INTRODUCTION
E NERGY STORAGES SYSTEM
L ITHIUM ION - ION BATTERIES
H IGH CAPACITY ANODE MATERIALS
The nanostructure alloy materials prevent critical pulverization and fracture formation while inserting Li ions into the electrode, and also enable Li ion to experience short ion diffusion length55. Doping elements affect the density of states of Si or Ge anodes, improving intrinsic electrochemical properties60-62.
R EFERENCE
Facile synthesis of silicon nanoparticles in graphene sheets as improved anode materials for lithium-ion batteries. Synthesis of silicon nanosheets from kaolinite as high-performance anode material for lithium-ion batteries.
REVEALING SALT-EXPEDITED REDUCTION MECHANISM FOR HOLLOW
I NTRODUCTION
Although several possibilities have been proposed in the previous works, they cannot fully elucidate the entire reaction mechanism of thermochemical process in the molten salt system at such a low temperature. Successive reduction reaction leads to the formation of aluminum oxychloride (AlOCl), the reduction of by-product, and the clustering of Si atoms to HPSS.
E XPERIMENTAL METHOD
The samples were loaded on Al wire as the working electrode, which occupied one side of the nanofactory STM container. Li metal was scratched out by the tungsten (W) tip mounted on the other side of the container from the counter electrode.
R ESULTS AND DISCUSSION
At the first intermediate state of the ligand dissociation mechanism (IM1-a), which had the activation energy (Ea) of 0.64 eV and heat of reaction (ΔE) of -0.41 eV, the ligand AlCl3 itself was detached from the [Al( AlCl3) 3] complex and exclusively adsorbed on the SiO2 surface. The typical polycrystalline nature of HPSS was observed in high-resolution transmission electron microscopy (HR-TEM) images with lattice fringes of 0.19 nm spacing, corresponding to (220) plane and selected area electron diffraction (SAED) pattern (Figure 2-4e). . During the post-treatments, its value gradually increased as the remaining components (Al, AlOCl, amorphous Al2O3 and SiO2) were etched out and the surface area of HPSS is 39.4 m2 g-.
Before measurement, carbon coating layers were introduced to improve the electrical conductivity of HPSS particles (denoted as HPSS@C, Supplementary Fig. 15). Magnified TEM images of (f) pristine, (g) fully lithiated and (h) delithiated HPSS@C particles illustrating the thickened shell (22% expansion after lithiation) and pore filling/restoration showing no structural collapse. i) Estimated volume and expansion ratio of HPSS@C particles during lithiation/delithiation.
C ONCLUSION
R EFERENCE
In particular, stable capacity retention with significant Coulombic efficiency in the full cell configuration with commercial LiCoO2 indicated a high feasibility of the NPGeNFs as high performance anodes for LIBs. Morphological changes of the NPGeNFs were investigated by in situ TEM during lithiation and delithiation processes. This excellent cycling performance of the NPGeNFs was further confirmed with electrochemical impedance spectroscopy (EIS) measurements (Figure S12).
The fracture toughness of macroscopic architectures of the NPGeNFs was further investigated similarly to the nanoscale dimension. The superior electrochemical properties of both half and full cells can be attributed to the rationally designed structural feature of the NPGeNFs.
ATOMIC-SCALE COMBINATION OF GERMANIUM-ZINC NANOFIBERS FOR
I NTRODUCTION
With the increase in energy consumption and the development of large-scale devices such as electric vehicles (EVs), the demand for rechargeable energy storage systems, especially lithium-ion batteries (LIBs), has increased significantly1-10. Furthermore, Ge-based anodes operate at a low operating voltage (< 0.5 V), resulting in a high potential window when assembled as whole cells14. However, pure Ge compounds are expensive and the synthesis of pure Ge nanostructures is quite complicated. However, GeOx also causes a large volume change during the lithiation process, resulting in fatal capacity breakdown during cycling with loss of electrical contacts, breakage, and dust, along with the continuous formation of unwanted solid interphase layers. electrolyte (SEI).
In addition, the poor electronic conductivity of GeOx limits electron transfer at high current density, which remains a challenge to realize high power/high energy density anode materials for advanced LIBs. In a full cell, a high energy density of 335 Wh kg-1 (565 Wh L-1) was achieved after the 1st cycle, and a stable charge/discharge characteristic with a Coulombic efficiency of 99.4% was observed during the of 400 cycles; the designed material shows great potential for practical energy storage systems.
E XPERIMENTAL METHOD
For in situ transmission electron microscopy (in situ TEM) measurements using ETEM, an open cell consisting of Li metal for the counter electrode and samples for the working electrode was fabricated to observe electrochemical reactions in real time. During the motion, a very thin layer of Li2O was coated on the Li metal and used as a solid electrolyte. The negative bias drove Li+ to the samples via the Li2O layer on the Li metal via the potential difference between the two electrodes and the samples reacted with Li+, consistent with lithiation.
The in situ conductivity test was almost the same as the in situ lithiation/delithiation observation, except that there was no loading of Li metal. For full cells, Li metal was replaced with LiCoO2 (LCO), while all other components were identical.
R ESULTS AND DISCUSSION
Furthermore, to investigate the effect of oxygen content on the electrochemical performance of O-. The total volume change of NF during a cycle in real time was shown in Figure 3-5n. The large volume expansion of O-dGNFs was attributed to the pulverization of the active materials, leading to unsustainable cycle retention (Figures 3–3d).
The overall RCT value of the O-dGZNF electrode including intermolecular Zn was significantly less than that of the O-dGNF electrode due to the improved electronic conductivity of O-dGZNFs. In contrast, the O-dGZNF electrode maintained a low value of RCT regardless of the formation of Li2O/Li2CO3, attributed to the intermolecular distribution of Zn, which has outstanding electronic conductivity.
C ONCLUSION
R EFERENCE
Preparation of nanostructured Ge/GeO2 composite in carbon matrix as anode material for lithium-ion batteries. A new strategy to achieve a high-performance anode for lithium-ion batteries by encapsulating germanium nanoparticles in carbon nanoboxes. Germanium nanoparticle/molybdenum disulfide (MoS2) nanocomposite as a high-performance, high-rate anode material for lithium-ion batteries.
A novel strategy to prepare Ge@C/rGO hybrids as high-performance anode materials for lithium ion batteries. In situ synthesis and characterization of Ge-embedded electrospun carbon nanostructures as high-performance anode material for lithium-ion batteries.
STRESS-TOLERANT NANOPOROUS GERMANIUM NANOFIBERS FOR LONG
I NTRODUCTION
In contrast to the conventional CVD method, our method provides high tunability and control in terms of macro/microscopic morphologies such as porosity, length, and diameter to improve the electrochemical performance of the electrodes. In this regard, we introduced nanoporosity in GeNF (NPGeNF), which facilitates electrolyte penetration and shortens the transport distance of Li ions, resulting in favorable charge transfer at the electrode/electrolyte interfaces, instead of leading to the serious side reaction that usually occurs in NW anodes. In addition, the nanopores formed in NPGeNFs efficiently adapt to volume expansion after lithium and ensure the reversibility of structural changes between cycles.
With this rational design, the NPGeNFs delivered a high initial reversible capacity of 1373 mAh g-1 and excellent capacity retention (80%) after 500 cycles at 3.0 C with an extremely low capacity decay rate of 0.039% per cycle.
E XPERIMENTAL METHOD
For the conformational atomic distribution, HAADF-STEM mapping was performed using the same TEM instrument. The open cell, which was composed of Li metal as counter electrode and samples as the working electrode, loaded on tungsten (W) tip and aluminum (Al) wire respectively, was fabricated to observe the lithiation/delithiation process in real time using a Nanofactory STM holder and tested by an environmental TEM (ETEM, Titan, FEI). Li metal was scratched out in an Ar-filled glove box and transferred to the ETEM.
While exposed to air (< 2 s), a lithium oxide solid electrolyte was formed on a Li metal surface. Then, the electrodes were transferred to an Ar-filled glove compartment for cell assembly using 2016 coin-type cells (Welcos), paired with a Li-metal counter/reference electrode.
R ESULTS AND DISCUSSION
The time-lapse TEM images of the NPGENFs demonstrate large volume expansion and morphology change during the lithiation/delithiation. Surprisingly, however, the previous nanopores in the NPGeNFs reappeared at the same locations with similar sizes and shapes. Such appreciable rate capability and cycling stability clearly confirm the excellent electrochemical property of the NPGeNFs.
The cyclic stability of the NPGeNFs was further evaluated at a much higher current density of 3 C, as shown in Figure 4-3e. Furthermore, TEM images of intact NPGeNFs after 100 cycles indicated high durability of the NPGeNFs against crushing ( Figure S15 ).
C ONCLUSION
R EFERENCE
Morphology- and porosity-tunable synthesis of 3D nanoporous SiGe alloy as a high-performance lithium-ion battery anode. Mesoporous germanium anode materials for lithium-ion batteries with exceptional cycling stability in a wide temperature range. Self-assembled germanium/carbon nanostructures as high-performance anode material for lithium-ion battery.
Core-Shell Ge@Graphene@TiO2 nanofibers as a high-capacity cycle-stable anode for lithium and sodium ion batteries. Long-life, high-speed superior Ge nanoarrays anchored on Cu/C nanowire frameworks for Li-ion battery electrodes.
I NTRODUCTION
Intramolecular deformation of zeotype borogermanate toward a three-dimensional porous germanium anode for rapid lithium storage. Here we demonstrate for the first time the synthesis of three-dimensional porous Ge material (referred to as 3D-pGe) from zeotype borogermanate (K2B2Ge3O10) by thermal deformation in a closed system, hot water etching, and subsequent hydrogen reduction steps. . The well-designed 3D-pGe is a micrometer-scale architecture composed of nanostructured Ge particles, demonstrating the high porosity in the overall frameworks. These micro-sized secondary particles have a high tapping density compared to simple Ge nanostructures, leading to a high volumetric density.
In addition, this architecture leads to a significant contribution of the surface-controlled reaction with pseudocapacitive behavior responsible for the rate performance (342 mAh g‒1 at 10 C). In particular, the well-designed 3D-pGe anode provides high reversible capacity (770 mAh g‒1) with exceptional Coulombic efficiency per cycle (> 99.8%) after 250 cycles at 1 C and solid electrolyte interfacial (SEI) layers formed in the first cycle it stably maintains its own shapes during repeated lithiation/delithiation without further reconstruction.
E XPERIMENTAL METHOD
A viscous slurry, which consists of active materials, conductive materials (Super-P) and poly(acrylic acid) (PAA)/carboxymethyl cellulose (CMC) (1:1 weight ratio) as an 8:1 weight ratio binder: 1, was cast on Cu paper to produce electrodes (loading mass: 1.2–1.4 mg cm‒2).
R ESULTS AND DISCUSSION
Additionally, the electrochemical properties of the 3D-pGe anode were evaluated where galvanostatic discharge/charge measurements were performed at 25°C. For the 3D-pGe anode comparison, micrometer-sized Ge was assembled in the same way (denoted as Bulk-Ge). In addition, the 3D-pGe electrode gave exceptional cycle retention without any capacity decay at C/5 (Figure 5-3c).
The 3D-pGe electrode had a capacitive current of 74%, while the bulk-Ge electrode showed a capacitive current of only 43% at 1.0 mV s‒1 (Figure 5-4d and 4e). A full cell fabricated with LiCoO2 (LCO) cathode and 3D-pGe anode was investigated for practical application.
CONCLUSION
Mesoporous germanium nanoparticles synthesized in molten zinc chloride at low temperature as a high-performance anode for lithium-ion batteries. Chemical synthesis of uniform-sized germanium nanoparticles as anode materials for lithium-ion batteries. A silicon-germanium bilayer sputtered on a carbon nanotube sheet as an anode material for lithium-ion batteries.
Two-dimensional Germanium Sulfide Nanosheets as an ultra-stable and high-capacity anode for lithium-ion batteries. Amorphous Ge/C Composite Sponges: Synthesis and Application in a High-Speed Anode for Lithium-Ion Batteries.
SUMMARY AND OUTLOOK
