Overview of the Oxygen Behavior in the Degradation of Li₂MnO₃ Cathode Material

The Li₂MnO₃ cathode material is vulnerable to complex degradation behaviors during the operation of battery although it has attracted much attention recently due to its potentially large capacity. In this study, we comprehensively examined the degradation process in Li₂MnO₃, using theoretical density functional computations as well as experimental techniques (<i>in situ</i> X-ray absorption near edge structure spectroscopy, X-ray diffraction, and Raman spectroscopy). Our study reveals that during the delithiation process, the Li ions mixed in the Mn layer are removed together with those in the Li layer, thereby inducing the release of oxygen atoms. The oxygen loss reaction is energetically favorable at the highly delithiated states, and it can reduce the plateau voltage in the charging curve. Such oxygen loss was observed during or even before the second cycle and furthermore it accelerates the phase transformation of the layered structure to a spinel one. Our results also suggest that oxygen release can be prevented when H ions are exchanged with Li ions during the charging process

Design of a Polymer–Carbon Nanohybrid Junction by Interface Modeling for Efficient Printed Transistors

Molecularly hybridized materials composed of polymer semiconductors (PSCs) and single-walled carbon nanotubes (SWNTs) may provide a new way to exploit an advantageous combination of semiconductors, which yields electrical properties that are not available in a single-component system. We demonstrate for the first time high-performance inkjet-printed hybrid thin film transistors with an electrically engineered heterostructure by using specially designed PSCs and semiconducting SWNTs (sc-SWNTs) whose system achieved a high mobility of 0.23 cm² V^–1 s^–1, no <i>V</i>_on shift, and a low off-current. PSCs were designed by calculation of the density of states of the backbone structure, which was related to charge transfer. The sc-SWNTs were prepared by a single cascade of the density-induced separation method. We also revealed that the binding energy between PSCs and sc-SWNTs was strongly affected by the side-chain length of PSCs, leading to the formation of a homogeneous nanohybrid film. The understanding of electrostatic interactions in the heterostructure and experimental results suggests criteria for the design of nanohybrid heterostructures

Modulation of the Dirac Point Voltage of Graphene by Ion-Gel Dielectrics and Its Application to Soft Electronic Devices

We investigated systematic modulation of the Dirac point voltage of graphene transistors by changing the type of ionic liquid used as a main gate dielectric component. Ion gels were formed from ionic liquids and a non-triblock-copolymer-based binder involving UV irradiation. With a fixed cation (anion), the Dirac point voltage shifted to a higher voltage as the size of anion (cation) increased. Mechanisms for modulation of the Dirac point voltage of graphene transistors by designing ionic liquids were fully understood using molecular dynamics simulations, which excellently matched our experimental results. It was found that the ion sizes and molecular structures play an essential role in the modulation of the Dirac point voltage of the graphene. Through control of the position of their Dirac point voltages on the basis of our findings, complementary metal–oxide–semiconductor (CMOS)-like graphene-based inverters using two different ionic liquids worked perfectly even at a very low source voltage (<i>V</i>_DD = 1 mV), which was not possible for previous works. These results can be broadly applied in the development of low-power-consumption, flexible/stretchable, CMOS-like graphene-based electronic devices in the future