With the ever-increasing demand for power sources of high energy density and stability for emergent electrical vehicles and portable electronic devices, rechargeable batteries (such as lithium-ion batteries, fuel batteries, and metal–air batteries) have attracted extensive interests. Among the emerging battery technologies, metal–air batteries (MABs) are under intense research and development focus due to their high theoretical energy density and high level of safety. Although significant progress has been achieved in improving battery performance in the past decade, there are still numerous technical challenges to overcome for commercialization. Herein, this mini-review summarizes major issues vital to MABs, including progress on packaging and crucial manufacturing technologies for cathode, anode, and electrolyte. Future trends and prospects of advanced MABs by additive manufacturing and nanoengineering are also discussed.

There is little doubt that there is significant potential for high-entropy alloys (HEAs) in cryogenic and aerospace applications. However, given the immense design space for HEAs, there is much more to be explored. This review will focus on four areas of application for HEAs that receive less attention. These focus areas include joining technologies, HEA nanomaterial synthesis, catalysis, and marine applications. The performance of HEAs as a filler metal for welding and brazing as well as their performance as a welded/brazed base metal will be discussed. Various methods for synthesizing HEA nanomaterials are reviewed with specifically highlighted applications in catalysis and energy storage. HEA catalysts, in particular, will be discussed in detail regarding their effectiveness, selectiveness, and stability. Marine applications are explored given the inherent corrosion resistance of HEAs as well as superior antifouling properties that make HEAs an intriguing marine-ready material.

This study investigated the characteristics and strength of the dissimilar joints between carbon fiber reinforced plastic (CFRP) epoxy composites and aluminum alloys using two different heating methods, Ni/Al reactive multilayer films (RMF) and a low power continuous wave diode laser. To enhance the adhesion, the top resin layer of the CFRP and the surface of the aluminum alloy were patterned by femtosecond laser. Polycarbonate (PC) was used as a filler material during the joining processes. ANSYS simulation was applied to elucidate the thermal kinetics of the self-propagation reaction and the thermal profile, and evaluate the possibility of joining CFRP to aluminum using Ni/Al RMFs. The SEM image of the cross-section shows that melted PC flowed into the CFRP–aluminum alloy interface, suggesting strong mechanical bonding. A tensile strength of 9.5 MPa was reached using Ni/Al multilayers as heat sources, which provides a new way for joining CFRPs and aluminum alloys in space or under water.

Self-powered brazing of Ti-6Al-4V was performed using Ni/Al reactive multilayer films (RMFs) as self-propagated heat resources. BAlSi-4 was first coated on Ti-6Al-4V by plasma welding, then alternating layers of Ni and Al were successfully deposited on BAlSi-4 up to 32.9 μm thick with e-beam deposition. The joint microstructure was investigated and the AlNi and Ni₅Al₃ phases were identified in the RMF. The cause for the two phases was determined to be differences in the diffusivity of Ni and Al, ultrafast brazing time, and faster cooling at the interface between brazing filler metal and the RMF. The maximum temperature of 683 °C was reached in the brazed joint, with a total RMF thickness of 135 μm, which is more than sufficient to melt the BAlSi-4 brazing material. The maximum bonding strength obtained was 10.6 MPa, with a self-power brazing procedure conducted in a minute. It is possible to further improve the bonding strength by using more ductile RMFs and/or modifying the bonding interface configuration.