Application Of Rice Husk Silica As Positive Additives In Lead-acid Batteries

Lead-acid batteries(LAB)and lead carbon battery(LCB)are widely used in start-stop system in hybrid vehicles,energy storage,communication,backup power,uninterrupted power system(UPS)due to the advantages of stability,low price,and high recycling rate.Current research on LABs and LCBs has focused on the negative plates and negative additives to enlarged battery performance by preventing sulfation.With the development and iteration of the negative plate,the failure of the positive plate is the critical factor that limits the battery performance and lifetime,limiting the development of batteries with high capacity,long cycle life and high specific energy.Curing and forming are the two important steps in the production of the plate.During the curing process,the lead powder reacts with sulfuric acid to form precursors of active materials with different degrees of chelation,such as tribasic lead sulfate(3BS),tetrabasic lead sulfate(4BS),etc.During the formation process,these materials are inclined to transform into different types of active phases,α-PbO2 predominantly derived from the conversion of 4BS,characterized by its extended cycle life,andβ-PbO2 formed from the conversion of 3BS,which is associated with a superior discharge capacity.The proportion of 3BS and 4BS in the cured plates and the efficiency of conversion to α-PbO2 and β-PbO2 in the formed plates are essential in deciding the capacity and cycle life of the positive plates of the battery.In this work,an ex-situ method is used to characterize the physicochemical reactions and inter-component transformations occurring during the positive plate curing process.A theoretical structure-function relationship is established between"cured intrinsic parameter-phase content-battery lifetime".Predictive model and optimal curing conditions for phase content in cured plates obtained.Based on the strategy of"carbon peaking and carbon neutrality goals" for sustainable development,the State Council issued the "Opinions on Accelerating the Construction of a Waste Recycling System".Make full use of rice husk agricultural biomass waste to produce RH-SiO2 active positive material additives with hierarchical pore structure,and design SnO2/RH-SiO2 compound.Both of the additives promote the conversion of 3BS and 4BS to PbO2 during the formation process to obtain positive plates with high capacity,long cycle lifetime,high capacity retention and cycle stability.To investigate the mechanism of rice husk silica and complex additives on the performance of positive plate and evaluate the performance under the actual application conditions,so as to provide theoretical support and technical support for the design and development of new additives.The main research results of this work are as follows:(1)The positive active material component is generated by the curing process,and its content depends on the intrinsic process parameters such as temperature,humidity and curing time during curing.Sampling by ex-situ continuous monitoring method was used to systematically investigate the mechanism of the role of intrinsic parameters on the formation of the content of the cathode active substance phase during the curing process.When the curing temperature was increased to 90℃,the components in the cured plate began to form 4BS crystal agglomerates,and the incomplete 4BS lattice was rapidly formed with 3BS during the 0-4 hours of elevated temperature.4-8 hours after heating,the rate of 4BS formation gradually slowed down toward large clusters.After the high temperature was applied for 8 hours and then the curing was resumed at low temperature,it was observed that the formed 4BS were dissolved again and transformed into 3BS.This phenomenon was analyzed from kinetic and thermodynamic points of view.A solid α-PbO2 skeleton holding smallβ-PbO2 particles with high reactivity was generated in the plates cured at high temperature at the 28th to 36th hour.At this time,the positive plate takes into account the capacity and cycle life.The powder of the cured plate,which was not removed in situ during the entire curing process,was modified by XRD slow scanning and Rietveld full spectrum matching.The changes in the phase contents of Pb,PbO,PbSO4,1BS,3BS and 4BS in the cured plate were calculated and a theoretical model was established for the changes in the contents of the active components of the anode with the changes in the intrinsic parameters such as curing time,temperature and humidity.This study develops a new idea and calculation method for the study of anode curing,which is of great significance for the theoretical study of batteries.(2)The superiority and mechanism of biomass-derived rice husk silica(RH-SiO2),which has a special three-dimensional pore structure,as an anode additive for lead-acid batteries were investigated.Compared with fumed silica,which has the same specific surface area but a different pore structure,the higher mesopore structure of rice husk silica can optimize the pore structure of the cured plate,establish better ionic and electronic conduction pathways,and give full play to the spatial resistance effect.It has been found that the pore structure built by rice husk silica can improve the conversion efficiency of drug precursors into α-PbO2 and β-PbO2 during formation through the "precipitation-dissolution effect",and thus can establish a more perfect phase-content ratio between the two.The addition of 1%mass fraction of RH-SiO2 to the cathode can increase the specific discharge capacity of the battery at 100%DoD from 57.75 mAh g-1 in the blank cell to 68.09 mAh g-1 with a growth rate of 17.9%.At the same time,the cycle life of the battery is significantly improved,from 91 to 245 cycles of the blank battery,an increase of 2.7 times.At a low discharge rate,the RH-SiO2 battery shows more obvious superiority.(3)SnO2/RH-SiO2 consisting of rice husk silica(RH-SiO2)coated with tin dioxide(SnO2)was developed and produced,which can compensate for the low electronic conductivity of rice husk silica as an additive for LABs.The conversion of α-PbO2 and β-PbO2 in the active material has been significantly improved,making it suitable for use at a higher discharge rate.It was shown that the specific discharge capacity of the positive plate with SnO2/RH-SiO2 additive reached 69.4 mAh g-1.The cycle life at 0.5 C 100%DoD was 339 cycles,which was 3.7 times that of the blank battery.The RH-SiO2 in SnO2/RH-SiO2 is able to form a stable physical bond and a backbone structure with PAM to increase the electrochemically active area of the positive plate.The SnO2 in the complex induces the formation of the intermediate phase of perovskite PbSnO3 and convert into the p-type semiconductor structure of SnPb2O4 during cycling.These two structures can accelerate the lead dioxide deposition rate and interphase conversion efficiency of PbO2/PbSO4,which can improve the lifetime and cycle reversibility of the positive plate.(4)Performance evaluation of RH-SiO2 and SnO2/RH-SiO2 in National Standard for energy storage and start-stop lead-acid batteries,respectively.RH-SiO2 is suitable for energy storage applications.All indexes of RH-SiO2 battery can meet the requirements of the national standard for energy storage,and in the most representative test for energy storage,the cycle life is increased to 477,nearly four times that of the blank battery.SnO2/RH-SiO2 is better suited for start-stop applications.The 17.5%DoD cycle life has been increased from 592 to 911 cycles for blank battery,and the 50%DoD cycle life is 368 cycles,which is 2.1 times more than the 174 cycles,meeting the requirements of the National Standards.The start-stop cycle life has increased by 4.7 times and there is still room for improvement.