Process for producing highly oriented graphene films

A process for producing a highly oriented graphene film (HOGF) with a thickness no greater than 0.1 mm, said process comprising:

• (a) preparing either a graphene oxide dispersion having graphene oxide sheets dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in a fluid medium, wherein said graphene oxide sheets or graphene oxide molecules contain an oxygen content higher than 5% by weight;
• (b) dispensing and depositing said graphene oxide dispersion or graphene oxide gel onto a surface of a supporting substrate to form a first layer of graphene oxide, wherein said dispensing and depositing procedure includes subjecting said graphene oxide dispersion or graphene oxide gel to an orientation-inducing stress;
• (c) partially or completely removing said fluid medium from the first layer of graphene oxide to form a first dried layer of graphene oxide having a layer thickness no greater than 200 μm and having an inter-plane spacing d002 of 0.4 nm to 1.2 nm as determined by X-ray diffraction and an oxygen content no less than 5% by weight;
• (d) preparing at least a second dried layer of graphene oxide by repeating steps (b) and (c) at least one time or preparing multiple sheets of dried graphene oxide by slicing said first dried layer of graphene oxide;
• (e) heat treating said first dried layer of graphene oxide and said at least second dried layer of graphene oxide or said multiple sheets of dried graphene oxide at a first heat treatment temperature higher than 100° C. under an optional first compressive stress to an extent that an inter-plane spacing d002 in said first dried layer, second dried layer, or multiple sheets of dried graphene oxide is decreased to a value less than 0.4 nm and the oxygen content is decreased to less than 5% by weight;
• and
• (f) stacking said first with said at least the second dried layer of graphene oxide or stacking said multiple sheets of dried graphene oxide under a second compressive stress to form said highly oriented graphene film, wherein said step (f) occurs after said step (e).