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The batteries are prone to being a fire hazard. Water-based electrolytes have been used as a safer alternative. Problems such as poor efficiency, short device longevity, and safety issues are caused by the problem of water being converted into hydrogen and oxygen within the battery.
It is necessary to remove salts from Li-ion batteries at high concentrations in order to suppress water electrolysis. Water-in-salt electrolytes are higher in volume and weight than salt, and they are referred to as water-in-salt electrolytes. In theory, the transport of lithium ion should be hampered by the high viscosity of the electrolyte. The conventional theory predicts that the water-electrolyte system will be a mixture. Water should be interacting with ion and thus hydrogen bonds should be disrupted.
Li-ion transport tends to be very fast in these areas. The extended stability window of the water molecule in wiSE was studied by using simulations of the water molecule's chemistry and by observing the isolated water molecule that is completely surrounded by ionized water. It wasn't enough to explain the rapid transport of the Li-ion.
The correlation between water dynamics and Li-ion transport has been discovered by a research team at the Center for Molecular Spectroscopy and Dynamics. They used IR-PP and DRS to observe water in a super-concentrated salt solution.
IR-PP can detect the dynamics of an individual water molecule, which is useful for determining its hydrogen bonding partner. The concentration of chemical species present in the electrolyte can be measured with the help of DRS.
The team observed that a lot of bulk-like water in the area exhibits the properties of pure water. There are pockets of bulk water molecule that form hydrogen bonds with other water molecule under high salt concentrations. The rotational dynamics of bulk-like water are faster than that of anion-bound water. The cause of fast Li-ion transport was identified by these observations.
The study is the first to explain the dynamics of water in superconcentrated aqueous electrolytes at amolecular level, and it is possible because IR-PP has the ability to distinguish and observe water molecule according to their hydrogen-bonding partner.
The water played an important role in Li-ion transport mechanisms. The design principle for other superconcentrated electrolytes is expected to be provided by this research.
The research was published in the online edition of the journal.
Jungyu Kim and her team have published a paper on Dynamic Water and its effects on ion transport.
The mechanism of ion transport in the batteries was revealed in the research.
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