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Li4Ti5O12 nanosheets (LTONS) embedded in three-dimensional amorphous carbon (3DAC) are fabricated by a facile hydrothermal method. Structure and morphology analyses confirm that the Li2TiO3 impurity phase is effectively suppressed in LTONS@3DAC and that the stacking of LTONS is also significantly inhibited in the porous matrix of the 3DAC, helpfully increasing the lithium ion diffusion coefficient. Compared to LTONS, LTONS@3DAC has a greatly enhanced electrochemical performance, including superior rate capabilities of 146, 142, and 140 mAh g−1 at the current rates of 32, 48, and 64 C, respectively, and an excellent cycling stability of 140 mAh g−1 after 700 cycles at 8 C. Therefore, the LTONS@3DAC composite is promising for applications in superior-rate lithium-ion batteries.

The application of tungsten (W) material is limited due to its intrinsic brittleness at low temperature. W-based multilayer composites are one of the solutions to improve the fracture toughness of W. In this study, a series of tungsten/tantalum (W/Ta) multilayer composites are prepared by diffusion bonding. The interfacial microstructure and fracture toughness under different deformation modes are investigated. It has been found that the flexural strength and fracture toughness loading perpendicular to the W/Ta interface are significantly higher than that loading parallel to the interface. The composites bonded at 1000 °C exhibits the highest flexural strength and fracture toughness. Both the flexural strength and fracture toughness decrease as bonding temperature increases. The decrease of flexural strength is due to recovery and recrystallization of the W layers. The decrease of fracture toughness is mainly attributed to the changes of the interfacial microstructure and fracture mechanism. For the composites bonded at 1000 °C, plastic deformation of the Ta layer and interfacial debonding are the main mechanisms for energy dissipation during crack propagation. As the bonding temperature increases, the decomposition of oxide scale and dynamic recrystallization occur at the vicinity of the W/Ta interface. A layer of fine recrystallization grains is developed at the W/Ta interface when the bonding temperature is higher than 1300 °C. As the interfacial bonding defects decreases, the interfacial bonding strength increases. Therefore, the interfacial debonding is inhibited in the composites bonded at a temperature higher than 1200 °C, instead, multiple tunnel micro-cracks appear in the W layers.

Multilayer composites are effective to improve the toughness of Tungsten (W). To demonstrate the toughing mechanism, a series of W/Ti multilayer composites are prepared by diffusion bonding at different temperatures in a spark plasma sintering system. It shows that the mechanical properties of the composites vary with the change of bonding temperature, which is closely related with the microstructures developed at different bonding temperatures. The bending strength of the composites bonding at 1100 °C is highest, which reaches 1847 MPa. However, the composites bonding at 1200 °C has absorbed the highest fracture energy during three-point bending tests. The different microstructures developed at different bonding temperatures are mainly due to the different diffusion behaviors of W and Ti elements. The activation energy of W diffusion into Ti and Ti diffusion into W is 87.69 KJ/mol and 152.20 KJ/mol, respectively. And the diffusion coefficient of W into Ti is two orders of magnitude higher than that of Ti into W. Thus, β-Ti has formed in the Ti layer due to W diffusion into Ti. Although α-Ti is precipitated in the β-Ti, solid solution strengthening is the main strengthening mechanism in the Ti layer. The toughening mechanism of the W/Ti multilayer composites is mainly crack deflection, and the plastic deformation of the Ti layer. Meanwhile, the fracture modes of these composites are proposed.

Mechanical properties of tungsten (W) multilayer composites can be modified by the toughening layers and interfacial microstructure between W layer and toughening layer. The W/Ta multilayer composite usually shows low tensile strength and toughness because of the low strength of Ta layers and large bonding strength between W layer and Ta layer. In order to improve the strength and toughness of the W/Ta multilayer composite, Ti intermediate layers with different thickness ranging from 30 µm to 100 µm have been added between W layer and Ta layer to get a kind of W/Ti/Ta/Ti multilayer composites. It can be found that the thickness of the Ti layer has a large effect on the microstructure and mechanical properties of the W/Ta multilayer composites. The solid solution with pure β-Ti and β-Ta are formed in the Ti layer when the thickness of Ti layer is lower than 50 µm. Ti layer composed of β-Ti, β-Ta and α precipitates is developed when the thickness of Ti layer is larger than 80 µm. The comprehensive mechanical properties of the W/Ta multilayer composites increase as the thickness of Ti intermediate layer increases. The tensile strength of the W/Ti/Ta/Ti multilayer composites is up to 642 MPa, which is much higher than that of the W/Ta multilayer composites (274 MPa). The tensile strength of these multilayer composites can be evaluated by a modified mix model considering the interfacial stress concentration factor. As the fracture mechanism of the W/Ta multilayer composites is also modified by addition of the Ti layer, the toughness of the W/Ti/Ta/Ti multilayer composites is improved because of the delamination along with the W/Ti interface and plastic deformation of the Ti/Ta/Ti layer in plane stress condition.

Li3.9Cr0.3Ti4.8O12 nanofibers with one-dimensional (1D) morphology and excellent electrical conductivity are prepared via a facile electrospinning technique. The as-prepared Li3.9Cr0.3Ti4.8O12 nanofibers exhibit excellent lithium storage performance with superior rate capability and low-temperature performance: 140 mAh g−1 at 10 C and 91 mAh g−1 at 50 C rates at room temperature, 100 mAh g−1 at 1 C rate at −20 °C. The superior electrochemical performance of Li3.9Cr0.3Ti4.8O12 nanofibers is attributed to the 1D nano-architectures composed of nanocrystals and the reduced grain size in Li3.9Cr0.3Ti4.8O12, both of which facilitate the Li+ ion transport. The Li3.9Cr0.3Ti4.8O12 nanofibers also have a high Ti3+ concentration and an in-situ surface coating layer of Li2CrO4, which could enhance intraparticle and interparticle electronic conductivities of Li3.9Cr0.3Ti4.8O12 grains, respectively.

In order to show the formation mechanism of {001}〈210〉 orientation, a Ta-2.5W alloy was cold rolled to a large strain when many microbands are aligned with rolling direction. The {001}〈210〉 orientation is usually developed in a deformation band with normal direction//〈001〉 next to {111}〈110〉 orientation. The {001}〈210〉 and {111}〈110〉 orientations share a common rotation axis of 〈111〉 and a highly stressed slip system of {110}〈111〉. The orientation relationship between {001}〈210〉 and {111}〈110〉 orientations could be a twin relationship (60°/〈111〉). The {001}〈210〉 orientation is probably developed by the rotation of intra-grain deformation bands, which is related with the shear banding and rigid body rotation. When the strain reaches 90%, deformation bands are crossed by shear bands and the orientations are changed. However, the {001}〈210〉 orientation can still be seen. The {001}〈210〉 oriented grains grow larger during subsequent annealing at 1223 K to 1323 K attribute to the coincident site lattice interfaces.

The work presents a detailed investigation of the microstructure characteristics of the γ-fiber (normal direction// ) in electron beam melted Ta-2.5W alloy subjected to cold rolling. With increasing strain, the average space of microbands decreases towards a saturation value which is about 0.5 μm. The typical microstructure in γ fiber is microbands and shear bands in different appearance. The microbands are relatively straight and aligned close with slip planes when the strain is lower than 60%. The non-crystallographic irregular microbands and shear bands prevail in γ fiber when the strain is larger than 70%. When the strain reaches 90%, a group of parallel macroshear bands are formed. The orientation of γ fiber can spread up to 60°. Both {111} and {001} new orientations are developed in {111} orientation. Many new developed high angle boundaries of these new grains are coincident site lattice boundaries (Σ3 and Σ9). Meanwhile, these new grains and matrix always share a common or with matrix.

Tungsten (W) laminate materials are very promising to improve the fracture toughness of tungsten. In this study, four kinds of tungsten laminated composites with different interlayers, including Ta, Ti, Ti/Ta/Ti, and W layers, are fabricated by spark plasma sintering (SPS). Compared with the W/W, W/Ti and W/Ta multilayer composites, the W/Ti/Ta composites exhibit the highest tensile strength (581 MPa) and elongation (7.9%). It shows that a gradual decrease of strength and a gradual increase of ductility from the W layer to the Ta layer can be obtained in the W/Ti/Ta multilayer composites. The tensile strength of these multilayer composites can be approximately predicted by the modified rule of mix. The toughening mechanism can be attributed to the energy dissipation caused by interfacial debonding, plastic deformation of interlayers, and crack bridging of the intermediate layer. The results show that the mechanical properties of the different tungsten-based multilayers are closely related to the toughening interlayers, which is beneficial to design tungsten laminates with high strength and toughness.

The effect of tungsten content on deformation texture and microstructure of Ta-W alloy is studied. It is found that the increase of tungsten content results in the strengthening of α-fiber and the weakening of γ-fiber in Ta-W alloys. The volume fraction of γ-fiber developed in Ta-10W alloy is lower than that in Ta-2.5W alloys. Meanwhile, a more significant through-thickness texture gradient is formed in Ta-10W alloy. The addition of tungsten has an important effect on the ability cross-slip of dislocations. Therefore, more dislocation loops and activated slip systems can be seen in Ta-2.5W alloy. The size of the dislocation cells in Ta-2.5W alloy is larger than that in Ta-10W alloy. As shear bands tends to appear in γ-fiber, the density of shear bands in the Ta-2.5W alloy is much higher than that of Ta-10W alloy at the same reduction strain. Meanwhile, the wavelength of the wavy shear bands in Ta-10W alloy is smaller than that in Ta-2.5W alloy. In Ta-10W alloy, new grains with Goss orientation can be seen in periodic shear bands developed in {111} orientations, which is different from that in Ta-2.5W alloy.

In this study, a series of the W/Ta multilayer composites are prepared by spark plasma sintering (SPS) at different temperature. The relationship between the sintering temperature and tensile properties are investigated in detail. Large equiaxed recrystallization grains appear in the W layers when the sintering temperature reaches 1200 °C. The W/Ta multilayer composites have a better comprehensive performance when the sintering temperature is 1100 °C. The fracture mechanisms of the W/Ta multilayer composites can be divided into two types based on the bonding strength of the interface. When the sintering temperature is lower than 1200 °C, delamination cracks can be seen. Meanwhile, necks and shear cracks appear in the Ta layers. When the sintering temperature reaches 1200 °C, delamination cracks disappear. Meanwhile, a lot of shear bands can be observed in the Ta layers. As the sintering temperature increases, the fracture mode of the W layers changes from transgranular cleavage fracture to intergranular fracture. And the fracture mode of the Ta layers is always ductility fracture. However, the ductility of the Ta layers decreases since the stress state changes from plane stress state to plane strain state. The tensile strength of the W/Ta multilayer composites can be calculated by the proposed model considering the stress concentration factor in the interface.

Nano-Li4Ti5O12 powders were synthesized by a simple gel route with acrylic acid, tetrabutyl titanate, and lithium nitrate as the precursors that were made into gels through thermal polymerization. The Li4Ti5O12 powders were obtained by calcination of the gels at 700, 750, and 800 °C. They were characterized by thermal gravimetric analysis, differential thermal analysis, X-ray diffraction, and field emission scanning electron microscopy. The electrochemical performance of these nano-Li4Ti5O12 powders was examined with galvanostatic cell cycling. The average particle size of the 700-, 750-, and 800 °C-calcined powders is about 70, 120, and 400 nm, respectively. The 750 °C-calcined powder exhibits a high capacity of over 160 mAh/g after 100 cycles and a good rate capability with a capacity of 122 mAh/g even at 10C rate.

The γ-Li 2 CuZrO 4 with a double rock-salt structure, as a lithium-ion compound, has never been reported on their physical and physicochemical properties. The γ-Li 2 CuZrO 4 was prepared by a solid-state reaction process. X-ray diffraction was used to analyze the structure of the products. Its electrical properties were characterized by both DC and AC measurements in the temperature range from 133 to 1273 K. Cyclic voltammetry and galvanostatic cell cycling were also employed to evaluate its electrochemical performance. It is found to be a pure electronic semiconductor with a fairly high conductivity (10 −5 S/cm at 133 K, 10 −2 S/cm at 300 K and 10 −1 S/cm at 1173 K). The average activation temperature is 14.4 kJ/mol. When increasing the temperature above 1073 K, a phase transition from γ to β takes place. When reacting with lithium in an electrochemical cell, γ-Li 2 CuZrO 4 decomposes into three phases during the initial discharge process, and possesses a reversible capacity of about 70 mAh/g.

Layered LiCo1/3Ni1/3Mn1/3O2 as a lithium insertion positive-electrode material was prepared by a radiated polymer gel method. The synthesis conditions and microstructure, morphology and electrochemical properties of the products were investigated by XRD, SEM and electrochemical cell cycling. It was found that the positive-electrode material annealed at 950 °C showed the best electrochemical property with the first specific discharge capacity of 178 mAh/g at C/6 and stable cycling ability between 2.8 and 4.5 V versus Li/Li+. The optimized LiCo1/3Ni1/3Mn1/3O2 exhibited rather good rate capability with the specific capacity of 173 mAh/g at 0.2C and 116 mAh/g at 4C under a fast charge and discharge mode in rate performance test.

By heating the admixture of a commercial liquid electrolyte (LB302, 1 M solution of LiPF6 in 1:1 EC/DEC), methyl methacrylate (MMA) and benzoyl peroxide (BPO, initiator), a poly(methyl methacrylate) (PMMA) based gel-polymer electrolyte (GPE) was obtained. AC impedance spectroscopy and cyclic voltammetry were used to evaluate its ionic conductivity and electrochemical stability window. Rechargeable cells LiNi0.8Co0.2O2/Li and LiNi0.8Co0.2O2/graphite with this MMA based GPE were also fabricated via the in-situ thermal polymerization process. This GPE exhibits a high ionic conductivity (over 10−3S cm−1) at room temperature. It is stable in the voltage range between 0 and 4.2 V (vs. Li+/Li). A phenomenon of large initial cell impedance (LICI) was observed for the LiNi0.8Co0.2O2/Li cells but not in LiNi0.8Co0.2O2/graphite cells. After the first several cycles, the cell impedance decreases substantially and reversible charge–discharge capacity can be obtained. This in-situ polymerization method provides a way to produce GPE cells.

A new type of Li 3 PO 4 -based composite electrolyte films was fabricated with an approach similar to Bellcore technology. The films are composed of Li 3 PO 4 fine powder, SiO 2 nanoparticles, dibutyl( o -)phthalate (DBP) and a polymer matrix poly(vinyldiene fluoride). X-ray diffraction, scanning electron microscopy and photo scattering techniques were employed to analyze the Li 3 PO 4 powder synthesized by a chemical precipitation method. AC impedance spectroscopy was used to measure the electrical properties of the composite electrolyte films. The effect of the addition of different concentration nanoparticles SiO 2 and DBP on the conductivities of the Li 3 PO 4 -based composite electrolyte was analyzed. It is found that the optimized starting composition with a mass ratio Li 3 PO 4 :SiO 2 :DBP:Kynar 2801 (PVDF–12% HFP):acetone equal to 30:5:30:35:100 gives rise to the highest ionic conductivity of 2.4 × 10 −8 S/cm at 30 °C and 1.7 × 10 −7 S/cm at 100 °C with an activation energy of 0.32 eV. It is comparable with that of Li 3 PO 4 thin films obtained from sputtering or electrostatic spray deposition (ESD) techniques. The presence of the plasticizer DBP and nanoparticles SiO 2 plays an important role to minimize the resistance for lithium-ion conduction between Li 3 PO 4 particles. In addition, for the graphite/composite/graphite measurement cell, the apparent conductivity for the charge-transfer process between the electrolyte film and the graphite electrode is about one order of magnitude lower than that of the composite electrolyte with an activation energy of 0.56 eV. The development of such composite films opens opportunities to thermally stable electrolytes for rechargeable lithium batteries.

The search for a reliable indicator of state of charge and even the remaining energy of a lithium-ion cell is of great importance for various applications. This study was an exploratory effort to use magnetic susceptibility as the indicator. In this work, for the first time the change of ac susceptibility of cells was in situ monitored during charge–discharge process. A strong permanent magnetic material, NdFeB alloy, was investigated as an anode material for rechargeable lithium batteries. Both original and partially oxidized NdFeB powders were made into electrodes. Structural characterization was performed on the NdFeB electrodes by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. An alloy (core)–oxide (shell) structure was found for those partially oxidized samples. The electrochemical cycling of cells made of the NdFeB electrodes against lithium was measured. The first lithium intercalation capacity of a treated NdFeB can be up to about 831 mAh/g, while a rather reversible capacity of up to 352 mAh/g can be obtained. With a specially designed cell, we were able to monitor in situ the change of relative ac susceptibility during charge and/or discharge steps. A clearly monotonous relationship is found between the ac susceptibility of a cell and its depth-of-discharge (DOD). A mechanism based on skin effect and eddy current change is proposed to explain this susceptibility versus DOD relationship.