Implementation of high Si-content anodes (> 10% v/v%) has been difficult to achieve at the loadings and manufacturing scale required for practical lithium-ion batteries (LIBs) applications. Three-dimensionally engineered electrically conductive porous scaffolds enable low silicon coating thicknesses (10-200 nm) and provide internal free volume to reduce the impact of Si volume changes upon cycling. Yet, scalable deposition of battery-grade silicon on these complex structures remains a challenge. Herein, we report a high energy-density Si-dominant electrodeposited material (EDEP-Si) onto 3D-structured Ni scaffolds and evaluate the impact of impurities inherent to the electrodeposition process on performance by comparing the behavior of the EDEP-Si with that of high-purity amorphous Si grown via static chemical vapor deposition (CVD). The long-term cycling stability and high reversible specific capacity of EDEP-Si and CVD-Si on a silicon basis are remarkably similar and near theoretical (~2400 mAh g^-1 Si^-1 after 100 cycles). However, the EDEP-Si exhibits a 13% lower first cycle efficiency and reduced round-trip efficiencies over the first 10-20 cycles relative to CVD-Si. Reactions between carbon (9-11 at%) and, more importantly, oxygen (42-44 at%) in the EDEP-Si with lithium are most likely responsible for the reduced early-cycle round trip efficiencies and low capacity relative to the mass of the total deposit. Based on our observations, we suggest directions for improving the composition and properties of EDEP-Si.