Effects of Phase Change and Cu Doping on the Li Storage Properties of Rutile TiO₂

Abstract

The crystal structure and Li storage properties of Cu-doped rutile TiO2 after a phase change caused by lithiation were investigated for the first time. Structural analysis results confirmed that undoped rutile TiO2 was transformed to a disordered layered rock-salt LixTiO2 structure with a small volume expansion of only 1 % when cycled in a potential range of 1.0−3.0 V vs. Li + /Li. A substitutional solid solution of Cu 2+ was formed in layered LixTiO2. The Cu doping increased both the interlayer distance and electronic conductivity of the layered LixTiO2. As an Li-ion battery anode, a Cu-doped TiO2 electrode exhibited a long cycle life, maintaining a reversible capacity of 120 mAh g −1 over 10000 cycles at 5C and an excellent rate capability of 108 mAh g −1 at 50C. Furthermore, this electrode could also be potentially used as a Na storage material. These attractive properties demonstrate high applicability of Cu-doped rutile TiO2 as a novel anode material.

Room-Temperature Preparation of All-Solid-State Lithium Batteries Using TiO2 Anodes and Oxide Electrolytes

“…We have recently developed rutile-type TiO 2 as high-performance anode materials for Li-ion batteries and Na-ion batteries using liquid electrolytes. In particular, it has been revealed that the impurity element doping into TiO 2 could remarkably enhance the anode performances. − We confirmed that doping has mainly two important effects: the enhancement in electronic conductivity and the expansion of the Li-ion diffusion path. It is expected that the material strategy of the impurity-doped TiO 2 anodes will be useful not only for liquid-type batteries but also for solid-type batteries.…”

“…In the initial charge curves, there are two potential plateaus at around 1.5 and 1.2 V vs Li + /Li. In the recent studies containing our works, the charge–discharge reaction mechanism of rutile TiO 2 electrodes has been clarified. ,− The first plateau at 1.5 V can be ascribed to a reversible phase change of rutile TiO 2 ( P 4 2 / mnm ) to monoclinic distorted rutile Li x TiO 2 ( P 2/ m ). The second plateau at 1.2 V can be attributed to an irreversible phase change from the distorted rutile Li x TiO 2 to monoclinic distorted Li x TiO 2 ( P 2/ m ) with a layered rock-salt structure (α-NaFeO 2 -type).…”

“…The second plateau at 1.2 V can be attributed to an irreversible phase change from the distorted rutile Li x TiO 2 to monoclinic distorted Li x TiO 2 ( P 2/ m ) with a layered rock-salt structure (α-NaFeO 2 -type). This layered rock-salt-type structure exists stably once it is formed and maintains this structure even during charge–discharge reactions (Li x TiO 2 ⇄ TiO 2 + x Li + + x e – ). , In addition to this, the authors have revealed that an impurity element was doped into the layered rock-salt TiO 2 to enhance its anode performances . Consequently, in this study, the crystal phases of Nb-doped TiO 2 and Ta-doped TiO 2 electrodes were investigated by XRD analysis.…”

“…This layered rock-salt-type structure exists stably once it is formed and maintains this structure even during charge−discharge reactions (Li x TiO 2 ⇄ TiO 2 + xLi + + xe − ). 10,22 In addition to this, the authors have revealed that an impurity element was doped into the layered rock-salt TiO 2 to enhance its anode performances. 10 Consequently, in this study, the crystal phases of Nb-doped TiO 2 and Ta-doped TiO 2 electrodes were investigated by XRD analysis.…”

“…10,22 In addition to this, the authors have revealed that an impurity element was doped into the layered rock-salt TiO 2 to enhance its anode performances. 10 Consequently, in this study, the crystal phases of Nb-doped TiO 2 and Ta-doped TiO 2 electrodes were investigated by XRD analysis. Figure 3a represents XRD patterns of the TiO 2 electrodes at the delithiation states after 10 cycles.…”