ABSTRACT
Layer-structured vanadium oxide (V2O5) nanoribbons with efficient electron transport and short lithium ion insertion lengths are promising candidates for high-performance lithium-ion battery applications. Despite the extensive investigation of its electrochemical properties, the chemical and structural evolution during lithiation-delithiation processes has rarely been characterized in real time. Herein, the lithiation-delithiation behaviors of V2O5 nanoribbons are probed by in situ transmission electron microscopy. We reveal that the V2O5 nanoribbons exhibit high lithiation speed (0.8 nm/s) without retardation along the [010] direction and can be fully lithiated to the Li3V2O5 phase. Fully reversible retraction of lithium is observed in these V2O5 nanoribbons during delithiation. The lithiation process accompanying the coherent strain is further simulated by our phase field model. The simulation results reveal that the specific rough lithiation interface between the V2O5 and Li3V2O5 phases originates from the lithiation inhomogeneity.
ABSTRACT
Through in situ transmission electron microscopy (TEM) observation, we report the behaviors of phosphorus (P)-doped silicon nanowires (SiNWs) during electrochemical lithiation/delithiation cycling. Upon lithiation, lithium (Li) insertion causes volume expansion and formation of the crystalline Li15Si4 phase in the P-doped SiNWs. During delithiation, vacancies induced by Li extraction aggregate gradually, leading to the generation of nanopores. The as-formed nanopores can get annihilated with Li reinsertion during the following electrochemical cycle. As demonstrated by our phase-field simulations, such first-time-observed reversible nanopore formation can be attributed to the promoted lithiation/delithiation rate by the P dopant in the SiNWs. Our phase-field simulations further reveal that the delithiation-induced nanoporous structures can be controlled by tuning the electrochemical reaction rate in the SiNWs. The findings of this study shed light on the rational design of high-power performance Si-based anodes.
ABSTRACT
By dispersing Li6.25Ga0.25La3Zr2O12 (Ga-LLZO) nanoparticles in poly(ethylene oxide) (PEO) matrix, PEO:Ga-LLZO composite polymer electrolytes are synthesized. The PEO: Ga-LLZO composite with 16 vol % Ga-LLZO nanoparticles shows a conductivity of 7.2 × 10-5 S cm-1 at 30 °C, about 4 orders of magnitude higher than the conductivity of PEO. The enhancement of the ionic conductivity is closely related to the space charge region (â¼3 nm) formed at the interface between the PEO matrix and the Ga-LLZO nanoparticles. The space charge region is observed by transmission electron microscope (TEM) and corroborated by the phase-field simulation. Using the random resistor model, the lithium-ion transport in the composite polymer electrolyte is simulated by the Monte Carlo simulation, demonstrating that the enhanced ionic conductivity can be ascribed to the ionic conduction in the space charge regions and the percolation of the space charge regions.
