Catalytic interfacial construction of a Li-Al-F-rich SEI for robust silicon dendrite anodes

The unstable solid-electrolyte interphase (SEI) on silicon anodes remains a bottleneck for sustainable lithium storage. Silicon dendrites (SD) derived from Al-Si alloys have been widely investigated, yet the residual Al from dealloying is typically overlooked or regarded as an inert impurity. Here, we introduce a defect-to-design strategy that repurposes this residual Al into an interfacial catalyst. By controlling HF etching kinetics, the native thick Li⁺-blocking SiO _x layer is tailored to an ultrathin thickness, while residual Al is in situ converted into uniformly distributed nanometric AlF₃ on the SD (SD@AlF₃). This AlF₃ precursor dynamically evolves into a Li-Al-F-rich interphase, which preferentially adsorbs FEC and PF₆ ^- and lowers their dissociation barriers, catalyzing a mechanically robust, inorganic-dominated SEI (Young's modulus of 12.0 GPa). Consequently, the optimized SD@AlF₃ anode exhibits ∼80% suppression in electrode swelling and 81.9% capacity retention after 200 cycles (in a half-cell configuration). Moreover, the SD@AlF₃‖LFP full cell retains 92.1% of its capacity after 100 cycles at 0.5C. This work highlights intrinsic defect repurposing as an effective route for interfacial regulation in high-capacity alloy anodes.