Autocombustion Synthesis of Nanostructured Na₂Ti₆O₁₃Negative Insertion Material for Na-Ion Batteries: Electrochemical and Diffusion Mechanism

Abstract

In the pursuit to develop practical sodium-ion batteries, safe negative insertion (anode) materials are essential. Recently, Na2Ti6O13 has been unveiled by conventional solid-state synthesis as a 0.85 V anode with 1-dimensional Na+ diffusion pathways. Here, an energy-savvy autocombustion synthesis has been successfully implemented to produce the target compound Na2Ti6O13 by restricting the annealing duration within 2 h. This drastic reduction in heat-treatment time involves minimal grain-growth hence forming homogeneous nanostructured particles (∼100 nm). It benchmarks the shortest synthesis of Ti-based anodes for sodium-ion batteries. The current work describes various aspects of autocombustion route. The as-prepared compound delivers near theoretical capacity (ca. 40 mAh g−1) involving a Ti4+/Ti3+ redox potential centered at 0.83 V (vs. Na/Na+) with excellent reversibility. Using both experiment and bond valence site energy (BVSE) modeling, the electrochemical, Na+ diffusion pathways and corresponding energy barriers have been explained.

Sonochemically synthesized Na2Ti6O13 nanorod: an efficient electrode material for Na-ion battery

“…The pattern showed a good match with CHI 2 = 25% and the details on the lattice and other parameter are shown in table 1. These values showed good match with the values reported earlier [10,14].…”

“…In the 2nd cycle, this potential value decreases to 0.85 V and this value remains constant up to 50th cycle. Similar potential value for redox activity has been reported previously [10,14,16]. The discharge capacity value is determined as 110 mAh g -1 for 1st cycle, shown in voltage-capacity profile of figure 4a.…”

“…The TEM image of these nanorods are shown in figure 3c, the particle size obtained from TEM analysis confirms the SEM analysis. Previously, nanorods have been prepared by solution-combustion [14] and soft-template methods [10], these have similar morphology as reported in this article. This nano-scale morphology accelerates Na-ion diffusion effecting excellent electrochemical performance.…”

“…This nanorod showed excellent retention property offering reversible capacity of 80% of the theoretical capacity. The NTO prepared by solution-combustion method [14] also showed similar electrochemical properties. Even NTO thin films in the nano-range obtained by pulse laser deposition technique have shown excellent results for Na-ion micro battery system [34].…”

“…These types of anode materials are economic, eco-friendly with a full cell operation voltage of 2.5 to 3.5 V when coupled with high voltage cathode materials [11][12][13]. In this respect, particularly Na-Ti-O-based anode materials showed plateau in the voltage range of 0.4-1 V with capacity ranging from 50 to 200 mAh g -1 [14,15]. In the quest for safe anode material, material should be chosen with moderate Na ?…”