e-mobility 2020

Battery technology PPG

Ahead of the pack

What role can special coatings play in improving EV battery cell and pack assembly? AMS discussed the challenges with Calum Munro, PPG senior scientist, research and technology for automotive

Electric vehicle battery technology is well established, but as these vehicles reach the mass market and greater demands are made of the battery systems in terms of range and charging speed, challenges arise in respect of safety, performance and efficiency. Coatings specialists PPG have announced a raft of solutions that they claim will address a number of technical and environmental issues with existing battery pack technology and simplify areas of assembly. PPG senior scientist Calum Munro discussed some of the most pressing challenges facing OEMs and tier suppliers.

Munro outlined the company’s approach to battery cell and pack assembly: “We’re seeing a lot of different challenges across the industry, some things that were anticipated, and a few surprises emerging. We (PPG) have focused on eight main areas to help address the most critical issues. A couple are at the cell level, but the majority are at the pack assembly level. 

Can new materials improve electrode performance?
The cell developments are aimed at improving the performance in electrodes and a cathode binder system, Munro explained: “We have developed an NMP free cathode binder system, which allows us to address some of the environmental health and safety concerns that are associated with the use of the traditional solvent of choice. In addition to addressing these concerns we’ve also been able to improve the overall performance of the electrode, and hence the performance of the battery”.

“Really these electrodes are just highly functional, very specialised coatings. They’re really highly pigmented coatings on a metal foil. So, it fits well with our expertise.”

Another material that PPG is working with is graphene. In recent years research and development has been progressing into the use of graphene in batteries and it has been reported that using the material in a battery’s electrodes can improve conductivity and performance while reducing the use of other materials, such as carbon.  

Munro noted that PPG is working on specific projects with customers but could not reveal any details: “We’re able to bring some graphene systems into play that really complement some of the newer emerging materials that are being utilised within the lithium-ion battery.”

The battery pack structure also has to meet a number of challenging technical requirements and perhaps the most basic being resistance to corrosion and impact. It is now common with some of the newer skateboard designs for the pack to be integrated into the floor structure of the vehicle. 

Calum Munro, PPG senior scientist, research and technology for automotive

We recognise there are not two packs that are the same and no two sets of challenges that are the same. The requirements and the preferences are going to vary by OEM and by the design of the individual vehicle. We’re now dealing with a very rapidly evolving field where, as an industry, we’re learning as we go on – Calum Munro, PPG

Munro pointed out that: “very often with those designs the battery pack casing is exposed under the vehicle. So, you can appreciate that as currently metals are still a material of choice for the overall casing of those battery packs, traditional challenges like corrosion and impact come into play.”

EMI and RFI shielding are another consideration. “When you have a lot of electrical components in close proximity to each other, very often you can get crosstalk between these components, and that’s something that we’re seeing becoming more important with the new vehicle designs that are coming through.

So, shielding becomes a real challenge,” explained Munro. He noted that ease of application of the shielding materials is something PPG had been working on, with the company offering spray-applied coatings. He added: “They can be applied to a broad range of substrates.

They are very thin, so they do not require a material change or an overall design change if you find that you have a shielding problem late within the overall design cycle. Also, we can tune these shielding materials, so that they cover certain frequencies or they give a higher level of shielding”.

Increasing efficiency requires high thermal conductivity material that accelerates the transfer of calories

Within the battery assembly, there are a number of components that have to be joined to each other in some way and depending on the battery design; there are a range of different approaches. In some cases, mechanical fixtures are still utilised, but according to Munro, there is a trend towards bonding: “That could be bonding from cell to cell within a module and you can get up to 20 modules, depending on the design within the unit. 

“There’s a lot of dissimilar materials that are utilised that could be bolted together as they aren’t necessarily conducive to welding. But using a structural adhesive means the process can be readily automated, allowing for scaling up of production as volumes increase.”

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