Atomic-Scale Clarification of Structural Transition of MoS₂ upon Sodium Intercalation

Two-dimensional (2D) transition-metal dichalcogenides hold enormous potential for applications in electronic and optoelectronic devices. Their distinctive electronic and chemical properties are closely related to the structure and intercalation chemistry. Herein, the controversial phase transition from semiconductive 2H to metallic 1T phase and occupancy of the intercalated sodium (Na) upon electrochemical Na intercalation into MoS₂ are clarified at the atomic scale by aberration-corrected scanning transmission electron microscope. In addition, a series of other complicated phase transitions along with lattice distortion, structural modulation, and even irreversible structural decomposition are recognized in MoS₂ depending on the content of Na ion intercalation. It is shown that <i>x</i> = 1.5 in Na_<i>x</i>MoS₂ is a critical point for the reversibility of the structural evolution. Our findings enrich the understanding of the phase transitions and intercalation chemistry of the MoS₂ and shed light on future material design and applications

Selecting Substituent Elements for Li-Rich Mn-Based Cathode Materials by Density Functional Theory (DFT) Calculations

Li₂MnO₃ is known to stabilize the structure of the Li-rich Mn-based cathode materials <i>x</i>Li₂MnO₃·(1 – <i>x</i>)­LiMO₂ (M = Ni, Co, Mn, etc.). However, its presence makes these materials suffer from drawbacks including oxygen release, irreversible structural transition, and discharge potential decay. In order to effectively address these issues by atomic substitution, density function theory (DFT) calculations were performed to select dopants from a series of transition metals including Ti, V, Cr, Fe, Co, Ni, Zr, and Nb. Based on the calculations, Nb is chosen as an dopant, because Nb substitution is predicted to be able to increase the electronic conductivity, donate extra electrons for charge compensation and postpone the oxygen release reaction during delithiation. Moreover, the Nb atoms bind O more strongly and promote Li diffusion as well. Electrochemical evaluation on the Nb-doped Li₂MnO₃ show that Nb doping can indeed improve the performances of Li₂MnO₃ by increasing its electrochemical activity and hindering the decay of its discharge potential

Solid-State Composite Electrolyte LiI/3-Hydroxypropionitrile/SiO₂ for Dye-Sensitized Solar Cells

A new compound, LiI(3-hydroxypropionitrile)2, is reported here. According to its single-crystal structure (C2/c), this compound has 3-D transporting paths for iodine. Further ab initio calculation shows that the activation energy for diffusion of iodine (0.73 eV) is much lower than that of lithium ion (8.39 eV) within the lattice. Such a mono-ion transport feature is favorable as solid electrolyte to replace conventional volatile organic liquid electrolytes used in dye-sensitized solar cells (DSSC). LiI and 3-hydroxypropionitrile (HPN) can form a series of solid electrolytes. The highest ambient conductivity is 1.4 × 10-3 S/cm achieved for LiI(HPN)4. However, it tends to form large crystallites and leads to poor filling and contact within porous TiO2 electrodes in DSSC. Such a drawback can be greatly improved by introducing micrometer-sized and nanosized SiO2 particles into the solid electrolyte. It is helpful not only in enhancing the conductivity but also in improving the interfacial contact greatly. Consequently, the light-to-electricity conversion efficiency of 5.4% of a DSSC using LiI(HPN)4/15 wt % nano-SiO2 was achieved under AM 1.5 simulated solar light illumination. Due to the low cost, easy fabrication, and relatively high conversion efficiency, the DSSC based on this new solid-state composite electrolyte is promising for practical applications

Solid-State Composite Electrolyte LiI/3-Hydroxypropionitrile/SiO₂ for Dye-Sensitized Solar Cells

A new compound, LiI(3-hydroxypropionitrile)2, is reported here. According to its single-crystal structure (C2/c), this compound has 3-D transporting paths for iodine. Further ab initio calculation shows that the activation energy for diffusion of iodine (0.73 eV) is much lower than that of lithium ion (8.39 eV) within the lattice. Such a mono-ion transport feature is favorable as solid electrolyte to replace conventional volatile organic liquid electrolytes used in dye-sensitized solar cells (DSSC). LiI and 3-hydroxypropionitrile (HPN) can form a series of solid electrolytes. The highest ambient conductivity is 1.4 × 10-3 S/cm achieved for LiI(HPN)4. However, it tends to form large crystallites and leads to poor filling and contact within porous TiO2 electrodes in DSSC. Such a drawback can be greatly improved by introducing micrometer-sized and nanosized SiO2 particles into the solid electrolyte. It is helpful not only in enhancing the conductivity but also in improving the interfacial contact greatly. Consequently, the light-to-electricity conversion efficiency of 5.4% of a DSSC using LiI(HPN)4/15 wt % nano-SiO2 was achieved under AM 1.5 simulated solar light illumination. Due to the low cost, easy fabrication, and relatively high conversion efficiency, the DSSC based on this new solid-state composite electrolyte is promising for practical applications

Atomic-Scale Recognition of Surface Structure and Intercalation Mechanism of Ti₃C₂X

MXenes represent a large family of functionalized two-dimensional (2D) transition-metal carbides and carbonitrides. However, most of the understanding on their unique structures and applications stops at the theoretical suggestion and lack of experimental support. Herein, the surface structure and intercalation chemistry of Ti₃C₂X are clarified at the atomic scale by aberration-corrected scanning transmission electron microscope (STEM) and density functional theory (DFT) calculations. The STEM studies show that the functional groups (e.g., OH^–, F^–, O^–) and the intercalated sodium (Na) ions prefer to stay on the top sites of the centro-Ti atoms and the C atoms of the Ti₃C₂ monolayer, respectively. Double Na-atomic layers are found within the Ti₃C₂X interlayer upon extensive Na intercalation via two-phase transition and solid-solution reactions. In addition, aluminum (Al)-ion intercalation leads to horizontal sliding of the Ti₃C₂X monolayer. On the basis of these observations, the previous monolayer surface model of Ti₃C₂X is modified. DFT calculations using the new modeling help to understand more about their physical and chemical properties. These findings enrich the understanding of the MXenes and shed light on future material design and applications. Moreover, the Ti₃C₂X exhibits prominent rate performance and long-term cycling stability as an anode material for Na-ion batteries

DataSheet_1_The relationship between weight-adjusted-waist index and diabetic kidney disease in patients with type 2 diabetes mellitus.docx

PurposeObesity, particularly abdominal obesity, is seen as a risk factor for diabetic complications. The weight-adjusted-waist index (WWI) is a recently developed index for measuring adiposity. Our goal was to uncover the potential correlation between the WWI index and diabetic kidney disease (DKD) risk.MethodsThis cross-sectional study included adults with type 2 diabetes mellitus (T2DM) who participated in the NHANES database (2007-2018). The WWI index was calculated as waist circumference (WC, cm) divided by the square root of weight (kg). DKD was diagnosed based on impaired estimated glomerular filtration rate (eGFR2), albuminuria (urinary albumin to urinary creatinine ratio>30 mg/g), or both in T2DM patients. The independent relationship between WWI index and DKD risk was evaluated.ResultsA total of 5,028 participants with T2DM were included, with an average WWI index of 11.61 ± 0.02. As the quartile range of the WWI index increased, the prevalence of DKD gradually increased (26.76% vs. 32.63% vs. 39.06% vs. 42.96%, P2) and WC. Subgroup analysis suggested that the relationship between the WWI index and DKD risk was of greater concern in patients over 60 years old and those with cardiovascular disease.ConclusionsOur findings suggest that higher WWI levels are linked to DKD in T2DM patients. The WWI index could be a cost-effective and simple way to detect DKD, but further prospective studies are needed to confirm this.</p

Electrochemical Lithium Deposition on Li<i>_x</i>Ti₅O₁₂

Lithium metal batteries (LMBs) have been regarded as one of the most promising next-generation high-energy-density storage devices. However, uncontrolled lithium dendrite growth leads to low Coulombic efficiencies and severe safety issues, hindering the commercialization of LMBs. Reducing the diffusion barrier of lithium is beneficial for uniform lithium deposition. Herein, a composite is constructed with Li4Ti5O12 as the skeleton of metallic lithium (Li@LixTi5O12) because Li4Ti5O12 is a “zero-strain” material and exhibits a low lithium diffusion barrier. It was found that the symmetric cells of Li@LixTi5O12 can stably cycle for over 400 h at 1 mA cm–2 in the carbonate electrolyte, significantly exceeding the usual lifespan (∼170 h) of the symmetric cell using a lithium metal electrode. In a full cell with Li@LixTi5O12 as the anode, the cathode LiFePO4 delivers a capacity retention of 78.2% after 550 cycles at 3.6C rate and an N/P ratio = 8.0. This study provides new insights for designing a practical lithium anode

Direct Evidence of Concurrent Solid-Solution and Two-Phase Reactions and the Nonequilibrium Structural Evolution of LiFePO₄

Lithium-ion batteries power many portable devices and in the future are likely to play a significant role in sustainable-energy systems for transportation and the electrical grid. LiFePO₄ is a candidate cathode material for second-generation lithium-ion batteries, bringing a high rate capability to this technology. LiFePO₄ functions as a cathode where delithiation occurs via either a solid-solution or a two-phase mechanism, the pathway taken being influenced by sample preparation and electrochemical conditions. The details of the delithiation pathway and the relationship between the two-phase and solid-solution reactions remain controversial. Here we report, using real-time in situ neutron powder diffraction, the simultaneous occurrence of solid-solution and two-phase reactions after deep discharge in nonequilibrium conditions. This work is an example of the experimental investigation of nonequilibrium states in a commercially available LiFePO₄ cathode and reveals the concurrent occurrence of and transition between the solid-solution and two-phase reactions

Insights into Lithium and Sodium Storage in Porous Carbon

The lithium and sodium storage behavior of porous carbon remains controversial, though it shows excellent cycling stability and rate performances. This Letter discloses the insertion, adsorption, and filling properties of porous carbon. 7Li nuclear magnetic resonance (NMR) spectroscopy recognized inserted and adsorbed lithium in this porous carbon but did not observe any other forms of lithium above 0.0 V vs. Li+/Li. In addition, although lithium insertion mainly takes place at low potentials, adsorption was found to be the main form of lithium storage throughout the investigated potential range. Such a storage feature is responsible for the excellent rate performance and high specific capacity of porous carbon. Raman spectroscopy further demonstrated the structural reversibility of the carbon in different potential ranges, verifying the necessity to optimize the potential range for a better cycling performance. These findings provide insights for the design and application of porous carbon