Carbon-Free Porous Zn2GeO4 Nanofibers as Advanced Anode Materials for High-Performance Lithium Ion Batteries

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.

In Situ Construction of Zn2Mo3O8/ZnO Hierarchical Nanosheets on Graphene as Advanced Anode Materials for Lithium-Ion Batteries

Transition-metal oxides as anodes for lithium-ion batteries (LIBs) have attracted enormous interest because of their high theoretical capacity, low cost, and high reserve abundance. Unfortunately, they commonly suffer from poor electronic and ionic conductivity and relatively large volume expansion during discharge/charge processes, thereby triggering inferior cyclic performance and rate capability. Herein, a molybdenum-zinc bimetal oxide-based composite structure (Zn₂Mo₃O₈/ZnO/rGO) with rectangular Zn₂Mo₃O₈/ZnO nanosheets uniformly dispersed on reduced graphene oxide (rGO) has been prepared by using a simple and controllable cyanometallic framework template method. The Zn₂Mo₃O₈/ZnO rectangular nanosheets with desirable porous features are composed of nanocrystalline subunits, facilitating the exposure of abundant active sites and providing sufficient contact with the electrolyte. Benefiting from the composition and structural merits as well as the induced synergistic effects, the Zn₂Mo₃O₈/ZnO/rGO composite as LIB anodes delivers superior electrochemical properties, including high reversible capacity (960 mA h g^-1 after 100 cycles at 200 mA g^-1), outstanding rate performance (417 mA h g^-1 at 10,000 mA g^-1), and admirable long-term cyclic stability (862 mA h g^-1 after 400 cycles at 1000 mA g^-1). The mechanism of lithium storage and the formation of SEI film are systematically elucidated. This work provides an effective strategy for synthesizing promising Mo-cluster compound-based anodes for high-performance LIBs.

Binder-Free Zinc-Iron Oxide as a High-Performance Negative Electrode Material for Pseudocapacitors

The interaction between cathode and anode materials is critical for developing a high-performance asymmetric supercapacitor (SC). Significant advances have been made for cathode materials, while the anode is comparatively less explored for SC applications. Herein, we proposed a high-performance binder-free anode material composed of two-dimensional ZnFe₂O₄ nanoflakes supported on carbon cloth (ZFO-NF@CC). The electrochemical performance of ZFO-NF@CC as an anode material for supercapacitor application was examined in a KOH solution via a three-electrode configuration. The ZFO-NF@CC electrode demonstrated a specific capacitance of 509 F g^-1 at 1.5 A g^-1 and was retained 94.2% after 10,000 GCD cycles. The ZFO-NF@CC electrode showed exceptional charge storage properties by attaining high pseudocapacitive-type storage. Furthermore, an asymmetric SC device was fabricated using ZFO-NF@CC as an anode and activated carbon on CC (AC@CC) as a cathode with a KOH-based aqueous electrolyte (ZFO-NF@CC||AC@CC). The ZFO-NF@CC||AC@CC yielded a high specific capacitance of 122.2 F g^-1 at a current density of 2 A g^-1, a high energy density of 55.044 Wh kg^-1 at a power density of 1801.44 W kg^-1, with a remarkable retention rate of 96.5% even after 4000 cycles was attained. Thus, our results showed that the enhanced electrochemical performance of ZFO-NF@CC used as an anode in high-performance SC applications can open new research directions for replacing carbon-based anode materials.

Size-controllable synthesis of Zn2GeO4 hollow rods supported on reduced graphene oxide as high-capacity anode for lithium-ion batteries

Germanium-based ternary oxides have aroused wide attention as an anode for high-performance lithium-ion batteries (LIBs). Nevertheless, they usually suffer a large volume expansion and rapid capacity fading during lithiation/delithiation cycles. To address this issue, herein, Zn₂GeO₄/RGO composites are synthesized with Zn₂GeO₄ hollow rods in-situ grown on reduced graphene oxide (RGO) sheets. The Zn₂GeO₄ hollow rods can be facilely adjusted from nano- to micro-size. The lithium storage performances of the composites strongly depend on the size of Zn₂GeO₄ hollow rods and the content of RGO. The optimized Zn₂GeO₄/RGO composite exhibits a pseudocapacitance-dominated Li⁺ storage performance, with a large reversible capacity of 1005 mAh g^-1 after 100 cycles at 0.5 A g^-1, an excellent rate capability (515 mAh g^-1 at a high rate of 5 A g^-1) and a good long cycling stability of 500 cycles with a low capacity loss of 0.05% per cycle at 1 A g^-1. The outstanding electrochemical performance can be attributed to the unique composition and microstructure of the material as well as the synergistic effect of the conductive RGO sheets and the hollow Zn₂GeO₄ nanostructure. This work provides a promising anode for high-performance LIBs and a useful inspiration for further improving the Ge-based ternary oxide anodes.

Selenium vacancy-rich and carbon-free VSe2 nanosheets for high-performance lithium storage

VSe2 is a typical transition metal dichalcogenide with metallic conductivity, which makes it a potentially promising electrode material for lithium-ion batteries (LIBs). However, further research into the VSe2 nanomaterial for electrochemical applications has been seriously impeded by the practical difficulty of synthesizing phase-pure VSe2. In this work, Se vacancy-rich VSe2 nanosheets were synthesized by a one-step solvothermal method with suitable reactants. Benefiting from the strong reduction ability of hydrazine hydrate, V4+ was partly reduced into V3+, resulting in abundant Se vacancies being generated in situ in the as-obtained VSe2 nanosheets. Positron annihilation lifetime spectroscopy, X-ray absorption spectroscopy and photoluminescence spectroscopy all confirmed the existence of Se vacancies. When applied as the anode material for LIBs, the VSe2 nanosheets can deliver a remarkable reversible capacity of 1020 mA h g-1 at 0.1 A g-1 after 100 cycles, and even at 2 A g-1 a high specific capacity of 430 mA h g-1 is reached. Electrochemical characterizations further reveal that the Se vacancies in the VSe2 nanosheets can significantly enhance lithium-ion diffusion kinetics and increase the number of electrochemical active sites, which are responsible for the good lithium-storage performance. This work may provide an alternative approach for rational design of other high-performance electrode materials for LIBs to satisfy demand for future sustainable development.

Bright persistent green emitting water-dispersible Zn2GeO4:Mn nanorods

This work reports on a green and facile approach for designing bright and persistent green luminescent Zn₂GeO₄:Mn²⁺ nano crystals with high quantum yield (∼52%) and water dispersibility designated for LEDs, security, and bio imaging.

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.