# Lowering of Proton and Deuteron Mean Kinetic Energy in the LiTFSI Water-in-Salt Electrolyte System

## TL;DR

This paper explores how salt concentration affects proton and deuteron energy in a water-in-salt electrolyte system.

## Contribution

The study reveals that proton and deuteron kinetic energy decreases with higher salt concentration in LiTFSI-H2O.

## Key findings

- Proton and deuteron mean kinetic energy decreases with increasing LiTFSI concentration.
- The hydrogen bond network disruption increases OH stretching frequency but lowers quantum kinetic energy.
- Zero-point energy and environmental effects influence proton/deuteron behavior in water-in-salt systems.

## Abstract

Water-in-salt electrolytes have emerged as promising
materials
for energy storage devices, significantly extending the electrochemical
stability window of water through confinement within a salt matrix.
While the structure and distribution of water molecules in these systems
is becoming increasingly better characterized, the molecular nature
and energetics of water present a greater challenge. Measurement of
the quantum kinetic energy of light atoms is a sensitive probe of
their environment, reflecting the potential experienced by the atoms
and inclusive of their zero-point energy. It is found that the mean
kinetic energy of the proton and deuteron in the archetypal water-in-salt
electrolyte system, LiTFSI-H2O, decreases as a function
of salt concentration. This indicates that while the disruption of
the hydrogen bond network of water is known to lead to an increasing
OH stretching frequency, other components to the quantum kinetic energy
must decrease to result in the overall lower measured average.