When an electric current is flowing, being it for powersupply (e.g. charging battery of an electrical vehicle) or data-transfer (e.g. in micro-electronics), heat is being generated. If the heat is not sufficiently “drained” the temperature of the surroundings will increase.
In many cases/ applications this increase in temperature is not a problem as the increase is marginal or the application is not really affected by it.
However higher processor-speeds and miniaturization in electronics have resulted in an increase in temperature and an increase of risk of local overheating, hereby not only affecting the reliability of the system and its lifespan, but worst case also leading to an increased catastrophic fire-risk.
The same line of thinking is true for e.g. batteries for electrical vehicles: to reduce the time for charging the battery the charging process takes place at higher voltage and more heat is generated during the process.
Therefore one of the major technological issues for the battery system is the control of its temperature between 15 dC and 35 dC to ensure optimal performance (engine power and distance traveled per charge) and battery-life. Heat is being generated in the battery during charging and discharging. Thermally conductive materials are applied in contact with the components of the battery system to allow for a good “drainage” of the heat.
The constituents of these thermal conductive material are a polymeric material (often a silicone, epoxy) combined with a highly thermally conductive filler (ceramic or metal-oxide). The material preferably is non electrically conductive and needs to have good flowability. The filler used should not interfere with the curing mechanism of the polymeric material.
If the filler particles are spherical in nature one can achieve higher loadings of the filler in the conductive material. This not only improves the thermal conductivity, but also the flowability of the material.
Sibelco offers two engineered fillers for highly thermally conductive materials: spherical alumina (under the product-name Megasil SA) and aluminium trihydrate (under the name Portaflame SG -E). Both fillers are available with different particle size distributions. The aluminium trihydrate has the additional benefit of being a flame-retardant material.
Megasil® SA products have narrow particle size distributions and close to perfect spherical shape. This allows for optimum packing and heat transfer between the particles.
Portaflame® SG-E ATH products haves been carefully designed to offer ultra-low surface area and large particle sizes, making them preferred materials for formulations needing good flowability. These products are also demetallized rendering them low electrically conductive.
Depending on the filler type, ratio between the two fillers and the filler-loading, thermal conductivities of up to 3.5 W/mk (pure Megasil® SA) can be obtained while maintaining good flowability.