In a recent study, functionalized graphene/nanofiber electrodes showed 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 (EV) 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 structures and batteries, and have a longer distance between charges. However, current electrodes used in batteries and supercapacitors have poor mechanical properties 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 College), used reduced graphene oxide (rGO), innovative chemical methods and aramid nanofibers to mimic the mother-of-pearl of natural materials, As a result, the Young's modulus and the ultimate tensile strength are 220% and 255% higher than that of the pure rGO electrode, respectively. Compared with the multifunctional electrode, the multifunctional efficiency value at <1 is 5-13.6.
Mother-of-pearl multifunctional composite material
In an article published in the journal Matter, Lutkenhaus and her team described the use of dopamine to functionalize rGO (chemical bonding) and then combine the material with aramid nanofibers to form a composite material. The paper explained: "We hypothesize 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 multifunctional efficiency values."
Mother-of-pearl (near-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 outstanding mechanical properties come from its layered composite structure: its constituent particles and matrix have different organization at each geometric scale or level (for example, nanometer, micrometer, meso, macro), and combine these levels The effective interface between to achieve high modulus and strength, while reducing crack propagation (see the blog "New Generation 3D Magnetic 3D Printing Tailored Composites").
The Lutkenhaus team knows that graphene-based simulated nacreous electrodes have been shown to perform well in terms of electricity. The challenge is to improve its mechanical properties. The team tried to use the hormone and neurotransmitter dopamine to functionalize rGO. Dopamine can also self-polymerize into a high-adhesive polymer polydopamine (PDA). Dopamine mimics the structure of adhesive proteins in mussels lined with pearls, while PDA has been used in lithium-ion batteries and supercapacitors as electrode materials, separator modifiers and adhesives. However, only a few studies focused on incorporating PDA into rGO composite materials.
As explained in Matter's technical paper, "For the first time, we seek to combine the excellent mechanical properties of PDA-modified rGO with high modulus, high strength Kevlar aramid nanofibers to improve multifunctional efficiency." Lun nanofibers also have been used in various applications, including energy storage.
Good structural performance
A nacre-like structure supercapacitor electrode based on branched aramid nanofibers and dopamine-functionalized rGO sheets was prepared by vacuum filtration, and its performance was evaluated. It is reported that the excellent mechanical properties are due to the increase in hydrogen bonds caused by dopamine functionalization and the chelation caused by Ca 2 ions.
The Lutkenhaus team reports that this method is applicable to other structures that imitate nacre, which should lead to a new and more powerful series of multi-functional nature-inspired materials. "Future work should focus on improving electrochemical performance, or improving ion mobility by increasing porosity, or increasing energy density by adding pseudo-capacitance materials. As far as we know, in low aramid nanofiber content Among the conductive composite materials, the obtained Young's modulus and multifunctional efficiency are the highest. This results in a strong structured supercapacitor electrode with high electrochemical performance."