CN106876705B - Preparation method of in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material - Google Patents
Preparation method of in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material Download PDFInfo
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- 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
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Abstract
The invention provides a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material, and relates to the technical field of battery materials. The preparation method comprises the steps of weighing raw materials of a lithium source, iron powder, phosphate and a carbon source; firstly, iron powder and phosphate are ball-milled, and hydrogen peroxide is added; adding a lithium source and a carbon source to obtain slurry, drying, and sintering under the protection of reducing/inert gas; the carbon/carbon nanotube-coated lithium iron phosphate composite material is prepared by an in-situ synthesis method, and the heat treatment time is short; the composite material has the advantages of high carbon coating rate, stable electrochemical performance, good consistency, greatly improved cycle performance and rate performance, simple whole preparation process flow, safety, high efficiency, low cost, environmental protection and the like.
Description
Technical Field
The invention relates to the technical field of battery materials, and relates to a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material.
Background
The lithium iron phosphate has the advantages of environmental friendliness, high safety, long cycle life and the like, and becomes the most widely applied anode material for the industrialization of the current lithium ion power battery. However, the rate performance of the lithium iron phosphate is poor due to the low electronic conductivity and the lithium ion diffusion rate of the lithium iron phosphate, and the market popularization and application capability of the lithium iron phosphate power battery is severely restricted. Currently, modification treatment is mainly performed on lithium iron phosphate from the following three aspects. (1) The lithium iron phosphate is doped with a conductive material or coated with the conductive material and the like to improve the conductivity of the material; (2) preparing nano-scale high-density spherical lithium iron phosphate, improving the specific surface area of the material and increasing the number of effective sites; (3) the electrochemical performance of the material is improved by carrying out lattice doping on the olivine type lithium iron phosphate. The interface conduction resistance can be reduced and the conductivity can be improved by coating the conductive carbon material, and meanwhile, the agglomeration of lithium iron phosphate nano particles can be reduced by coating the carbon material, so that the discharge and rate performance of the lithium iron phosphate can be improved due to the excellent lithium intercalation performance. For example Wang et al (Journal of Power Sources,2013,233:43-46.) in FeSO4·7H2O、H3PO4And LiOH as raw materials, preparing a precursor by a coprecipitation method, calcining to obtain the precursor with the particle size of 30-80 nm,LiFePO with specific capacities of 155mAh/g and 110mAh/g for 0.1C and 10C respectively4And C, material. Liu et al (Electrochimica Acta,2010,55: 4694-4699.) in FeSO4·7H2O、LiH2PO4LiFePO with the particle size of about 50nm is prepared by carrying out ultrasonic treatment, filtering and calcining on LiOH and LiFePO serving as raw materials4The specific capacities of the materials/C are 140 mAh/g and 135mAh/g respectively for 1C and 2C.
Carbon Nanotubes (CNTs) have a special tubular graphite structure and high electrical conductivity, and furthermore, directionally-grown three-dimensional CNTs have excellent mechanical properties, so that the CNTs are widely researched as electrode materials. Chen et al (Journal of Power sources,2013,223:100-106.) hydrothermally treated Fe (NO)3)3、NH4H2PO4Boiling with CNTs in one pot, separating and drying by a membrane to obtain FePO4/CNTs microspheres, then LiOH is added according to a certain proportion to be mixed and calcined at high temperature to obtain LiFePO4The material has larger nano-pore channels, improves the specific surface area and the electrolyte permeability of the material, and shows high lithium storage capacity during high-rate charge and discharge (the specific capacity reaches 155mAh cm during 5C-rate charge and discharge)-3) And cycle stability (capacity is maintained at 90% or more after 1000 cycles of charge and discharge). The composite material prepared by the method has insufficient contact between tubular CNTs and the surface of active substance particles, so Liu et al (ACS Sustainable Chemistry)&Engineering,2013,2(2): 200-. The carbon black (20-60 nm) particles provide short-range electron transmission among the lithium iron phosphate particles, and the CNTs (30-100 mu m) provide a one-dimensional conductive network to form a point-to-line long-range conductive path, so that the lithium iron phosphate mixed material has a better cycle retention rate. However, the binding capacity of CNTs as an additive to lithium iron phosphate is relatively weak, and in order to further improve the binding force of the material, CNTs can be grown on the surface of the lithium iron phosphate or active materials can be grown on the surface of the CNTs. Wang et al (Advanced Energy Materials,2016,6(16):1600426.) use CNTs as core, Li+And Fe3+Adsorbing onto CNTs surface due to electric charge, adding PO4 3-Hydrothermal treatment to form Li3PO4、FePO4Anchored to carbon nanotubesOn the tube, obtaining C @ LiFePO after ultrasonic dispersion carbon thermal reduction treatment4a/CNTs composite material. The 0.2C rate discharge capacity of the material is 155 mAh.g-1Much higher than C @ LiFePO4141 mAh.g of-1Meanwhile, the capacity is kept at 98% after 1000 times of 10C charging and discharging, and the cycle stability is high.
Most of the reported preparation methods are a coprecipitation method, a hydrothermal method and the like, and then a high-temperature carbon reduction reaction is carried out to generate a target product, although the morphology and the size of the material can be well controlled, and the electrical property of the material is improved, the method has relatively complex process and higher equipment requirement, and the used ferrous iron source, CNTs and the like have relatively higher cost, so that the industrial application is greatly limited, and therefore the method for preparing the carbon/carbon nanotube-coated lithium iron phosphate composite material with simple process and low cost needs to be developed urgently.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method for in-situ synthesis of a carbon/carbon nanotube coated lithium iron phosphate composite material, which solves the technical problems of complex preparation process and high cost of the carbon/carbon nanotube coated lithium iron phosphate composite material in the prior art.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material comprises the following steps:
s1, weighing a lithium source, iron powder, phosphate and a carbon source according to a molar ratio of Li to Fe to P to C of 1.02: 0.8-1: 1-1.5: 0.08-0.18;
s2, performing ball milling reaction on 300-800-mesh iron powder and phosphate for 1-3 hours, controlling the pH of the solution to be 1-3, and adding hydrogen peroxide to react to obtain ferric phosphate dihydrate ball milling liquid;
s3, adding a lithium source and a carbon source into the ferric phosphate dihydrate ball-milling liquid prepared in the step S2, and carrying out ball milling for 3-8 hours to obtain slurry;
s4, spray drying the slurry prepared in the step S3 at 200-300 ℃ to obtain lithium iron phosphate precursor powder;
and S5, sintering the lithium iron phosphate precursor powder prepared in the step S4 under the protection of reducing/inert gas.
Preferably, the iron powder is at least one of reduced iron powder with the iron mass percent of more than or equal to 98%, electrolytic iron powder with the iron mass percent of more than or equal to 98%, and nodular cast iron powder with the iron mass percent of more than or equal to 98%.
Preferably, the phosphate is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide.
Preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium nitrate.
Preferably, the carbon source comprises a first carbon source, a second carbon source and a third carbon source, wherein the first carbon source is at least one of glucose, maltose, rock candy and fructose; the second carbon source is at least one of polyvinyl alcohol, polyvinyl butyral and polypyrrole; the third carbon source is at least one of cyanamide, dicyandiamide and melamine.
Preferably, the inert gas is at least one of nitrogen, argon and helium.
Preferably, the reducing gas is hydrogen with the volume fraction of 0.5-1%.
Preferably, in the step S5, the prepared dried lithium iron phosphate precursor powder is heated to 200 to 600 ℃ and sintered for 3 to 5 hours, cooled to 50 to 100 ℃ by using circulating cooling water, heated to 600 to 1100 ℃ and sintered for 5 to 15 hours, and cooled to room temperature.
Preferably, in the step S5, the prepared dried lithium iron phosphate precursor powder is heated to 200-600 ℃ and sintered for 3-5 hours, and is cooled to 50-100 ℃ by using circulating cooling water, and pure inert gas is used for sintering protection in this stage; and then heating to 600-1100 ℃ for sintering for 5-15 hours, sintering reduction protection is carried out by using reducing/inert gas at the stage, and cooling to room temperature.
Preferably, the third type of carbon source contains ammonium radicals, ammonia gas is generated in the sintering process, and ammonium dihydrogen phosphate is obtained by reacting phosphate with the ammonia gas.
The invention provides a preparation method of a carbon/carbon nanotube coated lithium iron phosphate composite material, which has the following advantages compared with the prior art:
the carbon/carbon nanotube coated lithium iron phosphate composite material is prepared by adopting an in-situ synthesis method, the heat treatment time of the process method is short, and the large-scale production is easy to realize; the carbon/carbon nanotube coated lithium iron phosphate composite material has high carbon coating rate, stable electrochemical performance and good consistency, can obviously improve the capacity of the material, reduce irreversible capacity loss and improve cycle performance and rate capability, has simple whole preparation process flow, and has the advantages of safety, high efficiency, low cost, environmental protection and the like;
in the preparation method, the carbon source comprises a first type carbon source, a second type carbon source and a third type carbon source, the calcining process is segmented calcining, in the preparation process, a lithium source and an iron source are subjected to anaerobic sintering at the temperature of 200-600 ℃, and part of Fe in the first type carbon source in the agglomerate is converted into Fe in the first type carbon source3+Reduction to Fe2+The second kind of carbon source is carbonized to generate amorphous carbon coated on the surface of the particles, and a trace amount of Fe2+Catalyzing a third carbon source to generate graphene-like g-C3N4(ii) a In the range of 600-1100 ℃, the hydrogen further converts Fe3+Reduction to Fe2+And gradually nucleate to generate olivine type lithium iron phosphate and Fe2+-g-C3N4The carbon nano tube is formed by pyrolysis in-situ growth, and the preparation method can generate stable carbon/carbon nano tube, and is favorable for improving the cycle performance and rate capability of the carbon/carbon nano tube coated lithium iron phosphate composite material;
the invention selects the iron source with lower price, controls the proportion of lithium, iron and phosphorus, optimizes the addition of the organic and inorganic carbon sources, realizes the controllable adjustment of the generation ratio of the amorphous carbon and the carbon nano tube, and improves the comprehensive conductivity of the carbon/carbon nano tube coated lithium iron phosphate composite material. By adjusting the centrifugal rate of spray drying and controlling the temperature of air flow at an inlet and an outlet, the precursor of the carbon/carbon nanotube-coated lithium iron phosphate composite material can be efficiently prepared in batches, and the particle size of the dried material of the precursor is small and the distribution is stable, so that the particle crystallization is favorably realized through subsequent high-temperature calcination. The carbon/carbon nanotube coated lithium iron phosphate composite material with a loose net structure synthesized in situ by segmented high-temperature protection calcination ensures the normal growth of amorphous carbon and carbon nanotubes, and meanwhile, in the pyrolysis process, a carbon source is decomposed, part of gas is discharged to promote the material to generate micropores, so that the electrolyte infiltration and lithium ion exchange capacity are further improved, and the electrochemical performance of the material is improved. Amorphous carbon and carbon nanotubes are generated in situ in the calcining process, so that the adhesive force of the conductive material and the lithium iron phosphate and the electronic conduction efficiency of the composite material are improved, and the charge and discharge performance of the cathode material is improved.
The carbon/carbon nanotube coated lithium iron phosphate composite material prepared by the preparation method is prepared into a CR2016 type button battery with a lithium sheet as a negative electrode for charge-discharge test, the first charge specific capacity of 0.2C is 155-160 mAh/g, the first coulombic efficiency is 90-99%, the average discharge specific capacity is 150-160 mAh/g, the average discharge specific capacity of 1C is 145-155 mAh/g, the specific capacity of 50 cycles of circulation is still kept above 90%, the composite material shows excellent electrochemical characteristics, and is expected to be applied to the field of power batteries.
Drawings
FIG. 1 shows N of the in situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material of the present invention2Adsorption/desorption patterns and pore size distribution maps;
fig. 2 is an electrical property curve diagram of the in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material at charge and discharge rates of 0.2C and 1C.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described below clearly and completely with reference to the embodiments, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The method for manufacturing the button cell and testing the electrochemical performance of the material in the embodiment is as follows:
(1) and (3) preparing a battery positive plate, namely weighing the synthesized carbon/carbon nanotube coated lithium iron phosphate composite material and a binding agent polyvinylidene fluoride (PVDF) according to the mass ratio of 8: 2. And mixing and dissolving the binder and an organic solvent N-methylpyrrolidone (NMP), adding the carbon/carbon nanotube coated lithium iron phosphate composite material, fully stirring to form slurry, coating the slurry on the surface of the carbon-coated aluminum foil, drying and rolling to obtain the battery positive plate.
(2) And (4) battery assembly and performance test, namely testing the electrochemical performance of the carbon/carbon nanotube coated lithium iron phosphate composite material by using a CR2016 type button battery. And stamping the rolled positive plate into a positive plate with the diameter of 12mm, accurately weighing, and converting the effective mass of the carbon/carbon nanotube coated lithium iron phosphate composite material according to the composition of the positive plate. The prepared positive plate, electrolyte, a PE diaphragm with the diameter of 16mm and a lithium sheet with the diameter of 15mm are used for assembling the button cell in a glove box.
(3) The specific capacity test of the battery uses a Shenzhen Xinwei battery test system, the test temperature is 25 ℃, and 50 times of cycle test are respectively carried out on the charge-discharge multiplying power of 0.2C and 1C.
Example 1:
the in-situ synthesis of the carbon/carbon nanotube-coated lithium iron phosphate composite material of the embodiment comprises the following steps:
s1, weighing 10 parts of 500-mesh iron powder, adding the iron powder into 40 parts of phosphate, mixing, controlling the pH of the solution to be 2.0, carrying out high-speed ball milling for 3 hours, dropwise adding an oxidant hydrogen peroxide, continuously stirring and uniformly mixing until blackish green Fe (H) is obtained2PO4)3And (4) gradually reducing the color of the solution, and stopping adding hydrogen peroxide to generate an iron phosphate dihydrate insoluble substance.
S2, adding 200 parts of water, 6 parts of lithium carbonate, 0.5 part of glucose, 0.5 part of polyvinyl alcohol and 0.5 part of melamine into the dihydrate phosphoric acid insoluble substance, mixing and stirring for 3 hours, carrying out ball milling treatment for 3 hours, controlling the rotation speed to be 500rpm, and obtaining creamy yellow viscous slurry after the ball milling is finished;
s3, drying the slurry by adopting a centrifugal spray drying tower, controlling the air inlet temperature to be 350 ℃, the air outlet temperature to be 150 ℃ and the rotation speed of an atomizing disc to be 40000rpm, and obtaining a dried material with the particle size of about 15 mu m, namely the lithium iron phosphate precursor powder;
s4, placing the prepared dry material into a ceramic crucible and placing the ceramic crucible into a tube furnace, heating to 300 ℃ at a heating rate of 2.5 ℃/min in a nitrogen atmosphere with a gas flow rate of 0.2L/min, keeping the temperature for 3 hours, cooling to room temperature at 5 ℃/min, introducing mixed nitrogen-hydrogen gas (99:1) to heat to 500 ℃ at 5 ℃/min, keeping the temperature for 2 hours, heating to 800 ℃ at 2.5 ℃/min, keeping the temperature for 5 hours, controlling the cooling to 200 ℃ at a speed of 10 ℃/min, naturally cooling to room temperature, closing the gas, taking out a sintered sample, and fully grinding the sintered sample to obtain the in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material.
FIG. 1 is a graph of N detected by a American Kangta NOVA2200e specific surface area analyzer of the in situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material prepared in example 12Adsorption/desorption patterns and pore size distribution patterns. The specific surface area of the material is about 17.2m2The pore size distribution is mainly concentrated at 3-15 nm, and the micropores are favorable for electrolyte infiltration and lithium ion exchange.
Fig. 2 is a graph showing the charge-discharge curve at 0.2C rate, the charge-discharge curve at 1C rate and the charge-discharge specific capacity change at the 50 th circle of the in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material prepared in this example 1 by assembling a button-type half cell. The figure shows that the 0.2C specific discharge capacity is about 160mAh/g, the first-cycle coulombic efficiency is 99.02%, the 1C average specific discharge capacity is about 148mAh/g, and the specific capacity is kept at 95% after 50 cycles, which indicates that the carbon/carbon nanotube-coated lithium iron phosphate composite material has good electrochemical characteristics and can be applied to the field of power batteries.
Example 2:
this example is the same as example 1 except that the carbon source used in synthesizing the carbon/carbon nanotube-coated lithium iron phosphate composite was 0.6 parts glucose, 0.3 parts polyvinyl alcohol, and 0.6 parts melamine; the constant temperature of the nitrogen atmosphere is 400 ℃, the constant temperature of the nitrogen-hydrogen mixed gas atmosphere is 900 ℃, and the content of amorphous carbon and carbon nano tube is controlled to obtain the carbon/carbon nano tube coated lithium iron phosphate composite material.
The in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material obtained in this example was analyzed for specific surface area and electrical properties in the same test manner as in example 1, and the specific surface area of the carbon/carbon nanotube-coated lithium iron phosphate composite material prepared in this example was greater than that of example 1. The electrical property test result is that the average specific discharge capacity of 0.2C is about 165mAh/g, the first-cycle coulombic efficiency is 98.11%, the average specific discharge capacity of 1C is about 150mAh/g, and the specific capacity is kept 91% after 50 cycles, which shows that the in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material prepared by the embodiment also has good electrochemical characteristics and can be applied to the field of power batteries.
Example 3:
this example is the same as example 1 except that the carbon source used in synthesizing the carbon/carbon nanotube-coated lithium iron phosphate composite material was 1 part of glucose, 0.2 part of polyvinyl alcohol, and 0.3 part of melamine; the heating rate of the nitrogen atmosphere is 5 ℃/min, the heating rates of the nitrogen-hydrogen mixed gas atmosphere are 5 ℃/min uniformly, and the method is used for controlling the content ratio, the growth rate and the morphological characteristics of amorphous carbon and carbon nanotubes in the carbon/carbon nanotube coated lithium iron phosphate composite material.
The in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material obtained in this example was analyzed for specific surface area and electrical properties in the same test manner as in example 1, and the specific surface area of the carbon/carbon nanotube-coated lithium iron phosphate composite material prepared in this example was slightly smaller than that of example 1. Too fast temperature rise rate is not favorable for generating multiple holes, and the shape of the material is easy to collapse. The electrical property test result is that the average specific discharge capacity of 0.2C is about 150mAh/g, the first cycle coulombic efficiency is 95.20%, the average specific discharge capacity of 1C is about 146mAh/g, and the specific capacity is kept to 92% after 50 cycles, which shows that the in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material prepared by the embodiment also has good electrochemical characteristics and can be applied to the field of power batteries.
Example 4:
this example is the same as example 1 except that the carbon source used in the synthesis of the carbon/carbon nanotube-coated lithium iron phosphate composite was 0.5 parts sucrose, 0.5 parts polypyrrole, and 0.5 parts dicyanodiamine; the lithium source used was a mixture of 3 parts lithium hydroxide and 3 parts lithium phosphate; ball milling the slurry for 6 hours, controlling the rotating speed to be 800rpm, and reducing the granularity D50 of the slurry by about 3 mu m; the constant temperature time of the nitrogen atmosphere is increased to 5 hours, the constant temperature time of the nitrogen-hydrogen mixed gas atmosphere is increased to 5 hours, and the constant temperature time of the high temperature is increased to 10 hours.
The in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material obtained in this example was analyzed for specific surface area and electrical properties in the same test manner as in example 1, and the specific surface area of the carbon/carbon nanotube-coated lithium iron phosphate composite material prepared in this example was smaller than that of example 1. The long calcination time results in overburning of the material, causing the material space to collapse. The electrical property test result is that the average specific discharge capacity of 0.2C is about 148mAh/g, the first cycle coulombic efficiency is 94.00%, the average specific discharge capacity of 1C is about 145mAh/g, and the specific capacity is kept 90% after 50 cycles, which shows that the in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material prepared by the embodiment also has good electrochemical characteristics and can be applied to the field of power batteries.
Example 5:
this example is the same as example 3 except that 2 parts lithium dihydrogen phosphate and 5 parts lithium carbonate were added as lithium sources to provide more lithium sources for the preparation of lithium rich materials; ball milling the slurry for 5 hours, and controlling the rotating speed to be 800 rpm; all the heating rates in the high-temperature sintering stage are controlled to be 2.5 ℃/min, and the influence of the heating rates on the morphology of the material is reduced.
Specific surface area analysis and electrical property analysis were performed on the in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material obtained in this example in the same test manner as in example 1, the specific surface area of the carbon/carbon nanotube-coated lithium iron phosphate composite material prepared in this example was slightly larger than that of example 1, and the slower temperature rise rate was favorable for the carbonization of glucose and polyvinyl alcohol and the in-situ generation of carbon nanotubes by melamine under the catalysis of trace iron powder. The electrical property test result shows that the average discharge specific capacity of 0.2C is about 165mAh/g, the first-cycle coulombic efficiency is 98.10%, the average discharge specific capacity of 1C is about 155mAh/g, and the specific capacity after 50 cycles is kept 93%, which shows that the in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material prepared by the embodiment also has good electrochemical characteristics, and can be applied to the field of power batteries
Example 6:
a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material comprises the following steps:
s1, weighing a lithium source, iron powder, phosphate and a carbon source according to the molar ratio of Li to Fe to P to C of 1.02 to 0.9 to 1.2 to 0.13;
s2, performing ball milling reaction on 600-mesh iron powder and phosphate for 2 hours, controlling the pH of the solution to be 2, adding hydrogen peroxide to react to obtain ferric phosphate dihydrate ball milling liquid, wherein the pH of the solution is 2, the iron powder can be fully dissolved, and meanwhile, the subsequent hydrolysis of ferric phosphate to generate ferric hydroxide precipitate is effectively inhibited;
s3, adding a lithium source and a carbon source into the ferric phosphate dihydrate ball-milling liquid prepared in the step S2, and carrying out ball-milling for 6 hours to obtain slurry;
s4, spray drying the slurry prepared in the step S3 at 250 ℃ to obtain lithium iron phosphate precursor powder;
s5, heating the dried lithium iron phosphate precursor powder prepared in the step S4 to 400 ℃, sintering for 4 hours, cooling to 80 ℃ by using circulating cooling water, and sintering and protecting by using pure inert gas, wherein the inert gas is formed by mixing nitrogen, argon and helium; and heating to 850 ℃ and sintering for 10 hours, sintering and reducing and protecting by using reducing/inert gas at the stage, wherein the inert gas is nitrogen, and the reducing gas is hydrogen with the volume fraction of 0.8%, and cooling to room temperature.
Wherein the iron powder is nodular cast iron powder with the iron mass percentage of more than or equal to 98 percent; the phosphate is prepared by mixing phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; the lithium source is formed by mixing lithium carbonate, lithium hydroxide, lithium phosphate and dilithium hydrogen phosphate; the carbon source comprises a first carbon source, a second carbon source and a third carbon source, wherein the first carbon source is glucose; the second type of carbon source is polyvinyl alcohol; the third carbon source is formed by mixing cyanamide, dicyandiamide and melamine; the carbon source added in the method contains ammonium radicals, waste gases such as ammonia gas and the like can be generated in the high-temperature sintering process, ammonium dihydrogen phosphate can be obtained by carrying out acid-base neutralization treatment on phosphate with certain concentration, and the purified ammonium dihydrogen phosphate can be used as a raw material to protect productionEnvironment protection and low cost. In the temperature range of 200-600 ℃, a lithium source and an iron source are subjected to oxygen-free sintering, and a first type of carbon source in the agglomerate partially converts Fe3 +Reduction to Fe2 +The second kind of carbon source is carbonized to generate amorphous carbon coated on the surface of the particles, and a trace amount of Fe2 +Catalyzing a third carbon source to generate graphene-like g-C3N4(ii) a In the range of 600-1100 ℃, the hydrogen further converts Fe3 +Reduction to Fe2 +，Fe2 +-g-C3N4High-temperature cracking in-situ growth to form carbon nanotubes, and the carbon nanotubes can limit LiFePO4The direction and size of the crystals.
The in-situ synthesized carbon/carbon nanotube-coated lithium iron phosphate composite material prepared by the embodiment is prepared into a battery according to the method of the embodiment, the specific discharge capacity at 0.2C is not less than 150mAh/g, the specific discharge capacity at 1C is not less than 145mAh/g, and the specific capacity is still kept at 90% after 50 cycles.
The in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material obtained in the embodiment is spherical particles, the calcined material is crushed, the D50 is less than 1.0 μm, the D100 is less than 3.0 μm, the small particles are formed by the finer carbon/carbon nanotube coated lithium iron phosphate composite material nanoparticles, the size is about 100-150 nm, the material shows obvious nano-pore distribution in a nano range, micropores on the carbon/carbon nanotube provide capillary channels for the exchange of electrolyte and lithium ions, and the electrochemical performance of the lithium iron phosphate material is improved.
Example 7:
a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material comprises the following steps:
s1, weighing a lithium source, iron powder, phosphate and a carbon source according to the molar ratio of Li to Fe to P to C of 1.02 to 0.8 to 1 to 0.08;
s2, performing ball milling reaction on 300-mesh iron powder and phosphate for 1 hour, controlling the pH of the solution to be 1, adding hydrogen peroxide to react to obtain ferric phosphate dihydrate ball milling liquid, wherein the pH of the solution is 1, the iron powder can be fully dissolved, and meanwhile, the subsequent hydrolysis of ferric phosphate to generate ferric hydroxide precipitate is effectively inhibited;
s3, adding a lithium source and a carbon source into the ferric phosphate dihydrate ball-milling liquid prepared in the step S2, and carrying out ball milling for 3 hours to obtain slurry;
s4, spray drying the slurry prepared in the step S3 at 200 ℃ to obtain lithium iron phosphate precursor powder;
s5, heating the dried lithium iron phosphate precursor powder prepared in the step S4 to 200 ℃, sintering for 3 hours, cooling to 50 ℃ by using circulating cooling water, and sintering and protecting by using pure inert gas, wherein the inert gas is argon; and heating to 600 ℃ and sintering for 5 hours, sintering reduction protection is carried out by using reducing/inert gas at the stage, wherein the inert gas is argon, and the reducing gas is hydrogen with the volume fraction of 0.5%, and cooling to room temperature.
Wherein the iron powder is reduced iron powder with the iron mass percentage content of more than or equal to 98 percent; the phosphate is prepared by mixing phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; the lithium source is formed by mixing lithium carbonate, lithium hydroxide, lithium phosphate and dilithium hydrogen phosphate; the carbon source comprises a first carbon source, a second carbon source and a third carbon source, wherein the first carbon source is formed by mixing glucose, maltose and rock sugar; the second carbon source is formed by mixing polyvinyl alcohol, polypropylene alcohol and polyvinyl butyral; the third kind of carbon source is mixture of cyanamide, dicyandiamide and melamine.
Example 8:
a preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material comprises the following steps:
s1, weighing a lithium source, iron powder, phosphate and a carbon source according to the molar ratio of Li to Fe to P to C of 1.02 to 1 to 1.5 to 0.18;
s2, performing ball milling reaction on 800-mesh iron powder and phosphate for 3 hours, controlling the pH of the solution to be 3, adding hydrogen peroxide to react to obtain ferric phosphate dihydrate ball milling liquid, wherein the pH of the solution is 3, the iron powder can be fully dissolved, and meanwhile, the subsequent hydrolysis of ferric phosphate to generate ferric hydroxide precipitate is effectively inhibited;
s3, adding a lithium source and a carbon source into the ferric phosphate dihydrate ball-milling liquid prepared in the step S2, and carrying out ball-milling for 8 hours to obtain slurry;
s4, spray drying the slurry prepared in the step S3 at 300 ℃ to obtain lithium iron phosphate precursor powder;
s5, heating the dried lithium iron phosphate precursor powder prepared in the step S4 to 600 ℃, sintering for 5 hours, cooling to 100 ℃ by using circulating cooling water, and sintering and protecting by using pure inert gas, wherein the inert gas is helium; and heating to 1100 ℃ and sintering for 15 hours, sintering and reducing and protecting by using reducing/inert gas at the stage, wherein the inert gas is helium, and the reducing gas is hydrogen with the volume fraction of 1%, and cooling to room temperature.
Wherein the iron powder is nodular cast iron powder with the iron mass percentage of more than or equal to 98 percent; the phosphate is ammonium dihydrogen phosphate; the lithium source is dilithium hydrogen phosphate; the carbon source comprises a first carbon source, a second carbon source and a third carbon source, wherein the first carbon source is fructose; the second carbon source is polypyrrole; the third type of carbon source is dicyanodiamine.
In conclusion, the carbon/carbon nanotube coated lithium iron phosphate composite material is prepared by adopting an in-situ synthesis method, the heat treatment time of the process method is short, and the large-scale production is easy to realize; the carbon/carbon nanotube coated lithium iron phosphate composite material has the advantages of high carbon coating rate, stable electrochemical performance, good consistency, capability of obviously improving the capacity of the material, capability of reducing irreversible capacity loss and improving the cycle performance and the rate capability, simple whole preparation process flow, safety, high efficiency, low cost, environmental friendliness and the like.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A preparation method of an in-situ synthesized carbon/carbon nanotube coated lithium iron phosphate composite material is characterized by comprising the following steps:
s1, weighing a lithium source, iron powder, phosphate and a carbon source according to a molar ratio of Li to Fe to P to C of 1.02: 0.8-1: 1-1.5: 0.08-0.18; the carbon source comprises a first carbon source, a second carbon source and a third carbon source, wherein the first carbon source is at least one of glucose, maltose, rock candy and fructose; the second carbon source is at least one of polyvinyl alcohol, polyvinyl butyral and polypyrrole; the third carbon source is at least one of cyanamide, dicyandiamide and melamine;
s2, performing ball milling reaction on 300-800-mesh iron powder and phosphate for 1-3 hours, controlling the pH of the solution to be 1-3, and adding hydrogen peroxide to react to obtain ferric phosphate dihydrate ball milling liquid;
s3, adding a lithium source and a carbon source into the ferric phosphate dihydrate ball-milling liquid prepared in the step S2, and carrying out ball milling for 3-8 hours to obtain slurry;
s4, spray drying the slurry prepared in the step S3 at 200-300 ℃ to obtain lithium iron phosphate precursor powder;
s5, heating the lithium iron phosphate precursor powder prepared in the step S4 to 200-600 ℃, sintering for 3-5 hours, cooling to 50-100 ℃ by using circulating cooling water, and sintering and protecting by using pure inert gas or nitrogen at the stage; and heating to 600-1100 ℃ for sintering for 5-15 hours, sintering and reducing and protecting by using mixed gas consisting of reducing gas and pure inert gas or mixed gas consisting of reducing gas and nitrogen at the stage, and cooling to room temperature.
2. The method according to claim 1, wherein the iron powder is at least one of a reduced iron powder having an iron content of not less than 98% by mass, an electrolytic iron powder having an iron content of not less than 98% by mass, and a spheroidal graphite cast powder having an iron content of not less than 98% by mass.
3. The method according to claim 1, wherein the phosphate is at least one of monoammonium phosphate and diammonium phosphate.
4. The method according to claim 1, wherein the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, dilithium hydrogenphosphate, lithium dihydrogenphosphate, and lithium nitrate.
5. The method according to claim 1, wherein the pure inert gas is at least one of argon gas and helium gas.
6. The method according to claim 1, wherein the volume of the reducing gas in the mixed gas of the reducing gas and the pure inert gas is 0.5-1% of the total volume of the mixed gas; and the volume of the reducing gas in the mixed gas consisting of the reducing gas and the nitrogen accounts for 0.5-1% of the total volume of the mixed gas.
7. The preparation method of claim 1, wherein the third type of carbon source contains amino, ammonia gas is generated in the sintering process, and ammonium dihydrogen phosphate is obtained by reacting phosphate with ammonia gas.
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| CN109167027A (en) * | 2018-08-20 | 2019-01-08 | 合肥国轩电池材料有限公司 | A kind of redox graphene/carbon coating/composite ferric lithium phosphate material preparation method |
| EP3670454A1 (en) * | 2018-12-21 | 2020-06-24 | Höganäs AB (publ) | Pure iron containing compound |
| CN109786693A (en) * | 2018-12-28 | 2019-05-21 | 沈阳国科金能科技有限公司 | A kind of preparation method of carbon nanotube composite lithium iron phosphate cathode material |
| CN110745802A (en) * | 2019-10-14 | 2020-02-04 | 重庆特瑞电池材料股份有限公司 | Method for preparing lithium iron phosphate by electromagnetic induction self-heating |
| CN111554922B (en) * | 2020-04-14 | 2022-04-01 | 合肥国轩电池材料有限公司 | Preparation method of rate type lithium iron phosphate |
| CN112028045A (en) * | 2020-09-07 | 2020-12-04 | 厦门厦钨新能源材料股份有限公司 | Conductive lithium iron phosphate and preparation method and application thereof |
| CN112436132B (en) * | 2020-12-10 | 2021-07-02 | 桂林理工大学 | Method for preparing in-situ carbon-coated porous ferric phosphate material by adopting sweet osmanthus |
| CN114314554B (en) * | 2021-12-31 | 2024-04-09 | 欣旺达动力科技股份有限公司 | Lithium iron phosphate/carbon nanobelt composite material, preparation method and lithium ion battery |
| CN114843478B (en) * | 2022-05-23 | 2023-05-23 | 广东技术师范大学 | Nanometer FeP for lithium ion battery 2 Preparation method of/C/CNTs composite material |
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