Weiwei Gao

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.

Biomimetic Architectured Graphene Aerogel with Exceptional Strength and Resilience

Materials combining lightweight, robust mechanical performances, and multifunctionality are highly desirable for engineering applications. Graphene aerogels have emerged as attractive candidates. Despite recent progresses, the bottleneck remains how to simultaneously achieve both strength and resilience. While multiscale architecture designs may offer a possible route, the difficulty lies in the lack of design guidelines and how to experimentally achieve the necessary structure control over multiple length scales. The latter is even more challenging when manufacturing scalability is taken into account. The Thalia dealbata stem is a naturally porous material that is lightweight, strong, and resilient, owing to its architecture with three-dimensional (3D) interconnected lamellar layers. Inspired by such, we assemble graphene oxide (GO) sheets into a similar architecture using a bidirectional freezing technique. Subsequent freeze-drying and thermal reduction results in graphene aerogels with highly tunable 3D architectures, consequently an unusual combination of strength and resilience. With their additional electrical conductivity, these graphene aerogels are potentially useful for mechanically switchable electronics. Beyond such, our study establishes bidirectional freezing as a general method to achieve multiscale architectural control in a scalable manner that can be extended to many other material systems.

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.

Wet‐Spun Superelastic Graphene Aerogel Millispheres with Group Effect

Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high-performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost-effective scalable fabrication and miniaturization with group effect. This study shows millimeter-scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core-shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure-elastic and adsorbing materials. The GS shows a press-fly behavior with an extremely high jump velocity up to 1.2 m s-1 . For the first time, both free and oil-adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties.

Superconducting Continuous Graphene Fibers via Calcium Intercalation

Superconductors are important materials in the field of low-temperature magnet applications and long-distance electrical power transmission systems. Besides metal-based superconducting materials, carbon-based superconductors have attracted considerable attention in recent years. Up to now, five allotropes of carbon, including diamond, graphite, C60, CNTs, and graphene, have been reported to show superconducting behavior. However, most of the carbon-based superconductors are limited to small size and discontinuous phases, which inevitably hinders further application in macroscopic form. Therefore, it raises a question of whether continuously carbon-based superconducting wires could be accessed, which is of vital importance from viewpoints of fundamental research and practical application. Here, inspired by superconducting graphene, we successfully fabricated flexible graphene-based superconducting fibers via a well-established calcium (Ca) intercalation strategy. The resultant Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition at ∼11 K, which is almost 2 orders of magnitude higher than that of early reported alkali metal intercalated graphite and comparable to that of commercial superconducting NbTi wire. The combination of lightness and easy scalability makes Ca-GF highly promising as a lightweight superconducting wire.

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.

Highly stretchable carbon aerogels

Carbon aerogels demonstrate wide applications for their ultralow density, rich porosity, and multifunctionalities. Their compressive elasticity has been achieved by different carbons. However, reversibly high stretchability of neat carbon aerogels is still a great challenge owing to their extremely dilute brittle interconnections and poorly ductile cells. Here we report highly stretchable neat carbon aerogels with a retractable 200% elongation through hierarchical synergistic assembly. The hierarchical buckled structures and synergistic reinforcement between graphene and carbon nanotubes enable a temperature-invariable, recoverable stretching elasticity with small energy dissipation (~0.1, 100% strain) and high fatigue resistance more than 106 cycles. The ultralight carbon aerogels with both stretchability and compressibility were designed as strain sensors for logic identification of sophisticated shape conversions. Our methodology paves the way to highly stretchable carbon and neat inorganic materials with extensive applications in aerospace, smart robots, and wearable devices.Improved compressive elasticity was lately demonstrated for carbon aerogels but the problem of reversible stretchability remained a challenge. Here the authors use a hierarchical structure design and synergistic effects between carbon nanotubes and graphene to achieve high stretchability in carbon aerogels.

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.

Effect of flake size on the mechanical properties of graphene aerogels prepared by freeze casting

Aerogels enable a wide range of potential applications owing to their ultralow density, superelasticity, high specific surface area, energy-absorbability and so on. However, it is usually difficult to precisely control their mechanical performance, which largely hinders their applications. Here, we prepared anisotropic graphene aerogels assembled with flakes having different sizes ranging from sub-micron to ∼80 μm by the freeze casting technique, using ice as a template to assembling graphene oxide (GO) sheets into 3-dimensional (3D) aerogels. We found that graphene flake size has a profound effect on the mechanical performance of the assembled graphene aerogels, particularly their strength, modulus and fatigue resistance under compression. Larger flakes had stronger interaction when assembled, which made them more resistant to slipping between adjacent flakes during deformation. As a result, the graphene aerogel with larger flake size showed both higher strength and fatigue resistance. Our research provides a new way of controlling the mechanical properties of graphene aerogel by only adjusting the intrinsic properties of the flakes, e.g., size, without crosslinking agent or co-assembly with other materials as in previous studies.