(Invited) Electrolyte Additives for High-Voltage Lithium-Ion Battery Cathodes

In order to increase the energy density of lithium-ion batteries, novel cathode materials have attracted much attention due to their high operating voltage [1]. However, their practical application is still limited due to the poor stability of the cathode / alkyl carbonate-based electrolyte interface. In fact, the working potential of many high voltage cathode is beyond the electrochemical stability window of the conventional carbonate-based electrolytes (< 4.3 V vs. Li+/Li), thus leading to the electrolyte oxidative decomposition [2]. This phenomenon, besides reducing the energy stored in the cell, might even results in the formation of decomposition products (e.g., HF) leading to metal dissolution, and hence material capacity fading. Many strategies, such as the use of alternative electrolyte system or the coating of the material, have been proposed in order to enable the use of high-voltage cathodes [3]. However, using electrolyte additives is one of the most efficient and economic strategy for alleviating the undesired reactions among cathode and electrolyte [4]. In fact, electrolyte additives can be sacrificially decomposed to form a protective layer on cathode surface, thus avoiding further electrolyte decomposition reactions. In addition, electrolyte additives can even scavenge water or other impurities and/or stabilize the lithium salt, extending therefore the cycle life of the high-voltage cathodes. In this study, the investigation of additives’ effects in enhancing the cathode cycling stability and efficiency will be presented via a combination of electrochemical techniques, such as impedance spectroscopy and ex-situ analytical techniques, i.e. XRD, XPS and RAMAN. The feasibility of the electrolyte additives employment for practical application will be demonstrated showing full-cell studies with graphite as anode. [1] A. Kraytsberg, Y. Ein-Eli, Advanced Energy Materials, 2 (2012) 922-939. [2] S. Tan, Y.J. Ji, Z.R. Zhang, Y. Yang, ChemPhysChem, 15 (2014) 1956-1969. [3] N.-S. Choi, J.-G. Han, S.-Y. Ha, I. Park, C.-K. Back, RSC Advances, 5 (2015) 2732-2748. [4] S.S. Zhang, J. Power Sources, 162 (2006) 1379-1394.