“Nano‐Pearl‐String” TiNb₂O₇ as Anodes for Rechargeable Lithium Batteries

Abstract

Even though signifi cant enhancement of secondary lithium batteries has been achieved in the last decades, it remains a challenge to develop safe batteries for electric/hybrid vehicles with high energy and power density at lower cost. [1][2][3] As far as the anode is concerned, graphite, still the dominant anode material in commercial batteries, suffers from low kinetics at high power. [ 4 , 5 ] In addition, the passivating solid electrolyte interphase (SEI) formed on graphite in the initial charge due to the electrolyte decomposition, consumes a signifi cant amount of lithium irreversibly. The fact that the potential for lithium intercalation in graphite is close to metallic lithium is favorable for achieving a high voltage of the battery but also leads to the possibility of lithium plating during fast charge. Thus, lithium dendrite formation has to be concerned with which is an enormous safety hurdle for application in large electric vehicles. To avoid lithium plating, the anode charging potential must be less negative.In this regard, Li 4 Ti 5 O 12 appears to be an attractive alternative owing to phase thermodynamics structure and chemical stability. However, the theoretical capacity of Li 4 Ti 5 O 12 is relatively low (175 mAh/g) according to only three lithium atoms being insertable into the spinel structure at 1.5 V. [ 6-, 10 ] Recently, Goodenough et al. proposed TiNb 2 O 7 as a competitor for Li 4 Ti 5 O 12 with a higher capacity and an operating voltage range in which SEI formation does not occur. [ 1 ] TiNb 2 O 7 has a layered monoclinic structure in the space group C2/m, in which Ti 4 + and Nb 5 + both occupy octahedral sites sharing corners and edges. Anti-site disorder is probable owing to similar ionic radii of Ti 4 + and Nb 5 + . According to ref [12], lithium can be reversibly inserted into the ( -I10) plane of the TiNb 2 O 7 primitive cell and occupying the interstitial site there. [ 11 , 12 ] The theoretical capacity for TiNb 2 O 7 is 387.6 mAh/g according to the 5 electron transfer reaction (Ti 4 + /Ti 3 + , Nb 5 + /Nb 3 + ). Previous studies showed a reversible capacity of 280 mAh/g at 0.1C in the voltage range of 1-3 V, already a marked enhancement compared to Li 4 Ti 5 O 12 . [ 11 ] However, the development of rechargeable lithium ion batteries with TiNb 2 O 7 as an anode has been limited due to its low electronic conductivity and ionic conductivity, [ 12 ] which restricts the electrochemical kinetics. Ti doping (through Nb substitution, Ti Nb ′ ) and carbon coating improved the composite electronic conductivity, such that a reversible capacity of ∼ 150 mAh/g was achieved for TiNb 2 O 7 at a 2C rate. [ 11 ] It has been well demonstrated that nanostructure plays a prominent role in lithium insertion kinetics, by facilitating transport owing to shorter or simpler diffusion paths for lithium ions. [13][14][15] Specifi cally, one-dimensional (1D) nanostructures such as nano-wires, -fi bers, -rods or -tubes are quite attractive for electrode materials due to large surface-to-volume ratio, fa...

Constructing MoO2 Porous Architectures Using Graphene Oxide Flexible Supports for Lithium Ion Battery Anodes

“…The MoO 2 /GO architectures were achieved by decomposition of the preform at around 500 °C under the atmosphere of argon. Figure 1a shows the X-ray diffraction (XRD) patterns of the GO, bulk (NH 4 20:1, 10:1, and 5:1. The XRD patterns of the GO supports show the peak around 2θ = 9.8°, indicating interlayer spacing is 0.80 nm.…”

“…[28] In the experiments of the preparation of MoO 2 /GO, 0.36 g GO dispersed in ≈50 mL water under magnetic stirring at room temperature for 48 h. 4 The MoO 2 /GO-1, MoO 2 /GO-2, and MoO 2 /GO-3 were prepared by decomposition of preform-1, preform-2, and preform-3 at 500 °C for 40 min under the atmosphere of argon, respectively. The as-prepared products were washed by water for several times and dried under vacuum at 70 °C overnight.…”

“…The strategies to develop alternative anode materials with improved capacity have been achieved for several decades. [1][2][3][4][5][6][7][8] Among them, nanoscale metal oxides, including MnO, [9] SnO 2 , [10,11] Co 3 O 4 , [12] NiO, [13] and Fe 3 O 4 , [14,15] used as anode active materials for LIBs have been paid much attention attributed to their promising theoretical capacity. However, in most cases, the capacity decays rapidly as cycled due to high electrical resistivity and mechanism failure.…”

Electrospun Conformal Li4Ti5O12/C Fibers for High‐Rate Lithium‐Ion Batteries

“…The LTO grains connect with each other along the axial direction to construct the fibers, which is similar to the previous report on electrospun TiNb 2 O 7 nanofibers. [12] Carbon is hardly detectable on the surface of the LTO fibers that were obtained by thermal treatment at 800 8C in air. In contrast, the LTO/C-2 product, obtained in a nitrogen atmosphere, is comprised of well-crystallized LTO grains and a surface carbon layer.…”

Nanostructured electrode materials for lithium-ion and sodium-ion batteries via electrospinning

“…Similar to LTO, low electronic and ionic conductivity of TiNb 2 O 7 limit the electrochemical performance. To solve these problems, Tang and co-workers [144] firstly prepared "nano-pearl-string" 1D TiNb 2 O 7 nanofibers with attached TiNb 2 O 7 nanoparticles by the electrospinning method. A solution of PVP, niobium ethoxide (Nb(OC 2 H 5 ) 5 ) and tetrabutyl orthotitanate (Ti(OC 4 H 9 ) 4 ) dissolved in a mixed solvent of ethanol and acetic acid was firstly electrospun to nanofibers.…”