Ge Electrodes Research Articles

Three-Dimensional Self-Supported Ge Anode for Advanced Lithium-Ion Batteries.

Three-dimensional (3D) self-supported Ge anode is one of the promising candidates to replace the traditional graphite anode material for high-performance binder-free lithium-ion batteries (LIBs). The enlarged surface area and the shortened ions/electrons transporting distance of the 3D electrode would greatly facilitate the rapid transfer of abundant lithium ions during cycling, thus achieve enhanced energy and power density during cycling. Cycle stability of the 3D self-supported Ge electrode would be improved due to the obtained enough space could effectively accommodate the large volume expansion of the Ge anode. In this review, we first describe the electrochemical properties and Li ions storage mechanism of Ge anode. Moreover, the recent advances in the 3D self-supported Ge anode architectures design are majorly illustrated and discussed. Challenges and prospects of the 3D self-supported Ge electrode are finally provided, which shed light on ways to design more reliable 3D Ge-based electrodes in energy storage systems.

Controllable synthesis of crystalline germanium nanorods as anode for lithium-ion batteries with high cycling stability

Germanium (Ge) nanomaterials have emerged as promising anode materials for lithium-ion batteries (LIBs) due to their higher capacity compared to commercial graphite. However, their practical application has been limited by the high cost associated with harsh preparation conditions and the poor electrode cycling stability in charging and diacharging. In this study, we successfully synthesized crystalline Ge nanorods through the reaction of intermetallic compound CaGe and ZnCl2. Ge nanorods with different morphologies and crystallinity can be obtained through precisely controlling the reaction temperature. When employed as electrodes for LIBs, the Ge nanorods demonstrate exceptional long-term cyclic stability. Even after 1000 cycles at a high rate of 2C (1C = 1600 mA g−1), it exhibits a remarkable reversible capacity of around 1000 mAh/g. Furthermore, such Ge electrode displays excellent cycling performance across a wide temperature range. And it could achieve reversible capacities of 1267, 832, and 690 mAh/g, with the rate of 1C, at temperatures of 20, 0, and −20 °C, respectively. Above all, our study offers a cost-effective approach for the synthesis of crystalline Ge nanorods, addressing the concerns associated with high production costs. And the application of Ge nanorods as anode materials in LIBs over a wide temperature range opens up new possibilities for the development of advanced energy storage systems.

P‐7.9: The Specification Study of Taper Angle in Metal Wire Electrode of TFT‐LCD

The electrodes of Gate (GE) and Source & Drain (SE) in thin Film Transistor (TFT) devices which are made of metal wires are fabricated by getting patterned through WET Etching. The taper angle of these metal wires play key roles in liquid crystal display (LCD). Excessive taper angle of the metal wires after WET etching will lead to poor coverage of the insulating layer and light leakage at the edge of the metal and thus reduce the contrast of the LCD. The overlarge taper angle of the electrodes will result in a series of defects in the TFT LCD as stated above, however, the taper angle of the electrodes can not be too small. The lower taper will increase the resistance of the metal electrodes. Beyond that, the photoresist (PR) will peeling and thus the metal line disappearing if the taper angle are too small. This article mainly focus on developing the specifications of the taper angle in the GE and SE electrodes.

Three-electrode germanium-on-silicon avalanche photodiode array.

In this Letter, we report a bridge-connected three-electrode germanium-on-silicon (Ge-on-Si) avalanche photodiode (APD) array compatible with the complementary metal-oxide semiconductor (CMOS) process. In addition to the two electrodes on the Si substrate, a third electrode is designed for Ge. A single three-electrode APD was tested and analyzed. By applying a positive voltage on the Ge electrode, the dark current of the device can be reduced, and yet the response of the device can be increased. Under a dark current of 100 nA, as the voltage on Ge increases from 0 V to 15 V, the light responsivity is increased from 0.6 A/W to 1.17 A/W. We report, for the first time to the best of our knowledge, the near-infrared imaging properties of an array of three-electrode Ge-on-Si APDs. Experiments show that the device can be used for LiDAR imaging and low-light detection.

Surface Treatment of Polyimide Using Solid-source H2O Plasma for Fabrication of Ge Electrode

Surface Treatment of Polyimide Using Solid-source H2O Plasma for Fabrication of Ge Electrode

In Situ Synthesis of Germanium Particles Decorated in Conjugated N-doped Carbon Matrix: Boosting the Performance of the Lithium-Ion Battery

Germanium (Ge) has aroused great attention due to its high theoretical capacity, benign lithium diffusion, and low working potential. However, application of the Ge anode is hindered by volume expansion and the unstable solid electrolyte interphase (SEI) during the (de)lithiation process. Herein, Ge particles encapsulated tightly on an N-doped porous carbon matrix structure are obtained via a simple one-step in situ thermally driven reduction reaction of poly(vinylpyrrolidone) and carboxyethyl germanium sesquioxide. A protective N-doped carbon layer of suitable thickness is further rationally designed to improve the conductivity as well as enhance the transfer of lithium ions while alleviating the volume stress of Ge particles. The adsorption energy for the N-doped carbon obtained by density function theory (DFT) calculation has verified that heteroatom doping is helpful to considerable decrease the energy barrier of lithium ions and a remarkable electrochemical performance of the Ge electrode is achieved with this optimal designing. This facile easy-to-control method can further be applied for electrodes of silicon, tin, phosphorus etc., which have the volume expansion issue.

Enhanced Electrochemical Performance in Ge/GeO2 Nanotubes Anode Derived from C/Ge Nanofibers

Hollow discontinuous Ge/GeO2 nanotubes are successfully prepared after the facile oxidization process in air, which are derived from the C/Ge core–shell nanofibers. Electrospinning and chemical vapor deposition techniques are used to fabricate the carbon nanofiber templates and the Ge shell electrode, respectively. Compared with the C/Ge nanocomposites, the Ge/GeO2 nanotube anode demonstrates improved electrochemical performance due to the enlarged surface area and enough space, which can effectively retard the Ge electrode large volume change during repeated cycling. Full‐battery Ge/GeO2||LiCoO2 is also configured and displays good Li‐ion storage ability.

In-Situ Measurement and Modeling of Stress Evolution in Ge Electrode Due to Na/Na+ Redox Reactions

Sodium-ion batteries are one of the promising alternatives to Li-ion batteries and experience similar capacity fade mechanisms due to volume expansion induced stresses. It is imperative to understand the stress evolution in Na-ion battery electrodes and how these stresses affect the electrode performance to be able to develop durable batteries. To this end, amorphous germanium (a-Ge) was selected as a model electrode material to understand the mechanics of Na-ion battery electrodes. Stress evolution in Ge thin film electrode was measured in-situ during electrochemical sodiation/desodiation cycling. It was observed that the Ge electrode sustains as high as 0.6 GPa of compressive stress during insertion of sodium and 0.75 GPa of tensile stress during extraction of sodium. In spite of no experimental evidence suggesting phase changes in Ge electrodes, the stress response during the initial sodiation reaction with pristine a-Ge was significantly different from that of subsequent sodiation/desodiation cycling. To further understand this interesting stress behavior, a diffusion-deformation theory was formulated and implemented in a finite element code to predict the mechanical and electrochemical response. In this talk, we will present our finite element results and explain the mechanism responsible for the interesting stress behavior observed in our experiments.

Volume Expansion Induced Stresses in Ge Electrode Due Electrochemical Cycling Against Sodium

Li-ion battery has been widely used due to its high energy and power density. However, due to scarcity of Li reserves there has been increased focus on Li-ion alternatives. One of the promising alternatives is Na-ion battery (NIB). However, NIB also suffers from similar degradation phenomena’s as Li-ion when cycled with large volume expansion anodes like Ge. Electrodes undergoing large volume expansion are subjected to significant amount of stress during electrochemical cycling process which causes mechanical degradation and capacity fade. Here, we measured volume expansion and the associated stresses in Ge thin film electrodes during sodiation/desoadiaiton cycling. In spite of the bigger size, Na-ion generated lower stresses in Ge during cycling as compared to Li-ion. The mechanical dissipation losses were observed to be comparable to other polarization losses in the Na-ion cell.

Improving the cycling stability of three-dimensional nanoporous Ge anode by embedding Ag nanoparticles for high-performance lithium-ion battery

Due to huge volume expansion and poor electrical conductivity, the commercial application of the promising Germanium (Ge) anode is restrained in lithium ion battery (LIB) field. Generally, conductive metals can improve the electron mobility in Ge. In that way, whether active materials or conductive metals account for a higher proportion in the anode is controversial in this field and needs to be clarified urgently. Herein, three Ge-based anodes with different ratios in conductive Ag are fabricated by a facile melt spinning and one-step dealloying method. It is found that Ag nanoparticles embedded three-dimensional nanoporous Ge (Ag/np-Ge) electrode with high active material ratio exhibits the best cycling stability among tested samples, delivering a high capacity of 953 mAh g−1 after 100 cycles at a current density of 100 mA g−1 and an excellent reversible capacity of 522 mAh g−1 after 200 cycles even at the high current density of 1000 mA g−1. The enhanced cycling stability can be attributed to the synergistic effect of nanoporous network-like structure and embedded Ag nanoparticles. A dramatical increase in electrical conductivity and activity of Ge by doping of Ag is confirmed by density functional theory (DFT) calculations. The work provides us an idea to rationally design the three-dimensional structure of active materials assisting with a proper ratio of conductive metals, which may promote the development of promising Ge anodes for LIBs with excellent cycling stability.

Measurement of Volume Changes and Associated Stresses in Ge Electrodes Due to Na/Na+ Redox Reactions

In situ electrochemical cells were assembled with an amorphous germanium (a-Ge) film as working electrode and sodium foil as reference and counter electrode. The stresses generated in a-Ge electrodes due to electrochemical reaction with sodium were measured in real-time during the galvanostatic cycling. A specially designed patterned a-Ge electrode was cycled against sodium and the corresponding volume changes were measured using an AFM; it was observed that sodiation/desodiation of a-Ge results in more than 300% volume change, consistent with literature. The potential and stress response showed that the a-Ge film undergoes irreversible changes during the first sodiation process, but the subsequent desodiation/sodiation cycles are reversible. The stress response of the film reached steady-state after the initial sodiation and is qualitatively similar to the response of Ge during lithiation, i.e., initial linear elastic response followed by extensive plastic deformation of the film to accommodate large volume changes. However, despite being bigger ion, sodiation of Ge generated lower stress levels compared to lithiation. Consequently, the mechanical dissipation losses associated with plastic deformation are lower during sodiation process than it is for lithiation.

Critical roles of microstructure and interphase on the stability of microsized germanium anode

Creating a certain degree of porosity is a widely adopted strategy in maintaining the cyclic stability of alloy anodes in Li-ion batteries (LIBs). The free space provided by the nanopores enables to partly alleviate the large strains during lithiation for increasing structural integrity. Instead of fabricating a nanostructured electrode with pre-designed pores, nanopores are in-situ created during lithiation/de-lithiation of Ge electrodes, enabling the direct utilization of microsized Ge particles. Assisting by scanning transmission electron microscopy (STEM), we systematically explore the microstructure evolution of Ge particles during cycling. It reveals the vital role of pore development, which is closely related to the solid electrolyte interphase (SEI), in maintaining the stable cyclic performance. The nanostructure of SEI is further resolved by cryo-transmission electron microscopy (cryo-TEM), which suggests that the amorphous inorganic component is essential to the fast kinetics for inducing sufficient porosity. Compared to the classic lithium hexafluorophosphate (LiPF6) salt in the electrolyte, the lithium difluoro(oxalato)borate (LiDFOB) shows great advantages in constructing a highly ionic conductive SEI layer for facilitating the nanopore growth. This work demonstrates the critical roles of interphase and the resulted microstructure in stabilizing the alloy microparticles.

Boosting Superior Lithium Storage Performance of Alloy‐Based Anode Materials via Ultraconformal Sb Coating–Derived Favorable Solid‐Electrolyte Interphase

AbstractAlloy materials such as Si and Ge are attractive as high‐capacity anodes for rechargeable batteries, but such anodes undergo severe capacity degradation during discharge–charge processes. Compared to the over‐emphasized efforts on the electrode structure design to mitigate the volume changes, understanding and engineering of the solid‐electrolyte interphase (SEI) are significantly lacking. This work demonstrates that modifying the surface of alloy‐based anode materials by building an ultraconformal layer of Sb can significantly enhance their structural and interfacial stability during cycling. Combined experimental and theoretical studies consistently reveal that the ultraconformal Sb layer is dynamically converted to Li3Sb during cycling, which can selectively adsorb and catalytically decompose electrolyte additives to form a robust, thin, and dense LiF‐dominated SEI, and simultaneously restrain the decomposition of electrolyte solvents. Hence, the Sb‐coated porous Ge electrode delivers much higher initial Coulombic efficiency of 85% and higher reversible capacity of 1046 mAh g−1 after 200 cycles at 500 mA g−1, compared to only 72% and 170 mAh g−1 for bare porous Ge. The present finding has indicated that tailoring surface structures of electrode materials is an appealing approach to construct a robust SEI and achieve long‐term cycling stability for alloy‐based anode materials.

In Situ Focused Ion Beam-Scanning Electron Microscope Study of Crack and Nanopore Formation in Germanium Particle during (De)Lithiation

Germanium (Ge) has been considered a promising anode active material, due to its high capacity, low voltage, fast lithium ion diffusion, and high electrical conductivity. However, Ge based anode materials suffer from pulverization due to a large volume change, up to 300%. Although pulverization issues can be alleviated by nano-structuring the Ge-based anode materials, recent studies have shown that nanometer-sized pores are still formed in the nano-structured electrode due to vacancy-mediated diffusion, which could lead to pulverization during repeated cycling. In recent years, the reaction mechanism of the Ge anode has been studied by using different in situ and operando characterization methods such as X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). For instance, Lim et al. proposed the phase transformations of Ge that occur during lithiation and delithiation.1 They also studied the effect of cycling rate on Ge phase transformation during the charge/discharge process and proposed a mechanism to explain the C‐rate dependence phase transformation phenomenon. However, it is still necessary to correlate the microstructural evolution of the Ge electrode and its electrochemical performance. To this end, some advanced imaging technologies have been used to monitor the microstructural evolution of the Ge electrode during cycling such as transmission electron microscopy (TEM)2 and transmission X-ray microscopy (TXM).3 In situ TEM studies have shown the volume expansion during lithiation and formation of nanopores during delithiation in Ge nanowires in real time. But due to the small size of the sample used in the TEM, it is difficult to control the current rate. In situ TXM can obtain two dimensional (2D) or three dimensional (3D) microstructures of Ge particles during cycling with a large field of view. However, the resolution of TXM is not sufficient for monitoring nanometer-sized structures, such as nanopores. In this study, we developed an approach to build a single particle battery in the chamber of focused-ion beam-scanning electron microscope (FIB-SEM) to monitor the microstructural evolution of a single Ge micro-particle during cycling. The experiment was performed within a ZEISS Nvision FIB-SEM at the Center for Nanoscale Materials, Argonne National Laboratory. A Ge particle was attached to the tungsten probe by carbon coating using FIB deposition as positive electrode. The lithium metal was placed on the top of SEM stage as negative electrode. One drop of ionic liquid electrolyte (ILE) was placed on the top of lithium metal. The ILE was made by dissolving the lithium salt, lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), in a solvent of 1-butyl-1-methylpyrrolidinium bis (trifluoromethyl -sulfonyl) imide (P14TFSI). The tungsten probe and the SEM stage were connected to a Keithley 6430 sub-femtoamp remote sourcemeter. Galvanostatic mode was used in all electrochemical cycling. The particle was immersed in the ILE drop during cycling and lifted out for imaging at different states of charge. The particle was polished by FIB before imaging to remove ILE on the surface. This study reveals that germanium electrodes with low and high cycling rates have better microstructure integrity, which leads to better cycling performance. The nanopores tend to aggregate into large porous structures during cycling which leads to particle pulverization and capacity fading of the electrode. 1. Lim, L. Y.; Fan, S.; Hng, H. H.; Toney, M. F., Storage Capacity and Cycling Stability in Ge Anodes: Relationship of Anode Structure and Cycling Rate. Advanced Energy Materials 2015, 5 (15), 1500599. 2. Liu, X. H.; Huang, S.; Picraux, S. T.; Li, J.; Zhu, T.; Huang, J. Y., Reversible Nanopore Formation in Ge Nanowires during Lithiation-Delithiation Cycling: An In Situ Transmission Electron Microscopy Study. Nano Letters 2011, 11 (9), 3991-3997. 3.Weker, J. N.; Liu, N.; Misra, S.; Andrews, J. C.; Cui, Y.; Toney, M. F., In situ nanotomography and operando transmission X-ray microscopy of micron-sized Ge particles. Energy & Environmental Science 2014, 7 (8), 2771-2777.

Zinc Ferrite Nanorod‐Assembled Mesoporous Microspheres as Advanced Anode Materials for Sodium‐Ion Batteries

Mesoporous zinc ferrite (ZnFe2O4) microspheres assembled by nanorods are fabricated through a facile hydrothermal approach, followed by a calcination strategy. The fabricated mesoporous ZnFe2O4 has a diameter of approximately 500–800 nm with a high surface area of 91.6 m2 g−1. The utilization of the microspheres that serve as anode materials for sodium‐ion batteries is studied for the first time. The electrochemical results demonstrate that the ZnFe2O4 anode experiences a series of conversion and alloying reactions for reversible sodium storage and exhibits high sodium storage capacity and excellent stability. It exhibits a reversible capacity as high as 350 mAh g−1 after 300 cycles at 100 mA g−1, which is superior to other reported ZnO and ZnMxOy (M = Co, Sn, Ge) electrodes. The existence of the mesoporous structure is responsible for the excellent electrochemical properties of the microspheres, which not only enhances the electrochemical kinetics but also offers additional space to alleviate the strain associated with sodiation/desodiation.

Facile Synthesis of Amorphous Ge Supported by Ni Nanopyramid Arrays as an Anode Material for Sodium-Ion Batteries.

In this work, we introduce Ni nanopyramid arrays (NPAs) supported amorphous Ge anode architecture and demonstrate its effective improvement in sodium storage properties. The Ni−Ge NPAs are prepared by facile electrodeposition and sputtering method, which eliminates the need for any binder or conductive additive when used as a Na‐ion battery anode. The electrodes display stable cycling performance and enhanced rate capabilities in contrast with planar Ge electrodes, which can be owing to the rational design of the architectured electrodes and firm bonding between current collector and active material (i. e. Ni and Ge, respectively). To validate improvement of nanostructures on electrochemical performance, sodium insertion behavior of crystalline Ge derived from Mg2Ge precursor has been investigated, in which limited but effective enhancement of sodium storage properties are realized by introducing porous nanostructure in crystalline Ge. These results show that elaborately designed configuration of Ge electrodes may be a promising anode for Na‐ion battery applications.

Understanding the Mechanism of Stress Mitigation in Selenium-Doped Germanium Electrodes

This paper aims to investigate the mechanism of stress mitigation in micrometer (μm) sized Selenium (Se)-doped Germanium (Ge) electrode, which includes a self-forming inactive Li-Ge-Se network enveloping multiple nanometer-sized crystalline Ge (c-Ge) particles. Considering the electrode system contains multiply active particles, models based on single-particle are unable to fully understand elusive underpinning mechanism. Hence, a phase-field model is employed to investigate the effect of the Li-Ge-Se network on the particle-particle interaction, and the stress variation of the electrode upon lithiation. The amorphous Li-Ge-Se network provides an effective Li diffusion path for inter-particle diffusion, reducing stress difference between the surfaces of neighboring particles. Furthermore, the constraint between the adjacent particles induces a higher compressive stress at the reaction front impeding the mobile Li insertion during lithiation. Though small c-Ge nano-particle in the Ge0.9Se0.1 microparticle is lithiated quickly, the compressive stress is generated at its center for stress equilibrim causing more retardation effect. Meanwhile, the size difference between adjacent particles increases the principle and shear stresses in the inactive Li-Ge-Se, which could potentially lead to mechanical failure and debonding of the amorphous network. We believe that the results of this investigation can shed some light on the optimization design of electrodes.

Porous germanium enabled high areal capacity anode for lithium-ion batteries

The role of different mass loadings on the corresponding areal capacities, capacity retention, and rate performance in high-capacity Ge electrodes was studied. Micro-sized porous Ge powders were synthesized by a facile single-step reduction of GeO2 with hydrogen gas. The porous Ge electrode exhibited a high capacity retention over 1800 cycles at 8 A/g (∼73% retention) at the low loading of 0.56 mg/cm2. Even with the high loading of 4.45 mg/cm2, high areal capacity (>3 mAh/cm2) for over 100 cycles were observed. Excellent electrochemical stability for a full cell was also observed for about 180 cycles with a LiCoO2 cathode. Post cycling analysis reveals that the stability of the porous electrode stems from the ability of the grains to maintain their electrical contacts with each other even after undergoing transformation in the morphology and crystallinity.

Ionic Liquid–Organic Solvent Mixture-Based Polymer Gel Electrolyte with High Lithium Concentration for Li-Ion Batteries

In this paper, we have investigated the performance and solid electrolyte interphase formation (SEI) of a hybrid polymer gel electrolyte based on poly(vinylidene fluoride)-co-hexafluoropropylene, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide ([Py1,4]FSI), and lithium bis(fluorosulfonyl)imide (LiFSI) for all solid-state lithium-ion batteries. The effect of the addition of acetonitrile (AN) and different concentrations of LiFSI to such a polymer gel electrolyte was also examined. Compared to 1 M LiFSI in the ionic liquid–polymer electrolyte, the addition of 4 M LiFSI along with acetonitrile led to higher lithium storage capacity. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy were performed to analyze the SEI formation on a Ge electrode. The difference in the mechanical properties and SEI composition was observed upon changing the components of the polymer electrolyte. XPS analysis revealed a difference in the composition/thickness of the SEI layer, which varies upon increasing the Li-salt concentration and upon adding AN to [Py1,4]FSI. Such differences might have led to better Li storage capacity on using the concentrated IL–organic polymer electrolyte. Our study clearly shows that the addition of an organic solvent and high concentration of Li salt to the polymer gel electrolyte improves the performance of LIBs.

The Effect of Solvent on the Capacity Retention in a Germanium Anode for Lithium Ion Batteries

A thin and mechanically stable solid electrolyte interphase (SEI) is desirable for a stable cyclic performance in a lithium ion battery. For the electrodes that undergo a large volume expansion, such as Si, Ge, and Sn, the presence of a robust SEI layer can improve the capacity retention. In this work, the role of solvent choice on the electrochemical performance of Ge electrode is presented by a systematic comparison of the SEI layers in ethylene carbonate (EC)-based and fluoroethylene carbonate (FEC)-based electrolytes. The results show that the presence of FEC as a cosolvent in a binary or ternary solvent electrolyte results in an excellent capacity retention of ∼85% after 200 cycles at the current density of 500 mA g−1; while EC-based electrode suffers a rapid capacity degradation with a capacity retention of just 17% at the end of 200 cycles. Post analysis by an extensive use of X-ray photoelectron spectroscopy (XPS) was carried out, which showed that the presence of Li2O in FEC-based SEIs was the origin for the improved electrochemical performance.