Germanium Anodes Research Articles

Ti3C2Tx MXene coated 3D ordered macroporous germanium anodes for Li-ion batteries with enhanced cycling stability and fast Li-ion mobility

The current trend in electronic device development and electric vehicle technology has resulted in A growing need for negative electrode materials that possess high capacity and quick Li-ion transport properties. Ge-based materials are considered the very promising candidates owing to their high theoretical capacity and facile alloying reaction with Li. In order to enhance the rate of Li-ion diffusion and account for the volume change of over 300 %, a Ti3C2Tx MXene coated 3D ordered macroporous germanium (3DOM Ge@MXene) structure was successfully developed. The 3DOM Ge@MXene provides a 1490 mAh g−1 initial reversible capacity at 0.32 A g−1. Additionally, after 100 cycles, it displays a consistent cycling ability of 1034 mAh g−1. The MXene coating also improves the material's Li-ion rapid transfer performance, with Li-ion diffusion coefficient of 1.35 × 10−10 cm2s−1 for anodic and 2.2 × 10−10 cm2s−1 for cathodic.

Robust bond linkage between boron-based coating layer and lithium polyacrylic acid binder enables ultra-stable micro-sized germanium anodes

Micro-sized alloy type germanium (Ge) anodes possess appealing properties for next-generation lithium ions batteries, such as desirable capacity, easy accessibility and greater tapdensity. Nevertheless, volume expansion accompanied by severe pulverization and continuous growth of solid electrolyte interlayer (SEI) still represent fundamental obstacles to their practical applications. Herein, we propose a fresh strategy of constructing robust bond linkage between boron-based coating layer and lithiated polyacrylic acid (PAALi) binder to circumvent the pulverization problems of Ge anodes. Facile pyrolysis of boric acid can introduce an amorphous boron oxide interphase on Ge microparticles (noted as Ge@B2O3). Then in situ crosslinking reaction between B2O3 and PAALi via BOC bond linkage constructs a robust Ge anode (Ge@B-PAALi), which is proved by FTIR and Raman characterizations. Post morphological and compositional investigations reveal the minimized pulverization and a thinner SEI composition. The robust bond linkage strategy endows Ge anode with ultra-stable cycling properties of 1053.8 mAh/g after 500 cycles at 1 A/g vs. 500.7 mAh/g for Ge@PAALi and 372.7 mAh/g for Ge@B2O3, respectively. The proposed bond linkage strategy via artificial coating layer and functional binders unlocks huge potential of alloys and other anodes for next-generation battery applications.

Centrifugally Spun Binder-Free N, S-Doped Ge@PCNF Anodes for Li-Ion and Na-Ion Batteries.

Germanium has a high theoretical capacity as an anode material for sodium-ion batteries. However, germanium suffers from large capacity losses during cycling because of the large volume change and loss of electronic conductivity. A facile way to prepare germanium anodes is critically needed for next-generation electrode materials. Herein, centrifugally spun binder-free N, S-doped germanium@ porous carbon nanofiber (N, S-doped Ge@ PCNFs) anodes first were synthesized using a fast, safe, and scalable centrifugal spinning followed by heat treatment and N, S doping. The morphology and structure of the resultant N, S-doped Ge@ PCNFs were investigated by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray mapping, Raman spectroscopy, and X-ray diffraction, while electrochemical performance of N, S-doped Ge@ PCNFs was studied using galvanostatic charge-discharge tests. The results demonstrate that a nanostructured Ge homogeneously distributed on tubular structured porous carbon nanofibers. Moreover, N, S doping via thiourea treatment is beneficial for lithium- and sodium-ion kinetics. While interconnected PCNFs buffered volume change and provided fast diffusion channels for Li ions and Na ions, N, S-doped PCNFs further improved electronic conductivity and thus led to higher reversible capacity with better cycling performance. When investigated as an anode for lithium-ion and sodium-ion batteries, high reversible capacities of 636 and 443 mAhg-1, respectively, were obtained in 200 cycles with good cycling stability. Centrifugally spun binder-free N, S-doped Ge@ PCNFs delivered a capacity of 300 mAhg-1 at a high current density of 1 A g-1, indicating their great potential as an anode material for high-performance sodium-ion batteries.

An environment-friendly approach to produce nanostructured germanium anodes for lithium-ion batteries

A halogen-free process for the preparation of germanium nano-structured particles from germanium citrate, an easily accessible and environment-friendly precursor formed from germanium dioxide and citric acid in an aqueous medium, is proposed.

Ionic Liquid Based Polymer Gel Electrolytes for Use with Germanium Thin Film Anodes in Lithium Ion Batteries.

Thermally stable, flexible polymer gel electrolytes with high ionic conductivity are prepared by mixing the ionic liquid 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (C4mpyrTFSI), LiTFSI and poly(vinylidene difluoride‐co‐hexafluoropropylene (PVDF‐HFP). FT‐IR and Raman spectroscopy show that an amorphous film is obtained for high (60 %) C4mpyrTFSI contents. Thermogravimetric analysis (TGA) confirms that the polymer gels are stable below ∼300 °C in both nitrogen and air environments. Ionic conductivity of 1.9×10−3 S cm−2 at room temperature is achieved for the 60 % ionic liquid loaded gel. Germanium (Ge) anodes maintain a coulombic efficiency above 95 % after 90 cycles in potential cycling tests with the 60 % C4mpyrTFSI polymer gel.

Tailoring nanoporous structures of Ge anodes for stable potassium-ion batteries

We present here for the first time the electrochemical behavior of germanium anodes in potassium-ion batteries (KIBs). Nanoporous germanium (np-Ge) samples were fabricated by the chemical-dealloying method using Al as the sacrificial metal. Galvanostatic tests identified the reversible potassiation of the np-Ge anodes and the optimal sample with tuned porosities and ligaments demonstrated stable capacities of ~120 mAh g−1 over 400 cycles. Further analysis of the np-Ge electrode revealed amorphous KGe alloys were formed upon discharge. This study suggest germanium can be a potential anode in KIBs, but the structural tailoring is critical to overcome the kinetics problems of the large K-ions.

Synthesis of dual porous structured germanium anodes with exceptional lithium-ion storage performance

Dual-porous Ge nanostructures are synthesized via two straightforward steps. Compared with conventional approaches related to porous Ge materials, different types of pores can be readily generated by adjusting the relative ratio of the precursor amounts for GeO2 and SiO2. Unlike using hard templates with different sizes for introducing secondary pores, this system makes a uniformly blended structure of porogen and active sites in the nanoscale range. When GeO2 is subjected to zincothermic reduction, it is selectively converted to pure Ge still connected to unreacted SiO2. During the reduction process, primary pores (larger than 50 nm) are formed by eliminating zinc oxide by-products, while inactive SiO2 with respect to zinc metal could contribute to retaining the overall structure. Finally, the HF treatment completely leaches remaining SiO2 and formed secondary pores (micro/mesopores) to complete the dual-porous Ge structure. The resulting Ge structure is tested as an anode material for lithium-ion batteries. The Ge electrode exhibits an outstanding reversibility and an exceptional cycling stability corresponding to a capacity retention of 100% after 100 cycles at C/5 and of 94.4% after 300 cycles at C/2. Furthermore, multi-scale pores facilitate a facile Li-ion accessibility, resulting in an excellent rate capability delivering ∼740 mAh g−1 at 5C.

Hybridizing germanium anodes with polysaccharide-derived nitrogen-doped carbon for high volumetric capacity of Li-ion batteries

Hybridized Ge nanostructures with nitrogen-doped carbon have been demonstrated for high volumetric energy density of lithium ion batteries.

A novel strategy to prepare Ge@C/rGO hybrids as high-rate anode materials for lithium ion batteries

Abstract Germanium is considered as a promising anode material for lithium ion batteries (LIBs) due to its high-capacity. However, owing to the huge volume variation during cycling, the batteries based on germanium anodes usually show poor cyclability and inferior rate capability. Herein, we demonstrated a novel strategy to uniformly anchor the core-shell structured germanium@carbon (Ge@C) on the reduced graphene oxide (rGO) nanosheets by the strong adhesion of dopamine. In the resulting Ge@C/rGO hybrid, the amorphous carbon layer and rGO nanosheets can effectively reduce the agglomeration of germanium and provide buffer matrix for the volume change in electrochemical lithium reactions. When used as anode materials for LIBs, Ge@C/rGO hybrids deliver a reversible capacity of 1074.4 mA h g−1 at 2C after 600 cycles (with capacity retention of 96.5%) and high rate capability of 436 mA h g−1 at 20C after 200 cycles. The encouraging electrochemical performance clearly demonstrates that Ge@C/rGO hybrids could be a potential anode material with high capacity, excellent rate capability, and good cycling stability for LIBs.

Stable high-areal-capacity nanoarchitectured germanium anodes on three-dimensional current collectors for Li ion microbatteries

Ge nanoarrays anchored on 3D Cu nanoframework current collectors have demonstrated high areal capacity and stable cycling performance. The newly developed electrode design enabled high mass loading of active Ge and efficient conductive pathways for high-energy Li-ion microbatteries.

Elucidation of the Local and Long-Range Structural Changes that Occur in Germanium Anodes in Lithium-Ion Batteries

Metallic germanium is a promising anode material in secondary lithium-ion batteries (LIBs) due to its high theoretical capacity (1623 mAh/g) and low operating voltage, coupled with the high lithium-ion diffusivity and electronic conductivity of lithiated Ge. Here, the lithiation mechanism of micron-sized Ge anodes has been investigated with X-ray diffraction (XRD), pair distribution function (PDF) analysis, and in-/ex-situ high-resolution 7Li solid-state nuclear magnetic resonance (NMR), utilizing the structural information and spectroscopic fingerprints obtained by characterizing a series of relevant LixGey model compounds. In contrast to previous work, which postulated the formation of Li9Ge4 upon initial lithiation, we show that crystalline Ge first reacts to form a mixture of amorphous and crystalline Li7Ge3 (space group P3212). Although Li7Ge3 was proposed to be stable in a recent theoretical study of the Li–Ge phase diagram (Morris, A. J.; Grey, C. P.; Pickard, C. J. Phys. Rev. B: Condens. Matter Ma...

Nanostructured Si(1-x)Gex for Tunable Thin Film Lithium-Ion Battery Anodes

Both silicon and germanium are leading candidates to replace the carbon anode of lithium ions batteries. Silicon is attractive because of its high lithium storage capacity while germanium, a superior electronic and ionic conductor, can support much higher charge/discharge rates. Here we investigate the electronic, electrochemical and optical properties of Si(1-x)Gex thin films with x = 0, 0.25, 0.5, 0.75, and 1. Glancing angle deposition provided amorphous films of reproducible nanostructure and porosity. The film's composition and physical properties were investigated by X-ray photoelectron spectroscopy, four-point probe conductivity, Raman, and UV-vis absorption spectroscopy. The films were assembled into coin cells to test their electrochemical properties as a lithium-ion battery anode material. The cells were cycled at various C-rates to determine the upper limits for high rate performance. Adjusting the composition in the Si(1-x)Gex system demonstrates a trade-off between rate capability and specific capacity. We show that high-capacity silicon anodes and high-rate germanium anodes are merely the two extremes; the composition of Si(1-x)Gex alloys provides a new parameter to use in electrode optimization.

Residual Surface Recombination on Germanium Anodes

not Available.

The Anode Behavior of Germanium in Aqueous Solutions

The anode characteristics of n‐ and p‐type germanium are different. A large voltage barrier is observed at about 0.8 ma/cm2 current density at room temperature on n‐type but not on p‐type electrodes. The voltage barrier on 3 ohm‐cm n‐type germanium anodes breaks down at about 9 volts in many electrolytes. During anodic dissolution the germanium surface appears to be covered with about a monolayer of oxide or hydroxide. This suggests that germanium goes into solution as a complex ion with the hydroxyl or oxide radicals attached. A mechanism is proposed for the over‐all anode dissolution process involving two holes and two electrons for each germanium atom dissolving.