Hierarchically Nanoporous 3D Assembly Composed of Functionalized Onion-Like Graphitic Carbon Nanospheres for Anode-Minimized Li Metal Batteries

The Defect Chemistry of Carbon Frameworks for Regulating the Lithium Nucleation and Growth Behaviors in Lithium Metal Anodes

Carbon materials have been widely considered as the frameworks in lithium (Li) metal anodes due to their lightweight, high electrical conductivity, and large specific surface area. Various heteroatom-doping strategies have been developed to enhance the lithiophilicity of carbon frameworks, thus rendering a uniform Li nucleation in working Li metal batteries. The corresponding lithiophilicity chemistry of doping sites has been comprehensively probed. However, various defects are inevitably introduced into carbon materials during synthesis and their critical role in regulating Li nucleation and growth behaviors is less understood. In this contribution, the defect chemistry of carbon materials in Li metal anodes is investigated through first-principles calculations. The binding energy towards a Li atom and the critical current density are two key descriptors to reveal the defect chemistry of carbon materials. Consequently, a diagram of designing carbon frameworks with both high lithiophilicity and a large critical current density is built, from which the Stone-Wales defect is predicted to possess the best performance for delivering a uniform Li deposition. This work uncovers the defect chemistry of carbon frameworks and affords fruitful insights into defect engineering for achieving dendrite-free Li metal anodes.

Nitrogen-phosphorus doped graphitic nano onion-like structures: experimental and theoretical studies

Onion-like graphitic structures are of great importance in different fields. Pentagons, heptagons, and octagons are essential features of onion-like graphitic structures that could generate important properties for diverse applications such as anodes in Li metal batteries or the oxygen reduction reaction. These carbon nanomaterials are fullerenes organized in a nested fashion. In this work, we produced graphitic nano onion-like structures containing phosphorus and nitrogen (NP-GNOs), using the aerosol assisted chemical vapor deposition method. The NP-GNOs were grown at high temperature (1020 °C) using ferrocene, trioctylphosphine oxide, benzylamine, and tetrahydrofuran precursors. The morphology, structure, composition, and surface chemistry of NP-GNOs were characterized using different techniques. The NP-GNOs showed diameters of 110-780 nm with Fe-based nanoparticles inside. Thermogravimetric analysis showed that NP-GNOs are thermally stable with an oxidation temperature of 724 °C. The surface chemistry analysis by FTIR and XPS revealed phosphorus-nitrogen codoping, and several functionalities containing C-H, N-H, P-H, P-O, P[double bond, length as m-dash]O, C[double bond, length as m-dash]O, and C-O bonds. We show density functional theory calculations of phosphorus-nitrogen doping and functionalized C240 fullerenes. We present the optimized structures, electronic density of states, HOMO, and LUMO wave functions for P-doped and OH-functionalized fullerenes. The P[double bond, length as m-dash]O and P-O bonds attributed to phosphates or hydroxyl groups attached to phosphorus atoms doping the NP-GNOs could be useful in improving supercapacitor function.