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- ItemHigh-Entropy Metal-Organic Frameworks for Highly Reversible Sodium Storage(Weinheim : Wiley-VCH, 2021) Ma, Yanjiao; Ma, Yuan; Dreyer, Sören Lukas; Wang, Qingsong; Wang, Kai; Goonetilleke, Damian; Omar, Ahmad; Mikhailova, Daria; Hahn, Horst; Breitung, Ben; Brezesinski, TorstenPrussian blue analogues (PBAs) are reported to be efficient sodium storage materials because of the unique advantages of their metal-organic framework structure. However, the issues of low specific capacity and poor reversibility, caused by phase transitions during charge/discharge cycling, have thus far limited the applicability of these materials. Herein, a new approach is presented to substantially improve the electrochemical properties of PBAs by introducing high entropy into the crystal structure. To achieve this, five different metal species are introduced, sharing the same nitrogen-coordinated site, thereby increasing the configurational entropy of the system beyond 1.5R. By careful selection of the elements, high-entropy PBA (HE-PBA) presents a quasi-zero-strain reaction mechanism, resulting in increased cycling stability and rate capability. The key to such improvement lies in the high entropy and associated effects as well as the presence of several active redox centers. The gassing behavior of PBAs is also reported. Evolution of dimeric cyanogen due to oxidation of the cyanide ligands is detected, which can be attributed to the structural degradation of HE-PBA during battery operation. By optimizing the electrochemical window, a Coulombic efficiency of nearly 100% is retained after cycling for more than 3000 cycles.
- ItemStructural Aspects of P2-Type Na0.67Mn0.6Ni0.2Li0.2O2 (MNL) Stabilization by Lithium Defects as a Cathode Material for Sodium-Ion Batteries(Weinheim : Wiley-VCH, 2021) Yang, Liangtao; Kuo, Liang-Yin; López del Amo, Juan Miguel; Nayak, Prasant Kumar; Mazzio, Katherine A.; Maletti, Sebastian; Mikhailova, Daria; Giebeler, Lars; Kaghazchi, Payam; Rojo, Teófilo; Adelhelm, PhilippA known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemSodium-Vanadium Bronze Na9V14O35: An Electrode Material for Na-Ion Batteries(Basel : MDPI, 2021) Kirsanova, Maria A.; Akmaev, Alexey S.; Gorbunov, Mikhail V.; Mikhailova, Daria; Abakumov, Artem M.Na9V14O35 (η-NaxV2O5) has been synthesized via solid-state reaction in an evacuated sealed silica ampoule and tested as electroactive material for Na-ion batteries. According to powder X-ray diffraction, electron diffraction and atomic resolution scanning transmission electron microscopy, Na9V14O35 adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO5 tetragonal pyramids and VO4 tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate Na9V104.1+O19(V5+O4)4. Behavior of Na9V14O35 as a positive and negative electrode in Na half-cells was investigated by galvanostatic cycling against metallic Na, synchrotron powder X-ray diffraction and electron energy loss spectroscopy. Being charged to 4.6 V vs. Na+/Na, almost 3 Na can be extracted per Na9V14O35 formula, resulting in electrochemical capacity of ~60 mAh g−1. Upon discharge below 1 V, Na9V14O35 uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO4 tetrahedra and VO5 tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered Na9V14O35 structure transforms into a rock-salt type disordered structure and ultimately into amorphous products of a conversion reaction at 0.1 V. The discharge capacity of 490 mAh g−1 delivered at first cycle due to the conversion reaction fades with the number of charge-discharge cycles.
- ItemTiNb2O7 and VNB9O25 of ReO3 type in hybrid Mg−Li batteries: Electrochemical and interfacial insights(Washington, DC : American Chemical Society, 2020) Maletti, Sebastian; Herzog-Arbeitman, Abraham; Oswald, Steffen; Senyshyn, Anatoliy; Giebeler, Lars; Mikhailova, DariaAs one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid-state synthesis and, for the first time, comprehensively examined in hybrid Mg−Li batteries. Both materials adopt ReO3-related structures differing in the interconnection of oxygen polyhedra and the resulting guest ion diffusion paths. We show applicability of the compounds in hybrid cells providing capacities comparable to those reached in Li-ion batteries (LIBs) at room temperature (220 mAh g−1 for TNO and 150 mAh g−1 for VNO, both at 0.1 C), their operability in the temperature range between −10 and 60 °C, and even better capacity retention than in pure LIBs, rendering this hybrid technology superior for long-term application. Post mortem X-ray photoelectron spectroscopy reveals a cathode−electrolyte interface as a key ingredient for providing excellent electrochemical stability of the hybrid battery. A significant contribution of the intercalation pseudocapacitance to charge storage was observed for both materials in Li- and Mg−Li batteries. However, the pseudocapacitive part is higher for TNO than for VNO, which correlates with structural distinctions, providing better accessibility of diffusion pathways for guest cations in TNO and, as a consequence, a higher ionic transport within the crystal structure. © 2020 American Chemical Society
- ItemA Facile Chemical Method Enabling Uniform Zn Deposition for Improved Aqueous Zn-Ion Batteries(Basel : MDPI, 2021) Liu, Congcong; Lu, Qiongqiong; Omar, Ahmad; Mikhailova, DariaRechargeable aqueous Zn-ion batteries (ZIBs) have gained great attention due to their high safety and the natural abundance of Zn. Unfortunately, the Zn metal anode suffers from dendrite growth due to nonuniform deposition during the plating/stripping process, leading to a sudden failure of the batteries. Herein, Cu coated Zn (Cu–Zn) was prepared by a facile pretreatment method using CuSO4 aqueous solution. The Cu coating transformed into an alloy interfacial layer with a high affinity for Zn, which acted as a nucleation site to guide the uniform Zn nucleation and plating. As a result, Cu–Zn demonstrated a cycling life of up to 1600 h in the symmetric cells and endowed a stable cycling performance with a capacity of 207 mAh g−1 even after 1000 cycles in the full cells coupled with a V2O5-based cathode. This work provides a simple and effective strategy to enable uniform Zn deposition for improved ZIBs.
- ItemPreparation and Application of ZIF-8 Thin Layers(Basel : MDPI, 2021) Schernikau, Martin; Sablowski, Jakob; Gonzalez Martinez, Ignacio Guillermo; Unz, Simon; Kaskel, Stefan; Mikhailova, DariaHerein we compare various preparation methods for thin ZIF-8 layers on a Cu substrate for application as a host material for omniphobic lubricant-infused surfaces. Such omniphobic surfaces can be used in thermal engineering applications, for example to achieve dropwise condensation or anti-fouling and anti-icing surface properties. For these applications, a thin, conformal, homogeneous, mechanically and chemically stable coating is essential. In this study, thin ZIF-8 layers were deposited on a Cu substrate by different routes, such as (i) electrochemical anodic deposition on a Zn-covered Cu substrate, (ii) doctor blade technique for preparation of a composite layer containing PVDF binder and ZIF-8, as well as (iii) doctor blade technique for preparation of a two-layer composite on the Cu substrate containing a PVDF-film and a ZIF-8 layer. The morphology and topography of the coatings were compared by using profilometry, XRD, SEM and TEM techniques. After infusion with a perfluorinated oil, the wettability of the surfaces was assessed by contact angle measurements, and advantages of each preparation method were discussed.