Microbial-Copolyester-Based Eco-Friendly Binder for Lithium-Ion Battery Electrodes

Extensive research has been conducted in order to enhance the capacities of Li-ion batteries (LIBs). However, there is limited research on binders which are one of the main electrode components that contribute to the long life cycle of LIBs. Improving the binder properties enhances both long-term cycling performance and battery life. In this study, amorphous polyhydroxyalkanoate (aPHA), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), with a 4-hydroxybutyric acid content of approximately 47%, was used as a novel eco-friendly binder material. aPHA is an affinity polymer material synthesized by microorganisms and is suitable as a binder because of its electrochemical and thermal stability over the operating voltage and temperature ranges of LIBs. aPHA allowed strong adhesion between the active material and the current collector and maintained the structural stability of the electrode even after long-term cycling owing to its elastic properties. In addition, the high wettability of the aPHA binder toward the electrolyte reduced the resistance of the electrode, providing a shortened diffusion path for Li ions. As a result, aPHA exhibited a superior capacity over the commercially available polyvinylidene fluoride binder and displayed capacity retention with a high Coulombic efficiency (CE) of over 94% for 100 cycles. The PHA content was reduced from 10% to 5% by weight relative to that of the electrode, while the active material content was increased. The use of the aPHA binder increased the capacity and capacity retention with a CE of 94.1% over 100 cycles, indicating its potential as a next-generation eco-friendly binder for LIBs.