Voltage Sensitive Heating Device for Battery Overcharge Protection
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Solution Overview
Problem
Lithium ion batteries are vulnerable to overcharge, which can lead to accidental ignition or explosion due to the lack of effective safety devices that prevent overcharge, over-voltage, and over-current, posing risks in applications like portable electronics and electric vehicles.
Innovation Solution
A safety device comprising a voltage sensitive heating device and a temperature sensitive device, such as a PTC device, where the voltage sensitive heating device generates heat at a predetermined voltage level, triggering the temperature sensitive device to shut off current before overheating occurs, thereby preventing damage from overcharge, over-voltage, and over-current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zener diode with breakdown voltage close to maximum charge voltage is used, then overcharge protection is achieved, but leakage current occurs during normal operation reducing battery lifetime
Solution Approach 1:
A thermal fuse is introduced as an intermediary component between the zener diode and the battery circuit. The thermal fuse acts as a mediator that responds to heat generated by the zener diode's leakage current, providing overcharge protection only when necessary while allowing normal operation to proceed without interference.
Solution Approach 2:
The invention replaces the direct electrical protection mechanism with a thermal-based protection mechanism. Instead of using the zener diode's electrical characteristics directly for protection, the system converts the electrical leakage current into thermal energy, which then triggers the thermal fuse to provide protection, thereby eliminating the harmful electrical leakage effect.
2Reliability
If a zener diode is used for overcharge protection, then current can be shut off during overcharge, but the device is irreversible and cannot be reused
Solution Approach 1:
The invention introduces dynamic reversibility to the protection system. The thermal fuse can transition between conducting and non-conducting states based on temperature conditions, allowing the safety device to be reset and reused after the battery cools down, unlike permanently damaged components.
Solution Approach 2:
The system recovers the protective function after it has been activated. When the thermal fuse melts and interrupts the circuit due to overheating, it can be replaced or the system can be reset once the temperature returns to normal, allowing the safety device to continue protecting the battery in subsequent charging cycles.
3Reliability
If thermal bonding is used between zener diode and thermal fuse, then heat transfer is efficient, but the structure becomes complex and manufacturing difficult
Solution Approach 1:
The zener diode and thermal fuse are merged into a single integrated safety device component. This combination eliminates the need for separate mounting and thermal bonding processes, simplifying the manufacturing procedure while maintaining effective heat transfer between the components.
Solution Approach 2:
The integrated safety device performs multiple functions within a single component structure: voltage regulation through the zener diode and thermal protection through the thermal fuse. This multi-functionality reduces the overall component count and simplifies the manufacturing process while maintaining protection effectiveness.
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
The solution effectively prevents secondary batteries from being damaged by overcharge, over-voltage, and over-current, ensuring safety by using a reversible and reusable safety device with minimal leakage current, thus extending the battery's operating time and lifetime.
Implementation Method 1
a voltage sensitive heating device generating heat when a voltage difference between both ends thereof exceeds a predetermined voltage level
Implementation Method 2
a temperature sensitive device having a reversible current ON/OFF function according to a temperature, and having a reversible current ON/OFF function according to the temperature, wherein the temperature sensitive device detects the heat generated from the voltage sensitive heating device
Data Source
AI summary
Disclosed are a safety device and a secondary battery using the same. The safety device includes a voltage sensitive heating device generating heat when a voltage difference between both ends thereof exceeds a predetermined voltage level and a temperature sensitive device having a reversible current ON/OFF function according to a temperature. The temperature sensitive device is coupled with the voltage sensitive heating device such that the temperature sensitive device detects the heat generated from the voltage sensitive heating device.