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Nanoscale oxide-based negative electrodes are of great interest for lithium ion batteries due to their high energy density, power density and enhanced safety. In this work, we conducted a case study on mesoporous TiO2 nanoparticle negative electrodes with uniform size and varying crystallinity in order to investigate the trend in the electrochemical properties of oxide-based nanoscale negative electrodes with varying crystallinity. Mesoporous solid spherical TiO2 nanoparticles with a uniform particle size and varying crystallinity, i.e., amorphous TiO2 (A-TiO2), partially crystalline TiO2 (PC-TiO2) and fully crystalline TiO2 (FC-TiO2) nanoparticles were studied. At low current rate (quasi steady-state), the specific capacity of the samples drops with the decrease of crystallinity. Ex situ synchrotron pair distribution function analysis reveals that the 1D zigzag Li ion diffusion pathway becomes expanded with the increase of crystallinity, which promotes ion mobility and charge storage. At high current rates (away from equilibrium states), however, the A-TiO2 sample demonstrates slightly larger capacity than the FC-TiO2 sample, both of which show larger capacities than that of the PC-TiO2 sample. Both A-TiO2 and FC-TiO2 samples exhibit higher capacitive contribution to the charge storage and larger Li+ diffusivity than those of the PC-TiO2 sample, which explains their better rate capability. Moreover, the larger Li+ diffusivity of the A-TiO2 sample leads to the slightly larger specific capacity than the FC-TiO2 sample at the highest current rate. [ABSTRACT FROM AUTHOR]

The article features Donna Pierce, director of the Pierce Planetarium located in Dallas, Texas. Topics include her 35-year stint as the planetarium's director, why she considers the planetarium as an extension of the classroom, and the 2011 decision of Highland Park Integrated School District to name the planetarium after her.

Fundamental characterization of battery electrolyte is vital for rechargeable batteries. This work reports the chemical stability of sodium hexafluorophosphate (NaPF 6)-based non-aqueous electrolytes containing different solvent mixtures (e.g., cyclic and acyclic carbonates) in the presence of water for Na-ion batteries. A degradation study is conducted using NaPF 6 -based electrolytes, highlighting two electrolyte additives, 2,2,2-trifluoroethoxy-2,2,2-ethoxy phosphazene (FM2) and fluoroethylene carbonate (FEC), on degradation and cell performance of Na-ion batteries. Hydrolysis of NaPF 6 in acidic condition is particularly prone to form hydrofluoric acid (HF), and can be observed in electrolytes made with battery grade carbonate solvents (<20 ppm of water). Degradation mechanisms of NaPF 6 -based electrolytes are studied using liquid nuclear magnetic resonance (NMR). Noticeable degradation takes place in high purity electrolytes with the presence of moisture to form HF and organophosphates in timeframes below the current shelf-life of the Na electrolytes. FEC is not efficient to protect the electrodes from being exposed to HF. On the other hand, FM2 is revealed as a "scavenger" of HF, which helps stabilize the shelf life of electrolytes that might contain or become exposed to water. Our study underscores the importance to understanding the degradation of electrolyte and improving stability toward better shelf life for sodium ion batteries. Image 1 • NaPF 6 -based nonaqueous electrolytes are highly susceptible to HF with water presence. • NMR reveals an autocatalytic hydrolysis pathway of PF 6 − to form HF. • FM2 can serve as an HF scavenger to improve electrolyte chemical stability. • HF mitigation is closely related to the chemical stability of NaPF 6. • HF formation is observed in battery grade electrolytes with <20 ppm H 2 O. [ABSTRACT FROM AUTHOR]