Essential geometric and electronic properties in stage-n graphite alkali-metal-intercalation compounds

Beyond Conventional Carbon Activation: Creating Porosity without Etching Using Cesium Effect

Facile synthesis of porous carbon with high yield and high specific surface area (SSA) from low-cost molecular precursors offers promising opportunities for their industrial applications. However, conventional activation methods using potassium and sodium hydroxides or carbonates suffer from low yields (<20%) and poor control over porosity and composition especially when high SSAs are targeted (>2000 m2 g-1) because nanopores are typically created by etching. Herein, a non-etching activation strategy is demonstrated using cesium salts of low-cost carboxylic acids as the sole precursor in producing porous carbons with yields of up to 25% and SSAs reaching 3008 m2 g-1. The pore size and oxygen content can be adjusted by tuning the synthesis temperature or changing the molecular precursor. Mechanistic investigation unravels the non-classical role of cesium as an activating agent. The cesium compounds that form in situ, including carbonates, oxides, and metallic cesium, have extremely low work function enabling electron injection into organic/carbonaceous framework, promoting condensation, and intercalation of cesium ions into graphitic stacks forming slit pores. The resulting porous carbons deliver a high capacity of 252 mAh g-1 (567 F g-1) and durability of 100 000 cycles as cathodes of Zn-ion capacitors, showing their potential for electrochemical energy storage.

Fundamental features of AlCl4 --/AlCl4-graphite intercalation compounds of aluminum-ion-based battery cathodes

Up to now, many guest atoms/molecules/ions have been successfully synthesized into graphite to form various compounds. For example, alkali-atom graphite intercalation compounds are verified to reveal stage-n structures, including LiC6n and LiM8n [M = K, Rb, and Cs; n = 1, 2, 3; 4]. On the other side, AlCl4 --ion/AlCl4-molecule compounds are found to show stage-4 and stage-3 structures at room and lower temperatures, respectively. Stage-1 and stage-2 configurations, with the higher intercalant concentrations, cannot be synthesized in experimental laboratories. This might arise from the fact that it is quite difficult to build periodical arrangements along the longitudinal z and transverse directions simultaneously for large ions or molecules. Our work is mainly focused on stage-1 and stage-2 systems in terms of geometric and electronic properties. The critical features, being associated with the atom-dominated energy spectra and wave functions within the specific energy ranges, the active multi-orbital hybridization in distinct chemical bonds, and atom- & orbital-decomposed van Hove singularities, will be thoroughly clarified by the delicate simulations and analyses.