Charging and discharging batteries is really a chemical reaction, but lithium battery pack is claimed to become the exception. Battery scientists speak about energies flowing out and in of your battery included in ion movement between anode and cathode. This claim carries merits but if the scientists were totally right, then a battery would live forever. They blame capacity fade on ions getting trapped, but as with most battery systems, internal corrosion and other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till are involved. (See BU-808b: What may 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 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 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 promises to prolong battery lifespan and gain extra capacity with pulses and other gimmicks does not exist. Li-ion is really a “clean” system and merely takes what it 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 could go to 4.30V/cell and higher. Boosting the voltage increases capacity, but going beyond specification stresses battery and compromises safety. Protection circuits that are part of the pack do not allow exceeding the set voltage.
Figure 1 shows the voltage and current signature as lithium-ion passes throughout 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 approximately 2-three hours. Manufacturers of these cells recommend charging at .8C or less to extend battery; however, most Power Cells may take a higher charge C-rate with little stress. Charge efficiency is approximately 99 percent as well as the cell remains cool during charge.
Some Li-ion packs may experience a temperature rise of approximately 5ºC (9ºF) when reaching full charge. This might be because of the protection circuit and/or elevated internal resistance. Discontinue making use of the battery or charger when the temperature rises a lot more than 10ºC (18ºF) under moderate charging speeds.
Full charge occurs when the battery reaches the voltage threshold as well as the current drops to 3 percent of the rated current. A battery is likewise considered fully charged in the event the current levels off and cannot decline further. Elevated self-discharge might be the source of this disorder.
Enhancing the charge current will not hasten the entire-charge state by much. Although the battery reaches the voltage peak quicker, the saturation charge can take longer accordingly. With higher current, Stage 1 is shorter although the saturation during Stage 2 will require longer. A very high current charge will, however, quickly fill battery to around 70 %.
Li-ion will not need to be fully charged as is the case with lead acid, nor will it be desirable to accomplish this. Actually, it is far better not to fully charge just because a high voltage stresses battery. Selecting a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this reduces the runtime. Chargers for consumer products opt for maximum capacity and cannot be adjusted; extended service every day 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 coming to the Stage 2 saturation charge. “Ready” appears when the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this moment is about 85 percent, a level which may be sufficient for several users.
Certain industrial chargers set the charge voltage threshold lower on purpose to extend life of the battery. Table 2 illustrates the estimated capacities when charged to different voltage thresholds with and without saturation charge. (See also BU-808: How you can Prolong Lithium-based Batteries.)
When the battery is first put on charge, the voltage shoots up quickly. This behavior could be when compared with lifting a weight with a rubber band, causing a lag. The capacity may ultimately get caught up if the battery is almost fully charged (Figure 3). This charge characteristic is typical of batteries. The larger the charge current is, the larger the rubber-band effect is going to be. Cold temperatures or charging a cell with good internal resistance amplifies the effect.
Estimating SoC by reading the voltage of the charging battery is impractical; measuring the open circuit voltage (OCV) once the battery has rested for a couple hours is actually a better indicator. As with every batteries, temperature affects the OCV, so does the active material of Li-ion. SoC of smartphones, laptops along with 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 should be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To reduce stress, keep your lithium-ion battery on the peak cut-off as short as you can.
As soon as 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. Keep in mind that energy battery which has received a completely saturated charge helps keep the voltage elevated for a longer than one containing not received a saturation charge.
When lithium-ion batteries should be left from the charger for operational readiness, some chargers apply a brief topping charge to make up for that small self-discharge battery and its protective circuit consume. The charger may kick in when the open circuit voltage drops to 4.05V/cell and shut down again at 4.20V/cell. Chargers manufactured for operational readiness, or standby mode, often permit the battery voltage drop to 4.00V/cell and recharge to simply 4.05V/cell rather than the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.
Some portable devices sit in the charge cradle inside the ON position. The actual drawn from the system is referred to as parasitic load and may distort the charge cycle. Battery manufacturers advise against parasitic loads while charging since they induce mini-cycles. This cannot be avoided along with a laptop connected to the AC main is really a case. The battery may be charged to 4.20V/cell after which discharged through the device. The strain level around the battery is high because the cycles occur with the high-voltage threshold, often also at elevated temperature.
A transportable device ought to be turned off during charge. This allows the battery to reach the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing battery voltage and preventing the existing within the saturation stage to drop low enough by drawing a leakage current. A battery may be fully charged, although the prevailing conditions will prompt a continued charge, causing stress.
Even though the traditional lithium-ion includes a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception having a nominal cell voltage of 3.20V and charging to 3.65V. Relatively recent will be 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 certainly not compatible with regular 3.60-volt Li-ion. Provision has to be made to identify the systems and supply the appropriate voltage charging. A 3.60-volt lithium battery inside a charger created for Li-phosphate would not receive sufficient charge; a Li-phosphate within a regular charger would cause overcharge.
Lithium-ion operates safely in the designated operating voltages; however, battery becomes unstable if inadvertently charged into a beyond specified voltage. Prolonged charging above 4.30V with a Li-ion made for 4.20V/cell will plate metallic lithium around the anode. The cathode material becomes an oxidizing agent, loses stability and produces co2 (CO2). The cell pressure rises of course, if the charge is capable to continue, the existing interrupt device (CID) in charge of cell safety disconnects at one thousand-1,380kPa (145-200psi). Should the pressure rise further, the safety membrane on some Li-ion bursts open at about 3,450kPa (500psi) and the cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Safe.)
Venting with flame is associated with elevated temperature. An entirely charged battery includes a lower thermal runaway temperature and may vent sooner than one that is partially charged. All lithium-based batteries are safer in a 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 around 250ºC (482ºF). Li-phosphate enjoys similar and much 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 the sole battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries may also be recognized to melt down and cause fire if improperly handled. Properly designed charging devices 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 straight forward; voltage and current limitations are easier to accommodate than analyzing complex voltage signatures, which change as the battery ages. The charge process might be intermittent, and Li-ion fails to need saturation as is the situation with lead acid. This provides an important advantage for renewable energy storage for instance a solar power panel 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.