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Ameliorating the conductivity and terrible phase aggregation are the primary tasks of tin-based anodes for practical applications in lithium storage. Inspired by this, we have adopted an in-situ gas reduction strategy for fine SnS-SnO2 nanoparticles anchoring uniformly on N-doped graphene (C@SnS-SnO2@NGr) to realize superior rate performance in lithium-ion batteries (LIBs) applications. Especially, the better electric contact between SnS and SnO2 can avoid localized reaction of SnMx (M signifies O/S) and retard serious aggregation of Sn/LixSn. As a result, a higher initial Coulombic efficiency (ICE) (78%) was achieved with almost reversible conversion reaction of Sn/Li2M. The capacity retention reaches around 85% at the current density of 0.1 A g−1 for 500 cycles (1120 mA h g−1). Besides, the N-doped graphene as the skeleton benefits the well-distribution of p-n SnS-SnO2 nanoparticles and the conductivity of hybrids. Through high-rate and longest evaluation of 2.0 A g−1, the unique anode still keeps a high capacity of 630 mA h g−1 above 1000 cycles, which accordingly reveals a dominated surface-controlled redox reaction. Correspondingly, the evolution of electrode indicates that the ameliorate conductivity by N-doped graphene and the in-situ gas reduction procedure indeed enhance the charge-transfer kinetics and contribute to a durable high-rate performance.

Although the photochemical and ion exchange properties of layered KNb3O8 (KN) have been extensively studied, its potential lithium storage applications were ignored. Unlike typical acid hydrothermal method, this work demonstrate that interlayer-controlled KN nanoflakes can be prepared based on alkaline hydrothermal conditions. Pristine KN performs a high first-discharge capacity and superior cyclic stability. Moreover, polydopamine derived carbon as a conductive coating shell was firstly applied to modify KN for enhancing its lithium insertion ability. It performs outstanding rate character (310, 255, 110 mA h g−1 at the current density of 0.2, 1, 10 A g−1, respectively), as compared with pristine KN (96, 51, 13 mA h g−1). It also shows excellent long-term cycling feature (209 mA h g−1 after 3000 cycles, corresponds to 95% capacity retention). In addition, relevant energy storage mechanisms have been expounded. The present work could be helpful in developing potential multifunctional applications of KN-based and other similar niobates.

Boosting the lifespan of MnO-based materials for future lithium ion batteries is one of the primary challenges due to the intrinsic low ionic conductivity and volume expansion during the conversion process. Herein, superior lithium storage in a new quaternary MnO-Cu-CNT/graphene composite has been demonstrated, which is boosted by pseudocapacitance benefitting from the three-dimensional CNT/graphene and nanosized Cu additives. Such architecture offers highly interpenetrated porous conductive networks in intimate contact with MnO-Cu grains and abundant stress buffer space for effective charge transport upon cycling. The ternary MnO-Cu-graphene electrode contributes an ever-increasing reversible capacity of 938.3 mA h g-1 after 800 cycles at 0.8 A g-1. In particular, the quaternary MnO-Cu-CNT/graphene electrode demonstrates a high specific capacity of 1334 mA h g-1 at 0.8 A g-1 after 800 cycles and long lifetimes of more than 3500 cycles at 5 A g-1 with a capacity of 557.9 mA h g-1 and close-to-100% Coulombic efficiency. The boosted pseudocapacitive lithium storage together with the simple material fabrication method in a MnO-Cu-CNT/graphene hybrid could pave the way for the development of high-capacity and long-life energy storage devices.

Improving the conductivity and charge transfer kinetics is favourable for innovation of sustainable energy devices such as metal oxide/sulfide-based electrodes. Herein, with an intercalation pseudocapacitance effect, an in situ polymerization-carbonization process for novel carbon-sealed vertical MoS2-SnO2 anchored on graphene aerogel (C@MoS2-SnO2@Gr) has enabled excellent rate performance and durability of the anode of lithium ion batteries to be achieved. The integrated carbon layer and graphene matrix provide a bicontinuous conductive network for efficient electron/ion diffusion pathways. The charge transfer kinetics could be enhanced by the synergistic effects between vertical MoS2 nanosheets and well-dispersed SnO2 particles. Based on the crystal surface matching, the ameliorated electric contact between MoS2 and SnO2 can promote the extraction of Li+ from Li2O and restrain the serious aggregation of LixSn. As a result, the improved reversibility leads to a higher initial coulombic efficiency (ICE) of 80% (0.1 A g-1 current density) compared to that of other materials. In particular, with the dominating surface capacitive process, the C@MoS2-SnO2@Gr electrode delivers a stable capacity of 680 mA h g-1 at 2.5 A g-1 for 2000 cycles. Quantitative insight into the origin of the boosted kinetics demonstrated the high pseudocapacitance contribution (above 90%) which leads to the durable high rate Li ion storage.

Two-dimensional layered K4Nb6O17 (KN) possesses two different types of interlayer regions, which is of great interest for applications in energy conversion, environmental purification, etc. Although the photocatalytic properties of KN have been extensively studied, there still remain some pivotal problems that need to be clarified for future applications. Here we demonstrate that the KN nano-family (including KN nanolaminas and nano hollow spheres) can be derived from the same Nb2O5-based hydrothermal reaction. Different morphologies of KN show unique microstructures and optoelectronic properties. Remarkably, the initial pH of a dye solution has been proven to play a vital role in affecting the adsorption and photocatalytic performances of KN. Due to the effects of dye sensitization, KN shows superior photodegradation performance under both ultraviolet and visible light. Based on these crucial results, a highly-efficient and feasible scheme has been proposed to deal with dye wastewater. In addition, KN as a potential anode material for lithium ion batteries has been investigated for the first time. The present work could be helpful in broadening the multifunctional applications of KN and other layered niobate materials.

To accommodate huge volume change and boost the inferior electrochemical reaction kinetics of manganous oxide anodes for lithium-ion batteries, a unique 3D porous CNT/graphene-MnO architecture has been synthesized, with MnO nanoparticles homogeneously decorated on 3D interconnected CNT/graphene (3DCG) conductive networks. This porous 3DCG matrix with its abundant open pores and large surface area can provide efficient channels for fast charge transport and allow full contact between the electrode and electrolyte, leading to improved electrochemical activity. The robust 3D architecture offers abundant stress buffer space to tolerate volume expansion and ensures robust structural stability during the electrochemical processes. The synergistic effect between components endows the 3DCG/MnO electrodes with excellent electrochemical performance, retaining a high specific capacity of 526.7 mA h g-1 at 2.0 A g-1 with 98% capacity retention over 1400 cycles. This work provides a promising route for the practical application of fast and durable lithium-ion batteries and suggests insights for rational structural designs with other transition metal oxides.

Despite the extensive study of two-dimensional layered KNb3O8 (KN), there still remains some vital problems need to be clarified for future applications in environmental purification. Here we demonstrated the successful preparation of interlayer-controlled KN nanoflakes using alkaline hydrothermal conditions by adjusting the amount of thiourea in the reaction. This process resulted in KN nanoflakes with a larger specific surface area than previously reported. Moreover, the initial pH of dye solution and discrepant preferential orientation of interlayer peak have been proved to significantly influence the adsorption and photocatalysis performances of KN. In addition, relevant photocatalysis mechanisms have been expounded, by combined the first-principles calculation. The present work could be helpful in revealing the intrinsic adsorption-photocatalysis features of KN and other similar niobates.

Copper ferrites are emerging transition metal oxides that have potential applications in energy storage devices. However, it still lacks in-depth designing of copper ferrites based anode architectures with enhanced electroactivity for lithium-ion batteries. Here, we report a facile synthesis technology of copper ferrites anchored on reduced graphene oxide (CuFeO2@rGO and Cu/CuFe2O4@rGO) as the high-performance electrodes. In the resulting configuration, reduced graphene offers continuous conductive channels for electron/ion transfer and high specific surface area to accommodate the volume expansion of copper ferrites. Consequently, the sheet-on-sheet CuFeO2@rGO electrode exhibits a high reversible capacity (587 mAh g−1 after 100 cycles at 200 mA g−1). In particular, Cu/CuFe2O4@rGO hybrid, which combines the advantages of nano-copper and reduced graphene, manifests a significant enhancement in lithium storage properties. It reveals superior rate capability (723 mAh g−1 at 800 mA g−1; 560 mAh g−1 at 3200 mA g−1) and robust cycling capability (1102 mAh g−1 after 250 cycles at 800 mA g−1). This unique structure design provides a strategy for the development of multivalent metal oxides in lithium storage device applications.

Two-dimensional layered K4Nb6O17 (KN) was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing ferroelectric K x Na1−x NbO3 based ceramics and films. In this work, it was believed that KN film is with weak ferroelectricity and has a little effect on the ferroelectric properties of K x Na1−x NbO3 based films. Moreover, temperature dependent (77–500 K) dielectric functions of KN film have been firstly extracted by fitting ellipsometric spectra with the Adachi dielectric function model and a four-phase layered model. The high-frequency dielectric constant linearly increases and optical band gap slightly decreases with increasing the temperature. We also research its photoelectrochemical properties and its application in high-efficient light-induced H2 evolution. In addition, X-ray photoelectron spectroscopy, Raman scattering, temperature dependent transmittance and infrared reflectance spectra, and first-principles calculation were conjointly performed to further reveal the intrinsic optoelectronic features and relevant mechanisms of KN.

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567).

Developing high power-high energy electrochemical energy storage systems is an ultimate goal in the energy storage field, which is even more difficult but significant for low-cost sodium ion batteries. Here, fluoride is successfully prepared by the electrostatic spray deposition (ESD) technique, which greatly expands the application scope of ESD. A two-step strategy (solvothermal plus ESD method) is proposed to construct a bicontinuous ordered network of 3D porous Na3 (VO)2 (PO4 )2 F/reduced graphene oxide (NVOPF/rGO). This two-step strategy makes sure that NVOPF can be prepared by ESD, since it avoids the loss of F element during synthesis. The obtained NVOPF particles are as small as 15 nm, and the carbon content is only 3.5% in the final nanocomposite. Such a bicontinuous ordered network and small size of electroactive particles lead to the significant contribution of the pseudocapacitance effect to sodium storage, resulting in real high power-high energy sodium cathodes. The cathode exhibits excellent rate capability and cycling stability, whose rate performance is one of the best ever reported in both half cells and full cells. Moreover, this work provides a general and promising strategy for developing high power-high energy electrode materials for various electrochemical energy storage systems.

Niobium-based oxides including Nb2 O5 , TiNbx O2+2.5x compounds, M-Nb-O (M = Cr, Ga, Fe, Zr, Mg, etc.) family, etc., as the unique structural merit (e.g., quasi-2D network for Li-ion incorporation, open and stable Wadsley- Roth shear crystal structure), are of great interest for applications in energy storage systems such as Li/Na-ion batteries and hybrid supercapacitors. Most of these Nb-based oxides show high operating voltage (>1.0 V vs Li+ /Li) that can suppress the formation of solid electrolyte interface film and lithium dendrites, ensuring the safety of working batteries. Outstanding rate capability is impressive, which can be derived from their fast intercalation pseudocapacitive kinetics. However, the intrinsic poor electrical conductivity hinders their energy storage applications. Various strategies including structure optimization, surface engineering, and carbon modification are effectively used to overcome the issues. This review provides a comprehensive summary on the latest progress of Nb-based oxides for advanced electrochemical energy storage applications. Major impactful work is outlined, promising research directions, and various performance-optimizing strategies, as well as the energy storage mechanisms investigated by combining theoretical calculations and various electrochemical characterization techniques. In addition, challenges and perspectives for future research and commercial applications are also presented.

Due to the intrinsic low electrical conductivity and large volume expansion of the CoFe2O4 based active materials, designing more novel structures is still one of the most important challenges for its lithium ion battery application. In this work, the CoFe2O4/reduced graphene oxide/carbon (CFO/rGO/C) composite with integrated multi-layer structure has been synthesized through a facial two-step hydrothermal method. Benefiting from the introduction of the graphene network and amorphous carbon coating layer, as well as the accompanying synergistic effect, this composite can exhibit fast and reversible lithium intercalation/deintercalation reactions. With the aid of a surface-induced capacitive process, the CFO/rGO/C composite delivers a superior specific capacity (945 mA h g-1 at 0.1 A g-1) and excellent long-term cyclic stability (421 mA h g-1 at 4 A g-1 with closely 100% Coulombic efficiency after 2000 cycles). Significantly, at a high current density of 1 A g-1, the reversible capacity exhibits a rapid increasing after 100 cycles and finally shows an ultra-high-capacity of 1430 mA h g-1 over 500 cycles. This method could be generalized to the preparation of other similar transition metal oxide-based materials for the development of high-performance energy storage systems.

To overcome inferior rate capability and cycle stability of MnO-based anode materials for lithium-ion batteries (LIBs), we reported a novel 3D porous MnO@GS/CNT composite, consisting of MnO nanoparticles homogeneously distributed on the conductive interconnected framework based on 2D graphene sheets (GS) and 1D carbon nanotubes (CNTs). The distinctive architecture offers highly interpenetrated network along with efficient porous channels for fast electron transfer and ionic diffusion as well as abundant stress buffer space to accommodate the volume expansion of the MnO nanoparticles. The MnO@GS/CNT anode exhibits an ultrahigh capacity of 1115 mAh g-1 at 0.2 A g-1 after 150 cycles and outstanding rate capacity of 306 mAh g-1 at 10.0 A g-1. Moreover, a stable capacity of 405 mAh g-1 after 3200 cycles can still be achieved, even at a large current density of 5.0 A g-1. When coupled with LiMn2O4 (LMO) cathode, the LMO [Formula: see text] MnO@GS/CNT full cell characterizes an excellent cycling stability and rate capability, indicating the promising application of MnO@GS/CNT anode in the next-generation LIBs.