Susanne Dörfler

High Area Capacity Lithium-Sulfur Full-cell Battery with Prelitiathed Silicon Nanowire-Carbon Anodes for Long Cycling Stability

We show full Li/S cells with the use of balanced and high capacity electrodes to address high power electro-mobile applications. The anode is made of an assembly comprising of silicon nanowires as active material densely and conformally grown on a 3D carbon mesh as a light-weight current collector, offering extremely high areal capacity for reversible Li storage of up to 9 mAh/cm2. The dense growth is guaranteed by a versatile Au precursor developed for homogenous Au layer deposition on 3D substrates. In contrast to metallic Li, the presented system exhibits superior characteristics as an anode in Li/S batteries such as safe operation, long cycle life and easy handling. These anodes are combined with high area density S/C composite cathodes into a Li/S full-cell with an ether- and lithium triflate-based electrolyte for high ionic conductivity. The result is a highly cyclable full-cell with an areal capacity of 2.3 mAh/cm2, a cyclability surpassing 450 cycles and capacity retention of 80% after 150 cycles (capacity loss <0.4% per cycle). A detailed physical and electrochemical investigation of the SiNW Li/S full-cell including in-operando synchrotron X-ray diffraction measurements reveals that the lower degradation is due to a lower self-reduction of polysulfides after continuous charging/discharging.

Metal deposition by electroless plating on polydopamine functionalized micro- and nanoparticles

A novel approach for the fabrication of metal coated micro- and nanoparticles by functionalization with a thin polydopamine layer followed by electroless plating is reported. The particles are initially coated with polydopamine via self-polymerization. The resulting polydopamine coated particles have a surface rich in catechols and amino groups, resulting in a high affinity toward metal ions. Thus, they provide an effective platform for selective electroless metal deposition without further activation and sensitization steps. The combination of a polydopamine-based functionalization with electroless plating ensures a simple, scalable, and cost-effective metal coating strategy. Silver-plated tungsten carbide microparticles, copper-plated tungsten carbide microparticles, and copper-plated alumina nanoparticles were successfully fabricated, showing also the high versatility of the method, since the polymerization of dopamine leads to the formation of an adherent polydopamine layer on the surface of particles of any material and size. The metal coated particles produced with this process are particularly well suited for the production of metal matrix composites, since the metal coating increases the wettability of the particles by the metal, promoting their integration within the matrix. Such composite materials are used in a variety of applications including electrical contacts, components for the automotive industries, magnets, and electromagnetic interference shielding.

Trimodal hierarchical carbide-derived carbon monoliths from steam- and CO2-activated wood templates for high rate lithium sulfur batteries

Hierarchically structured biomorphic carbide-derived carbon (CDC) materials are obtained by applying a combined activation- and CDC approach on abundantly available, renewable and cheap raw materials. For the synthesis of these materials we mimic nature by using wood structures as templates which are already optimized for mass transport during their long-term evolutional process. The impregnation of steam- or carbon dioxide-pre-activated wood templates with a polycarbosilane precursor and the subsequent halogen treatment yields a hierarchical material that exhibits longitudinally orientated macropores from the wood structure as well as well-defined and narrowly distributed micro- and meso-pores derived from the activation and CDC approach. These materials offer specific surface areas up to 1750 m2 g−1, micro-/meso-pore volumes up to 1.0 cm3 g−1 and macropore volumes of 1.2 cm3 g−1. This sophisticated hierarchical pore system ensures both efficient mass transfer and high specific surface area, ideal for mass transport limited applications, such as the lithium sulfur battery. Testing steam activated wood-CDCs as cathode materials for Li–S batteries reveals excellent performance, especially a highly stable discharge capacity and sulfur utilization. Stable capacities of over 580 mA h gsulfur−1 at current densities exceeding 20 mA cm−2 (2C) are possible using only very low amounts of electrolyte of 6.8 μL mgsulfur−1.

Electrodeposition of copper on aligned multi-walled carbon nanotubes

Abstract In this work, the electrochemical deposition of copper on aligned multi-walled carbon nanotubes (MWCNTs) from an aqueous electrolyte is described. The addition of sodium dodecyl sulphate has been applied to enhance wettability of the hydrophobic MWCNT surface. The transfer of the MWCNT–copper composite film from nickel substrates, as applied for the chemical vapour deposition process for carbon nanotube synthesis, onto adhesive tapes is performed. Moreover, a sandwich layer consisting of copper top layers and copper incorporated MWCNT interlayer was produced. The structure of the resulting composite material of MWCNTs and copper was characterised by scanning electron microscopy. An electrochemical investigation of the MWCNTs on nickel foil and on conductive carbon ribbon by cyclic voltammetry is presented.

Pulse plating of platinum on aligned multiwalled carbon nanotubes

Abstract In the present study, the electrochemical deposition (ECD) of platinum particles on aligned multiwalled carbon nanotube (MWCNT) arrays as novel membrane electrode assembly (MEA) in polymer electrolyte membrane fuel cells was investigated. The ECD was performed using the pulse plating technique and an electrolyte based on potassium tetranitroplatinate(II) salt. The MWCNTs were produced on thin nickel foils by chemical vapour deposition. The MWCNT arrays were electrochemically characterised by cyclic voltammetry in sulphuric acid. The platinum functionalisation of the MWCNT arrays was also investigated by cyclic voltammetry and by scanning electron microscopy. The final preparation of the MEA functionalised MWCNT on Nafion was performed by a hot pressing process.

Topochemical conversion of an imine- into a thiazole-linked covalent organic framework enabling real structure analysis

Stabilization of covalent organic frameworks (COFs) by post-synthetic locking strategies is a powerful tool to push the limits of COF utilization, which are imposed by the reversible COF linkage. Here we introduce a sulfur-assisted chemical conversion of a two-dimensional imine-linked COF into a thiazole-linked COF, with full retention of crystallinity and porosity. This post-synthetic modification entails significantly enhanced chemical and electron beam stability, enabling investigation of the real framework structure at a high level of detail. An in-depth study by electron diffraction and transmission electron microscopy reveals a myriad of previously unknown or unverified structural features such as grain boundaries and edge dislocations, which are likely generic to the in-plane structure of 2D COFs. The visualization of such real structural features is key to understand, design and control structure–property relationships in COFs, which can have major implications for adsorption, catalytic, and transport properties of such crystalline porous polymers.Stabilization of covalent organic frameworks (COFs) by post-synthetic locking is a powerful tool to push the limits of COF utilization. Here the authors demonstrate a sulfur-assisted conversion of an imine-linked COF into a thiazole-linked COF, with retention of crystallinity and porosity, allowing for direct imaging of defects in COFs.

Sulfur: an intermediate template for advanced silicon anode architectures

The lithium–sulfur chemistry provides a next generation battery technology on the verge of commercialization with significantly increased specific energy. However, the cycle life mainly suffers from dendrite and continuous SEI formation in lithium anodes inducing active material and electrolyte depletion. Here, we report on a silicon–carbon composite anode as a stable alternative anode for safe Li–S cells. Well-defined sulfur coatings generate a shell for a silicon core (Si@S) to further form a carbon shell (Si@S@sucrose). After sulfur removal the void structure (Si@void@C) allows to compensate the mechanical stress imposed by the huge volume change during the lithiation of the silicon. In this case, sulfur is not only used as a low cost and high capacity cathode material but also as a template to create free volume. It is easily removed during the pyrolysis and no acid leaching steps are required. In half cell tests vs. lithium a high capacity of 2270 mA h gSi−1 (690 mA h g−1) was achieved in the 10th cycle and the reversible lithiation of the silicon particles could be ensured for more than 50 cycles. The prelithiated Si–C anode with a high areal capacity of 2 mA h cm−2 was successfully matched with a sulfur cathode in a SLS full cell on coin cell and on pouch cell levels. A high capacity of about 807 mA h gsulfur−1 (2nd cycle) was reached with a low lithium excess of only 76% compared to 2000% lithium excess in state-of-the-art Li–S cells.