Electrical Insulation Considerations in High-Voltage Electric Vehicle Battery Design
Increasing vehicle power and battery capacity, while reducing charging time and weight are priority considerations in electric vehicle battery design. While these considerations have always been important, battery technology, power supply capability, and semi-conductor capacity have been somewhat prohibitive of a solution impacting all: increasing the voltage of the battery.
350V batteries are still commonplace and 450V capacitors are most readily available. However, that has not stopped automakers from introducing batteries supporting up to 800V. Although this may seem premature given that peripheral support is limited, this evolution in battery design is inevitable and automakers such as Porsche and General Motors recognize this.
Benefits of High Voltage Batteries
At first glance, the benefits of a high voltage battery are attractive. Most apparent would be a reduction in copper area. By increasing the voltage rather than the current, the same amount of power can be transmitted in a smaller cross-sectional area. Not only will this reduce weight by copper reduction, but it will also reduce heat resulting in a more efficient battery. Similarly, charging speeds through DC fast chargers can be increased with the high voltage output. DC fast charger support is essentially a market requirement at this point, but an 800V battery will only improve this technology further where a full battery charge can be achieved in under 30 minutes.
Increasing the voltage will help increase the power of the motor as well. A disadvantage of electric vehicles has been their inferior power compared to petroleum-based motors particularly among truck, bus, and other heavy-duty applications. High voltage packs will continue to narrow that gap to a future where a gap may not exist at all.
Benefits of a high-voltage battery in an electric vehicle
– Less Weight
– Faster Charging
– More Power
– More Efficient
– More Range
Drawbacks of High Voltage Batteries
These advantages make the choice seem obvious – Higher-voltage batteries are a better option than lower-voltage batteries. However, higher voltage power inevitably leads to safety concerns. In an enclosed unit, these concerns can be compounded. Arguably the most significant danger related to EV batteries is thermal runaway. Left uncontrolled, thermal runaway within a battery can be deadly.
Thermal runaway – an incident where one exothermal process triggers other processes, finally resulting in an uncontrollable increase in temperature.
Thermal runaway often leads to fire and in some cases explosion. In a moving passenger vehicle, thermal runaway prevention may be the most important design consideration.
While it is by no means an excepted result, high voltage batteries have the potential to increase the likelihood of thermal runaway through arcing.
Arcing – When an electric current flows through the air from one conductive point to another.
Heat and energy emitted during arcing can be extreme. Left unmitigated, an arc can produce temperatures hotter than the surface of the sun and produce a blast pressure that exceeds 2000 psi. Very likely, these events would lead to thermal runaway.
Higher voltage increases the likelihood of an arc because the current can cross longer air gaps. Air is a natural insulator, but it doesn’t stop arcing alone. High voltage decreases the effectiveness of the air’s natural insulation. If high-voltage batteries are going to be used, subsequent electrical insulation must be implemented to prevent this arcing from occurring.
Electrical Insulation used in Electric Vehicle Batteries
There are many types of electrical insulation. Insulation can come in the form of thermosets, thermoplastics, films, adhesives, elastomers, and more, but while there are many options, few are suitable for electric vehicle battery packs.
1. Dielectric Strength – First and foremost, the material must accomplish what it is intended to do. In this case, the material must prevent arcing. Materials that exhibit a high dielectric strength are most suited for these applications. A material with sufficient dielectric strength will break down the flow of charge. An insulator with adequate strength located between 2 conductive points will prevent arcing between the points.
2. Relative Temperature Index – As an insulator absorbs current it also absorbs heat. Relative to the environment temperature, this generated heat can be extreme, and the material used must be able to withstand these temperatures. If it cannot, the material begins to break down. Even material with outstanding dielectric strength can be rendered useless if enough breakdown occurs
3. Flame resistance – In the event the insulating material ignites, it is paramount that the flame is extinguished before other components are exposed. Some insulating materials have flame retardant properties that self-extinguish. This can be achieved through the natural properties of the material or through additives.
Many materials meet the insulating requirements listed, however, not all of them are suited for a battery. High voltage insulation thermosets such as GPO-3 may be the best option from a dielectric performance standpoint, but a thick and heavy composite material is impractical for an electric vehicle battery. From a design standpoint, the material must exhibit the following:
1. Thin gauge – the material must have a thin profile so it can fit in tight spaces. Form factor and overall size of the pack are important considerations so any opportunity for reduction is key. Thin material can line the enclosure without increasing the size. A thin enough material can also be implemented in between cells and around modules for increased protection.
2. Formability – Ideally the material can form easily to contours within the battery. Optimizing the battery design to fit most cells often results in creative geometries. A thin, rigid material might be suitable for linear areas, but something flexible will be required to match the contours of the pack, module, or cell.
3. Manufacturability – Assuming the material can handle a high-voltage environment and functions in an optimized battery design, production of the material must match production volume requirements at an economical price point to keep the product cost-competitive. Materials ideal for manufacturing techniques such as those found here Article on fabrication methods are optimal.
After all the considerations, the candidate pool is few. Flame retardant polypropylene, such as The Gund Company’s PolyPro FR® family of materials, possesses thermal and dielectric properties that are ideal for high-voltage battery applications specifically in electric vehicles. These polymers offer superior dielectric strength to prevent arcing, a high-temperature rating, and exceptional moisture and chemical resistance. As such, these materials can be used as electrical insulation and thermal insulation in various applications in the battery cell, module, pack, and charger. Other insulation materials such as silicone foams, polyimide films, PET, polycarbonate, and aramid paper can also serve high-voltage battery applications.
High-voltage electric vehicle batteries are becoming more prevalent in the marketplace. Insulating materials such as PolyPro FR® are key to ensuring these high-functioning batteries operate safely.