Preparation And Energy Storage Of Lithium-based Composite Carbon Nanofibers

Li metal anode is one of the most promising anode materials because of its high theoretical specific capacity and low oxidation-reduction potential.However,Li metal anode has problems such as unlimited volume expansion,uncontrollable growth of Li dendrites and accumulation of dead Li,which result in short cycle life and high polarization voltage.These problems seriously hinder its commercial development.In this paper,aiming at the problems existing in Li metal anode,high-performance Ge-based composite carbon nanofibers are developed to obtain high-energy density Li-based composite electrode material by studying lithiophilic materials and combining with the electrospinning technology in dyeing and finishing functional finishing technology.The mechanism of Li nucleation and growth and the inhibition mechanism of Li dendrite are discussed by analyzing the deposition behavior of Li during cycling.(1)Preparation of 3D Li_xGe_y alloy framework and the study of its energy storage function.GeO₂ powder and Li metal are mixed to form 3D lithiophilic Li_xGe_yframework by melting and thermal infusion method.Compared with the morphology before and after the introduction of 3D Li_xGe_y framework,the Li dendrite is obviously inhibited after cycling,and the electrode thickness changes from 82?m to 9?m.The cycle life of symmetrical cell with GeO₂-Li composite electrode is 1100 h and the polarization overpotential is only 30 m V u at a current density of 1 m A cm^-2 with a fixed capacity of 1 m A h cm^-2.A high capacity of 108 m A h g^-1 at 8.0 C(?6.8 m A cm^-2)can be achieved for full cells when the LFP cathode is paired with the GeO₂-Li composite anode.The results show that the 3D Li_xGe_y framework as the transport channel of Li⁺,which can rapidly conduct Li⁺,alleviate volume expansion,guide Li⁺to strip from top to bottom and deposit from bottom to top,inhibiting the growth of Li dendrite.(2)Preparation of porous GeO₂ doped composite carbon nanofibers and the study of its energy storage function.CNF-GeO₂ was prepared by electrospinning of PAN,GeO₂ nanoparticles and Zn Ac₂ and carbonization at high temperature.CNF-GeO₂-Li was obtained by pre-lithium deposition of a certain amount of Li.The morphology analysis of CNF-GeO₂ shows that GeO₂ nanoparticles are uniformly dispersed on CNF.Li was uniformly coated on CNF by the morphology analysis of CNF-GeO₂-Li.At the current density of 0.5 m A cm^-2,the energy storage device containing CNF-GeO₂-5 electrode material can stablely cycle 250 cycles and the coulombic efficiency is maintained at 98.50%.The results show that the large specific surface area of CNF and doping of lithiophilic GeO₂ nanoparticles can improve the nucleation behavior,cycle stability and coulombic efficiency,which is beneficial to improve the utilization of Li and reduce the loss of Li resources.