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Lithium-oxygen batteries (LOBs) have been extensively studied as an attractive secondary battery due to their ultra-high energy density. However, its high charging voltage, poor cycle stability, and low rate performance make its practical applications very limited. Since the positive electrode is the main reaction site of LOBs, improving the structure and catalytic activity of the cathode catalyst is the key method to improve the electrochemical performance. In this work, colored titanium dioxide nanoparticles were synthesized by calcination in argon. Raman and XPS confirmed the existence of more oxygen vacancies and Ti3+ in black TiO2 than gray one. HRTEM analysis also reveals the defective layers of 2–3 nm on the TiO2 surface. Due to the high electrical conductivity and good catalytic activity promoted by oxygen vacancies and Ti3+ ions, the black TiO2-based cathodes have good electrochemical activity and enhanced cycling stability for LOBs. Compared with the gray TiO2 (4.3 V), the black TiO2 nanoparticles show a low overpotential with the charge voltage of 3.7 V. The charging voltage significantly reduced approximately 600 mV, which reduces the battery's side reactions and polarization, and thus enhances the cycling performance of the battery. When the cut-off capacity is 500 mAh g−1, it can run for 108 cycles without significant change in terminal voltage, indicating that black TiO2 is an efficient catalyst for LOBs.

Transition metal oxides have shown an extraordinary potential for lithium-storage capability to date. However, it remains enormous challenge to gain high capacities, good rate performance and cyclability due to their inferior conductivity. To address this issue, oxygen vacancies (VOs) implanted ultrathin WO3 nanorods (the diameter around 5 nm and the length less than 100 nm) composed with reduced graphene oxide (namely WO3-x/rGO), were synthesized by proposing a logical design. For the sake of better showing the outcome of such configuration, holy nanosheets of pure WO3 anode were proposed to compare with nanorods WO3-x/rGO one in terms of electrochemical properties, and they were obtained via annealing H2WO4/rGO precursor in air and argon atmosphere with the same annealing ramp, respectively. By contrast, both electron paramagnetic resonance and X-ray photoelectron spectroscopic characterizations demonstrate the existence of VOs in WO3-x/rGO composite. The generation of VOs together with the reserve of rGO, the conductivity of WO3-x/rGO anode is distinctly enhanced, which is then verified by the compared electrochemical performance in this work. It is clearly shown that the WO3-x/rGO nanocomposite displays a capacity of 745 mAh g−1 at a current density of 0.1 A g−1 after 200 cycles and excellent cycling stability up to 1000 cycles with capacity of 428 mAh g−1 at 1 A g−1. These findings exhibit that nanorods WO3-x/rGO nanocomposite is a promising candidate for high-performance Li-ion battery anode.

Application of the graphene-based composites in practice was hampered due to the lack of the controllable synthesis strategy. To solve the problem, we envisaged the organic nanodroplets as a nano-reaction environment to obtain the organic nanoframes by photo-polymerization, then to directly graphitize for the graphene-based materials. In such strategy, two-dimensional laminar matrix of graphene nanosheets (2DLMG) was obtained with millimeter-scale surface, which rendered the matrix high electron conductivity. Thanks to the confinement effect of the nanodroplets, the composited materials were homogeneously dispersed in the organic nanoframes. Then, the organic nanoframes converted directly to 2DLMG-based composites after calcination. In this paper, the transformation from organic nanoframes to 2DLMG has been revealed in detail by comprehensive analyses from SEM, XRD and XPS. To demonstrate the versatility of 2DLMG, the superiority in lithium ion battery has been indicated by the high specific capacity (565 mA h g−1), high cycling performance after 500 cycles and the 100% retention capacity in rate measurement. For the synthesis of the composites, Sn nanoparticles and γ-Fe2O3 nanoparticles were distributed in 2DLMG without the aggregation with high loading. The proposed organic molecule confinement reaction strategy was expected to point out a promising direction for the preparation of graphene-based materials.

A novel nitrogen and oxygen dual-doped porous carbon (NOPC) has been prepared from the aerial roots of ficus microcarpas through a facile carbonization and activation approach using KOH as the chemical activating agent. The obtained NOPC has very large specific surface area of 2294 m2 g−1 and high pore volume of 1.15 cm3 g−1. Thanks to the high specific surface area and the doping of nitrogen and oxygen, the prepared NOPC/S cathode with a sulfur content of 55.9% shows a high initial discharge capacity of 1338 mA h g−1 at 0.1 C and retains 1047 mA h g-1 after 200 cycles. What is more, the NOPC/S-62.9% cathode also remains high capacity of 1036 mA h g-1 and the coulomb efficiency remains 98.3% after 200 cycles. Taking into account of the low cost, green and sustainable development, NOPC/S composites show good prospects in the application of lithium-sulfur batteries.

Layered two-dimensional MoSe2 has raised much interest in lithium/sodium ion batteries (LIBs/SIBs) due to its unique structure and high theoretical capacity. In this work, we have fabricated MoSe2@carbon cloth (MoSe2@CC) composites through an in situ hydrothermal approach followed by an annealing treatment. The as-synthesized MoSe2@CC composites are constructed by MoSe2 nanoflowers anchored on CC network, which can be directly used as binder-free anodes for LIBs and SIBs. As an anode for LIBs, the MoSe2@CC performs excellent rate capacity (1337, 1092, 952, 831 and 749 mAh g−1 at current densities of 0.1, 0.2, 0.5, 1.0, and 2.0 A g−1) and super long-life cycling stability (638 mAh g−1 remains after 1200 cycles at 5 A g−1). As for SIBs, the MoSe2@CC electrode delivers a high initial discharge capacity of 839 mAh g−1 and excellent long-life cycling stability, retaining 202 mAh g−1 after 1000 cycles. Kinetics results indicate that the Li+ and Na+ storages in MoSe2@CC are both dominated by surface-based pseudocapacitive process, which greatly improves the rate performance of LIBs/SIBs. The CC provides a conductive network and an excellent utilization rate of the active material MoSe2 to improve the electrochemical performance.

Sn@Graphene composites as anode materials in Lithium-ion batteries have attracted intensive interest due to the inherent high capacity. On the other side, the high atomic ratio (Li4.4Sn) induces the pulverization of the electrode with cycling. Thus, suppressing pulverization by designing the structure of the materials is an essential key for improving cyclability. Applying the nanotechnologies such as electrospinning, soft/hard nano template strategy, surface modification, multi-step chemical vapor deposition (CVD), and so on has demonstrated the huge advantage on this aspect. These strategies are generally used for homogeneous dispersing Sn nanomaterials in graphene matrix or constructing the voids in the inner of the materials to obtain the mechanical buffer effect. Unfortunately, these processes induce huge energy consumption and complicated operation. To solve the issue, new nanotechnology for the composites by the bottom-up strategy (Organic Molecule Confinement Reaction (OMCR)) was shown in this report. A 3D organic nanoframes was synthesized as a graphene precursor by low energy nano emulsification and photopolymerization. SnO2 nanoparticles@3D organic nanoframes as the composites precursor were in-situ formed in the hydrothermal reaction. After the redox process by the calcination, the Sn nanoparticles with nanovoids (~100 nm, uniform size) were homogeneously dispersed in a Two-Dimensional Laminar Matrix of graphene nanosheets (2DLMG) by the in-situ patterning and confinement effect from the 3D organic nanoframes. The pulverization and crack of the composites were effectively suppressed, which was proved by the electrochemical testing. The Sn nanoparticles@2DLMG not delivered just the high cyclability during 200 cycles, but also firstly achieved a high specific capacity (539 mAh g−1) at the low loading Sn (19.58 wt%).

Lithium-sulfur (Li-S) battery is an appealing technology due to its conspicuous advantages in the area of energy storage. However, many challenges remain, such as the design of cathode with high sulfur loading, suppression of shuttle effects, enhanced performance and large scale preparation. Here, we report a novel 3D free-standing nitrogen-doped porous carbon foam (PCF) obtained by carbonization of the natural melaleuca bark, and apply it as a binder-free current collector to host sulfur for Li-S cells. This study shows that the obtained N-doped PCF possesses sheet-like porous carbon structures, high specific surface area, and large pore volume. Taking advantage of these properties, the resulting PCF/S electrodes exhibit an initial discharge capacity of 1330 mAh g−1, good reversible capacity of 880 mAh g−1 after 100 cycles at 0.2 C and deliver an excellent cycling stability (over 250 cycles at 0.5 C with 0.14% capacity fading per cycle). In addition, the PCF/S electrodes with large areal mass loading of 6 mg cm−2 show a high areal capacity of 4.14 mAh cm−2, revealing a great potential for high energy Li-S batteries.

Porous carbon materials are considered as a promising sulfur host for lithium–sulfur (Li–S) batteries. However, many porous carbon materials are prepared by complicated preparation processes, facing challenges including low yields, toxic chemicals, and high-energy consumption. In this work, a simple method is reported for the preparation of mesoporous carbon with a high surface area (2166 m2 g−1) and an ultra large pore volume (4.09 cm3 g−1) by the direct carbonization of an adipic acid and zinc powder mixture without further chemical/physical activation process. The mesoporous carbon is composed of nanosheets with abundant capsule-like nanopores of around 15 nm, exhibiting a hierarchically assembled flower-like structure. The porous carbon nanosheets (PCNSs) with a hierarchical structure are used as the host for sulfur to form a homogeneous composite (S/PCNS) through a conventional heat infiltration process. Excellent electrochemical performance is achieved with S/PCNS as the cathode of a Li–S battery. The S/PCNS composite with 62 wt% sulfur exhibits an initial discharge capacity of 1384 mA h g−1 and retains a reversible capacity of 657 mA h g−1 after 100 cycles at 0.2C rate. Remarkably, the S/PCNS composite exhibits a decay rate of only 0.046% per cycle within 500 cycles at 1C rate. The high surface area, large pore volume, and sheet-like two-dimensional (2D) structure of the micro/mesoporous carbon matrix render the sulfur-based cathode with superior electrochemical kinetics, rate capability, and long-life performance.

Sn-based anode for lithium-ion batteries (LIBs) has been received extensive concern, due to its high theoretical specific capacity. However, its poor stability induced by serious volume changes during charge/discharge process limits its application. MoS 2 possesses a 2-dimisional (2D) graphene-like layered structure facilitates lithium ions insertion and extraction and can be served as the buffer to alleviate the volume variation. Unfortunately, 2D MoS2 nanosheets are highly susceptible to stacking/restacking during cycles, which is fatal to their capacity retention. Herein, a novel MoS2@SnO2-SnS2 composite has been designed and fabricated via a two-step simple hydrothermal route. Due to the synergistic effect between the ultrathin MoS2 nanosheets and the SnO2-SnS2 nanosheets, the MoS2@SnO2-SnS2 composite exhibits excellent electrochemical performance as anode for LIBs.

ZnCo2O4/ZnO/carbon nanotubes (ZZCO/CNTs) nanocomposite is fabricated via a facile and rapid strategy of microwave-irradiation process followed by annealing. The nanocomposites are composed of ZnCo2O4/ZnO (ZZCO) nanocrystals (~ 5 nm) coated on the surfaces of carbon nanotubes, and the introduction of carbon nanotubes can greatly improve the conductivity and stability of the hybrid material and effectively prevent the aggregation of ZZCO nanoparticles. When considered as an anode material for lithium-ion batteries, the as-synthesized ZZCO/CNTs nanocomposite exhibits a high-reversible specific capacity of around 1440 mAh g−1 at the current density of 100 mA g−1, excellent cycling stability up to 200 cycles at a high current density of 500 mA g−1 and superior rate performance.

Lithium metal batteries (LMBs) are favored due to their high energy densities. However, how to inhibit the growth of Li dendrites, slow down the volume expansion and realize the reversible utilization of Li anode are still big challenges for the practical feasibility. Herein, a pre-lithiated edge-enriched ultra-thin MoS2 embedded carbon nanofiber (PCNF/MoS2) framework was prepared as a protective layer to stablize Li metal anode, Mo and Li2S was in situ formed on the surface of Li foil by a facile spontaneous chemical reaction of MoS2 and Li. Among them, Mo significantly reduces the overvoltage of the Li nucleation, achieves homogeneous Li plating/stripping, guides Li deposition in the cavity of three-dimensional (3D) framework, and thus inhibits the Li dendrites growth. More importantly, Li2S, as an effective additive, facilitates uniform and robust solid electrolyte interface (SEI) formation with excellent chemical stability and high ionic conductivity, which successfully realizes stable Li anode. Thereafter, the PCNF/MoS2-Li composite anode exhibits excellent long cycle life over 750 h at 1 mA cm−2 with a capacity of 1 mAh cm−2 in the symmetrical cell. In addition, when the PCNF/MoS2-Li composite anodes were paired with LiFePO4 and LiNi0.8Co0.1Mn0.1O2 cathodes, the batteries delivered improved cycling stability and rate performance, providing a promising new avenue to achieve pratical LMBs.

Lithium-oxygen (Li-O2) battery is regarded as one of the potential energy storage system due to the ultra-high theoretical energy density and environmental friendliness. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) severely limited the discharge/charge efficiency. Herein, the single-atom Ru anchored N-doped reduced graphene oxide nanosheets (Ru-N/rGO) was fabricated via a simple impregnation method. When employed as cathode for Li-O2 battery, the Ru-N/rGO delivers a higher discharge capacity, a lower overpotential and better rate performance in comparison with pure N-rGO without Ru atoms. Based on the in situ DEMS, the e-/O2 ratio of Ru-N/rGO (2.08) is close to the theoretical value for the desired O2 reduction to Li2O2 (2.00), suggesting the discharged product is mainly Li2O2. The density functional theory simulations reveal that the Ru single atoms offer high catalytic activity for OER and ORR. This work gives insight for the application of single atoms in advanced rechargeable Li-O2 batteries.

Probing the microstructure evolution, phase change, and fundamental conversion mechanism of anodes for lithium ion batteries (LIBs) during lithiation–delithiation cycles is important to gain insights into understanding how the electrode works and thus how it can be improved. The electrochemical reaction and phase evolution of Mn3O4 during lithiation–delithiation cycles remain unknown. To observe the real-time electrochemical behaviors of Mn3O4 during lithiation–delithiation cycles, a nanosized LIB was constructed inside a transmission electron microscope (TEM) using an individual Mn3O4/graphene moiety as the anode. Upon the first lithiation, Mn3O4 nanoparticles are lithiated into the crystallized Mn nanograins embedded within the Li2O matrix. However, Mn and Li2O cannot be recovered to the original Mn3O4 phase but to MnO after the first full delithiation, which results in an irreversible phase transformation. Such incomplete conversion reaction accounts for the huge capacity fading during the first cycle ...

SnO 2 quantum dots/reduced graphene oxide (SnO 2 /rGO) composite has been successfully prepared by a rapid microwave-irradiation process and subsequent annealing treatment. SEM and TEM results reveal that SnO 2 quantum dots with the sizes of 1–5 nm are uniformly anchored on rGO nanosheets. The SnO 2 /rGO composite as an anode material presents a high initial discharge capacity of 1628 mAh/g and maintains a reversible capacity of 797 mAh/g after 100 cycles. After being cycled at various rates for 100 cycles, the capacity can recover to 777 mAh/g at 100 mA/g. The high reversible capacity, long cycling life and good rate performance can be attributed to the size effect of SnO 2 quantum dots and the synergistic effect from rGO nanosheets.

Nanosized anode materials have been shown to be successful in addressing the problems of metal oxide anodes during electrochemical reactions. However, issues with low Coulombic efficiencies and poor cyclability of nanostructured metal oxide anodes still need to be resolved. Ultrafine CuCo 2 O 4 nanoparticles of 6∼9 nm uniformly anchored on graphene have been synthesized. CuCo 2 O 4 /graphene (CuCo 2 O 4 /G) composites show superior lithium-storage performances. A high reversible capacity of 1040 mAh g −1 is achieved at 0.1 C after 80 cycles, and can retain 211 mAh g −1 at a current density of 2 C. Furthermore, the lithiation process of CuCo 2 O 4 /G was recorded by TEM. It suggests the Li + diffuse through an individual CuCo 2 O 4 nanoparticle consists of three stages: (1) the insertion of Li + without crystalline structure change, (2) the nanoparticle’s crystalline lattice collapses, and (3) nanograins grow and reform from the collapsed nanoparticle. The lithium conversion resulting in the formation of a network of many ultrafine nanograins (2 nm) embedded in the Li 2 O matrix; also these ultrafine nanograins are confined in a layer of crystal, which is beneficial for the improved electrochemical performance. The macroscopic electrochemical performance of CuCo 2 O 4 /G was further correlated with the microcosmic in situ TEM results.

All solid-state composite polymer electrolyte (CPE) is considered to be the key to solving the high safety and long life of solid Li metal batteries (LMBs), but there are few CPEs that can suppress the side reactions of the cathode and achieve dendrite-free plating simultaneously. Here, a sandwiched structure CPE (SCPE) is prepared through a layer-by-layer coating process. Oxidation resistant polyacrylonitrile (PAN) and reduction resistant polyethylene oxide (PEO) are used to contact with cathode and anode respectively to protect “polymer-in-ceramic” (PIC)-CPE in SCPE. In which, PAN-CPE contacts with LiNi0.8Mn0.1Co0.1O2 (NCM811) to form a stable interface, and PEO-CPE contacts with lithium (Li) to avoid reduction, thus ensuring high-voltage tolerance. More importantly, the synergistic effect of different CPEs in SCPE significantly facilitates high Li ion conductivity, wide electrochemical window, strong mechanical property and stable electrolyte/electrode interface. As a result, the Li symmetric cell using SCPE can be cycled over 500 h without voltage hysteresis. The NCM811/Li battery assembled with SCPE exhibits excellent cycle stability (88% after 500 cycles), and high Coulombic efficiency (over 99.2% after 500 cycles). This work proposes an approach to develop a low-cost, safe, and promising CPE to achieve high safety LMBs.

CoFe2O4 quantum dots/N-doped graphene (CoFe2O4 QDs/N-G) composites have been successfully fabricated through a facile strategy involving a hydrothermal process and subsequent calcination at high temperature. Uniform nanoparticles with high density are homogeneously anchored on the surfaces of graphene sheets. The CoFe2O4 QDs with a distribution within 4–12 nm can be observed clearly, and there is no apparent aggregation of CoFe2O4 QDs on the graphene nanosheets. The CoFe2O4 QDs/N-G obtained as an anode material for LIBs presents an initial discharge capacity of 1616 mAh g−1 and maintains a reversible capacity of 1223 mAh g−1 after 90 cycles at a current of 100 mA g−1. The gradual capacity increase with cycling results primarily from the formation of Co3+ during the electrochemical process. After being cycled at various rates for 90 cycles, the capacity can recover to 1239 mAh g−1 when the current is switched to 100 mA g−1. This superior lithium-storage performance can be attributed to the quantum and size effects of CoFe2O4 quantum dots and the excellent electrochemical properties of N-doped graphene.

A carbon nanotube/polyaniline/graphene (MWCNT–PANI–G) composite as sulfur host has been prepared by a simple self-assembly approach with potential application for lithium–sulfur (Li–S) batteries. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the microstructures and morphology of the as-prepared samples. It is demonstrated that the sulfur can be evenly impregnated into the MWCNT–PANI–G composite with strong chemical bonding. The resultant S@MWCNT–PANI–G composite with a sulfur content of 68 wt% shows excellent electrochemical performance as cathode for Li–S batteries. It delivers a high initial discharge capacity up to 1290 mA h g−1, good capacity retention of 784 mA h g−1 after 100 cycles of charge/discharge at the current density of 330 mA g−1, and good rate capability of 663 mA h g−1 and 548 mA h g−1 at 1.65 and 3.3 A g−1, respectively. The remarkable electrochemical performances are mainly attributed to the unique architecture of MWCNT–PANI–G with an enhanced electronic and ionic conductivity. Furthermore, this special architecture can provide strong physical and chemical confinement to the active materials and the soluble lithium polysulphides. Therefore, our study demonstrates a facile and low-cost approach to fabricate cathode materials for high-performance Li–S batteries.

Three-dimensional (3D) porous carbon-coated ZnFe2O4 nanospheres/N-doped graphene aerogels (ZnFe2O4@C/N-G) have been synthesized via a facile hydrothermal method. The obtained ZnFe2O4@C hierarchical nanospheres with a size distribution of 150–210 nm are uniformly encapsulated within the graphene aerogels matrix. The ZnFe2O4@C/N-G composites as anode materials for Li-ion batteries demonstrate a high initial discharge capacity of ~1176 mA h g−1 with an initial coulombic efficiency of ~71.1% at a rate of 100 mA g−1. Moreover, a significantly enhanced reversible capacity of 952 mA h g−1 is retained after 100 cycles. After being cycled at various rates for 100 cycles, the capacity can reincrease to 955 mA h g−1 when the specific current returns back to 100 mA g−1. The improved electrochemical performance is attributed to the unique architectures of the carbon layer (~2 to 4 nm) and 3D porous N-doped graphene aerogels.

A freestanding nitrogen-doped graphene functional interlayer placed between the sulfur cathode and the separator has been investigated to enhance the electrochemical performance for lithium-sulfur (Li-S) batteries. The interlayer with three-dimensional porous structure and abundant of N-doping active sites, not only can increase electron transport pathway and the storage capacity of liquid electrolyte, but also can physically and chemically adsorb the highly soluble lithium polysulfides to reduce the loss of active material. With a pure sulfur electrode (high sulfur content of 70 wt%), the as-assembled Li-S battery delivers a high initial discharge capacity up to 1481 mAh g −1 at a rate of 0.1C, and maintains a reversible capacity of 956 mAh g −1 after 50 cycles of charge/discharge. Comparing with conventional cells, we have highly improved the electrochemical performance for Li-S batteries.

We present a novel strategy to prepare MnCo 2 O 4 /graphene composites on nickel foam. TEM analysis reveals that high density of MnCo 2 O 4 nanoparticles of ~5–10 nm are uniformly anchored on graphene nanosheets. The MnCo 2 O 4 /graphene-anchored Ni foams are used as binder-free integrated anodes for lithium ion batteries (LIBs) and exhibit superior lithium-storage performance. The MnCo 2 O 4 /graphene composites exhibit high cycling stability (868 mAh/g at 100 mA/g) and good rate capacity (607 mAh/g at 1.6 A/g) as anode materials for LIBs. The prominent electrochemical performance is associated with the synergistic effects of 3D porous Ni foam and graphene, which promote electron transfer and buffer the large volume fluctuation of metal oxides during the lithiation/delithiation progress.

A desirable oxygen electrode is critical for achieving high capacity Li-O2 battery. Here we have fabricated porous Mo2C/C nanoflowers assembled by ultrathin carbon nanosheets decorated with Mo2C quantum dots using in situ synthesis technique and the subsequent anneal treatment. When evaluated as cathode for Li-O2 battery, the Mo2C/C delivers a relatively high specific capacity of 7500 mAh g-1. With a cut-off capacity of 500 mAh g-1, the Li-O2 battery exhibits an excellent cycling stability for 100 cycles without obvious capacity fading. The battery shows the low discharge/charge gaps of 1.2 V in the first cycle, suggesting the excellent catalytic activity of Mo2C/C for ORR and OER. The excellent performance maybe ascribed to the synergistic effect of ultrathin carbon nanosheets, highly-dispersed Mo2C quantum dots and the special porous structure. The ultrathin carbon nanosheets not only effectively prevent the Mo2C quantum dots from agglomeration, but also improve the conductivity of Mo2C. In addition, the ultrathin carbon nanosheets and porous Mo2C/C nanoflowers could ensure the fast Li+ and O2 diffusion.

Lithium metal batteries (LMBs) are generally regarded as one of the alternatives for high energy density devices. However, the commercial application of LMBs is seriously restricted by volume changes and dendrite behavior of lithium metal, which cause low efficiency and poor safety. In the present study, and inspired by the structure of the lotus root (which has many interior parallel channels that significantly enlarges the contact area), we have designed lotus root-like 3D multichannel carbon fibers (MCNFs) that are decorated with lithiophilic Ag nanoparticles (Ag NPs). These adhered lithiophilic Ag nanoparticles will facilitate molten Li infusion into the carbon channels, forming stable lithium metal anodes. The ion concentration gradient near the surface Ag protrusions will become reduced, thereby inducing homogeneous nucleation and deposition of Li. The produced multi-channels will provide enough space for volume expansion of Li metal during cycling. As a result, when coupled with a LiFePO4 (LFP) cathode, the MCNF/Ag-Li composite anode maintained 94.7% of its capacity, and 99.1% of the Coulombic efficiency after 600 cycles at 1 C. Moreover, the MCNF/Ag-Li|Li symmetrical cell could be cycled for more than 600 h, with a low hysteresis of 20 mV (at 1 mA cm−1), and with the capacity of 1 mAh cm−1 during the whole cycle (without any short-circuit). These results suggest that anodes, made of a lotus root-like 3D multichannel lithium metal composite material, will have the potential to promote the practical applications of lithium metal batteries.

The working principle of Li–air (Li–O2) batteries is based on the formation/decomposition of Li2O2 on the catalytic electrode, which is basically different from the shuttle mechanism of Li-ion batteries. The successful operation of Li–O2 batteries requires an optimized cathode that is electrochemically/chemically stable, mechanically robust, and catalytically active. In this work, we proposed a unique design of a binder/carbon-free catalytic cathode consisting of knitted Co3O4 nanowires and decorated Ru nanoparticles. It was found that the Co3O4/Ru-catalyzed Li–O2 batteries exhibit considerably higher capacity and much improved cycling performance than the Co3O4-catalyzed ones. When the capacity is limited at 500 mA h g−1, the Co3O4/Ru-catalyzed battery can sustain a stable cycling of 29 times. The stable cycling can last 122 times at a limited capacity of 300 mA h g−1. This result indicates that the catalytic performance and structural stability of the cathodes are equally important to achieve a high performance of Li–O2 batteries.

ZnCo2O4/N-doped three-dimensional graphene (N-3DG) composite is successfully prepared by a facile two-step method involving a solvothermal process and subsequent annealing treatment. SEM and TEM results reveal that ZnCo2O4 nanoparticles with a size of 20–40 nm are uniformly embedded within 3D graphene matrix. The ZnCo2O4/N-3DG composite as an anode material presents a high initial discharge capacity of 1654 mAh/g and maintains a reversible capacity of 1102 mAh/g after 150 cycles. After being cycled at various rates for 90 cycles, the capacity can recover to 721 mAh/g at 80 mA/g. The high reversible capacity, long cycling life and good rate performance can be attributed to the 3D interconnected architecture and the excellent properties of N-doped graphene.

Porous Co3O4 nanosheets anchored on graphene nanosheets were synthesized by microwave irradiation method. The obtained Co3O4–graphene sheet-on-sheet nanocomposite as an anode material for LIBs demonstrates a high initial discharge capacity of 1359.6 mAh g−1 with a Columbic efficiency of 72.7% at a rate of 100 mA g−1. Moreover, a significantly enhanced reversible capacity of ∼1036.9 mAh g−1 is retained after 50 cycles, and the capacity can reincrease to 1068 mAh g−1 when the current density returns back to 100 mA g−1 after cycled at various rates for 50 cycles. The improved electrochemical performance is attributed to the unique architectures of the porous Co3O4 nanosheets and the incorporation of graphene nanosheets. Therefore, this nanocomposite is widely considered to be an attractive candidate as an anode material for next-generation LIBs.

The electrochemical conversion behavior of metal oxides as well as its influence on the lithium-storage performance remains unclear. In this paper, we studied the dynamic electrochemical conversion process of CuO/graphene as anode by in situ transmission electron microscopy. The microscopic conversion behavior of the electrode was further correlated with its macroscopic lithium-storage properties. During the first lithiation, the porous CuO nanoparticles transformed to numerous Cu nanograins (2-3 nm) embedded in Li2O matrix. The porous spaces were found to be favorable for accommodating the volume expansion during lithium insertion. Two types of irreversible processes were revealed during the lithiation-delithiation cycles. First, the nature of the charge-discharge process of CuO anode is a reversible phase conversion between Cu2O and Cu nanograins. The delithiation reaction cannot recover the electrode to its pristine structure (CuO), which is responsible for about ∼55% of the capacity fading in the first cycle. Second, there is a severe nanograin aggregation during the initial conversion cycles, which leads to low Coulombic efficiency. This finding could also account for the electrochemical behaviors of other transition metal oxide anodes that operate with similar electrochemical conversion mechanism.

Here we report a simple, low-cost and high yield strategy for porous carbon nanosheets (PCNS) with a high specific surface area using corncob waste material as carbon source. The PCNS are used as the conducting matrix for sulfur to form sulfur/porous carbon nanosheets (S/PCNS) composites, which are applied as cathodes for lithium–sulfur (Li–S) batteries. The S/PCNS composites exhibit a high initial discharge capacity of about 1600 mAh g−1 and maintain a reversible capacity of 554 mAh g−1 after 50 cycles. The superior performance is attributed to the highly porous structure of two-dimensional carbon nanosheets that not only enables stable and continue pathway for rapid electron and ion transportation, but also restrain soluble polysulfides and suppress the “shuttle effect”. The large surface area and unique sheet-like two-dimensional structure of PCNS also leads to a high utilization of sulfur, indicating a promising cathode material for Li–S batteries.

Ultrafine tin dioxide (SnO 2 ) nanocrystals anchored graphene composite is synthesized by a simple hydrothermal method. Well-defined SnO 2 nanocrystals with size of ∼5 nm are uniformly anchored on the graphene sheets. The two-dimensional nanostructure inherits the advantages of graphene, which possesses high electrical conductivity and large surface area. Furthermore, the ultrafine SnO 2 nanocrystals anchoring on graphene sheets facilitate fast ion transportation and prevent aggregation. As a result, the produced nanocomposite exhibits an excellent cycling stability and rate capability for lithium storage (808 mAh g −1 after 100 cycles at 200 mA g −1 , 1290 mAh g −1 at the current of 50 mA g −1 after being cycled at various current densities for 60 cycles).

Highlights: • A one-pot solvothermal route is developed for synthesizing ZnFe{sub 2}O{sub 4}/graphene nanocomposites. • ZnFe{sub 2}O{sub 4} nanospheres with a size of about 100–200 nm are uniformly dispersed on graphene nanosheets. • The nanocomposite delivers a reversible capacity of 704 mAh/g after 50 cycles. • The improved lithium-storage performance is ascribed to the confining and conducting effects of graphene nanosheets. - Abstract: We report a facile one-pot solvothermal route for synthesizing ZnFe{sub 2}O{sub 4}/graphene nanocomposites. XRD, SEM and TEM results demonstrate that ZnFe{sub 2}O{sub 4} nanospheres with a size of about 100–200 nm are uniformly dispersed on graphene nanosheets. Each ZnFe{sub 2}O{sub 4} nanosphere is assembled by many nanoparticles around 10 nm. When evaluated as anode for Li-ion batteries, ZnFe{sub 2}O{sub 4}/graphene nanocomposites deliver a first discharge capacity of 1400 mAh g{sup −1} and remain a reversible capacity up to 704.2 mAh g{sup −1} after 50 cycles. ZnFe{sub 2}O{sub 4}/graphene nanocomposites also exhibit ameliorative rate capacity of 271.8 mAh g{sup −1} at the current of 800 mA g{sup −1}, which can recover to 814 mAh g{sup −1} when the current density is reduced back to 100 mA g{sup −1}. The enhanced electrochemical performances of the nanocomposites are ascribed tomore » the confining and conducting effects of graphene and the synergistic effects between the conductive graphene and ZnFe{sub 2}O{sub 4} nanospheres.« less

Carbon-coated Fe 3 O 4 quantum dots/graphene composite was prepared via a hydrothermal and calcining process. XRD and TEM analysis revealed that carbon-coated Fe 3 O 4 quantum dots with a size around 7–10 nm were distributed uniformly on graphene nanosheets. The carbon shell can preserve structural stabilization of Fe 3 O 4 nanoparticles by preventing the aggregation and buffering the volume expansion during charge/discharge processes. In addition, the graphene nanosheets formed a three-dimensional network for the transportation of Li + ions and electrons. When evaluated as anode material for lithium-ion batteries, the nanocomposite showed an improved lithium-storage performance with high cycling stability and good rate capacity. Furthermore, it exhibited an initial discharge capacity of 1300 mA h/g and retained a reversible capacity of about 940 mA h/g after 100 cycles at a current density of 150 mA/g.

A sulfur/graphene composite is prepared by loading elemental sulfur into three-dimensional graphene (3D graphene), which is assembled using a metal ions assisted hydrothermal method. When used as cathode materials for lithium–sulfur (Li–S) batteries, the sulfur/graphene composite (S@3D-graphene) with 73 wt % sulfur shows a significantly enhanced cycling performance (>700 mAh g −1 after 100 cycles at 0.1C rate with a Coulombic efficiency > 96%) as well as high rate capability with a capacity up to 500 mAh g −1 at 2C rate (3.35 A g −1 ). The superior electrochemical performance could be attributed to the highly porous structure of three-dimensional graphene that not only enables stable and continue pathway for rapid electron and ion transportation, but also restrain soluble polysulfides and suppress the “shuttle effect”. Moreover, the robust structure of 3D graphene can keep cathode integrity and accommodate the volume change during high-rate charge/discharge processes, making it a promising candidate as cathode for high performance Li–S batteries.

Lithium–sulfur (Li–S) battery with high theoretical energy density is one of the most promising energy storage systems for electric vehicles and intermittent renewable energy. However, due to the poor conductivity of the active material, considerable weight of the electrode is occupied by the conductive additives. Here we report a graphene-wrapped sulfur nanospheres composite (S-nanosphere@G) with sulfur content up to 91 wt% as the high energy density cathode material for Li–S battery. The sulfur nanospheres with diameter of 400–500 nm are synthesized through a solution-based approach with the existence of polyvinylpyrrolidone (PVP). Then the sulfur nanospheres are uniformly wrapped by conductive graphene sheets through the electrostatic interaction between graphene oxide and PVP, followed by reducing of graphene oxide with hydrazine. The design of graphene wrapped sulfur nanoarchitecture provides flexible conductive graphene coating with void space to accommodate the volume expansion of sulfur and to minimize polysulfide dissolution. As a result, the S-nanosphere@G nanocomposite with 91 wt% sulfur shows a reversible initial capacity of 970 mA h g −1 and an average columbic efficiency > 96% over 100 cycles at a rate of 0.2 C. Taking the total mass of electrode into account, the S-nanosphere@G composite is a promising cathode material for high energy density Li–S batteries.

Despite the recent advancements in Li-O(2) (or Li-air) batteries, great challenges still remain to realize high-rate, long-term cycling. In this work, a binder-free, nanostructured RuO(2)/MnO(2) catalytic cathode was designed to realize the operation of Li-O(2) batteries at high rates. At a current density as high as 3200 mA g(-1) (or ∼1.3 mA cm(-2)), the RuO(2)/MnO(2) catalyzed Li-O(2) batteries with LiI can sustain stable cycling of 170 and 800 times at limited capacities of 1000 and 500 mA h g(-1), respectively, with low charge cutoff potentials of ∼4.0 and

Carbon-coated ZnFe2O4 spheres with sizes of ~110–180 nm anchored on graphene nanosheets (ZF@C/G) are successfully prepared and applied as anode materials for lithium ion batteries (LIBs). The obtained ZF@C/G presents an initial discharge capacity of 1235 mAh g−1 and maintains a reversible capacity of 775 mAh g−1 after 150 cycles at a current density of 500 mA g−1. After being tested at 2 A g−1 for 700 cycles, the capacity still retains 617 mAh g−1. The enhanced electrochemical performances can be attributed to the synergetic role of graphene and uniform carbon coating (~3–6 nm), which can inhibit the volume expansion, prevent the pulverization/aggregation upon prolonged cycling, and facilitate the electron transfer between carbon-coated ZnFe2O4 spheres. The electrochemical results suggest that the synthesized ZF@C/G nanostructures are promising electrode materials for high-performance lithium ion batteries.

Porous Co3O4 microrods have been prepared by an ultrasound-assisted route with subsequent calcination. The as-prepared Co3O4 microrods are composed of interconnected nanoparticles with porous characteristics. The ultrasonic irradiation is critical to determine the morphology and the electrochemical performance of the products. When tested as anode material for lithium-ion battery, the porous Co3O4 microrods show improved capacity and rate cycling performance. The reversible capacity of the materials retains 678 (±5) mAh g−1 after 50 cycles at 100 mA g−1. Even when cycled at various rate for more than 50 cycles, the reversible capacity recovers to 600 (±5) mAh g−1 for the current of 100 mA g−1. The improved lithium-storage performance can be attributed to the reduced electrochemical reaction resistance due to the unique porous architecture of Co3O4 microrods.

CuO–Cu 2 O/graphene composite has been successfully prepared by the combination of a microwave-assisted process and subsequent annealing. X-ray diffraction and electron microscopy reveals that copper oxide nanospheres with a size of 120–200 nm are uniformly anchored on graphene nanosheets. The copper oxide nanospheres are composed of numerous CuO and Cu 2 O nanocrystals of ∼10 nm. These nanospheres are hollow and the thickness of the shells is around 50–70 nm. The CuO–Cu 2 O/graphene composite shows a highly reversible capacity and excellent rate performance as anode for Li-ion battery. The reversible capacity of the composite retains 487 mA h g −1 after 60 cycles at 200 mA g −1 . Even when cycled at various rate (200, 500, 1000, 2000, 5000 mA g −1 ) for 60 cycles, the capacity can recover to 520 mA h g −1 at the current of 200 mA g −1 . The enhanced electrochemical performances are ascribed to the hollow spherical architectures, excellent conductivity of graphene sheets, and possible synergistic effects between CuO, Cu 2 O and graphene that enhance the intrinsic properties of each component.

A novel graphene-wrapped carbon nanotube/sulfur structure was designed to improve the electrochemical performance of the lithium–sulfur (Li–S) batteries. Owing to the introduction of the reduced graphene oxide (rGO) with the aim to restrain the polysulfide anions diffusion phenomenon, increase the overall electronic conductivity of the electrode and accommodate volume expansion between the delithiated S and lithiated Li 2 S phases, the resulted graphene-wrapped carbon nanotube/sulfur (S/CNT@rGO) composite makes the cycling performance of the Li–S batteries better than that without rGO. The S/CNT@rGO composite showed an initial discharge capacity of ~1299 mA h g −1 at 0.2 C rate. After 100 cycles of charge/discharge, the S/CNT@rGO composite retained a high specific capacity of ~670 mA h g −1 , much higher than that without rGO ( −1 ). The results show that the graphene-wrapped carbon nanotube/sulfur composite could be a promising cathode material for high-rate performance Li–S batteries.

Two kinds of graphene–sulfur composites with 50 wt% of sulfur are prepared using hydrothermal method and thermal mixing, respectively. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectra mapping show that sulfur nanocrystals with size of ∼5 nm dispersed on graphene sheets homogeneously for the sample prepared by hydrothermal method (NanoS@G). While for the thermal mixed graphene–sulfur composite (S–G mixture), sulfur shows larger and uneven size (50–200 nm). X-ray Photoelectron Spectra (XPS) reveals the strong chemical bonding between the sulfur nanocrystals and graphene. Comparing with the S–G mixture, the NanoS@G composite shows highly improved electrochemical performance as cathode for lithium–sulfur (Li–S) battery. The NanoS@G composite delivers an initial capacity of 1400 mAh g −1 with the sulfur utilization of 83.7% at a current density of 335 mA g −1 . The capacity keeps above 720 mAh g −1 over 100 cycles. The strong adherence of the sulfur nanocrystals on graphene immobilizes sulfur and polysulfides species and suppressed the “shuttle effect”, resulting higher coulombic efficiency and better capacity retention. Electrochemical impedance also suggests that the strong bonding enabled rapid electronic/ionic transport and improved electrochemical kinetics, therefore good rate capability is obtained. These results demonstrate that the NanoS@G composite is a very promising candidate for high-performance Li–S batteries.

Co 3 O 4 quantum dots/graphene composites were synthesized by a facile and efficient microwave irradiation method, and they were analyzed using XRD, TEM, HRTEM, and TG. Uniform Co 3 O 4 nanocrystals of about 3-8 nm with a high density are homogeneously dispersed on graphene nanosheets. When used as anode materials for Li-ion batteries, the Co 3 O 4 quantum dots/graphene composites show a significantly enhanced cycling performance (1785 mAh g −1 at 0.1 C after 90 cycles) as well as high rate capability (485 mAh g −1 at 5 C). The reversible capacity is found to be much higher than the theoretical value. The superior performance could be attributed to the interfacial lithium-storage and the quantum and size effects of quantum dots that lead to high activity during the lithiation/delithiation process. In addition, the flexible and conductive graphene nanosheets and well dispersed Co 3 O 4 nanodots as well as the synergetic effect between them also benefit the electrochemical performance by endowing a superior high surface area and shortening the diffusion pathway of lithium ions.

Co3O4 nanostructures have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanism remain unclear. In this paper, we report the direct observation of the dynamic behaviors and the conversion mechanism of porous Co3O4 nanoplates/graphene in LIBs by in situ transmission electron microscopy (TEM). The microstructures of the lithiated/delithiated electrode are analyzed by electron diffraction and electron energy-loss spectroscopy. It is revealed that well-crystalline Co3O4 transform into many Co nanograins embedded in Li2O matrix during the first lithiation. The subsequent electrochemical charge–discharge processes are found to be a reversible phase transition between Co nanograins and CoO nanograins, which is different from the previously recognized mechanism (namely a reversible conversion between Co and Co3O4). Pores within the Co3O4 nanoplates can accommodate the volume expansion, and benefit for the stability of electrode and thus the electrochemical performance. The irreversibility revealed by in situ TEM is further correlated with the half cell measurement, which can well explain the capacity loss in the first cycle.

Hierarchical ZnO hollow microspheres were prepared via a carbon microspheres-templated approach, and their microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The as-prepared ZnO products show well-defined hollow spherical morphology with a size of 2–4 µm. The thickness of ZnO shells is around 100 nm, and they are assembled by numerous nanoparticles of 30–50 nm. The optical properties of the ZnO hollow microspheres were studied, and they exhibit a narrowed band gap (2.96 eV) and a sharp violet emission at 434 nm. Moreover, the ZnO hollow microspheres show a stable and greatly enhanced photocurrent response to visible light, which can be attributed to the hierarchical structures and the narrowed band gap resulted from the carbothermic process.

In this work, we fabricated an all-solid-state nano lithium battery MnFe2O4/graphene–Li2O–Li to understand the electrochemical Li-storage mechanism and performance of MnFe2O4 using in situ transmission electron microscopy (TEM) technique. We found that single-crystalline MnFe2O4 is converted into polycrystalline Li2O/Mn/Fe with large volume expansion upon discharge and subsequently into polycrystalline MnO/Fe3O4 with volume shrinkage upon charge. Reversible conversion between MnO/Fe3O4 and Li2O/Mn/Fe occurs during the following cycles with small volume changes. We also found that both MnO/Fe3O4 and Li2O/Mn/Fe can be tightly confined by graphene despite the volume change and particle pulverization, and that free space that buffers the volume changes still exists even at deep lithiation state. In situ TEM characterization also indicates that graphene is a good conductor for both Li ion and electrons. The combined conducting, buffering and confining effects of graphene revealed by in situ TEM characterization can well explain the role it plays in improving the electrochemical properties of MnFe2O4.

The CuS nanoparticle-decorated reduced graphene oxide (CuS/rGO) composites have been successfully prepared via a sonochemical method. X-ray diffraction and electron microscopy observations confirm that CuS nanoparticles of 10–25 nm are well distributed on the rGO nanosheets. Ultraviolet–visible spectroscopy reveals the CuS/rGO nonocomposites show a strong and broad light absorption. Photocatalytic performance of the CuS/rGO nanocomposites is evaluated by measuring the decomposition of methylene blue solution under natural light. The experimental results reveal that the as-prepared nanocomposites show remarkably enhanced photocatalytic activity compared with pure CuS. This can be attributed to the enhanced light adsorption, strong dyestuff absorption, and efficient charge transport after the introduction of rGO.

ZnO nanocrystals anchored graphene composite (ZnO/G) was synthesized by a facile in situ solvothermal route. The nanocomposite was characterized by X-ray diffraction (XRD), scanning electron spectroscopy (SEM), transmission electron microscopy (TEM) and Raman spectra (RS). The results indicated that the ZnO particles with an average diameter of ca. 12.6 nm were well-dispersed on the surface of the graphene nanosheets. The optical properties were investigated by fluorescence (PL) and UV diffuse reflectance (UV-VIS). It showed that the nanocomposite displayed a fluorescence quenching property. Furthermore, the nanocomposite showed a remarkably enhanced photocatalytic activity to degrade organic pollutants (MB, MO, Rh-B) under visible light irradiation, with a percentage degradation of MB reaching as high as 99.8% in 60 min.

We performed a detailed in situ TEM observation of the growth of In 2 O 3 nanocrystals under high-energy electron beam irradiation. The In 2 O 3 nanocrystal growth on the In 2 S 3 nanosheets can be induced by the electron irradiation with a beam intensity of 450–635 pA/cm 2 . The individual nanocrystals grow up to 10–15 nm after 210 s of electron irradiation with an intensity of ~635 pA/cm 2 . The In 2 O 3 /In 2 S 3 nanocomposites or pure In 2 O 3 nanocrystals can be obtained by controlling the beam intensity and irradiation time. EELS experiments confirmed the conversion from In 2 S 3 to In 2 O 3 . This study demonstrates that electron beam irradiation within the TEM can be employed as an effective and promising tool to fabricate nanostructures.

In this work, in situ transmission electron microscopy (TEM) technique has been applied to investigate the structural and phase evolutions of lead selenide (PbSe) nanocrystals loaded on reduced graphene oxide (rGO) nanosheets. An all-solid-state nano lithium battery composed of a single PbSe/rGO sheet cathode, Li 2 O electrolyte and Li anode has been fabricated to real time monitor the electrochemical lithiation/de-lithiation process of PbSe. It is found that few-layered rGO is a suitable support for PbSe during the in situ TEM observation due to its large surface area and good Li ion and electron conductivity. Based on the in situ characterization, a lithiation/de-lithiation mechanism of PbSe has been proposed. In situ characterization results are correlated with the electrochemical performance of PbSe/rGO. The role that rGO plays in modifying the electrochemical performance of PbSe has also been clarified by the in situ TEM characterization.

The comprehension of fundamental electrochemical behavior and sodiation mechanism is critical for the design of high-performance electrode materials for sodium-ion (Na-ion) batteries. In this paper, the electrochemical sodiation process and microstructure evolution of individual Co9S8-filled carbon nanotubes (CNTs) have been directly visualized and studied using in situ transmission electron microscopy. Upon the first sodiation, a reaction front propagates progressively along the filling nanowire, causing the filled CNT to inflate. The filled CNTs behave differently depending on their structures and the magnitude of the sodiation voltage. For a Co9S8-filled CNT with an open end, the sodiated Co9S8 filler shows a substantial axial elongation of 120.8% and a small radial swelling due to the extrusion of CNT walls. In contrast, the closed CNT shows a major radial expansion of 40.6% and a small axial elongation because of the mechanical confinement of the carbon shells. After sodiation, the spacing between th...