Correlation between Microstructure and Electrochemical Behavior of the Mesoporous Co3O4 Sheet and Its Ionothermal Synthesized Hydrotalcite-like α-Co(OH)2 Precursor

An ionothermal strategy is developed to synthesize hydrotalcite-like α-Co(OH)2 sheets. The structure and interlayer chemistry of α-Co(OH)2 are facilely manipulated, thus determining its pseudocapacitive performance. Significantly, a very large space of 11.2 Å in (003) plane induced by various intercalated species is found in the ionothermal synthesized α-Co(OH)2 obtained at 210 °C (210-α-Co(OH)2), which delivers a better pseudocapacitive performance. Annealing the synthesized α-Co(OH)2 generates mesoporous Co3O4 sheets or nanoparticles, which depends on the structure of the precursors. More defects in the α-Co(OH)2 precursor provide larger driving force during the nucleation of Co3O4 nanocrystals, thus reducing the grain size. The architecture of the 210-Co3O4 derived from 210-α-Co(OH)2 is featured as self-supporting mesoporous nanosheets composed of ∼5 nm sized grains. The fine grains and ultralarge specific surface area of ∼113.5 m2 g–1 in the 210-Co3O4 can trigger the formation of CoO intermediate during lithium ion insertion into the Co3O4. The 210-Co3O4 exhibits superior cycling performance as electrode for lithium ion battery and supercapacitor over the other Co3O4 samples due to its nanocrystallite constructed mesoporous sheet structure, which has a higher strain accommodation capability. The underlying mechanism discussed in this work provides guidance on structural design of advanced energy storage materials.