Processing method for lithium secondary battery

Abstract

The purpose of the present invention is to provide a means that, when processing a lithium secondary battery including an electrode having an electrode active material layer in which a sulfide solid electrolyte and a binder are used, is capable of easily separating the electrode active material layer and a current collector from each other.　The present invention provides a processing method for a lithium secondary battery having an electrode including a current collector and an electrode active material layer that is laminated on the current collector and includes an electrode active material, a sulfide solid electrolyte, and a binder. The method includes a dissolution step for bringing the electrode into contact with a protic solvent to dissolve the sulfide solid electrolyte, and a separation step for separating the current collector and the electrode active material layer in which the sulfide solid electrolyte has been dissolved through the dissolution step.

Description

Disposal methods for lithium secondary batteries 【0001】 The present invention relates to a method for processing lithium secondary batteries. 【0002】 In recent years, research and development on lithium secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of ion conduction in a solid state. Therefore, lithium secondary batteries using solid electrolytes, such as all-solid-state batteries, have the advantage that, in principle, various problems caused by flammable organic electrolytes do not occur, unlike conventional liquid-based secondary batteries using non-aqueous electrolytes. In addition, generally, using high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials can significantly improve the power density and energy density of the battery. 【0003】 On the other hand, recycling of used batteries that have exceeded their service life has been carried out conventionally. The electrode active materials and solid electrolytes of lithium secondary batteries contain components such as rare metals, and it is desirable to recover and reuse these components from used batteries. In particular, the solid electrolytes used in lithium secondary batteries that use solid electrolytes, such as all-solid-state batteries, contain lithium at a much higher concentration than the lithium ions contained in the electrolyte of liquid-type secondary batteries, making lithium recovery important. Regarding lithium recovery in all-solid-state batteries, for example, International Publication No. 2010 / 106618 discloses a method for processing a battery component that contains at least a positive electrode active material having Li and a sulfide solid electrolyte material having Li, wherein the battery component and the processing liquid are brought into contact to dissolve the Li contained in the sulfide solid electrolyte material in the processing liquid, the positive electrode active material which is an insoluble component is recovered from the processing liquid in which the Li has been dissolved, and the Li compound is recovered from the processing liquid from which the positive electrode active material has been recovered. According to International Publication No. 2010 / 106618, this processing method allows for efficient separation of the positive electrode active material and the sulfide solid electrolyte material, and for efficient recovery of the Li contained in the positive electrode active material and the sulfide solid electrolyte material. 【0004】However, the method described in International Publication No. 2010 / 106618 is limited to a method for recovering a lithium compound derived from lithium contained in a positive electrode active material and a sulfide solid electrolyte from a positive electrode active material layer, and does not disclose separating an electrode active material layer (a positive electrode active material layer or a negative electrode active material layer) from a current collector (a positive electrode current collector or a negative electrode current collector). 【0005】 Therefore, an object of the present invention is to provide a means capable of easily separating an electrode active material layer from a current collector when treating a lithium secondary battery including an electrode having an electrode active material layer using a sulfide solid electrolyte and a binder. 【0006】 The present inventors conducted intensive studies to solve the above problems. As a result, by a method for treating a lithium secondary battery in which a sulfide solid electrolyte in an electrode active material layer is dissolved in a protic solvent and the electrode active material layer (a layer containing an electrode active material and a binder) after the sulfide solid electrolyte is dissolved is separated from a current collector, it was found that the above problems are solved, and the present invention was completed. 【0007】 That is, one aspect of the present invention is a method for treating a lithium secondary battery having an electrode including a current collector and an electrode active material layer laminated on the current collector and including an electrode active material, a sulfide solid electrolyte, and a binder, the method including a dissolution step of bringing the electrode into contact with a protic solvent to dissolve the sulfide solid electrolyte, and a separation step of separating the electrode active material layer and the current collector after the sulfide solid electrolyte is dissolved by the dissolution step. 【0008】 FIG. 1 is a diagram schematically showing separation of an electrode active material layer and a current collector in an electrode by the method of this aspect. FIG. 2 is a cross-sectional view schematically showing the overall structure of a laminated (internally parallel-connected type) all-solid-state lithium secondary battery (laminated secondary battery) which is an example of the lithium secondary battery in this aspect. 【0009】 Hereinafter, embodiments of the present invention will be described. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited only to the following embodiments. 【0010】One embodiment of the present invention is a method for processing a lithium secondary battery having a current collector and an electrode comprising an electrode active material layer laminated on the current collector and comprising an electrode active material layer comprising an electrode active material, a sulfide solid electrolyte, and a binder, comprising a dissolution step of contacting the electrode with a protic solvent to dissolve the sulfide solid electrolyte, and a separation step of separating the electrode active material layer in which the sulfide solid electrolyte has dissolved in the dissolution step from the current collector. According to the processing method of this embodiment, when processing a lithium secondary battery having an electrode with an electrode active material layer using a sulfide solid electrolyte and a binder, the electrode active material layer and the current collector can be easily separated. 【0011】 In lithium secondary batteries using a solid electrolyte, the solid interfaces of the positive electrode, solid electrolyte layer, and negative electrode are firmly bonded together. Furthermore, within the positive or negative electrode, the positive electrode active material layer or negative electrode active material layer, which contains the positive electrode active material or negative electrode active material, solid electrolyte, and binder, is firmly bonded at the interface with the positive electrode current collector or negative electrode current collector. Therefore, it is difficult to separate and recover the positive electrode current collector or negative electrode current collector from the positive electrode active material layer or negative electrode active material layer during recycling. 【0012】 In this embodiment of the method, an electrode having an electrode active material layer containing an electrode active material, a sulfide solid electrolyte, and a binder is brought into contact with a protic solvent to dissolve the sulfide solid electrolyte (dissolution step). This reduces the contact area between the electrode active material layer and the current collector, thereby decreasing the bonding force between them. As a result, a space (void) is created at the interface between the electrode active material layer and the current collector, allowing for easy separation of the electrode active material layer and the current collector (separation step). 【0013】Figure 1 schematically shows the separation of the electrode active material layer and the current collector in an electrode according to the method of this embodiment. Before processing, the electrode 101 has an electrode active material layer 103 on a current collector 102, and the electrode active material layer 103 contains an electrode active material 104, a sulfide solid electrolyte 105, and a binder 106. By performing the dissolution step S1 on the electrode 101, a gap 107 is created between the current collector 102 and the electrode active material layer 103' in which the sulfide solid electrolyte has dissolved. Subsequently, the current collector 102 and the electrode active material layer 103' in which the sulfide solid electrolyte has dissolved are separated by the separation step S2. 【0014】 The lithium secondary battery, including electrodes, in this embodiment will be described below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numeral, and redundant explanations are omitted. Furthermore, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from actual ratios. 【0015】 Figure 2 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked secondary battery"), which is an example of a lithium secondary battery. 【0016】As shown in Figure 2, the stacked battery 10a has a structure in which a flattened, roughly rectangular power generation element 21, in which the charge-discharge reaction actually takes place, is sealed inside a laminate film 29 which is the battery casing. Here, the power generation element 21 has a structure in which a positive electrode, a solid electrolyte layer 17 containing a solid electrolyte, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode active material layer 15 containing positive electrode active material is arranged on both sides of a positive electrode current collector 11''. The negative electrode has a structure in which a negative electrode active material layer 13 containing negative electrode active material is arranged on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 and the adjacent negative electrode active material layer 13 face each other via the solid electrolyte layer 17. As a result, adjacent positive electrode, solid electrolyte layer, and negative electrode This constitutes one single cell layer 19. Therefore, the stacked battery 10a shown in Figure 2 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel. The negative electrode current collector 11' and the positive electrode current collector 11'' are each fitted with a negative electrode current collector plate 25 and a positive electrode current collector plate 27, which are electrically connected to the respective electrodes (negative and positive electrodes), and have a structure that leads out to the outside of the laminate film 29 by being sandwiched between the edges of the laminate film 29. The stacked battery 10a is subjected to restraining pressure in the stacking direction of the power generation elements 21 by a pressurizing member (not shown). Therefore, the volume of the power generation elements 21 is kept constant. 【0017】 It should be noted that the lithium secondary battery processed by this processing method does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There are no particular restrictions on the amount of liquid electrolyte (electrolyte) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and no leakage of the liquid electrolyte (electrolyte) occurs. 【0018】<Method for Processing Lithium Secondary Batteries> One embodiment of the present invention is a method for processing a lithium secondary battery having a current collector and an electrode comprising an electrode active material layer laminated on the current collector and comprising an electrode active material layer comprising an electrode active material, a sulfide solid electrolyte, and a binder, the method comprising: a dissolution step of contacting the electrode with a protic solvent to dissolve the sulfide solid electrolyte; and a separation step of separating the electrode active material layer in which the sulfide solid electrolyte has dissolved in the dissolution step from the current collector. The steps in the processing method of this embodiment will be described below. 【0019】 [Electrodes] The electrodes of the lithium secondary battery processed by the method of this embodiment include a current collector and an electrode active material layer laminated on the current collector, which includes an electrode active material, a sulfide solid electrolyte, and a binder. The electrodes processed by this embodiment may be a positive electrode, a negative electrode, or both. Since the positive electrode active material often contains valuable components such as rare metals and more efficient recovery is often required, it is preferable that the electrodes processed by this embodiment include at least a positive electrode. 【0020】 [Current Collector] The current collector (positive electrode current collector, negative electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (positive electrode active material layer, negative electrode active material layer). There are no particular restrictions on the materials that make up the current collector. Examples of materials that can be used to make up the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but one example is 10 to 100 μm. 【0021】 [Electrode Active Material Layer] The electrode active material layer (positive electrode active material layer, negative electrode active material layer) comprises electrode active material (positive electrode active material, negative electrode active material), sulfide solid electrolyte, and binder, and optionally further comprises a conductive additive. 【0022】 (Positive electrode active material) The positive electrode active material has the function of releasing ions such as lithium ions during charging and absorbing ions such as lithium ions during discharge. A lithium transition metal composite oxide is preferred as the positive electrode active material. For example, LiCoO ２ LiMnO ２ LiNiO２ , LiVO ２ , Li(Ni-Mn-Co)O ２ and other layered rock salt type active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ and other spinel type active materials such as LiFePO ４ , LiMnPO ４ and other olivine type active materials such as lithium transition metal composite oxides can be mentioned. Among these, composite oxides containing lithium and nickel (lithium nickel composite oxides) are preferably used. As the lithium nickel composite oxide, Li(Ni-Mn-Co)O ２ and those in which some of these transition metals are substituted with other elements (hereinafter, simply referred to as "NMC composite oxide") can be preferably used. The NMC composite oxide has a layered crystal structure in which lithium atom layers and transition metal (Mn, Ni, and Co are arranged in an orderly manner) atom layers are alternately stacked via oxygen atom layers, and contains one Li atom per one atom of transition metal M. The amount of Li that can be extracted is twice that of spinel lithium manganese oxide, that is, the supply capacity is doubled, and it can have a high capacity. 【0023】 (Negative electrode active material) The type of the negative electrode active material is not particularly limited, and examples include carbon materials, metal oxides, and metal active materials. Further, as the negative electrode active material, a metal containing lithium may be used. Such a negative electrode active material is not particularly limited as long as it is an active material containing lithium, and examples include lithium metal and lithium-containing alloys. Examples of the lithium-containing alloy include an alloy of Li and at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. 【0024】 The average particle size of the electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm. In this specification, the average particle size of the particles shall be the median diameter (D50) measured by a particle size distribution measuring device using the laser diffraction / scattering method. 【0025】The content of the electrode active material in the electrode active material layer is not particularly limited, but is preferably 30 to 95% by mass, and more preferably 40 to 85% by mass. 【0026】 (Sulfide Solid Electrolyte) In this specification, a solid electrolyte refers to a material mainly composed of an ion conductor capable of conducting ions in a solid state, and in particular, a lithium ion conductivity of 1 × 10⁻¹⁶ at room temperature (25°C) －５ This refers to a material with a lithium ion conductivity of S / cm or higher, and this lithium ion conductivity is preferably 1 × 10⁻⁶. －４ The ionic conductivity is greater than or equal to S / cm. Here, the value of ionic conductivity can be measured by the AC impedance method. Sulfide solid electrolytes refer to solid electrolytes containing the element S. 【0027】 The sulfide solid electrolyte preferably contains Li, M, and S elements, wherein the M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I, and more preferably it is a sulfide solid electrolyte containing S, Li, and P elements. 【0028】 Sulfide solid electrolytes are Li ３ PS ４ It may have a skeleton, Li ４ P ２ S ７ It may have a skeleton, Li ４ P ２ S ６ It may have a skeleton. ３ PS ４ Examples of sulfide solid electrolytes with a skeleton include LiI-Li ３ PS ４ , LiI-LiBr-Li ３ PS ４ Li ３ PS ４ This can be cited. Also, Li ４ P ２ S ７ Examples of sulfide solid electrolytes having a framework include Li-P-S solid electrolytes called LPS. （４－ｘ） Ge （１－ｘ）P ｘ S ４ You may also use LGPS, etc., which is represented as (where x satisfies 0 < x < 1). More specifically, for example, LPS(Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ Li ３．２ P ０．９６ S, Li ３．２５ Ge ０．２５ P ０．７５ S ４ Li １０ GeP ２ S １２ , or Li ６ PS ５ Examples include X (where X is Cl, Br, or I). ２ S-P ２ S ５ The description of " is Li ２ S and P ２ S ５ This refers to a sulfide solid electrolyte made using a raw material composition containing the above, and the same applies to other descriptions. In particular, the sulfide solid electrolyte is preferably LPS (Li) because it has high ionic conductivity and a low bulk modulus, and can therefore follow the volume change of the electrode active material accompanying charging and discharging. ２ S-P ２ S ５ ), Li ６ PS ５ X (where X is Cl, Br, or I), Li ７ P ３ S １１ Li ３．２ P ０．９６ S and Li ３ PS ４ It is selected from the group consisting of the following. 【0029】 The average particle size (D50) of the sulfide solid electrolyte is not particularly limited, but is preferably 0.01 μm or more and 40 μm or less, and more preferably 0.1 μm or more and 20 μm or less. 【0030】The content of sulfide solid electrolyte in the electrode active material layer is not particularly limited, but is, for example, 1 to 60% by mass, and preferably 10 to 50% by mass. 【0031】 (Binder) The binder is not particularly limited, and known binders used in lithium secondary batteries using sulfide solid electrolytes can be used. Examples of binders include thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene (PTFE), polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated products, styrene-isoprene-styrene block copolymer and its hydrogenated products, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoro Examples include fluororesins such as polyethylene copolymer (ECTFE) and polyvinyl fluoride (PVF), vinylidene fluoride-based fluororubbers such as vinylidene fluoride-hexafluoropropylene-based fluororubbers (VDF-HFP-based fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-HFP-TFE-based fluororubbers), vinylidene fluoride-pentafluoropropylene-based fluororubbers (VDF-PFP-based fluororubbers), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), epoxy resins, and carboxymethylcellulose. 【0032】 In the processing method of this embodiment, it is preferable that the binder contained in the electrode active material layer does not dissolve in the protic solvent used to dissolve the sulfide solid electrolyte, as described later. In this specification, "does not dissolve" in a certain solvent means that the solubility of the binder in that solvent (at 25°C) is less than 0.1 g / 100 g of solvent. As such binders, depending on the type of protic solvent used, polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene (PTFE), polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride; fluororesin; vinylidene fluoride-based fluororubber, etc. are used. Among these, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene, etc. are preferred. If the binder is insoluble in protic solvents, it is less likely to contaminate the processing solution after the sulfide solid electrolyte has been dissolved. As a result, the recovery efficiency when recovering lithium from the processing solution is improved, which is preferable. 【0033】 It is preferable that at least a portion of the binder contained in the electrode active material layer is fibrillated. Binders such as polytetrafluoroethylene (PTFE) can be fibrillated (fibrousized) by applying shear force through kneading or other processes. When the binder is fibrillated, the electrode active material and sulfide solid electrolyte become entangled and held within the structure of the fibrillated binder. Therefore, even when in contact with a protic solvent, as described later, the shape and strength of the electrode active material layer are easily maintained, and separation from the current collector becomes easier. 【0034】In a preferred embodiment, the binder is polytetrafluoroethylene (PTFE). The PTFE may include a form in which part of the terminal or side chain is substituted (modified) with other substituents. In the form in which part of the terminal or side chain is substituted (modified) with other substituents, the proportion of constituent units in which the terminal or side chain is substituted (modified) with other substituents to 100 mol% of the total constituent units is preferably 10 mol% or less, more preferably 5 mol% or less, and most preferably 0 mol%. 【0035】 The binder content in the electrode active material layer is not particularly limited, but is, for example, 0.1 to 10% by mass, and preferably 0.1 to 5% by mass. In a preferred embodiment, the PTFE content in the electrode active material layer is, for example, 0.1 to 10% by mass, and preferably 0.1 to 5% by mass. 【0036】 (Conductive additives) Examples of conductive additives include carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNTs), and carbon black (specifically, acetylene black, Ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.). The content of conductive additives in the electrode active material layer is not particularly limited, but is for example 1 to 10% by mass. 【0037】 In a preferred embodiment, the electrode active material layer is manufactured by a dry method, i.e., without the use of a solvent. A dry-manufactured electrode active material layer is preferred because it is easier to maintain its shape even when in contact with a protic solvent, and the current collector is easier to remove in the separation process. The method for preparing the electrode active material layer when manufactured by a dry method is not particularly limited. For example, a method of pressure molding a mixture containing the electrode active material, a sulfide solid electrolyte, and a binder can be used. 【0038】 The thickness of the electrode active material layer is not particularly limited, but is, for example, 0.1 to 1000 μm, and preferably 10 to 200 μm. 【0039】<Dissolution Process> In the dissolution process, the electrode is brought into contact with a protic solvent to dissolve the sulfide solid electrolyte. 【0040】 The protic solvent is not particularly limited, but examples include water, alcohols such as methanol and ethanol, and carboxylic acids such as formic acid and acetic acid. Two or more protic solvents may be mixed and used. The protic solvent preferably contains water, and more preferably is water, because it is easy to handle and readily dissolves sulfide solid electrolytes. If an aprotic solvent is used in the dissolution process, the aprotic solvent will dissolve the binder, so the binder will also dissolve in the solution in which lithium ions are dissolved. Therefore, it becomes difficult to recover lithium ions. 【0041】 The method for bringing the electrode into contact with the protic solvent is not particularly limited. One example of a method for bringing the electrode into contact with the protic solvent is immersion in the protic solvent (immersion method). In the immersion method, the contact area of ​​the electrode with the protic solvent is large, so the sulfide solid electrolyte can be dissolved efficiently. As a result, a void is more easily formed between the electrode active material layer and the current collector, and separation of the electrode active material layer and the current collector becomes easier, which is preferable. It is also preferable because lithium can be easily recovered from the processing solution after immersion. That is, in a preferred embodiment of the present invention, the dissolution step includes immersing the electrode in a protic solvent. 【0042】 Furthermore, if the dissolution step includes immersing the electrode in a protic solvent, it is preferable to temporarily reduce the pressure of the processing solution containing the electrode and the protic solvent during immersion. When the electrode is brought into contact with the protic solvent, the sulfide solid electrolyte may react with the protic solvent to generate gases such as hydrogen sulfide, but reducing the pressure makes it easier to remove the current collector using the generated gas, which is therefore preferable. The means of reducing the pressure are not particularly limited. The pressure in the reduced pressure state and the time the reduced pressure state is maintained are also not particularly limited, but it is preferable that the protic solvent does not completely volatilize and remains in a liquid state. 【0043】If the dissolution step includes immersing the electrode in a protic solvent, and during the immersion, temporarily reducing the pressure of the treatment solution containing the electrode and the protic solvent, it is preferable to repeatedly reduce the pressure and then release it to the atmosphere during the immersion. Repeating the cycle of reducing the pressure and releasing it to the atmosphere makes it easier for the protic solvent to penetrate the pores in the electrode active material layer due to the pressure difference, and makes it easier to separate the electrode active material layer from the current collector, which is preferable. The number of times the above cycle is repeated is not particularly limited, but for example, it is 2 to 5 times. 【0044】 If the dissolution step includes immersing the electrode in a protic solvent, it is preferable to include vibrating the processing solution containing the electrode and the protic solvent during the immersion. This is preferable because vibrating facilitates the separation of the electrode active material layer from the current collector. The means of applying vibration are not particularly limited as long as they can deliver an impact to the processing solution. For example, any means that can physically impact the electrode from the outside, such as tapping the container containing the processing solution, would suffice. Alternatively, a method of applying ultrasonic vibration using, for example, an ultrasonic dispersion device, can be used. 【0045】 If the dissolution step includes immersing the electrode in a protic solvent, it is preferable to stir the treatment solution containing the electrode and the protic solvent during the immersion. Stirring the treatment solution is preferable because it can further promote the reaction between the sulfide solid electrolyte and the protic solvent, making it easier for voids to form between the electrode active material layer and the current collector, thus facilitating the separation of the electrode active material layer and the current collector. Furthermore, stirring allows for physical impact to be applied to the electrode from the outside, which is also preferable as it facilitates the separation of the electrode active material layer and the current collector. The means for stirring the treatment solution are not particularly limited. The stirring time is also not particularly limited and can be set as appropriate. 【0046】On the other hand, another example of a method for bringing an electrode into contact with a protic solvent is the method of spraying the electrode with a protic solvent (spray method). The spray method has the advantage of being suitable for continuous processing compared to the immersion method described above. For example, by fixing the spray nozzle and moving the electrode horizontally, the electrode can be processed continuously. Also, by placing the electrode on a filter and spraying the electrode with a protic solvent, a filtration process can be performed simultaneously. 【0047】 In the dissolution process, the heated protic solvent may be brought into contact with the electrode. This allows for more efficient dissolution of the sulfide solid electrolyte. If the dissolution process includes immersing the electrode in the protic solvent, the treatment solution containing the electrode and the protic solvent may be heated. The temperature of the treatment solution containing the electrode and the protic solvent is not particularly limited, and is, for example, 0 to 80°C, preferably 15 to 60°C. 【0048】 The dissolution process may be performed with the electrodes separated from the power generation element, or with the electrodes attached. Furthermore, the dissolution process may be performed with the power generation element removed from the battery casing, or with the power generation element remaining inside the battery casing after vacuum opening. In a preferred embodiment, the dissolution process is performed with the electrodes attached to the power generation element. In another preferred embodiment, the dissolution process is performed with the power generation element remaining inside the battery casing. This allows for simpler processing of lithium secondary batteries. 【0049】 <SOC Adjustment Step> In the case of the electrode described above, if the electrode contains a lithium transition metal composite oxide as the positive electrode active material, the processing method may further include an SOC adjustment step before the dissolution step to make the SOC of the lithium secondary battery 10% or less or 50% or more. 【0050】 By reducing the SOC to 10% or less, the positive electrode active material reacts more easily with the protic solvent during the dissolution process, and CO2 is formed at the interface between the current collector and the positive electrode active material layer. ２This makes it easier to generate gases such as lithium hydroxide. As a result, the current collector and the positive electrode active material layer become more prone to separation. There is no particular limit to the lower limit of SOC in this case, but for example, it is 0% or more. 【0051】 On the other hand, increasing the SOC to 50% or more increases the volume contraction of the positive electrode active material during charging, creating voids in the positive electrode active material layer. This allows the protic solvent to penetrate more easily during the dissolution process. As a result, the current collector and the positive electrode active material layer become easier to separate. There is no particular upper limit to the SOC in this case, but for example, it is 100% or less. 【0052】 The means of adjusting the SOC are not particularly limited. Furthermore, the charging and discharging conditions when adjusting the SOC are not particularly limited and may be the same as or different from the charging and discharging conditions during battery use. 【0053】 <Separation Process> The separation process is a process of separating the electrode active material layer, in which the sulfide solid electrolyte has dissolved by the above dissolution process, from the current collector. Here, "separating the electrode active material layer from the current collector" refers to the state in which the current collector is peeled off from the interface with the electrode active material layer. In the separation process, the current collector is peeled off from the interface with the electrode active material layer. Because the adhesion between the interface between the electrode active material layer and the current collector is reduced by the above dissolution process, the current collector can be easily peeled off and separated at the interface between the electrode active material layer and the current collector. 【0054】 The method for separating the current collector is not particularly limited, as long as it can separate the current collector from the interface. For example, the power generation element can be removed from the battery casing, the current collector plate (positive electrode current collector plate or negative electrode current collector plate) can be grasped, and the electrodes can be detached. 【0055】 Furthermore, the above dissolution step may also serve as a separation step. That is, the current collector may be separated from the electrode active material layer during the dissolution step, in which case a separate separation step may not be necessary. 【0056】The separation step may be performed after removing the protic solvent by methods such as filtering the processing solution in the dissolution step, but it is preferable to perform it in the processing solution containing the electrode and the protic solvent. This allows the dissolution step and the separation step to be performed continuously, reducing process costs. In particular, it is more preferable if the dissolution step also serves as the separation step (the current collector is detached from the electrode active material layer in the dissolution step), as this allows the dissolution step and the separation step to be performed in a single step. 【0057】 <Lithium Recovery Process> The present embodiment of the method may further include a lithium recovery process in which lithium is recovered from the processed liquid after the dissolution process or from the processed liquid after the separation process. 【0058】 The specific form of the lithium recovery process is not particularly limited. In one embodiment, the process first removes insoluble components from the processing solution. Examples of insoluble components include electrode active materials, binders, and conductive additives. One method for removing insoluble components from the processing solution is filtration. Next, lithium is recovered from the processing solution from which the insoluble components have been removed. One method for recovering lithium from the processing solution is to remove the protic solvent contained in the processing solution by drying and recover lithium as a lithium compound. The type of lithium compound obtained will vary depending on the type of sulfide solid electrolyte used. For example, if the sulfide solid electrolyte is Li ２ S-P ２ If it is an S compound, Li and P will dissolve in the treatment solution, so Li ３ PO ４ It is recovered as a lithium compound. 【0059】The treated solution from which insoluble components have been removed may contain impurities such as phosphoric acid. In such cases, it is preferable to perform purification treatment as necessary. The purification treatment is not particularly limited, but examples include recrystallization, reprecipitation, and column chromatography. In addition, depending on the type of sulfide solid electrolyte, multiple lithium compounds may be produced. In such cases, it is preferable to perform separation treatment as necessary. The separation treatment is not particularly limited, but examples include methods using differences in specific gravity, specifically wind classification, sedimentation classification, and centrifugal classification. 【0060】The following embodiments are also included in the scope of the present invention: Item 1: A method for processing a lithium secondary battery having a current collector and an electrode comprising an electrode active material layer laminated on the current collector and comprising an electrode active material, a sulfide solid electrolyte, and a binder, comprising: a dissolution step of contacting the electrode with a protic solvent to dissolve the sulfide solid electrolyte; and a separation step of separating the electrode active material layer in which the sulfide solid electrolyte has dissolved by the dissolution step from the current collector; Item 2: The method for processing a lithium secondary battery according to Item 1, wherein the binder does not dissolve in the protic solvent; Item 3: The method for processing a lithium secondary battery according to Item 1 or Item 2, wherein at least a portion of the binder contained in the electrode active material layer is fibrillated; Item 4: The method for processing a lithium secondary battery according to any one of Items 1 to 3, wherein the protic solvent is water; Item 5: The method for processing a lithium secondary battery according to any one of Items 1 to 4, wherein the dissolution step includes immersing the electrode in the protic solvent; Item 6: A method for processing a lithium secondary battery according to item 5, further comprising temporarily reducing the pressure of the processing solution containing the electrode and the protic solvent during the immersion; Item 7: A method for processing a lithium secondary battery according to item 6, further comprising repeatedly reducing the pressure and then releasing it to the atmosphere during the immersion; Item 8: A method for processing a lithium secondary battery according to any one of items 5 to 7, further comprising vibrating the processing solution containing the electrode and the protic solvent during the immersion; Item 9: A method for processing a lithium secondary battery according to any one of items 5 to 8, further comprising stirring the processing solution containing the electrode and the protic solvent during the immersion; Item 10: A method for processing a lithium secondary battery according to any one of items 1 to 9, wherein the electrode is a positive electrode containing a lithium transition metal composite oxide as a positive electrode active material, and further comprising an SOC adjustment step of making the SOC of the lithium secondary battery 10% or less or 50% or more before the dissolution step; Item 11: A method for processing a lithium secondary battery according to any one of items 1 to 10, wherein the separation step is performed in a processing solution containing the electrode and the protic solvent; Item 12: A method for processing a lithium secondary battery according to any one of items 1 to 11, wherein the dissolution step is performed without separating the electrode from the power generation element including the electrode;Item 13: The method for processing a lithium secondary battery according to any one of items 1 to 12, wherein the electrode is manufactured by a dry process. 【0061】 10a Stacked battery, 11' Negative electrode current collector, 11'' Positive electrode current collector, 13 Negative electrode active material layer, 15 Positive electrode active material layer, 17 Solid electrolyte layer, 19 Single cell layer, 21 Power generation element, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29 Laminate film, 101 Electrode, 102 Current collector, 103 Electrode active material layer, 103' Electrode active material layer with dissolved sulfide solid electrolyte, 104 Electrode active material, 105 Sulfide solid electrolyte, 106 Binder, 107 Void, S1 Dissolution process, S2 Separation process.

Claims

1. A method for processing a lithium secondary battery having a current collector and an electrode comprising an electrode active material layer laminated on the current collector and comprising an electrode active material layer comprising an electrode active material, a sulfide solid electrolyte, and a binder, the method comprising: a dissolution step of contacting the electrode with a protic solvent to dissolve the sulfide solid electrolyte; and a separation step of separating the electrode active material layer in which the sulfide solid electrolyte has been dissolved by the dissolution step from the current collector.

2. The method for processing a lithium secondary battery according to claim 1, wherein the binder does not dissolve in the protic solvent.

3. The method for processing a lithium secondary battery according to claim 1, wherein at least a portion of the binder contained in the electrode active material layer is fibrillated.

4. The method for processing a lithium secondary battery according to claim 1, wherein the protic solvent is water.

5. The method for processing a lithium secondary battery according to claim 1, wherein the dissolution step includes immersing the electrode in the protic solvent.

6. The method for processing a lithium secondary battery according to claim 5, comprising temporarily reducing the pressure of the processing solution containing the electrode and the protic solvent during the immersion.

7. The method for processing a lithium secondary battery according to claim 6, wherein the process of reducing the pressure and then releasing it to the atmosphere is repeated during the immersion.

8. The method for processing a lithium secondary battery according to claim 5, comprising applying vibration to the processing solution containing the electrode and the protic solvent during the immersion.

9. The method for processing a lithium secondary battery according to claim 5, comprising stirring the processing solution containing the electrode and the protic solvent during the immersion.

10. The method for processing a lithium secondary battery according to claim 1, wherein the electrode is a positive electrode containing a lithium transition metal composite oxide as a positive electrode active material, and further comprises an SOC adjustment step before the dissolution step to make the SOC of the lithium secondary battery 10% or less or 50% or more.

11. The method for processing a lithium secondary battery according to claim 1, wherein the separation step is carried out in a processing solution containing the electrode and the protic solvent.

12. The method for processing a lithium secondary battery according to claim 1, wherein the dissolution step is performed without separating the electrode from the power generation element including the electrode.

13. The method for processing a lithium secondary battery according to claim 1, wherein the electrode is manufactured by a dry process.

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