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

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

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

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

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

Reduction Depth Dependent Structural Reversibility of Sn₃(PO₄)₂

Conversion reaction is an important method for lithium storage. Tin-based compounds have been regarded as promising anode materials for lithium ion batteries due to their high specific capacities. Herein, we report the structural reversibility of Sn₃(PO₄)₂ after conversion and Li–Sn alloying reactions. It is found that the reversibility of Sn₃(PO₄)₂ is highly dependent on the cutoff discharge potential. The conversion reaction of Sn₃(PO₄)₂ is partially reversible when it is discharged to 1.55 and then recharged to 3.00 V but is not between 0.00 and 3.00 V

Synthesis and Lithium Storage Mechanism of Ultrafine MoO₂ Nanorods

Ultrafine MoO₂ nanorods with a diameter of ∼5 nm were successfully synthesized by a nanocasting method using mesoporous silica SBA-15 as hard template. This material demonstrates high reversible capacity, excellent cycling performance, and good rate capacity as an anode electrode material for Li ion batteries. The significant enhancement in the electrochemical Li storage performance in ultrafine MoO₂ nanorods is attributed to the nanorod structure with small diameter and efficient one-dimensional electron transport pathways. Moreover, density functional theory calculations were performed to elucidate the Li uptake/removal mechanism in the MoO₂ electrodes, which can help us understand the unique cycling behavior of MoO₂ material

Feasibility of Using Li₂MoO₃ in Constructing Li-Rich High Energy Density Cathode Materials

Layer-structured <i>x</i>Li₂MnO₃·(1 – <i>x</i>)­Li<i><b>M</b></i>O₂ are promising cathode materials for high energy-density Li-ion batteries because they deliver high capacities due to the stabilizing effect of Li₂MnO₃. However, the inherent disadvantages of Li₂MnO₃ make these materials suffer from drawbacks such as fast energy-density decay, poor rate performance and safety hazard. In this paper, we propose to replace Li₂MnO₃ with Li₂MoO₃ for constructing novel Li-rich cathode materials and evaluate its feasibility. Comprehensive studies by X-ray diffraction, X-ray absorption spectroscopy, and spherical-aberration-corrected scanning transmission electron microscopy clarify its lithium extraction/insertion mechanism and shows that the Mo⁴⁺/Mo⁶⁺ redox couple in Li₂MoO₃ can accomplish the task of charge compensation upon Li removal. Other properties of Li₂MoO₃ such as the nearly reversible Mo-ion migration to/from the Li vacancies, absence of oxygen evolution, and reversible phase transition during initial (de)­lithiation indicate that Li₂MoO₃ meets the requirements to an ideal replacement of Li₂MnO₃ in constructing Li₂MoO₃-based Li-rich cathode materials with superior performances

New Insight into the Atomic Structure of Electrochemically Delithiated O3-Li_{(1–<i>x</i>)}CoO₂ (0 ≤ <i>x</i> ≤ 0.5) Nanoparticles

Direct observation of delithiated structures of LiCoO₂ at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO₂ nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO₂, the Co-contained (003) planes distort from the bulk to the surface region and the <i>c</i>-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO₂ to O1-type Li_<i>x</i>CoO₂ (<i>x</i> ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li_<i>x</i>CoO₂ (<i>x</i> ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li_<i>x</i>CoO₂ in the phase diagram of O3-LiCoO₂, through which the two previously separated LiCoO₂ phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries