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Development of Nanostructured Lithium-Rich Cathode Material

Vahdatkhah, Parisa | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55509 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Sadrnezhaad, Khatiboleslam
  7. Abstract:
  8. This research is divided in three parts. In the first part of this research, we report the one-pot synthesis of carbonate-coated nanostructured LLO (Li2CO3@LLO) through a polyol-assisted method as a Li-ion battery cathode. Carbonate protects the cathode from adverse reactions with the electrolyte, also reduces the layered-to-spinel phase transition, thereby stabilizing the cathode structure. LLO nanostructure provides a fast Li+ diffusion. The target material exhibits excellent long-term stability with 77% capacity retention after 1000 cycles at 0.2C-rate. In the second part of research, Li(Na-doped)-Mn-Ni-O oxides were synthesized by different LiOH.H2O amount, type and amount of reducing agent, type of surfactant, calcination temperature and time. Based on the beneficial interface and structure, the Co-free LLO delivers a reversible capacity of 250 mAh g-1 with 99% capacity retention after 85 cycles at 0.1 C. We found that Ni surface enrichment improves the structural stability and reversibility of intra-cycle cation migration in the layered and spinel-layered Li-rich materials during the gradual de-lithiation process and Ni redox reaction. Furthermore, oxygen vacancies suppress gas release from the surface and reduce the resistance of electrode/electrolyte interface, thereby enhancing the cathode’s capacity. In the third part of this research, the surface functionalization of Li2CO3@LLO cathode is designed by polypyrrole (PPy) nanostructure coating due to its unique intrinsic properties such as high electrical conductivity, easy synthesis procedure, environmental stability, and good redox behavior. Li2CO3@LLO/PPy nanocomposites were produced with various morphologies (nanowire/nanorod/nanoparticle) and different weight percentage of PPy. We found that Li2CO3@LLO cathode with 5%PPy nanoparticles produced by H2O2 oxidant (PPy-NP(H2O2)) and sodium dodecyl sulfate (SDS) surfactant exhibits high-capacity retention, delivering a discharge capacity as high as 191 mAh g-1, with capacity retention of 96%, after ∼ 200 cycles at a current density of 20 mA g-1. Decreasing dimension and increasing dispersity of nanostructures lead to an increase in the interfacial area of the Li2CO3@LLO cathode by nanoparticles, thereby enhancing contact area with electrolyte and decreasing the diffusion length of Li+-ion.
  9. Keywords:
  10. Cathodes ; Oxygen Vacancy ; Lithium Ion Batteries ; Lithium Carbonate Coating ; Surface Nickel-Enrichment ; Polypyrrole Nanostructure ; Lithium-Rich Layered Oxide

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