Self-discharge test method:
1. Measuring Capacity Loss After a Period of Battery Rest: The original purpose of self-discharge research is to study the capacity loss of batteries after resting. However, the following reasons make it difficult to perform capacity loss testing: A. The irreversibility of the charging process is too great. Even if discharging occurs immediately after charging, it is difficult to guarantee that the discharge capacity/charge capacity ratio is within 100% ± 0.5%. Such a large error requires a very long rest period between tests, which obviously does not meet the needs of daily production. B. Testing capacity requires a large amount of electricity, manpower, and resources, and the process is complex and adds to costs. Based on the above two considerations, the measurement of the discharge capacity after resting compared to the previous charging capacity is generally not used as the standard for battery self-discharge.
2. Measuring the K-value over a period of time: A very important indicator for measuring the degree of self-discharge is the K-value = ΔOCV/Δt. The common unit for the K-value is mV/d, but this depends on the manufacturer's standards (or the manufacturer's personal preference), the battery's performance, and the measurement conditions. Calculating the K-value by measuring the voltage twice is simpler and has less error; therefore, the K-value is a conventional method for measuring battery self-discharge. Please note that the following text may use the terms K-value and self-discharge interchangeably.
The circuit mainly consists of a lithium-ion battery protection dedicated integrated circuit DW01, a charge and discharge control MOSFET1 (containing two N-channel MOSFETs), etc. The individual lithium-ion battery is connected between B+ and B-, and the battery pack outputs voltage from P+ and P-.
During charging, the charger output voltage is connected between P+ and P-. Current flows from P+ to the B+ and B- terminals of the individual battery, and then through the charging control MOSFET to P-. During charging, when the voltage of an individual battery exceeds 4.35V, the OC pin of the dedicated integrated circuit DW01 outputs a signal to turn off the charging control MOSFET, immediately stopping the lithium-ion battery from charging and preventing damage from overcharging.
During discharge, when the voltage of a single cell drops to 2.30V, the OD pin of DW01 outputs a signal to turn off the discharge control MOSFET, and the lithium-ion battery immediately stops discharging, thus preventing damage to the lithium-ion battery due to over-discharge. The CS pin of DW01 is a current detection pin. When the output is short-circuited, the on-state voltage drop of the charge/discharge control MOSFET increases sharply, the voltage at the CS pin rises rapidly, and the output signal of DW01 turns off the charge/discharge control MOSFET quickly, thereby achieving overcurrent or short-circuit protection.
