Flow battery cell and metal-air flow battery

Abstract

To increase the reaction efficiency of a metal active material and a negative electrode.SOLUTION: A flow battery cell includes: a positive electrode chamber; a negative electrode chamber opposite the positive electrode chamber; and a separator configured to separate the positive electrode chamber and the negative electrode chamber. The negative electrode chamber includes: a negative-electrode flow path through which a slurry containing a metal active material and an electrolytic solution flows; and a negative electrode constituting a part of a wall face of the negative-electrode flow path. While the negative electrode is disposed along a direction intersecting with a gravity direction and below the separator in terms of the gravity direction, the metal active material flows through the negative-electrode flow path in a sliding flow state.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a flow type battery cell and a flow type metal-air battery. [Background technology]

[0002] Conventionally, secondary batteries using a slurry containing an active material for the electrodes have been known. For example, Patent Document 1 discloses a secondary battery having a positive electrode, a negative electrode, and an electrolyte, the electrolyte containing at least one metal selected from the group consisting of Zn, Li, Na, Mg, Al, Ca, Cr, and Fe as an active material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-53868 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a flow battery, which is a type of secondary battery, a positive electrode active material and a negative electrode active material are supplied to a cell including a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode, respectively, to perform charging and discharging. If the contact efficiency between the negative electrode and the metal active material in the negative electrode slurry including the metal active material, which is one form of the negative electrode active material, and an electrolyte is low, the reaction efficiency may decrease, and the discharge characteristics may deteriorate.

[0005] An object of the present disclosure is to provide a flow type battery cell and a flow type metal-air battery that are capable of increasing the reaction efficiency between a metal active material and a negative electrode. [Means for solving the problem]

[0006] The flow type battery cell disclosed herein has a positive electrode chamber, a negative electrode chamber facing the positive electrode chamber, and a separator separating the positive electrode chamber and the negative electrode chamber. The negative electrode chamber is provided with a negative electrode flow path through which a slurry containing a metal active material and an electrolyte flows, and a negative electrode that constitutes part of a wall surface of the negative electrode flow path. The negative electrode is arranged in a direction intersecting the direction of gravity and is arranged below the separator in the direction of gravity, and the metal active material flows in a sliding flow state within the negative electrode flow path.

[0007] In addition, a flow type battery cell according to the present disclosure has a positive electrode chamber, a negative electrode chamber facing the positive electrode chamber, and a separator separating the positive electrode chamber and the negative electrode chamber. The negative electrode chamber is provided with a negative electrode flow path through which a slurry containing a metal active material and an electrolyte flows, and a negative electrode constituting a part of a wall surface of the negative electrode flow path. The negative electrode is disposed along a direction intersecting the direction of gravity and below the separator in the direction of gravity. The viscosity of the slurry is ηPa s, the particle diameter of the metal active material is D p When m is taken as 5×10^-9≦D p ^2 / η<2.5×10^-7 It is characterized by satisfying the following.

[0008] Furthermore, a flow-type metal-air battery including the flow-type battery cell also falls within the scope of the technical idea of ​​the present disclosure, and is characterized by having a power generation unit including the flow-type battery cell, a storage unit that contains an electrolyte that circulates through the power generation unit, and a charging unit to which the electrolyte is supplied from the storage unit. Effect of the Invention

[0009] According to the present disclosure, it is possible to increase the reaction efficiency between the metal active material and the negative electrode. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram illustrating a schematic configuration of a flow-type metal-air battery according to an embodiment. [Diagram 2]FIG. 1 is a cross-sectional view illustrating a flow type battery cell according to an embodiment. [Figure 3A] FIG. 2 is a cross-sectional explanatory diagram illustrating an example of a flow of a negative electrode slurry flowing through a negative electrode flow path in a flow type battery cell. [Figure 3B] FIG. 11 is a cross-sectional explanatory view showing another example of the flow of negative electrode slurry flowing through the negative electrode flow path in the flow type battery cell. [Figure 3C] FIG. 11 is a cross-sectional explanatory view showing a schematic diagram of still another example of the flow of negative electrode slurry passing through a negative electrode flow path in a flow type battery cell. [Figure 4] 1 is a table showing evaluation results regarding sedimentation and separation of negative electrode slurry and clogging of flow paths. [Diagram 5] 1 is a graph showing the relationship between the metal active material concentration and the viscosity in a negative electrode slurry. [Figure 6] 1 is a graph showing the relationship between the metal active material concentration in a negative electrode slurry and the discharge capacity. [Figure 7] 1 is a graph showing the relationship between the metal active material concentration in a negative electrode slurry and discharge characteristics. [Figure 8] 1 is a graph showing cross-sectional flow velocity and discharge characteristics of a negative electrode slurry. [Figure 9] FIG. 1 is a cross-sectional view illustrating a flow type battery cell according to an embodiment. [Figure 10] 1 is a graph showing the discharge characteristics and cross-sectional flow velocity of a negative electrode slurry. [Figure 11] 1 is a graph showing pressure loss and cross-sectional flow velocity of negative electrode slurry. [Figure 12] FIG. 4 is a plan view showing an example of a flow channel shape of a negative electrode flow channel. [Figure 13] FIG. 11 is a plan view showing another example of the flow channel shape of the negative electrode flow channel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A flow type battery cell and a flow type metal-air battery according to an embodiment of the present disclosure will be described with reference to the drawings.

[0012] (Flow type metal-air battery) 1 is an explanatory diagram showing a schematic configuration of a flow type metal-air battery 1 according to an embodiment. Note that components common to a plurality of embodiments described below are denoted by common reference symbols, and duplicated explanations will be omitted.

[0013] As illustrated in FIG. 1, the flow type metal-air battery 1 includes a storage unit 101, a power generation unit (discharge unit) 102, and a charging unit 103. The flow type metal-air battery 1 takes in air and generates electricity using the air taken in by the power generation unit 102. The charging unit 103 is responsible for charging and discharges oxygen. Anode slurry (slurry), which is a slurry-like fluid containing anode active material and electrolyte, is supplied from the storage unit 101 to the charging unit 103. A pipe is connected from the storage unit 101 to the charging unit 103, and the electrolyte and the like can be pumped through a pump or the like. The same can be done between the power generation unit 102 and the storage unit 101.

[0014] The storage unit 101 stores the negative electrode slurry. The negative electrode active material contained in the negative electrode slurry includes negative electrode active material ions dissolved in the electrolyte, and solid active material that does not dissolve and floats in a particulate state as a result of exceeding the saturation solubility in the electrolyte. The solid active material also includes a solid active material (metal active material) in a reduced state and a solid active material in an oxidized state.

[0015] The negative electrode active material is a metal species. The metal species is, for example, a zinc species, a cadmium species, a lithium species, a sodium species, a magnesium species, a lead species, a tin species, an aluminum species, or an iron species. The metal constituting the metal species may be a metal consisting of only a metal that is a main component, or may be an alloy of a metal that is a main component and a subcomponent. The metal species can be either a metal or an oxide. Whether the metal species is a metal or an oxide depends on the degree of progress of the discharge reaction or the charge reaction. However, in the discharge reaction described later, it is preferable that the metal species is in a reduced state.

[0016] In this embodiment, the metal species is a zinc species, and the flow type metal-air battery 1 is a flow type zinc-air battery. The metal constituting the zinc species may be, for example, a metal consisting of only zinc as a main component, or may be an alloy of zinc as a main component and a subcomponent. When the metal species is zinc, the negative electrode active material ions dissolved in the electrolyte are zincate ions, the solid active material in the reduced state is zinc, and the solid active material in the oxidized state is, for example, zinc oxide.

[0017] The average particle diameter of the metal species is several μm when it is a solid active material in an oxidized state (e.g., ZnO), and is several tens of μm to about 200 μm when it is a solid active material in a reduced state (e.g., Zn). The average particle diameter can be measured by a particle size distribution measuring device. The particle size distribution measuring device measures the particle size distribution by, for example, laser diffraction or dynamic light scattering, and calculates the median diameter D50 as the average particle diameter from the measured particle size distribution.

[0018] The electrolyte is selected according to the metal species. When the metal species is zinc species, the electrolyte is an alkaline aqueous solution, for example, a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution. When the metal species is lithium species, the electrolyte is a non-aqueous electrolyte. When the metal species is magnesium species, the electrolyte is a neutral aqueous solution, for example, a sodium chloride aqueous solution. The electrolyte may be replaced with a solid electrolyte.

[0019] In charging section 103, negative electrode slurry is supplied to the negative electrode from storage section 101. In charging section 103, separator 104 separates an area in which the negative electrode is provided from an area in which the positive electrode is provided.

[0020] When the metal species is zinc, the reaction at the negative electrode of charging unit 103 follows formulas (1) and (2). At the negative electrode, zinc oxide, which is a solid active material in an oxidized state, first reacts with water and hydroxide ions to generate zincate ions. Then, the zincate ions receive electrons to generate zinc and hydroxide ions. The anion involved in the charging reaction and the discharging reaction described later is the hydroxide ion. ZnO+H2O+2OH- →Zn(OH)4 2- …(1) Zn(OH)4 2- +2e - →Zn+4OH - …(2)

[0021] The reaction at the positive electrode of charging unit 103 follows formula (3). At the positive electrode, oxygen and water are produced from hydroxide ions, and electrons are released. 4OH - →O2+2H2O+4e - …(3)

[0022] The charging unit 103 is a zinc regeneration unit that uses zinc oxide, which is a solid active material in an oxidized state, for charging. A negative electrode slurry containing a negative electrode active material is supplied to the charging unit 103 from the storage unit 101. The solid active material contained in the storage unit 101 and supplied to the charging unit 103 is preferably in an oxidized state, or more of the solid active material in the oxidized state than the solid active material in the reduced state.

[0023] The power generation unit 102 supplies the negative electrode slurry from the storage unit 101 to the negative electrode, and supplies air to the positive electrode. In the power generation unit 102, a separator 104 separates an area where the negative electrode is provided from an area where the positive electrode is provided.

[0024] In the case of a flow-type zinc-air battery in which the metal species is zinc, the reaction at the negative electrode of the power generation unit 102 follows formulas (4) and (5). At the negative electrode, zinc, which is a solid active material in a reduced state, reacts with hydroxide ions to generate zincate ions and release electrons. The zincate ions generate zinc oxide, water, and hydroxide ions. The anion involved in the power generation reaction is the hydroxide ion. Zn+4OH- → Zn(OH)4 2- +2e - …(4) Zn(OH)4 2- →ZnO+H2O+2OH - …(5)

[0025] The reaction at the positive electrode of the power generation unit 102 follows formula (6): At the positive electrode, electrons are received and hydroxide ions are produced from oxygen and water. O2+2H2O+4 e- →4OH - …(6)

[0026] In the power generation unit 102, zinc, which is a solid active material in a reduced state, is used for discharging. A negative electrode slurry containing a negative electrode active material is supplied to the power generation unit 102 from the storage unit 101. The solid active material supplied to the power generation unit 102 and stored in the storage unit 101 is preferably in a reduced state, or preferably there is more of the solid active material in a reduced state than the solid active material in an oxidized state.

[0027] (Flow type battery cell) FIG. 2 is a cross-sectional view that illustrates a flow type battery cell 10 in a power generating section 102 of a flow type metal-air battery 1 according to an embodiment.

[0028] In the flow type metal-air battery 1, the power generation section 102 has, as its basic constituent unit, a flow type battery cell (power generation section cell) 10 including a positive electrode chamber 20, a negative electrode chamber 30, and a separator 40 that separates them. The flow type battery cell 10 is a flow type battery in which negative electrode slurry B flows through a negative electrode flow path 32 described later.

[0029] The positive electrode chamber 20 includes a positive electrode 21 where an oxygen reduction reaction occurs, and air A containing oxygen as a reactant flows through the positive electrode chamber 20. The positive electrode chamber 20 is provided with a positive electrode flow path 22. The positive electrode flow path 22 is a groove provided in a striped pattern, and is a flow path for flowing oxygen, which is a positive electrode active material.

[0030] The negative electrode chamber 30 includes a negative electrode 31 in which an oxidation reaction of metallic zinc occurs. The negative electrode 31 is arranged along the X direction intersecting with the gravity direction G. The negative electrode chamber 30 includes a negative electrode flow path 32 through which a negative electrode slurry B containing a metal active material and an electrolyte flows. The negative electrode flow path 32 is a flow path through which the negative electrode slurry B flows. For example, a negative electrode flow path layer 33 is provided between the negative electrode 31 and the separator 40, and the negative electrode flow path 32 is formed by grooves provided in the negative electrode 31, the separator 40, and the negative electrode flow path layer 33. The negative electrode flow path 32 is not limited to being provided by the negative electrode flow path layer 33 having a groove, and may be formed by a groove provided on the surface of the negative electrode 31.

[0031] The negative electrode flow path 32 is provided along the X direction (the direction perpendicular in FIG. 2 ) that intersects with the gravity direction G as the flow direction. The negative electrode flow path layer 33 provides an inlet 34 for the negative electrode slurry at one end of the negative electrode flow path 32 and an outlet 35 for the negative electrode slurry at the other end. The negative electrode slurry B flows through the negative electrode flow path 32 from the X1 side toward the X2 side.

[0032] The negative electrode 31 constitutes a part of the lower wall surface of the negative electrode flow path 32. The negative electrode 31 can be made of a conductive material made of a carbon material and a resin material. The separator 40 provided opposite the negative electrode 31 constitutes a part of the upper wall surface of the negative electrode flow path 32. The separator 40 separates the positive electrode chamber 20 from the negative electrode chamber 30, and suppresses the penetration of the negative electrode slurry from the negative electrode chamber 30 side to the positive electrode chamber 20 side. The separator 40 is provided along the positive electrode 21. It is preferable to use a material (e.g., a hydrous gel membrane) suitable for suppressing the penetration of the negative electrode slurry for the separator 40. The separator 40 and the positive electrode 21 are held and fixed by the sealing part 50.

[0033] In the negative electrode chamber 30, a current-carrying plate 36 may be provided along the negative electrode 31. A sealing portion 50 is disposed and fixed between the current-carrying plate 36 and the negative electrode flow path layer 33. Note that the negative electrode chamber 30 is not limited to a configuration including the negative electrode 31, the current-carrying plate 36, and the negative electrode flow path layer 33, and these may be configured as a single member.

[0034] 3A to 3C are cross-sectional explanatory views that diagrammatically show examples of the flow of negative electrode slurry flowing through the negative electrode flow path.

[0035] In the flow type battery cell 10, it is desirable that the negative electrode slurry flows smoothly and stably through the negative electrode flow path 32, and that the discharge characteristics of the power generation unit 102 are improved. In order to improve the discharge characteristics, it is desirable to increase the contact efficiency between the negative electrode 31 and the reduced solid active material (metal active material) in the flowing negative electrode slurry.

[0036] 3A, when negative electrode slurry B containing metal active material 60 and an electrolyte is supplied to the negative electrode flow path 32, the metal active material 60 settles downward in the direction of gravity G in the negative electrode flow path 32, and the metal active material 60 and the electrolyte are separated from each other, which may result in a difference in concentration of the metal active material 60 between the upper and lower layers in the negative electrode flow path 32. In this case, as shown in the figure, the metal active material 60 separated and settled from the upper layer consisting of the electrolyte is deposited on the negative electrode 31 disposed below the negative electrode flow path 32, and a sliding flow in which the deposited layer of the metal active material 60 gradually moves toward the X2 side is formed, which is desirable because it increases the reaction efficiency between the metal active material 60 and the negative electrode 31.

[0037] 3B, for example, when the action of the fluid (slurry) on the metal active material 60 is small, the movement of the metal active material 60 is retarded, forming a sediment layer, which may result in stagnation on the X2 side and blockage of the negative electrode flow path 32. When the action of the fluid (slurry) on the metal active material 60 is large, as shown in FIG. 3C, the metal active material 60 attempting to be deposited downward in the direction of gravity G is lifted up and becomes a floating flow, which may reduce the contact efficiency between the negative electrode 31 disposed below in the direction of gravity G and the metal active material 60, resulting in a deterioration in discharge characteristics.

[0038] When considering sedimentation in the negative electrode flow channel 32 for the purpose of stable liquid transfer in the negative electrode slurry, the terminal velocity (sedimentation velocity) V S " is calculated by the Stokes' equation shown in the following equation (7). pis the "average particle size of the main constituent particles (m)" and ρ p is the density of the main particles (g / cm 3 )" and ρ f is the density of the fluid (g / cm 3 )" and g is "gravitational acceleration (m / s 2 )=980cm / s 2 " and η is the "viscosity of the fluid (Pa s)".

[0039]

number

[0040] Based on the Stokes' law, if the viscosity η of the negative electrode slurry is small, the fluid action is small, and the flow may stop without becoming a sliding flow, and if the viscosity η is large, the fluid action is large, and it is likely that a floating flow will occur instead of a sliding flow. p If the diameter is large, the metal active material is likely to settle and cannot be transported, whereas if the diameter is small, the metal active material is unlikely to settle and a floating flow is likely to occur.

[0041] Here, if the concentration of the negative electrode slurry is low, the amount of metal active material in contact with the negative electrode 31 will decrease, resulting in a decline in discharge characteristics, and if the concentration is high, there is a risk of clogging the negative electrode flow path 32. If the density of the metal active material is low, it will not settle easily and a floating flow will be generated, and if the density is high, it will settle easily and the metal active material will not be able to be transported. If the flow speed (cross-sectional flow speed) of the negative electrode slurry is slow, the fluid action will be small and the flow may stop without becoming a sliding flow, and if it is fast, the fluid action will be large and a floating flow will be generated easily.

[0042] Therefore, in the flow type battery cell 10 according to this embodiment, the negative electrode slurry flowing through the negative electrode chamber 30 is mixed with a metal active material (e.g., zinc particles), a thickener (e.g., polyacrylic acid), and an electrolyte (e.g., an aqueous potassium hydroxide solution) and adjusted to fall within the following specified ranges, thereby increasing the contact efficiency between the metal active material and the negative electrode and improving the reaction efficiency.

[0043] That is, the viscosity of the negative electrode slurry is ηPa s, the particle diameter of the metal active material is D p m, the negative electrode slurry is formed so as to satisfy formula (8). 5×10^-9≦D p ^2 / η<2.5×10^-7 …(8)

[0044] In the following, in this embodiment, "D p ^2 / η" is called the characteristic equation d of the negative electrode slurry (d=D p ^2 / η).

[0045] Here, in the process of using the flow type metal-air battery 1, the negative electrode active material generates dissolved negative electrode active material ions (zinc acid ions) and oxidized solid active material (zinc oxide particles) that has exceeded its solubility and precipitated due to oxidation of zinc particles, which are the reduced solid active material. Therefore, the negative electrode slurry contains the negative electrode active material ions (zinc acid ions) that are dissolved active materials, the reduced solid active material (zinc particles) that is an undissolved solid component, and the oxidized solid active material (zinc oxide particles), a thickener (polyacrylic acid), and an electrolyte (potassium hydroxide aqueous solution) as the negative electrode active material. The reduced solid active material and the oxidized solid active material are obtained as a residue by preferentially dissolving the oxidized solid active material with excess potassium hydroxide, taking advantage of the fact that the dissolution rate of the reduced solid active material is significantly slower than that of the oxidized solid active material. Since the reduced solid active material is a metal active material, its density and particle size can be measured. In addition, the solid active material and the solution component can be separated by centrifugation. The density of the solution components can be measured using this.

[0046] In the characteristic formula d of the negative electrode slurry, by satisfying formula (8), when the particle diameter of the metal active material is large and when the viscosity of the negative electrode slurry is low, the terminal velocity at which the metal active material settles in the negative electrode slurry increases, and the metal active material accumulates below the direction of gravity G in the negative electrode chamber 30. The contact efficiency of the accumulated metal active material with the conductive flow path surface (i.e., the negative electrode 31 in this case) arranged below the direction of gravity G is increased. As a result, an electronic conduction path is formed between a large number of metal active materials and the negative electrode 31 due to contact between the metal active materials and between the metal active materials and the conductive flow path surface, and therefore a decrease in discharge voltage can be suppressed.

[0047] On the other hand, in the characteristic formula d of the negative electrode slurry, when the characteristic formula d is too small, that is, when the particle diameter of the metal active material is D p If the characteristic formula d of the negative electrode slurry is too large, that is, if the particle diameter of the metal active material is too small, or if the viscosity of the negative electrode slurry is too large, the settling speed of the metal active material is slowed down, so that the metal active material is suspended in the negative electrode slurry, and the contact efficiency with the negative electrode 31 is reduced. p If the viscosity of the negative electrode slurry is too large or if the viscosity of the negative electrode slurry is too small, the settling speed of the metal active material will increase and the force of the fluid acting on the metal active material will decrease, which may cause the transport of the metal active material to stop and the negative electrode flow path 32 to become clogged.

[0048] Therefore, in the flow type battery cell 10, by arranging the negative electrode 31 that constitutes part of the wall surface of the negative electrode flow path 32 along the X direction that intersects with the direction of gravity G, and by arranging the negative electrode 31 below the direction of gravity G and forming the negative electrode slurry to satisfy formula (8), it is possible to improve the flowability of the negative electrode slurry and increase the reaction efficiency between the metal active material and the negative electrode 31. Note that in the flow type battery cell 10, the negative electrode 31 is not limited to being arranged in a direction perpendicular to the direction of gravity G, and the negative electrode flow path 32 is not limited to having a flow direction perpendicular to the direction of gravity G, and may be arranged along other directions, such as a diagonal direction intersecting with the direction of gravity, as long as both are directions that intersect with the direction of gravity.

[0049] Example 1 Examples of the flow-type battery cell according to the present disclosure and comparative examples thereof will be described below.

[0050] As an example of a flow-type zinc-air battery, the positive electrode used was made by kneading and rolling manganese dioxide as a catalyst, acetylene black as a conductor, and PTFE as a water repellent and binder.

[0051] The negative electrode slurry flowing through the negative electrode flow passage in the negative electrode chamber is made of three different particle sizes D p A negative electrode slurry containing 20% ​​by weight of the metal active material (zinc powder) with different viscosities η was prepared in an amount of 50 cc, stirred, and then allowed to stand. The state of separation after standing was observed to evaluate whether the metal active material settled and whether a supernatant layer of the electrolyte appeared after 20 minutes had passed. In addition, when the same negative electrode slurry was passed through a 100 mm long flow path with a rectangular cross section of 10 mm x 4 mm for 20 minutes, an evaluation was performed as to whether the flow path was blocked. A list of the evaluation results is shown in Figure 4.

[0052] In Example 1, when a negative electrode slurry was prepared in which the characteristic formula d of the negative electrode slurry satisfied the condition of 5 x 10^-9 or more and 2.5 x 10^-7 or less, it was confirmed that sedimentation and separation were confirmed for any particle size and viscosity (sedimentation and separation "present") and that no flow path blockage occurred (flow path blockage "not present").

[0053] On the other hand, as a comparative example, in the case of a negative electrode slurry in which the particle size of the metal active material is 56 μm, when the viscosity is set to 1000 mPa·s, no sedimentation was observed (sedimentation "not confirmed"). In addition, in the case of a negative electrode slurry in which the particle size is 113 μm, flow path blockage occurred when the viscosity was set to 50 mPa·s (flow path blockage "present"), and no sedimentation was observed when the viscosity was set to 3000 mPa·s. In the case of a negative electrode slurry in which the particle size is 164 μm, flow path blockage occurred when the viscosity was set to 100 mPa·s. These negative electrode slurries do not satisfy the condition that the characteristic formula d is 5×10^-9 or more and 2.5×10^-7 or less.

[0054] Therefore, in a flow type battery cell, by satisfying the above condition of the characteristic formula d of the negative electrode slurry, it is possible to cause settling and separation in the negative electrode slurry to generate a sliding flow as shown in Fig. 3A. This increases the contact efficiency between the metal active material and the negative electrode, and enables stable liquid transfer without causing flow path blockage, thereby suppressing pressure loss during slurry transfer.

[0055] Example 2 In Example 2, negative electrode slurries were prepared by mixing metal active material (zinc powder) having a particle diameter (D50) of 164 μm at different weight fractions, and the viscosity was measured. The viscosity of the electrolyte at 0 wt% was adjusted with a thickener to 90 mPa·s or 4500 mPa·s. The viscosity was evaluated using a Viscotester VT-06 manufactured by RION Co., Ltd. The shear rate dependency of the viscosity was evaluated by changing the rotation speed of a Brookfield viscometer. The measurement using the Viscotester VT-06 is approximately equivalent to a rotation speed of 60 revolutions in a Brookfield viscometer.

[0056] Figure 5 is a graph showing the relationship between metal active material concentration (weight fraction of metal active material) and viscosity of the negative electrode slurry. It can be seen that the viscosity increases as the concentration of metal active material increases. Furthermore, under conditions with a high amount of thickener, the viscosity exceeded 4800 mPa s, resulting in a dispersed state and no sedimentation or separation of the metal active material could be observed, whereas under conditions with a low amount of thickener, the viscosity was less than 1000 mPa, and sedimentation or separation of the metal active material was observed.

[0057] That is, when the metal active material is dispersed in the negative electrode slurry, the slurry viscosity increases. In particular, it can be said that the viscosity increases as the weight fraction of the metal active material increases. On the other hand, by lowering the viscosity of the negative electrode slurry, if the metal active material can be deposited on the negative electrode even under the condition of a low weight fraction of the metal active material, the contact efficiency between the metal active material and the negative electrode can be improved.

[0058] Therefore, the discharge characteristics were evaluated using the negative electrode slurry shown in Figure 5. Figure 6 is a graph showing the relationship between the metal active material concentration in the negative electrode slurry and the discharge capacity.

[0059] As shown in Figure 6, the negative electrode slurry of the dispersion system tended to have a lower discharge capacity than the negative electrode slurry of the precipitation system. That is, in the negative electrode slurry of the precipitation system in which sedimentation was confirmed, the metal active material could be deposited on the negative electrode, and a discharge capacity exceeding 6000mAh was obtained regardless of the metal active material concentration. On the other hand, in the negative electrode slurry of the dispersion system in which sedimentation was not confirmed, the action of depositing the metal active material on the negative electrode did not work, and the contact efficiency between the negative electrode and the metal active material was low, so that the discharge capacity was significantly low when the metal active material concentration was 30% by weight or less, and the discharge capacity tended to increase when the metal active material concentration exceeded 35% by weight.

[0060] Therefore, the discharge capacity is largely dependent on the viscosity of the negative electrode slurry, in other words, the dispersibility of the metal active material. When the viscosity of the negative electrode slurry is high and the metal active material is dispersed, sufficient discharge characteristics cannot be obtained under conditions of low metal active material concentration. For the dispersion-type negative electrode slurry, the value of the characteristic formula d was 4.4 x 10^-9. In contrast, for the precipitation-type negative electrode slurry, a high discharge capacity was obtained even with a low metal active material concentration, and the value of the characteristic formula d for the negative electrode slurry was 6.1 x 10^-8.

[0061] As a result, it was confirmed that in a flow-type battery cell, by satisfying the condition that the characteristic formula d of the negative electrode slurry is between 5x10^-9 and 2.5x10^-7, the contact probability between the negative electrode and the metal active material can be increased even under conditions of low metal active material concentration, resulting in a high discharge capacity. Furthermore, by keeping the viscosity of the negative electrode slurry low, it is possible to achieve the additional effect of suppressing the pressure loss during slurry delivery. It was also confirmed that the viscosity of the negative electrode slurry that can promote the sedimentation of the metal active material in the negative electrode slurry and deposit the metal active material on the negative electrode is less than 1000m·Pa.

[0062] Example 3 As shown in Example 2, when the metal active material concentration is low, the amount of contact between the negative electrode and the metal active material is usually reduced, which is thought to result in a decrease in discharge characteristics. In Example 3, for a negative electrode slurry having a relatively low metal active material concentration and containing 5% to 40% by weight of the metal active material (zinc powder) relative to the total amount, a negative electrode slurry was prepared based on an electrolyte solution containing zinc particles with an average particle size of 50 μm as the metal active material and having a viscosity of 210 mPa·s, and was passed through a negative electrode flow path having a rectangular cross section of 10 mm×4 mm for a predetermined time. FIG. 7 is a graph showing the relationship between the metal active material concentration and discharge characteristics in this case.

[0063] As shown in Figure 7, when the current density is 30 mA / cm 2 When the weight fraction is 5% by weight, the voltage is 0.96 V, and when the weight fraction is 10% by weight or more, the voltage is about 1.0 V. When the current density is 50 mA / cm 2 When the weight fraction is 5% by weight, the voltage is 0.0.73 V, and when it is 10% by weight or more, the voltage is 0.76 V. On the other hand, when the current density is 70 mA / cm 2 When the weight fraction was 5 wt %, the voltage was 0.53 V, and even when the weight fraction was 10 wt % or more, the voltage showed a low value of 0.54 V.

[0064] It was confirmed that when the weight fraction is 15% or more, the voltage is 0.70V or more at all current densities, and sufficient discharge characteristics are obtained. If the weight fraction is too large, the metal active material may clog the negative electrode flow path. For example, if the weight fraction is increased to 40% by weight, the viscosity increases, resulting in a large pressure loss associated with the delivery of the negative electrode slurry.

[0065] For this reason, it is preferable to adjust the weight fraction of the negative electrode slurry so that it contains zinc powder, which is a metal active material, in an amount of 15% by weight or more and 30% by weight or less based on the total weight.

[0066] Example 4 In Example 4, negative electrode slurries with different characteristic formulas d were used to measure the discharge characteristics at various cross-sectional flow velocities (current density was 50 mA / cm 28 is a graph showing the discharge characteristics of the flow-type zinc-air battery for each example.

[0067] It contains 20% by weight of zinc particles with an average particle size of 50 μm, has a viscosity of 210 mPa s, and has a characteristic formula of d = 1.2 × 10 ―8 The negative electrode slurry (Example 4-1) contains 20% by weight of zinc particles having an average particle diameter of 50 μm, has a viscosity of 390 mPa s, and has a characteristic formula of d = 6.4 × 10 ―9 The negative electrode slurry (Example 4-2) contains 20% by weight of zinc particles having an average particle diameter of 175 μm, has a viscosity of 230 mPa s, and has a characteristic formula of d = 1.3 × 10 ―7 and a negative electrode slurry (Example 4-3) containing 20% ​​by weight of zinc particles having an average particle diameter of 175 μm, a viscosity of 330 mPa s, and a characteristic formula of d = 9.3 × 10 ―8 The negative electrode slurry (Example 4-4) was used.

[0068] In all of the examples, the negative electrode slurry satisfied the condition that the characteristic formula d was 5×10^-9 or more and 2.5×10^-7 or less, there was no flow path blockage, and a good discharge voltage was obtained.

[0069] Example 5 In Example 5, a thickener made of a polymer material was added to the electrolyte of the negative electrode slurry in addition to the configuration in Example 1. The viscosity of the negative electrode slurry was evaluated using a B-type viscometer to evaluate the thixotropy.

[0070] In a flow-type metal-air battery, when the negative electrode slurry is stored in the storage section for a long period of time, the concentration of the metal active material may become uneven between the upper and lower layers of the storage section due to the sedimentation or precipitation of the metal active material. If the viscosity of the negative electrode slurry is increased to slow down the sedimentation rate of the metal active material in the negative electrode slurry during storage, the sedimentation or precipitation of the metal active material can be suppressed, but when the negative electrode slurry is supplied to a flow-type zinc-air battery, the sedimentation or deposition of the metal active material on the negative electrode may not progress, resulting in a deterioration in discharge characteristics.

[0071] By using a polymer material such as polyacrylic acid as a thickener to adjust the viscosity of the negative electrode slurry, it is possible to impart shear thinning properties, in which the viscosity of the negative electrode slurry decreases under conditions where a shear force is applied, such as during liquid transfer, compared to the viscosity of the negative electrode slurry when it is left standing, such as during storage. This is because when a polymer material is used as a thickener, the randomly oriented polymer is oriented along the flow, decreasing the viscosity.

[0072] In the negative electrode slurry in which the viscosity is adjusted and shear thinning properties are imparted by using such a thickener made of a polymer material, the viscosity of the negative electrode slurry decreases during pumping compared to when stored (when left stationary), and sedimentation of the metal active material proceeds. As this type of thickener, it is preferable to include a polymer material containing at least one moiety selected from acrylic acid, carboxymethylcellulose-glucopyranose, β-D-mannuronic acid, α-L-guluronic acid, and acrylic methacrylate, such as polyacrylic acid, carboxymethylcellulose, sodium alginate, or acrylic acid-alkyl methacrylate copolymer. This makes it possible to suppress the concentration distribution of the metal active material during storage or other standing, while promoting the sedimentation of the metal active material in the flow type battery cell, and thus suppressing the decrease in discharge voltage.

[0073] Example 6 In Example 6, the flow rate of the negative electrode slurry per cross-sectional area of ​​the negative electrode flow path was evaluated in a negative electrode flow path in which the characteristic formula d of the negative electrode slurry satisfied the condition of 5 x 10^-9 or more and 2.5 x 10^-7 or less, and the negative electrode in the negative electrode chamber was arranged so as to intersect with the direction of gravity.

[0074] Fig. 9 is a cross-sectional view that shows a schematic diagram of a flow type battery cell of Example 6. Fig. 9 shows a cross section perpendicular to the flow direction (X direction, X2 direction in the illustrated embodiment) of the negative electrode slurry in the negative electrode flow channel 32 shown in Fig. 2. In this case, the negative electrode flow channel 32 appears in a state of being partitioned into multiple channels between the negative electrode 31 and the separator 40 that are arranged below in the gravity direction G. The partitioned negative electrode flow channel 32 has a channel cross-sectional area of ​​a cross section perpendicular to the flow direction (X direction) of the negative electrode slurry, which is expressed as W·h, where h is the distance between the negative electrode 31 and the separator 40 and W is the channel width of the negative electrode flow channel 32 perpendicular to the distance h.

[0075] As an example, a negative electrode slurry containing zinc particles with an average particle size of 50 μm as a metal active material and with a viscosity of 210 mPa s was passed through a negative electrode flow path having a rectangular cross-sectional area W h of 10 mm × 4 mm. The concentration of the zinc particles as a metal active material was varied from 5 to 40 wt%.

[0076] Figure 10 shows the discharge characteristics (current density 50 mA / cm) when five types of negative electrode slurries with different metal active material concentrations were passed through the negative electrode flow path. 2 ) and cross-sectional flow velocity, and FIG. 11 is a graph showing the pressure loss and cross-sectional flow velocity. In this case, if the cross-sectional flow velocity is less than 75 cm / min, the resistance of the flow to the metal active material is small, and the metal active material may be retained in the negative electrode flow path or may block the negative electrode flow path. If the cross-sectional flow velocity exceeds 500 cm / min, the flow of the fluid will lift up the metal active material that is trying to accumulate below the gravity (floating flow), and the contact efficiency between the negative electrode placed below in the direction of gravity and the metal active material will decrease.

[0077] Therefore, in a flow type battery cell, it is preferable that the flow rate of the negative electrode slurry passing through a cross section of the negative electrode flow path perpendicular to the flow direction of the negative electrode slurry is 75 cm / min or more and 500 cm / min or less per cross-sectional area of ​​the flow path.

[0078] In this way, by setting the cross-sectional flow velocity of the negative electrode flow path within the above range in addition to the characteristic formula d of the negative electrode slurry satisfying the condition of 5×10^-9 to 2.5×10^-7, the metal active material can flow in a sliding flow state above the negative electrode placed below the gravity direction G without blocking the negative electrode flow path. As a result, electron conduction paths are formed between many metal active materials and the negative electrode due to contact between the metal active materials and the metal active material and the negative electrode, making it possible to suppress a decrease in discharge voltage.

[0079] Example 7 9, in the flow type battery cell 10, one of the wall surfaces constituting the negative electrode flow path 32 is the negative electrode 31, and the other is the separator 40. In the region where the negative electrode 31 and the separator 40 face each other, it is preferable to arrange a plurality of flow paths constituting one negative electrode flow path 32. In this case, the distance (spacing) h between the negative electrode 31 and the separator 40 and the flow path width W affect the pressure loss when the negative electrode slurry is delivered.

[0080] If the distance h between the negative electrode 31 and the separator 40 is less than 1 mm, the metal active materials in the negative electrode slurry may come into contact with each other, and may easily become stagnant, which may result in blocking of the negative electrode flow path 32. In addition, in that case, the pressure loss during liquid transfer may be large. On the other hand, if the distance h between the negative electrode 31 and the separator 40 is 6 mm or more, the distance "(1 / 2)h" between the center of the negative electrode flow path 32 in the distance h direction and the wall surface of the negative electrode flow path 32 becomes long, so the force of the flow acting on the metal active material deposited on the negative electrode 31 becomes small. Therefore, the metal active material may not be transported by the flow in a sliding flow state, and the metal active material may be stagnated in the flow path. In addition, the negative electrode 31 is separated from the separator 40, and the cell resistance increases.

[0081] Furthermore, when the negative electrode flow path 32 is a single flow path, it is necessary to increase the flow rate per cross-sectional area of ​​the flow path, but if the flow path width W is too large, the flow of the negative electrode slurry is likely to become non-uniform, causing variation in the in-plane distribution of the metal active material and reducing the contact efficiency with the negative electrode 31. For this reason, the distance h between the negative electrode 31 constituting the wall surface of the negative electrode flow path 32 and the separator 40 facing the negative electrode 31 is preferably set to 1 mm or more and 6 mm or less.

[0082] In addition, in consideration of realizing a sliding flow in the negative electrode flow path 32, it is preferable that the flow path width W of the negative electrode flow path 32 perpendicular to the distance h is constant. This is because if the flow path width W of the negative electrode flow path 32 is constant from the inlet to the outlet, a large change in the flow rate does not occur.

[0083] 12 and 13 are plan views showing the flow path shape of the negative electrode flow path 32. As described above, the negative electrode flow path 32 is constituted by grooves formed in the negative electrode flow path layer 33, and the negative electrode flow path layer 33 is provided between the negative electrode 31 and the separator 40 to form a flow path with a flow path cross-sectional area W h.

[0084] 12, the negative electrode flow path 32 has a branched flow path, and the multiple flow paths are connected in parallel. The negative electrode slurry flows through a negative electrode manifold 37 that is connected to an inlet 34 and an outlet 35 of the negative electrode flow path 32. If the negative electrode flow path 32 has a flow path shape that includes such branched flow paths, a large change in flow rate is likely to occur before and after the branch. Therefore, it may be difficult to realize a sliding flow of the negative electrode slurry between the flow path region before the branch and the flow path region after the branch.

[0085] 13 does not include any branching flow paths from the inlet 34 to the outlet 35, and has a serpentine flow path structure in which one flow path groove is repeatedly folded back. In this case, multiple flow paths constituting one negative electrode flow path 32 can be arranged in the region where the negative electrode 31 and the separator 40 face each other, which is preferable because it is possible to increase the flow rate per flow path cross-sectional area W·h without increasing the total amount of negative electrode slurry supplied to the flow type battery cell. In addition, since the negative electrode flow path 32 does not have any branching flow paths, no large change in flow rate occurs within the negative electrode flow path 32, and it is possible to realize a sliding flow throughout the entire negative electrode flow path 32.

[0086] As described in the above examples, in the flow type battery cell of the present disclosure, it is possible to increase the contact efficiency between the metal active material and the negative electrode, improve the flowability of the negative electrode slurry, and increase the reaction efficiency between the metal active material and the negative electrode.

[0087] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the technical gist of the present disclosure, and all technical matters included in the technical ideas described in the claims are the subject of the present disclosure. The above-described embodiments are preferred examples, but various modifications can be realized from the disclosed contents, and such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0088] 1 Flow-type metal-air battery 101 Storage 102 Power Generation Division 103 Live parts 10 Flow type battery cell 20 Positive electrode chamber 21 Positive electrode 22 Positive electrode flow path 30 Negative electrode chamber 31 Negative electrode 32 Anode flow path 33 Negative electrode channel layer 34 Inlet 35 Outlet 36 Electricity plate 37 Negative manifold 40 Separator 50 Sealing part

Claims

1. A positive electrode chamber; a negative electrode chamber facing the positive electrode chamber; a separator that separates the positive electrode chamber from the negative electrode chamber, The negative electrode chamber is provided with a negative electrode flow path through which a slurry containing a metal active material and an electrolyte flows, and a negative electrode constituting a part of a wall surface of the negative electrode flow path, a flow type battery cell, characterized in that the negative electrode is arranged along a direction intersecting a direction of gravity and is arranged below the separator in the direction of gravity, and the metal active material flows in a sliding flow state within the negative electrode flow path.

2. A positive electrode chamber; a negative electrode chamber facing the positive electrode chamber; a separator that separates the positive electrode chamber from the negative electrode chamber, The negative electrode chamber is provided with a negative electrode flow path through which a slurry containing a metal active material and an electrolyte flows, and a negative electrode constituting a part of a wall surface of the negative electrode flow path, The negative electrode is arranged in a direction intersecting the direction of gravity and is arranged below the separator in the direction of gravity. The viscosity of the slurry is set to ηPa·s, and the particle diameter of the metal active material is set to D ｐ When m is taken as 5×10^-9≦D ｐ ^2 / <2.5×10^-7 A flow type battery cell characterized by satisfying the above.

3. The flow type battery cell according to claim 1 or 2, A flow type battery cell, characterized in that the viscosity of the slurry is less than 1000 m·Pa.

4. The flow type battery cell according to claim 1 or 2, The slurry contains the metal active material in an amount of 15% by weight or more and 30% by weight or less based on the total amount of the slurry.

5. The flow type battery cell according to claim 1 or 2, A flow type battery cell, wherein the slurry has shear thinning properties.

6. The flow type battery cell according to claim 1 or 2, The slurry comprises a thickening agent; The thickener is a polymer material containing at least one moiety selected from acrylic acid, carboxymethylcellulose glucopyranose, β-D-mannuronic acid, α-L-guluronic acid, and acrylic methacrylate.

7. The flow type battery cell according to claim 1 or 2, a flow rate of the slurry passing through a cross section of the negative electrode flow path perpendicular to a flow direction of the slurry is 75 cm / min or more and 500 cm / min or less per cross-sectional area of ​​the flow path of the cross section.

8. The flow type battery cell according to claim 1 or 2, a distance h between the negative electrode constituting a wall surface of the negative electrode flow path and the separator facing the negative electrode is 1 mm or more and 6 mm or less; The flow type battery cell according to claim 1, wherein the negative electrode flow path has a constant flow path width W perpendicular to the distance h.

9. The flow type battery cell according to claim 1 or 2, 2. The flow type battery cell according to claim 1, wherein the negative electrode flow path does not include a flow path that branches from the inlet to the outlet of the slurry.

10. A power generation section including the flow type battery cell according to claim 1 or 2; a storage section that contains the electrolyte solution that flows through the power generation section; a charging section to which the electrolyte is supplied from the storage section.

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