# Understanding Binding of Chitosan to Graphene in Li–Ion Battery Anodes from First-Principles

## TL;DR

This paper studies how chitosan, a biodegradable polymer, binds to graphene in lithium-ion battery anodes, comparing it to traditional materials.

## Contribution

The paper provides first-principles insights into chitosan's binding to graphene and how surface modifications affect this interaction.

## Key findings

- Chitosan physisorbs on graphene with hydrogen atoms and amino groups facing the surface.
- Functionalizing graphene with OH and LiF increases chitosan binding energy.
- Room temperature and pH environments significantly influence chitosan adhesion to graphene.

## Abstract

As a water-soluble, biodegradable, and abundant biopolymer,
chitosan
presents great advantages over the common PVDF as a possible binder
to be used in Li–ion battery graphite anodes. Using accurate
density functional theory, which includes a van der Waals long-range
energy functional, we have determined that chitosan molecules physisorb
on graphene/graphite and orient themselves horizontally, exposing
the hydrogen atoms and the amino group to the surface. The binding
energy is less than half that of PVDF. The binding is accompanied
by the transfer of 0.021 e from graphene to chitosan and is dominated
by the van der Waals long-range interactions. We have then investigated
how the functionalization of graphene using point defects, oxygen
atoms, and OH and LiF molecules as adsorbates affects the binding
properties of chitosan. We have found that the presence of carbon
vacancies and the functionalization with the OH and LiF molecular
adsorbates are effective at increasing the binding. Room temperature
significantly increases the chitosan binding energy on graphene functionalized
with atomic oxygen or OH groups. The interaction with charged ions
in low and high pH environments strongly increases chitosan adhesion
to graphene, to which the charge is transferred. The changes of the
binding properties of chitosan to the different surfaces are monitored
through the analysis of the electronic charge redistribution, Bader
charges, and changes in the electronic structure. Our results constitute
a baseline study for further investigations of the interaction between
the eco-friendly polymeric chitosan and the active material surfaces
of electrodes in energy devices.