Atomic Layer Deposition of Alumina Coatings onto SnS₂ for Lithium-Ion Battery Applications

Highlights: •First work to enhance the cyclability of SnS₂ anode by Al₂O₃ atomic layer deposition. •Al₂O₃ coated SnS₂ electrodes show better cycling/rate performances than uncoated ones. •Al₂O₃ coatings maintain kinetics of electrode reactions and prohibit SEI layer growth. -- Abstract: Tin disulfide (SnS₂) hierarchical structures have been synthesized via a simple hydrothermal route for their utilization in lithium-ion batteries. The issue of fast capacity degradation over cycling because of the dramatic volume change that causes particle pulverization and poor contact between the active material and current collector is explored and alleviated for the first time by surface modification of the whole SnS₂ electrode via a facile atomic layer deposition (ALD). ALD allows the uniform formation of conformal Al₂O₃ coatings onto the porous electrode, and thereby succeeds to enhance their electrochemical performance. As compared, within fifty battery cycles the bare SnS₂ electrode exhibits a final capacity of 219.2 mA h g⁻¹ at 100 mA g⁻¹, while the coated electrode can deliver the final capacity of 351.1 mA h g⁻¹ (60% larger). In addition, the capacity retention and rate capability of the coated electrode is found much better than that of the bare one. Electrochemical impedance spectroscopy analyses indicate that the resistance derived from solid-electrolyte interface (SEI) and charge transfer process remains fairly smaller in the coated electrode than in the bare one. The better electrode kinetics accounts for the strengthened Li-ion intercalation behaviors of the modified electrodes, and demonstrates that ALD oxide coatings are able to enhance the mechanical integrity and structural stability of SnS₂ electrodes, thus effectively impeding the pulverization of active particles and maintaining good electronic conduction paths and efficient charge transfer. Moreover, ALD coatings cover the entire electrode and reduce electrolyte decomposition to attenuate the SEI layer, which also contributes to the cyclability of SnS₂.