Amorphous GeOx-Coated Reduced Graphene Oxide Balls with Sandwich Structure for Long-Life Lithium-Ion Batteries

Amorphous RuPd bimetallene for hydrogen evolution reaction in acidic and alkaline conditions: a first-principles study

Metallene materials can provide a large number of active catalytic sites for the efficient use of noble metals as catalysts for hydrogen evolution reaction (HER), whereas the intrinsic activity on the surface is insufficient in crystal phase. The amorphous phase with an inherent long-range disorder can offer a rich coordinate environment and charge polarization on the surface is proposed for promoting the intrinsic catalytic activity on the surface of noble metals. Herein, we designed an amorphous RuPd (am-RuPd) structure by the first principles molecular dynamics method. The performance of the acidic HER on am-RuPd can have a huge enhancement due to the free energy change of hydrogen adsorption close to zero. In alkaline conditions, the H2O dissociation energy barrier on am-RuPd is just 0.49 eV, and it is predicted that the alkaline HER performance of am-RuPd will largely exceed that of Pt nanocrystalline sheets. This work provides a strategy for enhancing the intrinsic catalytic activity on the surface and a way to design an efficient HER catalyst based on metallene materials used in both acidic and alkaline conditions.

GeO2 Nanoparticles Decorated in Amorphous Carbon Nanofiber Framework as Highly Reversible Lithium Storage Anode

Germanium oxide (GeO2) is a high theoretical capacity electrode material due to its alloying and conversion reaction. However, the actual cycling capacity is rather poor on account of suffering low electron/ion conductivity, enormous volume change and agglomeration in the repeated lithiation/delithiation process, which renders quite a low reversible electrochemical lithium storage reaction. In this work, highly amorphous GeO2 particles are uniformly distributed in the carbon nanofiber framework, and the amorphous carbon nanofiber not only improves the conduction and buffers the volume changes but also prevents active material agglomeration. As a result, the present GeO2 and carbon composite electrode exhibits highly reversible alloying and conversion processes during the whole cycling process. The two reversible electrochemical reactions are verified by differential capacity curves and cyclic voltammetry measurements during the whole cycling process. The corresponding reversible capacity is 747 mAh g-1 after 300 cycles at a current density of 0.3 A g-1. The related reversible capacities are 933, 672, 487 and 302 mAh g-1 at current densities of 0.2, 0.4, 0.8 and 1.6 A g-1, respectively. The simple strategy for the design of amorphous GeO2/carbon composites enables potential application for high-performance LIBs.

Alloying Motif Confined in Intercalative Frameworks toward Rapid Li-Ion Storage

High-capacity alloying-type anodes suffer poor rate capability due to their great volume expansion, while high-rate intercalation-type anodes are troubled with low theoretical capacity. Herein, a novel mechanism of alloying in the intercalative frameworks is proposed to confer both high-capacity and high-rate performances on anodes. Taking the indium-vanadium oxide (IVO) as a typical system, alloying-typed In is dispersed in the stable intercalative V₂ O₃ to form a solid solution. The alloying-typed In element provides high lithium storage capacity, while the robust, Li-conductive V-O frameworks effectively alleviate the volume expansion and aggregation of In. Benefiting from the above merits, the anode exhibits a high specific capacity of 1364 mA h g^-1 at 1 A g^-1 and an extraordinary cyclic performance of 814 mA h g^-1 at 10 A g^-1 after 600 cycles (124.9 mA h g^-1 after 10 000 cycles at 50 A g^-1 ). The superior electrochemical rate capability of (In,V)₂ O₃ solid solution anode rivals that of the reported alloying anode materials. This strategy can be extended for fabricating other alloying/intercalation hybrid anodes, such as (Sn,V)O₂ and (Sn,Ti)O₂ , which demonstrates the universality of confining alloying motifs in intercalative frameworks for rapid and high-capacity lithium storage.

Microwave-Assisted Synthesis of Ge/GeO2-Reduced Graphene Oxide Nanocomposite with Enhanced Discharge Capacity for Lithium-Ion Batteries

Germanium/germanium oxide nanoparticles with theoretically high discharge capacities of 1624 and 2152 mAh/g have attracted significant research interest for their potential application as anode materials in Li-ion batteries. However, these materials exhibit poor long-term performance due to the large volume change of 370% during charge/discharge cycles. In the present study, to overcome this shortcoming, a Ge/GeO2/graphene composite material was synthesized. Ge/GeO2 nanoparticles were trapped between matrices of graphene nanosheets to offset the volume expansion effect. Transmission electron microscopy images revealed that the Ge/GeO2 nanoparticles were distributed on the graphene nanosheets. Discharge/charge experiments were performed to evaluate the Li storage properties of the samples. The discharge capacity of the bare Ge/GeO2 nanoparticles in the first discharge cycle was considerably large; however, the value decreased rapidly with successive cycles. Conversely, the present Ge/GeO2/graphene composite exhibited superior cycling stability.

Cu3(PO4)2: Novel Anion Convertor for Aqueous Dual-Ion Battery

A novel anion electrode Cu₃(PO₄)₂ is proposed at the first time. The reaction mechanism of Cu₃(PO₄)₂ electrode is investigated. The dual-ion cell is constructed by using pretreated Cu₃(PO₄)₂ and Na_0.44MnO₂.

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A Fast Charge/Discharge and Wide-Temperature Battery with a Germanium Oxide Layer on a Ti3C2 MXene Matrix as Anode

A rapid charge/discharge secondary battery is critical in portable electronic devices and electric vehicles. Germanium, due to the metallic property and facile alloying reaction with lithium, displays great potential in fast charge/discharge batteries in contrast to other intercalation batteries. In order to accommodate the over 300% volume change, a 2D hybrid composite electrode consisting of a homogeneous, amorphous GeO_x(x=1.57) layer bonded on Ti₃C₂ MXenes was successfully developed via an industry available method. The expanded interlayer space inside the MXene matrix accommodates the restricted isotropic expansion from the stress-released, ultrathin GeO_x layer. Owing to the improved e^-/Li⁺ conductivity from both metallic reduced Ge and MXene, the battery showed an excellent charge/discharge performance as fast as 3 min (20.0 C). A high-capacity retention of ∼1048.1 mAh/g along with a Coulombic efficiency (CE) of 99.8% at 0.5 C after 500 cycles was achieved. Under 1.0 C, the capacity was still up to 929.6 mAh/g with a CE of 99.6% (<0.02% capacity decay per cycle) after ultralong (1000) cycling. An almost doubled capacity of 671.6 mAh/g compared to graphite (372 mAh/g at 0.1 C) under 5.0 C and a capacity of 300.5 mAh/g under 10.0 C after 1000 cycles were respectively received. Under cold conditions, due to the low interface energy barrier, an efficient alloying reaction happens which prevents the Li plating on the electrode surface. High capacities of 631.6, 333.9, and 841.7 mAh/g under -20, -40, and 60 °C after 100 cycles demonstrate a wide temperature tolerance of the battery. In addition, a full-cell battery paired with LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) displayed a high capacity of 536.8 mAh/g after 200 cycles. A high capacity retention of a full pouch cell after 50 cycles was also obtained. The superhigh rate capability along with long cycling, wide temperature range, scalable production, and relatively low cost of this hybrid composite display promising potential in specific energy storage applications.

Graphene reinforced carbon nanofiber engineering enhances Li storage performances of germanium oxide

The rational design of electrode materials with high power and energy densities, good operational safety, and long cycle life remains a great challenge for developing advanced battery systems. As a promising electrode material for rechargeable batteries, germanium oxide (GeO₂) shows high capacity, but suffers from rapid capacity fading caused by its large volume variation during charge/discharge processes and poor rate performance owing to low intrinsic electronic conductivity. In this study, a novel one-dimensional (1D) carbon/graphene-nanocable–GeO₂ nanocomposite (denoted as GeO₂/nanocable) is rationally designed and prepared via a facile electrospinning method. Specifically, amorphous carbon and graphene spontaneously construct a nanocable structure, in which graphene acts as the “core” and amorphous carbon as the “shell”, and GeO₂ nanoparticles are encapsulated in the nanocable. The graphene “core” promises good electrical conductivity while the amorphous carbon “shell” guarantees fast Li ions diffusion. When tested as an anode material for rechargeable lithium ion batteries, the GeO₂/nanocable exhibits remarkable Li storage performance, including high reversible capacity (900 mA h g⁻¹), high capacity retention (91% after 100 cycles), and good rate performance (595 mA h g⁻¹ at 5000 mA g⁻¹).

In the GeO₂/nanocable, amorphous carbon and graphene spontaneously construct a nanocable structure, graphene “core” promises the good electrical conductivity while the amorphous carbon “shell” guarantees the fast Li ions diffusion.

Advances in the synthesis and design of nanostructured materials by aerosol spray processes for efficient energy storage

The increasing demand for energy storage has motivated the search for highly efficient electrode materials for use in rechargeable batteries with enhanced energy density and longer cycle life. One of the most promising strategies for achieving improved battery performance is altering the architecture of nanostructured materials employed as electrode materials in the energy storage field. Among numerous synthetic methods suggested for the fabrication of nanostructured materials, aerosol spray techniques such as spray pyrolysis, spray drying, and flame spray pyrolysis are reliable, as they are facile, cost-effective, and continuous processes that enable the synthesis of nanostructured electrode materials with desired morphologies and compositions with controlled stoichiometry. The post-treatment of spray-processed powders enables the fabrication of oxide, sulfide, and selenide nanostructures hybridized with carbonaceous materials including amorphous carbon, reduced graphene oxide, carbon nanotubes, etc. In this article, recent progress in the synthesis of nanostructured electrode materials by spray processes and their general formation mechanisms are discussed in detail. A brief introduction to the working principles of each spray process is given first, and synthetic strategies for the design of electrode materials for lithium-ion, sodium-ion, lithium-sulfur, lithium-selenium, and lithium-oxygen batteries are discussed along with some examples. This analysis sheds light on the synthesis of nanostructured materials by spray processes and paves the way toward the design of other novel and advanced nanostructured materials for high performance electrodes in rechargeable batteries of the future.

Research Advances of Amorphous Metal Oxides in Electrochemical Energy Storage and Conversion

Amorphous metal oxides (AMOs) have aroused great enthusiasm across multiple energy areas over recent years due to their unique properties, such as the intrinsic isotropy, versatility in compositions, absence of grain boundaries, defect distribution, flexible nature, etc. Here, the materials engineering of AMOs is systematically reviewed in different electrochemical applications and recent advances in understanding and developing AMO-based high-performance electrodes are highlighted. Attention is focused on the important roles that AMOs play in various energy storage and conversion technologies, such as active materials in metal-ion batteries and supercapacitors as well as active catalysts in water splitting, metal-air batteries, and fuel cells. The improvements of electrochemical performance in metal-ion batteries and supercapacitors are reviewed regarding the enhancement in active sites, mechanical strength, and defect distribution of amorphous structures. Furthermore, the high electrochemical activities boosted by AMOs in various fundamental reactions are elaborated on and they are related to the electrocatalytic behaviors in water splitting, metal-air batteries, and fuel cells. The applications in electrochromism and high-conducting sensors are also briefly discussed. Finally, perspectives on the existing challenges of AMOs for electrochemical applications are proposed, together with several promising future research directions.

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.

Graphene boosted Cu2GeS3 for advanced lithium-ion batteries

Ternary Cu₂GeS₃ (CGS) serves as lithium ion battery anode materials for the first time, whose electrochemical performance is significantly improved by the introduction of reduced graphene oxide.

Synthesis of Reduced Graphene Oxide-Modified LiMn0.75Fe0.25PO4 Microspheres by Salt-Assisted Spray Drying for High-Performance Lithium-Ion Batteries

Microsized, spherical, three-dimensional (3D) graphene-based composites as electrode materials exhibit improved tap density and electrochemical properties. In this study, we report 3D LiMn_0.75Fe_0.25PO₄/reduced graphene oxide microspheres synthesized by one-step salt-assisted spray drying using a mixed solution containing a precursor salt and graphene oxide and a subsequent heat treatment. During this process, it was found that the type of metal salt used has significant effects on the morphology, phase purity, and electrochemical properties of the synthesized samples. Furthermore, the amount of the chelating agent used also affects the phase purity and electrochemical properties of the samples. The composite exhibited a high tap density (1.1 g cm⁻³) as well as a gravimetric capacity of 161 mA h g⁻¹ and volumetric capacity of 281 mA h cm⁻³ at 0.05 C-rate. It also exhibited excellent rate capability, delivering a discharge capacity of 90 mA h g⁻¹ at 60 C-rate. Furthermore, the microspheres exhibited high energy efficiency and good cyclability, showing a capacity retention rate of 93% after 1000 cycles at 10 C-rate.

Ge/GeO2-Ordered Mesoporous Carbon Nanocomposite for Rechargeable Lithium-Ion Batteries with a Long-Term Cycling Performance

Germanium-based nanostructures are receiving intense interest in lithium-ion batteries because they have ultrahigh lithium ion storage ability. However, the Germanium-based anodes undergo the considerably large volume change during the charge/discharge processes, leading to a fast capacity fade. In the present work, a Ge/GeO2-ordered mesoporous carbon (Ge/GeO2-OMC) nanocomposite was successfully fabricated via a facile nanocasting route by using mesoporous carbon as a nanoreactor, and was then used as an anode for lithium-ion batteries. Benefited from its unique three-dimensional "meso-nano" structure, the Ge/GeO2-OMC nanocomposite exhibited large reversible capacity, excellent long-time cycling stability and high rate performance. For instance, a large reversible capacity of 1018 mA h g(-1) was obtained after 100 cycles at a current density of 0.1 A g(-1), which might be attributed to the unique structure of the Ge/GeO2-OMC nanocomposite. In addition, a reversible capacity of 492 mA h g(-1) can be retained when cycled to 500 cycles at a current density of 1 A g(-1).

Size-controllable synthesis of amorphous GeOx hollow spheres and their lithium-storage electrochemical properties

Size controllable synthesis of GeO_x hollow spheres was achieved using a solvothermal reaction. The GeO_x hollow spheres exhibit excellent lithium storage properties.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

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.

Green synthesis of GeO2/graphene composites as anode material for lithium-ion batteries with high capacity

A facile green solution route using only GeO₂ powder, graphene oxide and purified water has been developed to prepare a GeO₂/graphene composite, in which the GeO₂ particles are wrapped in graphene nanosheets.

Three-dimensional graphene-based spheres and crumpled balls: micro- and nano-structures, synthesis strategies, properties and applications

3D spherical and crumpled-ball graphene-based architectures with diverse, fascinating properties and applications are reviewed for the first time.

A new strategy of spray pyrolysis to prepare porous carbon nanosheets with enhanced ionic sorption capacity

We developed a new synthetic strategy to control the microstructure of carbon particles via ultrasonic spray pyrolysis. Porous carbon nanosheets with high ion-sorption capacitance were prepared by the one-pot spray pyrolysis process.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.

Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing

A nominal GeO_x (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO₂, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeO_x nanoparticles by chemical reduction of GeO₂, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeO_x, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeO_x. We find that the two initial GeO_x compounds have entirely different compositions: the fresh GeO_x contains large amorphous Ge clusters connected by GeO_x, while after air exposure; the Ge clusters are replaced by a GeO₂-GeO_x composite. In addition, the two GeO_x products undergo different structural rearrangement under H₂ annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeO_x, the amorphous Ge remains stable, with the GeO_x being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeO_x. The air-exposed GeO_x on the other hand, undergoes a GeO₂→GeO_x→Ge transition, in which H₂ induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature.