JP7706407B2 - How to dispose of used lithium-ion batteries - Google Patents

Description

The present invention relates to a method for treating waste lithium-ion batteries.

Lithium-ion batteries are composed of a positive electrode material made of aluminum foil coated with lithium, cobalt, nickel, etc., a negative electrode material made of copper foil coated with graphite, electrolyte, separator, etc. Lithium-ion batteries therefore contain valuable materials such as lithium, cobalt, nickel, and copper. For this reason, recycling discarded lithium-ion batteries (waste lithium-ion batteries) and recovering these valuable materials is extremely beneficial for a country like Japan, which has few resources.

Waste lithium-ion batteries are difficult to process because they can ignite, cause electric shock, and generate hydrogen fluoride during recycling. For this reason, waste lithium-ion batteries are rendered harmless by heating and roasting, and then separated and recovered by crushing, sieving, sorting, etc.

However, if a charged used lithium-ion battery is directly heated at high temperatures, there is a risk that the battery will heat up and explode. For this reason, by discharging the used lithium-ion battery before the heat treatment, the sudden heat generation during heating can be suppressed. Generally, discharging is performed by connecting the battery to an electric circuit, but this takes a long time, so it is not practical to use this method in a recycling system.

Patent documents 1 to 3 disclose discharging used lithium ion batteries by immersing them in an aqueous solution of sodium chloride or the like. Patent documents 2 to 4 disclose discharging used lithium ion batteries by immersing them in an aqueous solution of an inorganic compound such as sodium sulfate, ammonium nitrate, sodium carbonate, sodium bicarbonate, calcium carbonate, or magnesium oxide. Patent document 3 discloses discharging used lithium ion batteries by immersing them in an aqueous solution of an organic acid such as an aqueous solution of acetic acid.

Japanese Patent Application Publication No. 8-306394 Japanese Patent Application Publication No. 10-223264 Japanese Patent Application Publication No. 11-97076 JP 2005-347162 A

However, when an aqueous solution of an inorganic compound is used as the discharge liquid, the inorganic compound remains after the heat treatment, which may reduce the quality of the recovered resource. In particular, when an aqueous solution of sodium chloride is used as the discharge liquid, there is a risk of corrosion of the heating furnace used in the subsequent heat treatment process. Furthermore, when an aqueous solution of an organic acid is used as the discharge liquid, the electrolyte used in lithium-ion batteries is equivalent to kerosene, so there is a risk of it catching fire during the discharge process, thereby worsening the working environment.

The present invention aims to provide a method for processing used lithium-ion batteries that can prevent the deterioration of the quality of recovered resources and the deterioration of the working environment.

The method for treating used lithium ion batteries of the present invention is characterized by including a step of discharging the residual power of the used lithium ion batteries by immersing them in an amine-based aqueous solution containing carbamate anions or bicarbonate ions.

According to the method for treating waste lithium-ion batteries of the present invention, an amine-based aqueous solution containing carbamate anions or bicarbonate ions is used as the discharge liquid, and therefore the residual discharge liquid does not contain inorganic compounds, so there is no risk of the quality of the recovered resources decreasing after the heat treatment. In addition, since the residual discharge liquid does not contain chlorides, there is no risk of the heating furnace in which the heat treatment is performed corroding. In addition, even if the water concentration of the amine-based aqueous solution is high, it is possible to sufficiently discharge it, so it is possible to suppress deterioration of the working environment due to ignition, etc.

In the method for treating waste lithium ion batteries of the present invention, the amine-based aqueous solution is preferably an amine-based absorbing solution that has absorbed carbon dioxide.

In this case, the amine-based absorbing liquid that is used in the carbon dioxide separation and capture system and is discarded due to its reduced ability to absorb carbon dioxide can be reused as the discharge liquid, making it possible to reduce the cost required for the discharge liquid.

In addition, in the method for treating used lithium ion batteries of the present invention, it is preferable that the amine-based aqueous solution has a water content of 60% by weight or more.

In this case, the high water concentration of the amine-based aqueous solution makes it possible to further prevent deterioration of the working environment, such as ignition when the lithium-ion battery is discharged.

This article describes a method for treating used lithium-ion batteries according to an embodiment of the present invention.

In this processing method, first, a discharging process is performed in which used lithium ion batteries to be discarded (waste lithium ion batteries) are immersed in an amine-based aqueous solution and discharged. The details of the discharging process will be described later. It is preferable to wash the discharged waste lithium ion batteries with water to remove as much of the amine-based aqueous solution as possible.

Next, a heat treatment process is carried out in which the discharged waste lithium-ion batteries are roasted. By heating the waste lithium-ion batteries, the electrolyte inside them is removed and the waste lithium-ion batteries are rendered harmless. There are no particular limitations on the type or shape of the heating furnace used in the heat treatment process.

Next, a crushing process is performed in which the roasted waste lithium-ion batteries are crushed into appropriate sizes using a crusher, disintegrator, etc. Then, a classification process is performed in which the crushed material is classified using a sieve, an air classifier, etc. Furthermore, a sorting process is performed in which various metals and other components are sorted using a magnet, etc. This makes it possible to recover rare metals such as cobalt and base metals such as copper and iron contained in the waste lithium-ion batteries by material. The heat treatment process, crushing process, classification process, and sorting process may be performed in the same manner as conventional processes, and the order of these processes may be reversed, and other processes may be added.

The discharge process of the waste lithium-ion battery processing method according to the embodiment will be described in detail below.

In the discharging step, the used lithium ion batteries are immersed in an amine-based aqueous solution to discharge the remaining power of the used lithium ion batteries. Here, the amine-based aqueous solution is an amine-based aqueous solution containing carbamate anions (RNHCOO ^- ) or bicarbonate ions (HCO ₃ ^- ). As the amine-based aqueous solution, for example, an aqueous solution of an amine compound having a carbamate anion group is suitable.

Primary and secondary amines generate carbamate anions when they absorb carbon dioxide (CO ₂ ). On the other hand, tertiary amines generate bicarbonate ions when they absorb carbon dioxide. Therefore, it is preferable to use an amine aqueous solution that has absorbed carbon dioxide as the amine aqueous solution.

In particular, it is preferable to use an amine-based absorbing liquid that is used in a carbon dioxide capture and storage (CCS) system and is discarded due to a decrease in its ability to absorb carbon dioxide. This makes it possible to reuse the discarded amine-based absorbing liquid, thereby reducing the cost required for the discharge liquid.

The amine-based absorbing liquid used to separate and capture carbon dioxide from combustion exhaust gas generates ions such as carbamate anions and bicarbonate ions by absorbing carbon dioxide, which increases the electrical conductivity. Therefore, instead of using new amine-based absorbing liquid, used amine-based absorbing liquid that has absorbed carbon dioxide and has increased electrical conductivity is used as the discharge liquid.

Suitable examples of amine-based absorbing liquids include, but are not limited to, monoethanolamine (MEA), methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ/PIPA). These may also be used in combination.

It is preferable that the amine-based aqueous solution has an electrical conductivity of 0.2 S/m or more. This is because the higher the electrical conductivity, the faster the discharge of the used lithium-ion batteries can be completed, and if the electrical conductivity is 0.2 S/m or more, the discharge can be completed after immersion for about 20 hours, which is appropriate for an actual system.

Unlike the conventional technology described above, such an amine-based aqueous solution does not contain inorganic compounds, so there is no risk of the quality of the recovered resources after heat treatment being reduced by the residual discharge liquid. In addition, since the residual discharge liquid does not contain chlorides, there is no risk of corrosion of the heating furnace in which the heat treatment is performed. Furthermore, since the amine-based aqueous solution can be sufficiently discharged even if the water concentration is high, it is possible to suppress deterioration of the working environment due to ignition, etc. In particular, by making the amine-based aqueous solution 60% by weight or more, it is possible to further suppress the risk of ignition.

The present invention is not limited to the method for treating used lithium-ion batteries specifically described in the above embodiment, and may be modified as appropriate within the scope of the claims.

Below, we will explain examples and comparative examples of the method for treating used lithium-ion batteries of the present invention.

1.5 kg of used automotive lithium-ion batteries (one 40V lithium-ion battery each) were prepared as waste lithium-ion batteries. When these were measured with a residual voltage meter, the average residual voltage was 39.4V.

In Example 1, a used amine-based absorbing solution containing 30% by weight of MEA and having absorbed carbon dioxide was prepared as the amine-based aqueous solution of the present invention. When this amine-based absorbing solution was measured with an infrared spectrometer, the presence of carbamate anions was confirmed. When this amine-based absorbing solution was measured with an electrical conductivity meter, the electrical conductivity was 3.3 [S/m].

Then, 30 L of the amine-based aqueous solution was poured into a plastic container, and the waste lithium-ion batteries were immersed in the amine-based aqueous solution.

The residual voltage of the used lithium-ion batteries was then measured every minute using a residual voltage meter. Discharge was considered complete when the average residual voltage measured reached 0.5 V. It took 1.2 hours for discharge to be completed.

In Example 2, a used amine-based absorbing solution that had absorbed carbon dioxide and contained 15% by weight of MEA and diethanolamine (DEA) was prepared as the discharge solution. When this amine-based absorbing solution was measured with an infrared spectrometer, the presence of carbamate anions was confirmed. The electrical conductivity was 0.8 [S/m].

Then, similar to Example 1, the waste lithium-ion batteries were immersed in this mixed aqueous solution of used MEA and DEA. After 7.0 hours had elapsed, the average residual voltage of the waste lithium-ion batteries was 0.5 V or less, and discharging was deemed to be complete.

In Example 3, a used amine-based absorbing solution that contained 15% by weight each of DEA and MDEA and had absorbed carbon dioxide was prepared as the discharge solution. When this amine-based absorbing solution was measured with an infrared spectrometer, the presence of carbamate anions was confirmed. The electrical conductivity was 0.3 [S/m].

Then, similar to Example 1, the waste lithium-ion batteries were immersed in this used DEA and MDEA mixed aqueous solution. After 14.0 hours had elapsed, the average residual voltage of the waste lithium-ion batteries was 0.5 V or less, and the discharge was deemed to be complete.

In Comparative Example 1, a new amine-based absorbing solution that contained 30% by weight of MEA and had not absorbed any carbon dioxide was used as the discharge solution. When this amine-based absorbing solution was measured with an infrared spectrometer, the presence of carbamate anions was not confirmed. The electrical conductivity was 0.0 [S/m].

Then, similarly to Examples 1 to 3, the used lithium ion batteries were immersed in this new amine-based absorbing solution. However, even after 48 hours had passed, the average residual voltage of the used lithium ion batteries did not become 0.5 V or less, so it was determined that they could not be discharged.

In Comparative Example 2, industrial water was used as the discharge liquid. The electrical conductivity was 0.0 [S/m].

Then, similarly to Examples 1 to 3, the waste lithium-ion batteries were immersed in industrial water. However, even after 48 hours had passed, the average residual voltage of the waste lithium-ion batteries did not become 0.5 V or less, so it was determined that they could not be discharged.

In Comparative Example 3, an aqueous sodium chloride solution (saline solution) containing 3% by weight of sodium chloride (NaCl) was used as the discharge liquid. The electrical conductivity was 5.0 [S/m].

Then, similarly to Examples 1 to 3, the used lithium ion batteries were immersed in this sodium chloride aqueous solution. After 1.0 [hour] had elapsed, the average residual voltage of the used lithium ion batteries became 0.5 [V] or less, and the discharge was deemed to be completed.

The results of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1.

As can be seen from Table 1, in Examples 1 to 3 in which used amine-based absorbing liquid was used, discharging was completed in a reasonable time of 14 hours or less, unlike Comparative Example 1 in which new amine-based absorbing liquid was used and Comparative Example 2 in which industrial water was used. This shows that it is reasonable to use used amine-based absorbing liquid as a discharging liquid.

Also, from Table 1, Example 1, which used a used amine-based absorbing solution, took longer to complete discharge than Comparative Example 3, which used an aqueous sodium chloride solution, but only slightly longer. Comparative Example 3 used an aqueous sodium chloride solution, which may result in a deterioration in the quality of the recovered resources due to residual chlorides after the heat treatment, or corrosion of the heating furnace. On the other hand, if a used amine-based absorbing solution is used as the discharge solution, such problems do not occur, making it preferable.

Claims (2)

A method for treating waste lithium ion batteries, comprising the step of discharging residual power of the waste lithium ion batteries by immersing the waste lithium ion batteries in an amine-based aqueous solution containing a carbamate anion , wherein the amine-based aqueous solution is an amine-based absorbing solution that has absorbed carbon dioxide . The method for treating used lithium ion batteries according to claim 1, characterized in that the amine-based aqueous solution has a water content of 60% by weight or more.