Abstract
The layered intercalation compounds Li(Mn1-yCoy)O2; 0 ≤ y ≤ 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 ≤ y ≤ 0.5. Consideration of transition metal to oxygen bond lengths indicates that Mn3+ is replaced by cobalt in the trivalent state. Localized high spin Mn3+ (3d4) induces a cooperative Jahn-Teller distortion in layered LiMnO2, lowering the symmetry from rhombohedral R3̄m to monoclinic (C2/m). Substitution of as little as 10% Mn by Co is sufficient to suppress the distortion in Li0.9(Mn0.9Co0.1)O2, whereas half the Li must be extracted from LiMnO2 to achieve a single undistorted rhombohedral phase. On removing and reinserting Li in LiMnO2 only half the quantity of Li (equivalent to a specific charge of 130 mAhg-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-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 LiMnO2 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.
| Original language | English |
|---|---|
| Pages (from-to) | 549-556 |
| Number of pages | 8 |
| Journal | Journal of Solid State Chemistry |
| Volume | 145 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Jul 1999 |
| Externally published | Yes |
Fingerprint
Cite this
}
The layered intercalation compounds Li(Mn1-yCoy)Oz : positive electrode materials for lithium-ion batteries. / Armstrong, A. Robert; Robertson, Alastair D.; Gitzendanner, Robert; Bruce, Peter G.
In: Journal of Solid State Chemistry, Vol. 145, No. 2, 07.1999, p. 549-556.Research output: Contribution to journal › Article
TY - JOUR
T1 - The layered intercalation compounds Li(Mn1-yCoy)Oz
T2 - positive electrode materials for lithium-ion batteries
AU - Armstrong, A. Robert
AU - Robertson, Alastair D.
AU - Gitzendanner, Robert
AU - Bruce, Peter G.
PY - 1999/7
Y1 - 1999/7
N2 - The layered intercalation compounds Li(Mn1-yCoy)O2; 0 ≤ y ≤ 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 ≤ y ≤ 0.5. Consideration of transition metal to oxygen bond lengths indicates that Mn3+ is replaced by cobalt in the trivalent state. Localized high spin Mn3+ (3d4) induces a cooperative Jahn-Teller distortion in layered LiMnO2, lowering the symmetry from rhombohedral R3̄m to monoclinic (C2/m). Substitution of as little as 10% Mn by Co is sufficient to suppress the distortion in Li0.9(Mn0.9Co0.1)O2, whereas half the Li must be extracted from LiMnO2 to achieve a single undistorted rhombohedral phase. On removing and reinserting Li in LiMnO2 only half the quantity of Li (equivalent to a specific charge of 130 mAhg-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-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 LiMnO2 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.
AB - The layered intercalation compounds Li(Mn1-yCoy)O2; 0 ≤ y ≤ 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 ≤ y ≤ 0.5. Consideration of transition metal to oxygen bond lengths indicates that Mn3+ is replaced by cobalt in the trivalent state. Localized high spin Mn3+ (3d4) induces a cooperative Jahn-Teller distortion in layered LiMnO2, lowering the symmetry from rhombohedral R3̄m to monoclinic (C2/m). Substitution of as little as 10% Mn by Co is sufficient to suppress the distortion in Li0.9(Mn0.9Co0.1)O2, whereas half the Li must be extracted from LiMnO2 to achieve a single undistorted rhombohedral phase. On removing and reinserting Li in LiMnO2 only half the quantity of Li (equivalent to a specific charge of 130 mAhg-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-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 LiMnO2 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.
U2 - 10.1006/jssc.1999.8216
DO - 10.1006/jssc.1999.8216
M3 - Article
AN - SCOPUS:0001398007
VL - 145
SP - 549
EP - 556
JO - Journal of Solid State Chemistry
JF - Journal of Solid State Chemistry
SN - 0022-4596
IS - 2
ER -