Defects in Li4Ti5O12 induced by carbon deposition: an analysis of unidentified bands in Raman spectra.

Lithium titanate (Li4Ti5O12, LTO) has already occupied its niche as an anode material for high-power and long-lifespan lithium batteries, but some novel directions for basic and applied research are still open. One of the most promising approaches in improving its properties, e.g., electronic conductivity and rate capability, is based on controllable defect engineering. The "defects" may be intentionally introduced into LTO via doping, surface modifications, and the synergy between them. However, the defects, which have significant effects to the electrical and electrochemical properties, are usually extremely dilute. Reliable material characterizations are essential and challenging, but the instrumental tools for revealing dilute defects are still insufficient. Herein, detailed analyses on the surface or subsurface defects of carbon-coated LTO were performed using various material characterization methods. Raman spectroscopy has been identified as a unique tool for the probing of structural defects.

Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12:Al,Ta Interface in an All-Solid-State Lithium Battery.

All-solid-state lithium batteries are promising candidates for next-generation energy storage systems. Their performance critically depends on the capacity and cycling stability of the cathodic layer. Cells with a garnet Li7La3Zr2O12 (LLZO) electrolyte can show high areal storage capacity. However, they commonly suffer from performance degradation during cycling. For fully inorganic cells based on LiCoO2 (LCO) as cathode active material and LLZO, the electrochemically induced interface amorphization has been identified as an origin of the performance degradation. This study shows that the amorphized interface can be recrystallized by thermal recovery (annealing) with nearly full restoration of the cell performance. The structural and chemical changes at the LCO/LLZO heterointerface associated with degradation and recovery were analyzed in detail and justified by thermodynamic modeling. Based on this comprehensive understanding, this work demonstrates a facile way to recover more than 80% of the initial storage capacity through a thermal recovery (annealing) step. The thermal recovery can be potentially used for cost-efficient recycling of ceramic all-solid-state batteries.

Study of LiCoO2/Li7La3Zr2O12:Ta Interface Degradation in All-Solid-State Lithium Batteries.

The garnet-type Li7La3Zr2O12 (LLZO) ceramic solid electrolyte combines high Li-ion conductivity at room temperature with high chemical stability. Several all-solid-state Li batteries featuring the LLZO electrolyte and the LiCoO2 (LCO) or LiCoO2-LLZO composite cathode were demonstrated. However, all batteries exhibit rapid capacity fading during cycling, which is often attributed to the formation of cracks due to volume expansion and the contraction of LCO. Excluding the possibility of mechanical failure due to crack formation between the LiCoO2/LLZO interface, a detailed investigation of the LiCoO2/LLZO interface before and after cycling clearly demonstrated cation diffusion between LiCoO2 and the LLZO. This electrochemically driven cation diffusion during cycling causes the formation of an amorphous secondary phase interlayer with high impedance, leading to the observed capacity fading. Furthermore, thermodynamic analysis using density functional theory confirms the possibility of low- or non-conducting secondary phases forming during cycling and offers an additional explanation for the observed capacity fading. Understanding the presented degradation paves the way to increase the cycling stability of garnet-based all-solid-state Li batteries.

Plasmonic coupling of silver nanoparticles covered by hydrogen-terminated graphene for surface-enhanced Raman spectroscopy.

We report on strong plasmonic coupling from silver nanoparticles covered by hydrogen-terminated chemically vapor deposited single-layer graphene, and its effects on the detection and identification of adenine molecules through surface-enhanced Raman spectroscopy (SERS). The high resistivity of the graphene after subjecting to remote plasma hydrogenation allows plasmonic coupling induced strong local electromagnetic fields among the silver nanoparticles to penetrate the graphene, and thus enhances the SERS efficiency of adenine molecules adsorbed on the film. The graphene layer protects the nanoparticles from reactive and harsh environments and provides a chemically inert and biocompatible carbon surface for SERS applications.

The synthesis and electrical characterization of Cu2O/Al:ZnO radial p-n junction nanowire arrays.

Vertically aligned large-area p-Cu(2)O/n-AZO (Al-doped ZnO) radial heterojunction nanowire arrays were synthesized on silicon without using catalysts in thermal chemical vapor deposition followed by e-beam evaporation. Scanning electron microscopy and high-resolution transmission electron microscopy results show that poly-crystalline Cu(2)O nano-shells with thicknesses around 10 nm conformably formed on the entire periphery of pre-grown Al:ZnO single-crystalline nanowires. The Al doping concentration in the Al:ZnO nanowires with diameters around 50 nm were determined to be around 1.19 at.% by electron energy loss spectroscopy. Room-temperature photoluminescence spectra show that the broad green bands of pristine ZnO nanowires were eliminated by capping with Cu(2)O nano-shells. The current-voltage (I-V) measurements show that the p-Cu(2)O/n-AZO nanodiodes have well-defined current rectifying behavior. This paper provides a simple method to fabricate superior p-n radial nanowire arrays for developing nano-pixel optoelectronic devices and solar cells.