Non-Fluorinated Electrolytes Enable Long-Cycling Micron-Sized Silicon Anodes

Microsized silicon (µm-Si) anodes offer lower cost and higher tap density than their nanosized counterparts, however, their practical application remains challenging. A LiF-rich solid electrolyte interphase (SEI) is widely considered essential for µm-Si stable operation. However, potential environmental hazards of fluorides challenge the conventional use of lithium salts and additives for constructing LiF-rich SEIs. Here, we present a non-fluorinated electrolyte combining inorganic lithium salts (LiI/LiBr) with reduction-resistant monoether solvents (tetrahydrofuran and hexyl methyl ether) forms a LiF-free SEI that effectively addresses the rapid capacity fading of µm-Si anodes. Unlike conventional mosaic-structured SEI composed of oligomers and inorganic components (LiF and Li₂O), our electrolyte forms high-molecular-weight polymers with binder-like functionality at the silicon surface, preserving µm-Si particle integrity and maintaining electrical connectivity even after pulverization. As a result, the µm-Si electrode (D₅₀ = 4.65 µm) with an areal capacity of 3.15 mAh cm^-2 achieves a Coulombic efficiency exceeding 99.95% and retains 92.12% of its initial capacity after 300 cycles at 0.3°C and 25°C. Furthermore, Li_3.75Si||SPAN full cells achieve a capacity retention of over 79.43% after 150 cycles. This work provides an unconventional SEI design strategy for µm-Si anodes.