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ORIGINAL PAPER

TiO2 microbox/carbon nanotube composite-modified separator for high-performance lithium-sulfur batteries Jie Ni 1,2 & Liming Jin 1,2,3 & Mingzhe Xue 1,2 Cunman Zhang 1,2

&

Qiangfeng Xiao 1,2 & Junsheng Zheng 1,2,3 & Jim P. Zheng 2,3 &

Received: 7 March 2020 / Revised: 21 October 2020 / Accepted: 12 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Mesoporous hollow TiO2 microboxes are synthesized by a two-step solvothermal method via CaTiO3 intermediate. Composite consisting of TiO2 microboxes and carbon nanotubes (CNT) is applied as a coating layer on conventional polymer separator for lithium-sulfur batteries. The cell using a modified separator exhibits enhanced cycling performance and rate capability. A discharge capacity of 852.3 mAh g−1 is achieved at 0.2 C after 200 cycles and more than 500 mAh g−1 of discharge capacity could be retained after 1000 cycles at 1 C, much better than the cells employing untreated or sole CNT-coated separator. Even at a high C-rate of 10 C, the cell with CNT-TiO2-coated separator could deliver a high specific discharge capacity of 561 mAh g−1. Such enhanced electrochemical performance is ascribed to the synergistic effect of CNT and TiO2 on suppressing shuttle reactions of lithium polysulfides. Keywords TiO2 microboxes . Separator . Coating layer . Shuttle effect . Lithium-sulfur batteries

Introduction It is extremely critical to develop energy storage devices with admirable capacity and lifetime to meet the increasing demand from electronic equipment, electrical vehicle, and grid energy storage [1–4]. However, the traditional lithium-ion batteries have reached a bottleneck. The intercalation mechanism of graphite anode and transitional metal oxide cathode (e.g., Li2MnO4, LiCoO2) inherently limits the theoretical specific energy of traditional Li-ion battery, making it insufficient to many advanced technologies, such as unmanned aircraft, renewable energy storage, and mass marketization of electric Jie Ni and Liming Jin contributed equally to this work. * Mingzhe Xue [email protected] * Cunman Zhang [email protected] 1

Clean Energy Automotive Engineering Center, Tongji University, Shanghai 201804, People’s Republic of China

2

School of Automotive Studies, Tongji University, Shanghai 201804, People’s Republic of China

3

Department of Electrical and Computer Engineering, Florida State University, Tallahassee, FL 32304, USA

vehicles [5]. In this content, lithium-sulfur (Li-S) battery has drawn wide attention in the last few years due to the remarkable advantages of sulfur cathodes, including a high theoretical capacity of 1675 mAh g−1, nonpoisonous property, environment friendliness, and low price [6]. It is recognized as one of the most potential candidates for the next-generation lithium secondary battery, replacing commercial Li-ion battery [6]. Nevertheless, the rapid capacity fading during cycling and low efficiency of sulfur utilization block the practical application of Li-S battery [7], which stem from (i