Graphene nano-sheets such as graphene oxide, chemically converted graphene and pristine graphene improve the capacity utilization of the positive active material of the lead acid battery. At 0.2C, graphene oxide in positive active material produces the best capacity (41% increase over the control), and improves the high-rate performance due to higher reactivity at the graphene/active material interface. The in-situ changes in the graphen. Graphene nano-sheets such as graphene oxide, chemically converted graphene and pristine graphene improve the capacity utilization of the positive active material of the lead acid battery. At 0.2C, graphene oxide in positive active material produces the best capacity (41% increase over the control), and improves the high-rate performance due to higher reactivity at the graphene/active material interface. The in-situ changes in the graphene structure and oxygen states support these, as well as higher adsorptive surface area, better graphene/lead dioxide interfacial reaction, and finer & highly utilized lead dioxide phases. The multi-scale physio-chemical mechanisms improving capacity and cycle life is thus: Electrolyte/ionic permeation improvements results from increase in pre-formation porosity, and higher interfacial reactivity at gel zone which enhances active material reversibility. Our ion transfer model reveals the optimized redox reaction in the electro-active zone of graphene enhanced active materials. This work shows the best enhancement in the capacity of lead-acid battery positive electrode till date.••••Highest reported optimization for positive active material.••1 wt% GO additive results in 57% Capacity utilization increase at 0.2 C.••Lower Peukert dependencies, excellent rate performance and high current rate stability.••GO/PbO2 interfacial interaction caused increased electrochemical activity.••Increased utilization of lead oxide core and increased electrode structural inte. Technological demands in Hybrid Electric Vehicle (HEVs), renewable systems, and electrical storage systems, in addition to existing mature industrial process, recyclability and the low cost-per-energy, have extended the research interests in lead-acid battery (LAB). Efforts have been made to improve LAB positive active materials; that is, prolonging the life cycle by optimizing the utilization of the stoichiometric capacity of the PbO, which limits the competitiveness of the lead battery. The utilization (ActualCapacityStoichiometricCapacity) was less than 20% for the active material at high discharge rates, and lower than 55% at extremely low discharge rates. A commonly identified problem is the reduced access of electrolyte at high discharge rates. However, a more important emphasis is the conduction and desorption of ions (HSO4− and *OH) through the micro-channels in the active mass aggregate. Non-conductive additives have been utilized, but too high porosity had a detrimental effect on inter-particle cohesion, reducing conductivity, especially when there no chemical binder. The local problems include unreactive local materials, or electrochemically isolated electrode particles within the aggregate, resulting from increased crystallinity and size of passivated crystals. This reduced electrochemical reversibility of the electrode also shortens cyclic life, as capacity drops appreciably. Another resultant problem is low conductivity of the positive active mass which prompted the addition of conductive additives; how. 2.1. Active mass preparation1 wt% of the graphene additives were used to enhance the positive paste to obtain the respective active materials (GO-PAM, CCG-PAM and GX-PAM) in comparison with the control (CNTL-PAM), while 0–2.5 wt% GO loading in the GO-PAM was used to obtain the effect of GO wt% on utilization to determine the optimal graphene loading. The lead oxide preparation and mixing procedure were critical to the quality and composition of the composite electrode. Leady oxide and graphene additives (from the Energy Research Lab of HKUST) were prepared by mortar and pestling. The main objective of this procedure was to ensure proper blending of the graphene additives with the lead oxide resulting in uniform composition, proper interfacial interaction and enhanced strength of the composite electrode throughout manufacture and testing. The milling processes impact high energy that disperses the particles uniformly, with graphene additives disappearing into the composite. This ensures sufficient homogeneity in dry state as well as after addition of the H2O and H2SO4. To form 3BS paste (4PbO + H2SO4 → PbSO4.3PbO.H2O), less than 7 wt.% of 1.4 M H2SO4 (aq) and a calculated amount of de-ionized H2O is used and the temperature kept below 60 °C. Pastings were done on Pb-Sn grids of 15 mm X 13 mm to 2.2 mm electrode thickness on the anode and cathode. The thickne. 3.1. Analysis of electrochemical performanceThe electrochemical performance of the reference and graphene optimized electrodes (in Fig. 2a–b and Table 1) were as per compared the charge/discharge profile and the discharge capacity over 110 cycles. GO-PAM had the best performance with the highest utilization of 41.8%, followed by CCG-PAM (37.7%), CNTL-PAM (29.7%), and GX-PAM (28.7%). CCG-PAM seemed to have the best performance better on charging, lowest internal resistance (28.7 ohms at 5th cycle), due to the higher electron conductivity of reduced graphene compared to graphene oxide. Reduced graphene (CCG) has greater multiplicity (over 60%) of conductive and electron discharging sp2 carbon clusters. Curiously after 25 cycles, all the three optimized samples had increased discharge capacity and utilization, with graphene (GX-PAM) leading the control sample; despite a slight increase in internal resistance. This was due to increased electrochemical interaction and ionic activity of graphene additives within the active material. The cyclic performance of the optimized samples relative to the control is given in Fig. 2b. The GO-PAM had the most optimized cyclic performance with 87.6 mAg−1 capacity at 130 cycles, with CCG-PAM reaching such a decreasing in utilization at the same capacity only after ˜45 cycles. Greater interfacial interaction and increased electro-active surface are.
