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Graphene and 2D Tungsten Disulfide Electrodes in Lithium-Ion Batteries: An Interview with Gurpreet Singh

In this Thought Leader interview, Dr. Gurpreet Singh from Kansas State University talks to Will Soutter about his work on using 2D nanomaterials such as graphene and tungsten disulfide for electrodes in rechargeable lithium ion batteries.

WS: Can you give us a brief introduction to your work with lithium-ion batteries?

GS: We started working on lithium-ion batteries about 3 years ago. Our primary focus has been on designing the anode (negative electrode) material that can deliver improved electrochemical capacity with reduce polarization losses and no chemical or mechanical degradation over long periods of time. I have two PhD students (Romil Bhandavat and Lamuel David) working on this project.

WS: Why did you choose to study graphene in battery applications?

GS: Our initial work focused on use of molecular precursor derived glass ceramics (such as silicon oxycarbide) as rechargeable battery anodes. These high temperature glasses are unique because of their nanodomain structure consisting of graphene-like carbon domains.

In order to develop these anodes with tailored properties, we thought of first concentrating on understanding Li-ion storage mechanisms in single and multilayered graphene films. And that’s what got us into graphene film based anodes.

WS: How does the graphene manufacturing process you have developed make graphene more viable as a commercial electrode material?

GS: The process that we have developed allows synthesis of few-layer graphene without the use of high vacuum. The total time required for making these films is approximately 20 to 30 minutes. These graphene films can be used for corrosion prevention (grown on copper) and anodes for microbatteries (grown on nickel foil).

WS: What effects make graphene grown on nickel so much more effective than graphene grown on copper?

GS: We believe that sheets of graphene on nickel are relatively thick near the grain boundaries, and based on electron microscopy and spectroscopy data, these sheets are stacked in a well-defined manner called Bernal Stacking, which provides multiple sites for easy uptake and release of lithium ions as the cell is discharged and charged.

WS: How does the performance of your graphene electrodes compare to that of conventional electrode materials in lithium batteries?

GS: The purpose of this work was to study the underlying principles related to insertion and release of Li within individual sheets of few-layer graphene. A typical Li-ion battery anode is made from of a type of graphite slurry (along with conducting agent and binders) coated on a copper foil (current collector), and so a direct comparison with our graphene-based anode may not really be fair.

One clear advantage with graphene/Ni electrode is that it is less prone to delamination and does not require any binding or conducting agents (thereby saving weight). Flexible electrodes for microscale batteries are also possible with our graphene/Ni electrode.

Figure 1. Schematic representation showing likely paths for Li-ions to intercalate in single (SLG), bi (BLG) and few-layer (FLG) graphene on copper (Cu) and nickel (Ni) anodes. Smaller graphene grain size, Bernel stacking, and presence of edge defects in Ni-G specimen are responsible for better uptake and release of Li-ions as the cell is discharged and charged.

WS: You have also published work on tungsten disulfide, another 2D nanomaterial – how do the properties of this material differ from graphene?

GS: Tungsten disulfide (and also molybdenum disulfide) has a similar layered morphology to graphene, but its physical and chemical properties are quite different.

Firstly, each layer in Tungsten disulfide is 3 atoms thick (1 tungsten sandwiched between 2 sulfur atoms), while graphene is a one atom thick layer of carbon.

Secondly, tungsten disulfide is a semi-conductor whilst graphene is an excellent conductor of electricity. Tungsten disulfide is also much heavier and denser.

Now these materials can be combined together in the form of heterostructures and/ or layered composites to unravel some interesting applications – for example, the vertical field effect transistor demonstrated by Nobel Prize winning team of Novoselov and Geim in a recent article.


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