Eco-friendly production of high quality low cost graphene and its application in lithium ion batteries

Abstract

Large scale production of low cost and high quality graphene from abundant raw materials using eco-friendly methods is a critical step towards the widespread and sustainable use of this so-called “wonder material”. This paper for the first time reports a single step molten salt electrochemical method for the high yield preparation of graphene nanosheets having all the characteristics mentioned above. This process uses readily available commercial graphite electrodes as the carbon source which is both abundant and cheap. Surprisingly, apart from graphite, the other consumables are H₂ and electricity, and no by-product is produced. This method is not only eco-friendly but also very efficient. It offers a production rate of 450 g graphene per litre of molten salt per day. A molten salt volume of 10 L should be able to produce 4.5 kg graphene in a day. The graphene product showed a high conductivity of 5.8 × 10⁵ S m⁻¹. The bench-scale production of high quality graphene, on a scale of tens of grams, was achieved using a novel two working electrode electrolysis cell, operating at a current density of about 1 A cm⁻² which is at least an order of magnitude higher than any other electrochemical exfoliation method which has been used so far for the preparation of graphene. The mechanism involved in the process is discussed. The graphene nanosheets showed a high oxidation temperature of 663 °C when heated in air at 40 °C min⁻¹. A simple and green strategy was developed to anchor SnO₂ nanocrystals on the graphene nanosheets, and the lithium storage performance of the composite obtained was investigated. The composite displayed a high and stable lithium capacity of 1016 mA h g⁻¹ after 100 cycles of lithiation and de-lithiation.