The lithium-air (Li-O 2 ) battery has received enormous attention as a possible alternative to current state-of-the-art rechargeable Li-ion batteries given their high theoretical specific energy.However, the maximum discharge capacity in shapes and sizes in ethereal electrolytes and we suggest that this is likely due to varying levels of water contamination in the cells. Figure S1 in the SI shows a diminishment in toroid particle diameter with current at a fixed H 2 O content, with no toroids present at currents > 1 mA for 4000 ppm H 2 O concentration. At low H 2 O content, although toroids are still observed at very low currents, they disappear at currents much lower than 1 mA, where no toroid formation is apparent, an increase in discharge capacity is observed with water present (Fig. S10b). We argue that the improvement in capacity at both currents arises due to a solution-mediated mechanism for Li 2 O 2 formation (discussed later) that overcomes charge transport limitations inherent in surface growth of Li 2 O 2 . While trace H 2 O has a positive impact on capacity, it is also critical to understand its effect on the battery chemistry and rechargeability. Figure 3a shows X-ray diffractograms (XRD) near the Li 2 O 2 (100) and (101) peaks from Avcarb P50 paper cathodes extracted from batteries otherwise similar to those studied in Fig 1. The only additional H 2 O-induced XRD feature is a small peak at 30.65 degrees that has tentatively been identified as Li 2 NH (Fig. S6). These results confirm that the majority of the crystalline discharge product is Li 2 O 2 , regardless of electrolyte water content. Notably, no crystalline LiOH is observed in the XRD of the cathodes. The Li 2 O 2 diffractograms clearly show a decreasing peak width as a function of increasing water content in the electrolyte solution, implying that the Li 2 O 2 crystallite size increases, in

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Chemical advances are increasing the proportion of polymer waste that can be recycled

Li-air batteries have generated enormous interest as potential high specific energy alternatives to existing energy storage devices. However, Li-air batteries suffer from poor rechargeability caused by the instability of organic electrolytes and carbon cathodes. To understand and address this poor rechargeability, it is essential to elucidate the efficiency in which O2 is converted to Li2O2 (the desired discharge product) during discharge and the efficiency in which Li2O2 is oxidized back to O2 during charge. In this Letter, we combine many quantitative techniques, including a newly developed peroxide titration, to assign and quantify decomposition pathways occurring in cells employing a variety of solvents and cathodes. We find that Li2O2-induced electrolyte solvent and salt instabilities account for nearly all efficiency losses upon discharge, whereas both cathode and electrolyte instabilities are observed upon charge at high potentials.

Nitrogen-based thermoset polymers have many industrial applications (for example, in composites), but are difficult to recycle or rework. We report a simple one-pot, low-temperature polycondensation between paraformaldehyde and 4,4'-oxydianiline (ODA) that forms hemiaminal dynamic covalent networks (HDCNs), which can further cyclize at high temperatures, producing poly(hexahydrotriazine)s (PHTs). Both materials are strong thermosetting polymers, and the PHTs exhibited very high Young's moduli (up to ~14.0 gigapascals and up to 20 gigapascals when reinforced with surface-treated carbon nanotubes), excellent solvent resistance, and resistance to environmental stress cracking. However, both HDCNs and PHTs could be digested at low pH (<2) to recover the bisaniline monomers. By simply using different diamine monomers, the HDCN- and PHT-forming reactions afford extremely versatile materials platforms. For example, when poly(ethylene glycol) (PEG) diamine monomers were used to form HDCNs, elastic organogels formed that exhibited self-healing properties.

We present a comparative study of nonaqueous Li-O2 and Na-O2 batteries employing an ether-based electrolyte. The most intriguing difference between the two batteries is their respective galvanostatic charging overpotentials: a Na-O2 battery exhibits a low overpotential throughout most of its charge, whereas a Li-O2 battery has a low initial overpotential that continuously increases to very high voltages by the end of charge. However, we find that the inherent kinetic Li and Na-O2 overpotentials, as measured on a flat glassy carbon electrode in a bulk electrolysis cell, are similar. Measurement of each batteries' desired product yield, YNaO2 and YLi2O2, during discharge and rechargeability by differential electrochemical mass spectrometry (DEMS) indicates that less chemical and electrochemical decomposition occurs in a Na-O2 battery during the first Galvanostatic discharge-charge cycle. We therefore postulate that reactivity differences (Li2O2 being more reactive than NaO2) between the major discharge products lead to the observed charge overpotential difference between each battery.

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Hydrogels are useful materials as scaffolds for tissue engineering applications. The solid content used for hydrogels require a balance between scaffold stiffness and nanoporosity, which impacts nutrient diffusion into cell-laden scaffolds. Using hydrogels with additive manufacturing techniques has been a challenge, due to inconsistencies in print fidelity. In this study, agarosebased hydrogels commonly used for cartilage tissue engineering were compared to Pluronic, a hydrogel with established printing capabilities. Moreover, new material mixtures were developed for bioprinting by combining alginate and agarose. We compared mechanical and rheological properties, including yield stress, storage modulus, and shear thinning, to determine parameters that may predict better extrusion-based printability and to assess their potential as a bioink for cell-based tissue engineering. We found that all gels demonstrated shear-thinning behavior, yet recovered immediately upon the absence of a shear stress. Print fidelity of agarose-based gels improved with the addition of alginate, which did not significantly alter yield strength (p > 0.1).Alginate-agarose composites prepared with 5% w/v (3:2 agarose to alginate ratio) demonstrated high print fidelity with excellent cell viability that was maintained over a 28-day culture period (>~70% cell survival at day 28). Therefore, agarose-alginate mixtures showed the greatest potential as an effective bioink for additive manufacturing of biological materials for cartilage tissue engineering.