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Hydrogenated Na₂Ti₃O₇ Epitaxially Grown on Flexible N-Doped Carbon Sponge for Potassium-Ion Batteries
- Li, Peihao, Wang, Wei, Gong, Sheng, Lv, Fan, Huang, Hanxin, Luo, Mingchuan, Yang, Yong, Yang, Chao, Zhou, Jinhui, Qian, Chang, Wang, Bin, Wang, Qian, Guo, Shaojun
- ACS applied materials & interfaces 2018 v.10 no.44 pp. 37974-37980
- X-ray photoelectron spectroscopy, anodes, batteries, carbon, electrochemistry, hydrogenation, nanowires
- With its inherent zig-zag layered structure and open framework, Na₂Ti₃O₇ (NTO) is a promising anode material for potassium-ion batteries (KIBs). However, its poor electronic conductivity caused by large band gap (∼3.7 eV) usually leads to low-performance KIBs. In this work, we synthesize the fluff-like hydrogenated Na₂Ti₃O₇ (HNTO) nanowires grown on N-doped carbon sponge (CS) as a binder-free and current-collector-free flexible anode for KIBs (denoted as HNTO/CS). High-resolution X-ray photoelectron spectroscopy (XPS) and electron spin-resonance spectroscopy (ESR) confirm the existence of Ti–OHs and O vacancies in HNTO. The first-principles calculation discloses that both Ti–OHs and O vacancies are equivalent to n-type doping because they can shift the Fermi level up to the conduction band, thus leading to a higher electronic conductivity and better performance for KIBs. In addition, the N-doped CS can further reinforce the conductivity and avoid the aggregation of HNTO nanowires during cycling. As a result, the as-made HNTO/CS can deliver a capacity of 107.8 mAh g–¹ at 100 mA g–¹ after 20 cycles, and keep the capacity of 90.9% and 82.5% after 200 and 1555 cycles, respectively, much better than the samples without hydrogenation treatment or N-doped CS and reported KTiₓOy-based materials. Our work highlights the importance of hydrogenation treatment and N-doped CS in enhancing the electrochemical property for KIBs.