Zener Diode Voltage Balancing for Lithium-Ion Battery Modules
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Solution Overview
Problem
Lithium-ion battery modules with high-rate output applications face voltage variations among unit cells due to capacity and self-discharge differences, leading to safety issues like accelerated deterioration and overcharge/discharge, which existing monitoring systems cannot effectively address in small, space-saving applications.
Innovation Solution
Connecting Zener diodes in parallel to lithium-ion unit cells, with characteristics defined by each unit cell's capacity, allows for automatic and continuous voltage and capacity balancing, minimizing capacity loss and storage reductions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a system for individually monitoring the voltages of unit cells is used, then safety problems are addressed, but the battery module size increases
Solution Approach 1:
The patent extracts the voltage monitoring function from a complex external monitoring system and integrates it into individual Zener diodes connected to each unit cell. Each Zener diode independently monitors its associated unit cell's voltage, eliminating the need for a centralized monitoring system and reducing overall module size while maintaining safety.
Solution Approach 2:
Zener diodes serve as intermediary components between the unit cells and the external environment. They indirectly monitor voltage by utilizing their breakdown characteristic at a specific Zener voltage, providing safety monitoring without requiring complex measurement circuits or additional sensors.
2Reliability
If Zener diodes are connected to detect abnormal voltage rise, then overcharge protection is achieved, but leakage current increases causing capacity loss
Solution Approach 1:
The patent carefully selects and adjusts the Zener voltage parameter of the diodes to match the maximum safe operating voltage of the unit cells. By optimizing this parameter, the system achieves overcharge protection while minimizing the reverse leakage current that flows during normal operation, thereby reducing capacity loss.
Solution Approach 2:
The patent uses multiple identical Zener diodes, each with the same Zener voltage rating, connected to individual unit cells. This standardized approach allows for consistent protection characteristics across all cells while maintaining predictable and minimal leakage current values.
3Power
If unit cells are connected in series for high-rate output, then power supply capability is improved, but voltage variation among unit cells increases
Solution Approach 1:
The Zener diodes provide continuous voltage feedback for each unit cell in the series connection. When any unit cell's voltage approaches the Zener voltage threshold, the corresponding diode begins to conduct, effectively limiting further voltage increase and maintaining voltage uniformity across all cells in the series string.
Solution Approach 2:
By connecting Zener diodes with identical Zener voltages to each unit cell, the patent creates equipotential conditions across the series-connected cells. The diodes ensure that no single cell can exceed the Zener voltage threshold, thereby maintaining voltage equality and preventing harmful voltage variations among cells.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively balances voltages among unit cells, preventing overcharge and overdischarge, while maintaining battery performance and extending operational time by minimizing leakage current, making it suitable for small, low-profile battery applications.
Implementation Method 1
In Zener diodes, a reverse current rapidly increases in the case that a voltage exceeds a certain reverse voltage (referred to as a Zener voltage or a breakdown voltage)
Implementation Method 2
lithium-ion unit cells are, in general, connected in series into a battery module
Data Source
AI summary
Provided is a lithium-ion assembled battery including a plurality of lithium-ion unit cells connected to each other in series, and Zener diodes connected to the respective unit cells in parallel, and the Zener diode is characterized in that a current of 1/200 or less of a capacity of the unit cell flows at a mean voltage of the unit cell.