1. Capacity of lithium-ion batteries
The capacity of a battery can be divided into rated capacity and actual capacity. The rated capacity of a battery refers to the amount of electricity that the battery should provide when discharged at a rate of 5C to the termination voltage under an ambient temperature of 20 ℃± 5 ℃, expressed in 5C. The actual capacity of a battery refers to the actual amount of electricity released by the battery under certain discharge conditions, mainly influenced by the discharge rate and temperature (therefore, strictly speaking, the battery capacity should indicate the charging and discharging conditions). Capacity units: mAh, Ah (1Ah=1000mAh).
2. Internal resistance of lithium-ion battery
Internal resistance of a battery refers to the resistance experienced by the current flowing through the battery during operation. It consists of two parts: ohmic internal resistance and polarization internal resistance. A high internal resistance value of the battery can lead to a decrease in the discharge working voltage and a shortened discharge time. The size of internal resistance is mainly influenced by factors such as the material, manufacturing process, and battery structure of the battery. The internal resistance of a battery is an important parameter for measuring its performance.
3. Voltage of lithium-ion batteries
Open circuit voltage refers to the potential difference between the positive and negative terminals of a battery when there is no current flowing through the circuit and it is not in operation. In general, the open circuit voltage of lithium-ion batteries is about 4.2V after being fully charged, and about 3.0V after discharge. By detecting the open circuit voltage of the battery, the state of charge of the battery can be determined.
Working voltage, also known as terminal voltage, refers to the potential difference between the positive and negative terminals of a battery when there is current flowing through the circuit during operation. In the discharge state of the battery, when the current flows through the inside of the battery, there is no need to overcome the resistance caused by the internal resistance of the battery, so the working voltage is always lower than the open circuit voltage, and the opposite is true during charging. The discharge working voltage of lithium-ion batteries is around 3.6V.
4. Discharge plateau time of lithium-ion batteries
The discharge platform time refers to the discharge time to a certain voltage when the battery is fully charged. For example, measure the discharge platform time of a certain ternary battery at 3.6V. Charge it to a constant voltage of 4.2V and stop charging when the charging current is less than 0.02C. After fully charging, let it stand for 10 minutes. The discharge platform time at any rate of discharge current is the discharge platform time at that current. Due to the voltage requirements of some appliances using lithium-ion batteries, if the operating voltage is lower than the required value, it may cause malfunction. So the discharge platform is one of the important standards for measuring the performance of batteries.
5. Charging and discharging rate of lithium-ion batteries
The charge discharge ratio refers to the current required for a battery to discharge its rated capacity within a specified time. 1C is numerically equal to the battery's rated capacity, usually represented by the letter C. If the nominal rated capacity of the battery is 10Ah, then 10A is 1C (1 rate), 5A is 0.5C, 100A is 10C, and so on.
6. Self discharge rate of lithium-ion batteries
Self discharge rate, also known as charge retention capacity, refers to the ability of a battery to maintain the amount of electricity stored under certain conditions in an open circuit state. Mainly influenced by factors such as the manufacturing process, materials, and storage conditions of batteries. It is an important parameter for measuring battery performance.
Charging efficiency refers to a measure of the degree to which the electrical energy consumed by a battery during the charging process is converted into the chemical energy that the battery can store. Mainly affected by battery technology, formula, and working environment temperature of the battery. Generally, the higher the ambient temperature, the lower the charging efficiency.
Discharge efficiency refers to the ratio of the actual amount of electricity discharged to the terminal voltage under certain discharge conditions to the rated capacity of the battery. It is mainly affected by factors such as discharge rate, environmental temperature, internal resistance, etc. Generally, the higher the discharge rate, the lower the discharge efficiency. The lower the temperature, the lower the discharge efficiency.
7. The cycle life of lithium-ion batteries
The battery cycle life refers to the number of times a battery experiences charging and discharging under a certain charging and discharging system when its capacity drops to a specified value. According to the GB regulations for lithium-ion batteries, the capacity retention rate after 500 cycles under 1C conditions is above 60%.