Before the Spring Festival, PCauto and GeekNEV colleagues of The Pacific Automobile Network drove 6 new energy vehicles to run a long-distance "smart driving" Spring Festival, running a round trip between Guangzhou and Wuhan, of which the pure electric model in the southern winter under the smooth high-speed cruise conditions, the real endurance is about 50-60% of the NEDC's nominal endurance value.
If the northern media runs a pure electric endurance test, this proportion will be lower. Therefore, we can find that the correlation between the real endurance of new energy vehicles and the external temperature is very strong, when the external temperature is overheated in summer, the power battery needs to cool down, and the air conditioner needs to be opened in the car; when the external temperature is too low in winter, the power battery needs to be heated, and the car needs to open a warm air.
Today, we take a look at some of the things that battery heats:
01
Why do you need to keep your battery warm
At present, all new energy vehicles are equipped with lithium-ion battery packs, including BEV pure electric, PEHV plug-in hybrid, REEV extended range, HEV non-plug hybrid, FCV hydrogen fuel cell, and lithium batteries are very sensitive to temperature, especially squeamish, the temperature is too hot and too cold, it will immediately have no ideal, not good charging/discharging.
In general, the optimal operating temperature of lithium-ion batteries is about 20 ° C, such as the constant temperature of the power battery of the MEB platform is set at 23 ° C. If the battery cell temperature drops too much due to external cooling, the activity of the battery cell cathode material decreases, the number of lithium ions in the internal movement of the cell decreases, the diffusion of the charged ions in the positive and negative electrode materials becomes poorer, the power transfer speed decreases, the charged ion movement is not smooth, and the battery charge and discharge performance decreases. Low temperature not only affects the efficiency of charge and discharge, but also generates lithium dendrites due to low temperature lithium evolution, affecting the cycle life of the battery and even letting the battery be scrapped in advance.
From the "SoC-Voltage" coordinate chart below, it can be seen that the discharge curves at extreme low temperature -30 °C and ultra-low temperature -20 °C are very steep, -30 °C is only about 20-60% available soC, -20 °C is only about 15-80% available, and the voltage change is very large.
Because the chemical reaction of battery charge and discharge will heat up, so in a non-extreme low temperature environment, the battery after working for dozens of minutes can rely on its own heat to maintain a mild and comfortable "body temperature". However, the power battery in the cold car start state can not rely on its own heat to resist the outside winter, at this time we have to design thermal insulation measures for the battery.
Of course, the land area of the mainland is too large, and the weather forecast cannot be reported in three minutes, which gives different requirements to the power battery insulation strategy, and also allows us to form a battery technology route pattern of "south iron lithium / north ternary". The picture above is the voltage curve of lithium iron phosphate, the nominal voltage is only 3.2V (other power lithium batteries are 3.7V), and lithium iron is very afraid of cold.
You can look at the january average temperature distribution map below, the northeast of the mainland, north China, the plateau is undoubtedly a low temperature below 0 °C, the central plains can be maintained at about 0 °C, south of the Five Ridges all the way to the high.
In the Qinling Huaihe line north of the user, the winter use of lithium iron phosphate formula of electric vehicles to suffer, Model 3 lithium iron phosphate version of the owner should have the most say, and the ternary lithium version of the winter endurance gap is a bit large.
02
Mainstream battery insulation strategies
Qinling HuaiHe north of the region only one ripe a year, the winter temperature to minus celsius to go, the battery pack work self-generated heat is not enough to maintain the normal working temperature, car companies will basically use the following 6 schemes to solve the low temperature problem:
A Passive insulation device
Simply put, it is the shell itself at the three levels of the battery cell, module and battery pack, as well as the supporting thermal insulation device.
Thermal insulation materials must consider many factors, such as must be a bad conductor of heat, must be flame retardant, must be insulated, the best waterproof and dustproof and resistant to high temperature and low temperature, the cost of materials can not be too high, the best weight should be lighter...
Generally, the battery pack will release aerogel to insulate heat, and the aerogel is more interesting, it is the lowest density solid in the world (as low as 0.003g/cm2), most of which is gas, basically can isolate heat conduction, NASA fell in love with this new material in the 90s. Lyriq's Aotene platform also advertised that its own aerogel insulation material can block the impact of a 600 °C heat wave.
Mica is also a good insulation material, Lantu previously released the "mica battery" uses the "mica + aerogel" scheme to insulate.
Another material is called "Telite", which is a modified foam material, which is also used for thermal insulation and insulation, which is a relatively new type of material.
Wrapped in these materials, the heat generated by the battery can keep the battery charged and discharged in a more comfortable way.
Although the passive insulation material is a relatively "ancient" way, this is a necessary configuration of the power battery, and even the simple new energy will have a certain insulation material wrapping. In addition, the engineers also developed the resistance / liquid / external heat source system that I will mention later when it does not work, but these active insulation systems do not work for a long time, and when the temperature is sufficient, the energy supply will naturally be disconnected, and the battery pack still needs to rely on passive insulation materials to control the temperature.
B Resistance heating system
"Hot fast" used, right? That's it.
However, the traditional "hot fast" is very low-cost, without any protection, equivalent to an RPG rocket launcher held in the hands of elementary school students. There are generally two kinds of resistance heating systems for power batteries, commonly used called PTC thermistors (Positive Temperature Coefficient), which is a semiconductor resistance whose resistance surges with temperature rise (below).
The other is the heating film, which is metallic or silicon-based, and now there are also conductive particles added to the polymer organic material to make a heating film. These films are attached near the battery cell, heating more evenly than PTC, and the volume is relatively small (only 2mm thin).
There is also a heating device that uses the "Peltier effect", which is more thermally efficient, but has not yet been mass-produced.
A reader has asked before, power consumption to heat the battery, the battery life is not lower?
Very good question. As we said earlier, the charge and discharge performance of the battery at ultra-low temperature will be reduced by 50% or more, if I only use 5-10% of the power to heat the battery and let it recover 30% of the power, is it earned? It is such a simple truth, and the heating system does not need to work all the time, and when the temperature is almost over, the self-generated heat left for the battery to work in the second half to maintain body temperature.
I have photographed the temperature control device of the MEB platform before, and the heating part below uses PTC thermistors (red box, one large and one small) and the available heat pump (blue box), and the cooling part uses the R744 air conditioning compressor unit (blue box, the same one).
Why do PTC heaters have two? The big one is in the compartment, heating the car; the smaller one is in the front cabin, heating the battery. After the two units are independent, they can be heated on demand and consume less energy.
Because of the presence of PTC, even in the low temperature environment of -10 °C, the ID product can be charged with nearly 80% of the power in 1 hour.
C Liquid heating system
In the previous article, we talked about the liquid cooling scheme, the liquid can take away the heat (liquid cooling), but also can bring heat (liquid heating), so it can be changed to the two temperature control systems of cold and heat on the basis of the liquid cooling scheme power battery.
The liquid heating scheme is actually a combination of "PTC + liquid circulation system" (equivalent to an electric water heater), which heats the liquid in the package through PTC, and then transports heat to each battery cell through liquid circulation.
Compared with the simple PTC heating scheme, the heating of the "PTC + liquid circulation system" is more uniform, which can better ensure the consistency of the battery cell, delay the speed of capacity reduction, reduce the probability of thermal runaway, and improve the cycle life.
In the future, there may also be a mass production of immersion liquid heating schemes, and the heat transfer efficiency will be higher.
D External heat source heating
To put it a bit of a crepe crepe, it is actually the use of an internal combustion engine to heat the battery pack by burning fossil fuels to generate heat.
A typical example is the "polar electric heating system" that can be installed by the WM EX5, which is actually a small single-cylinder piston internal combustion engine, using diesel fuel with higher fuel efficiency, which is very useful in extreme low temperature environments below -30 °C.
The workflow of this system is also very simple, the small fuel tank with a capacity of 6L is filled with diesel, and the heat after diesel combustion is used to heat the liquid medium in the liquid circuit of the battery, and the liquid medium heats the battery. If you need to heat up for about 1 hour after starting every day, 6L diesel is enough for more than 1 month.
The advantage of the external heat source heating system is that it does not need to consume the power of the battery itself to heat the battery, the disadvantage is that the cost is relatively high, it cannot be disassembled, and it must be hung up when the system is not used in winter, reducing the mileage.
E pulses self-heating
The pulsed self-heating system is only recently mass-produced, BYD and Changan are developing this technology, in which BYD will be the battery module one-to-one arrangement, with the battery pack 1 pair of battery pack 2 charging, and then quickly with the battery pack 2 pairs of battery pack 1 charging, quickly left and right jump.
Because the internal resistance of the battery cell at low temperature is very large, the pulse charge will generate heat, and these heat is inside the battery cell, and there will be no transmission loss.
How Chang'an's pulsed self-heating system is, there is no information for the time being.
F Heat pump
Heat pumps have become popular in the field of new energy vehicles in recent years, which use liquid-gas phase transitions to exchange heat. The following figure is a diagram drawn by @on technology.
The outside and inside is an evaporator that liquefies the gas and exudes heat; outside the car is a condenser that vaporizes the liquid for heat absorption; the pump is used to compress the gas.
I have talked about the high efficiency of phase change heat transfer in the battery cooling article, and I will not say more here. What should be said here is that based on the global environmental protection needs, countries gradually banned R134a as a car air conditioning refrigerant, the main alternative refrigerant is R1234yf or CO2 (R744), CO2 boiling point under standard atmospheric pressure is lower than R134a and R1234yf, so the heating efficiency is higher in cold weather, and CO2 refrigerant is the most environmentally friendly, completely non-toxic, and subsequent use does not need to be recycled.
The efficiency of the heat pump is much higher than that of PTC heating, but the power of the heat pump is not high, before the author has seen the dismantling of the MEB platform, the lecturer said that in the case of extreme low temperatures, the heat pump air conditioner and PTC will work together, and after the temperature rise is sufficient, the PTC that costs electricity will be stopped.
The last two sentences of this section are added: heat insulation and thermal insulation are two independent projects with strong correlation, thermal insulation is a must in terms of safety, the stronger the thermal insulation performance, the better; but the insulation is not the stronger the better, high-latitude users of course hope that the battery insulation performance is pulled to full, but the low-latitude user's battery If the insulation is too strong, the performance and cost of the heat dissipation device will also rise, otherwise it will not be able to drain the heat smoothly in the summer.
03
Winter battery insulation and other things with the car
A intelligent pre-heating function
When charging at low temperature, the active substance inside the battery is very lazy, generally speaking, it can only trickle charge, at this time, it is very dangerous to charge at a large current, and the new energy vehicles that do not do well in electronic control may be risky when charging fast in the northern winter.
But the power of new energy vehicles is very precious, the vehicle in a static state will certainly not always start the heating device to maintain the battery body temperature, if you suddenly want to travel or suddenly access the power grid to charge, the cold car to start the battery will encounter ultra-low temperature failure problems, light power is greatly reduced, heavy can not start or produce lithium dendrite to reduce cycle life.
At present, high-end new energy vehicles will be equipped with battery pre-heating function, a little before you BOOK the time to use the vehicle, first open the battery heating device to heat it up, and even turn on the cabin heating in advance.
B How to charge efficiently
There is no doubt that the temperature in the open parking lot is much lower than the temperature inside the basement. Therefore, if you are a pure electric vehicle owner, you can choose the open air and the basement, please give priority to the basement (except if the parking fee in the basement is too high).
Because of the low temperature in winter, the charging speed is not only very slow, but the battery is easily charged at ultra-low temperatures
damage. Below the basement, not only is the temperature higher, the charging speed can be improved, and the battery safety is also guaranteed.
Winter snow melting will soak the charging equipment, in their own unfamiliar public charging pile operation, may wish to wear a pair of plastic insulating gloves (or can be put on the outside of the cold gloves oversized insulating gloves), on the one hand will not stain their hands or cotton gloves, on the one hand can do anti-electric shock. The maintenance of public facilities in China is worrying, and the management of relevant departments or profitable institutions is not effective, so the daily use of charging piles is still quite serious, and I am afraid that the insulation is not in place.
In addition, winter charging is generally slow, and many public charging piles use "one pile multi-line" charging parking spaces. Since "one pile and multiple lines" will take away part of the power, when charging, you may wish to pick a pile where both charging guns are idle to charge, so that the charging time can be shortened.
C temperature consistency
When the battery cell leaves the factory, there will be a difference in consistency, and it will be balanced by electronic control in the later stage.
D Different types of powertrains
New energy vehicles are installed with power batteries, of which BEV pure electric vehicles have the largest power battery, there is no other power system, so they are most afraid of low temperatures in winter, and need to consume their own electricity to keep warm.
PHEV plug-in hybrids (medium batteries), REEV range extender hybrids (small/medium batteries), and HEV unplugged hybrids (small batteries) are all equipped with internal combustion engines, and do not need to consider too much about the low temperature in winter.
FCV hydrogen fuel cell vehicles also need to be insulated, because the power system is equipped with a small power battery as an energy center, so there is also a problem of thermal insulation.
E Don't let the big foot "electric door" fly yourself
Low-temperature discharge and low-temperature charging as hurt the battery, and those loaded with electric heating system or external heat source of pure electric vehicles are not spared, because when the cold car starts, the heating system has not yet entered the state, the temperature inside the battery is still very low, at this time do not big foot "electric door" fly self and rush to say that "even the cold start is not smooth gasoline vehicles in winter are slag."
In addition, because of the winter driving, the inside and outside of the car need to be heated, the exterior mirror heating, the rear window heating wire, the air conditioning heating, the seat heating and other components will consume a lot of electrical energy, at this time also violent driving, the power consumption speed will be far beyond your imagination.
04
epilogue
After many people use electric vehicles, they adjust the dead force to the people around them regardless of any premise, which is not materialistic.
The advantages and disadvantages of electric vehicles are too obvious, so that people who need to use the scene are particularly consistent, so that they are particularly suitable for buying electric vehicles, such as a particularly long annual mileage, a car holding time of not less than 3 years, good charging conditions, no corona and so on. In addition, users with medium dimensions, the fun of using the tram will be greatly increased, no need to turn on the air conditioner in the summer, no need to turn on the heating in the winter, and the battery life will not be so stretched.