Research On Mechanism And Effect Of Additives On Hydrogen Evolution At Negative Plates Of Lead-acid Batteries

The negative plates of lead acid batteries are easy to be sulfated on their surface in the application of hybrid electric vehicles(HEV).Adding carbon additives to the negative plates can effectively inhibit the sulfation,but they can cause serious hydrogen evolution at negative plates and severe water loss which lead to battery failure.Moderate inhibitors of hydrogen evolution were added to the paste of negative plates or electrolyte can increase the hydrogen evolution potential of negative plate and reduce the rate of hydrogen evolution.The effect of different carbon materials and several additives on the hydrogen evolution at negative plates in 1.28 sp gr H2SO4 solution was studied.Also the influence of additives in the container formation and cycle life of 12V 12Ah VRLA battery was studied this work.The conclusions have been drawn as following:1.The Polarization curves of hydrogen evolution at negative plates containing different carbon materials in 1.28 sp gr H2SO4 solution were measured.The conclusions are as follows:(1)In comparison with the negative plate without carbon,the negative plates containing activated carbon,flake graphite or expanded graphite with high iron contents make the polarization potential of hydrogen evolution in 1.28 sp gr H2SO4 solution shift in the positive direction and promote the hydrogen evolution.The order of hydrogen evolution rate is activated carbon>expanded graphite>flake graphite>acetylene black>carbon black>no carbon.(2)The metal impurity content,particularly iron content,in purified carbon materials decreases sharply.The negative plate containing purified activated carbon can partly inhibit the hydrogen evolution;while the negative plates containing expanded graphite or flake graphite with part iron contents can significantly inhibit the hydrogen evolution;(3)In comparison with the negative plate without carbon,the negative plate containing activated carbon,flake graphite,acetylene black or carbon black with low contents of metal impurity make the polarization potential of hydrogen evolution on average decrease by 194mV?23mV?19mV?6mV respectively,but the negative plate containing expanded graphite increases by 32mV.2.The hydrogen evolution at negative plates containing different carbon materials in 1.28.sp gr H2SO4 solution containing different additives were measured.The conclusions are as follows:(1)La2O3,Sm2O3,Gd2O3,Nd2O3,Dy2O3 and polytetrafluoroethlene(PTFE)as electrolyte additives inhibit the hydrogen evolution obviously;(2)When the metal impurity content is high,which depends on their producing area and production processes.0.025%PTFE and 0.025%Dy2O3 additives in electrolyte increase its overpotential greatly;But the effects of low metal impurity contents are opposite,they can increase the polarization potential of hydrogen evolution at negative plates containing acetylene black and to some extent decrease the polarization potential of hydrogen evolution at negative plates containing activated carbon,expanded graphite or flake graphite with low contents of impurity.3.In the test of the container formation and cycle life of the 12V12Ah VRLA batteries with electrolyte containing 0.025%PTFE and 0.025%Dy2O3.the result shows that combined additive of PTFE and Dy2O3 reduces water loss and the volatilization of acid mist in the container formation and greatly increases the charge efficiency and thus decreases water loss simultaneously.