Ni-rich LiNi x Co y Mn1–x–y O2 cathodes (x = 0.6, 0.8, 0.9, and 0.95) were tested to characterize the capacity fading mechanism of extremely rich Ni compositions. Increasing the Ni fraction in the ...cathode delivered a higher discharge capacity (192.9 mA h g–1 for LiNi0.6Co0.2Mn0.2O2 versus 235.0 mA h g–1 for LiNi0.95Co0.025Mn0.025O2); however, the cycling stability was substantially reduced. LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2 retained more than 95% of their respective initial capacities after 100 cycles, while the capacity retention of LiNi0.9Co0.05Mn0.05O2 and LiNi0.95Co0.025Mn0.025O2 was limited to 85% during the same cycling period. The relatively inferior cycling stability of LiNi x Co y Mn1–x–y O2 with x > 0.8 is attributed to the phase transition near the charge-end, causing an abrupt anisotropic shrinkage (or expansion during discharge), which was suppressed for compositions of x < 0.8. Residual stress stemming from the phase transition destabilized the internal microcracks and allowed the microcracks to propagate to the surface, providing channels for electrolyte penetration and subsequent degradation of the exposed internal surfaces formed by the microcracks. Further developments in particle morphology are required to dissipate the intrinsic lattice strain, stabilize the surface, and modify the composition to attain a satisfactory long-term cycling stability, and hence battery life.
Kinetic resolution is a powerful strategy for the isolation of enantioenriched compounds from racemic mixtures, and the development of selective catalytic processes is an active area of research. ...Here, we present a nickel‐catalyzed kinetic resolution of racemic α‐substituted unconjugated carbonyl alkenes via the enantio‐, diastereo‐, and regioselective hydroamination. This protocol affords both chiral α‐substituted butenamides and syn‐β2,3‐amino acid derivatives with high enantiomeric purity (up to 99 % ee) and selectivity factor up to >684. The key to the excellent kinetic resolution efficiency is the distinctive architecture of the chiral nickel complex, which enables successful resolution and enantioselective C−N bond construction. Mechanistic investigations reveal that the unique structure of the chiral ligand facilitates a rapid migratory insertion step with one enantiomer. This strategy provides a practical and versatile approach to prepare a wide range of chiral compounds.
An efficient enantioselective catalysis using a chiral nickel complex has been developed via kinetic resolution of racemic α‐substituted unconjugated carbonyl alkenes. This hydroamination protocol produces a wide range of syn‐β2,3‐amino acid derivatives derivatives and α‐alkylated unconjugated carbonyl olefins with high enantiomeric purity.
Improving the thermal management of small-scale devices requires developing materials with high thermal conductivities. The semiconductor boron arsenide (BAs) is an attractive target because of ab ...initio calculation indicating that single crystals have an ultrahigh thermal conductivity. We synthesized BAs single crystals without detectable defects and measured a room-temperature thermal conductivity of 1300 watts per meter-kelvin. Our spectroscopy study, in conjunction with atomistic theory, reveals that the distinctive band structure of BAs allows for very long phonon mean free paths and strong high-order anharmonicity through the four-phonon process. The single-crystal BAs has better thermal conductivity than other metals and semiconductors. Our study establishes BAs as a benchmark material for thermal management applications and exemplifies the power of combining experiments and ab initio theory in new materials discovery.
Substituting W for Al in the Ni‐rich cathode LiNi0.885Co0.10Al0.015O2 (NCA89) produces LiNi0.9Co0.09W0.01O2 (NCW90) with markedly reduced primary particle size. Particle size refinement considerably ...improves the cathode's cycling stability such that the NCW90 cathode retains 92% of its initial capacity after 1000 cycles (compared to 63% for NCA89), while the cathode produces a high initial discharge capacity of 231.2 mAh g−1 (at 0.1 C). Thus, the proposed NCW90 can deliver high energy density and a long battery lifetime simultaneously, unlike other Ni‐rich layered oxide cathodes. This unprecedented cycling stability is mainly attributed to a series of interparticular microfractures that absorb the anisotropic lattice strain caused by a deleterious phase transition near the charge end, thereby improving the cathode's resistance to fracture. Microcrack suppression preserves the mechanical integrity of the cathode particles during cycling and protects the particle interior from detrimental electrolyte attack. The proposed NCW90 cathode provides an improved material from which a new series of Ni‐rich layered cathode can be developed for next‐generation electric vehicles.
Substituting W for Al in the Ni‐rich cathode LiNi0.885Co0.10Al0.015O2 (NCA89) produces LiNi0.9Co0.09W0.01O2 (NCW90) with markedly reduced primary particle size. Particle size refinement provides improved cycling stability such that the NCW90 cathode retains 92% of its initial capacity after 1000 cycles (compared to 63% for NCA89). Thus, the NCW90 cathode represents a new series of Ni‐rich layered cathodes for next‐generation electric vehicles.
The formation of C-N bonds is a fundamental aspect of organic synthesis, and hydroamination has emerged as a pivotal strategy for the synthesis of essential amine derivatives. In recent years, there ...has been a surge of interest in metal hydride-catalyzed hydroamination reactions of common alkenes and alkynes. This method avoids the need for stoichiometric organometallic reagents and overcomes problems associated with specific organometallic compounds that may impact functional group compatibility. Notably, recent developments have brought to the forefront olefinic hydroamination and hydroamidation reactions facilitated by nickel hydride (NiH) catalysis. The inclusion of suitable chiral ligands has paved the way for the realization of asymmetric hydroamination reactions in the realm of olefins. This review aims to provide an in-depth exploration of the latest achievements in C-N bond formation through intermolecular hydroamination catalyzed by nickel hydrides. Leveraging this innovative approach, a diverse range of alkene and alkyne substrates can be efficiently transformed into value-added compounds enriched with C-N bonds. The intricacies of C-N bond formation are succinctly elucidated, offering a concise overview of the underlying reaction mechanisms. It is our aspiration that this comprehensive review will stimulate further progress in NiH-catalytic techniques, fine-tune reaction systems, drive innovation in catalyst design, and foster a deeper understanding of the underlying mechanisms.
This review highlights recent progress in NiH-catalyzed hydroamination, focusing on its application to a variety of alkenes and alkynes.
Metal oxide nanosheets having high mesoporosity, grain size distribution of 5–10 nm, and ultrathin thickness have attracted much attention due to their intriguing properties such as high ...surface‐to‐volume ratio and superior chemical activities. However, 2D nanostructures tend to restack, inducing a decrease in accessible surface area and a number of pores. To solve this problem, herein, a unique synthetic method of crumpled metal oxide nanosheets using spray pyrolysis of metal ion–coated graphene oxide, followed by heat treatment, is reported. This method is applicable not only to single‐component metal oxides but also to heterogeneous multicomponent metal oxides in which composition can be controlled. Crumpled SnO2, ZnO, and Co3O4 as well as SnO2/ZnO and SnO2/Co3O4 nanosheets with heterogeneous interfaces are successfully synthesized and used as superior gas sensing layers. Because of the abundant reaction sites, well‐developed porosity for high gas accessibility, the formation of heterojunctions, the crumpled SnO2/ZnO and SnO2/Co3O4 nanosheets exhibit outstanding sensing performance (Rair/Rgas = 20.25 toward 5 ppm formaldehyde, and Rair/Rgas = 14.13 toward 5 ppm acetone, respectively). This study can contribute to the realization of a family of heterogeneous crumpled metal oxide nanosheets that can be applied to various research fields.
A general synthetic platform of hierarchically structured holey metal oxide nanosheets is achieved via a graphene oxide templating route and spray pyrolysis technique. The crumpled heterogeneous 2D metal oxide (crumpled H_2D MO) as a sensing layer exhibits improved sensing performance of formaldehyde (crumpled 2D SnO2/ZnO) and acetone (crumpled 2D SnO2/Co3O4) molecules due to the high porosity, surface area, and heterojunction effect.
Electrochemical properties and structural and thermal stability of LiNi0.65Co0.13Mn0.22O2 (FCG65), LiNi0.75Co0.08Mn0.17O2 (TSFCG75), and LiNi0.85Co0.05Mn0.10O2 (TSFCG85) with concentration ...gradients of Ni and Mn were evaluated to comprehensively demonstrate the effectiveness of compositional gradation for a wide range of Ni-rich LiNi x Co y Mn1–x–y O2 (NCM) cathodes. The discharge capacities of FCG65, TSFCG75, and TSFCG85 were 194.2, 206.8, and 222.2 mAh g–1, respectively with capacity retention of over 90% after 100 cycles. The high capacities and enhanced cycling stability relative to those of conventional Ni-rich NCM cathodes were attributed to the compositional partitioning, strong crystallographic texture, and unique particle morphology. In addition, the highly correlated particle orientation helped to reduce the anisotropic internal strain induced by Li removal/extraction from the Ni-rich NCM cathodes. The accelerated aging test (storing the delithiated cathodes in an electrolyte at elevated temperature) reconfirmed the superior stability of the TSFCG85 cathode compared to the commercial LiNi0.82Co0.14Al0.04O2 cathode, which exhibited fast structural degradation. Thus, NCM cathodes with concentration gradients represent a viable solution that simultaneously addresses the specific energy density, cycling and chemical stability, and safety issues of Ni-enriched NCM cathodes for general electromobility.
Detailed analysis of the microstructural changes during lithiation of a full‐concentration‐gradient (FCG) cathode with an average composition of LiNi0.75Co0.10Mn0.15O2 is performed starting from its ...hydroxide precursor, FCG Ni0.75Co0.10Mn0.15(OH)2 prior to lithiation. Transmission electron microscopy (TEM) reveals that a unique rod‐shaped primary particle morphology and radial crystallographic texture are present in the prelithiation stage. In addition, TEM detected a two‐phase structure consisting of MnOOH and Ni(OH)2, and crystallographic twins of MnOOH on the Mn‐rich precursor surface. The formation of numerous twins is driven by the lattice mismatch between MnOOH and Ni(OH)2. Furthermore, the twins persist in the lithiated cathode; however, their density decrease with increasing lithiation temperature. Cation disordering, which influences cathode performance, is observed to continuously decrease with increasing lithiation temperature with a minimum observed at 790 °C. Consequently, lithiation at 790 °C (for 10 h) produced optimal discharge capacity and cycling stability. Above 790 °C, an increase in cation disordering and excessive coarsening of the primary particles lead to the deterioration of electrochemical properties. The twins in the FCG cathode precursor may promote the optimal primary particle morphology by retarding the random coalescence of primary particles during lithiation, effectively preserving both the morphology and crystallographic texture of the precursor.
Crystallographic twins form by the precipitation of MnOOH in full‐concentration‐gradient precursors, Ni0.75Co0.10Mn0.15(OH)2, for Li‐ion batteries. The twins persist in cathodes through lithiation, but with varying density depending on the temperature of lithiation. The twin density influences the size and crystallographic orientation of primary particles in cathodes, which unequivocally affect their electrochemical properties.
Future generations of electric vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium ...batteries is mandatory while also maintaining similar or improved rate capability, lifetime, cost, and safety. The vast majority of electric vehicles that will appear on the market in the next 10 years will employ nickel-rich cathode materials, LiNi1–x–y Co x Al y O2 and LiNi1–x–y Co x Mn y O2 (x + y < 0.2), in particular. Here, the potential and limitations of these cathode materials are critically compared with reference to realistic target values from the automotive industry. Moreover, we show how future automotive targets can be achieved through fine control of the structural and microstructural properties.
Summary
Objective
To describe mesial temporal lobe ablated volumes, verbal memory, and surgical outcomes in patients with medically intractable mesial temporal lobe epilepsy (mTLE) treated with ...magnetic resonance imaging (MRI)–guided stereotactic laser interstitial thermal therapy (LiTT).
Methods
We prospectively tracked seizure outcome in 20 patients at Thomas Jefferson University Hospital with drug‐resistant mTLE who underwent MRI‐guided LiTT from December 2011 to December 2014. Surgical outcome was assessed at 6 months, 1 year, 2 years, and at the most recent visit. Volume‐based analysis of ablated mesial temporal structures was conducted in 17 patients with mesial temporal sclerosis (MTS) and results were compared between the seizure‐free and not seizure‐free groups.
Results
Following LiTT, proportions of patients who were free of seizures impairing consciousness (including those with auras only) are as follows: 8 of 15 patients (53%, 95% confidence interval CI 30.1–75.2%) after 6 months, 4 of 11 patients (36.4%, 95% CI 14.9–64.8%) after 1 year, 3 of 5 patients (60%, 95% CI 22.9–88.4%) at 2‐year follow‐up. Median follow‐up was 13.4 months after LiTT (range 1.3 months to 3.2 years). Seizure outcome after LiTT suggests an all or none response. Four patients had anterior temporal lobectomy (ATL) after LiTT; three are seizure‐free. There were no differences in total ablated volume of the amygdalohippocampus complex or individual volumes of hippocampus, amygdala, entorhinal cortex, parahippocampal gyrus, and fusiform gyrus between seizure‐free and non–seizure‐free patients. Contextual verbal memory performance was preserved after LiTT, although decline in noncontextual memory task scores were noted.
Significance
We conclude that MRI‐guided stereotactic LiTT is a safe alternative to ATL in patients with medically intractable mTLE. Individualized assessment is warranted to determine whether the reduced odds of seizure freedom are worth the reduction in risk, discomfort, and recovery time. Larger prospective studies are needed to confirm our preliminary findings, and to define optimal ablation volume and ideal structures for ablation.
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