Researchers in S. Korea have synthesized a divalent wolframite-structure zinc tungstate (ZnWO4) in the form of one-dimensional nanorods; used as anode material in Li-ion batteries, the nanorods deliver reversibly sustained high capacities of more than 420 mAh g–1 after 150 cycles—much higher than the capacities of graphite-based anodes which are limited to 372 mAh g-1.
Wolframite, a principal ore of tungsten, is an iron and manganese tungstate mineral that is monoclinic, with tabular crystals.
So far, research on metal oxides as anode materials has been focused on two approaches: those metal oxides that react with Li via the metal and subsequently form alloys (MO + 2Li→M + Li2O and M + xLi+ + xe-↔LixM, alloying/dealloying reaction) and those that react with Li via a displaced redox reaction, including Li2O and nanosized metal particles (MxOy + ne- + nLi+↔xM0 + LinOy, conversion reaction). Indeed, nanostructured metal oxides have shown high capacities and have therefore been identified as good candidates for use as anode materials. These nanometer-sized metal oxides have the advantages of high surface-to-volume ratio and short path length for Li+ transport compared with their bulk counterparts.
More recently, nanostructured ternary metal oxides containing transition metals (Ca3Co4O9 nanoplates, Zn2Ti3O8 nanowires, and so on) have been reported as promising anode materials, as well as other complex isostructural metal oxides. Therefore, the diverse crystal structures or phases of transition metal oxides can provide a large number of options for the study of Li-ion storage technologies.
In this context, the metal tungstates (AWO4-type compounds where A is a divalent metal ion) are an attractive group of materials because of their similarity to ternary oxides and the high oxidation state observed in the tungsten atom. This tungstate family is an important group of inorganic materials with high technological applications in various fields.—Shim et al.
Even after galvanostatic cycling over 30 cycles, the ZnWO4 nanorods sustained their 1-D nanostructure morphologies. The researchers suggested that these ZnWO4 nanorods may offer exciting possibilities for the development of new anode materials for Li-ion batteries. Their paper is published in the ACS Journal of Physical Chemistry C.
Hyun-Woo Shim, In-Sun Cho, Kug Sun Hong, Ah-Hyeon Lim, Dong-Wan Kim (2011) Wolframite-type ZnWO4 Nanorods as New Anodes for Li-Ion Batteries. The Journal of Physical Chemistry C Article ASAP doi: 10.1021/jp204656v