Morphology memory but reconstructing crystal structure: porous hexagonal GeO2 nanorods for rechargeable lithium-ion batteries

Structures and Properties of Planar Ge3O3 Cluster and Its Buckled Honeycomb Two-Dimensional Nanostructure

The discovery of graphene and its excellent properties inspired the search for more two-dimensional (2D) materials. Understanding the structures and properties of the smallest repeating units as well as crystal 2D materials is helpful for designing 2D materials. As germanium tends to form three-dimensional structures, the preparation of germanium-based 2D nanomaterials is still a challenge. Herein, we report a Ge3O3 cluster with the potential to construct a germanium oxide 2D nanostructure. We conduct a combined anion photoelectron spectroscopy and theoretical study on Ge3O3-/0. The structure of Ge3O3- is a Cs symmetric nonplanar six-membered ring, while that of Ge3O3 is a D3h symmetric planar six-membered ring. Chemical bonding analyses reveal that Ge3O3 exhibits π aromaticity. First-principle results suggest that a buckled honeycomb 2D nanostructure with a wide band gap of 3.14 eV may be produced based on Ge3O3, which is promising in optoelectronic applications especially in blue, violet, and ultraviolet regions.

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.

Crystalline Ammonium Peroxogermanate as a Waste-Free, Fully Recyclable Versatile Precursor for Germanium Compounds

High, nearly 100%, yield synthesis of ammonium peroxogermanate (APG), (NH₄)₆[Ge₆(μ-OO)₆(μ-O)₆(OH)₆]·6H₂O, is presented, and its crystal structure is determined by single crystal X-ray study. It comprises centrosymmetric hexanuclear peroxogermanate anions [Ge₆(μ-OO)₆(μ-O)₆(OH)₆]^6- with six μ-oxo- and six μ-peroxo groups forming negatively charged layers. The space between these layers is filled by ammonium cations and water molecules, forming a highly stable structure due to hydrogen bonding. Highly soluble macroporous amorphous germanium oxide (HSGO) is then synthesized by mild treatment of APG. The compound forms highly oversaturated metastable germanium oxide solution with a solubility of 100 g/L, over 20 times higher than the solubility of amorphous germanium oxide. HSGO solution is a versatile reagent that can react with basic and acidic reagents to give a diverse range of salts including, e.g., germanium sulfide, germanium hydrophosphate, and potassium germanate. In the absence of acid or base, the aqueous HSGO solution yields hexagonal germanium oxide under ambient conditions.

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.

Confined metal Ge quantum dots in carbon nanofibers for stable rechargeable batteries

As a promising alloy-type anode material for rechargeable batteries, the metal germanium (Ge) shows high capacity, but it suffers from a fast capacity fading problem caused by a large volume expansion during lithiation/delithiation cycles. In this study, via a facile electrospinning method, we optimized the combination structure of Ge quantum dots (QDs) and carbon nanofibers (CNFs). Specifically, Ge QDs with a diameter of 4-7 nm were highly dispersed in porous (pore size 10-150 nm) CNFs. The hybridized Ge/CNF nanocomposite exhibited remarkable Li storage performances such as high reversible capacity (1204 mA h g-1 at a current density of 200 mA g-1), high capacity retention (87.1% after 100 cycles) and excellent rate property (760 mA h g-1 at 3000 mA g-1). The improved electrochemical performance was due to the synergistic effects of Ge QDs and carbon nanofibers; this effectively alleviated the volume expansion problem, prevented the agglomeration of Ge, maintained the structural stability of the nanocomposite, and improved the electrode kinetics of diffusion of Li ions.