Plasma Assisted Synthesis of Sn Based Nanocomposites As High Performance Li-Ion Anodes
Authors: Hu Renzong , Sun Wei , Liu Hui , Zhu Min 
Published: February 2020

Sn-based alloys /oxides /composite, which have been regarded as potential alternative anode materials, not only have a high theoretical capacity, but also have moderate operation potential to avert the safety concern of Li deposition and co-insertion of solvents to the active materials as is the case with graphite anodes. However, the capacity and cycle performance of the Sn-based anodes should be further improved to meet widely application in Li-ion batteries.
For the Sn-based anode materials, further attention should not only be focussed on the exploration of new material system and the modification of currently available materials, but emphasis should also be placed on the microstructure design of the active materials of electrodes, in terms of tuning the volume stress/strain of electrodes and maintaining their integrity during cycling. We proposed that manipulating the multi-phase and multi-scale structures represents an important strategy for further improving the capacity and cycleability of Sn-based and other high-capacity alloy anodes, together with the development of new materials, new technology, and new mechanism.
Mechanical milling has long been a versatile method for synthesis of nanostructured materials for lithium ion electrodes. However, difficult control of subtle nanostructure, too long time of milling and the related contamination of materials have been barriers for its application. By combining discharge plasma with mechanical milling, referred as Plasma-milling, a synergetic effect between mechanical impact and plasma is generated, which shows unusual significant effect in the synthesis of nanostructured materials. With this method, we have synthesized a series of nanostructured materials, such as WC-based hardmetals, hydrogen storage materials and especially anode materials for Li ion batteries. And very significantly, this method shows great advantage in massive synthesis (kg scale in lab) of a series of Li storage anodes, such as Si-C, Ge-C, Fe2O3-C. All these materials show excellent electrode performances due to the unique multiscale structure created by the P-milling.
In this presentation, P-milling was used to prepare different kinds of Sn–C anode materials. By short-time Ar plasma-milling, a unique Sn–C nanocomposite is obtained with a microstructure of multi-scale Sn particles homogeneously dispersed in a graphite matrix (Figure1). Furthermore, an advanced Sn@SnOx/C nanocomposite was synthesized by using oxygen plasma-milling, in which Sn nanoparticles coated by an ultrathin amorphous/nanocrystalline SnOxlayer are homogeneously embedded within a graphite matrix (Figure 2a, b). As lithium ion anodes, both the plasma Sn-C and Sn@SnOx/C nanocomposites displayed superior electrochemical performance (Figure 2c) to Sn-C composites prepared by conventional ball milling methods. Our results demonstrate that plasma assisted milling is a simple and efficient method to prepare Sn–C composite anodes on a large scale with good performance for lithium ion battery applications.

References

(1) Liu, H., Hu, R. Z.; Zhu, M. J. Mater Chem. 2012, 22,8022.
(2) Liu, H., Hu, R. Z.; Zhu, M. J. Power Sources. 2013, 242,114.
(3) Hu, R.Z.; Sun, W.; Zhu, M. J. Mater Chem.A. 2014, 2,9118.
(4) Sun, W.; Hu, R. Z.; Zhu, M. J. Power Sources. 2014, I 268, 610.

Acknowledgements
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This work was supported by the National Science Foundation of China under projects No.51201065 and 51231003, by Doctorate Foundation of Ministry of Education under projects No. 20120172120007, by the Fundamental Research Funds for the Central Universities under project No.2014ZM0002.

Figure
1
. Back-scattering electron SEM images of Sn-C composites. (a) Plasma milling-10h; (b) Conventional milling-10h; (c) HRTEM images of P-10h Sn-C composites, (d) Histograms of Sn particle size distributions of P-10h.
Figure 2 (a) SEM , (b) TEM image of Sn@SnOx/C nanocomposite via plasma-milling 10h; (c) cycle performance of Sn-C and Sn@SnOx/C nanocomposite

Figure 1