Li(V0.5Ti0.5)S2 as a 1 v lithium intercalation electrode

Abstract

Graphite, the dominant anode in rechargeable lithium batteries, operates at ∼0.1 V versus Li+/Li and can result in lithium plating on the graphite surface, raising safety concerns. Titanates, for example, Li4Ti5O12, intercalate lithium at-1.6 V versus Li+/Li, avoiding problematic lithium plating at the expense of reduced cell voltage. There is interest in 1 V anodes, as this voltage is sufficiently high to avoid lithium plating while not significantly reducing cell potential. The sulfides, LiVS2 and LiTiS2, have been investigated as possible 1 V intercalation electrodes but suffer from capacity fading, large 1st cycle irreversible capacity or polarization. Here we report that the 50/50 solid solution, Li 1+x (V0.5Ti0.5)S2, delivers a reversible capacity to store charge of 220 mAh-1 (at 0.9 V), 99% of theoretical, at a rate of C/2, retaining 205 mAh-1 at C-rate (92% of theoretical). Rate capability is excellent with 200 mAh-1 at 3C. C-rate is discharge in 1 h. Polarization is low, 100 mV at C/2. To the best of our knowledge, the properties/performances of Li(V0.5Ti0.5)S2 exceed all previous 1 V electrodes.