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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - High-Rate Intercalation without Nanostructuring in Metastable Nb2O5 Bronze Phases
AU - Griffith, Kent J.
AU - Forse, Alexander C.
AU - Griffin, John M.
AU - Grey, Clare P.
PY - 2016/7/20
Y1 - 2016/7/20
N2 - 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.
AB - 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.
KW - SOLID-STATE NMR
KW - ELECTROCHEMICAL ENERGY-STORAGE
KW - LI ION DYNAMICS
KW - NIOBIUM PENTOXIDE
KW - LITHIUM INTERCALATION
KW - CRYSTAL-STRUCTURE
KW - CHARGE STORAGE
KW - ANODE MATERIAL
KW - PARTICLE-SIZE
KW - HIGH-POWER
U2 - 10.1021/jacs.6b04345
DO - 10.1021/jacs.6b04345
M3 - Journal article
VL - 138
SP - 8888
EP - 8899
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 28
ER -