Cation Co-Intercalation with Anions: The Origin of Low Capacities of Graphite Cathodes in Multivalent Electrolytes

• Published in: Journal of the American Chemical Society 2023-06, Vol.145 (22), p.12093-12104
• Main Authors: Yang, Yuanyuan, Wang, Jinzhi, Du, Xiaofan, Jiang, Hongzhu, Du, Aobing, Ge, Xuesong, Li, Na, Wang, Hao, Zhang, Yuchen, Chen, Zheng, Zhao, Jingwen, Cui, Guanglei
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.3c01555

Dual-ion batteries involving anion intercalation into graphite cathodes represent promising battery technologies for low-cost and high-power energy storage. However, the fundamental origins regarding much lower capacities of graphite cathodes in earth abundant and inexpensive multivalent electrolytes than in Li-ion electrolytes remain elusive. Herein, we reveal that the limited anion-storage capacity of a graphite cathode in multivalent electrolytes is rooted in the abnormal multivalent-cation co-intercalation with anions in the form of large-sized anionic complexes. This cation co-intercalation behavior persists throughout the stage evolution of graphite intercalation compounds and leads to a significant decrease of sites practically viable for capacity contribution inside graphite galleries. Further systematic studies illustrate that the phenomenon of cation co-intercalation into graphite is closely related to the high energy penalty of interfacial anion desolvation due to the strong cation–anion association prevalent in multivalent electrolytes. Leveraging this understanding, we verify that promoting ionic dissociation in multivalent electrolytes by employing high-permittivity and oxidation-tolerant co-solvents is effective in suppressing multivalent-cation co-intercalation and thus achieving increased capacity of graphite cathodes. For instance, introducing adiponitrile as a co-solvent to a Mg2+-based carbonate electrolyte leads to 83% less Mg2+ co-intercalation and a ∼29.5% increase in delivered capacity of the graphite cathode.