Improving Low‐temperature Performance and Stability of Na2Ti6O13 Anodes by the Ti−O Spring Effect through Nb‐doping

• Published in: Angewandte Chemie International Edition 2023-11, Vol.62 (46), p.n/a
• Main Authors: Hu, ChangYan, Li, Ying, Wang, Dong, Wu, Chunjin, Chen, Feng, Zhang, Linghong, Wan, Fang, Hua, Weibo, Sun, Yan, Zhong, Benhe, Wu, Zhenguo, Guo, Xiaodong
• Format: Article
• Language: English
• Subjects: Anodes; Charge density; Diffusion barriers; Discharge capacity; Doping; Electrochemical analysis; Electrochemistry; Low conductivity; Low-Temperature; Na2Ti6O13 Anode; Nb-Doping; Robust Spring Effect; Sodium-ion batteries; Structural stability
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202312310

Na2Ti6O13 (NTO) with high safety has been regarded as a promising anode candidate for sodium‐ion batteries. In the present study, integrated modification of migration channels broadening, charge density re‐distribution, and oxygen vacancies regulation are realized in case of Nb‐doping and have obtained significantly enhanced cycling performance with 92 % reversible capacity retained after 3000 cycles at 3000 mA g−1. Moreover, unexpected low‐temperature performance with a high discharge capacity of 143 mAh g−1 at 100 mA g−1 under −15 °C is also achieved in the full cell. Theoretical investigation suggests that Nb preferentially replaces Ti3 sites, which effectively improves structural stability and lowers the diffusion energy barrier. What's more important, both the in situ X‐ray diffraction (XRD) and in situ Raman furtherly confirm the robust spring effect of the Ti−O bond, making special charge compensation mechanism and respective regulation strategy to conquer the sluggish transport kinetics and low conductivity, which plays a key role in promoting electrochemical performance. Integrated effects of migration channels broadening, charge density re‐distribution, and oxygen vacancies modulation are achieved via high valence state ion‐doping in case of Nb5+. The modified samples optimized excellent long‐cycle stability, and superior low‐temperature performance in the full cell. Importantly, it is demonstrated for the first time that high‐valent transition metal preferentially replaces the Ti3 site of NTO, effectively improving electrical conductivity and ion diffusion rate. More interestingly, the “spring effect” of chemical bonding, which is twisted‐recovered‐twisted with the motion of Na+, is investigated for the first time by in situ Raman, and the stabilizing effect of Nb enables the more regular and reversible “spring effect”.