Partial atomic charges are widely used for the description of charge distributions of molecules and solids. These charges are useful to indicate the extent of charge transfer and charge flow during chemical reactions in batteries, fuel cells, and catalysts and to characterize charge distributions in capacitors, liquid-phase electrolytes, and solids and at electrochemical interfaces. However, partial atomic charges given by various charge models differ significantly, especially for systems containing metal atoms. In the present study, we have compared various charge models on both molecular systems and extended systems, including Hirshfeld, CM5, MK, ChElPG, Mulliken, MBS, NPA, DDEC, LoProp, and Bader charges. Their merits and drawbacks are compared. The CM5 charge model is found to perform well on the molecular systems, with a mean unsigned percentage deviation of only 9% for the dipole moments. We therefore formulated it for extended systems and applied it to study charge flow during the delithiation process in lithium-containing oxides used as cathodes. Our calculations show that the charges given by the CM5 charge model are reasonable and that during the delithiation process, the charge flow can occur not only on the transition metal but also on the anions. The oxygen atoms can lose a significant density of electrons, especially for deeply delithiated materials. We also discuss other methods in current use to analyze the charge transfer and charge flow in batteries, in particular the use of formal charge, spin density, and orbital occupancy. We conclude that CM5 charges provide useful information in describing charge distributions in various materials and are very promising for the study of charge transfer and charge flows in both molecules and solids.
Wearable electronic devices are evolving from current rigid configurations to flexible and ultimately stretchable structures. These emerging systems require soft circuits for connecting the various working units of the overall system. This paper presents fabrication of soft circuits by electrohydrodynamic (EHD) inkjet-printing technique. Multi-nozzle EHD printing head is employed for rapid fabrication of electric circuits on a wide set of materials, including glass substrate (rigid), flexible polyethylene terephthalate (PET) films, and stretchable thermoplastic polyurethane (TPU) films. To avoid the effects of substrate materials on the jettability, the proposed multi-nozzle head is equipped with integrated individual counter electrodes (electrodes are placed above the printing substrate). High-resolution circuits (50 ± 5 µm) with high electrical conductivity (0.6 Ω □−1) on soft substrate materials validate our well-controlled multi-nozzle EHD printing approach. The produced circuits showed excellent flexibility (bending radius ≈ 5 mm radius), high stretchability (strain ≈ 100%), and long-term mechanical stability (500 cycles at 30% strain). The concept is further demonstrated with a soft strain sensor based on a multi-nozzle EHD-printed circuit, employed for monitoring the human motion (finger bending), indicating the potential applications of these circuits in soft wearable electronic devices.
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