Structurally Adaptive Branched Polyimide Binder with Synergistic Elastic Buffering and Ionic Transport for Long‐Term Stability of Silicon Anodes

Abstract Overcoming the significant volume expansion and mitigating the poor interfacial stability are pivotal challenges that must be addressed to fully unlock the potential of silicon (Si) as an anode material for next‐generation lithium‐ion batteries (LIBs). Herein, a 3D branched polyimide binder with superior elasticity and ion conductivity is synthesized through the copolymerization of 3,3',4,4'‐biphenyltetracarboxylic dianhydride (BPDA) with tough 4,4'‐oxydianiline (ODA), polar isophthalic dihydrazide (IDP), and flexible poly(dimethylsiloxane)etherimide (DMS), while incorporating branched 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB) to construct a robust 3D crosslinked network. The 3D network of mPI‐T contains abundant aromatic benzene rings, providing high toughness and structural stability. The incorporation of IDP introduces numerous polar amide groups, which enhance the formation of robust interactions with the surfaces of SiO x . Additionally, the flexible Si‐O‐Si segments in DMS contribute exceptional elasticity, effectively preserving the structural integrity of the electrode while facilitating Li⁺ transport. The SiO x @mPI‐T electrode exhibits excellent cycling stability, achieving an unprecedented capacity retention of 88% after 600 cycles at 1C. Moreover, the Si/C@mPI‐T electrode demonstrates remarkable long‐term cycling stability with an exceptionally low capacity decay rate of 0.038% per cycle after 1000 cycles. The full cell of the SiO x @mPI‐T//NCM811 exhibits a remarkable capacity retention of 83.1% after 200 cycles, highlighting the potential of the 3D highly elastic PI binder with superior elasticity and ion conductivity for high‐energy‐density LIBs.