The Sound of Batteries: An Operando Acoustic Emission Study of the LiNiO₂ Cathode in Li–Ion Cells

Abstract

The development of advanced Li-ion batteries relies on the implementation of high-capacity Ni-rich layered oxide cathode materials, such as NCM and NCA, among others. However, fast performance decay because of intrinsic chemical and structural instabilities hampers their practical application. Hence, thoroughly understanding degradation processes is crucial to overcome current limitations. To monitor instabilities of electrode materials under realistic operating conditions, the application of nondestructive operando techniques is required. While structural changes of crystalline phases can be studied by X-ray diffraction, microstructural changes (e. g., particle fracture) cannot be easily accessed in situ and are therefore mostly investigated ex situ. Here, we use acoustic emission (AE) measurements to probe a potential next-generation cathode material in real-time. Specifically, we focus on LiNiO 2 (LNO) and demonstrate that AE events in different frequency ranges can be correlated with the formation of the cathode solid-electrolyte interphase and the mechanical degradation during electrochemical cycling.

Operando acoustic emission monitoring of degradation processes in lithium-ion batteries with a high-entropy oxide anode

“…Even if the outgassing can be excluded as a source of significant acoustic activity, the evolution of C 2 H 4 is a clear indication of the formation of a solid-electrolyte interphase (SEI) on the anode 13 , 35 , 36 . Both SEI formation and cracking are acoustically intense and detectable processes, as demonstrated by various AE studies 17 , 19 , 20 , 31 , 33 . The assignment to SEI formation is further supported by the fact that the appearance of acoustic activity in the second lithiation cycle is also consistent with the evolution of C 2 H 4 at E ≤ 0.2 V 13 .…”

“…Accordingly, it can be assumed that the increase in acoustic activity at E ≤ 0.3 V is due to the conversion reaction itself and the associated deformation of the crystal lattice 32 . In particular, the strong volumetric changes with Li uptake can lead to mechanical deformation, including particle fracture and pulverization, which strongly impacts on the AE 20 , 21 , 27 , 31 . Note that major contributions of the Li anode to the acoustic activity can be neglected 17 , 31 , 33 .…”

“…In particular, the strong volumetric changes with Li uptake can lead to mechanical deformation, including particle fracture and pulverization, which strongly impacts on the AE 20 , 21 , 27 , 31 . Note that major contributions of the Li anode to the acoustic activity can be neglected 17 , 31 , 33 . Furthermore, investigations into the gassing behavior of HEO half-cells by Breitung et al revealed that gas evolution (H 2 and C 2 H 4 ) due to reductive electrolyte decomposition starts at E ≈ 0.37 V in the initial cycle, with a maximum at the lower cutoff voltage of 0.01 V 13 .…”

“…Furthermore, investigations into the gassing behavior of HEO half-cells by Breitung et al revealed that gas evolution (H 2 and C 2 H 4 ) due to reductive electrolyte decomposition starts at E ≈ 0.37 V in the initial cycle, with a maximum at the lower cutoff voltage of 0.01 V 13 . However, the detection of both the formation and bursting of gas bubbles can be largely ruled out based on previous results 31 , 34 . Even if the outgassing can be excluded as a source of significant acoustic activity, the evolution of C 2 H 4 is a clear indication of the formation of a solid-electrolyte interphase (SEI) on the anode 13 , 35 , 36 .…”

“…The sensor coupling was probed using the pencil-lead break test 29 . For the calculation of hit rate and more details on the AE analysis, the reader is referred to the literature 17 , 20 , 21 , 27 , 30 , 31 .…”