4-(Trimethylsiloxy)-3-Pentene-2-One As a Novel Film-Forming Agent for High-Voltage LiNi0.5Mn1.5O4 Positive Electrode

As an effort to improve energy density of lithium-ion batteries (LIBs), the nickel-doped manganese spinel (LiNi0.5Mn1.5O4, LNMO) has been projected as a high-voltage positive electrode. The high working voltage (> 4.6 V vs. Li/Li+) and outstanding structural stability are advantageous with respect to energy density and cycle life. This advantage is, however, offset by the oxidative instability of electrolytes (> 4.3 V), which is even more serious at elevated temperatures.1 The commonly used electrolytes decompose and surface films deposit on the positive electrodes to lead to capacity fading.2, 3 In order to prevent electrolyte oxidation and film growth, the LNMO electrode should be passivated. To this end, the film-forming agents are added into electrolytes, which electrochemically decompose prior to the carbonate-based electrolytes to form passivation layer on the positive electrode. In this study, 4-(trimethylsiloxy)-3-pentene-2-one (TMSPO) was tested as a film-forming agent for LNMO electrode. TMSPO is oxidatively decomposed at 3.6 V (vs. Li/Li+) prior to the oxidation reaction of the carbonate-based electrolyte (1.3 M LiPF6 in EC : EMC : DEC = 3 : 2 : 5 (v/v/v)). The surface film derived from TMSPO shows good passivation ability to improve both Coulombic efficiency and cycle life of Li/LNMO cell (Fig. 1b). Electrolyte depletion and film growth are not serious in TMSPO-added cell. In contrast, the film derived from the carbonate-based electrolyte is poorly passivating. Cell polarization resulting from electrolyte decomposition/film deposition continues to cause capacity fading. References 1 .J. B. Goodenough and Y. Kim, J. Power Sources, 196, 6688-6694 (2011). 2. T. Yoon, S. Park, J. Mun, J. H. Ryu, W. Choi, Y.-S. Kang, J.-H. Park, and S. M. Oh, J. Power Sources, 215, 312-316 (2012). 3. D. Aurbach, B. Markovsky, Y. Talyossef, G. Salitra, H.-J. Kim, and S. Choi, J. Power Sources, 162, 780-789 (2006). Figure 1. (a); Differential capacity plot in the 1stcharging at 25℃, and (b) Coulombic efficiency and cycle performance at 60℃ Figure 1