Controlled Nano-Crystallization for Optimizing of Lead Acid Positive Active Material Using Graphene Nano-Composites
O.J. Dada, K.K. Yeung and MM-F Yuen ECS Meeting Abstracts, 2015
Posted: 19 Mar 2019
Date Written: July 27, 2015
Technological demands in HEVs, renewable systems, and electrical storage systems coupled with its mature industrial process, recyclability and low cost has furthered the interests in Lead acid (LAB) systems. The LAB Positive active materials, due to low utilization and life cycle, severely limits the competitiveness of the traditional battery. Reported attempts to optimize the lead acid system using nano-size materials including graphene and carbon nanotubes, has yielded increase in some performance metrics, but little is known about the responsible mechanisms . Based on the gel-crystal theory, Pavlov et al. has established that the lead acid active mass particles comprises interfaces made of intermediate amorphous molecules, within which the electrochemical reactions take place. Little or nothing is known about the effects of additives of micro- and sub-micro sizes on the redox activity in the gel zone, and how the chemistry of the active mass is improved to result in global increase in capacity and cycle life of the positive active mass.
This research demonstrates highly improved discharge capacity and cycle life obtained from careful combination of cathode materials with tailored graphene based additives: Graphene Oxide (GO), chemically converted graphene (CCG) and pristine graphene (GX). The chemical and electrochemical phenomena responsible for the high activity of the positive active particles in the cathode were established. PbO-GO had the best performance with highest utilization of 41.8%, followed by PbO-CCG (37.7%), PbOcontrol (29.7%), and PbO-GX (28.7%) at 2.5C rate. PbO-CCG seemed to have the best performance: better on charging, lower internal resistance, but poorer cycle life compared to PbO-GO. GO & CCG optimized samples had better discharge capacity and cyclic performance. Cycled at 2.5C rate, all samples but the control, had Increasing capacity till after ~50 cycles. This is due to electro-functionalization of the graphene sheets which tailored the growth of PbO2crystals in the gel zone. Also, there is a difference in the response of graphene composites to the chemistry of the reacting species on charging and discharging.
The extra-ordinary mobility of ions was facilitated by electrochemical functionalization and controlled nano-recrystallization of cathode particles along graphene sheets embedded with the gel-crystal interface. Porosity or surface area increase had no effects.
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