Recycling method of lithium ion battery

Abstract

The present invention addresses the problem of suppressing the influence of a sulfur component derived from a salt of an electrolyte solution when recovering a positive electrode active material from a positive electrode mixture. The present invention provides a method for recycling a lithium ion battery using LiFSI as a salt of an electrolyte solution, the method comprising: a treatment agent mixing step for mixing lithium carbonate with a positive electrode mixture recovered from a waste lithium ion battery; and a heating step for heating a mixture obtained by mixing lithium carbonate with the positive electrode mixture to a heating temperature that is equal to or higher than the melting point of LiFSI and equal to or lower than the melting point of lithium carbonate.

Description

Technical Field

[0001] This invention relates to a method for reusing lithium-ion batteries. Background Technology

[0002] Patent Document 1 discloses a method for recycling lithium-ion batteries using an electrode mixture obtained from waste electrodes to recover active materials, comprising: a mixing step in which an activating agent is mixed with a positive electrode mixture; and a heating step in which the mixture is heated to above the melting point of the activating agent. In the structure described in Patent Document 1, after the heating step, an active material recovery step is included to recover active materials from the mixture. This active material recovery step uses a slurry-based solid-liquid separation method to separate and recover active materials from the mixture after the heating step, and includes a slurry-based step, a solid-liquid separation step, a drying step, and a recalcination step.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2021-140996 Summary of the Invention

[0004] In the structure described in Patent Document 1, the fluorine component is stabilized into an alkali metal fluoride by contacting the molten activating agent with a fluorine compound derived from the electrolyte, thereby preventing the generation of hydrogen fluoride and inhibiting the deterioration of the crystal structure of the active material.

[0005] In lithium-ion batteries, electrolytes containing LiFSI (lithium bis(fluorosulfonyl)imide) are known to be used. In the structure described in Patent Document 1, LiPF6 (lithium hexafluorophosphate) is used as the salt of the electrolyte.

[0006] In lithium-ion batteries that use LiFSI as the electrolyte salt, sulfur remains in the positive electrode mixture after charging and discharging. The structure described in Patent Document 1 assumes that the heated mixture contains fluorine from the electrolyte, suppressing the degradation of the active material due to this fluorine, but does not consider the effects of sulfur from the electrolyte.

[0007] The present invention was made in view of the above circumstances, and its object is to provide a method for reusing lithium-ion batteries that can suppress the influence of sulfur components from electrolyte salts when recovering positive electrode active materials from positive electrode additives.

[0008] This invention relates to a method for reusing lithium-ion batteries, specifically a method for reusing lithium-ion batteries that use LiFSI as the electrolyte salt. The method comprises: a mixing step, in which lithium carbonate is mixed with a positive electrode mixture recovered from a spent lithium-ion battery; and a heating step, in which the mixture formed by mixing the lithium carbonate with the positive electrode mixture is heated to a temperature above the melting point of LiFSI and below the melting point of the lithium carbonate.

[0009] Invention Effects

[0010] In this invention, the influence of sulfur components from the electrolyte salts can be suppressed when recovering the positive electrode active material from the positive electrode mixture. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating the method for reusing lithium-ion batteries in the embodiments.

[0012] Figure 2 It is a graph showing the sulfur concentration in the recovered material relative to a combination of the type of treatment agent and the treatment temperature. Detailed Implementation

[0013] The following describes in detail the method for reusing lithium-ion batteries according to embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0014] The lithium-ion battery recycling method described in this embodiment targets lithium-ion batteries that use LiFSI as the electrolyte salt. This recycling method involves removing sulfur components contained in the positive electrode mixture and regenerating the positive electrode active material during the recovery of the positive electrode active material from spent lithium-ion batteries. The positive electrode active material can be either olivine-type or layered-type.

[0015] Furthermore, the lithium-ion battery reuse method in this embodiment is a material recycling method that involves direct reuse without restoring the active material to its original state. If direct reuse is used, the sulfur content contained in the electrolyte remains in the recycled active material, leading to a decrease in battery capacity, performance, and quality. Since LiFSI contained in the electrolyte is soluble in water, it should be easy to remove by washing, but it easily remains in the recycled active material. Due to the influence of carbon residues after charging and discharging, washing or ultrasonic cleaning alone cannot reduce the sulfur content to the same level as virgin active material. Therefore, the lithium-ion battery reuse method in this embodiment includes a step of removing sulfur from the positive electrode mixture using a dry process.

[0016] Figure 1 This is a flowchart illustrating the lithium-ion battery recycling method in the embodiment. The lithium-ion battery recycling method includes a harmless treatment process (step S1), a battery pack disassembly process (step S2), a battery module disassembly process (step S3), an electrolyte recovery process (step S4), a battery cell disassembly process (step S5), a positive electrode agent recovery process (step S6), a treatment agent mixing process (step S7), and a heating process (step S8).

[0017] The decontamination process involves discharging the battery pack to ensure its safe disposal (step S1). The decontamination process includes the discharge process of the battery pack. The battery pack comprises multiple battery modules. Each battery module comprises multiple battery cells. Each battery cell is a lithium-ion battery using LiFSI as the electrolyte.

[0018] The battery pack disassembly process is the process of disassembling the battery pack and separating the battery modules from the components of the battery pack (step S2).

[0019] The disassembly process of the battery module involves removing the constraints of the battery module and disassembling the battery module by battery cell (step S3).

[0020] The electrolyte recovery process involves removing the sealed state of the battery cell and recovering the electrolyte filling the spaces between the electrodes through heating, depressurization, and drying (step S4). In the electrolyte recovery process, the cell casing in the battery cell is opened, and the electrolyte using LiFSI as the electrolyte is recovered from the unsealed battery cell.

[0021] The battery cell disassembly process is the process of disassembling and recovering the battery cell after the electrolyte has been recycled (step S5). In this disassembly process, the battery cell is separated into a cell housing, terminals, resin components, electrodes, and a separator. The electrodes have a current collector made of metal foil such as aluminum foil or copper foil and an electrode binder layer disposed on the current collector.

[0022] The positive electrode flux recovery process is a process of recovering the positive electrode flux from the positive electrode (step S6). In the positive electrode flux recovery process, the positive electrode flux is separated and recovered from the positive electrode after charging and discharging. For example, the positive electrode flux is scraped off from the current collector and recovered. In this recovery process, the positive electrode flux layer is mechanically peeled off from the current collector. The positive electrode flux recovered through this recovery process is the recovered positive electrode flux (recovered active material).

[0023] The treatment agent mixing step involves mixing lithium carbonate (Li₂CO₃) as a treatment agent into the positive electrode mixture (step S7). Lithium hydroxide and lithium carbonate are commonly known as direct-reuse lithium sources. In the treatment agent mixing step, lithium carbonate is mixed into the positive electrode mixture as a direct-reuse lithium source. Lithium carbonate is an inorganic salt. In the treatment agent mixing step, only lithium carbonate is mixed into the positive electrode mixture. That is, in the treatment agent mixing step, lithium carbonate monomer is added to the positive electrode mixture. For example, the positive electrode mixture and lithium carbonate are mixed in a mortar.

[0024] The heating process is a process of heating the mixture containing the cathode agent and lithium carbonate to a temperature above the melting point of LiFSI and below the melting point of lithium carbonate (step S8). The heating process is a process of removing sulfur components remaining in the recycled cathode agent and a process of regenerating the cathode active material.

[0025] LiFSI has a melting point of 140°C. Lithium carbonate has a melting point of 723°C. LiFSI thermally decomposes at temperatures sufficiently lower than the melting point of lithium carbonate. During the heating process, if LiFSI thermally decomposes, SO2 is produced. The heating process is a sulfur removal method that utilizes the volatilization of the sulfur component of LiFSI in the form of SO2 gas.

[0026] For example, in the heating process, the mixture is heated at a rate of 300°C / h and calcined at a heating temperature of 700°C for a holding time of 4 hours. The positive electrode active material is regenerated through this heating process. Alternatively, lithium carbonate is added and treated at a high temperature of 700°C, thereby decomposing the LiFSI contained in the electrolyte and removing it as SO2 through vaporization. This reduces the sulfur content to the same level as before the addition of the electrolyte.

[0027] Regarding the relationship between the electrolyte salt and the lithium salt of the treatment agent, by adding a lithium salt that exists only in the melting temperature range of the electrolyte salt, the lithium salt does not hinder the thermal decomposition of the electrolyte salt. LiFSI, as the electrolyte salt, melts in a temperature range lower than the melting temperature range of lithium carbonate, which is the lithium salt of the treatment agent. This temperature range, below the melting temperature of lithium carbonate, is 300–600°C. In the heating process, the heating temperature for heating the mixture is preferably 600°C or higher.

[0028] Figure 2 This is a graph showing the sulfur concentration in the recovered material relative to a combination of the type of treatment agent and the treatment temperature. Figure 2 The diagram shows cases with lithium hydroxide as a treatment agent, cases with lithium carbonate, and cases without lithium salt. Furthermore, in... Figure 2 In this paper, the new positive electrode active material is shown as the new CAM, the positive electrode active material coated on the current collector is shown as the coated CAM, and the waste positive electrode active material is shown as the charged and discharged CAM.

[0029] like Figure 2 As shown, when LiOH is heated to 500℃, 600℃, and 700℃ using lithium hydroxide as a treatment agent, the sulfur content remaining in the electrode mixture does not decrease, and the sulfur content is close to that before direct reuse. Figure 2The residual level of CAM after charge and discharge is shown. Lithium hydroxide has a melting point of 462°C. The melting point of lithium hydroxide is lower than that of lithium carbonate. It is assumed that lithium hydroxide melts at a temperature lower than the melting point of lithium hydroxide, such as 300°C, through contact with the active material. In this case, since the thermal decomposition temperature of LiFSI is 300°C, it is assumed that because lithium hydroxide exists in a molten state (liquid state) at the thermal decomposition temperature of LiFSI, the SO2 gas generation caused by the thermal decomposition of LiFSI is suppressed, and sulfur components remain in the active material.

[0030] like Figure 2 As shown, when Li₂CO₃ is heated to 500℃, 600℃, and 700℃ using lithium carbonate as a treatment agent, the sulfur content remaining in the electrode mixture is reduced. The preferred heating temperature is 600℃ or higher.

[0031] Furthermore, if the process material is a pre-charge / discharge stage material (from the positive electrode to the electrolyte adhesion), sulfur can be removed from the positive electrode mixture to regenerate the positive electrode active material even without adding lithium carbonate. When calcined to 700°C without adding lithium salt, the sulfur concentration is 64 ppm. This is close to the value (26 ppm) obtained with mixed lithium carbonate.

[0032] As explained above, according to the embodiments, for lithium-ion batteries using LiFSI as an electrolyte salt, it is possible to recover the positive electrode active material from which sulfur components originating from the electrolyte have been removed, and the impact of sulfur components can be reduced, thereby restoring the battery's capacity / performance / quality. During the heating process, lithium carbonate does not melt during the thermal decomposition of LiFSI, thus sulfur components are easily removed from the positive electrode mixture.

[0033] Furthermore, lithium-ion batteries using electrolytes containing LiFSI can be directly reused using a method that does not require water washing (dry process). That is, since sulfur can be removed in a process that does not require water washing, this direct reuse method reduces costs. In the prior art, salts other than lithium are used as processing agents, specifically alkali metal compounds such as carbonates. Therefore, after the heating process, water washing is required to remove the alkali metal compounds.

[0034] Furthermore, while the prior art requires two heating processes, in this embodiment, sulfur can be removed and lithium replenished through a single heating process (calcination). According to this embodiment, the slurry preparation process, solid-liquid separation process, drying process, and recalcination process can be eliminated from the prior art.

[0035] Furthermore, olivine-type cathode materials do not contain sulfur, therefore, the sulfur content needs to be reduced in the cathode active material recovered through reuse. The increase in sulfur is limited to sulfur originating from the salts in the electrolyte; therefore, if this sulfur can be removed, the sulfur content can be reduced to levels close to those of virgin products.

Claims

1. A method for reusing lithium-ion batteries, specifically a method for reusing lithium-ion batteries that use LiFSI as the electrolyte salt, characterized in that... include: The mixing process involves mixing lithium carbonate with a positive electrode compound recovered from the spent lithium-ion batteries. and The heating process involves heating the mixture formed by mixing the lithium carbonate in the positive electrode agent to a temperature above the melting point of the LiFSI and below the melting point of the lithium carbonate.

2. The method for reusing lithium-ion batteries according to claim 1, characterized in that, In the mixing process, the inorganic salt mixed in the positive electrode mixture is only the lithium carbonate.

3. The method for reusing lithium-ion batteries according to claim 2, characterized in that, The heating temperature in the heating process is a temperature above the thermal decomposition temperature of LiFSI.

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