Novel nondestructive recycling methods for lithium ion batteries (LIBs) are under investigation but lack the process engineering specifications required for full-scale operation. Specifically, the ability of end-of-life LIB components to withstand the stresses inherent in industrial manufacturing techniques has not been established. In this paper, we mechanically characterize the electrodes of both fresh and "cycle-aged" (C-A) cells, and couple this with electrochemical analysis to establish reprocessing requirements in the context of roll-to-roll (R2R) direct recycling. Cycle-aging is found to significantly reduce the tensile strength of electrodes and C-A cathodes reach elastic deformation at a lower strain than do fresh cathodes. This implies that both roll tension and calendering force may need to be reduced for C-A components relative to fresh components to avoid irreversible damage. Electrochemical analysis suggests that phase change and buildup of electrolyte residues at both the primary particle and in the inter-particle pore space may contribute to cathode degradation. The combination of these mechanical and electrochemical findings is crucial to informing the process design of industrial-scale nondestructive LIB recycling methods.

The mechanical properties of aged and fresh lithium ion cell components are evaluated in this paper. Cells components were obtained from destructive physical analysis of 40Ah NMC/Graphite-based pouch cells before and after cycling and were subjected to mechanical testing. The aging tests comprised of cycling the cell across a voltage window of 4.1V to 3.0V at room temperature (25℃). Using a 2C charging rate and 1C discharging rate, the cells were subjected to over 5600 cycles before a 80% drop in the name-plate capacity was observed. Mechanical tests, including compression test, tensile test and indentation test, were conducted on the cell components to investigate differences in the mechanical performance. Comparison of the fresh and aged cells components shows that cycling the cells has different degrees of impact on the different cell components. Anodes suffered the most serious deterioration in mechanical properties while separators remained intact under the test condition investigated.

Lithium-ion batteries have been popular powering mobile electronics and electric vehicles owing to its high energy density and good electrochemical performance. However, thermal transport performance, especially in cross-plane direction, is not on a par with electrochemical ones. Poor thermal transport may result in overheating and even thermal runaway while there’s still a lack of methods studying battery electrode thermal conductivity under working condition1. Previous efforts provide measurement on either dry battery electrodes or reassembled electrodes with electrolyte but not being able to charge and discharge2, 3. Current study demonstrates a new method measuring thermal conductivity of a working battery cell through flash diffusivity technique. By minimizing contact resistance between electrode sample and holder, the work can contribute to comprehensive study of a working battery cell for better thermal performance. 1. V. Vishwakarma, C. Waghela, Z. Wei, R. Prasher, S. C. Nagpure, J. Li, F. Liu, C. Daniel, and A. Jain, Journal of Power Sources, 300 123-131 (2015). 2. H. Maleki, S. A. Hallaj, J. R. Selman, R. B. Dinwiddie, and H. Wang, Journal of The Electrochemical Society, 146 (3), 947-954 (1999). 3. S. C. Nagpure, R. Dinwiddie, S. S. Babu, G. Rizzoni, B. Bhushan, and T. Frech, Journal of Power Sources, 195 (3), 872-876 (2010).

Thermal management is a critical component of battery safety. Extensive amount of research has been done on the thermal aspects of battery safety,electrochemical stability of the cell components, initiation of internal electrical failure due to short-circuits, inadvertent inclusion of impurities during the fabrication process, and swelling of cells due to chemical reactions. However, limited results have been reported on how the safety of lithium ion cells changes with aging of the cells. The lowering of capacity as the cell ages may contribute to marginal improvements to the abuse performance of the cells; whereas the increase in resistance and changes to the mechanical and thermal stability window of the components result in narrower windows for safe operation. In this talk, we present some results on how the thermal, electrical and mechanical properties of lithium ion cells change under different cycling conditions. The testing on the components was performed after careful disassembly of large format (40 Ah) lithium ion cells. Thermal conductivities were measured using the xenon nanoflash technique. Compression and tensile tests were performed on cell components harvested from the cells before and after cycling. Electrochemical resistance build up was characterized using impedance spectroscopy. Cycling conditions included different depth of discharge windows, cycling temperatures as well as charge/discharge rates. Initial results (Fig. 1) show that for the cells tested, under the cycling conditions we used, the anode undergoes a significant amount of degradation in terms of thermal and mechanical properties. The subsequent build up of electrochemical resistance and over heating of the cells lead to lowering of the safety threshold. We then proceed to integrate the properties of cell components that were experimentally measured, into mathematical models that are used to assess cell-level performance under abuse. The models are used to perform several what-if analyses to identify safety thresholds for the individual cell components for our cell design. We conclude with case studies illustrating how safety thresholds for each cell component is different, how the different factors interact with each other to determine the outcome of cell-level safety, and how to best incorporate these findings to design safer lithium ion cells. Figure 1