Insights into Li⁺, Na⁺, and K⁺ Intercalation in Lepidocrocite-Type Layered TiO₂ Structures

Abstract

A lamellar lepidocrocite-type titanate structure with ~25% Ti 4+ vacancies was recently synthesized, and it showed potential for use as an electrode in rechargeable lithium-ion batteries.In addition to lithium, we explore this material's ability to accommodate other monovalent ions with greater natural abundance (e.g. sodium and potassium) in order to develop lower-cost alternatives to lithium-ion batteries constructed from more widely available elements.Galvanostatic discharge/charge curves for the lepidocrocite material indicate that increasing the ionic radius of the monovalent ion results in a deteriorating performance of the electrode. Using first-principles electronic structure calculations, we identify the relaxed geometries of the structure for various positions of the ion in the structure. We then use these geometries to compute the energy of formations. Additionally, we determine that all ions are favorable in the structure, but interlayer positions are preferred compared to vacancy positions. We also conclude that the exchange between the interlayer and vacancy positions is a process which involves the interaction between interlayer water and surface hydroxyl groups next to the titanate layer. We observe a cooperative effect between structural water and OH groups to assist alkali-ions to move from the interlayer to the vacancy site. Thus, the as-synthesized lepidocrocite serves as a prototypical structure to investigate both the migration mechanism of ions within a confined space along with the interaction between water molecules and the titanate framework.

Wire-in-Wire TiO2/C Nanofibers Free-Standing Anodes for Li-Ion and K-Ion Batteries with Long Cycling Stability and High Capacity

“…The comparison results of this work with previous reported TiO 2 anode materials in KHCs are listed in Table S3. This work shows better cycling stability than lepidocrocite-type layered TiO 2 and MXene-derived TiO 2 / RGO [19,20]. Hierarchical TiO 2 -C micro-tubes [18] could deliver 133 mAh g −1 after 1200 cycles at 0.5 A g −1 , which showed outstanding electrochemical properties.…”

“…Making every effort to investigate, there are only three reports about TiO 2 as anodes for KIBs. Hierarchical TiO 2 -C micro-tubes [18], lepidocrocite-type layered TiO 2 [19], and MXene-derived TiO 2 /RGO [20] have been synthesized and studied as anode materials for KIBs. It is noteworthy that free-standing TiO 2 anode in K-ions battery has not been reported as we know.…”

Size‐Independent Fast Ion Intercalation in Two‐Dimensional Titania Nanosheets for Alkali‐Metal‐Ion Batteries

“…The samples coagulated with other ions showed lower hydration and possessed a more ordered structure, for which relatively higher activation energy would be encountered, resulting in deterioration in both capacity and rate performances (Figure S10). The importance of water in crystal lattices to guest ion intercalations has been very recently demonstrated, for example, in layered TiO 2 , iron phosphate, and sodium manganese oxide, mainly through enlarging channel dimensions and screening the electrostatic interactions between guest ion and host framework. For the Mg 2+ ‐coagulated sample, performance deterioration would also be encountered upon the interlayer water was extracted (Figure S11).…”

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

“…Orthorhombic lepidocrocite structured minerals have been used in K-ion batteries. Diverse host materials, such as graphite, oxides, and sulfides (MoS2, SnS2), were identified as ideal insertion frameworks [172,173]. Recently, layered honeycomb structures (K2Ni2TeO6) have been found to exhibit high stability and ionic conductivity at an operating potential of 4V in potassium bis(trifluorosulfonly)imide, as shown in Figure 13 [174].…”