Today’s lithium-ion batteries are good, but their performance still needs to be improved; Developing new electrode materials is one way to improve their performance. Researchers of the King Abdullah University of Science and Technology KAUST have demons­trated the use of laser pulses to modify the structure of a promising alternative electrode material – two-dimensional transition metal carbides/nitrides, 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.

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 for laser scribing to create small nanodots of molybdenum carbide within the MXene. These nanodots, roughly 10 nanometers wide, were connected to the MXene’s layers by carbon materials. This offers several benefits. Firstly, 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. “This provides a cost-effective and fast way to tune battery performance,” says Bayhan.

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. 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,” explains Alshareef. (Source: KAUST)

Reference: Z. Bayhan et al.: A Laser-Induced Mo₂CT_x MXene Hybrid Anode for High-Performance Li-Ion Batteries, Small, online 14 May 2023; DOI: 10.1002/smll.202208253

Link: Materials Science and Engineering, Physical Science and Engineering (PSE) Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia