Lithium iron phosphate recovery method based on controllable atmosphere

Abstract

A lithium iron phosphate recovery method based on a controllable atmosphere comprises the following steps: feeding lithium iron phosphate waste into a manufacturing furnace, continuously introducing a reducing agent and water into the manufacturing furnace to form the controllable atmosphere in the manufacturing furnace, controlling the temperature to be 600-800 DEG C under the controllable atmosphere, carrying out heat treatment, and detecting the content of CO2 in the controllable atmosphere in the furnace in real time in the treatment process, according to the method, the content of CO2 in the controllable atmosphere is kept at 1.2-5% by adjusting the introduction amount of the reducing agent and the water in real time, waste lithium iron phosphate is directly converted into lithium iron phosphate, all Fe < 3 + > is converted into Fe < 2 + >, the conversion rate is increased, and the recycling time is saved.

Description

Technical Field

[0001] The invention relates to the technical field of regeneration treatment of scrapped lithium iron phosphate batteries, in particular to a lithium iron phosphate recovery method based on a controllable atmosphere. Background Art

[0002] Lithium iron phosphate has the advantages of low cost, long cycle life and safe use, which makes it widely used in batteries. As the battery life of electric vehicles gradually expires, the amount of power batteries scrapped is also increasing. The main reason for its scrapping is the reduction in the amount of active Li that can participate in chemical reactions, that is, Li is mainly intercepted by the polarization film formed on the surface of the positive electrode - SEI film, and cannot be normally embedded in the FePO4 skeleton during discharge. Lithium-ion batteries contain potassium hexafluorophosphate, carbonate organic matter, and heavy metals such as cobalt, lithium, and copper, as well as plastics, which are all valuable resources with extremely high recycling value. In particular, lithium iron phosphate has a higher recycling value, so it is necessary to convert the trivalent iron ions in the lithium iron phosphate waste into divalent iron ions. In the prior art, the recycled lithium iron phosphate is converted into lithium carbonate, and then the lithium carbonate is converted into lithium iron phosphate. Summary of the invention

[0003] In order to recycle lithium iron phosphate and reuse it, the present invention provides a lithium iron phosphate recovery method based on a controlled atmosphere, which recovers lithium iron phosphate in waste batteries, directly converts waste lithium iron phosphate into lithium iron phosphate, and converts all Fe 3+ Converted to Fe 2+ , improving the conversion rate and saving recycling time.

[0004] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present invention is: a lithium iron phosphate recovery method based on a controlled atmosphere, wherein lithium iron phosphate waste is fed into a manufacturing furnace, a reducing agent and water are continuously introduced into the manufacturing furnace to form a controllable atmosphere inside the furnace, and the temperature is controlled to be 600-800°C for heat treatment under the controlled atmosphere. During the treatment process, the CO2 content in the controlled atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2-5%.

[0005] As an optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the method for obtaining lithium iron phosphate waste is: adding the positive and negative electrode materials of the waste power battery into a solvent and dissolving them to obtain a raw material solution, and removing impurities and purifying the raw material solution to obtain lithium iron phosphate waste.

[0006] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the solvent is one or two of N-methylpyrrolidone and dimethylacetamide.

[0007] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the reducing agent is methanol.

[0008] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: when the CO2 content is less than 1.2%, the amount of reducing agent introduced is reduced and the amount of water introduced is increased.

[0009] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: when the CO2 content is greater than 5%, the amount of reducing agent introduced is increased and the amount of water introduced is reduced.

[0010] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the manufacturing furnace includes a base, a furnace shell inclined on the base and a furnace core coaxially arranged in the furnace shell. Lithium iron phosphate waste enters or flows out of the furnace core through a feeding and discharging unit. The furnace shell is provided with an air inlet cylinder for supplying reducing agent and water into the furnace core and a detector for detecting the CO2 content in the furnace core; the base is provided with a driving unit for driving the furnace shell and the furnace core to rotate.

[0011] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the feeding unit includes a feeding pipe that is coaxial with the furnace shell and extends into the furnace shell, and a spiral conveying assembly arranged in the feeding pipe, the spiral conveying assembly includes a rotating shaft and a spiral blade fixedly connected to the rotating shaft, during the rotation of the rotating shaft, the spiral blade conveys the lithium iron phosphate waste to the furnace shell or outputs it out of the furnace shell.

[0012] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: a feed port and a discharge port are provided at one end of the feed pipe extending out of the furnace shell.

[0013] As another optimization scheme of the above-mentioned lithium iron phosphate recovery method based on controlled atmosphere: the driving unit includes a gear ring arranged around the outer wall of the furnace shell and a transmission gear arranged on the base, and the transmission gear is driven and connected to a driving motor.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention provides a lithium iron phosphate recovery method based on a controlled atmosphere, wherein the lithium iron phosphate waste is fed into a manufacturing furnace, and a reducing agent and water are continuously introduced into the furnace to form a controllable atmosphere in the furnace, and the temperature is controlled to be 600-800°C for heat treatment under the controlled atmosphere, and the lithium iron phosphate waste reacts in the controlled atmosphere, and the CO2 content in the controlled atmosphere is maintained at 1.2-5%, the reducing agent is decomposed into carbon monoxide and hydrogen, water reacts with carbon in the lithium iron phosphate waste to generate carbon monoxide and hydrogen, and the trivalent iron ions in the lithium iron phosphate waste react with carbon monoxide to generate carbon dioxide. The basic reaction principle is as follows: 2C+3H2O→CO+CO2+3H2 CO+2FePO4+Li2O→2LiFePO4+CO2 H2+2FePO4+Li2O→2LiFePO4+H2O Only phosphate, divalent iron ions and metallic lithium ions can stably exist in a controlled atmosphere at a temperature of 600-800°C, and lithium iron phosphate has an olivine structure, so lithium iron phosphate waste can be recovered in one step, thereby improving the recovery efficiency; in the controlled atmosphere, all trivalent iron ions are converted into divalent iron ions, thereby improving the recovery rate; in the controlled atmosphere, the conversion rate of trivalent iron ions is high, thereby shortening the recovery time of lithium iron phosphate waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the manufacturing furnace;

[0017] Figure numerals: 1. furnace shell, 101. gear ring, 102. heating sleeve ring, 2. base, 201. transmission shaft, 202. transmission gear, 3. air intake cylinder. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further elaborated in detail below in conjunction with specific embodiments. The parts of the present invention that are not described and disclosed in detail in the following embodiments should be understood as the prior art known or should be known to those skilled in the art.

[0019] A lithium iron phosphate recovery method based on a controlled atmosphere is provided. The lithium iron phosphate waste is fed into a manufacturing furnace. The method for obtaining the lithium iron phosphate waste is as follows: positive and negative electrode materials of waste power batteries are added into a solvent to dissolve to obtain a raw material solution, and the raw material solution is removed and purified to obtain the lithium iron phosphate waste. Specifically, the waste power batteries are disassembled and the positive and negative electrode materials are sorted out, and the raw material solution is added into a solvent to dissolve, and the solvent is N-methylpyrrolidone to obtain a raw material solution, and the raw material solution is removed and purified to obtain the lithium iron phosphate waste. The obtained lithium iron phosphate waste is in powder form, and the lithium iron phosphate waste includes LiFePO4, FePO4 and a SEI film with Li2O as the main component.

[0020] A reducing agent and water are continuously introduced into the manufacturing furnace to form a controllable atmosphere inside the furnace. The temperature is controlled to be 600-800°C for heat treatment in the controlled atmosphere. The reducing agent is methanol or other alcohols. In this embodiment, methanol is selected as the reducing agent. Under the condition of 600-800°C, methanol is decomposed into carbon monoxide and hydrogen. Water reacts with carbon in lithium iron phosphate waste to generate carbon monoxide and hydrogen. Carbon monoxide reduces trivalent iron ions to divalent iron ions and generates carbon dioxide. In the controlled atmosphere, FePO4 - Form a stable framework, remove O from Li2O, and Li+ Re-embedding FePO4 - LiFePO4 is formed inside the furnace, completing the recovery of lithium iron phosphate waste. During the treatment process, the CO2 content in the controllable atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controllable atmosphere at 1.2-5%. At a temperature of 600-800°C and in a controlled atmosphere, only phosphate, divalent iron ions and metallic lithium ions can exist stably, and the lithium iron phosphate has an olivine structure. When the CO2 content is lower than 1.2%, it will lead to excessive presence of CO and H2. It is necessary to reduce the amount of reducing agent introduced and increase the amount of water introduced to make the reducing components in the controlled atmosphere appropriate so as not to cause Fe 2+ ions are over-reduced to elemental iron; when the CO2 content is higher than 5%, it indicates that the amount of CO and H2 in the controlled atmosphere is insufficient, resulting in Fe 2+ The ions cannot be fully reduced, so it is necessary to increase the amount of reducing agent introduced, reduce the amount of water introduced, and adjust the amount of CO and H2 in the controlled atmosphere. By adjusting the amount of reducing agent and water, the CO2 content is stabilized within a certain range. Only ferrous ions and lithium ions in the olivine structure are a stable phase, and other unstable structures and ionic states will transform to this stable state according to the laws of thermodynamics.

[0021] The reactions in the manufacturing furnace are calculated according to the following substances and participating reactions:

[0022] The specific calculation method is to use the GGA-PBE method to calculate the solid substance and the GGA-PW91 method to calculate the gaseous substance, wherein carbon is an amorphous solid single substance, and the Gibbs free energy G of the solid substance and the gaseous substance are shown in Tables 1 and 2.

[0023] Table 1 Gibbs free energy G(Ha) of solid substances

[0024] Table 2 Gibbs free energy G(Ha) of gaseous substances

[0025] Calculation of Gibbs free energy changes of four reactions and two limiting pressures of CO2 at 750°C:

[0026]

[0027]

[0028] 3LiFePO4+3CO≠3Fe+Li3PO4+3CO2+P2O5(p CO2 must be greater than 1.2%);

[0029] 3LiFePO4+3H2≠3Fe+Li3PO4+3H2O+P2O5;

[0030]

[0031] =-0.0959366Ha=-2.6106eV=-251.766kJ / mol;

[0032]

[0033] =-0.5192072Ha=-14.12866eV=-1362.568kJ / mol;

[0034] ΔG θ 3=(3G χ +3G ι +G δ +G κ )–(3G γ +3G β )

[0035] =-0.1672259Ha=-4.5505eV=-438.85kJ / mol;

[0036] ΔG θ 4=(3G χ +3G ι +G δ +G κ )–(3G η +3G β )

[0037] =-0.0437669Ha=-1.1910eV=-114.86kJ / mol;

[0038] The RT product at this temperature is 8.5 KJ / mol. Substituting the Gibbs free energy change of the above reaction into the following formula:

[0039] exp[-(Δ r G θ 2+Δ r G θ 3 / 3+Δ r G θ 4) / 2RΤ] <P CO2 / p θ <exp[-(Δ r G θ 1+Δ r G θ 2+2Δ r G θ 4 / 3) / 2RΤ]

[0040] Result: 1 / 255 <P CO2 / p θ <1 / 125.

[0041] like Figure 1 As shown, the manufacturing furnace includes a base 2, a furnace shell 1 obliquely arranged on the base 2, and a furnace core coaxially arranged in the furnace shell 1. The furnace shell 1 is a circular cylindrical structure. The top of the furnace shell 1 has a heating sleeve 102 for heating the manufacturing furnace to make the internal temperature reach 600-800°C, and the bottom of the furnace shell 1 has a furnace cover. The base 2 is provided with a driving unit for driving the furnace shell 1 and the furnace core to rotate. The driving unit includes a gear ring 101 arranged around the outer wall of the furnace shell 1 and a transmission gear 202 arranged on the base 2, and the transmission gear 202 is drivingly connected to a driving motor. Specifically, two mutually parallel transmission shafts 201 are arranged on the base 2, and the transmission gear 202 is sleeved on the transmission shaft 201 and fixedly connected to the rotating shaft, and the driving motor is drivingly connected to the transmission shaft 201. The driving motor drives the transmission shaft 201 and the transmission gear 202 to rotate, thereby driving the furnace shell 1 to rotate.

[0042] The lithium iron phosphate waste enters or flows out of the furnace through the feeding and discharging unit. The feeding unit includes a feeding pipe coaxial with the furnace shell 1 and extending into the furnace shell and a spiral conveying assembly arranged in the feeding pipe. One end of the feeding pipe extending out of the furnace shell 1 is provided with a feeding port and a discharging port. The spiral conveying assembly includes a rotating shaft and a spiral blade fixedly connected to the rotating shaft. During the rotation of the rotating shaft, the spiral blade conveys the lithium iron phosphate waste to the furnace shell or outputs it out of the furnace shell. When the rotating shaft rotates forward, the lithium iron phosphate waste is conveyed into the furnace shell, and when the rotating shaft rotates reversely, the reacted lithium iron phosphate is output out of the furnace shell.

[0043] The furnace shell 1 is provided with an air inlet 3 for supplying reducing agent and water into the furnace and a detector for detecting the CO2 content in the furnace. One end of the air inlet 3 extends out of the furnace shell 1, and the other end of the air inlet 3 extends into the furnace. The air inlet 3 is provided with two inlets, one of which is used to supply reducing agent into the furnace, and the other inlet is used to supply water into the furnace.

[0044] Example 1

[0045] 500 kg of lithium iron phosphate waste was fed into a manufacturing furnace, and a reducing agent and water were introduced into the manufacturing furnace. The flow rate of the reducing agent was 15-28 g / min in the initial stage, so that a controllable atmosphere was formed in the furnace. The temperature was controlled to be 600°C in the controllable atmosphere to carry out heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace was detected in real time, and the amount of reducing agent and water introduced was adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2%. As a result, all the trivalent iron ions in the lithium iron phosphate waste were converted into divalent iron ions. The battery evaluation of the lithium iron phosphate after the reaction showed normal charging and discharging.

[0046] Example 2

[0047] 500 kg of lithium iron phosphate waste was fed into a manufacturing furnace, and a reducing agent and water were introduced into the manufacturing furnace. The flow rate of the reducing agent was 15-28 g / min in the initial stage, so that a controllable atmosphere was formed in the furnace. The temperature was controlled to be 800°C under the controllable atmosphere to carry out heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace was detected in real time, and the amount of reducing agent and water introduced was adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2%. As a result, all the trivalent iron ions in the lithium iron phosphate waste were converted into divalent iron ions. The battery evaluation of the lithium iron phosphate after the reaction showed normal charging and discharging.

[0048] Example 3

[0049] 500 kg of lithium iron phosphate waste was fed into a manufacturing furnace, and a reducing agent and water were introduced into the manufacturing furnace. The flow rate of the reducing agent was 15-28 g / min in the initial stage, so that a controllable atmosphere was formed in the furnace. The temperature was controlled to be 600°C in the controllable atmosphere to carry out heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace was detected in real time, and the amount of reducing agent and water introduced was adjusted in real time to keep the CO2 content in the controlled atmosphere at 5%. As a result, all the trivalent iron ions in the lithium iron phosphate waste were converted into divalent iron ions. The battery evaluation of the lithium iron phosphate after the reaction showed normal charging and discharging.

[0050] Example 4

[0051] 500 kg of lithium iron phosphate waste was fed into a manufacturing furnace, and a reducing agent and water were introduced into the manufacturing furnace. The flow rate of the reducing agent was 15-28 g / min in the initial stage, so that a controllable atmosphere was formed in the furnace. The temperature was controlled to 700°C in the controllable atmosphere to carry out heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace was detected in real time, and the amount of reducing agent and water introduced was adjusted in real time to keep the CO2 content in the controlled atmosphere at 3%. As a result, all the trivalent iron ions in the lithium iron phosphate waste were converted into divalent iron ions. The battery evaluation of the lithium iron phosphate after the reaction showed normal charging and discharging.

[0052] Comparative Example 1

[0053] 500 kg of lithium iron phosphate waste is fed into a manufacturing furnace, and a reducing agent and water are introduced into the manufacturing furnace. The flow rate of the reducing agent is 15-28 g / min in the initial stage, so that a controllable atmosphere is formed in the furnace. The temperature is controlled to 500°C in the controllable atmosphere to perform heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2%. As a result, the lithium iron phosphate is unstable; the iron ions are reduced to atomic state.

[0054] Comparative Example 2

[0055] 500 kg of lithium iron phosphate waste is fed into a manufacturing furnace, and a reducing agent and water are introduced into the manufacturing furnace. The flow rate of the reducing agent is 15-28 g / min in the initial stage, so that a controllable atmosphere is formed in the furnace. The temperature is controlled to 900°C in the controllable atmosphere to perform heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2%. As a result, the lithium iron phosphate is unstable; the iron ions are reduced to atomic state.

[0056] Comparative Example 3

[0057] 500 kg of lithium iron phosphate waste was fed into a manufacturing furnace, and a reducing agent and water were introduced into the manufacturing furnace to form a controllable atmosphere in the furnace. The temperature was controlled to 600°C in the controllable atmosphere to perform heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controllable atmosphere in the furnace was detected in real time, and the amount of reducing agent and water introduced was adjusted in real time to keep the CO2 content in the controlled atmosphere at 1%. As a result, the lithium iron phosphate became unstable and the iron ions were reduced to an atomic state.

[0058] Comparative Example 4

[0059] 500 kg of lithium iron phosphate waste is fed into a manufacturing furnace, and reducing agent and water are introduced into the manufacturing furnace to form a controllable atmosphere in the furnace. The temperature is controlled to 600°C in the controllable atmosphere to perform heat treatment on the lithium iron phosphate waste. During the treatment, the CO2 content in the controlled atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controlled atmosphere at 6%. Trivalent iron ions will appear and the lithium iron phosphate will become unstable.

[0060] Comparative Example 5

[0061] 500 kg of lithium iron phosphate waste is fed into the manufacturing furnace, and reducing agent and water are introduced into the manufacturing furnace. The reducing agent and water are continuously and quantitatively introduced into the manufacturing furnace, and the temperature is controlled at 600°C to perform heat treatment on the lithium iron phosphate waste, so that the lithium iron phosphate becomes unstable and the iron ions are reduced to atomic state.

[0062] In summary, at a temperature of 600-800°C and a CO2 content of 1.2-5% in a controlled atmosphere, only phosphate, divalent iron ions and metallic lithium ions can exist stably, and the charging and discharging of the recovered lithium iron phosphate meets the requirements.

[0063] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lithium iron phosphate recovery method based on a controlled atmosphere, characterized in that: The lithium iron phosphate waste is fed into a manufacturing furnace, and a reducing agent and water are continuously introduced into the manufacturing furnace to form a controllable atmosphere inside the furnace. The temperature is controlled to be 600-800°C in the controllable atmosphere for heat treatment. During the treatment process, the CO2 content in the controlled atmosphere in the furnace is detected in real time, and the amount of reducing agent and water introduced is adjusted in real time to keep the CO2 content in the controlled atmosphere at 1.2-5%.

2. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 1, characterized in that: The method for obtaining lithium iron phosphate waste is as follows: adding positive and negative electrode materials of waste power batteries into a solvent to dissolve to obtain a raw material solution, and removing impurities and purifying the raw material solution to obtain lithium iron phosphate waste.

3. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 2, characterized in that: The solvent is one or both of N-methylpyrrolidone and dimethylacetamide.

4. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 1, characterized in that: The reducing agent is methanol.

5. A lithium iron phosphate recovery method based on a controlled atmosphere as claimed in claim 1, characterized in that: When the CO2 content is less than 1.2%, reduce the amount of reducing agent introduced and increase the amount of water introduced.

6. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 1, characterized in that: When the CO2 content is greater than 5%, increase the amount of reducing agent introduced and reduce the amount of water introduced.

7. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 1, characterized in that: The manufacturing furnace comprises a base (2), a furnace shell (1) arranged obliquely on the base (2), and a furnace core coaxially arranged in the furnace shell (1); lithium iron phosphate waste enters or flows out of the furnace core through a material inlet and outlet unit; the furnace shell (1) is provided with an air inlet cylinder (3) for supplying a reducing agent and water into the furnace core, and a detector for detecting the CO2 content in the furnace core; and the base (2) is provided with a driving unit for driving the furnace shell (1) and the furnace core to rotate.

8. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 7, characterized in that: The feeding unit comprises a feeding pipe coaxial with the furnace shell (1) and extending into the furnace core, and a spiral conveying assembly arranged in the feeding pipe. The spiral conveying assembly comprises a rotating shaft and a spiral blade fixedly connected to the rotating shaft. During the rotation of the rotating shaft, the spiral blade conveys the lithium iron phosphate waste into the furnace core or outputs it out of the furnace core.

9. A method for recovering lithium iron phosphate based on a controlled atmosphere as claimed in claim 8, characterized in that: One end of the feed pipe extending out of the furnace shell (1) is provided with a feed inlet and a discharge outlet.

10. A lithium iron phosphate recovery method based on a controlled atmosphere as claimed in claim 7, characterized in that: The driving unit comprises a gear ring (101) arranged around the outer wall of the furnace shell (1) and a transmission gear arranged on the base (2), and the transmission gear is drivingly connected to a driving motor.

Images