Lithium batteries have become indispensable in various applications, from consumer electronics to electric vehicles. Ensuring the performance and safety of lithium battery packs is crucial. In this article, we delve into traditional and dynamic sorting methods, and principles of module series paralleling, and address frequently asked questions regarding module concatenation and parallel connections in the context of Lithium-ion battery grouping and assembly.
Traditional Cell Sorting Methods
Parameters considered: Capacity difference of 1%, voltage difference of 10mV, internal resistance difference of 2 mΩ, charging constant current ratio of 1%.
Parameters considered: Open circuit voltage tolerance of ±10mV, internal resistance tolerance of ±0.5mΩ, self-discharge tolerance of ±5mV.
Parameters considered: Capacity difference rate (0.2C) ≤3%, internal resistance difference rate ≤5%, self-discharge rate difference rate ≤5%, average discharge voltage difference rate ≤5%.
Traditional Module Grouping and Sorting Method
In this approach, lithium battery modules are grouped based on specific criteria:
Capacity group difference ≤5Ah.
Voltage group difference ≤15mV.
Internal resistance group difference ≤0.2 mΩ.
Dynamic Sorting Method
A dynamic sorting method involves sampling points along the battery’s charge and discharge curve. By converting this data into an original matrix, one can calculate the Euclidean distance between curves to determine performance consistency. Smaller distances indicate better performance consistency.
Principle of Module Series Paralleling
Module series paralleling is a technique where single batteries are connected in series to achieve higher voltage and in parallel to create large-capacity battery packs. The decision to connect in series or parallel depends on the specific application. Factors to consider include:
Consistency between battery cells.
The “barrel effect” in battery pack behavior.
Economic and technical advantages of series-first or parallel-first connections.
Influence of internal resistance on voltage.
Frequently Asked Questions about Module Concatenation and Parallel Connection
Single Battery Failure:
In series-then-parallel connections, a single battery failure disconnects the entire branch, affecting the remaining batteries. In parallel-then-series, the impact is limited to the parallel module containing the failed battery.
Single Battery Short-Circuit:
In series-then-parallel connections, a short-circuited battery experiences higher current, potentially affecting other branches. In parallel-then-series, the shorted battery affects the parallel module, potentially leading to more significant safety issues.
Voltage inconsistency in parallel battery packs may lead to batteries charging each other. If one battery has a significantly lower voltage, other parallel batteries may charge it.
High Internal Resistance:
In series battery packs, a battery with high internal resistance may reach the charging cut-off voltage prematurely, necessitating early cessation of charging to avoid safety risks.
Parallel Battery Pack Charging:
In parallel battery packs, the end voltage of each battery is the same during charging and discharging. Variations in internal resistance result in different branch currents and charging/discharging capacities, impacting overall system energy efficiency.
Efficient and safe assembly of lithium battery packs is vital for various applications. Sorting methods, series paralleling principles, and an understanding of potential issues contribute to successful lithium battery assembly. By adhering to these principles and addressing common questions, we can maximize the performance and safety of lithium battery systems in diverse applications.
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