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The quest for both strength and toughness is perpetual in advanced material design; unfortunately, these two mechanical properties are generally mutually exclusive. So far there exists only limited success of attaining both strength and toughness, which often needs material-specific, complicated, or expensive synthesis processes and thus can hardly be applicable to other materials. A general mechanism to address the conflict between strength and toughness still remains elusive. Here we report a first-of-its-kind study of the dependence of strength and toughness of cellulose nanopaper on the size of the constituent cellulose fibers. Surprisingly, we find that both the strength and toughness of cellulose nanopaper increase simultaneously (40 and 130 times, respectively) as the size of the constituent cellulose fibers decreases (from a mean diameter of 27 µm to 11 nm), revealing an anomalous but highly desirable scaling law of the mechanical properties of cellulose nanopaper: the smaller, the stronger and the tougher. Further fundamental mechanistic studies reveal that reduced intrinsic defect size and facile (re)formation of strong hydrogen bonding among cellulose molecular chains is the underlying key to this new scaling law of mechanical properties. These mechanistic findings are generally applicable to other material building blocks, and therefore open up abundant opportunities to use the fundamental bottom-up strategy to design a new class of functional materials that are both strong and tough. [ABSTRACT FROM AUTHOR]

Sodium (Na)-ion batteries offer anattractive option for low cost grid scale storage due to the abundanceof Na. Tin (Sn) is touted as a high capacity anode for Na-ion batterieswith a high theoretical capacity of 847 mAh/g, but it has severallimitations such as large volume expansion with cycling, slow kinetics,and unstable solid electrolyte interphase (SEI) formation. In thisarticle, we demonstrate that an anode consisting of a Sn thin filmdeposited on a hierarchical wood fiber substrate simultaneously addressesall the challenges associated with Sn anodes. The soft nature of woodfibers effectively releases the mechanical stresses associated withthe sodiation process, and the mesoporous structure functions as anelectrolyte reservoir that allows for ion transport through the outerand inner surface of the fiber. These properties are confirmed experimentallyand computationally. A stable cycling performance of 400 cycles withan initial capacity of 339 mAh/g is demonstrated; a significant improvementover other reported Sn nanostructures. The soft and mesoporous woodfiber substrate can be utilized as a new platform for low cost Na-ionbatteries. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are promising candidatesfor the applicationsof large-scale energy storage due to their cost-effective and environmental-friendlycharacteristics. Nevertheless, it remains a practical challenge tofind a cathode material of SIBs showing ideal performance (capacity,reversibility, etc.). We report here a nanocomposite material of amorphous,porous FePO4nanoparticles electrically wired by single-wallcarbon nanotubes as a potential cathode material for SIBs. The hydrothermallysynthesized nanocomposite shows excellent cell performance with unprecedentedcycling stability and reversibility. The discharge capacity of ashigh as 120 mAh/g is delivered at a 0.1 C rate (10 mA/g). The capacityretentions are about 70 mAh/g, 60 mAh/g, and 55 mAh/g at higher currentsof 20 mA/g, 40 mA/g, and 60 mA/g, respectively. Even at a 1 C rate(100 mA/g), a capacity of about 50 mAh/g is still retained after 300cycles. With a simple synthetic procedure, cost-effective chemicals,and desirable cell performance, this method offers a highly promisingcandidate for commercialized cathode materials of SIBs. [ABSTRACT FROM AUTHOR]