Synthesis Of PbO@C Composite Recovered From The Spent Lead Paste By A Novel Short Route For Application In Lead-carbon Battery

Pyrometallurgical route is the most commonly used method for the recycling of spent lead-acid battery(LAB),however it causes challenging environmental problems such as the emissions of hazardous lead particulates and SO2 gas.Thus it is imperative to develop an environmentally-friendly alternative route for recycling LAB to reduce the emission.As the active material for LAB,ultrafine leady oxide is a viable solution to improve the capacity density,and lead-carbon composite is beneficial to extend the cycle life for application in hybrid electric vehicles.A novel short hydrometallurgical route for recycling of spent lead paste with organic acid was proposed by our research group,which can be used to prepare ultrafine leady oxide directly instead of an additional ball-milling process.However,the mechanism of calcination of lead citrate precursor and the effect of synthesized PbO@C composite on lead carbon battery are still unknown.This thesis focuses on the mechanism of calcination of lead citrate precursor,and on the effect of PbO@C composite in the lead carbon battery.The major contents of this thesis are as follows:1.Mechanism of phase control in calcination of lead citrate precursor and the mass transfer-reaction model about the thermal decomposition of lead citrate precursorThe influence of O2 concentration in the atmosphere of O2/N2 mixture on the phase distribution of PbO,metallic Pb and residual carbon in leady oxide product during calcination was studied at calcination temperature of 370,450 and 600?.It is found that the oxidizability and residual carbon content of obtained leady oxide decreases with the increasing of O2 concentration in the calcination atmosphere.High oxidizability and low recidual carbon content are contradictory in phase control of the preparation of leady oxide.PbO particle is anchored on porous carbon skeleton in the obtained leady oxide based on SEM analysis.A mass transfer-reaction model for the thermal decomposition of lead citrate is proposed based on the porous structure of leady oxide.A two-step calcination method is proposed to increase the oxidizability of the leady oxide in large scale calcination:pyrolyzing the lead citrate firstly to release the organic group,and then combusting the pyrolysis product in air.Pilot scale experiment of 20 kg per time confirms that the lower calcination temperature,longer pyrolysis time and lower ventilation volume in oxidation step is beneficial to achieve higher oxidizability(higher than 80 wt%)and lower residual carbon content(lower than 0.3 wt%)in the obtained leady oxide in two-step calcination method.2.Characterization of the PbO@C compositeThe structure and combination of the PbO@C composite was analyzed by XPS and TEM for the composite synthesized by pyrolyzing lead citrate precursor at 600? in N2.The nanostructured PbO with particle size of 20?50 nm is anchored on porous carbon skeleton via the formation of chemical bond between Pb and C elements.The porous carbon skeleton is amorphous with mass fraction of 8.0 wt%in composite.It is confirmed the adhesion force between PbO and C is at least 78.5?88.3 kPa via the thermal cycling test.The carbon material in the composite is 0?20%sp3 hybrid orbitals with a certain amount of organic groups such as—COO—.3.Mechanism of the effect of PbO@C composite on the performance of lead carbon batteryThe different effects of the two different PbO@C composites(P450 and P600)and the respective carbon materials(C450 and C600)as negative active material(NAM)additives were investigated with 0.5 wt%of carbon added in the ball-milled leady oxide.The 3D electrolyte pump effect of carbon,together with higher BET surface area and degree of graphitization can facilitate the absorption and transportation of electrolyte to improve the charge acceptance.Due to the chemical bonding between Pb and C and the consequently more active sites,the overgrowth of PbSO4 is restricted.The utilization of NAM in test cell is improved almost 50%times of 20 h rate(comparing with the blank control group without carbon additives).The cycle life at HRPSoC(High Rate Partial State of Charge)of the modified NAM is extended from 11 k to 41 k with the PbO@C composite additive of P600.4.The evolution of carbon and lead bonding in electrode and its influence on battery performanceThe evolution of C and Pb bonding was studied by XPS analysis of the electrode in the process of curing,formation and cycling.The chemical bonding between Pb and C in PbO@C composite is broken by chemical reaction during the mixing and curing process.Meanwhile,the previous sites of Pb and C can still act as the active site for the reaction of NAM in curing,formation and charge/discharge cycling in electrode.The concentration of carbon in the electrode is decreasing and the disordering effect is exacerbated after charge/discharge cycling,hence the effect of carbon in lead carbon battery fades out as the charge/discharge cycling proceeds.This research work provides a theoretical foundation to support the phase distribution of leady oxide as calcination product of organic lead precursor in a short-route recovery method.It also inspires the novel application of recovered spent lead paste in lead carbon battery via hydrometallurgical route with organic acid.