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Near-neutral electrolytes based on zinc chloride and ammonium chloride are examined for rechargeable zinc-air battery application.TheeffectsofpHvalue,saltconcentration,andpolyethyleneglycolandthioureaadditivesareinvestigatedandachlorideelectrolyteisdeveloped.Thereversiblezincdepositionandzincstrippingprocessesarestudiedbycyclicvoltammetrywithrotating-discelectrodetechnique. The zinc anode and air cathode behaviors in near-neutral chloride electrolyte are characterized by quasi steady-statepolarization and impedance spectroscopy. Prototyped zinc-air battery with near-neutral chloride electrolytes can sustain more than1000 hours and hundreds of discharge-charge cycles with minimized zinc dendrite formation and no carbonate formation problem,underdischarge-chargecapacityrangingfrom20to120mAh.Thenear-neutralchlorideelectrolyteprovidesasaferandmorerobustalternative to traditional alkaline electrolyte for rechargeable zinc-air batteries.© The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in anymedium, provided the original work is properly cited. [DOI: 10.1149/2.0311414jes] All rights reserved.Manuscript submitted June 17, 2014; revised manuscript received August 27, 2014. Published October 1, 2014.

In this work, we fabricate a solid-state, foldable, and rechargeable Zn-air battery which has similar discharge/charge curve after 100 times of repeated folding. Furthermore, the battery exhibits stable cycling performance after 100 times of folding. The foldable air cathodes are based on the directly grown bifunctional catalyst on the graphene coated carbon cloth. Random coating of graphene on the pretreated carbon cloth provides additional surface area to grow the catalyst while maintaining the electrically and mechanically interconnected 3D network in the air cathode. The directly grown catalyst on air cathode improves adhesion at air cathode/catalyst interface, preventing the de-attachment of catalyst during the continuous mechanical deformations. We grow manganese oxides (MnOx) on graphene coated carbon cloth as an active and low cost bifunctional catalyst for solid-state and rechargeable Zn-air batteries via simple immersion process. Solid-state electrolyte allows good flexibility and high safety without the need of costly sealing and the risk of electrolyte leakage. Cross-linked PAA-based electrolyte had given sufficient mechanical strength and conductivity (up to ≈0.46 S cm-1) to be used as solid-state electrolyte. Combining the advantage of MnOx grown on graphene coated carbon cloth and solid electrolyte result in the high performance all-solid-state, foldable, and rechargeable Zn-air batteries. The battery exhibits similar polarization curve and resistance at its fold and flat states. The fold battery is able to achieve to a power density of 32 mW cm-2, almost twice of the power density at its flat state. The cycling stability of the battery at its flat and fold state is better than the batteries with Pt/C on carbon cloth air cathode and the reported solid-state Zn-air batteries in the literature. Polyacrylic acid (PAA)-based electrolytes showed enhanced conductivity as compared to polyvinylalcohol (PVA) or polyethylene oxide (PEO)-based electrolytes due to their low crystallinity and high water retention, resulting in the high conductivity while maintaining desirable mechanical robustness. The obtained PAA-KOH solid electrolyte is transparent, free-standing, and flexible. Unlike gel electrolyte, the solid nature of crosslinked polymer electrolyte is able to prevent short circuit during continuous mechanical deformations. At the same applied current during polarization measurement, the folded battery has an almost similar discharge and charge voltage with the battery at its flat state. The polarization curve of the battery with MnOx-GCC air cathode is enhanced significantly as compared to the battery with GCC and MnOx-CC air cathodes, which only show slightly better performance than the battery with CC air cathode (i.e. without catalyst). At discharge voltage of 1 V, the batteries with GCC and MnOx-CC air cathode have low current (»2.0 and 2.2 mA), five times lower than the battery with MnOx-GCC air cathode. The small voltage gap (i.e. the difference between discharge and charge voltage) indicates an improved rechargeability of the battery with MnOx-GCC air cathode as compared to others batteries. Despite the similar discharge profile, the small footprint of the folded battery results in the high current per unit area. Thus, it has larger power density than the battery at its flat state. The folded battery delivers a power density as high as »32 mW cm-2, almost twice of power density at its flat state (»18 mW cm-2). Under the same device configuration, power density of battery with Pt/C-CC air cathode (»12 mW cm-2) is lower than the battery with MnOx-GCC air cathode, indicating the advantage of high loading density of thin MnOx layer on the dense and interconnected GCC. The battery with MnOx-GCC air cathode has higher discharge voltage and lower charge voltage than the batteries with MnOx-CC air cathode, agreeable to the measured polarization curve. It maintains the same voltages (i.e. discharge voltage of 1.3 V and charge voltage of 1.9 V) for about 170 cycles of discharge/charge test. On the other hand, voltage profile of the battery with Pt-C/CC air cathode degrades gradually over the time. At the end of 70th cycle, its discharge voltage reduces from 1.3 to 0.9 V while its charge voltage increases from 2.0 to 2.4 V, suggesting its low re-chargeability. Battery with MnOx-CC air cathode exhibits stable performance for up to 140 cycles. However, it has poorer discharge and charge voltages (i.e. 1.0 and 2.3 V) than the battery with MnOx-GCC and Pt/C-CC air cathodes. The battery with MnOx-GCC air cathode shows stable performance for up to 110 of discharge/charge cycles, 60 cycles lesser than the same battery at its flat state.

Amorphous and crystalline Sn{sub 2}P{sub 2}O{sub 7} can be considered as intrinsic P-doped classes, similar to the products from the binary solid state reaction between SnO and P{sub 2}O{sub 5}. Amorphous Sn{sub 2}P{sub 2}O{sub 7} was prepared by melt-quenching the crystalline form. IR spectroscopy and inductively coupled plasma measurements indicated that both forms are phase pure homogeneous materials. In the potential range 0-1.2 V (versus Li{sup +}/Li), amorphous and crystalline Sn{sub 2}P{sub 2}O{sub 7} can deliver reversible specific capacities of 520 and 400 mAh/g, respectively. However, both display nearly the same capacity and fade characteristics when the upper cutoff limit is increased to 1.4 V. Cyclic voltammetry and differential capacity plots indicated the presence of two energetically different Li{sup +} sites in crystalline Sn{sub 2}P{sub 2}O{sub 7}. A higher potential is required for the complete release of Li{sup +} in crystalline Sn{sub 2}P{sub 2}O{sub 7} and this explains the lower capacity of this polymorph. X-ray diffraction detected the presence of tin and tin alloy phases in charged and discharged samples, and an alloying mechanism is proposed to explain the reversibility in charge and discharge reactions. Dissociation of P{sub 2}O{sub 7}{sup 4{minus}} into PO{sub 4}{sup 3{minus}} and PO{sub 3}{sup {minus}} aftermore » repeated cycling was evidenced by IR spectroscopy. The large initial capacity loss could be explained by the requisite initial irreversible reaction to form metallic tin.« less

The fast and widespread commercialization of electric vehicles (EVs) demands high performance rechargeable batteries with good safety at low cost. Compared to the prevailing Li-ion battery, lithium-oxygen (Li-O2) battery promises significantly higher energy density in an open-system at notably reduced cost, and has thus become a focus of research on future battery technologies. Despite the encouraging progress in the development of electrocatalytic air-cathode, design of cathode architecture, and understanding of the related electrochemistry and stability of electrolytes, limited success was achieved in the practical aspects of Li-O2 batteries, as represented by low round-trip efficiency and unsatisfactory cycle life. The degradation of electrolyte during the charge/discharge processes is seen as one of the main causes for the battery performance deterioration, originating from the sources of its intrinsic instability, its reactions with discharge products, some synergistic reaction with oxygen, etc. It is worth pointing out that fast self-discharge may also notably contribute to a low round trip efficiency; while no report is available so far on this aspect of Li-O2 batteries. In this paper, we report how the storage condition and duration of Li-O2 cell affect their charge preservation and cell performance. This work also helps further improve the understanding on the stability of electrolyte in Li-O2 cells. Experiments were carried out using CR2032 coin-type cells with the cathode and anode being the stainless steel gauze supported multi-wall carbon nanotubes andlithium foil, respectively. Glass fiber (Whatman®, GF/B) was used as the separator, and the electrolyte was 1 M lithium trifluoromethane-sulfonate (LiOTf) in triethylene glycol dimethyl ether (Triglyme). Both electrolyte preparation and cell assembly were conducted in an Ar-filled glove box. Right after assembly the cells were stored under different conditions (varying storage temperature and time), with the electrochemical impedance spectra (EIS) and open circuit voltage (OCV) being recorded periodically. As the triglyme based electrolyte starts to degrade at a potential of about 4.7 V for cathode of CNTs, in the paper the upper limit of charge potential was set as 4.5 V to keep the electrolyte in a relatively stable state. The degree of self-discharge (DOSD) was quantified by calculating the differences between the discharge capacity of fresh assembled cell and that of the same cell after certain period of storage (Fig. 1a). One can clearly see that the cells lost approximately 44% of discharge capacity after 10 days storage atroom temperature under dry O2 atmosphere, and only ~31% of the discharge capacity can be retained after another 7 days of storage. The EIS spectra of Li-O2 cells showed steadily increased impedance as a result of continuous self-discharge (Fig. 1b). Here, for the real part of the impedance the intercept at high frequencies is generally associated with the separator and electrical contact resistances, as well as the electrolyte resistance. The semicircle in the high- and medium-frequency regions represents the interface resistances of Li-electrolyte, cathode-electrolyte, and charge-transfer resistance. Clearly, both electrolyte and interface resistances have increased. From the data of the first a few days, we can see the self-discharge was initially a slow process. The expedition in the following days indicates that some reactions were triggered by the intermediates of self-discharge, leading to notable electrolyte decomposition. Meanwhile, the accumulation of the self-discharged products elevated the interface resistance. This new understanding should facilitate research for further improvement of Li-O2 battery performance. Further study is in progress. This work was supported by the project IMRE/12-2P0504 under the SERC Advanced Energy Storage Research Programme, and Institute of Material Research and Engineering (IMRE), A*STAR, Singapore. Figure 1

This talk will focus on the design and synthesis of nanostructured non-precious metal-based hybrid catalysts for metal-air batteries. The presentation will describe some our works in nanostructured hybrid bifunctional electrocatalysts as air electrode for Zn-air rechargeable batteries, as well as nanostructured porous perovskite and spinel metal oxide catalytic materials as air electrode for Li-air batteries. In this presentation, I will introduce the fundamental and the most recent and significant scientific progresses made in the fields relevant to Zn-air and Li-air batteries, with emphasis placed on air electrodes. The preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries will be reported. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction in alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone. Other bifunctional catalysts for oxygen reduction and evolution reactions in Zn-air batteries include spinel MnCo2O4/ nanocarbon hybrids, perovskite lanthanum cobalt manganese oxides/nanocarbon hybrids (LCMO/NC), Co3O4 nanoparticles decorated carbon nanofiber and cobalt sulphide/N- or S-doped grapheme etc. I also will report porous cobalt-manganese oxide nanocubes derived from metal organic frameworks and porous perovskite LaNiO3 nanocubes as cathode catalysts for rechargeable Li-O2 batteries.

A dispersion of Mn and Co co-substituted Fe3O4 (MCF, Mn:Co:Fe=1:1:1) nanoparticles on nitrogen-doped reduced graphene oxide (N-rGO) nanosheets was prepared by a hydrothermal method. When tested for oxygen electrocatalysis in alkaline solution, the nanoparticles displayed 80% of the oxygen reduction reaction (ORR) activity of a typical 20 wt% Pt/C catalyst (Sigma); and 61% of the oxygen evolution reaction (OER) activity of a 20 wt% RuO2/C catalyst. Extensive material characterizations by field-emission transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) were carried out to provide some understanding of the good electrochemical performance. The MCF catalyst has successfully integrated the ORR activity of manganese oxide, the OER activity of cobalt oxide; and the electronic conductivity of bulk Fe3O4 into an effective bifunctional catalyst; and its good contact with the N-rGO nanosheets also reduces the external transport resistance in oxygen electrocatalysis. Hence the MCF catalyst also delivered good performance in zinc-air full cell tests where they were used in the air electrode.

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Carbon-supported Pd-rich pseudo-core-shell Pd-Pt (Pd@Pt/C) nanoparticles, with Pt coverage close to a monolayer, were prepared from a simple galvanic replacement reaction between Pd/C particles and PtCl 2- 4 at 100°C. The pseudo-core-shell architecture was confirmed by extensive microstructural characterization techniques. The binding energy shifts in the Pt 4f X-ray photoelectron spectra, in particular, suggest an electron exchange between Pd and Pt, and possible strain effects in Pt caused by the underlying Pd core. The activity of the pseudo-core-shell nanoparticles in the oxygen reduction reaction (ORR) was studied in acidic solutions with and without methanol. The electrocatalysts prepared as such were active for ORR at room temperature, even in the presence of 0.1 M methanol. The pseudo-core-shell Pd 70 @Pt 30 catalyst, in particular, compared rather favorably with a Pt/C catalyst with twice the Pt mass loading in terms of the ORR activity, cost, and methanol tolerance.