阅读说明：本技术 一种高碳低倍率性能的磷酸铁锂脱碳再造方法 (High-carbon low-rate lithium iron phosphate decarburization reconstruction method ) 是由 廖贻鹏 林文军 周玉琳 张桂海 王勇 于 2021-07-28 设计创作，主要内容包括：一种高碳低倍率性能的磷酸铁锂脱碳再造方法,包括以下步骤：将未注电解液的磷酸铁锂废极片在保护气氛下热解,热解完全的废极片振动筛分,得到磷酸铁锂废粉；将磷酸铁锂废粉和一定量的氧化锌粉末混合,并进行气流破碎,对破碎物料进行筛分,得到高碳低性能的混合磷酸铁锂废粉；将混合磷酸铁锂废粉在混合气体中进行烧结,烧结制度分为磷酸铁锂脱F温度680-720℃,脱碳温度820-880℃,纯化温度为740-780℃,然后冷却到100℃以下出炉。本发明工艺简单、流程短,制备的磷酸铁锂正极材料具有一致性好、电化学性能高等特点。(A high-carbon low-rate lithium iron phosphate decarburization reconstruction method comprises the following steps: pyrolyzing the lithium iron phosphate waste pole pieces without being injected with electrolyte under a protective atmosphere, and vibrating and screening the completely pyrolyzed waste pole pieces to obtain lithium iron phosphate waste powder; mixing the waste lithium iron phosphate powder with a certain amount of zinc oxide powder, performing airflow crushing, and screening the crushed material to obtain high-carbon low-performance mixed waste lithium iron phosphate powder; and sintering the mixed lithium iron phosphate waste powder in mixed gas, wherein the sintering system comprises the steps of removing F from lithium iron phosphate at 680-880 ℃, decarbonizing at 820-880 ℃, purifying at 740-780 ℃, and cooling to below 100 ℃ for discharging. The method has the characteristics of simple process, short flow, good consistency of the prepared lithium iron phosphate anode material, high electrochemical performance and the like.)

1. A high-carbon low-rate lithium iron phosphate decarburization reconstruction method is characterized by comprising the following steps:

A. pyrolysis separation: pyrolyzing the lithium iron phosphate waste pole pieces which are not injected with the electrolyte under the conditions of protective atmosphere, temperature of 420-500 ℃, time of 3-8h and oxygen concentration of less than 1500ppm, and vibrating and screening the completely pyrolyzed waste pole pieces on a screen to obtain lithium iron phosphate waste powder;

B. airflow crushing: b, mixing the waste lithium iron phosphate powder obtained in the step A with zinc oxide powder, performing airflow crushing, and screening the crushed material by using a screen to obtain high-carbon low-performance mixed waste lithium iron phosphate powder;

C. carbon reduction: and D, sintering the mixed lithium iron phosphate waste powder obtained in the step B in mixed gas, wherein the sintering system comprises the steps of defluorinating lithium iron phosphate at 680-720 ℃, decarbonizing at 820-880 ℃, purifying at 740-780 ℃, and cooling to a temperature below 100 ℃ for discharging.

2. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: the screen mesh in the step A is a vibrating screen with 3 meshes to 35 meshes; the screen in the step B is a 100-mesh screen.

3. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the step A, the lithium iron phosphate waste pole pieces which are not injected with the electrolyte comprise scrapped positive pole pieces in the manufacturing process of the lithium iron phosphate positive pole pieces, and the scrapped positive pole pieces of the battery which are not injected with the electrolyte in the preparation process of the battery are decomposed; the protective atmosphere is one or more mixed gases of nitrogen and rare gases.

4. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the step A, one of zirconia balls, rubber balls or stainless steel balls is required to be added on the screen in the screening process; the content of impurity aluminum in the obtained lithium iron phosphate waste powder is less than 0.1 percent.

5. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the step B, the adding amount of the zinc oxide is 0.3-0.35 time of the mole number of the impurity fluorine in the waste lithium iron phosphate powder; the medium particle size of the material after airflow crushing is 0.5-10 μm.

6. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the step C, the sintering system is that constant temperature rise is carried out at each liter of temperature stage, the time from the room temperature to the defluorination temperature is 6-8h, then the time to the decarburization temperature is 3-5h, and the mixture is naturally cooled to the purification temperature after decarburization; the holding time at the defluorination temperature, the decarbonization temperature and the purification temperature is 1-3h, 6-8h and 3-7h respectively, and then the cooling time is 7-12 h.

7. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the sintering system of the step C, the mixed gas refers to a gas formed by mixing one or more of nitrogen or rare gas and carbon dioxide, and the molar ratio of the carbon dioxide in the mixed gas is 10-60%.

8. The decarburization reconstruction method for lithium iron phosphate with high carbon and low rate capability according to claim 1, characterized in that: in the step C, when the mixed lithium iron phosphate waste powder is sintered in the mixed gas, the oxygen concentration is controlled to be 1-50ppm, and the micro-positive pressure in the furnace is controlled to be 10-100 Pa; and crushing and packaging the discharged material to obtain a lithium iron phosphate product.

Technical Field

The invention relates to the technical field of lithium ion battery materials, in particular to a high-carbon low-rate lithium iron phosphate decarburization reconstruction method.

Background

Lithium iron phosphate (LiFePO)₄LFP for short) is used as the anode material of the lithium ion battery, the theoretical specific capacity is 170 mAh.g < -1 >, the actual specific capacity exceeds 140 mAh.g < -1 > (0.2C, 25 ℃), and the lithium ion battery has the advantages of low price, good thermal stability, environmental protection, high safety and excellent cycle performance. At present, lithium iron phosphate is widely applied to the fields of electric buses, special vehicles, electric bicycles, ships, energy storage, 5G base stations and the like, the price of the lithium iron phosphate shows an increasing trend along with the wider application range of lithium iron phosphate anode materials, the preparation of lithium batteries is still expensive, and the lithium batteries have stronger competitiveness only if the price of 1WH of the lithium batteries is lower than 0.6 yuan in the future, so that the performance of the lithium iron phosphate needs to be improved, and the price of the lithium iron phosphate needs to be continuously reduced.

At present, the existing technology for preparing lithium iron phosphate by using low-temperature lithiation iron phosphate needs to use an organic solvent (such as absolute ethyl alcohol) and the mother solution is difficult to recycle, thereby causing waste. Meanwhile, most of lithium source-lithium-containing compounds used for lithiation in the preparation methods are simple inorganic substances, the solubility in organic solvents is not high, the solvent amount is large during mass preparation, heating is needed, the energy consumption is high, and the cost is high.

The patent CN 102104149A discloses a lithium iron phosphate composite anode material in a lithium ion battery and a preparation method thereof, the invention adopts raw materials containing lithium, iron and phosphorus to prepare lithium iron phosphate, then the lithium iron phosphate is uniformly mixed with nanowires, and the nanowire composite lithium iron phosphate anode material is prepared by annealing, so that the nanowire composite lithium iron phosphate anode material has excellent conductivity, and improves the reversible capacity, the rate capability and the cycle life of the battery. GuoxiuWang et al, university of horizontal Dragon hillock, Canada, prepared a one-dimensional lithium iron phosphate nanowire which was not coated with carbon by a hydrothermal method in an article published by Journal of Power sources in 2008, and the specific capacity of the nanowire was up to 140mAh/g, which indicates that the shape control of the lithium iron phosphate has a positive effect on improving the performance of the battery; then, researchers successfully synthesize various nano structures such as lithium iron phosphate nano rods, nano sheets and nano discs. Researchers dope the prepared lithium iron phosphate with the desired physical and chemical properties, such as "Effect of thermal treatment on the property" published by Changhean Zhang et al of the university of east Chinas of electrospun LiFePO₄The carbon nanofiber composite materials for lithium-ion batteries uses a mixed solution of a lithium iron phosphate precursor and polyacrylonitrile as a reaction solution, a nanowire is prepared in an electrostatic spinning mode, then two-stage heating and carbonization are carried out to obtain the lithium iron phosphate/C composite material, the material has better electrical property, the initial discharge capacity of the material at 0.5 ℃ is 146.3 mAh/g, and the material still has better stability after circulation for 100 circles, which means that the electrical property of the material can be properly improved by doping lithium iron phosphate. The traditional preparation method of the lithium iron phosphate by the solid phase method or the liquid phase method is further characterized in that the performance of the product is improved to a certain extent by a nanowire composite technology or a doping means, the cost is overhigh due to multiple sintering, and the whole preparation process is complex and tedious.

At present, the synthesis technology of the lithium iron phosphate anode material has various process technical routes, and the industrialized technical routes include an iron oxide red route, a ferrous oxalate route, a hydrothermal synthesis route and an iron orthophosphate route. The lithium iron phosphate prepared by the ferric orthophosphate route has the advantages of good electrical property, low impurity content, relatively simple process steps and the like, and gradually becomes a technical trend of industry unification. However, in the prior art, the method for recovering lithium iron phosphate generally comprises the steps of firstly preparing lithium salt and ferric sulfate by a wet method, and then preparing the lithium salt and the ferric sulfate by using a ferric sulfate route; the method is used for preparing the lithium iron phosphate product with high and medium quality, but the preparation cost is equivalent to the route of ferric phosphate, and the processing cost is higher, so that the lithium iron phosphate material with excellent performance is prepared by changing the original auxiliary material, improving the preparation process of the lithium iron phosphate and optimizing the technical conditions to overcome the defect of preparing the lithium iron phosphate anode material by recovering the lithium iron phosphate waste.

Disclosure of Invention

The invention aims to provide a high-carbon low-rate lithium iron phosphate decarburization reconstruction method aiming at the defects of the prior art, the preparation method can prepare a lithium iron phosphate anode material only through once defluorination, carbon reduction and purification processes, the process is simple, the flow is short, the production cost is low, and the prepared lithium iron phosphate anode material has high compaction density, good crystallinity and excellent rate performance.

The technical scheme of the invention is as follows:

a high-carbon low-rate lithium iron phosphate decarburization reconstruction method comprises the following steps:

step A, pyrolysis separation: pyrolyzing the lithium iron phosphate waste pole pieces without being injected with electrolyte under the conditions of protective atmosphere, temperature of 420-500 ℃, time of 3-8h and oxygen concentration of less than 1500ppm, and carrying out vibration screening on the waste pole pieces completely pyrolyzed on a screen mesh of 3-35 meshes to obtain lithium iron phosphate waste powder;

step B, airflow crushing: b, mixing the waste lithium iron phosphate powder obtained in the step A with a certain amount of zinc oxide powder, performing airflow crushing, and screening the crushed material by using a 100-mesh screen to obtain high-carbon low-performance mixed waste lithium iron phosphate powder;

step C, carbon reduction: and D, sintering the mixed lithium iron phosphate waste powder obtained in the step B in mixed gas, wherein the sintering system comprises the steps of removing F from lithium iron phosphate at 680-720 ℃, decarbonizing at 820-880 ℃, purifying at 740-780 ℃, and cooling to a temperature below 100 ℃ for discharging.

Preferably, the screen in the step A is a vibrating screen with 3 meshes to 35 meshes; the screen in the step B is a 100-mesh screen.

As a further improvement of the invention, the lithium iron phosphate waste pole pieces without being injected with the electrolyte in the step a comprise scrapped positive pole pieces in the manufacturing process of the lithium iron phosphate positive pole pieces, and the scrapped positive pole pieces of the battery without being injected with the electrolyte in the preparation process of the battery are decomposed; the protective gas is one or more mixed gases of rare gases such as nitrogen, argon and the like.

As a further improvement of the invention, in the screening process in the step a, one of zirconia balls, rubber balls or stainless steel balls is required to be added to the screen; the content of impurity aluminum in the obtained lithium iron phosphate waste powder is less than 0.1 percent.

As a further improvement of the invention, the adding amount of the zinc oxide in the step B is 0.3-0.35 times of the mole number of the impurity fluorine in the waste lithium iron phosphate powder; the medium particle size of the material after airflow crushing is 0.5-10 μm.

In the step C, the sintering system is that the temperature is raised at a constant speed in each liter of temperature stage, the time from the room temperature to the defluorination temperature is 6-8h, then the time to the decarburization temperature is 3-5h, and the decarburization temperature is naturally cooled to the purification temperature; the holding time at the defluorination temperature, the decarbonization temperature and the purification temperature is 1-3h, 6-8h and 3-7h respectively, and then the cooling time is 7-12 h.

As a further improvement of the present invention, in the step C, the mixed gas in the sintering system refers to: one or more of nitrogen, helium, neon and the like are mixed with carbon dioxide according to different proportions, and the molar ratio of the carbon dioxide in the mixed gas is 10-60%.

As a further improvement of the invention, in the step C, when the mixed lithium iron phosphate waste powder obtained in the step B is sintered in a mixed gas, the oxygen concentration is controlled to be 1-50ppm, and the micro positive pressure in the furnace is controlled to be 10-100 Pa; and (4) after the material is discharged from the furnace, conventionally crushing and packaging the material to obtain a lithium iron phosphate product.

In the pyrolysis separation process of the step A, a binder PVDF (polyvinylidene fluoride) is subjected to thermal decomposition, part of F enters a flue gas system along with flue gas and is discharged, the other part of F reacts with an aluminum foil to generate aluminum fluoride and reacts with lithium to generate lithium fluoride, the lithium fluoride enters waste lithium iron phosphate powder, the electrochemical performance of lithium iron phosphate is influenced to a certain extent by the generation of the lithium fluoride, and meanwhile, due to the fact that a certain amount of activated carbon is added in the coating process and part of C is generated by the thermal decomposition of the PVDF, the content of C in the waste lithium iron phosphate powder is often over 4%, and the content of C in the lithium iron phosphate anode material is generally within 2%.

The defluorination process is that under the condition of keeping a certain micro-positive pressure in the furnace at a high temperature of about 700 ℃, zinc oxide is subjected to physical and chemical changes in a sintering furnace, so that the fluorine compound is desorbed and returns to the gas phase, the low-boiling-point fluorine compound is volatilized, the fluorine compound of zinc is decomposed into a gas state, and the gas and the smoke enter a flue gas system together to be removed, so that Li in LiF is released and enters a lithium iron phosphate crystal lattice again, and the electrochemical performance is optimized.

The decarburization principle is as follows: c + CO₂→ CO, at the temperature of 820-.

The purification process is that ferric iron or ferroferric oxide reacts with carbon monoxide in the lithium iron phosphate anode material at the temperature of 740-780 ℃ in a reducing atmosphere to reduce the ferric iron into ferrous iron, so that a lithium iron phosphate product is generated; the ferroferric oxide has magnetism, and after purification, the ferroferric oxide completely reacts to generate the lithium iron phosphate anode material, so that the magnetic substances are reduced, and the rate capability of the material is obviously improved.

The sintering system process comprises the steps of defluorination temperature, decarburization temperature and purification temperature, so that the lithium iron phosphate has complete crystal lattice, more complete carbon coating, fast promotion of Li ion migration rate and more excellent electrical property.

The invention has the beneficial effects that:

1. the raw materials of the invention are lithium iron phosphate waste pole pieces which are not injected with liquid, certainly comprise defective lithium iron phosphate (LFP) raw materials, and also comprise a pure lithium iron phosphate anode material which is disassembled from a lithium iron phosphate battery and separated. Therefore, with the application of a large amount of lithium iron phosphate cathode materials in batteries, the raw materials are wide, and the project belongs to the field of green and environment-friendly circular economy.

2. According to the sintering process, the lithium iron phosphate is subjected to defluorination treatment through three stages of defluorination temperature, decarburization temperature and purification temperature, Li is recombined, the surfaces of lithium iron phosphate particles form compact carbon coating, carbon is uniformly distributed among the particles, the defect of the lithium iron phosphate is prevented, the purity of the product lithium iron phosphate is ensured, and the lithium iron phosphate material with high conductivity and low internal resistance can be obtained through the above technology, so that the lithium iron phosphate material has excellent electrical property. The lithium iron phosphate prepared by the process can be compacted to 2.48-2.56g/mL, the 1C discharge capacity exceeds 145mAh/g, the normal-temperature circulation can reach 3000 circles, and the performance of the lithium iron phosphate is equivalent to that of the medium-high-end lithium iron phosphate on the market. Can be well applied to the energy storage industry and the power battery industry.

3. The invention is particularly applied to the raw materials of the waste lithium iron phosphate positive electrode material, has the advantages of reasonable process, low manufacturing cost, environmental protection, no toxicity and the like, has the electrochemical performance meeting the requirements of olivine type lithium iron phosphate batteries sold in the market, and has very wide application prospect.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It is to be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention, and the present invention encompasses other embodiments and modifications thereof within the scope of the technical spirit thereof.

In the present invention, the decarburization step may be reduced or a magnetic iron removal step or a screening step of lithium iron phosphate may be added depending on the material, but the present invention can also be applied as long as the basic process flow is not changed.

The embodiment of the invention provides a high-carbon low-rate lithium iron phosphate decarburization reconstruction method, and please refer to fig. 1. The invention is further illustrated by the following specific examples.

Example 1

Step A, pyrolysis separation: taking the lithium iron phosphate waste pole pieces which are not injected with the electrolyte to pyrolyze under the conditions of the protection atmosphere of nitrogen, the temperature of 420 ℃, the time of 8 hours and the oxygen concentration of 1500ppm, and vibrating and screening the completely pyrolyzed waste pole pieces on a 3-mesh screen added with zirconium balls to obtain lithium iron phosphate waste powder with the Al content of 0.1 percent;

step B, airflow crushing: mixing the waste lithium iron phosphate powder obtained in the step A with zinc oxide powder which is 0.3 times of the mole number of F, performing airflow crushing, and screening the crushed material by using a 100-mesh screen to obtain high-carbon low-performance mixed waste lithium iron phosphate powder with the medium particle size of 0.5 mu m;

step C, carbon reduction: b, sintering the mixed lithium iron phosphate waste powder obtained in the step B in argon-containing mixed gas with the carbon dioxide molar ratio of 10%, wherein the oxygen concentration in the furnace is 1ppm, the pressure in the furnace is 100Pa, the time for heating the lithium iron phosphate to the F removing temperature is 6 hours, the F removing temperature is 720 ℃, and the F removing time is 1 hour; the temperature is raised to the decarburization temperature for 3 hours, the decarburization temperature is 880 ℃, and the decarburization time is 6 hours; the purification temperature is 780 ℃, and the purification time is 3 h; then cooling to below 100 ℃ and discharging, wherein the cooling time is 12 h.

And C, performing conventional crushing and packaging on the discharged material obtained in the step C to obtain a lithium iron phosphate product with D50=0.65 μm and the compacted density of 2.51 g/mL.

Example 2

Step A, pyrolysis separation: taking the lithium iron phosphate waste pole pieces which are not injected with the electrolyte, pyrolyzing the lithium iron phosphate waste pole pieces under the protection atmosphere of argon at the temperature of 500 ℃ for 3h and under the condition of oxygen concentration of 10ppm, and carrying out vibration screening on the waste pole pieces which are completely pyrolyzed on a 35-mesh screen added with rubber balls to obtain lithium iron phosphate waste powder with the Al content of 0.05%;

step B, airflow crushing: mixing the waste lithium iron phosphate powder obtained in the step A with zinc oxide powder which is 0.35 times of the mole number of F, performing airflow crushing, and screening the crushed material by using a 100-mesh screen to obtain high-carbon low-performance mixed waste lithium iron phosphate powder with the medium particle size of 10 mu m;

step C, carbon reduction: b, sintering the mixed lithium iron phosphate waste powder obtained in the step B in a nitrogen-containing mixed gas with the carbon dioxide molar ratio of 60%, wherein the oxygen concentration in the furnace is 50ppm, the pressure in the furnace is 10Pa, the time for heating the lithium iron phosphate to the F removing temperature is 8 hours, the F removing temperature is 680 ℃, and the F removing time is 3 hours; the temperature is raised to the decarburization temperature for 5 hours, the decarburization temperature is 820 ℃, and the decarburization time is 8 hours; the purification temperature is 740 ℃, and the purification time is 7 h; then cooling to below 100 ℃ and discharging, wherein the cooling time is 7 h.

And C, conventionally crushing and packaging the discharged material obtained in the step C to obtain a lithium iron phosphate product with D50=1.43 μm and the compacted density of 2.53 g/mL.

Example 3

Step A, pyrolysis separation: taking the lithium iron phosphate waste pole pieces which are not injected with the electrolyte to pyrolyze under the conditions of 480 ℃ of temperature, 5h of time and 100ppm of oxygen concentration in the protective atmosphere of helium, and vibrating and screening the completely pyrolyzed waste pole pieces on a 25-mesh screen added with stainless steel balls to obtain lithium iron phosphate waste powder with 0.07 percent of Al content;

step B, airflow crushing: mixing the waste lithium iron phosphate powder obtained in the step A with zinc oxide powder which is 0.33 times of the mole number of F, performing airflow crushing, and screening the crushed material by using a 100-mesh screen to obtain high-carbon low-performance mixed waste lithium iron phosphate powder with the medium particle size of 5 mu m;

step C, carbon reduction: b, sintering the mixed lithium iron phosphate waste powder obtained in the step B in a helium-containing mixed gas with the carbon dioxide molar ratio of 30%, wherein the oxygen concentration in the furnace is 20ppm, the pressure in the furnace is 50Pa, the time for heating the lithium iron phosphate to the F removing temperature is 7 hours, the F removing temperature is 700 ℃, and the F removing time is 2 hours; the temperature is raised to the decarburization temperature for 4 hours, the decarburization temperature is 860 ℃, and the decarburization time is 7 hours; the purification temperature is 760 ℃, and the purification time is 5 h; then cooling to below 100 ℃ and discharging, wherein the cooling time is 9 h.

And C, conventionally crushing and packaging the discharged material obtained in the step C to obtain a lithium iron phosphate product with D50=1.17 mu m and the compacted density of 2.55 g/mL.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.