ja9b13572_si_001.pdf (3.27 MB)
Revealing High Na-Content P2-Type Layered Oxides as Advanced Sodium-Ion Cathodes
journal contribution
posted on 2020-03-13, 17:38 authored by Chenglong Zhao, Zhenpeng Yao, Qidi Wang, Haifeng Li, Jianlin Wang, Ming Liu, Swapna Ganapathy, Yaxiang Lu, Jordi Cabana, Baohua Li, Xuedong Bai, Alán Aspuru-Guzik, Marnix Wagemaker, Liquan Chen, Yong-Sheng HuLayered
Na-based oxides with the general composition of NaxTMO2 (TM: transition metal) have
attracted significant attention for their high compositional diversity
that provides tunable electrochemical performance for electrodes in
sodium-ion batteries. The various compositions bring forward complex
structural chemistry that is decisive for the layered stacking structure,
Na-ion conductivity, and the redox activity, potentially promising
new avenues in functional material properties. In this work, we have
explored the maximum Na content in P2-type layered oxides and discovered
that the high-content Na in the host enhances the structural stability;
moreover, it promotes the oxidation of low-valent cations to their
high oxidation states (in this case Ni2+). This can be
rationalized by the increased hybridization of the O(2p)-TM(3d-eg*) states,
affecting both the local TM environment as well as the interactions
between the NaO2 and TMO2 layers. These properties
are highly beneficial for the Na storage capabilities as required
for cathode materials in sodium-ion batteries. It leads to excellent
Na-ion mobility, a large storage capacity (>100 mAh g–1 between 2.0-4.0 V), yet preventing the detrimental sliding of the
TMO2 layers (P2–O2 structural transition), as reflected
by the ultralong cycle life (3000 (dis)charge cycles demonstrated).
These findings expand the horizons of high Na-content P2-type materials,
providing new insights of the electronic and structural chemistry
for advanced cathode materials.