Charging and discharging of lithium ion battery – 12 charge/discharge methods
Table of Contents
As a kind of “chemical energy – electric energy” mutual conversion energy device, lithium batteries are bound to charge and discharge in the process of use. Reasonable charge and discharge method can not only reduce the degree of damage of lithium battery, but also give full play to the performance of lithium battery.
What is Charging and discharging of lithium ion battery
Lithium battery is composed of cathode, anode, separator and electrolyte. The lithium battery separator allows lithium ions to pass through, but not electrons.
When charging, under the action of an external power source, lithium atoms on the cathode break down into electrons and lithium ions so the lithium ions will move through the separator to the lithium ion battery anode, and the electrons will move through the outer circuit to the anode. When discharging, the lithium atoms on the lithium ion battery anode break down into electrons and lithium ions, which pass through an outer circuit to the positive end and through a separator to the cathode. This process is called the charging and discharging of lithium ion battery.
Charging method of lithium ion battery
Whether it is power battery or consumer battery, the industry and standard recommended charging method of lithium battery is constant current constant voltage (CC-CV) charging. In addition to the standard CC-CV charging mode, lithium battery can also be CC charged, CV charged, CP charged, CP-CV charged and so on.
Constant current charge
CC charge is short for constant current charge. During the whole charging process, the current is constant and the voltage increases gradually. Suggestion: Allow to use this method.
CC charge curve
Constant voltage charge
CV charge is short for constant voltage charge. The voltage at the moment of charging reaches the set value and the current is in the peak state. As shown in the figure below, after the discharge of lithium battery reaches 3.0V, the instantaneous charging current of 4.2V constant voltage reaches about 17.5C, and then the current gradually decreases until the charging ends after reaching the set value. Suggestion: Do not use this method.
CV charge curve
Constant current and constant voltage charge
CC-CV charge is short for constant current and constant voltage charge. This charging mode is the combination of CC charging and CV charging. During the charging process, the current first remains constant, and when the voltage is charged to the upper limit voltage, the voltage remains constant and unchanged. Finally, the charging ends after the current gradually decreases to the set value. Suggestion: Allow to use this method.
CC-CV charge curve
Constant power charge
CP charge is short for constant power charge. The power is kept constant during the charging process, and the current will gradually decrease as the voltage increases during charging. Suggestion: Allow to use this method.
CP charge curve
Constant power and constant voltage charge
CP-CV charge is short for constant power and constant voltage charge. It is a combination of constant power charging and constant voltage charging. First, constant power charging to the termination voltage, and then keep the voltage constant. When the current decreases to the set value, the charging ends. Suggestion: Allow to use this method.
CP-CV charge curve
Discharging method of lithium ion battery
In addition to the CC discharge mode required by the standard, lithium batteries can also perform CV discharge, CC-CV discharge, CP discharge, CP-CC-CV discharge, CR discharge, CR-CV discharge and so on.
Constant current discharge
CC discharge is short for constant current discharge. It is the most common discharge mode of lithium battery. During the whole discharge process, the current remains constant, the voltage gradually decreases to the termination voltage, and the discharge ends. Suggestion: Allow to use this method.
CC discharge curve
Constant voltage discharge
CV discharge is short for constant voltage discharge. The voltage reaches the set value and the current is in the peak state. As shown in the figure below, set the constant voltage discharge of lithium battery to 3.0V, and the instant discharge current reaches 30C-35C, then the current gradually decreases, and the discharge ends when it reaches the set value. Suggestion: Do not use this method.
CV discharge curve
Constant current and constant voltage discharge
CC-CV discharge is short for constant current and constant voltage discharge. It is a combination of CC discharge and CV discharge. First, discharge with a constant current to the termination voltage, keep the voltage unchanged, and then the current gradually decreases to the set value, the discharge ends. Suggestion: Allow to use this method.
CC-CV discharge curve
Constant power discharge
CP discharge is short for constant power discharge. The power is kept constant during discharge. As the voltage decreases during discharge, the current increases gradually. Suggestion: Allow to use this method.
CP discharge curve
Constant power and constant current and constant voltage discharge
CP-CC-CV discharge is short for constant power and constant current and constant voltage discharge. It is a combination discharge method of CP, CC and CV, The constant power is discharged to the termination voltage first. When the current at the end of CP is greater than the CC current at the next stage, the CC discharge voltage will first rise and then decrease to the termination voltage, and then the voltage is constant until the current decreases to the set value, and the discharge ends. Suggestion: Allow to use this method.
CP-CC-CV discharge curve
Constant resistance discharge
CR discharge is short for constant resistance discharge. It is equivalent to an external resistance. According to U=I* (R external +DCR), because the external resistance is large enough, the current value will gradually decrease with the decrease of voltage in the process of constant resistance discharge. Suggestion: Allow to use this method.
CR discharge curve
Constant resistance and constant voltage discharge
CR-CV discharge is short for constant resistance and constant voltage discharge. It is a combination of CR discharge and CV discharge, that is, first discharge to the termination voltage with constant resistance, and then keep the voltage constant and unchanged. When the current decreases to the set value, the discharge ends. Suggestion: Allow to use this method.
CR-CV discharge curve
To sum up, there are various methods for the charging and discharging of lithium ion battery, but in the final analysis, they are single-step or combined processes based on CC (constant current), CV (constant voltage), CP (constant power) or CR (constant resistance). The current and voltage changes of these charging and discharging methods are referred to the following table.
Current and voltage change
At present, the mainstream charging mode of lithium battery is still CC-CV, which is because the polarization phenomenon exists in lithium battery (the immediate voltage is not the steady-state voltage). In the CC stage, the current is large and the charging speed is fast. After the voltage rises to the upper voltage, the constant potential is maintained, and the external circuit electrons and Li+ react together at the negative electrode. The number of electrons involved in the reaction decreases and the current decreases gradually. When the current decreases to 0 (ideally), the polarization is completely eliminated and the lithium battery is fully charged.
However, CC mode is usually adopted in the discharge process of lithium batteries, which may be to facilitate the calculation of capacity or the estimation of SOC. In actual conditions, constant power discharge is mostly used.
Summary
The choice of charging and discharging of lithium ion battery should consider the convenience of data processing, charging/discharging efficiency and the risk of internal damage to lithium battery, which should not only give full play to the performance of lithium battery, but also rapid and accurate detection. At present, the detection of lithium battery is mainly based on CC-CV charging mode and CC discharge mode, but in the actual terminal use condition, CP mode is mainly used.
Charging and discharging of lithium ion battery – 12 charge/discharge methods
Table of Contents
As a kind of “chemical energy – electric energy” mutual conversion energy device, lithium batteries are bound to charge and discharge in the process of use. Reasonable charge and discharge method can not only reduce the degree of damage of lithium battery, but also give full play to the performance of lithium battery.
What is Charging and discharging of lithium ion battery
Lithium battery is composed of cathode, anode, separator and electrolyte. The lithium battery separator allows lithium ions to pass through, but not electrons.
When charging, under the action of an external power source, lithium atoms on the cathode break down into electrons and lithium ions so the lithium ions will move through the separator to the lithium ion battery anode, and the electrons will move through the outer circuit to the anode.
When discharging, the lithium atoms on the lithium ion battery anode break down into electrons and lithium ions, which pass through an outer circuit to the positive end and through a separator to the cathode.
This process is called the charging and discharging of lithium ion battery.
Charging method of lithium ion battery
Whether it is power battery or consumer battery, the industry and standard recommended charging method of lithium battery is constant current constant voltage (CC-CV) charging. In addition to the standard CC-CV charging mode, lithium battery can also be CC charged, CV charged, CP charged, CP-CV charged and so on.
Constant current charge
CC charge is short for constant current charge. During the whole charging process, the current is constant and the voltage increases gradually. Suggestion: Allow to use this method.
Constant voltage charge
CV charge is short for constant voltage charge. The voltage at the moment of charging reaches the set value and the current is in the peak state. As shown in the figure below, after the discharge of lithium battery reaches 3.0V, the instantaneous charging current of 4.2V constant voltage reaches about 17.5C, and then the current gradually decreases until the charging ends after reaching the set value. Suggestion: Do not use this method.
Constant current and constant voltage charge
CC-CV charge is short for constant current and constant voltage charge. This charging mode is the combination of CC charging and CV charging. During the charging process, the current first remains constant, and when the voltage is charged to the upper limit voltage, the voltage remains constant and unchanged. Finally, the charging ends after the current gradually decreases to the set value. Suggestion: Allow to use this method.
Constant power charge
CP charge is short for constant power charge. The power is kept constant during the charging process, and the current will gradually decrease as the voltage increases during charging. Suggestion: Allow to use this method.
Constant power and constant voltage charge
CP-CV charge is short for constant power and constant voltage charge. It is a combination of constant power charging and constant voltage charging. First, constant power charging to the termination voltage, and then keep the voltage constant. When the current decreases to the set value, the charging ends. Suggestion: Allow to use this method.
Discharging method of lithium ion battery
In addition to the CC discharge mode required by the standard, lithium batteries can also perform CV discharge, CC-CV discharge, CP discharge, CP-CC-CV discharge, CR discharge, CR-CV discharge and so on.
Constant current discharge
CC discharge is short for constant current discharge. It is the most common discharge mode of lithium battery. During the whole discharge process, the current remains constant, the voltage gradually decreases to the termination voltage, and the discharge ends. Suggestion: Allow to use this method.
Constant voltage discharge
CV discharge is short for constant voltage discharge. The voltage reaches the set value and the current is in the peak state. As shown in the figure below, set the constant voltage discharge of lithium battery to 3.0V, and the instant discharge current reaches 30C-35C, then the current gradually decreases, and the discharge ends when it reaches the set value. Suggestion: Do not use this method.
Constant current and constant voltage discharge
CC-CV discharge is short for constant current and constant voltage discharge. It is a combination of CC discharge and CV discharge. First, discharge with a constant current to the termination voltage, keep the voltage unchanged, and then the current gradually decreases to the set value, the discharge ends. Suggestion: Allow to use this method.
Constant power discharge
CP discharge is short for constant power discharge. The power is kept constant during discharge. As the voltage decreases during discharge, the current increases gradually. Suggestion: Allow to use this method.
Constant power and constant current and constant voltage discharge
CP-CC-CV discharge is short for constant power and constant current and constant voltage discharge. It is a combination discharge method of CP, CC and CV, The constant power is discharged to the termination voltage first. When the current at the end of CP is greater than the CC current at the next stage, the CC discharge voltage will first rise and then decrease to the termination voltage, and then the voltage is constant until the current decreases to the set value, and the discharge ends. Suggestion: Allow to use this method.
Constant resistance discharge
CR discharge is short for constant resistance discharge. It is equivalent to an external resistance. According to U=I* (R external +DCR), because the external resistance is large enough, the current value will gradually decrease with the decrease of voltage in the process of constant resistance discharge. Suggestion: Allow to use this method.
Constant resistance and constant voltage discharge
CR-CV discharge is short for constant resistance and constant voltage discharge. It is a combination of CR discharge and CV discharge, that is, first discharge to the termination voltage with constant resistance, and then keep the voltage constant and unchanged. When the current decreases to the set value, the discharge ends. Suggestion: Allow to use this method.
To sum up, there are various methods for the charging and discharging of lithium ion battery, but in the final analysis, they are single-step or combined processes based on CC (constant current), CV (constant voltage), CP (constant power) or CR (constant resistance). The current and voltage changes of these charging and discharging methods are referred to the following table.
At present, the mainstream charging mode of lithium battery is still CC-CV, which is because the polarization phenomenon exists in lithium battery (the immediate voltage is not the steady-state voltage).
In the CC stage, the current is large and the charging speed is fast. After the voltage rises to the upper voltage, the constant potential is maintained, and the external circuit electrons and Li+ react together at the negative electrode. The number of electrons involved in the reaction decreases and the current decreases gradually. When the current decreases to 0 (ideally), the polarization is completely eliminated and the lithium battery is fully charged.
However, CC mode is usually adopted in the discharge process of lithium batteries, which may be to facilitate the calculation of capacity or the estimation of SOC. In actual conditions, constant power discharge is mostly used.
Summary
The choice of charging and discharging of lithium ion battery should consider the convenience of data processing, charging/discharging efficiency and the risk of internal damage to lithium battery, which should not only give full play to the performance of lithium battery, but also rapid and accurate detection. At present, the detection of lithium battery is mainly based on CC-CV charging mode and CC discharge mode, but in the actual terminal use condition, CP mode is mainly used.