Abstract

Different from traditional lithium-ion batteries (LIBs) which rely on Li+ as the only charge carriers, dual-ion batteries (DIBs) which use both cations and anions as electroactive species have received increasing attention due to their high power- density and low cost. So far, graphite has been shown to accommodate anions such as PF6 - and BF4 - with a capacity of close to 100 mAh g-1 and a potential of above 4.5V vs. Li/Li+ on the positive electrode [1-3]. Since the anions originate from the electrolyte, the electrochemical performances of the graphite electrode depend highly on the type of solvent used. Figure 1a shows the cyclic voltammograms of graphite (KS6, Timcal) electrodes in 3M LiPF6 dissolved in linear carbonate solvents of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). We can see that by changing the solvent, the reaction peaks are completely changed. In particular, the lower onset potential at around 4.39 V vs. Li/Li+ suggests that it is easier for PF6 - anions to intercalate into graphite with EMC than DMC and DEC. Rate performances of graphite electrodes in the three different solvents are shown in Figure 1b. Interestingly, electrolyte with EMC solvent also gives much better rate capability than those with DMC and DEC. This is attributed to the difference in chemical interaction between the PF6 - anions and the solvent molecules. Further works on understanding how solvents’ properties, solvation structure and charge transfer impedances etc. affect the observed performances are underway and will be presented at the meeting.

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