Date of Award

12-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Materials Science and Engineering

Advisor

Luo, Jian

Committee Member

Kornev , Konstantin

Committee Member

Kennedy , Marian

Abstract

Rechargeable batteries that can charge and discharge at high rates have applications in hybrid and plug-in hybrid vehicles and they provide energy storages for wind energy. Various methods like reducing particle size, aliovalent doping and carbon coating have been researched in order to attain higher charge and discharge rates in rechargeable Li-ion batteries. In this work, the electrode materials were coated with amorphous films in an attempt to improve the rate capability of the batteries.
A study by Kang and Ceder suggested that a Li4P2O7-like 'fast-ion conducting surface phase' could form on the surface of LiFePO4 particles, which can improve the charging and discharging rates of these batteries to a great extent. This work demonstrates that these nanoscale surface films can indeed form spontaneously upon annealing; furthermore, they exhibit a self-selecting or 'equilibrium' thickness, similar to those previously observed Luo et al. in simpler binary oxide systems. Similar nanoscale intergranular films have also been observed. These nanoscale surficial and intergranular films can be used to tailor nanoparticles for battery and other applications.
In the second part of this study, LiMn2O4 particles were coated with Li4P2O7 or Li3PO4 particles. Then, coin cells and Swagelok cells were constructed to test these materials. It was found that amorphous Li4P2O7 formed non-uniform coatings on LiMn2O4 particles, but such coatings deteriorated the electrochemical properties of LiMn2O4. Furthermore, Li3PO4 coatings also deteriorated the electrochemical properties, but to a less extent. The electrochemical performances of the coated samples showed a dependency on the amount of Li3PO4. Additionally, it was found that HEBM decreased the capacity of LiMn2O4 by ~15%, more than half of which could be recovered by annealing.
In the third part of this study, the effect of particle size and V2O5 coatings on the electrochemical properties of anatase anodes was studied. The small increase in particle size did not affect the cell performance at low rates, while the particles with smaller size performed better at high rates. Nanoscale V2O5 coatings also deteriorated the electrochemical properties by reducing the capacity, especially at higher rates. At high loading levels, V2O5 participated and contributed to the total capacity in the first few cycles. Crystalline rutile and V2O5 phases were present in TiO2 with 18 wt. % V2O5, which further deteriorated the capacity.

Share

COinS