The Preparation Of Biomass-based Carbon Material And Its Application As Current Collector For Lithium Metal Batteries

At present,the energy density of advanced lithium-ion batteries can only reach 250Wh/kg,which cannot meet people’s needs for long-life electronic devices,and new battery systems need to be developed.Lithium metal batteries(LMBs,theoretical energy density to higher than 440 Wh/kg)are considered as one of the most promising high energy density batteries due to their extremely high theoretical specific capacity and low potential.However,there are several problems such as volume expansion and dendrite growth during cycling of Li metal anodes.To address the above problems,various strategies have been proposed to improve the electrochemical performance of lithium metal anodes.It mainly includes liquid electrolyte optimization,use of solid electrolyte,artificial solid electrolyte interface(SEI)and anode structure design.In the structural design of anodes,the construction of 3D current collectors is an effective method to alleviate the volume change and suppress dendrite growth during Li deposition/stripping.Among many three-dimensional current collectors,porous carbon materials with light weight,high conductivity,and adjustable structure can not only effectively reduce the current density,inhibit the growth of dendrites to prevent short-circuit of the battery,but also alleviate the volume expansion and improve the stability of the anode structure.Biomass-derived carbon materials have the advantages of high porosity,unique pore structure,and a wide range of sources.When used as three-dimensional current collectors,they can delocalize the distribution of lithium ions to improve electrochemical performance.However,excessive specific surface area will aggravate the occurrence of side reactions and reduce the coulombic efficiency.Therefore,it is necessary to design porous carbon with suitable specific surface area as the metal lithium anode.In addition,the nucleation of lithium in porous carbon is difficult due to the lithiphobic properties of carbon materials.The introduction of lithiophilic materials such as metal selenides into porous carbon can improve the affinity between lithium and carbon,thereby promoting the orderly deposition of lithium.(1)Different sources of agricultural waste(corn stalk,silkworm sand and basswood fungus residue)were researched as raw meterials for preparing the corn straw carbon,silkworm faeces carbon and basswood fungus residue carbon.Through the structural analysis and electrochemical performance test of the above biomass carbon materials,it was found that the basswood fungus residue carbon with a hierarchical porous structure had the highest coulombic efficiency and the lowest nucleation overpotential.The Coulombic efficiency of 98.7%can be maintained at a current density of 2 m A/cm~2 for180 cycles.The assembled basswood fungus residue carbon/Li symmetric cell exhibited an overpotential of only 12 m V after cycling at a current density of 1 m A/cm~2 for 700hours.At 2 m A/cm~2,the overpotential is only 15 m V,and it can cycle stably for 450 hours.The full battery assembled with lithium iron phosphate still has a capacity retention rate of 99.3%after 60 cycles at a rate of 0.2 C.(2)In order to further improve the electrochemical performance of basswood fungus residue carbon,cobalt selenide was used to modify basswood fungus residue carbon(BFC@Co Se)to improve its lithophilicity and achieve uniform deposition of metallic lithium.The cobalt selenide polyhedral framework with uniform distribution and particle size of 200 nm is obtained by a one-step carbonization-selenization process of zeolite imidazolate framework(ZIFs-67)which firstly is deposited on basswood fungus residue carbon.BFC@Co Se not only provides enough space for Li deposition and slows down the volume change of Li anode during cycling,but also induces uniform deposition of metallic Li by reducing the local current density.The as-prepared BFC@Co Se LMBs can maintain a coulombic efficiency of 99.3%after 70 cycles at a high capacity of 1 m A/cm~2and 10 m A h/cm~2.At a higher current density of 5 m A/cm~2,the Coulombic efficiency of more than 98.9%can still be maintained after 90 cycles.The assembled BFC@Co Se/Li symmetric cells can be stably cycled for 1500 and 1200 hours at current densities of 1m A/cm~2 and 2 m A/cm~2,respectively.The specific capacity of the full cell assembled BFC@Co Se/Li anode and lithium iron phosphate cathode can be delivered at 136.3 m A h/g after 200 cycles at a rate of 0.5 C with a capacity retention rate of 85.4%.