HOME / neutral zinc iron flow batteries advances and challenges
Flow batteries operate distinctively from “solid” batteries (e.g., lead and lithium) in that a flow battery's energy is stored in the liquid electrolytes that are pumped through the battery system (see image above) while a solid-state battery stores its energy in solid electrodes. There are several components that make up a flow battery system:
A new iron-based aqueous flow battery shows promise for grid energy storage applications. A commonplace chemical used in water treatment facilities has been repurposed for large-scale energy storage in a new battery design by researchers at the Department of Energy's Pacific Northwest National Laboratory.
Renewable Energy Source Integration: Flow batteries help the grid during periods of low generation, making it easier to integrate intermittent renewable energy sources like wind and solar. For example, flow batteries are used at the Sempra Energy and SDG&E plant to store excess solar energy, which is then released during times of high demand.
Iron-based flow batteries designed for large-scale energy storage have been around since the 1980s, and some are now commercially available. What makes this battery different is that it stores energy in a unique liquid chemical formula that combines charged iron with a neutral-pH phosphate-based liquid electrolyte, or energy carrier.
Lithium iron phosphate modules, each 700 Ah, 3.25 V. Two modules are wired in parallel to create a single 3.25 V 1400 Ah battery pack with a capacity of 4.55 kWh. Volumetric energy density = 220 Wh / L (790 kJ/L) Gravimetric energy density > 90 Wh/kg (> 320 J/g).
Multiple lithium iron phosphate modules are wired in series and parallel to create a 2800 Ah 52 V battery module. Total battery capacity is 145.6 kWh. Note the large, solid tinned copper busbar connecting the modules. This busbar is rated for 700 amps DC to accommodate the high currents generated in this 48 volt DC system.
Negative electrodes (anode, on discharge) made of petroleum coke were used in early lithium-ion batteries; later types used natural or synthetic graphite. Multiple lithium iron phosphate modules are wired in series and parallel to create a 2800 Ah 52 V battery module. Total battery capacity is 145.6 kWh.
Lithium-iron phosphate batteries officially surpassed ternary batteries in 2021, accounting for 52% of installed capacity. Analysts estimate that its market share will exceed 60% in 2024. The first vehicle to use LFP batteries was the Chevrolet Spark EV in 2014. A123 Systems made the batteries.
The history of zinc-based flow batteries is longer than that of the vanadium flow battery but has only a handful of demonstration systems. The currently available demo and application for zinc-based flow batteries are zinc-bromine flow batteries, alkaline zinc-iron flow batteries, and alkaline zinc-nickel flow batteries.
Neutral zinc–iron flow batteries (ZIFBs) remain attractive due to features of low cost, abundant reserves, and mild operating medium. However, the ZIFBs based on Fe (CN) 63– /Fe (CN) 64– catholyte suffer from Zn 2 Fe (CN) 6 precipitation due to the Zn 2+ crossover from the anolyte.
In addition to the energy density, the low cost of zinc-based flow batteries and electrolyte cost in particular provides them a very competitive capital cost. Taking the zinc-iron flow battery as an example, a capital cost of $95 per kWh can be achieved based on a 0.1 MW/0.8 MWh system that works at the current density of 100 mA cm-2 .
Benefiting from the uniform zinc plating and materials optimization, the areal capacity of zinc-based flow batteries has been remarkably improved, e.g., 435 mAh cm-2 for a single alkaline zinc-iron flow battery, 240 mAh cm -2 for an alkaline zinc-iron flow battery cell stack, 240 mAh cm -2 for a single zinc-iodine flow battery .
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