Nanocomposite Engineering of a High-Capacity Partially Ordered Cathode for Li-Ion Batteries.

Understanding the local cation order in the crystal structure and its correlation with electrochemical performances has advanced the development of high-energy Mn-rich cathode materials for Li-ion batteries, notably Li- and Mn-rich layered cathodes (LMR, e.g., Li1.2 Ni0.13 Mn0.54 Co0.13 O2 ) that are considered as nanocomposite layered materials with C2/m Li2 MnO3 -type medium-range order (MRO). Moreover, the Li-transport rate in high-capacity Mn-based disordered rock-salt (DRX) cathodes (e.g., Li1.2 Mn0.4 Ti0.4 O2 ) is found to be influenced by the short-range order of cations, underlining the importance of engineering the local cation order in designing high-energy materials. Herein, the nanocomposite is revealed, with a heterogeneous nature (like MRO found in LMR) of ultrahigh-capacity partially ordered cathodes (e.g., Li1.68 Mn1.6 O3.7 F0.3 ) made of distinct domains of spinel-, DRX- and layered-like phases, contrary to conventional single-phase DRX cathodes. This multi-scale understanding of ordering informs engineering the nanocomposite material via Ti doping, altering the intra-particle characteristics to increase the content of the rock-salt phase and heterogeneity within a particle. This strategy markedly improves the reversibility of both Mn- and O-redox processes to enhance the cycling stability of the partially ordered DRX cathodes (nearly ≈30% improvement of capacity retention). This work sheds light on the importance of nanocomposite engineering to develop ultrahigh-performance, low-cost Li-ion cathode materials.

Evaluation of the Dimensions of Anterior Loop of Mental Nerve in CBCT: A Radiographic Analysis.

BACKGROUND: Information on the dimensions of the anterior loop of mental nerve is important for dental implant placement. AIMS: The purpose of this study was to determine the total length of anterior loop of mental nerve from the mental foramen. MATERIALS AND METHODS: CBCT data of 150 patients were evaluated. RESULTS: We found that the anterior loop was absent in 56.4% of patients on the left side and 61.7% patients on the right side. 19.5% of the total patients (29 patients) had up to 4 mm length of the loop which was exactly same on both right and left sides. The remaining 16.8% on the left side (25 patients) and 14.1% on the right side (21 patients) had the length of the loop ranging between 4.1 and 8 mm. The rest 7.4% of patients on the left side and 4.7% patients on the right side had more than 8 mm of the loop length. CONCLUSIONS: Based on this study, the dimensions of the anterior loop are variable and hold great significance in dental implant planning in the mandibular premolar region.

Evaluation of Alveolar Ridge Height Gained by Vertical Ridge Augmentation Using Titanium Mesh and Novabone Putty in Posterior Mandible.

AIM: The purpose of this case series was to report the clinical and radiographical outcomes of vertical ridge augmentation in edentulous posterior mandible using a combination of titanium mesh with novabone putty. MATERIAL AND METHOD: Twenty patients were included, and grafting was done using alloplastic novabone putty supported by titanium mesh as the barrier for guided bone regeneration. RESULTS: Sixteen patients exhibited good soft tissue healing. Postoperative flap dehiscence occurred relatively early in the healing period in one patient followed by graft extrusion and delayed healing in other three patients. The mean vertical height of augmented bone was 4.825 ± 1.1387 mm. CONCLUSION: This report demonstrates the remarkable efficacy of guided bone regeneration using a combination of titanium mesh and novabone putty for vertical ridge augmentation, thus expanding the indications for implant therapy and allowing recovery of the three-dimensional esthetic architecture in a severely resorbed alveolar ridge.

Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges.

The rapidly expanding field of nonaqueous multivalent intercalation batteries offers a promising way to overcome safety, cost, and energy density limitations of state-of-the-art Li-ion battery technology. We present a critical and rigorous analysis of the increasing volume of multivalent battery research, focusing on a wide range of intercalation cathode materials and the mechanisms of multivalent ion insertion and migration within those frameworks. The present analysis covers a wide variety of material chemistries, including chalcogenides, oxides, and polyanions, highlighting merits and challenges of each class of materials as multivalent cathodes. The review underscores the overlap of experiments and theory, ranging from charting the design metrics useful for developing the next generation of MV-cathodes to targeted in-depth studies rationalizing complex experimental results. On the basis of our critical review of the literature, we provide suggestions for future multivalent cathode studies, including a strong emphasis on the unambiguous characterization of the intercalation mechanisms.

The structural and chemical origin of the oxygen redox activity in layered and cation-disordered Li-excess cathode materials.

Lithium-ion batteries are now reaching the energy density limits set by their electrode materials, requiring new paradigms for Li(+) and electron hosting in solid-state electrodes. Reversible oxygen redox in the solid state in particular has the potential to enable high energy density as it can deliver excess capacity beyond the theoretical transition-metal redox-capacity at a high voltage. Nevertheless, the structural and chemical origin of the process is not understood, preventing the rational design of better cathode materials. Here, we demonstrate how very specific local Li-excess environments around oxygen atoms necessarily lead to labile oxygen electrons that can be more easily extracted and participate in the practical capacity of cathodes. The identification of the local structural components that create oxygen redox sets a new direction for the design of high-energy-density cathode materials.

Role of Structural H2O in Intercalation Electrodes: The Case of Mg in Nanocrystalline Xerogel-V2O5.

Cointercalation is a potential approach to influence the voltage and mobility with which cations insert in electrodes for energy storage devices. Combining a robust thermodynamic model with first-principles calculations, we present a detailed investigation revealing the important role of H2O during ion intercalation in nanomaterials. We examine the scenario of Mg(2+) and H2O cointercalation in nanocrystalline Xerogel-V2O5, a potential cathode material to achieve energy density greater than Li-ion batteries. Water cointercalation in cathode materials could broadly impact an electrochemical system by influencing its voltages or causing passivation at the anode. The analysis of the stable phases of Mg-Xerogel V2O5 and voltages at different electrolytic conditions reveals a range of concentrations for Mg in the Xerogel and H2O in the electrolyte where there is no thermodynamic driving force for H2O to shuttle with Mg during electrochemical cycling. Also, we demonstrate that H2O shuttling with the Mg(2+) ions in wet electrolytes yields higher voltages than in dry electrolytes. The thermodynamic framework used to study water and Mg(2+) cointercalation in this work opens the door for studying the general phenomenon of solvent cointercalation observed in other complex solvent-electrode pairs used in the Li- and Na-ion chemical spaces.

First-principles evaluation of multi-valent cation insertion into orthorhombic V2O5.

A systematic first-principles evaluation of the insertion behavior of multi-valent cations in orthorhombic V2O5 is performed. Layer spacing, voltage, phase stability, and ion mobility are computed for Li(+), Mg(2+), Zn(2+), Ca(2+), and Al(3+) intercalation in the α and δ polymorphs.

Prevalence and predictors of left atrial thrombus in patients with atrial fibrillation: is transesophageal echocardiography necessary before cardioversion?

BACKGROUND: Systemic embolization threatens patients with atrial fibrillation (AF). The risk is enhanced at the time of cardioversion. Transesophageal echocardiography (TEE) prior to cardioversion to screen for left atrial thrombus (LAT), a marker of high risk for embolization, is recommended for many patients with AF. OBJECTIVE: To determine clinical and echocardiographic factors associated with LAT formation in AF. METHODS: Data from 600 consecutive patients with AF undergoing TEE prior to cardioversion for the detection of LAT were analyzed. Clinical, laboratory, and echocardiographic parameters were abstracted from the clinical record. RESULTS: TEE identified LAT in 70 (11.6%) and dense (LA) spontaneous echo contrast (SEC) in 156 (26%). Baseline characteristics and echocardiographic parameters of patients with or without LAT are compared. A prior myocardial infarction, 21 (29.4 %) vs. 31 (5.8), (p < 0.001); hypertension, 60 (85.7%) vs. 386 (72.8), (p 0.02); CHADS(2) ≥ 2, 56 (80%) vs. 308 (58.1%), (p < 0.001) prevalence was higher in patients with LAT. Patients with LAT had lower ejection fraction 38.2 ± 15.6 vs. 46.2 ± 14.5, (p < 0.001); higher LA diameter 4.98 ± 0.7 vs. 4.52 ± 0.7, (p <0.001); dense LA SEC 44 (62.8) vs. 112 (21.1), (p < 0.001); and low LA appendage emptying velocity 21.7 ± 12.9 vs. 37.5 ± 19.4, (p < 0.001). Multivariate analysis was done, and it revealed that low LA emptying velocity had the strongest independent association with LAT (HR 0.89 [CI 0.83-0.96], p value <0.001. CONCLUSION: LAT is not an uncommon finding of AF patients prior to cardioversion. The current practice of TEE examination may be justified since neither clinical nor routine 2D echo examinations reliably identify LAT.

Coronary blood flow in patients with severe aortic stenosis before and after transcatheter aortic valve implantation.

Patients with severe aortic stenosis and no obstructed coronary arteries are reported to have reduced coronary flow. Doppler evaluation of proximal coronary flow is feasible using transesophageal echocardiography. The present study aimed to assess the change in coronary flow in patients with severe aortic stenosis undergoing transcatheter aortic valve implantation (TAVI). The left main coronary artery was visualized using transesophageal echocardiography in 90 patients undergoing TAVI using the Edwards SAPIEN valve. The peak systolic and diastolic velocities of the coronary flow and the time-velocity integral were obtained before and after TAVI using pulse-wave Doppler. Mean aortic gradients decreased from 47.1 ± 15.7 mm Hg before TAVI to 3.6 ± 2.6 mm Hg after TAVI (p <0.001). The aortic valve area increased from 0.58 ± 0.17 to 1.99 ± 0.35 cm(2) (p <0.001). The cardiac output increased from 3.4 ± 1.1 to 3.8 ± 1.0 L/min (p <0.001). Left ventricular end-diastolic pressure (LVEDP) decreased from 19.8 ± 5.4 to 17.3 ± 4.1 mm Hg (p <0.001). The following coronary flow parameters increased significantly after TAVI: peak systolic velocity 24.2 ± 9.3 to 30.5 ± 14.9 cm/s (p <0.001), peak diastolic velocity 49.8 ± 16.9 to 53.7 ± 22.3 cm/s (p = 0.04), total velocity-time integral 26.7 ± 10.5 to 29.7 ± 14.1 cm (p = 0.002), and systolic velocity-time integral 6.1 ± 3.7 to 7.7 ± 5.0 cm (p = 0.001). Diastolic time-velocity integral increased from 20.6 ± 8.7 to 22.0 ± 10.1 cm (p = 0.04). Total velocity-time integral increased >10% in 43 patients (47.2%). Pearson's correlation coefficient revealed the change in LVEDP as the best correlate of change in coronary flow (R = -0.41, p = 0.003). In conclusion, TAVI resulted in a significant increase in coronary flow. The change in coronary flow was associated mostly with a decrease in LVEDP.

Kinetics of non-equilibrium lithium incorporation in LiFePO4.

Lithium-ion batteries are a key technology for multiple clean energy applications. Their energy and power density is largely determined by the cathode materials, which store Li by incorporation into their crystal structure. Most commercialized cathode materials, such as LiCoO(2) (ref. 1), LiMn(2)O(4) (ref. 2), Li(Ni,Co,Al)O(2) or Li(Ni,Co,Mn)O(2) (ref. 3), form solid solutions over a large concentration range, with occasional weak first-order transitions as a result of ordering of Li or electronic effects. An exception is LiFePO(4), which stores Li through a two-phase transformation between FePO(4) and LiFePO(4) (refs 5-8). Notwithstanding having to overcome extra kinetic barriers, such as nucleation of the second phase and growth through interface motion, the observed rate capability of LiFePO(4) has become remarkably high. In particular, once transport limitations at the electrode level are removed through carbon addition and particle size reduction, the innate rate capability of LiFePO(4) is revealed to be very high. We demonstrate that the reason LiFePO(4) functions as a cathode at reasonable rate is the availability of a single-phase transformation path at very low overpotential, allowing the system to bypass nucleation and growth of a second phase. The Li(x)FePO(4) system is an example where the kinetic transformation path between LiFePO(4) and FePO(4) is fundamentally different from the path deduced from its equilibrium phase diagram.

Particle size dependence of the ionic diffusivity.

Diffusion constants are typically considered to be independent of particle size with the benefit of nanosizing materials arising solely from shortened transport paths. We show that for materials with one-dimensional atomic migration channels, the diffusion constant depends on particle size with diffusion in bulk being much slower than in nanoparticles. This model accounts for conflicting data on LiFePO(4), an important material for rechargeable lithium batteries, specifically explaining why it functions exclusively on the nanoscale.