Anodized Ti₃SiC₂ As a Potential Anode Material for Li-Ion Microbatteries

To date, Li-ion microbatteries (µLIBs) are the most in demand storage systems for many microelectronic devices due to their high energy densities and cycling performances 1 . To enhance their performances beyond the current state of the art, there is an ongoing search to find alternative electrode materials. Recently, the synthesis and electrochemical performance of a new anode material based on MXene 2-4 , which are fabricated by chemical etching of A element from MAX phases 5 (Mn+1AXn: where n = 1, 2, or 3; M is an early transition metal; A is an A-group element; and the X is carbon and/or nitrogen), has been reported. In this work, a fully dense Ti 3 SiC 2 was electrochemically anodized in fluoride containing aqueous electrolyte to produce a thin oxide film based on titania, some silica and carbon. The anodization takes place in a two electrode electrochemical cell in the presence of aqueous electrolyte, 1 M NaOH, 1 M H 3 PO 4 , containing 0.1 v/v HF at an applied potential of 10 and 60 V for 3 h. Fig 1. a and b, shows the SEM image of Ti 3 SiC 2 anodized (A-312)at potential of 10 and 60 V, respectively. The morphology and thickness of the porous film formed by the anodization is dependent on the competition between electrochemical oxide formation and chemical dissolution which is strongly affected by the applied potential. At lower applied potential the oxide layer adopt a layered morphology which might due to the selective etching of one of its elements. When the anodizing potential is 60 V, the oxide formation is a dominant process leading to formation of pores. Fig. 1 SEM images of anodized Ti 3 SiC 2 for 3 h at potential of 10 (a) and 60 V (b). Fig. 2a shows the cyclic voltammgram curves obtained for pristine and Ti 3 SiC 2 anodized at 10 and 60 V, recorded at a scan rate of 1 mV.s -1 between 1 – 3 V vs Li/Li + . Unlike the pristine sample, the A-312 exhibits the presence of single cathodic and anodic peaks at 1.67 and 2.17 V vs Li/Li + corresponding to the insertion and extraction of Li + in/from anatase titania 6 . The cycle life performance tests were performed in two electrode Swagelok cell. The half-cells were assembled by using A-312 as a working electrode, Li foil as a counter electrode, and a Whatman glass microfiber soaked in 1 M LiPF 6 in EC:DEC electrolyte as separator. The cell was cycled at 200, 300, 500 A.cm -2 in a potential window of 1 – 3 V vs Li/Li + . It delivers a specific capacity of 460, 350, 380 and mAh.cm -2 after 1 st , 2 nd , and 140 th cycles, respectively, Fig2b. The cycle life performance shows a good capacity recovery after being cycled at faster rates. Furthermore, the capacity values are much higher than that reported for amorphous titania nanotubes 7 , and comparable to that for self-supported titania nanotubes fabricated by Wei and co-workers 8 . Fig. 2 (a) CVs of pristine material and Ti 3 SiC 2 anodized at 10 and 60 V. (b) Cycling performance of Ti 3 SiC 2 anodized at 60 V at various current density. Reference 1. Ellis, B. L.; Knauth, P.; Djenizian, T., Three-Dimensional Self-Supported Metal Oxides for Advanced Energy Storage. Adv. Mater. 2014, 26 (21), 3368-3397. 2. Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23 (37), 4248-4253. 3. Come, J.; Naguib, M.; Rozier, P.; Barsoum, M.; Gogotsi, Y.; Taberna, P.-L.; Morcrette, M.; Simon, P., A Non-Aqueous Asymmetric Cell with a Ti2C-Based Two-Dimensional Negative Electrode. J. Electrochem. Soc. 2012, 159 (8), A1368-A1373. 4. Naguib, M.; Halim, J.; Lu, J.; Cook, K. M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W., New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-ion Batteries. J. Am. Chem. Soc. 2013, 135 (43), 15966-15969. 5. Barsoum, M. W.; El-Raghy, T., The MAX Phases: Unique New Carbide and Nitride Materials-Ternary Ceramics Turn out to Be Surprisingly Soft and Machinable, yet Also Heat-Tolerant, Strong and Lightweight. Am. Sci. 2001, 89 (4), 334-343. 6. Kavan, L.; Grätzel, M.; Rathouský, J.; Zukalb, A., Nanocrystalline TiO2 (Anatase) Electrodes: Surface Morphology, Adsorption, and Electrochemical Properties. J. Electrochem. Soc. 1996, 143 (2), 394-400. 7. Ortiz, G. F.; Hanzu, I.; Djenizian, T.; Lavela, P.; Tirado, J. L.; Knauth, P., Alternative Li-ion Battery Electrode based on Self-Organized Titania Nanotubes. Chem. Mater. 2009, 21 (1), 63-67. 8. Wei, W.; Oltean, G.; Tai, C.-W.; Edstrom, K.; Bjorefors, F.; Nyholm, L., High Energy and Power Density TiO2 Nanotube Electrodes for 3D Li-ion Microbatteries. J. Mater. Chem. A 2013, 1 (28), 8160-8169. Figure 1