Abstract text (incl. figure legends and references)

Lithium-ion batteries (LIBs) are the state-of-art rechargeable batteries. With the ongoing growth of the electric vehicles market, driven by the global tendency aiming toward the decrease of fossil fuel consumption [1, 2], the improvement of the current LIBs technology is required and more particularly their performance, their safety and their lifetime[1, 2]. The research in this domain has mainly been focused on electrodes and electrolyte optimization. However, the role of the current collectors (CCs) on the LIBs performance remains poorly understood [3]. The intrinsic complex and interlinked chemistry of LIBs requires a deconvolution of all effects to gain insights on the mechanisms of their degradation. In bulk devices, the cathode side CC is aluminum, which overall presents good corrosion resistance [1]. However, its corrosion is still occurring and the exact mechanism and its implication on the whole LIB cell are yet not fully understood [2, 3].

To understand the impact of the degradation of the Al CC on the performance of LIB, we use liquid cell electron microscopy (LCEM) [4]. This technique is enabled by using specific transmission or scanning EM holders that are enclosing liquid solution between two micro-electromechanical systems (MEMS) chips. On one of these chips, electrodes can be patterned and electrically biased for performing in situ or operando electrochemical experiments.

First, we developed in-house microfabricated MEMS chips that include a Al electrode and two Pt electrodes, all having a thickness of 50 nm. To determine appropriate electrochemical conditions for Al corrosion in LCEM, we performed linear sweep voltammetry (LSV) and chronopotentiometry (CP) measurement on the bench in a simplified chloride-based aqueous environment. Al corrosion was thus performed ex situ in 0.1 M NaCl solution (>99.5%, Carl Roth) using the Al electrode of produced chip as working electrode (WE), a Pt wire as counter electrode (CE) and a Ag/AgCl reference electrode (RE). CP was also performed in situ in a SEM, using on chip Al WE and Pt CE, and a bulk Ag/AgCl RE.

LSV results showed that the current increases at the pitting potential, resulting in a large part of the Al electrode being corroded within less than 10 s. This timescale is very short for properly imaging Al corrosion using LCEM. In contrast, during CP measurements, pit formation occurred between tenths of seconds and several minutes, indicated by the potential increase as a function of time. The constant potential that follows is indicative of active corrosion of the aluminum electrode. The large pits density suggests that CP measurements can be used to study the corrosion using LCEM. It is noted that gas bubble formation on the corroded region was also observed and its role on the corrosion is being investigated.

In conclusion, we report the development of a MEMS chip containing an Al electrode for use as CC on the positive electrode of the lithium-ion microbatteries. We also report that galvanostatic experiments are more appropriate than potentiodynamic for imaging Al corrosion using LCEM.

References:

[1] V. Etacheri et al., Energy Environ. Sci. vol. 4 (2011), pp. 3243–3262, doi: 10.1039/c1ee01598b.

[2] L. Guo et al., J. Phys. Energy vol. 3 (Jul. 2021), p. 032015, doi: 10.1088/2515-7655/ac0c04.

[3] T. Ma et al., J. Phys. Chem. Lett. vol. 8 (2017), pp. 1072–1077, doi: 10.1021/acs.jpclett.6b02933.

[4] F. M. Ross, Science (80-. ). vol. 350 (2015), doi: 10.1126/science.aaa9886.