in that they store more watt-hours per unit volume, while supercapacitors are more power-dense, in that they generate more watts per unit volume. Power is related to the rate at which energy is used to do work, and supercapacitors can discharge much faster than batteries can, which makes them more powerful, even though they hold less energy. Supercapacitors are alsomuch longer-lived than batteries, withstanding many more charge/discharge cycles before their performance degrades. Greater safety is also a benefit of supercapacitors, as they don’t have the oxygen-releasing cathodes and flammable electrolytes that create the fire risks associated with lithium-ion batteries, for example. Therefore, a system that combines the energy density of a battery with the power density and safety of a supercapacitor would be very desirable; Gruber shows one of his cells continuing to operate normally after being shot with a 9mm bullet, contrasting it with a lithium-ion cell that goes into a dramatic thermal runaway. The make-up of the cell itself, as the company describes it, includes an aluminium anode, a separator, a graphite cathode and a liquid electrolyte, all contained in a flexible pouch. (It is not clear exactly how graphene is used here, but graphite has been described as multiple layers of graphene). Gruber Motors is now in the process of working out how many of these cells it can fit into the battery case of its Tesla Model S test mule. Beyond Gruber’s work, graphene is being used to extend battery life by reducing the amount of carbon needed in the electrodes to achieve the necessary conductivity; graphene’s extreme thinness and very high conductivity mean that much less needs to be used. In lithium-ion cathodes, a hybrid material made of vanadium oxide (VO2) and graphene is being incorporated to increase charge and discharge rates, while increasing durability. In supercapacitors, graphene can replace the activated carbon that coats the positive and negative plates, and its very large surface area allows it to store much more electrostatic charge, while its low weight, good elasticity and mechanical strength are bonus qualities. Whether or not the Gruber battery and/or technologies like it proves themselves, graphene enhanced batteries and supercapacitors and innovative hybrids promise to provide longer-lasting, more survivable power for soldier equipment and military vehicles of many kinds in the near future. Graphene has been touted as a wonder material for almost two decades. One area in which it seems to be starting to make good on this promise, and one that could lead to major improvements in military equipment, is its ability to enhance the energy density, power density, safety and service life of electrical storage devices, principally batteries but also supercapacitors. Soldiers dependent on electronic devices and burdened with the weight and bulk of the batteries they need to power them are just one group set to benefit. While graphene is just another form of carbon, this particular allotrope is unique because it consists of a single layer of atoms in hexagonal rings, each atom joined to its three immediate neighbours by a bond in which they share a pair of electrons. As well as being 100 times stronger than steel of the same thickness would be, graphene is a superlative conductor of electricity and heat, absorbs light at all visible wavelengths and has many unusual electronic properties. The market-driven desire to eliminate range anxiety as a barrier to the acceptance of electric cars is the main impetus behind the rapid progress in battery technology, from which the military can benefit. One developer recently made the startling claim that a battery his company is working on could provide a car with double the range, the ability to accept a full charge in 15 minutes, and a service life as long as 100 years, with graphene at the heart of this stellar (projected) performance. Other claims for the technology include retention of performance at very low temperatures (below 0°F), the ability to recover from discharge to 0V, which would kill most batteries today, and no requirement for cooling, all of which are very attractive in military applications. The person behind the claims is Pete Gruber of Gruber Motors, a US company whose business includes recovering and refurbishing battery packs for Tesla cars. His description of the technology is, of necessity, somewhat vague; the battery is made up of what he terms ‘graphene supercapacitor power cells,’ and refers to graphene batteries with performance more like supercapacitors. At this point it is worth digging into the differences between batteries and supercapacitors. The big one is that batteries store energy in chemical reactions, while supercapacitors do so in electric fields. Charging both involves using energy to separate positive and negative electric charges. Discharging them involves providing paths through which the charges can recombine at the electrodes, one for positively charged ions through the electrolyte and the other for the electrons through the load that needs the power. In terms of performance, batteries are much more energy-dense, With decades of experience in reporting on defence and security technologies, Peter Donaldson frequently turns his mind to their implications – which is why he is a frequent contributor to MilTech. Peter Donaldson The Implications of Graphene As the battlefields of tomorrow become ever more varied, and the forces inserted into them ever more conscious of the need to save weight and mass in order to enhance combat and operational efficiency – the benefits of a small, powerful and lightweight heigh-density power source become ever more attractive. (Photo: US Army Ft Hood Press Center) 54 · MT 2/2022 Analysis
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