THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Monday, May 7, 2018

10:00 AM
in MRDC 2407

will be held the

DISSERTATION DEFENSE

for

Anirudh Ramanujapuram

Electrochemical Behavior of Lithium Cobalt Oxide in Aqueous Electrolytes

Committee Members:

Prof. Gleb Yushin, Advisor, MSE

Prof. Faisal Alamgir, MSE

Prof. Preet Singh, MSE

Prof. Matthew McDowell, ME

Prof. Marta Hatzell, ME

Abstract:

Lithium-ion batteries are the most popular energy devices for almost all electronics today. From cell-phones and laptops, to advanced uses in automotive and aircraft applications, lithium-ion batteries have slowly taken over the market. Unfortunately, today’s lithium-ion batteries are also highly unsafe. They rely heavily on organic solvents for electrolytes in the battery. These organic solvents are inherently flammable in nature and have caused several fires reported in batteries over the past few years.

In this research, we aim to replace this flammable liquid with a safer alternative such as water. Water-based batteries offer greatly improved safety and much lower cost (from lower raw material cost to reduced manufacturing costs). In addition, water based electrolytes have higher ionic mobility for lithium ions and thus can be potentially used for much faster charging batteries or batteries with thicker electrodes. Lithium cobalt oxide (LCO) has long been proven to be an excellent material for cathodes in organic electrolytes. It has shown high volumetric capacity and good stability in non-aqueous environments of commercial lithium-ion (Li-ion) batteries. Unfortunately, the flammability of organic electrolytes in combination with a special propensity for batteries constructed with LCO to experience thermal runaway creates safety concerns.

In this work, we discuss the electrochemical performance characteristics and stability of LCO in aqueous environments. While LCO has been demonstrated to cycle for 20-100 cycles in aqueous electrolytes the causes of its degradation have not been investigated in detail. Our studies demonstrated that LCO cathodes with remarkably stable performance showing only 13% fading after over 1500 cycles. Post mortem analysis of the electrodes was conducted to understand the effect of cycling and the causes of degradation. Electrolyte composition was found to have a dramatic impact on the electrochemical performance and stability of LCO in aqueous environments.

Finally, the temperature range for aqueous electrolytes has also been investigated in detail. Through the use of the colligative properties of water, it has been demonstrated that aqueous electrolytes can function much below the freezing point of water down to -40oC.