Applications And Mechanisms Of Biomass-Derived Materials Prepared From Eucalyptus In Rechargeable Batteries

Biomass has great potentials for preparing rechargeable battery materials by virtue of its inherent renewability,natural microstructural and molecular structural characteristics,abundant reserves,and low cost.In this thesis,fast-growing eucalyptus wood was used as raw material to fabricate materials for rechargeable batteries.The lithium（Li）metal anodes and oxygen cathodes are suffering from the uneven Li deposition and sluggish kinetics,respectively.Taking the advantages of the natural ordered pore structure of wood,as well as the network structure and multi-functional groups of lignin macromolecules,the eucalyptus-derived materials are expected to play a role in effectively inducing uniform Li deposition and accelerating the electrochemical kinetics of oxygen cathodes.In this study,biomass-derived materials can not only solve the electrochemical problems of rechargeable batteries,but also improve the greenness of battery materials.On the other side,the applications of biomass-derived materials are further expanded in the field of energy storage.To address the uneven deposition behaviour of Li anode and the resulting battery problems,eucalyptus wood/Li composite anodes were prepared.The effects of eucalyptus wood host were verified by lithium–lithium symmetrical cells and lithium–copper half cells.Besides,the mechanism of wood hosts was further explained by finite element analysis method.The wood host was conducive to alleviating the electric field fluctuation near the electrode and inducing the uniform deposition of Li in the pores.Therefore,the volume expansion of the electrode after cycling was effectively relieved.Moreover,the polarization was reduced and the cycling lifespan of the electrode was prolonged.In order to further verify the role of the eucalyptus wood/Li composite anode in the full batteries,based on the strategy proposed in the previous chapter,the eucalyptus wood/Li composite anode was combined with nickel cobalt lithium manganate（NCM523）cathode,lithium iron phosphate（LFP）cathode,and sulfur（S）cathode to assemble full cells,respectively.Reduced polarization,improved cycling stability,and prolonged cycling lifespan were found in the full cells with eucalyptus wood/Li anode.Thus,the universality of eucalyptus wood host under different battery systems.In addition,an all-wood-based rechargeable Li|S cell with wood-derived sulfur host,separator,and Li host was developed.To address the sluggish kinetics of oxygen evolution reaction（OER）of oxygen cathode,the monolithic OER catalyst of eucalyptus wood/Ni Fe LDH was prepared by electrochemical deposition method using carbonized porous eucalyptus wood as framework.In addition,in order to optimize the catalytic performance of the monolithic catalyst,the effects of Ni²⁺/Fe³⁺ratio in the precursor solution,deposition potential,and deposition time were discussed.It was found that when Ni²⁺/Fe³⁺=5,the deposition potential was-0.86 V（vs Ag/Ag Cl）,and the deposition time was 300 s,the monolithic catalyst exhibited the best OER activity,which surpassed the noble metal catalyst of platinum-carbon.To promote the catalytic activity and optimizing the structure of air cathode in aqueous zinc–air batteries,the oxygen reduction reaction（ORR）catalytic sites Co_xN was introduced into the framework of carbonized eucalyptus wood by in-situ coating with polydopamine（PDA）-cobalt（II）.The effects of different Co²⁺concentrations on the catalytic activity of the materials were also discussed.On this basis,the OER catalytic sites were introduced by electrochemical deposition to obtain a monolithic air cathode with bifunctional catalysis.Moreover,an aqueous zinc–air battery with the eucalyptus-based bifunctional monolithic air cathode achieved 480 cycles at a current density of 5 m A cm^-2.Aiming at the sluggish kinetics of the ORR process of oxygen cathodes,cobalt-modified nitrogen-doped carbon nanosheets（L-NC-Co）was prepared as ORR catalysts.The lignin extracted form eucalyptus,with high molecular weight,high purity,and network molecular structure was used as precursor.The Co–N_x–C structure and uniformly embedded Co nanoparticles on L-NC-Co provided ORR catalytic activity.Compared with noble metal catalysts,the L-NC-Co was much closer to the four-electron transfer pathway.The L-NC-Co was further used in the air cathode of aqueous zinc–air battery,and contributed to stable cycling performance for 330 cycles at a current density of 5 m A cm^-2.This work demonstrated the application potentials of lignin-derived ORR catalytic materials.