Nanoparticles have been widely used as active materials for lithium ion batteries, as they provide shorter diffusion paths for both electrons and lithium ions transport, resulting in optimized high-rate capabilities.¹ From several possible nanomaterials, spinel lithium titanate (Li₄Ti₅O₁₂) has demonstrated extremely favourable characteristics as a promising negative electrode material for Li-ion batteries. Several different routes, such as hydrothermal synthesis² and sol-gel,³ have been widely used for preparing Li₄Ti₅O₁₂ nanoparticles. These techniques are very simple, cost-effective and usually lead to high-quality nanoparticles. However they are only suitable for fundamental research as they provide a very low yield.⁴ V. Nicolosi et al^5,6 were able to increase this yield by non-chemical, solution-phase exfoliation of layered materials in water or organic solvents upon ultrasonic irradiation. This method is usually referred as chemical or liquid phase exfoliation. Though it was initially applied for the production of monolayer, high surface area graphene, liquid phase exfoliation can be used to process any kind of two dimensional materials from a layered bulk sample.^4,5,7

In this work, the authors demonstrate that some of the principles behind liquid phase exfoliation (ultrasound irradiation and solvent stabilization) can be used as well to prepare highly stable dispersions from non-layered bulk materials, in this case spinel lithium titanate. Therefore, it is described the preparation and characterization of Li₄Ti₅O₁₂ nanoparticles via ultrasonic irradiation (37 kHz for 3 hours) in different solvents. A detailed structural characterization revealed that the obtained particles do not suffer any phase change upon processing. Moreover, the dispersions revealed to be highly stable, according to a zeta potential measurment (- 67 mV).

The obtained dispersions (in 2-propanol)were then mixed with single wall carbon nanotubes and sprayed onto copper disc electrodes (2.54 cm²), following a cost-effective spray deposition technology, suitable for the fabrication of both semi-industrial scale and laboratory size thin film electrodes. By testing electrodes with different mass fractions of carbon nanotubes it was found out that the electrochemical utilization is enhanced for a nanotubes load of 15% (wt). These electrodes (2 µg.cm^-2) present an outstanding capacity of 92 mAh.g^-1 at a relatively high current of 3.30 mA.cm² (100C). Besides the high rate capability, the nano LTO/carbon nanotubes composites also present a good stability and coulombic efficiency when cycled after 1000 cycles at 1C (35 µA.cm^-2).

References

(1) Haetge, J.; Hartmann, P.; Brezesinski, K.; Janek, J.; Brezesinski, T. Chemistry of Materials 2011, 23, 4384.

(2) Liu, W.; Shao, D.; Luo, G.; Gao, Q.; Yan, G.; He, J.; Chen, D.; Yu, X.; Fang, Y. Electrochim. Acta 2014, 133, 578.

(3) Wang, D.; Ding, N.; Song, X. H.; Chen, C. H. J Mater Sci 2009, 44, 198.

(4) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Science 2013, 340.

(5) Coleman, J. N.; Lotya, M.; O’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V. Science 2011, 331, 568.

(6) Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I.; Holland, B.; Byrne, M.; Gun'Ko, Y. K. Nature Nanotechnology 2008, 3, 563.

(7) Higgins, T. M.; McAteer, D.; Coelho, J. C. M.; Sanchez, B. M.; Gholamvand, Z.; Moriarty, G.; McEvoy, N.; Berner, N. C.; Duesberg, G. S.; Nicolosi, V.; Coleman, J. N. ACS Nano 2014.