ant is effective. This minimizes the system randomness which may localize the charge carriers, Li ϩ and e Ϫ . Second, The lattice instability in the discharged state of lithium-rich spinel manganese compounds, Li(Li x Mn 2؊x )O 4 , was investi-migration of non-Li ions to tetrahedral 8a sites, which gated with respect to the Jahn-Teller structural phase transilowers the rechargeable capacity in the 4-V region, can be tion (Fd3m to I4 1 /amd) around T t ؍ 280 K in LiMn 2 O 4 . A small prevented. That is, the migration or the exchange of doped amount of excess Li (0 Ͻ x Ͻ 0.035) substituted for Mn (16d Li ϩ between 16d and 8a sites, which would be prior to the sites) increased the average Mn valency, suppressing the Jahnmigration of Mn, results in no decrease in rechargeable ca-Teller effect and hence stabilizing the cubic phase to drastically pacity. decrease both the transition temperature T t from 282 to 214 K Gummow et al. recently synthesized Li-rich spinel and the latent heat ⌬H from 226 to 29 cal/mol. No transition Li(Li x Mn 2Ϫx )O 4 by reacting LiOH и H 2 O and Ͳ-MnO 2 was observed in the region x Ͼ 0.035, which corresponds to (CMD), and reported that cyclic stability in the 4-V region merely Ͻ2% Li substitution for Mn. The lattice instability in the is significantly enhanced at the expense of rechargeable charged state was also investigated by comparing the theoretical capacity (5). They also discussed the improved cyclic perand the experimental capacity of Li(Li x Mn 2؊x )O 4 . The cell caformance of Li(Li x Mn 2Ϫx )O 4 in terms of lattice stability in pacity showed a clear deviation from the theoretical value in the vicinity of y ϭ 3.5 in Mn yϩ , the onset of the Jahn-Teller the small x region (x Ͻ 0.15), indicating the mechanical lattice instability induced by scarcity of Li ؉ (8a).
The value of Li effect, in a deeply discharged state. However, nobody has substitution x which will maximize the cell performance is ever found quantitative evidence to directly indicate that discussed.