Do Protons released from DRX Cathode Surfaces Initiate Decomposition of Ethylene Carbonate Electrolyte in Lithium-Ion Batteries?

The cathode-electrolyte interphase (CEI) is a critical, but not fully understood component of Li-ion batteries (LIBs). Ethylene Carbonate (EC), a commonly used electrolyte in LIBs, starts to decompose at approx. 3.8 V vs Li/Li+ to form this CEI [1]. One of the initial products formed due to this decomposition is vinylene carbonate (VC) which has been experimentally observed by in-situ FT-IR(Fourier Transform Infrared Spectroscopy) measurements at potentials as low as 3.8 V vs Li/Li+[2]. In this talk, we explore the feasibility of this reaction occurring through a mechanism involving transition metal ions on the cathode surface through density functional theory calculations performed under realistic surface conditions. Previous ab initio studies on the EC decomposition on NMC surfaces have been performed[3,4,5]. As a prototype for next generation cathode, we study Disordered Rocksalt(DRX) surfaces as cathodes and explore the equilibrium between EC,VC and abstracted hydrogen as a function of the potential. We find that surface adsorbed hydrogen is released as protons at a potential of 3.7 V vs. Li/Li+, which drives the conversion of EC to VC. We study the thermodynamics of proton release from the DRX surface at different lithiation stages from ab initio calculations to understand the potential dependence of proton release and further understand the thermodynamics of EC to VC decomposition. This will allow us to better understand the reactions occurring at the cathode electrolyte interface as well as crosstalk between anode and cathode materials.<br/><br/><br/>Reference list<br/>[1]Y. Wu, X. Liu, L. Wang, X. Feng, D. Ren, Y. Li, X. Rui, Y. Wang, X. Han, G.-L. Xu, H. Wang, L. Lu, X. He, K. Amine, M. Ouyang, <i>Energy Storage Materials</i>. <b>37</b>, 77–86 (2021).<br/>[2] Y. Zhang, Y. Katayama, R. Tatara, L. Giordano, Y. Yu, D. Fraggedakis, J. G. Sun, F. Maglia, R. Jung, M. Z. Bazant, Y. Shao-Horn, Energy & Environmental Science. <b>13</b>, 183–199 (2020).<br/>[3] S. Xu, G. Luo, R. Jacobs, S. Fang, M. K. Mahanthappa, R. J. Hamers, D. Morgan, ACS Applied Materials & Interfaces. <b>9</b>, 20545–20553 (2017).<br/>[4] J. L. Tebbe, T. F. Fuerst, C. B. Musgrave, ACS Applied Materials & Interfaces. <b>8</b>, 26664–26674 (2016).<br/>[5] T. M. Ostergaard, L. Giordano, I. E. Castelli, F. Maglia, B. K. Antonopoulos, Y. Shao Horn, J. Rossmeisl Journal of Physical Chemistry C. <b>122</b>, 10442–10449 (2018)