Two-dimensional materials can have an excellent capability to handle high rates in ion batteries due to the absence of diffusion barrier. We studied two promising anode materials, namely Mxene and defective graphene. First, the adsorption of Li, as well as Na, K, and Ca on Ti3C2, one representative Mxene, is predicted by first-principles density functional calculations. We observe that these alkali ions exhibit different adsorption energy upon the coverage. The adsorption energies of Na, K and Ca decrease as coverage increases, while Li shows little sensitivity to variance in coverage. This observed relationship between adsorption energies and coverages of alkali ions on Ti3C2 can be explained by their effective ionic radii. A larger effective ionic radius increases interaction between alkali ions, thus lower capacity and coverage are obtained. Our calculated capacity values for Li, Na, K and Ca on Ti3C2 are 639.5, 319.8, 191.8 and 159.9 mAh g-1, respectively. Compared to the materials currently used in Li ion battery anodes, Mxene shows great promise in increasing overall battery performance. Second, the study of defective graphene is focused on the divacancy and Stone-Wales defects which are existing in the graphene grown by CVD method. Our results show that while adsorption of Na and Ca is not possible on pristine graphene, enhanced adsorption is observed on defective graphene due to the increased charge transfer between the adatoms and defects. We find that the capacity of graphene increases with the density of defects. For maximum possible divacancy defect densities, the capacities of 1459 mAh g-1 for Na-ion  and 2900 mAh g-1 for Ca-ion batteries can be achieved. For Stone-Wales defects, we find maximum capacities of 1071 mAh g-1 and 2142 mAh g-1 for Na and Ca, respectively. Our results provide guidelines to create better high-capacity anode materials for Na- and Ca-ion batteries for large-scale grid storage.

2D materials as promising ion battery anode: Mxene and defective graphene

247th National Meeting (2014)

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