Understanding the Li-storage in few layers graphene with respect to bulk graphite: experimental, analytical and computational study

Abstract

Greater Li-capacity of well-ordered fairly pristine few layers graphene is due to combined contributions of ‘classical’ bulk Li-intercalation (up to LiC6) and surface storage, especially near the exposed ‘stepped’ edges of each graphene layer (but not exactly at the edge sites).

Understanding the Cyclic (In)stability and the Effects of Presence of a Stable Conducting Network on the Electrochemical Performances of Na2Ti3O7

“…This was done to ensure a fair comparison between the two materials types, since for NTO (without MWCNTs) the features (i. e. current peaks) become very less prominent even in just the second CV scans; whereas it is not the case with NTO/MWCNT (compare Figures a, b with 4d, e). The maximum currents ( i ) recorded at the main peak position corresponding to the formation of Na 4 Ti 3 O 7 (i. e. at ∼0.17 V against Na/Na + ) during the cathodic scans at each of the scan rates ( υ ) have been plotted in terms of log ( i ) vs. log ( υ ) (see Figures c and d); as was done also in a couple of our recently published works ,. If power law is obeyed, the relationship between current ( ) and sweep rate ( ) may be expressed as in Equation (1); …”

“…where k is an adjustable (fitting) parameter and b gets determined by the slope of the best straight line fit for the data points in log ( i ) vs. log ( υ ) plots. A value of 0.5 for b indicates purely diffusion controlled mechanism of charge storage, whereas value of 1 for b indicates purely surface controlled phenomena; with intermediate values indicating partial contributions from both surface, as well as diffusion, controlled phenomena …”

Emergent Pseudocapacitance of 2D Nanomaterials

“…The lithium storage of few‐layer graphene is very similar to intercalation stage mechanism of graphite, while that of single layer graphene behaves electrochemical adsorption mainly on one side due to a repulsive force. Mukhopadhyay and co‐workers also investigated the effect of nanoscaling on the lithium storage of few‐layer graphene . At the reduced dimensional scale (≈7 layers as a model), classical intercalation mechanism was not observed, while both diffusion‐ and surface‐controlled mechanisms were shown.…”

“…[31] In addition, if the particle size of bulk LiCoO 2 , which is a common cathode in LIB, is less than 10 nm, the voltage profile shows the transition from the intercalation plateau to a sloped profile that is character iritic of pseudocapacitance, [32] Therefore, the pseudocapacitance of 2D nanomaterials is expected to be derived "extrinsically" from the nanoscale engineering of the redox-active layered materials. For instance, when bulk layered graphite used as a commercial anode in LIBs is exfoliated into 2D graphene, the diffusion-controlled intercalation becomes inactive while the typical EDLC feature appears.…”

“…Recently, the SC community has revisited bulk layered materials through various nanotechnologies such as nanostructuring, nanoarchitecturing, and compositional control at the nanoscale. For instance, when bulk layered graphite used as a commercial anode in LIBs is exfoliated into 2D graphene, the diffusion‐controlled intercalation becomes inactive while the typical EDLC feature appears . In addition, if the particle size of bulk LiCoO 2 , which is a common cathode in LIB, is less than 10 nm, the voltage profile shows the transition from the intercalation plateau to a sloped profile that is character iritic of pseudocapacitance, Therefore, the pseudocapacitance of 2D nanomaterials is expected to be derived “extrinsically” from the nanoscale engineering of the redox‐active layered materials.…”