Latest ArticlesThe supercapacitive properties of manganese oxides (MnOx) are strongly affected by their crystal structure. Nevertheless, the relationship between the crystal structure and supercapacitive performance of MnOx is elusive. Herein, a temperature-controlled fabrication method was developed to achieve MnO2, Mn3O4, MnO and Mn2O3 microspheres with various crystal structure as electrode materials tunable for supercapacitors. The detailed material and electrochemical characterizations revealed the structure-activity relationship of MnOx microspheres by systematically investigating the effect of valence state, specific surface area, conductivity and morphology on supercapacitive performance. Among these MnOx materials, nanoneedle-like MnO2 delivered a relatively high specific capacitance of 274.1 F/g at 1 A/g due to a high Mn valence state of +4, a large specific surface area of 113.4 m2/g and a desirable electronic conductivity of 1.73 × 10–5 S/cm. Furthermore, MnO2 presented a remarkable cycle stability with 115% capacitance retention after 10,000 cycles owing to the enhancement of wettability. This work not only provides a facile strategy to modulate MnOx crystal structure, but also offers a deep understanding of structure-dependent supercapacitive performance of MnOx.
Halide electrolytes in solid-state batteries with excellent oxidative stability and high ionic conductivity have been well reported recently. However, the high-cost rare-earth elements and long duration of high-rotation milling procure are the major obstacles. Herein, we have successfully synthesized the low cost Li2.25Zr0.75Fe0.25Cl6 electrolyte consisting of abundant elements with comparable Li-ion conductivity in a short milling duration of 4 h. Phase transition of the annealed sample was also carefully investigated. LiNi0.6Co0.2Mn0.2O2/Li2.25Zr0.75Fe0.25Cl6/Li5.5PS4.5Cl1.5/In-Li batteries using different halide electrolytes were constructed and cycled at different voltage windows. Solid-state battery using Li2.25Zr0.75Fe0.25Cl6 electrolyte obtained from long milling duration delivers higher discharge capacities and superior capacity retention than shorter milling time between 3.0 and 4.3 V. It delivers much higher discharge capacity when cycled at elevated temperature (60 ℃) and suffers fast capacity degradation when the upper cut-off voltage increases to 4.5 V at the same current density. This work provides an efficiency synthesis strategy for halide solid electrolyte and studies its applications in all-solid-state batteries in a wide temperature range.
Pyrochlore-structured polyantimonic acid (PAA) is a potential high-capacity electrode material, but its innately poor electroconductivity (~10−10 S/cm) seriously impairs its electrochemical reversibility for lithium-ion storage. Herein, we report design and synthesis of a novel V-substituted PAA (PAA-V), where V5+ are introduced to partially replace Sb5+. Owing to identical valence and close ionic radius relative to Sb5+, the V5+ cation can constitute the covalent VO6 octahedra framework without changing the pyrochlore crystal structure of PAA. As a result, the V5+-substitution is capable to modulate the electronic structure of PAA with significantly improved electrical conductivity (~10−6 S/cm for PAA-V) and meanwhile decreases the size of crystals with reduced diffusion length for Li+-ions. With varying the ratio of V5+-substitution, the PAA-V with optimized substitution molar ratio (18%) exhibits the best lithium-ion storage performance, delivering a long cycling life with high reversible capacity (731 mAh/g after 1200 cycles at 1 A/g) and outstanding rate capability (279 mAh/g at 15 A/g). More importantly, by pairing the PAA-V as anode and commercial LiFePO4 as cathode, the full cell with a limited negative/positive capacity ratio of 1.2 exhibits decent cycling stability at 1 C after 150 cycles with 85.5% capacity retention.
Separators is indispensable for the normal operation of lithium-ion batteries (LIBs). However, the widely used commercial polyolefin separators have some inherent deficiencies such as poor thermotolerance, high inflammability and inferior electrolyte wettability, which restrict their further applications of the advanced and safe batteries. Herein, we design a novel thermotolerant (a shrinkage percentage of 0% at 300 ℃) and flame retarded aerogel separator consisting of aramid nanofibers (ANFs). Because of its high porosity (86.5% ± 6.1%) and excellent electrolyte uptake (695%), the ANFs aerogel separator has an ionic conductivity of 1.04 mS/cm and a high lithium-ion transference number (0.67), which can endow LIBs with outstanding rate performance and superior cycling performance. Specifically, the ANFs aerogel separator-based batteries possess a discharge specific capacity of 102 mAh/g with a capacity retention of 90.7% and a Coulombic efficiency of 99.3% after 600 cycles at 5 C. In addition, under an operated temperature of 90 ℃, the battery with ANFs aerogel separator can still conduct the very steady charge-discharge, presenting a capacity retention of 90.1% and a Coulombic efficiency of 99.6% after 200 cycles at 3 C. Accordingly, the separator can probably serve as a potential candidate for application to advanced and safe LIBs.
Two erbium(Ⅲ) complexes [ErCl(OArAd)3][Na(THF)6] (1) and Er(OArAd)3 (2) are successfully prepared by using one variety of "hard" base ligand with large steric hindrance. The coordination geometry around the Er(Ⅲ) site changes from distorted tetrahedral to flat trigonal pyramid geometry in different solvent environment due to the removal of the coordinated chloride. Such an alternation significantly enhances the single-molecule magnet (SMM) behavior and makes the field-induced effective energy barrier (Ueff) arrive at 43(1) cm−1 for the latter. Together with theoretical calculations, this study shows that strong equatorial ligand field and high local symmetry are critical to suppress the quantum tunneling of the magnetization (QTM) and achieve high-performance erbium(Ⅲ) based SMMs.
Novel polyoxometalate (POM) Pickering interfacial catalyst (PIC) was fabricated through loading (NH4)5H6PMo4V8O40 (PMo4V8) on both alkyl and alkyl-amino groups functionalized silica nanoparticles. PMo4V8/SiO2(C8/C8NH2 with molar ratio as 1:1) PIC system provided a new catalytic model for aerobic conversion of 5-hydroxymethylfurfural (5-HMF), as well as its recovery and product separation in H2O/methyl isobutyl ketone (MIBK) biphase reaction. Balancing the ratio of PMo4V8, C8 and C8NH2 gave rise to variety in hydrophilicity and hydrophobicity for PMo4V8/SiO2(C8/C8NH2), which enhanced the transformation of 5-HMF to 2, 5-diformylfuran (DFF) in H2O/MIBK with 73.7% yield at 81.8% conversion than in H2O or MIBK single phase.
The discovery of new perovskite compounds under high pressure mainly focuses on the ABO3 compositions and the compositions highly deviated from ABO3 are less explored. Here we demonstrate that the La6Sr3Si6O24 silicate composition can be stabilized as a hexagonal perovskite-related structure with isolated tetrahedra anions under high pressure of 6 GPa. The compound adopts 9-layer shifted hexagonal perovskite-like structure with both B-cation and oxygen deficiencies and contains pseudo-cubic (c′) (La/Sr)O2 layers and hexagonal (h) (La/Sr)O3 layers stacked according to (c′hh)3 sequence. This structure features both B-cation vacancy ordering between the two consecutive hexagonal layers and oxygen vacancy ordering in c′-(La/Sr)O2 layers, resulting in isolated tetrahedral SiO4 anions and ionic conduction behavior. This work demonstrates the practicability of accessing new perovskite-related functional materials from the compositions highly deviated from ABO3 under high pressure.
Coating inorganic ceramic particles on commercial polyolefin separators has been considered as an effective strategy to improve thermostability of separator. However, the introduction of the coating layer could induce pore blockage on the surface of the polyolefin separator. Herein, a ceramic composite layer that consists of alumina nanoparticles (n-Al2O3) and halloysite nanotubes (HNTs) is designed to modify the polyethylene (PE) separator (the modified separator is denoted as AH-PE). The HNTs with hollow nanotubular structure construct a light skeleton and provide fast ion transport channels while Al2O3 particles function as heat-resistant fillers to inhibit the shrinkage of the separator at elevated temperatures. The total thickness of AH-PE separator is only 14 µm. Consequently, the mass increment of AH-PE separator decreases from 5 g/m2 to 3.5 g/m2, and the Gurley value reduces by 23%, compared with Al2O3 coated PE separator (A-PE). Due to the synergistic effects of Al2O3 and HNTs, AH-PE separator exhibits highly improved thermal stability (almost no shrinkage at 170 ℃ for 30 min), high Li+ transference number (up to 0.47), and long cycle life of 450 h for Li|Li cells. Moreover, the LiFePO4/Li cells assembled with AH-PE separators demonstrate improved rate capability and safety performance.
Benzimidazoles are very important chemical materials in the pharmaceutical industry, and the most common synthetic route is cyclization of o-phenylenediamine with carbon sources, in which utilization of inexpensive and abundant CO2 as C1 source is very impressive. Porous aromatic frameworks (PAFs) with highly desired skeletons have attracted great attentions in gas capture and catalysis. Herein, B-based PAF-165 and PAF-166 are designed and synthesized via Friedel-Crafts alkylation reaction, which present high surface areas as well as high stability. Benefiting from the abundant electron-deficient B centers, both PAFs exhibit excellent selective CO2 adsorption abilities. The presence of sterically hindered B units in PAFs can act as Lewis acid active sites for the frustrated Lewis pairs (FLPs) in situ formation with o-phenylenediamine, thus promoting the synthesis of benzimidazole. The optimal reaction conditions for o-phenylenediamine cyclization with PAF catalysts are explored, and the reaction mechanism is also proposed. This work provides feasible ideas for incorporating FLPs within porous materials as reusable heterogeneous catalysts for CO2 capture and conversion.
The growth of dendrites in the lithium (Li) metal anode hinders the commercialization of lithium metal batteries (LMBs). Electrolyte additives have proved to be an effective way to solve the problem of dendrites and improve the coulombic efficiency. Herein, we propose a strategy of using l-tyrosine (l-Tyr) as an additive to protect the lithium metal anode in situ, where l-Tyr can be electropolymerized in situ to form an ordered array of nanosheets on the surface of the lithium metal anode to uniformly deposit lithium ions. At the same time, the addition of l-Tyr changed the structure of the solvent in the electrolyte, because the carboxyl group on l-Tyr make DME form hydrogen bonds easily. Besides, the reduction of free DME makes more TFSI− involved in the formation of the SEI film on the electrode surface, which increases the proportion of LiF in the SEI film. With 2 wt% l-Tyr, Li||Li symmetric cells superior cycle stability in ether electrolytes, Li|Cu cells y improved stability up to 200 cycles with an average CE of 93.1% in ether electrolytes and Li||Li4Ti5O12 (LTO) demonstrated an excellent cycling capabilitie with 119 mAh/g capacity retention by the 5000th cycle.
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