The electrochemical properties of LiMn2O4 and LiMyMn2−yO4 false(M=normalTi,normalGe,normalFe,normalZn,normalor Nifalse) were studied for different conditions of sample preparation and different degrees of cation substitution false(yfalse) . In the voltage range 3.5–4.5 V, cells of either spinel LiMn2O4 or λ‐MnO2 (made by leaching the Li from LiMn2O4 ) reversibly insert 0.4 Li per Mn at an average voltage of 4.1 V, leading to an energy density of 480 Wh/kg of cathode. Cells cycled 50 times lost less than 10% of their initial capacity, suggesting that this material could be used instead of LiCoO2 or LiNiO2 as the cathode in the new generation of “rocking chair batteries.” Replacing Mn with cations of valence 2 (Ni, Zn) or 3 (Fe) reduces the amount of Mn+3 and correspondingly reduces the capacity of the cells at 4.1 V, but does not affect their cycling performance.

We show that the reaction mechanism in Li/[SnO:(B 2 O 3 ) x :(P 2 O 5 ) y glass (0.1 Յ x, y Յ 0.5)], Li/[SnO: B 2 O 3 ) 0.5 :(P 2 O 5 ) 0.5 :(K 2 CO 3 ) 0.04 glass] and Li/SnO cells is common. During the first discharge, the oxygen bonded to tin (as SnO) reacts with lithium to give metallic tin (which can be present as clusters of a few atoms) and lithia. The tin reacts with further lithium to the composition limit of Li 4.4 Sn. During charge the Li is removed from the lithium-tin alloy. The other components of the glass (e.g., B 2 O 3 , P 2 O 5 , Li 2 O, etc.) are inert with respect to lithium, and we call the atoms which make up these phases "spectator atoms." Using X-ray diffraction (XRD) and electrochemical methods, we show that size of the initial tin regions which form is inversely proportional to the spectator:Sn atom ratio. However, during cycling, all of these materials show the subsequent aggregation of the tin atoms into clusters which grow with cycle number until they reach a saturated size. The final cluster size is larger for materials with smaller X:Sn ratio. We propose a speculative model, which predicts the saturated Sn cluster size, as a function of the spectator:Sn ratio.

Using a new electrolyte composition, which is stable against oxidation up to 5 V, the full electrochemical deintercalation of lithium from the spinel LiMn204 is studied. The origin of two new reversible oxidation-reduction peaks near 4.5 and 4.9 V are examined. The capacity associated with these peaks depends on both the nominal composition x in Li=Mn204 and the synthesis conditions (annealing temperatures and cooling rates), and thereby can be used as an indicator for electrochemically optimized LiMn204 powders. We present evidence that these peaks are related to local structural defects. Thermogravimetric measurements (TGA) on Li~Mn20~ powders show a reversible loss of oxygen that can reach 5 % at 1000~ We find that some of this weight loss is associated with the conversion of cubic LiMn204 to a new tetragonal spinel phase and then to the decomposition of this phase into the orthorhombic LiMnO~ phase plus other products. This new tetragonal LiMn~O, spinel is prepared as a single phase, and its electrochemical properties are reported.