Detailed explanation of the application of supercapacitors in automobiles

Atez is considered a "technical geek" in its class. In addition to the Skyactiv-T, which makes people's ears calloused, its i-stop and i-ELOOP are also good "inventions". Some people say, isn't that automatic start-stop and brake energy recovery? Yes, but not entirely. For example, the ignition start of i-stop is very creative. What we really want to talk about here is its i-ELOOP. It is very different from the current mainstream brake energy recovery system in that the energy storage device is changed from a battery to a capacitor.

　　What’s wrong with battery energy storage?

　　The working principles of the current mainstream energy recovery systems are similar. We know that under normal circumstances, the generator works with the engine and provides power to the vehicle's electrical system and charges the battery when the engine is running normally. All of this energy comes from the normal operation of the engine and becomes one of the engine's loads, thereby increasing energy consumption. The brake energy recovery system uses the inverter principle of the generator to collect the remaining energy when the vehicle does not need power output (such as when coasting, braking, etc.) to achieve the purpose of saving energy.

　　Specifically speaking of the working mode. During normal driving, the generator no longer works, that is, it does not become a load on the engine. The electrical system is powered by the battery. When the throttle is reduced and the brake pedal is pressed, the generator generates electricity through inversion, which not only effectively utilizes the sliding inertia, but also has a braking effect, killing two birds with one stone. This surplus energy is converted into electrical energy and stored in the battery to provide electrical energy for the entire vehicle during acceleration. In this way, in theory, the engine no longer needs to actively provide energy to the generator, and the energy of the entire vehicle's electrical system comes entirely from the recovery of surplus energy. Not only does it achieve the effect of energy saving, but it can also reduce the engine load during acceleration and improve power.

　　However, this seemingly beautiful process has two problems:

　　1. Braking energy recovery can actually generate a lot of electricity (this is not difficult to judge through intuitive understanding), but it takes time to charge the battery. At this time, only a small part of the large amount of electricity generated instantly can be "charged into the battery", and the rest is still wasted. So even though the braking energy is much greater than the energy that needs to be charged, it may still cause the battery to run out of power. At this time, the system has to start the generator while still refueling, which increases energy consumption.

　　2. Lead-acid batteries will "shorten their life" during frequent charging and discharging, so this energy recovery system will shorten the battery's service life or increase the cost of replacing the battery (in order to extend the service life, better performance batteries are selected). These additional expenses are contrary to the original intention of energy saving = saving money.

　　What is a supercapacitor?

　　The energy storage device corresponding to the Atez's i-ELOOP is not a battery, but a double-layer capacitor. Double-layer capacitors are a type of supercapacitor. Why did Mazda use it, and why haven't we seen this thing on cars before?

　　What are the advantages of capacitors?

　　First of all, the charging speed is super fast. No matter how large the capacity is, as long as the current is enough, it can be done in one or two seconds. For example, if the battery of the mobile phone is replaced with a capacitor, it will be fully charged in a few seconds every day when plugged into the charger. What does it feel like? Secondly, it is durable and can be charged hundreds of thousands of times without any problem, and the energy does not decay. What does hundreds of thousands of times mean? According to the average level, it can be charged and discharged 20 times a day, which can be used for more than 50 years! The third is that the discharge speed is extremely fast, or the power it can carry is high, which is also unmatched by batteries. Fourth, it is highly efficient. Because it is a physical change, its energy conversion efficiency is far from comparable to that of batteries with chemical changes.

　　Looks perfect, right? But ordinary capacitors have a fatal flaw: their capacity is extremely small. This can be seen from the commonly used unit microfarad. 1 microfarad is only one millionth of 1 farad. And how much electricity is in 1 farad? Just 0.638 mAh. How many mAh are in our common No. 5 rechargeable batteries? 2500 mAh is not high. Converted, it is equivalent to the energy of a No. 5 rechargeable battery, which is equivalent to 400,000 10,000 microfarad capacitors. Such capacitors obviously cannot store energy for vehicles.

　　Supercapacitors are completely different from ordinary capacitors. They store energy through polarized electrolytes, but at the same time, like capacitors, they are physical changes rather than chemical changes like batteries. This interesting principle makes its characteristics between capacitors and batteries, or it combines the advantages of both. It is exactly the same as capacitors in terms of charging and discharging speed, impact resistance and discharge characteristics, but the capacity has been qualitatively improved. Judging from the current research and development situation, its specific energy has reached the level of lead-acid batteries.

　　In this way, supercapacitors have the potential to be used in automotive energy storage. In combination with Atez's i-ELOOP, let's take a closer look at its advantages.

　　When the throttle is released or the brakes are applied, a specially designed generator can generate enough electricity to fully charge the supercapacitor within a few seconds. Then, during acceleration, the generator does not work, and the supercapacitor provides power for all electrical systems. If the supercapacitor is used up and there is no chance to recharge (for example, if you keep refueling), the battery can still work together. Then, as long as there is another opportunity to release the throttle for a few seconds, the supercapacitor will be "full" again immediately. At this time, in addition to supplying power to the electrical system, it can also slowly release electricity to charge the battery. In this way, the two are coordinated and matched, so that it is completely unnecessary to use the energy of the normal operation of the engine to generate electricity, and the most ideal energy recovery can be achieved. According to official statements, this system can achieve a 10% reduction in fuel consumption. The data given by BMW for its brake energy recovery system is 3%. Although there are differences in standards, it also reflects that the energy saving rates of the two technologies are different.

　　Some people may ask: since supercapacitors have energy close to batteries and are so amazing, why do we need batteries? Isn't it a waste of effort? This has to mention the disadvantage of supercapacitors - they self-discharge much faster than batteries, or in layman's terms, they "cannot store electricity". If you don't use batteries, you may not be able to start your car after a few days of parking.

　　The characteristics of supercapacitors are fully suitable for hybrid power

　　Who is this energy storage device more suitable for, with fast charging, long-lasting charging, high energy conversion efficiency, and high self-discharge characteristics? That's right, it's hybrid power. The battery part of the current hybrid technology actually has similar problems. Even for masters like Prius, the proportion of braking energy absorbed is still very low. A large amount of energy is still converted into heat and lost in vain. And for Atez, since the recovered energy is only used for the electrical system, its recovery rate is also very low. If hybrid models use larger capacity supercapacitors to realize the recovery of braking energy, the energy saving effect will be very considerable. At the same time, car buyers don't have to worry about the expensive battery life.

　　The reason why this energy storage device has not been applied to cars is mainly due to its several shortcomings. One is safety. Too fast discharge speed and too low internal resistance, if not well designed, contain the hidden risk of "sudden burst of energy". The second is the low working voltage, which restricts its application in driving cars. But these are not fatal points. With the advancement of technology, these problems can be solved. After all, its advantages are too tempting. In fact, Toyota has developed a hybrid model using supercapacitors, and its core appeal is energy saving, energy saving, and energy saving again. The supercapacitor hybrid supercar jointly developed by BMW and Toyota values ​​its high discharge speed-it can be equipped with high-power motors as much as possible, and its instantaneous burst of energy can achieve a magical effect similar to "nitrogen acceleration".

　　summary:

　　When we always focus on lithium batteries, supercapacitors, an excellent energy storage device, have been ignored. In fact, it is not only suitable for the technologies mentioned above. If you think about it, it may become a solution for pure electric vehicles in the future. Although its high self-discharge characteristics are indeed not suitable for pure electric vehicles at present, don’t forget its ultra-fast charging characteristics - the charging time may be shorter than the refueling time, and there is no life problem. If its specific energy is further improved in the future, the voltage characteristics are better, and then combined with batteries, what will the effect be?