Stability Optimization Of Lithium Ion Battery Via Three-dimensional Micro-nano Structure

Lithium-ion battery has enormous applying in our lives.How to enhance capacity,charging rate and safety of battery is always the difficulty and hot spot in research field of lithium-ion battery.3D graphene has the large specific surface area,high electronic conductivity,high mechanical strength and more storage of Li+than graphite,since it is a ideal material to improve electrochemical stability of Lithium-ion battery.Silicon with high theoretical specific capacity 4200 mAh g-1 is regard as the promising anode.However,the volume of silicon occurs dramatical change as 300%during charging/discharging process.3D Gr/Si/Gr sandwich hybrid anode synthesized in this work improve the electrochemical stability of anode material.There are several paper revealing application of 3D micronano structure in optimizing performance of electrode,but little article reporting 3D micronano battery.In this work,we preliminarily prepared 3D micronano foam battery,and made the foundation for the further enhancement of electrochemical stability in full battery level.(1)In this work,3D graphene was fabricated with Ni skeleton via Chemical Vapor Deposition(CVD),and then Ni was removed in 10 wt%nitric acid.A layer of dispersed silicon particles were deposited on graphene surface via magnetron sputtering and followed by another CVD process.Finally,we synthesized 3D Gr/Si/Gr hybrid material liked sandwich.The 3D graphene deposited originally played an important role in support,collecting electron and reserving Li+.The outer graphene facilitated formation of solid electrolyte interface(SEI)on surface of hybrid anode.The introduction of nanometer silicon increased specific capacity additionally.(2)The electrochemical tests of Electrochemical Impedance Spectroscopy(EIS),Cyclic Voltammetry(CV),rate discharge/charge cycle and constant current long cycle showed that the 3D Gr/Si/Gr anode material has excellent electrochemical stability.This hybrid anode that showed a good performance in electrochemical test exhibited a capacity of 420 mAh g-1 at a current density of 0.5 A g-1,and maintained considerable capacity of 300 mAh g-1 after 294 cycle.Moreover,the Coulombic Efficiency(CE)of this anode still remained above 99%at high current density 2.0 A g-1.The material characterizations of 3D Gr/Si/Gr after long discharge/charge cycle proved that the material has good micro morphology stability,micronano structure stability and chemical components stability.The 3D Gr/Si/Gr displays the synergistic effect of 3D graphene and silicon nanoparticles.As a 3D porous flexible conductive framework,3D graphene not only acts as an active material in the electrode,but also provides electrons collection and expansion buffer support in the process of discharge/charge for silicon nanoparticles.While silicon nanoparticles contribute to lithium storage capacity,their nano size and dispersion distribution also reduce the electrode expansion in the discharge/charge process.The expansion alleviation of the composite electrode results in better cycle stability.(3)Lastly,designed and preliminarily prepared 3D micronano foam battery on the basis of 3D composite anode.The 3D micronano foam battery not only possesses the electrode of 3D micronano structure which has larger specific area and more active sites of Li+reaction,but also possesses a 3D interface between polymer electrolyte and electrodes in battery,which provides more pathways to Li+transfer in electrolyte and extends the area of electrochemical reaction.The distribution and drop coating of solid electrolyte and cathode are discussed.Furthermore,the micro morphology of each part and the overall structure of the 3D micronano foam battery are analyzed.It provided basis of material characteristics for the shape of complete 3D micronano foam structure battery.