JP2021144867A - All-solid type secondary battery - Google Patents

Abstract

To provide an all-solid type secondary battery superior in load characteristic and high-temperature characteristic.SOLUTION: An all-solid type secondary battery 1 comprises: a negative electrode 20 having a compact of a negative electrode mixture containing a negative electrode active substance, a conductive assistant and a solid electrolyte; a positive electrode 10 having a compact of a positive electrode mixture containing a positive electrode active material, a conductive assistant and a solid electrolyte; and a solid electrolyte layer 30 interposed between the positive and negative electrodes. The compact of the negative electrode mixture contains, as the solid electrolyte, a sulfide-based solid electrolyte (A) represented by the following general formula (1): Li7-xPS6-xClyBrz (1). [In the general formula (1), x=y+z, 1.0<x≤1.8 and 0.1≤z/y≤10.0.] The compact of the positive electrode mixture contains, as the solid electrolyte, a sulfide-based solid electrolyte (B) represented by the following general formula (2): Li7-a+bPS6-aCla+b (2). [In the general formula (2), 0.05≤b≤0.9 and -3.0a+1.8≤b≤-3.0a+5.7.]SELECTED DRAWING: Figure 1

Description

The present invention relates to an all-solid-state secondary battery having excellent load characteristics and high-temperature 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, as well as longer life and higher energy density. The reliability of lithium-ion secondary batteries with higher capacity and higher energy density is also highly required.

However, since the organic electrolyte used in the lithium ion secondary battery contains an organic solvent which is a flammable substance, the organic electrolyte 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 secondary battery) that does not use an organic solvent has attracted attention. The all-solid-state secondary 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. ..

Further, various improvements have been attempted in the all-solid-state secondary battery. For example, in Patent Document 1, the positive electrode active material layer and the solid electrolyte layer do not contain a sulfide-based solid electrolyte having oxygen, and further contain a sulfide-based solid electrolyte having no oxygen. , An all-solid-state battery in which the negative electrode active material layer contains graphite as the negative electrode active material and contains a sulfide-based solid electrolyte having oxygen is described.

Although the sulfide-based solid electrolyte having oxygen is thermally stable, the ionic conductivity is lower than that of the sulfide-based solid electrolyte having no oxygen, so that the battery resistance is large when used in an all-solid-state battery. Become. In the technique described in Patent Document 1, by containing a sulfide-based solid electrolyte having oxygen only in the negative electrode active material layer, a deinsertion reaction of Li occurs in the negative electrode active material (graphite) at a low potential. While suppressing the reductive decomposition of the solid electrolyte, the positive electrode active material layer and the solid electrolyte layer do not contain the sulfide-based solid electrolyte having oxygen, and are low by containing the sulfide-based solid electrolyte having no oxygen. It is said that battery resistance can be realized.

Further, Patent Document 2 contains a crystal phase having a cubic Argurodite type crystal structure _{and is represented by a composition formula of Li 7-x + y} PS _6-x Cl _{x + y} , which is a sulfide-based solid for a lithium ion battery. Electrolyte compounds in which x and y satisfy 0.05 ≦ y ≦ 0.9 and −3.0x + 1.8 ≦ y ≦ -3.0x + 5.7 are excellent in oxidation resistance and water resistance. Therefore, it is described that even if it comes into contact with the atmosphere, the amount of hydrogen sulfide generated due to the reaction with water in the atmosphere can be effectively suppressed.

Further, Patent Document 3, in cubic has a crystal phase of Arujirodaito (Argurodite) crystal _structure, sulfide compound represented by the composition formula _{Li 7-x PS 6-x} Cl y Br z, It is high by satisfying x = y + z and 1.0 <x ≦ 1.8, and defining the ratio (z / y) of the molar ratio of Br to the molar ratio of Cl in the range of 0.1 to 10.0. It is described that the Young rate can be lowered while maintaining the ionic conductivity. Further, in Patent Document 3, when the press pressure is applied when the electrode of the all-solid-state battery is produced by using the above-mentioned sulfide-based compound, the solid electrolyte is crushed and the gap between the active material particles is filled. It is said that the battery resistance can be lowered because the contact point and the contact area with the active material particles can be increased.

JP-A-2017-54626 International Publication No. 2016/104702 International Publication No. 2019/009228

By the way, at present, the fields of application of all-solid-state secondary batteries are expanding rapidly, and for example, they can be applied to applications that require discharge at a large current value. It is required to improve the characteristics, and there is also a demand to further improve the battery characteristics at high temperature.

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 secondary battery having excellent load characteristics and high-temperature characteristics.

The all-solid secondary battery of the present invention comprises a negative electrode having a molded body of a negative electrode mixture containing a negative electrode active material, a conductive auxiliary agent and a solid electrolyte, and a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent and a solid electrolyte. The molded body of the negative electrode mixture having a positive electrode having a molded body and a solid electrolyte layer interposed between the positive electrode and the negative electrode is the solid electrolyte of the following general formula (1).
_{Li 7-x PS 6-x} Cl y Br z (1)
The sulfide-based solid electrolyte (A) represented by [x = y + z, 1.0 <x≤1.8, 0.1≤z / y≤10.0 in the general formula (1)] is used. The molded body of the positive electrode mixture contained therein is used as the solid electrolyte according to the following general formula (2).
Li _{7-a + b} PS _6-a Cl _{a + b} (2)
The sulfide-based solid electrolyte (B) represented by [in the general formula (2), 0.05 ≦ b ≦ 0.9, −3.0a + 1.8 ≦ b ≦ -3.0a + 5.7] is used. It is characterized by containing.

According to the present invention, it is possible to provide an all-solid-state secondary battery having excellent load characteristics and high-temperature characteristics.

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

The all-solid secondary battery of the present invention comprises a negative electrode having a molded body of a negative electrode mixture containing a negative electrode active material, a conductive auxiliary agent and a solid electrolyte, and a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent and a solid electrolyte. It has a positive electrode having a molded body and a solid electrolyte layer interposed between the positive electrode and the negative electrode. The molded body of the negative electrode mixture contains the sulfide-based solid electrolyte (A) represented by the following general formula (1), and the molded body of the positive electrode mixture is represented by the following general formula (2). It contains a sulfide-based solid electrolyte (B).

_{Li 7-x PS 6-x} Cl y Br z (1)

In the general formula (1), x = y + z, 1.0 <x ≦ 1.8, 0.1 ≦ z / y ≦ 10.0.

Li _{7-a + b} PS _6-a Cl _{a + b} (2)

In the general formula (2), 0.05 ≦ b ≦ 0.9 and −3.0a + 1.8 ≦ b ≦ −3.0a + 5.7.

Since the sulfide-based solid electrolyte (A) has excellent ionic conductivity and high flexibility, when used in a molded body of a mixture of a positive electrode and a negative electrode, the ionic conductivity of the molded body of the mixture can be enhanced. At the same time, it is possible to satisfactorily fill the space between the active material particles with the sulfide-based solid electrolyte (A) while suppressing the intervention of voids, so that the filling rate of the mixture can be improved and the utilization rate of the positive electrode and the negative electrode can be improved. Can be enhanced.

However, since the sulfide-based solid electrolyte (A) tends to oxidize at a high potential to become an insulator, it is difficult to increase the ionic conductivity of the molded product of the positive electrode mixture when used for the positive electrode. .. Further, since the oxidation reaction of the sulfide-based solid electrolyte (A) is particularly likely to occur in a high temperature environment, if the all-solid secondary battery is left in such an environment for a long time, the battery characteristics are deteriorated.

Therefore, in the present invention, the sulfide-based solid electrolyte (A) is used for the molded body of the negative electrode mixture, and the sulfide-based solid electrolyte (B) is used for the molded body of the positive electrode mixture. The sulfide-based solid electrolyte (B) has higher stability than the sulfide-based solid electrolyte (A), and oxidation is less likely to occur even at a high potential. Therefore, by using the sulfide-based solid electrolyte (A) for the negative electrode, it is possible to improve the ionic conductivity and utilization rate of the molded product of the negative electrode mixture and improve the load characteristics of the negative electrode. By using the system-based solid electrolyte (B), deterioration of characteristics due to oxidation can be suppressed.

In the all-solid-state secondary battery of the present invention, the load characteristics and the high temperature characteristics can be improved by each of the above actions.

The details of the all-solid-state secondary battery of the present invention will be described below.

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

As the negative electrode active material, for example, graphite, pyrolytic carbons, cokes, glassy carbons, calcined organic polymer compounds, mesocarbon microbeads (MCMB), carbon fibers and other lithium can be stored and released. One or a mixture of two or more carbon-based materials is used. In addition, simple substances containing elements such as Si, Sn, Ge, Bi, Sb, and In, compounds and alloys thereof; compounds that can be charged and discharged at a low voltage close to that of lithium metals such as lithium-containing nitrides or lithium-containing oxides; lithium metals. Lithium / aluminum alloys; can also be used as the negative electrode active material.

Among these, it is preferable to use lithium titanium oxide. Examples of the lithium titanium oxide include those represented by the following general formula (3).

Li [Li _{1 / 3-c} M ¹ _c Ti _{5 / 3-d} M ² _d ] O ₄ (3)

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

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

Further, in the lithium titanium oxide represented by the general formula (3), the element M ² is a component for enhancing the electron conductivity of the lithium titanium oxide, and d representing the ratio of the ^{element M 2 is 0 ≦.} When d <5/3, the effect of improving the electron conductivity can be sufficiently ensured.

When a lithium titanium oxide and another negative electrode active material are used as the negative electrode active material, the ratio 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 45 to 65% by mass.

As the conductive auxiliary agent for the negative electrode, carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes can be used. The content of the conductive auxiliary agent in the negative electrode mixture is preferably 5% by mass or more, more preferably 7% by mass or more, from the viewpoint of improving the electron conductivity in the molded body of the negative electrode mixture. .. Further, if the amount of the conductive auxiliary agent in the negative electrode mixture is too large, voids tend to increase in the molded body of the negative electrode mixture, making it difficult to increase the density, and the volumetric energy density of the all-solid secondary battery. May become smaller. Therefore, from the viewpoint of reducing the porosity of the molded product of the negative electrode mixture, the content of the conductive auxiliary agent in the negative electrode mixture is preferably 15% by mass or less, and more preferably 12% by mass or less.

The sulfide-based solid electrolyte (A) represented by the general formula (1) is used as the negative electrode solid electrolyte, but the negative electrode mixture contains other solid electrolytes together with the sulfide-based solid electrolyte (A). You may be doing it. Examples of other solid electrolytes that can be used in combination with the sulfide-based solid electrolyte (A) include sulfide-based solid electrolytes, hydride-based solid electrolytes, oxide-based solid electrolytes, and the like, which are exemplified below.

Examples of the sulfide solid electrolyte other than the sulfide solid electrolyte (A) include the sulfide solid electrolyte (B) represented by the general formula (2); Li ₂ SP ₂ S ₅ , Li ₂ S-SiS. _{2, Li 2 S-P 2} S 5 -GeS 2, Li 2 S-B 2 S 3 type _{glass; Li 10 GeP 2 S 12 (} LGPS system); and the like.

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.). , Lithium amide, rubidium amide and at least one selected from the group consisting of 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 (A) in the total amount of the solid electrolyte used in the negative electrode mixture is preferably 30% by mass or less, and is other than the sulfide-based solid electrolyte (A). It does not have to contain the solid electrolyte of.

The content of the solid electrolyte in the negative electrode mixture is preferably 35 to 55% by mass.

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, in the negative 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 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 mixing, for example, a negative electrode active material, a conductive auxiliary agent, a solid electrolyte, and a binder added as needed, and the negative electrode mixture is compressed by pressure molding or the like. Can be formed by

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 the molded body 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 load characteristics of the battery are generally easily improved by thinning the positive electrode and the negative electrode, but according to the present invention, the load 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.

The porosity of the molded product of the negative electrode mixture is preferably 20% or less, and more preferably 15% or less. In the molded body of the negative electrode mixture, by using the sulfide-based solid electrolyte (A) having excellent flexibility, the filling density can be increased with the low void ratio as described above, so that the active material in the molded body can be increased. The utilization rate can be further increased. The lower the porosity of the molded product of the negative electrode mixture, the more preferable it is, but it is not easy to obtain the molded product in a state where there are no voids, and the lower limit value thereof is usually about 10%.

The void ratio of the molded body of the negative electrode mixture referred to in the present specification is the sum of each component i using the following formula (4) from the thickness of the molded body of the negative electrode mixture, the mass per area, and the density of the constituent components. It is a value calculated by finding.

P = 100- (Σai / ρi) × (m / t) (4)

Here, in the above formula (4), ai: the ratio of the component i expressed in% by mass, ρi: the density of the component i (g / cm ³ ), m: the mass per unit area of the molded body of the negative electrode mixture ( g / cm ² ), t: Thickness (cm) of the molded body of the negative electrode mixture.

(Positive electrode)
The positive electrode of the all-solid-state secondary battery has a molded body of a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent, a sulfide-based solid electrolyte (B), and the like. Examples thereof include a positive electrode having a structure in which the molded body and the current collector are integrated.

The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in a conventionally known lithium ion secondary battery, that is, an active material capable of storing and releasing Li ions. Specific examples of the positive electrode active material include LiM _x Mn _2-x O ₄ (where M is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al. , Sn, Sb, In, Nb, Mo, W, Y, Ru and Rh, which is at least one element selected from the group consisting of, and is represented by 0.01 ≦ x ≦ 0.5). manganese complex _{oxide, Li x Mn (1-y} -x) Ni y M z O (2-k) F l ( although, M is, Co, Mg, Al, B , Ti, V, Cr, Fe, Cu , Zn, Zr, Mo, Sn, Ca, Sr and W, at least one element selected from the group consisting of 0.8 ≦ x ≦ 1.2, 0 <y <0.5, 0 ≦ z. A layered compound represented by ≦ 0.5, k + l <1, −0.1 ≦ k ≦ 0.2, 0 ≦ l ≦ 0.1), LiCo _1-x M _x O ₂ (where M is Al. , Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, which is at least one element selected from the group consisting of 0 ≦ x ≦ 0.5. ), LiNi _1-x M _x O ₂ (where M is Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn. , Sb and Ba, at least one element selected from the group consisting of LiM _1-x N _x PO ₄ (where M is), a lithium nickel composite oxide represented by 0 ≦ x ≦ 0.5). , Fe, Mn and Co, at least one element selected from the group, N is Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba. At least one element selected from the group consisting of, such as an olivine type composite oxide represented by 0 ≦ x ≦ 0.5) and a lithium titanium composite oxide represented by _{Li 4} Ti ₅ O _12. Only one of these may be used, or two or more thereof may be used in combination.

The positive electrode active material may have a reaction suppressing layer on the surface thereof for suppressing the reaction between the positive electrode active material and the solid electrolyte. The reaction suppressing layer may be made of a material having ionic conductivity and capable of suppressing the reaction between the positive electrode active material and the solid electrolyte. As a material that can form the reaction suppression layer, for example, an oxide containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti and Zr, more specifically. Examples include LiNbO ₃ , Li ₃ PO ₄ , Li ₃ BO ₃ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , LiTIO ₃ , and LiZrO ₃ . The reaction suppression layer may contain only one of these oxides, or may contain two or more of these oxides, and a plurality of these oxides may be a composite compound. May be formed. Among these oxides, it is preferable to use a LiNbO _3.

When the reaction suppression layer is LiNbO ₃ , the coating amount of the reaction suppression layer is adjusted so that the ratio of the mass of Nb contained in the reaction suppression layer to the mass of the positive electrode active material is 0.5 to 2.5% by mass. It is preferable to adjust.

Examples of the method for forming the reaction suppressing layer on the surface of the positive electrode active material include a sol-gel method, a mechanofusion method, a CVD method, a PVD method and the like.

The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 85% by mass.

As the conductive auxiliary agent for the positive electrode, carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes can be used. The content of the conductive auxiliary agent in the positive electrode mixture is preferably 1 to 10% by mass.

The sulfide-based solid electrolyte (B) represented by the general formula (2) is used as the positive electrode solid electrolyte, but the positive electrode mixture contains other solid electrolytes together with the sulfide-based solid electrolyte (B). You may be doing it. Other solid electrolytes that can be used in combination with the sulfide-based solid electrolyte (B) include the sulfide-based solid electrolyte (A) and the same sulfide-based solid electrolyte as those exemplified above that can be contained in the positive electrode mixture. [The one that does not correspond to the sulfide-based solid electrolyte (B)], the hydride-based solid electrolyte, the oxide-based solid electrolyte, and the like can be mentioned.

However, the proportion of the solid electrolyte other than the sulfide-based solid electrolyte (B) in the total amount of the solid electrolyte used in the positive electrode mixture is preferably 30% by mass or less, and is other than the sulfide-based solid electrolyte (B). It does not have to contain the solid electrolyte of.

The content of the solid electrolyte in the positive electrode mixture is preferably 15 to 40% by mass.

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, punching metal, net, expanded metal, foamed metal; 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 conductive auxiliary agent, a solid electrolyte, and a binder added as needed, and the positive electrode mixture is compressed by pressure molding or the like. Can be formed by

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 the molded body 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 load characteristics of the battery are generally easily improved by thinning the positive electrode and the negative electrode, but according to the present invention, the load 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.

(Solid electrolyte layer)
The solid electrolyte in the solid electrolyte layer of the all-solid secondary battery includes the sulfide-based solid electrolyte (A), the sulfide-based solid electrolyte (B), and the same sulfide as those exemplified above as those that can be contained in the positive electrode mixture. One or more of physical solid electrolytes, hydride-based solid electrolytes, oxide-based solid electrolytes, and the like can be used. Among these, the sulfide-based solid electrolyte is preferable, and the sulfide-based solid electrolyte (A) is more preferable, because the ionic conductivity is particularly excellent and the load characteristics of the battery can be further enhanced.

Even if the solid electrolyte layer constructed by using the sulfide-based solid electrolyte (A) is brought into contact with the positive electrode, in the positive electrode (molded body of the positive electrode mixture), many parts of the surface of the positive electrode active material particles are sulfided. Since it is in contact with the physical solid electrolyte (B), there are not many direct contacts between the solid electrolyte layer and the positive electrode active material, so that the sulfide-based solid electrolyte (A) is unlikely to be oxidized.

Further, the solid electrolyte layer has a multilayer structure, and the layer on the surface side in contact with the positive electrode is a solid electrolyte other than the sulfide-based solid electrolyte (A) [for example, a sulfide-based solid electrolyte such as the sulfide-based solid electrolyte (B)]. By constructing the other layer and configuring the other layer with the sulfide-based solid electrolyte (A), it is possible to enhance the ionic conductivity of the solid electrolyte layer and suppress its oxidation to a higher degree.

Further, the solid electrolyte layer may have a porous body such as a resin non-woven fabric as a support.

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, and includes the solid electrolyte other than the sulfide-based solid electrolyte. You don't have to.

The solid electrolyte layer is a method of compressing the solid electrolyte by pressure molding or the like; a composition for forming a solid electrolyte layer prepared by dispersing the solid electrolyte in a solvent is applied onto a base material, a positive electrode, and a negative electrode, and dried. If necessary, it can be formed by a method of performing pressure molding such as press processing: or the like.

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 aprotic 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, fluorine-based solvents such as "Bertrel (registered trademark)" manufactured by Mitsui Dupont Fluorochemical, "Zeolola (registered trademark)" manufactured by Zeon Corporation, 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 secondary 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), polysulphon (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 form of the all-solid secondary battery is a form having 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-shaped battery or a button-shaped battery. Not limited to those, for example, those having an outer body made of a resin film or a metal-resin laminated film, metal outer cans having a bottomed cylinder (cylindrical or square cylinder), and their openings. It may have an exterior body having a sealing structure for sealing the above.

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

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

Example 1
<Making carbon particles>
An average particle diameter of 40nm of primary particles of carbon black having the following pore 2 nm: and 9 parts by _{mass, Co (CH 3 COO) 2} · 4H 2 O: 99.6 parts by mass, LiOH · _H 2 O: 32 parts by mass was mixed in distilled water, stirred for 1 hour, and then the mixed solution was filtered to obtain a mixture containing carbon black.

_{Next, 30 parts by mass of LiOH · H 2} O was added to the mixture, and the mixture was heated in air at 250 ° C. for 30 minutes using an evaporator to obtain a composite in which a lithium cobalt compound was supported on carbon black. This complex is put into a mixed aqueous solution having a volume ratio of 98% concentrated sulfuric acid, 70% concentrated nitrate and 30% hydrochloric acid in a volume ratio of 1: 1: 1 and irradiated with ultrasonic waves to form the complex. The lithium cobalt compound was dissolved, the remaining solid was filtered, washed with water and dried.

By repeating the steps of dissolving the lithium cobalt compound with the mixed aqueous solution, filtering, washing with water, and drying, the lithium cobalt compound was completely removed, and carbon particles containing a hydrophilic portion in a proportion of 10% by mass or more were obtained.

The obtained carbon particles: 0.1 g was added to 20 ml of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute, and then left for 5 hours to precipitate a solid phase portion.

After precipitation of the solid phase portion, the supernatant is removed and the residual portion is dried, the weight of the solid after drying is measured, and the amount reduced from the weight (0.1 g) of the carbon particles before the treatment is calculated as that of the hydrophilic portion. It was weighted. The ratio of the weight of the hydrophilic portion to the weight of the carbon particles before the treatment was determined to be 14.5% by mass.

<Preparation of positive electrode>
_{LiNi 0.33} Co _0.33 Mn _0.33 O ₂ (positive electrode active material) having an average particle diameter of 4 μm and a reaction suppression layer of LiNbO ₃ formed on the surface, and a sulfide-based solid electrolyte having an average particle diameter of 3 μm ( B): Li _7.0 PS _5.4 Cl _1.2 , carbon nanotubes [“VGCF” (trade name) manufactured by Showa Denko Co., Ltd.] (conductive aid), and carbon particles containing the hydrophilic portion (conductive aid). Agent) was mixed at a mass ratio of 65: 31.8: 2.1: 1.1 and kneaded well to prepare a positive electrode mixture. The mass ratio of Nb in the reaction suppressing layer to the mass of the positive electrode active material was 1.5% by mass.

Next, 92 mg of the positive electrode mixture was placed in a powder molding die and pressure-molded using a press to prepare a positive electrode made of a positive electrode mixture molded product.

<Formation of solid electrolyte layer>
Next, on the positive electrode mixture molded body in the powder molding die, a sulfide solid electrolyte (A) Li _5.4 PS _4.4 Cl _0.8 Br _{0. 8} : 16 mg was added and pressure molding was performed using a press machine to form a solid electrolyte layer on the positive electrode mixture molded product.

<Manufacturing of negative electrode>
_{The mass of lithium titanate (Li 4} Ti ₅ O ₁₂ , negative electrode active material) with an average particle size of 2 μm, the same sulfide solid electrolyte (A) used for the solid electrolyte layer, and graphene (conductive aid). The mixture was mixed at a ratio of 55:36: 9 and kneaded well to prepare a negative electrode mixture. Next, 129 mg of the negative electrode mixture was put onto the solid electrolyte layer in the powder molding die, pressure molding was performed using a press machine, and the void ratio was 16% on the solid electrolyte layer. By forming a negative electrode made of the negative electrode mixture molded body of the above, a laminated body in which a positive electrode, a solid electrolyte layer and a negative electrode were laminated was produced.

By sealing so that a porous carbon sheet having a thickness of 0.1 mm is arranged between the stainless steel sealing can and outer can and the positive electrode / solid electrolyte layer / negative electrode laminate. , A flat all-solid-state secondary battery was manufactured.

Comparative Example 1
A negative electrode mixture was prepared in the same manner as in Example 1 except that the same sulfide-based solid electrolyte used for the positive electrode was used instead of the sulfide-based solid electrolyte (A), except that this was used. A flat all-solid-state secondary battery was produced in the same manner as in Example 1. The porosity of the formed negative electrode mixture molded product was 22%.

Comparative Example 2
A positive electrode mixture was prepared in the same manner as in Example 1 except that the same sulfide-based solid electrolyte used for the negative electrode was used instead of the sulfide-based solid electrolyte (B), except that this was used. A flat all-solid-state secondary battery was produced in the same manner as in Example 1.

The following evaluations were performed on the all-solid-state secondary batteries of Examples and Comparative Examples.

<Load characterization>
For the prepared batteries of Examples and Comparative Examples, constant current charging is performed at a current value of 0.2 C until the battery voltage reaches 3.1 V, and constant current charging is performed at a voltage of 3.1 V until the current value reaches 0.02 C. Constant current-constant voltage charging combined with voltage charging was performed, and then constant current discharge was performed at a current value of 0.1 C until the battery voltage became 1.2 V, and the discharge capacity at 0.1 C was measured.

Next, the same constant current-constant voltage charge as described above is performed, and then constant current discharge is performed at a current value of 0.5 C until the battery voltage reaches 1.2 V, and the discharge capacity at 0.5 C is measured. bottom. The value (%) obtained by gradualizing the discharge capacity at 0.5 C with the discharge capacity at 0.1 C was obtained, and the load characteristics of each battery were evaluated.

<High temperature characteristic evaluation>
For the batteries of Examples and Comparative Examples, 50 cycles of charge / discharge cycles were repeated under the following conditions in an environment of 100 ° C.

Constant current charging is performed at a current value of 0.2C until the voltage reaches 3.1V, then constant voltage charging is performed at a voltage of 3.1V until the current value reaches 0.02C, and then 0.2C. The high temperature characteristics were evaluated by repeating the charge / discharge cycle of constant current discharge until the voltage became 1.2 V at the current value for 50 cycles, and the ratio of the discharge capacity of the 50th cycle to the discharge capacity of the second cycle (capacity retention rate). .. The results are shown in Table 1.

As shown in Table 1, the sulfide-based solid electrolyte (A) was used for the molded body of the negative electrode mixture, and the sulfide-based solid electrolyte (B) was used for the molded body of the positive electrode mixture. In the next battery, the ionic conductivity of the negative electrode mixture could be increased, and the filling rate of the mixture could be increased to improve the utilization rate of the negative electrode active material. Furthermore, since it was possible to suppress the deterioration of the characteristics due to the oxidation of the solid electrolyte at the positive electrode, it was possible to obtain a battery having excellent load characteristics and high temperature characteristics.

On the other hand, in the battery of Comparative Example 1 in which the sulfide-based solid electrolyte (B) was used for the molded body of the negative electrode mixture, the ionic conductivity of the negative electrode mixture was lower than that of the battery of Example 1, and the mixture was filled. Since the rate decreased and the utilization rate of the negative electrode active material decreased, the battery became inferior in load characteristics. Further, in the battery of Comparative Example 2 in which the sulfide-based solid electrolyte (A) was used for the molded body of the positive electrode mixture, a decrease in high temperature characteristics due to oxidation of the solid electrolyte at the positive electrode was observed.

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

Claims (4)

Negative electrode having a negative electrode mixture containing a negative electrode active material, a conductive auxiliary agent and a solid electrolyte, a positive electrode having a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent and a solid electrolyte, and the positive electrode. An all-solid secondary battery having a solid electrolyte layer interposed between the negative electrode and the negative electrode.
The molded body of the negative electrode mixture is used as the solid electrolyte according to the following general formula (1).
_{Li 7-x PS 6-x} Cl y Br z (1)
[In the general formula (1), x = y + z, 1.0 <x ≦ 1.8, 0.1 ≦ z / y ≦ 10.0]
Contains the sulfide-based solid electrolyte (A) represented by
The molded body of the positive electrode mixture is used as the solid electrolyte according to the following general formula (2).
Li _{7-a + b} PS _6-a Cl _{a + b} (2)
[In the general formula (2), 0.05 ≦ b ≦ 0.9, −3.0a + 1.8 ≦ b ≦ -3.0a + 5.7]
An all-solid-state secondary battery characterized by containing a sulfide-based solid electrolyte (B) represented by. The all-solid-state secondary battery according to claim 1, wherein the content of the conductive auxiliary agent in the molded body of the negative electrode mixture is 5 to 15% by mass. The all-solid-state secondary battery according to claim 1 or 2, wherein the porosity of the molded product of the negative electrode mixture is 20% or less. The all-solid-state secondary battery according to any one of claims 1 to 3, wherein the molded body of the negative electrode mixture contains lithium titanium oxide as the negative electrode active material.

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