A method for efficiently extracting active lithium from the negative electrode of waste lithium batteries

Abstract

The present invention belongs to the technical field of lithium battery recycling, and more specifically, relates to a method for efficiently extracting active lithium from the negative electrode of a waste lithium battery. First, a solvent capable of dissolving the SEI film is used to treat the SEI film on the surface of the negative electrode of the lithium battery, so that holes or solubility damage appear in the SEI film; then, a weakly polar solvent is used to dissolve polycyclic aromatic hydrocarbons to obtain a recovery liquid to soak the negative electrode of the lithium battery with the damaged SEI film, and the lithium in the negative electrode of the lithium battery is extracted by using the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons. Compared with the use of a strong polar organic solvent to dissolve polycyclic aromatic hydrocarbons, the present invention uses a weakly polar organic solvent to dissolve the polycyclic aromatic hydrocarbons to extract lithium. Due to the weak Lewis alkalinity of the solvent, the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons can be retained, thereby ensuring that it has a strong interaction with the lithium element in the negative electrode, which significantly improves the lithium leaching rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recycling, and more specifically, relates to a method for efficiently extracting active lithium from the negative electrode of waste lithium batteries. Background Art

[0002] The recycling of waste lithium-ion batteries has high economic and social benefits. Lithium in the electrode mainly exists in the form of a single substance rather than lithium ions, and the solvent can only react with lithium ions but not directly with lithium single substances, so the solvent cannot directly extract the lithium single substance from the negative electrode.

[0003] Patent document CN 113061726A disassembles waste lithium batteries, first performs plasma treatment on the electrode sheets, then uses a strong polar organic solvent to dissolve polycyclic aromatic hydrocarbons as a leaching solution, and leaches lithium from the lithium negative electrode under heating conditions. However, even under the condition of a leaching time of up to 2-10 hours, the lithium extraction rate is difficult to reach 90%, and the extraction efficiency is low. How to further improve the lithium extraction efficiency of polycyclic aromatic hydrocarbons is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a method for efficiently extracting active lithium from the negative electrode of waste lithium batteries, so as to solve the technical problems of the prior art such as low efficiency of lithium extraction through polycyclic aromatic hydrocarbons.

[0005] To achieve the above-mentioned purpose, the present invention provides a method for efficiently extracting active lithium from the negative electrode of waste lithium batteries. First, the SEI film on the surface of the negative electrode of the lithium battery is treated with a solvent that can dissolve the SEI film, so that holes appear in the SEI film or the solubility is damaged, thereby obtaining a negative electrode of the lithium battery with a damaged SEI film; then, the negative electrode of the lithium battery with a damaged SEI film is immersed in a recovery liquid obtained by dissolving polycyclic aromatic hydrocarbons in a weakly polar solvent with a dielectric constant less than 7, and the lithium in the negative electrode of the lithium battery is extracted by utilizing the electron-withdrawing effect of the large π bonds of the polycyclic aromatic hydrocarbons.

[0006] Preferably, the method comprises the following steps:

[0007] (1) After charging, the recycled waste lithium batteries are disassembled in a safe environment and the negative electrode sheets are separated;

[0008] (2) soaking, separating and drying the negative electrode sheet in step (1) in sequence using a cleaning agent to obtain a preliminarily treated negative electrode sheet; the cleaning agent comprises a first organic solvent capable of dissolving the SEI film;

[0009] (3) soaking the preliminarily treated negative electrode sheet in a recovery liquid containing polycyclic aromatic hydrocarbons to obtain a lithium-containing composite liquid; the recovery liquid contains a second organic solvent, the second organic solvent is used to dissolve the polycyclic aromatic hydrocarbons, and the second organic solvent is a weakly polar organic solvent with a dielectric constant of less than 7;

[0010] (4) separating the lithium-containing composite liquid into a solid-liquid state to obtain a lithium-containing enriched liquid.

[0011] Preferably, the safe environment in step (1) is an environment with a dew point of -50°C or below, or an environment with a relative humidity of less than 20%, more preferably an environment with a relative humidity of less than 10%.

[0012] Preferably, the first organic solvent is selected from carbonate solvents, phosphate solvents, nitrile solvents, carboxylate solvents and sulfone solvents.

[0013] Further preferably, the first organic solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, methyl propyl carbonate, ethyl propyl carbonate, triethyl phosphate, trimethyl phosphate, diethyl ethyl phosphate, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, ethyl acetate, methyl acetate, propyl acetate, sulfolane and dimethyl sulfoxide.

[0014] Preferably, the polycyclic aromatic hydrocarbon has 10 to 30 carbon atoms and contains 2 to 4 benzene rings; further preferably, it is selected from biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene, perylene, pyridine, bipyridine, thiophene, quinoline, isoquinoline, carbazole, pyrimidine, pteridine, acridine, phenazine, pyrazine and phenothiazine.

[0015] Preferably, the second organic solvent is selected from one or more of ether, ester and aromatic organic solvents with a dielectric constant less than 7, and more preferably one or more of ether and ester organic solvents with a dielectric constant less than 7.

[0016] Preferably, the second organic solvent is one or more of methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, ethyltetrahydrofuran, diethyltetrahydrofuran, phenyltetrahydrofuran, cyclopentyl methyl ether, hexafluoroisopropyl methyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl ether-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, tris(2,2,2-trifluoroethyl)orthoformate, fluorobenzene, chlorobenzene, bromobenzene, difluorobenzene, trifluorobenzene, hexafluorobenzene and trifluorotoluene.

[0017] Preferably, the concentration of PAHs in the recovery liquid in step (3) is 0.01 to 7 mol / L, more preferably 0.5 to 2 mol / L.

[0018] Preferably, the immersion temperature during the immersion treatment in step (3) is 20 to 80° C., the molar ratio of the lithium element in the preliminary treated negative electrode sheet to the polycyclic aromatic hydrocarbons in the recovery liquid is 1:1 to 3, the solid-liquid ratio of the immersion treatment is 1:1 to 3, and the immersion time is 0.5 to 2 hours.

[0019] In general, the above technical solution conceived by the present invention has the following advantages compared with the prior art:

[0020] Beneficial effects:

[0021] (1) The present invention first uses a solvent capable of dissolving the SEI film (solid electrolyte interface) to dissolve or partially dissolve and destroy the SEI film on the surface of the negative electrode, thereby opening a lithium extraction channel in the negative electrode, thereby significantly shortening the lithium extraction time.

[0022] (2) The present invention uses a weakly polar solvent to dissolve substituted or unsubstituted polycyclic aromatic hydrocarbons, which can retain the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons, ensure that it has a strong interaction with the lithium element in the negative electrode, and realize the discovery that the lithium extraction rate can be improved, and the lithium content extracted from the polycyclic aromatic hydrocarbons in a unit volume of solvent is greatly increased, thereby improving the lithium extraction efficiency.

[0023] (3) The present invention can efficiently and conveniently separate lithium from other substances. The entire process avoids high energy consumption and the use of corrosive chemical reagents. The processing process is simple to operate, highly safe, and has good compatibility with existing battery processes. It has low equipment requirements, is conducive to industrialization, and is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of the method for recovering active lithium from the negative electrode of waste lithium batteries. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] The prior art utilizes dissolved polycyclic aromatic hydrocarbons to extract active lithium from the negative electrode of a lithium-ion battery. The inventor of the present application has analyzed and speculated that it mainly relies on the large π bonds contained in the polycyclic aromatic hydrocarbons to react with the elemental lithium to extract the elemental lithium from the negative electrode. However, the prior art uses a highly polar solvent to dissolve substituted or unsubstituted polycyclic aromatic hydrocarbons. The highly polar solvent has a strong Lewis base and is easy to react with the large π bonds of the polycyclic aromatic hydrocarbons, thereby weakening the electron-accepting ability of the large π bonds, resulting in a weakening of the interaction between the large π bonds and the elemental lithium in the negative electrode, a decrease in the rate of extracting lithium, and a decrease in the content of lithium that can be extracted by the polycyclic aromatic hydrocarbons in a unit volume of solvent. In addition, since the surface of the negative electrode material is covered by a layer of solid electrolyte interface (abbreviated as: SEI film), the lithium extraction rate will be slowed down during the extraction process.

[0027] Based on the bottleneck of the prior art, the present invention first selects an organic solvent that can dissolve the SEI film to destroy the SEI film on the surface of the negative electrode, and then selects a weak polar solvent to dissolve the substituted or unsubstituted polycyclic aromatic hydrocarbons. Due to the weak Lewis basicity of the solvent, the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons can be retained, thereby ensuring that it has a strong interaction with the lithium element in the negative electrode. Experiments have found that this method of the present invention not only significantly improves the lithium leaching rate, but also greatly increases the lithium content extracted by the polycyclic aromatic hydrocarbons in the unit volume of solvent. The SEI membrane solvent mechanism is: the selected solvent can dissolve the organic components on the outer surface of the SEI membrane, so that the SEI membrane has holes, the contact with the negative electrode is weakened, and it becomes loose, thereby opening the lithium extraction channel and accelerating the extraction rate.

[0028] Specifically, the present invention provides a method for efficiently extracting active lithium from the negative electrode of a waste lithium battery. First, a solvent capable of dissolving the SEI film is used to treat the SEI film on the surface of the negative electrode of the lithium battery, so that holes or solubility damage appear in the SEI film, thereby obtaining a negative electrode of the lithium battery with a damaged SEI film; then, a weakly polar solvent is used to dissolve polycyclic aromatic hydrocarbons to obtain a recovered liquid, and the negative electrode of the lithium battery with a damaged SEI film is immersed in the recovered liquid, and the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons is utilized to extract the lithium from the negative electrode of the lithium battery.

[0029] In some embodiments, the method of the present invention for efficiently extracting active lithium from the negative electrode of a waste lithium battery comprises the following steps:

[0030] (1) After charging, the recycled waste lithium batteries are disassembled in a safe environment and the negative electrode sheets are separated;

[0031] (2) soaking, separating and drying the negative electrode sheet in step (1) in sequence using a cleaning agent to obtain a preliminarily treated negative electrode sheet; the cleaning agent comprises a first organic solvent capable of dissolving the SEI film;

[0032] (3) soaking the negative electrode sheet treated preliminarily in a recovery solution containing polycyclic aromatic hydrocarbons to obtain a lithium-containing composite solution; the recovery solution contains a second organic solvent, the second organic solvent is used to dissolve the polycyclic aromatic hydrocarbons, and the second organic solvent is a weakly polar organic solvent;

[0033] (4) separating the lithium-containing composite liquid into a solid-liquid state to obtain a lithium-containing enriched liquid.

[0034] In some embodiments, the recycled waste batteries are charged with a small current to a fully charged state of 100% SOC; then the fully charged batteries are disassembled in a safe environment and the negative electrode sheets are sorted out. The safe environment in step (1) is an environment with a dew point of -50°C or below, or an environment with a relative humidity of less than 20%, preferably less than 10%. The waste batteries are batteries in any SOC state, SOC = 0 to 100%.

[0035] The negative electrode material used in the negative electrode sheet separated from the waste lithium battery of the present invention is a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, a phosphorus-containing negative electrode, a sulfur-containing negative electrode, a vanadium-based negative electrode or a lithium titanate negative electrode; wherein, the carbon-based negative electrode includes but is not limited to a lithium battery negative electrode made of one or more materials selected from natural graphite, artificial graphite, soft carbon, hard carbon, and mesophase carbon microspheres; the silicon-based negative electrode includes but is not limited to a lithium battery negative electrode made of one or more materials selected from silicon element, silicon alloy, and silicon monoxide. During the service of the lithium battery, active lithium is embedded in the negative electrode of the lithium battery. As the battery charge and discharge cycle proceeds, the embedded active lithium cannot be effectively extracted, resulting in battery failure. The present invention is to recover the active lithium from the negative electrode of such waste lithium battery. The positive electrode material of the waste lithium battery is one or more selected from layered positive electrode material, spinel positive electrode material, and olivine positive electrode material. Specifically, the positive electrode material of the waste battery can be selected from Li x CoO2、Li x FePO4、Li x Mn2O4、LiNi y Co z Mn I O2(y+z+I=1), LiNi y Co z Al I O2(y+z+I=1), Li x NiO2、Li x VO2、Li x CrO2、Li x CoMnO4、Li x NiMn3O8 and Li x Ni 0.5 Mn 1.5 One or more combinations of O4, where 0<x≤1.

[0036] In some embodiments, the first organic solvent capable of dissolving the SEI film is selected from carbonate solvents, phosphate ester solvents, nitrile solvents, carboxylate solvents and sulfone solvents, including but not limited to one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, methyl propyl carbonate, ethyl propyl carbonate, triethyl phosphate, trimethyl phosphate, diethyl ethyl phosphate, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, ethyl acetate, methyl acetate, propyl acetate, cyclopentane sulfone and dimethyl sulfoxide.

[0037] In some embodiments, the carbon number of the polycyclic aromatic hydrocarbons is 10 to 30, and it contains 2 to 4 benzene rings; specifically selected from biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene, perylene, pyridine, bipyridine, thiophene, quinoline, isoquinoline, carbazole, pyrimidine, pteridine, acridine, phenazine, pyrazine and phenothiazine. The polycyclic aromatic hydrocarbons are substituted or unsubstituted polycyclic aromatic hydrocarbons. When the polycyclic aromatic hydrocarbons contain substituents, they are substituted by 1 to 4 substituents, and the substituent groups include but are not limited to alkyl (carbon number 1 to 5, such as methyl, ethyl, propyl, butyl), hydroxyl, nitro, halogen atoms (F, Cl, Br, I), amino, carboxyl, aldehyde, carbonyl, etc.

[0038] The second organic solvent used to dissolve polycyclic aromatic hydrocarbons in the present invention is a weakly polar organic solvent with a dielectric constant less than 7, and the second organic solvent is selected from one or more organic solvents such as ethers, esters, and aromatics with a dielectric constant less than 7. The aromatic organic solvent with a dielectric constant less than 7 includes but is not limited to fluorobenzene, chlorobenzene, bromobenzene, difluorobenzene, trifluorobenzene, hexafluorobenzene, and trifluorotoluene; preferably, it is one or more of the ether and ester organic solvents with a dielectric constant less than 7, including but not limited to methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, ethyltetrahydrofuran, diethyltetrahydrofuran, phenyltetrahydrofuran, cyclopentyl methyl ether, hexafluoroisopropyl methyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl ether-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, tris(2,2,2-trifluoroethyl)orthoformate, etc.

[0039] In some embodiments, the concentration of PAHs in the recovery liquid of step (3) is 0.01-7 mol / L, preferably 0.5-2 mol / L.

[0040] In some embodiments, the immersion temperature during the immersion treatment in step (3) is 20-80° C., the molar ratio of the lithium element in the preliminary treated negative electrode sheet (the lithium content of each lithium battery can be obtained according to its factory capacity calibration) and the polycyclic aromatic hydrocarbons in the recovery liquid is 1:1-3, the solid-liquid ratio of the immersion treatment (the solid phase is the preliminary treated negative electrode sheet, in g; the liquid phase is the recovery liquid, in g) is 1:1-3, and the immersion time is 0.5-2h.

[0041] The following are examples:

[0042] Example 1

[0043] A method for efficiently extracting active lithium from the negative electrode of waste lithium batteries, such as Figure 1 As shown, follow the steps below:

[0044] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0045] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0046] (3) Soak the cut negative electrode sheet in acetonitrile solvent to remove the SEI film on the negative electrode surface for 0.5 h. Then take out the electrode sheet and dry it at 60°C;

[0047] (4) Prepare the recovery solution: add 15.4 g of biphenyl and 100 ml of methyltetrahydrofuran (dielectric constant 6.97) solvent into a beaker and stir until a uniform solution is formed (the concentration of biphenyl is 1 mol / L);

[0048] (5) The negative electrode sheet obtained in step (3) is placed in a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to biphenyl in the recovery liquid is 1:1.2, the leaching time is 0.5h, and after the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0049] Example 2

[0050] A method for efficiently extracting active lithium from the negative electrode of waste lithium batteries is carried out according to the following steps:

[0051] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0052] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0053] (3) Soak the cut negative electrode sheet in acetonitrile solvent to remove the SEI film on the negative electrode surface for 0.5 h. Then take out the electrode sheet and dry it at 60°C;

[0054] (4) Prepare the recovery solution: add 15.4 g of biphenyl and 100 ml of 2,5-dimethyltetrahydrofuran (dielectric constant 5.5) solvent into a beaker and stir until a uniform solution is formed (the concentration of biphenyl is 1 mol / L);

[0055] (5) placing the negative electrode sheet obtained in step (3) into a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to biphenyl in the recovery liquid is 1:1.2, the leaching time is 0.5 hour, and after the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0056] Comparative Example 1

[0057] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0058] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0059] (3) Prepare the recovery solution: add 15.4 g of biphenyl and 100 ml of methyltetrahydrofuran solvent into a beaker and stir until a uniform solution is formed (the concentration of biphenyl is 1 mol / L);

[0060] (4) placing the negative electrode sheet obtained in step (2) into a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to biphenyl in the recovery liquid is 1:1.2, the leaching time is 0.5 hour, and after the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0061] Comparative Example 2

[0062] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0063] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0064] (3) Prepare the recovery solution: add 15.4 g of biphenyl and 100 ml of methyltetrahydrofuran solvent into a beaker and stir until a uniform solution is formed (the concentration of biphenyl is 1 mol / L);

[0065] (4) placing the negative electrode sheet obtained in step (2) into a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to biphenyl in the recovery liquid is 1:1.2, the leaching time is 5 hours, and after the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0066] Comparative Example 3

[0067] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0068] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0069] (3) Immerse the cut negative electrode sheet in a cleaning agent acetonitrile solvent to remove the SEI film on the negative electrode surface, and then remove the electrode sheet and dry it;

[0070] (4) Prepare a recovery solution by adding 12.8 g of naphthalene and 100 ml of tetrahydrofuran solvent into a beaker and stirring until a uniform solution is formed (the concentration of naphthalene is 1 mol / L);

[0071] (5) placing the negative electrode sheet obtained in step (3) into a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to naphthalene in the recovery liquid is 1:1.1, the leaching time is 5 hours, and after the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0072] Comparative Example 4

[0073] (1) charging the used nickel-cobalt-manganese ternary lithium battery to 4.3V by constant current charging, and then charging again by constant voltage until the charging current density drops to 10% of the initial constant current charging current density, the voltage remains stable, and charging is stopped;

[0074] (2) Dismantle the waste lithium-ion batteries in an environment with a dew point of -50°C, remove the negative electrode sheets, and cut them into appropriate sizes;

[0075] (3) Immerse the cut negative electrode sheet in a cleaning agent acetonitrile solvent to remove the SEI film on the negative electrode surface, and then remove the electrode sheet and dry it;

[0076] (4) Prepare a recovery solution by adding 20.3 g of pyrene and 100 ml of tetrahydrofuran solvent into a beaker and stirring until a uniform solution is formed (the concentration of pyrene is 1 mol / L);

[0077] (5) The negative electrode sheet obtained in step 3 is placed in a recovery liquid, the leaching temperature is room temperature, the solid-liquid ratio is 1:3, the molar ratio of lithium element in the negative electrode sheet to pyrene in the recovery liquid is 1:1.1, and the leaching time is 5 hours. After the leaching is completed, the solution is filtered to separate and obtain a high value-added lithium-enriched liquid.

[0078] The solute polycyclic aromatic hydrocarbons used in Examples 3 to 14, Comparative Examples 5 and 6, the types of the second organic solvent used to dissolve the polycyclic aromatic hydrocarbons, the first organic solvent used in the cleaning agent, and the lithium extraction time are shown in Table 1. Other conditions not listed are the same as in Example 1.

[0079] Table 1

[0080]

[0081] It is not difficult to see from Table 1 that when comparing Example 1 with Comparative Examples 1 and 2, it is not difficult to see that, under other conditions unchanged, when the cleaning agent is not used to first destroy the SEI film on the surface of the negative electrode, the lithium extraction rate under the same conditions drops from 95% in Example 1 to 80%, and even if the lithium extraction time is extended from 0.5 hours to 5 hours, the lithium extraction rate is only 90%. This shows that it is necessary to first use a cleaning agent that can dissolve the SEI film to treat the negative electrode of the lithium battery before extracting lithium from the negative electrode.

[0082] A cleaning agent is used to first destroy the SEI film on the surface of the negative electrode of the battery. Comparative Examples 5 and 6 use a strong polar organic solvent to dissolve polycyclic aromatic hydrocarbons. Compared with Examples 4 and 7 or 8 of the present invention, in which the SEI film is first destroyed and then a weak polar organic solvent with a dielectric constant of less than 7 is used to dissolve the polycyclic aromatic hydrocarbons to extract lithium from the recovered liquid, the lithium extraction rate in the embodiments of the present invention can be greatly improved in a shorter time. It is speculated that this may be due to the weak Lewis basicity of the weak polar organic solvent, which can retain the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons, thereby ensuring that it has a strong interaction with the lithium element in the negative electrode, which not only significantly improves the lithium leaching rate, but also greatly increases the lithium content extracted from the polycyclic aromatic hydrocarbons in the unit volume of solvent.

[0083] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for efficiently extracting active lithium from the negative electrode of waste lithium batteries, characterized in that: First, the SEI film on the surface of the negative electrode of the lithium battery is treated with a solvent capable of dissolving the SEI film, so that holes appear in the SEI film or the solubility is damaged, thereby obtaining a negative electrode of the lithium battery with a damaged SEI film; then, the negative electrode of the lithium battery with a damaged SEI film is soaked in a recovery solution obtained by dissolving polycyclic aromatic hydrocarbons with a weak polar solvent, and the lithium in the negative electrode of the lithium battery is extracted by utilizing the electron-withdrawing effect of the large π bond of the polycyclic aromatic hydrocarbons; The method comprises the following steps: (1) After charging, the recycled waste lithium batteries are disassembled in a safe environment and the negative electrode sheets are separated; (2) soaking, separating and drying the negative electrode sheet in step (1) in sequence with a cleaning agent to obtain a preliminarily treated negative electrode sheet; the cleaning agent comprises a first organic solvent capable of dissolving the SEI film; the first organic solvent is one or more of triethyl phosphate, trimethyl phosphate, diethyl ethyl phosphate, diethyl carbonate, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, ethyl acetate, methyl acetate, propyl acetate, sulfolane and dimethyl sulfoxide; the soaking time is 0.5 h; (3) soaking the negative electrode sheet treated preliminarily in a recovery solution containing polycyclic aromatic hydrocarbons to obtain a lithium-containing composite solution; the recovery solution contains a second organic solvent, the second organic solvent is used to dissolve the polycyclic aromatic hydrocarbons, and the second organic solvent is a weakly polar organic solvent with a dielectric constant of less than 7; the number of carbon atoms of the polycyclic aromatic hydrocarbons is 10 to 30, and it contains 2 to 4 benzene rings; the second organic solvent is methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, ethyltetrahydrofuran, diethyltetrahydrofuran, one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether and tris(2,2,2-trifluoroethyl)orthoformate; (4) Separating the lithium-containing composite liquid into a solid-liquid state to obtain a lithium-containing enriched liquid.

2. The method according to claim 1, characterized in that The safe environment in step (1) is an environment with a dew point of -50°C or an environment with a relative humidity of less than 20%.

3. The method according to claim 2, characterized in that The safe environment in step (1) is an environment with a relative humidity of less than 10%.

4. The method according to claim 1, characterized in that The polycyclic aromatic hydrocarbons are selected from biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene and perylene.

5. The method according to claim 1, characterized in that The concentration of polycyclic aromatic hydrocarbons in the recovery liquid of step (3) is 0.01~7 mol / L.

6. The method according to claim 1, characterized in that The soaking temperature during the soaking treatment in step (3) is 20-80° C., the molar ratio of lithium element in the preliminary treated negative electrode sheet to polycyclic aromatic hydrocarbons in the recovered liquid is 1:1-3, the solid-liquid ratio of the soaking treatment is 1:1-3, and the soaking time is 0.5-2h.

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