Recent progress on Ge oxide anode materials for lithium-ion batteries

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.

Microwave-Assisted Metal-Organic Frameworks Derived Synthesis of Zn2GeO4 Nanowire Bundles for Lithium-Ion Batteries

Germanium-based multi-metallic-oxide materials have advantages of low activation energy, tunable output voltage, and high theoretical capacity. However, they also exhibit unsatisfactory electronic conductivity, sluggish cation kinetics, and severe volume change, resulting in inferior long-cycle stability and rate performance in lithium-ion batteries (LIBs). To solve these problems, we synthesize metal-organic frameworks derived from rice-like Zn2GeO4 nanowire bundles as the anode of LIBs via a microwave-assisted hydrothermal method, minimizing the particle size and enlarging the cation's transmission channels, as well as, enhancing the electronic conductivity of the materials. The obtained Zn2GeO4 anode exhibits superior electrochemical performance. A high initial charge capacity of 730 mAhg-1 is obtained and maintained at 661 mAhg-1 after 500 cycles at 100 mA g-1 with a small capacity degradation ratio of ~0.02% for each cycle. Moreover, Zn2GeO4 exhibits a good rate performance, delivering a high capacity of 503 mA h g-1 at 5000 mA g-1. The good electrochemical performance of the rice-like Zn2GeO4 electrode can be attributed to its unique wire-bundle structure, the buffering effect of the bimetallic reaction at different potentials, good electrical conductivity, and fast kinetic rate.

Dual carbon decorated germanium-carbon composite as a stable anode for sodium/potassium-ion batteries

In the present work, we introduce a dual carbon accommodated structure in which germanium nanoparticles are encapsulated into an ordered mesoporous carbon matrix (Ge-CMK) and further coated with an amorphous carbon layer (Ge@C-CMK) through a nano-casting route followed by chemical vapor deposition (CVD) treatment. In the resultant Ge@C-CMK composite, the unique lane-like pore structure that cooperates with the amorphous carbon surface can not only mitigate the volume expansion of germanium particles, but also improve the electrical conductivity of germanium as well as facilitate Na⁺/K⁺ diffusion. When employed as the anode of sodium-ion batteries, the Ge@C-CMK electrode exhibits stable capacity as well as long-term cycling stability (a stable capacity of 176 mAh g^-1 at 1 A g^-1 after 5000 cycles). Furthermore, it also delivers a reversible capacity when used as the anode of potassium-ion batteries. This demonstrates that the Ge@C-CMK electrode possesses promising application potential as an alternative anode in sodium and potassium ion storage applications.

Facile synthesis of uniform N-doped carbon-coated TiO2 hollow spheres with enhanced lithium storage performance

Great efforts, such as nano-structuring and carbon coating, have been devoted to addressing the poor rate performance of TiO2 anodes in lithium ion batteries, which is mainly caused by sluggish Li ion diffusion and poor electrical conductivity of the bulk material. However, the complicated fabrication processes make most of these strategies much low practical significance. Herein, a scalable and facile strategy based on sacrificial template-accelerated hydrolysis and polydopamine coating is proposed to manufacture uniform N-doped carbon-coated TiO2 hollow spheres. The nanostructured hollow structure can shorten the path of Li+ insertion/extraction in the electrode material. More importantly, the uniform carbon layer can improve the electronic conductivity of TiO2 during long-term cycling. Thus, a reversible capacity can be obtained of as high as 390.2 mA h g-1 at a current density of 0.1 A g-1. Furthermore, a high capacity of 166.3 mA h g-1 after 2000 cycles at 5.0 A g-1 shows that the carbon-coated TiO2 hollow spheres deliver good capacity retention and cycling performance.

2-Carboxyethylgermanium Sesquioxide as A Promising Anode Material for Li-Ion Batteries

Various forms of germanium and germanium-containing compounds and materials are actively investigated as energy-intensive alternatives to graphite as the anode of lithium-ion batteries. The most accessible form-germanium dioxide-has the structure of a 3D polymer, which accounts for its rapid destruction during cycling, and requires the development of further approaches to the production of nanomaterials and various composites based on it. For the first time, we propose here the strategy of using 2-carboxyethylgermanium sesquioxide ([O_1.5 GeCH₂ CH₂ CO₂ H]_n , 2-CEGS), in lieu of GeO₂ , as a promising, energy-intensive, and stable new source system for building lithium-ion anodes. Due to the presence of the organic substituent, the formed polymer has a 1D or a 2D space organization, which facilitates the reversible penetration of lithium into its structure. 2-CEGS is common and commercially available, completely safe and non-toxic, insoluble in organic solvents (which is important for battery use) but soluble in water (which is convenient for manufacturing diverse materials from it). This paper reports the preparation of micro- (flower-shaped agglomerates of ≈1 μm thick plates) and nanoformed (needle-shaped nanoparticles of ≈500×(50-80) nm) 2-CEGS using methods commonly available in laboratories and industry such as vacuum and freeze-drying of aqueous solutions of 2-CEGS. Lithium half-cell anodes based on 2-CEGS show a capacity of ≈400 mAh g^-1 for microforms and up to ≈700 mAh g^-1 for nanoforms, which is almost two times higher than the maximal theoretical capacity of graphite. These anodes are stable during the cycling at various rates. The results of DFT simulations suggest that Li atoms form the stable Li₂ O with the oxygen atoms of 2-CEGS, and actual charge-discharge cycles involve deoxygenated GeC₃ H₅ molecules. Thus, C₃ chains loosen the anode structure compared to pure Ge, improving its ability to accommodate Li ions.

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.

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.