What problems will occur when lithium batteries are overcharged, overdischarged, and mixed?

What is overcharge and how does it affect battery performance?

Overcharge refers to the behavior of continuing to charge the battery after a certain charging process is fully charged.

Because the capacity of the negative electrode is higher than the capacity of the positive electrode in the design, the gas produced by the positive electrode penetrates the separator paper and is combined with the cadmium produced by the negative electrode. Therefore, under normal circumstances, the internal pressure of the battery will not increase significantly, but if the charging current is too large or the charging time is too long, the oxygen generated is too late to be consumed, which may cause the internal pressure to rise, battery deformation, and liquid leakage. And other undesirable phenomena. At the same time, its electrical performance will also be significantly reduced.

What is over-discharge and how does it affect battery performance?

The battery has discharged the internally stored power and the voltage reaches After a certain value, continued discharge will cause over-discharge, and the discharge cut-off voltage is usually determined according to the discharge current. 0.2C-2C discharge is generally set to 1.0V/piece, 3C or more, such as 5C or 10C discharge is set to 0.8V/piece, battery over-discharge may bring catastrophic consequences to the battery, especially high current over-discharge, or Repeated over-discharge has a greater impact on the battery. Generally speaking, over-discharge will increase the internal pressure of the battery, and the reversibility of the positive and negative active materials will be destroyed. Even if it is charged, it can only be partially restored, and the capacity will be significantly attenuated.

What will happen if batteries of different capacities are used in combination?

If batteries of different capacities or new and old batteries are mixed together Use, there may be leakage, zero voltage and other phenomena. This is because during the charging process, the capacity difference causes some batteries to be overcharged and some batteries are not fully charged. During discharging, some batteries with high capacity are not fully discharged, and batteries with low capacity are overdischarged. In such a vicious circle, the battery is damaged and leaks or has a low (zero) voltage.