What are the charging and discharging characteristics of lithium ion batteries?
LiCoO 2, LiNiO 2 and LiMnO 2 are used as the positive electrode of the core. LiCoO 2 is a crystal with stable layer structure, but the structure may change after removing x Li ions from LiCoO 2, but the change depends on the size of X.
It is found that when x > 0.5, the structure of Li1-xCoO2 is extremely unstable, and the crystal collapse occurs, and its external performance is the overwhelming end of the core. Therefore, the x value of Li1-xCoO2 should be controlled by limiting the charging battery voltage. Generally, the charging voltage is less than 4.2V and the x value is less than 0.5. At this time, the crystal form of Li1-xCoO2 is still stable.
Negative C6 has its own characteristics. When first formed, Li in positive LiCoO2 is charged to negative C6. When discharged, Li returns to positive LiCoO2, but after formed, a part of Li must remain in the center of negative C6 to ensure the normal embedding of Li in the next charge and discharge. Otherwise, the voltage of the battery will be very short, in order to ensure a part of it. In C6, Li is usually achieved by limiting the lower discharge voltage: the upper safe charge voltage is less than 4.2V, and the lower discharge voltage is more than 2.5V.
The principle of memory effect is crystallization, which is almost not produced in lithium batteries. However, the capacity of lithium ion batteries will drop after repeated charging and discharging. The reasons are complex and diverse. From the molecular level, the hole structure of lithium ion on the positive and negative electrode will gradually collapse and plug; from the chemical point of view, it is the passivation of the positive and negative electrode materials, resulting in side reactions to form stable other compounds. Physically, the cathode material will gradually peel off, which ultimately reduces the number of lithium ions in the battery that can move freely during charging and discharging.
Overcharge and overdischarge will cause permanent damage to the anode and cathode of lithium-ion batteries. From the molecular level, it can be intuitively understood that overdischarge will lead to excessive release of lithium ions from the anode carbon and lead to the collapse of its lamellar structure. Overcharge will push too many lithium ions into the anode carbon structure and cause the collapse of its lamellar structure. Some of the lithium ions can no longer be released.
Unsuitable temperatures will trigger other chemical reactions within the lithium-ion battery to produce compounds we do not want to see, so there are protective temperature-controlled diaphragms or electrolyte additives between the positive and negative electrodes of many lithium-ion batteries. When the temperature of the battery rises to a certain extent, the composite membrane hole closes or the electrolyte denatures, the internal resistance of the battery increases until the circuit is broken, and the battery is no longer heated to ensure the normal charging temperature of the battery.