Li2MSiO4 (M = Fe, Mn, etc.) are promising cathode materials for Li-ion batteries. One appealing strategy for improving their cathode properties is to develop mixed transition metal compounds. Density Functional Theory calculations were performed to evaluate the structural, magnetic and electrochemical properties of Li2M0.5N0.5SiO4 compounds. Our theoretical study allows us to individuate the most promising candidates for practical applications in lithium batteries.