Date: 2024-02-22 hits: 233
As a power source or energy storage device, the performance of lithium battery directly affects the operation effect of the entire system.
The internal resistance of lithium battery is one of the important parameters to evaluate its performance, which involves the battery's charging and discharging capacity, energy efficiency, operating stability and safety.
Definition: The internal resistance of lithium batteries refers to the resistance existing inside the battery, including electrode material resistance, electrolyte resistance, diaphragm resistance and other internal structure resistance.
The size of the internal resistance directly affects the charge-discharge performance and efficiency of the battery.
Measurement method: There are many ways to measure the internal resistance of lithium batteries, of which the commonly used DC internal resistance measurement and AC internal resistance measurement two.
Dc internal resistance measurement is to calculate the internal resistance of the battery by charging and discharging the battery with DC power supply and measuring the corresponding current and voltage value when the polarization effect of the battery is small.
The AC internal resistance measurement is to use AC signal to stimulate the battery, and calculate the internal resistance by measuring the response signal of the battery.
Evaluation of the internal resistance of lithium batteries
1, battery performance evaluation: the internal resistance of lithium batteries is one of the important evaluation indicators of its performance.
By testing the internal resistance, the energy transfer efficiency and heating of the battery can be evaluated, and the performance of the battery can be understood.
2, Health monitoring: With the use of lithium batteries, their performance will gradually decay, manifested as capacity attenuation and internal resistance increase.
By continuously monitoring the change of internal resistance, the health of the battery can be judged and the life of the battery can be predicted.
3, system SOC and SOP estimation: In practical applications, the DC internal resistance can be used to estimate the SOC (state of charge) and SOP (state of power) of the system.
Since the SOP and OCV-SOC tested by the battery factory are tested for a single cell, the overall value will be different after the battery group runs for a period of time. At this time, it is necessary to use the measured DC internal resistance to fit and correct the data.
4, balance management: the DC internal resistance of lithium batteries is of great help to the entire balance management.
In practical application, the DC internal resistance obtained by measurement can be used for balanced management to ensure the consistency of the battery.
5, protection logic: In the battery management system, the detection of DC internal resistance can determine the connection status of the module, and timely feedback can be made for the loose connection, and then trigger the corresponding protection logic.
6, power management: In power management, it is necessary to calculate the output capacity of the battery through the internal resistance of the battery.
The specific internal resistance model needs to be combined with the data of the single cell for group management.
In summary, the role of evaluating the internal resistance of lithium batteries is multi-faceted, involving battery performance evaluation, health monitoring, system SOC and SOP estimation, balance management, protection logic and power management.
Therefore, in practical applications, it is necessary to regularly test the internal resistance of lithium batteries.
Factors affecting the internal resistance of lithium batteries
1. Electrode material: Electrode material is one of the important factors affecting the internal resistance of lithium batteries. Different materials have different conductivity to electrons and ions, which affects the internal resistance of the battery. Commonly used electrode materials are graphite, lithium cobaltate, lithium iron phosphate and so on.
2. Electrolyte: electrolyte plays a role in the transmission of ions in lithium batteries, and its resistance directly affects the internal resistance of the battery. The higher the ionic conductivity of the electrolyte, the smaller the internal resistance of the battery.
3. Diaphragm: diaphragm is a material that separates the positive and negative electrodes, and it needs to have both electronic insulation and ion conductivity. Factors such as the quality of the diaphragm and the size of the aperture will also affect the internal resistance of the battery.
4. Temperature: Temperature has a greater impact on the internal resistance of lithium batteries. With the increase of temperature, the fluidity of the electrolyte is enhanced, the ionic conductivity is increased, and the internal resistance of the battery is reduced. However, too high a temperature will have a negative impact on battery performance, so it is necessary to control the temperature reasonably.
5. Battery capacity: There is a relationship between battery capacity and internal resistance. As the battery capacity increases, the surface area of the electrode material increases, thereby reducing the resistance of the electrode material to contact with the electrolyte, but too much capacity may increase the volume and weight of the battery, which is not conducive to practical applications
Methods to reduce the internal resistance of lithium batteries
1. Optimize electrode materials: The selection of electrode materials with good conductivity is an effective way to reduce the internal resistance of lithium batteries. For example, the use of porous electrode materials, nanostructured electrode materials, etc., can increase the surface area of the electrode material, improve the transmission efficiency of electrons and ions, and thus reduce the internal resistance.
2. Improve the ionic conductivity of the electrolyte: the selection of high ionic conductivity of the electrolyte, adding additives to improve the ionic conductivity of the electrolyte can effectively reduce the internal resistance of the battery. In addition, the use of homomorphic electrolytes can also significantly reduce internal resistance and improve battery performance.
3. Improve the diaphragm performance: By improving the diaphragm preparation process, increasing the diaphragm pore size and porosity, the diaphragm resistance can be reduced, thereby reducing the internal resistance of the battery. In addition, the multi-layer diaphragm structure can also improve the ion transport efficiency and reduce the internal resistance.
4. Control the temperature: During the operation of the lithium battery, reasonable control of the temperature can reduce the internal resistance changes caused by temperature changes. The advanced thermal management system can effectively control the temperature of the battery to ensure that the base works in the appropriate temperature range.
5. Reasonable design of battery structure and size: Reasonable design of battery structure and size according to actual needs can reduce the internal resistance of the battery. For example, using a laminated structure instead of a cylindrical structure, reducing the thickness of the electrode sheet and other methods can reduce the internal resistance of the battery.
