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Transition metal phosphides (TMPs) are promising candidates for sodium ion battery anode materials because of their high theoretical capacity and earth abundance. Similar to many other P-based conversion type electrodes, TMPs suffer from large volumetric expansion upon cycling and thus quick performance fading. Moreover, TMPs are easily oxidized in air, resulting in a surface phosphate layer that not only decreases the electric conductivity but also hinders the Na ion transport. In this work, we present a general electrode design that overcomes these two major challenges facing TMPs. Using metal hydroxide and glucose as precursors, we show that the metal hydroxide can be converted into phosphide whereas the glucose simultaneously decomposes and forms carbon shell on the phosphide particles under a plasma ambient. Ni2P@C core shell structures as a proof-of-concept are designed and synthesized. The in situ formed carbon shell protects the Ni2P from oxidation. Moreover, the high-energy plasma introduces porosity and vacancies to the Ni2P and more importantly produces phosphorus-rich nickel phosphides (NiPx). As a result, the Ni2P@C electrodes achieve high sodium capacity (693 mAh·g−1 after 50 cycles at 100 mA·g−1) and excellent cyclability (steady capacity maintained for at least 1, 500 cycles). Our work provides a general strategy for enhancing the sodium storage performance of TMPs, and in general many other conversion type electrode materials that are unstable in air and suffer from large volumetric changes upon cycling.

Publication history
Copyright
Acknowledgements

Publication history

Received: 17 June 2021
Revised: 07 July 2021
Accepted: 10 July 2021
Published: 12 August 2021
Issue date: March 2022

Copyright

© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Nos. 21805136 and 22001081), the Startup Foundation for Introducing Talent of NUIST (Nos. 1521622101002 and 1521622101003), and the open research fund of State Key Laboratory of Organic Electronics and Information Displays.

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