Scientists at the University of Maryland and the U.S. Army Research Laboratory have built safe, green cells with high concentrations of water and salt, and can play an important role in large-scale grid storage, spacecraft, and pacemakers. Many current batteries use designs that decompose the electrolyte near the cathode for energy, and form a so-called "SEI Layer" that allows the passage of ions despite the insulation.
SEI allows the battery to operate at higher voltages and self-discharges more slowly. It is so important that commercial lithium-ion batteries contain this structure, even if it has to use a flammable electrolyte that can (in rare cases) quickly overheat.
However, we can also use safer alternatives, such as aqueous electrolytes. However, no one believed that the solid electrolyte interface layer (SEI) could be formed in such a medium.
Now, Chunsheng Wang, Kang Xu and his team have successfully created SEI in a water-based battery for the first time. This study paves the way for safer and greener batteries.
Scientists took inspiration from seawater batteries and then used carefully selected lithium salts to bring this concept to the extreme and finally created a 6:1 aqueous solution of brine.
This high concentration of salt (near the saturation level) means that a solid electrolyte interface layer can be formed and the maximum voltage can be increased from 1.23V to 3V.
During the test, the team's prototype battery has achieved a voltage of 2.4V, the entire battery has an energy density of approximately 100Wh/kg, and can maintain stable performance over 1000 charge-discharge cycles.
Previously, in terms of voltage and energy density, aqueous batteries had only two advantages: high cycling and stability. The details of this study have been published in the recently published Science journal.
Of course, there are still many studies to follow, such as the use of non-flammable electrolytes to reduce manufacturing costs and improve the battery's recyclability. Potential applications include cheap and secure grid storage, or providing more secure energy for confined spaces (such as aircraft, spacecraft, and submarines).
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