97 research outputs found
Derbend-Nameh by Muhammad Avabi Aktashi: A Literary Reflection of Khazar History and How the City of Anji Was Destructed
No full textIntroduction. The paper attempts a scholarly insight into medieval historical chronicles for a new comprehension of Derbend-Nameh by Muhammad Avabi Aktashi (sixteenth–seventeenth centuries) that stands at the beginnings of Dagestani prose. Goals. The study seeks to identify the literary task set forth by the medieval author when he set to create the historical/literary narrative, reveal some meanings hidden therein, and show how the author influences a reader with the aid of stylistic techniques and expressive means. Methods. The work employs the cultural/historical and receptive methods, the latter be manifested (implemented) via ‘readers’ expectations’, certain derived genre norms, implied correlations between fiction and reality, text and context. The hermeneutic method proves most instrumental in revealing opportunities for multiple interpretations of one and the same text. Results. Our study attest to the author used not only documents and facts from the preceding Tawarikh-i Derbend-Nameh (The Book of Derbent Stories) but also invested his own knowledge of ancient fiction and undertones — to establish the genre of historical prose in Kumyk literature. This is evidenced by the author’s appeal to the key characteristic features of fiction: abundance of folklore legends, fragments from Arab, Oriental and European chronicles and fiction texts; hyperbolized narration about the size of Derbent and the Derbent Wall; fantastic elements, images of historical personalities, such as Zulkarnein Iskander (Alexander the Great), Kubad-Shah, Abu-Muslim and others; the formal and compositional division of the text (war between Arabs and Khazars, war between Persians and Khazars, ruling years of Abu Muslim); hidden meanings of the narrative about Khazars and the city of Anji (emotional narrative of battles attended by Khazars and Muslims); reflections on the turning point in history, impacts on the reader’s feelings by means of literary devices and artistic expressions. Conclusions. Despite the book by Muhammad Avabi Aktashi deals with the history of Derbent, it clearly shows the author’s intention and literary task to shed light on another city, the ancient Anji, as well as on the tragic collapse of the Khazar state. It is shown that the book served a landmark at the beginnings of Kumyk prose — and gave impulse to the latter’s further evolution
Unlocking the potential of weberite-type metal fluorides in electrochemical energy storage
No full textSodium-ion batteries (NIBs) are a front-runner among the alternative battery technologies suggested for substituting the state-of-the-art lithium-ion batteries (LIBs). The specific energy of Na-ion batteries is significantly lower than that of LIBs, which is mainly due to the lower operating potentials and higher molecular weight of sodium insertion cathode materials. To compete with the high energy density of LIBs, high voltage cathode materials are required for NIBs. Here we report a theoretical investigation on weberite-type sodium metal fluorides (SMFs), a new class of high voltage and high energy density materials which are so far unexplored as cathode materials for NIBs. The weberite structure type is highly favorable for sodium-containing transition metal fluorides, with a large variety of transition metal combinations (M, M’) adopting the corresponding Na2MM’F7 structure. A series of known and hypothetical compounds with weberite-type structure were computationally investigated to evaluate their potential as cathode materials for NIBs. Weberite-type SMFs show two-dimensional pathways for Na+ diffusion with surprisingly low activation barriers. The high energy density combined with low diffusion barriers for Na+ makes this type of compounds promising candidates for cathode materials in NIBs
Toward Improving the Areal Energy Density of Lithium–Sulfur Batteries with Ultramicroporous Carbon–Sulfur Composite Electrodes
No full textSulfur possesses high specific capacity (1672 mA h g−1) and high specific energy (2600 Wh kg−1), which makes it attractive as a cathode material for lithium–sulfur batteries. However, the areal energy density of sulfur electrodes is usually low due to an excess amount of inactive materials, mostly carbon, in the electrode composite. Typically, the electrode layers must be thin to achieve good specific capacity and cyclic stability. This further reduces the areal capacities, and it is challenging to design high areal density sulfur electrodes. Herein, the possibility of achieving high areal energy density by using ultramicroporous carbon–sulfur (UMC‐S) composite electrodes is investigated. For this purpose, the weight of sulfur per area is systematically varied by varying the amount of UMC‐S, and its electrochemical performance with respect to current density, cycling voltage window, electrolyte amount, and effect of temperature on cycling is investigated. A sulfur loading of up to 9.7 mg cm−2 and areal capacities above 4.5 mAh cm−2 are attained. The results indicate that a high areal energy density can be achieved with UMC‐S electrodes, however, at lower current rates. Higher current rates can be achieved by reducing the particle size and by improving the intrinsic electronic conductivity of the UMC host
Development of tysonite-type fluoride conducting thin film electrolytes for fluoride ion batteries
No full textElectrochemical synthesis of carbon-metal fluoride nanocomposites as cathode materials for lithium batteries
No full textHerein we have demonstrated an electrochemical method for the synthesis of carbon-metal fluoride nanocomposites (CMFNCs). Electrochemical intercalation of transition metal ions into graphite fluoride (CF) resulted in the formation of CMFNCs. As a proof-of-concept, we have synthesized C-FeF and C-NiF nanocomposites by the electrochemical intercalation of Fe and Ni into CF from corresponding non-aqueous electrolytes. The C-FeF and C-NiF nanocomposites synthesized by this method showed high reversible capacity and cycling stability compared to chemically synthesized analogs as cathode materials for lithium batteries. The reversible capacity of chemically synthesized C-FeF is 181 mAh g, whereas electrochemically synthesized material is 349 mAh g after 20 cycles. The better cycling performance of electrochemically synthesized C-FeF was attributed to the homogeneous distribution of FeF nanoparticles within the carbon matrix enabled by the electrochemical intercalation of Fe. The electrochemical method described here is emission-free, cost-effective, occurs at room temperature, and extendable to the synthesis of several other CMFNCs. Moreover, it might provide new avenues for the synthesis of advanced functional materials
Lithium Insertion into Niobates with Columbite-Type Structure: Interplay between Structure-Composition and Crystallite Size
No full textStructure and electrochemical properties of Na2±xV3P2O13 (x = 0 and 1): a promising cathode material for sodium-ion batteries
No full textOwing to the large abundance of sodium resources and its low cost, sodium-ion batteries (NIBs) are being considered as a promising, feasible alternative to lithium-ion batteries (LIBs), notably for stationary applications. Research activities on sodium-ion batteries are growing worldwide but do still require a great deal of basic and applied research. The design and synthesis of new cathode materials are of great interest to realize the structural requirements to build sustainable and safe NIBs. Herein, we report the synthesis, structure and electrochemical properties of sodium vanadium oxy-phosphate (NVOP), Na2±xV3P2O13 (x = 0 and 1), a stable host for the reversible insertion of sodium. Na3V3P2O13 delivers a reversible capacity of 132 mA h g−1 at an average potential of 2.7 V vs. Na/Na+, which amounts to a specific energy of 356 W h kg−1. Furthermore, NVOP compounds exhibit excellent cycling stability. Besides, NVOP shows a rich structural chemistry during the sodium insertion and deinsertion process. A reversible switching of V5+ and V4+ between two crystallographic sites during sodiation and desodiation reactions was observed, hitherto unknown in battery materials. Na2±xV3P2O13 (x = 0 and 1) compounds were characterized by various experimental tools to understand the structure and related properties. In addition, density functional theory (DFT) calculations were performed to complement experimental observations and to understand sodium diffusion behavior in Na2±xV3P2O13 (x = 0 and 1)
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