Abstract
The search for high-energy density batteries especially stimulates the design of electrode materials with enhanced electrochemical storage properties. Downsizing the material to extend its electrochemically active surface as well as creating vacancies to create more available insertion sites are common approaches to improve the performance of electrode materials. In this work, our strategy is to maximize the cationic vacancies into nano-sized spinel Fe2O3 through substituting iron by molybdenum, with the final objective of extending the electrochemical insertion domain and accessing higher specific capacities. Our electrode materials were prepared by a simple solvothermal route which allows a carefully tuning of the cationic precursors. The stabilization of molybdenum cations inside the spinel structure, and consequently the creation of cationic vacancies, were characterized by a wide range of complementary techniques, including pair distribution function analysis, X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy. Interestingly, it is possible to tune both size and crystallinity of such nanomaterials by modifying the synthesis conditions. Hence, we suggest that the synthetized compound is thermodynamically metastable, that is, kinetically trapped. Such a state is suggested to be a consequence of the tetrahedral site occupation by Mo ions. The population of these sites, known to be reactive sites enabling particle growth, is concomitant with the stabilization of very small particles.The positive influence of this nanoscale engineering was firstly verified by evaluating the synthesized materials as positive electrodes in lithium batteries, with a significant enhancement of the initial specific capacity (from 40 to 100 mAh/g) for Li insertion.