KAUST uses laser pulses to boost performance of MXene electrode

Aug 18, 2023

KAUST researchers have demonstrated the use of laser pulses to modify the structure of a promising alternative electrode material known as MXene, boosting its energy capacity and other key properties. The researchers hope that this strategy could help to engineer an improved anode material in next-generation batteries.

A paper on their work is published in the journal Small.

Graphite contains flat layers of carbon atoms, and during battery charging, lithium atoms are stored between these layers in a process called intercalation. MXenes also contain layers that can accommodate lithium, but these layers are made of transition metals such as titanium or molybdenum bonded to carbon or nitrogen atoms, which make the material highly conducting. The surfaces of the layers also feature additional atoms such as oxygen or fluorine. MXenes based on molybdenum carbide have particularly good lithium storage capacity, but their performance soon degrades after repeated charge and discharge cycles.

The team, led by Husam N. Alshareef and Ph.D. student Zahra Bayhan, discovered that this degradation is caused by a chemical change that forms molybdenum oxide within the MXene’s structure.

To tackle this problem, the researchers used infrared laser pulses to create small “nanodots“ of molybdenum carbide within the MXene, a process called laser scribing. These nanodots, roughly 10 nanometers wide, were connected to the MXene’s layers by carbon materials.

This offers several benefits. First, the nanodots provide additional storage capacity for lithium and speed up the charging and discharging process. The laser treatment also reduces the material’s oxygen content, helping to prevent the formation of problematic molybdenum oxide. Finally, strong connections between the nanodots and the layers improve the MXene’s conductivity and stabilize its structure during charging and discharging.

The researchers made an anode from the laser-scribed material and tested it in a lithium-ion battery over 1000 charge-discharge cycles. With the nanodots in place, the material had a four-fold higher electrical storage capacity than the original MXene and almost reached the theoretical maximum capacity of graphite. The laser-scribed material also showed no loss in capacity during the cycling test.

Herein, it is revealed that the unstable cycling performance of Mo2CTx is attributed to the partial oxidation into MoOx with structural degradation. A laser-induced Mo2CTx/Mo2C (LS-Mo2CTx) hybrid anode has been developed, of which the Mo2C nanodots boost redox kinetics, and the laser-reduced oxygen content prevents the structural degradation caused by oxidation. Meanwhile, the strong connections between the laser-induced Mo2C nanodots and Mo2CTx nanosheets enhance conductivity and stabilize the structure during charge–discharge cycling.

The as-prepared LS-Mo2CTx anode exhibits an enhanced capacity of 340 mAh g−1 vs 83 mAh g−1 (for pristine) and an improved cycling stability (capacity retention of 106.2% vs 80.6% for pristine) over 1000 cycles. The laser-induced synthesis approach underlines the potential of MXene-based hybrid materials for high-performance energy storage applications.

The researchers think that laser scribing could be applied as a general strategy to improve the properties of other MXenes. This could help to develop a new generation of rechargeable batteries that use cheaper and more abundant metals than lithium, for example. Unlike graphite, MXenes can also intercalate sodium and potassium ions, notes Alshareef.

Resources

Bayhan, Z., El-Demellawi, J. K., Yin, J., Khan, Y., Lei, Y., Alhajji, E., Wang, Q., Hedhili, M. N. & Alshareef, H. N. (2023) A laser-induced Mo2CTx MXene hybrid anode for high-performance Li-ion batteries. Small doi: 10.1002/smll.202208253

Posted on 28 July 2023 in Batteries, Market Background, Materials | Permalink | Comments (0)