Although often overlooked in anode research, the anode’s initial Coulombic efficiency (ICE) is a crucial factor dictating the energy density of a practical Li-ion battery. For next-generation anodes, a blend of graphite and Si/SiO_x represents the most practical way to balance capacity and cycle life, but its low ICE limits its commercial viability. Here, we develop a chemical prelithiation method to maximize the ICE of the blend anodes using a reductive Li–arene complex solution of regulated solvation power, which enables a full cell to exhibit a near-ideal energy density. To prevent structural degradation of the blend during prelithiation, we investigate a solvation rule to direct the Li⁺ intercalation mechanism. Combined spectroscopy and density functional theory calculations reveal that in weakly solvating solutions, where the Li⁺–anion interaction is enhanced, free solvated-ion formation is inhibited during Li⁺ desolvation, thereby mitigating solvated-ion intercalation into graphite and allowing stable prelithiation of the blend. Given the ideal ICE of the prelithiated blend anode, a full cell exhibits an energy density of 506 Wh kg^–1 (98.6% of the ideal value), with a capacity retention after 250 cycles of 87.3%. This work highlights the promise of adopting chemical prelithiation for high-capacity anodes to achieve practical high-energy batteries.