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1.
Artigo em Inglês | MEDLINE | ID: mdl-31961644

RESUMO

As a parent compound of Li-rich electrodes, Li2MnO3 exhibits high capacity during the initial charge; however, it suffers notoriously low Coulombic efficiency due to oxygen and surface activities. Here, we successfully optimize the oxygen activities toward reversible oxygen redox reactions by intentionally introducing protons into lithium octahedral vacancies in the Li2MnO3 system with its original structural integrity maintained. Combining structural probes, theoretical calculations, and resonant inelastic X-ray scattering results, a moderate coupling between the introduced protons and lattice oxygen at the oxidized state is revealed, which stabilizes the oxygen activities during charging. Such a coupling leads to an unprecedented initial Coulombic efficiency (99.2%) with a greatly improved discharge capacity of 302 mAh g-1 in the protonated Li2MnO3 electrodes. These findings directly demonstrate an effective concept for controlling oxygen activities in Li-rich systems, which is critical for developing high-energy cathodes in batteries.

2.
Adv Mater ; 31(29): e1805889, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31148266

RESUMO

Tracing the dynamic process of Li-ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state-of-charge (SOC). An ion-exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li-ion diffusion down to the atomic level. In a model LiNi1/3 Mn1/3 Co1/3 O2 cathode, dislocation-mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion-diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion-transport kinetics is stressed.

3.
Angew Chem Int Ed Engl ; 58(23): 7673-7677, 2019 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-30938003

RESUMO

Sulfide-based superionic conductors with high ionic conductivity have been explored as candidates for solid-state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide-based superionic conductor Li4 Cu8 Ge3 S12 with superior stability was developed based on the hard/soft acid-base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10-4  S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu-Ge-S open framework that increases its stability. Meanwhile, the weak bonding between Li+ and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid-state electrolytes.

4.
J Phys Chem Lett ; 10(3): 589-594, 2019 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-30668123

RESUMO

Nickel-rich transition metal oxides are the most promising high-voltage and high-capacity cathode materials for high-energy-density lithium batteries. Improving the chemical/electrochemical stability of the cathode-electrolyte interface has been the major technical focus to enable this class of cathode materials. In this work, LiCoO2 is adopted as the model cathode material to investigate the active sites for parasitic reactions between the delithiated cathode and the nonaqueous electrolyte. Both ab initio calculations and experimental results clearly show that the partially coordinated transition metal atoms at the surface are responsible for the parasitic reactions at the cathode-electrolyte interface. This finding lays out fundamental support for rational interfacial engineering to further improve the life and safety characteristics of nickel-rich cathode materials.

5.
Nat Nanotechnol ; 14(1): 50-56, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30420761

RESUMO

The solid-electrolyte interphase (SEI) is probably the least understood component in Li-ion batteries. Considerable effort has been put into understanding its formation and electrochemistry under realistic battery conditions, but mechanistic insights have mostly been inferred indirectly. Here we show the formation of the SEI between a graphite anode and a carbonate electrolyte through combined atomic-scale microscopy and in situ and operando techniques. In particular, we weigh the graphitic anode during its initial lithiation process with an electrochemical quartz crystal microbalance, which unequivocally identifies lithium fluoride and lithium alkylcarbonates as the main chemical components at different potentials. In situ gas analysis confirms the preferential reduction of cyclic over acyclic carbonate molecules, making its reduction product the major component in the SEI. We find that SEI formation starts at graphite edge sites with dimerization of solvated Li+ intercalation between graphite layers. We also show that this lithium salt, at least in its nascent form, can be re-oxidized, despite the general belief that an SEI is electrochemically inert and its formation irreversible.

6.
Chem Commun (Camb) ; 54(87): 12341-12344, 2018 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-30324196

RESUMO

A durable high-performance anode with a unique microstructure of a hetero-structured surface layer and exsolved Fe-Cu bimetal nano-fibers is fabricated from a self-assembled dual-phase precursor consisting of a single perovskite (SP) and a Ruddlesden-Popper (RP) layered perovskite component. This work opens up new opportunities to fabricate high-performance anodes for IT-SOFCs.

7.
J Am Chem Soc ; 140(39): 12484-12492, 2018 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-30165740

RESUMO

Metal (M) oxides are one of the most interesting and widely used solids, and many of their properties can be directly correlated to the local structural ordering within basic building units (BBUs). One particular example is the high-Ni transition metal layered oxides, potential cathode materials for Li-ion batteries whose electrochemical activity is largely determined by the cationic ordering in octahedra (e.g., the BBUs in such systems). Yet to be firmly established is how the BBUs are inherited from precursors and subsequently evolve into the desired ordering during synthesis. Herein, a multimodal in situ X-ray characterization approach is employed to investigate the synthesis process in preparing LiNi0.77Mn0.13Co0.10O2 from its hydroxide counterpart, at scales varying from the long-range to local individual octahedral units. Real-time observation corroborated by first-principles calculations reveals a topotactic transformation throughout the entire process, during which the layered framework is retained; however, due to preferential oxidation of Co and Mn over Ni, significant changes happen locally within NiO6 octahedra. Specifically, oxygen loss and the associated symmetry breaking occur in NiO6; as a consequence, Ni2+ ions become highly mobile and tend to mix with Li, causing high cationic disordering upon formation of the layered oxides. Only through high-temperature heat treatment, Ni is further oxidized, thereby inducing symmetry reconstruction and, concomitantly, cationic ordering within NiO6 octahedra. Findings from this study shed light on designing high-Ni layered oxide cathodes and, more broadly, various functional materials through synthetic control of the constituent BBUs.

8.
Int J Mol Sci ; 19(8)2018 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-30072674

RESUMO

Spinal cord injury (SCI) is a severe traumatic lesion of central nervous system (CNS) with only a limited number of restorative therapeutic options. Diosgenin glucoside (DG), a major bioactive ingredient of Trillium tschonoskii Max., possesses neuroprotective effects through its antioxidant and anti-apoptotic functions. In this study, we investigated the therapeutic benefit and underlying mechanisms of DG treatment in SCI. We found that in Sprague-Dawley rats with traumatic SCI, the expressions of autophagy marker Light Chain 3 (LC3) and Beclin1 were decreased with concomitant accumulation of autophagy substrate protein p62 and ubiquitinated proteins, indicating an impaired autophagic activity. DG treatment, however, significantly attenuated p62 expression and upregulated the Rheb/mTOR signaling pathway (evidenced as Ras homolog enriched in brain) due to the downregulation of miR-155-3p. We also observed significantly less tissue injury and edema in the DG-treated group, leading to appreciable functional recovery compared to that of the control group. Overall, the observed neuroprotection afforded by DG treatment warrants further investigation on its therapeutic potential in SCI.


Assuntos
Apoptose/efeitos dos fármacos , Autofagia/efeitos dos fármacos , Diosgenina/análogos & derivados , Glucosídeos/uso terapêutico , Fármacos Neuroprotetores/uso terapêutico , Traumatismos da Medula Espinal/prevenção & controle , Animais , Diosgenina/química , Diosgenina/uso terapêutico , Glucosídeos/química , MicroRNAs/genética , Fármacos Neuroprotetores/química , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos , Medula Espinal/efeitos dos fármacos , Medula Espinal/metabolismo , Medula Espinal/patologia , Traumatismos da Medula Espinal/genética , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/patologia , Trillium/química
9.
Angew Chem Int Ed Engl ; 57(37): 12033-12036, 2018 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-30066987

RESUMO

Relative solvating power, that is, the ratio of the coordination ratios between a solvent and the reference solvent, was used to probe the quantitative structure-activity relationship of electrolyte solvents and the lithium polysulfide (LiPS) dissolution in lithium-sulfur batteries. Internally referenced diffusion-ordered nuclear magnetic resonance spectroscopy (IR-DOSY) was used to determine the diffusion coefficient and coordination ratio, from which the relative solvating power can be easily measured. The higher the relative solvating power of an ethereal solvent, the more severe will be the LiPS dissolution and the lower the coulombic efficiency of the lithium-sulfur battery. A linear relationship was established between the logarithm of relative solvating power of a solvent and the degree of LiPS dissolution, rendering relative solvating power an important parameter in choosing the electrolyte solvent for lithium-sulfur batteries.

10.
J Phys Chem Lett ; 9(17): 5100-5104, 2018 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-30130117

RESUMO

Increasing the loading of active materials by thickening the battery electrode coating can enhance the energy density of a Li-ion cell, but the trade-off is the much reduced Li+ transport kinetics. To reach the optimum energy and power density for thick electrodes, the effective chemical diffusion coefficient of Li+ ( DLi) must be maximized. However, the diffusion of Li+ inside an electrode is a complex process involving both microscopic and macroscopic processes. Fundamental understandings are needed on the rate-limiting process that governs the diffusion kinetics of Li+ to minimize the negative impact of the large electrode thickness on their electrochemical performance. In this work, lithium Ni-Mn-Co oxide (NMC) cathodes of various thicknesses ranging from 100 to 300 µm were used as a model system to study the rate-limiting diffusion process during charge/discharge. The rate-limiting diffusion coefficient of Li+ was investigated and quantified, which was correlated to the electrochemical performance degradation of thick electrodes. It is revealed here that the under-utilization of the active material was caused by the limited diffusion of Li+ inside the porous electrode, leading to a critical electrode thickness, beyond which the specific capacity was significantly reduced.

11.
Angew Chem Int Ed Engl ; 57(37): 11918-11923, 2018 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-30040187

RESUMO

Na2 FePO4 F is a promising cathode material for Na-ion batteries owing to its relatively high discharge voltage and excellent cycling performance. Now, the long- and short-range structural evolution of Na2 FePO4 F during cycling is studied by in situ high-energy X-ray diffraction (XRD), ex situ solid-state nuclear magnetic resonance (NMR), and first-principles DFT calculations. DFT calculations suggest that the intermediate phase, Na1.5 FePO4 F, adopts the space group of P21 /c, which is a subgroup (P21 /b11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na2 FePO4 F, and this space group provides a good fit to the experimental XRD and NMR results. The two crystallographically unique Na sites in the structure of Na2 FePO4 F behave differently during cycling, where the Na ions on the Na2 site are electrochemically active while those on the Na1 site are inert. This study determines the structural evolution and the electrochemical reaction mechanisms of Na2 FePO4 F in a Na-ion battery.

12.
J Phys Chem Lett ; 9(13): 3714-3719, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29901395

RESUMO

A novel methodology is reported on the use of internally referenced diffusion-ordered spectroscopy (IR-DOSY) in divulging the solution structure of lithium-ion battery electrolytes. Toluene was utilized as the internal reference for 1H-DOSY analysis due to its exceptionally low donor number and reasonable solubility in various electrolytes. With the introduction of the internal reference, the solvent coordination ratio of different species in the electrolytes can be easily determined by 1H-DOSY or 7Li-DOSY. This new technique was applied to different carbonate electrolytes, and the results were consistent with a Fourier transform infrared (FTIR) analysis. Compared to conventional vibrational spectroscopy, this IR-DOSY technique avoids the complicated deconvolution of the spectrum and allows determination of the solvent coordination ratio of different species in electrolyte systems with two or more organic solvents.

13.
Small ; 14(21): e1704523, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29667305

RESUMO

O3-type NaNi1/3 Fe1/3 Mn1/3 O2 (NaNFM) is well investigated as a promising cathode material for sodium-ion batteries (SIBs), but the cycling stability of NaNFM still needs to be improved by using novel electrolytes or optimizing their structure with the substitution of different elements sites. To enlarge the alkali-layer distance inside the layer structure of NaNFM may benefit Na+ diffusion. Herein, the effect of Ca-substitution is reported in Na sites on the structural and electrochemical properties of Na1-x Cax/2 NFM (x = 0, 0.05, 0.1). X-ray diffraction (XRD) patterns of the prepared Na1-x Cax/2 NFM samples show single α-NaFeO2 type phase with slightly increased alkali-layer distance as Ca content increases. The cycling stabilities of Ca-substituted samples are remarkably improved. The Na0.9 Ca0.05 Ni1/3 Fe1/3 Mn1/3 O2 (Na0.9 Ca0.05 NFM) cathode delivers a capacity of 116.3 mAh g-1 with capacity retention of 92% after 200 cycles at 1C rate. In operando XRD indicates a reversible structural evolution through an O3-P3-P3-O3 sequence of Na0.9 Ca0.05 NFM cathode during cycling. Compared to NaNMF, the Na0.9 Ca0.05 NFM cathode shows a wider voltage range in pure P3 phase state during the charge/discharge process and exhibits better structure recoverability after cycling. The superior cycling stability of Na0.9 Ca0.05 NFM makes it a promising material for practical applications in sodium-ion batteries.

14.
Angew Chem Int Ed Engl ; 57(11): 2879-2883, 2018 03 05.
Artigo em Inglês | MEDLINE | ID: mdl-29378088

RESUMO

Sustainable sodium-ion batteries (SSIBs) using renewable organic electrodes are promising alternatives to lithium-ion batteries for the large-scale renewable energy storage. However, the lack of high-performance anode material impedes the development of SSIBs. Herein, we report a new type of organic anode material based on azo group for SSIBs. Azobenzene-4,4'-dicarboxylic acid sodium salt is used as a model to investigate the electrochemical behaviors and reaction mechanism of azo compound. It exhibits a reversible capacity of 170 mAh g-1 at 0.2C. When current density is increased to 20C, the reversible capacities of 98 mAh g-1 can be retained for 2000 cycles, demonstrating excellent cycling stability and high rate capability. The detailed characterizations reveal that azo group acts as an electrochemical active site to reversibly bond with Na+ . The reversible redox chemistry between azo compound and Na ions offer opportunities for developing long-cycle-life and high-rate SSIBs.

15.
Nano Lett ; 18(1): 336-346, 2018 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-29240435

RESUMO

Room-temperature sodium-ion batteries have attracted increased attention for energy storage due to the natural abundance of sodium. However, it remains a huge challenge to develop versatile electrode materials with favorable properties, which requires smart structure design and good mechanistic understanding. Herein, we reported a general and scalable approach to synthesize three-dimensional (3D) titania-graphene hybrid via electrostatic-interaction-induced self-assembly. Synchrotron X-ray probe, transmission electron microscopy, and computational modeling revealed that the strong interaction between titania and graphene through comparably strong van der Waals forces not only facilitates bulk Na+ intercalation but also enhances the interfacial sodium storage. As a result, the titania-graphene hybrid exhibits exceptional long-term cycle stability up to 5000 cycles, and ultrahigh rate capability up to 20 C for sodium storage. Furthermore, density function theory calculation indicated that the interfacial Li+, K+, Mg2+, and Al3+ storage can be enhanced as well. The proposed general strategy opens up new avenues to create versatile materials for advanced battery systems.

16.
Biomed Pharmacother ; 98: 516-522, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29287199

RESUMO

During the expansion of aging population, the study correlated with brain aging is one of the important research topics. Developing novel and effective strategies for delaying brain aging is highly desired. Brain aging is characteristics of impaired cognitive capacity due to dysfunctional autophagy regulated by Rheb-mTOR signal pathway in hippocampal tissues. In the present study, we have established a rat model with brain aging through subcutaneous injection of D-galactose (D-gal). Upon the intervention of Trillium tschonoskii Maxim (TTM) saponin, one of bioactive components from local natural herbs in China, the learning and memory capacity of D-gal-induced aging rats was evaluated through Morris water maze test, and the regulation of Rheb-mTOR signal pathway and functional status of autophagy in hippocampal tissues of D-gal-induced aging rats was explored by Western blot. TTM saponin revealed an obvious function to improve learning and memory capacity of D-gal-induced aging rats through up-regulating Rheb and down-regulating mTOR, thereby rescuing dysfunctional autophagy to execute anti-aging role. Meanwhile, this study confirmed the function of TTM saponin for preventing and treating brain aging, and provided a reference for the development and utilization of natural products in health promotion and aging-associated disease treatment.


Assuntos
Envelhecimento/efeitos dos fármacos , Autofagia/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Proteína Enriquecida em Homólogo de Ras do Encéfalo/metabolismo , Saponinas/farmacologia , Serina-Treonina Quinases TOR/metabolismo , Trillium/química , Envelhecimento/metabolismo , Animais , China , Galactose/farmacologia , Hipocampo/metabolismo , Memória/efeitos dos fármacos , Plantas Medicinais/química , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos
17.
ACS Appl Mater Interfaces ; 9(51): 44542-44549, 2017 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-29211441

RESUMO

Current developments of electrolyte additives to stabilize electrode-electrolyte interface in lithium-ion batteries highly rely on a trial-and-error search, which involves repetitive testing and intensive amount of resources. The lack of understandings on the fundamental protection mechanisms of the additives significantly increases the difficulty for the transformational development of new additives. In this study, we investigated two types of individual protection routes to build a robust cathode-electrolyte interphase at high potentials: (i) a direct reduction in the catalytic decomposition of the electrolyte solvent; and (ii) formation of a "corrosion inhibitor film" that prevents severely attack and passivation from protons that generated from the solvent oxidation, even the decomposition of solvent cannot be mitigated. Effect of two exemplary electrolyte additives, lithium difluoro(oxalato)borate (LiDFOB) and 3-hexylthiophene (3HT), on LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode were investigated to validate our hypothesis. It is demonstrated that understandings of both electrolyte additives and solvent are essential and careful balance between the cathode protection mechanism of additives and their side effects is critical to obtain optimum results. More importantly, this study opens up new directions of rational design of functional electrolyte additives for the next-generation high-energy-density lithium-ion chemistries.

18.
ACS Appl Mater Interfaces ; 9(50): 43632-43639, 2017 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-29164850

RESUMO

The development of highly reversible multielectron reaction per redox center in sodium super ionic conductor-structured cathode materials is desired to improve the energy density of sodium-ion batteries. Here, we investigated more than one-electron storage of Na in Na3VCr(PO4)3. Combining a series of advanced characterization techniques such as ex situ 51V solid-state nuclear magnetic resonance, X-ray absorption near-edge structure, and in situ X-ray diffraction, we reveal that V3+/V4+ and V4+/V5+ redox couples in the materials can be accessed, leading to a 1.5-electron reaction. It is also found that a light change on the local electronic and structural states or phase change could be observed after the first cycle, resulting in the fast capacity fade at room temperature. We also showed that the irreversibility of the phase changes could be largely suppressed at low temperature, thus leading to a much improved electrochemical performance.

19.
Nano Lett ; 17(10): 6018-6026, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28771015

RESUMO

Because of their enhanced kinetic properties, nanocrystallites have received much attention as potential electrode materials for energy storage. However, because of the large specific surface areas of nanocrystallites, they usually suffer from decreased energy density, cycling stability, and effective electrode capacity. In this work, we report a size-dependent excess capacity beyond theoretical value (170 mA h g-1) by introducing extra lithium storage at the reconstructed surface in nanosized LiFePO4 (LFP) cathode materials (186 and 207 mA h g-1 in samples with mean particle sizes of 83 and 42 nm, respectively). Moreover, this LFP composite also shows excellent cycling stability and high rate performance. Our multimodal experimental characterizations and ab initio calculations reveal that the surface extra lithium storage is mainly attributed to the charge passivation of Fe by the surface C-O-Fe bonds, which can enhance binding energy for surface lithium by compensating surface Fe truncated symmetry to create two types of extra positions for Li-ion storage at the reconstructed surfaces. Such surface reconstruction nanotechnology for excess Li-ion storage makes full use of the large specific surface area of the nanocrystallites, which can maintain the fast Li-ion transport and greatly enhance the capacity. This discovery and nanotechnology can be used for the design of high-capacity and efficient lithium ion batteries.

20.
Adv Mater ; 29(39)2017 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-28841754

RESUMO

Nickel-rich layered transition metal oxides, LiNi1-x (MnCo)x O2 (1-x ≥ 0.5), are appealing candidates for cathodes in next-generation lithium-ion batteries (LIBs) for electric vehicles and other large-scale applications, due to their high capacity and low cost. However, synthetic control of the structural ordering in such a complex quaternary system has been a great challenge, especially in the presence of high Ni content. Herein, synthesis reactions for preparing layered LiNi0.7 Mn0.15 Co0.15 O2 (NMC71515) by solid-state methods are investigated through a combination of time-resolved in situ high-energy X-ray diffraction and absorption spectroscopy measurements. The real-time observation reveals a strong temperature dependence of the kinetics of cationic ordering in NMC71515 as a result of thermal-driven oxidation of transition metals and lithium/oxygen loss that concomitantly occur during heat treatment. Through synthetic control of the kinetic reaction pathway, a layered NMC71515 with low cationic disordering and a high reversible capacity is prepared in air. The findings may help to pave the way for designing high-Ni layered oxide cathodes for LIBs.

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