Exfoliation and reassembly of cobalt oxide nanosheets into a reversible lithium-ion battery cathode

An exfoliation-reassembly-activation (ERA) approach to lithium-ion battery cathode fabrication is introduced, demonstrating that inactive HCoO ₂ powder can be converted into a reversible Li _1-xH _xCoO ₂ thin-film cathode. This strategy circumvents the inherent difficulties often associated with the powder processing of the layered solids typically employed as cathode materials. The delamination of HCoO ₂ via a combination of chemical and mechanical exfoliation generates a highly processable aqueous dispersion of [CoO ₂] ^- nanosheets that is critical to the ERA approach. Following vacuum-assisted self-assembly to yield a thin-film cathode and ion exchange to activate this material, the generated cathodes exhibit excellent cyclability and discharge capacities approaching that of low-temperature-prepared LiCoO ₂ (~83 mAh g ^-1), with this good electrochemical performance attributable to the high degree of order in the reassembled cathode. HCoO ₂ powder is successfully exfoliated in water to yield solution-processable aqueous dispersions of [CoO ₂] ^- nanosheets, which are reassembled into self-supporting thin films. Ion exchange with lithium generates Li _1-x H _x CoO ₂ thin films that can be used as reversible cathodes with excellent cyclability and discharge capacities approaching that of low-temperature-prepared LiCoO ₂.