Investigation of Titanate Family of Anode Materials for Li-Ion Batteries: Three Case Studies

Abstract

Lithium-ion batteries (LiBs) have been at the forefront of energy storage research since the early 80s. Lately, its ubiquitous overuse in portable electronics and rising cost has paved way for research on earth-abundant sodium ion batteries (SiBs), whereby finding new redox active materials have become imperative. In designing robust and safe batteries, anode plays a key role. Apart from graphitic carbons, myriad of mid-range voltages can be accessed by using Ti4+/Ti3+ redox couple in different Ti-based compounds. This is due to their diversity in structural framework and chemically dependent ionicity of the Ti-O bond. In this spirit, several titanates class of negative insertion materials have been reported. The current work focuses on three such titanate systems. (1) First, energy-savvy solvothermal synthesis of various ALi2Ti6O14 (A= Sr, Ba, 2Na) family of compounds will be described. Using either solution combustion and/or ultrasonic sonochemical techniques, these titanates have been prepared by annealing at 700-900 C for short duration of 1-2 h. They yield 100-300 nm homogeneous nanoparticles. Synchrotron XRD analysis confirmed the formation of phase-pure target products. We have employed bond valence site energy (BVSE) analysis to gauge the Li+ diffusion pathways in these titanates showing 0.1-0.6 eV one-dimensional migration pathways. They deliver reversible capacity in the range of 120-160 mAh/g (at C/10 rate, 25 C) with multi-step voltage profiles involving average Ti4+/Ti3+ redox plateaus around 1.3-1.45 V (vs. Li/Li+). The synthesis, structure, Li+ diffusion mechanism and electrochemical performance of the ALi2Ti6O14 (A= Sr, Ba, 2Na) family will be elaborated [1-4]. (2) Following, we have studied ATi3O7 (A = 2Na, Pb) layered titanates for Li- and Na-ion insertion at low voltage of 0.1-0.5 V involving a mixture of allowing and conversion reaction mechanism. They deliver low voltage operation with potential high capacity over 120-150 mAh/g. Using suites of experimental tools and first-principle analysis, we will describe the impediments and potential to use these titanates in Li-ion batteries [5]. (3) Next, scanning through several known minerals structure database, we have identified few open framework minerals containing Ti and Si. We have identified one novel anode for Li-ion batteries showing moderate capacity with extremely fast charging (patent in preparation). The solvothermal synthesis, tetragonal structure and electrochemical performance of this novel anode will be showcased. (4) Eventually, we will demonstrate the fabrication of micro-batteries using thin-films of above-mentioned titanates grown on stainless steel substrates. After optimizing several parameters, pulsed laser deposition (PLD) method was used to grown 100-300 nm thin films of titanates. They were used to assemble thin-film micro-batteries and their electrochemical performance was tested in half-cell architecture. The PLD growth and resulting performance of thin film batteries will be explained [6-8].