Proton-assisted calcium-ion storage in aromatic organic molecular crystal with coplanar stacked structure

Cuiping Han,Jiaxiong Zhu,Chunyi Zhi,Yu Li,Hongfei Li

doi:10.1038/s41467-021-22698-9

Cuiping Han, Jiaxiong Zhu + Show 3 more

Open Access

https://doi.org/10.1038/s41467-021-22698-9

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Abstract

Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries. However, the high charge density of divalent Ca2+ establishes a strong electrostatic interaction with the hosting lattice, which results in low-capacity Ca-ion storage. The ionic radius of Ca2+ further leads to sluggish ionic diffusion, hindering high-rate capability performances. Here, we report 5,7,12,14-pentacenetetrone (PT) as an organic crystal electrode active material for aqueous Ca-ion storage. The weak π-π stacked layers of the PT molecules render a flexible and robust structure suitable for Ca-ion storage. In addition, the channels within the PT crystal provide efficient pathways for fast ionic diffusion. The PT anode exhibits large specific capacity (150.5 mAh g-1 at 5 A g-1), high-rate capability (86.1 mAh g-1 at 100 A g-1) and favorable low-temperature performances. A mechanistic study identifies proton-assisted uptake/removal of Ca2+ in PT during cycling. First principle calculations suggest that the Ca ions tend to stay in the interstitial space of the PT channels and are stabilized by carbonyls from adjacent PT molecules. Finally, pairing with a high-voltage positive electrode, a full aqueous Ca-ion cell is assembled and tested.

Highlights

Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries
Theoretical calculations reveal that the negative charges of Ca-based enolate are delocalized across the stacks due to π–π stacking interactions such that one Ca2+ ion is stabilized by four carbonyls from adjacent PT molecules
Aromatic organic molecules with fewer electrondonating phenyl groups (–C6H5), such as DMQ and 2,5-dichloro BQ, show relatively higher redox potentials (Fig. 1a). Their capacity is limited to 40–60 mA h g−1, most likely due to the high charge density of Ca2+, causing strong electrostatic repulsion from the small molecules

Summary

Introduction

Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries. We report aromatic organic molecular crystals, represented by 5,7,12,14-pentacenetetrone (PT), as a high-rate and long-life CIB anode material in mild aqueous electrolytes.

Results

Conclusion