In the blink of an eye, the weather has turned cold again. Although there is heating indoors in the north, it is so warm that I want to eat ice cream every day, but when I go out, I face a temperature difference of about 40 degrees, which is still a bit scary.
If the smartphone in your pocket is truly a "smartphone", then it doesn't want to go out and get cold. why? Because the "life bar" power of mobile phones always drops at an alarming rate during this season.
This season, one thing is heavily discounted – battery life. The cruising range of electric vehicles in northern winter may only be less than 30% off that in summer.
There is a vivid description on the Internet: I have to go out for urgent matters in the winter. I pick up my phone and see that I still have 50+ batteries left. I go out with confidence. When I reach my destination, I pick up my phone and I don't know when the battery icon, which was green just now, has changed. Became 20% red. You stare in surprise, and it changes to 1% in front of you. You were shocked, breathing into the phone and rubbing your hands, but you still couldn't stop the phone from getting colder...
Several major challenges caused by low temperature
What's the problem? It turned out that the temperature was too low and the battery was "internally consumed".
Before exploring the causes of internal battery consumption, let's first understand how the battery works.
The battery mainly has these main components: negative electrode (mostly graphite is used as the negative electrode), positive electrode (lithium iron phosphate is used as an example), separator (lithium ions can pass through, but electrons cannot), and the battery casing.
When a lithium-ion battery is charged, lithium ions are released from the lithium iron phosphate in the positive electrode, move in the electrolyte solution to the negative electrode, and are embedded in the graphite. The graphite in the negative electrode will absorb the lithium ions running from the positive electrode and the electrons moving through the wire. During discharge, the lithium ions stored in the graphite escape again, pass through the separator through the electrolyte, and return to the positive electrode. The electrons cannot pass through the separator and can only return to the positive electrode from the external wire. This action generates current in the wire, causing the electrical appliance to work.
How will low temperatures affect the work of lithium-ion batteries? The materials and operating processes of the battery will be affected by the low-temperature environment. Just like fingers that are exposed to the elements for too long in the winter become less flexible, so too can the materials in the battery. In a low-temperature environment, it becomes more difficult for ions to escape and embed into materials, and it becomes more difficult to pass through the membrane, and the movement speed of ions will also be reduced.
During low-temperature discharge, the rate at which lithium ions are embedded in the cathode electrode material slows down. The lithium ions in the front arrive before the lithium ions in the front have time to be embedded in the material. Lithium ions begin to jam, and a large amount of lithium ions accumulate on the surface of the electrode material, which will accelerate the production of the passivation layer (called an SEI film in the industry, this film will slow down the insertion of lithium ions into the electrode). In this way Embedding is even more difficult. The macroscopic manifestation is that the internal resistance of the battery increases, the battery begins to "internally consume", and the power output to the outside becomes smaller.
During low-temperature charging, lithium ions migrate toward the graphite negative electrode, but the speed at which lithium ions are embedded in the graphite also slows down, while electrons can happily reach the negative electrode through the wire. When electrons encounter lithium ions on the surface of the negative electrode, metallic lithium will be generated to form lithium dendrites. Once the lithium dendrites grow, they will pierce the separator, causing the battery to short-circuit and malfunction.
Internal preheating
This technical route is called internal preheating. When making a battery, the manufacturer adds a thin piece of nickel foil to the battery structure and covers it with an electrically insulating polymer (to prevent the thin nickel foil from shorting out the battery). Once the battery temperature gets too low, the controller forces current through the nickel foil, generating a large amount of heat energy to rapidly heat the battery material. Let the battery always discharge within a relatively good operating temperature range.
If you want to charge at low temperatures, the charging equipment will first charge the battery with low power, use the heat generated by the battery itself during charging to preheat the battery and wait until the battery temperature rises to a suitable range before performing high-power fast charging.
Article 3: External heating. You can add preheating equipment to the battery (such as providing heaters and electric furnaces).
The battery first supplies low-power power to the preheating device. The preheating device generates heat and causes the battery temperature to rise. After reaching the appropriate operating temperature, the battery enters normal working status. Some electric cars are equipped with a battery-preheating function. In winter, the battery must be preheated before using the car to put the car into normal working condition.
