High Quality Graphene for Low Temperatures Lithium-Ion Batteries Application

The properties of high quality few-layers graphene, produced though multisteps process involving microwave irradiation of expandable graphite, are presented. Such innovative approach fulfills all desirable requirements (so far missing in the conventional methods, e.g. Hummers method) of being reproducible, low-cost, environmental friendly, with high yield, and scalable.

When used as anode material the so-obtained graphene (hereinafter GRAL), differently from the commonly employed reduced graphene oxide, is able, similarly to graphite, to intercalate/de-intercalate Li ions in the few-layers structure. Its peculiar features such as (i) presence of few defects, (ii) small sheets size, and (iii) nanometric thickness, enable the negative electrode to work at considerably lower temperatures than conventional graphite.

During galvanostatic charge-discharge experiments (specific current of 50 mA g^-1), performed in a temperature range comprised between +20°C and -30°C, GRAL exhibits remarkable capacity retention with comparison to commercial graphite. At temperatures above 0°C, GRAL performs quite similarly to graphite. However, at lower temperatures, graphite suffers from dramatic capacity decay resulting on only 9% of capacity retention at -30°C. On the contrary, GRAL is able to retain 65% and 34% of the room temperature capacity when operating at -20°C and -30°C, respectively.

The outstanding performances of this novel few-layers graphene are confirmed also by the very promising low temperature stability, with a coulombic efficiency close to 100%.