Electrolyte aggregates in weakly solvating electrolytes (WSEs) favor the formation of anion-derived inorganic-rich interphases, but their pronounced ion association can impede Li⁺ transport and exacerbate polarization under fast-charging conditions. Here we report an anion-sequestration strategy to tailor electrolyte aggregates in a tetrahydropyran (THP)-based WSE. Tris (pentafluorophenyl)borane (TPFPB) strongly binds FSI⁻ and lowers its effective activity, thereby weakening anion-bridged aggregation and shifting the association equilibrium from extended aggregates toward smaller contact ion pairs (CIPs). As a result, the Li⁺ desolvation barrier decreases from 59.86 to 55.12 kJ mol⁻¹, the CIP fraction increases from 44.9% to 52.6%, and the Li⁺ transference number increases from 0.31 to 0.63, collectively accelerating interfacial Li⁺ transport. As a proof of concept, the aggregate-tuned WSE enables Li||NCM523 full cells with a high-areal-capacity cathode (3 mAh cm⁻²) to sustain 3 C fast charging (9 mA cm⁻²), repeatedly reaching 70% state of charge within 18 min over 123 cycles while retaining 97.2% of capacity. In contrast, the pristine WSE becomes polarization-limited, accepting only 48% state of charge with 74.6% retention. These results establish anion sequestration as an effective lever to reconcile interphase-forming solvation chemistry with desolvation/transport kinetics for fast-charging lithium batteries.