Thermistor Layer Composition for Tunable Battery Switching Temperature
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Solution Overview
Problem
The existing PTC thermistors have limited design flexibility for switching temperature, which is largely determined by the melting point of crystalline polymers, restricting the ability to set the switching temperature lower than the melting point and limiting thermistor characteristics.
Innovation Solution
A thermistor layer is designed with thermosensitive particles coated by electro-conductive particles and a binder, where the thermoplastic resin on the surface softens at a lower temperature than the binder, allowing for a high degree of freedom in setting the resistance increase temperature and forming an electro-conductive network that becomes highly resistive upon softening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crystalline polymer is used to determine the switching temperature of a PTC thermistor, then the thermistor exhibits stable resistance increase at a specific temperature, but the degree of freedom in designing the switching temperature is small and the switching temperature cannot be set lower than the melting point of the polymer
Solution Approach 1:
The patent changes the fundamental parameter determining switching temperature from melting point (crystalline polymer) to softening point (amorphous polymer). By selecting different amorphous polymers with varying softening points, the switching temperature can be freely adjusted across a wide range without being constrained by a fixed melting point, thus resolving the contradiction between stability and design freedom.
Solution Approach 2:
The patent uses a composite structure consisting of amorphous polymer particles mixed with conductive filler particles. The amorphous polymer provides the temperature-dependent resistance change mechanism, while the conductive filler forms the conduction network. This composite approach enables independent optimization of switching temperature (via polymer selection) and conductivity (via filler content and distribution), achieving both stability and design flexibility.
2Temperature
If the switching temperature is set below the melting point of the crystalline polymer, then lower temperature protection is achieved, but the resistance increase mechanism becomes unreliable
Solution Approach 1:
The patent fundamentally changes the temperature-dependent mechanism from melting (crystalline) to softening (amorphous). Since amorphous polymers soften gradually over a temperature range rather than at a fixed melting point, the resistance increase occurs smoothly and reliably even at temperatures below what would be the melting point of a crystalline polymer, eliminating the reliability issue.
3Adaptability or versatility
If an electro-conductive resin layer with mixed electro-conductive filler in resin is used, then the layer can function as thermistor, electrode, heating element, or sensor, but the switching temperature is limited by the resin's melting point
Solution Approach 1:
The patent employs a composite material system where amorphous polymer particles are mixed with conductive filler. The amorphous polymer matrix provides temperature-dependent volume expansion during softening, while the conductive filler network provides electrical conductivity. This composite structure maintains the versatility of electro-conductive resin layers for multiple applications (thermistors, electrodes, heating elements, sensors) while expanding the achievable switching temperature range through selective polymer choice.
Solution Approach 2:
By changing from crystalline to amorphous polymer, the patent fundamentally alters the temperature parameter behavior. Amorphous polymers exhibit gradual softening over a temperature range rather than abrupt melting, enabling continuous adjustment of switching characteristics. This parameter change allows the same composite structure to serve multiple applications with different temperature requirements without being constrained by a fixed melting point.
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 design enables the thermistor layer to effectively reduce current flow and prevent abnormal heat generation, serving as an overheating protection and thermal sensor, while maintaining excellent conductivity at lower temperatures, and allows for precise control of the resistance increase temperature.
Implementation Method 1
the thermoplastic resin has the property of softening at a temperature lower than a temperature at which the binder softens. The thermistor layer is provided to become highly resistive due to softening and deformation of the thermoplastic resin.
Implementation Method 2
a plurality of electro-conductive particles covering a surface of the thermosensitive particle, wherein the plurality of electro-conductive particles form an electro-conductive network
Data Source
AI summary
A thermistor layer of the present invention is configured to be disposed in an electrical current path. The thermistor layer comprises a thermosensitive particle, a plurality of electro-conductive particles covering a surface of the thermosensitive particle, and a binder adhering the electro-conductive particles, the electro-conductive particles form an electro-conductive network, at least the surface of the thermosensitive particle is made of a thermoplastic resin, the thermoplastic resin softens at a temperature lower than a temperature at which the binder softens, and the thermistor layer is provided to become highly resistive due to softening and deformation of the thermoplastic resin.