CVD-based graphene has reached already a very high level of electrical conductivity. Produced under clean room conditions, this graphene type has found its way into the electronics and sensor industry.
Graphene manufactured by exfoliation technology is generally not as electrically conductive as CVD-based graphene materials. Depending on the exfoliation technique this is caused by edge breakage and disturbance of the sp².hybid orbitals within the structure. When such graphene types are used in bulk applications, re-agglomeration to more graphite-like materials may occur, which may further lower the electrical conductivity.
Researchers in the graphene bulk industry have been looking for quite some time, for methods by which they can improve the electrical conductivity of the graphene types and how to avoid re-agglomeration in bulk applications. They also keep an eye on competition like carbon nano-tubes and highly conductive carbon blacks or carbon nanostructures. Some carbon nano-tube types have excellent percolation properties. The goal of the research is to match or outperform these percolation properties at a significantly lower cost of use.
The Sixth Element uses a modified Hummers method to produce different graphene oxide and graphene types. The research and development department of The Sixth Element has analyzed the production process in detail and has found ways to reduce edge breakage and disturbance of the sp²-hybrid orbitals. They also managed to lower the particle thickness to a level close to single-layer graphene.
It is known from the literature that the lower the thickness the higher the surface area of graphene particles. A common standard to measure the surface area is BET, even though for graphene this will not represent the true value. The BET of SE1234 is above 800 m²/g, which is very high.
In the coating industry, the measurement of the oil absorption number indicates to the formulators how easily a pigment/product is dispersed in a resin/solvent system. The higher the oil absorption number, the more difficult the dispersion of the pigment is. Particle size and surface area influence the oil absorption number. The smaller the particle the lower the oil absorption number. On the other side the higher the surface area of a pigment the higher the oil absorption number. Using the DBP method, SE1234 shows an oil absorption number of 5000 ml/100g, indicating also the very high surface area of SE1234.
As expected, the high surface area of SE1234 also limits the addition level of solvents. Using a typical battery solvent – like NMP – a 1 % concentration still has acceptable viscosity ranges. Higher concentrations lead to very high viscous pastes.
Typical RAMAN and XRD spectra of SE1234 are shown in Figure 1.
Figure 1: Raman (left) and XRD (right) character of typical SE1234 sample. Image Credit: The Sixth Element (Changzhou) Materials Technology Co, Ltd
Internally SE1234 is compared with SE1233, our standard highly conductive graphene type. In the main target applications, batteries, SE1234 shows a significantly better performance than SE1233. Figure 2 displays some key values.
Figure 2: A comparison between SE1233 and SE1234 in battery applications. Image Credit: The Sixth Element (Changzhou) Materials Technology Co, Ltd
The researchers of The Sixth Element also compared the performance of SE1234 in a typical acrylic coating formulation. Again, SE1234 significantly outperforms SE1233. Within the anti-static range, the addition is very low allowing very light color coatings.
Figure 3. Surface resistance (Ω) by adding SE1234 into acrylic resin with the weight of 0%, 0.8%, and 1.575 %. The coating substrate is PET and the thickness of the film should be 0.5mm (wet state before drying). Image Credit: The Sixth Element (Changzhou) Materials Technology Co, Ltd