Overview: Battery Technology
Battery technology is one of the most important technologies of today with numerous implications on energy storage, electronics, clean energy, pollution control, managing of natural resources, oil and gas processing, and many others. An effective battery technology can lead to new era of our civilization in which fuel pollution would be minimized and alternative energy sources exploitation would be maximized. Currently, a clean energy movement is storming through the globe, without having answered the question of what would happen when alternative clean sources would produce more energy than could be consumed locally. One answer to this question is supplying extra energy through the grid to neighboring regions providing these regions do not exhibit excess energy production of their own. Another related issue to battery technology is the average life time in electronic devices; currently, the average users have to recharge their devices once in one and a half days. Electric cars, such as the heavyweight Tesla Motors are restrained from governing the global market due to requirements of often battery recharges. Tesla motors have an average autonomy of around 350 km between recharges. Such short driving distances call for a dense refueling network that is currently only available in the most developed regions of the richest countries such as California in the US. However, more than 95% of the global population resides in regions that a dense recharging network is at least decades away.
It is more than obvious that the next generation of batteries should be able to address these issues effectively; higher capacities are required in order to store all solar, wind or even bacterial energy generated at various locations globally. Higher currents should be achieved in order to offer higher power to cars and other vehicles. Shorter charging times can offer motivation for wider application in both vehicles and house applications. And of course, longer recharging cycles would allow for longer lifetimes and acceptance by the public.
The current most popular batteries rely on Lithium ions technology. Any battery of this type makes use of an electrochemical cell in which two electrodes, an anode and a cathode are separated by an electrolyte. In any electrochemical cell, stored chemical energy is transformed into electric current that is used to power an electronic device. The role of the two electrodes is to create a stream of ions through the electrolyte and a matching stream of electrons through the external circuit that joints the two electrodes. The process is quite simple to grasp; during charging lithium ions are generated in the LiCoO2 (or LiFePO4 quite commonly) electrode and they travel through the electrolyte towards the negative electrode. During discharging, the opposite process is observed; the lithium cations leave the negative electrode and transport back to the positive electrode with the simultaneous generation of ionic current of the opposite direction in the external circuit.
Lithium based batteries exhibit some shortcomings that include high cost, risks of explosion and an average capacity and current generation. For these reasons, different designs have been investigated, such as the Li-S batteries, graphite based batteries, and most recently graphene based batteries. Graphite batteries offered the advantage of deeper electronegative potentials and are the topic of increased research. Li-S batteries have attracted significant attention due to the fact that S is very cheap and secondly that its theoretical potential allows for capacities 1000% higher than conventional Lithium ions batteries.
The real and more recent technological revolution however has come from the use of graphene in electrochemical batteries. Graphene is a material with unique mechanical and electronic properties that has been characterized as ‘miracle material’. Some of its most attractive attributes include its transparency, high electrical and thermal conductivity, and its ultra-thinness. Graphene is a sheet of hexacyclic rings of one atom width; most of its properties are derived by its physical structure. Graphene has been used in varying scientific fields up to date: adsorption and storage of hydrogen, electronic applications, coatings, bio chemical sensors and many more.
‘Graphene batteries’ is the new advance in electrochemical rechargeable batteries. Graphene is used in different breakthroughs reported in the batteries technology recently. One of the most important applications comprises the use of graphene in the negative electrode instead of graphite to increase ion mobility and storage on the electrode surface. Graphene, being only one layer thick allows for more efficient charge transportation on the electrode surface, minimizing losses due to undesired recombination or delays due to longer kinetic times. Shorter adsorption times lead to higher current generation and thus to higher power for the end user. In addition to that, higher conductivity leads to higher capacity of the electrode itself and minimized charging times. All of these attributes are highly desired by various industries as explained earlier. Before graphene was utilized in this fashion, various research groups attempted to open ‘holes’ (defects) on graphitic structures in order to maximize charge transfer, adsorption and storage. It was found that creating defects of 100-200nm on these structures lead to kinetics faster by 20 times.
Graphene electrodes higher capacities are mostly due to its extremely high surface that allows for higher transportation, adsorption and storage of cations. Graphene’s specific surface reaches as high as 2670 m2g-1, making it one the most efficient adsorbents known. For comparison reasons, most activated carbons exhibit specific adsorption in the range of 500-2000 2670 m2g-1, mesoporous media [such as zeolites and silicas] in the range of 200-1000 2670 m2g-1 and only some highly microporous Metal Organic Frameworks reach surfaces higher than 3000 2670 m2g-1.
Another significant feature of graphene batteries is the encapsulation of silicon aggregates that lead to prolonged life times and efficiencies of the cell/ battery. Silicon has been used in rechargeable batteries in the negative electrode due their higher capacities in comparison to graphite. However, silicon aggregates tend to swell and crack during charging and recharging times leading to loss of capacity, and reduced life cycles. Different approaches have been used to face this issue, such as the design of a ‘free space’ around silicon aggregates in order to reduce contact and cracking of swollen aggregates. The solution however has been reached by graphene utilization as an encapsulation means. Graphene, being only one layer thick, provided an ideal wrapping membrane of silicon that protected it from damages during modification of its physical structure. Graphene battery in this case is based on improvement of properties of silicon rather than using its attributes themselves.
Market and Future
The future of Graphene batteries seems especially prominent. Different research groups and companies around the globe announce breakthroughs although significant skepticism still exists. A Spanish company recently announced not only that they have manufactured a graphene battery with an unprecedented capacity, but also with a charging time of a few minutes. Others have reported on their works on graphene encapsulation progress and on S utilization if their graphene batteries. If their claims are confirmed, scientific revolutions in many fields are about to be triggered. Electric and hybrid car manufacturers will make use of such long life, high power batteries to expand in traditional markets; electronics with advanced feature will appear shortly since the constraints of energy saving applications will become obsolete. Clean energy producers will enter a new era of financial growth due to affordable transportation of their excess generated energy. Fossil fuels consumption will accept another blow especially in the developed world. Our world as we know it is about to change soon.