An efficient, safe and low-corrosion discharging method for waste lithium-ion batteries

Abstract

The present invention discloses a method for efficiently, safely and low-corrosively discharging waste lithium-ion batteries, which comprises the following steps: dissolving zinc acetate in water to obtain a zinc acetate solution with a certain concentration, and then putting waste lithium-ion batteries into the solution for immersion discharging treatment. After the discharging is completed, the waste lithium-ion batteries that can be safely disassembled can be taken out. The present invention uses an acetate solution as the discharging medium. The discharging pretreatment process has the advantages of high efficiency, safety and low corrosion. The operation process is simple and no professional equipment is required. It will not cause corrosion of the battery shell and leakage of the electrolyte. While avoiding secondary pollution to the environment, it also improves the recovery rate of subsequent metal resources.

Description

Technical Field

[0001] The present invention belongs to the field of recycling of waste lithium-ion batteries, and particularly relates to a method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion. Background Art

[0002] Lithium-ion batteries have attracted much attention due to their significant advantages in energy density, rate performance and cycle life. In recent years, the rapid development of the new energy vehicle and electrochemical energy storage industries has greatly stimulated the demand for lithium-ion batteries. At the same time, a large number of waste batteries that need to be properly disposed of have been generated. With the depletion of mineral resources and the increase in mining costs, recycling waste lithium-ion batteries containing rich metal resources will be the key to solving the sustainable development of the industry. At present, the recycling technologies of waste lithium-ion batteries mainly include three types: wet method, pyrometallurgy and direct repair method. However, before the waste batteries enter the recycling process, a series of pretreatment processes, such as discharging, disassembling and sorting, are required to achieve the purpose of safe and efficient recycling.

[0003] Due to the differences in the state of charge and thermal stability of waste lithium-ion batteries, the residual charge in them is extremely likely to induce thermal runaway during storage, transportation and disassembly, which may lead to combustion and explosion accidents. As the first step in the pretreatment process, the discharging process is a key step to ensure the safe recycling of waste lithium-ion batteries. The safe discharging methods of waste lithium-ion batteries can be divided into physical discharging, freezing and inerting discharging and chemical discharging. CN108134154A proposes to use a conductive powder mixture of mica powder, calcium carbonate and sub-graphite as the discharging medium. By using its good electrical conductivity and under the condition of fully contacting the positive and negative electrodes of the waste lithium-ion battery, the discharging effect of quickly reducing the voltage to below 0.6V can be achieved. However, directly using the conductive powder to cause the battery to short-circuit discharge has a potential safety hazard of sudden temperature rise and combustion and explosion accidents; CN111430832A and CN107293819B respectively propose to use dry ice or liquid nitrogen as the coolant and introduce inert gas protection for crushing or discharging. Although this method can inhibit the exothermic reaction caused by the residual charge to a certain extent, it requires the investment of professional equipment and subsequent high operation costs, and cannot solve the potential safety problems in the storage and transportation links; CN106252772A proposes to soak the waste lithium-ion battery in a sodium chloride solution with a mass concentration of 3-5% for 10-15 days, and then puncture and stay for more than half an hour to completely release the residual charge. This method can ensure the safety of the operation process and subsequent links, but the whole process takes too long and the Cl - corrosion of the battery shell will cause electrolyte leakage, low efficiency and environmental pollution; CN113809426A uses CuSO 4 、FeSO 4 、ZnSO 4 、NiSO 4 、CoSO4 Soak the waste lithium-ion battery in a mixed salt solution, add solid conductive powder at the same time, and assist with ultrasonic and stirring. Under such a composite discharge method, a final voltage as low as 0V can be obtained in 8 hours. However, the complex metal salt solution brings great difficulties to the subsequent wastewater treatment. At the same time, numerous auxiliary devices also increase the investment and maintenance costs, which is not conducive to industrial batch treatment.

[0004] In summary, at present, chemical soaking is mostly used for the discharge pretreatment of waste lithium-ion batteries. Through the electrolysis process of anions and cations in the solution, the residual electrical energy of the battery is converted into chemical energy and heat energy. At the same time, the large specific heat capacity of water can conduct the heat generated during the battery discharge process in a timely manner, avoiding serious heat accumulation and thus ensuring the safety of the operation. However, during the electrolysis process of the inorganic salt solution used in the prior art, due to the corrosion reaction of the battery shell being more thermodynamically inclined than the electrolysis reaction of anions and cations in the solution, the corrosion problem has always hindered the large-scale application of chemical discharge. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a high-efficiency, safe and low-corrosion discharge method for waste lithium-ion batteries. The present invention uses an acetate solution as the discharge medium, and the discharge pretreatment process has the advantages of high efficiency, safety and low corrosion. The operation process is simple and no professional equipment is required. It will not cause battery shell corrosion and electrolyte leakage. While avoiding secondary pollution to the environment, it also improves the recovery rate of subsequent metal resources.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A high-efficiency, safe and low-corrosion discharge method for waste lithium-ion batteries, comprising the following steps: Dissolve zinc acetate in water to obtain a zinc acetate solution with a concentration of 0.8-1.2 mol / L; in a room temperature environment, place the waste lithium-ion battery in the zinc acetate solution for soaking and discharging treatment to discharge the waste lithium-ion battery. The discharge process ends when there is no obvious phenomenon, that is, the residual voltage is so low that the electrolysis reaction can no longer be maintained; after the discharge ends, take out the battery from the zinc acetate solution, and separate the solid powder precipitated by electrolysis from the zinc acetate solution through a funnel filtration. After adding zinc acetate, the zinc acetate solution continues to be used as the discharge medium; the battery after discharge treatment is rinsed with tap water, naturally dried after removing the residual solvent on the surface, and then enters the subsequent disassembly / crushing process to complete the entire recycling pretreatment process.

[0008] As a preferred technical solution, a platinum wire with a diameter of 0.1 mm is used as a lead wire to connect the positive and negative electrodes of the battery to a voltmeter for recording the voltage fluctuations during the discharging process. To verify the safety of the discharging process, a K-type thermocouple is used to measure the temperature change on the surface of the battery during discharging. The discharging process should be carried out in a well-ventilated place to facilitate the evacuation of a small amount of gas generated during the electrolysis process. For the lithium-ion battery after discharging, in order to ensure its safety in the subsequent disassembly / crushing process, a stainless steel needle with a diameter of 3 mm is used for a puncture test and the temperature fluctuations on the battery surface are recorded.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] (1) The present invention uses zinc acetate solution as a discharging pretreatment medium for waste lithium-ion batteries. Its remarkable feature is that it can inhibit the corrosion of the battery shell during the soaking process. The carboxylate salt solution will undergo a special reaction (Kolbe reaction) during electrolysis:

[0011]

[0012] During the electrolysis process of carboxylate ions, an adsorption layer will be formed on the electrode surface, which can effectively prevent the corrosion of the electrode material and thus achieve the corrosion inhibition effect. Through a series of experiments, it is proved that the zinc acetate solution adopted by the present invention can effectively solve the problem of battery leakage while discharging efficiently and safely, and avoid secondary pollution to the environment.

[0013] (2) The decision to use zinc acetate solution as the discharging medium in the present invention is a comprehensive consideration of conductivity, solubility and cost. During the discharging process of zinc ions, an oxidation reaction occurs, and the zinc metal powder deposited at the negative electrode can play a synergistic effect of physical discharging, greatly shortening the time-consuming of the discharging pretreatment process. The residual voltage can be reduced to 0 V within 30 minutes.

[0014] (3) The zinc acetate solution used in the present invention generates metal zinc powder with a nanoscale size during electrolysis, which can be used as a high-quality raw material in other chemical production processes, further reducing the operating cost and achieving the maximum utilization of resources.

[0015] (4) After the zinc acetate solution used in the present invention is used to treat waste lithium-ion batteries, since it does not cause the leakage of the battery electrolyte, it can be quickly recycled by replenishing reagents, fully saving water resources. Description of the Drawings

[0016] Figure 1 It is a voltage change diagram of the process of soaking waste lithium-ion batteries with zinc acetate solution in Example 1, sodium chloride solution in Comparative Example 1 and ferrous sulfate solution in Comparative Example 2;

[0017] Figure 2 It is the temperature change diagram of the battery surface during the soaking of the waste lithium-ion battery in the zinc acetate solution in Example 1 and the ferrous sulfate solution in Comparative Example 2;

[0018] Figure 3 They are the photos of the solution and the battery positive electrode before and after the soaking of the waste lithium-ion battery in the zinc acetate solution in Example 1, the sodium chloride solution in Comparative Example 1, and the ferrous sulfate solution in Comparative Example 2;

[0019] Figure 4 They are the XRD and SEM diagrams of the solid powder precipitated during the soaking of the waste lithium-ion battery in the zinc acetate solution;

[0020] Figure 5 It is the temperature change diagram of the battery surface when a 3mm stainless steel needle pierces the battery after discharge treatment. Specific implementation manners

[0021] The present invention will be described in detail below in conjunction with specific operation examples. The following implementation cases will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several deformations and improvements can still be made. Based on the claims, changes and modifications in the dimensions and models of the equipment involved in each step, the types of waste batteries, etc. all fall within the protection scope of the present invention.

[0022] Example 1:

[0023] Weigh 35.12 g of Zn(Ac) 2 ·2H 2 O at room temperature and transfer it to a reaction vessel. After adding 0.2 L of water, stir it with a glass rod to dissolve, and prepare a 0.8 mol / L Zn(Ac) 2 solution and let it stand for use. Put the waste 18650 cylindrical lithium-ion battery into the reaction vessel and completely immerse it. The discharge reaction immediately starts and gradually bubbles and solid powder precipitate. The whole operation is carried out in a well-ventilated place. When the reaction phenomenon is no longer significant, that is, the residual voltage of the waste battery is very low and is not enough to continue to maintain the electrolytic reaction, and then determine whether it is completely discharged again through the voltmeter reading. After that, take out the discharged battery, wash it with tap water and air-dry it naturally, then it can enter the next stage of disassembly / crushing process to complete the subsequent metal resource recovery. Add 30 g of Zn(Ac) 2 ·2H 2 O and stir evenly, then it can be used as the discharge medium again.

[0024] Comparative Example 1:

[0025] This comparative example explores discharging used lithium-ion batteries with a conventional sodium chloride solution, as follows:

[0026] At room temperature, 9.35 g of NaCl was weighed and transferred to a reaction vessel. After adding 0.2 L of water, it was stirred with a glass rod to dissolve, and a 0.8 mol / L NaCl solution was prepared and left standing for use. The used 18650 cylindrical lithium-ion battery was put into the reaction vessel and completely immersed in it. The discharging reaction immediately started and gradually bubbles and solid powder were precipitated. The whole operation was carried out in a well-ventilated place. When the reaction phenomenon was no longer significant, that is, the residual voltage of the used battery was very low and not enough to continue to maintain the electrolysis reaction, and it was determined again whether it was completely discharged through the voltmeter reading. Then, the discharged battery was taken out, washed with tap water and air-dried naturally.

[0027] Comparative Example 2:

[0028] This comparative example explores discharging used lithium-ion batteries with a conventional ferrous sulfate solution, as follows:

[0029] At room temperature, 44.46 g of FeSO 4 ·7H 2 O was weighed and transferred to a reaction vessel. After adding 0.2 L of water, it was stirred with a glass rod to dissolve, and a 0.8 mol / L FeSO 4 solution was prepared and left standing for use. The used 18650 cylindrical lithium-ion battery was put into the reaction vessel and completely immersed in it. The discharging reaction immediately started and gradually bubbles and solid powder were precipitated. The whole operation was carried out in a well-ventilated place. When the reaction phenomenon was no longer significant, that is, the residual voltage of the used battery was very low and not enough to continue to maintain the electrolysis reaction, and it was determined again whether it was completely discharged through the voltmeter reading. Then, the discharged battery was taken out, washed with tap water and air-dried naturally.

[0030] Result analysis

[0031] For the used lithium-ion batteries immersed in the solutions of Example 1, Comparative Example 1 and Comparative Example 2, platinum metal wires were used as leads to connect the positive and negative electrodes of the used lithium-ion batteries to the voltmeter to record the voltage fluctuations during the discharging process. The changes in the residual voltage of the used lithium-ion batteries in each solution are as Figure 1 shown. It can be seen from Figure 1 that 0.8 mol / L Zn(Ac) 2 has the highest discharging efficiency among the three solutions and can drop the voltage to 0 V within 30 minutes, fully ensuring the operation safety of the subsequent recovery process.

[0032] For the used lithium-ion batteries immersed in the solutions of Example 1 and Comparative Example 2, a K-type thermocouple was used to measure the temperature change on the battery surface during the discharging process. The results are asFigure 2 As shown, it can be seen that the surface temperature change during the discharge process of the zinc acetate solution immersion is milder than that of the ferrous sulfate solution. This is because more residual electrical energy is converted into chemical energy, reducing heat generation. Therefore, the process of zinc acetate solution immersion discharge is also safer and more stable.

[0033] The photos of the solutions and the battery positive electrodes before and after treating the used lithium-ion batteries by immersing them in the zinc acetate solution in Example 1, the sodium chloride solution in Comparative Example 1, and the ferrous sulfate solution in Comparative Example 2 are as Figure 3 shown. It can be seen that compared with the NaCl solution and the ferrous sulfate solution, the used lithium-ion battery after being immersed in the zinc acetate solution for 24 hours not only has a complete outer shell but also has no visible corrosion marks to the naked eye. The solution remains clear and transparent throughout the immersion and discharge process. On the contrary, the positive electrode of the battery after being immersed in the sodium chloride solution has been completely corroded, and even the internal electrode core can be observed. The solution is turbid and emits an organic electrolyte smell, proving that the immersion and discharge of the sodium chloride solution will cause serious battery leakage. The positive electrode of the battery after being immersed in the ferrous sulfate solution has corrosion marks but remains intact as a whole. The solution changes from the green of divalent iron ions at the beginning to the yellow of trivalent iron ions at the end, and the whole solution shows a slightly turbid appearance, which is also not suitable for long-term production use.

[0034] Figure 4 XRD and SEM diagrams of the solid powder precipitated during the process of immersing the used lithium-ion battery in the zinc acetate solution in Example 1. From Figure 4 it can be seen that the solid powder generated by the electrolytic reaction during the immersion process is zinc metal in nanometer size and shows a certain degree of agglomeration. Its good electrical conductivity ensures the efficient synergistic effect of chemical discharge and physical discharge.

[0035] Figure 5 The surface temperature change diagram of the battery when using a 3mm stainless steel needle to puncture the batteries after discharging the solutions in Example 1 and Comparative Examples 1 and 2. From Figure 5 it can be seen that the surface temperature of the used batteries after being immersed in the three solutions is below 30°C during the needle puncture process. Among them, the effect of the zinc acetate solution treatment is the most significant, indicating that the residual charge has been completely consumed, which can ensure the safety of the subsequent recycling process.

[0036] Obviously, the described embodiments are some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

Claims

1. A method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion, characterized in that: It includes the following steps: Dissolve zinc acetate in water to obtain a zinc acetate solution, and then put waste lithium-ion batteries into it for immersion discharge treatment. After the discharge is completed, the waste lithium-ion batteries that can be safely disassembled can be taken out; The concentration of the zinc acetate solution is 0.8 - 1.2 mol / L.

2. The method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion according to claim 1, characterized in that: The immersion discharge treatment is carried out in a room temperature environment, and the waste lithium-ion batteries are immersed in the zinc acetate solution during the immersion discharge treatment.

3. The method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion according to claim 1 or 2, characterized in that: During the discharge of the waste lithium-ion batteries, a platinum wire is used as a lead to connect the positive and negative electrodes of the waste lithium-ion batteries to a voltmeter for recording the voltage fluctuations during the discharge process.

4. The method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion according to claim 1 or 2, characterized in that: During the discharge of the waste lithium-ion batteries, a K-type thermocouple is used to measure the temperature change on the surface of the waste lithium-ion batteries during the discharge process.

5. The method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion according to claim 1 or 2, characterized in that: The immersion discharge treatment is carried out in a ventilated environment.

6. The method for discharging waste lithium-ion batteries with high efficiency, safety and low corrosion according to claim 1 or 2, characterized in that: A puncture experiment is carried out on the waste lithium-ion batteries taken out after the discharge is completed, and the surface temperature fluctuations are recorded.

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