PTC Over-Current Protection Layer for Low-Temperature Battery Tripping
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Solution Overview
Problem
Existing over-current protection devices using PTC conductive composite materials face challenges in maintaining low resistance and achieving low temperature trip protection, especially in low load applications, due to the high volume resistivity of carbon black and the resistance drift issue when subjected to thermal cycles, which can lead to battery explosion or burning.
Innovation Solution
Incorporating a high melting temperature crystalline polymer, such as LDPE and PVDF, with a conductive filler like titanium carbide, and a non-conductive filler for improved resistance repeatability and low temperature trip protection, forming a PTC material layer laminated between metal foils to create an over-current protection device with initial resistivity less than 0.1Ω-cm and a trip temperature closer to the low melting point of the first crystalline polymer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon black loaded PTC device is used to achieve over-current protection, then the device can provide protection function, but the volume resistivity is greater than 0.2Ω-cm which causes high energy consumption and shortened service life
Solution Approach 1:
The patent changes the conductive filler material from carbon black to metallic powder (such as nickel powder with volumetric resistivity less than 500μΩ-cm), fundamentally altering the electrical resistance parameter of the PTC composite material to achieve low initial resistivity and low energy consumption while maintaining protection function
Solution Approach 2:
The patent uses composite materials consisting of crystalline polymer matrix combined with metallic conductive filler, creating a new material system that achieves both low initial resistivity and stable resistance characteristics after thermal shock
2Stability of the object's composition
If HDPE is added to LDPE matrix to solve resistance drift problem, then resistance repeatability is improved, but the trip temperature increases above acceptable levels causing battery explosion or burning
Solution Approach 1:
The patent changes the polymer matrix from LDPE to PVDF, altering the melting temperature parameter from around 105°C to around 165°C, which enables achieving both low trip temperature and good resistance repeatability simultaneously
Solution Approach 2:
The patent uses a small amount (1-10% by weight) of high melting temperature PVDF as a additive to modify the polymer matrix, achieving the desired performance improvement with minimal material addition
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 reduces resistance after thermal shock, increases the device's lifetime, and maintains low temperature protection, avoiding the tradeoff between resistance repeatability and trip temperature, making it suitable for low load applications like lithium ion batteries.
Implementation Method 1
Because the resistance of positive temperature coefficient (PTC) conductive composite material is sensitive to temperature variation, it can be used for current sensing devices and is widely used for over-current protection devices or circuits. The resistance of PTC conductive composite materials can be kept extremely low at room temperature so that the circuit can operate normally. However, if an over-current or an over-temperature event occurs, the resistance will immediately increase to a high resistance state
Implementation Method 2
the PTC conductive composite material usually uses polymer of a low melting temperature as matrix thereof, e.g., low density polyethylene (LDPE). As a result, the trip temperature is reached at a relatively low temperature, so that explosion of or damage to the battery due to over-temperature can be avoided
Data Source
AI summary
An over-current protection device comprises two metal foils and a PTC material layer laminated between the two metal foils. The PTC material layer essentially comprises a polymer matrix and a conductive filler. The polymer matrix at least comprises a first crystalline polymer, e.g., LDPE, and a second crystalline polymer, e.g., PVDF, in which the melting temperature of the second crystalline polymer subtracting the melting temperature of the first crystalline polymer is equal to or more than 50° C. The conductive filler is selected from metallic grain of a volumetric resistivity less than 500 μΩ-cm, and is distributed in the polymer matrix. The initial volumetric resistivity of the PTC material layer is less than 0.1Ω-cm, and the trip temperature of the PTC material layer at which the resistance thereof increases to 1000 times the initial resistance subtracting the melting temperature of the first crystalline polymer is less than 15° C.