JP6421809B2 - Sulfide all-solid battery manufacturing method and sulfide all-solid battery - Google Patents

Description

  The present invention relates to a method for producing a sulfide all solid state battery and a sulfide all solid state battery.

In the field of all-solid-state batteries, there have been attempts to improve the performance of all-solid-state batteries by paying attention to battery charge / discharge.
For example, Patent Document 1 discloses a sulfide all solid state battery that performs charging and discharging in an argon gas atmosphere.

On the other hand, paying attention to the surface of the sulfide-based solid electrolyte, there is an attempt to improve the performance of the sulfide all-solid battery.
For example, Patent Document 3 discloses an all-solid battery including a sulfide-based solid electrolyte having an oxide layer formed by oxidation on its surface.

JP 2014-143133 A JP 2014-086209 A JP2012-094445A

However, the conventional sulfide all solid state battery disclosed in Patent Document 1 has a problem in that the capacity retention rate is reduced due to lithium deactivation at the negative electrode.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a method for producing a sulfide all-solid battery having a high capacity retention rate and a sulfide all-solid battery.

The method for producing a sulfide all solid state battery of the present invention includes a battery forming step for forming a sulfide all solid state battery,
And after the battery formation step, charging the sulfide all solid state battery for the first time,
The sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere during at least one of the initial charging step and after the initial charging step.

  The sulfide all solid state battery manufacturing method of the present invention is the initial charging step, wherein the sulfide all solid state battery is initially charged in an oxygen-containing gas atmosphere, and after the initial charging step, the sulfide all solid state battery is oxygenated. It is preferable to expose in a gas atmosphere.

In the method for producing a sulfide all solid state battery according to the present invention, in the initial charging step, the sulfide all solid state battery is placed in an oxygen-containing gas atmosphere, and the potential of the negative electrode provided in the sulfide all solid state battery is 0.85 V ( vs. Li ^/ Li ⁺ ) or less is preferably performed.

The sulfide all solid state battery of the present invention is disposed between a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and the positive electrode and the negative electrode. A solid electrolyte layer containing a solid electrolyte,
At least one of the negative electrode active material layer or the solid electrolyte layer contains a sulfide-based solid electrolyte,
The sulfide-based solid electrolyte has an oxygen-concentrated layer having a higher oxygen concentration than a portion other than the contact surface on the contact surface with the negative electrode active material.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a sulfide all-solid-state battery with a high capacity | capacitance maintenance factor and a sulfide all-solid-state battery can be provided.

It is a cross-sectional schematic diagram which shows an example of the sulfide all-solid-state battery formed at a battery formation process. It is a cross-sectional schematic diagram which shows an example of a sulfide all solid battery. It is a cross-sectional schematic diagram which shows another example of a sulfide all-solid-state battery. It is a dQ / dV curve at the time of the first charge in Examples 1-2. 6 is a TEM image showing a negative electrode obtained in Example 4. 6 is an EDX image showing the oxygen component of the negative electrode obtained in Example 4. It is a measurement result which shows the battery resistance in Example 4 and Comparative Example 2. It is a measurement result which shows the oxygen content rate in the solid electrolyte in Reference Examples 1-4.

  Hereinafter, the manufacturing method of a sulfide all solid state battery and the sulfide all solid state battery in the present invention will be described in detail.

A. Method for Producing Sulfide All-Solid Battery A method for producing a sulfide all-solid battery of the present invention includes a battery forming step for forming a sulfide all-solid battery,
And after the battery formation step, charging the sulfide all solid state battery for the first time,
The sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere during at least one of the initial charging step and after the initial charging step.

The inventors of the present invention charge the sulfide all solid state battery for the first time in an oxygen-containing gas atmosphere and / or expose the sulfide all solid state battery to the oxygen-containing gas atmosphere after the initial charge, thereby It has been found that the capacity retention rate of the solid battery is remarkably improved.
This is because by changing from an inert gas atmosphere such as argon gas to an oxygen-containing gas atmosphere, the solid electrolyte contained in the negative electrode of the sulfide all solid state battery is altered, and thereafter the solid electrolyte is less likely to change (deteriorate). It is estimated that. As a basis for this, when the voltage after the initial charge is adjusted to 3.65V and the sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere, the voltage of the sulfide all solid state battery is about 3.65V to 3.55V. It has been confirmed by the present inventors that this has changed.

  The manufacturing method of the all-solid-state battery of this invention has at least (1) battery formation process and (2) initial charge process.

(1) Battery formation process A battery formation process is a process of forming a sulfide all solid battery.
The sulfide all solid battery includes at least a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.
The sulfide all solid state battery formed in the battery forming process is a battery that can be charged and discharged.

FIG. 1 is a schematic cross-sectional view showing an example of a sulfide all solid state battery formed in the battery formation step of the present invention.
The sulfide all solid state battery 100 includes a positive electrode 16 including a positive electrode active material layer 12 and a positive electrode current collector 14, a negative electrode 17 including a negative electrode active material layer 13 and a negative electrode current collector 15, and between the positive electrode 16 and the negative electrode 17. A solid electrolyte layer 11 is provided.

The positive electrode has at least a positive electrode active material layer, and further includes a positive electrode current collector as necessary.
The positive electrode active material layer contains at least a positive electrode active material, and optionally contains a conductive material, a binder, and a solid electrolyte described later.
A conventionally known material can be used as the positive electrode active material. When the sulfide all solid state battery is a lithium battery, for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), Li _{1 + x} Ni _1/3 Mn _1/3 Co _1/3 O ₂ (0 ≦ x <0.3), lithium manganate (LiMn ₂ O ₄ ), Li _{1 + x} Mn _2−xy M _y O ₄ (M is at least selected from the group consisting of Al, Mg, Co, Fe, Ni, Zn) One element, hetero-element-substituted Li-Mn spinel having a composition represented by 0 ≦ x <0.5, 0 ≦ y <2), lithium titanate, lithium metal phosphate (LiMPO ₄ , M = Fe, Mn, Co , Ni) and the like.
The shape of the positive electrode active material is not particularly limited, and examples thereof include particles and plates.
The positive electrode active material preferably has a coating layer in which the surface of the positive electrode active material is coated with a solid electrolyte.
The method for coating the surface of the positive electrode active material with the solid electrolyte is not particularly limited. For example, a solid electrolyte such as LiNbO ₃ can be applied to the positive electrode active material in an atmospheric environment using a rolling fluid type coating apparatus (manufactured by POWREC, Inc.). Examples of the method include coating and firing in an atmospheric environment. Moreover, for example, a sputtering method, a sol-gel method, an electrostatic spray method, a ball milling method, and the like can be given.
The solid electrolyte that forms the coating layer may be any material that has lithium ion conductivity, does not flow even when in contact with the active material or the solid electrolyte, and can maintain the shape of the coating layer. _{LiNbO 3, Li 4 Ti 5 O} 12, Li 3 PO 4 and the like.
In addition, the thing similar to what is used for the solid electrolyte layer mentioned later can be used for the solid electrolyte used for a positive electrode active material layer.
The binder is not particularly limited, and examples thereof include butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene / butadiene rubber (SBR).
The conductive material is not particularly limited, and examples thereof include carbon materials and metal materials such as acetylene black, ketjen black, and carbon fiber.
Although the thickness of a positive electrode active material layer is not specifically limited, For example, it is preferable that it is 10-250 micrometers, especially 20-200 micrometers.
Although content of the positive electrode active material in a positive electrode active material layer is not specifically limited, For example, it is preferable that they are 50 volume%-90 volume%.
The positive electrode current collector has a function of collecting current of the positive electrode active material layer. Examples of the material for the positive electrode current collector include metal materials such as SUS, Ni, Cr, Au, Pt, Al, Fe, Ti, and Zn. Examples of the shape of the positive electrode current collector include a foil shape, a plate shape, and a mesh shape.
The positive electrode may further include a positive electrode lead connected to the positive electrode current collector.

  The average particle diameter of the particles in the present invention is calculated by a conventional method. An example of a method for calculating the average particle size of the particles is as follows. First, a transmission electron microscope (hereinafter referred to as TEM) with an appropriate magnification (for example, 50,000 to 1,000,000 times), an image or a scanning electron microscope (hereinafter referred to as SEM). In the image, for a certain particle, the particle diameter when the particle is regarded as spherical is calculated. Calculation of the particle size by such TEM observation or SEM observation is performed for 200 to 300 particles of the same type, and the average of these particles is taken as the average particle size.

The negative electrode includes at least a negative electrode active material layer and, if necessary, a negative electrode current collector that collects the negative electrode active material layer.
The negative electrode active material layer contains at least a negative electrode active material, and if necessary, contains a conductive material, a binder, and a solid electrolyte described later.
Examples of the negative electrode active material include carbon materials such as graphite and hard carbon, Si and Si alloys, Li ₄ Ti ₅ O _{12 and the} like.
The shape of the negative electrode active material is not particularly limited, and examples thereof include particles and plates.
As the conductive material and the binder used for the negative electrode active material layer, the same materials as those used for the positive electrode active material layer described above can be used. The same thing as what is used for the solid electrolyte layer mentioned later can be used for the solid electrolyte used for a negative electrode active material layer.
Although the thickness of a negative electrode active material layer is not specifically limited, For example, it is preferable that it is 10-100 micrometers, especially 10-50 micrometers.
Although content of the negative electrode active material in a negative electrode active material layer is not specifically limited, For example, it is preferable that they are 20 volume%-90 volume%.
Examples of the material for the negative electrode current collector include metal materials such as SUS, Cu, Ni, Fe, Ti, Co, and Zn. As the shape of the negative electrode current collector, the same shape as that of the positive electrode current collector described above can be adopted.

The solid electrolyte layer contains at least a solid electrolyte, and may contain a binder or the like as necessary.
The solid electrolyte is preferably a sulfide solid electrolyte. Examples of the sulfide-based solid electrolyte include Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ S—P ₂ S ₅ , LiI—Li ₂ S—P ₂ O ₅ , LiI— include _{Li 3 PO 4 -P 2 S 5} , LiI-Li 2 O-Li 2 S-P 2 S 5, LiBr-LiI-Li 2 S-P 2 S 5, Li 2 S-P 2 S 5 or the like . Specifically, 15LiBr · 10LiI · 75 (0.75Li ₂ S · 0.25P ₂ S ₅ ), 70 (0.06Li ₂ O · 0.69Li ₂ S · 0.25P ₂ S ₅ ) · 30LiI, etc. Can be mentioned.
The shape of the solid electrolyte is not particularly limited, and examples thereof include particles and plates.
The binder used for the solid electrolyte layer can be the same as that used for the positive electrode active material layer described above.

The sulfide all solid state battery includes an exterior body that accommodates a positive electrode, a negative electrode, and a solid electrolyte layer as necessary.
Although it does not specifically limit as a shape of an exterior body, A laminate type etc. can be mentioned.
The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.
When the outer package is a laminate-type sulfide all-solid battery, the sulfide all-solid battery is one that is laminated with vacuum suction after the initial charge in an oxygen-containing gas atmosphere described later, or an oxygen-containing gas. After the first charge in the atmosphere, the film may be laminated by changing to an argon gas atmosphere.

(2) Initial charging step The initial charging step is a step of initially charging the sulfide all solid state battery after the battery forming step.
In the present invention, the sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere at the time of the first charging step and / or at least one after the first charging step.
And from a viewpoint of the capacity maintenance rate improvement of a sulfide all-solid-state battery, it is preferable to expose a sulfide all-solid-state battery in oxygen-containing gas atmosphere both in the first charge process and after the first charge process.
The conditions for the initial charging are not particularly limited, and examples thereof include constant current and constant voltage charging. The current value is not particularly limited, but is preferably 0.1 mAh to 10 mAh, for example. This is because if the current value is too small, it takes time to charge, and if the current value is too large, the overvoltage increases.
Examples of the oxygen-containing gas include pure oxygen and air. The air is preferably dry air.

When the initial charging step is performed in an oxygen-containing gas atmosphere, charging is preferably performed until the potential of the negative electrode is 0.85 V (vs. Li ^/ Li ⁺ ) or less, and 0.70 V (vs. Li ^/ Li ⁺ ). It is more preferable to charge until it becomes the following. This is because the capacity retention rate can be further improved by charging the negative electrode potential until it falls within the above-described range.

(3) After the initial charging step The open circuit voltage of the sulfide all solid state battery after the initial charging step is not particularly limited, but is preferably maintained at 2.80 V or more and 3.8 V or less.
The exposure time in the oxygen-containing gas atmosphere after the initial charging step is not particularly limited, and is preferably 24 hours to 30 days.
The exposure temperature is not particularly limited and is preferably 0 to 60 ° C.
As the oxygen-containing gas, the same gas as that used in the initial charging step can be used.

  Examples of the sulfide all solid battery obtained by the production method of the present invention include a lithium battery, a sodium battery, a magnesium battery, and a calcium battery. Among them, a lithium battery is preferable.

B. Sulfide all-solid battery The sulfide all-solid battery of the present invention includes a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, the positive electrode, and the negative electrode. And a solid electrolyte layer containing a solid electrolyte,
At least one of the negative electrode active material layer or the solid electrolyte layer contains a sulfide-based solid electrolyte,
The sulfide-based solid electrolyte has an oxygen-concentrated layer having a higher oxygen concentration than a portion other than the contact surface on the contact surface with the negative electrode active material.

The present inventors charge the sulfide all solid state battery for the first time under an oxygen-containing gas atmosphere, so that the oxygen concentration is higher on the contact surface of the sulfide-based solid electrolyte with the negative electrode active material than on the portion other than the contact surface. It has been found that the capacity retention rate of the sulfide all solid state battery is remarkably improved by forming the oxygen concentrated layer.
This is presumably because the formed oxygen-concentrated layer suppresses the contact between the negative electrode active material and the sulfide-based solid electrolyte, and the sulfide-based solid electrolyte hardly changes (deteriorates).

FIG. 2 is a schematic cross-sectional view showing an example of the sulfide all solid state battery of the present invention.
The sulfide all solid state battery 200 includes a positive electrode 16 including a positive electrode active material layer 12 and a positive electrode current collector 14, a negative electrode 17 including a negative electrode active material layer 13 and a negative electrode current collector 15, and a positive electrode 16 and a negative electrode 17. A solid electrolyte layer 11 is provided. Furthermore, the negative electrode active material layer 13 includes a negative electrode active material 21 and a sulfide-based solid electrolyte 22, and includes an oxygen concentrating layer 18 on a contact surface between the negative electrode active material 21 and the sulfide-based solid electrolyte 22.

FIG. 3 is a schematic cross-sectional view showing another example of the sulfide all solid state battery of the present invention.
The sulfide all solid state battery 300 includes a positive electrode 16 including a positive electrode active material layer 12 and a positive electrode current collector 14, a negative electrode 17 including a negative electrode active material layer 13 and a negative electrode current collector 15, and a positive electrode 16 and a negative electrode 17. A solid electrolyte layer 11 is provided. Furthermore, the oxygen concentration layer 18 is provided on the contact surface of the solid electrolyte layer 11 with the negative electrode active material layer 13.
Hereinafter, the sulfide all solid state battery will be described for each configuration.

(1) Positive electrode The positive electrode includes at least a positive electrode active material layer, and includes a positive electrode current collector that collects the positive electrode active material layer as necessary.
The positive electrode active material layer contains at least a positive electrode active material, and contains a conductive material, a binder, and a solid electrolyte as necessary.
The positive electrode current collector, the positive electrode active material, the conductive material, the binder, and the solid electrolyte are the same as those described in the above-mentioned “A. Method for producing sulfide all-solid battery”.

(2) Negative Electrode The negative electrode includes at least a negative electrode active material layer, and includes a negative electrode current collector that collects current from the negative electrode active material layer as necessary.
The negative electrode active material layer contains at least a negative electrode active material, and contains a conductive material, a binder, and a solid electrolyte as necessary.
At least one of the negative electrode active material layer and the solid electrolyte layer described later contains a sulfide-based solid electrolyte.
The negative electrode current collector, the negative electrode active material, the conductive material, the binder, and the solid electrolyte are the same as those described in “A. Method for producing sulfide all solid battery” above.

(3) Solid electrolyte layer The solid electrolyte layer contains at least a solid electrolyte, and may contain a binder or the like as necessary.
At least one of the negative electrode active material layer and the solid electrolyte layer described above contains a sulfide-based solid electrolyte.
The solid electrolyte and the binder are the same as those described in the above “A. Method for producing sulfide all solid state battery”.

(4) Oxygen-concentrated layer The oxygen-concentrated layer is a layer formed on the contact surface with the negative electrode active material in the sulfide-based solid electrolyte and having a higher oxygen concentration than the portion other than the contact surface. The oxygen concentrating layer may be formed on a contact surface between the negative electrode active material and the sulfide solid electrolyte in the negative electrode active material layer, and includes a negative electrode active material layer and a solid electrolyte layer containing the sulfide solid electrolyte, It may be formed on the contact surface. Examples of the method for forming the oxygen-concentrated layer include exposing the sulfide all-solid-state battery to an oxygen-containing gas atmosphere during at least one of the first charging step and after the first charging step. Among these, it is preferable to expose the sulfide all solid state battery in an oxygen-containing gas atmosphere both in the first charging step and after the first charging step. This is because the oxygen-concentrated layer can be formed more efficiently.
Moreover, it is preferable that the oxygen concentration layer is formed only on the contact surface of the sulfide-based solid electrolyte with the negative electrode active material. This is because if the oxygen-concentrated layer is formed in many areas other than the contact surface with the negative electrode active material, the ionic conductivity of the sulfide-based solid electrolyte may be lowered.

  The average thickness of the oxygen-concentrated layer is not particularly limited, but is preferably 0.1 nm or more, more preferably 1 nm or more, and preferably 100 nm or less, preferably 10 nm or less. It is more preferable that The average thickness of the oxygen-concentrated layer can be determined by observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), for example.

  In addition, the formation state of the oxygen-enriched layer is, for example, X-ray diffraction (XRD) measurement, TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy, STEM-EDX (Scanning TransTransscope) ray Spectroscope), RBS (Rutherford Backscattering Spectrometry), PIXE (Particle Induced X-ray Emission), HFS (Hydrogen Forward Scattering), NRA (Natural Scattering) sis) can be confirmed by analysis or the like.

(5) Other members The sulfide all solid state battery includes an exterior body that accommodates the positive electrode, the negative electrode, and the solid electrolyte layer as necessary.
Although it does not specifically limit as a shape of an exterior body, For example, a coin type | mold, a laminate type | mold, a cylindrical shape, a square shape etc. can be mentioned.
The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

(6) Sulfide all-solid battery Examples of the sulfide all-solid battery include a lithium battery, a sodium battery, a magnesium battery, and a calcium battery. Among these, a lithium battery is preferable.
Examples of the shape of the sulfide all solid state battery include a coin type, a laminate type, a cylindrical type, and a square type.

Example 1
[Battery formation process]
[Production of positive electrode]
Using a rolling fluid type coating device (manufactured by POWREC Co., Ltd.), the cathode active material was coated with LiNbO ₃ as a solid electrolyte in the atmospheric environment, and baked in the atmospheric environment, and the surface of the cathode active material was coated with the solid electrolyte. .
A 5% by mass butyl butyrate solution of butyl butyrate, PVdF binder (manufactured by Kureha Co., Ltd.) in a polypropylene (PP) container, a positive electrode active material coated with the solid electrolyte, and a sulfide solid electrolyte (Li ₂ containing LiBr and LiI) S—P ₂ S ₅ glass ceramics) was added to the container, VGCF (trademark) (manufactured by Showa Denko KK) was added as a conductive material, and the mixture was stirred for 30 seconds with an ultrasonic dispersion device (UH-50 manufactured by SMT Corporation). .
Next, the container was shaken with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1) for 3 minutes, and further stirred with an ultrasonic dispersion device for 30 seconds.
After shaking for 3 minutes with a shaker, coating was performed on Al foil (manufactured by Nihon Foil Co., Ltd.) by the blade method using an applicator.
Then, the coated electrode was naturally dried.
Then, the positive electrode was obtained by making it dry on a 100 degreeC hotplate for 30 minutes.

[Production of negative electrode]
PP container with 5% butyl butyrate solution of butyl butyrate, PVdF binder (manufactured by Kureha Co., Ltd.), natural graphite carbon (Nippon Carbon Co., Ltd.) with an average particle size of 10 μm as a negative electrode active material, sulfide solid electrolyte as LiBr, adding _Li 2 _S-P 2 _{S 5} -based glass ceramic containing LiI in a vessel and stirred for 30 seconds with an ultrasonic dispersing device (manufactured by SMT Ltd. UH-50).
Next, the container was shaken for 30 minutes with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1).
It coated on Cu foil (made by Furukawa Electric Co., Ltd.) by the blade method using the applicator.
Then, the coated electrode was naturally dried.
Then, the negative electrode was obtained by making it dry for 30 minutes on a 100 degreeC hotplate.

[Production of solid electrolyte layer]
Heptane PP container made, butadiene rubber (BR) binder 5 wt% heptane solution of (JSR Co., Ltd.), _{Li 2 S-P} 2 containing LiBr and LiI as a sulfide-based solid electrolyte having an average particle diameter of 2.5μm It added S ₅ based glass ceramics, and stirred for 30 seconds with an ultrasonic dispersing device (manufactured by SMT Ltd. UH-50).
Next, the container was shaken for 30 minutes with a shaker (manufactured by Shibata Kagaku Co., Ltd., TTM-1).
Then, it coated on Al foil with the blade method using the applicator.
After coating, it was naturally dried.
Then, the solid electrolyte layer was obtained by making it dry for 30 minutes on a 100 degreeC hotplate.

[Preparation of sulfide all solid state battery]
The mold 1 cm ² putting a solid electrolyte layer and pressed at ^{1ton / cm 2 (≒ 98MPa)} , put a positive electrode on one side and pressed at ^{1ton / cm 2 (≒ 98MPa)} , then put in a negative longer on one side , 6 ton / cm ² (≈588 MPa) to obtain a sulfide all solid state battery.

[First charging process]
The obtained sulfide all solid state battery is placed in a glass container filled with argon gas, and is charged at a constant current and constant voltage (CCCV) up to 4.37 V at 1/3 C in an environment of 25 ° C. CCCV discharge was performed up to 3V at / 3C to determine the initial capacity.
The dQ / dV curve at the time of the first charge in Example 1 is shown in FIG.
[After initial charging process]
Thereafter, the open circuit voltage of the sulfide all solid state battery was adjusted to 3.65 V, and the atmosphere of the glass container was changed from an argon gas atmosphere to a dry air atmosphere. Then, as an endurance test, the open circuit voltage of the sulfide all solid state battery was readjusted to 4.25 V and stored at 60 ° C. for 28 days.

(Example 2)
In the initial charging step, a sulfide all solid state battery was manufactured in the same manner as in Example 1 except that the atmosphere of the glass container was changed to a dry air atmosphere.
The dQ / dV curve at the time of the first charge in Example 2 is shown in FIG.
As shown in FIG. 4, in Example 1, the peak of the dQ / dV curve does not appear at the first charge. On the other hand, in Example 2, it can be seen that the peak of the dQ / dV curve appears in the vicinity of 2.9 V (2.8-3.0 V) during the initial charge. This is presumably because the amount of reaction in the vicinity of 2.9 V was increased by performing the initial charge in an oxygen-containing gas atmosphere.
Therefore, it is presumed that the same effect as the first charge can be obtained by exposing the sulfide all solid state battery to an oxygen-containing gas atmosphere while maintaining a voltage of 2.8 to 3.0 V or more.

(Example 3)
A sulfide all solid state battery is manufactured in the same manner as in Example 1 except that the atmosphere of the glass container is changed to a dry air atmosphere in the initial charging process, and the atmosphere of the glass container is changed to an argon gas atmosphere after the initial charging process. did.

(Comparative Example 1)
After the initial charging step, a sulfide all solid state battery was manufactured in the same manner as in Example 1 except that the atmosphere of the glass container was kept in the argon gas atmosphere.

[Capacity maintenance rate]
About the sulfide all solid state battery obtained in Examples 1 to 3 and Comparative Example 1, CCCV discharge to 3 V at 25 ° C., CCCV charge to 4.37 V, CCCV discharge to 3 V, and the post-endurance capacity of each battery Asked.
And the capacity | capacitance maintenance factor was calculated | required from the capacity | capacitance after an endurance / initial stage capacity | capacitance. And ratio (capacity maintenance ratio) of the capacity maintenance rate of Examples 1-3 to comparative example 1 when the capacity maintenance rate of comparative example 1 was made into 100% was computed. The results are shown in Table 1.

As shown in Table 1, the ratio of the capacity retention ratio of Examples 1 to 3 with respect to Comparative Example 1 was 1.10 in Example 1, 1.13 in Example 2, and 1.11. .
As shown in Table 1, in Example 1, the capacity retention rate was improved by 1.10 times compared to Comparative Example 1, so the battery voltage (open circuit voltage) was adjusted to 3.65 V after the first charge. And it turns out that a capacity | capacitance maintenance factor improves significantly by changing from argon gas atmosphere to oxygen-containing gas atmosphere.
This is presumed that the voltage maintained after the first charge has an influence because the capacity maintenance rate is not improved before the first charge.
Further, as shown in Table 1, it can be seen that Example 2 has a higher capacity retention rate than Example 1. Therefore, immediately after the formation of the sulfide all solid state battery, the sulfide all solid state battery is placed in an oxygen-containing gas atmosphere, and the initial charge is performed in that state, thereby making the first charge in an argon gas atmosphere. It can be seen that the capacity retention rate is improved.
Furthermore, as shown in Table 1, Example 2 has a higher capacity retention rate than Example 3. Therefore, it can be seen that the capacity retention rate is improved by exposure to the oxygen-containing gas not only during the initial charge but also after the initial charge.

Example 4
In the first charging step, the obtained sulfide all solid state battery is put in a glass container in a dry air atmosphere (dew point −75 ° C.), and the negative electrode potential becomes 0.08 V (vs. Li / Li ⁺ ). The battery was discharged until the battery voltage reached 3 V, and the initial capacity was determined. Thereafter, the atmosphere in the glass container was replaced with argon gas, and the subsequent battery evaluation was performed. A battery was prepared and evaluated in the same manner as in Example 1.

(Example 5)
A battery was prepared and evaluated in the same manner as in Example 4 except that in the initial charging step, the negative electrode was charged until the potential of the negative electrode became 0.7 V (vs. Li ^/ Li ⁺ ).

(Example 6)
A battery was prepared and evaluated in the same manner as in Example 4 except that in the initial charging step, the negative electrode was charged until the potential of the negative electrode became 0.85 V (vs. Li ^/ Li ⁺ ).

(Example 7)
A battery was prepared and evaluated in the same manner as in Example 4 except that in the initial charging step, the negative electrode was charged until the potential of the negative electrode became 1.0 V (vs. Li ^/ Li ⁺ ).

[Capacity maintenance rate]
The sulfide all solid state batteries obtained in Examples 4 to 7 were charged to 4.1 V at 0.8 mA (end current condition: 0.016 mAh), and 3 V at 0.5 mA (end current condition: 0.16 mAh). Discharge was performed. Thereafter, the battery was charged to 3.9 V and stored at 60 ° C. for 28 days, and the post-endurance capacity of each battery was determined.
And the capacity | capacitance maintenance factor was calculated | required from the capacity | capacitance after an endurance / initial stage capacity | capacitance. And the ratio (capacity maintenance ratio) of the capacity maintenance ratio of Examples 4-6 with respect to Example 7 when the capacity maintenance ratio of Example 7 was set to 100% was calculated. The results are shown in Table 2.

As shown in Table 2, the capacity retention ratios of Examples 4 to 6 with respect to Example 7 were 1.19 in Example 4, 1.15 in Example 5, and 1.09 in Example 6. From the above results, it can be seen that the capacity retention rate is further improved by setting the negative electrode potential at the end of the initial charge to 0.85 V (vs. Li ^/ Li ⁺ ) or less. This is because when the potential of the negative electrode is charged to 0.85 V (vs. Li ^/ Li ⁺ ) or less, the sulfide solid electrolyte in contact with the negative electrode active material reacts with oxygen gas, and the oxygen concentrated layer This is presumed to be because of the efficient formation.

[TEM observation of interface]
The interface between the negative electrode active material and the sulfide-based solid electrolyte of the negative electrode of Example 4 in which the first charge / discharge in the [first charge step] was completed was observed using a TEM (transmission electron microscope). FIG. 5A shows a TEM image of the negative electrode, and FIG. 5B shows a TEM-EDX image showing the oxygen component. As shown in FIG. 5B, it was confirmed that an oxygen concentrating layer having a higher oxygen concentration than that of the portion other than the contact surface was formed on the contact surface of the sulfide-based solid electrolyte with the negative electrode active material. It was also confirmed that no oxygen-concentrated layer was formed on the inside of the sulfide-based solid electrolyte or on the surface not in contact with the negative electrode active material. This is because by performing the initial charging step in an oxygen-containing gas atmosphere, only the contact surface of the sulfide-based solid electrolyte with the negative electrode active material reacts with oxygen gas to selectively form an oxygen-enriched layer. It is estimated that.

(Comparative Example 2)
A battery was prepared and evaluated in the same manner as in Example 4 except that the initial charging step was not performed.

[Battery evaluation]
About the sulfide all solid state battery obtained in Example 4 and Comparative Example 2, it was charged to 4.1 V at 0.8 mA (end current condition: 0.016 mAh), and 0.5 mA (end current condition: 0.16 mAh). Was discharged to 3V. Thereafter, the voltage was adjusted by charging to 3.9 V, and the battery resistance was determined from the amount of voltage drop after 5 seconds when discharged at 4.8 mA. The results are shown in FIG.
As shown in FIG. 6, it was confirmed that the battery resistance of Example 4 showed a value almost equivalent to the battery resistance of Comparative Example 2 in which the initial charging step was not performed in a dry air atmosphere. In general, when the oxygen content in a sulfide-based solid electrolyte is increased, battery resistance tends to increase. However, by performing initial charging in an oxygen-containing gas atmosphere, the oxygen-concentrated layer becomes sulfide-based. Since it is selectively formed on the contact surface of the solid electrolyte with the negative electrode active material, the oxygen content in the sulfide-based solid electrolyte is minimized and the capacity retention rate is improved while suppressing an increase in battery resistance. I guess it is possible.

(Reference Example 1)
A Li ₂ S—P ₂ S ₅ glass ceramic containing LiBr and LiI as a sulfide-based solid electrolyte was placed in a 1 cm ² mold and pressed at 1 ton / cm ² (≈98 MPa) to produce a solid electrolyte pellet.
A SUS current collector, the solid electrolyte pellet produced above, a Li metal foil, and a SUS current collector were laminated in this order to produce a battery for evaluation.

(Reference Example 2)
The evaluation battery prepared in Reference Example 1 is placed in a glass container in a dry air atmosphere (dew point −75 ° C.) and charged until the potential of the negative electrode becomes 0.08 V (vs. Li / Li ⁺ ). Discharging was performed until the battery voltage reached 3V.
Thereafter, the atmosphere in the glass container was replaced with argon gas, and the subsequent analysis evaluation was performed.

(Reference Example 3)
The evaluation battery was prepared and evaluated in the same manner as in Reference Example 2 except that the prepared evaluation battery was placed in a glass container in a dry air atmosphere (dew point -75 ° C.) and charging / discharging was not performed. It was.

(Reference Example 4)
The prepared evaluation battery is put in a glass container filled with argon gas, charged until the negative electrode potential becomes 0.08 V (vs. Li / Li ⁺ ), and then discharged until the battery voltage becomes 3 V. A battery for evaluation was prepared and evaluated in the same manner as in Reference Example 2 except that.

[Analysis of electrolytes]
RBS, PIXE, HFS, NRA analysis was performed on the surface portion of the evaluation battery obtained in Reference Examples 1 to 4 that was in contact with the SUS current collector, and oxygen with respect to elemental sulfur in the sulfide-based solid electrolyte was analyzed. The content ratio (O / P) was calculated. The results are shown in FIG.
As shown in FIG. 7, it was confirmed that the oxygen content ratio in the sulfide-based solid electrolyte was significantly increased in Reference Example 2 as compared with Reference Example 1. On the other hand, in Reference Example 3 and Reference Example 4, it was confirmed that the oxygen content ratio in the sulfide-based solid electrolyte was slightly increased as compared with Reference Example 1. From these results, it was found that the oxygen content ratio in the sulfide-based solid electrolyte was significantly increased by performing the initial charge in an oxygen-containing gas atmosphere. This is because the sulfide-based solid electrolyte reacts with oxygen gas to form an oxygen-concentrated layer efficiently by bringing the sulfide-based solid electrolyte to a state below a certain potential in an oxygen-containing gas atmosphere. This is presumed to be due to this.

DESCRIPTION OF SYMBOLS 11 Solid electrolyte layer 12 Positive electrode active material layer 13 Negative electrode active material layer 14 Positive electrode current collector 15 Negative electrode current collector 16 Positive electrode 17 Negative electrode 18 Oxygen concentration layer 21 Negative electrode active material 22 Sulfide solid electrolyte 100 Sulfide all solid battery 200 Sulfide all-solid battery 300 Sulfide all-solid battery

Claims (4)

A battery forming process for forming a sulfide all solid state battery;
And after the battery formation step, charging the sulfide all solid state battery for the first time,
The method for producing a sulfide all solid state battery, wherein the sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere during at least one of the first charging step and after the first charging step. In the initial charging step, the sulfide all solid state battery is initially charged in an oxygen-containing gas atmosphere,
The method for producing a sulfide all solid state battery according to claim 1, wherein the sulfide all solid state battery is exposed to an oxygen-containing gas atmosphere after the initial charging step. In the initial charging step, initial charging is performed in which the sulfide all solid state battery is in an oxygen-containing gas atmosphere and the negative electrode potential of the sulfide all solid state battery is 0.85 V (vs. Li ^/ Li ⁺ ) or less. The method for producing a sulfide all solid state battery according to claim 1, wherein the method is performed. A positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, a solid electrolyte layer disposed between the positive electrode and the negative electrode and containing a solid electrolyte, With
At least one of the negative electrode active material layer or the solid electrolyte layer contains a sulfide-based solid electrolyte,
The sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid electrolyte has an oxygen-concentrated layer having a higher oxygen concentration than a portion other than the contact surface on a contact surface with the negative electrode active material.