Energy Efficiency of Flow Batteries Utilizing Non-Newtonian Fluids

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The four-part strategy to maximize efficiency constituted by (a) flow volume control, (b) suspension rheology, (c) interfacial slip promotion, and (d) active-material thermodynamics. In sub-figure (b) the fit of a Bingham-plastic model (yield stress τ0 and plastic viscosity μp) to the rheology of an aqueous suspension of 2 vol% Ketjen black and 10 vol% LiFePO4 from Ref. 9 is shown. The modeled equilibrium potentials shown in sub-figure (d) are from Refs. 39–41.(a) Voltage, (b) state-of-charge, and (c) solid-phase potential as a function of time for a 2-aliquot plug-flow cycle with an aliquot factor of m = 1.0. These curves and fields are shown for LiFePO4,LiCoO2, and V-redox suspensions from top to bottom.Performance as a function of aliquot factor for a Newtonian flow without slip: (a) charge capacity, (b) average polarization, (c) discharge energy,(d) energetic efficiency, and (e) fluid displacement profile. The red-dashed line indicates the critical aliquot factor m˜ for which the upstream aliquot edge is displaced to the downstream edge of the electroactive region. The limit of continuous flow (m → 0) is marked by the red arrow to which values of each performance parameter have been extrapolated (disconnected symbols). The red-dotted line shows the variation of average polarization predicted by the simplified model.
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Inventors
Professor Craig Carter
Department of Materials Science and Engineering, MIT
External Link (dmse.mit.edu)
Professor Yet-Ming Chiang
Department of Materials Science and Engineering, MIT
External Link (dmse.mit.edu)
Kyle Smith
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Flow Battery Using Non-Newtonian Fluids

US Patent Pending 2015-0125764
Publications
Maximizing Energetic Efficiency in Flow Batteries Utilizing Non-Newtonian Fluids
Journal of The Electrochemical Society, 2014 volume 161, issue 4, A486-A496

Applications

Flow batteries can provide scalable, low-cost energy storage for renewable energy sources (e.g. wind and solar).

Problem Addressed

Flow batteries are currently limited by their energy density. Introducing solid-state ion-insertion compounds in a mixed-conducting, flowable suspension increases the energy density. However, the increased viscosity of this suspension incurs two efficiency losses; the electroactive region extends the cell stack and non-uniformity of the flow field. These inefficiencies reduce the discharge energy and overall energetic efficiency. This technology models suspension flow batteries and determines the material properties and flow volume control needed to obtain both a discharge energy as a percentage of theoretical value and an energetic efficiency >95%.

Technology

A model of electrochemical kinetics and flow was developed to identify operating conditions and rheological behavior that maximizes electrochemical performance. This model was applied to three active materials, two solid state lithium-ion compounds (LiFePO­4 and LiCoO2) and one redox solution (VO2+/VO2+). From this model, precisely tuned flow volumes, large yield stresses, large Navier slip coefficients, and two-phase-like active-materials were seen to produce the greatest electrochemical efficiencies. Ideally, plug-flow is achieved, which maximizes energetic efficiency and capacity over cycling because there is no residual charged material. However, since plug-flow in most cases is unobtainable, the following conditions were determined to maximize efficiency and capacity: (β - Navier Slip Coefficient, w - channel width, µp - plastic viscosity, τo - yield stress, and ῡ - mean axial velocity component) β > wp, τo > 100µpῡ/w, and an aliquot factor, pump volume compared to volume between the current collector and separator, between 0.5-0.75. Adhering to these a conditions, a discharge energy (as a percentage of the theoretical value) and an energetic efficiency >95% was observed.

Advantages

  • Energetic efficiency that exceeds 95%
  • Discharge energy 95% of theoretical value
  • Applies to flow batteries with varying parameters