Composition and electrochemical properties of LiCu xMn 2- xO 4 and LiCu 0.5- yAl yMn 1.5O 4

In order to gain a better understanding of the parameters affecting the capacity and performance of spinel electrode materials, the chemical composition and cation distribution of three members of the LiCu_xMn_2–xO₄ and LiCu_0.5–yAl_yMn_1.5O₄ series have been studied by chemical analysis, X-ray diffraction and X-ray absorption spectroscopy. The synthesis used stoichiometric and lithium-excess precursors. The results evidence that lithium is always incorporated in lower contents than expected from the nominal stoichiometry, owing to the occurrence of significant amounts of copper in the tetrahedral sites of the structure. Manganese displays an oxidation state below 4+ in all these solids, while the lithium-excess synthesis leads to a slightly higher average oxidation state. The electrochemical results evidence the lack of improvement in capacity by using lithium-excess synthesis, while a significant increase in capacity is obtained by aluminium doping, reaching values of 100 mAh/g.