Mastering the use and maintenance technology of lithium-ion batteries can extend the life of lithium-ion batteries and maintain the superior performance of batteries.

Lithium-ion battery discharge

Discharge termination voltage: The rated voltage of the lithium-ion battery is 3.6V (some products are 3.7V), and the termination discharge voltage is 2.5-2.75V (the battery factory gives the working voltage range or gives the termination discharge voltage, and the parameters are slightly different. ). The discharge termination voltage of the battery should not be less than 2.5 (n is the number of batteries connected in series). The discharge below the termination discharge voltage is called overdischarge. Overdischarge will shorten the battery life and cause battery failure in severe cases. When the battery is not in use, the battery should be charged to 20% of the capacity, and then stored in moisture-proof packaging. The voltage is detected once every 3 to 6 months, and charged to ensure that the battery voltage is within the safe voltage value (3V or more).

Discharge current: Lithium-ion batteries are not suitable for high-current discharge. When excessive current is discharged, high internal temperature will be generated to lose energy, which will reduce the discharge time. If there is no protection element in the battery, it will overheat and damage the battery. Therefore, the battery production plant gives the maximum discharge current and cannot exceed the maximum discharge current given in the product characteristics table during use.

Discharge temperature: The discharge curves at different temperatures are different. At different temperatures, the discharge voltage and discharge time of the lithium ion battery are also different. The battery should be discharged (operating) within the temperature range of -20 ° C to +60 ° C.

Lithium-ion battery charging

In the use of lithium batteries, it should be noted that after the battery is placed for a period of time, it enters a sleep state. At this time, the capacity is lower than the normal value, and the use time is also shortened. However, the lithium battery is easy to activate, as long as the battery is activated after 3 to 5 normal charge and discharge cycles, and the normal capacity is restored. Due to the characteristics of the lithium battery itself, it is determined that it has almost no memory effect. Therefore, the new lithium battery in the user's mobile phone does not require special methods and equipment during the activation process.

To charge a Li-Ion battery, use a dedicated Li-Ion battery charger. Lithium-ion battery charging adopts “constant current/constant voltage” mode, first constant current charging, and changing to constant voltage charging when it is close to the termination voltage. For example, a battery of 800 mA.h capacity has a termination charging voltage of 4.2V. The battery is charged at 800mA (charge rate 1C) constant current. At the beginning, the battery voltage rises with a large slope. When the battery voltage is close to 4.2V, it is changed to 4.2V constant voltage charge. The lithium battery current gradually decreases, and the voltage does not change much. When the charging current drops to 1/10C (about 80mA), it is considered to be nearly full, and the charging can be terminated (some chargers start the timer after 10C, and end charging after a certain time). It is not possible to charge a lithium-ion battery with a charger filled with nickel-cadmium batteries (three-cell nickel-cadmium batteries) (although the rated voltage is 3.6V), it is easy to cause overcharging due to different charging methods.

Charging voltage: The charging voltage at full charge is related to the negative electrode material of the battery. The coke is 4.1V, and the graphite is 4.2V. It is generally called 4.1V lithium ion battery and 4.2V lithium ion battery. When charging, be aware that the 4.1V battery cannot be charged with the 4.2V charger, otherwise there is a danger of overcharging (4.1V is different from the charger IC used by the 4.2V charger). Lithium-ion batteries have high requirements for charging, and they require sophisticated charging circuits to ensure safe charging. The termination charge voltage accuracy tolerance is ±1% of the rated value (for example, a 4.2V lithium-ion battery with a tolerance of ±0.042V), and over-voltage charging can cause permanent damage to the lithium-ion battery.

Charging current: The charging current of the lithium ion battery should be based on the recommendations of the battery manufacturer and require a limited current circuit to avoid overcurrent (overheating). The commonly used charging rate is 0.25~1C, and the recommended charging current is 0.5C (C is the capacity of the battery, such as the battery with the nominal capacity of 1500mA.h, the charging current is 0.5*1500=750mA). It is often necessary to detect the battery temperature during high current charging to prevent damage to the battery or explosion due to overheating.

Charging temperature: When charging the battery, its ambient temperature must not exceed the temperature range listed in the product characteristics table. The battery should be charged within the temperature range of 0 to 45 ° C, away from high temperature (higher than 60 ° C) and low temperature ( -20 ° C).

If the lithium ion battery is overcharged, overdischarged or overcurrent during charging or discharging, it may cause damage to the battery or reduce the service life. To this end, various protection components and protection circuits consisting of protection ICs have been developed, which are installed in the battery or battery pack to provide complete protection of the battery. However, overcharge and overdischarge should be prevented as much as possible during use. For example, when the mobile phone battery is charging, it should be separated from the charger in time when it is fully charged. When the depth of discharge is shallow, the cycle life will be significantly improved. Therefore, when using, do not wait until the battery is low on the phone to charge, and do not continue to use this signal, although some residual capacity is available when this signal appears.

Storage and transportation

Lithium-ion batteries can be stored in a clean, dry and ventilated environment with a temperature of -5 to 35 ° C and a relative humidity of not more than 75%. Avoid contact with corrosive substances, keep away from fire and heat sources, and do not expose to direct sunlight. Place, you can't disassemble the battery at will. If the battery is stored for a long time, the battery should maintain 30% to 50% of the nominal capacity. The recommended battery should be charged every 6 months.

The battery should be packed into boxes for transportation. During transportation, it should be protected from severe vibration, impact or extrusion to prevent sun and rain. It can be transported by vehicles, trains, ships, airplanes and other means of transportation.

Short circuit

Regarding the safety of lithium-ion batteries, please pay attention to your friends. Lithium-ion batteries are prone to short-circuit conditions during charging.

Although most lithium-ion batteries have protection circuits that are short-circuit proof, there are also explosion-proof lines. But in many cases, this circuit does not necessarily work in various situations. Explosion-proof lines can also play a limited role.

Overcharge

All lithium-ion batteries, including polymer lithium-ion batteries, lithium-iron batteries, etc., are very afraid of overcharging.

If the lithium-ion battery is charged for too long, the possibility of an explosion will increase.

The chemical properties of lithium are very active and easy to burn. When the battery is charged and discharged, the inside of the battery continues to heat up, and the gas generated during the activation process expands, causing the internal pressure of the battery to increase. If the pressure reaches a certain level, if the outer casing is scratched, it will rupture, causing liquid leakage, fire, and even explosion.

Therefore, everyone should pay great attention to safety when using lithium-ion batteries.

Charging

Charging is an important step in the repeated use of batteries. The charging process of lithium-ion batteries is divided into two phases: a constant current fast charging phase and a constant voltage current decreasing phase. 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 the set value and finally finish charging. The power statistic chip can calculate the battery power by recording the discharge curve. After repeated use of lithium-ion batteries, the discharge curve will change. Although lithium-ion batteries do not have a memory effect, improper charging and discharging can seriously affect battery performance.

Charging precautions

Excessive charging and discharging of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. Over-discharge leads to collapse of the negative carbon sheet structure, and collapse can cause lithium ions to be inserted during charging; excessive charging causes excessive lithium ions to be embedded in the negative carbon structure, and some of the lithium ions can no longer be released.

The amount of charge is equal to the charging current multiplied by the charging time. When the charging control voltage is constant, the charging current is larger (the charging speed is faster), and the charging amount is smaller. If the battery charging speed is too fast and the termination voltage control point is improper, the battery capacity will also be insufficient. Actually, some of the electrode active materials of the battery are not fully reacted and the charging is stopped. This phenomenon of insufficient charging is aggravated as the number of cycles increases.

Discharge

For the first charge and discharge, if the time is long (usually 3 - 4 hours is sufficient), then the electrode can reach the highest oxidation state (full charge) as much as possible, and the discharge (or use) is forced to the regulation. The voltage, or until the automatic shutdown, can activate the battery usage capacity.

However, in the normal use of the lithium ion battery, it is not necessary to do so, and it can be charged as needed at any time, and it is not necessary to fully charge the battery during charging, and it is not necessary to discharge first. For the first charge and discharge operation, it is only necessary to perform 1 to 2 consecutive times every 3 to 4 months.

Internal short circuit protection

Lithium-ion batteries have the risk of internal short-circuit due to many factors such as material system and manufacturing process. Although lithium-ion batteries have undergone strict aging and self-discharge screening at the factory, due to process failure and other unpredictable use factors, there is still a certain probability of failure leading to internal short circuits during use. For the power battery, the lithium-ion battery in the battery pack has several hundred or even tens of thousands of knots, which greatly enlarges the probability that the battery pack will be short inside. Due to the great energy contained in the power battery pack, the occurrence of internal short circuit is easy to induce a malignant accident, resulting in casualties and property losses.

For a parallel lithium-ion battery module, when one or several batteries are short-lived, other batteries in the battery module will discharge them, and the energy of the battery pack will increase the temperature of the short battery. It is easy to induce thermal runaway, which eventually causes the battery to explode.

Conventional temperature detection, when the battery is warming up, can inform the IC to cut off the main circuit, but can not prevent the continuous discharge inside the parallel battery module, and because the main circuit is cut, all the energy of the battery module is concentrated on the inner short-circuit battery, but increase The probability of a thermal runaway occurring.

The ideal solution is to cut off the connection circuit between the battery and other batteries in the module when it is found that a certain battery is short and warm. As shown in Figure 2, TE PPTC or MHP-TA series products are assembled on a single battery. When an internal short circuit occurs, the TE protection device can effectively block the connection between the internal short circuit battery and other batteries in the module to prevent a malignant accident. occur. For a power battery pack with a large number of single cells, the consistency of the internal resistance of the battery and the device is required when the group is assembled, and the MHP-TA has a very good consistency of the device resistance due to its internal bimetal structure, which can greatly satisfy the Battery internal resistance requirements.

The system composition and actual road conditions of lithium-ion power batteries are complex, and the protection of passive devices is indispensable.

Lithium battery advantages

1) High voltage

The operating voltage of the single cell is as high as 3.7-3.8V (3.2V for lithium iron phosphate), which is three times that of Ni-Cd and Ni-MH batteries.

2) Larger than energy

The actual specific energy that can be achieved is about 555Wh/kg, that is, the material can reach a specific capacity of 150 mAh/g or more (3--4 times Ni-Cd, 2--3 times Ni-MH), which is close to its theory. A value of about 88%.

3) Long cycle life

Generally, it can reach more than 500 times, or even more than 1000 times, and lithium iron phosphate can reach more than 2000 times. For small current discharge appliances, the life of the battery will double the competitiveness of the appliance.

4) Good safety performance

No pollution, no memory effect. As the predecessor of Li-ion

New lithium ion battery

The lithium battery is short-circuited due to the formation of dendrites, which reduces the application of the metal: Li-ion contains no cadmium, lead, mercury and other environmentally polluting elements: Ni-Cd of some processes (such as sintered) One of the major drawbacks of the battery is the "memory effect", which severely constrains the use of the battery, but Li-ion does not have this problem at all.

5) Small self-discharge

The self-discharge rate of Li-ion fully charged at room temperature after storage for 1 month is about 2%, which is much lower than 25-30% of Ni-Cd and 30-35% of Ni-MH.

6) Fast charging

The 1C charging capacity can reach 80% of the nominal capacity in 30 minutes, and the ferrophosphorus battery can be charged to 90% of the nominal capacity in 10 minutes.

7) Working temperature

The working temperature is -25 to 45 ° C. With the improvement of the electrolyte and the positive electrode, it is expected to be widened to -40 to 70 ° C.

Lithium battery

1) Aging

Unlike other rechargeable batteries, the capacity of lithium-ion batteries