Trace ammonia-assisted binary solvothermal etching for highly stable micron-sized porous silicon/carbon anodes

A trace ammonia-assisted binary solvothermal etching constructs micron Si/C with in-situ CNT networks. • Multi-level architecture with C/SiC coating, porous framework, and 3D CNT network mitigates volume expansion. • Synergistic design achieves stable interfacial impedance and enhanced lithium storage kinetics. Rational structural design represents an effective strategy to mitigate the volume expansion of micron-sized silicon (Si) during charge/discharge cycling and to address its inherently poor electrical conductivity. Herein, we develop a trace-ammonia-assisted binary solvothermal etching method coupled with high-temperature carbonization to simultaneously construct a porous Si skeleton, a β-SiC-reinforced conformal carbon coating, and a three-dimensional interconnected carbon nanotube (CNT) conductive network within a single composite. Systematic investigation reveals the distinct yet complementary roles of each reaction component: the ethylene-glycol-dominated solvent system promotes uniform carbon coating formation; trace ammonia initiates Si etching to generate a porous framework; FeCl 3 catalyzes the in-situ growth of CNT; and the β-SiC phase formed during carbonization reinforces the mechanical integrity of the coating. Benefiting from these multi-level structural advantages, the material maintains intact particle morphology after 20 cycles, with an electrode thickness expansion rate of only 42.2%, substantially lower than that of conventional micron-sized Si/carbon composites (172.4%). Concurrently, it exhibits favorable charge transfer kinetics, as reflected by low and stable interfacial impedance throughout cycling. Electrochemical evaluation demonstrates outstanding cycling stability, with a reversible capacity of 960.4 mAh g −1 retained after 400 cycles at 2.0 A g −1 . Furthermore, a full cell assembled with an NCM622 cathode delivers satisfactory performance, underscoring the practical viability of the designed material. This work offers new insights into the controllable design of high-performance micron-sized Si/C anodes.