JP7328166B2 - All-solid secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an all-solid 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 commercialization of electric vehicles, there is a growing need for secondary batteries that are compact, lightweight, and have high capacity and high energy density. It has become to.

At present, in lithium secondary batteries, especially lithium ion secondary batteries, which can meet this demand, lithium-containing composite oxides such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) are used as positive electrode active materials. Graphite or the like is used as a negative electrode active material, and an organic electrolytic solution containing an organic solvent and a lithium salt is used as a non-aqueous electrolyte.

With the further development of lithium-ion secondary battery application equipment, there is a demand for longer life, higher capacity, and higher energy density of lithium-ion secondary batteries. Reliability of lithium-ion secondary batteries with increased capacity and increased energy density is also highly demanded.

However, since the organic electrolyte used in lithium-ion secondary batteries contains an organic solvent, which is a combustible substance, the organic electrolyte generates abnormal heat when an abnormal situation such as a short circuit occurs in the battery. there is a possibility. In addition, with the recent trends toward higher energy densities in lithium-ion secondary batteries and an increase in the amount of organic solvents in organic electrolytes, the reliability of lithium-ion secondary batteries is required to be even higher.

Under the circumstances described above, 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 secondary battery uses a solid electrolyte molded body that does not use an organic solvent instead of a conventional organic solvent-based electrolyte, and has a high degree of safety without the risk of abnormal heat generation of the solid electrolyte. .

Also, various improvements have been attempted in all-solid secondary batteries. 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 containing oxygen and contain a sulfide-based solid electrolyte that does not contain oxygen. , describes an all-solid battery in which the negative electrode active material layer contains graphite as the negative electrode active material and a sulfide-based solid electrolyte containing oxygen.

A sulfide-based solid electrolyte containing oxygen is thermally stable, but has a lower ionic conductivity than a sulfide-based solid electrolyte that does not contain oxygen. Therefore, when used in an all-solid battery, the battery resistance is large. Become. In the technique described in Patent Document 1, a sulfide-based solid electrolyte containing oxygen is contained only in the negative electrode active material layer, so that the negative electrode active material (graphite) undergoes a deinsertion reaction of Li at a base potential. In addition to suppressing the reductive decomposition of the solid electrolyte, the positive electrode active material layer and the solid electrolyte layer do not contain a sulfide-based solid electrolyte containing oxygen and contain a sulfide-based solid electrolyte that does not contain oxygen. It is said that the battery resistance can be realized.

Further, in Patent Document 2, a sulfide-based solid for lithium ion batteries containing a crystal phase of a cubic argurodite type crystal structure and represented by a composition formula of Li _7-x+y PS _6-x Cl _x+y An electrolyte compound in which x and y satisfy 0.05≦y≦0.9 and −3.0x+1.8≦y≦−3.0x+5.7 has excellent oxidation resistance and water resistance. Therefore, even if it comes into contact with air, it is possible to effectively suppress the amount of hydrogen sulfide generated due to reaction with moisture in the air.

Furthermore, in Patent Document 3, a sulfide compound having a crystal phase of a cubic Argurodite type crystal structure and represented by a composition formula of Li _7-x PS _6-x Cl _y Br _z , 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, a high It is stated that the Young's modulus can be lowered while maintaining ionic conductivity. Further, in Patent Document 3, by using the sulfide-based compound, when a press pressure is applied when creating an electrode of an all-solid-state battery, the solid electrolyte is crushed to fill the gaps between the active material particles. It is possible to increase the contact points and contact area with the active material particles, so that the battery resistance can be reduced.

JP 2017-54626 A WO2016/104702 WO2019/009228

By the way, at present, the application field of all-solid-state secondary batteries is rapidly expanding. There is a demand to improve the characteristics, and there is also a demand to further improve the battery characteristics at high temperatures.

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 secondary battery that is excellent in 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 aid and a solid electrolyte, a positive electrode mixture containing a positive electrode active material, a conductive aid and a solid electrolyte. A positive electrode having a molded body, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the molded body of the negative electrode mixture is represented by the following general formula (1) as the solid electrolyte
Li _7-x PS _6-x Cl _y Br _z (1)
A sulfide-based solid electrolyte (A) represented by [in the general formula (1), x = y + z, 1.0 < x ≤ 1.8, 0.1 ≤ z/y ≤ 10.0] The molded body of the positive electrode mixture contains, as the solid electrolyte, the following general formula (2)
Li _7-a+b PS _6-a Cl _a+b (2)
A sulfide-based solid electrolyte (B) represented by [0.05 ≤ b ≤ 0.9 and -3.0a + 1.8 ≤ b ≤ -3.0a + 5.7 in the general formula (2)] It is characterized by containing

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

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which represents 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 aid and a solid electrolyte, a positive electrode mixture containing a positive electrode active material, a conductive aid 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 negative electrode mixture contains a sulfide-based solid electrolyte (A) represented by the following general formula (1), and the molded 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, and 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 it is used in positive electrode and negative electrode mixture molded bodies, the ionic conductivity of the mixture molded bodies can be increased. In addition, since the space between the active material particles can be satisfactorily filled with the sulfide-based solid electrolyte (A) while suppressing the inclusion of voids, the filling rate of the mixture can be improved and the utilization rate of the positive electrode and the negative electrode can increase

However, since the sulfide-based solid electrolyte (A) is likely to be oxidized at a high potential and become an insulator, it is difficult to increase the ionic conductivity of the molded positive electrode mixture when used for the positive electrode. . In addition, since the oxidation reaction of the sulfide-based solid electrolyte (A) tends to occur particularly in a high-temperature environment, if the all-solid secondary battery is placed in such an environment for a long time, the battery characteristics will deteriorate.

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

In the all-solid secondary battery of the present invention, it is possible to improve load characteristics and high-temperature characteristics due to the above effects.

The details of the all-solid secondary battery of the present invention are described below.

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

Examples of negative electrode active materials include graphite, pyrolytic carbons, cokes, vitreous carbons, sintered organic polymer compounds, mesocarbon microbeads (MCMB), carbon fibers, and the like, which can occlude and release lithium. One or a mixture of two or more carbonaceous materials is used. Elements, compounds, and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In; compounds that can be charged and discharged at low voltages close to lithium metal, such as lithium-containing nitrides or lithium-containing oxides; lithium metal a lithium/aluminum alloy; can also be used as the negative electrode active material.

Among these, lithium titanium oxide is preferably used. Lithium titanium oxides 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), ^M1 is at least one element selected from the group consisting of Na, Mg, K, Ca, Sr and Ba, and ^M2 is Al, V, Cr, Fe, Co , Ni, Zn, Ym, Zr, Nb, Mo, Ta and W, and 0≦c<1/3 and 0≦d<5/3.

That is, in the lithium titanium oxide represented by the general formula (3), part of Li may be substituted with the element ^M1 . However, in the general formula (3), c representing the ratio of the element ^M1 is preferably less than 1/3. In the lithium titanium oxide represented by the general formula (3), Li may not be substituted with the element ^M1 , so c representing the ratio of the element ^M1 may be 0.

In the lithium-titanium oxide represented by the general formula (3), the element ^M2 is a component for increasing the electronic conductivity of the lithium-titanium oxide, and d representing the ratio of the element ^M2 is 0≤ When d<5/3, the effect of improving the electron conductivity can be satisfactorily secured.

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

Carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes can be used as the conductive aid for the negative electrode. The content of the conductive aid 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 negative electrode mixture molded body. . In addition, if the amount of the conductive additive in the negative electrode mixture is too large, voids tend to increase in the molded negative electrode mixture, making it difficult to increase the density, resulting in the volume energy density of the all-solid secondary battery. is likely to become smaller. Therefore, from the viewpoint of reducing the porosity of the molded negative electrode mixture, the content of the conductive aid in the negative electrode mixture is preferably 15% by mass or less, more preferably 12% by mass or less.

The solid electrolyte of the negative electrode uses the sulfide-based solid electrolyte (A) represented by the general formula (1), and the negative electrode mixture contains the sulfide-based solid electrolyte (A) and other solid electrolytes. You may have 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 exemplified below.

Sulfide solid electrolytes 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 SP ₂ S ₅ -GeS ₂ , Li ₂ S—B ₂ S ₃ system glass; Li ₁₀ GeP ₂ S ₁₂ (LGPS system);

Examples of hydride-based solid electrolytes include LiBH ₄ , solid solutions of LIBH ₄ and the following alkali metal compounds (for example, LiBH ₄ and alkali metal compounds having a molar ratio of 1:1 to 20:1), and the like. mentioned. Examples of alkali metal compounds in the solid solution include lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbiF, RbCl, etc.), and cesium halides (CsI, CsBr, CsF, CsCl, etc.). , lithium amide, rubidium amide and cesium amide.

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

However, the ratio 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 the sulfide-based solid electrolyte other than (A) solid electrolyte.

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 fluorine resin such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component even in the negative electrode mixture, its amount should be as small as possible. Therefore, it is preferable that the negative electrode mixture does not contain a resin binder, or if it contains a resin binder, 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 more preferably 0% by mass (that is, does not contain the resin binder).

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

The molded body of the negative electrode mixture is prepared by, for example, mixing the negative electrode active material, the conductive agent, the solid electrolyte, and the binder added as necessary, and compressing the negative electrode mixture 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 method described above to the current collector by pressure bonding or the like.

The thickness of the negative electrode mixture molded body (in the case of a negative electrode having a current collector, the thickness of the positive electrode mixture molded body per one side of the current collector; hereinafter the same) is determined from the viewpoint of increasing the capacity of the battery. , 200 μm or more. Generally, the load characteristics of a battery tend to be improved by making the positive electrode and the negative electrode thinner. 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 body 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 positive electrode mixture is 200 μm or more and the thickness of the molded negative electrode mixture is 200 μm or more. In addition, the thickness of the molded body of the negative electrode mixture is usually 3000 μm or less.

The molded body of the negative electrode mixture preferably has a porosity of 20% or less, more preferably 15% or less. In the molded body of the negative electrode mixture, by using the sulfide-based solid electrolyte (A) with excellent flexibility, the filling density can be increased with a low porosity as described above. Utilization rate can be increased. The void ratio of the negative electrode mixture compact is preferably as low as possible, but it is not easy to obtain a compact with no voids, and the lower limit is usually about 10%.

The porosity of the molded body of the negative electrode mixture referred to in this specification is the total 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. is a value calculated by finding

P = 100-(Σai/ρi)×(m/t) (4)

Here, in the above formula (4), ai is the ratio of component i expressed in mass %, ρi is the density of component i (g/cm ³ ), and m is the mass per unit area of the molded negative electrode mixture ( g/cm ² ), t: the 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 aid, a sulfide-based solid electrolyte (B), and the like. , a positive electrode having a structure in which the molded body and the current collector are integrated, and the like.

The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in conventionally known lithium ion secondary batteries, that is, an active material capable of intercalating/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, and is at least one element selected from the group consisting of 0.01 ≤ x ≤ 0.5). Manganese composite oxide, Li _x Mn _(1-y-x) Ni _y M _z O _(2-k) F _l (where M is Co, Mg, Al, B, Ti, V, Cr, Fe, Cu , Zn, Zr, Mo, Sn, Ca, Sr and W, and at least one element selected from the group consisting of 0.8≦x≦1.2, 0<y<0.5, 0≦z ≤ 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, and 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, and a lithium-nickel composite oxide represented by 0≦x≦0.5, LiM _1-x N _x PO ₄ (where M is , Fe, Mn and Co, wherein 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 an olivine-type composite oxide represented by 0≦x≦0.5), a lithium-titanium composite oxide represented by Li ₄ Ti ₅ O ₁₂ , etc. One of these may be used alone, or two or more thereof may be used in combination.

The positive electrode active material can have a reaction suppression layer on its surface for suppressing reaction between the positive electrode active material and the solid electrolyte. The reaction suppression layer may be composed of a material that has ion conductivity and that can suppress the reaction between the positive electrode active material and the solid electrolyte. Materials that can constitute the reaction suppression layer include, for example, oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti and Zr, more specifically include LiNbO ₃ , Li ₃ PO ₄ , Li ₃ BO ₃ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , LiTiO ₃ , LiZrO ₃ and the like. The reaction-suppressing layer may contain only one of these oxides, or may contain two or more of these oxides. may form Among these oxides, it is preferable to use _LiNbO3 .

When the reaction-suppressing layer is LiNbO ₃ , the coating amount of the reaction-suppressing layer is adjusted so that the ratio of the mass of Nb contained in the reaction-suppressing layer to the mass of the positive electrode active material is 0.5 to 2.5% by mass. Adjusting is preferred.

Sol-gel method, mechanofusion method, CVD method, PVD method, etc. are mentioned as a method of forming a reaction suppression layer on the surface of a positive electrode active material.

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

Carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofiber, carbon nanotube, and the like can be used as the conductive additive for the positive electrode. The content of the conductive aid 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 solid electrolyte of the positive electrode, and the positive electrode mixture contains the sulfide-based solid electrolyte (B) and other solid electrolytes. You may have 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 electrolytes as those previously exemplified as those that can be contained in the positive electrode mixture. [Sulfide-based solid electrolytes (B)], hydride-based solid electrolytes, oxide-based solid electrolytes, and the like.

However, the ratio 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 the sulfide-based solid electrolyte other than (B) solid electrolyte.

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 fluorine resin such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component in the positive electrode mixture, the amount thereof should be as small as possible. Therefore, it is preferable that the positive electrode mixture does not contain a resin binder, or if it contains a resin binder, 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 more preferably 0% by mass (that is, does not contain the resin binder).

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

The molded body of the positive electrode mixture is produced by, for example, compressing the positive electrode mixture prepared by mixing the positive electrode active material, the conductive agent, the solid electrolyte, and the binder added as necessary, by pressure molding or the like. can be formed by

In the case of a positive electrode having a current collector, it can be produced by bonding the positive electrode material mixture formed by the method described above to the current collector by pressure bonding or the like.

The thickness of the positive electrode mixture molded body (in the case of a positive electrode having a current collector, the thickness of the positive electrode mixture molded body per one side of the current collector; hereinafter the same) is determined from the viewpoint of increasing the capacity of the battery. , 200 μm or more. The load characteristics of a battery generally tend to be improved by making the positive electrode and the negative electrode thinner, 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 body of the positive electrode mixture is, for example, 200 μm or more. In addition, the thickness of the positive electrode mixture molded body is usually 2000 μm or less.

(Solid electrolyte layer)
The solid electrolyte in the solid electrolyte layer of the all-solid secondary battery includes a sulfide-based solid electrolyte (A), a sulfide-based solid electrolyte (B), and the same sulfides as those previously exemplified as those that can be contained in the positive electrode mixture. It is possible to use one or more of solid electrolytes, hydride solid electrolytes, oxide solid electrolytes, and the like. Among these, the sulfide-based solid electrolyte is preferable, and the sulfide-based solid electrolyte (A) is more preferable, because it has particularly excellent ion conductivity and can further improve the load characteristics of the battery.

Even when the solid electrolyte layer formed using the sulfide-based solid electrolyte (A) is brought into contact with the positive electrode, most of the surface of the positive electrode active material particles is sulfided in the positive electrode (positive electrode mixture molded body). Since the sulfide-based solid electrolyte (A) is in contact with the solid electrolyte (B), there are not many direct contact points between the solid electrolyte layer and the positive electrode active material, so oxidation of the sulfide-based solid electrolyte (A) is unlikely to occur.

In addition, the solid electrolyte layer has a multilayer structure, and the layer on the 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 forming the other layer with the sulfide-based solid electrolyte (A), the ionic conductivity of the solid electrolyte layer can be increased, and oxidation of the solid electrolyte layer can be suppressed to a higher degree.

Furthermore, the solid electrolyte layer may have a porous body such as resin nonwoven fabric as a support.

In addition, the ratio 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 the solid electrolyte other than the sulfide-based solid electrolyte is included. You don't have to.

The solid electrolyte layer is formed by 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 on the substrate, the positive electrode, and the negative electrode, and dried; It can be formed by a method in which pressure molding such as press processing is performed as necessary.

As for the solvent used in the solid electrolyte layer-forming composition, 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 are represented by hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene, since chemical reactions occur with minute amounts of moisture. Preference is given to using non-polar aprotic solvents. In particular, it is more preferable to use a super-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less. In addition, fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by Mitsui-DuPont Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Nippon Zeon, "Novec (registered trademark)" manufactured by Sumitomo 3M, and , dichloromethane, and diethyl ether can also be used.

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

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

When forming the electrode body, it is preferable from the viewpoint of increasing the mechanical strength of the electrode body that the positive electrode, the negative electrode, and the solid electrolyte layer are laminated and pressure-molded.

(Battery form)
A cross-sectional view schematically showing an example of the all-solid secondary battery of the present invention is shown in FIG. In the battery 1 shown in FIG. 1, a positive electrode 10, a negative electrode 20, and a positive electrode 10 and a negative electrode 20 are placed in an outer case formed of an outer can 40, a sealing can 50, and a resin gasket 60 interposed therebetween. A solid electrolyte layer 30 intervening between is encapsulated.

The sealing can 50 is fitted to the opening of the outer can 40 via a gasket 60, and the open end of the outer can 40 is tightened inward, whereby the gasket 60 abuts the sealing can 50. , the opening of the exterior can 40 is sealed to form a sealed structure inside the element.

A stainless steel can or the like can be used for the outer can and the sealing can. In addition, polypropylene, nylon, etc. can be used for gasket materials, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), etc., can be used when heat resistance is required in relation to battery applications. Heat resistance with a melting point exceeding 240°C such as fluorine resin, polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), etc. Resin can also be used. Moreover, when the battery is applied to applications requiring heat resistance, a glass hermetic seal can be used for the sealing.

The form of the all-solid-state secondary battery is, as shown in FIG. but not limited to, for example, those having an exterior body composed of a resin film or a metal-resin laminated film, or a metallic bottomed cylindrical (cylindrical or rectangular) exterior can and its opening It may have an exterior body having a sealing structure that seals the .

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

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

Example 1
<Production of carbon particles>
Carbon black having an average primary particle diameter of 40 nm and pores of 2 nm or less: 9 parts by mass, Co(CH ₃ COO) _{2.4H 2} O: 99.6 parts by mass, and LiOH.H ₂ O: After mixing 32 parts by mass in distilled water and stirring for 1 hour, the mixed liquid 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 of 98% concentrated sulfuric acid, 70% concentrated nitric acid, and 30% hydrochloric acid at a volume ratio of 1:1:1, and irradiated with ultrasonic waves. The lithium cobalt compound was dissolved and the remaining solid was filtered, washed with water and dried.

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

0.1 g of the obtained carbon particles were added to 20 ml of an aqueous ammonia solution having a pH of 11, and after ultrasonic irradiation for 1 minute, the mixture was allowed to stand for 5 hours to precipitate a solid phase portion.

After precipitation of the solid phase portion, the supernatant liquid is removed, the remaining portion is dried, the weight of the solid after drying is measured, and the decrease from the weight of the carbon particles before treatment (0.1 g) is taken as the hydrophilic portion. weight. The ratio of the weight of the hydrophilic portion to the weight of the carbon particles before treatment was found 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 size of 4 μm and having a reaction suppression layer of LiNbO ₃ formed on the surface, and a sulfide-based solid electrolyte having an average particle size of 3 μm ( B): Li _7.0 PS _5.4 Cl _1.2 , carbon nanotubes [“VGCF” (trade name) manufactured by Showa Denko Co., Ltd.] (conductivity aid), and carbon particles containing the hydrophilic portion (conductivity aid agent) were mixed at a mass ratio of 65:31.8:2.1:1.1 and well kneaded to prepare a positive electrode mixture. The mass ratio of Nb in the reaction suppression 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 composed of a molded positive electrode mixture.

<Formation of Solid Electrolyte Layer>
Next, a sulfide solid electrolyte (A) Li _5.4 PS _4.4 Cl _0.8 Br0 _{. 8} : 16 mg was added, and pressure molding was performed using a press to form a solid electrolyte layer on the positive electrode mixture molded body.

<Production of negative electrode>
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) as used in the solid electrolyte layer, and graphene (conductive assistant) They were mixed at a ratio of 55:36:9 and well kneaded to prepare a negative electrode mixture. Next, 129 mg of the negative electrode mixture is placed on the solid electrolyte layer in the powder molding mold, and pressure-molded using a press to obtain a porosity of 16% on the solid electrolyte layer. A laminated body in which the positive electrode, the solid electrolyte layer and the negative electrode are laminated was produced by forming the negative electrode from the negative electrode mixture molded product.

Sealing is performed by placing a porous carbon sheet having a thickness of 0.1 mm 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 fabricated.

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 as that used for the positive electrode was used instead of the sulfide-based solid electrolyte (A). A flat all-solid secondary battery was produced in the same manner as in Example 1. The porosity of the formed negative electrode mixture molded body 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 as that used for the negative electrode was used instead of the sulfide-based solid electrolyte (B). A flat all-solid secondary battery was produced in the same manner as in Example 1.

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

<Load characteristics evaluation>
The prepared batteries of Examples and Comparative Examples were subjected to constant current charging at a current value of 0.2 C until the battery voltage reached 3.1 V, and constant current charging at a voltage of 3.1 V until the current value reached 0.02 C. Constant current-constant voltage charging combined with voltage charging was performed, and then constant current discharging was performed at a current value of 0.1 C until the battery voltage reached 1.2 V, and the discharge capacity at 0.1 C was measured.

Next, constant current-constant voltage charging is performed in the same manner as above, and constant current discharging 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. did. The value (%) obtained by dividing the discharge capacity at 0.5C by the discharge capacity at 0.1C was obtained, and the load characteristics of each battery were evaluated.

<High temperature property evaluation>
The batteries of Examples and Comparative Examples were subjected to 50 charge-discharge cycles in an environment of 100° C. under the following conditions.

Constant-current charging was performed at a current value of 0.2C until the voltage reached 3.1V, followed by constant-voltage charging at a voltage of 3.1V until the current value reached 0.02C, and then charging at a voltage of 0.2C. A charge-discharge cycle of constant current discharge until the voltage reaches 1.2 V was repeated 50 cycles, and the high-temperature characteristics were evaluated by the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 2nd cycle (capacity retention rate). . Table 1 shows the results.

As shown in Table 1, the all-solid-state secondary battery of Example 1 in which the sulfide-based solid electrolyte (A) was used for the molded negative electrode mixture and the sulfide-based solid electrolyte (B) was used for the molded positive electrode mixture was used. In the secondary battery, the ionic conductivity of the negative electrode mixture was able to be increased, and the filling rate of the mixture was increased, thereby improving the utilization rate of the negative electrode active material. Furthermore, since deterioration of characteristics due to oxidation of the solid electrolyte at the positive electrode could be suppressed, a battery having excellent load characteristics and high temperature characteristics could be obtained.

On the other hand, in the battery of Comparative Example 1 in which the sulfide-based solid electrolyte (B) was used for the molded negative electrode mixture, the ionic conductivity of the negative electrode mixture was lower than that of the battery of Example 1, and the filling of the mixture was Since the rate decreased and the utilization rate of the negative electrode active material decreased, the battery was 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 positive electrode mixture, deterioration in high-temperature characteristics was observed due to oxidation of the solid electrolyte in the positive electrode.

1 All Solid Secondary Battery 10 Positive Electrode 20 Negative Electrode 30 Solid Electrolyte Layer 40 Outer Can 50 Sealing Can 60 Gasket

Claims (4)

a negative electrode having a molded body of a negative electrode mixture containing a negative electrode active material, a conductive aid and a solid electrolyte; a positive electrode having a molded body of a positive electrode mixture containing a positive electrode active material, a conductive aid and a solid electrolyte; An all-solid secondary battery having a solid electrolyte layer interposed between the negative electrode,
The molded body of the negative electrode mixture has the following general formula (1) as the solid electrolyte
Li _7-x PS _6-x Cl _y Br _z (1)
[In the general formula (1), x = y + z, 1.0 < x ≤ 1.8, and 0.1 ≤ z/y ≤ 10.0]
containing a sulfide-based solid electrolyte (A) represented by
The molded body of the positive electrode mixture has the following general formula (2) as the solid electrolyte
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]
All-solid secondary battery characterized by containing a sulfide-based solid electrolyte (B) represented by. 2. The all-solid secondary battery according to claim 1, wherein the content of said conductive aid in said negative electrode mixture compact is 5 to 15% by mass. 3. The all-solid secondary battery according to claim 1, wherein the negative electrode mixture molded body has a porosity of 20% or less. 4. The all-solid secondary battery in accordance with claim 1, wherein said negative electrode mixture compact contains lithium titanium oxide as said negative electrode active material.

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