, the environment is protected, the capacity is high, the cycle performance is good, but the low-temperature performance is poor. The improvement of the low-temperature performance and the rate capability of the lithium iron phosphate material is an urgent desire of material researchers and producers, and the current method for synthesizing the lithium iron phosphate comprises the following steps: high temperature solid phase method, sol-gel method, hydrothermal method, carbothermic method, spray pyrolysis method, etc., but only high temperature solid phase method is widely used in industrial production.
Disclosure of Invention
In order to solve the above problems, the present invention aims to provide a low-temperature lithium iron phosphate, and a preparation method and an application thereof. The low-temperature lithium iron phosphate has high multiplying power, and can keep good charge and discharge performance in a low-temperature environment.
In order to achieve the above object, the present invention provides a low-temperature lithium iron phosphate, which comprises lithium iron phosphate as a core, and CuInS coated on the surface of the core2Layer and cladding on CuInS2LiTaO on the surface of the layer3And (3) a layer.
In a specific embodiment of the invention, the CuInS is2The layer is used as an inner cladding layer of the lithium iron phosphate, which is beneficial to reducing the contact resistance between electrode materials and improving the surface conductivity of the lithium iron phosphate material, so that the diffusion rate of ions entering and exiting the lithium iron phosphate under the condition of low temperature (the low temperature is generally the temperature environment reaching-40 ℃), and the excessive thickness of the cladding layer can block Li+So that the thickness thereof is generally controlled to be 2nm to 4 nm.
In a specific embodiment of the invention, the LiTaO is3The layer is used as a surface modification layer of the lithium iron phosphate, and can provide power for the diffusion of lithium ions in the discharge process, so that the electrode material is made to be under the low-temperature conditionThe excellent rate capability is shown. The LiTaO3The extra power provided by the piezoelectric material is reduced by the excessively thick layer, and thus, the thickness thereof is generally controlled to be 2nm to 5 nm.
In a specific embodiment of the invention, the LiTaO is3LiTaO in layer3The mass purity of (A) is generally controlled to be more than 99.99% so as to avoid Fe2P、Li3PO4Excessive heterogeneous phase and the occurrence of Li clogging+The one-dimensional channel of de-intercalation and the crystal lattice are distorted, the ion diffusion rate is reduced, and the low-temperature performance is influenced.
In the embodiment of the present invention, the particle size of the lithium iron phosphate as the core is generally controlled to 400nm to 450nm to facilitate CuInS2The layer is uniformly coated on the surface of the inner core. In a specific embodiment, the lithium iron phosphate is generally subjected to ball milling treatment at a high rotation speed for a long time, so as to ensure that the particles of the lithium iron phosphate are uniform. The rotation speed of the ball milling is generally controlled to 3000-.
The invention also provides a preparation method of the low-temperature type lithium iron phosphate, which comprises the following steps:
mixing a mixed solution of a copper source, an indium source and a sulfur source with a lithium iron phosphate dispersion liquid to obtain slurry, spraying the slurry on a substrate, and drying to obtain a precursor film; heating the precursor film in a hydrazine hydrate atmosphere to obtain CuInS2Layer-coated lithium iron phosphate;
step two, dissolving the lithium source and the tantalum source in a protective atmosphere to obtain LiTaO3Sol prepared by dissolving the LiTaO3Sol in CuInS2The surface of the lithium iron phosphate coated with the layer is subjected to rotary coating to obtain LiTaO3Modified CuInS2A layer-coated lithium iron phosphate precursor;
step three, mixing the LiTaO in a protective atmosphere3Modified CuInS2Annealing the layer-coated lithium iron phosphate precursor to obtain the low-temperature lithium iron phosphate.
In a specific embodiment of the present invention, in step three, the annealing generally comprises two annealing steps: first step annealing for cracking organic matter in coating filmThe temperature of the first step annealing is generally controlled to be 350-390 ℃, and the time is generally controlled to be 12-15 min; second step anneal for CuInS2Layer and LiTaO3The temperature of the second step of annealing is controlled to be 700-770 ℃ and the time is controlled to be 10-15min, so as to avoid generating Fe at an excessive temperature2P、Li3PO4And the like, which affect the low-temperature performance of the lithium iron phosphate material.
In a particular embodiment of the invention, in step one, the copper source may comprise copper sulfate, e.g. Cu2SO4·5H2O, and the like.
In a particular embodiment of the invention, In step one, the indium source may comprise indium nitrate, for example In (NO)3)3·4.5H2O, and the like.
In a particular embodiment of the invention, in step one, the sulphur source may comprise thioacetamide or the like.
In a specific embodiment of the invention, in the first step, the mass ratio of the copper source, the indium source and the sulfur source is generally controlled to be (1.5-2.0): (2.5-2.8): (1.0-1.5), for example, 1.5: 2.5: 1.
in a specific embodiment of the invention, in the first step, the lithium iron phosphate dispersion liquid contains a dispersing agent, the lithium iron phosphate dispersion liquid is usually obtained by mixing lithium iron phosphate and the dispersing agent in water, and the specific dispersing condition may be that the mixture is stirred in a water bath at 40-60 ℃ for 8-10 h. The dispersant may be a nonionic dispersant, such as Tween-80. The mass concentration of the dispersing agent in the lithium iron phosphate dispersing liquid can be controlled to be 5-35%.
In the embodiment of the invention, the substrate for spray coating film formation is generally a monocrystalline silicon substrate, which is generally pretreated before use, for example, the substrate is cleaned 3-5 times with ultrapure water under ultrasonic conditions. The slurry is printed and sprayed on the substrate to form a wet film, and the thickness of the wet film can be controlled between 0.4 and 0.5 mu m. Drying the wet film at the temperature of 100-200 ℃ to obtain a precursor film (CuInS)2A precursor of layer-coated lithium iron phosphate).
In the specific embodiment of the invention, in the step one, the heating temperature is generally controlled to be 240-280 ℃, and the heating time is generally controlled to be 1-2 h.
In a specific embodiment of the invention, in step two, the LiTaO is3The preparation method of the sol may include: dissolving a lithium source and a tantalum source in a solvent, heating and refluxing to obtain the LiTaO3And (3) sol. The lithium source may be lithium ethoxide or the like, the tantalum source may be tantalum ethoxide or the like, and ethylene glycol monomethyl ether or the like may be used as a solvent for dissolving the lithium source and the tantalum source. The temperature of the heating reflux is generally 30-110 ℃, and the time of the heating reflux is generally 30-120 min. The molar ratio of the lithium source to the tantalum source is preferably 1: 1.
In the above LiTaO3In the preparation method of the sol, the lithium ethoxide can be obtained by the following processes: the lithium ethoxide is obtained by dissolving metallic lithium (generally, metallic lithium having a purity of 99.996% or more) in a solvent, and heating (preferably, 40 to 70 ℃).
In a specific embodiment of the present invention, step two produces a solution in CuInS2LiTaO coated on surface of layer-coated lithium iron phosphate3Layer of the LiTaO3Li in the layer+、Ta+5The stoichiometric ratio is 1:1, compared with LiTa3O8Film, LiTaO3The formed film has more uniform thickness and relatively simple preparation process, can bear higher polarization voltage in the polarization process, can avoid film breakdown, and improves the low-temperature performance of the material. The LiTaO3The thickness of the layer (2nm-5nm) is comparable to the particle size of the lithium tantalate crystalline material, LiTaO being comparable to lithium tantalate crystalline material3The formed film has more uniform and flat thickness and no crack, and can better improve the low-temperature performance of the material.
In the second and third steps of the present invention, the protective atmosphere may include nitrogen, argon, etc.
The invention further provides a lithium ion battery anode material which comprises the low-temperature lithium iron phosphate.
The invention has the beneficial effects that:
the preparation method provided by the invention coats CuInS on the surface of the lithium iron phosphate particles2The layer can reduce the side reaction of the lithium iron phosphate material and the electrolyte, improve the ionic conductivity and reduce the interface polarization effect; by adding in CuInS2Further coating LiTaO on the basis of layers3The layer can conduct stress generated by 'lattice respiration' of the lithium iron phosphate anode material in the charging and discharging processes to the piezoelectric modification layer at the interface, and an alternating local electric field is generated by in-situ induction at the electrode-electrolyte interface. During the charging process, lithium ions are continuously extracted to enable crystal lattices to gradually expand, the induced local potential is gradually increased corresponding to the gradual increase of stress, and the direction of a local electric field is opposite to the diffusion direction of the lithium ions at the moment, so that the occurrence of overcharge can be prevented to a certain extent. During the discharging process, lithium ions are gradually inserted back into the crystal lattice, so that the expansion of the crystal lattice is gradually reduced, corresponding to the gradual reduction of stress, the corresponding piezoelectric potential is gradually reduced, and at the moment, the direction of the built-in potential of the coating layer is consistent with the diffusion direction of the lithium ions, so that extra power is provided for the diffusion of the lithium ions during the discharging process, and the battery shows excellent rate performance and low-temperature performance.
Drawings
FIG. 1 is LiTaO prepared in example 13Modified CuInS2SEM image of the layer-coated lithium iron phosphate material.
FIG. 2 is a CuInS prepared in comparative example 12SEM image of the layer-coated lithium iron phosphate material.
FIG. 3 is LiTaO prepared in comparative example 33SEM image of the layer-coated lithium iron phosphate material.
Fig. 4 is a first charge-discharge curve diagram of the lithium iron phosphate materials of example 1 and comparative examples 1 to 3 at different multiplying factors.
Fig. 5 is a charge-discharge curve diagram of the lithium iron phosphate materials of example 1, comparative example 1 to comparative example 3 at-40 ℃.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
Example 1
The embodiment provides a preparation method of low-temperature lithium iron phosphate, which comprises the following steps:
s1 preparation of CuInS2A layer-coated lithium iron phosphate film; ball-milling the lithium iron phosphate powder material at the rotating speed of 3000-3500r/min for 20-22h, adding the ball-milled material into deionized water, adding a non-ionic dispersing agent Tween-80, and stirring the mixture in a water bath at 40 ℃ for 8h to obtain a lithium iron phosphate dispersion liquid, wherein the mass ratio of the Tween-80 in the lithium iron phosphate dispersion liquid is 5%.
1.5gCu2SO4·5H2O、2.5gIn(NO3)3·4.5H2O and 1gCH3CSNH2(thioacetamide) was uniformly mixed in 14g of deionized water to obtain a mixed solution. And mixing the mixed solution with a lithium iron phosphate dispersion liquid to obtain slurry.
Printing and spraying the slurry on a monocrystalline silicon substrate to obtain a wet film with the thickness of 0.4-0.5 μm, and drying at 100 ℃ to obtain a precursor film. Putting the precursor film into a sealable container containing hydrazine hydrate, heating to 240 ℃, preserving heat for 1h, and naturally cooling to obtain CuInS2A layer-coated lithium iron phosphate film.
S2 preparation of LiTaO3Modified CuInS2Layer-coated lithium iron phosphate precursor:
dissolving high-purity (more than 99.96 percent) lithium metal into 60 ℃ ethylene glycol monomethyl ether to obtain the lithium ethoxide. Mixing lithium ethoxide and tantalum ethoxide in ethylene glycol monomethyl ether according to the molar ratio of 1:1 in an argon atmosphere, and heating at 110 ℃ for 100min to obtain LiTaO3And (3) sol.
With CuInS2The lithium iron phosphate film coated with the layer is used as a substrate and LiTaO is utilized3Spin coating the sol on a substrate to obtain LiTaO3LiTaO with a layer thickness of 2nm3Modified CuInS2A layer-coated lithium iron phosphate precursor.
S3, preparing a modified lithium iron phosphate material: in the protective atmosphere of argon gas,LiTaO3modified CuInS2The lithium iron phosphate precursor coated with the layer is annealed at the first step of 350 ℃ for 12min and then annealed at the second step of 700 ℃ for 10min to obtain LiTaO3Modified CuInS2And the lithium iron phosphate coated with the layer is the low-temperature lithium iron phosphate material.
Example 2
The embodiment provides a preparation method of low-temperature lithium iron phosphate, which comprises the following steps:
s1 preparation of CuInS2A layer-coated lithium iron phosphate film; ball-milling the lithium iron phosphate powder material at the rotating speed of 3500r/min for 22h, adding the ball-milled material into deionized water, adding a non-ionic dispersing agent Tween-80, and stirring the mixture in a water bath at the temperature of 60 ℃ for 10h to obtain a lithium iron phosphate dispersion liquid, wherein the mass percentage of the Tween-80 in the lithium iron phosphate dispersion liquid is 35%.
1.5gCu2SO4·5H2O、2.5gIn(NO3)3·4.5H2O and 1gCH3CSNH2Mixed well in 14g of deionized water to give a mixed solution. And mixing the mixed solution with a lithium iron phosphate dispersion liquid to obtain slurry.
Printing and spraying the slurry on a monocrystalline silicon substrate to obtain a wet film with the thickness of 2 microns, and drying at 120 ℃ to obtain a precursor film. Putting the precursor film into a sealable container containing hydrazine hydrate, heating to 280 ℃, preserving heat for 2h, and naturally cooling to obtain CuInS2A layer-coated lithium iron phosphate film.
S2 preparation of LiTaO3Modified CuInS2Layer-coated lithium iron phosphate precursor:
dissolving high-purity (more than 99.96 percent) lithium metal into ethylene glycol monomethyl ether at 50 ℃ to obtain the lithium ethoxide. Mixing lithium ethoxide and tantalum ethoxide in ethylene glycol monomethyl ether according to the molar ratio of 1:1 in an argon atmosphere, and heating at 80 ℃ for 90min to obtain LiTaO3And (3) sol.
With CuInS2The lithium iron phosphate film coated with the layer is used as a substrate and LiTaO is utilized3Spin coating the sol on a substrate to obtain LiTaO3LiTaO with a layer thickness of 5nm3Modified CuInS2Layer coated phosphoric acidAnd (3) a lithium iron precursor.
S3, preparing a modified lithium iron phosphate material: in an argon protective atmosphere, LiTaO3Modified CuInS2The lithium iron phosphate precursor coated with the layer is annealed for 15min at 390 ℃ first, and then is annealed for 15min at 770 ℃ second to obtain LiTaO3Modified CuInS2And lithium iron phosphate coated with the layer, namely a low-temperature lithium iron phosphate material.
Example 3
The embodiment provides a preparation method of low-temperature lithium iron phosphate, which comprises the following steps:
s1 preparation of CuInS2A layer-coated lithium iron phosphate film; ball-milling the lithium iron phosphate powder material at the rotating speed of 3000-.
1.5gCu2SO4·5H2O、2.5gIn(NO3)3·4.5H2O and 1gCH3CSNH2Mixed well in 14g of deionized water to give a mixed solution. And mixing the mixed solution with a lithium iron phosphate dispersion liquid to obtain slurry.
Printing and spraying the slurry on a monocrystalline silicon substrate to obtain a wet film with the thickness of 4 microns, and drying at 120 ℃ to obtain a precursor film. Putting the precursor film into a sealable container containing hydrazine hydrate, heating to 240 ℃, preserving heat for 1h, and naturally cooling to obtain CuInS2A layer-coated lithium iron phosphate film.
S2 preparation of LiTaO3Modified CuInS2Layer-coated lithium iron phosphate precursor:
dissolving high-purity (more than 99.96 percent) lithium metal into ethylene glycol monomethyl ether at 70 ℃ to obtain the lithium ethoxide. Mixing lithium ethoxide and tantalum ethoxide in ethylene glycol monomethyl ether according to the molar ratio of 1:1 in an argon atmosphere, and heating at 110 ℃ for 120min to obtain LiTaO3And (3) sol.
With CuInS2The lithium iron phosphate film coated with the layer is used as a substrate and LiTaO is utilized3Spin coating the sol on a substrate to obtain LiTaO3LiTaO with a layer thickness of 2nm3Modified CuInS2A layer-coated lithium iron phosphate precursor.
S3, preparing a modified lithium iron phosphate material: in an argon protective atmosphere, LiTaO3Modified CuInS2The lithium iron phosphate precursor coated with the layer is annealed at 390 ℃ for 12min firstly and then annealed at 700 ℃ for 15min secondly to obtain LiTaO3Modified CuInS2And the lithium iron phosphate coated with the layer is the low-temperature lithium iron phosphate material.
Example 4
The embodiment provides a preparation method of low-temperature lithium iron phosphate, which comprises the following steps:
1. preparation of CuInS2Layer-coated lithium iron phosphate film: ball-milling the lithium iron phosphate powder material at the rotating speed of 3000-3500r/min for 20-22h, adding the ball-milled material into deionized water, adding a non-ionic dispersing agent Tween-80, and stirring the mixture in a water bath at 50 ℃ for 10h to obtain a lithium iron phosphate dispersion liquid, wherein the mass percentage of the Tween-80 in the lithium iron phosphate dispersion liquid is 25%.
1.5gCu2SO4·5H2O、2.5gIn(NO3)3·4.5H2O and 1gCH3CSNH2Mixed well in 14g of deionized water to give a mixed solution. And mixing the mixed solution with a lithium iron phosphate dispersion liquid to obtain slurry.
And printing and spraying the slurry on a monocrystalline silicon substrate to obtain a wet film with the thickness of 2.5 microns, and drying at 110 ℃ to obtain a precursor film. Putting the precursor film into a sealable container containing hydrazine hydrate, heating to 260 ℃, preserving heat for 1.5h, and naturally cooling to obtain CuInS2A layer-coated lithium iron phosphate film.
S2 preparation of LiTaO3Modified CuInS2Layer-coated lithium iron phosphate precursor:
dissolving high-purity (more than 99.96 percent) lithium metal into ethylene glycol monomethyl ether at 40 ℃ to obtain the lithium ethoxide. Mixing lithium ethoxide and tantalum ethoxide in ethylene glycol monomethyl ether according to the molar ratio of 1:1 in an argon atmosphere, and heating at 60 ℃ for 50min to obtain LiTaO3And (3) sol.
With CuInS2The lithium iron phosphate film coated with the layer is used as a substrate and LiTaO is utilized3Spin coating the sol on a substrate to obtain LiTaO3LiTaO with a layer thickness of 4nm3Modified CuInS2A layer-coated lithium iron phosphate precursor;
s3, preparing a modified lithium iron phosphate material: in an argon protective atmosphere, LiTaO3Modified CuInS2The lithium iron phosphate precursor coated with the layer is annealed for the first step of 370 ℃ and 14min and then annealed for the second step of 730 ℃ and 13min to obtain LiTaO3Modified CuInS2And the lithium iron phosphate coated with the layer is the low-temperature lithium iron phosphate material.
Comparative example 1
This comparative example provides a CuInS2The preparation method of the layer-coated lithium iron phosphate comprises the following steps:
ball-milling the lithium iron phosphate powder material at the rotating speed of 1000r/min for 8h, adding the ball-milled material into deionized water, adding a non-ionic dispersing agent Tween-80, and stirring the mixture in a water bath at 40 ℃ for 8h to obtain a lithium iron phosphate dispersion liquid, wherein the mass percentage of the Tween-80 in the lithium iron phosphate dispersion liquid is 5%.
1.5gCu2SO4·5H2O、2.5gIn(NO3)3·4.5H2O and 1gCH3CSNH2Mixed well in 14g of deionized water to give a mixed solution. And mixing the mixed solution with a lithium iron phosphate dispersion liquid to obtain slurry.
And printing and spraying the slurry on a monocrystalline silicon substrate to obtain a wet film with the thickness of 2 microns, and drying at 110 ℃ to obtain a precursor film. Putting the precursor film into a sealable container containing hydrazine hydrate, heating to 240 ℃, preserving heat for 1h, naturally cooling, transferring to a high-temperature furnace, and carrying out heat treatment at 700 ℃ for 2h in an argon atmosphere to obtain CuInS2A layer-coated lithium iron phosphate film.
Comparative example 2
This comparative example provides lithium iron phosphate, which is the lithium iron phosphate powder material used in examples 1 to 4 and comparative example 1.
Comparative example 3
This comparative example provides a LiTaO3The preparation method of the coated lithium iron phosphate comprises the following steps:
s1, dissolving high-purity (more than 99.96 percent) lithium metal in 60 ℃ ethylene glycol monomethyl ether to obtain the lithium ethoxide. Mixing lithium ethoxide and tantalum ethoxide in ethylene glycol monomethyl ether according to the molar ratio of 1:1 in an argon atmosphere, and heating at 100 ℃ for 100min to obtain LiTaO3And (3) sol.
Using lithium iron phosphate film as substrate and LiTaO3Spin coating the sol on a substrate to obtain LiTaO3LiTaO with a layer thickness of 4nm3A coated lithium iron phosphate film precursor;
s2, preparing a modified lithium iron phosphate material: in an argon protective atmosphere, LiTaO3The coated lithium iron phosphate film precursor is annealed at the first step of 370 ℃ for 14min and then annealed at the second step of 730 ℃ for 13min to obtain LiTaO3The coated lithium iron phosphate is a modified lithium iron phosphate material.
Test example 1
The test example provides the detection results of the physicochemical indexes of lithium iron phosphate of example 1, and is specifically summarized in table 1.
TABLE 1
Index (I) D10 D50 D90 D100 Tap density
Numerical value 1.249μm 2.752μm 3.131μm 3.991μm 1.016g/cc
BET High temperature moisture Magnetic substance PH Li Fe/P
3.5m2·g-1 412.0ppm 102.9ppb 9.15 4.37ppm 0.979ppm
The physical and chemical indexes of the lithium iron phosphate material prepared in the embodiment 2-4 are analyzed, and all indexes are similar to the corresponding indexes of the material prepared in the embodiment 1. I.e., also meets the battery grade requirements, the parameters of the materials of examples 2-4 are similar to those of the material of example 1, unless otherwise specified.
Fig. 1, 2, 3 are SEM photographs of the product materials of example 1, comparative example 1, and comparative example 3, respectively. As can be seen from FIG. 2, through CuInS2The particle surface of the lithium iron phosphate material coated with the layer is uniformly and smoothly coated; as can be seen from FIGS. 1 and 3, LiTaO3Modified CuInS2Layer-coated lithium iron phosphate material and LiTaO3The particle surfaces of the coated lithium iron phosphate material are all provided with obvious coating layers and coating effectsPreferably.
Electrochemical performance tests were performed on the lithium iron phosphate of example 1, comparative example 1, and comparative example 3 in a 28148115 specification lithium ion battery, and the results are shown in fig. 4 and 5.
As can be seen from fig. 4, at a 5C (25 ℃, 2.0-3.65V) rate, the lithium iron phosphate material of example 1 has a battery performance discharge capacity of 52.67Ah, while the lithium iron phosphate material of comparative example 1 only exerts a battery performance discharge capacity of 52.32Ah, the lithium iron phosphate material of comparative example 2 has a battery performance discharge capacity of only 51.80Ah, and the lithium iron phosphate material of comparative example 3 has a battery performance discharge capacity of only 51.56Ah, which indicates that the lithium iron phosphate material prepared in example 1 has good rate capability.
As can be seen from fig. 5, under the condition of 1C (-40 ℃, 1.8-3.65V), the discharge capacity corresponding to the battery performance of the lithium iron phosphate material of example 1 is 51.74Ah, while the discharge capacity corresponding to the battery of comparative example 1 is only 48.36Ah, the discharge capacity corresponding to the battery of comparative example 2 is only 44.05Ah, and the discharge capacity corresponding to the battery of the lithium iron phosphate material of comparative example 3 is only 26.99Ah, which indicates that the lithium iron phosphate material prepared in example 1 has good low-temperature performance.
The results of fig. 4 and 5 are summarized in table 2. As can be seen from table 2, the discharge capacity of the lithium iron lithiumate of example 1 at low temperature is increased by 3Ah to 25Ah compared to the discharge capacity at low temperature of comparative example 1 to comparative example 3, and this increase can generate a higher economic benefit. The results in Table 2 illustrate CuInS alone2Layer coating and LiTaO3The improvement degree of the lithium iron phosphate rate performance of the layer coating is very limited, and the modified lithium iron phosphate material provided by the invention can pass through CuInS2Layer and LiTaO3The synergistic effect between the layers greatly improves the rate capability of the lithium iron phosphate material in various temperature environments, and can better stabilize the rate capability of the lithium iron phosphate material in low-temperature environments.
TABLE 2
5C discharge capacity/Ah at 25 DEG C -40 ℃ to 1C discharge capacity/Ah
Comparative example 2 51.80 44.05
Comparative example 1 52.32 48.36
Comparative example 3 51.56 26.99
Example 1 52.67 51.74
Table 3 shows the discharge performance test results of the lithium iron phosphate materials of examples 2 to 4.
TABLE 3
Examples -40 ℃ to 1C discharge capacity/Ah
2 50.75
3 50.92
4 51.54
As can be seen from table 3, the discharge capacity of the lithium iron phosphate material prepared in examples 2 to 4 at-40 ℃ is similar to that of the lithium iron phosphate material prepared in example 1, and is at a higher level, which indicates that the modified lithium iron phosphate provided by the present invention has excellent low-temperature rate capability, and is very suitable for being used as a low-temperature lithium ion battery cathode material.

Claims (27)

1. The low-temperature lithium iron phosphate comprises lithium iron phosphate as a core and CuInS coated on the surface of the core2Layer and cladding on CuInS2LiTaO on the surface of the layer3A layer;
wherein the CuInS2The thickness of the layer is 2nm-4 nm; the LiTaO3The thickness of the layer is 2nm-5nm, and the low temperature is a temperature at least up to-40 ℃.
2. The low-temperature type lithium iron phosphate according to claim 1,
the LiTaO3LiTaO in layer3The mass purity of (A) is more than 99.9%.
3. The low-temperature lithium iron phosphate according to claim 1, wherein the particle size of the lithium iron phosphate as the core is 400nm to 450 nm.
4. The low-temperature lithium iron phosphate according to claim 1 or 3, wherein the lithium iron phosphate as the core is subjected to ball milling.
5. The low-temperature lithium iron phosphate according to claim 4, wherein the rotation speed of the ball milling is 3000r/min to 3500r/min, and the ball milling time is 20h to 22 h.
6. The method for preparing low-temperature type lithium iron phosphate according to any one of claims 1 to 5, comprising:
mixing a mixed solution of a copper source, an indium source and a sulfur source with a lithium iron phosphate dispersion liquid to obtain slurry, spraying the slurry on a substrate, and drying to obtain a precursor film; heating the precursor film in a hydrazine hydrate atmosphere to obtain CuInS2Layer-coated lithium iron phosphate;
step two, dissolving a lithium source and a tantalum source in a protective atmosphere to obtain LiTaO3Sol prepared by dissolving the LiTaO3Sol in CuInS2The surface of the lithium iron phosphate coated with the layer is subjected to rotary coating to obtain LiTaO3Modified CuInS2A layer-coated lithium iron phosphate precursor;
step three, mixing the LiTaO in a protective atmosphere3Modified CuInS2Annealing the layer-coated lithium iron phosphate precursor to obtain the low-temperature lithium iron phosphate.
7. The preparation method of claim 6, wherein in the third step, the annealing comprises two-step annealing, the temperature of the first step annealing is 350-390 ℃, and the time is 12-15 min; the temperature of the second step of annealing is 700-770 ℃, and the time is 10-15 min.
8. The production method according to claim 6 or 7, wherein in step one, the lithium iron phosphate dispersion liquid contains a dispersant.
9. The production method according to claim 8, wherein the dispersant comprises a nonionic dispersant.
10. The method of claim 9, wherein the non-ionic dispersant comprises Tween-80.
11. The preparation method according to claim 8, wherein the mass concentration of the dispersant in the lithium iron phosphate dispersion liquid is 5% to 35%.
12. The method of claim 6, wherein in step one, the copper source comprises copper sulfate; the indium source comprises indium nitrate; the sulfur source comprises thioacetamide.
13. The method of claim 8, wherein in step one, the copper source comprises copper sulfate; the indium source comprises indium nitrate; the sulfur source comprises thioacetamide.
14. The production method according to claim 8, wherein the mass ratio of the copper source, the indium source and the sulfur source is (1.5-2.0): (2.5-2.8): (1.0-1.5).
15. The production method according to claim 12, wherein the mass ratio of the copper source, the indium source and the sulfur source is (1.5-2.0): (2.5-2.8): (1.0-1.5).
16. The production method according to claim 13, wherein the mass ratio of the copper source, the indium source and the sulfur source is (1.5-2.0): (2.5-2.8): (1.0-1.5).
17. The production method according to any one of claims 14 to 16, wherein the mass ratio of the copper source, the indium source, and the sulfur source is 1.5: 2.5: 1.
18. the preparation method according to any one of claims 6 and 9 to 16, wherein in the first step, the heating temperature is 240 ℃ to 280 ℃, and the heating time is 1h to 2 h.
19. The preparation method according to claim 8, wherein in the first step, the heating temperature is 240-280 ℃, and the heating time is 1-2 h.
20. The preparation method of claim 17, wherein in the first step, the heating temperature is 240-280 ℃, and the heating time is 1-2 h.
21. The method of claim 6, wherein in step two, the LiTaO is present3The preparation method of the sol comprises the following steps: dissolving a lithium source and a tantalum source in a solvent, heating and refluxing to obtain the LiTaO3And (3) sol.
22. The preparation method according to claim 21, wherein in the second step, the temperature of the heating reflux is 30-110 ℃, and the time of the heating reflux is 30-120 min.
23. The production method according to claim 6 or 21, wherein the lithium source includes lithium ethoxide; the tantalum source comprises tantalum ethoxide; the solvent used to dissolve the lithium source and the tantalum source includes ethylene glycol monomethyl ether.
24. The method of claim 23, wherein the lithium ethoxide is prepared by dissolving lithium metal in a solvent and heating to obtain the lithium ethoxide.
25. The production method according to claim 24, wherein, in the production method of lithium ethoxide, the heating temperature is 40 ℃ to 70 ℃.
26. Low-temperature lithium iron phosphate obtained by the production method according to any one of claims 6 to 25.
27. A lithium ion battery positive electrode material comprising the low-temperature type lithium iron phosphate according to claim 26.
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