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Preface: Forum on New Materials and Approaches for Beyond Li-ion Batteries his issue of ACS Applied Materials & Interfaces features a Forum on New Materials and Approaches for beyond Liion Batteries. It is the second Forum issue on electrochemical energy storage. The first one was published in 2014 with an emphasis on Li-ion batteries. Li-ion technology is limited by its inherent energy density and cost. Therefore, batteries beyond Li-ion are being actively explored around the world. Examples include Li−S and metal−air batteries. This motivated the creation of this Forum to provide the readership with articles that highlight recent progress in new materials and approaches for the cathodes, anodes, and electrolytes of various emerging battery technologies. Four contributions to the Forum highlight new development in lithium−sulfur batteries. Qu et al. report their investigation of the Li−S battery mechanism by real-time monitoring of the changes in sulfur and polysulfide species during the discharge and charge using high-performance liquid chromatography. An existing issue is the uncontrollable passivation of electrodes by highly insulating Li2S, which limits sulfur utilization, increases polarization, and decreases cycling stability. Liu and Shao et al. report ammonium additives to dissolve lithium sulfide through hydrogen binding to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Another challenge in Li−S batteries is the dissolution of polysulfides into electrolytes, which results in shuttling of polysulfides between the electrode. An article contributed by Zhao et al. describes Prussian blue as an effective material to suppress the dissolution of polysulfides into liquid electrolyte by chemical adsorption. Another article contributed by Guo et al. reports ultrathin cobaltosic oxide nanosheets as an effective sulfur encapsulation matrix with strong affinity toward polysulfides. Alkali metal−oxygen batteries (Li−O2, Na−O2, and K−O2) are of great interests for energy storage because of their unparalleled theoretical energy densities. A major challenge is to identify electrolytes that are compatible with the reactive alkali metals. Superconcentrated electrolytes have recently emerged as a promising approach. In this aspect, Hu et al. report a concentrated Li[(FSO2)(n-C4F9SO2)N]-based ether electrolyte that forms a stable solid-electrolyte-interphase layer on metallic lithium anode. On the oxygen cathode side, Wu et al. report a systematic study on parameters that control rate performance and capacity to understand the limiting factors in superoxide-based K−O2 batteries. The influence of current density and oxygen diffusion on the nucleation, growth, and distribution of potassium superoxide (KO2) during the discharge process were applied to explain the inverse correlation between rate performance and capacity in K−O2 batteries. Shao-Horn et al. describe their investigation of the NaO2 oxidation mechanism using rotating ring disk electrode (RRDE) measurements of Na−O2 reaction products. Their results provide insight that the oxidation of NaO2 occurs predominantly via charge transfer at the interface between NaO2 and carbon electrode fibers. Yao et al. synthesized an
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activated carbon material with a porous honeycomblike structure, demonstrating high capacity and ultralong cycle life in Li−O2 battery. Aurbach et al. investigated the feasibility of full (Li-ion)−O2 cells comprising hard carbon anodes, which opens a new window for optimizing rechargeable nonaqueous batteries with oxygen reduction cathodes. Sodium, magnesium, and potassium have advantages in natural abundances and geological distributions over lithium. Therefore, the Li-based battery concepts have been expanded into these elements. Ji et al. contribute a timely mini review on potassium secondary batteries that highlight recent progress in K-ion, K−O2, and K−S batteries. The same group also reports a new polynanocrystalline graphite carbon anode with superior cycling performance for K-ion batteries. Magnesium has the dendrite-free characteristic in the electrochemical plating/ stripping process and high energy density. In this respect, Gogotsi et al. report a two-dimensional titanium carbide MXene as a cathode material for hybrid magnesium/lithiumion batteries, which combines the high capacity, high voltage, and fast Li+ intercalation of Li-ion cathodes and the highcapacity, low-cost, and dendrite-free Mg anodes. The sodium ion battery has shown great potential to become a low-cost electrochemical energy storage system. Takeuchi et al. investigated silver containing α-MnO2 structured materials (AgxMn8O16, x = 1.22 for L-Ag-OMS-2 or 1.66 for H-Ag-OMS2) as host materials for Li- and Na-ion insertion/deinsertion. A significant difference in the lithiation versus sodiation process was observed because of the more favorable formation of silver metal during the sodiation process relative to the lithiation process. Johnson et al. used a microwave synthetic process to make a metastable form of NaCoPO4 polyanion non-Maricite phase with a unique 5-coordinate Co compound for a potentially high-voltage Na-ion cathode. This Forum also features one contribution on supercapacitors from Deng et al. about the effect of pore depth on capacitance of nanoporous carbon derived from microalgae and its CoO composite, and one from Aurbach et al. about the substitution of Mn with Ni in Li-rich layered cathode materials, which results in impressive stability of the capacity upon cycling.
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Yiying Wu, Associate Editor Jun Lu, Associate Editor AUTHOR INFORMATION
ORCID
Yiying Wu: 0000-0001-9359-1863 Jun Lu: 0000-0003-0858-8577 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
Published: February 8, 2017 4281
DOI: 10.1021/acsami.7b01033 ACS Appl. Mater. Interfaces 2017, 9, 4281−4281
