# Flame-retardant Cl-substituted electrolyte for low-temperature and high-voltage lithium-ion batteries with fast interfacial kinetics

## TL;DR

A new flame-retardant electrolyte improves lithium-ion battery safety and performance at low temperatures and high voltages.

## Contribution

A chlorine substitution strategy in carbonate electrolytes enhances safety and interfacial kinetics in lithium-ion batteries.

## Key findings

- Cl-substituted electrolyte enables high-voltage (4.6 V) operation with LiNi0.8Co0.1Mn0.1O2 cathodes.
- Electrolyte retains 91.9% capacity at -20°C and passes nail penetration safety tests.
- Ah-level pouch cells show 84.6% capacity retention after 300 cycles.

## Abstract

Carbonate electrolytes such as ethylene carbonate and dimethyl carbonate are excellent at stabilizing the graphite (Gr) anode and thus enable the unprecedented success of lithium-ion batteries but suffer from high flammability and slow ion-transport kinetics at low temperature. Here, we propose a chlorine atom substitution strategy to address the long-standing challenge of carbonate-based electrolytes. Cl atom substitution with an electron-withdrawing effect can facilitate the interfacial reaction by weakening the interactions with Li+ and forming a solid electrolyte interphase involving LiCl, as well as terminating the chain reaction of combustion when releasing Cl radicals. At a conventional salt concentration (1 M), the Cl-substituted carbonate electrolyte achieves stable operation of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode at a high cut-off voltage (4.6 V) and low-temperature adaptation towards the Gr anode (91.9% capacity retention at −20°C). The Ah-level Gr/NCM811 pouch cell maintains 84.6% capacity retention over 300 cycles and can enable the rigorous nail penetration short-circuit test at a fully charged state. This work provides a promising approach to build cost-efficient electrolytes for safe and energy-dense lithium-ion batteries with wide-temperature application potentials.

This study reports a chlorine-substituted carbonate electrolyte for 4.6-V lithium-ion batteries, in which the released Cl• radicals act as flame retardants to increase safety, the weakened Li+-solvent coordination and a LiCl-involved SEI accelerate the interfacial reaction at low-temperature, and the anion-rich solvation structrue enables the formation of the robost CEI to suppress aluminum corrosion with enhanced high-voltage stability.