Carrageenans as Sustainable Water-Processable Binders for High-Voltage NMC811 Cathodes

Poly(vinylidene fluoride) (PVDF) is the most common binderforcathode electrodes in lithium-ion batteries. However, PVDF is a fluorinatedcompound and requires toxic N-methyl-2-pyrrolidone(NMP) as a solvent during the slurry preparation, making the electrodefabrication process environmentally unfriendly. In this study, wepropose the use of carrageenan biopolymers as a sustainable sourceof water-processable binders for high-voltage NMC811 cathodes. Threetypes of carrageenan (Carr) biopolymers were investigated,with one, two, or three sulfonate groups (SO3 (-)), namely, kappa, iota, and lambda carrageenans, respectively. Inaddition to the nature of carrageenans, this article also reportsthe optimization of the cathode formulations, which were preparedby using between 5 wt % of the binder to a lower amount of 2 wt %.Processing of the aqueous slurries and the nature of the binder, interms of the morphology and electrochemical performance of the electrodes,were also investigated. The Carr binder with 3SO(3) (-) groups (3SO(3) (-) Carr) exhibited the highest discharge capacities,delivering 133.1 mAh g(-1) at 3C and 105.0 mAh g(-1) at 5C, which was similar to the organic-based PVDFelectrode (136.1 and 108.7 mAh g(-1), respectively).Furthermore, 3SO(3) (-) Carr reached an outstanding capacity retention of 91% after 90 cyclesat 0.5C, which was attributed to a homogeneous NMC811 and a conductivecarbon particle dispersion, superior adhesion strength to the currentcollector (17.3 & PLUSMN; 0.7 N m(-1) vs 0.3 & PLUSMN; 0.1N m(-1) for PVDF), and reduced charge-transfer resistance.Postmortem analysis unveiled good preservation of the NMC811 particles,while the 1SO(3) (-) Carr and 2SO(3) (-) Carr electrodesshowed damaged morphologies.

Automated summary

This study proposes the use of carrageenan biopolymers as a sustainable and water-processable binder for high-voltage NMC811 cathodes in lithium-ion batteries. The binder with 3 sulfonate groups (3SO(3) (-) Carr) showed the highest discharge capacities and capacity retention.