Understand how mobile phone chargers work

Speaking of this lithium-ion battery, first briefly introduce the so-called lithium-ion battery is the use of carbon materials can absorb and dissociate lithium ion as the negative electrode active material, lithium ion symbol Li-ion. As we all know, batteries are generally composed of basic elements such as positive electrodes, negative electrodes, separators, and electrolytes. These materials used in lithium-ion batteries are generally the following:

Positive electrode: lithium cobalt oxide (LiCoO2), lithium nickelate (LiNiO2), lithium manganese oxide (LiMn2O4), etc.;

Negative electrode: artificial graphite series, natural graphite series, coke series, etc.;

Diaphragm: Single-layer or multi-layer microporous film composed of polyethylene (PE), polypropylene (PP), etc.;

Electrolyte: One or two of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), etc. A mixture of yuan or ternary.

Most of the lithium-ion batteries sold on the market are lithium cobalt oxide as the positive electrode and graphite series as the negative electrode battery.

The working mechanism of the lithium ion battery is as follows: when the battery is charged, lithium in the positive electrode material forms ions and is embedded in the negative electrode modified graphite layer; when the battery is discharged, lithium ions are extracted from the graphite layer and are filled back into the positive electrode through the separator. Lithium cobalt oxide in the layered structure. Lithium ions are continuously inserted and extracted from the positive electrode and the negative electrode as charging and discharging progress. Therefore, it is also known as a "rocking chair battery." The rated voltage of a lithium-ion battery cell is 3.6V, the charge limiting voltage is 4.2V, and the discharge limiting voltage is 2.5V.

Lithium-ion battery charging process is divided into two steps: first constant current charging, the current is constant, the voltage is rising, when the voltage is charged to 4.2V automatically converted to constant voltage charging, constant voltage charging, the voltage is constant, current It's getting smaller and smaller until the charging current is less than the preset value, so when someone charges the phone battery with direct charge, the battery display is full, but the display is still charging. In fact, the voltage at this time has reached 4.2V, so the battery shows a full grid. At that time, the constant voltage charging process was in progress. Then one might ask why it is easy to explain why the constant voltage charging is required to directly charge the constant current to 4.2V. Because each battery has a certain internal resistance, when charging to 4.2V with a constant current, the 4.2V is actually not the actual voltage of the battery, but the voltage of the battery plus the voltage consumed by the internal resistance of the battery. And, if the current is large, then the voltage consumed in the internal resistance is also very large, so that is the actual battery voltage may be much smaller than 4.2V, so use a constant voltage Electrical process, the charging current gradually down, so that the actual voltage of the battery is very close 4.2V.