Calcium-ion
batteries (CIBs) are under investigation as next-generation
energy storage devices due to their theoretically high operating potentials
and lower costs tied to the high natural abundance of calcium. However,
the development of CIBs has been limited by the lack of available
positive electrode materials. Here, for the first time, we report
two functional polyanionic phosphate materials as high-voltage cathodes
for CIBs at room temperature. NaV2(PO4)3 electrodes were found to reversibly intercalate 0.6 mol of
Ca2+ (81 mA h g–1) near 3.2 V (vs Ca2+/Ca) with stable cycling performance at a current density
of 3.5 mA g–1. The olivine framework material FePO4 reversibly intercalates 0.2 mol of Ca2+ (72 mA
h g–1) near 2.9 V (vs Ca2+/Ca) at a current
density of 7.5 mA g–1 in the first cycle. Structural,
electronic, and compositional changes are consistent with reversible
Ca2+ intercalation into these two materials.
Lattice
Mg2+ in a tailored solid solution spinel, MgCrMnO4, is electrochemically utilized at high Mn-redox potentials
in a nonaqueous electrolyte. Complementary evidence from experimental
and theoretical analyses supports bulk Mg2+ (de)intercalation
throughout the designed oxide frame where strong electrostatic interaction
between Mg2+ and O2– exists. Mg/Mn antisite
inversion in the spinel is lowered to ∼10% via postannealing
at 350 °C to further improve Mg2+ mobility. Spinel
lattice is preserved upon removal of Mg2+ without any phase
transformations, denoting structural stability at the charged state
at a high potential ∼3.0 V (vs Mg/Mg2+). Clear remagnesiation
upon first discharge, harvesting up to ∼180 Wh/kg at 60 °C
is shown. In the remagnesiated state, insertion of Mg2+ into interstitial sites in the spinel is detected, possibly resulting
in partial reversibility which needs to be addressed for structural
stability. The observations constitute a first clear path to the development
of a practical high voltage Mg-ion cathode using a spinel oxide.
Li-iodine chemistry is of interest for electrochemical energy storage because it has been shown to provide both high power and high energy density. However, Li-iodine batteries are typically formed using Li metal and elemental iodine, which presents safety and fabrication challenges (e.g., the high vapor pressure of iodine). These disadvantages could be circumvented by using LiI as a starting cathode. Here, we present fabrication of a reduced graphene oxide (rGO)/LiI composite cathode, enabling for the first time the use of LiI as the Li-ion battery cathode. LiI was coated on rGO by infiltration of an ethanolic solution of LiI into a compressed rGO aerogel followed by drying. The free-standing rGO/LiI electrodes show stable long-term cycling and good rate performance with high specific capacity (200 mAh g at 0.5 C after 100 cycles) and small hysteresis (0.056 V at 1 C). Shuttling was suppressed significantly. We speculate the improved electrochemical performance is due to strong interactions between the active materials and rGO, and the reduced ion and electron transport distances provided by the three-dimensional structured cathode.
We report that a Ni–InGaAs alloy can be used as a source/drain (S/D) metal for InGaAs metal–oxide–semiconductor field-effect transistors (MOSFETs), allowing us to employ the salicide-like self-align S/D formation. We also introduce Schottky barrier height (SBH) engineering process by increasing the indium content of InxGa1-xAs channels, which successfully reduces SBH down to zero. We propose a fabrication process for self-aligned metal S/D MOSFETs using Ni–InGaAs and demonstrate successful operation of the metal S/D InxGa1-xAs MOSFETs. The In0.7Ga0.3As MOSFETs exhibit an S/D resistance (RSD) that is 1/5 lower than that in P–N junction devices and a high peak mobility of 2000 cm2 V-1 s-1.
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