Abstract
Cathodes of Li- and Na-ion batteries usually have capacities <200 mAh/g, significantly less than the anodes. Two-dimensional materials can overcome this limitation but suffer from low voltages. In this context, we investigate NbS2 functionalized by O, F, and Cl as a cathode material by first-principles calculations, considering both the conversion and intercalation mechanisms. NbS2O2 shows a higher voltage than NbS2 for both Li and Na, but the voltage decreases drastically for increasing ion coverage. Even higher voltages and favorable dependences on the ion coverage are achieved by F and Cl functionalization. We obtain NbS2F2 and NbS2Cl2 energy densities of 1223 mWh/g and 823 mWh/g for lithiation and 1086 mWh/g and 835 mWh/g for sodiation, respectively. These values are higher than those for most state-of-the-art cathode materials (similar to 600 mWh/g). In addition, low diffusion barriers enable high cycling rates. Published by AIP Publishing.