Chinese knot-like electrode design for advanced Li-S batteries

Abstract

Rational design of Li-S batteries requires efficient prevention of sulfur mobility and fast redox kinetics while accommodating the volumetric expansion of the sulfur cathode. Herein, we propose a multifunctional Chinese knot-like electrode design for advanced Li-S batteries. NiCo2S4 nanotubes are closely interwoven to form Chinese knot-like designs as a sulfur host. The unique interconnectivity of the 2D Chinese knot-like networks constructed by 1D nanostructured nanotubes enables fast electron transfer for high capacity. Furthermore, the hollow structure can simultaneously provide enough space for volumetric expansion of sulfur and confine lithium polysulfides (LiPSs) in the internal void space by structural encapsulation. Besides these, experimental and theoretical analysis demonstrates that NiCo2S4 can effectively capture the LiPSs and then catalyze the captured LiPSs into solid Li2S2/Li2S. More importantly, the transition between low-spin and high-spin of Co ions, induced by extra sulfur atoms from LiPSs, provides an electronic way to stabilize the adsorption system and reduce system energy, leading to the inhibition of the shuttle effect in Li-S batteries. As a result, the Chinese knot-like S@NiCo2S4 electrodes show a high capacity of 1348 mA h g−1 at 0.1 C and long cycling life up to 1000 cycles with a slow capacity decay of 0.02% per cycle at 1 C. Even with a higher sulfur loading of 5 mg cm−2, the electrodes still deliver good electrochemical performance.