Abstract
Among the many studied Li-ion active materials, silicon presents the highest specific capacity, however it suffers from a great volume change during lithiation. In this work, we present two methods for the chemical modification of silicon nanoparticles. Both methods change the materials’ electrochemical characteristics. The combined XPS and SEM results show that the properties of the generated silicon oxide layer depend on the modification procedure employed. Electrochemical characterization reveals that the formed oxide layers show different susceptibility to electro-reduction during the first lithiation. The single step oxidation procedure resulted in a thin and very stable oxide that acts as an artificial SEI layer during electrode operation. The removal of the native oxide prior to further reactions resulted in a very thick oxide layer formation. The created oxide layers (both thin and thick) greatly suppress the effect of silicon volume changes, which significantly reduces electrode degradation during cycling. Both modification techniques are relatively straightforward and scalable to an industrial level. The proposed modified materials reveal great applicability prospects in next generation Li-ion batteries due to their high specific capacity and remarkable cycling stability.
Highlights
The majority of currently produced Li-ion cells contain layered transition metal oxides as cathodes [1] and graphite or semi-graphitized carbon as anode active materials [2,3]
The high specific capacity of silicon is a tremendous advantage compared to currently used materials, during the lithiation, formation of Li-Si alloy can lead to material expansion by up to 300% resulting in a fast mechanical degradation of the electrode layer or/and fast solid electrolyte interface (SEI) layer formation and internal resistance buildup [12]
The X-ray photoelectron spectroscopy (XPS) analysis of modified samples revealed a lower elemental silicon content (21.4 and 2.1% for Si-1 and Si-2 samples, respectively). This variation is the effect of the different silicon oxide layer thickness at the grain surface
Summary
The majority of currently produced Li-ion cells contain layered transition metal oxides as cathodes [1] and graphite or semi-graphitized carbon as anode active materials [2,3]. Group IV elements such as silicon, germanium, tin, and lead [4,5,6,7], as well as their corresponding oxides or nitrides [8,9,10]. In this group, the silicon presents the highest specific capacity (3590 mAh g−1 ), which is almost ten times greater than presently used graphite’s (372 mAh g−1 ) [11], and over three times higher than tin’s (993 mAh g−1 ) [5]. The high specific capacity of silicon is a tremendous advantage compared to currently used materials, during the lithiation, formation of Li-Si alloy can lead to material expansion by up to 300% resulting in a fast mechanical degradation of the electrode layer or/and fast solid electrolyte interface (SEI) layer formation and internal resistance buildup [12]
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