A. Abouimrane, S. A. Odom, H. Tavassol, M. V. Schulmerich, H. Wu, R. Bhargava, A. A. Gewirth, J. S. Moore, and K. Amine
Argonne National Laboratory and the University of Illinois at Urbana-Champaign
High-voltage cathode materials are being developed for lithium ion (Li-ion) batteries with the goal of significantly increasing battery energy density. Conventional Li-ion battery electrolyte systems are quite unstable at these high potentials, leading to short calendar and cycle lives, as well as potential safety issues. In this research project, we are studying the use of organic monomers as electrolyte additives that will oxidize and polymerize to form stable passivation films on the surface of high voltage cathode materials. Specifically, we studied 3-hexylthiophene (3HT) as an additive to stabilize the surface of the high-voltage cathode Li1.2Ni0.55Co0.1Mn0.55O2, when evaluated in half cells using a lithium metal anode. We conducted analyses of the treated cathode surface using scanning electron microscopy, matrix-assisted laser desorption/ionization (MALDI), and infrared and Raman spectroscopies. The results are consistent with the formation of poly(3HT) on the cathode surface. Electrochemical cycling, impedance measurements, and differential scanning calorimetry all confirm that the electrode/electrolyte interface is significantly stabilized by the use of 3HT as an electrolyte additive, when used at concentrations of 0.05–0.10 weight %. Future studies will evaluate additional polymerizable monomers, with the goal of further stabilization of the cathode surface.
Illustration of MALDI spectrum of cathode surface showing oligomers of poly(3HT): Insert shows electrochemical polymerization of 3HT; and (Right) capacity versus cycle number for Li/Li1.2Ni0.55Co0.1Mn0.55O2 half cells employing 0.00, 0.05, and 0.10 weight % of 3HT in the electrolyte.
A. Abouimrane, S. A. Odom, H. Tavassol, M. V. Schulmerich, H. Wu, R. Bhargava, A. A. Gewirth, J. S. Moore, K. Amine, J. Electrochem. Soc. 160(2), A268-A271 (2012).