Enhancing Catalytic Activity of Titanium Oxide in Lithium–Sulfur Batteries by Band Engineering

• Published in: Advanced energy materials Vol. 9; no. 24
• Main Authors: Wang, Yuankun, Zhang, Ruifang, Chen, Jie, Wu, Hu, Lu, Shiyao, Wang, Ke, Li, Huanglong, Harris, Christopher J., Xi, Kai, Kumar, Ramachandran Vasant, Ding, Shujiang
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-06-2019
• Subjects: Carbon nanotubes; Catalysis; Catalysts; Catalytic activity; Electrocatalysts; Electron states; electronic states; Energy storage; Heterojunctions; Ionic mobility; Lithium sulfur batteries; Metal oxides; nanosheets; Nanostructure; Organic chemistry; oxygen vacancies; Sulfur; Titanium dioxide; Titanium oxides; Vacancies
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201900953

The altering of electronic states of metal oxides offers a promising opportunity to realize high‐efficiency surface catalysis, which play a key role in regulating polysulfides (PS) redox in lithium–sulfur (Li–S) batteries. However, little effort has been devoted to understanding the relationship between the electronic state of metal oxides and a catalyst's properties in Li–S cells. Herein, defect‐rich heterojunction electrocatalysts composed of ultrathin TiO2‐x nanosheets and carbon nanotubes (CNTs) for Li–S batteries are reported. Theoretical simulations indicate that oxygen vacancies and heterojunction can enhance electronic conductivity and chemical adsorption. Spectroscopy and electrochemical techniques further indicate that the rich surface vacancies in TiO2‐x nanosheets result in highly activated trapping sites for LiPS and lower energy barriers for fast Li ion mobility. Meanwhile, the redistribution of electrons at the heterojunction interfaces realizes accelerated surface electron exchange. Coupled with a polyacrylate terpolymer (LA132) binder, the CNT@TiO2‐x–S electrodes exhibit a long cycle life of more than 300 cycles at 1 C and a high area capacity of 5.4 mAh cm−2. This work offers a new perspective on understanding catalyst design in energy storage devices through band engineering.
Defect‐rich heterojunction electrocatalysts based on CNT@TiO2‐x nanosheet hybrids are designed. This versatile interface can enhance the adsorption strength of polysulfides (PS), facilitate Li+/electron transfer, and promote of electrocatalytic activity for PS redox. As a result, CNT@TiO2‐x–S electrodes exhibit lower polarization, faster reaction kinetics, and longer cycle stability than that of CNT/TiO2‐x–S and CNT@TiO2–S electrodes.