An-Min Cao

Efficient 3D Conducting Networks Built by Graphene Sheets and Carbon Nanoparticles for High-Performance Silicon Anode

The utilization of silicon particles as anode materials for lithium-ion batteries is hindered by their low intrinsic electric conductivity and large volume changes during cycling. Here we report a novel Si nanoparticle-carbon nanoparticle/graphene composite, in which the addition of carbon nanoparticles can effectively alleviate the aggregation of Si nanoparticles by separating them from each other, and help graphene sheets build efficient 3D conducting networks for Si nanoparticles. Such Si-C/G composite shows much improved electrochemical properties in terms of specific capacity and cycling performance (ca. 1521 mA h g(-1) at 0.2 C after 200 cycles), as well as a favorable high-rate capability.

Spin-coated silicon nanoparticle/graphene electrode as a binder-free anode for high-performance lithium-ion batteries

Si has been considered as a promising anode material but its practical application has been severely hindered due to poor cyclability caused by the large volume change during charge/discharge. A new and effective protocol has been developed to construct Si nanoparticle/graphene electrodes with a favorable structure to alleviate this problem. Starting from a stable suspension of Si nanoparticles and graphene oxide in ethanol, spin-coating can be used as a facile method to cast a spin-coated Si nanoparticle/graphene (SC-Si/G) film, in which graphene can act as both an efficient electronic conductor and effective binder with no need for other binders such as polyvinylidenefluoride (PVDF) or polytetrafluoroethylene (PTFE). The prepared SC-Si/G electrode can achieve a high-performance as an anode for lithium-ion batteries benefiting from the following advantages: i) the graphene enhances the electronic conductivity of Si nanoparticles and the void spaces between Si nanoparticles facilitate the lithium ion diffusion, ii) the flexible graphene and the void spaces can effectively cushion the volume expansion of Si nanoparticles. As a result, the binder-free electrode shows a high capacity of 1611 mA·h·g−1 at 1 A·g−1 after 200 cycles, a superior rate capability of 648 mA·h·g−1 at 10 A·g−1, and an excellent cycle life of 200 cycles with 74% capacity retention.

One-nanometer-precision control of Al(2)O(3) nanoshells through a solution-based synthesis route.

Forming uniform metal oxide nanocoatings is a well-known challenge in the construction of core-shell type nanomaterials. Herein, by using buffer solution as a specific reaction medium, we demonstrate the possibility to grow thin nanoshells of metal oxides, typically Al2 O3 , on different kinds of core materials, forming a uniform surface-coating layer with thicknesses achieving one nanometer precision. The application of this methodology for the surface modification of LiCoO2 shows that a thin nanoshell of Al2 O3 can be readily tuned on the surface for an optimized battery performance.

Designable fabrication of flower-like SnS2 aggregates with excellent performance in lithium-ion batteries

Flower-like SnS2 aggregates have been prepared and show better electrochemical performances than nanoplates, which could be attributed to their structural matrix with the functions of facilitating the Li+ diffusion and electron transfer as well as reducing the crumbling and cracking of the electrode.

Copper-substituted Na0.67Ni0.3−xCuxMn0.7O2 cathode materials for sodium-ion batteries with suppressed P2–O2 phase transition

P2-type sodium layered oxides NaxMO2 (M = transition metal) are considered as one kind of promising cathode material for sodium-ion batteries because of their known structures, superior electrochemical properties, and their ease of synthesis. The Ni2+/Ni3+ and Ni3+/Ni4+ redox reactions endow the P2–Na2/3Ni1/3Mn2/3O2 electrode with a relatively high operating voltage and high specific capacity. However, the phase transition from P2 to O2 and Na+/vacancy ordering make P2–Na2/3Ni1/3Mn2/3O2 susceptible to severe voltage and capacity decay. Herein, we propose to employ the electrochemically active copper(II) as a unique substituent to stabilize the P2 phase, forming Na0.67Ni0.3−xCuxMn0.7O2 (x = 0, 0.1, 0.2 and 0.3). Our work highlights the importance of Cu(II) in the structural engineering of high performance cathode materials, whose existence can not only stabilize the P2 phase against the notorious phase transition, but also contribute to the rechargeable capacity due to the high potential Cu2+/Cu3+ redox. We identified that the cathode formulated as P2-type Na0.67Ni0.1Cu0.2Mn0.7O2 shows favorable battery performance with much-alleviated structural degradation.

Optimizing the carbon coating on LiFePO4 for improved battery performance

Core–shell structures as LiFePO4@carbon with a continuous and uniform carbon coating were achieved by means of the in situ polymerization of dopamine. Systematic control of the coating layer identified that a 5 nm carbon coating produces the best battery performance. Our results provide conclusive evidence for an optimal carbon coating for polyanion-type cathode materials.

Accurate surface control of core–shell structured LiMn0.5Fe0.5PO4@C for improved battery performance

Manganese-based mixed polyanion cathodes known as LiMn1−xFexPO4 can show much higher energy density as compared to the well-commercialized product of lithium iron phosphate. However, their much lower electronic conductivity has long plagued their further application. Here, by means of a facile solution-based synthesis route, we are able to introduce a uniform and conformal carbon coating layer onto LiMn1−xFexPO4 nanoparticles. The versatility in the synthesis control endows us with the capability of controlling the shell thickness with one nanometer accuracy, offering an effective way to optimize the battery performance through a systematic shell control. Detailed investigation reveals that the carbon nanoshells not only act as good electronic conducting media, but also contribute to the inhibition of the metal (Mn and Fe) dissolution and reduce the exothermic heat released during cycling. The core–shell structured cathode materials show promising potential for their application in lithium ion batteries as revealed by their high charge–discharge capacity, remarkable thermal stability, and excellent cyclability.

Controlling the Compositional Chemistry in Single Nanoparticles for Functional Hollow Carbon Nanospheres

Hollow carbon nanostructures have inspired numerous interests in areas such as energy conversion/storage, biomedicine, catalysis, and adsorption. Unfortunately, their synthesis mainly relies on template-based routes, which include tedious operating procedures and showed inadequate capability to build complex architectures. Here, by looking into the inner structure of single polymeric nanospheres, we identified the complicated compositional chemistry underneath their uniform shape, and confirmed that nanoparticles themselves stand for an effective and versatile synthetic platform for functional hollow carbon architectures. Using the formation of 3-aminophenol/formaldehyde resin as an example, we were able to tune its growth kinetics by controlling the molecular/environmental variables, forming resin nanospheres with designated styles of inner constitutional inhomogeneity. We confirmed that this intraparticle difference could be well exploited to create a large variety of hollow carbon architectures with desirable structural characters for their applications; for example, high-capacity anode for potassium-ion battery has been demonstrated with the multishelled hollow carbon nanospheres.

Ultrasmall Pd/Au bimetallic nanocrystals embedded in hydrogen-bonded supramolecular structures: facile synthesis and catalytic activities in the reduction of 4-nitrophenol

Melamine cyanurate (MCA) – a kind of hydrogen-bonded self-assembly supramolecular structure material – is readily synthesized by a hydrothermal method. Noble metal nanoparticles (NPs) (Pd, Au bimetallic and monometallic NPs) with an ultrasmall size below 5 nm are homogeneously distributed in the as-prepared MCA via a simple procedure at room temperature without any additional reductant and stabilizer. The as-prepared bimetallic noble metal NPs exhibit good catalytic activities toward the reduction of 4-nitrophenol to 4-aminophenol, and the resulting catalytic activities are even much better than those of monometallic counterparts. This unusual catalytic property should be relevant to the small size of noble nanoparticles and the electronic interaction between the support, Pd and Au nanoparticles.

Nanoarrays: design, preparation and supercapacitor applications

Increasing energy and power demands have continued to stimulate the development of new electrochemical energy storage devices. Supercapacitors, well-known energy storage systems characterized by a high power density and long cycle life, have experienced a rapid progress benefiting from fast advancements in electrode materials. However, for those conventional supercapacitors assembled through a thin film preparation technique, the conductive agent and polymer binder will inevitably account for a large amount of ‘dead volume’, which should be further diminished through a better design of the supercapacitor architecture. Here, we present a comprehensive review on recent research progress on the design of integrated electrode architectures, especially the binder-free nanoarray electrodes. By means of an integration of highly-ordered active nanomaterials and a current collector, the binder-free nanoarrays can provide a larger active surface area, faster electron-transport route, easier ion diffusion and superior structural stability, thus leading to a substantially improved cycling and rate performance. This work will narrow its focus on two independent aspects of binder-free architectures: the design of electrode materials and the construction of current collectors. In addition, we also discuss and review future research directions and the remaining challenges in materials development for advanced supercapacitors.