How Lithium-ion Batteries Work

Taking LiCoO system lithium-ion secondary battery as an example to illustrate its working principle. Generally, lithium-ion secondary batteries are composed of a positive electrode, an electrolyte, a separator, and a negative electrode. During charging, the lithium ions in the positive electrode are released from the LiCoO layered structure. The valence of the Co element increases from +III to +IV. The positive electrode material undergoes an oxidation reaction. At the same time, the lithium ions migrate to the negative electrode of the battery through the electrolyte. LiCx is generated by combining with carbon in the layered structure of the carbon material. When the battery is connected to a load, the reactions that occur on the two electrodes are the reverse reactions of the reactions that occur during charging. The separator is located between the positive and negative reaction electrodes. The separator can transmit ions but does not allow electrons to pass through. At the same time, when a certain degree of micro short circuit occurs between the positive and negative electrodes of the battery, the separator also plays a blocking and protective role.

Lithium-ion batteries are rated at 3.6V. The voltage when the battery is fully charged (called the termination voltage) is generally 4.2V; the termination voltage of the lithium-ion battery is 2.5V. If the lithium-ion battery continues to be used after the voltage has dropped to 2.5V during use, it is called over-discharge, which will cause damage to the battery.
Lithium-ion batteries are relatively expensive. If its charging and usage requirements are not met, it is easy to explode and reduce its lifespan. Because lithium-ion batteries are very sensitive to temperature, overvoltage, overcurrent and overdischarge, all batteries have integrated thermistors (monitoring charging temperature) and protection circuits against overvoltage, overcurrent and overdischarge.