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, use colloidal solid.
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: polymer battery ** can be bent around 900
5. It can be made into a single high voltage: liquid electrolyte battery can only obtain high voltage by connecting several batteries in series. Because the polymer battery has no liquid itself, it can be made into multiple layers in a single unit to achieve high voltage.
7. The capacity will be twice as high as the same size lithium-ion battery
The IEC standard lithium battery standard cycle life test is: 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)
After repeated cycles of 500 times, the capacity should be more than 60% of the initial capacity.
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 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. One of the main parameters to measure battery performance. Generally speaking, 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. BYD conventional battery requires storage. The temperature range is -20~45. After the battery is fully charged and left for a period of time, a certain degree of self-discharge is a normal phenomenon. The IEC standard stipulates that the 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. The self-discharge rate of the liquid electrolyte containing solar electrolyte is significantly lower than that of other rechargeable battery systems. October.
What is the internal resistance of the battery?
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 internal resistance of the AC 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 as follows: 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 processing such as voltage sampling rectification and 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 rise:
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, the effect of temperature 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 considered the heart of the battery. If the temperature drops, The reaction rate of the electrode also decreases. Assuming that the battery voltage is kept constant, the discharge current is reduced, and the power output of the battery is also decreased. 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 transmission temperature drops, the transmission slows down, and the battery charge and discharge performance is also affected. However, if the temperature is too high, exceeding 45, the chemical balance in the battery will be destroyed, resulting in side reactions.
What are the control methods for overcharging? In order to prevent overcharging of the battery, 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. Generally, there are six ways to prevent the battery from being charged. 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 **;
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 high temperature battery) charging, so when the battery temperature rises 60 should stop charging.
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 separator paper and the negative electrode. Therefore, in general, the internal pressure of the battery does not increase significantly, but if the charging current If it is too large, or the charging time is too long, the generated oxygen will not be consumed, which may cause an increase in internal pressure, battery deformation, liquid leakage, etc. 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. Generally, the discharge cutoff voltage is determined according to the discharge current. 0.2C-2C discharge is generally set to 1.0V/branch, and 3C or above is 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 over discharge has a greater impact on the battery. In general, over discharge will make the battery The internal pressure is increased, and the reversibility of the positive and negative active materials is 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 due to the difference in capacity during charging, some batteries are overcharged during charging, some batteries are not fully charged, and there is capacity when discharging. The high battery is not discharged, and the low capacity is over-discharged. Such a vicious cycle, the battery is damaged and leaked 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 25cm from the battery. It is called explosion. It is judged whether the battery is exploding or not. The experiment is carried out under the following conditions. The net is covered in the experimental battery, and the battery is in the middle. The mesh cover has a density of 6 cm on either side of the mesh. The density of the mesh is 6-7/cm. The mesh wire is made of soft aluminum wire with a diameter of 0.25 mm. If no solid part passes through the mesh 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 strict testing procedure, the voltage, resistance and capacity of each group of power supplies are the same, but after using it for a period of time, it will produce one way or another. The difference. Just like a mother's twins, they may grow exactly the same when they are born. It is difficult to distinguish them as mothers. However, when two children grow up, there will be one or another difference. In this way, after using a period of time to make a difference, the overall voltage control method is difficult to apply to a lithium-power battery. 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 It is 26V. With the overall voltage control mode, the initial phase of use is particularly good due to the battery consistency. Maybe there will be no problem. After using for a period of time, the internal resistance and voltage of the battery fluctuate, forming an inconsistent state. (Inconsistent is ** 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, two of the batteries are The voltage is 2.8V, the voltage of the four batteries is 3.2V, the fourth is only 3.4V, and the current voltage is 32V. We let it continue to discharge until it reaches 26V. Thus, the two 2.8V batteries are lower than 2.6V. In the over-discharge state. Lithium battery is over-discharged several times to be scrapped. Conversely, charging with the overall voltage-controlled charging method may also cause overcharging. For example, charging with the voltage state of the above 10 batteries. When the voltage reaches 42V, the two 2.8V batteries are in the state of \\\"hungry\\\", and the rapid absorption of electricity will exceed 4.2V, while the overcharged battery exceeding 4.2V is not only due to voltage High generation of scrap, and even danger, this is the characteristics of lithium-powered batteries.
The rated voltage of the lithium-ion battery is 3.6V (some products are 3.7V). The termination charging voltage when fully charged is related to the anode material of the battery: the anode material is 4.2V of graphite; the anode material is 4.1V of coke. Different anode materials The internal resistance is also different. The internal resistance of the coke anode is slightly larger, and the discharge curve is slightly different, as shown in Figure 1. It is generally called 4.1V lithium ion battery and 4.2V lithium ion battery. Most of the current use is 4.2. V, the termination discharge voltage of the lithium ion battery is 2.5V~2.75V (the battery factory gives the working voltage range or gives the termination discharge voltage, the parameters are slightly different). The discharge below the termination discharge voltage is called overdischarge. Over-discharge will damage the battery.
Portable electronic products use batteries as a power source. With the rapid development of portable products, the use of various batteries has increased greatly, and many new batteries have been developed. In addition to the familiar high-performance alkaline batteries, rechargeable nickel-cadmium batteries, nickel In addition to hydrogen batteries, there are lithium batteries developed in recent years. This article mainly introduces the basic knowledge about lithium batteries. This includes its characteristics, main parameters, meaning of the model, application range and precautions for use.
Lithium is a metal element with a chemical symbol of Li (its English name is lithium). It is a silver-white, very soft, chemically active metal. It is the lightest in metals. It is used in addition to the atomic energy industry. It can manufacture special alloys, special glass (fluorescent screen glass for TV sets) and lithium batteries. It is used as the anode of batteries in lithium batteries.
Lithium batteries are also divided into two categories: non-rechargeable and rechargeable. Non-rechargeable batteries are called disposable batteries. They can only convert chemical energy into electrical energy at one time, and cannot restore electrical energy back to chemical energy (or The reductive performance is very poor.) The 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. The main characteristics of lithium battery such as electric energy chemical energy.
Smart portable electronic products require a small size and light weight, but the size and weight of the battery are often the most ** and the heaviest compared with other electronic components. For example, the "big brother" of the year is quite "thick and bulky". Today's mobile phones are so lightweight. 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 characteristics of a lithium battery are higher than the energy. What is the specific energy? The specific energy refers to the 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), L is liter (volume unit). Here is an example to illustrate: No. 5 nickel-cadmium battery is rated at 12V, its capacity is 800mAh, then its The energy is 096Wh (12V×08Ah). The same size of the No. 5 lithium-manganese dioxide battery is rated at 3V, and its capacity is 1200mAh, its energy is 36Wh. The volume is the same, then 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. A lithium-manganese dioxide battery is 3V, and two nickel-cadmium batteries are only 24V. 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, 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. They are mainly used in handheld computers, PDAs, communication equipment, cameras, satellites, missiles, torpedoes, instruments, etc. With the development of technology, process improvement and production volume Increase, the price of lithium batteries will continue to decline, the application will be more common.
Non-rechargeable lithium battery
There are many kinds 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 two most commonly used ones.
1. Lithium-manganese dioxide battery (LiMnO2)
Lithium-manganese dioxide battery is a disposable battery with lithium as anode, manganese dioxide as cathode and organic electrolyte. The main characteristic of the battery is high battery voltage, rated voltage is 3V (it is generally alkaline) 2 times the battery); the termination discharge voltage is 2V; the specific energy is large (see the example above); the discharge voltage is stable and reliable; the storage performance is good (storage time is more than 3 years), and the self-discharge rate is low (year self-discharge) Rate ≤ 2%); working temperature range -20 ° C ~ +60 ° C.
The battery can be made into different shapes to meet different requirements. It has a rectangular shape, a cylindrical shape and a button shape (button type). The cylindrical shape also has different diameters and height dimensions. Here is a more familiar 1# (size code D) ), 2# (size code C) and 5# (size code AA) battery main parameters.
CR is expressed as a cylindrical lithium-manganese dioxide battery; of 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 505 mm (this Models are 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, the battery factory provides relevant data. For example, CR14505 produced by Lixing Power Company gives ** continuous discharge current of 1000mA, ** pulse discharge current up to 2500mA.
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.
Button type (button type) battery is small in size, its diameter is 125~245mm, height is 16~50mm. 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 dimension with a decimal point. For example, the CR1220 has a diameter of 125 mm (excluding the number after the decimal point). , its height is 20mm. This model representation method is internationally accepted.
Such button batteries are commonly used in clocks, calculators, electronic notebooks, cameras, hearing aids, video game consoles, IC cards, backup power supplies, etc.
2. Lithium-thionyl chloride battery (LiSOCl2)
Lithium-thionyl chloride battery is a kind of specific energy**, which can reach 500Wh/kg or 1000Wh/L. Its rated voltage is 36V, and it has extremely flat 34V discharge characteristics when discharged at medium current ( It can be discharged flatly within 90% capacity and keeps little change.) The battery can work in the range of -40 ° C ~ +85 ° C, but the capacity at -40 ° C is about 50% of the normal temperature capacity. Self-discharge Low rate (year self-discharge rate ≤ 1%), storage life of more than 10 years.
Compare the specific energy of 1# (size code D) nickel-cadmium battery with 1# lithium-thionyl chloride battery: 1# nickel-cadmium battery is rated at 12V, capacity is 5000mAh; 1# lithium-thionyl chloride The rated voltage is 36V 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!); no short circuit between positive and negative batteries; no excessive current discharge (more than ** discharge current discharge); battery use to termination discharge voltage When it is taken out, 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 during use to avoid damage to the circuit. Know the type and rated voltage of the CR and ER in the familiar model. When buying a new battery, be sure to press The original model to buy, otherwise it will affect the performance of electronic products.
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