The Application of Multi-scaled Transition Metal Oxides Based Anodes for Lithium-ion Batteries

多尺度過渡金屬氧化物基陽極在鋰離子電池中的應用

Student thesis: Doctoral Thesis

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Award date2 Aug 2021

Abstract

In recent decades, with the dramatically growing energy demands and increasingly environmental crisis, it is important to urge people to focus on the development of novel, efficient and environmentally friendly electric energy storage system (EES). Owing to the advantage of relatively high capacity density, high output voltage and excellent cycling stability, metal-ion battery has been widely researched and obtained great attentions. Specially, as a successfully commercial product, lithium-ion battery (LIB) is highly appreciated and used in all kinds of electronic equipment and power application. However, the commercial graphite anodes have seriously limited the potential application due to their low theoretical capacity (~ 372 mAh g-1). Herein, it is very important to explore novel anodes for LIB coupled with relatively high cycling stability, excellent electron conductivity and minor structural change during the electrochemical process, etc.

Currently, owing to the relatively high theoretical capacity, great structural stability and abundant mineral resources, transition metal oxides (TMOs, T = Zn, Co, Mn, Fe and M = Co, Ni, Fe, etc.) have been attached great attentions. However, each coin has two sides. Some fatal drawbacks of TMOs based electrodes also cannot be ignored, such as severe electrode volume expansion and electrode pulverization during the charging/discharging process, etc. To be more specific, much more efforts have been devoted to solve those intractable problems so as to obtain excellent electrodes for LIBs. In this thesis, three methods have been adopted here in an attempt to synthesize novel TMOs electrodes.

Firstly, chemically integrated hybrid nanostructures of Fe2O3/holey graphene framework (HGF) nanocomposites have been successfully synthesized via a glycerol activated process. Of which, defected graphene oxides were firstly etched by a certain volume of hydrogen peroxide. Subsequently, multi-dimensionally nanosized Fe2O3 particles were generated and anchored on the defected graphene layers. Based on this method, the ability in synthesizing the exquisitely tune Fe2O3 nanoparticles with highly controllable nanostructures and desirable properties was demonstrated, ranging from zero-dimensional quantum dots to one-dimensional nanorods, and eventually to two-dimensional nanosheets. As anodes for LIB, these hybrid Fe2O3/HGF electrodes exhibited excellent cycling stability and rate properties.

Secondly, self-template multi-scaled structure of ZnFe2O4 (ZFO) microspheres were synthesized through several solvothermal methods, subsequently accompanied by various annealing processes. Hollow spheres with controllable interior structures (ranging from solid, core-in-hollow wall and double wall hollow) are synthesized differently through a mutual cooperation of inward-outward ripening by a non-equilibrium heat-treatment process of different heating rates during the calcination process. Specifically, these as-synthesized ZFO electrodes exhibited excellent electrochemical stability than regular synthesized ZFO electrodes.

Thirdly, homogeneously hybrid NiCo2O4 (NCO) microspheres coupled by HGF (holey graphene framework) have been successfully synthesized via specific solvothermal methods. Meanwhile, tunable oxygen vacancies have been imported in reconstructed NiCo2O4 microspheres so as to increase the overall electronic/ionic conductivities. In addition to the conventional performance of graphene sheets, the role of holey defected graphene layers could not only alleviate the self-restacking of graphene sheets due to the Van der Waals force but increase the electrolyte penetration into the inner active electrodes, subsequently enhancing the reactivity of active sites in assembled electrodes.

In summary, the thesis demonstrated severally facile methods to synthesize TMOs based electrodes. In the first study, hybrid Fe2O3/HGF nanocomposites with complicated morphologies have been explored and synthesized. In the second study, multiscale structured ZnFe2O4 (ZFO) microspheres with finely internal structure have been researched. In the third study, homogeneously hybrid NCO microspheres coupled by HGF layers have been investigated, subsequently modified by tunable oxygen vacancies. As expected, those as-synthesized TMOs electrodes exhibited excellent cycling properties for LIB, demonstrating the possible approach to synthesizing TMOs based active electrodes for EES applications. On the whole, these works might provide a new strategy to modify superior TMOs based materials, hopefully accelerating the commercialization of TMOs based anodes for metal-ion batteries.