With the use of lithium iron phosphate battery, battery performance continues to decline, mainly manifested as capacity decline, internal resistance increase, power decline, etc., the change of battery internal resistance is affected by temperature, discharge depth and other operating conditions. Resistance is the resistance to the flow of current through the battery when the lithium battery is working.Generally, the internal resistance of lithium battery is divided into ohm internal resistance and polarization internal resistance.
How big is the internal resistance of lithium iron phosphate battery?
The internal resistance of lithium iron phosphate battery mainly includes two parts, the ohm resistance and the polarization resistance under the condition of constant temperature, the ohm resistance is basically stable and unchanged, and the polarization resistance will change with the factors affecting the polarization level. The internal resistance of lithium iron phosphate battery, static internal resistance and working internal resistance are often different, in different environments, the internal resistance of different temperature also has a change.Lithium iron phosphate battery refers to lithium ion battery which uses lithium iron phosphate as anode material. The anode materials of lithium ion battery mainly include lithium cobalt acid, lithium manganese acid, lithium nickel acid, ternary material, lithium iron phosphate and so on. Lithium cobalt oxide is the anode material used in most lithium ion batteries. The internal resistance of the battery refers to the resistance encountered by the current flowing through the battery when the battery is working, which includes the ohm internal resistance and the polarization internal resistance, which also includes the electrochemical polarization internal resistance and the concentration polarization internal resistance.
Ordinary 18650 lithium battery, such as samsung 18650 lithium battery, internal resistance is generally less than 80 millieuro, the actual production is less than 65 millieuro. Power 18650 lithium battery because the discharge current is generally large, so the internal resistance will be small, such as samsung 18650-2200-5c power, the internal resistance is less than 35 mmos.
What factors affect the internal resistance of lithium battery?
1, the temperature
The internal resistance of lithium iron phosphate battery, as the main parameter to measure the degree of conductive ions and electronic transmission in the battery, directly determines the power characteristics of the battery, so it has an important impact on the power performance of electric vehicles. Electric vehicles actually run in a wide range of ambient temperature, in different temperatures and working conditions, the internal resistance of the battery is different. Grasp the internal relationship between battery resistance and temperature, SOC and charge-discharge ratio. With the increase of temperature, the ohm resistance and polarization resistance of lithium iron phosphate battery during charging and discharging process all decrease, and the ohm resistance change rate at different temperatures is higher than that at polarization, and the ohm resistance change rate at low temperature is higher than that at high temperature.
2, the impact of the membrane on ion impedance
The main influencing factors of membrane on ionic impedance include: electrolyte distribution, membrane area, thickness, pore size, porosity and tortuous coefficient, etc. For ceramic diaphragm, it is also necessary to prevent ceramic particles from blocking the pore of the diaphragm, which is not conducive to the passage of ions. When the electrolyte is fully infiltrated into the diaphragm, there can be no residual electrolyte, which reduces the use efficiency of the electrolyte.
3. Influence of structural design
In the design of battery structure, in addition to the riveting and welding of battery structure parts, the number, size and position of battery pole lugs directly affect the internal resistance of lithium iron phosphate battery. To a certain extent, increasing the number of pole ears can effectively reduce the internal resistance of the battery. The position of the pole ear also affects the internal resistance of the battery. The coil battery with the pole ear at the head of the anode and cathode has the largest internal resistance, and compared with the coil battery, the stack battery is equivalent to dozens of small batteries in parallel, and its internal resistance is smaller.
4. battery factors
(1) membrane internal electrolyte
(2) the anode internal electrolyte
(3) cathode internal electrolyte
(4) the level of technology, the pole production technology, coating is uniform, compaction density, the level of technology in the processing of these cells, will also cause a direct impact on the polarization of internal resistance.