Structural Batteries Could Reduce Electric Vehicle Weight

GOTHENBURG, Sweden—Engineers at Chalmers University of Technology have produced a structural battery that performs 10 times better than all previous versions. It contains carbon fiber that serves simultaneously as an electrode, conductor and load-bearing material. The breakthrough paves the way for “massless” energy storage in electric vehicles.

Although engineers have been working on structural batteries for more than 10 years, it has been difficult to manufacture them with both good electrical and mechanical properties. The new battery has properties that far exceed anything yet seen in terms of electrical energy storage, stiffness and strength.

The battery has a negative electrode made of carbon fiber and a positive electrode made of aluminum foil coated with lithium iron phosphate. They are separated by a fiberglass fabric in an electrolyte matrix.

“The carbon fiber acts as a host for the lithium and thus stores the energy,” says Leif Asp, Ph.D., a professor of material and computational mechanics who is heading up the R&D project. “Since the carbon fiber also conducts electrons, the need for copper and silver conductors is avoided, reducing the weight even further.

“Both the carbon fiber and the aluminum foil contribute to the mechanical properties of the structural battery,” explains Asp. “The task of the electrolyte is to transport lithium ion between the two electrodes of the battery, but also to transfer mechanical loads between carbon fibers and other parts.

“The batteries in today’s electric cars constitute a large part of the vehicles’ weight, without fulfilling any load-bearing function,” Asp points out. “A structural battery, on the other hand, is one that works as both a power source and as part of the structure, such as a car body.

“This is termed massless energy storage, because in essence the battery’s weight vanishes when it becomes part of the load-bearing structure,” says Asp. “Calculations show that this type of multifunctional battery could greatly reduce the weight of an electric vehicle.

“It is absolutely conceivable that [future] electric cars, electric planes and satellites will be powered by structural batteries,” claims Asp.

The battery has an energy density of 24 watt-hours per kilogram (Wh/kg), meaning approximately 20 percent capacity compared to comparable lithium-ion batteries currently available. But, since the weight of vehicles can be greatly reduced, less energy will be required to drive an electric car, and lower energy density also results in increased safety. And, with a stiffness of 25 gigapascals (GPa), the structural battery can compete with many other commonly used construction materials, Asp believes.

A new project, financed by the Swedish National Space Agency, now underway aims to increase the performance of the structural battery even further. According to Asp, the aluminum foil will be replaced with carbon fiber as a load-bearing material in the positive electrode, providing both increased stiffness and energy density. In addition, the fiberglass separator will be replaced with an ultra-thin variant, which will provide faster charging cycles.

Asp estimates that such a battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa. “This would make the battery about as strong as aluminum, but with a comparatively much lower weight,” he claims.

Denso to Study 5G Use in Autonomous Vehicles

KARIYA, Japan—Engineers at Denso Corp. are studying how 5G technology can be used safely and securely in autonomous vehicle applications. They are working with KDDI Corp., a Japanese telecommunications company, on the project.

The two companies are building a test track at Denso’s global R&D center in Haneda, Japan. Engineers will verify driver assistance technologies using high-definition in-vehicle cameras and roadside sensors that detect conditions such as oncoming vehicles and pedestrians.

They will leverage low latency connections, which are achieved through edge computing technology for 5G, including AWS Wavelength. The goal is to build a system for distributing ever-changing road conditions to autonomous vehicles in real time and to verify the remote driver assistance technology.

Denso and KDDI plan to conduct verification using end-to-end network slicing. This advanced technology provides unique communication environment preferences, depending on the application and requirements, by virtually partitioning a network.

New Technology Enables High-Volume Fuel Cell Production

AACHEN, Germany—Traditionally, fuel cell manufacturing has been a complex, slow process. To address the issue, engineers at the Fraunhofer Institute for Production Technology (IPT) have developed a continuous assembly line that automatically makes fuel cell components and then assembles them into a stack. The goal is to produce fuel cells on an industrial scale at competitive prices.

A stack is the heart of a fuel cell. It consists of hundreds of bipolar plates arranged on top of one another.

Gas and air are pulled through an intricate system of millimeter-thick channels in the bipolar plates; hydrogen is fed in at one end and water produced by the chemical reaction in the stack is fed out at the other.

However, producing these bipolar plates is challenging. The plates are only about 100 microns thick and tend to resemble a film rather than a plate. They must be moved very carefully to make sure nothing gets creased or wrinkled.

First, presses are used to emboss channel structures onto the plate blanks. They are then coated under vacuum to reduce their electrical resistance and make them more corrosion-proof. A finished bipolar plate consists of a left half and a right half, with the fine channel system between. The two halves then need to be welded together with a high degree of precision. There are also multiple cleaning steps.

“We need nonstop production lines that are able to process components in cycles lasting just seconds,” says Christoph Baum, Ph.D., managing director of Fraunhofer IPT. “Right now, various components are manufactured by various producers and then assembled to create the fuel cell.

“Production steps, such as forming, cleaning, coating and joining the fuel cell components, are spatially separated from one another in various machine islands,” explains Baum. “All in all, the logistics within production facilities are complex. Parts have to be picked up, placed and buffered multiple times.”

Fraunhofer IPT engineers developed a production line that enables special pick-and-place handling devices to move all components and assemble bipolar plates in a fluid process.

“Because some process steps are faster than others, the challenge is to optimize the flow as a whole so that neither jams nor waiting times occur,” says Baum. “The blank pressing process, referred to as deep drawing, is done in just about 1 second, while the deposition of the protective layer takes much longer.

“We are predicting that hundreds of thousands of bipolar plates will be needed for the hydrogen economy of the future,” Baum points out. “For this reason, we are striving to achieve a throughput of at least one bipolar plate per second across all plants.”

In the CoBIP project (continuous roll-to-roll production of bipolar plates for fuel cells), Fraunhofer IPT engineers developed equipment for processing bipolar plates in a film strip off the roll. The film strip passes through the machine and through all process steps—from the blank to the forming, the deposition of the protective coating to the cleaning through to the laser welding process.

“Only at the very end are the bipolar plates cut off the strip and isolated,” explains Baum. “This continuous process from the roll to the finished item will save a number of handling steps.

“The plant is designed to be so flexible that [companies] are able to exchange and test individual production modules at will,” says Baum. “We are providing manufacturers with a tool they can use to design and optimize a nonstop production line to suit their requirements. A high cycle rate allows several devices to operate in parallel or to be connected in series, such as lasers for joining the plate halves.

“When it comes to fuel cells, the hurdle of industrial production scaling should not be underestimated,” warns Baum. “Similar to the situation with batteries, transferring systems from the laboratory to mass production is a complex matter.”

Rolls-Royce Tests Speedy Electric Aircraft

STAVERTON, England—Britain has a long history of setting speed records on land, sea and air. The latest chapter is being written by Rolls-Royce and its “Spirit of Innovation” electric aircraft.

Later this year, the engine manufacturer plans to set a world record by breaking the 300 mph barrier. The aircraft recently completed a successful taxi. For the first time, the plane powered along a runway propelled by its 400-kilowatt electric power train.

“The taxiing of the plane is a critical test of the integration of the aircraft’s propulsion system ahead of actual flight-testing,” says Rob Watson, director of Rolls-Royce Electrical. “For the first time, the plane propelled itself forward using the power from an advanced battery and propulsion system that is ground-breaking in terms of electrical technology.

“The first flight is planned for the spring,” explains Watson. “When at full power, the electric power train and advanced battery system will power the aircraft to more than 300mph, setting a new world speed record for electric flight.

“[We] will be using the technology from the project and applying it to products,” adds Watson. “We are bringing a portfolio of motors, power electronics and batteries into the general aerospace, urban air mobility and small commuter aircraft sectors as part of our electrification strategy.”

New Welding Processes Improve Battery Assembly

COLUMBUS, OH—Lithium batteries are made up of alternating layers of copper and aluminum foils that function as current collectors and substrates for the active materials inside the cell. These foils can be as thin as 7 microns, and generally no thicker than 25 microns.

Multiple layers of foils—from a few dozen to more than 150—must be welded (aluminum to aluminum, copper to copper) to collect the current in each layer and transfer it to one of two thicker collector tabs that exit the battery and are joined to busbars or other battery tabs.

“Welding of battery pack foils is usually accomplished using ultrasonic processes, but some stacks are laser welded,” says Tim Frech, senior engineer at EWI. “Neither process requires filler materials, and both weld at a high productivity rate.

“Laser and ultrasonic welding are both effective processes for attaching battery foils,” explains Frech. “However, neither joining method can be monitored in process. So, when a battery batch is defective, the problem is not identified until after material, time and money has been spent. A foil welding process with built-in weld quality measurement could be an enormous time- and money-saving benefit to [manufacturers].”

To address the issue, Frech and his colleagues recently tested a resistance spot welding technique that uses a capacitive discharge power supply. The system has the capacity to collect and measure data in process, thus offering the potential to monitor quality in real time, and ultimately reduce cost and waste.

“Resistance welding provides precise controls of all process inputs and reliable measurement of all process outputs,” notes Frech. “This data is critical for establishing and maintaining a weld quality standard not currently available with other processes for battery foil welding.”

Another new assembly process that could streamline EV battery production is pulsed arc welding. It creates a high-energy density arc between a tungsten electrode and the workpiece. This results in high local temperatures to melt the metals to be welded, with minimal heat-affected zones.

“Pulsed arc welding is typically used in small-scale welding processes,” says Frech. “Controlling current and welding duration allows for a stable welding process. Since the system is closed-loop, there is the possibility of providing in-process quality assurance.”

European Engineers Tackle EV Lightweighting

ZARAGOZA, Spain—Engineers at the Technological Institute of Aragon here are coordinating a new European Union initiative to develop lightweight components for electric vehicles. The goal of LEVIS is to create multimaterial production technologies that include recyclable resins and bio-based carbon fiber composites.

Thirteen other organizations are involved in the two-year project, including Cenex Nederland, Marelli Suspension Systems and Steinbeis-Europa-Zentrum.

“[Because] electric vehicles are powered by batteries that often carry considerable weight, car manufacturers and suppliers must seek new lightweighting technologies for other car components to compensate for this excess weight,” says Agustín Chiminelli, scientific coordinator of the LEVIS project. “These technologies can directly contribute to improving vehicle efficiency in terms of kilowatt hours consumed per kilometer, as well as vehicle autonomy, and also reduce environmental impact.”

Chiminelli and his colleagues will be focusing on three different components: a cross beam, a suspension control arm, and a battery clamping and packing system.

“We will use multimaterial solutions based on thermoplastic carbon-fiber compounds integrated with metals, which will be produced through a set of profitable and scalable manufacturing technologies,” explains Chiminelli. “Thanks to their excellent mechanical properties, these composites, properly combined with metals, are ideal for light applications.

“LEVIS aims to develop [new technology] for these multimaterial components based on resins and environmentally friendly reinforcement systems, cost-effective manufacturing processes, optimized joints, advanced simulation methodologies and structural integrity monitoring technologies,” Chiminelli points out. “The combination of these developments will allow us to obtain lightweight components.”

“The new lightweight components will be developed using a circular approach,” adds Theodora Skordili, business development manager at Cenex Nederland. “This means that we will pay special attention to the use of recyclable materials and the design of the components so that, at the end of the useful life of the components, nothing will be wasted and each part can be recycled or reused for the same component or for others. The useful life of these components will be optimized, and they will be designed to allow simple and efficient disassembly and reuse.”