Large-scale electrical energy storage devices are important for efficiently using existing power generation infrastructure, provide stability to renewable power generation, and displacing liquid fossil fuel use in the transportation sector. This project proposes a novel flow battery architecture that employs packed-beds of granular active materials as positive and negative electrodes. This design is expected to improve upon existing battery technologies and most importantly to increase the specific energy of flow battery technology to extend their use to vehicle applications.
This research validates the use of packed-bed electrodes in a flow battery configuration and determines the effects of electrode separation distance, stationary versus flowing electrolyte, ionically active electrode separation materials, separation distance using separation materials, and the direction of electrolyte circulation. These are fundamental parameters that must be determined to provide a packed-bed electrode flow battery (PBEFB) configuration to be used for continued development of the technology.
Zinc/alkaline/manganese dioxide battery chemistry was applied to the PBEFB design for all investigations presented in this dissertation. Two PBEFB configurations were used in these investigations: (1) 2-stainless steel cylinders with stainless steel piston tops (active material containment and current collection) were connected with non-conductive peristaltic pump hose, and (2) 2-stainless steel tubes (active material containment and current collection) were stacked vertically and connected by a non-conductive high-density polyethylene coupling. Overpotentials were revealed using voltage-time profiles and were used as the basis for performance discussions throughout this research. In all experiments, a 550-ohm load was used to discharge the PBEFB to obtain the voltage-time curves.
The effect of electrolyte flow was studied using the second PBEFB configuration. During discharge the PBEFB was subjected to 20-minutes of electrolyte flow, subsequent 20-minutes without electrolyte flow, and then final subsequent 20-minutes of electrolyte flow. This investigation was completed with 3 different electrolyte configurations; 2, 3, and 4 molar potassium hydroxide solutions. The results indicated that without electrolyte flow an increase in overpotential occurs and that higher concentration electrolytes exhibit less overpotential increase with a lack of electrolyte flow. The re-establishment of electrolyte flow immediately reduced the overpotentials associated with the lack of electrolyte flow and voltage profiles returned to similar discharge slopes as those seen prior to stopping electrolyte flow.
Electrode separation distance was investigated using the first PBEFB configuration. Varied lengths of peristaltic pump hose were used to determine the overpotentials associated with changing the distance between the electrodes. Results indicated an increase in overpotential with increased electrode separation distance. This behavior was attributed to an increased resistance to electrolyte charge balancing by the electrolyte counter-ion, K+.
Based on the results of the electrode separation distance study, it was hypothesized that adding a material with ionic activity between the electrodes would aid in electrolyte charge balancing and would result in reduction of overpotentials associated with electrode separation. The first PBEFB configuration was used in these studies. Initial results indicated that using an anion exchange resin, Amberlyst A-26(OH), exhibited lower overpotentials when compared against using a non-ionically active material, stainless steel shot, as the separation material. A survey of materials with different ionic activities was conducted based on these initial results. The survey of materials included: Amberlyst A-26(OH) basic ion exchange resin, Amberlite IR-120H acidic ion exchange resin, stainless steel shot, ethylene-acrylic acid copolymer beads, and ALL-CRAFT 4K activated carbon. The results indicated that Amberlyst A-26(OH) outperformed Amberlite IR-120H, but the ALL-CRAFT 4K activated carbon outperformed both of these materials. The copolymer beads and stainless steel shot performed about the same and exhibited the worst performance of materials tested. Particle size was ruled out as a possible reason for why ALL-CRAFT 4K outperformed Amberlyst A-26(OH) as a test with the use of similar particle sizes did not reveal similar results.
The effect of electrode separation distance while using ionically active separation materials was studied using the second PBEFB configuration. Amberlyst A-26(OH) and stainless steel shot were chosen as separation materials for these studies. Separation material beds of 2.2-, 2.8-, 4.1-, and 5.4-cm were used to separate the electrodes. The use of Amberlyst A-26(OH) as the separation material resulted in a 56% reduction in the voltage range (after 30 minutes of discharge) between 2.2- to 5.4-cm of electrode separation compared to the use of stainless steel shot. An important result of this study is that operating the PBEFB at 5.4-cm of electrode separation using Amberlyst A-26(OH) as the separation material exhibited better performance than using stainless steel shot as the separation material at only 2.2-cm of electrode separation.
The second PBEFB configuration was used to investigate the impact of electrolyte flow direction. It was hypothesize that electrolyte flow direction would have an impact on PBEFB performance due to possible differences in the mechanisms needed to maintain electrolyte charge balance. Using Amberlyst A-26(OH) and Amberlite IR-120H as electrode separation materials, the results were inconclusive. Neither flow direction with either separation material appeared to significantly affect PBEFB performance.
The research presented in this dissertation validates the use of packed-bed electrodes in a flow battery architecture and indicate that adequate electrode separation can be used by implementing ionically active electrode separation materials to reduce overpotentials. Adequate electrode separation is desired with the use of high energy dense metallic negative active materials. The vertically stacked electrode PBEFB configuration exhibits significant promise as an improve flow battery design.
|School:||University of Missouri - Columbia|
|School Location:||United States -- Missouri|
|Source:||DAI-B 73/04, Dissertation Abstracts International|
|Keywords:||Electrolytes, Flow batteries, Packed-bed electrodes|
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