Two birds with one stone: One-pot concurrent Ta-doping and -coating on Ni-rich LiNi0.92Co0.04Mn0.04O2 cathode materials with fiber-type microstructure and Li+-conducting layer formation

A novel scalable Taylor-Couette reactor (TCR) synthesis method was employed to prepare Ta-modified LiNi0.92Co0.04Mn0.04O2 (T-NCM92) with different Ta contents. Through experiments and density functional theory (DFT) calculations, the phase and microstructure of Ta-modified NCM92 were analyzed, showing that Ta provides a bifunctional (doping and coating at one time) effect on LiNi0.92Co0.04Mn0.04O2 cathode material through a one-step synthesis process via a controlling suitable amount of Ta and Li-salt. Ta doping allows the tailoring of the microstructure, orientation, and morphology of the primary NCM92 particles, resulting in a needle-like shape with fine structures that considerably enhance Li+ ion diffusion and electrochemical charge/discharge stability. The Ta-based surface-coating layer effectively prevented microcrack formation and inhibited electrolyte decomposition and surface-side reactions during cycling, thereby significantly improving the electrochemical performance and long-term cycling stability of NCM92 cathodes. Our as-prepared NCM92 modified with 0.2 mol% Ta (i.e., T2-NCM92) exhibits outstanding cyclability, retaining 84.5 % capacity at 4.3 V, 78.3 % at 4.5 V, and 67.6 % at 45 ℃ after 200 cycles at 1C. Even under high-rate conditions (10C), T2-NCM92 demonstrated a remarkable capacity retention of 66.9 % after 100 cycles, with an initial discharge capacity of 157.6 mAh g-1. Thus, the Ta modification of Ni-rich NCM92 materials is a promising option for optimizing NCM cathode materials and enabling their use in real-world electric vehicle (EV) applications.

Doping-Induced Surface and Grain Boundary Effects in Ni-Rich Layered Cathode Materials

In this work, the effects of dopant size and oxidation state on the structure and electrochemical performance of LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) are investigated. It is shown that doping with boron (B) which has a small ionic radius and an oxidation state of 3+, leads to the formation of a boron oxide-containing surface coating (probably Li3 BO3 ), mainly on the outer surface of the secondary particles. Due to this effect, boron only slightly affects the size of the primary particle and the initial capacity, but significantly improves the capacity retention. On the other hand, the dopant ruthenium (Ru) with a larger ionic radius and a higher oxidation state of 5+ can be stabilized within the secondary particles and does not experience a segregation to the outer agglomerate surface. However, the Ru dopant preferentially occupies incoherent grain boundary sites, resulting in smaller primary particle size and initial capacity than for the B-doped and pristine NCM811. This work demonstrates that a small percentage of dopant (2 mol%) cannot significantly affect bulk properties, but it can strongly influence the surface and/or grain boundary properties of microstructure and thus the overall performance of cathode materials.

Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12:Al,Ta Interface in an All-Solid-State Lithium Battery

All-solid-state lithium batteries are promising candidates for next-generation energy storage systems. Their performance critically depends on the capacity and cycling stability of the cathodic layer. Cells with a garnet Li₇La₃Zr₂O₁₂ (LLZO) electrolyte can show high areal storage capacity. However, they commonly suffer from performance degradation during cycling. For fully inorganic cells based on LiCoO₂ (LCO) as cathode active material and LLZO, the electrochemically induced interface amorphization has been identified as an origin of the performance degradation. This study shows that the amorphized interface can be recrystallized by thermal recovery (annealing) with nearly full restoration of the cell performance. The structural and chemical changes at the LCO/LLZO heterointerface associated with degradation and recovery were analyzed in detail and justified by thermodynamic modeling. Based on this comprehensive understanding, this work demonstrates a facile way to recover more than 80% of the initial storage capacity through a thermal recovery (annealing) step. The thermal recovery can be potentially used for cost-efficient recycling of ceramic all-solid-state batteries.

Study of LiCoO2/Li7La3Zr2O12:Ta Interface Degradation in All-Solid-State Lithium Batteries

The garnet-type Li₇La₃Zr₂O₁₂ (LLZO) ceramic solid electrolyte combines high Li-ion conductivity at room temperature with high chemical stability. Several all-solid-state Li batteries featuring the LLZO electrolyte and the LiCoO₂ (LCO) or LiCoO₂-LLZO composite cathode were demonstrated. However, all batteries exhibit rapid capacity fading during cycling, which is often attributed to the formation of cracks due to volume expansion and the contraction of LCO. Excluding the possibility of mechanical failure due to crack formation between the LiCoO₂/LLZO interface, a detailed investigation of the LiCoO₂/LLZO interface before and after cycling clearly demonstrated cation diffusion between LiCoO₂ and the LLZO. This electrochemically driven cation diffusion during cycling causes the formation of an amorphous secondary phase interlayer with high impedance, leading to the observed capacity fading. Furthermore, thermodynamic analysis using density functional theory confirms the possibility of low- or non-conducting secondary phases forming during cycling and offers an additional explanation for the observed capacity fading. Understanding the presented degradation paves the way to increase the cycling stability of garnet-based all-solid-state Li batteries.

Promoting the Transformation of Li2 S2 to Li2 S: Significantly Increasing Utilization of Active Materials for High-Sulfur-Loading Li-S Batteries

Lithium-sulfur (Li-S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether-based Li-S batteries involve sophisticated multistep solid-liquid-solid-solid electrochemical reaction mechanisms. Recently, studies on Li-S batteries have widely focused on the initial solid (sulfur)-liquid (soluble polysulfide)-solid (Li₂ S₂ ) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li-S batteries. Nonetheless, the sluggish kinetics of the solid-solid conversion from solid-state intermediate product Li₂ S₂ to the final discharge product Li₂ S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS₃ ) is proposed to decrease the dissociation energy of Li₂ S₂ and propel the electrochemical transformation of Li₂ S₂ to Li₂ S. The CoS₃ catalyst plays a critical role in improving the sulfur utilization, especially in high-loading sulfur cathodes (3-10 mg cm^-2 ). Accordingly, the Li₂ S/Li₂ S₂ ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS₃ catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g^-1 ) compared to the counterpart sulfur electrode without CoS₃ .

Unraveling the Role of Earth-Abundant Fe in the Suppression of Jahn-Teller Distortion of P'2-Type Na2/3MnO2: Experimental and Theoretical Studies

Layered Na_2/3MnO₂ suffers from capacity loss due to Jahn-Teller (J-T) distortion by Mn³⁺ ions. Herein, density functional theory calculations suggest Na_2/3[Fe _xMn_{1- x}]O₂ suppresses the J-T effect. The Fe substitution results in a decreased oxygen-metal-oxygen length, leading to decreases in the b and c lattice parameters but an increase in the a lattice constant. As a result, the capacity retention and rate capability are enhanced with an additional redox pair associated with Fe^4+/3+. Finally, the thermal properties are improved, with the Fe substitution delaying the exothermic reaction and reducing exothermic heat.

Stabilizing the Interface of NASICON Solid Electrolyte against Li Metal with Atomic Layer Deposition

Solid-state batteries have been considered as one of the most promising next-generation energy storage systems because of their high safety and energy density. Solid-state electrolytes are the key component of the solid-state battery, which exhibit high ionic conductivity, good chemical stability, and wide electrochemical windows. LATP [Li_1.3Al_0.3Ti_1.7 (PO₄)₃] solid electrolyte has been widely investigated for its high ionic conductivity. Nevertheless, the chemical instability of LATP against Li metal has hindered its application in solid-state batteries. Here, we propose that atomic layer deposition (ALD) coating on LATP surfaces is able to stabilize the LATP/Li interface by reducing the side reactions. In comparison with bare LATP, the Al₂O₃-coated LATP by ALD exhibits a stable cycling behavior with smaller voltage hysteresis for 600 h, as well as small resistance. More importantly, on the basis of advanced characterizations such as high-resolution transmission electron spectroscope-electron energy loss spectroscopy, the lithium penetration into the LATP bulk and Ti⁴⁺ reduction are significantly limited. The results suggest that ALD is very effective in improving solid-state electrolyte/electrode interface stability.

High Capacity, Dendrite-Free Growth, and Minimum Volume Change Na Metal Anode

Na metal anode attracts increasing attention as a promising candidate for Na metal batteries (NMBs) due to the high specific capacity and low potential. However, similar to issues faced with the use of Li metal anode, crucial problems for metallic Na anode remain, including serious moss-like and dendritic Na growth, unstable solid electrolyte interphase formation, and large infinite volume changes. Here, the rational design of carbon paper (CP) with N-doped carbon nanotubes (NCNTs) as a 3D host to obtain Na@CP-NCNTs composites electrodes for NMBs is demonstrated. In this design, 3D carbon paper plays a role as a skeleton for Na metal anode while vertical N-doped carbon nanotubes can effectively decrease the contact angle between CP and liquid metal Na, which is termed as being "Na-philic." In addition, the cross-conductive network characteristic of CP and NCNTs can decrease the effective local current density, resulting in uniform Na nucleation. Therefore, the as-prepared Na@CP-NCNT exhibits stable electrochemical plating/stripping performance in symmetrical cells even when using a high capacity of 3 mAh cm^-2 at high current density. Furthermore, the 3D skeleton structure is observed to be intact following electrochemical cycling with minimum volume change and is dendrite-free in nature.

Prognostic value of oxygen consumption and ventilatory equivalent slope in female candidates referred for heart transplantation--experience of a single Asian center

BACKGROUND

Ventilatory equivalent (ventilation/CO2 production, VE/VCO2) slope has been suggested to be a much more accurate predicator than peak oxygen consumption (VO2) during exercise for prognosis in patients with heart failure. However, patients tested were predominately male.

METHODS

To investigate whether peak VO2 and VE/VCO2 slope predict the prognosis of female patients with heart failure, we retrospectively collected data of 39 female candidates referred for heart transplantation (HTx) from 2004 to 2011. Both peak VO2 and VE/VCO2 slope were obtained from the results of an exercise pulmonary function test. The outcome was death or mechanical devices implantation or HTx. Logistic regression was used for data analysis.

RESULTS

Mean age and heart failure survival score were 55.8 ± 13.7 years and 7.3 ± 0.7, respectively. Each increment of VE/VCO2 slope decreased 2-year event-free rate (odds ratio [OR] = 0.88, 95% confidence interval [CI] = 0.79 to 0.98) in the female group. The predictions of VE/VCO2 slope for 1-year event-free survival did not reach statistical significance (OR = 0.92, 95% CI = 0.84 to 1.00). On the other hand, peak VO2 was not a strong predictor for 1- and 2-year event-free survival (OR = 1.22 and 1.16, 95% CI = 0.96 to 1.55 and 0.94 to 1.44, respectively).

CONCLUSIONS

Impairment in exercise ventilation holds a clinical and long-term prognostic impact in female patients with heart failure. The role of peak VO2 during exercise in prognostic prediction among the cohort should be further investigated.

Leaving group stabilization by metal ion coordination and hydrogen bond donation is an evolutionarily conserved feature of group I introns

To understand the behavior of group I introns on a biologically fundamental level, we must distinguish those traits that arise as the products of natural selection (selected traits) from those that arise as the products of neutral drift (non-selected traits). In practice, this distinction relies on comparing the similarities and differences among widely divergent introns to identify conserved traits. Here we address whether the strategies used by the eukaryotic group I intron from the Tetrahymena ciliate to stabilize the leaving group during splicing are maintained in the group I intron from the widely divergent Azoarcus bacterium. A substrate analogue containing a 3'-phosphorothiolate linkage, in which a sulfur atom replaces the bridging 3'-oxygen atom of the scissile phosphate, reacts 20-fold slower in the Azoarcus reaction than the corresponding unmodified substrate in the presence of Mg(II) as the only divalent cation. However, Mn(II) relieves this negative effect such that the 3'-S-P bond cleaves 21-fold faster than does the 3'O-P bond. Other thiophilic divalent metal ions such as Co(II), Cd(II), and Zn(II) similarly support cleavage of the S-P bond. These results indicate that a metal ion directly coordinates to the leaving group in the transition state of the Azoarcus ribozyme reaction. Additionally, the 3'-sulfur substitution eliminates the approximately 10(3)-fold contribution of the adjacent 2'-OH to transition state stabilization. Considering that sulfur accepts hydrogen bonds weakly compared to oxygen, this result suggests that the 2'-OH contributes to catalysis by donating a hydrogen bond to the 3'-oxygen leaving group in the transition state, presumably acting in conjunction with the metal ion to stabilize the developing negative charge. These same catalytic strategies of metal ion coordination and hydrogen bond donation operate in the Tetrahymena ribozyme reaction, suggesting that these features of catalysis have been conserved during evolution and thus extend to all group I introns. The two ribozymes also exhibit quantitative differences in their response to 3'-sulfur substitution. The Azoarcus ribozyme binds and cleaves the phosphorothiolate substrate more efficiently relative to the natural substrate than the Tetrahymena ribozyme under the same conditions, suggesting that the Azoarcus ribozyme better accommodates the phosphorothiolate at the active site both in the ground state and in the transition state. These differences may reflect either a less tightly knit Azoarcus structure and/or spatial deviations between backbone atoms in the two ribozymes that arise during divergent evolution, analogous to the well-documented relationship between protein sequence and structure.

Paraoxon and parathion hydrolysis by aqueous molybdenocene dichloride (Cp2MoCl2): first reported pesticide hydrolysis by an organometallic complex

We report the first case of an organometallic complex that effectively hydrolyzes the organophosphate pesticides parathion and paraoxon. The complex is the water-soluble compound bis(eta 5-cyclopentadienyl)molybdenum(IV) dichloride (1), which hydrolyzes parathion to produce ethanol and deethyl parathion in a biphasic reaction in D2O. Rate accelerations were 130 and 10(5) at pH 7 and 3, respectively. Paraoxon is readily hydrolyzed by 1 to yield p-nitrophenol and diethyl phosphate with rate accelerations of 2300 and 27 at pH 7 and 3, respectively. Kinetic data for paraoxon hydrolysis by 1 are consistent with a process that involves intermolecular (delta S++ = -49 +/- 10 eu) hydroxide attack on the phosphate triester in which the aquated 1 serves as a coordinated Lewis acid that activates the organophosphate. Interestingly parathion hydrolysis by 1 occurs via nucleophilic attack at the alpha-carbon of the phosphorothioate pesticide that involves C-O bond cleavage. These parathion results represent one of the few cases of this type of unusual hydrolytic chemistry and the first case of an organometallic complex that accelerates organophosphate pesticide hydrolysis.

Characterization of the Azoarcus ribozyme: tight binding to guanosine and substrate by an unusually small group I ribozyme

We report novel chemical properties of the ribozyme derived from the smallest group I intron (subgroup IC3) that comes from the pre-tRNA(Ile) of the bacterium Azoarcus sp. BH72. Despite the small size of the Azoarcus ribozyme (195 nucleotides (nt)), it binds tightly to the guanosine nucleophile (Kd = 15 +/- 3 microM) and exhibits activity at high temperatures (approximately 60-70 degrees C). These features may be due to the two GA3 tetraloop interactions postulated in the intron and the high GC content of the secondary structure. The second order rate constant for the Azoarcus ribozyme, ((k(cat)/Km)S = 8.4 +/- 2.1 x 10(-5) M(-1) min(-1)) is close to that found for the related ribozyme derived from the pre-tRNA(Ile) of the cyanobacterium Anabaena PCC7120. pH dependence studies and kinetic analyses of deoxy-substituted substrates suggest that the chemical cleavage step is the rate-determining process in the Azoarcus ribozyme. This may be due to the short 3-nt guide sequence-substrate pairing present in the Azoarcus ribozyme. Finally, the Azoarcus ribozyme shares features conserved in other group I ribozymes including the pH profile, the stereospecificity for the Rp-phosphorothioate at the cleavage site and the 1000-fold decrease in cleavage rate with a deoxyribonucleoside leaving group.

Conserved thermochemistry of guanosine nucleophile binding for structurally distinct group I ribozymes

We report thermodynamic values for binding of the guanosine nucleophile to the ribozyme derived from the Anabaena group I intron, and find that they are similar to those measured previously for the structurally distinct Tetrahymena ribozyme. The free energy of binding guanosine 5'-monophosphate (pG) at 30 degrees C is similar for the two ribozymes. The delta(H)degrees' and delta(S)degrees' for pG binding to the Anabaena ribozyme--RNA substrate complex (E x S) are 3.4 +/- 4 kcal/mol and 27 +/- 10 e.u., respectively. The negligible enthalpic contribution and positive entropy change were found previously for the Tetrahymena ribozyme, and are considered remarkable for a hydrogen-bonding interaction between a nucleotide and a nucleic acid. These thermodynamic values may reflect conformational changes or water release upon pG binding that are comparable for the two ribozymes. In addition, the apparent chemical steps of the two ribozyme reactions share similar activation energies and a positive deltaS++. It now appears that such thermochemical values for guanosine binding and activation may be intrinsic properties of the group I intron catalytic center.