A non-flammable hybrid electrolyte composed of water and 1,3-dioxolane (DOL) has been suggested by the researchers in the latest article published in the journal Energy Storage Materials to facilitate rapid transport of ions at temperatures as low as -50 °C.
Study: Expanding the Low-Temperature and High-Voltage Limits of Aqueous Lithium-ion Battery. Image Credit: Lightboxx/ Shutterstock.com
Importance and Utilization of Lithium-Ion Batteries
Owing to its successful uses in handheld tech gadgets and electric cars, lithium-ion batteries (LIB) have become an intrinsic part of our lives after thirty years of industrialization. LIBs are frequently used in compact protracted power storage because of their high capacity and high reliability.
Li-ion batteries are also used to power large maritime apparatus and warships. Aside from that, solar energy conveniently employs Li-ion cells for photovoltaic arrays due to their quick and effective recharging and storage. Reusable lithium batteries are ideal for global monitoring systems due to their extended life, simple structure, and absence of power outage due to self-discharge when the device is inactive. As a result, lithium-ion batteries have found use in practically every aspect of life.
Limitations of Lithium-Ion Batteries
Although LIBs are incredibly efficient and valuable, there are numerous restrictions to their use. One notable disadvantage is its extreme susceptibility to high temperatures, as well as the high expenses linked with it. The total production cost of these batteries is around 40% more than that of nickel-metal hydride batteries.
In addition, protection is critical to stop these batteries from being overcharged. In the event of overcharging, such batteries are also at risk of exploding. Even though these limits exist, the advantages of using batteries outweigh the downsides.
Limitations of Non-Aqueous Electrolytes
With its pervasiveness in our lives comes widespread public anxiety about its safety, which is sometimes exacerbated by media coverage of spontaneous combustion occurrences. The non-aqueous fluids employed in LIB should share significant blame for these massive failures, since they spark and burst under high-temperature conditions, voltage spikes, and chemical reactivity, all of which are present in the case of a cell overheating.
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Latest Focus on Novel Electrolytes
The hot topic of safety concerns has led to a great deal of interest in substituting extremely combustible non-aqueous solutions with the inherently non-flammable fluid, water. Aqueous lithium-ion batteries (ALIBs) increase safety at the material/cell level, but at the sacrifice of energy density due to the very limited electrochemical stability window (ESW) enforced by water oxidation and reduction of 1.23 V.
The development of water-in-salt-electrolyte (WiSE) has increased the ESW of aqueous electrolytes to 3 V by developing an anion-derived solid-electrolyte-interphase (SEI) that limits water decompositions kinetically.
Disadvantages of the Novel Electrolytes
Almost all these high-voltage ALIBs still exhibit stagnant reaction mechanisms, especially at higher charge/discharge percentages, due to a supplemental interlayer internal resistance caused by more resistive SEI as well as sluggish intracellular transport in high viscosity electrolytes at exceedingly high concentrations of salt, not to mention the organic drawback of electrolyte solution at stubby temperature applications caused by water's high freezing temperature point.
Keeping all of this in mind, the researchers developed a novel saturated aqueous/non-aqueous electrolyte that uses 1,3-dioxolane (DOL) as a co-solvent because of its robust nature against reductions, high permeability, and low freezing point (-95°C).
Analytical and empirical data reveal that the presence of DOL lowers the number of free molecules of water at the electrode surfaces, resulting in improved inter-phase reactivity and a wider ESW of 4.7 V. Although DOL is combustible, the mixed electrolyte is non-flammable because of its high-water content. Even though phase separation was detected in a hybrid at low temperatures, the leftover liquid solution in a semicrystalline electrolyte was shown to have high conductivity and to facilitate fast Li+ desolation at cryogenic temperatures.
Another benefit of the DOL solution is its minimum freezing temperature point, which may increase electrolyte solution permeability at low temperatures. The MD simulations agreed with the experimental conductivity results. Ion movement was significantly hindered in non-aqueous electrolytes below -20°C due to total electrolyte solidification caused by crystallization of the high melting ethylene carbonate.
A similar pattern is observed with WiSE, although at a higher temperature of 0°C, which appears to be caused by the crystallization of ice from the electrolyte.
In conclusion, a novel water/DOL hybrid electrolyte with broad ESW and low-temperature capacity has been discovered. This electrolyte has provided a good electrocatalytic activity for the LMO/LTO ALIBs at -20°C that stays functional at freezing temperatures around -50°C due to its broad ESW of 4.7 V and strong ionic conductance at cold temperatures.
Ma, Z. et al., 2021. Expanding the Low-Temperature and High-Voltage Limits of Aqueous Lithium-ion Battery. Energy Storage Materials. Available at: https://www.sciencedirect.com/science/article/pii/S2405829721006267