The average voltages, volume changes after delithiation and calculated theoretical capacities of the predicted phases are tabulated in Table . For Li-rich phases, only the capacity from the Fe 2+ /Fe 3+ redox is considered here, and Li orderings in the delithiated structures are enumerated for calculating the voltages. Li 2 FeSO is found to have a voltage of 2.3 V, which is in reasonable agreement with the experimentally obtained 2.5 V. We note that for disordered materials, voltages calculated using small ordered unit cell may not be accurate, and more rigorous approaches such as cluster expansion should provide better results. The two anti-RP phases, Li 2 Fe 2 S 2 O and Li 4 Fe 3 S 3 O 2 , are predicted to have voltages 2.9 V and 2.5 V respectively. Compared to the Li 2 FeSO phase (223 mAh/g), they have higher theoretical capacities (261 mAh/g and 249 mAh/g) because their Li:Fe ratios are closer to 1:1.