Mo₃Nb₁₄O₄₄: A New Li⁺ Container for High‐Performance Electrochemical Energy Storage

Abstract

To meet the application requirements of electric vehicles, tremendous efforts have so far been devoted to the development of high-performance lithium-ion batteries (LIBs) with elevated safety, large specific capacities, high energy-conversion efficiencies, fast-charging performance, and long-term cycle life. [1-6] The electrochemical properties of LIBs mainly rely on the nature of electrode materials. However, graphite, which is the most popular and commercial anode material, suffers from its unsatisfactory safety due to the probable lithium-dendrite formation when fast charged at its overly low operating potential (~0.1 V vs Li/Li +). [7] Li 4 Ti 5 O 12 , another commercial anode material, owns a safe operating potential of~1.6 V, but suffers from its overly small specific capacity (only 175 mAh g-1 theoretically). [8] Clearly, it is still very challenging to exploit practical anode materials with comprehensively good electrochemical properties (at least including both good safety and large specific capacities). Recently, intercalating Nb-based oxides, [1,9-18] such as T-Nb 2 O 5 , TiNb 2 O 7 , AlNb 11 O 29 W 5 Nb 16 O 55, and Cu 2 Nb 34 O 87 , have emerged as next-generation anode materials having both good safety and large specific capacities. The Nb 5+ /Nb 4+ and Nb 4+ /Nb 3+ redox couples in the Nb-based oxides are active in the potential range of 0.8-2.0 V, resulting in their good safety similar to Li 4 Ti 5 O 12. The two-electron transfer between Nb 5+ and Nb 3+ enables the large specific capacities (theoretically within 374-403 mAh g-1 and practically > 250 mAh g-1). Additionally, since the Nb element is heavy, the micron-sized Nb-based oxides always exhibit high tap density of >2.5 g cm-3 , much higher than that of graphite (~1.0 g cm-3) and Li 4 Ti 5 O 12 (~1.7 g cm-3) with similar particle sizes. [19] These desirable merits render the Nb-based oxides very promising for the practical application in the high-performance LIBs for electric vehicles. However, the exploited Nb-based oxide anode compounds are still very limited. Here, we exploit Mo 3 Nb 14 O 44 as a new niobium-based oxide anode compound for high-performance Li + storage. Mo 3 Nb 14 O 44 has two interesting features. First, besides the Nb-based redox couples, the Mo 6+ / Mo 5+ and Mo 5+ /Mo 4+ couples can also be active in Mo 3 Nb 14 O 44 , [11] benefiting its theoretical capacity (398 mAh g-1), which surpasses those of most Nb-based oxide anode compounds exploited. Secondly, Mo 3 Nb 14 O 44 owns an open and stable shear ReO 3 crystal structure, [20] benefiting its rate performance and cycling stability. In this work, two Mo 3 Nb 14 O 44 materials with distinct morphologies, that is, Mo 3 Nb 14 O 44 micron-sized particles (Mo 3 Nb 14 O 44-M) and Mo 3 Nb 14 O 44 nanowires (Mo 3 Nb 14 O 44-N), respectively, fabricated from the solid-state reaction and electrospinning processes (Figure 1), are demonstrated as prominent anode materials with not only safe operating potentials and large reversible capacities but also high initial coulombic efficien...

A general strategy to enhance the electrochemical activity and energy density of energy-storage materials through using sintering aids with redox activity: a case study of Mo4Nb26O77

“…In pristine Mo 4 Nb 26 O 77 at 25 °C, the characteristic peaks of Mo-3d 3/2 (236.59 eV), Mo-3d 5/2 (233.44 eV), Nb-3d 3/2 (210.49 eV) and Nb-3d 5/2 (207.71 eV) indicate that the valences of Mo and Nb are respectively +6 and +5, as expected. 33–36 After lithiation to 0.8 V, the characteristic peaks of Mo-3d 3/2 and Mo-3d 5/2 shift to lower binding energies of 232.60 and 229.45 eV, respectively, which match well with Mo 4+ . 35 Meanwhile, the complicated Nb-3d 3/2 and Nb-3d 5/2 peaks are perfectly fitted by the combination of minor Nb 4+ and major Nb 3+ .…”

“…At 25 C, three cathodic/anodic peakpairs are presented in the CV proles, which are located at 2.25/ 2.29 V originating from the Mo 5+ /Mo 6+ redox couple, 1.61/1.71 V attributed to both the Mo 4+ /Mo 5+ and Nb 4+ /Nb 5+ couples, and 1.16/1.26 V rooted in the Nb 3+ /Nb 4+ couple. [32][33][34] The cathodic/ anodic peak-pair at 1.16/1.26 V is intensive, indicating that many Nb 4+ ions are reduced to Nb 3+ ions during lithiation and that the average working potential of the Mo 4 Nb 26 O 77 submicron-sized particles is lowered, conrming the high electrochemical activity. In fact, at 0.1C, the reversible capacity of this Mo 4 Nb 26 O 77 material in the low-potential range of 1.5-0.8 V is up to 149 mA h g À1 , which surpasses those of the previously-reported niobate anode materials from solid-state reactions (Table S4 †), thus signicantly contributing to its very large reversible capacity of 366 mA h g À1 within 3.0-0.8 V. At À10 C, the positions of these three peak-pairs slightly shi to 2.17/2.28 V, 1.62/1.81 V and 1.12/1.44 V, suggesting a slightly larger polarization than that at 25 C. The CV peaks in the low potential region become weak due to the smaller capacity at À10 C, which causes the slightly higher average working potential at À10 C (Fig.…”

Shear-structured MoNb6O18 as a new anode for lithium-ion batteries

“…0 voltage ranges, the electrode exhibits the highest charge capacity of 137.6 mAh/g and retention rate of 93 % after 60 cycles between 1.0~3.0 V. The lithium storage properties of MNO also are compared with reported Nb-based and other anode electrodes (Table S1). [5,20,24,33,34] The Li-ion diffusion behavior of in MoNb 6 O 18 electrode was investigated CV measurement at the different voltage ranges at various scan speeds increased from 0.2 to 1.0 mV/s. As shown in Fig.…”

“…The propertied of the full-cell was comparable with LiMn 2 O 4 //porous MoNb 12 O 33 microspheres full cell (~170 mAh/g at 1 C after 100 cycles), [24] LiMn 2 O 4 //nanowires Mo 3 Nb 14 O 44 full cell (201 mAh/g at 0.1 C, 73 mAh/g at 5 C after 500 cycles). [33] The red-LED (Fig. 8 inset) was successfully lighted to certify the potential practicability of the full cell.…”

High-rate electrochemical lithium-ion storage through Li+ intercalation pseudocapacitance in the Pr1/3NbO3 anode

“…11 The detailed lattice constants of Pr 1/3 NbO 3 were obtained by rening the XRD spectra using a GSAS package with the graphical user interface. [12][13][14] The oxidation states of Pr, Nb and O in the Pr 1/3 NbO 3 were analyzed by PHI5000 Versaprobe X-ray photoelectron spectroscopy (XPS). Scanning transmission electron microscopy (STEM) and Z-contrast STEM images were obtained on a JEM 2100F (JEOL) and JEM-ARM 200F (JEOL), respectively.…”