E-magy produces a unique porous Si powder that can be used in Silicon-dominant (80-90%) Li-ion battery anodes. Although the powder has a D50 of well over 10 microns, there is no obvious fracture of even the largest particles after cycling, thus overcoming the most important limitation of Si in practical applications. This is achieved by balancing the cells to 1000-1500 mAh/gSi, approximately half the intrinsic capacity, thus maintaining a rigid, crystalline Si backbone that directs the expansion of the material towards the interior of the pores upon lithiation. First-cycle efficiencies comparable to commercial graphite (>90%) can be achieved in half-cell configuration. Full cells reach optimum lifetime of up to 250 cycles, defined as 80% of the discharge capacity immediately after formation, between 600-1100 mAh/gSi. Both at higher and lower Si utilization, the lifetime of the batteries declines. There is a very strong correlation between the maximum coulombic efficiency in the full cells and their cycle life. The absence of particle fracturing, as determined by Ion-Mill Cross-sectioning post-mortem, suggests that further improvements to battery life can be achieved by optimizing the balance between active material and binder and conductive additives, as well as electrolyte formulation.