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Different atomic arrangements lead to the changes of the electronic structures, which in turn affect the voltages, the diffusion dynamics, and relevant electrochemical properties of the materials. In this study, the inherent properties and lithium storage mechanism of polymorphic LiNbWO6, tetragonal and hexagonal phases, are investigated in detail via experimental techniques and density functional theory calculations. The specific capacity of LiNbWO6-T at a high mass loading of about 10 mg cm–2is 200.4 mA h g–1, and its Coulombic efficiency is 90.5% at 100 mA g–1. Conversely, the reversible capacity of LiNbWO6-H is only 20.5 mA h g–1with a Coulombic efficiency of 70.3% at 50 mA g–1. Our experiments show that tetragonal LiNbWO6manifests higher specific capacity, faster Li-ion storage kinetics, and superior electrochemical performance in comparison to the hexagonal phase. The results suggest that tetragonal LiNbWO6is a promising host for highly efficient lithium storage applications.

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, ZrNb14O37nanowires are fabricated via a facile electrospinning method, presenting a nanoparticle-in-nanowire architecture. As an anode for LIBs, the as-fabricated ZrNb14O37nanowires maintain a capacity of 244.9 mA h g–1at 100 mA g–1and 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 ZrNb14O37nanowires and LiCoO2suggests that ZrNb14O37nanowires 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.

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.

HTiNbO5has 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 H0.92K0.08TiNbO5nanowires via simple electrospinning followed by an ion-exchange reaction. The H0.92K0.08TiNbO5nanowires consist of many small “lumps” with a uniform diameter distribution of around 150 nm. Used as an anode for lithium-ion batteries, H0.92K0.08TiNbO5nanowires exhibit high capacity, fast electrochemical kinetics, and high performance of lithium-ion uptake. A capacity of 144.1 mA h g–1can be carried by H0.92K0.08TiNbO5nanowires at 0.5 C in the initial charge, and even after 150 cycles, the reversible capacity can remain at 123.7 mA h g–1with an excellent capacity retention of 85.84%. For H0.92K0.08TiNbO5nanowires, the diffusion coefficient of lithium ions is 1.97 × 10–11cm2s–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 H0.92K0.08TiNbO5nanowires can be a possible alternative anode material for rechargeable batteries.

TiNb24O62with large theoretical capacity and safe working potential is regarded as a candidate for lithium ion batteries. However, poor electronic conductivity of TiNb24O62restricts its widely application. Herein, we propose a novel methodology concerned about nitrogen-doped carbon coating to improve the electrochemical performance of TiNb24O62nanowires. 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 TiNb24O62nanowires. Meanwhile, both first principles calculations and in-situ XRD technique are applied to realize the structural evolution of nitrogen-doped carbon coated TiNb24O62nanowires. The obtained results show a high diffusion channel for lithium ions in the lattice of TiNb24O62and the good electrochemical reversibility of nitrogen-doped carbon coated TiNb24O62nanowires. In addition, a full lithium ion battery is assembled by using nitrogen-doped carbon coated TiNb24O62nanowires as anode and LiFePO4as cathode. Such a cell can deliver a high capacity, indicative of a great potential for practical applications. Therefore, nitrogen-doped carbon coated TiNb24O62nanowires can be a promising anode for high-rate lithium ion batteries.

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, K6Nb10.8O30groove 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 situtransmission electron microscopy (TEM). From in situobservations, the K6Nb10.8O30GNB, 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 K6Nb10.8O30GNB is as high as 69%. Furthermore, the lithium-storage mechanism is also investigated via in situX-ray diffraction (XRD). It is proved that the phase transition takes place from Li-poor K6Nb10.8O30phase to Li-rich Li22K6Nb10.8O30phase viatwo steps. In addition, the results obtained from ex situTEM and ex situX-ray photoelectron spectroscopy (XPS) also prove that the behavior of lithiation and de-lithiation for K6Nb10.8O30GNB is highly reversible, suggesting that it can be a possible anode material.

In this work, garnet-framework Li3Nd3W2O12as a novel insertion-type anode material has been prepared via a facile sol–gel method and examined as a lithium container for lithium ion batteries (LIBs). Li3Nd3W2O12shows a charge capacity of 225 mA h g–1at 50 mA g–1, and with the current density increasing up to 500 mA g–1, the charge capacity can still be maintained at 186 mA h g–1. After cycling at 500 mA g–1for 500 cycles, Li3Nd3W2O12retains about 85% of its first charge capacity changed from 190.2 to 161 mA h g–1. Furthermore, in situ X-ray diffraction technique is adopted for the understanding of the insertion/extraction mechanism of Li3Nd3W2O12. The full-cell configuration LiFePO4/Li3Nd3W2O12is also assembled to evaluate the potential of Li3Nd3W2O12for practical application. These results show that Li3Nd3W2O12is such a promising anode material for LIBs with excellent electrochemical performance and stable structure.

Hollow microstructure always exhibits some special properties in the field of electrochemistry. Here, this study reports the rational design and preparation of TiNb2O7nanofibers with one dimensional hollow structure via co-electrospinning. The as-electrospun TiNb2O7hollow nanofibers show high intercalation potential, low charge-charge resistance and fast electrochemical kinetics. The electrochemical results exhibit that the TiNb2O7hollow nanofibers deliver a reversible capacity of 210.1mAhg−1after 150 cycles at a current rate of 0.4C, and 158.4mAhg−1after 900 cycles even at a current rate of 10C with an outstanding capacity retention of 80.6%. The excellent electrochemical performance of nanofibers can be related to the unique morphology of hollow structure. Furthermore, the lithium ions storage mechanism of TiNb2O7hollow nanofibers is also systematically analyzed, which is related to one two-phase coexistence and two solid-solution processes during the whole charge-discharge cycle. In addition, it is also demonstrated by in situ and ex situ observations that TiNb2O7hollow nanofibers have outstanding structural stability and electrochemical reversibility. Therefore, the TiNb2O7hollow nanofibers can be applied as an alternative promising electrode material for the next rechargeable lithium ions batteries.

VNb9O25is a novel lithium storage material, which has not been systematically investigated so far. Via electrospinning technology, VNb9O25samples with two different morphologies, pored nanoribbon and rodlike nanoparticles, are prepared in relatively low temperature and time-saving calcination conditions. It is found that the formation process of different morphologies depends on the control of self-aggregation of the precursor by using different sample collectors. Compared with rodlike VNb9O25(RL-VNb9O25), pored nanoribbon VNb9O25(PR-VNb9O25) can deliver a higher specific capacity, lower capacity loss, and better cyclability. Even cycled at 1000 mA g–1, the reversible capacity of 132.3 mAh g–1is maintained by PR-VNb9O25after 500 cycles, whereas RL-VNb9O25only exhibits a capacity of 102.7 mAh g–1. The enhancement should be attributed to the pored nanoribbon structure with large specific surface area and shorter pathway for lithium ions transport. Furthermore, the lithium ions insertion/extraction process is verified from refinement results of in situX-ray diffraction data, which is associated with a lithium occupation process in type III and VI cavities through tunnels I, II, and III. In addition, high structural stability and electrochemical reversibility are also demonstrated. All of these advantages suggest that PR-VNb9O25is a promising anode material for lithium-ion batteries.

Via Li+, Cu2+, Y3+, Ce4+, and Nb5+dopings, a series of Na-site-substituted Na1.9M0.1Li2Ti6O14are prepared and evaluated as lithium storage host materials. Structural and electrochemical analyses suggest that Na-site substitution by high-valent metal ions can effectively enhance the ionic and electronic conductivities of Na2Li2Ti6O14. As a result, Cu2+-, Y3+-, Ce4+-, and Nb5+-doped samples reveal better electrochemical performance than bare Na2Li2Ti6O14, especially for Na1.9Nb0.1Li2Ti6O14, which can deliver the highest reversible charge capacity of 259.4 mAh g–1at 100 mA g–1among all samples. Even when cycled at higher rates, Na1.9Nb0.1Li2Ti6O14still can maintain excellent lithium storage capability with the reversible charge capacities of 242.9 mAh g–1at 700 mA g–1, 216.4 mAh g–1at 900 mA g–1, and 190.5 mAh g–1at 1100 mA g–1. In addition, ex situ and in situ observations demonstrate that the zero-strain characteristic should also be responsible for the outstanding lithium storage capability of Na1.9Nb0.1Li2Ti6O14. All of this evidence indicates that Na1.9Nb0.1Li2Ti6O14is a high-performance anode material for rechargeable lithium ion batteries.

•The Li+migration mechanism is determined by DFT together with MD.•Li frenkel defect, Li/V anti-site and Li+vacancies are the main intrinsic defects in the lattice.•The SOC (state of charge) dependency of Li+diffusion coefficients are fully revealed.•Li+intercalation/deintercalation mechanism and phase evolution are determined by cluster expansion.

In this paper, we reported on a comparison of LiVPO4F to Li4Ti5O12as anode materials for lithium-ion batteries. Combined with powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, galvanostatic discharge/charge tests and in situ X-ray diffraction technologies, we explore and compare the insertion/extraction mechanisms of LiVPO4F based on the V3+/V2+/V+redox couples and Li4Ti5O12based on the Ti4+/Ti3+redox couple cycled in 1.0–3.0 V and 0.0–3.0 V. The electrochemical results indicate that both LiVPO4F and Li4Ti5O12are solid electrolyte interphase free materials in 1.0–3.0 V. The insertion/extraction mechanisms of LiVPO4F and Li4Ti5O12are similar with each other in 1.0–3.0 V as proved by in situ X-ray diffraction. It also demonstrates that both samples possess stable structure in 0.0–3.0 V. Additionally, the electrochemical performance tests of LiVPO4F and Li4Ti5O12indicate that both samples cycled in 0.0–3.0 V exhibit much higher capacities than those cycled in 1.0–3.0 V but display worse cycle performance. The rate performance of Li4Ti5O12far exceeds that of LiVPO4F in the same electrochemical potential window. In particular, the capacity retention of Li4Ti5O12cycled in 1.0–3.0 V is as high as 98.2% after 20 cycles. By contrast, Li4Ti5O12is expected to be a candidate anode material considering its high working potential, structural zero-strain property, and excellent cycle stability and rate performance.

With the adoption of ABAQUS/Explicit as the simulation platform, a 3D finite element model has been established to simulate the stretch bending of square tube aluminum profile which is used as the door frame of fork lifter. Four characteristic points are put forward to evaluate the distortion of cross section during deformation, and the influence to distortion of cross section from some key parameters, such as bending radius and thickness of profile, is analyzed. An orthogonal experiment is designed to evaluate the influence to deformation from other forming parameters, including preload, fill rally and filling pressure which occurred in the stretch bending process. Then neural network based response surface method and genetic algorithm are used to optimize the parameters mentioned above. Finite element simulation proved that the optimized result is valuable to reduce the distortion of cross section of profile and improve formability.

This article proposed a liquid phase method to synthesize the small, even sized nano lead sulfide sol in high power (2KW) pulse ultrasonic reactor, which is designed by our research group. The characteristics of this method are the short time, the small granularity, the equal particle size and the mild synthesis condition. The particle size of lead sulfide sol is about 7～8 nanometer and the size distribution is narrow. Ultraviolet and visible spectroscopy shows that the absorption limit of this lead sulfide sol is about 670nm. Compared with the normal sized lead sulfide, the absorption limit is greatly blue shifted because of the quantum size effect.

The surface physical and chemical behaviors of conductive additive acetylene black (AB) are studied after the samples are cycled at different working temperatures (−20, 20, and 60 °C). Working at low temperature (−20 °C), AB shows high polarization and poor electrochemical property. In addition, plenty of inorganic compounds are formed on the surface of AB. For comparison, the surface film on AB after being worked at 60 °C is comprised of an outer organic layer and an inner inorganic layer. Moreover, it consumes large electrical energy and results in irreversible trapped lithium for surface film formation. Furthermore, much more organic components can induce lower thermal stability of conductive additive. During repeated electrochemical cycles, the surface structure of AB experiences a series of changes of surface electrolyte decomposition products. It is found that the organic polymer in outer layer will decompose into other stable species, and partial surface fluorides in the inner layer will transform into other fluorides. The working temperature has a great effect on the final transformation products.

The electrochemical behaviors and lithium-storage mechanism of LiCoO2in a broad voltage window (1.0−4.3 V) are studied by charge−discharge cycling, XRD, XPS, Raman, and HRTEM. It is found that the reduction mechanism of LiCoO2with lithium is associated with the irreversible formation of metastable phase Li1+xCoII IIIO2−yand then the final products of Li2O and Co metal. During the charging process, the Li2O/Co mixture can be oxidized into CoO, and then the Li2O/CoO mixture can result in the formation of Co3O4in the higher-voltage region. LixCoOyis the final product when the active material is charged to 4.3 V. During the subsequent cycles, the lithium uptake/release reactions are related to the reversible conversion of Co ↔ CoO ↔ Co3O4↔ LixCoOy.

Transition metal dichalcogenides (TMDs) with layered structure are regarded as a potential electrode material for high-performance energy storage devices, while intrinsic low electrical conductivity causes poor electrochemical performance. As we know, the change of atomic structure for TMDs can lead to the improvement of electrochemical properties. In this work, defect chemistry is employed to achieve this purpose. TiS2as a typical electrode material is chosen to complete the study of controllable defect engineering. Theoretical calculations and experimental analysis confirm that concentration and species of defects can be controlled via adjusting the experimental conditions. A series of concentrations of sulfur vacancies are introduced in TiS2by annealing methods. The introduction of sulfur vacancies enhances bond strength of Ti-S bonds near the defect area and improves electronic structure. Benefiting from the positive effect of sulfur vacancies, the electrochemical characteristics of TiS2are greatly optimized, including cycle ability and dynamic characteristics. In addition, it is found that the improvement of electrochemical performance is closely related to the concentration of defects. These results reveal that controllable defect engineering may be a fascinating strategy to promote the advancement of TMDs in energy storage application.

In recent years, potassium-ion batteries have been extensively studied as an alternative for lithium ion batteries, thus developing electrode materials for them has become important. TiS2as a typical electrode material is chosen due to the unique layered structure. However, 1T-TiS2(tetragonal (T)) is a metastable metallic phase, leading to poor long-term stability for alkali metal ions batteries. In order to alleviate this shortcoming, the functional cation defects are generated on the surface of TiS2via thermal annealing method in this work. Introduced titanium vacancies effectively improve cycle ability and enhance kinetic performance. The microscopic stress and strain can be weakened due to the existence of defects, demonstrating that defects can alleviate volume expansion during the ion intercalation process to maintain structural stability, thus obtaining excellent cycle ability. Meanwhile, titanium vacancies also can regulate alkali metal ions insertion sites to stabilize crystal structure. In addition, titanium vacancies could be conducive to the improvement of kinetics, including charge-transfer resistance and ions transport. These features are verified by electrochemical analysis combined with density functional theory calculations. Therefore, functional cation defects engineering as a facile and effective strategy can be advanced in various energy storage applications.

Electrochemical energy storage devices are currently an ideal tool to meet the energy needs of the people. It has been certified that niobium-based chalcogenides are generally used as the electrode materials for electrochemical energy storage devices due to their unique physical and chemical properties. This review summarizes the different synthesis methods and applications about the various niobium-based chalcogenides. In addition, in view of the existing problems of the niobium-based chalcogenides, many modification methods to improve the electrochemical properties of electrode materials are summarized, such as coating conductive matrixes, preparing composite materials, preparing porous or nanometer materials, and doping hetero atoms, etc. Finally, while summarizing the progress in recent years, the current bottlenecks and possible development directions in the future have also been proposed.