Search

The recently explored FeNb11O29 is an advanced anode material for lithium-ion batteries due to its large specific capacity and high safety. However, its poor electronic conductivity significantly limits its rate capability. To tackle this issue, a Cr3+ doping is employed, and CrxFe1-xNb11O29 (x = 0 and 0.2) materials were fabricated using a solid-state reaction. X-ray diffraction analyses combined with Rietveld refinements demonstrate that the Cr3+ doping does not destroy the orthorhombic shear ReO3 crystal structure (Amma space group) of FeNb11O29 or obviously change the unit cell volume. Scanning electron microscopy images combined with specific surface area tests reveal the similar particle size after the Cr3+ doping. Due to the free 3d electrons in the Cr3+ ions, the electronic conductivity of Cr0.2Fe0.8Nb11O29 is enhanced by three orders of magnitude comparing with FeNb11O29. Consequently, Cr0.2Fe0.8Nb11O29 exhibits improved electrochemical properties. At 0.1C, it delivers a large reversible capacity of 254 mAh g−1. At 10C, it still provides a large capacity of 123 mAh g−1 with large retention of 86.9% after 500 cycles. In contrast, FeNb11O29 shows a small capacity of 57 mAh g−1 and small retention of 41.6%. These results reveal that Cr0.2Fe0.8Nb11O29 can be a promising anode material for high-performance lithium-ion batteries.

Ti 2 Nb 10 O 29 is an advanced anode material for lithium-ion batteries due to its large specific capacity and high safety. However, its poor electronic/ionic conductivity significantly limits its rate capability. To tackle this issue, a Cr 3+ –Nb 5+ co-doping is employed, and a series of Cr x Ti 2–2 x Nb 10+ x O 29 compounds are prepared. The co-doping does not change the Wadsley–Roth shear structure but increases the unit-cell volume and decreases the particle size. Due to the increased unit-cell volumes, the co-doped samples show increased Li + -ion diffusion coefficients. Experimental data and first-principle calculations reveal significantly increased electronic conductivities arising from the formation of impurity bands after the co-doping. The improvements of the electronic/ionic conductivities and the smaller particle sizes in the co-doped samples significantly contribute to improving their electrochemical properties. During the first cycle at 0.1 C, the optimized Cr 0.6 Ti 0.8 Nb 10.6 O 29 sample delivers a large reversible capacity of 322 mAh g −1 with a large first-cycle Coulombic efficiency of 94.7%. At 10 C, it retains a large capacity of 206 mAh g −1 , while that of Ti 2 Nb 10 O 29 is only 80 mAh g −1 . Furthermore, Cr 0.6 Ti 0.8 Nb 10.6 O 29 shows high cyclic stability as demonstrated in over 500 cycles at 10 C with tiny capacity loss of only 0.01% per cycle.

Highly Li+-conductive HfNb24O62 is explored as a new intercalation-type niobium-based oxide anode material for superior Li+ storage. HfNb24O62 owns a Wadsley-Roth shear structure with a large unit-cell volume, leading to a large Li+ diffusion coefficient. HfNb24O62 shows a large capacity, safe operating potential, high rate performance and good cyclability.

Conductive Nb12O29 hierarchical microspheres with nanosheet shells were synthesized based on a hydrothermal process and a high-temperature hydrogen reduction treatment. The obtained materials demonstrated comprehensively good electrochemical properties, including a significant pseudocapacitive contribution, safe operating potential, high reversible capacity, superior initial coulombic efficiency, increased rate capability, and durable cycling stability.

Niobates with tungsten bronze crystal structures are regarded as prospective Li[Formula: see text]-storage anode candidates due to the rich chemistry of niobium and structural openness. However, the exploration of this type of materials is still insufficient. Here, BiNb[Formula: see text]O[Formula: see text] with a tetragonal tungsten bronze crystal structure (Cmmm space group) is explored. Abundant large-sized tunnels and a large interlayer spacing of [Formula: see text]3.97 Å are found in this open structure, enabling fast Li[Formula: see text] diffusivity (3.25 × 10[Formula: see text]/1.68 × 10[Formula: see text] cm2 ⋅ s[Formula: see text] during lithiation/delithiation). Additionally, this structure is very stable after the first lithiation process, resulting in excellent cyclability (95.4%/[Formula: see text]100% capacity retention after 100/1000 cycles at 1C/10C). BiNb[Formula: see text]O[Formula: see text] further exhibits a safe Li[Formula: see text]-storage potential ([Formula: see text]1.55 V) and a large reversible capacity (309.7 mAh ⋅ g[Formula: see text]@ 0.1C). Therefore, BiNb[Formula: see text]O[Formula: see text] can be a practical Li[Formula: see text]-stora ge anode compound for large-scale energy-storage applications.

A series of non-stoichiometric carbon-coated lithium iron phosphate (LiFexPO4/C) have been prepared by a solid-state reaction to study the variation of electrochemical performance at different x values. Characterized by XRD in conjunction with Rietveld refinement, Mossbauer, TEM, Raman, etc., it is indicated that the Li–O bond is elongated in the Fe-poor non-stoichiometric lithium iron phosphate with decreasing x value, while the content of Fe2P and graphitization degree of carbon layer in LiFexPO4/C samples is associated with the ratio of x. The powder electronic conductivity increases from 8.33 × 10−2 S cm−1 to 16.67 × 10−2 S cm−1 as the x value decreases from 1.04 to 0.98, which is due to a suitable amount of Fe2P and a superior graphitized carbon layer. Among different Fe/Li ratios, LiFe0.98PO4/C exhibits the highest rate capability of 163.5 mA h g−1 at 0.1C and 93.5 mA h g−1 at 20C, as well as the largest diffusion coefficient of 12.6 × 10−14 cm2 s−1. It is illustrated that the synergy effect of elongated Li–O bonds, moderate Fe2P and graphitized carbon layer results in the high performance of non-stoichiometric LiFexPO4/C.

The ever-increasing power and energy demands for modern consumer electronics and electric vehicles are driving the pursuit of energy-storage technologies beyond the current horizon. Pseudocapacitive charge storage is one of the most effective and promising approaches to fill this technology gap, owing to its potential to deliver both high power and energy densities. Typically, titanium niobium oxides (TiNbxO2+2.5x (x = 2, 5 and 24)) with intrinsic pseudocapacitance, high safety and theoretical capacities of 388–402 mA h g−1 are recognized as promising anode materials for lithium-ion batteries. However, their poor conductivity and low Li+-ion diffusion coefficient are known to be the major hurdles limiting the full utilization of their pseudocapacitive effects, leading to their lackluster rate capabilities. Herein, we employ a facile electrospinning method to prepare one-dimensional hierarchically porous ZrNb24O62 nanowires (P-ZrNb24O62) with an ultra-large Li+-ion diffusion coefficient as a new intercalating pseudocapacitive material for boosting Li+-ion storage. The P-ZrNb24O62 exhibits excellent electrochemical performances, including a high reversible capacity (320 mA h g−1 at 0.1C), safe working potential (∼1.67 V vs. Li/Li+), high initial coulombic efficiency (90.1%), outstanding rate capability (182 mA h g−1 at 30C) and durable long-term cyclability (90.2% capacity retention over 1500 cycles).

To explore advanced anode materials for lithium-ion batteries of electric vehicles, Cu 2+ /Nb 5+ co-doped TiNb 2 O 7 is studied. Cu 0.02 Ti 0.94 Nb 2.04 O 7 is successfully fabricated using a facile solid-state reaction. X-ray diffraction analyses combined with Rietveld refinements demonstrate that the trace Cu 2+ /Nb 5+ co-doping does not destroy the shear ReO 3 crystal structure of TiNb 2 O 7 but increases the lattice parameters and unit cell volume. Specific surface area tests and scanning electron microscopy images reveal a smaller average particle size in Cu 0.02 Ti 0.94 Nb 2.04 O 7 . Due to the increased unit cell volume and free 3d electrons in Cu 2+ ions, the Li + -ion diffusion coefficient and electronic conductivity of Cu 0.02 Ti 0.94 Nb 2.04 O 7 are respectively enhanced by 14.8 times and at least 220 times. Consequently, Cu 0.02 Ti 0.94 Nb 2.04 O 7 exhibits advanced electrochemical properties in terms of specific capacity, rate capability and cyclic stability. At 0.1 C, it delivers a large first-cycle discharge/charge capacity of 346/315 mAh g −1 . At 10 C, it still provides a large capacity of 182 mAh g −1 with tiny loss of only 1.2% over 1000 cycles. In sharp contrast, TiNb 2 O 7 shows a small capacity of only 90 mAh g −1 and large loss of 59.8%. Therefore, Cu 0.02 Ti 0.94 Nb 2.04 O 7 possesses great potential for the application in lithium-ion batteries for electric vehicles.

Flexible electrodes with high charge storage capacity, low solid-state diffusion resistance toward charges, and excellent mechanical properties are needed for fabricating flexible energy storage devices. In this paper, an approach is described to synthesize a composite material with hollow rutile TiO(2)cuboid arrays supported on carbon fiber cloth (H-TiO2@CFC). This composite material is used as a self-supporting and binder-free anode for sodium-ion storage, delivering reversible charge capacities of 287.3 at 0.1 C and 103.3 mAh g(-1)at 50 C, respectively. The observed excellent electrochemical performance of the H-TiO2@CFC electrode is mainly attributed to its unique architecture, which facilitates ion transport, improves electron conductivity, and enables active surface reactivity toward sodium ions. In situ X-ray diffraction characterization results reveal a nearly zero strain structure of the hollow rutile TiO(2)in H-TiO2@CFC against electrochemical cycling. An analysis of the charge storage mechanism reveals a significant pseudocapacitance contribution to the charge storage, accounting for the observed high-rate performance of the electrode. A flexible full cell fabricated with the H-TiO2@CFC as the anode and Na3V2(PO4)(3)as the cathode exhibits both excellent electrochemical properties and flexibility against mechanical deformation, demonstrating the great promise of the H-TiO2@CFC composite material for flexible battery cells.

A green and efficient route to the synthesis of boron carbonitride (BCN) nanoribbons was demonstrated using waste coconut shells, boric acid and urea as the raw materials. The BCN nanoribbons were then applied as anode materials for lithium-ion batteries (LIBs). The BCN nanoribbons possessed high specific surface area and porosity because of the inherent characteristics of the coconut shells, providing multiple active sites and diffusion channels for Li+ ions. High specific capacity, excellent rate capability and cycling stability were achieved especially when the carbon content in BCN is relatively high. The average reversible capacity and the retention rate reached 800 mAh g−1 at 0.1 A g−1 and 98% after 1000 cycles, respectively. This route not only paved a new way to the synthesis of BCN nanoribbons, but also realized the reuse of waste natural resources for fabricating LIBs anode materials with excellent performance.

Spherical vanadium phosphate (VPO4) particles grown on flexible electron-conductive carbon fiber cloth (CFC) is developed as a binder-free anode for lithium-ion batteries (LIBs). The flexible composite electrode (VP@CFC) exhibits an excellent performance, including high reversible lithium-ion storage capacity (541.2 mAh g−1 at 0.1C), high rate capability (350.2 mAh g−1 at 10C), and good cycling stability (a capacity retention ratio of 91.8% after 250 cycles at 1C). Moreover, a flexible full cell fabricated with the VP@CFC as anode and a commercial LiCoO2 (LCO) coated on CFC (LCO@CFC) as cathode displays good flexibility against mechanical bending at a wide range of angle while maintaining its good electrochemical performance. The flexible VP@CFC electrode holds a great promise in applications for flexible energy storage devices.

Transition-metal oxides based materials have recently been shown to be promising anode material for lithium ion batteries (LIBs) application to replace graphite material. In the present work, highly dispersed ultra-small MoOx nanoparticles anchored on N-doped three-dimensional (3D) hierarchically porous carbon (3D-MoOx@CN) are prepared on the basis of an efficient in-situ chelating and hard-templating strategy. The MoOx nanoparticles with particle sizes between 1.5 and 3.5 nm are observed to be anchored on the surface of the 3D N-doped carbon. The 3D-MoOx@CN composite anode electrode exhibits several appealing characteristics for lithium ion storage, including high specific capacity, good stability against cycling and fast charge transport kinetics. An optimized 3D-MoOx@CN sample (3D-MoOx@CN-700) delivers specific capacities of 742 mAh g−1 at current density of 100 mA g−1 and 431 mAh g−1 at 1000 mA g−1 after 1000 cycles, respectively. The observed excellent performance is due to the unique hierarchical pore structure with strong binding of the ultra-small MoOx nanoparticles onto N-doped carbon surface, which can avoid the agglomeration and alleviate the volume expansion of MoOx nanoparticles in the charge-discharge process. The composite electrode material described in this work holds a great potential for the development of high-performance lithium-ion batteries. Meanwhile, the synthesis method presents a common strategy to prepare other composite materials with highly dispersed metal oxide on the hierarchically porous carbon materials.

M-Nb-O compounds are advanced anode materials for lithium-ion batteries (LIBs) due to their high specific capacities, safe operating potentials, and high cycling stability. Nevertheless, the found M-Nb-O anode materials are very limited. Here, Mg

TiNb24O62 is explored as a new anode material for lithium-ion batteries. Microsized TiNb24O62 particles (M-TiNb24O62) are fabricated through a simple solid-state reaction method and porous TiNb24O62 microspheres (P-TiNb24O62) are synthesized through a facile solvothermal method for the first time. TiNb24O62 exhibits a Wadsley-Roth shear structure with a structural unit composed of a 3 × 4 octahedron-block and a 0.5 tetrahedron at the block-corner. P-TiNb24O62 with an average sphere size of ∼2 μm is constructed by nanoparticles with an average size of ∼100 nm, forming inter-particle pores with a size of ∼8 nm and inter-sphere pores with a size of ∼55 nm. Such desirable porous microspheres are an ideal architecture for enhancing the electrochemical performances by shortening the transport distance of electrons/Li+-ions and increasing the reaction area. Consequently, P-TiNb24O62 presents outstanding electrochemical performances in terms of specific capacity, rate capability and cyclic stability. The reversible capacities of P-TiNb24O62 are, respectively, as large as 296, 277, 261, 245, 222, 202 and 181 mA h g-1 at 0.1, 0.5, 1, 2, 5, 10 and 20 C, which are obviously larger than those of M-TiNb24O62 (258, 226, 210, 191, 166, 147 and 121 mA h g-1). At 10 C, the capacity of P-TiNb24O62 still remains at 183 mA h g-1 over 500 cycles with a decay of only 0.02% per cycle, whereas the corresponding values of M-TiNb24O62 are 119 mA h g-1 and 0.04%. These impressive results indicate that P-TiNb24O62 can be a promising anode material for lithium-ion batteries of electric vehicles.

Li4Ti5O12 suffers from its small theoretical capacity and low conductivity, limiting its practical applications in lithium-ion batteries. Although its conductivity has been improved, its theoretical capacity has not been increased so far. Here, for the first time, the capacity of Li4Ti5O12 is increased by combining Ti3+/Ti4+ and Cr2+/Cr3+ redox couples. Spinel Li5Cr9Ti4O24 with a larger theoretical capacity of 323 mAh g−1 is designed and fabricated through a facile solid-state reaction method. The as-fabricated Li5Cr9Ti4O24 delivers a large initial discharge capacity of 311 mAh g−1 between 3 and 0.001 V (vs. Li/Li+) at a current density of 62.5 mA g−1, which is larger than that of Li4Ti5O12. Furthermore, it exhibits good (electronic and ionic) conductivity and a high rate performance.

Lithium-ion batteries are not only popular for portable electronic devices, but also promising for electric vehicles. However, the current lithium-ion batteries for electric vehicles have limited safety performances. Due to the inherently safe performances, titanium-containing oxides are regarded as promising alternatives to the traditional carbonaceous anode materials. This paper reviews the characteristics, the crystal structures and the improvements of several popular titanium-containing complex oxides, including Li4Ti5O12, Li2MTi3O8, MLi2Ti6O14 and Ti2Nb2xO4+5x. An insight into the future research directions for titanium-containing complex oxides is also provided.

Potassium-ion batteries (KIBs) are receiving increasing interest in grid-scale energy storage owing to the earth abundant and low cost of potassium resources. However, their development still stays at the infancy stage due to the lack of suitable electrode materials with reversible depotassiation/potassiation behavior, resulting in poor rate performance, low capacity, and cycling stability. Herein, the first example of synthesizing single-crystalline metallic graphene-like VSe

RuxTi1−xNb2O7 (x = 0 and 0.01) materials have been synthesized via a solid-state reaction method. X-ray diffraction combined with Rietveld refinements demonstrates that both samples have a Wadsley–Roth shear structure with a C2/m space group without any impurities, and that the unit cell volume increases after the trace Ru4+ doping. Scanning electron microscopy and specific surface area tests reveal that the Ru4+ doping decreases the average particle size. The Li+ ion diffusion coefficient and electronic conductivity of Ru0.01Ti0.99Nb2O7 are respectively 64% and at least two orders of magnitude larger than those of the pristine TiNb2O7. First-principles calculations show that the increased electronic conductivity can result from the formation of impurity bands after the Ru4+ doping. Ru0.01Ti0.99Nb2O7 exhibits a large initial discharge capacity of 351 mA h g−1 at 0.1 C between 3.0 and 0.8 V vs. Li/Li+, approaching its theoretical capacity (388 mA h g−1). At 5 C, unlike the pristine TiNb2O7 with a small charge capacity of 115 mA h g−1, Ru0.01Ti0.99Nb2O7 delivers a large value of 181 mA h g−1, even exceeding the theoretical capacity of the popular spinel Li4Ti5O12 (175 mA h g−1). After 100 cycles, Ru0.01Ti0.99Nb2O7 shows a large capacity retention of 90.1%. These outstanding electrochemical performances can be attributed to its improved Li+ ionic and electronic conductivity as well as smaller particle size.

Ti-Nb-O binary oxide materials represent a family of promising intercalating anode materials for lithium-ion batteries. In additional to their excellent capacities (388-402 mAh g

Intercalation-type TiNb

Although spinel Li 4 Ti 5 O 12 is an attractive anode material for lithium-ion batteries (LIBs), it suffers from its poor rate performance. To improve the rate performance, a Li 3.9 Cu 0.1 Ti 5 O 12 and carbon nanotubes (CNTs) composite was fabricated through mixing CNTs with Li 3.9 Cu 0.1 Ti 5 O 12 particles. X-ray diffraction combined with Rietveld refinement, X-ray photoelectron spectroscopy, field emission scanning electron microscope, transmission electron microscope, nitrogen adsorption–desorption measurement, electrochemical impedance spectroscopy, two-terminal electronic conductivity test and galvanostatic discharge–charge test were employed for the characterizations. The Cu + substituting negligibly changed the particle size but modified the crystal structure. Consequently, the electronic and Li + ion conductivities of Li 3.9 Cu 0.1 Ti 5 O 12 were respectively increased to 4.0 × 10 −8 S cm −1 and 5.6 × 10 −7 S cm −1 , which are at least forty and four times larger than those of the pristine Li 4 Ti 5 O 12 . Through incorporating CNTs, the electrical conduction between the Li 3.9 Cu 0.1 Ti 5 O 12 particles was enhanced. As a result of these simultaneous improvements arising from the synergistic effect combining intrinsic improvement by Cu + substituting and extrinsic enhancement by CNTs compositing, Li 3.9 Cu 0.1 Ti 5 O 12 /CNTs shows a significantly improved rate performance, which is better than those of Li 3.9 Cu 0.1 Ti 5 O 12 , Li 4 Ti 5 O 12 /CNTs and Li 4 Ti 5 O 12 . The specific capacity of Li 3.9 Cu 0.1 Ti 5 O 12 /CNTs at 10 C is up to 103 mAh g −1 between 1.0 and 2.5 V ( vs. Li/Li + ), in contrast to those of Li 3.9 Cu 0.1 Ti 5 O 12 , Li 4 Ti 5 O 12 /CNTs and Li 4 Ti 5 O 12 to be only 29, 68, 12 mAh g −1 at the same rate. In addition, Li 3.9 Cu 0.1 Ti 5 O 12 /CNTs exhibits high cyclic stability with capacity retention of 96.3% over 100 cycles. These advanced electrochemical performances may render Li 3.9 Cu 0.1 Ti 5 O 12 /CNTs a promising candidate for the anodes of high-power LIBs.

Lithium-ion batteries (LIBs) have become popular electrochemical devices. Due to the unique advantages of LIBs in terms of high operating voltage, high energy density, low self-discharge, and absence of memory effects, their application range, which was primarily restricted to portable electronic devices, is now being extended to high-power applications, such as electric vehicles (EVs) and hybrid electrical vehicles (HEVs). Among various anode materials, Li4Ti5O12 (LTO) is believed to be a promising anode material for high-power LIBs due to its advantages of high working potential and outstanding cyclic stability. However, the rate performance of LTO is limited by its intrinsically low electronic conductivity and poor Li + ion diffusion coefficient. This review highlights the recent progress in improving the rate performance of LTO through doping, compositing, and nanostructuring strategies.

To improve the rate performance of Li4Ti5O12 (LTO), we employ a doping-compositing synergistic strategy that utilizes Cu2+ to alter intrinsic property and carbon nanotubes (CNTs) to engineer extrinsic conductivity. To realize cost-effective fabrication, solid state processing is adopted in the fabrication of the composite. X-ray diffraction measurement combined with Rietveld refinement shows that all doped samples have a spinel structure with F d 3 ¯ m space group without any impurities, and that both lattice parameter and occupancy of non-Li+ ions in 8a sites increase with the amount of Cu2+ dopant. Through the Cu2+ doping, the electronic conductivity and Li+ diffusion coefficient of the particles are improved by at least two orders of magnitude and four times, respectively. Through further CNTs compositing, the electrical conduction between the particles is enhanced. Between 1.0 and 2.5 V vs. Li/Li+, the specific capacity of Li3.8Cu0.3Ti4.9O12/CNTs composite at 10 C is as high as 114 mAh g−1 with little loss after 100 cycles, whereas that of pristine one is only 11 mAh g−1. The excellent electrochemical performance can be ascribed to its higher electronic conductivity and enhanced lithium ion conductivity in the particles, as well as its improved electrical conduction between the particles.

Li3VO4 has gained significant attention as a promising anode material for lithium-ion batteries owing to its high specific capacity, low cost and safe working potential. Unfortunately, its disappointing electronic conductivity limits its rate performance. To address this problem, a series of Cr[Formula: see text]-doped Li3VO4 compounds are synthesized by solid-state reaction. The obtained Li[Formula: see text]Cr[Formula: see text]V[Formula: see text]O4 compounds ([Formula: see text] and 0.02) have the same orthorhombic crystal structure (Pnm21 space group), suggesting the successful Cr[Formula: see text] doping in Li3VO4. Compared with Li3VO4, Li[Formula: see text]Cr[Formula: see text]V[Formula: see text]O4 exhibits a two orders of magnitude larger electronic conductivity. Additional benefits of the Cr[Formula: see text] doping include the increase of the Li[Formula: see text] diffusion coefficient and the decrease of the particle size. Consequently, Li[Formula: see text]Cr[Formula: see text]V[Formula: see text]O4 displays not only a large reversible capacity (363[Formula: see text]mAh g[Formula: see text] at 60[Formula: see text]mA g[Formula: see text] and superior cyclic stability (86.6% capacity retention after 1000 cycles at 1200[Formula: see text]mA g[Formula: see text] but also decent rate performance (147[Formula: see text]mAh g[Formula: see text] at 1200[Formula: see text]mA g[Formula: see text].

High-rate performance flexible lithium-ion batteries are desirable for the realization of wearable electronics. The flexibility of the electrode in the battery is a key requirement for this technology. In the present work, spinel lithium titanate (Li4 Ti5 O12 , LTO) cuboid arrays are grown on flexible carbon fiber cloth (CFC) to fabricate a binder-free composite electrode (LTO@CFC) for flexible lithium-ion batteries. Experimental results show that the LTO@CFC electrode exhibits a remarkably high-rate performance with a capacity of 105.8 mAh g-1 at 50C and an excellent electrochemical stability against cycling (only 2.2% capacity loss after 1000 cycles at 10C). A flexible full cell fabricated with the LTO@CFC as the anode and LiNi0.5 Mn1.5 O4 coated on Al foil as the cathode displays a reversible capacity of 109.1 mAh g-1 at 10C, an excellent stability against cycling and a great mechanical stability against bending. The observed high-rate performance of the LTO@CFC electrode is due to its unique corn-like architecture with LTO cuboid arrays (corn kernels) grown on CFC (corn cob). This work presents a new approach to preparing LTO-based composite electrodes with an architecture favorable for ion and electron transport for flexible energy storage devices.

Li3.33Cu1.005Ti4.665O12/CuO was fabricated via a one-step solid-state reaction. Li3.33Cu1.005Ti4.665O12 with the P4332 space group shows enhanced electronic conductivity and Li+ ion diffusion coefficient. The Cu particles reduced from CuO during the first lithiation process benefit the electrical conduction between Li3.33Cu1.005Ti4.665O12 particles. Consequently, Li3.33Cu1.005Ti4.665O12/CuO exhibits a small potential hysteresis and high rate performance.

To comprehensively improve the performance of Li4Ti5O12 (LTO), a synergistic method combining compositing, crystal structure modification and hierarchical particle structuring is employed in this work. Monodispersed/multidispersed mesoporous Li4Ti5O12-x/C submicrospheres were fabricated using monodispersed/multidispersed TiO2 submicrospheres, lithium hydroxide and sucrose as precursors. The Li4Ti5O12-x/C submicrospheres have a well-crystallized spinel structure, no blockages of Li(+) ion transport pathways, 2.69-3.03% O(2-) vacancy contents (vs. all 32e sites in the spinel structure), and 12.9-14.6% Ti(3+) ion contents (vs. all titanium ions). Thus, the electronic conductivity and Li(+) ion diffusion coefficient of particles can be significantly improved, and the working potential is 4.4-4.7 mV lower than that of LTO. Furthermore, these submicrospheres contain 1.06-1.44 wt% carbon as carbon coatings (2-3 nm in thickness) and carbon nanoparticles (∼20 nm in size), resulting in smaller primary particle sizes (100 nm), large specific surface areas (12-15 m(2) g(-1)), proper pore sizes (∼4 nm) and enhanced electrical conduction between particles. In addition, the submicrospherical morphology allows large tap densities (1.41-1.71 g cm(-3)). As a result of this desirable structure, these mesoporous Li4Ti5O12-x/C submicrospheres exhibit comprehensively improved electrochemical performances. The optimized sample, with an ideally graded sphere-size distribution ranging from 100 nm to 600 nm, shows the largest tap density of 1.71 g cm(-3), high first cycle Coulombic efficiency of 95.0% and 4.5 mV lower working potential. At 10 C, its capacity is as high as 119 mA h g(-1) with capacity retention of 95.9% over 100 cycles.

Doping, incorporating a conductive phase and reducing the particle size are three strategies for improving the rate capability of Li4Ti5O12 (LTO). Thus, the synergistic employment of these three strategies is expected to more efficiently improve the rate capability. To achieve this goal, Fe2+ doped LTO/multiwall carbon nanotube (MWCNT) composites were prepared by post-mixing MWCNTs with Fe2+ doped LTO particles from a solid-state reaction, while Cr3+ doped LTO/MWCNT composites were fabricated by a facile one-step solid-reaction using MWCNT premixing. Fe2+/Cr3+ doping not only remarkably improves the electronic conductivity and Li+ ion diffusion coefficient in LTO but also lowers its working potential. The carbon existed in the material fabrication processes leads to the reduction of the particle size. The introduction of MWCNTs in the Fe2+/Cr3+ doped LTO/MWCNT composite significantly enhances the electrical conduction between Fe2+/Cr3+ doped LTO particles. As a result of this novel synergistic strategy, performances of Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites are comprehensively improved. The Li3.8Fe0.3Ti4.9O12/MWCNT composite shows a working potential of 8.9 mV lower than that of pristine LTO. At 10 C, its capacity is up to 106 mA h g−1 with an unexpected capacity retention of 117% after 200 cycles in a potential window of 1.0–2.5 V (vs. Li/Li+). The corresponding values for LiCrTiO4/MWCNT composites are 46.2 mV, 120 mA h g−1 and 95.9%. In sharp contrast, the pristine counterpart shows a very disappointing capacity of only 11 mA h g−1 at 10 C. Therefore, the novel Li3.8Fe0.3Ti4.9O12/MWCNT and LiCrTiO4/MWCNT composites possess great potential for applications in high-power lithium-ion batteries.

Li4−2xNi3xTi5−xO12 (0 ≤ x ≤ 0.25) has been synthesized via solid-state reaction. X-ray diffractions (XRD) demonstrate that all doped samples have a spinel structure with Fd 3 ¯ m space group without any impurities. Through further Rietveld refinements, it is shown that both lattice parameter and occupancy of non-Li+ ions in the 8a sites negligibly change with the amount of Ni2+ dopants. Scanning electron microscope reveals that Ni2+ doping does not change the morphology of Li4Ti5O12. The best electronic conductivity of Ni2+ doped Li4Ti5O12 is at least one order of magnitude higher than that of the pristine one, while all samples have similar Li+ ion diffusion coefficients. The electrochemical performance of Ni2+ doped Li4Ti5O12 shows good rate capability. The specific capacity of Li3.9Ni0.15Ti4.95O12 at 5 C is as high as 72 mAh g−1, while that of the pristine one can only achieve 33 mAh g−1. This improved rate performance can be ascribed to its enhanced electronic conductivity.

Three-dimensional self-assembled graphene aerogels (GAs) are successfully developed by a simple chemical reduction with l -ascorbic acid at low temperature. And for the first time, the relationship among morphologies, electrical and thermal properties of GAs is studied comprehensively by controlling reaction conditions. The electrical conductivities of the GAs are also improved by four times after an annealing at 400 °C for 5 h under Ar environment. The results are very useful to optimize the best morphology, electrical and thermal properties of GAs for the best performance of GA-based electrodes of energy storage devices such as supercapacitors and batteries.

TiNb

Formation of ordered magnetic states in germanium nanostructures embedded in SiO2 has been investigated. Samples with the nanostructures were prepared by sputtering deposition on Si(100) substrates, followed by thermal annealing in vacuum. Transmission electron microscopy, energy dispersive X-ray spectrometry, and Raman spectroscopy have been used to characterize the samples. Magnetic measurements were performed using a superconducting quantum interference device. Size-effect induced magnetic orderings in the germanium nanostructures were found to be present at room temperatures and below. Superparamagnetic behavior was observed at temperatures above 230 K, whereas thermal excitation of spin reorientation and magnetic coupling has been revealed at temperatures below 60 K. Inverted hysteresis loops with negative remanences and multiple plateaus revealed the ferri- or antiferromagnetic nature of the coupling. Inter-domain coupling and effect of magnetic anisotropy will be discussed based on the experimental results and simulations with a spin reorientation model.

Three-dimensional (3D) porous self-supported MoS2 electrodes are constructed by electrodepositing coupled with high-temperature heat treatment using 3D porous Cu prepared via electroless plating as the substrate, and directly used as anode of sodium-ion battery. The 3D porous structure can accommodate the volumetric expansion/shrinkage and alleviate the stress caused from the large volumetric changes of MoS2 electrodes during electrochemical cycling. Meanwhile, large surface area of this unique configuration enables sufficient electrode/electrolyte interaction and fast electron transportation. Besides, the influence of heat treatment temperatures on the sodium storage performance of MoS2 electrode is also investigated. The electrochemical test result shows that the 3D porous self-supported MoS2 electrode heat treated at 350[Formula: see text]C has the best electrochemical performance. It demonstrates a high first reversible capacity of 714.1[Formula: see text]mAh g[Formula: see text] at 50[Formula: see text]mA g[Formula: see text] with a high first Coulombic efficiency of 84%, and a good capacity retention of 306.8[Formula: see text]mAh g[Formula: see text] after 100 cycles at 2[Formula: see text]A g[Formula: see text]. The reversible capacity at 3.2[Formula: see text]A g[Formula: see text] shows high value of 241[Formula: see text]mAh g[Formula: see text], which is 37% of that at 0.05[Formula: see text]A g[Formula: see text].

Potassium-ion batteries (KIBs) are receiving increasing interest in grid-scale energy storage owing to the earth abundant and low cost of potassium resources. However, their development still stays at the infancy stage due to the lack of suitable electrode materials with reversible depotassiation/potassiation behavior, resulting in poor rate performance, low capacity, and cycling stability. Herein, the first example of synthesizing single-crystalline metallic graphene-like VSe2 nanosheets for greatly boosting the performance of KIBs in term of capacity, rate capability, and cycling stability is reported. Benefiting from the unique 2D nanostructure, high electron/K+ -ion conductivity, and outstanding pseudocapacitance effects, ultrathin VSe2 nanosheets show a very high reversible capacity of 366 mAh g-1 at 100 mA g-1 , a high rate capability of 169 mAh g-1 at 2000 mA g-1 , and a very low decay of 0.025% per cycle over 500 cycles, which are the best in all the reported anode materials in KIBs. The first-principles calculations reveal that VSe2 nanosheets have large adsorption energy and low diffusion barriers for the intercalation of K+ -ion. Ex situ X-ray diffraction analysis indicates that VSe2 nanosheets undertake a reversible phase evolution by initially proceeding with the K+ -ion insertion within VSe2 layers, followed by the conversion reaction mechanism.

ZnO nanobelt array films were prepared using an electrodeposition method with liquid crystal template. The as-prepared sample was amorphous and changed to nanocrystalline ZnO after sintered at 500 degrees C for 1 h. The influences of reaction conditions to the morphology of the samples were checked in detail. When the distance between WE (working electrode) and CE (counter electrode) was 3 mm, the electrodeposition potential was -0.9 V versus SCE (saturated calomel electrode), the electrodeposition temperature was 65 degrees C and the surfactant concentration was 60 wt%, the ZnO nanobelt arrays were densest, most ordered and perpendicularly oriented. The sintered two-layer film was applied as a photoanode of a dye-sensitized solar cell (DSC), and a relatively high short-circuit photocurrent density of 10 mA/cm2 and an overall light-to-energy conversion efficiency of 2.1% were achieved.

ZnO nanobelt array films were prepared using an electrodeposition method with liquid crystal template. The as-prepared sample was amorphous and changed to nanocrystalline ZnO after sintered at 500 °C for 1 h. The sintered film with nanobelt width of about 5 nm was first applied as a photoanode of a dye-sensitized solar cell (DSC), and a high short-circuit photocurrent density of 17 mA/cm 2 and an overall light-to-energy conversion efficiency of 2.6% were achieved.

Externally bonded glass fiber-reinforced polymer (GFRP) fabrics are being increasingly used for seismic retrofit and rehabilitation of concrete structures due to their high strength to weight ratio and low cost in comparison to carbon and aramid fibers. However, previous studies have shown that glass fibers are vulnerable to attack caused by harsh environmental weathering agents such as freezing—thawing, wetting—drying, and exposure to alkaline and acidic environments. Concerned with durability, this study is based on a fracture mechanics approach to evaluate the interface durability of GFRP bonded to normal concrete (NC) and high-performance concrete (HPC), subjected to two types of weathering protocols: (1) freeze—thaw cycling under calcium chloride, which is used to simulate the deleterious effect of the de-icing agents used on highways in wintry weather; and (2) alternate wetting and drying in a sodium-hydroxide solution, which is used to simulate the naturally occurring alkalinity due to the presence of concrete pore water, that can cause degradation due to a combination of mechanisms such as leaching and pitting of the glass fibers, and cracking and spalling of the resin matrix. Durability of the GFRP—concrete interface is characterized based on the critical strain energy release rate, under Mode-I loading, and weight and strain measurements. Unconditioned companion specimens are fractured alongside their aged counterparts to provide baseline-feedback and also enable comparative analysis of the fracture surfaces. Considerable degradation of the interface bond integrity is found to have resulted with increasing cycling period.

A mesoporous nanocrystalline graded TiO 2 film was prepared on either a transparent conductive glass (ITO/glass) or a transparent conductive polymer (ITO/PEN, PEN = poly(ethylene naphthalene-2,6-dicarboxylate) through a doctor-blade method and then treated by chemical sintering at 150 °C. The graded film, which has a large specific surface area, high porosity, and proper strength, was composed of particles with different sizes and appropriate ratios. The effects of the smallest particles for binding and the largest particles for light scattering were studied. High light-to-energy conversion efficiencies of 4.10% and 3.05% were obtained within the dye-sensitized solar cells (DSSCs) fabricated by using the graded films on ITO/glass and ITO/PEN, respectively. The results show that the graded structure has promising applications in DSSCs.

Titanate nanotubes with an outer diameter of ca. 9 nm were obtained with hydrothermal method followed by an ion exchange reaction. The as-prepared sample was composed of H 2 Ti 2 O 4 (OH) 2 , which was thermally unstable. The effect of calcination temperature on its morphology and crystal form was investigated. Based on the results, especially the appearance of lotus-root-like structures, the transformation mechanism was proposed, which involved the dehydrations of intralayered and interlayered OH groups. The decrease in the interlayer distance and the transformation from titanate to anatase were ascribed to the interlayered dehydration, while the destruction of nanotubes into particles was caused by the intralayered one.

To explore anode materials with large capacities and high rate performances for the lithium-ion batteries of electric vehicles, defective Ti2Nb10O27.1 has been prepared through a facile solid-state reaction in argon. X-ray diffractions combined with Rietveld refinements indicate that Ti2Nb10O27.1 has the same crystal structure with stoichiometric Ti2Nb10O29 (Wadsley-Roth shear structure with A2/m space group) but larger lattice parameters and 6.6% O2– vacancies (vs. all O2– ions). The electronic conductivity and Li+ion diffusion coefficient of Ti2Nb10O27.1 are at least six orders of magnitude and ~2.5 times larger than those of Ti2Nb10O29, respectively. First-principles calculations reveal that the significantly enhanced electronic conductivity is attributed to the formation of impurity bands in Ti2Nb10O29–x and its conductor characteristic. As a result of the improvements in the electronic and ionic conductivities, Ti2Nb10O27.1 exhibits not only a large initial discharge capacity of 329 mAh g–1 and charge capacity of 286 mAh g–1 at 0.1 C but also an outstanding rate performance and cyclability. At 5 C, its charge capacity remains 180 mAh g–1 with large capacity retention of 91.0% after 100 cycles, whereas those of Ti2Nb10O29 are only 90 mAh g–1 and 74.7%.

Li4Ti5O12 suffers from its small theoretical capacity and low conductivity, limiting its practical applications in lithium-ion batteries. Although its conductivity has been improved, its theoretical capacity has not been increased so far. Here, for the first time, the capacity of Li4Ti5O12 is increased by combining Ti3+/Ti4+ and Cr2+/Cr3+ redox couples. Spinel Li5Cr9Ti4O24 with a larger theoretical capacity of 323 mAh g−1 is designed and fabricated through a facile solid-state reaction method. The as-fabricated Li5Cr9Ti4O24 delivers a large initial discharge capacity of 311 mAh g−1 between 3 and 0.001 V (vs. Li/Li+) at a current density of 62.5 mA g−1, which is larger than that of Li4Ti5O12. Furthermore, it exhibits good (electronic and ionic) conductivity and a high rate performance.

TiNb6O17 is prepared by calcination of TiO2 and Nb2O3 in the molar ratio Nb:Ti = 6:1 (1200 °C, 4 h).

In this paper, the effect of the annealing temperature on the phase transition and optical property of titanate nanotubes was discussed in detail. TGA results indicated that the dehydration process happened when titanate nanotubes were annealed. Up to 450 °C, the weight loss ceased entirely. XRD results showed that anatase and triclinic Ti 5 O 9 were formed in annealed samples. TEM was used to observe the micrographs of samples. SAED patterns indicated that the granular phase and the rod-shaped crystal were triclinic Ti 5 O 9 and anatase, respectively. In addition, UV–vis diffuse reflectance spectra were used to study the optical band gap of samples annealed at different temperature.

Here, we firstly reported a composite electrolyte prepared by adding α-zirconium phosphate into the iodide/triiodide liquid electrolyte including 4-tert-butylpyridine (TBP). The obtained composite electrolyte exhibited very good electrochemical property. The exchange current density (I0) and the diffusion coefficient of triiodide (DI3-) were both enhanced markedly. It was proved that the intercalation behavior of TBP into layered α-ZrP could be responsible for their enhancement. The mechanism for the enhancement of I0 and DI3- were investigated in detail, supported by X-ray diffraction (XRD) electrochemical impedance spectra (EIS) and limiting current measurements. Keywords: Exchange current density, Diffusion coefficient, Zirconium phosphate, Electrolyte

Analytical solutions for the deformation, penetration, and perforation of composite plates and sandwich panels subjected to quasi-static punch indentation and projectile impact are derived. Discrete spring-mass models are used to calculate the impact response of the composite plates and sandwich panels. Equivalent load resistance functions are obtained from the quasi-static analysis and adjusted for high strain rate. A generalized solution methodology for projectile impact of composite plates and sandwich panels are then proposed based on three key factors: (i) the contact load duration, (ii) the through-thickness transit time, and (iii) the lateral transit time. A two-dimensional wave propagation model is used to determine the ballistic limits of E-glass/polyester panels and GLARE fiber-metal laminates, and predicted values are found to be within 20 and 13% of the experimental results, respectively. A quasi-static impact model is used to predict the ballistic limit for E-glass/epoxy-aluminum honeycomb sandwich impacted by hemispherical nose projectile and the predicted values are within 11% of test results.