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Graphitic carbon nitride (g-C3N4) has attracted great interest in photocatalysis and photoelectrocatalysis. However, their poor hydrophilicity poses a great challenge for their applications in aqueous environment. Here, we demonstrate synthesis of a hydrophilic bi-functional hierarchical architecture by the assembly of B-doped g-C3N4 nanoplatelets. Such hierarchical B-doped g-C3N4 material enables full utilization of their highly enhanced visible light absorption and photogenerated carrier separation in aqueous medium, leading to an excellent photocatalytic H2O2 production rate of 4240.3 μM g−1 h−1, 2.84, 2.64 and 2.13 times higher than that of the bulk g-C3N4, g-C3N4 nanoplatelets and bulk B doped g-C3N4, respectively. Photoanodes based on these hierarchical architectures can generate an unprecedented photocurrent density of 1.72 mA cm−2 at 1.23 V under AM 1.5 G illumination for photoelectrochemical water splitting. This work makes a fundamental improvement towards large-scale exploitation of highly active, hydrophilic and stable metal-free g-C3N4 photocatalysts for various practical applications.

As an alternative for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have lately received tremendous interest due to their abundant reserves as well as low cost. Nevertheless, the lack of suitable anode materials severely hinders the application of sodium-ion batteries. TiS2 is elected as a representative material owing to its unique layered structure. But it always suffers from capacity fade due to poor electrochemical kinetics and structural stability. In this work, we fabricate a pre-potassiated TiS2 as a host material for sodium storage by an electrochemical pre-potassiation strategy. The intercalation/extraction mechanism, structural changes and reaction kinetics are completely investigated to reveal the outstanding electrochemical property of pre-potassiated TiS2 electrode. It turns out that the large interlayer space of pre-potassiated TiS2 is conducive to the diffusion of sodium ions, inducing the reduction of entropic barrier for the electrochemical reactions. In addition, the pre-potassiated host structure is still firmly maintained upon repeated cycles. Therefore, the pre-potassiated TiS2 presents superior rate capability (165.9 mA h g − 1 at 1 C and 132.1 mA h g − 1 at 20 C) and long-term cycling stability (85.3% capacity retention at 5 C after 500 cycles) for SIBs. This research provides an avenue to construct long-life sodium energy storage systems based on pre-potassiated TiS2.

Photocatalysis is deemed as a highly prominent technology to solve environmental problems such as pollutant removal, CO2 emission and bacterial inactivation. As an important photocatalyst, g-C3N4 has appealed a great...

In recent years, anion storage technology has been regarded as promising alternative for the typical metal ion batteries due to its high energy density in theory, including halogen anions (F−, Cl−, Br−, I−) and complex anions (PF6−, BF4−, FSI−, FTFSI−, TFSI−, FSA−, BETI−, HSO4−, ClO4−, AlCl4−, NO3−, [ZnCl4]2−). Research on the storage of anions can not only develop anion batteries, but also extend it to more novel battery concepts such as desalination batteries and dual-ion batteries (DIBs). However, the difference of theoretical and practical performance is a crucial problem for the development of anion storage. Thus, understanding the working mechanism of various batteries and the methods of performance improvement are necessary for the future development of anion battery systems. For this reason, this article reviews the research progress and challenges in electrode materials and electrolytes of various anion storage technologies in detail. Finally, possible development directions in this research area are also proposed.

The sodium dual ion battery (Na-DIB) technology is proposed as highly promising alternative over lithium-ion batteries for the stationary electrochemical energy-storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a novel Na-DIB based on TiSe2-graphite is reported for the first time. The unprecedentedly high diffusion coefficient of Na-ions (3.21 × 10-11 - 1.20 × 10-9 cm2 s-1) and the very low Na-ion diffusion barrier (0.50 eV) lead to very fast electrode kinetics, alike in conventional surface capacitive storage systems. In-situ investigations reveal that the fast Na-ion diffusion involves four insertion stage compositions. The prototype cell of novel and low-cost TiSe2-graphite Na-DIB shows a reversible capacity of 81.8 mAh g-1 at current density of 100 mA g-1, an excellent stability with 83.52% capacity retention over 200 cycles and excellent rate performance, suggesting its high potential for next-generation large scale high-performance stationary energy storage systems.

Aqueous dual-ion batteries are promising contenders for future applications due to their environmental friendliness, salient safety and cost-effectiveness. Herein, a novel anode-free aqueous dual-ion cell is proposed. Besides, electrolytes with inorganic/organic hybrid zinc salts are adopted to optimize its electrochemical performance. The electrochemical results suggest that this anode-free aqueous dual-ion cell exhibits decent reversible capacity and stable cyclability during galvanostatic cycles. Furthermore, the changes of the cathode and collector during charging and discharging are demonstrated via various in situ and ex situ routes. Without an anode, the weight and material cost of batteries can be reduced. Therefore, this work provides a new insight into the design of aqueous dual-ion batteries.

In this study, for the first time, Cu2Nb34O78 nanowires were fabricated via an electrospinning technique and exhibited outstanding electrochemical performance as an anode material. The nanowires presented a charge capacity of 279.8 mA h g−1 with remarkable long-life stability for 300 cycles (0.037% capacity loss per cycle). Significantly, ex situ X-ray diffraction, ex situ high-resolution transmission electron microscopy, and ex situ X-ray photoelectron spectroscopy were performed to unveil the reaction process and change in the microstructure during charge/discharge cycles in detail. The observed evidence demonstrates that the remarkable Li-storage capability is due to the enhanced contact-specific area and reduced transport path of Cu2Nb34O78 nanowires. In addition, the host mechanism is unraveled, in which the contribution of the reversible capacity is discussed based on the Nb5+/Nb4+, Nb4+/Nb3+ and Cu2+/Cu+ redox couples.

If the operating voltage of anode materials is below 1.0 V versus Li+/Li, the side reaction between electrolyte and anode materials will occur extensively. Thus, high-voltage anode materials have aroused interest recently. In this work, we report the preparation of PNb9O25 nanofiber via a facile electrospinning method. The PNb9O25 nanofiber shows the high rate performance and excellent cycling performance when it is used as anode in lithium ions batteries. For instance, the PNb9O25 nanofiber can deliver a capacity of 233, 212.1, 193.8, and 181.4 mA h g−1 at 0.2, 1, 3, and 6C, respectively. After 1000 cycles, it can reach at 134.3 mA h g−1 with capacity retention of 70.9%. Meanwhile, the ex situ X-ray photoelectron spectroscopy technique has been adopted to investigate the evolution in valence state of each element for PNb9O25 nanofiber. In addition, the PNb9O25 nanofiber is chosen as the anode material in lithium ion full cell in this work, demonstrating the potential for practical application.

Carbon coating always has a positive effect on improving the electrochemical performance of electrode materials for lithium ions batteries and its mechanism has once drawn great attention, yet few studies offer a model to elaborate on it. In this study, we select PNb9O25 nanowires as anode material and coat carbon on them to investigate how carbon layer does affect its electrochemical performance. Meanwhile, a theoretical model has proposed for the investigation of mass transfer and electron transfer at the surface of PNb9O25. The result suggests that due to the presence of carbon layer, mass transfer and electron transfer at the surface of PNb9O25 shows a decent boost, leading to the improvement of electrochemical performance at the high current density.

Carbon-based materials, as the traditional anodes for lithium and sodium ion batteries, have drawn extensive attention due to their low cost, available resources and superior cycling stability. Yet the inferior capacitance and sluggish kinetics of these materials severely restrict their further application in lithium and sodium ion batteries. For addressing the aforementioned issues, tremendous efforts have been made and many approaches are proposed, such as designing nanomaterials with various morphologies, creating numerous porosities, and heteroatoms doping. Among them, doping heteroatoms into the lattice of carbon-based materials is demonstrated to be an effective solution based on the results from the experimental and theoretical studies. This approach can modify several characteristics of carbon-based materials obviously, like expanding interlayer distance, generating numerous active sites, and improving electronic conductivity. Therefore, heteroatom-doped carbon-based materials present fantastic cycling stability, excellent rate performance and high capacities compared with pure carbon-based materials. Herein, we present the research progress of heteroatom-doped carbon-based materials for lithium and sodium ion batteries, including N, S, B, P, I, Br, Cl, and F doping/co-doping. The typical synthesis methods, characterization techniques, and electrochemical behaviors of heteroatom-doped carbon-based materials are summarized and clarified. In addition, the importance of heteroatom doping as well as the synergistic effects of co-doping in carbon-based materials is primary emphasized for lithium and sodium storage.

Nowadays, it is of great urgency to research for appropriate materials to construct high-performance lithium-ion batteries (LIBs) because of the growth of social demand. Among them, niobium type metal oxides are potential candidates for anode materials. Here, we propose GaNb11O29 with shear-ReO3 crystal structure as anode material. It is an intercalation-type material with high theoretical capacity and safe working voltage. In this work, GaNb11O29 nanowires are synthesized by electrospinning. The nanostructure design can effectively improve lithium storage behavior. Accordingly, GaNb11O29 nanowires provide a high reversible capacity (233.4 mAh g-1 at 100 mA g-1), outstanding rate capability (168.8 mAh g-1 at 700 mA g-1) and superior long-term stability (0.031% capacity loss per cycle after 500 cycles). Furthermore, the kinetic analysis confirms the pseudocapacitive contribution during cycling, which contributes to the rapid Li-storage. In addition, in-situ XRD characterization is conducted to further unveil the Li-storage mechanism in lithiation/delithiation processes. This work suggests that GaNb11O29 nanowires are potential anode material for rechargeable batteries, which enriches the choice for high-performance LIBs.

Na2Li2Ti6O14 nanowires prepared through electrospinning and subsequent calcination method are reported as an anode material for lithium ion storage. During the initial cycle, as-synthesized Na2Li2Ti6O14 nanowires deliver a quite flat charge platform at 1.32 V with the charge capacity of 94.0 mAh g-1 at 100 mA g-1. Specifically, after a long cycle of 2500 times, Na2Li2Ti6O14 nanowires still hold a reversible charge capacity of 88.8 mAh g-1 with a remarkable capacity retention of 94.47%, which also show a high Coulombic efficiency of 99.83%. The favorable electrochemical performance may stem from its unique nanostructures, which not only preserve structural integrity during repeated cycles but also reduce the distance of lithium ion transport.

The GaNb11O29 shows an open Wadsley-Roth shear structure, which is of great benefit to store ions in rechargeable batteries. In this work, we successfully synthesize GaNb11O29@C via a simple solid-state reaction method combined with carbon-coating modification. As anode for LIBs, the as-synthesized GaNb11O29@C sample exhibits wonderful electrochemical behaviors. It exhibits high reversible capacity (227.3 mA h g−1), outstanding rate capability (58.91% retention at 700 mA g−1) and excellent long cycle performance (0.036% capacity decay per cycle). The enhancement of diffusion kinetics and rate performance assigns to the increased surface reaction activity and electrical conductivity. The open and stable crystal framework structure guarantees rapid lithium-ion migration, excellent rate performance and long cycle performance. These results tell that GaNb11O29@C is promising anode material for the application in advanced LIBs.

The investigation of the lithiation mechanism for anode materials plays a key role in the field of lithium-ion batteries. It can always offer a new approach to design and develop anode materials to improve their electrochemical performance. Therefore, we have studied the lithiation mechanism of PNb9O25 during cycling by the adoption of the in situ X-ray diffraction technique coupled with the analysis of a structure model in this work. The results present that PNb9O25 reacts with lithium at 1.62 and 1.11 V with a small lattice volume expansion of 10.69%. Meanwhile, based on the evolutions of the selected reflections ((130), (141), and (370)), the position of the inserted lithium ions in the lattice is revealed and thus, the diffusion channels of lithium ions can be inferred from it. According to this lithiation mechanism, we can find out some new avenues to design and develop the morphology of PNb9O25 or other niobate materials.

Potassium ion batteries have suffered from a severe lack of proper insertion-type electrodes since the large-sized potassium ion cannot be accommodated in most of lithium/sodium ions anode materials. Here, we report commercial TiSe2 as a novel potassium insertion material. The electrochemical results show that commercial TiSe2 can electrochemically store the potassium ions reversibly with good cyclability and excellent rate performance. However, it is plagued by the low Coulombic efficiency in the first cycle. Upon investigation of in situ X-ray diffraction, its irreversible capacity loss is caused by the cracks of the TiSe2 host along with phase transitions. We design an efficient method to eliminate its irreversible capacity loss and then couple the as-pretreated TiSe2 with the as-pretreated Prussian blue for fabrication of full cell. The Coulombic efficiency of this full cell is improved and this full cell displays stable cyclability with good capacity retention of 94.5 % after 120 cycles.

This work reports the preparation of TiNb6O17 nanospheres via a facile electrostatic spraying route and their lithium storage mechanism. When selected as anode material in half-cell, TiNb6O17 nanospheres possess the high capacity, extraordinary rate performance, and outstanding cyclability. The results exhibit that TiNb6O17 nanospheres deliver an initial discharge capacity of 245 mAh g−1 with a high Coulombic efficiency of 86.37% at 0.5 C, and even after 150 cycles, a reversible capacity of 159.1 mAh g−1 is kept with Coulombic efficiency close to 100%. The outstanding electrochemical properties of TiNb6O17 nanospheres can be ascribed to their unique morphologies. In addition, the electrochemical kinetics of TiNb6O17 nanospheres is investigated by cyclic voltammetry. The results indicate that their electrochemical behavior is composed of two parts, lithium ion diffusion and pseudo-capacitive characteristic. Furthermore, lithium ion storage mechanism of TiNb6O17 nanospheres is studied by in situ X-ray diffraction instrument, revealing superior electrochemical reversibility and structure stability. Based on the aforementioned measurements, it can be concluded that TiNb6O17 nanospheres have the potential for practical use in lithium ion batteries.

Niobium-based compounds are extensively studied as anode materials for LIBs on account of the great structural stability and high theoretical capacity. Among them, VNb9O25 has an attractive theoretical capacity (416 mAh g−1). Unfortunately, low electronic conductivity and Li+ diffusivity hinder its practical application. To overcome above barriers, VNb9O25 nanowires were synthesized directly by electrospinning method. As expected, VNb9O25 nanowires deliver an outstanding capacity retention (92.1% after 200 cycles) and a robust rate property (90.7 mAh g−1 at 1000 mA g−1). Thus, as-electrospun VNb9O25 nanowires are alternative promising anode materials for LIBs.

The sodium dual ion battery (Na-DIB) technology is proposed as highly promising alternative over lithium-ion batteries for the stationary electrochemical energy-storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a Na-DIB based on TiSe

In this work, a novel zero-strain anode, LiY(MoO4)2 nanotubes, is firstly prepared by a simple electrospinning technique, which exhibits outstanding rate performance and stable cycling performance. After 580 cycles, the capacity retention of LiY(MoO4)2 nanotubes is up to 94%, while that of LiY(MoO4)2 bulks is only 30%. The enhancement can be attributed to the hollow structure of nanotubes. More importantly, in situ X-ray diffraction (XRD) technique is used for the first time to explore the mechanism of Li ion insertion/extraction for LiY(MoO4)2 nanotubes. It can be concluded that Li ions initially occupy vacant 8c sites for energy storage through tunnels built by Mo-O tetrahedra. With repeated lithiation, the Y(Li)O8 polyhedra are gradually distorted. The distortion of Y(Li)O8 polyhedra not only relieves the volume expansion caused by lithiation, but also induces the 8d site to be opened to allow more Li ions to be embedded. Moreover, in situ XRD and ex situ transmission electron microscopy (TEM) studies demonstrate that LiY(MoO4)2 nanotubes have outstanding structural stability with the maximum volume expansion of LiY(MoO4)2 nanotubes of only 0.53%, suggesting that LiY(MoO4)2 nanotubes, like Li4Ti5O12, are zero-strain insertion materials. All of these advantages suggest that LiY(MoO4)2 nanotubes are possible anode material for LIBs.

Here, LiY(WO4)2 nanotubes are prepared via a feasible electrospinning technique. This new anode material shows excellent electrochemical properties. The capacity loss of LiY(WO4)2 nanotubes is as low as 6.9% after 156 cycles, while bulk LiY(WO4)2 presents the capacity loss higher than 55.0%. Even after 600 long-life cycles, the capacity loss of the nanotubes is only 9%. It can be seen that the hollow structure with a rough surface and a porous morphology contributes to the improvement of electrochemical performance. Furthermore, online X-ray diffraction (XRD) method is firstly applied to understand the lithium ions insertion/extraction mechanism of LiY(WO4)2 nanotubes. It can be concluded that it is an asymmetrical two-phase reaction. A phase transformation from LiY(WO4)2 to Li3Y(WO4)2 can be obviously seen from the in situ XRD during discharge process. While Li2Y(WO4)2 appears as an intermediate phase with a reverse charge reaction. In addition, in situ XRD also demonstrates that LiY(WO4)2 nanotubes have surprised electrochemical reversibility. All the above results indicate that LiY(WO4)2 nanotubes can be expected to be anode candidate for rechargeable lithium ion batteries (LIBs).

Anode materials for lithium ion batteries with environmental benignity and great electrochemical performance are greatly desired. In this work, AgNb13O33 with open framework is reported as an anode material for the first time. It shows a triclinic lattice with 4i, 4f sites and 8j sites for lithium storage. At the current density of 100 mA g−1, AgNb13O33 delivers high initial charge/discharge capacity of 329.4/357.8 mAh g−1 with an initial Columbic efficiency of 92.06%. 500 cycles later, it still remains a reversible capacity of 214.2 mAh g−1. Moreover, at a higher rate of 1000 mA g−1, AgNb13O33 still maintains an initial charge capacity of 203 mAh g−1. Ex-situ transmission electron microscope (TEM) and in-situ X-ray diffraction (XRD) tests are performed to study the lithiation and delithiation reactions of AgNb13O33 during the cycling. The reversibility and structural stability of the AgNb13O33 make contributions to its excellent performance. All results show the promising possibility of applying AgNb13O33 as an anode material for lithium ion batteries.

Lithium ion batteries (LIBs) as the mainstream rechargeable batteries are widely used in industrial production and life. However, it is hard to meet the demand in the future due to the lack of lithium resources. At the same time, increasingly scarce lithium resources will increase the cost of LIBs. In contrast, potassium is abundant in the earth's crust, and available researches suggest that rechargeable potassium ion batteries (KIBs) may be a promising substitute for LIBs. In this paper, the research progress of non-aqueous KIBs is reviewed, including cathode materials, anode materials, electrolytes, binders, opportunities and future challenges. Firstly, cathode and anode materials are summarized according to the different reaction types. Secondly, the application and influence of electrolytes and binders for non-aqueous KIBs are also discussed. Moreover, in order to promote the advancement for non-aqueous KIBs, the main future challenges and some solutions are also proposed.

Based on the high theoretical capacity and relatively high safety voltage, niobium-based oxides are regarded as promising intercalation-type electrode materials for advanced lithium-ion batteries (LIBs). Here, ZrNb14O37 nanowires are fabricated via a facile electrospinning method, presenting a nanoparticle-in-nanowire architecture. As an anode for LIBs, the as-fabricated ZrNb14O37 nanowires maintain a capacity of 244.9 mA h g-1 at 100 mA g-1 and present excellent cycling capability (0.026% of capacity fading per cycle during 1000 cycles) as well as outstanding rate performance. In situ X-ray diffraction measurement is conducted to understand the fundamental reaction mechanism during the lithiation/delithiation process. The ex situ observations, including X-ray photoelectron spectroscopy and transmission electron microscopy, are further performed to provide more lines of evidence of the reaction mechanism. Moreover, the excellent electrochemical performance of the full cell constructed using ZrNb14O37 nanowires and LiCoO2 suggests that ZrNb14O37 nanowires are a promising anode material. This work sheds new light on understanding the lithium storage mechanism and may open new opportunities to develop new anode materials for LIBs.

Owing to the high theoretical capacity, molybdenum (Mo)-based materials are promising as high-performance anode for lithium-ion batteries (LIBs). Therefore, Y2(MoO4)3 is investigated as anode candidate for the first time in this work. Moreover, in an attempt to improve ionic diffusivity and capacity retention of Y2(MoO4)3, molybdenum-based Y2(MoO4)3 nanowires are successfully formed by a feasible electrospinning method. And the morphologies of as-prepared sample are observed by scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM). Herein, the Y2(MoO4)3 nanowires show a remarkable charge specific capacity of 480.1 mA h g−1 with 67.1% capacity retention at 100 mA g−1 after 100 cycles. While the capacity retention of Y2(MoO4)3 micro-particles is only 24.4% under the same conditions. Besides, ex-situ X-ray diffraction (XRD), ex-situ TEM and ex-situ X-ray photoelectron spectrometer (XPS) tests are carried to study lithium storage reaction of Y2(MoO4)3 upon the charge/discharge reactions. The results confirm that the Y2(MoO4)3 undergoes a typical conversion reaction, accompanied by the irreversible particle pulverization of structure.

Due to high capacity from multiple redox couples, niobium-based oxides are promising anode materials for lithium-ion batteries (LIBs). However, their poor electronic conductivity restricts their electrochemical performance. Here, we report the FeNb11O29 nanotubes as an advanced anode material. FeNb11O29 nanotubes exhibit an impressive charge capacity of 272.64 mAh g−1 with high initial cycle Coulombic efficiency of 90.13% at 0.1 C and outstanding cyclic stability (only 0.0123% of capacity decay per cycle during 2000 cycles). Furthermore, according to the in-situ XRD, the behavior of lithium atoms distribution in the FeNb11O29 framework during the insertion and extraction is studied in detail. In addition, full cells are assembled with commercially available cathodes. Coupled with LiFePO4, which is used as cathode, the full cell displays good electrochemical performance. In summary, FeNb11O29 nanotubes can be used as an ideal anode material due to the excellent electrochemical performance.

La2(MoO4)3 is a kind of transition metal molybdate. It has been proved to be a possible anode material for lithium ion batteries due to the high theoretical capacity. In this work, molybdenum-based La2(MoO4)3 material is successfully synthesized through a traditional solid-state reaction method. Carbon-coated La2(MoO4)3 is designed by using glucose as carbon source. By comparing the carbon-coated La2(MoO4)3 with the carbon-free La2(MoO4)3, carbon-coated La2(MoO4)3 delivers better cyclic stability and rate performance. Carbon-coated La2(MoO4)3 obtains a reversible charge capacity of 525.9 mA h g−1 at 100 mA g−1 after 100 cycles, corresponding to capacity retention of 75.2%. However, the capacity retention of carbon-free La2(MoO4)3 is only 33.4%. The results indicate that carbon layer can evidently alleviate the irreversibility of structure and improve capacity retention of La2(MoO4)3. It demonstrates that the carbon-coated La2(MoO4)3 composite can be a possible anode candidate for high capacity lithium ion batteries. In addition, in-situ X-ray diffraction investigation (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and ex-situ transmission electron microscopy (TEM) are employed to analyze the electrochemical behavior during process of cycling. These experimental results indicate that the conversion behavior of La2(MoO4)3 upon lithiation/delithiation is a process of structural pulverization. Based on that, our work provides guidance for the research of molybdenum-based electrode materials.

There is considerable interest in the titanium niobium oxides employed as the high performance anode hosts for lithium ion batteries in recent years. However, due to the low electronic conductivity, these compounds are also greatly compromised in practical application. Here, we successfully construct the CrNb49O124 nanotube, which has similar properties as titanium niobium oxides but higher electronic conductivity (1.78 × 10–2 S cm–1) via an electrospinning route with excellent long cycle life and high rate capacity. It delivers a high capacity of 340 mAh g–1 at 60 mA g–1, and the first cycle Coulombic efficiency is 88.9%, which is higher than the traditional Li4Ti5O12 anode material (capacity) and other Nb-based compounds (capacity and efficiency). Furthermore, it also exhibits a superior electrochemical kinetics (5.29 × 10–13 cm2 s–1). In addition, the Li storage mechanism of the CrNb49O124 nanotube is studied through a homemade in situ X-ray diffraction (XRD) experiment, which reveals an outstanding el...

Bismuth-based materials are promising alloy-type materials as lithium-ion batteries (LIBs) anode with a high theoretical capacity of about 385 mAh g−1 (Li3Bi). However, the severe volume change during the charge/discharge process limits their applications in LIBs. Nanostructured design is an effective strategy to relieve the volume change. Here, Bi5Ni3O15 nanowires are designed and fabricated via a sample electrospinning technique. When used as anode material, the Bi5Ni3O15 nanowires exhibit a charge/discharge capacity of 372 and 636 mAh g−1 at current density of 100 mA g−1. After 100 cycles, it still retains a capacity of 267 mAh g−1, revealing a good electrochemical performance. This is mainly attributed to the nanostructured design, which can suppress the pulverization resulting from volume variation during the repeated alloy/dealloy process and offers shorter lithium-ion diffusion path together. In addition, in-situ X-ray diffraction experiments are carried out to explore the phase change and lithium storage mechanism. The exploration of Bi5Ni3O15 nanowires as LIBs anode demonstrates that nanostructured design is an effective approach to improve electrochemical performance of alloy-type anodes, which will speed up the process to develop novel alloy-type anodes.

In recent years, the rechargeable aqueous batteries have attracted great attentions among quite a few researchers because of the abundant raw materials, low cost, simple operation, safety and environmental benignity. Compared with the battery system of monovalent ions, rechargeable aqueous polyvalent ion batteries have a greater significance of research in many aspects. Although some difficulties have been encountered in the development process, plenty of efforts have been made to improve the electrochemical performance by a variety of distinct methods, such as seeking for new electrode materials, modifying surface area of materials and exploring new type of electrolytes. This review is a summary of recently reported anode materials, cathode materials and electrolytes for rechargeable aqueous polyvalent ion batteries.

HTiNbO5 has been widely investigated in many fields because of its distinctive properties such as good redox activity, high photocatalytic activity, and environmental benignancy. Here, this work reports the synthesis of one-dimensional H0.92K0.08TiNbO5 nanowires via simple electrospinning followed by an ion-exchange reaction. The H0.92K0.08TiNbO5 nanowires consist of many small "lumps" with a uniform diameter distribution of around 150 nm. Used as an anode for lithium-ion batteries, H0.92K0.08TiNbO5 nanowires exhibit high capacity, fast electrochemical kinetics, and high performance of lithium-ion uptake. A capacity of 144.1 mA h g-1 can be carried by H0.92K0.08TiNbO5 nanowires at 0.5 C in the initial charge, and even after 150 cycles, the reversible capacity can remain at 123.7 mA h g-1 with an excellent capacity retention of 85.84%. For H0.92K0.08TiNbO5 nanowires, the diffusion coefficient of lithium ions is 1.97 × 10-11 cm2 s-1, which promotes the lithium-ion uptake effectively. The outstanding electrochemical performance is ascribed to its morphology and the formation of a stable phase during cycling. In addition, the in situ X-ray diffraction and ex situ transmission electron microscopy techniques are applied to reveal its lithium storage mechanism, which proves the structure stability and electrochemical reversibility, thus achieving high-performance lithium-ion uptake. All these advantages demonstrate that H0.92K0.08TiNbO5 nanowires can be a possible alternative anode material for rechargeable batteries.

High-performance anode materials for development of long cycling life and environmental benignity lithium-ion batteries (LIBs) are greatly desired. Here, the nanostructure, electrochemical performance and structural evolution of barium niobates in LIBs are reported of the first time. One-dimensional barium niobium oxide (BaNb3.6O10) nanowires are prepared by electrospinning technique, displaying the “nanoparticle-in-nanowire” morphology. The BaNb3.6O10 nanowires show high structural stability, high reversible specific capacity (263.8 mAh g−1 at 100 mA g−1), superior rate performance and long-term cycling capability (keeping 60% of the initial reversible capacity at a high current density of 1000 mA g−1 after 5000 cycles). In addition, the mechanism for lithium storage in BaNb3.6O10 is also studied by using ex-situ transmission electron microscopy (TEM), in-situ X-ray diffraction (XRD), in-situ TEM and theory calculations. The results show that BaNb3.6O10 nanowires have reversibility and structural stability for the lithiation and delithiation process. The fabricated BaNb3.6O10/LiMn2O4 full cell demonstrates a practical energy density of 270 Wh Kg−1. This work perfectly confirms that the one-dimensional BaNb3.6O10 nanowires are an ideal material for LIBs.

Alloying lithiation hosts have aroused much more interest due to their remarkable volumetric/gravimetric capacity. Among them, Sb-based binary or ternary alloys have become an appealing anode candidate owing to their good electronic conductivity. In this work, commercially available InSb is employed as an anode host material due to its excellent electrochemical capability proved via various electrochemical tests. InSb exhibits an initial specific charge capacity of 680.9 mA h g−1. Meanwhile, 78.6% of the initial charge capacity can be retained after the 80th cycle. By in situ X-ray diffraction (XRD), ex situ scanning electron microscopy (SEM), and ex situ transmission electron microscopy (TEM), InSb displays high structural stability and electrochemical reversibility. All these advantages suggest that InSb alloys as anode materials have great potential applications in the future.

The tungsten niobium oxides that belong to the well-known Wadsley-Roth shear structure have been already studied as the high-performance anode materials over the past several years since these materials can provide the additional vacuum site for accommodating lithium ions. Now, a novel anode material Nb18W16O93 which has a tetragonal tungsten bronze type structure is firstly reported in this paper. This material exhibits the good electrochemical performance. Upon the modification of its surface morphology, the electrochemical performance for Nb18W16O93 nanowire has been greatly improved. Nb18W16O93 nanowire shows the reversible specific capacity of 195 mAh g−1 when the current density is 100 mA g−1 and it can reach 153 mAh g−1 even at 1000 mA g−1. Meanwhile, the lithiation/delithiation mechanism and its corresponding structural change during the charge and discharge process are also carried out by an in-situ XRD technique. The result shows that Nb18W16O93 nanowire has excellent electrochemical reversibility and structural stability. Consequently, Nb18W16O93 nanowire can be employed as a novel anode material for lithium ion batteries.

TiNb24O62 with large theoretical capacity and safe working potential is regarded as a candidate for lithium ion batteries. However, poor electronic conductivity of TiNb24O62 restricts its widely application. Herein, we propose a novel methodology concerned about nitrogen-doped carbon coating to improve the electrochemical performance of TiNb24O62 nanowires. According to a series of analyses, it is found that nitrogen-doped carbon coating plays a key role on improving the electronic conductivity and electrochemical activity of TiNb24O62 nanowires. Meanwhile, both first principles calculations and in-situ XRD technique are applied to realize the structural evolution of nitrogen-doped carbon coated TiNb24O62 nanowires. The obtained results show a high diffusion channel for lithium ions in the lattice of TiNb24O62 and the good electrochemical reversibility of nitrogen-doped carbon coated TiNb24O62 nanowires. In addition, a full lithium ion battery is assembled by using nitrogen-doped carbon coated TiNb24O62 nanowires as anode and LiFePO4 as cathode. Such a cell can deliver a high capacity, indicative of a great potential for practical applications. Therefore, nitrogen-doped carbon coated TiNb24O62 nanowires can be a promising anode for high-rate lithium ion batteries.

Lithium ion batteries (LIBs), sodium ion batteries (SIBs) and potassium ion batteries (PIBs) can be proposed as substitutes to fossil fuels because of the gradual depletion of non-renewable energy. In this work, Pb3Nb4O13 is investigated as a new kind of anode material with the storage ability of lithium, sodium and potassium. Pb3Nb4O13 nanowires are prepared via a feasible electrospinning technique followed with calcinations. Furthermore, it's the first time for Pb3Nb4O13 to be applied as anode materials. At the current density of 50 mA g−1, Pb3Nb4O13 shows reversible capacities of 264.8, 171.4 and 100.1 mA h g−1 in the applications of LIBs, SIBs and PIBs, respectively. In addition, the storage mechanisms of Pb3Nb4O13 in different batteries are also investigated by in situ XRD. The results show that Pb3Nb4O13 nanowires have the reversible conversion reactions between PbO2 and Pb. This work perfectly confirms that Pb3Nb4O13 nanowires might be a potential anode material for LIBs, SIBs and PIBs.

Owing to the multiple redox couples of Nb5+/Nb4+ and Nb4+/Nb3+, Nb-based compounds have attracted great attention to be promising high-capacity anode materials for rechargeable batteries. Here, K6Nb10.8O30 groove nanobelts (GNB) are synthesized through heat-treating the adjustable electrospun potassium niobate nanofibers, thereupon the structural change in the lithiation and delithiation is evidently imaged via in situ transmission electron microscopy (TEM). From in situ observations, the K6Nb10.8O30 GNB, in virtue of its stability, is ascertained to be adopted as anode material in lithium-ion batteries (LIBs). Evaluated as lithium storage host, GNB outstrip nanowires (NW) in cyclicity and in reversible capacity. Even after 1000 cycles, the retention capacity of K6Nb10.8O30 GNB is as high as 69%. Furthermore, the lithium-storage mechanism is also investigated via in situ X-ray diffraction (XRD). It is proved that the phase transition takes place from Li-poor K6Nb10.8O30 phase to Li-rich Li22K6Nb10.8O30 phase via two steps. In addition, the results obtained from ex situ TEM and ex situ X-ray photoelectron spectroscopy (XPS) also prove that the behavior of lithiation and de-lithiation for K6Nb10.8O30 GNB is highly reversible, suggesting that it can be a possible anode material.

To fulfill the requirement for large-scale energy-storage systems, lithium ions batteries have been attracted great attentions. It is necessary to develop the anode material with high rate capability, long cycling life and outstanding safety. Here, N-doped carbon been successfully synthesized and estimated as an anode material for lithium ions batteries. PbLi2Ti6O14 is isostructural with SrLi2Ti6O14. After nitrogen-doped carbon coating, PbLi2Ti6O14@NC delivers a high capacity of 143.2 mAh g−1 at a current density of 100 mA g−1 and remains 104.8 mAh g−1 even at 700 mA g−1. In addition, PbLi2Ti6O14@NC also possesses excellent cyclic stability. The reversible capacity of PbLi2Ti6O14@NC can keep at 99.7 mAh g−1 after 1500 cycles. Such results are also proved by CV tests and EIS measurements. Meanwhile, the lithium storage mechanism of PbLi2Ti6O14@NC is investigated by an in situ XRD technique. It indicates that PbLi2Ti6O14@NC has a stable structural host. These aforementioned results suggest that PbLi2Ti6O14@NC has great potential working as an anode material for lithium ions batteries.