We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of ∼2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS2. The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physically adsorbed oxygen on an ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices.

Metallic lithium is a promising anode candidate for future high-energy-density lithium batteries. It is a light-weight material, and has the highest theoretical capacity (3,860 mAh g(-1)) and the lowest electrochemical potential of all candidates. There are, however, at least three major hurdles before lithium metal anodes can become a viable technology: uneven and dendritic lithium deposition, unstable solid electrolyte interphase and almost infinite relative dimension change during cycling. Previous research has tackled the first two issues, but the last is still mostly unsolved. Here we report a composite lithium metal anode that exhibits low dimension variation (∼20%) during cycling and good mechanical flexibility. The anode is composed of 7 wt% 'lithiophilic' layered reduced graphene oxide with nanoscale gaps that can host metallic lithium. The anode retains up to ∼3,390 mAh g(-1) of capacity, exhibits low overpotential (∼80 mV at 3 mA cm(-2)) and a flat voltage profile in a carbonate electrolyte. A full-cell battery with a LiCoO2 cathode shows good rate capability and flat voltage profiles.

Lithium metal has shown great promise as an anode material for high-energy storage systems, owing to its high theoretical specific capacity and low negative electrochemical potential. Unfortunately, uncontrolled dendritic and mossy lithium growth, as well as electrolyte decomposition inherent in lithium metal-based batteries, cause safety issues and low Coulombic efficiency. Here we demonstrate that the growth of lithium dendrites can be suppressed by exploiting the reaction between lithium and lithium polysulfide, which has long been considered as a critical flaw in lithium-sulfur batteries. We show that a stable and uniform solid electrolyte interphase layer is formed due to a synergetic effect of both lithium polysulfide and lithium nitrate as additives in ether-based electrolyte, preventing dendrite growth and minimizing electrolyte decomposition. Our findings allow for re-evaluation of the reactions regarding lithium polysulfide, lithium nitrate and lithium metal, and provide insights into solving the problems associated with lithium metal anodes.

For future applications in portable electronics, electric vehicles and grid storage, batteries with higher energy storage density than existing lithium ion batteries need to be developed. Recent efforts in this direction have focused on high-capacity electrode materials such as lithium metal, silicon and tin as anodes, and sulphur and oxygen as cathodes. Lithium metal would be the optimal choice as an anode material, because it has the highest specific capacity (3,860 mAh g(-1)) and the lowest anode potential of all. However, the lithium anode forms dendritic and mossy metal deposits, leading to serious safety concerns and low Coulombic efficiency during charge/discharge cycles. Although advanced characterization techniques have helped shed light on the lithium growth process, effective strategies to improve lithium metal anode cycling remain elusive. Here, we show that coating the lithium metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate the lithium metal depositions and facilitates the formation of a stable solid electrolyte interphase. We show that lithium dendrites do not form up to a practical current density of 1 mA cm(-2). The Coulombic efficiency improves to ∼ 99% for more than 150 cycles. This is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles. Our results indicate that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes.

Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizing minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm−2 in both carbonate and ether electrolyte. The advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes.