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We here demonstrate an unmediated photoelectrochemical oxidation approach to address the overpotential issue of Li–O2 batteries during the charge process. We show that photoexcited holes from the photoelectrode provide a direct oxidation of solid Li2O2, without the use of a redox mediator. The Li–O2 battery composed of carbon nitride on carbon paper as a cathode and also as a photoelectrode exhibits an ultralow charge voltage of 1.96 V resulting in a ‘negative’ overpotential and good cycling performance. These results could represent a new and promising avenue for the future development of photo-charging all-solid-state batteries. [ABSTRACT FROM AUTHOR]

A sponge-like V2O5 nanomaterial is prepared by a freeze-drying method and evaluated as a cathode material for sodium-ion batteries. The sponge-like structure is self-assembled from V2O5 nanosheets that can sustain high pressure (400 times their own weight), thus leading to a high structure stability. The numerous macropores in the spongy structure can effectively soak up the electrolyte. Moreover, the exposed (001) facet of the nanosheets is favorable for charge transfer at the electrolyte/electrode interface. The thin nanosheets along the [001] axis provide short diffusion pathways for sodium ions. Electrochemical experiments show that the material has a high discharge capacity of 216 mAh g−1 at a current density of 20 mA g−1. In addition, the material shows a good capacity retention of 73 % in 100 charge-discharge cycles at a current density of 100 mA g−1. [ABSTRACT FROM AUTHOR]

Hierarchically porous, metallic RuO2 hollow spheres are applied as a carbon‐free cathode for Li–O2 batteries for the first time. They exhibit low charge potentials of ≈3.5 V, corresponding to overpotentials of 0.13/0.54 V in discharging and charging processes, a large reversible capacity of ≈1400 mAh g−1, and 100 cycles of full discharge and charge. [ABSTRACT FROM AUTHOR]

Porous carbon-free cathodes are critical to achieve a high discharge capacity and efficient cycling for rechargeable Li-O2 battery. Herein, we present a very simple method to directly grow nanoporous Ru (composed of polycrystalline particles of ∼5 nm) on one side of a current collector of Ni foam via a galvanic replacement reaction. The resulting Ru@Ni can be employed as a carbon- and binder-free cathode for Li-O2 batteries and delivers a specific capacity of 3720 mAh gRu−1 at a current density of 200 mA gRu−1. 100 cycles of continuous discharge and charge are obtained at a very narrow terminal voltage window of 2.75∼3.75 V with a limited capacity of 1000 mAh gRu−1. The good performance of the nanoporous Ru@Ni cathode can be mainly attributed to the effective suppression of the by-products related to carbon or binder, the good adhesion of the catalyst to the current collector, and the good permeation of O2 and electrolyte into the active sites of the nanoporous Ru with the open pore system. This new type electrode provides a snapshot toward developing high-performance carbon- and binder-free Li-O2 batteries. [ABSTRACT FROM AUTHOR]

Antireflection TiO2 nanoparticle film was fabricated on silica glass substrate by using directed cluster beam deposition method. Self-shadowing becomes a dominant growth mechanism for nanoparticle deposition at sufficiently large incident angles, which results in extremely porous nanoparticle stacking and yields excellent control over the refractive index profile. Inclined columnar and porous microstructure was confirmed with SEM and AFM. The TiO2 nanoparticle films show ultra-high transmittance, broadband and omnidirectional characters, which can be attributed to its porous structure and modulated refractive index. We also found that the film displays an angular selective optical transmittance. The highest antireflection enhancement of the light transmission can be obtained for light incidence along the nanoparticle columns. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Rigid‐flexible coupled composite polymer electrolytes (CPEs, e.g., polyethylene oxide/Li6.4La3Zr1.4Ta0.6O12, PEO/LLZTO) hold the promise of integrating the respective merits of organic polymer electrolyte and inorganic ceramic fillers to achieve better all‐solid‐state batteries (ASSBs), but commonly suffer from poor synergistic effect owing to the ionically/electronically resistive layer on the ceramic surface. Representatively, the Li2CO3 passivation layer‐isolated LLZTO not only contributes minimally to the Li+ conduction in PEO/LLZTO CPE, but also narrows the available electrochemical window. Herein, an interfacial reconstruction strategy is disclosed based on mild liquid‐phase chemical reaction and subsequent self‐assembly, allowing the detrimental Li2CO3 to fully react with succinic anhydride (SA), and simultaneously constructing a robust ultra‐thin lithium succinate (SALi) ionic conductor shell to eradicate its regeneration. Accordingly, the obtained PEO/LLZTO@SALi (PLS) CPE shows a high room‐temperature ionic conductivity (1.2 × 10−4 S cm−1), a wide electrochemical window (4.8 V), a notable Li+ transference number (0.37), as well as nonflammability and exceptional compatibility with Li metal in Li/Li symmetric cells (2000 h at 0.2 mA cm−2). More encouragingly, the Li/PLS CPE/LiFePO4 full ASSB maintains an ultrahigh capacity retention of 84.3% after 1400 cycles at room temperature. This work propels the design of high‐performance CPEs through the interfacial modulation of inorganic ceramic fillers. [ABSTRACT FROM AUTHOR]

The self‐catalyzed growth of nanostructures on material surfaces is one of the most time‐ and cost‐effective ways to design multifunctional catalysts for a wide range of applications. Herein, the use of this technique to develop a multicomponent composite catalyst with CoSx core encapsulated in an ultrathin porous carbon shell entangled with Co, N‐codoped carbon nanotubes is reported. The as‐prepared catalyst has a superior catalytic activity for oxygen evolution and oxygen reduction reactions, an ultralow potential gap of 0.74 V, and outstanding durability, surpassing most previous reports. Such superiority is ascribed, in part, to the unique 3D electrode architecture of the composite, which is favorable for transporting oxygen species and electrons and creates a synergy between the components with different functionalities. Moreover, the flexible solid Zn–air battery assembled with such an air electrode shows a steady discharge voltage plateau of 1.25 V and a round‐trip efficiency of 70% at 1 mA cm−2. This work presents a simple strategy to design highly efficient bifunctional oxygen electrocatalysts and may pave the way for the practical application of these materials in many energy conversion/storage devices. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe 2 by studying the binary CoSe 2 -VSe 2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g -1 at 0.1 C and 1049 mAh g -1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe 2 nanowires and sulfur. In addition, Janus microspheres of C@TiO 2 were synthesized to capture polar polysulfides with their polar part of TiO 2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO 2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.

Redox mediators (RMs) have become a significant point in the now-established Li-O 2 battery system to reduce the charging overpotential in the oxygen evolution process. Nevertheless, a major inherent barrier of the RM is the redox shuttling between the Li metal anode and mobile RM, resulting in the corrosion of Li and depletion of RM. In this study, taking iodide/triiodide as a model RM, we propose an effective strategy by immersing the Li metal anode in I 2 steam to create a 1.5 μm thick surface protective layer. The resultant ionic conductive LiI layer on the Li metal anode can not only suppress Li dendrite growth but also act as a buffer layer between the RM and bare Li. By combining the iodide/triiodide RM with the LiI protective layer, the Li-O 2 battery shows low and steady charge voltage plateaus of ∼3.6 V over 70 cycles. Importantly, the symmetrical cell using the LiI-protected Li electrode exhibited small Li plating/stripping overpotentials (∼20 mV, 480 h), far superior to that of the bare Li electrode (∼70 mV, 300 h). The in situ interfacial observation shows that dendrite growth on the Li metal can be effectively suppressed by optimizing the LiI protective layer.

The cycling performance of Li-O 2 batteries (LOBs), which is an important parameter determining the practical use of this advanced energy technology with ultrahigh energy density, is strongly affected by the nature of the oxygen electrocatalyst. As a good oxygen electrode, it should possess good activity for both the oxygen evolution reaction and the oxygen reduction reaction and superior stability under operating conditions. During the past, oxygen electrodes for LOBs were generally fabricated by loading noble metal nanoparticles on the surface of a porous carbon support. However, the nanoparticles could easily lose contact with the carbon support during the reversible liquid-gas-solid reactions that involve lithium ions, oxygen gas, and Li 2 O 2 . Herein, we reported a novel Ru-metal-organic framework (MOF)-derived carbon composite, characterized by stereoscopic Ru nanoparticle distribution within the carbon matrix, as an alternative oxygen catalyst of LOBs, enabling superior operational stability and favorable activity. More specifically, the battery demonstrated stable charge-discharge cycling for up to 800 times (∼107 days) at a current density of 500 mA g -1 with low discharge/charge overpotentials (∼0.2/0.7 V vs Li). A mechanism of regenerative surface was further proposed to explain the excellent cycling stability of the LOBs through the use of the Ru-MOF-C catalyst. These encouraging results imply an accessible solution to address issues related to the oxygen catalyst for the realization of practical LOBs.

Gel-polymer electrolytes are considered as a promising candidate for replacing the liquid electrolytes to address the safety concerns in Li-O 2 /air batteries. In this work, by taking advantage of the hydrogen bond between thermoplastic polyurethane and aerogel SiO 2 in gel polymer, a highly crosslinked quasi-solid electrolyte (FST-GPE) with multifeatures of high ionic conductivity, high mechanical flexibility, favorable flame resistance, and excellent Li dendrite impermeability is developed. The resulting gel-polymer Li-O 2 /air batteries possess high reaction kinetics and stabilities due to the unique electrode-electrolyte interface and fast O 2 diffusion in cathode, which can achieve up to 250 discharge-charge cycles (over 1000 h) in oxygen gas. Under ambient air atmosphere, excellent performances are observed for coin-type cells over 20 days and for prototype cells working under extreme bending conditions. Moreover, the FST-GPE electrolyte also exhibits durability to protect against fire, dendritic Li, and H 2 O attack, demonstrating great potential for the design of practical Li-O 2 /air batteries., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lithium metal is an ultimate anode in "next-generation" rechargeable batteries, such as Li-sulfur batteries and Li-air (Li-O 2 ) batteries. However, uncontrollable dendritic Li growth and water attack have prevented its practical applications, especially for open-system Li-O 2 batteries. Here, it is reported that the issues can be addressed via the facile process of immersing the Li metal in organic GeCl 4 -THF steam for several minutes before battery assembly. This creates a 1.5 µm thick protection layer composed of Ge, GeO x , Li 2 CO 3 , LiOH, LiCl, and Li 2 O on Li surface that allows stable cycling of Li electrodes both in Li-symmetrical cells and Li-O 2 cells, especially in "moist" electrolytes (with 1000-10 000 ppm H 2 O) and humid O 2 atmosphere (relative humidity (RH) of 45%). This work illustrates a simple and effective way for the unfettered development of Li-metal-based batteries., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)