期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 138, 期 28, 页码 8888-8899出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.6b04345
关键词
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资金
- Winston Churchill Foundation of the United States
- Herchel Smith Scholarship
- EPSRC via Supergen consortium
- Sims Scholarship
- Engineering and Physical Sciences Research Council [EP/K002252/1, EP/L019469/1] Funding Source: researchfish
- EPSRC [EP/K002252/1, EP/L019469/1] Funding Source: UKRI
Nanostructuring and nanosizing have been widely employed to increase the rate capability in a variety of energy storage materials. While nanoprocessing is required for many materials, we show here that both the capacity and rate performance of low-temperature bronze-phase TT- and T-polymorphs of Nb2O5 are inherent properties of the bulk crystal structure. Their unique room-and-pillar NbO6/NbO7 framework structure provides a stable host for lithium intercalation; bond valence sum mapping exposes the degenerate diffusion pathways in the sites (rooms) surrounding the oxygen pillars of this complex structure. Electrochemical analysis of thick films of micrometer-sized, insulating niobia particles indicates that the capacity of the T-phase, measured over a fixed potential window, is limited only by the Ohmic drop up to at least 60C (12.1 A.g(-1)), while the higher temperature (Wadsley-Roth, crystallographic shear structure) H-phase shows high intercalation capacity (>200 mA.h.g(-1)) but only at moderate rates. High-resolution Li-6/7 solid-state nuclear magnetic resonance (NMR) spectroscopy of T-Nb2O5 revealed two distinct spin reservoirs, a small initial rigid population and a majority-component mobile distribution of lithium. Variable temperature NMR showed lithium dynamics for the majority lithium characterized by very low activation energies of 58(2)-98(1) meV. The fast rate, high density, good gravimetric capacity, excellent capacity retention, and safety features of bulk, insulating Nb2O5 synthesized in a single step at relatively low temperatures suggest that this material not only is structurally and electronically exceptional but merits consideration for a range of further applications. In addition, the realization of high rate performance without nanostructuring in a complex insulating oxide expands the field for battery material exploration beyond conventional strategies and structural motifs.
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