Crystallographic Insight of Reduced Lattice Volume Expansion in Mesoporous Cu²⁺‐Doped TiNb₂O₇ Microspheres during Li⁺ Insertion

Abstract

TiNb2O7 represents a promising anode material for lithium‐ion batteries (LIBs), but its practical applications are currently hampered by the non‐negligible volumetric expansion and contraction during the charge/discharge process and the sluggish ion/electron kinetics. A combination technique is reported by systematically optimizing the porous and spherical morphology, crystal structure, and surface decoration of mesoporous Cu2+‐doped TiNb2O7 microspheres to enhance the electrochemical Li+ storage performance and stability simultaneously. The Cu2+ dopants preferentially replace Ti4+ in crystal lattices, which decreases the Li+ diffusion barrier and increases the electronic conductivity, as confirmed by density functional theory (DFT) calculation and demonstrated by diverse electrochemical characterizations. The successful Cu2+ doping significantly reduces the lattice expansion coefficient from 7.26% to 4.61% after Li+ insertion along the b‐axis of TiNb2O7, as visualized from in situ and ex situ XRD analysis. The optimal 5% Cu2+‐doped TiNb2O7 with surface coating of N‐doped carbon exhibits significantly enhanced specific capacity and rate and cyclic performances in both half‐ and full‐cell configurations, demonstrating an excellent electrochemical behavior for fast‐charging LIB applications.

Bulk Modification of Porous TiNb2O7 Microsphere to Achieve Superior Lithium‐Storage Properties at Low Temperature

“…Specifically, both peaks of Ti 2p and Nb 3d (Figure 2d,e) move toward higher binding energy positions after doping, indicating their chemical environment changes induced by the replacement of Ti 4+ by Cu + . [ 24 ] In the spectrum of Cu 2p (Figure 2f), a pair of peaks at 951.5 and 932.3 eV resulting from Cu 2p 1/2 and Cu 2p 3/2 of Cu + appears in terms of Cu 0.06 TNO. [ 25 ] Since the appearance of Cu 2+ would cause signals at 934.2 and 953.5 eV accompanied with satellite peaks at 942.3 and 961.9 eV, [ 26 ] while no observation of characteristic peaks in these positions verifies the absence of Cu 2+ .…”

Correlations of Precursor and Carbon Coating with Electrochemical Property of 2D Graphitic Carbon Nitride (g-C3N4) Nanosheets as High-Reversibility Cathode of Nonaqueous Al-Ion Batteries

“…Many efforts have been devoted to novel electrochemical energy storage systems to satisfy the high demands of portable power devices including batteries and supercapacitors. Li-ion batteries (LIBs) are widely used in portable devices, electric vehicles, hybrid vehicles, and electrochemical battery solutions for renewable energy. − However, the applications of LIBs are greatly hampered by the ever-increasing costs, especially for lithium and cobalt . Given this challenge, alternative multivalent-ion batteries particularly Al-ion batteries (AIBs) have attracted considerable interest. , The three-electron transfer reactions could endow the higher volumetric and gravimetric capacities (8046 and 2980 mAh·cm –3 ) for AIBs theoretically. , Depending on the electrolyte solvent, AIBs can be divided into aqueous and nonaqueous AIBs (AAIBs & NAIBs).…”

Theoretical and Experimental Study of the Structure and Electrochemical Properties of V-Doped TiNb2O7 Anode for Lithium-Ion Batteries

“…In addition, the tap density does not decrease as in the case of the carbon black addition. Depending on the dopant, an increase in electronic conductivity can be achieved by narrowing the band gap by adding the impurity bands as in the case of V 5+ doping, , or by adding unpaired electrons as in the case of Ru 4+ , Cu 2+ , , Cr 3+ , , and Tb 3+ doping, or by charge compensation as in the case of heterovalent substitution of Ti/Nb atoms with Mo 6+ , ,, W 6+ , , Al 3+ , and La 3+ ions and self-doping of Ti 1– x Nb 2+ x O 7 , (Table ). Doping with ions with a larger ionic radius, for example, Cu 2+ , , Tb 3+ , La 3+ , and Zr 4+ , , leads to an increase in the cell volume, which eliminates the limitations on lithium diffusion.…”

“…Pan et al studied the Cu 2+ doping of TiNb 2 O 7 and using DFT calculations showed that Cu 2+ primarily substitutes the Ti 4+ ions. Hsiao et al explored a site-selective TiNb 2 O 7 substitution by W 6+ and showed that the electron conductivity of Ti-substituted Ti 0.9 W 0.1 Nb 2 O 7 is higher than that of Nb-substituted TiNb 1.9 W 0.1 O 7 .…”