Lead Acid Batteries Research Papers (original) (raw)

Graphene based nano-sheets have gained prominence in batteries and super-capacitors owing to their high aspect ratio, tunable transport properties, diverse ionic functionalities, and dependent surface characteristics. Variants like pristine graphene, graphene oxide, or chemically/thermally reduced graphene are not equal in ionic and transport properties owing to the presence or grafting of functional groups in the honey-comb carbon structure. Therefore, the conductivity or ionic functionality are synergistic in providing the combination of properties needed to function in energy systems or electronics. This research enhances the performance of lead acid battery using three graphene variants, demonstrates the in-situ electrochemical reduction of graphene, and furthering the understanding by the study of the electronic properties of electrochemically reduced graphene for opto-electronic applications.
Technological demands in hybrid electric vehicles, large scale storage and portable power stations has furthered more research interests in Lead Acid Batteries (LAB), in addition to the advantage of power rating per cost. The LAB positive active materials (PAM), due to low utilization and life cycle, severely limits the competitiveness of the traditional battery. The combination of cathode materials with tailored graphene based additives: Graphene Oxide (GO-PAM), chemically converted graphene (CCG-PAM) and pristine graphene (GX-PAM) resulted in improved discharge capacity and cycle life. PAM-GO had the best performance with the highest utilization of 41.8%, followed by CCG-PAM (37.7%), control-PAM (29.7%), and GX-PAM (28.7%) at 2.5C rate. CCG-PAM had better charging performance such as lower internal resistance, but poorer cycle life compared to GO-PAM. Cycled at 2.5C rate, all samples but the control, had increasing capacity till after ~50 cycles. Electrochemical interaction of the graphene sheets which changed the of PbO2 crystals in the gel zone. Ion transfer model was developed showing the optimization of gel zone ion transfer induced by the electrochemical activity of graphene additives.
The mechanistic interfacial characteristics of graphene enhancements in LABs were further evaluated based on the capacitance of the double layer (Cdl) and charge transfer resistance (Rct). The electrochemical impedance spectroscopy (EIS) curves were obtained from Pb/PbO2/HgSO4 system and evaluated using the Randles EIS circuit model, while Randles-Sevcik Equation also helped in understanding the cyclic voltametry (CV) curves. Enhanced samples had lower Rct and were marked by increased peak current values indicating increased faradaic and non-faradaic pseudo-capacitive processes. GO, CCG and GX within the electrode interphase enhanced charge storage in the presence of gel zone ions. The double layer capacitances of the graphene electrodes were higher at maximum charge partly due to agglomeration.
Graphene-based papers are notable for their mechanical strength and applications to large scale electronics. This work established the ex-situ electrochemical transition in the chemistry, electrical and fracture properties of graphene oxide paper (GO) in at the anode (aERGO) and cathode (cERGO). Higher thermal stability and lower weight loss of aERGO (34wt% at 800 °C) with XRD peak at 2ϴ = 10.5° showed the reduction of the ordinary GO paper (95wt% at 800 °C). The fractographs from the SEM showed that the cERGO failed by ductile rupture of a higher degree than the ordinary GO paper, while that of the aERGO was less ductile. UV-Vis, FT-IR and XPS showed the changes in functional groups, via the interaction of graphene oxide functional groups with protons, adsorbed oxygen containing ions. The aERGO and cERGO showed superior electrical conductivity of 1.61 x 106 S/m and 4.27 X 105 S/m respectively. The temperature and frequency dependent electronic characteristics of electrochemically reduced graphene paper (ERGO) were compared with those of graphene oxide paper (GO). The conductivity, permittivity and di-electric losses in ERGO papers were clearly leading those of GO paper by ~ 2 order of magnitude. Strongly polarized ionized cloud of charge carriers in the ERGO were due to higher concentration of conductive clusters. Frequency dependent properties were governed by dipole mobility while temperature dependent electronic characteristics were governed by thermally activated transport of charge carriers affecting their residence time, and increase in sp2 clusters.