Analyze the charging and discharging theory of lithium batteries

1.1 State-Of-Charge (SOC) The state-of-charge can mean the state of available electric energy in the battery, usually expressed as a percentage. Because the available electrical energy varies with charge and discharge current, temperature and aging phenomena, the meaning of the state of charge is also divided into two types: Absolute State-Of-Charge; ASOC) and Relative State-of-charge (RelativeState- Of-Charge; RSOC). Usually the relative state of charge ranges from 0% to 100%, while the battery is 100% when fully charged and 0% when fully discharged. The absolute state of charge is a reference value calculated based on 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. Shows the relationship between voltage and battery capacity at different discharge rates. The higher the discharge rate, the lower the battery capacity. When the temperature is low, the battery capacity will also decrease. 1.2 The maximum charging voltage (MaxChargingVoltage) 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. 1.3 FullyCharged (FullyCharged) 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. Shown as a typical lithium battery charging characteristic curve. When the battery voltage is equal to the highest charging voltage and the charging current is reduced to C/10, the battery is regarded as fully charged. 1.4 Minimum Discharging Voltage (MiniDischargingVoltage) The minimum discharge voltage can be defined by the cut-off discharge voltage, which is usually the voltage when the state of charge is 0%. This voltage value is not a fixed value, but changes with load, temperature, aging degree, or other factors. 1.5 Fully Discharge (FullyDischarge) When the battery voltage is less than or equal to the minimum discharge voltage, it can be called a full discharge. 1.6 Charge-discharge rate (C-Rate) Charge-discharge rate is an expression of charge-discharge current related to 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. 1.7 Cycle Life Cycle number is the number of times a battery has undergone complete charge and discharge, 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% to 20%. 1.8 Self-Discharge (Self-Discharge) The self-discharge of all batteries will increase as the temperature rises. Self-discharge is basically not a manufacturing defect, but the characteristics of the battery itself. However, improper solutions in the manufacturing process can also cause an increase in self-discharge. Normally, the self-discharge rate doubles every time the battery temperature increases by 10°C. The monthly self-discharge of lithium batteries is about 1~2%, while the monthly self-discharge of various nickel-based batteries is 10-15%. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: How to test and repair lithium batteries