packed structures was further extended by Goodenough's group to 3-D materials with the spinel structure (3). It was Lithium manganospinels belonging to the LiMn 2 O 4 -Li 2 Mn 4 O 9 -Li 4 Mn 5 O 12 system were prepared by solid-state reac-shown that lithium could be intercalated into the spinels tion of various lithium salts and manganese sources at tempera-Fe 3ϩ [Fe 2ϩ Fe 3ϩ ]O 4 (inverse) (4) and Mn 2ϩ [Mn 3ϩ Mn 3ϩ ]O 4 tures ranging from 400 to 900؇C. Their exact stoichiometry, (normal) (5), and either inserted or extracted into/from which is highly dependent on the preparation temperature, was the normal spinel Li[Mn 2 ]O 4 . Due to their lower determined by X-ray diffraction, atomic absorption spectroscost and toxicity, as compared to those of cobalt, nickel, or copy, and redox titration. Nearly stoichiometric LiMn 2 O 4 shows vanadium, the oxides of lithium and manganese, LiMn 2 O 4 a reversible phase transition at 30؇C upon heating and at 10؇C (7-11), Li 4 Mn 5 O 12 (12, 13), Li 2 Mn 4 O 9 (14-16), and upon cooling, which is associated with a tetragonal-cubic trans-LiMnO 2 (17-21), remain among the most promising mate-
formation. An increase in the average oxidation state of mangarials as 3-4 V vs Li/Li ϩ cathodes for rechargeable lithnese from 3.5؉ to 4؉ in the two systems Li 1؊␦ Mn 2؊2␦ (0 Յ ium batteries. ␦ Յ 0.11) and Li 1؉␦ Mn 2؊␦ O 4 (0 Յ ␦ Յ 0.33) results in (i) the Among these options, the spinel LiMn 2 O 4 (Li (8a) suppression of the Jahn-Teller distortion observed around [Mn 2 ] (16d) O 4 ) has been the most extensively studied: elecroom temperature for stoichiometric LiMn 2 O 4 and (ii) a progressive passage from antiferromagnetic (LiMn 2 O 4 , ؍ ؊ 266 K, trochemical extraction of one lithium ion from the tetrahen Mn ؉ ؍ 3.5) to ferromagnetic behavior (Li 4 Mn 5 O 12 , ؍ ؉ dral (8a) sites occurs in two steps at approximately 4 V vs 40 K, n Mn ؉ ؍ 4.0), where the lattice parameter is not too Li/Li ϩ (LiMn 2 O 4 Ǟ Mn 2 O 4 (-MnO 2 )) whereas the insersmall.