Structure-Performance Relationship of Aromatic Polymer Binder for Silicon Anode in Lithium-Ion Batteries

Abstract

Polymer binders are essential for Silicon (Si) anode-based lithium-ion batteries (LIBs). However, the synthetic guidance for aromatic polymer binder is relatively less explored compared to aliphatic polymer binders. In this study, polyimide-based aromatic polymer binders are developed that have strong binding affinity with Si particles, a conductive agent and copper (Cu) current collector, and they show an improved initial discharge capacity of 2663 mAh g(-1), which is 29% higher than that of Kapton-based one (2071 mAh g(-1)). The copolymerization between "hard" and "soft" segments is crucial to achieve reversible volume expansion/contraction during the repeated charging/discharging process, resulting in the best cycle performance. The new binder ensures both excellent volume retention after full-delithiation and allowed volume expansion at least to some extent upon full-lithiation. This Study finds a power-law relationship between the capacity of Si anode and the mechanical properties of the binder, i.e., the tensile stress (& sigma;) and strain (e). The initial discharge capacity is proportional to & sigma;(n) & BULL; e (n = 2.3-2.7). Such an understanding of the relationships between polymer structure, mechanical properties of the polymer and binder performance clearly revealed the importance of the soft-hard polymer structure for aromatic binders used in Si-based high-capacity lithium storage materials.