Single crystal H-Nb 2 O 5 growing along the [001] crystal direction for ultrafast lithium storage

Nb 2 O 5 has been deemed as a promising anode candidate for lithium ion batteries due to its fast charge–discharge capability, excellent structural stability, and high safety. Compared with the widely studied orthorhombic Nb 2 O 5 (T-Nb 2 O 5 ), the two-phase transition process during the charge/discharge processes in monoclinic Nb 2 O 5 (H-Nb 2 O 5 ) results in inadequate cycle stability and rate performance. Herein, the Li storage performance of H-Nb 2 O 5 is optimized by constructing single-crystalline structure via a simple and efficient one-pot annealing process. It has been demonstrated that the single-crystalline structure can more effectively maintain the structural integrity as well as suppress the continuous side reactions at the electrode/electrolyte interface in the charge–discharge processes. Besides, the growth along the [001] crystal direction can ensure that Li ions can penetrate directly into the center from the surface in the single-crystalline H-Nb 2 O 5 , resulting in a significantly improved Li + diffusion kinetics. As a result, the single-crystalline H-Nb 2 O 5 exhibits ultrahigh rate performance (119.8 mA h g −1 at 100C) and long cycle durability with a high capacity of 115.6 mA h g −1 at 25C for 3000 cycles. Besides, single-crystalline H-Nb 2 O 5 can deliver a remarkable areal capacity of 2.96 mA h cm −2 at a high mass loading of 12 mg cm −2 . The Li-ion capacitor paired with commercial activated carbon cathode also exhibits an exceptional energy density of 48.4 W h kg −1 at a high power density of 5.45 kW kg −1 . This work will further tap the commercial potential of the single-crystalline H-Nb 2 O 5 for fast lithium storage devices.