Synthesis of Polyvinylpyrrolidone-Stabilized Nonstoichiometric SnO₂ Nanosheets with Exposed {101} Facets and Sn(II) Self-Doping as Anode Materials for Li-Ion Batteries

Engineerings of facet exposure, nonstoichiometric defects and morphology are the key parameters affecting the SnO₂ performance. Development of synthetic procedures enabling to control all these variables in one pot towards enhanced physicochemical performance is a big challenge. Herein we report such a facile microwave hydrothermal preparation of 3D hierarchical architecture assembled from single-crystalline nonstoichiometric SnO₂ (denote as SnO_2-δ) nanosheets with self-doped Sn²⁺ and controllably exposed {101} facets. Polyvinylpyrrolidone (PVP) is used as capping agent allowing to stabilize the ultrathin and ultra-large SnO_2-δ nanosheets and avoid their dissolution in the highly alkaline environment due to the introduction of highly concentrated NaOH, which together with PVP contribute to the formation of nanosheet morphology with preferential growth plane (121) and dominant reactive {101} surfaces. The detailed structural characteristics are examined by XRD, SEM, TEM, FTIR, XPS and Mössbauer spectroscopy, revealing that SnO_2-δ contains 17 at.% of Sn²⁺ dopant. These nonstoichiometric SnO_2-δ hierarchical architectures capped with carbonized PVP manifest superior lithium storage properties compared with the stoichiometric SnO₂, owing to the novel open hierarchical structure composed of flexible and ultrathin nanosheets with large surface area (82 m²/g) and carbon-coating, which avoid the aggregation and provide porous channels facilitating the diffusion of electrolyte and lithium ions.