JP2021082555A - Processing method for sulfide all-solid-state lithium-ion battery - Google Patents

Abstract

To provide a processing method of a sulfide all-solid-state lithium-ion battery that can suppress the generation of hydrogen sulfide gas and treat it safely.SOLUTION: A processing method of a sulfide all-solid-state lithium-ion battery includes a control step of maintaining a sulfide all-solid-state lithium-ion battery by using a sulfide solid electrolyte at 60°C to 80°C, and applying a positive electrode voltage of 4.2 V to 4.5 V.SELECTED DRAWING: Figure 1

Description

The present application relates to a method for treating a sulfide all-solid-state lithium-ion battery using a sulfide solid electrolyte.

Since information-related devices such as personal computers, smartphones and tablets, and communication devices have extremely high performance and thinness, the batteries used therein are also required to be small, lightweight, and have high capacity. Further, in the automobile industry, the development and popularization of electric vehicles and hybrid vehicles are being promoted, and the development of batteries having higher output and higher capacity is required. Among the various batteries that have been developed in this way, lithium-ion batteries are attracting attention because of their high energy density.

Further, among lithium ion batteries, an all-solid-state lithium-ion battery that uses a solid electrolyte as an electrolyte does not use an organic solvent that is a liquid in the battery, so that the device can be simplified and the output characteristics and the like can be simplified. Is considered to be excellent in.

In this way, the use of all-solid-state lithium-ion batteries is expected to expand further, and it is expected that their disposal and recycling will become a problem. However, although it is necessary to disassemble the battery for recycling, the sulfide-based solid electrolyte material used as the solid electrolyte of the all-solid-state lithium-ion battery is hydrogen sulfide when it comes into contact with water. Is known to occur, and methods for suppressing the occurrence have been studied.

Patent Document 1 discloses that when a sulfide-based electrolyte material is exposed to a temperature higher than a predetermined temperature, its composition is changed to a composition in which hydrogen sulfide is easily generated. Then, in the all-solid-state lithium secondary battery provided with the sulfide-based electrolyte material-containing layer, when the internal temperature rises and reaches a predetermined temperature, the charge / discharge amount of the all-solid-state lithium secondary battery is reduced. It discloses a method of suppressing a temperature rise of an all-solid-state lithium secondary battery and suppressing a composition change of a sulfide-based solid electrolyte material.

Patent Document 2 encloses a metal salt in a battery case in advance in order to suppress the generation of hydrogen sulfide gas when a large amount of water infiltrates into the battery due to submersion caused by damage to the container, and dissociates when water invades. Discloses a method of suppressing the generation of hydrogen sulfide gas by reacting the metal cations generated in the above with sulfide ions. In Patent Document 3, in the Li _{2 SP 2} S _5- LiI-LiBr-based sulfide solid electrolyte, the generation of hydrogen sulfide can be suppressed by substituting a _{part of Li 2} S with K _{2 S.} Is disclosed. Further, Patent Document 4 discloses that the generation of hydrogen sulfide gas can be suppressed by setting the amount of lithium, phosphorus, and bismuth contained in a constant ratio.

On the other hand, from the viewpoint of recycling the all-solid-state lithium secondary battery, a treatment method capable of efficiently separating the negative electrode layer and the negative electrode current collector is disclosed (Patent Document 5).

International Publication No. 2011/027430 Japanese Unexamined Patent Publication No. 2008-198489 Japanese Unexamined Patent Publication No. 2019-160510 Japanese Unexamined Patent Publication No. 2014-154376 Japanese Unexamined Patent Publication No. 2016-157608

However, there is an effective method for decomposing a sulfide all-solid-state lithium-ion battery using a sulfide solid electrolyte, suppressing the generation of hydrogen sulfide gas that occurs when exposed to the atmosphere, and treating it safely. unknown.

Therefore, it is an object of the present invention to provide a method for treating a sulfide all-solid-state lithium-ion battery that can suppress the generation of hydrogen sulfide gas and treat it safely.

The present disclosure achieves the above object by the following means.

A sulfide all-solid-state lithium-ion battery having a control step of keeping a sulfide all-solid-state lithium-ion battery using a sulfide solid electrolyte at 60 ° C to 80 ° C and applying a positive electrode voltage of 4.2 V to 4.5 V. Processing method.

According to the treatment method of the present disclosure, it is possible to suppress the generation of hydrogen sulfide gas during the treatment. According to this, the sulfide all-solid-state lithium-ion battery can be safely treated.

The processing method 1 of the sulfide all-solid-state lithium ion battery is shown in the flowchart. It is a chart of the X-ray absorption fine structure (XAFS) analysis in Examples 1, 2 and Reference Example. It is a spectrum of X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron Spectroscopy) in the comparative example.

The present application comprises a control step of keeping a sulfide all-solid-state lithium-ion battery using a sulfide solid electrolyte at 60 ° C to 80 ° C and applying a positive electrode voltage of 4.2 V to 4.5 V. Disclose the processing method of the battery.

Here, the "treatment" is to deactivate (deactivate) the battery and dispose of or recycle the deactivated (inactivated) battery.

Hereinafter, the treatment method of the sulfide all-solid-state lithium-ion battery of the present disclosure will be described using the treatment method 1 of the sulfide all-solid-state lithium-ion battery according to the embodiment (hereinafter, may be referred to as “treatment method 1”). .. FIG. 1 shows a flowchart of the processing method 1.

In the treatment method 1 of the sulfide all-solid-state lithium-ion battery, the sulfide all-solid-state lithium-ion battery using the sulfide solid electrolyte is kept at 60 ° C to 80 ° C, and a positive electrode voltage of 4.2 V to 4.5 V is applied. It is characterized in that it includes at least a step (control step S2). Further, as shown in FIG. 1, a determination step (determination step S1) for determining the degree of deterioration of the sulfide all-solid-state lithium-ion battery is provided before the control step S2, and the resistance of the battery undergoing the control step S2. A confirmation step (confirmation step S3) for confirming the value may be provided. The determination step S1 and the confirmation step S3 are arbitrary steps.

<Sulfide all-solid-state lithium-ion battery>
First, the sulfide all-solid-state lithium-ion battery treated in the treatment method 1 will be described.
The sulfide all-solid-state lithium-ion battery treated in the treatment method 1 means an all-solid-state lithium-ion battery using at least a sulfide solid electrolyte. The sulfide solid electrolyte contains at least Li ₃ PS ₄ . In addition, a known sulfide-based solid electrolyte may be contained. For example, Li _{2 SP 2} S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Si _{2 SP 2} S ₅ , Li _{2 SP 2} S _5- LiI-LiBr. _{, LiI-Li 2 S-P} 2 S 5, LiI-Li 2 S-P 2 O 5, LiI-Li 3 PO 4 -P 2 S 5, Li 2 S-P 2 include the S 5 -GeS _2, etc. Can be done.

Such a battery has, for example, the following configuration. That is, it includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer. Further, at least among the surfaces of the ends of the sulfide all-solid-state lithium-ion battery in the stacking direction, the positive electrode current collector is arranged on the surface on the positive electrode side. Further, at least among the surfaces at the ends of the sulfide all-solid-state lithium-ion battery in the stacking direction, the negative electrode current collector is arranged on the surface on the negative electrode side. However, the positive electrode current collector and the negative electrode current collector may also be provided inside the sulfide all-solid-state lithium-ion battery.

The positive electrode layer contains at least the positive electrode active material. In addition to the positive electrode active material, the positive electrode layer may optionally contain a solid electrolyte, a binder, a conductive agent, and the like. As the positive electrode active material, a known positive electrode active material may be used. For example, when a lithium ion battery, lithium cobalt oxide as the positive electrode active material, lithium _{nickelate, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, lithium manganate, various such spinel type lithium compound Lithium-containing composite oxides can be used. The surface of the positive electrode active material may be coated with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer. The solid electrolyte that can be contained in the positive electrode layer is not particularly limited, but a sulfide solid electrolyte is preferable. As the sulfide solid electrolyte, a known sulfide solid electrolyte as described above can be used.
Examples of the binder that can be contained in the positive electrode layer include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-). HFP) and the like. Examples of the conductive agent that can be contained in the positive electrode layer include carbon materials such as acetylene black, ketjen black, and vapor phase carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel. The content of each component in the positive electrode layer may be the same as before. The shape of the positive electrode layer may be the same as the conventional one. In particular, a sheet-shaped positive electrode layer is preferable from the viewpoint that a sulfide all-solid-state lithium-ion battery can be easily constructed. In this case, the thickness of the positive electrode layer is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less.

The negative electrode layer contains at least the negative electrode active material. In addition to the negative electrode active material, the negative electrode layer may optionally contain a solid electrolyte, a binder, a conductive agent, and the like. As the negative electrode active material, a known negative electrode active material may be used. For example, in the case of forming a lithium ion battery, as a negative electrode active material, a silicon-based active material such as Si, Si alloy or silicon oxide; a carbon-based active material such as graphite or hard carbon; various oxide-based active materials such as lithium titanate. Material: Metallic lithium, lithium alloy, etc. can be used. The solid electrolyte that can be contained in the negative electrode layer is not particularly limited, but a sulfide solid electrolyte is preferable. As the sulfide solid electrolyte, a known sulfide solid electrolyte can be used. For example, the above-mentioned sulfide solid electrolyte can be exemplified. As the binder that can be contained in the negative electrode layer, for example, the above-mentioned binder can be exemplified. As the conductive agent that can be contained in the negative electrode layer, for example, the above-mentioned conductive agent can be exemplified. The content of each component in the negative electrode layer may be the same as the conventional one. The shape of the negative electrode layer may be the same as the conventional one. In particular, a sheet-shaped negative electrode layer is preferable from the viewpoint that a sulfide all-solid-state lithium-ion battery can be easily constructed. In this case, the thickness of the negative electrode layer is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 150 μm or less. However, it is preferable to determine the size (area and thickness) of the negative electrode layer so that the capacity of the negative electrode is larger than the capacity of the positive electrode.

The solid electrolyte layer contains a solid electrolyte. In addition to the solid electrolyte, the solid electrolyte layer may optionally contain a binder, a conductive agent and the like. The solid electrolyte contained in the solid electrolyte layer is not particularly limited, but is preferably a sulfide solid electrolyte. As the sulfide solid electrolyte, a known sulfide solid electrolyte as described above can be used. As the binder that can be contained in the solid electrolyte layer, for example, the above-mentioned binder can be exemplified. Examples of the conductive agent that can be contained in the solid electrolyte layer include the above-mentioned conductive agents. The content of each component in the solid electrolyte layer may be the same as before. The shape of the solid electrolyte layer may be the same as the conventional one. In particular, a sheet-shaped sulfide solid electrolyte layer is preferable from the viewpoint that a sulfide all-solid-state lithium-ion battery can be easily constructed. In this case, the thickness of the sulfide solid electrolyte layer is preferably, for example, 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 100 μm or less.

The positive electrode current collector and the negative electrode current collector may be formed of a metal foil, a metal mesh, or the like, and a metal foil is particularly preferable. Examples of the metal constituting the positive electrode current collector and the negative electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. Especially Cu and Al are preferable. The positive electrode current collector and the negative electrode current collector may have some coating layer on the surface thereof for adjusting the resistance. The thickness of each of the positive electrode current collector and the negative electrode current collector is not particularly limited. For example, it is preferably 0.1 μm or more and 1 mm or less, and more preferably 1 μm or more and 100 μm or less.

Such a sulfide all-solid-state lithium-ion battery can be produced by a known method. For example, it can be produced by laminating and pressing a positive electrode layer, a solid electrolyte layer, and a negative electrode layer that are separately produced. The positive electrode layer can be produced by applying a slurry containing a component constituting the positive electrode layer to a base material or a positive electrode current collector and drying the slurry. The negative electrode layer can be produced by applying a slurry containing a component constituting the negative electrode layer to a base material or a negative electrode current collector and drying the slurry. The solid electrolyte layer can be produced by applying a slurry containing a component constituting the solid electrolyte layer to a base material and drying it.

Further, the sulfide all-solid-state lithium-ion battery produced as described above may be sealed with a metal laminate film or the like.

Next, each step provided in the processing method 1 will be described.

<Judgment process S1>
The determination step S1 is a step of determining the degree of deterioration of the sulfide all-solid-state lithium-ion battery. In the determination step S1, it can be determined whether or not the sulfide all-solid-state lithium ion battery should be treated.

Here, "determining the degree of deterioration" means determining whether or not to perform the control step S2 on the battery depending on whether or not the degree of deterioration of the battery is equal to or higher than the reference value, and is equal to or higher than the reference value. If so, it can be determined that the battery should be processed. The degree of deterioration can be determined, for example, by the rate of decrease in capacity. Further, the reference value can be appropriately determined in consideration of the usage mode of the battery and the like, but in the present disclosure, the reduction rate of the capacity is set to 75%.

<Control process S2>
When the degree of deterioration is equal to or higher than the reference value determined above in the determination step S1, the control step S2 is performed.
The control step S2 is a step of activating (deactivating) the battery determined to be processed in the determination step S1.

Specifically, it is a step of holding a sulfide all-solid-state lithium-ion battery at 25 ° C to 180 ° C and applying a positive electrode voltage of 4.2 V to 4.5 V. The preferred temperature is 80 ° C to 100 ° C. The preferable voltage is 4.4 to 4.5V. The preferred energization type is cycle energization. The conditions for cycle energization are not particularly limited, but the conditions of SOC (State of Charge: charge rate) 0 to 100% and 2C may be used. There is no particular limitation on the number of times of energization, and the judgment is made while monitoring the resistance increase rate and the capacitance decrease rate.

_{When Li 3} PS ₄ contained in the sulfide-based solid electrolyte is _{exposed to the atmosphere, Li 3} + H ₂ O → Li ₃ PO ₄ + H ₂ S ... Equation (1) due to the moisture in the atmosphere.
This reaction causes hydrogen sulfide to be generated. Since hydrogen sulfide is extremely toxic, it is desirable to prevent this reaction from the viewpoint of work safety.

This time, the inventor performed the control step S2 to control Li ₃ PS ₄ .
Li ₃ PS ₄ → Li ₄ P ₂ S ₆ + 2S + 2Li ... Equation (2)
It was found that the generation of hydrogen sulfide can be suppressed during the treatment by promoting the reaction.
Li ₄ P ₂ S ₆ is a substance that does not decompose in air below 300 ° C. Therefore, even when the battery is disassembled for the purpose of recycling or the like, the work can be performed safely.

In the control step S2, Li ₄ P ₂ S ₆ and elemental sulfur are preferably produced up to about 0.8 to 2 times _{that of Li 3} PS ₄ at the peak of XAFS, up to 1.4 to 1.8. It is more preferable to generate it.

<Confirmation process S3>
The confirmation step S3 is performed after the control step S2, and is a step of determining whether or not the sulfide all-solid-state lithium-ion battery can be safely processed.

Specifically, it is a step of determining whether or not the resistance value of the sulfide all-solid-state lithium-ion battery is equal to or higher than a predetermined reference value. If the resistance value is equal to or higher than a predetermined reference value, the reaction of the formula (2) has proceeded sufficiently, and the sulfide all-solid-state lithium-ion battery can be safely treated. When the resistance value is less than a predetermined standard, it can be determined that the reaction of the formula (2) has not proceeded sufficiently and it is difficult to safely process the sulfide all-solid-state lithium-ion battery. Therefore, when the resistance value is less than a predetermined reference, the control step S2 is performed again to allow the reaction to proceed sufficiently. That is, the control step S2 and the confirmation step S3 are repeated until the value becomes equal to or higher than the reference value. The predetermined reference value can be appropriately determined in consideration of the processing environment of the battery and the like.
The resistance value is calculated by measuring the voltage and current, but the measuring method and the measuring device can be a general measuring method and the measuring device without limitation.

Hereinafter, the present invention will be described in more detail with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Examples 1 and 2, reference example)
<Manufacturing of sulfide all-solid-state lithium-ion battery>
Lithium nickel cobalt manganese oxide subjected to a surface treatment of LiNbO ₃ as a positive electrode material _{(LiNi 3 / 5Co 1 / 5Mn} 1 / 5O 2) 84.7 wt%, a solid electrolyte (10LiI-15LiBr-85 (0.75Li 2 S- 0.25P ₂ S ₅ )) 13.4% by weight, 1.3% by weight of vapor phase carbon fiber (VGCF), and 0.6% by weight of polyvinylidene fluoride (PVDF) as a binder are mixed in the positive electrode. A slurry was prepared using butyl butyrate as a material and a solvent. The obtained slurry was applied to an Al foil so as to have a thickness of 15 μm, and dried to obtain a positive electrode current collector foil.
Next, as the negative electrode active material, 71% by weight of lithium titanate (LTO), 1.7% by weight of VGCF, and 23.9% by weight of solid electrolyte (10LiI-15LiBr-85 (0.75Li ₂ S-0.25P ₂ S ₅ )). % And 3.4% by weight of the binder (PVDF) were mixed to prepare a slurry in the same manner as the positive electrode active material using butyl butyrate as a solvent, and Ni foil was used as the negative electrode current collecting foil so that the obtained slurry had a thickness of 15 μm. And dried to prepare a negative electrode. In addition, a solid electrolyte layer was prepared using a sulfide solid electrolyte ( _{a mixture of Li 3} PS ₄ and Li ₃ P ₇ S _11). Then, the positive electrode, the solid electrolyte, and the negative electrode were arranged in this order and sealed with a laminate to prepare a sulfide all-solid-state lithium-ion battery according to Examples 1 and 2, and Reference Example.

[An endurance test]
The prepared sulfide all-solid-state lithium-ion battery was heated at the temperatures shown in Table 1 and further subjected to cycle energization (positive electrode voltage 4.5 V) for 30 days under the conditions of SOC 0-100% and 2C. Then, the following measurements were carried out on the sulfide all-solid-state lithium-ion battery after the durability test.

< _{Amount ratio of Li 4} P ₂ S ₆ to 2 Li ₃ PS ₄ and rate of formation of _{Li 4} P ₂ S _6>
For the sulfide all-solid-state lithium-ion battery after the durability test, using AichiSR BL6N1 (soft X-ray XAFS / photoelectron spectroscopy beamline) of Aichi Synchroton Optical Center, X-ray energy 2-3 keV, beam size 2. X-ray absorption fine structure (XAFS) analysis was performed under the condition of 0 × 1.0 mm (width × height). The quantitative ratio of the produced Li ₄ P ₂ S ₆ to 2 Li ₃ PS _{4 and the production rate of Li 4} P ₂ S ₆ were analyzed from the peak intensities. The results are shown in Table 1. A chart of X-ray absorption fine structure (XAFS) analysis is shown in FIG.

<Discharge resistance>
Sulfide all-solid-state lithium-ion battery after the durability test The discharge resistance of the solid-state battery was measured under the conditions of SOC 60% and 2.5C, and compared with the resistance value before the durability test.

<Amount of hydrogen sulfide generated>
Sulfide after endurance test All-solid-state lithium-ion battery Put the sulfide solid electrolyte in the solid electrolyte layer of the solid-state battery into a 200 ml vial, pour air with a relative humidity (RH) of 30-40% into the bottle, and leave it for 1 hour. After that, the amount of hydrogen sulfide generated was measured with a mass flow meter. The results are shown in Table 1.

<The calorific value of the sulfide solid electrolyte>
The calorific value is measured by using a SUS gold-plated sealed container as a sample container, under conditions of a measurement temperature of 20 ° C. to 500 ° C. and a temperature rise rate of 10 ° C./min under an argon gas atmosphere, differential scanning calorimetry (DSC). Measured by method. The results are shown in Table 1.

As shown in Table 1, at the heating temperatures of 25 ° C, 60 ° C and 80 ° C, the higher the temperature, the faster the rate of formation of _{Li 4} P ₂ S _6. From this, it can be seen that the higher the temperature, the faster Li ₄ P ₂ S _{6 is produced.} This can be seen from the fact that the higher the temperature, the _{larger the proportion of Li 4} P ₂ S _{6 in the whole.} Also, from the value of the discharge resistance, _{it can be read that the higher the heated temperature, the more the decomposition of 2Li 3} PS ₄ progresses, and the solid electrolyte layer loses its function.

The amount of hydrogen sulfide generated is also less than 1/2 of that of Reference Example 3, which was heated at 25 ° C, which is almost room temperature, in Example 1 in which heating was performed at 80 ° C.

In addition, since the calorific value is significantly reduced, it is considered that the battery is more effectively alive and dead when heated at 80 ° C.

As for the resistance value after the durability test, as the temperature rises, the resistance value increases to about 2.36 times at 60 ° C and 2.76 times at 80 ° C as compared with the case where the voltage is applied at 25 ° C. The reaction of the formula (2) occurs even when heated to about 60 ° C., and decomposition starts, but it is considered that the reaction proceeds more at a higher temperature of 80 ° C.

(Comparative Examples 1 to 3)
Prepare positive electrode pellets using NCM, solid electrolyte (10LiI-15LiBr-85 (0.75Li ₂ S-0.25P ₂ S ₅ )), binder (PVDF), and 15 μm Al positive electrode current collector foil. , The heat treatment was performed under the temperature conditions shown in Table 2.
After the heat treatment, measurements were performed by X-ray Photoelectron spectroscopy (XPS) under the following conditions, and the peak intensities of S-Li, S = P, S-PS-C, and SO were measured. The results are shown in FIG. 3 and Table 2.

<XPS measurement conditions>
Equipment: ULVAC-PHI, Inc., PHI5000 scanning X-ray photoelectron spectrometer Measurement conditions: X-ray source AlKα, monochrome 1486.6 eV, 50 W
Analysis area: 1.0 x 0.4 mm ²
Use of charge neutralization mechanism (electronic neutralization gun)
Pretreatment conditions: Gas type: Ar
Gas flow rate: 130 sccm (about 1.0 atm)
Heating temperature: 60 ° C, 80 ° C, 120 ° C (2 hours each)

Here, the pellet sample was opened in an Ar glove box, sampled, and introduced into the XPS apparatus without exposure to the atmosphere using a transfer vessel. The XPS measurement was performed at the same location after heating at a specified temperature (60 ° C, 80 ° C, 120 ° C) for 2 hours using the reaction cell of the XPS pretreatment device.

As shown in Table 2, there was no difference in the amount _{of Li 4} P ₂ S ₆ produced due to the difference in temperature when the temperature was 80 ° C or lower. When heating was performed at 120 ° C., there was a slight difference in the peak of SO. It is considered that this is because the electrolyte oxidation reaction occurred.

Claims (1)

A sulfide all-solid-state lithium-ion battery having a control step of keeping a sulfide all-solid-state lithium-ion battery using a sulfide solid electrolyte at 60 ° C to 80 ° C and applying a positive electrode voltage of 4.2 V to 4.5 V. Processing method.

Images