Related characteristics of lithium batteries
1. State of charge SOC
The state of charge can be defined as the state of available electrical energy in the battery, usually expressed as a percentage. Because the available electrical energy varies with charge and discharge current, temperature and aging, the definition of state of charge is also divided into two types: Absolute State-Of-Charge (ASOC) and Relative State-Of-Charge (ASOC) State-Of-Charge; RSOC). Normally the relative state of charge range is 0%-100%, while the battery is 100% when fully charged and 0% when fully discharged. The absolute state of charge is a reference value calculated according to the designed fixed capacity value when the battery is manufactured. The absolute state of charge of a brand new fully charged battery is 100%; and even if an aging battery is fully charged, it cannot reach 100% under different charging and discharging conditions.
2. Max Charging Voltage
The maximum charging voltage is related to the chemical composition and characteristics of the battery. The charging voltage of lithium battery is usually 4.2V and 4.35V, and the voltage value will be different if the cathode and anode materials are different.
3. Fully Charged
When the difference between the battery voltage and the highest charging voltage is less than 100mV, and the charging current drops to C/10, the battery can be regarded as fully charged. The battery characteristics are different, and the full charge conditions are also different.
4. Charge and discharge rate (C-Rate)
The charge-discharge rate is an expression of the charge-discharge current relative to the battery capacity. For example, if 1C is used to discharge for one hour, ideally, the battery will be completely discharged. Different charge and discharge rates will result in different usable capacity. Generally, the greater the charge-discharge rate, the smaller the available capacity.
5. Cycle life
The number of cycles is the number of times a battery has undergone complete charging and discharging, which can be estimated from the actual discharge capacity and the design capacity. Whenever the accumulated discharge capacity is equal to the design capacity, the number of cycles is once. Usually after 500 charge and discharge cycles, the capacity of a fully charged battery drops by 10% ~ 20%.
The calculation method of the number of cycles is generally to count how much power the battery has discharged. For example, if the battery releases a total of 1C of power, the number of cycles is increased by 1;
6. Self-Discharge
The self-discharge of all batteries increases as the temperature rises. Self-discharge is basically not a manufacturing defect, but the characteristics of the battery itself. However, improper handling in the manufacturing process can also cause an increase in self-discharge. Generally, the self-discharge rate doubles for every 10°C increase in battery temperature. The monthly self-discharge of lithium-ion batteries is about 1~2%, while the monthly self-discharge of various nickel-based batteries is 10-15%.
6. Battery capacity (unit: mAh)
The capacity of the battery is determined by the amount of active material in the battery, usually expressed in milliampere-hour mAh or Ah. For example, 1000 mAh can be converted into a charge of about 3600 C with a current of 1 A for 1 h.
7. Battery open circuit voltage
When the battery is neither charged nor discharged, the positive and negative terminal voltages. When the battery is charging or discharging, due to the internal resistance of the battery, the voltage across the battery is greater than or less than the current open circuit voltage of the battery;
