The Effect of Doping LiMn2O4 spinel on its Use as a cathode in Li-ion Batteries: Neutron Diffraction and Electrochemical Studies

A series of compounds Li1+yMn2-xM'O-x(4) (x less than or equal to 0.1; y less than or equal to 0.02), have been synthesised by doping the parent LiMn2O4 spinel with various metal ions of variable oxidation state. Powder neutron diffraction data has been collected on these samples alongside a series of electrochemical experiments in order to elucidate the relationship between structure on the performance of these systems as Li batteries. Doping the LiMn2O4 spinel with a small amount of metal ions has a remarkable effect on the electrochemical properties. Whereas the capacity of the spinels doped with trivalent ions is much greater, the cycling fading properties are much enhanced with using divalent ions as dopants. The underlying reasons for this are discussed, and it is suggested that the occupancy of the tetrahedral site with divalent ions to form a more compact structure offers an improved structural stability to support greater Li insertion/extraction, but which ultimately prevents the free movement of Li also sited on the tetrahedral site of the lattice.