Preparation of Ge nanotube arrays from an ionic liquid for lithium ion battery anodes with improved cycling stability

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.

Binder-free germanium nanoparticle decorated multi-wall carbon nanotube anodes prepared via two-step electrophoretic deposition for high capacity Li-ion batteries

Germanium (Ge) has a high theoretical specific capacity (1384 mA h g-1) and fast lithium-ion diffusivity, which makes it an attractive anode material for lithium-ion batteries (LIBs). However, large volume changes during lithiation can lead to poor capacity retention and rate capability. Here, electrophoretic deposition (EPD) is used as a facile strategy to prepare Ge nanoparticle carbon-nanotube (Ge/CNT) electrodes. The Ge and CNT mass ratio in the Ge/CNT nanocomposites can be controlled by varying the deposition time, voltage, and concentration of the Ge NP dispersion in the EPD process. The optimized Ge/CNT nanocomposite exhibited long-term cyclic stability, with a capacity of 819 mA h g-1 after 1000 cycles at C/5 and a reversible capacity of 686 mA h g-1 after 350 cycles (with a minuscule capacity loss of 0.07% per cycle) at 1C. The Ge/CNT nanocomposite electrodes delivered dramatically improved cycling stability compared to control Ge nanoparticles. This can be attributed to the synergistic effects of implanting Ge into a 3D interconnected CNT network which acts as a buffer layer to accommodate the volume expansion of Ge NPs during lithiation/delithiation, limiting cracking and/or crumbling, to retain the integrity of the Ge/CNT nanocomposite electrodes.

Facile Synthesis of Ge@TiO2 Nanotube Hybrid Nanostructure Anode Materials for Li-Ion Batteries

Utilizing nanostructures of Li-alloying anode materials (e.g., Si, Ge, Sn, etc.) has been proposed as a key strategy to improve the electrochemical performance. However, the main challenge lies in the costly and complex nanostructure synthesis processes. Notably, the nanostructure growth processes are mainly supported by Li-inactive templates, which later need to be removed, and the template removal process results in the destruction of the desired nanostructures. In this report, we demonstrated the use of a Li-active, self-organized TiO2 nanotube template to fabricate germanium (Ge)-based nanostructured anodes. This has been achieved as follows: first, TiO2 nanotubes are fabricated via electrochemical anodization of titanium foil. Then, the nanotubes are coated with a Ge film in the second step via electrodeposition. Besides the effective nanostructure growth using a Li-active template, the implemented electrochemical synthesis methods are cost-effective, accessible, and scalable. Furthermore, the electrochemical methods allow the fabrication of nanostructures with well-controlled structures, morphology, and compositions. Accordingly, a Ge-coated TiO2 nanotube (Ge@TiO2) nanocomposite anode has been successfully fabricated, and its electrochemical performance has been tested for Li-ion batteries. The study has shown the important roles of TiO2 nanotube arrays in improving the performance by providing strong mechanical support to buffer the volume expansion and offering a high surface area to enhance Ge-active mass loading. Moreover, the direct contact of the nanotubes with a Ti current collector facilitates one-dimensional (1D) electron transport and avoids the need of adding inactive binders or conductive additives.

Germanium Nanowires via Molten-Salt Electrolysis for Lithium Battery Anode

Germanium (Ge)-based materials can serve as promising anode candidates for high-energy lithium-ion batteries (LIBs). However, the rapid capacity decay caused by huge volume expansion severely retards their application. Herein, we report a facile and controllable synthesis of Ge nanowire anode materials through molten-salt electrolysis. The optimal Ge nanowires can deliver a capacity of 1058.9 mAh g^-1 at 300 mA g^-1 and a capacity above 602.5 mAh g^-1 at 3000 mA g^-1 for 900 cycles. By in situ transmission electron microscopy and in situ X-ray diffraction, the multiple-step phase transformation and good structural reversibility of the Ge nanowires during charge/discharge are elucidated. When coupled with a lithium-rich Li_1.2Mn_0.567Ni_0.167Co_0.067O₂ cathode in a full battery, the Ge nanowire anode leads to a relatively stable capacity with a retention of 84.5% over 100 cycles. This research highlights the significance of molten-salt electrolysis for the synthesis of alloy-type anode materials toward high-energy LIBs.

Electrodeposition Technologies for Li-Based Batteries: New Frontiers of Energy Storage

Electrodeposition induces material syntheses on conductive surfaces, distinguishing it from the widely used solid-state technologies in Li-based batteries. Electrodeposition drives uphill reactions by applying electric energy instead of heating. These features may enable electrodeposition to meet some needs for battery fabrication that conventional technologies can rarely achieve. The latest progress of electrodeposition technologies in Li-based batteries is summarized. Each component of Li-based batteries can be electrodeposited or synthesized with multiple methods. The advantages of electrodeposition are the main focus, and they are discussed in comparison with traditional technologies with the expectation to inspire innovations to build better Li-based batteries. Electrodeposition coats conformal films on surfaces and can control the film thickness, providing an effective approach to enhancing battery performance. Engineering interfaces by electrodeposition can stabilize the solid electrolyte interphase (SEI) and strengthen the adhesion of active materials to substrates, thereby prolonging the battery longevity. Lastly, a perspective of future studies on electrodepositing batteries is provided. The significant merits of electrodeposition should greatly advance the development of Li-based batteries.

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.

Yolk-Shell Germanium@Polypyrrole Architecture with Precision Expansion Void Control for Lithium Ion Batteries

The key properties of yolk-shell architecture in improving electrochemical performance lies in its uniformity and the appropriate void space, which can expand/contract freely upon lithium alloying and leaching without damaging the outer shell, while being achievable with minimal sacrifice of volumetric energy density. Therefore, we developed a highly controllable strategy to fabricate a uniform porous germanium@polypyrrole (PGe@PPy) yolk-shell architecture with conformal Al₂O₃ sacrificial layer by atomic layer deposition (ALD) process. The PGe@PPy yolk-shell anode fabricated with 300 ALD cycles delivers excellent electrochemical performance: high reversible capacity (1,220 mA hr g⁻¹), long cycle performance (>95% capacity retention after 1,000 cycles), and excellent rate capability (>750 mA hr g⁻¹ at 32 A g⁻¹). Electrodes with high areal capacity and current density were also successfully fabricated, opening a new pathway to develop high-capacity electrode materials with large volume expansion.

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Porous germanium@polypyrrole (PGe@PPy) yolk-shell architecture was developed

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Precision expansion and void control make PGe@PPy stable during lithiation/delithiation

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PGe@PPy electrode shows high rate and areal capacity, cycling stability, and current density

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The full cell shows the stable capacity retention with high energy density

Electrochemical Synthesis of Battery Electrode Materials from Ionic Liquids

Electrode materials as well as the electrolytes play a decisive role in batteries determining their performance, safety, and lifetime. In the last two decades, different types of batteries have evolved. A lot of work has been done on lithium ion batteries due to their technical importance in consumer electronics, however, the development of post-lithium systems has become a focus in recent years. This chapter gives an overview of various battery materials, primarily focusing on development of electrode materials in ionic liquids via electrochemical route and using ionic liquids as battery electrolyte components.

Capillary-Induced Ge Uniformly Distributed in N-Doped Carbon Nanotubes with Enhanced Li-Storage Performance

Germanium (Ge) is a prospective anode material for lithium-ion batteries, as it possesses large theoretical capacity, outstanding lithium-ion diffusivity, and excellent electrical conductivity. Ge suffers from drastic capacity decay and poor rate performance, however, owing to its low electrical conductivity and huge volume expansion during cycling processes. Herein, a novel strategy has been developed to synthesize a Ge@N-doped carbon nanotubes (Ge@N-CNTs) composite with Ge nanoparticles uniformly distributed in the N-CNTs by using capillary action. This unique structure could effectively buffer large volume expansion. When evaluated as an anode material, the Ge@N-CNTs demonstrate enhanced cycling stability and excellent rate capabilities.

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.

UV-assisted, template-free electrodeposition of germanium nanowire cluster arrays from an ionic liquid for anodes in lithium-ion batteries

The structure of Ge nanowire cluster arrays is beneficial for capacity retention of the electrode.

Rational synthesis of carbon-coated hollow Ge nanocrystals with enhanced lithium-storage properties

High-capacity anode materials based on alloy-type group IV elements always have large volume expansion during lithiation when they are used in lithium-ion batteries. Designing hollow structures is a well-established strategy to accommodate the volume change because of sufficient internal void space. Here we report a facile template-free route to prepare hollow Ge nanospheres without using any templates through a quasi-microemulsion method. Ge nanocrystals are preferably self-assembled along the interface of liquid vesicles between water and tetrahydrofuran, and well-defined hollow architectures of ∼50 nm in diameter are formed. Both the wall thickness and hollow interiors can be easily tuned. After subsequent carbon coating via pyrolysis of acetylene, the as-formed Ge@C nanocomposite with hollow interiors exhibits a highly reversible capacity of about 920 mA h g(-1) at 200 mA g(-1) over 50 cycles, and excellent rate capability. The small size and the high structural integrity of hollow Ge@C structures contribute to the superior lithium-storage performances.

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.

Novel phosphorus-containing halogen-free ionic liquids: effect of sulfonate anion size on physical properties, biocompatibility, and flame retardancy

Phosphorus-containing sulfonate ILs with different anions size present different thermal stability, solubility, viscosity, melting points, and cytotoxicity. They show flame retardant effect for PA6 via accelerating decomposition of matrix.

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.

A double-layered Ge/carbon cloth integrated anode for high performance lithium ion batteries

A double-layered Ge coated carbon cloth composite as integrated electrode shows promising application in flexible lithium ion batteries.