Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 7, Issue 43, Pages 24016-24022Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.5b06847
Keywords
2D electride; anode material; diffusion barrier; open-circuit voltage; Na-ion batteries
Funding
- MOST Project of China [2014CB920903, 2011CBA00100]
- NSFC [11174337, 11225418, 11264014, 11574029]
- Specialized Research Fund for the Doctoral Program of Higher Education of China [20121101110046]
- [SUTD-SRG-EPD 2013062]
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Searching for suitable anodes with good performance is a key challenge for rechargeable Na-ion batteries (NIBs). Using the first-principles method, we predict that 2D nitrogen electride materials can be served as anode materials for NIBs. Particularly, we show that Ca2N meets almost all the requirements of a good NIB anode. Each formula unit of a monolayer Ca2N sheet can absorb up to four Na atoms, corresponding to a theoretical specific capacity of 1138 mAh.g(-1). The metallic character for both pristine Ca2N and its Na intercalated state Na2Ca2N ensures good electronic conduction. Na diffusion along the 2D monolayer plane can be very fast even at room temperature, with a Na migration energy barrier as small as 0.084 eV. These properties are key to the excellent rate performance of an anode material. The average open-circuit voltage is calculated to be 0.18 V vs Na/Na+ for the chemical stoichiometry of Na2Ca2N and 0.09 V for Na4Ca2N. The relatively low average open-circuit voltage is beneficial to the overall voltage of the cell. In addition, the 2D monolayers have very small lattice change upon Na intercalation, which ensures a good cycling stability. All these results,demonstrate that the Ca2N monolayer could be an excellent anode material for NIBs.
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