Ultrafast and Stable Li‐(De)intercalation in a Large Single Crystal H‐Nb₂O₅ Anode via Optimizing the Homogeneity of Electron and Ion Transport

Abstract

Lithium-ion batteries (LIBs) have profoundly affected most aspects of human's society in recent years. [1] With wide applications of smarter electronics and electric vehicles, the fast charging/discharging capability and safety issues became the key challenges for further commercialization of LIBs. [2] However, this requirement might be hardly satisfied if the anode were still graphite-based materials, because of the safety issues of short circuits caused by lithium dendrite formation at high charge rates when near the working potential of graphite (only 0.2 V higher than Li + /Li). [3] Although insertion-type Li 4 Ti 5 O 12 (LTO) anode has an outstanding high-rate performance and a safety working potential at about 1.55 V (vs Li + /Li), it exhibits a rather low theoretical specific capacity of 175 mAh g −1 , which would severely limit the energy density of batteries. [4] Recently, the conversion and alloying anode materials with high specific capacities have been reported to promote their rate performance via introducing nano or porous structures to shorten diffusion distances. However, they still face many problems such as huge volume changes, electrolyte decomposition, low initial Coulombic efficiency and limited cycling life. [5] Notably, nano or porous materials usually exhibit enhanced rate performance but are not preferred by industry for the intrinsic shortage of volumetric energy density. [6] Thus, it is essential to explore anode materials combined with high rate performance, satisfying capacity and safety.Recently, niobium pentoxide (Nb 2 O 5 ) has drawn wide attentions and is expected as a suitable alternative anode material for its ultrafast Li storage kinetics, promising capacity and safe operating potential. [7] The Nb 2 O 5 owns various configurations under different preparation conditions, which are denoted by letters TT, T, B, M, and H. [8] Among these crystals, the T-type Nb 2 O 5 (T-Nb 2 O 5 ) has received the highest attention because it shows little structural change on intercalation (no phase transition) and high-rate behavior so called as an "intercalation pseudocapacitance" material. [9] However, its specific capacity is still below 200 mAh g −1 (1.0-3.0 V vs Li + /Li). [10] In contrast, H-type Nb 2 O 5 (H-Nb 2 O 5 ) owns specific capacity of as high as over 250 mAh g −1 (1.0-3.0 V versus Li + /Li) and a flat charge/discharge Exploring anode materials with fast, safe, and stable Li-(de)intercalation is of great significance for developing next-generation lithium-ion batteries. Monoclinic H-type niobium pentoxide possesses outstanding intrinsic fast Li-(de) intercalation kinetics, high specific capacity, and safety; however, its practical rate capability and cycling stability are still limited, ascribed to the asynchronism of phase change throughout the crystals. Herein this problem is addressed by homogenizing the electron and Li-ion conductivity surrounding the crystals. An amorphous N-doped carbon layer is introduced on the micrometer single-crystal H-Nb 2 O 5 particle to optimize...

Designing Hierarchical Porous ZnO/ZnFe2O4 Hybrid Nanofibers with Robust Core/Shell Heterostructure as Competitive Anodes for Efficient Lithium Storage

“…Interestingly, the D Li + in pure ZnO NFs is obtained as ≈24 × 10 −16 cm 2 s −1 , which is even ≈17 times higher than that of ZnO/ZFO‐10, due to its 1D single‐crystalline nature, where the aligned lattice planes can offer high‐speed channels for ions, thereby affording a faster ion diffusion kinetic. [ 46,47 ] Thus, benefiting from the synergistic effect of crosslinked ZnFe 2 O 4 NSs and single‐crystalline ZnO NFs, the ZnO/ZFO hybrid anode can be endowed with faster electrochemical reaction kinetics, leading to remarkable rate performance.…”

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

“…[162] As described earlier, coating thin amorphous N-doped carbon layer on the surface of micron-level single-crystal H-Nb 2 O 5 particles can eliminate the spatial and temporal desynchrony of Li þ (de) intercalation from local inhomogeneity, and avoid the random phase transition of H-Nb 2 O 5 crystal. [29] Except for the direct influence on the electrochemical performance of Nb-based materials, carbon-based materials are also common growth substrate for morphology design (such as carbon nanotubes, [163] carbon cloth, etc.). There are also many composite preparation methods, such as hydrothermal method, gel method, electrostatic spinning, and so on.…”

“…The 4d 1 electron (Nb 4þ ) endows Nb 12 O 29 high electrical conductivity, three orders of magnitude higher than pure Nb 5þ . [19] In addition, Nb 12 O 29 has an open crystal structure derived from an A2/m space groups, which favors a large ions diffusion coefficient. Based on the aforementioned theoretical advantages, Lin and co-workers [20] reduced Nb 2 O 5 using H 2 /Ar at high temperature to prepare Nb 12 O 29 micron particles (0.5-3 μm) for LIB.…”

“…The anisotropy of electron and ion transport is the main cause of its asynchronous phase transition and real performance degradation. [14] To alleviate this problem, Zhang and co-workers [29] coated thin amorphous N-doped carbon layer on the surface of micron single-crystal H-Nb 2 O 5 particles to prepare N-C@MSC-Nb 2 O 5 composite materials (Figure 3d-i). The thin amorphous carbon layer eliminates the spatial and temporal unsynchronization of Li þ (de) intercalation due to local inhomogeneity, effectively inhibiting the capacity attenuation by reason of the random phase transition of H-Nb 2 O 5 .…”

“…In-situ XRD of T-Nb2O5; [28] d) Synthetic procedure, e-f ) HRTEM, g) GCD, h) CV and i) chemical diffusion coefficients D Li + versus potential (vs Li + /Li) plots of H-Nb 2 O 5 . [29] a-c) Reproduced with permission. [28] Copyright 2016, Royal Society of Chemistry.…”