Portable electronic products to the battery as a power source. With the rapid development of portable products, the amount of various battery greatly increased, and the development of many new battery. We are more familiar with the high-performance alkaline batteries, rechargeable nickel-cadmium batteries, nickel metal hydride battery, the recent development of lithium batteries. Here introduces the basic knowledge about lithium batteries. This includes its characteristics, the main parameters of the significance of the model, the range of applications and use precautions.
Lithium is a metallic element, its chemical symbol Li (English called lithium) is a silvery white, very soft, reactive metal and chemical properties, is the lightest metal. It is applied to the atomic energy industry, the manufacture of specialty alloys, specialty glass (on the TV screen glass) and lithium batteries. In the lithium battery
, which is used as the anode of the battery.
Lithium batteries can also be divided into two categories: two types of non-rechargeable and rechargeable. Called non-rechargeable batteries, disposable batteries, it can only chemical energy once converted into electrical energy, can not restore the energy back to chemical energy (or restore performance poor). Known as secondary batteries and rechargeable batteries (also called battery). Can convert electrical energy into chemical energy store, when in use, and then to convert chemical energy into electricity, it is reversible, the main characteristics of the lithium battery such as electricity chemical energy.
The most important feature of the lithium battery high specific energy. What is the ratio of energy? Refers to the ratio of the energy per unit weight or unit volume of energy. Wh / kg or Wh / L ratio of the energy. Wh is a unit of energy, W is watts, h is the hour; kg kg (unit of weight), L is the liter (volume unit). Here is an example to illustrate: 5 nickel-cadmium battery rated voltage of 1.2V, a capacity of 800mAh, the energy 0.96Wh (1? 2V x 0? 8Ah). Same size lithium - manganese dioxide battery rated voltage is 3V, capacity 1200mAh, its energy 3.6Wh. Both cell volume is the same, 3.75 times the specific energy of lithium - manganese dioxide battery is a nickel-cadmium battery!
A nickel-cadmium battery weighs about 23g, and a lithium - manganese dioxide battery weighs about 18g. A lithium - manganese dioxide battery 3V, the two nickel-cadmium batteries 2.4V. Small quantity of batteries using lithium batteries (portable electronic components
volume is reduced, weight reduction), and the long working life of the battery.
Other lithium batteries have a stable discharge voltage, wide operating temperature range, low self-discharge, long storage life, no memory effect and pollution-free advantages.
The disadvantage of lithium batteries is expensive, so is still not widely used, mainly used in handheld computers, PDAs, communication equipment, cameras, satellites, missiles, torpedoes, instruments. With the development of technology, process improvement and increase of production, the price of lithium batteries will continue to decline, applications will be more prevalent. Non-rechargeable lithium battery non-rechargeable lithium batteries have a variety of used lithium - manganese dioxide batteries, lithium - thionyl chloride battery and lithium and other compounds batteries. This paper describes only the most commonly used.
Lithium - manganese dioxide battery is a lithium anode, manganese dioxide as the cathode, and the organic electrolyte solution disposable batteries. The main characteristics of the battery is the battery voltage and rated voltage of 3V (2-fold) is generally alkaline batteries; terminate the discharge voltage of 2V; specific energy (see the above cited examples); stable discharge voltage; have better storage performance (more than 3 years of storage time), low self-discharge rate (annual self-discharge rate ≤ 2%); -20 ° C to +60 ° C operating temperature range.
The battery can be made into different shape to meet different requirements, it has a rectangular, cylindrical and button-shaped (snap). The cylindrical shape also has a different diameter and height.
The figure is Japan Maxell lithium - manganese dioxide battery, 3 volt, non-rechargeable, the volume of a single 15x40 mm.
Rechargeable lithium-ion battery
Rechargeable lithium-ion battery is currently the most widely used mobile phone applications battery, but it is more "squeamish" and not use the overcharge, over-discharge (may damage the battery or to make end-of-life). Therefore, the protection components or circuit protection to prevent costly damage to the battery in the battery. The lithium-ion battery is demanding, to ensure that the termination voltage accuracy of 1%, the current major semiconductor device factory has developed a variety of lithium-ion battery charging IC to ensure safe, reliable and fast charging.
The phone is now very common part of the phone is a nickel-metal hydride battery, but the smart phone is a lithium-ion battery. Correct use of the lithium-ion battery to extend the battery life is important. Lithium ion batteries are currently the most widely used lithium batteries, flat rectangular, cylindrical, rectangular and button it can be made according to the requirements of the different electronic products, and by several batteries in series with a battery pack
. The lithium-ion battery rated voltage of 3.6V (some products 3.7V). Related to termination when fully charged, the charging voltage and battery anode materials: anode material is graphite 4.2V; anode material as coke 4.1V. The internal resistance of the anode material is also different, slightly larger than the internal resistance of the anode of coke, and the discharge curve is also slightly different, as shown in Figure 1. Commonly referred to as 4.1V lithium-ion battery and 4.2V lithium-ion battery. Now use the majority of the termination of the discharge voltage of 4.2V, a lithium ion battery is 2.5V ~ 2.75V (cell factory given operating voltage range or a given discharge voltage, each parameter is slightly different). Below the termination of the discharge voltage to continue to discharge called over-discharge, over-discharge of the battery will be damage.
The lithium-ion battery is not suitable for large current discharge, reduce the discharge time when a large current discharge (internal will result in higher temperatures and loss of energy). Therefore, battery production plant gives the maximum discharge current, in use, should be less than the maximum discharge current. The lithium-ion battery temperature, the factory charging temperature range, the discharge temperature range Storage temperature range. The lithium-ion battery charging requirements is very high, and it requires a precision of the charging circuit in order to ensure the safety of charge. Terminate the charge voltage accuracy tolerance is the rated ± 1% (for example: the to charge 4.2V lithium-ion battery, the tolerance is ± 0.042V), over-voltage lithium ion battery charging will cause permanent damage. The lithium-ion battery charging current should be in accordance with the recommendations of the battery manufacturing plant, and requires current limiting circuit in order to avoid over-current (overheating). Commonly a charging rate of 0.25C to 1C (C is the capacity of the battery, such as C = 800mAh, 1C charging rate, the charging current of 800mA). Tend to detect high current charging battery temperature to prevent overheating and damage the battery or an explosion.
The lithium-ion battery is divided into two stages: the first constant current charging, to close termination voltage changed to constant voltage charging, the charging characteristics shown in Figure 2 as shown. This is a 800mAh capacity battery, its termination charge voltage of 4.2V. Batteries to 800mA (charging rate of 1C) constant-current charging, the battery voltage to start the larger the slope of the step-up, changed to 4.2V constant voltage charging when the battery voltage is close to 4.2V, the current is gradually decreased, the voltage change is not, 1/10C to the charging current is reduced (approximately 80mA), it is considered nearly full, the charging may be terminated (some charger to 1/10C after start timer, over a certain time after the end of charging). Lithium ion battery in the charging or discharging process the event of over-charge and over-discharge or over-current, will cause damage to the battery or reduce the service life.
Application Note:
Lithium-ion battery applications considerations in addition to the same with the non-rechargeable lithium batteries, in charge should also pay attention to the following points:
1. Lithium-ion battery 4.1V and 4.2V to terminate the charging of different varieties, charging 4.1V battery 4.2V charger can not be used, or there will be danger of overcharge (4.1V and 4.2V The charger with charger IC is different!)
2. Charge the battery, the ambient temperature can not exceed the temperature range listed in the table of product characteristics.
3. can not reverse charging.
4. Can not use rechargeable nickel-cadmium battery charger (charge three nickel-cadmium batteries) to charge the lithium-ion battery (rated voltage is 3.6V), but charging different ways, and easily lead to over-charge.
The discharge should note the following:
1. Lithium-ion battery discharge current can not exceed the maximum discharge current is given in the table of product characteristics. The discharge current is large, will produce a higher temperature (loss of energy), reducing the discharge time, and if the battery supplier
is no protection element will overheat and damage the battery.
2. Discharge curve is different at different temperatures, as shown in Figure 5. As can be seen from the figure, at different temperatures, the discharge voltage and the discharge time is also different. -20 ℃ discharge situation worst.
In storage:
1. Battery if long-term storage, to be maintained at 50% state of discharge.
2. Batteries should be stored in a cool, dry bad environment.
To Keep away from heat, do not be placed in direct sunlight.
The image of the working principle of analogy:
Now the principle and mechanism of charging and discharging of the lithium-ion battery, the bubble phenomenon common life metaphor. The lithium-ion battery is like a bunch of soap bubbles, electrical energy stored within the bubble. When charging, the bubble will lengthen as the charging time is increasing, the bubble will burst when more than its limit, that damage the lithium crystal form, resulting in permanent damage.
When excessive discharge will cause bubble collapse and disappear, so the next charging bubble also charge it up, and caused the failure of lithium. How to inadequate control bubble burst and the bubble but the degree of collapse? Must be used to protect the circuit to be strictly controlled. Of course, the quality of batteries and precise control circuit can be greatly extended battery life.
The owners like to use lithium-ion battery, lithium battery self-discharge small, large capacity, superior performance.