Everything you want to know about lithium battery safety is here

Everything you want to know about lithium battery safety is here

In the past two years, lithium batteries have been favored due to their comprehensive advantages of strong endurance and high cycle times. Because of the attention, some negative news of lithium batteries will also be amplified. The development of new things follows certain rules. Lithium batteries are improved in the market selection and continuous development. The safety of lithium batteries is also one of the most concerned issues. It is also the key point that the new energy industry attaches the most importance to urgently.

💥The main performance of the safety problems of lithium-ion batteries

⭐Fire, burns directly to the human body, or creates a fire hazard for battery-powered electronic products;

⭐Explosion, directly endangering the human body, or destroying equipment, and causing serious secondary hazards;

⭐Overheating, directly causing burns to the human body, or leading to a decrease in the insulation level and performance of safety components, or igniting flammable liquids;

⭐The leakage of liquid may cause chemical corrosion hazards caused by direct human contact or inhalation, or cause the internal insulation failure of battery-powered electronic products to indirectly cause electric shock, fire and other dangers;

⭐Electric shock, for battery packs whose output voltage exceeds the safe voltage limit, may also cause an electric shock hazard.

Lithium-ion battery failure causes

1. The first way: overheating and fire caused by internal short circuit;

Mainly related to the internal short circuit of lithium-ion batteries. The internal short circuit of lithium-ion batteries is the most important cause of its safety problems, and most of the safety problems are caused by internal short circuits. Internal short circuit is the short circuit of positive and negative electrodes in the battery, which is generally caused by metal impurities mixed in the production process, burrs caused by electrode metal foil during shearing, lithium dendrites formed during use, and unexpected mechanical stress such as extrusion. When an internal short circuit occurs, a large amount of heat is generated, which can cause safety problems.

2. The second way: fire and explosion caused by overcharge and overdischarge external short circuit;

In order to perform charge and discharge management and safety protection for lithium ions, a charge and discharge management circuit needs to be designed in the host device or adapter that uses the battery, and there is also a discharge load circuit in some devices.

3. The third way: fire and explosion caused by misuse and abuse;

In order to protect the lithium-ion battery, a protection circuit board needs to be added to the battery pack during the packaging process. The internal or external circuits of these battery packs may fail, resulting in over-voltage charging, over-charging, over-discharging, external short circuit, overload and other electrical stress conditions of the battery, which may also lead to overheating, fire, explosion, etc. Danger.

Under the condition of electrical stress, over-voltage charging and over-charging will produce violent side reactions and generate a lot of heat, which will lead to thermal runaway; over-discharge will cause the voltage of the battery to be lower than the discharge cut-off voltage specified by the manufacturer, and the side reactions at this time will The main reason is the decomposition of the electrolyte, which produces a large amount of gas, which causes the shell to bulge and rupture, causing leakage; external short circuits and overloads will increase the discharge current, which will cause the internal temperature of the battery or the temperature of the external conductor to increase sharply, causing thermal runaway.

4. The fourth way: leakage caused by shell rupture;

Mainly related to the rupture of the battery casing. Causes of shell rupture include internal and external stress. Internal stress refers to the internal and external pressure difference caused by side reactions such as excessive discharge; external stress refers to normal or unexpected mechanical stress during transportation and use, such as shell rupture caused by vibration, acceleration shock, and drop. A rupture of the casing can cause leakage of the electrolyte inside, creating a hazard.

5. The fifth way: over-voltage charging, under-voltage discharging, poor consistency of built-in resistor voltage capacity, resulting in explosion;

It has to do with consistency. In a battery pack composed of multiple cells (cells) in series, in parallel, and in series-parallel connection, the consistency of internal resistance, open-circuit voltage, and capacity between batteries will cause damage to a certain battery or battery inside the battery pack. Overvoltage charging, undervoltage discharging, etc. of the parallel block, thus causing safety problems.

Reasons for lithium battery failure

Lithium-ion batteries fail to bulge. First of all, it can be analyzed that the direct cause of the bulging of the battery is due to the decomposition of the electrolyte, which produces gas inside the sealed battery, causing the battery to bulge. There are many reasons for the decomposition of the electrolyte. All possible factors are shown in Figure 4. Obviously, the thermal decomposition of the electrolyte is the main possible cause.

The high temperature that causes the electrolyte to be decomposed by heat may come from battery overload, external short circuit, high temperature and internal short circuit of the battery. If the first three items can be excluded by the scene application before the failure, the most likely cause is the internal short circuit of the battery.

Deduction of the cause of lithium battery bulging

There are also several possibilities such as lithium dendrites, burrs and metal impurities that cause the internal short circuit of the battery. Further analysis of its possibility and causes is required. Taking the precipitation of lithium dendrites as an example, the direct cause of the precipitation of lithium dendrites may be caused by poor battery materials, or it may be that after lithium precipitation in the negative electrode, lithium metal grows along the gap of the separator, and lithium dendrites are formed in contact with the positive electrode. The reasons for the lithium precipitation of the negative electrode may include the charging rate being too high, or the charging at too low temperature. That is, the battery charging temperature and current are improperly managed. This inappropriateness is caused by a combination of protection circuit problems (no design or improper design), system charging circuit problems (faults or improper design) and user environment problems.

How to use lithium battery correctly

1. How to charge a new battery

When using lithium batteries, it should be noted that the battery will enter a dormant state after being placed for a period of time. At this time, the capacity is lower than the normal value, and the use time is also shortened. However, lithium batteries are easy to activate, as long as 3-5 normal charge-discharge cycles can be used to activate the battery and restore its normal capacity. Due to the characteristics of the lithium battery itself, it has almost no memory effect. Therefore, in the activation process of the new lithium battery in the user's mobile phone, no special method or equipment is required.

For the "activation" of lithium batteries, there are many sayings: the charging time must be more than 12 hours, and it must be repeated three times in order to activate the battery. This statement that "the first three charges should be charged for more than 12 hours" only applies to nickel batteries (such as nickel-cadmium and nickel-metal hydride). The charging and discharging characteristics of lithium batteries and nickel batteries are very different. Overcharge and overdischarge of lithium batteries will cause huge damage to lithium batteries, especially liquid lithium ion batteries. Therefore, it is best to charge according to the standard time and standard method, especially not to charge for more than 12 hours (the charger shows that it is fully charged).

In addition, lithium batteries or chargers will automatically stop charging when the battery is fully charged, and there is no so-called "trickle" charging that lasts for more than 10 hours for nickel battery chargers. That is to say, after the lithium battery is fully charged, it is also white-charged when it is placed on the charger. However, there is no guarantee that the characteristics of the battery's charge-discharge protection circuit will never change and the quality will be foolproof. Therefore, the lithium battery will be on the edge of danger for a long time. This is another reason why we are against long charging.

Finally, another aspect that cannot be ignored is that lithium batteries are also not suitable for over-discharge, and over-discharge is also very detrimental to lithium batteries.

2. When should you start charging in normal use?

This statement is often seen. Because the number of charging and discharging is limited, the battery of the mobile phone should be recharged as much as possible. In fact, the life of the lithium battery has nothing to do with this. The number of rechargeable times is related to the depth of discharge. The cycle life at 10% depth of discharge is much longer than that at 100% depth of discharge. Under normal circumstances, it should be recharged according to the principle of recharging after the remaining power of the battery is used up. If the battery cannot last for the whole day on the second day, it should be charged in time.

The principle of recharging after the remaining power of the battery is used up does not mean that it is really used up. A saying as widely circulated as long charging is to "use up the battery as much as possible". This practice is actually only used on nickel batteries, the purpose is to avoid the memory effect, and unfortunately it is also spread on lithium batteries. There has been an example of someone continuing to use the phone without charging after the warning that the battery power of the phone is too low has been used until it automatically shuts down. As a result, the mobile phone in this example did not respond during subsequent charging and booting, and had to be sent to customer service for maintenance. This is actually because the battery voltage is too low due to over-discharge, so that it does not have normal charging and power-on conditions.

The lithium-ion battery of the mobile phone should not be overcharged or used when it is out of power. Charging the battery before it runs out will not cause damage to the battery. It is advisable to charge it within 2-3 hours, and it does not have to be fully charged. However, the lithium battery should be fully charged (normal charging time) and discharged 1-2 times every 3-4 months or so.

3. Lithium batteries that are not used for a long time should be stored in a cool and dry place

It is best to use a half-charged state (70--80% of the full charge, if your mobile phone displays 4 bars when it is fully charged, then 3 bars is fine), it is best to store the battery with a full charge, and the battery will be damaged. Store the battery without electricity. will be destroyed. Every 3-6 months, check to see if you need to recharge.

4. Different types of lithium-ion batteries have different safety

According to the electrolyte, it can be divided into liquid lithium-ion battery and polymer lithium-ion battery. The electrolyte of polymer lithium-ion battery is colloid and does not flow, so there is no leakage problem and it is safer.

Storage of Lithium Batteries

Lithium primary batteries have very low self-discharge and can be stored for 3 years. The effect will be better when stored under refrigeration. It is a good idea to store lithium primary batteries in a low temperature place.

Lithium-ion batteries can be stored at 20°C for more than half a year due to their low self-discharge rate and most of their capacity can be recovered.

The self-discharge phenomenon that exists in lithium batteries, if the battery voltage is kept below 3.6V for a long time, it will lead to over-discharge of the battery and damage the internal structure of the battery, reducing the battery life. Therefore, long-term storage of lithium batteries should be recharged every 3 to 6 months, that is, charging to a voltage of 3.8 to 3.9V (the best storage voltage of lithium batteries is about 3.85V) is appropriate, not fully charged.

Lithium batteries have a wide range of application temperatures. They can still be used outdoors in winter, but their capacity will be reduced a lot. If they return to room temperature, the capacity can be restored.

Lithium battery maintenance instructions

1. The charging voltage shall not be higher than the maximum charging voltage, and the discharging voltage shall not be lower than the minimum working voltage.

2. Lithium-ion batteries must be kept above the minimum operating voltage at any time. Low-voltage over-discharge or self-discharge reactions will cause the decomposition and destruction of lithium-ion active substances, which may not be restored.

3. Any form of overcharge of the lithium-ion battery will cause serious damage to the battery performance and even explosion. Li-ion batteries must avoid overcharging the battery during the charging process.

4, do not often deep discharge, deep charge. However, after every 30 charging cycles, the power detection chip will automatically perform a deep discharge and deep charge to accurately assess the state of the battery.

5. Avoid high temperature, which will shorten the lifespan, and in severe cases may cause an explosion. Store in refrigerator if possible. If the notebook computer is running on AC power, please remove the lithium-ion battery bar to avoid being affected by the heat generated by the computer.

6. Avoid freezing, but the freezing point of most lithium-ion battery electrolyte solutions is -40 °C, which is not easy to freeze.

7. If it is not used for a long time, please store it with 40% to 60% of the charging capacity. When the battery is too low, it may cause over-discharge due to self-discharge.

8. Since lithium-ion batteries will naturally age when they are not in use, they should be purchased according to actual needs and should not be purchased too much.

To sum up, when using lithium batteries, you should avoid using them under severe conditions, such as: high temperature, high humidity, long-term exposure to the sun in summer, etc., and avoid putting the battery into fire. When removing the battery, make sure that the electrical appliances are turned off; the operating temperature should be kept between -20~50℃. Avoid prolonged "storage" of batteries in out-of-service electrical appliances. Buying lithium batteries choose regular channels, regular manufacturers, it is forbidden to modify lithium batteries without permission.

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