New amorphous mixed transition metal oxides and their Li derivatives: Synthesis, characterization, and electrochemical behavior

New amorphous MnV2O6+delta. nH(2)O (0 < delta < 1) compounds have been prep ared by a soft chemistry route including the precipitation of a crystallize d precursor, MnV2O6. 4H(2)O, and its ozonation at temperatures below 100 de grees C. A combination of techniques (TGA, magnetic measurements, IR, XANES , EXAFS, XPS, and EELS) was used for their characterization. At low voltage , very large amounts of Li (e.g., Li12MnV2O6.96) are stored into anhydrous MnV2O6+delta compounds. After the first Li uptake, subsequent charge/discha rge cycles correspond to fully reversible Li uptake between the two composi tions: LialphaMnV2O6+delta (alpha greater than or equal to 2) and Li12MnV2O 6+delta (from 600 to 900 mAh/g). The Li derivatives were characterized at v arious steps of the discharge/charge process. During the first discharge th e VOn polyhedron changes from VO5 to VO6, and reversibly from VO6 to VO4 du ring subsequent cycles. Meanwhile, the V oxidation state varies reversibly between +3 and +5, respectively. Upon the first discharge Mn4+ cations are reduced to Mn2+. During the subsequent cycles the average Mn oxidation stat e varies reversibly between +2 and similar to+2.6. The electron transfer fr om Li to the host matrix is shown to decrease with increasing Li uptake. It is shown that the same soft chemistry route enables the preparation of amo rphous CoV2O6+delta. nH(2)O (0 < delta < 1) compounds which exhibit similar storage properties.