Sodium ion batteries (SIB) have attracted more and more research interests recently as a low-cost alternative for LIB. The great challenge is to find proper electrode materials which can satisfy the requirements of commercial application. Among the current reported anodes for SIB, black phosphorus which holds a layered structure and possess high conductivity, can exhibit a large capacity as well as good rate performances, thus becomes the star material in SIB.[1-2] However, the critical requirements of synthesis and low thermo stability of black phosphorus would greatly limit its commercial utilization in battery industry. Recently, we proposed a new phosphorus-like material GeP₅ as the anode candidate for SIB. This material possesses a similar two-dimensional layered structure as black phosphorous and graphite.[3] The introducing of Ge element in the layered structure results in an even higher electronic conductivity than black phosphorus. Besides, the chemical and thermo stability of GeP₅ is much higher than that of black phosphorus. The higher conductivity and better stability made GeP₅ a high performance anode for SIB.

GeP₅ can be easily obtained in a large scale by simply mechanical milling of elemental Ge and low cost red P at ambient pressure. In a typical half cell, GeP₅ can deliver a reversible discharge capacity of 1200 mAh/g for SIB at a current density of 100 mA/g. The large capacity is attributed to the bi-active components of Ge and P in this material which can both store large capacity of sodium during the charge/discharge processes. More important, the first coulombic efficiency of this material reaches 95%, which is much higher than that of other reported anode materials for SIB and can even compete with the commercial anode in LIB industry. By further treating GeP₅ with carbon by high energy ball milling, the obtained GeP₅/C nanocomposite demonstrate much enhanced cycle performances and rate capabilities, due to the good volume accommodation effect of carbon matrix in the composite. Profit from the large capacity and low voltage of GeP₅, a full cell coupled with a GeP₅ anode and a Na₃V₂(PO₄)₃ cathode can deliver a high cell voltage and large cell energy density, which shows a promising potential of GeP₅ in SIB applications.

References:

[1] J. Qian, Y. Xiong, Y. Cao, X. Ai, H. Yang, Nano Lett., 2014, 14, 1865-1869.

[2] J. Sun, G. Zheng, H. Lee, N. Liu, H. Wang, H. Yao, W. Yang, Y. Cui, Nano Lett., 2014, 14, 4573-4580.

[3] W. Li, H. Li, Z. Lu, L. Gan, L. Ke, T. Zhai, H. Zhou, Energy Environ. Sci., 2015, 8, 3629-3636.