Demand for lightweight energy storage technology is driving the development
of carbon fiber composites for automotive batteries and other electronics.
Driven by the explosion of mobile and portable electronics and the
proliferation of drones and electric vehicles (EVs), the research race is on to
develop new lightweight materials for energy storage technologies, especially
ones with longer lifespan and higher High weight and volume efficient materials.
Carbon and composite materials have been an integral part of energy storage
systems for decades, with a notable example being graphitic carbon, which
contains the anode of lithium-ion batteries. The anode is usually made of a
carbon fiber composite made of metal or metal oxide, plus a polymer coating, a
barrier layer and some type of cathode to create an electrical potential that
allows electrons to flow through the circuit. Carbon fiber/polymer matrix
composites filled with conductive materials are also used as electromagnetic
interference (EMI) shielding materials and are widely used in special aerospace,
automotive, consumer electronics and other fields.
An emerging research approach to composite energy storage is to minimize
the mass of batteries, fuel cells, and capacitors through state-of-the-art
materials, with the ultimate goal of increasing overall power density. “One of
the problems today is that around 50% of a battery’s weight can go into
components that don’t produce energy,” said Dr. Rid Collins, senior technology
analyst at IDTechEx (London, UK), which conducts research on emerging
technologies, including advanced materials. Independent market research.
For example, in the battery packs that power electric and hybrid vehicles,
a necessary component of the total power system mass is the battery casing.
Simon Hiiemae, technical director at automotive thermal management specialist
Zircotec Group (Abingdon, UK), said: “High voltage batteries, performance EVs
can reach over 1,000 volts, generate a lot of radio frequency noise.” Hiiemae
points out that protecting sensitive controls integrated into EVs One approach
for electronic devices is to place the battery in a metal box, usually aluminum,
that acts as a Faraday cage to absorb electromagnetic fields or radio frequency
interference from the battery itself or surrounding sources; however, this adds
considerable weight. Replacing metal with lightweight carbon fiber composites
can save weight, but most composites are transparent to radio frequency noise
and do not provide the required level of interference protection.
Zircotec Group has introduced a solution to this technical challenge: a
conductive two-part coating system that can be easily applied to battery
housings made of carbon fiber or glass fiber filled composites. The first layer
of the coating is a thin aluminum alloy adhesive layer that is applied directly
to the composite material without any solvents or adhesives and provides the
conductivity needed to protect the battery from interference. Second, a ceramic
layer is applied over the first metal layer to protect it from wear and
corrosion; additionally, this ceramic layer can be modified to incorporate
thermal barrier protection to protect the battery from external heat sources.
Hiiemae reports that many car manufacturers are testing the coating; he says
composite battery casings can save up to 4kg/m2 in weight compared to
aluminum.
multifunctional materials
Also gaining traction in the energy storage industry are structural
laminates capable of generating electrical current or storing charge, an
approach that attempts to integrate structural and electrical systems into
power-consuming products. This type of multifunctional material was first
proposed and explored in research more than 20 years ago. It is mainly aimed at
special and advanced special aerospace applications. It still faces huge
technical challenges on the road to full commercialization. However, in the past
five to six years, the development of multifunctional materials has made
substantial progress on several fronts.
Composite structural supercapacitors (SSCs) have special development
potential, in part because of their relatively simple structure. SSCs store
energy through electrostatic charge accumulation at the electrode/electrolyte
interface and are typically designed as a sandwich structure of two carbon
porous electrodes separated by a membrane and embedded in a liquid electrolyte
with high ionic conductivity. Traditional commercial supercapacitors offer high
energy and power density, long cycle life, and reliable operation over a wide
range of temperatures and conditions. While SSC could one day be used to power
trains or cars, the earliest commercial SSC applications are likely to be in
special-purpose unmanned aerial vehicles (UAVs), idtechex's Collins said. "SSCs
integrated into UAVs can significantly extend range and mission time, which is a
critical performance requirement," Collins said. "Additionally, the first
commercial SSCs are expensive to build, so they are likely to be the most
suitable Special type of project.”
The accelerated pace of research into multifunctional materials is helping
to move this technology toward commercialization. For example, an EU-funded
project called Wizard is supporting research into lightweight structural energy
storage materials for electric and hybrid electric aircraft. The project aims to
develop advanced materials and technologies that can be used in structural
batteries and structural supercapacitors.
Another project involves a group of researchers from the IMDEA Institute of
Materials (Getafe, Spain) in collaboration with some special aerospace projects
funded by the European Union, such as Project Wizard, including the Airbus
project. The team demonstrated the structure of a new type of electric
double-layer capacitor (EDLC) made from thin sandwich structures. The structures
are staggered and include an ionic, liquid-based polymer electrolyte between a
veil of carbon nanotube (CNT) fibers and a carbon fiber layer infused with epoxy
resin. Dr. Juan Jose Vilatela, a member of the multifunctional nanocomposites
group, said the composites produced in this project are noteworthy for high
specific capacitance and power density of 88 mf/g and 30 wh/kg respectively.
This is one to three orders of magnitude higher than the best performing
structural materials. The material also has an energy density of 37.5Wh/kg, one
of the highest measured values for structural supercapacitors studied so
far.
Carbon nanotubes have the inherent advantage of having a surface area 1,000
times greater than carbon fiber fabrics, Vilatela said. Carbon nanotubes also
have high electrochemical stability. To fabricate EDLC composites, a thin EDLC
sandwich was set between eight layers (4+4) of Hexcel (Stamford, CT, US)
Hexforce high-strength carbon fiber fabric (G0926), vacuum infused by Ashland
Chemical (Columbus, OH, US) ) is supplied with epoxy vinyl ester resin Derakane
8084 and cures completely within 48 hours. room temperature. The middle layer
consists of a sandwich structure that includes a polymer electrolyte membrane
about 100-120 microns thick from the middle outward, set between two CNT fiber
plates, both of which are fixed to thin aluminum current collector plates.
superior. Carbon nanotube fibers were synthesized by direct spinning method
using iron, sulfur catalyst and butane as carbon sources.
A small amount of pressure is applied to the sandwich to impregnate the
soft electrolyte membrane into the porous CNT fiber sheet before being
positioned between the outer layers of carbon fiber fabric. The EDLC samples
prepared in this study were approximately 4 centimeters square (the size of a
typical laminate structural beam), although Vilatela said free-standing EDLCS
can be used without the need for additional structural support and can be as
large as 100 square centimeters. Field electromechanical measurements of EDLC
samples in four-point bending tests showed that the electrochemical performance
was maintained up to the breaking point. The trial is a key validation of the
material's performance, given its applications as a structural and energy
storage material.
IMDEA Group's use of unidirectional CNT fabrics to build the SSC
distinguishes the project from similar parallel work using various "active"
carbon fiber fabrics as energy storage materials. One such project cited by
Vilatela et al. A paper published in Scientific Reports (February 2018) uses
infusion technology to grow high-surface-area carbon aerogels (CAG) around
carbon fiber fabrics. Combined with an ethylene glycol matrix containing 10%
lithium ions, this technique produces a material with a calculated energy
density of only 0.84 m wh kg, which is low compared to that obtained with EDLC
containing CNT fibers. This technology, particularly when using
high-surface-area composites, resulted in a composite with a shear modulus of
895 MPa, which is comparable to conventional structural composites. In
comparison, the CNT composite in the IMDEA study had a flexural modulus of 60
gpa and a flexural strength of 153 mpa, values that are comparable to typical
unfilled polyimide and lower than those used in composites used in major
structural applications. required strength and stiffness properties.
The results of each project illustrate, in broad strokes, one of the
challenges in developing fully commercialized multifunctional materials suitable
for a wide range of applications: namely, it is difficult to build materials
with adequate electrical and structural properties. composite materials.
Collins believes that the current trade-off between structural and
electrical performance will not be a major barrier to adoption and
commercialization of the technology. "I don't think the degradation in the
structural properties of these new composite energy storage materials will limit
their effectiveness, because even the slightly inferior carbon fiber
reinforcements are still strong and stiff enough to be useful in some
applications," he said. Greater The problem, he believes, is how to design and
mechanically integrate solid polymer electrodes and separators that are
electrically insulating but ionically conductive. Other challenges include
cost-effective manufacturing and safety.
Leading automotive energy technology
In automotive racing, however, the future of advanced materials energy
storage is already here. The first all-electric Formula E car in the FIA
racing series since 2014, it is powered by an advanced multifunctional
composite 800V structural battery. The battery technology was developed and
manufactured by Williams Advanced Engineering (Grove, UK), the sole supplier of
vehicle batteries for the Formula E grid. A typical Formula E car has about 250
horsepower (190 kilowatts), can accelerate from 0 to 100 km/h (0 to 62 mph) in 3
seconds, and has a maximum speed of 225 km/h (140 mph). For more information
about Williams Advanced Engineering’s structural battery systems for consumer
vehicles, such as the battery-electric FW-EVX, see CW’s November 2018 Focus on
Design Story Design Story "Pushing EVS Forward".
On the other hand, Hyundai Motor Group (Seoul, South Korea) is using
hydrogen fuel cell technology provided by SGL Group (Wiesbaden, Germany) to
manufacture its zero-emission car Nexo. The production vehicle covers years of
development work and collaboration between the automaker and SGL, during which
Hyundai optimized the hydrogen powertrain and other components on the Ix35
demonstration fuel cell vehicle. Since starting production in March 2018,
Hyundai has reported average sales of about 45 units per month, and if it can
maintain this pace, it will reach sales of more than 500 units in 2018, which is
a new year for hydrogen fuel cell vehicle sales. Record.
NEXO's core technology is the Sigracet fuel cell, a polymer electrolyte
membrane fuel cell (PEMFC) developed and marketed by SGL. Proton exchange
membrane fuel cells (PEMFC) generate electrochemical power by converting
hydrogen fuel into electricity, with the only by-products being water and heat.
A single PEMFC cell consists of two flow fields, including two gas diffusion
layers (GDL) and two carbon-supported precious metal catalyst layers, each
separated by a proton exchange membrane. GDL, in turn, is a two-layer structure
consisting of a macroporous backing material (carbon fiber paper) and a
microporous carbon base layer. The membrane electrode assembly is constructed as
a layered laminate with one GDL layer serving as the anode and another GDL layer
serving as the cathode. PEMFCs are sandwiched between two bipolar plates (BPP)
made of graphite, coated steel or titanium. BPP forms the structural components
of the chimney and is designed with channels to accommodate coolant flow and
water outlets. Automotive PEMFC systems typically consist of up to 400 battery
packs with a power output of approximately 80 to 120 kilowatts.
Composites are making progress in energy storage, but making cleaner,
lighter energy a large-scale reality will depend on the details of advanced
technologies such as fuel cells, structural batteries and structural
supercapacitors.
IDTechEx studies and evaluates the Technology Readiness Level (TRL) of a
variety of multifunctional polymer composites. The rating system is based on a
range of criteria, including whether the research remains primarily academic
(resulting in a lower rating), whether the technology is being prototyped or
tested (resulting in a higher rating), or whether the technology has reached
commercialization (the highest rating). Data mining shows that multifunctional
materials for energy storage and energy storage are still in a relatively early
stage of development by IDTechEx standards - just ahead of self-healing
materials and fully embedded circuits, but behind power transmission and
embedded sensors . "When you look at electrodes for SSCs, for example, one of
the challenges is how to improve the surface area appropriately," Collins noted.
"CNTs show promise, but there are still ways to prove this commercially."
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