Charging and discharging batteries can be a chemical reaction, but 18650 lithium battery is claimed to become the exception. Battery scientists focus on energies flowing in 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 your battery would live forever. They blame capacity fade on ions getting trapped, but like all battery systems, internal corrosion and also other degenerative effects also known as parasitic reactions around the electrolyte and electrodes till be involved. (See BU-808b: The causes of Li-ion to die?.)
The Li ion charger is actually a voltage-limiting device that has 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 in terms of voltage shut down, manufacturers of Li-ion cells are extremely strict in the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that offers to prolong life of the battery and gain extra capacity with pulses and other gimmicks fails to exist. Li-ion is actually a “clean” system and simply 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 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 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 with 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 your Ah rating.
The advised charge rate of the Energy Cell is between .5C and 1C; the complete charge time is about 2-three hours. Manufacturers of the cells recommend charging at .8C or less to extend battery lifespan; however, most Power Cells may take a greater charge C-rate with little stress. Charge efficiency is around 99 percent and also the cell remains cool during charge.
Some Li-ion packs may experience a temperature rise of about 5ºC (9ºF) when reaching full charge. This could be as a result of protection circuit or elevated internal resistance. Discontinue utilizing the battery or charger when the temperature rises over 10ºC (18ºF) under moderate charging speeds.
Full charge occurs when the battery reaches the voltage threshold along with the current drops to 3 percent from the rated current. Battery power is likewise considered fully charged in case the current levels off and cannot drop further. Elevated self-discharge might be the source of this disorder.
Increasing the charge current is not going to hasten the total-charge state by much. Although the battery reaches the voltage peak quicker, the saturation charge will take longer accordingly. With higher current, Stage 1 is shorter nevertheless the saturation during Stage 2 will take longer. A high current charge will, however, quickly fill the battery to about 70 percent.
Li-ion does not should be fully charged as is the situation with lead acid, nor is it desirable to do so. Actually, it is far better to not fully charge just because a high voltage stresses battery. Picking a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery lifespan but this lessens the runtime. Chargers for consumer products go for maximum capacity and cannot 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 once the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this stage is approximately 85 percent, a level which may be sufficient for several users.
Certain industrial chargers set the charge voltage threshold lower on purpose to extend battery. 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.)
When the battery is first put on charge, the voltage shoots up quickly. This behavior can be compared to lifting a weight by using a rubber band, resulting in a lag. The capability may ultimately catch up as soon as the battery is nearly fully charged (Figure 3). This charge characteristic is typical of all the batteries. The greater the charge current is, the greater the rubber-band effect is going to be. Cold temperatures or charging a cell with higher internal resistance amplifies the outcome.
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 hours is 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: The way to Measure State-of-charge.)
Li-ion cannot absorb overcharge. When fully charged, the charge current has to be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To lower stress, keep the lithium-ion battery with the peak cut-off as short as is possible.
As soon as the charge is terminated, the battery voltage starts to drop. This eases the voltage stress. After a while, the open circuit voltage will settle to between 3.70V and 3.90V/cell. Remember that lithium battery storage which includes received an entirely saturated charge will keep the voltage elevated for an extended than one which has 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 your small self-discharge the battery and its protective circuit consume. The charger may start working if 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 enable the battery voltage drop to 4.00V/cell and recharge to only 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs battery lifespan.
Some portable devices sit within a charge cradle within the ON position. The existing drawn throughout the device is referred to as parasitic load and may distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because they induce mini-cycles. This cannot be avoided as well as a laptop linked to the AC main is certainly an instance. The battery could possibly be charged to 4.20V/cell and then discharged through the device. The worries level around the battery is high because the cycles occur at the high-voltage threshold, often also at elevated temperature.
A portable device ought to be switched off during charge. This allows 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 decrease low enough by drawing a leakage current. A battery could be fully charged, but the prevailing conditions will prompt a continued charge, causing stress.
As the traditional lithium-ion carries a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception using a nominal cell voltage of 3.20V and charging to 3.65V. Somewhat new is definitely the Li-titanate (LTO) using a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Kinds of Lithium-ion.)
Chargers for these non cobalt-blended Li-ions are not compatible with regular 3.60-volt Li-ion. Provision should be created to identify the systems and provide the proper voltage charging. A 3.60-volt lithium battery within a charger created 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, battery becomes unstable if inadvertently charged to some more than specified voltage. Prolonged charging above 4.30V on 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 co2 (CO2). The cell pressure rises and when the charge is able to continue, the actual interrupt device (CID) accountable for cell safety disconnects at 1,000-1,380kPa (145-200psi). When the pressure rise further, the safety 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 linked with elevated temperature. A fully charged battery has a lower thermal runaway temperature and definately will vent sooner than one that is partially charged. All lithium-based batteries are safer with a lower charge, and this is the 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 all about 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 really the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries may also be seen to melt down and cause fire if improperly handled. Properly designed charging equipment is paramount for all 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 simpler to accommodate than analyzing complex voltage signatures, which change as being the battery ages. The charge process may be intermittent, and Li-ion is not going to need saturation as is the case with lead acid. This provides an important advantage for alternative energy storage like 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.