As early as 2014, Professor Yury Gogotis proposed the idea of applying new batteries to MXene, and carried out related theoretical calculations and experimental research. Although it has been five years, it is still instructive for the design of the new MXene battery.



【Research Background】

       Rechargeable lithium-ion batteries (LIBs) are one of the most important energy storage systems and have been widely used in portable electronic devices to power electric vehicles. However, large-scale electrical energy storage applications for lithium-ion batteries can be affected by limited natural storage of lithium, high production costs, and safety issues. Therefore, a new generation of renewable energy technologies urgently needs to develop new battery systems. Currently, rechargeable sodium, potassium, magnesium, calcium and aluminum ion batteries have attracted attention due to their rich elements, high theoretical capacity, suitable negative redox potential, operational safety and environmental friendliness.

        In recent years, a two-dimensional transition metal carbonitride called MXene has been discovered and widely used in energy storage, catalysis, and sensors. Due to etching in an acidic solution, the surface of the MXene nanosheet is mainly covered by OH and F groups. In addition, MXene has good electrical conductivity and has the potential to produce materials with higher electrochemical properties.



[Introduction]

       The Yohan Dall’Agnese research team at the Oak Ridge National Laboratory Nanomaterials Center and Professor Yury Gogotis presented on ACS nano: Prediction and Characterization of MXene Nanosheet Anodes for Non-Lithium-Ion Batteries. In this paper, theoretical prediction and characterization of non-lithium ion battery MXene positive electrode. Here, the theoretical calculations of Na, K, Mg, Ca, and Al ion batteries are used to predict the energy storage behavior of various types of batteries under various conditions.


[Article Highlights]

       The theoretical analysis of the intercalation behavior of Na, K, Mg, Ca and Al ion batteries with different surface functional groups of different MXene was carried out.



[Graphic introduction]

Schematic diagram of multivalent ion intercalation and deintercalation

Figure 1. Theoretical simulation calculations for the surface of Ti2C, V2C, Nb2C, and Ti3C2 with -OH functional groups. Most of the adsorption energy is positive, indicating that these ions are not well adsorbed by MXenes. In particular, Mg and Al have higher adsorption energy than other ions. This may be related to their strong Coulomb repulsion between the MXene Ti atoms.

Fig. 2. Theoretical simulation calculations for the case where the surface of Ti2C, V2C, Nb2C and Ti3C2 is -O functional group. With the exception of Al, all atoms have a negative adsorption energy, indicating that they can form a complete adsorption layer on the O-functional MXenes. The positive adsorption of aluminum indicates that it is physically or partially chemisorbed.

Figure 3. Further studies have found that there may be two intercalated ions on the surface of the O-based functional group. It can be seen that the adsorption energy of the second layer of Mg ions is still negative.

Figure 4. Theoretical simulation calculations for the absence of functional groups on the surface of Ti2C, V2C, Nb2C, and Ti3C2. We immediately observed the difference from the oxy functional group. K cannot form a complete layer on any bare MXene; the maximum stable coverage is only 2/3. At the same time, Ca can only form a complete layer on Nb2C. For other MXenes, the coverage is 1/2. In contrast, Al does not form a stable full layer on the O functional group MXene, but forms a complete layer on the bare MXenes.

Figure 5. Both Mg and Al-ion batteries can embed two layers of ions on the exposed MXene surface. And the corresponding theoretical capacity has also increased.



[Article summary]

       In this paper, the storage behavior of sodium, potassium, magnesium, calcium and aluminum on MXene nanosheets was systematically studied by first-principles calculation. The results show that both oxy functional groups and non-functional MXene nanosheets are promising electrode materials for lithium-free battery electrodes. The non-functional MXene has higher capacity and stronger ion mobility than the oxy group-functional MXene. After selecting a suitable electrolyte, MXene nanoflakes can store multiple layers of Mg ions and Al ions, which in principle will exhibit energy storage mechanisms such as composite conversion reaction, insertion/extraction, electroplating/stripping metal ions. This study also provides the first theoretical approach to obtain MXene without functional groups from oxy MXene and reveals the storage mechanism of metal ions in MXene materials. In this paper, the storage behavior of sodium, potassium, magnesium, calcium and aluminum on MXene nanosheets was systematically studied by first-principles calculation. The results show that both the -O-based functional group and the non-functionalized MXene nanosheet are promising electrode materials for lithium-free battery electrodes.

Literature link:

https://doi.org/10.1021/nn503921