Tuesday, 30 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
In order to extend the lifetime and performance of lithium ion battery systems, the use of electrolyte additives continues to be one of the most effective and economical approaches currently under investigation. Common metrics used to measure the relative performance enhancement of these electrolyte additives include capacity retention and impedance rise. This study details efforts to 1) perform a combinatorial analysis of electrolyte additives for use in high voltage lithium ion battery systems, and 2) evaluate the performance of the tested electrolyte systems using two figures of merit (FOM) which address both capacity (energy) and impedance (power). Eight known additives were used throughout the course of the test: three additives known to work on the positive (cathode) electrode (TMSPi, TEPi, LiDFOB) and five additives known to work on the negative (anode) electrode (LiBOB, VC, tVCBO, PBE, PES). Electrochemical testing was performed on LiNi0.5Mn0.3Co0.2O2 /graphite full cells operating between 3.0-4.4 V. The cycling protocol combines several C rates (C/1, C/3, C/10) for capacity and rate information and intermittent hybrid pulse power characterization (HPPC) tests from which area specific impedance (ASI) values are calculated. Results from extensive testing reveal interesting trends in the electrolyte systems. In general, TMSPi performed well as an additive while a structurally analogous molecule, TEPi, performed poorly. Other trends, such as the effects of LiBOB on energy fade and VC on power fade, were found. Capacity, impedance and other electrochemical data will be presented to give a comprehensive overview of performance effects of the tested electrolyte additives. This work underscores the importance of developing evaluation methodologies in order to objectively view the performance of electrolyte systems and identify trends in electrolyte additive behavior.