JP2021144906A - Positive electrode for all-solid battery, and all-solid battery - Google Patents

Abstract

To provide a positive electrode which has a thick positive electrode mixture compact, and enables the formation of an all-solid battery superior in load characteristic, and an all-solid battery having the positive electrode.SOLUTION: A positive electrode for an all-solid battery according to the present invention comprises a compact of a positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte and a conductive assistant. In the positive electrode, fibrous carbon and granular carbon are included as the conductive assistant, and the positive electrode mixture compact is 250 μm or larger in thickness. An all-solid battery of the present invention comprises: a positive electrode; a negative electrode; and a solid electrolyte layer interposed between the positive and negative electrodes. At least one of the positive and negative electrodes is the positive electrode for an all-solid battery according to the present invention.SELECTED DRAWING: Figure 1

Description

The present invention relates to a positive electrode having a molded body of a thick positive electrode mixture and capable of forming an all-solid-state battery having excellent load characteristics, and an all-solid-state battery having the positive electrode.

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 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 because there is no risk of abnormal heat generation of the solid electrolyte.

By the way, in the secondary battery, not only the electrolyte but also various materials used for the electrodes have been improved. For example, in Patent Document 1, a paste-like conductive carbon derived from a specific oxidation-treated carbon is brought into contact with active material particles or coated with other conductive carbon such as carbon fiber to store electricity. It has been proposed to improve the energy density and cycle life of devices (secondary batteries).

Japanese Unexamined Patent Publication No. 2016-96125

By the way, as the solid electrolyte of the electrode of the all-solid-state battery, a sulfide-based one, a hydride-based one, and an oxide-based one are known. Is preferably a sulfide-based battery that is relatively soft and easily comes into contact with the active material.

However, when the sulfide-based solid electrolyte comes into contact with granular carbon generally used as a conductive auxiliary agent, it tends to oxidize and become an insulator. In such a case, for example, if the molded body of the positive electrode mixture used for the positive electrode of an all-solid-state battery is thin, the effect on the battery characteristics does not matter because it is relatively easy to take conductivity, but the molding of the positive electrode mixture is not a problem. When the body is as thick as 250 μm or more, the load characteristics of the battery are significantly reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to have a positive electrode having a molded body of a thick positive electrode mixture and capable of forming an all-solid-state battery having excellent load characteristics, and the positive electrode. The purpose is to provide an all-solid-state battery.

The positive electrode for an all-solid-state battery of the present invention has a molded body of a positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive auxiliary agent, and fibrous carbon and granules are used as the conductive auxiliary agent. It contains carbon and is characterized in that the thickness of the molded body of the positive electrode mixture is 250 μm or more.

Further, 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 at least one of the positive electrode and the negative electrode is the present invention. It is characterized by being an electrode for an all-solid-state battery.

According to the present invention, it is possible to provide a positive electrode having a molded body of a thick positive electrode mixture and capable of forming an all-solid-state battery having excellent load characteristics, and an all-solid-state battery having the positive electrode.

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

<Positive electrode for all-solid-state battery>
The positive electrode for an all-solid-state battery of the present invention has a molded body of a positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive auxiliary agent, and fibrous carbon and granular carbon are used as the conductive auxiliary agent. The thickness of the molded body of the positive electrode mixture is 250 μm or more.

In the positive electrode for an all-solid-state battery of the present invention, by using fibrous carbon and granular carbon as a conductive auxiliary agent, the ratio of granular carbon used can be reduced and the specific surface area of the entire conductive auxiliary agent can be reduced. It is possible to suppress the oxidation of the sulfide-based solid electrolyte by the agent.

Further, the positive electrode for an all-solid-state battery of the present invention has a molded body of a thick positive electrode mixture having a thickness of 250 μm or more, and the amount of the positive electrode active material in the positive electrode can be increased to increase the capacity. .. However, in a battery using a positive electrode having a molded body of such a thick positive electrode mixture, the load characteristics are deteriorated as described above. In the present invention, by using fibrous carbon and granular carbon together as a conductive auxiliary agent, a good conductive network can be formed in the molded body of the positive electrode mixture, thereby increasing the capacity of the battery. At the same time, it is possible to secure excellent load characteristics.

As described above, in the case of a molded body of a thin positive electrode mixture, it is difficult for the deterioration of the load characteristics to become apparent, but according to the present invention, the molded body of the positive electrode mixture having a thickness of 250 μm or more is simply loaded. In addition to suppressing the deterioration of the characteristics, the load characteristics can be improved as compared with the case of using a molded body of a thin positive electrode mixture.

Examples of the positive electrode for an all-solid-state battery include a molded body (pellet, etc.) formed by molding a positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive auxiliary agent, and a molded body (positive electrode combination) of the positive electrode mixture. Examples thereof include those having a structure in which the agent layer) is formed on the current collector.

The fibrous carbon used as a conductive auxiliary agent for a positive electrode for an all-solid-state battery has a ratio of fiber length to fiber diameter (fiber diameter) of 20 or more. The fiber length of the fibrous carbon is preferably 3 to 600 μm, and the fiber diameter is preferably 1 to 300 nm.

The fiber length and fiber diameter of the fibrous carbon referred to in the present specification are selected by selecting 50 fibers whose contours can be confirmed in an image of carbon observed at a magnification of 30,000 using a scanning electron microscope (SEM). It is a value obtained by measuring the particle size of fibers by the two-point method and calculating the average value (number average) of all fibers.

Specific examples of the fibrous carbon include vapor-grown carbon fibers, carbon nanofibers, and carbon nanotubes. As the fibrous carbon, only one of the above-exemplified ones may be used, or two or more of them may be used in combination.

Granular carbon used as a conductive auxiliary agent for a positive electrode for an all-solid-state battery has a ratio of the length of the longest diameter to the length of the shortest diameter of 1 to 1.3 in the state of primary particles. The average particle size of the granular carbon is preferably 10 nm to 1000 nm.

The particle size of the primary particles of granular carbon referred to in the present specification is a value obtained as follows. In an image of carbon observed at a magnification of 30,000 using a scanning electron microscope (SEM), 50 particles whose contours can be confirmed are selected, and the longest diameter and the shortest diameter of the selected particles are measured by a two-point method. The longest diameter of the granular carbon is the average value (number average) of all the longest diameters measured, and the shortest diameter is the average value (number average) of all the shortest diameters measured. The average particle size of the granular carbon is the longest diameter (average value of all the longest diameters) obtained as described above.

Specific examples of granular carbon include highly crystalline carbon materials such as graphite (natural graphite and artificial graphite) and graphene (single-layer graphene and multi-layer graphene); and low-crystalline carbon materials such as carbon black; ..

Further, as the granular carbon, it is preferable to use one containing a hydrophilic portion in a proportion of 10% by mass or more. By using granular carbon containing a hydrophilic portion in a proportion of 10% by mass or more, it becomes easier to lower the porosity of the molded product of the positive electrode mixture and increase the density. Further, as will be described later, it is more preferable that the granular carbon forms a composite with the fibrous carbon, but by using the granular carbon containing a hydrophilic portion in a proportion of 10% by mass or more, the fibrous carbon is used. The formation of a complex with is also easier.

The "hydrophilic portion" of the granular carbon referred to in the present specification is as follows. Granular carbon: 0.1 g is added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation is performed for 1 minute. The obtained liquid is left to stand for 5 hours to precipitate a solid phase portion. At this time, the portion dispersed in the liquid phase portion (supernatant liquid) without precipitating corresponds to the “hydrophilic portion”.

Further, the ratio of the "hydrophilic portion" in the total amount of granular carbon referred to in the present specification is a value obtained by the following method. The supernatant liquid is removed from the liquid after precipitation of the solid phase portion, the remaining portion is dried, and the weight of the dried solid is measured. The weight obtained by subtracting the weight obtained first from the weight of the granular carbon added first: 0.1 g is the weight of the "hydrophilic portion" dispersed in the supernatant liquid. Then, the weight of the "hydrophilic portion" is divided by the weight of the first added granular carbon: 0.1 g and expressed as a percentage, which corresponds to the ratio of the "hydrophilic portion" to the total amount of the granular carbon.

In the case of granular carbon having a hydrophilic portion of 10% by mass or more, the average particle size of the primary particles is preferably 10 nm or more, preferably 20 nm or more, from the viewpoint of further improving the moldability of the positive electrode mixture. On the other hand, since it is easy to increase the proportion of the hydrophilic portion, the average particle size of the primary particles in the case of granular carbon having a proportion of the hydrophilic portion of 10% by mass or more is preferably 400 nm or less. It is more preferably 300 nm or less.

In the electrodes of batteries such as lithium ion secondary batteries, conductive carbon such as graphite, carbon black, and carbon nanotubes, which are generally used as conductive aids, has a hydrophilic portion of 5% by mass or less. By subjecting such conductive carbon particles to an oxidation treatment, a hydroxy group, a carboxy group, an ether bond, etc. are introduced, and the conjugated double bond of carbon is oxidized to form a single bond, which is partially intercarbon. Since the hydrophilic portion is formed by breaking the bond, it is possible to obtain granular carbon in which the proportion of the hydrophilic portion satisfies the above value.

As a more specific method for producing granular carbon particles in which the proportion of the hydrophilic portion satisfies the above value, for example, a carbon raw material having voids (porous carbon powder, Ketjen black, furnace black having voids, etc.) can be used. Used, this is treated with an acid (nitrite, nitrate sulfuric acid mixture, hypochlorous acid aqueous solution, etc.) and then mixed with a transition metal compound (transition metal halide, transition metal inorganic salt, transition metal organic salt, etc.). Then, this mixture is mechanochemically reacted, and the product after the reaction is heated in a non-oxidizing atmosphere (nitrogen atmosphere, argon atmosphere, etc.), and the reaction formation of the transition metal compound or the transition metal compound is performed from the heated product. Examples thereof include a method of removing a substance by dissolving it with an acid, and then washing and drying it.

Further, the carbon raw material having the voids is mixed with the transition metal compound, and this is heated in an oxidizing atmosphere (under an oxygen-containing atmosphere such as under air), and the transition metal compound or transition metal is obtained from the heated product. Granular carbon in which the proportion of the hydrophilic portion satisfies the above-mentioned value can also be obtained by a method of removing the reaction product of the compound by dissolving it with an acid or the like, washing and drying.

Details of the method and conditions for producing granular carbon in which the proportion of the hydrophilic portion satisfies the above values are disclosed in International Publication No. 2015/133586, and the production may be performed in accordance with the description thereof.

The fibrous carbon tends to agglomerate, and even if it is mixed with a positive electrode active material or the like at the time of preparing a positive electrode mixture, it often exists in an agglomerated state without being crushed. When such an electrode mixture is used, since the agglomerated fibrous carbon is bulky, it becomes difficult to form a molded body of the positive electrode mixture having few voids and a high density. Therefore, it is preferable to use the fibrous carbon as a composite complex with granular carbon. When the fibrous carbon forms a composite with the granular carbon, the granular carbon adhering to the surface of the fibrous carbon suppresses the aggregation of the fibrous carbon. This facilitates the formation of a molded body of the positive electrode mixture having a low porosity of 16% or less and a high density, for example.

The composite of the fibrous carbon and the granular carbon can be obtained by dry-mixing the fibrous carbon and the granular carbon as described later.

Whether or not the "composite of fibrous carbon and granular carbon" is used in the molded product of the positive electrode mixture can be determined by the following method, for example, when the granular carbon is the above-mentioned low crystallinity. .. The molded body of the positive electrode mixture is taken out from the battery, and the cross section of the positive electrode is mapped and measured (measurement range: 80 × 80 μm, 2 μm steps) by micro-Raman spectroscopy. Fibrous carbon and particulate carbon, but any peak at 1340 cm ^-1 and 1590 cm ^-1 are observed, fibrous carbon is about 1 / 10-1 / 5 than the peak intensity of 1340 cm ^-1 is a granular carbon Is. Therefore, when the fibrous carbon and the granular carbon are present separately, it is possible to determine which carbon is by observing the peak intensity of ^{1340 cm -1.} When the fibrous carbon and the granular carbon form a composite, ^{the peak intensity of 1340 cm -1} is about 1/3 to 3/4 of that of the granular carbon, so that the observed carbon is It can be determined that it is a composite of fibrous carbon and granular carbon.

In the molded body of the positive electrode mixture in the positive electrode for all-solid-state batteries, the ratio of the fibrous carbon to the granular carbon is granular with respect to 100 parts by mass of the fibrous carbon from the viewpoint of better suppressing the aggregation of the fibrous carbon. The amount of carbon is preferably 10 parts by mass or more, and more preferably 30 parts by mass or more. Further, from the viewpoint of limiting the specific surface area of the entire conductive auxiliary agent and better suppressing the oxidation of the sulfide-based solid electrolyte in the molded body of the positive electrode mixture, the ratio of the fibrous carbon to the granular carbon is determined. The amount of granular carbon is preferably 100 parts by mass or less, and more preferably 70 parts by mass or less with respect to 100 parts by mass of fibrous carbon.

The ratio of fibrous carbon and granular carbon can be determined from the molded product of the positive electrode mixture by the following method. The electrode laminate is taken out from the battery, and only the molded body of the positive electrode mixture is separated with a precision knife. After the separated molded body of the positive electrode mixture is placed in ion-exchanged water, the same amount of toluene as the ion-exchanged water is added thereto for ultrasonic treatment. The liquid subjected to this treatment is separated into an aqueous phase containing granular carbon and a toluene phase containing fibrous carbon. The aqueous phase and the toluene phase are separated from this liquid. The aqueous phase thus obtained was centrifuged at a centrifugal acceleration of 50,000 G, and the operation of replacing the supernatant with ion-exchanged water was repeated three times, and then the remaining sample was dried to recover the solid content. Its mass Y (mg) is measured. Next, the solid content whose mass Y was measured was subjected to thermogravimetric (TG) analysis in an air atmosphere to determine the amount of change in mass from 120 ° C. to 700 ° C., which was calculated as the mass of granular carbon in the positive electrode mixture. Let it be Z (mg).

The toluene layer thus obtained was centrifuged at a centrifugal acceleration of 50,000 G, the operation of replacing the supernatant with toluene was repeated three times, and then the remaining sample was dried to recover the solid content, and its mass ( mg) is measured. Next, the solid content whose mass W was measured was subjected to thermogravimetric (TG) analysis in an air atmosphere to determine the amount of change in mass from 120 ° C. to 800 ° C., which was used as the fibrous carbon in the positive electrode mixture. Let the mass be X (mg).

Further, Z can be subtracted from Y to calculate the mass P (mg) of the positive electrode active material in the positive electrode mixture.

The total amount of the conductive auxiliary agent is preferably 1 to 10% by mass in the molded body of the positive electrode mixture of the positive electrode for all solid-state batteries.

As the positive electrode active material, a powder of an active material capable of occluding and releasing lithium ions, which is similar to that used in conventionally known lithium ion secondary batteries, can be used. Specifically, as the positive electrode active material, LiM ¹ _x Mn _2-x O ₄ (where M ¹ is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, It is at least one element selected from the group consisting of Cu, Al, Sn, Sb, In, Nb, Mo, W, Y, Ru and Rh, and is represented by 0.01 ≦ x ≦ 0.5). Spinel-type lithium manganese composite oxide, Li _a Mn _(1-ba) Ni _b M ² _c O _2-d F _f (where M ² is Co, Mg, Al, B, Ti, V, Cr, At least one element selected from the group consisting of Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W, 0.8 ≦ a ≦ 1.2, 0 <b <0.5, A layered compound represented by 0 ≦ c ≦ 0.5, d + f <1, −0.1 ≦ d ≦ 0.2, 0 ≦ f ≦ 0.1), LiCo _1-g M ³ _g O ₂ (however, where M ³ is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, and 0 ≦ _{LiNi 1-h} M ⁴ _h O ₂ (where M ⁴ is Al, Mg, Ti, Zr, Fe), a lithium cobalt composite oxide which is a kind of lithium transition metal oxide represented by g ≦ 0.5). , Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, which is at least one element selected from the group, and is a lithium transition metal represented by 0 ≦ h ≦ 0.5). ^{LiM 5} _1-m N _m PO ₄ (where M ⁵ is at least one element selected from the group consisting of Fe, Mn and Co, N is an element of LiM 5 1-m N m PO 4 which is a kind of oxide. It is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba, and is 0 ≦ m ≦ 0.5). Examples thereof include an olivine type composite oxide represented by, and a lithium titanium composite oxide represented by _{Li 4} Ti ₅ O _{12, and one or more of these can be used.} Among these, it is preferable to use a lithium transition metal oxide to secure the battery capacity. Further, when the positive electrode active material is a lithium transition metal oxide, if the molded body of the positive electrode mixture is contained in a ratio of 60% by mass or more, it tends to be difficult to secure conductivity. The effect of containing granular carbon can be obtained more remarkably.

It is preferable to provide a reaction suppressing layer on the surface of the positive electrode active material to suppress the reaction with the positive electrode active material and the solid electrolyte. Examples of the constituent material of the reaction suppression layer include _{lithium transition metal oxides represented by LiNbO 3} and Li ₄ Ti ₅ O ₁₂ , and one or more of these can be used.

The content of the positive electrode active material in the molded body of the positive electrode mixture of the positive electrode for an all-solid-state battery is preferably 60% by mass or more from the viewpoint of increasing the capacity of the battery. When the amount of the positive electrode active material in the molded body of the positive electrode mixture is within this range, it becomes difficult to secure the conductivity of the positive electrode mixture in the molded body. Therefore, fibrous carbon and granular carbon are used as conductive aids. The effect of improving the load characteristics becomes more remarkable. More preferably, it is 65% by mass or more. The content of the positive electrode active material in the molded product of the positive electrode mixture is usually 90% by mass or less.

The sulfide-based solid electrolyte in all-solid-state battery electrode, for _{example, 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 other mentioned particles, such as S ₃ based glass, in recent years, those LGPS system has attracted attention as a high lithium ion conductivity and _(such as Li ₁₀ GeP _{2 S 12),} those Arujirodaito system _[Li 6 PS _{5 Li 7-x + y} PS _6-x Cl _{x + y} (where 0.05 ≤ y ≤ 0.9, -3.0 x + 1.8 ≤ y ≤ -3.0 x + 5.7), such as Cl, Li _7-a PS _6-a Cl _b Br _c (where a = b + c, 0 <a≤1.8, 0.1≤b / c≤10.0, etc.) can also be used. can. Among these, a sulfide-based solid electrolyte containing lithium and phosphorus is preferable because of its high lithium ion conductivity, and an algyrodite-based material having high lithium ion conductivity and high chemical stability is more preferable.

The average particle size of the sulfide-based solid electrolyte is preferably 0.1 μm or more, more preferably 0.2 μm or more, from the viewpoint of reducing grain boundary resistance, while between the active material and the solid electrolyte. From the viewpoint of forming a sufficient contact interface in the above, it is preferably 10 μm or less, and more preferably 5 μm or less. The average particle size of the solid electrolyte referred to in the present specification is the volume when the integrated volume is obtained from particles having a small particle size distribution using a particle size distribution measuring device (such as the Microtrack particle size distribution measuring device "HRA9320" manufactured by Nikkiso Co., Ltd.). It means the value of 50% diameter (d _{50) in the standard integrated fraction.}

In addition to the sulfide-based solid electrolyte, other solid electrolytes (hydride-based solid electrolyte, oxide-based solid electrolyte, etc.) can also be used for the positive electrode for all-solid-state batteries. However, the ratio of the solid electrolyte other than the sulfide-based solid electrolyte in the polar positive electrode for the all-solid-state battery to the total amount of the solid electrolyte particles is preferably 30% by mass or less. Since all the solid electrolytes in the positive electrode for all-solid-state batteries may be sulfide-based solid electrolytes, the lower limit of the proportion of solid electrolytes other than the sulfide-based solid electrolytes in the total amount of solid electrolytes is 0% by mass. be.

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). Particles 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 particles such as _{Li 7} La ₃ Zr ₂ O ₁₂ , LiTi (PO ₄ ) ₃ , LiGe (PO ₄ ) ₃ , and LiLaTIO _3.

The average particle size of the solid electrolyte other than the sulfide-based solid electrolyte is preferably about the same as the average particle size of the sulfide-based solid electrolyte.

The content of the solid electrolyte in the molded product of the positive electrode mixture is preferably 4 to 30% by mass.

The molded body of the positive electrode mixture for the positive electrode for an all-solid-state battery may contain a binder, but it may not be contained because it can be satisfactorily molded by the action of a sulfide-based solid electrolyte. As the binder, various binders (fluororesin such as polyvinylidene fluoride and polytetrafluoroethylene) usually used for electrodes of lithium ion secondary batteries can be used. When the binder is contained in the molded product of the positive electrode mixture, the content is preferably 0.5% by mass or less.

In the positive electrode for all-solid-state batteries, the porosity of the molded product of the positive electrode mixture is preferably 16% or less, and more preferably 14% or less. As described above, when the fibrous carbon and the granular carbon form a complex, the granular carbon adhering to the surface of the fibrous carbon suppresses the aggregation of the fibrous carbon. As a result, for example, a molded body of a positive electrode mixture having a low void ratio of 16% or less and a high density can be formed, and the number of contacts between the positive electrode active material and the solid electrolyte is increased to ensure good ionic conductivity. You will be able to.

The lower limit of the void ratio of the positive electrode mixture molded body in the positive electrode for all-solid-state batteries is not particularly limited, but it is not easy to form the positive electrode mixture molded body having a void ratio of 0%, and usually , About 9%.

The void ratio of the molded body of the positive electrode mixture referred to in the present specification is calculated from the true density of the positive electrode mixture calculated from the ratio and true density of each material contained in the positive electrode mixture and the measured density of the molded body of the positive electrode mixture. Will be done.

The positive electrode for an all-solid-state battery is prepared by mixing a positive electrode active material, a sulfide-based solid electrolyte, fibrous carbon, granular carbon, and the like to prepare a positive electrode mixture, and molding the positive electrode mixture to form a positive electrode mixture. It can be manufactured by a manufacturing method including a step of forming a molded body.

When a composite of fibrous carbon and granular carbon is used as the conductive auxiliary agent, a step of mixing the fibrous carbon and the granular carbon to form the composite, and the composite and the positive electrode An all-solid-state battery by a manufacturing method including a step of mixing an active material and a sulfide-based solid electrolyte to prepare a positive electrode mixture and a step of molding the positive electrode mixture to form a molded body of the positive electrode mixture. Positive electrode can be manufactured.

The formation of a complex of fibrous carbon and granular carbon can be carried out by using a device such as a planetary ball mill or "Super Mascoroider (trade name)" manufactured by Masuko Sangyo, and dry-mixing them. The mixing time at the time of forming the complex may be, for example, 10 to 60 minutes.

The composite, the positive electrode active material, the sulfide-based solid electrolyte, etc. are mixed to prepare a positive electrode mixture, or the positive electrode active material, the sulfide-based solid electrolyte, fibrous carbon, granular carbon, etc. are mixed to prepare the positive electrode. When preparing the mixture, for example, they may be dry-mixed using the same apparatus as for forming the complex.

The molded body of the positive electrode mixture may be formed by using the positive electrode mixture prepared as described above and pressing the positive electrode mixture to form pellets or sheets. In the case of a positive electrode for an all-solid-state battery that does not have a current collector, the molded body of the positive electrode mixture can be used as it is as an electrode. On the other hand, in the case of a positive electrode for an all-solid-state battery having a current collector, it can be manufactured by crimping the obtained molded body of the positive electrode mixture with the current collector.

When the positive electrode for an all-solid-state battery has a current collector, examples of the current collector include metal foils such as aluminum and stainless steel, punching metal, mesh, expanded metal, foamed metal; carbon sheet; and the like. When the electrode for an all-solid-state battery is a negative electrode and a current collector is used, the current collector may be copper or nickel foil, punching metal, net, expanded metal, foamed metal; carbon sheet; etc. Can be mentioned.

The thickness of the molded product of the positive electrode mixture in the positive electrode for an all-solid-state battery is 250 μm or more, preferably 300 μm or more, and more preferably 400 μm or more. The larger the thickness of the molded body of the positive electrode mixture, the more the amount of the positive electrode active material can be increased, so that the capacity can be secured. Further, if the thickness of the molded body of the positive electrode mixture is smaller than 250 μm, ensuring conductivity is not a problem, while if the thickness is 250 μm or more, the load characteristics of the battery are significantly reduced due to the decrease in conductivity. According to this, the load characteristics of the battery can be improved as compared with the case of having a molded body of a thin positive electrode mixture. The thickness of the molded product of the positive electrode mixture can be appropriately changed according to the equipment to be used, but is preferably 5000 μm or less.

<All-solid-state battery>
The all-solid-state battery of the present invention is a secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the positive electrode is the positive electrode for the all-solid-state battery of the present invention.

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), 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.

Examples of the negative electrode of the all-solid-state battery include those having a molded body of a negative electrode mixture containing a negative electrode active material, a conductive auxiliary agent, a solid electrolyte, and the like. A negative electrode having a structure integrated with an electric body can be used.

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.

The content of the negative electrode active material in the negative electrode mixture is preferably 50 to 95% 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 1 to 10% by mass.

As the solid electrolyte of the negative electrode, one or more of the same solid electrolytes as those exemplified above can be used as the solid electrolyte that can be contained in the positive electrode mixture. Among the above-exemplified solid electrolytes, it is more preferable to use a sulfide-based solid electrolyte because it has high lithium ion conductivity and has a function of improving the moldability of the negative electrode mixture.

The content of the solid electrolyte in the negative electrode mixture is preferably 4 to 49% 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. The thickness of the molded product of the negative electrode mixture is usually 3000 μm or less.

The solid electrolyte layer for all-solid-state batteries is the same as the various solid electrolytes (sulfide-based solid electrolytes, hydride-based solid electrolytes, oxide-based solid electrolytes) exemplified above as the solid electrolytes for all-solid-state battery electrodes. One or more of the above can be used. However, in order to improve the battery characteristics, it is preferable to contain a sulfide-based solid electrolyte.

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 50 to 400 μm.

In the all-solid-state battery, the positive electrode and the negative electrode can be used 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.

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

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

(Example 1)
<Formation of solid electrolyte layer>
_{A sulfide-based solid electrolyte (Li 6} PS ₅ Cl) having an algyrodite-type structure with an average particle diameter of 4 μm was charged into a powder molding die, pressure-molded using a press machine, and a thickness of 0.2 mm. A solid electrolyte layer was formed.

<Preparation of positive electrode>
An average particle diameter of 200nm 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 granular carbon containing a hydrophilic portion was obtained in a proportion of 10% by mass or more. In the obtained granular carbon, the ratio of the length of the longest diameter to the length of the shortest diameter was 1.1 in the state of the primary particles, and the average particle size of the primary particles of the granular carbon was 200 nm.

Carbon nanotubes [“VGCF (trade name)” manufactured by Showa Denko Co., Ltd., fibrous carbon, the ratio of fiber length to fiber diameter is 30 or more] and the granular carbon are mixed by mass ratio of 2: using a planetary ball mill. Dry mixing was performed at a ratio of 1 for 60 minutes to obtain a composite of fibrous carbon and granular carbon.

LiCoO ₂ (positive electrode active material), a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an algyrodite-type structure with an average particle size of 4 μm, and a composite (conductive aid) of the fibrous carbon and granular carbon. And were mixed at a mass ratio of 70: 26.8: 3.2 to prepare a positive electrode mixture.

Next, 62 mg of the positive electrode mixture was put onto the solid electrolyte layer in the powder molding die, pressure molding was performed using a press machine, and the thickness was 0.46 mm on the solid electrolyte layer. A positive electrode was formed of a molded body of the positive electrode mixture of. The porosity of the obtained positive electrode was 14%.

<Manufacturing of negative electrode>
_{Li 4} Ti ₅ O ₁₂ having an average particle diameter of 2 μm, the sulfide solid electrolyte and the granular carbon were mixed at a mass ratio of 55:40: 5 and kneaded well to prepare a negative electrode mixture. Next, 88 mg of the negative electrode mixture was put onto the side of the powder molding die opposite to the positive electrode of the solid electrolyte layer, and pressure molding was performed using a press machine to obtain the solid electrolyte layer. By forming a negative electrode made of a negative electrode mixture molded body having a thickness of 0.89 mm on the electrode, an electrode laminate having a diameter of 7.5 mm and a thickness of 1.55 mm, in which a positive electrode, a solid electrolyte layer and a negative electrode are laminated, is formed. Made.

<Battery assembly>
A flexible graphite sheet "PERMA-FOIL (product name)" (thickness: 0.1 mm, apparent density: 1.1 g / cm ³ ) manufactured by Toyo Tanso Co., Ltd. punched to the same size as the electrode laminate. Two sheets were prepared, and one of them was placed on the inner bottom surface of a stainless steel sealing can fitted with an annular gasket made of polypropylene. Next, the electrode laminate is superposed on the graphite sheet with the negative electrode on the graphite sheet side, another sheet of the graphite sheet is placed on the graphite sheet, and an outer can made of stainless steel is further covered. By crimping the open end of the outer can inward to seal the can, between the inner bottom surface of the sealing can and the laminate, and between the inner bottom surface of the outer can and the laminate, respectively. A flat all-solid-state battery having a diameter of about 9 mm on which the graphite sheet was arranged was produced.

(Example 2)
LiCoO _{2 , a sulfide-based solid electrolyte (Li 6} PS ₅ Cl) having an algyrodite-type structure having an average particle diameter of 4 μm, the fibrous carbon, and the granular carbon in a mass ratio of 70: 26.8: A positive electrode mixture was prepared by mixing at a ratio of 2.1: 1.1. A positive electrode was formed in the same manner as in Example 1 except that this positive electrode was used. The porosity of the obtained positive electrode was 15%.

A flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Example 3)
LiCoO _{2 , a sulfide-based solid electrolyte (Li 6} PS ₅ Cl) having an algyrodite-type structure having an average particle diameter of 4 μm, the fibrous carbon, and the granular carbon in a mass ratio of 60: 36.8: A positive electrode mixture was prepared by mixing at a ratio of 2.1: 1.1. A positive electrode was formed in the same manner as in Example 1 except that this positive electrode was used. The porosity of the obtained positive electrode was 15%.

A flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Example 4)
LiCoO _{2 , a sulfide-based solid electrolyte (Li 6} PS ₅ Cl) having an algyrodite-type structure having an average particle diameter of 4 μm, the fibrous carbon, and the granular carbon in a mass ratio of 70: 26.8: A positive electrode mixture was prepared by mixing at a ratio of 2.1: 1.1.

Next, 40 mg of this positive electrode mixture was put onto the solid electrolyte layer in the powder molding die, pressure molding was performed using a press machine, and the thickness was 0.30 mm on the solid electrolyte layer. A positive electrode was formed of a molded body of the positive electrode mixture of. The porosity of the obtained positive electrode was 15%.

A flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Example 5)
LiCoO ₂ (positive electrode active material), a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an algyrodite-type structure with an average particle diameter of 4 μm, the fibrous carbon, and the granular carbon in a mass ratio of 70. A positive electrode mixture was prepared by mixing at a ratio of: 26.8: 2.1: 1.1.

Next, 33 mg of this positive electrode mixture was put onto the solid electrolyte layer in the powder molding die, pressure molding was performed using a press machine, and the thickness was 0.25 mm on the solid electrolyte layer. A positive electrode was formed of a molded body of the positive electrode mixture of. The porosity of the obtained positive electrode was 15%.

A flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Comparative Example 1)
Similar to Example 1, the thickness was 0.46 mm, except that the same carbon nanotubes used for forming the composite were used as the conductive auxiliary agent instead of the composite of fibrous carbon and granular carbon. A positive electrode made of a molded body of the positive electrode mixture of No. 1 was produced. The porosity of the obtained positive electrode was 19%. Then, a flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Comparative Example 2)
Similar to Example 1, the thickness was 0.46 mm, except that the same granular carbon used for forming the composite was used as the conductive auxiliary agent instead of the composite of the fibrous carbon and the granular carbon. A positive electrode made of a molded body of the positive electrode mixture of No. 1 was produced. The porosity of the obtained positive electrode was 15%. Then, a flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

(Comparative Example 3)
LiCoO ₂ (positive electrode active material), a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) having an algyrodite-type structure with an average particle diameter of 4 μm, and the granular carbon in a mass ratio of 70: 26.8: 3. A positive electrode mixture was prepared by mixing at a ratio of .2.

Next, 26 mg of this positive electrode mixture was put onto the solid electrolyte layer in the powder molding die, pressure molding was performed using a press machine, and the thickness was 0.20 mm on the solid electrolyte layer. A positive electrode was formed of a molded body of the positive electrode mixture of. The porosity of the obtained positive electrode was 15%.

A flat all-solid-state battery was produced in the same manner as in Example 1 except that this positive electrode was used.

The following evaluations were performed on 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 0.03 C until the voltage reaches 2.8 V, and then is charged with a constant voltage until the current value reaches 0.003 C. After that, the battery was discharged with a current value of 0.03C until the voltage became 1V, and the 0.03C discharge capacity (initial capacity) at that time was measured.

<Load characterization>
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 0.3 C until the voltage reaches 1 V. , The discharge capacity (0.3C discharge capacity) at this time was measured.

Then, for each battery, the value obtained by dividing the 0.3C discharge capacity by the 0.03C discharge capacity was expressed as a percentage to obtain the capacity retention rate, and the load characteristics were evaluated.

The results of each of the above evaluations are shown in Table 1.

As shown in Table 1, when a sulfide-based solid electrolyte is used and a molded body of a thick positive electrode mixture is used, the all-solid-state batteries of Comparative Examples 1 and 2 using only fibrous carbon or only granular carbon as the conductive auxiliary agent. The capacity retention rate at the time of load characteristic evaluation was small, and the load characteristic was inferior. On the other hand, in the battery of Comparative Example 3 using a positive electrode having a molded body of a thin positive electrode mixture, although only granular carbon was used as the conductive auxiliary agent as in the battery of Comparative Example 2, at the time of load characteristic evaluation. The capacity retention rate was relatively high.

On the other hand, the all-solid-state batteries of Examples 1 to 4 in which fibrous carbon and granular carbon are used in combination as the conductive auxiliary agent of the molded body of the positive electrode mixture use a sulfide-based solid electrolyte and are made of the positive electrode mixture. Despite the thick molded body, the capacity retention rate at the time of load characteristic evaluation was higher than that of the battery of Comparative Example 3 having the molded body of the thin positive electrode mixture, and had excellent load characteristics.

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

Claims (6)

It has a molded body of a positive electrode mixture containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive auxiliary agent.
The conductive auxiliary agent contains fibrous carbon and granular carbon, and contains
A positive electrode for an all-solid-state battery, characterized in that the thickness of the molded product of the positive electrode mixture is 250 μm or more. The positive electrode for an all-solid-state battery according to claim 1, wherein the fibrous carbon and the granular carbon form a complex. The positive electrode for an all-solid-state battery according to claim 1 or 2, wherein the binder content in the molded product of the positive electrode mixture is 0.5% by mass or less. The positive electrode for an all-solid-state battery according to any one of claims 1 to 3, which contains a sulfide-based solid electrolyte containing lithium and phosphorus as the solid electrolyte. The positive electrode for an all-solid-state battery according to any one of claims 1 to 4, which contains a lithium transition metal oxide as the positive electrode active material. 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.
An all-solid-state battery, wherein the positive electrode is the positive electrode for an all-solid-state battery according to any one of claims 1 to 5.

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