Study On The Application Of Rice Husk-based Activated Carbon Materials As Negative Electrode Additives For Lead-carbon Battery

Lead-acid batteries?LABs?for hybrid electric vehicles?HEVs?require a high-rate charge-discharge process under partial state of charge,which is also named as high-rate partial-state-of-charge operation?HRPSoC operation?.However,this operation will cause the accumulation of PbSO₄?sulfation?on the surface of negative electrode,which finally leads to the failure of LABs under HRPSoC operation.Adding carbonaceous materials into negative active mass?NAM?is an effective strategy to alleviate the sulfation of negative electrode.This type of LABs with negative electrode containing carbonaceous materials is also named as lead-carbon battery and an advanced lead-acid battery technology developed in the past 10 years.Lead-carbon battery originally adopts carbonaceous materials with high specific surface area and good conductivity as additives into NAM,thereby improving the utilization of NAM,suppressing the growth of PbSO₄ and prolonging the cycle life of lead-carbon battery under the HRPSoC operation.Studies have shown that the conductivity,specific surface area,capacitance characteristics,and electrocatalysis effect of carbonaceous materials have been considered as important factors affecting the performances of lead-carbon battery negative electrode.The researches about carbonaceous additives for lead-carbon battery negative electrode have become one of the hot topics of lead-carbon battery.Based on the understanding of those working mechanisms of carbonaceous materials,this paper studies the possibility of adopting rice husk-based activated carbon?RHAC?with porous structure and high specific surface area as additives in lead-carbon battery negative electrode.Some beneficial conclusions are acquired as follows:?1?RHAC is an effective carbonaceous material that can prolong the cycle life of negative electrode under HRPSoC operation.It is found that the well dispersed RHAC particles cause the increase of specific surface area of NAM.These particles can serve as active sites for lead deposition during HRPSoC operation.But the coating of RHAC with dense lead particles is an important factor that causes the quick failure of negative electrode with low RHAC proportion.2.0 wt.%is a suitable proportion for RHAC to enhance the cycle life?4.81 times that of the negative electrode?and improve the specific capacity(131 mAh g^-1 with a discharge current density of 5 mA g^-1).In addition,it is found that the addition of carbonaceous materials can effectively improve the charge-discharge reversibility,the charge acceptance and the conductivity of negative electrode under partial state of charge.Comparing to other carbon materials,the higher external specific surface area(407.4 m² g^-1)and porous structure of RHAC,which can facilitate the diffusion of electrolyte to the surface of RHAC and promote the deposition of lead on the surface of RHAC,are the main reasons for the prolonged HRPSoC cycle life.It is of great significance for the utilization of RHAC in lead-carbon battery.?2?Composites?PbO@RHAC?with different PbO ratios derived from RHAC are prepared controllably by simple chemical-deposition/pyrolysis method.The prepared PbO particles are deposited not only on the surface but also into the pores,which inhibit the hydrogen evolution reaction of RHAC effectively.When the ratio of PbO reaches9.9 wt.%,the PbO@RHAC composite exhibits the best effects on the performances of lead-carbon negative electrode,especially the capacity under high rate discharge and the cycle life under HRPSoC operation.Its cycle life exceeds 10000 cycles and is 9.2times that of the control battery.The good charge-discharge reversibility of the deposited PbO particles and the enhanced lead electrodeposition ability are the key factors for PbO@RHAC to improve the cycle life under HRPSoC operation.?3?A method of modifying carbonaceous material with BaSO₄ is proposed.The results show that the BaSO₄ particles on the surface of graphite electrodes can promote the lead deposition process and make the deposited lead particles have a good charge-discharge reversibility.The modification of BaSO₄ is beneficial to the formation of stable C-Pb structure between the deposited Pb and graphite electrode.Moreover,it is found that the BaSO₄ modified composite?EG-Ba?derived from expanded graphite?EG?can improve the quick charge acceptance and the cycle life under HRPSoC operation when added into NAM as an additive.During the HRPSoC cycle test,EG-Ba facilitates the deposition of lead particles on the surface of EG-Ba and the formation of connected EG-NAM structure.The lead particles deposited on the surface of EG-Ba can offer extra reaction area of lead during HRPSoC operation,which is useful for prolonging cycle life.?4?BaSO₄ modified composites?RHAC-Ba?based on porous RHAC is a suitable additive for negative electrode of lead-carbon battery.RHAC-Ba can promote the deposition of lead particles on the surface of RHAC and form a good connection structure between RHAC and NAM,then furher improving the HRPSoC cycle life.In addition,it is found that RHAC-Ba with clustered BaSO₄ particles is obviously inferior to RHAC-Ba composite with uniform small BaSO₄ particles in improving the cycle life of lead-carbon batteries.The uniformly deposited BaSO₄ particles on the surface of RHAC are the key to promote the deposition of lead particles on the surface of RHAC,and also the key to RHAC-Ba to enhance the HRPSoC cycle life of the negative electrode.