carbon nanotube reinforced structural composite supercapacitor - commercial energy storage systems

Carbon nanotubes have mechanical properties that are ideal for enhancing structural composites, and the specific surface area and conductivity are attractive to electrolytic capacitors.
Here we show the multi-functional synergy between these properties in composite materials that exhibit simultaneous mechanical and energy storage properties.
This includes an enhanced electrode that uses a tightly arranged carbon nanotubes grown on a stainless steel web that is layered with a Kefla or fiberglass pad in an ion-conductive epoxy
The resulting energy storage composite materials exhibit elastic modulus above 5 gpa and mechanical strength greater than 85 mpa, for the entire combination system including electrodes, collector, kaifla or fiberglass, energy and electrolyte matrix.
Also, from in-situ mechano-electro-
Chemical tests show that the performance of the super capacitor remains constant and stable throughout the elastic state.
Carbon fiber reinforced structural composites, with high strength-to-weight ratio and controllable form factor, are the benchmark materials for structural applications.
However, the extraordinary stiffness, strength and conductivity of carbon nanotubes (CNTs)
Make them the next obvious candidate.
Reinforced composite material.
In parallel with this, nano-activated carbon, due to its conductivity, high surface area and electro-chemical stability, provides a benchmark for high-power electro-capacitors, similarly, in this application, carbon nanotubes and graphene-based materials have also become viable candidates.
Generate high power energy storage.
Most carbon-based ultra-capacitor materials with ultra-high surface area are not compatible with the structural reinforced composite design, but carbon nanotubes make the non-
The Faradaic energy storage feature provides a high surface area advantage at the same time.
These concepts are a new class of CNT-
Based on energy storage materials, it can be developed using traditional composite processing routes, showing mechanical properties comparable to those of commercial composites, and having built-in
The ability to be dynamic and stable in the environment.
This solved "on-
In systems that have little tolerance to external payload weights, especially for high power applications that require a large number of battery footprints.
Early Consideration of structural energy storage composite materials derived from lithium in commercial packaging-
Ion batteries can be embedded in the wings of a driverless car (UAV)
The doors of the car, and the walls of the ocean boats.
The challenge of this approach is that battery packaging hinders the strength of these architectures.
Recently, a more elegant approach has emerged that the composite itself can act as both structural and energy storage materials, presumably light or non-external packaging materials.
In view of the initial efforts in this area to explore structural batteries, structural materials need to withstand environmental exposure and to maintain life synergy with structural components in the system (tens of years)
Incompatible with status-of-the-
Artistic durability of battery reports.
In this way, the electric double-layer capacitor (EDLCs)
As an attractive direction, because
The Faradaic storage mechanism of these devices leads to the stability of commercial systems, which are often cited for more than millions of cycles, which are integrated into structural components in expensive systems, such as buildings or vehicles.
Over the past few years, some limited approaches to developing EDLC devices with structural integrity have been demonstrated.
Most notably, the recent work of the greenhag group has brought together carbon fiber current collectors and high-surface-area gas gel electrodes-
Ethylene glycol diethyl ether (PEDGE)
-Ionic liquid (IL)electrolytes.
This route produces composite device performance with energy density up to 0.
1 mWh/kg, power density up to 3.
8 mw/kg, ultimate tensile strength 8.
71 mpa, the modulus is 0. 9u2009GPa.
However, this design is limited to very low operating voltages close to 0.
4 v and other related studies similar to this field show the mechanical and electro-chemical properties independently evaluated from each other.
Recently, Senokos.
, Developed a CNT-
Fiber super capacitors with energy density up to 11.
Based on the active mass of the electrode, the power density of 4wh wh/kg and 46 kw/kg highlights the potential of carbon-based materials, especially the potential of carbon nanotubes in structural energy storage.
The recent work of Wu is also concerned.
, Established the advantages of using directional carbon nanotubes in the application of super capacitors in obtaining high energy and power density.
However, despite some progress so far, there are still key challenges between the conceptual idea of structural energy storage materials and the actual design of such materials.
Specifically, structural materials must show stability under different environmental conditions without packaging and must show energy storage under mechanical stress, and must be able to achieve energy density, discharge voltage, structural integrity related to the application market of existing products at the same time.
In addition, unlike traditional energy storage devices usually encapsulated under compression, the mechanical integrity of the electrode/current collector and electrode/electrolyte interface is the basic design scheme of the composite material, the scheme has not yet become part of any previous research on structural energy storage materials.
In addition to choosing the ideal structural material, the interface engineering building containing this ideal structural material is a key design component of this multi-functional system.
Until now, even the basic premise of evaluating multi-functional performance by simultaneously testing the electro-chemical and mechanical properties of these materials is still elusive, although it is a way to store and release charges at the same time and maintain mechanical integrity.
In this report, we demonstrate the ability to synthesize high-density networks of carbon nanotubes arranged directly on the surface of stainless steel mesh materials to achieve enhanced structures and energy storage interfaces in multi-functional composites.
This design includes alternating CNT-
An enhanced electrode interface layered in ions with Kefla or fiberglass mesh
Conductive two sugar based on epoxy resin
Ionic liquid matrix.
The direct growth of carbon nanotubes creates an enhanced interface, which overcomes the realization of carbon nanotubes-
The matrix enhances and uses the high surface area of carbon nanotubes to achieve electrically accessible EDLC charge storage.
Our results show that the total energy density of the system is as high as 3 mWh/kg, the power density is as high as 1 w/kg, the modulus exceeds 5 gpa, the ultimate tensile strength exceeds 85 mpa, and the mechanical properties are available at the same time.
Our tests show that the energy storage performance remains in this device configuration in the elastic state of the entire device, and stable degradation is measured in the plastic state.
Our work lays an important framework for the design and key evaluation methods of a class of structural enhanced energy storage materials in the future.
Figure make-
Structural Composites with a photo and schematic diagram of the structural super capacitor shown in the figure.
For electrode materials, CNT chemical vapor deposition (CVD).
Three kinds of stainless steel mesh (
316 stainless steel (SS)
200 mesh, 316 SS 400 mesh, 304 SS 200 mesh and several different growth temperatures (740–790u2009°C)
Analysis and Optimization of CNT growth (Fig. ).
In 790 ℃ under growth in 316 SS 400 of and 770 ℃ under growth in 304 SS 200 of the of CNT was for we based on the highest CNT growth density of Device Research (
See SI, graph and table).
Average mass load of carbon nanotubes on stainless steel
The steel mesh is between 0. 30–0. 40u2009mg/cm (Fig. )
And the thickness of carbon nanotubes was measured between 15-80 μm.
Additional microstructure features (SEM, TEM)
The Raman spectra of cnt grown on stainless steel mesh are provided in the supporting information graph and in.
The picture shows three bird eyes and cross-
Compared to the uncoated SS, the SEM image of the section of the optimum CNT growth and the photo of the CNT coated SS Steel.
Here, the cnt is completely coated with steel mesh at a length of 15-30 µm.
In addition, the growth of CNT results in a uniform color change in mesh holes from silver to metal black.
Photo of epoxy resin
Compared with the photos of ordinary IL and pure epoxy materials, IL composites for electrolyte.
These pictures show the color of the epoxy resin containing IL, resulting in an opaque white material indicating that it came from the double-Phase material.
It should be noted that in this method, carbon nanotubes do not form aggregates in the polymer electrolyte matrix because they are bound on stainless steel
The steel base they grow. Finally Fig.
Two different types of insulating layered materials used in multi-functional composites are shown, namely, fiberglass and kaivelar.
In the IL electrolyte, the electrolytic test of cnt grown on the 316 SS 400 grid shows that the capacitance is about 120 mF/cm, and the capacitance is significantly increased on the SS grid without cnt (Fig. ).
For composite design, for polyethylene, fiberglass, and kaivelar (Fig. )
, It was found that the resistance of Kaifu fiber and glass fiber increased slightly, and the glass fiber separator showed an electrolytic window around 2 v.
After this, the structural composites are assembled with cnt grown on 316 SS 400 mesh electrodes, Kaifu fiber separator and 45-55 epoxy resin
The performance of IL electrolyte and electrolysis was evaluated (Fig. ).
Electrolyte is a key component of any multi-functional energy storage device, according to our previous work, non-
The choice of moisture-absorbing epoxy resin-based electrolyte containing ionic liquids is due to good environmental stability and the feasibility of effective integration of high-surface carbon nanotubes.
According to the measurement results reported in our previous work, the ionic conductivity of the 55% ionic liquid epoxy mixture is ~ 0. 1 mS/cmu2009.
Cyclic KVA (CV)
Curve reflection ~ The electrochemical window of 2.
5 v and maximum capacitance at a slow speed of 60 mF/cm (16 mF/g)
And the capacitance of 15 mF/cm (3 mF/g)
Under the fast rate of 500mv mv/s
Support information provides electrical properties of stainless steel grids with and without CNT growth in ionic liquid electrolyte (Fig. )for comparison.
The volume capacitance of the stainless steel mesh grown by CNT is 90 mF/cm, and when the scanning rate is 20 mv/s, the volume capacitance of the stainless steel mesh without CNT is 20 mF/cm.
This is equivalent to the best carbon gas gel based device with a similar capacitance of about 35 mF/cm in the literature (74 mF/g)
, But since their electrolytic windows are lower than 0, showing a lower energy density, the actual applicability is limited. 4u2009V.
Electrostatic charging-
The discharge curve of multiple current ranges from 1.
5 MoMA/cm, 8 MMA/cm (Fig. )
Shows the stable performance of the ultra-capacitor device.
It should be noted that the voltage drop or DCIR (
DC internal resistance)
As the distance between the two electrodes of the device increases.
Although, as shown in our previous work, the electrolyte itself can be used as a separation between the two electrodes, the mechanical strength requirements of this multi-functional equipment are improved, and therefore the mechanical solid separator material needs to be used, such as Kefla/fiberglass, this increases the separation between the two electrodes, resulting in an increase in pressure drop.
However, for this system dependent on mechanical properties, reliable mechanical behavior can be achieved by using this separator material without compromising the energy storage function due to preventing short circuit of the equipment.
The discharge curve is the basis of the volume energy and power calculation shown in the figure.
This compares with the performance of several other structural devices in the literature
State electrolyte.
Specifically, we also include projection values based on the previously reported voltage window assumption of the carbon gas gel device for increased energy and power density, and only assume that the active component mass of CNT fiber devices comes from the work of Senokos. .
Although the performance evaluation based on active quality is an important indicator of the ultra-capacitor device, due to the addition of several inactive design components, the predictive value based on full composite quality will be greatly reduced, these components become critical throughout the architecture of the device architecture.
For our equipment, we calculate energy density up to 3 mWh/kg (10 µWh/cm)
Power density of 1 W/kg (70u2009mW/cm)
Accurate energy and power performance are generated by directly integrating the discharge voltage distribution.
This is compared to an equivalent device with a liquid electrolyte of 10 mWh/kg (30 µWh/cm)
Energy and 10 w/kg (700u2009mW/cm)
Power density (Fig. ).
It is worth noting that our devices show considerable performance in power and energy density using specific and volume assessments compared to other statesof-the-
The art report in the literature and the corresponding data are summarized in the table. Stress-
Strain measurement of structural composite materials (Fig. )
And demonstrate an initial platform that corresponds to fiber alignment and stretching and then teaches the linear elastic properties of the composite, in which case the calculated elastic modulus is 6. 2u2009GPa.
Ultimate tensile strength (UTS)
Calculated ~ 85 mpa, which is the lowest in several tensile tests, the maximum value is close to 120mpa, and the limiting factor in this value is attributed to the steel mesh (Fig. )
Where a serious failure occurred.
This is confirmed by a controlled comparison of the mechanical properties of CNT-
Steel/Kefla/epoxy-
IL composite to simpler Kefla/epoxy-IL composite (Fig. ).
A key feature of our method is the presence of carbon nanotubes, which not only give energy storage properties to our composites, but also provide effective enhancements to the interface with the polymer matrix.
Many previous reports have shed light on the role of carbon nanotubes as effective reinforcement materials in polymer composite lamination.
In particular, the research team from John Hart's 'Brian waldel has demonstrated the sometimes pairs of carbon nanotubes in sheet-reinforced polymer composites ~ Compared to 153% tendons, there were no carbon nanotubes in this case.
In order to determine the interface properties of carbon nanotubes grown on stainless steel mesh, we performed a lap-
Joint shear measurement (
See support information. )
This shows that the mesh with carbon nanotubes has higher toughness compared with the ordinary stainless steel mesh.
These observations show that the carbon nanotubes in our system provide structural enhancements to the structural super capacitors, but also have the dual function of energy storage.
Further efforts to improve mechanical performance include increasing the number of insulation layers between the enhanced electrodes and comparing the performance with fiberglass (
Not Kefla)interlayers (Figs and ).
In this design route, the improvement of mechanical properties comes at the expense of the electrochemical properties and the increase of battery resistance.
When the EIS measurement of the device is compared with 1, 2 and 3 separators, this becomes more and more obvious (Fig. ).
Due to the increase in the thickness of the separator stack, the distance between the electrodes increases, and the equivalent series resistance (ESR)increases.
In general, these mechanical tests show that the route of growing carbon nanotubes on conductive carbon fiber materials rather than on stainless steel networks may lead to a simple route to improve mechanical properties, even if such a route is challenging without damaging carbon fiber.
Under the background of carbon gas gel, the further comparison of the energy storage and mechanical properties of these devices shows that the energy and power density are increased by nearly 2 orders of magnitude, the tensile strength and modulus were increased by 10 times and 5 times respectively (Fig. ).
These curves also show the goal of reflecting the minimum performance of commercial structure composites (~200u2009MPa)
And the commercial availability of the minimum performance of the super capacitor (~0.
Total system weight 5 wh/kg).
In view of the critical target of elastic modulus reached by our work and the order was provided (s)
For these important performance indicators, greater capacitance and better tensile properties are necessary to use this method to replace traditional structural composites with multi-functional energy storage composites.
In addition, the mass density of the fiberglass and kaifla fiber separators used in our work is ~ 83 mg/cm and ~ 54 mg/cm.
The adoption of a separator-free approach, as well as the use of carbon fiber, carbon cloth and other 3D carbon structures integrated with carbon nanotubes, is expected to further improve the performance of the entire system.
These methods provide a platform for further exploration of alternative pseudo-capacitance and faradaic energy storage chemistry, which significantly increases energy density.
Our results also show that the synthesis technology of carbon nanotubes that may lead to higher specific surface area (e. g. SWCNTs)
Using the general design approach outlined in this work to grow on carbon fiber electrodes, the performance that can ultimately produce synergy with all mechanical and electro-chemical targets can be achieved.
Simultaneous dual function of visual CNT-
Steel multi-function energy composite, the Instron load cell is configured with two 5 kg weights (10u2009kg in total)
Suspended from a material consisting of two series of structural super capacitors that are discharged to power the red LED (Fig. ).
The support infographic provides a specific description of the test settings. .
This reflects consistent observations made in these materials, demonstrating the critical operating conditions for multi-functional energy storage composites, I . e. , storing and releasing energy under mechanical stress.
To illustrate the potential applicability of this prototype device in load-bearing applications, concrete blocks (~10 Kg)
Is suspended to connect to the device (see Fig. ).
The equipment maintains good mechanical integrity, providing a feasible route for future work on integrating these devices into system-level engineering methods in practical bearer applications.
Double Power for further mechanical exploration-
Mechanical properties, testing of energy storage performance and mechanical properties at the same time (Fig. ).
Here, in the elastic state of the material, we observe the constant electrochemical and charge storage properties.
The super capacitor shows minimal degradation (
Capacitance degradation ~ 10%)
After 450 charge/discharge cycles in elastic state (Fig. )
Good stability
However, when the device enters the plastic state, the capacitance decreases steadily until the device is no longer charged and a complete electro-chemical failure occurs.
It is worth noting that this occurs after the main mechanical failure of the device near 0.
The strain of the 085 steel mesh begins to deform.
The initial degradation performance of the device performance is increased by internal resistance (DCIR)
And the corresponding large voltage drop (Fig. )
Related to failure of steel electrode.
To verify the consistency of this behavior, two similar mechanisms
Figure and electrochemical measurement of composite materials with ordinary SS/Kevin/epoxy
IL and CNT-
Fiberglass/epoxy-
IL composite showing similar properties.
In each case, the electro-chemical performance is compromised before the device is completely invalidated.
The results show that an important concept is that an electrolytic device failure occurs before a mechanical device fails, which occurs at the beginning of the plastic state.
To sum up, our work shows a CNT enhanced structural composite super capacitor, which exhibits stable energy storage device behavior under mechanical stress, and realizes the structural energy storage composite material.
This method includes enhanced ions-
A cnt conductive epoxy matrix grown from a stay on a steel mesh electrode and layered with an insulating Kaifu fiber or fiberglass material.
Our work utilizes carbon nanotubes grown on a conductive structure template as a mechanical enhanced interface for multi-functional structural energy storage devices and an electrolytic energy storage structure.
Our results show that the elastic modulus is higher than 5 gpa, the tensile strength is higher than 85 mpa, and the specific energy is up to 3 mWh/kg, showing synchronous energy storage and mechanical properties in the elastic state.
While the results of this work bridge the critical energy and mechanical objectives compared to past work, this general technology that uses high density CNT growth on a conductive surface as a layered reinforcement interface in structural composites reflects the way to utilize composite performance indicators at intersections of commercial composites and commercial super capacitor energy storage equipment.
As innovation in energy systems continues to be driven by easier access and seamless integration of energy and technology, our results support the extraordinary prospect of carbon nanotubes as a dual enhanced and energy storage material for the future
Composite structure.