Interpretation of the Aging Process Specifications for Lithium Battery Packs

The aging process of lithium battery packs is an indispensable part of battery production. Its purpose is to stabilize battery performance, eliminate defective products, and ensure the consistency of battery packs. The following is an interpretation from four aspects: aging purpose, method, parameter control and detection means:

First, the purpose of aging

Stabilizing battery performance: The internal electrochemical system of the battery after formation is still unstable. Aging can promote further interaction between electrode materials, electrolyte, etc., making the battery performance more uniform, for example, the internal resistance tends to be stable.

Optimizing the SEI film structure: The SEI film structure formed after formation is compact and has small pores. Through high-temperature aging, the SEI film structure can be reorganized to form a looser and more porous film, thereby enhancing battery performance.

Accelerated electrochemical performance stability: Aging can accelerate the active substances in the positive and negative electrode materials to undergo some side effect reactions, such as gas production and electrolyte decomposition, enabling the battery's electrochemical performance to quickly reach a stable state.

Eliminate defective products: During the aging process, batteries with severe self-discharge or micro-short circuits can be detected to ensure the consistency and safety of the battery pack.

Second, the way of aging

Room temperature aging: Place the battery in a room temperature environment (usually 20℃-25℃) and let it stand for a period of time. The duration generally ranges from 1 to 7 days, and the specific duration depends on the battery specifications and production process requirements.

High-temperature aging: Place the battery in an environment with a relatively high temperature (such as 40℃-60℃) for aging. High temperature can accelerate the reaction process inside the battery and shorten the aging time. However, the temperature and time must be strictly controlled to avoid adverse effects on the battery. The high-temperature aging time may range from several hours to tens of hours. Subsequently, it is often necessary to combine it with room-temperature aging to further stabilize the battery performance.

Charging and discharging aging: By performing multiple low-current charging and discharging cycles on the battery, it simulates the actual usage state of the battery, enabling it to reach a stable performance state more quickly. At the same time, it can also more effectively detect any abnormal conditions that may occur during the charging and discharging process of the battery. The parameters such as the current size for charging and discharging and the number of cycles need to be set reasonably according to the specific battery product.

Third, parameter control

Charging state: The charging state of the battery during aging will affect the aging rate and the change in voltage drop K value. It is necessary to set it reasonably according to the characteristics of the battery.

Storage temperature: Temperature is a key factor affecting battery performance and self-discharge rate. Under high or low temperature conditions, the chemical reaction rate of the battery will change, thereby affecting the voltage drop K value. Under the condition of a certain storage time, the K value increases with the rise of temperature. As the temperature rises, the activity of the system increases, the reaction rate accelerates, which speeds up the loss of active lithium and even causes some side reactions. The dissolution process of metal impurities at the positive electrode and the precipitation process at the negative electrode will also accelerate as the temperature rises.

Aging time: Aging time refers to the period during which a battery is stored under specific charging conditions and temperature conditions. Under certain temperature conditions, the K value decreases with the extension of the standing time, but this does not mean that the self-discharge rate of the battery has been fundamentally improved. The magnitude of self-discharge within a certain period of time is constant.

Fourth, detection methods

K value test: The K value is a physical quantity used to describe the self-discharge rate of a battery cell. Its calculation method is to divide the open-circuit voltage difference between two tests by the time interval between the two voltage tests. By precisely calculating the rate of voltage drop, it can be determined whether there is a micro-short circuit in the battery cell. If the voltage drop is too large, it indicates that there is a micro-short circuit inside, and the battery can be judged as a substandard product.

Voltage drop monitoring: By monitoring the voltage drop of batteries during the aging process, non-conforming products can be identified, ensuring that only batteries with stable performance can proceed to the next production stage.

Discharge capacity measurement: After leaving the battery open-circuited for a period of time at high or normal temperature, by discharging the battery to the cut-off voltage and measuring its discharge capacity, its self-discharge performance can be judged. However, this method has a long time cycle, many influencing factors, low accuracy, and occupies equipment and space for a long time, with poor test safety.