As the highly competitive global electric vehicle (EV) industry continues to mature, a major key to success is the ongoing advancement of battery technologies. Batteries are arguably the most important element in every EV, accounting for the lion’s share of total cost and weight, while also being the key to delivering higher driving range, which is a primary competitive factor.
During recent years, the rise of Cell-to-Pack (CTP) and Cell-to-Chassis (CTC) approaches have focused on eliminating intermediate modules that traditionally were grouped together to form battery packs. These larger sized CTP and CTC configurations can effectively reduce battery weight and cost while increasing energy density and efficiency.
However, the achievement of the high precision alignment and robust performance required for these larger size battery arrays necessitates a deep understanding of the design options and lamination alternatives that are available for creating Cell Contacting System (CCS) assemblies.
This article provides an overview of the various options and lamination approaches, including a deep dive into new adhesive-free lamination processes, along with a comparison of the trade-offs between different methodologies.
Why Cell Contacting Systems are Important
Regardless of the type or size of the battery configuration, the Cell Contacting System (CCS) is a critical element for bringing cells together in a battery module or pack.
Electrical Connection: The primary function of a CCS is to establish an efficient and reliable electrical connection between the individual cells in a battery pack. This ensures that the electrical current flows properly between the cells when charging and discharging. The CCS typically involves metal tabs or conductive straps that connect the anode and cathode terminals of each cell to the external connections of the module or pack.
Cell Balancing: The CCS plays a role in cell balancing, which ensures that all cells in a battery pack charge and discharge uniformly. Without proper balancing, some cells may become overcharged or over-discharged, leading to decreased performance, reduced lifespan, or potential safety issues. Balancing can be achieved using passive or active balancing methods, both of which may involve the CCS to manage voltage levels and current flow among cells.
Safety and Monitoring: The CCS may also integrate with the Battery Management System (BMS) to monitor the health and status of individual cells, mostly by voltage and temperature measurement. It helps with safety features such as detecting short circuits, preventing overcharging/over-discharging, and to avoid thermal runaway.
Mechanical Integrity: In addition to its electrical function, the CCS can provide mechanical support for the cells. Especially cylindrical cell modules may utilize the CCS as means to further secure the cells from the top and position them within assembly tolerances.
Overview of CCS Types, Characteristics, and Trade-offs
The two basic approaches for creating CCS assemblies are 1) Molded Plastic or Thermoformed Carriers and Trays, or 2) Lamination of the Current Collectors into a single assembly.
While plastic trays or carriers have long been viable options for smaller battery packs, these approaches are becoming problematic for creating the longer and thinner battery configurations needed for CTP and CTC battery arrays.
Plastic carriers and thermoformed trays are significantly limited regarding the length of battery arrays that can be supported whereas laminated assemblies can provide robust performance for battery packs up to 2000mm – 2500mm lengths. Preformed carriers and trays also are unable to support thinner heights of the CCS assembly that can be achieved with lamination. Lamination methods are leading the field when it comes to weight.
Within the three lamination approaches, hot lamination has the highest production cycle time and energy consumption compared to cold and adhesive-free lamination, while adhesive-free lamination also offers the simplest materials usage.
| PLASTIC TRAY | HOT LAMINATION | COLD LAMINATION | ADHESIVE-FREE LAMINATION | |
| CCS >1M | Does not support | Support | Support | Support |
| INSULATION CONCEPT | Distancing | Lamination | Distancing | Distancing |
| TOLERANCES & SWELLING | Tolerancing of collector pockets | Provides some resistance | Stretching of glue & foil | Tolerancing of collector pockets |
| APPLICATION | Cell positioning | Small cylindrical cell sizes | Larger cell sizes | Any cell form factor |
Of course, as can be seen from the various trade-offs, there is not a single best approach. Therefore, design engineers need to consider all factors against their specific battery design goals, production volume projections and product cost requirements.
A Closer Look at Adhesive-Free Lamination
Over many years of working closely with automotive manufacturers and Tier 1 suppliers, ENNOVI has been at the forefront of innovation in EV solutions, including CCS design and manufacturing alternatives. We have developed and delivered proven solutions that span the spectrum of plastic carriers, thermoformed trays, and both hot and cold lamination.
The idea for adhesive-free lamination had its genesis as a way to overcome the trade-offs between hot and cold lamination processes. The cost of cold lamination is low and the cycle time is fast, but the robustness and performance of hot lamination is better.
By leveraging ENNOVI’s 60 plus years of accumulated knowledge in laser welding and precision stamping, along with our deep experience with lamination and cell contacting system design, we innovated our Adhesive-Free Lamination Technology to eliminate trade-offs, while delivering both low cost and robustness.
ENNOVI’s Adhesive-Free Lamination Technology positions the current collector between 2 foils and joins the top foil to the bottom foil. The foils get sealed around the current collector, forming a tight pocket to secure the current collector and providing insulation between each current collector. This proprietary innovation is ideal for diverse designs and well suited for large assemblies in various battery form factors.
As shown in Figure 3, ENNOVI Adhesive-Free Lamination is a fully customizable process that can adapt to any size battery array (up to 2500mm) and accommodates various cell form factors (cylindrical, prismatic, and pouch), while also reducing weight and thickness by eliminating adhesive. The process also includes new innovations such as a patent-pending clamping feature to enhance robustness of the final CCS assembly.
Summary
The ENNOVI Adhesive-Free Lamination process is fast, efficient and designed with sustainability in mind. It uses less than 5% energy as compared to the conventional hot lamination processes, and the absence of adhesives eliminates any related environmental impacts.
Proven to be as robust and durable as conventional hot lamination, but with 50% lower cost, 80% reduced cycle time and 25% space savings. This patent-pending technology does not degrade the material properties as can occur with hot lamination.
While the adhesive-free approach is not necessarily a one-size-fits-all solution for every new EV battery project, it does give design engineers another important alternative to consider when weighing the trade-offs for each specific battery implementation project.