LiMn2O4 epitaxial thin films were synthesized on SrTiO3:Nb(1 1 1) and Al2O3(0 0 1) single crystal substrates by pulsed laser deposition (PLD) method and the electrochemical properties were discussed comparing with that of amorphous LiMn2O4 film on polycrystalline Au substrate. LiMn2O4 epitaxial film showed only a single plateau in charge-discharge curves and a single redox peak at the corresponding voltage of cyclic voltammograms. This phenomenon seems to originate from the effect of the epitaxy: the film is directly connected with the substrate by the chemical bond and this connection would suppress the phase transition of LixMn2O4 film during lithium (de-)intercalation. The discharge voltage of LiMn2O4 epitaxial film on SrTiO3 was lower than that of LiMn2O4 film on Al2O3. This lowered discharge voltage may be caused by the electronic interaction between LiMn2O4 film and SrTiO3:Nb n-type semiconductor Substrate.
We also attempted to measure the absorption spectrum change of LiMn2O4 epitaxial film on Al2O3 during the lithium (de-)intercalation. The absorption spectrum of LiMn2O4 hardly changed during charging and discharging. This suggests the d orbital of Mn does not concern the 4V region redox of LiMn2O4. (c) 2008 Elsevier B.V. All rights reserved.