Highly Reversible Lithium Storage in Hierarchical Ca2Ge7O16Nanowire Arrays/Carbon Textile Anodes

Electrospraying preparation of metal germanate nanospheres for high-performance lithium-ion batteries and room-temperature gas sensors

Metal germanate nanospheres including Ca₂Ge₇O₁₆, Zn₂GeO₄ and SrGe₄O₉ were successfully synthesized by a direct and large-scale electrospraying method. As anodes for lithium ion batteries, the prepared metal germanate nanospheres showed high electrochemical lithium storage performance including excellent cycling stability and high rate capacity. Especially, the Ca₂Ge₇O₁₆ nanosphere anode delivered a high specific capacity of ∼ 670 mA h g^-1 at 0.2 A g^-1. The capacity retention was maintained around 71% even after 500 cycles. Moreover, when applied as room-temperature ammonia gas sensors, all three prepared germinate nanospheres showed significant sensing response values (6.04 for SrGe₄O₉, 2.73 for Zn₂GeO₄ and 1.70 for Ca₂Ge₇O₁₆), fast response-recovery time, excellent stability and outstanding selectivity.

Enhanced lithium storage performances of novel layered nickel germanate anodes inspired by the spatial arrangement of lotus leaves

The rapid capacity degradation of Ge-based materials hinders their practical application for next generation lithium ion batteries, which could be solved by synthesizing Ge-containing ternary oxides, with new structures and hybridizing with carbon nanomaterials. Herein, novel Ni3Ge2O5(OH)4 nanosheets were synthesized and distributed in situ on reduced graphene oxide (RGO) sheets, with both flat-lying and vertically-grown spatial distributions to imitate the growth of lotus leaves. These two types of Ni3Ge2O5(OH)4 nanosheets enhance their efficient contact with RGO, and increase the mass loading of active materials. Furthermore, the interfacial bonds between RGO sheets and Ni3Ge2O5(OH)4 nanosheets are introduced to improve the diffusion rate of lithium ions. The RGO sheets act as a buffer matrix to sustain the volume change and prevent the nanosheets from aggregation. Consequently, the chemically bonded Ni3Ge2O5(OH)4/RGO hybrid delivers a high specific capacity of 863 mA h g-1 over 75 cycles, which is much higher than those for neat Ni3Ge2O5(OH)4 nanosheets or the hybrid without the interfacial bonding. This study provides a novel perspective for designing high-performance Ge-based anode materials for advanced lithium ion batteries.

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.

Reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density

This review summarizes the key challenges, effective modification strategies and perspectives regarding reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density.

Group IVA Element (Si, Ge, Sn)-Based Alloying/Dealloying Anodes as Negative Electrodes for Full-Cell Lithium-Ion Batteries

To satisfy the increasing energy demands of portable electronics, electric vehicles, and miniaturized energy storage devices, improvements to lithium-ion batteries (LIBs) are required to provide higher energy/power densities and longer cycle lives. Group IVA element (Si, Ge, Sn)-based alloying/dealloying anodes are promising candidates for use as electrodes in next-generation LIBs owing to their extremely high gravimetric and volumetric capacities, low working voltages, and natural abundances. However, due to the violent volume changes that occur during lithium-ion insertion/extraction and the formation of an unstable solid electrolyte interface, the use of Group IVA element-based anodes in commercial LIBs is still a great challenge. Evaluating the electrochemical performance of an anode in a full-cell configuration is a key step in investigating the possible application of the active material in LIBs. In this regard, the recent progress and important approaches to overcoming and alleviating the drawbacks of Group IVA element-based anode materials are reviewed, such as the severe volume variations during cycling and the relatively brittle electrode/electrolyte interface in full-cell LIBs. Finally, perspectives and future challenges in achieving the practical application of Group IVA element-based anodes in high-energy and high-power-density LIB systems are proposed.

Local Electric Field Facilitates High-Performance Li-Ion Batteries

By scrutinizing the energy storage process in Li-ion batteries, tuning Li-ion migration behavior by atomic level tailoring will unlock great potential for pursuing higher electrochemical performance. Vacancy, which can effectively modulate the electrical ordering on the nanoscale, even in tiny concentrations, will provide tempting opportunities for manipulating Li-ion migratory behavior. Herein, taking CuGeO₃ as a model, oxygen vacancies obtained by reducing the thickness dimension down to the atomic scale are introduced in this work. As the Li-ion storage progresses, the imbalanced charge distribution emerging around the oxygen vacancies could induce a local built-in electric field, which will accelerate the ions' migration rate by Coulomb forces and thus have benefits for high-rate performance. Furthermore, the thus-obtained CuGeO₃ ultrathin nanosheets (CGOUNs)/graphene van der Waals heterojunctions are used as anodes in Li-ion batteries, which deliver a reversible specific capacity of 1295 mAh g^-1 at 100 mA g^-1, with improved rate capability and cycling performance compared to their bulk counterpart. Our findings build a clear connection between the atomic/defect/electronic structure and intrinsic properties for designing high-efficiency electrode materials.

Mesoporous and Nanostructured TiO2 layer with Ultra-High Loading on Nitrogen-Doped Carbon Foams as Flexible and Free-Standing Electrodes for Lithium-Ion Batteries

A simple and green method is developed for the preparation of nanostructured TiO₂ supported on nitrogen-doped carbon foams (NCFs) as a free-standing and flexible electrode for lithium-ion batteries (LIBs), in which the TiO₂ with 2.5-4 times higher loading than the conventional TiO₂ -based flexible electrodes acts as the active material. In addition, the NCFs act as a flexible substrate and efficient conductive networks. The nanocrystalline TiO₂ with a uniform size of ≈10 nm form a mesoporous layer covering the wall of the carbon foam. When used directly as a flexible electrode in a LIB, a capacity of 188 mA h g^-1 is achieved at a current density of 200 mA g^-1 for a potential window of 1.0-3.0 V, and a specific capacity of 149 mA h g^-1 after 100 cycles at a current density of 1000 mA g^-1 is maintained. The highly conductive NCF and flexible network, the mesoporous structure and nanocrystalline size of the TiO₂ phase, the firm adhesion of TiO₂ over the wall of the NCFs, the small volume change in the TiO₂ during the charge/discharge processes, and the high cut-off potential contribute to the excellent capacity, rate capability, and cycling stability of the TiO₂ /NCFs flexible electrode.

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.

The binder-free Ca2Ge7O16 nanosheet/carbon nanotube composite as a high-capacity anode for Li-ion batteries with long cycling life

Ca₂Ge₇O₁₆ NS/CNT composites on Ni foam have been successfully fabricated for long cycling lithium-ion batteries.

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.

Porous mixed metal oxides: design, formation mechanism, and application in lithium-ion batteries

The relentless pursuit of new electrode materials for lithium ion batteries (LIBs) has been conducted for decades. Structures with either porous or nanostructure configurations have been confirmed as advantageous candidates for energy storage/conversion applications. The integration of the two features into one structure can provide another chance to improve the electroactivities. Recently, single-phased mixed metal oxides (MMOs) containing different metal cations, in particular, have confirmed high electrochemical activities because of their complex chemical composition, interfacial effects, and the synergic effects of the multiple metal species. In this review, we will focus on recent research advances of MMOs with porous architectures as anode materials in the matter of structural arrangement and compositional manipulation. Moreover, the application of self-supported MMO-based porous structures as LIB anodes is also explained herein. More importantly, investigations on the synthetic system and formation mechanism of porous MMOs will be highlighted. Some future trends for the innovative design of new electrode materials are also discussed in this review. The challenges and prospects will draw many researchers' attention.

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.

Flexible electronics based on inorganic nanowires

This review summarizes the latest research for exploiting the flexible electronic applications of inorganic nanowires.

Needle-like CoO nanowires grown on carbon cloth for enhanced electrochemical properties in supercapacitors

Needle-like CoO nanowires grown on carbon cloth have been successfully fabricated by a controllable hydrothermal method followed by an annealing process. The as-fabricated nanostructure showed enhanced specific capacitances and excellent cycling stability in supercapacitors.

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.

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 synthesis of hierarchical hollow MoS2 nanotubes as anode materials for high-performance lithium-ion batteries

Novel hierarchical hollow MoS₂ nanotubes have been fabricated, which exhibited excellent electrochemical performance as anode materials for lithium-ion batteries.

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.