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Synthesis of Electrode Materials for Rechargeable Batteries using Nanostructured Composites

Hassanzadeh Yazdi, Nafiseh | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49485 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Sadrnezhad, Khatiboleslam
  7. Abstract:
  8. Sodium-ion batteries are cost-effective rechargeable batteries which have attracted considerable interest in recent years due to the low cost and abundance of sodium resources on the earth. Na3MnCO3PO4 (NMCP) has been identified as a potential cathode material with a high theoretical capacity of 191 mAh g-1. In order to improve the conductivity and electrochemical properties of NMCP, fabrication of NMCP/reduced graphene oxide (rGO) composite is a novel and interesting research goal. Therefore, in the current study, rGO was produced by using modified Hummers method. Then, the kinetics of NMCP formation through hydrothermal process was investigated. Results indicate that the optimum temperature and time for hydrothermal process was 120 ̊C and 24 h. In the next step, the successful synthesis of NMCP/rGO nanocomposite was done for the first time via in-situ hydrothermal process. FESEM and TEM results indicate the formation of ~25 nm NMCP nanoparticles distributed on rGO sheets. The synergy arising from the formation of fine NMCP nanoparticles and NMCP/rGO hybridization makes this material a promising cathode for sodium-ion batteries. This nanocopmosite delivers specific discharge capacities of 156 and 114 mAh g-1 at C/30 and C/100 rates, respectively. Owing to the high electronic conductivity and extremely high surface/mass ratio of rGO, the obtained gravimetric capacities indicate 39% and 52% improvement at C/30 and C/100 rates, respectively, in comparison with the highest corresponding values reported in the literature. It should be noted that this material shows a medium cyclic behavior.In the next step, ball-milling synthesis of NMCP particles was done successfully, for the first time. The needle-like NMCP particles of ~15 nm diameter were anchored onto rGO sheets during hydrothermal reduction process under stirring and NMCP/rGO nanocomposite was produced. As a promising cathode candidate for sodium-ion batteries, NMCP and NMCP/rGO electrodes displayed initial capacities of 103 and 141 mAh g-1 at C/30 rate with capacity retention of 71% and 81% after 15 cycles, respectively. In comparison with the hydrothermally synthesized nanocomposite, improvement of the cycling performance is attributed mainly to the almost uniform distribution of NMCP nanoparticles on rGO conducting network and also lower agglomeration/stacking of rGO sheets as a result of stirring. In addition, the hierarchical morphology of the ball-milling synthesized NMCP resulted in improved structural stability of the electrode in comparison with the hydrothermally synthesized NMCP
  9. Keywords:
  10. Cathodes ; Graphene ; Nanocomposite ; Hydrothermal Method ; Milling ; Sodium-Ion Battery ; Carbonophosphate

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