Preparation And Electrochemical Properties Of Several Nanomaterials As Electrode Materials For Lithium Ion Batteries

Li-ion batteries have been widely used in portable electronics such as mobilecommunication devices due to their high energy density, friendly-environment and long cyclelife. Electrode materials determine the performance of lithium ion battery. Currently, theelectrochemical performance of lithium batteries is limited due to the low utilizationefficiency, slow diffusion of the lithium ion as well as severe polarization problem of thetraditional electrode materials. The high reactivity, favourable charge transport properties andnovel structural merits of nanomaterials make them suitable alternative to effectively improvethe performance of lithium batteries. The relationship between their composition, structure,morphology and properties needs to be further studied. Therefore, this dissertation focuses onthe preparation and electrochemical investigation of hollow Li₄Ti₅O₁₂, ZnCo₂O₄nanowiresand hollow LiMn₂O₄nanotubes. The main content is as follows.（1） Hollow structured spinel Li₄Ti₅O₁₂microspheres were synthesized via ahydrothermal route using carbon sphere template-assisted method followed by a subsequentcalcination process.The phase, structure, morphology and capacitance performance of theproducts were characterized and tested by XRD, SEM, TEM and Electrochimical AnalysisSystem. The results show that: the diameter of the hollow particles is480nm and these hollowspheres have an average shell thickness of50nm. Hollow microspheres exhibits the excellentrate capability at different current rates, especially at0.2C, its initial reversible capacity is174mAh/g and129mAh/g can be maintained after100cycles. It has a good circle stability andcyclic life. Hollow Li₄Ti₅O₁₂electrode materials can short the distance of lithium ion diffusionand be in favor of fast diffusion of the lithium ion，so it can improve the dynamicperformance. （2） ZnCo₂O₄cube was synthesized by a simple solvothermal method followed by acalcination process.1D ZnCo₂O₄nanowires was synthesized via annealing of a sacrificetemplate. The two materials were characterized and tested by XRD, SEM, TEM andElectrochimical Analysis System. The results indicate that the cubic spinel structure ZnCo₂O₄was obtained and the diameter of the ZnCo₂O₄cube and ZnCo₂O₄nanowires is2.5μm and150nm, respectively. The electrochemical results show that cyclic voltammetry have a strongsensitivity for different morphology and size of electrode materials. The diversity ofcapacities of different morphology and size of electrode materials mainly result from thestructure and size of materials. Hollow structure nanowires with porous structure on thesurface can immensely short the distance of lithium ion diffusion and improve the dynamicperformance. While the cube have low capacitance due to larger particles and difficulty ofintercalation and deintercalation.（3） Spinel LiMn₂O₄nanotubes and Co-LiMn₂O₄nanotubes with a diameter of about175nm, a wall thickness of about70nm and a length of1-3μm have been synthesized via atemplate-engaged reaction using α-MnO₂nanotubes as a self-sacrifice template. The optimaldoping amounts （LMO-1） was confirmed by galvanostatic charge/discharge measurements.The results indicate that LiMn₂O₄nanotubes exhibit superior electrochemical performance.About67%of its initial capacity （115mAh/g） can be retained after50cycles. For LMO-1, itsinitial reversible capacity is126.6mAh/g and100mAh/g can be maintained after50cycles, itscapacitance retention rate is still as high as79%, it has a better circle stability andelectrochemical performance than LMO. These results reveal that LiMn₂O₄and Co-LiMn₂O₄nanotubes will be one of the most promising cathode materials for high-power lithium ionbatteries.