A Lignosulfonate Binder for Hard Carbon Anodes in Sodium-Ion Batteries: A Comparative Study

An important factor in the development of sodium-ion batteries (SIBs) is the use of cheap and sustainable materials. Sodium lignosulfonate, a lignin derivative, is demonstrated here as an attractive, "green", water-soluble, and potentially cost-effective binder for use in hard carbon anodes for SIBs. A comparison of its battery cycling performance is made against other binders including sodium carboxymethyl cellulose and lignin, obtained from the kraft process, as well as sodium alginate, derived from algae. Apart from lignin, which requires processing in N-methyl-2-pyrrolidone, the other three binders are water-soluble. Lignosulfonate shows comparable or better performance, with high capacity retention and stability, when using 1 M NaPF6 in propylene carbonate or ethylene carbonate:diethyl carbonate electrolytes for both half- and full-cells (against a Prussian white cathode). Further improvements are observed when including styrene-butadiene rubber as a co-binder. X-ray photoelectron spectroscopy demonstrates similar solid electrolyte interphase compositions after the initial sodium insertion for both lignosulfonate and carboxymethyl cellulose binders. However, after subsequent cycling, the surface layer composition and thickness are found to be dependent on the binder. For the lignosulfonate-based electrode, the layer appears thicker but comprises a smaller fraction of carbon–oxygen species.