Unveiling the Formation Mechanism and Phase Purity Control of Nanostructured Li₄Ti₅O₁₂ via a Hydrothermal Process

Abstract

Although numerous efforts have been devoted to the spinal Li 4 Ti 5 O 12 anode material of lithium-ion batteries (LIBs), controllable synthesis of high-purity Li 4 Ti 5 O 12 nanoparticles under hydrothermal conditions has not yet been achieved. The current work systematically investigates the relationship between phase compositions of the Li−Ti−O system with the corresponding critical conditions. By determining the phase composition using the Rietveld refinement of XRD patterns, the relationship between key hydrothermal parameters and the resultant purity of Li 4 Ti 5 O 12 is revealed, and the formation mechanism of Li 4 Ti 5 O 12 using crystalline TiO 2 nanoparticles (Evonik Aeroxide P25, Hombikat 8602, and rutile TiO 2 ) and amorphous hydrous TiO 2 spheres (AHTS) as TiO 2 precursors in an aqueous LiOH solution is demonstrated accordingly. The hydrothermal process cannot generate Li 4 Ti 5 O 12 directly, while lithium titanium oxide intermediates (LTOIs), e.g., Li 2 TiO 3 and Li 2−x H x Ti 2 O 4 (OH) 2 , are obtained upon partial lithiation of crystalline or amorphous TiO 2 in the LiOH solution, respectively. Nanostructured TiO 2 @LTOIs can be formed since the underlying phase transition follows the classic in situ crystallization mechanism, as evidenced by the successful self-template synthesis using AHTS. Li 4 Ti 5 O 12 is formed by the solid-state reaction between the TiO 2 core and the LTOI shell at elevated temperatures (∼700 °C). At optimal conditions, the molar ratio of Li/Ti in all TiO 2 @LTOIs should be greater than a stoichiometric ratio of 4:5 since the solid-state reaction is found to promote the evaporation of lithium species. The comparative studies for the lithium storage properties of our assembled half-and full-cell LIBs demonstrate that the high phase purity of Li 4 Ti 5 O 12 enhances the electrochemical performances and that the spherical morphology delivers better cyclic stability.

Microwave-assisted self-template synthesis of mesoporous anatase TiO2 spheres for non-aqueous Al-ion batteries: Textural property optimization and enhanced reversible Al3+ storage

“…Attempts have been made to reveal the underlying Al insertion/ extraction mechanism of MATS cathodes in NAIBs. Our interest was mainly directed to phase and composition evolution in MATS during the charge/discharge process [35,53,56]. Thus, we disassembled the tested NAIBs after 50 cycles at 0.5C, and two MATS-450 cathodes were collected at their charging and discharging states, respectively.…”

“…Up to now, various energy materials have been studied as such as carbon [16][17][18], transition metal oxides [19,20], sulfides [21][22][23], selenides [24,25], tellurides [26], Prussian blue analogs [27], polyanion compounds [28], covalent organic frameworks (COFs) [29], 2D carbides and nitrides (Mxenes) [30], and organic polymer [31], of which TiO 2 is particularly interesting owing to its low cost, environmental benignity, excellent corrosion resistance, and high specific capacity [32][33][34][35]. The pioneering efforts were devoted to the aqueous AIBs (AAIBs) [36].…”

High Performance Ti3+ Self-Doped Li4Ti5O12 Anode Materials Synthesized by an Electrochemical Method in Molten Salt

“…4 However, poor Li-ion diffusion coefficient (about 10 −8 ∼ 10 −13 cm 2 •s −1 ) 5,6 and electron conductivity (2.65 × 10 −7 S•cm −1 ) 7 result in its unsatisfactory rate performance at high current density. To address this intractable problem, a variety of synthesis methods for the small size Li 4 Ti 5 O 12 have been used to shorten the path of Li + diffusion, such as ball millingassisted solid phase method, 8 sol-gel method, 9 solvothermal method 10 and spray drying synthesis method. 11,12 Moreover, the recombination with high conductivity materials 13 (Graphene, etc.…”