A previous article explains what you need to know about thermal runaway and thermal propagation, while a second installment covers standards of flammability testing. This article introduces Avery Dennison solutions for thermal protection. 

There are several trends in the EVB industry. One is a push to increase the energy density of the battery pack – by reducing the weight and thickness of many components, or by altering the footprint of the pack or the cell construction. Another one is the desire to charge faster. Drivers want to be able to achieve a full charge as quickly as possible. They also want long-lasting batteries. But fast charge or discharge cycles generate excess heat that can be detrimental to battery life and safety, as previously shown in our article on thermal runaway. 

The rate you can charge is also determined by thermal management; how much heat you can remove from the cell. 

Batteries work best at a specific temperature. Optimal performance is usually achieved at around 25 degrees Celsius. Cells that are thermally abused have shorter cycle lifetimes, but also an increased chance of a thermal runaway event. 

So, how do you protect cells from excess heat generated during the fast charge and discharge cycles required for high-performance day-to-day operations?

Managing heat flow is a large part of the fast-charge objectives, in turn leading to even more different approaches to thermal management – including innovation in material choices and applications. Materials historically being used elsewhere such as in the petrochemical industry are now being used in the battery pack, for instance, to improve battery performance and stop heat transfer to other cells by acting as thermal barriers or by carrying the heat away from the cells. From a tape perspective, we need to be ready to bond to the great variety of materials used in cells, packs and batteries. 

It is generally agreed there is no silver bullet in thermal runaway protection, as there are differences in vehicle size, pack size, modules per pack, cells per module, the degree of risk tolerance and so on. In other words, there is no one perfect solution. You need to find the perfect partner to help you find the balance you are looking for. 

Increasing battery performance and safety is a common concern, especially in the growing market for electric vehicles. Avoiding thermal runaway calls for safer cell chemistries, but that is especially difficult considering the aforementioned push for increased energy density of battery packs. 

Considering enough space between cells in a pack to prevent cell-to-cell propagation is equally difficult, as packs are becoming a structural vehicle element and much thinner – mostly as an element of the chassis and floor pan. Avoiding overcharging or simply storing batteries at safe temperatures aren’t, in everyday use, the realistic and easy solutions they would appear either. In addition, physical damage (crushing, penetration), another leading cause for thermal runaway, can be the result of the vehicle being involved in an accident.

In other words, avoiding thermal runaway by avoiding the causes of thermal runaway is a real challenge for the EVB industry. ‘Single cell’ runaway, however, is a maintenance issue, since defective cells can be replaced. It becomes a safety issue in the case of thermal propagation – the sequential occurrence of thermal runaway within a battery system triggered by the runaway of a single cell in that system, which can be prevented. 

EV and battery manufacturers have strict requirements against thermal runaway events and rely on mica, ceramic fibers, aerogels and other materials for protecting cells and passengers. Avery Dennison offers a variety of solutions for bonding and encapsulating these materials for cell, module and pack-level uses. Scott Krusinski, product manager at Avery Dennison Performance Tapes said:

Our range of solutions includes flame-retardant adhesives that enable composites and materials to meet UL 94 V and other flame requirements, single- and double-coated filmic tapes for fiber encapsulation and dielectric strength, and easy-release liners and pattern coating for preventing the cohesive failure of delicate fibrous based materials.

Avery Dennison offers a range of bonding and assembly solutions for thermal runaway propagation barriers, including double-coated tapes for mounting ceramic paper, mica, aerogel and other thermal barriers to various parts of pack, including cell-to-cell, module and pack levels. We offer easy-release liners and pattern-coated PSA to enable processing while preventing the tearing of delicate thermal barrier materials. 

Single-coated tapes can encapsulate thermal barriers, while the encapsulation layer provides dimensional stability and enables automated placement. Encapsulation also prevents shedding or linting from fibrous materials such as ceramic paper and aerogel composites throughout supply chain processes and in the pack.

Acrylic and silicone-based adhesives with Flame Tough™ flame-retardant properties allow composites and materials to meet UL 94 V and other requirements. Flame Tough™ Rubber is the latest addition to Avery Dennison’s Flame Tough™ adhesive platform. 

This rubber adhesive features flame-retardant properties that enable it and its composites to pass various flammability requirements, such as UL94 VTM and UL 94 which are common for EV battery pack applications. The adhesive is halogen-free and has higher tack and adhesion than the portfolio’s acrylic and silicone Flame Tough™ adhesives. Flame Tough™ Rubber is available in transfer tape and double-coated tape constructions and is recommended for thermal runaway barriers, compression pads and electrical insulation applications.

Choosing Avery Dennison means OEMs, engineers, converters and suppliers can be confident knowing their adhesive systems are engineered, manufactured, and supported by a global materials science leader. We deliver unmatched customer service and technical support to ensure the right product is chosen for the application, and service programs to help ensure the product is onsite when needed. We know our products, we understand the compatibility of our tapes, and we can mix and match, develop, and test. We have a solution to meet the wide variety of challenges, whatever they may be.