Session: 09-01-04: Electrochemical Energy Storage and Conversion Systems IV

Paper Number: 168187

Manufacturing and Measuring Lithium-Ion Batteries to Isolate Reduction of Performance From Mechanical Damage 

With the recent development of electric vehicles there has become a heightened demand for energy storage systems which can output high power with low weight. Traditionally lithium-ion batteries (LIBs) have been used to fill this role due to their high energy density and long cycle life. This high energy density, coupled with volatile electrolyte chemistries, can lead to explosive reactions if large mechanical loads were to be applied to their surfaces. However, many vehicular accidents may not lead to volatile battery failure such that car batteries could still be used for the remainder of their life cycles without seeing thermal runaway events. To determine the effects of mechanical loading conditions which do not lead to failure of LIBs, new experimental frameworks have been developed to isolate complex damage modes. Battery materials were obtained using pre calendared rolls of NMC 811 cathode and graphite anode with a 1:1 EC: DEC electrolyte to be manufactured in a pouch cell format. Electrodes were isolated into separate pouches and crushed under uniaxial loading prior to assembly to reduce risk of shorting from tearing of the separator in active cells. Uniaxial compression allowed for the focus of damage to consider electrode deterioration as a function of mechanical stress and ignores electrolyte migration, interlayer delamination and separator porosity changes which are common under complex and dynamic loading conditions of complete cells. To ensure a wide range of stresses the electrodes were compressed from 5 – 50 MPa. The damaged electrodes were examined using scanning electron microscopy and surface measuring techniques to determine degree of cracking/ fracture, porosity change and loss of active material from the compression. These measurements are often associated with heightened LIB performance reduction and allow for the prediction of reduction in capacity and life time of damaged cells prior to cycling. Crushed electrodes were then assembled and formed under a C/20 current formation cycle and characterized by a C/10 galvanostatic charge-discharge cycle at 30°C using rated current from the undamaged electrode. To validate the performance of these cells, additional batteries were manufactured undamaged and formed and cycled using the same cycling conditions. Minimal variation between characterization of pre crushed electrode LIBs and cells crushed after formation was noticed, allowing for pre damaged electrode to be used as a baseline for future work. The proposed manufacturing techniques can be further adapted to isolate electrolyte migration and delamination to provide a complete experimental framework to understand LIB performance change due to mechanical impact conditions. By coupling cells with differing controlled damage profiles performance of LIBs subject to varying loading conditions can also be measured which allows for better prediction of performance change from complex loading.

Presenting Author: John Sherman University of North Carolina at Charlotte

Presenting Author Biography: John Sherman is a Ph. D. student in Mechanical Engineering at the University of North Carolina at Charlotte. His work focuses on experimental and computational analysis of battery safety from impact conditions.

Authors:

John Sherman University of North Carolina at Charlotte
Anthony Bombik University of North Carolina at Charlotte