SnO2-QDs/Rgo Nanocomposites for Lithium Ion Battery Anodes
Authors: Hoque Md. Ikram Ul , Gibson Andrew , Donne Scott 
Published: November 2022

SnO2 is one of the most efficient materials for lithium ion battery (LIBs) anodes as it can theoretically provide a reversible capacity of 790 mAh/g (graphite, 372 mAh/g) for alloying reaction with lithium ion [(i) SnO
2 + 4 Li+
+ 4e
- = 2Li
2
O + Sn, (ii) Sn + xLi+
+ xe-
= LixSn (0 ≤ x ≤ 4.4)] during charge-discharge process [1]. In addition, SnO2 shows lowest operating potentials (average charge and discharge potentials: 0.3 V and 0.5 V vs. Li/Li+, respectively) in comparison with other transition metal oxides, facilitating a higher energy density when a full cell is constructed [2]. However, two issues: (1) poor electric conductivity, and (2) high volume fluctuation during lithiation-delithiation process (about 200-300%), limit its direct use as the anode material. To bit these issues, various carbon materials are employed to load the SnO2 [3].

Graphene, a carbon allotrope, which possesses high electrical conductivity (106 s/cm), excellent mechanical flexibility (Young’s modulus up to 1.0 TPa) and high surface area (2630 m2/g) and in addition, lithium storage capacity of a single layer graphene is theoretically found to be 744 mAh/g. Consequently, graphene can be most suitable host to incorporate the SnO2 [3]. We have tailored SnO2 quantum dots (TOQDs) encapsulated reduced graphene oxide (RGO) nanocomposite (TOQDs/RGO) by in-situ growth of the TOQDs in the RGO flakes. A nanofluidic synthesis approach has been developed using 1D-Sn(OH)4 nanofluid [4] and graphene oxide (GO) nanofluid [5] as prim precursors for the homogeneous encapsulation of the TOQDs in RGO flakes. The 1D-Sn(OH)4 nanofluid was dropwise added to the graphene oxide (GO) nanofluid with continuous stirring. Then the resultant mixture was sonicated to get a nanofluidic mixture which was freeze-dried followed by calcination at 600 °C for 6 hrs under nitrogen gas. During these processes, in-situ growth of the TOQDs was proceeded on the RGO plane, leading to give their homogeneous distribution with encapsulation on the RGO plane. The cyclic voltammetry (CV) and glavanostatic charge-discharge (GCD) were performed on an Iviumstat Multichannel Potentiostat using a three-electrode cell and two-electrode cell, respectively. It is found that the developed TOQDs/RGO nanocomposite provides high reversible specific capacity with excellent rate capability. The results of these electrochemical studies implied that the developed TOQDs/RGO nanocomposite could be utilized for high-performance LIBs.

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