Lithium battery overcharge and over discharge short circuit protection


The circuit is mainly composed of lithium battery protection ASIC DW01, charge and discharge control MOSFET1 (including two N-channel MOSFETs), etc. The single lithium battery is connected between B+ and B-, and the battery pack is from P+ and P. -The output voltage. When charging, the charger output voltage is connected between P+ and P-, current from P+ to B+ and B- of the single battery, and then through the charge control MOSFET to P-. During the charging process, when the voltage of the single cell exceeds 4.35V, the OC pin output signal of the ASIC DW01 turns off the charging control MOSFET, and the lithium battery stops charging immediately, thereby preventing the lithium battery from being damaged due to overcharging. During the discharge process, when the voltage of the single cell drops to 2.30V, the output signal of the OD pin of the DW01 causes the discharge control MOSFET to be turned off, and the lithium battery immediately stops discharging, thereby preventing the lithium battery from being damaged due to overdischarge, the CS pin of the DW01. For the current detection pin, when the output is short-circuited, the conduction voltage drop of the charge-discharge control MOSFET increases sharply, the CS pin voltage rises rapidly, and the DW01 output signal causes the charge-discharge control MOSFET to be quickly turned off, thereby achieving overcurrent or short-circuit protection.
What are the advantages of secondary lithium batteries?

High energy density

2. High operating voltage

3. No memory effect

4. Long cycle life

5. No pollution

6. Light weight

7. Self-discharge small

What are the advantages of lithium polymer batteries?

1. No battery leakage problem, the battery does not contain liquid electrolyte inside, using colloidal solids.

2. Can be made into a thin battery: with a capacity of 3.6V400mAh, its thickness can be as thin as 0.5mm.

3. The battery can be designed in a variety of shapes.

4. The battery can be bent and deformed: the polymer battery can be bent up to 900 or so.

5. A single high-voltage: liquid electrolyte battery can only be connected in series with several batteries to obtain a high voltage. Since the polymer battery has no liquid itself, it can be made into a multi-layer combination in a single unit to achieve a high voltage.

6. The capacity will be twice as high as the same size lithium-ion battery.

The IEC specifies the standard cycle life test for lithium batteries as:

After the battery is placed at 0.2C / 3.0V / support

1. 1C constant current constant voltage charging to 4.2V off current 20mA for 1 hour and then 0.2C discharge to 3.0V (one cycle), the capacity should be more than 60% of the initial capacity after repeated cycles of 500 times.

The national standard stipulates that the standard charge retention test for lithium batteries is (IEC has no relevant standards).

After the battery is placed at 3.0C to 3.0/branch at 25 degrees Celsius, it is charged to 4.2V with a constant current of 1C, the off current is 10mA, stored at a temperature of 20+_5 for 28 days, and then discharged to 0.25V at 0.2C. Calculate the discharge capacity.

What is the self-discharge rate of different types of batteries for self-discharge of secondary batteries?

Self-discharge, also known as charge retention, refers to the ability of the battery to store electricity under certain environmental conditions in an open state. In general, self-discharge is mainly affected by manufacturing processes, materials, and storage conditions. Self-discharge is one of the main parameters for measuring battery performance. In general, the lower the battery storage temperature, the lower the self-discharge rate, but it should also be noted that if the temperature is too low or too high, the battery may be damaged and cannot be used. The BYD conventional battery requires a storage temperature range of -20~45. After the battery is fully charged and left on for a period of time, a certain degree of self-discharge is normal. The IEC standard stipulates that nickel-cadmium and nickel-hydrogen batteries are fully charged, and the temperature is 20 degrees and the humidity is 65%. The open circuit is left for 28 days, and the 0.2C discharge time is greater than 3 hours and 3 hours and 15 minutes respectively.

Compared to other rechargeable battery systems, the self-discharge rate of liquid electrolyte-containing solar cells is significantly lower, at about 10%/month at 25.

What is the internal resistance of the battery measured?

The internal resistance of the battery refers to the resistance that the current is flowing through the inside of the battery during operation. It is generally divided into AC internal resistance and DC internal resistance. Since the internal resistance of the rechargeable battery is small, the DC internal resistance is polarized due to the electrode capacity. The polarization internal resistance is generated, so the true value cannot be measured, and the AC internal resistance can be removed to avoid the influence of the polarization internal resistance, and the true internal value is obtained.

The AC internal resistance test method is: using the characteristics of the battery equivalent to an active resistor, the battery is given a constant current of 1000HZ, 50mA, and a series of processes such as voltage sampling rectification filtering to accurately measure the resistance value.

What is the internal pressure of the battery? What is the normal internal pressure of the battery?

The internal pressure of the battery is the pressure formed by the gas generated during the charging and discharging process. It is mainly affected by the manufacturing process of the battery material, the structure and other process factors. Generally, the internal pressure of the battery is maintained at a normal level, in the case of overcharge or overdischarge. The internal pressure of the battery may increase (if the speed of the composite reaction is lower than the speed of the decomposition reaction, the generated gas is too late to be consumed, which will cause the internal pressure of the battery to rise)

What is the internal pressure test?

Lithium battery internal pressure test is: (UL standard)

The simulated battery is tested for leaking or damming the battery at an altitude of 15240 m (low pressure 11.6 kPa).

Specific steps: charge the battery 1C with constant current and constant voltage to 4.2V, cut off the current 10mA, and then store it in the low-pressure box with the air pressure of 11.6Kpa and the temperature of (20+_3) for 6 hours, the battery will not explode. Fire, crack, leaking.

What is the effect of ambient temperature on battery performance?

Among all environmental factors, temperature has the greatest influence on the charge and discharge performance of the battery. The electrochemical reaction at the electrode/electrolyte interface is related to the ambient temperature, and the electrode/electrolyte interface is regarded as the heart of the battery. If the temperature drops, the reaction rate of the electrode also decreases. Assuming that the battery voltage remains constant, the discharge current decreases, and the power output of the battery also decreases. If the temperature rises, the opposite is true, that is, the battery output power will rise, and the temperature also affects the transfer speed of the electrolyte. The temperature rises, the transfer temperature decreases, the transfer slows down, and the battery charge and discharge performance is also affected. However, if the temperature is too high, more than 45 will damage the chemical balance in the battery and cause side reactions.

What are the control methods for overcharging?

In order to prevent the battery from overcharging, it is necessary to control the charging end point. When the battery is full, some special information can be used to judge whether the charging reaches the end point. There are generally six ways to prevent the battery from being overcharged:

1. Peak voltage control: determine the end point of charging by detecting the peak voltage of the battery;

2. dT/dt control: determine the end point of charging by detecting the peak temperature change rate of the battery;

3. T control: When the battery is fully charged, the difference between temperature and ambient temperature will reach the maximum;

4. -V control: When the battery is fully charged to reach a peak voltage, the voltage will drop to a certain value;

5. Timing control: control the charging end point by setting a certain charging time, generally set the time required to charge 130% of the nominal capacity to control;

6. TCO Control: Considering the safety and characteristics of the battery should avoid high temperature (except for high temperature batteries), so the battery should stop charging when the battery temperature rises by 60.

What is the effect of overcharging on battery performance?

Overcharge refers to the behavior of the battery to continue charging after a certain charging process is fully charged.

Since the negative electrode capacity is higher than the positive electrode capacity at the time of design, the gas generated by the positive electrode is permeable to the cadmium generated by the negative electrode through the separator paper. Therefore, under normal circumstances, the internal pressure of the battery will not increase significantly, but if the charging current is too large, or the charging time is too long, the generated oxygen is too late to be consumed, which may cause the internal pressure to rise, the battery to deform, and the liquid to leak. And other undesirable phenomena. At the same time, its electrical performance will be significantly reduced.

What is the effect of overdischarge on battery performance?

After the battery has discharged the internal stored power, after the voltage reaches a certain value, the discharge will continue to cause overdischarge, and the discharge cutoff voltage is usually determined according to the discharge current. 0.2C-2C discharge is generally set to 1.0V / support, 3C or above, such as 5C or 10C discharge is set to 0.8V / support, battery over discharge may have catastrophic consequences for the battery, especially high current over discharge, or Repeated overdischarge has a greater impact on the battery. In general, over-discharge will increase the internal pressure of the battery, and the reversibility of the positive and negative active materials will be destroyed. Even if the charging is only partially restored, the capacity will be significantly attenuated.

What happens when batteries of different capacities are used together?

If different capacities or old and new batteries are used together, there may be leakage, zero voltage, etc. This is because some of the batteries are overcharged during charging due to the difference in capacity during charging. Some batteries are not fully charged. When the battery is discharged, the battery with high capacity is not discharged, and the battery with low capacity is over-discharged. In such a vicious circle, the battery is damaged and leaks or low (zero) voltage.

What is the explosion of the battery? How to prevent the battery from exploding?

The solid matter in any part of the battery is instantaneously discharged and pushed to a distance of more than 25 cm from the battery, which is called an explosion. To determine whether the battery exploded or not, the following conditions were used for the experiment. Cover the experimental battery with a net, the battery is in the middle, 25cm from either side of the mesh cover. The density of the net is 6-7/cm, and the net wire is made of soft aluminum wire with a diameter of 0.25 mm. If no solid part passes through the net cover, it proves that the battery has not exploded.

Lithium battery series problem

Since the battery is in the production process, there are many processes from the beginning of the film to the finished product. Even after a rigorous testing procedure, the voltage, resistance, and capacity of each group of power supplies are the same, but when used for a while, there will be one or the other difference. Like a mother's twins, they may grow exactly the same when they are born. It is difficult to distinguish them as mothers. However, as the two children grow up, there will be one or the other difference. Lithium-powered batteries are also the same. After using a period of time to make a difference, the overall voltage control method is difficult to apply to lithium-powered batteries. For example, a 36V battery stack must be connected in series with 10 batteries. The overall charge control voltage is 42V and the discharge control voltage is 26V. With the overall voltage control method, there may be no problem in the initial use phase due to the particularly good battery consistency. After a period of use, the internal resistance and voltage of the battery fluctuate, forming an inconsistent state (inconsistent is absolute, the consistency is relative). At this time, the overall voltage control is still unable to achieve its purpose. For example, when 10 batteries are discharged, the voltage of two of the batteries is 2.8V, the voltage of the four batteries is 3.2V, the fourth is only 3.4V, and the current overall voltage is 32V. We let it continue to discharge until 26V. In this way, the two 2.8V batteries are in an over-discharge state below 2.6V. A lithium battery that is over-discharged several times is equivalent to scrapping. Conversely, charging with the overall voltage control charging will also result in overcharging. For example, charging with the voltage state of the above 10 batteries. When the overall voltage reaches 42V, the two 2.8V batteries are in a "hungry" state, and the rapid absorption of power will exceed 4.2V, while the overcharged battery exceeding 4.2V will not only be scrapped due to excessive voltage. There is even danger, which is the characteristics of lithium-ion batteries.

Lithium-ion batteries are rated at 3.6V (some products are 3.7V). The termination charge voltage at full charge is related to the battery anode material: the anode material is 4.2V for graphite; the anode material is 4.1V for coke. The internal resistance of different anode materials is also different. The internal resistance of the coke anode is slightly larger, and the discharge curve is slightly different, as shown in Fig. 1. Generally known as 4.1V lithium ion battery and 4.2V lithium ion battery. Most of the current use is 4.2V, and the termination discharge voltage of the lithium ion battery is 2.5V to 2.75V (the battery factory gives the operating voltage range or gives the termination discharge voltage, and the parameters are slightly different). Continued discharge below the termination discharge voltage is called overdischarge, and overdischarge can damage the battery.

Portable electronics use batteries as a power source. With the rapid development of portable products, the amount of various batteries has increased, and many new batteries have been developed. In addition to the familiar high-performance alkaline batteries, rechargeable nickel-cadmium batteries, and nickel-hydrogen batteries, there are also lithium batteries developed in recent years. This article focuses on the basics of lithium batteries. This includes its characteristics, main parameters, the meaning of the model, the scope of application and precautions for use.

Lithium is a metal element with a chemical symbol of Li (English name is lithium). It is a silver-white, very soft, chemically active metal that is the lightest in metals. In addition to its application in the atomic energy industry, it can manufacture special alloys, special glass (fluorescent screen glass for TV sets) and lithium batteries. It is used as an anode of a battery in a lithium battery.

Lithium batteries are also divided into two categories: non-rechargeable and rechargeable. A non-rechargeable battery is called a disposable battery. It can only convert chemical energy into electrical energy at one time, and cannot restore electrical energy back to chemical energy (or very poor recovery performance). A rechargeable battery is called a secondary battery (also called a battery ). It converts electrical energy into chemical energy and, when used, converts chemical energy into electrical energy. It is reversible, such as the main feature of lithium-ion batteries for electrical energy.

Smart portable electronic products require a small size and light weight, but the size and weight of the battery are often the largest and heaviest compared to other electronic components. For example, the "big brother" of the year is quite "big and heavy", and today's mobile phones are so light. Among them, the improvement of the battery plays an important role: in the past it was a nickel-cadmium battery, and now it is a lithium-ion battery.

The biggest feature of lithium batteries is their high specific energy. What is specific energy? Specific energy refers to energy per unit weight or unit volume. The specific energy is expressed in Wh/kg or Wh/L. Wh is the unit of energy, W is watt, h is hour; kg is kilogram (weight unit), and L is liter (volume unit). Here is an example to illustrate: The No. 5 nickel-cadmium battery has a rated voltage of 12 V and a capacity of 800 mAh, and its energy is 0 96 Wh (1 2 V × 0 8 Ah). The same size of the No. 5 lithium-manganese dioxide battery is rated at 3V, and its capacity is 1200mAh, and its energy is 36Wh. The volume of these two batteries is the same, the specific energy of the lithium-manganese dioxide battery is 375 times that of the nickel-cadmium battery!

A No. 5 nickel-cadmium battery weighs about 23g, while a No. 5 lithium-manganese dioxide battery weighs about 18g. One lithium-manganese dioxide battery is 3V, and two nickel-cadmium batteries are only 2 4V. Therefore, when the lithium battery is used, the number of batteries is small (the portable electronic product is reduced in size and weight), and the battery has a long working life.

In addition, the lithium battery has the advantages of stable discharge voltage, wide operating temperature range, low self-discharge rate, long storage life, no memory effect and no pollution.

The disadvantage of lithium batteries is that they are expensive, so they are not widely used at present, and are mainly used in handheld computers, PDAs, communication devices, cameras, satellites, missiles, torpedoes, instruments, and the like. With the development of technology, process improvement and increased production, the price of lithium batteries will continue to decline, and the application will be more common.

Non-rechargeable lithium battery

There are many types of non-rechargeable lithium batteries. Currently, lithium-manganese dioxide batteries, lithium-thionyl chloride batteries, and lithium and other compound batteries are commonly used. This article only introduces the first two most commonly used ones.

1. Lithium-manganese dioxide battery (Li MnO2)

The lithium-manganese dioxide battery is a disposable battery using lithium as an anode, manganese dioxide as a cathode, and an organic electrolyte. The main feature of the battery is that the battery voltage is high, the rated voltage is 3V (2 times that of a typical alkaline battery); the termination discharge voltage is 2V; the specific energy is large (see the example above); the discharge voltage is stable and reliable; Storage performance (storage time more than 3 years), low self-discharge rate (annual self-discharge rate ≤ 2%); operating temperature range -20 ° C ~ +60 ° C.

The battery can be made in different shapes to meet different requirements. It has a rectangular shape, a cylindrical shape and a button shape (button type). Cylindrical also has different diameters and height dimensions. Here are the main parameters of the familiar 1# (size code D), 2# (size code C) and 5# (size code AA) batteries.

CR is represented by a cylindrical lithium-manganese dioxide battery; among the five digits, the first two digits indicate the diameter of the battery, and the last three digits indicate the height with one decimal. For example, the CR14505 has a diameter of 14 mm and a height of 50 5 mm (this model is universal). It should be pointed out here that the parameters of the same type of battery produced by different factories may have some differences. In addition, the standard discharge current value is small, the actual discharge current can be greater than the standard discharge current, and the allowable discharge current for continuous discharge and pulse discharge is also different, and the battery manufacturer provides relevant data. For example, the CR14505 produced by Lixing Power Co., Ltd. gives a maximum continuous discharge current of 1000 mA and a maximum pulse discharge current of up to 2500 mA.

Most of the lithium batteries used in the camera are lithium-manganese dioxide batteries. Here, the lithium-manganese dioxide batteries commonly used in cameras are listed in Table 2 for reference.

The button type (button type) battery has a small size, and has a diameter of 12 5 to 24 5 mm and a height of 16 to 50 mm. Several commonly used button batteries are shown in Table 3.

CR is a cylindrical lithium-manganese dioxide battery. The first two digits of the last four digits are the diameter dimensions of the battery, and the last two digits are the height dimensions with a decimal point. For example, CR1220 has a diameter of 12 5mm (excluding the number after the decimal point) and its height is 20 mm. This type of model representation is internationally accepted.

Such button batteries are commonly used in clocks, calculators, electronic notebooks, cameras, hearing aids, electronic game machines, IC cards, backup power supplies, and the like.

2. Lithium-thionyl chloride battery (Li SOCl2)

The lithium-thionyl chloride battery is the highest specific energy and can currently reach a level of 500 Wh/kg or 1000 Wh/L. It is rated at 3 6V and has an extremely flat 34V discharge characteristic at medium current discharge (flat discharge in a 90% capacity range with little change). The battery can operate from -40 ° C to +85 ° C, but the capacity at -40 ° C is about 50% of the normal temperature capacity. The self-discharge rate is low (year self-discharge rate ≤ 1%) and the storage life is up to 10 years. Compare the specific energy of 1# (size code D) nickel-cadmium battery with 1# lithium-thionyl chloride battery: 1# nickel-cadmium battery has a rated voltage of 12 V and a capacity of 5000 mAh; 1# lithium-thionyl chloride The rated voltage is 3 6V and the capacity is 10000mAh, then the latter's specific energy is 6 times larger than the former!

Application considerations

The above two kinds of lithium batteries are disposable batteries, which are not rechargeable (dangerous when charging!); there is no short circuit between the positive and negative terminals of the battery; no excessive current discharge (exceeding the maximum discharge current discharge); when the battery is used until the discharge voltage is terminated It should be taken out from the electronic product in time; the used battery should not be squeezed, incinerated and disassembled; it should not be used beyond the specified temperature range.

Since the voltage of the lithium battery is higher than that of the ordinary battery or the nickel-cadmium battery, do not make mistakes in use to avoid damaging the circuit. By knowing the CR and ER in the model, you can know its type and rated voltage. When buying a new battery, be sure to buy it according to the original model, otherwise it will affect the performance of the electronic product.

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