First Principles Studies of MXenes as Electrode Materials for Rechargeable Batteries


Student thesis: Doctoral Thesis

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Awarding Institution
Award date10 May 2021


MXenes are a large family of two-dimensional nanomaterials. Because of their excellent electronic conductivity, high specific surface area, and tunable physicochemical properties, MXenes have been extensively applied as electrode materials for various rechargeable batteries. Theoretical calculations play a significant role in revealing the storage mechanism of MXenes and predicting the electrochemical performance of them. However, the structure-property correlation of MXenes based electrode materials lacks exploration, and high-performance MXenes based electrode materials are still needed to develop.

In this thesis, electrochemical performance of a series of MXenes as anode materials for metal-ion batteries as well as anchoring materials for lithium-sulfur batteries by using density functional theory calculations is investigated. More importantly, the structural parameter of MXenes and their electrochemical performance is correlated. Based on this structure-property correlation, several high-performance MXenes based anode materials are designed.

Firstly, we find that different transition metal-based M3C2O2 MXenes possess greatly distinct structural properties, which significantly influences the adsorption and diffusion behaviors of Li, Na, and K atoms on them. More importantly, the structure parameters of M3C2O2 and their adsorption, diffusion behaviors are correlated. From this part of work, it can be concluded that the performance of M3C2O2 based anode materials can be optimized by selecting appropriate transition metal or applying biaxial strain to directly change the lattice constant of specific M3C2O2.

Then, we further design three titanium zirconium dual transition metal carbides (TiZrCO2, Ti2ZrC2O2, and TiZr2C2O2) as anode materials for Na-ion batteries. All these three systems are dynamically and thermodynamically stable and exhibit good conductivities. Besides, all of them can realize energetically favorable double-layer adsorptions of Na atoms on each side, which endows them with obviously higher capacity than corresponding mono titanium- and zirconium-based MXenes.

Besides, two heterostructures VS2/Ti2CT2 (T=O and S) are constructed and their electrochemical performance as anode materials for Li, Na, and Mg-ion batteries are explored based on first-principles calculations. First of all, the lattice mismatch of these two heterostructures is relatively small. Considering the strong adsorption properties, low diffusion energy barriers, suitable open-circuit voltages, and high capacities, VS2/Ti2CO2 and VS2/Ti2CS2 are proposed to be promising anode materials for Mg-ion batteries, and VS2/Ti2CS2 is a preferred anode material for Na-ion batteries.

Finally, we thoroughly investigate the interaction between various lithium polysulfides and Ti2CO2 substrate as well as other six M3C2O2 (M=Cr, V, Ti, Nb, Hf, and Zr) MXenes. It is found that all six M3C2O2 systems possess trapping ability towards soluble LiPSs, and Cr3C2O2 exhibits the strongest anchoring effect. More importantly, a monotonic correlation between the binding energy and the lattice constant of M3C2O2 is identified, which indicates that M3C2O2 with a smaller lattice constant tends to exhibit a stronger anchoring effect.

Taken together, we comprehensively investigate the electrochemical performance of a series of MXenes as anode materials for metal-ion batteries as well as anchoring materials for lithium-sulfur batteries. More importantly, the structure-property correlation of MXenes is identified. Overall, this thesis could provide helpful guidance on screening and designing high-performance MXenes based electrode materials for various rechargeable batteries.