阅读说明：本技术 一种磷酸铁锂的制备方法 (Preparation method of lithium iron phosphate ) 是由 李旭意 于 2019-09-19 设计创作，主要内容包括：本发明公开了一种磷酸铁锂的制备方法。将氯化铁与氯化锂按照摩尔比1：1.03-1.05加水搅拌混合,得到混合液,然后将磷酸三丁酯与N235萃取剂按照体积比6-10:1混合并搅拌均匀,得到萃取剂,然后将混合液与萃取剂6-8级逆流萃取,分相得到有机相和水相；将有机相喷雾状态进入燃烧炉内,同时通入空气进行燃烧,燃烧温度为300-450℃,经过收尘得到燃烧料；得到的燃烧料放入到辊道炉内,在惰性气氛保护下煅烧,冷却后得到煅烧料,煅烧料经过气流粉碎后,筛分除铁得到磷酸铁锂。本发明工艺简单,工艺流程短,可以得到高导电性、低内阻的磷酸铁锂材料,电性能优越。(The invention discloses a preparation method of lithium iron phosphate. Mixing ferric chloride and lithium chloride according to a molar ratio of 1: 1.03-1.05, adding water, stirring and mixing to obtain a mixed solution, then mixing tributyl phosphate and an N235 extractant according to the volume ratio of 6-10:1, uniformly stirring to obtain an extractant, then carrying out 6-8-level countercurrent extraction on the mixed solution and the extractant, and carrying out phase separation to obtain an organic phase and a water phase; feeding the organic phase into a combustion furnace in a spray state, introducing air for combustion at the combustion temperature of 300-450 ℃, and collecting dust to obtain a combustion material; and putting the obtained combustion material into a roller furnace, calcining under the protection of inert atmosphere, cooling to obtain a calcined material, and screening and deironing the calcined material after airflow crushing to obtain the lithium iron phosphate. The method has the advantages of simple process, short process flow, capability of obtaining the lithium iron phosphate material with high conductivity and low internal resistance and excellent electrical property.)

1. A preparation method of lithium iron phosphate is characterized by comprising the following steps:

1) mixing ferric chloride and lithium chloride according to a molar ratio of 1: 1.03-1.05, adding water, stirring and mixing to obtain a mixed solution, then mixing tributyl phosphate and an N235 extractant according to the volume ratio of 6-10:1, uniformly stirring to obtain an extractant, then carrying out 6-8-level countercurrent extraction on the mixed solution and the extractant, and carrying out phase separation to obtain an organic phase and a water phase;

2) feeding the organic phase into a combustion furnace in a spray state, introducing air for combustion at the combustion temperature of 300-450 ℃, and collecting dust to obtain a combustion material;

3) and putting the obtained combustion material into a roller furnace, calcining under the protection of inert atmosphere, cooling to obtain a calcined material, and screening and deironing the calcined material after airflow crushing to obtain the lithium iron phosphate.

2. The method for preparing lithium iron phosphate according to claim 1, wherein the method comprises the following steps: in the step (1), both ferric chloride and lithium chloride are in industrial grade, the countercurrent extraction process is carried out, the molar ratio of tributyl phosphate in the extractant to iron in the mixed solution added in the same time is 1.005-1.01:1, the mixing time of each stage of extraction is 5-10min, the extraction stirring speed is 100-200r/min, and the clarification time is 5-10 min.

3. The method for preparing lithium iron phosphate according to claim 1, wherein the method comprises the following steps: and (2) returning the water phase obtained in the step (1) to prepare a mixed solution, standing the organic phase for 2-5h, discharging water at the bottom of the organic phase, performing ultrasonic demulsification on the organic phase by using an ultrasonic device, and discharging the water at the bottom until the water content in the organic phase is lower than 300 ppm.

4. The method for preparing lithium iron phosphate according to claim 1, wherein the method comprises the following steps: keeping the particle size of fog drops to be 5-20 mu m during spraying in the step (2), introducing air to maintain the volume fraction of oxygen in the combustion furnace to be more than 15%, simultaneously starting an induced draft fan in the combustion furnace, controlling the induced draft of the induced draft fan to enable the carbon content in the combustion materials to be 3-4%, leading out the combusted waste gas, performing 3-5-level countercurrent absorption by pure water to obtain absorption liquid, collecting the combusted materials by a cyclone dust collector and a dust collection cloth bag to obtain the combustion materials, and cooling the combustion materials to the temperature of the materials to be less than or equal to 85 ℃ and then discharging.

5. The method for preparing lithium iron phosphate according to claim 1, wherein the method comprises the following steps: the calcination process in the step (3) is divided into a temperature rise section, a heat preservation section and a temperature reduction section, wherein the temperature rise speed is 60-100 ℃/h, the temperature rise is up to 700-plus-800 ℃, the heat preservation section process is carried out, the heat preservation time is 3-5h, the heat preservation temperature is up to 700-plus-800 ℃, the temperature reduction section process is carried out, the temperature rise speed is up to 120-plus-150 ℃/h, and the material is discharged after being cooled to the material temperature of less than or equal to 80 ℃.

6. The method for preparing lithium iron phosphate according to claim 1, wherein the method comprises the following steps: and (3) after the calcined material is pulverized to have a particle size of 1-1.5 microns by air flow, sieving the pulverized material by an ultrasonic vibration sieve, wherein the mesh number of the sieve is 100-150 meshes, and the iron removal is performed by adopting a battery iron remover until the magnetic substance is less than 1ppm, and then stopping removing the iron to obtain the lithium iron phosphate.

Technical Field

The invention relates to a preparation method of lithium iron phosphate, belonging to the technical field of lithium batteries.

Background

As the current mainstream battery cathode material, the lithium iron phosphate gradually shrinks the market share in the early period due to the guidance of the subsidy policy, but the cost advantage of the lithium iron phosphate battery gradually becomes prominent after subsidy is taken off the slope. Meanwhile, a new energy bus as one of the main application scenes of the lithium iron phosphate battery or a policy will further support, thereby benefiting the lithium iron phosphate battery industry; for consumers in three-four-wire cities and even villages and towns, the lithium iron phosphate battery with low price and long service life has higher competitiveness. In addition, overall, compared with foreign manufacturers, the lithium iron phosphate battery in China has obvious relevant technical advantages, high product cost performance and industrial maturity, and complete supporting measures related to power management.

As the main force of power batteries, lithium iron phosphate batteries and ternary batteries have occupied about 95% of the market share of the whole industry in recent years, and the comparison between the two has never stopped. In 2015-2016, the market occupancy of lithium iron phosphate batteries reaches about 70%. However, as the subsidies of the national new energy vehicles gradually incline to products with high energy density and high endurance mileage, the market proportion of the lithium iron phosphate batteries gradually slides down. In two years of 2017 and 2018, the market share of the lithium iron phosphate is respectively reduced to 45% and 39%.

But the lithium iron phosphate battery market has been showing signs of warmth again since this year. According to the latest data published by the society of automotive industry of China, in 2019, 1-2 months, the cumulative output of the power battery in China reaches 11.6GWh, wherein the cumulative output of the ternary battery is 6.6GWh, which accounts for 57.2 percent of the total output; the cumulative production of the lithium iron phosphate battery is 4.6GWh, which accounts for 39.6 percent of the total output and is slightly increased compared with 36.03 percent of the total output in the same period in the last year.

At present, a carbon coating method is generally adopted for preparing lithium iron phosphate, although the conductivity can be greatly improved, the conductivity in a single crystal particle of lithium iron phosphate is still poor due to the fact that the single crystal particle is a pure lithium iron phosphate particle, and the conventional method is realized by doping, but the lithium iron phosphate has impurity phases after doping, and some negative effects are generated on the cycle performance and the like of the lithium iron phosphate.

Disclosure of Invention

In view of the above, the invention provides a preparation method of lithium iron phosphate, which has the advantages of simple process, short process flow, capability of obtaining a lithium iron phosphate material with high conductivity and low internal resistance, and excellent electrical property.

The invention solves the technical problems by the following technical means:

the invention relates to a preparation method of lithium iron phosphate, which comprises the following steps:

1) mixing ferric chloride and lithium chloride according to a molar ratio of 1: 1.03-1.05, adding water, stirring and mixing to obtain a mixed solution, then mixing tributyl phosphate and an N235 extractant according to the volume ratio of 6-10:1, uniformly stirring to obtain an extractant, then carrying out 6-8-level countercurrent extraction on the mixed solution and the extractant, and carrying out phase separation to obtain an organic phase and a water phase;

2) feeding the organic phase into a combustion furnace in a spray state, introducing air for combustion at the combustion temperature of 300-450 ℃, and collecting dust to obtain a combustion material;

3) and putting the obtained combustion material into a roller furnace, calcining under the protection of inert atmosphere, cooling to obtain a calcined material, and screening and deironing the calcined material after airflow crushing to obtain the lithium iron phosphate.

In the step (1), both ferric chloride and lithium chloride are in industrial grade, the countercurrent extraction process is carried out, the molar ratio of tributyl phosphate in the extractant to iron in the mixed solution added in the same time is 1.005-1.01:1, the mixing time of each stage of extraction is 5-10min, the extraction stirring speed is 100-200r/min, and the clarification time is 5-10 min.

And (2) returning the water phase obtained in the step (1) to prepare a mixed solution, standing the organic phase for 2-5h, discharging water at the bottom of the organic phase, performing ultrasonic demulsification on the organic phase by using an ultrasonic device, and discharging the water at the bottom until the water content in the organic phase is lower than 300 ppm.

Keeping the particle size of fog drops to be 5-20 mu m during spraying in the step (2), introducing air to maintain the volume fraction of oxygen in the combustion furnace to be more than 15%, simultaneously starting an induced draft fan in the combustion furnace, controlling the induced draft of the induced draft fan to enable the carbon content in the combustion materials to be 3-4%, leading out the combusted waste gas, performing 3-5-level countercurrent absorption by pure water to obtain absorption liquid, collecting the combusted materials by a cyclone dust collector and a dust collection cloth bag to obtain the combustion materials, and cooling the combustion materials to the temperature of the materials to be less than or equal to 85 ℃ and then discharging.

The calcination process in the step (3) is divided into a temperature rise section, a heat preservation section and a temperature reduction section, wherein the temperature rise speed is 60-100 ℃/h, the temperature rise is up to 700-plus-800 ℃, the heat preservation section process is carried out, the heat preservation time is 3-5h, the heat preservation temperature is up to 700-plus-800 ℃, the temperature reduction section process is carried out, the temperature rise speed is up to 120-plus-150 ℃/h, and the material is discharged after being cooled to the material temperature of less than or equal to 80 ℃.

And (3) after the calcined material is pulverized to have a particle size of 1-1.5 microns by air flow, sieving the pulverized material by an ultrasonic vibration sieve, wherein the mesh number of the sieve is 100-150 meshes, and the iron removal is performed by adopting a battery iron remover until the magnetic substance is less than 1ppm, and then stopping removing the iron to obtain the lithium iron phosphate.

Compared with the solid-phase method preparation process of iron phosphate, the invention can shorten the flow, has simple process, adopts the mixed solution of ferric chloride and lithium chloride as the water phase, and realizes the extraction of the lithium iron ions by the extraction of the TBP extractantCo-extraction of (1) to form TBP₄The organic phase is added with a small amount of N235 simultaneously, the effects of synergistic extraction and a phase regulator can be realized, then water drops carried in the organic phase can be effectively reduced through standing and ultrasonic demulsification, the water content in the organic phase is reduced, then the organic phase enters the combustion furnace in a spraying mode, air is introduced simultaneously to burn nitrogen, hydrogen, oxygen and chlorine and part of carbon in the organic phase to form nitrogen oxide, water vapor, carbon dioxide, hydrogen chloride and other gases, then the acidic gases can be absorbed through absorption, meanwhile, the induced draft of a draught fan is controlled, so that the residence time of the combustion materials in the combustion furnace is controlled, the burning loss rate of the carbon is controlled, the carbon content in the combustion materials is 3-4%, and the carbon is remained in the lithium iron phosphorus compound through thermal decomposition and combustion of organic matters, so that the carbon is uniformly distributed in the lithium iron phosphorus compound, and the carbon is coated on the outer surface of the lithium iron phosphorus compound in the non-conventional solid phase method, so that the finally prepared lithium iron phosphate is non-coated but is carbon-doped lithium iron phosphate, and the method has two advantages:

1) the carbon of the coated lithium iron phosphate is only distributed on the outer surface of the lithium iron phosphate, the conductivity between particles is good, but the conductivity of single particle is poor, so that the conductivity of the whole material is reduced.

2) The coated lithium iron phosphate is of an amorphous carbon structure due to coating, so that the compactness of lithium iron phosphate powder is influenced, and the tap density and the compacted density of a lithium iron phosphate material are reduced.

Meanwhile, in the combustion thermal decomposition stage, the carbon is carbonized and uniformly distributed among particles, so that the temperature of the whole calcining process is lower, the time is shorter, the production efficiency is improved, and the reduction of the electrical property of the lithium iron caused by overlong sintering time and overhigh sintering temperature is avoided.

Meanwhile, the lithium iron phosphate material has larger BET, and the conventional lithium iron phosphate material has larger BET due to higher carbon content or higher carbon amorphization, so that agglomeration and poor dispersibility in the processing process are easily caused.

The invention has the beneficial effects that: the process is simple, the process flow is short, the lithium iron phosphate material with high conductivity and low internal resistance can be obtained, and the electrical property is excellent.

Detailed Description

The present invention will be described in detail with reference to specific examples, in which the preparation method of lithium iron phosphate of this example comprises the following steps:

1) mixing ferric chloride and lithium chloride according to a molar ratio of 1: 1.03-1.05, adding water, stirring and mixing to obtain a mixed solution, then mixing tributyl phosphate and an N235 extractant according to the volume ratio of 6-10:1, uniformly stirring to obtain an extractant, then carrying out 6-8-level countercurrent extraction on the mixed solution and the extractant, and carrying out phase separation to obtain an organic phase and a water phase;

2) feeding the organic phase into a combustion furnace in a spray state, introducing air for combustion at the combustion temperature of 300-450 ℃, and collecting dust to obtain a combustion material;

3) and putting the obtained combustion material into a roller furnace, calcining under the protection of inert atmosphere, cooling to obtain a calcined material, and screening and deironing the calcined material after airflow crushing to obtain the lithium iron phosphate.

In the step (1), both ferric chloride and lithium chloride are in industrial grade, the countercurrent extraction process is carried out, the molar ratio of tributyl phosphate in the extractant to iron in the mixed solution added in the same time is 1.005-1.01:1, the mixing time of each stage of extraction is 5-10min, the extraction stirring speed is 100-200r/min, and the clarification time is 5-10 min.

And (2) returning the water phase obtained in the step (1) to prepare a mixed solution, standing the organic phase for 2-5h, discharging water at the bottom of the organic phase, performing ultrasonic demulsification on the organic phase by using an ultrasonic device, and discharging the water at the bottom until the water content in the organic phase is lower than 300 ppm.

Keeping the particle size of fog drops to be 5-20 mu m during spraying in the step (2), introducing air to maintain the volume fraction of oxygen in the combustion furnace to be more than 15%, simultaneously starting an induced draft fan in the combustion furnace, controlling the induced draft of the induced draft fan to enable the carbon content in the combustion materials to be 3-4%, leading out the combusted waste gas, performing 3-5-level countercurrent absorption by pure water to obtain absorption liquid, collecting the combusted materials by a cyclone dust collector and a dust collection cloth bag to obtain the combustion materials, and cooling the combustion materials to the temperature of the materials to be less than or equal to 85 ℃ and then discharging.

The calcination process in the step (3) is divided into a temperature rise section, a heat preservation section and a temperature reduction section, wherein the temperature rise speed is 60-100 ℃/h, the temperature rise is up to 700-plus-800 ℃, the heat preservation section process is carried out, the heat preservation time is 3-5h, the heat preservation temperature is up to 700-plus-800 ℃, the temperature reduction section process is carried out, the temperature rise speed is up to 120-plus-150 ℃/h, and the material is discharged after being cooled to the material temperature of less than or equal to 80 ℃.

And (3) after the calcined material is pulverized to have a particle size of 1-1.5 microns by air flow, sieving the pulverized material by an ultrasonic vibration sieve, wherein the mesh number of the sieve is 100-150 meshes, and the iron removal is performed by adopting a battery iron remover until the magnetic substance is less than 1ppm, and then stopping removing the iron to obtain the lithium iron phosphate.