Open Access Dissertation
Date of Award
Physics and Astronomy
Lithium iron silicate (Li2FeSiO4) has the potential as cathode material for next generation lithium ion batteries because of its high specific theoretical capacity (330 mA h g-1), low cost, environmental benignity, and improved safety. However, itsintrinsically poor electronic conductivity and slow lithium ion diffusion in the solid phase limits its applications. To address these issues, we studied mesoporous Li2FeSiO4/C composites synthesized by sol-gel (SG) and solvothermal (ST) methods using tri-block copolymer (P123) as carbon source and structure directing agent. The Li2FeSiO4/C (ST) composites show improved electrochemical performance compared to Li2FeSiO4/C (SG). At C/30 rate, Li2FeSiO4/C (ST) delivered the discharge capacity ~276 mA h g-1whencycled between 1.5-4.6 V and shows better rate capability and stability at high rates. We attribute the improved electrochemical performance of Li2FeSiO4/C (ST) to its large surface area and reduced particle size. We also synthesized Mg-doped Li2MgxFe1-xSiO4/C, (x= 0.0, 0.01, 0.02, and 0.04) nano-composites by ST method to further improve their electrochemical performance. Li2Mg0.01Fe0.99SiO4/C nanocomposites exhibited the best rate capability and cycle stability (94% retention after 100 charge-discharge cycles at 1C) and also delivered the highest initial discharge capacity of 278 mA h g-1 (~84% of the theoretical capacity) at C/30 rate, which isattributed to its enhanced Li-ion diffusion coefficient and lower charge transfer resistance due to reduced impurity phases, increased electronic conductivity, and maintaining large surface area.
Motivated by outstanding electronic and mechanical properties as well as high specific surface area of carbon nano-fibers (CNF) and reduced graphene oxide (rGO), we also investigated the ternary Li2FeSiO4/CNF/rGOnano-compositesas possible cathode materials which showed high stability over 200 cycles and improved discharge capacity at high C-rates.
Kumar, Ajay, "Nanostructured Lithium Iron Silicate/carbon Composites As Cathode Material For Next Generation Of Lithium-Ion Batteries" (2017). Wayne State University Dissertations. 1828.