Compositional and Structural Aspects of Li-rich Anti-perovskites as Li-ion Battery Cathodes

Alkali-metal ion battery cathode is the part which mostly defines its specific characteristics, thus, studies in this field are always important, to make the batteries fulfill the needs of the rapidly accelerating progress and growing market. Current dissertation represents a comprehensive physicochemical study of novel inorganic compounds with general formula of Li2MChO (M – Mn, Fe, Co; Ch– S, Se) and Pm-3m anti-perovskite structure. One of their key properties is the electrochemical activity, and rather high specific capacity, explained by a high amount of lithium which can be reversibly extracted per formula unit. Although the practical application of these materials as Li-ion battery cathodes is limited due to relatively low operation voltage and high requirements to synthetic conditions, outstanding chemical flexibility of the crystal structure turns the cubic anti-perovskites into excelsior model for studying the synergetic effects of various transition metal cations on the structural stability against lithium removal, as well as on the mechanism of charge compensation. The named investigations are mostly based on operando methods, using synchrotron radiation facilities, and the electrochemical activity of anti-perovskites provides an opportunity to conduct such experiments: while lithium is removed or inserted into the crystal lattice, the electrochemical cell is irradiated, allowing to observe the changes constantly. Such studies may bring use for the battery research in general and give certain hints for creation of new battery materials, in particular, high-entropy ones (if two transition metal cations, or two chalcogenide anions are combined in Li2MChO formula, the compound formally becomes a high-entropy one). Besides, an attempt to extend the research topic was done, introducing the double anti-Ruddlesden-Popper phases (double anti-perovskites). Their structure is layered, which is favorable for the reversible electrochemical alkali-metal, which is in this specific case sodium, extraction, however, as their cationic and anionic sublattices are formed by the same transition metal cations and by the same anions, as in cubic anti-perovskites, they suffer from the same issue of low operation voltage. Nevertheless, from this type of structure it is also possible to expect chemical flexibility, which makes them model compounds as well, but for investigations on layered cathode materials, which are rather common nowadays: one of the most typical examples of those is NMC, which is commercialized, but still has much of unrealized potential. In the end, this dissertation is considered by its author as primarily fundamental research, which is supposed to expand the knowledge in the field of physical chemistry of novel battery compounds, and to give certain keys for their development

Structural Behaviour and Charge-Compensation Mechanism in Li2Fe1−xCoxSeO Solid Solutions during Reversible Delithiation

The constantly growing demand for renewable electrical energy keeps the continuation of battery-related research imperative. In spite of significant progress made in the development of Na- and K-ion systems, Li-ion batteries (LIBs) still prevail in the fields of portative devices and electric or hybrid vehicles. Since the amount of lithium on our planet is significantly limited, studies dedicated to the search for and development of novel materials, which would make LIBs more efficient in terms of their specific characteristics and life lengths, are necessary. Investigations of less industry-related systems are also important, as they provide general knowledge which helps in understanding directions and strategies for the improvement of applied materials. The current paper represents a comprehensive study of cubic Li2Fe1−xCoxSeO compounds with an anti-perovskite structure. These solid solutions demonstrate both cationic and anionic electrochemical activity in lithium cells while being applied as cathodes. Cobalt cations remain inactive; however, their amount in the structure defines if the Se0/Se2− or Fe3+/Fe2+ redox couple dominates the charge compensation mechanism upon (de)lithiation. Apart from that, cobalt affects the structural stability of the materials during cycling. These effects were evaluated by means of operando XRD and XAS techniques. The outcomes can be useful for both fundamental and practice-relevant research

Hidden nonlinear supersymmetries in pure parabosonic systems

The existence of intimate relation between generalized statistics and supersymmetry is established by observation of hidden supersymmetric structure in pure parabosonic systems. This structure is characterized generally by a nonlinear superalgebra. The nonlinear supersymmetry of parabosonic systems may be realized, in turn, by modifying appropriately the usual supersymmetric quantum mechanics. The relation of nonlinear parabosonic supersymmetry to the Calogero-like models with exchange interaction and to the spin chain models with inverse-square interaction is pointed out.Comment: 20 pages, one reference corrected, to appear in Int. J. Mod. Phys.

Flux Growth and Characterization of Bulk InVO4 Crystals

The flux growth of InVO4 bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V2O5:InVO4 = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO4 of typical size 0.5 × 1 × 7 mm3 were obtained using copper pyrovanadate (Cu2V2O7) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO4 crystals makes them excellent candidates for further study of their physical properties

Studies of Li2Fe0.9M0.1SO Antiperovskite Materials for Lithium–Ion Batteries: The Role of Partial Fe2+ to M2+ Substitution

Cubic Li2Fe0.9M0.1SO antiperovskites with M–Co2+, or Mn2+ were successfully synthesized by a solid-state technique, and studied as cathode materials in Li-batteries. The influence of the Co, and Mn cation substitution of Fe in Li2FeSO on the resulting electrochemical performance was evaluated by galvanostatic cycling, while the reaction mechanism was explored by applying operando X-ray absorption and X-ray diffraction techniques using synchrotron radiation facilities. Even 10% Fe-substitution by these metals completely changes the structural behavior of the material upon Li-removal and insertion, in comparison to Li2FeSO. The Co-substitution significantly improves cyclability of the material at high current densities in comparison to the non-substituted material, reaching a specific capacity of 250 mAh/g at 1C current density. In contrast, the Mn-substitution leads to deterioration of the electrochemical performance because of the impeded kinetics, which may be caused by the appearance of a second isostructural phase due to formation of Jahn-Teller Mn3+ cations upon delithiation

Sodium-Vanadium Bronze Na9V14O35: An Electrode Material for Na-Ion Batteries

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

Neurogenic dysfunction of the lower urinary tract in infectious and inflammatory diseases of the spine: is there a correlation with clinical and radiological variants of myelopathy? Preliminary result of the analysis of a single-center cohort

Objective. To study the relationship between clinical and radiation variants of myelopathy and types of the neurogenic dysfunction of the lower urinary tract in patients with infectious spondylitis. Material and Methods. A single-center cohort observational study was conducted with the analysis of medical records and a prospective examination of 20 patients with infectious spondylitis complicated by neurogenic dysfunction of the lower urinary tract. Results. Infectious spondylitis can be complicated by the development of various urodynamic disorders, including neurogenic detrusor hyperactivity (30 %), its combination with detrusor-sphincter dissinergia (30 %) and a decrease in detrusor contractility (40 %). In 50 % of patients, an urodynamic examination revealed an increase in detrusor pressure of more than 40 cm water. There was no connection between the development of any type of lower urinary tract dysfunction and MRI types of myelopathy according to Vendatam, as well as between the level of spinal cord compression and the severity of neurological disorders according to AIS. Conclusion. The results of the study do not confirm the existence of a relationship between the various characteristics of myelopathy in infectious spondylitis and the results of urodynamic examination. The limitation of the reliability of the results is the small number of observations. Studies with a larger sample are required to assess the relationship between the clinical and radiation characteristics of myelopathy and variants of neurogenic dysfunction of the lower urinary tract in patients with infectious spondylitis

P2-type layered high-entropy oxides as sodium-ion cathode materials

P2-type layered oxides with the general Na-deficient composition NaxTMO2 (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na+ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2 with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications

P2-type layered high-entropy oxides as sodium-ion cathode materials

P2-type layered oxides with the general Na-deficient composition NaxTMO2 (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na+ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2 with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications