Tieqi Huang

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.

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.

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).

Ultrafast all-climate aluminum-graphene battery with quarter-million cycle life

Trihigh tricontinuous graphene cathode enables a 1.1 s charge, 250,000 cycle life, wide temperature range Al-ion battery. Rechargeable aluminum-ion batteries are promising in high-power density but still face critical challenges of limited lifetime, rate capability, and cathodic capacity. We design a “trihigh tricontinuous” (3H3C) graphene film cathode with features of high quality, orientation, and channeling for local structures (3H) and continuous electron-conducting matrix, ion-diffusion highway, and electroactive mass for the whole electrode (3C). Such a cathode retains high specific capacity of around 120 mAh g−1 at ultrahigh current density of 400 A g−1 (charged in 1.1 s) with 91.7% retention after 250,000 cycles, surpassing all the previous batteries in terms of rate capability and cycle life. The assembled aluminum-graphene battery works well within a wide temperature range of −40 to 120°C with remarkable flexibility bearing 10,000 times of folding, promising for all-climate wearable energy devices. This design opens an avenue for a future super-batteries.

Hydrothermally Activated Graphene Fiber Fabrics for Textile Electrodes of Supercapacitors

Carbon textiles are promising electrode materials for wearable energy storage devices owing to their conductive, flexible, and lightweight features. However, there still lacks a perfect choice for high-performance carbon textile electrodes with sufficient electrochemical activity. Graphene fiber fabrics (GFFs) are newly discovered carbon textiles, exhibiting various attractive properties, especially a large variability on the microstructure. Here we report the fabrication of hierarchical GFFs with significantly enlarged specific surface area using a hydrothermal activation strategy. By carefully optimize the activation process, the hydrothermally activated graphene fiber fabrics (HAGFFs) could achieve an areal capacitance of 1060 mF cm-2 in a very thin thickness (150 μm) and the capacitance is easily magnified by overlaying several layers of HAGFFs, even up to a record value of 7398 mF cm-2. Meanwhile, a good rate capability and a long cycle life are also attained. As compared with other carbon textiles, including the commercial carbon fiber cloths, our HAGFFs present much better capacitive performance. Therefore, the mechanically stable, flexible, conductive, and highly active HAGFFs have provided an option for high-performance textile electrodes.

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.

MXene/graphene hybrid fibers for high performance flexible supercapacitors

Two dimensional MXene materials have demonstrated attractive electrical and electrochemical properties for various applications, particularly in energy storage, benefiting from their intrinsic 2D atomic thick topological structures. However, assembling MXene into macroscopic fibers with regular alignment still remains a huge challenge, inherently due to the insufficient interlaminar interaction between MXene sheets and the lack of well-developed assembling techniques. Herein, we report a wet-spinning assembly strategy for the continuous fabrication of MXene-based fibers through a synergistic effect between graphene oxides liquid crystals and MXene sheets. MXene sheets are orderly aligned between graphene oxides liquid crystalline templates and assembled into hybrid fibers with the highest MXene mass ratio achieving 95 w/w%. An excellent overall fiber electrical conductivity (2.9 × 104 S m−1) and superior volumetric capacitance (586.4 F cm−3) of the integrated fiber-constructed supercapacitor exceeding those of neat reduced graphene fibers were achieved.

Continuous fabrication of the graphene-confined polypyrrole film for cycling stable supercapacitors

A meter-length, graphene-confined polypyrrole (GP) film was fabricated by a scalable wet-spinning technology. The GP film-assembled supercapacitors had an extremely high cycling stability (115% retention after 50 000 cycles) due to the delicate graphene-confined polypyrrole-layered structures. Highly flexible supercapacitors with different sizes were further assembled with a gel electrolyte.