Understanding the Electrode/Electrolyte Interface Formation on Positive Electrodes of Li-Ion Batteries

Abstract

Understanding electrode/electrolyte interface (EEI) is crucial for the development of high-energy batteries for electric vehicle applications. The EEI layer formation of negative electrode (also referred as Solid Electrolyte Interphase) is comprehensively studied [1,2], whereas the electrolyte decomposition and formation of the EEI layer at the positive electrodes are still unknown [3,4]. Especially, at high potentials, the role of oxygen in the transition metal oxide becomes critical, leading to the evolution of oxygen from the oxide lattice or the formation of highly reactive species like surface peroxide and superoxide, which can modify the nature of the EEI layer. Here, we show how EEI layer depends on different positive electrodes (LiCoO2 and NMC electrodes with different Ni content) and different electrolyte additives (diphenyl carbonate and adiponitrile) by using X-ray Photoelectron Spectroscopy (XPS). We also highlight the importance of using carbon-free, binder-free electrodes to unambiguously pinpoint the reactivity of the electrolyte at the positive electrode [5]. The analysis of the XPS results points to a strong dependency of the surface reactivity on different electrode and electrolyte composition. [1] E. Peled, J. Electrochem. Soc. 126, 2047 (1979).[2] D. Aurbach et al., J. Power Sources 81-82, 95 (1999).[3] K. Xu et al., Chem. Rev., 114, 11503 (2014).[4] M. Gauthier, T. Carney, A. Grimaud et al., J. Phys. Chem. Lett. 6, 4653 (2015).[5] M. Gauthier et al., in preparation.