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

Abstract

TiNb2O7, as a promising alternative of Li4Ti5O12, exhibits giant potential as low‐temperature anode due to its higher theoretical capacity and comparable structural stability. However, the sluggish electronic conductivity still remains a challenge. Herein, bulk modification of Cu+ doping in porous TiNb2O7 microsphere is proposed via a simple one‐step solvothermal method with subsequent calcination treatment. The results show that the electronic conductivity is improved effectively due to the reduced band gap after doping, while enhanced lithium‐ion diffusion is achieved benefiting from the increased interplanar spacing. Therefore, the optimal sample of Cu0.06Ti0.94Nb2O7 exhibits a high reversible capacity of 244.4 mA h g−1 at 100 mA g−1 after 100 cycles, superior rate capability, and long‐term cycling stability at 1000 mA g−1 at room temperature. Particularly, it can also display good performance in a wide temperature range from 25 to –30 °C, including a reversible capacity of 76.6 mA h g−1 at –20 °C after 200 cycles at 200 mA g−1. Moreover, Cu0.06Ti0.94Nb2O7//LiFePO4 full cell can deliver a high reversible capacity of 177.5 mA h g−1 at 100 mA g−1. The excellent electrochemical properties at both ambient and low‐temperatures demonstrate the great potential of Cu+‐doped TiNb2O7 in energy‐storage applications.

Enhancing the Lithium Storage Performance of the Nb2O5 Anode via Synergistic Engineering of Phase and Cu Doping

“…Moreover, it is clearly observed in Figure b that the peaks for the (1 1 0) and (−4 0 5) planes of H–Cu 0.1 –Nb 2 O 5 slightly shift to a lower angle as compared with that of H–Nb 2 O 5 , indicating the expanded interplanar spacing, which can be explained by the fact that the ionic radius of Cu 2+ (72 pm) is larger than that of Nb 5+ (64 pm). Thus, the replacement of Nb 5+ by Cu 2+ would enlarge the interplanar spacing, which may facilitate the Li + insertion/extraction and fast electrochemical kinetics. , …”

“…27,58 After Cu doping, the Nb 3d peaks shift toward lower binding energies, indicating the chemical environment changes induced by the replacement of Nb 5+ by Cu 2+ . 39,59 As shown in the Cu 2p XPS spectra (Figures 2f and S8c), the two sharp peaks located at 931.6 and 951.3 eV can be indexed to Cu 2p 3/2 and Cu 2p 1/2 of Cu 2+ , while the other two peaks at 930.1 and 949.3 eV correspond to Cu 2p 3/2 and Cu 2p 1/2 of Cu + . 38 Especially, the Cu 2+ /Cu + ratio in H−Cu 0.1 −Nb 2 O 5 is close to 3.75/1.00, suggesting that copper is mainly in the form of Cu 2+ .…”

“…38 Especially, the Cu 2+ /Cu + ratio in H−Cu 0.1 −Nb 2 O 5 is close to 3.75/1.00, suggesting that copper is mainly in the form of Cu 2+ . 39,58,60,61 ), which is in inverse proportion to the square of the line slope of Z' − ω −1/2 . 68 Figure 4b shows the comparison of the slopes obtained by fitting the Z' − ω −1/2 plots, and the H−Cu 0.1 −Nb 2 O 5 electrode displays the smallest slope of 50.42, while H−Nb 2 O 5 shows the largest slope of 92.29, indicating that the Cu doping efficiently enhanced the lithium-ion diffusion coefficient of H−Nb 2 O 5 .…”

“…Thus, the replacement of Nb 5+ by Cu 2+ would enlarge the interplanar spacing, which may facilitate the Li + insertion/ extraction and fast electrochemical kinetics. 39,53 Figures 2c and S5b 55,56 The full width at half-maximum becomes broadened after Cu doping (Figure 2d), indicating a decreased bond ordered of Nb polyhedral and a more disordered crystal structure. 57 For comparison, the Raman spectra of T−Nb 2 O 5 and T−Cu 0.1 −Nb 2 O 5 are also provided in Figure S6b, which show two pairs of bands at 234/261 and 630/660 cm −1 and the additional bands at 305, 470, and 548 cm −1 in the middlewavenumber region, corresponding to the orthorhombic Nb 2 O 5 .…”

“…Heteroatom doping has been considered as an effective strategy to improve the intrinsic conductivity and electrochemical properties of electrode materials . Doping ions with different atomic radii could induce lattice distortion, change the unit cell structure, expand the lattice channels, and increase the ion diffusion coefficient, thus enhancing the conductivity and electrochemical performance of the electrode materials. − Cu exhibits excellent electronic conductivity and considerable electrochemical catalytic function because of the special electronic configuration of the Cu atom (3d 10 4s 1 ); thus, Cu doping would facilitate to generate the impurity energy band and shorten the band gap width. − Chen et al reported that the Cu-doped CoO displayed excellent rate performance and cycle life, while Chen et al also demonstrated the enhanced electron conductivity and improved cycle/rate performance of Li 4 Ti 5 O 12 –TiO 2 via Cu doping …”