Ball-milling: the behavior of graphite as a function of the dispersal media

The ball-milling in liquid media leads to well organized, thin and highly anisometric graphite (HAG) crystals. The presence in the milling container of a liquid, which acts as a lubricant and decreases the violence of the shocks, is relevant. Two liquids are used: n-dodecane and water. With dodecane, inert towards graphite and the metal of the milling tools, the powder consists of pure graphite whereas with water, the graphite particles are covered with nanocrystallites (15 nm) of a magnetic compound: the maghemite (γ Fe₂O₃). The electrochemical properties of those powders are interesting. The highly anisometric graphite leads to an irreversible capacity around half of that for the initial graphite powder, in contradiction with previous results claiming that higher the surface area, the higher the irreversible capacity. In fact, milling in the presence of dodecane provokes essentially a cleavage, which increases the global area, but does not drastically change the number of edge carbon atoms, responsible for the increase of the large irreversible capacity. The graphite–maghemite composites present a high capacity, partly reversible by oxidation–reduction between iron and wustite (FeO). This reaction is made possible by the nanometric size of the particles, and therefore their high reactivity.