Radical Anion Functionalization of Two-Dimensional Materials as a Means of Engineering Simultaneously High Electronic and Ionic Conductivity Solids

TL;DR

This study introduces a radical anion functionalization method for 2D materials that enhances both electronic and ionic conductivity, enabling advanced energy storage solutions without transition metals.

Contribution

It presents a novel radical anion functionalization approach for 2D materials, improving stability, conductivity, and energy storage capabilities in a transition metal free context.

Findings

Stable reduced state with reversible oxidation

High ionic conductivity due to cation mobility

Potential for high-energy, high-power batteries

Abstract

A radical anion based functionalization of the basal plane of two-dimensional (2D) materials is proposed in the present study. Simple charge neutral radical functionalizations typically detach from the basal planes upon reduction. For example, epoxy oxygens irreversibly detach from graphene when reduced by an alkali metal. The radical anion functionalization of 2D materials results in a stable reduced state that can reversibly be oxidized and has high ionic conductivity due to the great mobility of the cations between the negatively charged functional groups on the surface. Depending on the oxidation state of these systems, a high concentration of hole states can also be realized allowing for good electronic conductivity. These properties can further allow for improved energy storage devices via transition metal free cathode active species, solid electrolytes, electroconductive additives, separators, coatings for metal anodes and heat conductors through a single material. One possible realization of the above principles is the 2D salt An(BN)2OBX3, where A is an alkali atom (Li, Na, etc; 0=<n=<2) or alkaline earth (Mg, etc; 0=<n=<1) and X is a halide (typically F or Cl). This material can be derived from the basal plane functionalization of hexagonal boron nitride, h-BN, with .OBX3^- radical anions in the presence of the A cations. One potential source of .OBX3^- radical anions is their recombined form, the [X3B-O-O-BX3]2- anion, which can be found in the Lewis adduct of an AnO2 ionic peroxide with BX3: An[X3B-O-O-BX3]. The individual radical anions can be obtained by thermally splitting the O-O bond in the recombined anion. Transition metal free all-solid-state batteries with Li, Na and Mg anodes, thermal stability and high energy and power densities may be realizable using An(BN)2OBX3.