Using acoustic emission (AE) measurements enables to indirectly obtain information about degradation processes within a material. By placing a piezoelectric sensor outside a battery test cell, acoustic waves emitted from irreversible process within can be converted into a measurable voltage signal. These processes can be e. g., gas evolution or crack formation. The AE technique thus allows for non-destructive measurement without altering or affecting the studied material or process within a battery.

The AE technique is commonly being used to investigate infrastructure such as bridges or pressure vessels and has also been used to examine the aging behavior of battery systems. Multiple groups tested different electrochemical systems such as nickel-metal hydride and different lithium-based composite electrodes such as LiCoO2, Graphite and LiNiO2.[1-4] These measurements were conducted for different cell types (coin-cells, cylindrical cells, svagelock type and others) and different measurement setups with changing materials [2,5,6]. This variety makes a comparison and subsequent conclusion about the differences in acoustic behavior of the different materials difficult.

We present herein several, systematic long term AE measurements with commonly used lithium-ion battery electrodes to investigate the acoustic behavior during cycling under the same conditions. Commercially available electrodes containing nickel-cobalt-manganese (NCM), artificial graphite and lithium-iron-phosphate (LFP) were investigated by placing them into coin-cells and a custom-made cell holder for AE measurement. The setup allows a simultaneous connection of the electrochemical- and acoustic measurement system. The AE measurements were conducted using a threshold based AE hit acquisition method. The test-cells were cycled at room temperature for over 200 cycles / 350 hours.

The NCM electrodes show the most AE hits (300-600). These occur in part at the beginning of formation as well as at a SOC over 80% and under 20% with an almost constant number of hits during each cycle. Measurements on the graphite electrodes show fever hits (<100); they occur in large part under 20% SOC. Electrodes containing LFP show surprisingly close to no AE hits during cycling. Our results show that the different commonly used electrodes for lithium-ion batteries have different acoustic aging behaviors, and thus AE can be applied to reveal their characteristic degradation behavior. To further increase the applicability of the gathered information subsequent work is being done on how AE hits can be differentiated to even separate possible underlying processes, and to investigate other cell chemistries. References [1] A. Etiemble, P. Bernard, H. Idrissi, L. Roué, Electrochimica Acta 2015, 186, 112-116. [2] C.-Y. Choe, W.-S. Jung, J.-W. Byeon, MATERIALS TRANSACTIONS 2015, 56, 269-273. [3] N. Kircheva, P.-X. Thivel, S. Genies, D. Brun-Buisson, Y. Bultel, ECS Transactions 2011, 35, 19-26. [4] S. Schweidler, M. Bianchini, P. Hartmann, T. Brezesinski, J. Janek, Batteries & Supercaps 2020, 3, 1021-1027. [5] S. Komagata, N. Kuwata, R. Baskaran, J. Kawamura, K. Sato, J. Mizusaki, ECS Meeting Abstracts 2009, MA2009-02, 83. [6] C. Villevieille, M. Boinet, L. Monconduit, Electrochemistry Communications 2010, 12, 1336-1339.