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1.
Artigo em Inglês | MEDLINE | ID: mdl-32207203

RESUMO

Spinel LiNi0.5 Mn1.5 O4 (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd 3 ‾ m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb2 O7 counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices.

2.
Proc Natl Acad Sci U S A ; 117(6): 2815-2823, 2020 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-31996477

RESUMO

Existing lithium-ion battery technology is struggling to meet our increasing requirements for high energy density, long lifetime, and low-cost energy storage. Here, a hybrid electrode design is developed by a straightforward reengineering of commercial electrode materials, which has revolutionized the "rocking chair" mechanism by unlocking the role of anions in the electrolyte. Our proof-of-concept hybrid LiFePO4 (LFP)/graphite electrode works with a staged deintercalation/intercalation mechanism of Li+ cations and PF6 - anions in a broadened voltage range, which was thoroughly studied by ex situ X-ray diffraction, ex situ Raman spectroscopy, and operando neutron powder diffraction. Introducing graphite into the hybrid electrode accelerates its conductivity, facilitating the rapid extraction/insertion of Li+ from/into the LFP phase in 2.5 to 4.0 V. This charge/discharge process, in turn, triggers the in situ formation of the cathode/electrolyte interphase (CEI) layer, reinforcing the structural integrity of the whole electrode at high voltage. Consequently, this hybrid LFP/graphite-20% electrode displays a high capacity and long-term cycling stability over 3,500 cycles at 10 C, superior to LFP and graphite cathodes. Importantly, the broadened voltage range and high capacity of the hybrid electrode enhance its energy density, which is leveraged further in a full-cell configuration.

3.
Adv Mater ; : e1904528, 2019 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-31544298

RESUMO

The performance of rechargeable batteries is influenced by the structural and phase changes of components during cycling. Neutron powder diffraction (NPD) provides unique and useful information concerning the structure-function relation of battery components and can be used to study the changes to component phase and structure during battery cycling, known as in operando measurement studies. The development and use of NPD for in operando measurements of batteries is summarized along with detailed experimental approaches that impact the insights gained by these. A summary of the information gained concerning battery function using in operando NPD measurements is provided, including the structural and phase evolution of electrode materials and charge-carrying ion diffusion pathways through these, which are critical to the development of battery technology.

4.
Angew Chem Int Ed Engl ; 53(52): 14480-4, 2014 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-25469913

RESUMO

A stable visible-light-driven photocatalyst (λ≥450 nm) for water oxidation is reported. Rhodium substitution into the pyrochlore Y2 Ti2 O7 is demonstrated by monitoring Vegard's law evolution of the unit-cell parameters with changing rhodium content, to a maximum content of 3 % dopant. Substitution renders the solid solutions visible-light active. The overall rate of oxygen evolution is comparable to WO3 but with superior light-harvesting and surface-area-normalized turnover rates, making Y2 Ti1.94 Rh0.06 O7 an excellent candidate for use in a Z-scheme water-splitting system.

5.
Nat Mater ; 12(1): 74-80, 2013 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-23142842

RESUMO

Layered oxides are the subject of intense studies either for their properties as electrode materials for high-energy batteries or for their original physical properties due to the strong electronic correlations resulting from their unique structure. Here we present the detailed phase diagram of the layered P2-Na(x)VO(2) system determined from electrochemical intercalation/deintercalation in sodium batteries and in situ X-ray diffraction experiments. It shows that four main single-phase domains exist within the 0.5≤x≤0.9 range. During the sodium deintercalation (intercalation), they differ from one another in the sodium/vacancy ordering between the VO(2) slabs, which leads to commensurable or incommensurable superstructures. The electrochemical curve reveals that three peculiar compositions exhibit special structures for x = 1/2, 5/8 and 2/3. The detailed structural characterization of the P2-Na(1/2)VO(2) phase shows that the Na(+) ions are perfectly ordered to minimize Na(+)/Na(+) electrostatic repulsions. Within the VO(2) layers, the vanadium ions form pseudo-trimers with very short V-V distances (two at 2.581 Å and one at 2.687 Å). This original distribution leads to a peculiar magnetic behaviour with a low magnetic susceptibility and an unexpected low Curie constant. This phase also presents a first-order structural transition above room temperature accompanied by magnetic and electronic transitions. This work opens up a new research domain in the field of strongly electron-correlated materials. From the electrochemical point of view this system may be at the origin of an entire material family optimized by cationic substitutions.

6.
Inorg Chem ; 51(20): 11007-16, 2012 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-23009092

RESUMO

The electrochemical cycling in a sodium battery of the lamellar oxide NaVO(2) is reversible in the Na(x)VO(2) composition range 1/2 ≤ x ≤ 1. The complex electrochemical curve reveals the presence of several transitions taking place during deintercalation. With the help of in situ X-ray diffraction, we observed the structural transitions taking place between Na(2/3)VO(2) and Na(1/2)VO(2). The diffractograms show the presence of several monophasic domains separated by biphasic domains. All phases present a monoclinic distortion of the α-NaFeO(2) structure in the composition range 1/2 ≤ x ≤ 2/3. Moreover the presence of a superstructure is evidenced for Na(1/2)VO(2). It is the first time that an ordered structure is reported at the Na(1/2)MO(2) composition with an O'3 oxygen stacking. A thorough investigation of electrochemically obtained O'3-Na(1/2)VO(2) was performed. The structure refinement reveals the existence of a sodium/vacancy ordering, with a peculiar arrangement of the V-V distances hinting at a pairing of vanadium atoms. Our first measurements of the physical properties of O'3-Na(1/2)VO(2) show a semiconductor behavior and a complex thermal dependence of the magnetic susceptibility related to the pairing of the vanadium atoms.

7.
Risk Anal ; 29(10): 1347-54, 2009 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19572965

RESUMO

Even if most French mines are definitively closed, potential risks remain above the abandoned sites. In addition to surface instability, some mining sites may be affected by dangerous gas emissions, flooding events, or environmental impacts. Those kinds of disorders strongly influence the land-use management of the concerned areas. The present article presents the French mining historical context and identifies the major kinds of residual risks and harmful effects that may affect abandoned mine sites. The prevention policy applied on the national territory is then discussed and prospects for further developments are proposed.


Assuntos
Mineração , França , Medição de Risco
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