Freestanding flexible Si nanoparticles–multiwalled carbon nanotubes (SiNPs–MWNTs) composite paper anodes for Li-ion batteries (LIBs) have been prepared using a combination of ultrasonication and pressure filtration. No conductive additive, binder, or metal current collector is used. The SiNPs–MWNTs composite electrode material achieves first cycle specific discharge and charge capacities of 2298 and 1492 mAh/g, respectively. To address the first cycle irreversibility, stabilized Li metal powder (SLMP) has been utilized to prelithiate the composite anodes. As a result, the first cycle irreversible capacity loss is reduced from 806 to 28 mAh/g and the first cycle coulombic efficiency is increased from 65% to 98%. The relationship between different SLMP loadings and cell performance has been established to understand the prelithiation process of SLMP and to optimize the construction of Si-based cells. A cell containing the prelithiated anode is able to deliver charge capacity over 800 mAh/g without undergoing the initial discharge process, which enables the exploration of novel cathode materials.