The functionalized graphene/nano-fiber electrode shows 2 times the modulus, strength and 5 to 10 times the multifunctional efficiency.
Structural batteries and structural supercapacitors provide a potential solution for electric vehicles (EVs) because they can not only handle structural loads, but also store energy and/or generate electricity. For future ground and air mobility, this can reduce the weight and volume of the structure and battery, and have a longer distance between charging. However, the mechanical properties of current electrodes used in batteries and supercapacitors are poor because they are usually made of brittle materials.
A team led by Jodie Lutkenhaus, a chemical engineer at Texas A&M University (University of Texas University of America) used reduced graphene oxide (rGO), innovative chemical methods and aramid nanofibers to mimic natural mother-of-pearl, Thus, the Young's modulus and the ultimate tensile strength of the pure rGO electrode are 220% and 255% higher respectively. Compared with the multifunctional electrode, the multifunctional efficiency value of <1 is 5-13.6.
Multifunctional composite material of mother-of-pearl
In an article published in the Matter journal, Lutkenhaus and her team described the use of dopamine to functionalize (chemically bond) rGO and then combine the material with aramid nanofibers to form a composite. The paper explains: "We hypothesized that materials inspired by nature can transform the poor mechanical properties of supercapacitor electrodes into electrodes that mimic pearl, bone or wood to achieve extremely high multi-function efficiency values."
Mother of pearl (Mother of Pearl) is composed of 95% by volume of aragonite (calcium carbonate), chitin and protein, but its toughness is three orders of magnitude higher than that of aragonite alone. Its superior mechanical properties come from its layered composite structure: its constituent particles and matrix have different structures at each geometric scale or level (eg, nano, micro, meso, macro) and combine these levels An effective interface between them to achieve high modulus and strength while reducing crack propagation (see the blog "New Generation 3D Magnetic 3D Printing Tailored Composite Materials").
The Lutkenhaus team knows that it has been shown that graphene-based simulated nacreous electrodes perform very well electrically. The challenge is to improve its mechanical properties. The team tried to use hormones and the neurotransmitter dopamine to functionalize rGO. Dopamine can also be polymerized into a high adhesion polymer polydopamine (PDA). Dopamine mimics the structure of adhesion proteins in nacre-lined mussels, and PDAs have been used in lithium-ion batteries and supercapacitors as electrode materials, separator modifiers, and adhesives. However, only a few studies have focused on incorporating PDA into rGO composites.
As explained in the Matter technical paper, "For the first time, we seek to combine the excellent mechanical properties of PDA-modified rGO with high modulus, high-strength Kevlar fiber aramid nanofibers to improve multifunctional efficiency." Fang Polyester nanofibers have also been used in various applications, including energy storage.
Good structural performance
A pearl-like supercapacitor electrode based on branched aramid nanofibers and dopamine-functionalized rGO sheets was prepared by vacuum filtration method, and its performance was evaluated. It is reported that the excellent mechanical properties are due to the increase in hydrogen bonding caused by dopamine functionalization and chelation caused by Ca 2 ions.
The Lutkenhaus team reported that this method is applicable to other structures that imitate nacre, which should lead to a new and more powerful series of multi-functional natural inspiration materials. "Future work should focus on improving the electrochemical performance, either by increasing the porosity to improve the ion mobility, or by adding pseudo-capacitance materials to increase the energy density. To the best of our knowledge, at low aramid nanofiber content Among the conductive composite materials, the Young's modulus and multi-functional efficiency obtained are the highest. This results in a strong structural supercapacitor electrode with high electrochemical performance."