Charging and discharging batteries is actually a chemical reaction, but custom lithium battery is claimed to be the exception. Battery scientists speak about energies flowing inside and out from the battery within ion movement between anode and cathode. This claim carries merits however if the scientists were totally right, then the battery would live forever. They blame capacity fade on ions getting trapped, but as with every battery systems, internal corrosion and other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till play a role. (See BU-808b: What causes Li-ion to die?.)
The Li ion charger can be a voltage-limiting device which includes similarities for the lead acid system. The differences with Li-ion lie inside a higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead acid offers some flexibility regarding voltage cut off, 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 and gain extra capacity with pulses as well as other gimmicks does not exist. Li-ion is really a “clean” system and simply takes what it really can absorb.
Li-ion together with 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 might go to 4.30V/cell and better. Boosting the voltage increases capacity, but going beyond specification stresses the battery and compromises safety. Protection circuits built in the rest do not allow exceeding the set voltage.
Figure 1 shows the voltage and current signature as lithium-ion passes from the stages for constant current and topping charge. Full charge is reached when the current decreases to between 3 and 5 percent in the Ah rating.
The advised charge rate of any Energy Cell is between .5C and 1C; the entire charge time is all about 2-3 hours. Manufacturers of such cells recommend charging at .8C or less to prolong battery lifespan; however, most Power Cells can take an increased charge C-rate with little stress. Charge efficiency is around 99 percent and the cell remains cool during charge.
Some Li-ion packs may suffer a temperature rise around 5ºC (9ºF) when reaching full charge. This could be as a result of protection circuit and elevated internal resistance. Discontinue making use of the battery or charger in the event 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 additionally considered fully charged when the current levels off and cannot decrease further. Elevated self-discharge may be the reason behind this condition.
Boosting the charge current does not hasten the full-charge state by much. Even though the battery reaches the voltage peak quicker, the saturation charge is going to take longer accordingly. With higher current, Stage 1 is shorter but the saturation during Stage 2 can take longer. A high current charge will, however, quickly fill battery to around 70 %.
Li-ion is not going to need to be fully charged as is the situation with lead acid, nor will it be desirable to do so. Actually, it is best never to fully charge as a high voltage stresses the battery. Choosing a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this reduces the runtime. Chargers for consumer products select maximum capacity and can not be adjusted; extended service life is perceived less important.
Some lower-cost consumer chargers could use the simplified “charge-and-run” method that charges a lithium-ion battery in a single hour or less without going to the Stage 2 saturation charge. “Ready” appears if the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this point is about 85 percent, a level that could be sufficient for a lot of users.
Certain industrial chargers set the charge voltage threshold lower on purpose to extend battery lifespan. Table 2 illustrates the estimated capacities when charged to different voltage thresholds with and without saturation charge. (See also BU-808: The way to Prolong Lithium-based Batteries.)
Once the battery is first wear charge, the voltage shoots up quickly. This behavior may be when compared with lifting a weight having a rubber band, resulting in a lag. The ability will ultimately get caught up when the battery is almost fully charged (Figure 3). This charge characteristic is typical of all the batteries. The larger the charge current is, the larger the rubber-band effect will likely be. Cold temperatures or charging a cell rich in internal resistance amplifies the effect.
Estimating SoC by reading the voltage of any charging battery is impractical; measuring the open circuit voltage (OCV) after the battery has rested for a couple of hours can be a better indicator. As with all batteries, temperature affects the OCV, so does the active material of Li-ion. SoC of smartphones, laptops and also other devices is estimated by coulomb counting. (See BU-903: How to Measure State-of-charge.)
Li-ion cannot absorb overcharge. When fully charged, the charge current should be stop. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To lower stress, keep your lithium-ion battery at the peak cut-off as short as you possibly can.
When the charge is terminated, battery voltage begins to drop. This eases the voltage stress. After a while, the open circuit voltage will settle to between 3.70V and three.90V/cell. Remember that energy battery which has received a totally saturated charge helps keep the voltage elevated for a longer than a single that has not received a saturation charge.
When lithium-ion batteries has to be left inside the charger for operational readiness, some chargers apply a brief topping charge to compensate for the small self-discharge the battery and its particular protective circuit consume. The charger may kick in if the open circuit voltage drops to 4.05V/cell and shut down again at 4.20V/cell. Chargers created for operational readiness, or standby mode, often enable the battery voltage drop to 4.00V/cell and recharge just to 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.
Some portable devices sit inside a charge cradle within the ON position. The present drawn through the system is referred to as the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging since they induce mini-cycles. This cannot be avoided as well as a laptop coupled to the AC main is certainly a case. Battery could be charged to 4.20V/cell and after that discharged through the device. The stress level about the battery is high because the cycles occur in the high-voltage threshold, often also at elevated temperature.
A portable device must be switched off during charge. This gives battery to achieve the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing battery voltage and preventing the existing inside the saturation stage to decrease low enough by drawing a leakage current. Battery power can be fully charged, although the prevailing conditions will prompt a continued charge, causing stress.
While the traditional lithium-ion includes a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception having a nominal cell voltage of 3.20V and charging to 3.65V. Fairly new may be the Li-titanate (LTO) with a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Kinds of Lithium-ion.)
Chargers for such non cobalt-blended Li-ions are not works with regular 3.60-volt Li-ion. Provision needs to be intended to identify the systems and provide the proper voltage charging. A 3.60-volt lithium battery in the charger created for Li-phosphate would not receive sufficient charge; a Li-phosphate within a regular charger would cause overcharge.
Lithium-ion operates safely throughout the designated operating voltages; however, the battery becomes unstable if inadvertently charged to your more than specified voltage. Prolonged charging above 4.30V over a Li-ion designed for 4.20V/cell will plate metallic lithium around the anode. The cathode material becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises of course, if the charge is permitted to continue, the actual interrupt device (CID) in charge of cell safety disconnects at 1,000-1,380kPa (145-200psi). In case the pressure rise further, the security membrane on some Li-ion bursts open at about 3,450kPa (500psi) along with the cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Safe.)
Venting with flame is linked with elevated temperature. A totally charged battery includes a lower thermal runaway temperature and will vent sooner than one that is partially charged. All lithium-based batteries are safer in a lower charge, and this 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 around 250ºC (482ºF). Li-phosphate enjoys similar and better temperature stabilities than manganese. (See also BU-304a: Safety Concerns with Li-ion and BU-304b: Making Lithium-ion Safe.)
Lithium-ion is not the only real battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries are also proven to melt down and cause fire if improperly handled. Properly designed charging equipment is paramount for all those battery systems and temperature sensing is actually a reliable watchman.
Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is uncomplicated; voltage and current limitations are simpler to accommodate than analyzing complex voltage signatures, which change because the battery ages. The charge process might be intermittent, and Li-ion is not going to need saturation as is the case with lead acid. This provides a major advantage for alternative energy storage like a solar power and wind turbine, which cannot always fully charge the 26650 battery pack. The lack of trickle charge further simplifies the charger. Equalizing charger, as it is required with lead acid, is not necessary with Li-ion.