Construction of WS/NC@C nanoflake composites as performance-enhanced anodes for sodium-ion batteries.

The development of layered metal sulfides with stable structure and accessible active sites is of great importance for sodium-ion batteries (SIBs). Herein, a simple liquid-mixing method is elaborately designed to immobilize WS nanoflakes on N-doped carbon (NC), then further coat carbon to produce WS/NC@C. In the formation process of this composite, the presence of NC not only avoids the overlap and improves the dispersion of WS nanoflakes, but also creates a connection network for charge transfer, where the wrapped carbon provides a stable chemical and electrochemical reaction interface. Thus, the composite of WS/NC@C exhibits the desired Na storage capacity as anticipated. The reversible capacity reaches the high value of 369.8 mA h g at 0.2 A g after 200 cycles, while excellent rate performances and cycle life are also acquired in that capacity values of 256.7 and 219.6 mA h g at 1 and 5 A g are preserved after 1000 cycles, respectively. In addition, the assembled sodium-ion hybrid capacitors (SIHCs, AC//WS/NC@C) exhibit an energy/power density of 68 W h kg at 64 W kg, and capacity retention of 82.9% at 1 A g after 2000 cycles. The study provides insight into developing layered metal sulfides with eminent performance of Na storage.