A new type of morphological instability in Sn/2D graphene anodes

Sn-based anodes are well known for experiencing severe fracture during electrochemical cycling, due to the large-volume expansions that occur upon lithiation. This study, however, presents a new type of morphological instability for anodes composed of Sn nanoparticles attached on 2D graphene, as transmission and scanning electron microscopy reveal that after long-term cycling the Sn particles agglomerate to form clusters of up to 1 μm. Such clustering of Sn is quite the opposite of the fragmentation that is typically observed upon lithiation. This new microstructural instability mechanism can interpret the inability of Sn-2D graphene nanocomposites to retain their initial high capacity, since micro-scale particles do not allow for deep lithiation. For the present anodes, the initial capacity was ∼ 600 mAh/g (10% Sn-graphene) and ∼ 1100 (20% Sn-graphene) but stabilized to ∼ 230 mAh/g (10% Sn-graphene) and 255 mAh/g (20% Sn-graphene), while the initial Sn particle size was ∼ 50 nm but after 120 cycles it had increased to 1 μm. A detailed microscopy study for capturing Electrochemical coarsening has not been done before.