Cell Voltage Readings That Vary by More Than 0.2 Volts Indicate That the Battery Should Be Replaced.
Charging and discharging batteries is a chemical reaction, just Li-ion is claimed to be the exception. Battery scientists talk most energies flowing in and out of the battery equally office of ion movement between anode and cathode. This claim carries merits simply if the scientists were totally right, and then the bombardment would alive forever. They blame chapters fade on ions getting trapped, just as with all bombardment systems, internal corrosion and other degenerative effects likewise known as parasitic reactions on the electrolyte and electrodes till play a role. (See BU-808b: What causes Li-ion to dice?)
The Li ion charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion prevarication in a higher voltage per prison 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 cut off, manufacturers of Li-ion cells are very strict on the correct setting considering Li-ion cannot take overcharge. The so-called miracle charger that promises to prolong battery life and proceeds extra capacity with pulses and other gimmicks does non be. Li-ion is a "clean" system and only takes what it can absorb.
Charging Cobalt-blended Li-ion
Li-ion with the traditional cathode materials of cobalt, nickel, manganese and aluminum typically charge to 4.20V/prison cell. The tolerance is +/–50mV/jail cell. Some nickel-based varieties charge to 4.10V/cell; loftier capacity Li-ion may become to 4.30V/cell and college. Boosting the voltage increases chapters, merely going beyond specification stresses the battery and compromises rubber. Protection circuits congenital into the pack exercise not allow exceeding the set up voltage.
Effigy 1 shows the voltage and current signature equally lithium-ion passes through the stages for constant current and topping charge. Full charge is reached when the current decreases to between 3 and five pct of the Ah rating.
Li-ion is fully charged when the current drops to a set level. In lieu of trickle charge, some chargers use a topping charge when the voltage drops.
The advised charge rate of an Energy Jail cell is between 0.5C and 1C; the complete charge time is most 2–3 hours. Manufacturers of these cells recommend charging at 0.8C or less to prolong bombardment life; however, most Power Cells tin take a higher accuse C-rate with piddling stress. Accuse efficiency is about 99 percentage and the cell remains cool during charge.
Some Li-ion packs may experience a temperature rising of about 5ºC (9ºF) when reaching total charge. This could be due to the protection circuit and/or elevated internal resistance. Discontinue using the battery or charger if the temperature rises more than than 10ºC (18ºF) nether moderate charging speeds.
Total charge occurs when the bombardment reaches the voltage threshold and the current drops to 3 percent of the rated current. A bombardment is likewise considered fully charged if the current levels off and cannot go down further. Elevated self-discharge might be the crusade of this status.
Increasing the charge current does non hasten the full-charge country past much. Although the battery reaches the voltage peak quicker, the saturation accuse volition take longer accordingly. With college electric current, Phase ane is shorter but the saturation during Stage ii will take longer. A high electric current charge will, however, rapidly make full the battery to well-nigh 70 percent.
Li-ion does non need to be fully charged equally is the instance with atomic number 82 acid, nor is it desirable to do so. In fact, information technology is better not to fully charge because a high voltage stresses the battery. Choosing a lower voltage threshold or eliminating the saturation accuse altogether, prolongs battery life simply this reduces the runtime. Chargers for consumer products go for maximum capacity and cannot be adjusted; extended service 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 one hr or less without going to the Stage ii saturation charge. "Set up" appears when the battery reaches the voltage threshold at Phase 1. Country-of-charge (SoC) at this indicate is almost 85 percent, a level that may exist sufficient for many users.
Certain industrial chargers set up the charge voltage threshold lower on purpose to prolong battery life. T able 2 illustrates the estimated capacities when charged to different voltage thresholds with and without saturation charge. (See also BU-808: How to Prolong Lithium-based Batteries)
| Charge V/cell | Capacity at cut-off voltage* | Charge time | Capacity with full saturation |
|---|---|---|---|
| 3.80 | ~40% | 120 min | ~65% |
| 3.90 | ~threescore% | 135 min | ~75% |
| four.00 | ~70% | 150 min | ~lxxx% |
| iv.10 | ~eighty% | 165 min | ~90% |
| 4.xx | ~85% | 180 min | 100% |
* Readings may vary
Adding full saturation at the fix voltage boosts the capacity past almost 10 percent but adds stress due to high voltage.
When the battery is first put on accuse, the voltage shoots up quickly. This behavior tin be compared to lifting a weight with a rubber ring, causing a lag. The capacity will eventually take hold of upwards when the battery is most fully charged (Figure iii). This charge characteristic is typical of all batteries. The higher the charge current is, the larger the safe-band result will be. Cold temperatures or charging a jail cell with high internal resistance amplifies the upshot.
The capacity trails the charge voltage like lifting a heavy weight with a safe band.
Estimating SoC by reading the voltage of a charging battery is impractical; measuring the open circuit voltage (OCV) afterwards the battery has rested for a few hours is a better indicator. Every bit with all 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. (Run across BU-903: How to Mensurate Land-of-charge)
Li-ion cannot absorb overcharge. When fully charged, the charge current must exist cut off. A continuous trickle charge would cause plating of metallic lithium and compromise prophylactic. To minimize stress, proceed the lithium-ion battery at the peak cut-off as brusk as possible.
Once the charge is terminated, the battery voltage begins to drop. This eases the voltage stress. Over time, the open excursion voltage volition settle to between 3.70V and three.90V/cell. Annotation that a Li-ion battery that has received a fully saturated charge will proceed the voltage elevated for a longer than one that has not received a saturation charge.
When lithium-ion batteries must be left in the charger for operational readiness, some chargers apply a cursory topping charge to compensate for the small self-discharge the battery and its protective excursion eat. The charger may kick in when the open circuit voltage drops to iv.05V/cell and plow off again at 4.20V/cell. Chargers made for operational readiness, or standby mode, oft allow the battery voltage drop to 4.00V/cell and recharge to merely 4.05V/jail cell instead of the full four.20V/cell. This reduces voltage-related stress and prolongs battery life.
Some portable devices sit in a charge cradle in the ON position. The current drawn through the device is chosen the parasitic load and can misconstrue the accuse cycle. Battery manufacturers suggest against parasitic loads while charging because they induce mini-cycles. This cannot e'er be avoided and a laptop connected to the Air-conditioning chief is such a case. The battery might be charged to 4.20V/prison cell and so discharged by the device. The stress level on the battery is loftier because the cycles occur at the high-voltage threshold, often as well at elevated temperature.
A portable device should be turned off during charge. This allows the battery to attain the gear up voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the bombardment voltage and preventing the current in the saturation stage to driblet low plenty past drawing a leakage electric current. A battery may exist fully charged, but the prevailing weather will prompt a continued charge, causing stress.
Charging Non-cobalt-blended Li-ion
While the traditional lithium-ion has a nominal cell voltage of iii.60V, Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to three.65V. Relatively new is the Li-titanate (LTO) with a nominal cell voltage of ii.40V and charging to two.85V. (Come across BU-205: Types of Lithium-ion)
Chargers for these non cobalt-composite Li-ions are not compatible with regular three.sixty-volt Li-ion. Provision must be made to identify the systems and provide the correct voltage charging. A 3.60-volt lithium battery in a charger designed for Li-phosphate would not receive sufficient charge; a Li-phosphate in a regular charger would cause overcharge.
Overcharging Lithium-ion
Lithium-ion operates safely inside the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a college than specified voltage. Prolonged charging above 4.30V on a Li-ion designed for four.20V/prison cell will plate metallic lithium on the anode. The cathode cloth becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises and if the charge is allowed to continue, the current interrupt device (CID) responsible for prison cell safe disconnects at i,000–one,380kPa (145–200psi). Should the pressure rise further, the safety membrane on some Li-ion bursts open at about three,450kPa (500psi) and the jail cell might eventually vent with flame. (See BU-304b: Making Lithium-ion Rubber)
Venting with flame is connected with elevated temperature. A fully charged battery has a lower thermal runaway temperature and will vent sooner than one that is partially charged. All lithium-based batteries are safer at a lower charge, and this is why authorities will mandate air shipment of Li-ion at 30 percent state-of-accuse rather than at total charge. (Come across BU-704a: Shipping Lithium-based Batteries past Air)
The threshold for Li-cobalt at total charge is 130–150ºC (266–302ºF); nickel-manganese-cobalt (NMC) is 170–180ºC (338–356ºF) and Li-manganese is most 250ºC (482ºF). Li-phosphate enjoys similar and better temperature stabilities than manganese. (Encounter also BU-304a: Condom Concerns with Li-ion and BU-304b: Making Lithium-ion Safety)
Lithium-ion is not the only bombardment that poses a prophylactic hazard if overcharged. Atomic number 82- and nickel-based batteries are too known to melt down and cause fire if improperly handled. Properly designed charging equipment is paramount for all battery systems and temperature sensing is a reliable watchman.
Summary
Charging lithium-ion batteries is simpler than nickel-based systems. The charge circuit is straight forrard; voltage and electric current limitations are easier to accommodate than analyzing circuitous voltage signatures, which change every bit the battery ages. The charge process tin can be intermittent, and Li-ion does not need saturation every bit is the case with lead acid. This offers a major advantage for renewable energy storage such as a solar panel and wind turbine, which cannot always fully charge the battery. The absence of trickle charge further simplifies the charger. Equalizing charger, as is required with lead acid, is not necessary with Li-ion.
Consumer and most industrial Li-ion chargers charge the battery fully. They practise not offering adjustable end-of-charge voltages that would prolong the service life of Li-ion by lowering the end accuse voltage and accepting a shorter runtime. Device manufacturers fear that such an pick would complicate the charger. Exceptions are electric vehicles and satellites that avoid total charge to achieve long service life.
Simple Guidelines for Charging Lithium-based Batteries
- Turn off the device or disconnect the load on accuse to let the current to drib unhindered during saturation. A parasitic load confuses the charger.
- Accuse at a moderate temperature. Do not charge at freezing temperature. (Run across BU-410: Charging at High and Low Temperatures)
- Lithium-ion does non need to be fully charged; a partial charge is better.
- Not all chargers use a full topping accuse and the battery may non be fully charged when the "ready" signal appears; a 100 percent charge on a fuel gauge may exist a lie.
- Discontinue using charger and/or battery if the bombardment gets excessively warm.
- Employ some accuse to an empty battery before storing (40–50 pct SoC is platonic). (Come across BU-702: How to Store Batteries.)
References
[ane] Courtesy of Cadex
Source: https://batteryuniversity.com/article/bu-409-charging-lithium-ion
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