Abstract:
Disclosed herein is a redox flow battery, and more particularly, a cell frame channel design capable of efficiently distributing an electrolyte. 
     The present invention provides a cell frame of a redox flow battery providing an electrolyte to an electrode, the cell frame of a redox flow battery including: an electrolyte inlet part and an electrolyte outlet part disposed at both side surfaces of the electrode, respectively; a distribution channel connected to the electrolyte inlet part and dividing the electrolyte into a plurality of channels; a buffer channel formed in a shape in which the buffer channel is connected to an end of each distribution channel and a channel width thereof is increased toward the electrode; a mixing zone formed between the buffer channel and the electrode to mix electrolytes flowed from the buffer channels with each other.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application NO. 10-2013-0082169, filed on Jul. 12, 2013, entitled “Redox Flow Battery and Cell Frame” and Korean Patent Application NO. 10-2013-0082065, filed on Jul. 12, 2013, entitled “Cell Frame for Improved Flow Distributing and Redox Flow Battery Having the Same”, which are hereby incorporated by reference in their entirety into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a redox flow battery, and more particularly, to a cell frame channel design capable of efficiently distributing an electrolyte throughout the entire electrode area and efficiently distributing the electrolyte at various flow rate conditions at which a battery is operated. 
         [0004]    2. Description of the Related Art 
         [0005]    Uniform distribution of an electrolyte is an important factor associated with cell performance and efficiency in increasing a size of a redox flow battery. 
         [0006]    However, there is a limitation in uniformly distributing the electrolyte in a shape of an electrolyte flow channel of an existing redox flow battery frame. In addition, for high-power discharge of the battery, a flow velocity of the electrolyte should be faster than the existing operation condition (flow rate per electrode area: 0.5 cc/(min*cm 2 ), discharge current per electrode area: 80 mA/cm 2 ) but it is impossible to uniformly distribute the electrolyte using a longitudinal channel formed vertically to a transverse channel in the existing battery. When the electrolyte flows in a battery channel at a fast flow rate, fluid may be biased in a direction in which a pressure drop is small, such that a jet flow injected at a high pressure may be formed by an increased velocity of the electrolyte, thereby decreasing cell efficiency. As the related art, there is provided an ‘electrolyte-flowing device for a redox flow battery’ in Korean Patent Registration No. 10-1176575 (Aug. 23, 2012). 
         [0007]      FIG. 2  is a diagram showing a channel structure of the electrolyte-flowing device for a redox flow battery according to the related art. As shown in  FIG. 2 , a second longitudinal channel  507  is installed vertically to a second transverse channel  508 . 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention has been made in an effort to provide a channel design in which an electrolyte is distributed at the same pressure condition and the same channel length for efficient distribution of the electrolyte in a large size redox flow battery, an a channel structure in which a buffer section capable of allowing a velocity of the electrolyte to be uniform and a distribution section are mixed at a fast flow velocity condition of the electrolyte. 
         [0009]    In addition, the present invention has been made in an effort to provide a cell design including a block for preventing a jet flow of an electrolyte injected at a high pressure. 
         [0010]    According to an exemplary embodiment of the present invention, there is provided a cell frame of a redox flow battery, the cell frame of a redox flow battery comprising: an electrolyte inlet part disposed adjacent to a side of an electrode of the redox flow battery; an electrolyte outlet part disposed adjacent to the other side of the electrode; a multi-step distribution channel connected to the electrolyte inlet part, deployed in a transverse direction of the cell frame, and divided into a plurality of channels; multi-step buffer channels, each of which is connected to one of the divided channels of the distribution channel, deployed in a longitudinal direction of the cell frame, and divided into a plurality of sub-channels, wherein a width of each sub-channel is increased toward the electrode; a mixing zone disposed between the buffer channels and the electrode, and configured to mix electrolytes flowed from the buffer channels; and a mixing block disposed in the mixing zone, and configured to distribute and buffer the electrolytes in the mixing zone. 
         [0011]    The distribution channel may be divided into the plurality of channels at a divisional point, wherein a width of the distribution channel before the divisional point is same as a sum of widths of the divided channels of the distribution channel after the division point. 
         [0012]    Each of the buffer channels comprises at least one step-divisional point and has a shape in which a sum of widths of the sub-channels after the step-divisional point is greater than a width of the buffer channel connected to the sub-channels, it is preferable that a sum of widths of the sub-channels divided at an (n+1)-th step divisional point is greater than a sum of widths of sub-channels divided at an n-th step divisional point. 
         [0013]    It is preferable that a ratio between a width of a buffer channel before the step-divisional point and a sum of widths of sub-channels after the step-divisional point is in a range of 1:1.01 to 1:4. 
         [0014]    Meanwhile, a width of an outlet of the buffer channel is in a range of 5 to 30 times a width of an inlet of the buffer channel, and more preferably, the width of the outlet is in a range of 10 to 20 times the width of the inlet. The outlet is connected to the mixing zone, and the inlet is connected to the corresponding divided channel of the distribution channel. 
         [0015]    In addition, the mixing zone has the same width as that of the electrode, and one or more mixing blocks for preventing the electrolyte from being injected at a high pressure are arranged in the mixing zone so as to uniformly divide the mixing zone. It is preferable that the mixing block is positioned so that the mixing zone is uniformly divided for uniform re-distribution of the electrolyte and a central portion of the mixing block is overlapped with a central portion of each buffer channel, thereby preventing high-pressure injection of the electrolyte. In this case, a cross section of the mixing block has a circular shape or a polygonal shape. 
         [0016]    An area occupied by the mixing block in the mixing zone is in a range of 10% to 50% of the entire area of the mixing zone. 
         [0017]    It is preferable that one or more multi-step distribution channels have the same channel lengths, and all of the buffer channels have the same lengths. 
         [0018]    According to another exemplary embodiment of the present invention, there is provided a redox flow battery including: a cell frame of a redox flow battery; and an electrode supplied with an electrolyte from the cell frame, wherein the cell frame of a redox flow battery includes: an electrolyte inlet part disposed adjacent to a side of an electrode of the redox flow battery; an electrolyte outlet part disposed adjacent to the other side of the electrode a multi-step distribution channel connected to the electrolyte inlet part, deployed in a transverse direction of the cell frame, and divided into a plurality of channels; multi-step buffer channels, each of which is connected to one of the divided channels of the distribution channel, deployed in a longitudinal direction of the cell frame, and divided into a plurality of sub-channels, wherein a width of each sub-channel is increased toward the electrode; a mixing zone disposed between the buffer channels and the electrode, and configured to mix electrolytes flowed from the buffer channels; and a mixing block disposed in the mixing zone, and configured to distribute and buffer the electrolytes in the mixing zone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a diagram showing a rear surface of a cell frame of a redox flow battery according to an exemplary embodiment of the present invention. 
           [0021]      FIG. 2  is a diagram showing a channel structure of a cell frame of a redox flow battery according to the related art. 
           [0022]      FIG. 3  is a velocity distribution diagram showing velocity distribution when an electrolyte is introduced at a high velocity in the cell frame of the redox flow battery according to the related art. 
           [0023]      FIG. 4  is a diagram showing a front surface of the cell frame of the redox flow battery according to the exemplary embodiment of the present invention. 
           [0024]      FIG. 5  is a configuration diagram showing a coupling relation of the cell frame of the redox flow battery according to the exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Hereinafter, a cell frame for improved flow distribution according to an exemplary embodiment of the present invention, and a redox flow battery having the same will be described in detail with reference to the accompanying drawings. 
         [0026]    Uniform distribution of an electrolyte is an important factor associated with cell performance and efficiency in increasing a size of a redox flow battery. However, there was a limitation in uniformly distributing the electrolyte in a shape of an electrolyte flow channel of a cell frame of an existing redox flow battery. 
         [0027]    Further, for high-power operation of the battery, a flow velocity of the electrolyte should be faster than the existing operation condition, but a longitudinal channel formed vertically to a transverse channel in the existing battery forms a jet flow of the electrolyte injected at a high pressure as shown in  FIG. 2 , thereby deteriorating cell efficiency. 
         [0028]      FIG. 3  shows velocity distribution when an electrolyte is introduced at a high velocity in a cell frame of a redox flow battery according to the related art. 
         [0029]    Referring to  FIG. 3 , the jet flow is formed at some region, such that an electrode area may not be entirely utilized, thereby decreasing the cell efficiency. 
         [0030]    The present invention is to provide a channel design in which an electrolyte is distributed at the same pressure condition and the same channel length for efficient distribution of the electrolyte in a large size redox flow battery, an a channel structure in which a buffer section capable of allowing a rate of the electrolyte to be uniform and a distribution section are mixed at a fast flow velocity condition of the electrolyte. In addition, the present invention is characterized in that a mixing block for preventing the jet flow of the electrolyte injected at a high pressure is included. 
         [0031]      FIG. 1  is a diagram showing a rear surface of the cell frame of the redox flow battery according to an exemplary embodiment of the present invention, and  FIG. 4  is a diagram showing a front surface of the cell frame of the redox flow battery according to the exemplary embodiment of the present invention. Referring to  FIGS. 1 and 4 , the cell frame  100  of the redox flow battery according to the exemplary embodiment of the present invention may serve to uniformly supply an electrolyte to an electrode  200 . 
         [0032]    The cell frame  100  is disposed in a shape enclosing a peripheral portion of the electrode  200 , and in the case of the exemplary embodiment shown in  FIGS. 1 and 4 , the cell frame  100  has a structure in which the electrolyte is introduced downwardly from the electrode  200 , performs a reaction in the electrode  200 , and then, is discharged upwardly from the electrode  200 . Of course, the structure of the cell frame  100  is not limited thereto, but on the contrary, the cell frame  100  may have a structure in which the electrolyte is introduced upwardly and discharged downwardly. 
         [0033]    Referring to  FIG. 1 , an electrolyte inlet part  102  and an electrolyte outlet part  104  are formed at a right upper end and a left lower end of the cell frame  100 , respectively. The electrolyte inlet part and the electrolyte outlet part  102  and  104  are formed in a shape of a through hole penetrating through the cell frame  100 . 
         [0034]    The electrolyte introduced through the electrolyte inlet part  102  at the left lower end is supplied to the electrode  200  through a distribution channel  120 , a buffer channel  140 , and a mixing zone  160 . 
         [0035]    The distribution channel  120 , the buffer channel  140 , and the mixing zone  160  are formed on and beneath of the electrode  200  in a symmetrical shape. 
         [0036]    The distribution channel  120  is connected to the electrolyte inlet part  102  to serve to divide the electrolyte into a plurality of channels. The distribution channel  120  divides the electrolyte and uniformly disperses the electrolyte to thereby flow the electrolyte. 
         [0037]    The distribution channel  120  is designed in order to distribute the electrolyte to the entire electrode area, and only in the case in which a pressure drop (ΔP) applied to each distribution channel  120  is equal, uniform distribution of the electrolyte may be induced. 
         [0038]    In the case in which the pressure drop (ΔP) is non-uniform, the electrolyte may be biased toward a portion at which the pressure drop (ΔP) is small, and the electrolyte is not distributed to the entire surface of the electrode, such that the cell efficiency may be deteriorated. 
         [0039]    Total lengths of each distribution channel is need to be equal to each other, and it is preferable in view of uniform distribution that when the distribution channel is divided, a division direction of all the distribution channels is a transverse direction. 
         [0040]    In addition, in each of the distribution channels  120 , it is preferable that a bent portion of the distribution channel has a round shape. The reason is that in the case in which the channel is bent at a right angle, the pressure drop may be increased. 
         [0041]    Further, in the distribution channel  120 , in order to decrease the pressure drop of the electrolyte introduced from the electrolyte inlet part, it is preferable that a channel width before division and a sum of channel widths after division are the same as each other. The reason is that in the case in which the sum of the divided channel widths is smaller than the width of the channel before division, the pressure drop is significantly generated in the channel itself, a larger output is required in a pump in order to secure a predetermined flow rate, such that power consumption is increased. 
         [0042]    The distribution channel  120  includes a flow stabilization section  122  connected to the electrolyte inlet part  102  to stabilize a flow of the electrolyte supplied from the electrolyte inlet part  102 , a first channel  121  connected to the flow stabilization section  122  to maintain a first channel width w1, a second channel  123  divided from the first channel  121  so as to have a second channel width w2, and a third channel  125  divided from the second channel  123  so as to have a third channel width w3. 
         [0043]    The distribution channel  120  may be divided from the first channel  121  into two second channels  123 , and two second channels  123  are divided into four third channels  125 . In this case, the second channel width w2 is a half of the first channel width w1, and the third channel width w3 is a half of the second channel width w2. That is, even though the distribution channel is divided, the entire channel width is constantly maintained. Therefore, a constant flow velocity is maintained from the first channel  121  up to the third channel  125  in the distribution channel  120 , and a stable flow of the electrolyte may be formed. 
         [0044]    The distribution channel  120  according to the exemplary embodiment shown in  FIG. 1  has four routes to the buffer channel  140 , and in each of the routes, lengths of the routes are the same as each other. The reason is to allow the electrolyte distributed through the distribution channel  120  to flow at the same condition. 
         [0045]    The buffer channel  140  is a channel connecting the distribution channel  120  and the mixing zone  160 . 
         [0046]    The buffer channel  140  is formed so that a channel width is increased toward a downstream portion (a lower portion in the flow) unlike the distribution channel  120 , such that the buffer channel  140  serves to allow the velocity to be uniform while decreasing the flow velocity. 
         [0047]    It is ideal in view of uniform distribution of the electrolyte that all of the buffer channels  140  are divided in the longitudinal direction unlike the distribution channel  120 . The buffer channel  140  may be configured as a multi-step form, and it is advantageous in view of a buffer effect that a channel width increased in a multi-step is increased at a ratio smaller than an expansion width WO of a final buffer channel connected to the mixing zone  160 . 
         [0048]    An outlet width WO of the final buffer channel is in a range of, preferably, 5 to 30 times, and more preferably 10 to 20 times an inlet width WI of the buffer channel. Here, the inlet width WI of the buffer channel means a channel width at a position at which the buffer channel starts, and the outlet width WO of the buffer channel means a channel width at a position at which the buffer channel ends. 
         [0049]    In the multi-step buffer channel, a sum of widths of buffer channels divided at an (n+1)-th step is larger than a sum of widths of buffer channels divided at an n-th step. 
         [0050]    Further, it is preferable that a ratio between a width of a buffer channel before division and a sum of widths of buffer channels after division at a specific step is in a range of 1:1.01 to 1:4. 
         [0051]    The multi-step buffer channel is to distribute the electrolyte to the entire electrode area and improve the buffer effect, and in the case in which the ratio of the channel width is more than 1:4, distribution efficiency may be deteriorated. The reason is that a channel expanded at a ratio more than 1:4 instantly causes a pressure drop, thereby deteriorating distribution efficiency. 
         [0052]    On the contrary, in the case in which the ratio is less than 1:1.01, it is impossible to obtain the buffer effect. 
         [0053]    Since a distribution function is insignificant in the completely distributed buffer channel, that is, the final buffer channel, the final buffer channel may be expanded so that the outlet width thereof is 5 to 30 times the inlet width thereof, more preferably, 10 to 20 times the inlet width thereof. 
         [0054]    In the case in which the outlet width of the final buffer channel is less than 5 times the inlet width thereof, at the time of cell operation at a fast flow rate range (flow rate per electrode area &gt;1 cc/(min*cm 2 )), the buffer effect of the electrolyte is insignificant, thereby making it possible to cause a jet flow, and in the case in which the final buffer channel is more than 30 times, it is difficult to operate the battery while adjusting the flow rate at a slow flow rate range (flow rate per electrode area &lt;0.5 cc/(min*cm 2 )). 
         [0055]    The buffer channel  140  includes a fourth channel  141  divided from the third channel of the distribution channel  120  so as to have a fourth channel width w4, a fifth channel  143  divided from the fourth channel  141 , and a sixth channel  145  divided from the fifth channel  143  and expanded so that a channel width thereof is 10 to 20 times a fifth channel width w5. 
         [0056]    A penetration channel  150  is formed at an outlet portion of the sixth channel  145 , such that the electrolyte flowing along the distribution channel  120  and the buffer channel  140  formed at the rear surface of the cell frame  100  flows to the front surface of the cell frame  100 . 
         [0057]    The penetration channel  150  is connected to the outlet portion of the sixth channel  145 , and a width of the penetration channel  150  and the outlet width of the sixth channel  145  are the same as each other. 
         [0058]    In addition, the penetration channel  150  has the same width as a width of the mixing zone  160  at the front surface, and the mixing zone  160  is formed so as to have the same width as that of the electrode. 
         [0059]    The mixing zone  160  is formed at the front surface of the cell frame  100 , and mixing blocks  162  are provided in the mixing zone  160 . A mixture channel  164  is formed between the mixing blocks  162  in the mixing zone  160 . 
         [0060]    The mixing block  162  has a predetermined thickness, and a cross-section thereof has a circular or polygonal shape. The mixing blocks  162  are uniformly arranged in the mixing zone  160 , and the mixture channel  164  is formed between the mixing blocks  162 . 
         [0061]    Since the electrolyte moves between the mixing blocks  162 , a movement speed of the electrolyte is uniformly alleviated. 
         [0062]    It is preferable that an area occupied by the mixing block  162  in the mixing zone  160  is 10 to 50% of the entire area of the mixing zone  160 . 
         [0063]    The reason is that in the case in which the area of the mixing block is equal to or less than 10% of the area of the mixing zone, it is difficult to uniformly control the movement velocity of the electrolyte at the time of operation at a fast flow rate range (flow rate per electrode area &gt;1 cc/(min*cm 2 )), and in the case in which the area of the mixing block  162  is more than 50%, the mixture channel  164  becomes narrow, such that the velocity of the electrolyte may be locally increased. 
         [0064]    In the case in which the area of the mixing block  162  is more than 50%, a significant pressure drop may be generated in the flow of the electrolyte, and due to this pressure drop, Revolutions per minute (rpm) of the pump needs to be increased in order to secure the same amount of flow rate. Therefore, energy consumption in the pump is increased, which is a cause of deteriorating the entire system efficiency. 
         [0065]    Therefore, only in the case in which the area occupied by the mixing block  162  in the mixing zone  160  is in a range of 10 to 50% of the entire area of the mixing zone  160 , the pressure drop at a given flow rate may be decreased, and at the same time, the buffer effect may be obtained. 
         [0066]      FIG. 5  is a configuration diagram showing a coupling relation of the cell frame of the redox flow battery according to an exemplary embodiment of the present invention. 
         [0067]    In the cell frame  100  of a redox flow battery, the distribution channel ( 120  of  FIG. 1 ) and the buffer channel ( 140  of  FIG. 1 ) are formed in a groove shape at the rear surface, and a central frame  300  is adhered while covering the distribution channel  120  and the buffer channel  140  formed in the groove shape. An electrode plate  200  is adhered to the central frame  300 . 
         [0068]    A cell frame  100 - 1  in which an electrolyte having a different polarity flows is adhered to an opposite side of the central frame  300  while sharing the central frame  300  and the electrode plate  200 . 
         [0069]    The cell frame providing a flow path of the electrolyte is significantly important in view of improving battery efficiency through efficient distribution of the electrolyte. In the cell frame of the redox flow battery according to the related art, there is a problem that efficiency is deteriorated due to non-uniform distribution of the electrolyte, that is, a phenomenon that a flow of the electrolyte introduced at a high pressure is concentrated at some section at which the pressure of the electrolyte is relieved. However, the present invention solves this problem, such that the electrolyte may be uniformly distributed, and the jet flow may not be generated. 
         [0070]    The cell frame according to the present invention is to uniformly distribute the electrolyte and implement the buffer effect. According to the present invention, the electrolyte is uniformly distributed to all of the sections, such that electrolyte may maximally utilize the electrode area, thereby increasing battery efficiency. Maximization of electrode area utilization may decrease a charging time and a discharging time, and at the time of using power with high output, battery efficiency may be maintained through uniform distribution of the electrolyte at the required fast flow velocity condition. 
         [0071]    In the cell frame according to the present invention, the jet flow is not generated and the electrolyte may be uniformly distributed, even at the fast flow velocity condition of the electrolyte, by disposing the mixing zone and the mixing block while distributing the electrolyte through the channels having the same channel length as each other under the same pressure condition. 
         [0072]    Therefore, in the redox flow battery having the cell frame according to the present invention, the flow of the electrolyte is not concentrated on some section but uniformly distributed, such that the electrode area may be maximally utilized, thereby improving battery efficiency.