Charging and discharging batteries is a chemical reaction, but custom lithium battery is claimed to get the exception. Battery scientists speak about energies flowing inside and outside of your battery as an element 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 every battery systems, internal corrosion along with other degenerative effects also referred to as parasitic reactions about the electrolyte and electrodes till play a role. (See BU-808b: What causes Li-ion to die?.)
The Li ion charger is a voltage-limiting device that has similarities to 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 regarding voltage shut down, manufacturers of Li-ion cells are really strict in the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that offers to prolong battery life and gain extra capacity with pulses as well as other gimmicks will not exist. Li-ion is a “clean” system and merely takes just what it can absorb.
Li-ion using 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 higher. Boosting the voltage increases capacity, but going beyond specification stresses the battery and compromises safety. Protection circuits included in the pack do not allow 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 when the current decreases to between 3 and 5 percent of your Ah rating.
The advised charge rate of your Energy Cell is between .5C and 1C; the entire charge time is around 2-three hours. Manufacturers of such cells recommend charging at .8C or less to extend battery; however, most Power Cells will take a better charge C-rate with little stress. Charge efficiency is about 99 percent and also the cell remains cool during charge.
Some Li-ion packs may go through a temperature rise around 5ºC (9ºF) when reaching full charge. This could be because of the protection circuit and elevated internal resistance. Discontinue making use of the battery or charger in the event the temperature rises more than 10ºC (18ºF) under moderate charging speeds.
Full charge occurs when the battery reaches the voltage threshold and also the current drops to 3 percent in the rated current. Battery power is likewise considered fully charged in the event the current levels off and cannot go down further. Elevated self-discharge might be the cause of this condition.
Increasing the charge current is not going 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 nevertheless the saturation during Stage 2 will require longer. An increased current charge will, however, quickly fill battery to around 70 %.
Li-ion fails to have to be fully charged as is the case with lead acid, nor will it be desirable to accomplish this. In reality, it is far better not to fully charge since a high voltage stresses battery. Choosing a lower voltage threshold or eliminating the saturation charge altogether, prolongs battery but this reduces the runtime. Chargers for consumer products select 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 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 point is approximately 85 percent, a level which might be sufficient for several users.
Certain industrial chargers set the charge voltage threshold lower on purpose to extend battery lifespan. 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 place on charge, the voltage shoots up quickly. This behavior might be in comparison with lifting a weight having a rubber band, causing a lag. The capability may ultimately get caught up as soon as 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 will be. Cold temperatures or charging a cell with good internal resistance amplifies the effect.
Estimating SoC by reading the voltage of your charging battery is impractical; measuring the open circuit voltage (OCV) right after the battery has rested for a few hours can be a better indicator. As with every batteries, temperature affects the OCV, so does the active material of Li-ion. SoC of smartphones, laptops and 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 must be cut off. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To lower stress, maintain the lithium-ion battery on the peak cut-off as short as you can.
As soon as the charge is terminated, battery voltage starts to drop. This eases the voltage stress. After a while, the open circuit voltage will settle to between 3.70V and three.90V/cell. Keep in mind that lithium battery storage that has received a totally saturated charge helps keep the voltage elevated for a longer than a single containing not received a saturation charge.
When lithium-ion batteries should be left within the charger for operational readiness, some chargers apply a brief topping charge to make up for your small self-discharge the battery as well as its protective circuit consume. The charger may start working once the open circuit voltage drops to 4.05V/cell and switch off again at 4.20V/cell. Chargers made for operational readiness, or standby mode, often enable the battery voltage drop to 4.00V/cell and recharge to only 4.05V/cell rather than the full 4.20V/cell. This reduces voltage-related stress and prolongs battery lifespan.
Some portable devices sit in the charge cradle from the ON position. The present drawn from the system is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging mainly because they induce mini-cycles. This cannot often be avoided plus a laptop coupled to the AC main is really an instance. The battery may be charged to 4.20V/cell then discharged from the device. The worries level about the battery is high for the reason that cycles occur at the high-voltage threshold, often also at elevated temperature.
A portable device ought to be switched off during charge. This enables 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 current within the saturation stage to decrease low enough by drawing a leakage current. Battery power might be fully charged, although the prevailing conditions will prompt a continued charge, causing stress.
As the traditional lithium-ion features a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception having a nominal cell voltage of 3.20V and charging to 3.65V. Fairly new is definitely the Li-titanate (LTO) with a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Types of Lithium-ion.)
Chargers for these non cobalt-blended Li-ions are not suitable for regular 3.60-volt Li-ion. Provision needs to be created to identify the systems and provide the proper voltage charging. A 3.60-volt lithium battery within a charger designed 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 beyond specified voltage. Prolonged charging above 4.30V on the Li-ion designed for 4.20V/cell will plate metallic lithium about the anode. The cathode material becomes an oxidizing agent, loses stability and produces fractional co2 (CO2). The cell pressure rises of course, if the charge is able to continue, the present interrupt device (CID) in charge of 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 linked to elevated temperature. A completely charged battery has a lower thermal runaway temperature and may vent sooner than one which is partially charged. All lithium-based batteries are safer at the 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 about 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 really the only battery that poses a safety hazard if overcharged. Lead- and nickel-based batteries are also known to melt down and cause fire if improperly handled. Properly designed charging tools are paramount for all 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 since the battery ages. The charge process can be intermittent, and Li-ion is not going to need saturation as is the case with lead acid. This provides an important advantage for renewable power storage for instance a solar power and wind turbine, which cannot always fully charge the 26650 battery pack. The absence of trickle charge further simplifies the charger. Equalizing charger, as is required with lead acid, is not necessary with Li-ion.