Unveiling the Origin of Superior Electrochemical Performance in Polycrystalline Dense SnO₂ Nanospheres as Anodes for Lithium-ion Batteries

Development of feasible electrode materials is significant to realize high energy density Li-ion batteries (LIBs). Tin(IV) oxide, in particular, has a number of merits including higher theoretical capacity compared with graphite (1493 mAh g–1), low cost, and environmental friendliness. Nevertheless, huge volume changes and subsequent pulverization usually resulted in poor capacity retention of SnO2, where various nanostructures have been adopted to overcome its intrinsic limitations. Here we introduce the new insights into employing polycrystalline dense SnO2 nanospheres (NSs), rather than its hollow structures, as high-performance electrode for LIBs. Contrary to the previous notions, polycrystalline dense SnO2 NSs can exhibit highly stable cycle retention characteristics (1009.9 mAh g–1 after 300 cycles at 0.5 A g–1) as well as considerable rate capabilities (349 mAh g–1 at 5.0 A g–1), even superior to those of polycrystalline hollow SnO2 NSs. Based on the in situ TEM analyses and electrochemical/postmortem analyses, such improved electrochemical performance can be attributed to the (i) predominant isotropic volume changes of polycrystalline SnO2, (ii) formation of numerous nanograins within the NSs, and (iii) maintenance of structural integrity without pulverizations. This work sheds lights on the importance of using polycrystalline dense nanostructures to mitigate the effects of large volume changes and minimize pulverization, which can also be applied to other electrode materials.