Lithium-ion battery with high energy density, small size and light weight advantages, mobile phones, notebook computers market, it has completely Qudaiqita batteries, owns 100% of market share; the current, lithium-ion batteries are rapidly Yanshen into power tools, electric bicycles, and other applications, it is a promising market more and more recognized by the industry. However, with the nickel metal hydride, nickel cadmium, lead-acid battery compared to lithium-ion battery more quickly to promote the use and development, we must continuously improve its safety and service life. Charger from the perspective of this paper to discuss a new type of rechargeable solutions to improve the safety of lithium-ion battery, extended battery life, while reducing the cost of the charger.
The use of batteries, we often hear words like the battery industry: “the bad battery in less, more is to be fully bad.” This phrase could be interpreted as, incorrect charging conditions or methods will be easier to damage the battery, reducing battery life. To 18650 cobalt lithium-ion battery, for example, (1) charge-off temperature, at about 70 ℃: electrolyte interface (SEI) mode begins to decompose, and heat; 120 ℃ or so: electrolyte, cathode starting thermal decomposition, resulting in gas evolution and to temperature increased rapidly; to 260 ℃ in about: battery explosion. (2) over-voltage charge to look over voltage 5.5V, lithium metal precipitation, solvent is oxidized, the temperature rose, creating a vicious circle, battery fire, explosion. Shows poor characteristics of the battery charging method would have serious implications. Therefore, how to charge, we jointly investigate the following several important issues Vostro 1520 battery Vostro 1700 battery
(1) Why do we need pre-charge function?
Battery voltage from 2.5V (battery carbon anode: 3V) (power: 0%) to 4.2V (power: 100%). When the voltage is less than 2.5V, the discharge end. While the internal protection circuit is also reduced current consumption the lowest (discharge circuit closed). Of course, practical applications, due to different internal materials and better protect the battery, discharge termination voltage can be 2.5V ~ 3.0V range. When the voltage exceeds 4.2V, the charging circuit to terminate, to protect battery safety; and when the single battery voltage down to 3.0V below, we can state that over discharge, discharge circuit termination to protect the battery safety. battery when not in use, should charge the battery to maintain 20% of the electricity, further moisture preservation.
As the lithium ion battery has a higher energy than, and therefore the battery Shiyong in strictly avoid over charging and over discharging of the phenomenon. Guo Fang restoration of the active substance will Daozhi difficulties Cishi if Zhijie Jinrukuaisu red Dian Moshi (Da Dian Liu) , the battery will produce damage to life and may therefore affect the risk of bringing invisible. first, a small current (C/10) charge to 2.5V or 3.0V, then translate to fast charge is necessary.
Although lithium-ion battery with protection in the application of both board, under normal circumstances, the occurrence probability of release would be small, but without pre-charge function, in the following circumstances or possible over-discharge of the hidden dangers Vostro 1500 battery Vostro 1510 battery
1. Protection board failure.
2. A long time to place (5% ~ 10% / month) of the self-discharge rate.
Therefore, low current pre-charge function can be effectively solved the problem put the battery charge.
(2) whether the charge current the bigger the better?
To single lithium-ion battery, for example, charging method include constant current, constant voltage charging, constant voltage typically 4.2V (with LiCoO2 battery for example), set the value of constant current 0.1C ~ 1C. While current charging will shorten the charging time, but it can also shorten the battery life cycle and reduce capacity, so we need to select the appropriate charging constant current value.
The following is a 4.2V/900mAH LiCoO2 batteries and battery charging different current capacity curve (see Figure 1), we can see about 500 charge and discharge cycles, low current charge of battery capacity significantly higher than high current charging the battery capacity.
(3) constant charging voltage accuracy?
As a high energy density batteries, lithium ion battery overcharge has great harm, there may be swelling and leakage, are also an explosion, and over charge the battery inside is easy to speed up the reaction of electrolyte caused by the battery shorten life, so an accurate value of the constant voltage charging lithium-ion battery has an important significance.
In order to more fully fully charged, to ensure constant value and the termination voltage accuracy within 1%. With cobalt oxide lithium-ion battery, for example, preferably as close to 4.2V, but less than 4.2V, this kind of high-precision voltage charging method can reduce the dissolution of cobalt, stable LiCoO2 layered structure, it’s coated with non-phase transition, to improve cycling performance, and maintain high-capacity Vostro 1310 battery Vostro 1320 battery
Li-ion batteries in the multi-series cases, is guaranteed to the maximum battery capacity and life, sometimes 1% accuracy can not satisfy the application requirements, it sometimes required accuracy within 0.5%. Therefore, accurate control of charging voltage lithium-ion battery charger is a key.
Lithium battery charging voltage is present on a misunderstanding that has battery protection board, the voltage accuracy do not care, it is not desirable. Because the battery protection board for possible accidents on the timely protection, it is considered more of a safety factor, rather than performance factors. For example to 4.2V batteries, for example, over-voltage protection to protect board parameters are 4.30V (some may want to 4.4V), if every time overcharge to 4.30V cut-off point for charging, the battery capacity will also be very fast decay.
(4) Why charge timer?
Told me there was a battery charger manufacturers, they often encounter came before the user returns the charger that the charger is broken, because the battery charge of the day, the battery is not full charge, the charger does not turn light, has been a red light. Manufacturer of the charger can be measured, also found that it is normal to meet factory requirements. What is the problem? This is mainly because the charger did not take into account the aging of the battery self-discharge after the larger. If the deadline set charging current is too small, will make the aging battery charging has been completed not reach set point, allowing users to generate false positives, that the charger is bad.
The role of charge timer is to prevent damage or excessive cycle have lithium batteries, in charge of the closing paragraph, as self-discharge is too large, so that the battery is difficult to enter the state EOC (above determine current), on the one hand to the user battery charge is not full of false positives, it also may be due to long periods of charging, the battery overheating caused swelling, and even dangerous Vostro 1014 battery Vostro 1015 battery .
Consideration of these factors, embossing technology (O2Micro) introduced a new multi-series lithium-ion battery is a core OZ8981 the perfect solution. OZ8981 is a dedicated charge management integrated chip, which with precise voltage, current output, and multiple protection, and provide six-stage charge control model, system design, convenient and low cost. It is mainly used for light electric vehicles, electric bicycles and power tools on the multi-cell lithium ion battery pack.
OZ8981 specifically include the following features:
Single-chip integrated charge controller
The error amplifier output high
Support 0V pulse charging, pre-charge, constant current charging, constant voltage charging, closing charge, automatic recharge, six-stage intelligent charging control
Support for pre-charge start voltage, constant current charging value, constant voltage charging cut-off value and flexibility to set the charge current value
High-precision charge voltage (<1%) and current (<5%) output; through an external resistor to adjust the voltage output accuracy can be <0.5%
Dual charge timer protection – pre-charge time, constant voltage charging time (maximum: 5 hours, or not use)
Dual temperature protection – protection chip temperature (115 ℃), external over temperature protection (default: 44 ℃) and over-temperature protection (default: 2 ℃), the external temperature protection point can be set to external flexibility
Support the charge over-voltage protection, over current, short circuit protection
Support automatic access test Studio XPS 16 battery Vostro 1000 battery
Support the direct charging status LED display
Cost-effective, high reliability
Generic Package: SOP16
PWM chip through a combination of front-end, OZ8981 will help users quickly and cost to achieve safe and efficient lithium ion battery charger design Studio XPS 1640 battery .