Franziska Mueller

An Advanced Lithium-Air Battery Exploiting an Ionic Liquid-Based Electrolyte

A novel lithium-oxygen battery exploiting PYR14TFSI-LiTFSI as ionic liquid-based electrolyte medium is reported. The Li/PYR14TFSI-LiTFSI/O2 battery was fully characterized by electrochemical impedance spectroscopy, capacity-limited cycling, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results of this extensive study demonstrate that this new Li/O2 cell is characterized by a stable electrode-electrolyte interface and a highly reversible charge-discharge cycling behavior. Most remarkably, the charge process (oxygen oxidation reaction) is characterized by a very low overvoltage, enhancing the energy efficiency to 82%, thus, addressing one of the most critical issues preventing the practical application of lithium-oxygen batteries.

Challenges of “Going Nano”: Enhanced Electrochemical Performance of Cobalt Oxide Nanoparticles by Carbothermal Reduction and In Situ Carbon Coating

The electrochemical performance of nano- and micron-sized Co(3)O(4) is investigated, highlighting the substantial influence of the specific surface area on the obtainable specific capacities as well as the cycling stability. In fact, Co(3)O(4) materials with a high surface area (i.e. a small particle size) show superior specific features, which are, however, accompanied by a rapid capacity fading, owing to the increased formation of an insulating polymeric surface film that results from transition-metal-catalyzed electrolyte decomposition. The simultaneous coating with carbon of Co(3)O(4) nanoparticles and in situ reduction of the Co(3)O(4) by a carbothermal route yields a CoO-Co-C nanocomposite. The formation of this material substantially enhances the long-term cycling stability and coulombic efficiency of the lithium-ion active material used. Although the metallic cobalt enhances the electronic conductivity within the electrode and remains electrochemically inactive (as revealed by in situ powder X-ray diffraction analysis), it might have a detrimental effect on the long-term cycling stability by catalytically inducing continuous electrolyte decomposition.

Eco‐friendly Energy Storage System: Seawater and Ionic Liquid Electrolyte

As existing battery technologies struggle to meet the requirements for widespread use in the field of large-scale energy storage, novel concepts are urgently needed concerning batteries that have high energy densities, low costs, and high levels of safety. Here, a novel eco-friendly energy storage system (ESS) using seawater and an ionic liquid is proposed for the first time; this represents an intermediate system between a battery and a fuel cell, and is accordingly referred to as a hybrid rechargeable cell. Compared to conventional organic electrolytes, the ionic liquid electrolyte significantly enhances the cycle performance of the seawater hybrid rechargeable system, acting as a very stable interface layer between the Sn-C (Na storage) anode and the NASICON (Na3 Zr2 Si2 PO12) ceramic solid electrolyte, making this system extremely promising for cost-efficient and environmentally friendly large-scale energy storage.

Precursor Polymers for the Carbon Coating of Au@ZnO Multipods for Application as Active Material in Lithium-Ion Batteries

The synthesis of statistical and block copolymers based on polyacrylonitrile, as a source for carbonaceous materials, and thiol-containing repeating units as inorganic nanoparticle anchoring groups is reported. These polymers are used to coat Au@ZnO multipod heteroparticles with polymer brushes. IR spectroscopy and transmission electron microscopy prove the successful binding of the polymer onto the inorganic nanostructures. Thermogravimetric analysis is applied to compare the binding ability of the block and statistical copolymers. Subsequently, the polymer coating is transformed into a carbonaceous (partially graphitic) coating by pyrolysis. The obtained carbon coating is characterized by Raman spectroscopy and energy-dispersive X-ray (EDX) spectroscopy. The benefit of the conformal carbon coating of the Au@ZnO multipods regarding its application as lithium-ion anode material is revealed by performing galvanostatic cycling, showing a highly enhanced and stabilized electrochemical performance of the carbon-coated particles (still 831 mAh g(-1) after 150 cycles) with respect to the uncoated ones (only 353 mAh g(-1) after 10 cycles).

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Advanced metal oxide electrodes in Li-ion batteries usually show reversible capacities exceeding the theoretically expected ones. Despite many studies and tentative interpretations, the origin of this extra-capacity is not assessed yet. Lithium storage can be increased through different chemical processes developing in the electrodes during charging cycles. The solid electrolyte interface (SEI), formed already during the first lithium uptake, is usually considered to be a passivation layer preventing the oxidation of the electrodes while not participating in the lithium storage process. In this work, we combine high resolution soft X-ray absorption spectroscopy with tunable probing depth and photoemission spectroscopy to obtain profiles of the surface evolution of a well-known prototype conversion-alloying type mixed metal oxide (carbon coated ZnFe2O4) electrode. We show that a partially reversible layer of alkyl lithium carbonates is formed (∼5-7 nm) at the SEI surface when reaching higher Li storage levels. This layer acts as a Li reservoir and seems to give a significant contribution to the extra-capacity of the electrodes. This result further extends the role of the SEI layer in the functionality of Li-ion batteries.

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40u2009°C, revealing a very stable capacity of about 140u2005mAhu2009g(-1) and retention above 99u2009% over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Insights into the Effect of Iron and Cobalt Doping on the Structure of Nanosized ZnO

Here we report an in-depth structural characterization of transition metal-doped zinc oxide nanoparticles that have recently been used as anode materials for Li-ion batteries. Structural refinement of powder X-ray diffraction (XRD) data allowed the determination of small though reproducible changes in the unit cell dimensions of four ZnO samples (wurtzite structure) prepared with different dopants or different synthesis conditions. Moreover, large variations of the full width at half-maximum of the XRD reflections indicate that the crystallinity of the samples decreases in the order ZnO, Zn0.9Co0.1O, Zn0.9Fe0.1O/C, and Zn0.9Fe0.1O (the crystallite sizes as determined by Williamson-Hall plots are 42, 29, 15, and 13 nm, respectively). X-ray absorption spectroscopy data indicate that Co is divalent, whereas Fe is purely trivalent in Zn0.9Fe0.1O and 95% trivalent (Fe(3+)/(Fe(3+) + Fe(2+)) ratio = 0.95) in Zn0.9Fe0.1O/C. The aliovalent substitution of Fe(3+) for Zn(2+) implies the formation of local defects around Fe(3+) such as cationic vacancies or interstitial oxygen for charge balance. The EXAFS (extended X-ray absorption fine structure) data, besides providing local Fe-O and Co-O bond distances, are consistent with a large amount of charge-compensating defects. The Co-doped sample displays similar EXAFS features to those of pure ZnO, suggesting the absence of a large concentration of defects as found in the Fe-doped samples. These results are of substantial importance for understanding and elucidating the modified electrochemical lithiation mechanism by introducing transition metal dopants into the ZnO structure for the application as lithium-ion anode material.

Synthesis and characterization of carbon coated sponge-like tin oxide (SnOx) films and their application as electrode materials in lithium-ion batteries

Nanoporous metal oxides are widely used for the development of various functional nanostructures. We report on the synthesis of sponge-like tin oxide films on copper foil by anodization of electrochemically deposited tin films. The thin films are functionalized using a surface-anchoring carbon precursor-polymer (poly(acrylonitrile-b-dopamine acrylamide)) followed by annealing at elevated temperature to convert the polymer coating into a carbonaceous coating. The as prepared and the carbon coated films are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy. Subsequently, both SnOx films are employed as anode materials in lithium ion batteries. Carbon coating has a beneficial effect on the battery performance with respect to the rate capability, increasing the capacity by 200 mA h g−1 for all applied current densities. After 20 cycles, coated samples show a reversible specific charge capacity of 497 mA h g−1. Ex situ scanning electron microscopy reveals the retention of the sponge-like morphology even after cycling.

Facile hybridization of Ni@Fe2O3 superparticles with functionalized reduced graphene oxide and its application as anode material in lithium-ion batteries

In our present work we developed a novel graphene wrapping approach of Ni@Fe2O3 superparticles, which can be extended as a concept approach for other nanomaterials as well. It uses sulfonated reduced graphene oxide, but avoids thermal treatments and use of toxic agents like hydrazine for its reduction. The modification of graphene oxide is achieved by the introduction of sulfate groups accompanied with reduction and elimination reactions, due to the treatment with oleum. The successful wrapping of nanoparticles is proven by energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The developed composite material shows strongly improved performance as anode material in lithium-ion batteries (compared to unwrapped Ni@Fe2O3) as it offers a reversible capacity of 1051mAhg(-1) after 40 cycles at C/20, compared with 460mAhg(-1) for unwrapped Ni@Fe2O3. The C rate capability is also improved by the wrapping approach, as specific capacities for wrapped particles are about twice of those offered by unwrapped particles. Additionally, the benefit for the use of the advanced superparticle morphology is demonstrated by comparing wrapped Ni@Fe2O3 particles with wrapped Fe2O3 nanorice.

In Situ Coating of Li[Ni0.33Mn0.33Co0.33]O2Particles to Enable Aqueous Electrode Processing

The aqueous processing of lithium-ion battery (LIB) electrodes has the potential to notably decrease the battery processing costs and paves the way for a sustainable and environmentally benign production (and recycling) of electrochemical energy storage devices. Although this concept has already been adopted for the industrial production of LIB graphite anodes, the performance decay of cathode electrodes based on transition metal oxides processed in aqueous environments is still an open issue. In this study, we show that the addition of small quantities of phosphoric acid into the cathodic slurry yields Li[Ni0.33 Mn0.33 Co0.33 ]O2 electrodes that have an outstanding electrochemical performance in lithium-ion cells.