An Amphiphilic Binder with Complementary Polar–Nonpolar Interactions Enables Flexible Micron-Sized Silicon Anodes

Silicon anodes exhibit exceptional capacity but suffer from rapid degradation due to significant volumetric expansion. To address this challenge, an amphiphilic binder, poly(ethylene-alt-maleic acid) (PECH), is developed via one-step hydrolysis. The vicinal dicarboxyl groups form a high-modulus hydrogen-bonded network that maintains the electrode integrity, while the ethylene segments promote affinity with conductive additives through CH−π interactions, yielding a uniform three-dimensional conductive framework. Consequently, PECH significantly enhances conventional silicon anode performance, delivering 3,141 mAh g–1 with 82% retention over 100 cycles, while also enabling the fabrication of flexible, freestanding electrodes. A systematic particle-size evaluation identifies 1 μm silicon as the optimal choice─mitigating nano-Si agglomeration and coarse-particle fracture─achieving 3,059 mAh g–1 with 81% retention over 100 cycles and excellent durability over 10,000 bending cycles. Additionally, the versatility of PECH is further demonstrated in flexible LFP cathodes (146 mAh g–1 after 500 cycles) and LFP||Si full cells (∼1.2 mAh cm–2). This work provides a molecular-level binder design strategy for high-performance and flexible lithium-ion batteries.