WO2014038311A1 - All-solid cell - Google Patents

Description

All solid battery

The present invention relates to an all-solid battery.

In recent years, the demand for batteries as a power source for portable electronic devices such as mobile phones and portable personal computers has greatly increased. In a battery used for such an application, an electrolyte (electrolytic solution) such as an organic solvent has been conventionally used as a medium for moving ions.

However, the battery having the above configuration has a risk of leakage of the electrolyte. Moreover, the organic solvent etc. which are used for electrolyte solution are combustible substances. For this reason, it is required to further increase the safety of the battery.

Therefore, as one countermeasure for improving the safety of the battery, it has been proposed to use a solid electrolyte as the electrolyte instead of the electrolytic solution. Furthermore, development of an all-solid battery in which a solid electrolyte is used as an electrolyte and the other constituent elements are also made of solid is being promoted.

For example, JP 2010-219069 A (hereinafter referred to as Patent Document 1) discloses that a positive electrode active material is made into relatively large plate-like particles, whereby the active material filling rate in the positive electrode is increased and the lithium ion secondary material is increased. A method for producing a positive electrode active material capable of increasing the capacity of a battery is disclosed. Patent Document 1 does not limit the positive electrode active material obtained by the above manufacturing method to the case where a liquid electrolyte is used, but uses an inorganic solid, an organic polymer, or a gel electrolyte, that is, a solid electrolyte. It is described that the present invention can also be applied to a conventional solid battery.

In addition, for example, in Japanese Patent Application Laid-Open No. 2011-198692 (hereinafter referred to as Patent Document 2), there is a laminated all solid-state lithium ion secondary battery in which positive electrode layers and negative electrode layers are alternately stacked via a solid electrolyte layer. Are listed. This all solid-state lithium ion secondary battery is manufactured by firing a laminate of green sheets of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer. In Patent Document 2, a positive electrode layer is formed by firing various oxides such as titanium oxide, niobium oxide, and vanadium oxide as a positive electrode active material.

JP 2010-219069 A JP 2011-198692 A

In an all solid state battery manufactured by firing as described in Patent Document 2, in order to promote the supply of ions to the electrode active material or the release of ions from the electrode active material, It is important that the electrode active material and the solid electrolyte are closely joined to form an interface.

As a result of repeated studies by the inventors, in order to obtain an all-solid battery in which the electrode active material and the solid electrolyte are intimately joined in the electrode layer, as disclosed in Patent Document 1, a positive electrode of plate-like particles is used. It is not sufficient to use only the active material, and as disclosed in Patent Document 2, it is not sufficient to merely fire oxides such as titanium oxide, niobium oxide, and vanadium oxide as the positive electrode active material. I understood.

Therefore, an object of the present invention is to provide an all-solid battery capable of improving charge / discharge characteristics by forming an interface in which an electrode active material and a solid electrolyte are closely joined in an electrode layer. .

As a result of various studies conducted by the inventors to solve the above problems, a solid electrolyte layer containing a solid electrolyte and an electrode layer containing a solid electrolyte and an electrode active material having a rod-like or strip-like form were laminated. When fired, the contact interface between the solid electrolyte and the electrode active material in the electrode layer increases, and the solid electrolyte and the electrode active material are closely bonded by firing to form an interface, improving the bondability at that interface It was found that the charge / discharge characteristics can be improved. Based on such knowledge of the inventors, the present invention has the following features.

An all-solid battery according to the present invention includes an electrode layer including at least one of a positive electrode layer and a negative electrode layer including an electrode active material and a solid electrolyte, and a solid electrolyte layer including the solid electrolyte laminated on the electrode layer. Prepare. The electrode active material has a rod-like or strip-like form.

In the all solid state battery of the present invention, the electrode active material preferably has a long side and a short side, and the ratio of the long side to the short side is preferably 3 or more.

In addition, it is preferable that the long side of the electrode active material is oriented in a direction substantially orthogonal to the stacking direction of the electrode layer and the solid electrolyte layer.

Furthermore, the electrode active material is preferably an oxide containing at least one metal selected from the group consisting of titanium and niobium.

The volume occupancy of the solid electrolyte in the electrode layer is preferably 22% by volume to 56% by volume.

The electrode active material is preferably monoclinic niobium oxide.

The solid electrolyte preferably contains a lithium-containing phosphate compound, and more preferably contains a lithium-containing phosphate compound having a NASICON type structure.

According to the present invention, the bondability at the interface between the solid electrolyte and the electrode active material can be improved in the electrode layer, and the charge / discharge characteristics can be improved.

It is sectional drawing which shows typically the cross-section of an all-solid-state battery laminated body as one embodiment of this invention. It is the photograph which observed the electrode active material material used by the Example and comparative example of this invention with the scanning electron microscope. It is the photograph which observed the cross section of the electrode-solid electrolyte laminated body produced by the Example and comparative example of this invention with the scanning electron microscope. It is a figure which shows the charging / discharging curve of the all-solid-state battery produced by the Example and comparative example of this invention.

As shown in FIG. 1, an all-solid battery stack 10 according to one embodiment of the present invention is composed of a stack in which a positive electrode layer 11, a solid electrolyte layer 13, and a negative electrode layer 12 are stacked in this order. The positive electrode layer 11 is disposed on one surface of the solid electrolyte layer 13, and the negative electrode layer 12 is disposed on the other surface opposite to the one surface of the solid electrolyte layer 13. In other words, the positive electrode layer 11 and the negative electrode layer 12 are provided at positions facing each other with the solid electrolyte layer 13 interposed therebetween. Note that each of the positive electrode layer 11 and the negative electrode layer 12 includes a solid electrolyte and an electrode active material. The solid electrolyte layer 13 includes a solid electrolyte. Each of the positive electrode layer 11 and the negative electrode layer 12 may contain carbon, a metal, an oxide, etc. as an electronic conductive material.

In the all-solid-state battery stack 10 configured as described above, at least one of the positive electrode layer 11 and the negative electrode layer 12 includes an electrode active material having a rod-like or strip-like form.

By configuring in this way, an all-solid battery showing good charge / discharge characteristics can be obtained. This can improve the bondability at the interface between the solid electrolyte and the electrode active material in the electrode layer of at least one of the positive electrode layer 11 and the negative electrode layer 12, and can improve the charge / discharge characteristics. It is considered a thing. The reason why such an effect can be obtained is based on the following knowledge and consideration of the inventors.

The solid electrolyte material used in all solid state batteries is inferior in ionic conductivity as compared to non-aqueous electrolytes used in conventional secondary batteries. For this reason, it is presumed that the overvoltage generated when the all-solid battery is charged and discharged is mainly caused by the high internal resistance due to the low ionic conductivity of the solid electrolyte material.

However, when an all-solid battery produced by firing is charged and discharged, the electrode layer is actually compared to the internal resistance estimated from the low ionic conductivity of the solid electrolyte material existing inside the electrode layer of the all-solid battery. Have been found by the inventors to have a higher internal resistance. This suggests that, in an all-solid battery produced by firing, the high internal resistance of the electrode layer cannot be sufficiently explained only by the low ionic conductivity of the solid electrolyte material.

As a result of further investigation, the inventor increased the contact interface between the solid electrolyte material and the electrode active material in the electrode layer, and the solid electrolyte material and the electrode active material were closely bonded by firing, Promoting the transfer of ions between the solid electrolyte material and the electrode active material and promoting the movement of ions inside the electrode active material improve the charge / discharge characteristics of the all-solid battery produced by firing It was found to be extremely important.

According to the present invention, an all-solid-state battery having excellent charge / discharge characteristics can be obtained by including an electrode active material in a rod-like or strip-like form, for example, a columnar or scale-like anisotropy in an electrode layer. Can be provided. The reason why this effect is obtained is estimated as follows.

In contrast to an electrode active material having no anisotropy such as a spherical shape, an electrode active material having an anisotropy in the form of a rod or a band has a larger surface area than an electrode active material having the same volume. For this reason, it is presumed that the contact area between the solid electrolyte material and the electrode active material can be increased by including the electrode active material in the form of a rod or strip in the electrode layer. In addition, since an ion conduction path inside the electrode active material is secured toward the long side direction of the electrode active material, exchange of ions between the solid electrolyte material and the electrode active material, and the electrode active material It is estimated that the movement of ions inside is promoted. Furthermore, since the electron conduction path inside the electrode active material is secured in the long side direction of the electrode active material, the movement of electrons inside the electrode layer is promoted. It is estimated that it contributes to the improvement of the charge / discharge characteristics.

In the present invention, the rod-like or belt-like form defines the shape of the elements (particles, etc.) constituting the electrode active material, and specifically, the outer surface of the component of the electrode active material is defined. The ratio of the dimension of the longest side to the dimension of the shortest side of the rectangular parallelepiped when surrounded by the rectangular parallelepiped, that is, the shape having an anisotropy with an aspect ratio exceeding 1, and the outer shape of the constituent elements of the electrode active material is a rod shape or It means a strip shape, for example, a columnar body or a scale-like body. For example, when the outer shape of the component of the electrode active material has anisotropy of a strip or scale, the longest side corresponds to the length of the component of the electrode active material, and the shortest side is the electrode active material Generally, it corresponds to the thickness of the component of the material. The longest side and the shortest side can be measured from, for example, an image obtained by observing components of the electrode active material using a scanning electron microscope (SEM).

The electrode active material is preferably oriented in a direction (plane direction of each layer) substantially orthogonal to the stacking direction of the electrode layer and the solid electrolyte layer. In this case, the ionic conduction path and the electron conduction path are secured in the long side direction of the constituent elements of the electrode active material, that is, the surface direction of the electrode layer, so that the area current density in the electrode layer is increased. The charge / discharge characteristics of the all-solid battery can be improved, and the electrode active material contained in the electrode layer can be filled at a high density to improve the volume energy density of the all-solid battery. Can do.

The electrode active material preferably has a long side and a short side, and the ratio of the long side to the short side is preferably 3 or more. In this case, the ion conduction path and the electron conduction path are more effectively ensured in the long side direction of the constituent elements of the electrode active material, that is, the surface direction of the electrode layer, inside the electrode layer.

Furthermore, the electrode active material is not particularly limited as long as it is a material that can occlude and release ions and can be fired, but includes at least one metal selected from the group consisting of titanium and niobium. An oxide is preferable. In particular, the electrode active material is preferably monoclinic niobium oxide.

The volume occupancy of the solid electrolyte in the electrode layer is preferably 22% by volume to 56% by volume. In this case, a good ion conduction path can be secured inside the electrode layer.

The solid electrolyte contained in the solid electrolyte layer 13 or the solid electrolyte contained in at least one of the positive electrode layer 11 and the negative electrode layer 12 preferably contains a lithium-containing phosphate compound.

The lithium-containing phosphate compound as a solid electrolyte included in the solid electrolyte layer 13 or the lithium-containing phosphate compound as a solid electrolyte included in the positive electrode layer 11 or the negative electrode layer 12 is a lithium-containing phosphate compound having a NASICON structure. Can be used. Lithium-containing phosphoric acid compound having a NASICON-type structure, the chemical formula _{Li x M y (PO 4)} 3 ( Formula, x 1 ≦ x ≦ 2, y is a number in the range of 1 ≦ y ≦ 2, M Includes one or more elements selected from the group consisting of Ti, Ge, Al, Ga and Zr), for example, Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ . In this case, part of P in the above chemical formula may be substituted with B, Si, or the like. For example, two or more compounds having different compositions of lithium-containing phosphate compounds having a NASICON type structure such as Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and Li _1.2 Al _0.2 Ti _1.8 (PO ₄ ) ₃ are mixed. You may use the mixture.

In addition, the lithium-containing phosphate compound having a NASICON structure used in the above solid electrolyte includes a crystal phase of a lithium-containing phosphate compound having a NASICON structure, or a lithium-containing phosphate having a NASICON structure by heat treatment You may use the glass which precipitates the crystal phase of a phosphoric acid compound.

In addition, as a material used for said solid electrolyte, it is possible to use the material which has ion conductivity and is so small that electronic conductivity can be disregarded other than the lithium-containing phosphate compound which has a NASICON structure. Examples of such a material include lithium oxyacid salts and derivatives thereof. In addition, Li-PO system compounds such as lithium phosphate (Li ₃ PO ₄ ), LIPON (LiPO _4−x N _x ) in which nitrogen is mixed with lithium phosphate, and Li—Si—O such as Li ₄ SiO _{4 Such} as La-based compounds, Li-P-Si-O based compounds, Li-V-Si-O based compounds, La _0.51 Li _0.35 TiO _2.94 , La _0.55 Li _0.35 TiO ₃ , Li _3x La _{2 / 3-x} TiO ₃ Examples thereof include a compound having a lobskite structure, a compound having a garnet structure having Li, La, and Zr, such as Li ₇ La ₃ Zr ₂ O ₁₂ .

When an oxide containing at least one metal selected from the group consisting of titanium and niobium is used as the positive electrode active material included in the positive electrode layer 11, the negative electrode active material included in the negative electrode layer 12 is MOx. (M includes at least one element selected from the group consisting of Ti, Si, Sn, Cr, Fe, Nb, and Mo, and x is a numerical value in a range of 0.9 ≦ x ≦ 2.0. ) Can be used. For example, a mixture in which two or more active materials having a composition represented by MOx containing different elements M such as TiO ₂ and SiO ₂ may be used. As the negative electrode active material, graphite-lithium compounds, lithium alloys such as Li-Al, oxidation of Li ₃ V ₂ (PO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₄ Ti ₅ O _12, etc. Thing, etc. can be used. The negative electrode layer 12 may be formed from metallic lithium.

When an oxide containing at least one metal selected from the group consisting of titanium and niobium is used as the negative electrode active material included in the negative electrode layer 12, the positive electrode active material included in the positive electrode layer 11 may be Li Lithium-containing phosphate compounds having a nasicon structure such as ₃ V ₂ (PO ₄ ) _3, lithium-containing phosphate compounds having an olivine structure such as LiFePO ₄ and LiMnPO ₄ , LiCoO ₂ , LiCo _1/3 Ni _1/3 A layered compound such as Mn _1/3 O ₂ or a lithium-containing compound having a spinel structure such as LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , or Li ₄ Ti ₅ O ₁₂ can be used.

In the all-solid-state battery stack 10 of the present invention, the solid electrolyte layer 13 includes a solid electrolyte made of a lithium-containing phosphate compound having a NASICON structure, and at least one of the positive electrode layer 11 and the negative electrode layer 12 is a NASICON type. It is preferable to include a solid electrolyte composed of a lithium-containing phosphate compound having a structure.

In order to manufacture the all-solid battery stack 10 configured as described above, in the present invention, first, an unsintered electrode layer that is an unsintered body of at least one of the positive electrode layer 11 and the negative electrode layer 12, and a solid An unsintered solid electrolyte layer that is an unsintered body of the electrolyte layer 13 is fabricated (unsintered layer fabrication step). In particular, in the present invention, an unsintered solid electrolyte layer that is an unsintered body of the solid electrolyte layer 13 is produced from a material containing the above lithium-containing phosphate compound, and at least one selected from the group consisting of the above titanium and niobium An unsintered electrode layer, which is an unsintered body of the electrode layer, is prepared from a material including an oxide containing the above metal and a material including the lithium-containing phosphate compound. Thereafter, the produced unfired electrode layer and the unfired solid electrolyte layer are laminated to form a laminate (laminated body forming step). And the obtained laminated body is baked (baking process). The positive electrode layer 11 and / or the negative electrode layer 12 and the solid electrolyte layer 13 are joined by firing. Finally, the fired laminate is sealed, for example, in a coin cell. The sealing method is not particularly limited. For example, you may seal the laminated body after baking with resin. Alternatively, an insulating paste having an insulating property such as Al ₂ O ₃ may be applied or dipped around the laminate, and the insulating paste may be heat-treated for sealing.

In order to efficiently draw current from the positive electrode layer 11 and the negative electrode layer 12, a current collector layer such as a carbon layer, a metal layer, or an oxide layer may be formed on the positive electrode layer 11 and the negative electrode layer 12. Examples of the method for forming the current collector layer include a sputtering method. Alternatively, the metal paste may be applied or dipped and heat-treated.

In the laminated body forming step, it is preferable to laminate the unfired bodies of the positive electrode layer 11, the solid electrolyte layer 13, and the negative electrode layer 12 to form an unfired laminated body having a single cell structure. Furthermore, in the laminated body forming step, a laminated body may be formed by laminating a plurality of laminated bodies having the above single cell structure with an unfired body of the current collector interposed therebetween. In this case, a plurality of laminates having a single battery structure may be laminated electrically in series or in parallel.

The method for forming the unfired electrode layer and the unfired solid electrolyte layer is not particularly limited, but a doctor blade method, a die coater, a comma coater, etc. for forming a green sheet, or a screen for forming a printing layer. Printing or the like can be used. The method for laminating the unfired electrode layer and the unfired solid electrolyte layer is not particularly limited, but the unfired electrode layer and the unfired electrode layer may be formed using a hot isostatic press, a cold isostatic press, an isostatic press, or the like. A fired solid electrolyte layer can be laminated.

The slurry for forming the green sheet or the printing layer is obtained by wet-mixing an organic vehicle in which an organic material is dissolved in a solvent and (a positive electrode active material and a solid electrolyte, a negative electrode active material and a solid electrolyte, or a solid electrolyte). Can be produced. Media can be used in wet mixing, and specifically, a ball mill method, a viscomill method, or the like can be used. On the other hand, a wet mixing method that does not use media may be used, and a sand mill method, a high-pressure homogenizer method, a kneader dispersion method, or the like can be used. The organic material contained in the slurry for forming the green sheet or the printing layer is not particularly limited, and polyvinyl acetal resin, cellulose resin, acrylic resin, urethane resin, and the like can be used.

The slurry may contain a plasticizer. Although the kind of plasticizer is not particularly limited, phthalic acid esters such as dioctyl phthalate and diisononyl phthalate may be used.

In the firing step, the atmosphere is not particularly limited, but it is preferably performed under conditions that do not change the valence of the transition metal contained in the electrode active material. The firing temperature is preferably 400 ° C. or higher and 1000 ° C. or lower.

Next, specific examples of the present invention will be described. In addition, the Example shown below is an example and this invention is not limited to the following Example.

Hereinafter, examples and comparative examples of all-solid batteries manufactured using titanium dioxide (TiO ₂ ) powder and niobium pentoxide (Nb ₂ O ₅ ) powder as electrode active materials will be described.

First, the electrode active materials used in the all solid state batteries of Examples and Comparative Examples were evaluated as follows.

<Evaluation of electrode active material>
As an electrode active material, in Example 1, each particle is a scaly titanium dioxide powder having an anatase type crystal structure, and in Example 2, each particle is a columnar body and a monoclinic crystal structure of niobium pentoxide, In Example 1, a titanium dioxide powder having spherical particles and anatase type crystal structure was used in Example 1, and in Comparative Example 2, niobium pentoxide powder having a substantially cubic shape and a monoclinic crystal structure was used. The photograph which observed each powder with the scanning electron microscope (SEM) is shown in FIG. In the photograph of each powder, the dimensions of the long side and the short side of the particles were measured, and the aspect ratio (= long side / short side) was calculated. The aspect ratio was about 30 in Example 1, about 10 in Example 2, about 1 in Comparative Example 1, and about 1 in Comparative Example 2. The long side dimension of the particles was about 25 μm in Example 1 and about 5 μm in Example 2.

Next, an electrode sheet and a solid electrolyte sheet were prepared as follows in order to produce the all-solid battery of the example and the comparative example.

<Preparation of electrode sheet and solid electrolyte sheet>
As a solid electrolyte, a glass powder of Li _1.4 Al _0.4 Ge _1.6 (PO ₄ ) ₃ , which is an example of a NASICON type lithium-containing phosphate compound, was prepared. The main material of the electrode material of Example 1 and Comparative Example 1 was prepared by mixing the electrode active material, the solid electrolyte, and carbon in a weight ratio of 30:60:10. The electrode active material, the solid electrolyte, and carbon were mixed at a weight ratio of 70: 23: 7 to prepare the main material of the electrode material of Example 2 and Comparative Example 2.

The electrode materials of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared by mixing the main material of each electrode material obtained above, polyacetal resin and ethanol in a weight ratio of 85: 15: 140.

The solid electrolyte slurries of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared by mixing the solid electrolyte obtained above, polyacetal resin and ethanol in a weight ratio of 85: 15: 140.

Each of the obtained electrode slurry of Example 1 and Comparative Examples 1 and 2 and the solid electrolyte slurry of Examples 1, 2 and Comparative Examples 1 and 2 was formed into a green sheet having a thickness of 10 μm by the doctor blade method. The electrode sheets of Example 1 and Comparative Examples 1 and 2 and the solid electrolyte sheets of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared by cutting into a square shape with a side of 25 mm. The electrode slurry of Example 2 was formed into a green sheet having a thickness of 5 μm by the doctor blade method and cut into a square shape having a side of 25 mm, thereby producing the electrode sheet of Example 2.

In Example 1, since the long side dimension of the electrode active material particles contained in the electrode slurry is about 25 μm and the thickness of the electrode sheet is 10 μm, the long side of the electrode active material particles has a thickness within the electrode sheet. Orientation in the direction is suppressed and the film is oriented in the plane direction. In Example 2, since the long side dimension of the electrode active material particles contained in the electrode slurry is about 5 μm and the thickness of the electrode sheet is 5 μm, the long side of the electrode active material particles is in the thickness direction within the electrode sheet. Orientation is suppressed and the film is oriented in the plane direction.

Using the electrode sheet and the solid electrolyte sheet obtained as described above, all-solid batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were produced.

<Preparation of electrode-electrolyte laminate>
On one side of the solid electrolyte layer formed by laminating 8 sheets of solid electrolyte sheets, 10 electrode sheets (20 sheets in Example 2) were laminated, cut into a square shape with a side of 10 mm, and 80 ° C. An electrode-electrolyte laminate as a molded body was produced by applying a pressure of 1 ton at this temperature and thermocompression bonding.

Firing is performed for 2 hours at a temperature of 500 ° C. in a nitrogen gas atmosphere containing 1% by volume of oxygen gas in a state where the electrode-electrolyte laminate as a compact is sandwiched between two alumina ceramic plates. After removing the polyacetal resin in 1), the electrode layer and the solid electrolyte layer were joined by firing in a nitrogen gas atmosphere at a temperature of 700 ° C. for 2 hours (firing step 2). Thus, an electrode-electrolyte laminate as a fired body was produced.

<Evaluation of electrode layer>
The cross sections of the obtained electrode-electrolyte laminates of Examples 1 and 2 and Comparative Examples 1 and 2 were observed using a scanning electron microscope (SEM). FIG. 3 shows a photograph of a cross section of the electrode-solid electrolyte laminate produced in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention, observed with a scanning electron microscope (SEM). In Example 1, an enlarged cross section of the electrode-solid electrolyte laminate is also shown.

In each photograph shown in FIG. 3, the vertical direction is the stacking direction, the upper side of the photograph is the electrode layer side, and the lower side is the solid electrolyte layer side.

As shown in FIG. 3, in Comparative Example 1, titanium dioxide, which is a spherical electrode active material, and a solid electrolyte material are in a randomly sintered state, in the stacking direction or with respect to the stacking direction. In the vertical direction (the surface direction of the fired body), no particular orientation of the electrode active material was observed.

In Example 1, titanium dioxide which is a scale-like anisotropic electrode active material was oriented in a direction perpendicular to the stacking direction and sintered with a solid electrolyte material.

In Comparative Example 2, niobium pentoxide, which is a substantially cubic electrode active material, and a solid electrolyte material are randomly sintered, in the stacking direction, or in the direction perpendicular to the stacking direction, In particular, the orientation of the electrode active material was not observed.

In Example 2, niobium pentoxide, which is a columnar anisotropic electrode active material, was oriented in a direction perpendicular to the stacking direction and sintered with the solid electrolyte material.

On the other hand, the volume occupancy of the solid electrolyte material in the electrode layers of Examples 1 and 2 and Comparative Examples 1 and 2 was calculated by the following formula, and the calculated values are shown in Table 1 below.

(Volume occupation ratio of solid electrolyte material in electrode layer)
= (Volume of solid electrolyte material in electrode layer) / (Volume of electrode layer)
= (Weight of solid electrolyte material in electrode layer) ÷ (specific gravity of solid electrolyte material) ÷ (volume of electrode layer)

From Table 1 below, it can be seen that the volume occupancy of the solid electrolyte material in the electrode layers of Examples 1 and 2 and Comparative Examples 1 and 2 is 22 to 56% by volume.

<Preparation of all-solid battery>
The electrode-electrolyte laminate as a fired body was dried at a temperature of 100 ° C. to remove moisture, and then a platinum (Pt) layer was formed as a current collector layer on the electrode side surface by sputtering. A polymethyl methacrylate resin (PMMA) gel electrolyte is applied on a metal lithium plate as a counter electrode, and the electrode-electrolyte laminate and the metal lithium plate as a fired body so that the surface on the electrolyte side is in contact with this application surface Were sealed with a 2032 type coin cell, and all-solid batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were produced.

<Evaluation of all solid state battery>
The characteristics of the obtained all-solid-state batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated as follows. In the evaluation of the battery, charging is performed when lithium is inserted into the electrode active material constituting the electrode layer serving as the working electrode, and the potential is increased due to lithium desorption from the metal lithium plate serving as the counter electrode. This is defined as discharge.

The all solid state battery was charged to a voltage of 1.4 V with a current of 100 μA, held at a voltage of 1.4 V for 5 hours, and left for several hours until the voltage value stabilized. Thereafter, the battery was discharged at a current of 100 μA to a voltage of 3.0 V, held at a voltage of 3.0 V for 5 hours, and left for several hours until the voltage value was stabilized. Such a charge / discharge cycle test was carried out for two cycles. Here, 100 μA corresponds to a current value of about 0.1 C with respect to the weight of the electrode active material contained in the electrode layer.

As a result, it was confirmed that all the all-solid-state batteries can be charged and discharged without any problem. The charge / discharge curves of the second cycle of the obtained all-solid-state batteries of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG.

From FIG. 4A, the all-solid battery of Example 1 in which the electrode active material particles are scaly is different from the all-solid battery of Comparative Example 1 in which the electrode active material particles are spherical. Is small and it is understood that the charge and discharge characteristics are excellent. From FIG. 4B, the all solid state battery of Example 2 in which the electrode active material particles are columnar bodies is similarly charged and discharged in contrast to the all solid state battery of Comparative Example 2 in which the electrode active material particles are spherical. It can be seen that the overvoltage is small and the charge / discharge characteristics are excellent.

Moreover, about 50% of the discharge capacity of each all-solid-state battery shown in FIG. 4, that is, 75 mAh / g in the all-solid-state batteries of Example 1 and Comparative Example 1 as shown by the arrows in FIG. As shown by the arrows in FIG. 4B, the discharge voltage (discharge flat voltage) at 100 mAh / g in the all solid state batteries of Example 2 and Comparative Example 2 is shown in Table 1 below.

From Table 1 above, the discharge flat potential of Example 1 is lower than that of Comparative Example 1, and the discharge flat potential of Example 2 is lower than that of Comparative Example 2. Therefore, compared with the case where a spherical electrode active material is used. Thus, it can be seen that the use of scale-like or columnar electrode active material particles can increase the discharge voltage and is excellent in discharge characteristics.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

Since the bondability at the interface between the solid electrolyte and the electrode active material in the electrode layer can be improved and the charge / discharge characteristics can be improved, the present invention is particularly useful for the production of an all-solid battery.

10: all-solid battery stack, 11: positive electrode layer, 12: negative electrode layer, 13: solid electrolyte layer.

Claims (8)

An electrode layer containing an electrode active material and a solid electrolyte, and at least one of a positive electrode layer and a negative electrode layer;
A solid electrolyte layer laminated on the electrode layer and containing a solid electrolyte, and
An all-solid-state battery in which the electrode active material has a rod-like or strip-like form. The all-solid-state battery according to claim 1, wherein the electrode active material has a long side and a short side, and a ratio of the long side to the short side is 3 or more. The all-solid-state battery according to claim 1 or 2, wherein a long side of the electrode active material is oriented in a direction substantially perpendicular to a stacking direction of the electrode layer and the solid electrolyte layer. The all-solid-state battery according to any one of claims 1 to 3, wherein the electrode active material is an oxide containing at least one metal selected from the group consisting of titanium and niobium. The all-solid-state battery according to any one of claims 1 to 4, wherein a volume occupation ratio of the solid electrolyte in the electrode layer is 22% by volume or more and 56% by volume or less. The all-solid-state battery according to any one of claims 1 to 5, wherein the electrode active material is monoclinic niobium oxide. The all-solid-state battery according to any one of claims 1 to 6, wherein the solid electrolyte includes a lithium-containing phosphate compound. The all-solid-state battery according to claim 7, wherein the solid electrolyte includes a lithium-containing phosphate compound having a NASICON structure.

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