Lithium-ion batteries (LIBs) are extensively employed to power small electric and stationary devices as well as electric vehicles (EVs), due to their high energy density, long cycle life, and relatively low self-discharge. The rapid expansion of the EV market is expected to increase significantly the global demand for LIBs, with sales projected to reach 245 million units by 2030, according to the International Energy Agency. In order to meet this demand, it is essential to reduce manufacturing scrap rates and extend battery life. [1,2] Production efficiency can be increased by limiting production failures and detecting process deflections at early stages of manufacturing chain, for example through rigorous control of the electrode homogeneity. On the other hand, the prolongation of a battery life assumes deep knowledge of the degradation processes, such as dendrite formation and electrolytes degradation, directly correlated with a change in the elemental distribution inside the battery. [3] As techniques capable of in-depth elemental analysis at scales from a few nm to 100 μm, Glow Discharge Optical Emission Spectroscopy (GD-OES) and Glow Discharge Mass Spectrometry (GD-MS) are suited for investigating both the homogeneity of the cathodic material in the manufacturing phase, as well as changes in its elemental distribution caused by aging. Focus has been given to lithium and fluorine distribution, whose migration inside the battery is correlated to the cycling and the electrolyte and binder degradation, respectively. 

A few previous reports described depth profiling of positive and negative electrodes in LIBs using GD-OES. [4-6] In this work, GD-OES spectroscopic analysis has been performed on self-made cathodes for LIBs to gain insight into the quality of the manufacturing process, targeting a standardized electrodes production. With the same cathode material, coin cells have been built and artificially aged. Post-mortem analysis conducted by GD-OES with the use of an argon/neon mixture as discharge gas, helped correlating the variation of fluorine distribution with the battery state of health (SOH). GD-MS analysis was employed to gain insight into battery degradation phenomena upon aging, such as transition metal dissolution from the positive electrode and lithium isotopic fractionation [3,7]. This work marks GD-techniques as versatile and efficient tools to study LIBs, unveiling significant application in both academical research and industrial manufacture.

References
[1] X. Duan, W. Zhu, Z. Ruan, M. Xie, J. Chen, X. Ren Energies 2022, 15, 1611.
[2] L. Yu, Y. Bai, B. Polzin, I. Belharouak J. of Power Sources, 2024, 593, 233955.
[3] J. S. Edge, G. J. Offer et al. Phys. Chem. Chem. Phys., 2021, 23, 8200.
[4] H. Takahara, Y. Kobayashi, T. Nakamura et al. Journal of The Electrochemical Society, 2014, 161, A1716.
[5] K. Richter, T. Waldmann, P. Axmann, M. Wohlfahrt-Mehrens et al. J. Phys. Chem. C, 2019, 123, 18795.
[6] Z. You, V. Hoffmann, D. Morcillo, L. A. Jácome, R. Leonhardt, A. Winckelmann, S. Richter, S. Recknagel, C. Abad Spectrochim. Acta, Part B, 2023, 205, 106681.
[7] K. Okano, Y. Takami, S. Yanase, T. Oi, Energy Procedia 2015, 71, 140.