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 (σ) and strain (ɛ). The initial discharge capacity is proportional to σⁿ · ɛ (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.