Design, Synthesis And Electrochemical Performance Of Conversion-type Anode Materials

This dissertation aims to improve the electrochemical performance of conversion-type anode materials.Constructing nanomaterials,porous structure and composites can effectively improve the reaction kinetics and structural stability of electrode materials,realizing its high cycle reversibility,superior rate performance and long-life cycling performance.In addition,we also systematically investigated the electrochemical storage lithium/sodium mechanism of electrode materials,revealing the correlation between the structure and electrochemical performance.The important achievements are summarized as follows:?1?FeSe₂ clusters consisting of nanorods are synthesized by a facile hydrothermal method.The FeSe₂ clusters deliver high electrochemical performance with an ether-based electrolyte in a voltage range of 0.5-2.9 V.A high discharge capacity of515 mAh g^-1 is obtained after 400 cycles at 1 A g^-1.Even at an ultrahigh rate of 35 A g^-1,a specific capacity of 128 mAh g^-1 is achieved.Using calculations,we reveal that the pseudocapacitance significantly contributed to the sodium-ion storage,especially at high current rates,leading to a high rate capability.In situ XRD is performed to further investigate the intrinsic reaction mechanisms of the FeSe₂ cluster electrodes.These results indicate that the amorphization of the FeSe₂ electrode occurred after the electrochemical sodium-ion insertion.?2?Iron sulfide porous nanowires@N-doped carbon composites?FeS@N-C nanowire?are synthesized by a facile amine-assisted solvothermal reaction and subsequent calcination strategy.The different reaction time experiments are carried out to confirm the formation mechanism of FeS@N-C nanowire.This facile strategy is then generally applied to obtain various porous metal sulfide?Co₉S₈,Ni₃S₂?nanowires for the first time.The as-obtained FeS@N-C nanowires as a LIB anode exhibit ultrahigh reversible capacity,excellent rate capability and long-term cycling stability.In particular,a high reversible capacity of 1061 mAh g^-1 can be reached at 1A g^-1 after 500 cycles.Most impressively,it delivers a high specific capacity of 433mAh g^-1 even at 5 A g^-1.In addition,the involved lithium-storage mechanism has been systematically investigated via ex-situ X-ray diffraction?XRD?and high-resolution transmission electron microscopy?HRTEM?technologies.?3?The yolk-shell zinc and cobalt sulfides@nitrogen-doped carbon composites?Zn-Co-S@N-C?are synthesized by adopting MOFs as a precursor,PDA coating and subsequent calcination strategy.As LIB anode,Zn-Co-S@N-C composites deliver a high initial specific capacity of 1193 mAh g^-1 at 0.2 A g^-1,and 747 mAh g^-11 can be retained after 400 cycles.The high specific capacity of 707 mAh g^-1 can be obtained at 1 A g^-1 after 100 cycles.The results demonstrate that the Zn-Co-S@N-C composites possess excellent electrochemical performance,which is attributed to continuous electron transport pathway,improved electric conductivity,and excellent stress relaxation.?4?Zinc selenide Microspheres/Multi-Walled Carbon Nanotubes Composites?ZnSe/MWCNTs?are successfully synthesized by a facile hydrothermal method and subsequent grinding process.The electrochemical performance of the as-prepared ZnSe/MWCNTs as SIB anode is studied for the first time.As a result,ZnSe/MWCNTs exhibit excellent rate capacity,high Coulombic efficiency,and long cycling life.In particular,it still delivers a high capacity of 382 mAh g^-1 at a high current density of 0.5 A g^-1 after 180 cycles.The initial Coulombic efficiency of ZnSe/MWCNTs can reach 88%and nearby 100%in the following cycles.The superior electrochemical properties are attributed to its unique structure,synergistic effect of bimetallic sulfides,and the protective effect of the nitrogen-doped carbon.?5?Hierarchical copper silicate hydrate hollow spheres-reduced graphene oxide?RGO?composite is successfully fabricated by a facile hydrothermal method using silica as in-situ sacrificing template.The electrochemical performance of the composite as lithium-ion battery anode was studied for the first time.Benefiting from the synergistic effect of the hierarchical hollow structure and conductive RGO matrix,the composite exhibits excellent long-life performance and rate capability.A capacity of 890 mAh g^-1 is achieved after 200 cycles at 200 mA g^-1 and a capacity of429 mAh g^-1 is retained after 800 cycles at 1000 mA g^-1.In combination of the XPS and ex-situ XRD results,the possibility of intercalation/de-intercalation reaction can be ruled out.It's speculated that the copper silicate hydrate stores lithium through the combination of alloying/de-alloying and conversion reaction.