JPWO2016080300A1 - Secondary battery - Google Patents

Abstract

In a secondary battery using lithium as a negative electrode active material and bromine as a positive electrode active material, a reduction in battery capacity due to a charge / discharge cycle is suppressed. And a liquid active material 50 and a complexing agent. The solid electrolyte 40 is a lithium ion conductive film. The positive electrode 20 is made of porous carbon and is provided to face one surface of the solid electrolyte 40. The negative electrode 30 is made of metallic lithium and is provided to face the surface of the solid electrolyte on the side opposite to the positive electrode 20. The liquid active material 50 contains lithium ions and bromide ions and is sealed between the solid electrolyte 40 and the positive electrode 20. The complexing agent forms a bromine complex compound immobilized on the positive electrode 20 together with bromine in the liquid active material 50. The complexing agent is a quaternary ammonium salt added in the liquid active material 50. [Selection] Figure 1

Description

  The present invention relates to a secondary battery using lithium as a negative electrode active material and bromine as a positive electrode active material.

  In recent years, lithium-ion secondary batteries have been widely used as power storage devices for hybrid vehicles, electric vehicles, and portable terminal devices. However, as energy density is reaching the theoretical limit, secondary batteries based on new operating principles have been developed. It is being advanced. In the case of a secondary battery for an electric vehicle, the target energy density is 500 Wh / kg or more based on the weight of the entire battery (Non-Patent Document 1).

  A zinc-bromine secondary battery uses zinc as a negative electrode active material and bromine as a positive electrode active material, and has a configuration of a flow battery in which an electrolytic solution is forcibly circulated by an external pump (Non-patent Document 2). . In order to prevent bromine from causing a self-discharge reaction that dissolves zinc produced by the charging reaction of the negative electrode and corroding the electrode constituent materials and the electrolyte circulation system, a quaternary ammonium salt compound is added to the electrolyte. It is known to react with bromine in an electrolytic solution to form a bromine complex compound (complex) (Non-patent Document 3).

  On the other hand, lithium-bromine secondary batteries have been proposed as those capable of achieving a larger theoretical energy density (Non-Patent Document 4, Non-Patent Document 5, and Non-Patent Document 6). In these, carbon is used for the positive electrode and metallic lithium is used for the negative electrode, a lithium ion conductive solid electrolyte is provided between the two, and a liquid active material is sealed between the solid electrolyte and the positive electrode. No external pump is required, and it is excellent in portability and miniaturization. Patent Document 1 proposes an example in which a lithium-bromine secondary battery having the same configuration is used as a flow battery. As in Non-Patent Document 2, in order to prevent bromine generated on the positive electrode from passing through the solid electrolyte and causing self-discharge, a quaternary amine is used as a carbon binder for the positive electrode, and a bromine complex compound is formed on the positive electrode surface. The formation of (complex) is disclosed.

International Publication No. 2011/142797 International Publication No. 2010/150859

Kuniaki Kaki, “Innovation Technology of Lithium Ion Battery”, Innovation Technology of Lithium Ion Secondary Battery and Latest Technology of Next Generation Secondary Battery, Chapter 1, 2.2, Technology Education Publisher, Tokyo, 2013. Wendy Pell, “ZINC / BROMINE BATTERYELECTROLYTES: ELECTROCHEMICAL, PHYSICO-CHEMICAL ANDSPECTROSCOPIC STUDIES”, Ph.D. Thesis, University of Ottawa, 1994. Kuniaki Minato, `` Zinc-bromine battery / zinc-chlorine battery '', Battery Handbook, Electrochemical Society, Battery Technical Committee, Chapter 7, Chapter 2, Ohmsha, Tokyo, 2010. Y. Zhao, Y. Ding, J. Song, L. Peng, J. B. Goodenough, G. Yu, Energy & Environmental Science, 7 (2014) pp 1990-1995. Z. Chang, X. Wang, Y. Yang, J. Gao, M. Li, L. Liu, Y. Wu, Journal of Materials Chemistry A, DOI: 10.1039 / c4ta04419c. Takayoshi Takemoto, Hirotoshi Yamada, “Electrochemical characteristics of new lithium-bromine secondary battery”, 2014 Electrochemical Fall Conference, 2Q19, Sapporo, 2014.

In the lithium-bromine secondary battery of Non-Patent Document 4, 1.0M KBr and 0.3M LiBr are added to the liquid active material. Of these, only Br ⁻ ions for LiBr contribute to the battery capacity. Since the Br ⁻ ions derived from KBr are excessive, the potential at the time of charging is suppressed, and the concentration of Br ₂ generated at the time of charging is suppressed by the reaction of Br ₂ + Br ⁻ → Br ₃ ⁻ . Similarly, in the lithium-bromine secondary battery of Non-Patent Document 5, 1.0 M Br ₂ and 7.0 M LiBr are added to the liquid active material. Of these, 1.0 M contributes to the battery capacity. it is only of Br _2. In these lithium-bromine secondary batteries, the capacity per active material is as high as 300 mAh / g or more, but the energy density of the whole battery remains at about 100 Wh / kg on a weight basis and about 200 Wh / L on a volume basis.

The saturated solubility of the lithium bromide aqueous solution is 160 g / 100 g-H ₂ O. If a concentrated liquid active material close to the saturated solution can be used, the energy density of the entire battery is 682 Wh / kg on a weight basis and on a volume basis. 1070 Wh / L can be expected. However, when such a thick liquid active material is used, the liberation of Br ₂ cannot be suppressed during charging. In the lithium-bromine secondary battery of Non-Patent Document 6, when the charge / discharge cycle is repeated under conditions where bromine is generated, the resistance value at the interface between the solid electrolyte and the liquid active material is greatly increased, and the battery capacity is decreased. There's a problem.

  In Patent Document 1, a polymer mainly composed of a quaternary amine as a complexing agent is used as a binder to fix particles made of non-porous carbon or graphite. The amount of the binder can only be added up to about 10 to 50 percent by mass, since it must be an amount that does not inhibit the electron conduction between them. In addition, since the particles are bonded to each other, there is almost no liquid active material at a position in contact with the binder. For this reason, even if a complexing agent is used as a binder or as a part thereof, the effect of complexing bromine and immobilizing it is limited.

  Accordingly, an object of the present invention is to suppress a decrease in battery capacity due to a charge / discharge cycle in a secondary battery using lithium as a negative electrode active material and concentrated bromine as a positive electrode active material.

  In order to achieve the above-described object, the present invention provides a secondary battery, which is formed of a lithium ion conductive solid electrolyte and a porous conductor having a plurality of macropores, and is opposed to one surface of the solid electrolyte. An electron conductive positive electrode provided on the opposite side of the surface of the solid electrolyte opposite to the positive electrode, and a solid electrolyte containing lithium ions and bromide ions. A liquid active material sealed between the positive electrode and bromine disposed at a position in contact with the liquid active material and immobilized as a water-insoluble solid together with the bromide ions in the liquid active material And a complexing agent that forms a complex compound.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the battery capacity by a charging / discharging cycle can be suppressed in the secondary battery which uses lithium for a negative electrode active material and bromine for a positive electrode active material.

It is a longitudinal cross-sectional view of 1st Embodiment of the secondary battery which concerns on this invention. It is sectional drawing which shows typically the laminated structure of the 1st Embodiment of the secondary battery which concerns on this invention, and the electric circuit at the time of charge. It is a graph which shows the constant current charging / discharging curve of 1st Embodiment of the secondary battery which concerns on this invention. It is a graph which shows the cycle characteristic of 1st Embodiment of the secondary battery which concerns on this invention. It is a graph which shows the example of the constant current charging / discharging curve of 1st Embodiment of the secondary battery which concerns on this invention. It is typical sectional drawing which shows the flow of the manufacturing method of the positive electrode in 2nd Embodiment of the secondary battery which concerns on this invention. It is a longitudinal cross-sectional view of 2nd Embodiment of the secondary battery which concerns on this invention.

  Several embodiments of a secondary battery according to the present invention will be described with reference to the drawings. This embodiment is merely an example, and the present invention is not limited to this. The same or similar components are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a longitudinal sectional view of a first embodiment of a secondary battery according to the present invention. FIG. 2 is a cross-sectional view schematically showing the laminated structure of the secondary battery and the electric circuit during charging in the present embodiment.

  The secondary battery 10 of the present embodiment has a positive electrode 20, a negative electrode 30, a solid electrolyte 40, and a liquid active material 50. The solid electrolyte 40 is formed in a disk shape, for example.

  The solid electrolyte 40 is sandwiched between the first cell body 61 and the second cell body 62. The central portion of the solid electrolyte 40 faces the through holes 71 and 72 in the center of the first cell body 61 and the second cell body 62. The outer peripheral portion of the solid electrolyte 40 is in contact with a portion outside the central through holes 71 and 72 of the first cell body 61 and the second cell body 62. A plurality of fixing holes 73 are provided between the central through holes 71 and 72 and the outer periphery of the first cell body 61 and the second cell body 62. Bolts 74 pass through the fixing holes 73. A nut 76 is screwed into the end of the bolt 74 opposite to the head 75. The first cell body 61 and the second cell body 62 are pressed against the solid electrolyte 40 side by the head portion 75 and the nut 76 of the bolt 74.

  Between the 1st cell body 61 and the volt | bolt 74, the press plate 77 in which the through-hole was formed in the position corresponding to the hole 73 for fixation may be arrange | positioned. Between the second cell body 62 and the nut 76, a press plate 78 in which a through hole is formed at a position corresponding to the fixing hole 73 may be disposed.

  A first electrode cover 81 is fitted in the central through hole 71 of the first cell body 61. An O-ring 83 is sandwiched between the inner surface of the first cell body 61 and the outer surface of the first electrode cover 81. A plurality of O-rings 83 are arranged, for example, at different positions in the axial direction.

  A second electrode cover 82 is fitted in the central through hole 72 of the second cell body 62. An O-ring 84 is sandwiched between the inner surface of the second cell body 62 and the outer surface of the second electrode cover 82. A plurality of O-rings 84 are arranged, for example, at different positions in the axial direction.

  An electrode lead 85 extending in the axial direction passes through the center of the first electrode cover 81. An electrode lead 86 extending in the axial direction passes through the center of the second electrode cover 82.

  A space surrounded by the end of the first electrode cover 81 facing the solid electrolyte 40, the inner surface of the first cell body 61, and the solid electrolyte 40 is formed watertight together with the O-ring 83. A liquid active material 50 is enclosed. The space surrounded by the end of the second electrode cover 82 facing the solid electrolyte 40, the inner surface of the second cell body 62, and the solid electrolyte 40 is formed in a watertight manner together with the O-ring 84. A solid electrolyte protective layer 52 is enclosed.

  The positive electrode 20 is fixed to the end of the first electrode cover 81 on the side facing the solid electrolyte 40. The positive electrode 20 is formed in a columnar shape having a short axial length, for example. The positive electrode 20 is connected to an electrode lead 85 that penetrates the first electrode cover 81.

  The negative electrode 30 is fixed to the end of the second electrode cover 82 on the side facing the solid electrolyte 40. The negative electrode 30 is formed in a disk shape, for example. The negative electrode 30 is connected to an electrode lead 86 that penetrates the second electrode cover 82. The conductive plate 32 may be disposed between the negative electrode 30 and the second electrode cover 82.

  The positive electrode 20 is formed of a porous conductor such as porous carbon. The positive electrode 20 may be composed of a columnar carbon electrode and porous carbon formed on the surface thereof. The positive electrode 20 may be an electron conductive substance having a high surface area. For example, fine particle carbon, graphite or metal, or porous graphite or metal may be used. The negative electrode 30 is made of metallic lithium. The negative electrode 30 is not limited to metallic lithium, and is preferably a substance having a low electrode potential for reaction with lithium ions and a large capacity. For example, graphite, tin, silicon, or the like may be used.

  The solid electrolyte 40 is formed of an insulator having lithium ion conductivity. The solid electrolyte 40 is dense. That is, the solid electrolyte 40 does not penetrate the liquid active material. The solid electrolyte 40 is, for example, a lithium ion conductive film-like glass ceramic sheet. The thickness of the solid electrolyte 40 is, for example, 150 μm.

The solid electrolyte protective layer 52 is an organic liquid electrolyte in which a glass filter is impregnated with an electrolyte in which 1M LiPF ₆ is dissolved in EC (ethylene carbonate) and DMC (dimethyl carbonate). When there is no possibility that the metallic lithium of the negative electrode 30 reacts with the elements in the solid electrolyte 40, the negative electrode 30 and the solid electrolyte 40 may be contacted except for the solid electrolyte protective layer 52. The solid electrolyte protective layer 52 only needs to have lithium ion conductivity and be stable even in contact with metallic lithium. For example, a dry polymer electrolyte film may be used. Alternatively, another solid electrolyte may be laminated by sputtering or the like.

  The first cell body 61, the second cell body 62, the first electrode cover 81, and the second electrode cover 82 are made of an insulating material such as ceramics that does not allow liquid to pass through. The O-rings 83 and 84 are made of an insulating material such as rubber that does not pass liquid and has a certain degree of elasticity.

  The bolt 74 and the nut 76 are made of a material having a certain degree of rigidity such as stainless steel. The holding plate 77 is made of a material having a certain degree of rigidity such as stainless steel. The electrode leads 85 and 86 and the conductive plate 32 are made of a conductive material such as copper.

The liquid active material 50 is a liquid containing lithium ions and bromide ions, and is, for example, a lithium bromide (LiBr) aqueous solution. A complexing agent is added to the liquid active material 50. The concentration of the lithium bromide aqueous solution is, for example, 1M. The complexing agent is a quaternary ammonium salt (Q ⁺ -Br ⁻ ). Tetraethylammonium bromide can be used as the complexing agent. By adding the complexing agent to the liquid active material 50, bromine (Br ₂ ) generated during charging forms a complex with the complexing agent by the following multistage reaction.

Q ⁺ −Br ⁻ + Br ₂ → Q ⁺ −Br ₃ ^{−
_{Q + -Br 3 - + Br 2}} → Q + -Br 5 -
...
Q ⁺ −Br _2n−1 ⁻ + Br ₂ → Q ⁺ −Br _{2n + 1} ⁻
At this time, the complex becomes a water-insoluble solid or liquid depending on the molecular weight and molecular structure of the complexing agent, and is immobilized on the surface of the porous carbon as the positive electrode 20. The complexing agent only needs to form a complex with bromine, and may be 1,4-dioxane, 1,3,5-triazine and analogs thereof. In order to securely fix the complex to the surface of the positive electrode 20 and facilitate the release of bromine ions in the next discharge cycle, the complex is preferably a complexing agent that becomes a water-insoluble solid.

  The secondary battery 10 uses bromine as a positive electrode active material, lithium as a negative electrode active material, and lithium ion conductive ceramics as a solid electrolyte. When the solid electrolyte also serves as a separator, the metallic lithium and the aqueous solution of the negative electrode 30 are separated. This lithium-bromine secondary battery has an operating voltage as high as 4.1 V and a theoretical energy density as high as 683 Wh / kg.

  FIG. 3 is a graph showing a constant current charge / discharge curve of the secondary battery of the present embodiment. In FIG. 3, the horizontal axis represents capacity, and the vertical axis represents voltage. FIG. 4 is a graph showing the cycle characteristics of the secondary battery of the present embodiment. The horizontal axis in FIG. 4 is the number of charge / discharge cycles, and the vertical axis is the discharge capacity and coulomb efficiency (ratio of discharge capacity to charge capacity). 3 and 4 also show the charge / discharge curves of the secondary battery in which the complexing agent is not added to the liquid active material 50.

  When the complexing agent was not added, the initial charge capacity was 253 mAh / g-LiBr, the initial discharge capacity was 147 mAh / g-LiBr, and the Coulomb efficiency was 58%. As the charge / discharge cycle was repeated, the capacity decreased, and the discharge capacity at the fifth cycle was 79 mAh / g-LiBr, which was reduced to 54% at the first cycle. The coulombic efficiency at the fifth cycle was less than 90%.

  On the other hand, when tetraethylammonium bromide was added as a complexing agent, the initial charge capacity was 193 mAh / g-LiBr, the initial discharge capacity was 161 mAh / g-LiBr, and the Coulomb efficiency was 83%. The discharge capacity slightly decreased as the cycle was repeated, but the discharge capacity at the fifth cycle was 139 mAh / g-LiBr, and maintained 86% at the first cycle. The coulomb efficiency reached 99.6%.

From these results, it can be seen that the addition of the quaternary ammonium salt to the liquid active material 50 stabilizes charge and discharge, and in particular improves the cycle characteristics. When the quaternary ammonium salt is not added to the liquid active material 50, the cycle characteristic is that bromine (Br ₂ ) generated during charging increases the interface resistance between the solid electrolyte 40 and the liquid active material 50. Conceivable.

On the other hand, when a quaternary ammonium salt is added to the liquid active material 50, bromine (Br ₂ ) is fixed (trapped) to the surface of the porous carbon pores that are the positive electrodes 20 and stabilized. As a result, bromine produced by the positive electrode reaction does not move through the liquid active material 50 and reach the interface of the solid electrolyte 40. Therefore, it is considered that the resistance value at the interface between the solid electrolyte 40 and the liquid active material 50 does not increase greatly and exhibits good cycle characteristics.

  Thus, according to the present embodiment, in a secondary battery using lithium as the negative electrode active material and bromine as the positive electrode active material, it is possible to suppress a decrease in battery capacity due to charge / discharge cycles.

  Further, most of the weight of the lithium-bromine secondary battery is occupied by the exterior parts such as the liquid active material 50 and the cell bodies 61 and 62. Since the exterior portion varies greatly depending on the size and design, when considered excluding it, the weight of the lithium-bromine secondary battery is mainly the liquid active material 50.

Lithium bromide (LiBr) has a very high water solubility and dissolves 160 g per 100 g of water at 20 ° C. For example, when a 54 wt% solution (density 1.57 g / cm ³ ) is used as the liquid active material, the ratio of water in the liquid active material is reduced to 50% or less. As a result, the energy density of the entire cell is 682 Wh / kg on a weight basis and 1070 Wh / L on a volume basis, which can satisfy the value required for a next-generation storage battery. By using such a concentrated solution, it is considered that the lithium-bromine battery has significance.

However, when such a thick liquid active material is simply used, Br ₂ is liberated during charging. When the charge / discharge cycle is repeated under conditions where bromine is generated, the resistance value at the interface between the solid electrolyte and the liquid active material is greatly increased, and the battery capacity is decreased.

Thus, for example, in Non-Patent Documents 4 and 5, excess Br ⁻ is added to suppress free bromine during charging. That means

The equilibrium reaction (equilibrium constant K-16) is used to bias the equilibrium to the right by excess Br ⁻ . In this way, reversibility of electrochemical reaction and cycle characteristics are enhanced by suppressing free bromine. However, in order to utilize this reaction, an excess of Br ^{− that} is about 7 times the amount of bromine at the time of charging is required, and this excess Br ⁻ does not contribute to the oxidation / reduction reaction. Therefore, simply increasing the amount of bromine does not significantly improve the energy density.

On the other hand, in the present embodiment, a complexing agent is added to the liquid active material 50. For this reason, free bromine (Br ₂ ) at the time of charging forms a complex and is fixed to the surface of the positive electrode 20. As a result, Br ₂ in the liquid active material 50 is substantially reduced, so that Br ⁻ contributing to the capacity in the liquid active material 50 increases. That is, the effective active material concentration increases and a high energy density is realized.

  The complexing agent is added to the liquid active material 50. For this reason, compared with the case where a complexing agent is arrange | positioned inside the positive electrode 20, for example, it becomes possible for more complexing agents to reach the surface of the positive electrode 20. As a result, according to the amount of free bromine generated, the complexing agent captures free bromine and the free bromine complexing rate is improved.

A water-soluble salt that contains lithium ions but does not contain bromide ions and has an oxidation potential higher than that of the liquid active material 50 and a lower reduction potential may be added to the liquid active material 50. This salt is, for example, lithium nitrate (LiNO ₃ ). By adding such a salt to the liquid active material 50, the lithium ion concentration in the liquid active material 50 is maintained even at the end of charging, and the resistance of the liquid active material 50 and the resistance between the liquid active material 50 and the solid electrolyte 40 are maintained. Suppresses the increase in As a result, the charge capacity of the battery increases and the charge / discharge cycle characteristics are improved.

  FIG. 5 is a graph showing an example of a constant current discharge curve in the present embodiment. In FIG. 5, the horizontal axis represents capacity, and the vertical axis represents voltage.

FIG. 5 shows the measurement results of the discharge capacity when 1 M LiBr, 1 M LiNO ₃ , and 0.25 M tetraethylammonium bromide were used as the liquid active material 50. In the result shown in FIG. 3, the initial discharge capacity was about 150 mAh / g-LiBr. However, the discharge capacity became about 280 mAh / g-LiBr by adding LiNO ₃ . Thus, by adding a water-soluble salt that contains lithium ions but does not contain bromide ions and has a higher oxidation potential and a lower reduction potential than the liquid active material 50 to the liquid active material 50, the discharge capacity can be increased. You can see it grows.

[Second Embodiment]
FIG. 6 is a schematic cross-sectional view showing a flow of a method for manufacturing a positive electrode in the second embodiment of the secondary battery according to the present invention.

First, a colloidal solution containing silicon oxide (SiO ₂ ) having an average particle diameter of, for example, 100 nm or more and 450 nm or less is centrifuged, and then dried under reduced pressure, so that the average particle diameter is, for example, as shown in FIG. An aggregate of SiO ₂ particles of 100 nm or more and 450 nm or less (hereinafter referred to as SiO ₂ opal 91) is obtained. This SiO ₂ opal 91 functions as a so-called mold. Further, a carbon source solution is prepared by preparing a mixed solution in which phenol and formaldehyde are mixed at a molar ratio of, for example, 1: 0.85, and adding a small amount of hydrochloric acid to the mixed solution.

Next, as shown in FIG. 6B, the SiO ₂ opal 91 is immersed in the carbon source solution 92 for 12 hours, for example. Thereafter, the SiO ₂ opal 91 immersed in the carbon source solution 92 is filtered and, for example, heat treated at 128 ° C. for 12 hours, for example, to remove moisture and to make the carbon source resin. Thus, as shown in FIG. 6 (c), the complex 93 of phenolic resin 94 and SiO ₂ opal 91 is obtained.

Next, the phenol resin 94 is carbonized by heat-treating the composite 93 of the phenol resin 94 and the SiO ₂ opal 91 in, for example, an argon atmosphere at 400 ° C. for 5 hours, for example. As a result, a composite 95 of carbon and SiO ₂ opal 91 as shown in FIG. 6D is obtained.

Next, the SiO ₂ opal 91 is removed from the composite 95 by wet etching using a hydrogen fluoride (HF) aqueous solution. As a result, the SiO ₂ opal 91 functioning as a mold is removed. As a result, as shown in FIG. 6E, pores 96 are formed in the portions where the SiO ₂ opal 91 is present, and macroporous carbon 97 is formed. In the first embodiment, the macroporous carbon 97 particles are solidified with an appropriate binder to form the positive electrode 20. The pores 96 are so-called macropores having a diameter of 50 nm or more, and the positive electrode 20 is formed of macroporous carbon 97.

  In the present embodiment, as shown in FIG. 6 (f), the macroporous carbon 97 particles are then impregnated with an ammonium salt polymer 98. Thereafter, by pulling up the macroporous carbon 97, as shown in FIG. 6G, particles 99 in which the ammonium salt polymer 98 adheres to the particle surfaces and the surfaces of the pores 96 to form the complexing agent film 54 are obtained. It is done. By solidifying the particles 99 using an appropriate binder 90, the positive electrode 20 of the present embodiment as shown in FIG. 6 (h) is formed.

  FIG. 7 is a vertical cross-sectional view of the secondary battery in the present embodiment.

  The secondary battery 12 of the present embodiment is different from the secondary battery 10 of the first embodiment (see FIG. 1) in the introduction position of the complexing agent. In the first embodiment, the complexing agent is added to the liquid active material 50 (see FIG. 1). However, in this embodiment, a quaternary ammonium salt, which is a complexing agent, is polymerized to produce porous carbon. A complexing agent film 54 (see FIG. 6) is bound to the surfaces of the particles constituting the positive electrode 20 and the surfaces of the pores formed in the particles. The polymer used for coating the positive electrode 20 as the complexing agent film 54 preferably contains a large amount of quaternary amine. Further, this polymer preferably has low water solubility.

  Even in such a secondary battery 12, when the liquid active material 51 to which no complexing agent is added is sealed, ammonium ions and bromine exposed on the surface of the complexing agent film 54 form a complex to be immobilized. To do. For this reason, the fall of the battery capacity by a charging / discharging cycle can be suppressed similarly to 1st Embodiment.

  When the positive electrode 20 is in contact with the liquid active material 51, the liquid active material 51 penetrates into the positive electrode 20 which is porous carbon. As a result, the liquid active material 51 comes into contact with the surface of the positive electrode 20, the surface of the particles 97 constituting the positive electrode 20, and the pores 96 formed in the particles 97 constituting the positive electrode 20.

  The complexing agent is present as a complexing agent film 54 on the surfaces of the particles constituting the positive electrode 20 and the surfaces of the pores 96 formed in the particles. As a result, bromine is immobilized as a complex not only on the macroscopic surface of the positive electrode 20 but also on the surfaces of the particles constituting the positive electrode 20 and the surfaces of the pores 96 formed in the particles.

  Since the binder binds the particles to each other, the liquid active material 51 hardly exists at the position where it comes into contact with the binder. For this reason, even if a complexing agent is used as a binder or as a part thereof, the effect of complexing bromine and immobilizing it is limited. However, in the present embodiment, more complexing agent is present at a position in contact with the liquid active material 51. As a result, the complexing agent can capture more free bromine, and the complexation rate of free bromine is improved.

DESCRIPTION OF SYMBOLS 10 ... Secondary battery, 12 ... Secondary battery, 20 ... Positive electrode, 30 ... Negative electrode, 32 ... Conductive plate, 40 ... Solid electrolyte, 50 ... Liquid active material, 51 ... Liquid active material, 52 ... Solid electrolyte protective layer, 54 ... Complexing agent film, 61 ... First cell body, 62 ... Second cell body, 71, 72 ... Through hole, 73 ... Fixing hole, 74 ... Bolt, 75 ... Head, 76 ... Nut, 77 ... Presser plate, 81 ... 1st electrode cover, 82 ... 2nd electrode cover, 83 ... O-ring, 84 ... O-ring, 85 ... Electrode lead, 86 ... Electrode lead

Claims (5)

A lithium ion conductive solid electrolyte;
An electronically conductive positive electrode formed of a porous conductor having a plurality of macropores and provided opposite to one surface of the solid electrolyte;
An electron-conductive negative electrode provided to face the surface of the solid electrolyte opposite to the positive electrode;
A liquid active material containing lithium ions and bromide ions and sealed between the solid electrolyte and the positive electrode;
A complexing agent disposed at a position in contact with the liquid active material to form a bromine complex compound that is immobilized on the positive electrode as a water-insoluble solid together with the bromide ions in the liquid active material;
A secondary battery comprising:   A water-soluble salt that contains lithium ions, does not contain bromide ions, and has a higher oxidation potential and a lower reduction potential than the liquid active material, and has a salt added to the liquid active material The secondary battery according to claim 1.   The secondary battery according to claim 1, wherein the complexing agent is added to the liquid active material.   3. The secondary battery according to claim 1, wherein the complexing agent is a polymer bound to the surfaces of the particles constituting the positive electrode and the surfaces of the pores formed in the particles. The secondary battery according to any one of claims 1 to 4, wherein the complexing agent is a quaternary ammonium salt.