Lingzhi Zhang

Nanostructured silicon/porous carbon spherical composite as a high capacity anode for Li-ion batteries

A nanostructured silicon/porous carbon spherical composite was prepared by a simple hydrothermal method using glucose as a carbon source and Pluronic F127 as a soft template/pore forming agent in the presence of silicon nanoparticles, and a subsequent carbonization process. In this composite, silicon nanoparticles were individually and separately coated with a porous carbon shell with a thickness of 15–20 nm and a pore size of 3–5 nm. The composite electrode exhibited excellent cycling stability and rate capability, delivering a stable capacity of 1607 mA h g−1 at a current density of 0.4 A g−1 after 100 cycles, and a reversible capacity of 1050 mA h g−1 even at a high current density of 10 A g−1. Detailed analysis of cyclic voltammetry and electrochemical impedance spectroscopy revealed that the composite showed favorable electrochemical kinetics due to the nano-sized porous carbon shell, which facilitated the formation of a solid electrolyte interface film and the transportation of Li ions and electrons, and decreased the charge transfer resistance, thus significantly improving the electrochemical performance compared with the bare nano-Si electrode.

Nano-silicon composites using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as elastic polymer matrix and carbon source for lithium-ion battery anode

Nano-silicon composites, Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Si/C, were prepared by an in situ chemical polymerization of 3,4-ethylenedioxythiophene (EDOT) with nano-Si particles in a PSS aqueous solution and subsequent carbonization of Si/PEDOT:PSS, respectively. The nano-Si particles were embedded in a shapeless PEDOT:PSS matrix and amorphous carbon in the corresponding composite. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements revealed that 2.66 wt% of the element sulfur was doped in the carbon matrix for Si/C composite. Both the Si/PEDOT:PSS and Si/C composite electrodes exhibited higher initial coulombic efficiency and better cycling performance than the bare nano-Si anode. The Si/C composite showed the best electrochemical performance, retaining a specific capacity of 768 mA h g−1 and a Coloumbic efficiency of 99.2% after 80 cycles, with a very small initial capacity loss of 2.80% and a capacity fade of 0.48% per cycle.

Hole-transport properties of a furan-containing oligoaryl

We report the carrier transport properties of a furan-containing oligoaryl PF6, which contains no arylamine moiety in the molecular structure but exhibits competitive hole-transport capability in comparison with conventional arylamine-based hole-transport materials often used in organic light-emitting devices (OLEDs) and xerography. Thin films of this compound exhibit both morphological stability and appropriate energy levels for OLED applications. OLEDs using PF6 as the hole-transport layer show low turn-on voltage, high efficiency, and high brightness competitive with those using conventional hole-transport materials, strongly indicating superior hole-transport properties of PF6. The carrier mobility of PF6 was directly measured by the time-of-flight transient photocurrent technique under various temperatures and electric fields. Nondispersive hole transport was observed and a room-temperature hole mobility in excess of 10−3 cm2/V s was obtained under high fields. The field and temperature dependence of...

Highly conductive trimethylsilyl oligo(ethylene oxide) electrolytes for energy storage applications

Monomethyl ethers of oligoethylene glycols with different chain lengths were converted to trimethylsilyl derivatives by reacting with trimethylchlorosilane in the presence of triethylamine, or by directly refluxing with excess trimethylchlorosilane or hexamethyldisilazane. Similarly, two oligoethylene glycols were converted to bis(trimethylsilyl) derivatives. When doped with lithium bis(trifluoromethanesulfonyl)imide, these electrolytes have very high conductivity, generally >10−3 S cm−1. A full cell performance test using one of these new electrolytes (1NM3) showed excellent cyclability at room temperature. Introducing a second trimethylsilyl group decreases the conductivity of trimethylsilylated compounds. The thermal properties, viscosities and dielectric constants of the compounds were measured, and the effect of those on the conductivity is reported. Cyclic voltammetry experiments show that the trimethylsilylated compound (1NM2) of diethylene glycol monomethyl ether has greater electrochemical stability than its germanium and carbon analogues.

Non-amine-based furan-containing oligoaryls as efficient hole transporting materialsElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b2/b207489c/

A new class of highly stable furan-based hole transporting oligomeric materials, synthesized from the corresponding propargylic dithioacetals, serve as efficient hole transporting materials in electroluminescent devices. The performance of the devices using these furan materials is comparable with or somewhat better than those employing the conventional triarylamines (e.g. alpha-NPD).

W6+ & Br− codoped Li4Ti5O12 anode with super rate performance for Li-ion batteries

We report a novel Li4Ti5−xWxO12−xBrx (x = 0.025, 0.050 and 0.100) anode material simultaneously doped with W6+ and Br− ions prepared by a simple solid-state reaction in air, aiming to significantly improve electrical conductivity of Li4Ti5O12. Our theoretical calculation predicts that codoping with W6+ on the Ti4+ site and Br− on the O2− site can remarkably narrow down the band gap, and thus facilitate the electron transport in the lattice of LTO. The comparative experiments prove that W & Br-codoped LTO exhibits higher electrical conductivity compared with undoped LTO as expected, thus leading to improved rate capability and specific capacity. Particularly, Li4Ti5−xWxO12−xBrx (x = 0.05) exhibits the best rate capability and cycling stability with an outstanding capacity retention of 88.7% even at 10 C rate after 1000 cycles. This codoping strategy with high valence transition metal and halide ions holds promise to be applied to other insulating cathode materials suffering from inferior electrical conductivity.

Micro/nano-structured SnS2 negative electrodes using chitosan derivatives as water-soluble binders for Li-ion batteries

Micro/nano-structured SnS2 was prepared by a hydrothermal method using biomolecular l-cysteine and SnCl4·5H2O as sulfur source and tin source, respectively. The electrochemical performances of SnS2 electrodes were investigated using water-soluble binders of carboxymethyl chitosan (C-chitosan) and chitosan lactate, and compared with the conventional water-soluble sodium carboxymethyl cellulose (CMC) and non-aqueous polyvinylidene difluoride (PVDF). SnS2 electrode using the water-soluble binders (C-chitosan, chitosan lactate, and CMC) showed higher initial coulombic efficiency, larger reversible capacity, and better rate capabilities than that of PVDF. In addition, SnS2 electrode using C-chitosan binder exhibited somewhat worse cycling stability, but better rate capability at a high rate of 5C than CMC.

Synthesis and characterization of alkylsilane ethers with oligo(ethylene oxide) substituents for safe electrolytes in lithium-ion batteries

Alkylsilane ethers, containing one or three carbon spacer groups between the silicon atom and oligo(ethylene oxide) moiety, were designed and synthesized. These compounds are non-hydrolyzable and less flammable than their alkoxysilane counterparts. A full cell test using them as electrolyte solvents showed good cycling performance in lithium-ion batteries.

Photocrosslinked polymer and interpenetrating polymer network for nonlinear optics

Two photocrosslinkable NLO polymers of poly(glycidyl methacrylate) substituted with 4-nitro-4′-hydroxyl stilbene (PGMAS) and acryloyl-functionalized epoxy-based polymer (PENAA) carrying 4-nitroaniline moieties were synthesized and characterized. By using the sulfonium salt cationic photoinitiator BDS · 2PF6 which can induce cationic or/and radical polymerization, the photocrosslinking of PGMAS and the interpenetrating polymer network (IPN) formed by the photocrosslinking of PGMAS and PENAA simultaneously were reported. The poled and photocrosslinked polymer films and IPN films exhibit relatively stable second-order nonlinear optical activity. The influence of stilbene isomerization in PGMAS films with different crosslink densities on the SHG stability was also investigated.

New crosslinked polymer systems with high and stable optical nonlinearity

Abstract Thermo-crosslinkable copolymers (PGMAA and PGMAS) of glycidyl methacrylate containing azobenzene chromophores (20 mol%) and stilbene chromophores (19 mol%) respectively were synthesized and characterized. In order to obtain crosslinked polymers with high and stable second-order nonlinear optical (NLO) property, PGMAA and PGMAS were doped with a reactive nonlinear optical (NLO) dye, 4-nitro-4′-aminobiphenyl (20 mol% of the glydidyl group). In the poled state, these doped polymers systems (PGMAD and PGMSD) can be thermo-crosslinked to yield materials with high second-order (NLO) coefficient (d33) of 4.33×10−7 esu and 4.74×10−7 esu respectively. The investigation of SHG decay at room temperature and 100°C showed that the polymer networks much improved the SHG stability.