Li-Zhen Fan

Nitrogen‐Containing Hydrothermal Carbons with Superior Performance in Supercapacitors

[ ∗] L. Zhao , Prof. M. Antonietti , Dr. M.-M. Titirici Colloid Chemistry Department Max-Planck Institute for Colloids and Interfaces Am Muehlenberg 1, 14424 Potsdam (Germany) E-mail: Magdalena.Titirici@mpikg.mpg.de Prof. L.-Z. an , F M.-Q. Zhou , H. Guan , Qiao S. . YSchool of Materials Science and Engineering University of Science and Technology Beijing 100083 Beijing (China) E-mail: fanlizhen@ustb.edu.cn L. Zhao Institute of Coal Chemistry Chinese Academy of Sciences 27th Taoyuan South Road, 030001 Taiyuan (China)

Thermal, electrical and mechanical properties of plasticized polymer electrolytes based on PEO/P(VDF-HFP) blends

Abstract The polymer electrolytes composed of a blend of poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as a host polymer, mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and LiClO 4 as a salt were prepared by a solution casting technique. SEM micrographs show that P(VDF-HFP) is very compatible with PEO. The ionic conductivity of the electrolytes increases with increasing plasticizer content, while the mechanical properties become obviously worse. By addition of a certain content of PEO in P(VDF-HFP) matrix, a good compromise between high ionic conductivity and mechanical stability can be obtained.

Dielectric behavior of novel three-phase MWNTs/BaTiO3/PVDF composites

Abstract A three-phase composite with multi-walled carbon nanotubes (MWNTs) and BaTiO 3 particles embedded into polyvinylidene fluoride was prepared by using a simple blending and hot-molding technique. The dielectric measurement results show that the effective dielectric constant of the composite is slightly dependence on the frequency below 1 MHz but increases rapidly with the MWNTs concentration when the concentration is very close to the percolation threshold. The temperature has a little effect on the variation of the dielectric behavior. The percolation theory is used to explain the experimental results.

Self-Wound Composite Nanomembranes as Electrode Materials for Lithium Ion Batteries

www.MaterialsViews.com C O M M U Self-Wound Composite Nanomembranes as Electrode Materials for Lithium Ion Batteries N IC A T By Heng-Xing Ji , Xing-Long Wu , Li-Zhen Fan , Cornelia Krien , Irina Fiering , Yu-Guo Guo , * Yongfeng Mei , * and Oliver G. Schmidt IO N Bending and rolling is commonly employed in nature to release strain in fi lms to maintain structure stability. Recently, rolledup nanotechnology has proven to be an intriguing approach on the micro-/nanoscale for various promising future applications and concepts. [ 1–5 ] Nanomembranes composed of various functional stacks can self wind (or roll up) into micro/nanotubes upon detaching from a holding substrate by releasing intrinsic differential strain. The deposition and process methods for nanomembranes are compatible to industrial-level technologies like e-beam evaporation, sputtering deposition and atomic layer deposition, etc., which are demanded by advanced materials used for applications. Moreover, the intrinsic strain accommodated in multi-layer nanomembranes is effi ciently released by self winding and thus offers a minimization of the system energy. [ 6 ] Such tubular and strain-relaxed structures are liable to improve the materials tolerance against stress cracking and are therefore promising candidates for increasing the stability of energy storage devices such as lithium ion batteries. Lithium ion batteries are attractive for applications ranging from electric vehicles to microchips. [ 7–10 ] One of the big challenges is strain accommodation during electrode lithiation, which would prevent the electrodes in batteries from being pulverized which causes capacity fading. [ 10–12 ] For example, transition-metal oxides and lithium alloys are attractive anode materials owing to their high theoretical charge capacity, which is several times larger than existing graphite anodes. [ 13–16 ]

Hollow core-shell structured Si/C nanocomposites as high-performance anode materials for lithium-ion batteries.

Hollow core-shell structured Si/C nanocomposites were prepared to adapt for the large volume change during a charge-discharge process. The Si nanoparticles were coated with a SiO2 layer and then a carbon layer, followed by etching the interface SiO2 layer with HF to obtain hollow core-shell structured Si/C nanocomposites. The Si nanoparticles are well encapsulated in a carbon matrix with an internal void space between the Si core and the carbon shell. The hollow core-shell structured Si/C nanocomposites demonstrate a high specific capacity and excellent cycling stability, with capacity decay as small as 0.02% per cycle. The enhanced electrochemical performance can be attributed to the fact that the internal void space can accommodate the volume expansion of Si during lithiation, thus preserving the structural integrity of electrode materials, and the carbon shell can increase the electronic conductivity of the electrode.

Dielectric behavior of Li and Ti co-doped NiO/PVDF composites

Abstract The dielectric behavior of two kinds of Li and Ti co-doped NiO (LTNO)/polyvinylidene fluoride (PVDF) composite was studied at various different frequencies and temperatures. The effective dielectric constant of the percolative composite at 100 Hz is very high, i.e., e eff ≈600, which is 60 times higher than that of the PVDF. The results also show that there is a remarkable difference in the dielectric constant of the composites with different LTNO fillers. Boundary layer capacitor effect and percolation theory can be used to explain the experimental results.

Facile fabrication of ultrathin graphene papers for effective electromagnetic shielding

Ultrathin electromagnetic interference (EMI) shielding materials promise great application potential in portable electronic devices and communication instruments. Lightweight graphene-based materials have been pursued for their exclusive microstructures and unique shielding mechanism. However, the large thickness of the current low-density graphene-based composites still limits their application potential in ultrathin devices. In this work, a novel approach has been taken to use conductive graphene paper (GP) in the fabrication of ultrathin EMI shielding materials. The as-prepared flexible GPs exhibit highly effective shielding capabilities, reaching ∼19.0 dB at ∼0.1 mm in thickness and ∼46.3 dB at ∼0.3 mm in thickness, thus the thinnest GPs having the best shielding performance among graphene-based shielding materials. Double-layered shielding attenuators have been designed and fabricated for a high shielding performance of up to ∼47.7 dB at a GP thickness of ∼0.1 mm. Mechanistically, the high performance should be due to Fabry–Perot resonance, which is unusual in carbon-based shielding materials. The preparation of conductive GPs of superior shielding performance is relatively simple, amenable to large-scale production of ultrathin materials for EMI shielding and electromagnetic attenuators, with broad applications in lightweight portable electronic devices.

Rational design of graphene/porous carbon aerogels for high-performance flexible all-solid-state supercapacitors

Lightweight flexible energy storage devices have aroused great attention due to the remarkably increasing demand for ultrathin and portable electronic devices. As typical new two-dimensional carbon materials, graphene-based porous structures with ultra-light weight and exclusive electrochemical properties have demonstrated outstanding capacitive ability in supercapacitors. Thus far, the performance of all-solid-state supercapacitors achieved from graphene-based materials is still unsatisfactory. In this work, we have rationally designed graphene/porous carbon (GN/PC) aerogels via a simple green strategy to achieve flexible porous electrode materials. The ordered porous carbon (PC) with high specific surface area and good capacitance was introduced as a spacer to efficiently inhibit the restacking of graphene (GN) sheets, which significantly enhanced the specific surface area and facilitated the transport and diffusion of ions and electrons in the as-synthesized porous hybrid structure. The all-solid-state electrodes fabricated by the as-prepared GN/PC aerogels presented excellent flexibility, high specific capacitance and good rate performance in a polyvinyl alcohol/KOH gel electrolyte. Implication of the specific capacitances of ∼187 F g−1 at 1 A g−1 and 140 F g−1 at 10 A g−1 suggests that the GN/PC aerogels promise great potentials in the development of lightweight high-performance flexible energy storage devices.

Interfacial engineering of carbon nanofiber-graphene-carbon nanofiber heterojunctions in flexible lightweight electromagnetic shielding networks.

Lightweight carbon materials of effective electromagnetic interference (EMI) shielding have attracted increasing interest because of rapid development of smart communication devices. To meet the requirement in portable electronic devices, flexible shielding materials with ultrathin characteristic have been pursued for this purpose. In this work, we demonstrated a facile strategy for scalable fabrication of flexible all-carbon networks, where the insulting polymeric frames and interfaces have been well eliminated. Microscopically, a novel carbon nanofiber-graphene nanosheet-carbon nanofiber (CNF-GN-CNF) heterojunction, which plays the dominant role as the interfacial modifier, has been observed in the as-fabricated networks. With the presence of CNF-GN-CNF heterojunctions, the all-carbon networks exhibit much increased electrical properties, resulting in the great enhancement of EMI shielding performance. The related mechanism for engineering the CNF interfaces based on the CNF-GN-CNF heterojunctions has been discussed. Implication of the results suggests that the lightweight all-carbon networks, whose thickness and density are much smaller than other graphene/polymer composites, present more promising potential as thin shielding materials in flexible portable electronics.

Hollow Core–Shell SnO2/C Fibers as Highly Stable Anodes for Lithium-Ion Batteries

Given their competitive prospects for energy storage, lithium-ion batteries (LIBs) have attracted ever-intensive research interest. However, the large volume changes during cycling and structural pulverization significantly hinder the cycling stability and high capacity for lithium-alloy electrodes. Herein, novel one-dimensional (1D) hollow core-shell SnO2/C fibers were synthesized by facile coaxial electrospinning. The as-prepared fibers that possess sufficient hollow voids and nanosized SnO2 particles on the inner shell are able to serve as an anode in LIBs. The results suggest a reversible capacity of 1002 mAh g(-1) (for the initial cycle at 100 mA g(-1)), excellent rate capability, and a highly stable cycling performance with a discharge capacity of 833 mAh g(-1) after 500 cycles at 600 mA g(-1). The superior electrochemical performance is attributed to the unique hollow core-shell structure, which offers sufficient voids for alleviating the volume changes of SnO2 nanoparticles during lithiation/delithiation processes. The promising strategies and associated opportunities here demonstrate great potential in the fabrication of advanced anode materials for long-life LIBs.