Chitosan as Enabling Polymeric Binder Material for Silicon‐Graphite‐Based Anodes in Lithium‐Ion Batteries

Abstract

Massive volume change during (de-)lithiation and subsequent challenges, such as pulverization of active materials, delamination of electrode from the current collector, and fragile solid electrolyte interphase, are among the main impediments hindering the large-scale commercialization of silicon-containing anode materials in lithium-ion batteries. In this regard, designer polymeric binders with unique chemistries are considered as enabling solutions. Polymeric materials endowed with functional groups such as –OH, –COOH/COO−, and –NH2/NH3+, capable of building strong H bonds, are hailed as effective binders for Si-containing anode materials. Herein, chitosan biopolymers are investigated as a green and environmentally friendly binder in a silicon/graphite (Si/Gr) anode and compared to lithium poly(acrylic acid)/sodium carboxymethyl cellulose binders. The effect of degree of acetylation (DA) and degree of polymerization of chitosan on the electrochemical performance of Si/Gr anode-based cells is investigated. Anodes with chitosan binder with DA of 50% show the most promising electrochemical performance in Si/Gr||lithium metal and lithium nickel manganese cobalt oxide (NMC622)||Si/Gr cells. Crosslinking of chitosan binder with citric acid monohydrate in combination with free-standing electrodes results in improved electrochemical performance in full cells. The surface chemistry of electrochemically cycled Si/Gr anodes with/without chitosan binder is investigated by X-ray photoelectron spectroscopy.