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.

Sensing as the key to battery lifetime and sustainability

“…As highlighted by Choe et al 41 , with LiCoO2/C cells, two types of AE events could be unveiled over two different frequency regions, based on waveform analysis, which when combined with scanning electron microscope (SEM) measurements, were assigned to LiCoO2 fracture and SEI growth, respectively. Of course, the AE spectra will depend on cell chemistry, as highlighted by a recent study on LiNiO2/Li cells 42 where three distinct types of acoustic events are discerned during cycling. In addition to particle fracture, the growth of a cathode electrolyte interphase (CEI) at the positive electrode was also evidenced.…”

Advances and challenges in multiscale characterizations and analyses for battery materials

“…Such a combination of reduction-expansion-cracking of sulfide solid electrolyte is repeated and, eventually, large cracks form and Li metal forms inside the large cracks, which causes short circuiting. There are other advanced characterization techniques that are non-destructive and can be done operando: such as acoustic emission [139], ultrasound- [140,141] and thermal waves characterization [142]. These techniques can scan large areas and even practical full cell dimensions during battery operation.…”