Study On The Energy Storage Mechanisms Of Porous Carbon In Negative Plates Of Lead-carbon Batteries

As the energy crisis and environmental pollution problems become increasingly serious,photovoltaic,wind energy storage and hybrid electric vehicles have become hot research point at home and abroad,which require the energy storage batteries with long cycle life,high output power and good charge acceptance at High-rate Partial-state-of-Charge?HRPSoC?conditions.The traditional lead-acid batteries are mainly used for automobile and various internal combustion engine starting,and wireless communication base stations.However,their negative plates are easily sulfated under HRPSoC conditions,and then their charging capacity and cycle life were greatly reduced.Lead-carbon battery is a new type of lead-acid battery,which adds carbon materials with high specific surface area or high conductivity into negative plate with excellent rate performance and high HRPSoC cycle life.Lead-carbon batteries have a good application prospect in energy storage and hybrid electric vehicle,so the mechanisms of carbon materials in lead-carbon batteries have been widely studied mainly in aspects of the construction of conductive network,H+ double-layer capacitance storage,improvement of pore structure and increase of electrochemical reaction dynamics.But the interaction between lead and porous carbon and its related mechanisms have not been deeply studied.This study is focused on the energy storage mechanisms of porous carbon and lead in negative plates of lead-carbon batteries,which is divided into four parts as follows.?1?A series of porous carbon materials with the comparable physicochemical parameters were used to test the electrochemical properties in pure sulfuric acid environment for the follow-up mechanism studies.The study indicate that in pure sulfuric acid environment,porous carbon with higher SBET and pore volume has higher specific capacitance,but that with lower SBET and pore volume has the moderate hydrogen evolution.More mesoporosity and pore volume would improve the rate performance,but lead to the serious hydrogen evolution.Less acidic functional groups would improve the specific capacitance and rate performance,and inhibit the hydrogen evolution.High conductivity could improve rate performance,but lead to the serious hydrogen evolution.?2?The effect of surface functional groups on the lead-carbon batteries was studied from hydrogen evolution and lead electrodeposition on the surface of PC.Porous carbon?PC?materials were modified by four oxidation and reduction methods.We used cyclic voltammetry and a three-electrode system to prepare lead eletrodeposits on the surface of PC.The results show that in a Pb2+ containing H2SO4 electrolyte,appropriate acidic groups on the surface of PC are beneficial to the lead electrodeposition.The lead deposits with high activity could inhibit the hydrogen evolution and the irreversible sulfation in the negative plates of lead-carbon batteries,and then result in the long cycle life under HRPSoC conditions.?3?Mesoporous carbon?MC?materials were selected to prepare Pb@MC composite through vacuum impregnation followed by chemical-precipitation method.Pb@MC were used to assemble three-electrode device to simulate the electrochemical process of carbon additives in the negative plates.The results show that during higher-rate charge-discharge testing,the lead on the external surface of carbon could be not only electrodeposited into the pores in the form of nano-particle,but also attached on the pore wall with atomic state in the sequence of the lead electrodeposition from macropores to mesopores,and then to micropores.And these nano-lead particles could maintain their size under the limitation of nano-sized pores of carbon,which could inhibit the hydrogen evolution,provide the pseudocapacitance contribution,enhance the reversibility of Pb/PbSO₄,and then result in the longer cycle performance of lead-carbon batteries.?4?According to the above results of mechanisms study,MC materials were modified by NaOH activation and air oxidation methods to prepare Modified-MC materials,and the effect of microscopic modification of porous carbon for lead electrodeposition on the internal surface and its applications in lead-carbon batteries were studied.The results show that through the micro-modification,there were more mesoporous volume and appropriate acidic groups in Modified-MC than MC materials.During higher-rate charge-discharge testing,more nano-lead particles with smaller size could be electrodeposited on the external and internal surface of the Modified-MC materials,which could effectively slow down the degradation of the hydrogen evolution and the pseudocapacitance contribution.This phenomenon could more effectively improve the reversibility of Pb/PbSO₄ and slow down the irreversible sulfation,and then result in the excellent cycle performance of lead-carbon batteries.