(684d) Impedance Behavior and Analysis of Binder-Free Ni-Mo Composite Cathode for Li-O2 Batteries

AIChE Annual Meeting Abstract ? Materials for Energy
Storage; Electronics & Photonics

Title

Impedance Behavior and Analysis of Binder-free Ni-Mo Composite
Cathode for Li-O₂ Batteries

Authors

Ruben Nelson, Mark H. Weatherspoon, Joyce Kosivi, Eric E.
Kalu, Jim P. Zheng

Abstract

            Lithium oxygen (Li-O₂) batteries have
significant promise for energy storage, with a high theoretical energy density
above 10 KW/kg. However, their many shortcomings from a cyclability and
efficiency perspective leave the technology in the research stage.  It is generally
understood that significant electrochemical activity occurs at the cathode
side; hence, there is much work in the area of cathode design. Specifically,
cathodes with metal oxide deposits have provided improved capacity and
efficiency, leading to enhanced performance over cells with bare carbon
cathodes.

            We present a porous carbon cathode with an
electroless deposited nickel and molybdenum composite that was also
electrolytically oxidized for use in Li-O₂ batteries promising a
specific capacity of approximately 1 Ah/g in the fist discharge.  However, scanning
electron microscope images show several changes in surface composition before
and after 15 charge-discharge cycles indicating several sources. To follow up,
impedance spectroscopy measurements are performed to gather frequency dependent
impedance behavior.  Equivalent circuit models are developed to associate intrinsic
cell phenomena to physical models.  Cathode influence on ohmic resistance,
charge-transfer resistance, and double layer capacitance, and constant phase
element behavior trends are investigated.  We expect that throughout cell
cycling, there is greater polarization from product buildup.  This would
increase the various physical resistances of the cell and lead to a decrease in
capacity.  Also unique to our study, we include the impedance response of the
cell to high frequency voltage signals greater than at least 10 kHz, where
capacitive behavior is recessive. Other previous studies attribute behavior at
these frequencies to be inductive behavior from instrumentation, cathode
design, or other factors. We aim to gain more insight on the relationship and
significance between high frequency and inductive behavior to decreasing cell
capacitance response in efforts to associate physical cell changes with electric
circuit principles. 

Ni-Mo Composite Oxide
Catalyst Cathode Prior to Discharge (left) and After 15 Discharge/Charge Cycles
(right)

Predischarged Li-O₂ cell with Ni-Mo Composite
Oxide Catalyst Impedance Spectrum

Impedance Spectrum of Li-O₂ Cell with Ni-Mo
Composite Oxide Catalyst Discharged 15 Times