Liquid phase exfoliation of GeS nanosheets in ambient conditions for lithium ion battery applications

The propensity of many 2D materials to oxidize in ambient conditions can complicate production and limit applications potential. Here we describe ambient liquid phase exfoliation of GeS, a layered material known for its chemical instability. Ambient exfoliation in organic solvents such as N-methyl-pyrrolidone yields good quality multi-layer GeS nanosheets. Although oxidation appears to occur with a time constant of similar to 10 d, the data suggests it to be limited to nanosheet edges leaving the basal plane intact. The rate of oxidation is slow enough to allow processing of the dispersions. For example, it was possible to size-select GeS nanosheets and characterize the size-dependence of nanosheet optical properties, leading to the observation of significant changes in bandgap with nanosheet thickness. Additionally, we were able to fabricate the nanosheets into lithium ion battery anodes using carbon nanotubes as both binder and conductive additive. These electrodes were relatively stable, showing similar to 0.2% capacity decay per cycle, and displayed low-rate capacity of 1523 mAh g(-1) which is within 93% of the theoretical value. However, detailed analysis showed relatively poor rate performance, possibly due to nanosheet alignment.