 | |
 | |
| Names | |
|---|---|
| IUPAC name lithium cobalt(III) oxide | |
| Other names lithium cobaltite | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.032.135 |
| EC Number |
|
| |
| |
| Properties | |
| LiCoO 2 | |
| Molar mass | 97.87 g mol−1 |
| Appearance | dark blue or bluish-gray crystalline solid |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | harmful |
| GHS labelling: | |
  | |
| Danger | |
| H317,H350,H360 | |
| P201,P202,P261,P272,P280,P281,P302+P352,P308+P313,P321,P333+P313,P363,P405,P501 | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Lithium cobalt oxide, sometimes calledlithium cobaltate[2] orlithium cobaltite,[3] is achemical compound with formulaLiCoO
2. Thecobalt atoms are formally in the +3 oxidation state, hence theIUPAC namelithium cobalt(III) oxide.
Lithium cobalt oxide is a dark blue or bluish-gray crystalline solid,[4] and is commonly used in the positiveelectrodes oflithium-ion batteries especially inhandheld electronics.
The structure ofLiCoO
2 has been studied with numerous techniques includingx-ray diffraction,electron microscopy, neutronpowder diffraction, andEXAFS.[5]
The solid consists of layers of monovalentlithium cations (Li+
) that lie between extended anionic sheets of cobalt and oxygen atoms, arranged as edge-sharingoctahedra, with two faces parallel to the sheet plane.[6] The cobalt atoms are formally in the trivalent oxidation state (Co3+
) and are sandwiched between two layers of oxygen atoms (O2−
).
In each layer (cobalt, oxygen, or lithium), the atoms are arranged in a regular triangular lattice. The lattices are offset so that the lithium atoms are farthest from the cobalt atoms, and the structure repeats in the direction perpendicular to the planes every three cobalt (or lithium) layers. The point group symmetry is inHermann-Mauguin notation, signifying a unit cell with threefoldimproper rotational symmetry and a mirror plane. The threefold rotational axis (which is normal to the layers) is termed improper because the triangles of oxygen (being on opposite sides of each octahedron) are anti-aligned.[7]
Fully reduced lithium cobalt oxide can be prepared by heating a stoichiometric mixture oflithium carbonateLi
2CO
3 andcobalt(II,III) oxideCo
3O
4 or metallic cobalt at 600–800 °C, thenannealing the product at 900 °C for many hours, all under an oxygen atmosphere.[6][3][7]
_synthesis_route.png)
Nanometer-size particles more suitable for cathode use can also be obtained by calcination ofhydratedcobalt oxalate β-CoC
2O
4·2H
2O, in the form of rod-like crystals about 8 μm long and 0.4 μm wide, withlithium hydroxideLiOH, up to 750–900 °C.[9]
A third method useslithium acetate,cobalt acetate, andcitric acid in equal molar amounts, in water solution. Heating at 80 °C turns the mixture into a viscous transparent gel. The dried gel is then ground and heated gradually to 550 °C.[10]
The usefulness of lithium cobalt oxide as an intercalation electrode was discovered in 1980 by anOxford University research group led byJohn B. Goodenough andTokyo University'sKoichi Mizushima.[11]
The compound is now used as the cathode in some rechargeablelithium-ion batteries, with particle sizes ranging fromnanometers tomicrometers.[10][9] During charging, the cobalt is partially oxidized to the +4 state, with somelithium ions moving to the electrolyte, resulting in a range of compoundsLi
xCoO
2 with 0 <x < 1.[3]
Batteries produced withLiCoO
2 cathodes have very stable capacities, but have lower capacities and power than those with cathodes based on (especially nickel-rich)nickel-cobalt-aluminum (NCA) ornickel-cobalt-manganese (NCM) oxides.[12] Issues withthermostability are better forLiCoO
2 cathodes than other nickel-rich chemistries although not significantly. This makesLiCoO
2 batteries susceptible tothermal runaway in cases of abuse such as high temperature operation (>130 °C) orovercharging. At elevated temperatures,LiCoO
2decomposition generatesoxygen, which then reacts with the organic electrolyte of the cell, this reaction is often seen inLithium-Ion batteries where the battery becomes highly volatile and must be recycled in a safe manner. The decomposition of LiCoO2 is a safety concern due to the magnitude of this highlyexothermic reaction, which can spread to adjacent cells or ignite nearby combustible material.[13] In general, this is seen for many lithium-ion battery cathodes.
The delithiation process is usually by chemical means,[14] although a novel physical process has been developed based on ion sputtering and annealing cycles,[15] leaving the material properties intact.
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