RESUMEN
Ag doped Co3O4 nanoparticles (NPs) were synthesized via a co-precipitation method changing the concentration of Ag. The crystal structure, morphology, surface area, functional group, optical band gap, and thermal property were investigated by XRD, SEM, BET, FTIR, UV-Vis, and TGA/DTA techniques. The XRD results showed the formation of single-cubic Co3O4 nanostructured materials with an average crystal size of 19.37 nm and 12.98 nm for pristine Co3O4 and 0.25 M Ag-doped Co3O4 NPs. Morphological studies showed that pristine Co3O4 and 0.25 M Ag-doped Co3O4 NPs having a porous structure with small spherical grains, porous structures with sponge-like structures, and loosely packed porous structures, respectively. The pristine and 0.25 M Ag-doped Co3O4 NPs showed BET surface areas of 53.06 m2/g, and 407.33 m2/g, respectively. The band gap energy of Co3O4 NPs were 2.96 eV, with additional sub-bandgap energy of 1.95 eV. Additionally, it was discovered that the band gap energies of 0.25 M Ag-doped Co3O4 NPs ranged from 2.2 to 2.75 eV, with an extra sub-band with energies ranging from 1.43 to 1.94 eV for all as-prepared samples. The Ag-doped Co3O4 as prepared samples show improved thermal properties due to the doping effect of silver. The CV test confirmed that the 0.25 M Ag-doped Co3O4 NPs exhibited the highest specific capacitance value of 992.7 F/g at 5 mV/s in a 0.1 M KOH electrolyte solution. The energy density and power density of 0.25 M Ag-doped Co3O4 NPs were 27.9 W h/kg and 3816.1 W/kg, respectively.
RESUMEN
Understanding the mechanism of Li nucleation and growth is essential for providing long cycle life and safe lithium ion batteries or lithium metal batteries. However, no quantitative report on Li metal deposition is available, to the best of our knowledge. We propose a model for quantitatively understanding the Li nucleation and growth mechanism associated with the solid-electrolyte interphase (SEI) formation, which we name the Li-SEI model. The current transients at various overpotentials initiate the nucleation and growth of Li metal on bare Cu foil. The Li-SEI model considering a three-dimensional diffusion-controlled instantaneous process (J3D-DC) with the simultaneous reduction of electrolyte decomposition (JSEI) due to the SEI fracture is employed for investigating the Li nucleation and growth mechanism. The individual contributions of experimental and theoretical transient states, i.e., the fundamental kinetic values of diffusion coefficient (D), rate of nucleation (N0), and rate constant of electrolyte decomposition (kSEI), can be determined from the Li-SEI model. Interestingly, JSEI increases with time, indicating that the current contributing from the electrolyte decomposition increases with time due to the SEI fracture upon Li deposition. Meanwhile, the kSEI increases with overpotential, indicating the SEI fracture is more serious at higher overpotential or higher growth rate. The kSEI is smaller in the electrolyte with fluoroethylene carbonate (FEC) additive, indicating that FEC additive can significantly suppress the SEI fracture during Li metal deposition. This proposed model opens a new way to quantitatively understand the Li nucleation and growth mechanism and electrolyte decomposition on various substrates or in different electrolytes.
