The layered intercalation compounds Li(Mn{sub 1{minus}y}Co{sub y})O{sub 2}: Positive electrode materials for lithium-ion batteries
- Univ. of St. Andrews (United Kingdom). School of Chemistry
The layered intercalation compounds Li(Mn{sub 1{minus}y}Co{sub y})O{sub 2}; 0 {le} y {le} 0.5 cannot be prepared by conventional solid state reaction but have been synthesized using a solution-based route coupled with ion exchange. A continuous range of solid solutions with rhombohedral symmetry exists for 0.1 {le} y {le} 0.5. Consideration of transition metal to oxygen bond lengths indicates that Mn{sup 3+} is replaced by cobalt in the trivalent state. Localized high spin Mn{sup 3+} (3d{sup 4}) induces a cooperative Jahn-Teller distortion in layered LiMnO{sub 2}, lowering the symmetry from rhombohedral R{bar 3}m to monoclinic (C2/m). Substitution of as little as 10% Mn by Co is sufficient to suppress the distortion in Li{sub 0.9}(Mn{sub 0.9}Co{sub 0.1})O{sub 2}, whereas half the Li must be extracted from LiMnO{sub 2} to achieve a single undistorted rhombohedral phase. On removing and reinserting Li in LiMnO{sub 2} only half the quantity of Li (equivalent to a specific charge of 130 mAhg{sup {minus}1}) may be reinserted on the first cycle; this substantial drop in capacity is eliminated with only 10% Co substitution. The latter material can sustain a large capacity on cycling (200 mAhg{sup {minus}1}). Higher Co contents have somewhat lower capacities but fade less at higher cycle numbers. The marked improvement in capacity retention of the Co-doped materials compared with pure LiMnO{sub 2} may be related in part to the absence of the Jahn-Teller distortion. Electrochemical data indicate conversion to a spinel-like structure on cycling. Such conversion is progressively slower with increasing Co content. Cycling of this spinel-like material is significantly better than Co-doped spinel of the same composition. These materials are of interest as electrodes in rechargeable lithium batteries.
- OSTI ID:
- 679244
- Journal Information:
- Journal of Solid State Chemistry, Vol. 145, Issue 2; Other Information: PBD: Jul 1999
- Country of Publication:
- United States
- Language:
- English
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