A two-dimensional MXene/BN van der Waals heterostructure as an anode material for lithium-ion batteries.

Titanium carbide (Ti3C2Tx) is highly regarded as a promising anode material for lithium-ion batteries but suffers from sluggish kinetics with low storage capacity. In this work, a BN/Ti3C2Tx heterostructure is effectively fabricated by high energy ball-milling, which plays a series of roles in enlarging the interlayer spacing, reducing the size of the nanosheets and maintaining the structural integrity. Benefiting from the synergistic effect between the BN and Ti3C2Tx monolayers, it delivers a high reversible capacity of 521.6 mA h g-1 at 0.1 A g-1, excellent rate capabilities (344.9 mA h g-1 at 1 A g-1 and 251.3 mA h g-1 at 2.5 A g-1) and a robust long-term cycling stability with 84.4% capacity retention after 1400 cycles. In particular, the theoretical calculations further confirm that the BN/Ti3C2Tx heterostructure manifests improved adsorption energies, an ultralow diffusion barrier and a high charge-discharge rate. These findings provide an important new strategy for further design and rational fabrication of MXenes for energy storage applications.

First-principles calculation on the lithium storage properties of high-entropy MXene Ti3C2(N0.25O0.25F0.25S0.25)2.

Experimental studies had shown that a variety of surface functional groups exist simultaneously on the surface of Ti3C2Tx MXenes. However, current theoretical calculations on MXenes, used as anode materials for lithium-ion batteries, consider only one surface functional group, which fails to take into account the actual situation. In this study, combining the characteristics of high-entropy materials and two-dimensional MXene material, a model of MXene with multiple surface functional groups was constructed, and its electrochemical performance as an anode material for lithium-ion batteries was further explored. The Ti3C2(N0.25O0.25F0.25S0.25)2 monolayer exhibited metallic properties. Meanwhile, Li atoms could be stably adsorbed on the surface and the diffusion energy barrier of Li on the surface was only 0.17 eV. First-principles calculation showed that Ti3C2(N0.25O0.25F0.25S0.25)2 monolayer had good rate performance and low open-circuit voltage (1 V), corresponding to a lithium storage capacity of 385.38 mA h g-1. The results of our work might inspire further studies on the Li storage performance of high-entropy MXenes experimentally and theoretically.

MXene/graphene oxide heterojunction as a high performance anode material for lithium ion batteries.

MXene/graphene oxide composites with strong interfacial interactions were constructed by ball milling in vacuum. Graphene oxide (GO) acted as a bridge between Ti3C2Tx nanosheets in the composite material, which could buffer the mechanical shear force during the ball milling process, avoid the structural damage of nanosheets and improve the structural stability of the composite material during the lithium process. Partial oxidation of Ti3C2Tx nanosheets is caused by high temperatures during ball milling, which is beneficial to improve the intercalation of lithium ions in the material, reduce the stress and electrostatic repulsion between adjacent layers, and cause the composite to have better lithium storage performance. Under the high current density of 2.5 A g-1, the reversible capacity of the Ti3C2Tx/GO composite material after 2000 cycles was 116.5 mA h g-1, and the capacity retention was as high as 116.6%.