Facilely synthesis of SnO₂ dots decorated reduced graphene oxide with ultra-long lithium storage life

In lithium-ion batteries (LIBs), commercial anodic graphite has reached its limit of theoretical capacity and some metal-based composites are drawing substantial attention due to their higher Li storage ability and better cyclic performance. In this work, SnO dots modified reduced graphene oxide (rGO/SnO) is prepared using a modified colloidal precipitation (MCP) method followed by calcination in air. After 1000 cycles, rGO/SnO-70 can retain reversible discharge specific capacities of 584 (1 A·g) and 378 mAh·g (2 A·g), respectively. This study can provide a reference for the design of anode composite materials with high-capacity and ultra-long cyclic life.

rGO/SnO is prepared using a MCP method followed by calcination in air. The rGO/SnO composites are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The specific surface area of rGO/SnO are measured using Brunauer Emmett Teller (BET) analysis and the mass percent of SnO is calculated through thermogravimetric (TG) analysis, respectively. CR-2032 batteries are assembled in a glove box. The electrochemical performance of the electrode is tested and analyzed using constant current charge discharge technology and cyclic voltammetry in the range of 0.02-3 V.

The XRD results indicate that rGO/SnO is successfully fabricated. The Raman spectra confirm the existence of the graphene components. The mass percentage of SnO is analyzed by TG. The specific surface area of rGO/SnO is tested by BET, which is benefit for the transfer of Li. The SEM and TEM images further confirms the formation of rGO/SnO. As anode for LIB, rGO/SnO-70 exhibits a higher specific capacity than rGO/SnO-40 and more stable cycling performance than rGO/SnO-100. After 1000 cycles, the capacity of rGO/SnO-70 are 584 (1 A·g) and 379 mAh·g (2 A·g), respectively. The lithium storage processes of rGO/SnO-70 is studied through its initial 3 charge/discharge curves and the corresponding dQ/dV curves. The results indicate that the interconversion between SnO and Sn in rGO/SnO-70 is highly reversible, leading to high lithium storage capacity. After the rate activation process, the CV curves show higher alloying peak of Sn, leading to high specific capacity of SnO. Compared with the reported SnO-based composite, rGO/SnO shows advantages including low-cost, no additives and high performance. The Sn 3d characteristic peak in the XPS curve of rGO/SnO-70 after 20 cycles confirms the presence of SnO. As a result, the lithium storage mechanism of rGO/SnO-70 is: SnO + ( + 4)Li + ( + 4)e ↔ SnLi + 2LiO (0 ≤ x ≤ 4.4). The conversion between SnO and Sn is reversible, and SnO shows a fully reversible specific capacity of 1495 mAh·g, resulting in high specific capacity of rGO/SnO-70. rGO/SnO shows two advantages for lithium storage. On the one hand, the rGO "cores" can not only serve as electronic conductors to accelerate reaction kinetics during lithium insertion/extraction processes, but also effectively buffer the volume changes of SnO, thereby achieving stable lithium storage performance of rGO/SnO. On the other hand, the SnO quantum dots can prevent the re stacking of rGO, shorten the diffusion distance of Li, and increase the contact area between the electrode and the electrolyte, thereby improving the rate specific capacity of rGO/SnO.

The rGO/SnO composite materials are prepared using a MCP process followed by a calcination process in air. The rGO/SnO-70 exhibits high capacities of 584 (1 A·g) and 379 mAh·g (2 A·g) after 1000 cycles, respectively. This study provides a reference for the novel anodic carbonaceous materials with high capacity at high current density and ultra-long cyclic life.