The Power Struggle of Energy Storages
Electrical energy storages are the hidden heroes of today`s society. Ever present, ever useful but only noticed at particular moments such as when the TV remote stops working. Electrical energy storages have been the key to so many advancements in the world, ranging from electric cars to robots to space travel. Indeed, energy storages are the key to the integration of renewable energy into the Global power grid. I would like to discuss the development of electrical energy storages, in particular, the current battle between chemical batteries and supercapacitors. While this hidden technology seems to slip past popular view it is essential to everyone and for every portable device. As I will try to show to you batteries and supercapacitors have opposing positives and negatives and ultimately I believe it will be the marriage of these two technologies that will produce the best power source.
Yes, I`m aware that most people just want their electronics to work. Please note that is the purpose of this discussion to make sure that your devices have the optimum option.To start this discussion we will ask the question: How does a battery differ from a supercapacitor? To answer this we must look at the internal structures of both. lt;/p>
Most chemical batteries contain three basic parts: electrodes, an electrolyte and a separator. As we know there is a positive cathode and negative anode which make up the electrodes. Between these electrodes, as well as inside them, is the electrolyte. This is a liquid or gel-like substance that contains electrically charged particles, or ions. The ions combine with the materials that make up the electrodes, producing chemical reactions that allow a battery to generate an electric current. The separator material stops the current flowing through the battery. Over time the anode loses electrons and is oxidised. The cathode is reduced and is usually made of metal oxides. This creates the fundamental separation of charge required to create a potential difference. Interestingly, the first battery was called the voltaic pile and was produced in 1800 by Volta. The first device called a battery was actually a capacitor developed by Benjamin Franklin. He called his device a battery as he put multiple capacitors in series which worked together like an artillery battery.
Inside a supercapacitor, there are two conducting metal plates with an insulating material called a dielectric. You can increase the energy a capacitor will store either by using a better material for the dielectric or by using bigger metal plates. The dielectric is made from ceramics or even air. Charge builds up on one plate until it overcomes the capacitance and a current flows between the plates, similar to how lightning strikes the ground. In fact lightning clouds could be considered part of the largest capacitors on the planet. Therefore the fundamental difference between a super capacitor and batteries is in how they store energy. Super capacitors store energy as electrostatic energy and chemical batteries store energy in the chemicals within.
In order to fully appreciate the debate, it is best to understand several major properties to consider for batteries and supercapacitors: Charge density, which determines the energy per meter cubed& power density, which affects charge and discharge rates& efficiency& sustainability& size & and longevity. For an engineer choosing an energy storage these factors will be some of the most important.
Firstly, let us talk about power density. Supercapacitors have a much higher power density than chemical batteries. This is due to the fact that there is no need for the energy to be transferred to or from chemical energy meaning energy can be transferred out and in much faster. The implication of this, for you and I, is the possibility of instant charging. No more hour long waits for phones, electric cars that can be charged faster than filling a tank and, most importantly, no arguments over household chargers. A chemical battery’s power capacity is determined by the speed at which the lithium can be oxidized. But it’s not so simple to turn up the speed. Doing this too quickly can cause the battery to develop flaws and eventually break down. It’s one reason why the longer we use our smartphone, laptop, or electric car, the worse their battery life gets. It`s shocking that Apple are breaking our phones on purpose. Every charge and discharge causes the chemical battery to reduce in performance. Supercapacitors do not have this problem and thus are able to output at higher rates without any fear of damage.
The difference in charge density is where batteries currently reign supreme. Simply put, per unit volume of battery you can store more energy than per unit volume of supercapacitor. This in the past has given batteries the edge in most applications. The other factor I mentioned that is highly related to charge density is the size of the unit. Capacitors have to be much larger than batteries in order to increase the area of their charged plates. This also makes them impractical. lt;/p>
However, a new material has entered the market. Like a knight in shining armor graphene has stepped into the energy stage. With an electron mobility that is off the charts, a tensile strength that is unbelievable and an ability to be shaped and molded, graphene could pave the way to the supercapacitors triumph. Graphene is now being incorporated into the metal plates of supercapacitors to increase surface area. This ultimately will increase charge density. However graphene is also being integrated into batteries. Graphene batteries have a much higher energy density compared to a lithium-ion battery. This is due to it having a high surface area to volume ratio. Lithium ion batteries store up to 180 Wh per kilogram, graphene’s capable of storing up to an incredible 1,000 Wh per kilogram. The Tesla model S has the longest range for an electric car of 390 miles with an 85 kWh 540kg battery. The same weighted graphene battery would easily surpass 390 miles and would theoretically be able to travel further than the longest range vehicle the Ford Focus.
Now to discuss the issue of longevity. Ironically, this will be the shortest paragraph. Evidence unequivocally shows that supercapacitors have better longevity than batteries. In addition they are far safer than batteries as they do not contain harmful chemicals. They also have fewer malfunctions. This is because of the supercapacitors innate ability to handle high voltages and sharp peaks.
For the final comparison, I would like to talk about sustainability of the products. It is no secret that batteries are not good for the environment. From the mining and extraction of materials to the disposal of them, batteries create waste and use up fossil fuels. In addition batteries are not heavily recycled due to the cheapness of their raw materials making it not economically viable. Most of the batteries that do get recycled undergo a high-temperature melting-and-extraction, or smelting, process similar to ones used in the mining industry. Those operations are very bad for the environment. The plants are also costly to build and operate and require dangerous equipment to treat harmful emissions generated by the smelting process. And despite the high costs, these plants don’t recover all valuable battery materials. In particular lithium is rarely recovered which is the hardest to extract material in a battery. On the other hand supercapacitors are far more sustainable. To begin with, they have a much larger life span. In addition supercapacitors can be manufactured using recycled bottles. It is even believed that supercapacitors could be able to biodegrade.
I would now like to talk about some specific uses and or electrical storages. To begin with, I will talk about the most popular chemical battery, the lithium ion battery. While all chemical batteries follow the same structure described above over the years many changes have been made to increase the batteries performance. Arguably the biggest revolution was the development of the rechargeable Li ion battery. Firstly I would like to talk about the rechargeability of a battery. The key principal for a battery to be recharged is that the chemical reaction can be undone using electricity. The small size allows lithium ions to move back across the electrolyte and be reduced by the anode when a potential difference is applied. As hinted in the name lithium is used at the positive electrode and graphite is used at the negative electrode. Li ion batteries are used in most portable devices. The main advantage of them is their high charge density, rechargeability and low maintenance. The main reason for these advantages is lithium`s small size. The small size is also what was responsible for the high charge density as they have a high surface area to volume ratio. Li ion batteries have essentially dominated the market. You can find them everywhere, in your phones, laptops and if you are lucky enough your Tesla. However for me the most thrilling use lies in space. Currently most of the International space station is powered by lithium ion batteries. They are favoured over other batteries and supercapacitors mainly due to their small size making them easy to transport. In space lithium batteries have a magnified risk factor of blowing up. To solve this NASA have manufactured special casing which will contain the potential fires and mitigate risk. This process of blowing up is called thermal runaway and is caused by defects in the battery. This is why supercapacitors are so interesting. In our current world we need bigger batteries. But bigger batteries are more susceptible to defects and therefore thermal runaways. Perhaps as the need for large energy stores increases we will be forced to use supercapacitors.
While in its current state the battery`s use is obvious the supercapacitor is not. One use of supercapacitors is in capturing the energy in braking electric cars. Due to their fast charging times they can quickly capture the energy in braking and then discharge the collected energy into the main battery. Another incredible use of supercapacitors is in wind turbines. Super capacitors are also being used in wind farms to make short pitch adjustments in the angle of the rotor blades maximising performance. Here they are more suited than batteries as they are much better at handling fast short expulsions of energy. In addition their increased longevity means that they will be able to last much longer than batteries which is important when wind turbines are often in remote locations and very high up. Supercapacitors have also become a vital part of the electrical grid. Supercapacitors can smooth out power outputs by storing excess energy and releasing it when there are dips in the power output. This is becoming increasingly important as we move towards renewable energies dependent on the wind and sun. Having supercapacitors will allow these renewable storages to be integrated with little to no disturbance to our daily lives.
You may have noticed something interesting in the last paragraph. The idea of a super capacitor working with a battery to maximise performance. Like Hardy and Ramanujan, Einstein and Marcel Grossman and Batman and Robin, these two incredible technologies are stronger together. This is where I believe the future of electrical energy storage lies. The basic idea of capitalising on the charge density of batteries and the power density of capacitors has led to the creation of li-ion supercapacitors. Inside these devices you find a beautiful blend of both technologies like a perfectly balanced dinner. A positive electrode made of activated carbon from a super capacitor, immersed in an electrolyte you would find in a battery. A negative electrode doped with lithium ions. Pre-doping the negative electrode with lithium ions reduces its electrical potential, meaning a higher output voltage can be obtained without a high potential at the positive electrode. The energy density is proportional to the output voltage. Therefore Li-ion capacitors have a greater energy density than supercapacitors, with a similar power density to li-ion batteries. Li-ion capacitors are ideal for applications that demand high energy density, high power density, low leakage, longevity, durability and safety, as well as anywhere where the operating temperature is too high for efficient operation of EDLCs. What else could you want?
