The Key Role of Nanoparticles in Reactivity of 3D Metal Oxides Toward Lithium

In response to the needs of today's mobile society and the emergence of ecological concerns such as global warming, one of the major technological challenges in this new century is undoubtedly energy generation and storage. Ninety percent of today's electrical power generation still comes from fossil fuels, and we are constantly struggling to reduce the carbon dioxide emissions per unit of electric power so as to help curtail global warming. It is now mandatory that new and environmentally friendly energy/storage sources be found. Hence, the fast developing research in that field involving, among others, fuel cells, primary and rechargeable batteries, and supercapacitors. As a result of this worldwide ecological priority, political concerns have come into play, and science has suffered from prioritisation based on both industrial pressure and media reports, rather than on the clear and rigorous scientific identification of technological stoppers inherent in each storage system. Needless to say, this applies to battery systems as well.

In the past two decades, intensive efforts have given birth to the rechargeable Li-ion battery technology that has dominated the market place, and can be regarded as one of the great successes in modern electrochemistry to date. But these Li-based systems still suffer from the lack of suitable electrode and electrolyte materials, which they require if they are ever to accommodate the increasing user's demands. Aware of this limitation, chemists have been acting at several levels to incrementally improve the Li-ion performance. They have followed a dual approach, dealing with either positive or negative electrode materials, with efforts centered around: 1) the modification of existing materials through cationic/anionic substitution, texture modification and surface treatments, 2) the making of composite electrodes or electrolytes made of several chemical components, and 3) the design of new electrode materials. Such approaches were pursued at the macroscopic scale on electrode materials^1–3 having a dual electronic-ionic conductivity, a void structure to insert/de-insert Li ions, or the ability to alloy with Li. They led to the identification of layered LiMn_1−x Cr _x 0₂ oxides^4–5 or three-dimensional iron phosphates (LiFeP0₄)⁶, that stand as a possible alternative to LiCo0₂ or negative electrode materials such as tin-based oxides (Sn0₂, SnO),^7–8 intermetallics (CuSb⁹, Cu₆Sn₅ ¹⁰, ...), nitrides¹¹ and phosphides,^12'13 which could be used as alternatives to carbonaceous materials, once their initial large irreversibility and poor cycle life have been overcome.