A method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte

Abstract

The application provides a method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte, belongs to the technical field of waste liquid comprehensive utilization, and is used for lithium ion battery production and lithium battery recycling processes, wherein part of waste electrolyte is generated, mainly containing carbonate organic solvent and lithium salt; the application first separates the carbonate and lithium salt by adopting thin film evaporation; after neutralization, the light component carbonate solvent enters a rectification system to realize the separation of carbonates, and various carbonate products meeting the national standard requirements are obtained; after high-temperature incineration cracking and removal of residual organic impurities, the heavy component lithium salt is recycled in the form of lithium fluoride; the process realizes comprehensive utilization of the waste electrolyte, and avoids waste of lithium elements and carbonate solvents.

Description

Technical Field

[0001] This invention belongs to the field of waste liquid resource comprehensive utilization technology, specifically involving a method for recovering lithium salts and carbonate solvents from waste electrolyte of lithium batteries. Background Technology

[0002] Lithium-ion battery electrolyte is the carrier of ion transport in the battery. It is generally composed of lithium salt and organic solvent. The electrolyte plays the role of conducting ions between the positive and negative electrodes of the lithium battery, which is the guarantee for the high voltage and high specific energy of lithium-ion batteries. The electrolyte is generally prepared by mixing high-purity organic solvent, electrolyte lithium salt, necessary additives and other raw materials under certain conditions and in certain proportions. Lithium-ion battery electrolyte consists of three parts, mainly solvent, lithium salt and additives. The solvent accounts for 80-85%, the lithium salt, which is the solute, accounts for 10-12%, and the additives account for 3-5%. The role of the solvent in the composition of lithium-ion battery electrolyte is mainly to dissolve lithium salt. Currently, commonly used organic solvents on the market include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), etc., and their physicochemical parameters are shown in Table 1 below.

[0003]

[0004] High-quality lithium salts have a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. Commonly contained elements in lithium salts include LiPF6, LiClO4, LiBF4, and LiAsF6, with LiPF6 being the most prevalent lithium salt at present.

[0005] Lithium hexafluorophosphate is a thermosensitive substance that decomposes readily when heated. The decomposition equation is as follows:

[0006]

[0007] When the electrolyte contains a small amount of water, the generated phosphorus pentafluoride will undergo a further reaction, as shown in the following equation:

[0008]

[0009] If the electrolyte contains too much water, a further reaction will occur, producing more hydrogen fluoride and other substances. Lithium hexafluorophosphate will eventually hydrolyze into lithium fluoride, hydrogen fluoride, and fluorophosphate compounds.

[0010]

[0011] The main types of additives used in lithium battery electrolytes include film-forming additives, conductive additives, flame-retardant additives, overcharge protection additives, additives that control the H2O and HF content in the electrolyte, additives that improve low-temperature performance, and multifunctional additives.

[0012] Thin-film evaporators are a new type of evaporator that uses a rotating scraper to force film formation and high-speed flow, resulting in high heat transfer efficiency, short residence time, and the ability to perform falling film evaporation under vacuum conditions. A thin-film evaporator is a type of evaporator characterized by the material liquid flowing in a film along the heating tube wall for heat transfer and evaporation. Its advantages include high heat transfer efficiency, fast evaporation rate, and short material residence time, making it particularly suitable for the evaporation of heat-sensitive substances. Distillation is an important method for organic solvent recovery. Due to the different relative volatility of the main carbonate solvents in the electrolyte, multi-stage series distillation can achieve the gradual separation of mixed solvents, obtaining products that meet purity requirements and achieving the goal of recycling.

[0013] Existing treatment processes primarily rely on direct incineration. Carbonate-based organic solvents are incinerated into carbon dioxide and water, while lithium salts, after incineration and alkali absorption, are used as building materials. Therefore, current processes cannot achieve the recycling of lithium resources and carbonate solvents, resulting in a significant waste of resources. Summary of the Invention

[0014] To address the aforementioned problems, this invention discloses a method for separating lithium salts and carbonate organic solvents from waste electrolytes of lithium batteries, thereby achieving the recovery of lithium resources and organic solvents.

[0015] To achieve the above objectives, the technical solution of the present invention is as follows:

[0016] A method for separating lithium salts and carbonate organic solvents from waste electrolyte of lithium batteries includes the following steps:

[0017] Step 1: The waste electrolyte of lithium battery is separated into light components and heavy components by passing it through a thin film evaporator. The light components include any one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, and hydrofluoric acid. The heavy components include any one or more of propylene carbonate and ethylene carbonate containing lithium salts and some high-boiling-point propylene carbonate.

[0018] Step 2: Transfer the light component obtained in step (1) into a neutralization vessel, heat it to 50-60℃, add water and alkali, adjust the pH value to 7-8, mix thoroughly for 0.5h, let it stand for 0.5h, and then separate the water layer to obtain a carbonate solvent without hydrofluoric acid.

[0019] Step 3: The carbonate solvent without hydrofluoric acid obtained in step (2) is put into the distillation system for further distillation and purification.

[0020] Step 4: The heavy components obtained in step (1) are put into a high-temperature incineration system at 800-1000℃. After high-temperature incineration for 3-5 hours, the residual organic solvent is decomposed into carbon dioxide and water. After high-temperature incineration, lithium hexafluorophosphate is decomposed into lithium fluoride solid and any one of the following gases: phosphorus pentafluoride, phosphorus trifluoride, and hydrogen fluoride. After the gas is absorbed by the alkali absorption tower, inorganic salt is obtained.

[0021] Furthermore, the evaporation temperature of the thin-film evaporator in step (1) is 130-160℃, and the working pressure is 5-10kpa.

[0022] Furthermore, the thin-film evaporator is a scraped-film evaporator and / or a hinged-film evaporator.

[0023] Furthermore, the alkali mentioned in step (2) is any one or more of ammonia, sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate, triethylamine, and dimethylamine. The amount of alkali added is 1-5% of the mass of the carbonate solvent, and the amount of water added is 5-10% of the mass of the carbonate solvent.

[0024] Furthermore, the preferred incineration temperature of the high-temperature incineration system in step (3) is 900°C, and the preferred incineration time is 3-5 hours.

[0025] This invention also provides a process flow for a waste electrolyte treatment system, as per [reference]. Figure 1 As shown, the waste electrolyte is first stored in a raw material tank, then pumped into a thin-film evaporator for evaporation and separation into light and heavy components. The light components are condensed by a condenser and then enter a light component receiving tank. They are then transferred in batches to a neutralization vessel via a light component transfer pump for neutralization. After passing through a filter, the light components are temporarily stored in a solvent transfer tank and then pumped into a distillation system via a solvent transfer pump. The heavy components enter a heavy component final tank and are then transferred in batches to an incineration system for incineration.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Compared with existing direct incineration processes, this invention achieves simultaneous recovery of lithium salts and carbonate organic solvents, avoiding the loss of lithium resources and realizing the recycling of carbonate solvents;

[0028] 2. The thin-film evaporator used in this invention is a scraped-film evaporator or a hinged-film evaporator. Its characteristics are that the material liquid flows in a film along the heating tube wall for heat transfer and evaporation, with high heat transfer efficiency, fast evaporation speed and short material residence time. Therefore, it is particularly suitable for the evaporation of heat-sensitive substances, which greatly reduces the decomposition of lithium hexafluorophosphate and reduces the occurrence of side reactions. Attached Figure Description

[0029] Figure 1A simplified process flow diagram of the waste electrolyte treatment system provided in an embodiment of the present invention;

[0030] Figure 2 This is a typical gas phase spectrum of the waste electrolyte of this invention.

[0031] List of identifiers in attached diagrams:

[0032] 1. Raw material storage tank; 2. Raw material pump; 3. Thin film evaporator; 4. Light component condenser; 5. Light component receiving tank; 6. Heavy component receiving tank; 7. Light component transfer pump; 8. Heavy component transfer pump; 9. Neutralization vessel; 10. Filter; 11. Solvent transfer tank; 12. Solvent delivery pump. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0034] Example 1

[0035] The main components of a waste electrolyte, after analysis using gas chromatography and ion chromatography, are shown in Table 2 below.

[0036] As shown:

[0037]

[0038] A thin-film evaporator was used to separate lithium salts and carbonate solvents. The process conditions were as follows: the heat exchange area of ​​the thin-film evaporator was 1 m². 2 10m³ primary condenser 2 The cooling medium is circulating water, and the secondary condenser is 10m². 2 The cooling medium is low-temperature water (-10℃), the equipment material is Monel 400 alloy, the distributor is hinged, the rotation speed is 60 rpm, the jacket is heated by 140℃ heat transfer oil, the pressure is 8 kPa (absolute pressure), the feed flow rate is 200 L / h, after a feed rate of 1000 kg, the mass of the light component is approximately 805 kg and the mass of the heavy component is approximately 147 kg, with a volatilization loss of 48 kg. Its composition is shown in Table 3 below:

[0039]

[0040] Take 800 kg of the above light component and add it to a neutralization vessel. Heat the vessel to 50°C, add 50 kg of water, and mix thoroughly. Then add 33 kg of sodium carbonate, adjust the pH to 7-8, and stir thoroughly for 0.5 h. After standing for 0.5 h, separate the lower water layer. Ion chromatography analysis shows that the fluoride ion content in the organic phase is ≤5 ppm. The process parameters for distillation separation of the mixed solvent are shown in Table 4 below.

[0041]

[0042] Take 50 kg of the above-mentioned heavy components and add them to a high-temperature incinerator for thermal pyrolysis. The incinerator temperature is 900℃. After continuous incineration for 3 hours, cool to room temperature. The remaining substance is a white powder. According to the analytical method in GBT 4293-1984, the sodium fluoride content is ≥95%, which meets the requirements of industrial products.

[0043] Example 2

[0044] The main components of a waste electrolyte, after analysis using gas chromatography and ion chromatography, are shown in Table 5 below:

[0045]

[0046] A thin-film evaporator was used to separate lithium salts and carbonate solvents. The process conditions were as follows: the heat exchange area of ​​the thin-film evaporator was 1 m². 2 10m³ primary condenser 2 The cooling medium is circulating water. The secondary condenser is 10m², using low-temperature water (-10℃). The equipment is made of Monel 400 alloy, with a scraper-type distributor operating at 40rpm. The jacket is heated by 140℃ heat transfer oil. The pressure is 6kPa (absolute pressure). The feed flow rate is 180L / h. After a feed rate of 1000kg, the light component weighs approximately 791kg and the heavy component weighs approximately 181kg, with a volatilization loss of 66kg. The composition is shown in Table 6 below.

[0047]

[0048] Take 700 kg of the above light component and add it to a neutralization vessel. Heat the vessel to 50°C, add 40 kg of water, and mix thoroughly. Then add 21 kg of sodium carbonate, adjust the pH to 7-8, and stir thoroughly for 0.5 h. After standing for 0.5 h, separate the lower water layer. Ion chromatography analysis shows that the fluoride ion content in the organic phase is ≤5 ppm. The process parameters for distillation separation of the mixed solvent are shown in Table 7 below.

[0049]

[0050] Take 50 kg of the above-mentioned heavy components and add them to a high-temperature incinerator for thermal pyrolysis. The incinerator temperature is 900℃. After continuous incineration for 3 hours, cool to room temperature. The remaining substance is a white powder. According to the analytical method in GBT 4293-1984, the sodium fluoride content is ≥95%, which meets the requirements of industrial products.

[0051] Example 3

[0052] The process flow of the waste electrolyte treatment system in this embodiment of the invention is as follows: Figure 1As shown, the waste electrolyte is first stored in the raw material tank 1, and then enters the thin film evaporator 3 via the raw material pump 2 for evaporation and separation into light components and heavy components. The light components are condensed by the condenser 4 and then enter the light component receiving tank 5. They are then transferred in batches to the neutralization vessel 9 via the light component transfer pump 7 for neutralization treatment. After passing through the filter 10, they are temporarily stored in the solvent transfer tank 11 and then sent to the distillation system via the solvent transfer pump 12. The heavy components enter the heavy component receiving tank 6 and are then sent in batches to the incineration system for incineration treatment.

[0053] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for separating lithium salts and carbonate-based organic solvents from spent electrolyte of lithium batteries, characterized by: The method comprises the following steps: (1) The lithium battery waste electrolyte is separated into light components and heavy components by a thin film evaporator, wherein the light components comprise multiple carbonic acid ester solvents in carbonic acid dimethyl ester, carbonic acid methyl ethyl ester, carbonic acid diethyl ester, carbonic acid propylene ester and carbonic acid vinyl ester, and hydrogen fluoride acid, and the heavy components comprise lithium salt and part of high-boiling-point carbonic acid propylene ester and carbonic acid vinyl ester; (2) The light components obtained in step (1) are transferred into a neutralization kettle, and water and alkali are added to adjust the pH value to 7-8, and the mixture is fully mixed for 0.5 h, and the water layer is separated after standing for 0.5 h to obtain carbonic acid ester solvents without hydrogen fluoride acid, wherein the alkali is any one or more of ammonia, sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, potassium bicarbonate, calcium bicarbonate or triethylamine, and dimethylamine; (3) The carbonic acid ester solvents without hydrogen fluoride acid obtained in step (2) are subjected to subsequent rectification and purification in a rectification system; (4) The heavy components obtained in step (1) are subjected to high-temperature incineration in a high-temperature incineration system with an incineration temperature of 800-1000℃, and after high-temperature treatment for 3-5 h, the residual organic solvents are decomposed into carbon dioxide and water after incineration, and lithium hexafluorophosphate is decomposed into lithium fluoride solid and any one or more of phosphorus pentafluoride, trifluoro phosphine oxide and hydrogen fluoride gas after high-temperature incineration, and the gas is absorbed by an alkali absorption tower to obtain inorganic salt.

2. The method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte according to claim 1, characterized in that: The evaporation temperature of the thin film evaporator in step (1) is 130-160℃, and the working pressure is 5-10kpa.

3. The method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte according to claim 1, characterized in that: The thin film evaporator is a scraper type thin film evaporator and / or a hinged type thin film evaporator.

4. The method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte according to claim 1, characterized in that: The addition amount of the alkali in step (2) is 1-5% of the mass of the light components, and the addition amount of the water is 5-10% of the mass of the light components.

5. The method for separating lithium salt and carbonate organic solvent from lithium battery waste electrolyte according to claim 1, characterized in that: The incineration temperature of the incineration system in step (3) is 900℃, and the incineration time is 3-5 h.

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