Flexible Printed Circuit Technology to Enable Cell-to-Pack EV Batteries

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The days of the internal combustion engine are drawing near to an end. According to a forecast in September 2021 made by investment bank UBS, by 2025 20% of all new cars sold globally will be electric. That figure will leap to 40% by 2030, and by 2040 virtually every new car sold globally will be electric, the report continues. And it’s not just private cars that are embracing electrification, other eMobility vehicles such as buses, lorries, trams, industrial vehicles, and aircraft are also ‘going electric’.

The big issues

Two of the biggest issues consumers see are range and charging time. To address this, EV manufacturers are including bigger batteries, but of course, this takes space and weight. Power density is therefore very important.

Cell-to-pack technology aims to increase battery pack power density. This approach directly integrates cells into a battery pack, eliminating the modules commonly used in most current pack designs. Many major EV companies, including names such as Tesla, Hyundai, and Volvo, plus CATL, a global leader in lithium-ion battery development and manufacturing, and other similar battery producers, have all recently issued press releases or statements referring to cell-to-pack battery programs. A simple web search will reveal many more.

However, there are challenges to solve. First, the traditional internal module construction provides a very rugged structure. Second, if a cell fails, using a modular structure it is very simple to replace the failing cell with a new, functioning unit. Third, modules permit ‘Lego’-style flexibility as modules can be arranged to create packs of all sizes and shapes. Lastly, all the individual cells will need to be connected using rugged, reliable, and easy-to-use systems.

Flexible Printed Circuits

To address these concerns, the industry is turning to flexible printed circuit (FPC) technology. FPCs such as Trackwise’s IHT (Improved Harness Technology™) offer many advantages. FPCs are much lighter – up to 75% less – than wiring looms and take up much less space. Both of these factors are paramount for EVs and electric aircraft where the power-to-weight ratio is critical and where power density is – as we have already mentioned – a real selling factor.

The concept of FPCs originated in the early 20th century and, over the ensuing decades, FPCs have been adopted for use in a wide variety of industrial and consumer electronic products. FPC manufacturing techniques traditionally limited their length to less than one meter, but an innovation in the manufacturing process by Trackwise has removed these restrictions, enabling many new applications. The patented IHT process enables multi-layer FPCs of almost any length to be produced. The current record length stands at 72m for an industrial application, but the same roll-to-roll manufacturing process is used no matter what length of FPC is required by the application.

Cell-to-pack applications for EVs using FPCs are benefitting not only from the weight and space savings already mentioned. FPCs are very reliable and because they are constructed using a printing process, they are very repeatable – every FPC will perform similarly within a tight performance variation tolerance. Traditional wiring looms are limited to commonly-used minimum wire gauges such as AWG24-26 for reasons of mechanical strength. With FPCs, exactly the correct amount of copper to carry the required current can be left on the dielectric substrate base after etching to form the necessary tracking.

Active as well as passive

Components can also be mounted onto either side of the FPC, forming an FPCA. For the battery manufacturer, this means that they can buy a single part which is, in effect, a subsystem with extra functionality such as, perhaps, filtering or monitoring systems. Strengthening elements can be included to make the end structure more rugged and robust.

One very significant advantage of FPCs is that they are simple to install. This saves a huge amount of time and increases reliability. Finally, of course, since each IHT FPC is a custom design, there is ultimate flexibility in layout.

All these benefits mean that EV makers are turning to roll-to-roll FPCs for their next-generation cell-to-pack batteries. The designs vary – some are fairly simple, while others are more complex including bus bars and other electronics systems.

To meet the mass volume requirements of the EV industry, Trackwise is building a new UK manufacturing facility near its headquarters and current manufacturing site in Tewkesbury. This will be of tremendous benefit to European EV manufacturing companies as they will have access to a world-class, high-volume plant for one of their key battery subsystems, notably one capable of delivering cell-to-pack interconnect.