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Understanding Power Battery Pack Consistency and Its Causes

Nov 08 - 2023


Lithium-ion batteries play a significant role in various applications, including new energy vehicles and smart grids, but inconsistencies in battery parameters remain a critical factor affecting battery pack longevity. While advancements in thermal management enhance the safety of battery packs, achieving greater consistency within these packs is essential for their widespread utilization.

By simulating a 10-series, 10-parallel battery pack,Battery recycling machine we can examine the impact of temperature distribution within the battery pack on its performance and cycle life. It's observed that lower average temperatures result in higher temperature inhomogeneity and increased inconsistencies in single-cell depth of discharge. Conversely, higher average temperatures lead to greater temperature inhomogeneity and shorter battery pack cycle life. It's important to note that non-uniform temperature distribution can also disrupt current distribution among parallel branches, further deteriorating single-cell aging rate consistency.

Within the context of battery pack thermal management, we've introduced a rapid estimation method for flow and temperature fields in parallel air-cooled battery packs. This method, comprised of a flow resistance network model and a transient heat transfer model,cylindrical battery pack mahcine offers a balance between computational fluid dynamics methods, which are often computationally intensive, and estimation accuracy.

With this method, we investigate how an inhomogeneous flow field affects temperature uniformity within the battery pack. We also explore structural parameters for air-cooling systems aimed at enhancing temperature uniformity.

Battery inconsistency arises from variations in parameter values among batteries of the same type and specification, such as voltage, internal resistance, and capacity. These differences often lead to performance discrepancies in electric vehicles,cell stacking machine preventing these vehicles from reaching the full potential of individual batteries.

Lithium-ion battery consistency encompasses a range of performance indicators such as capacity, impedance, electrode electrical characteristics, electrical connections, temperature traits, decay rates, and more. Inconsistent factors directly impact the differences in electrical output parameters during battery operation.

The inconsistency in lithium-ion battery packs, or the discreet performance among batteries, relates to single batteries of the same specifications exhibiting differences in voltage, charge, capacity, rate of decline, internal resistance, and the change of these factors over time, life expectancy, temperature effects, self-discharge rate, and the rate of change over time.

From a chronological perspective, the inconsistency among single cells within a battery pack primarily results from two factors: issues in the manufacturing process and material variations. Variations in the activation of battery plate active material, thickness, microporosity, connecting strips, and spacers lead to internal structural and material inconsistencies. During usage, individual cells within the battery pack experience disparities in electrolyte density, temperature, ventilation conditions, self-discharge levels, and the charging/discharging process.

What causes variations in capacity, internal resistance, and self-discharge among batteries of the same model and batch? Many believe that battery inconsistency is primarily a production process problem, while others attribute it to dispensing issues. Certain measures, such as strict process control through statistical process control (SPC), are assumed to eliminate inconsistencies. However, real-world evidence suggests that even with strict control over ingredients, slurry consistency, coating, cutting, and rolling processes, these measures reduce standard deviations between batches but do not completely eliminate inconsistencies. When a random variable is influenced by numerous random factors, and the individual impact of each factor is insufficient to make a decisive difference, these factors accumulate, causing the random variable to follow a normal distribution with parameters such as the standard deviation (σ) and mean (μ). The voltage values of batteries during the charging and discharging process are the result of the thermodynamic and kinetic state of the battery, which is influenced by various production process conditions and battery charging and discharging currents. As a result, each battery's voltage value within a battery pack cannot be precisely identical due to various accidental factors introduced by the battery charging and discharging process, including current, temperature, time, and operational conditions.