There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

羟氨苄青霉素引起大疱性类天疱疮样疹

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

The submicrometer gate HEMT is fabricated with an ultrathin-barrier (UTB) AlGaN/gallium nitride (GaN) combined with in situ SiN passivation. The sheet resistance of the UTB Al0.2Ga0.8N (4 nm)/GaN heterostructure is effectively reduced by the SiNx passivation layer grown by metal organic chemical vapor deposition (MOCVD), from 6500 to $312~ \Omega $ /⬜. With the 20-nm stress-engineered in situ SiN, the device not only provides a large output current of 1.05 A/mm but also demonstrates promising potential on the RF applications, which gives AlGaN material two records high cutoff frequency ${f} _{\text {T}}/{f} _{\text {max}}$ of 157 GHz/334 GHz for 100-nm gated device and 211 GHz/379 GHz for 70-nm gated device. During the continuous wave (CW) power measurement at 30 GHz, the 70-nm devices exhibit a large output power of 4.6 W/mm associated with a peak power-added efficiency (PAE) of 48.1% and a gain of 11.6 dB ( ${V} _{\text {ds}} =20$ V), and a high PAE of 53.8% with an output power density of 1.9 W/mm and a gain of 10.8 dB ( ${V} _{\text {ds}} =10$ V), respectively. The huge potential of the UTB-AlGaN/GaN is demonstrated for high-frequency and large-output power applications when it is combined with the in situ SiN, which is necessary for future communication systems.

A High RF-Performance AlGaN/GaN HEMT With Ultrathin Barrier and Stressor In Situ SiN

At present, the physical mechanism of complementary resistive switching (CRS) devices remains controversial. In this Letter, stable CRS can be achieved in Pt/AlOxNy/Ta resistive random access memory (RRAM). A dynamic evolution from bipolar resistive switching to CRS can be evidently observed in non-inert electrodes RRAM. The causes of CRS behavior are analyzed in detail, and these phenomena are attributed to the different oxidation degrees of the top electrode and propose that the transition state can be used as a signal for the emergence of CRS behavior. Moreover, the model is partially supported by measured switching behavior of the Pt/AlOxNy/TaOx device. This research contributes to the understanding of the CRS behavior physical mechanism in non-inert electrodes RRAM devices.

Dynamic evolution process from bipolar to complementary resistive switching in non-inert electrode RRAM

The effect of 3 MeV proton irradiation on interface traps under a Schottky contact in an AlGaN/GaN heterostructure has been investigated in this work. Utilizing the frequency-dependent conductance technique, the detailed information about interface traps under different proton doses has been evaluated. When the proton irradiation dose is increased to 5 × 1014 H+/cm2, it is observed that the deepest energy level of interface traps changes from 0.375 eV to 0.346 eV and the shallowest energy level changes from 0.284 eV to 0.238 eV. The corresponding energy range expands from 0.091 eV to 0.108 eV. Especially, the trap density at the deepest energy level and that at the shallowest energy level are reduced by 65% and 93%, respectively. Transmission electron microscopy and energy dispersive x-ray spectroscopy are also used to assess the Schottky contact interface, and no element inter-diffusion is observed after proton irradiation. The reverse gate leakage current decreases with an increase in the proton irradiation dose, which agrees with the reduction in interface trap density.

Proton irradiation impact on interface traps under Schottky contact in AlGaN/GaN heterostructure

Ordered TiO2 nanostructure arrays such as hydrothermal nanorod arrays (NRAs) and anodic nanotube arrays have attracted great attentions in solar cells, photocatalysis and etc., mainly due to their vertically-aligned 1-D architectures. However, the device performances are limited by their poor electronic properties, due to the morphology collapse and surface adsorbates. In this work, a novel freeze-drying technique has been used to post-treat the hydrothermal TiO2 NRAs. The freeze-drying treatment not only leads to well-preserved nano-array morphology, but also induces complete removal of adsorbed chlorine on TiO2 surface. The light scattering feature and the energy band structure have thus changed after freeze-drying as compared to common air-drying. As a result, the charge transfer at TiO2/electrolyte interface and the collection efficiency of photo-excited electrons through the TiO2 NRAs are substantially improved, leading to the performance enhancement of model solar cells.

Freeze Drying as a Novel Approach to Improve Charge Transport in Titanium Dioxide Nanorod Arrays

A novel AlGaN/GaN high electron mobility transistor (HEMT) with double buried p-type layers (DBPLs) in the GaN buffer layer and its mechanism are studied. The DBPL AlGaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8 μm.

https://iopscience.iop.org/article/10.1088/0256-307X/33/6/067301/pdf

Xiaohua Ma

Papers

A High RF-Performance AlGaN/GaN HEMT With Ultrathin Barrier and Stressor In Situ SiN

Dynamic evolution process from bipolar to complementary resistive switching in non-inert electrode RRAM

Proton irradiation impact on interface traps under Schottky contact in AlGaN/GaN heterostructure

Freeze Drying as a Novel Approach to Improve Charge Transport in Titanium Dioxide Nanorod Arrays

Enhancement of Breakdown Voltage in AlGaN/GaN High Electron Mobility Transistors Using Double Buried p-Type Layers