A novel aqueous aspartic acid modified biomass binder for high-performance Li-S batteries

Abstract

The commercial feasibility of lithium-sulfur (Li-S) batteries is still hindered by three long-standing problems: substantial volumetric expansion of sulfur cathodes during cycling, serious polysulfide shuttle phenomenon, and sluggish redox kinetics. Addressing these limitations through innovative material engineering, this study presents a sustainable approach by developing a novel aqueous multifunctional binder (designated AG-DAA) derived from aloe vera gel crosslinked with D-aspartic acid. The rationally designed AG-DAA binder demonstrates dual functionality to overcome existing barriers. Mechanically, its superior elastic modulus (1.2 GPa) and tensile strength (156 MPa) enable effective accommodation of sulfur cathode volume fluctuations, thereby maintaining structural integrity throughout extended cycling. Chemically, the abundance of polar functional groups (-COOH, -OH) facilitates three critical interactions: 1) Enhanced Li+ transport through enhanced lithium affinity, 2) Strong chemisorption of lithium polysulfides via Lewis acid-base interaction, and 3) Catalytic acceleration of sulfur redox reactions. The AG-DAA based cathode achieves an initial specific capacity of 1130.8 mAh·g⁻¹ at 0.5 C, maintaining 600.3 mAh·g⁻¹ after 500 cycles with a coulombic efficiency exceeding 98.7%. Remarkably, under high-rate conditions (4 C), the system demonstrates exceptional stability with capacity retention of 51.3% after 1000 cycles, corresponding to an ultralow cycle degradation rate of 0.049% per cycle-representing a 20% improvement over conventional PVDF binders. This investigation establishes a paradigm for eco-friendly binder engineering in Li-S batteries systems, demonstrating that rational design of functionalized natural polymers can simultaneously address multiple electrochemical challenges.