An article has been published in the journal ACS Energy Letters by researchers in China regarding the incorporation of solid Li storage technology with aqueous redox flow battery systems to advocate for the creation of an unconventional battery structure.
Study: Hypersaline Aqueous Lithium-Ion Slurry Flow Batteries. Image Credit: Veleri/Shutterstock.com
The Need for Storage Devices
With a rapid boom in the need for a transformation from fossil fuels to sustainable means of energy such as sporadic wind and solar power, the advancement of cost-optimized and self-sustaining supplementary battery storage is direly needed to meet the ever-increasing demand for decentralized energy storage systems in microgrids.
Solar panels and renewable energy have improved tremendously as a consequence of regulatory benefits and lower program costs. This is primarily due to higher industrial utilization and an increased power demand as a result of both professional and personal activities. Electric energy storage technology is designed to alleviate this adverse situation by smoothing the generation of electricity.
What are Redox Flow Batteries?
Owing to their dependable stability and modulable battery systems with decoupled efficiency and electricity outputs, redox flow batteries based on liquid electrolytes are very promising for industrial applications. Because of their mono-element nature and great durability, all-vanadium redox flow batteries (VRFBs) have especially received a lot of attention.
A redox flow battery (RFB) is one of the most important technologies for electricity and power storage due to the variance of power and energy. In typical RFBs, redox-active materials (RAMs) submerged in solution are placed into battery structures, and electrolytic conditions change on the terminals while the cell packages operate. This implies that both RAMs and electrodes are necessary for RFBs.
Organic RAMs have a low price, are associated with "greenness," and have unique flexibility. The bulk of organic RAM research is now focused on functional studies, medicinal chemistry, and manufacturing.
Limitations of the Technology
However, the persistent crossover phenomenon, relatively poor Coulombic effectiveness (typically 85 percent), and expensive cost of ion-exchange barriers (500 to 700 USD m2) continue to limit the deployment of VRFBs. The organic solution in Li-RFBs, on the other hand, may provide a fire danger and raise system costs.
As a result, it is preferable to replace organic solutions with aqueous electrolytes that are safe, environmentally friendly, and competitively priced. Furthermore, the electrolytic capabilities of aqueous LIBs are limited by the short, wide electrochemical range of water (1.23V) and aquatic side reactions. Furthermore, the use of hypersaline aqueous electrolytes in dynamic RFBs aimed at large-scale energy storage has yet to be investigated.
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It was also discovered that increasing the salt content and adding MWCNTs improved the dispersion stability of slurries and inhibited vanadium dissolution.
Advantages of Aqueous Electrolyte-Containing Batteries
Vanadium-containing polyanion lithium combinations are used to fully utilize the enlarged potential window of high-salinity aqueous electrolytes.
The tightly compacted frameworks of -Li compounds result in a high working potential, quick lithium-ion diffusion, and exceptional phase stability. The incorporation of extra electronegative F ions with a significant induction impact into the solidus covalently linked crystal structure resulted in further enhancements in the oxidation potential of LiVPO4F.
Furthermore, the hypersaline aqueous electrolyte efficiently prevents vanadium-based active compounds from dissolving into the electrolyte. Using ball milling, a specific proportion of MWCNTs was homogeneously incorporated into the slurries and acted as a conductive agent to produce dense electron-transfer channels in the slurries.
The open-circuit voltage of the hypersaline ALISFBs was greater than 1.5 V, with a total energy density of up to 84.6 Wh. Kg-1. During long-term cycling, a phenomenal Coulombic efficiency of over 100 percent was retained.
Importantly, the ALISFBs demonstrated extraordinary cycle stability due to the great structural stability of the particles and the excellent size exclusion of the dialysis membrane. The presence of Li-ion in the batteries, in particular, demonstrated a good capacity retention ratio of almost 100% after more than 1000 cycles, with essentially negligible degradation per cycle and per day.
Furthermore, the combination of a flow cell with a commercialized, low-cost dialysis membrane significantly decreased the ALISFBs' system cost, which is crucial for their practical implementation in large-scale energy storage devices.
In short, an unconventional aqueous slurry flow battery design has been proposed. The pricing of the ALISFBs for grid-scale energy storage devices is conservative because of the special cell design. Furthermore, particles in slurries may be easily recycled using basic liquid-solid extraction procedures such as filtering and centrifugation, considerably facilitating the recovery and recycling of active components.
Wei, J. et al., 2022. Hypersaline Aqueous Lithium-Ion Slurry Flow Batteries. ACS Energy Letters, Volume 7, pp. 862-870. Available at: https://pubs.acs.org/doi/10.1021/acsenergylett.2c00032
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