Charge-engineered cellulose nanofibril binders for PFAS-free, high-loading lithium battery positive electrodes

Area of Science:

• Materials Science
• Electrochemistry
• Sustainable Chemistry

Background:

• Growing demand for high-energy lithium-ion batteries faces environmental concerns from per- and polyfluoroalkyl substances (PFAS) and toxic solvents like N-methyl-2-pyrrolidone (NMP) used in polyvinylidene fluoride (PVDF) binders.
• PVDF binders exhibit limited structural integrity under high-mass-loading conditions, hindering battery performance.

Purpose of the Study:

• To develop a sustainable, PFAS- and NMP-free electrode binder for lithium-ion batteries using charge-engineered cellulose nanofibrils (CE-CNF).
• To evaluate the performance of CE-CNF binders as a renewable alternative to PVDF, focusing on structural integrity, processing, and electrochemical properties.

Main Methods:

• Charge-engineered cellulose nanofibrils derived from natural wood were synthesized.
• CE-CNF binders were characterized for their ability to promote particle dispersion via electrostatic repulsion and form hydrogen bonds for structural reinforcement.
• LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_{2}$ positive electrodes utilizing CE-CNF binders were fabricated and tested for high mass loading and density.
• Electrochemical performance, including areal capacity and volumetric energy density, was evaluated.

Main Results:

• CE-CNF binders enabled NMP-free slurry processing, reducing environmental footprint.
• Electrodes with CE-CNF binders achieved high mass loading (113 mg cm⁻²) and density (3.65 g cm⁻³).
• Competitive electrochemical performance was demonstrated, with an areal capacity of 22.5 mAh cm⁻² and volumetric energy density of 1781.5 Wh L⁻¹ at 0.05 C.

Conclusions:

• Charge-engineered cellulose nanofibrils provide a sustainable, high-performance alternative to conventional PVDF binders in lithium-ion batteries.
• The CE-CNF binder's unique properties enhance electrode structural integrity and facilitate ion transport.
• This approach significantly reduces the environmental impact of battery manufacturing by eliminating PFAS and NMP.