Bamboo Weaving Inspired Design of a Carbonaceous Electrode with Exceptionally High Volumetric Capacity.

A highly densified electrode material is desirable to achieve large volumetric capacity. However, pores acting as ion transport channels are critical for high utilization of active material. Achieving a balance between high volume density and pore utilization remains a challenge particularly for hollow materials. Herein, capillary force is employed to convert hollow fibers to a bamboo-weaving-like flexible electrode (BWFE), in which the shrinkage of hollow space results in high compactness of the electrode. The volume of the electrode can be decreased by 96% without sacrificing the gravimetric capacity. Importantly, the conductivity of BWFE after thermal treatment can reach up to 50,500 S/m which exceeds that for most other carbon materials. Detailed mechanical analysis reveals that, due to the strong interaction between nanoribbons, Young's modulus of the electrode increases by 105 times. After SnO2 active materials is impregnated, the BWFE/SnO2 electrode exhibits an exceptionally ultrahigh volumetric capacity of 2000 mAh/cm3.

Ultra-Thin Wrinkled Carbon Sheet as an Anode Material of High-Power-Density Potassium-Ion Batteries.

Although K+ is readily inserted into graphite, the volume expansion of graphite of up to 60% upon the formation of KC8, together with its slow diffusion kinetics, prevent graphite from being used as an anode for potassium-ion batteries (PIBs). Soft carbon with low crystallinity and an incompact carbon structure can overcome these shortcomings of graphite. Here, ultra-thin two-dimensional (2D) wrinkled soft carbon sheets (USCs) are demonstrated to have high specific capacity, excellent rate capability, and outstanding reversibility. The wrinkles themselves prevent the dense stacking of micron-sized sheets and provide sufficient space to accommodate the volume change of USCs during the insertion/extraction of K+. The ultra-thin property reduces strain during the formation of K-C compounds, and further maintains structural stability. The wrinkles and heteroatoms also introduce abundant edge defects that can provide more active sites and shorten the K+ migration distance, improving reaction kinetics. The optimized USC20-1 electrode exhibits a reversible capacity of 151 mAh g-1 even at 6400 mA g-1, and excellent cyclic stability up to 2500 cycles at 1000 mA g-1. Such comprehensive electrochemical performance will accelerate the adoption of PIBs in electrical energy applications.

Efficient removal of lead and copper ions from water by enhanced strength-toughness alginate composite fibers.

In this study, we designed and synthesized an enhanced strength-toughness alginate composite fiber by using graphene oxide as reinforcing filler for removing heavy metal ions from water media. The as-prepared alginate composite fiber exhibits high affinity to Pb2+ ion, and the maximum adsorption capacity for Pb2+ reached 386.2 mg/g, which is higher than the reported Pb2+-sorbent. The prepared round-shaped nanofibers have relatively uniform distribution with a diameter of 400 nm, and the interlaced fibers form porous structure that conducive to the rapid transport of heavy metal ions. Adsorption mechanism analysis shows that the alginate composite fibers combine heavy metals mainly by ion exchange and chemical coordination effects. Owing to the excellent mechanical properties of graphene oxide, the alginate composite fibers can be used repeatedly with minimal loss in performance.

Prolonging the Cycle Life of a Lithium-Air Battery by Alleviating Electrolyte Degradation with a Ceramic-Carbon Composite Cathode.

Carbon materials with a high specific surface area are usually preferred to construct the air cathode of lithium-air batteries due to their abundant sites for oxygen reduction and discharge product growth. However, the high surface area also amplifies electrolyte degradation during charging, which would become the threshold of cyclability after addressing the issue of electrode passivation and pore clogging, but is usually overlooked in relevant research. Herein, it is proven that the critical influence of cathode surface area on electrolyte consumption by adopting carbon-ceramic composites to reduce the surface area of the air cathode. After screening several potential ceramic materials, an optimal composite of Ketjenblack (KB) and La0.7 Sr0.3 MnO3 (LSM) delivered a discharge capacity that was even higher than that of pure KB. This composite effectively mitigated the parasitic reaction current by 45 % if polarized at 4.4 V versus Li+ /Li. Correspondingly, this composite prolonged the cycle life of the cell by 156 %. The results demonstrate that electrolyte consumption during charging is one of the critical boundary conditions to restrain the cyclic stability of lithium-air batteries.

Seed-Free Selective Deposition of Lithium Metal into Tough Graphene Framework for Stable Lithium Metal Anode.

Graphene has been wildly used as a host to suppress dendrite growth to stabilize the lithium metal anode. However, the high overpotential of lithium deposition on pure graphene has to be lowered by doping or employing precious metals. Additionally, the soft nature of graphene rendered itself to aggregate, consequently squeezing room for lithium accommodation. Herein, a tough graphene framework composed of 3D periodic hollow spheres was reported as a free-standing host to stabilize lithium metal anodes. The prepared 3D periodic hollow structure not merely reinforces the framework to maintain hollow structure under pressure caused by assembling battery, but also lowers the overpotential without the help of dopant or precious metals. It is worthy to note that high efficiency of ion diffusion, thanks to the channels interconnecting hollow spheres by holes on the walls, benefits both suppression of lithium dendrite and rate capability. The properties of low density and high mechanical strength make graphene frameworks electrode a promising lightweight Li host material, which reveals a new avenue for designing high-energy density electrode materials.

Efficient Removal of Lead, Copper and Cadmium Ions from Water by a Porous Calcium Alginate/Graphene Oxide Composite Aerogel.

In this study, we fabricated a porous calcium alginate/graphene oxide composite aerogel by using polystyrene colloidal particles as sacrificial template and graphene oxide as a reinforcing filler. Owing to the excellent metal chelation ability of calcium alginate and controlled nanosized pore structure, the as-prepared calcium alginate/graphene oxide composite aerogel (mp-CA/GO) can reach the adsorption equilibrium in 40 min, and the maximum adsorption capacity for Pb2+, Cu2+ and Cd2+ is 368.2, 98.1 and 183.6 mg/g, respectively. This is higher than most of the reported heavy metal ion sorbents. Moreover, the mp-CA/GO can be regenerated through simple acid-washing and be used repeatedly with little loss in performance. The adsorption mechanism analysis indicates that the mp-CA/GO adsorb the heavy metal ions mainly through the ion exchange and chemical coordination effects.