The development of high-voltage and long-life cathode materials remains a key challenge for advanced lithium-ion batteries. Herein, we report surfactant-regulated two-dimensional BiOCl nanosheets (BiOCl-A) synthesized via a facile hydrothermal method and applied as a cathode in a full-cell configuration. Tetramethylammonium iodide (TMAI) effectively directs crystal growth, yielding well-defined nanosheets with enhanced electrochemically active surface exposure. Coupled with a tailored DME/DMF-based LiCl/ LiOTf electrolyte, the BiOCl-A electrode exhibits a conversion-assisted redox process and delivers a stable discharge plateau at ∼3.4 V. The full cell achieves a reversible capacity of ∼200 mAh g −1 based on the mass of the BiOCl-A cathode active material and maintains stable cycling over 1000 cycles with ∼95%–98% retention at 1 A g −1 . Electrochemical impedance analysis reveals reduced charge-transfer resistance and improved apparent interfacial Li + transport kinetics compared with control samples. These results demonstrate that morphology engineering combined with interfacial electrolyte optimization provides an effective strategy for regulating conversion-type cathodes for high-voltage and durable energy storage systems.