Rechargeable Li-O2 batteries have been considered as the most promising chemical power owing to their ultrahigh specific energy density. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) result in high overpotential (∼1.5 V), poor rate capability, and even a short cycle life, which critically hinder their practical applications. Herein, we propose a synergistic strategy to boost the electrocatalytic activity of Co3O4 nanosheets for Li-O2 batteries by tuning the inner oxygen vacancies and the exterior Co3+/Co2+ ratios, which have been identified by Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption near edge structure spectroscopy. Operando X-ray diffraction and ex situ scanning electron microscopy are used to probe the evolution of the discharge product. In comparison with bulk Co3O4, the cells catalyzed by Co3O4 nanosheets show a much higher initial capacity (∼24051.2 mAh g–1), better rate capability (8683.3 mAh g–1@400 mA g–1) and cycling stability (150 cycles@400 mA g–1), and lower overpotential. The large enhancement in the electrochemical performances can be mainly attributed to the synergistic effect of the architectured 2D nanosheets, the oxygen vacancies, and Co3+/Co2+ difference between the surface and the interior. Moreover, the addition of LiI to the electrolyte can further reduce the overpotential, making the battery more practical. This study offers some insights into designing high-performance electrocatalysts for Li-O2 batteries through a combination of the 2D nanosheet architecture, oxygen vacancies, and surface electronic structure regulation.Keywords: Co3O4 nanosheets; Li-O2 battery; oxygen vacancy; surface electronic modulation; synergetic effect;

Radioresistance is one of the undesirable impediments in hypoxic tumors, which sharply diminishes the therapeutic effectiveness of radiotherapy and eventually results in the failure of their treatments. An attractive strategy for attenuating radioresistance is developing an ideal radiosensitization system with appreciable radiosensitization capacity to attenuate tumor hypoxia and reinforce radiotherapy response in hypoxic tumors. Therefore, we describe the development of Gd-containing polyoxometalates-conjugated chitosan (GdW10@CS nanosphere) as a radiosensitization system for simultaneous extrinsic and intrinsic radiosensitization, by generating an overabundance of cytotoxic reactive oxygen species (ROS) using high-energy X-ray stimulation and mediating the hypoxia-inducible factor-1a (HIF-1a) siRNA to down-regulate HIF-1α expression and suppress broken double-stranded DNA self-healing. Most importantly, the GdW10@CS nanospheres have the capacity to promote the exhaustion of intracellular glutathione (reduced GSH) by synergy W6+-triggered GSH oxidation for sufficient ROS generation, thereby facilitating the therapeutic efficiency of radiotherapy. As a result, the as-synthesized GdW10@CS nanosphere can overcome radioresistance of hypoxic tumors through a simultaneous extrinsic and intrinsic strategy to improve radiosensitivity. We have demonstrated GdW10@CS nanospheres with special radiosensitization behavior, which provides a versatile approach to solve the critical radioresistance issue of hypoxic tumors.Keywords: GdW10@CS nanosphere; gene therapy; glutathione; hypoxic tumor; polyoxometalates; radiosensitization; radiotherapy;

•A Li-O2 battery based on amorphous LiO2 has been built for the first time.•Amorphous LiO2 has been identified by In-situ Raman spectrum, linear sweep voltammetry and UV–vis measurements.•The LiO2-based Li-O2 battery shows an ultralow overpotential, high rate capability and long cycling stability.•A synchronized reduction strategy was proposed to prepare 3D-architectured Pd-rGO catalyst.•The side reactions have been mitigated due to the significant decrease of the oxidation potential.Replacing Li2O2 with LiO2 as the discharge product is a very promising strategy to tackle the problems of high overpotential (~ 1.5 V), inferior rate capability and short cycle life in the current Li-O2 batteries based on Li2O2. But it's very difficult to control LiO2 due to its thermodynamic instability. Herein, we have successfully built a facile rechargeable Li-O2 battery based on the formation and decomposition of amorphous LiO2 with an ultralow overpotential (~ 0.3 V), long cycle life and high rate capability under the catalysis of 3D-architectured Pd-rGO. In-situ Raman spectrum, linear sweep voltammetry, UV–vis measurements and SAED (Selected Area Electron Diffraction) all have identified the amorphous LiO2-based electrochemical process. Amorphous LiO2 shows a lower oxidation potential and a faster ionic conductivity contributing to the excellent electrochemical performances and the mitigation of undesirable side reactions. This study opens a new horizon to solve the intrinsic problems of the current Li-O2 batteries.Download high-res image (224KB)Download full-size image

Noble-metal-free bifunctional cathode catalysts, which can promote both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), are quite necessary for lithium–air batteries. In this study, we propose a novel strategy to improve the catalytic performance of CoO through the integration with the dotted carbon species and oxygen vacancies. We have successfully prepared carbon-dotted defective CoO with oxygen vacancies (CoO/C) by sintering the pink precursors obtained from the ethanol-mediated Co(Ac)2·4H2O. In comparison with the commercial or oxygen-vacancies-only CoO, the cycling stability, the initial capacity, and the rate capability of CoO/C-catalyzed cathode have all been greatly enhanced, and the overpotential has also been decreased, which can be attributed to the synergetic effect of the dotted carbon species and oxygen vacancies on both ORR and OER. Oxygen vacancies can enhance the mobility of e– and Li+ and bind to O2 and Li2O2 as active sites. The dotted carbon species not only improve the conductivity of CoO but also stabilize the oxygen vacancies during ORR/OER. In addition, our further investigation on the evolution of the morphology and phase composition of CoO/C and commercial CoO based cathodes under different charge/discharge states confirms that CoO/C can largely accelerate the formation and decomposition of Li2O2 during discharge–charge cycles.Keywords: carbon dotting; CoO; Li−O2 battery; oxygen vacancy; synergetic effect

Recently, the design and synthesis of high performance cathode materials for sodium ion batteries have attracted great interest. In this study, we propose a novel strategy to design high-rate performance cathode materials for sodium ion batteries through enlarging the d-spacing of the Na-ion diffusion layer. More importantly, some new insights into the expansion mechanism of the interplanar spacing for Na0.67Mn0.8Ni0.1Mg0.1O2 induced by Ni and Mg co-doping and the resulting high-rate capability have been presented for the first time. We find that Mg and Ni co-doping leads to the shortening of the TM–O (TM = transition metal) bond lengths and the shrinkage of the TMO6 octahedrons, which might be largely responsible for the expansion of the interplanar spacing of the Na-ion diffusion layer. In comparison with Na0.67Mn0.8Ni0.2O2 and Na0.67Mn0.8Mg0.2O2, Mg and Ni co-doped Na0.67Mn0.8Ni0.1Mg0.1O2 has a higher Na-ion diffusion coefficient and can deliver around 160, 145, 133 and 124 mA h g−1 at 24, 48, 120 and 240 mA g−1, respectively. In particular, at the high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C), MMN can still offer reversible capacities of 110, 66 and 37 mA h g−1, respectively. In addition, the cycling stability has also been enhanced via Mg and Ni co-doping at the same time, which means that Mg and Ni co-doping also has a positive effect on the stability of the layered structure.

Co substitution has been extensively used to improve the electrochemical performances of cathode materials for sodium-ion batteries (SIBs), but the role of Co has not been well understood. Herein, we have comprehensively investigated the effects of Co substitution for Ni on the structure and electrochemical performances of Na0.7Mn0.7Ni0.3–xCoxO2 (x = 0, 0.1, 0.3) as cathode materials for SIBs. In comparison with the Co-free sample, the high-rate capability and cycle performance have been greatly improved by the substitution of Co, and some new insights into the role of Co have been proposed for the first time. With the substitution of Co3+ for Ni2+ the lattice parameter a decreases; however, c increases, and the d-spacing of the sodium-ion diffusion layer has been enlarged, which enhances the diffusion coefficient of the sodium ion and the high-rate capability of cathode materials. In addition, Co substitution shortens the bond lengths of TM–O (TM = transition metal) and O–O due to the smaller size of Co3+ than Ni2+, which accounts for the decreased thickness and volume of the TMO6 octahedron. The contraction of TM–O and O–O bond lengths and the shrinkage of the TMO6 octahedron improve the structure stability and the cycle performance. Last but not least, the aliovalent substitution of Co3+ for Ni2+ can improve the electronic conductivity during the electrochemical reaction, which is also favorable to enhance the high-rate performance. This study not only unveils the role of Co in improving the high-rate capability and the cycle stability of layered Na0.7Mn0.7Ni0.3–xCoxO2 cathode materials but also offers some new insights into designing high performance cathode materials for SIBs.

•CoO has been confined into bimodal mesoporous carbon frameworks to form CoO@BMC hybrid.•CoO@BMC based cathode shows higher initial capacity and cycling stability than CoO, BMC and CoO@CMK.•CoO@BMC based cathode also shows higher rate capability and lower overpotential than CoO@CMK.•The enhanced performance can be attributed to the synergetic effect of CoO and hierarchical BMC on both ORR and OER.Rechargeable Li-O2 batteries show great potential owing to the super high energy density. However, the poor kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) limits their practical application. The exploration of noble metals-free cathode catalysts with high catalytic activity on both ORR and OER is still a big challenge. Herein, CoO has been confined into bimodal mesoporous carbon frameworks (CoO@BMC) via a wet-chemistry impregnation approach and the performance of CoO@BMC as cathode catalyst for Li-O2 batteries has been largely improved. For comparison, CoO@CMK-3 composite has also been prepared. In comparison with bulk CoO, BMC and CoO@CMK-3, CoO@BMC based cathode shows a higher initial capacity (∼4000 mA h g−1), much higher cycling stability, higher rate capability and lower overpotential,which can be largely attributed to the synergetic effect of CoO and hierarchical BMC on both ORR and OER. In addition, the formation and decomposition of Li2O2 and side products in the process of ORR and OER have also been analyzed and the results indicate that CoO@BMC nanocomposite can efficiently promote the decomposition of Li2O2 and even some side products of carbonates.Download high-res image (199KB)Download full-size image

•LiCoO2 is coated by Li+-conductive Li2ZrO3 by a synchronous lithiation strategy.•Multiple effects of Li2ZrO3 coating on high-voltage LiCoO2 are discovered.•The synchronous lithiation coating strategy combines bulk doping and surface modifications.•The interplanar spacing, layered structure stability and Li-ion diffusion coefficient are enhanced.•The cycle performance, polarization, rate capability and thermo-stability have been significantly improved.The poor cycle performance, low rate capability and thermo-instability limit the practical application of LiCoO2 as high-voltage cathode materials for lithium-ion batteries. Herein, we propose an integrated modification strategy which combines the advantages of elements doping, surface modifications and even the high Li+-diffusion of the coating layer. In this study, Li+-conductive Li2ZrO3 has been successfully coated on the surface of LiCoO2 (Li2ZrO3@LCO) through a synchronous lithiation strategy and the multiple effects of Li2ZrO3 coating on the structural and electrochemical performances of LiCoO2 as high-voltage cathode materials for Li-ion batteries have been discovered. In compared to bare LiCoO2, the cycle performance, polarization, rate capability and thermo-stability of Li2ZrO3@LZO have been significantly improved. Li2ZrO3@LCO shows a much higher capacity retention than bare LiCoO2 both at 25 °C (85.2% vs.32.6% at 5 C, 1 C = 200 mA g−1) and 55 °C (71.3% vs.13.9% at 5 C), and the specific capacity at 10 C has also been largely increased from 33.9 mAh g−1 to 103.4 mAh g−1. The enhancement of the electrochemical performances can be largely attributed to the multiple effects of Li+-conductive Li2ZrO3 coating: the alleviation of side reactions and transition metal dissolution, the enhancement of Li-ion diffusion coefficient and electronic conductivity, Zr4+ migration and doping, the resulting interplanar spacing expansion and the improvement of the layered structure stability.

Lithium-rich Mn-based layered cathode materials have attracted wide attention due to their high specific capacity for lithium-ion batteries. However, some critical issues i.e. poor rate capability and voltage fade have limited their practical applications. Herein, we propose a synchronous lithiation strategy to coat Li-rich Li1.2Mn0.6Ni0.2O2 (LMNO) with a thin layer of Li+-conductive Li2ZrO3. The obtained syn-Li2ZrO3@LMNO integrates the advantages of the Li2ZrO3 coating and Zr4+ doping, and shows a much higher rate capability and cycling stability than those of the counterpart post-Li2ZrO3@LMNO fabricated by a post-coating method. More importantly, the average voltage of syn-Li2ZrO3@LMNO has been enhanced by 0.15 V and the voltage decay has also been mitigated. New insights into the synergetic modification mechanism of the Li2ZrO3 coating and Zr4+ doping have been proposed. The coating layer of Li+-conductive Li2ZrO3 alleviates the surface side reactions, suppresses the transition metal dissolution and enhances the Li-ion conductivity. Meanwhile, the doping and incorporation of Zr4+ into the host structure accompanied by the Li2ZrO3 coating expands the interplanar spacing and decreases Li/Ni mixing which facilitates Li+ diffusion. In addition, the integration of the Li2ZrO3 coating and Zr4+ doping also further enhances the layered structure stability and mitigates the voltage fade during lithiation/delithiation cycles. Moreover, the proposed synchronous lithiation coating route avoids the duplicated high-temperature calcinations and can also be widely used to modify some other cathode materials.

Strongly yellow fluorescent carbon dots (CDs) have been directly synthesized from o-phenylenediamine (o-PD) through a facile microwave-assisted method. The as-prepared o-CDs exhibit excitation-dependent photoluminescent behavior and excellent water-solubility due to some amino or hydroxy functional groups on the surface. An emission peak appears at 573 nm when the o-CDs solution is excited at 400 nm, and the quantum yield (QY) is 38.5%. Owing to their low toxicity and water solubility the as-prepared o-CDs can be directly used for cell imaging. More importantly, the as-prepared o-CDs solution also shows sensitivity for H2O2. The limits of detection (LOD) for Fe3+ and H2O2 are 16.1 nM and 28.1 nM, respectively, which is much lower than what's reported in previous studies. The fluorescence intensity also shows a dependence on pH and the strongest fluorescence intensity appears at pH 9. In addition, we also find that the fluorescent properties of CDs prepared from m-phenylenediamine (m-PDs) and p-phenylenediamine (p-PDs) are quite different from those of o-CDs.

A ZnFe2O4–reduced graphene oxide (ZnFe2O4–RGO) hybrid has been successfully synthesized through a facile syn-graphenization strategy. In this preparation procedure, N2H4·H2O works as both a base source and a reductant, and the reduction of graphene oxide (GO) into RGO is accompanied by the formation of ZnFe2O4. In comparison with bare ZnFe2O4, the ZnFe2O4–RGO hybrid shows ultrahigh cycling stability and rate capability as an anode material for lithium ion batteries. The cycling capacity of the ZnFe2O4–RGO hybrid at the 100th cycle is considerably enhanced to 1025 mA h g−1, compared with only 166 mA h g−1 for bare ZnFe2O4. The rate performance can also be significantly improved to 800 mA h g−1 at the current density of 1000 mA g−1. The much better cycling stability and rate capability can be largely attributed to the well dispersed conductive RGO and the tight binding between ZnFe2O4 and RGO, which is a benefit of the subtle syn-graphenization strategy. In addition, the effects of RGO content on the electrochemical performance are presented.

•Graphene quantum dots (GQDs) were synthesized by microwave-assisted pyrolysis of aspartic acid.•GQDs can serve as a fluorescent probe for sensitive detection of Fe3+ and pH value.•GQDs can be directly used for live cells imaging.Recently, carbon nanomaterials have received considerable attention as fluorescent probes owing to their low toxicity, water solubility and stable photochemical properties. However, the development of graphene quantum dots (GQDs) is still on its early stage. In this work, GQDs were successfully synthesized by one-step microwave assisted pyrolysis of aspartic acid (Asp) and NH4HCO3 mixture. The as-prepared GQDs exhibited strongly blue fluorescence with high quantum yield up to 14%. Strong fluorescence quenching effect of Fe3+ on GQDs can be used for its high selectivity detection among of general metal ions. The probe exhibited a wide linear response concentration range (0–50 μM) to Fe3+ and the limit of detection (LOD) was calculated to be 0.26 μM. In addition, GQDs are also sensitive to the pH value in the range from 2 to 12 indicating a great potential as optical pH sensors. More importantly, the GQDs possess lower cellular toxicity and high photostability and can be directly used as fluorescent probes for cell imaging.Aspartic acid-derived graphene quantum dots show great sensing property for Fe3+, pH value and bioimaging as fluorescent probes.

The effects of Li substitution for Ti on the structure and electrochemical performances of Co-free Na0.67Mn0.55Ni0.25Ti0.2–xLixO2 (x = 0, 0.1, 0.2) layered cathode materials for sodium ion batteries have been comprehensively investigated. X-ray diffraction and Rietveld refinement results demonstrate that Li mainly occupies TM (TM = transition metal) sites in the crystal structure to maintain the P2 structure majority and a small amount of Li atoms enter Na sites to generate some O3 phase. The discharge voltage, reversible capacity, rate capability, cycling performance, and Coulombic efficiency all have been improved by Li substitution, which can be largely attributed to the integration of P2 and O3. Li substitution also raises the average discharge voltage from 2.6 to 3.1 V. Na0.67Mn0.55Ni0.25Li0.2O2 (L02) can deliver an initial capacity of about 158 mA h g–1 at 0.05C (12 mA g–1) in comparison with the Li-free sample (147 mA h g–1). Even at the high rates of 480 (2C), 1200 (5C), and 1920 (8C) mA g–1, L02 can also display ca. 93, 65, and 38 mA h g–1 discharge capacities, respectively. The rate capability is higher than what is reported in the previous Li-substituted cathode materials. In addition, Li substitution in transition-metal sites generates more defects to maintain the charge neutrality, which enhances the electronic conductivity and also has a positive effect on the Na ion diffusion coefficient. The electronic conductivity and Na ion diffusion coefficient have been enhanced by 122% and 29%, respectively, with the substitution of Li for Ti. Our results also show that the oxidation peaks become sharper with increasing Li content, which indicates the feasibility of Na ion intercalation/deintercalation in the integrated P2/O3 phase. This study also offers some new insights into designing high-performance cathode materials for sodium ion batteries.

The design and facile synthesis of noble metal-free efficient cathode catalysts to accelerate the sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a big challenge for lithium–air batteries. In this study, oxygen vacancy-bearing CoO (CoO-A) has been successfully synthesized through a simple calcination of Co(Ac)2·4H2O in Ar, and the oxygen vacancies have been confirmed by Raman spectroscopy, HRTEM, X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS). In comparison with defect-free CoO-N, which is derived from the decomposition of Co(NO3)2·6H2O, an oxygen-deficient CoO-A based cathode shows much higher cycling stability, higher rate capability, higher coulombic efficiency, and lower charge–discharge overpotential. The enhanced performances of the CoO-A based cathode can be largely attributed to the synergetic effect of CoO itself and oxygen vacancies on the promotion of both ORR and OER. CoO provides catalytic activity for ORR, and at the same time the oxygen vacancies not only facilitate the electron and Li+ migration but also act as active sites binding to O2 and Li2O2, which accelerates the OER process. Furthermore, the formation and decomposition of Li2O2 during discharge–charge cycles have also been studied and the results indicate that CoO-A shows a high catalytic activity in the decomposition of Li2O2.

A high performance layered P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material for sodium ion batteries with high rate capability and excellent long-life cyclic performance has been successfully designed and synthesized by a simple sol–gel method. In comparison with the reported Na0.7MnO2, the designed P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material can be charged and discharged in an extended voltage range of 1.5–4.2 V and shows reversible capacities of 155, 144, 137, 132 and 126 mA h g−1 at different current densities of 12, 24, 48, 120 and 240 mA g−1, respectively. Even at high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C) it can still deliver capacities of 117, 93 and 70 mA h g−1, respectively, which are much higher than those of the recently reported Na0.5[Ni0.23Fe0.13Mn0.63]O2. In addition, the Na0.67Mn0.65Ni0.2Co0.15O2 cathode material also displays an excellent capacity retention ca. 85% and 78% after 100 cycles at 0.05C and 0.5C, respectively. It is also proposed that Mn4+ may be “activated” in a low voltage range, especially below 2.0 V, which contributes to the additional capacity. The Na-ion diffusion coefficient, DNa+, is ca. 10−14 cm2 s−1 as calculated by the PITT and the discharge diffusion coefficient is a little larger than the charge one. The designed Na0.67Mn0.65Ni0.2Co0.15O2 shows great potential as a cathode material for sodium ion batteries.

A facile and efficient exfoliation process has been reported to produce single- and few-layer nanosheets of MoS2, WS2 and BN using liquid alloys of alkali metals at room temperature. The colloidal dispersions of MoS2 and WS2 layers were highly stable over several months, which allowed us to easily prepare films of MoS2 and WS2 by vacuum filtration or spraying.

0.3Li2MnO3·0.7LiNi0.5−xMn0.5−xM2xO2 (M = Mg or Al, x = 0–0.08) samples have been synthesized by a combination of co-precipitation (CP) and solid-state reaction. Electrochemical measurements show that not only can the charge–discharge capacity of lithium-rich materials be enhanced, but more importantly, the rate capacity can be greatly improved by doping with magnesium and aluminum. At a current density of 400 mA g−1, the 0.3Li2MnO3·0.7LiNi0.46Mn0.46Mg0.08O2 and 0.3Li2MnO3·0.7LiNi0.49Mn0.49Al0.02O2 electrodes deliver discharge capacities of 135 mA h g−1 and 127 mA h g−1, respectively, while the pristine electrode delivers a discharge capacity of only 10 mA h g−1. Through studying the structure of lithium-rich materials, we find that the Li/Ni mixing of lithium-rich materials is reduced by doping with magnesium and aluminum, in turn, the performance of doped lithium-rich materials is improved greatly. Furthermore, compared with Al-doped lithium-rich materials, the Li/Ni mixing of Mg-doped materials is further reduced. So the performance improvement of Mg-doped lithium-rich materials is more obvious than that of Al-doped materials.

CdS nanodots (CNDs) were directly synthesized through a facile one-pot method using BSA as a template without adding an external sulfur source. The as-synthesized green fluorescent CNDs show much better water solubility and lower cell cytotoxicity, and can be directly used for live HeLa cell imaging without any further modifications.

Hg2+ is one of the most ubiquitous pollutants in the environment and is a danger to human health. There is a need for a simple highly sensitive method of for the detection of aqueous Hg2+. Carbon dots (CDs) have attracted widespread attention due to their potential application in bioimaging, chemisensors and photocatalyst design. We have now developed a simple and efficient method for the preparation of P-doped carbon dots (CDs) with tunable fluorescence, using L-valine as the carbon source and H3PO4 (85%) as oxidant. The fluorescence of CDs can be tuned from green (CDs-1) to yellow (CDs-2) by simply controlling the reaction time at a relatively mild temperature (90 °C). The CDs obtained exhibit bright photoluminescence with quantum yield (QY) up to 44.8% for CDs-1 and 31% for CDs-2, together with excellent biocompatibility and water solubility. pH and NaCl solution had no significant effect on the fluorescence intensity of CDs-1. More importantly, the green CDs show high sensitivity and selectivity in the detection of Hg2+. Two different fluorescence quenching modes have been established, the lower limit of detection (LOD) being about 1.51 nM.

Porous metal oxides have attracted great interest as anode materials for lithium ion batteries owing to their improved electrochemical properties. In this study, we propose a Prussian blue analogue (PBA)-derived strategy to successfully prepare hollow porous FexCo3−xO4 (FCO) with controlled morphologies (nanospheres and nanocubes) using surfactants as “soft templates”. In comparison with FCO nanocubes (FCO-NCs) and FCO nanoparticles (FCO-NPs), FCO spheres (FCO-NSs) show a much better cycling stability and rate capability as an anode material for lithium ion batteries. The cycling capacity of FCO-NSs at the 50th cycle has been largely enhanced to 1060 mA h g−1 from only 721 (FCO-NCs) and 389 mA h g−1 (FCO-NPs). The capacity of FCO-NSs at a current density of 1000 mA g−1 has been considerably improved to 823 mA h g−1 from 504 and 152 mA h g−1 for FCO-NCs and FCO-NPs, respectively, indicating a much better rate capability. The greatly enhanced cycling stability and rate capability can be largely attributed to the hollow porous structure of FCO-NSs with a wider pore distribution, a slightly higher Co content (compared to FCO-NCs) and higher mechanical strength, which facilitates Li+ and electron diffusion and migration.

Confining Fe3O4 into nanoporous carbon frameworks has been achieved through self-assembly and the use of a subsequent syn-carbonization strategy, where Fe3O4 and carbon frameworks are generated simultaneously and Fe3O4 particles are confined into porous carbon frameworks (Fe3O4@C). Both the composition and microstructure have a significant effect on the electrochemical performances. In comparison with bulk Fe3O4, Fe3O4@C-2 with optimal void pore volume and oxide content shows a significant enhancement in both cycling stability and high-rate capacity. The reversible capacity of Fe3O4@C-2 is retained at 932 mA h g−1 after 100 cycles compared to only 410 mA h g−1 for bulk Fe3O4. The capacity of Fe3O4@C-2 at the current density of 2 A g−1 has been significantly improved to 478 mA h g−1 from only 26 mA h g−1 for bulk Fe3O4. The considerable enhancement of both the cyclability and high-rate capability can be attributed to the synergic effect of nanoconfinement as well as the optimized composition and microstructure: the good dispersion of oxide particles, and the efficient volume change alleviation during the discharge–charge process.

•Na and K co-doping has a cooperative effect on the enlargement of lattice parameters of Li3.98Na0.01K0.01Ti5O12.•Na and K co-doping has a synergic effect on the improvement of electrochemical performances of Li3.98Na0.01K0.01Ti5O12.•Rietveld refinement of neutron diffraction indicates both Na and K prefer to take 8a site in Li3.98K0.01Na0.01Ti5O12.The effects of Na and K co-doping on the crystal structure and electrochemical properties of Li4Ti5O12 have been comprehensively investigated by means of X-ray diffraction (XRD), neutron diffraction (ND), scanning electron microscope (SEM) and galvanostatic charge–discharge tests. Rietveld refinements of XRD and ND data indicate that the lattice parameters increase with the doping of Na and K, and Na or K prefers to take 8a site (tetrahedral site) in Li3.98K0.01Na0.01Ti5O12. The lattice parameter and unit cell volume of Li3.98Na0.01K0.01Ti5O12 are even larger than that of Li3.98Na0.02Ti5O12 and Li3.98K0.02Ti5O12 indicating a cooperative effect of Na and K co-doping on the enlargement of lattice parameters and unit cell volume. The electrochemical property results demonstrate that Na and K co-doped Li3.98Na0.01K0.01Ti5O12 has a larger reversible capacity and rate capability as anode material for lithium ion battery compared to un-doped Li4Ti5O12, Na-doped Li3.98Na0.02Ti5O12 or K-doped Li3.98Ka0.02Ti5O12, which indicates the significant synergic effect of Na and K co-doping on the improvement of the electrochemical performances of Li4Ti5O12.

•Pure and Co doped MgMn2O4 are studied as negative materials for lithium ion battery for the first time.•Co doping induces a phase transition of MgMn2O4 from a tetragonal to a cubic spinel-structure.•Co content has a significant effect on the electrochemical performance.•The anti-sites defects resulting from the Co substitution for Mn is discovered by neutron diffraction.MgMn2O4 and Co doped Mg(Mn2 − xCox)O4 (x = 0.5, 1.0 and 2.0) compounds have been successfully synthesized and studied as negative materials for lithium ion battery for the first time. Co doping induced a phase transition of MgMn2O4 from a tetragonal spinel-structure with a space group of I41/amd to a cubic spinel structure with a space group of Fd-3m. Electrochemical measurements indicate that the reversible capacity and cyclability of Mg(Mn2 − xCox)O4 first increases and then decreases with increasing Co content indicating that Co content has a significant effect on the electrochemical performance. MgMn1.5Co0.5O4 shows the best electrochemical performance compared to the other three samples. This might be largely attributed to the phase transition and anti-sites defects of spinel crystal cell resulting from the Co substitution for Mn, which was further confirmed by Rietveld refinement of neutron diffraction.

A novel synchronous lithiation route has been successfully used to coat Li+-conductive Li2ZrO3 on the surface of LiNi1/3Co1/3Mn1/3O2 (Li2ZrO3@LNCMO). In this strategy, Li2ZrO3 layer and LiNi1/3Co1/3Mn1/3O2 host simultaneously form from ZrO2@Ni1/3Co1/3Mn1/3C2O4·xH2O precursor. In compared to bare LNCMO, the reversible capacity, cycling performance, thermal stability, rate capability, and polarization of Li2ZrO3@LNCMO have all been greatly improved. At 0.1 and 10 C, the specific capacity of Li2ZrO3@LNCMO is 192 and 106 mAh g–1, respectively, while they are 178 and 46 mAh g–1 for bare LNCMO. At a current density of 5 C, the capacity retention of Li2ZrO3@LNCMO at 25 and 55 °C after 400 cycles is enhanced to 93.8% and 85.1%, respectively, compared to 69.2% and 37.4% of bare LNCMO. The largely enhanced electrochemical performances of Li2ZrO3@LNCMO cathode can be attributed to the high Li-ion conductivity as well as the proctection of Li2ZrO3 coating. Li+ conductivity of Li2ZrO3@LNCMO is about 20 times higher than that of bare LNCMO. Moreover, the migration of partial Zr4+ to the host LNCMO phase not only benefits Li-ion or electron conductivity but also alleviates the Li–Ni cation mixing and improves the structure stability. The cations migration, doping effect, and the reduced cation mixing further contribute to the electrochemical performance enhancement.

The facet-dependent performance has aroused great interest in the fields of catalyst, lithium ion battery and electrochemical sensor. In this study, the well-defined Co3O4 cubes with exposed (001) plane and octahedrons with exposed (111) plane have been successfully synthesized and the facet-dependent electrocatalytic performance of Co3O4 for rechargeable Li–O2 battery has been comprehensively investigated by the combination of experiments and theoretical calculations. The Li–O2 battery cathode catalyzed by Co3O4 octahedron with exposed (111) plane shows much higher specific capacity, cycling performance, and rate capability than Co3O4 cube with exposed (001) plane, which may be largely attributed to the richer Co2+ and more active sites on (111) plane of Co3O4 octahedrons. The DFT-based first-principles calculations further indicate that Co3O4 (111) has a lower activation barrier of O2 desorption in oxygen evolution reaction (OER) than Co3O4 (001), which is very important to refresh active sites of catalyst and generate a better cyclic performance. Also, our calculations indicate that Co3O4 (111) surface has a stronger absorption ability for Li2O2 than Co3O4 (001), which may be an explanation for a larger initial capacity in Co3O4 (111) plane by experimental observation.

Fluorescent carbon dots (CDs) have attracted great attention in the biomedical field owing to their remarkable fluorescence property, low toxicity, and excellent water solubility. Because of the “water window” effect, the CDs with upconversion fluorescence or longer wavelength downconversion fluorescence are particularly more suitable for bioimaging because they can weaken the auto-fluorescence interferences and penetrate the cell or tissue more deeply. In this study, we reported a facile method to simultaneously enhance the upconversion fluorescence and tune the downconversion luminescence of CDs from blue to green light by simply adding H2O2 in a hydrothermal process. The H2O2-treated green fluorescent CDs with excellent upconversion property showed a high yield of 34% and a quantum yield of 16.5%, and low cell cytotoxicity, which could be directly used for live Hela cell imaging.

NiAl–LDH films with hierarchical morphology have been fabricated by immersion of an Al substrate in Ni2+-containing solutions under strong acidic conditions, and the growth processes of the films are discussed in this communication. The as-prepared LDH films exhibit high activity in the photocatalytic degradation of organic contaminants.

•NiFe2O4 octahedrons have been successfully synthesized by a one-step hydrothermal method.•Hydrogenation modifies the surface structure of NiFe2O4 and generates some oxygen vacancies and metallic Ni.•Hydrogenation largely improves the cycling capacity (60% higher at 50th cycle) and rate capability (3 times higher at 1 A/g).•The simple hydrogenation modification method might also be applied to other transition metal oxides electrodes.Nanocrystal NiFe2O4 (NFO) octahedron with a spinel structure has been successfully synthesized by a one-step hydrothermal method. The effects of hydrogenation on the crystal structure, morphology, surface structure, and the electrochemical performance of NFO are comprehensively investigated for the first time. After hydrogenation, the well-defined octahedron morphology of NFO disappears and a small fraction of metallic Ni and some oxygen vacancies are generated after hydrogenation which has been characterized by X-ray diffraction (XRD), X-ray photoelectronic spectrometer (XPS) and Positron annihilation lifetime spectroscopy (PALS). Compared to the pristine NFO or the annealed NFO in air, the hydrogenated samples exhibit much better capacity retention (60% higher than un-hydrogenated NFO at 50th cycle) and rate capability (3 times higher at 1 A/g), which can be largely attributed to the synergetic effect of the conductive metallic Ni and oxygen vacancies resulting from H2 reduction. Furthermore, this facile hydrogenation modification method may also be applied to improve the electrochemical performances of other transition metal oxides electrodes.

•Nd2−xYxFe17−yAly (0 ≤ x ≤ 1.5,0 ≤ y ≤ 3.0) compounds crystallize in Th2Zn17-type structure.•The site occupancies are determined by X-ray diffraction and neutron diffraction.•Al prefers to take 18h sites and avoids 9d sites.•Y and Al co-doping has a well synergic effect on the crystal structure and magnetic properties.The synergic effects of Y and Al co-doping on the structural and magnetic properties of Nd2−xYxFe17−yAly compounds (0 ≤ x ≤ 1.5, 0 ≤ y ≤ 3.0) have been comprehensively investigated by means of X-ray diffraction, neutron diffraction and magnetic measurement. Rietveld refinements indicate that all the prepared samples crystallize in Th2Zn17-type structure (R3¯m space group). For a given Al content (y), the lattice parameter a, c and unit cell volume V of Nd2−xYxFe17−yAly all decrease linearly with increasing Y concentration while the c/a ratio increases. For a given Y content (x), the lattice parameter a, c and unit cell volume V of Nd2−xYxFe17−yAly all increase linearly with increasing Al content. Al atoms prefer to take 18h sites and completely avoid the 9d sites. For a given Al content, Ms of Nd2−xYxFe17−yAly first increases to a maximum and then decreases with increasing Y content. This is quite different from what's observed in other mixed rare earth systems. For a given Y content, TC of Nd2−xYxFe17−yAly first increases rapidly and then increases slowly with increasing Al content but Ms first increases and then decreases. This can be attributed to the competition between the positive effect resulting from the optimization of bond lengths and the negative effect caused by magnetic dilution of nonmagnetic substituent.

We present the crystal structure, diborane (B2H6) and triborane (B3Hn) evolution, and dehydrogenation kinetics, of both bulk and nanoconfined Li/Mg(BH4)3 in a highly ordered nanoporous carbon template. The bialkali borohydride Li/Mg(BH4)3 mainly forms a structure similar to that of α-Mg(BH4)2. The decomposition temperature of Li/Mg(BH4)3 lies between that of LiBH4 and Mg(BH4)2. A direct line-of-site residual gas analyzer mass spectrometer shows that very little diborane and no detectable triborane are released during the decomposition of bulk Li/Mg(BH4)3, which is quite different from Mg(BH4)2 or LiBH4, indicating that the dual-cation borohydride undergoes a different decomposition pathway, and that the reaction pathway related to diborane or triborane formation was suppressed. The nanoconfined Li/Mg(BH4)3 shows a higher cycling capacity as well as a lower decomposition temperature but, in contrast, produces more diborane and triborane in comparison with bulk Li/Mg(BH4)3.

LiVO3 has been considered as a promising cathode material owing to the high specific capacity. But it suffers from the poor rate capability and cyclability. Carbon coating is an effective approach to improve the electrochemical performance, but the synthesis of carbon-coated LiVO3 has not been reported. Herein, we propose a novel method to synthesize carbon-coated LiVO3 (C@LVO) using a simple solution evaporation of LiNO3, VOC2O4 and resol precursors followed by a sync-carbonization strategy. In this approach, VOC2O4 is utilized as the precursor for the first time. Carbon layers and encapsulated LVO are simultaneously generated. An amorphous carbon layer with thickness around 10 nm is observed on the surface of LVO particles using TEM. Compared to bare LVO, C@LVO shows a higher rate capability and more stable cyclability. C@LVO exhibits initial charge and discharge capacities of 281.3 and 339.5 mA h g−1 and features long-term cyclability (125.2 and 125.4 mA h g−1 at 200 mA g−1 after 120 cycles). They possess lower charge-transfer resistance in comparison with bare LVO due to enhanced conductivity of the carbon layer. The higher specific capacity, improved cyclability and rate capability can be greatly attributed to the coated carbon layer, which resists the aggregation of LVO particles, and prevents the side reaction with electrolyte.

A facile and efficient exfoliation process has been reported to produce single- and few-layer nanosheets of MoS2, WS2 and BN using liquid alloys of alkali metals at room temperature. The colloidal dispersions of MoS2 and WS2 layers were highly stable over several months, which allowed us to easily prepare films of MoS2 and WS2 by vacuum filtration or spraying.

Lithium-rich Mn-based layered cathode materials have attracted wide attention due to their high specific capacity for lithium-ion batteries. However, some critical issues i.e. poor rate capability and voltage fade have limited their practical applications. Herein, we propose a synchronous lithiation strategy to coat Li-rich Li1.2Mn0.6Ni0.2O2 (LMNO) with a thin layer of Li+-conductive Li2ZrO3. The obtained syn-Li2ZrO3@LMNO integrates the advantages of the Li2ZrO3 coating and Zr4+ doping, and shows a much higher rate capability and cycling stability than those of the counterpart post-Li2ZrO3@LMNO fabricated by a post-coating method. More importantly, the average voltage of syn-Li2ZrO3@LMNO has been enhanced by 0.15 V and the voltage decay has also been mitigated. New insights into the synergetic modification mechanism of the Li2ZrO3 coating and Zr4+ doping have been proposed. The coating layer of Li+-conductive Li2ZrO3 alleviates the surface side reactions, suppresses the transition metal dissolution and enhances the Li-ion conductivity. Meanwhile, the doping and incorporation of Zr4+ into the host structure accompanied by the Li2ZrO3 coating expands the interplanar spacing and decreases Li/Ni mixing which facilitates Li+ diffusion. In addition, the integration of the Li2ZrO3 coating and Zr4+ doping also further enhances the layered structure stability and mitigates the voltage fade during lithiation/delithiation cycles. Moreover, the proposed synchronous lithiation coating route avoids the duplicated high-temperature calcinations and can also be widely used to modify some other cathode materials.

The design and facile synthesis of noble metal-free efficient cathode catalysts to accelerate the sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a big challenge for lithium–air batteries. In this study, oxygen vacancy-bearing CoO (CoO-A) has been successfully synthesized through a simple calcination of Co(Ac)2·4H2O in Ar, and the oxygen vacancies have been confirmed by Raman spectroscopy, HRTEM, X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS). In comparison with defect-free CoO-N, which is derived from the decomposition of Co(NO3)2·6H2O, an oxygen-deficient CoO-A based cathode shows much higher cycling stability, higher rate capability, higher coulombic efficiency, and lower charge–discharge overpotential. The enhanced performances of the CoO-A based cathode can be largely attributed to the synergetic effect of CoO itself and oxygen vacancies on the promotion of both ORR and OER. CoO provides catalytic activity for ORR, and at the same time the oxygen vacancies not only facilitate the electron and Li+ migration but also act as active sites binding to O2 and Li2O2, which accelerates the OER process. Furthermore, the formation and decomposition of Li2O2 during discharge–charge cycles have also been studied and the results indicate that CoO-A shows a high catalytic activity in the decomposition of Li2O2.

A high performance layered P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material for sodium ion batteries with high rate capability and excellent long-life cyclic performance has been successfully designed and synthesized by a simple sol–gel method. In comparison with the reported Na0.7MnO2, the designed P2-Na0.67Mn0.65Ni0.2Co0.15O2 cathode material can be charged and discharged in an extended voltage range of 1.5–4.2 V and shows reversible capacities of 155, 144, 137, 132 and 126 mA h g−1 at different current densities of 12, 24, 48, 120 and 240 mA g−1, respectively. Even at high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C) it can still deliver capacities of 117, 93 and 70 mA h g−1, respectively, which are much higher than those of the recently reported Na0.5[Ni0.23Fe0.13Mn0.63]O2. In addition, the Na0.67Mn0.65Ni0.2Co0.15O2 cathode material also displays an excellent capacity retention ca. 85% and 78% after 100 cycles at 0.05C and 0.5C, respectively. It is also proposed that Mn4+ may be “activated” in a low voltage range, especially below 2.0 V, which contributes to the additional capacity. The Na-ion diffusion coefficient, DNa+, is ca. 10−14 cm2 s−1 as calculated by the PITT and the discharge diffusion coefficient is a little larger than the charge one. The designed Na0.67Mn0.65Ni0.2Co0.15O2 shows great potential as a cathode material for sodium ion batteries.

NiAl–LDH films with hierarchical morphology have been fabricated by immersion of an Al substrate in Ni2+-containing solutions under strong acidic conditions, and the growth processes of the films are discussed in this communication. The as-prepared LDH films exhibit high activity in the photocatalytic degradation of organic contaminants.

Fluorescent carbon dots (CDs) have attracted great attention in the biomedical field owing to their remarkable fluorescence property, low toxicity, and excellent water solubility. Because of the “water window” effect, the CDs with upconversion fluorescence or longer wavelength downconversion fluorescence are particularly more suitable for bioimaging because they can weaken the auto-fluorescence interferences and penetrate the cell or tissue more deeply. In this study, we reported a facile method to simultaneously enhance the upconversion fluorescence and tune the downconversion luminescence of CDs from blue to green light by simply adding H2O2 in a hydrothermal process. The H2O2-treated green fluorescent CDs with excellent upconversion property showed a high yield of 34% and a quantum yield of 16.5%, and low cell cytotoxicity, which could be directly used for live Hela cell imaging.

Recently, the design and synthesis of high performance cathode materials for sodium ion batteries have attracted great interest. In this study, we propose a novel strategy to design high-rate performance cathode materials for sodium ion batteries through enlarging the d-spacing of the Na-ion diffusion layer. More importantly, some new insights into the expansion mechanism of the interplanar spacing for Na0.67Mn0.8Ni0.1Mg0.1O2 induced by Ni and Mg co-doping and the resulting high-rate capability have been presented for the first time. We find that Mg and Ni co-doping leads to the shortening of the TM–O (TM = transition metal) bond lengths and the shrinkage of the TMO6 octahedrons, which might be largely responsible for the expansion of the interplanar spacing of the Na-ion diffusion layer. In comparison with Na0.67Mn0.8Ni0.2O2 and Na0.67Mn0.8Mg0.2O2, Mg and Ni co-doped Na0.67Mn0.8Ni0.1Mg0.1O2 has a higher Na-ion diffusion coefficient and can deliver around 160, 145, 133 and 124 mA h g−1 at 24, 48, 120 and 240 mA g−1, respectively. In particular, at the high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C), MMN can still offer reversible capacities of 110, 66 and 37 mA h g−1, respectively. In addition, the cycling stability has also been enhanced via Mg and Ni co-doping at the same time, which means that Mg and Ni co-doping also has a positive effect on the stability of the layered structure.