When battery capacity cannot grow without limit, fast charging technology will definitely develop. The development of smart phones has proved the feasibility of this path, so when will electric vehicles with slower progress in battery technology see substantial progress in fast charging technology?
Tong Jiren Automobile Review丨Tatsumi
Faced with the endurance anxiety of electric vehicles, the increase in power battery energy density and the increase in charging speed, which one will take the lead in a breakthrough?
If counting from the release of GM EV1 in 1990, in the first 25 years of the development of electric vehicles, improving battery energy density has been the focus of the industry, and the core idea is to continuously explore new battery cathode materials.
However, each battery material has a theoretical upper limit of its energy density, and the higher the energy density, the more active the battery characteristics, and the higher the requirements for battery control and management. By 2020, lithium iron phosphate batteries have returned to the mainstream market's vision, which is to abandon the single pursuit of energy density, and instead consider the balance of battery safety, cost and energy density.
So, the improvement of charging speed began to get more attention.
Compared with the bottleneck encountered in the improvement of battery energy density, there are actually many unknowns in the development of fast charging technology. These unknowns exist not only at the technical level-the synergy of batteries, charging piles, and power components, but also at the level of standards and regulations.
▎Improve the charging power, first increase the voltage
Before 2019, the high-voltage systems of mainstream electric vehicles are all 400V, and the increase in charging power is the increase in charging current. For example, the increase of Tesla overcharge from the second-generation 120kW to the third-generation 250kW is to increase the charging current under the 400V voltage platform.
However, when the charging power reaches 250kW, the maximum charging current has exceeded 500A. If you want to further increase the power, you can only rely on increasing the voltage. According to the current public information, luxury brand electric vehicles including Porsche, Audi, Genesis and other luxury brands have announced the use of 800V high-voltage systems, and the general electric version of Hummer and Lynk&Co's SEA architecture also use 800V high-voltage systems. The improvement of
from 400V to 800V looks very good, but it means that all high-voltage components and management systems of electric vehicles must raise the standard, and the inverter is the first to bear the brunt.
In electric vehicles, the power battery is undoubtedly the most expensive component, and the inverter ranked second.
Traditional IGBTs usually adapt to high-voltage platforms around 600-700V. When the high voltage reaches 800V, MOSFET semiconductors made of silicon carbide materials must be used. In September last year, Delphi announced the launch of an 800V inverter and announced that it would supply a new car launched by a “global high-end brand” in 2022. BYD also used silicon carbide as a high-voltage system for the first time in Han EV, but the high-voltage only reached Up to 600V level.
However, silicon carbide devices are currently facing two problems that all new things will have: low supply and high prices. The initial production capacity of Han EV is insufficient, and the supply of silicon carbide devices cannot keep up. One of the important reasons is that Delphi silicon carbide devices' initial orders are mainly concentrated in European luxury brands, and they have sufficient bicycle premium capabilities to support cost increases. However, the increase in production capacity and the decrease in prices will also show a positive correlation.
To increase the charging power, first increase the voltage. Therefore, the top-down popularity of 800V high-voltage platforms in electric vehicles will be a major trend in the electric vehicle industry.
▎What is the impact of high-power charging on the battery?
high-power charging requires a higher charging rate for power batteries, which contradicts the traditional characteristics of pure electric vehicles using energy batteries.
takes Tesla’s third-generation supercharger up to 250kW as an example. The maximum charging current is about 520A. According to the model 3 long-life battery rated capacity of 216.2Ah, the charging rate is about 2.4C. As the charging power is further increased, the requirements for the charging rate are also increasing. The current industry consensus is that the charging rate needs to reach 4C to meet the 400kW charging power.
But if the charging speed is too fast, the movement speed of lithium ions from the positive electrode to the negative electrode in the battery will increase, and crystals will form on the surface of the negative electrode.Negative efficiency, thereby reducing the actual capacity of the battery.
China Automotive Technology and Research Center once did a test. Three test cars were charged to full charge under the same initial conditions with different power conditions, and then the same NEDC cycle was performed to calculate the driving range in slow charge and fast charge. The difference in conditions. The results of
show that the driving range of the three cars after fast charging has decreased by 13.7%, 16.5%, and 4.5% compared to the slow full range. The difference between the driving range of the car with the biggest difference between fast and slow charging exceeds 40km. The end of charging of the
battery pack depends on the battery cell with the worst performance, and different charging power will cause the voltage of each battery cell in the battery pack to be unbalanced. Under low-power charging, the charging time is long, and the individual cells in the battery pack can slowly maintain the voltage tends to be balanced; when the charging power is greatly increased, the cells cannot maintain a balanced state in a short time, and the entire battery pack cannot reach the maximum capacity. It is no longer possible to continue charging.
still takes Tesla overcharge as an example. Although the maximum power of V3 overcharge is twice that of V2 overcharge, after 55% of electricity, the charging power of the two is almost the same, which means that the battery can be fully charged as much as possible.
Therefore, in addition to the bottleneck of increasing the voltage of the battery system, the increase in battery charging rate and the problem of reduced capacity to be solved for this will be another bottleneck in the increase of charging speed. The
▎ standard lags behind technology, and manufacturers are watching
. At present, the electric vehicle charging standard adopted in my country is the "National Standard for Conductive Charging System for Electric Vehicles" promulgated in 2015. Its Chinese standard DC charging port is developed and widely used in reference to the CHAdeMO organization in Japan. The charging port design in Japan, North America and other places, the maximum voltage and current are 950V and 250A respectively. In other words, under the framework of the existing national standard, the maximum fast charging power is limited to 240kW.
Therefore, even if the industry has the ability to fast charge R&D and supporting, the relative lag of the national standard will increase their wait-and-see sentiment. At this time, car companies and charging suppliers have two choices: implement their own standards, or wait for the national standard to be updated.
In China, the world’s largest electric vehicle market, implementing its own standards including hardware interfaces and software protocols is obviously not a wise move. Tesla, which once chose its own charging interface, eventually switched to the national standard interface. It is even more impossible for other smaller foreign brands to stand on their own in this matter.
Therefore, car companies and charging suppliers generally choose the second way-wait. Xingxing Charging has conducted counterpart tests on its own 500kW high-power charging piles. Potevio New Energy and Special Call also have technical reserves of charging piles above 400kW, which will be released in due course according to the progress of the national standard.
At this time, the release plan of the new national standard is particularly important. The promotion of national standards is closely related to the technological promotion of key enterprises. According to previous media reports, the new version of the fast charging standard is expected to be launched in the next year. The voltage and current upper limits have been increased to 1500V and 600A respectively, and the maximum power can reach 900kW.
Once the new national standard is launched, the current high-power charging piles of related companies will steadily advance, and car companies will also accelerate their pace of adapting to fast charging.
▎ is written at the end of
In the early years, everyone’s requirement for smart phones was that the battery was large enough to ensure battery life. However, after the energy density reaches the bottleneck, in recent years, the promotion of fast charging of 30W, 60W and even 120W has been deeply rooted in the hearts of the people and has become the mainstream of the smartphone industry. Because of the rapid increase in charging power, quantitative changes and qualitative changes, consumers' habits of using mobile phones are also changing, which has given birth to many new ecology. The same is true for
electric vehicles. Now the long-range Model 3 can be charged to 120km in 5 minutes on supercharging, which has actually changed the car usage habits of many Tesla consumers. If charging piles with a charging power of more than 400kW are gradually popularized, charging for 5 minutes and a battery life of 200 kilometers will be achieved, which will have a qualitative change in the technology trend of the entire industry and the ecology of electric vehicles.
