# Molecularly Engineered Amphiphilic Anions Enable Flame-Retarding Fluorous Electrolytes for Lithium Metal Batteries

## TL;DR

Scientists designed a new type of electrolyte for lithium metal batteries that is both safe and efficient, using molecularly engineered anions to prevent fires and improve battery performance.

## Contribution

The paper introduces a novel fluorous electrolyte design using amphiphilic anions that improves both safety and performance in lithium metal batteries.

## Key findings

- The designed electrolyte is nonflammable and enables dendrite-free lithium plating with high Coulombic efficiency.
- Molecular engineering of anions enhances compatibility between solvents and diluents, improving battery stability.
- LiF-rich interphases formed at the electrode interface delay thermal runaway and improve safety.

## Abstract

Developing high-energy-density lithium metal batteries
(LMBs) is
challenging due to critical safety concerns and cycling instability.
A highly fluorinated diluent offers improved safety features but fails
to form miscible electrolytes. Herein, we address these key issues
through the design of miscible fluorous electrolytes enabled by molecular
engineering of anions with fluoro-alkyl moieties, creating an effective
molecular bridge between solvents and fluorous diluents. Detailed
spectroscopy and molecular dynamics simulations reveal the critical
amphiphilic anion chemistry inward and outward of the Li+ solvation sheath: fluorophilic interactions (F···F)
with the diluent and atypical hydrogen-bonding (F···H)
with the solvent. The designed miscible fluorous electrolyte, featuring
diluents with ultrahigh F/H atomic ratios of 4.33 or higher, exhibits
not only remarkable nonflammability safety properties, but also dendrite-free
Li plating/stripping with a high Coulombic efficiency (CE) of 99.53%
and long-term cycling stability in Li||NCM811 batteries. LiF-rich
interphases formed at the electrode–electrolyte interface and
the unique electrolyte formulation greatly enhance the battery performance
and safety profile, as characterized by delayed onset and peak temperatures
of thermal runaway reactions. This study demonstrates a general approach
for engineering high-safety electrolytes, advancing next-generation
LMBs that overcome the traditional trade-off between performance and
safety.