Hybrid cathode architectures for lithium batteries based on TiS2 and sulfur

Abstract

Great efforts have been devoted towards development of rechargeable lithium–sulfur (Li–S) battery designs that offer extended cycling. The poor electronic and ionic conductivity of sulfur and its reduction compounds with lithium, solubility of some sulfides in the most commonly used Li–S electrolyte solvents, and the volume changes that accompany lithiation and delithiation processes in a sulfur cathode, pose significant challenges that have so far impeded commercialization of rechargeable Li–S batteries. We demonstrate that TiS₂, which uses an intercalation chemistry and is known for its high rate capability and stable performance as a lithium battery cathode, and sulfur, which has very high capacity (1675 mA h g⁻¹) when coupled in a conversion-based electrochemical reaction with lithium metal, can be combined to produce hybrid cathodes in which the two materials function synergistically in the same electrolyte and within the same working voltage. We further show that co-generation of interconnected S₈/TiS₂ hybrid foams through thermal reaction of Ti precursor foams and S₈ yields 3D hybrid cathode structures in which sulfur is infused into porous TiS₂ foams. In galvanostatic electrochemical cycling studies the hybrid cathodes demonstrate high areal specific capacity (9 mA h cm⁻²) and high retention ratios, even at a relatively large areal mass loading of ∼40 mg sulfur per cm² and high current density (10 mA cm⁻²). We attribute the improved performance of the materials to the synergistic effect in which TiS₂ not only improves the conductivity and rate capability of the cathode, but exerts a strong affinity for soluble lithium polysulfides, which limit their loss to the electrolyte.