Lithium Storage Mechanism And Performance Of Iron Carbonate Anodes For Lithium-ion Batteries

Transition metal carbonates(TMCO3,TM=Fe,Co,and Mn,etc.)are considered as promising anode candidates for next-generation high-energy-density lithium-ion batteries,due to their high lithium storage capacities,simple preparations,environmental friendliness and low cost.However,carbonate-based anode materials encounter high initial irreversible capacity,dramatic volume change,and easy pulverization during electrochemical lithium storage,which lead to poor cycling stability and rate capability.This thesis aims at solving aforementioned problems for potential applications of TMCO3 anode materials,The iron carbonate(FeCO3)is selected as the research object,which is further composited with highly-conductive MXene materials and carbon nanotube(CNT)through in-situ preparations.The structural design and associated formation mechanism of FeCO3-based composite anode materials are studied,coupled with exploring their lithium storage mechanism and kinetics.The main content in this thesis is as follows:1.The composite structure is designed to combine iron carbonate particles and transition metal carbide nanosheets,in order to significantly improve long-term cycling performance of the FeCO3 anode material.Specifically,FeCO3 microparticles are obtained in a solvothermal preparation,followed by the structural reconstruction into nanorods and in situ anchoring on the Ti3C2 nanosheets through a one-step sonication-induced electrostatic self-assembly(SIEA),resulting in the formation of FeCO3@Ti3C2 nanocomposite.Electrochemical performance shows that the Ti3C2 substrate with high conductivity can significantly improve long-term cycling and high-rate performance of the FeCO3 anode material.The FeCO3@Ti3C2 composite anode material still retain a reversible lithium storage capacity of 954 mAh/g after 50 cycles at a current density of 0.1 C.After 500 cycles at 1 C rate,its capacity retention is up to 65.7%,and the average capacity decay rate is only 0.06%/cycle.The ζ potential analysis and density function theory(DFT)calculations together show that the chemical bond between Ti3C2 and FeCO3 components in the composite is formed by the O bridge at their surface interface,which is beneficial to the electron transfer of active FeCO3 anode material and thus contributes to enhanced electrochemical lithium storage performance of the carbonate anode material.2.Based on the above research achievements,carbon nanotubes are further in-situ introduced to the synthesis of iron carbonate@titanium carbide@carbon nanotubes(FeCO3@Ti3C2@CNT)composite material with a three-dimensional structure by a one-step hydrothermal method.The results of material characterizations show that FeCO3 particles are anchored on Ti3C2 nanosheet and also encapsulated by the CNT network.Electrochemical performance shows that as compared with the pure FeCO3 particles,the synergistic effect of Ti3C2 and CNT components can effectively reduce the volume expansion and particle agglomeration of massive FeCO3 anode materials during the lithium storage,and can significantly improve the lithium storage reversibility,specific capacity,long-term cycling stability and dynamic behavior of the FeCO3 anode material.Under the testing conditions of 1 C in a voltage range of 0.01-3.0 V vs.Li+/Li,the FeCO3@Ti3C2@CNT can deliver a reversible specific capacity of 562 mAh/g,and the capacity retention is 66.2%after 500 cycles,which are superior to that of the pure FeCO3 anode.3.The actual performance and application prospect of as-prepared two iron carbonate composite anode materials,i.e.,FeCO3@Ti3C2 and FeCO3@Ti3C2@CNT are evaluated in the full cells by using the high-Ni Li2TiO3-coated LiNi0.83Co0.07Mn0.1O2(Ni83@Li2TiO3)as the cathode material.The corresponding electrochemical performance shows that the initial specific capacity of FeCO3@TI3C2//Ni83@Li2TiO3 cell is 212 mAh/g(calculated based on the mass of active anode material)at 0.2 C in a voltage range of 0.5-3.9 V,and the working voltage is near 2.0 V.However,the initial Coulomb efficiency in the first cycle and cycling stability of two full cells are still needed to improve.The full FeCO3@Ti3C2@CNT//Ni83@Li2TiO3 cell shows better electrochemical performance compared to that of the FeCO3@Ti3C2//Ni83@Li2TiO3.After 50 cycles at 0.2 C,the specific capacity can reach 132 mAh/g,and the capacity decay is to a certain extent improved,which proves the potential application of iron-carbonate-based composite anode materials for high-energy lithium-ion batteries.