Spider Silk-Inspired Binder Design for Flexible Lithium-Ion Battery with High Durability.

The development of flexible lithium-ion batteries (LIBs) imposes demands on energy density and high mechanical durability simultaneously. Due to the limited deformability of electrodes, as well as the flat and smooth surface of the metal current collectors, stable/durable/reliable contact between electrode materials and the current collectors remains a challenge, in particular, for electrodes with high loading mass and heavily deformed batteries. Binders play an essential role in binding particles of electrode materials and adhering them to current collectors. Herein, inspired by spider silk, a binder for flexible LIBs is developed, which equips a cross-linked supramolecular poly(urethane-urea) to the polyacrylic acid. The binder imparts super high elastic restorability originating from the meticulously engineered hydrogen-bonding segments as well as extraordinary adhesion. The developed binder provides excellent flexibility and intact electrode morphologies without disintegration even when the electrode is largely deformed, enabling a stable cycling and voltage output even when the batteries are put under tough dynamic deformation tests. The flexible LIBs exhibit a high energy density of 420 Wh L-1 , which is remarkably higher than reported numbers. The unique binder design is greatly promising and offers a valuable material solution for LIBs with high-loading mass and flexible designs.

Fabricated High-Strength, Low-Elastic Modulus Biomedical Ti-24Nb-4Zr-8Sn Alloy via Powder Metallurgy.

With the huge demands of an aging society, it is urgent to develop a new generation of non-toxic titanium alloy to match the modulus of human bone. Here, we prepared bulk Ti2448 alloys by powder metallurgy technology, and focused on the influence of the sintering process on the porosity, phase composition, and mechanical properties of the initial sintered samples. Furthermore, we performed solution treatment on the samples under different sintering parameters to further adjust the microstructure and phase composition, so as to achieve strength enhancement and reduction of Young's modulus. Solution treatment can effectively inhibit the continuous α phase precipitated along the grain boundaries of the ß matrix, which is beneficial to the fracture resistance. Therefore, the water-quenched sample exhibits good mechanical properties due to the absence of acicular α-phase. Samples sintered at 1400 °C and subsequently water quenched have excellent comprehensive mechanical properties, which benefit from high porosity and the smaller feature size of microstructure. To be specific, the compressive yield stress is 1100 MPa, the strain at fracture is 17.5%, and the Young's modulus is 44 GPa, which are more applicable to orthopedic implants. Finally, the relatively mature sintering and solution treatment process parameters were screened out for reference in actual production.

3D Printing Soft Matters and Applications: A Review.

The evolution of nature created delicate structures and organisms. With the advancement of technology, especially the rise of additive manufacturing, bionics has gradually become a popular research field. Recently, researchers have concentrated on soft robotics, which can mimic the complex movements of animals by allowing continuous and often responsive local deformations. These properties give soft robots advantages in terms of integration and control with human tissue. The rise of additive manufacturing technologies and soft matters makes the fabrication of soft robots with complex functions such as bending, twisting, intricate 3D motion, grasping, and stretching possible. In this paper, the advantages and disadvantages of the additive manufacturing process, including fused deposition modeling, direct ink writing, inkjet printing, stereolithography, and selective laser sintering, are discussed. The applications of 3D printed soft matter in bionics, soft robotics, flexible electronics, and biomedical engineering are reviewed.

Novel High-Energy-Density Rechargeable Hybrid Sodium-Air Cell with Acidic Electrolyte.

Low-cost, high-energy-density, and highly efficient devices for energy storage have long been desired in our society. Herein, a novel high-energy-density hybrid sodium-air cell was fabricated successfully on the basis of acidic catholytes. Such a hybrid sodium-air cell possess a high theoretical voltage of 3.94 V, capacity of 1121 mAh g-1, and energy density of 4418 Wh kg-1. First, the buffering effect of an acidic solution was demonstrated, which provides relatively long and stable cell discharge behaviors. Second, the catholytes of hybrid sodium-air cells were optimized systematically from the solutions of 0.1 M H3PO4 + 0.1 M Na2SO4 to 0.1 M HAc + 0.1 M NaAc and it was found that the cells with 0.1 M H3PO4 + 0.1 M Na2SO4 displayed a maximum power density of 34.9 mW cm-2. The cell with 0.1 M H3PO4 + 0.1 M Na2SO4 displayed higher discharge capacity of 896 mAh g-1. Moreover, the fabricated acidic hybrid sodium-air cells exhibited stable cycling performance in ambient air and they delivered a low voltage gap around 0.3 V when the current density is 0.13 mA cm-2, leading to a high energy efficiency up to 90%. Therefore, the present study provides new opportunities to develop highly cost-effective energy storage technologies.

Nature-Inspired Hierarchical Steels.

Materials can be made strong, but as such they are often brittle and prone to fracture when under stress. Inspired by the exceptionally strong and ductile structure of byssal threads found in certain mussels, we have designed and manufactured a multi-hierarchical steel, based on an inexpensive austenitic stainless steel, which defeats this "conflict" by possessing both superior strength and ductility. These excellent mechanical properties are realized by structurally introducing sandwich structures at both the macro- and nano-scales, the latter via an isometric, alternating, dual-phase crystal phases comprising nano-band austenite and nano-lamellar martensite, without change in chemical composition. Our experiments (transmission and scanning electron microscopy, electron back-scattered diffraction, nano-indentation and tensile tests) and micromechanics simulation results reveal a synergy of mechanisms underlying such exceptional properties. This synergy is key to the development of vastly superior mechanical properties, and may provide a unique strategy for the future development of new super strong and tough (damage-tolerant), lightweight and inexpensive structural materials.