Superionic Lithium Intercalation through 2 × 2 nm² Columns in the Crystallographic Shear Phase Nb₁₈W₈O₆₉

Abstract

Nb18W8O69 (9Nb2O5×8WO3) is the tungsten-rich end-member of the Wadsley-Roth crystallographic shear (cs) structures within the Nb2O5-WO3 series. It has the largest block size of any known, stable Wadsley-Roth phase, comprising 5 ´ 5 units of corner-shared MO6 octahedra between the shear planes, giving rise to 2 nm ´ 2 nm blocks. Rapid lithium intercalation is observed in this new candidate battery material and 7 Li pulsed field gradient nuclear magnetic resonance spectroscopy-measured in a battery electrode for the first time at room temperature-reveals superionic lithium conductivity with Li diffusivities at 298 K predominantly between 10-10 and 10-12 m 2 •s-1. In addition to its promising rate capability, Nb18W8O69 adds a piece to the larger picture of our understanding of high-performance Wadsley-Roth complex metal oxides.

Fast lithium-ion conductivity in the ‘empty-perovskite’ n = 2 Ruddlesden–Popper-type oxysulphide Y2Ti2S2O5

“…Recently, Griffith and Grey have applied 7 Li pulsed-eldgradient nuclear-magnetic-resonance (PFG-NMR) spectroscopy to probe Li + diffusion in Nb 18 W 8 O 69 at room temperature (298 K). 19 The technique is generally not suitable for measuring diffusion in battery electrodes, since Li + mobility is too slow in most electrode materials. However, since the diffusion coefficients for Li + in Wadsley-Roth type materials are orders of magnitude greater than in many battery electrode materials, PFG-NMR spectroscopy measurements are possible.…”

“…Recently, rapid lithium mobility has been identied in a selection of niobium-based complex oxides with open framework structures, including H-and T-Nb 2 O 5 , [13][14][15] 19 High charging and discharging rates can be achieved in many of these materials even in large, micrometer-sized particles. They display low voltage vs. Li/Li + and as such, they are of interest as high-rate Li-ion anode materials.…”

“…14,17,21,29 This structural property is key to their performance in battery applications, and means the low activation barriers for Li diffusion are retained across different states of charge, leading to exceptional charging and discharging rates. 14,17,19 Computational and experimental studies have revealed that Li diffusion is very fast down the centre of the columns in W-R phases, where type I, II or III cavities are linked through corners of their constituent octahedra. However, the diffusion is slower into 'pocket'-like sites at block edges formed by the cornersharing motifs of type II and III cavities.…”

“…However, the diffusion is slower into 'pocket'-like sites at block edges formed by the cornersharing motifs of type II and III cavities. 19,29 Furthermore, Liion hopping is inhibited between blocks in W-R phases, leading to effectively 1D diffusion down the columns. 29,30 The implications are thus; whilst shear planes provide structural rigidity that is key to the high Li-ion diffusion across different states of charge, they also restrict Li-ion mobility to 1D channels and introduce sites which Li-ions are slower to transfer in and out of.…”

Optimization Design and Application of Niobium‐Based Materials in Electrochemical Energy Storage

“…This report confirmed that T-Nb 2 O 5 stores lithium mainly through intercalated pseudocapacitance (Nb 2 O 5 þ xLi þ þ xe À ⇔Li x Nb 2 O 5 ) through in situ XRD and kinetic studies. Specifically, the diffraction peaks of the crystal plane (001) and (180) are slightly periodically shifted due to the embedding Li þ in the energy storage process. Clearly, the crystal structure of T-Nb 2 O 5 will not be damaged during the Li þ embedding process and maintains good cyclic stability (retains 98% capacity after 1000 cycles).…”