How lithium ion batteries are charged?

Although lithium ions are rechargeable batteries, lithium ion batteries are not chemical reactions. Battery scientists believe that as ions move between the positive and negative poles, energy flows in and out. Battery scientists have a point. Battery chemists blame trapped ions for the decline in lithium-ion battery capacity, but internal corrosion and other degradation effects can continue to work in lithium-ion battery systems, as in all other types of batteries.

Lithium ion charger and lead acid battery system has a lot in common are a kind of voltage limiting device, but one difference is that, unlike lithium ion, the battery voltage is higher, at the same time the voltage tolerance is greater, the form of trickle or float charge and then full charge does not exist. Lithium-ion battery manufacturers are very strict about the correct setup because lithium-ion batteries cannot accept overcharging, although lead acid offers some flexibility in terms of voltage cutoff. Lithium ion is a “clean” system because it absorbs only what it can.

Charging Cobalt-blended Li-ion

Lithium ions with traditional cathode materials such as cobalt, nickel, manganese and aluminum are usually charged to 4.20V/ battery. +/ -50mV /cell is a tolerance. The battery capacity can be increased by increasing the voltage, but exceeding certain specifications will also cause pressure to the battery, which will endanger the safety of the battery. The protection circuit in the bag shall not exceed the set voltage value.

Figure 1 shows the voltage and current characteristics of lithium ions passing through the constant current and charging stages. The state of full charge is the recurrent drops to between 3% and 5% of rated Ah.

Figure 1: Charge stages of lithium-ion [1]

Lithium ions charge when the current drops to a set level. Some chargers also do top charging when the voltage drops, rather than trickle charging.

It is recommended that the charging rate of the energy battery be between 0.5℃ and 1C. Second, the recommended time for full charging is about two to three hours. But battery manufacturers recommend 0.8C or even lower to delay battery life. Most Power cells can also withstand a high charge rate of about 99% under low pressure conditions, and the battery stays cool during the charging phase.

Some lithium-ion batteries may experience a temperature increase of around 5 ° C (9ºF) after a full charge due to increased protection circuits or internal resistance. And if the charging speed is in moderate conditions, if the temperature of the battery or charger is higher than 10℃, it should stop using.

When the battery is fully charged, increasing the charging current has no significant promotion effect on it. Although the battery reaches the maximum voltage faster, it also extends the corresponding saturation charging time. At the same time, the higher the current, the shorter the stage 1, but also prolong the saturation time of stage 2. However, the high-current mode charges quickly, reaching 70 percent of the battery’s capacity.

When the voltage of the battery reaches a threshold, the current drops to about 3 percent of the rated current, and the battery is fully charged. There is also a fully charged state, that is, the current gradually becomes stable and does not drop further. The cause of this condition is high self-discharge.

Lead-acid batteries need to be fully charged. Lithium-ion batteries do not need to be fully charged, but this is not desirable. Actually, best not to charge batteries, will only because of high voltage battery to bring greater pressure, but by eliminating the saturated charging or choose a low voltage threshold method can extend the life of the battery, but the way the operation time, less money in all types of battery chargers, consumer type of charger capacity is the largest, is unable to adjust, But extending service life is not so important now.

Charging a lithium-ion battery in an hour or less is a simplified “plug and go” approach that is commonly adopted by low-cost consumer chargers and does not require saturation charging stage 2. When the voltage threshold for phase 1 is reached, Ready appears. At this point, the charging status is around 85%, which is sufficient for most users.

To extend battery life, some industrial chargers set the voltage threshold low. Table 2 shows the estimated capacity of saturated charge at different voltage thresholds.

Charge V/cell Capacity at cut-off voltage* Charge time Capacity with full saturation
3.80 ~40% 120 min ~65%
3.90 ~60% 135 min ~75%
4.00 ~70% 150 min ~80%
4.10 ~80% 165 min ~90%
4.20 ~85% 180 min 100%

Table 2: Typical charge characteristics of lithium-ion
* Readings may vary

Increasing saturation at a set voltage will increase the capacity by about 10%, but the pressure will also increase because the voltage is too high.

The voltage rises rapidly when the battery is first charged, similar to lifting a heavy object with a rubber band, causing a lag. Capacity will eventually catch up when the battery is fully charged. (See Figure 3). This charging characteristic is typical of all batteries. The higher the current of the charge, the greater the rubber band effect, which is amplified at low temperatures by batteries with high internal resistance.

Figure 3: Volts/capacity vs. time when charging lithium-ion [1]

Like lifting a weight with a rubber band, the capacity follows the charging voltage.

Estimating SoC by reading the voltage of a rechargeable battery is out of touch with reality, and measuring open circuit voltage (OCV) is a better indicator that can be measured several hours after the battery has rested. As with other batteries, OCV is affected by temperature and the active species of lithium ions. Coulomb counting is used to estimate devices such as laptops and smart phones.

To reduce the pressure, keep the lithium ion battery at its maximum cutoff time as short as possible. The elegant battery will drop during charging, but will reduce the voltage pressure. The brief charging and discharging of the charger protects the circuit from small self-discharges while the lithium-ion battery remains in the charger and is ready at the same time.

When a portable device ON a charging rack is “ON,” the current passing through is called parasitic load and distorts the charge cycle, which is unavoidable. The portable device should be turned off while charging so that the battery is not impeded when it reaches current protection and voltage thresholds.

Charging Non-cobalt-blended Li-ion

3.60V is the nominal battery voltage for conventional lithium ion, with the exception of lithium phosphate (LiFePO), which has a nominal voltage of 3.20V, and lithium titanate (LTO), which is newer, which has a nominal battery voltage of 2.40V.

Conventional 3.60 volt lithium ion and non-cobalt hybrid lithium ion chargers are not compatible and therefore must be specified for the identification system and can provide the correct identification system.

Overcharging Lithium-ion

Lithium ion can operate normally and safely within the specified operating voltage, but the battery can become unstable if it is inadvertently charged above the specified voltage. If lithium metal is present on the anode, lithium ions designed for 4.20V batteries can be charged over 4.2V for a long time. At the same time, the cathode material acts as an oxidant and loses its stability, producing carbon dioxide (CO2).

By combining high temperature with flame exhaust, a fully charged battery has a lower thermal runaway temperature and will exhaust faster than a partially charged battery. All lithium-ion batteries are safer at low power levels, which is why authorities have set a 30% charge requirement for airborne lithium ions.

The lithium cobalt battery has a threshold of 130-150ºC(266-302ºF) when fully charged; Lithium manganese is about 250ºC(482ºF); Nickel-manganese-cobalt (NMC) is 170-180ºC(338-356ºF). Phosphoric acid batteries have temperature stability similar to but better than manganese.

Like other batteries, lithium-ion batteries pose a safety hazard if overcharged, and lead and nickel batteries can melt and cause fires if not handled properly. Therefore, proper charging equipment is essential for all types of battery systems.


Lithium-ion batteries are simpler to charge than nickel batteries, the circuits of charge are straight, and voltage and current limits are easier to adapt to than complex circuits, which change as the battery ages. Lithium ions are not saturated like lead acid and are intermittent during the charging process. This provides a major advantage for renewable energy sources such as solar panels and wind turbines.

Most industrial and consumer lithium-ion batteries can fully charge the battery, and they extend the life of the lithium ion by lowering the end-of-charge voltage and accepting a shorter running time, without providing adjustable end-of-charge voltage.

Simple Guidelines for Charging Lithium-based Batteries

To allow the current to drop unimpeded during saturation, the device should be shut down or the live load disconnected. Parasitic loads confuse chargers.

You can’t charge it at freezing temperature, you charge it at the right temperature.

For lithium ions, a partial charge is better than a full charge.

When the “ready” signal appears, the battery may not be fully charged and the fuel gauge is 100% false, so not all chargers are fully charged.

When the battery temperature is too high, stop using the charger and battery immediately.

An empty battery is ideally charged 40-50% of the SoC before storage.

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