Mesoporous Ge/GeO2/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility

Dendritic Copper Current Collectors as a Capacity Boosting Material for Polymer-Templated Si/Ge/C Anodes in Li-Ion Batteries

Dendritic copper offers a highly effective method for synthesizing porous copper anodes due to its intricate branching structure. This morphology results in an elevated surface area-to-volume ratio, facilitating shortened electron pathways during aqueous and electrolyte permeation. Here, we demonstrate a procedure for a time- and cost-efficient synthesis routine of fern-like copper microstructures as a host for polymer-templated Si/Ge/C thin films. Dissolvable Zintl clusters and sol-gel chemistry are used to synthesize nanoporous coating as the anode. Cyclic voltammetry (CV) with KOH as the electrolyte is used to estimate the surface area increase in the dendritic copper current collectors (CCs). Half cells are assembled and tested with battery-related techniques such as CV, galvanostatic cycling, and electrochemical impedance spectroscopy, showing a capacity increase in the dendritic copper cells. Energy-dispersive X-ray spectroscopy is used to estimate the removal of K in the bulk after oxidizing the Zintl phase K12Si8Ge9 in the polymer/precursor blend with SiCl4. Furthermore, scanning electron microscopy images are provided to depict the thin films after synthesis and track the degradation of the half cells after cycling, revealing that the morphological degradation through alloying/dealloying is reduced for the dendritic Cu CC anodes as compared with the bare reference. Finally, we highlight this time- and cost-efficient routine for synthesizing this capacity-boosting material for low-mobility and high-capacity anode coatings.

Spinodal Decomposition-Driven Structural Hierarchy of Mesoporous Inorganic Materials for Energy Applications

ConspectusMesoporous inorganic materials (MIMs) directed by block copolymers (BCPs) have attracted tremendous attention due to their high surface area, large pore volume, and tunable pore size. The structural hierarchy of inorganic materials with designed meso- and macrostructures combines the benefits of mesoporosity and tailored macrostructures in which macropores have increased ion/mass transfer and large capacity to carry guest material and have a macroscale particle morphology that permits close packing and a low surface energy. Existing methods for hierarchically structured MIMs require complicated multistep procedures including preparation of sacrificial macrotemplates (e.g., foams and colloidal spheres). Despite considerable efforts to control the macrostructures of mesoporous materials, major challenges remain in the formation of a structural hierarchy with ordered mesoporosity.In polymer science, spinodal decomposition (SD) is a physical phenomenon that spontaneously produces a wide variety of macroscale heterostructures from interconnected networks to isolated droplets. Exploitation of SD is a promising method to achieve precise control of the macrostructure (e.g., macropore, particle morphology) and mesostructure (e.g., pore size and structure, composition) of inorganic materials. However, this approach for tailoring the structural hierarchy of MIMs is unexplored due to the lack of effective systems that can control the complex thermodynamic interactions of inorganic precursor/polymer blends and the phase-separation kinetics.In this Account, we present our recent research progress on the development of synthesis systems that combine unique SD behaviors and BCP self-assembly in polymer blends. To generate macropores in MIMs, we have exploited interconnected macrostructures of SD induced by designed quench conditions of multicomponent blends containing BCP. These strategies enable control of the size of the macropores of the nanostructures independently and can be extended to various compositions (e.g., carbon, SiO2, TiO2, WO3, TiNb2O7, TiN). We also control the macroscopic morphology of the MIMs into spherical particles (e.g., solid and hollow mesoporous spheres) by using SD induced by increasing the mixing entropy penalty of polymer blends that consist BCP, homopolymer(s), and inorganic precursors. Furthermore, interfacial tension between polymers determines the macroscopic morphology of MIMs, from isotropic to anisotropic mesoporous particles (e.g., oblate, bowl, 2D nanosheet). The interfacial states of the homopolymer determine the pore orientation and particle morphology of BCP-directed MIMs.We also highlight the application of the hierarchically structured MIMs in energy storage devices. Generated macropores facilitate ion/mass transfer in lithium-ion batteries and stable accommodation of a large amount of sulfur in lithium-sulfur batteries. Designed morphologies of MIMs are beneficial to achieve high packing density as electrode materials in potassium-ion batteries and thereby achieve high volumetric capacities.Recent advances in SD-driven synthesis for the structural hierarchy of MIMs will inspire how polymer science can be used as a platform for preparing the designed inorganic materials. Additionally, broadening the polymer and composition repertoire will guide in novel frontiers in the design and applications of MIMs in various fields.

Spinodal Decomposition Method for Structuring Germanium-Carbon Li-Ion Battery Anodes

To increase the energy density of lithium-ion batteries (LIBs), high-capacity anodes which alloy with Li ions at a low voltage against Li/Li⁺ have been actively pursued. So far, Si has been studied the most extensively because of its high specific capacity and cost efficiency; however, Ge is an interesting alternative. While the theoretical specific capacity of Ge (1600 mAh g^-1) is only half that of Si, its density is more than twice as high (Ge, 5.3 g cm^-3; Si, 2.33 g cm^-3), and therefore the charge stored per volume is better than that of Si. In addition, Ge has a 400 times higher ionic diffusivity and 4 orders of magnitude higher electronic conductivity compared to Si. However, similarly to Si, Ge needs to be structured in order to manage stresses induced during lithiation and many reports have achieved sufficient areal loadings to be commercially viable. In this work, spinodal decomposition is used to make secondary particles of about 2 μm in diameter that consist of a mixture of ∼30 nm Ge nanoparticles embedded in a carbon matrix. The secondary structure of these germanium-carbon particles allows for specific capacities of over 1100 mAh g^-1 and a capacity retention of 91.8% after 100 cycles. Finally, high packing densities of ∼1.67 g cm^-3 are achieved in blended electrodes by creating a bimodal size distribution with natural graphite.

Bamboo Weaving Inspired Design of a Carbonaceous Electrode with Exceptionally High Volumetric Capacity

A highly densified electrode material is desirable to achieve large volumetric capacity. However, pores acting as ion transport channels are critical for high utilization of active material. Achieving a balance between high volume density and pore utilization remains a challenge particularly for hollow materials. Herein, capillary force is employed to convert hollow fibers to a bamboo-weaving-like flexible electrode (BWFE), in which the shrinkage of hollow space results in high compactness of the electrode. The volume of the electrode can be decreased by 96% without sacrificing the gravimetric capacity. Importantly, the conductivity of BWFE after thermal treatment can reach up to 50,500 S/m which exceeds that for most other carbon materials. Detailed mechanical analysis reveals that, due to the strong interaction between nanoribbons, Young's modulus of the electrode increases by 105 times. After SnO₂ active materials is impregnated, the BWFE/SnO₂ electrode exhibits an exceptionally ultrahigh volumetric capacity of 2000 mAh/cm³.

Three-dimensional porous structured germanium anode materials for High-Performance Lithium-Ion Full-cell

Germanium (Ge) has a high specific capacity when used as an alloying anode in lithium ion batteries. Despite this, the large volume of expansion that occurs during charging and discharging...

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Graphene-Based Two-Dimensional Mesoporous Materials: Synthesis and Electrochemical Energy Storage Applications

Graphene (G)-based two dimensional (2D) mesoporous materials combine the advantages of G, ultrathin 2D morphology, and mesoporous structures, greatly contributing to the improvement of power and energy densities of energy storage devices. Despite considerable research progress made in the past decade, a complete overview of G-based 2D mesoporous materials has not yet been provided. In this review, we summarize the synthesis strategies for G-based 2D mesoporous materials and their applications in supercapacitors (SCs) and lithium-ion batteries (LIBs). The general aspect of synthesis procedures and underlying mechanisms are discussed in detail. The structural and compositional advantages of G-based 2D mesoporous materials as electrodes for SCs and LIBs are highlighted. We provide our perspective on the opportunities and challenges for development of G-based 2D mesoporous materials. Therefore, we believe that this review will offer fruitful guidance for fabricating G-based 2D mesoporous materials as well as the other types of 2D heterostructures for electrochemical energy storage applications.

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.

First-principles view of the interaction between Li and Bi4Ge3O12 anodes

As a novel anodic electrode for Li-ion storage, the cubic Bi4Ge3O12 phase can experimentally deliver a remarkably high reversible specific capacity of 586 mA h g-1 at 200 mA h g-1 with a coulombic efficiency of 99.8% after 500 cycles, and has recently attracted attention for its stable electrochemical performance. Here we calculated its lithiation/delithiation reactions by using density functional theory studies, through the structural changes as the conversion and alloying reaction takes place during the Li-ion insertion and extraction process. The obtained theoretical capacity of Li is 48.75 mol (∼1043 mA h g-1) for 1 mol Bi4Ge3O12. The decomposed Bi2O3 (P3[combining macron]m1) and GeO2 (P3121) in the lithiation process of Bi4Ge3O12 are the active materials to react with the Li atoms via a conversion reaction. Besides Li2O with both Fm3[combining macron]m and Pnma phases, the final lithiation products of Bi4Ge3O12 should include Li3Bi (Fm3[combining macron]m) and Li4.25Ge (F4[combining macron]3m), through the alloying reactions of multi-valence elements of Bi and Ge with Li. Bi and Ge metals are also helpful in the decomposition of Li2O into Li during the delithiation process, increasing the reversibility of the conversion reactions. Our research provides theoretical support to understand the working mechanism of Bi4Ge3O12 and related mixed-metal anode materials.

Interface Coassembly and Polymerization on Magnetic Colloids: Toward Core-Shell Functional Mesoporous Polymer Microspheres and Their Carbon Derivatives

Core-shell structured magnetic mesoporous polymer or carbon-based microspheres not only possess the combined merits of magnetic particles and stable mesoporous shell but also provide various organic functional groups for further modification and immobilization of active sites, thus opening up more possibility for various applications. Herein, a bottom-up soft-templating strategy is developed to controllably synthesize core-shell magnetic mesoporous polydopamine microspheres (MMP) and their derivative magnetic mesoporous carbon (MMC) microspheres via an amphiphilic block copolymer-directed interface assembly and polymerization (denoted as abc-DIAP) approach. The obtained uniform MMP microspheres have a well-defined structure consisting of magnetic core, silica middle layer and mesoporous PDA shell, uniform mesopores of 11.9 nm, high specific surface areas (235.6 m2 g-1) and rich functional groups. They show fast magnetic separation speed and superior performance in selective adsorption of Cyt.C from complex biosample solutions. Moreover, they can be in situ converted into core-shell magnetic mesoporous carbon (MMC) for efficient in-pore immobilization of ultrafine Au nanoparticles for high-efficiency catalytic epoxidation of styrene with high conversion (88.6%) and selectivity (90.1%) toward styrene oxide.

Insight into the antiviral activity of synthesized schizonepetin derivatives: A theoretical investigation

The antiviral activity of schizonepetin derivatives 1A-1C were investigated via theoretical methods and results are compared with experimental results. The derivatives 1 A and 1 C have the highest and the lowest antiviral activity, respectively. The interactions of derivatives 1A-1C and BN-nanotube are examined. Results show that, derivatives 1A-1C can effectively interact with BN-nanotube (9, 9) and their adsorptions are favorable. The energy of derivative 1 A is higher than derivatives 1B and 1 C. The derivative 1 A has highest absolute µ, ω and ∆N values and it has lowest absolute ƞ value. Results show that, theoretical and experimental trends of antiviral activity of derivatives 1A-1C were similar, successfully.

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.

An artificial sea urchin with hollow spines: improved mechanical and electrochemical stability in high-capacity Li-Ge batteries

Metallic germanium (Ge) as the anode can deliver a high specific capacity and high rate capability in lithium ion batteries. However, the large volume expansion largely restrains its further application. Herein, we constructed a three-dimensional sea urchin structure consisting of double layered Ge/TiO₂ nanotubes as the spines via a ZnO template-removing method, which displays a capacity as high as 1060 mA h g^-1 over 130 cycles. The robust, hollow oxide backbone serves as a strong support to accommodate the morphological change of Ge while the enhanced electron-transfer kinetics is attributed to the Ge content and the intimate contact between Ge and TiO₂ during charging/discharging, which were confirmed using in situ transmission electronic microscopy observations and first-principles simulations. In addition, a high capacity retention of batteries using this hybrid composite as the anode was also achieved at low temperature.

Self-assembly of block copolymers towards mesoporous materials for energy storage and conversion systems

This paper reviews the progress in the field of block copolymer-templated mesoporous materials, including synthetic methods, morphological and pore size control and their potential applications in energy storage and conversion devices.

Constraint spaces in carbon materials

Nano-sized pores in carbon materials are recently known to give certain constraints to the encapsulated materials by keeping them inside, accompanied with some changes in their structure, morphology, stability, etc. Consequently, nano-sized pores endow the constrained materials with improved performances in comparison with those prepared by conventional processes. These pores may be called "constraint spaces" in carbon materials. Here, we review the experimental results related to these constraint spaces by classifying as nanochannels in carbon nanotubes, nanopores and nanochannels in various porous carbons, and the spaces created by carbon coating.

Production of germanium nanoparticles via laser pyrolysis for anode materials of lithium-ion batteries and sodium-ion batteries

Germanium nanoparticles were synthesized and subjected to study as anode materials for lithium ion batteries and sodium ion batteries. Laser pyrolysis of GeH₄ was used to produce germanium nanoparticles and the average diameter of these nanoparticles was easily controlled by regulating sensitizer gas flow rates during the process. 60 and 10 nm diameter nanoparticles were synthesized and micron-size powder was purchased and these three pure germanium powder samples were tested as the anode materials of lithium ion batteries and sodium ion batteries in terms of cycle retention, long term cycles and the kinetics of reactions. Experimental results showed that the smallest powder sample which is synthesized, average 10 nm, exhibited excellent performances in both kinds of batteries. According to the results, the characteristics of batteries improved as the size of germanium powder decreased consistently. Pure germanium was thoroughly investigated as an anode of metal-ion batteries with regard to its powder size. The experimental data and synthesis approach of germanium nanoparticles suggested in this research would be a good example for the utilization of elemental germanium in high performance batteries.

Amorphous Tin Oxide Nanohelix Structure Based Electrode for Highly Reversible Na-Ion Batteries

An array of amorphous tin oxide (a-SnO_x) nanohelixes (NHs) was fabricated on copper foil as an electrode for Na-ion batteries via the oblique angle deposition method, a solution- and surfactant-free process. The combination of the amorphous phase SnO_x with a low oxidation number and its vertically aligned NH geometry with a large surface area and high porosity, which facilitate Na-ion dynamics and accommodate the volume changes, enabled a reversible capacity of up to 915 mA h g^-1 after 50 cycles, fast rate capability with 48.1% retention at 2 A g^-1, and high stability, which are superior to those of crystalline nanoparticle-based electrodes.

Atomic-scale combination of germanium-zinc nanofibers for structural and electrochemical evolution

Alloys are recently receiving considerable attention in the community of rechargeable batteries as possible alternatives to carbonaceous negative electrodes; however, challenges remain for the practical utilization of these materials. Herein, we report the synthesis of germanium-zinc alloy nanofibers through electrospinning and a subsequent calcination step. Evidenced by in situ transmission electron microscopy and electrochemical impedance spectroscopy characterizations, this one-dimensional design possesses unique structures. Both germanium and zinc atoms are homogenously distributed allowing for outstanding electronic conductivity and high available capacity for lithium storage. The as-prepared materials present high rate capability (capacity of ~ 50% at 20 C compared to that at 0.2 C-rate) and cycle retention (73% at 3.0 C-rate) with a retaining capacity of 546 mAh g⁻¹ even after 1000 cycles. When assembled in a full cell, high energy density can be maintained during 400 cycles, which indicates that the current material has the potential to be used in a large-scale energy storage system.

Alloy anode materials are receiving renewed interest. Here the authors show the design of Ge-Zn nanofibers for lithium ion batteries. Featured by a homogeneous composition at the atomic level and other favorable structural attributes, the materials allow for impressive electrochemical performance.

Temperature-Dependent Li Storage Performance in Nanoporous Cu-Ge-Al Alloy

The performance fading process and safety concerns of lithium ion batteries at low temperature (LT) prohibit their application in cold climates. The alloy-type electrodes demonstrate great potentials in stable and dendrite-free anodes at LT. Herein, we report a temperature-dependent Li storage performance in Al-based nanoporous alloy anode. The nanoporous-structured Cu-Ge-Al ternary alloys (NP-CuGeAl) have been designed and prepared by selectively etching Al out. The high-Al-content NP-CuGeAl (acid etching for 6 h, named CGA-6) is composed of multi-intermetallic compounds (denoted as M _xN _y, M, N = Cu, Al, Ge) with bimodal porous architectures. Investigated as anode at room temperature, the CGA-6 delivers a capacity as high as 479.7 mAh g^-1 at 0.5 A g^-1 of over 1020 cycles, and the low-Al-content ones show improved LT electrochemical performance. At -20 °C, the CGA-48 (acid etching for 48 h) shows much better performance as compared with the CGA-6. In Situ transmission electron microscopy and ex situ characterizations confirm that the M _xN _y/Li _zM _xN _y couples are highly reversible and the porous structure is durable upon battery cycling.

A hierarchical composite of GeO2 nanotubes/N-doped carbon microspheres with high-rate and super-durable performance for lithium-ion batteries

A new composite of hierarchical microspheres assembled by GeO₂ tubes/nitrogen doped carbon was fabricated for the first time and showed a promising electrochemical performance.

Improved pseudocapacitive charge storage in highly ordered mesoporous TiO2/carbon nanocomposites as high-performance Li-ion hybrid supercapacitor anodes

A Li-ion hybrid supercapacitor (Li-HSCs), an integrated system of a Li-ion battery and a supercapacitor, is an important energy-storage device because of its outstanding energy and power as well as long-term cycle life. In this work, we propose an attractive material (a mesoporous anatase titanium dioxide/carbon hybrid material, m-TiO₂-C) as a rapid and stable Li⁺ storage anode material for Li-HSCs. m-TiO₂-C exhibits high specific capacity (∼198 mA h g⁻¹ at 0.05 A g⁻¹) and promising rate performance (∼90 mA h g⁻¹ at 5 A g⁻¹) with stable cyclability, resulting from the well-designed porous structure with nanocrystalline anatase TiO₂ and conductive carbon. Thereby, it is demonstrated that a Li-HSC system using a m-TiO₂-C anode provides high energy and power (∼63 W h kg⁻¹, and ∼4044 W kg⁻¹).

A mesoporous TiO₂/carbon nanocomposite prepared by block copolymer self-assembly improves pseudocapacitive behavior and achieves high energy/power density Li-ion hybrid supercapacitors.

Stress-Tolerant Nanoporous Germanium Nanofibers for Long Cycle Life Lithium Storage with High Structural Stability

Nanowires (NWs) synthesized via chemical vapor deposition (CVD) have demonstrated significant improvement in lithium storage performance along with their outstanding accommodation of large volume changes during the charge/discharge process. Nevertheless, NW electrodes have been confined to the research level due to the lack of scalability and severe side reactions by their high surface area. Here, we present nanoporous Ge nanofibers (NPGeNFs) having moderate nanoporosity via a combination of simple electrospinning and a low-energetic zincothermic reduction reaction. In contrast with the CVD-assisted NW growth, our method provides high tunability of macro/microscopic morphologies such as a porosity, length, and diameter of the nanoscale 1D structures. Significantly, the customized NPGeNFs showed a highly suppressed volume expansion of less than 15% (for electrodes) after full lithation and excellent durability with high lithium storage performance over 500 cycles. Our approach offers effective 1D nanostructuring with highly customized geometries and can be extended to other applications including optoelectronics, catalysis, and energy conversion.

Synthesis of the ZnO@ZnS Nanorod for Lithium-Ion Batteries

The ZnO@ZnS nanorod is synthesized by solvothermal method as an anode material for lithium ion batteries. ZnS is deposited on ZnO and assembles in nanorod geometry successfully. The nanosized rod structure supports ion diffusion by substantially reducing the ion channel. The close-linking of ZnS and ZnO improves the synergetic effect. ZnS is in the middle of the ZnO core and the external environment, which would greatly relieve the volume change of the ZnO core during the Li+ intercalation/de-intercalation processes; therefore, the ZnO@ZnS nanorod is helpful in maintaining excellent cycle stability. The ZnO@ZnS nanorod shows a high discharge capacity of 513.4 mAh g−1 at a current density of 200 mA g−1 after 100 cycles, while a reversible capacity of 385.6 mAh g−1 is achieved at 1000 mA g−1.

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.

Tunable conductivity in mesoporous germanium

Germanium-based nanostructures have attracted increasing attention due to favourable electrical and optical properties, which are tunable on the nanoscale. High densities of germanium nanocrystals are synthesized via electrochemical etching, making porous germanium an appealing nanostructured material for a variety of applications. In this work, we have demonstrated highly tunable electrical conductivity in mesoporous germanium layers by conducting a systematic study varying crystallite size using thermal annealing, with experimental conductivities ranging from 0.6 to 33 (×10^-3) Ω^-1 cm^-1. The conductivity of as-prepared mesoporous germanium with 70% porosity and crystallite size between 4 and 10 nm is shown to be ∼0.9 × 10^-3 Ω^-1 cm^-1, 5 orders of magnitude smaller than that of bulk p-type germanium. Thermal annealing for 10 min at 400 °C further reduced the conductivity; however, annealing at 450 °C caused a morphological transformation from columnar crystallites to interconnecting granular crystallites and an increase in conductivity by two orders of magnitude relative to as-prepared mesoporous germanium caused by reduced influence of surface states. We developed an electrostatic model relating the carrier concentration and mobility of p-type mesoporous germanium to the nanoscale morphology. Correlation within an order of magnitude was found between modelled and experimental conductivities, limited by variation in sample uniformity and uncertainty in void size and fraction after annealing. Furthermore, theoretical results suggest that mesoporous germanium conductivity could be tuned over four orders of magnitude, leading to optimized hybrid devices.

Bismuth germanate (Bi4Ge3O12), a promising high-capacity lithium-ion battery anode

Cubic Bi₄Ge₃O₁₂ lithiation-host electrode material with micron size, low surface area (3 m² g⁻¹) and high tap density yielded a reversible capacity of 586 mA h g⁻¹ at a current density of 200 mA g⁻¹ after 500 charge–discharge cycles. Density functional theory calculations detected distorted [BiO₆]⁹⁻ octahedra with two types of Bi–O bonds.

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.

GeO2 Thin Film Deposition on Graphene Oxide by the Hydrogen Peroxide Route: Evaluation for Lithium-Ion Battery Anode

A peroxogermanate thin film was deposited in high yield at room temperature on graphene oxide (GO) from peroxogermanate sols. The deposition of the peroxo-precursor onto GO and the transformations to amorphous GeO₂, crystalline tetragonal GeO₂, and then to cubic elemental germanium were followed by electron microscopy, XRD, and XPS. All of these transformations are influenced by the GO support. The initial deposition is explained in view of the sol composition and the presence of GO, and the different thermal transformations are explained by reactions with the graphene support acting as a reducing agent. As a test case, the evaluation of the different materials as lithium ion battery anodes was carried out revealing that the best performance is obtained by amorphous germanium oxide@GO with >1000 mAh g^-1 at 250 mA g^-1 (between 0 and 2.5 V vs Li/Li⁺ cathode), despite the fact that the material contained only 51 wt % germanium. This is the first demonstration of the peroxide route to produce peroxogermanate thin films and thereby supported germanium and germanium oxide coatings. The advantages of the process over alternative methodologies are discussed.

Amorphous Ge/C Composite Sponges: Synthesis and Application in a High-Rate Anode for Lithium Ion Batteries

A Ge/C spongelike composite is prepared by the facile and scalable single-step pyrolysis of the GeO_x/ethylenediamine gel process, which has a feature with three-dimensional interconnected pore structures and is hybridized with nitrogen-doped carbon. A detailed investigation shows that the pore in the sponge is formed for the departure of the gaseous products at the evaluated temperature. As an anode for lithium ion batteries, the obtained composite exhibits superior specific capacity in excess of 1016 mA h g^-1 at 100 mA g^-1 after 100 cycles. Moreover, the amorphous Ge/C sponge electrode also has a good rate capacity and stable cycling performance. The obtained amorphous Ge/C sponges are a good candidate anode for next-generation lithium ion batteries.

ZnO decorated germanium nanoparticles as anode materials in Li-ion batteries

Germanium exhibits high charge capacity and high lithium diffusivity, both are the key requirements for electrode materials in high performance lithium ion batteries (LIBs). However, high volume expansion and segregation from the electrode during charge-discharge cycling have limited use of germanium in LIBs. Here, we demonstrate that ZnO decorated Ge nanoparticles (Ge@ZnO NPs) can overcome these limitations of Ge as an LIB anode material. We produced Ge NPs at high rates by laser pyrolysis of GeH₄, then coated them with solution phase synthesized ZnO NPs. Half-cell tests revealed dramatically enhanced cycling stability and higher rate capability of Ge@ZnO NPs compared to Ge NPs. Enhancements arise from the core-shell structure of Ge@ZnO NPs as well as production of metallic Zn from the ZnO layer. These findings not only demonstrate a new surface treatment for Ge NPs, but also provide a new opportunity for development of high-rate LIBs.

Structural evolution of reduced GeOx nanoparticles

GeO_x nanoparticles (NPs) are of growing interest in lithium storage and optoelectronics. GeO_x NPs prepared by chemical reduction, exposed to air or retained under N₂, then annealed under H₂ at various temperatures are studied herein using soft X-ray spectroscopy. We find that fresh and air-exposed GeO_x NPs evolve rather differently under annealing. The fresh GeO_x NPs start as a very amorphous heterogeneous mixture of GeO_x and Ge, and during annealing both the valence band and conduction band edges evolve. In contrast, the air-exposed GeO_x NPs initially contain quartz-phase GeO₂, and during annealing only the conduction band edge evolves due to increased oxygen vacancies forming unoccupied defect states (the valence band does not change until annealing at high temperture, at which point almost all of the GeO₂ is removed). These findings suggest a preparation and annealing strategy that could be used to tailor GeO_x NPs for their intended use in lithium storage or optoelectronic applications.

Unlocking the potential of SnS2: Transition metal catalyzed utilization of reversible conversion and alloying reactions

The alloying-dealloying reactions of SnS₂ proceeds with the initial conversion reaction of SnS₂ with lithium that produces Li₂S. Unfortunately, due to the electrochemical inactivity of Li₂S, the conversion reaction of SnS₂ is irreversible, which significantly limit its potential applications in lithium-ion batteries. Herein, a systematic understanding of transition metal molybdenum (Mo) as a catalyst in SnS₂ anode is presented. It is found that Mo catalyst is able to efficiently promote the reversible conversion of Sn to SnS₂. This leads to the utilization of both conversion and alloying reactions in SnS₂ that greatly increases lithium storage capability of SnS₂. Mo catalyst is introduced in the form of MoS₂ grown directly onto self-assembled vertical SnS₂ nanosheets that anchors on three-dimensional graphene (3DG) creating a hierarchal nanostructured named as SnS₂/MoS₂/3DG. The catalytic effect results in a significantly enhanced electrochemical properties of SnS₂/MoS₂/3DG; a high initial Coulombic efficiency (81.5%) and high discharge capacities of 960.5 and 495.6 mA h g⁻¹ at current densities of 50 and 1000 mA g⁻¹, respectively. Post cycling investigations using ex situ TEM and XPS analysis verifies the successful conversion reaction of SnS₂ mediated by Mo. The successful integration of catalyst on alloying type metal sulfide anode creates a new avenue towards high energy density lithium anodes.