Study On Lithium-Ions Storage Properties Of New Zirconium-Manganese Hydride Electrode Materials

Metal hydrides based on conversion reaction mechanism generally have high theoretical specific capacity and low voltage platform,which are potential electrode materials for lithium-ion battery.However,the poor conductivity,the instability in air and the volume expansion in the process of lithium extraction/insertion caused their low electrochemical cycle properties.In this paper,based on the review of the recently literature research and existing problems of metal hydride anode materials for lithium-ion batteries,we prepared a new ternary zirconium manganese alloy hydride(ZrMn₂H_3.6)and its composite graphene anode materials for the first time.The electrochemical properties of the materials were systematically studied by X-ray diffraction(XRD),Scanning Electron Microscope(SEM),Cyclic Voltammetry(CV),Electrochemical Impedance Spectroscopy(EIS).The behavior of lithium storage,the reason of capacity decay and mechanism of electrochemical lithium storage performance enhancement were discussed.The main conclusions are as follows:(1)ZrMn₂ alloy and ZrMn₂ hydride-based anode materials for lithium-ion batteries were prepared by melting method and high-pressure hydrogen balloon grinding method,furthermore their lithium storage behavior and attenuation internal reasons were further studied.The results show that ZrMn₂ alloy has no electrochemical lithium storage activity,while ZrMn₂H_3.6 can realize reversible lithium storage based on the conversion mechanism.The first discharge specific capacity of ZrMn₂ hydride can reach 475.8 mAh g^-1,but the capacity decays seriously,and only 92 mAh g^-1 remains after 100 cycles.This is mainly due to the poor conductivity of ZrMn₂H_3.6 electrode,the comparatively sluggish transmission speed of lithium ion,and the construction damage of electrode material caused by cycle induced volume expansion.(2)A series of ZrMn₂H_3.6 with shell core structure with different ratios was prepared by adding reduced graphene(GR).The reduced graphene materials were used to improve the conductivity and electrochemical activity.Besides the micro morphology and lithium storage property were in depth research.The study found that when the gravity of graphene is 25 wt%,the lithium storage performance of the 3ZrMn₂H_3.6@GR composite electrode material is the best.After 100 cycles,the capacity of 3ZrMn₂H_3.6@GR composite electrode is stable at 560 mAh g^-1 at the current density of 100 mAh g^-1.In addition,graphene coating treatment can alleviate the problem of volume expansion and collapse,these presenting excellent cycle behavior and better rate capacity(after 500 cycles of stable,the specific capacity of 430 mAh g^-1 at current density of 500 mAh g^-1).(3)LiBH₄ was selected as solid electrolyte to construct ZrMn₂H_3.6-based all solid state battery,and thus electrochemical performance and reversible lithium extraction/insertion improvement mechanism were in depth reasearch.It is found that the first discharge capacity of pure ZrMn₂H_3.6 solid-state battery is increased by 25%to 626.4mAh g^-1,and it reduces to 240 mAh g^-1 after 100 cycles,and the coulomb efficiency is only95%.The lithium intercalation potential of pure ZrMn₂H_3.6 solid-state battery remains unchanged(?0.5 V),but the electrode polarization is significantly reduced.In contrast,the3ZrMn₂H_3.6@BP based solid-state battery has a considerable capacity,and the capacity after cycling can be stabilized at 618 mAh g^-1;graphene coated ZrMn₂H_3.6(3ZrMn₂H_3.6@GR)based all solid-state battery also has excellent electrochemical performance.After 500 cycles,the capacity can still be maintained at 465 mAh g^-1,and the coulomb efficiency can reach 99.5%.