Freestanding TiO2 Nanoparticle-Embedded High Directional Carbon Composite Host for High-Loading Low-Temperature Lithium–Sulfur Batteries

Abstract

Improving the low-temperature performance of lithium–sulfur batteries is significant for future applications. Meanwhile, a low temperature often leads to sluggish charge transfer kinetics and low energy output. Herein, we designed a thick freestanding TiO2 nanoparticle-embedded three-dimensional carbon composite (TiO2@C@CSC) host with high directional channels, aiming at achieving a high-performance low-temperature lithium–sulfur battery. The carbon-coated TiO2 nanoparticles (TiO2@C) are derived from polyimide-coated TiO2 nanoparticles and embedded in the channels. The chitosan-foam-derived carbon framework (CSC) has vertically aligned channels, which kinetically accelerates ion/electron transport and precisely confines sulfur/polysulfides within its channels. TiO2@C nanoparticles could facilitate the adsorption and conversion of polysulfides. The combination of vertically aligned channels and TiO2@C nanoparticles further provides a chemical gradient that prevents the diffusion of polysulfides and enhances the reaction kinetics at low temperatures. The designed host also has enough accommodation space, which is beneficial to improving the mass loading and utilization efficiency of active sulfur. Finally, the energy storage performance of TiO2@C@CSC as a sulfur host was investigated under 30, −20, and −40 °C. Under 30 °C, the initial discharge capacity of TiO2@C@CSC is 679 mAh g–1 at 1C with 4.0 mg cm–2 sulfur, and an initial capacity of 969 mAh g–1 could be obtained at 0.1C with the sulfur loading mass of 10.0 mg cm–2. Under −20 °C, the performance of TiO2@C@CSC with loading masses of 2.5, 5.0, 10.0, and 20.0 mg cm–2 was investigated, and the corresponding initial capacities at 0.05C were 1573, 924, 242, and 13 mAh g–1, respectively. As the temperature drops to −40 °C, the efficiency becomes lower but the charge–discharge process can still be complete. This work presents a promising direction for developing high-energy low-temperature lithium–sulfur batteries.