Lithium-ion battery recycling methods

Abstract

To suppress the influence of sulfur components derived from electrolyte salts when recovering the positive electrode active material from the positive electrode composite material. [Solution] A method for recycling lithium-ion batteries using LiSFI as the electrolyte salt, comprising: a processing agent mixing step (step S7) in which lithium carbonate is mixed with the positive electrode composite material recovered from a used lithium-ion battery; and a heating step (step S8) in which the mixture of the positive electrode composite material and lithium carbonate is heated to a heating temperature above the melting point of LiSFI and below the melting point of lithium carbonate.

Description

Technical Field

[0001] The present invention relates to a method for recycling lithium - ion batteries.

Background Art

[0002] In Patent Document 1, in a method for recycling a lithium - ion battery that recovers an active material using an electrode mixture obtained from a waste electrode, a mixing step of mixing an activation treatment agent with a positive electrode mixture and a heating step of heating the mixture to a temperature not lower than the melting start temperature of the activation treatment agent are disclosed. In the configuration described in Patent Document 1, after the heating step, an active material recovery step of recovering the active material from the mixture is included. This active material recovery step uses a slurry solid - liquid separation method when separating and recovering the active material from the mixture that has undergone the heating step, and includes a slurrying step, a solid - liquid separation step, a drying step, and a re - firing step.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration described in Patent Document 1, when the molten activation treatment agent comes into contact with a fluorine compound derived from an electrolytic solution, the fluorine component is stabilized as an alkali metal fluoride, the generation of hydrogen fluoride is prevented, and the deterioration of the crystal structure of the active material can be suppressed.

[0005] By the way, in a lithium - ion battery, it is known to use an electrolytic solution containing LiSFI (lithium bis(fluorosulfonyl)imide). The configuration described in Patent Document 1 uses LiPF6 (lithium hexafluorophosphate) as a salt of the electrolytic solution.

[0006] In lithium-ion batteries using LiSFI as the electrolyte salt, sulfur components remain in the positive electrode mixture after charging and discharging. The configuration described in Patent Document 1 assumes that the mixture after heating contains fluorine components derived from the electrolyte and suppresses the degradation of the active material due to these fluorine components, but it did not take into account the effects of sulfur components derived from the electrolyte.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a lithium-ion battery recycling method that can suppress the influence of sulfur components derived from electrolyte salts when recovering positive electrode active material from positive electrode composite material. [Means for solving the problem]

[0008] The present invention relates to a method for recycling lithium-ion batteries using LiSFI as an electrolyte salt, and is characterized by comprising a mixing step of mixing lithium carbonate with a positive electrode composite material recovered from a used lithium-ion battery, and a heating step of heating the mixture of the positive electrode composite material and lithium carbonate to a heating temperature above the melting point of LiSFI and below the melting point of lithium carbonate. [Effects of the Invention]

[0009] In this invention, the influence of sulfur components derived from electrolyte salts can be suppressed when recovering the positive electrode active material from the positive electrode mixture. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart illustrating a lithium-ion battery recycling method in an embodiment. [Figure 2] This graph shows the sulfur concentration in the recovered material for different combinations of treatment agent type and treatment temperature. [Modes for carrying out the invention]

[0011] The following describes in detail the lithium-ion battery recycling method in embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0012] The lithium-ion battery recycling method in this embodiment applies to lithium-ion batteries using LiSFI as the electrolyte salt. This recycling method involves recovering the positive electrode active material from a used lithium-ion battery by removing the sulfur component contained in the positive electrode composite material and regenerating the positive electrode active material. The positive electrode active material may be either olivine type or layered type.

[0013] Furthermore, the lithium-ion battery recycling method in this embodiment is a material recovery method in direct recycling, which regenerates the active material without returning it to its raw material state. In direct recycling, if sulfur components contained in the electrolyte remain in the recovered active material, it can lead to a decrease in the battery's capacity, performance, and quality. LiSFI contained in the electrolyte is soluble in water, so it should be easy to remove by washing with water, but due to the influence of carbon residues after charging and discharging, it tends to remain in the recycled active material, and washing with water or ultrasonic cleaning alone cannot reduce the sulfur component to the same level as new active material. Therefore, the lithium-ion battery recycling method in this embodiment includes a step of removing sulfur components from the positive electrode composite material by a dry method.

[0014] Figure 1 is a flowchart illustrating a lithium-ion battery recycling method in an embodiment. The lithium-ion battery recycling method includes a detoxification step (step S1), a battery pack dismantling step (step S2), a battery module dismantling step (step S3), an electrolyte recovery step (step S4), a battery cell dismantling step (step S5), a positive electrode composite material recovery step (step S6), a treatment agent mixing step (step S7), and a heating step (step S8).

[0015] The detoxification process is a process of discharging the battery pack to make it safe to handle (step S1). The detoxification process includes the battery pack discharge process. The battery pack comprises multiple battery modules. Each battery module comprises multiple battery cells. The battery cells are composed of lithium-ion batteries using LiSFI as the electrolyte salt.

[0016] The battery pack dismantling process involves dismantling the battery pack and separating the battery module from the battery pack's components (step S2).

[0017] The battery module dismantling process involves releasing the constraints on the battery module and dismantling the battery module into individual battery cells (step S3).

[0018] The electrolyte recovery process involves releasing the sealed state of the battery cell and recovering the electrolyte that fills the space between the electrodes by heating, vacuum drying, etc. (Step S4). In the electrolyte recovery process, the cell case of the battery cell is opened, and the electrolyte, which uses LiSFI as the electrolyte, is recovered from the battery cell whose sealed state has been released.

[0019] The battery cell dismantling process is the process of dismantling the battery cell after the electrolyte has been recovered (step S5). In this dismantling process, the battery cell is separated into the cell case, terminals, resin components, electrodes, and separator. The electrodes consist of a current collector, which is a metal foil such as aluminum foil or copper foil, and an electrode composite layer provided on the current collector.

[0020] The positive electrode composite material recovery process is the process of recovering the positive electrode composite material from the positive electrode (step S6). In the positive electrode composite material recovery process, the positive electrode composite material is separated from the positive electrode after charging and discharging and recovered. For example, the positive electrode composite material is scraped off and recovered from the current collector. In this recovery process, the positive electrode composite material layer is mechanically peeled off from the current collector. The positive electrode composite material recovered in this recovery process is the recovered positive electrode composite material (recovered active material).

[0021] The treatment agent mixing step is a step of mixing lithium carbonate (Li2CO3) as a treatment agent with the positive electrode composite material (step S7). As lithium sources for direct recycling, lithium hydroxide and lithium carbonate are generally known. In the treatment agent mixing step, lithium carbonate is mixed with the positive electrode composite material as a lithium source for direct recycling. Lithium carbonate is an inorganic salt. In the treatment agent mixing step, only lithium carbonate is mixed with the positive electrode composite material. That is, in the treatment agent mixing step, elemental lithium carbonate is added to the positive electrode composite material. For example, the positive electrode composite material and lithium carbonate are mixed in a mortar.

[0022] The heating step is a step of heating the mixture of the positive electrode composite material and lithium carbonate to a heating temperature that is not lower than the melting point of LiSFI and not higher than the melting point of lithium carbonate (step S8). The heating step is a step of removing the sulfur component remaining in the recovered positive electrode composite material and a step of regenerating the positive electrode active material.

[0023] The melting point of LiSFI is 140 °C. The melting point of lithium carbonate is 723 °C. LiSFI thermally decomposes at a temperature sufficiently lower than the melting point of lithium carbonate. When LiSFI is thermally decomposed in the heating step, SO2 is generated. The heating step is a sulfur removal method that utilizes the volatilization of the sulfur component of LiSFI as SO2 gas.

[0024] For example, in the heating step, the mixture is heated at a heating rate of 300 °C / h, and fired at a heating temperature of 700 °C and a holding time of 4 hours. The positive electrode active material is regenerated by the heating step. By adding lithium carbonate as direct recycling and treating it at a high temperature of 700 °C, LiSFI contained in the electrolyte can be decomposed and removed as gasified SO2. As a result, the sulfur component can be reduced to the same level as before adding the electrolyte.

[0025] Regarding the relationship between the electrolyte salt and the lithium salt of the treatment agent, by adding a lithium salt that has a temperature range in which only the electrolyte salt melts, the lithium salt does not interfere with the thermal decomposition of the electrolyte salt. LiSFI, which is the electrolyte salt, melts at a temperature range lower than the temperature range in which lithium carbonate, the lithium salt of the treatment agent, melts. The temperature range lower than the melting temperature of lithium carbonate is 300 to 600°C. In the heating process, it is preferable that the heating temperature for heating the mixture is 600°C or higher.

[0026] Figure 2 is a graph showing the sulfur concentration in the recovered material for different combinations of treatment agent type and treatment temperature. Figure 2 shows the cases when lithium hydroxide is mixed as the treatment agent, when lithium carbonate is mixed, and when no lithium salt is mixed. Also, in Figure 2, new positive electrode active material is shown as new CAM, positive electrode active material coated on a current collector is coated CAM, and used positive electrode active material is charged and discharged CAM.

[0027] As shown in Figure 2 for LiOH 500℃, LiOH 600℃, and LiOH 700℃, when lithium hydroxide is used as the treatment agent, the sulfur component remaining in the electrode mixture is not reduced, and the sulfur component remains at a level close to that before direct recycling (CAM after charge / discharge shown in Figure 2). The melting point of lithium hydroxide is 462℃. The melting point of lithium hydroxide is lower than that of lithium carbonate. It is thought that when lithium hydroxide comes into contact with the active material, it melts at a temperature lower than its melting point, for example, in the 300℃ range. In this case, since the thermal decomposition temperature of LiSFI is 300℃, it is thought that the presence of lithium hydroxide in a molten state (liquid state) at the thermal decomposition temperature of LiSFI suppresses the generation of SO2 gas due to the thermal decomposition of LiSFI, and sulfur components remain in the active material.

[0028] As shown in Figure 2, when lithium carbonate is used as the treatment agent at Li2CO3500℃, Li2CO3600℃, and Li2CO3700℃, the amount of sulfur remaining in the electrode mixture is reduced. A heating temperature of 600℃ or higher is preferable.

[0029] Furthermore, if the process scraps before charging and discharging (from the positive electrode to the electrolyte adhesion stage) are processed without adding lithium carbonate, it is possible to remove the sulfur component from the positive electrode composite and regenerate the positive electrode active material. When calcined to 700°C without adding lithium salt, the sulfur concentration was 64 ppm. This is close to the value obtained when lithium carbonate was mixed in (26 ppm).

[0030] As described above, according to the embodiment, in a lithium-ion battery using LiSFI as the electrolyte salt, it is possible to recover the positive electrode active material from which sulfur components derived from the electrolyte have been removed, and the influence of sulfur components can be reduced, enabling the recovery of the battery's capacity, performance, and quality. In the heating process, lithium carbonate does not melt when LiSFI is thermally decomposed, so sulfur components are easily removed from the positive electrode mixture.

[0031] Furthermore, direct recycling of lithium-ion batteries using electrolytes containing LiSFI becomes possible using a dry method that does not involve water washing. In other words, since sulfur components can be removed in a process that does not involve water washing, the cost of direct recycling can be reduced. In conventional technology, salts other than lithium, specifically alkali metal compounds such as carbonates, are used as processing agents, so it is necessary to remove the alkali metal compounds by washing with water after the heating process.

[0032] Furthermore, while conventional technology requires two heating steps, this embodiment allows for the removal of sulfur components and the replenishment of lithium in a single heating step (calcination). According to this embodiment, the slurrying step, solid-liquid separation step, drying step, and re-calcination step can be reduced from the process of conventional technology.

[0033] Furthermore, since olivine-type cathode materials do not contain sulfur, the sulfur content of the cathode active material recovered through recycling must be reduced. The increase in sulfur is limited to sulfur derived from the salts in the electrolyte, so if this sulfur can be removed, the sulfur content can be reduced to a level close to that of a new product.

Claims

1. A method for recycling lithium-ion batteries using LiSFI as the electrolyte salt, A mixing step of mixing lithium carbonate with the positive electrode composite material recovered from the used lithium-ion battery, A heating step involves heating the mixture of the positive electrode material and the lithium carbonate to a heating temperature that is above the melting point of the LiSFI and below the melting point of the lithium carbonate. A method for recycling lithium-ion batteries, characterized by including [a specific component].

2. In the mixing step, the only inorganic salt mixed into the positive electrode mixture is lithium carbonate. A method for recycling lithium-ion batteries according to feature 1.

3. The heating temperature in the heating step is a temperature equal to or greater than the thermal decomposition temperature of the LiSFI. The method for recycling lithium-ion batteries according to feature 2.

Images