Answering fans’ questions: In-depth interpretation of lithium battery internal resistance

Answering fans' private message questions and inquiries: What impact does the internal resistance of lithium batteries have on battery capacity and battery life, and how to choose new lithium batteries.

Lithium Meaning of battery internal resistance

The internal resistance of a lithium battery refers to the resistance encountered when the current flows inside the battery. It is like a water pipe. The rougher the inner wall, the greater the resistance to the water flow . The same is true when the current flows inside the battery. The size of the internal resistance will directly affect the performance of the battery.

The internal resistance mainly consists of the following two parts:

Ohmic internal resistance: It is mainly composed of electrode materials, electrolyte, diaphragm resistance and contact resistance of each part. It is the main part of battery internal resistance and is relatively stable.

Polarization internal resistance: resistance caused by electrochemical reactions, including electrochemical polarization and concentration polarization. It changes with the battery's charge and discharge state, temperature and other factors.

The influence of internal resistance and current on battery capacity attenuation

Internal resistance and capacity attenuation:

The greater the internal resistance, the more serious the battery heat: when charging and discharging with high current, the heat generated by the internal resistance will accelerate the decomposition of the electrolyte, causing the battery capacity to decay.

The internal resistance increases and the polarization phenomenon intensifies: the polarization phenomenon will reduce the utilization rate of the battery and will also cause capacity decay in the long run.

If the internal resistance is too large, the battery self-discharge will increase: If the internal resistance is too large, self-discharge will occur inside the battery, resulting in loss of battery capacity.

Current and capacity decay:

High current charging and discharging: will cause the internal temperature of the battery to rise, accelerate polarization and side reactions, and aggravate capacity decay.

Frequent high-current charging and discharging: will cause mechanical damage to the battery, accelerate the pulverization of the electrode material, and thus lead to capacity decay.

Internal resistance of a newly purchased battery: Is smaller the better or is a moderate value better?

Generally speaking, the smaller the internal resistance of a newly purchased battery, the better. The smaller the internal resistance, the better the battery performance, including:

Strong high current discharge capability: suitable for equipment that requires instantaneous bursts of high power, such as power tools, electric vehicles, etc.

Long cycle life: small internal resistance and less heat, which is beneficial to the life of the battery.

High energy conversion efficiency: The internal resistance is small, and the battery has high energy conversion efficiency, which can provide more available power.

Since the different manufacturing processes of lithium batteries with different forms and uses will directly affect the internal resistance of lithium batteries, the battery internal resistance data can be found in the data provided by the manufacturer, or the average value can be taken as a reference in the same battery rules.

Under the same capacity, the smaller the internal resistance, the better the performance?

Generally speaking, at the same capacity, the battery with smaller internal resistance has better performance.

Reference data:

18650 lithium-ion battery: The internal resistance is generally around 12 milliohms, and is generally around 13-15 milliohms.

Impact of internal resistance: For every 10 milliohms increase in internal resistance, the performance of the battery will decrease to a certain extent.

However, internal resistance is not the only indicator to measure battery performance. Other factors, such as the battery's chemical composition, structural design, production process, etc., will also affect the battery's performance.

Summarize:

When choosing a lithium battery, internal resistance is an important reference indicator. However, you cannot just look at the internal resistance, but also need to consider the battery capacity, voltage, cycle life, safety and other factors. It is recommended to choose a battery product produced by a regular manufacturer with a good reputation.

Kind tips:

Battery operating environment: Temperature that is too high or too low will have an adverse effect on battery performance.

Charging method: Using a suitable charger and charging method can extend the battery life.

Avoid over-discharge: Over-discharge can cause permanent damage to the battery.

I hope the above information is helpful to you. If you have any other questions, please feel free to ask them in private messages or on the message board.