CN110620276A - Method for recycling waste lithium ion battery electrolyte - Google Patents

Abstract

The invention discloses a method for recycling and reusing the electrolyte of waste lithium-ion batteries, which is mainly aimed at failing to correctly treat the organic solvents and conductive salts that pollute the environment in the recovery process of eliminated digital lithium-ion batteries and power lithium-ion batteries. question. The recycling steps are as follows: 1. Put the used lithium-ion battery into a liquid nitrogen tank and fully discharge it. 2. Disassemble the fully discharged battery in a glove box, put the disassembled battery into a supercritical extraction device, use acetone as an entrainer, and adjust the corresponding pressure, temperature and time parameters of the instrument for supercritical static extraction. 3. Remove acid and water from the extracted and recovered electrolyte, and conduct component analysis. The present invention uses acetone as the entraining agent to realize the maximum benefit recovery and reuse of the electrolyte after the digital lithium-ion battery and the power lithium-ion battery are disassembled, and achieves the pre-treatment of the battery material recovery without damaging other battery components. Require.

Description

A method for recovering and reusing the electrolyte of waste lithium-ion batteries

technical field

The invention relates to a method for recycling the electrolyte solution of waste lithium-ion batteries, belonging to the field of clean production in the lithium-ion battery industry.

Background technique

With the rapid development of the digital industry and the electric vehicle industry, the application of lithium-ion batteries has a broader space. Lithium-ion batteries have attracted extensive attention because of their high energy density, small size, and light weight. Digital lithium-ion batteries contain more precious metals, which is very necessary for the recovery of their materials. At the same time, power lithium-ion batteries have a higher design capacity, so the volume is relatively large, and the production cost is high. With the increase of usage , battery material recycling is also a must. The electrolyte of lithium-ion batteries is volatile. When the battery is recycled and disassembled, lithium hexafluorophosphate will produce HF, PF ₅ and other gases in the presence of air or water, which are harmful to the human body and the environment. The current studies commonly used for recycling have omitted the electrolyte treatment, because this is a difficult part to deal with effectively. For example, the Chinese patent application CN101212074A published "a method for recycling positive electrode materials of lithium-ion batteries" mechanically decomposes the battery, takes out the pole pieces and puts them into organic matter or soaked in water to obtain current collectors and active materials. take out. There is also a patent CN101847763A published "a comprehensive recovery method for waste lithium iron phosphate batteries", which uses an organic solvent to dissolve the binder on the cell fragments, and sieves to obtain lithium iron phosphate materials and clean aluminum, copper, and the like. The electrolyte has not been effectively and reasonably utilized. Therefore, how to dispose of the battery after opening the battery can reduce the harm of the electrolyte, and recycle the electrolyte to reduce the cost of the enterprise and reduce environmental pollution. In the long run, it is also a problem that needs to be solved.

Contents of the invention

The purpose of the present invention is to solve the problems of poor recovery effect and too many missing important components in the process of recycling waste lithium ion battery electrolyte. Due to the limitations of its own physical properties, supercritical carbon dioxide itself is not very polar, so it cannot achieve a good extraction effect on highly polar substances in waste electrolytes. In order to make up for this shortcoming, low-level ketone acetone is introduced as entrainment agent to change the density of supercritical carbon dioxide, improve its ability to dissolve strong polar substances, thereby increasing the extraction rate of the electrolyte.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for recycling the electrolyte of a waste lithium-ion battery, which is characterized in that it comprises the following steps:

(1) Put the used lithium-ion battery into liquid nitrogen and fully discharge it.

(2) Disassemble the battery in the glove box, so that the supercritical fluid can more fully contact the inside of the battery during extraction.

(3) Put the cell in step (2) and the collected frozen electrolyte debris and electrolyte-containing firmware into the extraction kettle of the supercritical extraction device, and add a certain amount of acetone as an entrainer;

(4) Under the condition that the pressure is 10-40MPa and the temperature is 31-50°C, the co-extraction of supercritical carbon dioxide and entrainer is carried out, the electrolyte in the electrolyte is separated, and the extract is obtained, and the extraction time is 30-50°C. 70min;

(5) After the extraction is finished, avoid the secondary pollution of the tail gas to process and then discharge it;

(6) Distill the extract obtained in step (4) under reduced pressure to remove the entrainer acetone in the extract, supplement the missing content through subsequent component analysis, and prepare an electrolyte.

Further, the discharge in the liquid nitrogen kettle described in step (1), the discharge time should be greater than 30min.

Further, the entrainer acetone mass consumption in the step (3) is 2%-10% of the supercritical carbon dioxide fluid mass.

Further, the tail gas treatment described in step (5) is to absorb the acid gas that may be generated through a sleeve equipped with an alkaline desiccant.

Further, the missing components required to be supplemented in step (6) mainly include conductive salts and carbonates, and the conductive salts are LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(SO ₂ F) ₂ , LiC ₂ O ₄ Any one of BC ₂ O ₄ or a combination of several, carbonates are any of ethylene carbonate, ethylene propyl carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate or ethyl methyl carbonate A combination of two or more.

Advantages of the present invention: 1. Use the principle of entrainer modification to adjust the dissolving capacity of supercritical carbon dioxide. The density of supercritical carbon dioxide is close to that of liquid, but its viscosity is similar to that of gas. This unique supercritical fluid has both gas-liquid dual Due to the strong compressibility of supercritical carbon dioxide, increasing the pressure of supercritical carbon dioxide can effectively increase its density and improve its solubility. However, when the pressure of supercritical carbon dioxide increases to a certain level, the viscosity of the fluid will increase, which is not conducive to extraction. At this time, an entrainer is needed to change the polarity of supercritical carbon dioxide, and at the same time, it will not significantly increase the viscosity of supercritical fluid. viscosity. 2. By changing the polarity and using the principle of similar compatibility, the more polar carbonate substances (used as organic solvents) and electrolytes can be continuously extracted to achieve the purpose of recycling. 3. Acetone was selected as the entrainer because of its low viscosity, low boiling point, easy separation and medium polarity. At the same time, this experiment was carried out in a dry carbon dioxide atmosphere, avoiding the conductive salt (conductive salt refers to the electrolyte in this case) in the air or When encountering water and water vapor, it will decompose and produce toxic gases (such as HF, PF ₅ , etc.), so as to achieve the purpose of recycling and reducing the harm of the electrolyte after the battery is disassembled. Some HF and PF ₅ gases may be produced in the process of electrolyte extraction and collection, but they are finally absorbed by alkali in the tail gas treatment device, which avoids the harm to people and the environment. The tail gas treatment device can be equipped with alkaline absorbent sleeve. In addition, the residual acetone in the extract after distillation is only at the ppm level, which has no effect on the properties of the electrolyte. Using acetone as an entrainer can remove acetone at a temperature lower than the decomposition temperature of lithium hexafluorophosphate, and the removal is more thorough.

Description of drawings

Fig. 1 is a schematic diagram of the extraction device in the embodiment of the present invention; the marks in the figure are: 1. Condenser, 2. Compressor, 3. Extraction kettle, 4. Tail gas treatment device, 5. Extraction liquid receiving device.

Fig. 2 is a comparison of the extraction rates under different dosages of entrainer in the examples of the present invention and comparative examples.

Fig. 3 is a schematic diagram of a vacuum distillation device for removing residual entrainer in an embodiment of the present invention.

Fig. 4 is the gas chromatogram before and after extract vacuum distillation among the example 3, EMC, EC refer to ethyl methyl carbonate and ethylene carbonate respectively among the figure.

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the following examples.

In the following examples, the device for reclaiming the lithium-ion battery electrolyte, as shown in Figure 1, includes a condenser 1, a compressor 2, an extraction kettle 3 and an extract receiving device 5 connected in sequence through pipelines, and the extraction kettle is also A tail gas treatment device 4 is connected. The tail gas treatment device 4 is filled with an alkaline absorbent inside, and the alkaline absorbent can be Ca(OH) ₂ , but can also be one or a combination of two or three of CaO, NaOH and Ca(OH) ₂ . The device used for vacuum distillation is shown in Figure 3.

Example 1

(1) Put the 18650 lithium-ion battery into liquid nitrogen and fully discharge it for 50 minutes.

(2) Disassemble the battery in the glove box, separate the battery shell from the battery cell, and collect the frozen electrolyte debris and firmware containing the electrolyte.

(3) Put the disassembled battery cell, the collected frozen electrolyte debris and the firmware containing the electrolyte into the inner tank of the supercritical extraction device, add 2% (that is, the mass dosage of acetone is supercritical carbon dioxide Fluid mass of 2% acetone, sealed well.

(4) Adjust the temperature of the condensing device at 1-10° C. to ensure that the carbon dioxide is in a liquid state.

(5) Take out the liner in step (3) quickly from the glove box and put it into a supercritical carbon dioxide extraction kettle, feed dry carbon dioxide with a certain air flow to evacuate, then continue to inject carbon dioxide to a supercritical state, set The pressure of the extraction kettle is 24±1MPa, the temperature is 40±4°C, and the extraction time is 50min. Connect the extract with the extract receiving device 5, and turn on the tail gas treatment device when receiving the extract, so that the toxic gas hydrogen fluoride is absorbed by calcium hydroxide to form calcium fluoride precipitation.

(6) extract is carried out underpressure distillation to remove residual entrainer acetone, then through gas chromatograph, ion chromatography and ICP analysis missing component and the amount that needs supplementing (by dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): Ethylene Carbonate (EC) = 1:1:1 (volume ratio), LiPF ₆ : 1mol/L, the requirements are supplemented).

As shown in Figure 2, the extraction rate of carbonates and lithium hexafluorophosphate in this example is 68.17%.

Example 2

Compared with Example 1, the difference is that the amount of acetone added in step (3) is increased to 4%, as shown in Figure 2, and the extraction rate of carbonates and lithium hexafluorophosphate is increased to 72.81% compared with Example 1.

Example 3

Compared with Example 1, the difference is that the amount of acetone added in step (3) is increased to 6%, as shown in Figure 2, and the extraction rate of carbonates and lithium hexafluorophosphate is increased to 82.13% compared with Example 1.

Example 4

Compared with Example 1, the difference is that the amount of acetone added in step (3) is increased to 8%, as shown in Figure 2, and the extraction rate of carbonates and lithium hexafluorophosphate is increased to 83.25% compared with Example 1.

Example 5

Compared with Example 1, the difference is that the amount of acetone added in step (3) is increased to 10%, as shown in Figure 2, and the extraction rate of carbonates and lithium hexafluorophosphate is increased to 84.56% compared with Example 1.

Because the difference between the boiling point of acetone and the organic carbonates exceeds 30°C, the vacuum distillation process of the extract obtained in the above example is as follows: controlling the heating temperature at 35-40°C under vacuum can effectively remove residual acetone. The concentration of lithium hexafluorophosphate in the extract is 0.46-0.63mol/L as tested by ICP.

As a small part of the generated toxic gases HF and PF ₅ are absorbed by the tail gas absorption liquid, the purpose of harmlessness is achieved. The reaction equation is as follows:

LiPF ₆ →LiF+PF ₅

PF5 _{+ H2O} →HF+ _PF4O

2HF+Ca(OH) ₂ → _CaF2 ↓ ₊ 2H2O.

Comparative Example 1:

Compared with Example 1, the difference is that the amount of acetone added in step (3) is 0%, as shown in Figure 2, the extraction rate of carbonates and lithium hexafluorophosphate is 59.23%.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Equivalent replacements or changes to the concepts thereof shall fall within the protection scope of the present invention.

Claims (5)

1. A method for recycling waste lithium ion battery electrolyte is characterized by comprising the following steps: the method comprises the following steps:

(1) putting the waste lithium ion battery into a liquid nitrogen kettle for full discharge;

(2) disassembling the battery in the glove box, separating the battery shell from the battery core, and collecting frozen electrolyte scraps and electrolyte-containing firmware;

(3) putting the battery core in the step (2) and the collected frozen electrolyte scraps and firmware containing the electrolyte into supercritical CO under the protection of inert gas₂Adding acetone as an entrainer into an extraction kettle of the extraction device;

(4) co-extracting supercritical carbon dioxide and entrainer under the conditions of 10-40MPa of pressure and 31-50 ℃ of temperature, separating electrolyte in the electrolyte, and obtaining extract for 30-70 min;

(5) introducing tail gas generated in the extraction process into a tail gas treatment device, wherein the tail gas absorption device is filled with CaO, NaOH and Ca (OH)₂One or a combination of two or three of (a);

(6) and (4) carrying out reduced pressure distillation on the extract obtained in the step (4), removing an entrainer acetone in the extract, and then supplementing missing components through subsequent component analysis to prepare electrolyte.

2. The method for recycling the electrolyte of the waste lithium ion battery according to claim 1, wherein the method comprises the following steps: the waste lithium ion battery in the step (1) is a power type lithium ion battery and a digital type lithium ion battery.

3. The method for recycling the electrolyte of the waste lithium ion battery according to claim 1, wherein the method comprises the following steps: discharging in a liquid nitrogen kettle in the step (1), wherein the discharging time is more than 30 min.

4. The method for recycling the electrolyte of the waste lithium ion battery according to claim 1, wherein the method comprises the following steps: in the step (3), the mass amount of the acetone is 2-10% of the mass of the supercritical carbon dioxide fluid.

5. The method for recycling the electrolyte of the waste lithium ion battery according to claim 1, wherein the method comprises the following steps: the deficiency components required to be supplemented in the step (6) comprise conductive salt and carbonate substance, wherein the conductive salt is LiPF₆、LiBF₄、LiClO₄、LiAsF₆、LiN(SO₂F)₂、LiC₂O₄BC₂O₄Any one or combination of a plurality of the substances, and the carbonate substance is any two or combination of a plurality of the substances of ethylene carbonate, ethyl propyl carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate or methyl ethyl carbonate.