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

In this work, we, for the first time, demonstrate <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3 lateral superjunction (SJ) -equivalent metal–oxide–semiconductor field-effect transistors (MOSFETs). The electric field engineering is implemented by the alternatively arranged p-NiO/n-Ga2O3 lateral hetero-SJ, which is constructed through the selective epitaxial filling of p-NiO pillars into the trenched drift region of <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3. The static electrical characteristics indicate that <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3 SJ-equivalent MOSFETs outperform the control transistor without the SJ structure. In particular, the Ga2O3SJ-equivalent MOSFET with a p-NiO pillar width of 2 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> demonstrates a breakdown voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {br}}$ </tex-math></inline-formula>) of 1362 V and a power figure-of-merit (PFOM) of 39 MW/cm2, which are 2.42 and 4.86 times higher, respectively, than those of the control device. The large divergence of the experimental performance from the theoretical predictions is attributed to the charge imbalance caused by the substrate-assisted depletion effect and superimposed interfacial charges. With the proper interface engineering and controlled doping, it is expected that utilizing p-NiO/n-Ga2O3 hetero-SJ is a promising technological strategy to allow a favorable trade-off between <inline-formula> <tex-math notation="LaTeX">${V}_{\text {br}}$ </tex-math></inline-formula> and ON-state loss of Ga2O3 transistors for the high-efficiency power conversion.

Demonstration of β-Ga₂O₃ Superjunction-Equivalent MOSFETs

Here, we present a systematical investigation of AlN/GaN double-barrier resonant tunneling diodes (RTDs) grown by plasma-assisted molecular beam epitaxy on metal-organic chemical vapor deposition GaN-on-sapphire templates. The processed devices featured an active region composed of 2.5 nm GaN quantum well sandwiched by two 1.5 nm AlN barriers and RTD mesa diameter ranging from 1 to 20 μm. Room temperature current–voltage characteristics exhibited a repeatable negative differential resistance (NDR) free of degradation and hysteresis after 1000 times subsequently up-to-down voltage sweeps across different sizes. High peak-to-valley current ratios of 1.93 and 1.58 were obtained at room temperature for 1 and 12 μm diameter devices, respectively, along with peak current densities of 48 and 36 kA/cm2 corresponding to peak voltages of 4.65 and 5.9 V. The peak current density decreased quickly initially and then was less susceptible to this averaging effect with increasing the device diameter. Temperature-dependent measurements revealed that the valley current density displayed a positive relationship to the temperature, and an abruptly increasement was observed for the devices with a diameter of 20 μm when the temperature rose over 230 K. We attributed this abnormal phenomenon to the increased contribution from acoustic and longitudinal optical (LO) phonon scattering, especially for the LO phonon scattering. The area dependence of electrical performance suggested that the leakage pathway through dislocations played a vital role for charge transport and there existed a threshold of dislocation density for NDR characteristics. These results promote further study for future implementation of III-nitride-based RTD oscillators into high-frequency and high-power terahertz radiation.

Demonstration of highly repeatable room temperature negative differential resistance in large area AlN/GaN double-barrier resonant tunneling diodes

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Si-rich SiN/Si3N4 bilayer passivation were studied in this article. The use of a Si-rich SiN interlayer leads to improved channel transport property, current collapse, power performance, and temperature-dependent stability. Devices without Si-rich SiN interlayer passivation exhibit an increase in the gate leakage current by over three orders of magnitudes with temperature increasing from 300 to 420 K, leading to an increase in a current collapse from 9.7% to 24.7%, while the devices with Si-rich SiN passivation exhibit a weak temperature dependence of leakage current and a constant current collapse about 5%. Small signal characterization shows that Si-rich SiN passivation results in a remarkable decrease in the effective gate length by ~15% with temperature up to 420 K. At 17 GHz, devices with Si-rich SiN interlayer passivation exhibit an output power density of 7 W/mm and a peak power-added efficiency (PAE) of 56%. The improved power performance of devices using Si-rich SiN interlayer passivation is attributed to the suppressed current collapse and superior device stability under high channel temperature.

Improved Power Performance and the Mechanism of AlGaN/GaN HEMTs Using Si-Rich SiN/Si3N4 Bilayer Passivation

A combination of high maximum oscillation frequency (fmax) and breakdown voltage (Vbr) was achieved in AlGaN/GaN high electron mobility transistors (HEMTs) with N2O plasma treatment on the access region. The breakdown voltage is improved from 37 V to 80 V due to the formation of oxide layer in the gate region. A suppressed current collapse is obtained due to plasma treatment on the gate-source and the gate-drain regions. The effect of the present passivation method is almost the same with that of the conventional SiN passivation method, meanwhile it can avoid introducing additional parasitic capacitance due to thinner thickness. The small signal measurement shows that HEMT can yield fT and fmax of 98 and 322 GHz, respectively, higher than that of 70 and 224 GHz for the non-treated HEMT. By using the plasma treatment technique, the HEMT can simultaneously exhibit high fmax and Vbr with a record fmax⋅Vbr of 25 THz⋅V.

Xiaohua Ma

Papers

Demonstration of β-Ga₂O₃ Superjunction-Equivalent MOSFETs

Demonstration of highly repeatable room temperature negative differential resistance in large area AlN/GaN double-barrier resonant tunneling diodes

Improved Power Performance and the Mechanism of AlGaN/GaN HEMTs Using Si-Rich SiN/Si3N4 Bilayer Passivation

Record combination fmax · Vbr of 25 THz·V in AlGaN/GaN HEMT with plasma treatment

MoS2@PDA thin-film nanocomposite nanofiltration membrane for simultaneously improved permeability and selectivity