JP2019021435A - All-solid secondary battery - Google Patents

Abstract

To provide a safe and inexpensive all-solid secondary battery.SOLUTION: The all-solid secondary battery is provided that comprises: a positive electrode including a carbon material as a positive electrode active material; a negative electrode including a metal hydroxide as a negative electrode active material and further including a conduction aid and a hydroxide ion conductive solid electrolyte; and a separator provided between the positive electrode and the negative electrode and including a hydroxide ion conductive solid electrolyte.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an all solid state secondary battery.

  In recent years, lithium ion secondary batteries have been widely used in various applications such as mobile devices, automobiles, and stationary storage batteries. However, since a lithium ion secondary battery uses a flammable organic electrolyte, there is a risk of ignition due to manufacturing defects or overcharge, and an accident has actually occurred. As countermeasures, nickel-hydrogen batteries, which are water-based secondary batteries that do not use organic electrolytes, are used in part, but the volume capacity density and weight capacity density are inferior, and the material cost is high and the cost is low. There is a limit. Therefore, a cheaper nickel zinc secondary battery has also been developed.

  On the other hand, various secondary batteries that use lithium but do not use an organic electrolyte have been developed. For example, all-solid batteries have attracted attention, and among them, the performance of lithium all-solid batteries using sulfide solid electrolytes has increased. However, there is a risk that sulfides react with moisture to generate hydrogen sulfide or burn when exposed to the atmosphere. An all-solid battery using an oxide solid electrolyte has been studied, but has not yet achieved sufficient performance.

A safe and inexpensive secondary battery does not yet exist in the world, and it has been reported that graphite intercalates hydroxide ions (OH ⁻ ) between various layers as various studies are being carried out (non- Patent Document 1 (Asuka Iizuka, Junpei Miyazaki, Tomokazu Fukuzuka and Takeshi Abe, “Synthesis of Acceptor-Type Graphite Intercalation Compounds in Alkaline Mixed Aqueous Solution (2)”, Abstracts of the 83rd Annual Meeting of the Electrochemical Society, 1P01, 20163 (March 23)). Specifically, when a voltage of 1.1 V was applied between a graphite sheet (working electrode) and carbon paper (counter electrode) using Hg / HgO as a reference electrode, insertion of OH ⁻ between the graphite layers was confirmed. It has been reported that graphite is expected as a positive electrode of an aqueous secondary battery.

  By the way, in recent years, the use of hydroxide ion conductive inorganic solid electrolyte separators, particularly layered double hydroxide (LDH) separators, has been proposed in the fields of nickel zinc secondary batteries and air zinc secondary batteries. According to the hydroxide ion conductive inorganic solid electrolyte separator such as the LDH separator, it is possible to prevent the penetration of zinc dendrite extending from the negative electrode in the alkaline electrolyte while selectively allowing the hydroxide ions to permeate. The problem of short circuit between positive and negative electrodes due to zinc dendrite can be solved. For example, Patent Document 1 (International Publication No. 2016/076047) discloses a separator structure including an LDH separator fitted or bonded to a resin outer frame, and the LDH separator is a porous substrate. It is also disclosed that it is provided in the form of a composite material. Furthermore, Patent Document 2 (International Publication No. 2016/067884) discloses various methods for obtaining a composite material by forming an LDH dense film on the surface of a porous substrate. In this method, a starting material capable of giving a starting point for crystal growth of LDH is uniformly attached to the porous substrate, and the porous substrate is hydrothermally treated in the raw material aqueous solution to form the LDH dense film on the surface of the porous substrate. The process of making it form is included.

International Publication No. 2016/076047 International Publication No. 2016/067884

Asuka Iizuka, Junpei Miyazaki, Tomokazu Fukutsuka and Takeshi Abe, “Synthesis of Acceptor-Type Graphite Intercalation Compounds in Alkali Mixed Aqueous Solution (2)”, Proceedings of the 83rd Annual Meeting of the Electrochemical Society, 1P01, March 23, 2016

  As described above, Non-Patent Document 1 reports that graphite is expected as a positive electrode of an aqueous secondary battery. However, in an aqueous solution, water may be electrolyzed due to an overvoltage of the positive electrode. The electrolysis of water causes the battery container to expand in a sealed secondary battery, while the electrolyte solution decreases in an open secondary battery. For this reason, like other conventional aqueous secondary batteries, a device for dealing with the above problem is required.

  The present inventors have recently used an all-solid-state secondary battery capable of solving the problems associated with the above-described aqueous solution-based secondary battery by using a hydroxide ion-conducting solid electrolyte instead of an electrolyte as a hydroxide ion transfer medium. We obtained knowledge that secondary batteries could be provided. That is, a positive electrode including a carbon material such as graphite as a positive electrode active material, a negative electrode including a metal hydroxide, a conductive additive and a hydroxide ion conductive solid electrolyte, and a separator including a hydroxide ion conductive solid electrolyte; The knowledge that it can provide a safe and inexpensive all-solid-state secondary battery by combining them was obtained.

  Accordingly, an object of the present invention is to provide a safe and inexpensive all-solid secondary battery.

According to one embodiment of the present invention, a positive electrode including a carbon material as a positive electrode active material;
A negative electrode containing a metal hydroxide as a negative electrode active material, and further comprising a conductive additive and a hydroxide ion conductive solid electrolyte;
A separator provided between the positive electrode and the negative electrode and containing a hydroxide ion conductive solid electrolyte;
An all-solid secondary battery is provided.

It is a figure which shows notionally the all-solid-state secondary battery by this invention.

  FIG. 1 conceptually shows an all-solid secondary battery 10 according to the present invention. As shown in FIG. 1, the all solid state secondary battery 10 includes a positive electrode 12, a negative electrode 14, and a separator 16. The positive electrode 12 includes a carbon material as a positive electrode active material. The negative electrode 14 includes a metal hydroxide as a negative electrode active material, and further includes a conductive additive and a hydroxide ion conductive solid electrolyte. The separator 16 includes a hydroxide ion conductive solid electrolyte and is provided between the positive electrode 12 and the negative electrode 14. As described above, by using a hydroxide ion conductive solid electrolyte instead of an electrolyte as a hydroxide ion transfer medium, the all-solid-state secondary battery 10 capable of solving the problems associated with the above-described aqueous secondary battery is obtained. Can be provided. That is, a positive electrode 12 containing a carbon material such as graphite as a positive electrode active material, a negative electrode 14 containing a metal hydroxide, a conductive additive and a hydroxide ion conductive solid electrolyte, and a hydroxide ion conductive solid electrolyte. By combining with the separator 16, a safe and inexpensive all-solid secondary battery can be provided.

  The positive electrode 12 includes a carbon material as a positive electrode active material. That is, in the all solid state secondary battery 10 of the present invention, the carbon material functions as a positive electrode active material rather than as a conductive additive. The carbon material as the positive electrode active material is not particularly limited as long as it can insert and desorb hydroxide ions between layers. Therefore, the carbon material as the positive electrode active material is preferably graphite having a layered structure, and may be either graphite or amorphous carbon as long as it is layered. Further, it may be nanotube-like carbon or fullerene. That is, preferable examples of the carbon material include graphite, amorphous carbon, carbon nanotubes, fullerenes, and combinations thereof, and graphite is particularly preferable. The graphite may be either natural graphite or artificial graphite, and for example, a flexible graphite sheet (manufactured by Graftech) marketed under the product name of Graphofoil is preferably used. As the positive electrode active material, the carbon material may be in the form of particles or a sheet, and the form thereof is not particularly limited. When the carbon material is in a particulate form, a preferable average particle diameter of the positive electrode active material particles is 0.1 to 10 μm, and more preferably 1 to 5 μm.

  The carbon material as described above has electronic conductivity and intercalates hydroxide ions. For this reason, the positive electrode 12 does not necessarily need to contain a conductive support agent and a hydroxide ion conductive solid electrolyte. But the positive electrode 12 may contain the conductive support agent and / or the hydroxide ion conductive solid electrolyte. In this case, the conductive assistant and / or hydroxide ion conductive solid electrolyte for the positive electrode 12 is the same as the conductive assistant and / or hydroxide ion conductive solid electrolyte contained in the negative electrode 14 described later. Can be used.

The negative electrode 14 includes a metal hydroxide as a negative electrode active material. The metal hydroxide is not particularly limited as long as it can reversibly release and bond hydroxide ions, and various metal hydroxides can be used. Preferable examples of such metal hydroxides include hydroxides of at least one metal selected from Li, Na, K, Ca, Mg, Al, Zn, and Fe. Typical examples of these hydroxides include LiOH, KOH, Ca (OH) ₂ , Mg (OH) ₂ , Al (OH) ₃ , Zn (OH) ₂ , Fe (OH) ₃ , Fe (OH) _2. , And combinations thereof. A particularly preferred metal hydroxide is LiOH. These metal hydroxides are inexpensively available elements and are therefore particularly suitable for the realization of safe and inexpensive secondary batteries. For example, the charging reaction formula when LiOH is used as the positive electrode active material is as follows.
・ Negative electrode: LiOH + e ⁻ → Li + OH ⁻
・ Positive electrode: xC + OH ⁻ → C _x OH + e ⁻
(Where x is a positive real number, ie x> 0)

  Alternatively, the metal hydroxide as the negative electrode active material may be an oxide hydroxide or a layered double hydroxide (LDH). Examples of the oxide hydroxide as the negative electrode active material include AlO (OH), FeO (OH), NiO (OH) and the like. Examples of LDH as the negative electrode active material include Li—Al based LDH, Mg—Al based LDH, Mg—Fe based LDH, Ni—Ti based LDH, and the like. In the case of LDH, since the discharge product LDH has hydroxide ion conductivity, there is an advantage that the reaction proceeds to the inside of the negative electrode active material particles. As will be described later, LDH can also be used as the hydroxide ion conductive solid electrolyte contained in the negative electrode 14, but in this case, LDH as the negative electrode active material and LDH as the hydroxide ion conductive solid electrolyte are used. It is preferable that they are of different types. For example, it is preferable to select two types of LDH, that is, LDH that electrochemically reacts at a predetermined overvoltage and LDH that does not electrochemically react at the same overvoltage, and assign the roles to each LDH. That is, it is preferable to use LDH that electrochemically reacts at a predetermined overvoltage as the negative electrode active material and LDH that does not electrochemically react at the same overvoltage as the hydroxide ion conductive solid electrolyte.

  The metal hydroxide that is the negative electrode active material may be in the form of particles. In this case, since the discharge reaction is a reaction in which the metal particles return to the hydroxide, if a dense hydroxide is generated on the metal surface, the hydroxide ions do not reach the inside of the metal particles and the reaction cannot be performed. There is. Therefore, it is desired that the particles of the negative electrode active material are fine. Specifically, the preferable average particle diameter of the negative electrode active material particles is 0.1 to 5 μm, and more preferably 0.1 to 2 μm.

  The negative electrode 14 further includes a conductive additive and a hydroxide ion conductive solid electrolyte. That is, since the metal hydroxide that is the negative electrode active material is poor in electron conductivity and hydroxide ion conductivity, the negative electrode 14 includes the electron conductivity and the hydroxide ion conductive solid electrolyte. Gives hydroxide ion conductivity. From the viewpoint of improving hydroxide ion conductivity in the negative electrode 14, the hydroxide ion conductive solid electrolyte contained in the negative electrode 14 preferably forms a network in the negative electrode. Typically, such a network is formed by connecting hydroxide ion conductive solid electrolyte particles together. In addition, from the viewpoint of improving the conductivity in the negative electrode 14, it is preferable that the conductive additive contained in the negative electrode 14 forms a network in the negative electrode. Typically, such a network is formed by connecting conductive aid particles (eg, conductive carbon particles) to each other. Particularly preferred is a mixed state in which each of the hydroxide ion conductive solid electrolyte and the conductive auxiliary agent is in contact with the active material while forming a network.

  The conductive additive contained in the negative electrode 14 is preferably at least one selected from the group consisting of a carbon material, aluminum, and copper. Examples of the carbon material include various conductive carbons such as graphite, carbon black, carbon nanotube, and graphene. The conductive aid is preferably in the form of particles. It is preferable to mix negative electrode active material particles and conductive carbon particles. The average particle diameter of the conductive auxiliary agent particles is preferably 0.005 to 1 μm, more preferably 0.005 to 0.5 μm.

  The solid electrolyte contained in the negative electrode 14 is not particularly limited as long as it has hydroxide ion conductivity, and may be either an inorganic solid electrolyte or an organic solid electrolyte. Examples of hydroxide ion conductive inorganic solid electrolytes include layered double hydroxides (LDH) and layered perovskite oxides. LDH is most preferable because it is inexpensive and exhibits high hydroxide ion conductivity. On the other hand, examples of the hydroxide ion conductive organic solid electrolyte include anion conductive polymers. However, since anion conductive polymers may be deteriorated by hydroxide ions, it can be said that hydroxide ion conductive inorganic solid electrolytes such as LDH are preferable. The hydroxide ion conductive solid electrolyte or LDH is preferably in the form of particles. The preferable average particle diameter of the hydroxide ion conductive solid electrolyte particles or LDH particles is 0.1 to 5 μm, more preferably 0.1 to 2 μm.

  The separator 16 includes a hydroxide ion conductive solid electrolyte and is provided between the positive electrode 12 and the negative electrode 14. The separator 16 is a member necessary for preventing a short circuit between the positive electrode 12 and the negative electrode 14. That is, the separator 16 is a film-like, layer-like, or plate-like member that separates the positive electrode 12 and the negative electrode 14 so as to allow hydroxide ion conduction and not allow electronic conduction. This member may be dense or porous, and the structure is not limited as long as it does not contain an electron conductive substance. For example, the separator 16 may be a green compact layer in which hydroxide ion conductive solid electrolyte particles are deposited in a thin layer and pressed, or integrated by a technique such as heating or hydrothermal treatment. It may be a thing. In particular, since the secondary battery 10 of the present invention does not require the use of an electrolytic solution, no particular problem (for example, deterioration or collapse due to electrolyte penetration) occurs even when a green compact layer is used. Alternatively, a hydroxide ion conductive solid electrolyte formed into a film may be disposed as the separator 16. The hydroxide ion conductive solid electrolyte is not particularly limited as long as it is a solid electrolyte having hydroxide ion conductivity, but an inorganic solid electrolyte is preferable. Examples of the hydroxide ion conductive inorganic solid electrolyte include layered double hydroxide (LDH), layered perovskite oxide, and the like. LDH is most preferable because it is inexpensive and exhibits high hydroxide ion conductivity. In particular, as described above, LDH separators are known in the fields of nickel zinc secondary batteries and air zinc secondary batteries (see Patent Documents 1 and 2), and this LDH separator is used as the secondary battery 10 of the present invention. Also preferably used. This LDH separator may be a composite with a porous substrate as disclosed in Patent Documents 1 and 2, but in that case, pores are formed over the entire region in the thickness direction of the porous substrate. It is desirable that the inside be filled with LDH. By doing so, it is possible to smoothly exchange hydroxide ions with the positive electrode 12 and the negative electrode 14 in contact with the separator 16. Therefore, when there is a portion in the porous base material that is not filled with LDH, it is desirable to remove such a portion by cutting, polishing, or the like and use it as the separator 16.

  As described above, the hydroxide ion conductive solid electrolyte contained in the negative electrode 14 and the separator 16 is preferably a layered double hydroxide (LDH). In this case, from the viewpoint of improving battery characteristics by improving hydroxide ion conductivity, the hydroxide ion conductive solid electrolyte contained in the negative electrode 14 and the separator 16 is composed of a plurality of LDH particles connected to each other. preferable.

LDH has the following general formula:
^{_{M 2+ 1-x M 3+ x}} (OH) 2 A n- x / n · mH 2 O
^{(Wherein, M 2+} is a divalent ^{cation, M 3+} is a trivalent ^{cation, A n-n-valent} anion, x is 0.1 to 0.4, n is an integer of 1 or more, m is 0 or more Is)
However, the present invention is not limited to this and may be a hydroxide containing at least two types of valence cations. Therefore, a composition having three or more kinds of cations may be used. For example, LDH may have a composition generally called hydrotalcite composed of divalent Mg (ie, Mg ²⁺ ), trivalent Al (ie, Al ³⁺ ), and an anion of CO ₃ ²⁻ . Alternatively, the LDH may have a composition composed of divalent Ni (ie, Ni ²⁺ ), tetravalent or trivalent Ti (ie, Ti ⁴⁺ or Ti ³⁺ ), and trivalent Al (ie, Al ³⁺ ). Not limited to these, LDH may have any composition as long as hydroxide ion conductivity is acceptable.

  The hydroxide ion conductive solid electrolyte contained in the negative electrode 14 and the hydroxide ion conductive solid electrolyte contained in the separator 16 may be the same material or different materials. However, from the viewpoint of improving the electronic conductivity in the negative electrode 14 and improving the insulating property of the separator 16, the electronic conductivity of the hydroxide ion conductive solid electrolyte contained in the negative electrode 14 is the same as the hydroxide ion conductivity contained in the separator 16. It is preferably higher than the electronic conductivity of the conductive solid electrolyte. In particular, it is more preferable that the hydroxide ion conductive solid electrolyte contained in the negative electrode 14 has high electron conductivity, and the hydroxide ion conductive solid electrolyte contained in the separator 16 has as low electronic conductivity as possible.

  The all-solid-state secondary battery 10 of the present invention is preferably manufactured in a discharged state. That is, by using a carbon material such as graphite for the positive electrode 12, using a metal hydroxide for the negative electrode 14, and interposing the separator 16 between the positive electrode 12 and the negative electrode 14, the all-solid-state secondary battery 10 is in a discharged state. Can be manufactured.

When the negative electrode 14 and / or the separator 16 includes LDH powder, the battery constituent may be subjected to water vapor treatment. This is because the LDH powder has a property that the powders are connected to each other by the steam treatment in the compacted state, and thus the hydroxide ion conductivity can be increased by performing the steam treatment. As the steam treatment, any method in which high-temperature steam is brought into contact with an untreated material can be adopted. For example, the steam treatment can be preferably performed by placing water in the bottom of the autoclave, placing the non-treated product in a state where it is not immersed in water, sealing it, and heating it to 100 ° C. or higher.

Claims (7)

A positive electrode containing a carbon material as a positive electrode active material;
A negative electrode containing a metal hydroxide as a negative electrode active material, and further comprising a conductive additive and a hydroxide ion conductive solid electrolyte;
A separator provided between the positive electrode and the negative electrode and containing a hydroxide ion conductive solid electrolyte;
An all-solid-state secondary battery.   The all-solid-state secondary battery according to claim 1, wherein the carbon material as the positive electrode active material is at least one selected from the group consisting of graphite, amorphous carbon, carbon nanotubes, and fullerenes.   The all-solid-state secondary battery according to claim 1 or 2, wherein the hydroxide ion conductive solid electrolyte contained in the negative electrode and the separator is a layered double hydroxide (LDH).   The all-solid-state secondary battery as described in any one of Claims 1-3 whose said conductive support agent contained in the said negative electrode is at least 1 sort (s) selected from the group which consists of a carbon material, aluminum, and copper.   The all-solid-state secondary battery as described in any one of Claims 1-4 in which the said hydroxide ion conductive solid electrolyte contained in the said negative electrode forms the network in the said negative electrode.   The all-solid-state secondary battery as described in any one of Claims 1-5 in which the said conductive support agent contained in the said negative electrode forms the network in the said negative electrode. The all-solid-state secondary battery according to any one of claims 1 to 6, wherein the hydroxide ion conductive solid electrolyte contained in the negative electrode and the separator is composed of a plurality of LDH particles connected to each other. .

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