Taking a lithium-ion battery with LiFePO4 as the cathode material as an example, charging begins ↓
Before charging, lithium ions are embedded in the layered structure of the cathode material.
After charging begins, the positive electrode material loses electrons,and lithium ions are extracted from it.
Positive electrode reaction: Lithium ion extraction, LiFePO4- xe⁻→ Li1-xFePO4 + xLi ⁺
Fe²⁺ ions lose electrons. Since not all lithium ions are extracted, the charging efficiency is not 100%.
Lithium ions pass through the electrolyte and separator to reach the negative electrode graphite material.
Lithium ions are inserted into the graphite layer, while electrons reach the negative electrode through the external circuit. The electrode reaction is: xLi⁺+ x e⁻+ 6C →LixC6
The lithium ions gain electrons, forming a relatively stable lithium-intercalated (lithium with a valence of 0, i.e., a special form of elemental lithium) graphite.
As charging continues, the cathode material continuously loses electrons, and lithium ions continuously intercalate and deintercalate until charging is complete.
As the electric vehicle is in motion, the lithium-ion battery begins to discharge↓
Electrons leave (de-intercalate) from the negative electrode material and flow to the positive electrode through the external circuit. The electrode reaction is: LixC6 – xe⁻→ xLi⁺ + 6C
The lithium ions generated after losing electrons also de-intercalate from the graphite layers.
After being deintercalated from the negative electrode, lithium ions return to the positive electrode through the electrolyte and separator. The electrode reaction is as follows: Li₁₋xFePO4+xLi⁺+ xe⁻ →LiFePO4
After lithium ion intercalation, a relatively stable lithium-intercalated positive electrode material, LiFePO4, is formed.
The above describes the microscopic movement of lithium ions during charging and discharging.
