JP2021034326A - All-solid battery - Google Patents

Abstract

To provide a high-capacity all-solid battery superior in output characteristic.SOLUTION: An all-solid battery according to the present invention comprises: a positive electrode; a negative electrode; and a solid electrolyte layer interposed between the positive and negative electrodes. The positive electrode contains a lithium nickel cobalt manganese composite oxide, which is a positive electrode active material of a particular composition, a sulfide-based solid electrolyte, and a conductive assistant. The content of the positive electrode active material in a positive electrode mixture is 60-75 mass%. The negative electrode has a mold of a negative electrode mixture containing a lithium titanium oxide which is a negative electrode active material, a sulfide-based solid electrolyte and a conductive assistant. The content of the negative electrode active material in the negative electrode mixture is 40-60 mass%. The solid electrolyte layer contains a sulfide-based solid electrolyte.SELECTED DRAWING: Figure 1

Description

The present invention relates to an all-solid-state battery having a high capacity and excellent output characteristics.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers and the practical application of electric vehicles, small and lightweight secondary batteries with high capacity and high energy density are required. It has become to.

Currently, lithium secondary batteries that can meet this demand, especially lithium ion secondary batteries, use lithium-containing composite oxides such as lithium _{cobalt oxide (LiCoO 2} ) and lithium nickel oxide (LiNiO _{2) as the positive electrode active material.} Graphite or the like is used as the negative electrode active material, and an organic electrolytic solution containing an organic solvent and a lithium salt is used as the non-aqueous electrolyte.

With the further development of equipment to which lithium-ion secondary batteries are applied, further extension of life, higher capacity, and higher energy density of lithium-ion secondary batteries are required, and at the same time, longer life and higher life are required. The reliability of lithium-ion secondary batteries with higher capacity and higher energy density is also highly required.

However, since the organic electrolytic solution used in the lithium ion secondary battery contains an organic solvent which is a flammable substance, the organic electrolytic solution abnormally generates heat when an abnormal situation such as a short circuit occurs in the battery. there is a possibility. Further, with the recent increase in energy density of lithium ion secondary batteries and the increasing tendency of the amount of organic solvent in organic electrolytic solutions, the reliability of lithium ion secondary batteries is further required.

Under the above circumstances, an all-solid-state lithium secondary battery (all-solid-state battery) that does not use an organic solvent has attracted attention. The all-solid-state battery uses a molded body of a solid electrolyte that does not use an organic solvent instead of the conventional organic solvent-based electrolyte, and has high safety without the risk of abnormal heat generation of the solid electrolyte.

Various improvements have also been attempted in all-solid-state batteries. For example, Patent Document 1 proposes that a binder having a specific structure and an antioxidant are contained in a solid electrolyte composition for forming a positive electrode, a negative electrode, and a solid electrolyte layer. According to Patent Document 1, by adopting the above configuration, an all-solid-state battery having excellent stability of battery voltage over time can be configured. In Patent Document 1, various positive electrode active materials and negative electrode active materials are combined. We are verifying the effect.

Further, Patent Document 2 describes a specific composition as a solid electrolyte for a lithium ion battery that can suppress the generation of hydrogen sulfide when exposed to the atmosphere and can maintain high conductivity even when left in dry air. A sulfide-based solid electrolyte having an Argurodite type crystal structure has been proposed.

JP-A-2018-88306 International Publication No. 2016/104702

At present, the fields of application of all-solid-state batteries are expanding rapidly, and for example, they can be applied to applications that require discharge at large current values. Therefore, the output characteristics should be improved to meet this demand. Is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an all-solid-state battery having a high capacity and excellent output characteristics.

The all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the positive electrode contains a positive electrode active material, a solid electrolyte, and a conductive auxiliary agent. It has a molded body of a positive electrode mixture, and the positive electrode mixture contains a lithium nickel cobalt manganese composite oxide represented by the following general composition formula (1) as the positive electrode active material, and as the solid electrolyte, The negative electrode mixture contains a sulfide-based solid electrolyte, the content of the positive electrode active material in the positive electrode mixture is 60 to 75% by mass, and the negative electrode is a negative electrode active material, a solid electrolyte, and a conductive auxiliary agent. The negative electrode mixture contains lithium titanium oxide as the negative electrode active material and a sulfide-based solid electrolyte as the solid electrolyte, and the negative electrode active material in the negative electrode mixture. The content is 40 to 60% by mass, and the solid electrolyte layer is characterized by containing a sulfide-based solid electrolyte.

Li _{1 + x} M ¹ O ₂ (1)

In the general composition formula (1), −0.3 ≦ x ≦ 0.3, M ¹ is a group of three or more elements including at least Ni, Co, and Mn, and each element constituting ^{M 1.} Among them, when the ratios (mol%) of Ni, Co and Mn are a, b and c, respectively, 0.3 ≦ a ≦ 0.5, 0.2 ≦ b ≦ 0.4 and 0.2. ≦ c ≦ 0.4.

According to the present invention, it is possible to provide an all-solid-state battery having a high capacity and excellent output characteristics.

It is sectional drawing which shows typically an example of the all-solid-state battery of this invention.

The all-solid-state battery of the present invention has a positive electrode having a molded body of a positive electrode mixture containing a positive electrode active material, a solid electrolyte and a conductive auxiliary agent, and a negative electrode mixture containing a negative electrode active material, a solid electrolyte and a conductive auxiliary agent. It has a negative electrode having a body and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

Then, in the all-solid-state battery of the present invention, the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) is used as the positive electrode active material, and the content of the positive electrode active material in the positive electrode mixture is determined. Lithium titanium oxide is used as the negative electrode active material, and the content of the negative electrode active material in the negative electrode mixture is set to a specific value, and the solid electrolyte in the positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer is further set. As a sulfide-based solid electrolyte is used. In the present invention, by adopting these matters, in addition to increasing the capacity at the time of light load discharge, the capacity at the time of heavy load discharge is also increased to improve the output characteristics.

(Positive electrode)
The positive electrode of an all-solid-state battery has a molded body of a positive electrode mixture containing a positive electrode active material, a solid electrolyte, a conductive auxiliary agent, and the like. For example, a positive electrode having a structure in which and is integrated with each other.

As the positive electrode active material, a lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) is used.

In the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Ni and Co are components that contribute to the capacity improvement of the lithium nickel cobalt manganese composite oxide.

Further, in the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Mn is a component that enhances the thermal stability of the lithium nickel cobalt manganese composite oxide. Furthermore, since the lithium nickel-cobalt-manganese composite oxide contains Co together with Mn, Co acts so as to suppress fluctuations in the valence of Mn due to Li doping and dedoping during charging and discharging of the battery. Therefore, the average valence of Mn can be stabilized to a value close to tetravalent, and the reversibility of charge and discharge can be further enhanced. Therefore, by using such a lithium nickel cobalt manganese composite oxide, it is possible to construct a battery having more excellent charge / discharge cycle characteristics.

In the lithium nickel-cobalt-manganese composite oxide represented by the general composition formula (1), the ratios (mol%) of Ni, Co and Mn in each element constituting ^{M 1 are set to a, b and c, respectively.} When this is done, 0.3 ≦ a ≦ 0.5, 0.2 ≦ b ≦ 0.4, and 0.2 ≦ c ≦ 0.4. When the ratios of Ni, Co and Mn in the element group M ¹ are within the above ranges, the above-mentioned actions of Ni, Co and Mn are effectively exhibited, and the output characteristics of the all-solid-state battery are improved. ..

In the lithium nickel-cobalt-manganese composite oxide represented by the general composition formula (1), the element group M ¹ may be composed of only Ni, Co and Mn, but together with these elements, Mg and Ti , Zr, Nb, Mo, W, Al, Si, Ga, Ge and Sn may contain at least one element selected from the group. However, when the total number of elements in the element group M ¹ is 100 mol%, the total ratio d of Mg, Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge and Sn is 5 mol% or less. It is preferably 1 mol% or less, and more preferably 1 mol% or less. Elements other than Ni, Co and Mn in the element group M ¹ may be uniformly distributed in the lithium-nickel-cobalt-manganese composite oxide, also may be segregated like particles surfaces.

The lithium nickel-cobalt-manganese composite oxide having the above composition has a ^{large true density of 4.55 to 4.95 g / cm 3,} and is a material having a high volumetric energy density. The true density of the lithium nickel-cobalt-manganese composite oxide containing Mn in a certain range varies greatly depending on the composition, but the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. For example, it is considered that the value becomes a large value close to the true density of _{LiCoO 2.} Further, the capacity per mass of the lithium nickel-cobalt-manganese composite oxide can be increased, and the material can be made into a material having excellent reversibility.

The true density of the lithium nickel-cobalt-manganese composite oxide increases particularly when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (1), −0.3 ≦ x. It is preferable that ≦ 0.3, and by adjusting the value of x in this way, the true density and reversibility can be improved. It is more preferable that x is −0.05 or more and 0.05 or less, and in this case, the true density of the lithium nickel cobalt manganese composite oxide is set to a higher value of ^{4.6 g / cm 3 or more.} Can be done.

The lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) contains Li-containing compounds (such as lithium hydroxide), Ni-containing compounds (such as nickel sulfate), Co-containing compounds (such as cobalt sulfate), and Mn. It can be produced by mixing a compound (manganese sulfate or the like) and a compound (oxide, hydroxide, sulfate, etc.) containing other elements contained in the ^{element group M 1 and firing the compound.} Further, in synthesizing the lithium-nickel-cobalt-manganese composite oxide with a higher purity, a composite compound containing a plurality of elements included in the element group M ¹ (hydroxides, such as an oxide) and mixing the Li-containing compound , Preferably fired.

The firing conditions can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but preheating is performed by heating to a temperature lower than the firing temperature (for example, 250 to 850 ° C.) and holding at that temperature. After that, it is preferable to raise the temperature to the firing temperature to allow the reaction to proceed. The preheating time is not particularly limited, but is usually about 0.5 to 30 hours. Further, the atmosphere at the time of firing can be an atmosphere containing oxygen (that is, in the atmosphere), a mixed atmosphere of an inert gas (argon, helium, nitrogen, etc.) and oxygen gas, an oxygen gas atmosphere, and the like. The oxygen concentration (based on volume) is preferably 15% or more, and preferably 18% or more.

As the positive electrode active material, only the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) may be used, or the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) may be used. And other positive electrode active materials may be used in combination. As another positive electrode active material that can be used in combination with the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), various positive electrode active materials used as the positive electrode active material of the lithium ion secondary battery [ Lithium-containing composite oxides other than the lithium nickel-cobalt-manganese composite oxide represented by the general composition formula (1)] can be mentioned. However, the proportion of the positive electrode active material other than the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1) in the total amount of the positive electrode active material is preferably 30% by mass or less.

The content of the positive electrode active material in the positive electrode mixture is 60% by mass or more, preferably 65% by mass or more, and more preferably 65% by mass or more, from the viewpoint of enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is 75% by mass or less, preferably 70% by mass.

A sulfide-based solid electrolyte is used as the solid electrolyte of the positive electrode. The sulfide-based solid electrolyte is particularly excellent in ionic conductivity among the solid electrolytes that can be used for all-solid-state batteries, and by using this not only for the positive electrode but also for the negative electrode and the solid electrolyte layer, the output characteristics of the battery Is improved.

The sulfide-based solid electrolyte, _such as _{Li 2 S-P 2 S 5} , Li 2 S-SiS 2, Li 2 S-P 2 S 5 -GeS 2, Li 2 S-B 2 S 3 based glass _{In addition to these, Li 10} GeP ₂ S ₁₂ (LGPS system), which has been attracting attention as having high lithium ion conductivity in recent years, and a sulfide-based solid electrolyte having an algyrodite-type crystal structure can also be used.

Examples of the sulfide-based solid electrolyte having an algyrodite type crystal structure include a material represented by the following general composition formula (2).

Li _{7-p + q} PS _6-p Cl _{p + q} (2)

In the general composition formula (2), 0.05 ≦ q ≦ 0.9 and −3.0p + 1.8 ≦ q ≦ −3.0p + 5.7.

The sulfide-based solid electrolyte referred to in the present specification may be composed of a single phase of a crystal phase having an algyrodite-type crystal structure (cubic-based algyrodite-type crystal structure), but may be a crystal phase having an algyrodite-type crystal structure. It may consist of a mixed phase containing and a crystal phase represented by LiCl. The mixed phase contains only a crystal phase having an algyrodite type crystal structure and a crystal phase represented by LiCl, a crystal phase having an algyrodite type crystal structure and a crystal phase represented by LiCl, and a crystal phase other than these. Including the case of

In the case of a sulfide-based solid electrolyte composed of a mixed phase containing a crystal phase having an algyrodite type crystal structure and a crystal phase represented by LiCl, 0.05 ≦ p ≦ 0.4 in the general composition formula (2). It is preferable that −3.0p + 3.9 ≦ q ≦ −3.0p + 5.7 is satisfied.

Details of the sulfide-based solid electrolyte having an algyrodite-type crystal structure represented by the general composition formula (2) are disclosed in Patent Document 2, and can be produced by the method described in Patent Document 2.

As the sulfide-based solid electrolyte, one or more of the above-exemplified ones can be used, but it is represented by the general composition formula (2) because the output characteristics of the battery are further improved. It is more preferable to use a sulfide-based solid electrolyte having an algyrodite type crystal structure.

Only the sulfide-based solid electrolyte may be used for the positive electrode, but other solid electrolytes can be used together with the sulfide-based solid electrolyte. Examples of the solid electrolyte that can be used in combination with the sulfide-based solid electrolyte include a hydride-based solid electrolyte and an oxide-based solid electrolyte.

Examples of the hydride-based solid electrolyte include a solid solution of LiBH ₄ , LIBH ₄ and the following alkali metal compound (for example, _{one having a molar ratio of LiBH 4} to the alkali metal compound of 1: 1 to 20: 1). Can be mentioned. Examples of the alkali metal compound in the solid solution include lithium halide (LiI, LiBr, LiF, LiCl, etc.), rubidium halide (RbI, RbBr, RbiF, RbCl, etc.), and cesium halide (CsI, CsBr, CsF, CsCl, etc.). , At least one selected from the group consisting of lithium amide, rubidium amide and cesium amide.

Examples of the oxide-based solid electrolyte include Li ₇ La ₃ Zr ₂ O ₁₂ , LiTi (PO ₄ ) ₃ , LiGe (PO ₄ ) ₃ , and LiLaTIO ₃ .

However, the proportion of the solid electrolyte other than the sulfide-based solid electrolyte in the total amount of the solid electrolyte used in the positive electrode mixture is preferably 30% by mass or less.

The content of the solid electrolyte in the positive electrode mixture is 25 parts by mass or more when the content of the positive electrode active material is 100 parts by mass from the viewpoint of further enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, preferably 65 parts by mass or less, and more preferably 60 parts by mass or less. , 50 parts by mass or less is more preferable.

A carbon material such as carbon black can be used as the conductive auxiliary agent for the positive electrode.

The content of the conductive auxiliary agent in the positive electrode mixture is 2.5 when the content of the positive electrode active material is 100 parts by mass from the viewpoint of further enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is preferably 3 parts by mass or more, more preferably 3.0 parts by mass or more, further preferably 4.0 parts by mass or more, and preferably 6.5 parts by mass or less, 6 It is more preferably 0.0 parts by mass or less, and further preferably 5.0 parts by mass or less.

The positive electrode mixture may or may not contain a resin binder. Examples of the resin binder include fluororesins such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component in the positive electrode mixture, it is desirable that the amount thereof be as small as possible. Therefore, in the positive electrode mixture, it is preferable that the binder made of resin is not contained, or if it is contained, the content thereof is 0.5% by mass or less. The content of the resin binder in the positive electrode mixture is more preferably 0.3% by mass or less, and further preferably 0% by mass (that is, the resin binder is not contained).

When a current collector is used for the positive electrode, a metal foil such as aluminum or stainless steel, a punching metal, a net, an expanded metal, a foamed metal; a carbon sheet; or the like can be used as the current collector.

The molded body of the positive electrode mixture is prepared by mixing, for example, a positive electrode active material, a solid electrolyte and a conductive auxiliary agent, and a binder added for non-vaginal use, and the positive electrode mixture is prepared by pressure molding or the like. It can be formed by compressing.

In the case of a positive electrode having a current collector, it can be manufactured by bonding the molded body of the positive electrode mixture formed by the above method by crimping it with the current collector.

The thickness of the molded body of the positive electrode mixture (in the case of a positive electrode having a current collector, the thickness of the molded body of the positive electrode mixture per one side of the current collector; the same applies hereinafter) is from the viewpoint of increasing the capacity of the battery. , 200 μm or more is preferable. The output characteristics of the battery are generally easily improved by thinning the positive electrode and the negative electrode, but according to the present invention, the output characteristics can be improved even when the molded body of the positive electrode mixture is as thick as 200 μm or more. It is possible. Therefore, in the present invention, the effect becomes more remarkable when the thickness of the molded product of the positive electrode mixture is, for example, 200 μm or more. The thickness of the molded product of the positive electrode mixture is usually 2000 μm or less.

(Negative electrode)
The negative electrode of the all-solid-state battery has a molded body of a negative electrode mixture containing lithium titanium oxide as a negative electrode active material, a solid electrolyte, a conductive auxiliary agent, and the like. Examples thereof include a negative electrode having a structure in which a molded body and a current collector are integrated.

Examples of the lithium titanium oxide include those represented by the following general composition formula (3).

Li [Li _{1 / 3-a} M ² _a Ti _{5 / 3-b} M ³ _b ] O ₄ (3)

In the general composition formula (3), M ² is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba, and M ³ is Al, V, Cr, Fe, It is at least one element selected from the group consisting of Co, Ni, Zn, Ym, Zr, Nb, Mo, Ta and W, and has 0 ≦ a <1/3 and 0 ≦ b <5/3.

That is, in the lithium titanium oxide represented by the general composition formula (3), a part of the Li site may be replaced with the ^{element M 2.} However, in the general composition formula (3), a ^{representing the ratio of the element M 2} is preferably less than 1/3. In the lithium titanium oxide represented by the general composition formula (3), Li does not have to be substituted with the ^{element M 2} , so that a representing the ratio of the ^{element M 2 may be 0.}

Further, in the lithium titanium oxide represented by the general composition formula (3), the element M ³ is a component for enhancing the electron conductivity of the lithium titanium oxide, and b representing the ratio of the ^{element M 3 is 0.} When ≦ b <5/3, the effect of improving the electron conductivity can be satisfactorily ensured.

As the negative electrode active material, a negative electrode active material other than lithium titanium oxide used in lithium ion secondary batteries and the like can also be used together with lithium titanium oxide. However, the proportion of the negative electrode active material other than the lithium titanium oxide in the total amount of the negative electrode active material is preferably 30% by mass or less.

The content of the negative electrode active material in the negative electrode mixture is preferably 40% by mass or more, preferably 45% by mass or more, from the viewpoint of enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is 60% by mass or less, preferably 55% by mass.

A sulfide-based solid electrolyte is used as the solid electrolyte of the negative electrode. The sulfide-based solid electrolyte is particularly excellent in ionic conductivity among the solid electrolytes that can be used for all-solid-state batteries. As described above, by using this not only for the negative electrode but also for the positive electrode and the solid electrolyte layer, The output characteristics of the battery are improved.

As the sulfide-based solid electrolyte, one or more of the same solid electrolytes as those exemplified above can be used as the solid electrolyte that can be used for the positive electrode. Among the above-exemplified sulfide-based solid electrolytes, since the output characteristics of the battery are further improved, it is more preferable to use the sulfide-based solid electrolyte having an algyrodite type crystal structure represented by the general composition formula (2). preferable.

Only the sulfide-based solid electrolyte may be used for the negative electrode, but other solid electrolytes can be used together with the sulfide-based solid electrolyte. Examples of the solid electrolyte that can be used in combination with the sulfide-based solid electrolyte include the same hydride-based solid electrolyte and oxide-based solid electrolyte as those exemplified above as those that can be used for the positive electrode.

However, the proportion of the solid electrolyte other than the sulfide-based solid electrolyte in the total amount of the solid electrolyte used in the negative electrode mixture is preferably 30% by mass or less.

The content of the solid electrolyte in the negative electrode mixture is 50 parts by mass or more when the content of the negative electrode active material is 100 parts by mass from the viewpoint of further enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, preferably 130 parts by mass or less, and more preferably 120 parts by mass or less. , 110 parts by mass or less is more preferable.

A carbon material such as carbon black can be used as the conductive auxiliary agent for the negative electrode.

The content of the conductive auxiliary agent in the negative electrode mixture is 10 parts by mass when the content of the negative electrode active material is 100 parts by mass from the viewpoint of further enhancing the output characteristics of the all-solid-state battery and further increasing the capacity. It is preferably 12 parts by mass or more, more preferably 15 parts by mass or more, more preferably 30 parts by mass or less, and more preferably 25 parts by mass or less. It is preferably 22 parts by mass or less, and more preferably 22 parts by mass or less.

The negative electrode mixture may or may not contain a resin binder. Examples of the resin binder include fluororesins such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component even in the negative electrode mixture, it is desirable that the amount thereof is as small as possible. Therefore, as in the case of the positive electrode mixture, the negative electrode mixture does not contain a resin binder, or when it is contained, the content thereof is preferably 0.5% by mass or less. The content of the resin binder in the negative electrode mixture is more preferably 0.3% by mass or less, and further preferably 0% by mass (that is, the resin binder is not contained).

When a current collector is used for the negative electrode, a copper or nickel foil, punching metal, net, expanded metal, foamed metal; carbon sheet; or the like can be used as the current collector.

The molded body of the negative electrode mixture is prepared by, for example, a negative electrode mixture prepared by mixing a negative electrode active material, a solid electrolyte and a conductive auxiliary agent, and a binder added for non-vaginal use by pressure molding or the like. It can be formed by compressing.

In the case of a negative electrode having a current collector, it can be manufactured by bonding the molded body of the negative electrode mixture formed by the above method by crimping it with the current collector.

The thickness of the molded body of the negative electrode mixture (in the case of a negative electrode having a current collector, the thickness of the molded body of the positive electrode mixture per one side of the current collector; the same applies hereinafter) is from the viewpoint of increasing the capacity of the battery. , 200 μm or more is preferable. The output characteristics of the battery are generally easily improved by thinning the positive electrode and the negative electrode, but according to the present invention, the output characteristics can be improved even when the molded body of the negative electrode mixture is as thick as 200 μm or more. It is possible. Therefore, in the present invention, the effect becomes more remarkable when the thickness of the molded product of the negative electrode mixture is, for example, 200 μm or more. In the present invention, the effect is particularly remarkable when the thickness of the molded product of the positive electrode mixture is 200 μm or more and the thickness of the molded product of the negative electrode mixture is 200 μm or more. The thickness of the molded product of the negative electrode mixture is usually 3000 μm or less.

(Solid electrolyte layer)
A sulfide-based solid electrolyte is also used as the solid electrolyte in the solid electrolyte layer of the all-solid-state battery. The sulfide-based solid electrolyte is particularly excellent in ionic conductivity among the solid electrolytes that can be used in all-solid-state batteries. The output characteristics of the battery are improved.

As the sulfide-based solid electrolyte, one or more of the same solid electrolytes as those exemplified above can be used as the solid electrolyte that can be used for the positive electrode. Among the above-exemplified sulfide-based solid electrolytes, since the output characteristics of the battery are further improved, it is more preferable to use the sulfide-based solid electrolyte having an algyrodite type crystal structure represented by the general composition formula (2). preferable.

Only the sulfide-based solid electrolyte may be used for the solid electrolyte layer, but other solid electrolytes can be used together with the sulfide-based solid electrolyte. Examples of the solid electrolyte that can be used in combination with the sulfide-based solid electrolyte include the same hydride-based solid electrolyte and oxide-based solid electrolyte as those exemplified above as those that can be used for the positive electrode.

However, the proportion of the solid electrolyte other than the sulfide-based solid electrolyte in the total amount of the solid electrolyte used in the solid electrolyte layer is preferably 30% by mass or less.

For the solid electrolyte layer, a composition for forming a solid electrolyte layer prepared by dispersing a solid electrolyte in a solvent is applied onto a base material, a positive electrode, and a negative electrode, dried, and if necessary, pressure molding such as press treatment is performed. It can be formed by doing.

As the solvent used in the composition for forming the solid electrolyte layer, it is preferable to select a solvent that does not easily deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes cause a chemical reaction with a very small amount of water, and are therefore represented by hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is preferable to use a non-polar aproton solvent. In particular, it is more preferable to use a super dehydration solvent having a water content of 0.001% by mass (10 ppm) or less. In addition, fluorosolvents such as "Bertrel (registered trademark)" manufactured by Mitsui Dupont Fluorochemical, "Zeorolla (registered trademark)" manufactured by Nippon Zeon, and "Novec (registered trademark)" manufactured by Sumitomo 3M, as well as , Dichloromethane, diethyl ether and other non-aqueous organic solvents can also be used.

The thickness of the solid electrolyte layer is preferably 100 to 300 μm.

(Electrode body)
The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body laminated via a solid electrolyte layer or a wound electrode body in which the laminated electrode body is wound.

When forming the electrode body, it is preferable to perform pressure molding in a state where the positive electrode body, the negative electrode body, and the solid electrolyte layer are laminated from the viewpoint of increasing the mechanical strength of the electrode body.

(Battery form)
FIG. 1 shows a cross-sectional view schematically showing an example of the all-solid-state battery of the present invention. The battery 1 shown in FIG. 1 has a positive electrode 10, a negative electrode 20, and a positive electrode 10 and a negative electrode 20 in an outer body formed of an outer can 40, a sealing can 50, and a resin gasket 60 interposed between them. A solid electrolyte layer 30 interposed between the two is enclosed.

The sealing can 50 is fitted to the opening of the outer can 40 via a gasket 60, and the opening end of the outer can 40 is tightened inward, whereby the gasket 60 comes into contact with the sealing can 50. The opening of the outer can 40 is sealed, and the inside of the element has a sealed structure.

Stainless steel cans can be used for the outer can and the sealing can. In addition, polypropylene, nylon, etc. can be used as the material of the gasket, and if heat resistance is required in relation to the application of the battery, tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), etc. can be used. Heat resistance of fluororesin, polyphenylene ether (PEE), polysulfone (PSF), polyallylate (PAR), polyethersulphon (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), etc. with a melting point of more than 240 ° C. Resin can also be used. Further, when the battery is applied to an application requiring heat resistance, a glass hermetic seal can be used for the sealing.

The all-solid-state battery has an outer body composed of an outer can, a sealing can, and a gasket as shown in FIG. 1, that is, a form generally called a coin-type battery or a button-type battery. Not limited to, for example, those having an exterior body made of a resin film or a metal-resin laminate film, or a metal bottomed tubular (cylindrical or square tubular) exterior can and its opening are sealed. It may have an exterior body having a sealing structure for stopping.

The all-solid-state battery of the present invention can be applied to the same applications as conventionally known secondary batteries, but has excellent heat resistance because it has a solid electrolyte instead of an organic electrolyte, and has a high temperature. It can be preferably used for applications that are exposed to.

Hereinafter, the present invention will be described in detail based on Examples. However, the following examples do not limit the present invention.

Example 1
<Cathode preparation>
_{LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (positive electrode active material) with an average particle size of 4 μm _{, sulfide solid electrolyte (Li 6} PS ₅ Cl), and carbon nanotubes as a conductive aid [Showa Denko Co., Ltd.] Manufactured by "VGCF" (trade name)] was mixed at a mass ratio of 65:32: 3 and kneaded well to prepare a positive electrode mixture. Next, 80 mg of the positive electrode mixture was placed in a powder molding die having a diameter of 6 mm and pressure molding was performed using a press to prepare a positive electrode made of a positive electrode mixture molded product.

<Formation of solid electrolyte layer>
Next, the sulfide solid electrolyte: 15 mg was put onto the positive electrode mixture molded body in the powder molding die, pressure molding was performed using a press machine, and the positive electrode mixture molded body was topped. A solid electrolyte layer was formed on the surface.

<Manufacturing of negative electrode>
_{Mass ratio of lithium titanate (Li 4} Ti ₅ O ₁₂ , negative electrode active material) with an average particle diameter of 7 μm, the sulfide solid electrolyte, and carbon nanotubes as a conductive aid [“VGCF” (trade name) manufactured by Showa Denko Co., Ltd.] The mixture was mixed at a ratio of 50:41: 9 and kneaded well to prepare a negative electrode mixture. Next, the negative electrode mixture: 150 mg was put onto the solid electrolyte layer in the powder molding mold, pressure molding was performed using a press machine, and the negative electrode mixture molded body was placed on the solid electrolyte layer. By forming the negative electrode, a laminated body in which the positive electrode, the solid electrolyte layer, and the negative electrode were laminated was produced. At this time, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

A copper foam base material manufactured by Sumitomo Electric Co., Ltd. [Copper Celmet (trade name), thickness: 1 mm, pore ratio: 97%] is punched to a size of 6 mmφ and placed on the inner bottom surface of a stainless steel sealing can. An aluminum foam group manufactured by Sumitomo Electric Co., Ltd., in which a laminate of the positive electrode / solid electrolyte layer / negative electrode was laminated so that the negative electrode was on the base material side, and further punched to the same size as described above. After placing the material [Aluminum Celmet (trade name), thickness: 1 mm, porosity: 97%] on the positive electrode of the laminate, it is sealed by covering it with a stainless steel outer can. , A flat all-solid-state battery was produced.

Example 2
The positive electrode / solid electrolyte layer / negative electrode in the same manner as in Example 1 except that the ratio of the positive electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the positive electrode mixture was changed to 75:23: 2 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Example 3
The positive electrode / solid electrolyte layer / negative electrode is the same as in Example 1 except that the ratio of the negative electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the negative electrode mixture is changed to 60:33:72 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Example 4
The positive electrode / solid electrolyte layer / negative electrode is the same as in Example 1 except that the ratio of the negative electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the negative electrode mixture is changed to 40:49:11 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Example 5
Positive electrode / solid electrolyte in the same manner as in Example 1 except that the ratio of the positive electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the positive electrode mixture was changed to 60: 36.5: 3.5 in terms of mass ratio. A layer / negative electrode laminate was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that this laminate was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Comparative Example 1
Positive electrode / solid electrolyte in the same manner as in Example 1 except that the ratio of the positive electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the positive electrode mixture was changed to 80: 18.5: 1.5 in terms of mass ratio. A layer / negative electrode laminate was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that this laminate was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Comparative Example 2
The positive electrode / solid electrolyte layer / negative electrode is the same as in Example 1 except that the ratio of the negative electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the negative electrode mixture is changed to 65:30: 5 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Comparative Example 3
The positive electrode / solid electrolyte layer / negative electrode in the same manner as in Example 1 except that the ratio of the positive electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the positive electrode mixture was changed to 55:41: 4 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

Comparative Example 4
The positive electrode / solid electrolyte layer / negative electrode is the same as in Example 1 except that the ratio of the negative electrode active material, the sulfide-based solid electrolyte, and the conductive auxiliary agent in the negative electrode mixture is changed to 35:53:12 in terms of mass ratio. A laminated body was produced, and a flat all-solid-state battery was produced in the same manner as in Example 1 except that the laminated body was used. In the laminated body, the thickness of the laminated body was 3300 μm, the thickness of the positive electrode mixture molded body was 850 μm, the thickness of the negative electrode mixture molded body was 2250 μm, and the thickness of the solid electrolyte layer was 200 μm.

The initial capacity was measured and the output characteristics were evaluated by the following methods for each of the flat all-solid-state batteries of Examples and Comparative Examples.

<Initial capacity measurement>
Each of the flat all-solid-state batteries of Examples and Comparative Examples is constantly charged with a current value of 0.02 C until the voltage reaches 2.8 V, and then is charged with a constant voltage until the current value reaches 0.002 C. After that, the battery was discharged with a current value of 0.02 C until the voltage became 1 V, and the discharge capacity (initial capacity) at that time was measured.

<Output characteristic evaluation>
Each of the flat all-solid-state batteries of Examples and Comparative Examples is charged with constant current and constant voltage under the same conditions as at the time of initial capacity measurement, and then discharged at a current value of 0.2 C until the voltage reaches 1 V. , The discharge capacity (0.2C discharge capacity) at this time was measured.

Then, for each battery, the value obtained by dividing the 0.2C discharge capacity by the initial capacity was expressed as a percentage to obtain the capacity retention rate, and the output characteristics were evaluated.

The compositions of the positive electrode mixture and the negative electrode mixture in each of the flat all-solid-state batteries of Examples and Comparative Examples are shown in Table 1, and the evaluation results of each of the above are shown in Table 2. Of the compositions of the positive electrode mixture in Table 1, the content of the "positive electrode active material" is the content (mass%) in 100% by mass of the positive electrode mixture, and the contents of the "solid electrolyte" and the "conductive aid" are. The amount (parts by mass) with respect to 100 parts by mass of the positive electrode active material, and the content of the "negative electrode active material" in the composition of the negative electrode mixture is the content (mass%) in 100% by mass of the negative electrode mixture, and is "solid". The contents of the "electrolyte" and the "conductive aid" are the amounts (parts by mass) with respect to 100 parts by mass of the negative electrode active material.

As shown in Tables 1 and 2, using a lithium nickel cobalt manganese composite oxide (positive electrode active material) having an appropriate composition and a sulfide-based solid electrolyte, the content of the positive electrode active material in the positive electrode mixture is set to an appropriate value. Examples 1 to 5 using the positive electrode, the lithium titanium oxide (negative electrode active material), and the sulfide-based solid electrolyte, and the negative electrode having the content of the negative electrode active material in the negative electrode mixture set to an appropriate value. The flat all-solid-state battery had a large initial capacity and a high capacity, and also had a large capacity retention rate at the time of evaluating the output characteristics and had excellent output characteristics.

On the other hand, the battery of Comparative Example 1 using a positive electrode having an excessively high content of the positive electrode active material in the positive electrode mixture, and the battery of Comparative Example 2 using a negative electrode having an excessively high content of the negative electrode active material in the negative electrode mixture. The capacity retention rate at the time of output characteristic evaluation was small, and the output characteristics were inferior. Further, the battery of Comparative Example 3 using a positive electrode in which the content of the positive electrode active material in the positive electrode mixture is too low, and the battery of Comparative Example 4 in which the negative electrode in which the content of the negative electrode active material in the negative electrode mixture is too low are used. The initial capacity was small.

1 All-solid-state battery 10 Positive electrode 20 Negative electrode 30 Solid electrolyte layer 40 Exterior can 50 Sealed can 60 Gasket

Claims (5)

An all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.
The positive electrode has a molded body of a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and a conductive auxiliary agent.
The positive electrode mixture is used as the positive electrode active material in the following general composition formula (1).
Li _{1 + x} M ¹ O ₂ (1)
[In the general composition formula (1), −0.3 ≦ x ≦ 0.3, M ¹ is a group of three or more elements containing at least Ni, Co, and Mn, and each of them constitutes ^{M 1.} When the ratios (mol%) of Ni, Co and Mn in the elements are a, b and c, respectively, 0.3 ≦ a ≦ 0.5, 0.2 ≦ b ≦ 0.4, 0. 2 ≦ c ≦ 0.4], and contains a sulfide-based solid electrolyte as the solid electrolyte.
The content of the positive electrode active material in the positive electrode mixture is 60 to 75% by mass.
The negative electrode has a molded body of a negative electrode mixture containing a negative electrode active material, a solid electrolyte, and a conductive auxiliary agent.
The negative electrode mixture contains lithium titanium oxide as the negative electrode active material and contains a sulfide-based solid electrolyte as the solid electrolyte.
The content of the negative electrode active material in the negative electrode mixture is 40 to 60% by mass.
The solid electrolyte layer is an all-solid-state battery characterized by containing a sulfide-based solid electrolyte. When the content of the positive electrode active material in the positive electrode mixture is 100 parts by mass, the content of the solid electrolyte is 25 to 65 parts by mass, and the content of the conductive auxiliary agent is 2.5 to 6. The all-solid-state battery according to claim 1, which is 5 parts by mass. When the content of the negative electrode active material in the negative electrode mixture is 100 parts by mass, the content of the solid electrolyte is 50 to 130 parts by mass, and the content of the conductive auxiliary agent is 10 to 30 parts by mass. The all-solid-state battery according to claim 1 or 2. The positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer have the following general composition formula (2).
Li _{7-p + q} PS _6-p Cl _{p + q} (2)
[In the general composition formula (2), 0.05 ≦ q ≦ 0.9, −3.0p + 1.8 ≦ q ≦ -3.0p + 5.7]
The all-solid-state battery according to any one of claims 1 to 3, which contains a sulfide-based solid electrolyte having an algyrodite type crystal structure represented by. As the lithium titanium oxide, the following general composition formula (3)
Li [Li _{1 / 3-a} M ² _a Ti _{5 / 3-b} M ³ _b ] O ₄ (3)
[In the general composition formula (3), M ² is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba, and M ³ is Al, V, Cr and Fe. , Co, Ni, Zn, Ym, Zr, Nb, Mo, Ta and W, at least one element selected from the group consisting of 0≤a <1/3, 0≤b <5/3. ]
The all-solid-state battery according to any one of claims 1 to 4, which contains the one represented by.

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