Kassie Nigus Shitaw

Bio: Kassie Nigus Shitaw is an academic researcher from National Taiwan University of Science and Technology. The author has contributed to research in topics: Electrolyte & Anode. The author has an hindex of 4, co-authored 7 publications receiving 32 citations.

Decoupling the origins of irreversible coulombic efficiency in anode-free lithium metal batteries.

Abstract: Anode-free lithium metal batteries are the most promising candidate to outperform lithium metal batteries due to higher energy density and reduced safety hazards with the absence of metallic lithium anode during initial cell fabrication. In general, researchers report capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of anode-free lithium metal batteries. However, evaluating the behavior of batteries from limited aspects may easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, we present an integrated protocol combining different types of cell configuration to determine various sources of irreversible coulombic efficiency in anode-free lithium metal cells. The decrypted information from the protocol provides an insightful understanding of the behaviors of LMBs and AFLMBs, which promotes their development for practical applications.

Al–Sc dual-doped LiGe2(PO4)3 – a NASICON-type solid electrolyte with improved ionic conductivity

Abstract: LiGe2(PO4)3 (LGP), a NASICON-type solid electrolyte, has many advantages such as its superior electrochemical and thermal stability for use in all solid-state lithium batteries. However, its low ionic conductivity is one of the challenges that can hinder its practical application commercially. In this work, the influence of adding different amounts of scandium and aluminum on the Li+ conductivity of LGP was investigated computationally and experimentally. Substituting 25% of Ge4+ ions in the LGP structure with Al3+ and/or Sc3+ ions to obtain doped LGP in the form of Li1+x+yAlxScyGe2−x−y(PO4)3, where x + y = 0.5, led to more Li+ ions in the 36f vacant sites (M2) and resulted in enhanced ionic conductivity of the material. In both approaches, the highest bulk Li+ conductivity of 5.826 mS cm−1 was obtained for Li1.5Al0.33Sc0.17Ge1.5(PO4)3 from the experimental measurement. The activation energy was also investigated theoretically using the nudged elastic band method, and the lowest value (0.279 eV) was obtained for this composition. Furthermore, the Li1+x+yAlxScyGe2−x−y(PO4)3 electrolytes were synthesized using a melt-quenching method and subsequently transformed into a glass–ceramic material through heat treatment. X-ray diffraction, electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the structure, measure the Li+ conductivity and determine the electrochemical window of the synthesized glass–ceramic material, respectively. There was a remarkable agreement between the computationally calculated and experimentally measured values of ionic conductivity, activation energy and electrochemical window. Finally, its applicability in a solid-state battery was tested, and it showed good electrochemical performance.

A new high-Li+-conductivity Mg-doped Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte with enhanced electrochemical performance for solid-state lithium metal batteries

Abstract: Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising solid electrolyte for use in next-generation lithium batteries. Nevertheless, its lower bulk and grain-boundary ionic conductivities are major restrictions preventing its practical utilization. Mg was introduced into LAGP to form Li1.6Al0.4Mg0.1Ge1.5(PO4)3 (LAMGP) based on computational analysis. The doping of LAGP with Mg results in advantages such as increasing the Li+ concentration and expanding the material dimensions due to the larger ionic radius of Mg, leading to enhanced ionic conductivity. Mg had a two-birds-with-one-stone effect in the LAMGP electrolyte, not only generating super high bulk ionic conductivity of 7.435 mS cm−1, compared to 2.896 mS cm−1 in LAGP, but also generating low grain-boundary resistance due to improved densification. The lowering of the grain-boundary resistance and the increased densification are related to choosing the right precursor for the dopant. Using LAMGP as a hybrid solid electrolyte, a solid battery delivered great electrochemical performance in comparison to when LAGP was used. Interfacial analysis was also conducted, which revealed that the formation of an interface prevented the reduction of components in LAMGP by Li metal, therefore ensuring the long-term durability of LAMGP in liquid electrolyte. These results suggest that LAMGP is an auspicious solid electrolyte for achieving practical solid-state lithium batteries.

Separating bulk from grain boundary Li ion conductivity in the sol-gel prepared solid electrolyte Li1.5Al0.5Ti1.5(PO4)3

Abstract: Lithium aluminium titanium phosphate (LATP) belongs to one of the most promising solid electrolytes. Besides sufficiently high electrochemical stability, its use in lithium-based all-solid-state batteries crucially depends on the ionic transport properties. While many impedance studies can be found in literature that report on overall ion conductivities, a discrimination of bulk and grain boundary electrical responses via conductivity spectroscopy has rarely been reported so far. Here, we took advantage of impedance measurements that were carried out at low temperatures to separate bulk contributions from the grain boundary responses. It turned out that bulk ion conductivity is by at least three orders of magnitude higher than ion transport across the grain boundary regions. At temperatures well below ambient long-range Li ion dynamics is governed by activation energies ranging from 0.26 to 0.29 eV depending on the sintering conditions. As an example, at temperatures as low as 173 K, the bulk ion conductivity, measured in N2 inert gas atmosphere, is in the order of 8.1 × 10−6 S cm−1. Extrapolating this value to room temperature yields ca. 3.4 × 10−3 S cm−1 at 293 K. Interestingly, exposing the dense pellets to air atmosphere over a long period of time causes a significant decrease of bulk ion transport. This process can be reversed if the phosphate is calcined at elevated temperatures again.

Lanthanum nitrate as aqueous electrolyte additive for favourable zinc metal electrodeposition

Abstract: Aqueous zinc batteries are appealing devices for cost-effective and environmentally sustainable energy storage. However, the zinc metal deposition at the anode strongly influences the battery cycle life and performance. To circumvent this issue, here we propose the use of lanthanum nitrate (La(NO3)3) as supporting salt for aqueous zinc sulfate (ZnSO4) electrolyte solutions. Via physicochemical and electrochemical characterizations, we demonstrate that this peculiar electrolyte formulation weakens the electric double layer repulsive force, thus, favouring dense metallic zinc deposits and regulating the charge distribution at the zinc metal|electrolyte interface. When tested in Zn||VS2 full coin cell configuration (with cathode mass loading of 16 mg cm-2), the electrolyte solution containing the lanthanum ions enables almost 1000 cycles at 1 A g-1 (after 5 activation cycles at 0.05 A g-1) with a stable discharge capacity of about 90 mAh g-1 and an average cell discharge voltage of ∼0.54 V.

Chemical Stability of Sulfide Solid-state Electrolytes: Stability Toward Humid Air and Compatibility with Solvents and Binders

Abstract: Sulfide solid electrolytes (S-SEs) based all-solid-state batteries (ASSBs) have received particular attention due to their outstanding ionic conductivity and higher energy density over conventional lithium-ion batteries. Nevertheless, chemical instability toward...