High-Rate Li⁺Storage Capacity of Surfactant-Templated Graphene-TiO₂Nanocomposites

Abstract

Graphene-TiO 2 nanocomposites are a promising anode material for Li-ion batteries due to their good high-rate capacity, inherent safety, and mechanical and chemical robustness. However, despite a large number of scientific reports on the material, the mechanism of the enhanced high-rate Li + storage capacity that results from the addition of graphene to TiO 2 -typically attributed to improved electrical conductivity -is still not well understood. In this work, we focus on optimizing the processing of surfactant-templated graphene-TiO 2 hybrid nanocomposites. Towards this end, we examine the influence of various processing parameters, in particular the surfactant-mediated colloidal dispersion of graphene, on the material properties and electrochemical performance of grapheneTiO 2 . We investigate the influence of electrode mass loading on Li + storage capacity, focusing mainly on high-rate performance. Furthermore, we demonstrate an approach for estimating power loss during charge/discharge cycling, which offers a succinct method for characterizing the high-rate performance of Li-ion battery electrodes. Metal oxides have been studied extensively as anode materials for Li-ion batteries due to their comparably high Li-insertion/extraction potentials, 1,2 which make them inherently safe from Li-electroplating and dendrite formation, thus preventing membrane perforation and cell shorting even at high lithiation currents. Additionally, good mechanical and chemical stability during operation enables long cycling lifetimes.2-4 However, large oxide particles are restricted to slow charge/discharge rates (< C/5, meaning charge/discharge times > 5 h) because of low diffusion rates of Li +5-8 and poor electrical conductivity in oxides. Much work has therefore been done to address these limitations, with significant attention placed on titanium dioxide (TiO 2 ) 9-12 because it is abundant and chemically inert, and the availability of simple processes for producing nanostructured (i.e., nano-sized or nano-porous) TiO 2 make it attractive for large-scale use.Nanostructuring of TiO 2 improves Li + transport mainly by decreasing the length of Li + diffusion pathways through the oxide during lithiation/delithiation. 8,[13][14][15] In addition, the diffusivity of Li + in TiO 2 can be enhanced by using surfactant templates to orient the growth of the oxide. [16][17][18] To improve electron transport in TiO 2 electrodes, on the other hand, conductive coatings [19][20][21][22] at [SDS] just below the cmc, however, micelles will only be present on FGSs. 37 As such, the [SDS] used in the processing of FGS-TiO 2 will strongly influence where TiO 2 growth occurs and how intimately interconnected FGSs and TiO 2 will be, which will significantly affect the Li + storage performance of the nanocomposites. Furthermore, as the practical energy density of the system depends, in part, on the fraction of active mass present, 38 it is also necessary to investigate the effect of electrode mass loading, i.e., the amount of active material per unit ...

Reversible Cluster Aggregation and Growth Model for Graphene Suspensions

“…In such aggregated structures, a deterministic control of the topological features is of paramount importance to define properties by controlling parameters such as accessible area for chemical reactions, load transfer for mechanical properties, electron and heat transfer for electronic and thermal properties. To this end, research efforts have been exclusively experimental to observe the effects of dispersion quality on the final properties of the products …”