Challenges faced by electric vehicle fast charging
The necessity of fast charging,
First, let’s understand why fast charging is needed.
If we want to drive a long distance, we may change our trip plan because we are driving a EV. Can a large-capacity battery solve this mileage problem? The battery of an electric vehicle not only accounts for one-third of the weight of the entire vehicle, but its cost is also close to 40% of the entire vehicle. If the battery capacity increases, the price of the vehicle may increase exponentially. It is estimated that everyone will also like this kind of vehicle. Wouldn't want to buy it.
The reason why there are concerns about the mileage of electric trains is that the convenience of charging is too poor. According to the 2020 research report of the British Department of Transport, there are several reasons for people to buy electric vehicles: Awareness & knowledge. Financial factors. Charging infrastructure. Vehicle attributes. Consumer attitudes. The third and fourth items are currently the biggest obstacles. We use data to understand this barrier. The number of public charging piles has reached 807,000. The number of public charging piles is 2.8 times the number of gas stations. But even so, the efficiency of charging stations is still not as good as that of gas stations. According to statistics, medium-sized gas stations generally cover an area of 2,500 square meters, are equipped with four channels and 8 refueling positions, and can serve a maximum of 120 vehicles per hour. A charging station with the same area is equipped with 50 charging parking spaces, and the number of concurrent charging stations is 6 times that of a gas station. However, based on the speed of charging one car in one hour, the charging station can only serve up to 50 vehicles in one hour, which is less than half of the service capacity of the gas station. If we use fast charging to charge a car in 20 minutes, then the service capacity commission will be 125%, and we can serve 150 cars in one hour. In this way, the charging station will exceed the level of gas stations. If we make further progress in the future and can charge a car in 5 minutes, then the service level of charging stations will far exceed that of gas stations.
working principle
For mobile phones, adding fast charging is just a matter of buying a new mobile phone or charger. For electric vehicles, fast charging is a multi-faceted challenge, including battery materials, battery cells, battery pack design, vehicle heat dissipation devices, charging piles, charging station design, and the entire power grid.
Challenges faced by fast charging
Since fast charging is so good, why has it always been unsatisfactory? Let’s take a look at the challenges faced by fast charging. We all know that power is equal to current times voltage (P=I*V). If you want faster charging, either increase the voltage or increase the current. This principle seems very clear, but as the current or voltage increases, we will encounter the following three challenges: technology, cost, and energy. As we all know, the biggest fear of lithium batteries is not charging too fast, but the high temperature generated by fast charging. This high temperature will have an irreversible impact on the battery. The process of charging and discharging is the process of lithium ions moving back and forth through the electrolyte between the positive and negative electrodes. As the temperature increases, the negative electrode will easily form a solid electrolyte interface (sei) and lithium ions will precipitate to form lithium metal. These two All changes are irreversible. This will ultimately affect conductivity. If the precipitation of lithium metal is too serious, it will cause a short circuit between the positive and negative electrodes, and even cause thermal runaway.
The cost of DC charging piles. When we charge the electric car at home, we need to convert the alternating current into direct current through the rectifier installed in the car. However, public charging piles have built-in rectifiers, so that DC power can be directly supplied to bicycles. At the same time, the cost of investing in charging piles will increase as the voltage and current increase. Therefore, the wires required for super fast charging will also become very thick, and the cost will also increase. For battery packs in trams, it is necessary to ensure that each battery is evenly dissipated through a complex liquid cooling system.
As for the energy challenge, if we use a 480-watt charging pile to charge, it is equivalent to 48 households using normal electricity at the same time. Electricity consumption can also fluctuate by more than 30% throughout the day. The consideration of increasing electric vehicle charging will be a huge challenge for the entire power grid.
solution
Therefore, in order to meet the needs of fast charging, the battery materials have been re-selected to make the resistance of ions moving between the positive and negative electrodes smaller, the energy density has been adjusted lower, and the volume has been made larger.
Under the same conditions, fast charging will indeed shorten the life of the battery, but if the life span exceeds the industry standard, it is qualified.