The performance of electric vehicles in cold climates has been attracting attention in China, with government-affiliated public and private organizations conducting evaluations and publishing the results. 2019 changes to the EV-TEST Administrative Regulations will see the government agency CATARC include charging at low temperatures and the accuracy of remaining range indication as test items. The new test items include the accuracy of charging and remaining range indication at low temperatures. In this issue, we will introduce and discuss the results of the 2022 range evaluation conducted by 懂车tei, a private evaluation organization.

Why does the range of electric vehicles decrease at low temperatures?

Reason 1: Increased internal resistance of lithium-ion batteries

　Batteries also have a resistance, called internal resistance. When a battery is discharged, this internal resistance causes the voltage of the battery itself to drop. The smaller this internal resistance is, the better the battery is in the sense that the voltage does not drop when discharging, but the battery’s internal resistance basically increases at low temperatures.
　The structure of a lithium-ion battery uses nickel chromium manganese or iron phosphate as the positive electrode, and carbon as the negative electrode. The negative electrode is made of carbon, and lithium-ion electrolyte is used in between. At low temperatures, both the individual resistance of the electrode and the resistance of the electrolyte increase.
　The black line in the graph below shows the relationship between temperature and battery voltage drop.

　Thus, when energy is extracted from the lithium-ion battery at low temperatures, the voltage tends to drop more easily than when the temperature is higher, and the voltage drop makes it impossible to maintain the system voltage, which causes the cruising range to decrease.

Reason 2: Air conditioning function

In engine-operated cars, about 60% of the gasoline burned by the engine to produce power is discarded as heat. This waste heat could be used to heat the interior of the car. Electric vehicles, on the other hand, have no heat source. Therefore, it is necessary to generate heat from electricity, which consumes battery power. Currently, two types of heating systems are used in electric vehicles: PTC heaters and heat pumps, which can be further divided into hot water PTC to produce hot water and air PTC to heat the air directly. PTC heaters consume more electricity than heat pumps.

Reason 3: Battery temperature control

I mentioned in Reason 1 that a battery cannot be discharged when its temperature drops, and modern electric vehicles are equipped with a function that uses antifreeze or refrigerant to regulate the battery temperature. It is like an air conditioner for the battery. This cools the battery when the battery temperature is too high and warms the battery when the battery temperature is too low, but the energy source for the temperature control is also the battery. The energy source for temperature control is also the battery, which consumes power from the electric vehicle’s running battery to heat the battery itself, which also reduces the cruising range.

懂车帝’s 2022 valuation results

In this issue, we will look at the results of the cruising range test conducted by 懂车tei.The data for 29 car models has been compiled, and not only TESLA but also Toyota bZ4X and Nissan ARIYA have been evaluated.

Test Contents

The test was conducted in Inner Mongolia’s Fanggezhi and Nehe regions, which are very cold regions with an average annual temperature of -3°C. This test was conducted in November in an environment ranging from -15°C to -10°C. The vehicle was driven along the route shown in the figure below, with a speed limit of 80 km/h in the green section and 100 km/h in the red section. The test was conducted in November in an environment ranging from -15°C to -10°C. The test was conducted along the route shown in the figure below, with a speed limit of 80 km/h in the green section and 100 km/h in the red section, and an overall average speed of 50 km/h. The video shows that all the cars were driving in a series. The video shows that all the cars are running in a row and are tested under the same conditions.

Test method: Driving on the above course. Average vehicle speed for the course was 50 km/h. Mixed dry and snowy road surface.
Exit condition: Test ended when vehicle speed of 50 km/h became impossible or SOC display on meter reached 0%.
Vehicle condition: Charged until automatically finished, soaked overnight in a warehouse at 0°C, and started.
Vehicle settings: ECO mode and other fuel efficiency priority modes
Air conditioner is set to auto 24°C
Tires are replaced with snow tires of the same size as those from the factory and set to the specified air pressure.
*If the cabin temperature is too low, the air conditioner temperature and drive mode can be changed.

test result

　This test measures the distance actually traveled in this test and the average cost of electricity during the test, and shows what percentage of the manufacturer’s nominal range was achieved in the NEDC driving mode.
　We mentioned earlier that the more current drawn from the battery, the easier it is for the voltage to drop. The “C-rate” is used to determine whether the current drawn from the battery is high or low. For example, the current value for a fully charged battery that is discharged completely in one hour is called 1 C. C-rate = discharge current (A) / battery capacity (Ah). Therefore, when a small amount of current is drawn from a battery with a large capacity, the voltage drop is less likely to occur.
　A vehicle with a longer manufacturer’s nominal cruising range has more battery power than the energy required to run the vehicle. Therefore, a larger capacity battery draws less current, and if the effects of air conditioning and battery temperature control are ignored, a vehicle with a longer nominal range tends to have a longer actual driving range in cold climates. (There is a limit to how much the voltage drop can be reduced, so above a certain point there may not be much change.)

　Therefore, we will compare the nominal driving distance on the horizontal axis and the actual driving distance, the degree of achievement of the nominal distance, and the electricity cost on the vertical axis.
　First is a graph of the actual cruising range. The diagonal black line indicates exactly half of the actual range, and below the black line, the actual range is less than half of the nominal range in the catalog. The red circles indicate vehicles with iron phosphate lithium-ion batteries, and the blue circles indicate vehicles with ternary lithium-ion batteries. Here, the three vehicles with the lowest range (Changan Lumin, Chery New Energy QQ, and Hongguang MINIEV) are small vehicles with batteries of less than 20 kWh.
　The results of this study show no predominant difference between the vehicles with ternary batteries and those with iron phosphate batteries, but the soaking at 0°C as the experimental condition may be the reason for the lack of difference. The difference in performance degradation between the ternary and iron phosphate batteries at low temperatures is particularly noticeable under conditions where the battery temperature is negative, and it is thought that the conditions used in this experiment were such that there was little difference in the performance of the two types of batteries. Also, if the battery is well insulated, the battery will warm up as it runs and consumes power, so the more it runs, the more the effect of the battery’s performance degradation due to low temperatures will disappear.

　Next is a graph of actual range achieved versus catalog range. Here, too, the black horizontal line is the 50% line of the nominal catalog range. Looking at the ratios, a local Chinese manufacturer called 几何E has the poorest range performance, followed by Toyota’s bZ4X.

　Next is a graph of actual electric cost. The smaller the value of the actual electric power cost, the better the electric power cost is, in other words, the less energy is required to run the car. The actual cost of electricity is calculated by dividing the capacity of the battery installed in each model by the distance traveled. Therefore, the higher this number is, the longer distance could not be traveled in spite of the large capacity of the battery. For example, the Nissan ARIYA, which has the worst electric cost, also achieved a poor cruising range, and it can be assumed that a lot of battery energy is used for interior air conditioning and battery temperature control. The Toyota bZ4X has almost the same power consumption as the NIO ET5, but there is a big difference in the achievement of the nominal cruising range.
　Also, the Tesla ModelY and BYD’s sealion have a 1.6 %しかないにもかかわらず、公称航続距離の達成度では4%difference in power cost, and I am wondering if the Tesla vehicle was consuming batteries during the overnight soak, as the battery temperature control may operate to maintain battery temperature while in storage. Battery temperature control usually consumes 1kW to 2kW of electricity, so if the soak time is 8 hours and 1kW is used for temperature control, the electricity consumption would be 8kWh. The backward calculation from the electricity cost yields a mileage of about 33 km, which is close to the difference between the mileage of the Tesla Model Y and the BYD sealion, 22 km.
　Lithium-ion iron phosphate batteries can hardly transfer electricity in and out at temperatures ranging from -10°C to -15°C. We do not know how the battery temperature control of BYD’s seal was controlled in this experiment, but if the soak condition was -15°C, the BYD seal with lithium-ion iron phosphate batteries would also have to operate the battery temperature control, so the results may have been different.

　Finally, the graph compares the achievement level of the catalog range and the catalog range divided by the battery capacity. The index of catalog range divided by battery capacity on the horizontal axis indicates how many kilometers could be driven per 1 kWh of battery capacity at the time of certification, and the larger the value, the less energy was used at the time of certification. Excluding the group of vehicles with batteries of 20 kWh or less, which are small cars, there appears to be an inverse correlation between this horizontal axis index and the vertical axis achievement of the catalog distance under low temperatures. There is a large gap between the NIO ET5 and the Toyota bZ4x mentioned earlier in this index, and it appears that the actual range at low temperatures for the Toyota car that was able to run on less power during the certification test is noticeably lower, i.e., the power used increases relative to that during the certification test.

postscript

　Japanese Toyota and Nissan vehicles seem to use more energy for interior air conditioning and battery temperature control. As a whole, it is interesting to note that the better a vehicle’s catalog power consumption is, the worse its cruising range performance tends to deteriorate during actual driving at low temperatures.
　In addition, when battery performance is degraded due to low temperatures, it is necessary to be more careful about charging than discharging. This is because charging with more power than the battery can accept may lead to lithium precipitation and destroy the battery. 懂车车帝’s website also publishes the results of charging tests and reports that BYD vehicles equipped with lithium-ion iron phosphate batteries performed well, but there is no information on whether soaking was done to match the conditions before charging or, if soaked, at what temperature, which makes the test unreliable and The reliability of the test appears to be lacking.

　The year 2022 has come to a close. We would like to thank you all for your great support this year. I wish you a happy New Year. We look forward to working with you again next year.

Reference Links

懂车帝 2022新能源车冬测结果公布_懂车帝 (dongchedi.com)

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