Synthesis And Electrochemical Properties Of MoO₂ Loaded On Foam Metal As The Direct Electrode

As a new and green energy storage devices,lithium ion batteries is currently attracting extensive attentions from researchers due to their advantages of high power density,good cycle performance,safety and stability.The electrode materials as the main part of lithium storage determin the electrochemical performance of LIBs.Molybdeum dioxde?MoO₂?as anode material for lithium ion batteries has high theoretical specific capacity and high energy density,etc.,which raise the interest from researchers.However,as anode material,bulk MoO₂ has poor cycle stability and rate performance,which restrict the practical application.Therefore,in order to develop the high-performance anode for lithium ion batteries,the synthesis of MoO₂and Ag/MoO₂ loaded on Ni foam as direct electrode by hydrothermal method and dip-coating method are studied.And the effect of electrode preparation and Ag modification on its electrochemical performance are investigated.The main contents of this thesis are as follows:1.MoO₂ nanomaterials were synthesized via a hydrothermal method with different precursors of the peroxymolybdic acid and ammonium molybdate?named as a-MoO₂ and b-MoO₂?.MoO₂ loaded on Ni foam?MoO₂/NF?were prepared by a dip-coating method,which can be directly assembled lithium ion batteries as binder-free anode.Actually,many¹0 nm nanocrystals were aggregated to a-MoO₂nanoparticles,while b-MoO₂ showed nanoflake-like structure with interconnected nanocrystals.After dip-coating process,a-MoO₂ nanoparticles and b-MoO₂nanoflakes were uniformly loaded on Ni foam to form a three-dimensional network,which enlarged the specific surface area of the electrode materials.The particular structure can not only offer more active sites and shorten the diffusion path for Li⁺,but also provided larger buffer space for the volume expansion of MoO₂ during charging/discharging process.The results showed that b-MoO₂/NF electrode exhibited better electrochemical performance in comparison with a-MoO₂/NF electrode.The b-MoO₂/NF electrode retained reversible capacity of 924 mAh g^-1?about 93%of the original high capacity?after 100 cycles at a current density of 0.1 C.More importantly,the capacity recovered to 910 mAh g^-11 from 370 mAh g^-11 when the current density returned from 2 C to 0.1 C,suggesting excellent reversibility and rate capability.2.Ag/MoO₂ nanocomposites with different Ag contents?molar ratio of Ag versus MoO₂:1%,2.5%,5%and 7.5%?were prepared by hydrothermal method with precursors of the peroxymolybdic acid and AgNO₃,which were loaded on Ni foam by dip-coating method to prepare the direct electrode?Ag/MoO₂/NF?as binder-free anode.Ag/MoO₂ nanocomposites were uniformly loaded on Ni foam to form the three dimensional networks structure,and Ag modification did not change the structure and micro morphology of direct electrode.The introduction of Ag was beneficial to improve the electrical conductivity of the electrode.It was found that Ag/MoO₂/NF electrode had the optimal cycle stability and rate performance when the Ag content was 5%.At a current density of 0.1 C,Ag_0.05/MoO₂/NF maintained reversible capacity of 805 mAh g^-11 after 100 cycles.Meanwhile,the discharge capacity still retained 468 mAh g^-11 at a high current density of 2 C.When the current density reduced to 0.1 C,the capacity recovered to 820 mAh g^-1,indicating its excellent electrochemical performance of Ag_0.05/MoO₂/NF electrode.