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The electrochemical study of LiCrIIIyMnIII1−yMnIVO4compounds, 0≤y≤1, between 3.5 and 5.4 V vs Li metal, shows that the Cr substitution is beneficial to the overall performances (capacity, specific energy, and cyclability) fory≤0.62, and thaty=0.25 gives the best results. Fory>0.62, the cyclability is worse than for LiMn2O4, and fory≥0.75 the capacity fading becomes very fast. The electron energy loss spectroscopy study confirms that the deintercalation in the range 3.5–4.3 V corresponds to a MnIII–MnIVoxidation. Further deintercalation between 4.3 and 5.1 V mainly corresponds to a CrIII–CrIVoxidation with, however, the formation of a significant amount of CrVIfor the highest Cr contenty=0.75. In the starting compounds LiM2O4,M=Cr, Mn, Rietveld refinements show that the 8aand 16dsites of the spinel structure are occupied by Li andM, respectively. The Li deintercalation up to 5.1 V induces structural defects which do not disappear completely upon the subsequent intercalation down to 3.5 V; their concentration increases upon cycling. Such defects consist ofMcations occupying an 8asite (“Td defect”) or a 16csite (“16cdefect”), instead of 16d. Both defects imply a lowering of the tetrahedral Li concentration which accounts for the experimental capacity loss upon cycling.

MnV2O6 + δ· nH2O (0 < δ< 1) amorphous oxides were prepared by a two-step process including the precipitation of a crystallized precursor MnV2O6· 4H2O and its ozonation at temperatures below 100 °C. Their characterization by spectroscopic techniques (XAS and EELS) shows that V5+retains a VO5environment and that Mn, which remains in octahedral coordination, is oxidized to Mn4+mainly. MnV2O6 + δcompounds insert reversibly large amounts of Li per formula unit (e.g. Li12MnV2O6.96) at low voltage. After the first insertion/de-insertion cycle, subsequent cycles correspond to fully reversible lithium insertion between the two compositions: LiαMnV2O6 + δ(α≥ 2) and Li12MnV2O6 + δ(from 600 to 900 mAh/g). Investigations on the Li derivatives by XAS and EELS show that during the insertion/de-insertion cycles the V oxidation state varies reversibly between +5 and +3. Mn4+cations are reduced to Mn2+upon the first discharge. During the subsequent cycles the average Mn oxidation state varies reversibly between +2 and about +2.6. It clearly appears that the electron transfer from Li to the host matrix decreases with increasing xin LixMnV2O6 + δ.