Bingna Zheng

Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics

Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm−2 and energy densities of 5.91 and 3.84 μWh cm−2, respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics.

Graphene fiber-based asymmetric micro-supercapacitors

Fiber-based micro-supercapacitors (F-mSCs) are new members of the energy storage family, which facilitate SCs with flexibility and expand their application to fields such as tiny, flexible and wearable devices. One of the biggest challenges for F-SCs is to enhance the energy density (E) and keep the flexibility at the same time. Here, for the first time we assembled a type of fiber-based asymmetric micro-supercapacitors (F-asym-mSCs) with two different graphene fiber-based electrodes. The excellent electrochemical performances (59.2 mF cm−2 and 32.6 mF cm−2) of both electrodes offered a chance to achieve high performance two-ply F-asym-mSCs. The potential window of F-asym-mSCs was expanded to 1.6 V, and both the area energy density (EA: 11.9 μW h cm−2) and the volume energy density (EV: 11.9 mW h cm−3) are the highest E ever reported in F-SCs. The F-asym-mSCs exhibit good cycling stability with a 92.7% initial capacitance retention after 8000 cycles and can be integrated into a fiber-like device to realize the flexibility of fibers.

Flexible high performance wet-spun graphene fiber supercapacitors

We have explored a new method to produce flexible and all-solid-state graphene fiber supercapacitors (GFSs) from wet-spun graphene fibers. The GFSs exhibited high capacitance (3.3 mF cm−2) and good stability (almost no changes occur after 5000 charge cycles and bending cycles). Moreover, we decorated GFSs with polyaniline nanoparticles and the resulting pseudocapacitors exhibited a capacitance of 66.6 mF cm−2.

Macroscopic assembled, ultrastrong and H 2 SO 4 -resistant fibres of polymer-grafted graphene oxide

Nacre realizes strength and toughness through hierarchical designs with primary “brick and mortar” structures of alternative arrangement of nanoplatelets and biomacromolecules, and these have inspired the fabrication of nanocomposites for decades. However, to simultaneously solve the three critical problems of phase separation, low interfacial strength and random orientation of nanofillers for nanocomposites is a great challenge yet. Here we demonstrate that polymer-grafted graphene oxide sheets are exceptional building blocks for nanocomposites. Their liquid crystalline dispersions can be wet-spun into continuous fibres. Because of well-ordering and efficient load transfer, the composites show remarkable tensile strength (500 MPa), three to four times higher than nacre. The uniform layered microstructures and strong interlayer interactions also endow the fibres good resistance to chemicals including 98% sulfuric acid. We studied the enhancing effect of nanofillers with fraction in a whole range (0–100%), and proposed an equation to depict the relationship.

A Defect-Free Principle for Advanced Graphene Cathode of Aluminum-Ion Battery

A conceptually new defect-free principle is proposed for designing graphene cathode of aluminum-ion battery: the fewer the defects, the better the performances. Developed through scalable approach, defect-free graphene aerogel cathode affords high capacity of 100 mAh g-1 under an ultrahigh rate of 500 C, exceeding defective graphene and previous reports. This defect-free principle can guide us to fabricate better graphene-based electrodes.

Polyelectrolyte-Stabilized Graphene Oxide Liquid Crystals against Salt, pH, and Serum

Stabilization of colloids is of great significance in nanoscience for their fundamental research and practical applications. Electrostatic repulsion-stabilized anisotropic colloids, such as graphene oxide (GO), can form stable liquid crystals (LCs). However, the electrostatic field would be screened by ions. To stabilize colloidal LCs against electrolyte is an unsolved challenge. Here, an effective strategy is proposed to stabilize GO LCs under harsh conditions by association of polyelectrolytes onto GO sheets. Using sodium poly(styrene sulfonate) (PSS) and poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PMEDSAH), a kind of polyzwitterion, GO LCs were well-maintained in the presence of NaCl (from 0 M to saturated), extreme pH (from 1 to 13), and serum. Moreover, PSS- or PMEDSAH-coated chemically reduced GO (rGO) also showed stability against electrolyte.

High rate capability supercapacitors assembled from wet-spun graphene films with a CaCO3 template

We fabricated continuous wrinkle-structured graphene film electrodes by a wet-spinning method. The assembled supercapacitors showed an excellent rate performance (79% retention from 1 to 100 A g−1) with a high specific capacitance (177 F g−1 at 1 A g−1). When further functionalized with polyaniline, the electrodes maintained their wrinkled structure and showed an improved rate capability (90% retention from 1 to 100 A g−1) with a superior capacitance as high as 505 F g−1 (1 A g−1).

Oxide Film Efficiently Suppresses Dendrite Growth in Aluminum-Ion Battery

Aluminum metal foil is the optimal choice as an anode material for aluminum-ion batteries for its key advantages such as high theoretical capacity, safety, and low cost. However, the metallic nature of aluminum foil is very likely to induce severe dendrite growth with further electrode disintegration and cell failure, which is inconsistent with previous reports. Here, we discover that it is aluminum oxide film that efficiently restricts the growth of crystalline Al dendrite and thus improves the cycling stability of Al anode. The key role of surficial aluminum oxide film in protecting Al metal anode lies in decreasing the nucleation sites, controlling the metallic dendrite growth, and preventing the electrode disintegration. The defect sites in aluminum oxide film provide channels for electrolyte infiltration and further stripping/depositing. Attributed to such a protective aluminum oxide film, the Al-graphene full cells can attain up to 45 000 stable cycles.