Nano-Structuring Strategies of Ti/Sn Oxides Produced from MAX Phases to Achieve Efficient Anodes for Alkaline Ion Batteries
Authors: Gentile Antonio , Vallana Nicholas , Ostroman Irene , Ferrara Chiara , Ruffo Riccardo , Marchionna Stefano 
Published: December 2024

One of the most promising technologies to support lithium-ion batteries (LIB) to follow the growing demand of electrochemical storage devices, particularly for stationary applications, are sodium-ion batteries (NIB). Despite both technologies sharing operating principles, first of all the ion rocking chair mechanism between cathode and anode, it is always difficult to find materials able to exchange ions between battery electrodes quickly and reversibly. While the use of graphite as an anode is a well-established application in LIB; for NIB, hard carbons are currently the most exploited solution, both in laboratory research and upcoming industrial products expected to hit the market in the coming years. The performance of these compounds is heavily reliant on fine control over the synthesis process and the nature of carbonaceous precursors.

Over the years, as materials generations change, the anodic side of LIB has also been under study to increase volumetric capacity beyond that of graphite, as well as to improve device safety by reducing the flammability of constituents [1].

Another way to develop high-performance LIB and NIB anodes is to exploit the conversion/alloying processes that some compounds/elements exhibit with lithium and sodium. This approach has always been less promising due to strong irreversible capacity lost cycle by cycle due to the poor stability of the materials and the strong volumetric expansions involved. To minimize these phenomena, it is essential to push the grain size of electro-chemically active compounds to the nanometer scale. The strategy used in this work to easily produce nano-structured oxides able to convert/alloy with Li/Na was based on a controlled thermal treatment in air of lamellar carbides known as MAX phases. Specifically, for the first time, powders of Ti3Al(1-x)SnxC2 MAXPhase (synthesized by Spark Plasma Sintering method) were oxidized treated at various temperatures at tested as NIB anode. Samples obtained by varying the Sn concentration and the thermal process parameters were characterized both at a chemical-physical and electrochemical level in half-cells. XRD, SEM, EDX, TEM and Raman (in operando) measurements were used to study the self-nano-structuration process of the oxides on the surface of the original MAX phase [2] and to deeply investigate the storage mechanisms involved. The structural analysis revealed the presence of mixed Ti/Sn oxides with variable composition and structure depending on the process parameters. The aim of the study was to correlate the properties of the oxidized powders with the electrochemical performances in order to maximize the final ion accumulation properties. Preliminary electrochemical tests led to current C/10 capacity values of ≈300 mAh/g (vs Li+/Li) and ≈170 mAh/g (vs Na+/Na) with both cases Coulombic Efficiency >99%.

[1] X. Ding, Q. Zhou, X. Li, and X. Xiong, “Fast-charging anodes for lithium ion batteries: progress and challenges,” Chemical Communications, vol. 60, no. 18, pp. 2472–2488, 2024, doi: 10.1039/D4CC00110A.

[2] I. Ostroman et al., “Highly Reversible Ti/Sn Oxide Nanocomposite Electrodes for Lithium Ion Batteries Obtained by Oxidation of Ti 3 Al (1‐x) Sn x C 2 Phases,” Small Methods, vol. 7, no. 10, pp. 1–15, Oct. 2023, doi: 10.1002/smtd.202300503.