Zn2GeO4 Nanorods synthesized by low-temperature hydrothermal growth for high-capacity anode of lithium battery

Controllable synthesis and morphology-dependent light emission efficiency of Zn2GeO4 nanophosphors

Zn2GeO4 is considered a very promising alternative to current luminescent semiconductors. Previous results suggest that its emitted wavelength may depend on different variables, such as particle size and morphology, among others. In this work, we have prepared pure and highly homogeneous Zn2GeO4 nanorods under hydrothermal synthesis conditions with a willemite-like structure. Their luminescent properties have been explored and their band gap is estimated, which are distinct from those of previously reported Zn2GeO4 bulk particles. Therefore, our results identify particle morphology as a crucial factor for maximizing and fine-tuning the luminescence of Zn2GeO4 nano-phosphors.

Microwave-Assisted Metal-Organic Frameworks Derived Synthesis of Zn2GeO4 Nanowire Bundles for Lithium-Ion Batteries

Germanium-based multi-metallic-oxide materials have advantages of low activation energy, tunable output voltage, and high theoretical capacity. However, they also exhibit unsatisfactory electronic conductivity, sluggish cation kinetics, and severe volume change, resulting in inferior long-cycle stability and rate performance in lithium-ion batteries (LIBs). To solve these problems, we synthesize metal-organic frameworks derived from rice-like Zn2GeO4 nanowire bundles as the anode of LIBs via a microwave-assisted hydrothermal method, minimizing the particle size and enlarging the cation's transmission channels, as well as, enhancing the electronic conductivity of the materials. The obtained Zn2GeO4 anode exhibits superior electrochemical performance. A high initial charge capacity of 730 mAhg-1 is obtained and maintained at 661 mAhg-1 after 500 cycles at 100 mA g-1 with a small capacity degradation ratio of ~0.02% for each cycle. Moreover, Zn2GeO4 exhibits a good rate performance, delivering a high capacity of 503 mA h g-1 at 5000 mA g-1. The good electrochemical performance of the rice-like Zn2GeO4 electrode can be attributed to its unique wire-bundle structure, the buffering effect of the bimetallic reaction at different potentials, good electrical conductivity, and fast kinetic rate.

Identification of Ge═O Double Bonds in Planar MnGe3O and MnGe4O Clusters: Anion Photoelectron Spectroscopy and Ab Initio Calculations

The structures, chemical bonding, and magnetic properties of MnGe₃O^-/0 and MnGe₄O^-/0 are investigated by photoelectron spectroscopy and ab initio calculations. The experimental vertical electron detachment energies of MnGe₃O^- and MnGe₄O^- are measured to be 2.06 ± 0.04 and 2.64 ± 0.04 eV, respectively. The structures of MnGe₃O^-/0 and MnGe₄O^-/0 can be viewed as evolved from quadrilateral MnGe₃ or tetrahedral MnGe₃. It is found that both MnGe₃O^- and MnGe₃O have C_s symmetric planar structures with an O atom attached to quadrilateral MnGe₃. The structure of MnGe₄O^- is nonplanar with an O atom and an additional Ge atom attached to tetrahedral MnGe₃, while that of MnGe₄O is planar with an O atom and an additional Ge atom attached to quadrilateral MnGe₃. Chemical bonding analyses reveal the existence of Ge═O double bonds in MnGe₃O and MnGe₄O. Magnetic property analyses suggest that MnGe₃O and MnGe₄O are ferromagnetic with total spin magnetic moments of 5 μ_B.

Enhancing the Areal Capacity and Stability of Cu2ZnSnS4 Anode Materials by Carbon Coating: Mechanistic and Structural Studies During Lithiation and Delithiation

The widespread use of energy storage technologies has created a high demand for the development of novel anode materials in Li-ion batteries (LIBs) with high areal capacity and faster electron-transfer kinetics. In this work, carbon-coated Cu₂ZnSnS₄ with a hierarchical 3D structure (CZTS@C) is used as an anode material for LIBs. The CZTS@C microstructures with enhanced electrical conductivity and improved Li-ion diffusivity exhibit high areal and gravimetric capacities of 2.45 mA h/cm² and 1366 mA h/g, respectively. The areal capacity achieved in the present study is higher than that of previously reported CZTS-based materials. Moreover, in situ X-ray diffraction results show that lithium ions are stored in CZTS through the insertion reaction, followed by the alloying and conversion reactions at ∼1 V. The structural evolution of Li₂S and Cu-Sn/Cu-Zn alloy phases occurs during the conversion and alloying reactions. The present work provides a cost-effective and simple method to prepare bulk CZTS and highlights the conformal carbon coating over CZTS, which can enhance the electrical and ionic conductivities of CZTS materials and increase the mass loading (1-2.3 mg/cm²). The improved stability and rate capability of CZTS@C anode materials can therefore be achieved.

Characterization of structural and optical properties of Mn2+ doped Zn2 GeO4 nanorods as an efficient green phosphor for solid-state lighting

A series of Mn²⁺ doped zinc germinate ZGO:xMn²⁺ (x = 0-0.05) nanorods were synthesized successfully by the hydrothermal method. X-ray diffraction, Rietveld refinement were used to describe the structural information of the ZGO:xMn²⁺ nanocrystals. XRD revealed that crystal phases of the ZGO:xMn²⁺ is rhombohedral and in the R-3 space group. The unit cell size did not significantly change as the concentration of Mn²⁺ doping increased. The Williamson-Hall equation was also used to explain the strain, nanocrystalline size, and stacking fault. Green LEDs were successfully fabricated by coating ZGO:Mn²⁺ nanorods onto UV-LEDS chip. High color purity, CIE coordinates of the fabricated green LEDs are (0.2404, 0.5428) which is one of the promising candidate for fabrication of UV-based green LEDs.

Decoding of Oxygen Network Distortion in a Layered High-Rate Anode by In Situ Investigation of a Single Microelectrode

Sluggish conversion reactions severely impair the rate capability for lithium storage, which is the main disadvantage of the conversion-type anode materials. Here, the microplatform based on a single microelectrode is designed and utilized for the fundamental understanding of the conversion reaction. The kinetic-favorable layered structure of the anode material is on-site synthesized in the microplatform. The in situ characterization reveals that introducing an oxygen network distortion in the layered oxide anode effectively circumvents the severe passivation of the electrode material by lithium oxide, thus leading to highly reversible conversion reactions. As a result, the high-rate capability of the conversion-type anode materials is realized. The on-site synthesis strategy is further applied in the large-scale synthesis of nanomaterials for lithium-ion batteries. As such, oxide nanorods with the layered structure are synthesized by a facile chemical strategy, showing high rate performance (574 mAh g^-1 at 10 A g^-1). This work unveils the beneficial effect of oxygen network distortion in the layered anode for conversion reactions over cycling, thus providing an alternative strategy to enhance the rate capability of conversion-type anodes for lithium storage.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

Bright persistent green emitting water-dispersible Zn2GeO4:Mn nanorods

This work reports on a green and facile approach for designing bright and persistent green luminescent Zn₂GeO₄:Mn²⁺ nano crystals with high quantum yield (∼52%) and water dispersibility designated for LEDs, security, and bio imaging.

Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO

Functionalizing transparent conducting oxides (TCOs) is an intriguing approach to expand the tunability and operation of optoelectronic devices. For example, forming nanoparticles that act as quantum wells or barriers in zinc oxide (ZnO), one of the main TCOs today, may expand its optical and electronic tunability. In this work, 800 keV Ge ions have been implanted at a dose of 1 × 10¹⁶ cm^-2 into crystalline ZnO. After annealing at 1000 °C embedded disk-shaped particles with diameters up to 100 nm are formed. Scanning transmission electron microscopy shows that these are particles of the trigonal Zn₂GeO₄ phase. The particles are terminated by atomically sharp facets of the type {11 [Formula: see text] 0}, and the interface between the matrix and particles is decorated with misfit dislocations in order to accommodate the lattice mismatch between the two crystals. Electron energy loss spectroscopy has been employed to measure the band gap of individual nanoparticles, showing an onset of band-to-band transitions at 5.03 ± 0.02 eV. This work illustrates the advantages of using STEM characterization methods, where information of structure, growth, and properties can be directly obtained.

CTAB-assisted growth of self-supported Zn2GeO4 nanosheet network on a conductive foam as a binder-free electrode for long-life lithium-ion batteries

The Ge-based compounds show great potential as replacements for traditional graphite anode in lithium-ion batteries (LIBs). However, large volume changes and low conductivity of such materials result in a poor electrochemical cycling and rate performance. Herein, we fabricate a self-supported and three-dimensional (3D) sponge-like structure of interlinked Zn₂GeO₄ ultrathin nanosheets anchored vertically on a nickel foam (ZGO NSs@NF) via a simple hydrothermal process assisted by cetyltrimethyl ammonium bromide (CTAB). Such robust self-supported hybrid structures greatly improve the structural tolerance of the active materials and accommodate the volume variation that occurs during repeated electrochemical cycling. As expected, the self-supported ZGO NSs@NF composites demonstrate an excellent lithium storage with a high discharge capacity, a long cycling life, and a good rate capability when used as binder-free anodes for LIBs. A high reversible discharge capacity of 794 mA h g^-1 is maintained after 500 cycles at 200 mA g^-1, corresponding to 81% capacity retention of the second cycle. Further evaluation at a higher current density (2 A g^-1) also delivers a reversible discharge capacity (537 mA h g^-1) for this binder-free anode. This novel 3D structure of the self-supported ultrathin nanosheets on a conductive substrate, with its volume buffer effect and good interfacial contacts, can stimulate the progress of other energy-efficient technologies.

Luminescence properties and the thermal quenching mechanism of Mn2+ doped Zn2GeO4 long persistent phosphors

Luminescence and thermal quenching mechanisms for excitation and emission in ZGO:2% Mn²⁺ phosphors.

Hierarchical Structural Evolution of Zn2GeO4 in Binary Solvent and Its Effect on Li-ion Storage Performance

Zinc germinate (Zn₂GeO₄) with a hierarchical structure was successfully synthesized in a binary ethylenediamine/water (En/H₂O) solvent system by wet chemistry methods. The morphological evolution process of the Zn₂GeO₄ was investigated in detail by tuning the ratio of En to H₂O in different solvent systems, and a series of compounds with awl-shaped, fascicular, and cross-linked hierarchical structures was obtained and employed as anode materials in lithium-ion batteries. The materials with fascicular structure exhibited excellent electrochemical performance, and a specific reversible capacity of 1034 mA h g^-1 was retained at a current density of 0.5 A g^-1 after 160 cycles. In addition, the as-prepared nanostructured electrode also delivered impressive rate capability of 315 mA h g^-1 at the current density of 10 A g^-1. The remarkable electrochemical performances could be ascribed to the following aspects. First, each unit in the three-dimensional fascicular structure can effectively buffer the volume expansions during the Li⁺ extraction/insertion process, accommodate the strain induced by the volume variation, and stabilize its whole configuration. Meanwhile, the small fascicular units can enlarge the electrode/electrolyte contact area and form an integrated interlaced conductive network which provides continuous electron/ion pathways.

Carbon-Free Porous Zn2GeO4 Nanofibers as Advanced Anode Materials for High-Performance Lithium Ion Batteries

In this work, carbon-free, porous, and micro/nanostructural Zn₂GeO₄ nanofibers (p-ZGONFs) have been prepared via a dissolution-recrystallization-assisted electrospinning technology. The successful electrospinning to fabricate the uniform p-ZGONFs mainly benefits from the preparation of completely dissolved solution, which avoids the sedimentation of common Ge-containing solid-state precursors. Electrochemical tests demonstrate that the as-prepared p-ZGONFs exhibit superior Li-storage properties in terms of high initial reversible capacity of 1075.6 mA h g^-1, outstanding cycling stability (no capacity decay after 130 cycles at 0.2 A g^-1), and excellent high-rate capabilities (e.g., still delivering a capacity of 384.7 mA h g^-1 at a very high current density of 10 A g^-1) when used as anode materials for lithium ion batteries (LIBs). All these Li-storage properties are much better than those of Zn₂GeO₄ nanorods prepared by a hydrothermal process. The much enhanced Li-storage properties should be attributed to its distinctive structural characteristics including the carbon-free composition, plentiful pores, and macro/nanostructures. Carbon-free composition promises its high theoretical Li-storage capacity, and plentiful pores cannot only accommodate the volumetric variations during the successive lithiation/delithiation but can also serve as the electrolyte reservoirs to facilitate Li interaction with electrode materials.

Flexible and free-standing ternary Cd₂GeO₄ nanowire/graphene oxide/CNT nanocomposite film with improved lithium-ion battery performance

To realize flexible lithium-ion batteries (LIBs), the design of flexible electrode/current collector materials with high mechanical flexibility, superior conductivity and excellent electrochemical performance and electrical stability are highly desirable. In this work, we developed a new ternary Cd2GeO4 nanowire/graphene oxide/carbon nanotube nanocomposite (Cd2GeO4 NW/GO/CNT) film electrode. Benefiting from the efficient combination of GO and Cd2GeO4 NWs, our Cd2GeO4 NW/GO/CNT composite film exhibits a capacity of 784 mA h g(-1) after 30 cycles at 200 mA g(-1), which is 2.7 times higher than that of Cd2GeO4 NW/CNT film (290 mA h g(-1)). At a higher rate of 400 mA g(-1) and 1 A g(-1), the Cd2GeO4 NW/GO/CNT film delivers a stable capacity of 617 and 397 mA h g(-1), respectively. Even at 2.5 A g(-1), it still exhibits a high rate capacity of 180 mA h g(-1). The flexible Cd2GeO4 NW/GO/CNT film clearly demonstrates good cycling stability and rate performance for anode materials in LIBs. This route may be extended to design other flexible free-standing metal germanate nanocomposite anode materials.

Germanium-based multiphase material as a high-capacity and cycle-stable anode for lithium-ion batteries

Cu-incorporated porous Ge-based anodes with high electrical conductivity are prepared by a simple carbothermic reduction process of CuGeO₃. The Cu–Ge-based anodes exhibit outstanding capacity retention at 25 °C and 60 °C.

An overview of AB2O4- and A2BO4-structured negative electrodes for advanced Li-ion batteries

Energy-storage devices are state-of-the-art devices with many potential technical and domestic applications.

Ultrathin Hexagonal 2D Co₂GeO₄ Nanosheets: Excellent Li-Storage Performance and ex Situ Investigation of Electrochemical Mechanism

Two-dimensional (2D) nanostructures are a desirable configuration for lithium ion battery (LIB) electrodes due to their large open surface and short pathway for lithium ions. Therefore, exploring new anode materials with 2D structure could be a promising direction to develop high-performance LIBs. Herein, we synthesized a new type of 2D Ge-based double metal oxides for lithium storage. Ultrathin hexagonal Co2GeO4 nanosheets with nanochannels are prepared by a simple hydrothermal method. When used as LIB anode, the sample delivers excellent cyclability and rate capability. A highly stable capacity of 1026 mAhg(-1) was recorded after 150 cycles. Detailed morphology and phase evolutions were detected by TEM and EELS measurements. It is found that Co2GeO4 decomposed into Ge NPs which are evenly dispersed in amorphous Co/Li2O matrix during the cycling process. Interestingly, the in situ formed Co matrix could serve as a conductive network for electrochemical process of Ge. Moreover, aggregations of Ge NPs could be restricted by the ultrathin configuration and Co/Li2O skeleton, leading to unique structure stability. Hence, the large surface areas, ultrathin thickness, and atomically metal matrix finally bring the superior electrochemical performance.

Unique Urchin-like Ca2Ge7O16 Hierarchical Hollow Microspheres as Anode Material for the Lithium Ion Battery

Germanium is an outstanding anode material in terms of electrochemical performance, especially rate capability, but its developments are hindered by its high price because it is rare in the crust of earth, and its huge volume variation during the lithium insertion and extraction. Introducing other cheaper elements into the germanium-based material is an efficient way to dilute the high price, but normally sacrifice its electrochemical performance. By the combination of nanostructure design and cheap element (calcium) introduction, urchin-like Ca2Ge7O16 hierarchical hollow microspheres have been successfully developed in order to reduce the price and maintain the good electrochemical properties of germanium-based material. The electrochemical test results in different electrolytes show that ethylene carbonate/dimethyl carbonate/diethyl carbonate (3/4/3 by volume) with 5 wt% fluoroethylene carbonate additive is the most suitable solvent for the electrolyte. From the electrochemical evaluation, the as-synthesized Ca2Ge7O16 hollow microspheres exhibit high reversible specific capacity of up to 804.6 mA h g(-1) at a current density of 100 mA g(-1) after 100 cycles and remarkable rate capability of 341.3 mA h g(-1) at a current density of 4 A g(-1). The growth mechanism is proposed based on our experimental results on the growth process.

One-pot solvothermal synthesis of graphene wrapped rice-like ferrous carbonate nanoparticles as anode materials for high energy lithium-ion batteries

Well dispersed rice-like FeCO3 nanoparticles were produced and combined with reduced graphene oxide (RGO) via a one-pot solvothermal route. SEM characterization shows that rice-like FeCO3 nanoparticles are homogeneously anchored on the surface of the graphene nanosheets; the addition of RGO is helpful to form a uniform morphology and reduce the particle size of FeCO3 to nano-grade. As anode materials for lithium-ion batteries, the FeCO3/RGO nanocomposites exhibit significantly improved lithium storage properties with a large reversible capacity of 1345 mA h g(-1) for the first cycle and a capacity retention of 1224 mA h g(-1) after 50 cycles with a good rate capability compared with pure FeCO3 particles. The superior electrochemical performance of the FeCO3/RGO nanocomposite electrode compared to the pure FeCO3 electrode can be attributed to the well dispersed RGO which enhances the electronic conductivity and accommodates the volume change during the conversion reactions. Our study shows that the FeCO3/RGO nanocomposite could be a suitable candidate for high capacity lithium-ion batteries.

Coaxial Zn2GeO4@carbon nanowires directly grown on Cu foils as high-performance anodes for lithium ion batteries

Zn₂GeO₄@carbon nanowires directly grown on Cu foil using CVD method exhibit high reversible capacity and high-rate capability as LIB anode.

In-situ one-step hydrothermal synthesis of a lead germanate-graphene composite as a novel anode material for lithium-ion batteries

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100-200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01-1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g(-1) at 100 mA g(-1) after 50 cycles. Even at a high current density of 1600 mA g(-1), a capacity of 406 mAh g(-1) can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

CuGeO₃ nanowires covered with graphene as anode materials of lithium ion batteries with enhanced reversible capacity and cyclic performance

A facile one-step route was developed to synthesize crystalline CuGeO₃ nanowire/graphene composites (CGCs). Crystalline CuGeO₃ nanowires were tightly covered and anchored by graphene sheets, forming a layered structure. Subsequently, CGCs were exploited as electrode materials for lithium ion batteries (LIBs). The reversible formation of Li₂O buffer layer and elastic graphene sheets accommodated the volume change during the charge and discharge processes. CGC containing 37 wt% graphene exhibited a superior electrochemical performance, that is, a remarkable reversible capacity (1265 mA h g(-1) for the first cycle), an outstanding cyclic performance (853 mA h g(-1) after 50 cycles under a current density of 200 mA g(-1)), a high coulombic efficiency, and an excellent rate capability. Clearly, CGCs may stand out as a promising anode material for LIBs.

Partially crystalline Zn₂GeO₄ nanorod/graphene composites as anode materials for high performance lithium ion batteries

Zn2GeO4 nanorod/graphene composites (ZGCs) were yielded by a two-step hydrothermal processing. Crystalline and amorphous regions were found to coexist in a single Zn2GeO4 nanorod. The surface of the Zn2GeO4 nanorod was compactly covered and anchored by graphene sheets. The ZGCs were then utilized as anodes for lithium ion batteries (LIBs). Intriguingly, partially crystalline ZGC containing 10.2 wt % graphene possessed excellent electrochemical performance, namely, high reversible capacity (1020 mA h g(-1) in the first cycle), favorable cyclic performance (768 mA h g(-1) after 50 cycles), and commendable rate capability (780 mA h g(-1) at the current density of 0.8A g(-1)). The amorphous region in partially crystalline Zn2GeO4 nanorods and the elastic graphene sheets provided the accommodation of volume change during the charge and discharge processes. These advantageous attributes make ZGCs the potential anode materials for LIBs.

Facile synthesis of sandwiched Zn2GeO4-graphene oxide nanocomposite as a stable and high-capacity anode for lithium-ion batteries

Traditional metal anode materials in lithium-ion batteries are plagued by instability upon discharge-charge cycling. We report that a unique sandwiched Zn2GeO4-graphene oxide nanocomposite has been synthesized on a large scale through a simple ion-exchange reaction, whereby Zn2GeO4 nanorods with lengths of 600 nm and widths of 40 nm are homogeneously sandwiched into the graphene oxide matrix. Compared with bare Zn2GeO4 nanorods, a dramatic improvement in the electrochemical performance of the resulting nanocomposite has been achieved. In the voltage window of 0.001-3 V, the electrode of the Zn2GeO4-graphene oxide nanocomposite delivers a specific capacity as high as 1150 mA h g(-1) at 200 mA g(-1) after 100 discharge-charge cycles. Even at a high current density of 3.2 A g(-1), a capacity of 522 mA h g(-1) can be retained. The unusual electrochemical performance including highly reversible capacity and excellent rate capability arise from synergetic chemical coupling effects between Zn2GeO4 and graphene oxide.

Facile microwave-assisted synthesis and effective photocatalytic hydrogen generation of Zn2GeO4 with different morphology

Single-crystalline hexagonal prism Zn₂GeO₄ nanorods and hierarchical Zn₂GeO₄ microspheres have been successfully synthesized via a facile microwave-assisted solution-phase approach.

Core-shell Zn2GeO4 nanorods and their size-dependent photoluminescence properties

Size-tunable crystalline core-crystalline shell Zn2GeO4 nanorods were synthesized via a facile hydrothermal reaction. High purity Zn2GeO4 nanorods were obtained at pH = 7. The length of Zn2GeO4 nanorods (L = 50-100 nm) can be controlled through a one-step process, while micro-sized nanorods with an aspect ratio of the length to the diameter of 10 were yielded in a two-step process. The single crystalline nature of Zn2GeO4 nanorods with a core-shell structure was verified by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) measurements. The Raman study revealed that there is no oxygen defect in Zn2GeO4 nanocrystals, suggesting that photoluminescence emission of Zn2GeO4 can be attributed to the presence of the interstitial Zn defect in Zn2GeO4 nanocrystals. As the diameter of nanorods decreased, the excitation and emission peaks appeared to be redshifted due to the quantum size effect.

Single-crystalline metal germanate nanowire-carbon textiles as binder-free, self-supported anodes for high-performance lithium storage

Single-crystalline metal germanate nanowires, including SrGe4O9, BaGe4O9, and Zn2GeO4 were successfully grown on carbon textile via a simple low-cost hydrothermal method on a large scale. The as-grown germanate nanowires-carbon textiles were directly used as binder-free anodes for lithium-ion batteries, which exhibited highly reversible capacity in the range of 900-1000 mA h g(-1) at 400 mA g(-1), good cyclability (no obvious capacity decay even after 100 cycles), and excellent rate capability with a capacity of as high as 300 mA h g(-1) even at 5 A g(-1). Such excellent electrochemical performance can be ascribed to the three-dimensional interconnected conductive channels composed of the flexible carbon microfibers, which not only serve as the current collector but also buffer the volume change of the active material upon cycling. Additionally, the one-dimensional nanostructures grown directly on the carbon microfibers also ensure fast charge carrier (e(-) and Li(+)) transport, large surface areas, better permeabilities, and more active sites, which also contributed to the improved electrochemical performance.

Rational design of anode materials based on Group IVA elements (Si, Ge, and Sn) for lithium-ion batteries

Lithium-ion batteries (LIBs) represent the state-of-the-art technology in rechargeable energy-storage devices and they currently occupy the prime position in the marketplace for powering an increasingly diverse range of applications. However, the fast development of these applications has led to increasing demands being placed on advanced LIBs in terms of higher energy/power densities and longer life cycles. For LIBs to meet these requirements, researchers have focused on active electrode materials, owing to their crucial roles in the electrochemical performance of batteries. For anode materials, compounds based on Group IVA (Si, Ge, and Sn) elements represent one of the directions in the development of high-capacity anodes. Although these compounds have many significant advantages when used as anode materials for LIBs, there are still some critical problems to be solved before they can meet the high requirements for practical applications. In this Focus Review, we summarize a series of rational designs for Group IVA-based anode materials, in terms of their chemical compositions and structures, that could address these problems, that is, huge volume variations during cycling, unstable surfaces/interfaces, and invalidation of transport pathways for electrons upon cycling. These designs should at least include one of the following structural benefits: 1) Contain a sufficient number of voids to accommodate the volume variations during cycling; 2) adopt a "plum-pudding"-like structure to limit the volume variations during cycling; 3) facilitate an efficient and permanent transport pathway for electrons and lithium ions; or 4) show stable surfaces/interfaces to stabilize the in situ formed SEI layers.

Electrospun eggroll-like CaSnO3 nanotubes with high lithium storage performance

Novel eggroll-like CaSnO(3) nanotubes have been prepared by a single spinneret electrospinning method followed by calcination in air for the first time. The electrospun sample as a lithium-ion battery electrode material exhibited improved cycling stability and rate capability by virtue of the high surface area and unique hollow interior structure, compared to nanorod-structured CaSnO(3).

Facile approach to prepare porous CaSnO₃ nanotubes via a single spinneret electrospinning technique as anodes for lithium ion batteries

CaSnO₃ nanotubes are successfully prepared by a single spinneret electrospinning technique. The characterized results indicate that the well-crystallized one-dimensional (1D) CaSnO₃ nanostructures consist of about 10 nm nanocrystals, which interconnect to form nanofibers, nanotubes, and ruptured nanobelts after calcination. The diameter and wall thickness of CaSnO₃ nanotubes are about 180 and 40 nm, respectively. It is demonstrated that CaSnO₃ nanofiber, nanotubes, and ruptured nanobelts can be obtained by adjusting the calcination temperature in the range of 600-800 °C. The effect of calcination temperature on the morphologies of electrospun 1D CaSnO₃ nanostructures and the formation mechanism leading to 1D CaSnO₃ nanostructures are investigated. As anodes for lithium ion batteries, CaSnO₃ nanotubes exhibit superior electrochemical performance and deliver 1168 mAh g⁻¹ of initial discharge capacity and 565 mAh g⁻¹ of discharge capacity up to the 50th cycle, which is ascribed to the hollow interior structure of 1D CaSnO₃ nanotubes. Such porous nanotubular structure provides both buffer spaces for volume change during charging/discharging and rapid lithium ion transport, resulting in excellent electrochemical performance.

Zn2GeO4 and In2Ge2O7 nanowire mats based ultraviolet photodetectors on rigid and flexible substrates

Ternary metal oxide, Zn2GeO4, In2Ge2O7, have potential applications in many research areas. Using a single chemical vapor deposition method, high-quality single crystalline Zn2GeO4 nanowire (NW) mats and In2Ge2O7 NW mats were synthesized on a large scale. Nanowires mats based ultraviolet photodetectors were fabricated on rigid silicon substrates. By simply transferring the nanowire mats to a transparent adhesive PET tape, flexible photodetectors were also fabricated. Both the rigid and flexible photodetectors exhibited excellent photoconductive performance in terms of high sensitivity to the UV light, excellent stability and reproducibility, and fast response and recovery time.

Ternary Cu₂SnS₃ cabbage-like nanostructures: large-scale synthesis and their application in Li-ion batteries with superior reversible capacity

In this paper, novel ternary Cu(2)SnS(3) cabbage-like nanostructures are synthesized on a large scale via a facile solvothermal route. The individual Cu(2)SnS(3) cabbage-like hierarchitecture is constructed from 2D nanosheets with thickness of about 15.6 nm. The Cu(2)SnS(3) electrodes exhibit an initial reversible capacity of 842 mAh g(-1) and still reach 621 mAh g(-1) after 50 cycles. Such an admirable performance could be related to their 3D porous structural features as well as the high electrical conductivity induced by Cu. The electrochemical properties of the 3D hierarchical nanostructures imply its potential application in high energy density Li-ion batteries.