JP2017059368A - Secondary battery and electrolytic solution for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an inexpensive secondary battery, which operates even at an atmospheric temperature, and works according to a novel energy-saving principle; and an electrolytic solution for such a secondary battery.SOLUTION: A secondary battery 1 according to the present invention comprises: a positive electrode 11 including a metal as a positive electrode active material; a negative electrode 12; and an electrolytic solution 13. The electrolytic solution 13 contains an electrolyte. The electrolyte includes an ionic compound MX (where M is a metal ion substance; and X is an anion substance). In the secondary battery 1, the ionic compound MX includes at least one sodium chloride, and it further includes an ionic compound MX in which an element lower than sodium in oxidation-reduction potential makes the metal ion substance M.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a secondary battery and an electrolytic solution such as a secondary battery, and relates to a secondary battery that operates based on a new charge / discharge reaction, and an electrolytic solution used in the secondary battery.

  Secondary batteries are used in various electronic devices such as portable devices, notebook computers, and portable devices. In particular, a lithium ion battery has a high energy density and a high voltage, and there is no so-called memory effect because the battery capacity gradually decreases when charged before being completely discharged during charging and discharging. It is often used as a power source for electronic devices.

Currently, as a measure to prevent global warming, efforts are being made to reduce CO ₂ emissions on a global scale. Under such circumstances, there is an urgent need to develop and popularize next-generation clean energy vehicles such as plug-in hybrid vehicles and electric vehicles that have low dependence on petroleum and can contribute to CO ₂ reduction. For example, lithium ion batteries are also expected as a driving force for such next-generation clean energy vehicles.

  Specifically, the lithium ion battery includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution (see, for example, Patent Document 1). The positive electrode is configured such that a mixture layer containing a positive electrode active material, a binder, and a conductive agent is provided on a current collector such as an aluminum foil. The negative electrode is configured by providing a current collector such as a copper foil with a mixture layer containing a negative electrode active material, a binder, and a conductive agent. Lithium transition metal composite oxides such as lithium cobaltate and lithium nickelate are used as the positive electrode active material, and graphite and various alloy materials are used as the negative electrode active material. In a lithium ion battery, during charging, lithium ions contained in the positive electrode active material are released (desorbed) from the positive electrode and inserted in the negative electrode. On the other hand, the reverse movement occurs during discharge. In the lithium ion battery, electric energy is created by repeating occlusion / release of lithium ions between the positive electrode and the negative electrode.

  However, the lithium transition metal composite oxide used in such a lithium ion battery is a special compound and has a drawback of being expensive.

  On the other hand, molten salt batteries such as zebra batteries have been proposed as secondary batteries other than lithium ion batteries. The zebra battery has a positive electrode made of nickel (Ni) and a negative electrode made of molten sodium (Na), and uses sodium aluminum chloride (melting point: about 160 ° C.) as an electrolyte and operates at a temperature of about 250 ° C.

  However, such a molten salt battery does not operate at room temperature and is not sufficient as an energy-saving secondary battery.

  In addition, as secondary batteries, techniques such as Patent Documents 2 to 4 have been proposed.

JP 2006-310010 A International Publication No. 2013/108309 International Publication No. 2010/073978 JP 2007-200966 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a secondary battery that is inexpensive, operates at room temperature, and operates on a new energy-saving principle, and an electrolyte for the secondary battery.

  (1) A first invention of the present invention includes a positive electrode containing a metal as a positive electrode active material, a negative electrode, and an electrolytic solution, and the electrolytic solution contains an electrolyte, and the electrolyte contains an ionic compound MX (M : Metal ionic substance, X: anionic substance), and at least one of the ionic compounds MX is sodium chloride, and the ionic compound MX is further contained in the electrolyte as the ionic compound MX. The secondary battery includes a compound having a metal ion substance M as an element having a low oxidation-reduction potential.

  (2) The second invention of the present invention is the secondary battery according to the first invention, wherein the sodium chloride as the ionic compound MX is provided in contact with the negative electrode as a solid in the electrolytic solution. .

  (3) The third invention of the present invention is the secondary battery according to the first or second invention, wherein the element having a lower oxidation-reduction potential than sodium is selected from calcium, barium, potassium, and lithium. It is.

  (4) A fourth aspect of the present invention is a secondary battery according to any one of the first to third aspects, wherein the negative electrode is made of a material that reduces and metalizes the metal ion substance M. is there.

  (5) According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the standard electrode potential of each of the metal constituting the positive electrode active material and the metal constituting the negative electrode is the ionicity. The secondary battery is larger than the standard electrode potential of the metal ion substance M constituting the compound MX.

  (6) According to a sixth aspect of the present invention, in any one of the first to fifth aspects, at least a part of the positive electrode or a surface of the positive electrode opposite to the electrolyte side is electrically conductive. It is a secondary battery provided with a substance.

  (7) According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the electrolyte contains an anionic substance relative to the anionic substance X constituting the ionic compound MX. The secondary battery includes a compound having a Lewis acidity stronger than that of the compound BX in which X and an ionic substance of metal B as the positive electrode active material are combined.

  (8) The eighth invention of the present invention is based on any one of the first to seventh inventions. (I) Anionic substance X dissociated from the ionic compound MX and ionization from the positive electrode active material during charging When the metal ionic substance B is bonded at the positive electrode, a compound precipitate BX is generated, and the metal ionic substance M dissociated from the ionic compound MX is reduced at the negative electrode, whereby the negative electrode collector The metal deposit is deposited on the electric body, and (II) upon discharge, the anionic substance X is ionized from the compound precipitate BX generated by the charging and returns to the electrolyte, and the compound precipitate The ionic substance of BX is ionized and returned to the metal by being reduced at the positive electrode, and the metal ionic substance M is ionized from the metal precipitate deposited on the negative electrode current collector by the charging. Back in the electrolyte Te, a secondary battery.

  (9) A ninth invention of the present invention is an electrolytic solution used for a secondary battery composed of a positive electrode containing a metal as a positive electrode active material, a negative electrode, and an electrolytic solution, containing an electrolyte, The electrolyte contains an ionic compound MX (M: metal ionic substance, X: anionic substance), at least one of the ionic compounds MX is sodium chloride, and the ionic compound MX is further sodium. An electrolyte solution for a secondary battery, characterized in that a compound containing a metal ion substance M as an element having a lower oxidation-reduction potential is contained.

  (10) According to a tenth aspect of the present invention, in the ninth aspect, the sodium chloride that is the ionic compound MX is a solid, and is an electrolyte for a secondary battery in contact with the negative electrode constituting the secondary battery. It is.

  According to the present invention, it is possible to provide a novel secondary battery that operates at a low temperature and operates at a normal temperature to save energy and operates on a new principle, and an electrolyte for the secondary battery. Further, according to the present invention, it is possible to suppress the generation of dendrites and to provide a highly safe secondary battery.

It is a figure for demonstrating the structure and operating principle of the secondary battery which concern on this invention. It is a figure which shows an example of a structure of the secondary battery which concerns on this invention. It is a figure which shows an example of the other structure of the secondary battery which concerns on this invention. It is a figure which shows an example of the other structure of the secondary battery which concerns on this invention. In the secondary battery which concerns on this invention, it is a figure for demonstrating the structure at the time of providing solid NaCl as an electrolyte layer in contact with a negative electrode, and an operation principle.

  Hereinafter, specific embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention.

<1. Secondary battery>
The secondary battery according to the present invention includes a positive electrode containing a metal as a positive electrode active material, a negative electrode, and an electrolytic solution. The electrolytic solution contains an electrolyte, and the electrolyte contains an ionic compound MX (M: Metal ion substance, X: anionic substance). In this secondary battery, at least one of the ionic compounds MX as an electrolyte is sodium chloride, and an element having a lower oxidation-reduction potential than sodium is included in the electrolyte as the ionic compound MX. A compound to be a metal ion substance M is further included.

  In the present specification, “metal” means a single metal and an alloy, and those single metals and alloys doped with other elements are included.

  Specifically, FIG. 1 is a schematic configuration diagram showing an example of the configuration of the secondary battery according to the present invention. The secondary battery 1 includes a positive electrode 11, a negative electrode 12, and an electrolyte solution 13.

  The positive electrode 11 is formed in a sheet shape as shown in FIG. 1, for example, and is composed of a positive electrode current collector (not shown) and a positive electrode active material bonded to the positive electrode current collector. Note that the positive electrode active material includes metal B.

  Similarly, the negative electrode 12 is formed in a sheet shape as shown in FIG. 1, and is made of, for example, a negative electrode current collector. Note that. In the secondary battery 1, the negative electrode 12 may not include the negative electrode active material. By not including the negative electrode active material, the negative electrode 12 can be thinned, and the size of the secondary battery 1 can be further reduced, and the energy density can be increased.

  The electrolytic solution 13 includes an electrolyte and a solvent that dissolves the electrolyte. In the secondary battery 1, the electrolyte contains an ionic compound MX (M: metal ion substance, X: anion substance). At least one of the ionic compounds MX is sodium chloride (NaCl), and the ionic material M includes a compound having an element having a lower redox potential than sodium as the metal ionic material M. In the electrolytic solution 13, when the ionic compound MX is an ionic liquid, the electrolytic solution 13 does not necessarily include a solvent.

  In the secondary battery 1 having such a configuration, for example, as shown in FIGS. 1 to 3, a charge and discharge reaction occurs, and the reaction is activated to produce electric energy.

That is, (I) at the time of charging, the anion substance X dissociated from the ionic compound MX and the ionic substance of the metal B ionized from the positive electrode active material contained in the positive electrode 11 are combined at the positive electrode 11, thereby forming a compound precipitate. BX generates. At the same, the dissociated metal ion material from ionic compound MX (positive ion material) M, by being reduced at the negative electrode 12, the metal deposit M _d.

On the other hand, at the time of (II) discharge, the anionic substance X is ionized from the compound precipitate BX generated at the positive electrode 11 by charging and returns to the electrolytic solution 13, and the metal B ionic substance is converted from the compound precipitate BX. The dissociated metal ion substance that has dissociated is returned to the metal B by being reduced by the positive electrode 11. On the other hand, metal deposit M _d precipitated generated at the negative electrode 12 by charging, anionic substance on the anode 12 without returning metal ion material M back into the electrolyte 13, or into the electrolyte 13 by ionization Combines with X to return to ionic compound MX.

  FIG. 1 is a diagram for explaining the configuration and operating principle of a secondary battery including an ionic compound MX, at least one of which is NaCl, as an electrolyte, and FIG. 2 specifically shows the ionic compound. It is a figure which shows the mode at the time of charging / discharging reaction of NaCl which is MX. FIG. 3 shows the configuration of the secondary battery and its operating principle when LiCl (ionic compound MX) is used as the electrolyte other than NaCl, provided as solid electrolyte in contact with the negative electrode 12 as the electrolyte layer 14. FIG.

  In the secondary battery 1 according to the present invention, charging and discharging are performed by such a new reaction mechanism without using an expensive active material. A part of the compound precipitate BX may be dissolved.

In particular, in the secondary battery 1 according to the present invention, at least one of the ionic compounds MX that is an electrolyte is NaCl, and an element having a lower oxidation-reduction potential than sodium is used as the metal ionic substance M as the ionic compound MX. Contains compounds such as LiCl. In such a secondary battery 1, sodium ions preferentially become metallic sodium and precipitate on the negative electrode 12 by the reaction mechanism described above, while LiCl and the like carry Cl ⁻ to the positive electrode 11 side. Since it acts as a medium, for example, it is possible to effectively suppress that Li ⁺ becomes metal Li and precipitates on the negative electrode 12 and becomes dendrite (acicular crystal growth product) due to excessive growth. it can. Thereby, generation | occurrence | production of a short circuit etc. can be prevented and it can be set as a highly safe secondary battery.

  Below, each structure of the secondary battery 1 is demonstrated more concretely.

<2. Positive electrode>
[Configuration of positive electrode]
The positive electrode 11 includes a positive electrode active material. The positive electrode active material is provided by being bonded to, for example, a sheet-like positive electrode current collector or by being applied to the positive electrode current collector. In addition, the positive electrode 11 itself may have a current collector and an active material.

  The positive electrode 11 contains the metal B as a positive electrode active material. The standard electrode potential of the metal B is larger than the standard electrode potential of the metal ion substance M constituting the ionic compound MX contained in the electrolyte, and does not spontaneously elute in the electrolyte solution 13. Specifically, as such a metal B, nickel (Ni) having a standard electrode potential of about −0.25 V or a metal nobler than the nickel (standard electrode potential of −0.25 V or more) is preferably mentioned. . For example, nickel (Ni, -0.25V), copper (Cu, + 0.340V), silver (Ag, + 0.799V), platinum (Pt, + 1.188V), gold (Au, + 1.520V), etc. It is done. Among these, nickel and copper are preferable from the viewpoint of cost and the like.

  When the positive electrode current collector is provided in the positive electrode 11, a material made of a material that does not cause an electrode reaction can be applied. Examples of such a positive electrode current collector include metals, conductive polymers, carbon, and the like, which are more precious than the metal B contained in the positive electrode active material. The positive electrode current collector is joined to the above-described positive electrode active material to constitute the positive electrode 11. In addition, a joining means and a joining aspect with a positive electrode active material are not specifically limited.

  The shape of the positive electrode 11 is not particularly limited, and may be, for example, a sheet shape or a granular shape, but is preferably a sheet shape. Here, the sheet shape does not limit the thickness, hardness, width, length, etc., for example, it means that it is formed into a rectangular shape having an arbitrary thickness with a metal foil, A layer can be formed. Moreover, it is not restricted to foil shape like metal foil, A film | membrane shape, a film shape, plate shape, etc. are also contained in the sheet-like concept. The positive electrode 11 may be porous. Further, the size and thickness of the positive electrode 11 are not particularly limited, and can be appropriately determined according to the desired size of the secondary battery 1.

  Further, a conductive material may be provided on at least a part of the positive electrode 11 or on the surface of the positive electrode 11 opposite to the electrolyte solution 13 side as shown in FIG. In the configuration illustrated in FIG. 4, the conductive material provided on the positive electrode 11 is described as “conductive material 15”. This conductive substance is provided so as to be in contact with the positive electrode 1 and acts like a current collector to supplement the current collecting function when most of the positive electrode 1 is used for the reaction. In particular, it can be suitably used when nickel or copper is used as the metal B contained in the positive electrode active material.

  The conductive substance may be provided on the entire surface (one surface) opposite to the electrolyte solution 13 side of the positive electrode 11 or may be provided on a part of the one surface. In particular, from the viewpoint of increasing the field where the ionic compound MX contained in the electrolyte in the electrolyte solution 13 and the metal B contained in the positive electrode active material directly react and fulfill the function as a current collector, It is preferable to be provided. For example, FIG. 4 shows an example in which the sheet-like conductive material 15 is provided on one side of the sheet-like positive electrode 11 in a laminated manner. As another example, although not shown, a large number of particles constituting the positive electrode 11 and a large number of particles of the conductive material may be mixed to form a sheet as a whole. Thus, a conductive material may be provided on at least a part of the positive electrode 11.

  The conductive substance is not particularly limited, and examples thereof include carbon such as acetylene black, ketjen black and graphite, a conductive polymer such as polyaniline, and a metal such as gold. This conductive substance is formed by mixing in a solvent such as NMP (N-methyl-2-pyrrolidone) containing a resin binder such as polyvinylidene fluoride to form a conductive paste, and applying the conductive paste to the positive electrode 11. Can do. Examples of the solvent include NMP, MEK (methyl ethyl ketone), IPA (isopropyl alcohol), water, and the like. The obtained conductive paste is applied on the positive electrode 11 and then dried to volatilize and remove all or most of it. be able to. Note that the conductive paste may contain a binder component that does not reduce the conductivity so much, and examples of the binder component include polyvinylidene fluoride, polyethylene oxide, and polyvinyl alcohol.

[Reaction mechanism at the positive electrode]
In the positive electrode 11, during charging, for example, as shown in FIGS. 1 and 2, the anionic substance X (for example, “Cl ⁻ ”) dissociated from the ionic compound MX (for example, “NaCl”) in the electrolytic solution 13, and the positive electrode 11 is combined with an ionic substance of metal B (for example, “Cu”) included in the positive electrode active material 11, and a compound precipitate BX (for example, “CuCl”) is generated on the positive electrode 11. That is, in the secondary battery 1, the ionic substance of the metal B combines with the anionic substance X to become the compound precipitate BX at the positive electrode 11, and the charged state is maintained by holding the compound precipitate BX on the positive electrode 11. . Therefore, the charged state is maintained for a long time by the ionic substance of the metal B. FIG. 2 shows an example when NaCl is used as the ionic compound MX.

For example, as shown in FIG. 2, when the metal B is Cu and the anionic substance X is Cl ⁻ , CuCl (copper chloride) or CuCl ₂ (cupric chloride) is added to the positive electrode 11 as the compound precipitate BX. Generate. Further, when the metal B is Ni and the anionic substance X is Cl ⁻ , NiCl ₂ (nickel chloride) is generated on the positive electrode 11 as the compound precipitate BX. And the produced | generated compound precipitate BX copper chloride and nickel chloride are hold | maintained as the compound precipitate BX by the effect | action of the copper or nickel which is the metal B, and a charged state is maintained.

  The compound precipitate BX such as copper chloride or nickel chloride generated on the positive electrode 11 may be partially or wholly dissolved in the electrolytic solution 13 while maintaining a charged state. By dissolving the compound precipitate BX in the electrolytic solution 13, the progress of the discharge reaction can be accelerated.

On the other hand, at the time of discharging, as shown in FIGS. 1 and 2, the anionic substance X (for example, “Cl ⁻ ”) is ionized and jumped out from the compound precipitate BX (for example, “CuCl”) generated in the positive electrode 11, Return to the electrolyte 13. Further, the ionic substance of the metal B is ionized from the compound precipitate BX (for example, “CuCl”), and the ionized substance of the metal B (for example, “Cu ion”) is reduced at the positive electrode 11 to be a metal (for example, “Cu”). with return to, Na ions ionized from the metal Na is a metal deposit M _d generated are reduced in the negative electrode 12 is returned to the electrolytic solution 13.

  In the positive electrode 11, a charging reaction and a discharging reaction occur by a new reaction mechanism different from the conventional one.

<3. Negative electrode>
[Configuration of negative electrode]
The negative electrode 12 is composed of at least a negative electrode current collector. The negative electrode 12 may include a negative electrode current collector and a negative electrode active material.

Negative electrode current collector constituting the negative electrode 12 does not naturally eluted into the electrolyte solution 13, it is precipitated as a metal deposit M _d by a reduction reaction of the metal ion material M of the ionic compound MX contained in the electrolyte 13 It is made of a material that can be used. The standard electrode potential of such a negative electrode current collector is larger than the standard electrode potential of the metal ion substance M constituting the ionic compound MX and does not spontaneously elute in the electrolyte solution 13.

  Specifically, the negative electrode current collector is made of nickel (Ni) having a standard electrode potential of −0.25 V or a metal that is nobler than the nickel (standard electrode potential is −0.25 V or more). For example, metals such as nickel (Ni, -0.25V), copper (Cu, + 0.340V), silver (Ag, + 0.799V), platinum (Pt, + 1.188V), gold (Au, + 1.520V) Among them, those made of nickel and copper are preferable from the viewpoint of cost and the like.

In the negative electrode 12, the metal ion material M dissociated from ionic compound MX at the time of charge would metal ion material M is generated deposited on the negative electrode current collector as metal deposit M _d generated by reduction . Specifically, Na ⁺ dissociated from NaCl which is the ionic compound MX contained in the electrolytic solution 13 is reduced to metal Na and deposited on the negative electrode current collector. In this regard, as in conventional lithium ion batteries, for example, a negative electrode active material such as carbon is included, and lithium ions released from the positive electrode active material by charging are stored in the negative active material carbon in an ionic state It is different from the embodiment. Note that “storage” means that the metal ion substance is not a metal, that is, becomes a compound in an ionic state.

  The shape of the negative electrode 12 is not particularly limited, and may be, for example, a sheet shape or a granular shape, but an electrolyte layer (for example, the electrolyte layer 14 in FIG. 3) using NaCl, which is one of the ionic compounds MX, as a solid. ) And the electrolyte layer is provided adjacent to the negative electrode, it is preferably a sheet-like negative electrode. The negative electrode 12 may be porous. Further, the size and thickness of the negative electrode 12 are not particularly limited, and can be appropriately determined according to the desired size of the secondary battery 1.

[Reaction mechanism at the negative electrode]
In the negative electrode 12, during charging, for example, as shown in FIGS. 1 and 2, Na, which is a metal ion substance M, is ionized from NaCl, which is an ionic compound MX in the electrolytic solution 13, to become metal ion Na ions. Na ions are precipitated by reduction on the negative electrode 12 on the negative electrode 12 as metal Na is metal deposit M _d. In the secondary battery 1, the ionic compound MX further includes a compound composed of an element having a lower oxidation reduction than sodium. However, since sodium has a higher oxidation reduction potential, the ionic compound MX is Metal Na based on the contained NaCl is preferentially deposited.

On the other hand, at the time of discharge, eluted metal Na is in the electrolyte 13 is a metal deposit M _d are deposited on the negative electrode 12 as a metal ion (e.g., "Na ions"), having gone out from the positive electrode 11 to ionize It combines with the anion Cl ion to return to the ionic compound MX (NaCl).

  In the negative electrode 12, a charging reaction and a discharging reaction occur by such a new reaction mechanism different from the conventional one.

Here, in the secondary battery 1 as described above, by charging the metal Na is generated deposited on the negative electrode 12, the negative electrode 12 before charging in advance, the metal Na and the same kind is a metal deposit M _d The metal M ′ may be disposed as a solid. By arranging the solid metal M ′ in this way, when the amount of precipitation of the metal Na on the negative electrode 12 at the time of charging, in particular, the initial charging is insufficient, the metal M ′ can be compensated. it can.

  As will be described in detail later, the negative electrode 12 may be provided with an electrolyte layer 14 made of NaCl, which is the ionic compound MX, as a solid (see FIG. 3). In this case, the electrolyte layer 14 made of NaCl may be mixed with a conductive material such as carbon particles.

<4. Electrolyte>
The electrolytic solution 13 contains an electrolyte and a solvent that dissolves the electrolyte. Further, the electrolyte contains an ionic compound MX (M: metal ion substance, X: anion substance).

  The ionic compound MX causes a charging reaction and a discharging reaction based on the above-described mechanism. In the secondary battery 1 according to the present invention, at least NaCl is included as the ionic compound MX as the electrolyte. Further, as the ionic compound MX, a compound in which an element having a lower redox potential than sodium is used as the metal ion substance M is included.

Specifically, the element having a lower redox potential than sodium is preferably selected from calcium (Ca), barium (Ba), potassium (K), and lithium (Li). Examples of the ionic compound MX in which the metal ion substance M is Li include, for example, inorganic lithium salts such as LiCl, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , and LiBr, LiB (C ₆ H ₅ ). ₄ , LiN (SO ₃ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiOSO ₂ CF ₃ , LiOSO ₂ C ₂ F ₅ , LiOSO ₂ C ₄ F ₉ , LiOSO ₂ C ₅ F ₁₁ , LiOSO ₂ C ₆ Examples thereof include organic lithium salts such as F ₁₃ and LiOSO ₂ C ₇ F ₁₅ .

For example, as shown in FIGS. 1 and 2, in the secondary battery 1, NaCl, which is at least one of the ionic compounds MX, is preferentially deposited on the negative electrode 12 as metallic sodium by the reaction mechanism described above. It becomes like this. On the other hand, in other ionic compounds MX containing Li or the like having a lower oxidation-reduction potential than that of sodium, for example, a reaction to Li ⁺ → Li (metal Li) is suppressed, and Cl ⁻ is conveyed to the positive electrode 11 side. To act as. By such an action, in the secondary battery 1, it is possible to effectively suppress that Li ⁺ becomes metal Li and precipitates on the negative electrode 12 and becomes dendrite due to excessive growth. In such a secondary battery 1, it is possible to prevent the occurrence of a short circuit or the like based on dendrite, and the secondary battery is highly safe.

  Further, in the secondary battery 1, it is preferable that the electrolyte layer 14 is formed of NaCl, which is the ionic compound MX, as a solid and is provided in contact with the negative electrode 12. FIG. 3 is a diagram illustrating an example of a configuration in which NaCl of the ionic compound MX that is an electrolyte is solid and an electrolyte layer 14 made of NaCl is provided in contact with the negative electrode 12. The solid electrolyte layer 14 is an electrolyte contained in the electrolytic solution 13 as described above.

Here, FIG. 5 shows an example of the secondary battery 1 in which the electrolyte layer 14 made of NaCl is provided in contact with the negative electrode 12, wherein NaCl is divided into Na ⁺ and Cl ⁻ and each is schematically expressed. It is the figure which showed the behavior at the time of discharge. The secondary battery 1 further includes LiCl as the ionic compound MX other than NaCl.

As shown in FIG. 5, in the secondary battery 1, when charging is started, Na ions, which are the metal ion substance M, are deposited on the negative electrode 12 as metal Na (metal precipitate M _d ) from the electrolyte layer 14 made of NaCl. . On the other hand, Cl ions that are the anionic substance X are released into the electrolytic solution 13 and react with the metal B (Cu) on the positive electrode 11 side to form CuCl that is the compound precipitate BX. When NaCl is provided adjacent to the negative electrode 12 as the solid electrolyte layer 14, the Cl ion is released into the electrolytic solution 13 by charging and becomes metallic Na, so that the volume reduction is about 10%. Seen.

As can be seen from the schematic diagram of FIG. 5, NaCl, which is the ionic compound MX, is provided adjacent to the negative electrode 12 as the solid electrolyte layer 14, so that Na remains on the negative electrode 12 and remains in the metallic Na state. Therefore, the generation of dendrite can be suppressed more effectively. More specifically, the electrolytic solution 13 further includes LiCl (a compound in which Li having a lower redox potential than sodium is used as the metal ion substance M) as the ionic compound MX. The reaction is such that Na which does not move from the negative electrode 12 becomes metal Na based on Na ⁺ → Na rather than Li ion dissociated from LiCl becomes metal Li based on Li ⁺ → Li. Therefore, generation of dendrite that occurs when metal Li is deposited on the negative electrode 12 by the reaction of Li ⁺ → Li does not occur. As described above, the LiCl acts as a medium for transporting Cl ⁻ dissociated from NaCl.

  Therefore, the formation of the dendrite can be more effectively suppressed by forming the electrolyte layer 14 with the NaCl, which is the ionic compound MX, as a solid and in contact with the negative electrode 12. Therefore, a secondary battery having a higher lifetime and a longer lifetime can be obtained.

  When the electrolyte layer 14 is provided with solid NaCl, the thickness of the electrolyte layer (NaCl layer) 14 is preferably about 0.01 mm to 0.5 mm, for example. If the thickness of the NaCl electrolyte layer 14 is less than 0.01 mm, it may be difficult to obtain a sufficient capacity because it is too thin. On the other hand, if the thickness exceeds 0.5 mm, the reaction may be slow. is there.

  The NaCl electrolyte layer 14 can be provided in contact with the negative electrode 12 by various film forming methods.

The electrolytic solution 13 preferably contains a Lewis acidic compound together with the ionic compound MX. Specifically, a compound having a Lewis acidity stronger than that of the compound BX in which the anionic substance X constituting the ionic compound MX is combined with the ionic substance of the metal B as the positive electrode active material. Is preferably included. Such a Lewis acidic compound acts to assist the reaction of the ionic compound MX during the charge / discharge reaction. The Lewis acidic compound is determined by the relationship between the metal B as the positive electrode active material and the compound precipitate BX in which the ionic compound MX is bonded to the anionic material X. For example, AlCl ₃ , CuCl, ZnCl _{2 and the} like can be mentioned, and an aluminum compound is particularly preferable.

  For example, when copper (Cu) is used as the metal B as the positive electrode active material and NaCl (M: Na, X: Cl) is used as the ionic compound MX that is the electrolyte, the positive electrode 11 is charged by charging by the mechanism described above. Produces CuCl as a compound precipitate BX.

As described above, during charging, NaCl, which is the ionic compound MX, dissociates into Na ⁺ and Cl ^−, and Na ⁺ precipitates as metal Na on the negative electrode 12 due to the reaction of Na ⁺ → Na. ^- are stored in the positive electrode 11 becomes compound precipitates CuCl in combination with Cu metal of the positive electrode active material. On the other hand, during discharge, precipitated metal Na is eluted as Na ⁺ and Cl ⁻ is ejected from CuCl accumulated in the positive electrode 11. Note that Cu ⁺ → Cu. However, NaCl, which is the ionic compound MX, behaves as a Lewis base in an organic solvent, whereas CuCl deposited on the positive electrode 11 is a Lewis acid, so that they react to become Na ⁺ and CuCl ₂ ^— , and Cu Is easily dissolved from the positive electrode 11.

On the negative electrode 12 side, Na⇔Na ⁺ reaction occurs, and the amount of Na accumulated in the negative electrode 12 becomes equal to the charge capacity. However, Cu is ionized (CuCl ₂ ⁻ ) from the CuCl generated in the positive electrode 11, and thus in the electrolytic solution 13. When elution occurs, the Cu ions migrate to the negative electrode 12 and a reaction occurs in which the deposited metal Na is replaced by Cu. Then, as the amount of accumulated Na decreases, the charge capacity decreases, and the portion that should have been charged cannot be discharged. Moreover, the accumulation of Cu in the negative electrode 12 causes a short circuit.

At this time, by containing a Lewis acidic compound in the electrolytic solution 13, it is possible to effectively prevent elution of CuCl which is a compound precipitate. That is, by including AlCl ₃ as a Lewis acidic compound in the electrolyte solution 13, the contained AlCl ₃ is more preferential than CuCl which is a compound precipitate of the positive electrode 11 with respect to NaCl acting as a Lewis base. To respond to. That is, AlCl ₃ becomes a reaction medium with NaCl which is a Lewis base. Then, while the reaction between NaCl and AlCl ₃ produces AlCl ₄ ⁻ , the reaction of the compound precipitate CuCl of the positive electrode 11 is suppressed, and as a result, the elution of Cu ions into the electrolyte solution 13 is suppressed. Is done. Thereby, charge capacity can be raised.

  Examples of the solvent include cyclic esters, chain esters, cyclic ethers, and chain ethers. Specific examples include γ-butyrolactone, cyclohexanone, tetrahydrofuran, crown ether, ethylene carbonate, propylene carbonate, and ethylene glycol dimethyl ether. These solvents may be used alone or in combination of two or more. In addition, when the ionic compound MX which is an electrolyte is an ionic liquid, the electrolyte solution 13 does not necessarily contain a solvent.

  Further, as shown in FIG. 3, when the electrolyte layer 14 is provided in contact with the negative electrode 12 with solid NaCl, the solvent in the electrolytic solution 13 at that time is propylene carbonate, ethylene carbonate, or diethylene carbonate. preferable. In addition, it is preferable that NaCl, which is a solid electrolyte, contains a conductive substance such as carbon or a conductive polymer as long as the action is not hindered, thereby increasing the speed of charging and discharging. Can do.

  The blending ratio of the ionic compound MX and the solvent constituting the electrolytic solution 13 is not particularly limited, but when the total amount is 100% by mass, the ionic compound MX is preferably blended at 30% by mass or more. More preferably, it is blended at a ratio of at least mass%. By mixing the electrolyte solution 13 at such a ratio, good charge / discharge can be realized.

  In addition, you may circulate electrolyte solution like the electrolyte solution which comprises a redox flow battery. By circulating the electrolyte, the battery capacity and battery life can be increased. The electrolytic solution may be a gel such as a polymer gel by mixing a gelling agent such as a polymer. According to the gel electrolyte, the fluidity is lowered, so that the seepage from the outer container or the like can be suppressed and the short circuit between the positive electrode 11 and the negative electrode 12 can be prevented, and the safety of the battery can be improved. it can.

<4. Other configurations>
The secondary battery 1 may be configured to increase the voltage and current by stacking a plurality of single cell structures constituted by the positive electrode 11, the negative electrode 12, and the electrolytic solution 13 described above. For example, a single cell structure can be laminated by sandwiching a separator therebetween. Specifically, the laminate of the positive electrode 11, the separator (not shown), and the negative electrode 12 may be accommodated in the outer container while remaining in a plate shape, or is accommodated in the outer container in a spirally wound state. May be.

  Further, lead wires (not shown) are connected to the positive electrode 11 and the negative electrode 12, respectively. The lead wire connected to the positive electrode 11 is usually connected to the positive electrode terminal of the outer container, and the lead wire connected to the negative electrode 12 is usually connected to the negative electrode terminal of the outer container.

  The separator has a function of dissociating the positive electrode 11 and the negative electrode 12, and is not particularly limited as the separator, and a conventionally known separator can be appropriately selected and used in the field of secondary batteries. In addition, a separator is not an essential structure, For example, it can also be set as the aspect which does not use a separator by using gel-like electrolyte solution.

  Moreover, you may use the solid electrolyte etc. which are generally used as a diaphragm. Such a diaphragm can effectively prevent a short circuit of the battery and can improve safety.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples of the present invention, but the present invention is not limited to the following examples.

[Example 1]
Solid NaCl is used as the electrolyte, and LiCl is further dissolved in the electrolyte as the electrolyte to obtain aluminum foil (negative electrode current collector) / NaCl-containing film / separator / copper foil (positive electrode active material) / nickel foil (positive electrode) A bipolar soft package cell was assembled by laminating the current collectors in this order.

  Specifically, a nickel foil (thickness 8 μm) was used as a positive electrode current collector, and a copper foil (thickness 10 μm) as a positive electrode active material was bonded to the nickel foil. In addition, an aluminum foil (thickness: 15 μm) was used as a current collector for the negative electrode. A negative electrode active material was not used.

Further, a sodium chloride (NaCl) -containing film as an electrolyte was adjacent to the negative electrode current collector. Specifically, it was provided by applying sodium chloride to the aluminum foil of the negative electrode current collector. As its configuration, a mixture obtained by mixing 80 parts by mass of sodium chloride, 10 parts by mass of graphite, and 10 parts by mass of polyvinylidene fluoride was coated on an aluminum foil with an application amount of 110 g / m ² .

  As the separator, a non-woven fabric (manufactured by Nippon Bayleen Co., Ltd., OA-0711) was used.

  The electrolyte was prepared in a glove box filled with argon gas. First, 20 parts by mass of aluminum chloride, 10 parts by mass of lithium chloride, 60 parts by mass of triethylene glycol dimethyl ether, and 10 parts by mass of EC (ethylene carbonate) were prepared as the electrolyte solution, and they were mixed and stirred. Prepared by heating at 60 ° C. for 1 hour.

  A soft package cell was assembled from the positive electrode, negative electrode, and electrolyte solution thus prepared (aluminum foil (negative electrode current collector) / NaCl-containing film / separator / copper foil (positive electrode active material) / nickel foil (positive electrode collection)). Electrical body)). The size of the electrode was 4 cm square, the separator was 5 cm square, and the injection volume was 1 g. The liquid injection operation during cell assembly was also performed in a glove box filled with argon gas.

  The assembled soft package cell was subjected to a charge test and a discharge test. Charging was performed to a voltage of 4.3 V under a constant current control of 5 mA. Thereafter, there was a pause for 300 seconds. Subsequently, the battery was discharged to 0 V under 5 mA constant current control.

  As a result, the battery was charged at a charging voltage of about 3.1V and discharged at a discharging voltage of about 2.4V. From the X-ray diffraction (XRD) measurement, the precipitate deposited on the negative electrode (negative electrode current collector) upon completion of charging was metallic sodium, and the precipitate deposited on the positive electrode nickel current collector was copper chloride (CuCl). there were. Furthermore, sodium chloride was confirmed on the negative electrode current collector when the subsequent discharge was completed.

  This is because sodium chloride, which is an electrolyte, is divided into sodium ions and chlorine ions during charging, and chlorine ions combine with copper ions on the positive electrode side to become copper chloride, while sodium ions are reduced at the negative electrode. It is shown that it was deposited as metallic sodium on the negative electrode. Moreover, the reverse reaction occurs at the time of discharge, and it returns to solid sodium chloride.

  In addition, when the charging was completed, generation of dendrites at the negative electrode was not confirmed.

[Example 2]
In Example 2, NaCl is used as an electrolyte dissolved in an electrolytic solution, and lithium bis (trifluoromethanesulfonyl) imide is further dissolved in an electrolytic solution as an electrolyte to obtain a copper foil (negative electrode current collector) / separator. A bipolar soft package cell in which / copper foil (positive electrode active material) / nickel foil (positive electrode current collector) was laminated in this order was assembled.

  Specifically, a nickel foil (thickness 8 μm) was used as a positive electrode current collector, and a copper foil (thickness 10 μm) as a positive electrode active material was bonded to the nickel foil. Further, a copper foil (thickness: 10 μm) was used as a negative electrode current collector. A negative electrode active material was not used.

  Sodium chloride (NaCl) was used as an electrolyte, and an electrolyte containing the electrolyte was prepared in a glove box filled with argon gas. That is, first, 10 parts by mass of aluminum chloride, 30 parts by mass of EC (ethylene carbonate), 30 parts by mass of PC (propylene carbonate), and 30 parts by mass of lithium bis (trifluoromethanesulfonyl) imide were prepared, and 30 parts by mixing them. Stir at 24 ° C. for 24 hours. Next, 30 parts by weight of sodium chloride was mixed with 70 parts by weight of the liquid to prepare an electrolytic solution.

  A soft package cell was assembled from the positive electrode, negative electrode, and electrolyte solution thus prepared (copper foil (negative electrode current collector) / separator / copper foil (positive electrode active material) / nickel foil (positive electrode current collector)). . The size of the electrode was 4 cm square, the separator was 5 cm square, and the injection volume was 1 g. The liquid injection operation during cell assembly was also performed in a glove box filled with argon gas.

  The assembled soft package cell was subjected to a charge test and a discharge test. Charging was performed to a voltage of 4.3 V under a constant current control of 5 mA. Thereafter, there was a pause for 300 seconds. Subsequently, the battery was discharged to 0 V under 5 mA constant current control.

  As a result, the battery was charged at a charging voltage of about 3.1V, and discharged at a discharging voltage of about 2.6V. From the XRD measurement, the deposit deposited on the negative electrode (negative electrode current collector) upon completion of charging was metallic sodium, and the deposit deposited on the nickel current collector of the positive electrode was copper chloride (CuCl). Furthermore, when the subsequent discharge was completed, sodium chloride was confirmed as the current collector copper in the negative electrode, sodium chloride was confirmed in both the negative electrode and the positive electrode, and copper was confirmed in the positive electrode current collector.

  This is because sodium chloride, which is an electrolyte, is divided into sodium ions and chlorine ions during charging, and chlorine ions combine with copper ions on the positive electrode side to become copper chloride, while sodium ions are reduced at the negative electrode. It is shown that it was deposited as metallic sodium on the negative electrode. Moreover, the reverse reaction occurs at the time of discharge, and returns to sodium chloride.

  In addition, when the charging was completed, generation of dendrites at the negative electrode was not confirmed.

DESCRIPTION OF SYMBOLS 1 Secondary battery 11 Positive electrode 12 Negative electrode 13 Electrolytic solution 14 Electrolyte layer 15 Conductive substance

Claims (10)

A positive electrode containing a metal as a positive electrode active material, a negative electrode, and an electrolyte solution,
The electrolytic solution contains an electrolyte, and the electrolyte contains an ionic compound MX (M: metal ion substance, X: anion substance),
At least one of the ionic compounds MX is sodium chloride,
The secondary battery, wherein the electrolytic solution further includes, as the ionic compound MX, a compound having a metal ionic substance M as an element having a lower oxidation-reduction potential than sodium. The secondary battery according to claim 1, wherein sodium chloride that is the ionic compound MX is provided in contact with the negative electrode as a solid in the electrolytic solution. The secondary battery according to claim 1, wherein the element having a lower redox potential than sodium is any one selected from calcium, barium, potassium, and lithium. The secondary battery according to any one of claims 1 to 3, wherein the negative electrode has a configuration made of a material that reduces and metalizes the metal ion substance M. The standard electrode potential of each of the metal constituting the positive electrode active material and the metal constituting the negative electrode is larger than the standard electrode potential of the metal ion material M constituting the ionic compound MX. The secondary battery according to claim 1. 6. The secondary battery according to claim 1, wherein a conductive substance is provided on at least a part of the positive electrode or a surface of the positive electrode opposite to the electrolyte solution side. In the electrolytic solution, Lewis acidity stronger than the compound BX in which the anionic substance X and the ionic substance of the metal B as the positive electrode active material are combined with the anionic substance X constituting the ionic compound MX. The secondary battery according to any one of claims 1 to 6, wherein a compound having the following is included. At the time of charging, an anionic substance X dissociated from the ionic compound MX and a metal ionic substance B ionized from the positive electrode active material are combined at the positive electrode, whereby a compound precipitate BX is generated and the ions When the metal ion substance M dissociated from the conductive compound MX is reduced at the negative electrode, the metal deposit is deposited on the negative electrode current collector,
At the time of discharging, the anionic substance X is ionized from the compound precipitate BX generated by the charging and returns to the electrolyte, and the ionic substance of metal B is ionized from the compound precipitate BX and reduced at the positive electrode. The metal ion substance M is ionized from the metal deposit deposited on the negative electrode current collector by the charging and returned to the electrolytic solution as well as returning to the metal. Secondary battery described in 1. An electrolytic solution used for a secondary battery composed of a positive electrode containing a metal as a positive electrode active material, a negative electrode, and an electrolytic solution,
An electrolyte, the electrolyte contains an ionic compound MX (M: metal ion substance, X: anion substance),
At least one of the ionic compounds MX is sodium chloride,
An electrolyte solution for a secondary battery, wherein the ionic compound MX further includes a compound having a metal ion substance M as an element having a lower oxidation-reduction potential than sodium. Sodium chloride as the ionic compound MX is a solid,
The electrolytic solution for a secondary battery according to claim 9, which is in contact with the negative electrode constituting the secondary battery.

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