Research to develop alternative electrode materials with high energy densities in Li-ion batteries has been actively pursued to satisfy the power demands for electronic devices and hybrid electric vehicles. This critical review focuses on anode materials composed of Group IV and V elements with their composites including Ag and Mg metals as well as transition metal oxides which have been intensively investigated. This critical review is devoted mainly to their electrochemical performances and reaction mechanisms (313 references).

Li-air(O2) and Li-S batteries have gained much attention recently and most relevant research has aimed to improve the electrochemical performance of air(O2) or sulfur cathode materials. However, many technical problems associated with the Li metal anode have yet to be overcome. This review mainly focuses on the electrochemical behaviors and technical issues related to metallic Li anode materials as well as other metallic anode materials such as alkali (Na) and alkaline earth (Mg) metals, including Zn and Al when these metal anodes were employed for various types of secondary batteries.

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A promising stress control process is demonstrated to achieve near-zero stress levels in thick porous silicon (PS) films. Stress reduction is necessary for thick PS structures to be used for radio-frequency applications such as on-chip inductors and transmission lines that require very thick (>100 μm) insulating materials. This study employs a standard sample structure with 50-μm-thick PS films formed on p+ substrates through anodization under 50 mA/cm2 and 25% HF concentration. Mass spectroscopy analysis shows that the desorption of hydrogen is correlated with the stress evolution in PS films. As-prepared PS films are under compressive stress. Thermal annealing in N2 ambient turns it into tensile stress. Further annealing in an oxidizing ambient restores the compressive stress. Such stress evolution can be explained by the atomic structure changes on the pore walls of PS films: H2-passivated and oxidized Si surfaces result in compression in PS films, whereas reconstructed state results in tension. These findings are used to fabricate thick PS films with negligible stress (<1 MPa) at room temperature.

Porous Si is the semi-insulating state of Si, with low thermal expansion mismatch with bulk Si. As a result, it is an excellent material for crosstalk isolation in mixed-signal integrated circuits. We study the formation of isolated porous Si regions in p−-type and p+-type Si substrates with emphasis on the cross-sectional profile of the porous regions. Our study reveals that in addition to the primary undercut due to the isotropic nature of the anodization process, there exists a secondary undercut that is similar in shape to the bird’s beak commonly observed at the edge of field oxides in conventional Si complementary-metal-oxide-semiconductor process. The shape and the extent of the secondary undercut are dependent on the type of mask materials used during selective formation of porous Si as well as the substrate resistivity. The combined experimental and simulation studies pointed to two likely origins of secondary undercuts: the weak adhesion of some of the mask materials and current crowding in bulk Si substrates near the edge of the mask openings. Secondary undercuts result in the erosion of the precious Si chip surface area when a porous Si trench is used for rf crosstalk isolation, and should be minimized.

Sodium rechargeable batteries can be excellent alternatives to replace lithium rechargeable ones because of the high abundance and low cost of sodium; however, there is a need to further improve the battery performance, cost-effectiveness, and safety for practical use. Here we demonstrate a new type of room-temperature and high-energy density sodium rechargeable battery using an SO2-based inorganic molten complex catholyte, which showed a discharge capacity of 153 mAh g−1 based on the mass of catholyte and carbon electrode with an operating voltage of 3 V, good rate capability and excellent cycle performance over 300 cycles. In particular, non-flammability and intrinsic self-regeneration mechanism of the inorganic liquid electrolyte presented here can accelerate the realization of commercialized Na rechargeable battery system with outstanding reliability. Given that high performance and unique properties of Na–SO2 rechargeable battery, it can be another promising candidate for next generation energy storage system.

Articles you may be interested inMonolithic integration of common mode filters with electrostatic discharge protection on silicon/porous silicon hybrid substrate Appl. Phys. Lett.An isolation technology for radio frequency ͑rf͒ applications based on unoxidized porous Si ͑PS͒ is demonstrated. This study examines all the important issues pertinent to incorporating PS with Si very-large-scale integration ͑VLSI͒ technology, where PS is used as a semi-insulating material. Specifically, the issues on rf isolation performance of PS as a function of porosity ͓from coplanar waveguide ͑CPW͒ line measurements͔ and PS thickness ͑from on-chip inductors͒ and the stress generated from incorporating PS regions by anodization are discussed in detail. CPW line measurements show that the relative dielectric constant of PS films decreases from 9 to 3 with increasing porosity from 24% to 78%. PS is a very low loss material with loss tangent Ͻ0.001 at 20 GHz when its porosity is above 51%. rf crosstalk through a Si substrate can be reduced to that through air by inserting a PS trench between noise generating circuit and noise sensing circuit. On-chip spiral inductors fabricated on top of PS regions of through-the-wafer thickness have Q max of about 29 at 7 GHz and resonant frequency higher than 20 GHz. With the additional advantage of planar topography and mechanical integrity, we show that unoxidized PS is an outstanding material for rf isolation in Si VLSI.

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