Exploring the Efficient Na/K Storage Mechanism and Vacancy Defect-Boosted Li+ Diffusion Based on VSe2/MoSe2 Heterostructure Engineering.

As typical 2D materials, VSe2 and MoSe2 both play a complementary role in Li/Na/K storage. Therefore, we designed and optimized the VSe2/MoSe2 heterostructure to gain highly efficient Li/Na/K-ion batteries. Most importantly, achieving fast Li/Na/K-ion diffusion kinetics in the interlayer of VSe2/MoSe2 is a key point. First of all, first-principles calculations were carried out to systematically investigate the packing structure, mechanical properties, band structure, and Li/Na/K storage mechanism. Our calculated results suggest that a large interlayer spacing (3.80 A), robust structure, and metallic character pave the way for achieving excellent charge-discharge performance for the VSe2/MoSe2 heterostructure. Moreover, V and Mo ions both suffer a very mild redox reaction even if Li/Na/K ions fill the interlayer space. These structures were all further verified to show thermal stability (300 K) by means of the AIMD method. By analyzing the Li/Na/K diffusion behavior and the effect of vacancy defect on the structural stability and energy barrier for Li interlayer diffusion, it is found that the VSe2/MoSe2 heterostructure exhibits very low-energy barriers for Na/K interlayer diffusion (0.21 eV for Na and 0.11 eV for K). Compared with the VSe2/MoSe2 heterostructure, the V0.92Se1.84/MoSe2 heterostructure not only can still maintain a stable structure and metallic character but also has much lower energy barrier for Li interlayer diffusion (0.07 vs 0.48 eV). These discoveries also break new ground to eliminate the obstacles preventing Li+ diffusion in the interlayer of other heterostructure materials. Besides, both VSe2/MoSe2 and V0.92Se1.84/MoSe2 heterostructures have low average open-circuit voltage (OCV) values during Li/Na/K interlayer diffusion (1.07 V for V0.92Se1.84/MoSe2 vs Li+, 0.86 V for VSe2/MoSe2 vs Na+, and 0.54 V for VSe2/MoSe2 vs K+), such low OCV values are beneficial for anode materials with excellent electrochemical properties. The above findings offer a new route to design anode materials for Li/Na/K-ion batteries.