ABSTRACT
The notorious issues of lithium (Li) dendrite growth and volume change hinder the practical applications of Li metal anodes. LiF as a key component of the solid electrolyte interface (SEI) governs Li+ transport and deposition, yet the formation of LiF consumes the anions (PF6-/TFSI-) in the electrolyte, preventing the stable cycling of Li anodes. Herein, fluorine (F)-doped hollow carbon (FHC) was synthesized and used to construct a composite current collector with FHC as an F-rich buffer layer for modifying the Cu foil. The F content provided by FHC not only mitigates the anion (PF6-/TFSI-) consumption but also enhances the stability of SEI. The hollow structure of FHC with abundant internal space can accommodate deposited Li to relieve the volume change during cycling. Besides, the significantly improved specific surface area of the electrode effectively reduces the local current density to achieve a homogeneous Li deposition. Due to the above cooperation, the symmetrical cell of Cu@FHC-Li||Cu@FHC-Li maintains stable cycling for more than 1800 h with a hysteresis voltage of 19 mV. In addition, full cell coupling with LiFePO4 cathode delivers excellent long-term cycling and rate performance. This work provides an effective route for developing stable Li metal anodes.
ABSTRACT
Objective@#To investigate the age related changes in cervical range of motion (CROM) and its relationship with cervical spondylosis in school students aged 12-18 in Nanyang City, to provide reference for prevention, early diagnosis and treatment evaluation of cervical spondylosis.@*Methods@#Stratified sampling was adopted in 13 counties and districts of Nanyang City and 890 students aged 12-18 were assessed for CROM using the Coda Motion Analyzer. SPSS 19.0 was used to data analyze.@*Results@#A decreasing trend was observed in CROM among boys and girls aged 12-18 years in Nanyang. For boys aged 15 and 18 years old, higher anterior flexion ( t =2.02, 2.70), posterior extension ( t =2.01, 2.81), left flexion ( t =3.51, 2.99), right flexion ( t =5.07, 2.66), sinistral ( t =2.28, 2.92) and dextral ( t =2.91,3.60) were found compared with younger age groups ( P <0.05). Similar findings were found in girls aged 15 and 18-years old [anterior flexion ( t =2.38, 2.20), posterior extension ( t =2.09,2.02), left flexion ( t =2.33, 2.55), right flexion ( t =7.34, 4.60), sinistral ( t =3.73, 2.35) and dextral ( t =2.31, 3.99, P <0.05). Except for the right flexion, the CROM of boys in was higher than that of girls at the same age group. The prevalence of cervical spondylosis showed an increasing trend (boys: χ 2 trend =13.93, girls: χ 2 trend =12.87, P <0.05). Except for 14-year-old group, the prevalence of cervical spondylosis in girls was higher than that in boys, with significant differences observed in 15 and 17-year-old groups ( χ 2=10.35, 9.64, P <0.05).@*Conclusion@#With the increase of age, the CROM of male and female students shows a downward trend in general. The prevalence of cervical spondylosis increases with the decrease of CROM. CROM measurement is conducive to the prevention, early diagnosis and treatment of juvenile cervical spondylosis.
ABSTRACT
Pseudocapacitive lithium storage is an effective way to promote the improvement of electrochemical performance for lithium ion batteries. However, the intrinsically sluggish lithium ionic diffusion and the low electronic conductivity of TiO2 limit its capability of pseudocapacitive behavior with fast surface redox reaction. In this work, TiO2 quantum dots confined in 3-dimensional carbon framework have been synthesized by a facile process of reverse microemulsion method combined with heat treatment. The obtained composites effectively combine electrochemical redox with surface pseudocapacitive, showing excellent electrochemical properties. An ultra-high discharge capacity of 370.5 mAh/g can be retained after 200 cycles at a current density of 0.1 A/g. Ultra-long life extends to 10,000 cycles with an average capacity loss of as low as 0.00314% per cycle can be obtained at a high current density of 5.0 A/g, due to the high pesudocapacitance contribution of fast surface redox reaction. Furthermore, the practice application of the obtained electrode is also investigated in a full cell with LiCoO2 as the cathode and a high capacity retention of 93.5% is maintained after 100 cycles at the current density of 0.1 A/g.
ABSTRACT
TiO2 as the promising anode material candidate of sodium-ion battery suffers from poor conductivity and slow ion diffusion rate, which severely hampers its development. Highly compacted TiO2/C microspheres without inner pores/tunnels are synthesized by a very facile one-pot rapid processing method based on novel in-situ surface-confined inter-growth mechanism. This highly compacted TiO2/C microspheres exhibit an excellent electrochemical performance of reversible Na+ storage despite with relatively large particle/aggregation size from submicrometer to micrometer. An outstanding cycling stability extending to 10,000 cycles is gained with a high retention capacity of 140.5 mAh g-1 at a current rate of 2 A g-1. An ultra-high reversible capacity of 362 mAh g-1 close to its theoretic specific capacity is obtained at a current rate of 0.05 A g-1. The successful combination of highly compacted structure with large particle size, excellent electrochemical performance as well as rapid cost-effective preparing process might provide a potential industrial approach for efficiently synthesizing electrode materials for Na ion batteries.
ABSTRACT
Poor electrochemical kinetics caused by the unstable structure for the dramatically volumetric expansion (>300%) hinders the application of silicon in rechargeable lithium ion batteries. Si@C-Ni-MOF composites with petal-like Ni-MOFs as the skeleton and Si@C nanoparticles as the active center were synthesized via facile solvothermal process. The resulting Ni-MOF-Si@C material maintains admirable stability on cycling, and its capacity remains 1545.3 mAh g-1 with a high capacity retention rate of 99.79% after 300 cycles at the current density of 200 mA g-1. The enhancement on the kinetics is obtained, attributing to the porous structure created by the petal-like Ni-MOFs and the strong interface bonding between Si@C and Ni-MOFs.
ABSTRACT
The liquid-phase epoxidation of cyclopentene (CPE) was performed in the Ti-zeolite/H2O2 catalytic system for the clean synthesis of cyclopentene oxide. Among all the Ti-zeolites (Ti-Beta, Ti-MOR, Ti-MCM-68, TS-1, TS-2, and Ti-MWW) investigated in the present study, Ti-MWW provided relatively lower CPE conversion of 13% due to the diffusion constrains but a higher CPO selectivity of 99.5%. The catalytic performance of Ti-MWW was significantly enhanced by piperidine (PI) treatment, with the CPE conversion and CPO selectivity increased to 97.8 and 99.9%, respectively. The structural rearrangement upon PI treatment converted the 3-dimensional (3D) MWW structure to a 2D lamellar one, which enlarged the interlayer space and greatly alleviated the diffusion constrains of cyclic cyclopentene. Furthermore, the newly constructed "open site" six-coordinated Ti active sites with PI as the ligand exhibited higher catalytic activity. The two factors contributed to more significant enhancement of the activity upon PI-assisted structural arrangement compared to the cases in linear alkenes.
ABSTRACT
Fe3O4@CNF anode material for Li-ion batteries (LIBs) was designed and fabricated using lyotropic cellulose acetate as the carbon nanofiber (CNF) phase and Fe(acac)3 as the Fe3O4 phase through the electrospinning approach. Because the CNFs could retard the change of Fe3O4 volume during the electrochemical cycling and improve the electrical conductivity and the introduction of Fe3O4 could offer a larger specific surface area and more mesopores to promote electrolyte penetration and Li+ diffusion, the Fe3O4@CNFs electrode showed high reversible capacities (RCs) of 773.6 and 596.5 mAh g-1 after 300 cycles and capacity residuals of 98.0 and 99.0% at high current densities 1 and 2 A g-1, respectively. This simple method to fabricate Fe3O4@CNFs composite as anode material can be widely applied to fabricate metal oxides and bio-carbon composite nanofibers for high-performance energy storage materials.
ABSTRACT
This study proposes a novel strategy for preparing Ti-Beta zeolite with nanosized crystals and incredibly stable isolated Ti4+ ions under solvent-free conditions via intensified interzeolite transformation from a commercially available Ti-MWW source. The obtained Ti-Beta exhibited unique catalytic performance in the oxidation of cyclohexene with aqueous hydrogen peroxide.
