The Manipulation of Individual Layers in Two-dimensional Metamaterial Batteries

The studentship is part of the UK’s Centre of Doctoral Training in Metamaterials (XM2) based in the Departments of Physics and Engineering on the Streatham Campus in Exeter. Its aim is to undertake world-leading research, while training scientists and engineers with the relevant research skills and knowledge, and professional attributes for industry and academia.

The world is facing an energy crisis. A key component in this crisis is the lack of a light weight energy storage mechanism. The UK and other governments have announced that they are phasing out petrol and diesel vehicles in the next 30 years. This requires electric cars which in turn need an efficient rechargeable battery.

The current generation of electric cars is estimated to go at best up to 200 miles, which corresponds to an energy density of roughly 300 Wh/kg. In order to become really competitive, this needs to rise 500 Wh/kg. Two-dimensional systems, ranging from bilayers to many layer systems provide ideal candidates for battery applications, in particular the anodes of the battery cell. This is because it is possible to intercalated lithium (or sodium) ions between the layers without causing significant structural reconfiguration [1] (thus allowing for a high number of recharges), driven by the van der Waals pressure which stabilises unusual phases between the layers [2]. However, these devices still rely on traditional bulk components, but what is needed to take this forward is a 2D metamaterial battery.

Systems such as phosphorene and the transitional metal dichalogenides (TMDCs) often offer higher operating voltages [3] but at the cost of becoming insulating during intercalation (which is not suitable for battery activities). The project envisages using a combination of two or three different 2D materials in a layered format, with graphene initially forming the outer most layers of the stack to ensure conductivity. The inner layers will consist of TMDC’s, phosphorene and other 2D systems. Initial calculations will focus on the density of ions that can be intercalated, the operating voltage and the expansion of the system. From this set up, the inner layers will be either oxidised or severed to explore potential geometries which allow greater amounts of intercalation, whilst maintaining the structure. These devices will be characterised using optical techniques.

The manipulation of individual 2D layers, tuning the layers, and examining how carving individual flakes in half etc. may seem experimentally verging on impossible, but if a design can be found to enable high energy densities of 500 Wh/kg then it can be assured that military applications will immediately lead these to be developed, and in the long term picture, the car industry will also be keen to be ahead of their competitors.

[1] Mayo et al. Chem. Of Mat. 28, 2011 (2016)
[2] Vasu et al. Nature Comm. 7, 12168 (2016).
[3] Fan et al. J. Phys. Chem. C 121, 13599 (2017)