Charging and discharging batteries can be a chemical reaction, but 18650 lithium battery is claimed being the exception. Battery scientists discuss energies flowing inside and out of your 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 like all battery systems, internal corrosion as well as other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till be a factor. (See BU-808b: What can cause Li-ion to die?.)
The Li ion charger is a voltage-limiting device that has similarities towards the lead acid system. The differences with Li-ion lie in the higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead acid offers some flexibility in terms of voltage cut off, manufacturers of Li-ion cells are incredibly strict around the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks is not going to exist. Li-ion is really a “clean” system and simply takes just what it can absorb.
Li-ion 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 could go to 4.30V/cell and better. Boosting the voltage increases capacity, but going beyond specification stresses the battery and compromises safety. Protection circuits included 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 as soon as the current decreases to between 3 and 5 percent of the Ah rating.
The advised charge rate of any Energy Cell is between .5C and 1C; the whole charge time is about 2-three hours. Manufacturers of such cells recommend charging at .8C or less to prolong battery lifespan; however, most Power Cells can take a greater charge C-rate with little stress. Charge efficiency is about 99 percent as well as the cell remains cool during charge.
Some Li-ion packs can experience a temperature rise around 5ºC (9ºF) when reaching full charge. This may be as a result of protection circuit and elevated internal resistance. Discontinue while using battery or charger in the event the temperature rises more than 10ºC (18ºF) under moderate charging speeds.
Full charge happens when the battery reaches the voltage threshold and also the current drops to 3 percent of the rated current. Battery power can also be considered fully charged in the event the current levels off and cannot decline further. Elevated self-discharge might be the source of this problem.
Boosting the charge current does not hasten the entire-charge state by much. Even though the battery reaches the voltage peak quicker, the saturation charge will require longer accordingly. With higher current, Stage 1 is shorter but the saturation during Stage 2 can take longer. A very high current charge will, however, quickly fill battery to about 70 percent.
Li-ion is not going to have to be fully charged as is the case with lead acid, nor will it be desirable to do so. In fact, it is best to never fully charge just because a high voltage stresses battery. Picking a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this cuts down on the runtime. Chargers for consumer products go for maximum capacity and should not be adjusted; extended service life is perceived less important.
Some lower-cost consumer chargers may use the simplified “charge-and-run” method that charges a lithium-ion battery in just one hour or less without visiting the Stage 2 saturation charge. “Ready” appears once the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this time is all about 85 percent, a level which might be sufficient for most users.
Certain industrial chargers set the charge voltage threshold lower on purpose to extend battery life. Table 2 illustrates the estimated capacities when charged to several voltage thresholds with and without saturation charge. (See also BU-808: The best way to Prolong Lithium-based Batteries.)
As soon as the battery is first place on charge, the voltage shoots up quickly. This behavior may be in comparison to lifting a weight with a rubber band, causing a lag. The capacity will ultimately catch up as soon as the battery is nearly fully charged (Figure 3). This charge characteristic is typical of most batteries. The greater the charge current is, the larger the rubber-band effect will be. Cold temperatures or charging a cell with high internal resistance amplifies the result.
Estimating SoC by reading the voltage of any charging battery is impractical; measuring the open circuit voltage (OCV) following the battery has rested for a couple of hours is a better indicator. As with most 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: The best way to Measure State-of-charge.)
Li-ion cannot absorb overcharge. When fully charged, the charge current must be shut down. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To reduce stress, retain the lithium-ion battery with the peak cut-off as short as possible.
After the charge is terminated, battery voltage actually starts to drop. This eases the voltage stress. Over time, the open circuit voltage will settle to between 3.70V and 3.90V/cell. Note that energy battery that has received an entirely saturated charge can keep the voltage elevated for a longer than one containing not received a saturation charge.
When lithium-ion batteries must be left inside the charger for operational readiness, some chargers use a brief topping charge to compensate for that 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 allow the battery voltage drop to 4.00V/cell and recharge to merely 4.05V/cell rather than full 4.20V/cell. This reduces voltage-related stress and prolongs life of the battery.
Some portable devices sit in the charge cradle inside the ON position. The current drawn throughout the device is referred to as parasitic load and might distort the charge cycle. Battery manufacturers advise against parasitic loads while charging simply because they induce mini-cycles. This cannot be avoided plus a laptop attached to the AC main is really a case. Battery could be charged to 4.20V/cell and then discharged by the device. The strain level on the battery is high since the cycles occur with the high-voltage threshold, often also at elevated temperature.
A transportable device should be turned off during charge. This allows the battery to arrive at the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing battery voltage and preventing the actual inside the saturation stage to lower low enough by drawing a leakage current. Battery power might be fully charged, although the prevailing conditions will prompt a continued charge, causing stress.
Whilst the traditional lithium-ion features a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception having a nominal cell voltage of three.20V and charging to 3.65V. Relatively recent 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 particular non cobalt-blended Li-ions are not suitable for regular 3.60-volt Li-ion. Provision needs to be made to identify the systems and offer the correct voltage charging. A 3.60-volt lithium battery within a charger intended 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, battery becomes unstable if inadvertently charged into a beyond specified voltage. Prolonged charging above 4.30V on the Li-ion intended for 4.20V/cell will plate metallic lithium in the anode. The cathode material becomes an oxidizing agent, loses stability and produces fractional co2 (CO2). The cell pressure rises and when the charge is permitted to continue, the current interrupt device (CID) accountable for cell safety disconnects at 1,000-1,380kPa (145-200psi). In case the pressure rise further, the protection membrane on some Li-ion bursts open at about 3,450kPa (500psi) and also the cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Safe.)
Venting with flame is associated with elevated temperature. A completely charged battery has a lower thermal runaway temperature and may vent sooner than the one that is partially charged. All lithium-based batteries are safer at the lower charge, and for this reason 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 approximately 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 just not really the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries will also be recognized to melt down and cause fire if improperly handled. Properly designed charging tools are paramount for many battery systems and temperature sensing is a reliable watchman.
Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is simple; voltage and current limitations are easier to accommodate than analyzing complex voltage signatures, which change since the battery ages. The charge process might be intermittent, and Li-ion does not need saturation as is the case with lead acid. This offers an important advantage for renewable power storage for instance a solar power and wind turbine, which cannot always fully charge the 18500 battery. The absence of trickle charge further simplifies the charger. Equalizing charger, as it is required with lead acid, is not necessary with Li-ion.