Analyze the maintenance and misunderstanding of lithium batteries

The battery is also a serious consumable part in the notebook computer. After the battery is used for a period of time, the power supply time will be gradually shortened until it is unavailable. Therefore, the maintenance and reasonable use of laptop batteries is also a topic that is often discussed. However, some users' understanding of some maintenance is wrong, and the following explanation is given.

First, nickel-hydrogen battery

Compared to lithium batteries, nickel-metal hydride batteries can't get rid of the inherent disadvantages. The first is the memory effect: Ni-MH batteries have the same memory effect as nickel-cadmium batteries, but they are much more slightly, but they still have to be charged before they are exhausted. The lithium battery has no memory effect at all, so you can ignore the residual power and charge it directly. The disadvantage is that the self-discharge rate is high: the nickel-hydrogen battery is 25 to 35% a month, and the lithium battery is only 2 to 5% a month, so that the nickel-hydrogen battery loses its power quickly and needs to be charged frequently. The models equipped with nickel-metal hydride batteries are almost never seen, and lithium-ion batteries are commonly used.

Second, lithium battery

Lithium batteries can generally be charged and discharged 300 to 500 times in one life cycle. Therefore, many people believe that as long as the battery is used less, this can play a role in extending battery life to a certain extent. But they ignore the nature of the aging of lithium batteries.

As a chemical component, the battery is greatly affected by the working environment. The increase of the internal resistance of the battery due to the oxidation reaction is the main cause of battery loss. When the cell resistance reaches a certain point, although the battery can still be fully charged at this time, the battery can no longer release the stored power. This is why many users complain that their fully charged batteries are out of power at all. So it's a good idea to understand this problem. When the lithium battery is assembled and the production line is gone, its life clock will start to move. Its remaining life is currently estimated by the number of times of charging.

Avoiding frequent use of the battery is the most fundamental method, but even if you usually use an external power supply, it seems that you have not used the battery, but in fact, the aging process of the battery has been going on over time. If the battery is left unused, it can only delay the loss of the battery to a certain extent, but it cannot be stopped. Generally, it will be dead after two to three years. Therefore, it is not necessary to purchase a spare lithium battery for storage. Actually, this battery is wasted. In addition, if you always leave the battery unused, what is the meaning of the mobile phone? Therefore, it is still necessary to talk about maintenance issues in the case of use.

Knowing ourselves and knowing each other, there is no war. The positive electrode material of a lithium ion battery is usually composed of an active compound of lithium, and the negative electrode is carbon of a special molecular structure. The main component of the common positive electrode material is LiCoO2. When charging, the potential applied to the two poles of the battery forces the compound of the positive electrode to release lithium ions, and is embedded in the carbon in which the negative electrode molecules are arranged in a sheet structure. At the time of discharge, lithium ions are precipitated from the carbon of the sheet structure and recombined with the compound of the positive electrode. The movement of lithium ions produces a current.

Although the principle of chemical reaction is very simple, in actual industrial production, there are many practical problems to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charge and discharge, and the material of the negative electrode needs to be designed at the molecular structure level. In order to accommodate more lithium ions; the electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, also needs to have good electrical conductivity, reducing the internal resistance of the battery.

Lithium-ion batteries rarely have the memory effect of nickel-cadmium batteries. The cause of the memory effect is crystallization, which is hardly produced in a lithium battery. However, the capacity of lithium-ion batteries will still decrease after multiple charging and discharging, which is complicated and diverse, mainly the change of the positive and negative materials themselves. From the molecular point of view the holes structure containing lithium ions on the positive and negative electrodes will gradually collapse and block; from the chemical point of view, the positive and negative materials are passively activated, and side reactions are generated. Other compounds that are stable, physically, the positive electrode material gradually peels off, and finally, the number of lithium ions that the battery can freely move during charging and discharging is finally reduced.

Unsuitable temperatures will cause other chemical reactions inside the lithium-ion battery to produce compounds that we don't want to see. Therefore, there are protective temperature-controlled separators or electrolyte additives between the positive and negative electrodes of many lithium-ion batteries. When the temperature of the battery is raised to a certain extent, the pores of the composite membrane are closed or the electrolyte is denatured, and the internal resistance of the battery is increased until the circuit is broken, and the battery is no longer heated to ensure that the charging temperature of the battery is normal.

Therefore, lithium-ion batteries also have congenital defects. Since the lithium-ion battery has been degraded since it was shipped from the factory, even if it is not recycled, part of its power will be permanently lost. This phenomenon is called the "aging effect" of the battery. Like the "memory effect" of NiMH batteries, it causes a reduction in battery power. But the principle is different, and the disposal methods are different. The way to avoid the "memory effect" of nickel-metal hydride batteries is to perform deep charging and discharging, but lithium batteries must not do this. This will be explained in detail later.

Third, the preservation of lithium batteries

The rate at which the lithium battery ages is determined by the temperature and the state of charge when left on hold, test data shows that the magnitude of aging of lithium-ion batteries is proportional to temperature and charge saturation. This means that the higher the temperature and the more fully charged the battery, the greater the loss of capacity. I will give a table to illustrate the effect of different factors on battery capacity.

Store the temperature after charging 40%, put it on hold, save the charge 100%, and put it on hold.

Remaining capacity after one year of remaining capacity after one year

0 degrees 98% 94%

25 degrees 96% 80%

40 degrees 85% 65%

60 degrees 75% 60% (three months later)

As can be seen from the table, the high state of charge and the excessive temperature accelerate the decline in battery capacity. Therefore, for long-term storage of lithium-ion batteries, users should control their power at 40% and store them at 15 ° C or lower, so that the protection circuit of the battery itself can be operated. If the battery is placed at a high temperature after being fully charged, it will cause great damage to the battery. It has also been seen in the table that 100% of the charge is stored at 60 ° C, and the battery capacity has dropped by 40% after 3 months.

Fourth, the use of lithium batteries

After solving the problem of how to save the battery, it also brought out another focus that everyone has been arguing. Is it necessary to remove the battery when we use a fixed power supply? This is indeed a headache. In principle, the life of the battery is mainly calculated by the number of times of charging. Removing the battery with an external power supply can reduce the chance of the battery being charged. In addition, we can analyze the environment in which the battery is placed in the computer when using a fixed power supply: due to the charging protection circuit of the notebook computer, the battery is maintained at a state of full charge of 95% to 100%, and the battery is in a state of being at this time. The ambient temperature is at least between 25 ° C and 30 ° C. If the temperature is higher in hot weather, then you should naturally come to a conclusion from the above table that is to do so. The damage to the battery is greatest, causing a significant drop in its capacity.

However, after removing the battery, there are some dangers when using only the external power supply. Sudden power outages and unstable AC voltages cause hardware damage to the notebook, so manufacturers generally warn users not to remove the battery. Of course, the result is that your battery is often in such a relatively harsh environment, it will not be long before it will be over, then you need to go to the repair center to replace the new battery, so that the benefit is naturally the manufacturer. It is. This is also a headache.

It can only be said that under the premise of stable AC power supply, you can consider removing the battery, provided that the data is ready to be backed up at any time. If you do not intend to use the battery for a long time, store the battery in 40% and store it in a cool, dry place below 25 °C, but remember not to put it in the refrigerator.

Since dust and moisture also act as battery killers, they can damage the panel circuit and accelerate the oxidation inside the battery, so for those batteries that have been stored for a long time, it is necessary to put a film on the low-grade dust and moisture. During the storage period, since the passivation voltage of the battery itself will drop, the battery should be installed every other month to perform a charge and discharge loop, and then continue to save to maintain the capacity and ionic activity of the battery, just like exercising the battery for the body. Just recharge it.

The following special emphasis: prohibiting overcharging and discharging

The last focus of everyone's attention is on how to properly charge and discharge lithium batteries. Overcharge and over discharge will cause permanent damage to the positive and negative terminals of the lithium ion battery. This is very different from the practice of nickel-metal hydride and nickel-cadmium batteries. From a molecular perspective, it can be intuitively understood that excessive discharge will cause the anode carbon to release lithium ions excessively and collapse its sheet structure; overcharging will hardly plug too much lithium ions into the negative carbon structure. Some of these lithium ions can no longer be released. Therefore, lithium ion batteries are usually equipped with charge and discharge control circuits. For lithium batteries it is best to perform a partial discharge instead of a full discharge. The actual test shows that if the battery is placed below 2.5 volts per unit, although the internal safety circuit of the battery will start, the battery will become somewhat useless at this time. As a result, the battery retirement period can only be advanced. The correct way is to not drain the battery before storing it. Instead, charge it before storing it and fully charge it before using it again.

Deep charging and discharging are harmful to the battery, but why do some people misunderstand?

First of all, it is believed that deep charging and discharging can stimulate battery activity and increase the actual capacity of lithium-ion batteries. According to the experts' answer, this is just an interesting imagination that does not understand the mechanism of lithium batteries. Deep charging and discharging will only cause permanent and negative permanent damage of lithium-ion batteries.

Secondly, the battery display of the new battery is sometimes incorrect. For example, if the battery is fully charged, it still shows 96%. After several cycles of charging and discharging, it will slowly reach 99%-100%. In fact, this is because the detection circuit in the battery has not sampled enough data, and it will be caused by correcting the value in the register in the future. The battery level is still determined by the chemistry of the battery, and the displayed value is only a reference. The so-called new battery is “activated” for three full charge and discharge before use. In the eyes of experts, it is also rumored. Many people have found that the capacity indicated in Battery Information has changed after deep charging and putting it down. Why? Because lithium-ion batteries for notebook computers generally have management chips and charging control chips among them

(1) There are a series of registers in the management chip, which contain values such as battery capacity, temperature, ID, state of charge, and number of discharges. These values will gradually change during use.

(2) The charging control chip mainly controls the charging process of the battery. The charging process of a lithium-ion battery is divided into two phases, a constant current fast charging phase (when the battery indicator is yellow) and a constant voltage current decreasing phase (the battery indicator flashes green). During the constant current fast charge phase, the battery voltage is gradually increased to the standard voltage of the battery, and then transferred to the constant voltage stage under the control chip, the voltage is no longer raised to ensure that it does not overcharge, and the current is gradually weakened as the battery power rises. Go to 0 and finish charging. This effectively prevents overcharging.

(3) The electricity statistics chip can calculate the battery power by recording the discharge curve (voltage, current, time), which is the Wh value we read in Battery Information. The lithium-ion battery will change its discharge curve after repeated use. If the chip has no chance to read the complete discharge curve again, the calculated power is not accurate. So you need to deep charge and put the chip to calibrate the battery.

Therefore, I personally think that the main function of the "use should be fully charged and put one time after using one month" in the notebook's instructions for use should be to correct the improper values in these registers, so that the battery's charging control and nominal capacity match the battery the actual situation.

In addition, how should the lithium battery be properly charged and discharged? Since the electrical memory effect of a lithium-ion battery is negligibly small, the damage caused by half-way charging is not great, and the most feared is over-discharge (complete discharge). Frequently, the result of excessively low discharge of lithium-ion batteries is that the batteries are scrapped in advance. Those such as BIOS discharge, program discharge, and even the discharge of small bulbs are not the last resort. Therefore, it is not necessary to wait for 0% recharging for the lithium ion battery.

In summary, there are several suggestions for battery maintenance:

1. In the ACAdapter (external power adapter) mode, if the battery is not subjected to the charging/discharging process, the life will be longer than the normal battery.

2. The increase of the internal resistance of the battery is the main cause of battery loss. The half-way charging and the use of the proximity alarm line are not much different. Only the count of the management chip will be different;

3. Avoid full discharge;

4. For a period of time, you can do a deep charge under the control of the protection circuit, and put it to correct the battery's power statistics, but this will not increase the actual capacity of the battery;

5. At a high temperature of 40 degrees Celsius, the battery loss rate will be much faster than normal temperature. When used in a car with a higher temperature in Singapore, South China, etc., the battery temperature can easily reach 65 degrees Celsius, which will cause the battery fast loss. Avoid placing your notebook in a hot car;

6. If you are using a fixed power supply most of the time and the AC power is stable, you can remove the battery and charge the remaining battery to 40%.

The page contains the contents of the machine translation.