LiMn2O4-based spinels have been extensively studied as positive electrode materials for lithium-ion batteries. Our investigations have shown that, by using the Pechini process, the performance of these materials can be improved significantly through adjustments to the synthesis conditions and composition by means of selective doping. This paper reports the results of neutron and ex situ X-ray diffraction studies performed to examine the structural changes that occur during lithium ion insertion into various LiMn,O4 compositions. It appears that an ordering intercalation of lithium ions occurs in the lithium concentration range of 0.15-0.35, followed by a second-order phase transformation when the lithium population is close to 0.5, leading to a random lithium insertion into a single-spinel phase from x = 0.5 to 1.0. * Electrochemical Society Student Member. * * Electrochemical Society Active Member.agreement with many literature reports,4"°13 including results obtained from the ionic modeling of various lithium manganese spinel compounds.'3 However, the reason is not cleat One goal of this study was to explore the intrin-

LiMn2O4 ‐based spinels are of great interest as positive electrode materials for lithium‐ion batteries. We describe here what is believed to be the first synthesis of these materials using the Pechini process, a low temperature synthetic method that often yields inorganic oxides of excellent phase purity and well‐controlled stoichiometry. Using this process, it has been possible to synthesize phase‐pure crystalline spinel LiMn2O4 by calcining the appropriate polymeric precursors in air at 250°C for several hours. The influence of different firing temperatures and the effect of substituting a small amount of Mn with Ni have also been explored. Electrochemical studies show that the Pechini‐synthesized materials appear to offer not only high quality performance but also significant analytical advantages which allow us to understand the structural mechanism of Li intercalation.

The discovery of inorganic solids with ionic conductivities comparable to those of aqueous electrolytes has revolutionized solid-state electrochemistry. Sodium beta alumina, a Na(+) conductor, and LixTiS(2), an intercalation compound with simultaneous Li(+) and electronic conductivity, are two of the best and most versatile fast ionic conductors. A wide variety of cations can replace Na(+) in beta alumina and Li(+) in LixTiS(2) and change the properties of the materials. Sodium beta alumina and LixTiS(2) are currently used in the development of high-energy density batteries for electric vehicles and electrical utility load leveling. Current research in solid ionic conductors is exploring new intercalation compounds, solid polymer electrolytes, and alkali ion and proton transport in crystalline solids.

No abstract