The vehicle’s range and the autonomy – the distance a vehicle can travel on a single charge – are critical features for EVs. Typically, range is increased by either decreasing the weight of a vehicle to make it more efficient, or by adding more batteries so the vehicle can store more energy.
EVs have traditionally used what is called a Cell- to- Module (CTM) method for their batteries. CTM batteries configure the cells into small groups called modules. Those modules are then assembled to create a full vehicle’s battery pack. The modular nature of this method allows for flexibility in manufacture because there is only one design of battery being made and can be used for multiple vehicles and trim styles. With the Cell -to -Pack method, cells are configured directly into one large pack for the vehicle. Many times, this means the batteries are attached to and assembled directly to the body or chassis of the vehicle. The major benefit is that you eliminate many of the parts and components used to assemble the multiple modules of each vehicle. This is important for an electric vehicle because 1) less parts equal less overall vehicle weight, 2) the increased space allows for more cells to be added, and 3) few parts means few steps and less complexity in manufacturing. However, with these benefits there also come some challenges.
Three of the biggest issues that come with a cell to pack design include the loss of structural support to the battery, effective sealing, and increased risk of battery fire.
The loss of structural support comes from the loss of the side wall and enclosure of the modules. This will cause issues over time because the cells will experience more of the shock and vibration of the regular use of the vehicle. This can eventually cause damage to cells, wire bonds and the electrical systems. To restore much of the NVH (noise, vibration, and harshness) capabilities, many of these battery packs will use structural polyurethane potting material like the EV Protect 5006. The EV Protect 5006 provides high structural strength to help keep cells and other infrastructure in place while having high compressibility to allow for shock absorption.
The loss of sealing effectiveness is caused by removal of the module’s lids. In a modular design, each module would have a sealed lid as well as the entire pack having a sealed lid. With cell to pack designs there is only one a seal on the pack lid. The use of a sealant like the EV Seal 500 can help to ensure sealing of a battery pack. It has consistently been tested to and passed IP 67 (Leak testing), dust, and water sealing, and has passed testing through IP 69 (Watertight) rating in many applications. The EV Seal 500 also performed excellently in long term aging and weather testing to help seal your battery for the lifetime of the vehicle.
Increased risk of battery fire is caused by the cells being in direct contact with the frame or body of the vehicle. If there an accident, even a small one, there is an increased chance that cells will be damaged resulting in thermal runaway and eventually thermal propagation. In this situation, the use of a battery encapsulant like the EV Protect 5006 and the EV Protect 4006 could help mitigate some of these risks. Both materials form a flame retardant barrier around the cells to prevent thermal propagation. In the event of a small accident where a cell was damaged to the point it enters thermal runaway, the EV Protect 5006 and 4006 would help to stop a battery fire caused by full cell thermal propagation.
CTP battery designs are a great way to improve range in a vehicle, but they do come with their own risks. With some battery design work and help from specially engineered encapsulant and sealant material, it can be a great design choice.
This article first appeared on H.B Fuller’s The GlueTalk Blog.
