Charged and ready: Engineering resins for electric and hybrid vehicles

As any blackjack player could tell you, doubling down involves a big risk. But it’s one thing to chance it at the local casino for half a day’s pay, quite another when careers, reputations, and hundreds of millions of dollars are on the line.

Automakers are doing just that, though, with plug-in electric vehicles (PEVs) and hybrid electric vehicles (HEVs). Despite the fact that overall sales of PEVs and HEVs in North America haven’t lived up to their expectations nor politicians’ proclamations so far — the U.S. federal government forecasts that only one per cent of all new cars sold in 2014 will be of the plug-in electric variety, for example — the auto industry is betting the market will expand steadily as fuel prices remain high and consumers increasingly seek alternatives to internal combustion engines. Adoption forecasts vary (and we’ve summarized one of them at the bottom of pg. 13), but several industry forecasters predict that power-split hybrids and full electrics could account for up to 25 per cent of global vehicle production by 2020. Analysts from the glass half empty school, on the other hand, note the lack of progress to date and point to the overwhelming likelihood of almost every governmental electric car adoption target being missed between now and 2020.

Taken as a whole, the resin manufacturing industry is on the fence, too. Germany’s second-biggest chemical company, Evonik Industries AG, is seeking a buyer for its battery activities, including a joint venture with Daimler AG. Six years ago, the company said it wanted to become Europe’s leading producer of lithium-ion battery components; fast forward to today and Evonik is abandoning the project. At the other end of the spectrum — and in a double down that would’ve made blackjack legend Ken Uston proud — BASF, Germany’s largest chemical maker, has made battery materials one of 10 areas it’s targeting for growth in 2014.

But whether the cars stall in the marketplace or not, you can bet on at least two things. First, the number of vehicle models will increase from 20 to 60 or more by the middle of this decade. And second, materials and polymer science — chief among them engineering resins — will be critical in automakers’ quests to boost battery kilowatt-per-hour and power capabilities, improve product safety, and reduce overall vehicle weight. The good news? “Traditional engineering resins are well-suited for use in a wide variety of electric vehicle applications, and offer properties that can enable automakers to overcome some key challenges in vehicle electrification,” said Scott Fallon, general manager of automotive marketing with Sabic Innovative Plastics.

BATTERY OF IMPROVEMENTS

Let’s start with the area of greatest challenge: the battery. Rechargeable batteries are usually the most expensive components of PEVs and HEVs, accounting for about half the retail cost of each vehicle. It’s also the vehicle’s core, in that its power capacity determines the driving range. But it’s not exactly as light as a feather — battery pack structures can weigh up to 300 kg on a mid-sized car — and this is a drawback that can undermine environmental benefits. “Because battery modules present a significant weight increase, one of the most important challenges is to find engineering resins that are less dense, to offset the added weight, while still structurally strong,” Fallon said.

And they are indeed finding them. “Sabic’s Noryl resin addresses this challenge, and is being used today on vehicles like the 2013 Nissan Leaf,” Fallon continued. “Noryl resin, by design, has a lower density than other engineering resin materials like polyamides or nylon 6/6, and also exhibits low moisture absorption, a property which may allow for thinner wall design for even greater weight savings.”

Similarly, DuPont’s Zytel HTN PPA resins and new Zytel PLUS nylon resins can offer up to 40 per cent lower mass in a PEV or HEV battery pack than aluminum, the company said, as well as the design freedom to enable parts integration and improve packaging to save space and component cost.

Another battery-related challenge is that, unlike traditional automotive lead-acid batteries, higher energy density battery packs for PEVs and HEVs are composed of many separate battery cells — up to 200 in some cases — and the structure around these cells and their electronic control systems must maintain stringent dimensional stability. The problem? With so many stacked components in limited spaces, even a little instability could potentially cause misfits, leakage, or possible damage due to limited clearances. “Sabic’s Noryl and Noryl GTX resins — the latter a blend of polyamide and PPE — offer lower initial mold shrink and warp, lower moisture uptake that minimizes dimensional and mechanical property changes, and a lower and more stable coefficient of thermal expansion,” Fallon said. “These high-end properties help keep the performance of the battery pack system stable regardless of potential changes in environment such as temperature, humidity, and load.”

A much-publicized problem afflicting PEVs and HEVs of late is fires in battery packs that use lithium-ion. For example, electric vehicle maker Tesla Motors Inc. is currently awaiting results of a U.S. probe into crash-related battery fires — and a February 2014 report of a fire happening in a Toronto garage involving a PEV that wasn’t even plugged in for recharging hasn’t helped.

The trouble stems from the fact that higher power and energy density requirements in battery pack structures challenge the upper performance limits of some materials, which means they require protection from exposure to high voltage systems as well as electrical isolation and thermal conductivity — something neither metals nor plastics have been able to do alone.

The fires are a public relations disaster that newer engineering resins might just alleviate. “Many automakers across the world are now using UL 94 — which is a plastic flammability standard set by Underwriters Laboratories — to qualify polymers for battery packs and related components, especially for battery packs that use lithium-ion,” Fallon said. “Flame tests under UL 94 are used to determine a material’s tendency to either extinguish or spread a flame once it has been ignited. Sabic’s Noryl resin meets the stringent flame retardant requirements of the UL 94V-0 rating.”

Also, DuPont offers Energain separators for high performance lithium-ion batteries, which the company said can improve safety by providing stability at high temperatures, as well as increasing battery power 15 to 30 per cent and battery life by up to 20 per cent.

LIGHTEN UP

Getting away from battery packs, it seems a safe bet that engineering resins will also play increasing roles in virtually every other aspect of PEV and HEV manufacturing. For example, BASF now offers its Ultradur HR polybutylene terephthalate with integrated flame retardancy and laser transparency, qualities that the company said make the material well-suited for PEV and HEV control housings and charging plugs.

But the dominant need is for overall weight reduction. “Removing weight is critical to the auto industry in general, but even more so for electric and hybrid cars,” said Ignacio Osio, key growth program manager, polycarbonates, with Bayer Material­Science LLC. “A wide variety of today’s engineering resins can be used throughout the vehicle — for trim, lighting, thermal management systems, hoses and tubing, interior components, and more. Anything that goes into the electric or hybrid car is going to be scrutinized by the automaker for weight savings.”

A case in point is Nissan&r
squo;s 2013 Leaf, the top-selling PEV in the world. The updated Nissan Leaf is 80 kg lighter than the outgoing model, a reduction made possible by changes to the powertrain and integrated functions, a streamlined battery module and case structure, and the use of lighter parts — including up to 20 per cent weight savings for the terminal cover and spacer of the Leaf’s battery system through the use of Sabic’s Noryl resin.

The finished PEVs and HEVs rolling down the highway are the end results — what we see. Less visible, but just as important, are the charging stations that give the vehicles their power. Located outdoors, and with cars backing towards them — and sometimes into them — they need to be rugged and able to withstand the elements. ChargePoint, the world’s largest network of PEV charging stations with over 15,000 charging locations and a 70 per cent market share, uses Bayer MaterialScience’s Makrolon 6487 polycarbonate for the top cap and plug holsters on its CT4021 Bollard Dual Charging Station, and Makrolon 6557 clear polycarbonate for the front-facing panels. The Makrolon 6487 polycarbonate was selected for its flame retardant UL 94V-0/1.5 mm and 5VA/3.0 mm ratings, Bayer MaterialScience said, and the Makrolon 6557 clear polycarbonate for its impact resistance, flame retardancy, and UL 94V-0/3.0 mm rating.

Despite disappointing sales, these are still early days for PEVs and HEVs, and it’s anyone’s guess as to whether or not tomorrow’s consumers will overcome today’s concerns that zero-emission cars are too expensive, less efficient, and less practical than conventional gas and diesel vehicles. But most automakers are all in, at least for now, so expect them to demand more engineering resins for more and more vehicle parts. It’s all part of the high-stakes double down.