iPhone suddenly shuts down at low temperature. In fact, lithium (ion) batteries not only caused trouble for Apple at low temperatures, but Samsung’s mobile phones were once criticized for not being able to charge at low temperatures. My wife’s old iPad, after being fully charged this winter, will suddenly lose power, and it will not be able to turn on after plugging in the charger. It will only resume work after baking it on the heater for a while. My daughter calls it the most “exquisite” Electronic equipment.
This article focuses on the impact of temperature, especially low temperature on lithium batteries, and clarifies some misunderstandings in the use of lithium batteries. This article does not explain the basic principles and development history of batteries. If you are interested, please Google. There are many interesting stories here. Let’s start with a set of concepts.
Energy Density
The unit of lithium battery capacity is generally “mAh” (milliampere hour) or “Ah” (ampere hour), and there is a difference between the rated capacity and the actual capacity when in use. Energy density refers to the amount of electricity that a battery per unit volume or unit weight can store and release. There are two units: Wh/kg and Wh/L, which represent weight specific energy and volume specific energy respectively. In application, the index of energy density is more meaningful than capacity. If the capacity is not enough, it can be made bigger, and the improvement of energy density requires technological progress.
The development of lithium batteries has entered a slow growth period in recent years after a rapid period. For example, Samsung increases its energy density by an average of 6.5% per year, far behind Moore’s Law in the semiconductor industry:
The energy density of lithium batteries in mobile phones is already quite high,
Conditions of Use of Lithium Batteries
Such a high energy density lithium battery, its use should be very careful. A little carelessness can affect the lifespan, or it may explode and catch fire, such as Samsung’s battery door. Among all the conditions of use, voltage and temperature are the two most important related conditions, as shown in the following figure:
The horizontal axis is voltage, and the vertical axis is temperature. It can be seen that in this quadrant, there is only a small safe area in the middle of the large red warnings that indicate various terrible consequences. It is the comfort zone of lithium batteries, and getting out of it poses risks:
- High and low voltage:
The voltage of lithium-ion batteries includes open circuit voltage and working voltage, which will not be described in detail here. The open circuit voltage is usually defined as 3.7V, but a brand-new battery can reach 4.2V after it is fully charged; the lithium battery can be said to be dead after reaching 3.4V, in fact, 3.0V is really called completely dead. Discharge curve of lithium battery
Both higher than 4.2V and lower than 3.4V will have an impact on the life of lithium batteries. Higher than 4.2V is called overcharge, which will have an irreversible impact on battery life. In severe cases, it will cause thermal runaway (thermal runaway), which may cause bubbles, liquid leakage, fire and explosion.
The low temperature causes the reduction of the internal resistance of the electrolyte of the battery cell, and may form lithium condensation on the cathode, which irreversibly affects the battery life. High temperature may cause thermal runaway such as explosion. very dangerous.
in conclusion
Lithium batteries used at low temperatures have poor performance regardless of charging or discharging, and may affect their lifespan, so they should be avoided. The following are some popular sayings in the use of lithium batteries, let’s identify them one by one:
The first use should be fully charged three times to activate the lithium battery. Wrong, lithium batteries have no memory effect and do not need to be activated.
It is best to recharge after use up. Wrong, cycle life is not a vulgar number of recharges, but a whole cycle, that is, the process of running out of battery power and then refilling it, rather than plugging in the charger and unplugging it once. Can be recharged at any time. If it is used up and recharged, it may also lead to over-discharge and affect the battery life if it is left for too long.
Don’t keep charging, just unplug it when it’s done. A few are right, most are wrong. General mobile phone charging is not a simple constant voltage charging, but in order to prolong the battery life, there are optimized charging algorithms, including CC, CV and MC and so on. After judging that it is full, it will not keep rushing all the time. Don’t worry at all, you can always plug in the power supply. Due to the lack of charging management equipment for some cottages and low-cost devices, it is recommended to charge them as soon as possible.
Charge your phone when you are not using it. correct. When the lithium battery is not used, the power will flow quietly, and it will be over-discharged when it is lower than 2.0V, which will seriously affect the battery life. It is best to charge regularly.
