Submicro-sized Si-Ge solid solutions with high capacity and long cyclability for lithium-ion batteries

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Xiao-Chen Liud) College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, China

Mark Geppert Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29208, USA

James J. Wu Electrochemistry Division, NASA Glenn Research Center, Cleveland, Ohio 44135, USA

Jun-Tao Li, Ling Huang, and Shi-Gang Sun State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, China

Xiao-Dong Zhoub) State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, China; and Department of Chemical Engineering, Institute for Materials Research and Innovation, University of Louisiana, Lafayette, Louisiana 70503, USA

Fu-Sheng Kec) College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, China (Received 23 February 2018; accepted 24 April 2018)

Mastery of strengthening strategies to achieve high-capacity anodes for lithium-ion batteries can shed light on understanding the nature of diffusion-induced stress and offer an approach to use submicro-sized materials with an ultrahigh capacity for large-scale batteries. Here, we report solute strengthening in a series of silicon (Si)–germanium (Ge) alloys. When the larger solute atom (Ge) is added to the solvent atoms (Si), a compressive stress is generated in the vicinity of Ge atoms. This local stress field interacts with resident dislocations and subsequently impedes their motion to increase the yield stress in the alloys. The addition of Ge into Si substantially improves the capacity retention, particularly in Si0.50Ge0.50, aligning with literature reports that the Si/Ge alloy showed a maximum yield stress in Si0.50Ge0.50. In situ X-ray diffraction studies on the Si0.50Ge0.50 electrode show that the phase change undergoes three subsequent steps during the lithiation process: removal of surface oxide layer, formation of cluster-size Lix(Si,Ge), and formation of crystalline Li15(Si,Ge)4. Furthermore, the lithiation process starts from higher index facets, i.e., (220) and (311), then through the low index facet (111), suggesting the orientationdependence of the lithiation process in the Si0.50Ge0.50 electrode.

I. INTRODUCTION

Development of anode materials for high performance lithium-ion batteries has been driven by the recognition of mitigating the adverse effects of pulverization in highcapacity materials, such as silicon (Si) and tin (Sn). Significant progress has been made since 20081 toward improving capacity retention in Si. Si is an attractive anode candidate because of its high theoretical capacity of 4200 mAh/g, corresponding to Li22Si5 composition Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] c) e-mail: [email protected] d) These authors contributed equally to this work. DOI: 10.1557/jmr.2018.145

with a lattice constant of 18.66 Å and 3580 mAh/g for Li15Si4 with a lattice constant of 10.777 Å.2,3 As a result, a large volume change (;400%) from Si (lattice constant 5.431 Å and four silicon at