Magnèli phase TiOx in carbon as highly efficient cathode for Li/S batteries

Natural abundance of elemental sulfur in the Earth’s crust make Li-S technology as an attractive low cost alternative to Li-ion batteries. Some of setbacks in Li-S technology include: (i) a low degree of sulfur utilization, (ii) quick capacity fading during cycling, (iii) relatively poor rate capability and (iv) a low Coulombic efficiency [1-2]. These limitations mainly arise because of the low conductivity of S8 (5 × 10−18 S cm−1), the solubility of polysulfide intermediates, shuttling of dissolved polysulfides, and a general lack of morphological restoration of the sulfur-containing host material during long term cycling [2]. In this work, we demonstrate integration of multiple design strategies to form a cost effective and sustainable sulfur-containing electrode of carbon and Magnéli phase TinO2n-1, that offers exceptional long life and good rate performance with high S loading for Li-S batteries. Electrically conductive Magnéli phase nanoparticle-loaded carbon matrices (TinO2n-1@C/S) were synthesized by simple heat treatment of the mixture of TiO2 nanotubes and polyvinyl alcohol (PVA) in inert environment. The approach also suppresses the sintering and grain growth in TinO2n-1 nanoparticles ensuring high surface area for LiPS docking that mitigates shuttling effect for high capacity Li/S batteries. Sulfur is introduced into the carbon matrix by a simple thermal infusion process, allowing a high areal sulfur loading (>2.3 mg cm-2) with effective LiPS adsorption. The cells were efficiently charged and discharged for 1000 cycles up to 1 C, even for low E/S ratio. This study also demonstrates how physical entrapment of porous carbon in addition to the chemical binding capability of several Magnéli phase oxides contribute synergistically to realize long cycle life Li-S batteries. [1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nat Mater 2012, 11, 19. [2] N. S. Choi, Z. H. Chen, S. A. Freunberger, X. L. Ji, Y. K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho, P. G. Bruce, Angew Chem Int Edit 2012, 51, 9994.