JP2021057142A - Positive electrode for all-solid-state battery and all-solid-state battery - Google Patents

Abstract

To provide an all-solid-state battery having a high capacity and excellent output characteristics, and a positive electrode for an all-solid-state battery that can constitute the all-solid-state battery.SOLUTION: A positive electrode for an all-solid-state battery has a molded body of a positive electrode mixture containing positive electrode active material particles, solid electrolyte particles, and electrical conduction assistant particles. The electrical conduction assistant particles contain the following carbon A and carbon B, the content of the carbon A in the positive electrode mixture is 3 mass% or less, and the amount of the carbon B relative to 100 parts by mass of the carbon A is 40 to 60 parts by mass. Carbon A: a ratio ID/IG of a signal intensity ID of a D-band and a signal intensity IG of a G-band in a Raman spectrum is 1 or more, and an average particle diameter is 10 to 100 nm. Carbon B: the ratio ID/IG of the signal intensity ID of the D-band and the signal intensity IG of the G-band in the Raman spectrum is less than 1, and a length is 500 nm or more. Further, an all-solid-state battery has the positive electrode for an all-solid-state battery.SELECTED DRAWING: Figure 1

Description

The present invention relates to an all-solid-state battery having a high capacity and excellent output characteristics, and a positive electrode for an all-solid-state battery that can constitute the all-solid-state battery.

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 safety and reliability of lithium-ion secondary batteries with higher capacity and higher energy density are also highly required.

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

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

In batteries such as all-solid-state batteries, it is common to include a conductive auxiliary agent in the positive electrode and the negative electrode, but studies have been made to improve the characteristics of the battery by improving this. For example, in Patent Document 1, in order to increase the capacity retention rate during a charge / discharge cycle of an all-solid-state battery, a carbon material having a carboxyl group on the surface and a cup-laminated carbon nanofiber are used to assist the conductivity of a positive electrode or a negative electrode. It has been proposed to be used in combination as an agent.

Further, Patent Document 2 proposes a conductive carbon mixture in which another conductive carbon is coated with an oxidation-treated carbon having conductivity, and an electrode having an electrode active material whose surface is coated with this conductive carbon mixture is provided. By using it to configure a power storage device such as a secondary battery, the cycle life can be extended.

Japanese Unexamined Patent Publication No. 2018-206537 Japanese Unexamined Patent Publication No. 2019-21420

By the way, at present, the fields of application of all-solid-state batteries are rapidly expanding, and for example, they can be applied to applications that require discharge at a large current value. It is required to increase.

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

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 solid electrolyte, and a conductive auxiliary agent, and the conductive auxiliary agent contains the following carbon A and carbon B. It is characterized in that the content of carbon A in the positive electrode mixture is 3% by mass or less, and the amount of carbon B is 40 to 60 parts by mass with respect to 100 parts by mass of the amount of carbon A. ..

Carbon A: the ratio _I D / _{I G} of the signal intensity _{I G} of the D-band signal intensity _{I D} and G bands in the Raman spectrum is 1 or more, an average particle diameter of 10 to 100 nm.

Carbon B: the ratio _I D / _{I G} is less than 1 and the signal strength _{I G} of signal intensity _{I D} D to G band in Raman spectrum, has a more portions 500nm long.

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 has the positive electrode for the all-solid-state battery of the present invention as the negative electrode. It is a feature.

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

It is sectional drawing which shows typically an example of the all-solid-state battery of this invention. It is a top view schematically showing another example of the all-solid-state battery of this invention. FIG. 2 is a cross-sectional view taken along the line II of FIG.

<Positive electrode for all-solid-state battery>
The positive electrode for an all-solid-state battery of the present invention (hereinafter, may be simply referred to as “positive electrode”) has a molded body of a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and a conductive auxiliary agent. Then, carbon A and carbon B are used in the conductive auxiliary agent in a specific ratio.

Carbon A is the ratio _I D / _{I G} of the signal intensity _{I G} of the D-band signal intensity _{I D} and G bands in the Raman spectrum is 1 or more, an average particle diameter of 10 to 100 nm.

_{Carbon having an ID} / _IG of 1 or more has high hydrophilicity, and by using such carbon as a conductive auxiliary agent, it is possible to improve the moldability of the molded product of the positive electrode mixture. Thereby, for example, the density of the molded body of the positive electrode mixture can be increased, and the volumetric energy density of the all-solid-state battery can be improved.

However, carbon A has a good affinity with the positive electrode active material due to its high hydrophilicity. Therefore, when such carbon is used as a conductive auxiliary agent for the positive electrode for an all-solid battery, the positive electrode active material particles can be used. The surface is covered with carbon particles, which makes it difficult for the positive electrode active material particles to come into contact with each other, or makes it difficult for the positive electrode active material particles and the solid electrolyte to come into contact with each other. Therefore, for example, in the positive electrode (molded body of the positive electrode mixture), the proportion of the positive electrode active material particles that do not come into contact with the solid electrolyte and other positive electrode active material particles and exist independently increases. The ionic conductivity in the molded body is reduced, and the utilization rate of the positive electrode active material is reduced.

Therefore, in order to use carbon A having high hydrophilicity as a conductive auxiliary agent for the positive electrode, the amount of carbon A in the positive electrode mixture is limited to some extent from the viewpoint of ensuring ionic conductivity in the molded body of the positive electrode mixture. It is necessary, and this also limits the electron conductivity in the molded body of the positive electrode mixture to some extent. As described above, when carbon A having high hydrophilicity is used as a conductive auxiliary agent for the positive electrode, it is difficult to secure a good balance between ionic conductivity and electron conductivity, it is difficult to reduce the DC resistance at the positive electrode, and the output characteristics are poor. It is difficult to form expensive batteries.

Therefore, in the present invention, it is decided to use carbon B together with carbon A. Carbon B is the ratio _I D / _{I G} is less than 1 and the signal strength _{I G} of the D-band signal intensity _{I D} and G bands in the Raman spectrum has a more portions 500nm long.

Since _{carbon B having an ID} / _IG of less than 1 has low hydrophilicity, it does not selectively collect around the positive electrode active material particles unlike carbon A, and has relatively high uniformity in the molded body of the positive electrode mixture. Easy to disperse. Compared to carbon A, which has an average particle size of 10 to 100 nm, which is relatively small in size, carbon B has a portion having a length of 500 nm or more, and is relatively large in size. Therefore, by limiting the amount of carbon A in order to secure ionic conductivity, for example, a solid electrolyte adheres to the surroundings, making it difficult to come into contact with other positive electrode active material particles or carbon A, and ensuring electron conductivity. Even for positive electrode active material particles, which have become difficult to achieve, carbon B makes it possible to form a conductive path with other positive electrode active material particles.

Therefore, by using carbon A and carbon B in an appropriate ratio, the amount of carbon A can be reduced to ensure good ionic conductivity and electron conductivity can be increased in the molded body of the positive electrode mixture. Therefore, it is possible to reduce the DC resistance at the positive electrode, increase the utilization rate of the positive electrode active material, and construct an all-solid-state battery having a high capacity and excellent output characteristics.

The positive electrode of the present invention is formed by forming a molded body (pellet or the like) formed by molding a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and the conductive auxiliary agent, or a layer of the positive electrode mixture on a current collector. The structure of the above is mentioned.

The shape of carbon A, which is a conductive auxiliary agent for the positive electrode, is, for example, a particle shape. For such carbon A, for example, conductive carbon particles containing a hydrophilic portion in a proportion of 10% by mass or more can be used. The proportion of the hydrophilic portion in the conductive carbon particles is more preferably 12% by mass or more, and more preferably 30% by mass or less.

The "hydrophilic portion" of the conductive carbon referred to in the present specification is as follows. Conductive 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 conductive 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 conductive 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 conductive carbon first added: 0.1 g and expressed as a percentage, which corresponds to the ratio of the "hydrophilic portion" to the total amount of the conductive carbon. ..

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 oxidation treatment, hydroxy groups, carboxy groups, ether bonds, etc. are introduced, and the conjugated double bonds of carbon are oxidized to form single bonds, which are partially intercarbon. Since the hydrophilic portion is formed by breaking the bond, it is possible to obtain conductive carbon particles in which the proportion of the hydrophilic portion satisfies the above value.

As a more specific method for producing conductive 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, carbon) Nanofibers, carbon nanotubes, etc.) are used, which are treated with acids (nitric acid, nitrate-sulfuric acid mixture, hypochlorous acid aqueous solution, etc.), and then transition metal compounds (transition metal halides, transition metal inorganic salts, transitions, etc.). It is mixed with an organic salt of a metal, etc.), and this mixture is mechanochemically reacted. The product after the reaction is heated in a non-oxidizing atmosphere (nitrogen atmosphere, argon atmosphere, etc.), and the transition metal is transferred from the heated product. Examples thereof include a method of removing the reaction product of the compound or the transition metal compound 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. Conductive carbon particles 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 conductive carbon particles in which the proportion of the hydrophilic portion satisfies the above values are disclosed in International Publication No. 2015/133586, and the particles may be produced in accordance with the description thereof.

The average particle size of the carbon A is preferably 10 nm or more, more preferably 20 nm or more, while "hydrophilic", from the viewpoint of further improving the moldability of the positive electrode mixture. The average particle size of the primary particles is preferably 100 nm or less, and more preferably 35 nm or less, because it is easy to increase the proportion of “parts”.

The average particle size of carbon A referred to in the present specification is a carbon A whose outline can be confirmed in an image obtained by observing a cross section of a molded body of a positive electrode mixture at a magnification of 30,000 times using a scanning electron microscope (SEM). It means an average value obtained by selecting 50 particles and measuring the particle size on the major axis side for each selected particle.

The content of carbon A in the positive electrode mixture is 3% by mass from the viewpoint of limiting the area ratio of the surface of the positive electrode active material particles coated with carbon A and enhancing the ionic conductivity in the molded body of the positive electrode mixture. It is less than or equal to 2.5% by mass or less. Further, from the viewpoint of improving the electron conductivity in the molded body of the positive electrode mixture, the content of carbon A in the positive electrode mixture is preferably 0.5% by mass or more, preferably 1% by mass or more. Is more preferable.

Further, the carbon B, which is the conductive auxiliary agent for the positive electrode, may have an _ID / _IG of less than 1 and at least a part having a length of 500 μm or more. The shape of the carbon B is not particularly limited, and examples thereof include a sheet shape, a scale shape, a needle shape, and a fibrous shape.

Specific examples of carbon B include graphite (natural graphite, artificial graphite), graphene, carbon nanofibers, carbon nanotubes and the like used as a conductive auxiliary agent in the positive electrode of a battery such as a lithium ion secondary battery. It is preferable that carbon B does not form an agglomerate.

The fact that "carbon B has a portion having a length of 500 μm or more" as used herein means that the powder obtained by crushing the positive electrode mixture in a dairy pot is obtained by using a scanning electron microscope (SEM). In the image observed at a magnification of 3000 times, 50 carbon B particles whose contours can be confirmed are selected, the particle size on the long axis side is measured for each selected particle, and the particle size is grasped by the sixth value from the minimum value. The "major axis side particle size" of the carbon B particles means, for example, the length of the portion corresponding to the fiber length when the carbon B particles have a fibrous (including rod-shaped) morphology. However, when the carbon B particles are flat, it means the length of the longest part of the flat plate.

In the positive electrode mixture, when the amount of carbon A is 100 parts by mass, the amount of carbon B is preferably 40% by mass or more, preferably 42% by mass or more, and 60% by mass or less, 58% by mass. % Or less is preferable. When the ratio of carbon A and carbon B in the positive electrode mixture satisfies the above values, it is possible to form a positive electrode capable of enhancing the output characteristics of the all-solid-state battery while increasing its capacity.

The carbon B content in the positive electrode mixture is within the range in which the ratio of carbon A to carbon B in the positive electrode mixture satisfies the above value and the carbon A content in the positive electrode mixture satisfies the above value. You can set it with.

The positive electrode mixture may contain only carbon A and carbon B as the conductive auxiliary agent, or may contain other conductive auxiliary agent together with carbon A and carbon B. Other conductive aids that can be used with carbon A and carbon B include, for example, _{carbon black with an ID} / _IG of less than 1 and no portion of length of 500 nm or more. However, the content of the conductive auxiliary agent other than carbon A and carbon B in the total amount of the conductive auxiliary agent in the positive electrode mixture is preferably 1% by mass or less.

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

The content of the positive electrode active material in the positive electrode mixture is 70% by mass or more, preferably 75% by mass or more, from the viewpoint of enabling the construction of a high-capacity all-solid-state battery. However, if the amount of the positive electrode active material in the positive electrode mixture is too large, the amount of the solid electrolyte and the amount of the conductive auxiliary agent become too small, and the ionic conductivity and the electron conductivity in the molded body of the positive electrode mixture become too small. The content of the positive electrode active material in the positive electrode mixture is preferably 90% by mass or less because the effect of ensuring a well-balanced condition may be reduced.

The solid electrolyte of the positive electrode is not particularly limited as long as it has lithium ion conductivity, and for example, a sulfide-based solid electrolyte, a hydride-based solid electrolyte, an oxide-based solid electrolyte, and the like can be used.

The sulfide-based solid electrolyte, _such as _{Li 2 S-P 2 S 5} , Li 2 S-SiS 2, Li 2 S-P 2 S 5 -GeS 2, Li 2 S-B 2 S 3 based glass _{In addition to these, Li 10} GeP ₂ S ₁₂ (LGPS system) and Li ₆ PS ₅ Cl (algirodite system), which have been attracting attention in recent years as having high lithium ion conductivity, can also be used. Among these, an algyrodite-based material having particularly high lithium ion conductivity and high chemical stability is preferably used.

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

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

As the solid electrolyte, one or more of the above-exemplified ones can be used. Among the above-exemplified solid electrolytes, the lithium ion conductivity is high, and the function of enhancing the moldability of the positive electrode mixture is enhanced. Therefore, it is more preferable to use a sulfide-based solid electrolyte.

The positive electrode mixture may or may not contain a binder. When the positive electrode mixture contains a binder, a fluororesin such as polyvinylidene fluoride (PVDF) can be used as the binder. When a binder is used, the content of the binder in the positive electrode mixture is preferably 0 to 1% by mass. More preferably, it is 0 to 0.5% by mass. It is most preferable not to contain a binder from the viewpoint that the ratio of the material to be charged and discharged can be increased and the lithium ion conductivity is kept high.

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

In the positive electrode, when the total surface area of all positive electrode active materials contained in the positive electrode mixture is S (cm ² ) and the carbon A content in the positive electrode mixture is Z (g), Z / S <1. It is preferable that the relationship is satisfied. In this case, since the proportion of the portion of the surface of the positive electrode active material particles that is not coated with carbon A can be increased to some extent, the ions in the molded body of the positive electrode mixture are combined with the action of carbon B. The balance between conductivity and electron conductivity becomes better.

In addition, S and Z in "Z / S <1" are values obtained by the following methods.

A molded body of the positive electrode mixture constituting the positive electrode is taken out and placed in ion-exchanged water, and then the same amount of toluene as the ion-exchanged water is added thereto to perform sonication. The liquid subjected to this treatment is separated into an aqueous phase containing hydrophilic carbon A and a toluene phase containing hydrophobic carbon B. 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 carbon A in the positive electrode mixture. Let it be Z (mg).

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

Further, for the test piece obtained from the molded body of the positive electrode mixture, the component composition of the positive electrode active material was determined by using an inductively coupled plasma atomic emission spectroscopic analysis (ICP-AES) apparatus, and an X-ray diffraction (XRD) apparatus was used. The lattice constant of the positive electrode active material is obtained, and the density d _XRD (g / cm ³ ) of the positive electrode active material is calculated from these.

Further, 50 positive electrode active material particles whose contours can be confirmed in an image obtained by observing a cross section of a molded body of a positive electrode mixture at a magnification of 2000 times using a scanning electron microscope (SEM) are selected and selected. _{The average particle size of the positive electrode active material particles D SEM} (μm) is obtained by measuring the particle size on the major axis side of the particles and calculating the average value of all the particles.

Then, from the mass P of the obtained positive electrode active material, the density d _{XRD of the} positive electrode active material, and the average particle size D _SEM , the total surface area of the total positive electrode active material contained in the positive electrode mixture is S (cm ² ) by the following formula. Is calculated.
S = 0.6 x P ÷ (d _XRD x D _SEM )

By adjusting the particle size and amount of the positive electrode active material used in the positive electrode mixture (content of the positive electrode active material in the positive electrode mixture) and the content of carbon A in the positive electrode mixture, the Z / S value can be adjusted as described above. Can be adjusted to satisfy the relationship.

The positive electrode can be manufactured by mixing a positive electrode active material, a solid electrolyte, a conductive additive, and the like without using a solvent, for example, to prepare a positive electrode mixture, and molding the positive electrode mixture into pellets or the like. Further, the molded body of the positive electrode mixture obtained as described above may be bonded to the current collector to form a positive electrode.

Further, the positive electrode mixture and the solvent are mixed to prepare a positive electrode mixture-containing composition, which is applied onto a substrate such as a current collector or a solid electrolyte layer facing the positive electrode, dried, and then pressed. By performing the above, a molded body of the positive electrode mixture may be formed.

As the solvent used in the positive electrode mixture-containing 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 cause a chemical reaction with a very small amount of water, and are therefore represented by hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene. It is preferable to use a non-polar aproton solvent. In particular, it is more preferable to use a super dehydration solvent having a water content of 0.001% by mass (10 ppm) or less. In addition, fluorosolvents such as "Bertrel (registered trademark)" manufactured by Mitsui Dupont Fluorochemical, "Zeorolla (registered trademark)" manufactured by Nippon Zeon, and "Novec (registered trademark)" manufactured by Sumitomo 3M, as well as , Dichloromethane, diethyl ether and other non-aqueous organic solvents can also be used.

The thickness of the molded body of the positive electrode mixture (including both the case where the positive electrode does not have a current collector and the case where the positive electrode has a current collector) is preferably 50 to 2000 μm.

<All-solid-state battery>
The all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the positive electrode 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 all-solid-state battery 1 shown in FIG. 1 has a positive electrode 10, a negative electrode 20, and a positive electrode 10 and a negative electrode 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 20 and 20 is enclosed.

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

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

In addition, FIGS. 2 and 3 show drawings schematically showing other examples of the all-solid-state battery of the present invention. FIG. 2 is a plan view of the all-solid-state battery, and FIG. 3 is a sectional view taken along line II of FIG.

In the all-solid-state battery 100 shown in FIGS. 2 and 3, the electrode body 200 composed of the positive electrode, the solid electrolyte layer, and the negative electrode of the present invention is housed in the laminate film exterior body 500 composed of two metal laminate films. The laminated film exterior body 500 is sealed at the outer peripheral portion thereof by heat-sealing the upper and lower metal laminated films. In addition, in FIG. 3, in order to avoid complicating the drawings, each layer constituting the laminated film exterior body 500, and the positive electrode, the negative electrode, and the separator constituting the electrode body are not shown separately.

The positive electrode of the electrode body 200 is connected to the positive electrode external terminal 300 in the battery 100, and although not shown, the negative electrode of the electrode body 200 is also connected to the negative electrode external terminal 400 in the battery 100. There is. Then, one end side of the positive electrode external terminal 300 and the negative electrode external terminal 400 is pulled out to the outside of the laminated film exterior body 500 so that it can be connected to an external device or the like.

(Negative electrode)
As the negative electrode of the all-solid-state battery, a negative electrode active material used in a conventionally known lithium ion secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions is 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 compounds containing elements such as Si, Sn, Ge, Bi, Sb, and In, compounds and their alloys; compounds capable of charging and discharging at low voltages close to lithium metals such as lithium-containing nitrides or lithium-containing oxides; lithium metals. Lithium / aluminum alloy ;; lithium titanate; can also be used as the negative electrode active material.

For the negative electrode, a solid electrolyte, a binder such as butyl rubber, chloropyrene rubber, acrylic resin and fluororesin, and a conductive auxiliary agent (carbon material such as carbon black, etc.) are appropriately added to the negative electrode active material. The mixture is compressed by pressure molding to form a pellet-shaped molded body (negative electrode mixture molded body), or the current collector is used as a core material to form a molded body (negative electrode mixture layer). Alternatively, the above-mentioned various alloys or lithium metal foils can be used alone or laminated on a current collector as an active material layer.

When the negative electrode contains a solid electrolyte, 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. In order to improve the battery characteristics, it is desirable to contain a sulfide-based solid electrolyte.

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.

A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a solid electrolyte is prepared by dispersing, for example, a negative electrode active material and a solid electrolyte, and a binder or a conductive auxiliary agent to be used as necessary in a solvent. The prepared negative electrode mixture-containing composition (paste, slurry, etc.) can be applied to a substrate such as a current collector, dried, and pressed if necessary. In the negative electrode mixture-containing composition in this case, the binder may be dissolved in a solvent.

As with the solvent used for the positive electrode mixture-containing composition, it is desirable to select a solvent that does not easily deteriorate the solid electrolyte as the solvent used for the negative electrode mixture-containing composition. It is preferable to use various solvents exemplified in the above, and it is particularly preferable to use a super-dehydrated solvent having a water content of 0.001% by mass (10 ppm) or less.

In the case of a negative electrode mixture molded body containing a negative electrode active material and a solid electrolyte, or a negative electrode having a layer (negative electrode mixture layer) composed of a negative electrode mixture molded body on the surface of the current collector, the composition of the negative electrode mixture For example, the content of the negative electrode active material is preferably 50 to 80% by mass, and the content of the solid electrolyte is preferably 20 to 50% by mass. When the negative electrode mixture contains a binder, the content thereof is preferably 0.1 to 10% by mass. Further, when the negative electrode mixture contains a conductive auxiliary agent, the content thereof is preferably 0.1 to 10% by mass.

The thickness of the molded body of the negative electrode mixture (including both the case where the negative electrode does not have a current collector and the case where the negative electrode has a current collector) is preferably 50 to 2000 μm.

(Solid electrolyte layer)
As the solid electrolyte in the solid electrolyte layer of the all-solid-state battery, one or more of the same ones as those exemplified above can be used as the solid electrolyte of the positive electrode. However, in order to improve the battery characteristics, it is desirable to contain a sulfide-based solid electrolyte, and it is more desirable to contain the sulfide-based solid electrolyte in all of the positive electrode, the negative electrode, and the solid electrolyte layer.

For the solid electrolyte layer, 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, dried, and if necessary, pressure molding such as press treatment is performed. It can be formed by doing.

As for the solvent used for the composition for forming the solid electrolyte layer, it is desirable to select a solvent that does not easily deteriorate the solid electrolyte, like the solvent used for the composition containing the positive electrode mixture, and the solvent for the composition containing the positive electrode mixture. It is preferable to use various solvents exemplified above, and it is particularly preferable to use a super-dehydrating solvent having a water content of 0.001% by mass (10 ppm) or less.

The thickness of the solid electrolyte layer is preferably 20 to 200 μm.

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

When forming the electrode body, it is preferable to perform pressure molding in a state where the positive electrode body, the negative electrode body, and the solid electrolyte layer are laminated from the viewpoint of increasing the mechanical strength of the electrode body. Further, the positive electrode (for example, a molded body of a pellet-shaped positive electrode mixture), the solid electrolyte layer, and the negative electrode (for example, a molded body of a pellet-shaped negative electrode mixture) can be integrated by the above-mentioned pressure molding. In this case, for example, a positive electrode mixture (or a negative electrode mixture) is formed, a solid electrolyte layer is formed on the formed body of the positive electrode mixture, and a negative electrode mixture is formed on the further formed solid electrolyte layer. By forming a body (or a molded body of a positive electrode mixture), an electrode body in which a positive electrode, a solid electrolyte layer, and a negative electrode are integrated may be used.

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

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

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

_{Next, 30 parts by mass of LiOH · H 2} O was added to the mixture, and the mixture was heated in air at 250 ° C. for 30 minutes using an evaporator to obtain a composite in which a lithium cobalt compound was supported on carbon black. This complex is put into a mixed aqueous solution having a volume ratio of 98% concentrated sulfuric acid, 70% concentrated nitric acid 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 to obtain carbon A. The resulting carbon A has an average particle diameter of _{28nm, I} D / I _G was 1.5.

Further, 0.1 g of the obtained carbon A: 0.1 g was added to 20 ml of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute and then left for 5 hours to precipitate a solid phase portion. After precipitation of the solid phase portion, the supernatant liquid is removed to dry the residual portion, the weight of the solid after drying is measured, and the amount reduced from the weight (0.1 g) of carbon A before treatment is calculated as that of the hydrophilic portion. It was weighted. The ratio of the weight of the hydrophilic portion to the weight of carbon A before the treatment was determined and found to be 14.5% by mass.

<Cathode preparation>
_{LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (positive electrode active material) whose surface is coated with an oxide containing Li and Nb with an average particle size of 4 μm, and a sulfide-based solid electrolyte (Li ₆ PS _5). Cl), carbon A, and graphene (carbon B) were mixed at a mass ratio of 75: 21.5: 2.3: 1.2 and kneaded well to prepare a positive electrode mixture. Next, 15 mg of the positive electrode mixture was placed in a powder molding die having a diameter of 10 mm and pressure-molded using a press to prepare a positive electrode made of a cylindrical positive electrode mixture molded body. Note that the graphene was used as the carbon _B, and 0.2 I D / _{I G,} had a portion of the 500nm long.

<Formation of solid electrolyte layer>
_{Next, 80 mg of a sulfide-based solid electrolyte (Li 6} PS ₅ Cl) was charged onto the positive electrode mixture molded body in the powder molding die, and pressure molding was performed using a press machine. A solid electrolyte layer was formed on the positive electrode mixture molded body.

<Formation of laminated electrode body>
As the negative electrode, a Li metal and an In metal were formed into a cylindrical shape and bonded together. This negative electrode was put onto the surface of the solid electrolyte layer in the powder molding die on the side opposite to the positive electrode, and pressure molding was performed using a press machine to prepare a laminated electrode body.

<Assembly of all-solid-state battery>
Using the laminated electrode body, an all-solid-state battery having a planar structure similar to that shown in FIG. 2 was produced. Laminated film A positive electrode current collector foil (SUS foil) and a negative electrode current collector foil (SUS foil) are placed laterally on the inner surface of the aluminum laminate film constituting the exterior body with a certain distance between them. I pasted them side by side. Each of the current collecting foils includes a main body portion facing the positive electrode side surface or the negative electrode side surface of the laminated electrode body, and a positive electrode external terminal 300 and a negative electrode external terminal 400 protruding from the main body portion toward the outside of the battery. The one cut into a shape having a portion was used.

The laminated electrode body is placed on the negative electrode current collecting foil of the laminated film outer body, and the laminated electrode body is wrapped with the laminated film outer body so that the positive electrode current collecting foil is arranged on the positive electrode of the laminated electrode body. The remaining three sides of the laminated film exterior body were sealed by heat fusion under vacuum to obtain an all-solid-state battery.

Example 2
A positive electrode mixture was prepared in the same manner as in Example 1 except that carbon B was changed to carbon nanotubes [“VGCF” (trade name) manufactured by Showa Denko Co., Ltd.], and the same as Example 1 except that this positive electrode mixture was used. A positive electrode was produced in the same manner, and an all-solid-state battery was produced in the same manner as in Example 1 except that the positive electrode was used. The carbon nanotubes used as carbon B had an _ID / _IG of 0.1 and had a portion having a length of 500 nm.

Comparative Example 1
The positive electrode mixture was prepared in the same manner as in Example 1 except that the ratio of the positive electrode active material, the solid electrolyte, and carbon A was changed to 75: 21.5: 3.5 by mass ratio without using carbon B. Was prepared, and a positive electrode was prepared in the same manner as in Example 1 except that this positive electrode mixture was used, and an all-solid-state battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
The positive electrode mixture was prepared in the same manner as in Example 1 except that the ratio of the positive electrode active material, the solid electrolyte, carbon A and carbon B was changed to 75: 21.5: 2.6: 0.9 in terms of mass ratio. A positive electrode was prepared in the same manner as in Example 1 except that this positive electrode mixture was used, and an all-solid-state battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 3
The positive electrode mixture was prepared in the same manner as in Example 1 except that the ratio of the positive electrode active material, the solid electrolyte, carbon A and carbon B was changed to 75: 21.5: 2.1: 1.4 in terms of mass ratio. A positive electrode was prepared in the same manner as in Example 1 except that this positive electrode mixture was used, and an all-solid-state battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

Each of the all-solid-state batteries of Examples and Comparative Examples was evaluated as follows ^{under pressure (1 t / cm 2).}

(Volume capacity measurement)
Each of the all-solid-state batteries of Examples and Comparative Examples is charged with a constant current at a current value of 0.05 C until the voltage reaches 3.68 V, and then is charged with a constant voltage until the current value reaches 0.01 C. The battery was discharged at a current value of 0.05 C until the voltage reached 1.88 V, and the discharge capacity (initial capacity) at that time was measured. Then, the obtained discharge capacity was divided by the volume of the positive electrode to obtain the volume capacity of each battery.

(Measurement of resistivity)
After the initial capacity measurement, each all-solid-state battery is charged with constant current and constant voltage under the same conditions as at the time of initial capacity measurement, and then at a current value of 0.05 C until the charging depth (SOC) reaches 50%. After discharging, it was allowed to rest for 1 hour. After that, for each battery, the voltage was measured after performing pulse discharge for 10 sec with a current value of 0.05 C, and the voltage obtained by subtracting the voltage drop attributable to the solid electrolyte layer and the negative electrode from the voltage difference before and after the pulse discharge. Was obtained, and DCR was calculated from the value.

Then, from the obtained DCR of each battery, the resistivity of each battery was calculated using the following formula.
ρ = DCR × (s / t)

In the above formula, ρ: resistivity, t: thickness of the laminated electrode body (cm), S: area of the laminated electrode body in a plan view (cm ² ).

It can be said that the smaller the resistivity obtained by this method, the better the output characteristics of the all-solid-state battery (the larger the capacity at the time of large current discharge).

The above evaluation results are shown in Table 1 together with the compositions of carbon A and carbon B used in the positive electrode mixture. In Table 1, the volume capacity of each battery is shown as a relative value when the value of the battery of Comparative Example 1 is 100, and the resistivity of each battery is the value of the battery of Comparative Example 1. It is shown as a relative value when it is set to 0.

As shown in Table 1, the all-solid-state batteries of Examples 1 and 2 having a positive electrode using carbon A and carbon B in an appropriate ratio as the conductive auxiliary agent have a positive electrode using only carbon A as the conductive auxiliary agent. Compared with the battery of Example 1, the volume capacity was large, the capacity was high, the resistivity was small, and the output characteristics were excellent.

The resistivity of the battery of Comparative Example 2 having a positive electrode in which the amount of carbon B is too small with respect to the amount of carbon A and the battery of Comparative Example 3 having a positive electrode in which the amount of carbon B is too large with respect to the amount of carbon A. Was large and the output characteristics were inferior.

1,100 All-solid-state battery 10 Positive electrode 20 Negative electrode 30 Solid electrolyte layer 40 Exterior can 50 Sealing can 60 Gasket 200 Electrode body 300 Positive electrode external terminal 400 Negative electrode external terminal 500 Laminate film exterior

Claims (5)

A positive electrode used for all-solid-state batteries
It has a molded body of a positive electrode mixture containing a positive electrode active material, a solid electrolyte and a conductive auxiliary agent.
The conductive auxiliary agent contains the following carbon A and carbon B, and contains the following carbon A and carbon B.
A positive electrode for an all-solid-state battery, wherein the content of carbon A in the positive electrode mixture is 3% by mass or less, and the amount of carbon B is 40 to 60 parts by mass with respect to 100 parts by mass of carbon A.
Carbon A: the ratio _I D / _{I G} of the signal intensity _{I G} of the D-band signal intensity _{I D} and G bands in the Raman spectrum is 1 or more, an average particle size of 10~100nm
Carbon B: the ratio _I D / _{I G} is less than 1 and the signal strength _{I G} of the D-band signal intensity _{I D} and G bands in the Raman spectrum, has a more portions 500nm length The positive electrode for an all-solid-state battery according to claim 1, wherein the content of the positive electrode active material in the positive electrode mixture is 70% by mass or more. When the total surface area of all the positive electrode active materials contained in the positive electrode mixture is S (cm ² ) and the carbon A content in the positive electrode mixture is Z (g), the relationship of Z / S <1. The positive electrode for an all-solid-state battery according to claim 1 or 2. The positive electrode for an all-solid-state battery according to any one of claims 1 to 3, wherein the content of the binder in the positive electrode mixture is 0 to 1% by mass. It is characterized by having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and having the positive electrode for an all-solid-state battery according to any one of claims 1 to 4 as the positive electrode. All-solid-state battery.

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