Graphite as a Long-Life Ca 2+ -Intercalation Anode and its Implementation for Rocking-Chair Type Calcium-Ion Batteries

• Published in: Advanced science 2019-12, Vol.6 (24), p.1902129
• Main Authors: Richard Prabakar, S J, Ikhe, Amol Bhairuba, Park, Woon Bae, Chung, Kee-Choo, Park, Hwangseo, Kim, Ki-Jeong, Ahn, Docheon, Kwak, Joon Seop, Sohn, Kee-Sun, Pyo, Myoungho
• Format: Article
• Language: English
• Subjects: Batteries; Electrodes; Electrolytes; Graphite; Solvents
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.201902129

Herein, graphite is proposed as a reliable Ca -intercalation anode in tetraglyme (G ). When charged (reduced), graphite accommodates solvated Ca -ions (Ca-G ) and delivers a reversible capacity of 62 mAh g that signifies the formation of a ternary intercalation compound, Ca-G ·C . Mass/volume changes during Ca-G intercalation and the evolution of in operando X-ray diffraction studies both suggest that Ca-G intercalation results in the formation of an intermediate phase between stage-III and stage-II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca-G has a planar structure with Ca surrounded by G , which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g at 1.0 A g s vs 62 mAh g at 0.05 A g ) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca -shuttling calcium-ion batteries with a graphite anode, a full-cell is constructed by coupling with an organic cathode and its electrochemical performance is presented.