Normal Li-ion cells with a positive electrode and a negative electrode normally have a voltage near 4.0 V. There are many surprising things about lithium-ion cells. One of these is that unwanted chemical reactions between one charged electrode (say the positive) and the electrolyte can create reaction products that migrate to the other electrode (say the negative) and affect it dramatically [1,2]. In order to eliminate this “cross-talk”, “symmetric” cells, which have two positive (or two negative electrodes) electrodes and hence an average voltage of zero, are used [3,4]. The charge discharge cycle performance of a symmetric cell is exclusively determined by the compatibility of the electrode of interest with the electrolyte of choice.
In this study, the compatibility of various electrolyte additives with Li[Ni0.6Mn0.2Co0.2]O2 positive electrodes were studied using positive-positive symmetric cells built in-house. Symmetric cell testing is a method to effectively evaluate materials made in an academic laboratory when machine-made electrodes and full Li-ion cells are not readily available.
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