Reinvestigation of the electrochemical lithium intercalation in 2H- and 3R-NbS2

Layered sulfides, 2H-Li0.7NbS2 (s.g.: P63/mmc) and 3R-NbS2 (s.g: R3m) were synthesized and characterized as electrode materials for a lithium-ion battery. 2H-NbS2 has been known as a poor electrode material for Li+-intercalation. However, both 2H-Li0.7NbS2 and 3R-NbS2 show reversible charge/discharge reactions based on the Nb(IV)/Nb(III) redox couple. They present distinctive differences in the voltage curves as a result of local structural differences. Galvanostatic charge/discharge tests between 1.0 and 3.0 V versus Li showed that discharge capacities were 169.5 mAh g−1 for 2H-LixNbS2 and 169.0 mAh g−1 for 3R-LixNbS2 at 0.05 C rate and room temperature. At 10 C rate, 2H-LixNbS2 delivered a discharge capacity of 84.0 mAh g−1 while 3R-LixNbS2 kept 74.9 mAh g−1. After 200 cycles at 1 C, 9% of capacity fade was observed for 2H-LixNbS2 (from 141.5 to 129.4 mAh g−1) and 3R-LixNbS2 showed 14% fade from 139.4 to 120.1 mAh g−1. The key to improvement of the electrochemical performance of the 2H-LixNbS2 electrode is an initial synthesis of Li0.7NbS2.