Flow-type battery cell

Abstract

To increase reaction efficiency of a metal active material with a negative electrode.SOLUTION: A flow-type battery cell includes a positive electrode chamber, a negative electrode chamber facing the positive electrode chamber, and a separator for dividing the positive electrode chamber and the negative electrode chamber. A negative electrode channel through which slurry containing a metal active material and an electrolyte is circulated, and a negative electrode which constitutes a part of a wall surface of the negative electrode channel are provided within the negative electrode chamber. In a state in which the negative electrode is arranged along a direction crossing a gravity direction and arranged below the separator in the gravity direction, the slurry has shear-thinning properties.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a flow-type battery cell. [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 including a positive electrode, a negative electrode, and an electrolyte solution, in which the electrolyte solution contains at least one metal selected from the group consisting of Zn, Li, Na, Mg, Al, Ca, Cr, and Fe as the active material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-53868 Summary of the Invention [Problem to be solved by the invention]

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

[0005] An object of the present disclosure is to provide a flow-type battery cell that can increase 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 includes 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 forms 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 located below the separator in the direction of gravity, and the slurry exhibits shear thinning properties.

[0007] Furthermore, in the flow type battery cell, it is preferable that the slurry contains a thickener, and 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.

[0008] In the flow type battery cell, the distance h between the negative electrode that forms the wall surface of the negative electrode flow path and the separator facing the negative electrode is preferably 1 mm or more and 6 mm or less.

[0009] In the flow-type battery cell, the negative electrode flow path preferably has a constant flow path width W perpendicular to the distance h.

[0010] In the flow-type battery cell, the negative electrode flow path preferably does not include a flow path that branches from the inlet to the outlet of the slurry. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to increase the reaction efficiency between the metal active material and the negative electrode. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram schematically illustrating the general configuration of a flow-type metal-air battery according to an embodiment. [Figure 2] FIG. 1 is a cross-sectional view schematically showing a flow-type battery cell according to an embodiment. [Figure 3A] FIG. 2 is a cross-sectional view illustrating an example of a flow of anode slurry flowing through a cathode flow path in a flow-type battery cell. [Figure 3B] FIG. 10 is a cross-sectional view illustrating another example of the flow of negative electrode slurry flowing through the negative electrode flow path in a flow-type battery cell. [Figure 3C] FIG. 10 is a cross-sectional explanatory view schematically illustrating yet another example of the flow of negative electrode slurry flowing through the 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. [Figure 5] 1 is a graph showing the relationship between the metal active material concentration and viscosity in a negative electrode slurry. [Figure 6] 1 is a graph showing the relationship between the metal active material concentration in the negative electrode slurry and the discharge capacity. [Figure 7] 1 is a graph showing the relationship between the metal active material concentration in the negative electrode slurry and the discharge characteristics. [Figure 8] 1 is a graph showing the cross-sectional flow velocity and discharge characteristics of a negative electrode slurry. [Figure 9] FIG. 1 is a cross-sectional view schematically showing 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. 2 is a plan view showing an example of a flow channel shape of a negative electrode flow channel. [Figure 13] FIG. 10 is a plan view showing another example of the flow channel shape of the negative electrode flow channel. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] (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 multiple embodiments described below are designated by common reference numerals, and redundant explanations will be omitted.

[0015] As shown 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. Pipes are connected from the storage unit 101 to the charging unit 103, and the electrolyte and the like can be pressure-fed via a pump or the like. The same can be done between the power generation unit 102 and the storage unit 101.

[0016] The storage unit 101 stores a 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 has exceeded its saturated solubility in the electrolyte and is suspended in a particle state without dissolving. The solid active material also includes a reduced solid active material (metal active material) and an oxidized solid active material.

[0017] The negative electrode active material is a metal species. Examples of the metal species include zinc species, cadmium species, lithium species, sodium species, magnesium species, lead species, tin species, aluminum species, and iron species. The metal constituting the metal species may be a metal consisting of only the main component metal, or may be an alloy of the main component metal and a subcomponent. The metal species can be either a metal or an oxide. Whether the metal species becomes 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 below, the metal species is preferably in a reduced state.

[0018] 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 only of zinc as the main component, or may be an alloy of zinc as the 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 reduced solid active material is zinc, and the oxidized solid active material is, for example, zinc oxide.

[0019] The average particle size of the metal species is several μm when it is an oxidized solid active material (e.g., ZnO), and is several tens of μm to 200 μm when it is a reduced solid active material (e.g., Zn). The average particle size can be measured using a particle size distribution analyzer. The particle size distribution analyzer measures the particle size distribution by, for example, laser diffraction or dynamic light scattering, and calculates the median diameter D50 from the measured particle size distribution as the average particle size.

[0020] The electrolyte is selected depending on the metal species. When the metal species is zinc, the electrolyte is an alkaline aqueous solution, such as a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution. When the metal species is lithium, the electrolyte is a non-aqueous electrolyte. When the metal species is magnesium, the electrolyte is a neutral aqueous solution, such as a sodium chloride aqueous solution. The electrolyte may be replaced with a solid electrolyte.

[0021] 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 where the negative electrode is provided from an area where the positive electrode is provided.

[0022] 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. The zincate ions then receive electrons to generate zinc and hydroxide ions. The anion involved in the charging reaction and the discharging reaction described below is hydroxide ions. ZnO+H2O+2OH- →Zn(OH)4 2- …(1) Zn(OH)4 2- +2e - →Zn+4OH - …(2)

[0023] 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)

[0024] The charging unit 103 is a zinc regeneration unit that charges using zinc oxide, which is a solid active material in an oxidized state. 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 preferably there is more oxidized solid active material than reduced solid active material.

[0025] 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. The power generation unit 102 is separated by a separator 104 into an area where the negative electrode is provided and an area where the positive electrode is provided.

[0026] 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, the reduced zinc active material 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 hydroxide ions. Zn+4OH- → Zn(OH)4 2- +2e - …(4) Zn(OH)4 2- →ZnO+H2O+2OH - …(5)

[0027] 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)

[0028] In the power generation unit 102, zinc, which is a solid active material in a reduced state, is used for discharge. 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.

[0029] (Flow battery cell) FIG. 2 is a cross-sectional view that schematically shows a flow-type battery cell 10 in the power generation section 102 of the flow-type metal-air battery 1 according to the embodiment.

[0030] 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, which will be described later.

[0031] The positive electrode chamber 20 is equipped with a positive electrode 21 where an oxygen reduction reaction occurs, and air A containing oxygen as a reactant flows through it. The positive electrode chamber 20 is provided with a positive electrode flow path 22. The positive electrode flow path 22 is a groove formed in a striped pattern, and is a flow path for flowing oxygen, which is a positive electrode active material.

[0032] The anode chamber 30 includes an anode 31 in which an oxidation reaction of metallic zinc occurs. The anode 31 is arranged along the X direction intersecting with the gravity direction G. An anode flow path 32 is provided within the anode chamber 30, through which an anode slurry B containing a metal active material and an electrolyte flows. The anode flow path 32 is a flow path through which the anode slurry B flows. For example, an anode flow path layer 33 is provided between the anode 31 and the separator 40, and the anode flow path 32 is formed by grooves provided in the anode 31, the separator 40, and the anode flow path layer 33. Note that the anode flow path 32 is not limited to being formed by the anode flow path layer 33 having grooves, and the flow path may be formed by grooves provided on the surface of the anode 31, or the like.

[0033] The negative electrode flow path 32 has a flow direction in the X direction (a direction perpendicular to the gravity direction G in FIG. 2 ) and is provided along the X direction. An inlet 34 for the negative electrode slurry is provided at one end of the negative electrode flow path 32 by the negative electrode flow path layer 33, and an outlet 35 for the negative electrode slurry is provided 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.

[0034] The negative electrode 31 forms part of the lower wall surface of the negative electrode flow path 32. The negative electrode 31 can be made of a conductive material such as a carbon material and a resin material. A separator 40, provided opposite the negative electrode 31, forms 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 prevents the negative electrode slurry from permeating 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 (such as a hydrous gel membrane) suitable for preventing the permeation of the negative electrode slurry for the separator 40. The separator 40 and the positive electrode 21 are held and fixed by a sealing portion 50.

[0035] A current-carrying plate 36 may be provided in the negative electrode chamber 30 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. 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.

[0036] 3A to 3C are cross-sectional explanatory views that schematically show examples of the flow of negative electrode slurry flowing through the negative electrode flow path.

[0037] 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. 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.

[0038] 3A , when anode slurry B containing a metal active material 60 and an electrolyte solution is supplied to the anode flow path 32, the metal active material 60 may settle downward in the direction of gravity G within the anode flow path 32, causing separation of the metal active material 60 from the electrolyte solution, resulting in a difference in concentration of the metal active material 60 between the upper and lower layers within the anode flow path 32. In this case, as shown in the figure, the metal active material 60 that has separated and settled from the upper layer consisting of the electrolyte solution is deposited on the anode 31 disposed below the anode 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 anode 31.

[0039] 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 hindered, 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 that attempts to deposit 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.

[0040] When considering sedimentation in the negative electrode flow path 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 (m) of the main constituent particles" and ρ p is the density of the main constituent 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)".

[0041]

number

[0042] 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 forming a sliding flow, while 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.

[0043] 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 poor discharge characteristics, while 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 be difficult to settle and a floating flow will be generated, while if the density is high, it will be prone to settling and the metal active material will not be able to be transported. If the flow velocity (cross-sectional flow velocity) of the negative electrode slurry is slow, the fluid action will be small and the flow may stop without becoming a sliding flow, while if it is fast, the fluid action will be large and a floating flow will be generated easily.

[0044] 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., potassium hydroxide aqueous solution), and adjusted to the following predetermined ranges, thereby increasing the contact efficiency between the metal active material and the negative electrode and improving the reaction efficiency.

[0045] That is, the viscosity of the negative electrode slurry is ηPa·s, and the particle diameter of the metal active material is D p Assuming that m is the mass ratio, the negative electrode slurry is formed so as to satisfy the formula (8). 5×10^-9≦D p ^2 / η<2.5×10^-7 …(8)

[0046] In the following, in this embodiment, "D p ^2 / η" is called the characteristic formula d of the negative electrode slurry (d=D p ^2 / η).

[0047] During use of the flow-type metal-air battery 1, the negative electrode active material, which is the reduced-state solid active material, undergoes oxidation, resulting in the formation of dissolved negative electrode active material ions (zincate ions) and oxidized solid active material (zinc oxide particles) that has exceeded its solubility and precipitated. Therefore, the negative electrode slurry contains the dissolved negative electrode active material ions (zincate ions), the undissolved solid components of the reduced-state solid active material (zinc particles) and oxidized solid active material (zinc oxide particles), a thickener (polyacrylic acid), and an electrolyte (potassium hydroxide aqueous solution). Taking advantage of the significantly slower dissolution rate of the reduced-state solid active material than that of the oxidized-state solid active material, the oxidized-state solid active material is preferentially dissolved with excess potassium hydroxide, leaving the reduced-state solid active material as residue. Because this reduced-state solid active material is a metal active material, its density and particle size can be measured. The solid active material and the solution components can be separated by centrifugation. The density of the solution components can be measured using this.

[0048] 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 or 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 downward in the direction of gravity G in the negative electrode chamber 30. The accumulated metal active material has improved contact efficiency with the conductive flow path surface (i.e., the negative electrode 31 in this case) arranged below the direction of gravity G. As a result, contact between the metal active materials and between the metal active materials and the conductive flow path surface forms an electron conduction path between a large number of metal active materials and the negative electrode 31, thereby suppressing a decrease in discharge voltage.

[0049] On the other hand, in the characteristic formula d of the negative electrode slurry, if the characteristic formula d is too small, that is, if 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 large, the settling speed of the metal active material is slow, and the metal active material is suspended in the negative electrode slurry, resulting in a decrease in the contact efficiency with the negative electrode 31. p If the viscosity of the negative electrode slurry is too large or too small, the settling rate of the metal active material increases and the force of the fluid acting on the metal active material decreases, which may cause the transport of the metal active material to stop and block the negative electrode flow path 32.

[0050] Therefore, in the flow type battery cell 10, by arranging the negative electrode 31, which forms part of the wall surface of the negative electrode flow path 32, along the X direction intersecting with the direction of gravity G, and by arranging the negative electrode 31 below the direction of gravity G and configuring 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 does not necessarily have to have a flow direction perpendicular to the direction of gravity G, but may be arranged in another direction, such as a diagonal direction intersecting with the direction of gravity, as long as both directions intersect with the direction of gravity.

[0051] Example 1 Examples of the flow-type battery cell of the present disclosure and comparative examples thereof will be described.

[0052] 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 acting as a conductor, and PTFE acting as a water repellent and binder.

[0053] The negative electrode slurry flowing through the negative electrode flow path in the negative electrode chamber was made of three different particle diameters D p 50 cc of negative electrode slurry containing 20 wt% of the metal active material (zinc powder) with varying viscosities (η) was prepared, stirred, and allowed to stand. The separation behavior after standing was observed to determine whether the metal active material settled and a supernatant layer of electrolyte appeared after 20 minutes. The same negative electrode slurry was also passed through a 100 mm long flow path with a rectangular cross section of 10 mm x 4 mm for 20 minutes, and the occurrence of flow path blockage was evaluated. A summary of the evaluation results is shown in Figure 4.

[0054] 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 5×10^-9 or more and 2.5×10^-7 or less, sedimentation and separation were confirmed for all particle sizes and viscosities (sedimentation and separation "present"), and it was confirmed that no flow path blockage occurred (flow path blockage "not present").

[0055] On the other hand, as a comparative example, in the case of a negative electrode slurry with a metal active material particle size of 56 μm, when the viscosity was set to 1000 mPa·s, no sedimentation was observed (sedimentation "not observed"). Furthermore, in the case of a negative electrode slurry with a particle size of 113 μm, flow path clogging occurred when the viscosity was set to 50 mPa·s (flow path clogging "present"), and no sedimentation was observed when the viscosity was set to 3000 mPa·s. In the case of a negative electrode slurry with a particle size of 164 μm, flow path clogging 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 between 5×10^-9 and 2.5×10^-7.

[0056] Therefore, in a flow-type battery cell, by satisfying the above condition of characteristic formula d for the negative electrode slurry, it is possible to cause sedimentation and separation within the negative electrode slurry, generating a sliding flow as shown in Fig. 3A. This increases the contact efficiency between the metal active material and the negative electrode, enables stable liquid transport without flow path clogging, and suppresses pressure loss during slurry transport.

[0057] Example 2 In Example 2, negative electrode slurries were prepared by mixing different weight fractions of a metal active material (zinc powder) with a particle diameter (D50) of 164 μm, and the viscosities were measured. The viscosity of the 0 wt% electrolyte was adjusted to 90 mPa·s or 4500 mPa·s using a thickener. 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. Measurements using the Viscotester VT-06 roughly correspond to a rotation speed of 60 rpm using a Brookfield viscometer.

[0058] 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, when there was 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 was observed. However, when there was a low amount of thickener, the viscosity was less than 1000 mPa, and sedimentation or separation of the metal active material was observed.

[0059] That is, when the metal active material is dispersed in the negative electrode slurry, the viscosity of the slurry increases. In particular, it can be said that the viscosity also increases as the weight fraction of the metal active material increases. On the other hand, by reducing the viscosity of the negative electrode slurry, even under conditions of a low weight fraction of the metal active material, if the metal active material can be deposited on the negative electrode, the contact efficiency between the metal active material and the negative electrode can be improved.

[0060] Therefore, 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.

[0061] As shown in Figure 6, the discharge capacity of the dispersion-based negative electrode slurry tended to be lower than that of the precipitation-based negative electrode slurry. That is, the precipitation-based negative electrode slurry, in which sedimentation was confirmed, allowed the metal active material to deposit on the negative electrode, resulting in a discharge capacity of over 6000 mAh regardless of the metal active material concentration. On the other hand, the dispersion-based negative electrode slurry, in which sedimentation was not confirmed, did not function to deposit the metal active material on the negative electrode, resulting in low contact efficiency between the negative electrode and the metal active material. Therefore, when the metal active material concentration was 30 wt% or less, the discharge capacity was significantly low. However, when the metal active material concentration exceeded 35 wt%, the discharge capacity tended to increase.

[0062] 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 equation 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 equation d for the negative electrode slurry was 6.1 x 10^-8.

[0063] This confirmed that in a flow-type battery cell, by satisfying the condition that the characteristic formula d of the negative electrode slurry is between 5 x 10^-9 and 2.5 x 10^-7, the probability of contact between the negative electrode and the metal active material can be increased even when the metal active material concentration is low, 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 pressure loss during slurry delivery. It was also confirmed that the viscosity of the negative electrode slurry, which promotes sedimentation of the metal active material in the negative electrode slurry and allows the metal active material to deposit on the negative electrode, needs to be less than 1000 m·Pa.

[0064] Example 3 As shown in Example 2, a low metal active material concentration typically reduces the amount of contact between the negative electrode and the metal active material, which is thought to result in poor discharge characteristics. In Example 3, a negative electrode slurry with a relatively low metal active material concentration (zinc powder) was prepared using an electrolyte solution containing zinc particles with an average particle size of 50 μm as the metal active material and with a viscosity of 210 mPa·s. The negative electrode slurry was then passed through a negative electrode flow path with a rectangular cross section of 10 mm × 4 mm for a predetermined period of time. Figure 7 is a graph showing the relationship between the metal active material concentration and discharge characteristics in this case.

[0065] As shown in Figure 7, when the current density is 30 mA / cm 2 When the weight fraction is 5 wt%, the voltage is 0.96 V, and when it is 10 wt% or more, the voltage becomes about 1.0 V. When the current density is 50 mA / cm 2 When the weight fraction is 5 wt%, the voltage is 0.0.73 V, and when it is 10 wt% or more, the voltage becomes 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 at 10 wt % or more, the voltage remained low at 0.54 V.

[0066] It was confirmed that when the weight fraction is 15% or more, the voltage is 0.70 V or more at all current densities, and sufficient discharge characteristics are obtained. If the weight fraction is too high, the metal active material may clog the negative electrode flow path. For example, if the weight fraction is increased to 40% or more, the viscosity increases, resulting in a large pressure loss associated with the delivery of the negative electrode slurry.

[0067] 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 to 30% by weight based on the total weight.

[0068] 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 50 mA / cm 2) was evaluated. Fig. 8 is a graph showing the discharge characteristics of the flow-type zinc-air batteries for each example.

[0069] 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 with an average particle diameter of 50 μm, has a viscosity of 390 mPa·s, and has a characteristic formula d=6.4×10 ―9 The negative electrode slurry (Example 4-2) contains 20 wt % zinc particles with an average particle diameter of 175 μm, has a viscosity of 230 mPa s, and has a characteristic formula d = 1.3 × 10 ―7 and a negative electrode slurry (Example 4-3) containing 20 wt % zinc particles with an average particle diameter of 175 μm, a viscosity of 330 mPa s, and a characteristic formula d = 9.3 × 10 ―8 The negative electrode slurry (Example 4-4) was used.

[0070] 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 clogging, and a good discharge voltage was obtained.

[0071] Example 5 In Example 5, a thickener made of a polymer material was added to the electrolyte solution of the negative electrode slurry in addition to the configuration of Example 1. The viscosity of the negative electrode slurry was evaluated using a B-type viscometer to evaluate the thixotropy.

[0072] In a flow-type metal-air battery, when the negative electrode slurry is stored in the storage section for a long period of time, settling or precipitation of the metal active material occurs, which may result in uneven concentration of the metal active material between the upper and lower layers of the storage section. If the viscosity of the negative electrode slurry is increased to slow the settling rate of the metal active material in the negative electrode slurry during storage, the settling 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 settling or deposition of the metal active material on the negative electrode may not progress, which may result in a deterioration in discharge characteristics.

[0073] 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, which means that the viscosity of the negative electrode slurry decreases under conditions where shear force is applied, such as during liquid transport, compared to the viscosity when the slurry is left standing, such as during storage. This is because when a polymer material is used as a thickener, the randomly oriented polymer becomes oriented along the flow, resulting in a decrease in viscosity.

[0074] In a negative electrode slurry whose viscosity is adjusted and whose shear thinning properties are imparted using a thickener made of such a polymer material, the viscosity of the negative electrode slurry decreases during pumping compared to when stored (at rest), promoting sedimentation of the metal active material. This type of thickener preferably includes 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 suppresses the concentration distribution of the metal active material during resting, such as storage, while promoting sedimentation of the metal active material within the flow-type battery cell, thereby suppressing a decrease in discharge voltage.

[0075] 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.

[0076] Fig. 9 is a cross-sectional view schematically illustrating a flow-type battery cell of Example 6. Fig. 9 illustrates a cross section perpendicular to the flow direction (X direction, or X2 direction in the illustrated embodiment) of the negative electrode slurry in the negative electrode flow channel 32 illustrated in Fig. 2. In this case, the negative electrode flow channel 32 appears in a state of being partitioned into multiple sections between the negative electrode 31, which is disposed below in the direction of gravity G, and the separator 40. The partitioned negative electrode flow channel 32 has a cross-sectional area perpendicular to the flow direction (X direction) of the negative electrode slurry, expressed as W·h, where h is the distance between the negative electrode 31 and the separator 40 and W is the width of the negative electrode flow channel 32 perpendicular to the distance h.

[0077] In this example, a negative electrode slurry containing zinc particles with an average particle size of 50 μm as the metal active material and having a viscosity of 210 mPa·s was passed through a negative electrode flow path with a rectangular cross-sectional area W·h of 10 mm × 4 mm. The concentration of the zinc particles as the metal active material was varied from 5 to 40 wt%.

[0078] 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 drag force acting on the metal active material from the flow is small, and the metal active material may stagnate in the negative electrode flow path or block the negative electrode flow path. Furthermore, if the cross-sectional flow velocity exceeds 500 cm / min, the fluid flow will lift up the metal active material that would otherwise be deposited below gravity (floating flow), reducing the contact efficiency between the metal active material and the negative electrode located below in the direction of gravity.

[0079] Therefore, in a flow-type battery cell, it is preferable that the flow rate of the negative electrode slurry passing through the 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.

[0080] 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 or more and 2.5 × 10^-7 or less, the metal active material can flow in a sliding flow state over the negative electrode placed below in the direction of gravity G without clogging the negative electrode flow path. As a result, contact between the metal active materials and between the metal active material and the negative electrode forms numerous electron conduction paths between the metal active material and the negative electrode, making it possible to suppress a decrease in discharge voltage.

[0081] Example 7 9, in a 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 multiple 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.

[0082] If the distance h between the negative electrode 31 and the separator 40 is less than 1 mm, the metal active material in the negative electrode slurry may come into contact with each other, which may cause stagnation and block the negative electrode flow path 32. This may also increase the pressure loss during liquid transfer. On the other hand, if the distance h between the negative electrode 31 and the separator 40 is 6 mm or greater, the distance "(1 / 2)h" between the center of the negative electrode flow path 32 in the direction of the distance h and the wall surface of the negative electrode flow path 32 becomes longer, thereby reducing the force acting on the metal active material deposited on the negative electrode 31. Therefore, a sliding flow state in which the metal active material is transported by the flow does not occur, and the metal active material may stagnate in the flow path. Furthermore, the distance between the negative electrode 31 and the separator 40 increases the cell resistance.

[0083] 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 variations in the in-plane distribution of the metal active material and reducing the contact efficiency with the negative electrode 31. Therefore, 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 1 mm or more and 6 mm or less.

[0084] Furthermore, in consideration of realizing sliding flow in the anode flow path 32, it is preferable that the flow path width W of the anode flow path 32, which is perpendicular to the distance h, is constant. This is because if the flow path width W of the anode flow path 32 is constant from the inlet to the outlet, no large change in flow rate occurs.

[0085] 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 composed of 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, thereby forming a flow path with a flow path cross-sectional area W h.

[0086] 12 , the anode flow path 32 has branched flow paths, and the multiple flow paths are connected in parallel. The anode slurry flows through an anode manifold 37 that is connected to an inlet 34 and an outlet 35 of the anode flow path 32. When the anode 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 branching. This may make it difficult to achieve a sliding flow of the anode slurry between the flow path region before and after the branching.

[0087] In contrast, the anode flow path 32 shown in Fig. 13 does not include any branching flow paths between the inlet 34 and the outlet 35, but has a serpentine flow path structure in which a single flow path groove repeatedly turns back. In this case, multiple flow paths constituting one anode flow path 32 can be arranged in the region where the anode 31 and the separator 40 face each other, which is preferable because it allows for a large flow rate per flow path cross-sectional area W·h without increasing the total amount of anode slurry supplied to the flow battery cell. Furthermore, because the anode flow path 32 does not have any branching flow paths, no large changes in flow rate occur within the anode flow path 32, making it possible to achieve sliding flow throughout the entire anode flow path 32.

[0088] 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, thereby improving the flowability of the negative electrode slurry and increasing the reaction efficiency between the metal active material and the negative electrode.

[0089] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the technical gist thereof, 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]

[0090] 1 Flow-type metal-air battery 101 Storage Unit 102 Power Generation Department 103 Live parts 10 Flow-type battery cells 20 Positive electrode chamber 21 Positive electrode 22 Positive electrode flow path 30 Anode chamber 31 Negative electrode 32 Anode flow path 33 Negative electrode channel layer 34 Inlet 35 Outlet 36 Electricity plate 37 Negative electrode 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 that forms 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, A flow-type battery cell characterized in that the slurry has shear thinning properties.

2. 2. The flow type battery cell according to claim 1, the slurry comprises a thickener; 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.

3. 3. The flow type battery cell according to claim 1, a distance h between the negative electrode forming 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.

4. The flow type battery cell according to claim 3, a flow path width W of the negative electrode flow path perpendicular to the distance h is constant;

5. 3. The flow type battery cell according to claim 1, A flow-type battery cell, characterized in that the negative electrode flow path does not include a flow path that branches from the inlet to the outlet of the slurry.

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