Abstract:
A flow battery employs a solid suspension charge material to maintain high charge density via stability of a suspension including a binder, conductive carbon and an electrolyte. A cathodic suspension employs carbon powder as a stabilizing agent in a suspension form to avoid precipitation of solids and maintain a high surface area of the suspended solids. The stabilizing agent undergoes agitation and milling to reduce a particle size and increase the change density due to the conductive nature of the fine powdered stabilizing agent exhibiting high energy density. The resulting suspensions are circulated in a charge cell connected to a load for providing electrical power.

Description:
RELATED APPLICATIONS 
     This patent application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent App. No. 61/646,496, filed May 14, 2012, entitled “HIGH ENERGY DENSITY FLOW BATTERIES,” incorporated herein by reference in entirety. 
    
    
     BACKGROUND 
     Flow batteries circulate charge material in the form of a liquid electrolyte for reacting the charge material in a cell to generate electricity from an electrochemical reaction between anode and cathode charge materials. Flow batteries, in contrast to conventional sealed cells such as commonly employed in automobiles, portable electronics, and flashlights, separate the charge materials from an ionic transfer cell or containment where electrochemical reactions occur. Flow batteries decouple power and energy because the charge material is maintained separately and may be stored as an arbitrary volume, in contrast to conventional sealed cells which have a fixed quantity of charge material. Therefore, the charge volume, or capacity, is independent from the energy density, or delivery rate of electrical energy (current and voltage) being drawn of the battery. 
     SUMMARY 
     A solid suspension charge material for a flow battery maintains high charge density via stability of a suspension including a binder, conductive carbon and an electrolyte. In the example arrangement, zinc oxide (ZnO) is employed as the anodic (anode) charge material and nickel hydroxide (Ni(OH) 2 ) is employed as the cathodic (cathode) charge material, and form respective anodic and cathodic suspensions using carbon powder and additives to form suspensions having high stability and high energy density. The resulting suspensions are circulated in a charge cell connected to a load for providing electrical power. 
     Conventional approaches to flow battery usage employ electrolyte solutions circulated through a charge cell for producing an electrochemical reaction and corresponding electrical generation via ion transfer. Unfortunately, conventional approaches suffer from the shortcoming that the charge density of the conventional electrolyte solutions tend to be relatively weak per unit volume of electrolyte. Such electrolyte solutions tend to become saturated and precipitate out, limiting the quantity of charge material that may be dissolved. Therefore, large volumes of electrolyte solution must be employed and circulated to generate a useful energy component in the form of electric charge. Accordingly, configurations herein substantially overcome the shortcomings of conventional solution based flow batteries by introducing a charge suspension having a high charge density for generating substantial electrical energy from a relatively manageable volume of charge material via anodic (anode) and cathodic (cathode) suspensions. 
     Flow batteries are used for large-scale applications that require high-capacity storage and also high power storage. However, they have low power density (˜40 mA/cm 2 ) and energy density (˜30 Wh/L) because of the solubility limit of active materials in solution, which prevents widespread use. 
     In a particular configuration disclosed below, a nickel/zinc (Ni/Zn) flow battery includes an anodic charge material and a cathodic charge material, such that the anodic charge material is different than the cathode charge material and the anodic and cathodic charge materials are defined by a suspension including a conductive carbon powder and additives for stabilizing the suspension. In the example arrangement, the anodic charge material is zinc oxide (ZnO) and the cathode charge material is nickel hydroxide (Ni(OH) 2 ), however alternate charge materials may be employed. 
     The anodic and cathodic charge material are prepared using a mixer for a predetermined time and adding carbon powder and other stabilizing agents for stabilizing the suspension and avoiding settling, in which the charge materials are responsive to the carbon powder for forming a solid suspension network having high energy density properties. The anodic and cathodic charge materials are then supplied to a flow battery for distributing the charge materials through a voltage cell, such that the voltage cell has positive and negative terminals for connection to a load, in which the anodic and cathodic charge materials are circulated via a respective pump for maintaining a potential in the voltage cell for powering the load. 
     Configurations herein substantially overcome the above described shortcomings of conventional solution-based flow batteries by providing a flow battery with Ni/Zn chemistry. The configurations disclosed below present Ni/Zn flow batteries that approximate the following characteristics: Energy density: 260 Wh/L, Power density: 100 mW/cm 2 , cycle life: 5000 cycles, cost: $100/kW and further promote a high safety factor due to the involatility of the water based electrolyte suspension. 
     In the configurations disclosed below, a method of generating an electrochemical charge is disclosed which includes combining a cathode material with an electrolyte and a stabilizing agent to form an electrolyte mixture, and generating a suspension by agitating the electrolyte mixture. A similar suspension is generated for the anode side. The charge material suspensions are circulated the suspension through a voltage cell having charge plates responsive to the electrolyte mixture for generating the electrochemical charge. To prepare a proper suspension for the charge material, combining the cathode material further includes adding a stabilizing agent to a water base, and adding an electrolyte based on the suspension properties of the electrolyte and the stabilizing agent in the water base. Following mixture and agitation, the cathode material is added to form a suspension, and the suspension further agitated decreasing a particle size of the suspension and increasing a charge density of the suspension. Preparation of the anode material involves similar steps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a context diagram of an environment suitable for use with configurations herein; 
         FIG. 2  is a flowchart of charge generation in the environment of  FIG. 1 ; 
         FIG. 3  is a diagram of a flow battery in the environment of  FIG. 1 ; and 
         FIGS. 4-5  are a flowchart of charge material suspension development in the flow battery of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Flow batteries are generally applicable to large-scale projects that require high-capacity storage and also high power storage. However, conventional flow batteries have low power density, being on the order of (˜40 mA/cm 2 ) and having an energy density around ˜30 Wh/L because of the solubility limit of active materials in solution, which presents obstacles to common usage of conventional flow batteries. In the examples disclosed below, a flow battery employs charge material in the form of separate volumes of anode and cathode material circulated through a voltage cell for drawing electrical energy from electrodes attached to the voltage cell. 
     In the approach disclosed below, the active materials for the anode and cathode in Ni/Zn batteries are ZnO and Ni(OH) 2 , respectively. For the anode, carbon powder is added to form the electrical network to increase the electronic conductivity of the electrode. For the cathode, Ni(OH) 2  powder coated with cobalt oxide hydroxide (CoOOH) is used since CoOOH has higher electronic conductivity. Carbon is added in the cathode to form the electric network to further increase the electronic conductivity. The mixtures are added into 6 mol/L potassium hydroxide (KOH) solution (electrolyte for Ni/Zn battery) with different additives to prepare the suspension. The resulting suspensions will be stirred for 10 hours prior to use. Our results showed that suspension can be successfully fabricated. In order to increase the stability of the suspension, several methods including reducing particle size by ball milling, adding effective dispersants (for example poly (acrylic acid) or polyethylene glycol), such that surface modification is utilized. The disclosed approach combines the advantages of high energy density suspension and Ni/Zn chemistry and offers a distinguishable design of flow batteries with high energy and power densities and low cost. 
       FIG. 1  is a context diagram of an environment suitable for use with configurations herein. Referring to  FIG. 1 , in a managed energy environment  100 , a high-density flow battery  110  (flow battery) as disclosed herein may be employed in an electric or hybrid vehicle  112 , for example. The charge material  120 , including the cathode material  122  and anode material  124  take the form of a suspension that can be tuned for range or power delivery. Options for delivery of the charge material  120  to customers could then take a range of forms similar to the manner that petroleum based fuels are rated in octane. The charge material  120  could also be recharged at a charging facility or device  130 , and eventually reserviced, refurbished or recycled at a recycling facility  132 . 
     In the flow battery  110 , such as a flow battery disposed in the vehicle  112 , power delivery can be tuned, or sized to correspond to the needs of the vehicle by the arrangement of charge plates  142 - 1  (anode) and  142 - 2  (cathode),  142  generally, inside a voltage cell  140 . Electrochemical reactions, typically ionic transfers, occur within the voltage cell  140  for generating a voltage for powering a load, such as an electric motor  144 . Power delivery is increased by increasing the area of the charge plates  142 , and charge capacity is increased by additional volumes of the charge material  120  suspension. Qualitative differences in the suspension, such as an amount of suspended charge material per unit volume, affect the total charge capacity, or stored electrical energy. 
       FIG. 2  is a flowchart of charge generation in the environment of  FIG. 1 . Referring to  FIGS. 1 and 2 , in a particular configuration, the flow battery  110  performs a method of generating an electrochemical charge by combining a cathode material with an electrolyte and a stabilizing agent to form an electrolyte mixture, such as the cathode material (mixture)  122 , and the anode material (mixture)  124 , as disclosed at step  200 , and generates a suspension by agitating the electrolyte mixture. The stabilizing agent, discussed further below, facilitates formation of a suspension having a greater charge density than a conventional solution, which are prone to precipitate out charge materials when the concentration becomes too high. The flow battery  110  circulates the suspension through a voltage cell  140 , in which that the voltage cell  140  has charge plates  142  responsive to the electrolyte mixture for generating the electrochemical charge, as depicted at step  202 . 
     In a particular configuration, disclosed herein, there is an electrolyte suspension mixture for both the anode material  124  and the cathode material  122 , corresponding to the anode and cathode poles (electrodes) of the voltage cell  140 . Suspension properties disclosed herein are generally applicable to both, however the examples below will illustrate particular aspects of handling the individual suspensions. In particular, the cathode material suspension  122  requires a more delicate process for maintaining an effective high-density suspension. 
       FIG. 3  is a diagram of a flow battery in the environment of  FIG. 1 . Referring to  FIGS. 1 and 3 , the charge cell  110  circulates the charge material  120  via pumps  146 - 1 ,  146 - 2  ( 146  generally) to maintain the anode material  124  and cathode material  122  in the voltage cell  140 . The voltage cell  140  has a separator  150 , such as an ion selective membrane, for allowing ionic transfer between the cathode material  122  and anode material  124 . The ion transfer causes a complementary electron (electrical) flow from the electrodes  152 - 1 ,  152 - 2  ( 152  generally) for powering the load  144  as the electrodes exhibit a voltage at terminals  162  (positive) and  164  (negative). As indicated above, the power (volts and amps) available from the voltage cell  140  is driven by the size and number of charge plates  142  for scaling the ion transfer, while the energy available is driven by the volume of charge material, thus decoupling power from energy. 
       FIGS. 4-5  are a flowchart of charge material suspension development in the flow battery of  FIG. 3 . Referring to  FIGS. 3-5 , the method of generating an electrochemical charge as disclosed in  FIG. 2  further includes combining the cathode material  122  with an electrolyte and a stabilizing agent to form an electrolyte mixture, as begun at step  300 . Combining further includes adding a stabilizing agent to a water base, as disclosed at step  301 . In an example configuration, the stabilizing agent includes carbon powder, however other suitable additives may be employed. For example, the stabilizing agent may include polymers for maintaining the charge material in solution, as depicted at step  303 , so as to achieve a greater density (concentration) of the suspended cathode material. 
     In the particular example shown, the cathode material is Nickel Hydroxide (Ni(OH) 2 ) and the anode material is Zinc Oxide (ZnO), however other battery chemistries may benefit from the high-density suspension disclosed herein. The method then adds an electrolyte based on the suspension properties of the electrolyte and the stabilizing agent in the water base, as depicted at step  304 . Suspension density properties benefit from the addition of the carbon powder to the water first, then adding electrolyte followed by the charge material. Accordingly, step  305  provides for adding a cathode material to result in a mixture adapted to form a suspension. The method combines the stabilizing agent with the electrolyte, agitating the combination before adding the cathode material, adding the cathode material and further agitating the mixture including the added cathode material for increasing the charge density. The resulting the suspension has a concentration greater than 2 moles/liter of the cathode material. Thus, generation of the cathode material suspension includes combining the cathode material with a water based electrolyte, and agitating the combination with a stabilizing agent, such that the stabilizing agent is for increasing the charge density of the suspended charge material. Similar steps apply for generating an anode suspension by combining an anode material with the stabilizing agent. 
     Accordingly, configurations herein generate a suspension by agitating the electrolyte mixture, as shown at step  306 , thus agitating the suspension for decreasing a particle size of the suspension and increasing a charge density of the suspension, as clarified at step  307 . The cathode materials  122  and anode materials  124  undergo various preparations for increasing a surface area of the materials for increasing density, and enhancing the ability of the electrolyte to maintain the charge material in suspension. Accordingly, agitation further include ball milling to increase granularity of the suspension. In the example configuration, the anodic and cathodic charge materials are prepared using a mixer for a predetermined time and adding carbon powder for stabilizing the suspension for avoiding settling, as depicted at step  308 , such that in the example configuration, the charge materials are responsive to the carbon powder for forming a solid suspension network having high energy density properties of at least 100 watt hours per liter of charge material suspension, as disclosed at step  309 . 
     Following preparation of the cathode  122  and anode  124  material, the pump  146  circulates the suspension through the voltage cell  140 , in which the voltage cell  140  has charge plates  142  responsive to the electrolyte mixture for generating the electrochemical charge, as depicted at step  310 . In the example structure of the flow battery  110  shown, the anode materials  124  and cathode materials  122  are responsive to the flow battery  110  for distributing the charge materials through the voltage cell  140 , such that the voltage cell has positive  162  and negative terminals  164  for connection to a load  144 , in which the anodic  124  and cathode charge materials  122  are circulated via a respective pump  146  for maintaining a potential in the voltage cell  140  for powering the load  144 , as shown at step  311 . 
     In the example battery chemistry shown, the flow battery  110  circulates the suspension through a nickel/zinc (Ni/Zn) flow battery, as shown at step  312 , such that the flow battery  110  includes an anode charge material, as depicted at step  313 , and a cathode charge material, as shown at step  314 , such that the anode (anodic)  124  and cathode (cathodic)  122  charge materials are defined by a suspension including a conductive carbon powder for stabilizing the suspension, as disclosed at step  315 . In the example shown, the cathode charge material  122  includes nickel hydroxide (Ni(OH) 2 ), as shown at step  316 , and the anode charge material  124  is zinc oxide ZnO, as depicted at step  317 . However, as indicated above, other battery chemistries may be employed by preparing the charge material suspension for high density, as discussed above. 
     The above description discloses an example configuration and method for generating and using a high density charge material suspension in a flow battery  140 . While various permutations and combinations of preparing the charge material suspension may be attempted within the scope of the disclosure above, one particular approach to building the flow battery  110  is as follows. Begin forming the cathode material solution by adding carbon to water to form a stabilizing agent. Next, potassium hydroxide (KOH) electrolyte is added, such that the carbon is approximately 3% of the KOH to form an electrolyte suspension. A milling apparatus ball mills the electrolyte suspension using mill balls having a mass of approximately half of the electrolyte solution for substantially around 24 hours, and the resulting the electrolyte solution is sonicated for 1 hour. Following milling, a quantity of nickel hydroxide Ni(OH) 2  is added to the electrolyte suspension to form a substantially 10% nickel hydroxide suspension. The mill is used to further ball milling the electrolyte solution for substantially around 24 hours, and a pump  146  circulates the electrolyte solution through a voltage cell as a cathode material  122 , in which the voltage cell further has anode material  124  and charge plates  142  for connection a voltage load  144 . 
     An alternative suspension may be formed by adding granulated carbon to form a 5% suspension. Therefore, the anode and cathode charge materials are responsive to a flow battery  110  for distributing the charge materials ( 122 ,  124 ) through the voltage cell  140 , in which the voltage cell  140  has positive  162  and negative  164  terminals for connection to a load  144 , and the anodic  124  and cathodic charge materials  122  are circulated via a respective pump  146 - 2 ,  146 - 1  for maintaining a potential in the voltage cell  140  for powering the load  144 . 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present application as defined by the appended claims. Such variations are intended to be covered by the scope of this present application. As such, the foregoing description of embodiments of the present application is not intended to be limiting, the full scope rather being conveyed by the appended claims.