In applications demanding high power and large capacity, individual lithium-ion batteries often fall short of meeting the requirements. Consequently, lithium-ion batteries are combined in series and parallel to achieve the desired power output. Unfortunately,Battery recycling machine the inconsistencies between individual batteries can lead to rapid capacity degradation and a shorter lifespan for the battery pack during cycling. Addressing these inconsistencies by selecting batteries with the most consistent performance for grouping is crucial for the widespread use of lithium-ion batteries in power applications.
1. Defining Inconsistency
In the context of lithium-ion battery packs, inconsistency refers to differences in various parameters when a battery pack is formed using the same model of single-cell batteries. These differences manifest in parameters such as voltage, capacity,cylindrical battery pack mahcine internal resistance, life expectancy, temperature effects, and self-discharge rate.
Single-cell batteries inherently exhibit performance variations upon manufacture. As these batteries are used, these differences accumulate, and because they operate in slightly varying environments within the battery pack, these variations amplify, hastening the performance degradation of the battery and, ultimately, causing premature battery pack failure.
2. Inconsistency in Performance
Lithium-ion battery inconsistency primarily manifests in two ways: disparities in the performance parameters of individual battery cells (capacity, internal resistance, self-discharge rate, etc.)cell stacking machine and differences in the state of charge (SOC) of the batteries.
The capacity difference between battery cells typically adheres to a distribution close to the Will distribution. Meanwhile, internal resistance disparities tend to be more significant than capacity variations, with the internal resistance of the same batch of batteries generally following a normal distribution pattern. Self-discharge rates also tend to approximate a normal distribution.
SOC characterizes the state of charge in the battery, representing the ratio of the battery's remaining capacity to its rated capacity. This ratio is pivotal as batteries with small capacity changes tend to experience a faster rate of change in SOC. These batteries reach the cut-off voltage more swiftly during charging and discharging compared to batteries with larger capacity.
3. Causes of Inconsistency
Inconsistencies in lithium-ion batteries can be attributed to multiple factors, particularly within the manufacturing and usage processes. Various aspects of the manufacturing process, such as the uniformity of slurry during batching, control of coating surface density and surface tension, can lead to performance differences in individual cells.
Research has delved into the impact of lithium-ion battery production and manufacturing processes on battery consistency, with a focus on the implications of the water-based binder system. During battery usage, the connection method, structural components/devices, working conditions, and the operating environment can influence battery pack consistency. Variability in energy consumption at different connection points, differential performance and aging rates of each component or structural member, and variations in temperature and performance degradation across individual cells all contribute to the amplification of inconsistency within the battery pack.