Charging and discharging batteries is really a chemical reaction, but lithium battery pack is claimed to get the exception. Battery scientists talk about energies flowing out and in in the battery as part of 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 most battery systems, internal corrosion along with other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till be involved. (See BU-808b: The causes of Li-ion to die?.)
The Li ion charger is really a voltage-limiting device containing similarities towards 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 with regards to voltage cut off, manufacturers of Li-ion cells are incredibly strict in 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 also other gimmicks is not going to exist. Li-ion is actually a “clean” system and merely takes exactly 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 rest do not let exceeding the set voltage.
Figure 1 shows the voltage and current signature as lithium-ion passes through the stages for constant current and topping charge. Full charge is reached once the current decreases to between 3 and 5 percent in the Ah rating.
The advised charge rate of your Energy Cell is between .5C and 1C; the total charge time is all about 2-3 hours. Manufacturers of such cells recommend charging at .8C or less to extend battery; however, most Power Cells might take a higher charge C-rate with little stress. Charge efficiency is around 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 could be because of the protection circuit and elevated internal resistance. Discontinue while using battery or charger if the temperature rises greater than 10ºC (18ºF) under moderate charging speeds.
Full charge takes place when the battery reaches the voltage threshold and also the current drops to 3 percent from the rated current. Battery power is likewise considered fully charged if the current levels off and cannot go down further. Elevated self-discharge may be the cause of this condition.
Boosting the charge current fails to hasten the total-charge state by much. Even though 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 take longer. A very high current charge will, however, quickly fill battery to about 70 %.
Li-ion fails to have to be fully charged as is the situation with lead acid, nor would it be desirable to do this. In fact, it is advisable to not fully charge since a high voltage stresses the battery. Choosing a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery life but this cuts down on the runtime. Chargers for consumer products opt for maximum capacity and can not be adjusted; extended service every day life is perceived less important.
Some lower-cost consumer chargers can make use of the simplified “charge-and-run” method that charges a lithium-ion battery in a single 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 point is approximately 85 percent, a level which might be sufficient for most users.
Certain industrial chargers set the charge voltage threshold lower on purpose to prolong battery lifespan. 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.)
Once the battery is first place on charge, the voltage shoots up quickly. This behavior might be in comparison with lifting a weight having a rubber band, creating a lag. The ability may ultimately get caught up if the battery is nearly fully charged (Figure 3). This charge characteristic is typical of all batteries. The higher 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 a charging battery is impractical; measuring the open circuit voltage (OCV) right after the battery has rested for several hours is really 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, maintain the lithium-ion battery in the peak cut-off as short as possible.
After the charge is terminated, battery voltage begins to drop. This eases the voltage stress. As time passes, the open circuit voltage will settle to between 3.70V and three.90V/cell. Be aware that lithium battery storage that has received a totally saturated charge can keep the voltage elevated for a longer than a single containing not received a saturation charge.
When lithium-ion batteries should be left inside the charger for operational readiness, some chargers apply a brief topping charge to make up for your small self-discharge the battery and its particular protective circuit consume. The charger may kick in once the open circuit voltage drops to 4.05V/cell and switch off 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 just to 4.05V/cell as opposed to the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.
Some portable devices sit in a charge cradle in the ON position. The present drawn with the system is known as the parasitic load and may distort the charge cycle. Battery manufacturers advise against parasitic loads while charging simply because they induce mini-cycles. This cannot continually be avoided and a laptop linked to the AC main is such a case. Battery could be charged to 4.20V/cell and after that discharged with the device. The strain level in the battery is high as the cycles occur on the high-voltage threshold, often also at elevated temperature.
A transportable device ought to be switched off during charge. This enables 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 from the saturation stage to decrease low enough by drawing a leakage current. Battery power can be fully charged, but the prevailing conditions will prompt a continued charge, causing stress.
While the traditional lithium-ion includes a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception using a nominal cell voltage of three.20V and charging to 3.65V. Somewhat new will be the Li-titanate (LTO) having a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Forms of Lithium-ion.)
Chargers for these non cobalt-blended Li-ions are not appropriate for regular 3.60-volt Li-ion. Provision should be made to identify the systems and give the appropriate voltage charging. A 3.60-volt lithium battery within a charger intended for Li-phosphate would not receive sufficient charge; a Li-phosphate in the regular charger would cause overcharge.
Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Prolonged charging above 4.30V over a Li-ion made for 4.20V/cell will plate metallic lithium in the anode. The cathode material becomes an oxidizing agent, loses stability and produces co2 (CO2). The cell pressure rises and when the charge is permitted to continue, the existing interrupt device (CID) accountable for cell safety disconnects at one thousand-1,380kPa (145-200psi). Should the pressure rise further, the protection 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 connected with elevated temperature. An entirely charged battery includes a lower thermal runaway temperature and definately will vent earlier than the one that is partially charged. All lithium-based batteries are safer with 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 temperature stabilities than manganese. (See also BU-304a: Safety Concerns with Li-ion and BU-304b: Making Lithium-ion Safe.)
Lithium-ion will not be really the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries will also be known to melt down and cause fire if improperly handled. Properly designed charging tools are paramount for all those battery systems and temperature sensing is really 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 as the battery ages. The charge process may be intermittent, and Li-ion fails to need saturation as is the situation with lead acid. This offers a serious advantage for renewable energy storage for instance a solar power and wind turbine, which cannot always fully charge the 18650 battery pack. The absence of trickle charge further simplifies the charger. Equalizing charger, as is also required with lead acid, is not required with Li-ion.