The feasibility of iron substitution by 50% vanadium in lithium iron silicates (Li2FeSiO4) to improve the capacity is investigated by first-principles calculations based on density functional theory (DFT) within the generalized gradient approximation adding Hubbard-like correlation (GGA+U). The structural evolutions of LixFe0.5V0.5SiO4 upon the selected delithiation states, namely x = 0, 0.5, 1.0, 1.5, 2.0, are analyzed in detail. It is demonstrated that 50% vanadium substitution of iron in Li2FeSiO4 may be thermodynamically possible to achieve higher capacity corresponding to more than one lithium ion extractions and improve electronic conductivity with lower band gap. More importantly, minor local structural distortions resulted by vanadium substitution might be beneficial to stabilize the delithiated phases and to achieve better cycling performance. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.025202jes] All rights reserved.