Charging and discharging batteries is actually a chemical reaction, but custom lithium battery is claimed being the exception. Battery scientists discuss energies flowing out and in of the battery as an element of ion movement between anode and cathode. This claim carries merits however if the scientists were totally right, then this battery would live forever. They blame capacity fade on ions getting trapped, but as with all battery systems, internal corrosion and other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till be a factor. (See BU-808b: The causes of Li-ion to die?.)
The Li ion charger is really a voltage-limiting device that has similarities on 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 in terms of voltage shut down, manufacturers of Li-ion cells are extremely 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 as well as other gimmicks fails to exist. Li-ion can be a “clean” system and just takes exactly 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 may 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 with the stages for constant current and topping charge. Full charge is reached once the current decreases to between 3 and 5 percent of the Ah rating.
The advised charge rate of the Energy Cell is between .5C and 1C; the total charge time is about 2-3 hours. Manufacturers of such cells recommend charging at .8C or less to prolong life of the battery; however, most Power Cells will take a higher charge C-rate with little stress. Charge efficiency is about 99 percent along with 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/or elevated internal resistance. Discontinue utilizing the battery or charger in case the temperature rises over 10ºC (18ºF) under moderate charging speeds.
Full charge happens when the battery reaches the voltage threshold as well as the current drops to 3 percent of your rated current. A battery is likewise considered fully charged when the current levels off and cannot decrease further. Elevated self-discharge may be the reason for this condition.
Boosting the charge current fails to hasten the complete-charge state by much. While the battery reaches the voltage peak quicker, the saturation charge is going to take longer accordingly. With higher current, Stage 1 is shorter although the saturation during Stage 2 is going to take longer. A high current charge will, however, quickly fill the battery to about 70 percent.
Li-ion does not need to be fully charged as is the case with lead acid, nor will it be desirable to do so. In reality, it is far better never to fully charge just because a high voltage stresses battery. Selecting a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery but this decreases the runtime. Chargers for consumer products choose maximum capacity and can not be adjusted; extended service every day 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 a single hour or less without going to 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 approximately 85 percent, a level which might be sufficient for many users.
Certain industrial chargers set the charge voltage threshold lower on purpose to prolong battery. Table 2 illustrates the estimated capacities when charged to various 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 might be compared to lifting a weight by using a rubber band, causing a lag. The ability may ultimately get caught up once the battery is nearly fully charged (Figure 3). This charge characteristic is typical of batteries. The better 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 result.
Estimating SoC by reading the voltage of a charging battery is impractical; measuring the open circuit voltage (OCV) after the battery has rested for a couple of hours is really a better indicator. As with every 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 lessen stress, keep your lithium-ion battery on the peak cut-off as short as is possible.
As soon as 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. Note that energy storage companies containing received a completely saturated charge helps keep the voltage elevated for an extended than a single which has not received a saturation charge.
When lithium-ion batteries needs 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 protective circuit consume. The charger may kick in as soon as the open circuit voltage drops to 4.05V/cell and shut 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 simply 4.05V/cell as opposed to the full 4.20V/cell. This reduces voltage-related stress and prolongs life of the battery.
Some portable devices sit in a charge cradle from the ON position. The actual drawn from the system is known as the parasitic load and might distort the charge cycle. Battery manufacturers advise against parasitic loads while charging since they induce mini-cycles. This cannot always be avoided plus a laptop linked to the AC main is really an instance. The battery might be charged to 4.20V/cell and then discharged with the device. The worries level on the battery is high for the reason that cycles occur at the high-voltage threshold, often also at elevated temperature.
A transportable device should be turned off during charge. This enables battery to attain the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing battery voltage and preventing the current within the saturation stage to drop low enough by drawing a leakage current. A battery might be fully charged, but the prevailing conditions will prompt a continued charge, causing stress.
Even though the traditional lithium-ion features a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception by using a nominal cell voltage of 3.20V and charging to 3.65V. Relatively recent will be the Li-titanate (LTO) using a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Forms 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 created to identify the systems and provide the appropriate voltage charging. A 3.60-volt lithium battery within a charger designed for Li-phosphate would not receive sufficient charge; a Li-phosphate inside 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 on a Li-ion intended for 4.20V/cell will plate metallic lithium about 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 allowed to continue, the actual interrupt device (CID) liable for cell safety disconnects at 1,000-1,380kPa (145-200psi). If 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 associated with elevated temperature. A totally charged battery includes a lower thermal runaway temperature and may vent earlier than one that is partially charged. All lithium-based batteries are safer with a lower charge, and that 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 just not the sole 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 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 easier to accommodate than analyzing complex voltage signatures, which change since the battery ages. The charge process may be intermittent, and Li-ion does not need saturation as is the case with lead acid. This offers a major advantage for renewable energy storage like a solar panel and wind turbine, which cannot always fully charge the 26650 battery pack. The absence of trickle charge further simplifies the charger. Equalizing charger, as it is required with lead acid, is not necessary with Li-ion.