Polarizable Additive with Intermediate Chelation Strength for Stable Aqueous Zinc‑Ion Batteries

Aqueous zinc-ion batteries are promising due to inherent safety,low cost,low toxicity,and high volumetric capacity.However,issues of dendrites and side reactions between zinc metal anode and the electrolyte need to be solved for extended storage and cycle life.Here,we proposed that an electrolyte additive with an intermediate chelation strength of zinc ion—strong enough to exclude water molecules from the zinc metal-electrolyte interface and not too strong to cause a significant energy barrier for zinc ion dissociation—can benefit the electrochemical stability by suppressing hydrogen evolution reaction,overpotential growth,and den-drite formation.Penta-sodium diethylene-triaminepentaacetic acid salt was selected for such a purpose.It has a suitable chelating ability in aqueous solutions to adjust solvation sheath and can be readily polarized under electrical loading conditions to further improve the passivation.Zn||Zn symmetric cells can be stably operated over 3500 h at 1 mA cm^(-2).Zn||NH4V4O10 full cells with the additive show great cycling stability with 84.6%capacity retention after 500 cycles at 1 A g^(-1).Since the additive not only reduces H2 evolution and corrosion but also modifies Zn2+diffusion and deposition,highlyreversible Zn electrodes can be achieved as verified by the experimental results.Our work offers a practical approach to the logical design of reliable electrolytes for high-performance aqueous batteries.

Grain size refinement of additive manufactured Ce-TZP ceramics by coupled two-step pre-sintering and HIP

Ceria-stabilized tetragonal zirconia polycrystal(Ce-TZP)has exceptional fracture toughness and flaw tolerance due to facile t‒m phase transformation toughening.However,its wider-range applications are limited by its relatively low strength due to its large grain size and low transformation stress,which results in yield-like failure.Here,we combined additive manufacturing(AM),pressureless two-step sintering,and hot isostatic pressing(HIP),and addressed the challenging grain size refinement problem in Ce-TZPs.We successfully produced dense ultrafine-grained Ce-TZP ceramics with an average grain size below 500 nm,a three-point bending strength above 800 MPa,and a single-edge-notch-beam fracture toughness in the range of 11‒12 MPa·m^(1/2).The critical roles of processing design,mixed Ce valences,and under-vs.over-stabilization of tetragonal polymorphs were noted.Our work offers insights and strategies for the future development of stronger and tougher Ce-TZP ceramics that can compete with tetragonal yttria-stabilized zirconia in various applications,including additive manufacturing.

Resolving the sintering conundrum of high-rhenium tungsten alloys

Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.

Recent progress in Ti-based nanocomposite anodes for lithium ion batteries

Studying on the anode materials with high energy densities for next-generation lithium-ion batteries(LIBs) is the key for the wide application for electrochemical energy storage devices.Ti-based compounds as promising anode materials are known for their outstanding high-rate capacity and cycling stability as well as improved safety over graphite. However, Ti-based materials still suffer from the low capacity, thus largely limiting their commercialized application. Here, we present an overview of the recent development of Ti-based anode materials in LIBs, and special emphasis is placed on capacity enhancement by rational design of hybrid nanocomposites with conversion-/alloying-type anodes. This review is expected to provide a guidance for designing novel Ti-based materials for energy storage and conversion.

Pressureless two-step sintering of ultrafine-grained refractory metals:Tungsten-rhenium and molybdenum

The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.

Unveiling exceptional sinterability of ultrafine a-Al2O_(3) nanopowders

Scalable pressureless sintering of nanocrystalline alumina(Al2O_(3))ceramics is a challenging problem with great scientific and technological interest.This challenge was addressed in our recent works utilizing ultrafine a-Al2O_(3) nanopowders with exceptional sinterability combined with two-step sintering technique.Here the sintering mechanism and kinetic parameters(grain boundary diffusivity and its activation energy)were analyzed from constant heating-rate sintering experiments by three different sintering models and compared with existing sintering data in the literature.We found that the lowtemperature sintering of 4.7 nm a-Al2O_(3) nanopowders can be well explained by conventional sintering mechanism via grain boundary diffusion,with reasonable activation energy of 4e5 eV that is smaller than that of coarse Al2O_(3) powders and enhanced diffusivity.However,unphysically small activation energy could be obtained if an inappropriate model was used.Lastly,successful two-step sintering was demonstrated under different heating rates.Our work illustrates that the exceptional sinterability of ultrafine a-Al2O_(3) nanopowders are most likely contributed by small size(short diffusion distance),large surface area(large sintering driving force)and good dispersity rather than new sintering mechanism,and highlights the importance of fast firing and the non-equilibrium nature for the low-temperature sintering of such nanopowders.