Monolayer TiSi 2 P 4 as a High-Performance Anode for Na-Ion Batteries.

Exploring anode materials with overall excellent performance remains a great challenge for rechargeable Na-ion battery technologies. Herein, we have identified that monolayer TiSi 2 P 4 is just such a prospective anode candidate via first-principles calculations. It is showed to be dynamically, thermally, mechanically, and energetically stable, which provides feasibility for experimental realization. The Na diffusion on the its surface is proved to be ultrafast, with a migration energy barrier as low as 73 meV. Electronic structure confirms that the pristine system undergoes a transition from the semiconductor to metal during the whole sodiation process, which is a significant advantage to the electrode conductivity. More excitingly, monolayer TiSi 2 P 4 can accommodate up to double-sided 5-layer adatoms, resulting in an ultrahigh theoretical capacity of 1176 mA h g -1 and a low average open-circuit voltage of 0.195 V. Moreover, the maximally sodiated electrode monolayer yields rather small in-plane lattice expansion of only 1.40%, which ensures reversible deformation and excellent cycling stability as further corroborated by structural relaxation and ab initio molecular dynamics simulation. Overall, all of these results point to the potential that monolayer TiSi 2 P 4 can serve as a promising anode candidate for application in high-performance low-cost Na-ion batteries.