Extended life lithium-ion battery new charging solution

　　Author ：Iflowpower – Portable Power Station Supplier

Lithium-ion batteries have high energy density, small size, weight and other advantages, in mobile phones, laptop markets have completely replaced other batteries, accounting for almost 100%. At present, the lithium-ion battery is rapidly extending to electric tools and other applications, and its broad market prospect is increasingly recognized. However, compared with nickelin, nickel-cadmium, lead-acid batteries, it is necessary to push the application and development of lithium-ion batteries faster, and must constantly improve its safety and service life.

This article will discuss a new type of charging solution from the angle of charger, to increase the safety of lithium-ion batteries, extend battery life, while reducing the cost of charger. In the process of using the battery, we often hear a sentence such as the battery industry: "There is less in the use of the battery, more is contrastic". This sentence we can understand that incorrect charging conditions or methods will be more likely to damage the battery and reduce the life of the battery.

Take a 1,8650 lithium-cobalt-free battery as an example, when the charge is over temperature, at 70 ¡ã C, the electrolyte interface (SEI) is used to decompose and heat; 120 ¡ã C, the electrolyte, the positive electrode begins thermal decomposition, causing the gas and rapidly increase the temperature ; Around 260 ¡ã C: Battery explosion. Or charge over pressure, in terms of overvoltage 5.5V, easy to precipitate lithium metal, solvent is oxidized, temperature rise, malignant circulation, or even batteries, explosion.

Therefore, for how to charge, we will discuss the following important issues together. Why do you want to precharge? Battery operating voltage from 2.5V (carbon negative battery: 3V, power is 0%) to 4.

2V (100% power). When the voltage is less than 2.5V, the battery discharge is terminated.

At the same time, because the discharge loop is closed, the current loss of the internal protection circuit is also reduced to the lowest. Of course, due to different internal materials, the discharge termination voltage can be in the range of 2.5V-3.

0V due to different internal materials. When the voltage exceeds 4.2V, the charging loop is terminated to protect the battery security; and when the unit cell operating voltage drops below 3.

0V, we can think that the discharge is terminated, the discharge loop is terminated to protect battery safety. Therefore, when the battery is not used, the battery should be charged 20% electricity, and then moisture-proof storage. Since the lithium-ion battery has a higher energy ratio, it is necessary to prevent overcharge and over-placing in the battery life.

Overlant causes difficulties in recovery of active substances, if they go directly into the fast power mode (large current), it will damage the battery, affecting the service life and may therefore bring safety hazards. First charge the small current (C / 10) to 2.5V to 3.

0V, and then convert to fast charge is necessary. Although the current lithium-ion battery has a protective board in the application, in general, the chance of overlapping will be small, but does not add precharge, in these two cases, the situation may also bring over Hidden danger. First, the protective board is invalid, and the second is to place (5% -10% / month) self-discharge rate.

Therefore, small current precharge can effectively solve the charging problem of over-discharge cells. However, charging current is not bigger, better. Taking the monomer lithium ion battery as an example, its charging method includes constant current, constant voltage charging process, constant voltage is usually 4.

2V (as an example of LiCoO2 battery), the constant current setting value is 0.1c ~ 1c. Although the charging of the large current will shorten the charging time, it will also cause a reduction in the shortement and capacity of the battery lifecycle, so we need to choose the appropriate constant current value to charge.

Below is a relationship curve of different current charging and battery capacity of 4.2V / 900mAhlicoo2 cell (Figure 1), we can see that the battery capacity of small current charging is significantly greater than the battery capacity of high current charging after approximately 500 fees. The voltage accuracy of constant voltage charging requires a high energy density battery, and the overchaul will have a great harm to the lithium-ion battery, and it is possible to expand the leakage or even explosion.

Moreover, it is easy to cause the electrolytic substance in the battery to speed up the battery life, and therefore the accurate constant voltage value is important for the life of the lithium-ion battery. In order to be more fully charged, to ensure that the constant voltage value and the accuracy of the termination voltage value are within 1%. Taking the lithium-cobalt-free ion battery as an example, it is best to be as close as possible to 4.

2V, but no more than 4.2V, this high-precision voltage charging method can reduce the dissolution of cobalt, stabilize the layered structure of LiCoO2, make it The coating does not change, improves cycle performance, and maintains high capacity. In addition, even slight overvoltage will bring two phenomena, the battery initial capacity is reduced and the battery cycle life is lowered.

In the case of multi-elevative ion battery, in order to ensure the maximum battery capacity and life, sometimes even the accuracy is less than 0.5%. Therefore, the accuracy control of the charging voltage is a key technology for lithium-ion battery chargers.

At present, people have such a misunderstanding for the charging voltage of lithium ion battery. It is considered that there is a battery protection board. It doesn't care in voltage accuracy.

This is not advisable. Because the battery protection board is used to make timely protection against possible accidents, it considers more security factors, not performance factors. For example, as an example of 4.

2V, the overvoltage protection parameter of the protective plate is 4.30V (some may be 4.4V), if each time is full, with 4.

30V as a charging cut-off point, the battery capacity will be very Faster. Why do you have a charger vendor that they have repeatedly touched the charger user to return, saying that the charger is broken because the battery is charged one day, the battery is not full, the charger does not turn the light, always Red light. When the manufacturer actually measures the charger, it finds that it is normal and meets the factory requirements.

What is this problem? This is important because this charger does not take into account the aging of the battery. If the current of the deadly charge is too small, it will make the aging battery will not reach the set point of the charging completed, so that the user has misjudge, and it is considered that the charger has been bad. The purpose of the charging press is to prevent the damaged or too much cycling of lithium-ion batteries, in the off-specific section of the charging, due to the self-discharge, it is difficult to enter the state of EOC (higher than judging current), on the one hand to the user On the other hand, it is also possible to expand the battery overheating due to overhang charging.

Aiming at these factors, the new multi-lithium-ion battery charging chip OZ8981 launched by the unevenness technology (O2Micro) is already a perfect solution. OZ8981 is a dedicated charging management integrated chip with precise voltage, current output, and multiple protection, and supply six-stage charging control mode with convenient system design and low cost. It is important for multi-lithium ion battery packs for light electric vehicles, electric bicycles and electric tools.

High cost-effective and high reliability OZ8981 contain single-chip integrated charging controllers that achieve efficient error amplifier output. It supports 0V pulse charging, precharge, constant current charging, constant voltage charging, deadline, and automatic recharging control. Intelligent charging control.

Supports flexible settings for pre-charged startup voltage, constant current charge, constant voltage charging value, and cut-off charging current value. In addition, the OZ8981 has a high precision charging voltage ("1%) and current (" 5%) output; by external resistance adjustment, voltage output accuracy can be "0.5%).

Support for dual charging press: precharge, constant voltage charging is on time (maximum 5 hours, or not). Support for dual temperature protection: internal temperature protection (115 ¡ã C), exterior high temperature protection (default: 44 ¡ã C) and low temperature protection (default: 2 ¡ã C). External temperature protection point can be external flexible settings.

Support charging overpressure protection, overcurrent protection, short circuit protection. Support battery automatic access detection, direct LED display for charging state. The device adopts universal package SOP16.

Fig. 4 is a graph showing the charging graph of OZ8981 lithium ion battery. By combining with the front-end PWM chip, OZ8981 will help users quickly achieve safe and efficient and low-cost lithium-ion battery charger d.