In Situ Engineering of a 3D Branched Polyimide/Silver Interface Layer with Dual Ion‐Electron Conductivity for Superior Structural Integrity and Long‐Cycle Stability of Silicon Anodes

Abstract Silicon (Si) has been regarded as a remarkable potential anode material for next‐generation lithium‐ion batteries (LIBs) owing to its exceptional capacity. However, overcoming excessive volume expansion and continuous interfacial side reactions is a prerequisite for achieving practical applicability. Herein, an ion‐electron dual conductive 3D crosslinked interface layer (PMTI‐Ag), derived from branched polyimide (abbreviated as PMTI) and silver (Ag), is synthesized by copolymerizing pyromellitic dianhydride (PMDA), 4,4′‐oxydianiline (ODA), poly(dimethylsiloxane)etherimide (DMS), and 1,3,5‐tris(4‐aminophenoxy) benzene (TAPOB). Trifluoroacetylacetonate silver (AgTFA) is incorporated and in situ reduced to form ultra‐small silver nanoclusters within the PMTI. The 3D crosslinked network of PMTI‐Ag contains abundant aromatic benzene rings, which provide excellent modulus and toughness. The flexible Si‐O‐Si segments in DMS provide elasticity to accommodate volume expansion of Si. The uniform distribution of nanosilver enhances charge‐carrier mobility and promotes the formation of a robust solid electrolyte interface (SEI). The Si@PMTI‐Ag anode exhibits long‐term cycling stability with a specific capacity of 1103.9 mAh g⁻¹ after 350 cycles at 1 A g⁻¹, and this strategy is also suitable for enhancing SiO _x anodes achieving a capacity retention of 89.3% after 400 cycles at 1 C. Moreover, the Si@PMTI‐Ag//LiNi _0.8 Mn _0.1 Co _0.1 O ₂ pouch cell delivers an impressive 82.6% capacity retention after 100 cycles.