Eutectic solvent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery recovery, and discloses a deep eutectic solvent as well as a preparation method and application thereof. The eutectic solvent is prepared from the following components: polyol, organic acid and water, the molar ratio of the polyol to the organic acid to the water is (4-10): 1: (2-160). Compared with a conventional two-component mixture, the eutectic solvent provided by the invention has the advantages that the viscosity of a solvent system is reduced after water is added, and leaching and recovery of metal are facilitated; according to the recovery method of the lithium cobalt oxide, the deep eutectic solvent is adopted for carrying out leaching and solid-liquid separation on the lithium cobalt oxide, so that lithium and cobalt can be recovered, the leaching rate of the lithium is close to 100%, the cobalt is converted into cobalt oxalate dihydrate with high purity in a precipitation form, the leaching efficiency of the lithium and the cobalt is high, and the separation effect is good; when the recovery method of the eutectic solvent and the lithium cobalt oxide is applied to the recovery of the waste lithium ion battery, the valuable metal elements lithium and cobalt in the positive electrode material can be recovered, the resource waste is reduced, and the environmental pollution is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling, and particularly relates to a deep eutectic solvent and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have excellent electrochemical performance, are widely used, and have a large market demand. With the increase in their production, the number of waste batteries has also increased. Waste lithium-ion batteries contain harmful substances such as electrolytes and heavy metals. If not properly treated, they will have an adverse impact on the environment and human health. In addition, the cathode materials of waste lithium-ion batteries contain valuable metal elements such as Li, Ni, Co, and Mn. Therefore, the recycling of waste lithium-ion batteries is crucial for environmental sustainability and alleviating resource shortages.

[0003] At present, the main methods for recycling waste lithium-ion batteries are pyrometallurgy and hydrometallurgy. Among them, pyrometallurgy has the advantages of large processing capacity, simple operation, and large recycling scale, and is widely used in the industrial recycling of waste lithium-ion batteries, but it has problems such as high energy consumption and large environmental pollution. Hydrometallurgy is a process in which valuable metals in the cathode materials of waste lithium-ion batteries are dissolved in a solution or precipitated in a new solid phase through acid leaching or alkali leaching, and then the metal components are recovered through extraction and precipitation. It has the advantages of low energy consumption and simple process flow, but requires a large amount of extractants and precipitants, and will increase the number of metal types in the solution, making the subsequent reactions complicated. Therefore, it is urgent to develop a green and efficient method for recycling waste lithium-ion batteries.

[0004] Deep eutectic solvents (DESs) are a new type of green solvent composed of hydrogen bond donors and hydrogen bond acceptors, with the characteristics of biodegradability, high-temperature chemical stability, easy preparation, and customizability, and have been widely used in fields such as catalytic chemistry, organic synthesis, and electrochemistry. In the absence of reducing agents or extractants, deep eutectic solvents also have excellent solubility for metal oxides, so they have the potential to be applied in the field of lithium battery recycling. However, deep eutectic solvents usually have high viscosities, making the recovery of metals after leaching a difficult problem, and steps such as extraction and precipitation are required, increasing the difficulty of recovering valuable metals. Summary of the Invention

[0005] The present invention aims to at least solve one of the above technical problems existing in the prior art. For this reason, one of the purposes of the present invention is to provide a deep eutectic solvent; the second purpose of the present invention is to provide a preparation method of this deep eutectic solvent; the third purpose of the present invention is to provide a method for recycling lithium cobaltate; the fourth purpose of the present invention is to provide the application of the deep eutectic solvent or the method for recycling lithium cobaltate.

[0006] In order to achieve the above purposes, the technical solutions adopted by the present invention are:

[0007] The first aspect of the present invention provides a deep eutectic solvent, comprising the following components: polyol, organic acid and water;

[0008] The molar ratio of the polyol, organic acid and water is (4 - 10):1:(2 - 160).

[0009] In some embodiments of the present invention, the deep eutectic solvent consists of polyol, organic acid and water.

[0010] In some embodiments of the present invention, the molar ratio of the polyol, organic acid and water is (4 - 8):1:(16 - 80).

[0011] In some specific embodiments of the present invention, the molar ratio of the polyol, organic acid and water is (4 - 6):1:(16 - 48).

[0012] In some embodiments of the present invention, the polyol is selected from at least one of glycerol, ethylene glycol, butanediol, xylitol.

[0013] In some specific embodiments of the present invention, the polyol is glycerol.

[0014] In some embodiments of the present invention, the organic acid is selected from at least one of oxalic acid, phenylacetic acid, malic acid, citric acid, succinic acid.

[0015] In some specific embodiments of the present invention, the organic acid is oxalic acid.

[0016] The second aspect of the present invention provides a preparation method of the deep eutectic solvent according to the first aspect of the present invention, comprising the following steps:

[0017] Under heating conditions, first mix the polyol and the organic acid, and then add water and continue to mix to obtain the deep eutectic solvent.

[0018] In some embodiments of the present invention, the heating temperature is 60 - 80 °C.

[0019] In some specific embodiments of the present invention, the heating temperature is 65 - 75 °C.

[0020] In some embodiments of the present invention, the heating method is water bath heating.

[0021] In some embodiments of the present invention, the mixing time of the polyol and the organic acid is 0.5 - 1.5 h.

[0022] In some embodiments of the present invention, the mixing time after adding water and continuing to mix is 0.5 - 1.5 h.

[0023] In some embodiments of the present invention, the mixing process is assisted by stirring, and the stirring speed is 300-500 r / min.

[0024] The third aspect of the present invention provides a method for recycling lithium cobaltate, which includes adding lithium cobaltate into the deep eutectic solvent described in the first aspect of the present invention, heating and reacting, and separating solid from liquid.

[0025] In some embodiments of the present invention, the solid-liquid ratio of lithium cobaltate to the deep eutectic solvent is (10-80) g:1 L.

[0026] In some specific embodiments of the present invention, the solid-liquid ratio of lithium cobaltate to the deep eutectic solvent is (10-40) g:1 L.

[0027] In some embodiments of the present invention, the temperature of the heating reaction is 80-120 °C, and the time is 5-120 min.

[0028] In some specific embodiments of the present invention, the temperature of the heating reaction is 100-120 °C, and the time is 45-120 min.

[0029] In some embodiments of the present invention, the heating reaction process is assisted by stirring, and the stirring speed is 700-900 r / min.

[0030] In some embodiments of the present invention, the heating method is oil bath heating.

[0031] When the deep eutectic solvent provided by the present invention is used for the recycling of lithium cobaltate, polyol acts as a hydrogen bond acceptor to enhance the ability to provide protons, and organic acid acts as a hydrogen bond donor to provide hydrogen ions, while providing reduction ability and complexing ability. It reduces the high-valent cobalt to a low-valent state and complexes to form cobalt oxalate precipitate for separation from lithium. Water can effectively reduce the viscosity of the system and reduce the dosage of reagents, realizing the efficient separation and recycling of lithium and cobalt.

[0032] The fourth aspect of the present invention provides the application of the deep eutectic solvent described in the first aspect of the present invention, or the method for recycling lithium cobaltate described in the third aspect, in the recycling of waste lithium-ion batteries.

[0033] In some embodiments of the present invention, the recycling of waste lithium-ion batteries specifically includes the following steps:

[0034] Disassemble the waste lithium-ion battery, strip the lithium cobaltate from the positive electrode material, crush it to obtain lithium cobaltate powder, soak it in the deep eutectic solvent, heat and react, separate solid from liquid, and recycle lithium and cobalt respectively.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1) The eutectic solvent provided by the present invention, compared with the conventional two-component mixture, can reduce the viscosity of the solvent system after adding water, thus being more conducive to the leaching and recovery of metals;

[0037] 2) The preparation method of the eutectic solvent provided by the present invention has simple steps, the material components are cheap and easy to obtain, and it is environmentally friendly;

[0038] 3) The recovery method of lithium cobaltate provided by the present invention uses the eutectic solvent to leach lithium cobaltate and perform solid-liquid separation, then the recovery of lithium and cobalt can be achieved. The leaching rate of lithium is close to 100%, and cobalt is converted into cobalt oxalate dihydrate with high purity in the form of precipitation, and the separation effect of lithium and cobalt is good;

[0039] 4) When the recovery method of the eutectic solvent and lithium cobaltate provided by the present invention is applied to the recovery of waste lithium-ion batteries, valuable metal elements lithium and cobalt in the positive electrode material can be recovered, reducing resource waste and environmental pollution. Description of the Drawings

[0040] Figure 1 For the leaching rate results of lithium and cobalt in the filtrate of Example 1;

[0041] Figure 2 For the infrared detection results of glycerol-oxalic acid eutectic solvent in Example 1;

[0042] Figure 3 For the leaching rate results of lithium and cobalt in the filtrate of Example 2;

[0043] Figure 4 For the leaching rate results of lithium and cobalt in the filtrate of Example 3;

[0044] Figure 5 For the leaching rate results of lithium and cobalt in the filtrate of Example 4;

[0045] Figure 6 For the leaching rate results of lithium and cobalt in the filtrate of Example 5;

[0046] Figure 7 For the XRD test results of the solid-phase product in the application example. Detailed Description of the Invention

[0047] The content of the present invention will be further described in detail through specific examples below. The raw materials, reagents or devices used in the examples can be obtained from conventional commercial channels or can be obtained by existing technical methods without special instructions. Unless otherwise specified, the test or measurement methods are all conventional methods in the art.

[0048] Example 1

[0049] In this example, oxalic acid and glycerol are taken as examples to explore the optimal molar ratio of polyol and organic acid in the eutectic solvent:

[0050] Glycerol was added to oxalic acid, and the molar ratios of glycerol to oxalic acid were 4:1, 6:1, 8:1, and 10:1, respectively. The mixture was heated and stirred in a water bath at 70 °C for 1 h at a rotation speed of 400 r / min to obtain anhydrous glycerol-oxalic acid deep eutectic solvent (G-DES) with different molar ratios. Lithium cobaltate powder was added to the glycerol-oxalic acid deep eutectic solvent according to a solid-liquid ratio of 20 g:1 L, and the mixture was heated and stirred in an oil bath at 110 °C for 2 h at a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation, and the leaching rates of lithium and cobalt in the filtrate were detected.

[0051] Figure 1 For the results of the leaching rates of lithium and cobalt in the filtrate of Example 1, from Figure 1 it can be seen that when the molar ratio of glycerol to oxalic acid is 4:1, the leaching rate of lithium (Li) is 84%, and the leaching rate of cobalt (Co) is 0.88%. At this time, the separation efficiency of lithium and cobalt is the best. As the molar ratio of glycerol to oxalic acid increases, the leaching rate of lithium gradually decreases, the leaching rate of cobalt gradually increases, and the separation effect of lithium and cobalt becomes worse.

[0052] Figure 2 For the infrared detection results of the glycerol-oxalic acid deep eutectic solvent in Example 1, from Figure 2 it can be seen that the glycerol-oxalic acid deep eutectic solvent still retains the characteristic peaks of glycerol and oxalic acid. Among them, the vibration peak of -OH moves from 3510 cm -1 of oxalic acid and 3290 cm -1 of glycerol to 3380 cm -1 , and the characteristic peak of -OH becomes wider and larger, indicating that the intramolecular hydrogen bond of the components of the glycerol-oxalic acid deep eutectic solvent weakens, while the intermolecular hydrogen bond strengthens, confirming that glycerol and oxalic acid have successfully formed a deep eutectic solvent.

[0053] Example 2

[0054] This example explores the optimal molar ratios of polyols, organic acids, and water in the deep eutectic solvent:

[0055] Under the condition of heating in a water bath at 70 °C, glycerol and oxalic acid were first mixed and stirred for 1 h at a rotation speed of 400 r / min, and then water was added and the mixture was continuously stirred for 1 h with the rotation speed maintained at 400 r / min to obtain a deep eutectic solvent. Among them, the molar ratios of glycerol, oxalic acid, and water were 4:1:2, 4:1:4, 4:1:8, 4:1:16, 4:1:32, 4:1:48, 4:1:80, and 4:1:160, respectively.

[0056] Lithium cobaltate powder was added to the above-mentioned eutectic solvent according to a solid-liquid ratio of 20 g:1 L, heated and stirred in an oil bath at 110 °C for 2 h, with a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation, and the leaching rates of lithium and cobalt in the filtrate were detected.

[0057] Figure 3 For the results of the leaching rates of lithium and cobalt in the filtrate of Example 2, from Figure 3 it can be seen that when the amount of water added gradually increases, the leaching rate of lithium gradually rises. When the molar ratio of glycerol, oxalic acid and water is 4:1:16, the leaching rate of lithium remains at about 98%. When the molar ratio of glycerol, oxalic acid and water is 4:1:160, the leaching rate of lithium drops to 82%, while the leaching rate of cobalt increases from 0.8% to 3%. This indicates that when the amount of water used is excessive, it will damage the structure of the eutectic dissolution, resulting in a worse separation effect of lithium and cobalt.

[0058] Example 3

[0059] This example explores the optimal solid-liquid ratio when the eutectic solvent is used for the recovery of lithium cobaltate:

[0060] Lithium cobaltate powder was added to the eutectic solvent (molar ratio of glycerol, oxalic acid and water is 4:1:16) according to solid-liquid ratios of 10 g:1 L, 20 g:1 L, 40 g:1 L and 80 g:1 L respectively, heated and stirred in an oil bath at 110 °C for 2 h, with a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation, and the leaching rates of lithium and cobalt in the filtrate were detected.

[0061] Figure 4 For the results of the leaching rates of lithium and cobalt in the filtrate of Example 3, from Figure 4 it can be seen that when the solid-liquid ratio is 20 g:1 L, the leaching rate of lithium is 98% and the leaching rate of cobalt is 0.7%. At this time, the separation effect of lithium and cobalt is the best; when the solid-liquid ratio gradually increases, the leaching rate of lithium gradually decreases, and the leaching rate of cobalt first decreases and then increases, and the overall separation effect of lithium and cobalt becomes worse.

[0062] Example 4

[0063] This example explores the optimal leaching time when the eutectic solvent is used for the recovery of lithium cobaltate:

[0064] Lithium cobaltate powder was added to the eutectic solvent (molar ratio of glycerol, oxalic acid and water is 4:1:16) according to a solid-liquid ratio of 20 g:1 L, and heated and stirred in an oil bath at 110 °C for 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 45 min, 60 min, 90 min and 120 min respectively, with a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation, and the leaching rates of lithium and cobalt in the filtrate were detected.

[0065] Figure 5 For the leaching rate results of lithium and cobalt in the filtrate of Example 4, it can be seen from Figure 5 that when the leaching time is greater than 45 min, the leaching rate of lithium can reach more than 90%, and shows a gradually increasing trend, while the leaching rate of cobalt gradually decreases. When the leaching time is 2 h, the leaching rate of lithium is 98% and the leaching rate of cobalt is 0.5%. At this time, the separation effect of lithium and cobalt is the best.

[0066] Example 5

[0067] This example explores the optimal leaching temperature when using deep eutectic solvents for the recovery of lithium cobaltate:

[0068] Lithium cobaltate powder was added to the deep eutectic solvent (the molar ratio of glycerol, oxalic acid and water is 4:1:16) according to the solid-liquid ratio of 20 g:1 L, and heated and stirred in an oil bath at 80 °C, 90 °C, 100 °C, 110 °C and 120 °C for 120 min, with a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation, and the leaching rates of lithium and cobalt in the filtrate were detected.

[0069] Figure 6 For the leaching rate results of lithium and cobalt in the filtrate of Example 5, it can be seen from Figure 6 that when the leaching temperature is greater than or equal to 100 °C, the leaching rate of lithium can reach more than 90%, and shows a gradually increasing trend, while the leaching rate of cobalt gradually decreases. When the leaching temperature is 110 °C, the leaching rate of lithium is 98% and the leaching rate of cobalt is 0.7%. At this time, the separation effect of lithium and cobalt is the best.

[0070] Application Example

[0071] S1. Under the condition of heating and stirring in a water bath at 70 °C, glycerol and oxalic acid were mixed, and then water was added and mixed continuously to obtain a deep eutectic solvent. Among them, the molar ratio of glycerol, oxalic acid and water is 4:1:16, the mixing time of glycerol and oxalic acid is 1 h, the mixing time after adding water is 1 h, and the stirring speed is 400 r / min;

[0072] S2. The waste lithium-ion battery was disassembled, the lithium cobaltate in the positive electrode material was peeled off, and the lithium cobaltate powder was obtained by crushing. The lithium cobaltate powder was added to the deep eutectic solvent according to the solid-liquid ratio of 20 g:1 L, and heated and stirred in an oil bath at 110 °C for 120 min, with a rotation speed of 800 r / min. After the reaction was completed, suction filtration was carried out for solid-liquid separation to achieve the leaching and separation of lithium and cobalt.

[0073] Figure 7 For the XRD test results of the solid-phase product in the application example, it can be seen from Figure 7It can be seen that the solid-phase product obtained by solid-liquid separation is cobalt oxalate dihydrate with relatively high purity. That is, the high-valence cobalt in lithium cobaltate has been reduced to a low valence state and complexed to form cobalt oxalate precipitation, while lithium is leached out and in the liquid phase. Through solid-liquid separation, the separation of lithium and cobalt can be achieved.

Claims

1. A deep eutectic solvent, characterized in that The invention comprises the following components: polyol, organic acid and water; The molar ratio of the polyol, the organic acid and water is (4-10):1:(2-160).

2. The deep eutectic solvent according to claim 1, characterized in that The molar ratio of the polyol, the organic acid and water is (4-8):1:(16-80).

3. The deep eutectic solvent according to claim 1 or 2, characterized in that The polyol is selected from at least one of glycerol, ethylene glycol, butylene glycol and xylitol.

4. The deep eutectic solvent according to claim 1 or 2, characterized in that The organic acid is selected from at least one of oxalic acid, phenylacetic acid, malic acid, citric acid and succinic acid.

5. The method for preparing the deep eutectic solvent according to any one of claims 1 to 4, characterized in that: The following steps are involved: Under heating conditions, the polyol and the organic acid are first mixed, and then water is added and mixed continuously to obtain the low eutectic solvent.

6. The preparation method according to claim 5, characterized in that: The heating temperature is 60-80°C.

7. A method for recovering lithium cobalt oxide, characterized in that: The method comprises adding lithium cobalt oxide to the low eutectic solvent according to any one of claims 1 to 4, heating for reaction, and solid-liquid separation.

8. The recycling method according to claim 7, characterized in that: The solid-to-liquid ratio of the lithium cobalt oxide to the low eutectic solvent is (10-80) g:1L.

9. The recycling method according to claim 7, characterized in that: The temperature of the heating reaction is 80-120° C. and the time is 5-120 min.

10. Use of the low eutectic solvent according to any one of claims 1 to 4, or the lithium cobalt oxide recovery method according to any one of claims 7 to 9 in the recovery of waste lithium-ion batteries.

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