Charging and discharging batteries can be a chemical reaction, but custom lithium battery is claimed to be the exception. Battery scientists speak about energies flowing out and in of your battery as part of ion movement between anode and cathode. This claim carries merits but if the scientists were totally right, then the 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 called parasitic reactions in the electrolyte and electrodes till play a role. (See BU-808b: What may cause Li-ion to die?.)
The Li ion charger is actually a voltage-limiting device which includes similarities to the lead acid system. The differences with Li-ion lie in 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 when it comes to voltage cut off, manufacturers of Li-ion cells are incredibly strict on 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 as well as other gimmicks fails to exist. Li-ion is a “clean” system and just takes just 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 may go to 4.30V/cell and higher. Boosting the voltage increases capacity, but going beyond specification stresses battery and compromises safety. Protection circuits built in 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 when the current decreases to between 3 and 5 percent of your Ah rating.
The advised charge rate of an Energy Cell is between .5C and 1C; the total charge time is all about 2-3 hours. Manufacturers of those cells recommend charging at .8C or less to prolong battery life; however, most Power Cells will take a higher charge C-rate with little stress. Charge efficiency is around 99 percent along with the cell remains cool during charge.
Some Li-ion packs can experience a temperature rise of approximately 5ºC (9ºF) when reaching full charge. This could be due to the protection circuit and elevated internal resistance. Discontinue making use of the battery or charger in the event the temperature rises over 10ºC (18ºF) under moderate charging speeds.
Full charge happens when the battery reaches the voltage threshold and also the current drops to 3 percent of your rated current. A battery is additionally considered fully charged when the current levels off and cannot decline further. Elevated self-discharge may be the cause of this issue.
Boosting the charge current is not going to hasten the full-charge state by much. Even though 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 can take longer. A higher current charge will, however, quickly fill battery to around 70 percent.
Li-ion will not have to be fully charged as is the situation with lead acid, nor would it be desirable to accomplish this. The truth is, it is far better not to fully charge just because a high voltage stresses battery. Deciding on a lower voltage threshold or eliminating the saturation charge altogether, prolongs life of the battery but this decreases the runtime. Chargers for consumer products select 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 if the battery reaches the voltage threshold at Stage 1. State-of-charge (SoC) at this time is around 85 percent, a level which might be sufficient for many 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 placed on charge, the voltage shoots up quickly. This behavior may be when compared with lifting a weight with a rubber band, resulting in a lag. The capacity could eventually get caught up as soon as the battery is practically fully charged (Figure 3). This charge characteristic is typical of batteries. The larger the charge current is, the greater the rubber-band effect will likely be. Cold temperatures or charging a cell with good internal resistance amplifies the result.
Estimating SoC by reading the voltage of any charging battery is impractical; measuring the open circuit voltage (OCV) once the battery has rested for a few 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 way to Measure State-of-charge.)
Li-ion cannot absorb overcharge. When fully charged, the charge current should be shut down. A continuous trickle charge would cause plating of metallic lithium and compromise safety. To lessen stress, keep your lithium-ion battery at the peak cut-off as short as you possibly can.
After the charge is terminated, the battery voltage starts to drop. This eases the voltage stress. With time, the open circuit voltage will settle to between 3.70V and three.90V/cell. Be aware that energy battery that has received a totally saturated charge can keep the voltage elevated for an extended than a single that has not received a saturation charge.
When lithium-ion batteries needs to be left within the charger for operational readiness, some chargers use a brief topping charge to make up for your small self-discharge battery and its protective circuit consume. The charger may kick in as soon as 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 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 life of the battery.
Some portable devices sit in a charge cradle from the ON position. The existing drawn through the system is referred to as the parasitic load and will distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because they induce mini-cycles. This cannot often be avoided along with a laptop connected to the AC main is certainly an instance. Battery may be charged to 4.20V/cell after which discharged with the device. The worries level around the battery is high since the cycles occur in the high-voltage threshold, often also at elevated temperature.
A portable device needs to be switched off during charge. This allows the battery to arrive at the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing battery voltage and preventing the present in the saturation stage to decrease low enough by drawing a leakage current. A battery may be fully charged, but the prevailing conditions will prompt a continued charge, causing stress.
Whilst the traditional lithium-ion carries a nominal cell voltage of three.60V, Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to 3.65V. Fairly new will be the Li-titanate (LTO) having a nominal cell voltage of 2.40V and charging to 2.85V. (See BU-205: Types of Lithium-ion.)
Chargers for such non cobalt-blended Li-ions are not appropriate for regular 3.60-volt Li-ion. Provision must be made to identify the systems and supply the right voltage charging. A 3.60-volt lithium battery within a charger made for Li-phosphate would not receive sufficient charge; a Li-phosphate within a regular charger would cause overcharge.
Lithium-ion operates safely within the designated operating voltages; however, battery becomes unstable if inadvertently charged into a greater than specified voltage. Prolonged charging above 4.30V on 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 if the charge is allowed to continue, the existing interrupt device (CID) accountable for cell safety disconnects at one thousand-1,380kPa (145-200psi). If the pressure rise further, the safety 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 linked to elevated temperature. A totally charged battery includes a lower thermal runaway temperature and may vent earlier than one who is partially charged. All lithium-based batteries are safer at 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 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 only real 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 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 is not going to need saturation as is the situation with lead acid. This provides a major advantage for renewable power storage like a solar cell 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 required with Li-ion.