A Gradient Doping Strategy toward Superior Electrochemical Performance for Li-Rich Mn-Based Cathode Materials.

Lithium-rich layered oxides (LLOs) are concerned as promising cathode materials for next-generation lithium-ion batteries due to their high reversible capacities (larger than 250 mA h g-1 ). However, LLOs suffer from critical drawbacks, such as irreversible oxygen release, structural degradation, and poor reaction kinetics, which hinder their commercialization. Herein, the local electronic structure is tuned to improve the capacity energy density retention and rate performance of LLOs via gradient Ta5+ doping. As a result, the capacity retention elevates from 73% to above 93%, and the energy density rises from 65% to above 87% for LLO with modification at 1 C after 200 cycles. Besides, the discharge capacity for the Ta5+ doped LLO at 5 C is 155 mA h g-1 , while it is only 122 mA h g-1 for bare LLO. Theoretical calculations reveal that Ta5+ doping can effectively increase oxygen vacancy formation energy, thus guaranteeing the structure stability during the electrochemical process, and the density of states results indicate that the electronic conductivity of the LLOs can be boosted significantly at the same time. This strategy of gradient doping provides a new avenue to improve the electrochemical performance of the LLOs by modulating the local structure at the surface.

Oxocarbon-functionalized graphene as a lithium-ion battery cathode: a first-principles investigation.

In recent years, organic-based, especially carbonyl-based, Li-ion battery electrode materials have attracted great attention due to their low-cost, environmentally friendly nature and strong Li-ion bonding abilities. However, new research is required to further increase the electron mobility and cycling performance of organic materials. The performance of a high-carbonyl C6O6 molecule-functionalized graphene electrode for Li-ion batteries is investigated using the density functional theory. The binding energy calculations indicate that the C6O6 molecule is adsorbed on graphene via physisorption. C6O6@graphene maintains excellent electronic conductivity with 1 to 6 Li ions. By our statistical method, the reduced voltage of the C6O6@graphene cathode displays a voltage between 2.6 V and 1.5 V with 2 phases from 1 to 6 Li ions with energy density of approximately 155 mA h g-1. The results obtained reveal that C6O6@graphene is a promising electrode material for renewable Li-ion batteries.

Variation of the coordination environment and its effect on the white light emission properties in a Mn-doped ZnO-ZnS complex structure.

Mn-doped ZnO-ZnS complex nanocrystals were fabricated through coating of dodecanethiol on Mn-doped ZnO nanocrystals. The relationship between the component of white light emission and the coordination environments of Mn-dopants were experimentally investigated. It was shown that Mn ions mainly formed Mn(3+)O6 octahedra in as prepared Mn-doped ZnO, while the Mn(3+) ions on the surface of ZnO transferred into Mn(2+) ions at the interface between ZnO and ZnS after dodecanethiol coating. The Mn(2+)S4 tetrahedron density and the orange emission intensity increased upon enhancing the dodecanethiol content. These results provide an alternative way to optimize the white emission spectrum from nanocrystals of Mn-doped ZnS-ZnO complex structures through modulation of the coordination environment of Mn ions.

Al doped ZnO nanogranular film fabricated by layer-by-layer self-assembly method and its application for gas sensors.

ZnO is one of the most promising materials for gas sensor. Nanogranular films with ultrahigh surface-to-volume ratio have great potential in gas sensor application. In this paper, Al doped ZnO nanogranular films were fabricated by layer-by-layer (LBL) self-assembly method and the gas sensitivity of ZnO films were investigated. The results show that sensitivity of Al:ZnO gas sensors is up to 12 against 20000 ppm hydrogen, while the response time and recovery time of the sensor are only 12 s and 25 s respectively. The high sensitivity is attributed to the high surface-to-volume ratio of nanogranular and porous structure of self-assembled films.

Fabrication and photoluminescence of Er(3+)-doped Al2O3 thin films with sol-gel method.

Erbium doped Al2O3 thin films were fabricated on quartz substrates in dip-coating process by sol-gel method, using the aluminum isopropoxide [Al(OC3H7)3]-derived AlOOH sols with the addition of erbium nitrate [Er(NO3)3 x 5H2O]. The as-deposited films, which erbium concentration was between 20 and 43 mol%, were annealed in air from 600 to 1200 degrees C. The phase structure was detected by X-ray diffraction (XRD) and the PL spectra in the wavelength range of 1400-1700 nm were investigated by spectrophotometer, which was exited by a 760 nm semiconductor LD. The PL spectrum shows a broadband extending from 1.430 to 1.670 microm and centered at 1.55 microm, corresponding to the intra-4f transition between the first excited (4I(13/2)) and the ground state (4I(15/2)) of Er3+. The full width at half maximum (FWHM) of PL peaks increase from 60 to 100 nm with temperature increased from 600 to 1200 degrees C.

A Flexible Li-Air Battery Workable under Harsh Conditions Based on an Integrated Structure: A Composite Lithium Anode Encased in a Gel Electrolyte.

Flexible lithium-air batteries (FLABs) with ultrahigh theoretical energy density are considered as the most promising energy storage devices for next-generation flexible and wearable electronics. However, their practical application is seriously hindered by various obstacles, including bulky and rigid electrodes, instability/low conductivity of electrolytes, and especially, the inherent semi-open structure. When operated in ambient air, moisture penetrated from an air cathode inevitably corrodes a Li metal anode, and most of the reported FLABs can only work under a pure oxygen or specific air (relative humidity: <40%) atmosphere, which cannot be regarded as a real "lithium-air battery". Herein, the author designed an innovative battery configuration by the synergy of a 3D open-structured Co3O4@MnO2 cathode and an integrated structure: a composite lithium anode encased in a gel electrolyte. A composite lithium anode fabricated through a simple, low-cost, and effective rolling method significantly relieves the fatigue fracture of the lithium electrode. Subsequently, an in situ-formed gel electrolyte encloses the composite lithium electrode, which not only reduces the electrode/electrolyte interfacial resistance but also acts as a protective layer, effectively preventing the lithium anode from corrosion. Consequentially, the battery can achieve more than 100 stable cycles in ambient air with a high relative humidity of 50%. To our surprise, the FLAB remains operational under extreme conditions, such as bending, twisting, clipping, and even soaking in water, demonstrating widespread applications in flexible electronics.

ZnO quantum dot-modified rGO with enhanced electrochemical performance for lithium-sulfur batteries.

Lithium-sulfur batteries are considered the most promising next-generation energy storage devices. However, problems like sluggish reaction kinetics and severe shuttle effect need to be solved before the commercialization of Li-S batteries. Here, we successfully prepared ZnO quantum dot-modified reduced graphene oxide (rGO@ZnO QDs), and first introduced it into Li-S cathodes (rGO@ZnO QDs/S). Due to its merits of a catalysis effect and enhancing the reaction kinetics, low surface impedance, and efficient adsorption of polysulfide, rGO@ZnO QDs/S presented excellent rate capacity with clear discharge plateaus even at a high rate of 4C, and superb cycle performance. An initial discharge capacity of 998.8 mA h g-1 was delivered, of which 73.3% was retained after 400 cycles at a high rate of 1C. This work provides a new concept to introduce quantum dots into lithium-sulfur cathodes to realize better electrochemical performance.

MnO nanoparticles interdispersed in 3D porous carbon framework for high performance lithium-ion batteries.

Interdispersed MnO nanoparticles that are anchored and encapsulated in a three-dimensional (3D) porous carbon framework (MnO@CF) have been constructed, which display nanosphere architecture with rich porosity, well-defined carbon framework configuration, and excellent structure stability. When evaluated as an anode material, the MnO@CF exhibits relatively high specific capacity of 939 mA h g(-1) at current rate of 0.2 A g(-1) over 200 cycles and excellent rate capability of 560.2 mA h g(-1) at 4 A g(-1). By virtue of its mechanical stability and desirable ionic/electronic conductivity, the specific design can be a promising approach to fabricate high-performance lithium-ion batteries.

Improving the solubility of Mn and suppressing the oxygen vacancy density in Zn(0.98)Mn(0.02)O nanocrystals via octylamine treatment.

Zn(0.98)Mn(0.02)O nanocrystals were synthesized by the wet chemical route and were treated with different content of octylamine. The environment around Mn and the defect type and concentration were characterized by photoluminescence, Raman, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. It is found that N codoping effectively enhances the solubility of Mn substituting Zn via reducing donor binding energy of impurity by the orbital hybridization between the N-acceptor and Mn-donor. On the other hand, the O atoms released from MnO(6) and the N ions from octylamine occupy the site of oxygen vacancies and result in reduction of the concentration of oxygen vacancies in Zn(0.98)Mn(0.02)O nanocrystals.