High‐Performance Microsized Si Anodes for Lithium‐Ion Batteries: Insights into the Polymer Configuration Conversion Mechanism

Microsized silicon particles are desirable Si anodes because of their low price and abundant sources. However, it is challenging to achieve stable electrochemical performances using a traditional microsized silicon anode due to the poor electrical conductivity, serious volume expansion, and unstable solid electrolyte interface. Herein, a composite microsized Si anode is designed and synthesized by constructing a unique polymer, poly(hexaazatrinaphthalene) (PHATN), at a Si/C surface (PCSi). The Li+ transport mechanism of the PCSi is elucidated by using in situ characterization and theoretical simulation. During the lithiation of the PCSi anode, CN groups with high electron density in the PHATN first coordinate Li+ to form CNLi bonds on both sides of the PHATN molecule plane. Consequently, the original benzene rings in the PHATN become active centers to accept lithium and form stable Li‐rich PHATN coatings. PHATN molecules expand due to the change of molecular configuration during the consecutive lithiation process, which provides controllable space for the volume expansion of the Si particles. The PCSi composite anode exhibits a specific capacity of 1129.6 mAh g−1 after 500 cycles at 1 A g−1, and exhibits compelling rate performance, maintaining 417.9 mAh g−1 at 16.5 A g−1. A poly(hexaazatrinaphthalene) (PHATN) coating is constructed at the surface of a Si/C anode to design a high‐performance microsized Si composite anode for Li‐ion batteries. The Li‐rich PHATN coating can form during the initial lithiation, promote interfacial diffusion kinetics for Li‐ions, generate free space to accommodate the volume expansion of microsized Si, and mitigate possible side reactions.