Charging and discharging batteries can be a chemical reaction, but custom lithium battery is claimed to become the exception. Battery scientists talk about energies flowing inside and out in the battery included in ion movement between anode and cathode. This claim carries merits however if the scientists were totally right, then a battery would live forever. They blame capacity fade on ions getting trapped, but as with all battery systems, internal corrosion and also other degenerative effects also called parasitic reactions on the electrolyte and electrodes till play a role. (See BU-808b: What causes Li-ion to die?.)
The Li ion charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion lie within a higher voltage per cell, tighter voltage tolerances and the lack of trickle or float charge at full charge. While lead acid offers some flexibility with regards to voltage stop, manufacturers of Li-ion cells are really strict on the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that offers to prolong battery life and gain extra capacity with pulses as well as other gimmicks does not exist. Li-ion is a “clean” system and merely takes exactly what it can absorb.
Li-ion with all the traditional cathode materials of cobalt, nickel, manganese and aluminum typically charge to 4.20V/cell. The tolerance is /-50mV/cell. Some nickel-based varieties charge to 4.10V/cell; high capacity Li-ion may go to 4.30V/cell and better. Boosting the voltage increases capacity, but going beyond specification stresses battery and compromises safety. Protection circuits that are part of the rest do not allow exceeding the set voltage.
Figure 1 shows the voltage and current signature as lithium-ion passes with the stages for constant current and topping charge. Full charge is reached if the current decreases to between 3 and 5 percent in the Ah rating.
The advised charge rate of an Energy Cell is between .5C and 1C; the complete charge time is approximately 2-3 hours. Manufacturers of these cells recommend charging at .8C or less to extend life of the battery; however, most Power Cells may take a greater charge C-rate with little stress. Charge efficiency is about 99 percent and the cell remains cool during charge.
Some Li-ion packs may go through a temperature rise around 5ºC (9ºF) when reaching full charge. This might be because of the protection circuit and elevated internal resistance. Discontinue making use of the battery or charger when the temperature rises more than 10ºC (18ºF) under moderate charging speeds.
Full charge occurs when the battery reaches the voltage threshold and the current drops to 3 percent of your rated current. Battery power is likewise considered fully charged in the event the current levels off and cannot go down further. Elevated self-discharge may be the source of this problem.
Boosting the charge current will not hasten the complete-charge state by much. While the battery reaches the voltage peak quicker, the saturation charge will take longer accordingly. With higher current, Stage 1 is shorter although the saturation during Stage 2 will take longer. A very high current charge will, however, quickly fill the battery to around 70 %.
Li-ion fails to must be fully charged as is the situation with lead acid, nor could it be desirable to achieve this. In fact, it is best never to fully charge just because a high voltage stresses battery. Deciding on a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery lifespan but this decreases the runtime. Chargers for consumer products choose maximum capacity and should not be adjusted; extended service every day life is perceived less important.
Some lower-cost consumer chargers might use the simplified “charge-and-run” method that charges a lithium-ion battery in just one hour or less without seeing the Stage 2 saturation charge. “Ready” appears as soon as the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this stage is all about 85 percent, a level that could be sufficient for most users.
Certain industrial chargers set the charge voltage threshold lower on purpose to prolong life of the battery. Table 2 illustrates the estimated capacities when charged to several voltage thresholds with and without saturation charge. (See also BU-808: How to Prolong Lithium-based Batteries.)
As soon as the battery is first wear charge, the voltage shoots up quickly. This behavior can be when compared with lifting a weight with a rubber band, creating a lag. The ability will eventually get caught up once the battery is practically fully charged (Figure 3). This charge characteristic is typical of batteries. The higher the charge current is, the greater the rubber-band effect will probably be. Cold temperatures or charging a cell with higher internal resistance amplifies the effect.
Estimating SoC by reading the voltage of a charging battery is impractical; measuring the open circuit voltage (OCV) following the battery has rested for a couple hours can be a better indicator. As with every batteries, temperature affects the OCV, so does the active material of Li-ion. SoC of smartphones, laptops as well as other devices is estimated by coulomb counting. (See BU-903: How you can Measure State-of-charge.)
Li-ion cannot absorb overcharge. When fully charged, the charge current has to be shut down. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To lessen stress, keep the lithium-ion battery in the peak cut-off as short as you can.
Once the charge is terminated, the battery voltage actually starts to drop. This eases the voltage stress. With time, the open circuit voltage will settle to between 3.70V and three.90V/cell. Keep in mind that energy storage companies that has received a totally saturated charge helps keep the voltage elevated for an extended than one which includes not received a saturation charge.
When lithium-ion batteries must be left within the charger for operational readiness, some chargers apply a brief topping charge to make up to the small self-discharge the battery and its protective circuit consume. The charger may kick in as soon as the open circuit voltage drops to 4.05V/cell and shut down again at 4.20V/cell. Chargers designed for operational readiness, or standby mode, often allow the battery voltage drop to 4.00V/cell and recharge to simply 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs life of the battery.
Some portable devices sit in a charge cradle within the ON position. The actual drawn throughout the device is called the parasitic load and will distort the charge cycle. Battery manufacturers advise against parasitic loads while charging mainly because they induce mini-cycles. This cannot always be avoided as well as a laptop coupled to the AC main is unquestionably an instance. Battery may be charged to 4.20V/cell and after that discharged through the device. The anxiety level in the battery is high as the cycles occur in the high-voltage threshold, often also at elevated temperature.
A portable device needs to be switched off during charge. This gives battery to attain the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the battery voltage and preventing the actual in the saturation stage to lower low enough by drawing a leakage current. A battery might be fully charged, nevertheless the prevailing conditions will prompt a continued charge, causing stress.
Even though the traditional lithium-ion carries a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception using a nominal cell voltage of three.20V and charging to 3.65V. Somewhat new is definitely the Li-titanate (LTO) having a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Varieties of Lithium-ion.)
Chargers for these non cobalt-blended Li-ions are not works with regular 3.60-volt Li-ion. Provision should be intended to identify the systems and offer the correct voltage charging. A 3.60-volt lithium battery inside a charger made for Li-phosphate would not receive sufficient charge; a Li-phosphate in a regular charger would cause overcharge.
Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a beyond specified voltage. Prolonged charging above 4.30V on the Li-ion intended for 4.20V/cell will plate metallic lithium about the anode. The cathode material becomes an oxidizing agent, loses stability and produces co2 (CO2). The cell pressure rises and if the charge is capable to continue, the current interrupt device (CID) in charge of cell safety disconnects at one thousand-1,380kPa (145-200psi). When the pressure rise further, the security membrane on some Li-ion bursts open at about 3,450kPa (500psi) as well as the cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Safe.)
Venting with flame is linked to elevated temperature. A fully charged battery includes a lower thermal runaway temperature and will vent earlier than the one that is partially charged. All lithium-based batteries are safer at a lower charge, and that is why authorities will mandate air shipment of Li-ion at 30 percent state-of-charge rather dexkpky82 at full charge. (See BU-704a: Shipping Lithium-based Batteries by Air.).
The threshold for Li-cobalt at full charge is 130-150ºC (266-302ºF); nickel-manganese-cobalt (NMC) is 170-180ºC (338-356ºF) and Li-manganese is about 250ºC (482ºF). Li-phosphate enjoys similar and temperature stabilities than manganese. (See also BU-304a: Safety Concerns with Li-ion and BU-304b: Making Lithium-ion Safe.)
Lithium-ion is not really the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries can also be recognized to melt down and cause fire if improperly handled. Properly designed charging devices are paramount for those battery systems and temperature sensing can be a reliable watchman.
Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is easy; voltage and current limitations are easier to accommodate than analyzing complex voltage signatures, which change because the battery ages. The charge process can be intermittent, and Li-ion does not need saturation as is the case with lead acid. This offers a major advantage for renewable energy storage say for example a solar power and wind turbine, which cannot always fully charge the 26650 battery pack. The absence of trickle charge further simplifies the charger. Equalizing charger, as is also required with lead acid, is not necessary with Li-ion.