JP6978007B2 - Manganese secondary battery - Google Patents

Description

The present invention relates to a manganese secondary battery.

Manganese dioxide (MnO ₂ ) is widely used in manganese batteries. Manganese dioxide has the advantage of being an inexpensive positive electrode material. However, since manganese dioxide cannot be reversibly charged and discharged, all of the commercialized manganese batteries remain in the primary battery. That is, manganese secondary batteries such as manganese-zinc secondary batteries have not been commercialized.

On the other hand, a layered double hydroxide containing Mn is known. For example, in Non-Patent Document 1 (Chihiro Obayashi et al., "Preparation of the Electrochemically Precipitated Mn-Al LDHs and Their Electrochemical Behaviors", Electrochemistry, 80 (11), pp.879-882 (2012)), Mn A layered double hydroxide (Mn-Al-LDH) containing Al as a constituent element has been disclosed, and its electrochemical properties have been reported.

By the way, in the field of zinc secondary batteries, a layered double hydroxide (LDH) separator having ^{hydroxide ion (OH −) conductivity has been proposed.} For example, Patent Document 1 (International Publication No. 2013/118561) discloses that an LDH separator is provided between a positive electrode and a negative electrode in a nickel-zinc secondary battery for the purpose of preventing a short circuit due to zinc dendrite. Further, Patent Document 2 (International Publication No. 2016/076047) discloses a separator structure including an LDH separator compounded with a porous substrate, and the LDH separator is gas impermeable and / or. It is disclosed that it has a high degree of density enough to have water impermeableness.

International Publication No. 2013/118561 International Publication No. 2016/076047

Chihiro Obayashi et al., "Preparation of the Electrochemically Precipitated Mn-Al LDHs and Their Electrochemical Behaviors", Electrochemistry, 80 (11), pp.879-882 (2012)

The present inventors have now found that by using Mn-based layered double hydroxide (Mn-LDH) for the positive electrode, charging and discharging can be performed reversibly, and therefore a manganese secondary battery can be realized. Got

Therefore, an object of the present invention is to realize a manganese secondary battery by using a manganese-based positive electrode material which is inexpensive and rich in elemental resources.

According to one aspect of the present invention, there is provided a manganese secondary battery including a positive electrode containing a Mn-based layered double hydroxide (Mn-LDH), a negative electrode, and an electrolytic solution containing an aqueous alkali metal hydroxide solution. Will be done.

It is a figure which shows one aspect of the manganese secondary battery of this invention. 6 is an SEM image of the Mn-Al-LDH powder produced in Example 1 taken at a magnification (20,000 times) suitable for observing primary particles. 6 is an SEM image of the Mn-Al-LDH powder produced in Example 1 taken at a magnification (40,000 times) suitable for observing primary particles. 6 is an SEM image of the Mn-Al-LDH powder produced in Example 1 taken at a magnification (5000 times) suitable for observing secondary particles. 6 is an SEM image of the Mn-Al-LDH powder produced in Example 1 taken at a magnification (5000 times) suitable for observing secondary particles. It is a graph which shows the charge / discharge characteristic in the reversibility evaluation performed in Example 1. 6 is an SEM image of the Ni-Mn-Al-LDH powder produced in Example 7 taken at a magnification (20,000 times) suitable for observing primary particles. 6 is an SEM image of the Ni-Mn-Al-LDH powder produced in Example 7 taken at a magnification (40,000 times) suitable for observing primary particles. 6 is an SEM image of the Ni-Mn-Al-LDH powder produced in Example 7 taken at a magnification (5000 times) suitable for observing secondary particles. 6 is an SEM image of the Ni-Mn-Al-LDH powder produced in Example 7 taken at a magnification (5000 times) suitable for observing secondary particles.

FIG. 1 conceptually shows a manganese secondary battery according to the present invention. As shown in FIG. 1, the manganese secondary battery 10 includes a positive electrode 12, a negative electrode 14, and an electrolytic solution 16. The positive electrode 12 contains a Mn-based layered double hydroxide (Mn-LDH). The electrolytic solution 16 contains an aqueous alkali metal hydroxide solution. According to such a configuration, by using Mn-LDH for the positive electrode, charging and discharging can be performed reversibly, and therefore a manganese secondary battery can be realized. As described above, although manganese dioxide is an inexpensive positive electrode material, it has been difficult to commercialize a manganese secondary battery because it cannot be reversibly charged and discharged. However, according to the present invention, it is inexpensive and also in terms of elemental resources. A manganese secondary battery can be realized by using abundant manganese-based positive electrode materials.

The positive electrode 12 contains Mn-LDH. Mn-LDH is a layered double hydroxide (LDH) containing Mn as a constituent element. That is, as is generally known, LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers. The basic hydroxide layer is mainly composed of metal elements (typically metal ions) and OH groups. Intermediate layer of LDH is composed of anionic and _{H 2} O. The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anions in LDH contain OH ⁻ and / or CO ₃ ^2- . Therefore, Mn-LDH contains Mn or its ions as a part of the metal element constituting the hydroxide basic layer.

Mn-LDH preferably has a particulate morphology. Since it is in the form of particles, the surface area increases and it becomes possible to cope with a large current discharge. The particulate form of Mn-LDH preferably has an average primary particle size of 0.1 to 3 μm, more preferably 0.1 to 1 μm, still more preferably 0.1 to 0.7 μm, and particularly preferably 0. It is 1 to 0.5 μm. Since LDH generally has poor conductivity, it is considered that the particulate form (particularly the one having a small primary particle size as described above) is more reactive than the film-like microstructure. In the present specification, the primary particle size is the longest distance of the diameter of Mn-LDH primary particles (plate-like particles), and is observed with a scanning electron microscope (SEM) at a magnification (for example, 40,000 times) at which the primary particles can be observed. , Can be measured using the length measurement function of SEM software. Further, the average primary particle size shall be measured for 10 primary particles per field of view, and the average value of the primary particle size for two fields of view (that is, a total of 20 primary particles) shall be calculated. It is desirable to decide.

It is preferable that Mn-LDH also contains Al as a constituent element. That is, Mn-LDH is preferably Mn-Al-LDH containing Mn and Al. In this case, the metal elements constituting the hydroxide basic layer of LDH contain Mn and Al. This facilitates the production of Mn-Al-LDH powder having a desired composition, and can improve the discharge capacity when used for the positive electrode 12 of the manganese secondary battery 10. From these viewpoints, the molar ratio of Al / (Mn + Al) is preferably 0.15 to 0.85, more preferably 0.25 to 0.80, still more preferably 0.25 to 0.75, and particularly preferably 0.25 to 0.75. It is 0.30 to 0.70. Within these ranges, the discharge capacity can be further improved when used for the positive electrode 12 of the manganese secondary battery 10 such as a manganese-zinc secondary battery.

The method for producing Mn-Al-LDH powder is not particularly limited, but for example, Mn-Al-LDH powder can be preferably produced by the following procedure.
1) Mn (II) metal salt and Al (III) metal salt are added in an arbitrary ratio to distilled water, mixed, and bubbled with an inert gas to degas dissolved oxygen to obtain a metal ion solution. .. As the metal salt, any metal salt such as chloride and nitrate can be used.
2) Degas the dissolved oxygen by bubbling the alkaline solution with an inert gas.
3) The metal ion solution obtained in 1) above is placed in an oil bath at 130 ° C., and the alkaline solution of 2) above is added dropwise to pH = 11.0 while stirring under an inert atmosphere to form an LDH precipitate. Precipitate.
4) The solution containing the LDH precipitate is subjected to centrifugation to recover the LDH precipitate, washed with water, further washed with ethanol, and then dried in vacuum at 80 ° C. to obtain Mn-Al-LDH powder.

It is more preferable that Mn-LDH further contains Ni as a constituent element in addition to Al. That is, Mn-LDH is more preferably Ni-Mn-Al-LDH containing Mn, Al and Ni. In this case, the metal elements constituting the hydroxide basic layer of LDH contain Mn, Al and Ni. In this case, the molar ratio of Al / (Ni + Mn + Al) is preferably 0.15 to 0.85, more preferably 0.15 to 0.50, still more preferably 0.15 to 0.40, and particularly preferably 0. It is 20 to 0.30. The molar ratio of Ni / (Ni + Mn + Al) is preferably 0.15 to 0.85, more preferably 0.15 to 0.70, still more preferably 0.15 to 0.50, and particularly preferably 0.20. ~ 0.50. Within these ranges, the discharge capacity can be further improved when used for the positive electrode 12 of the manganese secondary battery 10 such as a manganese-zinc secondary battery.

The method for producing the Ni-Mn-Al-LDH powder is not particularly limited, but for example, the Ni-Mn-Al-LDH powder can be preferably produced by the following procedure.
1) A metal salt of Ni (II), a metal salt of Mn (II) and a metal salt of aluminum (III) are added to distilled water in an arbitrary ratio and mixed to obtain a metal ion solution. As the metal salt, any metal salt such as chloride and nitrate can be used.
2) Mix ethylene glycol, aqueous ammonia and sodium carbonate solution to obtain a mixed solvent.
3) Mix the mixed solvent of 2) and the metal ion solution of 1), put the mixed solution in a pressure-resistant container, bubbling with an inert gas, and then seal the pressure-resistant container.
4) The mixed solution in the pressure-resistant container is heated at 120 to 200 ° C. (for example, 170 ° C.) for 10 to 30 hours (for example, 18 hours) and naturally cooled to room temperature.
5) The obtained precipitate is recovered by centrifugation, washed with degassed acetone, and then vacuum dried to obtain Ni-Mn-Al-LDH powder.

The negative electrode 14 is not particularly limited as long as it has characteristics that can be charged and discharged in combination with the positive electrode 12 and the electrolytic solution 16. Preferred examples of the active material contained in the negative electrode 14 include zinc and / or zinc oxide, a hydrogen storage alloy, iron, and cadmium, and more preferably zinc and / or zinc oxide. When the negative electrode 14 contains zinc and / or zinc oxide, the manganese secondary battery 10 becomes a manganese zinc secondary battery. Zinc may be contained in any form of zinc metal, zinc compound and zinc alloy as long as it has an electrochemical activity suitable for the negative electrode. Preferred examples of the negative electrode material include zinc oxide, zinc metal, calcium zincate and the like, but a mixture of zinc metal and zinc oxide is more preferable. The negative electrode 14 may be formed in the form of a gel, or may be mixed with the electrolytic solution 16 to form a negative electrode mixture. The shape of the negative electrode material is not particularly limited, but it is preferably in the form of powder, which increases the surface area and makes it possible to cope with a large current discharge.

The electrolytic solution 16 contains an aqueous alkali metal hydroxide solution. That is, the aqueous solution containing the alkali metal hydroxide is used as the electrolytic solution 16 (for example, the positive electrode electrolytic solution 16a and the negative electrode electrolytic solution 16b). Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide and the like, but potassium hydroxide is more preferable.

The electrolytic solution 16 may include a positive electrode electrolytic solution 16a in which the positive electrode 12 is immersed and a negative electrode electrolytic solution 16b in which the negative electrode 14 is immersed. In particular, the electrolytic solution 16 is preferably separated into a positive electrode electrolytic solution 16a and a negative electrode electrolytic solution 16b. This configuration is extremely advantageous in a manganese-zinc secondary battery. That is, Zn dissolved in the electrolytic solution may react with Mn of LDH to form heterolite on the electrode surface. In this respect, if the positive electrode electrolytic solution 16a and the negative electrode electrolytic solution 16b are separated, such a reaction between Mn and Zn can be suppressed, and the structure of Mn-LDH is effectively maintained in the electrolytic solution 16. be able to.

It is preferable that Al is dissolved in the positive electrode electrolyte 16a. By doing so, the elution of Al from the positive electrode 12 can be effectively suppressed, and the structural change of the positive electrode 12 to trimanganese tetraoxide can be effectively prevented. The concentration of Al dissolved in the positive electrode electrolyte 16a is preferably 0.02 to 1.5 mol / L, more preferably 0.02 to 1.2 mol / L, and further preferably 0.05 to 1.0 mol. / L.

On the other hand, it is preferable to add a zinc compound such as zinc oxide or zinc hydroxide to the negative electrode electrolytic solution 16b in order to suppress the self-dissolution of zinc and / or zinc oxide.

The positive electrode electrolytic solution 16a and the negative electrode electrolytic solution 16b may be mixed with the positive electrode 12 and / or the negative electrode 14 and exist in the form of a positive electrode mixture and / or a negative electrode mixture. Further, the electrolytic solution may be gelled in order to prevent leakage of the electrolytic solution.

When the electrolytic solution 16 is separated into a positive electrode electrolytic solution 16a and a negative electrode electrolytic solution 16b, the positive electrode 12 and the positive electrode electrolytic solution 16a are watered by the negative electrode 14 and the negative electrode electrolytic solution 16b and the layered double hydroxide (LDH) separator 28. It is preferable to be isolated so that the oxide ion can be conducted. As described above, the LDH separator 28 is known as a dense separator having hydroxide ion conductivity in the field of zinc secondary batteries, and a preferred embodiment thereof will be described below.

The LDH separator 28 is a ceramic separator containing a layered double hydroxide (LDH), and separates the positive electrode 12 and the negative electrode 14 so that hydroxide ions can be conducted. The preferred LDH separator 28 has gas impermeable and / or water impermeable. In other words, the LDH separator 28 is preferably densified to have gas impermeableness and / or water impermeableness. In addition, as described in Patent Document 2 (International Publication No. 2016/076047), "having gas impermeable" in the present specification means an object to be measured in water (that is, LDH separator 28 and / or porous). It means that even if the helium gas is brought into contact with one surface side of the quality substrate 30) at a differential pressure of 0.5 atm, no bubbles are generated due to the helium gas from the other surface side. Further, as described in Patent Document 2 (International Publication No. 2016/076047), “having water impermeable” in the present specification means an object to be measured (for example, LDH film and / or a porous substrate). ) Means that water in contact with one side does not permeate the other side. That is, the fact that the LDH separator 28 has gas impermeableness and / or water impermeability means that the LDH separator 28 has a high degree of porosity that does not allow gas or water to pass through, and has water permeability. It means that it is not a porous film or other porous material. By doing so, the LDH separator 28 selectively passes only hydroxide ions due to its hydroxide ion conductivity, and can exhibit a function as a battery separator. Therefore, the configuration is extremely effective in physically preventing the penetration of the separator by the zinc dendrite generated and propagating from the negative electrode 14 during charging to prevent a short circuit between the positive and negative electrodes. However, it goes without saying that the LDH separator 28 may be composited with the porous base material 30 as shown in FIG. In any case, since the LDH separator 28 has hydroxide ion conductivity, the positive electrode 12 and the negative electrode enable efficient transfer of the required hydroxide ion between the positive electrode electrolytic solution 16a and the negative electrode electrolytic solution 16b. The charge / discharge reaction in No. 14 can be realized.

The LDH separator 28 contains layered double hydroxides (LDH) and is preferably composed of LDH. As described above, LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers. The basic hydroxide layer is mainly composed of metal elements (typically metal ions) and OH groups. Intermediate layer of LDH is composed of anionic and _{H 2} O. The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anions in LDH contain OH ⁻ and / or CO ₃ ^2- . LDH also has excellent ionic conductivity due to its unique properties. In general, LDH is M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · mH ₂ O (in the formula, M ²⁺ is a divalent cation and M ³⁺ is a trivalent cation. is a ^{cation, a n-is} the n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, m is the base composition formula is 0 or more) It is known as a representative. In the above basic composition formula, M ²⁺ can be any divalent cation, but preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ can be any trivalent cation, with preferred examples being Al ³⁺ or Cr ³⁺ , more preferably Al ³⁺ . A ^n- may be any anion, preferred examples OH ^- and _CO ^{3 2-} and the like. Accordingly, in the above basic ^{formula, M 2+} comprises ^{Mg 2+, M 3+} comprises ^{Al 3+, A n-is} OH ^- and / or _CO preferably contains ^{3 2-.} n is an integer of 1 or more, but is preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is any number that means the number of moles of water and is a real number greater than or equal to 0, typically greater than or equal to 0 or greater than or equal to 1. However, the above-mentioned basic composition formula is merely a formula of the "basic composition" generally exemplified with respect to LDH, and the constituent ions can be appropriately replaced. For example, it may be replaced with some or all of the M ³⁺ tetravalent or higher valency cations in the basic formula, in which case, the anion A coefficient of ^n-x / n in the general formula May be changed as appropriate.

The LDH separator 28 may be in any form of a plate, a film or a layer, and when the LDH separator 28 is in a film or layered form, the film or layered LDH separator 28 is composited with the porous substrate 30. For example, it is preferably formed on or in the porous substrate 30. The plate-like form can secure sufficient hardness and more effectively prevent the penetration of zinc dendrites. On the other hand, the film-like or layered form, which is thinner than the plate-like form, has the advantage that the resistance of the separator can be significantly reduced while ensuring the minimum necessary hardness to prevent the penetration of zinc dendrites. be. The thickness of the plate-shaped LDH separator 28 is preferably 0.01 to 0.5 mm, more preferably 0.02 to 0.2 mm, still more preferably 0.05 to 0.1 mm. Further, the higher the hydroxide ion conductivity of the LDH separator 28 is, the more desirable it is, but it typically ^{has a conductivity of 10 -4} to ^-1 S / m. On the other hand, in the case of a film-like or layered form, the thickness is preferably 100 μm or less, more preferably 75 μm or less, still more preferably 50 μm or less, particularly preferably 25 μm or less, and most preferably 5 μm or less. With such a thin thickness, it is possible to realize a low resistance of the LDH separator 28. The lower limit of the thickness is not particularly limited because it varies depending on the application, but it is preferably 1 μm or more, more preferably 2 μm or more in order to secure a certain degree of hardness desired as a separator film or layer. be.

The LDH separator 28 is preferably composited with the porous base material 30. For example, the porous base material 30 may be provided on one side or both sides of the LDH separator 28. When the porous base material 30 is provided on one side of the LDH separator 28, the porous base material 30 may be provided on the surface of the LDH separator 28 on the negative electrode 14 side or on the surface of the LDH separator 28 on the positive electrode 12 side. May be good. It goes without saying that the porous substrate 30 has water permeability and therefore the positive electrode electrolyte 16a and the negative electrode electrolyte 16b can reach the LDH separator 28, but the presence of the porous substrate 30 causes LDH. It is also possible to more stably retain the hydroxide ion on the separator 28. Further, since the strength can be imparted by the porous base material 30, the LDH separator 28 can be thinned to reduce the resistance. Further, a dense film or a dense layer of LDH can be formed on or in the porous substrate 30. When a porous base material is provided on one side of the LDH separator 28, a method of preparing a porous base material and forming LDH on the porous base material can be considered. On the other hand, when the porous base material is provided on both sides of the LDH separator 28, it is conceivable to sandwich the LDH raw material powder between the two porous base materials to perform densification. Although the porous substrate 30 is provided over the entire surface of one side of the LDH separator 28 in FIG. 1, it may be provided only on a part of one side of the LDH separator 28 (for example, a region involved in the charge / discharge reaction). .. For example, when LDH is formed in a film or layer on or in the porous substrate 30, the porous substrate 30 is provided over the entire surface of one side of the LDH separator 28 due to the manufacturing method thereof. Is typical. On the other hand, when LDH is formed into a self-supporting plate shape (which does not require a base material), the porous base material 30 is retrofitted only to a part of one side of the LDH separator 28 (for example, a region involved in a charge / discharge reaction). Alternatively, the porous base material 30 may be retrofitted over the entire surface of one side.

When the porous base material 30 is provided on one side of the LDH separator 28, the LDH separator 28 may be provided on either the positive electrode 12 side or the negative electrode 14 side of the porous base material 30. However, it is preferable that the LDH separator 28 is provided on the negative electrode 14 side of the porous base material 30. By doing so, it is possible to more effectively suppress the peeling of the LDH separator 28 from the porous substrate 30. That is, when zinc dendrites derived from the negative electrode 14 grow and reach the LDH separator 28, the stress that can be generated due to the growth of the zinc dendrites acts in the direction of pressing the LDH separator 28 against the porous substrate 30. As a result, the LDH separator 28 is less likely to peel off from the porous substrate 30.

The porous substrate 30 is preferably composed of at least one selected from the group consisting of ceramic materials, metal materials, and polymer materials, more preferably ceramic materials and / or polymer materials, and even more preferably. It is a polymer material. The porous substrate is more preferably composed of a ceramic material. In this case, preferred examples of the ceramic material include alumina, zirconia, titania, magnesia, spinel, calcia, cordylite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, and any combination thereof, which is more preferable. Is alumina, zirconia, titania, and any combination thereof, particularly preferably alumina and zirconia, and most preferably alumina. When these porous ceramics are used, it is easy to form the LDH separator 28 having excellent denseness. Preferred examples of metallic materials include aluminum, zinc, and nickel. Preferred examples of the polymer material are polystyrene, polyether sulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrophilized fluororesin (tetrafluororesin: PTFE, etc.), cellulose, nylon, polyethylene and any combination thereof. Can be mentioned. It is more preferable to appropriately select a material having excellent alkali resistance as resistance to the electrolytic solution of the battery from the various preferable materials described above.

Preferably, the LDH separator 28 is composed of an aggregate of a plurality of LDH plate-like particles, and the plurality of LDH plate-like particles have the surface of the porous base material 30 (ignoring the fine irregularities due to the porous structure). It is oriented so as to intersect vertically or diagonally with the main surface of the porous substrate when observed macroscopically to the extent possible. The LDH separator 28 may be incorporated at least partially in the pores of the porous substrate 30, and in that case, LDH plate-like particles may also be present in the pores of the porous substrate 30.

The method for producing the LDH separator 28, for example, the LDH separator 28 composited with the porous substrate 30, is not particularly limited, and the LDH separator 28 is produced by referring to already known methods for producing LDH separators (for example, Patent Documents 1 and 2). be able to.

The present invention will be described in more detail with reference to the following examples.

Example 1
(1) Preparation of Mn-Al-LDH powder Mn-Al-LDH having Mn: Al = 2: 1 was prepared by the following procedure. Distilled water 100ml manganese chloride (II) 4 hydrate _(MnCl 2 · _4H 2 O, manufactured by Kishida Chemical Co., Ltd., special grade) 10 mmol of aluminum chloride (III) 6-hydrate _(AlCl 3 · _6H 2 O, Kishida Chemical (Made by Co., Ltd., special grade) 5 mmol was added and mixed to obtain a metal ion solution. On the other hand, the 2M sodium hydroxide solution was bubbled with an inert gas to degas the dissolved oxygen. A metal ion solution was placed in an oil bath at 130 ° C., and the sodium hydroxide solution was added dropwise and reacted until the pH reached 11.0 while stirring under an inert atmosphere to precipitate a precipitate. The precipitate-containing solution thus obtained was subjected to centrifugation to recover the precipitate. The recovered LDH precipitate was washed with water, further washed with ethanol, and then dried in vacuum at 80 ° C. to obtain Mn-Al-LDH powder.

(2) SEM observation and particle size measurement The obtained Mn-Al-LDH powder was observed with a scanning electron microscope (SEM) (JSM-6610LV, manufactured by JEOL Ltd.). 2A and 2B show SEM images of LDH powder taken at magnifications (20,000 times and 40,000 times) suitable for primary particle observation. As shown in FIGS. 2A and 2B, the primary particle size of the Mn-Al-LDH powder was 0.2 to 0.6 μm. The average primary particle size of the Mn-Al-LDH powder was 0.36 μm. The average primary particle size was measured by measuring the longest distance of the diameter of the plate-like particles in the SEM image. The magnification of the SEM image used for this measurement is 40,000 times, and the primary particle size is measured for 10 primary particles per field, and the primary particle size for 2 fields (that is, a total of 20 primary particles). The average value was calculated and used as the average primary particle size. The length measurement function of the SEM software was used for the length measurement.

Further, FIGS. 3A and 3B show SEM images of Mn-Al-LDH powder taken at a magnification (5000 times) suitable for observing secondary particles. From the results shown in FIGS. 3A and 3B, the secondary particle size of the Mn-Al-LDH powder was 0.5 to 5 μm.

(3) LDH structure retention in electrolytic solution (3a) Preparation of electrolytic solution As shown in Table 1, electrolytic solutions 1 to 5 having different Al concentrations were prepared.

(3b) Preparation and Immersion of Test Pieces A polytetrafluoroethylene solution (EC-TE-TFE manufactured by Toyo Technica Co., Ltd.) was mixed with Mn-Al-LDH powder to form a paste. The obtained paste was applied to a Cu mesh and molded into a sheet. This sheet was cut into a size of about 10 mm × 10 mm × 0.7 mm and used as a test piece. This test piece was immersed in 10 ml of each electrolytic solution at 70 ° C. for 1 week, washed with ion-exchanged water, and dried at 80 ° C. in an inert atmosphere.

(3c) Evaluation by X-ray diffraction X-ray diffraction measurement was performed to confirm to what extent the test piece after immersion in the electrolytic solution maintained the LDH structure. Specifically, using an X-ray diffractometer (Rigaku Co., Ltd., RINT TTR III), an XRD profile of the test piece is obtained under the measurement conditions of voltage: 50 kV, current value: 300 mA, and measurement range: 10 to 70 °. rice field. _{As a result, trimanganese tetraoxide (Mn 3} O ₄ ) was generated as a different phase in the test piece immersed in the electrolytic solution 4 (KOH aqueous solution), and the different phase was generated in the test piece immersed in the electrolytic solution 5 (Zn saturated KOH aqueous solution). It was found that heterolite (Znmn ₂ ^{+ 3} O _{4) was formed.} In each of the different phases, the strongest line peak in the XRD profile was present near 2θ = 36 °. From the XRD profile, the LDH (003) reflection peak value (2θ = about 11 °) and the heterogeneous strongest peak value due to _{trimanganese tetraoxide (Mn 3} O ₄ ) or heterolite (Zn _{Mn 2} ^{+ 3} O _{4) (Zn Mn 2 + 3 O 4).} 2θ = about 36 °) was read. The ratio of the out-of-phase strongest line peak value to the (003) reflection peak value of LDH was obtained, and the degree to which the LDH structure was maintained was used as an index, and the determination was made according to the following evaluation criteria.
-Evaluation A: It was judged that there was no abnormality.
-Evaluation B: It was determined to be a mixed phase of LDH and a different phase.
-Evaluation C: It was judged that only the phase was different.

(4) Evaluation of reversibility (4a) Preparation of electrode Mn-Al-LDH powder and acetylene black (AB) are mixed at a weight ratio of 20:80, polytetrafluoroethylene (PTFE) is added and kneaded, and then a sheet is obtained. It was molded into a shape. The obtained sheet was pressed on nickel foam to prepare an LDH electrode.

(4b) Preparation of electrochemical cell An electrochemical cell using an LDH electrode as a working electrode (WE), a Pt electrode as a counter electrode (CE), Hg / HgO as a reference electrode (RE), and a 6 mol / L KOH solution as an electrolytic solution. Was configured.

(4c) Charge / discharge test A charge / discharge test was performed on the obtained electrochemical cell. In the charge / discharge test, 0Z0-A19 manufactured by Interface was used, and charging and discharging were repeated at a current density of 50 mA / g. The charging time was 10 hours and the cutoff was 0 to 0.7V. The obtained charge / discharge curve was as shown in FIG.

(5) Manganese-zinc secondary battery preparation and evaluation (5a) Electrode preparation Mn-Al-LDH powder and acetylene black (AB) are mixed at a weight ratio of 20:80, and polytetrafluoroethylene (PTFE) is added. After kneading, it was formed into a sheet. The obtained sheet was pressed on nickel foam to prepare an LDH electrode.

(5b) Preparation of Zinc Oxide Secondary Battery LDH electrode as positive electrode, Zn-ZnO electrode (including a mixture of zinc metal and zinc oxide) as negative electrode, and zinc oxide saturated and dissolved in 6M KOH aqueous solution as electrolytic solution. It was used to construct a manganese-zinc secondary battery.

(5c) Charge / discharge test A charge / discharge test was performed on the obtained manganese-zinc secondary battery. The charge / discharge test was performed at a 10-hour rate using a 580-inch Battery Test System manufactured by Toyo Corporation. The discharge side had a cutoff of 1.0 V. The measured discharge capacity at the 50th cycle is shown in Table 3 as a relative value with respect to the case where _{the MnO 2 positive electrode is used (Example 6 described later).}

Examples 2-5
A manganese-zinc secondary battery was prepared and evaluated in the same manner as in Example 1 except that the Mn—Al-LDH composition was changed so as to have the Mn: Al ratio (molar ratio) shown in Table 3. The results are as shown in Table 2. The average primary particle size of the Mn-Al-LDH powder was in the range of 0.1 to 3 μm.

Example 6 (comparison)
Manganese-zinc secondary batteries were prepared and evaluated in the same manner as in Example 1 except _{that MnO 2} powder was used instead of Mn-Al-LDH powder. The results are as shown in Table 3.

Example 7
(1) Preparation of Ni-Mn-Al-LDH powder A Ni-Mn-Al-LDH powder having Ni: Mn: Al = 2: 1: 1 was prepared by the following procedure. Distilled water 10ml nickel chloride (II) 6 hydrate _(NiCl 2 · _6H 2 O, manufactured by Wako Pure Chemical Industries, Ltd., special grade) 4 mmol, manganese chloride (II) tetrahydrate _(MnCl 2 · _4H 2 O, Kishida chemical Co., Ltd., special grade) 2mmol and aluminum (III) chloride hexahydrate _(AlCl 3 · _6H 2 O, manufactured by Kishida chemical Co., Ltd., special grade) was added 2mmol were mixed to obtain a metal ion solution. Next, 20 ml of ethylene glycol, 15 ml of aqueous ammonia and 5 ml of a 1 M aqueous sodium carbonate solution were mixed to obtain a mixed solvent. The obtained mixed solvent and the metal ion solution were mixed to prepare a mixed solution. This mixed solution was placed in a pressure-resistant container, Ar bubbling was performed, and then the pressure-resistant container was sealed. The mixed solution in the pressure-resistant container was heated at 170 ° C. for 18 hours and naturally cooled to room temperature. The obtained precipitate was recovered by centrifugation. The recovered LDH precipitate was washed with degassed acetone and then vacuum dried to obtain a Ni-Mn-Al-LDH powder.

(2) SEM observation and measurement of particle size The obtained Ni-Mn-Al-LDH powder was SEM-observed in the same manner as in Example 1 (2). 5A and 5B show SEM images of Ni-Mn-Al-LDH powder taken at magnifications (20,000 times and 40,000 times) suitable for primary particle observation. As shown in FIGS. 5A and 5B, the primary particle size of the Ni-Mn-Al-LDH powder was 0.1 to 0.4 μm. The average primary particle size of the Ni-Mn-Al-LDH powder was 0.19 μm.

Further, FIGS. 6A and 6B show SEM images of Ni-Mn-Al-LDH powder taken at a magnification (5000 times) suitable for observing secondary particles. From the results shown in FIGS. 6A and 6B, the secondary particle size of the Ni-Mn-Al-LDH powder was 1 to 5 μm.

(3) LDH structure retention in electrolytic solution The LDH structure retention in the electrolytic solution of Ni-Mn-Al-LDH was evaluated in the same manner as in Example 1 (3). The results are as shown in Table 2. In particular, in the electrolytic solution 5 (KOH + Zn), unlike Mn-Al-LDH (Example 1), a result was obtained in which a different phase was less likely to be generated. It is presumed that this is because the structure of LDH was stabilized by the inclusion of Ni in LDH.

＜評価基準＞
・評価Ａ：異相が無いものと判定された。
・評価Ｂ：ＬＤＨと異相の混相であると判定された。
・評価Ｃ：異相のみと判定された。

<Evaluation criteria>
-Evaluation A: It was judged that there was no abnormality.
-Evaluation B: It was determined to be a mixed phase of LDH and a different phase.
-Evaluation C: It was judged that only the phase was different.

(4) Manganese-Zinc Secondary Battery Preparation and Evaluation The manganese-zinc secondary battery was prepared and evaluated in the same manner as in Example 1 except that Ni-Mn-Al-LDH powder was used instead of Mn-Al-LDH powder. Evaluation was performed. The results are as shown in Table 3.

Examples 8 and 9
Manganese-zinc secondary batteries were prepared and evaluated in the same manner as in Example 7 except that the Ni—Mn-Al-LDH composition was changed so as to have the Ni: Mn: Al ratio (molar ratio) shown in Table 3. gone. The results are as shown in Table 3.

Claims (9)

A positive electrode containing a Mn-based layered double hydroxide (Mn-LDH) , a negative electrode containing zinc and / or zinc oxide , and an electrolytic solution containing an aqueous alkali metal hydroxide solution are provided .
A manganese- zinc secondary battery in which the Mn-LDH is Mn-Al-LDH or Ni-Mn-Al-LDH having a molar ratio of Ni / (Ni + Mn + Al) of 0.15 to 0.70. The manganese-zinc secondary battery according to claim 1, wherein the Mn-LDH has a particulate form. The manganese-zinc secondary battery according to claim 2, wherein the Mn-LDH in the form of particles has an average primary particle size of 0.1 to 3 μm. The electrolytic solution contains a positive electrode electrolytic solution in which the positive electrode is immersed and a negative electrode electrolytic solution in which the negative electrode is immersed, and
The manganese- zinc secondary battery further comprises a layered double hydroxide (LDH) separator that sequesterably separates the positive electrode and the positive electrode electrolyte from the negative electrode and the negative electrode electrolyte so as to be able to conduct hydroxide ions. The manganese- zinc secondary battery according to any one of 1 to 3. The manganese- zinc secondary battery according to claim 4 , wherein Al is dissolved in the positive electrode electrolytic solution. The manganese- zinc secondary battery according to claim 5 , wherein the concentration of Al dissolved in the positive electrode electrolytic solution is 0.02 to 1.5 mol / L. The manganese-zinc secondary battery according to any one of claims 4 to 6 , wherein the LDH separator has gas impermeableness and / or water impermeableness. The manganese-zinc secondary battery according to any one of claims 4 to 7 , wherein the LDH separator is composited with a porous substrate. The LDH separator is composed of an aggregate of a plurality of LDH plate-like particles, and the plurality of LDH plate-like particles are oriented so that their plate surfaces intersect the surface of the porous substrate vertically or diagonally. The manganese- zinc secondary battery according to claim 8 , which is oriented.

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