The values of charging current and discharging current in aging testing have a significant impact on battery capacity, as follows:
1、 The influence of charging current size
Higher charging current
1. Initial capacity increase: In the early stages of aging testing, larger charging currents may cause the battery capacity to appear to increase. This is because high current charging can inject more charge into the battery in a shorter period of time, causing the terminal voltage of the battery to rise rapidly, which appears to increase the capacity on the surface. For example, for lithium-ion batteries, when a larger charging current is used, lithium ions quickly embed into the negative electrode material, and the state of charge (SOC) of the battery rapidly increases.
2. Accelerated capacity decay: However, long-term use of larger charging currents can lead to accelerated capacity decay of the battery. High current charging can cause structural changes in electrode materials, such as lithium dendrite growth and increased polarization of electrode materials in lithium-ion batteries. These changes will hinder the normal insertion and extraction of lithium ions, reducing the reversible capacity of the battery. At the same time, excessive heat generated by high current charging can accelerate internal side reactions of the battery, such as electrolyte decomposition and dissolution of active substances, further damaging the battery capacity. For example, after multiple high current charging cycles, the capacity of the battery may decrease by 10% -20% or even more.
3. Impact on battery consistency: In battery modules composed of multiple batteries, larger charging currents may lead to increased capacity differences between different batteries, affecting the overall performance and lifespan of the battery module. Due to slight differences in the internal resistance, capacity, and other characteristics of each battery, these differences can be amplified during high current charging, causing some batteries to reach full charge prematurely while others may not be fully charged yet. In the subsequent use process, the capacity decay rate of different batteries will also be different, which reduces the capacity consistency of the battery module.
Smaller charging current
1. Stable Capacity Growth: Low current charging is beneficial for the stable growth of battery capacity. In aging testing, low current charging can make lithium ions more evenly embedded in the negative electrode material, reducing structural damage and polarization phenomena of the electrode material. This helps to maintain the reversible capacity of the battery, allowing the battery capacity to gradually and steadily increase with the progress of charge and discharge cycles. For example, by conducting aging tests on lithium-ion batteries using low current slow charging, the capacity of the battery can maintain a relatively stable upward trend for a long time.
2. Extend battery life: Low current charging generates less heat, causing less damage to the internal structure and materials of the battery, thereby extending its service life. Throughout its entire lifespan, the battery is able to maintain a high level of capacity. For example, some application scenarios that require high battery life, such as energy storage systems, typically use low current charging to maintain battery capacity and performance.
3. Improve battery consistency: Low current charging can reduce the differences between batteries and improve the capacity consistency of battery modules. Due to the gentle charging process, the charging status of different batteries can be better synchronized, reducing capacity differences caused by uneven charging. For example, in electric vehicle battery packs, using low current balanced charging can effectively improve the overall capacity and performance of the battery pack.
2、 The Influence of Discharge Current Size
Larger discharge current
1. Temporary decrease in capacity: During aging testing, larger discharge currents can cause a temporary decrease in battery capacity. This is because during high current discharge, the polarization phenomenon inside the battery intensifies, and the speed of voltage drop accelerates. In order to meet the power demand of the load, the battery needs to operate at a higher discharge rate, which can cause the terminal voltage of the battery to rapidly decrease, resulting in a decrease in apparent capacity. For example, in high-power applications such as power tools, the capacity of the battery may decrease by 10% -20% when discharged at high currents compared to when discharged at low currents.
2. Accelerated capacity decay: Long term high current discharge will accelerate the decay of battery capacity. High current discharge can cause structural changes in electrode materials, such as electrode particle rupture and active material detachment in lithium-ion batteries. At the same time, the heat generated by high current discharge can accelerate the internal side reactions of the battery, damaging its capacity. For example, after multiple high current discharge cycles, the capacity of the battery may significantly decrease and even fail to meet the requirements of the device.
3. Impact on battery performance: High current discharge can also affect other performance indicators of the battery, such as increased internal resistance and shortened cycle life. These factors will further reduce the actual available capacity of the battery. For example, under high rate discharge, the internal resistance of the battery may rapidly increase, resulting in increased energy loss during discharge and a decrease in actual output capacity.
Smaller discharge current
1. Stable Capacity Output: When discharging with low current, the battery can output at a relatively stable capacity. Due to the mild discharge process, the polarization phenomenon inside the battery is relatively light, and the voltage drop rate is slow. This enables the battery to maintain a high terminal voltage for a longer period of time, thereby providing stable capacity output. For example, in some low-power electronic devices, the battery discharges with a small current, and its capacity can remain relatively stable for a long time.
2. Extend battery life: Low current discharge causes less damage to the battery and is beneficial for extending its lifespan. Throughout its entire lifespan, the battery is able to maintain a high level of capacity. For example, some application scenarios that require high battery life, such as smart watches, medical devices, etc., usually use low current discharge to extend the battery's usage time.
3. Improve battery reliability: Low current discharge can reduce the risk of battery use and improve battery reliability. Due to the relatively stable discharge process, the probability of battery overheating, overdischarging, and other issues is low. For example, in some application scenarios that require high safety, such as aerospace and military equipment, small current discharge is usually used to ensure the safe and reliable operation of the battery.