Charging and Discharging Li-ion Cells / Batteries Systems

Find out how to extend your Battery Systems using the best charging methods

When charging and discharging batteries a chemical reaction occurs, but with lithium ions there is an exception. Scientists speak of the energies flowing into and out of the battery as part of the movement of ions between the anode and the cathode. If scientists were right, according to this statement the battery would live forever but it is not. They blame the fading of the trapped ions, but as with all battery systems, internal corrosion and other degenerative effects also known as parasitic reactions on the electrolyte and electrodes play a role.

The lithium ion charger is a voltage limiting device that has similarities to the lead-acid battery system. Differences from Li-ion are found in higher voltage per cell, tighter voltage tolerances, and the absence of drip or float charge at full charge. While lead acid offers some flexibility in terms of cut-off voltage, Li-ion manufacturers are very decisive in the correct setting because Li-ion cannot accept any overload. The so-called "miracle charger" that promises to extend Battery Systems life and increase extra capacity does not exist. The Li-ion system is a "clean" system and only takes what it can absorb.

Charging cobalt batteries mixed with Li-ion

Specifically, we refer to Li-ion batteries made with the traditional cathode materials of cobalt, nickel, manganese and aluminum, charging typically at 4.20V / cell. Tolerance is +/- 50mV / cell. Some nickel-based varieties are charged at 4.10V / per cell; The high capacity Li-ion can go to 4.30V / per cell. Increasing the voltage also increases the capacity, but going beyond the specification can overcharge the battery. Protection circuits incorporated in the package do not allow exceeding the set voltage.

the variation of voltage and current when lithium ion passes through the current phases. Full load is reached when the current drops to between 3% and 5% of the Ah rating.

The temperature oscillation in the charge of a power cell is between 0.5C and 1C and the full charge time is approximately 2-3 hours. The manufacturers of these cells recommend charging at 0.8C or lower to prolong battery life. Most power cells can take a more powerful charger. The charging efficiency is around 99% and the cell stays cool during charging.

Some Li-ion batteries may experience a temperature rise of approximately 5ºC when fully charged. Discontinue use of the battery or charger if the temperature rises above 10ºC under moderate charging speeds.

Full charge occurs when the battery reaches the voltage threshold and the current drops to 3% of the rated current. A Battery Systems is also considered fully charged if the levels turn off and cannot drop any further. An increase in charge current does not advance a full charge. Although the battery reaches peak voltage faster, as a result the saturation charge will take longer. With higher current, Stage 1 is shorter, but saturation during Stage 2 will take longer. A high current charge, however, will quickly fill the battery to approximately 70%.

A Li-ion battery does not need to be fully charged as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge it because high voltage will overload the Battery Systems. Choosing a lower voltage threshold or eliminating saturation charging entirely prolongs battery life, but this reduces runtime. Chargers for other products go to maximum capacity and cannot be adjusted; so the useful life of the product itself is perceived as less important.

Some low-cost consumer chargers can use the simplified "charge and run" method that charges a lithium-ion battery in one hour or less without going to Stage 2 saturation charging. "Ready" appears when the Battery reaches threshold voltage in Stage 1. The state of charge (SoC) at this point is approximately 85%, a level that may be sufficient for many users. Some industrial chargers purposely set the charge voltage threshold lower to prolong battery life. Table 2 illustrates the estimated capacities when charged at different voltage thresholds with and without saturation charging.