LiCoO₂ (lithium cobalt oxide): structure, capacity and uses

LiCoO₂ is the archetypal layered oxide cathode (Huang et al. 2026). Its oxygen ions form a cubic close-packed array, and the cations fill the octahedral holes between them in an ordered way: one plane of Li⁺, then one plane of Co³⁺, and so on along the stacking direction. Seen another way, it is a stack of edge-sharing CoO₂ sheets with lithium in the gaps between them. This ordered rock-salt arrangement is called the O3 structure (Manthiram 2020) and is of the α-NaFeO₂ type (Hashem et al. 2019), with space group R-3m, Li on the 3a sites, Co on 3b and O on 6c (Hashem et al. 2019; Liao et al. 2022).

Because Li⁺ and Co³⁺ differ a lot in size and charge they order well, and the Li planes stay clean, so lithium moves quickly in two dimensions, hopping from one octahedral site to the next through an empty tetrahedral site. Co–Co contact across shared octahedral edges makes the CoO₂ sheets good electronic conductors, and LiCoO₂ turns metallic as it is charged (Manthiram 2020). Many of its properties, from ion transport to mechanical behaviour, differ along and across the CoO₂ planes (Huang et al. 2026).

On charging, Li⁺ leaves the gaps between the CoO₂ sheets, crosses the electrolyte and enters the anode while Co³⁺ is oxidized towards Co⁴⁺; on discharge the process runs backwards (Lin et al. 2026). The oxide was the key to the modern cell for two reasons: it raised the voltage from below 2.5 V for the sulfide cathodes of the 1970s to about 4 V, and because it is made with lithium already in it, it can be paired with a lithium-free anode such as graphite (Manthiram 2020).

LiCoO₂ came from John Goodenough’s group at Oxford in the 1980s, in work by Koichi Mizushima, and in 1991 Sony announced lithium-ion batteries with a LiCoO₂ cathode and a graphite anode (Manthiram 2020). It remains the main cathode for portable electronics because of its high Li-ion and electronic conductivity, high density (4.2 g cm⁻³) and good cycling (Lin et al. 2026). For an overview of the other cathodes, anodes and electrolytes, see battery materials.

The theoretical capacity of LiCoO₂, one lithium per formula unit, is 274 mAh g⁻¹ (Lin et al. 2026; also calculated from the molar mass of 97.87 g mol⁻¹). Classic cells charged to 4.2 V take out only about half of it, roughly 140 mAh g⁻¹ (Lin et al. 2026; Manthiram 2020).

The reason is chemical: the Co³⁺/Co⁴⁺ band overlaps the top of the oxygen 2p band, so pulling out more than about 50% of the lithium starts to oxidize the oxide ions and release oxygen from the lattice (Manthiram 2020). Structurally, near 4.2 V (about half the Li removed) the crystal goes through a hexagonal–monoclinic–hexagonal order–disorder transition, and near 4.55 V the O3 stacking glides into the H1-3 phase, which builds up anisotropic stress and slows Li diffusion; that is why early commercial cells stopped at 4.2 V (Lin et al. 2026).

Raising the charge cut-off voltage is the most direct way to get more out of LiCoO₂ with existing manufacturing (Lin et al. 2026). In layered oxides, going from 4.2 V to 4.6 V raises the lithium extracted from about 50% to about 80% (Lin et al. 2026); for LCO, 4.6 V gives about 220 mAh g⁻¹ against 175 mAh g⁻¹ at 4.45 V (Zhang et al. 2022), and cathode energy densities reach 740 Wh kg⁻¹ at 4.45 V and 840 Wh kg⁻¹ at 4.55 V (Lin et al. 2026).

The price is faster degradation, through three linked processes (Lin et al. 2026):

• Phase transitions and strain. The O3 → H1-3 transition and large changes of the c axis cause interlayer sliding and microcracks; charging beyond 4.6 V damages the structure irreversibly.
• Cobalt dissolution and oxygen loss. The surface becomes unstable, Co dissolves into the electrolyte and lattice oxygen is released; the surface turns into a defective spinel.
• Electrolyte oxidation. A cathode–electrolyte interphase (CEI) forms, cracks as the particles breathe, and keeps regrowing, consuming lithium and electrolyte and raising the impedance.

The fixes are doping with traces of Mg, Al, Ti and other elements (Al suppresses Co dissolution; Mg on Li sites props the layers apart), surface coatings, particle design and electrolyte additives (Lin et al. 2026). One hybrid coating, a sol-gel coating on the powder followed by an ultrathin atomic-layer-deposited oxide on the electrode, improved energy density and voltage retention at 4.55 V and 45 °C (Kalluri et al. 2017).

Cobalt is the weak point of LiCoO₂. Its drawbacks listed in the literature are high cost and toxicity, limited practical capacity and poor thermal stability (Hashem et al. 2019). The high cost and limited capacity have driven the substitution of cobalt by nickel and manganese in NMC (LiNiₓMnᵧCo_zO₂); manganese, used in the LiMn₂O₄ spinel, is about two orders of magnitude cheaper than cobalt (Manthiram 2020). Nickel-based layered oxides offer higher capacity, greater abundance and lower cost than the costly and toxic LiCoO₂ (Wang et al. 2025), and polyanion cathodes such as LiFePO₄ are built on abundant iron (Manthiram 2020).

For a paper, slide or poster, show LiCoO₂ side on so the stacking is visible: a CoO₂ sheet of edge-sharing CoO₆ octahedra, a plane of Li⁺ ions, the next CoO₂ sheet, and so on. Drawing the CoO₆ units as polyhedra and the lithium as separate spheres makes the layers and the 2D lithium pathways obvious; an arrow through the Li plane shows where the ions move on charge and discharge. The LabCanvas figure editor’s Library has battery crystal objects, including the layered oxide structure shared by LiCoO₂ and NMC, which you can drop into a figure as high-resolution vector drawings and recolour. The LabCanvas 3D Studio has battery models you can rotate, show as polyhedra and export as high-resolution images.