Solid-state NMR study on sodium intercalation at low voltage window for Na_(3)V_(2)(PO_(4))_(3) as an anode

In-situ XRD,^(31)P NMR and ^(23)Na NMR were used to analyze the interaction behavior of Na_(3)V_(2)(PO_(4))_(3) at low voltage,and then a new intercalation model was proposed.During the transition from Na_(3)V_(2)(PO_(4))_(3) to Na_(4)V_(2)(PO_(4))_(3),Na ions insert into M1,M2 and M3 sites simultaneously.Afterwards,during the transition of Na_(4)V_(2)(PO_(4))_(3)to Na_(5)V_(2)(PO_(4))_(3),Na ions mainly insert into M3 site.

Unexpected temperature dependence of^(1)H paramagnetic shift in MAS NMR of nickelocene

This work revisits the temperature dependence of^(1)H paramagnetic shift in nickelocene as a potential nuclear magnetic resonance(NMR)thermometer under fast magic angle spinning(MAS)rate.Surprisingly,an abnormal temperature dependence of^(1)H paramagnetic shift has been observed.In addition to a 1/T dependence term,a 1/T^(2)dependence term must be included to correctly describe the curvature behavior of the δ^(1)H-T correlation under fast MAS rate.

One-Pot Synthesis of Co-Based Coordination Polymer Nanowire for Li-Ion Batteries with Great Capacity and Stable Cycling Stability

Nanowire coordination polymer cobalt–terephthalonitrile(Co-BDCN) was successfully synthesized using a simple solvothermal method and applied as anode material for lithium-ion batteries(LIBs). A reversible capacity of 1132 mAh g^(-1) was retained after 100 cycles at a rate of 100 mAg^(-1), which should be one of the best LIBs performances among metal organic frameworks and coordination polymers-based anode materials at such a rate. On the basis of the comprehensive structural and morphology characterizations including fourier transform infrared spectroscopy,~1 H NMR,^(13)C NMR, and scanning electron microscopy, we demonstrated that the great electrochemical performance of the as-synthesized Co-BDCN coordination polymer can be attributed to the synergistic effect of metal centers and organic ligands, as well as the stability of the nanowire morphology during cycling.

Three-dimensional clogging structures of granular spheres near hopper orifice

The characteristic clogging structures of granular spheres blocking three-dimensional granular flow through hopper outlet are analyzed based on packing structures reconstructed using magnetic resonance imaging techniques.Spheres in clogging structures are arranged in a way with typical features of load-bearing,such as more contacting bonds close to the horizontal plane and more mutually-stabilized contact configurations than packing structures away from the orifice.The requirement of load-bearing inevitably leads to the cooperativity of clogging structures with a correlation length of several particle diameters.This correlation length being comparable with the orifice diameter suggests that a clogging structure is composed of several mutually-stabilized structural motifs to span the orifice perimeter,instead of a collection of independent individual spheres to cover the whole orifice area.Accordingly,we propose a simple geometric model to explain the unexpected linear dependence of the average size of three-dimensional clogging structures on orifice diameter.

Molecular fluorescence significantly enhanced by gold nanoparticles@zeolitic imidazolate framework-8

Noble metal nanoparticles exhibit unique surface plasmon resonance dependent optical properties.On this basis,gold nanoparticles(AuNPs)encapsulated in metal–organic frameworks(MOFs)can form AuNPs@MOFs composites to modulate the optical properties of fluorescent molecules,which is less reported.In this paper,based on the fluorescence enhancement effect of AuNPs on 2-(2-hydroxyphenyl)-1H-benzimidazole(HPBI)molecules,zeolitic imidazolate framework-8(ZIF-8)crystals with structural stability were introduced.AuNPs@ZIF-8 exhibited a significantly pronounced fluorescence enhancement of the HPBI molecules.In addition,by comparing the fluorescence characteristics of the HPBI molecules adsorbed on AuNPs@ZIF-8 and those captured in AuNPs@ZIF-8,we found that the ZIF-8 can act as a spacer layer with highly effective near-field enhancement.All our preliminary results shed light on future research on the composite structures of noble metal particles and MOFs for fluorescent probes and sensing applications.

Probing microstructure of solid-state synthesized LiCoO_(2)with MAS NMR spectroscopy

LiCoO_(2)is an important category of active cathode materials in lithium-ion batteries due to its high compacted electrode density,good thermal stability,and stable voltage platform.Recent works on LiCoO_(2)have focused on the realization of higher charging voltages to fully utilize its high theoretical capacity.However,an unambiguous atomic-level local probe is essential for the understanding of structure-function correlation.Here we employ highresolution solid-state nuclear magnetic resonance(NMR)spectroscopy to study the local atomic environments in LiCoO_(2)synthesized with three common sintering methods.While one-dimensional 7Li NMR shows distinct linewidth and subtle dependence on lithium over-stoichiometry,both 7Li and 59Co relaxation times are highly dependent on the sintering method.We prove that the two-step sintering method favors the elimination of unreacted Co3O4,thereby enabling the best discharge capacity in all-solid-state lithium batteries assembled with LiCoO_(2)/LGPS/LiIn,which is in accordance with its narrowest 7Li linewidth and the longest 7Li/59Co T1.

The study of electrochemical cycle for LiCoO_(2) by dual-mode EPR

Dual-mode electron paramagnetic resonance(EPR)spectroscopy was employed to analyze redox mechanisms in lithium cobalt oxide LiCoO_(2)(LCO)cathode material during delithiation and lithiation.It was found that the O_(3)-II could not fully convert back to the pristine O_(3) -I phase while oxygen vacancies quickly generate and accumulate during the cycling.Our study paves the way for better understanding the doping effects of different elements on LiCoO_(2) in the future.

In Situ Electron Paramagnetic Resonance Reveals Fading Mechanism of Mn-Based Prussian Blue Analogue:Accelerated Mn Dissolution Due to Charge Delocalization

Contrasting with Fe-based Prussian blue analogues(PBAs),Mn-based PBAs with higher energy density are more promising cathode materials for Na-ion batteries.However,fast capacity fading has severely impeded its practical use,which is still not well understood.To elucidate the fading mechanism,in situ and ex situ electron paramagnetic resonance are employed here.The results first demonstrate the charge delocalization of Mn2+and Mn dissolution during cycles,which are further proved to be highly related.Our work reveals the inherent shortcoming of Mn-based PBA cathodes in liquid electrolyte.

Bimetallic zeolite imidazolate framework for enhanced lithium storage boosted by the redox participation of nitrogen atoms

In this work, a bimetallic zeolitic imidazolate framework （ZIF） CoZn-ZIF was synthesized via a facile sol-vothermal approach and applied in lithiumion batteries. The as-prepared CoZn-ZIF shows a high reversible capacity of 605.8 mA b g-i at a current density of 100 mA g^-1, far beyond the performance of the corresponding monometallic Co-ZIF- 67 and Zn-ZIF-8. Ex-situ synchrotron soft X-ray absorption spectroscopy, X-ray diffraction, and electron paramagnetic resonance techniques were employed to explore the Li^storage mechanism. The superior performance of CoZn-ZIF over Co-ZIF-67 and Zn-ZIF-8 could be mainly attributed to lithiation and delithiation of nitrogen atoms, accompanied by the breakage and recoordination of metal nitrogen bond. Morever, a few metal nitrogen bonds without recoordination will lead to the amorphization of CoZn-ZIF and the formation of few nitrogen radicals.